WO2022099586A1

WO2022099586A1 - Method, device and computer readable medium for communication

Info

Publication number: WO2022099586A1
Application number: PCT/CN2020/128581
Authority: WO
Inventors: Zhe Chen; Gang Wang
Original assignee: Nec Corporation
Priority date: 2020-11-13
Filing date: 2020-11-13
Publication date: 2022-05-19

Abstract

Embodiments of the present disclosure relate to methods, devices and computer readable media for communication. According to embodiments of the present disclosure, a source network device receives a first PDU of tunneling protocol comprising a first sequence number. The source network device transmits a second PDU of PDCP comprising a second sequence number which is at least partially same as the first sequence number. In this way, it ensures that the PDCP sequence number is aligned with the tunneling protocol sequence number.

Description

METHOD, DEVICE AND COMPUTER READABLE MEDIUM FOR COMMUNICATION

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to methods, devices and computer storage media for ensuring reliability of services.

BACKGROUND

With development of communication technologies, several solutions have been proposed to provide efficient and reliable solutions for communication. For example, Multicast and Broadcast Service (MBS) has been proposed to make it possible for efficient use of radio and network resources while transmitting audio and video content to a large group of end users. MBS is a point-to-multipoint communication scheme where data packets are transmitted simultaneously from a single source to multiple destinations. The term broadcast refers to the ability to deliver content to all users. Multicast, on the other hand, refers to distribution of content among a specific group of users that are subscribed to those services.

SUMMARY

In general, embodiments of the present disclosure provide methods, devices and computer storage media for ensuring reliability of services.

In a first aspect, there is provided a method of communication. The method comprises: receiving, at a source network device and from a core network device, a first protocol data unit of tunneling protocol comprising a first sequence number; and transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) comprising a second sequence number which is assigned based on the first sequence number.

In a second aspect, there is provided a method of communication. The method comprises: receiving, from the source network device a protocol data unit of packet data convergence protocol (PDCP) for the service comprising a second sequence number which is assigned based on a first sequence number comprised in a protocol data unit of tunneling protocol for the service.

In a third aspect, there is provided a method of communication. The method comprises: receiving, at a target network device, from a core network device, a first protocol data unit of tunneling protocol for a service comprising a first sequence number; and transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) for the service comprising a second sequence number which is assigned based on the first sequence number, the terminal device to handed over from the source network device to the target network device.

In a fourth aspect, there is provided a source network device. The source network device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor, cause the source network device to perform: receiving, from a core network device, a first protocol data unit of tunneling protocol comprising a first sequence number; and transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) comprising a second sequence number which is assigned based on the first sequence number.

In a fifth aspect, there is provided a terminal device. The terminal device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor, cause the terminal to perform: receiving, from the source network device, a protocol data unit of packet data convergence protocol (PDCP) for the service comprising a second sequence number which is at least partially same as a first sequence number comprised in a protocol data unit of tunneling protocol for the service.

In a sixth aspect, there is provided a target network device. The target network device comprises a processor and a memory coupled to the processor. The memory stores instructions that when executed by the processor, cause the target network device to perform: receiving, at a target network device, from a core network device, a first protocol data unit of tunneling protocol for a service comprising a first sequence number; and transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) for the service comprising a second sequence number which is at least partially same as the first sequence number, the terminal device to handed over from the source network device to the target network device.

In a seventh aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to perform the method according to the first aspect of the present disclosure.

In an eighth aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to perform the method according to the second aspect of the present disclosure.

In a ninth aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor, cause the at least one processor to perform the method according to the third aspect of the present disclosure.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

Fig. 1 is a schematic diagram of a communication environment in which embodiments of the present disclosure can be implemented;

Fig. 2 illustrates a flow chart of an example method of communication implemented at a source network device in accordance with some embodiments of the present disclosure;

Fig. 3 illustrates a schematic diagram of a PDCP protocol data unit in accordance with some embodiments of the present disclosure;

Fig. 4 illustrates a schematic diagram of a PDCP protocol data unit in accordance with other embodiments of the present disclosure;

Fig. 5 illustrates a flow chart of an example method of communication implemented at a terminal device in accordance with some embodiments of the present disclosure;

Fig. 6 illustrates a schematic diagram of a PDU in accordance with some embodiments of the present disclosure;

Fig. 7 illustrates a schematic diagram of a PDU in accordance with other embodiments of the present disclosure;

Fig. 8 illustrates a schematic diagram of a PDU in accordance with further embodiments of the present disclosure;

Fig. 9 illustrates a flow chart of an example method of communication implemented at a target network device in accordance with some embodiments of the present disclosure;

Fig. 10 illustrates a schematic diagram illustrating a process for handover between the source network device and the target network device according to embodiments of the present disclosure; and

Fig. 11 is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitations as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

As used herein, the term “terminal device” refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, or image capture devices such as digital cameras, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device. In addition, the term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an Evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a Transmission Reception Point (TRP) , a Remote Radio Unit (RRU) , a radio head (RH) , a remote radio head (RRH) , a low power node such as a femto node, a pico node, and the like.

