Handover method and related apparatus

Abstract

Provided in the present application are a handover method and a related apparatus, which can enable an access network device to release a cache in a timely manner, thereby improving the resource utilization rate. The method comprises: a first access network device sending a first handover request message to a second access network device, wherein the first handover request message comprises the serial number of the last first data packet among at least one first data packet sent by the first access network device to the terminal; the first access network device sending at least one second data packet to the terminal; the first access network device sending a second serial number to the second access network device, wherein the second serial number is the serial number of the last second data packet among the at least one second data packet sent by the first access network device to the terminal, and the at least one first data packet and the at least one second data packet belong to the same MBS session; and on the basis of the received second serial number, the second access network device deleting a data packet, which is identified by means of a serial number less than or equal to the second serial number, among cached data packets of the MBS session.

Description

Switching method and related device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 28, 2023, with application number 202311295095.X and application name “Switching Method and Related Devices”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of communication technology, and in particular to a switching method and related devices. Background Art

[0003] During the handover process, the deterioration of the wireless environment between the terminal and the access network device may cause the terminal's measurement report to fail to reach the access network device; or after the access network device receives the measurement report, the handover command sent to the terminal cannot reach it, resulting in handover failure, and the terminal needs to re-initiate radio resource control (RRC) reconstruction.

[0004] To reduce the probability of unicast service handover failure, conditional handover (CHO) was proposed. CHO allows the source access network device to preemptively send a handover command to the terminal before the wireless environment between the terminal and the access network device deteriorates. This allows the terminal to know how to access the target access network device in advance. Once the terminal finds a candidate access network device that meets the handover trigger conditions among multiple candidate target access network devices, it can initiate the handover autonomously. This significantly improves the success rate of handovers.

[0005] With the increasing demand for lossless handover of multicast and broadcast services (MBS), CHO can be applied to handovers involving MBS sessions to ensure the success rate of handovers for terminals receiving MBS sessions. When CHO is applied to handovers involving MBS sessions, after the source access network device determines the handover conditions, it will continue to forward MBS data packets to the terminal device for a period of time. Data forwarding between the source access network device and the candidate target access network device may also continue. However, the forwarded MBS data packets may accumulate on the candidate target access network device side, resulting in excessive burden on multiple candidate target access network devices and excessive data buffering resources.

[0006] Summary of the Invention

[0007] The present application provides a switching method and related devices, which can enable access network equipment to release cache in a timely manner and improve resource utilization.

[0008] In a first aspect, the present application provides a handover method that can be applied to a first access network device. For example, the method can be performed by the first access network device, or by a component configured in the first access network device (such as a chip, a chip system, etc.), or by a logic module or software capable of implementing all or part of the functions of the first access network device, which is not limited by the present application.

[0009] Exemplarily, the method includes: sending a first switching request message to a second access network device, the first switching request message being used to request switching the terminal from the first access network device to the second access network device, the first switching request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one first data packet sent by the first access network device to the terminal; sending at least one second data packet to the terminal; and sending a second sequence number to the second access network device, the second sequence number being the sequence number of the last second data packet in the at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number.

[0010] In this application, the data packet of the MBS session sent by the first access network device to the first terminal before the first access network device sends the first switching request message to the second access network device is referred to as the first data packet; the data packet of the MBS session sent by the first access network device after sending the first switching request before the first terminal accesses the second target access network device is referred to as the second data packet, and at least one first data packet and at least one second data packet belong to the same MBS session.

[0011] The second sequence number is used by the second access network device to delete cached data packets of the MBS session.

[0012] The first switching request message is a switching request message that the first access network device sends to multiple target access network devices for the first time after determining the conditional switching.

[0013] In the present application, after sending the first sequence number to the second access network device, the first access network device can continue to send the second sequence number to the second access network device. Since the first sequence number and the second sequence number are respectively the data packets of the last MBS session sent by the first access network device to the terminal at different time periods, and the second sequence number is greater than the first sequence number, the second access network device can delete the data packets corresponding to the sequence numbers smaller than the second sequence number in the cache of the local end after receiving the second sequence number. Compared with the method in which the second access network device deletes the data packets cached on the local end based only on the first sequence number, the first access network device can release the cache in time, effectively improve resource utilization, and at the same time avoid the second access network device sending duplicate MBS session data packets to the terminal after the terminal accesses the second access network device.

[0014] In combination with the first aspect, in some implementations of the first aspect, before sending the first switching request to the second access network device, the method further includes: determining to perform conditional switching.

[0015] In combination with the first aspect, in certain implementations of the first aspect, after sending a first switching request message to the second access network device, the method also includes: receiving a switching response message from the second access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first (packet data convergence protocol, PDCP) service data unit (service data unit, SDU) not submitted to the upper layer in the receiving window; and sending the first initial value of the first variable to the terminal.

[0016] The initial value of the first variable is the latest value of RX_DELIV on the second access network device side when the second access network device sends the handover response message. When the second access network device transparently transmits the first initial value of the first variable to the first terminal through the first access network device, the first terminal can use the first initial value as the initial value of RX_DELIV on the first terminal side when accessing the second access network device.

[0017] In combination with the first aspect, in some implementations of the first aspect, the method further includes: receiving a second initial value from the second access network device, the second initial value being greater than the first initial value; and sending the second initial value to the terminal.

[0018] The second initial value is the latest value of the first variable on the second access network device side when the second access network device decides to send the second initial value of the first variable.

[0019] This method can promptly update the second initial value to the terminal when the first initial value of the first variable expires. In this way, after the terminal accesses the second access network device, it can accurately receive the data packets of the MBS session based on the second initial value of the first variable, avoiding the terminal receiving disordered data packets.

[0020] In combination with the first aspect, in some implementations of the first aspect, the method further includes: determining whether the number of the at least one second data packet is greater than a preset value; if the number of the at least one second data packet is greater than the preset value, sending first information to the second access network device, the first information being used to request a second initial value of the first variable, the second initial value being greater than the first initial value; receiving the second initial value from the second access network device; and sending the second initial value to the terminal.

[0021] The second initial value is the latest value of the first variable on the second access network device side when the second access network device receives the first information.

[0022] Exemplarily, the preset value is the size of the receiving window; or, the preset value and the size of the receiving window satisfy a preset relationship.

[0023] Exemplarily, the preset relationship is: preset value = k × size of receiving window. Wherein, k is greater than 0 and less than or equal to 1, N is the size of receiving window, and N satisfies: N = 2 p-1 , P is the number of bits used to identify the first sequence number. For example, if the first sequence number is represented by 12 bits, then P=12.

[0024] In a second aspect, the present application provides a handover method that can be applied to a second access network device. For example, the method can be performed by the first access network device, or by a component configured in the second access network device (such as a chip, chip system, etc.), or by a logic module or software capable of implementing all or part of the functions of the second access network device, which is not limited by the present application.

[0025] Exemplarily, the method includes: receiving a first switching request message from a first access network device, the first switching request message being used to request switching the terminal from the first access network device to the second access network device, the first switching request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one data packet sent by the first access network device to the terminal; receiving a second sequence number from the first access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number; and deleting all data packets identified by sequence numbers less than or equal to the second sequence number in the cached data packets of the MBS session.

[0026] The at least one first data packet and the at least one second data packet belong to the same MBS session. The description of the first data packet and the second data packet can refer to the description of the first aspect and will not be repeated here.

[0027] In the present application, after the second access network device receives the first sequence number from the first access network device, it can continue to receive the second sequence number. Since the first sequence number and the second sequence number are respectively the data packets of the last MBS session sent by the first access network device to the terminal at different time periods, and the second sequence number is greater than the first sequence number, the second access network device can delete the data packets corresponding to the sequence numbers cached on the local end that are less than the second sequence number after receiving the second sequence number. Compared with the method in which the second access network device deletes the data packets cached on the local end based only on the first sequence number, the resources occupied by the data packets of the MBS session cached on the first access network device side can be effectively reduced, and at the same time, it can also avoid the second access network device sending duplicate data packets of the MBS session to the terminal after the terminal accesses the second access network device.

[0028] In combination with the second aspect, in some implementations of the second aspect, the first switching request is sent by the first access network device after determining to perform conditional switching.

[0029] In combination with the second aspect, in certain implementations of the second aspect, after receiving a first switching request message from a first access network device, the method further includes: sending a switching response message to the first access network device, the switching response message including a first initial value of a first variable, and the first variable indicating an identification value of the first PDCP SDU that is not submitted to the upper layer in the receiving window.

[0030] For the description of the first initial value, please refer to the first aspect and will not be repeated here.

[0031] In combination with the second aspect, in some implementations of the second aspect, the method also includes: receiving first information from the first access network device, the first information being used to request a second initial value of the first variable, the second initial value being greater than the first initial value; and sending the second initial value to the first access network device.

[0032] The second initial value is the latest value of the first variable on the second access network device side when the second access network device receives the first information.

[0033] In combination with the second aspect, in some implementations of the second aspect, the method further includes: after the terminal accesses the second access network device, sending a second initial value to the terminal, and the second initial value is greater than the first initial value.

[0034] Optionally, the second initial value may be carried in an RRC reconfiguration message.

[0035] It can be understood that after the second access network device sends a switching success message to the first access network device, it is considered that the terminal is switched from the first access network device to the second access network device, that is, the terminal accesses the network to the second access network; otherwise, it is considered that the terminal has not accessed the second access network device.

[0036] In combination with the second aspect, in some implementations of the second aspect, the method further includes: before the terminal accesses the second access network device, sending a second initial value to the first access network device, and the second initial value is greater than the first initial value.

[0037] The second initial value is a reference value of the first variable on the second access network device side when the second access network device decides to send the second initial value of the first variable. The difference between the reference value and the latest value of the first variable on the second access network device side is less than or equal to 2 p-1 , and the reference value is less than or equal to the latest value. Wherein, P is the number of bits used to identify the first sequence number. For example, if the first sequence number is represented by 12 bits, then P=12.

[0038] In combination with the second aspect, in some implementations of the second aspect, the method further includes: determining that the number of data packets of the MBS session sent by the second access network device is greater than a preset value.

[0039] For the description of the preset value, please refer to the first aspect and will not be repeated here.

[0040] In combination with the second aspect, in certain implementations of the second aspect, the second serial number is carried in a second switching request message, the second switching request message is used to request that the terminal be switched from the first access network device to the second access network device, and the second switching request message indicates that the second access network device does not update the RRC configuration.

[0041] Alternatively, the second handover request message instructs the second access network device to only update the progress of the MBS radio bearer (MRB).

[0042] In combination with the second aspect, in certain implementations of the second aspect, the second sequence number is carried through early status transfer signaling or MBS early status transfer signaling.

[0043] In a third aspect, the present application provides a handover method that can be applied to a second access network device. For example, the method can be performed by the second access network device, or by a component configured in the second access network device (such as a chip, chip system, etc.), or by a logic module or software that can implement all or part of the functions of the second access network device, which is not limited by the present application.

[0044] Exemplarily, the method includes: receiving a third switching request message from a first access network device, the third switching request message being used to request switching the first terminal to a second access network device; sending a switching response message to the first access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first PDCP SDU that is not submitted to the upper layer in a receiving window; and sending a second initial value of the first variable to the first terminal.

[0045] The switching response message is a request confirmation of the first switching request message by the second access network device.

[0046] Exemplarily, the second access network device may directly send the second initial value of the first variable to the first terminal after the first terminal accesses the second access network device; or, the second access network device may send the second initial value of the first variable to the first terminal through the first access network device before the first terminal accesses the second access network device.

[0047] In the present application, the second access network device may send the second initial value of the first variable to the first terminal again after sending the initial value of the first variable to the first terminal, so that the first terminal can update the initial value of the first variable, so that after accessing the second access network device, the first terminal can use the updated second initial value to receive data packets of the MBS session from the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets.

[0048] Fourthly, the present application provides a handover method that can be applied to a first access network device. For example, the method can be performed by the first access network device, or by a component configured in the first access network device (such as a chip, chip system, etc.), or by a logic module or software that can implement all or part of the functions of the first access network device, which is not limited by the present application.

