WO2021168257A1

WO2021168257A1 - Multicast service handover and data forwarding

Info

Publication number: WO2021168257A1
Application number: PCT/US2021/018791
Authority: WO
Inventors: Xipeng Zhu; Prasad Reddy KADIRI; Miguel Griot; Umesh PHUYAL; Haris Zisimopoulos; Le LIU; Alberto Rico Alvarino
Original assignee: Qualcomm Incorporated
Priority date: 2020-02-21
Filing date: 2021-02-19
Publication date: 2021-08-26

Abstract

Methods, systems, and devices for wireless communications are described. A source base station may serve multicast traffic associated with one or more multicast radio bearers to a UE. The source base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. The source base station may transmit, to the target base station, a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. The target base station may transmit, to the source base station, a handover complete message, where the handover complete message is indicative that the target base station is serving the UE the multicast traffic associated with the one or more multicast radio bearers.

Description

MULTICAST SERVICE HANDOVER AND DATA FORWARDING

CROSS REFERENCE

[0001] The present Application for Patent claims the benefit of Greek Patent Application Serial No. 20200100095 by ZHU et al., entitled “MULTICAST SERVICE HANDOVER AND DATA FORWARDING,” filed February 21, 2020, assigned to the assignee hereof.

FIELD OF TECHNOLOGY

[0002] The following relates generally to wireless communications and more specifically to multicast service handover and data forwarding.

BACKGROUND

[0003] Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple- access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM). A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).

[0004] In some cases, a UE may undergo handover from a source base station to a target base station, in which the UE may cease communications with the source base station and may initiate communications with the target base station. Handover in which the source base station initiates the handover may be referred to as radio access network (RAN)-based handover. If the RAN-based handover is performed in a manner such that no packets are lost, the handover may be referred to as lossless handover. SUMMARY

[0005] The described techniques relate to improved methods, systems, devices, and apparatuses that support multicast service handover and data forwarding. Generally, the described techniques provide for a source base station to perform handover with a user equipment (UE) from a multicast radio bearer of the source base station to a multicast radio bearer of a target base station; from a multicast radio bearer of the source base station to a dedicated radio bearer of the target base station; from a dedicated radio bearer of the source base station to a multicast radio bearer of the source base station. In some examples, performing handover may involve a source base station serving multicast traffic (or multicast/broadcast traffic) associated with one or more multicast radio bearers to a UE. The source base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. The source base station may transmit, to the target base station, a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. The target base station may transmit, to the source base station, a handover complete message, where the handover complete message may indicate that the target base station is serving the UE the multicast traffic associated with the one or more multicast radio bearers and associated configurations.

[0006] A method for wireless communication at a source base station is described. The method may include serving multicast traffic associated with one or more multicast radio bearers to a UE, determining that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE, transmitting a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and receiving a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

[0007] An apparatus for wireless communication at a source base station is described.

The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to serv multicast traffic associated with one or more multicast radio bearers to a UE, determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the EE, transmit a handover request to the target base station, where the handover request includes a current multicast context of the EE identifying the one or more multicast radio bearers associated with the multicast traffic, and receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the EE the multicast traffic associated with the one or more multicast radio bearers.

[0008] Another apparatus for wireless communication at a source base station is described. The apparatus may include means for serving multicast traffic associated with one or more multicast radio bearers to a UE, means for determining that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE, means for transmitting a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and means for receiving a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

[0009] A non-transitory computer-readable medium storing code for wireless communication at a source base station is described. The code may include instructions executable by a processor to serv multicast traffic associated with one or more multicast radio bearers to a UE, determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE, transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

[0010] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request to the target base station further may include operations, features, means, or instructions for including, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

[0011] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request to the target base station further may include operations, features, means, or instructions for including, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE may be being served the multicast traffic.

[0012] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request to the target base station further may include operations, features, means, or instructions for including, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE may be being served the multicast traffic.

[0013] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request to the target base station further may include operations, features, means, or instructions for including, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE may be being served the multicast traffic and one or more dedicated radio bearers.

[0014] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for forwarding a portion of the multicast traffic to the target base station for service to the UE in accordance with the current multicast context of the UE, where the portion of the multicast traffic that may be forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

[0015] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a sequence number status transfer message to the target base station, where the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE may be being served. [0016] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for forwarding the portion of the multicast traffic to the target base station occurs after transmission of the sequence number status transfer message. [0017] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a sequence number status update message from the target base station, where the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE may be being served.

[0018] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for forwarding the portion of the multicast traffic to the target base station occurs after receipt of the sequence number status update message.

[0019] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, forwarding the portion of the multicast traffic to the target base station further may include operations, features, means, or instructions for identifying that a mismatch exists between multicast radio bearers served by the target base station and multicast radio bearers served by the source base station, where forwarding the portion of the multicast traffic may be based on the mismatch.

[0020] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the mismatch may be based on the target base station not serving, at a time of the handover request, one or more multicast radio bearers that the source base station was serving to the UE.

[0021] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the mismatch may be based on the target base station serving one or more multicast radio bearers in advance of service of the same one or more multicast radio bearers by the source base station. [0022] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, identifying the mismatch may include operations, features, means, or instructions for receiving, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to one or more multicast radio bearers served by the target base station, and comparing the one or more current sequence numbers of data packets served by the target base station with sequence numbers served by the source base station.

[0023] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for participating in a data forwarding negotiation that occurs between the source base station and the target base station, where forwarding the portion of the multicast traffic to the target base station may be based on the data forwarding negotiation.

[0024] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, participating in the data forwarding negotiation may include operations, features, means, or instructions for transmitting, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, where the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station, and receiving, via a handover request acknowledgment, a confirmation that data forwarding from the source base station may be to occur based on N3 tunnel availability at the target base station for respective multicast radio bearers.

[0025] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the forwarding request further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0026] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the confirmation includes at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station. [0027] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a stop data forwarding message from the target base station, indicating that the data forwarding from the source base station may be to stop, where the stop data forwarding message may be received via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

[0028] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, participating in the data forwarding negotiation may include operations, features, means, or instructions for transmitting, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station, and determining, from a handover request acknowledgement responding to the handover request, whether data forwarding from the source base station to the target base station may be to occur.

[0029] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, determining whether data forwarding may be to occur may include operations, features, means, or instructions for receiving, via the handover request acknowledgement, a confirmation that data forwarding may be to occur.

[0030] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, determining whether data forwarding may be to occur may include operations, features, means, or instructions for identifying that the handover request acknowledgement does not include a data forwarding message, and determining that data forwarding from the source base station to the target base station may be to occur based on an absence of the data forwarding message in the handover request acknowledgement.

[0031] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, in response to a determination that data forwarding may be to occur, a forwarding indication from the source base station to the target base station, where the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station, and receiving, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0032] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the forwarding indication further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0033] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for forwarding, from the source base station to the target base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) based on a determination that data forwarding may be to occur and without further data forwarding negotiations between the source base station and the target base station, receiving, from the target base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station may be to stop data forwarding, and continuing data forwarding until the source base station reaches the termination PDCP sequence number.

[0034] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for data packets having first data, associated with a first multicast radio bearer, and received at the source base station may have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

[0035] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, a data packet associated with a multicast radio bearer may have a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the source base station.

[0036] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, via a handover request acknowledgement from the target base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station, and transmitting a radio resource control (RRC) reconfiguration message to the UE, where the RRC reconfiguration message includes an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for the target base station. [0037] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the indication may be a delta indication with respect to a previous multicast flow-to-radio bearer mapping or MRB/DRB configuration.

[0038] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, determining that the UE may be to be handed over to the target base station may include operations, features, means, or instructions for receiving a measurement report from the UE, and determining UE handover based on the measurement report.

[0039] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

[0040] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for disconnecting from an N3 tunnel providing the multicast traffic after receiving the handover complete message.

[0041] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the multicast traffic may be multicast/broadcast traffic.

[0042] A method for wireless communication at a target base station is described. The method may include receiving, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, receiving, from the UE, a radio resource control reconfiguration complete message, transmitting, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and serving the multicast traffic to the UE based on the current multicast context of the UE.

[0043] An apparatus for wireless communication at a target base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, receive, from the UE, a radio resource control reconfiguration complete message, transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and serv the multicast traffic to the UE based on the current multicast context of the UE.

[0044] Another apparatus for wireless communication at a target base station is described. The apparatus may include means for receiving, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, means for receiving, from the UE, a radio resource control reconfiguration complete message, means for transmitting, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and means for serving the multicast traffic to the UE based on the current multicast context of the UE.

[0045] A non-transitory computer-readable medium storing code for wireless communication at a target base station is described. The code may include instructions executable by a processor to receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, receive, from the UE, a radio resource control reconfiguration complete message, transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and serv the multicast traffic to the UE based on the current multicast context of the UE.

[0046] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the handover request from the source base station further may include operations, features, means, or instructions for receiving, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

[0047] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the handover request from the source base station further may include operations, features, means, or instructions for receiving, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE may be being served the multicast traffic.

[0048] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the handover request from the source base station further may include operations, features, means, or instructions for receiving, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE may be being served the multicast traffic.

[0049] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the handover request from the source base station further may include operations, features, means, or instructions for receiving, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE may be being served the multicast traffic and one or more dedicated radio bearers.

[0050] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a portion of the multicast traffic forwarded from the source base station for service to the UE in accordance with the current multicast context of the UE, where the portion of the multicast traffic that may be forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station. [0051] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a sequence number status transfer message from the source base station, where the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE may be being served.

[0052] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving the portion of the multicast traffic forwarded from the source base station occurs after receipt of the sequence number status transfer message.

[0053] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a sequence number status update message to the source base station, where the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE may be being served.

[0054] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving the portion of the multicast traffic forwarded from the source base station occurs after transmission of the sequence number status update message.

[0055] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, receiving the portion of the multicast traffic forwarded from the source base station further may include operations, features, means, or instructions for identifying that a mismatch exists between multicast radio bearers served by the target base station and multicast radio bearers served by the source base station, where receiving the portion of the multicast traffic may be based on the mismatch.

[0056] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the mismatch may be based on the target base station not serving, at a time of the handover request, one or more multicast radio bearers that the source base station was serving to the UE. [0057] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the mismatch may be based on the target base station serving one or more multicast radio bearers in advance of service of the same one or more multicast radio bearers by the source base station.

[0058] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to one or more multicast radio bearers served by the target base station.

[0059] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for participating in a data forwarding negotiation that occurs between the source base station and the target base station, where receiving the portion of the multicast traffic forwarded from the source base station may be based on the data forwarding negotiation.

[0060] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, participating in the data forwarding negotiation may include operations, features, means, or instructions for receiving, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, where the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station, and transmitting, via a handover request acknowledgment, a confirmation that data forwarding from the source base station may be to occur based on N3 tunnel availability at the target base station for respective multicast radio bearers.

[0061] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the forwarding request further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0062] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the confirmation includes at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0063] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a stop data forwarding message to the source base station, indicating that the data forwarding from the source base station may be to stop, where the stop data forwarding message may be transmitted via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

[0064] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, participating in the data forwarding negotiation may include operations, features, means, or instructions for receiving, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station, and transmitting a handover request acknowledgement responding to the handover request, the handover request acknowledgement being indicative of whether data forwarding from the source base station to the target base station may be to occur.

[0065] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request acknowledgement may include operations, features, means, or instructions for transmitting, via the handover request acknowledgement, a confirmation that data forwarding may be to occur.

[0066] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, transmitting the handover request acknowledgement may include operations, features, means, or instructions for transmitting the handover request acknowledgement without a data forwarding message, where an absence of the data forwarding message in the handover request acknowledgement may be indicative that data forwarding from the source base station to the target base station may be to occur.

[0067] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a forwarding indication from the source base station, where the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station, and transmitting, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0068] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the forwarding indication further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0069] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the source base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) without further data forwarding negotiations between the source base station and the target base station, and transmitting, to the source base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station may be to stop data forwarding.

[0070] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for data packets having first data, associated with a first multicast radio bearer, and received at the source base station may have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

[0071] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, a data packet associated with a multicast radio bearer may have a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the target base station.

[0072] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, via a handover request acknowledgement to the source base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station. [0073] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, an N3 tunnel for receipt of multicast traffic to the UE may be already established at the target base station prior to receiving the handover request.

[0074] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, an N3 tunnel for receipt of multicast traffic to the UE may be established at the target base station after receiving the handover request but before transmission of a handover request acknowledgement.

[0075] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for establishment of the N3 tunnel may be based on the current multicast context for the UE.

[0076] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the current multicast context for the UE used to establish the N3 tunnel may be received from a core network.

[0077] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, from the UE and after transmitting the handover complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE, transmitting, via a unicast transmission to the UE and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE, and transmitting ongoing packet data units of the multicast traffic to the UE via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

[0078] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the multicast traffic may be multicast/broadcast traffic.

[0079] A method for wireless communication at a UE is described. The method may include receiving, from a source base station, multicast traffic associated with one or more multicast radio bearers, transmitting a measurement report to the source base station, receiving, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, transmitting, to the target base station, a radio resource control reconfiguration complete message, and receiving, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0080] An apparatus for wireless communication at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive, from a source base station, multicast traffic associated with one or more multicast radio bearers, transmit a measurement report to the source base station, receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, transmit, to the target base station, a radio resource control reconfiguration complete message, and receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0081] Another apparatus for wireless communication at a UE is described. The apparatus may include means for receiving, from a source base station, multicast traffic associated with one or more multicast radio bearers, means for transmitting a measurement report to the source base station, means for receiving, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, means for transmitting, to the target base station, a radio resource control reconfiguration complete message, and means for receiving, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0082] A non-transitory computer-readable medium storing code for wireless communication at a UE is described. The code may include instructions executable by a processor to receive, from a source base station, multicast traffic associated with one or more multicast radio bearers, transmit a measurement report to the source base station, receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, transmit, to the target base station, a radio resource control reconfiguration complete message, and receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0083] Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, to the target base station and after transmitting the radio resource control reconfiguration complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE, receiving, via a unicast transmission from the target base station and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE, and receiving ongoing packet data units of the multicast traffic from the target base station via either multicast radio bearers, dedicated radio bearers, or combinations thereof. [0084] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

[0085] In some examples of the method, apparatuses, and non-transitory computer- readable medium described herein, the multicast traffic may be multicast/broadcast traffic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] FIG. 1 illustrates an example of a wireless communications system that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. [0087] FIGs. 2A and 2B illustrate examples of wireless communications systems that support multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0088] FIG. 3 illustrates an example of an architecture that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. [0089] FIG. 4 illustrates an example of a handover procedure that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0090] FIG. 5 illustrates an example of a handover procedure that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. [0091] FIG. 6 illustrates an example of a process flow that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0092] FIGs. 7 and 8 show block diagrams of devices that support multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0093] FIG. 9 shows a block diagram of a communication manager that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0094] FIG. 10 shows a diagram of a system including a device that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0095] FIGs. 11 and 12 show block diagrams of devices that support multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0096] FIG. 13 shows a block diagram of a communication manager that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0097] FIG. 14 shows a diagram of a system including a device that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure.

