CN110089151B

CN110089151B - System and method for packet forwarding during handover procedure

Info

Publication number: CN110089151B
Application number: CN201780079141.9A
Authority: CN
Inventors: S·帕拉; R·伯比奇; 姚丽娟; 张玉健; S·班格来; 许允亨; M·马丁内斯塔拉德利; A·S·斯托扬诺夫斯基
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2016-12-20
Filing date: 2017-12-20
Publication date: 2022-05-31
Anticipated expiration: 2037-12-20
Also published as: CN110089151A; WO2018119123A1

Abstract

The techniques described herein may enable packet forwarding during a Handover (HO) procedure involving fifth generation (5G) techniques. During the HO procedure, a source Radio Access Network (RAN) node may send user data packets intended for a User Equipment (UE) to a target RAN node. Each packet may be assigned a Sequence Number (SN) based on a quality of service (QoS) or Data Radio Bearer (DRB) used by the source RAN node to send the packet to the UE. The target RAN node may use the same DRB to forward the packet to the UE, a different DRB to forward the packet to the UE, or a different QoS to forward the packet to the UE. The target RAN node may also or alternatively create a record of packets forwarded to the UE to effect retransmission of the packets as appropriate.

Description

System and method for packet forwarding during handover procedure

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application No. 62/436,900 filed on 2016, 12, 20, the contents of which are incorporated herein by reference as if fully set forth herein.

Technical Field

The present application relates to systems and methods for packet forwarding during a handoff procedure.

Background

The wireless communication network may include User Equipment (UE) (e.g., a smartphone, a tablet, a laptop, etc.), a Radio Access Network (RAN) node (e.g., a base station), and a core network. The UE may connect to the core network by communicating with the RAN node and registering with the core network. Communication between the UE and the RAN node (also referred to herein as an access node) may be over signal carriers corresponding to the frequency bands.

As the UE moves to different coverage areas within the wireless communication network, the UE may participate in one or more Handover (HO) procedures. A Handover (HO) procedure may include a process in which a UE transfers from one access node to another access node, generally referred to herein as a source node and a target node, respectively. The source node may receive information directed to the UE from the core network prior to conducting the HO procedure and temporarily store the information in a buffer memory prior to transmitting the information to the UE. When the source node determines to handover the UE to the target node, some information intended for the UE may still be stored in the buffer memory of the source node. Thus, in addition to enabling the UE to connect to the target node, the HO process may include the source node providing buffered data to the target node and the target node sending data to the UE (after a connection between the target node and the UE has been established).

Disclosure of Invention

According to an aspect of the present disclosure, there is provided an apparatus of a radio access network, RAN, node, the apparatus comprising: an interface to a radio frequency RF circuit; and one or more processors configured to: inserting a sequence number, SN, into each of a plurality of user data packets directed to a user equipment, UE, connected to a RAN node, the SN being based on a relative sequential position of each of the plurality of user data packets; and prior to causing at least one of the plurality of user data packets to be transmitted to the UE via the RF circuitry, determining that the UE is to be transferred to a target RAN node as part of a handover procedure, and causing the at least one user data packet to be transferred to the target RAN node during the handover procedure along with an indication of how the at least one user data packet would have been transmitted to the UE by the RAN node via the interface of the RF circuitry prior to the handover procedure.

According to another aspect of the present disclosure, there is provided an apparatus of a radio access network, RAN, node, the apparatus comprising: an interface to a radio frequency RF circuit; and one or more processors configured to: receiving a plurality of user data packets from a source RAN node of a handover procedure, the plurality of user data packets being directed to a user equipment, UE, corresponding to the handover procedure, each user data packet of the plurality of user data packets comprising a sequence number, SN, based on a relative sequential position of each user data packet of the plurality of user data packets; receiving, from the source RAN node, an indication of how each user data packet of the plurality of user data packets would otherwise be transmitted by the source RAN node to the UE prior to the handover procedure; determining, based on the indication, a data radio bearer, DRB, for transmission of the plurality of user data packets to the UE; receiving, via the interface of the RF circuitry, an indication that the UE is ready to communicate with the RAN node as part of the handover procedure; and cause the plurality of user data packets to be transmitted to the UE via the interface of the RF circuitry using the DRB.

According to another aspect of the present disclosure, there is provided an apparatus of a user equipment, UE, the apparatus comprising: an interface to a radio frequency RF circuit; and one or more processors configured to: receiving, via the interface of the RF circuitry, a plurality of first user data packets from a first Radio Access Network (RAN) node, each user data packet of the plurality of first user data packets comprising a Sequence Number (SN) based on an order position of each user data packet of the plurality of first user data packets; receiving, via the interface of the RF circuitry, an instruction to participate in a handover procedure involving the first RAN node and a second RAN node; receiving, as part of the handover procedure, a plurality of second user data packets from the second RAN node via the interface of the RF circuitry, each user data packet of the plurality of second user data packets comprising a SN based on a sequential position of each user data packet relative to the plurality of first user data packets and the plurality of second user data packets, wherein the second RAN node receives the plurality of second user data packets from the first RAN node and an indication of how each user data packet of the plurality of second user data packets would have been transmitted to the UE by the first RAN node prior to the handover procedure, and wherein the second RAN node sends each user data packet of the plurality of second user data packets to the UE based on the indication; and merging the plurality of first user data packets with the plurality of second user data packets based on the SN of each of the plurality of first user data packets and the plurality of second user data packets.

Drawings

The embodiments described herein will be readily understood by the following detailed description in conjunction with the accompanying drawings. For convenience of description, the same reference numerals may denote the same structural elements. Embodiments are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings.

FIG. 1 illustrates an architecture of a system of networks according to some embodiments;

fig. 2 is a sequential flow diagram of an example process of packet forwarding during a handover procedure in which a source node and a target node communicate with a User Equipment (UE) using the same Data Radio Bearer (DRB);

FIG. 3 is a sequential flow diagram of an example process of quality of service (QoS) ID based packet forwarding during a handoff process;

FIG. 4 is a sequential flow diagram of an exemplary process of packet forwarding during a handoff procedure in which a source node and a target node use different DRBs;

fig. 5 and 6 are sequential flowcharts of an example of a detailed process of packet forwarding during a handover process;

FIG. 7 illustrates example components of a device according to some embodiments;

FIG. 8 illustrates an example interface of a baseband circuit according to some embodiments; and

fig. 9 is a block diagram illustrating components capable of reading instructions from a machine-readable or computer-readable medium (e.g., a non-transitory machine-readable storage medium) and performing any one or more of the methodologies discussed herein, according to some example embodiments.

Detailed Description

The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims and their equivalents.

In a wireless communication network, a Handover (HO) procedure may include a process in which a UE transfers from one access node to another access node (often referred to as a source node and a target node, respectively). When the source node determines to handover the UE, some information intended for the UE may still be stored in the buffer memory of the source node. Thus, in addition to enabling the UE to connect to the target node, the HO process may include the source node providing the target node with buffered data for the UE, and the target node sending the data to the UE after a connection between the target node and the UE has been established.

In some scenarios, for example using Long Term Evolution (LTE) Radio Access Technology (RAT), providing buffered data to a UE may involve using Packet Data Convergence Protocol (PDCP) to assign Sequence Numbers (SNs) to Packet Data Units (PDUs) intended for the UE. The SN may enable the UE to determine which PDUs have been received and which have not been received, and take appropriate action (such as requesting that one or more PDUs be re-transmitted to the UE). Further, each Data Radio Bearer (DRB) used to transmit data to the UE may have its own PDCP instance, such that the SNs assigned to PDUs transmitted through a particular DRB may be independent of or related to the SNs assigned to PDUs transmitted through different DRBs. The SN may be assigned to the PDU before and/or while the PDU is stored in the memory buffer in preparation for transmission of the PDU to the UE.

With respect to the HO process, where PDUs stored in a memory buffer of the source node are forwarded to the target node and then to the UE, it is useful to preserve the SN of the PDUs so that the UE can combine the PDUs from the source node with the PDUs from the target node to arrange the PDUs in the proper order and/or determine whether all PDUs in a given order have been successfully received. When the UE determines that one or more PDUs are missing, the UE may request that the PDUs be retransmitted by the target node, and in response, the target node may retransmit all PDUs in a given set or only the missing PDUs. When all PDUs are retransmitted, the UE may detect (based on the SN) which PDUs are duplicate and delete/ignore the duplicate PDUs. Since the above procedure enables the UE to arrange PDUs from the source node and the target node in the proper order and request retransmission of lost packets, the procedure is sometimes characterized as delivering data to the UE participating in the HO procedure in sequence without loss.

Aspects of LTE that may enable the SN assigned by the source node to be used by the target node may include ensuring that the source node and the target node are using the same DRB to send data to the UE. However, in new air interface (NR) technologies (e.g., next generation node bs (gnbs) and enbs connected to NR core networks), the mapping of data to DRBs may go to the RAN nodes (i.e., enbs, gnbs, etc.). Therefore, the source node and the target node may eventually use different DRBs to transmit data to the UE undergoing the HO procedure. In such a scenario, if the target node uses a different DRB than the source node, the target node may assign a SN to a PDU that does not correspond to the SN of the PDU previously sent by the source node to the UE. Thus, the UE may not be able to merge PDUs from the source node with PDUs from the target node to arrange the PDUs in the proper order and/or determine whether all PDUs for a given transmission have been successfully received.

The techniques described herein may be used to enable sequential lossless delivery of data to UEs participating in HO procedures involving NR technology (e.g., gNB, eNB connected to NR core network, etc.). In one example, the source node can indicate which DRBs are being used by the source node to transmit the PDUs to the UE, and the target node can use the same DRBs to forward the PDUs received from the source node to the UE. Once the UE has successfully received the PDU, the target node may reconfigure which DRBs are used to send subsequent PDUs to the UE according to its own preferences.

In another example, the access nodes (e.g., source node and target node) can assign SNs to the PDUs based on criteria, attributes, characteristics, etc., other than the DRBs used to transmit the PDUs. For example, the SN assigned to a PDU can be based on the QoS flow corresponding to the PDU. In this way, two different QoS flows can have different numbering orders in PDCP even/when the two QoS flows belong to the same DRB. Since the QoS flow can be maintained during and after the HO procedure, SNs of PDUs transmitted to the UE can be sequential and lossless.

In another example, each PDU can include a SN assigned by the source node and a SN assigned by the target node. For example, a PDU sent from a source node to a target node can include a SN assigned by the source node and an indication of the manner in which the PDU was sent by the source node to the UE (e.g., one or more conditions under which, etc.). An example of this indication may include a DRB ID corresponding to a DRB used by the source node to transmit the PDU to the UE. In some embodiments, different types of identifiers (e.g., in addition to DRB IDs) may be used to map data packets to DRBs. In another example, this indication may include a quality of service (QoS) ID corresponding to a QoS used by the source node to transmit the PDU to the UE. In some embodiments, different types of identifiers (e.g., in addition to QoS IDs) may be used to map data packets to DRBs.

The destination node may then assign another SN to the PDUs such that each PDU includes two SNs, one assigned by the source node and the other assigned by the destination node. The target node may transmit the PDU to the UE, and the UE may use the DRB ID and SN from the source node to combine the PDU previously received from the source node with the PDU received from the target node. Further, when the UE finds that a particular PDU is not received, the UE may request retransmission of the PDU based on the SN assigned by the source node or the SN assigned by the target node.

In some embodiments, the source node may use one or more techniques to determine which buffered PDUs to send to the target node for transmission to the UE. In one example, when the source node transmits PDUs to the UE, the source node may monitor the UE for which PDUs are acknowledged (e.g., successfully received). In this way, the source node may determine that the oldest PDU for acknowledgement has not been received from the UE and may send all PDUs beginning with the oldest PDU that has not yet been acknowledged by the UE to the target node, if/when the time for the HO procedure involving the UE comes. In this case, some of the PDUs sent to the target node may include PDUs that have been acknowledged by the UE but are not as old as the oldest, unacknowledged PDUs. In another example, the source node may send only unacknowledged PDUs to the target node. In some embodiments, some PDUs received from the source node may not have been assigned a SN, and the target node may identify such PDUs and process them appropriately (e.g., according to one of the examples described above). Further, the techniques described herein may be applied in conjunction with existing HO procedure techniques (such as those described above with reference to LTE RAT).