[0049] Exemplarily, the method includes: sending a third switching request message to a second access network device, the third switching request message being used to request that the first terminal be switched to the second access network device; receiving a switching response message from the second access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first PDCP SDU not submitted to the upper layer in a receiving window, receiving a second initial value from the second access network device, the second initial value being greater than the first initial value; and sending the second initial value to the terminal.

[0050] In the present application, after sending the initial value of the first variable to the first terminal, the second access network device may again send the second initial value of the first variable to the first terminal, so that the first terminal can update the initial value of the first variable. This allows the first terminal to use the updated second initial value after accessing the second access network device to receive data packets of the MBS session from the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets. In a fifth aspect, the present application provides a communication device, including modules or units for implementing the method of any aspect and any possible implementation of any aspect. It should be understood that each module or unit can implement the corresponding function by executing a computer program.

[0051] In a fifth aspect, the present application provides a communication device, comprising a processor, wherein the processor is configured to execute the method described in any aspect and any possible implementation of any aspect.

[0052] The apparatus may further include a memory for storing instructions and data. The memory is coupled to the processor, and when the processor executes the instructions stored in the memory, the method described in the above aspects may be implemented.

[0053] The apparatus may further include a communication interface, where the communication interface is used for the apparatus to communicate with other devices. Exemplarily, the communication interface may be a transceiver, a circuit, a bus, a module, or other types of communication interfaces.

[0054] In a sixth aspect, the present application provides a chip system comprising at least one processor for supporting the implementation of the functions involved in any of the above aspects and any possible implementation of any of the aspects, for example, receiving or processing the data and / or information involved in the above method.

[0055] In one possible design, the chip system further includes a memory, which is used to store program instructions and data, and the memory is located inside or outside the processor.

[0056] The chip system can be composed of chips, or can include chips and other discrete devices.

[0057] In a seventh aspect, the present application provides a computer-readable storage medium comprising a computer program, which, when executed on a computer, enables the computer to implement the method in the first aspect and any possible implementation manner of the first aspect.

[0058] In an eighth aspect, the present application provides a computer program product, comprising: a computer program (also referred to as code, or instructions), which, when executed, enables a computer to execute the method in the first aspect and any aspect and any possible implementation of any aspect.

[0059] In a ninth aspect, the present application provides a communication system, comprising the aforementioned first access network device and second access network device.

[0060] It should be understood that the fifth to ninth aspects of the present application correspond to the technical solutions of the first to fourth aspects of the present application, and the beneficial effects achieved by each aspect and the corresponding feasible implementation methods are similar and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] FIG1 is a schematic diagram of the architecture of a communication system applicable to an embodiment of the present application;

[0062] FIG2 is a schematic diagram of the MBS transmission process;

[0063] FIG3 is a schematic diagram of a multicast service transmission architecture;

[0064] FIG4 is a schematic diagram of a lossless switching process based on an Xn interface provided in an embodiment of the present application;

[0065] FIG5 is a schematic diagram of a lossless switching process based on the N2 interface provided in an embodiment of the present application;

[0066] FIG6 is a schematic flow chart of a conditional switching method provided in an embodiment of the present application;

[0067] 7 to 11 are schematic flow charts of a switching method according to an embodiment of the present application;

[0068] 12 and 13 are schematic block diagrams of devices provided in embodiments of the present application;

[0069] FIG14 is a schematic structural diagram of a wireless access network device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0070] The technical solution in this application will be described below with reference to the accompanying drawings.

[0071] To facilitate understanding of the embodiments of the present application, the following points are first explained:

[0072] First, in the embodiments of this application, prefixes such as "first" and "second" are used solely to distinguish between different items belonging to the same category and do not restrict the order, size, or quantity of the items. For example, "first access network device" and "second access network device" are simply different devices, and do not restrict the number of devices or their priority.

[0073] Second, the "sending" and "receiving" in the embodiments of the present application indicate the direction of signal transmission. For example, "sending at least one second data packet to the terminal" can be understood as the destination end of the second data packet is the terminal, which can include direct sending through the air interface, and also include indirect sending through the air interface by other units or modules. "Receiving the second initial value from the second access network device" can be understood as the source end of the second initial value is the second access network device, which can include receiving it directly from the second access network device through the air interface, and also include receiving it indirectly from the second access network device through the air interface from other units or modules. "Sending" can also be understood as the "output" of the chip interface, and "receiving" can also be understood as the "input" of the chip interface.

[0074] In other words, sending and receiving can be performed between devices, for example, between the first access network device and the terminal; it can also be performed within the device, for example, sending or receiving between components, modules, chips, software modules or hardware modules within the device through a bus, wiring or interface.

[0075] It is understood that before information is sent from the source to the destination, it may undergo necessary processing, such as encoding and modulation. After receiving the information from the source, the destination may also perform corresponding processing, such as decoding and demodulation, to interpret the valid information from the source. Similar expressions in this application can be understood similarly and will not be repeated here.

[0076] Third, in the embodiments of the present application, "at least one" refers to one or more, and "more" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship, but does not exclude the situation where the previous and next associated objects are in an "and" relationship. The specific meaning can be understood in conjunction with the context. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c can represent: a, b, c; a and b; a and c; b and c; or a and b and c. Where a, b, c can be single or multiple.

[0077] Fourth, in the embodiments of the present application, "indication" may include direct indication and indirect indication, and may also include explicit indication and implicit indication. The information indicated by a certain information (such as the indication information described below) is called information to be indicated. In the specific implementation process, there are many ways to indicate the information to be indicated, such as but not limited to, directly indicating the information to be indicated, such as the information to be indicated itself or the index of the information to be indicated. The information to be indicated may also be indirectly indicated by indicating other information, wherein the other information has an association relationship with the information to be indicated; or only a part of the information to be indicated may be indicated, while the other parts of the information to be indicated are known or agreed in advance. For example, the indication of specific information may be achieved by means of the arrangement order of each information agreed in advance (such as predefined by the protocol), thereby reducing the indication overhead to a certain extent. The present application does not limit the specific method of indication.

[0078] It can be understood that, for the sender of the indication information, the indication information can be used to indicate the information to be indicated, and for the receiver of the indication information, the indication information can be used to determine the information to be indicated.

[0079] Fifth, the tables in the embodiments of the present application are only examples. The values ​​of the information in each table are only examples and can be configured as other values, which are not limited by the present application. The tables do not limit the scope of protection of the present application. For example, appropriate deformation adjustments can be made based on the tables in the above text, such as splitting, merging, etc. For another example, the parameter names shown in the titles of the tables can also use other names that can be understood by the communication device, and the values ​​or representations of the parameters can also use other values ​​or representations that can be understood by the communication device. For another example, when implementing the above tables, other data structures can also be used, such as arrays, queues, containers, stacks, linear lists, pointers, linked lists, trees, graphs, structures, classes, heaps, hash tables or hash tables.

[0080] Sixth, in the embodiments of the present application, descriptions such as "when...", "in the case of...", "if" and "if" all mean that the device (such as an access network device or terminal) will make corresponding processing under certain objective circumstances. It does not limit the time, and does not require the device (such as a network device or terminal) to have a judgment action when implementing it, nor does it mean that there are other limitations.

[0081] Seventh, the predefined in this application can be understood as: define, predefine, store, pre-store, pre-negotiate, pre-configure, solidify, or pre-burn.

[0082] Eighth, the storage involved in this application may refer to storage in one or more memories. The one or more memories may be provided separately or integrated into an encoder or decoder, a processor, or a communication device. The one or more memories may also be provided in part separately and in part integrated into a decoder, a processor, or a communication device. The type of memory may be any form of storage medium, and this application is not limited thereto.

[0083] The technical solutions provided in this application can be applied to various communication systems, such as: long term evolution (LTE) system, LTE frequency division duplex (FDD) system, LTE time division duplex (TDD) system, sidelink (SL) communication system, world-wide interoperability for microwave access (WiMAX) communication system, fifth generation (5G) mobile communication system or new radio access technology (NR), satellite communication system, etc. Among them, the 5G mobile communication system can include non-standalone (NSA) and / or standalone (SA) networking.

[0084] The technical solution provided in this application can also be applied to future communication systems, such as the sixth generation (6G) mobile communication system, etc. This application does not limit this.

[0085] In this application, a radio access network (RAN) device is a device with wireless transceiver capabilities. It can provide wireless communication services and connect terminals to a wireless network. It can be a node in a radio access network, referred to as a RAN node.

[0086] In one possible scenario, a RAN node can be a base station (BS), an evolved NodeB (eNodeB), a transmission reception point (TRP), a home evolved NodeB (HNB), a wireless fidelity (Wi-Fi) access point (AP), a mobile switching center, a next-generation NodeB (gNB) in a 5G mobile communication system, a next-generation NodeB in a 6G mobile communication system, or a base station in a future mobile communication system. A RAN node can also be a device that performs base station functions in device-to-device (D2D) communication systems, vehicle-to-everything (V2X) communication systems, machine-to-machine (M2M) communication systems, and Internet of Things (IoT) communication systems. A RAN node can also be a RAN node in a non-terrestrial network (NTN), meaning that the RAN node can be deployed on a high-altitude platform or satellite. A RAN node can be a macro base station, a micro base station, an indoor base station, a relay node, a donor node, or a radio controller in a cloud radio access network (CRAN) scenario, or a node in an open radio access network (O-RAN or ORAN) scenario. Alternatively, a RAN node can be a server, a wearable device, a vehicle, or an onboard device. For example, a RAN node in V2X technology can be a roadside unit (RSU). Of course, a RAN node can also be a node in the core network.

[0087] In another possible scenario, multiple RAN nodes collaborate to assist the terminal in achieving wireless access, and different RAN nodes respectively implement part of the functions of the base station. For example, the RAN node can be a centralized unit (CU), a distributed unit (DU), a CU-control plane (CP), a CU-user plane (UP), or a radio unit (RU). The CU and DU can be set separately, or they can be included in the same network element, such as a baseband unit (BBU). The RU can be included in a radio frequency device or radio frequency unit, such as a remote radio unit (RRU), an active antenna unit (AAU), or a remote radio head (RRH).

[0088] In different systems, CU (or CU-CP and CU-UP), DU, or RU may have different names, but those skilled in the art will understand their meanings. For example, in the ORAN system, CU may be referred to as Open CU (O-CU), DU may be referred to as Open DU (O-DU), CU-CP may be referred to as Open CU-CP (O-CU-CP), CU-UP may be referred to as Open CU-UP (O-CU-UP), and RU may be referred to as Open RU (O-RU).

[0089] Among them, any unit among CU (or CU-CP, CU-UP), DU and RU can be implemented by a software module, a hardware module, or a combination of a software module and a hardware module. That is, the wireless access network device in this application can be a virtualized device, for example, implemented by general hardware and instantiated virtualization functions, or by dedicated hardware and instantiated virtualization functions. Among them, the general hardware can be a server, such as a cloud server. The name of the wireless access network device in the future evolving communication system does not constitute a limitation, and it can also be called a network device or a core network device.

[0090] The terminal in this application may also be referred to as user equipment (UE), access terminal, user unit, user station, mobile station, mobile station, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent or user device.

[0091] A terminal can be a device that provides voice / data connectivity to a user, such as a handheld device or vehicle-mounted device with wireless connection function. At present, some examples of terminals may include: mobile phones, tablet computers, computers with wireless transceiver functions (such as laptops, PDAs, etc.), mobile internet devices (MIDs), virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving, drones, wireless terminals in remote medical care, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, cellular phones, cordless phones, session initiation protocol (SIP) phones, wireless local loop (WLL) stations, personal digital assistants (PDAs), handheld devices with wireless communication functions, computing devices or other processing devices connected to wireless modems, vehicle-mounted devices, wearable devices, terminals in 5G networks or future evolved public land mobile communication networks (PLMNs). terminals in network, PLMN, etc.