In one embodiment, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In one embodiment, the first network device may be a first RAT device and the second network device may be a second RAT device. In one embodiment, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device and the second network device. In one embodiment, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In one embodiment, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

As used herein, the singular forms ‘a’ , ‘an’ and ‘the’ are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term ‘includes’ and its variants are to be read as open terms that mean ‘includes, but is not limited to. ’ The term ‘based on’ is to be read as ‘at least in part based on. ’ The term ‘one embodiment’ and ‘an embodiment’ are to be read as ‘at least one embodiment. ’ The term ‘another embodiment’ is to be read as ‘at least one other embodiment. ’ The terms ‘first, ’ ‘second, ’ and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In some examples, values, procedures, or apparatus are referred to as ‘best, ’ ‘lowest, ’ ‘highest, ’ ‘minimum, ’ ‘maximum, ’ or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

As mentioned above, the MBS has been proposed. In LTE, a new protocol, i.e. SYNC is defined additionally on transport network layer to support content synchronization mechanism. It enables network devices to identify the timing for radio frame transmission and detect packet loss. The network devices may buffer MBMS packet and waits for the transmission timing indicated in the SYNC protocol. Such protocol may be extended to support sequence number (SN) synchronization among radio access network (RAN) nodes which perform point-to-multipoint (PTM) transmission for the same 5G MBS service. According to conventional technologies, the terminal device specific unsuccessfully transmitted packet data convergence protocol (PDCP) protocol data unit (PDU) from the source network device may be forwarded to the target network device. Core network may transmit the data to the target network device after the path switch. However, in MBS, the PDCP PDU is not UE specific, the target network device may keep transmit the MBS PDCP PDU regardless the UE mobility. As the MBS progress gap is hard to avoid, filling in the gap should be an important direction to work with.

In order to solve at least part of above problems, solutions on ensuring reliability of services are needed. According to embodiments of the present disclosure, a source network device receives a first PDU of tunneling protocol comprising a first sequence number. The source network device transmits a second PDU of PDCP comprising a second sequence number which is at least partially same as the first sequence number. In this way, it ensures that the PDCP sequence number is aligned with the tunneling protocol sequence number.

Fig. 1 illustrates a schematic diagram of a communication system in which embodiments of the present disclosure can be implemented. The communication system 100, which is a part of a communication network, comprises a terminal device 110-1, a terminal device 110-2, ..., a terminal device 110-N, which can be collectively referred to as “terminal device (s) 110. ” The number N can be any suitable integer number.

The communication system 100 further comprises a network device 120-1, a network device 120-2, a network device 120-3, ..., a network device 120-M, which can be collectively referred to as “network device (s) 120. ” The number M can be any suitable integer number. The communication system 100 also comprises a core network device 130. Only as an example, the core network device 130 may be a User Plan Function (UPF) entity. In other embodiments, the communication system 100 may comprise another core network device (not shown) which may be an Access and Mobility Management Function (AMF) entity. In the communication system 100, the network devices 120 and the terminal devices 110 can communicate data and control information to each other. The numbers of devices shown in Fig. 1 are given for the purpose of illustration without suggesting any limitations.

Communications in the communication system 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , the third generation (3G) , the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Divided Multiple Address (CDMA) , Frequency Divided Multiple Address (FDMA) , Time Divided Multiple Address (TDMA) , Frequency Divided Duplexer (FDD) , Time Divided Duplexer (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Divided Multiple Access (OFDMA) and/or any other technologies currently known or to be developed in the future.

Embodiments of the present disclosure can be applied to any suitable scenarios. For example, embodiments of the present disclosure can be implemented at reduced capability NR devices. Alternatively, embodiments of the present disclosure can be implemented in one of the followings: NR multiple-input and multiple-output (MIMO) , NR sidelink enhancements, NR systems with frequency above 52.6GHz, an extending NR operation up to 71GHz, narrow band-Internet of Thing (NB-IOT) /enhanced Machine Type Communication (eMTC) over non-terrestrial networks (NTN) , NTN, UE power saving enhancements, NR coverage enhancement, NB-IoT and LTE-MTC, Integrated Access and Backhaul (IAB) , NR Multicast and Broadcast Services, or enhancements on Multi-Radio Dual-Connectivity.

Fig. 2 shows a flowchart of an example method 200 in accordance with an embodiment of the present disclosure. The method can be implemented at any suitable network devices. Only for the purpose of illustrations, the method 200 can be implemented at the network device 120-1 which can be regarded as a source network device as shown in Fig. 1.

At block 210, the network device 120-1 receives a first protocol data unit of tunneling protocol from the core network device 130. For example, the tunneling protocol may be General Packet Radio Service (GPRS) Tunneling Protocol User Plan (GTP-U) . The first protocol data unit comprises a first sequence number (SN) . The first SN may have a first length. For example, the first length may be 16 bits.

At block 220, the network device 120-1 transmits a second protocol data unit of PDCP to the terminal device 110-1. The second protocol data unit comprises a second SN. The second SN is as assigned based on the first SN. For example, the second SN may be the same as the first SN. Alternatively, a portion of the second SN may be the same as the first SN. The second SN may have a second length. In some embodiments, the second length may be the same as the first length, for example 16 bits. Alternatively, the second length may be longer than the first length, for example 18 bits. It should be noted that the first length and the second length can be any suitable values.

Fig. 3 illustrates a schematic diagram of a PDCP protocol data unit 300 in accordance with some embodiments of the present disclosure. As shown in Fig. 3, the second SN is 16 bits. The network device 120-1 may set values of the first SN to be the same values of the second SN. The filed 310 may indicate it belongs to a control PDU or a data PDU. The fields 320-1, 320-2, 320-3, 320-4, 320-5, 320-6 and 320-7 may be reserved. The fields 330-1 and 330-2 may comprise 16-bit PDCP SN (i.e., the second SN) which may be the same as 16-bit GTP-U SN (i.e., the first SN) . The field 340 may be a data field. The fields 350-1, 350-2, 350-3 and 350-4 may be Medium Access Control fields which are optional.

