Communication method and apparatus

Abstract

Provided in the present application are a communication method and apparatus. The method comprises: receiving first downlink data of a terminal device; and when a first condition is met, sending a first message to a first satellite or a second network device on the first satellite, wherein the first message comprises the first downlink data of the terminal device and context information of the terminal device, the context information comprises access stratum security context information and / or non-access stratum context information of the terminal device, and the first condition comprises one or more of the following: the terminal device accessing a network by means of a satellite and supporting a store and forward mode, or a communication link between a first network device and the first satellite being available, and a communication link between the terminal device and the first satellite cannot be currently established. By means of the present application, the security and reliability of data transmission between a satellite and a terminal device can be ensured in a store and forward scenario.

Description

Communication methods and devices

[0001] This application claims priority to Chinese Patent Application No. 202410521273.4, filed on April 26, 2024, entitled "Communication Method and Apparatus", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of communication technology, and in particular to a communication method and apparatus. Background Technology

[0003] Small packet data transmission in terrestrial mobile communication networks for cellular Internet of Things (CIoT) devices can include two types: one is user data transmission based on the user plane, known as User Plane CIoT Evolved Packet System (EPS) optimization; the other is user data transmission based on the control plane, known as Control Plane CIoT EPS optimization. The characteristic of Control Plane CIoT EPS optimization is that it does not require establishing a data bearer. After the data arrives at the user's serving gateway, the Mobility Management Entity (MME) network element includes the data in a Non-Access Stratum Packet Data Unit (NAS PDU) and sends it to the base station. The base station then transmits the NAS PDU to the CIoT user via an RRC message.

[0004] In a non-terrestrial network (NTN), the link between a satellite and a terminal device is called a service link, the link between a satellite and a ground network gateway station is called a feeder link, and the link between satellites is called an inter-satellite link (ISL). When a terminal device accesses the network through an NTN, it can utilize the above communication links to achieve end-to-end connectivity between the terminal device, the satellite, and the network, i.e., terminal device - service link - satellite 1 (- inter-satellite link - satellite 2) - feeder link - ground network.

[0005] However, for some extremely remote areas where no gateway stations are deployed nearby, there is a limitation of discontinuous feeder links. For example, when satellites cover users in these areas (i.e., when the service link is available), it is impossible to connect to the terrestrial network providing services to these users via the feeder link; similarly, when satellites cover gateway stations of the terrestrial network (i.e., when the feeder link is available), it is impossible to cover users in these areas. To meet the communication needs of these extremely remote areas, NTN can transmit CIoT small packet data to users in these areas through store and forward (S&F). For uplink signaling / data transmission, "store" refers to storing uplink signaling / data from the terminal device on the satellite, and "forward" refers to forwarding the cached uplink signaling / data to the terrestrial network; for downlink signaling / data transmission, "store" refers to storing downlink signaling / data from the terrestrial network on the satellite, and "forward" refers to forwarding the cached downlink signaling / data to the terminal device.

[0006] In the S&F scenario, ensuring the security and reliability of data transmission between satellites and terminal equipment is a problem that those skilled in the art are currently addressing. Summary of the Invention

[0007] This application proposes a communication method and apparatus that can ensure the security and reliability of data transmission between satellites and terminal devices in a store-and-forward scenario.

[0008] In a first aspect, embodiments of this application provide a communication method applicable to a first network device. This method can be executed by the first network device, by components within the first network device (e.g., a processor, chip, or chip system), or by a logic module or software capable of implementing all or part of the functions of the first network device. The method includes: receiving first downlink data from a terminal device; and, when a first condition is met, sending a first message to a first satellite or a second network device on the first satellite. The first message includes the first downlink data from the terminal device and context information of the terminal device. The context information includes access layer security context information and / or non-access layer context information of the terminal device. The first condition includes one or more of the following: the terminal device accesses the network via a satellite and supports store-and-forward mode; or a communication link between the first network device and the first satellite is available, and a communication link cannot currently be established between the terminal device and the first satellite.

[0009] For example, the first network device is a Mobility Management Entity (MME) network element.

[0010] In the above method, by sending a first message to the first satellite or the network device on the first satellite, the first satellite or the network device on the first satellite can establish a secure communication link with the terminal device based on the uplink and downlink information in the first message. Then, when the service link is available, the first satellite or the network device on the first satellite and the terminal device can transmit data on the established secure communication link. That is, on the secure communication link, the first satellite or the network device on the first satellite sends first downlink data to the terminal device, thereby ensuring the security and reliability of data transmission between the satellite and the terminal device.

[0011] In one possible implementation, the method further includes: caching the first downlink data.

[0012] In another possible implementation, the method further includes: determining a first downlink data transmission record and starting a timer, wherein the first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device.

[0013] For example, one first downlink data corresponds to one first downlink data transmission record, and one first downlink data transmission record corresponds to one timer.

[0014] In the above method, it is possible to accurately determine whether the first downlink data has been successfully sent in a store-and-forward scenario based on whether the timer has timed out. This avoids the situation where the user has to wait indefinitely because it is impossible to determine whether the first downlink data has been successfully sent, thus ensuring data transmission latency and improving data transmission reliability.

[0015] In another possible implementation, the duration of the timer is determined based on satellite coverage information and paging strategy information; wherein the duration of the timer is greater than a first duration, which is the duration from the start time of the timer to the moment when the first satellite covers the first network device again.

[0016] In another possible implementation, the method further includes: receiving a service request message from a terminal device, the service request message indicating that the first downlink data was successfully transmitted; deleting the first downlink data transmission record and the cached first downlink data.

[0017] The above method can free up storage space, thereby ensuring maximum resource utilization.

[0018] In another possible implementation, receiving the service request message from the terminal device includes: receiving the service request message from the terminal device before the timer expires.

[0019] In the above method, if the service request message from the terminal device is received before the timer expires, that is, if the first downlink data is successfully sent before the timer expires, the latency of data transmission can be guaranteed and the reliability of data transmission can be improved.

[0020] In another possible implementation, the method further includes: receiving a second message before the timer expires; and determining whether the first downlink data was successfully sent based on the second message.

[0021] For example, the second message is a tracking area update request message.

[0022] For example, before the first network device receives the second message, the terminal device may remove itself from the original tracking area list, detect that it has entered a new tracking area that is not in the original tracking area list, or trigger the terminal device to initiate a tracking area update process due to periodic tracking area update timers, etc.

[0023] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0024] In another possible implementation, the second message includes a timestamp and / or the identification information of the last serving device. The timestamp indicates the moment when the terminal device was removed from the tracking area list, and the identification information of the last serving device indicates the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list. The timestamp includes one or more of the following: the moment when the terminal device last received satellite network service before being removed from the tracking area list; the moment when the terminal device first received satellite network service after being removed from the tracking area list; the moment when the terminal device sent the second message, or the moment when the satellite received the second message.

[0025] In another possible implementation, the second message includes a timestamp, and determining that the first downlink data was not successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the time indicated by the timestamp, determining that the first downlink data was not successfully transmitted, and the location of the terminal device includes the last tracked area accessed by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list.

[0026] In the above method, the first network device can identify downlink data that could not be successfully sent due to the movement of the terminal device during the tracking area update process, and retransmit the first downlink data, thus ensuring data integrity. Moreover, it does not need to wait for the timer corresponding to the first downlink data to expire, thereby reducing data transmission latency and improving data transmission reliability.

[0027] In another possible implementation, the second message includes a timestamp, and determining that the first downlink data was successfully transmitted based on the second message includes: if the first satellite receives the first downlink data and the time when the terminal device location is first covered is before the time indicated by the timestamp, receiving a service request message from the terminal device, wherein the terminal device location includes the last tracked area accessed by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list; and determining that the first downlink data was successfully transmitted.

[0028] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0029] In another possible implementation, the second message includes the identification information of the last serving device. The determination that the first downlink data was not successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, the determination that the first downlink data was not successfully transmitted is made. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

[0030] In the above method, the first network device can identify downlink data that could not be successfully sent due to the movement of the terminal device during the tracking area update process, and retransmit the first downlink data to ensure data integrity. Moreover, it does not need to wait for the timer corresponding to the first downlink data to expire, thereby reducing the latency of data transmission and improving the reliability of data transmission.

[0031] In another possible implementation, the second message includes the identification information of the last serving device. Determining that the first downlink data was successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, receiving a service request message from the terminal device, wherein the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; and determining that the first downlink data was successfully transmitted.

[0032] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0033] In another possible implementation, the method further includes: if it is determined from the second message that the first downlink data was not successfully sent, retransmitting the first downlink data.

[0034] The above method ensures data integrity and eliminates the need to wait for the timer corresponding to the first downlink data to time out, thereby reducing data transmission latency and improving data transmission reliability.

[0035] In another possible implementation, the method further includes: retransmitting the first downlink data until the timer expires and no service request message is received from the terminal device.

[0036] The above method ensures data integrity and eliminates the need to wait for the timer corresponding to the first downlink data to time out, thereby reducing data transmission latency and improving data transmission reliability.

[0037] In another possible implementation, the method further includes: when retransmissions exceed N times, or the time for caching the first downlink data exceeds duration T, deleting the first downlink data transmission record and the cached first downlink data, and ceasing retransmission operations, where N is a positive integer greater than 0, and T is greater than 0. This approach ensures efficient resource utilization and avoids resource waste.

[0038] In another possible implementation, the method further includes: receiving a third message from a third network device; and sending a fourth message to the third network device, the fourth message including context information of the terminal device, first downlink data of the terminal device, the first downlink data transmission record, and the timer. This approach ensures the normal operation of the system.

[0039] In another possible implementation, the method further includes sending a fifth message, which includes identification information of a third network device, and this fifth message is used to instruct the sending of a service request message from the terminal device to the third network device. This approach ensures the normal operation of the system.

[0040] Secondly, embodiments of this application provide a communication method applicable to a third network device. This method can be executed by the third network device, by components within the third network device (e.g., processors, chips, or chip systems), or by a logic module or software capable of implementing all or part of the functions of the third network device. The method includes: receiving a second message, the second message including a timestamp and / or identification information of the last serving device; the timestamp indicating the moment a terminal device is removed from the tracking area list, and the identification information of the last serving device indicating the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list; receiving a fourth message from a first network device, the fourth message including context information of the terminal device, first downlink data of the terminal device, a first downlink data transmission record corresponding to the first downlink data, and a timer corresponding to the first downlink data transmission record, the first downlink data transmission record including identification information of the terminal device, identification information of the first downlink data, and identification information of the first satellite or the second network device; and determining whether the first downlink data was successfully transmitted based on the second message.

[0041] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0042] In one possible implementation, the timestamp includes one or more of the following: the last time the terminal device received satellite network service before being removed from the tracking area list; the first time the terminal device received satellite network service after being removed from the tracking area list; the time the terminal device sent the second message; or the time the satellite received the second message.

[0043] In another possible implementation, the second message includes a timestamp, and determining that the first downlink data was not successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the time indicated by the timestamp, determining that the first downlink data was not successfully transmitted, and the location of the terminal device includes the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list.

[0044] In the above method, the third network device can identify downlink data that could not be successfully sent due to the movement of the terminal device during the tracking area update process, and retransmit the first downlink data, thus ensuring data integrity. Moreover, it does not need to wait for the timer corresponding to the first downlink data to expire, thereby reducing data transmission latency and improving data transmission reliability.

[0045] In another possible implementation, the second message includes a timestamp, and determining that the first downlink data was successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the time indicated by the timestamp, receiving a service request message from the terminal device, wherein the location of the terminal device includes the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list; and determining that the first downlink data was successfully transmitted.

[0046] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0047] In another possible implementation, the third message includes the identification information of the last serving device. The determination that the first downlink data was not successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, the determination that the first downlink data was not successfully transmitted is made. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

[0048] In the above method, the third network device can identify downlink data that could not be successfully sent due to the movement of the terminal device during the tracking area update process, and retransmit the first downlink data to ensure data integrity. Moreover, it does not need to wait for the timer corresponding to the first downlink data to expire, thereby reducing the latency of data transmission and improving the reliability of data transmission.

[0049] In another possible implementation, the third message includes the identification information of the last serving device. The determination that the first downlink data was successfully transmitted based on the second message includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, receiving a service request message from the terminal device, wherein the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; and determining that the first downlink data was successfully transmitted.

[0050] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0051] In another possible implementation, the method further includes: if it is determined from the second message that the first downlink data was not successfully sent, retransmitting the first downlink data.

[0052] The above method ensures data integrity and eliminates the need to wait for the timer corresponding to the first downlink data to time out, thereby reducing data transmission latency and improving data transmission reliability.

[0053] In another possible implementation, the method further includes: receiving a service request message from the terminal device, the service request message indicating that the first downlink data was successfully transmitted; and deleting the first downlink data transmission record and the cached first downlink data. By employing the above methods, storage space can be freed up, thereby ensuring maximum resource utilization.

[0054] In another possible implementation, receiving the service request message from the terminal device includes: receiving the service request message from the terminal device before the timer expires.

[0055] In the above method, if the service request message from the terminal device is received before the timer expires, that is, if the first downlink data is successfully sent before the timer expires, the latency of data transmission can be guaranteed and the reliability of data transmission can be improved.

[0056] In another possible implementation, the method further includes: retransmitting the first downlink data until the timer expires and no service request message is received from the terminal device.

[0057] The above method ensures data integrity and eliminates the need to wait for the timer corresponding to the first downlink data to time out, thereby reducing data transmission latency and improving data transmission reliability.

[0058] In another possible implementation, the method further includes: when retransmissions exceed N times, or the time for caching the first downlink data exceeds duration T, deleting the first downlink data transmission record and the cached first downlink data, and ceasing retransmission operations, where N is a positive integer greater than 0, and T is greater than 0. This approach ensures efficient resource utilization and avoids resource waste.