[0092] Wearable devices, also known as wearable smart devices, are a general term for wearable devices that use wearable technology to intelligently design and develop wearable devices for daily wear, such as glasses, gloves, watches, clothing, and shoes. Wearable devices are portable devices that are worn directly on the body or integrated into the user's clothing or accessories. Wearable devices are not just hardware devices, but also achieve powerful functions through software support, data interaction, and cloud interaction. In a broad sense, wearable smart devices include those that are fully functional, large in size, and can achieve full or partial functions without relying on smartphones, such as smart watches or smart glasses, as well as those that only focus on a certain type of application function and need to be used in conjunction with other devices such as smartphones, such as various smart bracelets and smart jewelry for vital sign monitoring.

[0093] Furthermore, terminals can also be terminals in IoT systems. IoT is a crucial component of future information technology development. Its primary technical feature is connecting objects to the internet through communications, enabling intelligent networks that interconnect humans and machines, and objects and things. IoT technology, for example, utilizes narrowband (NB) technology to achieve massive connectivity, deep coverage, and power-saving terminals.

[0094] In addition, the terminal can also include sensors such as smart printers, train detectors, and gas stations. Its main functions include collecting data (partial terminals), receiving control information and downlink data from network devices, and sending electromagnetic waves to transmit uplink data to network devices.

[0095] The terminal in this application may be a virtualized device, for example, implemented by general-purpose hardware and instantiated virtualization functions, or by dedicated hardware and instantiated virtualization functions. The general-purpose hardware may be a server, for example, a cloud server.

[0096] It should be understood that the present application does not limit the specific forms of the wireless access network device and the terminal.

[0097] Figure 1 is a schematic diagram of the architecture of a communication system 100 applicable to the method provided in an embodiment of the present application. As shown in Figure 1 , the communication system 100 includes a radio access network 10 and a core network 20. Optionally, the communication system 100 may also include the Internet 30. The radio access network 10 may include at least one radio access network device (such as 110a and 110b in Figure 1 ) and at least one terminal (such as 120a-120j in Figure 1 ).

[0098] Terminals can connect to radio access network equipment wirelessly, and radio access network equipment can connect to the core network wirelessly or via wired connections. Core network equipment and radio access network equipment can be independent, distinct physical devices, or they can integrate the core network equipment's functions and the radio access network equipment's logical functions into the same physical device. Alternatively, a single physical device can integrate some core network equipment functions and some radio access network equipment functions. Terminals and radio access network equipment can connect to each other via wired or wireless connections.

[0099] Wireless access network devices and terminals, wireless access network devices, and terminals can communicate through authorized spectrum, unauthorized spectrum, or both. They can communicate through spectrum below 6 gigahertz (GHz), spectrum above 6 GHz, or both. The embodiments of this application do not limit the spectrum resources used for wireless communications.

[0100] The wireless access network device may be a base station deployed in the air, such as a satellite base station 110a; or a base station deployed indoors, such as a micro base station or an indoor station 110b.

[0101] The terminal can be a terminal deployed in the air, such as the helicopter or drone 120i in Figure 1; it can also be a terminal deployed on the ground, such as the mobile phones 120a, 120e, 120f and 120j, vehicle 120b, computer 120g, printer 120h, etc. in Figure 1.

[0102] Wireless access network equipment and terminals can be fixed or mobile. For example, they can be deployed on land, indoors or outdoors, handheld or vehicle-mounted; on water; or in the air on aircraft, balloons, and satellites.

[0103] The roles of radio access network devices and terminals can be relative. For example, the helicopter or drone 120i in Figure 1 can be configured as a mobile base station. For devices 120j accessing the radio access network 10 via 120i, 120i is a base station; however, for 110a, 120i is a terminal. That is, communication between 110a and 120i occurs via a wireless air interface protocol. Of course, communication between 110a and 120i can also occur via an interface protocol between radio access network devices. In this case, 120i is also a base station relative to 110a. Therefore, radio access network devices and terminals can be collectively referred to as communication devices. 110a, 110b, and 120a-120j in Figure 1 can be referred to as communication devices having their respective corresponding functions, such as communication devices having base station functions or communication devices having terminal functions.

[0104] It should be understood that FIG1 is only a schematic diagram, and the communication system may further include other devices, such as wireless relay devices and wireless backhaul devices, which are not shown in FIG1 .

[0105] MBS is a service for multiple terminals, such as live broadcast services, public safety services, and batch software update services. In this application, the terms MBS, multicast, MBS service, MBS session, multicast service, and multicast session are interchangeable. The following describes the MBS transmission process and architecture in conjunction with Figures 2 and 3.

[0106] Figure 2 is a schematic diagram of the MBS transmission process. As shown in Figure 2, the server first sends the MBS data packet to the core network, then the core network device sends the MBS data packet to the access network, and finally the access network sends the MBS data packet to at least one terminal.

[0107] As shown in Figure 2, the server sends the MBS service to the core network. When the core network sends MBS data packets to the access network device, they can be transmitted through a common transmission channel MBS session. Each MBS session can contain at least one MBS quality of service (QoS) flow. When the access network device sends MBS data packets to the terminal, the data packets are transmitted through the MBS radio bearer (MRB). An MRB has two transmission modes: 1. Point to multi-point (PTM) transmission; 2. Point to point (PTP) transmission.

[0108] Multicast services are designed for services with high QoS requirements and offer the same QoS level as unicast services. For multicast services, the core network manages the entry and exit of terminals into and out of the multicast service, and access network equipment and core network devices maintain information about terminals in the multicast service group. Transmission between the core and access networks relies on protocol data unit (PDU) sessions, introducing MBS QoS flows. The RAN supports both PTP and PTM transmission methods for sending data to terminals, and supports dynamic switching between PTP and PTM, controlled by the RAN.

[0109] Figure 3 illustrates a multicast service transmission architecture. As shown in Figure 3, between the core network and the access network, multicast services are transmitted via MBS sessions. MBS sessions include MBS QoS flows (also known as multicast QoS flows). MBS sessions can be associated with a terminal's PDU session, and MBS QoS flows can be associated with unicast QoS flows within the PDU session. Core network devices can control the MBS session's status to active or deactivated, while the terminal is unaware of the MBS session's status.

[0110] When access network devices send multicast services to terminals, they can use either PTM or PTP transmission modes. In PTM mode, multicast service data is scrambled using the group radio network temporary identifier (G-RNTI); in PTP mode, multicast service data is scrambled using the cell radio network temporary identifier (C-RNTI). Furthermore, access network devices can dynamically switch the transmission mode between PTM and PTP.

[0111] In the lossless switching scenario of MBS, the source access network device and the target access network device need to exchange service progress in the switching signaling, which is used by the source access network device to determine the data packets to be forwarded to the target access network device, and by the target access network device to determine the data packets to be forwarded to the terminal.

[0112] Taking Xn handover as an example, FIG4 is used to describe information that needs to be exchanged between the source access network device and the target access network device during the Xn lossless handover process.

[0113] FIG4 is a schematic diagram of a lossless switching process based on an Xn interface provided by an embodiment of the present application. As shown in FIG4 , the method 400 may include S401 and S402. Each step in the method 400 is described in detail below.

[0114] S401: The source access network device sends a handover request message to the target access network device. The handover request message carries one or more of the following information:

[0115] Group 1: MBS session identity (ID), area session ID, and MBS session associated information. The multicast session associated information includes the MBS QFI and mapped unicast QFI.

[0116] Group 2: MBS session ID, area session ID, MBS service area, QoS flow parameters; or

[0117] Group 3: MRB ID, MRB mapping information, and MRB progress information. The MRB progress information includes the PDCP SN. The MRB progress information is used by the target access network device to determine the packet number of the largest data packet that the source access network device has sent to the terminal.

[0118] Correspondingly, the target access network device receives the handover request message. Exemplarily, the target access network device may determine whether to send the forwarding address and / or the local MRB progress information to the source access network device based on the MRB progress information.

[0119] S402: The target access network device sends a handover response message to the source access network device. The handover response message carries at least one of the following information: MBS session ID, MRB ID, downlink (DL) data forwarding address, and MRB progress information.

[0120] The MRB progress information includes the PDCP SN; the downlink data forwarding address is used by the source access network device to forward data packets; and the MRB progress information is the packet number of the oldest data packet currently cached on the target access network device side.

[0121] Correspondingly, the source access network device receives the handover response message. Exemplarily, the source base station may determine whether to forward data to the target access network device and which data to forward based on the received MRB progress information.

[0122] It can be understood that the above-mentioned handover response message can also be called a handover request confirmation message.

[0123] Taking N2 handover as an example, FIG5 illustrates the process of N2 lossless handover. In this process, the source access network device needs to provide information to the target access network device.

[0124] FIG5 is a schematic diagram of a lossless handover process based on the N2 interface provided by an embodiment of the present application. As shown in FIG5 , the method 500 may include S501 to S504. Each step shown in the method 500 is described in detail below.

[0125] S501: A source access network device sends a handover request message to a core network device. Correspondingly, the core network device receives the handover request message.

[0126] S502: The core network device sends a handover request message to the target access network device. Correspondingly, the target access network device receives the handover request message.

[0127] The source access network device may carry at least one group of information in the handover request message and send it to the target access network device through the core network device: Group 1, MBS session ID, area session ID, MBS service area, QoS flow parameters; Group 2, MRB ID, MRB mapping information, MRB progress information.

[0128] For the next generation application protocol (NGAP) interface, the core network device may also carry at least one group of information in the handover request message and send it to the target access network device: Group 1: MBS session ID, area session ID; Group 2: MBS session associated information.

[0129] S503: The target access network device sends a handover response message to the core network device. Correspondingly, the core network device receives the handover request message.

[0130] S504: The core network device sends the handover response message to the source access network device. Correspondingly, the source access network device receives the handover response message.

[0131] The target access network device may carry at least one of the following information in the handover response message and send it to the source access network device through the core network device: MBS session ID, MRB ID, DL data forwarding address, and MRB progress information.

[0132] During a New Radio (NR) handover, the radio environment between the terminal and the access network device may deteriorate, causing the measurement report reported by the terminal to fail to reach the access network device, or the handover command issued by the access network device after receiving the measurement report to fail to reach the terminal. This can lead to handover failure. In this case, the terminal will recognize the radio link failure and initiate RRC reestablishment.

[0133] To reduce the probability of handover failure and improve handover reliability, CHO has been proposed. CHO allows the access network device to pre-send a handover command (containing the wireless parameter configuration of candidate target base stations and handover trigger conditions) to the terminal before the wireless environment between the terminal and the access network device deteriorates further. This allows the terminal to know how to access the target access network device in advance. Once the terminal finds a target access network device that meets the handover trigger conditions among the candidate target access network devices, it can independently decide to initiate the handover.

[0134] Figure 6 is a schematic flow chart of a conditional switching method provided by an embodiment of the present application. As shown in Figure 6, the method 600 may include steps S601 to S611. The steps shown in step 600 are described in detail below.

[0135] S601: The source access network device transmits data with the terminal. The data is unicast service data.

[0136] S602: The source access network device determines a conditional handover.

[0137] S603: The source access network device sends a handover request to multiple target access network devices. The handover request is used to request handover of the terminal from the source access network device to the target access network device.

[0138] The switching request carries the sequence number of the last data packet sent by the source access network device to the terminal before sending the switching request message; in other words, the switching request carries the maximum sequence number among the sequence numbers corresponding to the data packets of the unicast service sent by the source access network device to the terminal.

[0139] S604: Multiple target access network devices send a handover response message to the source access network device. The response message is used to confirm the handover request.

[0140] S605: The source access network device sends an RRC reconfiguration message to the terminal.

[0141] The RRC reconfiguration message carries the radio parameter configurations and handover execution triggering conditions of multiple candidate target access network devices.

[0142] S606: The terminal sends an RRC reconfiguration completion message to the source access network device.

[0143] After the terminal sends an RRC reconfiguration completion message to the source access network device, the terminal begins to evaluate the switching conditions and still maintains the connection with the source access network device. The source access network device can continue to send unicast service data packets to the terminal.

[0144] S607: The source access network device sends an early status transfer message, or an early status indication message, to multiple target access network devices.

[0145] The early status transfer message may be triggered after the source access network device continues to send data packets of a unicast service to the terminal, and is used to update the target access network device on the progress of data packets sent by the source access network device to the terminal.

