Switching method and related device

Abstract

The invention provides a switching method and a related device, which can enable access network equipment to release a cache in time and improve the resource utilization rate. The method comprises the following steps: a first access network device sends a first switching request message to a second access network device, wherein the first switching request message comprises the serial number of the last first data packet in at least one first data packet sent by the first access network device to a terminal; the first access network equipment sends at least one second data packet to the terminal; the first access network equipment sends a second serial number to second access network equipment, wherein the second serial number is the serial number of the last second data packet in at least one second data packet sent by the first access network equipment to the terminal; wherein the at least one first data packet and the at least one second data packet belong to the same MBS session; and based on the received second serial number, the second access network equipment deletes the data packets identified by the serial number smaller than or equal to the second serial number in the cached data packets of the MBS session.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a switching method and related devices. Background Art

[0002] During the switching 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 switching command sent to the terminal fails to reach the access network device, resulting in a switching failure, requiring the terminal to re-initiate radio resource control (RRC) reconstruction.

[0003] In order to reduce the probability of unicast service handover failure, conditional handover (CHO) is proposed. CHO can allow the source access network device to send a handover command to the terminal in advance before the wireless environment between the terminal and the access network device deteriorates, so that the terminal can know how to access the target access network device in advance. After the terminal finds a candidate target access network device that meets the handover triggering conditions among multiple candidate target access network devices, it can initiate handover autonomously. Therefore, the success rate of handover can be greatly improved.

[0004] At present, with the increasing demand for lossless switching of multicast and broadcast service (MBS), CHO can be applied to the switching including MBS sessions to ensure the success rate of the switching of the terminal receiving the MBS session. When CHO is applied to the switching including MBS sessions, after the source access network device determines the conditional switching, it will continue to forward the MBS data packets to the terminal device for a period of time, and the data forwarding performed between the source access network device and the candidate target access network device may also be performed all the time, but the forwarded MBS data packets may accumulate a lot on the candidate target access network device side, resulting in excessive burden on multiple candidate target access network devices and excessive resources occupied by cached data. Summary of the invention

[0005] 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.

[0006] In a first aspect, the present application provides a switching method, which can be applied to a first access network device. For example, it can be performed by the first access network device, or it can also be performed by a component (such as a chip, a chip system, etc.) configured in the first access network device, or it can also be implemented by a logic module or software that can implement all or part of the functions of the first access network device, and the present application does not limit this.

[0007] 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 of a 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 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; and sending a second sequence number to the second access network device, the second sequence number being the sequence number of a 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.

[0008] In the present 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.

[0009] The second sequence number is used by the second access network device to delete cached data packets of the MBS session.

[0010] The first switching request message is a switching request message that is sent to multiple target access network devices for the first time after the first access network device determines the conditional switching.

[0011] 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 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 first access network device can release the cache in time, effectively improving resource utilization. At the same time, it can also prevent the second access network device from sending duplicate MBS session data packets to the terminal after the terminal accesses the second access network device.

[0012] 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.

[0013] In combination with the first aspect, in certain implementations of the first aspect, after sending a first switching request message to a second access network device, the method further 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 a first (packet data convergence protocol, PDCP) service data unit (service data unit, SDU) in a receiving window that is not submitted to an upper layer; and sending the first initial value of the first variable to a terminal.

[0014] 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 a switching 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.

[0015] 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.

[0016] 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.

[0017] The method can update the second initial value to the terminal in a timely manner 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, thereby avoiding the terminal receiving disordered data packets.

[0018] In combination with the first aspect, in some implementations of the first aspect, the method also includes: 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, 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.

[0019] 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.

[0020] 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.

[0021] Exemplarily, the preset relationship is: preset value = k × size of receiving window. Where 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.

[0022] In a second aspect, the present application provides a switching method, which can be applied to a second access network device. For example, it can be performed by the first access network device, or it can also be performed by a component (such as a chip, a chip system, etc.) configured in the second access network device, or it can also be implemented by a logic module or software that can implement all or part of the functions of the second access network device, and the present application does not limit this.

[0023] 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 of a 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 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, the second sequence number being the sequence number of a 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 among the cached data packets of the MBS session.

[0024] 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, which will not be repeated here.

[0025] 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 side 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 side 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. 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.

[0026] 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.

[0027] 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 indicates an identification value of the first PDCP SDU that is not submitted to the upper layer in the receiving window.

[0028] For the description of the first initial value, please refer to the first aspect and will not be repeated here.

[0029] 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.

[0030] 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.

[0031] 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, the second initial value being greater than the first initial value.

[0032] Optionally, the second initial value may be carried in an RRC reconfiguration message.

[0033] 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 switches 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.

[0034] 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, the second initial value being greater than the first initial value.

[0035] 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.

[0036] 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.

[0037] For the description of the preset value, please refer to the first aspect and will not be repeated here.

[0038] In combination with the second aspect, in certain implementations of the second aspect, the second sequence number is carried in a second switching request message, the second switching request message is used to request to switch 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 RRC configuration.

[0039] Alternatively, the second handover request message instructs the second access network device to only update the progress of an MBS radio bearer (MRB).

[0040] In combination with the second aspect, in certain implementations of the second aspect, the second sequence number is carried via early status transfer signaling or MBS early status transfer signaling.

[0041] In a third aspect, the present application provides a switching method, which can be applied to a second access network device. For example, it can be performed by the second access network device, or it can also be performed by a component (such as a chip, a chip system, etc.) configured in the second access network device, or it can also be implemented by a logic module or software that can implement all or part of the functions of the second access network device, and the present application does not limit this.

[0042] 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 of a 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 a first PDCP SDU that is not submitted to an upper layer in a receiving window; and sending a second initial value of the first variable to the first terminal.

[0043] The switching response message is a request confirmation of the first switching request message by the second access network device.

[0044] 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.

[0045] In the present application, after sending the initial value of the first variable to the first terminal, the second access network device can send the second initial value of the first variable to the first terminal again, 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 disordered data packets.

[0046] In a fourth aspect, the present application provides a switching method, which can be applied to a first access network device. For example, it can be performed by the first access network device, or it can also be performed by a component (such as a chip, a chip system, etc.) configured in the first access network device, or it can also be implemented by a logic module or software that can implement all or part of the functions of the first access network device, and the present application does not limit this.

[0047] Exemplarily, the method includes: sending a third switching request message to a second access network device, the third switching request message is used to request to switch the first terminal 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 in a receiving window that is not submitted to the upper layer, 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.

[0048] In the present application, after sending the initial value of the first variable to the first terminal, the second access network device can send the second initial value of the first variable to the first terminal again, so that the first terminal can update the initial value of the first variable, so that after the first terminal accesses the second access network device, it can use the updated second initial value to receive the data packet of the MBS session from the second access network device, effectively avoiding the possibility of the terminal receiving disordered data packets. In a fifth aspect, the present application provides a communication device, including a module or unit for implementing the method in any aspect and any possible implementation method of any aspect. It should be understood that each module or unit can implement the corresponding function by executing a computer program.

[0049] In a fifth aspect, the present application provides a communication device, comprising a processor, wherein the processor is used to execute the method described in any aspect and any possible implementation manner of any aspect.

[0050] The device 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 methods described in the above aspects may be implemented.

[0051] The apparatus may further include a communication interface, and 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.

[0052] 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 methods of any of the aspects, for example, receiving or processing the data and / or information involved in the above methods.

