Communication methods and communication devices

Abstract

This application provides a communication method and a communication device. In this method, before or when transmitting a first message, a second network device transmits indication information to a first network device so that the first network device can determine, based on the indication information, the configuration of a first mapping relationship used to transmit the first message. In this way, the first message is transmitted correctly so that the first terminal device can re-establish or resume the first connection using the second terminal device and correctly access the corresponding access network device.

Description

Technical Field

[0001] This application relates to the field of communication technologies, and particularly to communication methods and communication apparatuses.

Background Art

[0002] This application claims the priority of Chinese Patent Application No. 202310402926.2, titled "COMMUNICATION METHOD AND COMMUNICATION APPARATUS", filed with the China National Intellectual Property Administration on April 6, 2023, which is incorporated herein by reference in its entirety.

[0003] Sidelink UE (user equipment)-to-network relay (SL-U2N Relay) is a technology in which a UE helps another UE communicate with a base station, and is also called relay technology. The communication architecture of U2N relay includes a remote device (remote UE), a relay device (relay UE), and a base station. The base station includes a distributed unit (DU) and a central unit (CU). For example, the CU and DU are connected via an F1 interface. The relay UE is connected to the DU, and the corresponding interface is the Uu interface. The remote UE and the relay UE are directly connected (for example, connected via a sidelink), and the corresponding interface is the PC5 interface. For example, in a CU-DU separation architecture, when a remote UE requests to re-establish or resume a radio resource control (RRC) connection via a relay UE, how the DU forwards the RRC connection re-establishment or resume message to the relay UE and / or the remote UE becomes an issue to be solved.

Summary of the Invention

[0004] This application provides a communication method and a communication apparatus. In this method, an access network device can correctly forward a first connection re-establishment or restart message so that a remote UE can correctly access the corresponding access network device when performing a first connection re-establishment / RRC restart via a relay UE.

[0005] According to a first aspect, the present application provides a communication method which is applied to a first network device. The first network device may be an access network device. The first network device may be a distributed unit, a component of an access network device (e.g., a processor, chip, or chip system), or a logic module which can implement all or some of the functions of a distributed unit. The first network device receives indication information from a second network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. The first network device receives a first message from the second network device and transmits the first message based on the first mapping relationship. The first message is a first downlink message sent from the second network device to a first terminal device in a first connection re-establishment or restart procedure, and the first connection is a connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0006] In this method, a first network device (e.g., a DU) receives indication information and determines, based on this indication information, the configuration of a first mapping relationship used to transmit a first message, so that a first terminal device can re-establish or resume the first connection via a second terminal device and correctly access the corresponding access network device. Optionally, the mapping relationship (mapping) in this application may also be referred to as a mapping relationship configuration (mapping configuration).

[0007] In a possible implementation, the first network device receives first indication information from the second network device, where the first indication information indicates a first identifier of the first terminal device, which the first network device uses to associate the first terminal device on the interface between the first and second network devices. For example, the first identifier is used to identify the first terminal device on the F1 interface between the first and second network devices, and the first network device may interact with the first terminal device based on the first identifier.

[0008] In possible implementations, the first terminal device may re-establish or resume the first connection via an associated relay terminal device before re-establishing or resuming the first connection itself. In this case, the first indication information received by the first network device carries the first identifier of the first terminal device (e.g., the old gNB-DU UE F1AP ID of the remote UE). This helps the first network device obtain context information for the first terminal device.

[0009] In a possible implementation, the first network device obtains context information for the first terminal device based on the first identifier, and determines the first mapping relationship based on the context information for the first terminal device.

[0010] In this method, if the first terminal device re-establishes or resumes the first connection via a relay terminal device associated with the first terminal device before the first connection is re-established or resumed, the first network device may look up context information for the first terminal device based on the first identifier. The context information includes previously configured mapping relationships between SRB1 and the Uu relay RLC channel (for example, mapping relationships between SRB1 and the Uu relay RLC channel configured by the remote UE before the first connection was re-established or resumed). The first network device may use this previously configured mapping relationship as the first mapping relationship. This helps the first terminal device re-establish or resume the first connection and correctly access the corresponding access network device.

[0011] In a possible implementation, the first network device determines a first mapping relationship based on second indication information and context information of the first terminal device, where the second indication information instructs the first network device to apply the first mapping relationship.

[0012] In this method, if the first terminal device re-establishes or resumes the first connection via a relay terminal device associated with the first terminal device before the first connection is re-established or resumed, the second network device may indicate to the first network device that the previously configured mapping relationship between SRB1 and the Uu relay RLC channel should be used as the first mapping relationship. This helps the first terminal device re-establish or resume the first connection and correctly access the corresponding access network device.

[0013] In a possible implementation, the first network device determines a first mapping relationship based on a first identifier of the first terminal device, context information of the first terminal device, and information corresponding to the second terminal device. For example, the information corresponding to the second terminal device includes one or more of the second identifier of the second terminal device, service information of the second terminal device, and context information of the second terminal device.

[0014] In this method, the first network device may determine that the first terminal device should perform access by re-establishing the first connection or restarting a previously associated relay terminal device, based on information corresponding to the first identifier and the associated second terminal device (e.g., the relay UE F1AP ID of the associated relay UE, historical service information, and UE context information of the second terminal device). Therefore, the first network device may use a previously established mapping relationship between SRB1 and the Uu relay RLC channel as the first mapping relationship to help the first terminal device re-establish or restart the first connection and correctly access the corresponding access network device.

[0015] In possible implementations, indication information includes a first mapping relationship.

[0016] In this method, the indication information received by the first network device includes a new mapping relationship between SRB1 and the Uu relay RLC channel. The first network device uses this new mapping relationship between SRB1 and the Uu relay RLC channel as the first mapping relationship, so that the first terminal device can re-establish or restart the first connection via the second terminal device and correctly access the corresponding access network device.

[0017] In a possible implementation, the first network device decides to release the second mapping relationship based on the first identifier of the first terminal device and the information corresponding to the second terminal device. The second mapping relationship is included in the context information of the first terminal device, and the first mapping relationship is distinct from the second mapping relationship.

[0018] In this method, the first network device may decide that the first terminal device will perform access through the second terminal device (the new relay UE) based on a second identifier (e.g., the relay UE F1AP ID of the new relay UE). The context information of the first terminal device includes another mapping relationship (i.e., a second mapping relationship), for example, the second mapping relationship includes the originally configured mapping relationship between the SRB2 / DRB and the Uu relay RLC channel, so the first network device may release the second mapping relationship.

[0019] In a possible implementation, the first network device receives third indication information from the second network device, which instructs the first network device to release the second mapping relationship, the second mapping relationship being included in the context information of the first terminal device, and the first mapping relationship being different from the second mapping relationship.

[0020] In this method, the second network device may instruct the first network device to release the second mapping relationship. When the first network device receives the third indication information, it may release the originally configured mapping relationship between the SRB2 / DRB and the Uu relay RLC channel based on the indication.

[0021] In a possible implementation, the first network device receives a context information establishment or update request message from the second network device, which is used to establish a second mapping relationship, the second mapping relationship being different from the first mapping relationship.

[0022] In this method, the first network device decides to release another originally configured mapping relationship, and may then reconfigure the second mapping relationship of the first terminal device based on a context information establishment or update procedure triggered by the second network device. This helps the first terminal device re-establish or resume the first connection through the second terminal device and correctly access the corresponding access network device.

[0023] In a possible implementation, the first downlink message is the first connection re-establishment message, the first connection reopen message, or the first connection release message, and the first bearer is the signaling radio bearer SRB1 message of the first terminal device.

[0024] In a possible implementation, the first downlink message is the first connection establishment message, and the first bearer is the SRB0 message from the first terminal device.

[0025] In a possible implementation, the first downlink message is the first connection rejection message, and the first bearer is the SRB0 message from the first terminal device.

[0026] According to a second aspect, the present application provides another communication method which is applied to a second network device. The second network device may be an access network device. The second network device may be a central unit, a component of an access network device (e.g., a processor, chip, or chip system), or a logic module which can implement all or some of the functions of the central unit. The second network device transmits indication information to the first network device, where the indication information is used to determine a first mapping relationship between a first bearer and a second bearer. The second network device transmits a first message to the first network device, where the first message is a first downlink message transmitted from the second network device to a first terminal device in a first connection re-establishment or restart procedure, where the first connection is the connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0027] In this method, the second network device sends indication information to the first network device so that the first network device can determine the configuration of a first mapping relationship used to transmit the first message based on this indication information, and the first terminal device can re-establish or restart the first connection via the second terminal device and correctly access the corresponding access network device.

[0028] In a possible implementation, the second network device transmits first indication information to the first network device, where the first indication information indicates a first identifier of the first terminal device, and the first identifier is used by the first network device to associate the first terminal device on an interface between the first network device and the second network device.

[0029] In a possible implementation, the first terminal device may re - establish or resume the first connection via a relaying terminal device associated before the re - establishment or resumption of the first connection. In this case, the relaying terminal device associated before the re - establishment or resumption of the first connection may indicate the first identifier of the first terminal device to the first network device. This helps the first network device to obtain the context information of the first terminal device.

[0030] In a possible implementation, the first identifier of the first terminal device is used by the first network device to obtain the context information of the first terminal device, and the context information of the first terminal device includes a first mapping relationship.

[0031] In this method, when the first terminal device re - establishes or resumes the first connection via a relaying terminal device associated before the re - establishment or resumption of the first connection, the context information of the first terminal device includes a mapping relationship between SRB1 and the Uu relaying RLC channel set by a remote UE before the re - establishment or resumption of the first connection. This mapping relationship is used as the first mapping relationship to help the first terminal device re - establish or resume the first connection and correctly access the corresponding access network device.

[0032] In a possible implementation, the second network device determines, based on the second message and the second identifier of the second terminal device, which relay terminal device is associated with the first terminal device before the first connection re-establishment or restart procedure. The second message is used by the first terminal device to request that the first connection re-establishment or restart procedure be performed.

[0033] In this method, the second network device may decide, based on the second message and information corresponding to the second terminal device, that the first terminal device should access the relay terminal device associated with the first terminal device before the first connection is re-established or restarted.

[0034] In a possible implementation, the second network device sends second indication information to the first network device, which instructs the first network device to apply the first mapping relationship.

[0035] In this method, if the first terminal device re-establishes or resumes the first connection via a relay terminal device associated with the first terminal device before the first connection re-establishment or resumption procedure, the second network device may indicate to the first network device that the previously configured mapping relationship between SRB1 and the Uu relay RLC channel should be used as the first mapping relationship. This helps the first terminal device re-establish or resume the first connection and correctly access the corresponding access network device.

[0036] In possible implementations, indication information includes a first mapping relationship.

[0037] In this method, the indication information transmitted by the second network device includes a new mapping relationship between SRB1 and the Uu relay RLC channel (different from the previously established mapping relationship between SRB1 and the Uu relay RLC channel), which helps the first terminal device re-establish or resume the first connection via the second terminal device and correctly access the corresponding access network device.

[0038] In a possible implementation, the second network device determines, based on the second message and the second identifier of the second terminal device, that the relay terminal device associated with the second terminal device is different from the relay terminal device associated with the first terminal device before the first connection re-establishment or restart procedure, where the second message is used by the first terminal device to request the first connection re-establishment or restart. The second network device then decides to update the first mapping relationship.

[0039] In this method, the second network device may determine, based on the second message and the information corresponding to the second terminal device, that the first terminal device needs to access the second terminal device (a new relay UE) and that the first mapping relationship needs to be updated.

[0040] In a possible implementation, the second network device sends a third indication to the first network device, which instructs the first network device to release the second mapping relationship, the second mapping relationship being included in the context information of the first terminal device, and the first mapping relationship being different from the second mapping relationship.

[0041] In this method, the second network device may instruct the first network device to release the second mapping relationship, so the first network device may release the second mapping relationship based on the indication, for example, the originally configured mapping relationship between the SRB2 / DRB and the Uu relay RLC channel.

[0042] In possible implementations, the second network device sends a context information establishment or update request message to the first network device, where the context information establishment or update request message is used to establish a second mapping relationship, which is different from the first mapping relationship.

[0043] In this method, assuming that the first terminal device performs access via the second terminal device, the second network device determines that mapping relationships other than the first mapping relationship need to be updated. For example, updating the second mapping relationship in a context information establishment or update procedure includes facilitating correct data transmission between the first terminal device and the second terminal device by sending a context information establishment or update request message from the first terminal device to the second network device.

[0044] In a possible implementation, the second network device transmits first configuration information to the second terminal device, where the first configuration information includes a first mapping relationship. Optionally, the first configuration information further includes a third mapping relationship between the first bearer and the third bearer, which is used to transmit the first message between the first terminal device and the second terminal device.

[0045] In this method, the second network device may configure the re-determined first mapping relationship for the new relay UE to help the first terminal device correctly transmit data between the second and first terminal devices. Optionally, the second network device may further reconfigure a third mapping relationship (for example, the mapping relationship between SRB1 and the PC5 relay RLC channel).

