A communication method, device and system

Abstract

The present application relates to a communication method, apparatus and system. When the first terminal device determines that the second terminal device can no longer provide relay services for the first terminal device, the first terminal device initiates RRC re-establishment through a first method, and the first method is determined according to the first information. The first method is a method of initiating RRC re-establishment through a Uu interface, or a method of initiating RRC re-establishment through a new terminal device, or a method of initiating RRC re-establishment through a second terminal device. In the embodiment of the present application, the first terminal device can choose a method of initiating RRC re-establishment, so that the method of initiating RRC re-establishment by the first terminal device is more flexible.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to a Chinese patent application filed with the State Intellectual Property Office of China on December 15, 2020, with application number 202011479765.X and application name “A method for UE to reestablish RRC connection under layer 2 relay”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of communication technology, and in particular to a communication method, device and system. Background Art

[0004] When a terminal device is far away from a network device, for example, the terminal device is not within the coverage of the network device, or the terminal device is at the edge of the coverage of the network device, or the link quality between the terminal device and the network device is poor, the terminal device can communicate with the network device through another terminal device, that is, the other terminal device can provide a relay service for the terminal device, so that the terminal device can communicate with the network device. A terminal device that communicates with a network device through another terminal device can be called a remote terminal device, and a terminal device that provides a relay service for a remote terminal device can be called a relay terminal device.

[0005] During the communication between the remote terminal device and the network device via the relay terminal device, if the remote terminal device detects that a radio link failure (RLF) occurs in the sidelink (SL) between the remote terminal device and the relay terminal device, the service of the remote terminal device may be interrupted. There is currently no solution to this problem. Summary of the invention

[0006] Embodiments of the present application provide a communication method, apparatus, and system for improving service continuity of remote terminal equipment.

[0007] In a first aspect, a first communication method is provided. For example, the method may be applicable to a first communication system, and the first communication system, for example, includes a first terminal device and a second terminal device. The method includes: when the first terminal device determines that the second terminal device can no longer provide relay services for the first terminal device, the first terminal device initiates RRC re-establishment through a first method, and the first method is a method of initiating RRC re-establishment through a Uu interface, or a method of initiating RRC re-establishment through a new terminal device, or a method of initiating RRC re-establishment through the second terminal device. Among them, the method also includes: the first terminal device receives the first information from the first network device through the second terminal device, and the first information is used to indicate the initiation of RRC re-establishment through Uu, or the initiation of RRC re-establishment through a new terminal device, or the initiation of RRC re-establishment through the second terminal device; or, the first information includes the RSRP of the cell selected by the first terminal device and / or the RSRP of the third terminal device selected by the first terminal device.

[0008] In an embodiment of the present application, if the first terminal device determines that the second terminal device can no longer provide relay services for the first terminal device, the first terminal device can initiate RRC re-establishment to restore the service of the first terminal device as soon as possible. Moreover, the first terminal device can choose a way to initiate RRC re-establishment, such as initiating RRC re-establishment through the Uu interface, or initiating RRC re-establishment through a new terminal device, or continuing to initiate RRC re-establishment through the second terminal device, etc., so that the way in which the first terminal device initiates RRC re-establishment is more flexible. Moreover, for example, the first terminal device can select a better way to initiate RRC re-establishment based on factors such as network quality, thereby improving the success rate of RRC re-establishment, improving the service continuity of the first terminal device, and reducing packet loss caused by service discontinuity. For example, the first way can be indicated by a network device, such as in the process of the first terminal device communicating with the first network device through the second terminal device, the first network device sends the first information to the first terminal device through the second terminal device, and accordingly, the first terminal device receives the first information from the first network device through the second terminal device. The first terminal device can determine the first way according to the indication of the first information, thereby initiating RRC re-establishment. The network performs instructions, and the first terminal device does not need to determine the method of initiating RRC re-establishment by itself, which can simplify the execution process of the terminal device, so that the method of the embodiment of the present application can be applied to more terminal devices (for example, even terminal devices with limited capabilities can apply the solution of the embodiment of the present application). For another example, the first method can also be determined by the first terminal device itself, without the need for instructions from the network device, which can save signaling overhead.

[0009] In combination with the first aspect, in a first optional implementation of the first aspect, when the first information includes the RSRP of the cell selected by the first terminal device and / or the RSRP of the third terminal device selected by the first terminal device, wherein: when the RSRP of the first cell is less than or equal to a first RSRP threshold and the first terminal device has not selected a terminal device that can provide relay service, the first method is a method of initiating RRC re-establishment through the Uu interface, and the first cell is the cell selected by the first terminal device; or, when the RSRP of the first cell is greater than the first RSRP threshold, the first method is a method of initiating RRC re-establishment through the Uu interface, and the first cell is the cell selected by the first terminal device. The first method is to initiate RRC re-establishment through the third terminal device; or, when the RSRP of the cell selected by the first terminal device is less than or equal to the first RSRP threshold, and the first terminal device selects a third terminal device that can provide relay services, the first method is to initiate RRC re-establishment through the third terminal device; or, when the difference between the RSRP of the cell selected by the first terminal device and the RSRP of the third terminal device is less than or equal to the first RSRP threshold, the first method is to initiate RRC re-establishment through the third terminal device, and the third terminal device is a new terminal device that can provide relay services selected by the first terminal device, or the third terminal device and the second terminal device are the same terminal device. The first method can also be determined by the first terminal device itself, for example, the first terminal device can determine the first method according to the RSRP of the cell selected by the first terminal device and / or the RSRP of the third terminal device selected by the first terminal device, so that the first terminal device can perform RRC re-establishment in a better way according to RSRP to improve the success rate of RRC re-establishment.

[0010] In combination with the first aspect or the first optional implementation of the first aspect, in a second optional implementation of the first aspect, the first terminal device determines that the second terminal device cannot continue to provide relay services for the first terminal device, including: the first terminal device detects the SL RLF between the first terminal device and the second terminal device; or, the first protocol layer of the first terminal device requests to release the connection between the first terminal device and the second terminal device. The first terminal device can determine that the second terminal device cannot continue to provide relay services for the first terminal device according to a variety of different situations, thereby reducing the delay for the first terminal device to initiate RRC re-establishment.

[0011] In combination with the first aspect or the first optional implementation manner of the first aspect or the second optional implementation manner of the first aspect, in the third optional implementation manner of the first aspect, when the first method is a method of initiating RRC re-establishment through the Uu interface, the method also includes: the first terminal device starts a first timer; wherein the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device selects a new terminal device that can provide relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device completes the connection establishment with the new terminal device that can provide relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device obtains the identification of the service cell of the new terminal device that can provide relay service selected by the first terminal device; the first terminal device selects the first cell and stops the first timer. When the terminal device initiates RRC re-establishment through the Uu interface, the first timer can be started. If the first terminal device selects a suitable cell (e.g., the first cell) before the first timer times out, the first terminal device can stop the first timer. If the first terminal device has not selected a suitable cell when the first timer times out, the first terminal device can stop the cell selection. For example, the first terminal device can enter the RRC idle state, or the first terminal device can instead initiate RRC re-establishment through the terminal device. The first timer can effectively control the cell selection time of the first terminal device and improve the success rate of RRC re-establishment.

[0012] In combination with the third optional implementation of the first aspect, in a fourth optional implementation of the first aspect, the first terminal device starts the first timer, including: the first terminal device starts the first timer when initiating RRC re-establishment through the first method; or, the first terminal device starts the first timer when determining that the second terminal device cannot continue to provide relay service for the first terminal device; or, the first terminal device starts the first timer after initiating RRC re-establishment through the first method and before performing cell selection. The first terminal device can start the first timer in different situations, and the embodiments of the present application do not limit this.

[0013] In combination with the first aspect or the first optional implementation of the first aspect or the second optional implementation of the first aspect, in a fifth optional implementation of the first aspect, in the case where the first method is a method of initiating RRC re-establishment through a Uu interface, after the first terminal device initiates RRC re-establishment through the first method, the method further includes: the first terminal device does not select a cell, or the cell selected by the first terminal device is no longer suitable, or the first terminal device does not receive an RRC re-establishment message from a second network device, or the RSRP of the cell selected by the first terminal device is less than or equal to a second RSRP threshold, and the second network device is the network device where the first terminal device initiates the RRC re-establishment; the first terminal device selects a new terminal device that can provide relay services; in the case where the first terminal device selects a third terminal device, the first terminal device initiates RRC re-establishment through the third terminal device, and the third terminal device can provide relay services for the first terminal device. If the first terminal device does not select a suitable cell in the process of initiating RRC re-establishment through the Uu interface, the first terminal device may not be able to continue to initiate RRC re-establishment through the Uu interface. In this case, the first terminal device can select another terminal device to initiate RRC re-establishment through the terminal device, thereby improving the success rate of RRC re-establishment of the terminal device. The third terminal device and the second terminal device can be the same terminal device, or can also be different terminal devices.

[0014] In combination with the fifth optional implementation of the first aspect, in the sixth optional implementation of the first aspect, the first terminal device fails to select a cell, including: when the first timer times out, the first terminal device fails to select a cell, the first timer is started when the first terminal device initiates RRC re-establishment through the first method, or the first timer is started when the first terminal device determines that the second terminal device cannot continue to provide relay service for the first terminal device, or the first timer is started after the first terminal device initiates RRC re-establishment through the first method and before performing cell selection. The first terminal device fails to select a suitable cell, which may mean that the first terminal device fails to select a suitable cell when the first timer times out. The first timer can effectively control the cell selection time of the first terminal device to prevent the terminal device from performing cell selection indefinitely.

[0015] In combination with the fifth optional implementation of the first aspect, in the seventh optional implementation of the first aspect, the first terminal device does not receive the RRC re-establishment message from the second network device, including: when the second timer times out, the first terminal device does not receive the RRC re-establishment message from the second network device, and the second timer is started after the first terminal device selects a cell. If the first terminal device selects a suitable cell, the second timer can be started. If the first terminal device receives an RRC re-establishment message from the network before the second timer times out, the first terminal device can stop the second timer. If the first terminal device has not received the RRC re-establishment message from the network when the second timer times out, the first terminal device has not received the RRC re-establishment message from the network. For example, the first terminal device can change to initiate RRC re-establishment through the terminal device, or the first terminal device can enter the RRC idle state, etc. The second timer can effectively control the time when the terminal device receives the RRC re-establishment message from the network, avoiding the terminal device from waiting for messages from the network indefinitely.

[0016] In combination with the first aspect or the first optional implementation manner of the first aspect or the second optional implementation manner of the first aspect, in the eighth optional implementation manner of the first aspect, when the first method is a method of initiating RRC re-establishment through a new terminal device, the method further includes: when the first terminal device initiates RRC re-establishment through the first method, or, when the first terminal device determines that the second terminal device can no longer provide relay service for the first terminal device, or, before the first terminal device reselects a terminal device that can provide relay service, the first terminal device starts a second timer; when the first terminal device selects a third terminal device, or when the first terminal device completes establishing a connection with the third terminal device, or when the first terminal device obtains the identifier of the service cell of the third terminal device, the first terminal device stops the second timer. When the terminal device initiates RRC re-establishment through the terminal device (new terminal device or second terminal device), the second timer can be started. If the first terminal device selects a suitable terminal device (such as a third terminal device) before the second timer times out, the first terminal device can stop the second timer. If the first terminal device has not selected a suitable terminal device when the second timer times out, the first terminal device can stop selecting the terminal device. For example, the first terminal device can enter the RRC idle state, or the first terminal device can instead initiate RRC re-establishment through the Uu interface, etc. The second timer can effectively control the terminal device selection time of the first terminal device and improve the success rate of RRC re-establishment.

[0017] In combination with the eighth optional implementation manner of the first aspect, in a ninth optional implementation manner of the first aspect, the first terminal device initiates RRC re-establishment through the first method, including: the first terminal device establishes an SL RLC bearer of the first SRB; the first terminal device sends an RRC re-establishment request message to a second network device through the third terminal device, and the second network device is a network device accessed by the third terminal device; the first terminal device receives an RRC re-establishment message from the second network device through the third terminal device, and the RRC re-establishment message is transmitted on the first SRB. If the first terminal device initiates RRC re-establishment through the third terminal device, the first terminal device can communicate with the second network device through the third terminal device.

[0018] In combination with the first aspect or the first optional implementation manner of the first aspect or the second optional implementation manner of the first aspect, in the tenth optional implementation manner of the first aspect, when the first method is a method of initiating RRC re-establishment through a new terminal device, the method further includes: the first terminal device starts a first timer; wherein the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device selects a new terminal device that can provide relay services; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device completes the connection with the new terminal device that can provide relay services; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the connection between the first terminal device and the new terminal device that can provide relay services is established. When the first terminal device obtains the identifier of the service cell of the new terminal device that can provide relay service selected by the first terminal device, the first terminal device stops the first timer; the first terminal device reselects the terminal device that can provide relay service, and when the third terminal device is selected, the first terminal device stops the first timer; or the first terminal device reselects the terminal device that can provide relay service, and when the third terminal device is selected and the connection with the third terminal device is established, the first terminal device stops the first timer; or the first terminal device reselects the terminal device that can provide relay service, and when the third terminal device is selected and the identifier of the service cell of the third terminal device is obtained, the first terminal device stops the first timer. In this way, the process of selecting a cell and selecting a terminal device can be carried out by the terminal device, and the terminal device can initiate RRC re-establishment in the way of which succeeds first (for example, if the terminal device selects a suitable cell first, the cell selection process is considered to be successful, and if the terminal device selects a suitable terminal device first, the terminal device selection process is considered to be successful), thereby further reducing the delay of RRC re-establishment.

[0019] In combination with the tenth optional implementation of the first aspect, in the eleventh optional implementation of the first aspect, the first terminal device starts the first timer, including: the first terminal device starts the first timer when initiating RRC re-establishment through the first method; or, the first terminal device starts the first timer when determining that the second terminal device can no longer provide relay service for the first terminal device; or, the first terminal device starts the first timer after initiating RRC re-establishment through the first method and before reselecting a terminal device that can provide relay service.

[0020] In combination with the first aspect or the first optional implementation manner of the first aspect or the second optional implementation manner of the first aspect, or in combination with any optional implementation manner from the eighth optional implementation manner of the first aspect to the eleventh optional implementation manner of the first aspect, in the twelfth optional implementation manner of the first aspect, when the first method is a method of initiating RRC re-establishment through a new terminal device, the method further includes: the first terminal device sends data of a second SRB to a third terminal device, the second SRB is an SRB between the first terminal device and the second network device, the second network device is a network device accessed by the third terminal device, and the third terminal device is a new terminal device selected by the first terminal device; the third terminal device receives data from the first terminal device; The third terminal device establishes or reconstructs the RLC bearer of the first SRB corresponding to the first terminal device, the RLC bearer of the first SRB includes the first RLC bearer between the first terminal device and the third terminal device and the second RLC bearer between the first terminal device and the second network device, and the first SRB is the SRB between the first terminal device and the second network device; the third terminal device sends the data of the second SRB to the second network device; the third terminal device receives the data of the first SRB from the second network device through the second RLC bearer; the third terminal device sends the data of the first SRB to the first terminal device through the first RLC bearer. If the first terminal device initiates RRC re-establishment through the third terminal device, the third terminal device can establish or reconstruct the RLC bearer corresponding to the first SRB of the first terminal device, so as to forward information between the first terminal device and the second network device through the RLC bearer. The first SRB is, for example, SRB1, or it can also be other SRBs. The second SRB is, for example, SRB0, or it can also be other SRBs. In this embodiment, the third terminal device can also belong to the first communication system.

[0021] In combination with the twelfth optional implementation manner of the first aspect, in the thirteenth optional implementation manner of the first aspect, the third terminal device establishes or reconstructs the RLC bearer corresponding to the first SRB of the first terminal device, including: the third terminal device receives data of the second SRB from the first terminal device, and the third terminal device establishes or reconstructs the RLC bearer of the first SRB; or, the third terminal device receives first indication information from the second network device, and the third terminal device establishes or reconstructs the RLC bearer of the first SRB, wherein the first indication information is used to indicate the establishment of the RLC bearer of the first SRB, or to indicate the reception of data of the first SRB sent by the second network device to the first terminal device. The third terminal device may establish or reconstruct the RLC bearer of the first SRB corresponding to the first terminal device according to different triggering conditions. For example, one triggering method is that the third terminal device receives the data of the second SRB from the first terminal device, then the first terminal device and other devices do not need to specifically trigger the third terminal device, the first terminal device only needs to send the data of the second SRB to the third terminal device, and the third terminal device knows that the RLC bearer corresponding to the first SRB of the first terminal device needs to be established or reconstructed, thereby reducing the signaling overhead. Alternatively, the second network device or the first terminal device may also indicate the third terminal device through indication information, so that the third terminal device can more clearly know when to establish or reestablish the RLC bearer corresponding to the first SRB of the first terminal device. In this embodiment, the third terminal device may also belong to the first communication system.

[0022] In combination with the first aspect or the first optional implementation manner of the first aspect or the second optional implementation manner of the first aspect, in the fourteenth optional implementation manner of the first aspect, when the first method is a method of initiating RRC re-establishment through the second terminal device, the method further includes: the second terminal device detects the RLF between the second terminal device and the first network device; the second terminal device initiates RRC re-establishment. For example, the second terminal device cannot continue to provide relay service for the first terminal device, and the first terminal device may discover it first, or the second terminal device may discover it first. For example, if the second terminal device detects the RLF between the second terminal device and the first network device, the second terminal device may also determine that it cannot continue to provide relay service for the first terminal device, which makes the solution of the embodiment of the present application more flexible.

[0023] In combination with the fourteenth optional implementation of the first aspect, in the fifteenth optional implementation of the first aspect, the method further includes: the second terminal device sends third indication information to the first terminal device, and the third indication information is used to indicate RRC re-establishment, or to indicate that RLF occurs in the second terminal device. If the second terminal device determines that it cannot continue to provide relay service for the first terminal device, the second terminal device can promptly inform the first terminal device so that the first terminal device can take corresponding measures as soon as possible, thereby reducing the probability of service interruption of the first terminal device.

[0024] In combination with the fifteenth optional implementation of the first aspect, in the sixteenth optional implementation of the first aspect, the first terminal device determines that the second terminal device cannot continue to provide relay services for the first terminal device, including: the first terminal device determines that the second terminal device cannot continue to provide relay services for the first terminal device according to the third indication information. If the second terminal device first finds that it cannot provide relay services for the first terminal device, the second terminal device can notify the first terminal device through the third indication information, and the first terminal device can determine that the second terminal device cannot continue to provide relay services for the first terminal device according to the third indication information.

[0025] In combination with the sixteenth optional implementation of the first aspect, in the seventeenth optional implementation of the first aspect, the method further includes: after the first terminal device receives the third indication information, starting a fifth timer; when the fifth timer times out, if the first terminal device has not received the identifier of the second cell from the second terminal device, the first terminal device enters the RRC idle state; or, before the fifth timer times out, if the first terminal device receives the identifier of the second cell from the second terminal device, the first terminal device turns off the fifth timer; wherein the second cell is the cell selected by the second terminal device. If RLF occurs between the second terminal device and the network, the second terminal device will initiate RRC re-establishment. The second terminal device may succeed in RRC re-establishment or fail in RRC re-establishment. In this embodiment, the first terminal device may start the fifth timer after receiving the third indication information. If the first terminal device has not received the identifier of the second cell from the second terminal device when the fifth timer times out, the RRC re-establishment process of the second terminal device may fail, and the first terminal device may enter the RRC idle state by itself, or the first terminal device may reselect a terminal device to initiate RRC re-establishment, or the first terminal device may initiate RRC re-establishment through the Uu interface, etc. Through the fifth timer, the first terminal device can take corresponding measures in a timely manner, reducing the probability of service interruption of the first terminal device. And through the fifth timer, the second terminal device does not need to inform the first terminal device of whether the RRC re-establishment is successful, reducing signaling overhead.

[0026] In combination with any one of the fourteenth optional implementation manner of the first aspect to the seventeenth optional implementation manner of the first aspect, in the eighteenth optional implementation manner of the first aspect, the method further includes: the second terminal device sends the identifier of the second cell to the first terminal device after the RRC re-establishment is completed; or, the second terminal device sends the identifier of the second cell to the first terminal device when selecting the second cell; wherein the second cell is the cell selected by the second terminal device by initiating RRC re-establishment. If the second terminal device selects a suitable cell (e.g., the second cell) by initiating RRC re-establishment, the second terminal device may send the identifier of the second cell to the first terminal device, so that the first terminal device can calculate the shortMAC-I that needs to be carried in the RRC re-establishment request message.

[0027] In combination with the eighteenth optional implementation of the first aspect, in the nineteenth optional implementation of the first aspect, after the second terminal device initiates RRC re-establishment, the method further includes: the second terminal device fails to select a cell, the second terminal device sends a fourth indication message to the first terminal device, and the fourth indication message is used to indicate that the RRC re-establishment fails, or indicates the release of the connection with the first terminal device; after receiving the fourth indication message, the first terminal device enters the RRC idle state, or selects a new terminal device to initiate RRC re-establishment, or initiates RRC re-establishment through the Uu interface. If the second terminal device fails to select a suitable cell, the second terminal device may send a fourth indication message to the second terminal device to indicate that the RRC re-establishment fails, so that the first terminal device can take corresponding measures in time to reduce the probability of service interruption of the first terminal device.