[0053] In one possible design, the chip system also includes a memory, which is used to store program instructions and data, and the memory is located inside or outside the processor.

[0054] The chip system may be composed of the chip, or may include the chip and other discrete devices.

[0055] 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.

[0056] In an eighth aspect, the present application provides a computer program product, comprising: a computer program (also referred to as code, or instruction), which, when executed, enables a computer to execute the method in the first aspect and any aspect and any possible implementation of any aspect.

[0057] In a ninth aspect, the present application provides a communication system, comprising the aforementioned first access network device and second access network device.

[0058] 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

[0059] Figure 1 is a schematic diagram of the architecture of a communication system applicable to an embodiment of the present application;

[0060] Figure 2 It is a schematic diagram of the MBS transmission process;

[0061] Figure 3 It is a schematic diagram of a multicast service transmission architecture;

[0062] Figure 4 This is a schematic diagram of a lossless switching process based on an Xn interface provided in an embodiment of the present application;

[0063] Figure 5 This is a schematic diagram of a lossless switching process based on the N2 interface provided in an embodiment of the present application;

[0064] Figure 6 is a schematic flow chart of a conditional switching method provided in an embodiment of the present application;

[0065] Figures 7 to 11 is a schematic flow chart of a switching method provided in an embodiment of the present application;

[0066] Fig.12 and Fig.13 is a schematic block diagram of a device provided in an embodiment of the present application;

[0067] Fig.14 It is a structural diagram of the wireless access network device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0068] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0069] To facilitate understanding of the embodiments of the present application, the following points are first explained:

[0070] First, in the embodiments of the present application, the use of prefixes such as "first" and "second" is only to facilitate the distinction and description of different things belonging to the same name category, and does not restrict the order, size or quantity of the things. For example, "first access network device" and "second access network device" are just different devices, and do not limit the number of devices or the priority relationship.

[0071] 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 includes indirect sending through the air interface by other units or modules. "Receiving a second initial value from a 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 directly receiving from the second access network device through the air interface, and also includes indirectly receiving 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.

[0072] 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.

[0073] It is understandable that before the information is sent from the source end to the destination end, it may be subjected to necessary processing, such as encoding, modulation, etc. After receiving the information from the source end, the destination end may also perform corresponding processing, such as decoding, demodulation, etc., so as to interpret the valid information from the source end. Similar expressions in this application can be understood similarly and will not be repeated.

[0074] 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: A exists alone, A and B exist at the same time, and B exists 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 it 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" 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.

[0075] 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 with the information to be indicated; it may also be possible to indicate only a part of the information to 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.

[0076] 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.

[0077] 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. Each table does 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 each table can also use other names that can be understood by the communication device, and the values ​​or representations of its parameters can also be 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.

[0078] Sixth, in the embodiments of the present application, descriptions such as "when...", "in the case of...", "if" and "if" all mean that under certain objective circumstances, the device (such as an access network device or terminal) will make corresponding processing, which is not a limited 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.

[0079] Seventh, the pre-defined in the present application can be understood as: define, pre-define, store, pre-store, pre-negotiate, pre-configure, solidify, or pre-burn.

[0080] Eighth, the storage involved in this application may refer to storage in one or more memories. The one or more memories may be set separately or integrated in an encoder or decoder, a processor, or a communication device. The one or more memories may also be partially set separately and partially integrated in a decoder, a processor, or a communication device. The type of memory may be any form of storage medium, which is not limited by this application.

[0081] The technical solution 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), sidelink (SL) communication system, worldwide 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).

[0082] 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.

[0083] The radio access network (RAN) device in this application is a device with wireless transceiver function. The radio access network device can provide wireless communication function services and can access the terminal to the wireless network. The radio access network device can be a node in the radio access network, referred to as a RAN node.

[0084] In a possible scenario, a RAN node may be a base station (BS), an evolved NodeB (eNodeB), a transmission reception point (TRP), a home evolved NodeB (or home Node B, HNB), an access point (AP) of wireless fidelity (Wi-Fi), 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 may also be a device that performs base station functions in a device to device (D2D) communication system, a vehicle to everything (V2X) communication system, a machine to machine (M2M) communication system, and an Internet of Things (IoT) communication system. A RAN node may also be a RAN node in a non terrestrial network (NTN), that is, a RAN node may be deployed on a high altitude platform or a satellite. The RAN node can be a macro base station, a micro base station or an indoor station, a relay node or a donor node, or a wireless controller in a cloud radio access network (CRAN) scenario, a node in an open radio access network (O-RAN or ORAN) scenario, etc. Optionally, the RAN node can also be a server, a wearable device, a vehicle or an onboard device, etc. For example, the RAN node in the V2X technology can be a road side unit (RSU). Of course, the RAN node can also be a node in the core network.

[0085] 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 can also be included in the same network element, such as a baseband unit (BBU). The RU can be included in a radio frequency device or a radio frequency unit, such as a remote radio unit (RRU), an active antenna unit (AAU) or a remote radio head (RRH).

[0086] In different systems, CU (or CU-CP and CU-UP), DU or RU may also have different names, but those skilled in the art can understand their meanings. For example, in the ORAN system, CU may also be called an open CU (O-CU), DU may also be called an open DU (O-DU), CU-CP may also be called an open CU-CP (O-CU-CP), CU-UP may also be called an open CU-UP (O-CU-UP), and RU may also be called an open RU (O-RU).

[0087] Among them, any unit in 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 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.

[0088] 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.

[0089] A terminal can be a device that provides voice / data connectivity to a user, for example, a handheld device with wireless connection function, a vehicle-mounted device, etc. At present, some examples of terminals can be: mobile phones, tablet computers (pad), computers with wireless transceiver functions (such as laptops, PDAs, etc.), mobile Internet devices (mobile internet devices, MIDs), virtual reality (virtual reality, VR) devices, augmented reality (augmented reality, AR) devices, wireless terminals in industrial control, wireless terminals in self-driving, drones, wireless terminals in remote medical, 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 (session initiation protocol, SIP) phones, wireless local loop (wireless local loop, WLL) stations, personal digital assistants (personal digital assistants) assistant, PDA), handheld devices with wireless communication function, computing devices or other processing devices connected to a wireless modem, vehicle-mounted devices, wearable devices, terminals in 5G networks or terminals in future evolved public land mobile communication networks (public land mobile network, PLMN), etc.

[0090] Among them, wearable devices can also be called wearable smart devices, which are a general term for the intelligent design and development of wearable devices for daily wear using wearable technology, 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 clothes or accessories. Wearable devices are not only hardware devices, but also realize powerful functions through software support, data interaction, and cloud interaction. Broadly speaking, wearable smart devices include full-featured, large-sized, and independent of smartphones to achieve complete or partial functions, 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.

[0091] In addition, the terminal can also be a terminal in the IoT system. IoT is an important part of the future development of information technology. Its main technical feature is to connect objects to the network through communication technology, thereby realizing an intelligent network of human-machine interconnection and object-to-object interconnection. IoT technology can achieve massive connections, deep coverage, and terminal power saving through narrow band (NB) technology, for example.

[0092] 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.

[0093] The terminal in the present application may be a virtualized device, for example, implemented by general hardware and instantiated virtualization functions, or by dedicated hardware and instantiated virtualization functions. The general hardware may be a server, for example, a cloud server.

[0094] It should be understood that the present application does not limit the specific forms of the wireless access network equipment and terminals.

