Handover method and related apparatus

Abstract

This application provides a handover method and related apparatus that enables access network devices to release cache in a timely manner, thereby improving resource utilization. The method includes: a first access network device sending a first handover request message to a second access network device, the first handover request message including the sequence 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 device sending at least one second data packet to the terminal; the first access network device sending a second sequence number to the second access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device 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 the second access network device, based on the received second sequence number, deleting data packets in the cached MBS session whose sequence number is less than or equal to the second sequence number.

Description

Technical Field

[0001] This application relates to the field of communication technology, and in particular to a switching method and related apparatus. Background Technology

[0002] During the handover process, the deterioration of the wireless environment between the terminal and the access network equipment may cause the terminal's measurement report to fail to reach the access network equipment; or the handover command issued by the access network equipment to the terminal after receiving the measurement report may fail to reach the terminal, resulting in handover failure and requiring the terminal to re-initiate radio resource control (RRC) reconstruction.

[0003] To reduce the probability of unicast service handover failure, conditional handover (CHO) was proposed. CHO allows the source access network device to send a handover command to the terminal before the wireless environment between the terminal and the access network device deteriorates. This enables the terminal to know in advance how to access the target access network device. Once 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 the handover independently. Therefore, it can significantly improve the handover success rate.

[0004] Currently, with the increasing demand for lossless handover in multicast and broadcast services (MBS), Callable Hash (CHO) can be applied to handovers involving MBS sessions to ensure a high success rate for terminals receiving MBS sessions. When applying CHO to handovers involving MBS sessions, after the source access network device decides on conditional handover, it will continue to forward MBS data packets to the terminal device for a period of time. Data forwarding between the source access network device and the candidate target access network device may also continue indefinitely. However, the forwarded MBS data packets may accumulate significantly on the candidate target access network device side, leading to an excessive burden on multiple candidate target access network devices and excessive resource consumption due to cached data. Summary of the Invention

[0005] This application provides a switching method and related apparatus that enable access network devices to release cache in a timely manner and improve resource utilization.

[0006] Firstly, this application provides a switching method that can be applied to a first access network device. For example, it can be executed by the first access network device, or by a component (such as a chip, chip system, etc.) configured in the first access network device, or by a logic module or software capable of implementing all or part of the functions of the first access network device; this application does not limit this.

[0007] For example, the method includes: sending a first handover request message to a second access network device, the first handover request message being used to request a handover of a terminal from the first access network device to the second access network device, the first handover request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one first data packet sent by the first access network device to the terminal; sending at least one second data packet to the terminal; and sending a second sequence number to the second access network device, the second sequence number being the sequence number of the last second data packet in the at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number.

[0008] This application defines the data packets of the MBS session sent by the first access network device to the first terminal before the first access network device sends the first handover request message to the second access network device as the first data packet; and the data packets of the MBS session sent by the first access network device after sending the first handover request before the first terminal accesses the second target access network device 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 for the data packets of the second access network device to delete the cached MBS session.

[0010] The first handover request message is the first handover request message sent by the first access network device to multiple target access network devices after deciding on the conditional handover.

[0011] In this application, after sending a first sequence number to a second access network device, the first access network device can continue to send a second sequence number to the second access network device. Since the first sequence number and the second sequence number are respectively the 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 with sequence numbers less than the second sequence number in its local cache after receiving the second sequence number. Compared with the method of the second access network device deleting the data packets in its local cache based only on the first sequence number, the first access network device can release the cache in a timely manner, effectively improving resource utilization. At the same time, it can also avoid the second access network device sending duplicate MBS session data packets to the terminal after the terminal accesses the second access network device.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: determining to perform a conditional handover before sending the first handover request to the second access network device.

[0013] In conjunction with the first aspect, in some implementations of the first aspect, after sending a first handover request message to the second access network device, the method further includes: receiving a handover response message from the second access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first (packet data convergence protocol, PDCP) service data unit (SDU) that has not been submitted to the upper layer in the receiving window; and sending the first initial value of the first variable to the 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 handover response message. When the second access network device 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 conjunction 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] Wherein, 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] This 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 connects to 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, thus avoiding the terminal receiving garbled data packets.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: determining whether the number of the at least one second data packet is greater than a preset value; if the number of the at least one second data packet is greater than the preset value, sending first information to the second access network device, the first information being used to request a second initial value for 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] For example, 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] For example, the preset relationship is: preset value = k × size of the receiving window. Where k is greater than 0 and less than or equal to 1, N is the size of the 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] Secondly, this application provides a switching method that can be applied to a second access network device. For example, it can be executed by a first access network device, or by a component (such as a chip, chip system, etc.) configured in the second access network device, or by a logic module or software capable of implementing all or part of the functions of the second access network device; this application does not limit this.

[0023] For example, the method includes: receiving a first handover request message from a first access network device, the first handover request message being used to request a handover of a terminal from the first access network device to a second access network device, the first handover request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one data packet sent by the first access network device to the terminal; receiving a second sequence number from the first access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number; and deleting all data packets identified by sequence numbers less than or equal to the second sequence number in the cached data packets of the MBS session.

[0024] In this case, at least one first data packet and at least one second data packet belong to the same MBS session. A description of the first and second data packets can be found in the description of the first aspect, and will not be repeated here.

[0025] In this application, after receiving the first sequence number from the first access network device, the second access network device 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 that are less than the second sequence number in its local cache after receiving the second sequence number. Compared with the method of the second access network device deleting the data packets in its local cache based only on the first sequence number, this can effectively reduce the resources occupied by the data packets of the MBS session cached by the first access network device. At the same time, it can also avoid the second access network device sending duplicate MBS session data packets to the terminal after the terminal accesses the second access network device.

[0026] In conjunction with the second aspect, in some implementations of the second aspect, the first handover request is sent by the first access network device after determining that a conditional handover is to be performed.

[0027] In conjunction with the second aspect, in some implementations of the second aspect, after receiving the first handover request message from the first access network device, the method further includes: sending a handover response message to the first access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first PDCP SDU that has not been submitted to the upper layer in the receiving window.

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

[0029] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes: receiving first information from the first access network device, the first information being used to request a second initial value for 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 conjunction 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, wherein the second initial value is greater than the first initial value.

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

[0033] It is understandable that after the second access network device sends a handover success message to the first access network device, it is considered that the terminal has switched from the first access network device to the second access network device, that is, the terminal accesses the second access network; otherwise, it is considered that the terminal has not accessed the second access network device.

[0034] In conjunction 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, wherein the second initial value is greater than the first initial value.

[0035] Wherein, the second initial value is a reference value for 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 this 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-1And the reference value is less than or equal to the latest value. Where 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 conjunction 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 a description of the preset values, please refer to the first aspect; it will not be repeated here.

[0038] In conjunction with the second aspect, in some implementations of the second aspect, the second sequence number is carried in the second handover request message, which is used to request the terminal to be switched from the first access network device to the second access network device, and the second handover 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 update only the progress of the MBS radio bearer (MRB).

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

[0041] Thirdly, this application provides a switching method that can be applied to a second access network device. For example, it can be executed by the second access network device, or by a component (such as a chip, chip system, etc.) configured in the second access network device, or by a logic module or software capable of implementing all or part of the functions of the second access network device; this application does not limit this.

[0042] For example, the method includes: receiving a third handover request message from a first access network device, the third handover request message being used to request a handover of a first terminal to a second access network device; sending a handover response message to the first access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first PDCP SDU that has not been submitted to the upper layer in the receiving window; and sending a second initial value of the first variable to the first terminal.

[0043] The handover response message is the second access network device's confirmation of the first handover request message.

[0044] For example, the second access network device may send the second initial value of the first variable directly 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 this application, after sending the initial value of the first variable to the first terminal, the second access network device can send a 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. This allows the first terminal to use the updated second initial value to receive data packets from the MBS session of the second access network device after accessing the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets.

[0046] Fourthly, this application provides a switching method that can be applied to a first access network device. For example, it can be executed by the first access network device, or by a component (such as a chip, chip system, etc.) configured in the first access network device, or by a logic module or software capable of implementing all or part of the functions of the first access network device; this application does not limit this.

[0047] For example, the method includes: sending a third handover request message to a second access network device, the third handover request message being used to request a handover of a first terminal to the second access network device; receiving a handover response message from the second access network device, the handover response message including a first initial value of a first variable, the first variable indicating an identifier value of a first PDCP SDU that has not been submitted to the upper layer in the receiving window; receiving a second initial value from the second access network device, the second initial value being greater than the first initial value; and sending the second initial value to the terminal.

[0048] In this application, the second access network device can send a second initial value of the first variable to the first terminal after sending the initial value of the first variable, so that the first terminal can update the initial value of the first variable. This allows the first terminal to use the updated second initial value to receive data packets from the MBS session of the second access network device after accessing the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets. Fifthly, this application provides a communication apparatus, including modules or units for implementing any aspect and any possible implementation of the method in any aspect. It should be understood that each module or unit can implement its corresponding function by executing a computer program.

[0049] Fifthly, this application provides a communication device including a processor, the processor being configured to perform the method described in any aspect and any possible implementation thereof.

[0050] The apparatus may further include a memory for storing instructions and data. The memory is coupled to the processor, which, when executing the instructions stored in the memory, can implement the methods described in the foregoing aspects.

[0051] The device may also include a communication interface for communicating with other devices. For example, the communication interface may be a transceiver, circuit, bus, module or other type of communication interface.