[0028] In combination with the fifteenth optional implementation of the first aspect or the sixteenth optional implementation of the first aspect, in the twentieth optional implementation of the first aspect, the method further includes: the first terminal device sends fifth indication information to the second terminal device, and the fifth indication information is used to indicate not to re-establish RRC through the second terminal device, or to indicate to release the connection with the second terminal device. If the first terminal device receives the third indication information, it can send the fifth indication information to the second terminal device in response to the third indication information.

[0029] In combination with the fourteenth optional implementation manner of the first aspect, in the twenty-first optional implementation manner of the first aspect, the method further includes: the second terminal device does not provide relay service before selecting a suitable cell during the RRC re-establishment process or before the RRC re-establishment is completed. If a terminal device establishes a connection with a second terminal device that is in RLF or in the process of RRC re-establishment, the terminal device may not be able to immediately transmit data through the second terminal device or may not be able to connect to the network device through the second terminal device, causing a large delay to the service of the terminal device. The technical solution of the embodiment of the present application can solve this problem, so that other terminal devices can select a more suitable terminal device to provide relay service as soon as possible, thereby reducing the service interruption time of the terminal device.

[0030] In combination with the twenty-first optional implementation of the first aspect, in the twenty-second optional implementation of the first aspect, the second terminal device does not provide relay service, including: the second terminal device does not send a discovery message related to the relay service, or refuses to establish a connection with a terminal device requesting to provide relay service. For example, for a terminal device capable of providing relay service, a discovery message may be sent, and the discovery message may include information related to the relay service, such as indicating that the terminal device sending the discovery message is capable of providing relay service, etc. Then, in an embodiment of the present application, the second terminal device does not send a discovery message related to the relay service before selecting a suitable cell or before the RRC re-establishment process is completed.

[0031] In combination with the twenty-first optional implementation of the first aspect, in the twenty-third optional implementation of the first aspect, the second terminal device does not provide a relay service, including: the second terminal device sends sixth indication information to the first terminal device, and the sixth indication information is used to indicate that the second terminal device is in an RLF state, or indicates that the second terminal device is re-establishing RRC, or indicates that the connection between the second terminal device and the first network device is unavailable. The second terminal device can actively send the sixth indication information so that the first terminal device can promptly be informed that it is temporarily unable to access the network through the second terminal device.

[0032] In combination with the twenty-third optional implementation of the first aspect, in the twenty-fourth optional implementation of the first aspect, the sixth indication information is included in a first message, and the first message is a discovery message, or a message for establishing a connection between terminal devices. Alternatively, the sixth indication information may also be included in other messages.

[0033] In combination with the twenty-first optional implementation of the first aspect, in the twenty-fifth optional implementation of the first aspect, the second terminal device does not provide a relay service, including: the second terminal device sends seventh indication information to the first terminal device, the seventh indication information is used to indicate not to send a connection establishment request message, or to indicate not to perform a PC5 connection establishment process. The second terminal device can actively send the seventh indication information, so that the first terminal device can promptly know that it is temporarily unable to establish a connection with the second terminal device.

[0034] In combination with the twenty-fifth optional implementation of the first aspect, in the twenty-sixth optional implementation of the first aspect, the seventh indication information is included in a second message, and the second message is a discovery message, or a message for establishing a connection between terminal devices. Alternatively, the seventh indication information may also be included in other messages.

[0035] In combination with the twenty-first optional implementation of the first aspect, in the twenty-seventh optional implementation of the first aspect, the second terminal device does not provide a relay service, including: the second terminal device does not respond to a message from the first terminal device for establishing a connection with the second terminal device. If the second terminal device does not respond to the message for establishing a connection, other terminal devices will not be able to establish a connection with the second terminal device. This method does not require the second terminal device to send indication information, which can save signaling overhead.

[0036] In combination with the twenty-seventh optional implementation of the first aspect, in the twenty-eighth optional implementation of the first aspect, the method further includes: after the second terminal device selects a new cell or after RRC re-establishment is completed, responding to a message from the first terminal device for establishing a connection with the second terminal device. If the terminal device does not respond to messages from other terminal devices for establishing a connection before selecting a suitable cell during the RRC re-establishment process, it can respond to these messages to establish a connection with other terminal devices after the RRC re-establishment is completed or after a new cell is selected, without the need for other terminal devices to send messages again, so as to save signaling overhead.

[0037] In a second aspect, a second communication method is provided, which can be executed by a terminal device, or by a chip system that can implement the functions of the terminal device, or by a larger device including the terminal device. The method includes: the second terminal device receives a shortMAC-I from the first terminal device; the second terminal device reconstructs the RLC bearer corresponding to the first SRB of the first terminal device, the RLC bearer of the first SRB includes the RLC bearer between the first terminal device and the second terminal device and the second RLC bearer between the first terminal device and the second network device, the second network device is the network device accessed by the second terminal device; the second terminal device sends an RRC re-establishment request message to the second network device, the RRC re-establishment request message includes the shortMAC-I; the second terminal device receives the RRC re-establishment message from the second network device through the second RLC bearer; the second terminal device sends the RRC re-establishment message to the first terminal device through the first RLC bearer.

[0038] In combination with the second aspect, in a first optional implementation manner of the second aspect, the second terminal device establishes or reconstructs the RLC bearer of the first SRB corresponding to the first terminal device, including: the second terminal device receives data of the second SRB from the first terminal device, and the second terminal device establishes or reconstructs the RLC bearer of the first SRB; or, the second terminal device receives first indication information from the second network device, and the second terminal device establishes or reconstructs the RLC bearer of the first SRB, wherein the first indication information is used to indicate the establishment of the RLC bearer of the first SRB, or indicates the reception of data of the first SRB sent by the second network device to the first terminal device, or indicates the reception of an RRC re-establishment message sent by the second network device to the first terminal device, or indicates that the first terminal device has sent an RRC re-establishment request message through the second terminal device; or, the second terminal device receives second indication information from the first terminal device, and the second terminal device establishes or reconstructs the RLC bearer of the first SRB, and the second indication information is used to indicate the establishment of the RLC bearer of the first SRB, or indicates the reception of data of the first SRB sent by the second network device to the first terminal device, or indicates the reception of an RRC re-establishment message sent by the second network device to the first terminal device, or indicates that the first terminal device has sent an RRC re-establishment request message through the second terminal device.

[0039] Regarding the technical effects brought about by the second aspect or various optional implementations of the second aspect, reference may be made to the introduction to the technical effects of the first aspect or corresponding implementations.

[0040] In a third aspect, a third communication method is provided, which can be executed by a terminal device, or by a chip system that can implement the functions of the terminal device, or by a larger device including the terminal device. The method includes: a first terminal device communicates with a first network device through a second terminal device, and the second terminal device provides a relay service for the first terminal device; the first terminal device determines that the second terminal device cannot continue to provide a relay service for the first terminal device; the first terminal device enters an RRC idle state; wherein the first terminal device determines that the second terminal device cannot continue to provide a relay service for the first terminal device, including one or more of the following: the first terminal device detects an SL RLF between the first terminal device and the second terminal device; or, the first protocol layer of the first terminal device requests to release the connection between the first terminal device and the second terminal device; or, the connection between the first terminal device and the second terminal device is released.

[0041] If the first terminal device determines that the second terminal device can no longer provide relay services for the first terminal device, the first terminal device can release the connection with the second terminal device and return to the RRC idle state, which is relatively simple to implement and can save power consumption. After the first terminal device returns to the RRC idle state, it can re-establish an RRC connection with the network device, or it can also reselect a terminal device to continue the service of the first terminal device.

[0042] In a fourth aspect, a fourth communication method is provided, which can be executed by a terminal device, or by a chip system that can implement the functions of the terminal device, or by a larger device including the terminal device. The method includes: the second terminal device detects the RLF between the second terminal device and the first network device; the second terminal device initiates RRC re-establishment; the second terminal device does not provide relay service before selecting a suitable cell during the RRC re-establishment process, or before the RRC re-establishment is completed.

[0043] In combination with the fourth aspect, in a first optional implementation of the fourth aspect, the second terminal device does not provide relay service, including: the second terminal device does not send a discovery message related to the relay service, or refuses to establish a connection with a terminal device requesting to provide relay service.

[0044] In combination with the fourth aspect, in a second optional implementation of the fourth aspect, the second terminal device does not provide relay service, and the second terminal device does not provide relay service, including: the second terminal device sends sixth indication information to the first terminal device, and the sixth indication information is used to indicate that the second terminal device is in an RLF state, or indicates that the second terminal device is performing RRC re-establishment, or indicates that the connection between the second terminal device and the first network device is unavailable.

[0045] In combination with the second optional implementation of the fourth aspect, in a third optional implementation of the fourth aspect, the sixth indication information is included in a first message, and the first message is a discovery message, or a message for establishing a connection between terminal devices.

[0046] In combination with the fourth aspect, in a fourth optional implementation of the fourth aspect, the second terminal device does not provide relay service, including: the second terminal device sends a seventh indication information to the first terminal device, and the seventh indication information is used to indicate not to send a connection establishment request message, or to indicate not to perform a PC5 connection establishment process.

[0047] In combination with the fourth optional implementation of the fourth aspect, in a fifth optional implementation of the fourth aspect, the seventh indication information is included in a second message, and the second message is a discovery message, or a message for establishing a connection between terminal devices.

[0048] In combination with the fourth aspect, in a sixth optional implementation of the fourth aspect, the second terminal device does not provide a relay service, including: the second terminal device does not respond to a message from the first terminal device for establishing a connection with the second terminal device.

[0049] In combination with the sixth optional implementation of the fourth aspect, in the seventh optional implementation of the fourth aspect, the method also includes: after the second terminal device selects a new cell or completes RRC re-establishment, responds to a message from the first terminal device for establishing a connection with the second terminal device.

[0050] Regarding the technical effects brought about by the fourth aspect or various optional implementations of the fourth aspect, reference may be made to the introduction to the technical effects of the first aspect or corresponding implementations.

[0051] In a fifth aspect, a communication system is provided, for example, referred to as a first communication system. The first communication system may include the first terminal device described in the first aspect above, or include an electronic device (for example, a chip system) configured in the first terminal device, or include a larger device including the first terminal device; and the first communication system also includes the second terminal device described in the first aspect above, or includes an electronic device (for example, a chip system) configured in the second terminal device, or includes a larger device including the second terminal device. Optionally, the first communication system may also include the third terminal device described in the first aspect above, or include an electronic device (for example, a chip system) configured in the third terminal device, or include a larger device including the third terminal device. The first terminal device and / or the second terminal device include corresponding means (means) or modules for performing the above method.

[0052] For example, the first terminal device is used to initiate RRC re-establishment through a first method when it is determined that the second terminal device cannot continue to provide relay service for the first terminal device, the first method is determined according to the first information, the first method is a method of initiating RRC re-establishment through a Uu interface, or a method of initiating RRC re-establishment through a new terminal device, or a method of initiating RRC re-establishment through the second terminal device; wherein,

[0053] The first terminal device is further used to receive the first information from the first network device through the second terminal device, the first information is used to indicate initiating RRC re-establishment through Uu, or initiating RRC re-establishment through a new terminal device, or initiating RRC re-establishment through the second terminal device; or,

[0054] The first information includes the RSRP of the cell selected by the first terminal device and / or the RSRP of a third terminal device selected by the first terminal device.

[0055] In a sixth aspect, a communication device is provided. The communication device may be the second terminal device described in the second aspect above, or an electronic device (e.g., a chip system) configured in the second terminal device, or a larger device including the second terminal device. The communication device includes corresponding means or modules for executing the above method. For example, the communication device includes a processing unit (sometimes also referred to as a processing module) and a transceiver unit (sometimes also referred to as a transceiver module).

[0056] For example, the transceiver unit is used to receive a shortMAC-I from the first terminal device;

[0057] The processing unit is configured to reconstruct an RLC bearer of a first SRB corresponding to the first terminal device, where the RLC bearer of the first SRB includes an RLC bearer between the first terminal device and the second terminal device and a second RLC bearer between the first terminal device and the second network device, where the second network device is a network device accessed by the second terminal device;

[0058] The transceiver unit is further configured to send an RRC re-establishment request message to the second network device, wherein the RRC re-establishment request message includes the shortMAC-I;

[0059] The transceiver unit is further configured to receive an RRC re-establishment message from the second network device through the second RLC bearer;

[0060] The transceiver unit is further used to send the RRC re-establishment message to the first terminal device through the first RLC bearer.

[0061] For another example, the communication device includes: a processor coupled to a memory, configured to execute instructions in the memory to implement the method performed by the second terminal device in the second aspect. Optionally, the communication device also includes other components, such as an antenna, an input / output module, an interface, etc. These components may be hardware, software, or a combination of software and hardware.

[0062] In a seventh aspect, a communication device is provided. The communication device may be the first terminal device described in the third aspect above, or an electronic device (e.g., a chip system) configured in the first terminal device, or a larger device including the first terminal device. The communication device includes corresponding means or modules for executing the above method. For example, the communication device includes a processing unit (sometimes also referred to as a processing module) and a transceiver unit (sometimes also referred to as a transceiver module).

[0063] For example, the transceiver unit is used to communicate with the first network device through the second terminal device, and the second terminal device provides a relay service for the first terminal device;

[0064] The processing unit is used to determine that the second terminal device cannot continue to provide a relay service for the first terminal device;

[0065] The processing unit is configured to enable the first terminal device to enter an RRC idle state; wherein the processing unit is configured to determine that the second terminal device cannot continue to provide a relay service for the first terminal device through one or more of the following:

[0066] Detecting the SL RLF between the second terminal device; or,

[0067] The first protocol layer of the first terminal device requests to release the connection between the first terminal device and the second terminal device; or,

[0068] The connection with the second terminal device is released.

[0069] For another example, the communication device includes: a processor coupled to a memory, configured to execute instructions in the memory to implement the method performed by the first terminal device in the third aspect. Optionally, the communication device also includes other components, such as an antenna, an input / output module, an interface, etc. These components may be hardware, software, or a combination of software and hardware.

[0070] In an eighth aspect, a communication device is provided. The communication device may be the second terminal device described in the fourth aspect, or an electronic device (e.g., a chip system) configured in the first terminal device, or a larger device including the first terminal device. The communication device includes corresponding means or modules for executing the above method. For example, the communication device includes a processing unit (sometimes also referred to as a processing module) and a transceiver unit (sometimes also referred to as a transceiver module).

[0071] For example, the processing unit is used to detect the RLF between the first network device and the first network device;

[0072] The processing unit is further used to initiate RRC re-establishment (or the processing unit is further used through the transceiver unit);

[0073] The processing unit is further configured to not provide relay service before a suitable cell is selected during the RRC re-establishment process or before the RRC re-establishment is completed.

[0074] For another example, the communication device includes: a processor coupled to a memory, configured to execute instructions in the memory to implement the method performed by the second terminal device in the fourth aspect. Optionally, the communication device also includes other components, such as an antenna, an input / output module, an interface, etc. These components may be hardware, software, or a combination of software and hardware.

[0075] In a ninth aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium is used to store computer programs or instructions, and when the computer-readable storage medium is executed, the methods performed by the terminal device or network device in the above aspects are implemented.

[0076] According to a tenth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the methods described in the above aspects to be implemented.

[0077] In the embodiment of the present application, the first terminal device can select a method for initiating RRC re-establishment, so that the method for initiating RRC re-establishment by the first terminal device is more flexible. Moreover, for example, the first terminal device can select a better method for initiating RRC re-establishment according to factors such as network quality, thereby improving the success rate of RRC re-establishment, improving the service continuity of the first terminal device, and reducing packet loss caused by service discontinuity. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A schematic diagram of a scenario in which a remote UE connects to a network via a relay UE;

[0079] Figure 2A and Figure 2B Two schematic diagrams of the control plane protocol stack architecture of layer 2 relay technology;

[0080] Figure 3A and Figure 3B Schematic diagrams of two application scenarios of the embodiments of the present application;

[0081] Figures 4 to 17 Flowcharts of various communication methods provided in embodiments of the present application;

[0082] Fig.18 A schematic block diagram of a communication device provided in an embodiment of the present application;

[0083] Fig.19 A schematic block diagram of a terminal device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0085] Below, some terms or concepts in the embodiments of the present application are explained to facilitate understanding by those skilled in the art.

[0086] In the embodiment of the present application, the terminal device is a device with wireless transceiver function, which can be a fixed device, a mobile device, a handheld device (such as a mobile phone), a wearable device, a vehicle-mounted device, or a wireless device built into the above device (for example, a communication module, a modem, or a chip system, etc.). The terminal device is used to connect people, objects, machines, etc., and can be widely used in various scenarios, such as but not limited to the following scenarios: cellular communication, device-to-device communication (device-to-device, D2D), vehicle to everything (vehicle to everything, V2X), machine-to-machine / machine-type communication (machine-to-machine / machine-type communications, M2M / MTC), Internet of Things (Internet of Things, IoT), virtual reality (virtual reality, VR), augmented reality (augmented reality, AR), industrial control (industrial control), self-driving, remote medical, smart grid (smart grid), smart furniture, smart office, smart wear, smart transportation, smart city (smart city), drones, robots and other scenarios of terminal devices. The terminal device may sometimes be referred to as user equipment (UE), terminal, access station, UE station, remote station, wireless communication device, or user device, etc. For ease of description, the terminal device is described by taking UE as an example in the embodiments of the present application.

[0087] Among them, when a terminal device is far away from a network device (for example, not within the coverage of the network device), or the terminal device is at the edge of the coverage of the network device, or the link quality between the terminal device and the network device is poor, or the terminal device cannot be directly served by the network device, or the terminal device is not equipped with a Uu interface, or the terminal device has low power, or the terminal device is in energy-saving mode, or the terminal device hopes to save power consumption, etc., the terminal device can communicate with the network device through a relay terminal device (UE-to-Network Relay UE). In an embodiment of the present application, a relay terminal device may also be referred to as a relay user device (relay UE), and a relay terminal device may be a terminal device that provides network access to a remote terminal device. A remote terminal device may also be referred to as a remote user device (remote UE). In other words, a remote UE refers to a UE that requires other UEs to provide relay services in order to access the network; a relay UE refers to a UE that provides relay services to other UEs. The relay service provided by the relay UE to the remote UE can be understood as follows: information sent by the remote UE to the network device is forwarded to the network device through the relay UE, and information sent by the network device to the remote UE is also forwarded to the remote UE through the relay UE.

[0088] The network device in the embodiment of the present application includes, for example, an access network device and / or a core network device. The access network device is a device with a wireless transceiver function, which is used to communicate with the terminal device. The access network device includes but is not limited to the base station (BTS, Node B, eNodeB / eNB, or gNodeB / gNB) in the above-mentioned communication system, a transmission reception point (TRP), a base station of the subsequent evolution of the third generation partnership project (3GPP), an access node in the wireless fidelity (Wi-Fi) system, a wireless relay node, a wireless backhaul node, etc. The base station can be: a macro base station, a micro base station, a micro-micro base station, a small station, a relay station, etc. Multiple base stations can support the same access technology mentioned above, or they can support the networks of different access technologies mentioned above. The base station may include one or more co-station or non-co-station transmission reception points. The network device may also be a wireless controller, a centralized unit (CU), and / or a distributed unit (DU) in a cloud radio access network (CRAN) scenario. The network device can also be a server, a wearable device, or a vehicle-mounted device. For example, the network device in the vehicle to everything (V2X) technology can be a road side unit (RSU). The following describes the access network device taking the base station as an example. The base station can communicate with the terminal device, or it can communicate with the terminal device through a relay station. The terminal device can communicate with multiple base stations in different access technologies. The core network device is used to implement functions such as mobility management, data processing, session management, policy and billing. The names of the devices that implement the core network functions in systems with different access technologies may be different, and the embodiments of the present application do not limit this. Taking the 5G system as an example, the core network device includes: access and mobility management function (AMF), session management function (SMF), policy control function (PCF) or user plane function (UPF), etc.

[0089] In the embodiment of the present application, the communication device for realizing the function of the network device may be a network device, or may be a device capable of supporting the network device to realize the function, such as a chip system, which may be installed in the network device. In the technical solution provided in the embodiment of the present application, the technical solution provided in the embodiment of the present application is described by taking the device for realizing the function of the network device as an example that the network device is used as the device.

[0090] Device-to-device (D2D) communication based on cellular networks, also known as proximity service (ProSe) in the 3rd generation partnership project (3GPP), is a technology that allows terminal devices to communicate directly under the control of the network. It can increase the spectrum efficiency of cellular communication systems, reduce the transmission power of terminal devices, and to a certain extent solve the problem of scarce spectrum resources in wireless communication systems.