Fig. 1 illustrates an architecture of a system 100 of networks according to some embodiments. The system 100 is shown to include a UE101 and a UE 102. The

UEs

101 and 102 are illustrated as smart phones (e.g., handheld touch screen mobile computing devices connectable to one or more cellular networks), but may also include any mobile or non-mobile computing device, such as a Personal Data Assistant (PDA), pager, laptop computer, desktop computer, wireless handheld device, or any computing device that includes a wireless communication interface.

In some embodiments, any of

UEs

101 and 102 may include an internet of things (IoT) UE, which may include a network access layer designed for low power IoT applications that utilize short-term UE connections. IoT UEs may utilize technologies such as machine-to-machine (M2M) or Machine Type Communication (MTC) to exchange data with MTC servers or devices via Public Land Mobile Network (PLMN), proximity services (ProSe) or device-to-device (D2D) communication, sensor networks, or IoT networks. The M2M or MTC data exchange may be a machine initiated data exchange. An IoT network describes interconnected IoT UEs that may include uniquely identifiable embedded computing devices (within the internet infrastructure) with short-term connections. The IoT UE may execute background applications (e.g., keep-alive messages, status updates, etc.) to facilitate connection of the IoT network.

UEs

101 and 102 may be configured to connect with (e.g., communicatively couple with) a Radio Access Network (RAN) 110-RAN 110 may be, for example, an evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (E-UTRAN), a NextGen RAN (NG RAN), or other type of RAN.

UEs

101 and 102 utilize

connections

103 and 104, respectively, each of which includes a physical communication interface or layer (discussed in further detail below); in this example,

connections

103 and 104 are shown as air interfaces for implementing communicative coupling, and may conform to a cellular communication protocol, such as a global system for mobile communications (GSM) protocol, a Code Division Multiple Access (CDMA) network protocol, a push-to-talk (PTT) protocol, a PTT over cellular (poc) protocol, a Universal Mobile Telecommunications System (UMTS) protocol, a 3GPP Long Term Evolution (LTE) protocol, a fifth generation (5G) protocol, a new air interface (NR) protocol, and so forth.

In this embodiment, the

UEs

101 and 102 may also exchange communication data directly via the ProSe interface 105. The ProSe interface 105, which may alternatively be referred to as a side link interface, includes one or more logical channels including, but not limited to, a physical side link control channel (PSCCH), a physical side link shared channel (PSCCH), a physical side link discovery channel (PSDCH), and a physical side link broadcast channel (PSBCH).

UE 102 is shown configured to access an Access Point (AP)106 via a connection 107. Connection 107 may comprise a local wireless connection, such as a connection conforming to any IEEE 802.11 protocol, wherein AP 106 will include wireless fidelity

A router. In this example, the AP 106 is shown connected to the internet without being connected to the core network of the wireless system (described in further detail below).

RAN 110 may include one or more access nodes that enable

connections

103 and 104. These Access Nodes (ANs) may be referred to as Base Stations (BSs), nodebs, evolved nodebs (enbs), next generation nodebs (gnbs), RAN nodes, etc., and may include ground stations (e.g., terrestrial access points) or satellite stations that provide coverage within a geographic area (e.g., a cell). RAN 110 may include one or more RAN nodes (e.g., macro RAN node 111) to provide a macro cell and one or more RAN nodes (e.g., Low Power (LP) RAN node 112) to provide a femto cell or a pico cell (e.g., a cell with less coverage area, less user capacity, or higher bandwidth than a macro cell).

Either of RAN nodes 111 and 112 may terminate the air interface protocol and may be the first point of contact for

UEs

101 and 102. In some embodiments, any of RAN nodes 111 and 112 may perform various logical functions of RAN 110, including but not limited to Radio Network Controller (RNC) functions such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management.

According to some embodiments, the

UEs

101 and 102 may be configured to: according to various communication techniques, such as, but not limited to, Orthogonal Frequency Division Multiple Access (OFDMA) communication techniques (e.g., for downlink communications) or single carrier frequency division multiple access (SC-FDMA) communication techniques (e.g., for uplink and ProSe or sidelink communications), Orthogonal Frequency Division Multiplexed (OFDM) communication signals are used over a multicarrier communication channel to communicate with each other or with any of RAN nodes 111 and 112, although the scope of the embodiments is not limited in this respect.

In some embodiments, the downlink resource grid may be used for downlink transmissions from any of RAN nodes 111 and 112 to UEs 101 and 102, while uplink transmissions may utilize similar techniques. The grid may be a time-frequency grid, referred to as a resource grid or time-frequency resource grid, which is a physical resource in each slot in the downlink. Such a time-frequency plane representation is common practice for OFDM systems, which makes radio resource allocation intuitive. Each column and each row of the resource grid corresponds to one OFDM symbol and one OFDM subcarrier, respectively. The duration of the resource grid in the time domain corresponds to one slot in the radio frame. The smallest time-frequency unit in a resource grid is called a resource element. Each resource grid includes a plurality of resource blocks, which describe the mapping of certain physical channels to resource elements. Each resource block comprises a set of resource elements; in the frequency domain, this may represent the minimum amount of resources that can currently be allocated. There are several different physical downlink channels transmitted using such resource blocks.

The Physical Downlink Shared Channel (PDSCH) may carry user data and higher layer signaling to UEs 101 and 102. A Physical Downlink Control Channel (PDCCH) may carry information on a transport format and resource allocation related to a PDSCH channel, and the like. It may also inform

UEs

101 and 102 about the transport format, resource allocation and H-ARQ (hybrid automatic repeat request) information related to the uplink shared channel. In general, downlink scheduling (assigning control channel resource blocks and shared channel resource blocks to UEs 102 within a cell) may be performed at any of RAN nodes 111 and 112 based on channel quality information fed back from any of

UEs

101 and 102. The downlink resource assignment information may be sent on a PDCCH used for (e.g., assigned to) each of

UEs

101 and 102.

The PDCCH may use Control Channel Elements (CCEs) to convey control information. The PDCCH complex-valued symbols may first be organized into quadruplets before being mapped to resource elements, and then may be arranged using a sub-block interleaver for rate matching. Each PDCCH may be transmitted using one or more of these CCEs, where each CCE may correspond to nine sets of four physical resource elements called Resource Element Groups (REGs). Four Quadrature Phase Shift Keying (QPSK) symbols may be mapped to each REG. The PDCCH may be transmitted using one or more CCEs, depending on the size of Downlink Control Information (DCI) and channel conditions. Four or more different PDCCH formats with different numbers of CCEs (e.g., aggregation levels, L ═ 1, 2, 4, or 8) may be defined in LTE.

Some embodiments may use the concept as an extension of the above concept for resource allocation for control channel information. For example, some embodiments may utilize an Enhanced Physical Downlink Control Channel (EPDCCH) that uses PDSCH resources for control information transmission. The EPDCCH may be transmitted using one or more Enhanced Control Channel Elements (ECCEs). Similar to the above, each ECCE may correspond to nine sets of four physical resource elements called Enhanced Resource Element Groups (EREGs). In some cases, ECCE may have other numbers of EREGs.

RAN 110 is shown communicatively coupled to Core Network (CN)120 via S1 interface 113. In embodiments, the CN120 may be an Evolved Packet Core (EPC) network, a next generation packet core (NPC) network, or some other type of CN. In this embodiment, the S1 interface 113 is divided into two parts: an S1-U interface 114 that carries traffic data between RAN nodes 111 and 112 and serving gateway (S-GW) 122; and S1 Mobility Management Entity (MME) interface 115, which is a signaling interface between RAN nodes 111 and 112 and MME 121.

In this embodiment, CN120 includes MME 121, S-GW 122, Packet Data Network (PDN) gateway (P-GW)123, and Home Subscriber Server (HSS) 124. MME 121 may be similar in function to the control plane of a legacy serving General Packet Radio Service (GPRS) support node (SGSN). MME 121 may manage mobility aspects in access such as gateway selection and tracking area list management. HSS 124 may include a database for network users, including subscription-related information for supporting network entities in handling communication sessions. The CN120 may include one or more HSS 124 depending on the number of mobile subscribers, the capabilities of the devices, the organization of the network, etc. For example, the HSS 124 may provide support for routing/roaming, authentication, authorization, naming/addressing solutions, location dependencies, and the like.

The S-GW 122 may terminate S1 interface 113 to RAN 110 and route data packets between RAN 110 and CN 120. In addition, S-GW 122 may be a local mobility anchor for inter-RAN node handovers and may also provide an anchor for inter-3 GPP mobility. Other responsibilities may include lawful interception, charging, and certain policy enforcement.

The P-GW 123 may terminate the SGi interface to the PDN. P-GW 123 may route data packets between EPC network 123 and an external network, such as a network including application server 130 (alternatively referred to as an Application Function (AF)), via Internet Protocol (IP) interface 125. In general, the application server 130 may be an element that provides applications (e.g., UMTS Packet Service (PS) domain, LTE PS data services, etc.) that use IP bearer resources to the core network. In this embodiment, P-GW 123 is shown communicatively coupled to application server 130 via an IP communications interface 125. The application server 130 may also be configured to support one or more communication services (e.g., voice over internet protocol (VoIP) sessions, PTT sessions, group communication sessions, social networking services, etc.) for the

UEs

101 and 102 via the CN 120.

P-GW 123 may also be a node for policy enforcement and charging data collection. Policy and Charging Rules Function (PCRF)126 is a policy and charging control element of CN 120. In a non-roaming scenario, there may be a single PCRF in a Home Public Land Mobile Network (HPLMN) associated with an internet protocol connectivity access network (IP-CAN) session of the UE. In a roaming scenario where traffic is off-local, there may be two PCRFs associated with the IP-CAN session of the UE: a home PCRF (H-PCRF) within the HPLMN and a visited PCRF (V-PCRF) in a Visited Public Land Mobile Network (VPLMN). PCRF 126 may be communicatively coupled to application server 130 via P-GW 123. Application server 130 may signal PCRF 126 to indicate the new service flow and select the appropriate quality of service (QoS) and charging parameters. PCRF 126 may provide the rules to a Policy and Charging Enforcement Function (PCEF) (not shown) with appropriate Traffic Flow Templates (TFTs) and QoS Class Identifiers (QCIs), which initiates the QoS and charging specified by application server 130.

The number of devices and/or networks shown in fig. 1 is for illustration purposes only. Indeed, system 100 may include additional devices and/or networks; fewer devices and/or networks; different devices and/or networks; or a different arrangement of devices and/or networks than those shown in fig. 1. For example, although not shown, system 100 may include devices, such as routers, modems, gateways, switches, hubs (hubs), etc., that facilitate or enable communication between the various components shown in system 100. Alternatively or additionally, one or more devices of system 100 may perform one or more functions described as being performed by another one or more devices of system 100. Further, the devices of system 100 may be interconnected to each other and/or other devices via wired connections, wireless connections, or a combination of wired and wireless connections. In some embodiments, one or more devices of system 100 may be physically integrated in one or more other devices of system 100, and/or may be physically attached to one or more other devices of system 100. Further, while "direct" connections are shown between certain devices of FIG. 1, in practice, some of the devices may communicate with each other via one or more additional devices and/or networks.

Fig. 2 is a sequential flow diagram of an example process for packet forwarding during a handover procedure in which the source node and target node 111 communicate with the UE101 using the same DRB(s). As shown, the example of FIG. 2 may include a UE101, a source node 111-1, and a target node 111-2. Both the source node 111-1 and the target node 111-2 may be examples of the macro RAN node 111 or the LP RAN node 112 described above with reference to fig. 1. The example of fig. 2 is provided as a non-limiting example. Indeed, the example of fig. 2 may include fewer, additional, and/or alternative operations or functions, such as one or more of the operations or functions of fig. 3-6. Additionally, one or more operations or functions of fig. 2 may be performed by fewer, additional, or alternative devices, which may include one or more of the devices described above with reference to fig. 1.

