Data transmission method, apparatus and communication system

Abstract

A data transmission method, an apparatus and a communication system, relating to the technical field of wireless communication. A first terminal communicates with a first network device by means of a relay device; the first network device determines that the first terminal switches from the first network device to a third network device, and sends first indication information to a second network device; and the first terminal communicates with the second network device by means of the relay device, the first indication information being used for indicating a downlink transmission requirement of the first terminal or a downlink transmission parameter, so as to instruct the first network device to send first downlink data to the third network device, and the first downlink data comprising downlink data for which a reception success acknowledgment indication has been received from the relay device. Thus, the first network device can indicate to the second network device the downlink transmission requirement of the first terminal or the downlink transmission parameter, so as to enable the second network device to know how to forward downlink data of the first terminal to the third network device, thus reducing the phenomenon of packet loss, and ensuring the downlink data transmission performance of the first terminal.

Description

Data transmission method, device and communication system

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on September 20, 2023, with application number 202311230128.2 and application name "A data transmission method, device and communication system", the entire contents of which are incorporated by reference into this application; this application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on September 27, 2023, with application number 202311288591.2 and application name "A data transmission method, device and communication system", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The embodiments of the present application relate to the field of wireless communication technology, and in particular to a data transmission method, device, and communication system. Background Art

[0004] In wireless communication systems, user equipment (UE) can communicate with a base station via a relay device. This UE is called a remote UE, and communication between the relay device and the remote UE can be via a sidelink. When the remote UE moves, the communication link needs to be switched based on the configuration of the source base station. When inter-base handover is involved, to ensure service continuity, the source base station can also use data forwarding to send the remote UE's downlink data to the target base station. After the remote UE successfully connects to the target base station, the target base station sends the downlink data to the remote UE.

[0005] When the source base station sends downlink data to the remote UE based on the source link and the relay device, it only receives acknowledgment (ACK) and negative acknowledgment (NACK) messages for the downlink data packets from the relay device, and cannot perceive the data transmission status between the relay device and the remote UE. If the data packets transmitted between the relay device and the remote UE are lost and the source base station cannot promptly learn of this situation, the source base station will not be able to forward the lost data packets between the relay device and the remote UE to the target base station when implementing the data forwarding mechanism, resulting in the remote UE still not being able to obtain the required data packets after the handover is completed, which is called packet loss.

[0006] Therefore, how to reduce packet loss is still an important issue that needs to be solved urgently.

[0007] Summary of the Invention

[0008] The embodiments of the present application provide a data transmission method, apparatus, and communication system for reducing packet loss and ensuring downlink data transmission performance of terminal devices.

[0009] In a first aspect, an embodiment of the present application provides a data transmission method, which can be executed by a first network device, or by a component of the first network device, such as a chip or a processor. In this method, a first terminal communicates with the first network device through a relay device, and the first network device can be a control plane of a centralized unit of a source base station. The first network device determines that the first terminal switches from the first network device to a third network device; and sends first indication information to the second network device, wherein the first terminal communicates with the second network device through the relay device, and the first indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal, and the downlink transmission requirements or downlink transmission parameters of the first terminal are used to instruct the second network device to send first downlink data to the third network device, and the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0010] Based on the above scheme, the first network device can indicate the downlink transmission requirements or downlink transmission parameters of the first terminal to the second network device, so that the second network device knows how to forward the downlink data of the first terminal to the third network device, thereby reducing packet loss and ensuring the downlink data transmission performance of the first terminal, such as downlink lossless transmission. Optionally, the first network device can also instruct the second network device to cache the first downlink data of the first terminal, so that part or all of the cached first downlink data can be forwarded to the first terminal when switching to another station, thereby reducing packet loss and ensuring the downlink data transmission performance of the first terminal, such as downlink lossless transmission. It should be understood that in the embodiment of the present application, the relay device can be a relay terminal device or a relay network device, and the embodiment of the present application does not limit the specific implementation of the relay device.

[0011] It can be understood that the above scheme is introduced by taking the CU-CP function and CU-UP function of the target network device as an example in which they are not deployed separately. In actual applications, if the CU-CP function and CU-UP function of the target network device are deployed separately, for example, the CU-CP function is deployed on the third network device and the CU-UP function is deployed on the fourth network device, the downlink transmission requirement or downlink transmission parameter of the above-mentioned first terminal can be specifically used to instruct the second network device to send the first downlink data to the fourth network device. In one example, the first indication information can also be used to indicate the first downlink data of one or more wireless bearers of the first terminal to be cached. Exemplarily, the first wireless bearer represents one or more wireless bearers of the first terminal, and the first indication information may include an identifier of the first wireless bearer.

[0012] Based on the above solution, the first network device can cache and forward downlink data of certain radio bearers of the first terminal as needed, so as to ensure downlink data transmission performance of certain radio bearers of the first terminal and reduce cache overhead.

[0013] In a possible scenario, the method may further include: sending a first message to the third network device, where the first message includes a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0014] Based on the above scheme, the first network device can inform the third network device of the downlink transmission requirements or downlink transmission parameters of the first terminal through the first message, so that the third network device can cooperate with the first network device to implement the data forwarding mechanism to ensure lossless downlink transmission of the first terminal.

[0015] In one example, the first message may include identifiers of one or more radio bearers of the first terminal. Exemplarily, the transmission mode of the first radio bearer is an acknowledgement mode, or the quality of service of the first radio bearer meets a first transmission requirement.

[0016] Based on the above solution, the first network device can inform the third network device of the downlink transmission requirements or downlink transmission parameters of certain radio bearers of the first terminal as needed, so that the third network device can cooperate with the first network device to implement a data forwarding mechanism based on these radio bearers to ensure the downlink data transmission performance of certain radio bearers of the first terminal. Among them, the transmission mode or quality of service is only an example of how to determine these radio bearers and is not a limitation. In specific implementation, the first network device can also determine the radio bearer in combination with specific application requirements or business scenarios, and this embodiment of the application does not specifically limit this.

[0017] In one possible scenario, the first message is further used to request handover of the first terminal to the third network device. That is, the first message may be a handover request message from the first network device. It should be understood that this is merely an example of an implementation of the first message and does not constitute a limitation. In a specific implementation, the first message may also be, for example, a newly added E1 message between the first network device and the third network device that indicates the first terminal's downlink lossless transmission requirements or downlink lossless transmission parameters.

[0018] In one possible scenario, the method may further include: sending second indication information to the second network device, wherein the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0019] Based on the above scheme, the first network device can indicate the reception status of the downlink data of one or more wireless bearers of the first terminal to the second network device, so that the second network device can forward the downlink data of the first terminal to the target base station based on the reception status of the downlink data of the first terminal, so as to reduce packet loss and ensure the downlink data transmission performance of the first terminal.

[0020] In one possible scenario, the method may also include: determining the reception status of downlink data of one or more wireless bearers of the first terminal; and sending the second indication information to the second network device includes: sending the second indication information to the second network device according to the reception status.

[0021] In one example, the method may further include: receiving a second message from the third network device, wherein the second message includes a reception status of downlink data of one or more radio bearers of the first terminal. Exemplarily, the reception status may include at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of a first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0022] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0023] In a possible scenario, the method may further include: sending third indication information to the second network device, where the third indication information is used to instruct the second network device to stop buffering the first downlink data.

[0024] In one example, sending the third indication information to the second network device may include: receiving a third message, wherein the third message is used to indicate the release of the terminal context; or, the third message is used to indicate the release of the connection between the first network device and the core network device; and sending the third indication information to the second network device.

[0025] In one example, sending the third indication information to the second network device may include: sending a fourth message to the first terminal, the fourth message being used to instruct the first terminal to switch from the first network device to the third network device, and / or instructing the first terminal to switch from the second network device to the fourth network device; sending the third indication information to the second network device.

[0026] In one example, the sending of third indication information to the second network device may include: receiving a fifth message from the first terminal, the fifth message being used to confirm that the first terminal has switched from the first network device to the third network device, and / or confirming that the first terminal has switched from the second network device to the fourth network device; and sending third indication information to the second network device.

[0027] In a possible scenario, the method may further include: sending fourth indication information to the second network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0028] In a second aspect, an embodiment of the present application further provides a data transmission method, which can be executed by a second network device, or by a component of the second network device, such as a chip or a processor. In this method, a first terminal communicates with the second network device through a relay device, and the second network device receives first indication information from the first network device, wherein the first terminal communicates with the first network device through the relay device, and the first indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal, and the downlink transmission requirements or downlink transmission parameters of the first terminal are used to instruct the second network device to send first downlink data to the fourth network device, and the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device; and the first downlink data of the first terminal is cached. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0029] Based on the above solution, when the CU-CP function and the CU-UP function of the source base station are deployed separately, for example, the CU-CP function is deployed on the first network device and the CU-UP function is deployed on the second network device, the second network device can know how to forward the downlink data of the first terminal to the fourth network device according to the instruction of the first network device, thereby reducing packet loss and ensuring the downlink data transmission performance of the first terminal, such as downlink lossless transmission. Thus, the second network device can cache the first downlink data of the first terminal according to the first instruction information, so that after switching, part or all of the cached first downlink data of the first terminal can be forwarded to the first terminal, thereby reducing packet loss and ensuring the downlink data transmission performance of the first terminal.

[0030] It is understandable that the above solution is introduced by taking the CU-CP function and CU-UP function of the target network device as an example of separate deployment. In actual application, if the CU-CP function and CU-UP function of the target network device are not separately deployed, for example, the CU-CP function and CU-UP function are deployed on a third network device, the downlink transmission requirement or downlink transmission parameter of the first terminal can specifically be used to instruct the second network device to send the first downlink data to the third network device.

[0031] In an example, the first indication information may also be used to indicate caching of first downlink data of one or more radio bearers of the first terminal.

[0032] In an example, the transmission mode of the first radio bearer may be an acknowledged mode, or the quality of service of the first radio bearer may meet a first transmission requirement, which may specifically be a downlink lossless transmission requirement.

[0033] In one example, the first indication information may include an identifier of the first radio bearer. In other embodiments, the first indication information may indicate the first radio bearer in other ways, which is not limited in this embodiment of the present application.

[0034] In one possible scenario, the method may further include: determining the reception status of downlink data of one or more wireless bearers of the first terminal; and sending part or all of the first downlink data to a fourth network device according to the reception status, wherein the fourth network device is the target network device to which the first terminal switches from the second network device. The fourth network device here can be understood as a target network device. For example, if the CU-CP function and the CU-UP function of the target network device are deployed separately, the target network device may be a fourth network device for implementing the CU-UP function. If the CU-CP function and the CU-UP function of the target network device are not deployed separately, the target network device may be a third network device for implementing the CU-CP function and the CU-UP function of the target network device.

[0035] In a possible scenario, the method may further include: receiving second indication information from the first network device, where the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0036] In a possible scenario, the method may further include: receiving a sixth message from the fourth network device, wherein the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0037] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet.

[0038] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0039] In one possible scenario, the method may further include: receiving third indication information sent from the first network device, the third indication information being used to instruct the second network device to stop buffering the first downlink data; and stopping buffering the first downlink data.

[0040] In one possible scenario, the method may further include discarding cached data packets in the first downlink data according to a data volume cache threshold of the second network device, and using the cache space after packet loss to cache newly arrived data packets in the first downlink data.

[0041] In a possible scenario, the method may further include: receiving fourth indication information from the first network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0042] In a third aspect, an embodiment of the present application provides a data transmission method, which can be executed by a third network device, or by a component of the third network device, such as a chip or processor. In this method, a first terminal switches from the first network device to the third network device, and the first terminal communicates with the first network device through a relay device. The third network device can determine the reception status of the first terminal's downlink data; and send a second message to the first network device based on the reception status, wherein the second message includes the reception status of the downlink data of one or more radio bearers of the first terminal.

[0043] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0044] In one possible scenario, the method may further include: sending fifth indication information to a fourth network device, wherein the fourth network device is the target network device to which the first terminal performs switching, and the fifth indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal.

[0045] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0046] In one example, determining the reception status of downlink data of one or more wireless bearers of the first terminal may also include: receiving sixth indication information from a fourth network device, the sixth indication information being used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal; and determining the reception status of downlink data of one or more wireless bearers of the first terminal based on the sixth indication information.

[0047] In a possible scenario, the method may further include: receiving a first message from a first network device, where the first message is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0048] In one example, the first message may include identifiers of one or more radio bearers of the first terminal.

[0049] In an example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer may meet the first transmission requirement.

[0050] In an example, the first message may also be used to request that the first terminal be handed over to the third network device.

[0051] In a fourth aspect, an embodiment of the present application provides a data transmission method, which can be executed by a third network device, or by a component of a fourth network device, such as a chip or a processor. In this method, a first terminal switches from a first network device to the third network device, the first terminal communicates with the first network device through a relay device, the third network device receives a first message from the first network device, the first message includes a downlink transmission requirement or downlink transmission parameter of the first terminal; and sends seventh indication information to a fourth network device, wherein the fourth network device is the target network device to which the first terminal performs the handover, and the seventh indication information is used to indicate the downlink transmission requirement or downlink transmission parameter of the first terminal.

[0052] In one example, the seventh indication information may include identifiers of one or more radio bearers of the first terminal.

[0053] In one possible scenario, the method may further include: sending an eighth indication message to a fourth network device, wherein the eighth indication message is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the first network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of one or more wireless bearers of the downlink data of the first terminal. In another possible scenario, when the CU-CP function and the CU-UP function of the source network device are deployed separately, they are represented as a first network device and a second network device. The eighth indication message can specifically be used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of one or more wireless bearers of the downlink data of the first terminal.

[0054] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0055] In a fifth aspect, an embodiment of the present application provides a data transmission method, which can be executed by a fourth network device, or by a component of the fourth network device, such as a chip or a processor. In this method, a first terminal switches to the fourth network device, the first terminal communicates with the source network device through a relay device, and the fourth network device determines the reception status of downlink data of one or more radio bearers of the first terminal; according to the reception status, sixth indication information is sent to a third network device, wherein the third network device is the target network device to which the first terminal performs the handover, and the sixth indication information is used to indicate the reception status of downlink data of one or more radio bearers of the first terminal. If the CU-CP function and the CU-UP function of the source network device are not deployed separately, the source network device can be referred to as a first network device, which is used to implement the CU-CP function and the CU-UP function. If the CU-CP function and the CU-UP function of the source network device are deployed separately, the source network device can include a first network device and a second network device, the first network device can be used to implement the CU-CP function, and the second network device can be used to implement the CU-UP function.

[0056] In a possible scenario, the method may further include: receiving a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0057] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0058] In a possible scenario, the method may further include: receiving fifth indication information from the third network device, where the fifth indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0059] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0060] In a sixth aspect, an embodiment of the present application provides a data transmission method, which can be executed by a fourth network device or a chip having functions similar to those of the fourth network device. In this method, a first terminal switches to the fourth network device, the first terminal communicates with a second network device via a relay device, the fourth network device determines the reception status of downlink data of one or more radio bearers of the first terminal, and sends a sixth message to the second network device, wherein the sixth message includes the reception status of downlink data of one or more radio bearers of the first terminal.

[0061] In a possible scenario, the method may further include: receiving a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0062] In an example, the receiving status may include at least one of the following:

[0063] identifiers of one or more radio bearers of the first terminal;

[0064] The sequence number of the first unsuccessfully received data packet corresponding to one or more radio bearers;

[0065] Bitmap information corresponding to one or more radio bearers, where the bitmap information is used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0066] In one possible scenario, the method may further include: receiving seventh indication information from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the seventh indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the wireless bearer of the first terminal.

[0067] In one possible scenario, if the CU-CP function and the CU-UP function of the source network device are deployed separately, represented as a first network device and a second network device, the first network device can be used to implement the CU-CP function, and the second network device can be used to implement the CU-UP function. The method may also include: establishing a user plane tunnel from the fourth network device to the second network device, wherein the second network device is the source network device for the first terminal to perform switching, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal.

[0068] In another possible case, when the CU-CP function and CU-UP function of the source network device are not deployed separately, it is represented as a first network device for implementing the CU-CP function and the CU-UP function. The method may also include: establishing a user plane tunnel from the fourth network device to the first network device, wherein the first network device is the source network device for performing switching by the first terminal, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal.

[0069] In one possible scenario, the method may also include: receiving an eighth indication message sent from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the eighth indication message is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device.

[0070] In a seventh aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. A first terminal communicates with a first network device via a relay device, and the first network device may be a control plane of a centralized unit of a source base station.

[0071] A processing unit is configured to determine that the first terminal switches from the first network device to a third network device; a transceiver unit is configured to send first indication information to the second network device, wherein the first terminal communicates with the second network device via the relay device, the first indication information is used to indicate a downlink transmission requirement or downlink transmission parameter of the first terminal, the downlink transmission requirement or downlink transmission parameter of the first terminal is used to instruct the second network device to send first downlink data to the third network device, the first downlink data including downlink data for which a successful reception confirmation indication is received from the relay device. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0072] In an example, the first indication information may also be used to indicate that first downlink data of one or more radio bearers of the first terminal is to be buffered. Exemplarily, the first indication information may include an identifier of the first radio bearer.

[0073] In a possible scenario, the transceiver unit is configured to send a first message to the third network device, where the first message includes a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0074] In one example, the first message may include identifiers of one or more radio bearers of the first terminal. Exemplarily, the transmission mode of the first radio bearer is an acknowledgement mode, or the quality of service of the first radio bearer meets a first transmission requirement.

