Network device, terminal device and method for communication

Abstract

The embodiment of the invention relates to a scheme for communication. In one aspect of the approach, a first network device receives at least one packet of a set of packets from a third network device. The first network device then forwards the subset of the at least one data packet to the second network device. And the first network equipment further sends information about the transmission state of the data packet set from the first network equipment to the terminal equipment to the second network equipment. The second network device then transmits at least one data packet in the subset to the terminal device based on the information about the transmission status.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to the field of communications, and in particular, to a network device, a terminal device, and a method for communication. BACKGROUND

[0002] In some cases, a terminal device can need all data packets in a data packet set to operate. For example, an application layer of the terminal device can need all data packets to use the data packet set. For another example, the terminal device can enter a discontinuous reception (DRX) sleep mode after receiving all data packets in the set. Therefore, in a case of data forwarding due to a handover or a change of bearer type, a network device receiving the forwarded data needs to know whether the transmission of the data packet set to the terminal device has been completed. SUMMARY

[0003] Generally, embodiments of the present disclosure provide a scheme for communication.

[0004] In a first aspect, a first network device is provided. The first network device includes a processor and a transceiver coupled to the processor. The processor is configured to: receive, via the transceiver, at least one data packet in a data packet set from a third network device; forward, via the transceiver, a subset of the at least one data packet to a second network device; and send, via the transceiver, information about a transmission status of the data packet set from the first network device to a terminal device to the second network device.

[0005] In a second aspect, a second network device is provided. The second network device includes a processor and a transceiver coupled to the processor. The processor is configured to: receive, via the transceiver, a subset of a data packet set from a first network device; receive, from the first network device, information about a transmission status of the data packet set from the first network device to a terminal device; and transmit, via the transceiver, at least one data packet in the subset to the terminal device based on the information about the transmission status.

[0006] In a third aspect, a terminal device is provided. The terminal device includes a processor and a transceiver coupled to the processor. The processor is configured to: determine a reception status of a data packet set; and send, via the transceiver, an indication of the reception status of the data packet set to a second network device.

[0007] In a fourth aspect, a method performed by a first network device is provided. The method includes: receiving, from a third network device, at least one data packet in a data packet set; forwarding, to a second network device, a subset of the at least one data packet; and sending, to the second network device, information about a transmission status of the data packet set from the first network device to a terminal device.

[0008] In a fifth aspect, a method performed by a second network device is provided. The method comprises receiving, from a first network device, a subset of a set of data packets; receiving, from the first network device, information about a transmission status of the set of data packets from the first network device to a terminal device; and transmitting, to the terminal device, at least one data packet in the subset based on the information about the transmission status.

[0009] In a sixth aspect, a method performed by a terminal device is provided. The method comprises determining a reception status of a set of data packets; and transmitting, to a second network device, an indication of the reception status of the set of data packets.

[0010] In a seventh aspect, a computer readable medium is provided. The computer readable medium has instructions stored thereon. The instructions, when executed on at least one processor of an apparatus, cause the apparatus to perform the method of the fourth or fifth aspect.

[0011] It should be understood that the Summary is not intended to identify key or essential features of embodiments of the disclosure, nor is it intended to limit the scope of the disclosure. Other aspects of the disclosure will become readily apparent to those skilled in the art by review of the following description. BRIEF DESCRIPTION OF DRAWINGS

[0012] Some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

[0013] FIG. 1A and 1B respectively illustrate examples of downlink data transmission;

[0014] FIG. 2 shows a schematic diagram of a communication environment in which some embodiments of the disclosure can be implemented;

[0015] FIG. 3 shows a signalling diagram illustrating an example procedure for communication according to some embodiments of the disclosure;

[0016] FIGS. 4-8 shows a signalling diagram illustrating example implementations of example procedures for communication according to some embodiments of the disclosure;

[0017] FIG. 9 shows a flow diagram of a method implemented at a network device according to some embodiments of the disclosure;

[0018] FIG. 10 shows a flow diagram of a method implemented at a network device according to other embodiments of the disclosure;

[0019] FIG. 11 shows a flow diagram of a method implemented at a terminal device according to some embodiments of the disclosure; and

[0020] FIG. 12A simplified block diagram of a device suitable for implementing embodiments of the present disclosure is shown.

[0021] In all of the drawings, like or similar reference numerals are used to refer to like or similar elements throughout the several views. DETAILED DESCRIPTION

[0022] The principles of the present disclosure will now be described with reference to some embodiments. It should be understood that the embodiments described are only for illustration and help the person skilled in the art to understand and implement the present disclosure, and do not imply any limitation on the scope of the present disclosure. The disclosure described herein can be implemented in various ways different from those described below. In the following description and claims, all technical and scientific terms used herein have the same meaning as generally understood by a person of ordinary skill in the art to which the present disclosure belongs, unless otherwise defined.

[0023] In the present disclosure, the reference to “one embodiment”, “an example embodiment”, “an embodiment”, “some embodiments” and the like means that the described embodiment can include a particular feature, structure or characteristic, but it is not necessary that every embodiment include the particular feature, structure or characteristic. In addition, these phrases do not necessarily refer to the same embodiment. Furthermore, when a particular feature, structure or characteristic is described in connection with an embodiment, it is contemplated that it is within the knowledge of those skilled in the art to affect such feature, structure or characteristic in connection with other embodiments, whether or not explicitly described.

[0024] It should be understood that although the terms “first” and “second” and the like can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could also be termed a second element, and, similarly, a second element could also be termed a first element, without departing from the scope of the embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the associated terms. In some examples, a value, process, or apparatus is referred to as “best”, “lowest”, “highest”, “smallest”, “largest”, etc. It should be understood that such a description is intended to indicate that a selection can be made among a number of used functional alternatives, and that such a selection is not necessarily better, smaller, higher, or more preferred than other alternatives.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of embodiments. 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. It will be further understood that the terms "comprises", "comprising", "includes" and / or "including", when used herein, specify the presence of stated features, elements, components, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, elements, components, and / or combinations thereof. For example, the term "comprises" and variations thereof are to be construed as open-ended terms that mean "comprising, but not limited to." The term "based on" is to be understood as "based, at least in part, on." The terms "one embodiment" and "an embodiment" are to be understood as "at least one embodiment." The term "another embodiment" is to be understood as "at least one other embodiment." Use of the expression "A and / or B" can mean "A or B" or "both A and B". Other explicit and implicit definitions can be included below.

[0026] As used herein, the term "communication network" refers to a network that follows any suitable communication standard, such as 5G NR, Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT), etc. In addition, communication between terminal devices and network devices in a communication network can be performed according to any suitable generation communication protocol, including but not limited to first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, fifth generation (5G), sixth generation (6G) communication protocols, and / or any other protocols that are currently known or are to be developed in the future. Embodiments of the present disclosure can be applied in various communication systems. In consideration of the rapid development of communication, there will also be future types of communication technology and systems in which the present disclosure can be implemented. It should not be considered as limiting the scope of the present application to only the aforementioned systems.

[0027] As used herein, the term "network device" generally refers to a node in a communication network via which a terminal device can access a communication network and receive services therefrom. Depending on the terminology applied and the technology, the network device can refer to a base station (BS) or an access point (AP), for example, a Node B (NodeB or NB), a radio access network (RAN) node, an evolved Node B (eNodeB or eNB), an NR NB (also known as gNB), a remote radio unit (RRU), a radio head (RH), an infrastructure equipment for V2X (vehicle-to-everything) communication, a transmission and reception point (TRP), a reception point (RP), a remote radio head (RRH), a relay, an integrated access and backhaul (IAB) node, a low power node such as a femto BS, a pico BS, etc.

[0028] As used herein, the term "terminal device" generally refers to any terminal device capable of wireless communication. By way of example, and without limitation, a terminal device can also be referred to as a communication device, user equipment (UE), end user device, subscriber station (SS), unmanned aerial vehicle (UAV), portable subscriber station, mobile station (MS), or access terminal (AT). The terminal device can include, but is not limited to, a mobile phone, a cellular phone, a smart phone, a voice over Internet Protocol (VoIP) phone, a wireless local loop phone, a tablet, a wearable terminal device, a personal digital assistant (PDA), a portable computer, a desktop computer, an image capture terminal device such as a digital camera, a game terminal device, a music storage and playback appliance, a vehicle-mounted wireless terminal device, a wireless endpoint, a mobile station, a laptop-embedded equipment (LEE), a laptop-mounted equipment (LME), a USB dongle, a smart device, a wireless customer-premises equipment (CPE), an Internet of Things (IoT) device, a watch or other wearable device, a head-mounted display (HMD), a vehicle, a target, a medical device (e.g., a remote surgery device), an industrial device (e.g., a robot and / or other wireless devices operating in an industrial and / or automated processing chain environments, consumer electronic devices, devices operating on a business and / or industrial wireless network, etc. In the following description, the terms "terminal device", "communication device", "terminal", "user equipment" and "UE" can be used interchangeably.