In some embodiments, the network device 120-1 may configure 18 bits PDCP SN (i.e., the second SN) length. In some embodiments, the first left two bits of the PDCP SN may be always set to a default value. For example, the firs left two bits may be “00. ” It should be noted that the first two bits can be any suitable values. The rest 16 bits PDCP SN may be set to be the same value of the GTP-U SN. In this situation, the terminal device 110-1 may understand that the last 16 bits of the PDCP SN are useful and the first two bits can be regardless. When a radio bearer (RB) is configured for an multicast radio bearer (MRB) or for a data radio bearer (DRB) associated with a MRB, the terminal device 110-1 may follow the “first two PDCP SN is always 00” rule. In some embodiments, values of a portion of the second SN can be assigned the same as values of the first SN. Only as an example, if the first SN is 16 bits and the second SN is 18 bits, values of the last 16 bits of the second SN can be the same as values of the first SN. Alternatively, values of the first 16 bits of the second SN can be the same as values of the first SN. In this situation, if values of first length bits of the second SN reaches maximum values, the network device 120-1 may assign a next PDU of the PDCP with a minimum SN. Only as an example, if the second SN is “001111111111111111, ” the network device 120-1 may assign the next PDU with the SN starting from “000000000000000000. ”

Fig. 4 illustrates a schematic diagram of a PDCP protocol data unit 400 in accordance with other embodiments of the present disclosure. As shown in Fig. 4, the second SN is 18 bits. The filed 410 may indicate it belongs to control PDCP or data PDCP. The fields 420-1, 420-2, 420-3, 420-4 and 320-5, may be reserved. The fields 430-1, 430-2, 430-3 and 430-4 may comprise 18-bit PDCP SN (i.e., the second SN) . The fields 430-1 and 430-2 may be set to “00. ” The fields 430-3 and 430-4 may be the same as 16-bit GTP-U SN (i.e., the first SN) . The field 440 may be a data field. The fields 450-1, 450-2, 450-3 and 450-4 may be Medium Access Control fields which are optional.

In some embodiments, if the terminal device 110-1 is in Radio Resource Control (RRC) _IDLE mode, and due to an Xn interface information exchange, the network device 120-1 may know which point-to-multipoint service the network device 120-2 is providing. The network device 120-1 may transmit a paging message to the terminal device 110-1 which enforces the terminal device 110-1 to enter a RRC connected mode. The network device 120-1 may transmit an indication of a multimedia broadcast service which the terminal device 110-1 requires to the network device 120-2. The terminal device 110-1 may be handed over from the network device 120-1 to the network device 120-2.

In other embodiments, due to the Xn interface information exchange, the network device 120-1 may know which PTM services that the network device 120-2 is providing. The network device 120-1 may transmit a handover request to the network device 120-2. The handover request may indicate a list of services which the terminal device 110-1. For example, the handover request may comprise a temporary mobile group identity (TMGI) list.

If the network device 120-2 has already supported point-to-point (PTP) for a service in the handover request, and the network device 120-2 may determine to switch from PTM to PTP during the handover. The network device 120-1 may receive a handover request from the network device 120-2. The handover request may comprise a dedicated radio bearer (DRB) configuration for the service. The service may be switched from PTM communication to PTP communication by the network device 120-2. The network device 120-1 may transmit a RRC configuration message to the terminal device 110-1. The RRC configuration message may comprise the DRB configuration for the service.

In some embodiments, in order to ensure reliability of a PTM service, the target network device may need to establish a complementary PTP channel for the PTM service. For example, during the handover procedure, the network device 120-1 may transmit a handover request to the network device 120-2. In some embodiments, the handover request may indicate a PTM service and request an additional PTP channel for the PTM service. Only as an example, the handover request may comprise a PTM TMGI list and a PTM with PTP TMGI list. The handover request may include a list of services that the network device 120-2 should ensure the reliability. The network device 120-1 may receive a handover response from the network device 120-2. The handover response may comprise a DRB configuration for the service. The network device 120-1 may transmit a RRC configuration message comprising the DRB configuration for the service to the terminal device 110-1.

Alternatively, if the network device 120-1 supports PTP communication for a service and the network device 120-2 supports PTM communication for the service, the network device 120-1 may transmit a RRC release indication to the terminal device 110-1. The RRC release indication may comprise a PTM communication configuration for the service. Table 1 below shows an example of the RRC release message. It should be noted that Table 1 is only an example not limitation.

Table 1

In some embodiments, for some of the MBMS services, the reliability may require to be guaranteed, while the others do not require reliability. So high reliability services should be controlled by the network to enforce the terminal device to be RRC connected. The hybrid automatic repeat request (HARQ) /ARQ mechanism can be enhanced for high reliability services, thus the reliability requirement enforces the terminal device to be in RRC_CONNECTED to enable HARQ/ARQ feedback. In an example embodiment, the network device 120-1 may transmit configuration information at least indicating a reliability level of a MBMS service. For example, for high reliability level MBMS service, the terminal device 110-1 may be RRC connected for the service. For low reliability level MBMS service, the terminal device 110-1 may be RRC_IDLE for the service. For medium reliability level MBMS service, the terminal device 110-1 may select the RRC_IDLE or RRC_CONNECTED mode by itself. Table 2 below shows an example of the configuration information. Table 3 below shows example configuration singling. It should be noted that Table 2 and Table 3 are only examples not limitations.