[0046] In a possible implementation, the first downlink message is the first connection re-establishment message, the first connection reopen message, or the first connection release message, and the first bearer is the signaling radio bearer SRB1 message of the first terminal device.

[0047] In a possible implementation, the first downlink message is the first connection establishment message, and the first bearer is the SRB0 message from the first terminal device.

[0048] In a possible implementation, the first downlink message is the first connection rejection message, and the first bearer is the SRB0 message from the first terminal device.

[0049] According to a third aspect, the present application provides a communication device, which may be an access network device (e.g., a DU), an access network device apparatus, or an apparatus that can be used in conjunction with an access network device. In possible implementations, the communication device may include a functional module, which may be implemented by hardware circuitry, software, or a combination of hardware circuitry and software.

[0050] In a possible implementation, the communication device includes a communication unit and a processing unit. The communication unit is configured to receive indication information from a second network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. The communication unit is further configured to receive a first message from the second network device. The processing unit is configured to transmit a first message based on the first mapping relationship via the communication unit. The first message is a first downlink message sent from the second network device to a first terminal device in a first connection re-establishment or restart procedure, where the first connection is the connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0051] In possible implementations, the communication unit is configured to receive indication information from a second network device. The process includes receiving first indication information from a second network device, wherein the first indication information indicates a first identifier of a first terminal device, which is used by the first network device to associate the first terminal device on an F1 interface between the first network device and the second network device.

[0052] In possible implementations, the processing unit is configured to determine a first mapping relationship between a first bearer and a second bearer. Obtaining context information of a first terminal device based on a first identifier, This includes determining a first mapping relationship based on context information of a first terminal device.

[0053] In possible implementations, the processing unit is configured to determine a first mapping relationship based on context information of a first terminal device. This includes determining a first mapping relationship based on second indication information and context information of a first terminal device, wherein the second indication information instructs the first network device to apply the first mapping relationship.

[0054] In possible implementations, the processing unit is configured to determine a first mapping relationship based on context information of a first terminal device. The process includes determining a first mapping relationship based on a first identifier of a first terminal device, context information of the first terminal device, and information corresponding to a second terminal device, wherein the information corresponding to the second terminal device includes one or more of the second identifier of the second terminal device, service information of the second terminal device, and context information of the second terminal device.

[0055] In possible implementations, indication information includes a first mapping relationship.

[0056] In possible implementations, the processing unit is further configured to decide to release the second mapping relationship based on the first identifier of the first terminal device and the information corresponding to the second terminal device. The second mapping relationship is contained in the context information of the first terminal device, and the first mapping relationship is distinct from the second mapping relationship.

[0057] In a possible implementation, the communication unit is further configured to receive third indication information from a second network device, where the third indication information instructs the first network device to release a second mapping relationship, the second mapping relationship being contained in the context information of the first terminal device, and the first mapping relationship being distinct from the second mapping relationship.

[0058] In possible implementations, the communication unit is further configured to receive context information establishment or update request messages from a second network device, where the context information establishment or update request messages are used to establish a second mapping relationship, which is distinct from the first mapping relationship.

[0059] In a possible implementation, the first downlink message is the first connection re-establishment message, the first connection reopen message, or the first connection release message, and the first bearer is the signaling radio bearer SRB1 message of the first terminal device.

[0060] In a possible implementation, the first downlink message is the first connection establishment message, and the first bearer is the SRB0 message from the first terminal device.

[0061] In a possible implementation, the first downlink message is the first connection rejection message, and the first bearer is the SRB0 message from the first terminal device.

[0062] According to a fourth aspect, the present application provides another communication device, which may be an access network device (e.g., a CU), a device for an access network device, or a device that can be used in conjunction with an access network device. In possible implementations, the communication device may include a functional module, which may be implemented by hardware circuitry, software, or a combination of hardware circuitry and software.

[0063] In possible implementations, the communication device may include a communication unit and a processing unit. The communication unit is configured to transmit indication information to a first network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. The communication unit is further configured to transmit a first message to the first network device, which is a first downlink message transmitted from the second network device to the first terminal device in a first connection re-establishment or restart procedure, where the first connection is the connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0064] In possible implementations, the communication unit is configured to send indication information to the first network device. The process includes transmitting first indication information to a first network device, wherein the first indication information indicates a first identifier of a first terminal device, which is used by the first network device to associate the first terminal device on an F1 interface between the first network device and the second network device.

[0065] In a possible implementation, a first identifier of a first terminal device is used by a first network device to obtain context information for the first terminal device, and the context information for the first terminal device includes a first mapping relationship.

[0066] In possible implementations, the processing unit is configured to determine, based on the second message and a second identifier of the second terminal device, that the second terminal device is a relay terminal device associated with the first terminal device prior to the first connection re-establishment or restart procedure. The second message is used by the first terminal device to request that the first connection re-establishment or restart procedure be performed.

[0067] In possible implementations, the communication unit transmits indication information to the first network device. This includes transmitting second indication information to a first network device, where the second indication information instructs the first network device to apply a first mapping relationship.

[0068] In possible implementations, indication information includes a first mapping relationship.

[0069] In a possible implementation, the processing unit is further configured to determine, based on a second message and a second identifier of the second terminal device, that the relay terminal device associated with the second terminal device is different from the relay terminal device associated with the first terminal device prior to the first connection re-establishment or restart procedure, where the second message is used by the first terminal device to request the first connection to be re-established or restarted. The processing unit is configured to determine to update the first mapping relationship.

[0070] In a possible implementation, the communication unit is further configured to transmit a third indication to a first network device, which instructs the first network device to release a second mapping relationship. The second mapping relationship is contained in the context information of the first terminal device and is distinct from the second mapping relationship.

[0071] In possible implementations, the communication unit is further configured to send a context information establishment or update request message to a first terminal device, where the context information establishment or update request message is used to establish a second mapping relationship, which is different from the first mapping relationship.

[0072] In a possible implementation, the communication unit is further configured to transmit first configuration information to a second terminal device, where the first configuration information includes a first mapping relationship. Optionally, the first configuration information further includes a third mapping relationship between a first bearer and a third bearer, the third bearer being used to transmit a first message between the first terminal device and the second terminal device.

[0073] In a possible implementation, the first downlink message is the first connection re-establishment message, the first connection reopen message, or the first connection release message, and the first bearer is the signaling radio bearer SRB1 message of the first terminal device.

[0074] In a possible implementation, the first downlink message is the first connection re-establishment message, and the first bearer is the SRB0 message from the first terminal device.

[0075] In a possible implementation, the first downlink message is the first connection rejection message, and the first bearer is the SRB0 message from the first terminal device.

[0076] According to a fifth aspect, the present application provides a communication device including a processor configured to execute instructions. Optionally, the communication device further includes a memory configured to store instructions. When instructions are executed by the processor, the communication device becomes capable of implementing a method according to the first aspect and any one of the possible implementations thereof. Optionally, the processor is coupled to the memory.

[0077] According to a sixth aspect, the present application provides a communication device including a processor configured to execute instructions. Optionally, the communication device further includes a memory configured to store instructions. When instructions are executed by the processor, the communication device becomes capable of implementing a method according to the second aspect and any one of the possible implementations thereof. Optionally, the processor is coupled to the memory.

[0078] According to the seventh aspect, the present application provides a communication system, which includes a plurality of devices or apparatus according to the third to sixth aspects. These devices or apparatus can implement methods according to any one of the first and second aspects, and possible implementations of the first and second aspects.

[0079] According to the eighth aspect, the present application provides a computer-readable storage medium that stores instructions. When the instructions are executed on a computer, the computer can implement any one of the first and second aspects, or possible implementations thereof.

[0080] According to the ninth aspect, the present application provides a chip comprising a processor and an interface, optionally further comprising memory, and configured to implement a method according to any one of the first aspect, the second aspect, and possible implementations of the first and second aspects.

[0081] According to a tenth aspect, the present application provides a chip system, which includes a processor and an interface, and optionally further includes memory, and is configured to implement a method according to any one of the first aspect, the second aspect, and possible implementations of the first and second aspects. The chip system may include a chip, or it may include a chip and other separate components.

[0082] According to the eleventh aspect, the present application provides a computer program product including instructions. When the instructions are executed on a computer, the computer becomes capable of executing any one of the first and second aspects, and any possible implementations of the first and second aspects. [Brief explanation of the drawing]

[0083] [Figure 1] This is a diagram of the communication system according to this application. [Figure 2] This is a diagram of the user plane protocol stack for L2 U2N relay. [Figure 3] This is a diagram illustrating the routing process for downlink data from a remote UE. [Figure 4] This is a diagram of the CU-DU isolation architecture. [Figure 5] This is a diagram of the protocol stacks for the user plane and control plane in a CU-DU isolation architecture. [Figure 6A] This is a schematic flowchart of the RRC connection re-establishment process performed by the UE in a CU-DU isolation architecture. [Figure 6B] This is a schematic flowchart of the RRC connection re-establishment process performed by the UE in a CU-DU isolation architecture. [Figure 7] This is a schematic flowchart of the communication method described in this application. [Figure 8] This is a schematic flowchart of another communication method according to this application. [Figure 9] This is a schematic flowchart of yet another communication method according to this application. [Figure 10A] This is a schematic flowchart of yet another communication method according to this application. [Figure 10B] This is a schematic flowchart of yet another communication method according to this application. [Figure 10C] This is a schematic flowchart of yet another communication method according to this application. [Figure 11] This is a diagram of a communication device according to this application. [Figure 12]This is a diagram of another communication device according to this application. [Modes for carrying out the invention]

[0084] In embodiments of this application, “ / ” may represent an “or” relationship between related objects. For example, A / B may represent A or B. “And / or” may be used to indicate that there are three relationships between related objects. For example, “A and / or B” may represent the following three cases: the case where only A exists, the case where both A and B exist, and the case where only B exists, where A and B may be singular or plural. In order to facilitate the description of the technical solutions of this application, in embodiments of this application, terms such as “first” and “second” may be used to distinguish technical features that have the same or similar function. Terms such as “first” and “second” are not intended to limit the quantity and order of execution, nor are they intended to limit clear differences. In embodiments of this application, terms such as “example” or “for example” may be used to represent an example, evidence, or explanation. None of the embodiments or design solutions described as “examples” or “for example” are described as being preferable or having more advantages than other embodiments or design solutions. Terms such as “examples” or “for example” are used to present the relevant concepts in a particular way to facilitate understanding.

[0085] The technical solutions in the embodiments of this application will be described below with reference to the accompanying drawings of the embodiments of this application.

[0086] To resolve the issue of how a DU forwards a first downlink message to a relay UE and / or remote UE in a remote UE RRC connection re-establishment / restart scenario, this application provides a communication method. In this method, the gNB-DU may apply the SRB1 mapping relationship settings of the remote UE's original UE context, or obtain the SRB1 mapping relationship settings based on the gNB-CU indication, so that the remote UE can correctly access the DU and CU when performing RRC re-establishment / restart using the relay UE.

[0087] The communication method provided in this application may be applied to the communication system shown in Figure 1. For example, this communication system includes network devices (e.g., gNB-DU and gNB-CU), relay devices (e.g., relay UE), and remote devices (e.g., remote UE). The network device includes a distributed unit DU and a central unit CU, where the CU and DU communicate with each other via the F1 interface. The relay devices and remote devices may also be terminal devices. For example, as shown in Figure 1, the relay device communicates with the remote device via the PC5 interface, and the relay device communicates with the network device via the Uu interface. Optionally, in this application, the remote device may also be referred to as the first terminal device, and the relay device may also be referred to as the second terminal device. In possible implementations, the network device is an access network device that provides user access functions, such as a base station. The network devices and terminal devices may perform signal / data transmission. Optionally, the communication method provided in this application is also applicable to scenarios where the remote device communicates with the network device via relays from multiple relay devices. Figure 1 is merely an example and does not limit the solutions of this application.

[0088] The communication systems of this application may include, but are not limited to, communication systems using various radio access technologies (RATs), such as LTE communication systems, 5G (or new radio, NR) communication systems, transition systems between LTE and 5G communication systems, sometimes referred to as 4.5G communication systems, or future communication systems such as 6th generation (6G) or even 7th generation (7G) systems. The network architectures and service scenarios described in the embodiments of this application are for the purpose of further clarifying the technical solutions of the embodiments of this application and do not limit the technical solutions provided in the embodiments of this application. Those skilled in the art will understand that, with advances in communication network architectures and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application may also be applicable to similar technical problems.

[0089] Terminal devices, sometimes called user equipment (UE), mobile station (MS), or mobile terminal (MT), are devices that provide voice and / or data connectivity to the user, such as handheld devices or in-vehicle devices with wireless connectivity. Currently, examples of terminal devices include mobile phones, tablet computers, notebook computers, palmtop computers, mobile internet devices (MIDs), wearable devices, unmanned aerial vehicles, virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving, wireless terminals in remote medical surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, terminal devices for 5G networks, terminal devices for future advanced PLMN networks, or terminal devices for future communication systems.