[0098] FIGs. 15 through 19 show flowcharts illustrating methods that support multicast service handover and data forwarding in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

[0099] A user equipment (UE) may receive traffic from a base station over a dedicated radio bearer (DRB) or a multicast radio bearer (MRB). The base station may transmit unicast traffic to the UE over the DRB and multicast traffic to the UE over the MRB or a DRB. In some cases, the UE may undergo radio access network (RAN)-based handover from an MRB or a DRB of a source base station to an MRB or a DRB of a target base station. The methods as described herein may relate to procedures that enable lossless handover of a UE from an MRB to an MRB; an MRB to a DRB; a DRB to an MRB; or a combination thereof.

[0100] In one example, a source base station may serve multicast traffic (also referred to herein as multicast/broadcast traffic) associated with one or more MRBs to a UE. The source base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic. The source base station may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more MRBs associated with the multicast traffic.

The target base station may transmit a handover complete message to the source base station, where the handover complete message may include an indication that the target base station is serving to the UE the multicast traffic associated with the one or more MRBs and/or an associated MRB configuration.

[0101] Aspects of the disclosure are initially described in the context of wireless communications systems. Additional aspects of the disclosure are described in the context of an architecture, handover procedures, and a process flow. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to multicast service handover and data forwarding.

[0102] FIG. 1 illustrates an example of a wireless communications system 100 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE- Advanced (LTE- A) network, an LTE-A Pro network, or a New Radio (NR) network. In some examples, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

[0103] The base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

[0104] The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment), as shown in FIG. 1.

[0105] The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an SI, N2, N3, or other interface). The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105), or indirectly (e.g., via core network 130), or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

[0106] One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB), a next- generation NodeB or a giga-NodeB (either of which may be referred to as a gNB), a Home NodeB, a Home eNodeB, or other suitable terminology.

[0107] A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

[0108] The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

[0109] The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP)) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR). Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information), control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

[0110] Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT- S-OFDM)). In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both). Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams), and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

[0111] The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T_s =

1 /{ f_{max '} Nf) seconds, where A/_ma may represent the maximum supported subcarrier spacing, and JV- may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms)). Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023).

[0112] Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period). In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., Nf) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

[0113] A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI). In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs)).

[0114] Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET)) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs)) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

[0115] In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

[0116] The wireless communications system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timings, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timings, and transmissions from different base stations 105 may, in some examples, not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

[0117] The wireless communications system 100 may be configured to support ultra reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra reliable low-latency communications (URLLC) or mission critical communications. The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions). Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT), mission critical video (MCVideo), or mission critical data (MCData). Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low- latency may be used interchangeably herein.

[0118] In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol). One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1 :M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

[0119] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC), which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME), an access and mobility management function (AMF)) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW), a Packet Data Network (PDN) gateway (P-GW), or a user plane function (UPF)). The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to the network operators IP services 150. The operators IP services 150 may include access to the Internet, Intranet(s), an IP Multimedia Subsystem (IMS), or a Packet- Switched Streaming Service. [0120] Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC). Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs). Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105).

[0121] The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

[0122] The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA), LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA). Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples. [0123] A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

[0124] Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation).

[0125] The wireless communications system 100 may be a packet-based network that operates according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP -based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use error detection techniques, error correction techniques, or both to support retransmissions at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE 115 and a base station 105 or a core network 130 supporting radio bearers for user plane data. At the physical layer, transport channels may be mapped to physical channels.

[0126] The UEs 115 and the base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. Hybrid automatic repeat request (HARQ) feedback is one technique for increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (e.g., automatic repeat request (ARQ)). HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., low signal-to-noise conditions). In some examples, a device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

[0127] Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). A wireless network, for example a wireless local area network (WLAN), such as a Wi-Fi (i.e., Institute of Electrical and Electronics Engineers (IEEE) 802.11) network may include an access point (AP) that may communicate with one or more wireless or mobile devices. The AP may be coupled to a network, such as the Internet, and may enable a mobile device to communicate via the network (or communicate with other devices coupled to the access point). A wireless device may communicate with a network device bi-directionally. For example, in a WLAN, a device may communicate with an associated AP via downlink (e.g., the communication link from the AP to the device) and uplink (e.g., the communication link from the device to the AP). A wireless personal area network (PAN), which may include a Bluetooth connection, may provide for short range wireless connections between two or more paired wireless devices. For example, wireless devices such as cellular phones may utilize wireless PAN communications to exchange information such as audio signals with wireless headsets.

[0128] In LTE networks, multimedia broadcast multicast service (MBMS) and single cell point to multipoint (SC-PTM) may support UE-based service continuity. Such continuity may be applicable for RRC CONNECTED ( MBMSInterestlndication based) and RRC IDLE states. UE-assisted RAN based lossless or seamless handover may be used for unicast DRBs, but not MRBs. Additionally, multicast-broadcast single frequency network (MBSFN) may be supported.

[0129] For NR, for some cases, multicast/broadcast service (MBS) may rely on RAN based handover. For instance, RAN based handover may be used if a UE 115 is in RRC CONNECTED when downlink data arrives. Alternatively, if the UE 115 is in RRC IDLE or RRC INACTIVE, the UE 115 may be paged to enter RRC CONNECTED when downlink data arrives and may then perform RAN based handover. The disclosure herein describes methods by which lossless handover and/or seamless handover may be performed.

[0130] In some examples, a source base station 105 may serve multicast traffic (or multicast/broadcast traffic) associated with one or more multicast radio bearers to a UE 115. The source base station may determine that the UE 115 is to be handed over to a target base station 105 for continued service of the multicast traffic to the UE 115. The source base station 105 may transmit, to the target base station 105, a handover request to the target base station, where the handover request includes a current multicast context of the UE 115 identifying the one or more multicast radio bearers associated with the multicast traffic and/or a User Plane Function (UPF) context for receiving MBS service. The target base station 105 may transmit, to the source base station 105, a handover complete message, where the handover complete message is indicative whether the target base station 105 is serving the UE 115 the multicast traffic associated with the one or more multicast radio bearers. Additionally or alternatively, the handover complete message may include an indication about whether data forwarding is optional and/or whether data forwarding is to be used or not and an MRB configuration used in a target cell (e.g., the cell of the target base station 105). [0131] FIGs. 2A and 2B illustrate examples of wireless communications systems 200 that support multicast service handover and data forwarding in accordance with aspects of the present disclosure. In some examples, wireless communications system 200 may implement aspects of wireless communications system 100. For instance, base stations 105-a and 105-b may be examples of base stations as described with reference to FIG. 1 and UE 115-a may be an example of a UE 115 as described with reference to FIG. 1.

[0132] Initially, as depicted in FIG. 2A, UE 115-a may communicate with source base station 105-a via radio bearer 215-a, where radio bearer 215-a may be a multicast radio bearer (MRB). Source base station 105-a may communicate with User Plane Function (UPF) 205 via tunnel 210-a, which may be an example of an MB-N3 tunnel. UPF 205 may use tunnel 210-a to transmit multicast/broadcast service (MBS) data to source base station 105-a. Source base station 105-a, in turn, may serve multicast traffic (or multicast/broadcast traffic) received from the UPF 205 (e.g., MBS data) to UE 115-a. A more detailed architecture may be described with reference to FIG. 3.

[0133] Source base station 105-a may trigger a handover procedure for UE 115-a towards target base station 105-b to enable UE 115-a to have a radio bearer 215 (e.g., an MRB or a dedicated radio bearer (DRB)) connection with target base station 105-b. Base station 105-a may trigger the handover procedure based on a UE mobility and/or a measurement report received from UE 115-a. As depicted in FIG. 2B, after handover is complete, UE 115-a may communicate with target base station 105-b via radio bearer 215-b. The methods as described with reference to FIGs. 4 and 5 may correspond to methods by which a UE 115, such as UE 115-a, may perform lossless handover from an MRB to an MRB and/or a DRB.

[0134] In cases where a tunnel 210-b (e.g., an MB-N3 tunnel) is not established prior to the handover procedure, target base station 105-b and UPF 205 may establish the tunnel 210-b as part of the handover procedure. Additionally, in some cases, source base station 105-a may cease communicating with UPF 205 via tunnel 210-a.

[0135] Herein, lossless handover and seamless handover scenarios may be described. For instance, source MRB to target MRB or DRB handover may be described. A first case may involve a target base station 105 already serving MBS and having an established MB-N3 tunnel when a handover request is received. A second case may involve the MB-N3 session joining procedure being ongoing and a target base station 105 receiving a handover request for an MBS session. A third case may involve the target base station joining the session once a handover request has been received. The second and third case may be described with reference to FIG. 5.

[0136] By performing lossless handover for an MRB, no packets of multicast traffic to be transmitted to UE 115-a by base stations 105-a and/or 105-b may be lost. As such, performing lossless handover for the MRB may increase the efficiency of communications.

[0137] FIG. 3 illustrates an example of an architecture 300 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. In some examples, architecture 300 may implement aspects of wireless communications system 100. For instance, base station 105-c may be an example of a base station 105 as described with reference to FIG. 1 and UEs 115-b, 115-c, 115-d, and 115-e may be examples of UEs 115 as described with reference to FIG. 1.

[0138] Architecture 300 may include a UPF 205-a, which may be an example of a UPF 205 as described with reference to FIG. 2. UPF 205-a may communicate with a central unit (CU) of base station 105-c via tunnel 210-c, which may be an example of a tunnel 210 as described with reference to FIG. 2. For instance, the CU of base station 105-a may receive a multicast/broadcast (MB) flow identified by a quality of service (QoS) flow (e.g., a 5G QoS flow) and/or a temporary mobile group identity (TMGI) over tunnel 210 and may map to MRB or DRB accordingly (e.g., depending on a number of UEs 115 receiving MBS service). Architecture 300 may also include an access and mobility management function (AMF) 305. AMF 305 may communicate with the CU of base station 105-c via N2 interface 310. For instance, AMF 305 may provide control signaling for MB-flow, TMGI setup, TMGI modification or a combination thereof.

[0139] One or more distributed units (DU) of base station 105-c may communicate with one or more sets of UEs 115 via radio bearers 215. For instance, a first DU of base station 105-c may communicate with a first set of UEs 115 including UE 115-b and 115-c through radio bearer 215-c, and a second DU of base station 105-a may communicate with a second set of UEs 115 including UE 115-d and 115-e through radio bearer 215-d. Radio bearers 215-c and 215-d may be examples of MRBs.

[0140] Implementing architecture 300 may enable mixed broadcast and unicast on physical downlink shared channel (PDSCH). In such cases, LTE SC-PTM may be used as a baseline. Additionally or alternatively, architecture 300 may enable more flexible switching between DRB and MRB and/or may enable unicast assistance to MRB in lower layers.

[0141] FIG. 4 illustrates an example of a handover procedure 400 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. In some examples, handover procedure 400 may implement aspects of wireless communications system 100. For instance, UE 115-f may be an example of a UE 115 as described with reference to FIG. 1 and base stations 105-d and 105-e may be examples of base stations 105 as described with reference to FIG. 1. Additionally, UPF 205-b may be an example of a UPF 205 as described with reference to FIG. 2 and AMF 305-a may be an example of an AMF 305 as described with reference to FIG. 3. In some cases, a session management function (SMF) may perform the functions of AMF 305-a as described herein. Handover procedure 400 may depict methods for performing lossless handover when a target base station 105 has established a tunnel 210 with a UPF 205 prior to the target base station 105 receiving a handover request.

[0142] At 405, UPF 205-b may transmit MB user data to source base station 105-d. UPF 205-b may transmit the MB user data via a tunnel 210 (e.g., an MB-N3 tunnel). At 410, source base station 105-d may transmit multicast traffic (e.g., MBS data) to UE 115-f. Source base station 105-d may transmit the multicast traffic over a radio bearer 215 (e.g., an MRB). Source base station 105-d may derive the multicast traffic from the MB user data received at 405. At 415, UPF 205-b may transmit MB user data to target base station 105-e. UPF 205-b may transmit the MB user data via a tunnel 210 (e.g., an MB-N3 tunnel).

[0143] At 420, UE 115-f may transmit a measurement report to source base station 105-d. Source base station 105-d, after receiving the measurement report, may determine, at 425, to perform handover towards target base station 105-e and may initiate handover preparation towards target base station 105-e by transmitting a handover request (e.g., at 425) to target base station 105-e (e.g., over Xn). Additionally, the handover request message may include a UE MBS context to target base station 105-e containing a source cell MRB configuration, a list of MBS services, a UPF context used by the source cell for receiving MBS data from the core network, or a combination thereof. The MBS context may include MBS bearer and session information and/or a UPF context. The MBS context may, additionally or alternatively, include UE interested and/or receiving MRBs, MRB-DRB association (e.g., an MB flow to QoS flow mapping), a unicast assistance configuration, or a combination thereof. A decision whether to transmit the handover request at 425 may be based on existing reference signal received power (RSRP) or reference signal received quality (RSRQ) measurements and/or MBS measurements included in the measurement report received from UE 115-f. In some examples, for an NR MBS session, each session may have one or more MB flows, where each flow may be associated with a respective QoS flow. In some examples, a DRB configuration may be associated with point to point (PTP) communications and an MRB configuration may be associated with point to multipoint (PTM) communications and/or PTP communications.

[0144] At 430, target base station 105-e may transmit to source base station 105-d a handover request acknowledgement indicating that target base station 105-e successfully received the handover request. In some cases, the handover request acknowledgement may include an indication of a data forwarding tunnel, an indication of establishment of MB-N3 at the target cell (e.g., at target base station 105-e), data forwarding tunneling information between source and target cells (e.g., between source base station 105-d and target base station 105-e), a current PDCP sequence number (SN) per MRB, a target cell MRB and/or DRB configuration, or a combination thereof to source base station 105-d (e.g., the current SN per MRB may be included in or multiplexed with the handover request acknowledgement).

[0145] At 435, source base station 105-d may transmit an RRC reconfiguration message to UE 115-f. The RRC reconfiguration may include parameters that UE 115-f may use to initiate communications with target base station 105-e. At 440, source base station 105-d may transmit a sequence number (SN) status transfer message to target base station 105-e. The SN status transfer message may include a downlink delivery status per MRB and/or a last PDCP SN served to UE 115-f by source base station 105-d. At 445, source base station 105-d may forward MB data to target base station 105-e. At 450, target base station 105-e may transmit an SN status update or SN transfer information message to source base station 105-d. The SN status update or SN transfer information message may indicate an expected PDCP SN range per MRB (e.g., the NACKed PDCP SNs at target cell until current target cell serves PDCP SN), PDCP SNs that target base station 105-e is currently serving, PDCP SNs used for data tunneling, or any combination thereof. At 455, source base station 105-d may forward MB data (e.g., or, may continue to serve if forwarding MB data at 445) to target base station 105-e.