[0029] Extended Reality (XR), including Augmented Reality (AR) and Virtual Reality (VR), as well as Cloud Gaming (CG), provide a new promising connectivity for devices, applications, and services. Protocol Data Unit (PDU) sets and Quality of Service (QoS) characteristics for PDU sets can be introduced for XR services.

[0030] In some embodiments, a PDU set can include one or more PDUs carrying a payload of an information unit generated at an application layer. For example, the information unit can be a frame or a video slice for an XR service. In some implementations, all PDUs in a PDU set are needed by the application layer to use the corresponding information unit. In other implementations, the application layer can still recover part or all of the information unit when some PDUs in the PDU set are lost.

[0031] To support PDU set based QoS handling, a User Plane Function (UPF) can identify PDUs belonging to a PDU set, determine PDU set information, and send the PDU set information in a General Packet Radio Service (GPRS) Tunneling Protocol User Plane (GTP-U) header (which also includes a GTP-U extension header) to a gNB. The PDU set information can be used by the gNB for PDU set handling.

[0032] In some embodiments, the PDU set information may include at least one of the following: -PDU set number, - indicates the end PDU of a PDU set, - the PDU sequence number within the PDU set, - the PDU aggregate size in bytes, or -PDU set importance, which identifies the importance of the PDU set in the QoS flow.

[0033] In some embodiments, the UPF may send a PDU aggregate QoS parameter called "PDU aggregate uniform handling indication" (PSIHI) to the gNB. The PSIHI indicates whether all PDUs are required for the PDU aggregate to be used by the application layer on the receiver side.

[0034] To support QoS processing based on PDU aggregation, the UPF provides the gNB with an indication of the end PDU of a PDU aggregation in the GTP-U header. This indication indicates the complete transmission of the PDU aggregation for unified processing of the PDU aggregation. To support lossless handover, data is forwarded from the source gNB to the target gNB. When data is forwarded from the source gNB to the target gNB, how the target gNB is informed of the complete transmission of the PDU aggregation needs to be addressed. This will be referred to in the following section. FIG. 1A and 1B Provide a description.

[0035] FIG. 1A and 1B The following examples illustrate downlink data transmission. FIG. 1A As shown, in step 1, the source gNB (S-gNB) 110 receives PDUs #1, #2, and #3 in the PDU set from the UPF 130. PDU #3 is the last PDU in the PDU set.

[0036] In step 2, before handover, source gNB 110 sends PDUs #1, #2, and #3 to UE 140. PDUs #1 and #3 have been successfully sent to UE 140, while PDU #2 preceding PDU #3 (i.e., the last PDU) has not been acknowledged by UE 140.

[0037] In step 3, the source gNB forwards PDU#2 to the target gNB (T-gNB) 120 during data forwarding.

[0038] In step 4, target gNB 120 sends PDU#2 to UE 140.

[0039] Since the last PDU is not forwarded to the target gNB 120, the target gNB 120 does not know whether the transmission of the PDU set is completed, and thus cannot perform PDU set unified processing on the PDU set.

[0040] As shown in FIG. 1, at step 1, the source gNB 110 receives PDU#1 and #2 in the PDU set and an end marker (EM) packet from the UPF 130. The source gNB 110 does not receive the last PDU in the PDU set from the UPF 130. FIG. 1B

[0041] At step 2, before the handover, the source gNB 110 sends PDU#1 and #2 to the UE 140. PDU#1 has been successfully sent to the UE 140, while PDU#2 is not acknowledged by the UE 140.

[0042] At step 3, the source gNB forwards PDU#2 and the EM packet to the target gNB 120 during data forwarding.

[0043] At step 4, the UPF 130 can send the last packet to the target gNB 120.

[0044] However, the target gNB 120 does not know whether the last packet of the PDU set is expected to be received from the UPF 130, and thus cannot perform PDU set unified processing on the PDU set before receiving the last packet.

[0045] In addition to the example of FIG. 1A and 1B , in the case of sending a data burst, in the case of data forwarding, the network device receiving the forwarded data also needs to know whether the transmission of the data burst to the terminal device is complete.

[0046] Taking a split bearer terminated at a master node (MN) in NR dual connectivity (NR-DC) as an example. The MN receives an indication of the end of a data burst from the UPF. The MN can send a PDU with the indication of the end of the data burst to the terminal device via a master cell group (MCG) leg. However, the secondary node (SN) still needs to know the complete transmission of the data burst for power saving purposes, for example, so that the terminal device enters a DRX sleep mode with respect to a DRX group with a secondary cell group (SCG).

[0047] ​In view of the above, embodiments of the present disclosure provide a scheme for communication. In the scheme, a first network device receives at least one data packet in a set of data packets from a third network device. The first network device then forwards a subset of the at least one data packet to a second network device. The first network device in turn sends information about a transmission status of the set of data packets from the first network device to a terminal device to the second network device. Based on the information about the transmission status, the second network device can determine whether the transmission of the set of data packets to the terminal device is complete. The second network device then sends at least one data packet in the subset to the terminal device based on the information about the transmission status. In this way, the scheme can ensure that all data packets in the set are received by the terminal device. The terminal device can then operate based on the set of data packets.

[0048] In the following, some embodiments of the present disclosure will be described with reference to FIGS. 2-12 the principles of the present disclosure will be described.

[0049] FIG. 2 A schematic diagram of a communication environment 200 in which some embodiments of the present disclosure can be implemented is shown. The environment 200 can include a first network device 210, a second network device 220, a third network device 230, a fourth network device 240, and a terminal device 250.

[0050] In some embodiments, each of the first network device 210 and the second network device 220 can be implemented as a network device in a radio access network, e.g., a gNB. In such embodiments, the first network device 210 can communicate with the second network device 220 via an Xn interface between them.

[0051] In some embodiments, each of the third network device 230 and the fourth network device 240 can be implemented as a network device in a core network. For example, the third network device 230 can be implemented as a UPF, while the fourth network device 240 can be implemented as an access and mobility management function (AMF). In such embodiments, the third network device 230 can communicate with the fourth network device 240 via a session management function (SMF, not shown).

[0052] In some embodiments, the third network device 230 can communicate with each of the first network device 210 and the second network device 220 via a respective next generation user plane (NG-U) interface. The fourth network device 240 can communicate with each of the first network device 210 and the second network device 220 via a respective next generation control plane (NG-C) interface.

[0053] In some embodiments, the terminal device 250 can perform a handover from the first network device 210 to the second network device 220. In such embodiments, the first network device 210 can be referred to as a source network device, while the second network device 220 can be referred to as a target network device.

[0054] In some embodiments, the terminal device 250 can operate in a dual connectivity (DC) mode. In the DC mode, the terminal device 250 can communicate with both the first network device 210 and the second network device 220 simultaneously. In such embodiments, one of the first network device 210 and the second network device 220 can be implemented as a packet data convergence protocol (PDCP) termination node for bearers, while the other can be implemented as a peer node. For example, one of the first network device 210 and the second network device 220 can be implemented as a master node (MN), while the other can be implemented as a secondary node (SN).

[0055] The first network device 210 receives at least one data packet of a set of data packets from the third network device 230. The first network device 210 then forwards a subset of the at least one data packet to the second network device 220. The first network device 210 sends information about a transmission status of the set of data packets from the first network device 210 to the terminal device 250 to the second network device 220. Based on the information about the transmission status, the second network device 220 sends at least one data packet of the subset to the terminal device. In this way, the scheme can ensure that all data packets of the set are received by the terminal device. The terminal device can then operate based on the set of data packets.

[0056] It should be appreciated that the number of network devices and terminal devices is merely for ease of understanding and does not imply any limitation. The communication environment 200 can include any suitable number or type of network devices and terminal devices suitable for implementing embodiments of the present disclosure.

[0057] Communications in the communication environment 200 can be implemented according to any suitable communication protocol, including but not limited to cellular communication protocols of first generation (1G), second generation (2G), third generation (3G), fourth generation (4G), fifth generation (5G), or future sixth generation (6G) wireless local area network communication protocols (e.g., Institute of Electrical and Electronics Engineers (IEEE) 802.11, etc.), and / or any other protocol currently known or to be developed in the future. Moreover, the communications can utilize any suitable wireless communication techniques, including but not limited to code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), frequency division duplexing (FDD), time division duplexing (TDD), multiple-input multiple-output (MIMO), orthogonal frequency division multiplexing (OFDM), discrete Fourier transform spread OFDM (DFT-s-OFDM), and / or any other techniques currently known or to be developed in the future.

[0058] FIG. 3 A signaling diagram illustrating an exemplary procedure 300 for communication according to some embodiments of the present disclosure is shown. For purposes of discussion, reference will be made to FIG. 2 The procedure 300 is described. The procedure 300 can involve the first network device 210, the second network device 220, the third network device 230, and the terminal device 250.

[0059] As FIG. 3 shown, the first network device 210 receives 310 at least one data packet of a data packet set from the third network device 230.