As shown, UE101 and source node 111-1 may transmit packets to each other (route 205). As described herein, a packet may comprise a PDU transmitted between devices (e.g., UE101, source node 111-1, target node 111-2, devices of CN120, etc.) over a user plane of a wireless communication network. Such packets may be referred to herein as User Data (UD). Both UE101 and source node 111-1 may implement a protocol such as PDCP to assign SNs to each packet. The SN may be included in a packet at a location reserved for SN information. For example, the SN may be 12 bits in length and may occupy bits 4-8 of the first octet of the packet and all 8 bits of the second octet of the packet. In this embodiment, the first bit of the first octet may be dedicated to indicating whether the packet corresponds to user data or control data, and the second, third and fourth bits of the first octet may be reserved for other purposes. In some embodiments, the grouping may be configured in different ways.

Source node 111-1 may receive packets intended for UE101 (from CN 120) and may temporarily store the packets in a local buffer memory of source node 111-1. The source node 111-1 may assign a SN to each packet before sending the packet to the UE 101. According to PDCP, the SN assigned to each packet can be based on the DRB used by the source node 111-1 to send the packet to the UE 101. The SNs of the packets may be dispatched in a relative order (e.g., 1, 2, 3, etc.) consistent with the manner (e.g., order) in which the packets are to be sent, received, read, and/or processed by the UE 101. In transmitting packets to the UE101, the source node 111-1 may monitor which packets have been transmitted (and the time of transmission) and whether any transmitted packets have been acknowledged by the UE 101. When the UE101 indicates that one or more packets have not been received, the source node 111-1 may retransmit the identified packets, record the time of the retransmission, and continue to monitor whether the UE101 acknowledges the retransmitted packets. When the buffered packets are acknowledged by the UE101, the source node 111-1 may (immediately or periodically) remove the packets from the buffer.

The SN may be assigned by the PDCP layer of the protocol stack implemented by source node 111-1. In such an embodiment, the PDCP layer may operate above a Radio Link Control (RLC) layer of the protocol stack, the RLC layer may operate above a Medium Access Control (MAC) layer of the protocol stack, and the MAC layer may operate above a Physical (PHY) layer of the protocol stack. The UE101 may implement similar protocol stacks (e.g., PDCP layer, RLC layer, MAC layer, and PHY layer) and may transmit, process, and receive packets in a similar manner as the source node 111-1. In some embodiments, source node 111-1 may assign SNs to packets before and during the handoff process. In some embodiments, the source node 111-1 may begin assigning SNs to packets only after determining that the UE101 is to be handed off to another RAN node 111.

Assume that source node 111-1 determines that UE101 should undergo a handover procedure involving target node 111-2 (block 210). In response, the source node 111-1 may stop sending user data packets to the UE101 and determine which buffered packets to send to the target node 111-2. In some embodiments, the source node 111-1 may determine that the packets to be sent to the target node 111-2 include all packets sent to the UE101 measured from the oldest packet that has not yet been acknowledged by the UE 101. For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), the target node may determine that packet 4-10 is to be sent to the target node 111-2 because packet 4 is the oldest packet that has not yet been acknowledged by the UE 101. In contrast, in some embodiments, the source node 111-1 may determine that packets to be sent to the target node 111-2 include only packets that have not been acknowledged by the UE 101. For example, continuing the example in which the source node 111-1 sends packets 1-10 to the UE101, and the UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), the target node may determine to send only packets 4, 5, and 8-10 to the target node 111-2 because packets 1-3 and 6-7 have been acknowledged by the UE 101.

Source node 111-1 may transmit the determined packet to destination node 111-2 (route 220). As shown, each packet may include a corresponding SN and DRB ID. The DRB ID may indicate the DRB that source node 111-1 uses to determine the SN and that source node 111-1 will use to send the packet to UE 101. In some embodiments, the source node 111-1 may only insert the DRB ID into packets transmitted by the target node 111-2 to the UE101 (e.g., after the source node 111-1 determines to perform the handover procedure). In some embodiments, the source node 111-1 may include the DRB ID in all packets directed to the UE101 (e.g., packets received even before the source node 111-1 determines to perform the handover procedure). The target node 111-2 may buffer each packet and map each packet to a corresponding DRB based on the DRB ID associated with each packet (block 225). Additionally, the target node 111-2 may assign the same DRB as the source node 111-1 for sending the packet to the UE101 based on the DRB ID (block 230). As such, the target node 111-2 may transmit the packet to the UE101 using the same DRB as the source node 111-1 (route 255).

The source node 111-1 may inform the UE101 of the HO procedure (route 235), which may include configuration information for establishing a connection with the target node 111-2, by sending an RRC connection reconfiguration request message to the UE 101. In some embodiments, the UE101 may respond to the message from the source node 111-1 by, for example, detaching from the source node 111-1 and transmitting an RRC connection reconfiguration complete message to the target node 111-2, examples of which are described in detail below with reference to FIGS. 5 and 6.

In embodiments in which (as described above) the source node 111-1 is configured to determine that packets to be sent to the target node 111-2 include all packets sent to the UE101 since the oldest packet that has not yet been acknowledged by the UE101, the UE101 may similarly operate by dropping packets based on the oldest packet sent by the source node 111-1 that the UE101 has not successfully received (and thus has not yet been acknowledged) (block 240). For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 only receives packets 1-3 and 6-7 (but does not receive 4, 5, or 8-10), the UE101 may drop packets 4-10 because packet 4 is the oldest packet that the UE101 has not yet received/acknowledged. Doing so may free up storage capacity of the UE101, as in such an embodiment, the target node 111-2 may be configured to retransmit packets starting with the oldest, unacknowledged packet (e.g., packets 4-10). In contrast, in embodiments where the source node 111-1 sends only unacknowledged packets (e.g., packets 4, 5, and 8-10) to the target node 111-2 such that the target node 111-2 may send only unacknowledged packets to the UE101, the UE101 may process and send successfully received packets (e.g., packets 1-3 and 6-7) from the source node 111-1 to an upper layer (e.g., IP layer or another type of layer 3 protocol) or the like without waiting for lost packets (e.g., packets 4, 5, and 8-10) from the target node 111-2 (block 245).

After the target node 111-2 has successfully sent the packets to the UE101, the source node 111-1, and the target node 111-2 may complete the HO procedure. Doing so may include one or more of various operations (such as the UE101 detaching from the source node 111-1 and transmitting an RRC connection reconfiguration complete message to the target node 111-2) (route 250). A detailed example of such operation is described below with reference to fig. 5 and 6. The target node 111-2 may send a data packet to the UE101 (route 255). In some embodiments, the target node 111-2 may send all data packets (route 220) that the target node 111-2 receives from the source node 111-1 to the UE 101. In some embodiments, prior to the target node 111-2 sending data packets to the UE101, the UE101 may send an acknowledgement message to the target node 111-2 for one or more data packets that the target node 111-2 has received from the source node 111-1, and the target node 111-2 may send only data packets to the UE101 for which acknowledgements have not been received (i.e., unacknowledged packets).

In some embodiments, the UE101 may notify the target node 111-2 of the time when all data packets (e.g., all packets with SNs from the source node) have been received. In some embodiments, the notification or indication may be provided by the UE101 via an end-marker packet or another type of indicator. Additionally or alternatively, after the UE101 has successfully received the packet from the target node 111-2 (route 255), the target node 111-2 may reconfigure the DRB for communication with the UE101 (block 260). For example, the DRB with which the source node 111-1 communicates with the UE101 may be a non-optimal or preferred DRB with which the target node 111-2 communicates with the UE 101. As such, after the packet from the source node 111-1 has been successfully received by the UE101, the target node 111-2 may reconfigure (e.g., reassign, reallocate, etc.) the DRBs that the target node 111-2 and the UE101 may use to transmit user data to each other (block 260). In some embodiments, target node 111-2 may perform these operations at an earlier time. For example, prior to transmitting the data packet to the UE101 (route 255), the target node 111-2 may determine the DRBs that the target node 111-2 will use after transmitting the data packet to the UE101 (e.g., after the HO procedure is complete), and after the UE101 has received the data packet (e.g., after the HO procedure is complete), the target node 111-2 may provide the UE101 with configuration information for using the new DRBs.

Fig. 3 is a sequential flow diagram of an example process for packet forwarding based on QoS ID during a handoff process. As shown, the example of FIG. 3 may include a UE101, a source node 111-1, and a target node 111-2. Both the source node 111-1 and the target node 111-2 may be examples of the macro RAN node 111 or the LP RAN node 112 described above with reference to fig. 1. The example of fig. 3 is provided as a non-limiting example. In practice, the example of fig. 3 may include fewer, additional, and/or alternative operations or functions, such as one or more of the operations or functions of fig. 2 and 4-6. Additionally, one or more of the operations or functions of fig. 3 may be performed by fewer, additional, or alternative devices, which may include one or more of the devices described above with reference to fig. 1.

As shown, UE101 and source node 111-1 may transmit user data packets to each other over the user plane (route 305). Both UE101 and source node 111-1 may implement a protocol to assign a SN to each packet. Instead of the SN for each packet being based on the DRB used to transmit the packet, the SN for each packet may be based on the QoS flow associated with the packet. The QoS flow associated with a packet may be determined or identified based on a QoS flow filter or QoS indicator or other QoS marking information included in the packet. This information may also or alternatively be transmitted in the user plane or as part of the configuration information exchanged between the UE101 and the CN120 over a wireless protocol. Since the SN may be based on a QoS flow associated with the packet (rather than, for example, a DRB), user data packets corresponding to multiple different numbering sequences may be transmitted using one DRB.

Assume that the source node 111-1 determines that the UE101 is to undergo a HO procedure involving the target node 111-2 (block 310). In response, the source node 111-1 may stop sending packets of user data to the UE101 and determine which buffered packets to send to the target node 111-2. In some embodiments, source node 111-1 may determine that the packets to be sent to target node 111-2 include all packets sent to UE101 since the oldest packet that has not yet been acknowledged by UE 101. For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), the target node 111-2 may determine that packet 4-10 is to be sent to the target node 111-2 because packet 4 is the oldest packet that has not yet been acknowledged by the UE 101. In contrast, in some embodiments, the source node 111-1 may determine that packets to be sent to the target node 111-2 include only packets that have not been acknowledged by the UE 101. For example, continuing the example in which source node 111-1 sends packets 1-10 to UE101, and UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), then target node 111-2 may determine to send only packets 4, 5, and 8-10 to target node 111-2 because packets 1-3 and 6-7 have been acknowledged by UE 101.

The source node 111-1 may inform the UE101 of the HO procedure (path 320), which may include configuration information for establishing a connection with the target node 111-2, by sending an RRC connection reconfiguration request message to the UE 101. The configuration information may include instructions as to which packet forwarding technique is being implemented by the source and target nodes 111 (e.g., whether the target node 111-2 is to forward only unacknowledged packets, etc.). The packet forwarding technique may inform the UE101 of which packets are expected from the target node 111-2. In some embodiments, the UE101 may respond to the message from the source node 111-1 by, for example, detaching from the source node 111-1 and transmitting an RRC connection reconfiguration complete message to the target node 111-2, examples of which are described in detail below with reference to FIGS. 5 and 6.