[0091] ProSe Direct Communication: Direct communication between two or more ProSe-enabled UEs in close proximity without passing through any network nodes. ProSe Direct Communication can be implemented through the sidelink communication access layer function.

[0092] 5G ProSe Direct Communication: Direct communication between two or more adjacent ProSe-enabled UEs without going through any network nodes, using NR technology.

[0093] ProSe UE-to-Network Relay (hereinafter referred to as relay UE), or 5G ProSe UE-to-Network Relay, is a UE that provides the function of supporting remote UE to connect to the network.

[0094] Sidelink communication: Direct communication between two or more adjacent UEs without going through any network nodes.

[0095] For example, you can refer to Figure 1 , is a schematic diagram of a scenario in which a remote UE connects to a network through a relay UE. Figure 1In the example, the core network accessed by the relay UE is the 5G core network (5G core, 5GC) or the evolved packet core network (evolved packet core, EPC). The remote UE and the relay UE can use NR sidelink communication or sidelink communication at the PC5 interface. The remote UE and the relay UE are connected through the PC5 interface, and the relay UE and the radio access network (radio access network, RAN) are connected through the Uu interface.

[0096] SL transmission is carried out between a pair of source and destination. The source can be identified by the source layer 2 identity (ID), and the destination can be identified by the destination layer-2 ID. The source layer-2 ID can be used to identify the sender of the data in the SL communication, and the destination layer-2 ID can be used to identify the target or receiver of the data in the SL communication. The sender refers to the source of the SL communication (or a media access control (MAC) protocol data unit (PDU)), and the receiver refers to the destination of the SL communication (or a MAC PDU).

[0097] NR sidelink communication is the access layer function that enables vehicle to everything (V2X) communication between two or more UEs. Using NR technology, it does not pass through any network nodes. NR sidelink communication can also enable 5G ProSe Direct Communication.

[0098] PC5 reference point / interface, reference point / interface between UEs.

[0099] Uu reference point / interface, a reference point / interface between the UE and a radio access network (e.g., next generation (NG)-RAN, evolved universal mobile telecommunications system terrestrial radio access network (E-UTRAN)).

[0100] A PC5-radio resource control (RRC) connection is a logical connection between two UEs in a source and destination pair. After a PC5 unicast link is established between the two UEs, a corresponding PC5-RRC connection is established. There is a one-to-one correspondence between a PC5-RRC connection and a PC5 unicast link.

[0101] Currently, UE relay technology includes layer 2 relay technology and layer 3 relay technology.

[0102] Layer 2 relay technology is also called Layer 2 UE-to-Network Relay (L2 UE-to-Network Relay). In the Layer 2 relay technology, the remote UE can establish an RRC connection with the base station through the relay UE, and the remote UE is controlled by the serving cell of the relay UE.

[0103] For reference Figure 2A or Figure 2B, which are two schematic diagrams of the control plane protocol stack architecture of layer 2 UE-to-Network Relay. The control plane data between the remote terminal device and the wireless access network device is forwarded on the radio link control (RLC) layer or adaptation layer through the relay terminal device. The service data adaptation layer (SDAP), packet data convergence protocol (PDCP) layer and RRC layer on the Uu interface of the remote terminal device are end-to-end connected between the remote terminal device and the wireless access network device. The RLC layer, MAC layer and physical (PHY) layer are end-to-end between the remote terminal device and the relay terminal device, and between the relay terminal device and the wireless access network device. After the relay terminal device and the remote terminal device respectively establish corresponding RLC entities and logical channels, and the relay terminal device and the wireless access network device respectively establish corresponding RLC entities and logical channels, the control signaling between the remote terminal device and the wireless access network device can be transmitted. The Uu radio bearer (RB) of the remote terminal device is transmitted through the RLC bearer between the remote terminal device and the relay terminal device and the RLC bearer between the relay terminal device and the access network device. The adaptation layer on the Uu interface is used to identify the remote terminal device and the Uu RB of the remote terminal device. Figure 2A In the PC5 interface, the adaption layer is not supported. Figure 2B In the case of IEEE 802.11ac, the PC5 interface can support the adaptation layer. Figure 2A or Figure 2B The RLC channel here refers to RLC channel.

[0104] Uu RB refers to the RB between the UE and the access network device. The Uu RB of the remote terminal device described in this article can also be called the end-to-end radio bearer of the remote terminal device. At the access layer, RB defines the data packet processing method, and an RB provides services for data packets in the same data packet processing method. RB is divided into signaling radio bearer (SRB) and data radio bearer (DRB). Among them, SRB is used to transmit control plane data, and can also be used to transmit RRC messages and non-access stratum (NAS) messages. DRB is used to transmit user plane data. The PDCP sublayer provides RB to the SDAP sublayer.

[0105] Layer 3 relay technology is also called Layer 3 UE-to-Network Relay (L3 UE-to-Network Relay). In layer 3 relay technology, the relay terminal device performs relaying based on the Internet protocol (IP) layer. There is no equivalent protocol layer between the base station and the remote terminal device. Therefore, the access network device cannot sense the existence of the remote terminal device, but can only sense the existence of the relay terminal device. In other words, when the information sent by the remote terminal device reaches the access network device, the access network device does not parse it and directly forwards it to the core network device. In this case, it can be considered that the remote terminal device communicates with the core network device through the relay terminal device.

[0106] In addition, the embodiments of the present application also involve SL RLF, which is briefly introduced below.

[0107] Once situation 1 occurs, the UE considers that an RLF with a certain destination has been detected, and that the PC5-RRC connection with the destination has been released, then the UE's physical layer may indicate to the upper layer of the UE's RRC layer that the PC5-RRC connection with the destination has been released (that is, PC5 is unavailable). In this case, if the UE is in the RRC connection (RRC_CONNECTED) state, the UE sends a sidelink UE information NR (sidelink UE information NR) message to the base station, which includes a sidelink failure list (sl-FailureList), and the sl-FailureList includes one or more SL-Failure information elements (information element, IE), wherein each SL-Failure IE may include an SL destination identity IE (sl-DestinationIdentity IE) and an sl-Failure, and the sl-Failure included in the SL-Failure IE may also be regarded as an IE, or as an information. Among them, sl-DestinationIdentity is used to indicate the destination information of the unicast connection where the SL failure occurs, and sl-Failure is used to indicate the cause of the SL failure. The UE can set the value of the sidelink target identity (sl-DestinationIdentity) in the SL-Failure to the destinationidentity of the destination, and can set the value of the sl-Failure in the SL-Failure IE to rlf. Setting the value of sl-Failure to rlf can be used to indicate that the cause of the SL failure is the occurrence of SL RLF.

[0108] Among them, situation 1 can be any one of the following four situations: 1. The number of sidelink RLC retransmissions of the UE's destination reaches the maximum number; 2. The timer T400 of the destination times out; 3. The number of discontinuous transmissions (DTX) of the hybrid automatic repeat request (HARQ) connection of the destination reaches the maximum number; 4. The SL-signaling radio bearer (SRB) 2 or SL-SRB3 integrity check of the destination fails.

[0109] In the embodiments of the present application, the number of nouns, unless otherwise specified, means "singular noun or plural noun", that is, "one or more". "At least one" means one or more, and "plural" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. For example, A / B means: A or B. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c means: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, c can be single or multiple.

[0110] The ordinal numbers such as "first" and "second" mentioned in the embodiments of the present application are used to distinguish multiple objects, and are not used to limit the size, content, order, timing, priority or importance of multiple objects. For example, the first RSRP threshold and the second RSRP threshold can be the same RSRP threshold or different RSRP thresholds, and this name does not indicate the difference in the amount of information, value, priority or importance of the two RSRP thresholds. In addition, the numbering of the steps in the various embodiments introduced in the present application is only to distinguish different steps, and is not used to limit the order of the steps. For example, step S501 may occur before step S502, or may occur after S502, or may occur at the same time as S502.

[0111] For reference Figure 3A , is a schematic diagram of an application scenario of an embodiment of the present application. Figure 3AIn the example, the remote terminal device is connected to the relay terminal device, and the remote terminal device can communicate with the network device through the relay terminal device. Figure 3B , is a schematic diagram of another application scenario of the embodiment of the present application. Figure 3B In the process, the remote terminal device is connected to the relay terminal device, and the remote terminal device can communicate with the network device through the relay terminal device. Figure 3A and Figure 3B The difference is that Figure 3A In the case of a remote terminal device being within the coverage area (in-coverage), Figure 3B In the case of a wireless access control, the remote terminal device is out-of-coverage.

[0112] Figure 3A or Figure 3B The network device in the example is an access network device, and the access network device is, for example, a base station. Among them, the access network device corresponds to different devices in different systems. For example, in a 4G system, it can correspond to an eNB, and in a 5G system, it corresponds to an access network device in 5G, such as a gNB. Of course, the technical solution provided in the embodiment of the present application can also be applied to future mobile communication systems, so Figure 3A or Figure 3B The access network device in the embodiment of the present application may also correspond to a network device in a future mobile communication system. In the embodiment of the present application, the access network device is a base station as an example. In fact, referring to the introduction in the foregoing text, the access network device may also be a device such as an RSU.

[0113] The method provided by the embodiment of the present application is introduced below in conjunction with the accompanying drawings. In the accompanying drawings corresponding to the various embodiments of the present application, all optional steps are represented by dotted lines. In the various embodiments of the present application, the RLC bearer is the lower layer part of the wireless bearer, and the RLC bearer configuration is the lower layer part of the wireless bearer configuration, including RLC configuration and logical channel configuration. Establishing an RLC bearer includes establishing an RLC entity and configuring a corresponding logical channel, and releasing an RLC bearer includes releasing an RLC entity and releasing a corresponding logical channel. In addition, for ease of understanding, in the following text, remote UE and relay UE are used for description. The "remote UE" mentioned below can be replaced by a "first terminal device", the "relay UE" or "relay UE 1" mentioned below can be replaced by a second terminal device, and the "new relay UE" or "relay UE 2" mentioned below can be replaced by a third terminal device. The various embodiments of the present application are applicable to Figure 2A or Figure 2B The control plane protocol stack architecture shown.

[0114] The present application embodiment provides a first communication method, see Figure 4, which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0115] S401. A remote UE communicates with a first network device through a relay UE.

[0116] For example, if the remote UE is far away from the network device (for example, it is not within the coverage of the network device), or the remote UE is at the edge of the coverage of the network device, or the link quality between the remote UE and the network device is poor, or the remote UE cannot be directly served by the network device, or the remote UE is not equipped with a Uu interface, or the remote UE has low battery, or the remote UE is in energy-saving mode, or the remote UE wants to save power consumption, etc., then the remote UE can access the network through the relay UE, and the relay UE provides relay service for the remote UE. The remote UE can establish an RRC connection with the first network device through the relay UE. When the remote UE is in the RRC connection state, data can be transmitted to the first network device through the relay UE.

[0117] For example, the remote UE may send first data to the relay UE, and the first data needs to be sent to the first network device. Then, after the relay UE receives the first data from the remote UE, it sends the first data to the first network device. For another example, the first network device sends second data to the relay UE, and the second data needs to be sent to the remote UE. Then, after the relay UE receives the second data from the first network device, it may send the second data to the remote UE. In this way, the remote UE and the first network device achieve communication through the relay UE.

[0118] S402, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE. In various embodiments of the present application, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, which can also be understood as the remote UE determining that a link failure occurs between the remote UE and the first network device, or the remote UE determines that the link fails, or the remote UE determines that normal communication is impossible, or the remote UE determines that the RRC connection needs to be reestablished.

[0119] For example, if the remote UE detects SL RLF between the remote UE and the relay UE, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the first protocol layer of the remote UE requests to release the connection between the remote UE and the relay UE, the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the connection between the remote UE and the relay UE is released, the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the relay UE detects Uu RLF between the relay UE and the first network device, the relay UE may send a third indication message to the remote UE, and the third indication message may indicate RRC re-establishment (in this case, the third indication message may also be referred to as RRC re-establishment indication message), or may indicate that the relay UE has RLF (in this case, the third indication message may also be referred to as RLF indication message). After the remote UE receives the third indication message, it may determine that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the relay UE detects Uu RLF between the relay UE and the first network device, the relay UE may initiate RRC connection re-establishment, for example, the relay UE may perform cell selection. If the relay UE selects a suitable cell, the relay UE may send the identifier of the cell to the remote UE. After the remote UE receives the identifier of the cell, it may determine that the relay UE cannot continue to provide relay services for the remote UE. The above specific contents will be introduced in the corresponding embodiments below.

[0120] Alternatively, the remote UE may also determine in other ways that the relay UE cannot continue to provide relay services for the remote UE. The connection between the remote UE and the relay UE is, for example, a PC5-RRC connection or a PC5 unicast link, and the first protocol layer is, for example, a PC5-S layer, or may be other protocol layers in the remote UE.

[0121] S403: The remote UE initiates RRC re-establishment in the first manner.

[0122] The first method is, for example, a method of initiating RRC re-establishment through the Uu interface, or a method of initiating RRC re-establishment through a new relay UE, or a method of continuing to initiate RRC re-establishment through the relay UE. In various embodiments of the present application, the method of initiating RRC connection re-establishment through the Uu interface means that the remote UE is directly connected to the network device, and is not connected to the network device through the relay UE, that is, the RB of the remote UE is transmitted through the RLC bearer between the remote UE and the network device. In various embodiments of the present application, the method of initiating RRC connection re-establishment through a new relay UE means that the remote UE is connected to the network device through the new relay UE, and can be used Figure 2A or Figure 2B The layer 2 relay protocol stack architecture shown in the figure, wherein the RB of the remote UE is transmitted through the sidelink RLC bearer between the remote UE and the new relay UE and the RLC bearer between the new relay UE and the network device. In various embodiments of the present application, the method of initiating RRC connection reestablishment through the relayUE refers to the remote UE connecting to the network device through the relay UE and using Figure 2A or Figure 2B The layer 2 relay protocol stack architecture shown in the figure, wherein the RB of the remote UE is transmitted via the sidelink RLC bearer between the remote UE and the relay UE and the RLC bearer between the relay UE and the network device.

[0123] For example, if the remote UE detects SL RLF between the remote UE and the relay UE, or the first protocol layer of the remote UE requests to release the connection between the remote UE and the relay UE, or the connection between the remote UE and the relay UE is released, the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE, and the first method may be, for example, a method of initiating RRC re-establishment through the Uu interface, or a method of initiating RRC re-establishment through a new relay UE. For another example, if the relay UE detects Uu RLF between the relay UE and the first network device, the relay UE may send a third indication message to the remote UE, and the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE based on the third indication message, and the first method may be, for example, a method of initiating RRC re-establishment through the Uu interface, or a method of initiating RRC re-establishment through a new relay UE, or a method of continuing to initiate RRC re-establishment through the relay UE.

[0124] The first method is determined, for example, based on the first information. As an optional implementation, the first information may be specified by a protocol. For example, the protocol specifies that if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE initiates RRC re-establishment through the Uu interface, or initiates RRC re-establishment through a new relay UE, or continues to initiate RRC re-establishment through the relay UE. In other words, if the first information is specified in the protocol, the remote UE may not have to perform the step of determining the first method. Accordingly, in fact, the embodiment of the present application may not involve the first information, and the remote UE only needs to perform corresponding operations according to the provisions of the protocol.

[0125] As another optional implementation, the first information may come from a network device. For example, in the process of the remote UE communicating with the first network device through the relay UE, the first network device sends the first information to the remote UE through the relay UE, and accordingly, the remote UE receives the first information from the first network device through the relay UE. The first information may indicate that RRC re-establishment is initiated through the Uu interface, or indicates that RRC re-establishment is initiated through a new relay UE, or indicates that RRC re-establishment is initiated through the relay UE. Then the remote UE may determine the first method according to the indication of the first information, thereby initiating RRC re-establishment.

[0126] If the first information adopts any of the above two methods, for example, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE based on the third indication information, then after the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, it can initiate RRC re-establishment through the Uu interface, or initiate RRC re-establishment through a new relay UE, or continue to initiate RRC re-establishment through the relay UE. If the remote UE does not initiate RRC re-establishment through the relay UE (for example, the remote UE initiates RRC re-establishment through the Uu interface, or initiates RRC re-establishment through a new relay UE), then optionally, the remote UE can also send information to the relay UE, the information, for example, indicating not to perform RRC re-establishment through the relay UE, or the information, for example, indicating to release the PC5 unicast link between the remote UE and the relay UE, or the information, for example, indicating to release the PC5-RRC connection between the remote UE and the relay UE. After receiving the information, the relay UE can determine that the remote UE does not re-establish the RRC through the relay UE.

[0127] As another optional implementation, the first information may be obtained by the remote UE. For example, the first information includes the reference signal receiving power (RSRP) of the cell selected by the remote UE, or the first information includes the RSRP of the new relay UE selected by the remote UE, or the first information includes the RSRP of the cell selected by the remote UE and the RSRP of the new relay UE selected by the remote UE. In various embodiments of the present application, the RSRP of the relay UE is, for example, the SL-RSRP of the relay UE, or the RSRP corresponding to the discovery message from the relay UE.

[0128] For example, if the remote UE selects a suitable cell, and the RSRP of the selected cell is less than or equal to the first RSRP threshold, but the remote UE does not select a new relay UE, the first method is to re-establish RRC through the Uu interface, and the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, and the RSRP of the selected cell is less than or equal to the first RSRP threshold, the first method is to re-establish RRC through the Uu interface, and the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, and the RSRP of the selected cell is less than or equal to the first RSRP threshold, and the remote UE selects a new relay UE, the first method is to re-establish RRC through the new relay UE, and the remote UE can re-establish RRC through the new relay UE. Alternatively, if the remote UE selects a suitable cell but fails to select a new relay UE, the first method is to re-establish RRC through the Uu interface, and the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, and the RSRP of the selected cell is greater than the first RSRP threshold, the first method is to re-establish RRC through the Uu interface, and the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, and the remote UE cannot serve as a remote terminal device, or the remote UE cannot communicate with the network through other UEs, the first method is to re-establish RRC through the Uu interface, and the remote UE can re-establish RRC through the Uu interface.

[0129] For another example, if the remote UE selects a new relay UE and fails to select a suitable cell, the first method is to reestablish RRC through the new relay UE, and the remote UE can reestablish RRC through the new relay UE. Alternatively, if the remote UE selects a new relay UE and a suitable cell, and the difference between the RSRP of the selected cell and the RSRP of the new relay UE is less than or equal to the first RSRP threshold, indicating that the signal quality will be better if the remote UE reestablishes RRC through the new relay UE, the first method is to reestablish RRC through the new relay UE, and the remote UE can reestablish RRC through the new relay UE.

[0130] The first RSRP threshold may be specified by a protocol, for example, or may be configured by a network device.

[0131] Alternatively, the first method may not be determined based on the first information, but may be determined based on the cell selection process of the remote UE and / or the selection process of the new relay UE. For example, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may perform cell selection and may select a new relay UE. If the remote UE first selects a suitable cell, the first method is a method of initiating RRC re-establishment through the Uu interface, and if the remote UE first selects a new relay UE, the first method is a method of initiating RRC re-establishment through the new relay UE. For another example, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may perform cell selection, and the first method is a method of initiating RRC re-establishment through the Uu interface. If the remote UE fails to initiate RRC re-establishment through the Uu interface, the remote UE may select a new relay UE again, and the first method is a method of initiating RRC re-establishment through the new relay UE. These specific contents will be introduced in other embodiments below.

[0132] In various embodiments of the present application, the remote UE initiates RRC re-establishment, for example, including the remote UE sending an RRC re-establishment request message. For example, the remote UE initiates RRC re-establishment through the Uu interface, which may include the remote UE sending an RRC re-establishment request message to the corresponding network device through the Uu interface; for another example, the remote UE initiates RRC re-establishment through a new relay UE, which may include the remote UE sending an RRC re-establishment request message to the network device corresponding to the service cell of the new relay UE through the new relay UE; for another example, the remote UE initiates RRC re-establishment through the original relay UE, which may include the remote UE sending an RRC re-establishment request message to the network device corresponding to the service cell of the original relay UE through the original relay UE.

[0133] It should be noted that in various embodiments of the present application, the new relay UE (e.g., relay UE 2 in the following text) selected by the remote UE and the original relay UE (e.g., relay UE 1 in the following text) may be the same UE or different UEs. In addition, the specific process of the remote UE initiating RRC re-establishment will also be introduced in other embodiments in the following text.

[0134] In an embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE can initiate RRC re-establishment to restore the remote UE's service as soon as possible. Moreover, the remote UE can choose a method to initiate RRC re-establishment, such as initiating RRC re-establishment through the Uu interface, or initiating RRC re-establishment through a new relay UE, or continuing to initiate RRC re-establishment through the original relay UE, etc., so that the remote UE can initiate RRC re-establishment in a more flexible manner. Moreover, for example, the remote UE can choose a better method to initiate RRC re-establishment based on factors such as network quality, thereby improving the success rate of RRC re-establishment, improving the service continuity of the first terminal device, and reducing packet loss caused by service discontinuity.