[0095] Figure 1 1 is a schematic diagram of the architecture of a communication system 100 applicable to the method provided in the embodiment of the present application. Figure 1 As shown, the communication system 100 includes a wireless access network 10 and a core network 20. Optionally, the communication system 100 may also include the Internet 30. The wireless access network 10 may include at least one wireless access network device (such as Figure 1 110a and 110b), and may further include at least one terminal (such as Figure 1 120a-120j in FIG.

[0096] The terminal can be connected to the wireless access network equipment by wireless means, and the wireless access network equipment can be connected to the core network by wireless or wired means. The core network equipment and the wireless access network equipment can be independent and different physical devices, or the functions of the core network equipment and the logical functions of the wireless access network equipment can be integrated on the same physical device, or part of the functions of the core network equipment and part of the functions of the wireless access network equipment can be integrated on one physical device. Terminals and wireless access network equipment can be connected to each other by wired or wireless means.

[0097] The wireless access network equipment and the terminal, the wireless access network equipment, and the terminals can communicate through the authorized spectrum, through the unlicensed spectrum, or through both the authorized spectrum and the unlicensed spectrum; they can communicate through the spectrum below 6 gigahertz (GHz), through the spectrum above 6 GHz, or through the spectrum below 6 GHz and the spectrum above 6 GHz at the same time. The embodiments of the present application do not limit the spectrum resources used for wireless communication.

[0098] The wireless access network device may be a base station deployed in the air, such as a satellite base station 110a; or may be a base station deployed indoors, such as a micro base station or an indoor station 110b.

[0099] The terminal may be a terminal deployed in the air, such as Figure 1 The helicopter or drone 120i in the example; it can also be a terminal deployed on the ground, such as Figure 1 The mobile phones 120a, 120e, 120f and 120j, the vehicle 120b, the computer 120g, the printer 120h, etc.

[0100] Wireless access network equipment and terminals can be fixed or mobile. For example, wireless access network equipment and terminals can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; they can also be deployed on the water surface; they can also be deployed in the air on aircraft, balloons and artificial satellites.

[0101] The roles of wireless access network equipment and terminals can be relative. For example, Figure 1 The helicopter or drone 120i in the figure can be configured as a mobile base station. For those 120j that access the wireless access network 10 through 120i, 120i is a base station; but for 110a, 120i is a terminal, that is, 110a and 120i communicate through the wireless air interface protocol. Of course, 110a and 120i can also communicate through the interface protocol between wireless access network devices. In this case, relative to 110a, 120i is also a base station. Therefore, wireless access network devices and terminals can be collectively referred to as communication devices. Figure 1 110a, 110b and 120a-120j in the figure can be called communication devices having their respective corresponding functions, such as communication devices having base station functions, or communication devices having terminal functions.

[0102] It should be understood that Figure 1 This is just a schematic diagram. The communication system may also include other devices, such as wireless relay devices and wireless backhaul devices. Figure 1 Not drawn in.

[0103] MBS is a service for multiple terminals, such as live broadcast service, public safety service, batch software update service, etc. In this application, MBS, multicast, MBS service, MBS session, multicast service, and multicast session can be interchangeable. Figure 2 and Figure 3 Introduce the transmission process and transmission architecture of MBS.

[0104] Figure 2 is a schematic diagram of the MBS transmission process. Figure 2 As shown, first the server 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.

[0105] like Figure 2 As shown, the server sends the MBS service to the core network. When the core network sends the MBS data packet to the access network device, it 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 the MBS data packet to the terminal, the data packet is transmitted through the MBS radio bearer (abbreviated as MRB). An MRB has two transmission modes: 1. point to multi-point (PTM) transmission; 2. point to point (PTP) transmission.

[0106] Multicast services are designed for services with high QoS requirements and can provide the same QoS level as unicast services. For multicast services, the core network can manage the terminals joining and exiting the multicast services, and the access network equipment and core network equipment can maintain the information of the terminals in the multicast service group. The transmission between the core network and the access network relies on the protocol data unit (PDU) session, thereby introducing the MBS QoS flow; RAN supports both PTP and PTM transmission modes to send data to the terminal, and supports dynamic switching between PTP and PTM controlled by the RAN.

[0107] Figure 3 FIG. 1 shows a multicast service transmission architecture. Figure 3 As shown, Figure 3As shown, between the core network and the access network, the multicast service is transmitted through the MBS session, and the MBS session includes the MBS QoS flow (or multicast QoS flow). The MBS session can be associated with the PDU session of the terminal, and the MBS QoS flow is associated with the unicast QoS flow in the PDU session. The core network device can control the state of the MBS session to be activated or deactivated, and the terminal does not perceive the state of the MBS session.

[0108] When the access network device sends multicast services to the terminal, it can use the PTM or PTP transmission mode. In the PTM mode, the multicast service data can be scrambled using the group radio network temporary identifier (G-RNTI); in the PTP mode, the multicast service data is scrambled using the cell radio network temporary identifier (C-RNTI). In addition, the access network device can control the transmission mode to dynamically switch between PTM and PTP.

[0109] 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.

[0110] Take Xn switching as an example, combined with Figure 4 This section describes the information that needs to be exchanged between the source access network device and the target access network device during Xn lossless switching.

[0111] Figure 4 FIG. 1 is a schematic diagram of a lossless switching process based on an Xn interface provided in an embodiment of the present application. Figure 4 As shown, the method 400 may include S401 and S402. Each step in the method 400 is described in detail below.

[0112] 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:

[0113] Group 1: MBS session identity (ID), area session ID, MBS session associated information, where the multicast session associated information includes MBS QFI and mapped unicast QFI;

[0114] Group 2: MBS session ID, area session ID, MBS service area, QoS flow parameters; or,

[0115] Group 3: MRB ID, MRB mapping information, and MRB progress information, wherein the MRB progress information includes the PDCP SN, and 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.

[0116] 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.

[0117] 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 (data forwarding address), MRB progress information.

[0118] 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.

[0119] 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 what data to forward based on the received MRB progress information.

[0120] It can be understood that the above-mentioned switching response message can also be called a switching request confirmation message.

[0121] Take N2 switching as an example, combined with Figure 5 During the N2 lossless switching process, the source access network device needs to provide information to the target access network device.

[0122] Figure 5 A schematic diagram of a lossless switching process based on the N2 interface provided in an embodiment of the present application. Figure 5 As shown, the method 500 may include S501 to S504. The steps shown in the method 500 are described in detail below.

[0123] 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.

[0124] 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.

[0125] 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: the first group, MBS session ID, area session ID, MBS service area, QoS flow parameters; the second group, MRB ID, MRB mapping information, MRB progress information.

[0126] For the next generation application protocol (NGAP) interface, the core network device may also carry at least one group of information in the switching request message and send it to the target access network device: Group 1: MBSsession ID, area session ID; Group 2: MBS session associated information.

[0127] 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.

[0128] S504, the core network device sends the switching response message to the source access network device. Correspondingly, the source access network device receives the switching response message.

[0129] 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, MRB progress information.

[0130] During the new radio (NR) handover process, the wireless 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 will lead to handover failure. At this time, the terminal will recognize the failure of the wireless link and initiate RRC reconstruction.

[0131] At present, in order to reduce the probability of handover failure and improve the reliability of handover, CHO is proposed. CHO can allow the access network device to send the handover command (with the wireless parameter configuration of the candidate target base station and the triggering conditions for handover execution) to the terminal in advance before the wireless environment between the terminal and the access network device further deteriorates, so that the terminal can know how to access the target access network device in advance. After the terminal finds the target access network device that meets the handover triggering conditions among the candidate target access network devices, it can independently decide to initiate the handover.