[0059] Thirdly, embodiments of this application provide a communication method applicable to a terminal device. This method can be executed by the terminal device itself, by components within the terminal device (e.g., processors, chips, or chip systems), or by a logic module or software capable of implementing all or part of the terminal device's functions. The method includes: sending a second message to determine whether first downlink data was successfully transmitted; the second message including a timestamp and / or the identification information of the last serving device; the timestamp indicating the moment the terminal device was removed from the tracking area list; and the identification information of the last serving device indicating the identification information of the last satellite or network device to receive satellite network services before the terminal device was removed from the tracking area list; if the first downlink data was not successfully transmitted, receiving retransmitted first downlink data. Through the above method, data integrity and data transmission reliability can be guaranteed.

[0060] Fourthly, embodiments of this application provide a communication method applicable to a first satellite or a second network device on the first satellite. This method can be executed by the first satellite or the second network device on the first satellite, or by components (e.g., processors, chips, or chip systems) within the first satellite or the second network device on the first satellite, or by a logic module or software capable of implementing all or part of the functions of the first satellite or the second network device on the first satellite. The method includes: receiving a first message, the first message including first downlink data from a terminal device and context information of the terminal device, the context information including access layer security context information and / or non-access layer security context information of the terminal device; establishing a secure connection with the terminal device based on the context information; and sending the first downlink data to the terminal device.

[0061] In the above method, when the service link is available, the first satellite or the network device on the first satellite and the terminal device can transmit data on the established secure communication link. That is, on the secure communication link, the first satellite or the network device on the first satellite sends the first downlink data to the terminal device, thereby ensuring the security of data transmission between the satellite and the terminal device.

[0062] In one possible implementation, the method further includes: receiving a service request message from a terminal device; and sending the service request message from the terminal device to indicate that the first downlink data was successfully transmitted.

[0063] In the above method, the relevant resources corresponding to the first downlink data can be further determined through the above approach, thereby reasonably optimizing the resources.

[0064] Fifthly, embodiments of this application provide a communication method applicable to a first satellite or a second network device on the first satellite. This method can be executed by the first satellite or the second network device on the first satellite, or by components (e.g., processors, chips, or chip systems) within the first satellite or the second network device on the first satellite, or by a logic module or software capable of implementing all or part of the functions of the first satellite or the second network device on the first satellite. The method includes: receiving a second message to determine whether first downlink data was successfully transmitted; the second message including a timestamp and / or the identification information of the last serving device; the timestamp indicating the time when the terminal device was removed from the tracking area list; and the identification information of the last serving device indicating the identification information of the satellite that last received satellite network service before the terminal device was removed from the tracking area list; if the first downlink data was not successfully transmitted, sending retransmitted first downlink data. Through the above method, data integrity and data transmission reliability can be guaranteed.

[0065] In one possible implementation, the method further includes: receiving a fifth message, the fifth message including identification information of a third network device; and sending a service request message from a terminal device to the third network device.

[0066] Sixthly, embodiments of this application provide a communication method applicable to a second satellite or a fourth network device on the second satellite. This method can be executed by the second satellite or the fourth network device on the second satellite, or by components (e.g., processors, chips, or chip systems) within the second satellite or the fourth network device on the second satellite, or by a logic module or software capable of implementing all or part of the functions of the second satellite or the fourth network device on the second satellite. The method includes: receiving a second message to determine whether first downlink data was successfully transmitted; the second message including a timestamp and / or the identification information of the last serving device; the timestamp indicating the time when the terminal device was removed from the tracking area list; and the identification information of the last serving device indicating the identification information of the satellite that last received satellite network service before the terminal device was removed from the tracking area list; if the first downlink data was not successfully transmitted, sending retransmitted first downlink data. Through the above method, data integrity and data transmission reliability can be guaranteed.

[0067] In a seventh aspect, embodiments of this application provide a communication device, which may be a first network device, a component of the first network device (e.g., a processor, chip, or chip system), or a logic module or software capable of implementing all or part of the functions of the first network device. The device includes a processing unit and a transceiver unit. The transceiver unit is configured to receive first downlink data from a terminal device. The processing unit is further configured to, under a first condition, send a first message to a first satellite or a second network device on the first satellite via the transceiver unit. The first message includes the first downlink data from the terminal device and context information of the terminal device. The context information includes access layer security context information and / or non-access layer context information of the terminal device. The first condition includes one or more of the following: the terminal device accesses the network via a satellite and supports store-and-forward mode; or a communication link between the first network device and the first satellite is available, and a communication link cannot currently be established between the terminal device and the first satellite.

[0068] In one possible implementation, the transceiver unit is also used to cache the first downlink data.

[0069] In another possible implementation, the processing unit is further configured to determine a first downlink data transmission record and start a timer, wherein the first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device.

[0070] In another possible implementation, the duration of the timer is determined based on satellite coverage information and paging strategy information; wherein the duration of the timer is greater than a first duration, which is the duration from the start time of the timer to the moment when the first satellite covers the first network device again.

[0071] In another possible implementation, the transceiver unit is further configured to receive a service request message from the terminal device, the service request message being used to indicate that the first downlink data was successfully transmitted; the processing unit is further configured to delete the first downlink data transmission record and the cached first downlink data.

[0072] In another possible implementation, the transceiver unit is also configured to receive a service request message from the terminal device before the timer expires.

[0073] In another possible implementation, the transceiver unit is further configured to receive a second message before the timer expires; the processing unit is further configured to determine, based on the second message, whether the first downlink data was successfully transmitted.

[0074] In another possible implementation, the second message includes a timestamp and / or the identification information of the last serving device. The timestamp indicates the moment when the terminal device was removed from the tracking area list, and the identification information of the last serving device indicates the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list. The timestamp includes one or more of the following: the moment when the terminal device last received satellite network service before being removed from the tracking area list; the moment when the terminal device first received satellite network service after being removed from the tracking area list; the moment when the terminal device sent the second message; or the moment when the satellite received the second message.

[0075] In another possible implementation, the second message includes a timestamp, and the processing unit is configured to determine that the first downlink data was not successfully transmitted if the time at which the terminal device location is first covered after the first satellite receives the first downlink data is after the time indicated by the timestamp. The terminal device location includes the last tracked area accessed by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list.

[0076] In another possible implementation, the second message includes a timestamp. The processing unit is configured to receive a service request message from the terminal device via the transceiver unit if the time when the terminal device location is first covered by the first satellite after the first satellite receives the first downlink data is before the time indicated by the timestamp. The terminal device location includes the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list. The processing unit is configured to determine that the first downlink data was successfully transmitted.

[0077] In another possible implementation, the second message includes the identification information of the last serving device. The processing unit is configured to determine that the first downlink data was not successfully transmitted if the time when the first satellite first covers the location of the terminal device is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

[0078] In another possible implementation, the second message includes the identification information of the last serving device. The processing unit is configured to receive a service request message from the terminal device via a transceiver unit if the time when the first satellite first covers the location of the terminal device is before the last moment when the satellite corresponding to the last serving device covers the location of the terminal device. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list. The processing unit is configured to determine that the first downlink data was successfully transmitted.

[0079] In another possible implementation, the transceiver unit is also configured to retransmit the first downlink data if it is determined based on the second message that the first downlink data was not successfully transmitted.

[0080] In another possible implementation, the transceiver unit is also configured to retransmit the first downlink data if no service request message from the terminal device is received before the timer expires.

[0081] In another possible implementation, the processing unit is further configured to delete the first downlink data transmission record and the cached first downlink data, and cease performing retransmission operations, if the retransmission exceeds N times or the time for caching the first downlink data exceeds duration T.

[0082] In another possible implementation, the transceiver unit is further configured to receive a third message from a third network device; the transceiver unit is further configured to send a fourth message to the third network device, the fourth message including context information of the terminal device, first downlink data of the terminal device, the first downlink data transmission record, and the timer.

[0083] In another possible implementation, the transceiver unit is further configured to send a fifth message, which includes identification information of a third network device, and the fifth message is used to instruct the third network device to send a service request message of a terminal device.

[0084] For the technical effects of the seventh aspect or possible implementation, please refer to the introduction of the technical effects of the first aspect or corresponding implementation.

[0085] Eighthly, embodiments of this application provide a communication device, which can be a third network device, a component of the third network device (e.g., a processor, chip, or chip system), or a logic module or software capable of implementing all or part of the functions of the third network device. The device includes: a processing unit and a transceiver unit. The transceiver unit is configured to receive a second message, the second message including a timestamp and / or the identification information of the last serving device. The timestamp indicates the time when the terminal device is removed from the tracking area list, and the identification information of the last serving device indicates the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list. The transceiver unit is further configured to receive a fourth message from a first network device, the fourth message including context information of the terminal device, first downlink data of the terminal device, a first downlink data transmission record corresponding to the first downlink data, and a timer corresponding to the first downlink data transmission record. The first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device. The processing unit is configured to determine whether the first downlink data was successfully transmitted based on the second message.

[0086] In one possible implementation, the timestamp includes one or more of the following: the last time the terminal device received satellite network service before being removed from the tracking area list; the first time the terminal device received satellite network service after being removed from the tracking area list; the time the terminal device sent the second message; or the time the satellite received the second message.

[0087] In another possible implementation, the second message includes a timestamp, and the processing unit is configured to determine that the first downlink data was not successfully transmitted if the time at which the terminal device location is first covered after the first satellite receives the first downlink data is after the time indicated by the timestamp. The terminal device location includes the last tracked area accessed by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list.

[0088] In another possible implementation, the second message includes a timestamp. The processing unit is configured to receive a service request message from the terminal device via the transceiver unit if the time when the terminal device location is first covered by the first satellite after the first satellite receives the first downlink data is before the time indicated by the timestamp. The terminal device location includes the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list. The processing unit is configured to determine that the first downlink data was successfully transmitted.

[0089] In another possible implementation, the third message includes the identification information of the last serving device. The processing unit is configured to determine that the first downlink data was not successfully transmitted if the time when the first satellite first covers the location of the terminal device is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

[0090] In another possible implementation, the third message includes the identification information of the last serving device. The processing unit is configured to receive a service request message from the terminal device via a transceiver unit if the time when the first satellite first covers the terminal device's location after receiving the first downlink data is before the last moment when the satellite corresponding to the last serving device covers the terminal device's location. The terminal device's location includes the tracking area last accessed by the terminal device in the terminal device's tracking area list, or any tracking area included in the terminal device's tracking area list. The processing unit is configured to determine that the first downlink data was successfully transmitted.

[0091] In another possible implementation, the transceiver unit is also configured to determine, based on the second message, that the first downlink data was not successfully transmitted, and to retransmit the first downlink data.

[0092] In another possible implementation, the transceiver unit is further configured to receive a service request message from the terminal device, the service request message being used to indicate that the first downlink data was successfully transmitted; the processing unit is further configured to delete the first downlink data transmission record and the cached first downlink data.

[0093] In another possible implementation, the transceiver unit is configured to receive a service request message from the terminal device before the timer expires.

[0094] In another possible implementation, the transceiver unit is also configured to retransmit the first downlink data if no service request message from the terminal device is received before the timer expires.

[0095] In another possible implementation, the processing unit is further configured to delete the first downlink data transmission record and the cached first downlink data, and cease performing retransmission operations, if the retransmission exceeds N times or the time for caching the first downlink data exceeds duration T.

[0096] For the technical effects of the eighth aspect or possible implementation, please refer to the introduction of the technical effects of the second aspect or corresponding implementation.

[0097] Ninthly, embodiments of this application provide a communication device, which may be a terminal device, a component within the terminal device (e.g., a processor, chip, or chip system), or a logic module or software capable of implementing all or part of the terminal device's functions. The device includes: a processing unit and a transceiver unit. The processing unit is configured to send a second message via the transceiver unit. The second message is used to determine whether first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp indicates the moment the terminal device was removed from the tracking area list. The identification information of the last serving device indicates the identification information of the satellite or network device that last received satellite network services before the terminal device was removed from the tracking area list. The transceiver unit is configured to receive retransmitted first downlink data if the first downlink data was not successfully transmitted.

[0098] For the technical effects of the ninth aspect or possible implementation, please refer to the introduction of the technical effects of the third aspect or corresponding implementation.

[0099] In a tenth aspect, embodiments of this application provide a communication device, which may be a first satellite or a second network device on the first satellite, or a component (e.g., a processor, chip, or chip system) in the first satellite or the second network device on the first satellite, or a logic module or software capable of implementing all or part of the functions of the first satellite or the second network device on the first satellite, comprising: a processing unit and a transceiver unit, the transceiver unit being configured to receive a first message, the first message including first downlink data of a terminal device and context information of the terminal device, the context information including access layer security context information and / or non-access layer context information of the terminal device; the processing unit being configured to establish a secure connection with the terminal device based on the context information; the transceiver unit being further configured to send the first downlink data to the terminal device.

[0100] In one possible implementation, the transceiver unit is further configured to receive a service request message from the terminal device; the transceiver unit is further configured to send a service request message from the terminal device, the service request message from the terminal device being used to indicate that the first downlink data was successfully sent.

[0101] For the technical effects of the tenth aspect or possible implementation, please refer to the description of the technical effects of the fourth aspect or corresponding implementation.

[0102] Eleventhly, embodiments of this application provide a communication device, which may be a first satellite or a second network device on the first satellite, or a component (e.g., a processor, chip, or chip system) in the first satellite or the second network device on the first satellite, or a logic module or software capable of implementing all or part of the functions of the first satellite or the second network device on the first satellite, including: a processing unit and a transceiver unit. The processing unit is used to receive a second message through the transceiver unit. The second message is used to determine whether the first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the time when the terminal device is removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the satellite that last received satellite network service before the terminal device was removed from the tracking area list. The transceiver unit is used to send retransmitted first downlink data if the first downlink data is not successfully transmitted.

[0103] In one possible implementation, the transceiver unit is further configured to receive a fifth message, the fifth message including the identification information of the third network device; the transceiver unit is further configured to send a service request message from the terminal device to the third network device.

[0104] For the technical effects of the eleventh aspect or possible implementation, please refer to the introduction of the technical effects of the fifth aspect or corresponding implementation.