[0135] Next, the present application embodiment provides a second communication method, please refer to Figure 5 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0136] S501. A remote UE communicates with a first network device through a relay UE.

[0137] For more information about S501, please refer to Figure 4 Introduction of S401 in the illustrated embodiment.

[0138] S502: The remote UE determines that the relay UE cannot continue to provide relay service for the remote UE.

[0139] For example, if the remote UE detects SL RLF between the remote UE and the relay UE, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the first protocol layer of the remote UE requests to release the connection between the remote UE and the relay UE, the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE. For another example, if the connection between the remote UE and the relay UE is released, the remote UE may determine that the relay UE cannot continue to provide relay services for the remote UE. Alternatively, the remote UE may also determine that the relay UE cannot continue to provide relay services for the remote UE in other ways. Among them, the connection between the remote UE and the relay UE is, for example, a PC5-RRC connection or a PC5 unicast link, and the first protocol layer is, for example, a PC5-S layer, or it may also be other protocol layers within the remote UE.

[0140] The embodiments of the present application can be Figure 4 The embodiments shown in the figure are combined with the application, for example, the embodiments of the present application can be regarded as Figure 4 If this is the case, then after S502, the remote UE may determine the first mode. For details on how the remote UE determines the first mode, please refer to Figure 4 For example, in the embodiment of the present application, the first method determined by the remote UE is to initiate RRC re-establishment through the Uu interface. Figure 4 The embodiments shown may also not be combined, but applied separately. In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the remote UE does not need to select a method of initiating RRC re-establishment, but initiates RRC re-establishment through the Uu interface.

[0141] It can be seen that in the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE does not need to reselect a new relay UE, nor does it need to initiate RRC re-establishment through the original relay UE. Instead, it initiates RRC re-establishment through the Uu interface by itself, which reduces the probability of service interruption of the remote UE due to the inability of the network device to configure a new relay UE, and also reduces the probability of failure when performing RRC re-establishment through the original relay UE, thereby improving the service continuity of the remote UE and reducing the packet loss caused by the service interruption of the remote UE. The following describes the process of the remote UE performing RRC re-establishment through the Uu interface.

[0142] S503: The remote UE starts a first timer. The first timer may be stopped when the remote UE selects a suitable cell.

[0143] For example, once the remote UE initiates RRC re-establishment, the first timer is started; or, once the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the remote UE will perform cell selection, then before performing cell selection, the remote UE starts the first timer. Alternatively, the remote UE may also start the first timer in other circumstances. The first timer is, for example, timer T311, or may also be other timers.

[0144] S504, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. In various embodiments of the present application, the second SRB is, for example, SRB0, or may be other SRBs. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0145] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0146] S505: The remote UE performs cell selection.

[0147] S506: The remote UE selects a suitable cell.

[0148] For example, the cell selected by the remote UE is called the first cell, and the first cell corresponds to the second network device. In various embodiments of the present application, a cell corresponds to a network device, which can be understood as the network device providing services for the cell, for example, the network device is an access network device, such as a base station. Taking the first cell corresponding to the second network device as an example, it can be understood that the second network device provides services for the second cell, for example, the second network device is an access network device. Figure 3A or Figure 3B The second network device is not given in the above description, which can be understood as that the second network device can communicate with the remote terminal device. The second network device and the first network device can be the same network device, or can be different network devices. If the remote UE selects a suitable cell, the first timer can be stopped. Enter S508.

[0149] S507: If the first timer times out, the remote UE returns to the RRC idle (RRC_IDLE) state, and the process ends.

[0150] Among them, S506 and S507 are two parallel solutions, and one of the solutions is executed according to the cell selection situation of the remote UE.

[0151] S508. The remote UE establishes an RLC bearer of SRB0.

[0152] For example, the remote UE may apply the common control channel (CCCH) configuration specified by the protocol to establish the RLC bearer of SRB0, and this configuration may be referred to as a specified configuration.

[0153] Alternatively, the RLC bearer of SRB0 may always exist and does not need to be established, and the remote UE may not execute S508. Therefore, S508 is an optional step.

[0154] S509: The remote UE determines a value of short MAC-I (shortMAC-I).

[0155] The remote UE performs RRC reestablishment and needs to send an RRC reestablishment request message to the second network device corresponding to the selected first cell, and the RRC reestablishment request message includes shortMAC-I, so the remote UE needs to determine the value of shortMAC-I. For example, the remote UE can determine the value of shortMAC-I according to the identifier of the first cell (such as the ID of the first cell, etc.).

[0156] S510: The remote UE establishes or reestablishes a PDCP entity of the first SRB. In various embodiments of the present application, the first SRB is, for example, SRB1, or may be other SRBs. In the embodiment of the present application, the first SRB is SRB1 as an example.

[0157] S511. The remote UE establishes or reestablishes the SL RLC bearer of SRB1.

[0158] S512: The remote UE applies the default configuration of SRB1. The default configuration may be specified in the protocol.

[0159] S513. The remote UE restores SRB1.

[0160] The remote UE may have suspended SRB1 in S504, and the remote UE needs to send an RRC re-establishment request message to the second network device corresponding to the selected first cell for RRC re-establishment. After receiving the RRC re-establishment request message, the second network device needs to send an RRC re-establishment message (RRC reestablishment) to the remote UE, and the RRC re-establishment message will be transmitted through SRB1. Therefore, the remote UE needs to restore SRB1 before receiving the RRC re-establishment message.

[0161] S514: The remote UE sends an RRC re-establishment request message to the second network device, and correspondingly, the second network device receives the RRC re-establishment request message from the remote UE. The RRC re-establishment request message may be transmitted via SRB0 of the remote UE.

[0162] S515: The second network device sends an RRC reestablishment message to the remote UE, and correspondingly, the remote UE receives the RRC reestablishment message from the second network device. The RRC reestablishment message may be transmitted via SRB1 of the remote UE.

[0163] S516: The remote UE sends an RRC reestablishment complete message to the second network device. Correspondingly, the second network device receives the RRC reestablishment complete message from the remote UE.

[0164] Through the above process, the remote UE completes the RRC re-establishment process through the Uu interface. Afterwards, the second network device can establish the RB of the remote UE through the RRC reconfiguration process, or modify the RB of the remote UE, or release the RB of the remote UE, etc., so as to restore the data transmission of the remote UE.

[0165] In an embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the remote UE can initiate RRC re-establishment through the Uu interface, which is equivalent to the remote UE being able to re-establish the RRC connection with the network device by itself without selecting a new relay UE, thereby reducing the probability that the remote UE's service cannot continue due to the inability to configure the new relay UE, improving the service continuity of the remote UE, and reducing packet loss caused by service discontinuity.

[0166] Next, the present application embodiment provides a third communication method, see Figure 6 , which is the flow chart of this method. Figure 5 The embodiment shown is different in that Figure 6 In the embodiment shown, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may select a new relay UE and access the network through the new relay UE. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B The relay UE 2 and the second network device described below are Figure 3A or Figure 3B Not drawn in the middle.

[0167] S601. A remote UE communicates with a first network device through relay UE 1.

[0168] For more information about S601, please refer to Figure 4 S401 in the illustrated embodiment.

[0169] S602: The remote UE determines that relay UE 1 cannot continue to provide relay service for the remote UE.

[0170] For information on the circumstances under which the remote UE may determine that relay UE 1 is unable to continue to provide relay services for the remote UE, see Figure 5 S502 in the illustrated embodiment.

[0171] The embodiments of the present application can be Figure 4 The embodiments shown in the figure are combined with the application, for example, the embodiments of the present application can be regarded as Figure 4 If this is the case, then after S602, the remote UE may determine the first mode. For details on how the remote UE determines the first mode, please refer to Figure 4 For example, in the embodiment of the present application, the first method determined by the remote UE is to initiate RRC re-establishment through a new relay UE. Alternatively, the embodiment of the present application is similar to Figure 4 The embodiments shown may also not be combined, but applied separately. In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the remote UE does not need to choose to initiate RRC re-establishment, but initiates RRC re-establishment through a new relay UE.

[0172] It can be seen that in the embodiment of the present application, if the remote UE determines that relay UE 1 cannot continue to provide relay services for the remote UE, the remote UE can select a new relay UE to initiate RRC re-establishment through the new relay UE. In other words, if the remote UE determines that relay UE 1 cannot continue to provide relay services for the remote UE, the remote UE can select a new relay UE to resume the service, which improves the service continuity of the remote UE and reduces the packet loss caused by the service interruption of the remote UE. The following introduces the process of the remote UE selecting a new relay UE and re-establishing RRC through the new relay UE.

[0173] S603: The remote UE starts a second timer. The second timer may be stopped when the remote UE selects a new relay UE.

[0174] For example, once the remote UE initiates RRC re-establishment, the second timer is started; or, once the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the second timer is started; or, before the remote UE selects a new relay UE, the second timer is started. Alternatively, the remote UE may also start the second timer in other circumstances. The second timer may be, for example, timer T311, or may be other timers.

[0175] S604, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. The second SRB is, for example, SRB0, or may be another SRB. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0176] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0177] S605: The remote UE selects or reselects a new relay UE.

[0178] For example, the remote UE may measure other relay UEs, etc., to reselect a UE that can provide relay service for the remote UE as a new relay UE.

[0179] S606: The remote UE stops the second timer.

[0180] For example, if the remote UE selects a new relay UE, the second timer can be stopped. Hereinafter, the new relay UE is referred to as a third terminal device, or relay UE 2. For another example, if the remote UE selects relay UE 2 and the remote UE has established a connection with relay UE 2, the second timer can be stopped. The connection between the remote UE and relay UE 2 is, for example, a PC5-RRC connection or a PC5 unicast link. For another example, if the remote UE selects relay UE 2 and the remote UE obtains the identifier of the serving cell of relay UE 2, the second timer can be stopped.

[0181] In addition, no matter under what circumstances the remote UE stops the second timer, after stopping the second timer or when stopping the second timer, the remote UE can start a third timer, and the third timer is, for example, timer T301, or may be other timers. For example, the third timer is not timer T301, and the timing duration of the third timer is greater than or equal to the timing duration of timer T301. The third timer can be used for the remote UE to receive the RRC re-establishment message.

[0182] The remote UE may first establish a connection with the relay UE 2, and then obtain the identification of the serving cell of the relay UE 2 from the relay UE 2 after the connection is established. Alternatively, the remote UE may obtain the identification of the serving cell of the relay UE 2 from the relay UE 2 before establishing a connection with the relay UE 2. Alternatively, the remote UE may obtain the identification of the serving cell of the relay UE 2 from the relay UE 2 during the process of establishing a connection with the relay UE 2. The identification of the cell is, for example, the ID of the cell.

[0183] For example, the relay UE may send the ID of the service cell of the relay UE via a 5G ProSe Direct Communication message or a PC5 direct discovery message. For example, a cell ID announcement request procedure is performed between the remote UE and the relay UE, the remote UE sends a CELL_ID_ANNOUNCEMENT_REQUEST message to the relay UE 2, and after the relay UE receives the message, it sends a cell ID notification response (CELL_ID_ANNOUNCEMENT_RESPONSE) message to the remote UE, wherein the CELL_ID_ANNOUNCEMENT_RESPONSE message may include or indicate the ID of the service cell of the relay UE 2. Alternatively, the relay UE 2 sends a relay discovery additional information message, which includes or indicates the ID of the service cell of the relay UE 2, and the remote UE may obtain the ID of the service cell of the relay UE 2 after receiving the message.

[0184] If the remote UE stops the second timer when it selects a new relay UE, or the remote UE stops the second timer when it selects relay UE 2 and completes establishing a connection with relay UE 2, the process proceeds to S608; or, if the remote UE stops the second timer when it selects relay UE 2 and obtains the identifier of the serving cell of relay UE 2, the process proceeds to S609.

[0185] S607: If the second timer times out, the remote UE returns to the RRC idle state and the process ends.

[0186] S606 and S607 are two parallel solutions, and one of the solutions is executed according to the selection of the relay UE by the remote UE.

[0187] S608: The remote UE obtains the identifier of the serving cell of the relay UE 2.

[0188] If the remote UE wants to perform RRC re-establishment through relay UE 2, the remote UE will initiate the transmission of an RRC re-establishment request message. The RRC re-establishment request message contains shortMAC-I, and the remote UE needs to calculate shortMAC-I based on the ID of the cell that initiates the RRC re-establishment. Since the remote UE performs RRC re-establishment through relay UE 2, the cell that initiates the RRC re-establishment is the serving cell of relay UE 2, so the remote UE needs to obtain the ID of the serving cell of relay UE 2.

[0189] If the remote UE stops the second timer when a new relay UE is selected, or the remote UE stops the second timer when the relay UE 2 is selected and the connection with the relay UE 2 is established, the remote UE has not yet obtained the identifier of the serving cell of the relay UE 2, and the remote UE needs to execute S608. For the method for the remote UE to obtain the identifier of the serving cell of the relay UE 2, refer to the introduction of S606.

[0190] After the remote UE obtains the identifier of the serving cell of relay UE 2, it can determine the shortMAC-I according to the identifier of the serving cell of relay UE 2.

[0191] S609, the remote UE reestablishes the PDCP entity of the first SRB, establishes the first RLC bearer of the first SRB, and restores SRB1. The first RLC bearer of the first SRB is, for example, the SL RLC bearer of the first SRB. The first SRB is, for example, SRB1, or may be another SRB. In the embodiment of the present application, the first SRB is SRB1 as an example.

[0192] After sending the RRC re-establishment request message, the remote UE needs to receive the RRC re-establishment message. The RRC re-establishment message is transmitted through SRB1, so the remote UE can restore SRB1. For example, the remote UE can apply the PDCP default configuration (default configuration) or specified configuration (specified configuration) of SRB1, and the default configuration or specified configuration can be specified by the protocol. Among them, the remote UE can apply the SL RLC default configuration (default configuration) or specified configuration (specified configuration) of SRB1, and the default configuration or specified configuration can be specified by the protocol.

[0193] After the remote UE establishes a PC5 unicast link or a PC5-RRC connection with relay UE 2, if the remote UE wants to initiate RRC re-establishment or RRC connection recovery, then optionally, the remote UE may apply a default configuration or a specified configuration to establish a SL RLC bearer of SRB1 before sending an RRC re-establishment request message or an RRC recovery request message, when sending an RRC re-establishment request message or an RRC recovery request message, or after sending an RRC re-establishment request message or an RRC recovery request message. The SL RLC bearer of the SRB may be a SL RLC bearer that is equivalent to the relay UE (e.g., relay UE 2). Alternatively, if the remote UE wants to initiate RRC connection establishment, the remote UE establishes the SL RLC bearer of SRB1 after receiving indication information 1 of re-establishing the SL RLC bearer of SRB1 or indication information 2 of establishing the SL RLC bearer of SRB1 from the serving cell of relay UE 2 forwarded by relay UE 2. If indication information 1 or indication information 2 indicates configuration information, the remote UE may apply the configuration information to establish the SL RLC bearer of SRB1; if indication information 1 or indication information 2 does not indicate configuration information, the remote UE may apply the default configuration or the specified configuration to establish the SL RLC bearer of SRB1. Indication information 1 or indication information 2 may be sent via an RRC connection establishment message.

[0194] If the remote UE does not initiate the RRC re-establishment process, for example, the remote UE initiates the RRC connection establishment process, then after the remote UE establishes a PC5 unicast link or a PC5-RRC connection with the relay UE 2, and before the remote UE sends an RRC connection establishment request message or when the remote UE sends an RRC connection establishment request message or after the remote UE sends the RRC connection establishment request message, the remote UE may not re-establish the PDCP entity of SRB1, but may establish the SL RLC bearer of SRB1 to restore SRB1, or the remote UE may not re-establish the PDCP entity of SRB1 nor establish the SL RLC bearer of SRB1 to restore SRB1.

[0195] According to the above description, the remote UE can initiate different processes such as RRC re-establishment, RRC connection recovery or RRC connection establishment. The embodiment of the present application takes the remote UE initiating RRC re-establishment as an example.

[0196] S610, the remote UE sends the data of SRB0 to the relay UE 2, and correspondingly, the relay UE 2 receives the data of SRB0 from the remote UE. The data of SRB0 is, for example, an RLC service data unit (SDU), and the RLC PDU may include an RRC re-establishment request message. For example, the remote UE may send the RLC SDU to the relay UE 2 via the SL RLC bearer corresponding to SRB0, and the relay UE 2 receives the RLC SDU. The RLC SDU is to be sent to the second network device, and the second network device is the network device to which the relay UE 2 accesses. The remote UE needs to relay the message to the second network device through the relay UE 2, so the remote UE 2 sends the data of SRB0 to the relay UE 2.

[0197] S611, relay UE 2 establishes or reconstructs the RLC bearer corresponding to SRB1 of the remote UE. For example, relay UE2 may establish or reconstruct the RLC bearer using a default configuration or a specified configuration, and the default configuration or the specified configuration may be specified by a protocol. The RLC bearer of SRB1 may include at least one of the first RLC bearers between the remote UE and relay UE 2, and may also include a second RLC bearer between the remote UE and the second network device. The first RLC bearer is, for example, an SL RLC bearer, and the second RLC bearer is, for example, a Uu RLC bearer.

[0198] Relay UE 2 may establish or reestablish the RLC bearer of SRB1 in different triggering modes, which are described below with examples.

[0199] For example, one triggering method is that after relay UE 2 receives the data of SRB0, it can establish or reconstruct the RLC bearer of SRB1. After relay UE 2 receives the data of SRB0, it can determine that the data is the data of SRB0 of remote UE according to the SL logical channel where the data of SRB0 is located. Optionally, relay UE 2 can establish or reconstruct the RLC bearer of SRB1 after receiving the data of SRB0 and before relay UE 2 sends the data of SRB0 to the second network device or when relay UE 2 sends the data of SRB0 to the second network device or after relay UE 2 sends the data of SRB0 to the second network device. In this triggering method, the RLC bearer of SRB1 established or reconstructed by relay UE 2 may include the SL RLC bearer of SRB1, or include the Uu RLC bearer of SRB1, or include the SL RLC bearer of SRB1 and the Uu RLC bearer of SRB1.

[0200] For another example, another triggering method is that the second network device sends the first indication information to relay UE 2, and accordingly, relay UE 2 receives the first indication information from the second network device, and the first indication information may indicate the establishment or reconstruction of the RLC bearer of SRB1, or indicate the reception of the SRB1 data sent by the second network device to the remote UE, or indicate the reception of the RRC reconstruction message sent by the second network device to the remote UE, or indicate that the remote UE has sent the RRC reconstruction message through relay UE 2, etc. After receiving the first indication information, relay UE 2 can establish or reconstruct the RLC bearer of SRB1. For example, if the first indication information indicates the establishment or reconstruction of the RLC bearer of SRB1, or indicates the reception of data of SRB1 sent by the second network device to the remote UE, or indicates the reception of the RRC reconstruction message sent by the second network device to the remote UE, or indicates that the remote UE has sent an RRC reconstruction message through relay UE 2, then the RLC bearer of SRB1 established or reconstructed by relay UE 2 may include the SL RLC bearer of SRB1, or include the Uu RLC bearer of SRB1, or include the SL RLC bearer of SRB1 and the Uu RLC bearer of SRB1; or, if the first indication information indicates the establishment or reconstruction of the SL RLC bearer of SRB1 (for example, for the SL RLC bearer of SRB1 and the Uu RLC bearer of SRB1, the second network device may indicate through different indication information. If this is the case, the second network device may send only one of the indication information, or may send two indication information. If two indication information are sent, the two indication information may be carried in one message, or may be carried in different messages), then the relay UE 2. The RLC bearer of SRB1 established or rebuilt by relay UE 2 may include the SL RLC bearer of SRB1; or, if the first indication information indicates to establish or rebuild the Uu RLC bearer of SRB1, the RLC bearer of SRB1 established or rebuilt by relay UE 2 may include the Uu RLC bearer of SRB1; or, if the first indication information indicates to establish or rebuild the SL RLC bearer of SRB1 and the Uu RLC bearer of SRB1, the RLC bearer of SRB1 established or rebuilt by relay UE 2 may include the SL RLC bearer of SRB1 and the Uu RLC bearer of SRB1. For example, the second network device may send the first indication information to relay UE 2 after receiving the data of SRB0 forwarded by relay UE2. That is to say, if this triggering method is adopted, relay UE 2 has sent the data of SRB0 in S610 to the second network device, and the second network device has also received the data of SRB0.

[0201] If this triggering method is used, and the first indication information indicates the corresponding configuration (for example, indicating the configuration of the SL RLC bearer of SRB1 and / or the configuration of the Uu RLC bearer of SRB1), the relay UE 2 may establish or re-establish the RLC bearer of SRB1 according to the configuration indicated by the first indication information. If the first indication information does not indicate the configuration, the relay UE 2 may establish or re-establish the RLC bearer of SRB1 according to the default configuration or the specified configuration.