[0132] Figure 6 is a schematic flow chart of the conditional switching method provided in the embodiment of the present application. Figure 6 As shown, the method 600 may include S601 to S611. The steps shown in 600 are described in detail below.

[0133] S601, the source access network device transmits data with the terminal, and the data is unicast service data.

[0134] S602, the source access network device determines a conditional switch.

[0135] S603: The source access network device sends a switching request to multiple target access network devices. The switching request is used to request to switch the terminal from the source access network device to the target access network device.

[0136] 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.

[0137] 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.

[0138] S605: The source access network device sends an RRC reconfiguration message to the terminal.

[0139] The RRC reconfiguration message carries the radio parameter configurations and switching execution trigger conditions of multiple candidate target access network devices.

[0140] S606: The terminal sends an RRC reconfiguration completion message to the source access network device.

[0141] After the terminal sends an RRC reconfiguration completion message to the source access network device, the terminal starts 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 data packets of unicast services to the terminal.

[0142] S607, the source access network device sends an early status transfer message, or an early status indication message, to multiple target access network devices.

[0143] The early status transfer message may be triggered after the source access network device continues to send data packets of unicast services to the terminal, and is used to update the target access network device with the progress of the data packets sent by the source access network device to the terminal.

[0144] 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.

[0145] S608, completing the conditional switching, and the terminal switches from the source access network device to the first target access network device.

[0146] 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.

[0147] 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.

[0148] S610, the source access network device sends an SN status sending message to the first target access network device.

[0149] S611, the source access network device sends a switching cancellation message to other target access network devices.

[0150] In order to ensure the success rate of MBS handover, it is proposed that CHO can be applied to handovers involving MBS sessions. However, there is currently no solution for CHO to make additional enhancements or adaptations for MRB handovers. From the current RRC signaling format, the CHO configuration directly references the RRC reconfiguration message (that is, the CHO configuration includes the RRC reconfiguration message), and there is no restriction that the CHO configuration cannot include the MRB configuration. In other words, the target access network device can include the MRB configuration in the CHO configuration to support multicast CHO.

[0151] For the CHO switching process of multicast, please refer to the above Figure 6The description of the CHO switching process shown in FIG. 1 is different from the description of the CHO switching process in FIG. 1 . 1. In the multicast CHO switching process, the switching request message sent by the source access network device to multiple candidate target access network devices includes MBS information (i.e., the switching request message sent by S603 also carries relevant information about MBS); 2. Multiple candidate target access network devices will include MBS information in the switching response message sent (i.e., the switching response message sent by S604 also carries MBS information). 3. During the terminal's evaluation of the switching conditions, the source access network device can continue to send MBS data packets to the terminal, and the source access network device will send MBS data packets to multiple target access network devices based on the MBS information carried in the switching request message, so that after the terminal accesses the target access network device, the target access network device can directly send data packets to the terminal.

[0152] For the description of MBS information, please refer to the above Figure 5 The information carried in the switching request message and the switching response message will not be repeated here.

[0153] However, when CHO is applied to handovers involving MBS sessions, the following problems are found:

[0154] 1. In combination with the above description of lossless switching of MBS, it can be obtained that in order to ensure that there is no data packet loss when the terminal switches from the source access network device to the candidate target access network device. Therefore, in 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 the MRB on the local side 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, so that 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.

[0155] However, when CHO is applied to a handover involving an MBS session, the terminal may continue to receive data packets of multicast services from the source access network device for a period of time during the CHO condition evaluation phase, and the data forwarding performed between the source access network device and the candidate target access network device may also be performed continuously. Since the progress information of the MRB 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 data packets of the MBS session based on the progress information of the MRB carried in the handover request message. However, since the terminal continues to receive data packets from the source access network device during the CHO condition evaluation phase, resulting in changes in the progress of the MRB, if the candidate target access network device still caches the data packets of the MBS session based on the progress information of the MRB previously received, more MBS data packets will be cached, and more resources will be required.

[0156] In view of this, the present application provides a switching method and related devices. In the method, the source access network device can send MRB progress information to the target access network device in a timely manner, so that the target access network device can delete the data packets cached at the local end based on the MRB progress information, so as to reduce the resources required for the target access network device to cache the data packets.

[0157] 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.

[0158] Exemplarily, the identification value of the PDCP SDU can be called COUNT. COUNT is composed of HFN and PDCP SN. Among them, the PDCP SN will be added to the PDU for transmission, and the HFN is maintained by the transmitter and the receiver. The PDCP PDU sent by the transmitter to the receiver contains the SN number, but does not contain COUNT or HFN. The receiving side calculates the HFN based on the received SN number and restores the COUNT value. That is, the receiving side combines the calculated HFN and the SN number carried in the PDCP PDU into the COUNT corresponding to the PDCP PDU. PDCP receives the PDCP PDU submitted by the lower layer in the form of a receiving window plus a reordering timer. The receiving window moves according to the update of the lower boundary state variable of the receiving window (i.e., RX_DELIV). Since the state variable is described by the COUNT value, after the PDCP receives the PDCP PDU, it needs to determine the correct HFN and COUNT based on the SN in the PDCP PDU subheader and the current receiving window state variable, so as to perform decryption and integrity verification based on the obtained COUNT.

[0159] 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 at the source access network device for a period of time. At this time, the selected 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 by the handover response message is greater than or equal to 2 p-1 , then the RX_DELIV carried by the switching response message is considered expired. In other words, if the terminal still determines the HFN according to the initial value received before, an incorrect HFN will be obtained, resulting in confusion in the received data packets.

[0160] In view of this, the present application provides a switching method and related apparatus. In the method, the source access network device can send the updated value of RX_DELIV to the target access network device in a timely manner, so that the terminal can use the updated value of RX_DELIV to receive data packets after accessing the target access network device.

[0161] 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 activated again, 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 allow 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 the following Fig.11 The method shown is implemented.

[0162] In view of this, the present application provides a switching method and related apparatus. In the method, the access network device can send an MRB configuration to the terminal after the MBS service is activated, so that the terminal can continue to receive data packets of the MBS session after accessing the target access network device.

[0163] Combine the following Figures 7 to 11 , describes in detail the method provided in the embodiment of the present application. The method can be applied to Figure 1 The communication system shown, but the embodiments of the present application are not limited to this.

[0164] exist Figures 7 to 11 In the flowchart shown, the method is shown from the perspective of the interaction of the communication device, but the present application does not limit the execution subject of the method. Figures 7 to 11 The access network device in the method may be a chip, a chip system, or a processor that supports the access network device to implement the method, or may be a logic module or software that can implement all or part of the functions of the access network device; Figures 7 to 11 The terminal in the method may be a chip, a chip system, or a processor that supports the terminal to implement the method, or may be a logic module or software that can implement all or part of the terminal functions.

[0165] Figure 7 is a schematic flow chart of the switching method provided in the embodiment of the present application. Figure 7 As shown, the method 700 may include S701 to S704. Each step in the method 700 is described in detail below.

[0166] 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.

[0167] 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 first terminal. In other words, the first sequence number is the maximum sequence number among the sequence numbers corresponding to at least one first data packet sent by the first access network device to the first terminal. In other words, 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 switching request message.