Table 2

	MBMS Service	Reliability Level
Entry
1	TMGI 1	Low
Entry 2	TMGI 2	Medium
Entry
3	TMGI 3	High

Table 3

Alternatively or in addition, the configuration information may indicate a service reliability threshold for the terminal device 110-1 to enter a RRC connected mode. For the MBMS services with higher or equal to the reliability threshold, the terminal device 110-1 should enter RRC_CONNECTED. Table 4 below shows an example of the configuration information. Table 5 below shows an example reliability threshold in system information block. It should be noted that Table 4 and Table 5 are only examples not limitations.

Table 4

	MBMS Service	Reliability Level
Entry
1	TMGI 1	1
Entry 2	TMGI 2	2
Entry 3	TMGI 3	3
…	…	…
Entry 14	TMGI 14	15
Entry 15	TMGI 15	15
Entry 16	TMGI 16	16

Table 5

Fig. 5 shows a flowchart of an example method 500 in accordance with an embodiment of the present disclosure. The method 500 can be implemented at any suitable terminal devices. Only for the purpose of illustrations, the method 500 can be implemented at a terminal device 110-1 as shown in Fig. 1.

In some embodiments, the terminal device 110-1 transmits a request for a service to the network device 120-1. For example, the terminal device 110-1 may request a MBMS service. In some embodiments, the service may be a PTP service. Alternatively, the service may be a PTM service.

At block 510, the terminal device 110-1 receives a second protocol data unit of PDCP from the network device 120-1. The second protocol data unit comprises a second SN. The second SN is at least partially same as the first SN. The first SN may have a first length. The second SN may have a second length. In some embodiments, the second length may be the same as the first length, for example 16 bits. Alternatively, the second length may be longer than the first length, for example 18 bits.

In some embodiments, the network device 120-1 may configure 18 bits PDCP SN (i.e., the second SN) length. In some embodiments, the first left two bits of the PDCP SN may be always set to a default value. For example, the firs left two bits may be “00. ” The rest 16 bits PDCP SN may be set to be the same value of the GTP-U SN. In this situation, the terminal device 110-1 may understand that the last 16 bits of the PDCP SN are useful and the first two bits can be regardless. When a radio bearer (RB) is configured for an multicast radio bearer (MRB) or for a data radio bearer (DRB) associated with a MRB, the terminal device 110-1 may follow the “first two PDCP SN is always 00” rule. In this situation, if values of first length bits of the second SN reaches maximum values, the terminal device 110-1 may receive a next PDU of the PDCP for the service with a minimum SN. Only as an example, if the second SN is “001111111111111111, ” the terminal device 110-1 may receive the next PDU with the SN starting from “000000000000000000. ” The terminal device 110-1 will not wait for a PDU with the SN “010000000000000000. ”

In some embodiments, if the terminal device 110-1 is in RRC_IDLE mode, the terminal device 110-1 may receive a paging message from the network device 120-1 which enforces the terminal device 110-1 to enter a RRC connected mode. In some embodiments, if the service is switched from PTM communication to PTP communication by the network device 120-2, the terminal device 110-1 may receive a RRC configuration message which comprises a DRB configuration for the service.

In some embodiments, in PTM physical downlink control channel (PDCCH) /physical downlink shared channel (PDSCH) transmission mode, each network device may schedule the PTM data transmission individually, in result that the PTM data transmission is unsynchronized between network devices. In some embodiments, at block 520, the terminal device 110-1 may transmit a PDCP status report to indicate lost packets. Only for the purpose of illustrations, the terminal device 110-1 may perform handover after received packet 3 from the network device 120-1. However, after the handover, the terminal device 110-1 may start receiving packet 9 from the network device 120-2. In this situation, the terminal device 110-1 may lose packets 4 to 8. The terminal device 110-1 may transmit the PDCP status report at least indicating the lost packets 4 to 8.

In other embodiments, the terminal device 110-1 may receive a first plurality of PDUs of the PDCP for a service from the network device 120-1. The terminal device 110-1 may monitor a second plurality of PDUs of the PDCP. The terminal device 110-1 may determine at least one missing PDU based on the first plurality of PDUs and the second plurality of PDUs. For example, as mentioned above, the terminal device 110-1 may receive packets 1-3 from the network device 210-1 and receive packet 9 from the network device 210-2, the terminal device 110-1 may determine the missing PDUs are 4 to 8. The terminal device 110-1 may transmit a control PDU to the network device 120-2. The control PDU may comprise an indication where the PDU is a PDCP status report. In addition, the control PDU may indicate an identity of the service. The control PDU may also comprise an indication of at least one missing PDU.

In some embodiments, a new PDU type is proposed. The new PDU type may indicate that the control PDU is a PDCP status report. Table 6 illustrates examples of PDU type. It should be noted that Table 6 is only an example not limitation.