[0202] For another example, another triggering method is that the remote UE sends a second indication message to the relay UE 2, and accordingly, the relay UE 2 receives the second indication message from the remote UE, and the second indication message may indicate the establishment or reconstruction of the RLC bearer of SRB1, or indicate the reception of the data of SRB1 sent by the second network device to the remote UE, or indicate the reception of the RRC reconstruction message sent by the second network device to the remote UE, or indicate that the remote UE has sent the RRC reconstruction message through the relay UE 2, etc. After receiving the second indication message, the relay UE 2 can establish or rebuild the RLC bearer of SRB1. For the relationship between the reconstruction of the RLC bearer by the relay UE 2 and the second indication message, please refer to the introduction of the first indication message. For example, the second indication information may not be carried in the SRB0 data, so the remote UE may first send the SRB0 data to relay UE 2, and then send the second indication information to relay UE 2, or the remote UE may first send the second indication information to relay UE 2, and then send the SRB0 data to relay UE 2, or the remote UE may send the second indication information and SRB0 data to relay UE 2 at the same time; or, the second indication information may also be carried in the SRB0 data, then the remote UE sends the SRB0 data to relayUE 2, and also sends the second indication information. This method can save signaling overhead.

[0203] In addition, for the Uu RLC bearer of SRB1, if the SRB1 of multiple remote UEs reuses the same Uu RLC bearer of the relay UE 2, it is possible that other remote UEs have communicated with the second network device through the relay UE 2, and the relay UE 2 has established the Uu RLC bearer, so the relay UE 2 does not need to establish the Uu RLC bearer. If the relay UE 2 has not established the Uu RLC bearer, the relay UE 2 can establish the Uu RLC bearer.

[0204] It should be noted that if relay UE 2 has not entered the RRC connected state when receiving the data of SRB0 from the remote UE, relay UE 2 may first enter the RRC connected state and then establish the Uu RLC bearer corresponding to SRB1 of the remote UE.

[0205] S612: Relay UE 2 sends the SRB0 data from the remote UE to the second network device, and correspondingly, the second network device receives the SRB0 data from relay UE 2. For example, relay UE 2 may send the SRB0 data to the second network device via the Uu RLC bearer of SRB0.

[0206] Among them, if the second network device sends the first indication information to relay UE 2 to indicate the establishment or reconstruction of the RLC bearer of SRB1, the second network device may send the first indication information to relay UE 2 after receiving the data of SRB0 forwarded by relay UE 2. In other words, if this triggering method is adopted, relay UE 2 has sent the data of SRB0 in S610 to the second network device, and the second network device has also received the data of SRB0, then S612 may occur before S611. If the other two triggering methods introduced in S611 are adopted, S612 may occur before S611, or after S611, or at the same time as S611.

[0207] S613: The second network device sends the data of SRB1 to the remote UE through relay UE 2. Correspondingly, the remote UE receives the data of SRB1 from the second network device through relay UE 2.

[0208] The data of SRB1 is, for example, an RLC SDU, and the RLC PDU may include an RRC re-establishment message. Specifically, the second network device sends the data of SRB1 to relay UE 2, and relay UE2 receives the data of SRB1 from the second network device; relay UE 2 sends the data of SRB1 to the remote UE, and the remote UE receives the data of SRB1 from relay UE 2. For example, relay UE 2 may receive the data of SRB1 from the second network device via the Uu RLC bearer corresponding to the SRB1 of the remote UE, relay UE 2 may send the data of SRB1 to the remote UE via the SL RLC bearer corresponding to the SRB1 of the remote UE, and the remote UE receives the data of SRB1 from the remote UE 2 via the SL RLC of SRB1. After receiving the data of SRB1, the remote UE may deliver the data of SRB1 to the PDCP entity of SRB1 for processing.

[0209] In addition, after receiving the data of the SRB1, the remote UE may stop the third timer and execute S614. If the remote UE does not receive the data of the SRB1 when the third timer times out, the remote UE may enter the RRC idle state and the process ends.

[0210] S614. The remote UE sends an RRC re-establishment completion message to the second network device through the relay UE 2, and correspondingly, the second network device receives the RRC re-establishment completion message from the remote UE through the relay UE 2. Specifically, the remote UE sends the RRC re-establishment completion message to the relay UE 2, and the relay UE 2 receives the RRC re-establishment completion message from the remote UE 2; the relay UE 2 sends the RRC re-establishment completion message to the second network device, and the second network device receives the RRC re-establishment completion message from the relay UE 2.

[0211] Through the above process, the remote UE completes the RRC re-establishment process through the Uu interface. Afterwards, the second network device can establish the RB of the remote UE through the RRC reconfiguration process, or modify the RB of the remote UE, or release the RB of the remote UE, etc., so as to restore the data transmission of the remote UE.

[0212] In the embodiment of the present application, if the remote UE determines that the relay UE 1 cannot continue to provide the relay service for the remote UE, the remote UE may select the relay UE 2 and initiate the RRC re-establishment through the relay UE 2. Since the relay UE 2 can only act as the relay UE when the signal quality of the cell is good or the relay UE 2 is in the RRC connected state, the occurrence of the RRC connection re-establishment failure caused by the poor cell signal quality when the remote UE performs RRC re-establishment through the Uu can be reduced, thereby improving the service continuity of the remote UE.

[0213] Figure 5 The embodiments shown and Figure 6 The embodiments shown can be applied alone or in combination. Figure 5 The embodiment shown is Figure 6 Alternatively, the following embodiments can be regarded as Figure 5 The embodiment shown is Figure 6 The embodiment shown in combination with the embodiment of the application can also be regarded as Figure 4 Several examples of embodiments are shown.

[0214] This application embodiment provides a fourth communication method, see Figure 7 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B The relay UE 2 and the second network device described below are Figure 3A or Figure 3B Not drawn in the middle.

[0215] S701. A remote UE communicates with a first network device through relay UE 1.

[0216] For more information about S701, please refer to Figure 4 S401 in the illustrated embodiment.

[0217] S702: The remote UE determines that relay UE 1 cannot continue to provide relay service for the remote UE.

[0218] For information on the circumstances under which the remote UE may determine that relay UE 1 is unable to continue to provide relay services for the remote UE, see Figure 5 S502 in the illustrated embodiment.

[0219] If the embodiments of the present application are compared with Figure 4 The embodiments shown are combined, or the embodiments of the present application are regarded as Figure 4 An example of the embodiment shown in FIG. 1 is a first embodiment of the present invention. If the remote UE determines that the relay UE cannot continue to provide the relay service for the remote UE, the remote UE may determine the first method according to the cell selection process of the remote UE and / or the selection process of the remote UE for the new relay UE. Alternatively, it may also be considered that Figure 5 The embodiment shown does not have Figure 4 The illustrated embodiment combines, and Figure 6 The embodiment shown is also not related to Figure 4 The embodiments shown are combined, and the embodiments of the present application are Figure 5 The embodiment shown is Figure 6 The first embodiment shown is a combined application mode.

[0220] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may initiate RRC re-establishment through Uu, or may select a new relay UE to initiate RRC re-establishment through the new relay UE. This can provide the remote UE with more opportunities for RRC re-establishment and improve the success rate of the remote UE performing RRC re-establishment. This is described below.

[0221] S703, the remote UE starts a first timer. The first timer can be used to stop when the remote UE selects a suitable cell, or can be used to stop when the remote UE selects a new relay UE. The first timer is, for example, timer T311, or can also be other timers. It can be understood that, Figure 7 The first timer described in the embodiment shown can achieve Figure 5The function of the first timer in the embodiment shown can be realized by Figure 6 Function of the second timer in the embodiment shown.

[0222] For example, once the remote UE initiates RRC re-establishment, the first timer is started; or, once the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the remote UE will perform cell selection, and before performing cell selection, the remote UE starts the first timer; or, before selecting a new relay UE, the remote UE starts the first timer; or, before performing cell selection and before selecting a new relay UE, the remote UE starts the first timer. Alternatively, the remote UE may also start the first timer in other situations.

[0223] S704, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. The second SRB is, for example, SRB0, or may be another SRB. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0224] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0225] S705: The remote UE selects or reselects a new relay UE; or the remote UE performs cell selection; or the remote UE selects or reselects a new relay UE and performs cell selection. The following takes the remote UE selecting or reselecting a new relay UE and performing cell selection as an example.

[0226] S706: The remote UE stops the first timer.

[0227] For example, if the remote UE selects a new relay UE, or selects a suitable cell, the first timer can be stopped. Hereinafter, the new relay UE is referred to as a third terminal device, or relay UE 2. For another example, if the remote UE selects relay UE 2, and the remote UE has completed the connection with relay UE 2, or the remote UE selects a suitable cell, the first timer can be stopped. The connection between the remote UE and relay UE 2 is, for example, a PC5-RRC connection or a PC5 unicast link. For another example, if the remote UE selects relay UE 2, and the remote UE obtains the identifier of the serving cell of relay UE 2, or the remote UE selects a suitable cell, the first timer can be stopped.

[0228] Among them, if the remote UE stops the first timer when a new relay UE is selected, the remote UE can establish a connection with the relay UE 2, for example, a PC5 unicast link establishment process or a layer 2 link (layer-2link) establishment process can be performed. If the remote UE2 stops the first timer when the identifier of the serving cell of the relay UE 2 is obtained, the remote UE can determine the shortMAC-I according to the identifier of the serving cell of the relay UE2.

[0229] In addition, no matter under what circumstances the remote UE stops the first timer, after the remote UE stops the first timer, or when the remote UE stops the first timer, the remote UE can also start a second timer, the second timer is, for example, timer T301, or can also be other timers. For example, the second timer is not timer T301, and the timing duration of the second timer is greater than or equal to the timing duration of timer T301. The second timer in the embodiment of the present application is, for example, used for the remote UE to receive the RRC re-establishment message. For example, the second timer in the embodiment of the present application can be implemented Figure 6 Function of the third timer in the embodiment shown.

[0230] S707: If the first timer times out, the remote UE returns to the RRC idle (RRC_IDLE) state, and the process ends.

[0231] S706 and S707 are two parallel solutions, and one of the solutions is executed according to the cell selection of the remote UE or the selection of the new relay UE.

[0232] If the remote UE stops the first timer after selecting a suitable cell, it can continue to execute Figure 5 S508 to S516 in the embodiment shown; if the remote UE stops the first timer after selecting a new relay UE, or the remote UE stops the first timer after selecting a new relay UE and the remote UE completes the connection establishment with the new relay UE, or the remote UE stops the first timer after selecting a new relay UE and the remote UE obtains the identifier of the serving cell of the new relay UE, then the execution may continue Figure 6 S608 to S614 in the embodiment shown.

[0233] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may initiate RRC re-establishment through Uu, or may select a new relay UE to initiate RRC re-establishment through the new relay UE. This can provide the remote UE with more opportunities to perform RRC re-establishment and improve the success rate of the remote UE performing RRC re-establishment.

[0234] This application embodiment provides a fifth communication method, see Figure 8 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B The relay UE 2 and the second network device described below are Figure 3A or Figure 3B Not drawn in the middle.

[0235] S801. A remote UE communicates with a first network device through relay UE 1.

[0236] For more information about S801, please refer to Figure 4 S401 in the illustrated embodiment.

[0237] S802: The remote UE determines that relay UE 1 cannot continue to provide relay service for the remote UE.

[0238] For information on the circumstances under which the remote UE may determine that relay UE 1 is unable to continue to provide relay services for the remote UE, see Figure 5 S502 in the illustrated embodiment.

[0239] If the embodiments of the present application are compared with Figure 4 The embodiments shown are combined, or the embodiments of the present application are regarded as Figure 4 An example of the embodiment shown in FIG. 1 is a first embodiment of the present invention. If the remote UE determines that the relay UE cannot continue to provide the relay service for the remote UE, the remote UE may determine the first method according to the cell selection process of the remote UE and / or the selection process of the remote UE for the new relay UE. Alternatively, it may also be considered that Figure 5 The embodiment shown does not have Figure 4 The illustrated embodiment combines, and Figure 6 The embodiment shown is also not related to Figure 4 The embodiments shown are combined, and the embodiments of the present application are Figure 5 The embodiment shown is Figure 6 The second embodiment shown is a combined application mode.

[0240] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may initiate RRC re-establishment through Uu, or may select a new relay UE to initiate RRC re-establishment through the new relay UE. This can provide the remote UE with more opportunities for RRC re-establishment and improve the success rate of the remote UE performing RRC re-establishment. This is described below.

[0241] S803, the remote UE starts a first timer and a second timer. The first timer can be used to stop when the remote UE selects a suitable cell, and the second timer can be used to stop when the remote UE selects a new relay UE. The first timer is, for example, timer T311, or can also be other timers. It can be understood that, Figure 8 The first timer described in the embodiment shown can achieve Figure 5 The function of the first timer in the embodiment shown is, Figure 8 The second timer described in the embodiment shown can achieve Figure 6 Function of the second timer in the embodiment shown.

[0242] For example, once the remote UE initiates RRC re-establishment, the first timer and the second timer are started; or, once the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the first timer and the second timer are started; or, after initiating RRC re-establishment, the remote UE will perform cell selection, then before performing cell selection, the remote UE starts the first timer; before selecting a new relay UE, the remote UE starts the second timer. Alternatively, the remote UE may also start the first timer and the second timer in other situations.

[0243] S804, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. The second SRB is, for example, SRB0, or may be another SRB. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0244] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0245] S805: The remote UE selects or reselects a new relay UE; or, the remote UE performs cell selection; or, the remote UE selects or reselects a new relay UE, and performs cell selection. The following takes the remote UE selecting or reselecting a new relay UE, and performing cell selection as an example.

[0246] S806: The remote UE stops the first timer and the second timer.

[0247] For example, if the remote UE selects a new relay UE, or selects a suitable cell, the first timer and the second timer may be stopped. Hereinafter, the new relay UE is referred to as a third terminal device, or relay UE 2. For another example, if the remote UE selects relay UE 2, and the remote UE has completed establishing a connection with relay UE 2, or the remote UE selects a suitable cell, the first timer and the second timer may be stopped. The connection between the remote UE and relay UE 2 is, for example, a PC5-RRC connection or a PC5 unicast link. For another example, if the remote UE selects relay UE 2, and the remote UE obtains the identifier of the serving cell of relay UE 2, or the remote UE selects a suitable cell, the first timer and the second timer may be stopped.

[0248] Among them, if the remote UE stops the first timer and the second timer when a new relay UE is selected, the remote UE can establish a connection with the relay UE 2, for example, a PC5 unicast link establishment process or a layer 2 link (layer-2link) establishment process can be performed. If the remote UE2 stops the first timer and the second timer when the identifier of the serving cell of the relay UE 2 is obtained, the remote UE can determine the shortMAC-I according to the identifier of the serving cell of the relay UE2.

[0249] In addition, no matter under what circumstances the remote UE stops the first timer and the second timer, after the remote UE stops the first timer and the second timer, or when the remote UE stops the first timer and the second timer, the remote UE can also start a third timer, and the third timer is, for example, timer T301, or it can also be other timers. For example, the third timer is not timer T301, and the timing duration of the third timer is greater than or equal to the timing duration of timer T301. The third timer in the embodiment of the present application is, for example, used for the remote UE to receive the RRC re-establishment message. For example, the third timer in the embodiment of the present application can be implemented Figure 6 Function of the third timer in the embodiment shown.

[0250] S807: If the first timer and the second timer expire, the remote UE returns to the RRC idle state, and the process ends.

[0251] If the remote UE does not select a suitable cell when the first timer times out, the remote UE stops selecting cells. If the remote UE does not select a suitable relay UE when the second timer times out, or the remote UE does not establish a connection with the new relay UE when the second timer times out, or the remote UE does not obtain the identifier of the service cell of the new relay UE when the second timer times out, the remote UE stops selecting a new relay UE. If the first timer times out but the second timer does not, the remote UE will no longer select a cell, but can continue to select a new relay UE; if the second timer times out but the first timer does not, the remote UE will no longer select a new relay UE, but can continue to select a cell; and if both the first timer and the second timer times out, the remote UE returns to the RRC idle state and the process ends.

[0252] S806 and S807 are two parallel solutions, and one of the solutions is executed according to the cell selection of the remote UE or the selection of the new relay UE.

[0253] If the remote UE stops the first timer and the second timer after selecting a suitable cell, it can continue to execute Figure 5 S508 to S516 in the embodiment shown; if the remote UE stops the first timer and the second timer after selecting a new relay UE, or the remote UE selects a new relay UE and stops the first timer and the second timer after the remote UE completes the connection establishment with the new relay UE, or the remote UE selects a new relay UE and stops the first timer and the second timer after obtaining the identifier of the serving cell of the new relay UE, then the execution may continue Figure 6 S608 to S614 in the embodiment shown.

[0254] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may initiate RRC re-establishment through Uu, or may select a new relay UE to initiate RRC re-establishment through the new relay UE. This can provide the remote UE with more opportunities to perform RRC re-establishment and improve the success rate of the remote UE performing RRC re-establishment.

[0255] This application embodiment provides a sixth communication method, see Fig. 9 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B The relay UE 2 and the second network device described below are Figure 3A or Figure 3B Not drawn in the middle.

[0256] S901. A remote UE communicates with a first network device through relay UE 1.

[0257] For more information about S901, please refer to Figure 4 S401 in the illustrated embodiment.

[0258] S902: The remote UE determines that relay UE 1 cannot continue to provide relay service for the remote UE.

[0259] For information on the circumstances under which the remote UE may determine that relay UE 1 is unable to continue to provide relay services for the remote UE, see Figure 5 S502 in the illustrated embodiment.

[0260] If the embodiments of the present application are compared with Figure 4 The embodiments shown are combined, or the embodiments of the present application are regarded as Figure 4 An example of the embodiment shown in FIG. 1 is a first embodiment of the present invention. If the remote UE determines that the relay UE cannot continue to provide the relay service for the remote UE, the remote UE may determine the first method according to the cell selection process of the remote UE and / or the selection process of the remote UE for the new relay UE. Alternatively, it may also be considered that Figure 5 The embodiment shown does not have Figure 4 The illustrated embodiment combines, and Figure 6The embodiment shown is also not related to Figure 4 The embodiments shown are combined, and the embodiments of the present application are Figure 5 The embodiment shown is Figure 6 The third combined application mode of the embodiment is shown.

[0261] S903: The remote UE starts a first timer. The first timer may be stopped when the remote UE selects a suitable cell.

[0262] For more information about S903, please refer to Figure 5 S503 in the illustrated embodiment.

[0263] S904, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. The second SRB is, for example, SRB0, or may be another SRB. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0264] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0265] S905: The remote UE performs cell selection. If the remote UE selects a suitable cell, S906 is executed. If the remote UE does not select a suitable cell, S907 is executed.

[0266] S906: The remote UE selects a suitable cell.

[0267] If the remote UE selects a suitable cell, it can stop the first timer and continue to execute Figure 5 S508 to S516 in the embodiment shown.

[0268] S907: The remote UE selects or reselects a new relay UE.

[0269] If the remote UE does not select a suitable cell, or the cell selected by the remote UE is no longer suitable (for example, the remote UE has originally selected a suitable cell, but the cell becomes no longer suitable), or the remote UE does not receive an RRC re-establishment message from the network device that initiates RRC re-establishment by the remote UE, or the RSRP of the cell selected by the remote UE is less than or equal to the second RSRP threshold, S907 may be executed. The network device that initiates RRC re-establishment by the remote UE is, for example, the second network device. The second RSRP threshold is, for example, specified by a protocol, or may be configured by the network device, etc.

[0270] The remote UE not selecting a suitable cell can be understood as the remote UE not selecting a suitable cell when the first timer times out. The remote UE not receiving an RRC re-establishment message from the second network device can be understood as the remote UE not receiving an RRC re-establishment message from the second network device when the second timer times out, and the second timer is, for example, started by the remote UE after selecting a suitable cell.

[0271] For example, if the remote UE does not select a suitable cell, or the cell selected by the remote UE is no longer suitable (for example, the remote UE has originally selected a suitable cell, but the cell becomes no longer suitable), or the remote UE does not receive an RRC re-establishment message from the network device from which the remote UE initiates RRC re-establishment, the remote UE may start a third timer, and the remote UE begins to reselect or select a new relay UE, and the following may be continued: Figure 6 In addition, since the second network device in the embodiment of the present application is a network device for the remote UE to initiate RRC re-establishment through Uu, when executing Figure 6 In S606 to S614 in the illustrated embodiment, the second network device in S606 to S614 may be replaced by a third network device, and the third network device and the second network device may be the same network device, or may be different network devices.

[0272] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may initiate RRC re-establishment through Uu, and if the remote UE fails to initiate RRC re-establishment through Uu, the remote UE may also select a new relay UE to initiate RRC re-establishment through the new relay UE. This can provide the remote UE with more opportunities to perform RRC re-establishment and improve the success rate of the remote UE performing RRC re-establishment.

[0273] This application embodiment provides a seventh communication method, see Fig.10 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3AIn the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 , the relay UE 1 described below may be Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B The relay UE 2 and the second network device described below are Figure 3A or Figure 3B Not drawn in the middle.

[0274] S1001. A remote UE communicates with a first network device through relay UE 1.