[0105] In a twelfth aspect, embodiments of this application provide a communication device, which may be a second satellite or a fourth network device on the second satellite, or a component (e.g., a processor, chip, or chip system) in the second satellite or the fourth network device on the second satellite, or a logic module or software capable of implementing all or part of the functions of the second satellite or the fourth network device on the second satellite, comprising: a processing unit and a transceiver unit, the processing unit being configured to receive a second message through the transceiver unit, the second message being used to determine whether first downlink data was successfully transmitted, the second message including a timestamp and / or the identification information of the last serving device; the timestamp being used to indicate the time when the terminal device was removed from the tracking area list; the identification information of the last serving device being used to indicate the identification information of the satellite that last received satellite network service before the terminal device was removed from the tracking area list; the transceiver unit being configured to send retransmitted first downlink data if the first downlink data was not successfully transmitted.

[0106] For the technical effects of the twelfth aspect or possible implementation, please refer to the description of the technical effects of the sixth aspect or corresponding implementation.

[0107] In a thirteenth aspect, embodiments of this application provide a communication device, which includes at least one processor and a communication interface, wherein the at least one processor invokes a computer program or instructions stored in a memory to execute the method described in any of the above aspects or possible implementations of any of the above aspects.

[0108] In a fourteenth aspect, embodiments of this application provide a chip device including at least one processor for executing computer programs or instructions to implement the method described in any of the above aspects or possible implementations of any of the above aspects.

[0109] In a fifteenth aspect, embodiments of this application provide a computer-readable storage medium storing a computer program or instructions which, when executed on a processor, implement the method described in any of the above aspects or possible implementations thereof.

[0110] In a sixteenth aspect, embodiments of this application provide a computer program product that includes a computer program or instructions which, when executed on a computer, implement the method described in any of the above aspects or possible implementations of any of the above aspects. Attached Figure Description

[0111] Figure 1 is a schematic diagram of the architecture of a communication system provided in this application;

[0112] Figure 2 is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0113] Figure 3 is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0114] Figure 4 is a schematic diagram of a communication method provided in an embodiment of this application;

[0115] Figure 5 is a schematic diagram of the architecture of a 4G communication system;

[0116] Figure 6 is a schematic diagram of the architecture of a 5G communication system;

[0117] Figure 7 is a schematic diagram of CIoT EPS optimization for a terrestrial mobile communication network control plane.

[0118] Figure 8 is a schematic diagram of control plane CIoT EPS optimization in an S&F scenario;

[0119] Figure 9 is a schematic diagram of the tracking area update process;

[0120] Figure 10 is a schematic diagram of a communication method provided in an embodiment of this application;

[0121] Figure 11 is a schematic diagram of another communication method provided in an embodiment of this application;

[0122] Figure 12 is a schematic diagram of a first downlink data failure provided in an embodiment of this application;

[0123] Figure 13 is a schematic diagram of a successful first downlink data transmission according to an embodiment of this application;

[0124] Figures 14-18 are schematic diagrams of another communication method provided in the embodiments of this application;

[0125] Figure 19 is a schematic diagram of the structure of a communication device provided in an embodiment of this application;

[0126] Figure 20 is a schematic diagram of the structure of another communication device provided in an embodiment of this application. Detailed Implementation

[0127] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0128] References to "one embodiment" or "some embodiments" as described in this application mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0129] In the description of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. "And / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Furthermore, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can represent: a, b, c; a and b; a and c; b and c; or a and b and c. Where a, b, and c can be single or multiple.

[0130] It is understood that in this application, "instruction" can include direct instruction, indirect instruction, explicit instruction, and implicit instruction. When describing a certain instruction information for the purpose of instructing A, it can be understood that the instruction information carries A, directly instructs A, or indirectly instructs A.

[0131] In this application, the information indicated by the instruction information is called the information to be instructed. In specific implementations, there are many ways to instruct the information to be instructed, such as, but not limited to, directly instructing the information to be instructed, such as the information to be instructed itself or its index; indirectly instructing the information to be instructed by instructing other information, where there is a relationship between the other information and the information to be instructed; or instructing only a part of the information to be instructed, while the other parts are known or pre-agreed upon. For example, the instruction of specific information can be achieved by using a pre-agreed (e.g., protocol-defined) arrangement of various pieces of information, thereby reducing instruction overhead to some extent.

[0132] The information to be instructed can be sent as a whole or divided into multiple sub-information messages, and the sending period and / or timing of these sub-information messages can be the same or different. This application does not limit the specific sending method. The sending period and / or timing of these sub-information messages can be predefined, for example, according to a protocol, or configured by the transmitting device by sending configuration information to the receiving device.

[0133] It is understood that "send" and "receive" in this application refer to the direction of signal transmission. For example, "send information to XX" can be understood as the destination of the information being XX, which can include direct transmission via the air interface or indirect transmission via the air interface from other units or modules. "Receive information from YY" can be understood as the source of the information being YY, which can include direct reception from YY via the air interface or indirect reception from YY via the air interface from other units or modules. "Send" can also be understood as the "output" of the chip interface, and "receive" can also be understood as the "input" of the chip interface.

[0134] In other words, sending and receiving can occur between devices, such as between network devices and terminal devices, or within a device, such as between components, modules, chips, software modules, or hardware modules within the device via buses, wiring, or interfaces.

[0135] It is understandable that information may undergo necessary processing, such as encoding and modulation, between the source and destination, but the destination can understand the valid information from the source. Similar statements in this application can be interpreted in a similar way and will not be elaborated further.

[0136] The communication method provided in this application can be applied to cellular communication systems related to the 3rd Generation Partnership Project (3GPP), such as 4th generation (4G) communication systems, including Long Term Evolution (LTE) systems. It can also be applied to 5th generation (5G) communication systems, such as 5G New Radio (NR) systems, or to various future communication systems, such as 6th generation (6G) systems. The method provided in this application can also be applied to Bluetooth systems, Wireless Fidelity (WiFi) systems, LoRa systems, or vehicle-to-everything (V2X) systems, as well as communication systems supporting the integration of multiple wireless technologies, and device-to-device (D2D) systems. The method provided in this application can also be applied to satellite communication systems, wherein the satellite communication system can be integrated with the aforementioned communication systems. The wireless communication systems involved in this application also include, but are not limited to: narrowband Internet of Things (NB-IoT), Global System for Mobile Communications (GSM), Enhanced Data Rate for GSM Evolution (EDGE), Wideband Code Division Multiple Access (WCDMA), Code Division Multiple Access 2000 (CDMA2000), or Time Division-Synchronization Code Division Multiple Access (TD-SCDMA).

[0137] Please refer to Figure 1, which is a schematic diagram of the architecture of a communication system provided in an embodiment of this application. The application scenario used in this application will be described using the communication system architecture shown in Figure 1 as an example. The communication system includes a terminal device 101, a first network device 102, and a first satellite 103. Optionally, the first satellite 103 may include a second network device. Optionally, the first satellite 103 may have the processing functions of a network device. The first satellite can function as a network device, and this embodiment of the application does not limit this. For example, the first network device 102 is a mobility management entity (MME) network element. In a non-terrestrial network (NTN), the link between the first satellite and the terminal device is called a service link, the link between the satellite and the ground network gateway station is called a feeder link, and the link between satellites is called an inter-satellite link (ISL). When a terminal device accesses the network via NTN, it can use the above communication links to achieve end-to-end connectivity between the terminal device, the satellite, and the network, namely, the terminal device - service link - satellite 1 (- inter-satellite link - satellite 2) - power supply link - ground network.

[0138] Optionally, the communication system may also include a third network device. For example, if a terminal device detects that it has entered a new tracking area (TA) that is not in the tracking area identity list (TAI List) registered with the network by the terminal device, or if the periodic TA update timer expires, the terminal device will initiate a TAU procedure. If the MME network element has changed, the first network device is the original MME network element, or in other words, the first network device is the old MME network element, and the third network device is the changed network element, or in other words, the third network device is the new MME network element.

[0139] Optionally, the communication system may further include a second satellite. Optionally, the second satellite may include a fourth network device. The second satellite and the first satellite may be the same satellite or different satellites. When the second satellite and the first satellite are different satellites, the second satellite can be any satellite other than the first satellite. When the second satellite and the first satellite are the same satellite, the fourth network device on the second satellite is the same network device as the second network device on the first satellite; when the second satellite and the first satellite are different satellites, the fourth network device on the second satellite can be any network device other than the second network device on the first satellite.

[0140] In this system, the first and / or second satellite can be regenerative satellites without inter-satellite links, as shown in Figure 2. These satellites possess network device processing capabilities and can function as network devices. Alternatively, they can be regenerative satellites with inter-satellite links, as shown in Figure 3. Again, these satellites possess network device processing capabilities and can function as network devices. Figure 3 supports service to users via multiple satellites; the network can select any one or more satellites to send downlink data / signaling, and the terminal device can select one or more satellites to send uplink signaling / data. The difference between the communication system architecture shown in Figure 2 and Figure 3 is that the communication system architecture shown in Figure 3 includes inter-satellite communication links, while the communication system architecture shown in Figure 2 does not. The first and / or second satellite can also be a regenerative satellite (NG-RAN with a regenerative satellite based on gNB-DU) with distributed unit (DU) processing capabilities. In this scenario, the first and / or second satellite can be a distributed unit (DU). The first and / or second satellite can also be equipment with integrated access and backhaul (IAB) node functionality. It should be noted that in some scenarios, the first satellite and the second network equipment on the first satellite can be collectively referred to as access network equipment, or the second satellite and the fourth network equipment on the second satellite can be collectively referred to as access network equipment; this application does not limit this.

[0141] Please refer to Figure 4, which is a schematic diagram of a communication method provided in an embodiment of this application, specifically including two scenarios, as follows:

[0142] Scenario 1: When the MME network element remains unchanged, for example, the terminal device does not move or the terminal device moves but the MME network element does not change. After the first network device sends a first message to the first satellite or the second network device on the first satellite, it caches the first downlink data, determines the first downlink data transmission record, and starts a timer. Before the timer expires, if the first network device receives a service request message from the terminal device, it deletes the first downlink data transmission record and the cached first downlink data. If no service request message from the terminal device is received before the timer expires, the first downlink data is retransmitted. Before the timer expires, if the first network device receives a second message, it determines whether the first downlink data was successfully transmitted based on the second message. The determination of whether the first downlink data was successfully transmitted based on the second message can include the following two methods: Method 1: The second message includes a timestamp, which indicates the time when the terminal device leaves the tracking area list, and the first network device determines whether the first downlink data was successfully transmitted based on the timestamp. Method 2: The second message includes the identification information of the last serving device. This identification information indicates the identification information of the satellite or network device that last received satellite network services before the terminal device was removed from the tracking area list. The first network device determines whether the first downlink data was successfully transmitted based on the identification information of the last serving device. For a detailed description, please refer to the relevant descriptions in subsequent embodiments; they will not be repeated here.

[0143] Scenario 2: When the MME network element changes, for example, due to the movement of the terminal device. The first network device is the old MME network element, and the third network device is the new MME network element. The first network device sends a fourth message to the third network device. The fourth message includes the context information of the terminal device, the first downlink data of the terminal device, the first downlink data transmission record, and a timer. Before the timer expires, if the third network device receives a service request message from the terminal device, it deletes the first downlink data transmission record and the cached first downlink data. Further, the first network device sends a fifth message to the first satellite or a second network device on the first satellite. The fifth message includes the identification information of the third network device. Accordingly, the first satellite or the second network device on the first satellite sends a service request message from the terminal device to the third network device based on the fifth message. If the third network device receives the second message, it determines whether the first downlink data was successfully transmitted based on the second message. If the first network device does not receive a service request message from the terminal device before the timer expires, it determines that the first downlink data was not successfully transmitted and retransmits the first downlink data.

[0144] It is understood that Figure 1 only illustrates a possible communication system architecture to which the embodiments of this application can be applied. In other possible scenarios, the communication system architecture may also include other devices. The method in the embodiments of this application can be applied to the communication system shown in Figure 1. The terminal device mentioned above can be any of the following terminal devices, and the second network device or the fourth network device mentioned above can be any of the following network devices.

[0145] 1) Terminal equipment, also known as user equipment (UE), mobile station (MS), mobile terminal (MT), etc., is a device that provides voice or data connectivity to a user. Specifically, it includes devices that provide voice connectivity, devices that provide data connectivity, or devices that provide both voice and data connectivity. For example, it may include handheld devices with wireless connectivity or processing devices connected to a wireless modem. This terminal equipment can communicate with the core network via a radio access network (RAN), exchanging voice or data with the RAN, or interacting with the RAN to exchange voice and data. Currently, terminal devices can include: mobile phones, tablets, laptops, PDAs, mobile internet devices (MIDs), wearable devices (such as smartwatches, smart bracelets, pedometers, etc.), in-vehicle devices (such as cars, bicycles, electric vehicles, airplanes, ships, trains, high-speed trains, etc.), virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, smart home devices (such as refrigerators, televisions, air conditioners, electricity meters, etc.), intelligent robots, workshop equipment, wireless terminals in autonomous driving, wireless terminals in remote surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, or wireless terminals in smart homes, and flying equipment (such as intelligent robots, hot air balloons, drones, airplanes), etc. Terminal devices can also be other devices with terminal functions; for example, a terminal device can also be a device that performs terminal functions in D2D communication.Terminal devices can also include vehicle-to-everything (V2X) terminal devices, machine-to-machine / machine-type communications (M2M / MTC) terminal devices, internet of things (IoT) terminal devices, light UEs, reduced capability UEs (REDCAP UEs), subscriber units, subscriber stations, mobile stations, remote stations, access points (APs), remote terminals, access terminals, user terminals, user agents, or user devices, and drone equipment. For example, this can include mobile phones (or "cellular" phones), computers with mobile terminal devices, portable, pocket-sized, handheld, and computer-embedded mobile devices, etc. Examples include personal communication service (PCS) telephones, cordless phones, session initiation protocol (SIP) phones, wireless local loop (WLL) stations, and personal digital assistants (PDAs). It also includes limited devices, such as devices with low power consumption, limited storage capacity, or limited computing power. Examples include information sensing devices such as barcode scanners, radio frequency identification (RFID), sensors, global positioning systems (GPS), and laser scanners. In this application, terminal devices with wireless transceiver capabilities and chips that can be installed in the aforementioned terminal devices are collectively referred to as terminal devices.