[0052] Sixthly, this application provides a chip system including at least one processor for supporting the implementation of the functions involved in any of the above aspects and any possible implementations of any of the above aspects, such as receiving or processing data and / or information involved in the above methods.

[0053] In one possible design, the chip system also includes a memory for storing program instructions and data, which may be located within or outside the processor.

[0054] The chip system can consist of chips or include chips and other discrete components.

[0055] In a seventh aspect, this application provides a computer-readable storage medium including a computer program that, when run on a computer, causes the computer to implement the methods of the first aspect and any possible implementation of the first aspect.

[0056] Eighthly, this application provides a computer program product comprising: a computer program (also referred to as code or instructions) that, when the computer program is run, causes a computer to perform the method in the first aspect and any other aspect and any possible implementation thereof.

[0057] Ninthly, this application provides a communication system including the aforementioned first access network device and second access network device.

[0058] It should be understood that the fifth to ninth aspects of this application correspond to the technical solutions of the first to fourth aspects of this application, and the beneficial effects obtained by each aspect and the corresponding feasible implementation are similar, and will not be repeated here. Attached Figure Description

[0059] Figure 1 This is a schematic diagram of the architecture of a communication system applicable to embodiments of this application;

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

[0061] Figure 3 This 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 the Xn interface provided in an embodiment of this application;

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

[0064] Figure 6 This is a schematic flowchart of the condition switching method provided in the embodiments of this application;

[0065] Figures 7 to 11 This is a schematic flowchart of the switching method provided in the embodiments of this application;

[0066] Figure 12 and Figure 13 This is a schematic block diagram of the device provided in the embodiments of this application;

[0067] Figure 14 This is a schematic diagram of the structure of the wireless access network device provided in an embodiment of this application. Detailed Implementation

[0068] The technical solutions in this application will now be described with reference to the accompanying drawings.

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

[0070] First, in the embodiments of this application, the use of prefixes such as "first" and "second" is merely for the purpose of distinguishing and describing different things belonging to the same name category, and does not constrain the order, size, or quantity of things. For example, "first access network device" and "second access network device" are simply different devices, and do not limit the number of devices or their priority relationship.

[0071] Second, in the embodiments of this application, "send" and "receive" indicate the direction of signal transmission. For example, "send at least one second data packet to the terminal" can be understood as the destination of the second data packet being the terminal, which may include direct transmission via the air interface or indirect transmission via the air interface by other units or modules. "Receive a second initial value from a second access network device" can be understood as the source of the second initial value being the second access network device, which may include direct reception from the second access network device via the air interface or indirect reception from the second access network device via the air interface by other units or modules. "Send" can also be understood as the "output" of the chip interface, and "receive" can also be understood as the "input" of the chip interface.

[0072] In other words, sending and receiving can be done between devices, such as between a first access network device and a terminal; or they can be done within a device, such as between components, modules, chips, software modules, or hardware modules within the device via a bus, wiring, or interface.

[0073] It is understandable that information may undergo necessary processing, such as encoding and modulation, before being sent from the source to the destination. Similarly, the destination, upon receiving information from the source, can also perform corresponding processing, such as decoding and demodulation, to interpret the valid information from the source. Similar expressions in this application can be understood in a similar way and will not be elaborated further.

[0074] Third, in the embodiments of this application, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates an "or" relationship between the preceding and following related objects, but it does not exclude the possibility of indicating an "and" relationship. The specific meaning can be understood in conjunction with the context. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single 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. Here, a, b, and c can be single or multiple.

[0075] Fourth, in the embodiments of this application, "instruction" can include direct instruction and indirect instruction, as well as explicit instruction and implicit instruction. The information indicated by a certain piece of information (as described below, the instruction information) is called the information to be instructed. In the specific implementation process, there are many ways to indicate the information to be instructed, such as, but not limited to, directly indicating the information to be instructed, such as the information to be instructed itself or its index. It can also indirectly indicate the information to be instructed by indicating other information, where there is a correlation between the other information and the information to be instructed; or it can only indicate a part of the information to be instructed, while the other parts of the information to be indicated are known or pre-agreed upon. For example, the instruction of specific information can be achieved by using a pre-agreed (e.g., protocol predefined) arrangement of various pieces of information, thereby reducing the instruction overhead to a certain extent. This application does not limit the specific method of instruction.

[0076] It is understandable that, for the sender of the instruction information, the instruction information can be used to indicate the information to be indicated, and for the receiver of the instruction information, the instruction information can be used to determine the information to be indicated.

[0077] Fifth, the tables in the embodiments of this application are merely examples. The values ​​of the information in each table are only examples and can be configured to other values; this application is not limited thereto. The tables do not limit the scope of protection of this application. For example, appropriate modifications and adjustments can be made based on the tables described above, such as splitting, merging, etc. Furthermore, the parameter names shown in the headings of each table can also use other names understandable to the communication device, and the values ​​or representations of the parameters can also be other values ​​or representations understandable to the communication device. Moreover, in the implementation of 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, etc.

[0078] Sixth, in the embodiments of this application, descriptions such as "when," "under the circumstances," "if," and "if" all refer to the fact that the device (e.g., access network device or terminal) will make corresponding processing under certain objective circumstances. They are not time limits, nor do they require the device (e.g., network device or terminal) to make a judgment action when implementing it, nor do they mean that there are other limitations.

[0079] Seventh, the predefined terms in this application can be understood as: definition, pre-defined, storage, pre-storage, pre-negotiation, pre-configuration, solidification, or pre-firing.

[0080] Eighth, the term "storage" in this application can refer to storage in one or more memory devices. These memory devices can be separate installations or integrated into an encoder, decoder, processor, or communication device. Alternatively, some memory devices can be separately installed, while others can be integrated into the decoder, processor, or communication device. The type of memory can be any form of storage medium, and this application does not limit this.

[0081] The technical solutions provided in this application can be applied to various communication systems, such as: Long Term Evolution (LTE) systems, LTE Frequency Division Duplex (FDD) systems, LTE Time Division Duplex (TDD) systems, sidelink (SL) communication systems, Worldwide Interoperability for Microwave Access (WiMAX) communication systems, 5th Generation (5G) mobile communication systems or new radio access technology (NR), satellite communication systems, etc. Among them, 5G mobile communication systems can include non-standalone (NSA) and / or standalone (SA) networking.

[0082] The technical solutions provided in this application can also be applied to future communication systems, such as sixth-generation (6G) mobile communication systems. This application does not limit the application in this regard.

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

[0084] In one possible scenario, a RAN node can be a base station (BS), an evolved NodeB (eNodeB), a transmission reception point (TRP), a home evolved NodeB (or home Node B, HNB), a Wi-Fi access point (AP), a mobile switching center, a next-generation NodeB (gNB) in a 5G mobile communication system, a next-generation base station in a 6G mobile communication system, or a base station in a future mobile communication system. A RAN node can also be a device that performs base station functions in device-to-device (D2D) communication systems, vehicle-to-everything (V2X) communication systems, machine-to-machine (M2M) communication systems, and internet-to-things (IoT) communication systems. A RAN node can also be a RAN node in a non-terrestrial network (NTN), meaning that a RAN node can be deployed on a high-altitude platform or a satellite. RAN nodes can be macro base stations, micro base stations, indoor stations, relay nodes, donor nodes, etc., or radio controllers in cloud radio access network (CRAN) scenarios, or nodes in open radio access network (O-RAN or ORAN) scenarios. Optionally, RAN nodes can also be servers, wearable devices, vehicles, or in-vehicle equipment. For example, in V2X technology, RAN nodes can be roadside units (RSUs). Of course, RAN nodes can also be nodes in the core network.

[0085] In another possible scenario, multiple RAN nodes collaborate to assist the terminal in achieving wireless access, with different RAN nodes each implementing a portion of the base station's functions. For example, RAN nodes can be central units (CUs), distributed units (DUs), CU-control plane (CPs), CU-user plane (UPs), or radio units (RUs), etc. CUs and DUs can be set up separately or included in the same network element, such as a baseband unit (BBU). RUs can be included in radio frequency equipment or radio frequency units, such as remote radio units (RRUs), active antenna units (AAUs), or remote radio heads (RRHs).

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

[0087] Any one of the CU (or CU-CP, CU-UP), DU, and RU units can be implemented through software modules, hardware modules, or a combination of software and hardware modules. That is, the wireless access network device in this application can be a virtualized device, for example, implemented through general-purpose hardware and instantiated virtualization functions, or dedicated hardware and instantiated virtualization functions. The general-purpose hardware can be a server, such as a cloud server. The name of the wireless access network device in future evolved communication systems is not limited and can also be called a network device or 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 equipment, user agent, or user device.

[0089] A terminal can be a device that provides voice / data connectivity to a user, such as a handheld device or in-vehicle device with wireless connectivity. Currently, some examples of terminals include: mobile phones, tablets, computers with wireless transceiver capabilities (such as laptops and PDAs), mobile internet devices (MIDs), virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving, drones, wireless terminals in remote medical care, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, cellular phones, cordless phones, session initiation protocol (SIP) phones, wireless local loop (WLL) stations, and personal digital assistants (PDAs). The following are examples of mobile communication devices: assistant (PDA), handheld devices with wireless communication capabilities, computing devices or other processing devices connected to a wireless modem, in-vehicle devices, wearable devices, terminals in 5G networks, or terminals in future public land mobile networks (PLMNs).