[0075] In one possible scenario, the first message is further used to request handover of the first terminal to the third network device. That is, the first message may be a handover request message from the first network device. It should be understood that this is merely an example of an implementation of the first message and does not constitute a limitation. In a specific implementation, the first message may also be, for example, a newly added E1 message between the first network device and the third network device that indicates the first terminal's downlink lossless transmission requirements or downlink lossless transmission parameters.

[0076] In one possible scenario, the transceiver unit is further configured to send second indication information to the second network device, wherein the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0077] In one possible scenario, the processing unit is also used to: determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit sends second indication information to the second network device, including: sending the second indication information to the second network device according to the reception status.

[0078] In one example, the transceiver unit is further configured to: receive a second message from the third network device, wherein the second message includes a reception status of downlink data of one or more radio bearers of the first terminal. Exemplarily, the reception status may include at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0079] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0080] In a possible scenario, the transceiver unit is further configured to: send third indication information to the second network device, where the third indication information is configured to instruct the second network device to stop buffering the first downlink data.

[0081] In one example, the transceiver unit sends a third indication information to the second network device, which may include: receiving a third message, wherein the third message is used to indicate the release of the terminal context; or, the third message is used to indicate the release of the connection between the first network device and the core network device; and sending a third indication information to the second network device.

[0082] In one example, the transceiver unit sends third indication information to the second network device, which may include: sending a fourth message to the first terminal, the fourth message being used to instruct the first terminal to switch from the first network device to the third network device, and / or instructing the first terminal to switch from the second network device to the fourth network device; sending third indication information to the second network device.

[0083] In one example, the transceiver unit sends third indication information to the second network device, which may include: receiving a fifth message from the first terminal, the fifth message being used to confirm that the first terminal switches from the first network device to the third network device, and / or confirming that the first terminal switches from the second network device to the fourth network device; and sending third indication information to the second network device.

[0084] In one possible scenario, the transceiver unit is further configured to send fourth indication information to the second network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0085] In an eighth aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. The first terminal communicates with the second network device through a relay device, and the transceiver unit is used to receive first indication information from the first network device, wherein the first terminal communicates with the first network device through the relay device, and the first indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal, and the downlink transmission requirements or downlink transmission parameters of the first terminal are used to instruct the second network device to send first downlink data to the fourth network device, and the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device; the processing unit is used to cache the first downlink data of the first terminal. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0086] In an example, the first indication information may be used to indicate caching of first downlink data of one or more radio bearers of the first terminal.

[0087] In an example, the transmission mode of the first radio bearer may be an acknowledged mode, or the quality of service of the first radio bearer may meet a first transmission requirement, which may specifically be a downlink lossless transmission requirement.

[0088] In one example, the first indication information may further include an identifier of the first radio bearer. In other embodiments, the first indication information may indicate the first radio bearer in other ways, which is not limited in this embodiment of the present application.

[0089] In one possible scenario, the processing unit is used to: determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit is used to send part or all of the first downlink data to a fourth network device based on the reception status, and the fourth network device is the target network device to which the first terminal switches from the second network device.

[0090] In one possible scenario, the transceiver unit is further configured to: receive second indication information from the first network device, where the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0091] In a possible scenario, the transceiver unit is further configured to: receive a sixth message from the fourth network device, wherein the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0092] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet.

[0093] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0094] In one possible scenario, the transceiver unit is further used to: receive third indication information sent from the first network device, where the third indication information is used to instruct the second network device to stop buffering the first downlink data; and stop buffering the first downlink data.

[0095] In one possible scenario, the transceiver unit is further used to: discard cached data packets in the first downlink data according to a data volume cache threshold of the second network device, and the cache space after packet loss is used to cache newly arrived data packets in the first downlink data.

[0096] In a possible scenario, the transceiver unit is further configured to: receive fourth indication information from the first network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0097] In a ninth aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. A first terminal switches from a first network device to a third network device, and the first terminal communicates with the first network device via a relay device. The processing unit is configured to determine a reception status of downlink data of the first terminal; and the transceiver unit is configured to send a second message to the first network device based on the reception status, wherein the second message includes the reception status of downlink data of one or more radio bearers of the first terminal.

[0098] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0099] In one possible scenario, the transceiver unit is further used to: send fifth indication information to a fourth network device, wherein the fourth network device is the target network device to which the first terminal performs switching, and the fifth indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal.

[0100] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0101] In one example, the transceiver unit is also used to: receive sixth indication information from a fourth network device, wherein the sixth indication information is used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal; and the processing unit is also used to determine the reception status of downlink data of one or more wireless bearers of the first terminal based on the sixth indication information.

[0102] In a possible scenario, the transceiver unit is further configured to: receive a first message from a first network device, where the first message is configured to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0103] In one example, the first message may include identifiers of one or more radio bearers of the first terminal.

[0104] In an example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer may meet the first transmission requirement.

[0105] In an example, the first message may also be used to request that the first terminal be handed over to the third network device.

[0106] In a tenth aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. A first terminal switches from a first network device to a third network device, and the first terminal communicates with the first network device through a relay device. The transceiver unit is configured to receive a first message from the first network device, where the first message includes a downlink transmission requirement or downlink transmission parameter of the first terminal; and to send seventh indication information to a fourth network device, where the fourth network device is the target network device to which the first terminal performs the handover, and the seventh indication information is configured to indicate the downlink transmission requirement or downlink transmission parameter of the first terminal.

[0107] In one example, the seventh indication information may include identifiers of one or more radio bearers of the first terminal.

[0108] In one possible scenario, when the CU-CP function and the CU-UP function of the source network device are not deployed separately, it is represented as a first network device, and the first network device can be used to implement the CU-CP function and the CU-UP function. The transceiver unit is further used to: send an eighth indication information to the fourth network device, wherein the eighth indication information is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the first network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of one or more radio bearers of the downlink data of the first terminal. In another possible scenario, when the CU-CP function and the CU-UP function of the source network device are deployed separately, it is represented as a first network device and a second network device, and the first network device can be used to implement the CU-CP function, and the second network device can be used to implement the CU-UP function. The eighth indication information can specifically be used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of one or more radio bearers of the downlink data of the first terminal.

[0109] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0110] On the eleventh aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. Wherein, the first terminal switches to the fourth network device, the first terminal communicates with the source network device through the relay device, and the processing unit is used to determine the reception status of the downlink data of one or more wireless bearers of the first terminal; the transceiver unit is used to send a sixth indication information to the third network device according to the reception status, wherein the third network device is the target network device to which the first terminal performs the switch, and the sixth indication information is used to indicate the reception status of the downlink data of one or more wireless bearers of the first terminal. Wherein, if the CU-CP function and the CU-UP function of the source network device are deployed separately, the source network device here may refer to the first network device, which is used to implement the CU-CP function.

[0111] In one possible scenario, the transceiver unit is further configured to: receive a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0112] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0113] In a possible scenario, the transceiver unit is further used to: receive fifth indication information from the third network device, where the fifth indication information is used to indicate a downlink transmission requirement or downlink transmission parameter of the first terminal.

[0114] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0115] In a twelfth aspect, an embodiment of the present application provides a communication device, which may include a processing unit and a transceiver unit. A first terminal switches to the fourth network device, and the first terminal communicates with a second network device via a relay device. The processing unit is configured to determine a reception status of downlink data of one or more wireless bearers of the first terminal; and the transceiver unit is configured to send a sixth message to the second network device, wherein the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal.

[0116] In one possible scenario, the transceiver unit is further configured to: receive a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0117] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0118] In one possible scenario, the transceiver unit is also used to: receive seventh indication information from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the seventh indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the wireless bearer of the first terminal.

[0119] In one possible scenario, when the CU-CP function and the CU-UP function of the source network device are deployed separately, it is represented as a first network device and a second network device, the first network device can be used to implement the CU-CP function, and the second network device can be used to implement the CU-UP function, and the processing unit is further used to: establish a user plane tunnel from the fourth network device to the second network device, wherein the second network device is the source network device for the first terminal to perform switching, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of downlink data of one or more radio bearers of the first terminal. In another possible scenario, when the CU-CP function and the CU-UP function of the source network device are not deployed separately, it is represented as a first network device, used to implement the CU-CP function and the CU-UP function, and the processing unit is further used to: establish a user plane tunnel from the fourth network device to the first network device, wherein the first network device is the source network device for the first terminal to perform switching, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of downlink data of one or more radio bearers of the first terminal. In one possible scenario, the transceiver unit is also used to: receive an eighth indication message sent from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the eighth indication message is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device.

[0120] In aspect 13, an embodiment of the present application provides a communication device comprising at least one processor, wherein the at least one processor is used to call a computer program or instruction in a memory to execute the method described in the first aspect and any possible method of the first aspect, or to execute the method described in the second aspect and any possible method of the second aspect, or to execute the method described in the third aspect and any possible method of the third aspect, or to execute the method described in the fourth aspect and any possible method of the fourth aspect, or to execute the method described in the fifth aspect and any possible method of the fifth aspect, or to execute the method described in the sixth aspect and any possible method of the sixth aspect.

[0121] Optionally, the communication device may include the memory, which is used to store computer programs or instructions.

[0122] In the fourteenth aspect, an embodiment of the present application provides a chip system, which includes at least one processor, and the at least one processor is used to call one or more computer programs or instructions in the memory to implement the method as described in the first aspect and any possible method of the first aspect, or implement the method as described in the second aspect and any possible method of the second aspect, or implement the method as described in the third aspect and any possible method of the third aspect, or implement the method as described in the fourth aspect and any possible method of the fourth aspect, or implement the method as described in the fifth aspect and any possible method of the fifth aspect, or implement the method as described in the sixth aspect and any possible method of the sixth aspect.

[0123] In aspect fifteen, an embodiment of the present application provides a communication system, comprising a communication device for use as described in the seventh aspect and any possible design of the seventh aspect, or comprising a communication device for implementing the communication device described in the eighth aspect and any possible design of the eighth aspect; or comprising a communication device for implementing the communication device described in the ninth aspect and any possible design of the ninth aspect, or comprising a communication device for implementing the communication device described in the tenth aspect and any possible design of the tenth aspect, or comprising a communication device for implementing the communication device described in the eleventh aspect and any possible design of the eleventh aspect; or comprising a communication device for implementing the communication device described in the twelfth aspect and any possible design of the twelfth aspect.

[0124] In the sixteenth aspect, an embodiment of the present application provides a communication system, comprising one or more of the following: a network device for implementing the method described in the first aspect and any possible method of the first aspect, a network device for implementing the method described in the second aspect and any possible method of the second aspect, a network device for implementing the method described in the third aspect and any possible method of the third aspect, a network device for implementing the method described in the fourth aspect and any possible method of the fourth aspect, a network device for implementing the method described in the fifth aspect and any possible method of the fifth aspect, and a network device for implementing the method described in the sixth aspect and any possible method of the sixth aspect.

[0125] In the seventeenth aspect, an embodiment of the present application provides a computer-readable storage medium, which stores computer-executable instructions. When the computer-executable instructions are called by an electronic device, the electronic device executes the method as described in the first aspect and any possible design of the first aspect, or the electronic device executes the method as described in the second aspect and any possible design of the second aspect, or the electronic device executes the method as described in the third aspect and any possible design of the third aspect, or the electronic device executes the method as described in the fourth aspect and any possible design of the fourth aspect, or the electronic device executes the method as described in the fifth aspect and any possible design of the fifth aspect, or the electronic device executes the method as described in the sixth aspect and any possible design of the sixth aspect.

[0126] In aspect 18, an embodiment of the present application provides a computer program product, which includes computer execution instructions. When the computer execution instructions are run on a computer, the computer executes the method described in the first aspect and any possible design of the first aspect, or the computer executes the method described in the second aspect and any possible design of the second aspect, or the computer executes the method described in the third aspect and any possible design of the third aspect, or the computer executes the method described in the fourth aspect and any possible design of the fourth aspect, or the computer executes the method described in the fifth aspect and any possible design of the fifth aspect, or the computer executes the method described in the sixth aspect and any possible design of the sixth aspect.

[0127] Based on the implementations provided in the above aspects, the embodiments of the present application can be further combined to provide more implementations.

[0128] The technical effects that can be achieved by any possible implementation method in any of the second to eighteenth aspects mentioned above can be referred to the description of the technical effects that can be achieved by any possible implementation method in any of the first aspect mentioned above, and the repetitions will not be discussed. BRIEF DESCRIPTION OF THE DRAWINGS

[0129] FIG1 is a schematic diagram of the architecture of a communication system used in an embodiment of the present application;

[0130] FIG2 is a schematic diagram of the structure of a PDCP status report;

[0131] Figure 3 is a schematic diagram of the communication architecture of SL U2N Relay;

[0132] Figure 4 is a schematic diagram of the L2 SL U2N Relay protocol stack;

[0133] FIG5 is a schematic diagram of a same-site handover scenario;

[0134] FIG6 is a schematic diagram of an inter-site handover scenario;

[0135] FIG7 is a schematic diagram of a communication interface;

[0136] Figure 8 is a schematic diagram of the protocol stack;

[0137] FIG9 is a schematic diagram of the CP-UP separation architecture of the CU;

[0138] FIG10 is a flow chart showing the implementation of a data forwarding mechanism in an inter-site handover scenario;

[0139] FIG11 is a schematic diagram of a packet loss situation;

[0140] FIG12 is a schematic flow chart of a data transmission method according to an embodiment of the present application;

[0141] FIG13 is a schematic diagram of a flow chart of a data transmission method according to an embodiment of the present application;

[0142] FIG14 is a schematic flow chart of a data transmission method according to an embodiment of the present application;

[0143] FIG15 is a flow chart of a data transmission method according to an embodiment of the present application;

[0144] FIG16 is a schematic flow chart of a data transmission method according to an embodiment of the present application;

[0145] FIG17 is a schematic diagram of a communication device provided in an embodiment of the present application;

[0146] FIG18 is a schematic diagram of a communication device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0147] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0148] To facilitate a clear description of the technical solutions of the embodiments of the present application, in the embodiments of the present application, words such as "first" and "second" are used to distinguish between identical or similar items with substantially the same functions and effects. For example, the first information and the second information are merely used to distinguish different information and do not limit their order. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity or execution order, and words such as "first" and "second" do not necessarily limit differences.

[0149] In the embodiments of the present application, "at least one" refers to one or more, and "more" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following items" or similar expressions refers 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, b, and c. Among them, a, b, and c can be single or multiple.

[0150] To facilitate understanding of the data transmission method provided in the embodiments of the present application, the system architecture and application scenarios of the data transmission method provided in the embodiments of the present application are described below. It is understood that the system architecture and application scenarios described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application and do not constitute a limitation on the technical solutions provided in the embodiments of the present application.

[0151] Figure 1 is a schematic diagram of the architecture of a communication system 1000 used in an embodiment of the present application. As shown in Figure 1 , the communication system includes a radio access network 100 and a core network 200. Optionally, the communication system 1000 may also include the Internet 300. The radio access network 100 may include at least one radio access network device (such as 110a and 110b in Figure 1 ) and at least one terminal (such as 120a-120j in Figure 1 ). The terminal is wirelessly connected to the radio access network device, and the radio access network device is wirelessly or wiredly connected to the core network. The core network device and the radio access network device may be independent, distinct physical devices, or the core network device's functions and the radio access network device's logical functions may be integrated into the same physical device, or a single physical device may integrate some of the core network device's functions and some of the radio access network device's functions. Terminals and radio access network devices may be interconnected via wired or wireless connections. Figure 1 is merely a schematic diagram. The communication system may also include other network devices, such as wireless relay devices and wireless backhaul devices, which are not shown in Figure 1 .

[0152] A radio access network device may be a device with wireless transceiver functions. The radio access network device may be a device that provides wireless communication function services, typically located on the network side, and may include but is not limited to: a next-generation base station (gNodeB, gNB) in a fifth-generation (5G) communication system, a next-generation base station in a sixth-generation (6G) mobile communication system, a base station in a future mobile communication system, or an access node in a WiFi system, an evolved node B (eNB) in an LTE system, a radio network controller (RNC), a node B (NB), a base station controller (BSC), a home base station (e.g., home evolved NodeB, or home Node B, HNB), a base band unit (BBU), a transmission reception point (TRP), a transmitting point (TP), a base transceiver station (BTS), etc.

[0153] In a network structure, the access network device may include a centralized unit (CU) node, a distributed unit (DU) node, a RAN device including a CU node and a DU node, or a control plane CU node and a user plane CU node, and a RAN device including a DU node, or a RAN device including a radio unit (RU). In different systems, CU (or CU-CP and CU-UP), DU or RU may also have different names, but those skilled in the art can understand their meanings. For example, in an ORAN system, CU may also be called O-CU (open CU), DU may also be called O-DU, CU-CP may also be called O-CU-CP, CU-UP may also be called O-CU-UP, and RU may also be called O-RU. For convenience of description, this application uses CU, CU-CP, CU-UP, DU and RU as examples for description. Any of the CU (or CU-CP, CU-UP), DU and RU in this application may be implemented by a software module, a hardware module, or a combination of a software module and a hardware module.