[0146] Terminal devices can also be Internet of Things (IoT) devices, which can also be called Ambient Internet of Things (Ambient IoT) devices.

[0147] It should be noted that the terminal device may be a device or apparatus with a chip, or a device or apparatus with integrated circuitry, or a chip, module or control unit in the device or apparatus shown above. This application does not limit the specific device.

[0148] 2) A network device is a device deployed in a radio access network to provide wireless communication functions for terminal devices. Network devices can also be called radio access network (RAN) entities, access nodes, network nodes, or communication devices, etc.

[0149] Specifically, the network equipment can be access network equipment for cellular systems related to the 3rd Generation Partnership Project (3GPP). For example, fourth-generation (4G) mobile communication systems or 5G mobile communication systems. The network equipment can also be access network equipment in open RAN (O-RAN or ORAN) or cloud radio access network (CRAN). Alternatively, the network equipment can also be access network equipment in a communication system formed by the integration of two or more of the above communication systems.

[0150] Network equipment includes, but is not limited to: evolved Node B (eNB), radio network controller (RNC), Node B (NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved NodeB, or home Node B, HNB), baseband unit (BBU), access point (AP) in wireless fidelity (WIFI) systems, macro base station, micro base station, wireless relay node, donor node, radio controller in CRAN scenarios, wireless backhaul node, transmission point (TP), or transmission and receiving point (TRP). Network equipment can also be access network equipment in 5G mobile communication systems. For example, next-generation Node B (gNB), TRP, TP in new radio (NR) systems, or one or more antenna panels (including multiple antenna panels) of a base station in a 5G mobile communication system. Alternatively, network devices can also be network nodes constituting a gNB or transmission point. Examples include centralized units (CUs), distributed units (DUs), CU-control plane (CPs), CU-user plane (UPs), or radio units (RUs). CUs and DUs can be separate entities or included in the same network element, such as a BBU. RUs can be included in radio equipment or radio units, such as remote radio units (RRUs), active antenna units (AAUs), or remote radio heads (RRHs). Alternatively, network devices can also be servers, wearable devices, vehicles, or in-vehicle equipment. For example, in V2X technology, network devices can be roadside units (RSUs).

[0151] It should be noted that CU (or CU-CP and CU-UP), DU, or RU may have different names in different systems, but those skilled in the art will understand their meaning. For example, in an ORAN system, CU can also be called an open centralized unit (O-CU) or an open CU, DU can also be called an open distributed unit (O-DU), centralized unit control plane (CU-CP) can also be called an open centralized unit control plane (O-CU-CP) or an open CU-CP, centralized unit user plane (CU-UP) can also be called an open centralized unit user plane (O-CU-UP) or an open CU-UP, and RU can also be called an open radio unit (O-RU). This application does not impose any specific limitations. Any of the units CU, CU-CP, CU-UP, DU, and RU in this application can be implemented through software modules, hardware modules, or a combination of software and hardware modules.

[0152] In some deployments, the CU and DU implement some of the functions of the gNB. For example, the CU implements the functions of the radio resource control (RRC) and packet data convergence protocol (PDCP) layers, while the DU implements the functions of the radio link control (RLC), media access control (MAC), and physical (PHY) layers. Since RRC layer information ultimately becomes PHY layer information, or is derived from PHY layer information, in this architecture, higher-layer signaling, such as RRC or PDCP signaling, can also be considered to be sent by the DU, or by the DU+RU. It is understood that network devices can be CU nodes, DU nodes, or devices including both CU and DU nodes. Furthermore, the CU can be classified as a network device in the access network (RAN) or a network device in the core network (CN); no restrictions are placed here.

[0153] It should be noted that the network device can be the device or apparatus shown above, or a component (e.g., a chip), module, or unit in the device or apparatus shown above; this application does not limit the specifics.

[0154] 3) Network equipment can also be core network equipment. Core network equipment is responsible for access control, registration management, service management, mobility management, etc. of terminal equipment accessing the network.

[0155] For example, please refer to Figure 5, which is a schematic diagram of the architecture of a 4G communication system. Optionally, the core network equipment can be the MME network element, Serving Gateway (S-GW), Packet Data-Network Gateway (P-GW), Policy and Charging Rule Function (PCRF) network element, or Home Subscriber Server (HSS) shown in Figure 5. The specific functions of each network element are as follows:

[0156] MME network elements: mainly used for mobility management and control, including user authentication, paging, location updates and handover.

[0157] S-GW: Primarily used for context session management and packet routing and forwarding.

[0158] P-GW: Primarily used for connecting to external networks. P-GW can be divided into control plane P-GW (P-GW-C) and user plane P-GW (P-GW-U).

[0159] PCRF network elements are mainly used for policy control and flow-based charging control functions.

[0160] HSS: Primarily used to store and manage user subscription data, including user authentication information, location information, and routing information.

[0161] For example, please refer to Figure 6, which is a schematic diagram of the architecture of another 5G communication system provided in an embodiment of this application. Optionally, the core network equipment can also be the user plane function (UPF) network element, access and mobility management function (AMF) network element, session management function (SMF) network element, authentication server function (AUSF) network element, unified data management (UDM) network element, and policy control function (PCF) network element shown in Figure 6. The specific functions of each network element are as follows:

[0162] UPF network elements are primarily used for routing and forwarding user plane data packets, similar to the functions implemented by the P-GW in the aforementioned 4G communication system.

[0163] AMF (Automatic Management Module) network elements are primarily used for registration management, connection management, accessibility management, mobility management, and various functions related to security, access management, and authorization. They perform functions similar to those of the MME (Mechanical Management Module) network elements in the aforementioned 4G communication system.

[0164] SMF network elements: Primarily used for session establishment, modification, and release management. Similar to the functions implemented by MME and P-GW in the aforementioned 4G communication system.

[0165] AUSF network element: mainly used for unified authentication service functions.

[0166] UDM network elements are primarily responsible for managing user identifiers, subscription data, authentication data, and user service network element registration management. This is similar to the function implemented by the HSS in the aforementioned 4G communication system.

[0167] PCF network element: Primarily used to support unified policy management of network behavior, providing policy rules to control plane functions. Similar to the functions implemented by the PCRF network element in the aforementioned 4G communication system.

[0168] It should be noted that in this application, network elements can also be referred to as entities or functional entities. For example, an MME network element can also be referred to as an MME entity or an AMF functional entity.

[0169] To better understand the solutions provided in the embodiments of this application, some terms, concepts or processes involved in the embodiments of this application will be introduced below.

[0170] I. Two Data Transmission Modes for Cellular IoT Devices in Terrestrial Mobile Communication Networks

[0171] Small packet data transmission in terrestrial mobile communication networks for cellular Internet of Things (CIoT) devices can include two types: one is user data transmission based on the user plane, known as user plane CIoT evolved packet system (EPS) optimization; the other is user data transmission based on the control plane, known as control plane CIoT EPS optimization. The characteristic of control plane CIoT EPS optimization is that it does not require establishing a data bearer. After the data arrives at the user's serving gateway, the MME network element includes the data in a non-access stratum packet data unit (NAS PDU) and sends it to the base station. The base station then transmits the NAS PDU to the CIoT user via an RRC message.

[0172] II. Optimization of CIoT EPS for Terrestrial Mobile Communication Network Control Plane

[0173] Please refer to Figure 7, which is a schematic diagram of CIoT EPS optimization for a terrestrial mobile communication network control plane, as shown below:

[0174] Step 1: The terminal device is attached to the EPS and is in an idle state.

[0175] Step 2: The P-GW sends downlink data or signaling to the S-GW.

[0176] The downlink data or signaling is sent from the terminal device to the P-GW. After receiving the downlink data or signaling from the P-GW, the S-GW caches the downlink data or signaling and identifies the MME network element serving the terminal device.

[0177] Step 3: The S-GW sends a downlink data notification message to the MME network element.

[0178] The downlink data notification message is used to notify the MME network element that downlink data has arrived. This message may include the Address Resolution Protocol (ARP) and the EPS bearer identifier (ID).

[0179] Step 4: The MME element sends a downlink data notification ack message to the S-GW.

[0180] Step 5: The MME network element sends a paging message to the base station.

[0181] Specifically, the MME network element sends a paging message to each base station within the tracking area (TA) registered by the terminal device. This paging message is used to request the base station to page the terminal device over the air interface.

[0182] Step 6: The base station sends a paging message to the terminal device.

[0183] Optionally, if the base station receives a paging message from an MME network element, the base station sends a paging message to the terminal device.

[0184] Step 7: The terminal device establishes an RRC connection with the base station.

[0185] Since the terminal device is in an idle state, once it receives a paging instruction, it sends a Non-Access Stratum Control Plane Service Request (NAS) to the base station via a Radio Resource Control Connection Request (RRC) message and an S1-AP initial message. Under CIoT EPS optimization in the control plane, the NAS control plane service request does not trigger the MME network element to establish a data radio bearer; instead, the MME network element sends the received downlink data to the base station via the NAS PDU.

[0186] Step 8: The MME network element sends the context information of the terminal device to the base station.

[0187] This step is optional.

[0188] If the base station is a narrowband Internet of Things (NB-IoT) network element, the base station can obtain the quality of service profile negotiated by EPS from the MME network element based on the configuration information.

[0189] Step 9: The base station sends the S1-AP initial message to the MME network element.

[0190] The S1-AP initial message includes the NAS control plane service request from the terminal device.

[0191] Step 10: The MME network element sends a modify bearer request message to the S-GW.

[0192] This step is optional.

[0193] The modify bearer request message is used to request the establishment of an S11-U channel.

[0194] Step 11: The S-GW sends a modify bearer response message to the MME network element.

[0195] This step is optional.

[0196] Step 12: The S-GW sends downlink data to the MME network element.

[0197] The downlink data is cached by the MME network element.

[0198] Step 13: The MME network element performs data encryption and integrity protection on the downlink data.

[0199] Step 14: The MME network element sends a downlink S1-AP message to the base station.

[0200] The S1-AP message includes a NASDATA PDU, which contains downlink data and the corresponding Evolved Packet System Bearer ID (EBI).

[0201] Step 15: The base station sends an RRC message to the terminal device.

[0202] The RRC message includes a NAS PDU, which contains downlink data.

[0203] Step 16: The base station sends a Non-Access Stratum Delivery Notification (NAS delivery notification) message to the MME network element.

[0204] The NAS delivery notification message is used to notify the MME network element whether the NAS PDU has been successfully sent.

[0205] As can be seen from the above process, the base station notifies the MME network element whether downlink data has been successfully transmitted via a NAS delivery notification message. For example, the S1-AP channel through which the base station sends the NAS delivery notification message in step 16 is the same as the S1-AP channel through which the base station receives the S1-AP message from the MME network element in step 14. Therefore, the MME network element can determine whether the NASDATA PDU included in the S1-AP message has been successfully transmitted through the NAS delivery notification message.

[0206] III. The main process of optimizing the control plane CIoT EPS in the store and forward (S&F) scenario is as follows:

[0207] Please refer to Figure 8, which is a schematic diagram of control plane CIoT EPS optimization in a S&F scenario, as follows:

[0208] Step 1: The terminal device is attached to the EPS and is in an idle state.

[0209] Step 2: The MME network element receives downlink data or signaling.

[0210] That is, downlink data or signaling arrives from the S-GW and is cached in the MME.

[0211] Step 3: The MME network element performs data encryption and integrity protection on the downlink data.

[0212] The MME network element selects a suitable satellite for the terminal device based on its location and ephemeris information, and performs data encryption and integrity protection on the downlink data when the satellite's feed link is available. This satellite is a regenerated satellite, meaning it has the processing capabilities of a base station and can function as such.

[0213] Step 4: The MME network element sends a paging message and NAS PDU to the satellite.

[0214] The paging message includes the location information of the terminal device, such as a tracking area identity list (TAI List), and the NAS PDU includes downlink data.

[0215] Step 5: Satellite cache NAS PDU.

[0216] Step 6: The satellite sends a paging message to the terminal device.

[0217] When the satellite reaches the location of the terminal device (e.g., TAI List), the satellite can send a paging message via broadcast.

[0218] Step 7: The terminal device sends a NAS control plane service request message to the satellite.

[0219] After receiving the paging message, the terminal device establishes an RRC connection with the satellite and sends a NAS control plane service request message to the satellite.

[0220] Step 8: The satellite sends the NAS PDU to the terminal device.

[0221] This NAS PDU includes downlink data.

[0222] Step 9: Cache the NAS control plane service request message on the satellite.

[0223] This step is optional.

[0224] Step 10: The satellite sends a NAS delivery notification message or a NAS control plane service request message to the MME network element.

[0225] IV. Tracking Area Updates

[0226] Please refer to Figure 9, which is a schematic diagram of a tracking area update process, as follows:

[0227] Step 1: The terminal device triggers the TAU process.

[0228] In one example, the terminal device detects the arrival of a new TA that is not in the TAI List, or the periodic TA update timer expires, which will trigger the terminal device to initiate the TAU process.

[0229] Step 2: The terminal device sends a TAU request message to the base station.

[0230] Optionally, the TAU request message includes Last Visited TAI information, which is used to indicate the last TA visited by the terminal device in the TAI List.

[0231] Step 3: The base station sends a TAU request message to the new MME network element.

[0232] Step 4: The new MME element sends a context request message to the old MME element.

[0233] The context request message is used to request context information from the terminal device.

[0234] Step 5: The old MME element sends a context response message to the new MME element.

[0235] Step 6: Trigger the authentication or security process.

[0236] This step is optional.

[0237] If the integrity check of the TAU message fails, the authentication and security process is triggered.