In embodiments in which (as described above) the source node 111-1 is configured to determine that packets to be sent to the target node 111-2 include all packets sent to the UE101 since the oldest packet that has not yet been acknowledged by the UE101, the UE101 may similarly operate by dropping packets based on the oldest packet sent by the source node 111-1 that the UE101 has not successfully received (and thus has not yet been acknowledged) (block 325). For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 only receives packets 1-3 and 6-7 (but does not receive 4, 5, or 8-10), the UE101 may drop packets 4-10 because packet 4 is the oldest packet that the UE101 has not yet received/acknowledged. Doing so may free up storage capacity of the UE101, as in such an embodiment, the target node 111-2 may be configured to retransmit packets starting with the oldest, unacknowledged packet (e.g., packets 4-10). In contrast, in embodiments where the source node 111-1 sends only unacknowledged packets (e.g., packets 4, 5, and 8-10) to the target node 111-2 such that the target node 111-2 may send only unacknowledged packets to the UE101, the UE101 may process and send successfully received packets (e.g., packets 1-3 and 6-7) from the source node 111-1 to an upper layer (e.g., IP layer or another type of layer 3 protocol) or the like without waiting for lost packets (e.g., packets 4, 5, and 8-10) from the target node 111-2 (block 330).

Source node 111-1 may transmit the user data packet to destination node 111-2 (route 335). As shown, each packet may include a corresponding SN and QoS flow ID. Destination node 111-2 may buffer each packet and map each packet to a corresponding QoS flow ID based on the QoS flow ID already associated with each packet (block 340). Additionally, the target node 111-2 may determine and assign a preferred DRB for sending the data user packet to the UE101 (block 345). In contrast to the example of fig. 2, the target node 111-2 may select a different set of DRBs for transmission of user data packets to the UE101 than the source node 111-1.

The UE101, source node 111-1, and target node 111-2 may complete the HO procedure. Doing so may include one or more of various operations (such as the UE101 detaching from the source node 111-1 and transmitting an RRC connection reconfiguration complete message to the target node 111-2) (route 350). A detailed example of such operation is described below with reference to fig. 5 and 6. The target node 111-2 may transmit the user data packet to the UE101 (on route 355). In the event that the UE101 fails to successfully receive one or more transmitted packets, the UE101 may send a retransmission request for the failed packet to the target node 110, and the target node 111-2 may respond by retransmitting the failed packet (route 360).

Fig. 4 is a sequential flow diagram of an example process for packet forwarding during a handoff procedure in which the source node and target node 111 use different DRBs. As shown, the example of fig. 4 may include UE101, source node 111-1, and target node 111-2, which may each be an example of macro RAN node 111 or LP RAN node 112 described above with reference to fig. 1. The example of fig. 4 is provided as a non-limiting example. Indeed, the example of fig. 4 may include fewer, additional, and/or alternative operations or functions, such as one or more of the operations or functions of fig. 2, 3, 5, and 6. Additionally, one or more of the operations or functions of fig. 4 may be performed by fewer, additional, or alternative devices, which may include one or more of the devices described above with reference to fig. 1.

As shown, UE101 and source node 111-1 may transmit packets to each other (route 405). For example, source node 111-1 may receive packets intended for UE101 (from CN 120) and may temporarily store the packets in a local buffer memory of source node 111-1. The source node 111-1 may assign a SN to each packet before sending the packet to the UE 101. According to PDCP, the SN assigned to each packet can be based on the DRB used by source node 111-1 to send the packet to UE 101. The SN of a packet may be dispatched in an order consistent with the manner in which the packet is to be received, read, and/or processed by the UE 101. In transmitting packets to the UE101, the source node 111-1 may monitor which packets have been transmitted (and the time of transmission) and whether any transmitted packets have been acknowledged by the UE 101. When the UE101 indicates that one or more packets have not been received, the source node 111-1 may retransmit the identified packets, record the time of the retransmission, and continue to monitor whether the UE101 acknowledges the retransmitted packets. When the buffered packets are acknowledged by the UE101, the source node 111-1 may (immediately or periodically) remove the packets from the buffer.

Assume that source node 111-1 determines that UE101 should undergo a handover procedure involving target node 111-2 (block 410). In response, the source node 111-1 may stop sending packets of user data to the UE101 and determine which buffered packets to send to the target node 111-2. In some embodiments, the source node 111-1 may determine that the packets to be sent to the target node 111-2 include all packets sent to the UE101 measured from the oldest packet that has not yet been acknowledged by the UE 101. For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), the target node 111-2 may determine that packet 4-10 is to be sent to the target node 111-2 because packet 4 is the oldest packet that has not yet been acknowledged by the UE 101. In contrast, in some embodiments, source node 111-1 may determine that packets to be sent to target node 111-2 include only packets that have not been acknowledged by UE 101. For example, continuing with the example in which source node 111-1 sends packets 1-10 to UE101, and UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not 4, 5, or 8-10), target node 111-2 may determine to send only packets 4, 5, and 8-10 to target node 111-2 because packets 1-3 and 6-7 have been acknowledged by UE 101.

Source node 111-1 may transmit the determined packet to destination node 111-2 (route 420). As shown, each packet may include a corresponding SN and DRB ID. The DRB ID may indicate the DRB that source node 111-1 uses to determine the SN and that source node 111-1 will use to send the packet to UE 101. The source node 111-1 may inform the UE101 of the HO procedure (route 425), which may include configuration information for establishing a connection with the target node 111-2, by sending an RRC connection reconfiguration request message to the UE 101.

In some embodiments, where source node 111-1 is configured to determine that packets to be sent to target node 111-2 include all packets sent to UE101 since the oldest packet that has not yet been acknowledged by UE101, UE101 may operate similarly by dropping packets based on the oldest packet sent by source node 111-1 that has not been successfully received by UE101 (and thus has not been acknowledged) (block 430). For example, if source node 111-1 sends packets 1-10 to UE101, and UE101 only receives packets 1-3 and 6-7 (but does not receive 4, 5, or 8-10), UE101 may drop packets 4-10 because packet 4 is the oldest packet that UE101 has not yet received/acknowledged. In contrast, in embodiments where the source node 111-1 sends only unacknowledged packets (e.g., packets 4, 5, and 8-10) to the target node 111-2 such that the target node 111-2 may send only unacknowledged packets to the UE101, the UE101 may process and send successfully received packets (e.g., packets 1-3 and 6-7) from the source node 111-1 to an upper layer (e.g., IP layer or another type of layer 3 protocol) or the like without waiting for lost packets (e.g., packets 4, 5, and 8-10) from the target node 111-2 (block 435).

In response to receiving the packets from the source node 111-1, the target node 111-2 may buffer each packet and determine a DRB for forwarding the packet to the UE101 (block 440). As such, the DRB used by the target node 111-2 may be different from the DRB used by the source node 111-1. In addition, enabling the target node 111-2 to assign, determine and use preferred DRBs at this point in the HO procedure may mitigate the target node 111-2 from handing over DRBs later (e.g., after the HO procedure), as described above with reference to fig. 2.

Additionally, the target node 111-2 may determine a new SN for the packet based on the newly determined DRB and assign the new SN to each packet (block 445). In some embodiments, for each packet, target node 111-2 may map (e.g., create a record) the SN (and/or DRB) of source node 111-1 with the new SN (and/or DRB) from target node 111-2. Doing so may enable the target node 111-2 to ensure that the packet was successfully sent to the UE101, which may involve an acknowledgement message from the UE101, a retransmission from the target node 111-2. As part of the HO procedure, the UE101 may transmit an RRC connection reconfiguration complete message to the target node 111-2 (route 450), and the target node 111-2 may transmit packets to the UE101 using the same DRB as the source node 111-1 (block 455). In the event that the UE101 does not successfully receive the one or more transmitted packets, the UE101 may send a retransmission request for the failed packet to the target node 110, and the target node 111-2 may respond by retransmitting the failed packet (route 460).

Fig. 5 and 6 are sequential flow charts of examples of detailed procedures for packet forwarding during a handoff procedure. As shown, the example of FIG. 5 may include UE101, source node 111-1, target node 111-2, SGW 112, and user plane function device(s) 510.

Both the source node 111-1 and the target node 111-2 may be examples of the macro RAN node 111 or the LP RAN node 112 described above with reference to fig. 1. Similarly, SGW 122 may be an example of S-GW 122 of FIG. 1. The user plane function device(s) 510 may include one or more server devices that implement user plane functions (as opposed to, for example, control plane functions) of a 5G (or Next Generation (NG)) CN. According to embodiments, the SGW 122 and the user plane function device(s) 510 may correspond to the same CN or different CNs. For example, SGW 122 may correspond to an EPC supporting source node 111-1 and user plane function device(s) 510 may correspond to a 5G CN supporting target node 111-2.

The examples of fig. 5 and 6 are provided as non-limiting examples. In practice, the examples of fig. 5 and 6 may include fewer, additional, and/or alternative operations or functions, such as one or more of the operations or functions of fig. 2-4. Additionally, one or more of the operations or functions in fig. 5 and 6 may be performed by fewer, additional, or alternative devices, which may include one or more of the devices described above with reference to fig. 1.

Referring to FIG. 5, the UE101 may send information to and receive information from the CN120 via a connection with the source node 111-1 (route 505). Information may be transmitted through a User Data (UD) plane. For example, source node 111-1 may receive packets intended for UE101 (from CN 120) and may temporarily store the packets in a local buffer memory of source node 111-1. The source node 111-1 may assign a SN to each packet before sending the packet to the UE 101. According to PDCP, the SN assigned to each packet can be based on the DRB that source node 111-1 can use to send packets to UE 101. The SN of a packet may be dispatched in an order consistent with the manner in which the packet is to be received, read, and/or processed by the UE 101. In transmitting packets to the UE101, the source node 111-1 may monitor which packets have been transmitted (and the time of transmission) and whether any transmitted packets have been acknowledged by the UE 101. When the UE101 indicates that one or more packets have not been received, the source node 111-1 may retransmit the identified packets, record the time of the retransmission, and continue to monitor whether the UE101 acknowledges the retransmitted packets. When the buffered packets are acknowledged by the UE101, the source node 111-1 may (immediately or periodically) remove the packets from the buffer.

Assume that source node 111-1 determines that UE101 should undergo a handover procedure involving target node 111-2 (block 510). In response, source node 111-1 may stop sending packets of user data to UE101 and determine which buffered packets to send to target node 111-2. In some embodiments, the source node 111-1 may determine that the packets to be sent to the target node 111-2 include all packets sent to the UE101 measured from the oldest packet that has not yet been acknowledged by the UE 101. For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), the target node 111-2 may determine that packet 4-10 is to be sent to the target node 111-2 because packet 4 is the oldest packet that has not yet been acknowledged by the UE 101. In contrast, in some embodiments, the source node 111-1 may determine that packets to be sent to the target node 111-2 include only packets that have not been acknowledged by the UE 101. For example, continuing the example in which source node 111-1 sends packets 1-10 to UE101, and UE101 has acknowledged receipt of packets 1-3 and 6-7 (but not receipt of 4, 5, or 8-10), then target node 111-2 may determine to send only packets 4, 5, and 8-10 to target node 111-2 because packets 1-3 and 6-7 have been acknowledged by UE 101.

The source node 111-1 may send a layer 3(L3) HO request to the target node 111-2 (route 515). The request may include DRB mapping information, which may include an indication of the UE101 and the DRBs used by the source node 111-1 to communicate with the UE 101. In response, the target node 111-2 may perform admission control operations (block 520), which may include determining whether to accept or reject the HO request. The determination may be based on various factors, such as the availability of radio resources to communicate with the UE101, the level of congestion associated with the target node 111-2, and so forth. Assume that target node 111-2 determines to accept the HO request. As shown, the target node 111-2 may respond to the source node 111-1 by transmitting an L3 HO request confirm message (route 525), and in response, the source node 111-1 may send an L3RRC connection reconfiguration message to the UE 101. (route 530). The L3RRC connection reconfiguration message may include mobility control information, which may include instructions for UE101 to communicate with target node 111-2.