[0154] Among them, the access network equipment provides services for the cell, and the user equipment communicates with the base station through the transmission resources used by the cell (for example, frequency domain resources, or spectrum resources). The cell can be a cell corresponding to a base station (for example, a base station), and the cell can belong to a macro base station or a base station corresponding to a small cell. The small cell here can include: a metro cell, a micro cell, a pico cell, a femto cell, etc. These small cells have the characteristics of small coverage and low transmission power, and are suitable for providing high-speed data transmission services. The wireless access network equipment can be a macro base station (such as 110a in Figure 1), a micro base station or an indoor station (such as 110b in Figure 1), a relay node or a donor node, a device that provides wireless communication services to user equipment in a V2X communication system, a wireless controller in a cloud radio access network (CRAN) scenario, a relay station, a vehicle-mounted device, a wearable device, and a network device in a future evolution network. The embodiments of this application do not limit the specific technology and specific device form adopted by the wireless access network equipment. For ease of description, the following description uses a base station as an example of a wireless access network device.

[0155] The terminal may also be referred to as a terminal device, user equipment (UE), mobile station (MS), mobile terminal (MT), etc., which may be an entity on the user side for receiving or transmitting signals, such as a mobile phone. The terminal device may be a user equipment (UE), wherein the UE includes a handheld device, a vehicle-mounted device, a wearable device, or a computing device with wireless communication capabilities. Exemplarily, the UE may be a mobile phone, a tablet computer, or a computer with wireless transceiver capabilities. The terminal device may also be a virtual reality (VR) terminal device, an augmented reality (AR) terminal device, a wireless terminal in industrial control, a wireless terminal in unmanned driving, a wireless terminal in telemedicine, a wireless terminal in a smart grid, a wireless terminal in a smart city, a wireless terminal in a smart home, and the like. The terminal can be widely used in various scenarios, such as device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart office, smart wearable, smart transportation, smart city, etc. The terminal can be a mobile phone, tablet computer, computer with wireless transceiver function, wearable device, vehicle, drone, helicopter, airplane, ship, robot, robotic arm, smart home device, etc. In the embodiment of the present application, the device for implementing the function of the terminal can be a terminal; it can also be a device that can support the terminal to implement the function, such as a chip system, or a communication module, or a modem, which can be installed in the terminal. In the embodiment of the present application, the chip system can be composed of a chip, or it can include a chip and other discrete devices. In the technical solutions provided in the embodiments of the present application, the device for implementing the function of the terminal is a terminal, and the terminal is a UE as an example to describe the technical solutions provided in the embodiments of the present application. The embodiments of the present application do not limit the specific technology and specific device form adopted by the terminal device.

[0156] Optionally, the UE may also be configured to act as a base station. For example, the UE may act as a scheduling entity that provides sidelink signals between UEs in vehicle-to-everything (V2X), device-to-device (D2D), or peer-to-peer (P2P) scenarios.

[0157] Base stations and terminals can be fixed or mobile. They can be deployed on land, indoors or outdoors, handheld or vehicle-mounted; on water; or in the air on aircraft, balloons, and satellites. The embodiments of this application do not limit the application scenarios of base stations and terminals.

[0158] The roles of base stations and terminals can be relative. For example, the helicopter or drone 120i in Figure 1 can be configured as a mobile base station. For terminals 120j accessing the wireless access network 100 via 120i, 120i is a base station. However, for base station 110a, 120i is a terminal, meaning that communication between 110a and 120i occurs via a wireless air interface protocol. Of course, communication between 110a and 120i can also occur via a base station-to-base station interface protocol. In this case, 120i is also a base station relative to 110a. Therefore, base stations and terminals can be collectively referred to as communication devices. 110a, 110b, and 120a-120j in Figure 1 can be referred to as communication devices having their respective functions, such as communication devices having base station functions or communication devices having terminal functions.

[0159] Communication between base stations and terminals, between base stations, and between terminals can be carried out through authorized spectrum, unlicensed spectrum, or both. Communication can be carried out through spectrum below 6 gigahertz (GHz), spectrum above 6 GHz, or spectrum below 6 GHz and spectrum above 6 GHz. The embodiments of the present application do not limit the spectrum resources used for wireless communication.

[0160] In the embodiments of the present application, the functions of the base station may also be performed by a module (such as a chip) in the base station, or by a control subsystem that includes the base station function. The control subsystem that includes the base station function here can be a control center in the application scenarios of the above-mentioned terminals such as smart grid, industrial control, intelligent transportation, and smart city. The functions of the terminal may also be performed by a module (such as a chip or a modem) in the terminal, or by a device that includes the terminal function.

[0161] To facilitate understanding of the solutions of the embodiments of the present application, the nouns or terms involved in the embodiments of the present application are first explained below.

[0162] 1. Sidelink communication:

[0163] In a wireless communication system, data communication can be carried out between UEs through the network, or directly between UEs without the help of the network. The interface between UEs is called the PC5 interface, which is similar to the Uu interface between UEs and base stations. The link between UEs is called sidelink. A typical application scenario of sidelink communication is vehicle-to-everything (V2X). In the vehicle network, each vehicle is a UE, and data can be transmitted directly between UEs through sidelink without going through the network, which can effectively reduce communication delays. It is understandable that the side link can also be called side link, side link, side link, etc.

[0164] 2. Broadcast, unicast, and multicast on sidelink:

[0165] Broadcast communication on the sidelink is similar to the base station broadcasting system information, that is, the UE sends broadcast service data without encryption. Any other UE within the effective reception range that is interested in the broadcast service can receive the broadcast service data.

[0166] Unicast communication on the sidelink is similar to data communication after a radio resource control (RRC) connection is established between a UE and a base station. It requires a unicast connection to be established between the two UEs. After the unicast connection is established, the two UEs can communicate data based on the negotiated identifier, and the data can be encrypted or unencrypted.

[0167] Multicast communication on the sidelink refers to communication between all UEs in a communication group. Any UE in the group can send or receive data for the multicast service.

[0168] In the embodiment of the present application, the sidelink communication between UEs is not limited to the above-mentioned broadcast, unicast, or multicast methods.

[0169] 3. Radio Bearer (RB):

[0170] A radio bearer is a general term for a series of protocol entities and configurations allocated by a base station to a UE, including the radio resource control (RRC) or service data adaptation protocol (SDAP) protocol entity, the packet data convergence protocol (PDCP) entity, the radio link control (RLC) protocol entity, the medium access control (MAC) protocol entity, and a series of resources allocated by the physical layer (PHY). Radio bearers are divided into data radio bearers (DRBs) and signaling radio bearers (SRBs). The former is used to carry data, and the latter is used to carry signaling messages. In a sidelink communication scenario, communication between UEs is carried out through sidelink radio bearers (SLRBs), which include sidelink DRBs and sidelink SRBs. In the protocol text, the radio bearer configuration generally only includes the configuration of the PDCP layer and the service data adaptation protocol (SDAP) layer. The protocol entity below the RLC layer is called the RLC bearer, and the corresponding configuration is given in the RLC bearer configuration.

[0171] 4. PDCP status report:

[0172] During the communication process, the receiving end may send a PDCP status report to the transmitting end. The PDCP status report may be used to indicate the receiving end's reception status of the data packet from the transmitting end.

[0173] Exemplarily, the format of the PDCP status report may be as shown in FIG2 . The format may include 5+N bytes (for example, represented as Oct1-Oct5, and Oct6-Oct5+N), each byte may include 8 bits for carrying different content, and N is an integer greater than or equal to 1.

[0174] For example, the Oct1 field can carry D / C indication information and PDU type indication information. The D / C indication information occupies one bit and can be used to indicate whether the PDCP PDU type is a PDCP Data PDU or a PDCP Control PDU. If it is a PDCP Control PDU, the PDU type indication information occupies three bits and can be used to indicate the type of PDCP control PDU. For example, 000 corresponds to a PDCP status report, or 001 corresponds to an interspersed ROHC feedback / ROHC feedback PDU. The R field is a reserved bit and can be set to all 0s.

[0175] For example, the Oct2-Oct5 fields may carry the first missing count (FMC) (cont.), that is, the COUNT value corresponding to the first lost PDCP PDU. The COUNT value may be composed of two parts: the Hyper Frame Number (HFN) and the PDCP sequence number (SN). HFN and SN are the sequence numbers assigned by the transmitter to each PDCP PDU.

[0176] Optionally, the Oct6 field - Oct5+N field can carry bitmap information. The bitmap consists of 0 and 1, which is used to indicate the reception status of each PDCP SDU starting from FMC in sequence. 0 represents packet loss and 1 represents successful reception.

[0177] 5. Sidelink UE to Network Relay (also known as sidelink UE-to-Network Relay, SL UE-to-Network Relay, or SL U2N Relay):

[0178] SL U2N Relay, also known as relay technology, is a technology in which a UE helps another UE communicate with a base station. Figure 3 shows the communication architecture of SL U2N Relay. A remote UE (Remote UE) communicates with a base station through the collaboration of a relay UE (Relay UE). The Remote UE and Relay UE communicate via sidelink, the corresponding interface being called PC5. The Relay UE is directly connected to the base station, communicating through the Uu port.

[0179] Embodiments of the present application can be used in Layer 2 (L2) scenarios of SL U2N Relay, hereinafter referred to as L2SL U2N Relay. Figure 4 is a schematic diagram of the L2SL U2N Relay protocol stack. Data packets from the Remote UE are relayed below the PDCP layer of the Relay UE. That is, the Relay UE only maintains the relayed RLC bearer, including the RLC layer, MAC layer, and PHY layer. Therefore, there are end-to-end PDCP layers, SDAP layers, and RRC layers between the Remote UE and the base station, but no end-to-end RLC layers, MAC layers, and PHY layers.

[0180] This protocol architecture adds the Sidelink Relay Adaptation Protocol (SRAP) layer between the RLC layer and the PDCP layer. The SRAP layer's primary function is to multiplex and demultiplex radio bearers, enabling the multiplexing of different radio bearers onto a single RLC bearer and the corresponding demultiplexing process. The RLC bearer between the Remote UE and the Relay UE is called the PC5 Relay RLC channel / bearer, and the RLC bearer between the Relay UE and the base station is called the Uu Relay RLC channel / bearer.

[0181] 6. Remote UE path switching:

[0182] The "path" in the embodiments of the present application refers to a communication path or a communication link. Among them, the Remote UE can communicate with the base station through a direct link, which is called a direct link or a direct link. Alternatively, the Remote UE can communicate with the base station through an indirect link with the assistance of the Relay UE, which is called a non-direct link or an indirect link, and the Remote UE and the Relay UE are located within the cell coverage of the same base station. On the direct link, the Remote UE communicates with the base station directly through the Uu port. On the indirect link, the Remote UE communicates with the base station through the Relay UE, wherein the Remote UE and the Relay UE can be connected and communicated through the PC5 interface and the sidelink, or can communicate through a non-3GPP link.

[0183] The remote UE in L2SL U2N Relay has a service continuity requirement, that is, it needs to switch paths based on the configuration of the base station in the connected state. For example, in the intra-site handover scenario shown in Figure 5, in case (a), the remote UE can switch from a non-direct link to a direct link; in case (b), the remote UE can switch from a direct link to a non-direct link; in case (c), the remote UE can switch from a non-direct link through the source relay device under the same base station to another non-direct link through the target relay device. Alternatively, in the inter-site handover scenario shown in Figure 6, in case (a), the remote UE can switch from a non-direct link with the source base station to a direct link with the target base station; in case (b), the remote UE can switch from a direct link with the source base station to a non-direct link with the target base station; in case (c), the remote UE can switch from a non-direct link with the source base station to a non-direct link with the target base station.

[0184] 7. CU-DU separation architecture:

[0185] The CU-DU split architecture divides a base station into a centralized unit (CU) and a distributed unit (DU). Part of the base station's functions are deployed in the CU, while the remaining functions are deployed in the DU. Multiple DUs share a single CU, saving costs and facilitating network expansion. As shown in Figure 7, the gNB-CU and gNB-DU can be connected via the F1 interface, while the CU-CP represents the gNB's connection to the core network (EPC or 5GC) via the NG interface.

[0186] In this CU-DU split architecture, as shown in Figure 8, the gNB-CU is responsible for the RRC, SDAP, and PDCP protocol layer functions, while the gNB-DU is responsible for the RLC, MAC, and PHY protocol layer functions. In particular, the SRAP layer, newly introduced in the SL U2N relay, is located in the gNB-DU. Furthermore, for the control plane protocol stack, the gNB-CU-CP is responsible for the RRC and PDCP entities corresponding to SRBs; for the user plane protocol stack, the gNB-CU-UP is responsible for the PDCP entities corresponding to SDAP and DRBs.

[0187] 8. gNB-CU CP-UP Separation Architecture

[0188] The CU can also be divided into the control plane (CU-CP) and the user plane (CU-UP). The CU-CP is responsible for control plane functions, primarily including RRC and the PDCP corresponding to the control plane (or SRB), namely PDCP-C. PDCP-C is responsible for control plane data encryption, integrity protection, and data transmission. The CU-UP is responsible for user plane functions, primarily including SDAP and the PDCP corresponding to the user plane (or DRB), namely PDCP-U. SDAP is responsible for processing core network data and mapping flows to bearers. PDCP-U is responsible for data plane encryption, integrity protection, header compression, sequence number maintenance, and data transmission. As shown in Figure 9, the CU-CP and CU-UP are connected via the E1 interface. The CU-CP connects to the DU via the F1 interface control plane, namely F1-C. The CU-UP connects to the DU via the F1 interface user plane, namely F1-U. Alternatively, PDCP-C may also reside in the CU-UP.

[0189] 9. Data forwarding mechanism:

[0190] Taking the inter-site handover scenario of situation (a) shown in FIG6 as an example, as shown in FIG10 , the path handover process of the remote UE may include the following steps:

[0191] S1001: With the assistance of a source relay UE, a remote UE transmits uplink (UL) data and downlink (DL) data with a source base station via a source link (ie, a non-direct link based on the source relay UE).

[0192] S1002: The remote UE performs measurement and reports according to the configuration of the source base station.

[0193] For example, if the remote UE measures that the sidelink signal quality of the current serving relay UE (ie, source relay UE) is poor and there is a more suitable cell nearby, measurement and reporting are triggered to enable the source base station to switch the communication path for the remote UE.

[0194] S1003: The source base station decides to hand over the remote UE to a cell managed by the target base station based on the measurement report information of the remote UE.

[0195] S1004: The source base station sends a handover (HO) request message to the target base station. The message may carry configuration information of the remote UE on the source base station side.

[0196] S1005: The target base station performs admission control and decides to execute handover of the remote UE.

[0197] S1006: The target base station sends an acknowledgement (ACK) message corresponding to the handover request to the source base station. The ACK message carries radio resource control (RRC) configuration information of the remote UE on the target base station side.

[0198] S1007: With the assistance of the source relay UE, the source base station sends an RRC reconfiguration message to the remote UE through an indirect link. The RRC reconfiguration message is used to instruct the remote UE to access the target cell managed by the target base station. The RRC reconfiguration message includes information such as the cell ID information of the target cell.

[0199] S1008: The remote UE accesses the target cell managed by the target base station based on the received RRC reconfiguration message.

[0200] S1009: The remote UE sends an RRC reconfiguration completion message to the target base station.

[0201] S1010: The target base station instructs the source base station to release the UE context of the remote UE.

[0202] S1011: The source base station sends an RRC reconfiguration message to the source relay UE, instructing the source relay UE to release the remote UE and relay-related configurations.

[0203] S1012: The source relay UE or the remote UE triggers the process of releasing the PC5 connection.

[0204] During the above switching process, data transmission continuity is achieved between base stations through data forwarding.

[0205] Specifically, before implementing the above S1007, the source base station maintains a connection with the remote UE and sends downlink data to the remote UE via a non-direct link between the source base station and the remote UE. After S1007, the source base station will send the downlink data to the target base station via data forwarding, that is, the downlink data of the remote UE will be sent through the GTP-U tunnel via the Xn port. The GTP-U tunnel can be configured by the source base station instructing the target base station in S1004-S1006, and each radio bearer data is transmitted over a GTP-U tunnel. When the remote UE successfully accesses the target base station, the target base station can send the downlink data sent by the source base station to the remote UE, thus completing data forwarding. This technology may cause packet loss.

[0206] In a possible downlink data transmission scenario on a source link, as shown in FIG11(a), a downlink data packet is represented by a rectangular box. Assume that before the source base station sends RRC reconfiguration information to the remote UE based on the source link (corresponding to S1007), the source base station sends downlink data packets numbered 0-8 to the relay UE and receives ACK information corresponding to data packets numbered 0, 1, 3, 5, 6, and 8, as well as negative acknowledgment (NACK) information corresponding to data packets numbered 2, 4, and 7 from the relay UE. The ACK information indicates that the relay UE successfully receives data packets numbered 0, 1, 3, 5, 6, and 8, and the NACK information indicates that the relay UE fails to successfully receive data packets numbered 2, 4, and 7 (the symbol "×" in the figure indicates unsuccessful transmission / reception). The relay UE forwards the data packets to the remote UE. Assume that only data packet numbered 0 is successfully transmitted, while the remaining data packets (data packets numbered 1, 3, 5, 6, and 8) all fail to transmit.

[0207] According to the above-mentioned data forwarding mechanism, as shown in Figure 11 (b), the source base station will only forward the downlink data packets for which the ACK information was not successfully received (for example, data packets numbered 2, 4, and 7) and the new downlink data packets (represented by the dotted box) to the target base station via data forwarding. After the remote UE accesses the target base station, the target base station will retransmit the data packets numbered 2, 4, and 7 and the new downlink data packets to the remote UE via the target link. However, for the remote UE, whether before or after the link switch, the data packets numbered 1, 3, 5, 6, and 8 were not successfully received, resulting in the loss of these data packets.