[0238] Step 7: The new MME element sends a context confirmation message to the old MME element.

[0239] Step 8: The new MME network element interacts with the S-GW to complete the creation of a new session.

[0240] Step 9: The new MME network element sends an update location request message to the HSS.

[0241] The Update Location Request message is used to notify the HSS MME of a change.

[0242] Step 10: The HSS sends the location cancellation information to the old MME network element.

[0243] Step 11: The old MME network element sends a location cancellation confirmation message to the HSS.

[0244] Upon receiving the location cancellation information, the old MME network element deletes the mobility management and bearer context of the terminal device and sends a location cancellation confirmation message to the HSS.

[0245] Step 12: The HSS sends an update location confirmation message to the new MME network element.

[0246] Step 13: The new MME network element sends a TAU acceptance message to the terminal device.

[0247] The TAU receives messages to indicate that the TAU process is complete.

[0248] In NTN, for some extremely remote areas without surrounding gateway stations, there is a limitation of discontinuous feeder links. For example, when satellites cover users in these areas (i.e., when the service link is available), it is impossible to connect to the terrestrial network providing services to these users via the feeder link. Similarly, when satellites cover gateway stations of the terrestrial network (i.e., when the feeder link is available), it is impossible to cover users in these areas. To meet the communication needs of these extremely remote areas, NTN can transmit CIoT small packet data to users in these areas via S&F (Short-Side and Forwarding). For uplink signaling / data transmission, "storage" refers to storing uplink signaling / data from the terminal device on the satellite, and "forwarding" refers to forwarding the cached uplink signaling / data to the terrestrial network. For downlink data transmission, "storage" refers to storing downlink signaling / data from the terrestrial network on the satellite, and "forwarding" refers to forwarding the cached downlink signaling / data to the terminal device.

[0249] In S&F scenarios, since the service link and power supply link are not available simultaneously, ensuring the security of data transmission between the satellite and terminal equipment is a problem that those skilled in the art are addressing. To solve the above problem, the embodiments of this application propose the following solutions.

[0250] Please refer to Figure 10, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0251] Step S1001: The first network device receives the first downlink data from the terminal device.

[0252] The first network device receives the first downlink data from the terminal device of the S-GW.

[0253] Optionally, the first downlink data of the terminal device can be carried in a non-access stratum (NAS) message, and correspondingly, the first downlink data of the terminal device can be a NAS PDU.

[0254] Optionally, prior to step S1001, the terminal device is attached to the EPS and is in an idle state.

[0255] Step S1002: When the first condition is met, the first network device sends a first message to the first satellite or the second network device on the first satellite.

[0256] In other words, when the first condition is met, the first network device sends the first message to the first satellite, or when the first condition is met, the first network device sends the first message to the second network device on the first satellite.

[0257] The first message includes the terminal device's first downlink data and the terminal device's context information. This context information is used to establish a secure communication link between the first satellite and the terminal device. The context information includes the terminal device's access stratum security context information and / or non-access stratum context information. The access stratum security context information may include a key, a security algorithm identifier, and uplink / downlink sequence count values ​​(COUNT values). The non-access stratum context information may include mobility management context, EPS bearer context information, and non-access stratum security algorithms.

[0258] The first condition includes one or more of the following: the terminal device accesses the network via satellite and supports store-and-forward mode; or the communication link between the first network device and the first satellite is available, and a communication link cannot currently be established between the terminal device and the first satellite. The availability of the communication link between the first network device and the first satellite means that the feeder link is available, or it can also mean that the feeder link is available and the inter-satellite link is available. In this case, the availability of both the feeder link and the inter-satellite link means that the feeder links between the first network device and other satellites are available, and the inter-satellite link between the other satellite and the first satellite is available. The terminal device accessing the network via satellite can mean that the terminal device accesses the network via the first satellite or other satellites. Supporting store-and-forward mode can mean that for downlink signaling / data transmission, "store" refers to storing downlink signaling / data from the terrestrial network on the satellite, and "forward" refers to forwarding the cached downlink signaling / data to the terminal device. For uplink signaling / data transmission, "store" refers to storing uplink signaling / data from the terminal device on the satellite, and "forward" refers to forwarding the cached uplink signaling / data to the terrestrial network. The inability to establish a communication link between the terminal device and the first satellite can mean that the first satellite fails to cover the location of the terminal device, i.e., the service link is unavailable, or it can mean that the first satellite fails to establish an inter-satellite link with the satellite that covers the location of the terminal device.

[0259] For example, when the first condition is met, after the first network device sends a first message to the second network device on the first satellite, the method further includes: the first network device caching the first downlink data. Optionally, the first network device caching the first downlink data can also be described as the first network device backing up the first downlink data, the first network device temporarily storing the first downlink data, or the first network device archiving the first downlink data.

[0260] Optionally, when the first network device sends a first message to the first satellite or a second network device on the first satellite, it may also send a paging message to the first satellite or a second network device on the first satellite. The paging message may include the location information of the terminal device, for example, the location information of the terminal device may be a TAI List.

[0261] For example, before step S1002, the first network device performs data encryption and integrity protection on the first downlink data. That is, the first network device selects a suitable satellite for the terminal device based on the terminal device's location information and satellite coverage information, and performs data encryption and integrity protection on the first downlink data when the satellite's feed link is available. Here, satellite coverage information refers to the mapping relationship between satellite coverage range and time. This satellite coverage information can be directly configured to the first network device, or it can be calculated and determined by the first network device based on ephemeris information.

[0262] In one possible implementation, after the first network device sends a first message to the first satellite or a second network device on the first satellite when the first condition is met, the method further includes: the first network device determining a first downlink data transmission record and starting a timer.

[0263] The first downlink data transmission record is used to record the first satellite or the second network device on the first satellite receiving the first downlink data from the receiving terminal device, as well as the corresponding terminal device. The first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device.

[0264] In this context, one first downlink data transmission record corresponds to one first downlink data, one first downlink data transmission record corresponds to one timer, and one downlink data transmission record corresponds to one NAS message.

[0265] The timer's duration is determined based on satellite coverage information and paging strategy information. In one example, the timer's duration is longer than a first duration, which is the time between the timer's start time and the moment the first satellite again covers the first network device.

[0266] In one example, a NAS message includes NAS PDU#1 and NAS PDU#2. The first downlink data transmission record is shown in Table 1, as follows:

[0267] Table 1

[0268] In the above method, it is possible to accurately determine whether the first downlink data has been successfully sent in a store-and-forward scenario based on whether the timer has timed out. This avoids the situation where the user has to wait indefinitely because it is impossible to determine whether the first downlink data has been successfully sent, thus ensuring data transmission latency and improving data transmission reliability.

[0269] Step S1003: The first satellite or the second network device on the first satellite receives the first message from the first network device.

[0270] Optionally, after receiving the first message from the first network device, the first satellite or the second network device on the first satellite caches the first downlink data.

[0271] The first message includes the first downlink data of the terminal device and the context information of the terminal device, as described above.

[0272] Step S1004: The first satellite or the second network device on the first satellite establishes a secure connection with the terminal device based on context information.

[0273] The first satellite or the second network device on the first satellite verifies the legitimacy of the terminal device based on context information and uses the corresponding encryption algorithm to encrypt and decrypt the signaling / data.

[0274] Step S1005: The first satellite or the second network device on the first satellite sends the first downlink data to the terminal device.

[0275] Correspondingly, the terminal device receives first downlink data from the first satellite or a second network device on the first satellite.

[0276] Optionally, before step S1005, the first satellite or the second network device on the first satellite sends a paging message. For example, when the first satellite covers the location of the terminal device, the first satellite or the second network device on the first satellite can send a paging message to the terminal device. Accordingly, after receiving the paging message, the terminal device establishes an RRC connection with the first satellite or the second network device on the first satellite.

[0277] In another possible implementation, the method further includes: the first satellite or a second network device on the first satellite receiving a service request message from a terminal device; the first satellite or the second network device on the first satellite sending a service request message to the first network device; correspondingly, the first network device receiving the service request message from the terminal device on the first satellite or the second network device on the first satellite; and then the first network device deleting the first downlink data transmission record and the cached first downlink data. This method frees up storage space, thereby maximizing resource utilization.

[0278] This service request message is used to indicate that the first downlink data transmission was successful. For example, this service request message can be a NAS message, such as a NAS Control Plane Service Request message.

[0279] Optionally, the first satellite or the second network device on the first satellite may receive the service request message from the terminal device after the terminal device receives the paging message and establishes an RRC connection with the first satellite or the second network device on the first satellite.

[0280] Optionally, after receiving a service request message from a terminal device, the first satellite or the second network device on the first satellite may send first downlink data to the terminal device.

[0281] Optionally, after receiving a service request message from a terminal device, the first satellite or a second network device on the first satellite may cache the service request message and send it to the first network device when the power supply link is available.

[0282] Optionally, the first network device may receive the service request message from the first satellite or a second network device on the first satellite before the timer expires. This approach ensures data transmission latency and improves data transmission reliability.

[0283] Optionally, if the first network device does not receive a service request message from the terminal device of the first satellite or the second network device on the first satellite before the timer expires, the first network device retransmits the first downlink data. This can be understood as the first network device determining that the first downlink data transmission failed before the timer expires, and retransmitting the first downlink data. Optionally, the first network device selects a suitable satellite and retransmits the first downlink data to that satellite. Optionally, the selected suitable satellite can be the first satellite, the second satellite, or other satellites besides the first and second satellites. This method ensures data integrity and eliminates the need to wait for the timer corresponding to the first downlink data to expire, thereby reducing data transmission latency and improving data transmission reliability. Optionally, if retransmissions exceed N times, or the time for caching the first downlink data exceeds duration T, the first downlink data transmission record and the cached first downlink data are deleted, and no further retransmissions are performed, where N is a positive integer greater than 0, and T is greater than 0. This method makes efficient use of resources and avoids resource waste.

[0284] In another possible implementation, after the first satellite or the second network device on the first satellite sends the first downlink data to the terminal device, the method further includes: the first satellite or the second network device on the first satellite sending a transmission notification message to the first network device.

[0285] Accordingly, the first network device can receive a transmission notification message from the first satellite or a second network device on the first satellite. Optionally, the first network device can receive a transmission notification message from the first satellite or a second network device on the first satellite before the timer expires. If no transmission notification message is received from the first satellite or a second network device on the first satellite before the timer expires, the first network device retransmits the first downlink data.

[0286] The delivery notification message is used to indicate whether the first downlink data was successfully sent. Optionally, the delivery notification message can be a NAS message, such as a NAS delivery notification message.

[0287] In the method shown in Figure 10, by sending a first message to the first satellite or the network device on the first satellite, the first satellite or the network device on the first satellite can establish a secure communication link with the terminal device based on the uplink and downlink information in the first message. Then, when the service link is available, the first satellite or the network device on the first satellite and the terminal device can transmit data on the established secure communication link. That is, on the secure communication link, the first satellite or the network device on the first satellite sends first downlink data to the terminal device, thereby ensuring the security and reliability of data transmission between the satellite and the terminal device.

[0288] This embodiment applies to scenarios where the MME network element remains unchanged after the terminal device triggers the TAU process, and the first network device is the original MME network element.

[0289] Please refer to Figure 11, which is a schematic diagram of another communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0290] Steps S1101-S1103 can be referred to the relevant descriptions in steps S1001-S1003, and will not be repeated here.

[0291] Step S1104: The terminal device sends a second message to the second satellite or the fourth network device on the second satellite.

[0292] In this embodiment, the second satellite and the first satellite can be the same satellite or different satellites. When the second satellite and the first satellite are different satellites, the second satellite can be any other satellite besides the first satellite. The fourth network device on the second satellite can be the same as or different from the second network device on the first satellite. When the fourth network device is different from the second network device, the fourth network device can be any network device on the second satellite besides the second network device on the first satellite. This embodiment does not impose any limitations.

[0293] For example, the second message is a TAU request message. Before the terminal device sends the second message to the second satellite or the fourth network device on the second satellite, the terminal device is removed from the TAI List registered with the network, a new TA is detected entering the network, the TA is not in the TAI List registered with the network, or the periodic TA update timer expires, etc., triggering the terminal device to initiate the TAU process, and the terminal device establishes a connection with the second satellite or the fourth network device on the second satellite.

[0294] The second message includes a timestamp and / or the identification information of the last servicing RAN / SAT. The timestamp indicates the moment the terminal device was removed from the tracking area list. The identification information of the last servicing RAN indicates the identification information of the satellite or network device that last received satellite network services before the terminal device was removed from the tracking area list. This last satellite or network device that received satellite network services before the terminal device was removed from the tracking area list can refer to the satellite or network device where the terminal device last camped or established a connection.

[0295] The timestamp includes one or more of the following: the last time the terminal device received satellite network service before leaving the tracking area list; the first time the terminal device received satellite network service after leaving the tracking area list; the time the terminal device sent the second message; or the time the satellite received the second message. The tracking area list is a list that combines a group of tracking areas. A tracking area consists of multiple base station cells. For example, TAI List1 = {TA1, TA2, TA3} means that Tracking Area List 1 consists of three tracking areas: TA1, TA2, and TA3. "Terminal device leaving the tracking area list" means that the terminal device leaves the tracking areas included in the tracking area list. When the terminal device moves within a tracking area included in the tracking area list, no TAU procedure is required. When the terminal device leaves a tracking area included in the tracking area list, a TAU procedure is required.

[0296] Among them, receiving satellite network services by terminal equipment refers to the terminal equipment residing in or accessing a satellite network cell;

[0297] The last time a terminal device received satellite network services before being removed from the tracking area list refers to the last time the terminal device remained within the tracking area list or accessed a satellite network cell.

[0298] The moment when a terminal device first receives satellite network service after being removed from the tracking area list can refer to the moment when the terminal device is removed from the TAI List registered to the network and a new TA is detected, which is not in the TAI List registered to the network, and the moment when satellite network service is first received in that TA.

[0299] Optionally, when the timestamp includes the moment the satellite receives the second message, the moment the satellite receives the second message is added to the timestamp by the satellite. Optionally, the satellite can be a second satellite.