[0090] A network device is a radio access network (RAN) node (or device) that connects terminal devices to a wireless network, and may be, for example, a base station. For example, RAN nodes include continuously evolving node B (gNB), transmission reception point (TRP), evolved node B (eNB), radio network controller (RNC), node B (NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved node B or home node B, HNB), baseband unit (BBU), wireless fidelity (Wi-Fi) access point (AP), satellites in satellite communication systems, radio controllers in cloud radio access network (CRAN) scenarios, wearable devices, unmanned aerial vehicles, vehicle internet (e.g., vehicle-to-everything (V2X) devices), or communication devices for device-to-device (D2D) communication. Access network devices may include central unit (CU) nodes, distributed units (DUs), or RAN devices containing both CU and DU nodes. In possible configurations, RAN devices containing CU and DU nodes divide the protocol layers of the eNB in ​​a long-term evolution (LTE) system. Some protocol layer functions are centrally controlled by the CU, while some or all of the remaining protocol layer functions are controlled by the DU. The CU centrally controls the DU.

[0091] In possible scenarios, multiple RANs collaborate to help terminals perform wireless access, with different RAN nodes independently performing some of the base station's functions. For example, a RAN node could be a CU, DU, CU control plane (CP), CU user plane (UP), or radio unit (RU). CUs and DUs may be located separately or be included in the same network element, such as a baseband unit (BBU). An RU may be included in a radio frequency device or radio frequency unit, such as a remote radio unit (RRU), active antenna unit (AAU), or remote radio head (RRH).

[0092] In different systems, CU (or CU-CP and CU-UP), DU, or RU may have different names as alternatives, but their meanings will be understood by those skilled in the art. For example, in the ORAN system, CU may be called open-radio CU (O-CU), DU may be called O-DU, CU-CP may be called O-CU-CP, CU-UP may be called O-CU-UP, and RU may be called O-RU. For ease of explanation, CU, CU-CP, CU-UP, DU, and RU are used as illustrative examples in this application. Any one of CU (or CU-CP or CU-UP), DU, and RU in this application may be implemented using a software module, a hardware module, or a combination of a software module and a hardware module.

[0093] The access network device in the embodiment may, alternatively, be an open-radio access network (O-RAN) device, and the O-RAN device may include an O-DU and an O-CU. In the embodiments of this application, the functions of the base station may be performed by a module (e.g., a chip) within the base station, or by a control subsystem that includes the functions of the base station. The control subsystem that includes the functions of the base station as described herein may be a control center in the above application scenarios such as smart grids, industrial control, smart transport, and smart cities. For ease of explanation, the following description will use an example in which the base station is used as a radio access network device.

[0094] I. For ease of understanding, the definitions of the terms used in this application are described in detail below.

[0095] 1. Sidelink communication

[0096] In wireless communication systems, UEs (Environmental Users) may perform data communication via network devices, or they may communicate directly with each other without using network devices as relays. The interface between UEs is called a PC5 interface, similar to the Uu interface between a UE and a base station. The link between UEs is called a sidelink. For example, a typical application scenario for sidelink communication is vehicle-to-everything (V2X) communication. In vehicle-to-everything / vehicle-to-infrastructure communication, each vehicle represents one UE, and data may be transmitted directly between UEs via sidelinks without using a network. In this way, communication delay can be effectively reduced. For example, in the communication system shown in Figure 1, relay devices and remote devices may communicate directly with each other via sidelinks.

[0097] Specifically, sidelinks support broadcast, unicast, and multicast communications. Broadcast communications are similar to broadcast system notifications by base stations. Specifically, a UE transmits broadcast service data externally without encryption, and any other UE within effective reception range can receive that broadcast service data if it is interested in that UE's broadcast service. Unicast communications are similar to data communications performed after an RRC connection is established between a UE and a base station, and the unicast connection must first be established between the two UEs. After the unicast connection is established, the two UEs can perform data communications based on an agreed-upon identifier. The data may or may not be encrypted. Compared to broadcast communications, unicast communications can only be performed between two UEs with an established unicast connection. Multicast communications are communications between all UEs in a communication group, and any UE in the group can receive and transmit multicast service data.

[0098] A single unicast communication on a sidelink corresponds to a source L2 ID (layer-2 identifier) ​​and a destination L2 ID pair. The subheader of the media access control protocol data unit (MACPDU) for each sidelink contains the source L2 ID and destination L2 ID, ensuring that data is transmitted from the transmitter to the correct receiver.

[0099] 2. Radio Bearer (RB)

[0100] A radio bearer is a general term for a series of protocol entities and configurations allocated to a UE by a base station, providing a Layer 2 service used to transmit user data between the UE and the base station. Radio bearers include packet data convergence protocol (PDCP) entities, radio link control (RLC) protocol entities, and MAC protocol entities, as well as a series of resources allocated by the physical layer (PHY). Radio bearers are classified into data radio bearers (DRBs) and signaling radio bearers (SRBs). DRBs are used to carry data, while SRBs are used to carry signaling messages. In sidelink communication scenarios, UEs communicate with each other using sidelink radio bearers (SLRBs), which include sidelink data radio bearers (SL DRBs) and sidelink signaling radio bearers (SL SRBs). In protocol text, radio bearer configurations generally include only the configurations for the PDCP layer and the Service Data Adaptation Protocol (SDAP) layer. Protocol entities below the RLC layer are called RLC bearers, and their corresponding configurations are provided in the RLC bearer configuration. An RLC bearer includes protocol entities and configurations below the RLC layer and is the lower-layer portion of a radio bearer, containing a series of resources such as RLC protocol entities and logical channels. One RLC bearer is associated with one logical channel at the MAC layer. One RLC bearer is associated with one PDCP entity, i.e., one RLC serves one radio bearer RB.

[0101] 3. Relay Technology

[0102] In existing protocol standards, R17 Sidelink UE-Network Relay (SL U2N Relay) is a technique where one UE helps another UE communicate with a base station, and is also called a relay technique. For example, the communication system shown in Figure 1 can be considered a U2N relay communication architecture, where the remote UE communicates with the base station through the cooperation of the relay UE. The remote UE and the relay UE communicate with each other via a sidelink, and the corresponding interface is PC5. The relay UE and the base station are directly connected and communicate with each other via the Uu interface.

[0103] U2N relay technology includes two designs: L2 and Layer 3 (L3). This application primarily relates to the protocol architecture of L2 U2N relay. The protocol architecture of L2 U2N relay is described below. For example, Figure 2 is a diagram of the user plane protocol stack of L2 U2N relay. Data packets from the remote UE are relayed and forwarded below the PDCP layer of the relay UE. In other words, the relay UE maintains only a relay RLC bearer, including the RLC, MAC, and PHY layers. In other words, there are end-to-end SDAP and PDCP layers between the remote UE and the base station, but no end-to-end RLC, MAC, and PHY layers. Optionally, the control plane protocol stack of L2 U2N relay is similar to that in Figure 2, the difference being the presence of end-to-end RLC and PDCP layers between the remote UE and the base station. Details are not repeated in this specification.

[0104] Furthermore, a sidelink relay adaptation protocol layer (SRAP) is added between the RLC and PDCP layers of the protocol stack. The main function of the SRAP layer is to support the multiplexing and demultiplexing of radio bearers, i.e., the multiplexing of different end-to-end radio bearers into a single RLC bearer, and the corresponding demultiplexing process. RLC bearers between remote UEs and relay UEs are called PC5 relay RLC channels / bearers, and RLC bearers between relay UEs and base stations are called Uu relay RLC channels / bearers. Multiplexing allows different radio bearers of one remote UE to be multiplexed into a single PC5 relay RLC channel. Alternatively, in a scenario where one relay UE is connected to multiple remote UEs, different radio bearers of one or more remote UEs can be multiplexed into a single Uu relay RLC channel.

[0105] During downlink transmission, the base station's SRAP layer may multiplex data from multiple radio bearers of one or more remote UEs onto a single Uu relay RLC bearer. On each remote UE's sidelink, data from one or more radio bearers of the remote UE may be mapped onto a single PC5 relay RLC bearer. Similarly, during uplink transmission, the remote UE's SRAP layer may map data from multiple radio bearers of the remote UE onto a single PC5 relay RLC channel. The relay UE's adaptation layer may perform bearer multiplexing by multiplexing data from different radio bearers of one or more remote UEs onto a single Uu relay RLC bearer.

[0106] To distinguish data from different remote UEs, the base station assigns a single remote UE ID, also called a local identifier (local ID), to each remote UE. This local ID is carried during the data packet routing process to identify the remote UE to which the data belongs. Existing protocols specify that the local ID of a remote UE is assigned by the base station where the relay UE is located, and that the assigned local ID may be unique at that base station or unique at the relay UE. In possible implementations, after a remote UE establishes a unicast connection with the relay UE, the relay UE sends an RRC message (e.g., a SidelinkUEInformationNR (SUI) message) to the base station, which carries the L2 ID of the remote UE, used to request the base station to assign a local ID to the remote UE.

[0107] Before data transmission, the base station performs SRAP configuration on the remote UE and relay UE for data routing. SRAP configuration may include mapping relationships between the remote UE's radio bearer ID (RB ID including SRB ID / DRB ID) and the Uu relay RLC channel / PC5 ​​relay RLC channel. Specifically, the base station configures the mapping relationship between the radio bearer (SRB or DRB) and the remote UE's PC5 relay RLC channel, as well as the remote UE's local ID and the mapping relationship between the remote UE's radio bearer and the relay UE's Uu / PC5 relay RLC channel. When transmitting uplink or downlink data, the remote UE or base station adds the remote UE's local ID and RB ID to the SRAP header. Based on this SRAP configuration, the remote UE's data can be correctly relayed and forwarded by the relay UE.

[0108] For example, Figure 3 illustrates the routing process for downlink data from a remote UE. The base station's SRAP layer receives the PDCP PDU of remote UE1 from the PDCP layer, adds the remote UE1's local ID and radio bearer (SRB or DRB) information to the SRAP header, and delivers the PDCP PDU to the Uu relay RLC channel based on the mapping relationship. After receiving the data packet from the Uu relay RLC channel, the relay UE's adaptation layer may deliver the data packet to the correct PC5 relay RLC channel based on the mapping relationship set up by the base station. After receiving the data packet from the PC5 relay RLC channel, the remote UE delivers the data packet to the corresponding PDCP layer for processing based on the bearer ID information in the SRAP header. Optionally, the routing process for uplink data is similar to that for downlink data. Further details are not repeated in this specification.

[0109] 4. CU-DU Isolation Architecture

[0110] For example, Figure 4 is a diagram of a CU-DU separation architecture. This architecture includes a 5G core network and a next-generation radio access network (NG-RAN). The NG-RAN includes a series of gNBs (gNB-CUs and gNB-DUs) connected to the 5G core network. The gNBs are connected to the 5G core network via NG interfaces, and these gNBs are connected to each other via Xn interfaces. Specifically, in the CU-DU separation architecture, one gNB may be divided into one gNB-CU and one or more gNB-DUs. The gNB-CUs and gNB-DUs are connected via F1 interfaces.

[0111] In possible implementations, for example, in a CU-DU separation architecture, the gNB-CU is responsible for the RRC, SDAP, and PDCP protocol layers, while the gNB-DU is responsible for the RLC, MAC, and PHY protocol layers. In another example, in the control plane (CP), the gNB-CU-CP is responsible for the PDCP entities corresponding to RRC and SRB, while in the user plane (UP), the gNB-CU-UP is responsible for the PDCP entities corresponding to SDAP and DRB.

[0112] For example, in a CU-DU isolation architecture, the protocol stack of the CU-DU isolation architecture is shown in Figure 5. This protocol stack, while not limited to these, includes the following design principles.

[0113] (1) SRAP is positioned on the DU side.

[0114] (2) The gNB-CU determines the mapping relationship settings at the SRAP layer.

[0115] (3) The gNB-DU determines the PC5 / Uu relay RLC channel configuration based on the gNB-CU indication.

[0116] (4) The gNB-CU assigns a local ID to the remote UE.

[0117] (5) SRAP layer configuration and PC5 relay RLC channel configuration are performed for the remote UE using the remote UE's F1AP message (this message carries the remote UE's identifier (F1AP ID) on the F1 interface and is used to generate the relevant configuration for the remote UE).

[0118] (6) SRAP layer configuration and PC5 / Uu relay RLC channel configuration are performed for the relay UE using the relay UE's F1AP message (this message carries the identifier of the relay UE on the F1 interface and is used to generate the relevant configuration for the relay UE).

[0119] Please note that the CU-DU isolation architecture and protocol stack shown in Figures 4 and 5 are merely examples. The protocol stack partitioning scheme and naming conventions are not limited in this application.