[0146] Source base station 105-d may perform data forwarding for MRB (e.g., at 445 and/or 455) if an MB-N3 tunnel for a UE interested or receiving MRB is not available at target base station 105-e and/or the target base station 105-e broadcasts or multicasts packets ahead of source base station 105-d. With regards to PDCP SN continuity, at UPF 205-b, a same payload (e.g., an internet protocol (IP) packet) may be assigned with a same GTP-U SN in each N3 tunnel between base stations 105 and UPF 205-b. Base station PDCP SN allocation and N3 GTP-U SN allocation at UPF 205-b may have a one-to-one mapping. In some cases, UE 115-f may use a sync protocol between UPF 205-b and base stations 105 for synchronizing data transmission from UPF 205-b to multiple base stations 105.

[0147] In some examples, the handover request transmitted at 425 may indicate a current PDCP SN and/or one or more previously non-ACKed (or missed) packets. Additionally or alternatively, target base station 105-e may determine, based on receiving the handover request, an indication that source base station 105-d is requesting to forward data per MRB.

In the handover response (e.g., the handover request acknowledgement transmitted at 430), target base station 105-e may indicate that it accepts data forwarding based on N3-tunnel availability and current PDCP SN at target base station 105-e. Additionally, target base station 105-e may indicate a current PDCP SN, a desired PDCP SN range, explicit PDCP SNs, or a combination thereof. Target base station 105-e may indicate to source base station 105-d to stop data forwarding if target base station 105-e has received the corresponding packets from UPF 205-b. Such information may be indicated by a control plane (e.g., the SN status update transmitted at 450) or a user plane (e.g., a downlink data delivery status (DDDS) message). In such cases, target base station 105-e may not receive an endmark as there may be no path switch for the MRB at UPF 205-b from source base station 105-d to target base station 105-e.

[0148] In other examples, source base station 105-d may indicate a MRB bearer type in the handover request transmitted at 425. Additionally, target base station 105-e may indicate whether MRB data forwarding is optional and/or to be utilized in the handover request acknowledgement message transmitted at 430. If a data forwarding request (if MRB data forwarding is to be utilized) is received from target base station 105-e, source base station 105-d may indicate a PDCP SN and/or non-ACKed (or missed) packets in the SN status transfer message transmitted at 440. Alternatively, without a data forwarding request received from target base station 105-e, source base station 105-d may indicate PDCP SN and/or previously not-ACKed (or missed) packets in SN status transfer message transmitted at 440. In the SN status update message at 450, target base station 105-e may request for which packets to be forwarded by a current PDCP SN, a desired start SN range, explicit SNs requested, or a combination thereof.

[0149] In yet other examples, source base station 105-d may indicate MRB bearer type in the handover request message transmitted at 425. Target base station 105-e may indicate whether MRB data forwarding is to be used or not in the handover request acknowledgement message transmitted at 430. If source base station 105-d receives a data forwarding request, as described herein, from target base station 105-e, source base station 105-d may forward downlink PDCP service data units (SDU) to target base station 105-e. After successful handover completion to target base station 105-e, UE 115-f may transmit a PDCP status report (e.g., at 470) that indicates which PDCP SNs are not received yet. In such cases, target base station 105-e may transmit a new SN status update and/or a handover complete message to source base station 105-d indicating at which PDCP SN to stop data forwarding.

[0150] For lossless handover, the SN status transfer (e.g., at 440) and PDCP status report (e.g., at 470) may be extended to support MRB PDCP SN status transfer. Target base station 105-e may start MB protocol data unit (PDU) buffering based on the handover request (e.g., at 425) or SN status transfer (e.g., at 440) from source base station 105-d. Target base station 105-e may deliver missed PDUs to UE 115-f based on the PDCP status report (e.g., at 470) and/or the SN status report or transfer (e.g., at 440).

[0151] At 460, UE 115-f may transmit an RRC reconfiguration complete message to target base station 105-e. The RRC reconfiguration complete message may indicate that UE 115-f has successfully completed handover with target base station 105-e. At 465, target base station 105-e may transmit a handover complete message to source base station 105-d, which may indicate to source base station 105-d that handover has occurred successfully. At 470,

UE 115-f may transmit a PDCP status report to target base station 105-e. PDCP status report may indicate one or more PDUs that UE 115-f has not successfully received and decoded. [0152] At 475, target base station 105-e may transmit PDUs to UE 115-f that source base station 105-d transmitted to UE 115-f but that UE 115-f did not successfully receive and decode (e.g., PDUs that source base station 105-d transmitted to UE 115-f and forwarded to base station 105-e due to UE 115-f failing to successfully receive and decode the PDUs). Target base station 105-e may transmit the PDUs via unicast. At 480, target base station 105-e may transmit new PDUs (e.g., PDUs that source base station 105-d did not transmit but forwarded to target base station 105-e or PDUs that target base station 105-e received directly from UPF 205-b) to UE 115-f. At 485, source base station 105-d may release (e.g., leave) a tunnel 210 (e.g., the MB-N3 broadcast tunnel) between target base station 105-e and 5GC (e.g., UPF 205-b). In some cases, source base station 105-d may leave the tunnel 210 if there are not any other UEs continuing to receive the MBS service.

[0153] In some cases, an MB-flow and/or TMGI specified service may be carried by a DRB or a different MRB in target base station 105-e than the MRB used by source base station 105-d. Target base station 105-e may include the new mapping and/or the MRB or DRB configuration in the handover command included with the handover request acknowledgement transmitted at 430, which may be referred to as RRCReconfiguration. The full-configuration and delta configuration may be supported for MRB and for the MB flow and/or TMGI.

[0154] Source base station 105-d may perform target base station selection based on an MB configuration exchanged between base station 105-d and the target base stations (e.g., via Xn or next generation (NG)) or based on pre-configured information in source base station 105-d. There may be an MBS configuration per cell which may include supported MB-flow and/or TMGIs as well as an MRB configuration. Signaling for setting up the configuration may be done via Xn or NG.

[0155] In some cases, a DRB to MRB handover may occur. Such a procedure may be similar to the procedure outlined with regards to FIG. 4 and/or FIG. 5. In DRB to MRB handover, target base station 105-e may configure MBS measurements to UE 115-f. Source base station 105-d may make handover decisions based on a unicast/MBS measurement report and/or MRB availability. Target base station 105-e may determine whether to map MB-flow and/or TMGI to a MRB. Data forwarding may be performed when target base station 105-e does not have an MB-N3 tunnel for the MB-flow and/or the TMGI or when the PDCP SN is ahead of source base station 105-d by a threshold amount. A one-to-one mapping between N3 GTP-U SN and PDCP SN may be utilized. Lossless handover may be supported based on the SN status transfer and PDCP status report. In some cases, DRB to MRB handover may happen intra-cell. In such cases, data forwarding may not be applicable or may otherwise not be used.

[0156] In some examples, in order to support lossless handover for 5G MBS services, the network may ensure support for downlink PDCP SN synchronization and continuity between a source cell (e.g., source base station 105-d) and a target cell (e.g., target base station 105-e). From the network side, the source cell (e.g., gNB) may forward data to the target cell (e.g., gNB) and the target cell may deliver the forwarding data. Additionally, an SN status transfer between the target cell and the source cell may cover the PDCP SN for MBS data. In some examples, a UE 115 (e.g., UE 115-f) may receive the MBS in the target by the target cell according to the target configuration. Additionally the UE 115 may support a PDCP status report.

[0157] In a 5G core network, MBS data may be delivered to a base station 105 (e.g., a gNB) using a shared MBS session (e.g., a multicast PDU session common to some or each UE 115 of a set of UEs 115) or a unicast PDU session (e.g., specific to one UE 115 of a set of UEs 115). Data received by the base station 105 from a shared MBS session may be delivered to UEs 115 using MRB, which may be associated with PTM communications, PTP communications, or PTM and PTP communications. Additionally or alternatively, data received by the base station 105 from a unicast PDU session may be delivered to UEs 115 using a unicast DRB, which may be UE-specific and may share one or more similarities with a PTP link of an MRB. The techniques described herein may correspond to lossless handover from a source base station 105 (e.g., gNB) to a target base station 105 (e.g., gNB) supporting MBS (e.g., MBS to MBS handover). Accordingly, in the present disclosure, a DRB may correspond to a unicast DRB or may correspond to the PTP communications performed with an MRB.

[0158] FIG. 5 illustrates an example of a handover procedure 500 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. In some examples, handover procedure 500 may implement aspects of wireless communications system 100. For instance, UE 115-g may be an example of a UE 115 as described with reference to FIG. 1 and base stations 105-f and 105-g may be examples of base stations 105 as described with reference to FIG. 1. Additionally, UPF 205-c may be an example of a UPF 205 as described with reference to FIG. 2 and AMF 305-b may be an example of an AMF 305 as described with reference to FIG. 3. In some cases, a session management function (SMF) may perform the functions of AMF 305-b as described herein. Handover procedure 500 may depict methods for performing lossless handover when a target base station 105 has not established a tunnel 210 with a UPF 205 prior to the target base station 105 receiving a handover request.

[0159] At 505, UPF 205-c may transmit MB user data to source base station 105-f. UPF 205-c may transmit the MB user data via a tunnel 210 (e.g., an MB-N3 tunnel). At 410, source base station 105-f may transmit MBS data to UE 115-g. Source base station 105-f may transmit the MBS data over a radio bearer 215 (e.g., an MRB). Source base station 105-f may derive the MBS data from the MB user data received at 505. At 515, UE 115-g may transmit a measurement report to source base station 105-f. Source base station 105-f, after receiving the measurement report, may determine, at 520, to perform handover towards target base station 105-g and may initiate handover preparation towards target base station 105-g by transmitting a handover request to target base station 105-g. Additionally, the handover request message may include a UE MBS context to target base station 105-g containing a source cell MRB configuration, a list of MBS services, a UPF context used by the source cell for receiving MBS data from the core network, or a combination thereof. The MBS context may include MBS bearer and session information and/or a UPF context. The MBS context may, additionally or alternatively, include UE interested and/or receiving MRBs, MRB-DRB association, a unicast assistance configuration, or a combination thereof. A decision whether to transmit the handover request at 520 may be based on existing RSRP, RSRQ, or MBS measurements included in the measurement report received from UE 115-g.

[0160] At 525, target base station 105-g may perform a tunnel establishment procedure. Performing the tunnel establishment procedure may establish a tunnel 210 (e.g., an MB-N3 tunnel) between target base station 105-g and UPF 205-c. Target base station 105-g may perform the tunnel establishment procedure based on receiving the handover request. Alternatively, target base station 105-g may perform the tunnel establishment procedure before receiving the handover request but may fail to establish the tunnel before receiving the handover request (e.g., the MB-N3 session joining may be ongoing). Additionally or alternatively, at 525, target base station 105-g may perform admission control. A decision whether to transmit the handover request at 525 may be based on existing RSRP or RSRQ measurements and/or MBS measurements.

[0161] In cases where target base station 105-g has not established an MB-N3 tunnel (e.g., not joined a multicast tree) by the time the handover request is received, target base station 105-g may join a multicast tree before sending a handover response (e.g., the handover request acknowledgement transmitted at 530) to source base station 105-f. The multicast context received in the handover request may be used to join the multicast tree, where the multicast context may be sent to target base station 105-g by CN before or by source base station 105-f. Target base station 105-g may establish an MB-N3 tunnel and request data forwarding details in the SN transfer message transmitted at 540. Target base station 105-g may have broadcast data carried over MRB or DRB. In other cases, target base station 105-g may join the multicast tree after handover. Once target base station 105-g has joined the multicast tree, the methods of FIG. 4 may be employed.

[0162] At 530, target base station 105-g may transmit to source base station 105-f an handover request acknowledgement indicating that target base station 105-g successfully received the handover request. In some cases, the handover request acknowledgement may include an indication of a data forwarding tunnel, an indication of establishment of MB-N3 at the target cell (e.g., at target base station 105-g), data forwarding tunneling information between source and target cells (e.g., between source base station 105-f and target base station 105-g), a current PDCP SN per MRB, a target cell MRB and/or DRB configuration, or a combination thereof to source base station 105-g (e.g., the current SN per MRB may be included in or multiplexed with the handover request acknowledgement).

[0163] At 535, source base station 105-f may transmit an RRC reconfiguration message to UE 115-g. The RRC reconfiguration may include parameters that UE 115-g may use to initiate communications with target base station 105-g. At 537, UE 115-g may stop the connection with source base station 105-f. At 538, UE 115-g may perform adjustments according to the target configuration.

[0164] At 540, source base station 105-f may transmit an SN status transfer message to target base station 105-g. The SN status transfer message may include a downlink delivery status per MRB and/or a last PDCP SN served to UE 115-g by source base station 105-f. At 545, target base station 105-g may transmit an SN status update or SN transfer information message to source base station 105-f. The SN status update or SN transfer information message may indicate an expected PDCP SN range per MRB (e.g., the NACKed PDCP SNs at the target cell until the current target cell serves PDCP SN), PDCP SNs that target base station 105-g is currently serving, an indication about data tunneling, PDCP SNs used for data tunneling, or any combination thereof. At 550, source base station 105-f may forward MB data to target base station 105-g.

[0165] Source base station 105-f may perform data forwarding for MRB (e.g., at 550) if an MB-N3 tunnel for a UE interested or receiving MRB is not available at target base station 105-g and/or the target base station 105-g broadcasts or multicasts packets ahead of source base station 105-f. With regards to PDCP SN continuity, at UPF 205-c, a same payload (e.g., an internet protocol (IP) packet) may be assigned with a same GTP-U SN in each N3 tunnel between base stations 105 and UPF 205-b. Base station PDCP SN allocation and N3 GTP-U SN allocation at UPF 205-c may have a one-to-one mapping. In some cases, UE 115-g may use a sync protocol between UPF 205-c and base stations 105 for synchronizing data transmission from UPF 205-c to multiple base stations 105.

[0166] In some examples, the handover request transmitted at 520 may indicate a current PDCP SN and/or one or more previously non-ACKed (or missed) packets. Additionally or alternatively, target base station 105-g may determine, based on receiving the handover request, an indication that source base station 105-f is requesting to forward data per MRB. In the handover response (e.g., the handover request acknowledgement transmitted at 530), target base station 105-g may indicate that it accepts data forwarding based on N3-tunnel availability and current PDCP SN at target base station 105-g. Additionally, target base station 105-g may indicate a current PDCP SN, a desired PDCP SN range, explicit PDCP SNs, or a combination thereof. Target base station 105-g may indicate to source base station 105-f to stop data forwarding if target base station 105-g has received the corresponding packets from UPF 205-a. Such information may be indicated by a control plane (e.g., the SN status update or SN transfer info transmitted at 545) or a user plane (e.g., a downlink data delivery status (DDDS) message). In such cases, target base station 105-g may not receive an endmark as there may be no path switch for the MRB at UPF 205-c from source base station 105-f to target base station 105-g. [0167] In other examples, source base station 105-f may indicate a MRB bearer type in the handover request transmitted at 520. Additionally, target base station 105-g may indicate whether MRB data forwarding is optional and/or to be utilized in the handover request acknowledgement message transmitted at 530. If a data forwarding request (if MRB data forwarding is to be utilized) is received from target base station 105-g, source base station 105-f may indicate a PDCP SN and/or non-ACKed (or missed) packets in the SN status transfer message transmitted at 540. Alternatively, without a data forwarding request received from target base station 105-g, source base station 105-f may indicate PDCP SN and/or previously not-ACKed (or missed) packets in SN status transfer message transmitted at 540. In the SN status update message at 545, target base station 105-g may request for which packets to be forwarded by a current PDCP SN, a desired start SN range, explicit SNs requested, or a combination thereof.