[0060] In some embodiments, the data packet set can comprise a PDU set. In some embodiments, the PDU set can comprise one or more PDUs carrying a payload of an information unit generated at an application layer. For example, the information unit can be a frame or a video slice for an XR service.

[0061] Alternatively, in some embodiments, the data packet set can comprise a data burst. The data burst can comprise a plurality of PDUs generated and transmitted by an application within a short time period. The data burst can comprise one or more PDU sets.

[0062] The first network device 210 then forwards 320 a subset of the at least one data packet to the second network device 220.

[0063] In some embodiments, the subset of the at least one data packet can comprise all or part of the data packets received from the third network device 230.

[0064] The first network device 210 in turn transmits 330, to the second network device 220, information about a transmission status of the data packet set from the first network device 210 to the terminal device 250.

[0065] Based on the information about the transmission status, second network device 220 sends 340 at least one data packet of the subset to terminal device 250 .

[0066] Process 300 can ensure that all packets in the set are received by terminal device 250. Terminal device 250 can then perform operations based on the set of packets.

[0067] It should be noted that although act 330 is shown after act 320 , act 330 may be performed in parallel with act 320 or before act 320 .

[0068] In some embodiments, the information about the transmission status may include an indication of the last data packet that has not been successfully sent by the first network device 210 to the terminal device 250 .

[0069] In some embodiments, the first network device 210 may have sent a data packet to the terminal device 250 but has not yet received a positive acknowledgement from the terminal device 250. In such embodiments, the data packet may be referred to as a data packet that has not yet been successfully sent by the first network device 210 to the terminal device 250.

[0070] Alternatively, in some embodiments, the first network device 210 may have received a data packet from the third network device 230 but has not sent it to the terminal device 250. In such an embodiment, the data packet may also be referred to as a data packet that has not yet been successfully sent by the first network device 210 to the terminal device 250.

[0071] Hereinafter, for the sake of brevity, “data packets that have not been successfully sent by the first network device 210 to the terminal device 250 ” are also referred to as “data packets that have not been successfully sent”.

[0072] In some embodiments, the indication of the last data packet that has not been successfully sent may include an indication of the end of the data packet set. FIG. 4 Provide a description.

[0073] FIG. 4 A signaling diagram illustrating an exemplary process 400 for communication according to some embodiments of the present disclosure is shown. Process 400 may be considered an example implementation of process 300. For the purposes of this discussion, reference will be made to FIG. 2 The process 400 is described. The process 400 may involve the first network device 210, the second network device 220, the third network device 230, the fourth network device 240, and the terminal device 250. The process 400 may be described by taking a PDU set as an example of a data packet set.

[0074] like FIG. 4As shown, the PDU set includes PDU#1, PDU#2, PDU#3, and PDU#4. The first network device 210 receives (410) PDU#1, PDU#2, PDU#3, and PDU#4 in the PDU set from the third network device 230. PDU#4 is the last PDU in the PDU set. The GTP-U extension header of the PDCP service data unit (SDU) associated with PDU#4 can include an indication of the last packet, which indicates that PDU#4 is the last PDU in the PDU set.

[0075] In addition, the first network device 210 also receives an EM packet from the third network device 230. The EM packet is used to mark the last packet sent from the third network device 230 to the first network device 210 before the path switch.

[0076] The first network device 210 successfully transmits 415 PDU#1 and PDU#4 to the terminal device 250. In other words, the first network device 210 has transmitted PDU#1 and PDU#4 to the terminal device 250 and receives a positive acknowledgement from the terminal device 250.

[0077] However, the first network device 210 has transmitted PDU#2 and PDU#3 to the terminal device 250 but does not receive a positive acknowledgement from the terminal device 250. In other words, PDU#2 and PDU#3 are not successfully transmitted by the first network device 210 to the terminal device 250.

[0078] In response to the trigger of the handover procedure, the first network device 210 transmits 420 a handover request message to the second network device 220. Upon receiving the handover request message, the second network device 220 transmits 425 a handover request acknowledgement (Ack) message to the first network device 210.

[0079] Upon receiving the handover request acknowledgement message, the first network device 210 transmits 430 a radio resource control (RRC) reconfiguration message (with synchronization) to the terminal device 250. In addition, the first network device 210 transmits 435 a sequence number (SN) status transfer message to the second network device 220.

[0080] Upon receiving the RRC reconfiguration message, the terminal device 250 transmits 440 an RRC reconfiguration complete message to the second network device 220.

[0081] Upon receiving the RRC reconfiguration complete message, the second network device 220 transmits 445 a path switch request message to the fourth network device 240. In response, the fourth network device 240 transmits 450 a path switch request acknowledgement message to the second network device 220.

[0082] To support lossless handover, the first network device 210 can perform data radio bearer (DRB) based data forwarding to the second network device 220. For example, the first network device 210 forwards 455 PDU#2 and PDU#3 and the end marker packet to the second network device 220. PDU#2 and PDU#3 are PDUs that have not been successfully transmitted by the first network device 210 to the terminal device 250. In particular, PDU#3 is the last PDU that has not been successfully transmitted by the first network device 210 to the terminal device 250.

[0083] To transmit information about the transmission status of the PDU set, the first network device 210 adds an end of PDU set indication in PDU#3. The end of PDU set indication can indicate that PDU#3 is the last PDU that has not been successfully transmitted for the PDU set.

[0084] For example, the GTP-U extension header of the PDCP SDU associated with PDU#3 can include the end of PDU set indication. For example, the GTP-U extension header can include a PDCP SN GTP-U extension header or a PDU session container GTP-U extension header.

[0085] It should be noted that the meaning of the “end of PDU set indication” can be different from the meaning of the “indication of the last PDU in the PDU set”. As described above, the “end of PDU set indication” can indicate the last PDU that has not been successfully transmitted, while the “indication of the last PDU in the PDU set” indicates the complete transmission of the PDU set. The complete transmission of the PDU set is used for PDU set uniform handling. In this regard, the PDU including the “end of PDU set indication” can be different from the last PDU including the “indication of the last PDU in the PDU set”.

[0086] For example, in the example process 400, the PDU including the “end of PDU set indication” is PDU#3, and PDU#3 is the last PDU that has not been successfully transmitted. The last PDU including the “indication of the last PDU in the PDU set” is PDU#4, and PDU#4 has been successfully transmitted.

[0087] For another example, before the path switch, the first network device 210 can not have received the end marker packet from the third network device 230. Therefore, after the path switch, the second network device 220 will receive the end marker packet from the third network device 230. In this example, the PDU including the “end of PDU set indication” is different from the last PDU including the “indication of the last PDU in the PDU set”.

[0088] In some embodiments, to distinguish from the "indication of the last PDU in the PDU set", the "end indication of the PDU set" can be referred to as "time end indication of the PDU set" or "assumed end indication of the PDU set".

[0089] With continued reference to FIG. 4 Upon receiving PDU#2 and PDU#3 including the end indication of the PDU set, the second network device 220 determines that PDU#2 and PDU#3 are PDUs that have not been successfully transmitted. Further, the second network device 220 determines 460 that PDU#3 is the last PDU that has not been successfully transmitted by the first network device 210 to the terminal device 250. Then, the second network device 220 transmits 465 PDU#2 and PDU#3 to the terminal device 250.

[0090] In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250. Then, the terminal device 250 can operate based on the PDU set.

[0091] In other embodiments, the indication of the last packet that has not been successfully transmitted can be an implicit indication. For example, the indication of the last packet that has not been successfully transmitted can include a last sequence number (SN) of the last packet. The last SN is higher than the SNs of the other packets in the subset. In other words, the last SN is the highest one among the SNs of the packets in the subset.

[0092] In such embodiments, if any PDU has been transmitted to the terminal device 250, the first network device 210 can continue to assign PDCP SNs for the PDUs in the PDU set received from the third network device 230. When forwarding the PDUs to the second network device 220, the first network device 210 can put the PDCP SNs into the GTP-U extension header of the PDCP SDU associated with the PDUs.

[0093] For example, the second network device 220 can identify the PDUs belonging to the PDU set by the PDU set sequence number in the GTP-U header. The second network device 220 can determine that the PDU with the highest PDCP SN among the PDUs forwarded by the first network device 210 is the last packet that has not been successfully transmitted.

[0094] The procedure 400 is described by taking the PDU set as an example of the packet set. Alternatively, in some embodiments, the packet set can include a data burst. The data burst can include one or more PDU sets. The procedure 400 can be applied to embodiments in which the packet set can include a data burst.

[0095] In embodiments using MN terminated split bearers in the case of NR-DC, the first network device 210 can be implemented as an MN, while the second network device 220 can be implemented as an SN.

[0096] In such embodiments, the indication of the last data packet can comprise an end of data burst indication. The end of data burst indication can indicate that PDU#3 is the last PDU in the data burst to be transmitted in the SCG.