Table 6

Bit	Description
000	PDCP status report
001	Interspersed ROHC feedback
010	MBS PDCP status report
011-111	Reserved

In some embodiments, if radio logic control (RLC) acknowledgment (for example, ACK/NACK) is allowed and the terminal device 110-1 successfully receives a first PDU in the second plurality of PDUs, the terminal device 110-1 may transmit the control PDU to the network device 120-2. Fig. 6 illustrates a schematic diagram of a PDCP status report in accordance with some embodiments of the present disclosure. As shown in Fig. 6, the field 610 may indicate whether the PDU 600 is a control PDU or a data PDU. For example, if the PDU is the control PDU, the field 610 may be set to “1. ” The filed 620 may indicate the PDU type. For example, if the field 620 is set to “010” , it may indicate that the PDU 600 is the MBS PDCP status report. The fields 630-1, 630-2, 630-3 and 630-4 may be reserved bits. The fields 640-1 and 640-2 may indicate the identity of the service. For example, the field 640-1 and 640-2 may indicate the TMGI. The fields 650-1, 650-2, 650-3 and 650-4 may indicate the first missing count value which identifies the first missing PDU. The first missing count may comprise hyper frame number and PDCP SN. The field 660 may comprise bitmap to indicate that whether a specific PDU is received or not. For example, the value “1” in the bitmap may represent the PDU is received and the value “0” in the bitmap may represent the PDU is not received.

Fig. 7 illustrates an example PDCP status report. It should be noted the values in Fig. 7 are only examples not limitations. The field “1” may indicate that the PDU is a control PDU. The field “010” may indicate that the PDU is a MBS PDCP status report. The identity of the service may be “TMGI. ” The first missing count “00000000 00000000 00000000 00000010” may indicate that the first missing PDU is 2. According to the bitmap section shown in Fig. 7, the 3 ^rd, 5 ^th, 7 ^th, 9 ^th and 13 ^th PDUs are received by the terminal device 110-1 and the 2 ^nd, 4 ^th, 6 ^th, 8 ^th, 10 ^th, 11 ^th, 12 ^th, 14 ^th, 15 ^th, 16 ^th, and 17 ^th PDUs are not received by the terminal device 110-1.

Alternatively, the terminal device 110-1 may receive a subset of the second plurality of PDUs for the service retransmitted based on the PDCP status report. The terminal device 110-1 may discard at least one PDU in the subset of the PDCP which has been successfully received previously. For example, the network device 220 may re-transmit all PDCP PDUs with count value whose value is 0 in the bit map with count value less than 13 (

count

2, 4, 6, 8, 10, 11, 12) as shown in Fig. 7. However, the terminal device 110-41 has received count 13 PDCP PDU from the network device 120-2 and the network device 120-2 doesn’t know without RLC ACK. The network device 120-2 may re-transmit

count value

2, 4, 6, 8, 10, 11, 12 14, 15, 16, 17 PDCP PDUs by PTP to the terminal device 110-1. The terminal device 110-1 may discard

count value

14, 15, 16, 17 PDCP PDUs if they are received by PTM.

In some embodiments, the terminal device 110-1 may monitor a plurality of PDUs of the PDCP for a service from the network device 120-2. If the RLC acknowledgment for the service is not allowed and the terminal device 110-1 may successfully receive a first PDU in the plurality of PDUs, the terminal device 110-1 may transmit the control PDU. The control PDU may comprise an indication where the control PDU is a PDCP status report. Additionally, the control PDU may indicate the identity of the service. The control PDU may also comprise an indication of the first received PDU.

Fig. 8 illustrates a PDU 800 in accordance with further embodiments of the present disclosure. As shown in Fig. 8, the field 810 may indicate whether the PDU 800 is a control PDU or a data PDU. For example, if the PDU is the control PDU, the field 810 may be set to “1. ” The filed 820 may indicate the PDU type. For example, if the field 820 is set to “010” , it may indicate that the PDU 800 is the MBS PDCP status report. The fields 830-1, 830-2, 830-3 and 830-4 may be reserved bits. The fields 840-1 and 840-2 may indicate the identity of the service. For example, the field 840-1 and 840-2 may indicate the TMGI. The fields 850-1, 850-2, 850-3 and 850-4 may indicate the first missing count value which identifies the first missing PDU. The first missing count may comprise hyper frame number and PDCP SN. The fields 860-1, 860-2, 860-3 and 860-4 may indicate the first received count value which identifies the first PDU that is successfully received from the network device 120-2. The field 870 may comprise bitmap to indicate that whether a specific PDU is received or not. For example, the value “1” in the bitmap may represent the PDU is received and the value “0” in the bitmap may represent the PDU is not received.

In some embodiments, in order to ensure the reliability of the service, the network device 120-2 may establish a complementary PTP for the PTM service. The terminal device 110-1 may receive a RRC release indication from the network device 120-1. The RRC release indication may comprise a PTM communication configuration for the service. The terminal device 110-1 may move to the network device 120-2 to monitor the PTM service.

Fig. 9 shows a flowchart of an example method 900 in accordance with an embodiment of the present disclosure. The method 900 can be implemented at any suitable target network devices. Only for the purpose of illustrations, the method 900 can be implemented at the network device 120-2 as shown in Fig. 1.

At block 910, the network device 120-2 receives a first protocol data unit of tunneling protocol from the core network device 130. For example, the tunneling protocol may be General Packet Radio Service (GPRS) Tunneling Protocol User Plan (GTP-U) . The first protocol data unit comprises a first sequence number (SN) . The first SN may have a first length. For example, the first length may be 16 bits.

At block 920, the network device 120-2 transmits a second protocol data unit of PDCP to the terminal device 110-1. The second protocol data unit comprises a second SN. The second SN is at least partially same as the first SN. The second SN may have a second length. In some embodiments, the second length may be the same as the first length, for example 16 bits. Alternatively, the second length may be longer than the first length, for example 18 bits. The terminal device 110-1 may handover from the network device 120-1 to the network device 120-2.