In response to the L3RRC connection reconfiguration message, the UE101 may detach from the source node 111-1 and synchronize to the target node 111-2 (block 535). In some embodiments, where the source node 111-1 is configured to determine that the packets to be sent to the target node 111-2 include all packets sent to the UE101 since the oldest packet that has not yet been acknowledged by the UE101, the UE101 may similarly operate by dropping packets based on the oldest packet sent by the source node 111-1 that the UE101 has not successfully received (and thus has not yet been acknowledged) (block 540). For example, if the source node 111-1 sends packets 1-10 to the UE101, and the UE101 only receives packets 1-3 and 6-7 (but does not receive 4, 5, or 8-10), the UE101 may drop packets 4-10 because packet 4 is the oldest packet that the UE101 has not yet received/acknowledged. In contrast, in embodiments where the source node 111-1 sends only unacknowledged packets (e.g., packets 4, 5, and 8-10) to the target node 111-2 such that the target node 111-2 may send only unacknowledged packets to the UE101, the UE101 may process and send successfully received packets (e.g., packets 1-3 and 6-7) from the source node 111-1 to upper layers (e.g., IP layer or another type of layer 3 protocol) and the like without waiting for lost packets (e.g., packets 4, 5, and 8-10) from the target node 111-2 (block 545).

The source node 111-1 may send L3 SN status transfer information (route 550), which may include communication standard information for performing a handover procedure, to the target node 111-2. The source node 111-1 may send UD packet data for forwarding purposes to the target node 111-2 (route 555). As described above, this may include all buffered packets (e.g., packets 1-3 and 6-7 instead of 4, 5, or 8-10) sent to the UE101 since the oldest packet that has not yet been acknowledged by the UE 101. Alternatively, this may include only packets buffered by the source node 111-1 and not acknowledged by the UE101 (e.g., packets 4, 5, and 8-10 instead of 1-3, 6, and 7). Upon receiving the packet from the source node 111-1, the target node 111-2 may buffer the packet (e.g., for processing and/or subsequent transmission to the UE 101).

According to an embodiment, target node 111-2 may process the received packet based on the packet data forwarding technique being implemented. For example, the target node 111-2 may map and/or assign packets to the same DRB used by the source node 111-1 to send the packets to the UE101 (see, e.g., FIG. 2). Alternatively, the target node may map the received packets to the QoS used by the source node 111-1 to send the packets to the UE101, and then allocate the received packets to a DRB preferred by the target node 111-2 (which may be the same or a different DRB as the DRB used by the source node 111-1 to send the packets to the UE 101) (see, e.g., FIG. 3). Yet another alternative, the target node 111-2 can determine and assign a preferred DRB for forwarding packets to the UE101 (which can be the same or a different DRB as used by the source node 111-1 to send packets to the UE 101), assign (e.g., insert) a new SN into the packet based on the determined DRB, and for each received packet, create a record that maps the SN assigned by the source node 111-1 to the new SN assigned by the target node 111-2 (see, e.g., FIG. 4).

Referring now to fig. 6, based on the RRC connection reconfiguration message from the source node 111-1, the UE101 may reconfigure itself for the handover procedure and send an L3RRC connection reconfiguration complete message to the target node 111-2 (route 605). In response, the target node 111-2 and the UE101 may transmit the user data packet to each other (route 610). For example, the target node 111-2 may forward packets received from the source node 111-1 to the UE101 in the Downlink (DL) direction. Additionally or alternatively, the UE101 may transmit packets to the target node 111-2 in the Uplink (UL) direction. The target node 111-2 may process packets received from the UE101 and/or forward packets received from the UE101 to the SGW 122 of the target node 111-2 (route 615).

The target node 111-2 may also send an L3 path switch request message to the user plane function device(s) 510 (route 620), and the user plane function device(s) 510 may respond by sending an L3 modify bearer request message to the SGW 122 (route 625). These messages may enable/cause devices of the CN120 to switch to a DL path for transmitting packets to the UE101 via the target node 111-2 according to a handover procedure. In addition, in response to the L3 modifying the bearer response message, the SGW 112 may switch DL path information (e.g., information indicating the DL path from the CN120 to the UE 101) based on the handover procedure (e.g., including the target node 111-2) and may send a UD end marker packet to the source node 111-1 (block and route 630). The end-marker packet may include an indication of the last packet for UE101 provided to source node 111-1 by CN 120.

The source node 111-1 may forward the UD end marker packet to the target node 111-2 (route 635), and the target node 111-2 and SGW 122 may transmit the packet to each other (route 640). The UD end marker packet may inform the target node 111-2 of the last packet for the UE101 provided by the CN120 to the source node 111-1. As such, target node 111-2 may use the end-marker packet to determine whether the packets from source node 111-1 include the last packet sent from CN120 to source node 111-1, and/or whether subsequent packets for UE101 received by target node 111-2 from CN120 start with the end-marker packet (e.g., whether packets provided from CN120 in the DL direction were lost during the handover procedure). If/when the target node 111-2 determines that a packet from the CN120 has been lost, the target node 111-2 may request retransmission of the lost packet.

The SGW 122 may send an L3 modify bearer response message to the user plane function device(s) 510 (route 645), which may correspond to the previous L3 modify bearer request message (see route 625). In response, the user plane function device(s) 510 may send an L3 path switch request confirm message to the target node 111-2 (route 650), which may correspond to the previous L3 switch request message (see route 620). In turn, the target node 111-2 may send an L3 UE context release message to the source node 111-1 (route 655), and the source node 111-1 may respond by releasing the radio resources used by the source node 111-1 to communicate with the UE101 (block 660).

As used herein, the terms "circuit," "processing circuit" or "logic" may refer to, be part of or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and/or memory (shared, dedicated, or group) that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. In some embodiments, the circuitry may be implemented in, or functions associated with, one or more software or firmware modules. In some embodiments, the circuitry may comprise logic operable, at least in part, in hardware.

The embodiments described herein may be implemented in a system using any suitably configured hardware and/or software. Fig. 7 illustrates example components of a device 700 according to some embodiments. In some embodiments, device 700 may include application circuitry 702, baseband circuitry 704, Radio Frequency (RF) circuitry 706, front-end module (FEM) circuitry 708, one or more antennas 710, and Power Management Circuitry (PMC)712, coupled together at least as shown. The illustrated components of the apparatus 700 may be included in a UE or RAN node. In some embodiments, the apparatus 700 may include fewer elements (e.g., the RAN node may not utilize the application circuitry 702, but instead include a processor/controller to process IP data received from the EPC). In some embodiments, device 700 may include additional elements, such as memory/storage, a display, a camera, sensors, or an input/output (I/O) interface. In other embodiments, the components described below may be included in more than one device (e.g., for a cloud RAN (C-RAN) implementation, the circuitry may be included in more than one device individually).

The application circuitry 702 may include one or more application processors. For example, the application circuitry 702 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor may include any combination of general-purpose processors and special-purpose processors (e.g., graphics processors, application processors, etc.). The processor may be coupled with or may include memory/storage and may be configured to: the instructions stored in the memory/storage are executed to enable various applications or operating systems to run on the device 700. In some embodiments, the processor of the application circuitry 702 may process IP data packets received from the EPC.

The baseband circuitry 704 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. Baseband circuitry 704 may include one or more baseband processors or control logic to process baseband signals received from the receive signal path of RF circuitry 706 and to generate baseband signals for the transmit signal path of RF circuitry 706. Baseband circuitry 704 may interface with application circuitry 702 to generate and process baseband signals and to control operation of RF circuitry 706. For example, in some embodiments, the baseband circuitry 704 may include a third generation (3G) baseband processor 704A, a fourth generation (4G) baseband processor 704B, a fifth generation (5G) baseband processor 704C, or other baseband processors 704D for other existing, developing, or future developed generations (e.g., second generation (2G), sixth generation (6G), etc.). The baseband circuitry 704 (e.g., one or more of the baseband processors 704A-D) may process various radio control functions that enable communication with one or more radio networks via the RF circuitry 706. In other embodiments, some or all of the functionality of the baseband processors 704A-D may be included in modules that are stored in the memory 704G and executed via a Central Processing Unit (CPU) 704E. The radio control functions may include, but are not limited to, signal modulation/demodulation, encoding/decoding, radio frequency shifting, and the like. In some embodiments, the modulation/demodulation circuitry of the baseband circuitry 704 may include Fast Fourier Transform (FFT), precoding, or constellation mapping/demapping functionality. In some embodiments, the encoding/decoding circuitry of baseband circuitry 704 may include convolution, tail-biting convolution, turbo, viterbi, or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functions are not limited to these examples, and other suitable functions may be included in other embodiments.

In some embodiments, the baseband circuitry 704 may include one or more audio Digital Signal Processors (DSPs) 704F. The audio DSP 704F may include elements for compression/decompression and echo cancellation, and may include other suitable processing elements in other embodiments. In some embodiments, the components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on the same circuit board. In some embodiments, some or all of the constituent components of baseband circuitry 704 and application circuitry 702 may be implemented together, for example, on a system on a chip (SOC).

In some embodiments, the baseband circuitry 704 may provide communications compatible with one or more radio technologies. For example, in some embodiments, baseband circuitry 704 may support communication with an Evolved Universal Terrestrial Radio Access Network (EUTRAN) or other Wireless Metropolitan Area Network (WMAN), Wireless Local Area Network (WLAN), Wireless Personal Area Network (WPAN). Embodiments in which the baseband circuitry 704 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry.

RF circuitry 706 may enable communication with a wireless network using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 706 may include switches, filters, amplifiers, and the like to facilitate communication with the wireless network. RF circuitry 706 may include a receive signal path that may include circuitry to down-convert RF signals received from FEM circuitry 708 and provide baseband signals to baseband circuitry 704. RF circuitry 706 may also include a transmit signal path that may include circuitry to upconvert baseband signals provided by baseband circuitry 704 and provide an RF output signal to FEM circuitry 708 for transmission.

In some embodiments, the receive signal path of RF circuit 706 may include a mixer circuit 706A, an amplifier circuit 706B, and a filter circuit 706C. In some embodiments, the transmit signal path of RF circuitry 706 may include filter circuitry 706C and mixer circuitry 706A. RF circuitry 706 may also include synthesizer circuitry 706D to synthesize the frequencies used by mixer circuitry 706A for the receive signal path and the transmit signal path. In some embodiments, mixer circuit 706A of the receive signal path may be configured to: the RF signal received from the FEM circuit 708 is downconverted based on the synthesized frequency provided by the synthesizer circuit 706D. The amplifier circuit 706B may be configured to amplify the downconverted signal, and the filter circuit 706C may be a Low Pass Filter (LPF) or a Band Pass Filter (BPF) configured to: unwanted signals are removed from the down-converted signal to generate an output baseband signal. The output baseband signal may be provided to baseband circuitry 704 for further processing. In some embodiments, the output baseband signal may be a zero frequency baseband signal, but this is not required. In some embodiments, mixer circuit 706A of the receive signal path may comprise a passive mixer, although the scope of the embodiments is not limited in this respect.

In some embodiments, the mixer circuit 706A of the transmit signal path may be configured to: the input baseband signal is upconverted based on the synthesized frequency provided by the synthesizer circuit 706D to generate an RF output signal for the FEM circuit 708. The baseband signal may be provided by baseband circuitry 704 and may be filtered by filter circuitry 706C.

In some embodiments, mixer circuit 706A of the receive signal path and mixer circuit 706A of the transmit signal path may include two or more mixers and may be arranged for quadrature down-conversion and up-conversion, respectively. In some embodiments, mixer circuit 706A of the receive signal path and mixer circuit 706A of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, mixer circuit 706A of the receive signal path and mixer circuit 706A of the transmit signal path may be arranged for direct down-conversion and direct up-conversion, respectively. In some embodiments, mixer circuit 706A of the receive signal path and mixer circuit 706A of the transmit signal path may be configured for superheterodyne operation.

In some embodiments, the output baseband signal and the input baseband signal may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternative embodiments, the output baseband signal and the input baseband signal may be digital baseband signals. In these alternative embodiments, RF circuitry 706 may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry, and baseband circuitry 704 may include a digital baseband interface to communicate with RF circuitry 706.

In some dual-mode embodiments, separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect.

In some embodiments, synthesizer circuit 706D may be a fractional-N synthesizer or a fractional-N/N +1 synthesizer, although the scope of embodiments is not so limited as other types of frequency synthesizers may be suitable. For example, the synthesizer circuit 706D may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer including a phase locked loop with a frequency divider.