[0120] 5. In a CU-DU isolation architecture, the procedure for the UE to re-establish the RRC connection is as follows:

[0121] For example, Figures 6A and 6B are schematic flowcharts of the RRC connection re-establishment performed by the UE in a CU-DU isolation architecture. This procedure includes the following steps:

[0122] Step 1: The UE accesses the base station via random access (for example, the UE sends a preamble to the gNB-DU).

[0123] Step 2: The gNB-DU assigns a new cell-radio network temporary identifier (C-RNTI) to the accessed UE and sends a random access response (RAR) message to the UE.

[0124] Step 3: The UE sends an RRC Reestablishment Request message to the gNB-DU, which includes the UE's original C-RNTI and physical cell identifier (PCI).

[0125] Step 4: The gNB-DU sends an INITIAL UL RRC MESSAGE TRANSFER message to the gNB-CU, which includes the RRCReestablishmentRequest message sent by the UE, the lowest layer configuration determined by the gNB-DU, and a new C-RNTI allocated by the gNB-DU.

[0126] Step 5: The gNB-CU generates an RRC reestablishment message and sends it to the gNB-DU using a DL RRC MESSAGE TRANSFER message. If the UE accesses the original gNB-DU (i.e., the gNB-DU accessed when the UE established the RRC connection), the gNB-CU sends the old gNB-DU UE F1AP ID to the gNB-DU (for example, the UEs in Figures 6A and 6B perform RRC reestablishment on the original gNB-DU, i.e., RRC establishment and RRC reestablishment are performed on the same gNB-DU).

[0127] Step 6: The gNB-DU retrieves the UE context information based on the old gNB-DU UE F1AP ID (for example, the UE context information may include settings related to the UE that are maintained by the gNB-DU), and updates the UE's original C-RNTI / PCI to the new C-RNTI / PCI.

[0128] Step 7: The UE sends an RRC connection re-establishment complete message to the gNB-DU.

[0129] Step 8: The gNB-DU transmits the UE's RRC message to the gNB-CU using the UL RRC MESSAGE TRANSFER message.

[0130] Step 9: The gNB-CU triggers the UE context modification procedure, for example, by sending a UE Context Modification Request message to the gNB-DU, which includes radio bearer establishment indication information.

[0131] Step 10: The gNB-DU sends a UE Context Modification Response message to the gNB-CU.

[0132] Steps 9 and 10 are optional. For example, the UE context information may not be modified; i.e., the procedure in Figures 6A and 6B may not include steps 9 and 10. Optionally, the gNB-DU triggers the UE context modification procedure. In this case, the sender and receiver of the message in steps 9 and 10 are swapped (e.g., steps 9' and 10' in Figure 6B). Optionally, if the UE accesses the base station using a new gNB-DU, a further UE context re-establishment must be performed.

[0133] Step 11: The gNB-CU generates an RRCReconfiguration message for the UE and sends the RRCReconfiguration message to the gNB-DU.

[0134] Step 12: The gNB-DU sends an RRCReconfiguration message to the UE.

[0135] Step 13: The UE sends an RRCReconfigurationComplete message to the gNB-DU to indicate that the configuration is complete.

[0136] Step 14: The gNB-DU sends the RRCReconfigurationComplete message to the gNB-CU.

[0137] II. Communication method provided in this application

[0138] Figure 7 is a schematic flowchart of the communication method according to this application. This communication method may be applied to the communication system shown in Figure 1. For example, this communication method may be implemented through interaction between a first network device (e.g., DU) and a second network device (e.g., CU). This communication method includes the following steps:

[0139] S101: The second network device transmits indication information to the first network device, which is used to determine a first mapping relationship between the first bearer and the second bearer. In response, the first network device receives indication information from the second network device.

[0140] S102: The second network device sends a first message to the first network device, where the first message is a first downlink message sent from the second network device to the first terminal device in a first connection re-establishment or restart procedure.

[0141] The first connection is a connection between a first terminal device and a second network device, the first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0142] For example, in the communication system shown in Figure 1, the first terminal device may be a remote UE, the second terminal device may be a relay UE, the first network device is a DU (DU is used in this application as an illustrative example), and the second network device is a CU (CU is used in this application as an illustrative example). For example, the first connection is an RRC connection between the remote UE and the gNB-CU, and correspondingly, the first message is an RRC connection re-establishment message, an RRC connection restart message, or an RRC connection release message. For example, the first bearer is a signaling radio bearer SRB of the remote UE, and is used to transmit RRC connection re-establishment messages, RRC connection restart messages, or RRC connection release messages between the remote UE and the gNB-CU. The second bearer is a Uu relay RLC channel, and is used to transmit RRC connection re-establishment messages, RRC connection restart messages, or RRC connection release messages between the relay UE and the gNB-DU. The first bearer may be multiplexed to the second bearer, that is, the SRB on the remote UE may be multiplexed to the Uu relay RLC channel. The gNB-CU may perform SRAP configuration on the relay UE. The SRAP configuration includes a first mapping relationship between the first bearer and the second bearer, which may be a mapping relationship between the SRB on the remote UE and the Uu relay RLC channel (sometimes called a mapping relationship configuration or mapping configuration). Optionally, the gNB-DU may also need to acquire the first mapping relationship so that the gNB-DU transmits the first message to the relay UE based on the first mapping relationship.

[0143] For example, if indication information sent from a second network device to a first network device is used to determine a first mapping relationship between the first bearer and the second bearer, the first network device may determine the mapping relationship between the SRB of the remote UE used to send the RRC re-establishment message or RRC re-restart message and the Uu relay RLC channel, so that the remote UE can use the relay UE to complete the RRC re-establishment / RRC re-restart procedure, before sending the RRC re-establishment message or RRC re-restart message.

[0144] Specifically, the first message is a first downlink message sent from the second network device to the first terminal device during the first connection re-establishment or restart procedure, and may include, but is not limited to, the following messages:

[0145] (1) The first message is an RRC connection re-establishment message.

[0146] For example, in the RRC connection re-establishment procedure, the gNB-CU generates an RRC connection re-establishment message and transmits this message to the remote UE via the gNB-DU and relay UE. In this scenario, the first message is sometimes referred to as the first downlink SRB1 message in the RRC connection re-establishment procedure. The first mapping relationship is the mapping relationship between SRB1 and the Uu relay RLC channel. In this example, the first downlink message is the downlink SRB1 message sent from the CU to the DU.

[0147] (2) The first message is an RRC connection restart message.

[0148] For example, in the RRC reactivation procedure (which is used by the UE to transition from an inactive state (RRC_INACTIVE) to a connected state), the gNB-CU generates an RRC reactivation message and transmits this message to the remote UE via the gNB-DU and relay UE. In this scenario, the first message is sometimes referred to as the first downlink SRB1 message in the RRC reactivation procedure. The first mapping relationship is the mapping relationship between SRB1 and the Uu relay RLC channel. In this example, the first downlink message is the downlink SRB1 message sent from the CU to the DU.

[0149] (3) The first message is an RRC connection release message.

[0150] For example, in the RRC connection reactivation procedure, if the gNB-CU instructs the first terminal device to resume the disconnected state or enter an idle state (e.g., instructing the UE to release or suspend the RRC connection), the gNB-CU generates an RRC connection release (RRCrelease with suspend or RRCrelease) message. Furthermore, the gNB-DU and the relay UE transmit the RRC connection release message to the remote UE. In this scenario, the first message is sometimes referred to as the first downlink SRB1 message in the RRC connection reactivation procedure. The first mapping relationship is the mapping relationship between SRB1 and the Uu relay RLC channel. In this example, the first downlink message is the downlink SRB1 message sent from the CU to the DU.

[0151] (4) The first message is the RRC setup message.

[0152] For example, in the RRC connection re-establishment or restart procedure, if the gNB-CU cannot find the UE context information of the remote UE (e.g., the gNB-CU makes a decision and is unable to determine the UE context information of the remote UE and instruct the gNB-DU to obtain the UE context of the remote UE), the gNB-CU generates and sends an RRC setup (RRCsetup) message and uses the relay UE to transmit the RRC setup message to the remote UE. In this scenario, the first message may also be called the first downlink SRB0 message in the RRC connection re-establishment or restart procedure. Optionally, the gNB-CU may determine the mapping relationship between SRB0 and the Uu relay RLC channel and send this mapping relationship to the gNB-DU. In this example, the first downlink message is the downlink SRB0 message sent from the CU to the DU.

[0153] (5) The first message is an RRC rejection message.

[0154] For example, in the RRC connection reactivation procedure, if the gNB-CU refuses to reactivate the remote UE's RRC connection, the gNB-CU may send an RRC reject message to the remote UE. In this scenario, the first message is sometimes referred to as the first downlink SRB0 message in the RRC connection reactivation procedure. Optionally, the gNB-CU may determine the mapping relationship between SRB0 and the Uu relay RLC channel and send this mapping relationship to the gNB-DU. In this example, the first downlink message is the downlink SRB0 message sent from the CU to the DU.

[0155] Optionally, in (1), (2), (3), and (5), whether the first mapping relationship in the remote UE's UE context information is used or whether the first mapping relationship is re-determined may be determined based on the status of the relay UE.

[0156] There may be an optional order in which S101 and S102 are performed. For example, S101 is performed before S102. Alternatively, S101 and S102 may be performed simultaneously. For example, the second network device transmits indication information and the first message simultaneously. Alternatively, S102 may be performed before S101. In this case, after receiving the first message, the first network device determines the first mapping relationship after the second network device has transmitted the indication information, and transmits the first message based on the first mapping relationship. The specific implementation is not limited in this application.

[0157] S103: The first network device transmits the first message based on the first mapping relationship.

[0158] For example, the gNB-DU sends RRC connection re-establishment messages, RRC connection restart messages, RRC connection release messages, RRC setup messages, or RRC rejection messages to the relay UE via the corresponding Uu relay RLC channel based on the mapping relationship between the remote UE's SRB and the Uu relay RLC channel.

[0159] It should be understood that the above examples do not limit the solutions of this application.

[0160] In this embodiment, before transmitting the first message, the second network device may transmit indication information to the first network device so that the first network device can determine, based on the indication information, the settings of the first mapping relationship used to transmit the first message and thus transmit the first message correctly. In this way, the first terminal device re-establishes or restarts the first connection via the second terminal device and correctly accesses the base station.

[0161] 3. If the second network device does not update the first mapping relationship, a specific implementation of the communication method provided in this application is as follows:

[0162] Specifically, in this embodiment, the second network device may apply the original SRAP configuration in the context of the UE (i.e., the SRAP configuration used before the first connection re-establishment or restart procedure). The SRAP configuration includes a first mapping relationship between the first bearer and the second bearer.

[0163] For example, Figure 8 is a schematic flowchart of another communication method according to this application. This method includes the following steps:

[0164] S201: The second network device decides to apply the adaptation layer settings before the first connection re-establishment or restart procedure.

[0165] Optionally, the second network device may determine, based on the second message and information corresponding to the second terminal device, that the second terminal device is a relay terminal device associated with the first terminal device prior to the first connection re-establishment or restart procedure. In this case, the second network device decides to apply the adaptation layer settings prior to the first connection re-establishment or restart procedure. For example, the second message is an SRB0 message, which includes an RRC connection re-establishment or restart request message sent by the remote UE. Optionally, the SRB0 message further includes information about the remote UE, e.g., the remote UE's I-RNTI / C-RNTI. Information corresponding to the second terminal device includes, for example, the second identifier of the second terminal device (e.g., the relay UE gNB-DU F1AP ID), the service information of the second terminal device (e.g., the relay UE's historical service information), and the context information of the second terminal device (e.g., the relay UE's UE context information). For example, gNB-DU sends the SRB0 message and the relay UE gNB-DU F1AP ID to gNB-CU using the F1AP message. Based on the relay UE gNB-DU F1AP ID and the remote UE's I-RNTI / C-RNTI in the SRB0 message, the original SRAP settings may be applied if the remote UE uses the original relay UE to re-establish or restart the RRC connection. The original relay UE is the relay terminal device that provided relay services to the remote UE before the RRC connection re-establishment or restart procedure.

[0166] S202: The second network device transmits first indication information to the first network device, where the first indication information indicates a first identifier of the first terminal device, which is used by the first network device to associate the first terminal device on the F1 interface between the first network device and the second network device.

[0167] For example, the first identifier of the first terminal device is the old gNB-DU UE F1AP ID of the remote UE (i.e., the F1AP ID assigned to the remote UE by the original gNB-DU before the remote UE's RRC connection re-establishment or restart procedure), and this old gNB-DU UE F1AP ID is used in the RRC connection re-establishment or restart procedure to instruct the original gNB-DU to look up the remote UE's UE context information. The UE context information includes the original SRAP configuration, which includes a first mapping relationship between the first bearer and the second bearer. For example, the first mapping relationship includes a mapping relationship between the remote UE's SRB1 (used to carry RRC connection re-establishment messages, RRC connection restart messages, or RRC connection release messages) and the Uu relay RLC channel. In another example, the first mapping relationship includes a mapping relationship between the remote UE's SRB0 (used to carry RRC setup messages or RRC reject messages) and the Uu relay RLC channel.