[0300] Step S1105: The second satellite or the fourth network device on the second satellite receives the second message from the terminal device.

[0301] Step S1106: The second satellite or the fourth network device on the second satellite sends a second message to the first network device.

[0302] For example, when the power supply link between the second satellite and the first network device is available, the second satellite or a fourth network device on the second satellite sends a second message to the first network device.

[0303] Step S1107: The first network device receives a second message from the second satellite or a fourth network device on the second satellite.

[0304] Optionally, the first network device receives a second message from the second satellite or a fourth network device on the second satellite before the timer expires.

[0305] Step S1108: The first network device determines whether the first downlink data was successfully sent based on the second message.

[0306] The first network device may determine whether the first downlink data was successfully sent based on the second message in the following ways:

[0307] Method 1: The second message includes a timestamp. The first network device determines that the first downlink data was not successfully transmitted based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the time indicated by the timestamp, it is determined that the first downlink data was not successfully transmitted.

[0308] It can also be described as the first satellite failing to cover the terminal device's location until the time indicated by the timestamp, indicating that the first downlink data was not successfully transmitted.

[0309] The first network device can determine whether the first satellite can cover the location of the terminal device based on satellite coverage information or indication information from other network devices. If it can cover the location of the terminal device, it can also determine the time when the first satellite covers the location of the terminal device and / or the time when it first covers the location of the terminal device.

[0310] The location of the terminal device covered by the first satellite may refer to the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; or, it may refer to the first satellite being able to establish a communication link with a satellite that reaches the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; or, it may refer to the first satellite being able to provide services to the terminal devices in the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

[0311] The term "first satellite first coverage of terminal device location" can refer to the first satellite arriving at the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list; or, it can refer to the first satellite establishing a communication link with a satellite arriving at the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list; or, it can refer to the first satellite providing services to a terminal device in the last tracked area visited by the terminal device in the terminal device tracking area list, or any tracked area included in the terminal device tracking area list.

[0312] The terminal device location includes the last tracked area (UE Last Visited TAI) in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list. The last tracked area visited by the terminal device in the terminal device tracking area list can refer to the tracking area last visited before the terminal device was removed from the tracking area list. In one example, TAI List1 = {TA1, TA2, TA3} indicates that tracking area list 1 consists of three tracking areas: TA1, TA2, and TA3. In this tracking area list 1, the last tracked area visited by the terminal device is TA3.

[0313] Specifically, if, after the first satellite receives the first downlink data, the time until it first covers the location of the terminal device is after the time indicated by the timestamp, determining that the first downlink data was not successfully transmitted can be understood as the time when the first satellite first arrives at the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is after the time indicated by the timestamp; it can also be understood as the time when the first satellite first establishes a communication link with a satellite arriving at the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is after the time indicated by the timestamp; or it can be understood as the time when the first satellite first provides service to a terminal device in the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is after the time indicated by the timestamp, determining that the first downlink data was not successfully transmitted.

[0314] Specifically, determining that the first downlink data transmission failed could mean that the first satellite failed to reach the last tracked area visited by the terminal device in the terminal device tracking area list or any tracked area included in the terminal device tracking area list by the time indicated ...

[0315] In one example, please refer to Figure 12, which is a schematic diagram of a first downlink data failure provided by an embodiment of this application. The terminal device location includes any tracking area included in the terminal device tracking area list, such as TAI List1 = {TA1, TA4, TA5}. The timestamp indicates the time T1, which represents the time when the terminal device was removed from the tracking area list, for example, the time when the terminal device last received satellite network service before being removed from the tracking area list. If the first satellite, such as satellite #1, fails to cover any tracking area in the tracking area list TAI List1 until T1, then the first network device determines that the first downlink data has not been successfully transmitted.

[0316] In another example, the timestamp indicates the time T1, which represents the time when the terminal device was removed from the tracking area list. For example, the last time the terminal device received satellite network service before it was removed from the tracking area list, and the time T2 when the first satellite first covered the location of the terminal device after receiving the downlink data of the terminal device. T2 is after T1, indicating that the first downlink data was not successfully transmitted.

[0317] In the above method, by determining that the first downlink data was not successfully transmitted by the first satellite failing to cover the location of the terminal device by the time indicated by the timestamp, the first network device can identify downlink data that could not be successfully transmitted due to the movement of the terminal device during the TAU process and retransmit the first downlink data without waiting for the timer corresponding to the first downlink data to expire, thereby reducing the latency of data transmission and improving the reliability of data transmission.

[0318] Method 2: The second message includes a timestamp. The first network device determines that the first downlink data was successfully sent based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the time indicated by the timestamp, the device receives a service request message from the terminal device and determines that the first downlink data was successfully sent.

[0319] Alternatively, it can be described as the first satellite covering the terminal device's location until the time indicated by the timestamp, receiving the terminal device's service request message, and determining that the first downlink data was successfully sent.

[0320] The first network device can determine whether the first satellite can cover the location of the terminal device based on satellite coverage information or indication information from other network devices. If it can cover the location of the terminal device, it can also determine the time of coverage of the terminal device location and / or the time of the first coverage of the terminal device location.

[0321] The explanation of the location of the terminal device can be found above and will not be repeated here.

[0322] In this context, receiving a service request message from a terminal device can refer to the first network device receiving a service request message from a terminal device on a first satellite or a second network device on the first satellite. This service request message from the terminal device is used to indicate that the first downlink data was successfully transmitted.

[0323] Wherein, if after the first satellite receives the first downlink data, the time until it first covers the location of the terminal device is before the time indicated by the timestamp, it can be understood that the time when the first satellite first arrives at the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is before the time indicated by the timestamp; it can also be understood that the time when the first satellite first establishes a communication link with a satellite that arrives at the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is before the time indicated by the timestamp; it can also be understood that the time when the first satellite first provides services to the terminal device in the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list, is before the time indicated by the timestamp.

[0324] Wherein, "if the first satellite can cover the location of the terminal device up to the time indicated by the timestamp" can mean that the first satellite can reach the last tracked area visited by the terminal device in the terminal device tracking area list or any tracked area included in the terminal device tracking area list up to the time indicated by the timestamp; or, it can also be understood as the first satellite being able to provide services to the terminal device in the last tracked area visited by the terminal device in the terminal device tracking area list or any tracked area included in the terminal device tracking area list up to the time indicated by the timestamp. Alternatively, it can also be understood as the first satellite being able to establish a communication link with a satellite that reaches the last tracked area visited by the terminal device in the terminal device tracking area list or any tracked area included in the terminal device tracking area list up to the time indicated by the timestamp. In one example, please refer to Figure 13, which is a schematic diagram of a successful first downlink data transmission provided by an embodiment of this application. The location of the terminal device includes any tracking area included in the terminal device tracking area list, such as TAI List1 = {TA1, TA4, TA5}. The timestamp indicates the time T1, which represents the time when the terminal device leaves the tracking area list, for example, the time when the terminal device last received satellite network service before leaving the tracking area list. If the first satellite, such as satellite #1, can cover any tracking area in the tracking area list TAI List1 until T1, then the first network device determines that the first downlink data transmission is successful.

[0325] In another example, the timestamp indicates the time T1, which represents the time when the terminal device was removed from the tracking area list, for example, the last time the terminal device received satellite network service before it was removed from the tracking area list, and the time T3 when the first satellite first covered the location of the terminal device. T3 is before T1, when the first satellite receives the service request message from the terminal device and determines that the first downlink data was successfully transmitted.

[0326] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0327] Method 3: The second message includes the identification information of the last serving device. The first network device determines that the first downlink data was not successfully transmitted based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, the first downlink data is determined to have not been successfully transmitted.

[0328] Alternatively, it can be described as follows: If the time of the location of the first satellite-covered terminal device is after the last moment of the location of the satellite-covered terminal device corresponding to the last serving device, it is determined that the first downlink data was not successfully transmitted.

[0329] Specifically, the first network device can determine the time when the first satellite covers the location of the terminal device, and / or the time when the terminal device's location is first covered, based on satellite coverage information or indications from other network devices. The first network device can also determine the time period for the satellite coverage of the terminal device corresponding to the last service device, based on satellite coverage information or indications from other network devices.

[0330] The explanations regarding the location of the terminal device and the location of the terminal device initially covered by the first satellite can be found above and will not be repeated here.

[0331] The last moment of the satellite coverage terminal location corresponding to the last servicing device can refer to the last moment within the time period of the satellite coverage terminal location corresponding to the last servicing device, or it can refer to the last moment within the time range of the satellite coverage terminal location corresponding to the last servicing device. In one example, the time period of the satellite coverage terminal location corresponding to the last servicing device includes [T2, T3], where T3 is after T2. Therefore, the last moment within the time range of the satellite coverage terminal location corresponding to the last servicing device is T3.

[0332] In one example, if the first satellite first covers the location of the terminal device at time T4, and the last time the satellite corresponding to the last serving device covers the location of the terminal device is at time T3, where T4 is after T3, then the first network device determines that the first downlink data was not successfully sent.

[0333] In the above method, the first network device can identify downlink data that could not be successfully sent due to the movement of the terminal device during the tracking area update process, and retransmit the first downlink data to ensure data integrity. Moreover, it does not need to wait for the timer corresponding to the first downlink data to expire, thereby reducing the latency of data transmission and improving the reliability of data transmission.

[0334] Method 4: The second message includes the identification information of the last serving device. Based on the second message, it is determined that the first downlink data was successfully sent. This includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, a service request message from the terminal device is received, and it is determined that the first downlink data was successfully sent.

[0335] Alternatively, it can be described as follows: if the time when the location of the first satellite covers the terminal device is before the last moment when the location of the last service device is covered by the satellite, receive the service request message from the terminal device and determine that the first downlink data was successfully sent.

[0336] In this context, receiving a service request message from a terminal device can refer to the first network device receiving a service request message from a terminal device on a first satellite or a second network device on the first satellite. This service request message from the terminal device is used to indicate that the first downlink data was successfully transmitted.

[0337] In one example, if the time when the first satellite first covers the location of the terminal device is T5, and the last time when the satellite corresponding to the last serving device covers the location of the terminal device is T3, where T5 is before T3, the first network device receives the service request message from the terminal device and determines that the first downlink data was successfully sent.

[0338] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used to optimize the resources.

[0339] Step S1109: If it is determined from the second message that the first downlink data was not successfully sent, the first network device retransmits the first downlink data to the second satellite or the fourth network device on the second satellite.

[0340] Optionally, when the first network device retransmits the first downlink data to the second satellite or the fourth network device on the second satellite, it may send a TAU accept message to the second satellite or the fourth network device on the second satellite.

[0341] Accordingly, the second satellite or the fourth network device on the second satellite receives the retransmitted first downlink data from the first network device.

[0342] Step S1110: The second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device.

[0343] Correspondingly, the terminal device receives the first downlink data retransmitted from the second satellite or the fourth network device on the second satellite.

[0344] Optionally, when the second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device, it may send a Tracking Area Update Accept (TAU Accept) message to the terminal device.

[0345] For example, before the second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device, an RRC connection is established with the terminal device when the second satellite or the fourth network device on the second satellite covers the location of the terminal device.

[0346] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0347] The applicable scenario for this embodiment is: after the terminal device triggers the TAU process, the MME network element changes, the first network device is the original MME network element, or the first network device is the old MME network element, and the third network device is the changed network element, or the third network device is the new MME network element.

[0348] Please refer to Figure 14, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0349] Steps S1401-S1405 can be referred to the relevant descriptions in steps S1101-S1105, and will not be repeated here.

[0350] Step S1406: The second satellite or the fourth network device on the second satellite sends a second message to the third network device.

[0351] The second message includes a timestamp and / or the identification information of the last servicing device. The timestamp indicates the moment the terminal device was removed from the tracking area list. The identification information of the last servicing device indicates the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list. The timestamp includes one or more of the following: the moment the terminal device last received satellite network service before being removed from the tracking area list; the moment the terminal device first received satellite network service after being removed from the tracking area list; the moment the terminal device sent the second message; or the moment the satellite received the second message. For explanations regarding the timestamp and the identification information of the last servicing device, please refer to step S1104 above.

[0352] Step S1407: The third network device receives a second message from the second satellite or a fourth network device on the second satellite.

[0353] Step S1408: The third network device sends a third message to the first network device.

[0354] Correspondingly, the first network device receives a third message from the third network device.

[0355] For example, the third message is a context request message.

[0356] Step S1409: The first network device sends a fourth message to the third network device.

[0357] Step S1410: The third network device receives a fourth message from the first network device.

[0358] The fourth message includes the context information of the terminal device, the first downlink data of the terminal device, the first downlink data transmission record corresponding to the first downlink data, and the timer corresponding to the first downlink data transmission record. The first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the second network device on the first satellite. For details regarding the first downlink data of the terminal device, please refer to the relevant description in step S1002. For explanations regarding the first downlink data transmission record and the timer, please refer to the relevant description in step S1005.

[0359] For example, the fourth message can be a context response message, which is a response to the third message. Optionally, the context information of the terminal device included in the fourth message can be the same as or different from the context information of the terminal device included in the first message in step S1001, and this embodiment of the application does not limit it.

[0360] In one possible implementation, after the third network device receives the fourth message from the first network device, the third network device can send a context confirmation message to the first network device. Then, the third network device, the first network device, and other network devices continue to interact to complete other TAU processes.

[0361] Step S1411: The third network device determines whether the first downlink data was successfully sent based on the second message.

[0362] The third network device can determine whether the first downlink data was successfully sent based on the second message in the following ways:

[0363] Method 1: The second message includes a timestamp. The third network device determines that the first downlink data was not successfully transmitted based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the time indicated by the timestamp, it is determined that the first downlink data was not successfully transmitted.

[0364] Method 2: The second message includes a timestamp. The third network device determines that the first downlink data was successfully sent based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the time indicated by the timestamp, the device receives a service request message from the terminal device and determines that the first downlink data was successfully sent.