[0146] Exemplarily, the early status transfer message may carry the sequence number of the last data packet among the data packets that the source access network device continues to send to the terminal.

[0147] S608: The conditional switching is completed, and the terminal switches from the source access network device to the first target access network device.

[0148] When there are multiple target access network devices, the terminal determines one target access network device (for example, the first target access network device) from the multiple target access network devices to access.

[0149] S609: The first target access network device sends a handover completion message to the source access network device. The handover completion message is used to notify the source access network device of successful access to the first target access network device.

[0150] S610: The source access network device sends an SN status sending message to the first target access network device.

[0151] S611: The source access network device sends a handover cancellation message to other target access network devices.

[0152] To ensure the success rate of MBS handovers, CHO has been proposed for handovers involving MBS sessions. However, there is currently no solution to enhance or adapt CHO for MRB handovers. Based on the current RRC signaling format, the CHO configuration directly references the RRC reconfiguration message (i.e., the CHO configuration includes the RRC reconfiguration message), and there is no restriction against including the MRB configuration in the CHO configuration. This means that the target access network device can include the MRB configuration in the CHO configuration to support multicast CHO.

[0153] The multicast CHO handover process can refer to the description of the CHO handover process shown in Figure 6 above. The differences between the two are: 1. In the multicast CHO handover process, the handover request message sent by the source access network device to multiple candidate target access network devices includes MBS information (i.e., the handover request message sent in S603 also carries MBS-related information); 2. The multiple candidate target access network devices will include MBS information in the handover response messages they send (i.e., the handover response message sent in S604 also carries MBS information). 3. While the terminal is evaluating the handover conditions, the source access network device can continue to send MBS data packets to the terminal. Moreover, based on the MBS information carried in the handover request message, the source access network device will send MBS data packets to multiple target access network devices, so that after the terminal accesses the target access network device, the target access network device can directly send data packets to the terminal.

[0154] For the description of MBS information, reference may be made to the information carried in the handover request message and the handover response message in FIG. 5 , which will not be repeated here.

[0155] However, when applying CHO to handovers involving MBS sessions, the following problems are found:

[0156] 1. Based on the above description of lossless switching of MBS, it can be concluded that in order to ensure that no data packet loss occurs when the terminal switches from the source access network device to the candidate target access network device, during the lossless switching process of MBS, the source access network device needs to send the progress information of the current MRB to the candidate target access network device, and the candidate target access network device will also send the progress information of its own MRB to the source access network device, so that the source access network device can send data packets to the candidate target access network device based on the progress information of the MRB from the candidate target access network device side, and the candidate target access network device can continue to send data packets to the terminal based on the progress information and data packets from the source access network device.

[0157] However, when CHO is applied to a handover involving an MBS session, the terminal may continue to receive data packets for the multicast service from the source access network device for a period of time while evaluating the CHO condition, and data forwarding between the source access network device and the candidate target access network device may also continue. Since the MRB progress information is carried to the candidate target access network device in the first handover request sent by the source access network device, the candidate target access network device will cache the MBS session data packets based on the MRB progress information carried in the handover request message. However, since the terminal continues to receive data packets from the source access network device while evaluating the CHO condition, the progress of the MRB changes. If the candidate target access network device still caches the MBS session data packets based on the previously received MRB progress information, it will cache more MBS data packets, requiring more resources.

[0158] In view of this, the present application provides a handover method and related apparatus. In this method, a source access network device can promptly send MRB progress information to a target access network device, so that the target access network device can delete data packets cached locally based on the MRB progress information, thereby reducing the resources required by the target access network device to cache data packets.

[0159] 2. In the lossless switching of MBS, after the source access network device sends a switching request message to the candidate target access network device, it will receive a switching response message sent by the second access network device. The switching response message may include MRB configuration information, and the MRB configuration information indicates the initial value of RX_DELIV. When the candidate target access network device transmits the initial value of RX_DELIV to the terminal through the source access network device, the terminal can use the initial value as the initial value of RX_DELIV on the terminal side after accessing the candidate target access network device. Among them, the initial value of RX_DELIV is the reference value of RX_DELIV on the candidate target access network device side when the candidate target access network device sends a switching response message. The difference between the reference value and the latest value of RX_DELIV on the candidate target access network device side is less than or equal to 2 p-1 , and the reference value is less than or equal to the latest value. Wherein, P is the number of bits used to identify the PDCP SN. For example, if the PDCP SN is represented by 12 bits, then P=12.

[0160] For example, the identification value of a PDCP SDU can be called a COUNT. The COUNT consists of the HFN and the PDCP SN. The PDCP SN is added to the PDU for transmission, while the HFN is maintained by the transmitter and receiver. The PDCP PDU sent by the transmitter to the receiver contains the SN number but does not contain the COUNT or HFN. The receiver calculates the HFN based on the received SN number and restores the COUNT value. That is, the receiver combines the calculated HFN and the SN number carried in the PDCP PDU to form the COUNT corresponding to the PDCP PDU. PDCP uses a receive window plus a reordering timer to receive PDCP PDUs delivered by lower layers. The receive window moves based on updates to the receive window lower boundary state variable (i.e., RX_DELIV). Since the state variable is described by the COUNT value, after receiving the PDCP PDU, the PDCP needs to determine the correct HFN and COUNT based on the SN in the PDCP PDU subheader and the current receive window state variable, and then perform decryption and integrity verification based on the obtained COUNT.

[0161] When CHO is applied to a handover involving an MBS session, after the terminal receives the initial value of RX_DELIV from the candidate target access network device, it will remain on the source access network device for a period of time. At this time, the target access network device may continue to send MBS data packets to the terminal connected to it, causing the value of RX_DELIV on the candidate target access network device to change to the second value. If the difference between the second value and the initial value carried in the handover response message is greater than or equal to 2 p-1 , then the RX_DELIV carried by the handover response message is considered expired. In other words, if the terminal still determines the HFN according to the initial value received before, it will get an incorrect HFN, causing confusion in the received data packets.

[0162] In view of this, the present application provides a switching method and related apparatus. In this method, the source access network device can promptly send an updated value of RX_DELIV to the target access network device, so that the terminal can use the updated value of RX_DELIV to receive data packets after accessing the target access network device.

[0163] 3. When CHO is applied to a handover involving an MBS session, the access network device may release or retain the MRB after the MBS service is deactivated. If the candidate target access network device deletes the MRB configuration in the RRC configuration after the MBS service is deactivated, then when the MBS service is reactivated, the access network device may not carry the MRB configuration in the RRC reconfiguration message, resulting in the terminal being unable to receive data packets of the MRB session after accessing the target access network device. MBS service deactivation means that the data of the MBS session is not transmitted, but the MBS session is retained. In order to enable the terminal of the target access network device to continue to receive data packets of the MBS session after the MBS service is activated, the present application proposes a method implementation as shown in FIG11 below.

[0164] In view of this, the present application provides a switching method and related apparatus. In this method, after the MBS service is activated, the access network device can send an MRB configuration to the terminal, so that the terminal can continue to receive data packets of the MBS session after accessing the target access network device.

[0165] The method provided in the embodiment of the present application is described in detail below in conjunction with Figures 7 to 11. The method can be applied to the communication system shown in Figure 1, but the embodiment of the present application is not limited thereto.

[0166] The flowcharts shown in Figures 7 to 11 illustrate the method from the perspective of communication device interaction, but this application does not limit the execution entity of the method. For example, the access network device in Figures 7 to 11 can be a chip, chip system, or processor that supports the access network device to implement the method, or a logic module or software that can implement all or part of the access network device functions; the terminal in Figures 7 to 11 can be a chip, chip system, or processor that supports the terminal to implement the method, or a logic module or software that can implement all or part of the terminal functions.

[0167] FIG7 is a schematic flow chart of a handover method according to an embodiment of the present application. As shown in FIG7 , the method 700 may include steps S701 to S704. Each step in the method 700 is described in detail below.

[0168] S701: A first access network device sends a first handover request message to a second access network device, wherein the first handover request message includes a first sequence number. Correspondingly, the second access network device receives the first handover request message from the first access network device.

[0169] The first sequence number is the sequence number of the last first data packet among the at least one first data packet sent by the first access network device to the first terminal. Alternatively, the first sequence number is the maximum sequence number among the sequence numbers corresponding to the at least one first data packet sent by the first access network device to the first terminal. Alternatively, the first sequence number is the sequence number of the last first data packet sent by the first access network device to the first terminal before sending the first handover request message.

[0170] The first sequence number may be a PDCP SN number, COUNT, or hyper frame number (HFN), or other parameters that can be used to identify the transmission order of data packets, which is not limited in this application.

[0171] It is understood that the first terminal in this application is a terminal connected to the first access network device. When multiple first terminals connected to the first access network device all have CHO, the first sequence number sent by the first access network device can be the first sequence number corresponding to each of the multiple first terminals connected to the first access network device.

[0172] It can also be understood that the first handover request message is the first handover request message sent by the first access network device to multiple target access network devices after the first access network device determines the conditional handover. The first handover request message is used to request handover of the first terminal from the first access network device to the second access network device.

[0173] The first access network device may also be referred to as a source access network device, and the second access network device may also be referred to as a target access network device.

[0174] It can be understood that the first access network device can send a first switching request message to multiple candidate target access network devices, and the second access network device in this application can be an access network device accessed by the first terminal among the multiple candidate target access network devices.

[0175] Optionally, before S701 , the method 700 further includes: the first access network device determining to perform conditional switching.

[0176] S702: The first access network device sends at least one second data packet to the first terminal. Correspondingly, the first terminal receives at least one second data packet from the first access network device.

[0177] The at least one first data packet and the at least one second data packet belong to the same MBS session (eg, the first MBS session).

[0178] It can be understood that in this application, the data packet of the first MBS session sent by the first access network device to the first terminal before the first access network device sends the first switching request message to the second access network device is referred to as the first data packet; the data packet of the first MBS session sent by the first access network device after sending the first switching request message to the second access network device and before the first terminal accesses the second access network device is referred to as the second data packet.

[0179] S703: The first access network device sends a second sequence number to the second access network device. Correspondingly, the second access network device receives the second sequence number from the first access network device.

[0180] The second sequence number is the sequence number of the last second data packet among the at least one second data packet sent by the first access network device to the first terminal, and the second sequence number is greater than the first sequence number. Alternatively, the second sequence number is the maximum sequence number among the sequence numbers corresponding to the at least one second data packet sent by the first access network device to the first terminal. Alternatively, the second sequence number is the sequence number of the last second data packet sent by the first access network device to the first terminal before the second sequence number is sent.

[0181] Similar to the first sequence number, the second sequence number may be a PDCP SN number, COUNT or HFN, or other parameters that may be used to identify the transmission order of data packets, which is not limited in this application.

[0182] It can be understood that when CHO exists in multiple first terminals connected to the first access network device, the second sequence number sent by the above-mentioned first access network device can be the second sequence number corresponding to the terminal with the slowest progress among the multiple first terminals connected to the first access network device.

[0183] It can also be understood that, after receiving the first handover request message, the second access network device may send a handover response message in response to the first handover request to the first access network device. The handover response message may carry the second sequence number.

[0184] Illustratively, after S701, the first access network device may send the second sequence number to the second access network device when any of the following conditions is met: 1. every interval of a first duration; 2. every time a first number of second data packets are sent. The first duration and the first number may be predefined or instructed by the second access network device to the first access network device.

[0185] For example, if the first access network device sends the second sequence number to the second access network device at intervals of a first duration after sending the first handover request message, and if the first access network device does not send at least one second data packet to the first terminal within the first duration, then step S702 may not be executed. That is, after step S701, step S703 is executed, and at this point, the first sequence number is equal to the second sequence number.

[0186] S704: The second access network device deletes the cached data packet of the MBS session based on the second sequence number. In other words, the second access network device deletes the cached data packet of the MBS session based on the second sequence number.

[0187] It can be understood that the data packet of the MBS session deleted by the second access network device and the at least one second data packet (or at least one first data packet) belong to the same MBS session.