[0168] In yet other examples, source base station 105-f may indicate MRB bearer type in the handover request message transmitted at 520. Target base station 105-g may indicate whether MRB data forwarding is to be used or not in the handover request acknowledgement message transmitted at 530. If source base station 105-f receives a data forwarding request, as described herein, from target base station 105-g, source base station 105-f may forward downlink PDCP service data units (SDU) to target base station 105-g. After successful handover completion to target base station 105-g, UE 115-g may transmit a PDCP status report (e.g., at 560) that indicates which PDCP SNs are not received yet. In such cases, target base station 105-g may transmit a new SN status update and/or a handover complete message to source base station 105-f indicating at which PDCP SN to stop data forwarding.

[0169] For lossless handover, the SN status transfer (e.g., at 540) and PDCP status report (e.g., at 560) may be extended to support MRB PDCP SN status transfer. Target base station 105-g may start MB PDU buffering based on the handover request (e.g., at 520) or SN status transfer (e.g., at 540) from source base station 105-f. Target base station 105-g may deliver missed PDUs to UE 115-g based on the PDCP status report (e.g., at 560) and/or the SN status report or transfer (e.g., at 540).

[0170] At 555, UE 115-g may transmit an RRC reconfiguration complete message to target base station 105-g. The RRC reconfiguration complete message may indicate that UE 115-g has successfully completed handover with target base station 105-g. At 560, UE 115-g may transmit a PDCP status report to target base station 105-g. PDCP status report may indicate one or more PDUs that UE 115-g has successfully received and decoded. At 565, target base station 105-g may transmit a handover complete message to source base station 105-f, which may indicate to source base station 105-f that handover has occurred successfully.

[0171] At 570, target base station 105-g may transmit PDUs to UE 115-g that source base station 105-f transmitted to UE 115-g but UE 115-g did not successfully receive and decode (e.g., PDUs that source base station 105-f transmitted to UE 115-g and forwarded to base station 105-g due to UE 115-g failing to successfully receive and decode the PDUs). Target base station 105-g may transmit the PDUs via unicast. At 575, target base station 105-g may transmit new PDUs (e.g., PDUs that source base station 105-f did not transmit but forwarded to target base station 105-g or PDUs that target base station 105-g received directly from UPF 205-b) to UE 115-g.

[0172] At 580, source base station 105-f may determine whether to continue an MRB for other UEs 115 or whether to leave the MB-N3 broadcast tunnel. If determining to leave the MB-N3 broadcast tunnel, at 585, source base station 105-f may release (e.g., leave) a tunnel 210 (e.g., the MB-N3 tunnel) between target base station 105-g and 5GC (e.g., UPF 205-b). It should be noted that, in some cases, source base station 105-f of FIG. 4 may perform 580 prior to performing 485.

[0173] FIG. 6 illustrates an example of a process flow 600 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. In some examples, process flow 600 may implement aspects of wireless communications system 100. For instance, UE 115-h may be an example of a UE 115 as described with reference to FIG. 1 and base stations 105-h and 105-i may be examples of base stations 105 as described with reference to FIG. 1.

[0174] At 605, source base station 105-h may serve multicast traffic associated with one or more MRBs to UE 115-h. The multicast traffic may be multicast/broadcast traffic. UE 115-h may receive the multicast traffic.

[0175] At 610, UE 115-h may transmit a measurement report to base station 105-h. The measurement report may include one or more of RSRP measurements, RSRQ measurements, or multicast service measurements (e.g., MBS measurements). [0176] At 615, source base station 105-h may determine that UE 115-h is to be handed over to target base station 105-i for continued service of the multicast traffic to UE 115-h. In some cases, determining UE handover at 615 may be based on the measurement report.

[0177] At 620, source base station 105-h may transmit a handover request to target base station 105-i, where the handover request includes a current multicast context of UE 115-h identifying the one or more MRBs associated with the multicast traffic. In some cases, the current multicast context may include at least one of a TMGI or a multicast flow identity as identification for the one or more MRBs. In some cases, the current multicast context may include an MRB configuration of one or more MRBs for which UE 115-h is being served the multicast traffic. In some cases, the current multicast context may include a QoS profile of one or more MRBs for which UE 115-h is being served the multicast traffic. In some cases, the current multicast context may include at least one of a unicast assistance configuration or an association between one or more MRBs for which UE 115-h is being served the multicast traffic and one or more DRBs. Source base station 105-h may transmit the handover request to initiate handover preparation towards target base station 105-i. In some cases, the handover request may include a source cell MRB configuration, a list of MBS services, a UPF context used by the source cell (e.g., source base station 105-h) for receiving MBS data from the core network, or a combination thereof.

[0178] In some cases, an N3 tunnel for receipt of multicast traffic to UE 115-h may already be established at target base station 105-i prior to receiving the handover request. Alternatively, the N3 tunnel for receipt of multicast traffic to UE 115-h may be established at target base station 105-i after receiving the handover request but before transmission of a handover request acknowledgement. The establishment of the N3 tunnel may be based on the current multicast context for UE 115-h, The current multicast context for UE 115-h used to establish the N3 tunnel may be received from the core network.

[0179] At 625, target base station 105-i may transmit a handover request acknowledgement to source base station 105-h. The handover request acknowledgement may include at least one of a multicast flow-to-radio bearer mapping or a MRB/DRB configuration, which may also be referred to as an MRB-DRB configuration, for target base station 105-i. In some cases, the handover request acknowledgement may include a handover command, an indication of a data forwarding tunnel, an indication of establishment of MB- N3 at the target cell (e.g., at target base station 105-i), data forwarding tunneling information between source and target cells (e.g., between source base station 105-h and target base station 105-i), a current PDCP sequence number (SN) per MRB, a target cell MRB and/or DRB configuration, or a combination thereof.

[0180] At 630, source base station 105-h may transmit an RRC reconfiguration message to UE 115-h. The RRC reconfiguration message may include an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for target base station 105-i. The indication may be a delta indication with respect to a previous multicast flow-to-radio bearer mapping or MRB/DRB configuration.

[0181] At 635, source base station 105-h may transmit an SN status transfer message to target base station 105-i. The SN status transfer message may include a downlink delivery status of one or more MRBs for which UE 115-h is being served.

[0182] At 640, target base station 105-i may transmit an SN status update message to source base station 105-h. The SN status update message may include a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at target base station 105-i from source base station 105-h for one or more MRBs for which UE 115-h is being served.

[0183] At 645, source base station 105-h may forward a portion of the multicast traffic to target base station 105-i for service to UE 115-h in accordance with the current multicast context of UE 115-h. The portion of the multicast traffic that is forwarded may include traffic received at source base station 105-h after determination of UE handover (e.g., at 615) and before receipt of the handover complete message from target base station 105-i (e.g., at 655). In some cases, forwarding the portion of the multicast traffic to target base station 105-i may occur after transmission of the SN status transfer message. In some cases, forwarding the portion of the multicast traffic to target base station 105-i may occur after receipt of the SN status update message.

[0184] In some cases, forwarding the portion of the multicast traffic to target base station 105-i may include identifying, by source base station 105-h, that a mismatch exists between MRBs served by target base station 105-i and MRBs served by source base station 105-h, where forwarding the portion of the multicast traffic may be based on the mismatch. In some cases, the mismatch may be based on target base station 105-o not serving, at the time of the handover request (e.g., at 620), one or more MRBs that source base station 105-h was serving to UE 115-h. In some cases, the mismatch may be based on target base station 105-i serving one or more MRBs in advance of service of the same one or more MRBs by source base station 105-h. In some cases, identifying the mismatch may involve receiving, via the handover request acknowledgement transmitted at 625, one or more current SNs of data packets corresponding to one or more MRBs served by target base station 105-i and comparing the one or more current SNs of data served packets served by target base station 105-i with SNs served by source base station 105-h. Target base station 105-i, in some cases, may identify that the mismatch exists between MRBs served by target base station 105-i and MRBs served by source base station 105-h, and may receive the portion of the multicast traffic based on the mismatch.

[0185] In some cases, source base station 105-h and target base station 105-i may participate in a data forwarding negotiation that occurs between source base station 105-h and target base station 105-i, where forwarding the portion of the multicast traffic to target base station 105-i is based on the data forwarding negotiation. Participating in the data forwarding negotiation may involve transmitting, with the handover request at 620, a forwarding request for forwarding of data per MRB from source base station 105-h to target base station 105-i. The forwarding request may include a current PDCP SN for one or more MRBs at source base station 105-h. The forwarding request may further include an identification of additional PDCP SNs served by source base station 105-a but not acknowledgement by UE 115-h. Additionally, participating in the data forwarding negotiation may involve receiving, via the handover request acknowledgement at 625, a confirmation that data forwarding from source base station 105-h is to occur based on N3 tunnel availability at target base station 105-i for respective MRBs. In some cases, the confirmation may include at least one of a current PDCP SN for respective MRBs at target base station 105-i, a desired PDCP SN range for respective MRBs at target base station 105-i, one or more explicitly-indicated PDCP SNs for respective MRBs at target base station 105-i, or a combination thereof. In some cases, target base station 105-i may transmit a stop data forwarding message to source base station 105-h. The stop data forwarding message may indicate that the data forwarding from source base station 105-h is to stop. The stop data forwarding message may be received via one of an SN status update message (e.g., at 640) or a DDDS message. [0186] In some cases, participating in the data forwarding negotiation may involve transmitting, with the handover request at 620, an indication of MRB bearer-type for one or more MRBs at source base station 105-h. In such cases, base station 105-h may determine, from the handover request acknowledgement at 625, whether data forwarding from source base station 105-h to target base station 105-i is to occur. Determining whether data forwarding is to occur may include receiving, via the handover request acknowledgement at 625, a confirmation that data forwarding is to occur. Additionally or alternatively, determining whether data forwarding is to occur may involve identifying that the handover request acknowledgement at 625 does not include a data forwarding message and determining that data forwarding from source base station 105-h to target base station 105-i is to occur based on an absence of the data forwarding message in the handover request acknowledgement.

[0187] In some cases, in response to a determination that data forwarding is to occur, source base station 105-h may transmit a forwarding indication to target base station 105-i. The forwarding indication may include a current PDCP SN for one or more MRBs at source base station 105-h. The forwarding indication may further include an identification of additional PDCP SNs served by source base station 105-h but not yet acknowledged by UE 115-h.

[0188] In some cases, source base station 105-h may forward downlink PDCP SDUs to target base station 105-i based on a determination that data forwarding is to occur and without further data forwarding negotiations between source base station 105-h and target base station 105-i. In such cases, target base station 105-i may transmit, to source base station 105-h, a SN status update message at 640 indicating to source base station 105-h a termination PDCP SN at which source base station 105-h is to stop data forwarding. Source base station 105-h may continue data forwarding until source base station 105-h reaches the termination PDCP SN.

[0189] At 650, UE 115-h may transmit an RRC reconfiguration complete message to target base station 105-i.

[0190] At 655, target base station 105-i may transmit a handover complete message to source base station 105-h, where the handover complete message is indicative that target base station 105-i is serving to UE 115-h the multicast traffic associated with the one or more multicast radio bearers.

[0191] At 660, UE 115-h may transmit, to target base station 105-i, a PDCP status report that includes an MRB receiving status for UE 115-h. In some cases, transmitting the PDCP status report may occur after transmitting the RRC reconfiguration complete message. In some cases, target base station 105-i may transmit, via a unicast transmission and in response to the PDCP status report, any PDUs identified by the PDCP status report as having not been received or decoded at UE 115-h.

[0192] At 665, target base station 105-i may serve the multicast traffic to UE 115-h based on the current multicast context of UE 115-h. In some cases, target base station 105-i may transmit ongoing PDUs of the multicast traffic from target base station 105-i via MRBs, DRBs, or a combination thereof. UE 115-h may receive the multicast traffic.

[0193] At 670, source base station 105-h may disconnect from an N3 tunnel providing the multicast traffic. Source base station 105-h may perform the disconnection from the N3 tunnel after receiving the handover complete message at 655.

[0194] In some cases, data packets having first data associated with a first MRB, and received at source base station 105-h may have same SNs as data packets having the first data, associated with the first MRB, and received at target base station 105-i. In some cases, a data packet associated with an MRB may have a GTP-U SN that maps in a one-to-one relationship with a PDCP SN at source base station 105-h.

[0195] FIG. 7 shows a block diagram 700 of a device 705 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 705 may be an example of aspects of a base station 105 as described herein. The device 705 may include a receiver 710, a communication manager 715, and a transmitter 720. The device 705 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0196] The receiver 710 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast service handover and data forwarding, etc.). Information may be passed on to other components of the device 705. The receiver 710 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 710 may utilize a single antenna or a set of antennas.

[0197] The communication manager 715 may serve multicast traffic (or multicast/broadcast traffic) associated with one or more multicast radio bearers to a UE, determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE, transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The communication manager 715 may also serve the multicast traffic to the UE based on the current multicast context of the UE, receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and receive, from the UE, a radio resource control reconfiguration complete message. The communication manager 715 may be an example of aspects of the communication manager 1010 described herein.

[0198] In some examples, the communication manager 715 performing the methods described herein may be associated with one or more advantages. For instance, the methods described herein may enable communication manager 715 to perform lossless handover for an MRB. Accordingly, no packets of multicast traffic to be transmitted by a UE may be lost. Thus, by performing lossless handover, the communication manager 715 may increase the efficiency of communications.

[0199] The communication manager 715, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communication manager 715, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field- programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0200] The communication manager 715, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communication manager 715, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communication manager 715, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

[0201] The transmitter 720 may transmit signals generated by other components of the device 705. In some examples, the transmitter 720 may be collocated with a receiver 710 in a transceiver module. For example, the transmitter 720 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 720 may utilize a single antenna or a set of antennas.

[0202] FIG. 8 shows a block diagram 800 of a device 805 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a device 705, or a base station 105 as described herein. The device 805 may include a receiver 810, a communication manager 815, and a transmitter 845. The device 805 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0203] The receiver 810 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast service handover and data forwarding, etc.). Information may be passed on to other components of the device 805. The receiver 810 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 810 may utilize a single antenna or a set of antennas. [0204] The communication manager 815 may be an example of aspects of the communication manager 715 as described herein. The communication manager 815 may include a multicast traffic serving component 820, a handover determination component 825, a handover request component 830, a handover complete component 835, and a RRC reconfiguration complete component 840. The communication manager 815 may be an example of aspects of the communication manager 1010 described herein.