In some embodiments, the network device 120-2 may configure 18 bits PDCP SN (i.e., the second SN) length. In some embodiments, the first left two bits of the PDCP SN may be always set to a default value. For example, the firs left two bits may be “00. ” The rest 16 bits PDCP SN may be set to be the same value of the GTP-U SN. In this situation, the terminal device 110-1 may understand that the last 16 bits of the PDCP SN are useful and the first two bits can be regardless. When a radio bearer (RB) is configured for an multicast radio bearer (MRB) or for a data radio bearer (DRB) associated with a MRB, the terminal device 110-1 may follow the “first two PDCP SN is always 00” rule.

In other embodiments, due to the Xn interface information exchange, the network device 120-1 may know which PTM services that the network device 120-2 is providing. The network device 120-2 may receive a handover request from the network device 120-1. The handover request may indicate a list of services which the terminal device 110-1. For example, the handover request may comprise a temporary mobile group identity (TMGI) list. If the network device 120-2 does not support PTM communication or PTP communication for this service, the network device 120-2 may establish a session with a core network device, for example, AMF. Alternatively, if the network device 120-2 may support PTP of the service, and determine to switch from PTM to PTP during the handover, the network device 120-2 may configure a DRB for the service. The network device 120-2 may transmit a handover response to the network device 120-1. The handover response may comprise a DRB configuration.

Alternatively, in order to ensure reliability of a PTM service, the target network device may need to establish a complementary PTP channel for the PTM service. For example, during the handover procedure, the network device 120-1 may transmit a handover request to the network device 120-2. In some embodiments, the handover request may indicate a PTM service and request an additional PTP channel for the PTM service. Only as an example, the handover request may comprise a PTM TMGI list and a PTM with PTP TMGI list. The handover request may include a list of services that the network device 120-2 should ensure the reliability. The network device 120-2 may determine the DRB for the service. The network device 120-2 may transmit a handover response to the network device 120-1. The handover response may comprise the DRB configuration for the service.

In some embodiments, the network device 120-2 may transmit a plurality of PDUs of the PDCP for the service. If the RLC acknowledgment for the service is allowed, the network device 120-2 may receive a control PDU from the terminal device 110-1. The control PDU may comprise an indication where the PDU is a PDCP status report. In addition, the control PDU may indicate an identity of the service. The control PDU may also comprise an indication of at least one missing PDU.

In other embodiments, the network device 220 may re-transmit all PDCP PDUs with count value whose value is 0 in the bit map with count value less than 13 (

count

count value

2, 4, 6, 8, 10, 11, 12 14, 15, 16, 17 PDCP PDUs by PTP to the terminal device 110-1.

In other embodiments, the network device 120-2 may transmit a plurality of PDUs of the PDCP for the service. If the RLC acknowledgment for the service is not allowed, the network device 120-2 may receive the control PDU from the terminal device 110-1. The control PDU may comprise an indication where control PDU is a PDCP status report. Additionally, the control PDU may indicate the identity of the service. The control PDU may also comprise an indication of the first received PDU.

Fig. 10 shows a signaling chart illustrating process 1000 among devices according to some example embodiments of the present disclosure. Only for the purpose of discussion, the process 1000 will be described with reference to Fig. 1. The process 1000 may involve the communication device 120-1 and the core network device 130 in Fig. 1. It should be noted that the process 1000 is only an example not limitation.

The core network device 130 may transmit 1005 a first PDU of the GTP-U to the network device 120-1. The first PDU may comprise a first SN. The network device 120-1 may transmit 1008 a second PDU of the PDCP to the terminal device 110-1. The second PDU may comprise a second SN which at least partially the same as the first SN.

The terminal device 110-1 may transmit 1010 a measurement report to the network device 120-1. The measurement report may be any suitable types of measurement report for handover. The network device 120-1 may transmit 1015 a paging message to the terminal device 110-1 which enables the terminal device 110-1 to enter a RRC connected mode.

The network device 120-1 may determine 1020 to handover the terminal device 110-1 to the network device 120-2 based on the measurement report. The network device 120-1 may transmit 1025 a handover request to the network device 120-2. In some embodiments, the handover request may indicate a list of services which the terminal device 110-1. For example, the handover request may comprise a temporary mobile group identity (TMGI) list. Alternatively, the handover request may indicate a PTM service and request an additional PTP channel for the PTM service.

In some embodiments, if the network device 120-2 does not support PTM communication or PTP communication for this service, the network device 120-2 may establish a session with the AMF 1400. The network device 120-2 may transmit 1030 a handover response to the network device 120-1. In some embodiments, if the network device 120-2 may support PTP of the service, and determine to switch from PTM to PTP during the handover, the network device 120-2 may configure a DRB for the service. The handover response may comprise a DRB configuration. Alternatively, if the handover request may comprise a PTM TMGI list and a PTM with PTP TMGI list and the network device 120-2 may establish the PTP channel for the PTM service, the handover response may comprise the DRB configuration for the service.

The network device 120-1 may transmit 1035 a RRC configuration message which comprises a DRB configuration for the service. The network device 120-1 may transmit 1040 SN status transfer information to the network device 120-2. The terminal device 110-1 may transmit 1045 a RRC reconfiguration complete message to the network device 120-2.

The core network device 130 may transmit 1050 a first PDU of the GTP-U to the network device 120-2. The first PDU may comprise a first SN. The network device 120-1 may transmit 1055 a second PDU of the PDCP to the terminal device 110-1. The second PDU may comprise a second SN which at least partially the same as the first SN.