[0365] Method 3: The second message includes the identification information of the last serving device. The third network device determines that the first downlink data was not successfully transmitted based on the second message, including: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, it is determined that the first downlink data was not successfully transmitted.

[0366] Method 4: The second message includes the identification information of the last serving device. Based on the second message, it is determined that the first downlink data was successfully sent. This includes: if the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is before the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, a service request message from the terminal device is received, and it is determined that the first downlink data was successfully sent.

[0367] For example, step S1411 can refer to step S1108, which will not be repeated here.

[0368] Step S1412: If it is determined from the second message that the first downlink data was not successfully sent, the third network device retransmits the first downlink data to the second satellite or the fourth network device on the second satellite.

[0369] Optionally, when the third network device retransmits the first downlink data to the second satellite or the fourth network device on the second satellite, it may send a TAU accept message to the second satellite or the fourth network device on the second satellite.

[0370] Correspondingly, the second satellite or the fourth network device on the second satellite receives the retransmitted first downlink data from the third network device.

[0371] Step S1413: The second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device.

[0372] Optionally, when the second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device, it may send a Tracking Area Update Accept (TAU Accept) message to the terminal device.

[0373] For example, before the second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device, an RRC connection is established with the terminal device when the second satellite or the fourth network device on the second satellite covers the location of the terminal device.

[0374] Step S1414: The first network device sends a fifth message to the first satellite or a second network device on the first satellite.

[0375] Correspondingly, the first satellite or the second network device on the first satellite receives the fifth message from the first network device.

[0376] The fifth message includes the identification information of the third network device, which is used to instruct the first satellite or the second network device on the first satellite to send a service request message from the terminal device to the third network device.

[0377] Optionally, before the first network device sends the fifth message to the first satellite or the second network device on the first satellite, the first network device receives a service request message or a delivery notification message from the terminal device of the first satellite or the second network device on the first satellite. The service request message of the terminal device is used to indicate that the first downlink data was successfully sent, and the delivery notification message is used to indicate whether the first downlink data was successfully sent.

[0378] For example, there is no obvious sequential relationship between steps S1413 and S1414.

[0379] Step S1415: The first satellite or the second network device on the first satellite sends a service request message from the terminal device to the third network device.

[0380] Optionally, the first satellite or a second network device on the first satellite sends a service request message or a notification message from the terminal device to the third network device. Correspondingly, the third network device receives the service request message or notification message from the first satellite or the second network device on the first satellite.

[0381] For example, when the power supply link between the first satellite and the third network device is available, the first satellite or the second network device on the first satellite sends a service request message or a notification message to the third network device.

[0382] In one possible implementation, after receiving a service request message or notification message from the first satellite or a second network device on the first satellite, the third network device can update the first downlink data transmission record. The specific update process is as follows: if a service request message from the terminal device is received before the timer expires, the first downlink data transmission record and the cached first downlink data are deleted; if no service request message from the terminal device is received before the timer expires, the first downlink data is retransmitted. For details, please refer to the relevant description in step S1005.

[0383] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0384] Please refer to Figure 15, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0385] Step S1501: The first network device receives the first downlink data from the terminal device of the S-GW.

[0386] For details, please refer to the relevant description in step S1001.

[0387] Step S1502: The first network device performs data encryption and integrity protection on the first downlink data.

[0388] For details, please refer to the relevant description in step S1002.

[0389] Step S1503: When the first condition is met, the first network device sends a first message to the first satellite or the second network device on the first satellite.

[0390] Accordingly, after receiving the first message from the first network device, the first satellite or the second network device on the first satellite caches the first downlink data in the first message.

[0391] For details, please refer to the relevant description in step S1002.

[0392] Step S1504: The first network device determines the first downlink data transmission record and starts a timer.

[0393] For details, please refer to the relevant description in step S1002.

[0394] Step S1505: The first satellite or the second network device on the first satellite sends a paging message to the terminal device.

[0395] Accordingly, the terminal device receives a paging message from the first satellite or a second network device on the first satellite. For example, when the first satellite covers the location of the terminal device, the first satellite or a second network device on the first satellite can send a paging message to the terminal device. After receiving the paging message, the terminal device establishes an RRC connection with the first satellite or the second network device on the first satellite.

[0396] Step S1506: The terminal device sends a service request message to the first satellite or the second network device on the first satellite.

[0397] For details, please refer to the relevant description in step S1005.

[0398] Accordingly, the first satellite or the second network device on the first satellite receives and caches the service request message from the terminal device.

[0399] Step S1507: The first satellite or the second network device on the first satellite establishes a secure connection with the terminal device based on context information.

[0400] For details, please refer to the relevant description in step S1004.

[0401] Step S1508: The first satellite or the second network device on the first satellite sends the first downlink data to the terminal device.

[0402] For details, please refer to the relevant description in step S1005.

[0403] Step S1509: The first satellite or the second network device on the first satellite sends a service request message from the terminal device to the first network device.

[0404] Optionally, the first satellite or a second network device on the first satellite sends a transmission notification message to the first network device.

[0405] For details, please refer to the relevant description in step S1005.

[0406] Step S1510: The first network device receives a service request message from a terminal device of the first satellite or a second network device on the first satellite.

[0407] For details, please refer to the relevant description in step S1005.

[0408] Step S1511: The first network device deletes the first downlink data transmission record and the cached first downlink data.

[0409] For details, please refer to the relevant description in step S1005.

[0410] In the above method, by sending a first message to the first satellite or the network device on the first satellite, the first satellite or the network device on the first satellite can establish a secure communication link with the terminal device based on the uplink and downlink information in the first message. Then, when the service link is available, the first satellite or the network device on the first satellite and the terminal device can transmit data on the established secure communication link. That is, on the secure communication link, the first satellite or the network device on the first satellite sends first downlink data to the terminal device, thereby ensuring the security and reliability of data transmission between the satellite and the terminal device.

[0411] This embodiment applies to scenarios where the MME network element remains unchanged after the terminal device triggers the TAU process, and the first network device is the original MME network element.

[0412] Please refer to Figure 16, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0413] Steps S1601-S1604 can be referred to the relevant descriptions in steps S1501-S1504.

[0414] Step S1605: The terminal device sends a second message to the second satellite or the fourth network device on the second satellite.

[0415] Correspondingly, the second satellite or the fourth network device on the second satellite receives the second message from the terminal device.

[0416] For details, please refer to the relevant description in step S1104.

[0417] Step S1606: The second satellite or the fourth network device on the second satellite sends a second message to the first network device.

[0418] Correspondingly, the first network device receives a second message from the second satellite or a fourth network device on the second satellite.

[0419] For details, please refer to the relevant description in step S1106.

[0420] Step S1607: The first network device determines whether the first downlink data was successfully sent based on the second message.

[0421] For details, please refer to the relevant description in step S1108.

[0422] Step S1608: If it is determined based on the second message that the first downlink data was not successfully transmitted, the first network device retransmits the first downlink data to the second satellite or the fourth network device on the second satellite.

[0423] Accordingly, the second satellite or the fourth network device on the second satellite receives the retransmitted first downlink data from the first network device.

[0424] For details, please refer to the relevant description in step S1109.

[0425] Step S1609: The second satellite or the fourth network device on the second satellite sends the retransmitted first downlink data to the terminal device.

[0426] For details, please refer to the relevant description in step S1110.

[0427] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0428] The applicable scenario for this embodiment is: after the terminal device triggers the TAU process, the MME network element changes, the first network device is the original MME network element, or the first network device is the old MME network element, and the third network device is the changed network element, or the third network device is the new MME network element.

[0429] Please refer to Figure 17, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0430] Steps S1701-S1704 can be referred to the relevant descriptions in steps S1501-S1504.

[0431] Step S1705: The terminal device sends a second message to the second satellite or the fourth network device on the second satellite.

[0432] Correspondingly, the second satellite or the fourth network device on the second satellite receives the second message from the terminal device.

[0433] For details, please refer to the relevant description in step S1404.

[0434] Steps S1706-S1715 refer to the relevant descriptions in steps S1406-S1415, and will not be repeated here.

[0435] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0436] Please refer to Figure 18, which is a schematic diagram of a communication method provided in an embodiment of this application. The method includes, but is not limited to, the following steps:

[0437] Step S1801: The terminal device sends a second message to the satellite or network device on the satellite.

[0438] Correspondingly, the satellite or network equipment on the satellite receives a second message from the terminal device.

[0439] The satellite can be either a first satellite or a second satellite. Accordingly, when the satellite is the first satellite, the network equipment on the satellite can be the network equipment on the first satellite; when the satellite is the second satellite, the network equipment on the satellite can be the network equipment on the second satellite.

[0440] The second message includes a timestamp and / or the identification information of the last servicing RAN / SAT. The timestamp indicates the moment the terminal device was removed from the tracking area list. The identification information of the last servicing RAN / SAT indicates the identification information of the satellite or network device that last received satellite network service before the terminal device was removed from the tracking area list. See the relevant description in step S1104 for details.

[0441] Step S1802: The satellite or a network device on the satellite sends a second message to the first network device or the third network device.

[0442] Step S1803: The first network device or the third network device determines whether the first downlink data was successfully sent based on the second message.

[0443] For details, please refer to the relevant description in step S1108.

[0444] Step S1804: If it is determined based on the second message that the first downlink data was not successfully transmitted, the first network device or the third network device retransmits the first downlink data to the satellite or the network device on the satellite.

[0445] Step S1805: The satellite or network equipment on the satellite sends the retransmitted first downlink data to the terminal equipment.

[0446] In the above method, if it is determined that the first downlink data was successfully sent based on the second information, the relevant resources corresponding to the first downlink data can be used, thereby optimizing resources. Furthermore, if it is determined that the first downlink data was not successfully sent based on the second message, the first downlink data is retransmitted, ensuring data integrity and eliminating the need to wait for the timer corresponding to the first downlink data to time out, thus reducing data transmission latency and improving data transmission reliability.

[0447] The methods of the embodiments of this application have been described in detail above, and the apparatus of the embodiments of this application is provided below.

[0448] Please refer to Figure 19, which is a schematic diagram of the structure of a communication device 1900 provided in an embodiment of this application. The communication device 1900 may include a processing unit 1901 and a transceiver unit 1902, and the specific details of each unit are as follows:

[0449] The processing unit 1901 is used for data processing. The transceiver unit 1902 can implement corresponding communication functions. The transceiver unit 1902 can also be called a communication interface or a communication module.

[0450] Optionally, the communication device 1900 may further include a storage unit, which can be used to store instructions and / or data. The processing unit 1901 can read the instructions and / or data in the storage module to enable the implementation of the aforementioned method embodiments.

[0451] Optionally, the transceiver unit 1902 may include a sending unit and a receiving unit. The sending unit is used to perform the sending operation in the above method embodiments. The receiving unit is used to perform the receiving operation in the above method embodiments.

[0452] It should be noted that the communication device 1900 may include a transmitting unit but not a receiving unit. Alternatively, the communication device 1900 may include a receiving unit but not a transmitting unit. Specifically, it depends on whether the above-described scheme executed by the communication device 1900 includes both transmitting and receiving actions.

[0453] Optionally, the communication device 1900 is used to perform the actions performed by the first network device in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18, which will not be elaborated here. For example, the communication device 1900 is used to perform the following scheme:

[0454] The transceiver unit 1902 is used to receive first downlink data from the terminal device; the processing unit 1901 is further used to send a first message to a first satellite or a second network device on the first satellite through the transceiver unit 1902 when a first condition is met. The first message includes the first downlink data of the terminal device and the context information of the terminal device. The context information includes the access layer security context information and / or non-access layer context information of the terminal device. The first condition includes one or more of the following: the terminal device accesses the network through the satellite and supports store-and-forward mode; or the communication link between the first network device and the first satellite is available, and a communication link cannot be established between the terminal device and the first satellite at present.

[0455] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17 or 18.

[0456] Optionally, the communication device 1900 is used to perform the actions performed by the third network device in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18, which will not be elaborated here. For example, the communication device 1900 is used to perform the following scheme:

[0457] The transceiver unit 1902 is configured to receive a second message, the second message including a timestamp and / or the identification information of the last serving device; the timestamp is used to indicate the time when the terminal device is removed from the tracking area list, and the identification information of the last serving device is used to indicate the identification information of the last satellite or network device that received satellite network service before the terminal device was removed from the tracking area list; the transceiver unit 1902 is also configured to receive a fourth message from the first network device, the fourth message including the context information of the terminal device, the first downlink data of the terminal device, the first downlink data transmission record corresponding to the first downlink data, and the timer corresponding to the first downlink data transmission record, the first downlink data transmission record including the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device; the processing unit 1901 is configured to determine whether the first downlink data was successfully transmitted based on the second message.

[0458] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17 or 18.

[0459] Optionally, the communication device 1900 is used to perform the actions performed by the terminal device in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18; these will not be elaborated upon here. For example, the communication device 1900 is used to perform the following scheme:

[0460] The processing unit 1901 is configured to send a second message through the transceiver unit 1902. The second message is used to determine whether the first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the time when the terminal device was removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the last satellite or network device that received satellite network service before the terminal device was removed from the tracking area list. The transceiver unit 1902 is configured to receive retransmitted first downlink data if the first downlink data was not successfully transmitted.

[0461] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17 or 18.

[0462] Optionally, the communication device 1900 is used to perform the actions performed by the first satellite or the second network device on the first satellite in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18, which will not be elaborated here. For example, the communication device 1900 is used to perform the following scheme:

[0463] The transceiver unit 1902 is configured to receive a first message, the first message including first downlink data of the terminal device and context information of the terminal device, the context information including access layer security context information and / or non-access layer security context information of the terminal device; the processing unit 1901 is configured to establish a secure connection with the terminal device based on the context information; the transceiver unit 1902 is further configured to send the first downlink data to the terminal device.

[0464] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17 or 18.