[0208] Similarly, there is also a packet loss problem in the inter-site handover scenario of situation (c) shown in Figure 6. In this situation, when implementing the above S1008, the remote UE accesses the target cell managed by the target relay UE and the target base station based on the received RRC reconfiguration message. When implementing the above S1009, the remote UE sends an RRC reconfiguration completion message to the target base station through the target relay UE. The other steps are similar to the other steps shown in Figure 10, and can refer to each other and are not repeated here. Optionally, the source base station side can also be a multi-path connection. For example, the remote UE communicates with the source base station through multiple relay devices, or communicates with the source base station through a direct link and an indirect link. There may be packet loss problems on the indirect link between the remote UE and the source base station. After the handover, the remote UE and the target base station may have a direct link, an indirect link, or multiple paths, and the multiple paths may include a direct link and / or an indirect link.

[0209] The embodiments of the present application address the packet loss problem that exists when the CU-CP function and CU-UP function of the source base station and / or the target base station implement the data forwarding mechanism under the CP-UP separation architecture as shown in Figure 9, and propose some solutions to reduce packet loss and ensure the downlink data transmission performance of the remote UE, such as downlink lossless transmission.

[0210] For ease of understanding, the following describes the interaction process involved when the source base station and / or the target base station adopt different structures in conjunction with different method flow charts.

[0211] FIG12 is a flow chart of a data transmission method according to an embodiment of the present application. Referring to FIG12 , taking the CU-CP function and CU-IP function of the source base station as an example (the CP-UP separation architecture shown in FIG9 ), the data transmission method may include the following steps:

[0212] S1210: The first network device determines that the first terminal is switched from the first network device to the third network device.

[0213] In this example, the first network device can provide control plane communication services for the first terminal, and the first network device can be implemented as the CU-CP of the source base station. The second network device can provide user plane communication services for the first terminal, and the second network device can be implemented as the CU-UP of the source base station. The third network device can be implemented as the target base station.

[0214] When S1210 is specifically implemented, the first network device may determine that the first terminal is switched from the first network device to the third network device through direct or indirect information interaction with the first terminal, or the second network device, or the third network device.

[0215] For example, the first network device can communicate with the first terminal through the source relay device, receive measurement reporting information from the first terminal, and analyze whether the quality of the communication link between the first terminal and the relay device, or the communication link between the relay device and the source DU, has deteriorated based on the measurement reporting information, so as to decide whether it is necessary to switch the communication link for the first terminal, for example, switching the first terminal to the third network device. The first network device can directly determine whether it is necessary to switch the communication link for the first terminal based on the measurement reporting information, or the first network device can also determine whether it is necessary to switch the communication link for the first terminal after communicating with the second network device.

[0216] Alternatively, for example, the first network device may send a handover request message to a third network device when it is necessary to switch the communication link for the first terminal. The third network device may receive the handover request message from the first network device, and if the third network device confirms the handover, it may send a handover request confirmation message to the first network device. The first network device may determine, based on the handover request confirmation message, that the first terminal is to be handed over from the first network device to the third network device.

[0217] In the embodiment of the present application, the type of communication link between the first terminal and the third network device is not limited. In one example, after switching, the first terminal and the third network device may be a direct link, for example, the first terminal communicates directly with the third network device through the Uu port. In another example, after switching, the first terminal and the third network device may be a non-direct link, for example, the first terminal communicates with the third network device through the target relay device. For ease of distinction, the relay device on the source link before the first terminal switches can be referred to as the first relay device or the source relay device, and the relay device on the target link after the first terminal switches can be referred to as the second relay device or the target relay device.

[0218] S1220: The first network device sends first indication information to the second network device. Correspondingly, the second network device may receive the first indication information from the first network device.

[0219] In an embodiment of the present application, the first indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal. The downlink transmission requirements or downlink transmission parameters of the first terminal are used to instruct the second network device to send the first downlink data to the third network device, so that the second network device knows how to forward the downlink data of the first terminal to the third network device, thereby reducing packet loss and ensuring the downlink data transmission performance of the first terminal, such as downlink lossless transmission. Furthermore, the second network device can send the first downlink data of the first terminal to the third network device based on the first indication information. Alternatively, the second network device can send part or all of the first downlink data of the first terminal to the third network device based on the first indication information.

[0220] In an embodiment of the present application, the first indication information may be an explicit or implicit indication of the downlink transmission requirements or downlink transmission parameters of the first terminal. In an optional implementation, the first indication information may indicate the downlink transmission requirements or downlink transmission parameters of all radio bearers of the first terminal, and accordingly, the first downlink data may include the downlink data of all radio bearers of the first terminal. In another optional implementation, the first indication information may indicate the downlink transmission requirements or downlink transmission parameters of some radio bearers of the first terminal, and accordingly, the first downlink data may include the downlink data of one or more radio bearers of the first terminal.

[0221] Taking the example of the first indication information indicating the downlink transmission requirements or downlink transmission parameters of all radio bearers of the first terminal, for example, when an explicit indication method is used, the first indication information may be enabling information. When the second network device receives the enabling information, it may be considered that the first network device indicates the downlink transmission requirements or downlink transmission parameters of all radio bearers of the first terminal, so that the second network device guarantees the downlink lossless transmission requirements of the first terminal. Or, for example, the first indication information may include information for stopping the operation of discarding downlink data packets based on the receipt of a successful reception confirmation instruction from the source relay device, so as to indicate the downlink transmission requirements or downlink transmission parameters of all radio bearers of the first terminal. For example, when an implicit indication method is used, the first indication information may include the link switching type of the first terminal, such as the inter-station switching type from a non-direct link to a direct link, or the inter-station switching type from a non-direct link to a non-direct link. After the second network device receives the first indication information, it may be considered that the second network device has received the downlink transmission requirements or downlink transmission parameters of the first terminal, so that the second network device guarantees the downlink lossless transmission requirements of the first terminal. Similarly, the first network device may use a similar method to indicate the downlink transmission requirements or downlink transmission parameters of some wireless bearers of the first terminal through the first indication information. Optionally, the first indication information may also include the identifiers of one or more wireless bearers of the first terminal.

[0222] In an embodiment of the present application, the first indication information can also be used to indicate the first downlink data of all radio bearers of the first terminal to be cached. The radio bearer of the first terminal may include the data radio bearer and / or the signaling radio bearer of the first terminal. The "cache" here can be understood as saving or storing, which is a temporary storage. For example, the first downlink data may include downlink data of a successful reception confirmation indication received from the source relay device. In another understanding, "cache" may be not deleted when an ACK indication is received. For example, the first downlink data may include downlink data of a successful reception confirmation indication received from the source relay device but no discard operation is performed. Optionally, the cached first downlink data may be cleared when the packet loss condition is met, such as regular clearing or clearing when the data volume cache threshold is exceeded. For details, please refer to the following introduction and will not be repeated here.

[0223] Based on the cached first downlink data, the second network device can send part or all of the first downlink data to the third network device. For example, if necessary, the second network device can forward the downlink data of the cached first downlink data that receives a reception failure indication (such as NACK) from the source relay device, and the downlink data that receives a reception success confirmation indication (such as ACK) from the source relay device to the third network device, so that after the first terminal switches to the third network device, the third network device sends part or all of these downlink data to the first terminal to avoid packet loss, so as to ensure the downlink data transmission performance of the first terminal, such as downlink lossless transmission.

[0224] In a specific implementation, the first indication information may be an explicit indication. For example, the first indication information may be enabling information. Upon receiving the enabling information, the second network device may determine that it is necessary to cache the first downlink data of all radio bearers of the first terminal. Alternatively, for example, the first indication information may include information instructing to stop discarding downlink data packets based on a successful reception confirmation from the source relay device, thereby instructing the first downlink data of all radio bearers of the first terminal to be cached.

[0225] Alternatively, the first indication information may be an implicit indication. For example, the first indication information may include the link switching type of the first terminal, such as an inter-station switching type from a non-direct link to a direct link, or an inter-station switching type from a non-direct link to a non-direct link. After receiving the first indication information, the second network device may consider that it is necessary to cache the first downlink data of all radio bearers of the first terminal.

[0226] In another example, the first network device can ensure downlink lossless transmission of the first terminal based on the radio bearer granularity. For example, the first network device can determine one or more radio bearers that need to meet the first transmission requirement from all the radio bearers of the first terminal, and the first indication information can be used to indicate the downlink transmission requirements or downlink transmission parameters of the one or more radio bearers of the first terminal. Optionally, the first indication information can also be used to indicate the first downlink data of the one or more radio bearers of the first terminal to be cached. For ease of distinction, in an embodiment of the present application, the one or more radio bearers that meet the first transmission requirement may be referred to as the first radio bearer.

[0227] Exemplarily, the first transmission requirement may be a downlink lossless transmission requirement agreed upon in a protocol or a downlink lossless transmission requirement determined based on an internal implementation of a base station, such as a transmission mode requirement or a quality of service (QoS) requirement. For example, if the protocol agrees or the internal implementation of the base station determines that a radio bearer using an acknowledgement mode (AM) needs to meet the downlink lossless transmission requirement, the first network device may determine that the radio bearer using the AM mode of the first terminal is the radio bearer that needs to meet the first transmission requirement. Or, for example, the QoS parameter may include a packet loss rate, and the first network device may determine that a radio bearer having a packet loss rate greater than or equal to the packet loss rate threshold is the first radio bearer that needs to guarantee the downlink lossless transmission requirement. If the packet loss rate is less than the packet loss rate threshold, it is considered that the probability of packet loss on the corresponding radio bearer is low, and the downlink lossless transmission requirement may be temporarily ignored. The packet loss rate threshold may be a protocol agreement or a configuration determined by the source base station. In another possible implementation, the first network device determines which radio bearers need to meet the first transmission requirement based on the implementation and indicates it to the second network device, which is not limited here.

[0228] In this example, the first indication information sent by the first network device to the second network device may include the identification information of the first radio bearer. For example, DRB1 and DRB2 represent the identifications of the two radio bearers of the first terminal. If DRB1 and DRB2 are in AM transmission mode, the first indication information may include the identification information of DRB1 and DRB2 to indicate the downlink transmission requirements or downlink transmission parameters of DRB1 and DRB2 of the first terminal. Optionally, the first indication information may also instruct the second network device to cache the downlink data of DRB1 and DRB2 to ensure lossless downlink transmission on DRB1 and DRB2.

[0229] Or, for example, the first indication information may include first transmission requirement indication information and / or the transmission mode of the radio bearer of the first terminal, such as AM mode or unacknowledged mode (UM). In one possible manner, the second network device may consider that the radio bearer adopting the AM mode needs to ensure downlink lossless transmission, that is, determine the radio bearer adopting the AM mode as the first radio bearer, and determine the downlink transmission requirement or downlink transmission parameters of the radio bearer adopting the AM mode of the first terminal, or cache the downlink data of the radio bearer adopting the AM mode. Alternatively, the first indication information may only indicate the radio bearer adopting the AM mode, and the second network device may determine the downlink transmission requirement or downlink transmission parameters of the radio bearer adopting the AM mode of the first terminal based on the indicated AM mode, or cache the downlink data of the radio bearer adopting the AM mode. Alternatively, the first transmission requirement indication information is used to indicate downlink lossless transmission guarantee, and the second network device may confirm that the radio bearer adopting the AM mode is determined as the first radio bearer based on the first transmission requirement indication information.

[0230] It can be understood that the above S1210 and S1220 are only examples of the steps included in the data transmission method of the embodiment of the present application and are not any limitation. In the specific implementation, S1210 can be executed first and then S1220, or S1220 can be executed first and then S1210, or S1210 and S1220 can be executed at the same time.

[0231] Taking the example of the first network device executing S1220 first and then executing S1210, specifically, the first network device can implement S1220 after establishing a non-direct link with the first terminal to indicate the downlink transmission requirements or downlink transmission parameters of all or part of the radio bearers of the first terminal. Optionally, if the first indication information indicates to cache the first downlink data of one or more radio bearers of the first terminal, the second network device can cache the downlink data of all or part of the radio bearers of the first terminal according to the first indication information. Subsequently, the first network device can implement S1210 based on the quality detection result of the source link between it and the first terminal to switch the communication link for the first terminal.

[0232] In this method, in order to avoid caching a large amount of first downlink data on the second network device side, the cached first downlink data can be cleared based on the data reception status of the first terminal. In one possible implementation, the first network device requests the first terminal to report data reception status information at regular intervals. The data reception status information can be implemented as a PDCP status report, for example. The second network device can receive the data reception status information from the first terminal and, based on the data reception status information of the first terminal, clear the first downlink data that has been successfully received by the first terminal, i.e., no longer cache it. In another possible implementation, the first network device can configure the first terminal to periodically report data reception status information / report (specifically, the first network device can send configuration information to the first terminal, the configuration information including a period T, for instructing the first terminal to report data reception status information every T time period), such as a PDCP status report. The second network device can, based on the data reception status information / report of the first terminal, clear the first downlink data that has been successfully received by the first terminal, i.e., no longer cache it. In another possible embodiment, the second network device can instruct the first terminal device to report data reception status information each time the cached data volume reaches the data volume cache threshold, so that the second network device can clear the first downlink data, that is, no longer cache it.

[0233] Optionally, limited by the cache capacity of the second network device, or limited by the cache capacity allocated to the first terminal by the second network device, or limited by the maximum cache data volume of each radio bearer, the first network device may further indicate a data volume cache threshold to the second network device. For example, the first network device may send fourth indication information to the second network device, where the fourth indication information includes the data volume cache threshold of the second network device. When the amount of first downlink data to be cached exceeds the data volume cache threshold, the second network device may discard data packets in the cached first downlink data based on the data volume cache threshold of the second network device, and use the cache space after the packet loss to cache data packets in newly arrived first downlink data. For ease of distinction, the newly arrived first downlink data may also be referred to as second downlink data. In one possible implementation, the first network device may further indicate a data volume cache threshold for a first radio bearer to the second network device, to constrain the maximum cache data volume of a single radio bearer. In this case, the fourth indication information may include an identifier of a first radio bearer and the data volume cache threshold of the first radio bearer. Similarly, when the amount of cached data corresponding to the first wireless bearer exceeds the data amount cache threshold corresponding to the wireless bearer, the second network device can discard the cached downlink data packets of the first wireless bearer according to the data amount cache threshold of the second network device, and the cache space after the packet loss is used to cache the downlink data packets newly arriving at the first wireless bearer.

[0234] Optionally, in an embodiment of the present application, several levels of cache data volume may be set, such as a first cache level, a second cache level, and a third cache level. Each cache level may be associated with a data volume cache threshold. For example, the cache threshold corresponding to the first cache level is smaller than the cache threshold corresponding to the second cache level, and the cache threshold corresponding to the second cache level is smaller than the cache threshold corresponding to the third cache level. The first network device may also indirectly indicate the data volume cache threshold by indicating to the second network device the cache level used by the radio bearer of the first terminal. The second network device may determine the corresponding data volume cache threshold based on the cache level indicated by the first network device.

[0235] Taking the example of the first network device executing S1210 first and then executing S1220, specifically, the first network device may implement S1210 when deciding to switch the first terminal to the cell managed by the target base station based on the measurement reporting information of the first terminal, that is, determining that the first terminal is switched from the first network device to the third network device. In order to ensure the downlink lossless transmission of the wireless bearer of the first terminal, the first network device may implement S1220 before sending the relevant configuration information for switching to the first terminal (such as RRC reconfiguration information) to instruct the second network device to cache the relevant downlink data of the first terminal, so as to facilitate the retransmission of part or all of these downlink data to the first terminal through the third network device after the switching is completed, thereby reducing packet loss and ensuring the downlink lossless transmission of the first terminal.

[0236] In an embodiment of the present application, the first network device may also send a first message to a third network device, where the first message may include the downlink transmission requirements or downlink transmission parameters of the first terminal. Accordingly, the third network device may receive the first message from the first network device. Based on the downlink transmission requirements or downlink transmission parameters of the first terminal, the third network device may subsequently collaborate with the first network device to implement a data forwarding mechanism to retransmit the relevant downlink data of the first terminal, thereby reducing packet loss and ensuring lossless downlink transmission.

[0237] Exemplarily, the first message can be implemented as a handover request (HO request) message sent by the first network device to the third network device in Figure 10, and the first message can also be used to request that the first terminal be handed over to the third network device. The first message may include the downlink transmission requirements or downlink transmission parameter indications of all radio bearers of the first terminal, and the downlink transmission requirements or downlink transmission parameter indications are used to instruct the second network device to ensure downlink lossless transmission of all radio bearers of the first terminal. Alternatively, if the first network device ensures downlink lossless transmission of the first terminal based on radio bearer granularity, the first message may include the identifiers of one or more radio bearers of the first terminal, and the one or more radio bearers may be referred to as first radio bearers. Similar to the above introduction, the first radio bearer may be determined based on the performance requirements of the radio bearer. For example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer meets the first transmission requirement, which will not be repeated here.

[0238] In other embodiments, the first network device may also implicitly indicate the downlink transmission requirement or downlink transmission parameter of the first terminal to the third network device.

[0239] For example, when the first network device sends a first message to the third network device, the first message may carry the switching configuration information of the first network device. The switching configuration information may include the link switching type of the first terminal, such as the inter-station switching type from a non-direct link to the third network device. The third network device may determine the downlink transmission requirements or downlink transmission parameters of the first terminal based on the protocol agreement, such as determining that the downlink lossless transmission of the first terminal needs to be guaranteed when the link switching type is used.