[0090] Wearable devices, also known as wearable smart devices, are a general term for devices that utilize wearable technology to intelligently design and develop everyday wearables, such as glasses, gloves, watches, clothing, and shoes. Wearable devices are portable devices worn directly on the body or integrated into the user's clothing or accessories. Wearable devices are not merely hardware devices; they achieve powerful functions through software support, data interaction, and cloud interaction. Broadly defined, wearable smart devices include those with comprehensive functions, large sizes, and the ability to perform complete or partial functions without relying on a smartphone, such as smartwatches or smart glasses. They also include devices focused on a specific application function that require the use of other devices, such as smart bracelets and smart jewelry for vital sign monitoring.

[0091] Furthermore, a terminal can also be a terminal in an IoT system. IoT is an important component of future information technology development. Its main technical characteristic is connecting objects to networks through communication technologies, thereby realizing an intelligent network that enables human-machine interconnection and machine-to-machine interconnection. IoT technology can achieve massive connectivity, deep coverage, and low terminal power consumption through technologies such as narrowband (NB).

[0092] In addition, the terminal may also include sensors such as smart printers, train detectors, and gas stations. Its main functions include collecting data (for some 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 this application can be a virtualized device, for example, implemented through general-purpose hardware and instantiated virtualization functions, or dedicated hardware and instantiated virtualization functions. The general-purpose hardware can be a server, such as a cloud server.

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

[0095] Figure 1 This is a schematic diagram of the architecture of a communication system 100 applicable to the methods provided in the embodiments of this application. For example... 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 an Internet 30. The wireless access network 10 may include at least one wireless access network device (such as...). Figure 1 110a and 110b in the above), may also include at least one terminal (such as Figure 1 (120a-120j in the middle).

[0096] Terminals can connect to wireless access network (WLAN) devices wirelessly, and WLAN devices can connect to the core network wirelessly or via wired connections. Core network devices and WLAN devices can be independent, separate physical devices, or they can integrate the functions of the core network device and the logical functions of the WLAN device onto the same physical device. Alternatively, a single physical device can integrate some core network device functions and some WLAN device functions. Terminals and WLAN devices can connect to each other via wired or wireless connections.

[0097] Communication between wireless access network devices and terminals, between wireless access network devices, and between terminals can be conducted using licensed spectrum, unlicensed spectrum, or both simultaneously. Communication can be conducted using spectrum below 6 GHz, spectrum above 6 GHz, or both simultaneously. The embodiments of this application do not limit the spectrum resources used for wireless communication.

[0098] Among them, the wireless access network equipment can be a base station deployed in the air, such as a satellite base station 110a; or it can be a base station deployed indoors, such as a micro base station or an indoor station 110b.

[0099] The terminal can be a terminal deployed in the air, such as... Figure 1 The 120i can be a helicopter or drone; it can also be a terminal deployed on the ground, such as... Figure 1 The following are examples: mobile phones 120a, 120e, 120f and 120j, vehicle 120b, computer 120g, 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 water; and they can also be deployed in the air on airplanes, balloons, and satellites.

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

[0102] It should be understood that Figure 1 This is just an illustration; the communication system may also include other devices, such as wireless repeaters and wireless backhaul devices. Figure 1 It is not shown in the middle.

[0103] Multicast Broadcast System (MBS) is a service that targets multiple terminals, such as live streaming, public safety services, and batch software update services. In this application, MBS, multicast, MBS service, MBS session, multicast service, and multicast session are interchangeable. The following section will combine... Figure 2 and Figure 3 This section introduces the transmission process and architecture of MBS.

[0104] Figure 2 This is a schematic diagram of an MBS transmission process. (Example) Figure 2 As shown, the server first sends the MBS data packet to the core network, then the core network device sends the MBS data packet to the access network, and finally the access network sends the MBS data packet to at least one terminal.

[0105] like Figure 2 As shown, the server sends MBS services to the core network. When the core network sends MBS data packets to the access network equipment, it can transmit them through a common transmission channel, the MBS session. Each MBS session can contain at least one MBS quality of service (QoS) stream. When the access network equipment sends MBS data packets to the terminal, the data packets are transmitted through the MBS radio bearer (MRB). An MRB has two transmission modes: 1. Point-to-multipoint (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 terminals joining and leaving multicast services, and access network equipment and core network equipment can maintain information about terminals in the multicast service group. Transmission between the core network and the access network relies on protocol data unit (PDU) sessions, thus introducing MBS QoS streams; the RAN supports both PTP and PTM transmission modes to send data to terminals and supports dynamic switching between PTP and PTM controlled by the RAN.

[0107] Figure 3 This illustrates a multicast service transmission architecture. For example... Figure 3 As shown, Figure 3As shown, multicast services are transmitted between the core network and the access network through MBS sessions, which include MBS QoS streams (or multicast QoS streams). MBS sessions can be associated with a terminal's PDU session, and MBS QoS streams are associated with unicast QoS streams within the PDU session. Core network devices can control the state of the MBS session to be active or deactivated; the terminal is unaware of the MBS session's state.

[0108] When access network devices send multicast services to terminals, they can use either PTM or PTP transmission modes. In PTM mode, multicast service data can be scrambled using the group radio network temporary identifier (G-RNTI); in PTP mode, multicast service data is scrambled using the cell radio network temporary identifier (C-RNTI). Furthermore, access network devices can dynamically switch between PTM and PTP transmission modes.

[0109] In the lossless handover scenario of MBS, the source access network device and the target access network device need to exchange service progress during the handover signaling. This 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] Taking 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 the Xn lossless handover process.

[0111] Figure 4 This is a schematic diagram of a lossless switching process based on the Xn interface provided in an embodiment of this application. Figure 4 As shown, method 400 may include steps S401 and S402. The steps in method 400 are described in detail below.

[0112] S401, the source access network device sends a handover request message to the target access network device. This handover request message carries one or more of the following sets of information:

[0113] Group 1: MBS session identifier (ID), area session ID, MBS session associated information, where 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 info, MRB progress information. The MRB progress information includes the PDCP SN. The MRB progress information is used by the target access network device to determine the packet number of the largest data packet that the source access network device has sent to the terminal.

[0116] Correspondingly, the target access network device receives the handover request message. For example, the target access network device can determine whether to send a forwarding address and / or its own 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. This handover response message carries at least one of the following pieces of information: MBS session ID, MRB ID, downlink (DL) data forwarding address, and 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 by the target access network device.

[0119] Correspondingly, the source access network device receives the handover response message. For example, the source base station can determine, based on the received MRB progress information, whether to forward data to the target access network device, and which data to forward.

[0120] It is understandable that the above-mentioned handover response message can also be called a handover request confirmation message.

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

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

[0123] S501, the source access network device sends a handover request message to the 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 set of information in the handover request message and send it to the target access network device through the core network device: the first set is MBS session ID, area session ID, MBS service area, and QoS flow parameters; the second set is MRB ID, MRB mapping information, and MRB progress information.

[0126] For the Next Generation Application Protocol (NGAP) interface, the core network device can also send the following set of information to the target access network device in the handover request message: Set 1: MBS session ID, area session ID; Set 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 handover response message to the source access network device. Correspondingly, the source access network device receives the handover response message.

[0129] The target access network device may include at least one of the following information in the handover response message and send it to the source access network device through the core network device: MBS session ID, MRB ID, DL data forwarding address, and MRBprogress information.

[0130] During the handover process with a new radio (NR), the radio environment between the terminal and the access network equipment may deteriorate, causing the measurement reports submitted by the terminal to fail to reach the access network equipment, or the handover commands issued by the access network equipment after receiving the measurement reports to fail to reach the terminal. This can lead to handover failure, at which point the terminal will recognize the radio link failure and initiate an RRC (Radio Relay Call) reconstruction.

[0131] Currently, to reduce the probability of handover failure and improve handover reliability, CHO (Call for Handover) has been proposed. CHO allows the access network device to send a handover command (containing the radio 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 deteriorates further. This enables the terminal to know in advance how to access the target access network device. After the terminal finds a target access network device that meets the handover triggering conditions among the candidate target access network devices, it can decide to initiate the handover independently.

[0132] Figure 6 This is a schematic flowchart of the condition switching method provided in the embodiments of this application. Figure 6 As shown, method 600 may include steps 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. This data is unicast service data.

[0134] S602, the source access network equipment determines the switching conditions.

[0135] S603, the source access network device sends a handover request to multiple target access network devices. This handover request is used to request the terminal to be handed over from the source access network device to the target access network device.

[0136] The handover request carries the sequence number of the last data packet sent by the source access network device to the terminal before the handover request message was sent; or, in other words, the handover request carries the maximum sequence number among the sequence numbers of the unicast service data packets sent by the source access network device to the terminal.

[0137] S604, Multiple target access network devices send handover response messages to the source access network device. This 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 handover execution trigger conditions for multiple candidate target access network devices.

[0140] S606, the terminal sends an RRC reconfiguration complete message to the source access network device.

[0141] After the terminal sends an RRC reconfiguration complete message to the source access network device, the terminal begins to evaluate the handover conditions and maintains the connection with the source access network device. The source access network device can continue to send unicast service data packets to the terminal.

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

[0143] The early status transfer message can be triggered after the source access network device continues to send unicast service data packets to the terminal. It is used to update the target access network device on the progress of the data packets sent by the source access network device to the terminal.

[0144] For example, the early status transfer message may carry the sequence number of the last data packet in the data packets that the source access network device continues to send to the terminal.