[0097] The first network device 210 can add the end of data burst indication in a user plane protocol, e.g. in a GTP-U extension header. For example, a new bit can be added in the DL_USER_DATA frame for the end indication.

[0098] The first network device 210 can transmit the end of data burst indication in the GTP-U extension header of the last forwarded PDCP PDU or after the last forwarded PDCP PDU.

[0099] In embodiments using SN terminated split bearers in the case of NR-DC, the first network device 210 can be implemented as an SN, while the second network device 220 can be implemented as an MN. In such embodiments, the end of data burst indication can indicate that PDU#3 is the last PDU in the data burst to be transmitted in the MCG.

[0100] In some embodiments, the subset of data packets forwarded by the first network device 210 can comprise an end data packet of the set of data packets, and the information about the transmission status can comprise an indication of the end data packet.

[0101] For example, in embodiments where the set of data packets comprises a set of PDUs, the end data packet of the set of data packets can be an end PDU of the set of PDUs, and the information about the transmission status can comprise an indication of the end PDU. This will be described with reference to FIG. 5 .

[0102] FIG. 5 A signaling diagram illustrating an exemplary procedure 500 for communication according to some embodiments of the present disclosure is shown. The procedure 500 can be considered an example implementation of the procedure 300. For purposes of discussion, the procedure 500 will be described with reference to FIG. 2 the first network device 210, the second network device 220, the third network device 230, the fourth network device 240, and the terminal device 250. The procedure 500 can be described by considering the set of PDUs as an example of the set of data packets.

[0103] Actions 410, 415, 420, 425, 430, 435, 440, 445, and 450 in process 500 are the same as those in process 400. Therefore, details of these actions are omitted for brevity.

[0104] Actions 555, 560, and 565 in process 500 are different from actions 455, 460, and 465 in process 400.

[0105] Specifically, during data forwarding, the first network device 210 forwards 555, in addition to PDU#2, PDU#3, and the EM packet, PDU#4 to the second network device 220. PDU#4 is the last PDU in the PDU set that has been successfully transmitted to the terminal device 250.

[0106] The indication of the last packet (i.e., PDU#4) can have been removed by a service data adaptation protocol (SDAP) layer of the first network device 210. To transmit information about the transmission status of the PDU set, the first network device 210 re-adds the indication of the last packet in the GTP-U extension header of the PDCP SDU associated with PDU#4. For example, the first network device 210 can re-add the indication of the last packet in the PDCP SN GTP-U extension header or the PDU session container GTP-U extension header of the PDCP SDU associated with PDU#4.

[0107] Upon receiving PDU#4 including the indication of the last packet, the second network device 220 determines 560 that PDU#4 is the last PDU in the PDU set. The second network device 220 can in turn transmit 565 PDU#2, PDU#3, and PDU#4 to the terminal device 250.

[0108] In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250. The terminal device 250 can then operate based on the PDU set.

[0109] In other embodiments, the second network device 220 can receive, from the terminal device 250, an indication of a reception status of the PDUs in the PDU set. The second network device 220 can transmit, to the terminal device 250, at least one of the PDUs received from the first network device 210 based on the indication of the reception status.

[0110] In some embodiments, the second network device 220 can receive the indication of the reception status via a PDCP status report (SR). The PDCP SR can include a PDU set sequence number and a PDU sequence number within the PDU set. The PDCP SR can also include a bitmap indicating whether each PDU in the PDU set has been successfully received. If a bit in the bitmap indicates “true” or “yes”, it means that the PDU in the PDU set has been successfully received by the terminal device 250. Otherwise, it means that the PDU (e.g., named as a missing PDU) has not been received, and then the second network device 220 sends the missing PDU in the PDU set to the terminal device 250.

[0111] For example, if the PDCP SR indicates that PDU#1 and PDU#4 (i.e., the last PDU) have been successfully received but PDU#2 and PDU#3 are missing, the second network device 220 can send PDU#2 and PDU#3 to the terminal device 250.

[0112] Alternatively, in some embodiments, the second network device 220 can receive the indication of the reception status of the PDU set from the terminal device 250. Then, the second network device 220 can send at least one of the PDUs received from the first network device 210 to the terminal device 250 based on the indication of the reception status of the PDU set.

[0113] In such embodiments, the second network device 220 can receive the indication of the reception status via a PDCP SR. The PDCP SR can include a PDU set sequence number and a bit indicating whether the PDU set identified by the sequence number has been successfully received. If the bit indicates “true” or “yes”, it means that all PDUs in the PDU set have been successfully received by the terminal device 250. Otherwise, it means that one or more PDUs in the PDU set have not been successfully received. Then, the second network device 220 sends all the forwarded PDUs in the PDU set received from the first network device 210 to the terminal device 250.

[0114] The procedure 500 is described by taking the PDU set as an example of the data packet set. Alternatively, in some embodiments, the data packet set can include a data burst. The data burst can include one or more PDU sets. The procedure 500 can be applied to embodiments in which the data packet set can include a data burst.

[0115] In embodiments using MN-terminated split bearers in the case of NR-DC, the first network device 210 can be implemented as an MN, and the second network device 220 can be implemented as an SN.

[0116] In such embodiments, the information about the transmission status can comprise an indication of an end packet of the data burst. The indication of the end packet of the data burst can indicate to the second network device 220 (SN) that the transmission of the data burst is completed in the SCG.

[0117] In such embodiments, the first network device 210 can transmit to the second network device 220 the end packet of the data burst comprising the indication.

[0118] In embodiments of split bearer using SN termination, the first network device 210 can be implemented as an SN, while the second network device 220 can be implemented as an MN. In such embodiments, the indication of the end packet of the data burst can indicate to the second network device 220 (MN) that the transmission of the data burst is completed in the MCG.

[0119] In some embodiments, the subset forwarded by the first network device 210 can comprise all packets of the set of packets, and the information about the transmission status of the set of packets can comprise an indication of an end packet of the set of packets. This will be described with reference to FIG. 6

[0120] FIG. 6 A signaling diagram illustrating an exemplary procedure 600 for communication according to some embodiments of the present disclosure is shown. The procedure 600 can be considered an example implementation of the procedure 300. For purposes of discussion, the procedure 600 will be described with reference to FIG. 2 the first network device 210, the second network device 220, the third network device 230, the fourth network device 240, and the terminal device 250. The procedure 600 can be described by considering the set of PDUs as an example of a set of packets.

[0121] The actions 410, 415, 420, 425, 430, 435, 440, 445, and 450 in the procedure 600 are the same as in the procedure 400. The action 560 in the procedure 600 is the same as in the procedure 500. Therefore, details of these actions are omitted for brevity.

[0122] The actions 655 and 665 in the procedure 600 are different from the actions 455 and 465 in the procedure 400, and from the actions 555 and 565 in the procedure 500.

[0123] Specifically, during the data forwarding, the first network device 210 forwards 655 PDU#1 and PDU#4 to the second network device 220 in addition to PDU#2, PDU#3, and the EM packet. PDU#4 is the end PDU of the set of PDUs that has been successfully transmitted to the terminal device 250.

[0124] ​In other words, the first network device 210 forwards all PDUs in the PDU set. In this case, PDU session level data forwarding can be performed, which means that the PDU set information in the GTP-U header received from the third network device 230 is maintained. The second network device 220 identifies the PDU set by reading the GTP-U header. The indication of the last packet is also saved in the GTP-U header of PDU #4.

[0125] Similar to the procedure 500, in the procedure 600, upon receiving PDU #4 including the indication of the last packet, the second network device 220 determines 560 that PDU #4 is the last PDU in the PDU set. Then, the second network device 220 can transmit 665 PDU #1, PDU #2, PDU #3, and PDU #4 to the terminal device 250.

[0126] In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250. Then, the terminal device 250 can operate based on the PDU set.

[0127] In other embodiments, similar to the procedure 500, in the procedure 600, the second network device 220 can receive an indication of a reception status of the PDUs in the PDU set from the terminal device 250. The second network device 220 can transmit at least one of the PDUs received from the first network device 210 to the terminal device 250 based on the indication of the reception status. In such embodiments, the second network device 220 can receive the indication of the reception status via a PDCP SR. For example, if the PDCP SR indicates that PDU #1 and PDU #4 (i.e., the last PDU) have been successfully received but PDU #2 and PDU #3 are missing, the second network device 220 can transmit PDU #2 and PDU #3 to the terminal device 250.

[0128] Alternatively, in some embodiments, the second network device 220 can receive an indication of a reception status of the PDU set from the terminal device 250. Then, the second network device 220 can transmit at least one of the PDUs received from the first network device 210 to the terminal device 250 based on the indication of the reception status of the PDU set.

[0129] In such embodiments, the second network device 220 can receive the indication of the reception status via the PDCP SR. The PDCP SR can comprise a PDU set sequence number and a bit indicating whether the PDU set identified by the sequence number has been successfully received. If the bit indicates "true" or "yes", it means that all PDUs in the PDU set have been successfully received by the terminal device 250. Otherwise, it means that there is still one or more PDUs in the PDU set that have not been successfully received. Then, the second network device 220 transmits all PDUs in the PDU set to the terminal device 250.