[0205] The multicast traffic serving component 820 may serve multicast traffic associated with one or more multicast radio bearers to a UE. The multicast traffic serving component 820 may serve the multicast traffic to the UE based on the current multicast context of the UE.

[0206] The handover determination component 825 may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE.

[0207] The handover request component 830 may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. The handover request component 830 may receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic.

[0208] The handover complete component 835 may receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The handover complete component 835 may transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station.

[0209] The RRC reconfiguration complete component 840 may receive, from the UE, a radio resource control reconfiguration complete message.

[0210] The transmitter 845 may transmit signals generated by other components of the device 805. In some examples, the transmitter 845 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 845 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 845 may utilize a single antenna or a set of antennas.

[0211] FIG. 9 shows a block diagram 900 of a communication manager 905 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The communication manager 905 may be an example of aspects of a communication manager 715, a communication manager 815, or a communication manager 1010 described herein. The communication manager 905 may include a multicast traffic serving component 910, a handover determination component 915, a handover request component 920, a handover complete component 925, a data traffic forwarding component 930, a SN status transfer component 935, a SN status update component 940, a handover request acknowledgement (ACK) component 945, a SN comparing component 950, a RRC reconfiguration component 955, a measurement report component 960, a tunnel disconnection component 965, a RRC reconfiguration complete component 970, a PDCP status report receiver 975, and a PDU transmitter 980. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0212] The multicast traffic serving component 910 may serve multicast traffic associated with one or more multicast radio bearers to a UE. In some examples, the multicast traffic serving component 910 may serve the multicast traffic to the UE based on the current multicast context of the UE.

[0213] The handover determination component 915 may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. In some examples, the handover determination component 915 may determine UE handover based on the measurement report.

[0214] The handover request component 920 may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. In some examples, the handover request component 920 may receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic.

[0215] In some examples, the handover request component 920 may include, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity. In some examples, the handover request component 920 may include, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE is being served the multicast traffic. In some examples, the handover request component 920 may include, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE is being served the multicast traffic. In some examples, the handover request component 920 may include, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

[0216] In some examples, the handover request component 920 may transmit, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station. In some examples, the handover request component 920 may receive, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity. In some examples, the handover request component 920 may receive, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE is being served the multicast traffic. In some examples, the handover request component 920 may receive, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE is being served the multicast traffic.

[0217] In some examples, the handover request component 920 may receive, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers. In some examples, the handover request component 920 may receive, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station. [0218] The handover complete component 925 may receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. In some examples, the handover complete component 925 may transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station.

[0219] The data traffic forwarding component 930 may forward a portion of the multicast traffic to the target base station for service to the UE in accordance with the current multicast context of the UE, where the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station. In some examples, the data traffic forwarding component 930 may identify that a mismatch exists between first multicast radio bearers served by the target base station and second multicast radio bearers served by the source base station, where forwarding the portion of the multicast traffic is based on the mismatch. In some examples, the data traffic forwarding component 930 may participate in a data forwarding negotiation that occurs between the source base station and the target base station, where forwarding the portion of the multicast traffic to the target base station is based on the data forwarding negotiation. In some examples, the data traffic forwarding component 930 may transmit, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, where the forwarding request includes a current PDCP sequence number for the one or more multicast radio bearers at the source base station. In some examples, the forwarding request further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE. In some examples, the confirmation may include at least one of a current PDCP sequence number for the respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station. In some examples, the mismatch is based on the target base station not serving, at a time of the handover request, the first multicast radio bearers that the source base station was serving to the UE. In some examples, the mismatch may be based on the target base station serving the second multicast radio bearers in advance of service of the same second radio bearers by the source base station.

[0220] In some examples, the data traffic forwarding component 930 may receive a stop data forwarding message from the target base station, indicating that the data forwarding from the source base station is to stop, where the stop data forwarding message is received via one of a sequence number status update message or a downlink data delivery status (DDDS) message. In some examples, the data traffic forwarding component 930 may determine, from a handover request acknowledgement responding to the handover request, whether data forwarding from the source base station to the target base station is to occur. In some examples, the data traffic forwarding component 930 may receive, via the handover request acknowledgement, a confirmation that data forwarding is to occur. In some examples, the data traffic forwarding component 930 may determine that data forwarding from the source base station to the target base station is to occur based on an absence of the data forwarding message in the handover request acknowledgement.

[0221] In some examples, the data traffic forwarding component 930 may transmit, in response to a determination that data forwarding is to occur, a forwarding indication from the source base station to the target base station, where the forwarding indication includes a current PDCP sequence number for one or more multicast radio bearers at the source base station. In some examples, the forwarding indication further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE. In some examples, the data traffic forwarding component 930 may forward, from the source base station to the target base station, downlink PDCP service data units (SDUs) based on a determination that data forwarding is to occur and without further data forwarding negotiations between the source base station and the target base station. In some examples, the data traffic forwarding component 930 may continue data forwarding until the source base station reaches the termination PDCP sequence number. In some examples, the data traffic forwarding component 930 may receive a portion of the multicast traffic forwarded from the source base station for service to the UE in accordance with the current multicast context of the UE, where the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station. [0222] In some examples, the data traffic forwarding component 930 may identify that a mismatch exists between multicast radio bearers served by the target base station and multicast radio bearers served by the source base station, where receiving the portion of the multicast traffic is based on the mismatch. In some examples, the data traffic forwarding component 930 may transmit, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to second multicast radio bearers served by the target base station. In some examples, the data traffic forwarding component 930 may participate in a data forwarding negotiation that occurs between the source base station and the target base station, where receiving the portion of the multicast traffic forwarded from the source base station is based on the data forwarding negotiation.

[0223] In some examples, the data traffic forwarding component 930 may receive, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, where the forwarding request includes a current PDCP sequence number for one or more multicast radio bearers at the source base station. In some examples, the data traffic forwarding component 930 may transmit a stop data forwarding message to the source base station, indicating that the data forwarding from the source base station is to stop, where the stop data forwarding message is transmitted via one of a sequence number status update message or a downlink data delivery status (DDDS) message. In some examples, the data traffic forwarding component 930 may receive a forwarding indication from the source base station, where the forwarding indication includes a current PDCP sequence number for one or more multicast radio bearers at the source base station.

[0224] In some examples, the data traffic forwarding component 930 may receive, from the source base station, downlink PDCP service data units (SDUs) without further data forwarding negotiations between the source base station and the target base station. In some cases, the forwarding request further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE. In some cases, the forwarding indication further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE. In some cases, the forwarding request further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE. In some cases, the forwarding indication further includes an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0225] The SN status transfer component 935 may transmit a sequence number status transfer message to the target base station, where the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE is being served. In some examples, forwarding the portion of the multicast traffic to the target base station may occur after transmission of the sequence number status transfer message. In some examples, the SN status transfer component 935 may receive a sequence number status transfer message from the source base station, where the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE is being served.

[0226] The SN status update component 940 may receive a sequence number status update message from the target base station, where the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE is being served. In some examples, forwarding the portion of the multicast traffic to the target base station occurs after receipt of the sequence number status update message. In some examples, the SN status update component 940 may receive, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station. In some examples, the SN status update component 940 may receive, from the target base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding.

[0227] In some examples, the SN status update component 940 may transmit a sequence number status update message to the source base station, where the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE is being served. In some examples, the SN status update component 940 may transmit, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station. In some examples, the SN status update component 940 may transmit, to the source base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding.

[0228] The handover request ACK component 945 may receive, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to one or more multicast radio bearers served by the target base station. In some examples, the handover request ACK component 945 may receive, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based on N3 tunnel availability at the target base station for respective multicast radio bearers. In some examples, the handover request ACK component 945 may identify that the handover request acknowledgement does not include a data forwarding message.

[0229] In some examples, the handover request ACK component 945 may receive, via a handover request acknowledgement from the target base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station. In some examples, the handover request ACK component 945 may transmit, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based on N3 tunnel availability at the target base station for respective multicast radio bearers. In some examples, the handover request ACK component 945 may transmit a handover request acknowledgement responding to the handover request, the handover request acknowledgement being indicative of whether data forwarding from the source base station to the target base station is to occur. In some examples, the indication may be a delta indication with respect to a previous multicast flow- to-radio bearer mapping or the MRB/DRB configuration.

[0230] In some examples, the handover request ACK component 945 may transmit, via the handover request acknowledgement, a confirmation that data forwarding is to occur. In some examples, the handover request ACK component 945 may transmit the handover request acknowledgement without a data forwarding message, where an absence of the data forwarding message in the handover request acknowledgement is indicative that data forwarding from the source base station to the target base station is to occur. In some examples, the handover request ACK component 945 may transmit, via a handover request acknowledgement to the source base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station.

[0231] In some cases, the confirmation includes at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station. In some cases, the confirmation includes at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0232] The SN comparing component 950 may compare the one or more current sequence numbers of data packets served by the target base station with sequence numbers served by the source base station.

[0233] The RRC reconfiguration component 955 may transmit a RRC reconfiguration message to the UE, where the RRC reconfiguration message includes an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for the target base station.

[0234] The measurement report component 960 may receive a measurement report from the UE. In some examples, the measurement report may include one or more of RSRP or RSRQ measurements or multicast service measurements.

[0235] The tunnel disconnection component 965 may disconnect from an N3 tunnel providing the multicast traffic after receiving the handover complete message.

[0236] The RRC reconfiguration complete component 970 may receive, from the UE, a radio resource control reconfiguration complete message. [0237] The PDCP status report receiver 975 may receive, from the UE and after transmitting the handover complete message, a PDCP status report that includes a multicast radio bearer receiving status for the UE.

[0238] The PDU transmitter 980 may transmit, via a unicast transmission to the UE and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE. In some examples, the PDU transmitter 980 may transmit ongoing packet data units of the multicast traffic to the UE via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

[0239] In some examples, a data packed associated with a multicast radio bearer may have a GTP-U sequence number that maps in a one-to-one relationship with a PDCP sequence number at the source base station. In some examples, the multicast traffic may be multicast/broadcast traffic.

[0240] FIG. 10 shows a diagram of a system 1000 including a device 1005 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 1005 may be an example of or include the components of device 705, device 805, or a base station 105 as described herein. The device 1005 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communication manager 1010, a network communications manager 1015, a transceiver 1020, an antenna 1025, memory 1030, a processor 1040, and an inter-station communications manager 1045. These components may be in electronic communication via one or more buses (e.g., bus 1050).

[0241] The communication manager 1010 may serve multicast traffic (or multicast/broadcast traffic) associated with one or more multicast radio bearers to a UE, determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE, transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The communication manager 1010 may also serve the multicast traffic to the UE based on the current multicast context of the UE, receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station, and receive, from the UE, a radio resource control reconfiguration complete message.

[0242] The network communications manager 1015 may manage communications with the core network (e.g., via one or more wired backhaul links). For example, the network communications manager 1015 may manage the transfer of data communications for client devices, such as one or more UEs 115.

[0243] The transceiver 1020 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1020 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1020 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

[0244] In some cases, the wireless device may include a single antenna 1025. However, in some cases the device may have more than one antenna 1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0245] The memory 1030 may include random-access memory (RAM) and read-only memory (ROM). The memory 1030 may store computer-readable, computer-executable code 1035 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1030 may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0246] The code 1035 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1035 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1035 may not be directly executable by the processor 1040 but may cause a computer (e.g., when compiled and executed) to perform functions described herein. [0247] The processor 1040 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 1040 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1040. The processor 1040 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1030) to cause the device 1005 to perform various functions (e.g., functions or tasks supporting multicast service handover and data forwarding).

[0248] The inter-station communications manager 1045 may manage communications with other base station 105, and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1045 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1045 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

[0249] FIG. 11 shows a block diagram 1100 of a device 1105 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 1105 may be an example of aspects of a UE 115 as described herein. The device 1105 may include a receiver 1110, a communication manager 1115, and a transmitter 1120. The device 1105 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0250] The receiver 1110 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast service handover and data forwarding, etc.). Information may be passed on to other components of the device 1105. The receiver 1110 may be an example of aspects of the transceiver 1415 described with reference to FIG. 14. The receiver 1110 may utilize a single antenna or a set of antennas.

[0251] The communication manager 1115 may receive, from a source base station, multicast traffic associated with one or more multicast radio bearers, receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers, transmit a measurement report to the source base station, receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, and transmit, to the target base station, a radio resource control reconfiguration complete message. The communication manager 1115 may be an example of aspects of the communication manager 1410 described herein.

[0252] In some examples, the communication manager 1115 performing the methods described herein may be associated with one or more advantages. For instance, the methods described herein may enable communication manager 1115 to perform lossless handover for an MRB. Accordingly, no packets of multicast traffic to be transmitted to a UE 115 (e.g., to communication manager 1115) may be lost. Thus, by participating in lossless handover, the communication manager 1115 may increase the efficiency of communications.

[0253] The communication manager 1115, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communication manager 1115, or its sub-components may be executed by a general-purpose processor, a DSP, an application-specific integrated circuit (ASIC), a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

[0254] The communication manager 1115, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communication manager 1115, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communication manager 1115, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure. [0255] The transmitter 1120 may transmit signals generated by other components of the device 1105. In some examples, the transmitter 1120 may be collocated with a receiver 1110 in a transceiver module. For example, the transmitter 1120 may be an example of aspects of the transceiver 1415 described with reference to FIG. 14. The transmitter 1120 may utilize a single antenna or a set of antennas.

[0256] FIG. 12 shows a block diagram 1200 of a device 1205 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 1205 may be an example of aspects of a device 1105, or a UE 115 as described herein. The device 1205 may include a receiver 1210, a communication manager 1215, and a transmitter 1240. The device 1205 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

[0257] The receiver 1210 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to multicast service handover and data forwarding, etc.). Information may be passed on to other components of the device 1205. The receiver 1210 may be an example of aspects of the transceiver 1415 described with reference to FIG. 14. The receiver 1210 may utilize a single antenna or a set of antennas.

[0258] The communication manager 1215 may be an example of aspects of the communication manager 1115 as described herein. The communication manager 1215 may include a multicast traffic receiver 1220, a measurement report transmitter 1225, a RRC reconfiguration receiver 1230, and a RRC reconfiguration complete transmitter 1235. The communication manager 1215 may be an example of aspects of the communication manager 1410 described herein.

[0259] The multicast traffic receiver 1220 may receive, from a source base station, multicast traffic associated with one or more multicast radio bearers and receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0260] The measurement report transmitter 1225 may transmit a measurement report to the source base station. [0261] The RRC reconfiguration receiver 1230 may receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station.

[0262] The RRC reconfiguration complete transmitter 1235 may transmit, to the target base station, a radio resource control reconfiguration complete message.