[0145] S608, conditional handover completed, 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 selects one target access network device (e.g., the first target access network device) from among 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. This handover completion message is used to notify the source access network device that it has successfully connected to the first target access network device.

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

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

[0150] To ensure a high success rate for MBS handovers, it has been proposed to apply CHOs to handovers involving MBS sessions. However, currently there are no solutions for additional enhancements or adaptations to MRB handovers using CHOs. From the current RRC signaling format, CHO configurations directly reference RRC reconfiguration messages (i.e., CHO configurations contain RRC reconfiguration messages), and there is no restriction preventing the inclusion of MRB configurations in CHO configurations. In other words, target access network devices can include MRB configurations in their CHO configurations to support multicast CHOs.

[0151] For the CHO switching procedure for multicast, please refer to the above. Figure 6The descriptions of the CHO handover procedures shown differ in the following ways: 1. In the multicast CHO handover procedure, the handover request message sent by the source access network device to multiple candidate target access network devices includes MBS information (i.e., the handover request message sent by S603 also carries MBS-related information); 2. Multiple candidate target access network devices will include MBS information in their handover response messages (i.e., the handover response message sent by S604 also carries MBS information); 3. During the terminal's evaluation of handover conditions, the source access network device can continue to send MBS data packets to the terminal. Furthermore, based on the MBS information carried in the handover request message, the source access network device will send MBS data packets to multiple target access network devices so that after the terminal accesses the target access network device, the target access network device can directly send data packets to the terminal.

[0152] The description of MBS information can be found above. Figure 5 The information carried in the handover request message and the handover response message will not be elaborated here.

[0153] However, when applying CHOs to handovers involving MBS sessions, the following issues were found:

[0154] 1. Based on the above description of lossless handover in MBS, to ensure that no data packets are lost when the terminal hands over from the source access network device to the candidate target access network device, the source access network device needs to send its current MRB progress information to the candidate target access network device during the lossless handover process. Similarly, the candidate target access network device will send its own MRB progress information back to the source access network device. This allows the source access network device to send data packets to the candidate target access network device based on the MRB progress information from the candidate target access network device, and the candidate target access network device to continue sending data packets to the terminal based on the progress information and data packets from the source access network device.

[0155] However, when applying CHO to handovers involving MBS sessions, during the CHO condition evaluation phase, the terminal may continue receiving multicast service packets from the source access network device for a period of time, and data forwarding between the source access network device and the candidate target access network device may also continue indefinitely. Since the MRB progress information is carried to the candidate target access network device in the initial handover request sent by the source access network device, the candidate target access network device will cache MBS session packets based on the MRB progress information carried in the handover request message. However, because the terminal continues to receive packets from the source access network device during the CHO condition evaluation phase, causing changes in the MRB progress, if the candidate target access network device continues to cache MBS session packets based on previously received MRB progress information, it will cache a large number of MBS packets, requiring more resources.

[0156] In view of this, this application provides a handover method and related apparatus. In this 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 on its own end based on the MRB progress information, thereby reducing the resources required for the target access network device to cache data packets.

[0157] 2. In lossless handover of MBS, after the source access network device sends a handover request message to the candidate target access network device, it receives a handover response message from the second access network device. This handover response message may include MRB configuration information, which indicates the initial value of RX_DELIV. When the candidate target access network device transparently transmits the initial value of RX_DELIV to the terminal through the source access network device, the terminal can use this initial value as the initial value of RX_DELIV on the terminal side after accessing the candidate target access network device. The initial value of RX_DELIV is a reference value for the RX_DELIV on the candidate target access network device side when the candidate target access network device sends the handover response message. The difference between this 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. Where 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] For example, the identifier value of a PDCP SDU can be called COUNT. COUNT consists of HFN and PDCP SN. The PDCP SN is added to the PDU for transmission, while the HFN is maintained by both the transmitter and receiver. The PDCP PDU sent from the transmitter to the receiver contains the SN, but not COUNT or HFN. The receiver calculates the HFN based on the received SN and restores the COUNT value. That is, the receiver combines the calculated HFN with the SN carried in the PDCP PDU to form the COUNT corresponding to the PDCP PDU. PDCP uses a receive window plus a reordering timer to receive PDCP PDUs submitted from lower layers. The receive window moves according to the update of the lower boundary state variable (i.e., RX_DELIV). Since the state variable is described by the COUNT value, after receiving the PDCP PDU, PDCP needs to determine the correct HFN and COUNT based on the SN in the PDCP PDU subheader and the current receive window state variable, and then perform decryption and integrity verification based on the obtained COUNT.

[0159] When applying a CHO to a handover involving an MBS session, after the terminal receives the initial value of RX_DELIV from the candidate target access network device, it will remain on the source access network device for a period of time. During this period, the candidate 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 side to change to a second value. If the difference between the second value and the initial value previously carried in the handover response message is greater than or equal to 2... p-1 If the RX_DELIV carried in the handover response message is not found to be valid, then the terminal will consider it expired. In other words, if the terminal still determines the HFN based on the previously received initial value, it will receive an incorrect HFN, resulting in disordered received data packets.

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

[0161] 3. When applying a CHO to a handover involving an MBS session, after MBS service deactivation, the access network device can release or retain the MRB. If the candidate target access network device deletes the MRB configuration in the RRC configuration after MBS service deactivation, then when MBS service is reactivated, the access network device may not carry the MRB configuration in the RRC reconfiguration message, resulting in the terminal being unable to receive MRB session data packets after accessing the target access network device. MBS service deactivation means not transmitting MBS session data, but retaining the MBS session. To ensure that the terminal of the target access network device can continue to receive MBS session data packets after MBS service activation, this application proposes the following... Figure 11 The method shown is implemented.

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

[0163] The following is combined Figures 7 to 11 This application describes in detail the method provided in its embodiments. This method can be applied to... Figure 1 The communication system shown is not limited to this embodiment.

[0164] exist Figures 7 to 11 The flowchart shown illustrates the method from the perspective of communication device interaction, but this application does not limit the subject that performs the method. For example, Figures 7 to 11 The access network device in the text can be a chip, chip system, or processor that supports the implementation of the method in the access network device, or it can 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 text can be a chip, chip system, or processor that supports the implementation of the method on the terminal, or it can be a logic module or software that can implement all or part of the terminal functions.

[0165] Figure 7 This is a schematic flowchart illustrating the switching method provided in an embodiment of this application. Figure 7 As shown, method 700 may include steps S701 to S704. The steps in method 700 are described in detail below.

[0166] S701, the first access network device sends a first handover request message to the second access network device, the first handover request message including a first sequence number. Correspondingly, the second access network device receives the first handover request message from the first access network device.

[0167] Wherein, the first sequence number is the sequence number of the last first data packet among the at least one first data packets sent by the first access network device to the first terminal. Alternatively, the first sequence number is the largest sequence number among the sequence numbers corresponding to the at least one first data packet sent by the first access network device to the first terminal. Or, 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 up to the time the first handover request message was sent.

[0168] The first sequence number can be a PDCP SN, COUNT, or hyperframe number (HFN), or other parameters that can be used to identify the transmission order of data packets; this application does not limit this. Here, COUNT is the identifier value of the PDCP SDU.

[0169] It is understood that the first terminal in this application is a terminal connected to the first access network device. When multiple first terminals connected to the first access network device all have a 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 aforementioned first handover request message is the first handover request message sent by the first access network device to multiple target access network devices after deciding on the conditional handover. This first handover request message is used to request the first terminal to be handed over from the first access network device to the second access network device.

[0171] The first access network device can also be called the source access network device, and the second access network device can also be called the target access network device.

[0172] It is understood that the first access network device can send a first handover request message to multiple candidate target access network devices, while the second access network device in this application can be one of the access network devices accessed by the first terminal among multiple candidate target access network devices.

[0173] Optionally, prior to S701, the method 700 further includes: the first access network device determining to perform a conditional handover.

[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] In this case, at least one first data packet and at least one second data packet belong to the same MBS session (e.g., the first MBS session).

[0176] It is understood that, in this application, the data packet of the first MBS session sent by the first access network device to the first terminal before the first access network device sends the first handover request message to the second access network device is referred to as the first data packet; and the data packet of the first MBS session sent by the first access network device after sending the first handover 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] Wherein, the second sequence number is the sequence number of the last second data packet among at least one second data packet sent by the first access network device to the first terminal, and the second sequence number is greater than the first sequence number. Alternatively, the second sequence number is the largest sequence number among the sequence numbers corresponding to the at least one second data packet sent by the first access network device to the first terminal. Or, 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 up to the point of sending the second sequence number.

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

[0180] It is understood that when multiple first terminals connected to the first access network device all have CHO, the second sequence number sent by the 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, upon receiving the first handover request message, the second access network device can send a handover response message in response to the first access network device. This handover response message may carry a second sequence number.

[0182] For example, after S701, the first access network device may send a second sequence number to the second access network device when any of the following conditions are met: 1. every first time interval; 2. every first number of second data packets. The first time interval 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 a second sequence number to the second access network device at first intervals after sending the first handover request message, and if the first access network device does not send at least one second data packet to the first terminal within the first interval, then the above-mentioned S702 can be omitted. That is, after S701, S703 is executed, at which point the first sequence number and the second sequence number are equal.

[0184] S704, the second access network device deletes cached MBS session data packets based on the second sequence number. Alternatively, the second access network device deletes cached MBS session data packets based on the second sequence number.