[0168] The first sequence number may be a PDCP SN number, COUNT or a hyper frame number (HFN), or other parameters that can be used to identify the transmission order of data packets, which is not limited in the present application. COUNT is an identification value of the PDCP SDU.

[0169] It can be understood that the first terminal in the present 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.

[0170] It can also be understood that the first switching request message is the first switching request message sent to multiple target access network devices after the first access network device determines the conditional switching. The first switching request message is used to request the first terminal to be switched from the first access network device to the second access network device.

[0171] 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.

[0172] 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 the present application can be an access network device to which the first terminal accesses among the multiple candidate target access network devices.

[0173] Optionally, before S701, the method 700 further includes: the first access network device determines to perform conditional switching.

[0174] 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.

[0175] 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).

[0176] It can be understood that, in the present 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.

[0177] 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.

[0178] 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 first terminal, and the second sequence number is greater than the first sequence number. In other words, the second sequence number is the maximum sequence number among the sequence numbers corresponding to at least one second data packet sent by the first access network device to the first terminal. In other words, 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.

[0179] Similar to the first sequence number, the second sequence number may be a PDCP SN number, a COUNT or a HFN, or other parameters that may be used to identify the transmission order of data packets, which is not limited in the present application.

[0180] 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.

[0181] It can also be understood that, after receiving the first switching request message, the second access network device may send a switching response message in response to the first switching request to the first access network device. The switching response message may carry the second sequence number.

[0182] Exemplarily, 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 indicated by the second access network device to the first access network device.

[0183] For example, if the first access network device sends the second sequence number to the second access network device at intervals of the first time length after sending the first switching 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 time length, the above S702 may not be executed. That is, after S701, S703 is continued to be executed, and at this time the first sequence number is equal to the second sequence number.

[0184] 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.

[0185] 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.

[0186] 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 packet of the first MBS session based on the second sequence number.

[0187] Optionally, the second access network device may delete, from the cached data packets of the first MBS session, data packets whose sequence numbers are less than or equal to the second sequence number.

[0188] The method 700 provided in the present application is applied to the conditional switching scenario to solve the problem of excessive resources required by the target access network device to cache the data packets of the MBS session. In the embodiment of 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 last MBS data packets sent by the first access network device to the terminal in 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 of the cached 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 first access network device side to cache the data packets of the MBS session can be effectively reduced, and the resource utilization rate can be improved. At the same time, it can also prevent the second access network device from sending duplicate MBS data packets to the terminal after the terminal accesses the second access network device.

[0189] Optionally, the second sequence number may be carried by the following messages or signaling: a second switching request message, an early status transfer signaling, or an MBS early status transfer signaling.

[0190] In the first possible implementation, the second sequence number is carried through early status transfer signaling.

[0191] Among them, early status transfer signaling Figure 6 The flowchart shown is used to update the signaling of the data radio bearer (DRB) progress. Figure 6 The early status transfer signaling shown includes the procedure stage information element indicating the progress of DRB transmission.

[0192] The present 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 sage information element, and include a COUNT value (HFN and SN) or SN for the MRB in the DL discarding branch. Based on this solution, the progress information of the MRB 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 data packet of the MRB session.

[0193] In a second possible implementation, the present application introduces new signaling to carry the second sequence number. The new signaling is related to the MBS and can be used to indicate the progress of one MBS session or the progress of multiple MBS sessions.

[0194] For example, the new signaling may be an MBS early status transfer signaling. The MBS early status transfer signaling may include an MBS procedure sage information element, the MBS procedure sage information element may include a DL Discarding branch, and the DL discarding branch includes a COUNT value (HFN and SN) or SN for the MRB.

[0195] 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 MBSsession, thereby saving the signaling overhead when updating the MRB progress.

[0196] In a third possible implementation, 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 first terminal from the first access network device to the second access network device.

[0197] The second switching request message is a switching request message sent again by the first access network device to the second access network device after sending the first switching request message based on the trigger condition of sending the second sequence number, wherein the trigger condition of sending the second sequence number is the first duration or sending the first number of second data packets.

[0198] 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 to only update the MRB progress.

[0199] 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.

[0200] Optionally, before S704, the method 700 further includes: the second access network device sends 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.

[0201] The third data packet and the first data packet (or the second data packet) are data packets of the same MBS session.

[0202] Similar to the first sequence number, the third sequence number may be a PDCP SN number, a COUNT or a HFN, or other parameters that may be used to identify the transmission order of data packets, which is not limited in the present application.

[0203] Optionally, before S704, the method 700 further includes: the first access network device sends 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 at least one third data packet from the first access network device.

[0204] The at least one third data packet and the at least one first data packet belong to the same MBS session.

[0205] 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.

[0206] Optionally, the second access network device may cache the received at least one third data packet.

[0207] The following will be Figure 7 Based on the embodiment shown, combined with Figure 8 The specific process of the switching method provided by this application is introduced. Figure 7 The contents already introduced in the illustrated embodiment will not be repeated here. Figure 8 In the switching method shown, 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 explanation.

[0208] Figure 8 FIG. 1 is another schematic flow chart of the switching method provided in an embodiment of the present application. Figure 8 As shown, the method 800 may include S801 to S812. The steps shown in the method 800 are described in detail below.

[0209] S801, the source access network device transmits data with the terminal, and the data is the data of the MBS session.

[0210] S802, the source access network device determines the conditional switching.

[0211] S803: The source access network device sends a first switching request message to multiple target access network devices. Correspondingly, the multiple target access network devices receive the first switching request message from the source access network device.

[0212] 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.

[0213] The first switching request is used to request to switch the terminal from the source access network device to any target access network device among multiple target access network devices.

[0214] For the description of the first switching request, please refer to the relevant description in S701, which will not be repeated here.

[0215] 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.

[0216] 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.

[0217] Exemplarily, each of 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.

[0218] For the description of the third serial number and the first variable, please refer to the relevant description in method 700, which will not be repeated here.

[0219] 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.

[0220] The RRC reconfiguration message includes a plurality of radio parameter configurations of target access network devices and a switching command of a switching execution trigger condition.

[0221] S806, the terminal sends a message indicating that the RRC reconfiguration is completed to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0222] After S806, the terminal still maintains the connection with the source access network device and starts to evaluate the switching condition. During the process of the terminal evaluating the switching condition, the source target access network device can continue to send at least one second data packet to the terminal; and the first access network device continues 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.

[0223] 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.

[0224] 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.

[0225] For the description of the second serial number, please refer to the relevant description in the previous method 700, which will not be repeated here.

[0226] 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.

[0227] The process may refer to the description of S704 and will not be described again here.

[0228] S809, completing the conditional switching, and the terminal switches from the source access network device to the first target access network device.

[0229] S810. The first target access network device sends a switching success message to the source access network device.

[0230] The switching success message is used to notify the source access network device of successfully accessing the first target access network device.

[0231] 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.

[0232] S812, the source access network device sends a switching cancellation message to other target access network devices. Correspondingly, the other target access network devices receive the switching cancellation message from the source access network device.

[0233] 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 for the target access network device to cache MBS data packets, and improve resource utilization.

[0234] Fig. 9 FIG. 1 is another schematic flow chart of the switching method provided in the embodiment of the present application. Fig. 9 As shown, the method 900 may include S901 to S904. Each step in the method 900 is described in detail below.

[0235] S901, a first access network device sends a third handover request message to a second access network device, the third handover request message being 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.

[0236] 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.