[0188] In conjunction with the example in which the at least one first data packet and the at least one second data packet belong to the first MBS session, the above S704 may be replaced by the second access network device deleting the cached data packets of the first MBS session based on the second sequence number.

[0189] Optionally, the second access network device may delete data packets of the first MBS session that are cached and whose sequence numbers are less than or equal to the second sequence number.

[0190] The method 700 provided in the present application is applied to a conditional switching scenario to solve the problem of excessive resources required by a target access network device to cache MBS session packets. In an embodiment of the present application, after sending a first sequence number to a second access network device, the first access network device may continue to send a second sequence number to the second access network device. Since the first sequence number and the second sequence number are respectively the last MBS packets sent by the first access network device to the terminal at different time periods, and the second sequence number is greater than the first sequence number, the second access network device may delete the packets corresponding to sequence numbers less than the second sequence number cached on its own end after receiving the second sequence number. Compared with the method in which the second access network device deletes the packets cached on its own end based only on the first sequence number, the resources occupied by the first access network device for caching MBS session packets can be effectively reduced, thereby improving resource utilization. At the same time, it can also prevent the second access network device from sending duplicate MBS packets to the terminal after the terminal accesses the second access network device.

[0191] Optionally, the second sequence number may be carried by the following messages or signaling: a second handover request message, an early status transfer signaling, or an MBS early status transfer signaling.

[0192] In the first possible implementation, the second sequence number is carried through early status transfer signaling.

[0193] The early status transfer signaling is used to update the data radio bearer (DRB) progress signaling in the flowchart shown in Figure 6. The early status transfer signaling shown in Figure 6 includes a procedure stage information element indicating the DRB transmission progress.

[0194] This application can add an MBS procedure stage information element in parallel with the procedure stage information element in the early status transfer signaling, and include a DL discarding branch in the MBS procedure stage information element. The DL discarding branch includes the MRB COUNT value (HFN and SN) or SN. Based on this solution, the MRB progress information of each terminal can be independently sent to the candidate target access network device, so that the candidate target access network device can delete the MRB session data packet.

[0195] In a second possible implementation, the present application introduces new signaling to carry the second sequence number. The new signaling is related to MBS and can be used to indicate the progress of one MBS session or the progress of multiple MBS sessions.

[0196] For example, the new signaling may be MBS early status transfer signaling, which may include an MBS procedure sage information element, which may include a DL discarding branch, which may include a COUNT value (HFN and SN) or SN for an MRB.

[0197] Based on this method, the source access network device can update the MRB progress according to the MBS session granularity. Since the data forwarding between stations is actually also at the MBS session granularity, the source access network device will not forward multiple copies of data to different terminals receiving a certain MBS session, thereby saving the signaling overhead when updating the MRB progress.

[0198] In a third possible implementation, the second sequence number is carried in a second handover request message, where the second handover request message is used to request handover of the first terminal from the first access network device to the second access network device.

[0199] The second handover request message is a handover request message sent again by the first access network device to the second access network device after sending the first handover request message based on a trigger condition for sending a second sequence number, wherein the trigger condition for sending the second sequence number is a first duration or sending a first number of second data packets.

[0200] Optionally, the second handover request message may further include indication information, where the indication information may instruct the second access network device not to update the RRC configuration, or instruct the second access network device only to update the MRB progress.

[0201] It can be understood that in the CHO switching process, the source access network device will re-trigger the switching request message (referred to as the second switching request message in this application) to the candidate target access network device. After receiving the switching request message, the candidate target access network device will send a switching response message to the source access network device, and carry the RRC reconfiguration message on the target access network device side in the switching response message. Since the purpose of carrying the second sequence number in the second switching request message in the multicast CHO switching process is to update the MRB progress, the second switching request can carry indication information for indicating not to update the RRC configuration or only to update the MRB progress, so as to avoid the second access network device from repeatedly sending the RRC reconfiguration message.

[0202] Optionally, before S704, method 700 further includes: the second access network device sending a third sequence number to the first access network device, where the third sequence number is the oldest sequence number cached by the second access network device. In other words, the third sequence number is the smallest sequence number among the sequence numbers corresponding to the data packets of the MBS session cached by the second access network device. Correspondingly, the first access network device receives the third sequence number from the second access network device.

[0203] The third data packet and the first data packet (or the second data packet) are data packets of the same MBS session.

[0204] Similar to the first sequence number, the third sequence number may be a PDCP SN number, COUNT or HFN, or other parameters that may be used to identify the transmission order of data packets, which is not limited in this application.

[0205] Optionally, before S704, the method 700 further includes: the first access network device sending at least one third data packet to the second access network device based on the first sequence number and the third sequence number. Correspondingly, the second access network device receives the at least one third data packet from the first access network device.

[0206] The at least one third data packet and the at least one first data packet belong to the same MBS session.

[0207] Exemplarily, when the first sequence number is smaller than the third sequence number, the first access network device may send a data packet of the MBS session identified by a sequence number smaller than the third sequence number to the second access network device.

[0208] Optionally, the second access network device may cache the received at least one third data packet.

[0209] The following will be based on the embodiment shown in Figure 7 and combined with Figure 8 to introduce the specific process of the switching method provided by this application. The content already introduced in the embodiment shown in Figure 7 will not be repeated. In the switching method shown in Figure 8, the source access network device is used as the first access network device and the first target access network device is used as the second access network device for illustration.

[0210] FIG8 is another schematic flow chart of a handover method according to an embodiment of the present application. As shown in FIG8 , the method 800 may include steps S801 to S812. The steps shown in the method 800 are described in detail below.

[0211] S801: The source access network device transmits data with the terminal, where the data is MBS session data.

[0212] S802: The source access network device determines a conditional handover.

[0213] S803: The source access network device sends a first handover request message to multiple target access network devices. Correspondingly, the multiple target access network devices receive the first handover request message from the source access network device.

[0214] The multiple target access network devices include a first target access network, and the first target access network device may be a target access network device to which the terminal switches from a source access network device.

[0215] The first handover request is used to request handover of the terminal from a source access network device to any one of a plurality of target access network devices.

[0216] For the description of the first switching request, please refer to the relevant description in S701, which will not be repeated here.

[0217] It can be understood that the first switching request may also carry an identifier of an MBS session, which is used to identify the service type to which the at least one first data packet belongs.

[0218] S804: Multiple target access network devices send a handover response message to the source access network device. The handover response message is used to confirm the first handover request. Correspondingly, the source access network device receives the handover response messages from the multiple target access network devices.

[0219] Exemplarily, each target access network device among the multiple target access network devices may carry the third sequence number and the first initial value of the first variable in its respective handover response message.

[0220] For the description of the third serial number and the first variable, please refer to the relevant description in method 700 and will not be repeated here.

[0221] S805: The source access network device sends an RRC reconfiguration message to the terminal. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0222] The RRC reconfiguration message includes radio parameter configurations of multiple target access network devices and a handover command of a handover execution triggering condition.

[0223] S806: The terminal sends an RRC reconfiguration completion message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0224] After S806, the terminal remains connected to the source access network device and begins evaluating handover conditions. While the terminal is evaluating the handover conditions, the source target access network device may continue to send at least one second data packet to the terminal; and the first access network device may continue to send at least one third data packet to multiple target access network devices based on the first sequence number and the third sequence number.

[0225] For the description of at least one second data packet and at least one third data packet, reference may be made to the relevant description in method 700 and will not be repeated here.

[0226] S807: The source access network device sends the second sequence number to the multiple target access network devices. Correspondingly, the multiple target access network devices receive the second sequence number from the source access network device.

[0227] For the description of the second serial number, please refer to the relevant description in the above method 700, which will not be repeated here.

[0228] S808 , the multiple target access network devices delete, based on the third sequence number, data packets of the cached MBS session whose sequence numbers are less than or equal to the second sequence number.

[0229] This process can be referred to the description of S704 and will not be repeated here.

[0230] S809: The conditional switching is completed, and the terminal switches from the source access network device to the first target access network device.

[0231] S810: The first target access network device sends a handover success message to the source access network device.

[0232] The handover success message is used to notify the source access network device of successful access to the first target access network device.

[0233] S811: The source access network device sends an SN status sending message to the first target access network device. Correspondingly, the first target access network device receives the SN status sending message from the source access network device.

[0234] S812: The source access network device sends a handover cancellation message to the other target access network devices. Correspondingly, the other target access network devices receive the handover cancellation message from the source access network device.

[0235] The method provided by the embodiment of the present application can effectively prevent the target access network device from caching too many data packets, reduce the resources required by the target access network device to cache MBS data packets, and improve resource utilization.

[0236] FIG9 is another schematic flow chart of a handover method provided in an embodiment of the present application. As shown in FIG9 , the method 900 may include steps S901 to S904. Each step in the method 900 is described in detail below.

[0237] S901: A first access network device sends a third handover request message to a second access network device, wherein the third handover request message is used to request handover of a first terminal to the second access network device. Correspondingly, the second access network device receives the third handover request message from the first access network device.

[0238] For the description of the first terminal, the first access network device, and the second access network device, please refer to the relevant description in method 700 and will not be repeated here.

[0239] Optionally, before S901 , the method 900 further includes: the first access network device determining to perform conditional switching.

[0240] S902: The second access network device sends a handover response message to the first access network device, where the handover response message includes a first initial value of the first variable. Correspondingly, the first access network device receives the handover response message from the second access network device.

[0241] The first variable indicates an identification value of the first PDCP SDU in the receiving window that has not been delivered to the upper layer. For example, the first variable is RX_DELIV.

[0242] S903: The first access network device sends a first initial value of the first variable to the first terminal. The first initial value of the first variable may be carried in an RRC reconfiguration message.

[0243] S904: The second access network device sends a second initial value of the first variable to the first terminal. Correspondingly, the first terminal receives the second initial value from the second access network device.

[0244] Optionally, the second initial value is greater than the first initial value. The second initial value is a reference value of the first variable on the second access network device side after the first terminal accesses the second access network device.

[0245] For the description of the reference value, please refer to the previous description and will not be repeated here.

[0246] Exemplarily, the second access network device may directly send the second initial value of the first variable to the first terminal after the first terminal accesses the second access network device; or, the second access network device may send the second initial value of the first variable to the first terminal through the first access network device before the first terminal accesses the second access network device.

[0247] It can be understood that after the second access network device sends a switching success message to the first access network device, it can be considered that the first terminal is connected to the second access network device; otherwise, it is considered that the first terminal is not connected to the second access network device.

[0248] The method 900 provided in this application is applied to a conditional handover scenario to address the issue of the initial value of a first variable expiring on the terminal side. In this embodiment of the application, after sending the initial value of the first variable to the first terminal, the second access network device can again send the second initial value of the first variable to the first terminal, so that the first terminal can update the initial value of the first variable. This allows the first terminal to use the updated second initial value to receive data packets for the MBS session from the second access network device after accessing the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets.

[0249] Two methods in which the second access network device updates the initial value of the first variable to the first terminal are described in detail below.

[0250] Method 1: The second access network device directly sends the initial value of the first variable to the first terminal. That is, the first terminal accesses the second access network device.

[0251] Exemplarily, after the first terminal accesses the second access network device, the second access network device sends the second initial value to the first terminal, and correspondingly, the first terminal receives the second initial value.

[0252] Optionally, the second initial value may be carried in an RRC reconfiguration message. The RRC reconfiguration message may be sent directly to the first terminal by the second access network device after the first terminal accesses the second access network device.

[0253] In a second approach, the second access network device sends the initial value of the first variable to the first terminal via the first access network device. That is, the first terminal does not access the second access network device.

[0254] In example 1, the second access network device sends a second initial value to the first access network device. Correspondingly, the first access network device receives the second initial value and sends the second initial value to the first terminal.

[0255] Optionally, in the above-mentioned method 1 and the method shown in Example 1, before the second access network device sends the second initial value of the first variable (to the first access network device or to the first terminal), the method 900 also includes: the second access network device determines whether the number of data packets sent for the MBS session is greater than a preset value.

[0256] Exemplarily, when the number of MBS session data packets sent by the second access network device is greater than a preset value, the second access network device sends the second initial value of the first variable; or, when the number of MBS data packets sent by the second access network device is less than or equal to the preset value, the second access network device does not send the second initial value of the first variable.