[0275] For more information about S1001, please refer to Figure 4 S401 in the illustrated embodiment.

[0276] S1002: The remote UE determines that relay UE 1 cannot continue to provide relay service for the remote UE.

[0277] For information on the circumstances under which the remote UE may determine that relay UE 1 is unable to continue to provide relay services for the remote UE, see Figure 5 S502 in the illustrated embodiment.

[0278] If the embodiments of the present application are compared with Figure 4 The embodiments shown are combined, or the embodiments of the present application are regarded as Figure 4 An example of the embodiment shown in FIG. 1 is a first embodiment of the present invention. If the remote UE determines that the relay UE cannot continue to provide the relay service for the remote UE, the remote UE may determine the first method according to the RSRP of the cell selected by the remote UE and / or the RSRP of the new relay UE selected by the remote UE. Alternatively, it may also be considered that Figure 5 The embodiment shown does not have Figure 4 The illustrated embodiment combines, and Figure 6 The embodiment shown is also not related to Figure 4 The embodiments shown are combined, and the embodiments of the present application are Figure 5 The embodiment shown is Figure 6 The fourth combined application mode of the embodiment is shown.

[0279] S1003, the remote UE starts a first timer. The first timer can be used to stop when the remote UE selects a suitable cell, or can be used to stop when the remote UE selects a new relay UE. The first timer is, for example, timer T311, or can also be other timers. It can be understood that, Fig.10 The first timer described in the embodiment shown can achieve Figure 5 The function of the first timer in the embodiment shown can be realized by Figure 6 Function of the second timer in the embodiment shown.

[0280] For example, once the remote UE initiates RRC re-establishment, the first timer is started; or, once the remote UE determines that the relay UE cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the remote UE will perform cell selection, and before performing cell selection, the remote UE starts the first timer; or, before selecting a new relay UE, the remote UE starts the first timer; or, before performing cell selection and before selecting a new relay UE, the remote UE starts the first timer. Alternatively, the remote UE may also start the first timer in other situations.

[0281] S1004, the remote UE suspends all RBs except the second SRB. The RB suspended by the remote UE is a UuRB. The second SRB is, for example, SRB0, or may be another SRB. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0282] For example, the remote UE may also release the SL RLC bearer of the suspended RB.

[0283] S1005, the remote UE selects or reselects a new relay UE; or the remote UE performs cell selection; or the remote UE selects or reselects a new relay UE and performs cell selection. The following takes the remote UE selecting or reselecting a new relay UE and performing cell selection as an example.

[0284] S1006. The remote UE re-establishes RRC via the Uu interface, or re-establishes RRC via a new relay UE.

[0285] For example, if the remote UE selects a suitable cell, and the RSRP of the selected cell is less than or equal to the first RSRP threshold, but the remote UE does not select a new relay UE, the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, but does not select a new relay UE, the remote UE can re-establish RRC through the Uu interface. Alternatively, if the remote UE selects a suitable cell, and the RSRP of the selected cell is greater than the first RSRP threshold, the remote UE can re-establish RRC through the Uu interface.

[0286] For another example, if the remote UE selects a new relay UE and fails to select a suitable cell, the remote UE may perform RRC re-establishment through the new relay UE. Alternatively, if the remote UE selects a new relay UE and also selects a suitable cell, and the difference between the RSRP of the selected cell and the RSRP of the new relay UE is less than or equal to the first RSRP threshold, it indicates that the signal quality will be better if the remote UE performs RRC re-establishment through the new relay UE, and the remote UE may perform RRC re-establishment through the new relay UE.

[0287] For another example, if the remote UE selects a suitable cell and the RSRP of the selected cell is greater than the first RSRP threshold, the remote UE can re-establish RRC through Uu. Alternatively, if the remote UE selects a suitable cell and the remote UE cannot be used as a remote terminal device, or the remote UE cannot communicate with the network through other UEs, the remote UE can re-establish RRC through Uu.

[0288] For another example, if the remote UE selects a suitable cell, the RSRP of the selected cell is less than or equal to the second RSRP threshold, and the remote UE selects a new relay UE, the remote UE can perform RRC re-establishment through the new relay UE. Alternatively, if the remote UE selects a suitable cell, and the RSRP of the selected cell is less than or equal to the first RSRP threshold, the remote UE can perform RRC re-establishment through Uu.

[0289] The first RSRP threshold may be specified by a protocol, or may be configured by a network device. Fig. 9The illustrated embodiment also mentions a second RSRP threshold, and the first RSRP threshold and the second RSRP threshold may be equal or unequal.

[0290] If the remote UE selects a new relay UE or a suitable cell, the first timer may be stopped. If the remote UE reestablishes RRC via Uu, the execution may continue. Figure 5 S508 to S516 in the embodiment shown; or, if the remote UE re-establishes RRC through a new relay UE, it may continue to execute Figure 6 S608 to S614 in the embodiment shown. If the remote UE does not select a new relay UE or a suitable cell when the first timer times out, the remote UE enters the RRC idle state and the process ends.

[0291] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE can choose whether to initiate RRC re-establishment through Uu or through a new relay UE according to the signal quality (such as RSRP). This can provide more opportunities for the remote UE to perform RRC re-establishment, and can improve the signal quality of the remote UE performing RRC re-establishment, thereby improving the success rate of the remote UE performing RRC re-establishment.

[0292] In the embodiment of the present application, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE can choose whether to initiate RRC re-establishment through Uu or through a new relay UE according to the signal quality (such as RSRP). This can provide more opportunities for the remote UE to perform RRC re-establishment, and can improve the signal quality of the remote UE performing RRC re-establishment, thereby improving the success rate of the remote UE performing RRC re-establishment.

[0293] Figure 5 The embodiment shown to Fig.10 In any of the embodiments shown, the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE. There is another possibility that the relay UE may determine that it cannot continue to provide relay services for the remote UE. Next, how the relay UE and the remote UE will handle this scenario will be described.

[0294] This application embodiment provides an eighth communication method, see Fig.11 , which is a flow chart of the method. If the embodiment of the present application is applied in Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0295] S1101. A remote UE communicates with a first network device through a relay UE.

[0296] For more information about S1101, please refer to Figure 4 S401 in the illustrated embodiment.

[0297] S1102: The relay UE determines that it cannot continue to provide relay service for the remote UE.

[0298] For example, if the relay UE detects RLF between the relay UE and the first network device, it can be determined that it is no longer possible to provide relay service to the remote UE. Next, the relay UE can perform RRC re-establishment. After initiating RRC re-establishment, the relay UE can perform cell selection. For example, during the cell selection process, the relay UE can give priority to cells that support layer 2 relay technology. For example, the relay UE selects a cell that supports layer 2 relay technology. If there is no suitable cell that supports layer 2 relay technology, the relay UE can select a cell that does not support layer 2 relay technology. For more information about the process of relay UE performing RRC re-establishment, please refer to Figure 5 The illustrated embodiment introduces a process of performing RRC re-establishment by a remote UE.

[0299] Optionally, if the relay UE detects RLF between the relay UE and the first network device, the relay UE may also send a third indication message to the remote UE, and the third indication message may indicate RRC re-establishment (in this case, the third indication message may also be referred to as RRC re-establishment indication message), or may indicate that RLF has occurred in the relay UE (in this case, the third indication message may also be referred to as RLF indication message), wherein the relay UE has Uu RLF. After receiving the third indication message, the remote UE may suspend all RBs except the second SRB. Among them, the RB suspended by the remote UE is the UuRB. The second SRB may be, for example, SRB0, or it may be other SRBs. The embodiment of the present application takes the second SRB being SRB0 as an example. After receiving the third indication message, the remote UE may send response information of the third indication message to the relay UE, or it may not send response information of the third indication message to the relay UE.

[0300] Alternatively, when the relay UE detects the RLF between the relay UE and the first network device, it may not send the third indication information to the remote UE, but may send the third indication information to the remote UE after the RRC re-establishment is completed. At this time, the third indication information may indicate that the RRC re-establishment is to be performed, or indicate that the relay UE has completed the RRC re-establishment, etc. At this time, the third indication information may include the identifier of the serving cell of the relay UE. After receiving the third indication information, the remote UE may determine the shortMAC-I according to the identifier of the serving cell. In addition, the remote UE may start the first timer and execute S1103. The first timer is, for example, T301, or it may be other timers. The first timer can be used for the remote UE to receive an RRC re-establishment message. For example, the relay UE sends an RRC re-establishment message to the second network device, and after the second network device receives the RRC re-establishment message, it sends an RRC re-establishment message to the relay UE. After receiving the RRC re-establishment message, the relay UE sends an RRC re-establishment completion message to the second network device. After the relay UE sends the RRC re-establishment completion message to the second network device, it can be regarded that the relay UE completes the RRC re-establishment. The second network device is a network device corresponding to the cell (for example, called the second cell) selected by the relay UE through the cell selection during the RRC re-establishment process. The second network device and the first network device can be the same network device, or can also be different network devices. The RRC re-establishment process of the relay UE will not be described in detail.

[0301] If the relay UE sends the third indication information to the remote UE after detecting the RLF between the relay UE and the first network device, the relay UE may also send the identifier of the serving cell of the relay UE to the remote UE after completing the RRC re-establishment. After the remote UE receives the identifier of the serving cell of the relay UE, it may determine the shortMAC-I according to the identifier of the serving cell. In addition, the remote UE may start the first timer and execute S1103.

[0302] The embodiments of the present application can be Figure 4 The embodiments shown in the drawings can be used in combination or can also be used alone. Figure 4 The embodiment shown is combined with an application, then after the relay UE sends the third indication information to the remote UE, the remote UE can determine that the relay UE cannot continue to provide relay services for the remote UE according to the third indication information, so that the remote UE can initiate RRC re-establishment according to the first method. The first method can be selected by the remote UE. In the embodiment of the present application, the first method is to initiate RRC re-establishment through the original relay UE as an example.

[0303] In addition, if during the RRC re-establishment process, the relay UE's timer T311 times out, or the relay UE's T301 times out, or the cell selected by the relay UE is no longer suitable, or the relay UE enters the RRC idle state, etc., these all indicate that the relay UE has failed to re-establish the RRC. The relay UE may send a fourth indication message to the remote UE, and the fourth indication message may indicate that the RRC re-establishment has failed (in this case, the fourth indication message may also be referred to as the RRC re-establishment failure indication message), or indicate (or request) to release the connection with the remote UE (for example, a PC5-RRC connection). If the remote UE receives the fourth indication message, it may enter the RRC idle state, and the process ends. Alternatively, if the remote UE receives the fourth indication message, it may select or reselect a new relay UE, and then re-establish the RRC through the new relay UE. This process may refer to Figure 6 Alternatively, if the remote UE receives the fourth indication information, it can initiate RRC re-establishment through Uu. The process can refer to Figure 5 The embodiment shown.

[0304] If the relay UE has other services besides the relay service, the relay UE needs to enter the RRC connected state. If the relay UE does not select a suitable cell, or selects a cell that does not support the layer 2 relay technology, the relay UE can initiate RRC re-establishment again; or, if the relay UE has other services besides the relay service, if the relay UE selects a cell that does not support the layer 2 relay technology, the relay UE can continue to re-establish RRC; or, if the relay UE only has the relay service, if the relay UE does not select a suitable cell, or selects a cell that does not support the layer 2 relay technology, the relay UE can enter the RRC idle state.

[0305] S1103, the remote UE reestablishes the PDCP entity of the first SRB, and establishes or reestablishes the first RLC bearer of the first SRB, and restores SRB1. The first RLC bearer of the first SRB is, for example, the SL RLC bearer of the first SRB. The first SRB is, for example, SRB1, or may be another SRB. In the embodiment of the present application, the first SRB is SRB1 as an example.

[0306] For example, after sending an RRC re-establishment request message to the relay UE (the message needs to be sent to the second network device), the remote UE may also re-establish the PDCP layer of SRB1 and establish or re-establish the SL RLC bearer of SRB1 to restore SRB1.

[0307] For more information about S1103, please refer to Figure 6 S609 in the illustrated embodiment.

[0308] S1104. The remote UE sends the SRB0 data to the relay UE, and correspondingly, the relay UE receives the SRB0 data from the remote UE. The SRB0 data is, for example, an RLC SDU, and the RLC PDU may include an RRC re-establishment request message. For example, the remote UE may send the RLC SDU to the relay UE via the SL RLC bearer corresponding to the SRB0, and the relay UE receives the RLC SDU. The RLC SDU is to be sent to the second network device, and the second network device is the network device accessed by the relay UE. The remote UE needs to relay the message to the second network device through the relay UE, so the remote UE sends the SRB0 data to the relay UE.

[0309] S1105. The relay UE establishes or reestablishes the RLC bearer corresponding to the SRB1 of the remote UE.

[0310] For more information about S1105, please refer to Figure 6 In S611 of the illustrated embodiment, the relay UE 2 in S611 may be replaced by the relay UE in the embodiment of the present application.

[0311] S1106: The relay UE sends the SRB0 data from the remote UE to the second network device, and correspondingly, the second network device receives the SRB0 data from the relay UE. For example, the relay UE may send the SRB0 data to the second network device via the Uu RLC bearer of SRB0.

[0312] For more information about S1106, please refer to Figure 6 In S612 of the illustrated embodiment, the relay UE 2 in S612 may be replaced by the relay UE in the embodiment of the present application.

[0313] S1107: The second network device sends the SRB1 data to the remote UE through the relay UE. Correspondingly, the remote UE receives the SRB1 data from the second network device through the relay UE.

[0314] For more information about S1107, please refer to Figure 6 In S613 of the illustrated embodiment, the relay UE 2 in S613 may be replaced by the relay UE in the embodiment of the present application, and the third timer in S613 may be replaced by the first timer in the embodiment of the present application.

[0315] S1108: The remote UE sends an RRC re-establishment completion message to the second network device through the relay UE. Correspondingly, the second network device receives the RRC re-establishment completion message from the remote UE through the relay UE.

[0316] For more information about S1108, please refer to Figure 6 In S614 of the illustrated embodiment, the relay UE 2 in S614 may be replaced by the relay UE in the embodiment of the present application.

[0317] In the embodiment of the present application, if the relay UE determines that it cannot continue to provide relay service for the remote UE, the relay UE can perform RRC re-establishment, and can trigger the remote UE to also perform RRC re-establishment, and the remote UE can continue to access the network through the relay UE that has completed RRC re-establishment, without selecting other relay UEs, thereby reducing the power consumption of the remote UE due to selecting other relay UEs. Moreover, since the remote UE accesses the network through the relay UE, relay UE 1 is in the RRC connection state, therefore, it can reduce the occurrence of RRC re-establishment failures due to poor cell signal quality when the remote UE initiates RRC re-establishment through Uu, thereby improving the service continuity of the remote UE.

[0318] This application embodiment provides a ninth communication method, see Fig.12 , which is a flowchart of the method. In the method, the relay UE still determines that it cannot continue to provide relay services for the remote UE. Through this method, the efficiency of the remote UE in performing RRC re-establishment can be improved. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relayUE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0319] S1201. A remote UE communicates with a first network device through a relay UE.

[0320] For more information about S1201, please refer to Figure 4 S401 in the illustrated embodiment.

[0321] S1202: The relay UE determines that it cannot continue to provide relay service for the remote UE.

[0322] For example, if the relay UE detects the RLF between the relay UE and the first network device, it may be determined that the relay service cannot be continued to be provided for the remote UE.

[0323] S1203: The relay UE starts a first timer. The first timer may be stopped when the relay UE selects a suitable cell.

[0324] For example, once the relay UE initiates RRC re-establishment, the first timer is started; or, once the relay UE determines that it cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the relay UE will perform cell selection, then before performing cell selection, the relay UE starts the first timer. Alternatively, the relay UE may also start the first timer in other circumstances. The first timer is, for example, timer T311, or may also be other timers.

[0325] S1204: The relay UE suspends all RBs except SRB0. The RBs suspended by the relay UE are Uu RBs. For example, the relay UE may also release the SL RLC bearer of the suspended RBs.

[0326] S1205, the relay UE performs cell selection. For example, in the process of performing cell selection, the relay UE may preferentially select a cell that supports the layer 2 relay technology. For example, the relay UE selects a cell that supports the layer 2 relay technology. If there is no suitable cell that supports the layer 2 relay technology, the relay UE may select a cell that does not support the layer 2 relay technology.

[0327] S1206. The relay UE sends a third indication message to the remote UE, and correspondingly, the remote UE receives the third indication message from the relay UE. The third indication message may indicate RRC re-establishment (in this case, the third indication message may also be referred to as RRC re-establishment indication message), or may indicate that RLF has occurred in the relay UE (in this case, the third indication message may also be referred to as RLF indication message), wherein the relay UE has Uu RLF. After receiving the third indication message, the remote UE may suspend all RBs except the second SRB. The RB suspended by the remote UE is a Uu RB. The second SRB may be, for example, SRB0, or may be other SRBs. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0328] The embodiments of the present application can be Figure 4The embodiments shown in the drawings can be used in combination or can also be used alone. Figure 4 The embodiment shown is combined with an application, then after the relay UE sends the third indication information to the remote UE, the remote UE can determine that the relay UE cannot continue to provide relay services for the remote UE according to the third indication information, so that the remote UE can initiate RRC re-establishment according to the first method. The first method can be selected by the remote UE. In the embodiment of the present application, the first method is to initiate RRC re-establishment through the original relay UE as an example.

[0329] S1207: The remote UE sends response information of the third indication information to the relay UE, and correspondingly, the relay UE receives the response information of the third indication information from the remote UE.

[0330] After receiving the third indication information, the remote UE may send response information of the third indication information to the relay UE, or may not send response information of the third indication information to the relay UE. That is, S1207 is an optional step.

[0331] S1208: The relay UE selects a suitable cell. For example, the relay UE selects a cell that supports the layer 2 relay technology. For example, the cell selected by the relay UE is called a second cell, and the second cell corresponds to a second network device.

[0332] S1209, the relay UE sends the identifier of the second cell to the remote UE, and correspondingly, the remote UE receives the identifier of the second cell from the relay UE. If the relay UE selects a suitable cell, the identifier of the selected cell may be sent to the remote UE, so that the remote UE determines the shortMAC-I according to the identifier of the cell. Then enter S1211.

[0333] S1210: When the first timer times out, the relay UE does not select a suitable cell (for example, the relay UE does not select a cell supporting layer 2 relay technology), the relay UE sends fourth indication information to the remote UE, and correspondingly, the remote UE receives the fourth indication information from the relay UE.

[0334] The fourth indication information may indicate that the RRC re-establishment has failed (in this case, the fourth indication information may also be referred to as the RRC re-establishment failure indication information), or indicate (or request) to release the connection with the remote UE (for example, the PC5-RRC connection). If the remote UE receives the fourth indication information, it may enter the RRC idle state and the process ends. Alternatively, if the remote UE receives the fourth indication information, it may select or reselect a new relay UE and then re-establish the RRC through the new relay UE. The process may refer to Figure 6 Alternatively, if the remote UE receives the fourth indication information, it can initiate RRC re-establishment through Uu. The process can refer to Figure 5 The embodiment shown.

[0335] In addition, if the relay UE has other services of its own in addition to the relay service, and therefore the relay UE needs to enter the RRC connected state, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may perform RRC re-establishment again, but the RRC re-establishment process is not the process introduced in S1211; or, if the relay UE has other services of its own in addition to the relay service, then if the relay UE selects a cell that does not support the layer 2 relay technology before the first timer times out, the relay UE may continue to perform RRC re-establishment, but the RRC re-establishment process is not the process introduced in S1211; or, if the relay UE has only the relay service, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may enter the RRC idle state.

[0336] S1208 to S1209 and S1210 are two parallel solutions, and one of them is executed according to the cell selection of the relay UE. In addition, S1211 is not executed after S1210 is executed.

[0337] S1211. The relay UE establishes or reestablishes the RLC bearer corresponding to SRB1 of the remote UE.

[0338] For more information about S1211, please refer to Figure 6 S611 in the embodiment shown, or reference Fig.11 S1105 in the illustrated embodiment. In addition, the RRC re-establishment process of the relay UE will not be described in detail.

[0339] S1212. The remote UE determines shortMAC-I according to the identifier of the second cell.

[0340] After receiving the identity of the serving cell of the relay UE, the remote UE can determine the shortMAC-I according to the identity of the serving cell. Fig.11 Steps S1103 to S1104 and S1106 to S1108 in the illustrated embodiment are not described in detail.

[0341] In an embodiment of the present application, if the relay UE cannot continue to provide relay service for the remote UE, the relay UE can send a third indication message to the remote UE when initiating RRC re-establishment, so that the remote UE can initiate RRC re-establishment as soon as possible, thereby improving the efficiency of the remote UE in performing RRC re-establishment, and correspondingly improving the service continuity of the remote UE.

[0342] This application embodiment provides a tenth communication method, see Fig.13 , which is a flowchart of the method. In the method, the relay UE still determines that it cannot continue to provide relay services for the remote UE. Through this method, the efficiency of the remote UE in performing RRC re-establishment can be improved. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relayUE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0343] S1301. A remote UE communicates with a first network device through a relay UE.