[0168] S203: The first network device obtains context information for the first terminal device based on the first identifier.

[0169] For example, gNB-DU looks up UE context information for the remote UE based on the remote UE's old gNB-DU UE F1AP ID, where UE context information includes the originally configured mapping relationships between the remote UE's radio bearer and the Uu relay RLC channel.

[0170] S204: The first network device determines the first mapping relationship based on the context information of the first terminal device.

[0171] In possible implementations, S204 specifically includes the following steps:

[0172] The first network device determines a first mapping relationship based on the second indication information and the context information of the first terminal device, where the second indication information instructs the first network device to apply the first mapping relationship.

[0173] For example, the gNB-CU may instruct the gNB-DU to apply the originally configured first mapping relationship based on second indication information. In this case, the gNB-DU may decide to apply the originally configured mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel included in the UE context information, based on the UE context information found for the remote UE.

[0174] Optionally, when the gNB-DU searches for a UE context and actively releases the mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel by default, the gNB-CU may instruct the gNB-DU to retain the originally configured mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel. In this case, the gNB-DU may decide to apply the originally configured mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel based on the UE context information found for the remote UE.

[0175] If the gNB-CU optionally instructs the gNB-DU not to release the originally configured SRAP configuration (for example, by sending additional 1-bit indication information to instruct it not to release the SRAP configuration), the gNB-DU may decide to apply the originally configured mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel based on the discovered UE context information of the remote UE.

[0176] In another possible implementation, S204 specifically includes the following steps:

[0177] The first network device determines a first mapping relationship based on the first identifier of the first terminal device, the context information of the first terminal device, and the information corresponding to the second terminal device.

[0178] For example, gNB-DU may determine that the remote UE is performing access from the original relay UE based on the remote UE's old gNB-DU UE F1AP ID and information corresponding to the relay UE (e.g., a second identifier for the second terminal device (e.g., relay UE F1AP ID), service information for the second terminal device (e.g., relay UE history service information), and context information for the second terminal device (e.g., relay UE UE UE context information)). Therefore, the first mapping relationship set up in the UE context of the first terminal device may be applied. Based on the UE context information found for the remote UE, gNB-DU determines that the first mapping relationship is the originally set up mapping relationship between the remote UE's radio bearer and the Uu relay RLC channel.

[0179] Optionally, if gNB-DU discovers that gNB-CU has not established a mapping relationship and that a mapping relationship is unavailable in the remote UE's UE context, gNB-DU may, for example, decide that the remote UE will perform access through a new relay UE, and gNB-DU may further request gNB-CU to provide a first mapping relationship.

[0180] Optionally, the first network device may decide to release a second mapping relationship based on the first identifier of the first terminal device and the information corresponding to the second terminal device. The second mapping relationship is included in the context information of the first terminal device, and the first mapping relationship is distinct from the second mapping relationship. For example, it is assumed that, prior to the RRC connection re-establishment or restart procedure, the context information of the first terminal device includes mapping relationships between the remote UE's radio bearers and Uu relay RLC channels (e.g., mapping relationships between SRB0 / SRB1 / SRB2 and Uu relay RLC channels). The first mapping relationship includes the mapping relationship between SRB1 and the Uu relay RLC channels, and the second mapping relationship includes the mapping relationship between SRB0 / SRB2 and the Uu relay RLC channels. Based on the information corresponding to the remote UE's old gNB-DU UE F1AP ID and relay UE, the gNB-DU may decide that the remote UE should perform access from the original relay UE and may release the mapping relationship between SRB0 / SRB2 and the Uu relay RLC channel.

[0181] Optionally, the first network device receives third indication information from the second network device, where the third indication information instructs the first network device to release the second mapping relationship. For example, the gNB-CU may further send 1-bit indication information to the gNB-DU instructing it to release the mapping relationship between SRB0 / SRB2 and the Uu relay RLC channel.

[0182] S205: The second network device sends a first message to the first network device, where the first message is a first downlink message sent from the second network device to the first terminal device in a first connection re-establishment or restart procedure. For example, the first message is an RRC connection re-establishment message, an RRC connection restart message, an RRC connection release message, or an RRC rejection message. For a specific description of the first message and the specific implementation of S205, see the first message in S102 (including the descriptions of (1), (2), (3), and (5) of the first downlink message) and the procedure by which the second network device sends the first message to the first network device. Details are not repeated in this specification.

[0183] S206: The first network device transmits the first message based on the first mapping relationship.

[0184] For specific implementation details of S206, please refer to the corresponding explanation in S103. Further details will not be repeated in this specification.

[0185] There may be an optional order in which S202 and S205 are performed. For example, S202 is performed before S205. Alternatively, S202 and S205 may be performed simultaneously. For example, the second network device transmits indication information and the first message simultaneously. Alternatively, S205 may be performed before S202. In this case, after receiving the first message, the first network device determines the first mapping relationship after the second network device has transmitted the indication information, and transmits the first message based on the first mapping relationship. The specific implementation is not limited in this application.

[0186] In this embodiment, when the first terminal device re-establishes or resumes the first connection via the second terminal device, if the second network device does not update the first mapping relationship and the first network device has an available first mapping relationship, the second network device may instruct the first network device to forward the first message using the first mapping relationship in the original UE context information. In this way, the first terminal device re-establishes or resumes the first connection via the second terminal device and correctly accesses the base station. Optionally, when the first message is an RRC setup message or an RRC rejection message, the first network device can correctly send the first downlink SRB message.

[0187] 4. When a second network device updates the first mapping relationship, the specific implementation of the communication method provided in this application is as follows:

[0188] Specifically, in this embodiment, the second network device may update the SRAP configuration. The SRAP configuration includes a first mapping relationship between the first bearer and the second bearer. In other words, the second network device updates the first mapping relationship.

[0189] For example, Figure 9 is a schematic flowchart of another communication method according to this application. This method includes the following steps:

[0190] S301: The second network device decides to update the first mapping relationship.

[0191] In possible implementations, when a remote UE re-establishes or resumes RRC connectivity via the original relay UE, the second network device may update the first mapping relationship using the originally configured first mapping relationship (e.g., S201), or it may not update the first mapping relationship using the originally configured first mapping relationship. For example, the second network device re-determines the mapping relationship between the remote UE's SRB1 and the Uu relay RLC channel.

[0192] In another possible implementation, when a remote UE re-establishes or restarts the RRC connection via a new relay UE, the second network device decides to update the first mapping relationship. Optionally, the second network device decides to update the first mapping relationship based on the first identifier of the first terminal device, the context information of the first terminal device, and the information corresponding to the second terminal device. The relay terminal device associated with the second terminal device is different from the relay terminal device associated with the first terminal device before the first connection re-establishment or restart procedure. In other words, the relay UE is a new relay UE.

[0193] For example, the second message is an SRB0 message, which contains an RRC connection re-establishment or restart request message sent by the remote UE. Optionally, the SRB0 may further include information about the remote UE, such as the remote UE's I-RNTI / C-RNTI. For example, information corresponding to the second terminal device may include a new relay UE F1AP ID, which may be carried in an INITIAL UL RRC message. For example, gNB-DU sends the SRB0 message and the new relay UE F1AP ID to gNB-DU using an INITIAL UL RRC message.

[0194] In this case, the gNB-CU may re-determine the mapping relationship between the remote UE's SRB1 and the new Uu relay RLC channel (based on the new relay UE).

[0195] Optionally, when a remote UE re-establishes or restarts an RRC connection via a new relay UE, the new relay UE may be connected to a new first network device. In this case, the second network device may further reconfigure the first mapping relationships for the first network device. For example, the second network device sends the first network device a mapping relationship between the remote UE's SRB1 and a new Uu relay RLC channel (based on the new relay UE).

[0196] S302: The second network device transmits indication information to the first network device, where the indication information includes a first mapping relationship.

[0197] It can be understood that the first mapping relationship is an updated first mapping relationship. For example, the gNB-CU may directly transmit the mapping relationship between the remote UE's SRB1 and the new Uu relay RLC channel to the gNB-DU.

[0198] Optionally, the first network device may decide to release the second mapping relationship based on the first identifier of the first terminal device and the information corresponding to the second terminal device. For example, if the gNB-DU decides that a remote UE re-establishes or resumes the RRC connection via a new relay UE, the gNB-DU decides to release the mapping relationship between SRB0 / SRB2 in the context information of the first terminal device and the original Uu relay RLC channel. Optionally, the first network device may receive third indication information from the second network device, which instructs the first network device to release the second mapping relationship. For example, the gNB-CU may further send 1-bit indication information to the gNB-DU instructing it to release the mapping relationship between SRB0 / SRB2 in the context information of the first terminal device and the original Uu relay RLC channel.

[0199] S303: The second network device sends a first message to the first network device, where the first message is a first downlink message sent from the second network device to the first terminal device in a first connection re-establishment or restart procedure. For example, the first message is an RRC connection re-establishment message, an RRC connection restart message, an RRC connection release message, an RRC setup message, or an RRC rejection message. For a specific description of the first message and the specific implementation of S303, see the description of the first message in S102 (including the description of (1) to (5) of the first downlink message) and the description of the procedure by which the second network device sends the first message to the first network device. Details are not repeated in this specification.

[0200] S304: The first network device transmits the first message based on the first mapping relationship.

[0201] For specific implementation details of S304, please refer to the corresponding explanation in S103. Further details will not be repeated in this specification.

[0202] There may be an optional order in which S302 and S303 are performed. For example, S302 may be performed before S303. Alternatively, S302 and S303 may be performed simultaneously. For example, the second network device transmits the indication information and the first message simultaneously. Alternatively, S303 may be performed before S302. In this case, after receiving the first message, the first network device determines the first mapping relationship after the second network device has transmitted the indication information, and transmits the first message based on the first mapping relationship. This is not limited to the present application.

[0203] In this embodiment, when the second network device updates the first mapping relationship, the second network device may directly transmit the updated first mapping relationship to the first network device so that the first network device transmits the first message based on the updated first mapping relationship. In this way, the first terminal device re-establishes or resumes the first connection via the second terminal device and correctly accesses the base station.

[0204] The following provides a detailed explanation of how the communication methods described in sections 2 through 4 apply to the RRC connection re-establishment procedure in a CU-DU isolation architecture.

[0205] 5. Regardless of whether the second network device updates the first mapping relationship or not, it is assumed that the originally configured SRAP settings are not released. A specific implementation of the communication method provided in this application is as follows:

[0206] Figures 10A to 10C are schematic flowcharts of yet another communication method according to the present application. This procedure includes the work of a first terminal device (remote UE) re-establishing an RRC connection via a second terminal device (relay UE), and a base station (including gNB-CU and gNB-DU) setting up SL relay for the remote UE in a CU-DU separation architecture.

[0207] Step 1: The remote UE uses a discovery procedure on the sidelink to search for a suitable relay UE and establishes a unicast connection with the selected relay UE.

[0208] Step 2: The remote UE sends an RRC connection re-establishment request message to the relay UE via the PC5 relay RLC channel corresponding to the SRB (e.g., SRB0), requesting the relay UE to forward the RRC connection re-establishment request message to the first network device.

[0209] Step 3: The relay UE sends an SUI message to the base station, where the SUI message carries the source L2 ID identifier of the remote UE.

[0210] Step 4: The gNB-DU sends an uplink RRC information transfer message (UL RRC MESSAGE TRANSFER message) carrying the SUI message to the gNB-CU. After receiving this message, the gNB-CU assigns a local ID to the remote UE and configures the relay UE to provide relaying to the remote UE.

[0211] Step 5 / 6: Perform the UE Context Modification procedure on the relay UE to generate the relay configuration on the relay UE side. Specifically, the gNB-CU sends a UE Context Modification Request message to the gNB-DU requesting the establishment of a Uu relay RLC channel. The Uu relay RLC channel is used to carry SRB0 messages from the remote UE (optionally, it may also include a Uu relay RLC channel used to carry SRB1 messages). The gNB-DU sends a UE Context Modification Response message to the gNB-CU to provide the required Uu relay RLC channel configuration to the gNB-CU.

[0212] Step 7 / 8: The gNB-CU generates the RRC configuration (RRCReconfiguration) for the relay UE and sends this RRC configuration to the relay UE via the gNB-DU. For example, the gNB-CU sends a Downlink RRC Transfer Message (DL RRC MESSAGE TRANSFER) to the gNB-DU, which carries the RRC configuration for the relay UE. The gNB-DU then sends the RRC configuration for the relay UE to the relay UE.

[0213] Step 9 / 10: The relay UE feeds back RRC configuration completion to the gNB-CU. For example, the relay UE sends an RRC Reconfiguration Complete message to the gNB-DU, and the gNB-DU sends an Uplink RRC Transfer Message (UL RRC MESSAGE TRANSFER) to the gNB-CU, which carries the RRC Reconfiguration Complete message.