The synthesizer circuit 706D may be configured to: the output frequency is synthesized based on the frequency input and the divider control input for use by mixer circuit 706A of RF circuit 706. In some embodiments, the synthesizer circuit 706D may be a fractional N/N +1 synthesizer.

In some embodiments, the frequency input may be provided by a Voltage Controlled Oscillator (VCO), but this is not required. The divider control input may be provided by the baseband circuitry 704 or the application processor 702, depending on the desired output frequency. In some embodiments, the divider control input (e.g., N) may be determined from a look-up table based on the channel indicated by the application processor 702.

Synthesizer circuit 706D of RF circuit 706 may include a divider, a Delay Locked Loop (DLL), a multiplexer, and a phase accumulator. In some embodiments, the divider may be a dual-mode divider (DMD) and the phase accumulator may be a Digital Phase Accumulator (DPA). In some embodiments, the DMD may be configured to: the input signal is divided by N or N +1 (e.g., based on a carry) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded tunable delay elements, a phase detector, a charge pump, and a D flip-flop. In these embodiments, the delay elements may be configured to decompose the VCO period into Nd equal phase groups, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

In some embodiments, synthesizer circuit 706D may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with a quadrature generator and divider circuit to generate a plurality of signals at the carrier frequency having a plurality of different phases relative to each other. In some embodiments, the output frequency may be the LO frequency (fLO). In some embodiments, the RF circuitry 706 may include an IQ/polar converter.

FEM circuitry 708 may include a receive signal path, which may include circuitry configured to operate on RF signals received from one or more antennas 710, amplify the received signals, and provide amplified versions of the received signals to RF circuitry 706 for further processing. FEM circuitry 708 may also include a transmit signal path, which may include circuitry configured to amplify signals provided by RF circuitry 706 for transmission by one or more of the one or more antennas 710. In various embodiments, amplification through either the transmit signal path or the receive signal path may be done in only the RF circuitry 706, only the FEM 708, or both the RF circuitry 706 and the FEM 708.

In some embodiments, FEM circuitry 708 may include a TX/RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include an LNA for amplifying the received RF signal and providing the amplified received RF signal as an output (e.g., to RF circuitry 706). The transmit signal path of the FEM circuitry 708 may include: a Power Amplifier (PA) to amplify an input RF signal (e.g., provided by RF circuitry 706); and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 710).

In some embodiments, PMC 712 may manage power provided to baseband circuitry 704. In particular, PMC 712 may control power selection, voltage scaling, battery charging, or DC-DC conversion. PMC 712 may generally be included when device 700 is capable of being powered by a battery, such as when the device is included in a UE. PMC 712 may improve power conversion efficiency while providing desired implementation size and heat dissipation characteristics.

Although fig. 7 shows PMC 712 coupled only to baseband circuitry 704, in other embodiments PMC 712 may additionally or alternatively be coupled to other components and perform similar power management operations for other components, such as, but not limited to, application circuitry 702, RF circuitry 706, or FEM 708.

In some embodiments, PMC 712 may control, or be part of, various power saving mechanisms of device 700. For example, if the device 700 is in an RRC _ Connected state (where it is still Connected to the RAN node because it is expected to receive traffic soon thereafter), it may enter a state called discontinuous reception mode (DRX) after a period of inactivity. During this state, the device 700 may be powered down for a brief interval of time, thereby saving power.

If there is no data traffic activity for an extended period of time, the device 700 may transition to the RRC _ Idle state (where it is disconnected from the network and no operations such as channel quality feedback, handover, etc. are performed). The device 700 enters a very low power state and it performs paging, where it again periodically wakes up to listen to the network and then powers down again. The device 700 may not receive data in this state and in order to receive data it must transition back to the RRC Connected state.

The additional power-save mode may allow the device to be unavailable to the network for a period longer than the paging interval (ranging from a few seconds to a few hours). During this time, the device is completely inaccessible to the network and may be completely powered down. Any data sent during this time will incur a large delay and it is assumed that the delay is acceptable.

The processor of the application circuitry 702 and the processor of the baseband circuitry 704 may be used to execute elements of one or more instances of a protocol stack. For example, the processor of the baseband circuitry 704 (alone or in combination) may be configured to perform layer 3, layer 2, or layer 1 functions, while the processor of the application circuitry 704 may utilize data (e.g., packet data) received from these layers and further perform layer 4 functions (e.g., Transmission Communication Protocol (TCP) and User Datagram Protocol (UDP) layers). As mentioned herein, layer 3 may include a Radio Resource Control (RRC) layer, described in further detail below. As mentioned herein, layer 2 may include a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, and a Packet Data Convergence Protocol (PDCP) layer, as will be described in further detail below. As mentioned herein, layer 1 may comprise the Physical (PHY) layer of the UE/RAN node, as will be described in further detail below.

Fig. 8 illustrates an example interface of a baseband circuit according to some embodiments. As discussed above, the baseband circuitry 704 of fig. 7 may include processors 704A-704E and memory 704G used by the processors. Each of the processors 704A-704E may include a memory interface to send and receive data to and from the memory 704G, respectively.

Baseband circuitry 704 may also include one or more interfaces to communicatively couple to other circuitry/devices, such as a memory interface 812 (e.g., an interface to send/receive data to/from memory external to baseband circuitry 704), an application circuitry interface 814 (e.g., an interface to send/receive data to/from application circuitry 702 of fig. 7), an RF circuitry interface 816 (e.g., an interface to send/receive data to/from RF circuitry 706 of fig. 7), a wireless hardware connection interface 819 (e.g., an interface to send/receive data to/from Near Field Communication (NFC) components, a wireless interface, a wireless transceiver, a wireless interface, a wireless transceiver, a wireless interface, a wireless transceiver, a wireless interface, a wireless transceiver, a wireless,

Components (e.g. low power consumption)

)、

Component and other communication component routingAn interface to receive data) and a power management interface 820 (e.g., an interface to send/receive power or control signals to/from PMC 712).

Fig. 9 is a block diagram illustrating components capable of reading instructions from a machine-readable or computer-readable medium (e.g., a non-transitory machine-readable storage medium) and performing any one or more of the methodologies discussed herein, according to some example embodiments. In particular, fig. 9 shows a graphical representation of hardware resources 900, including one or more processors (or processor cores) 910, one or more memory/storage devices 920, and one or more communication resources 930, each of which may be communicatively coupled via a bus 940. For embodiments utilizing node virtualization (e.g., NFV), hypervisor 902 may be executed to provide an execution environment for one or more network slices/subslices to utilize hardware resources 900.

Processor 910 (e.g., a Central Processing Unit (CPU), a Reduced Instruction Set Computing (RISC) processor, a Complex Instruction Set Computing (CISC) processor, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP) such as a baseband processor, an Application Specific Integrated Circuit (ASIC), a Radio Frequency Integrated Circuit (RFIC), another processor, or any suitable combination thereof) may include, for example, processor 912 and processor 914.

Memory/storage 920 may include a main memory, a disk storage, or any suitable combination thereof. Memory/storage 920 may include, but is not limited to, any type of volatile or non-volatile memory, such as Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, solid state storage, and the like.

The communication resources 930 may include interconnection or network interface components or other suitable devices to communicate with one or more peripheral devices 904 or one or more databases 906 via the network 908. For example, communication resources 930 may include wired communication components (e.g., for coupling via a Universal Serial Bus (USB)), cellular communication components, NFC components, and/or the like,

Components (e.g. low power consumption)

)、

Components and other communication components.

The instructions 950 may include software, a program, an application, an applet, an app, or other executable code for causing at least any one of the processors 910 to perform any one or more of the methodologies discussed herein. The instructions 950 may reside, completely or partially, within at least one of the processor 910 (e.g., within a cache of the processor), the memory/storage 920, or any suitable combination thereof. Further, any portion of instructions 950 may be transmitted to hardware resource 900 from any combination of peripherals 904 or database 906. Thus, the memory of the processor 910, memory/storage 920, peripherals 904, and database 906 are examples of computer-readable and machine-readable media.

Next, many examples will be given regarding embodiments of the above-described technology.

In a first example, an apparatus of a Radio Access Network (RAN) node may comprise: an interface for Radio Frequency (RF) circuitry; and one or more processors configured to: inserting a Sequence Number (SN) into each of a plurality of user data packets directed to a User Equipment (UE) connected to a RAN node, the SN based on a relative sequential position of each of the plurality of user data packets; and prior to causing at least one of the plurality of user data packets to be transmitted to the UE via the RF circuitry, determining that the UE is to be transferred to a target RAN node as part of a handover procedure during which the at least one user data packet is transferred to the target RAN node along with an indication of how at least one data packet would have been transmitted to the UE by the RAN node prior to the handover procedure.

In example 2, the subject matter of example 1 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the RAN node for transmission of the plurality of user data packets to the UE.

In example 3, the subject matter of example 2 or any example herein, wherein the indication comprises an identifier of the DRB.

In example 4, the subject matter of example 1 or any example herein, wherein the SN of each user data packet is further based on a quality of service (QoS) associated with transmitting the plurality of user data packets to the UE.

In example 5, the subject matter of example 4 or any example herein, wherein the indication comprises an identifier of a QoS class associated with transmitting the plurality of user data packets to the UE.

In example 6, the subject matter of example 1 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having caused the at least one user data packet to be sent to the UE.

In example 7, the subject matter of example 1 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding the at least one user data packet.

In example 8, the subject matter of example 1 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding a user data packet preceding the at least one user data packet.

In example 9, an apparatus of a Radio Access Network (RAN) node may include: an interface for Radio Frequency (RF) circuitry; and one or more processors configured to: receiving a plurality of user data packets from a source RAN node of a handover procedure, the plurality of user data packets directed to a User Equipment (UE) corresponding to the handover procedure, each user data packet of the plurality of user data packets comprising a Sequence Number (SN) based on a relative sequential position of each user data packet of the plurality of user data packets; determining a Data Radio Bearer (DRB) for transmitting the plurality of user data packets to the UE; receiving, via an interface of the RF circuitry, an indication that the UE is ready to communicate with the RAN node as part of the handover procedure; and causing the plurality of user data packets to be transmitted to the UE via the interface of the RF circuitry using the DRB.

In example 10, the subject matter of example 9 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the source RAN node for transmission of the plurality of user data packets to the UE.

In example 11, the subject matter of example 10 or any example herein, wherein each user data packet of the plurality of user data packets comprises an identifier associated with a DRB assigned by the source RAN node.

In example 12, the subject matter of example 11 or any example herein, wherein the one or more processors determine the DRB based on the identifier, such that the one or more processors cause the plurality of user data packets to be transmitted to the UE using a DRB allocated by the source RAN node.

In example 13, the subject matter of example 11 or any example herein, wherein: a DRB for transmitting the plurality of user data packets to the UE is different from the DRB allocated by the source RAN node, and the one or more processors are further to: mapping the SN to another Sequence Number (SN) that is based on a DRB used to transmit the plurality of user data packets; and inserting the further Sequence Number (SN) into each of the plurality of user data packets.

In example 14, the subject matter of example 9 or any example herein, wherein the SN of each user data packet is based on a quality of service (QoS) associated with a source RAN node transmitting the plurality of user data packets to the UE.

In example 15, the subject matter of example 14 or any example herein, wherein the one or more processors are further to: determining a quality of service (QoS) with which the RAN node is to transmit the plurality of user data packets to the UE; and mapping an identifier associated with the QoS included in the plurality of user data packets to a QoS with which the RAN node is to transmit the plurality of user data packets to the UE.

In example 16, the subject matter of example 9 or any example herein, wherein the one or more processors are further to: determining that the UE has received the plurality of user data packets; determining another DRB for communication with the UE and different from the DRB; and causing the other DRB to be used in place of the DRB for communication with the UE.