[0130] In some embodiments, the information about the transmission status of the data packet set can comprise at least one of: - a first indication indicating whether the data packet set has been successfully transmitted by the first network device 210 to the terminal device 250; - a second indication of the transmission status of the data packets in the set, or - a third indication of the transmission status of the last data packet in the set.

[0131] In some embodiments, the third indication can comprise one of: - a fourth indication indicating whether the first network device 210 has successfully transmitted the last data packet to the terminal device 250; - a fifth indication indicating that the first network device 210 has received the last data packet from the third network device 230, but has not transmitted the last data packet to the terminal device 250, or - a sixth indication indicating that the last data packet has not been received from the third network device 230.

[0132] FIG. 7 A signaling diagram illustrating an exemplary procedure 700 for communication according to some embodiments of the present disclosure is shown. The procedure 700 can be considered an example implementation of the procedure 300. For the purpose of discussion, reference will be made to FIG. 2 The procedure 700 is described. The procedure 700 can involve the first network device 210, the second network device 220, the third network device 230, the fourth network device 240 and the terminal device 250. The procedure 700 can be described by considering a PDU set as an example of a data packet set.

[0133] The actions 410, 415, 420, 425, 430, 440, 445 and 450 in the procedure 700 are the same as in the procedure 400. Therefore, the details of these actions are omitted for brevity.

[0134] The actions 735, 755, 760 and 765 in the procedure 700 are different from the actions 435, 455, 460 and 465 in the procedure 400.

[0135] In the process 700, to send information about the transmission status of the set of PDUs to the second network device 220, the first network device 210 sends a first indication to the second network device 220 via control signaling. The first indication indicates whether the set of PDUs has been successfully transmitted by the first network device 210 to the terminal device 250.

[0136] The first network device 210 can send 735 a SN status transfer message to the second network device 220. The SN status transfer message can include the first indication. Alternatively, the first indication can be included in control signaling different from the SN status transfer message.

[0137] In some embodiments, the first indication can include a PDU set sequence number and a bit to indicate whether the PDU set identified by the sequence number has been successfully transmitted to the terminal device 250. If the bit indicates "true" or "yes", it means that all PDUs in the PDU set have been successfully transmitted to the terminal device 250. Otherwise, it means that there still exists one or more PDUs in the PDU set that have not been successfully transmitted. For example, in the process 700, the bit can indicate "false" or "no", which means that there still exists one or more PDUs in the PDU set that have not been successfully transmitted.

[0138] During data forwarding, the first network device 210 forwards 755 PDU#2 and PDU#3 to the second network device 220.

[0139] Based on the first indication and the received PDU#2 and PDU#3, the second network device 220 determines 760 that PDU#2 and PDU#3 have not been successfully transmitted. Then, the second network device 220 sends 765 PDU#2 and PDU#3 to the terminal device 250. In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250.

[0140] Alternatively, to send information about the transmission status of the set of PDUs to the second network device 220, the first network device 210 sends a second indication of the transmission status of the PDUs in the set of PDUs to the second network device 220 via control signaling.

[0141] In some embodiments, the second indication can comprise a PDU set sequence number, a PDU sequence number within the PDU set, and a bitmap for indicating whether each PDU in the PDU set has been successfully transmitted to the terminal device 250. If a bit in the bitmap indicates "true" or "yes", it means that the PDU associated with the bit in the PDU set has been successfully transmitted to the terminal device 250. Otherwise, it means that the PDU has not been successfully transmitted. For example, in the procedure 700, the bits associated with PDU#2 and PDU#3 can indicate "false" or "no", which means that PDU#2 and PDU#3 have not been successfully transmitted.

[0142] The first network device 210 can send 735 a SN status transfer message to the second network device 220. The SN status transfer message can comprise the second indication. Alternatively, the second indication can be included in control signaling different from the SN status transfer message.

[0143] Based on the second indication and the received PDU#2 and PDU#3, the second network device 220 determines 760 that PDU#2 and PDU#3 have not been successfully transmitted. Then, the second network device 220 sends 765 PDU#2 and PDU#3 to the terminal device 250. In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250.

[0144] Alternatively, to send information about the transmission status of the PDU set to the second network device 220, the first network device 210 can send a third indication of the transmission status of the last packet in the PDU set to the second network device 220 via control signaling.

[0145] In some embodiments, the third indication of the transmission status of the last packet can comprise one of: - a fourth indication indicating whether the first network device 210 has successfully transmitted the last packet to the terminal device 250; - a fifth indication indicating that the last packet has been received from the third network device 230 but has not yet been transmitted by the first network device 210 to the terminal device 250, or - a sixth indication indicating that the last packet has not yet been received from the third network device 230.

[0146] ​In some embodiments, the third indication can comprise the PDU set sequence number and a fourth indication. The fourth indication can comprise a bit indicating whether the last packet in the PDU set identified by the sequence number has been successfully transmitted to the terminal device 250. If the bit indicates "true" or "yes", it means that the last packet has been successfully transmitted to the terminal device 250. Otherwise, it means that the last packet has not been successfully transmitted. For example, in the procedure 700, the bit can indicate "true" or "yes", which means that the last packet (i.e., PDU#4) has been successfully transmitted to the terminal device 250.

[0147] During data forwarding, the first network device 210 forwards 755 PDU#2 and PDU#3 to the second network device 220.

[0148] Based on the received PDU#2 and PDU#3, the second network device 220 determines 760 that PDU#2 and PDU#3 have not been successfully transmitted. Based on the third indication, the second network device 220 determines that the last packet (i.e., PDU#4) has been successfully transmitted to the terminal device 250.

[0149] Then, the second network device 220 transmits 765 PDU#2 and PDU#3 to the terminal device 250. In this way, the second network device 220 can ensure that all PDUs in the PDU set are received by the terminal device 250.

[0150] Alternatively, to transmit information about the transmission status of the PDU set to the second network device 220, the first network device 210 can transmit the first indication and the second indication to the second network device 220 via control signaling.

[0151] For example, in the procedure 700, based on the first indication, the second network device 220 determines that the PDU set has not been successfully transmitted to the terminal device 250. Based on the first indication and the second indication, the second network device 220 determines that only PDU#2 and PDU#3 in the PDU set have not been successfully transmitted to the terminal device 250. The second network device 220 in turn transmits PDU#2 and PDU#3 to the terminal device 250.

[0152] Alternatively, to transmit information about the transmission status of the PDU set to the second network device 220, the first network device 210 can transmit the first indication, the second indication and the third indication to the second network device 220 via control signaling.

[0153] For example, in the procedure 700, based on the first indication, the second network device 220 determines that the set of PDUs has not been successfully transmitted to the terminal device 250. Based on the second indication, the second network device 220 determines that PDU#2 and PDU#3 in the set of PDUs have not been successfully transmitted to the terminal device 250. Based on the third indication, the second network device 220 determines that the last packet (i.e., PDU#4) in the set of PDUs has been successfully transmitted to the terminal device 250.

[0154] Next, the second network device 220 transmits 765 PDU#2 and PDU#3 to the terminal device 250. In this way, the second network device 220 can ensure that all PDUs in the set of PDUs are received by the terminal device 250.

[0155] The procedure 700 is described by taking the set of PDUs as an example of the set of packets. Alternatively, in some embodiments, the set of packets can include a data burst. A data burst can include one or more sets of PDUs. The procedure 700 can be applied to embodiments in which the set of packets can include a data burst.

[0156] In embodiments in which split bearers with MN termination are used in NR-DC, the first network device 210 can be implemented as an MN, and the second network device 220 can be implemented as an SN.

[0157] In such embodiments, the information about the transmission status can include the first indication. The first indication can indicate whether the data burst has been successfully transmitted to the terminal device 250 in the SCG.

[0158] In embodiments in which split bearers with SN termination are used in NR-DC, the first network device 210 can be implemented as an SN, and the second network device 220 can be implemented as an MN. In such embodiments, the first indication can indicate whether the data burst has been successfully transmitted to the terminal device 250 in the MCG.

[0159] In some embodiments, the first network device 210 can obtain, from the third network device 230, information about a second size of the set of PDUs. The first network device 210 can determine a first size (e.g., in bytes) of remaining PDUs in the set of PDUs based on the second size of the set of PDUs and a third size of the PDUs in the set of PDUs that have been successfully transmitted to the terminal device 250 by the first network device 210. For example, the first network device 210 can determine the first size after stopping the data transmission to the terminal device 250. In such embodiments, the information about the transmission status can include the first size of the remaining PDUs.

[0160] In some embodiments, the first network device 210 can send the information on the transmission status including the first size of the remaining PDUs in the SN status transfer message. Alternatively, the first network device 210 can send the information on the transmission status including the first size of the remaining PDUs in control signaling different from the SN status transfer message.