[0214] Step 11: The relay UE sends an RRC connection re-establishment request message for the remote UE to the gNB-DU based on the base station configuration (including the remote UE's local ID, the Uu relay RLC channel configuration, and the mapping relationship between SRB0 and the Uu relay RLC channel).

[0215] Step 12: The gNB-DU adds a remote UE's RRC connection re-establishment request message to the initial uplink RRC transfer message (INITIAL UL RRC MESSAGE TRANSFER message) and sends this message to the gNB-CU. Furthermore, this message further includes the relay UE F1AP ID and the remote UE's local ID, indicating to the gNB-CU that the remote UE is associated with the relay UE. In Step 4, this local ID is assigned by the gNB-CU. This message may further include the PC5 relay RLC channel configuration corresponding to the remote UE's SRB1 message.

[0216] Steps 1 through 12 include, but are not limited to, the following cases:

[0217] Case 1: The remote UE accesses the original gNB-DU via the original relay UE and performs RRC connection re-establishment.

[0218] In Case 1, when the remote UE requests to re-establish the RRC connection via the original relay UE, the remote UE may not release the previously established sidelink connection with the original relay UE. Therefore, step 1 may not be performed in Case 1. Furthermore, the remote UE performs the re-establishment via the original relay UE. Thus, the remote UE's relay forwarding settings are configured on the original relay UE side. Therefore, when the original relay UE receives an RRC connection re-establishment request message from the remote UE, it forwards the RRC connection re-establishment request message directly based on the original SRB0 mapping relationship settings (including the mapping relationship between SRB0 and the Uu relay RLC channel) (steps 3 through 10 can be skipped, and step 11 is performed directly). In other words, in step 11, the relay UE sends the remote UE's RRC connection re-establishment request message to the original gNB-DU based on the original mapping relationship between SRB0 and the Uu relay RLC channel.

[0219] In step 12, the original gNB-DU includes SRB0 in the INITIAL UL RRC MESSAGE TRANSFER message and forwards this message to the gNB-CU. Furthermore, this message further includes the original relay UE F1AP ID and the remote UE's local ID. The remote UE's local ID is the local ID that is added to the adaptation layer header when the relay UE forwards the SRB0 message. Based on step 12, the gNB-CU decides that the remote UE will re-establish the RRC connection through the original relay UE (similar to S201).

[0220] Case 2: The remote UE accesses the original gNB-DU via a new relay UE and performs RRC connection re-establishment.

[0221] In Case 2, when a remote UE accesses the original gNB-DU via a new relay UE, the Uu relay RLC channel between the new relay UE and the original gNB-DU (considered a new Uu relay RLC channel) is used to carry the remote UE's data over the Uu. Therefore, the mapping relationship between the relay UE and the gNB-DU needs to be reconfigured. In other words, steps 1 through 12 must be performed sequentially in Case 2. For example, in steps 5 / 6, a new relay configuration must be generated on the relay UE side (including generating the mapping relationship between SRB0 / SRB1 and the new Uu relay RLC channel). In steps 7 / 8, a new RRC configuration must be generated on the relay UE side, and so on. For specific implementations, please refer to the protocol standard description. Details will not be repeated in this specification.

[0222] In step 12, the gNB-DU adds the remote UE's RRC connection re-establishment request message, the new relay UE's gNB-DU UE F1AP ID, and the remote UE's local ID to the INITIAL UL RRC MESSAGE TRANSFER message. Based on the information carried in the RRC message sent from the remote UE and the relay UE's F1AP ID information, the gNB-CU determines that the remote UE will perform RRC re-establishment via the new relay UE and that the SRAP mapping relationship settings need to be updated (similar to S301).

[0223] Case 3: The remote UE accesses a new gNB-DU via a new relay UE and performs RRC connection re-establishment.

[0224] In Case 3, when a remote UE accesses a new gNB-DU via a new relay UE, the new gNB-DU cannot directly obtain the remote UE's UE context. Therefore, the gNB-CU needs to re-determine the SRAP mapping relationship settings on both the relay UE and gNB-DU sides.

[0225] For example, in step 12, the gNB-CU determines, based on the remote UE information carried in the RRC re-establishment request message and the new relay UE F1AP ID indicated by the gNB-DU, that the remote UE will perform RRC re-establishment via the new gNB-DU (similar to the explanation of optional selection in S301).

[0226] Step 13: The gNB-CU configures the relay UE to forward the PC5 relay RLC channel and the Uu relay RLC channel to relay SRB1 messages from the remote UE, and sets up the mapping relationship between SRB1 and the PC5 / Uu relay RLC channels. Furthermore, the gNB-CU sends the above configuration to the relay UE via the gNB-DU to transmit SRB1 messages (including, for example, RRC connection re-establishment messages and RRC connection re-establishment complete messages).

[0227] Step 14 / 15: The gNB-CU generates an RRC connection reestablishment message for the remote UE and transmits the RRC connection reestablishment message to the remote UE via the gNB-DU and the relay UE. For example, the gNB-CU sends a downlink RRC forwarding message (DL RRC MESSAGE TRANSFER) to the gNB-DU, and the gNB-DU transmits an RRC connection reestablishment message (RRCReestablishment) to the remote UE via the relay UE.

[0228] Steps 13 through 15 also show different implementations for Cases 1 through 3, including the following:

[0229] Regarding Case 1:

[0230] In step 13, since both the relay UE and the gNB-DU are the original devices, the gNB-CU does not need to reconfigure the mapping relationship between SRB1 and the PC5 / Uu relay RLC channel on the relay UE side. For example, in step 14, the gNB-CU generates an RRC connection re-establishment message for the remote UE, appends the RRC connection re-establishment message to the DL RRC MESSAGE TRANSFER message, and sends the DL RRC MESSAGE TRANSFER message to the gNB-DU. Optionally, if the procedure is an RRC connection reactivation procedure, in step 14, the gNB-CU generates an RRC connection reactivation message or an RRC connection release message for the remote UE, appends the RRC connection reactivation message or RRC connection release message to the DL RRC MESSAGE TRANSFER message, and sends the DL RRC MESSAGE TRANSFER message to the gNB-DU. Optionally, in the RRC connection re-establishment or restart procedure, the gNB-CU generates and transmits a first downlink SRB0 message in step 14, which may be an RRC rejection message. For a specific description of the above message, see the description of the first message in S102 (including the descriptions of (1), (2), (3), and (5) of the first downlink message). Details are not repeated in this specification.

[0231] Optionally, the gNB-CU may send further indication information to the gNB-DU to indicate the old gNB-DU UE F1AP ID of the remote UE. The old gNB-DU UE F1AP ID of the remote UE is used by the gNB-DU to find the UE context of the remote UE. The UE context includes the previously configured SRAP mapping relationship settings (similar to S202 through S205).

[0232] In possible implementations, the gNB-CU decides to apply the original settings. Therefore, the gNB-CU does not need to update the SRB1 mapping relationship (the mapping relationship between SRB1 and the Uu relay RLC channel) on the gNB-DU side. Correspondingly, the original SRB1 mapping relationship is also used on the relay UE side.

[0233] Optionally, in step 13, the gNB-CU updates only the PC5 relay RLC channel settings. Optionally, step 13 is not performed.

[0234] Optionally, in step 14, the gNB-CU does not send an SRAP mapping relationship configuration update indication to the gNB-DU.

[0235] Optionally, in step 14, the gNB-CU may send indication information to the gNB-DU, and the gNB-DU may apply the SRB1 mapping relationship settings in the UE context information based on this indication information (similar to the possible implementations described in S204).

[0236] Optionally, in step 14, the gNB-DU may decide that the remote UE will perform access from the original relay UE based on the old gNB-DU UE F1AP ID and associated relay UE. Therefore, the SRB1 mapping relationship setting in the UE context information may be applied (similar to another possible implementation described in S204).

[0237] Optionally, in step 14, in this embodiment, after the gNB-DU has looked up the UE context information of the remote UE based on the old gNB-DU UE F1AP ID indicated by the gNB-CU, it is assumed that the SRAP settings in the UE context information are not released by default, and the gNB-CU may instruct the gNB-DU to retain the SRB1 mapping relationship settings or indicate settings that can be retained (for example, instructing it to retain the SRB0 mapping relationship settings).

[0238] Optionally, in step 15, the gNB-DU sends an RRC connection re-establishment message from the remote UE to the relay UE based on the SRB1 mapping relationship setting in the UE context information.

[0239] In another possible implementation, the gNB-CU decides to update the SRB1 mapping relationship (the mapping relationship between SRB1 and the Uu relay RLC channel). Therefore, in step 13, the gNB-CU determines the new mapping relationship between SRB1 and the Uu relay RLC channel and updates the mapping relationship of SRB1 on the relay UE side.

[0240] Optionally, in step 14, the gNB-CU sends indication information to the gNB-DU instructing it to update the SRAP mapping relationship settings. This indication information includes the new mapping relationship between SRB1 and the Uu relay RLC channel (similar to S301 and S302).

[0241] Optionally, in step 15, the gNB-DU transmits an RRC connection re-establishment message to the remote UE via the relay UE based on the new mapping relationship between SRB1 and the Uu relay RLC channel indicated by the gNB-CU.

[0242] Regarding Case 2:

[0243] In step 13, the gNB-CU updates the SRB1 mapping relationship settings on the relay UE side, including updating the mapping relationships between SRB1 and the Uu relay RLC channel and between SRB1 and the PC5 relay RLC channel.

[0244] In step 14, the gNB-CU sends indication information to the gNB-DU, which includes a new mapping relationship between the SRB1 and the Uu relay RLC channel. Optionally, the gNB-CU sends the old gNB-DU UE F1AP ID of the remote UE to the gNB-DU so that the gNB-DU can explore the UE context.

[0245] Optionally, in this embodiment, it is assumed that after the gNB-DU looks up UE context information based on the old gNB-DU UE F1AP ID indicated by the gNB-CU, and after the UE context information of the remote UE, the SRAP settings in the UE context information are not released by default. When the mapping relationships between SRB1 and the Uu relay RLC channel, and between SRB1 and the PC5 relay RLC channel are updated, the gNB-CU may further instruct the gNB-DU to release all SRAP mapping relationship settings obtained by looking up the UE context (e.g., including the original mapping relationship between SRB1 / SRB0 and the Uu relay RLC channel) and apply the newly set SRB1 mapping relationship settings. Alternatively, the gNB-DU may decide that the remote UE will access the base station via the new relay UE based on the old gNB-DU UE F1AP ID indicated by the gNB-CU and the relay UE associated with the UE, and autonomously release the SRAP mapping relationship settings obtained by looking up the UE context information.

[0246] For example, in step 15, the gNB-DU transmits an RRC connection re-establishment message to the remote UE via the relay UE based on the new mapping relationship between SRB1 and the Uu relay RLC channel. Optionally, if an RRC connection restart procedure is performed, in step 15, the gNB-DU transmits an RRC connection restart message or an RRC connection release message to the remote UE via the relay UE based on the new mapping relationship between SRB1 and the Uu relay RLC channel. Optionally, in an RRC connection re-establishment or restart procedure, the gNB-DU transmits a first downlink SRB0 message in step 15, which may also be an RRC rejection message. For a specific description of the above messages, see the description of the first message in S102 (including the descriptions of (1), (2), (3), and (5) of the first downlink message). Details are not repeated in this specification.

[0247] Regarding Case 3:

[0248] In step 13, the gNB-CU determines the new SRB1 mapping relationship settings (including the new mapping relationship between SRB1 and the Uu relay RLC channel) and updates the SRB1 mapping relationship on the relay UE side.

[0249] In step 14, the gNB-CU sends the new mapping relationship between SRB1 and the Uu relay RLC channel to the gNB-DU.

[0250] Optionally, if the gNB-CU decides, based on the message received in step 12, that the remote UE will re-establish the RRC connection via a new gNB-DU, the gNB-CU must determine and transport a new mapping relationship between the SRB0 and the Uu relay RLC channel in step 14.

[0251] For example, in step 15, the gNB-DU transmits an RRC connection re-establishment message to the remote UE via the relay UE based on the new mapping relationship between SRB1 and the Uu relay RLC channel. Optionally, if an RRC connection restart procedure is performed, in step 15, the gNB-DU transmits an RRC connection restart message or an RRC connection release message to the remote UE via the relay UE based on the new mapping relationship between SRB1 and the Uu relay RLC channel. Optionally, in an RRC connection re-establishment or restart procedure, the gNB-DU transmits a first downlink SRB0 message in step 15, which may be an RRC rejection message. For a specific description of the above messages, see the description of the first message in S102 (including the descriptions of (1), (2), (3), and (5) of the first downlink message). Details are not repeated in this specification.

[0252] Step 16 / 17: The remote UE transmits an RRC re-establishment complete message to the gNB-CU via the relay UE and gNB-DU. For example, the remote UE transmits the RRCReestablishmentComplete message to the gNB-DU via the relay UE. The gNB-DU sends an uplink RRC transfer message (UL RRC MESSAGE TRANSFER) to the gNB-CU, which carries the RRCReestablishmentComplete message.