[0240] Or for example, when the first network device sends a first message to the third network device, the first message may carry the switching configuration information of the first network device, and the switching configuration information may include the transmission mode information of the wireless bearer of the first terminal, such as AM mode or UM mode. The third network device may adopt the downlink transmission requirements or downlink transmission parameters of the wireless bearer in AM mode by default, for example, it is necessary to ensure the downlink lossless transmission of the wireless bearer in AM mode by default.

[0241] Optionally, the first network device may instruct the first terminal to report data reception status information, such as a PDCP status report, before the handover. After receiving the data reception status information of the first terminal, the first network device may send the first message to the third network device, and by carrying the reception status of downlink data of one or more radio bearers of the first terminal in the first message, indicate the downlink transmission requirements or downlink transmission parameters of the first terminal to the third network device, or indicate the downlink transmission requirements or downlink transmission parameters of one or more radio bearers of the first terminal to the third network device.

[0242] Optionally, the third network device may or may not support the function of providing downlink lossless transmission for the first terminal. The third network device may indicate this in the handover request confirmation message fed back to the first network device. If the third device does not support the function of providing downlink lossless transmission for the first terminal, the first network device may stop caching the first downlink data of the first terminal.

[0243] Optionally, the third network device may further configure data recovery indication information, such as PDCP data recovery indication information, for the first terminal after determining to provide the function of ensuring downlink lossless transmission for the first terminal. The data recovery indication information may be carried in the switching request confirmation message sent by the third network device to the first network device, that is, carried in the configuration of the first terminal by the third network device, so that the first terminal can report data reception status information to the third network device after accessing the third network device. Optionally, the third network device may configure the data recovery indication information for one or more radio bearers that provide downlink lossless transmission guarantee for the first terminal based on the granularity of the radio bearer, for example, configuring the data recovery indication information for the first radio bearer. The embodiment of the present application does not limit this specific implementation.

[0244] Optionally, the first network device can also determine the reception status of downlink data of one or more wireless bearers of the first terminal through interaction with the third network device, and based on the reception status, instruct the second network device to send part or all of the cached first downlink data to the third network device.

[0245] For example, after switching to the third network device, the first terminal may send data reception status information to the third network device. The data reception status information may be, for example, a PDCP status report. The data reception status information may be carried in, for example, the seventh message from the first terminal. The third network device may send a second message to the first network device based on the data reception status information from the first terminal. The second message may include sixth indication information. The sixth indication information may be used to indicate the reception status of downlink data of one or more radio bearers of the first terminal. The reception status may include, for example, at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more radio bearers; and bitmap information corresponding to one or more radio bearers, the bitmap information being used to indicate the reception status of the subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0246] The first network device may send second indication information to the second network device based on the received second message, and the second indication information may include the reception status of the downlink data of one or more wireless bearers of the first terminal. Accordingly, the second network device may receive the second indication information from the first network device, and send part or all of the cached first downlink data to the third network device based on the second indication information. It should be understood that in the embodiments of the present application, "message" or "indication information" is only an example of the information carrier and not any limitation. In specific implementation, the content contained in the two may be the same or different, and the format may be the same or different. The embodiments of the present application do not limit this.

[0247] In another possible implementation, the second network device may determine the reception status of the downlink data of one or more radio bearers of the first terminal through interaction with the third network device, and send part or all of the cached first downlink data to the third network device based on the reception status. For example, the second network device may receive a sixth message from the third network device, and the sixth message may include ninth indication information, and the ninth indication information may be used to indicate the reception status of the downlink data of the first or more radio bearers of the first terminal. The reception status may include, for example, at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of the subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0248] Accordingly, the second network device may send part or all of the cached first downlink data to the third network device based on the ninth indication information in the received sixth message. Similarly, in the embodiments of the present application, "message" or "indication information" is merely an example of an information carrier and does not limit it. In specific implementations, the content contained in the two may be the same or different, and the formats may be the same or different, and the embodiments of the present application do not limit this.

[0249] In the embodiment of the present application, in order to avoid excessive buffering of downlink data and the resulting high requirements on the buffering capacity of the source base station, in some embodiments, the second network device side also needs to stop buffering the first downlink data of the first terminal. The triggering timing of stopping buffering can be flexibly set, as shown below:

[0250] For example, the second network device may stop caching the first downlink data after determining the reception status of the downlink data of one or more radio bearers of the first terminal. The second network device may determine the reception status of the downlink data of one or more radio bearers of the first terminal upon receiving the second indication information from the first network device, and stop caching the first downlink data corresponding to the indicated one or more radio bearers. Or, for example, the second network device may determine the reception status of the downlink data of one or more radio bearers of the first terminal upon receiving the sixth message from the third network device, and stop caching the first downlink data corresponding to the indicated one or more radio bearers.

[0251] Or for example, the second network device may receive a third indication message from the first network device, and the third indication message may be used to instruct the second network device to stop caching the first downlink data. The first network device may send the third indication message to the second network device after receiving the third message, and the third message may be used to instruct the release of the terminal context; or, the three messages are used to instruct the release of the connection between the first network device and the core network device. Alternatively, the first network device may send the third indication message to the second network device after sending the fourth message to the first terminal, and the fourth message is used to instruct the first terminal to switch from the first network device and the second network device to the third network device. Alternatively, the first network device may send the third indication message to the second network device after receiving the fifth message from the first terminal, and the fifth message is used to confirm that the first terminal switches from the first network device and the second network device to the third network device.

[0252] Or for example, before sending an RRC reconfiguration message to the first terminal, the first network device may instruct the first terminal to report data reception status information, and the data reception status information may be, for example, a PDCP status report. Further, the first network device may instruct the second network device to discard downlink data that has been successfully received by the first terminal and cached on the second network device side based on the data reception status information reported by the first terminal. Alternatively, before sending an RRC reconfiguration message to the first terminal, the first network device may instruct the source relay device to report the downlink data forwarding status, that is, which downlink data packets the source relay device has successfully forwarded to the first terminal. The first network device may, based on the downlink data forwarding status, instruct the second network device to discard downlink data that has been successfully received by the first terminal and cached on the second network device side.

[0253] Therefore, through the above scheme, when the CU-CP function and CU-UP function of the source base station are deployed separately, through the interaction between the first network device and the first terminal, or the second network device, or the third network device, the source base station and the target base station can implement the data forwarding mechanism according to the downlink lossless transmission requirements of the first terminal and the reception status of the downlink data of the first terminal on one or more wireless bearers, so as to reduce packet loss and ensure the downlink lossless transmission of the first terminal as much as possible.

[0254] FIG13 shows a flow chart of a data transmission method according to an embodiment of the present application. Wherein, if the functions of the first network device and the second network device shown in FIG12 are deployed in the same source base station (for example, represented as the first network device), the CU-CP function and the CU-UP function of the third network device are deployed separately, for example, represented as the third network device and the fourth network device, the third network device can be used to implement the CU-CP function of the target base station, and the fourth network device can be used to implement the CU-UP function of the target base station. Referring to FIG13, the data transmission method may include the following steps:

[0255] S1310: The first network device determines that the first terminal is switched from the first network device to the third network device and the fourth network device.

[0256] In this example, the first network device can provide control plane and user plane communication services for the first terminal, and the first network device can be implemented as a source base station. The third network device can provide control plane communication services for the first terminal, for example, it can implement the CU-CP of the target base station, and the fourth network device can provide user plane communication services for the first terminal, for example, it can be implemented as the CU-UP of the target base station.

[0257] When S1310 is specifically implemented, the first network device may determine that the first terminal switches from the first network device to the third network device and the fourth network device through direct or indirect information interaction with the first terminal, or the third network device, or the fourth network device.

[0258] For example, the first network device can communicate with the first terminal through the source relay device, receive measurement reporting information from the first terminal, and based on the measurement reporting information, analyze whether the quality of the communication link between the first terminal and the source relay device, or the communication link between the source relay device and the first network device has decreased, to decide whether it is necessary to switch the communication link for the first terminal, for example, switching the first terminal to the third network device and the fourth network device.

[0259] Or, for example, the first network device may send a switching request message to the third network device when it is necessary to switch the communication link for the first terminal. The third network device may receive the switching request message from the first network device. If the third network device confirms the switching, it may send a switching request confirmation message to the first network device. The first network device may determine that the first terminal switches from the first network device to the third network device and the fourth network device based on the switching request confirmation message. The third network device may send the switching request confirmation message directly to the first network device, or may send the switching request confirmation message to the first network device after communicating with the fourth network device. This embodiment of the present application does not limit this.

[0260] In the embodiment of the present application, the type of communication link between the first terminal and the third network device / fourth network device is not limited. In one example, after switching, the first terminal and the third network device / fourth network device may be a direct link, for example, the first terminal directly communicates with the target DU through the Uu port, the target DU is connected to the third network device / fourth network device, and the first terminal communicates with the third network device / fourth network device through the target DU. In another example, after switching, the first terminal and the third network device / fourth network device may be a non-direct link, for example, the first terminal communicates with the target relay device through the PC5 interface, the target relay device is connected to the target DU through the Uu port, the target DU is connected to the third network device / fourth network device, that is, the first terminal communicates with the third network device / fourth network device through the target relay device target DU. In another example, there may also be multi-path communication between the first terminal and the third network device / fourth network device, and the multi-path may include the above-mentioned direct link and / or non-direct link, which is not limited in the embodiment of the present application. For ease of distinction, the relay device on the source link before the first terminal switches can be called the first relay device or source relay device, and the relay device on the target link after the first terminal switches can be called the second relay device or target relay device.

[0261] S1320: The first network device buffers the first downlink data of the first terminal.

[0262] In the embodiment of the present application, the first network device may cache the first downlink data of the first terminal according to the downlink transmission requirement or downlink transmission parameter of the first terminal.

[0263] The meaning of "cache" here is the same as that described in FIG12 . Please refer to the relevant description in conjunction with FIG12 and will not be repeated here.

[0264] Based on the cached first downlink data, the first network device can send part or all of the first downlink data to the fourth network device. For example, if necessary, the first network device can forward the downlink data of the cached first downlink data that receives a reception failure indication (such as NACK) from the source relay device and the downlink data that receives a reception success confirmation indication (such as ACK) from the source relay device to the fourth network device, so that after the first terminal switches to the third network device and the fourth network device, the fourth network device sends part or all of these downlink data to the first terminal to reduce packet loss and ensure lossless downlink transmission of the first terminal.

[0265] In an example, the first network device may cache first downlink data of all radio bearers of the first terminal. The radio bearers of the first terminal may include data radio bearers and / or signaling radio bearers of the first terminal.

[0266] In another example, the first network device can ensure lossless downlink transmission of the first terminal based on the radio bearer granularity. For example, the first network device can determine one or more radio bearers that need to meet the first transmission requirement from all the radio bearers of the first terminal, and cache the first downlink data of the one or more radio bearers of the first terminal. For ease of distinction, in an embodiment of the present application, the one or more radio bearers that meet the first transmission requirement may be referred to as the first radio bearer. The meaning of the first transmission requirement is the same as that described in Figure 12, and reference may be made to the relevant description in conjunction with Figure 12, which will not be repeated here.

[0267] It can be understood that the above S1310 and S1320 are only examples of the steps included in the data transmission method of the embodiment of the present application and are not any limitations. In the specific implementation, S1310 can be executed first and then S1320, or S1320 can be executed first and then S1310, or S1310 and S1320 can be executed at the same time.

[0268] Taking the example of the first network device executing S1320 first and then executing S1310, specifically, the first network device can implement S1320 after establishing a non-direct link with the first terminal to cache all or part of the downlink data of the wireless bearer of the first terminal. Subsequently, the first network device can implement S1310 based on the quality detection result of the source link between the first terminal and the first terminal to switch the communication link for the first terminal, such as switching the first terminal from the first network device to the third network device and the fourth network device. In this method, in order to avoid caching a large amount of first downlink data on the first network device side, the cached first downlink data can be cleaned up based on the data reception situation of the first terminal, or the cache level, or the data volume cache threshold, etc. The relevant implementation details are the same as those described in Figure 12, and you can refer to the relevant description in conjunction with Figure 12, which will not be repeated here.

[0269] Taking the first network device executing S1310 first and then executing S1320 as an example, specifically, the first network device may implement S1310 when deciding to switch the first terminal to the cell managed by the target base station based on the measurement reporting information of the first terminal, that is, determining that the first terminal is switched from the first network device to the third network device and the fourth network device. In order to ensure the downlink lossless transmission of the wireless bearer of the first terminal, the first network device may implement S1320 before sending the relevant configuration information for switching to the first terminal (such as the RRC reconfiguration message in Figure 10) to cache the relevant downlink data of the first terminal, so as to facilitate the retransmission of part or all of these downlink data to the first terminal through the fourth network device after the switching is completed, thereby reducing packet loss and ensuring the downlink lossless transmission of the first terminal.

[0270] In an embodiment of the present application, the first network device may also send a first message to a third network device, where the first message may include the downlink transmission requirements or downlink transmission parameters of the first terminal. Accordingly, the third network device may receive the first message from the first network device. Based on the downlink transmission requirements or downlink transmission parameters of the first terminal, the third network device may subsequently collaborate with the first network device to implement a data forwarding mechanism to retransmit the relevant downlink data of the first terminal, thereby reducing packet loss and ensuring lossless downlink transmission.

[0271] Exemplarily, the first message can be implemented as a handover request message sent by the first network device to the third network device in Figure 10. The first message can also be used to request that the first terminal be handed over to the third network device and the fourth network device. The first message may include the downlink transmission requirements or downlink transmission parameter indications of all radio bearers of the first terminal, and the indicated downlink transmission requirements or downlink transmission parameters are used to instruct the third network device to ensure downlink lossless transmission of all radio bearers of the first terminal. Alternatively, if the first network device ensures downlink lossless transmission of the first terminal based on radio bearer granularity, the first message may include the identifiers of one or more radio bearers of the first terminal, and the one or more radio bearers may be referred to as first radio bearers. Similar to the above description in conjunction with Figure 12, the first radio bearer may be determined based on the performance requirements of the radio bearer. For example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer meets the first transmission requirement, which will not be repeated here.

[0272] In other embodiments, the first network device may also implicitly indicate the downlink transmission requirement or downlink transmission parameter of the first terminal to the third network device. The relevant implementation details are the same as those described in FIG12 , and can be referred to the relevant description in conjunction with FIG12 , which will not be repeated here.

[0273] Optionally, the third network device may or may not support the function of providing downlink lossless transmission for the first terminal. The third network device may indicate this in the handover request confirmation message fed back to the first network device. If the third device does not support the function of providing downlink lossless transmission for the first terminal, the first network device may stop caching the first downlink data of the first terminal.

[0274] Optionally, the third network device may further configure data recovery indication information, such as PDCP data recovery indication information, for the first terminal after determining to provide the function of ensuring downlink lossless transmission for the first terminal. The data recovery indication information may be carried in the switching request confirmation message sent by the third network device to the first network device, that is, carried in the configuration of the first terminal by the third network device, so that the first terminal reports data reception status information to the fourth network device after receiving the third network device and the fourth network device. Optionally, the third network device may configure the data recovery indication information for one or more radio bearers that provide downlink lossless transmission guarantee for the first terminal based on the granularity of the radio bearer, for example, configuring the data recovery indication information for the first radio bearer. The embodiment of the present application does not limit this specific implementation.

[0275] Optionally, the first network device can also determine the reception status of the downlink data of one or more wireless bearers of the first terminal through interaction with the third network device and / or the fourth network device, and send part or all of the cached first downlink data to the fourth network device based on the reception status.

[0276] For example, after switching to the third network device and the fourth network device, the first terminal may send a seventh message to the fourth network device, where the seventh message may include data reception status information, such as a PDCP status report. The fourth network device may determine the reception status of downlink data of one or more radio bearers of the first terminal based on the data status reception information from the first terminal. The reception status may include, for example, at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, where the bitmap information is used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0277] In one possible implementation, the fourth network device may send sixth indication information to the third network device based on the reception status. The sixth indication information may be used to indicate the reception status of downlink data for one or more radio bearers of the first terminal. Accordingly, the third network device may receive the sixth indication information from the fourth network device. The third network device may determine the reception status of downlink data for one or more radio bearers of the first terminal based on the sixth indication information. Furthermore, the third network device may send a second message to the first network device based on the reception status. The second message may include the reception status of downlink data for one or more radio bearers of the first terminal. Accordingly, the first network device receives a second message from the third network device. The second message may include the sixth indication information. The sixth indication information may be used to indicate the reception status of downlink data for one or more radio bearers of the first terminal. Exemplarily, the reception status may include at least one of the following: identifiers of one or more radio bearers of the first terminal; sequence numbers of the first unsuccessfully received data packets corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information indicating the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1. In a specific implementation, the second message may be an XnAP message, including the content of the PDCP status report of one or more radio bearers, such as the radio bearer identifier, the first packet loss FMC of the corresponding radio bearer, and a bitmap. Optionally, the content of the PDCP status report is included in the XnAP message in the form of a container.

[0278] The first network device may transmit, to the fourth network device, part or all of the cached first downlink data based on the reception status of downlink data of one or more radio bearers of the first terminal, for example, including downlink data for which a successful reception confirmation indication has been received from the source relay device. Accordingly, the fourth network device may receive downlink data from the first network device and transmit part or all of the downlink data from the first network device to the first terminal, thereby reducing packet loss and ensuring downlink data transmission performance of the first terminal as much as possible.