[0161] Alternatively, in some embodiments, the information on the transmission status can include a second size of the set of PDUs and a third size of the PDUs in the set of PDUs that have been successfully transmitted by the first network device 210 to the terminal device 250. Upon receiving the information on the transmission status, the second network device 220 can determine the first size based on the second size and the third size.

[0162] In some embodiments, the first network device 210 can forward the PDUs in the set of PDUs that have not been successfully transmitted to the terminal device 250 to the second network device 220. The second network device 220 can receive new PDUs in the set of PDUs that have not been transmitted to the first network device 210 from the third network device 230. Then, the second network device 220 can complete the transmission of the set of PDUs according to the first size of the remaining PDUs.

[0163] In some embodiments, if the size of the PDUs in the set of PDUs that have not been successfully transmitted to the terminal device 250 (and new PDUs, if any) is less than the first size of the remaining PDUs, the second network device 220 can not completely process the set of PDUs transmission, and can accordingly trigger discarding the set of PDUs.

[0164] In some embodiments, before the last packet in the set of PDUs is forwarded to the second network device 220, the first network device 210 can determine that a timer associated with discarding of the set of PDUs expires. The first network device 210 can in turn send an indication to the second network device 220 indicating that the set of PDUs is to be discarded. Upon receiving the indication, the second network device 220 can discard all buffered PDUs in the set of PDUs. This will be described with reference to FIG. 8 .

[0165] FIG. 8 A signaling diagram illustrating an exemplary procedure 800 for communication according to some embodiments of the present disclosure is shown. The procedure 800 can be considered an example implementation of the procedure 300. For purposes of discussion, the procedure 800 will be described with reference to FIG. 2 the devices 210, 220, 230, 240, and 250. The procedure 800 can be described by taking the set of PDUs as an example of the set of packets.

[0166] Actions 420, 425, 430, 435, 440, 445, and 450 in process 800 are the same as the actions in process 400. Therefore, the details of these actions are omitted for brevity.

[0167] Actions 810, 815, 855, 860, and 865 in process 800 are different from actions 410, 415, 455, 460, and 465 in process 400. In addition, actions 812 and 852 in process 800 are newly added.

[0168] In particular, the PDU set includes PDU#1, PDU#2, PDU#3, and PDU#4. The first network device 210 receives 810 PDU#1, PDU#2, and PDU#3 in the PDU set from the third network device 230. PDU#4 is the last PDU in the PDU set. The GTP-U extension header of the PDCP SDU associated with PDU#4 can include an indication indicating that the last PDU in the PDU set is the end packet of PDU#4.

[0169] Upon receiving PDU#1, the first network device 210 starts 812 a timer associated with the discard of the PDU set. For example, the timer can include a PDCP discard timer of the PDU set.

[0170] The first network device 210 successfully transmits 815 PDU#1 to the terminal device 250.

[0171] However, the first network device 210 has transmitted PDU#2 and PDU#3 to the terminal device 250, but does not receive a positive acknowledgement from the terminal device 250. In other words, PDU#2 and PDU#3 are not successfully transmitted to the terminal device 250 by the first network device 210.

[0172] During the handover procedure, the first network device 210 receives 852 PDU#4 (i.e., the end packet) and the EM packet from the third network device 230.

[0173] The first network device 210 forwards 855 PDU#2 and PDU#3 to the second network device 220.

[0174] Before the end packet (i.e., PDU#4) in the PDU set is forwarded to the second network device 220, the first network device 210 determines 860 that the timer expires.

[0175] In some embodiments, the expiration of the timer associated with the discard of the PDU set can mean the expiration of the PDCP discard timer of any PDU in the PDU set.

[0176] Based on the determination, the first network device 210 sends 865 an indication to the second network device 220 that the set of PDUs is to be discarded. For brevity, the “indication that the set of PDUs is to be discarded” is also referred to as a PDU set discard indication.

[0177] In some embodiments, the PDU set discard indication can include a sequence number of the set of PDUs to be discarded.

[0178] In some embodiments, the PDU set discard indication can be included in a GTP-U extension header (e.g., a RAN container) or in control plane signaling (e.g., in an Xn-AP message).

[0179] Upon receiving the PDU set discard indication, the second network device 220 can discard all buffered PDUs in the set of PDUs identified by the sequence number.

[0180] In some embodiments, the information about the transmission status can include information about a remaining time of a timer associated with the discard of the set of PDUs.

[0181] In some embodiments, the information about the remaining time of the timer can be included in a GTP-U extension header (e.g., a RAN container) or in control plane signaling (e.g., in an Xn-AP message).

[0182] In some embodiments, the information about the remaining time of the timer can include a remaining time of the timer.

[0183] In some embodiments, the information about the remaining time of the timer can include a duration of the timer and an elapsed time of the timer. The second network device 220 can determine the remaining time of the timer based on the duration of the timer and the elapsed time of the timer.

[0184] In some embodiments, if the remaining time is exhausted, the second network device 220 can discard all buffered PDUs in the set of PDUs.

[0185] In some embodiments, the path switch based on the set of PDUs can be performed by the third network device 230. If there is an ongoing data transmission of the set of PDUs, the third network device 230 can send one or more EM packets to the first network device 210 only after the last PDU of the set of PDUs.

[0186] Currently, the second network device 220 sends a path switch request message to the fourth network device 240 to trigger the third network device 230 to switch a downlink (DL) data path to the second network device 220. The third network device 230 switches the DL data path to the second network device 220. The third network device 230 sends one or more EM packets to the first network device 210 on the old path per PDU session or per tunnel (TNL). Then, the third network device 230 can release any U-plane / TNL resources to the first network device 210.

[0187] In some embodiments, the third network device 230 can switch the DL data path only after the transmission of the PDU set is completed. This means that only when all PDUs of the PDU set have been sent to the first network device 210, the third network device 230 switches the DL data path from the old path (i.e., the GTP-U tunnel between the third network device 230 and the first network device 210 for DL data transmission) to the new path (i.e., the GTP-U tunnel between the third network device 230 and the second network device 220 for DL data transmission).

[0188] In case of a switch, the SMF can instruct the third network device 230 to switch the DL data path and provide an indication to the third network device 230 to send one or more EM packets on the old data path. If there is an ongoing data transmission of the PDU set, the third network device 230 sends the one or more EM packets to the first network device 210 only after the last PDU of the PDU set. The third network device 230 starts sending PDUs of a new PDU set to the second network device 220 via the new path.

[0189] FIG. 9 A flowchart illustrating an example method implemented at a network device, in accordance with some embodiments of the disclosure, is shown. For discussion purposes, reference will be made to FIG. 2 The method 900 is described from the perspective of the first network device 210.

[0190] At block 910, the first network device 210 receives at least one data packet of a data packet set from the third network device 230.

[0191] At block 920, the first network device 210 forwards a subset of the at least one data packet to the second network device 220.

[0192] At block 930, the first network device 210 sends information about a transmission status of the data packet set from the first network device 210 to the terminal device 250 to the second network device 220.

[0193] In some embodiments, the information on the transmission status can comprise an indication of a last data packet that has not been successfully sent by the first network device 210 to the terminal device 250.

[0194] In some embodiments, the indication of the last data packet can comprise an end indication of the set of data packets.

[0195] In some embodiments, the indication of the last data packet can comprise a last sequence number of the last data packet, the last sequence number being higher than sequence numbers of other data packets in the subset.

[0196] In some embodiments, the subset can comprise an end data packet in the set of data packets, and the information on the transmission status can comprise an indication of the end data packet.

[0197] In some embodiments, the subset can further comprise all data packets in the set of data packets, and the information on the transmission status can comprise an indication of an end data packet in the set of data packets.

[0198] In some embodiments, the information on the transmission status can comprise at least one of: - a first indication of whether the set of data packets has been successfully sent by the first network device 210 to the terminal device 250; - a second indication of the transmission status of the data packets in the set, or - a third indication of the transmission status of an end data packet in the set.

[0199] In some embodiments, the third indication can comprise one of: - a fourth indication of whether the first network device 210 has successfully sent the end data packet to the terminal device 250; - a fifth indication of whether the first network device 210 has received the end data packet from the third network device 230 but has not sent the end data packet to the terminal device 250, or - a sixth indication of whether the end data packet has not been received from the third network device 230.

[0200] In some embodiments, the set of data packets can comprise a set of PDUs.

[0201] In some embodiments, the method 900 further comprises determining a first size of remaining PDUs in the set of PDUs based on a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully sent by the first network device 210 to the terminal device 250.

[0202] In some embodiments, the information on the transmission status can comprise the first size of the remaining PDUs.

[0203] In some embodiments, the information about the transmission status can comprise a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device 210 to the terminal device 250.

[0204] In some embodiments, the method 900 further comprises determining, prior to the last PDU in the set of PDUs being forwarded to the second network device 220, that a timer associated with discarding of the set of PDUs has expired; based on the determination, sending, to the second network device 220, an indication that the set of PDUs is to be discarded.