[0185] It is understandable that the data packets of the MBS session deleted by the second access network device belong to the same MBS session as at least one second data packet (or at least one first data packet).

[0186] Based on the example above where at least one first data packet and at least one second data packet belong to the first MBS session, the above S704 can be replaced by the second access network device deleting the cached data packets of the first MBS session based on the second sequence number.

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

[0188] The method 700 provided in this application is applied to a conditional handover scenario to solve the problem of excessive resources required for the target access network device to cache MBS session data packets. In the embodiments of this application, after the first access network device sends a first sequence number to the second access network device, it can continue to send a second sequence number to the second access network device. Since the first sequence number and the second sequence number are respectively the last MBS data packets sent by the first access network device to the terminal at different time periods, and the second sequence number is greater than the first sequence number, the second access network device can delete the data packets corresponding to the sequence numbers less than the second sequence number that are cached on its own side after receiving the second sequence number. Compared with the method of the second access network device deleting the data packets cached on its own side based only on the first sequence number, this can effectively reduce the resources occupied by the first access network device to cache MBS session data packets, improve resource utilization, and at the same time avoid 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 aforementioned second sequence number can be carried by the following messages or signaling: second handover request message, early status transfer signaling, or MBS early status transfer signaling.

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

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

[0192] This application can add an MBS procedure stage cell parallel to the procedure stage cell in the early status transfer signaling, and include a DL discarding branch in the MBS procedure stage cell. The DL discarding branch contains the COUNT value (HFN and SN) or SN for the MRB. Based on this scheme, the MRB progress information of each terminal can be independently sent to the candidate target access network device, which then uses the data packets for deleting the MRB session.

[0193] In a second possible implementation, this application introduces a new signaling system that carries a second sequence number. This new signaling is associated with MBS and can be used to indicate the progress of one or more MBS sessions.

[0194] For example, the new signaling could be an MBS early status transfer signaling. This MBS early status transfer signaling could contain an MBS procedure sage cell, which could contain a DL Discarding branch, and the DL Discarding branch could contain the 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 at the MBS session granularity. Since the data forwarding between stations is also at the MBS session granularity, the source access network device will not forward multiple copies of data for different terminals receiving a certain MBS session, thereby saving the signaling overhead when updating the MRB progress.

[0196] In a third possible implementation, the second sequence number is carried in the second handover request message, which is used to request the first terminal to be switched from the first access network device to the second access network device.

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

[0198] Optionally, the second handover request message may also include indication information, which 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 is understandable that during the CHO handover process, the source access network device will re-trigger a handover request message (referred to as the second handover request message in this application) to the candidate target access network device. After receiving the handover request message, the candidate target access network device will send a handover response message to the source access network device, carrying the RRC reconfiguration message from the target access network device side in the handover response message. Since the purpose of carrying the second sequence number in the second handover request message in the multicast CHO handover process is to update the MRB progress, indication information indicating whether to update the RRC configuration or only update the MRB progress can be carried in the second handover request to avoid the second access network device repeatedly sending the RRC reconfiguration message.

[0200] Optionally, prior to S704, method 700 further includes: the second access network device sending a third sequence number to the first access network device, wherein 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 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] Among them, 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 can be a PDCP SN, COUNT, or HFN, or other parameters that can be used to identify the transmission order of data packets, which are not limited in this application.

[0203] Optionally, prior to S704, the method 700 further includes: the first access network device sending at least one third data packet to the second access network device based on a first sequence number and a third sequence number. Correspondingly, the second access network device receives at least one third data packet from the first access network device.

[0204] In this case, at least one third data packet and at least one first data packet belong to the same MBS session.

[0205] For example, if the first sequence number is less than the third sequence number, the first access network device may send a data packet of the MBS session identified by the sequence number which is less than the third sequence number to the second access network device.

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

[0207] The following will be based on Figure 7 Based on the illustrated embodiments, combined with Figure 8 The specific process of the switching method provided in this application is described below. Figure 7 The content already described in the illustrated embodiments will not be repeated. Figure 8 The switching method shown is illustrated by an example where 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.

[0208] Figure 8 This is another illustrative flowchart of the switching method provided in the embodiments of this application. For example... Figure 8 As shown, the method 800 may include steps S801 to S812. The steps of method 800 are described in detail below.

[0209] S801, the source access network device and the terminal transmit data. This data is from the MBS session.

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

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

[0212] Among the multiple target access network devices, there is a first target access network, which can be a target access network device that the terminal switches from the source access network device to.

[0213] The first handover request is used to request the terminal to be switched from the source access network device to any one of the multiple target access network devices.

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

[0215] It is understood that the first handover request may also carry an identifier of the MBS session, which is used to identify the service type to which at least one first data packet belongs.

[0216] In step S804, multiple target access network devices send handover response messages to the source access network device. These handover response messages are used to confirm the first handover request. Correspondingly, the source access network device receives handover response messages from the multiple target access network devices.

[0217] For example, each of the multiple target access network devices may carry a third sequence number and a first initial value of a first variable in its respective handover response message.

[0218] For a 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 the radio parameter configurations for multiple target access network devices and the handover command that triggers the handover execution conditions.

[0221] S806, the terminal sends an RRC reconfiguration completion message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0222] Following S806, the terminal maintains its connection with the source access network device and begins evaluating handover conditions. During this evaluation, the source target access network device may continue to send at least one second data packet to the terminal; and the first access network device may continue to send at least one third data packet to multiple target access network devices based on a first sequence number and a third sequence number.

[0223] For a description of at least one second data packet and at least one third data packet, please refer to the relevant description in method 700, which will not be repeated here.

[0224] S807, the source access network device sends a second sequence number to 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 a description of the second serial number, please refer to the relevant description in Method 700 above, which will not be repeated here.

[0226] S808: Multiple target access network devices delete data packets in the cached MBS session based on the third sequence number, where the sequence number is less than or equal to the second sequence number.

[0227] This process can be referred to in S704, and will not be repeated here.

[0228] S809, conditional handover completed, 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 handover success message to the source access network device.

[0230] The successful handover message is used to notify the source access network device that it has successfully connected to the first target access network device.

[0231] S811, the source access network device sends an SN status transmission message to the first target access network device. Correspondingly, the first target access network device receives the SN status transmission message from the source access network device.

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

[0233] The method provided in this application can effectively avoid the target access network device 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] Figure 9 This is another illustrative flowchart of the switching method provided in the embodiments of this application. For example... Figure 9 As shown, method 900 may include steps S901 to S904. The steps in method 900 are described in detail below.

[0235] S901, the first access network device sends a third handover request message to the second access network device, which requests that the first terminal be switched 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 a 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, which will not be repeated here.

[0237] Optionally, prior to S901, the method 900 further includes: the first access network device determining to perform a conditional handover.

[0238] S902, the second access network device sends a handover response message to the first access network device, the handover response message including a first initial value of a first variable. Correspondingly, the first access network device receives the handover response message from the second access network device.

[0239] The first variable indicates the flag value of the first PDCP SDU that has not been submitted to the upper layer in the receive window. For example, the first variable is RX_DELIV.

[0240] S903, the first access network device sends the first initial value of the first variable to the first terminal. This first initial value of the first variable can be carried in the 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 for the first variable on the second access network device side after the first terminal accesses the second access network device.

[0243] The description of the reference values ​​can be found in the previous text and will not be repeated here.

[0244] For example, the second access network device may send the second initial value of the first variable directly 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 is understandable that after the second access network device sends a handover success message to the first access network device, the first terminal can be considered to have accessed the second access network device; otherwise, the first terminal is considered not to have accessed the second access network device.

[0246] The method 900 provided in this application is applied to a conditional switching scenario to solve the problem of expired initial values ​​of the first variable on the terminal side. In the embodiments of this application, after sending the initial value of the first variable to the first terminal, the second access network device can send a 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. This allows the first terminal to use the updated second initial value to receive data packets from the MBS session of the second access network device after accessing the second access network device, effectively avoiding the possibility of the terminal receiving garbled data packets.

[0247] The following details two methods by which the second access network device updates the initial value of the first variable to the first terminal.

[0248] Method 1: The second access network device directly sends the initial value of the first variable to the first terminal. That is, the first terminal connects to the second access network device.

[0249] For example, after the first terminal connects to the second access network device, the second access network device sends a second initial value to the first terminal. Correspondingly, the first terminal receives the second initial value.

[0250] Optionally, the second initial value can be carried in the RRC reconfiguration message. This RRC reconfiguration message can be sent directly from the second access network device to the first terminal after the first terminal has accessed the second access network device.

[0251] Method 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 connect to the network via the second access network device.

[0252] Example 1: The second access network device sends a second initial value to the first access network device. Correspondingly, the first access network device receives the second initial value and sends it to the first terminal.

[0253] Optionally, in the manner described in Method 1 and Example 1 above, 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 further includes: the second access network device determining whether the number of data packets of the MBS session being sent is greater than a preset value.

[0254] For example, if the number of MBS session data packets sent by the second access network device is greater than a preset value, the second access network device sends a second initial value of the first variable; or, if the number of MBS data packets sent by the second access network device is less than or equal to the preset value, the second access network device does not send a second initial value of the first variable.

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

[0256] For example, the preset relationship is: preset value = k × size of the receiving window. Where k is greater than 0 and less than or equal to 1, N is the size of the 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 packets of the MBS session sent by the second access network device refer to the data packets of the MBS session sent by the second access network device to the second terminal, and the data packets of the MBS session belong to the same MBS session as at least one first data packet (or at least one second data packet).