[0263] The transmitter 1240 may transmit signals generated by other components of the device 1205. In some examples, the transmitter 1240 may be collocated with a receiver 1210 in a transceiver module. For example, the transmitter 1240 may be an example of aspects of the transceiver 1415 described with reference to FIG. 14. The transmitter 1240 may utilize a single antenna or a set of antennas.

[0264] FIG. 13 shows a block diagram 1300 of a communication manager 1305 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The communication manager 1305 may be an example of aspects of a communication manager 1115, a communication manager 1215, or a communication manager 1410 described herein. The communication manager 1305 may include a multicast traffic receiver 1310, a measurement report transmitter 1315, a RRC reconfiguration receiver 1320, a RRC reconfiguration complete transmitter 1325, a PDCP status report transmitter 1330, and a PDU receiver 1335. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

[0265] The multicast traffic receiver 1310 may receive, from a source base station, multicast traffic associated with one or more multicast radio bearers. In some examples, the multicast traffic receiver 1310 may receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0266] The measurement report transmitter 1315 may transmit a measurement report to the source base station.

[0267] The RRC reconfiguration receiver 1320 may receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station.

[0268] The RRC reconfiguration complete transmitter 1325 may transmit, to the target base station, a radio resource control reconfiguration complete message.

[0269] The PDCP status report transmitter 1330 may transmit, to the target base station and after transmitting the radio resource control reconfiguration complete message, a PDCP status report that includes a multicast radio bearer receiving status for the UE.

[0270] The PDU receiver 1335 may receive, via a unicast transmission from the target base station and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE. In some examples, the PDU receiver 1335 may receive ongoing packet data units of the multicast traffic from the target base station via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

[0271] FIG. 14 shows a diagram of a system 1400 including a device 1405 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The device 1405 may be an example of or include the components of device 1105, device 1205, or a UE 115 as described herein. The device 1405 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communication manager 1410, a transceiver 1415, an antenna 1420, memory 1425, and a processor 1435. These components may be in electronic communication via one or more buses (e.g., bus 1440).

[0272] The communication manager 1410 may receive, from a source base station, multicast traffic associated with one or more multicast radio bearers, receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers, transmit a measurement report to the source base station, receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station, and transmit, to the target base station, a radio resource control reconfiguration complete message. [0273] The transceiver 1415 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1415 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1415 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

[0274] In some cases, the wireless device may include a single antenna 1420. However, in some cases the device may have more than one antenna 1420, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

[0275] The memory 1425 may include RAM and ROM. The memory 1425 may store computer-readable, computer-executable code 1430 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1425 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

[0276] The code 1430 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1430 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1430 may not be directly executable by the processor 1435 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

[0277] The processor 1435 may include an intelligent hardware device, (e.g., a general- purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof). In some cases, the processor 1435 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1435. The processor 1435 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1425) to cause the device 1405 to perform various functions (e.g., functions or tasks supporting multicast service handover and data forwarding). [0278] FIG. 15 shows a flowchart illustrating a method 1500 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1500 may be performed by a communication manager as described with reference to FIGs. 7 through 10. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the described functions. Additionally or alternatively, a base station may perform aspects of the described functions using special-purpose hardware.

[0279] At 1505, the base station may serve multicast traffic associated with one or more multicast radio bearers to a UE. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by a multicast traffic serving component as described with reference to FIGs. 7 through 10.

[0280] At 1510, the base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a handover determination component as described with reference to FIGs. 7 through 10.

[0281] At 1515, the base station may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a handover request component as described with reference to FIGs. 7 through 10.

[0282] At 1520, the base station may receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a handover complete component as described with reference to FIGs. 7 through 10. [0283] FIG. 16 shows a flowchart illustrating a method 1600 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1600 may be performed by a communication manager as described with reference to FIGs. 7 through 10. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the described functions. Additionally or alternatively, a base station may perform aspects of the described functions using special-purpose hardware.

[0284] At 1605, the base station may serve multicast traffic associated with one or more multicast radio bearers to a UE. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by a multicast traffic serving component as described with reference to FIGs. 7 through 10.

[0285] At 1610, the base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a handover determination component as described with reference to FIGs. 7 through 10.

[0286] At 1615, the base station may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, where the current multicast context includes as identification for the one or more multicast radio bearers at least one of a TMGI or an multicast flow identity. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a handover request component as described with reference to FIGs. 7 through 10.

[0287] At 1620, the base station may receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The operations of 1620 may be performed according to the methods described herein. In some examples, aspects of the operations of 1620 may be performed by a handover complete component as described with reference to FIGs. 7 through 10.

[0288] FIG. 17 shows a flowchart illustrating a method 1700 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1700 may be performed by a communication manager as described with reference to FIGs. 7 through 10. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the described functions. Additionally or alternatively, a base station may perform aspects of the described functions using special-purpose hardware.

[0289] At 1705, the base station may serve multicast traffic associated with one or more multicast radio bearers to a UE. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed by a multicast traffic serving component as described with reference to FIGs. 7 through 10.

[0290] At 1710, the base station may determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed by a handover determination component as described with reference to FIGs. 7 through 10.

[0291] At 1715, the base station may transmit a handover request to the target base station, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic, and where the current multicast context includes a multicast radio bearer configuration of one or more multicast radio bearers for which the UE is being served the multicast traffic. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be performed by a handover request component as described with reference to FIGs. 7 through 10.

[0292] At 1720, the base station may receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers. The operations of 1720 may be performed according to the methods described herein. In some examples, aspects of the operations of 1720 may be performed by a handover complete component as described with reference to FIGs. 7 through 10.

[0293] FIG. 18 shows a flowchart illustrating a method 1800 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The operations of method 1800 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1800 may be performed by a communication manager as described with reference to FIGs. 7 through 10. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the described functions. Additionally or alternatively, a base station may perform aspects of the described functions using special-purpose hardware.

[0294] At 1805, the base station may receive, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, where the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed by a handover request component as described with reference to FIGs. 7 through 10.

[0295] At 1810, the base station may receive, from the UE, a radio resource control reconfiguration complete message. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed by a RRC reconfiguration complete component as described with reference to FIGs. 7 through 10.

[0296] At 1815, the base station may transmit, based on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be performed by a handover complete component as described with reference to FIGs. 7 through 10.

[0297] At 1820, the base station may serve the multicast traffic to the UE based on the current multicast context of the UE. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be performed by a multicast traffic serving component as described with reference to FIGs. 7 through 10.

[0298] FIG. 19 shows a flowchart illustrating a method 1900 that supports multicast service handover and data forwarding in accordance with aspects of the present disclosure. The operations of method 1900 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1900 may be performed by a communication manager as described with reference to FIGs. 11 through 14. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the described functions. Additionally or alternatively, a UE may perform aspects of the described functions using special-purpose hardware.

[0299] At 1905, the UE may receive, from a source base station, multicast traffic associated with one or more multicast radio bearers. The operations of 1905 may be performed according to the methods described herein. In some examples, aspects of the operations of 1905 may be performed by a multicast traffic receiver as described with reference to FIGs. 11 through 14.

[0300] At 1910, the UE may transmit a measurement report to the source base station.

The operations of 1910 may be performed according to the methods described herein. In some examples, aspects of the operations of 1910 may be performed by a measurement report transmitter as described with reference to FIGs. 11 through 14.

[0301] At 1915, the UE may receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, where the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station. The operations of 1915 may be performed according to the methods described herein. In some examples, aspects of the operations of 1915 may be performed by a RRC reconfiguration receiver as described with reference to FIGs. 11 through 14.

[0302] At 1920, the UE may transmit, to the target base station, a radio resource control reconfiguration complete message. The operations of 1920 may be performed according to the methods described herein. In some examples, aspects of the operations of 1920 may be performed by a RRC reconfiguration complete transmitter as described with reference to FIGs. 11 through 14. [0303] At 1925, the UE may receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers. The operations of 1925 may be performed according to the methods described herein. In some examples, aspects of the operations of 1925 may be performed by a multicast traffic receiver as described with reference to FIGs. 11 through 14.

[0304] The following provides an overview of aspects of the present disclosure:

[0305] Aspect 1 : A method for wireless communication at a source base station, comprising: serving multicast traffic associated with one or more multicast radio bearers to a UE; determining that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE; transmitting a handover request to the target base station, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; and receiving a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

[0306] Aspect 2: The method of aspect 1, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

[0307] Aspect 3 : The method of any of aspects 1 through 2, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE is being served the multicast traffic.

[0308] Aspect 4: The method of any of aspects 1 through 3, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE is being served the multicast traffic.

[0309] Aspect 5 : The method of any of aspects 1 through 4, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

[0310] Aspect 6: The method of any of aspects 1 through 5, further comprising: forwarding a portion of the multicast traffic to the target base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

[0311] Aspect 7: The method of aspect 6, further comprising: transmitting a sequence number status transfer message to the target base station, wherein the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE is being served.

[0312] Aspect 8: The method of aspect 7, wherein forwarding the portion of the multicast traffic to the target base station occurs after transmission of the sequence number status transfer message.

[0313] Aspect 9: The method of any of aspects 7 through 8, further comprising: receiving a sequence number status update message from the target base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE is being served.

[0314] Aspect 10: The method of aspect 9, wherein forwarding the portion of the multicast traffic to the target base station occurs after receipt of the sequence number status update message.

[0315] Aspect 11 : The method of any of aspects 6 through 10, wherein forwarding the portion of the multicast traffic to the target base station further comprises: identifying that a mismatch exists between multicast radio bearers served by the target base station and multicast radio bearers served by the source base station, wherein forwarding the portion of the multicast traffic is based at least in part on the mismatch. [0316] Aspect 12: The method of aspect 11, wherein the mismatch is based on the target base station not serving, at a time of the handover request, one or more multicast radio bearers that the source base station was serving to the UE.

[0317] Aspect 13: The method of any of aspects 11 through 12, wherein the mismatch is based on the target base station serving one or more multicast radio bearers in advance of service of the same one or more multicast radio bearers by the source base station.

[0318] Aspect 14: The method of any of aspects 11 through 13, wherein identifying the mismatch comprises: receiving, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to one or more multicast radio bearers served by the target base station; and comparing the one or more current sequence numbers of data packets served by the target base station with sequence numbers served by the source base station.

[0319] Aspect 15: The method of any of aspects 6 through 14, further comprising: participating in a data forwarding negotiation that occurs between the source base station and the target base station, wherein forwarding the portion of the multicast traffic to the target base station is based at least in part on the data forwarding negotiation.

[0320] Aspect 16: The method of aspect 15, wherein participating in the data forwarding negotiation comprises: transmitting, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station; and receiving, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers.

[0321] Aspect 17: The method of aspect 16, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0322] Aspect 18: The method of any of aspects 16 through 17, wherein the confirmation comprises at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0323] Aspect 19: The method of any of aspects 16 through 18, further comprising: receiving a stop data forwarding message from the target base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is received via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

[0324] Aspect 20: The method of any of aspects 15 through 19, wherein participating in the data forwarding negotiation comprises: transmitting, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station; and determining, from a handover request acknowledgement responding to the handover request, whether data forwarding from the source base station to the target base station is to occur.

[0325] Aspect 21 : The method of aspect 20, wherein determining whether data forwarding is to occur comprises: receiving, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

[0326] Aspect 22: The method of any of aspects 20 through 21, wherein determining whether data forwarding is to occur comprises: identifying that the handover request acknowledgement does not include a data forwarding message; and determining that data forwarding from the source base station to the target base station is to occur based on an absence of the data forwarding message in the handover request acknowledgement.

[0327] Aspect 23: The method of any of aspects 20 through 22, further comprising: transmitting, in response to a determination that data forwarding is to occur, a forwarding indication from the source base station to the target base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station; and receiving, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station. [0328] Aspect 24: The method of aspect 23, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0329] Aspect 25: The method of any of aspects 20 through 24, further comprising: forwarding, from the source base station to the target base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) based on a determination that data forwarding is to occur and without further data forwarding negotiations between the source base station and the target base station; receiving, from the target base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding; and continuing data forwarding until the source base station reaches the termination PDCP sequence number.

[0330] Aspect 26: The method of any of aspects 1 through 25, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

[0331] Aspect 27: The method of any of aspects 1 through 26, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the source base station. [0332] Aspect 28: The method of any of aspects 1 through 27, further comprising: receiving, via a handover request acknowledgement from the target base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station; and transmitting an RRC reconfiguration message to the UE, wherein the RRC reconfiguration message includes an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for the target base station.

[0333] Aspect 29: The method of aspect 28, wherein the indication is a delta indication with respect to a previous multicast flow-to-radio bearer mapping or MRB/DRB configuration. [0334] Aspect 30: The method of any of aspects 1 through 29, wherein determining that the UE is to be handed over to the target base station comprises: receiving a measurement report from the UE; and determining UE handover based at least in part on the measurement report. [0335] Aspect 31 : The method of aspect 30, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

[0336] Aspect 32: The method of any of aspects 1 through 31, further comprising: disconnecting from an N3 tunnel providing the multicast traffic after receiving the handover complete message.

[0337] Aspect 33: The method of any of aspects 1 through 32, wherein the multicast traffic is multicast/broadcast traffic.

[0338] Aspect 34: A method for wireless communication at a target base station, comprising: receiving, at the target base station, a handover request from a source base station serving, to a UE, multicast traffic associated with one or more multicast radio bearers, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; receiving, from the UE, a radio resource control reconfiguration complete message; transmitting, based at least in part on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station; and serving the multicast traffic to the UE based at least in part on the current multicast context of the UE.

[0339] Aspect 35: The method of aspect 34, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

[0340] Aspect 36: The method of any of aspects 34 through 35, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, a multicast radio bearer configuration of one or more multicast radio bearers for which the UE is being served the multicast traffic. [0341] Aspect 37: The method of any of aspects 34 through 36, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, a quality of service profile of one or more multicast radio bearers for which the UE is being served the multicast traffic.

[0342] Aspect 38: The method of any of aspects 34 through 37, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, at least one of a unicast assistance configuration or an association between one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

[0343] Aspect 39: The method of any of aspects 34 through 38, further comprising: receiving a portion of the multicast traffic forwarded from the source base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

[0344] Aspect 40: The method of aspect 39, further comprising: receiving a sequence number status transfer message from the source base station, wherein the sequence number status transfer message includes a downlink delivery status of one or more multicast radio bearers for which the UE is being served.

[0345] Aspect 41 : The method of aspect 40, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after receipt of the sequence number status transfer message.

[0346] Aspect 42: The method of any of aspects 40 through 41, further comprising: transmitting a sequence number status update message to the source base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for one or more multicast radio bearers for which the UE is being served. [0347] Aspect 43 : The method of aspect 42, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after transmission of the sequence number status update message.