[0279] In another possible implementation, the fourth network device may send a sixth message to the first network device, where the sixth message may include ninth indication information, which may be used to indicate the reception status of downlink data of one or more radio bearers of the first terminal. The reception status may include, for example, at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more radio bearers; and bitmap information corresponding to one or more radio bearers, where the bitmap information is used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1. Accordingly, the first network device may send part or all of the cached first downlink data to the fourth network device based on the ninth indication information in the received sixth message. Similarly, in the embodiments of the present application, "message" or "indication information" is merely an example of an information carrier and is not intended to be limiting. In specific implementations, the content contained in the two may be the same or different, and the formats may be the same or different. The embodiments of the present application do not limit this.

[0280] Optionally, the third network device may send fifth indication information to the fourth network device. The fifth indication information may be used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal, or may indicate the downlink transmission requirements or downlink transmission parameters of one or more radio bearers of the first terminal. Accordingly, the fourth network device may receive the fifth indication information from the third network device. Further, the fourth network device may send the sixth message to the first network device based on the fifth indication information.

[0281] During specific implementation, the fourth network device may pre-establish a user plane tunnel (e.g., GTP-U tunnel) from the fourth network device to the first network device, and send the sixth message to the first network device through the user plane tunnel. The sixth message may, for example, be user plane control information on the Xn interface. In one possible implementation, the first network device may instruct the third network device and the fourth network device to establish the user plane tunnel. For example, the first message sent by the first network device to the third network device may also include the target address of the user plane tunnel. After receiving the first message, the third network device may send eighth indication information to the fourth network device based on the target address of the user plane tunnel. The eighth indication information may be used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the first network device. Accordingly, the fourth network device may receive the eighth indication information from the third network device and establish a user plane tunnel from the fourth network device to the first network device based on the eighth indication information. Further, the fourth network device may send a sixth message to the first network device through the user plane tunnel. The sixth message may include the reception status of downlink data of one or more radio bearers of the first terminal.

[0282] Optionally, the user plane tunnel corresponds one-to-one to the first radio bearer of the first terminal, and the first radio bearer is a radio bearer that needs to meet a first transmission requirement.

[0283] Optionally, when the user plane tunnel and the first radio bearer have a one-to-one correspondence, the sixth message does not include identification information of the radio bearer. After receiving the sixth message from the user plane tunnel, the second network device may learn, based on the correspondence between the user plane tunnel and the first radio bearer, that the sixth message includes the reception status of the downlink data corresponding to the first radio bearer.

[0284] In the embodiment of the present application, in order to avoid excessive buffering of downlink data and the resulting high requirements on the buffering capacity of the source base station, in some embodiments, the first network device side also needs to stop buffering the first downlink data of the first terminal. The triggering timing of stopping buffering can be flexibly set, as shown below:

[0285] For example, the first network device may stop caching the first downlink data after determining the reception status of the downlink data of one or more radio bearers of the first terminal. The first network device may determine the reception status of the downlink data of one or more radio bearers of the first terminal upon receiving the second message from the third network device, and stop caching the first downlink data corresponding to the indicated one or more radio bearers.

[0286] Alternatively, for example, the first network device may stop buffering the first downlink data after receiving the third message. The third message may be used to instruct the release of the terminal context; or the third message may be used to instruct the release of the connection between the first network device and the core network device.

[0287] Alternatively, for example, the first network device may stop caching the first downlink data after sending a fourth message to the first terminal. The fourth message may be used to instruct the first terminal to switch to the third network device, and / or the fourth message may be used to instruct the first terminal to switch to the fourth network device. Alternatively, the first network device may stop caching the first downlink data after receiving a fifth message from the first terminal. The fifth message is used to confirm that the first terminal has switched to the third network device, and / or the fifth message is used to confirm that the first terminal has switched to the fourth network device.

[0288] Or for example, before sending an RRC reconfiguration message to the first terminal, the first network device may instruct the first terminal to report data reception status information, such as a PDCP status report. Furthermore, the first network device may discard downlink data that has been successfully received by the first terminal and cached on the first network device side based on the content of the data reception status information reported by the first terminal. Alternatively, before sending an RRC reconfiguration message to the first terminal, the first network device may instruct the source relay device to report the downlink data forwarding status, that is, which downlink data packets the source relay device has successfully forwarded to the first terminal. The first network device may discard downlink data that has been successfully received by the first terminal and cached on the first network device side based on the downlink data forwarding status.

[0289] Therefore, through the above scheme, when the CU-CP function and CU-UP function of the target base station are deployed separately, through the interaction between the first network device and the first terminal, or the third network device, or the fourth network device, the source base station and the target base station can implement the data forwarding mechanism according to the downlink lossless transmission requirements of the first terminal and the reception status of the downlink data of the first terminal on one or more wireless bearers, so as to reduce packet loss and ensure the downlink lossless transmission of the first terminal as much as possible.

[0290] FIG14 is a flow chart of a data transmission method according to an embodiment of the present application. If the CU-CP function and the CU-UP function of the third network device shown in FIG12 are deployed separately, for example, as a third network device and a fourth network device, the third network device can be used to implement the CU-CP function of the target base station, and the fourth network device can be used to implement the CU-UP function of the target base station. Referring to FIG14 , the data transmission method may include the following steps:

[0291] S1410: The first network device determines that the first terminal switches from the first network device to the third network device, and switches from the second network device to the fourth network device.

[0292] In this example, the first network device can provide control plane communication services for the first terminal, and the first network device can be implemented as the CU-CP of the source base station. The second network device can provide user plane communication services for the first terminal, and the second network device can be implemented as the CU-UP of the source base station. The third network device can provide control plane communication services for the first terminal, for example, it can implement the CU-CP of the target base station, and the fourth network device can provide user plane communication services for the first terminal, for example, it can be implemented as the CU-UP of the target base station.

[0293] When S1410 is specifically implemented, the first network device can determine whether the first terminal switches from the first network device to the third network device, or from the second network device to the fourth network device through direct or indirect information interaction with the first terminal, or the second network device, or the third network device, or the fourth network device.

[0294] For example, the first network device can communicate with the first terminal through the source relay device, receive measurement reporting information from the first terminal, and analyze whether the quality of the communication link between the first terminal and the source relay device or the communication link between the source relay device and the source DU has decreased based on the measurement reporting information, so as to decide whether it is necessary to switch the communication link for the first terminal, for example, switching the first terminal from the first network device to the third network device, or from the second network device to the fourth network device. The first network device can directly determine whether it is necessary to switch the communication link for the first terminal based on the measurement reporting information, or the first network device can also determine whether it is necessary to switch the communication link for the first terminal after communicating with the second network device.

[0295] Or, for example, the first network device may send a switching request message to the third network device when it is necessary to switch the communication link for the first terminal. The third network device may receive the switching request message from the first network device, and if the third network device confirms the switching, it may send a switching request confirmation message to the first network device. The first network device may receive the switching request confirmation message from the third network device, and determine based on the switching request confirmation message that the first terminal switches from the first network device to the third network device, and from the second network device to the fourth network device. The third network device may send the switching request confirmation message directly to the first network device, or may send the switching request confirmation message to the first network device after communicating with the fourth network device.

[0296] After switching, the link type supported between the first terminal and the third network device / fourth network device is similar to the link type introduced in Figure 13. For detailed implementation details, please refer to the relevant introduction in the previous text combined with Figure 13, which will not be repeated here.

[0297] S1420: The first network device sends first indication information to the second network device. Correspondingly, the second network device may receive the first indication information from the first network device.

[0298] In an embodiment of the present application, the first indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal, and the downlink transmission requirements or downlink transmission parameters of the first terminal are used to instruct the second network device to send the first downlink data to the fourth network device, so that the second network device knows how to forward the downlink data of the first terminal to the fourth network device, reduce packet loss, and ensure the downlink data transmission performance of the first terminal, such as downlink lossless transmission. Optionally, the first downlink data may include downlink data of one or more wireless bearers of the first terminal. Further, the second network device may send the first downlink data of the first terminal to the fourth network device based on the first indication information, or the second network device may send part or all of the first downlink data of the first terminal to the fourth network device based on the first indication information. The meaning of the "first indication information" here is the same as that described in Figure 12, and you can refer to the relevant description in conjunction with Figure 12, which will not be repeated here.

[0299] Similar to the method described in conjunction with FIG12 , in an optional embodiment, the first indication information may also be used to indicate caching of first downlink data of all radio bearers of the first terminal. The radio bearers of the first terminal may include data radio bearers and / or signaling radio bearers of the first terminal. The meaning of "caching" here is the same as that described in conjunction with FIG12 , and reference may be made to the relevant description in conjunction with FIG12 , and will not be repeated here.

[0300] Based on the cached first downlink data, the second network device can send part or all of the cached first downlink data to the fourth network device. For example, if necessary, the second network device can forward the downlink data of the cached first downlink data that receives a reception failure indication (such as NACK) from the source relay device and the downlink data that receives a reception success confirmation indication (such as ACK) from the source relay device to the fourth network device, so that after the first terminal switches from the second network device to the fourth network device, the fourth network device sends part or all of these downlink data to the first terminal to reduce packet loss and ensure the downlink data transmission performance of the first terminal.

[0301] In another example, the first network device can ensure lossless downlink transmission of the first terminal at the radio bearer granularity. For example, the first network device can determine one or more radio bearers that need to meet the first transmission requirement from all the radio bearers of the first terminal, and the first indication information can be used to indicate the downlink transmission requirements or downlink transmission parameters of the one or more radio bearers of the first terminal. Optionally, the first indication information can also be used to indicate the first downlink data of the one or more radio bearers of the first terminal to be cached. Similar descriptions can be found in the relevant introduction in the previous text combined with Figure 12, which will not be repeated here. For the sake of distinction, in an embodiment of the present application, the one or more radio bearers that meet the first transmission requirement may be referred to as the first radio bearer.

[0302] It can be understood that the above S1410 and S1420 are merely examples of the steps included in the data transmission method of the embodiment of the present application and are not any limitation. In specific implementation, S1410 can be executed first and then S1420, or S1420 can be executed first and then S1410, or S1410 and S1420 can be executed at the same time.

[0303] Taking the example of a first network device executing S1420 before executing S1410, specifically, the first network device may implement S1420 after establishing a non-direct link between the first network device, the second network device, and the first terminal to indicate the downlink transmission requirements or downlink transmission parameters of all or part of the radio bearers of the first terminal. Optionally, if the first indication information indicates to cache the first downlink data of one or more radio bearers of the first terminal, the second network device may cache the downlink data of all or part of the radio bearers of the first terminal based on the first indication information. Subsequently, the first network device may implement S1410 based on the quality detection result of the source link between the first terminal and the first terminal to switch the communication link for the first terminal, for example, from the first network device to a third network device, or from the second network device to a fourth network device. Similarly, to avoid caching a large amount of first downlink data on the second network device side, the cached first downlink data may be cleared based on the data reception status of the first terminal, the cache level, or the data volume cache threshold. The relevant implementation details are the same as those described in Figure 12, and can be referred to in conjunction with the relevant description of Figure 12 or Figure 13, and will not be repeated here.

[0304] Taking the first network device executing S1410 first and then executing S1420 as an example, specifically, the first network device may implement S1410 when deciding to switch the first terminal to the cell managed by the target base station based on the measurement reporting information of the first terminal, that is, determining that the first terminal switches from the first network device to the third network device and from the second network device to the fourth network device. In order to ensure the downlink lossless transmission of the wireless bearer of the first terminal, the first network device may implement S1420 before sending the relevant configuration information for switching to the first terminal (such as the RRC reconfiguration message shown in Figure 10) to instruct the second network device to cache the relevant downlink data of the first terminal, so that after the switching is completed, some or all of the downlink data can be retransmitted to the first terminal through the fourth network device, thereby reducing packet loss and ensuring the downlink lossless transmission of the first terminal.

[0305] In an embodiment of the present application, the first network device may also send a first message to the third network device, and the first message may include a downlink transmission requirement or downlink transmission parameter indication of the first terminal, and the downlink transmission requirement or downlink transmission parameter is used to instruct the second network device to ensure downlink lossless transmission of all wireless bearers of the first terminal. Accordingly, the third network device may receive the first message from the first network device, and determine the downlink transmission requirement or downlink transmission parameter of the first terminal based on the first message. Based on the downlink transmission requirement or downlink transmission parameter of the first terminal, the third network device and the fourth network device may subsequently cooperate with the first network device to implement a data forwarding mechanism to retransmit the relevant downlink data of the first terminal to reduce packet loss and ensure downlink lossless transmission.

[0306] Exemplarily, the first message can be implemented as a handover request (HO request) message sent by the first network device to the third network device in Figure 10. The first message can also be used to request that the first terminal be handed over to the third network device and the fourth network device. The first message may include the downlink transmission requirements or downlink transmission parameter indications of all radio bearers of the first terminal, and the indicated downlink transmission requirements or downlink transmission parameters are used to instruct the second network device to ensure downlink lossless transmission of all radio bearers of the first terminal. Alternatively, if the first network device ensures downlink lossless transmission of the first terminal based on radio bearer granularity, the first message may include the identifiers of one or more radio bearers of the first terminal, and the one or more radio bearers may be referred to as first radio bearers. Similar to the above description in conjunction with Figure 12, the first radio bearer may be determined based on the performance requirements of the radio bearer. For example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer meets the first transmission requirement, which will not be repeated here.

[0307] In other embodiments, the first network device may also implicitly indicate the downlink transmission requirement or downlink transmission parameter of the first terminal to the third network device. The relevant implementation details are the same as those described in FIG12 , and can be referred to the relevant description in conjunction with FIG12 , which will not be repeated here.

[0308] Optionally, the third network device may or may not support the function of providing downlink lossless transmission for the first terminal. The third network device may indicate this in the handover request confirmation message fed back to the first network device. If the third device does not support the function of providing downlink lossless transmission for the first terminal, the first network device may stop caching the first downlink data of the first terminal.

[0309] Optionally, the third network device may further configure data recovery indication information, such as PDCP data recovery indication information, for the first terminal after determining to provide the function of ensuring downlink lossless transmission for the first terminal. The data recovery indication information may be carried in the switching request confirmation message sent by the third network device to the first network device, that is, carried in the configuration of the first terminal by the third network device, so that the first terminal can report data reception status information to the third network device after accessing the third network device. Optionally, the third network device may configure the data recovery indication information for one or more radio bearers that provide downlink lossless transmission guarantee for the first terminal based on the granularity of the radio bearer, for example, configuring the data recovery indication information for the first radio bearer. The embodiment of the present application does not limit this specific implementation.

[0310] Optionally, the third network device may also send fifth indication information / seventh indication information to the fourth network device, and the fifth indication information / seventh indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal. Accordingly, the fourth network device may receive the fifth indication information / seventh indication information from the third network device. Thus, the fourth network device may be aware of the need to ensure downlink lossless transmission of the wireless bearer of the first terminal. The fifth indication information / seventh indication information may be carried in an E1 message (such as an E1AP message or an E1 port control signaling). Optionally, based on the wireless bearer granularity, the fifth indication information / seventh indication information may include the identifiers of one or more wireless bearers of the first terminal. Thus, through the above method, the first network device, the second network device, the third network device and the fourth network device may know the wireless bearer of the first terminal that needs to ensure downlink lossless transmission.

[0311] Furthermore, the first network device and the second network device may transmit downlink data involved in implementing data forwarding, such as part or all of the first downlink data, to the fourth network device, which may include downlink data for which a successful reception confirmation indication from the source relay device has been received. Alternatively, the second network device may transmit downlink data involved in implementing data forwarding, such as part or all of the first downlink data, to the fourth network device based on an indication from the first network device or the fourth network device, which may include downlink data for which a successful reception confirmation indication from the source relay device has been received.

[0312] For example, when the first network device and the second network device send downlink data involved in implementing data forwarding to the fourth network device based on the implementation, the first network device can instruct the second network device to initiate the data forwarding process, and the second network device can send the cached first downlink data to the fourth network device. After the first terminal switches from the second network device to the fourth network device, the fourth network device can retransmit the downlink data based on the PDCP status report reported by the first terminal.

[0313] Alternatively, the fourth network device may also send all downlink data received from the second network device to the first terminal, and the first terminal may discard the repeatedly received downlink data packets based on the PDCP sequence number.

[0314] The second network device may send downlink data involved in implementing data forwarding to the fourth network device based on the instruction from the first network device or the fourth network device in the following two ways:

[0315] Method 1: The first network device determines the reception status of downlink data of one or more radio bearers of the first terminal and, based on the reception status, sends second indication information to the second network device. The second indication information includes the reception status of the downlink data of the one or more radio bearers of the first terminal. The second network device may, based on the reception status, send some or all packets of the cached first downlink data to the fourth network device.

[0316] As shown in FIG15 , the first method may include the following steps:

[0317] S1501: A first terminal sends a seventh message to a fourth network device. In response, the fourth network device receives the seventh message from the first terminal. The seventh message includes the reception status of downlink data for one or more radio bearers of the first terminal. Exemplarily, the seventh message may include data reception status information, such as a PDCP status report.

[0318] S1502: The fourth network device determines the reception status of downlink data of one or more radio bearers of the first terminal according to the seventh message, and sends sixth indication information to the third network device. Correspondingly, the third network device receives the sixth indication information.