[0205] In some embodiments, the information about the transmission status can comprise information about a remaining time of a timer associated with discarding of the set of PDUs.

[0206] In some embodiments, the set of data packets can comprise a data burst.

[0207] FIG. 10 A flowchart illustrating an example method implemented at a network device, in accordance with some embodiments of the present disclosure, is shown. For discussion purposes, reference will be made to FIG. 2 Method 1000 is described from the perspective of the second network device 220.

[0208] At block 1010, the second network device 220 receives, from the first network device 210, a subset of the set of data packets.

[0209] At block 1020, the second network device 220 receives, from the first network device 210, information about a transmission status of the set of data packets from the first network device 210 to the terminal device 250.

[0210] At block 1030, the second network device 220 sends, to the terminal device 250, at least one data packet in the subset based on the information about the transmission status.

[0211] In some embodiments, the information about the transmission status can comprise an indication of a last data packet that has not been successfully transmitted by the first network device 210 to the terminal device 250.

[0212] In some embodiments, the indication of the last data packet can comprise an end indication of the set of data packets.

[0213] In some embodiments, the indication of the last data packet can comprise a last sequence number of the last data packet, the last sequence number being higher than sequence numbers of other data packets in the subset.

[0214] In some embodiments, the subset can comprise a last data packet in the set of data packets, and the information about the transmission status can comprise an indication of the last data packet.

[0215] In some embodiments, the subset can include all data packets in the set of data packets, and the information about the transmission status can include an indication of a last data packet in the set of data packets.

[0216] In some embodiments, the method 1000 further includes receiving, from the terminal device 250, an indication of a reception status of the data packets in the set of data packets. In such embodiments, transmitting the at least one data packet in the subset includes transmitting the at least one data packet based on the indication of the reception status.

[0217] In some embodiments, the method 1000 further includes receiving, from the terminal device 250, an indication of a reception status of the set of data packets. In such embodiments, transmitting the at least one data packet in the subset includes transmitting the at least one data packet based on the indication of the reception status.

[0218] In some embodiments, the information about the transmission status can include at least one of: - a first indication indicating whether the set of data packets has been successfully transmitted by the first network device 210 to the terminal device 250; - a second indication of a transmission status of the data packets in the set, or - a third indication of a transmission status of a last data packet in the set.

[0219] In some embodiments, the third indication can include one of: - a fourth indication indicating whether the first network device 210 has successfully transmitted the last data packet to the terminal device 250; - a fifth indication indicating that the first network device 210 has received the last data packet from the third network device 230 but has not transmitted the last data packet to the terminal device 250, or - a sixth indication indicating that the last data packet has not been received from the third network device 230.

[0220] In some embodiments, the set of data packets can include a set of PDUs.

[0221] In some embodiments, the information about the transmission status can include a first size of remaining PDUs in the set of PDUs. The first size of the remaining PDUs is determined based on a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device 210 to the terminal device 250.

[0222] In some embodiments, the information about the transmission status can comprise a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device 210 to the terminal device 250. In such embodiments, the method 1000 further comprises determining a first size of remaining PDUs in the set of PDUs based on the second size and the third size.

[0223] In some embodiments, the method 1000 further comprises receiving an indication from the first network device 210 that the set of PDUs is to be discarded.

[0224] In some embodiments, the method 1000 further comprises discarding all PDUs in the set of PDUs based on the indication.

[0225] In some embodiments, the information about the transmission status can comprise information about a remaining time of a timer associated with the discarding of the set of PDUs.

[0226] In some embodiments, the method 1000 further comprises discarding all PDUs in the set of PDUs based on determining that the remaining time has run out.

[0227] In some embodiments, the set of data packets can comprise a data burst.

[0228] FIG. 11 A flowchart of an example method implemented at a terminal device according to some embodiments of the present disclosure is shown. For the purpose of discussion, reference will be made to FIG. 2 The method 1100 is described from the perspective of the terminal device 250.

[0229] At block 1110, the terminal device 250 determines a reception status of the set of data packets.

[0230] At block 1120, the terminal device 250 sends an indication of the reception status of the set of data packets to the second network device 220.

[0231] In some embodiments, the method 1100 further comprises determining a reception status of a data packet in the set of data packets; and sending an indication of the reception status of the data packet to the second network device 220.

[0232] FIG. 12 A simplified block diagram of an apparatus 1200 suitable for implementing embodiments of the present disclosure is shown. The apparatus 1200 can be considered another example implementation of the first network device 210, the second network device 220, or the terminal device 250 as shown. FIG. 2 Thus, the apparatus 1200 can be implemented at or as at least a part of the first network device 210, the second network device 220, or the terminal device 250.

[0233] As illustrated, the apparatus 1200 includes a processor 1210, a memory 1220 coupled to the processor 1210, a suitable transceiver (TX) and receiver (RX) 1240 coupled to the processor 1210, and a communication interface coupled to the TX / RX 1240. The memory 1210 stores at least a portion of a program 1230. The TX / RX 1240 is for bidirectional communication. The TX / RX 1240 has at least one antenna to facilitate communication, although in practice the access node mentioned in the present disclosure can have several antennas. The communication interface can represent any interface needed for communication with other network elements, such as an X2 interface for bidirectional communication between eNBs, an S1 interface for communication between a mobility management entity (MME) / serving gateway (S-GW) and an eNB, an Un interface for communication between an eNB and a relay node (RN), or a Uu interface for communication between an eNB and a terminal device.

[0234] The program 1230 is assumed to include program instructions that, when executed by the associated processor 1210, enable the apparatus 1200 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGS. 1 to FIG. 11 The embodiments herein discussed can be implemented through computer software executable by the processor 1210 of the apparatus 1200, or by hardware, or by a combination of software and hardware. The processor 1210 can be configured to perform various embodiments of the present application. Further, the combination of the processor 1210 and the memory 1220 can form a processing arrangement 1250 suitable for implementing various embodiments of the present disclosure.

[0235] The memory 1220 can be of any type suitable to the local technical requirements and can 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 1220 is shown in the apparatus 1200, there can be several physically different memory modules in the apparatus 1200. The processor 1210 can be of any type suitable to the local technical requirements and can include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), and processors based on multi-core processor architectures, as non-limiting examples. The apparatus 1200 can have multiple processors for internal parallel processing, such as a master integrated circuit chip that is time-synchronized with a clock to a slave integrated circuit chip.

[0236] In summary, the embodiments of the present disclosure can provide the following solutions.

[0237] Clause 1. A first network device comprising: a processor; and a transceiver coupled to the processor, wherein the processor is configured to: receive, via the transceiver, at least one data packet of a set of data packets from a third network device; forward, via the transceiver, a subset of the at least one data packet to a second network device; and send, via the transceiver, to the second network device, information about a transmission status of the set of data packets from the first network device to an end device.

[0238] Clause 2. The first network device of clause 1, wherein the information about the transmission status comprises an indication of a last data packet that has not been successfully sent by the first network device to the end device.

[0239] Clause 3. The first network device of clause 2, wherein the indication of the last data packet comprises an end indication of the set of data packets.

[0240] Clause 4. The first network device of clause 2, wherein the indication of the last data packet comprises a last sequence number of the last data packet, the last sequence number being higher than sequence numbers of other data packets in the subset.

[0241] Clause 5. The first network device of clause 1, wherein the subset comprises an end data packet in the set of data packets, and the information about the transmission status comprises an indication of the end data packet.

[0242] Clause 6. The first network device of clause 1, wherein the subset further comprises all data packets in the set of data packets, and the information about the transmission status comprises an indication of an end data packet in the set of data packets.

[0243] Clause 7. The first network device of clause 1, wherein the information about the transmission status comprises at least one of: a first indication indicating whether the first network device has successfully sent the set of data packets to the end device, a second indication indicating a transmission status of data packets in the set, or a third indication indicating a transmission status of an end data packet in the set.

[0244] Clause 8. The first network device of clause 7, wherein the third indication comprises one of: a fourth indication indicating whether the first network device has successfully sent the end data packet to the end device, a fifth indication indicating that the end data packet has been received from a third network device but has not been sent by the first network device to the end device, or a sixth indication indicating that the end data packet has not been received from the third network device.

[0245] Clause 9. The first network device of clause 1, wherein the set of data packets comprises a set of protocol data units (PDUs).

[0246] Clause 10. The first network device of clause 9, wherein the processor is further configured to determine a first size of remaining PDUs in the set of PDUs based on a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device to the terminal device; and wherein the transmission status information comprises the first size of remaining PDUs.

[0247] Clause 11. The first network device of clause 9, wherein the information about the transmission status comprises a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device to the terminal device.

[0248] Clause 12. The first network device of clause 9, wherein the processor is further configured to determine that a timer associated with discarding of the set of PDUs expires before a last PDU in the set of PDUs is forwarded to the second network device; and based on the determination, send, via the transceiver, an indication to the second network device indicating that the set of PDUs is to be discarded.