[0237] Optionally, before S901, the method 900 further includes: the first access network device determines to perform conditional switching.

[0238] 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.

[0239] The first variable indicates an identification value of the first PDCP SDU in the receiving window that is not delivered to the upper layer. For example, the first variable is RX_DELIV.

[0240] S903: The first access network device sends a first initial value of a first variable to the first terminal. The first initial value of the first variable may be carried in an RRC reconfiguration message.

[0241] 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.

[0242] 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.

[0243] For the description of the reference value, please refer to the previous description and will not be repeated here.

[0244] 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.

[0245] 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.

[0246] The method 900 provided in the present application is applied to the conditional switching scenario to solve the problem of the initial value of the first variable on the terminal side being out of date. In the embodiment of the present application, after sending the initial value of the first variable to the first terminal, the second access network device can send the second initial value of the first variable to the first terminal again, so that the first terminal can update the initial value of the first variable, so that after the first terminal accesses the second access network device, it can use the updated second initial value to receive the data packet of the MBS session from the second access network device, effectively avoiding the possibility that the terminal receives a disordered data packet.

[0247] 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.

[0248] Mode 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.

[0249] 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. Correspondingly, the first terminal receives the second initial value.

[0250] 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.

[0251] Mode 2: The second access network device sends the initial value of the first variable to the first terminal through the first access network device. That is, the first terminal does not access the second access network device.

[0252] Example 1: 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.

[0253] 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.

[0254] Exemplarily, when the number of data packets of the MBS session 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 data packets of the MBS session 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.

[0255] The preset value and the size of the receiving window satisfy a preset relationship.

[0256] Exemplarily, the preset relationship is: preset value = k × size of receiving window. Where 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.

[0257] 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.

[0258] Example 2: When 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.

[0259] The first information is used to request a second initial value of the first variable.

[0260] 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.

[0261] Among them, the description of the preset value can refer to the description in the above example one, which 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 is necessary to first determine the size of the preset value. The preset value and the size of the receiving window satisfy a preset relationship. The preset relationship can refer to the description in method one. When calculating the size N of the interface window, if the first access network device is not sure 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.

[0262] Because 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.

[0263] The following will be Fig. 9 Based on the embodiment shown, combined with Fig.10 The specific process of the switching method provided by this application is introduced. Fig. 9 The contents already introduced in the illustrated embodiment will not be repeated here. Fig.10 In the switching method shown, 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 explanation.

[0264] Fig.10 FIG. 1 is another schematic flow chart of the switching method provided in an embodiment of the present application. Fig.10 As shown, the method 1000 may include S1001 to S1019. The steps shown in the method 1000 are described in detail below.

[0265] S1001, the source access network device transmits data with the terminal, and the data is MBS data.

[0266] S1002, the source access network device determines a conditional switch.

[0267] S1003: The source access network device sends a first switching request message to multiple target access network devices. Correspondingly, the multiple target access network devices receive the first switching request message from the source access network device.

[0268] The above S1001 to S1003 are the same as the process shown in the above S801 to S803, and will not be repeated here.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] The RRC reconfiguration message includes a plurality of radio parameter configurations of target access network devices and a switching command of a switching execution trigger condition.

[0273] Optionally, the RRC reconfiguration message includes initial values ​​of first variables configured by multiple target access network devices for the terminal.

[0274] 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.

[0275] S1006, the terminal sends a message indicating that the RRC reconfiguration is completed to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0276] After S1006, the terminal still maintains the connection with the source access network device and starts to evaluate the switching condition. During the process of the terminal evaluating the switching condition, multiple target access network devices can continue to send MBS data packets to the terminals connected thereto; the first access network device can continue to send at least one second data packet to the terminal.

[0277] The description of the at least one second data packet may refer to the description of method 700 and will not be repeated here.

[0278] S1007: The multiple target access network devices determine that the number of MBS data packets sent is greater than a preset value.

[0279] S1008, the multiple target access network devices send the second initial value of the first variable to the source access network device respectively. Correspondingly, the source access network device receives the second initial value of the first variable from the multiple target access network devices.

[0280] For the description of the second initial value, please refer to the description in method 700, which will not be repeated here.

[0281] 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 as to calculate the COUNT value using the initial value of the first variable from the first target access network device after switching to the first target access network device among the multiple target access network devices.

[0282] S1010: The source access network device determines that the number of at least one second data packet is greater than a preset value.

[0283] 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.

[0284] For the description of the first information, please refer to the description in method 700, which will not be repeated here.

[0285] 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.

[0286] 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.

[0287] For the description of the second initial value, please refer to the description in method 700, which will not be repeated here.

[0288] S1014, completing the conditional switching, the terminal switches from the source access network device to the first target access network device.

[0289] 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.

[0290] 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.

[0291] The switching success message is used to notify the source access network device of successfully accessing the first target access network device.

[0292] 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.

[0293] S1017, the source access network device sends a switching cancellation message to other target access network devices. Correspondingly, the other target access network devices receive the switching cancellation message from the source access network device.

[0294] S1018: The first target access network device determines that the data packet sent for the MBS session is greater than a preset value.

[0295] 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.

[0296] It should be noted that the above steps S107 to S1013, as well as S1018 and S1019 are optional steps. For example, after S106, when S107 to S1010 are continued to be executed, S1011 to S1013, as well as S1018 and S1019 may not be executed; for another example, after S106, when S1011 to S1013 are continued to be executed, S107 to S1010, as well as S1018 and S1019 may not be executed; for another example, after S106, when S107 to S1013 are not continued to be executed, S1018 and S1019 may be continued after S1017.

[0297] The improved method of the embodiment of the present application can effectively avoid the possibility of the terminal receiving disordered data packets.

[0298] It is understandable that the above Figure 7 and Fig. 9 (or Figure 8 and Fig.10 ) can be implemented in combination with each other or independently. Figure 7 and Fig. 9 ( Figure 8 and Fig.10 ) can be executed separately. Figure 7 or Fig. 9 ( Figure 8 or Fig.10 ) more or less of the steps shown; when Figure 7 and Fig. 9 (or Figure 8 and Fig.10 ), the communication method provided by the present application may include: the first access network device sends a switching request message (for example, a first switching request message or a third switching request message) to the second access network device for the first time, including a first sequence number, the second access network device sends a switching response message to the first access network device, including a second sequence number and a first initial value of the first variable, and the first access network device sends an RRC reconfiguration message to the first terminal. The first initial value of the first variable is carried. For other more detailed processes, please refer to the above Figure 7 and Fig. 9 (or Figure 8 and Fig.10 )Description of the embodiment shown.

[0299] Fig.11 FIG. 1 is a schematic flow chart of another switching method provided in an embodiment of the present application. Fig.11 As shown, the method 1100 may include S1101 to S1116. The steps shown in the method 1100 are described in detail below.

[0300] S1101, the source access network device transmits data with the terminal, and the data is MBS data.

[0301] S1102, the source access network device determines the conditional switching.

[0302] S1103, the source access network device sends a first switching request message to multiple target access network devices. The first switching request message carries a first identifier. Correspondingly, the multiple target access network devices receive the first switching request message from the source access network device.

[0303] The first identifier is used to identify an MBS session, and the state of the MBS session is deactivated.

[0304] 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 multiple target access network devices.

[0305] 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 state of the MBS session is deactivated, and carry the MRB configuration in the switching response message sent to the source access network device.

[0306] 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.

[0307] 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.