[0253] Step 18 / 19: The gNB-CU may trigger a UE context change in a remote UE. For example, the gNB-CU may send a UE Context Modification Request message to the gNB-DU, and the gNB-DU may send a UE Context Modification Response message to the gNB-CU.

[0254] Steps 18 and 19 also show different implementations for Cases 1 through 3, including the following:

[0255] Regarding Case 1:

[0256] Optionally, the gNB-CU may update SRAP mapping relationship settings other than the SRB1 mapping relationship settings (for example, the mapping relationship between SRB2 / DRB and the Uu relay RLC channel). Specifically, this update may be performed in the UE context update procedure in steps 18 and 19. Optionally, the gNB-CU may not update SRAP mapping relationship settings other than the SRB1 mapping relationship settings, and may not perform steps 18 and 19.

[0257] Regarding Case 2:

[0258] Steps 18 and 19 are mandatory because the originally configured SRAP mapping relationship settings need to be updated, and are used to update at least the SRAP mapping relationship settings on the gNB-DU side.

[0259] Regarding Case 3:

[0260] The gNB-CU triggers the UE CONTEXT SETUP procedure, specifically step 18, which is the UE CONTEXT SETUP REQUEST procedure, instructing the gNB-DU to establish a new SRB / DRB mapping relationship for the remote UE. Step 19 is the UE CONTEXT SETUP RESPONSE procedure, used by the gNB-DU to provide lower-layer configuration at the command of the gNB-CU. For specific implementations, please refer to the corresponding description in the protocol standard. Details are not repeated here.

[0261] Step 20 / 21: The gNB-CU generates an RRC reconfiguration message for the remote UE and sends this message to the remote UE. For example, the gNB-CU sends a downlink RRC transfer message (DL RRC MESSAGE TRANSFER) to the gNB-DU, which carries the RRC Reconfiguration. The gNB-DU then transmits the RRC reconfiguration message to the remote UE via the relay UE.

[0262] Step 22 / 23: The remote UE sends an RRC Reconfiguration Complete message. For example, the remote UE transmits the RRC Reconfiguration Complete message to the gNB-DU via the relay UE. The gNB-DU sends an uplink RRC transfer message (UL RRC MESSAGE TRANSFER) to the gNB-CU, which carries the RRC Reconfiguration Complete message.

[0263] Step 24: The base station updates the relay settings on the relay UE side and configures the Uu / PC5 relay RLC channel used to carry the DRB and SRB and SRAP mapping relationships of the remote UE. For specific implementations, please refer to the corresponding description in the protocol standard. Details are not repeated in this specification.

[0264] Optionally, in the CU-DU isolation architecture, the procedure for the first terminal device to re-establish the RRC connection via the second terminal device is the same. For details, please refer to the procedure shown in Figures 10A to 10C. The difference is that the RRC connection re-establishment request message in step 2 / 11, the RRC connection re-establishment message in step 15, and the re-establishment completion message in step 16 are the RRC connection resumption request message (RRCResumeRequest), the RRC connection resumption message (RRCResume), and the RRC connection resumption completion message (RRCResumeComplete).

[0265] Optionally, in this embodiment, it is assumed that the gNB-CU cannot discover the UE context information of the remote UE. In steps 13 to 15, the gNB-CU generates and sends an RRC setup message, which is transmitted to the remote UE via the relay UE. Optionally, the gNB-CU needs to determine the mapping relationship between SRB0 and the Uu relay RLC channel and transmit this mapping relationship to the gNB-DU.

[0266] 6. Regardless of whether the second network device updates the first mapping relationship, it is assumed that the originally configured SRAP configuration is released. A specific implementation of the communication method provided in this application is as follows:

[0267] The overall procedure of this embodiment is the same as that shown in Figures 10A to 10C. The differences between this embodiment and the fifth partial embodiment will be described in detail below.

[0268] Steps 1 through 24 are the same as steps 1 through 24 in Figures 10A through 10C. The difference is that when gNB-DU searches for UE context information of a remote UE, the originally configured SRAP mapping relationship settings are not enabled by default; they are unavailable or need to be released. In other words, in steps 13 through 15, cases 1 through 3 are different implementations, including the following:

[0269] Regarding Case 1:

[0270] In possible implementations, gNB-CU decides to apply the original settings. However, if the originally configured SRAP mapping relationship settings are released, the processing methods of gNB-CU and gNB-DU are not limited to, but include several of the following methods:

[0271] Method 1: The gNB-CU explicitly instructs the gNB-DU to apply the mapping relationship between SRB1 and the Uu relay RLC channel in the original UE context information. For example, the gNB-CU sends a second indication information to the gNB-DU (for example, the second indication information is 1-bit indication information, which is similar to S204). However, the gNB-DU releases any SRAP mapping relationship settings other than the SRB1 mapping relationship. The gNB-DU may use the mapping relationship between SRB1 and the Uu relay RLC channel in the original UE context information to transmit an RRC connection re-establishment message, an RRC connection restart message, or an RRC connection release message.

[0272] Method 2: The gNB-CU does not send an explicit indication to the gNB-DU, but the gNB-DU decides to apply the mapping relationship between SRB1 and the Uu relay RLC channel in the original UE context information based on the remote UE's access status. For example, the gNB-DU decides, based on the old gNB-DU UE F1AP ID and the relay UE associated with the remote UE indicated by the gNB-CU in step 14, that the remote UE will perform access via the original relay UE and therefore decides not to release the SRB1 mapping relationship. However, the gNB-DU will release any other SRAP mapping relationship settings besides the SRB1 mapping relationship. The gNB-DU may use the mapping relationship between SRB1 and the Uu relay RLC channel in the original UE context information to transmit an RRC connection re-establishment message, an RRC connection restart message, or an RRC connection release message.

[0273] Method 3: Since the gNB-DU has released all original settings, the gNB-CU may directly send the mapping relationship between SRB1 and Uu relay RLC channel in the original UE context information to the gNB-DU. The gNB-DU may use the mapping relationship between SRB1 and Uu relay RLC channel in the original UE context information to transmit RRC connection re-establishment messages, RRC connection restart messages, or RRC connection release messages.

[0274] In another possible implementation, the gNB-CU decides to update the SRB1 mapping relationship (the mapping relationship between SRB1 and the Uu relay RLC channel). For example, in step 14, the gNB-CU directly sends the new mapping relationship between SRB1 and the Uu relay RLC channel to the gNB-DU. The gNB-DU may use the new mapping relationship between SRB1 and the Uu relay RLC channel to transmit an RRC connection re-establishment message, an RRC connection reopening message, or an RRC connection release message.

[0275] Optionally, the gNB-CU decides to transmit a mapping relationship between SRB0 or ​​SRB1 and the Uu relay RLC channel based on whether the first message sent to the gNB-DU is specifically an RRC connection re-establishment message, an RRC connection restart message, an RRC connection release message, an RRC setup message, or an RRC reject message. For example, if the gNB-CU generates an RRC connection re-establishment message, an RRC connection restart message, or an RRC connection release message for a remote UE, the gNB-CU transmits that RRC connection re-establishment message, an RRC connection restart message, or an RRC connection release message to the gNB-DU. In addition, the mapping relationship between SRB1 and the Uu relay RLC channel is transmitted to the gNB-DU. Optionally, in an RRC connection re-establishment or restart procedure, the gNB-CU generates and transmits a first downlink SRB0 message, which may be an RRC reject message. In this case, the gNB-CU sends an RRC setup message or an RRC rejection message to the gNB-DU and transmits the mapping relationship between SRB0 and the Uu relay RLC channel.

[0276] Regarding Cases 2 and 3:

[0277] When a remote UE accesses the original gNB-DU via a new relay UE, or accesses a new gNB-DU via a new relay UE, the mapping relationships on the gNB-DU side need to be reconfigured. Therefore, even if the originally configured SRAP mapping relationship settings are released, the reconfiguration of the mapping relationships is not affected. In this case, please refer to the corresponding explanation in Part 5 for specific implementations in Case 2 or Case 3. Details will not be repeated in this specification.

[0278] To implement the functions in the method provided in this application, the apparatus or device provided in this application may include hardware structures and / or software modules, and the above functions may be implemented in the form of hardware structures, software modules, or a combination of hardware structures and software modules. Whether the above functions are performed using hardware structures, software modules, or a combination of hardware structures and software modules depends on the individual application and design constraints of the technical solution. The division into modules in this application is merely a logical division of functions, and actual implementations may be other divisions. Furthermore, the functional modules of the embodiments of this application may be integrated into a single processor, exist physically independently, or two or more modules may be integrated into a single module. The integrated module may be implemented in hardware form or in the form of a software functional module.

[0279] Figure 11 is a diagram of a communication device according to this application. This device may include modules that correspond one-to-one with the methods / operations / steps / actions described in any one of the embodiments shown in Figures 7 to 10C. These modules may be implemented by hardware circuitry, software, or a combination of hardware circuitry and software.

[0280] The apparatus 1100 includes a communication unit 1101 and a processing unit 1102, configured to perform the method performed by the device in the above embodiment.

[0281] In possible implementations, this device is an access network device (e.g., a DU) or is located within an access network device. Specifically, the communication unit 11101 is configured to receive indication information from a second network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. The communication unit 1101 is further configured to receive a first message from the second network device, which is a first downlink message sent from the second network device to a first terminal device in a first connection re-establishment or restart procedure. The first connection is a connection between a first terminal device and a second network device, the first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device. The processing unit 1102 is configured to transmit a first message based on a first mapping relationship via the communication unit 1101.

[0282] For specific execution procedures of the communication unit 1101 and processing unit 1102 in this implementation, please refer to the description of the steps performed by the first network device in the embodiment of the method described above, and the corresponding description in the summary of the invention. Details will not be repeated in this specification. In the communication method implemented by this device, the access network device receives indication information and, based on this indication information, determines the setting of a first mapping relationship used to transmit a first message, so that the first terminal device re-establishes or resumes the first connection via the second terminal device and correctly accesses the corresponding access network device.

[0283] In another possible implementation, this device is an access network device (e.g., CU) or is located within an access network device. Specifically, the communication unit 1101 is configured to send indication information to a first network device, where this indication information is used to determine a first mapping relationship between a first bearer and a second bearer. The communication unit 1101 is further configured to send a first message to the first network device, where the first message is a first downlink message sent from a second network device to a first terminal device in a re - establishment or resumption procedure of a first connection, and the first connection is a connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides a relay service to the first terminal device.

[0284] For the specific execution procedures of the communication unit 1101 and the processing unit 1102 in this implementation, refer to the description of the steps executed by the second network device in the above - mentioned method embodiments and the corresponding description in the summary of the invention. In this specification, details will not be repeated. In the communication method implemented by this device, since the second network device sends indication information to the first network device, the first network device can determine the setting of the first mapping relationship used to transmit the first message based on this indication information, and the first terminal device can re - establish or resume the first connection via the second terminal device and correctly access the base station.

[0285] FIG. 12 is a diagram of another communication device according to the present application. This communication device is configured to implement the communication method of the above-described method embodiment. It can be understood that the communication device 1200 includes necessary forms such as modules, units, elements, circuits, or interfaces that are appropriately configured together to execute the method of the present application. For example, the communication device 1200 may be a RAN node, a terminal, a core network device, or another network device for implementing the method described in the above method embodiment, or may be a component (such as a chip) in these devices. The communication device 1200 includes one or more processors 1201. The processor 1201 can be a general-purpose processor or a dedicated processor. For example, the processor may be a baseband processor or a central processing unit. The baseband processor may be configured to process communication protocols and communication data. The central processing unit may be configured to control the communication device (such as a RAN node, a terminal, or a chip), execute a software program, and process the data of the software program.

[0286] Optionally, the processor 1201 may include a program 1202 (which may sometimes be called code or instructions). When the program 1202 is executed on the processor 1201, the communication device 1200 may execute the method described in the above embodiment. In yet another possible design, the communication device 1200 includes a circuit (not shown in FIG. 12). This circuit is configured to implement the functions of the CU or DU in the above embodiment.

[0287] Optionally, the communication device 1200 may include one or more memories 1203, and the memory 1203 stores a program 1204 (which may sometimes be called code or instructions). When the program 1204 is executed on the processor 1201, the communication device 1200 may execute the method described in the above method embodiment.

[0288] Optionally, processor 1201 and / or memory 1203 may include AI modules 1205 and 1206. The AI ​​modules are configured to implement AI-related functions. AI modules may be implemented by software, hardware, or a combination of software and hardware. For example, an AI module may include an RIC module. For example, an AI module may be a near real-time RIC or a non-real-time RIC.

[0289] Optionally, the communication device 1200 further includes a transceiver 1207 and an antenna 1208. The transceiver 1207 and antenna 1208 can implement transceiver functions, such as communicating with another device via a transmission medium, thereby enabling the device 1200 to communicate with another device.