[0258] Example 2: When the second access network device receives the first information from the first access network device, it sends a second initial value to the first access network device. Correspondingly, the first access network device receives the second initial value and sends the second initial value to the first terminal.

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

[0260] Optionally, the method 900 further includes: the first access network device determining whether the number of at least one second data packet sent to the first terminal is greater than a preset value; if the number of at least one second data packet is greater than the preset value, the first access network device sends first information to the second access network device, or if 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 first information to the second access network device.

[0261] The description of the preset value can be found in Example 1 above, and will not be repeated here. However, it should be noted that when the second access network device determines whether the number of at least one second data packet is greater than the preset value, it needs to first determine the size of the preset value. The preset value and the size of the receiving window satisfy a preset relationship, which can be found in Method 1. When calculating the size N of the interface window, if the first access network device is unsure of the number of bits used by the second access network device to identify the first sequence number, 12 bits can be used for calculation.

[0262] Since the second initial value of the first variable is actively requested by the first access network device in the manner shown in Example 2, the second initial value may be the same as the first initial value.

[0263] The following will be based on Figure 9 Based on the illustrated embodiments, combined with Figure 10 The specific process of the switching method provided in this application is described below. Figure 9 The content already described in the illustrated embodiments will not be repeated. Figure 10 The switching method shown is illustrated by an example where 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.

[0264] Figure 10 This is another illustrative flowchart of the switching method provided in the embodiments of this application. For example... Figure 10 As shown, the method 1000 may include steps S1001 to S1019. The steps of method 1000 are described in detail below.

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

[0266] S1002, the source access network equipment determines the switching conditions.

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

[0268] The processes described in S1001 to S1003 are the same as those described in S801 to S803, and will not be repeated here.

[0269] S1004, multiple target access network devices send handover response messages to the source access network device. These handover response messages are used to confirm the first handover request. Correspondingly, the source access network device receives handover response messages from the multiple target access network devices.

[0270] The switching response message carries the first initial value of the first variable. A description of the first variable and its first initial value can be found in the relevant description in method 700, and 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 the radio parameter configurations for multiple target access network devices and the handover command that triggers the handover execution conditions.

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

[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 an RRC reconfiguration completion message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration message from the terminal.

[0276] Following S1006, the terminal maintains its connection with the source access network device and begins evaluating handover conditions. During this evaluation, multiple target access network devices can continue sending MBS data packets to the terminal connected to them; the first access network device can continue sending at least one second data packet to the terminal.

[0277] For a description of at least one second data packet, please refer to the description of method 700, which will not be repeated here.

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

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

[0280] For a 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 a 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 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, the 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 a description of the first information, please refer to the description in method 700, which will not be repeated here.

[0285] S1012, multiple target access network devices send a 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 a description of the second initial value, please refer to the description in Method 700, which will not be repeated here.

[0288] S1014, conditional handover completed, 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 select one target access network device (e.g., the first target access network device) from among 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 successful handover message is used to notify the source access network device that it has successfully connected to the first target access network device.

[0292] S1016, the source access network device sends an SN status transmission message to the first target access network device. Correspondingly, the first target access network device receives the SN status transmission message from the source access network device.

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

[0294] S1018, the first target access network device determines that the data packets sent for the MBS session are greater than a preset value.

[0295] S1019, the first target access network device sends a 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 steps S107 to S1013, as well as S1018 and S1019, are optional. For example, if S107 to S1010 are executed after S106, steps S1011 to S1013, S1018, and S1019 do not need to be executed; or if S1011 to S1013 are executed after S106, steps S107 to S1010, S1018, and S1019 do not need to be executed; or if S107 to S1013 are not executed after S106, steps S1018 and S1019 can be executed after S1017.

[0297] The method improved in this application can effectively avoid the possibility of the terminal receiving garbled data packets.

[0298] It is understandable that the above Figure 7 and Figure 9 (or Figure 8 and Figure 10 The embodiments shown can be combined with each other or implemented independently. Wherein, when Figure 7 and Figure 9 ( Figure 8 and Figure 10 When implemented alone, it can perform better than Figure 7 or Figure 9 ( Figure 8 or Figure 10 More or fewer steps than shown in the steps; when Figure 7 and Figure 9 (or Figure 8 and Figure 10 When combined with the embodiments shown above, the communication method provided in this application may include: a handover request message (e.g., a first handover request message or a third handover request message) sent by the first access network device to the second access network device for the first time includes a first sequence number; a handover response message sent by the second access network device to the first access network device includes a second sequence number and a first initial value of a first variable; and an RRC reconfiguration message sent by the first access network device to the first terminal carries the first initial value of the first variable. More detailed procedures can be found above. Figure 7 and Figure 9 (or Figure 8 and Figure 10 The embodiment shown is described below.

[0299] Figure 11 This is a schematic flowchart illustrating another switching method provided in an embodiment of this application. Figure 11 As shown, method 1100 may include steps S1101 to S1116. The steps of method 1100 are described in detail below.

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

[0301] S1102, the source access network equipment determines the switching conditions.

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

[0303] The first identifier is used to identify the MBS session, which is in a deactivated state.

[0304] S1104, multiple target access network devices send handover response messages to the source access network device. These handover response messages are used to confirm the first handover request. Correspondingly, the source access network device receives handover response messages from the multiple target access network devices.

[0305] When the first handover request message is a handover request message sent under conditional handover, after receiving the first handover request message, if the MBS session is in a deactivated state, multiple target access network devices will send a handover response message to the source access network device carrying the MRB configuration.

[0306] S1105, the source access network device sends an RRC reconfiguration message to the terminal. This 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 complete message to the source access network device. Correspondingly, the source access network device receives the RRC reconfiguration complete message from the terminal.

[0308] After S1106, the terminal maintains its connection with the source access network equipment and begins to assess the handover conditions.

[0309] S1107, when the first condition is met, the source access network device sends second information to multiple target access network devices. Correspondingly, the multiple target access network devices receive the second information from the source access network device. This second information is used to request the multiple target access network devices to update their RRC configuration.

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

[0311] For example, the source access network device may consider the first condition to be met when it receives a notification message to activate the MBS session, or when the source access network device determines that the MBS session is in an active state, or when the source access network device receives a group paging message from another access network device.

[0312] S1108, 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. This RRC reconfiguration message carries the MRB configuration.

[0313] S1109, the source access network device forwards the received RRC reconfiguration message 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, multiple target access network devices send an RRC reconfiguration message to the source access network device again. This RRC reconfiguration message carries 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 be found in S1107, and will not be repeated here. That is, when the MBS session is in an active state, multiple target access network devices send RRC reconfiguration messages to the source access network device again.

[0316] For example, multiple target access network devices may consider the first condition to be met when they receive a notification message to activate the MBS session, or when multiple target access network devices determine that the MBS session is in an active state, or when multiple target access network devices receive a group paging message from other access network devices.

[0317] Optionally, when multiple target access network devices receive an activation notification for an MBS session, they can determine whether the handover response message sent by the multiple target access network devices in S1104 carries the MBS configuration; if the MBS configuration is carried, then in S1110, the multiple target access network devices can omit the MRB configuration in the RRC reset message they send.

[0318] S1111, the source access network device forwards the received RRC reconfiguration message to the terminal. Correspondingly, the terminal receives the RRC reconfiguration message from the source access network device.

[0319] S1112, conditional handover completed, 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 select one target access network device (e.g., the first target access network device) from among 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 successful handover message is used to notify the source access network device that it has successfully connected to the first target access network device.

[0323] S1114, the source access network device sends an SN status transmission message to the first target access network device. Correspondingly, the first target access network device receives the SN status transmission message from the source access network device.

[0324] S1115, the source access network device sends a handover cancellation message to other target access network devices. Correspondingly, the other target access network devices receive the handover 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, which 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 can be found in S1107, and will not be repeated here. That is, when the MBS session is in an active state, the first target access network device sends an RRC reconfiguration message to the terminal.

[0327] For example, the first target access network device may consider the first condition to be met when it receives a notification message to activate the MBS session, or when the first target access network device determines that the MBS session is in an active state, or when the first target access network device receives a group paging message from another access network device.

[0328] Optionally, after the terminal accesses the first target access network device, if the MBS session is in an active state, the first target access network device can determine whether the handover response message sent in S1104 carries the MRB configuration. If it carries the MRB configuration, the RRC configuration message sent in S1116 may not include the MRB configuration; and / or, the first target access network device can determine whether the RRC reconfiguration message sent in S1110 carries the MRB configuration. If it carries the MRB configuration, the RRC configuration message sent in S1116 may not include the MRB configuration.

[0329] It should be noted that if the handover response messages sent by multiple target access network devices to the source access network device in S1104 carry MRB configuration, then S1107 to S1111 and S1116 are optional steps. That is, if the handover response message in S1104 carries MRB configuration, S1107 to S1111 and S1016 do not need to be executed; or, if the handover response message in S1104 carries MRB configuration, S1107 to S1111 and S1016 can continue to be executed, and the specific execution process is as follows: 1. After S1106, when continuing to execute S1107 to S1109, steps (…) are not required. S1110 and S1111), and / or S1116; or, 2, when continuing to execute S1110 and S1111 after S1106, (S1107 to S1109) and / or S1116 may not be executed; or, 3, when not continuing to execute (S1107 to S1109) and / or (S1110 and S1111) after S1106, S1116 may continue to be executed after S1115.