[0257] The preset value and the size of the receiving window satisfy a preset relationship.

[0258] Exemplarily, the preset relationship is: preset value = k × size of receiving window. Wherein, k is greater than 0 and less than or equal to 1, N is the size of receiving window, and N satisfies: N = 2 p-1 , P is the number of bits used to identify the first sequence number. For example, if the first sequence number is represented by 12 bits, then P=12.

[0259] It can be understood that the data packet of the MBS session sent by the above-mentioned second access network device refers to the data packet of the MBS session sent by the second access network device to the second terminal, and the data packet of the MBS session and at least one first data packet (or at least one second data packet) belong to the same MBS session.

[0260] In Example 2, upon receiving the first information from the first access network device, the second access network device sends the second initial value to the first access network device. Correspondingly, the first access network device receives the second initial value and sends the second initial value to the first terminal.

[0261] The first information is used to request a second initial value of the first variable.

[0262] Optionally, the method 900 also includes: the first access network device determines whether the number of at least one second data packet sent to the first terminal is greater than a preset value; when the number of at least one second data packet is greater than the preset value, the first access network device sends the first information to the second access network device, or when the number of at least one second data packet is less than or equal to the preset value, the first access network device does not send the first information to the second access network device.

[0263] The description of the preset value can refer to the description in Example 1 above and will not be repeated here. However, it should be noted that when the second access network device determines whether the number of at least one second data packet is greater than the preset value, it needs to first determine the size of the preset value. The preset value and the size of the receiving window satisfy a preset relationship. This preset relationship can refer to the description in Method 1. When calculating the size N of the interface window, if the first access network device is unsure of the number of bits used by the second access network device to identify the first sequence number, 12 bits can be used for calculation.

[0264] Since, in the manner shown in Example 2, the second initial value of the first variable is actively requested by the first access network device, the second initial value may be the same as the first initial value.

[0265] The following will be based on the embodiment shown in Figure 9 and combined with Figure 10 to introduce the specific process of the switching method provided by this application. The content already introduced in the embodiment shown in Figure 9 will not be repeated. In the switching method shown in Figure 10, the source access network device is used as the first access network device and the first target access network device is used as the second access network device for illustration.

[0266] Figure 10 is another schematic flow chart of a handover method provided in an embodiment of the present application. As shown in Figure 10, the method 1000 may include steps S1001 to S1019. The steps shown in the method 1000 are described in detail below.

[0267] S1001: The source access network device transmits data with the terminal, where the data is MBS data.

[0268] S1002: The source access network device determines a conditional handover.

[0269] S1003: The source access network device sends a first handover request message to multiple target access network devices. Correspondingly, the multiple target access network devices receive the first handover request message from the source access network device.

[0270] The above S1001 to S1003 are the same as the process shown in the above S801 to S803, and will not be repeated here.

[0271] S1004: Multiple target access network devices send a handover response message to the source access network device. The handover response message is used to confirm the first handover request. Correspondingly, the source access network device receives the handover response messages from the multiple target access network devices.

[0272] The handover response message carries the first initial value of the first variable. For the description of the first variable and the first initial value, refer to the relevant description in method 700, which will not be repeated here.

[0273] S1005: The source access network device sends an RRC reconfiguration message to the terminal. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0274] The RRC reconfiguration message includes radio parameter configurations of multiple target access network devices and a handover command of a handover execution triggering condition.

[0275] Optionally, the RRC reconfiguration message includes initial values ​​of the first variables configured by multiple target access network devices for the terminal.

[0276] Correspondingly, the terminal receives and caches the first initial value of the first variable from multiple target access network devices, and after switching to the first target access network device among the multiple target access network devices, calculates the COUNT value using the initial value of the first variable from the first target access network device.

[0277] S1006: The terminal sends an RRC reconfiguration completion message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0278] After S1006, the terminal remains connected to the source access network device and begins evaluating handover conditions. While the terminal is evaluating handover conditions, multiple target access network devices may continue to send MBS data packets to the terminals connected thereto; and the first access network device may continue to send at least one second data packet to the terminal.

[0279] For the description of the at least one second data packet, reference may be made to the description of method 700 and will not be repeated here.

[0280] S1007: The multiple target access network devices determine that the number of MBS data packets sent is greater than a preset value.

[0281] S1008: The multiple target access network devices respectively send the second initial value of the first variable to the source access network device. Correspondingly, the source access network device receives the second initial value of the first variable from the multiple target access network devices.

[0282] For the description of the second initial value, please refer to the description in method 700 and will not be repeated here.

[0283] S1009: The source access network device sends the second initial value of the first variable to the terminal. Correspondingly, the terminal receives the second initial value of the first variable from the first access network device, so that after switching to a first target access network device among the multiple target access network devices, the terminal calculates a COUNT value using the initial value of the first variable from the first target access network device.

[0284] S1010: The source access network device determines that the number of at least one second data packet is greater than a preset value.

[0285] S1011: A source access network device sends first information to multiple target access network devices. Correspondingly, the multiple target access network devices receive the first information from the source access network device.

[0286] For the description of the first information, please refer to the description in method 700 and will not be repeated here.

[0287] S1012: The multiple target access network devices send the second initial value to the source access network device. Correspondingly, the source access network device receives the second initial value from the multiple target access network devices.

[0288] S1013: The source access network device sends a second initial value to the terminal. Correspondingly, the terminal receives the second initial value from the source access network device.

[0289] For the description of the second initial value, please refer to the description in method 700 and will not be repeated here.

[0290] S1014: The conditional switching is completed, and the terminal switches from the source access network device to the first target access network device.

[0291] When there are multiple target access network devices, the terminal will only determine one target access network device (for example, the first target access network device) from the multiple target access network devices to access.

[0292] S1015: The first target access network device sends a handover success message to the source access network device. Correspondingly, the source access network device receives the handover success message from the first target access network device.

[0293] The handover success message is used to notify the source access network device of successful access to the first target access network device.

[0294] S1016: The source access network device sends an SN status sending message to the first target access network device. Correspondingly, the first target access network device receives the SN status sending message from the source access network device.

[0295] S1017: The source access network device sends a handover cancellation message to the other target access network devices. Correspondingly, the other target access network devices receive the handover cancellation message from the source access network device.

[0296] S1018: The first target access network device determines that the data packet sent for the MBS session is greater than a preset value.

[0297] S1019: The first target access network device sends the second initial value of the first variable to the terminal. Correspondingly, the terminal receives the second initial value of the first variable from the first target access network device.

[0298] It should be noted that the above steps S107 to S1013, as well as S1018 and S1019 are optional. For example, after S106, when S107 to S1010 is continued, S1011 to S1013, as well as S1018 and S1019 may not be performed. For another example, after S106, when S1011 to S1013 is continued, S107 to S1010, as well as S1018 and S1019 may not be performed. For another example, after S106, when S107 to S1013 is not continued, S1018 and S1019 may be continued after S1017.

[0299] The improved method of the embodiment of the present application can effectively avoid the possibility of the terminal receiving disordered data packets.

[0300] It is understood that the embodiments shown in Figures 7 and 9 (or Figures 8 and 10) above can be combined with each other or implemented independently. Specifically, when Figures 7 and 9 (Figures 8 and 10) are implemented separately, more or fewer steps than those shown in Figures 7 or 9 (Figures 8 or 10) can be performed; when the embodiments shown in Figures 7 and 9 (or Figures 8 and 10) are combined, the communication method provided in this application may include: a first handover request message (e.g., a first handover request message or a third handover request message) sent by a first access network device to a second access network device for the first time includes a first sequence number, a handover response message sent by the second access network device to the first access network device includes a second sequence number and a first initial value of the first variable, and an RRC reconfiguration message sent by the first access network device to the first terminal carries the first initial value of the first variable. For other more detailed processes, please refer to the description of the embodiments shown in Figures 7 and 9 (or Figures 8 and 10) above.

[0301] FIG11 is a schematic flow chart of another switching method provided by an embodiment of the present application. As shown in FIG11 , the method 1100 may include steps S1101 to S1116. The steps shown in the method 1100 are described in detail below.

[0302] S1101: The source access network device transmits data with the terminal, where the data is MBS data.

[0303] S1102: The source access network device determines a conditional handover.

[0304] S1103: The source access network device sends a first handover request message to multiple target access network devices. The first handover request message carries a first identifier. Correspondingly, the multiple target access network devices receive the first handover request message from the source access network device.

[0305] The first identifier is used to identify an MBS session, and the state of the MBS session is deactivated.

[0306] S1104: Multiple target access network devices send a handover response message to the source access network device. The handover response message is used to confirm the first handover request. Correspondingly, the source access network device receives the handover response messages from the multiple target access network devices.

[0307] When the first switching request message is a switching request message sent under conditional switching, after receiving the first switching request message, multiple target access network devices determine that the status of the MBS session is deactivated, and carry the MRB configuration in the switching response message sent to the source access network device.

[0308] S1105: The source access network device sends an RRC reconfiguration message to the terminal. The RRC reconfiguration message includes the MRB configuration. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0309] S1106: The terminal sends an RRC reconfiguration completion message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration completion message from the terminal.

[0310] After S1106 , the terminal still maintains the connection with the source access network device and starts to evaluate the switching condition.

[0311] S1107: When the first condition is met, the source access network device sends second information to the multiple target access network devices. Correspondingly, the multiple target access network devices receive the second information from the source access network device. The second information is used to request the multiple target access network devices to update RRC configurations.

[0312] The first condition is that the state of the MBS session is active, that is, when the state of the MBS session is active, the source access network device sends the second information to the multiple target access network devices.

[0313] Exemplarily, the source access network device may consider that the above-mentioned first condition is met when it receives a notification message to activate the MBS session, or the source access network device determines that the status of the MBS session is activated, or the source access network device receives a group paging message from other access network devices.

[0314] S1108: The multiple target access network devices send an RRC reconfiguration message to the source access network device again. Correspondingly, the source access network device receives the RRC reconfiguration message from the multiple target access network devices. The RRC reconfiguration message carries the MRB configuration.

[0315] S1109: The source access network device forwards the RRC reconfiguration message received again to the terminal. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0316] S1110: When the first condition is met, the multiple target access network devices resend an RRC reconfiguration message to the source access network device, the RRC reconfiguration message carrying the MRB configuration. Correspondingly, the source access network device receives the RRC reconfiguration messages from the multiple target access network devices.

[0317] For the description of the first condition, reference may be made to the description in S1107 and will not be repeated here. That is, when the state of the MBS session is active, the multiple target access network devices resend the RRC reconfiguration message to the source access network device.

[0318] Exemplarily, multiple target access network devices may consider that the above-mentioned first condition is met when they receive a notification message to activate the MBS session, or when multiple target access network devices determine that the status of the MBS session is activated, or when multiple target access network devices receive a group paging message from other access network devices.

[0319] Optionally, when receiving the activation notification of the MBS session, multiple target access network devices can determine whether the switching response message sent by the multiple target access network devices in S1104 carries the MBS configuration; if the MBS configuration is carried, the multiple target access network devices may not carry the MRB configuration in the RRC reset message sent in S1110.

[0320] S1111: The source access network device forwards the RRC reconfiguration message received again to the terminal. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0321] S1112, completing the conditional switching, the terminal switches from the source access network device to the first target access network device.

[0322] When there are multiple target access network devices, the terminal will only determine one target access network device (for example, the first target access network device) from the multiple target access network devices to access.

[0323] S1113: The first target access network device sends a handover success message to the source access network device. Correspondingly, the source access network device receives the handover success message from the first target access network device.

[0324] The handover success message is used to notify the source access network device of successful access to the first target access network device.

[0325] S1114: The source access network device sends an SN status sending message to the first target access network device. Correspondingly, the first target access network device receives the SN status sending message from the source access network device.

[0326] S1115: The source access network device sends a handover cancellation message to the other target access network devices. Correspondingly, the other target access network devices receive the handover cancellation message from the source access network device.