The network device 120-2 may perform path switch with the AMF 1400. The network device 120-2 may transmit 1060 a UE context release message to the network device 120-1. The terminal device 110-1 may transmit 1065 a control PDU to the network device 120-2. In some embodiments, the control PDU may indicate that the PDU is a PDCP status report. In addition, the control PDU may indicate an identity of the service. The control PDU may also indicate at least one missing PDU. Alternatively, the control PDU may also comprise an indication of the first received PDU.

The network device 120-2 may retransmit 1065 the PDUs based on the PDCP status report. In some embodiments, the network device 220 may re-transmit all PDCP PDUs with count value whose value is 0 in the bitmap.

Fig. 11 is a simplified block diagram of a device 1100 that is suitable for implementing embodiments of the present disclosure. The device 1100 can be considered as a further example implementation of the network device 120, the core network device 130 or the terminal device 110 as shown in Fig. 1. Accordingly, the device 1100 can be implemented at or as at least a part of the terminal device 110, the network device 120, or the core network device 130.

As shown, the device 1100 includes a processor 1110, a memory 1120 coupled to the processor 1110, a suitable transmitter (TX) and receiver (RX) 1140 coupled to the processor 1110, and a communication interface coupled to the TX/RX 1140. The memory 1110 stores at least a part of a program 1130. The TX/RX 1140 is for bidirectional communications. The TX/RX 1140 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN) , or Uu interface for communication between the eNB and a terminal device.

The program 1130 is assumed to include program instructions that, when executed by the associated processor 1110, enable the device 1100 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to Figs. 2 to 10. The embodiments herein may be implemented by computer software executable by the processor 1110 of the device 1100, or by hardware, or by a combination of software and hardware. The processor 1110 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1110 and memory 1120 may form processing means adapted to implement various embodiments of the present disclosure.

The memory 1120 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1120 is shown in the device 1100, there may be several physically distinct memory modules in the device 1100. The processor 1110 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1100 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to Figs. 2 to 10. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A communication method, comprising:

receiving, at a source network device and from a core network device, a first protocol data unit of tunneling protocol comprising a first sequence number; and

transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) comprising a second sequence number which is assigned based on the first sequence number.
The method of claim 1, wherein the first sequence number has a first length and the second sequence number has a second length which is the same as the first length, and values of the second sequence number are assigned to be the same as values of the first sequence number.
The method of claim 1, wherein the first sequence number has a first length and the second sequence number has a second length which is longer than the first length, and values of the first length from end of the second sequence number value are assigned to be the same as values of the first sequence number.
The method of claim 2 or 3, wherein the first length is 16 bits and the second length is 16 bits, or the second length is 16 bits and the second length is 18 bits.
The method claim 3, further comprising:

in accordance with a determination that the value of the first length from end of the second sequence number reaches maximum, assigning a next protocol data unit of the PDCP for the service with a minimum sequence number.
The method of claim 1, further comprising:

transmitting, to the terminal device, a paging message to enforce the terminal device to enter a radio resource control (RRC) connected mode; and

transmitting, to a target network device which the terminal device is handed over to, an indication of a multimedia broadcast service which the terminal device requires.
The method of claim 1, further comprising:

transmitting, to a target network device which the terminal device is handed over to, a handover request indicating a list of services which the terminal device requires;

receiving, from the target network device, a handover response comprising a data radio bearer configuration for a service in the list of services, the service being switched from point-to-multipoint communication in the source network device to point-to-point communication by the target network device during the handover; and

transmitting, to the terminal device, a radio resource control (RRC) configuration message comprising the data radio bearer configuration for the service.
The method of claim 1, further comprising:

transmitting, to a target network device which the terminal device is handed over to, a handover request indicating a point-to-multipoint service and requesting an additional point-to-point channel for the point-to-multipoint service;

receiving, from the target network device, a handover response comprising a data radio bearer configuration for the point-to-multipoint service; and

transmitting, to the terminal device, a radio resource control (RRC) configuration message comprising the data radio bearer configuration for the service.
The method of claim 1, further comprising:

in accordance with a determination that the source network device supports point-to-point communication for a service and a target network device supports point-to-multipoint communication for the service, transmitting, to the terminal device, a radio resource control (RRC) release indication comprising a point-to-multipoint communication configuration for the service.
The method of claim 1, further comprising:

transmitting, to the terminal device, configuration information at least indicating a reliability level of a multimedia broadcast multicast service.
The method of claim 1, further comprising:

transmitting, to the terminal device, configuration information indicating: a reliability level of a service and a reliability threshold for the terminal device to enter a radio resource control (RRC) connected mode.
A communication method, comprising:

receiving, at a terminal device and from the source network device, a second protocol data unit of packet data convergence protocol (PDCP) comprising a second sequence number which is assigned based on a first sequence number comprised in a first protocol data unit of tunneling protocol.
The method of claim 12, wherein the first sequence number has a first length and the second sequence number has a second length which is the same as the first length, and values of the second sequence number is assigned to be the same as values of the first sequence number.
The method of claim 12, wherein the first sequence number has a first length and the second sequence number has a second length which is longer than the first length, and values of the first length from end of the second sequence number value are assigned to be the same as values of the first sequence number.
The method of claim 13 or 14, wherein the first length is 16 bits and the second length is 16 bits, or the second length is 16 bits and the second length is 18 bits.
The method of claim 14, further comprising:

in accordance with a determination that the value of the first length from end of the second sequence number reaches maximum, receiving, from the source network device, a next protocol data unit of the PDCP for the service assigned with a minimum sequence number.
The method of claim 12, further comprising:

receiving, from the source network device, a paging message to enforce the terminal device to enter a radio resource control (RRC) connected mode; and