In example 17, the subject matter of example 9 or any example herein, wherein prior to causing the plurality of user data packets to be transmitted to the UE, the one or more processors are further to: determining the other DRB; transmitting configuration information for handover to the other DRB to the UE; and communicating with the UE using the other DRB after transmitting the plurality of user data packets to the UE.

In example 18, the subject matter of example 9 or any example herein, wherein the one or more processors are further to receive an acknowledgement from the UE regarding at least one user data packet of the plurality of user data packets and exclude the at least one user data packet from being sent to the UE.

In example 19, the subject matter of example 9 or any example herein, wherein the one or more processors are further to receive an end-marker packet indicating that the UE has received the plurality of user data packets.

In example 20, the subject matter of example 1 or 9, or any example herein, wherein the RAN node comprises a new air interface (NR) base station.

In example 21, the subject matter of example 1 or 9, or any example herein, wherein the plurality of user data packets are transmitted via a user plane of a wireless telecommunications network.

In example 22, an apparatus of a User Equipment (UE) may include: an interface for Radio Frequency (RF) circuitry; and one or more processors configured to: receiving, via an interface of the RF circuitry, a plurality of first user data packets from a first Radio Access Network (RAN) node, each user data packet of the plurality of first user data packets comprising a Sequence Number (SN) based on an order position of each user data packet of the plurality of first user data packets; receiving, via an interface of the RF circuitry, an instruction to participate in a handover procedure involving the first RAN node and a second RAN node; receiving, as part of a handover procedure, a plurality of second user data packets from the second RAN node via an interface of the RF circuitry, each user data packet of the plurality of second user data packets comprising a SN based on a sequential position of each user data packet relative to the plurality of first user data packets and the plurality of second user data packets; and merging the plurality of first user data packets with the plurality of second user data packets based on the SN of each of the plurality of first user data packets and the plurality of second user data packets.

In example 23, the subject matter of example 22 or any example herein, wherein the one or more processors are further configured to: based on the instruction, cause a message to be transmitted to the second RAN node via an interface of the RF circuitry indicating that the UE is configured to communicate with the second RAN node.

In example 24, the subject matter of example 22 or any example herein, wherein the one or more processors are further to: determining whether a transmission failure occurs based on a SN of each of the plurality of first user data packets and the plurality of second user data packets; and transmitting a retransmission request for a user data packet corresponding to the transmission failure to the second RAN node.

In example 25, the subject matter of example 22 or any example herein, wherein the one or more processors are further to: for at least one user data packet of the plurality of first user data packets, deleting the at least one user data packet based on the at least one user data packet in accordance with the UE not sending an acknowledgement message to the first RAN node; and receiving another copy of the at least one user data packet as part of a plurality of second user data packets from the second RAN node.

In example 26, the subject matter of example 25 or any example herein, wherein the one or more processors are further to: deleting another user data packet of the first plurality of user data packets based on the another user data packet having a SN after the SN of the at least one user data packet.

In example 27, the subject matter of example 22 or any example herein, wherein the one or more processors are further to: determining that all of the plurality of first user data packets and the plurality of second user data packets have been received, and causing an end-marker packet to be transmitted to the second RAN node indicating that all of the plurality of first user data packets and the plurality of second user data packets have been received.

In example 28, a computer-readable medium may contain program instructions to cause one or more processors associated with a Radio Access Network (RAN) node to: inserting a Sequence Number (SN) into each of a plurality of user data packets directed to a User Equipment (UE) connected to a RAN node, the SN based on a relative sequential position of each of the plurality of user data packets; and prior to causing at least one of the plurality of user data packets to be transmitted to the UE, determining that the UE is to be transferred to a target RAN node as part of a handover procedure, and causing the at least one user data packet to be transferred to the target RAN node during the handover procedure, along with an indication of how at least one data packet would have been transmitted to the UE by the RAN node prior to the handover procedure.

In example 29, the subject matter of example 28 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the RAN node for transmission of the plurality of user data packets to the UE.

In example 30, the subject matter of example 29 or any example herein, wherein the indication comprises an identifier of the DRB.

In example 31, the subject matter of example 28 or any example herein, wherein the SN of each user data packet is further based on a quality of service (QoS) associated with transmitting the plurality of user data packets to the UE.

In example 32, the subject matter of example 31 or any example herein, wherein the indication comprises an identifier of a QoS class associated with transmitting the plurality of user data packets to the UE.

In example 33, the subject matter of example 28 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having caused the at least one user data packet to be sent to the UE.

In example 34, the subject matter of example 28 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding the at least one user data packet.

In example 35, the subject matter of example 28 or any example herein, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding a user data packet preceding the at least one user data packet.

In example 36, a computer-readable medium may contain program instructions to cause one or more processors associated with a Radio Access Network (RAN) node to: receiving a plurality of user data packets from a source RAN node of a handover procedure, the plurality of user data packets being directed to a User Equipment (UE) corresponding to the handover procedure, each user data packet of the plurality of user data packets comprising a Sequence Number (SN) based on a relative ordinal position of each user data packet of the plurality of user data packets; determining a Data Radio Bearer (DRB) for transmitting the plurality of user data packets to the UE; receiving, as part of the handover procedure, an indication that the UE is ready to communicate with the RAN node; and causing the plurality of user data packets to be transmitted to the UE using the DRB.

In example 37, the subject matter of example 36 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the source RAN node for transmission of the plurality of user data packets to the UE.

In example 38, the subject matter of example 37 or any example herein, wherein each user data packet of the plurality of user data packets comprises an identifier associated with a DRB assigned by the source RAN node.

In example 39, the subject matter of example 38 or any example herein, wherein the one or more processors determine the DRB based on the identifier, such that the one or more processors cause the plurality of user data packets to be transmitted to the UE using a DRB allocated by the source RAN node.

In example 40, the subject matter of example 38 or any example herein, wherein: the DRBs for transmitting the plurality of user data packets to the UE are different from the DRBs allocated by the source RAN node, and the one or more processors are further configured to: mapping the SN to another Sequence Number (SN) that is based on a DRB used to transmit the plurality of user data packets; and inserting the further Sequence Number (SN) into each of the plurality of user data packets.

In example 41, the subject matter of example 36 or any example herein, wherein the SN of each user data packet is based on a quality of service (QoS) associated with a source RAN node transmitting the plurality of user data packets to the UE.

In example 42, the subject matter of example 41 or any example herein, wherein the one or more processors are further to: determining a quality of service (QoS) with which the RAN node is to transmit the plurality of user data packets to the UE; and mapping an identifier associated with the QoS included in the plurality of user data packets to a QoS with which the RAN node is to transmit the plurality of user data packets to the UE.

In example 43, the subject matter of example 36 or any example herein, wherein the one or more processors are further to: determining that the UE has received the plurality of user data packets; determining another DRB for communication with the UE and different from the DRB; and causing the other DRB to be used in place of the DRB for communication with the UE.

In example 44, the subject matter of example 36 or any example herein, wherein, prior to causing the plurality of user data packets to be transmitted to the UE, the one or more processors are further to: determining the other DRB; transmitting configuration information for handover to the other DRB to the UE; and communicating with the UE using the other DRB after transmitting the plurality of user data packets to the UE.

In example 45, the subject matter of example 36 or any example herein, wherein the one or more processors are further to receive an acknowledgement from the UE regarding at least one user data packet of the plurality of user data packets and exclude the at least one user data packet from being sent to the UE.

In example 46, the subject matter of example 36 or any example herein, wherein the one or more processors are further to receive an end-marker packet indicating that the UE has received the plurality of user data packets.

In example 47, the subject matter of example 28 or 36, or any example herein, wherein the RAN node comprises a new air interface (NR) base station.

In example 48, the subject matter of example 28 or 36, or any example herein, wherein the plurality of user data packets are transmitted via a user plane of a wireless telecommunications network.

In an example 49, a computer-readable medium may contain program instructions to cause one or more processors associated with a User Equipment (UE) to: receiving a plurality of first user data packets from a first Radio Access Network (RAN) node, each of the plurality of first user data packets comprising a Sequence Number (SN) based on an order position of each of the plurality of first user data packets; receiving an instruction to participate in a handover procedure involving the first RAN node and a second RAN node; receiving, as part of the handover procedure, a plurality of second user data packets from the second RAN node, each user data packet of the plurality of second user data packets comprising a SN based on an ordinal position of each user data packet with respect to the plurality of first user data packets and the plurality of second user data packets; and merging the plurality of first user data packets with the plurality of second user data packets based on the SN of each of the plurality of first user data packets and the plurality of second user data packets.

In example 50, the subject matter of example 49 or any example herein, wherein the one or more processors are further to: based on the instruction, cause a message to be transmitted to the second RAN node indicating that the UE is configured to communicate with the second RAN node.

In example 51, the subject matter of example 49 or any example herein, wherein the one or more processors are further to: determining whether a transmission failure occurs based on a SN of each of the plurality of first user data packets and the plurality of second user data packets; and transmitting a retransmission request for a user data packet corresponding to the transmission failure to the second RAN node.

In example 52, the subject matter of example 49 or any example herein, wherein the one or more processors are further to: for at least one user data packet of the plurality of first user data packets, deleting the at least one user data packet based on the at least one user data packet in accordance with the UE not sending an acknowledgement message to the first RAN node; and receiving another copy of the at least one user data packet as part of a plurality of second user data packets from the second RAN node.

In example 53, the subject matter of example 52 or any example herein, wherein the one or more processors are further to: deleting another user data packet of the plurality of first user data packets based on the another user data packet having a SN after the SN of the at least one user data packet.

In example 54, the subject matter of example 49 or any example herein, wherein the one or more processors are further to: determining that all of the plurality of first user data packets and the plurality of second user data packets have been received, and causing an end-marker packet to be transmitted to the second RAN node indicating that all of the plurality of first user data packets and the plurality of second user data packets have been received.

In example 55, the apparatus of the Radio Access Network (RAN) node may comprise: means for inserting a Sequence Number (SN) into each of a plurality of user data packets directed to a User Equipment (UE) connected to a RAN node, the SN based on a relative sequential position of each of the plurality of user data packets; means for determining that the UE is to be transferred to a target RAN node as part of a handover procedure prior to causing at least one of the plurality of user data packets to be transmitted to the UE; and means for causing the at least one user data packet to be transferred to the target RAN node during the handover procedure, along with an indication of how at least one data packet would have been transmitted by the RAN node to the UE prior to the handover procedure.

In example 56, the subject matter of example 55 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the RAN node for transmission of the plurality of user data packets to the UE.

In example 57, the subject matter of example 56 or any example herein, wherein the indication comprises an identifier of the DRB.

In example 58, the subject matter of example 55 or any example herein, wherein the SN of each user data packet is further based on a quality of service (QoS) associated with transmitting the plurality of user data packets to the UE.

In example 59, the subject matter of example 58 or any example herein, wherein the indication comprises an identifier of a QoS class associated with transmitting the plurality of user data packets to the UE.

In example 60, the subject matter of example 55, or any example herein, further comprising: means for causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having caused the at least one user data packet to be sent to the UE.

In example 61, the subject matter of example 55, or any example herein, further comprising: means for causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding the at least one user data packet.

In example 62, the subject matter of example 55, or any example herein, further comprising: means for causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding a user data packet preceding the at least one user data packet.

In example 63, the apparatus of the Radio Access Network (RAN) node may comprise: means for receiving a plurality of user data packets from a source RAN node of a handover procedure, the plurality of user data packets directed to a User Equipment (UE) corresponding to the handover procedure, each user data packet of the plurality of user data packets comprising a Sequence Number (SN) based on a relative sequential position of each user data packet of the plurality of user data packets; means for determining a Data Radio Bearer (DRB) for transmitting the plurality of user data packets to the UE; means for receiving an indication that the UE is ready to communicate with the RAN node as part of the handover procedure; and means for causing the plurality of user data packets to be transmitted to the UE using the DRB.

In example 64, the subject matter of example 63 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the source RAN node for transmission of the plurality of user data packets to the UE.

In example 65, the subject matter of example 64 or any example herein, wherein each user data packet of the plurality of user data packets comprises an identifier associated with a DRB assigned by the source RAN node.