[0465] Optionally, the communication device 1900 is used to perform the actions performed by the first satellite or the second network device on the first satellite in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18, which will not be elaborated here. For example, the communication device 1900 is used to perform the following scheme:

[0466] The processing unit 1901 is configured to receive a second message through the transceiver unit 1902. The second message is used to determine whether the first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the time when the terminal device was removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the last satellite that received satellite network service before the terminal device was removed from the tracking area list. The transceiver unit 1902 is configured to send retransmitted first downlink data if the first downlink data was not successfully transmitted.

[0467] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17 or 18.

[0468] Optionally, the communication device 1900 is used to perform the actions performed by the second satellite or the fourth network device on the second satellite in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. For details, please refer to the relevant descriptions in the embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18, which will not be elaborated here. For example, the communication device 1900 is used to perform the following scheme:

[0469] The processing unit 1901 is configured to receive a second message through the transceiver unit 1902. The second message is used to determine whether the first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the time when the terminal device was removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the last satellite that received satellite network service before the terminal device was removed from the tracking area list. The transceiver unit 1902 is configured to send retransmitted first downlink data if the first downlink data was not successfully transmitted.

[0470] It should be noted that the implementation and beneficial effects of each module can also be described in accordance with the corresponding descriptions of the method embodiments shown in Figures 10, 11, 14, 15, 16, 17, or 18. It should be understood that the specific processes by which each module performs the above-described corresponding procedures have been described in detail in the above method embodiments, and for the sake of brevity, will not be repeated here.

[0471] The processing unit 1901 in the above embodiments can be implemented by at least one processor or processor-related circuitry. The transceiver unit 1902 can be implemented by a transceiver or transceiver-related circuitry. The transceiver unit 1902 can also be referred to as a communication module or communication interface. The storage module can be implemented by at least one memory.

[0472] Please refer to Figure 20, which is a schematic diagram of the structure of a communication device 2000 provided in an embodiment of this application. The communication device 2000 includes at least one processor 2001 and a communication interface 2003. Optionally, it also includes a memory 2002. The processor 2001, memory 2002, and communication interface 2003 are interconnected via a bus 2004. Optionally, the processor 2001 and the memory 2002 can be integrated together.

[0473] The memory 2002 includes, but is not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), or compact disc read-only memory (CD-ROM), which is used for related computer programs and data. The communication interface 2003 is used for receiving and sending data.

[0474] Processor 2001 can be one or more central processing units (CPUs). When processor 2001 is a CPU, the CPU can be a single-core CPU or a multi-core CPU.

[0475] The processor 2001 in the communication device 2000 is used to read computer programs or instructions stored in the memory 2002 to implement the functions of the aforementioned processing unit, and the communication interface 2003 in the communication device 2000 is used to implement the functions of the aforementioned transceiver unit.

[0476] This application also provides a chip device including at least one processor, which is used to call a computer program or instructions stored in a memory to cause the processor to execute the method provided in the above embodiments.

[0477] In one possible implementation, the input of the chip device corresponds to the receiving operation in any of the above embodiments, and the output of the chip device corresponds to the sending operation in any of the above embodiments.

[0478] Optionally, the processor is coupled to the memory via an interface.

[0479] Optionally, the chip device may also include a memory storing computer program instructions.

[0480] This application also provides a computer-readable storage medium storing a computer program or instructions that, when executed on a processor, implement the method provided in the above-described method embodiments.

[0481] This application also provides a computer program product, which includes a computer program or instructions that, when run on a processor, implement the method provided in the above-described method embodiments.

[0482] It is understood that the processor in the embodiments of this application may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor may be a microprocessor or any conventional processor.

[0483] The method steps in the embodiments of this application can be implemented in hardware or by a processor executing software instructions. The software instructions can consist of corresponding software modules, which can be stored in random access memory, flash memory, read-only memory, programmable read-only memory, erasable programmable read-only memory, electrically erasable programmable read-only memory, registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in a base station or terminal. Of course, the processor and storage medium can also exist as discrete components in the base station or terminal.

[0484] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of this application are performed entirely or partially. The computer can be a general-purpose computer, a special-purpose computer, a computer network, a network device, a user equipment, or other programmable device. The computer program or instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another. For example, the computer program or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; it can also be an optical medium, such as a digital video optical disc; or it can be a semiconductor medium, such as a solid-state drive. The computer-readable storage medium may be a volatile or non-volatile storage medium, or may include both types of storage media.

[0485] In the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions of different embodiments are consistent and can be referenced by each other. The technical features of different embodiments can be combined to form new embodiments according to their inherent logical relationship.

[0486] In the description of this application, terms such as "first", "second", "S1001" or "S1002" are used only for the purpose of distinguishing descriptions and for the convenience of context. Different sequence numbers do not have specific technical meanings themselves and should not be construed as indicating or implying relative importance, nor should they be construed as indicating or implying the order of execution of operations. The order of execution of each process should be determined by its function and internal logic.

[0487] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. Additionally, the character " / " in this document indicates that the preceding and following related objects have an "or" relationship.

[0488] In this application, "transmission" can include the following three situations: sending data, receiving data, or both sending and receiving data. In this application, "data" can include business data and / or signaling data.

[0489] The terms “comprising” or “having” and any variations thereof in this application are intended to cover a non-exclusive inclusion, such as a process / method that includes a series of steps, or a system / product / equipment that includes a series of units, not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes / methods / products / equipment.

[0490] In the description of this application, unless otherwise specified, the number of nouns refers to "singular nouns or plural nouns," that is, "one or more." "At least one" means one or more. "Including at least one of the following: A, B, C" means that it may include A, or B, or C, or A and B, or A and C, or B and C, or A, B, and C. A, B, and C may be single or multiple.

Claims

1. A communication method, characterized in that, Applied to the first network device, including: Receive the first downlink data from the terminal device; When a first condition is met, a first message is sent to a first satellite or a second network device on the first satellite. The first message includes first downlink data from the terminal device and context information of the terminal device. The context information includes access layer security context information and / or non-access layer context information of the terminal device. The first condition includes one or more of the following: The terminal device accesses the network via satellite and supports store-and-forward mode; or The communication link between the first network device and the first satellite is available, and the communication link between the terminal device and the first satellite cannot be established at present.

2. The method according to claim 1, characterized in that, The method further includes: A first downlink data transmission record is determined, and a timer is started. The first downlink data transmission record includes the identification information of the terminal device, the identification information of the first downlink data, and the identification information of the first satellite or the identification information of the second network device.

3. The method according to claim 2, characterized in that, The duration of the timer is determined based on satellite coverage information and paging strategy information; wherein, the duration of the timer is greater than a first duration, the first duration being the time between the start time of the timer and the moment when the first satellite covers the first network device again.

4. The method according to any one of claims 1-3, characterized in that, The method further includes: Receive a service request message from the terminal device, the service request message being used to indicate that the first downlink data was successfully sent; Delete the first downlink data transmission record and the cached first downlink data.

5. The method according to claim 4, characterized in that, The service request message received by the terminal device includes: Before the timer expires, a service request message from the terminal device is received.

6. The method according to any one of claims 1-3, characterized in that, The method further includes: Receive the second message before the timer expires; Based on the second message, determine whether the first downlink data was successfully sent.

7. The method according to claim 6, characterized in that, The second message includes a timestamp and / or the identification information of the last serving device. The timestamp indicates the moment when the terminal device is removed from the tracking area list, and the identification information of the last serving device indicates the identification information of the satellite or network device that last received satellite network services before the terminal device was removed from the tracking area list. The timestamp includes one or more of the following: The last time the terminal device received satellite network service before it was removed from the tracking area list; The moment when the terminal device first receives satellite network service after being removed from the tracking area list; The moment when the terminal device sends the second message; or The moment the satellite receives the second message.

8. The method according to claim 6 or 7, characterized in that, The second message includes a timestamp, and determining that the first downlink data was not successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is after the time indicated by the timestamp, it is determined that the first downlink data was not successfully transmitted. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

9. The method according to claim 6 or 7, characterized in that, The second message includes a timestamp, and determining that the first downlink data was successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is before the time indicated by the timestamp, and receives the service request message of the terminal device, the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; It has been confirmed that the first downlink data was successfully transmitted.

10. The method according to any one of claims 6-9, characterized in that, The second message includes the identification information of the last serving device, and the step of determining that the first downlink data was not successfully sent based on the second message includes: If the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, it is determined that the first downlink data was not successfully transmitted. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

11. The method according to any one of claims 6-9, characterized in that, The second message includes the identification information of the last serving device, and determining that the first downlink data was successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is before the last time when the satellite corresponding to the last service device covers the location of the terminal device, and the terminal device receives the service request message of the terminal device, the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; It has been confirmed that the first downlink data was successfully transmitted.

12. The method according to any one of claims 6-11, characterized in that, The method further includes: If it is determined from the second message that the first downlink data was not successfully sent, the first downlink data is retransmitted.

13. The method according to any one of claims 1-3, characterized in that, The method further includes: No service request message was received from the terminal device until the timer expired; Retransmit the first downlink data.

14. The method according to claim 13, characterized in that, The method further includes: If the retransmission exceeds N times, or the time for caching the first downlink data exceeds duration T, the first downlink data transmission record and the cached first downlink data are deleted, and no further retransmission operation is performed. Here, N is a positive integer greater than 0, and T is greater than 0.

15. The method according to any one of claims 1-3, characterized in that, The method further includes: Receive a third message from a third network device; A fourth message is sent to the third network device. The fourth message includes the context information of the terminal device, the first downlink data of the terminal device, the first downlink data transmission record, and the timer.

16. The method according to claim 15, characterized in that, The method further includes: Send a fifth message, which includes the identification information of the third network device, and the fifth message is used to instruct the sending of a service request message of the terminal device to the third network device.

17. A communication method, characterized in that, Applied to third-party network devices, including: Receive a second message, the second message including a timestamp and / or the identification information of the last serving device; the timestamp is used to indicate the moment when the terminal device is removed from the tracking area list, and the identification information of the last serving device is used to indicate the identification information of the satellite or network device that last received satellite network services before the terminal device was removed from the tracking area list; A fourth message is received from a first network device. The fourth message includes context information of the terminal device, first downlink data of the terminal device, a first downlink data transmission record corresponding to the first downlink data, and a timer corresponding to the first downlink data transmission record. The first downlink data transmission record includes identification information of the terminal device, identification information of the first downlink data, and identification information of the first satellite or identification information of the second network device. Based on the second message, determine whether the first downlink data was successfully sent.

18. The method according to claim 17, characterized in that, The timestamp includes one or more of the following: The last time the terminal device received satellite network service before it was removed from the tracking area list; The moment when the terminal device first receives satellite network service after being removed from the tracking area list; The moment when the terminal device sends the second message; or The moment the satellite receives the second message.

19. The method according to claim 17 or 18, characterized in that, The second message includes a timestamp, and determining that the first downlink data was not successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is after the time indicated by the timestamp, it is determined that the first downlink data was not successfully transmitted. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

20. The method according to claim 17 or 18, characterized in that, The second message includes a timestamp, and determining that the first downlink data was successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is before the time indicated by the timestamp, and receives the service request message of the terminal device, the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; It has been confirmed that the first downlink data was successfully transmitted.

21. The method according to any one of claims 17-20, characterized in that, The third message includes the identification information of the last serving device, and the step of determining that the first downlink data was not successfully sent based on the second message includes: If the time when the first satellite first covers the location of the terminal device after receiving the first downlink data is after the last moment when the satellite corresponding to the last serving device covers the location of the terminal device, it is determined that the first downlink data was not successfully transmitted. The location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list.

22. The method according to any one of claims 17-20, characterized in that, The third message includes the identification information of the last serving device, and the step of determining that the first downlink data was successfully sent based on the second message includes: If the first satellite receives the first downlink data and the time when it first covers the location of the terminal device is before the last time when the satellite corresponding to the last service device covers the location of the terminal device, and the terminal device receives the service request message of the terminal device, the location of the terminal device includes the tracking area last visited by the terminal device in the terminal device tracking area list, or any tracking area included in the terminal device tracking area list; It has been confirmed that the first downlink data was successfully transmitted.

23. The method according to any one of claims 17-22, characterized in that, The method further includes: If it is determined from the second message that the first downlink data was not successfully sent, the first downlink data is retransmitted.

24. A communication method, characterized in that, Applied to terminal devices, including: Send a second message, which is used to determine whether the first downlink data was successfully sent. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the moment when the terminal device is removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the last satellite or network device that received satellite network service before the terminal device was removed from the tracking area list. If the first downlink data is not successfully sent, the retransmitted first downlink data will be received.

25. A communication method, characterized in that, A second network device applied to or on the first satellite, including: Receive a first message, the first message including first downlink data of the terminal device and context information of the terminal device, the context information including access layer security context information and / or non-access layer context information of the terminal device; Establish a secure connection with the terminal device based on the context information; The first downlink data is sent to the terminal device.

26. The method according to claim 25, characterized in that, The method further includes: Receive service request messages from terminal devices; A service request message from the terminal device is sent, which indicates that the first downlink data was successfully sent.

27. A communication method, characterized in that, A second network device applied to or on the first satellite, including: A second message is received, which is used to determine whether the first downlink data was successfully transmitted. The second message includes a timestamp and / or the identification information of the last serving device. The timestamp is used to indicate the time when the terminal device was removed from the tracking area list. The identification information of the last serving device is used to indicate the identification information of the last satellite that received satellite network service before the terminal device was removed from the tracking area list. If the first downlink data is not successfully sent, retransmit the first downlink data.

28. The method according to claim 27, characterized in that, The method further includes: Receive a fifth message, the fifth message including the identification information of the third network device; Send a service request message from the terminal device to the third network device.

29. A communication device, characterized in that, The apparatus includes a transceiver unit and a processing unit, wherein the processing unit is configured to perform the processing operation in the method as described in any one of claims 1-28, and the transceiver unit is configured to perform the transceiver operation in the method as described in any one of claims 1-28.

30. A communication device, characterized in that, The apparatus includes at least one processor and a communication interface, wherein the at least one processor invokes a computer program or instructions stored in a memory to perform the method as described in any one of claims 1-28.

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