[0327] S1116: When the first condition is met, the first target access network device sends an RRC reconfiguration message to the terminal, where the RRC reconfiguration message carries the MRB configuration. Correspondingly, the terminal receives the RRC reconfiguration message from the first target access network device.

[0328] For the description of the first condition, reference may be made to the description in S1107 and will not be repeated here. That is, when the state of the MBS session is active, the first target access network device sends an RRC reconfiguration message to the terminal.

[0329] Exemplarily, the first target access network device may consider that the above-mentioned first condition is met when it receives a notification message to activate the MBS session, or the first target access network device determines that the status of the MBS session is activated, or the first target access network device receives a group paging message from other access network devices.

[0330] Optionally, after the terminal accesses the first target access network device, if the status of the MBS session is in an activated state, the first target access network device can determine whether the switching response message sent in S1104 carries the MRB configuration; if it carries the MRB configuration, the RRC configuration message sent in S1116 may not include the MRB configuration; and / or, the first target access network device can determine whether the RRC reconfiguration message sent in S1110 carries the MRB configuration; if it carries the MRB configuration, the RRC configuration message sent in S1116 may not include the MRB configuration.

[0331] It should be noted that if the handover response message sent by multiple target access network devices to the source access network device in S1104 carries the MRB configuration, then the above S1107 to S1111, and S1116 are optional steps. That is, if the handover response message in S1104 carries the MRB configuration, S1107 to S1111, and S1016 may not be executed; or, if the handover response message in S1104 carries the MRB configuration, S1107 to S1111, and S1016 may continue to be executed, and the specific execution process is as follows: 1. After S1106, when continuing to execute S1107 to S1109, it is not necessary to execute ( S1110 and S1111), and / or S1116; or, 2. After S1106, when continuing to execute S1110 and S1111, it is not necessary to execute (S1107 to S1109), and / or S1116; or, 3. After S1106, when not continuing to execute (S1107 to S1109), and / or (S1110 and S1111), it is possible to continue to execute S1116 after S1115.

[0332] Alternatively, if the switching response message sent by multiple target access network devices to the source access network device in S1104 does not carry the MRB configuration, then the specific execution process of the above S1107 to S1111, and S1116 is as follows: 1. After S1106, when continuing to execute S1107 to S1109, (S1110 and S1111) and / or S1116 may not be executed; or, 2. After S1106, when continuing to execute S1110 and S1111, (S1107 to S1109) and / or S1116 may not be executed; or, 3. After S1106, when not continuing to execute (S1107 to S1109) and / or (S1110 and S1111), S1116 may be continued after S1115.

[0333] It should also be noted that when CHO is applied to a handover involving an MBS session, the CHO handover process may include more or fewer steps than those shown in FIG. 11 .

[0334] The method 1100 provided herein is applied to a conditional handover scenario to address the issue of an access network device failing to update the MRB configuration when an MBS service transitions from a deactivated state to an activated state. In this embodiment of the present application, after the MBS service is activated, the MRB configuration can be included in the RRC configuration so that the terminal can normally receive data packets for the MBS session after accessing the target access network device.

[0335] The method provided in the embodiment of the present application is described in detail above in conjunction with Figures 1 to 11. The device provided in the embodiment of the present application is introduced below in conjunction with Figures 12 to 14.

[0336] Figures 12 and 13 are schematic diagrams of possible devices provided by embodiments of the present application. These devices can be used to implement the functions of the first access network device or the second access network device in the above method embodiments, thereby also achieving the beneficial effects of the above method embodiments.

[0337] FIG12 is a schematic block diagram of an apparatus according to an embodiment of the present application. As shown in FIG12 , the apparatus 1200 includes a transceiver module 1210 and a processing module 1220 .

[0338] One possible design is that the apparatus 1200 is used to implement the functions of the first access network device in the method embodiments shown in FIG. 7 to FIG. 11 .

[0339] Exemplarily, the transceiver module 1210 is used to: send a first switching request message to the second access network device, the first switching request message is used to request to switch the terminal from the first access network device to the second access network device, the first switching request message includes a first sequence number, the first sequence number is the sequence number of the last first data packet in at least one first data packet sent by the first access network device to the terminal; send at least one second data packet to the terminal; and send a second sequence number to the second access network device, the second sequence number is the sequence number of the last second data packet in the at least one second data packet sent by the first access network device to the terminal, and the second sequence number is greater than the first sequence number; wherein the at least one first data packet and the at least one second data packet belong to the same multicast broadcast service MBS.

[0340] Optionally, the processing module 1220 is configured to determine whether to perform conditional switching.

[0341] Optionally, the transceiver module 1210 is also used to: receive a switching response message from the second access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first Packet Data Convergence Protocol PDCP Service Data Unit SDU that is not submitted to the upper layer in the receiving window; and send the first initial value of the first variable to the terminal.

[0342] Optionally, the transceiver module 1210 is further configured to: receive a second initial value from the second access network device, where the second initial value is greater than the first initial value; and send the second initial value to the terminal.

[0343] Optionally, the processing module 1220 is also used to: determine whether the number of the at least one second data packet is greater than a preset value; the transceiver module 1210 is also used to: when the number of the at least one second data packet is greater than the preset value, send first information to the second access network device, the first information being used to request a second initial value of the first variable, the second initial value being greater than the first initial value; receive the second initial value from the second access network device; and send the second initial value to the terminal.

[0344] Exemplarily, the transceiver module 1210 is used to: send a third switching request message to the second access network device, the third switching request message is used to request that the first terminal be switched to the second access network device; receive a switching response message from the second access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first PDCP SDU not submitted to the upper layer in the receiving window, receive a second initial value from the second access network device, the second initial value is greater than the first initial value; and send the second initial value to the terminal.

[0345] A more detailed description of the transceiver module 1210 and the processing module 1220 can be directly obtained by referring to the relevant descriptions in the embodiments shown in Figures 7 to 11, and will not be repeated here.

[0346] Another possible design is that the apparatus 1200 is used to implement the functions of the second access network device in the method embodiments shown in FIG. 7 to FIG. 11 .

[0347] Exemplarily, the transceiver module 1210 is used to: receive a first switching request message from a first access network device, the first switching request message is used to request that the terminal be switched from the first access network device to the second access network device, the first switching request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one data packet sent by the first access network device to the terminal; and receive a second sequence number from the first access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number, and the at least one first data packet and the at least one second data packet belonging to the same multicast broadcast service MBS; the processing module 1220 is used to: delete the data packets of the cached MBS, the data packets identified by the sequence numbers less than or equal to the second sequence number.

[0348] Optionally, the transceiver module 1210 is also used to: send a switching response message to the first access network device, the switching response message including a first initial value of a first variable, and the first variable indicating the identification value of the first packet data convergence protocol PDCP service data unit SDU that is not submitted to the upper layer in the receiving window.

[0349] Optionally, the transceiver module 1210 is also used to: receive first information from the first access network device, the first information is used to request a second initial value of the first variable, the second initial value being greater than the first initial value; and send the second initial value to the first access network device.

[0350] Optionally, the transceiver module 1210 is further configured to: after the terminal accesses the second access network device, send a second initial value to the terminal, where the second initial value is greater than the first initial value.

[0351] Optionally, the transceiver module 1210 is further configured to: before the terminal accesses the second access network device, send a second initial value to the first access network device, where the second initial value is greater than the first initial value.

[0352] Optionally, the processing module 1220 is further configured to: determine that the number of the MBS data packets sent by the second access network device is greater than a preset value.

[0353] Exemplarily, the transceiver module 1210 is also used to: receive a third switching request message from the first access network device, the third switching request message being used to request that the first terminal be switched to the second access network device; send a switching response message to the first access network device, the switching response message including a first initial value of a first variable, the first variable indicating an identification value of the first PDCP SDU that is not submitted to the upper layer in the receiving window; and, send a second initial value of the first variable to the first terminal.

[0354] A more detailed description of the transceiver module 1210 and the processing module 1220 can be directly obtained by referring to the relevant descriptions in the embodiments shown in Figures 7 to 11, and will not be repeated here.

[0355] It should be noted that device 1200 may include a sending module but not a receiving module. Alternatively, device 1200 may include a receiving module but not a sending module. This may depend on whether the above-mentioned solution executed by device 1200 includes both sending and receiving actions. It is understood that because device 1200 has communication functionality, it can also be referred to as a communication device.

[0356] FIG13 is another schematic block diagram of an apparatus provided in an embodiment of the present application. As shown in FIG13 , apparatus 1300 includes one or more processors 1310. Processor 1310 may be a general-purpose processor or a dedicated processor. For example, it may be a baseband processor or a central processing unit. The baseband processor may be used to process communication protocols and communication data, and the central processing unit may be used to control an apparatus (e.g., a first access network device, a second access network device, or a chip), execute software programs, and process data from the software programs.

[0357] Optionally, in one design, the processor 1310 may include a program (also referred to as code or instructions), which may be executed on the processor 1310 to cause the apparatus 1300 to perform the method performed by the first access network device or the second access network device in the above method embodiment. In another possible design, the apparatus 1300 includes a circuit (not shown in FIG. 13 ) configured to implement the functions of the first access network device or the second access network device in the above method embodiment.

[0358] Exemplarily, the processor 1310 may be configured to execute a computer program or instruction in a memory to implement the steps performed by the first access network device or the second access network device in the method embodiment shown in any one of the embodiments shown in FIG. 7 to FIG. 11 .

[0359] Optionally, the device 1300 may include one or more memories 1320 on which programs (sometimes also referred to as codes or instructions) are stored. The programs can be run on the processor 1310, so that the device 1300 executes the method executed by the first access network device or the second access network device in the above embodiment.

[0360] Optionally, the processor 1310 and / or the memory 1320 may include an artificial intelligence (AI) module, which is used to implement AI-related functions. The AI ​​module may be implemented through software, hardware, or a combination of software and hardware. For example, the AI ​​module may include a wireless intelligent controller (RIC) module. For example, the AI ​​module may be a near real-time RIC or a non-real-time RIC.

[0361] Optionally, data may be stored in the processor 1310 and / or the memory 1320. The processor and memory may be provided separately or integrated together.

[0362] Optionally, the apparatus 1300 may further include a communication interface 1330. The processor 1310 may also be sometimes referred to as a processing unit, which controls the apparatus (e.g., the first access network device or the second access network device). The communication interface 1330 may also be sometimes referred to as a transceiver unit, a transceiver, a transceiver circuit, or a transceiver, etc., which is used to implement the transceiver function of the apparatus.

[0363] Optionally, the apparatus 1300 further includes a communication interface 1330. The processor 1310 and the communication interface 1330 are coupled to each other. It is understood that the communication interface 1330 may be a transceiver or an input / output interface.

[0364] It is understandable that, since the device 1300 has a communication function, it can also be called a communication device.

[0365] When apparatus 1300 is used to implement the methods of Figures 7 to 11, processor 1310 is used to perform the functions of the aforementioned processing unit, and communication interface 1330 is used to perform the functions of the aforementioned transceiver module. Whether communication interface 1330 is used for sending or receiving can be determined by whether it is used to perform a sending action or a receiving action in the solution implemented by apparatus 1300.

[0366] When the apparatus 1300 is a chip implemented in a first access network device, the chip implements the functions of the first access network device in the above method embodiment. The chip of the first access network device receives a signal from another module (such as a radio frequency module or antenna) in the first access network device. The signal may be sent from the second access network device to the first access network device; or the chip of the first access network device sends a signal to another module (such as a radio frequency module or antenna) in the first access network device. The signal may be sent from the first access network device to the second access network device.

[0367] When the apparatus 1300 is a chip implemented in a second access network device, the chip implements the functions of the second access network device in the above method embodiments. The chip of the second access network device receives a signal from another module (such as a radio frequency module or antenna) in the second access network device. The signal may be sent from the first access network device to the second access network device. Alternatively, the chip of the second access network device sends a signal to another module (such as a radio frequency module or antenna) in the second access network device. The signal may be sent from the second access network device to the first access network device.

[0368] It is understood that when the apparatus 1300 is a first access network device or a second access network device, the communication interface 1330 may be a transceiver, specifically including a transmitter and a receiver, where the transmitter is used to transmit signals and the receiver is used to receive signals. When the apparatus 1300 is a chip used in the first access network device or the second access network device, the communication interface 1330 may be an input / output circuit, where the input circuit may be used for receiving and the output interface may be used for transmitting.