[0348] Aspect 44: The method of any of aspects 39 through 43, wherein receiving the portion of the multicast traffic forwarded from the source base station further comprises: identifying that a mismatch exists between multicast radio bearers served by the target base station and multicast radio bearers served by the source base station, wherein receiving the portion of the multicast traffic is based at least in part on the mismatch.

[0349] Aspect 45: The method of aspect 44, wherein the mismatch is based on the target base station not serving, at a time of the handover request, one or more multicast radio bearers that the source base station was serving to the UE.

[0350] Aspect 46: The method of any of aspects 44 through 45, wherein the mismatch is based on the target base station serving one or more multicast radio bearers in advance of service of the same one or more multicast radio bearers by the source base station.

[0351] Aspect 47: The method of any of aspects 44 through 46, further comprising: transmitting, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to one or more multicast radio bearers served by the target base station.

[0352] Aspect 48: The method of any of aspects 39 through 47, further comprising: participating in a data forwarding negotiation that occurs between the source base station and the target base station, wherein receiving the portion of the multicast traffic forwarded from the source base station is based at least in part on the data forwarding negotiation.

[0353] Aspect 49: The method of aspect 48, wherein participating in the data forwarding negotiation comprises: receiving, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station; and transmitting, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers. [0354] Aspect 50: The method of aspect 49, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0355] Aspect 51 : The method of any of aspects 49 through 50, wherein the confirmation comprises at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0356] Aspect 52: The method of any of aspects 49 through 51, further comprising: transmitting a stop data forwarding message to the source base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is transmitted via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

[0357] Aspect 53: The method of any of aspects 48 through 52, wherein participating in the data forwarding negotiation comprises: receiving, with the handover request, an indication of multicast radio bearer bearer-type for one or more multicast radio bearers at the source base station; and transmitting a handover request acknowledgement responding to the handover request, the handover request acknowledgement being indicative of whether data forwarding from the source base station to the target base station is to occur.

[0358] Aspect 54: The method of aspect 53, wherein transmitting the handover request acknowledgement comprises: transmitting, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

[0359] Aspect 55: The method of any of aspects 53 through 54, wherein transmitting the handover request acknowledgement comprises: transmitting the handover request acknowledgement without a data forwarding message, wherein an absence of the data forwarding message in the handover request acknowledgement is indicative that data forwarding from the source base station to the target base station is to occur.

[0360] Aspect 56: The method of any of aspects 53 through 55, further comprising: receiving a forwarding indication from the source base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for one or more multicast radio bearers at the source base station; and transmitting, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for respective multicast radio bearers at the target base station.

[0361] Aspect 57: The method of aspect 56, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

[0362] Aspect 58: The method of any of aspects 53 through 57, further comprising: receiving, from the source base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) without further data forwarding negotiations between the source base station and the target base station; and transmitting, to the source base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding.

[0363] Aspect 59: The method of any of aspects 34 through 58, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

[0364] Aspect 60: The method of any of aspects 34 through 59, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the target base station.

[0365] Aspect 61 : The method of any of aspects 34 through 60, further comprising: transmitting, via a handover request acknowledgement to the source base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station.

[0366] Aspect 62: The method of any of aspects 34 through 61, wherein an N3 tunnel for receipt of multicast traffic to the UE is already established at the target base station prior to receiving the handover request. [0367] Aspect 63: The method of any of aspects 34 through 62, wherein an N3 tunnel for receipt of multicast traffic to the UE is established at the target base station after receiving the handover request but before transmission of a handover request acknowledgement.

[0368] Aspect 64: The method of aspect 63, wherein establishment of the N3 tunnel is based on the current multicast context for the UE.

[0369] Aspect 65: The method of aspect 64, wherein the current multicast context for the UE used to establish the N3 tunnel is received from a core network.

[0370] Aspect 66: The method of any of aspects 34 through 65, further comprising: receiving, from the UE and after transmitting the handover complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; transmitting, via a unicast transmission to the UE and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and transmitting ongoing packet data units of the multicast traffic to the UE via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

[0371] Aspect 67: The method of any of aspects 34 through 66, wherein the multicast traffic is multicast/broadcast traffic.

[0372] Aspect 68: A method for wireless communication at a UE, comprising: receiving, from a source base station, multicast traffic associated with one or more multicast radio bearers; transmitting a measurement report to the source base station; receiving, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, wherein the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station; transmitting, to the target base station, a radio resource control reconfiguration complete message; and receiving, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

[0373] Aspect 69: The method of aspect 68, further comprising: transmitting, to the target base station and after transmitting the radio resource control reconfiguration complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; receiving, via a unicast transmission from the target base station and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and receiving ongoing packet data units of the multicast traffic from the target base station via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

[0374] Aspect 70: The method of any of aspects 68 through 69, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

[0375] Aspect 71 : The method of any of aspects 68 through 70, wherein the multicast traffic is multicast/broadcast traffic.

[0376] Aspect 72: A source base station, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the source base station to perform a method of any of aspects 1 through 33.

[0377] Aspect 73 : A source base station, comprising at least one means for performing a method of any of aspects 1 through 33.

[0378] Aspect 74: A non-transitory computer-readable medium storing code for wireless communication at a source base station, the code comprising instructions executable by a processor to perform a method of any of aspects 1 through 33.

[0379] Aspect 75: A target base station, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the target base station to perform a method of any of aspects 34 through 67.

[0380] Aspect 76: A target base station, comprising at least one means for performing a method of any of aspects 34 through 67.

[0381] Aspect 77: A non-transitory computer-readable medium storing code for wireless communication at a target base station, the code comprising instructions executable by a processor to perform a method of any of aspects 34 through 67.

[0382] Aspect 78: A UE, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the UE to perform a method of any of aspects 68 through 71. [0383] Aspect 79: A UE, comprising at least one means for performing a method of any of aspects 68 through 71.

[0384] Aspect 80: A non-transitory computer-readable medium storing code for wireless communication at a UE, the code comprising instructions executable by a processor to perform a method of any of aspects 68 through 71.

[0385] It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

[0386] Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

[0387] Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0388] The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0389] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

[0390] Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media. [0391] As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of’ or “one or more of’) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on.”

[0392] In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

[0393] The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration,” and not “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

[0394] The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

CLAIMS What is claimed is:

1. A method for wireless communication at a source base station, comprising: serving multicast traffic associated with one or more multicast radio bearers to a user equipment (UE); determining that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE; transmitting a handover request to the target base station, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; and receiving a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

2. The method of claim 1, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

3. The method of claim 1, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, a multicast radio bearer configuration of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

4. The method of claim 1, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, a quality of service profile of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

5. The method of claim 1, wherein transmitting the handover request to the target base station further comprises: including, in the current multicast context, at least one of a unicast assistance configuration or an association between the one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

6. The method of claim 1, further comprising: forwarding a portion of the multicast traffic to the target base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

7. The method of claim 6, further comprising: transmitting a sequence number status transfer message to the target base station, wherein the sequence number status transfer message includes a downlink delivery status of the one or more multicast radio bearers for which the UE is being served.

8. The method of claim 7, wherein forwarding the portion of the multicast traffic to the target base station occurs after transmission of the sequence number status transfer message.

9. The method of claim 7, further comprising: receiving a sequence number status update message from the target base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for the one or more multicast radio bearers for which the UE is being served.

10. The method of claim 9, wherein forwarding the portion of the multicast traffic to the target base station occurs after receipt of the sequence number status update message.

11. The method of claim 6, wherein forwarding the portion of the multicast traffic to the target base station further comprises: identifying that a mismatch exists between first multicast radio bearers served by the target base station and second multicast radio bearers served by the source base station, wherein forwarding the portion of the multicast traffic is based at least in part on the mismatch.

12. The method of claim 11, wherein the mismatch is based on the target base station not serving, at a time of the handover request, the first multicast radio bearers that the source base station was serving to the UE.

13. The method of claim 11, wherein the mismatch is based on the target base station serving the second multicast radio bearers in advance of service of the same second radio bearers by the source base station.

14. The method of claim 11, wherein identifying the mismatch comprises: receiving, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to the second multicast radio bearers served by the target base station; and comparing the one or more current sequence numbers of data packets served by the target base station with sequence numbers served by the source base station.

15. The method of claim 6, further comprising: participating in a data forwarding negotiation that occurs between the source base station and the target base station, wherein forwarding the portion of the multicast traffic to the target base station is based at least in part on the data forwarding negotiation.

16. The method of claim 15, wherein participating in the data forwarding negotiation comprises: transmitting, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and receiving, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers.

17. The method of claim 16, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

18. The method of claim 16, wherein the confirmation comprises at least one of a current PDCP sequence number for the respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

19. The method of claim 16, further comprising: receiving a stop data forwarding message from the target base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is received via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

20. The method of claim 15, wherein participating in the data forwarding negotiation comprises: transmitting, with the handover request, an indication of multicast radio bearer bearer-type for the one or more multicast radio bearers at the source base station; and determining, from a handover request acknowledgement responding to the handover request, whether data forwarding from the source base station to the target base station is to occur.

21. The method of claim 20, wherein determining whether data forwarding is to occur comprises: receiving, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

22. The method of claim 20, wherein determining whether data forwarding is to occur comprises: identifying that the handover request acknowledgement does not include a data forwarding message; and determining that data forwarding from the source base station to the target base station is to occur based on an absence of the data forwarding message in the handover request acknowledgement.

23. The method of claim 20, further comprising: transmitting, in response to a determination that data forwarding is to occur, a forwarding indication from the source base station to the target base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and receiving, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

24. The method of claim 23, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

25. The method of claim 20, further comprising: forwarding, from the source base station to the target base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) based on a determination that data forwarding is to occur and without further data forwarding negotiations between the source base station and the target base station; receiving, from the target base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding; and continuing data forwarding until the source base station reaches the termination PDCP sequence number.

26. The method of claim 1, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

27. The method of claim 1, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the source base station.

28. The method of claim 1, further comprising: receiving, via a handover request acknowledgement from the target base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station; and transmitting a radio resource control (RRC) reconfiguration message to the UE, wherein the RRC reconfiguration message includes an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for the target base station.

29. The method of claim 28, wherein the indication is a delta indication with respect to a previous multicast flow-to-radio bearer mapping or the MRB/DRB configuration.

30. The method of claim 1, wherein determining that the UE is to be handed over to the target base station comprises: receiving a measurement report from the UE; and determining UE handover based at least in part on the measurement report.

31. The method of claim 30, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

32. The method of claim 1, further comprising: disconnecting from an N3 tunnel providing the multicast traffic after receiving the handover complete message.

33. The method of claim 1, wherein the multicast traffic is multicast/broadcast traffic.

34. A method for wireless communication at a target base station, comprising: receiving, at the target base station, a handover request from a source base station serving, to a user equipment (UE), multicast traffic associated with one or more multicast radio bearers, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; receiving, from the UE, a radio resource control reconfiguration complete message; transmitting, based at least in part on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station; and serving the multicast traffic to the UE based at least in part on the current multicast context of the UE.

35. The method of claim 34, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

36. The method of claim 34, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, a multicast radio bearer configuration of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

37. The method of claim 34, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, a quality of service profile of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

38. The method of claim 34, wherein receiving the handover request from the source base station further comprises: receiving, in the current multicast context, at least one of a unicast assistance configuration or an association between the one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

39. The method of claim 34, further comprising: receiving a portion of the multicast traffic forwarded from the source base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

40. The method of claim 39, further comprising: receiving a sequence number status transfer message from the source base station, wherein the sequence number status transfer message includes a downlink delivery status of the one or more multicast radio bearers for which the UE is being served.

41. The method of claim 40, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after receipt of the sequence number status transfer message.

42. The method of claim 40, further comprising: transmitting a sequence number status update message to the source base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for the one or more multicast radio bearers for which the UE is being served.

43. The method of claim 42, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after transmission of the sequence number status update message.

44. The method of claim 39, wherein receiving the portion of the multicast traffic forwarded from the source base station further comprises: identifying that a mismatch exists between first multicast radio bearers served by the target base station and second multicast radio bearers served by the source base station, wherein receiving the portion of the multicast traffic is based at least in part on the mismatch.

45. The method of claim 44, wherein the mismatch is based on the target base station not serving, at a time of the handover request, the first multicast radio bearers that the source base station was serving to the UE.

46. The method of claim 44, wherein the mismatch is based on the target base station serving the second multicast radio bearers in advance of service of the same second multicast radio bearers by the source base station.

47. The method of claim 44, further comprising: transmitting, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to the second multicast radio bearers served by the target base station.

48. The method of claim 39, further comprising: participating in a data forwarding negotiation that occurs between the source base station and the target base station, wherein receiving the portion of the multicast traffic forwarded from the source base station is based at least in part on the data forwarding negotiation.

49. The method of claim 48, wherein participating in the data forwarding negotiation comprises: receiving, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and transmitting, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers.

50. The method of claim 49, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

51. The method of claim 49, wherein the confirmation comprises at least one of a current PDCP sequence number for the respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

52. The method of claim 49, further comprising: transmitting a stop data forwarding message to the source base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is transmitted via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

53. The method of claim 48, wherein participating in the data forwarding negotiation comprises: receiving, with the handover request, an indication of multicast radio bearer bearer-type for the one or more multicast radio bearers at the source base station; and transmitting a handover request acknowledgement responding to the handover request, the handover request acknowledgement being indicative of whether data forwarding from the source base station to the target base station is to occur.

54. The method of claim 53, wherein transmitting the handover request acknowledgement comprises: transmitting, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

55. The method of claim 53, wherein transmitting the handover request acknowledgement comprises: transmitting the handover request acknowledgement without a data forwarding message, wherein an absence of the data forwarding message in the handover request acknowledgement is indicative that data forwarding from the source base station to the target base station is to occur.

56. The method of claim 53, further comprising: receiving a forwarding indication from the source base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and transmitting, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

57. The method of claim 56, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

58. The method of claim 53, further comprising: receiving, from the source base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) without further data forwarding negotiations between the source base station and the target base station; and transmitting, to the source base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding.

59. The method of claim 34, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

60. The method of claim 34, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the target base station.

61. The method of claim 34, further comprising: transmitting, via a handover request acknowledgement to the source base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station.

62. The method of claim 34, wherein an N3 tunnel for receipt of multicast traffic to the UE is already established at the target base station prior to receiving the handover request.

63. The method of claim 34, wherein an N3 tunnel for receipt of multicast traffic to the UE is established at the target base station after receiving the handover request but before transmission of a handover request acknowledgement.

64. The method of claim 63, wherein establishment of the N3 tunnel is based on the current multicast context for the UE.

65. The method of claim 64, wherein the current multicast context for the UE used to establish the N3 tunnel is received from a core network.