[0344] For more information about S1301, please refer to Figure 4 S401 in the illustrated embodiment.

[0345] S1302: The relay UE determines that it cannot continue to provide relay service for the remote UE.

[0346] For example, if the relay UE detects the RLF between the relay UE and the first network device, it may be determined that the relay service cannot be continued to be provided for the remote UE.

[0347] S1303: The relay UE starts a first timer. The first timer may be stopped when the relay UE selects a suitable cell.

[0348] For example, once the relay UE initiates RRC re-establishment, the first timer is started; or, once the relay UE determines that it cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the relay UE will perform cell selection, then before performing cell selection, the relay UE starts the first timer. Alternatively, the relay UE may also start the first timer in other circumstances. The first timer is, for example, timer T311, or may also be other timers.

[0349] S1304: The relay UE suspends all RBs except SRB0. The RBs suspended by the relay UE are Uu RBs. For example, the relay UE may also release the SL RLC bearer of the suspended RBs.

[0350] S1305. The relay UE performs cell selection.

[0351] S1306. The relay UE sends a third indication message to the remote UE, and correspondingly, the remote UE receives the third indication message from the relay UE. The third indication message may indicate RRC re-establishment (in this case, the third indication message may also be referred to as RRC re-establishment indication message), or may indicate that RLF has occurred in the relay UE (in this case, the third indication message may also be referred to as RLF indication message), wherein the relay UE has Uu RLF. After receiving the third indication message, the remote UE may suspend all RBs except the second SRB. The RB suspended by the remote UE is a Uu RB. The second SRB may be, for example, SRB0, or may be other SRBs. The embodiment of the present application takes the second SRB being SRB0 as an example.

[0352] The embodiments of the present application can be Figure 4 The embodiments shown in the drawings can be used in combination or can also be used alone. Figure 4The embodiment shown is combined with an application, then after the relay UE sends the third indication information to the remote UE, the remote UE can determine that the relay UE cannot continue to provide relay services for the remote UE according to the third indication information, so that the remote UE can initiate RRC re-establishment according to the first method. The first method can be selected by the remote UE. In the embodiment of the present application, the first method is to initiate RRC re-establishment through the original relay UE as an example.

[0353] S1307: The remote UE starts a fifth timer. The timing duration of the fifth timer may be specified by a protocol, or may be configured by a network device.

[0354] S1308. The remote UE sends response information of the third indication information to the relay UE. Correspondingly, the relay UE receives the response information of the third indication information from the remote UE.

[0355] After receiving the third indication information, the remote UE may send response information of the third indication information to the relay UE, or may not send response information of the third indication information to the relay UE. That is, S1308 is an optional step. If S1308 is executed, S1307 may be executed before S1308, or S1307 may be executed after S1308, or S1307 and S1308 may be executed simultaneously.

[0356] S1309: The relay UE selects a suitable cell. For example, the relay UE selects a cell that supports the layer 2 relay technology. For example, the cell selected by the relay UE is called a second cell, and the second cell corresponds to a second network device.

[0357] S1310, the relay UE sends the identifier of the second cell to the remote UE, and correspondingly, the remote UE receives the identifier of the second cell from the relay UE. If the relay UE selects a suitable cell, the identifier of the selected cell may be sent to the remote UE, so that the remote UE can determine the shortMAC-I according to the identifier of the cell. If the remote UE receives the identifier of the second cell before the fifth timer expires, enter S1312.

[0358] S1311: When the fifth timer times out, the remote UE does not receive the cell identifier from the relay UE, and the remote UE enters the RRC idle state.

[0359] For example, if the relay UE does not select a suitable cell before the first timer times out, the relay UE may not send the identifier of the selected cell to the remote UE. For the remote UE, when the fifth timer times out, if the remote UE has not received the identifier of the serving cell of the relay UE from the relay UE, the remote UE may enter the RRC idle state, or the remote UE may initiate RRC re-establishment through the Uu interface, or the remote UE may also select a new relay to initiate RRC re-establishment, etc. S1311 takes the remote UE entering the RRC idle state as an example.

[0360] In addition, if the relay UE has other services of its own in addition to the relay service, and therefore the relay UE needs to enter the RRC connected state, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may perform RRC re-establishment again, but the RRC re-establishment process is not the process introduced in S1312; or, if the relay UE only has the relay service, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may enter the RRC idle state.

[0361] S1309-S1310 and S1311 are two parallel solutions, and one of them is executed according to whether the fifth timer has timed out. In addition, S1311 is not executed after S1310 is executed.

[0362] S1312: The relay UE establishes or reestablishes the RLC bearer corresponding to the SRB1 of the remote UE.

[0363] For more information about S1312, please refer to Figure 6 S611 in the embodiment shown, or reference Fig.11 S1105 in the illustrated embodiment. In addition, the RRC re-establishment process of the relay UE will not be described in detail.

[0364] S1313. The remote UE stops the fifth timer and determines shortMAC-I according to the identifier of the second cell.

[0365] After receiving the identifier of the second cell, the remote UE may stop the fifth timer and determine the shortMAC-I according to the identifier of the serving cell. Fig.11Steps S1103 to S1104 and S1106 to S1108 in the illustrated embodiment are not described in detail.

[0366] In the embodiment of the present application, if the relay UE cannot continue to provide relay service for the remote UE, the relay UE can send the third indication information to the remote UE when initiating RRC re-establishment, so that the remote UE can initiate RRC re-establishment as soon as possible, thereby improving the efficiency of the remote UE in performing RRC re-establishment, and correspondingly improving the service continuity of the remote UE. Moreover, if the relay UE does not select a suitable cell, the relay UE does not need to notify the remote UE, and the remote UE can decide on subsequent actions based on the fifth timer, thereby reducing signaling overhead.

[0367] The present application embodiment provides an eleventh communication method, see Fig.14 , which is a flowchart of the method. In the method, the relay UE still determines that it cannot continue to provide relay services for the remote UE. Through this method, the efficiency of the remote UE in performing RRC re-establishment can be improved. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relayUE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0368] S1401. A remote UE communicates with a first network device through a relay UE.

[0369] For more information about S1401, please refer to Figure 4 S401 in the illustrated embodiment.

[0370] S1402: The relay UE determines that it cannot continue to provide relay service for the remote UE.

[0371] For example, if the relay UE detects the RLF between the relay UE and the first network device, it may be determined that the relay service cannot be continued to be provided for the remote UE.

[0372] S1403: The relay UE starts a first timer. The first timer may be stopped when the relay UE selects a suitable cell.

[0373] For example, once the relay UE initiates RRC re-establishment, the first timer is started; or, once the relay UE determines that it cannot continue to provide relay service for the remote UE, the first timer is started; or, after initiating RRC re-establishment, the relay UE will perform cell selection, then before performing cell selection, the relay UE starts the first timer. Alternatively, the relay UE may also start the first timer in other circumstances. The first timer is, for example, timer T311, or may also be other timers.

[0374] S1404: The relay UE suspends all RBs except SRB0. The RBs suspended by the relay UE are Uu RBs. For example, the relay UE may also release the SL RLC bearer of the suspended RBs.

[0375] S1405. The relay UE performs cell selection.

[0376] S1406: The relay UE selects a suitable cell. For example, the relay UE selects a cell that supports the layer 2 relay technology. For example, the cell selected by the relay UE is called a second cell, and the second cell corresponds to a second network device.

[0377] S1407, the relay UE sends the identifier of the second cell to the remote UE, and correspondingly, the remote UE receives the identifier of the second cell from the relay UE. If the relay UE selects a suitable cell, the identifier of the selected cell may be sent to the remote UE, so that the remote UE determines the shortMAC-I according to the identifier of the cell. Then enter S1409.

[0378] S1408: When the first timer times out, the relay UE does not select a suitable cell (for example, the relay UE does not select a cell supporting layer 2 relay technology), the relay UE sends fourth indication information to the remote UE, and correspondingly, the remote UE receives the fourth indication information from the relay UE.

[0379] The fourth indication information may indicate that the RRC re-establishment has failed (in this case, the fourth indication information may also be referred to as the RRC re-establishment failure indication information), or indicate (or request) to release the connection with the remote UE (for example, the PC5-RRC connection). If the remote UE receives the fourth indication information, it may enter the RRC idle state and the process ends. Alternatively, if the remote UE receives the fourth indication information, it may select or reselect a new relay UE and then re-establish the RRC through the new relay UE. The process may refer to Figure 6 Alternatively, if the remote UE receives the fourth indication information, it can initiate RRC re-establishment through Uu. The process can refer to Figure 5 The embodiment shown.

[0380] In addition, if the relay UE has other services of its own in addition to the relay service, and therefore the relay UE needs to enter the RRC connected state, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may perform RRC re-establishment again, but the RRC re-establishment process is not the process introduced in S1409; or, if the relay UE only has the relay service, then if the relay UE fails to select a suitable cell when the first timer times out, or selects a cell that does not support the layer 2 relay technology, the relay UE may enter the RRC idle state.

[0381] S1406 to S1407 and S1408 are two parallel solutions, and one of them is executed according to the cell selection of the relay UE. In addition, S1409 is not executed after S1408 is executed.

[0382] S1409: The relay UE establishes or reestablishes the RLC bearer corresponding to the SRB1 of the remote UE.

[0383] For more information about S1409, please refer to Figure 6 S611 in the embodiment shown, or reference Fig.11 S1105 in the illustrated embodiment. In addition, the RRC re-establishment process of the relay UE will not be described in detail.

[0384] S1410. The remote UE determines shortMAC-I according to the identifier of the second cell.

[0385] The embodiments of the present application can be Figure 4 The embodiments shown in the drawings can be used in combination or can also be used alone. Figure 4The embodiment shown is combined with the application, then after the relay UE sends the identifier of the second cell to the remote UE, the remote UE can determine that the relay UE cannot continue to provide relay services for the remote UE, so that the remote UE can initiate RRC re-establishment according to the first method. The first method can be selected by the remote UE. In the embodiment of the present application, the first method is to initiate RRC re-establishment through the original relay UE as an example.

[0386] After receiving the identity of the serving cell of the relay UE, the remote UE can determine the shortMAC-I according to the identity of the serving cell. Fig.11 Steps S1103 to S1104 and S1106 to S1108 in the illustrated embodiment are not described in detail.

[0387] Optionally, the remote UE may send confirmation information to the relay UE, where the confirmation information is used to confirm RRC re-establishment through the relay UE.

[0388] In an embodiment of the present application, if the relay UE cannot continue to provide relay service for the remote UE, the relay UE can initiate RRC re-establishment by itself. If the relay UE selects a suitable cell, the relay UE can implicitly indicate that the original RRC connection of the relay UE cannot continue to provide relay service for the remote UE by sending the identifier of the selected cell to the remote UE, without sending the third indication information to the remote UE, thereby reducing signaling overhead and enabling the remote UE to initiate RRC re-establishment as soon as possible, thereby improving the efficiency of the remote UE in performing RRC re-establishment.

[0389] This application embodiment provides a twelfth communication method, see Fig.15 , which is a flowchart of the method. In the method, the relay UE still determines that it cannot continue to provide relay services for the remote UE. Through this method, the efficiency of the remote UE in performing RRC re-establishment can be improved. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relayUE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3BThe network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0390] S1501. The relay UE sends an identifier of a second cell to the remote UE. Correspondingly, the remote UE receives the identifier of the second cell from the relay UE.

[0391] The second cell is, for example, a cell selected by the relay UE. Fig.11 The embodiment shown to Fig.14 In combination with any one of the embodiments shown, the manner in which the relay UE sends the identifier of the second cell to the remote UE may refer to the introduction of the corresponding embodiment.

[0392] S1502. The remote UE determines shortMAC-I according to the identifier of the second cell.

[0393] S1503: The remote UE sends a shortMAC-I to the relay UE, and correspondingly, the relay UE receives the shortMAC-I from the remote UE.

[0394] S1504: The relay UE establishes or reestablishes an RLC bearer corresponding to the first SRB of the remote UE. The first SRB is, for example, SRB1.

[0395] For more information about S1504, please refer to Figure 6 S611 in the embodiment shown, or reference Fig.11 S1105 in the illustrated embodiment. In addition, the RRC re-establishment process of the relay UE will not be described in detail.

[0396] S1505: The relay UE sends an RRC re-establishment request message to the second network device. Correspondingly, the second network device receives the RRC re-establishment request message from the relay UE.

[0397] The RRC re-establishment request message may include the shortMAC-I determined by the relay UE, and the identifier of the relay UE, for example, the identifier of the relay UE is the cell-radio network temporary identifier (C-RNTI) of the relay UE. In addition, the RRC re-establishment request message may also include the shortMAC-I determined by the remote UE, and the identifier of the remote UE, for example, the local ID (local ID) or C-RNTI of the remote UE. Of course, the RRC re-establishment request message may also include other corresponding information, which is not limited in the embodiments of the present application.

[0398] S1506: The second network device sends an RRC re-establishment message to the relay UE, and correspondingly, the relay UE receives the RRC re-establishment message from the second network device. For example, the relay UE may receive the RRC re-establishment message via a Uu RLC bearer corresponding to the remote UE.

[0399] The RRC re-establishment message may indicate that the relay UE is allowed to perform RRC re-establishment, and may also indicate that the remote UE is allowed to perform RRC re-establishment. Optionally, the relay UE may send the RRC re-establishment message to the remote UE, for example, the relay UE may send the RRC re-establishment message to the remote UE, so that the remote UE determines that the RRC re-establishment can be performed. For example, the relay UE may send the RRC re-establishment message to the remote UE via the SL RLC bearer corresponding to the remote UE.

[0400] S1507: The relay UE sends an RRC re-establishment completion message to the second network device. Correspondingly, the second network device receives the RRC re-establishment completion message from the relay UE.

[0401] In the embodiment of the present application, both the remote UE and the relay UE need to perform RRC re-establishment, so the remote UE does not need to send an RRC re-establishment request message to the second network device, but the relay UE can carry the information of the remote UE in the RRC re-establishment request message of the relay UE and send it to the second network device. In this way, the signaling overhead can be reduced, and the remote UE can perform RRC re-establishment, so that the service of the remote UE can be restored, and the packet loss caused by service interruption is reduced.

[0402] This application embodiment provides a thirteenth communication method, see Fig.16 , which is a flowchart of the method. In the method, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may enter the RRC idle state to save power consumption. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0403] S1601. A remote UE communicates with a first network device through a relay UE.

[0404] For more information about S1601, please refer to Figure 4 Introduction of S401 in the illustrated embodiment.

[0405] S1602: The remote UE determines that the relay UE cannot continue to provide relay service for the remote UE.

[0406] For more information about S1602, please refer to Figure 4 Introduction to S402 in the illustrated embodiment.

[0407] S1603. The remote UE enters the RRC idle state.

[0408] If the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE can release the PC5-RRC connection with the relay UE and return to the RRC idle state, which is relatively simple to implement and can save power consumption. After the remote UE returns to the RRC idle state, it can re-establish an RRC connection with the network device, or re-select the relay UE to continue the remote UE's service.

[0409] This application embodiment provides a fourteenth communication method, see Fig.17 , which is a flowchart of the method. In the method, if the remote UE determines that the relay UE cannot continue to provide relay services for the remote UE, the remote UE may enter the RRC idle state to save power consumption. Figure 3A The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3A The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3A In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3A Alternatively, if the embodiment of the present application is applied to Figure 3B The network architecture shown in FIG. 1 is shown in FIG. 1 , the remote UE described below may be Figure 3B The remote terminal device in the network architecture shown in FIG. 1 may be a relay UE described below. Figure 3B In the network architecture shown in FIG. 1 , the first network device described below may be a relay terminal device. Figure 3B Network devices in the network architecture shown.

[0410] S1701. The remote UE communicates with the first network device through the relay UE.

[0411] For more information about S1701, please refer to Figure 4 Introduction of S401 in the illustrated embodiment.

[0412] S1702: The relay UE determines that the relay UE cannot continue to provide relay service for the remote UE.

[0413] For example, if the relay UE detects the RLF between the relay UE and the first network device, it may be determined that the relay service cannot be continued to be provided for the remote UE.

[0414] S1703, the relay UE initiates RRC re-establishment. For the process of the relay UE performing RRC re-establishment, please refer to Fig.11 The embodiment shown.

[0415] S1704: The relay UE does not provide relay service before selecting a suitable cell during the RRC re-establishment process or before the RRC re-establishment is completed.

[0416] During the RRC re-establishment process, the relay UE will select a cell. Therefore, before the relay UE selects a suitable cell, the relay UE does not provide relay service. Alternatively, before the RRC re-establishment process of the relay UE is completed, the relay UE does not provide relay service. For example, after the relay UE sends an RRC re-establishment completion message to the second network device, the RRC re-establishment process of the relay UE is deemed to be completed. The second network device is the network device corresponding to the cell selected by the relay UE during the RRC re-establishment process.

[0417] Relay UE does not provide relay service. There are many ways to implement it. The following examples are introduced.

[0418] Method 1: The relay UE does not send a discovery message related to the relay service, or the relay UE refuses to establish a connection with the UE requesting the relay service. Alternatively, the relay UE does not send a discovery message related to the relay service, and the relay UE refuses to establish a connection with the UE requesting the relay service.

[0419] For example, for a UE capable of providing a relay service (e.g., a relay UE), a discovery message may be sent, and the discovery message may include information related to the relay service, such as indicating that the UE sending the discovery message is capable of providing the relay service, etc. Then, in an embodiment of the present application, the relay UE does not send a discovery message related to the relay service before selecting a suitable cell or before the RRC re-establishment process is completed.

[0420] For another example, other UEs may request to establish a PC5 unicast link with the relay UE. The purpose of other UEs requesting to establish a PC5 unicast link may be to request the relay UE to provide a relay service, or it may be for other purposes, such as to perform D2D communication with the relay UE. Then, the relay UE may refuse to establish a connection with the UE requesting the relay service, and the relay UE may continue to establish a connection with the UE that does not request the relay service; or, the relay UE may also refuse to establish a connection with all UEs requesting a connection.

[0421] Mode 2: The relay UE sends sixth indication information, where the sixth indication information may indicate that the relay UE is in the RLF state, or indicates that the relay UE is re-establishing RRC, or indicates that the connection between the relay UE and the first network device is unavailable.

[0422] For example, the relay UE may send the sixth indication information to the remote UE, for example, the sixth indication information may be included in the first message, and the first message may be, for example, a message for establishing a connection between UEs; or, the relay UE may also broadcast the sixth indication information, for example, the sixth indication information may be included in the first message, and the first message may be, for example, a discovery message or a system message, so that more UEs can know the status of the relay UE. The UE (for example, the remote UE) that receives the sixth indication information may not select the relay UE to provide relay service. Or the UE that receives the sixth indication information may continue to select the relay UE to provide relay service, for example, it may request the relay UE to provide relay service again after a period of time.

[0423] Method three: the remote UE sends seventh indication information, and the seventh indication information may indicate not to send a connection establishment request message, or indicate not to perform a PC5 connection establishment process.

[0424] For example, the relay UE may send the seventh indication information to the remote UE, for example, the seventh indication information may be included in the second message, and the second message may be, for example, a message for establishing a connection between UEs; or, the relay UE may also broadcast the sixth indication information, for example, the seventh indication information may be included in the second message, and the second message may be, for example, a discovery message or a system message, so that more UEs can know the status of the relay UE. The UE (for example, the remote UE) receiving the sixth indication information may not select the relay UE to provide relay service, or may not initiate the PC5-unicast link establishment process with the relay UE, for example, may not send a connection establishment request message to the relay UE (the connection establishment request message is used to request the establishment of a PC5 connection), etc. Alternatively, the UE receiving the sixth indication information may continue to select the relay UE to provide relay service, for example, it may request the relay UE to provide relay service again after a period of time.

[0425] Mode 4: The relay UE does not respond to the message used to establish a connection with the relay UE.

[0426] For example, the relay UE does not respond to the message from the remote UE for establishing a connection with the relay UE, or the relay UE does not respond to all messages for establishing a connection with the relay UE. For example, before the relay UE selects a suitable cell, if it receives a connection establishment request message from the remote UE, or the relay UE and the remote UE are in the process of establishing a PC5 unicast link (that is, the PC5 unicast link has not been established), the relay UE may not respond to the remote UE first, for example, the relay UE does not send a message to the remote UE. Afterwards, if the relay UE selects a suitable cell, it can continue to respond to the messages that were not responded to before. For another example, before the RRC re-establishment is completed, if the relay UE receives a connection establishment request message from the remote UE, or the relay UE and the remote UE are in the process of establishing a PC5 unicast link (that is, the PC5 unicast link has not been established), the relay UE may not respond to the remote UE first, for example, the relay UE does not send a message to the remote UE. Afterwards, if the RRC re-establishment of the relay UE is completed, it can continue to respond to the message that was not responded to before.