In example 66, the subject matter of example 65, or any example herein, further comprising: means for determining the DRB based on the identifier, such that the one or more processors cause the plurality of user data packets to be transmitted to the UE using the DRB allocated by the source RAN node.

In example 67, the subject matter of example 65 or any example herein, wherein: the DRBs for transmitting the plurality of user data packets to the UE are different from the DRBs allocated by the source RAN node, and the apparatus further comprises: means for mapping the SN to another Sequence Number (SN) that is based on a DRB used to transmit the plurality of user data packets; and means for inserting the further Sequence Number (SN) into each of the plurality of user data packets.

In example 68, the subject matter of example 63 or any example herein, wherein the SN of each user data packet is based on a quality of service (QoS) associated with a source RAN node transmitting the plurality of user data packets to the UE.

In example 69, the subject matter of example 68, or any example herein, further comprising: means for determining a quality of service (QoS) with which the RAN node is to transmit the plurality of user data packets to the UE; and means for mapping an identifier associated with the QoS included in the plurality of user data packets to a QoS utilized by a RAN node to transmit the plurality of user data packets to the UE.

In example 70, the subject matter of example 63, or any example herein, further comprising: means for determining that the UE has received the plurality of user data packets; means for determining another DRB for communicating with the UE and different from the DRB; and means for causing the other DRB to be used in place of the DRB for communication with the UE.

In example 71, the subject matter of example 63, or any example herein, further comprising: means for determining the other DRB prior to causing the plurality of user data packets to be transmitted to the UE; means for causing configuration information for handover to the other DRB to be sent to the UE; and means for communicating with the UE using the other BRD after transmitting the plurality of user data packets to the UE.

In example 72, the subject matter of example 63, or any example herein, further comprising: means for receiving an acknowledgement from the UE regarding at least one user data packet of the plurality of user data packets and excluding the at least one user data packet from being sent to the UE.

In example 73, the subject matter of example 63, or any example herein, further comprising: means for receiving an end-marker packet indicating that the UE has received the plurality of user data packets.

In example 74, the subject matter of example 55 or 66 or any example herein, wherein the RAN node comprises a new air interface (NR) base station.

In example 75, the subject matter of example 55 or 66 or any example herein, wherein the plurality of user data packets are transmitted via a user plane of a wireless telecommunications network.

In example 76, a method performed by a Radio Access Network (RAN) node may comprise: inserting a Sequence Number (SN) into each of a plurality of user data packets directed to a User Equipment (UE) connected to a RAN node, the SN based on a relative sequential position of each of the plurality of user data packets; and prior to causing at least one of the plurality of user data packets to be transmitted to the UE, determining that the UE is to be transferred to a target RAN node as part of a handover procedure, and causing the at least one user data packet to be transferred to the target RAN node during the handover procedure, along with an indication of how at least one data packet would have been transmitted to the UE by the RAN node prior to the handover procedure.

In example 77, the subject matter of example 76 or any example herein, wherein the SN of each user data packet is further based on a Data Radio Bearer (DRB) allocated by the RAN node for transmission of the plurality of user data packets to the UE.

In example 78, the subject matter of example 77 or any example herein, wherein the indication comprises an identifier of the DRB.

In example 79, the subject matter of example 76 or any example herein, wherein the SN of each user data packet is further based on a quality of service (QoS) associated with transmitting the plurality of user data packets to the UE.

In example 80, the subject matter of example 79 or any example herein, wherein the indication comprises an identifier of a QoS class associated with transmitting the plurality of user data packets to the UE.

In example 81, the subject matter of example 76 or any example herein, further comprising: causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding the at least one user data packet.

In example 82, the subject matter of example 76 or any example herein, further comprising: causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding a user data packet preceding the at least one user data packet.

In example 83, the subject matter of example 76 or any example herein, further comprising: causing the at least one user data packet to be transferred to the target RAN node based on the RAN node not having caused the at least one user data packet to be sent to the UE.

In the foregoing specification, various embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

For example, while a series of signals and/or operations have been described with respect to fig. 2-6, the order of the signals/operations may be modified in other implementations. Furthermore, independent signals may be executed in parallel.

It will be apparent that the example aspects described above may be implemented in many different forms of software, firmware, and hardware in the implementations illustrated in the figures. The actual software code or specialized control hardware used to implement these aspects should not be construed as limiting. Thus, the operation and behavior of the aspects were described without reference to the specific software code — it being understood that software and control hardware may be designed to implement the aspects based on the description herein.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to be limiting. Indeed, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification.

No element, act, or instruction used in the present application should be construed as critical or essential unless explicitly described as such. An example of the use of the word "and" as used herein does not necessarily exclude interpretation of the phrase "and/or" in that example. Similarly, an instance of use of the word "or" as used herein does not necessarily exclude interpretation of the phrase "and/or" in that instance. Further, as used herein, the article "a" is intended to include one or more items, and may be used interchangeably with the phrase "one or more. Where there is only one item, the words "a," "an," "only," or similar language are used.

Claims

1. An apparatus of a radio access network, RAN, node, the apparatus comprising:

an interface to a radio frequency RF circuit; and

one or more processors configured to:

inserting a sequence number, SN, into at least one of a plurality of user data packets directed to a user equipment, UE, connected to a RAN node, the SN being based on a relative sequential position of the plurality of user data packets; and is

Prior to causing the at least one of the plurality of user data packets to be transmitted to the UE via the RF circuitry,

determining, as part of a handover procedure, that the UE is to be transferred to a target RAN node,

causing the at least one user data packet to be transferred to the target RAN node during the handover procedure, along with an indication of how the at least one user data packet would have been transmitted to the UE by the RAN node via the interface prior to the handover procedure, wherein the indication comprises an identifier of a data radio bearer, DRB, allocated by the RAN node for transmission of the plurality of user data packets to the UE, and wherein the target RAN node determines whether to use the DRB or another DRB different from the DRB for transmission of the at least one user data packet to the UE.

2. The apparatus of claim 1, wherein the SN of the at least one user data packet is further based on the DRB.

3. The apparatus of claim 1, wherein the SN of the at least one user data packet is further based on a quality of service (QoS) associated with transmitting the plurality of user data packets to the UE.

4. The apparatus of claim 3, wherein the indication comprises an identifier of a QoS class associated with transmitting the plurality of user data packets to the UE.

5. The apparatus of claim 1 or 4, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having caused the at least one user data packet to be transmitted to the UE.

6. The apparatus of claim 1 or 4, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding the at least one user data packet.

7. The apparatus of claim 1 or 4, wherein the one or more processors cause the at least one user data packet to be transferred to the target RAN node based on the RAN node not having received an acknowledgement message from the UE regarding a user data packet preceding the at least one user data packet.

8. The apparatus of claim 1, wherein the RAN node comprises a new air interface, NR, base station.

9. The apparatus of claim 1 or 8, wherein the plurality of user data packets are transmitted via a user plane of a wireless telecommunications network.

10. An apparatus of a radio access network, RAN, node, the apparatus comprising:

an interface to a Radio Frequency (RF) circuit; and

one or more processors configured to:

receiving a plurality of user data packets from a source RAN node of a handover procedure, the plurality of user data packets being directed to a user equipment, UE, corresponding to the handover procedure, at least one of the plurality of user data packets comprising a sequence number, SN, based on a relative sequential position of the plurality of user data packets;

receiving, from the source RAN node, an indication of how the at least one of the plurality of user data packets would otherwise be transmitted by the source RAN node to the UE prior to the handover procedure, wherein the indication comprises an identifier of a data radio bearer, DRB, allocated by the RAN node for transmission of the plurality of user data packets to the UE;

determining, based on the indication, whether to use the DRB or another DRB different from the DRB for transmitting the plurality of user data packets to the UE;

receiving, via the interface, an indication that the UE is ready to communicate with the RAN node as part of the handover procedure; and is

Causing the plurality of user data packets to be transmitted to the UE via the interface using the DRB.

11. The apparatus of claim 10, wherein the SN of the at least one user data packet is further based on the DRB.

12. The apparatus of claim 10, wherein:

the one or more processors are further to:

mapping the SN to another Sequence Number (SN) that is based on the DRB used to transmit the plurality of user data packets; and

inserting the further sequence number SN into the at least one of the plurality of user data packets.

13. The apparatus of claim 10, wherein the SN of the at least one user data packet is based on a quality of service, QoS, associated with the source RAN node transmitting the plurality of user data packets to the UE.

14. The apparatus of claim 13, wherein the one or more processors are further configured to:

determining a quality of service, QoS, with which the RAN node is to transmit the plurality of user data packets to the UE; and

mapping an identifier associated with the QoS included in the plurality of user data packets to the QoS with which the RAN node is to transmit the plurality of user data packets to the UE.

15. The apparatus of claim 10 or 14, wherein the one or more processors are further configured to:

determining that the UE has received the plurality of user data packets;

determining another DRB different from the DRB for communication with the UE; and

causing the other DRB to be used in place of the DRB for communication with the UE.

16. The apparatus of claim 10 or 14, wherein prior to causing the plurality of user data packets to be transmitted to the UE, the one or more processors are further to:

determining another DRB;

configuration information for handover to the other DRB is transmitted to the UE; and

communicating with the UE using the other DRB after transmitting the plurality of user data packets to the UE.

17. The apparatus of claim 10 or 14, wherein the one or more processors are further to receive an acknowledgement from the UE regarding at least one user data packet of the plurality of user data packets and exclude the at least one user data packet from being sent to the UE.

18. The apparatus of claim 10 or 14, wherein the one or more processors are further to receive an end-marker packet indicating that the UE has received the plurality of user data packets.

19. The apparatus of claim 10, wherein the RAN node comprises a new air interface, NR, base station.

20. The apparatus of claim 10, wherein the plurality of user data packets are transmitted via a user plane of a wireless telecommunications network.

21. An apparatus of a User Equipment (UE), the apparatus comprising:

an interface to a radio frequency RF circuit; and

one or more processors configured to:

receiving a plurality of first user data packets from a first radio access network, RAN, node via the interface, at least one of the plurality of first user data packets comprising a sequence number, SN, based on an order position of the at least one of the plurality of first user data packets;

receiving, via the interface, an instruction to participate in a handover procedure involving the first RAN node and a second RAN node;

receiving, as part of the handover procedure, a plurality of second user data packets from the second RAN node via the interface, at least one of the plurality of second user data packets comprising a SN based on a sequential position of the at least one user data packet relative to the plurality of first user data packets and the plurality of second user data packets, wherein the second RAN node receives the plurality of second user data packets from the first RAN node and an indication of how the at least one of the plurality of second user data packets would otherwise be transmitted to the UE by the first RAN node prior to the handover procedure, wherein the indication comprises an identifier of a Data Radio Bearer (DRB) allocated by the RAN node for transmission of the plurality of user data packets to the UE, and wherein the second RAN node sends the at least one of the plurality of second user data packets to the UE based on the indication by determining whether to use the DRB or another DRB different from the DRB; and is

Merging the plurality of first user data packets with the plurality of second user data packets based on the SN of the at least one of the plurality of first user data packets and the plurality of second user data packets.

22. The apparatus of claim 21, wherein the one or more processors are further configured to:

based on the instruction, cause a message to be transmitted to the second RAN node via the interface, the message indicating that the UE is configured to communicate with the second RAN node.

23. The apparatus of claim 21, wherein the one or more processors are further configured to:

determining whether a transmission failure occurs based on a SN of the at least one of the plurality of first user data packets and the plurality of second user data packets; and

transmitting a retransmission request for a user data packet corresponding to the transmission failure to the second RAN node.

24. The apparatus of claim 21, wherein the one or more processors are further configured to:

for at least one user data packet of the plurality of first user data packets, deleting the at least one user data packet based on the at least one user data packet in accordance with the UE not sending an acknowledgement message to the first RAN node; and

receiving another copy of the at least one user data packet as part of the plurality of second user data packets from the second RAN node.