[0330] Alternatively, if the handover response messages sent by multiple target access network devices to the source access network device in S1104 do not carry MRB configuration, then the specific execution process of 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 not continuing to execute (S1107 to S1109) and / or (S1110 and S1111), S1116 can be executed after S1115.

[0331] It should also be noted that when applying a CHO to a handover involving an MBS session, the CHO handover process may include more than Figure 11The steps shown may include more or fewer steps.

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

[0333] The above text combined Figures 1 to 11 The method provided in the embodiments of this application has been described in detail below, in conjunction with... Figures 12 to 14 The apparatus provided in the embodiments of this application is described.

[0334] Figure 12 and Figure 13 The diagram illustrates possible apparatuses provided for embodiments of this application. These apparatuses 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 of the above method embodiments.

[0335] Figure 12 This is a schematic block diagram of the apparatus provided in the embodiments of this application. Figure 12 As shown, the device 1200 includes a transceiver module 1210 and a processing module 1220.

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

[0337] For example, the transceiver module 1210 is configured to: send a first handover request message to a second access network device, the first handover request message being used to request a handover of the terminal from the first access network device to the second access network device, the first handover request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one first data packet sent by the first access network device to the terminal; 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 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 whether to perform a condition switch.

[0339] Optionally, the transceiver module 1210 is further configured to: receive a handover response message from the second access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) that has not been submitted to the upper layer in the receiving window; and send the first initial value of the first variable to the terminal.

[0340] Optionally, the transceiver module 1210 is further configured to: receive a second initial value from the second access network device, the second initial value being greater than the first initial value; and send the second initial value to the terminal.

[0341] Optionally, the processing module 1220 is further configured to: determine whether the number of the at least one second data packet is greater than a preset value; the transceiver module 1210 is further configured to: send first information to the second access network device when the number of the at least one second data packet is greater than the preset value, the first information being used to request a second initial value for 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] For example, the transceiver module 1210 is configured to: send a third handover request message to the second access network device, the third handover request message being used to request the first terminal to be switched to the second access network device; receive a handover response message from the second access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first PDCP SDU that has not been submitted to the upper layer in the receiving window; receive a second initial value from the second access network device, the second initial value being 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 mentioned above, please refer to the following: Figures 7 to 11 The relevant descriptions in the illustrated embodiments are directly obtained and will not be repeated here.

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

[0345] For example, the transceiver module 1210 is configured to: receive a first handover request message from a first access network device, the first handover request message being used to request a handover of the terminal from the first access network device to a second access network device, the first handover request message including a first sequence number, the first sequence number being the sequence number of the last first data packet in at least one data packet sent by the first access network device to the terminal; and receive a second sequence number from the first access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number, the at least one first data packet and the at least one second data packet belonging to the same multicast broadcast service (MBS); the processing module 1220 is configured to: delete data packets identified by a sequence number less than or equal to the second sequence number in the cached MBS data packets.

[0346] Optionally, the transceiver module 1210 is further configured to: send a handover response message to the first access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) that has not been submitted to the upper layer in the receiving window.

[0347] Optionally, the transceiver module 1210 is further configured to: receive first information from the first access network device, the first information being used to request a second initial value for the first variable, the second initial value being greater than the first initial value; and send the second initial value to the first access network device.

[0348] Optionally, the transceiver module 1210 is further configured to: after the terminal accesses the second access network device, send a second initial value to the terminal, wherein the second initial value is greater than the first initial value.

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

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

[0351] For example, the transceiver module 1210 is further configured to: receive a third handover request message from a first access network device, the third handover request message being used to request the first terminal to be switched to a second access network device; send a handover response message to the first access network device, the handover response message including a first initial value of a first variable, the first variable indicating the identifier value of the first PDCP SDU that has not been 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 mentioned above, please refer to [link / reference needed]. Figures 7 to 11 The relevant descriptions in the illustrated embodiments are directly obtained and will not be repeated here.

[0353] It should be noted that device 1200 may include a transmitting module but not a receiving module. Alternatively, device 1200 may include a receiving module but not a transmitting module. Specifically, it depends on whether the above-described scheme executed by device 1200 includes both transmitting and receiving actions. It is understood that because device 1200 has communication capabilities, it can also be called a communication device.

[0354] Figure 13 This is another schematic block diagram of the device provided in the embodiments of this application. For example... Figure 13 As shown, device 1300 includes one or more processors 1310. The processor 1310 can be a general-purpose processor or a dedicated processor, such as a baseband processor or a central processing unit. The baseband processor can be used to process communication protocols and communication data, while the central processing unit can be used to control the device (e.g., a first access network device, a second access network device, or a chip), execute software programs, and process data from the software programs.

[0355] Optionally, in one design, processor 1310 may include a program (also referred to as code or instructions) that can be executed on processor 1310, causing device 1300 to perform the methods performed by the first access network device or the second access network device in the above method embodiments. In yet another possible design, device 1300 includes circuitry (…). Figure 13 (Not shown), the circuit is used to implement the functions of the first access network device or the second access network device in the above method embodiments.

[0356] For example, processor 1310 can be used to execute computer programs or instructions in memory to achieve Figures 7 to 11 The steps performed by the first access network device or the second access network device in any of the embodiments shown.

[0357] Optionally, the device 1300 may include one or more memories 1320 storing programs (sometimes referred to as code or instructions) that can be run on the processor 1310, causing the device 1300 to perform the methods performed by the first access network device or the second access network device in the above embodiments.

[0358] Optionally, the processor 1310 and / or memory 1320 may include an artificial intelligence (AI) module, which is used to implement AI-related functions. The AI ​​module may be implemented through software, hardware, or a combination of both. For example, the AI ​​module may include a radio intelligent controller (RIC) module. For example, the AI ​​module may be a near real-time RIC or a non-real-time RIC.

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

[0360] Optionally, the device 1300 may further include a communication interface 1330. The processor 1310, sometimes referred to as a processing unit, controls the device (e.g., a first access network device or a second access network device). The communication interface 1330, sometimes referred to as a transceiver unit, transceiver, transceiver circuit, or transceiver, is used to implement the transceiver function of the device.

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

[0362] It is understandable that since device 1300 has communication capabilities, it can also be called a communication device.

[0363] When device 1300 is used to achieve Figures 7 to 11 In this method, the processor 1310 performs the functions of the aforementioned processing unit, and the communication interface 1330 performs the functions of the aforementioned transceiver module. Whether the communication interface 1330 is used for sending or receiving depends on whether the device 1300 is used to perform a sending or receiving action in the execution scheme.

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

[0365] When the aforementioned device 1300 is a chip applied to a second access network device, the chip implements the functions of the second access network device in the above method embodiments. The chip of the second access network device receives signals from other modules (such as radio frequency modules or antennas) in the second access network device, and these signals may be sent from the first access network device to the second access network device; or, the chip of the second access network device sends signals to other modules (such as radio frequency modules or antennas) in the second access network device, and these signals may be sent from the second access network device to the first access network device.

[0366] It is 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, specifically including a transmitter and a receiver, with the transmitter used to send signals and the receiver 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] Figure 14 This is a schematic diagram of the structure of a wireless access network device provided in an embodiment of this application, such as a schematic diagram of the structure of a base station. The base station 1400 can be applied to, for example... Figure 1In the system shown, the functions of the second access network device in the above method embodiment are executed. As shown in the figure, the base station 1400 may include one or more of the following: one or more (DU+RU) 1410s and one or more CUs 1420s. CUs 1420 can communicate with the next-generation core (NG core). The DU may include at least one antenna 1411, at least one radio frequency unit 1412, at least one processor 1414, and at least one memory 1414. The DU is mainly used for transmitting and receiving radio frequency signals, converting radio frequency signals to baseband signals, and performing some baseband processing. CUs 1420 may include at least one processor 1422 and at least one memory 1421. CUs 1420 and DUs can communicate through an interface. The control plane (CP) interface can be Fs-C, such as F1-C, and the user plane (UP) interface can be Fs-U, such as F1-U. DUs and RUs can cooperate to implement the functions of the physical (PHY) layer. One DU can be connected to one or more RUs. The functions of the DU and RU can be configured in various ways depending on the design. For example, the DU can be configured to implement baseband functions, and the RU can be configured to implement mid-RF functions. As another example, the DU can be configured to implement higher-level functions in the PHY layer, and the RU can be configured to implement lower-level and RF functions in the PHY layer. Higher-level functions in the PHY layer may include a portion of the PHY layer's functions that are closer to the MAC layer, while lower-level functions in the PHY layer may include another portion of the PHY layer's functions that are closer to the mid-RF side.

[0368] The CU 1420 is mainly used for baseband processing and base station control. The DU and CU 1420 can be physically installed together or physically separated, i.e., a distributed base station. The CU 1420 serves as the control center of the base station and can correspond to... Figure 12 The processing module or Figure 13 The processor in the unit, also known as a processing unit, is mainly used to perform baseband processing functions. For example, the CU 1420 can be used to control the base station to execute the operation procedures of the access network equipment in the above method embodiments.

[0369] Specifically, baseband processing on the CU and DU can be divided according to the protocol layers of the wireless network. For example, the functions of the Packet Data Convergence Protocol (PDCP) layer and above are set in the CU, while the functions of protocol layers below PDCP, such as the RLC layer and MAC layer, are set in the DU. Alternatively, the CU may implement the functions of the RRC layer and PDCP layer, while the DU may implement the functions of the RLC layer, MAC layer, and PHY layer.