[0319] Among them, the sixth indication information is used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal, and the reception status may, for example, include at least one of the following contents: the identification of one or more wireless bearers of the first terminal; the sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; the bitmap information corresponding to one or more wireless bearers, and the bitmap information is used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0320] Exemplarily, the sixth indication information may be carried in an E1 message (e.g., an E1AP message or E1 interface control signaling), and the sixth indication information may include PDCP status reports of one or more radio bearers. Alternatively, the content of the PDCP status reports of one or more radio bearers may be included in the E1 message in the form of a container and indicate the identifier of the corresponding radio bearer.

[0321] Optionally, the fourth network device may indicate to the third network device only the content of the first PDCP status report of each radio bearer received from the first terminal, where the radio bearer is a radio bearer with lossless transmission requirements.

[0322] S1503: The third network device determines the reception status of downlink data of one or more radio bearers of the first terminal according to the sixth indication information, and sends a second message to the first network device according to the reception status. Correspondingly, the first network device receives the second message from the third network device.

[0323] Among them, the second message includes the reception status of downlink data of one or more wireless bearers of the first terminal, and the reception status may, for example, include at least one of the following contents: the identification of one or more wireless bearers of the first terminal; the sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; the bitmap information corresponding to one or more wireless bearers, and the bitmap information is used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0324] Exemplarily, the second message may be an XnAP message, including the content of the PDCP status report of one or more radio bearers, such as the radio bearer identifier, the first packet loss FMC of the corresponding radio bearer, and a bitmap. Optionally, the content of the PDCP status report is included in the XnAP message in the form of a container.

[0325] Optionally, the third network device may indicate to the first network device only the content of the first PDCP status report of each radio bearer received from the first terminal, where the radio bearer is a radio bearer with lossless transmission requirements.

[0326] S1504: The first network device sends second indication information to the second network device according to the receiving status included in the second message. Correspondingly, the second network device receives the second indication information from the first network device.

[0327] The second indication information includes the reception status of downlink data of one or more radio bearers of the first terminal. The second indication information can be carried in an E1 message (such as an E1AP message or E1 port control signaling). The reception status may include, for example, at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of the subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0328] S1505: The second network device sends part or all of the buffered first downlink data to the fourth network device based on the receiving status included in the second indication information. Correspondingly, the fourth network device receives part or all of the first downlink data from the second network device.

[0329] Furthermore, the fourth network device may transmit part or all of the first downlink data received from the second network device to the first terminal. For example, the fourth network device may transmit the downlink data based on the PDCP status report reported by the first terminal and the downlink transmission requirements or downlink transmission parameters of the first terminal. Alternatively, the fourth network device may transmit all downlink data received from the second network device to the first terminal, with the first terminal discarding duplicate downlink data packets based on the PDCP sequence number.

[0330] Method 2: The second network device receives a sixth message from the fourth network device, where the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal. Based on the reception status, the second network device may selectively send some or all packets of the cached first downlink data to the fourth network device.

[0331] As shown in FIG16 , the second method may include the following steps:

[0332] S1601 (optional): The third network device sends eighth instruction information to the fourth network device. In response, the fourth network device receives the eighth instruction information from the third network device. The eighth instruction information is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device.

[0333] In one possible implementation, the first network device may carry the user plane tunnel target address in the first message sent to the third network device. When implementing S1601, the third network device may send the eighth indication information to the fourth network device according to the user plane tunnel target address after receiving the first message. In another possible implementation, the third network device may determine that a user plane tunnel needs to be established based on the downlink transmission requirements or downlink transmission parameters of the first terminal, and send the eighth indication information to the fourth network device. The embodiment of the present application does not limit the triggering method and triggering timing of the eighth indication information.

[0334] S1602 (optional step): The fourth network device establishes a user plane tunnel from the fourth network device to the second network device. The user plane tunnel is used to send a sixth message from the fourth network device to the second network device, where the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0335] S1603: The first terminal sends a seventh message to the fourth network device. In response, the fourth network device receives the seventh message from the first terminal. The seventh message includes the reception status of downlink data for one or more radio bearers of the first terminal. Exemplarily, the seventh message may include data reception status information, such as a PDCP status report.

[0336] S1604: The fourth network device determines the reception status of downlink data of one or more radio bearers of the first terminal based on the seventh message, and sends a sixth message to the second network device. Accordingly, the second network device receives the seventh message from the fourth network device. Exemplarily, the sixth message may be user plane control information on the Xn interface.

[0337] The sixth message includes the reception status of downlink data of one or more radio bearers of the first terminal. The sixth message can be carried on the user plane tunnel from the fourth network device to the second network device. The reception status includes at least one of the following: the identifier of one or more radio bearers of the first terminal; the sequence number of the first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of the subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0338] Optionally, the fourth network device may indicate to the second network device only the content of the first PDCP status report of each radio bearer received from the first terminal, where the radio bearer is a radio bearer with lossless transmission requirements.

[0339] S1605: The second network device sends part or all of the buffered first downlink data to the fourth network device according to the receiving status. Correspondingly, the fourth network device receives part or all of the first downlink data from the second network device.

[0340] Furthermore, the fourth network device may transmit part or all of the first downlink data received from the second network device to the first terminal. For example, the fourth network device may transmit the downlink data based on the PDCP status report reported by the first terminal. Alternatively, the fourth network device may transmit all downlink data received from the second network device to the first terminal, with the first terminal discarding duplicate downlink data packets based on the PDCP sequence number.

[0341] In the embodiment of the present application, in order to avoid excessive buffering of downlink data on the buffering capacity of the source base station, in some embodiments, the second network device may also stop buffering the first downlink data. The triggering timing for the second network device to stop buffering the first downlink data can be flexibly set, as shown below:

[0342] (1) After determining the reception status of downlink data of one or more radio bearers of the first terminal, the second network device stops buffering the first downlink data.

[0343] The second network device may determine the reception status of downlink data of one or more radio bearers of the first terminal upon receiving the second indication information from the first network device, and stop caching the first downlink data corresponding to the indicated one or more radio bearers. The second indication information may include the reception status of downlink data of one or more radio bearers of the first terminal. Or, for example, the second network device may determine the reception status of downlink data of one or more radio bearers of the first terminal upon receiving the sixth message from the fourth network device, and stop caching the first downlink data corresponding to the indicated one or more radio bearers. The sixth message includes the reception status of downlink data of one or more radio bearers of the first terminal.

[0344] (2) After receiving the third instruction information from the first network device, the second network device stops buffering the first downlink data.

[0345] Among them, the third indication information can be generated in the following manner: the first network device sends the third indication information to the second network device after receiving the third message, wherein the third message is used to indicate the release of the terminal context; or, the third message is used to indicate the release of the connection between the first network device and the core network device.

[0346] Alternatively, the third indication information may be generated by: the first network device sends a fourth message to the first terminal and then sends a third indication information to the second network device, wherein the fourth message is used to instruct the first terminal to switch from the first network device to the third network device, and / or to instruct the first terminal to switch from the second network device to the fourth network device.

[0347] Alternatively, the third indication information may be generated in the following manner: the first network device sends the third indication information to the second network device after receiving the fifth message from the first terminal, wherein the fifth message is used to confirm that the first terminal switches from the first network device to the third network device, and / or confirm that the first terminal switches from the second network device to the fourth network device.

[0348] Alternatively, the third indication information may be generated by: after determining that the handover of the first terminal has failed or the handover has been aborted, the first network device sends the third indication information to the second network device. The handover failure or handover abort may be, for example, the first network device receiving handover failure indication information or handover abort indication information from the third network device.

[0349] Alternatively, before sending the RRC reconfiguration message as shown in Figure 10 to the first terminal, the first network device may instruct the first terminal to report data reception status information, such as a PDCP status report. Furthermore, the second network device may discard the downlink data that has been successfully received by the first terminal and cached on the second network device side based on the content of the data reception status information of the first terminal. Alternatively, before sending the RRC reconfiguration message as shown in Figure 10 to the first terminal, the first network device may instruct the source relay device to report the downlink data forwarding status, that is, which downlink data packets the source relay device has successfully forwarded to the first terminal. The second network device may discard the downlink data that has been successfully received by the first terminal and cached on the second network device side based on the downlink data forwarding status.

[0350] Therefore, through the above method, when the source base station and the target base station both implement the data forwarding mechanism under the CP-UP separation architecture as shown in Figure 9, the first network device can instruct the second network device to send the first downlink data to the fourth network device through the first indication information, and the second network device can further cache the first downlink data of the first terminal so as to forward the first downlink data of the first terminal to the first terminal as comprehensively as possible during switching, reduce packet loss, and ensure lossless downlink transmission of the first terminal.

[0351] The following describes the communication device used to implement the above method in the embodiment of the present application with reference to the accompanying drawings. Therefore, the above contents can be used in subsequent embodiments, and repeated contents will not be repeated.

[0352] Figure 17 is a schematic block diagram of a communication device 1700 provided in an embodiment of the present application. The communication device 1700 can implement the functions or steps implemented by the first network device, or the second network device, or the third network device, or the fourth network device in the above-mentioned various method embodiments. The communication device may include a processing unit 1710 and a transceiver unit 1720. Optionally, it may also include a storage unit, which can be used to store instructions (codes or programs) and / or data. The processing unit 1710 and the transceiver unit 1720 can be coupled to the storage unit. For example, the processing unit 1710 can read the instructions (codes or programs) and / or data in the storage unit to implement the corresponding method. The above-mentioned units can be set independently or partially or fully integrated.

[0353] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the first network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a first network device, or a component (such as a chip or circuit) used in the first network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the first network device in the embodiments shown in Figures 12 to 16. For example, S1220 in the embodiment shown in Figure 12, and / or other processes for supporting the technology described herein; wherein, the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the first network device in the embodiments shown in Figures 12 to 16, such as S1210 in the embodiment shown in Figure 12, and / or other processes for supporting the technology described herein.

[0354] For example, if the first terminal communicates with the first network device through a relay device, the first network device may be the control plane of the centralized unit of the source base station. The processing unit 1710 may determine that the first terminal switches from the first network device to the third network device; the transceiver unit 1720 may send first indication information to the second network device, wherein the first terminal communicates with the second network device through the relay device, and the first indication information is used to indicate the downlink transmission requirement or downlink transmission parameter of the first terminal, and the downlink transmission requirement or downlink transmission parameter of the first terminal is used to instruct the second network device to send first downlink data to the third network device, and the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0355] In an example, the first indication information may also be used to indicate that first downlink data of one or more radio bearers of the first terminal is to be buffered. Exemplarily, the first indication information may include an identifier of the first radio bearer.

[0356] In a possible scenario, the transceiver unit 1720 is configured to send a first message to the third network device, where the first message includes a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0357] In one example, the first message may include identifiers of one or more radio bearers of the first terminal. Exemplarily, the transmission mode of the first radio bearer is an acknowledgement mode, or the quality of service of the first radio bearer meets a first transmission requirement.

[0358] In one possible scenario, the first message is further used to request handover of the first terminal to the third network device. That is, the first message may be a handover request message from the first network device. It should be understood that this is merely an example of an implementation of the first message and does not constitute a limitation. In a specific implementation, the first message may also be, for example, a newly added E1 message between the first network device and the third network device that indicates the first terminal's downlink lossless transmission requirements or downlink lossless transmission parameters.

[0359] In one possible scenario, the transceiver unit 1720 is further configured to send second indication information to the second network device, wherein the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0360] In one possible scenario, the processing unit 1710 is also used to: determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit sends second indication information to the second network device, including: sending the second indication information to the second network device according to the reception status.

[0361] In one example, the transceiver unit 1720 is further configured to: receive a second message from the third network device, wherein the second message includes a reception status of downlink data of one or more radio bearers of the first terminal. Exemplarily, the reception status may include at least one of the following: an identifier of one or more radio bearers of the first terminal; a sequence number of a first unsuccessfully received data packet corresponding to the one or more radio bearers; and bitmap information corresponding to the one or more radio bearers, the bitmap information being used to indicate the reception status of N subsequent data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0362] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0363] In a possible scenario, the transceiver unit is further configured to: send third indication information to the second network device, where the third indication information is configured to instruct the second network device to stop buffering the first downlink data.

[0364] In one example, the transceiver unit 1720 sends a third indication information to the second network device, which may include: receiving a third message, wherein the third message is used to indicate the release of the terminal context; or, the third message is used to indicate the release of the connection between the first network device and the core network device; and sending a third indication information to the second network device.

[0365] In one example, the transceiver unit 1720 sends third indication information to the second network device, which may include: sending a fourth message to the first terminal, the fourth message being used to instruct the first terminal to switch from the first network device to the third network device, and / or instructing the first terminal to switch from the second network device to the fourth network device; sending third indication information to the second network device.

[0366] In one example, the transceiver unit 1720 sends third indication information to the second network device, which may include: receiving a fifth message from the first terminal, the fifth message being used to confirm that the first terminal switches from the first network device to the third network device, and / or confirming that the first terminal switches from the second network device to the fourth network device; and sending third indication information to the second network device.

[0367] In a possible scenario, the transceiver unit 1720 is further configured to send fourth indication information to the second network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0368] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the second network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a second network device, or a component (such as a chip or circuit) used in the second network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the second network device in the embodiments shown in Figures 12 to 16. For example, S1220 in the embodiment shown in Figure 12, and / or other processes for supporting the technology described herein; wherein, the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the second network device in the embodiments shown in Figures 12 to 16, such as S1210 in the embodiment shown in Figure 12, and / or other processes for supporting the technology described herein.

[0369] For example, if the first terminal communicates with the second network device through a relay device, the transceiver unit 1720 is configured to receive first indication information from the first network device, wherein the first terminal communicates with the first network device through the relay device, the first indication information is used to indicate a downlink transmission requirement or downlink transmission parameter of the first terminal, the downlink transmission requirement or downlink transmission parameter of the first terminal is used to instruct the second network device to send first downlink data to the fourth network device, the first downlink data including downlink data for which a successful reception confirmation indication is received from the relay device; and the processing unit 1710 is configured to cache the first downlink data of the first terminal. Optionally, the first downlink data includes downlink data of one or more radio bearers of the first terminal.

[0370] In an example, the first indication information may also be used to indicate caching of first downlink data of one or more radio bearers of the first terminal.

[0371] In an example, the transmission mode of the first radio bearer may be an acknowledged mode, or the quality of service of the first radio bearer may meet a first transmission requirement, which may specifically be a downlink lossless transmission requirement.

[0372] In one example, the first indication information may further include an identifier of the first radio bearer. In other embodiments, the first indication information may indicate the first radio bearer in other ways, which is not limited in this embodiment of the present application.

[0373] In one possible scenario, the processing unit 1710 is used to: determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit is used to send part or all of the first downlink data to a fourth network device based on the reception status, and the fourth network device is the target network device to which the first terminal switches from the second network device.

[0374] In one possible scenario, the transceiver unit 1720 is further configured to: receive second indication information from the first network device, where the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0375] In a possible scenario, the transceiver unit 1720 is further configured to: receive a sixth message from the fourth network device, wherein the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0376] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet.

[0377] In an example, the reception status of downlink data of one or more radio bearers of the first terminal may originate from the first terminal.

[0378] In one possible scenario, the transceiver unit 1720 is further used to: receive third indication information sent from the first network device, where the third indication information is used to instruct the second network device to stop buffering the first downlink data; and stop buffering the first downlink data.

[0379] In one possible scenario, the transceiver unit 1720 is further used to discard cached data packets in the first downlink data according to a data volume cache threshold of the second network device, and the cache space after packet loss is used to cache newly arrived data packets in the first downlink data.

[0380] In a possible scenario, the transceiver unit 1720 is further configured to: receive fourth indication information from the first network device, where the fourth indication information includes a data volume cache threshold of the second network device.

[0381] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the third network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a third network device, or a component (such as a chip or circuit) used in a third network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the third network device in the embodiments shown in Figures 12 to 16. For example, S1502 and S1503 in the embodiment shown in Figure 15, and / or other processes for supporting the technology described herein; wherein the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the third network device in the embodiments shown in Figures 12 to 16.

[0382] For example, if the first terminal switches from the first network device to the third network device, the first terminal communicates with the first network device through the relay device, and the processing unit 1710 is used to determine the reception status of the downlink data of the first terminal; the transceiver unit 1720 is used to send a second message to the first network device according to the reception status, wherein the second message includes the reception status of the downlink data of one or more wireless bearers of the first terminal.

[0383] Exemplarily, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0384] In one possible scenario, the transceiver unit 1720 is also used to: send fifth indication information to a fourth network device, wherein the fourth network device is the target network device to which the first terminal performs switching, and the fifth indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal.

[0385] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0386] In one example, the transceiver unit 1720 is also used to: receive sixth indication information from a fourth network device, wherein the sixth indication information is used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal; the processing unit is also used to determine the reception status of downlink data of one or more wireless bearers of the first terminal based on the sixth indication information.

[0387] In a possible scenario, the transceiver unit is further configured to: receive a first message from a first network device, where the first message is configured to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

[0388] In one example, the first message may include identifiers of one or more radio bearers of the first terminal.

[0389] In an example, the transmission mode of the first radio bearer may be a confirmation mode, or the quality of service of the first radio bearer may meet the first transmission requirement.

[0390] In an example, the first message may also be used to request that the first terminal be handed over to the third network device.

[0391] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the third network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a third network device, or a component (such as a chip or circuit) used in a third network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the third network device in the embodiments shown in Figures 12 to 16. For example, S1502 and S1503 in the embodiment shown in Figure 15, and / or other processes for supporting the technology described herein; wherein the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the third network device in the embodiments shown in Figures 12 to 16.