[0308] After S1106 , the terminal still maintains the connection with the source access network device and starts to evaluate the switching condition.

[0309] 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 configuration.

[0310] The first condition is that the state of the MBS session is activated. That is, when the state of the MBS session is activated, the source access network device sends the second information to the multiple target access network devices.

[0311] Exemplarily, the source access network device may consider that the first condition is met when it receives a notification message for activating the MBS session, or when the source access network device determines that the state of the MBS session is activated, or when the source access network device receives a group paging message from other access network devices.

[0312] S1108, the multiple target access network devices send RRC reconfiguration messages to the source access network device again. Correspondingly, the source access network device receives RRC reconfiguration messages from the multiple target access network devices. The RRC reconfiguration message carries the MRB configuration.

[0313] 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.

[0314] 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.

[0315] The description of the first condition can refer to the description in S1107, which will not be repeated here. That is, when the state of the MBS session is activated, multiple target access network devices send RRC reconfiguration messages to the source access network device again.

[0316] 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.

[0317] 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.

[0318] 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.

[0319] S1112, completing the conditional switching, the terminal switches from the source access network device to the first target access network device.

[0320] 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.

[0321] 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.

[0322] The switching success message is used to notify the source access network device of successfully accessing the first target access network device.

[0323] 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.

[0324] S1115, the source access network device sends a switching cancellation message to other target access network devices. Correspondingly, the other target access network devices receive the switching cancellation message from the original access network device.

[0325] S1116: When the first condition is met, the first target access network device sends an RRC reconfiguration message to the terminal, wherein the RRC reconfiguration message carries the MRB configuration. Correspondingly, the terminal receives the RRC reconfiguration message from the first target access network device.

[0326] The description of the first condition may refer to the description in S1107, which will not be repeated here. That is, when the state of the MBS session is activated, the first target access network device sends an RRC reconfiguration message to the terminal.

[0327] Exemplarily, the first target access network device may consider that the above-mentioned first condition is met when it receives a notification message for activating 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.

[0328] 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 MRB configuration may not be included in the RRC configuration message sent in S1116; 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 MRB configuration may not be included in the RRC configuration message sent in S1116.

[0329] 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 possible not 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.

[0330] 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 do not need to be executed; or, 2. After S1106, when continuing to execute S1110 and S1111, (S1107 to S1109) and / or S1116 do not need to be executed; or, 3. After S1106, when (S1107 to S1109) and / or (S1110 and S1111) are not continued, S1116 can be continued after S1115.

[0331] It should also be noted that when CHO is applied to a handover involving an MBS session, the CHO handover process may include: Fig.11More or fewer steps may be performed than those shown.

[0332] The method 1100 provided in the present application is applied to the conditional switching scenario to solve the problem that the access network device does not update the MRB configuration when the MBS service changes from the deactivated state to the activated state. In the embodiment of the present application, after the MBS service is activated, the MRB configuration can be carried in the RRC configuration so that the terminal can normally receive the data packets of the MBS session after accessing the target access network device.

[0333] Combination of the above Figures 1 to 11 The method provided in the embodiment of the present application is described in detail. Figure 12 to Figure 14 The device provided in the embodiment of the present application is introduced.

[0334] Fig.12 and Fig.13 Schematic diagram 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, and thus can also achieve the beneficial effects possessed by the above method embodiments.

[0335] Fig.12 is a schematic block diagram of the device provided in the embodiment of the present application. Fig.12 As shown, the device 1200 includes a transceiver module 1210 and a processing module 1220 .

[0336] One possible design is that the device 1200 is used to implement the above Figures 7 to 11 The function of the first access network device in the method embodiment shown in FIG.

[0337] Exemplarily, the transceiver module 1210 is used to: send a first switching request message to a second access network device, the first switching request message being used to request switching of a terminal from the first access network device to the second access network device, the first switching request message comprising 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; 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 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; wherein the at least one first data packet and the at least one second data packet belong to the same multicast broadcast service MBS.

[0338] Optionally, the processing module 1220 is used to: determine to perform conditional switching.

[0339] 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 in the receiving window that has not been submitted to the upper layer; and send the first initial value of the first variable to the terminal.

[0340] Optionally, the transceiver module 1210 is further used 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.

[0341] 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.

[0342] Exemplarily, the transceiver module 1210 is used to: send a third switching request message to a second access network device, the third switching request message is used to request to switch the first terminal to the second access network device; receive a switching response message from the second access network device, the switching response message includes a first initial value of a first variable, the first variable indicates an identification value of the first PDCP SDU in a receiving window that is not submitted to the upper layer, 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.

[0343] For a more detailed description of the transceiver module 1210 and the processing module 1220, please refer to Figures 7 to 11 The relevant description in the illustrated embodiment is directly obtained and will not be repeated here.

[0344] Another possible design is that the device 1200 is used to implement the above Figures 7 to 11 The function of the second access network device in the method embodiment shown in FIG.

[0345] 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 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 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 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; 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.

[0346] 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 indicates 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.

[0347] 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 is greater than the first initial value; and send the second initial value to the first access network device.

[0348] Optionally, the transceiver module 1210 is further used 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.

[0349] Optionally, the transceiver module 1210 is further used to: before the terminal accesses the second access network device, send a second initial value to the first access network device, and the second initial value is greater than the first initial value.

[0350] Optionally, the processing module 1220 is further used to: determine that the number of the MBS data packets sent by the second access network device is greater than a preset value.

[0351] 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 is used to request to switch the first terminal 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.

[0352] For a more detailed description of the transceiver module 1210 and the processing module 1220, please refer to Figures 7 to 11 The relevant description in the illustrated embodiment is directly obtained and will not be repeated here.

[0353] It should be noted that the device 1200 may include a sending module but not a receiving module. Alternatively, the device 1200 may include a receiving module but not a sending module. Specifically, it may depend on whether the above solution executed by the device 1200 includes a sending action and a receiving action. It is understandable that since the device 1200 has a communication function, it can also be called a communication device.

[0354] Fig.13 is another schematic block diagram of the device provided in the embodiment of the present application. Fig.13 As shown, the device 1300 includes one or more processors 1310. The processor 1310 may be a general-purpose processor or a dedicated processor, etc. For example, it may be a baseband processor or a central processing unit. The baseband processor may be used to process the communication protocol and communication data, and the central processing unit may be used to control the device (such as the first access network device, the second access network device or the chip, etc.), execute the software program, and process the data of the software program.

[0355] Optionally, in one design, the processor 1310 may include a program (also referred to as code or instruction), which may be executed on the processor 1310 to enable 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 ( Fig.13 (not shown), the circuit is used to implement the function of the first access network device or the second access network device in the above method embodiment.

[0356] For example, the processor 1310 may be configured to execute computer programs or instructions in the memory to implement Figures 7 to 11 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 illustrated embodiments.

[0357] 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 embodiments.

[0358] Optionally, the processor 1310 and / or the memory 1320 may include an artificial intelligence (AI) module, and the AI ​​module is used to implement AI-related functions. The AI ​​module may be implemented by 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.

[0359] Optionally, data may also be stored in the processor 1310 and / or the memory 1320. The processor and the memory may be provided separately or integrated together.

[0360] Optionally, the device 1300 may further include a communication interface 1330. The processor 1310 may also be sometimes referred to as a processing unit, which controls the device (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 device.

[0361] Optionally, the device 1300 further includes a communication interface 1330. The processor 1310 and the communication interface 1330 are coupled to each other. It can be understood that the communication interface 1330 can be a transceiver or an input-output interface.