[0370] Alternatively, the base station 1400 may include one or more radio frequency units (RUs), one or more DUs, and one or more CUs. A DU may include at least one processor 1414 and at least one memory 1413, an RU may include at least one antenna 1411 and at least one radio frequency unit 1412, and a CU may include at least one processor 1422 and at least one memory 1421.

[0371] In one example, the CU 1420 can be composed of one or more single boards. Multiple single boards can collectively support a single access-indicating wireless access network (such as a 5G network), or they can each support wireless access networks with different access standards (such as LTE, 5G, or other networks). The memory 1421 and processor 1422 can serve one or more single boards. That is, each single board can have its own memory and processor, or multiple single boards can share the same memory and processor. Furthermore, each single board can also have necessary circuitry. Similarly, the DU can be composed of one or more single boards. Multiple single boards can collectively support a single access-indicating wireless access network (such as a 5G network), or they can each support wireless access networks with different access standards (such as LTE, 5G, or other networks). The memory 1413 and processor 1414 can serve one or more single boards. That is, each single board can have its own memory and processor, or multiple single boards can share the same memory and processor. Furthermore, each single board can also have necessary circuitry.

[0372] It should be understood that Figure 14 The base station 1400 shown can achieve Figures 7 to 11 The methods illustrated in the embodiments involve various processes related to 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 for implementing the corresponding processes in the above method embodiments. For details, please refer to the descriptions in the above method embodiments; to avoid repetition, detailed descriptions are appropriately omitted here.

[0373] It should be understood that Figure 14The base station 1400 shown is merely one possible architecture for a wireless access network device and should not be construed as limiting this application. The method provided in this application can be applied to network devices with other architectures, such as wireless access network devices including CU, DU, and AAU. This application does not limit the specific architecture of the wireless access network device.

[0374] It should be understood that Figure 14 This is for illustrative purposes only and not as a limitation; wireless access network devices may not rely on this. Figure 14 The structure shown is different. For example, a wireless access network device may also include an AAU, a CU, and / or a DU, or a BBU and an adaptive radio unit (ARU). This application does not limit this.

[0375] The aforementioned CU and / or DU can be used to perform the actions implemented internally by the radio access network device as described in the preceding method embodiments, while the AAU can be used to perform the actions described in the preceding method embodiments whereby the radio access network device sends data to or receives data from the terminal. For details, please refer to the descriptions in the preceding method embodiments; they 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. A processor may be an integrated circuit chip with signal processing capabilities. During implementation, each step of the above method embodiments can be completed by integrated logic circuits in the processor's hardware or by software instructions.

[0377] The aforementioned processor can 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 devices, discrete gate or transistor logic devices, discrete hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0378] The steps of the method disclosed in the embodiments of this application can be directly manifested as being executed by a hardware decoding processor, or executed by a combination of hardware and software modules in the decoding processor. The software modules can reside in mature storage media in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, or registers. This storage medium is located in memory, and the processor reads information from the memory and, in conjunction with its hardware, completes the steps of the above method.

[0379] The memory in this application embodiment can be volatile memory or non-volatile memory, or it can include both volatile and non-volatile memory. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDRSDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous linked dynamic random access memory (SLDRAM), and direct rambus RAM (DR RAM). It should be noted that the memory used in 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 methods provided in the above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any combination thereof. When implemented in software, they can be implemented, in whole or in part, in the form of a computer program product. The computer program product may include one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. 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. For example, the computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. 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 integrates one or more available media. The available medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic disk), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid-state disk (SSD)).

[0381] This application also provides a computer-readable medium having a computer program stored thereon, which, when executed by a computer, implements the functions of the above-described method embodiments.

[0382] This application also provides a computer program product containing instructions that, when executed by a computer, implements the functions of the above-described method embodiments.

[0383] Those skilled in the art will recognize that the units and algorithm steps of the various examples 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 implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0384] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0385] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

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

[0387] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0388] If the aforementioned functions are implemented as 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 this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0389] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A handover method, characterized by, Applied to a first access network device, the method includes: Send a first handover request message to the second access network device. The first handover request message is used to request the terminal to be switched from the first access network device to the second access network device. The first handover request message includes a first sequence number, which is the sequence number of the last first data packet in at least one first data packet sent by the first access network device to the terminal. Send at least one second data packet to the terminal; Send a second sequence number to the second access network device. The second sequence number is the sequence number of the last second data packet in the at least one second data packet sent by the first access network device to the terminal. The second sequence number is greater than the first sequence number. Wherein, the at least one first data packet and the at least one second data packet belong to the same Multicast Broadcast Service (MBS) session; The second sequence number is used by the second access network device to delete the cached data packets of the MBS session.

2. The method of claim 1, wherein, Before sending the first handover request to the second access network device, the method further includes: Confirm to switch conditions.

3. The method according to claim 1 or 2, characterized in that, After sending the first handover request message to the second access network device, the method further includes: Receive a handover response message from the second access network device. The handover response message includes a first initial value of a first variable, whereby the first variable indicates the identifier value of the first Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) that has not been submitted to the upper layer in the receiving window. Send the first initial value of the first variable to the terminal.

4. The method of claim 3, wherein, The method further includes: Receive a second initial value from the second access network device, wherein the second initial value is greater than the first initial value; The second initial value is sent to the terminal.

5. The method of claim 3, wherein, The method further includes: Determine whether the number of the at least one second data packet is greater than a preset value; If the number of at least one second data packet is greater than the preset value, a first message is sent to the second access network device, the first message being used to request a second initial value for 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; The second initial value is sent to the terminal.

6. The method of claim 5, wherein, The preset value is the size of the receiving window.

7. The method of any one of claims 1-2, 4-5, wherein, The second sequence number is carried in the second handover request message, which is used to request the terminal to be switched from the first access network device to the second access network device. The second handover request message indicates that the second access network device does not update the Radio Resource Control (RRC) configuration.

8. The method of any one of claims 1-2, 4-5, wherein, The second sequence number is carried in the early state transmission signaling.

9. The method of any one of claims 1-2, 4-5, wherein, The second sequence number is carried in the MBS early state transmission signaling.

10. A handover method, characterized by, Applied to a second access network device, the method includes: A first handover request message is received from a first access network device. The first handover request message is used to request the terminal to be switched from the first access network device to the second access network device. The first handover request message includes a first sequence number, which 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. Receive a second sequence number from the first access network device, the second sequence number being the sequence number of the last second data packet in at least one second data packet sent by the first access network device to the terminal, the second sequence number being greater than the first sequence number, and the at least one first data packet and the at least one second data packet belonging to the same Multicast Broadcast Service (MBS) session; Delete the data packets in the cached MBS session that are identified by a sequence number whose sequence number is less than or equal to the second sequence number.

11. The method of claim 10, wherein, The first handover request is sent by the first access network device after it determines that a conditional handover is to be performed.

12. The method according to claim 10 or 11, characterized in that, After receiving the first handover request message from the first access network device, the method further includes: A handover response message is sent to the first access network device. The handover response message includes a first initial value of a first variable, which indicates the identifier value of the first Packet Data Convergence Protocol (PDCP) Service Data Unit (SDU) that has not been submitted to the upper layer in the receiving window.

13. The method of claim 12, wherein, The method further includes: Receive first information from the first access network device, the first information being used to request a second initial value for the first variable, the second initial value being greater than the first initial value; Send the second initial value to the first access network device.

14. The method of claim 12, wherein, The method further includes: After the terminal connects to the second access network device, a second initial value is sent to the terminal, the second initial value being greater than the first initial value.

15. The method of claim 12, wherein, The method further includes: Before the terminal connects to the second access network device, it sends a second initial value to the first access network device, the second initial value being greater than the first initial value.

16. The method according to claim 14 or 15, characterized in that The method further includes: It is determined that the number of data packets sent by the second access network device for the MBS session is greater than a preset value.

17. The method of claim 16, wherein, The preset value is the size of the receiving window.

18. The method of any one of claims 10-11, 13-15, wherein, The second sequence number is carried in the second handover request message, which is used to request the terminal to be switched from the first access network device to the second access network device. The second handover request message indicates that the second access network device does not update the Radio Resource Control (RRC) configuration.

19. The method of any one of claims 10-11, 13-15, wherein, The second sequence number is carried in the early state forwarding signaling.

20. The method of any one of claims 10-11, 13-15, wherein, The second sequence number is carried through the MBS early state forwarding signaling.

21. A communication device, characterized in that, Includes modules for implementing the method as described in any one of claims 1 to 20.

22. A communication device, characterized in that, Includes a processor for causing the communication device to implement the method as described in any one of claims 1 to 20 by executing a computer program and / or by logic circuitry.

23. The apparatus according to claim 22, characterized in that, It also includes a memory for storing computer programs and / or configuration files for the logic circuitry.

24. The apparatus according to claim 22 or 23, characterized in that, It also includes a communication interface for inputting and / or outputting signals.

25. A computer-readable storage medium storing a computer program thereon, characterized in that, When the computer program is executed by a processor, the method of any one of claims 1 to 9 is executed, or the method of any one of claims 10 to 20 is executed.

26. A computer program product, characterized in that, The method includes a computer program, which, when run, performs the method according to any one of claims 1 to 9, or the method according to any one of claims 10 to 20.

27. A communication system, characterized in that, It includes a first access network device and a second access network device, wherein the first access network device is used to implement the method as described in any one of claims 1 to 9, and the second access network device is used to implement the method as described in any one of claims 10 to 20.

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