[0392] For example, if the first terminal switches from the first network device to the third network device, the first terminal communicates with the first network device through the relay device, and the transceiver unit 1720 is used to receive a first message from the first network device, where the first message includes the downlink transmission requirements or downlink transmission parameters of the first terminal; and send seventh indication information to the fourth network device, where the fourth network device is the target network device to which the first terminal switches, and the seventh indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the first terminal.

[0393] In one example, the seventh indication information may include identifiers of one or more radio bearers of the first terminal.

[0394] In one possible scenario, when the CU-CP function and the CU-UP function of the source network device are deployed separately, they are represented as a first network device and a second network device, and the transceiver unit 1720 is also used to: send an eighth indication message to the fourth network device, wherein the eighth indication message is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of one or more wireless bearers of the downlink data of the first terminal. In another possible scenario, when the CU-CP function and the CU-UP function of the source network device are not deployed separately, the eighth indication message can specifically be used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the first network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of one or more wireless bearers of the downlink data of the first terminal.

[0395] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0396] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the fourth network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a third network device, or a component (such as a chip or circuit) used in a fourth network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the fourth network device in the embodiments shown in Figures 12 to 16. For example, S1602 and S1603 in the embodiment shown in Figure 16, and / or other processes for supporting the technology described herein; wherein the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the fourth network device in the embodiments shown in Figures 12 to 16.

[0397] For example, if the first terminal switches to the fourth network device, the first terminal communicates with the first network device through the relay device, and the processing unit 1710 is used to determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit 1720 is used to send sixth indication information to the third network device according to the reception status, wherein the third network device is the target network device to which the first terminal performs switching, and the sixth indication information is used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal.

[0398] In one possible scenario, the transceiver unit 1720 is further configured to: receive a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0399] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0400] In a possible scenario, the transceiver unit 1720 is further configured to: receive fifth indication information from the third network device, where the fifth indication information is configured to indicate a downlink transmission requirement or downlink transmission parameter of the first terminal.

[0401] In one example, the fifth indication information may include identifiers of one or more radio bearers of the first terminal.

[0402] In some possible implementations, the communication device 1700 can implement the behaviors and functions of the fourth network device in the above-mentioned method embodiment. For example, the communication device 1700 can be a third network device, or a component (such as a chip or circuit) used in a fourth network device. The transceiver unit 1720 can be used to perform all receiving or sending operations performed by the fourth network device in the embodiments shown in Figures 12 to 16. For example, S1602 and S1603 in the embodiment shown in Figure 16, and / or other processes for supporting the technology described herein; wherein the processing unit 1710 is used to perform all operations except the receiving and sending operations performed by the fourth network device in the embodiments shown in Figures 12 to 16.

[0403] For example, if the first terminal switches to the fourth network device, the first terminal communicates with the second network device through the relay device, and the processing unit 1710 is used to determine the reception status of downlink data of one or more wireless bearers of the first terminal; the transceiver unit 1720 is used to send a sixth message to the second network device, wherein the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal.

[0404] In one possible scenario, the transceiver unit 1720 is further configured to: receive a seventh message from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

[0405] In one example, the receiving status may include at least one of the following: an identifier of one or more wireless bearers of the first terminal; a sequence number of the first unsuccessfully received data packet corresponding to one or more wireless bearers; and bitmap information corresponding to one or more wireless bearers, the bitmap information being used to indicate the reception status of subsequent N data packets starting from the first unsuccessfully received data packet, where N is an integer greater than or equal to 1.

[0406] In one possible scenario, the transceiver unit 1720 is also used to: receive seventh indication information from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the seventh indication information is used to indicate the downlink transmission requirements or downlink transmission parameters of the wireless bearer of the first terminal.

[0407] In one possible scenario, when the CU-CP function and the CU-UP function of the source network device are deployed separately, represented as a first network device and a second network device, the processing unit 1710 is further used to: establish a user plane tunnel from the fourth network device to the second network device, wherein the second network device is the source network device for performing switching by the first terminal, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal. In another possible scenario, the CU-CP function and the CU-UP function of the source network device are not deployed separately, represented as a first network device, and the processing unit 1710 is further used to: establish a user plane tunnel from the fourth network device to the first network device, wherein the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal. In one possible scenario, the transceiver unit 1720 is also used to: receive an eighth indication message sent from a third network device, wherein the third network device is the target network device to which the first terminal performs switching, and the eighth indication message is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device.

[0408] Figure 18 provides a schematic diagram of the structure of a communication device. The communication device can be applied to the operations performed by the first network device, the second network device, the third network device, or the fourth network device in any of the above method embodiments. For ease of illustration, Figure 18 only shows the main components of the communication device.

[0409] As shown in FIG18 , the apparatus 1800 includes at least one processor 1810 and an interface circuit 1820. In an optional design, a memory 1830 may also be included.

[0410] The specific connection medium between the processor 1810 and the memory 1830 is not limited in the embodiment of the present application.

[0411] In the apparatus as shown in FIG. 18 , the processor 1810 may transmit data through the interface circuit 1820 when communicating with other devices.

[0412] When the communication device adopts the form shown in Figure 18, the processor 1810 in Figure 18 can call the computer-executable instructions stored in the memory 1830, so that the device 1800 can execute any of the above method embodiments.

[0413] An embodiment of the present application also relates to a chip system, which includes a processor for calling a computer program or computer instructions stored in a memory so that the processor executes the method of any of the above embodiments.

[0414] In a possible implementation, the processor may be coupled to the memory via an interface circuit.

[0415] In a possible implementation, the chip system may also directly include a memory, in which a computer program or computer instructions are stored.

[0416] For example, the memory may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. The non-volatile memory may be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache memory. By way of example and not limitation, many forms of RAM are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link dynamic random access memory (SLDRAM), and direct rambus RAM (DR RAM).

[0417] An embodiment of the present application further relates to a processor, which is used to call a computer program or computer instruction stored in a memory so that the processor executes the method described in any of the above embodiments.

[0418] For example, in the embodiments of the present application, the processor is an integrated circuit chip with signal processing capabilities. For example, the processor can be an FPGA, a general-purpose processor, a DSP, an ASIC or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component, a system on chip (SoC), a CPU, a network processor (NP), a microcontroller unit (MCU), a PLD or other integrated chip, and can implement or execute the various methods, steps and logic block diagrams disclosed in the embodiments of the present application. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor. The steps of the method disclosed in the embodiments of the present application can be directly embodied as being executed by a hardware decoding processor, or can be executed by a combination of hardware and software modules in the decoding processor. The software module can be located in a storage medium mature in the art, such as random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory, registers, etc. The storage medium is located in the memory, and the processor reads the information in the memory and completes the steps of the above method in combination with its hardware.

[0419] It should be understood that the embodiments of the present application may be provided as methods, systems, or computer program products.

[0420] In one possible implementation, an embodiment of the present application provides a computer-readable storage medium, which stores program code. When the program code runs on the computer, the computer executes the above method embodiment.

[0421] In a possible implementation, an embodiment of the present application provides a computer program product. When the computer program product is run on a computer, the computer is caused to execute the above method embodiment.

[0422] In one possible implementation, an embodiment of the present application provides a chip system, which may include at least one processor, and the at least one processor may be used to implement the above method embodiment. Optionally, the chip system may also include a processor, and the processor may be used to store computer programs or instructions.

[0423] Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0424] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0425] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0426] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the scope of the embodiments of the present application. Thus, if these modifications and variations of the embodiments of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these changes and variations. In the various embodiments of the present application, unless otherwise specified or logically conflicting, the terms and / or descriptions between the various embodiments are consistent and can be referenced to each other, and the technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

Claims

1. A data transmission method, characterized in that: Applied to a first network device, a first terminal communicates with the first network device through a relay device, and the method includes: Determine that the first terminal switches from the first network device to a third network device; Sending first indication information to a second network device, wherein the first terminal communicates with the second network device through the relay device, the first indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal, the downlink transmission requirement or the downlink transmission parameter of the first terminal is used to instruct the second network device to send first downlink data to the third network device, the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device.

2. The method according to claim 1, characterized in that The first downlink data includes downlink data of one or more radio bearers of the first terminal.

3. The method according to claim 1 or 2, characterized in that: The first indication information is further used to indicate caching of first downlink data of one or more radio bearers of the first terminal.

4. The method according to any one of claims 1 to 3, characterized in that The method further comprises: A first message is sent to the third network device, where the first message includes a downlink transmission requirement or a downlink transmission parameter of the first terminal.

5. The method according to claim 4, characterized in that The first message includes identifiers of one or more radio bearers of the first terminal.

6. The method according to any one of claims 1 to 5, characterized in that The method further comprises: Send second indication information to the second network device, wherein the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

7. The method according to any one of claims 1 to 5, characterized in that The method further comprises: A second message is received from the third network device, wherein the second message includes a reception status of downlink data of one or more radio bearers of the first terminal.

8. The method according to any one of claims 1 to 7, characterized in that The method further comprises: Send third indication information to the second network device, where the third indication information is used to instruct the second network device to stop buffering the first downlink data.

9. A data transmission method, characterized in that: Applied to a second network device, a first terminal communicates with the second network device through a relay device, and the method includes: Receiving first indication information from a first network device, wherein the first terminal communicates with the first network device through the relay device, the first indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal, the downlink transmission requirement or the downlink transmission parameter of the first terminal is used to instruct the second network device to send first downlink data to the fourth network device, the first downlink data includes downlink data of a successful reception confirmation indication received from the relay device; The first downlink data of the first terminal is cached.

10. The method according to claim 9, characterized in that The first downlink data includes downlink data of one or more radio bearers of the first terminal.

11. The method according to claim 9 or 10, characterized in that: The first indication information is also used to indicate caching of first downlink data of one or more radio bearers of the first terminal.

12. The method according to any one of claims 9 to 11, characterized in that: The method further comprises: Determining a reception status of downlink data of one or more radio bearers of the first terminal; According to the receiving state, part or all of the first downlink data is sent to a fourth network device, and the fourth network device is a target network device to which the first terminal performs switching from the second network device.

13. The method according to claim 12, characterized in that The method further comprises: Second indication information is received from the first network device, where the second indication information includes a reception status of downlink data of one or more radio bearers of the first terminal.

14. The method according to claim 12, characterized in that The method further comprises: A sixth message is received from the fourth network device, wherein the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

15. The method according to any one of claims 9 to 14, characterized in that: The method further comprises: receiving third indication information sent from the first network device, where the third indication information is used to instruct the second network device to stop buffering the first downlink data; Stop buffering the first downlink data.

16. A data transmission method, characterized in that: Applied to a third network device, a first terminal switches from the first network device to the third network device, and the first terminal communicates with the first network device through a relay device, and the method includes: Determine a reception status of downlink data of one or more radio bearers of the first terminal; A second message is sent to the first network device according to the reception status, wherein the second message includes a reception status of downlink data of one or more radio bearers of the first terminal.

17. The method according to claim 16, characterized in that The method further comprises: Send fifth indication information to a fourth network device, wherein the fourth network device is a target network device to which the first terminal performs switching, and the fifth indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

18. The method according to claim 17, characterized in that The fifth indication information includes identifiers of one or more radio bearers of the first terminal.

19. The method according to any one of claims 16 to 18, characterized in that: The determining the reception status of downlink data of one or more radio bearers of the first terminal further includes: receiving sixth indication information from a fourth network device, wherein the fourth network device is a target network device to which the first terminal performs handover, and the sixth indication information is used to indicate a reception status of downlink data of one or more radio bearers of the first terminal; Based on the sixth indication information, a reception status of downlink data of one or more radio bearers of the first terminal is determined.

20. The method according to any one of claims 16 to 19, characterized in that The method further comprises: A first message is received from a first network device, where the first message is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

21. The method according to claim 20, characterized in that The first message includes identifiers of one or more radio bearers of the first terminal.

22. A data transmission method, characterized in that: Applied to a third network device, a first terminal switches from the first network device to the third network device, and the first terminal communicates with the first network device through a relay device, and the method includes: receiving a first message from the first network device, where the first message includes a downlink transmission requirement or a downlink transmission parameter of the first terminal; Send seventh indication information to a fourth network device, wherein the fourth network device is a target network device to which the first terminal performs switching, and the seventh indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

23. The method according to claim 22, characterized in that The seventh indication information includes identifiers of one or more radio bearers of the first terminal.

24. The method according to claim 22 or 23, characterized in that The method further comprises: Sending eighth indication information to the fourth network device, wherein the eighth indication information is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the first network device, and the user plane tunnel is used to send a sixth message from the fourth network device to the first network device, and the sixth message includes the reception status of one or more radio bearers of the downlink data of the first terminal.

25. A data transmission method, characterized in that: Applied to a fourth network device, a first terminal switches to the fourth network device, and the first terminal communicates with a source network device through a relay device, and the method includes: Determining a reception status of downlink data of one or more radio bearers of the first terminal; Send sixth indication information to a third network device according to the reception status, wherein the third network device is a target network device to which the first terminal performs switching, and the sixth indication information is used to indicate the reception status of downlink data of one or more wireless bearers of the first terminal.

26. The method according to claim 25, characterized in that The method further comprises: A seventh message is received from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

27. The method according to claim 25 or 26, characterized in that The method further comprises: Receive fifth indication information from the third network device, the fifth indication information being used to indicate downlink transmission of the first terminal Request or downlink transmission parameters.

28. The method according to claim 27, characterized in that The fifth indication information includes identifiers of one or more radio bearers of the first terminal.

29. A data transmission method, characterized in that: Applied to a fourth network device, a first terminal switches to the fourth network device, and the first terminal communicates with a second network device through a relay device, and the method includes: Determining a reception status of downlink data of one or more radio bearers of the first terminal; A sixth message is sent to the second network device, wherein the sixth message includes a reception status of downlink data of one or more radio bearers of the first terminal.

30. The method according to claim 29, characterized in that The method further comprises: A seventh message is received from the first terminal, wherein the seventh message includes a reception status of downlink data of one or more radio bearers of the first terminal.

31. The method according to claim 29 or 30, characterized in that The method further comprises: Receive seventh indication information from a third network device, wherein the third network device is a target network device to which the first terminal performs switching, and the seventh indication information is used to indicate a downlink transmission requirement or a downlink transmission parameter of the first terminal.

32. The method according to any one of claims 29 to 31, characterized in that The method further comprises: Establish a user plane tunnel from the fourth network device to the second network device, wherein the second network device is a source network device for performing switching by the first terminal, and the user plane tunnel is used to send a sixth message from the fourth network device to the second network device, and the sixth message includes the reception status of downlink data of one or more wireless bearers of the first terminal.

33. The method according to claim 32, characterized in that The method further comprises: Receive eighth indication information sent from a third network device, wherein the third network device is a target network device to which the first terminal performs switching, and the eighth indication information is used to instruct the fourth network device to establish a user plane tunnel from the fourth network device to the second network device.

34. A communication device, characterized in that: Comprising a unit for performing the method as claimed in any one of claims 1 to 8, or comprising a unit for performing the method as claimed in any one of claims 9 to 15, or comprising a unit for performing the method as claimed in any one of claims 16 to 21, or comprising a unit for performing the method as claimed in any one of claims 22 to 24, or comprising a unit for performing the method as claimed in any one of claims 25 to 28, or comprising a unit for performing the method as claimed in any one of claims 29 to 33.

35. A communication device, characterized in that: include: The device includes at least one processor, wherein the at least one processor is used to call a computer program or instruction in a memory to execute a method as described in any one of claims 1 to 8, or to execute a method as described in any one of claims 9 to 15, or to execute a method as described in any one of claims 16 to 21, or to execute a method as described in any one of claims 22 to 24, or to execute a method as described in any one of claims 25 to 28, or to execute a method as described in any one of claims 29 to 33.

36. A chip system, characterized in that: The chip system includes at least one processor, and the at least one processor is used to call one or more computer programs or instructions in the memory to implement the method as described in any one of claims 1-8, or implement the method as described in any one of claims 9-15, or implement the method as described in any one of claims 16-21, or implement the method as described in any one of claims 22-24, or implement the method as described in any one of claims 25-28, or implement the method as described in any one of claims 29-33.

37. A communication system, characterized in that: It includes one or more of the following: a network device for implementing the method as described in any one of claims 1 to 8, a network device for implementing the method as described in any one of claims 9 to 15, a network device for implementing the method as described in any one of claims 16 to 21, a network device for implementing the method as described in any one of claims 22 to 24, a network device for implementing the method as described in any one of claims 25 to 28, and a network device for implementing the method as described in any one of claims 29 to 33.

38. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, which, when called by an electronic device, cause the electronic device to execute the method as described in any one of claims 1-8, or cause the electronic device to execute the method as described in any one of claims 9-15, or cause the electronic device to execute the method as described in any one of claims 16-21, or cause the electronic device to execute the method as described in any one of claims 22-24, or cause the electronic device to execute the method as described in any one of claims 25-28, or cause the electronic device to execute the method as described in any one of claims 29-33.

39. A computer program product, characterized in that The method comprises computer execution instructions, which, when executed on a computer, cause the computer to execute the method as claimed in any one of claims 1 to 8, or cause the computer to execute the method as claimed in any one of claims 9 to 15, or cause the computer to execute the method as claimed in any one of claims 16 to 21, or cause the computer to execute the method as claimed in any one of claims 22 to 24, or cause the computer to execute the method as claimed in any one of claims 25 to 28, or cause the computer to execute the method as claimed in any one of claims 29 to 33.

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