[0369] Figure 14 is a schematic diagram of the structure of a wireless access network device provided in an embodiment of the present application, for example, a base station. Base station 1400 can be used in the system shown in Figure 1 to perform the functions of the second access network device in the above-described method embodiment. As shown in the figure, base station 1400 may include one or more of the following: one or more (DU+RU) units 1410 and one or more CUs 1420. CU 1420 can communicate with a next-generation core (NG core). The DU may include at least one antenna 1411, at least one radio frequency unit 1412, at least one processor 1414, and at least one memory 1414. The DU portion is primarily used for transmitting and receiving radio frequency signals, converting radio frequency signals into baseband signals, and performing partial baseband processing. CU 1420 may include at least one processor 1422 and at least one memory 1421. CU 1420 and the DU may communicate via an interface. The control plane (CP) interface may be an Fs-C, such as F1-C, and the user plane (UP) interface may be an Fs-U, such as F1-U. The DU and RU can work together to implement the functions of the physical (PHY) layer. A DU can be connected to one or more RUs. The functions of the DU and RU can be configured in various ways according to the design. For example, the DU is configured to implement the baseband function, and the RU is configured to implement the mid-RF function. For another example, the DU is configured to implement the high-layer functions in the PHY layer, and the RU is configured to implement the low-layer functions and RF functions in the PHY layer. The high-layer functions in the PHY layer may include a part of the functions of the PHY layer, which is closer to the MAC layer, and the low-layer functions in the PHY layer may include another part of the functions of the PHY layer, which is closer to the mid-RF side.

[0370] The CU 1420 is primarily used for baseband processing and base station control. The DU and CU 1420 may be physically located together or physically separated, i.e., a distributed base station. The CU 1420 is the control center of the base station and may correspond to the processing module in FIG12 or the processor in FIG13 , and may also be referred to as a processing unit, primarily for performing baseband processing functions. For example, the CU 1420 may be used to control the base station to execute the operational procedures for the access network device in the above-described method embodiment.

[0371] Specifically, baseband processing on the CU and DU can be divided according to the protocol layers of the wireless network. For example, the functions of the packet data convergence protocol (PDCP) layer and above are set in the CU, while the functions of the protocol layers below PDCP, such as the RLC layer and the MAC layer, are set in the DU. For another example, the CU implements the functions of the RRC layer and the PDCP layer, while the DU implements the functions of the RLC layer, the MAC layer, and the PHY layer.

[0372] In addition, optionally, the base station 1400 may include one or more radio frequency units (RUs), one or more DUs, and one or more CUs. The DU may include at least one processor 1414 and at least one memory 1413, the RU may include at least one antenna 1411 and at least one radio frequency unit 1412, and the CU may include at least one processor 1422 and at least one memory 1421.

[0373] In one example, the CU 1420 may be composed of one or more single boards, and the multiple single boards may jointly support a wireless access network with a single access indication (such as a 5G network), or may respectively support wireless access networks with different access standards (such as an LTE network, a 5G network, or other networks). The memory 1421 and the processor 1422 may serve one or more single boards. That is, a memory and a processor may be separately set on each single board. It is also possible that multiple single boards share the same memory and processor. In addition, necessary circuits may be provided on each single board. The DU may be composed of one or more single boards, and the multiple single boards may jointly support a wireless access network with a single access indication (such as a 5G network), or may respectively support wireless access networks with different access standards (such as an LTE network, a 5G network, or other networks). The memory 1413 and the processor 1414 may serve one or more single boards. That is, a memory and a processor may be separately set on each single board. It is also possible that multiple single boards share the same memory and processor. In addition, necessary circuits may be provided on each single board.

[0374] It should be understood that base station 1400 shown in Figure 14 is capable of implementing the various processes involving the first access network device or the second access network device in the method embodiments shown in Figures 7 to 11. The operations and / or functions of the various modules in base station 1400 are respectively for implementing the corresponding processes in the aforementioned method embodiments. For details, please refer to the description of the aforementioned method embodiments; to avoid repetition, detailed descriptions are omitted here.

[0375] It should be understood that the base station 1400 shown in FIG14 is only one possible architecture of a radio access network device and does not constitute any limitation on the present application. The method provided in the present application is applicable to network devices of other architectures. For example, radio access network devices including CUs, DUs, and AAUs are not limited in the present application to the specific architecture of the radio access network device.

[0376] It should be understood that Figure 14 is merely an example and not a limitation, and the radio access network device may not rely on the structure shown in Figure 14. For example, the radio access network device may also include an AAU, a CU, and / or a DU, or the radio access network device may also include a BBU and an adaptive radio unit (ARU). This application is not limited to this.

[0377] The CU and / or DU described above can be used to perform the actions implemented within the radio access network device described in the previous method embodiments, while the AAU can be used to perform the actions described in the previous method embodiments where the radio access network device sends or receives information to or from the terminal. For details, please refer to the description in the previous method embodiments and will not be repeated here.

[0378] It should be noted that the above method embodiments can be applied to or implemented by a processor. The processor may be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above method embodiments can be completed by hardware integrated logic circuits in the processor or by software instructions.

[0379] The processor may be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0380] The steps of the method disclosed in the embodiments of this application can be directly implemented and executed by a hardware decoding processor, or by a combination of hardware and software modules in the decoding processor. The software module can be located in a storage medium well-known in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, etc. The storage medium is located in the memory, and the processor reads the information in the memory and, in conjunction with its hardware, completes the steps of the above method.

[0381] The memory in the embodiments of the present application may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. Among them, the non-volatile memory may be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example and not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), and direct RAM bus RAM (DR RAM). It should be noted that the memory of the systems and methods described herein is intended to include, but is not limited to, these and any other suitable types of memory.

[0382] The methods provided in the above embodiments can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, they can be implemented in whole or in part in the form of a computer program product. The computer program product may include one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website, computer, server or data center to another website, computer, server or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated therein. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a magnetic disk), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state disk (SSD)).

[0383] The present application also provides a computer-readable medium having a computer program stored thereon, which implements the functions of the above-mentioned method embodiment when executed by a computer.

[0384] The present application also provides a computer program product comprising instructions, which implements the functions of the above method embodiments when executed by a computer.

[0385] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0386] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0387] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0388] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0389] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0390] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0391] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A switching method, characterized in that: Applied to a first access network device or a chip of the first access network device, the method comprising: Sending a first switching request message to a second access network device, where the first switching request message is used to request that the terminal be switched from the first access network device to the second access network device, where the first switching request message includes a first sequence number, where the first sequence number is a sequence number of a last first data packet in at least one first data packet sent by the first access network device to the terminal; Sending at least one second data packet to the terminal; Sending a second sequence number to the second access network device, where the second sequence number is the sequence number of the last second data packet in the at least one second data packet sent by the first access network device to the terminal, and the second sequence number is greater than the first sequence number; The at least one first data packet and the at least one second data packet belong to the same multicast broadcast service MBS session.

2. The method according to claim 1, characterized in that The second sequence number is used by the second access network device to delete cached data packets of the MBS session.

3. The method according to claim 1 or 2, characterized in that: Before sending the first switching request to the second access network device, the method further includes: Confirm the conditional switching.

4. The method according to any one of claims 1 to 3, characterized in that After sending the first switching request message to the second access network device, the method further includes: receiving a handover response message from the second access network device, wherein the handover response message includes a first initial value of a first variable, wherein the first variable indicates an identification value of a first Packet Data Convergence Protocol (PDCP) service data unit (SDU) that is not delivered to an upper layer in a receiving window; A first initial value of the first variable is sent to a terminal.

5. The method according to claim 4, characterized in that The method further comprises: receiving a second initial value from the second access network device, where the second initial value is greater than the first initial value; The second initial value is sent to the terminal.

6. The method according to claim 4, characterized in that The method further comprises: Determining whether the number of the at least one second data packet is greater than a preset value; When the number of the at least one second data packet is greater than the preset value, sending first information to the second access network device, where the first information is used to request a second initial value of the first variable, and the second initial value is greater than the first initial value; receiving the second initial value from the second access network device; The second initial value is sent to the terminal.

7. The method according to claim 6, characterized in that The preset value is the size of the receiving window.

8. The method according to any one of claims 1 to 7, characterized in that The second sequence number is carried in a second switching request message, where the second switching request message is used to request switching of the terminal from the first access network device to the second access network device, and the second switching request message indicates that the second access network device does not update the radio resource control RRC configuration.

9. The method according to any one of claims 1 to 7, characterized in that The second sequence number is carried by early state signaling.

10. The method according to any one of claims 1 to 7, characterized in that The second sequence number is carried by MBS early state signaling.

11. A switching method, characterized in that: The method applied to the second access network device or the chip of the second access network device includes: Receiving a first handover request message from a first access network device, where the first handover request message is used to request that a terminal be handed over from the first access network device to the second access network device, where the first handover request message includes a first sequence number, where the first sequence number is a sequence number of a last first data packet in at least one data packet sent by the first access network device to the terminal; receiving a second sequence number from the first access network device, where the second sequence number is the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number is greater than the first sequence number, and the at least one first data packet and the at least one second data packet belong to the same multicast broadcast service MBS session; Delete the data packets of the MBS session in the cache, the data packets identified by the sequence numbers which are less than or equal to the second sequence number.

12. The method according to claim 11, characterized in that The first switching request is sent by the first access network device after determining to perform conditional switching.

13. The method according to claim 11 or 12, characterized in that: After receiving the first switching request message from the first access network device, the method further includes: A switching response message is sent to the first access network device, wherein the switching response message includes a first initial value of a first variable, and the first variable indicates an identification value of a first Packet Data Convergence Protocol PDCP Service Data Unit SDU that is not delivered to an upper layer in a receiving window.

14. The method according to claim 13, characterized in that The method further comprises: receiving first information from the first access network device, where the first information is used to request a second initial value of the first variable, where the second initial value is greater than the first initial value; Send the second initial value to the first access network device.

15. The method according to claim 13, characterized in that The method further comprises: After the terminal accesses the second access network device, a second initial value is sent to the terminal, where the second initial value is greater than the first initial value.

16. The method according to claim 13, characterized in that The method further comprises: Before the terminal accesses the second access network device, a second initial value is sent to the first access network device, where the second initial value is greater than the first initial value.

17. The method according to claim 15 or 16, characterized in that The method further comprises: It is determined that the number of data packets of the MBS session sent by the second access network device is greater than a preset value.

18. The method according to claim 17, characterized in that The preset value is the size of the receiving window.

19. The method according to any one of claims 11 to 18, characterized in that The second sequence number is carried in a second switching request message, where the second switching request message is used to request switching of the terminal from the first access network device to the second access network device, and the second switching request message indicates that the second access network device does not update the radio resource control RRC configuration.

20. The method according to any one of claims 11 to 18, characterized in that The second sequence number is carried by early state forwarding signaling.

21. The method according to any one of claims 11 to 18, characterized in that The second sequence number is carried by MBS early status forwarding signaling.

22. A communication device, characterized in that: Comprising modules for implementing the method as claimed in any one of claims 1 to 21.

23. A communication device, characterized in that: The device comprises a processor configured to cause the communication device to implement the method according to any one of claims 1 to 21 by executing a computer program and / or a logic circuit.

24. The device according to claim 23, characterized in that The system also includes a memory for storing a computer program and / or a configuration file of the logic circuit.

25. The device according to claim 23 or 24, characterized in that A communication interface is also included for inputting and / or outputting signals.

26. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 10 is executed, or the method according to any one of claims 11 to 21 is executed.

27. A computer program product, characterized in that The invention comprises a computer program. When the computer program is executed, the method according to any one of claims 1 to 10 is executed, or the method according to any one of claims 11 to 21 is executed.

28. A communication system, characterized in that: It comprises a first access network device and a second access network device, wherein the first access network device is used to implement the method as claimed in any one of claims 1 to 10, and the second access network device is used to implement the method as claimed in any one of claims 11 to 21.

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