[0362] It can be understood that since the device 1300 has a communication function, it can also be called a communication device.

[0363] When the device 1300 is used to implement Figures 7 to 11 When the method is used, the processor 1310 is used to execute the functions of the above processing unit, and the communication interface 1330 is used to execute the functions of the above transceiver module. Whether the communication interface 1330 is used to send or receive can be specifically determined by whether it is used to perform a sending action or a receiving action in the solution executed by the device 1300.

[0364] When the above-mentioned device 1300 is a chip applied to the first access network device, the chip implements the functions of the first access network device in the above-mentioned method embodiment. The chip of the first access network device receives a signal from other modules (such as a radio frequency module or an antenna) in the first access network device, and the signal may be sent by the second access network device to the first access network device; or, the chip of the first access network device sends a signal to other modules (such as a radio frequency module or an antenna) in the first access network device, and the signal may be sent by the first access network device to the second access network device.

[0365] When the above-mentioned device 1300 is a chip applied to the second access network device, the chip implements the functions of the second access network device in the above-mentioned method embodiment. The chip of the second access network device receives a signal from other modules (such as a radio frequency module or an antenna) in the second access network device, and the signal may be sent by the first access network device to the second access network device; or, the chip of the second access network device sends a signal to other modules (such as a radio frequency module or an antenna) in the second access network device, and the signal may be sent by the second access network device to the first access network device.

[0366] It can be understood that when the device 1300 is a first access network device or a second access network device, the communication interface 1330 can be a transceiver, which can specifically include a transmitter and a receiver, the transmitter is used to send signals, and the receiver is used to receive signals. When the device 1300 is a chip applied to the first access network device or the second access network device, the communication interface 1330 can be an input-output circuit, wherein the input circuit can be used for receiving, and the output interface can be used for sending.

[0367] Fig.14 1400 is a schematic diagram of the structure of a wireless access network device provided in an embodiment of the present application, for example, a schematic diagram of the structure of a base station. The base station 1400 can be applied to Figure 1In the system shown, the function of the second access network device in the above method embodiment is performed. As shown in the figure, the base station 1400 may include one or more of the following: one or more (DU+RU) 1410, one or more CU 1420. CU 1420 can communicate with the next generation core network (NG core). The DU may include at least one antenna 1411, at least one radio unit 1412, at least one processor 1414 and at least one memory 1414. The DU part is mainly used for receiving and transmitting radio frequency signals, converting radio frequency signals to baseband signals, and partial baseband processing. CU 1420 may include at least one processor 1422 and at least one memory 1421. CU 1420 and DU may communicate through an interface. Among them, the control plane (CP) interface may be Fs-C, such as F1-C, and the user plane (UP) interface may be Fs-U, such as F1-U. DU and RU may cooperate to jointly implement the functions of the physical (PHY) layer. A DU may be connected to one or more RUs. The functions of DU and RU can be configured in a variety of ways according to the design. For example, DU is configured to implement baseband functions, and RU is configured to implement mid-RF functions. For another example, DU is configured to implement high-level functions in the PHY layer, and RU is configured to implement low-level functions and RF functions in the PHY layer. The high-level functions in the PHY layer may include a portion of the functions of the PHY layer, which is closer to the MAC layer, and the low-level functions in the PHY layer may include another portion of the functions of the PHY layer, which is closer to the mid-RF side.

[0368] The CU 1420 is mainly used for baseband processing and controlling the base station. The DU and CU 1420 can be physically arranged together or physically separated, that is, a distributed base station. The CU 1420 is the control center of the base station and can correspond to Fig.12 The processing module in Fig.13 The processor in the CU 1420 may also be referred to as a processing unit, which is mainly used to complete the baseband processing function. For example, the CU 1420 may be used to control the base station to execute the operation flow of the access network device in the above method embodiment.

[0369] Specifically, the baseband processing on the CU and DU can be divided according to the protocol layer of the wireless network, for example, the functions of the packet data convergence protocol (PDCP) layer and above are set in the CU, and the functions of the protocol layers below the 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, and the DU implements the functions of the RLC layer, the MAC layer, and the PHY layer.

[0370] 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.

[0371] In one example, the CU 1420 may be composed of one or more boards, and the multiple 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 boards. In other words, a memory and a processor may be separately set on each board. It may also be that multiple boards share the same memory and processor. In addition, necessary circuits may be set on each board. The DU may be composed of one or more boards, and the multiple 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 boards. In other words, a memory and a processor may be separately set on each board. It may also be that multiple boards share the same memory and processor. In addition, necessary circuits may also be set on each board.

[0372] It should be understood that Fig.14 The base station 1400 shown is capable of implementing Figures 7 to 11 The method embodiment shown involves various processes of the first access network device or the second access network device. The operations and / or functions of each module in the base station 1400 are respectively to implement the corresponding processes in the above method embodiment. For details, please refer to the description in the above method embodiment. To avoid repetition, the detailed description is appropriately omitted here.

[0373] It should be understood that Fig.14The base station 1400 shown is only a possible architecture of a wireless access network device and should not constitute any limitation to the present application. The method provided in the present application can be applied to network devices of other architectures. For example, wireless access network devices including CU, DU and AAU, etc. The present application does not limit the specific architecture of the wireless access network device.

[0374] It should be understood that Fig.14 For example only and not limitation, the wireless access network device may not rely on Fig.14 For example, the wireless access network device may include an AAU, and may also include a CU and / or a DU, or the wireless access network device may include a BBU, and may also include an adaptive radio unit (ARU). This application is not limited to this.

[0375] The above CU and / or DU can be used to perform the actions implemented by the wireless access network device in the previous method embodiment, and the AAU can be used to perform the actions of the wireless access network device sending to or receiving from the terminal described in the previous method embodiment. Please refer to the description in the previous method embodiment for details, which will not be repeated here.

[0376] It should be noted that the above method embodiments can be applied to a processor or implemented by a processor. The processor may be an integrated circuit chip with signal processing capabilities. In the implementation process, each step of the above method embodiment can be completed by an integrated logic circuit of hardware in the processor or an instruction in the form of software.

[0377] 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.

[0378] The steps of the method disclosed in the embodiments of the present application can be directly embodied as being executed by a hardware decoding processor, or can be executed by a combination of hardware and software modules in the decoding processor. The software module can be located in a mature storage medium in the art such as a random access memory, a flash memory, a read-only memory, a programmable read-only memory, or an electrically erasable programmable memory, a register, etc. The storage medium is located in a memory, and the processor reads the information in the memory and completes the steps of the above method in combination with its hardware.

[0379] 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 (DDRSDRAM), 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.

[0380] The method provided in the above embodiment can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it 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 a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital user (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. 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. 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 hard disk (SSD)), etc.

[0381] The present application also provides a computer-readable medium on which a computer program is stored. When the computer program is executed by a computer, the functions of the above method embodiments are implemented.

[0382] 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.

[0383] Those of ordinary skill 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 to be beyond the scope of this application.

[0384] Those skilled in the art can 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.

[0385] In the several embodiments provided in the present 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 only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, 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.

[0386] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0387] 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.

[0388] 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 can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the various embodiments of the present application. The aforementioned storage media include: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM), random access memories (RAM), magnetic disks or optical disks.

[0389] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A switching method, characterized in that: Applied to a first access network device, the method includes: 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: Applied to a second access network device, the method comprises: 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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