[0290] In possible implementations, this device is a DU, or is located within a DU. Specifically, transceiver 1207 and antenna 1208 are configured to receive indication information from a second network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. Transceiver 1207 and antenna 1208 are further configured to receive a first message from the second network device, which is a first downlink message sent from the second network device to the first terminal device in a first connection re-establishment or restart procedure. The first connection is the connection between the first terminal device and the second network device, the first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device. The processor 1201 is configured to transmit a first message based on a first mapping relationship.

[0291] For specific execution procedures of the communication device 1200 in this implementation, please refer to the description of the steps performed by the first network device in the embodiment of the method described above, and the corresponding description in the summary of the invention. Details will not be repeated in this specification. In the communication method implemented by this device, the DU receives indication information and, based on this indication information, determines the setting of a first mapping relationship used to transmit a first message, so that the first terminal device re-establishes or resumes the first connection via the second terminal device and correctly accesses the base station.

[0292] In possible implementations, this device is a CU, or is located within a CU. Specifically, the transceiver 1207 and antenna 1208 are configured to transmit indication information to a first network device, which is used to determine a first mapping relationship between a first bearer and a second bearer. The transceiver 1207 and antenna 1208 are further configured to transmit a first message to the first network device, where the first message is a first downlink message transmitted from the second network device to the first terminal device in a first connection re-establishment or restart procedure, and the first connection is the connection between the first terminal device and the second network device. The first bearer is used to transmit the first message between the first terminal device and the second network device, and the second bearer is used to transmit the first message between the second terminal device and the first network device. The second terminal device provides relay services to the first terminal device.

[0293] For specific procedures of the communication device 1200 in this implementation, please refer to the description of the steps performed by the second network device in the embodiment of the method described above, and the corresponding description in the summary of the invention. Details will not be repeated in this specification. In the communication method implemented by this device, the second network device transmits indication information to the first network device so that the first network device can determine the configuration of a first mapping relationship used to transmit a first message based on this indication information, and the first terminal device re-establishes or restarts the first connection via the second terminal device and correctly accesses the base station.

[0294] In this application, the processor may be a general-purpose processor, a digital signal processor, an application-specific integrated circuit, a field-programmable gate array or another programmable logic device, a discrete gate or transistor logic device, or a separate hardware component that can implement the methods, steps, and logic block diagrams disclosed herein. The general-purpose processor may be a microprocessor or any conventional processor. The steps of the methods disclosed with reference to this application may be implemented directly by the hardware processor or by a combination of hardware and software modules within the processor.

[0295] In this application, memory may be non-volatile memory such as a hard disk drive (HDD) or solid-state drive (SSD), or volatile memory such as random-access memory (RAM). Memory may be any other medium that can carry or store a desired program code in the form of instructions or data structures, and which can be accessed by a computer, but is not limited to these. Alternatively, memory in this application may be a circuit or any other device that can implement a storage function and is configured to store program instructions and / or data.

[0296] This application also provides another communication device, which includes a processor and an interface. Optionally, it further includes memory. The processor is coupled to the memory and is configured to read and execute computer instructions stored in the memory to implement the communication method of the embodiment shown in Figures 7 to 10C.

[0297] This application provides a communication system, which includes one or more of the devices of the embodiments shown in Figures 7 to 10C.

[0298] This application provides a computer-readable storage medium. The computer-readable storage medium stores a program or instruction. When the program or instruction is executed on a computer, the computer becomes capable of executing the communication method of the embodiment shown in Figures 7 to 10C.

[0299] This application provides a computer program product. The computer program product includes instructions. When the instructions are executed on a computer, the computer becomes capable of executing the communication method of the embodiment shown in Figures 7 to 10C.

[0300] This application provides a chip or chip system, which includes at least one processor and an interface. The interface and this at least one processor are interconnected via a line. This at least one processor is configured to execute a computer program or instructions to perform the communication method of the embodiment shown in Figures 7 to 10C.

[0301] The chip's interface can be an input / output interface, pins, or circuitry.

[0302] A chip system may be a system-on-a-chip (SOC) or a baseband chip. A baseband chip may include a processor, channel encoder, digital signal processor, media, and interface modules.

[0303] In one implementation, the chip or chip system described in this application further includes at least one memory, which stores instructions. The memory may be a storage unit within the chip, such as a register or a cache, or it may be a storage unit of the chip (e.g., read-only memory or random-access memory).

[0304] All or part of the technical solutions provided in this application may be implemented using software, hardware, firmware, or any combination thereof. When software is used to implement an embodiment, all or part of the embodiment may be implemented in the form of a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded into a computer and executed, all or part of the procedures or functions according to this application are generated. The computer may be a general-purpose computer, a special-purpose computer, a computer network, a network device, a terminal device, or another programmable device. Computer instructions may be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions may be transmitted from one website, computer, server, or data center to another website, computer, server, or data center by a wired method (e.g., coaxial cable, optical fiber, or digital subscriber line (DSL)) or a wireless method (e.g., infrared, radio, or microwave). Computer-readable storage media can be any available medium accessible by a computer, or a data storage device such as a server or data center that integrates one or more available media. Available media can be magnetic media (e.g., floppy disks, hard disks, or magnetic tapes), optical media (e.g., digital video discs (DVDs)), or semiconductor media.

[0305] In this application, embodiments may be referenced to one another, provided that no logical inconsistency arises. For example, methods and / or terms may be referenced to one another between embodiments of methods. For example, functions and / or terms may be referenced to one another between embodiments of apparatus. For example, functions and / or terms may be referenced to one another between embodiments of apparatus and embodiments of methods.

[0306] It will be apparent to those skilled in the art that various modifications and alterations can be made to this application without departing from its scope. Therefore, to the extent that such modifications and alterations fall within the scope of the claims of this application and their equivalent art, this application is intended to cover such modifications and alterations to this application.

Claims

1. A communication method applicable to a first network device, A step of receiving indication information from a second network device, wherein the indication information is used to determine a first mapping relationship between a first bearer and a second bearer. The steps include: receiving a first message from the second network device, wherein the first message is a first downlink message transmitted from the second network device to the first terminal device in a first connection re-establishment or restart procedure, the first connection is a connection between the first terminal device and the second network device, the first bearer is used to transmit the first message between the first terminal device and the second network device, the second bearer is used to transmit the first message between the second terminal device and the first network device, and the second terminal device provides relay services to the first terminal device; The steps include transmitting the first message based on the first mapping relationship and A communication method that includes this.

2. The step of receiving the indication information from the second network device is: Steps of receiving first indication information from the second network device, wherein the first indication information indicates a first identifier of the first terminal device, and the first identifier is used by the first network device to associate the first terminal device on the interface between the first network device and the second network device. The method according to claim 1, including the method described in claim 1.

3. The indication information is used to determine the first mapping relationship between the first bearer and the second bearer. A step of obtaining context information of the first terminal device based on the first identifier, The steps include determining the first mapping relationship based on the context information of the first terminal device and The method according to claim 2, including the method described in claim 2.

4. The step of determining the first mapping relationship based on the context information of the first terminal device is: A step of determining the first mapping relationship based on second indication information and the context information, wherein the second indication information instructs the first network device to apply the first mapping relationship. The method according to claim 3, including the method described in claim 3.

5. The step of determining the first mapping relationship based on the context information of the first terminal device is: A step of determining a first mapping relationship based on the first identifier of the first terminal device, the context information of the first terminal device, and information corresponding to the second terminal device, wherein the information corresponding to the second terminal device includes one or more of the second identifier of the second terminal device, the service information of the second terminal device, and the context information of the second terminal device. The method according to claim 3, including the method described in claim 3.

6. The method according to claim 1 or 2, wherein the indication information includes the first mapping relationship.

7. The aforementioned method, A step of deciding to release a second mapping relationship based on the first identifier of the first terminal device and the information corresponding to the second terminal device, wherein the second mapping relationship is included in the context information of the first terminal device and the first mapping relationship is different from the second mapping relationship. The method according to claim 5 or 6, further comprising:

8. The aforementioned method, A step of receiving third indication information from the second network device, wherein the third indication information instructs the first network device to release the second mapping relationship, the second mapping relationship is included in the context information of the first terminal device, and the first mapping relationship is different from the second mapping relationship. The method according to claim 5 or 6, further comprising:

9. The method according to any one of claims 1 to 8, wherein the first downlink message is a first connection re-establishment message, a first connection restart message, or a first connection release message, and the first bearer is a signaling radio bearer SRB1 message of the first terminal device.

10. The method according to any one of claims 1 to 8, wherein the first downlink message is a first connection establishment message, and the first bearer is an SRB0 message from the first terminal device.

11. The method according to any one of claims 1 to 8, wherein the first downlink message is a first connection rejection message, and the first bearer is an SRB0 message from the first terminal device.

12. A communication method applicable to a second network device, A step of transmitting indication information to a first network device, wherein the indication information is used to determine a first mapping relationship between a first bearer and a second bearer. The steps include: sending a first message to the first network device, wherein the first message is a first downlink message sent from the second network device to the first terminal device in a first connection re-establishment or restart procedure, the first connection is a connection between the first terminal device and the second network device, the first bearer is used to transmit the first message between the first terminal device and the second network device, the second bearer is used to transmit the first message between the second terminal device and the first network device, and the second terminal device provides relay services to the first terminal device; A communication method that includes this.

13. The step of transmitting the indication information to the first network device is: Steps of transmitting first indication information to the first network device, wherein the first indication information indicates a first identifier of the first terminal device, and the first identifier is used by the first network device to associate the first terminal device on an interface between the first network device and the second network device. The method according to claim 12, including the method described in claim 12.

14. The method according to claim 13, wherein the first identifier is used by the first network device to obtain context information of the first terminal device, and the context information of the first terminal device includes the first mapping relationship.

15. The step of transmitting the indication information to the first network device is: A step of transmitting second indication information to the first network device, wherein the second indication information instructs the first network device to apply the first mapping relationship. The method according to claim 12, including the method described in claim 12.

16. The aforementioned method, A step of determining, based on a second message and a second identifier of the second terminal device, that the second terminal device is a relay terminal device associated with the first terminal device prior to the re-establishment or restart procedure of the first connection, wherein the second message is used by the first terminal device to request that the re-establishment or restart procedure of the first connection be performed. The method according to claim 15, further comprising:

17. The method according to claim 12 or 13, wherein the indication information includes the first mapping relationship.

18. The aforementioned method, A step of determining, based on a second message and a second identifier of the second terminal device, that a relay terminal device associated with the second terminal device is different from a relay terminal device associated with the first terminal device prior to the re-establishment or restart procedure of the first connection, wherein the second message is used by the first terminal device to request the re-establishment or restart of the first connection. The method according to claim 17, further comprising:

19. The aforementioned method, A step of transmitting third indication information to the first network device, wherein the third indication information instructs the first network device to release the second mapping relationship, the second mapping relationship being included in the context information of the first terminal device, and the first mapping relationship being different from the second mapping relationship. The method according to claim 18, further comprising

20. The aforementioned method, A step of sending a context information establishment or update request message for the first terminal device to the first network device, wherein the context information establishment or update request message is used to establish a second mapping relationship, and the second mapping relationship is different from the first mapping relationship. The method according to claim 17, further comprising:

21. The method according to any one of claims 12 to 20, wherein the first downlink message is a first connection re-establishment message, a first connection restart message, or a first connection release message, and the first bearer is an SRB1 message from the first terminal device.

22. The method according to any one of claims 12 to 20, wherein the first downlink message is a first connection establishment message, and the first bearer is an SRB0 message from the first terminal device.

23. The method according to any one of claims 12 to 20, wherein the first downlink message is a first connection rejection message, and the first bearer is an SRB0 message from the first terminal device.

24. A communication device comprising a communication unit and a processing unit, wherein the communication unit and the processing unit are configured to perform the method described in any one of claims 1 to 11 or 12 to 23.

25. A communication device comprising a processor and memory, wherein the memory is configured to store instructions, and when the instructions are executed by the processor, the communication device is capable of performing the method according to any one of claims 1 to 11 or 12 to 23.

26. A communication system comprising one or more of a first network device, a second network device, a first terminal device, and a second terminal device, wherein the first network device is configured to perform the method described in any one of claims 1 to 11, and the second network device is configured to perform the method described in any one of claims 12 to 23.

27. A computer-readable storage medium, wherein the computer-readable storage medium stores instructions, and when the instructions are executed in a computer, the computer is able to perform the method according to any one of claims 1 to 11 or 12 to 23.

28. A chip comprising an interface with a processor, wherein the processor is configured to execute a computer program or instructions, and the chip is configured to carry out the method according to any one of claims 1 to 11 or 12 to 23.

29. A chip system comprising a processor and an interface, wherein the processor is configured to execute a computer program or instructions, and the chip system is configured to carry out the method according to any one of claims 1 to 11 or 12 to 23.

30. A computer program product comprising instructions, wherein when the instructions are executed in a computer, the computer becomes capable of carrying out the method according to any one of claims 1 to 11 or 12 to 23.

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