[0249] Clause 13. The first network device of clause 9, wherein the information about the transmission status comprises information about a remaining time of a timer associated with discarding of the set of PDUs.

[0250] Clause 14. The first network device of clause 1, wherein the set of data packets comprises a data burst.

[0251] Clause 15. A second network device comprising: a processor; and a transceiver coupled to the processor, wherein the processor is configured to: receive, via the transceiver, a subset of a set of data packets from a first network device; receive, via the transceiver, information about a transmission status of the set of data packets from the first network device to a terminal device from the first network device; and based on the information about the transmission status, send, via the transceiver, at least one data packet in the subset to the terminal device.

[0252] Clause 16. The second network device of clause 15, wherein the information about the transmission status comprises an indication of a last data packet that has not been successfully transmitted by the first network device to the terminal device.

[0253] Clause 17. The second network device of clause 16, wherein the indication of the last data packet comprises an end indication of the set of data packets.

[0254] Clause 18. The second network device of clause 16, wherein the indication of the last data packet comprises a last sequence number of the last data packet, the last sequence number being higher than sequence numbers of other data packets in the subset.

[0255] Clause 19. The second network device of clause 15, wherein the subset comprises an end data packet in the set of data packets, and the information about the transmission status comprises an indication of the end data packet.

[0256] Clause 20. The second network device of clause 15, wherein the subset comprises all data packets in the set of data packets, and the information about the transmission status comprises an indication of an end data packet in the set of data packets.

[0257] Clause 21. The second network device of clause 19 or 20, wherein the processor is further configured to: receive, from the terminal device, an indication of a reception status of data packets in the set of data packets; and wherein the processor is configured to transmit the at least one data packet in the subset via the transceiver by transmitting the at least one data packet based on the indication of the reception status.

[0258] Clause 22. The second network device of clause 20, wherein the processor is further configured to: receive, from the terminal device, an indication of a reception status of the set of data packets; and wherein the processor is configured to transmit the at least one data packet in the subset via the transceiver by transmitting the at least one data packet based on the indication of the reception status.

[0259] Clause 23. The second network device of clause 15, wherein the information about the transmission status comprises at least one of: a first indication indicating whether the first network device has successfully transmitted a set of data packets to the terminal device, a second indication indicating a transmission status of data packets in the set, or a third indication indicating a transmission status of an end data packet in the set.

[0260] Clause 24. The second network device of clause 23, wherein the third indication comprises one of: a fourth indication indicating whether the first network device has successfully transmitted the end data packet to the terminal device, a fifth indication indicating that the end data packet has been received from a third network device but has not been transmitted to the terminal device by the first network device, or a sixth indication indicating that the end data packet has not been received from the third network device.

[0261] Clause 25. The second network device of clause 15, wherein the set of data packets comprises a set of protocol data units (PDUs).

[0262] Clause 26. The second network device of clause 25, wherein the information about the transmission status comprises a first size of remaining PDUs in the set of PDUs, the first size of remaining PDUs being determined based on a second size of the set of PDUs and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device to the terminal device.

[0263] Clause 27. The second network device of clause 25, wherein the information about the transmission status comprises: a second size of the set of PDUs, and a third size of PDUs in the set of PDUs that have been successfully transmitted by the first network device to the terminal device; and wherein the processor is further configured to: determine a first size of remaining PDUs in the set of PDUs based on the second size and the third size.

[0264] Clause 28. The second network device of clause 25, wherein the processor is further configured to: receive, via the transceiver, an indication from the first network device indicating that the set of PDUs is to be discarded.

[0265] Clause 29. The second network device of clause 28, wherein the processor is further configured to: discard all PDUs in the set of PDUs based on the indication.

[0266] Clause 30. The second network device of clause 25, wherein the information about the transmission status comprises information about a remaining time of a timer associated with a discard of the set of PDUs.

[0267] Clause 31. The second network device of clause 30, wherein the processor is further configured to: discard all PDUs in the set of PDUs based on a determination that the remaining time is exhausted.

[0268] Clause 32. The second network device of clause 15, wherein the set of data packets comprises a data burst.

[0269] Clause 33. A terminal device comprising: a processor; and a transceiver coupled to the processor, wherein the processor is configured to: determine a reception status of a set of data packets; and transmit, via the transceiver, an indication of the reception status of the set of data packets to a second network device.

[0270] Clause 34. The terminal device of clause 33, wherein the processor is further configured to: determine a reception status of a data packet of the set of data packets; and send, via the transceiver, an indication of the reception status of the data packet to the second network device.

[0271] In general, the various embodiments of the disclosure can be implemented in hardware or special-purpose circuits, software, logic or any combination thereof. Some aspects can be implemented in hardware, while other aspects can be implemented in firmware or software which can be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the disclosure are illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it will be understood that the blocks, apparatus, systems, techniques or methods described herein can 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.

[0272] The disclosure also provides at least one computer program product which is 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, executed by devices in a target real or virtual processor to perform processes or methods as described above. 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 can be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules can be executed within the local or distributed device. In a distributed device, program modules can be located in local and remote memory storage devices.

[0273] Program code for carrying out methods of the disclosure can be written in any combination of one or more programming languages. The program code can be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing device to produce a machine, such that the program code, when executed by the processor or controller, causes the machine to perform the functions / acts specified in the flowcharts and / or block diagrams. The program code can execute entirely on a machine, partly on a machine, as a stand-alone software package, partly on a machine, partly on a remote machine or entirely on a remote machine or server.

[0274] The program code mentioned above can be contained on a machine-readable medium, which can be any tangible medium that can contain or store the program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium can include, but is 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 will 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.

[0275] Moreover, while operations have been described 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 can be advantageous. Likewise, while several specific implementation details have been included for the purpose of illustration, this should not be understood as a limitation on the scope of the disclosure. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Accordingly, the disclosure is not to be seen as being limited to the particular combinations of features specified in the description, but can include any combination of the features specified.

[0276] Although the present disclosure has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject of the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as example forms of implementing the claims.

Claims

1. A first network device, comprising: processor; as well as a transceiver coupled to the processor, wherein the processor is configured to: receiving, via the transceiver, at least one data packet from the set of data packets from a third network device; forwarding a subset of the at least one data packet to a second network device via the transceiver; as well as Information about a transmission status of the set of data packets from the first network device to the terminal device is sent to the second network device via the transceiver.

2. The first network device according to claim 1, wherein the information about the transmission status comprises: An indication of a last data packet that has not been successfully sent by the first network device to the terminal device.

3. The first network device of claim 2, wherein the indication of the last data packet comprises: An indication of the end of the set of data packets.

4. The first network device of claim 1 , wherein the subset comprises: The last data packet in the set of data packets, and the information about the transmission status includes: an indication of the last data packet.

5. The first network device of claim 1 , wherein the subset further comprises: All data packets in the set of data packets, and the information about the transmission status includes: an indication of an end data packet in the set of data packets.

6. The first network device according to claim 1, wherein the information about the transmission status comprises at least one of the following: a first indication, indicating whether the data packet set has been successfully sent from the first network device to the terminal device; a second indication of the transmission status of said data packets in said set, or A third indication of a transmission status of a last packet in the set.

7. The first network device according to claim 6, wherein the third indication comprises one of the following: a fourth indication, indicating whether the last data packet has been successfully sent from the first network device to the terminal device; a fifth indication indicating that the last data packet has been received from the third network device but has not yet been sent by the first network device to the terminal device, or A sixth indication indicates that the last data packet has not been received from the third network device.

8. The first network device of claim 1, wherein the set of data packets comprises a set of protocol data units (PDUs).

9. The first network device of claim 8, wherein the processor is further configured to: Determine a first size of remaining PDUs in the PDU set based on the second size of the PDU set and a third size of the PDUs in the PDU set that have been successfully sent by the first network device to the terminal device; and The information about the transmission status includes: The first size of the remaining PDU.

10. The first network device according to claim 8, wherein the information about the transmission status comprises: a second size of the PDU set, and The third size of the PDU in the PDU set that has been successfully sent by the first network device to the terminal device.

11. The first network device of claim 8, wherein the processor is further configured to: Before a last PDU in the PDU set is forwarded to the second network device, determining that a timer associated with discarding the PDU set expires; and Based on the determination, an indication is sent to the second network device via the transceiver indicating that the set of PDUs is to be discarded.

12. The first network device according to claim 8, wherein the information about the transmission status comprises: Information about the remaining time of a timer associated with discarding the set of PDUs.

13. The first network device of claim 1, wherein the set of data packets comprises a burst of data.

14. A terminal device comprising: processor; as well as a transceiver coupled to the processor, wherein the processor is configured to: determining a receive status of a set of data packets; as well as An indication of the reception status of the set of data packets is sent to a second network device via the transceiver.

15. The terminal device according to claim 14, wherein the processor is further configured to: determining a reception status of the data packets in the set of data packets; and An indication of the reception status of the data packet is sent to the second network device via a transceiver.

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