switching from a RRC idle mode into the RRC connected mode based on the paging message.
The method of claim 12, further comprising:

in accordance with a determination that a service is switched from point-to-multipoint communication to point-to-point communication by a target network device during handover, receiving, from the source network device, a radio resource control (RRC) configuration message comprising the data radio bearer configuration for the service.
The method of claim 12, further comprising:

receiving, from the source network device, a first plurality of protocol data units of the PDCP for a service; and

in accordance with a determination that an acknowledgment for the service is allowed and a first protocol data unit in a second plurality of protocol data units from a target network device is successfully received,

transmitting, to the target network device, a control protocol data unit comprising:

an indication where the control protocol data unit is a PDCP status report, an identity of the service, and an indication of at least one missing protocol data unit which is determined based on the first plurality of protocol data units and the second plurality of data units.
The method of claim 12, further comprising:

receiving, from the source network device, a first plurality of protocol data units of the PDCP for a service;

in accordance with a determination that an acknowledgment for the service is not allowed and a first protocol data unit in a second plurality of protocol data units from a target network device is successfully received,

transmitting, to the target network device, a control protocol data unit comprising:

an indication where the control protocol data unit is a PDCP status report, an identity of the service, and at least one missing protocol data unit which is determined based on the first plurality of protocol data units and the second plurality of data units;

receiving, from the target network device, a subset of the second plurality of protocol data units of the PDCP for the service retransmitted based on the PDCP status report; and

discarding at least one protocol data unit in the subset the second plurality of protocol data units of the PDCP, the at least one protocol data unit being successfully received previously.
The method of claim 12, further comprising:

in accordance with a determination that an acknowledgment for the service is not allowed and a first protocol data unit in a plurality of protocol data units from a target network device is successfully received,

transmitting, to the target network device, a control protocol data unit comprising:

an indication where the control protocol data unit is a PDCP status report, an identity of the service, and an indication of the first received protocol data unit.
The method of claim 12, further comprising:

in accordance with a determination that an additional point-to-point channel for a point-to-multipoint service is required,

receiving, from the source network device, a radio resource control (RRC) configuration message comprising a data radio bearer configuration for the point-to-multipoint service.
The method of claim 12, further comprising:

in accordance with a determination that the source network device supports point-to-point communication for a service and a target network device supports point-to-multipoint communication for the service,

receiving, from the source network device, a radio resource control (RRC) release indication comprising a point-to-multipoint communication configuration for the service.
The method of claim 12, further comprising:

receiving, from the source network device, configuration information indicating a reliability level of each multimedia broadcast multicast service.
The method of claim 12, further comprising:

receiving, from the source network device, configuration information indicating : a reliability level of a service and a reliability threshold for the terminal device to enter a radio resource control (RRC) connected mode; and

in accordance with a determination that the reliability level of the service exceeds the reliability threshold, entering into the RRC connected mode.
A communication method comprising:

receiving, at a target network device, from a core network device, a first protocol data unit of tunneling protocol for a service comprising a first sequence number; and

transmitting, to a terminal device, a second protocol data unit of packet data convergence protocol (PDCP) for the service comprising a second sequence number which is as assigned based on the first sequence number, the terminal device to handed over from the source network device to the target network device.
The method of claim 26, further comprising:

determining whether the service is supported by the target network device; and

in accordance with a determination that the service is supported, establishing a session for the service with a core network device.
The method of claim 26, further comprising:

receiving, from the source network device, a handover request indicating that the source network device supports point-to-point communication for the service;

determining that the target network device support point-to-point communication for the service; and

transmitting, to the source network device, a handover response comprising the data radio bearer configuration for the service.
The method of claim 26, further comprising:

receiving, from the source network device, a handover request indicating a point-to-multipoint service and requesting an additional point-to-point channel for the point-to-multipoint service,

determining the data radio bearer configuration; and

transmitting, to the source network device, a handover response comprising the data radio bearer configuration for the service.
The method of claim 26, further comprising:

transmitting, to the terminal device, a plurality of protocol data units of the PDCP for the service; and

in accordance with a determination that an acknowledgment for the service is allowed, receiving, from the terminal device, a control protocol data unit comprising:

an indication where the control protocol data unit is a PDCP status report, an identity of the service, and an indication of at least one missing protocol data unit in the plurality of protocol data units.
The method of claim 30, further comprising:

retransmitting, to the terminal device, a subset of the plurality of protocol data units of the PDCP for the service based on the PDCP status report.
The method of claim 26, further comprising:

transmitting, to the terminal device, a plurality of protocol data units of the PDCP for the service; and

in accordance with a determination that an acknowledgment for the service is not allowed, receiving, from the terminal device, a control protocol data unit comprising:

an indication where the control protocol data unit is a PDCP status report, an identity of the service, and an indication of a first received protocol data units in the plurality of protocol data units.
A source network device comprising:

a processor; and

a memory coupled to the processor and storing instructions thereon, the instructions, when executed by the processor, causing the source network device to perform the method according to any of claims 1-11.
A terminal device comprising:

a processor; and

a memory coupled to the processor and storing instructions thereon, the instructions, when executed by the processor, causing the terminal device to perform the method according to any of claims 12-25.
A target network device comprising:

a processor; and

a memory coupled to the processor and storing instructions thereon, the instructions, when executed by the processor, causing the target network device to perform the method according to any of claims 26-32.
A computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method according to any of claims 1-11, or the method according to any of claims 12-25, or the method according to any of claims 26-32.