66. The method of claim 34, further comprising: receiving, from the UE and after transmitting the handover complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; transmitting, via a unicast transmission to the UE and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and transmitting ongoing packet data units of the multicast traffic to the UE via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

67. The method of claim 34, wherein the multicast traffic is multicast/broadcast traffic.

68. A method for wireless communication at a user equipment (UE), comprising: receiving, from a source base station, multicast traffic associated with one or more multicast radio bearers; transmitting a measurement report to the source base station; receiving, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, wherein the radio resource control reconfiguration message includes an indication of at least one multicast flow-to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station; transmitting, to the target base station, a radio resource control reconfiguration complete message; and receiving, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

69. The method of claim 68, further comprising: transmitting, to the target base station and after transmitting the radio resource control reconfiguration complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; receiving, via a unicast transmission from the target base station and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and receiving ongoing packet data units of the multicast traffic from the target base station via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

70. The method of claim 68, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

71. The method of claim 68, wherein the multicast traffic is multicast/broadcast traffic.

72. A source base station, comprising: a processor, memory coupled with the processor, and instructions stored in the memory and executable by the processor to cause the source base station to: serve multicast traffic associated with one or more multicast radio bearers to a user equipment (UE); determine that the UE is to be handed over to a target base station for continued service of the multicast traffic to the UE; transmit a handover request to the target base station, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; and receive a handover complete message from the target base station, the handover complete message indicative that the target base station is serving to the UE the multicast traffic associated with the one or more multicast radio bearers.

73. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: include, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

74. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: include, in the current multicast context, a multicast radio bearer configuration of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

75. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: include, in the current multicast context, a quality of service profile of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

76. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: include, in the current multicast context, at least one of a unicast assistance configuration or an association between the one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

77. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: forward a portion of the multicast traffic to the target base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

78. The source base station of claim 77, wherein the instructions are further executable by the processor to cause the source base station to: transmit a sequence number status transfer message to the target base station, wherein the sequence number status transfer message includes a downlink delivery status of the one or more multicast radio bearers for which the UE is being served.

79. The source base station of claim 78, wherein forwarding the portion of the multicast traffic to the target base station occurs after transmission of the sequence number status transfer message.

80. The source base station of claim 78, wherein the instructions are further executable by the processor to cause the source base station to: receive a sequence number status update message from the target base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for the one or more multicast radio bearers for which the UE is being served.

81. The source base station of claim 80, wherein forwarding the portion of the multicast traffic to the target base station occurs after receipt of the sequence number status update message.

82. The source base station of claim 77, wherein the instructions are further executable by the processor to cause the source base station to: identify that a mismatch exists between first multicast radio bearers served by the target base station and second multicast radio bearers served by the source base station, wherein forwarding the portion of the multicast traffic is based at least in part on the mismatch.

83. The source base station of claim 82, wherein the mismatch is based on the target base station not serving, at a time of the handover request, the first multicast radio bearers that the source base station was serving to the UE.

84. The source base station of claim 82, wherein the mismatch is based on the target base station serving the second multicast radio bearers in advance of service of the same second multicast radio bearers by the source base station.

85. The source base station of claim 82, wherein the instructions to identify the mismatch are executable by the processor to cause the source base station to: receive, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to the second multicast radio bearers served by the target base station; and compare the one or more current sequence numbers of data packets served by the target base station with sequence numbers served by the source base station.

86. The source base station of claim 77, wherein the instructions are further executable by the processor to cause the source base station to: participate in a data forwarding negotiation that occurs between the source base station and the target base station, wherein forwarding the portion of the multicast traffic to the target base station is based at least in part on the data forwarding negotiation.

87. The source base station of claim 86, wherein the instructions to participate in the data forwarding negotiation are executable by the processor to cause the source base station to: transmit, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and receive, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers.

88. The source base station of claim 87, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

89. The source base station of claim 87, wherein the confirmation comprises at least one of a current PDCP sequence number for the respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

90. The source base station of claim 87, wherein the instructions are further executable by the processor to cause the source base station to: receive a stop data forwarding message from the target base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is received via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

91. The source base station of claim 86, wherein the instructions to participate in the data forwarding negotiation are executable by the processor to cause the source base station to: transmit, with the handover request, an indication of multicast radio bearer bearer-type for the one or more multicast radio bearers at the source base station; and determine, from a handover request acknowledgement responding to the handover request, whether data forwarding from the source base station to the target base station is to occur.

92. The source base station of claim 91, wherein the instructions to determine whether data forwarding is to occur are executable by the processor to cause the source base station to: receive, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

93. The source base station of claim 91, wherein the instructions to determine whether data forwarding is to occur are executable by the processor to cause the source base station to: identify that the handover request acknowledgement does not include a data forwarding message; and determine that data forwarding from the source base station to the target base station is to occur based on an absence of the data forwarding message in the handover request acknowledgement.

94. The source base station of claim 91, wherein the instructions are further executable by the processor to cause the source base station to: transmit, in response to a determination that data forwarding is to occur, a forwarding indication from the source base station to the target base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and receive, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

95. The source base station of claim 94, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

96. The source base station of claim 91, wherein the instructions are further executable by the processor to cause the source base station to: forward, from the source base station to the target base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) based on a determination that data forwarding is to occur and without further data forwarding negotiations between the source base station and the target base station; receive, from the target base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding; and continue data forwarding until the source base station reaches the termination PDCP sequence number.

97. The source base station of claim 72, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

98. The source base station of claim 72, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the source base station.

99. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: receive, via a handover request acknowledgement from the target base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station; and transmit a radio resource control (RRC) reconfiguration message to the UE, wherein the RRC reconfiguration message includes an indication of the at least one of the multicast flow-to-radio bearer mapping or the MRB/DRB configuration for the target base station.

100. The source base station of claim 99, wherein the indication is a delta indication with respect to a previous multicast flow-to-radio bearer mapping or the MRB/DRB configuration.

101. The source base station of claim 72, wherein the instructions to determine that the UE is to be handed over to the target base station are executable by the processor to cause the source base station to: receive a measurement report from the UE; and determine UE handover based at least in part on the measurement report.

102. The source base station of claim 101, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

103. The source base station of claim 72, wherein the instructions are further executable by the processor to cause the source base station to: disconnect from an N3 tunnel providing the multicast traffic after receiving the handover complete message.

104. The source base station of claim 72, wherein the multicast traffic is multicast/broadcast traffic.

105. An target base station, comprising: a processor, memory coupled with the processor, and instructions stored in the memory and executable by the processor to cause the target base station to: receive, at the target base station, a handover request from a source base station serving, to a user equipment (UE), multicast traffic associated with one or more multicast radio bearers, wherein the handover request includes a current multicast context of the UE identifying the one or more multicast radio bearers associated with the multicast traffic; receive, from the UE, a radio resource control reconfiguration complete message; transmit, based at least in part on receipt of the radio resource control reconfiguration complete message, a handover complete message to the source base station; and serve the multicast traffic to the UE based at least in part on the current multicast context of the UE.

106. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive, in the current multicast context and as identification for the one or more multicast radio bearers, at least one of a temporary mobile group identity (TMGI) or an multicast flow identity.

107. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive, in the current multicast context, a multicast radio bearer configuration of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

108. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive, in the current multicast context, a quality of service profile of the one or more multicast radio bearers for which the UE is being served the multicast traffic.

109. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive, in the current multicast context, at least one of a unicast assistance configuration or an association between the one or more multicast radio bearers for which the UE is being served the multicast traffic and one or more dedicated radio bearers.

110. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive a portion of the multicast traffic forwarded from the source base station for service to the UE in accordance with the current multicast context of the UE, wherein the portion of the multicast traffic that is forwarded includes traffic received at the source base station after determination of UE handover and before receipt of the handover complete message from the target base station.

111. The target base station of claim 110, wherein the instructions are further executable by the processor to cause the target base station to: receive a sequence number status transfer message from the source base station, wherein the sequence number status transfer message includes a downlink delivery status of the one or more multicast radio bearers for which the UE is being served.

112. The target base station of claim 111, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after receipt of the sequence number status transfer message.

113. The target base station of claim 111, wherein the instructions are further executable by the processor to cause the target base station to: transmit a sequence number status update message to the source base station, wherein the sequence number status update message includes a range of sequence numbers corresponding to the portion of the multicast traffic expected to be received at the target base station from the source base station for the one or more multicast radio bearers for which the UE is being served.

114. The target base station of claim 113, wherein receiving the portion of the multicast traffic forwarded from the source base station occurs after transmission of the sequence number status update message.

115. The target base station of claim 110, wherein the instructions are further executable by the processor to cause the target base station to: identify that a mismatch exists between first multicast radio bearers served by the target base station and second multicast radio bearers served by the source base station, wherein receiving the portion of the multicast traffic is based at least in part on the mismatch.

116. The target base station of claim 115, wherein the mismatch is based on the target base station not serving, at a time of the handover request, the first multicast radio bearers that the source base station was serving to the UE.

117. The target base station of claim 115, wherein the mismatch is based on the target base station serving the second multicast radio bearers in advance of service of the same second multicast radio bearers by the source base station.

118. The target base station of claim 115, wherein the instructions are further executable by the processor to cause the target base station to: transmit, via a handover request acknowledgement, one or more current sequence numbers of data packets corresponding to the second multicast radio bearers served by the target base station.

119. The target base station of claim 110, wherein the instructions are further executable by the processor to cause the target base station to: participate in a data forwarding negotiation that occurs between the source base station and the target base station, wherein receiving the portion of the multicast traffic forwarded from the source base station is based at least in part on the data forwarding negotiation.

120. The target base station of claim 119, wherein the instructions to participate in the data forwarding negotiation are executable by the processor to cause the target base station to: receive, with the handover request, a forwarding request for forwarding of data per multicast radio bearer from the source base station to the target base station, wherein the forwarding request includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and transmit, via a handover request acknowledgment, a confirmation that data forwarding from the source base station is to occur based at least in part on N3 tunnel availability at the target base station for respective multicast radio bearers.

121. The target base station of claim 120, wherein the forwarding request further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

122. The target base station of claim 120, wherein the confirmation comprises at least one of a current PDCP sequence number for the respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

123. The target base station of claim 120, wherein the instructions are further executable by the processor to cause the target base station to: transmit a stop data forwarding message to the source base station, indicating that the data forwarding from the source base station is to stop, wherein the stop data forwarding message is transmitted via one of a sequence number status update message or a downlink data delivery status (DDDS) message.

124. The target base station of claim 119, wherein the instructions to participate in the data forwarding negotiation are executable by the processor to cause the target base station to: receive, with the handover request, an indication of multicast radio bearer bearer-type for the one or more multicast radio bearers at the source base station; and transmit a handover request acknowledgement responding to the handover request, the handover request acknowledgement being indicative of whether data forwarding from the source base station to the target base station is to occur.

125. The target base station of claim 124, wherein the instructions to transmit the handover request acknowledgement are executable by the processor to cause the target base station to: transmit, via the handover request acknowledgement, a confirmation that data forwarding is to occur.

126. The target base station of claim 124, wherein the instructions to transmit the handover request acknowledgement are executable by the processor to cause the target base station to: transmit the handover request acknowledgement without a data forwarding message, wherein an absence of the data forwarding message in the handover request acknowledgement is indicative that data forwarding from the source base station to the target base station is to occur.

127. The target base station of claim 124, wherein the instructions are further executable by the processor to cause the target base station to: receive a forwarding indication from the source base station, wherein the forwarding indication includes a current packet data convergence protocol (PDCP) sequence number for the one or more multicast radio bearers at the source base station; and transmit, via a sequence number status update message, at least one of a current PDCP sequence number for respective multicast radio bearers at the target base station, a desired PDCP sequence number range for the respective multicast radio bearers at the target base station, or one or more explicitly-indicated PDCP sequence numbers for the respective multicast radio bearers at the target base station.

128. The target base station of claim 127, wherein the forwarding indication further comprises an identification of additional PDCP sequence numbers served by the source base station but not yet acknowledged by the UE.

129. The target base station of claim 124, wherein the instructions are further executable by the processor to cause the target base station to: receive, from the source base station, downlink packet data convergence protocol (PDCP) service data units (SDUs) without further data forwarding negotiations between the source base station and the target base station; and transmit, to the source base station, a sequence number status update message indicating to the source base station a termination PDCP sequence number at which the source base station is to stop data forwarding.

130. The target base station of claim 105, wherein data packets having first data, associated with a first multicast radio bearer, and received at the source base station have same sequence numbers as data packets having the first data, associated with the first multicast radio bearer, and received at the target base station.

131. The target base station of claim 105, wherein a data packet associated with a multicast radio bearer has a general packet radio service (GPRS) tunneling protocol (GTP) user plane (GTP-U) sequence number that maps in a one-to-one relationship with a packet data convergence protocol (PDCP) sequence number at the target base station.

132. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: transmit, via a handover request acknowledgement to the source base station, at least one of a multicast flow-to-radio bearer mapping or a multicast radio bearer/dedicated radio bearer (MRB/DRB) configuration for the target base station.

133. The target base station of claim 105, wherein an N3 tunnel for receipt of multicast traffic to the UE is already established at the target base station prior to receiving the handover request.

134. The target base station of claim 105, wherein an N3 tunnel for receipt of multicast traffic to the UE is established at the target base station after receiving the handover request but before transmission of a handover request acknowledgement.

135. The target base station of claim 134, wherein establishment of the N3 tunnel is based on the current multicast context for the UE.

136. The target base station of claim 135, wherein the current multicast context for the UE used to establish the N3 tunnel is received from a core network.

137. The target base station of claim 105, wherein the instructions are further executable by the processor to cause the target base station to: receive, from the UE and after transmitting the handover complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; transmit, via a unicast transmission to the UE and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and transmit ongoing packet data units of the multicast traffic to the UE via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

138. The target base station of claim 105, wherein the multicast traffic is multicast/broadcast traffic.

139. A user equipment (UE), comprising: a processor, memory coupled with the processor, and instructions stored in the memory and executable by the processor to cause the

UE to: receive, from a source base station, multicast traffic associated with one or more multicast radio bearers; transmit a measurement report to the source base station; receive, responsive to the measurement report, a radio resource control reconfiguration message from the source base station, wherein the radio resource control reconfiguration message includes an indication of at least one multicast flow- to-radio bearer mapping or multicast radio bearer/dedicated radio bearer configuration for a target base station; transmit, to the target base station, a radio resource control reconfiguration complete message; and receive, from the target base station, the multicast traffic associated with the one or more multicast radio bearers.

140. The UE of claim 139, wherein the instructions are further executable by the processor to cause the UE to: transmit, to the target base station and after transmitting the radio resource control reconfiguration complete message, a packet data convergence protocol (PDCP) status report that includes a multicast radio bearer receiving status for the UE; receive, via a unicast transmission from the target base station and in response to the PDCP status report, any packet data units identified by the PDCP status report as having not been received or decoded at the UE; and receive ongoing packet data units of the multicast traffic from the target base station via either multicast radio bearers, dedicated radio bearers, or combinations thereof.

141. The UE of claim 139, wherein the measurement report includes one or more of reference signal received power (RSRP)/ reference signal received quality (RSRQ) measurements or multicast service measurements.

142. The UE of claim 139, wherein the multicast traffic is multicast/broadcast traffic.