[0427] Alternatively, the relay UE may also have other implementations for not providing the relay service, which are not limited in the embodiments of the present application. As for the above-mentioned method by which the relay UE implements not providing the relay service, it may be specified by the protocol, or configured by the network device, or determined by the relay UE and the remote UE in advance through negotiation, or determined by the relay UE itself.

[0428] The embodiments of the present application can be Figures 4 to 16 Any of the embodiments shown in the examples may be used in combination, or may not be used in combination with any of the embodiments, but may be used alone. Moreover, the technical solutions of the embodiments of the present application can be applied to both layer 2 relay technology and layer 3 relay technology.

[0429] If the remote UE establishes a PC5 unicast link with a relay UE that is in the process of RLF or RRC reestablishment, the remote UE may not be able to immediately transmit data through the relay UE or cannot connect to the network device through the relay UE, causing a large delay to the remote UE's service. The technical solution of the embodiment of the present application can solve this problem, so that the remote UE can select a more suitable UE to provide relay service as soon as possible, reducing the service interruption time of the remote UE.

[0430] Fig.18 A schematic diagram of the structure of a communication device provided in an embodiment of the present application is given. The communication device 1800 may be Figure 4 The embodiment shown to Fig.17 The first terminal device or the chip system of the first terminal device described in any one of the embodiments shown in the figure is used to implement the method for the first terminal device in the above method embodiment. Alternatively, the communication device may also be Figure 4 The embodiment shown to Fig.17 The second terminal device or the chip system of the second terminal device described in any one of the embodiments shown in the figures is used to implement the method corresponding to the second terminal device in the above method embodiment. Alternatively, the communication device may also be Figure 4 The embodiment shown to Fig.17 The third terminal device or the chip system of the third terminal device described in any of the embodiments shown is used to implement the method corresponding to the third terminal device in the above method embodiment. For specific functions, please refer to the description in the above method embodiment.

[0431] The communication device 1800 includes one or more processors 1801. The processor 1801 may also be referred to as a processing unit, and may implement certain control functions. The processor 1801 may be a general-purpose processor or a dedicated processor, etc. For example, it may include: a baseband processor, a central processing unit, etc. The baseband processor may be used to process the communication protocol and the communication data. The central processing unit may be used to control the communication device 1800, execute software programs and / or process data. Different processors may be independent devices, or may be arranged in one or more processing circuits, for example, integrated in one or more dedicated integrated circuits.

[0432] Optionally, the communication device 1800 includes one or more memories 1802 for storing instructions 1804, and the instructions 1804 can be executed on the processor so that the communication device 1800 performs the method described in the above method embodiment. Optionally, data can also be stored in the memory 1802. The processor and the memory can be set separately or integrated together.

[0433] Optionally, the communication device 1800 may include instructions 1803 (sometimes also referred to as codes or programs), and the instructions 1803 may be executed on the processor so that the communication device 1800 executes the method described in the above embodiment. The processor 1801 may store data.

[0434] Optionally, the communication device 1800 may further include a transceiver 1805 and an antenna 1806. The transceiver 1805 may be referred to as a transceiver unit, a transceiver, a transceiver circuit, a transceiver, an input / output interface, etc., and is used to implement the transceiver function of the communication device 1800 through the antenna 1806.

[0435] Optionally, the communication device 800 may also include one or more of the following components: a wireless communication module, an audio module, an external memory interface, an internal memory, a universal serial bus (USB) interface, a power management module, an antenna, a speaker, a microphone, an input / output module, a sensor module, a motor, a camera, or a display screen, etc. It is understood that in some embodiments, the communication device 1800 may include more or fewer components, or some components may be integrated, or some components may be separated. These components may be implemented in hardware, software, or a combination of software and hardware.

[0436] The processor 1801 and the transceiver 1805 described in the embodiments of the present application may be implemented in an integrated circuit (IC), an analog IC, a radio frequency integrated circuit (RFID), a mixed signal IC, an application specific integrated circuit (ASIC), a printed circuit board (PCB), or an electronic device, etc. The communication device described herein may be an independent device (e.g., an independent integrated circuit, a mobile phone, etc.), or may be a part of a larger device (e.g., a module that can be embedded in other devices). For details, please refer to the aforementioned description of the terminal device and the network device, which will not be repeated here.

[0437] The present application embodiment provides a terminal device, which can be used in the above embodiments (for the convenience of description, referred to as UE). The terminal device includes a Figure 4 The embodiment shown to Fig.17 The corresponding means, units and / or circuits of the first terminal device, the second terminal device or the third terminal device functions described in any of the embodiments shown in the embodiments. For example, the terminal device includes a transceiver module to support the terminal device to implement the transceiver function, and a processing module to support the terminal device to process the signal.

[0438] Fig.19 A schematic diagram of the structure of a terminal device provided in an embodiment of the present application is given.

[0439] The terminal device 1900 can be applied to Figure 1 , Figure 3A or Figure 3B In the architecture shown in any of the accompanying drawings. For ease of explanation, Fig. 9 Only the main components of the terminal device 1900 are shown. Fig.19 As shown, the terminal device 1900 includes a processor, a memory, a control circuit, an antenna, and an input-output device. The processor is mainly used to process the communication protocol and communication data, and to control the entire terminal device 1900, execute the software program, and process the data of the software program. The memory is mainly used to store software programs and data. The control circuit is mainly used for converting baseband signals and radio frequency signals and processing radio frequency signals. The antenna is mainly used to send and receive radio frequency signals in the form of electromagnetic waves. The input-output device, such as a touch screen, a display screen, a microphone, a keyboard, etc., is mainly used to receive data input by the user and output data to the user.

[0440] Those skilled in the art will appreciate that for ease of description, Fig.19 Only one memory and processor are shown. In some embodiments, the terminal device 1900 may include multiple processors and memories. The memory may also be referred to as a storage medium or a storage device, etc., which is not limited in the embodiments of the present application.

[0441] In one example, the antenna with transceiver functions and the control circuit can be regarded as the transceiver unit 1910 of the terminal device 1900, and the processor with processing function can be regarded as the processing unit 1920 of the terminal device 1900. Fig.19 As shown, the terminal device 1900 includes a transceiver unit 1910 and a processing unit 1920. The transceiver unit may also be referred to as a transceiver, a transceiver, a transceiver device, etc. Optionally, the device used to implement the receiving function in the transceiver unit 1910 may be regarded as a receiving unit, and the device used to implement the sending function in the transceiver unit 1910 may be regarded as a sending unit, that is, the transceiver unit 1910 includes a receiving unit and a sending unit. Exemplarily, the receiving unit may also be referred to as a receiver, a receiver, a receiving circuit, etc., and the sending unit may be referred to as a transmitter, a transmitter, or a transmitting circuit, etc.

[0442] When several embodiments provided in this application are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. The computer software product is stored in a storage medium, including several instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of this application. The aforementioned computer-readable storage medium may be any available medium that can be accessed by a computer. Taking this as an example but not limited to: a computer-readable medium may include a random access memory (RAM), a read-only memory (ROM), or any other medium that can be used to carry or store a desired program code in the form of an instruction or data structure and can be accessed by a computer.

[0443] The above is only a specific implementation of the present application, but the protection scope of the embodiments of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the embodiments of the present application, which should be included in the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application should be based on the protection scope of the claims.

Claims

1. A communication method, characterized in that: include: When the first terminal device determines that the second terminal device cannot continue to provide relay services for the first terminal device, the first terminal device initiates RRC re-establishment through a first method, where the first method is determined according to the first information, and the first method is a method of initiating RRC re-establishment through a Uu interface, or a method of initiating RRC re-establishment through a new terminal device, or a method of initiating RRC re-establishment through the second terminal device; wherein, The method further includes: the first terminal device receiving the first information from the first network device through the second terminal device, the first information being used to indicate initiating RRC re-establishment through Uu, or initiating RRC re-establishment through a new terminal device, or initiating RRC re-establishment through the second terminal device; or, The first information includes the RSRP of the cell selected by the first terminal device and / or the RSRP of a third terminal device selected by the first terminal device; Wherein, when the first manner is a manner of initiating RRC re-establishment through a Uu interface, the method further includes: The first terminal device starts a first timer; wherein the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device selects a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device completes establishing a connection with a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device obtains an identifier of a service cell of a new terminal device that can provide a relay service selected by the first terminal device; The first terminal device selects the first cell and stops the first timer.

2. The method according to claim 1, characterized in that In the case where the first information includes the RSRP of the cell selected by the first terminal device and / or the RSRP of a third terminal device selected by the first terminal device, When the RSRP of the first cell is less than or equal to the first RSRP threshold and the first terminal device has not selected a terminal device that can provide a relay service, the first manner is a manner of initiating RRC re-establishment through a Uu interface, and the first cell is a cell selected by the first terminal device; or, In a case where the RSRP of the first cell is greater than a first RSRP threshold, the first manner is a manner of initiating RRC re-establishment through a Uu interface, and the first cell is a cell selected by the first terminal device; or, When the RSRP of the cell selected by the first terminal device is less than or equal to the first RSRP threshold, and the first terminal device selects a third terminal device that can provide a relay service, the first manner is to initiate RRC re-establishment through the third terminal device; or, When the difference between the RSRP of the cell selected by the first terminal device and the RSRP of the third terminal device is less than or equal to the first RSRP threshold, the first method is a method of initiating RRC re-establishment through the third terminal device, and the third terminal device is a new terminal device selected by the first terminal device that can provide relay service, or the third terminal device and the second terminal device are the same terminal device.

3. The method according to claim 1 or 2, characterized in that: The first terminal device determines that the second terminal device cannot continue to provide a relay service for the first terminal device, including: The first terminal device detects the SL RLF between the first terminal device and the second terminal device; or, The first protocol layer of the first terminal device requests to release the connection between the first terminal device and the second terminal device.

4. The method according to claim 1 or 2, characterized in that: The first terminal device starts a first timer, including: When the first terminal device initiates RRC re-establishment in the first manner, the first timer is started; or, When the first terminal device determines that the second terminal device cannot continue to provide relay service for the first terminal device, starting the first timer; or, The first terminal device starts the first timer after initiating RRC re-establishment in the first manner and before performing cell selection.

5. The method according to claim 1 or 2, characterized in that: In a case where the first manner is a manner of initiating RRC re-establishment through a Uu interface, after the first terminal device initiates RRC re-establishment through the first manner, the method further includes: The first terminal device does not select a cell, or the cell selected by the first terminal device is no longer suitable, or the first terminal device does not receive an RRC re-establishment message from the second network device, or the RSRP of the cell selected by the first terminal device is less than or equal to a second RSRP threshold, and the second network device is the network device for the first terminal device to initiate the RRC re-establishment; The first terminal device selects a new terminal device capable of providing a relay service; In the case that the first terminal device selects the third terminal device, the first terminal device initiates RRC re-establishment through the third terminal device, and the third terminal device can provide relay service for the first terminal device.

6. The method according to claim 5, characterized in that The first terminal device fails to select a cell, including: When the first timer times out, the first terminal device has not selected a cell, and the first timer is started when the first terminal device initiates RRC re-establishment through the first method, or the first timer is started when the first terminal device determines that the second terminal device cannot continue to provide relay service for the first terminal device, or the first timer is started after the first terminal device initiates RRC re-establishment through the first method and before performing cell selection.

7. The method according to claim 5, characterized in that The first terminal device does not receive an RRC re-establishment message from the second network device, including: When the second timer times out, the first terminal device has not received the RRC re-establishment message from the second network device, and the second timer is started after the first terminal device selects a cell.

8. The method according to claim 1 or 2, characterized in that: In the case where the first manner is a manner of initiating RRC re-establishment by a new terminal device, the method further includes: When the first terminal device initiates RRC re-establishment by the first method, or when the first terminal device determines that the second terminal device cannot continue to provide relay service for the first terminal device, or before the first terminal device reselects a terminal device that can provide relay service, the first terminal device starts a second timer; When the first terminal device selects the third terminal device, or when the first terminal device completes establishing a connection with the third terminal device, or when the first terminal device obtains the identifier of the service cell of the third terminal device, the first terminal device stops the second timer.

9. The method according to claim 8, characterized in that The first terminal device initiating RRC re-establishment by using the first method includes: The first terminal device establishes a SL RLC bearer for the first SRB; The first terminal device sends an RRC re-establishment request message to a second network device through the third terminal device, where the second network device is a network device accessed by the third terminal device; The first terminal device receives an RRC re-establishment message from the second network device through the third terminal device, and the RRC re-establishment message is transmitted on the first SRB.

10. The method according to claim 1 or 2, characterized in that: In the case where the first manner is a manner of initiating RRC re-establishment by a new terminal device, the method further includes: The first terminal device starts a first timer; wherein the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device selects a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device completes establishing a connection with a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device obtains an identifier of a service cell of a new terminal device that can provide a relay service selected by the first terminal device; The first terminal device reselects a terminal device capable of providing relay services, and when the third terminal device is selected, the first terminal device stops the first timer; or, the first terminal device reselects a terminal device capable of providing relay services, and when the third terminal device is selected and a connection is established with the third terminal device, the first terminal device stops the first timer; or, the first terminal device reselects a terminal device capable of providing relay services, and when the third terminal device is selected and an identifier of a service cell of the third terminal device is obtained, the first terminal device stops the first timer.

11. The method according to claim 10, characterized in that The first terminal device starts a first timer, including: When the first terminal device initiates RRC re-establishment in the first manner, the first timer is started; or, When the first terminal device determines that the second terminal device cannot continue to provide relay service for the first terminal device, starting the first timer; or, The first terminal device starts the first timer after initiating RRC re-establishment through the first method and before reselecting a terminal device that can provide relay service.

12. The method according to any one of claims 1, 2, 9 and 11, characterized in that: In the case where the first manner is a manner of initiating RRC re-establishment by a new terminal device, the method further includes: The first terminal device sends data of a second SRB to a third terminal device, where the second SRB is an SRB between the first terminal device and a second network device, the second network device is a network device accessed by the third terminal device, and the third terminal device is a new terminal device selected by the first terminal device; The third terminal device receives data of the second SRB from the first terminal device; The third terminal device establishes or reconstructs an RLC bearer corresponding to a first SRB of the first terminal device, the RLC bearer of the first SRB including a first RLC bearer between the first terminal device and the third terminal device and a second RLC bearer between the first terminal device and the second network device, and the first SRB is an SRB between the first terminal device and the second network device; The third terminal device sends the data of the second SRB to the second network device; The third terminal device receives data of the first SRB from the second network device through the second RLC bearer; The third terminal device sends the data of the first SRB to the first terminal device through the first RLC bearer.

13. The method according to claim 12, characterized in that The third terminal device establishing or re-establishing an RLC bearer corresponding to the first SRB of the first terminal device includes: The third terminal device receives data of the second SRB from the first terminal device, and the third terminal device establishes or reconstructs the RLC bearer of the first SRB; or, The third terminal device receives first indication information from the second network device, and the third terminal device establishes or reconstructs the RLC bearer of the first SRB, wherein the first indication information is used to indicate the establishment of the RLC bearer of the first SRB, or indicates receiving the data of the first SRB sent by the second network device to the first terminal device, or indicates receiving the RRC re-establishment message sent by the second network device to the first terminal device, or indicates that the first terminal device sends an RRC re-establishment request message through the third terminal device; or, The third terminal device receives second indication information from the first terminal device, and the third terminal device establishes or reconstructs the RLC bearer of the first SRB, and the second indication information is used to indicate the establishment of the RLC bearer of the first SRB, or indicates the reception of data of the first SRB sent by the second network device to the first terminal device, or indicates the reception of an RRC re-establishment message sent by the second network device to the first terminal device, or indicates that the first terminal device has sent an RRC re-establishment request message through the third terminal device.

14. The method according to claim 1 or 2, characterized in that: In a case where the first manner is a manner of initiating RRC re-establishment by the second terminal device, the method further includes: The second terminal device detects RLF between the second terminal device and the first network device; The second terminal device initiates RRC re-establishment.

15. The method according to claim 14, characterized in that The method further comprises: The second terminal device sends third indication information to the first terminal device, where the third indication information is used to indicate RRC re-establishment or to indicate that RLF occurs in the second terminal device.

16. The method according to claim 15, characterized in that The first terminal device determines that the second terminal device cannot continue to provide a relay service for the first terminal device, including: The first terminal device determines, based on the third indication information, that the second terminal device cannot continue to provide relay service for the first terminal device.

17. The method according to claim 16, characterized in that The method further comprises: After receiving the third indication information, the first terminal device starts a fifth timer; When the fifth timer times out, if the first terminal device has not received the identifier of the second cell from the second terminal device, the first terminal device enters the RRC idle state; or, before the fifth timer times out, if the first terminal device receives the identifier of the second cell from the second terminal device, the first terminal device turns off the fifth timer; wherein the second cell is the cell selected by the second terminal device.

18. The method according to any one of claims 15 to 17, characterized in that: The method further comprises: After the RRC re-establishment is completed, the second terminal device sends an identifier of the second cell to the first terminal device; or, When the second terminal device selects the second cell, the second terminal device sends an identifier of the second cell to the first terminal device; The second cell is a cell selected by the second terminal device by initiating RRC re-establishment.

19. The method according to claim 18, characterized in that After the second terminal device initiates RRC re-establishment, the method further includes: The second terminal device fails to select a cell, and the second terminal device sends fourth indication information to the first terminal device, where the fourth indication information is used to indicate that the RRC re-establishment fails, or to indicate to release the connection with the first terminal device; After receiving the fourth indication information, the first terminal device enters the RRC idle state, or selects a new terminal device to initiate RRC re-establishment, or initiates RRC re-establishment through the Uu interface.

20. The method according to claim 15 or 16, characterized in that The method further comprises: The first terminal device sends fifth indication information to the second terminal device, where the fifth indication information is used to indicate not to perform RRC re-establishment through the second terminal device, or to indicate to release the connection with the second terminal device.

21. The method according to claim 14, characterized in that The method further comprises: The second terminal device does not provide relay service before selecting a suitable cell during the RRC re-establishment process or before the RRC re-establishment is completed.

22. The method according to claim 21, characterized in that The second terminal device does not provide a relay service, including: The second terminal device does not send a discovery message related to the relay service, or refuses to establish a connection with the terminal device requesting to provide the relay service.

23. The method according to claim 21, characterized in that The second terminal device does not provide a relay service, including: The second terminal device sends sixth indication information to the first terminal device, where the sixth indication information is used to indicate that the second terminal device is in an RLF state, or indicates that the second terminal device is performing RRC re-establishment, or indicates that the connection between the second terminal device and the first network device is unavailable.

24. The method according to claim 23, characterized in that The sixth indication information is included in a first message, where the first message is a discovery message or a message used to establish a connection between terminal devices.

25. The method according to claim 21, characterized in that The second terminal device does not provide a relay service, including: The second terminal device sends seventh indication information to the first terminal device, where the seventh indication information is used to indicate not to send a connection establishment request message or to indicate not to perform a PC5 connection establishment process.

26. The method according to claim 25, characterized in that The seventh indication information is included in a second message, and the second message is a discovery message, or a message used to establish a connection between terminal devices.

27. The method according to claim 21, characterized in that The second terminal device does not provide a relay service, including: The second terminal device does not respond to a message from the first terminal device for establishing a connection with the second terminal device.

28. The method according to claim 27, characterized in that The method further comprises: After selecting a new cell or completing RRC re-establishment, the second terminal device responds to a message from the first terminal device for establishing a connection with the second terminal device.

29. A communication system, characterized in that: It includes a first terminal device and a second terminal device, wherein: The second terminal device is used to receive first data from the first terminal device and send the first data to the first network device, or to receive second data from the first network device and send the second data to the first terminal device, wherein the second terminal device provides a relay service for the first terminal device; The first terminal device is used to determine that the second terminal device cannot continue to provide a relay service for the first terminal device, and initiate RRC re-establishment through a first manner, where the first manner is determined according to first information, the first information comes from the first network device, and the first manner is a manner of initiating RRC re-establishment through a Uu interface, or a manner of initiating RRC re-establishment through a new terminal device, or a manner of initiating RRC re-establishment through the second terminal device; Wherein, when the first mode is a mode of initiating RRC re-establishment through the Uu interface: The first terminal device is further used to start a first timer; wherein the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device selects a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device completes establishing a connection with a new terminal device that can provide a relay service; or, the first timer is used to stop when the first terminal device selects a cell, or is used to stop when the first terminal device obtains an identifier of a service cell of a new terminal device that can provide a relay service selected by the first terminal device; The first terminal device is also used to select the first cell and stop the first timer.

30. A communication device, characterized in that: It includes a transceiver unit and a processing unit, and the transceiver unit and the processing unit are coupled and can execute the method executed by the first terminal device as described in any one of claims 1 to 28, or execute the method executed by the second terminal device as described in any one of claims 1 to 28, or execute the method executed by the third terminal device as described in any one of claims 1 to 28.

31. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store a computer program. When the computer program is run on a computer, the computer executes the method executed by the first terminal device as described in any one of claims 1 to 28, or the computer executes the method executed by the second terminal device as described in any one of claims 1 to 28, or the computer executes the method executed by the third terminal device as described in any one of claims 1 to 28.

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