Communication method, apparatus and system

Abstract

The present application relates to the technical field of communications. Provided in the embodiments are a communication method, an apparatus, and a system, which can transmit data from a core network to a terminal device in scenarios of non-continuous feeder links. The method comprises: a mobility management network element receives a first notification message, the first notification message being used for instructing receiving downlink data of a first terminal device; when the mobility management network element determines that a communication connection between a first access network device located on a satellite and the first terminal device is unavailable, and the downlink data can be cached in the first access network device, the mobility management network element sends first instruction information to the first access network device, the first instruction information being used for instructing caching the downlink data to the first access network device.

Description

Communication method, device and system

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on December 29, 2023, with application number 202311870572.0 and application name “Communication Methods, Devices and Systems”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of communication technologies, and in particular to communication methods, devices, and systems. Background Art

[0003] In the terrestrial cellular internet of things (CIoT), user data can be transmitted over either the user plane or the control plane. Control-plane transmission eliminates the need to establish a data bearer. After the data reaches the user's serving gateway (S-GW), it is passed from the control-plane network element to the base station, which then transmits the data to the terminal device via non-access stratum (NAS) signaling.

[0004] With the development of communication technology, CIoT data can be transmitted through non-terrestrial networks (NTN). In the NTN network, the satellite can be connected to the ground station on the network side through a feeder link, and can be connected to the terminal device on the ground through a service link, thereby realizing end-to-end connectivity between the terminal device, the satellite, and the network. However, the feeder link and the service link may not be available at the same time. This scenario can also be called feeder link discontinuity. For example, in some remote areas where there are no ground stations deployed around, when the satellite covers the terminal devices in this area (the service link is available at this time), it may not be able to connect to the available ground stations at the same time (the feeder link is unavailable at this time). For another example, when the satellite is connected to the ground station (the feeder link is available at this time), there is no terminal device within the coverage of the satellite (the service link is unavailable at this time).

[0005] In CIoT, for downlink data transmitted via the control plane, the base station needs to obtain data from the control plane network element after successfully paging the terminal device. However, in a discontinuous feeder link scenario, after the base station successfully pages the terminal device, it cannot establish a connection with the control plane network element via the feeder link, and data cannot be sent from the core network (CN) to the terminal device. Therefore, how to send data from the core network to the terminal device in a discontinuous feeder link scenario is an urgent problem to be solved. Summary of the Invention

[0006] The embodiments of the present application provide a communication method, apparatus, and system that can transmit data from a core network to a terminal device in a scenario where the feeder link is discontinuous.

[0007] The embodiments of this application adopt the following technical solutions:

[0008] In the first aspect, a communication method is provided, which can be executed by a mobile management network element, or by a component of the mobile management network element (such as a processor, a chip, or a chip system, etc.), or by a logic module or software that can implement all or part of the functions of the mobile management network element. The following is an illustration using the mobile management network element as an example of the execution subject of the method, and the method includes: the mobile management network element receives a first notification message, and the first notification message is used to indicate the reception of downlink data of the first terminal device. When the mobile management network element determines that the communication connection between the first access network device located on the satellite and the first terminal device is unavailable, and the downlink data can be cached in the first access network device, the mobile management network element sends a first indication message to the first access network device, and the first indication message is used to indicate the caching of downlink data to the first access network device.

[0009] Based on the communication method provided in the embodiment of the present application, if the communication connection between the first access network device and the first terminal device is unavailable, the mobility management network element can instruct the first access network device to pre-receive and cache downlink data. Thus, after the communication connection between the first access network device and the first terminal device is restored, the first access network device can immediately send the cached data to the first terminal device after paging the first terminal device. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time required to complete a data transmission will not be very long.

[0010] In one possible implementation, the mobility management network element determines that downlink data can be cached in the first access network device, including at least one of the following: the mobility management network element determines that the first access network device supports a first function, and the first function includes a storage and forwarding function; or, the mobility management network element determines that the downlink data supports transmission through storage and forwarding operations.

[0011] In this solution, the mobility management network element may consider multiple factors: whether the first access network device supports store and forward, and / or whether the data supports store and forward, to determine whether the downlink data can be cached in the first access network device.

[0012] In one possible implementation, the mobile management network element determines that downlink data supports transmission through storage and forwarding operations, including: the mobile management network element determines that downlink data supports transmission through storage and forwarding operations based on one or more of the following: subscription information of the first terminal device, latency requirements of the downlink data, or the context of the first terminal device.

[0013] This solution provides multiple pieces of information that can be used to determine whether downlink data supports transmission through the store and forward operation.

[0014] In a possible implementation, the first indication information is carried in a first paging message, and the first paging message is used to request the first access network device to page the first terminal device.

[0015] Based on this solution, the first indication information can be carried in a paging message and sent to the first access network device, thereby saving signaling overhead.

[0016] In one possible implementation, the method further includes: a mobility management network element receiving a first request message from a first access network device, the first request message being used to request the mobility management network element to establish a data transmission channel with the first access network device. After the mobility management network element obtains downlink data from the first terminal device, the mobility management network element sends the downlink data to the first access network device.

[0017] Based on this solution, the first request message sent by the first access network device can trigger the transmission of downlink data.

[0018] In one possible implementation, the method further includes: a mobility management network element determining, based on the satellite coverage availability information corresponding to the first access network device and the location information of the first terminal device, whether the first terminal device is within the coverage range corresponding to the first access network device; wherein the satellite coverage information of the first access network device includes a mapping relationship between the coverage range corresponding to the first access network device and time. If the first terminal device is within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is available; or, if the first terminal device is not within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is unavailable.

[0019] This solution provides a method for determining whether a communication connection between an access network device and a terminal device is available.

[0020] In a possible implementation, the method further includes: the mobile management network element determines one or more access network devices that are available for communication connection with the mobile management network element. The mobile management network element determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that there is no access network device whose current coverage includes the first terminal device, among the one or more access network devices, wherein the satellite coverage information of the access network device includes a mapping relationship between the coverage corresponding to the access network device and time. The mobile management network element determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that the access network device whose earliest coverage is expected to include the first terminal device is the first access network device.

[0021] Based on this solution, the mobile management network element can determine the access network device that is expected to restore the communication connection with the first terminal device the earliest as the first access network device, so as to shorten the time required for the access network device to cache the downlink data after receiving the downlink data until the downlink data is sent to the first terminal device.

[0022] In one possible implementation, the location information of the first terminal device includes one or more of the following: information about the tracking area where the first terminal device is located when it enters the idle state, or information about the updated tracking area obtained according to the tracking area update process of the first terminal device.

[0023] This solution provides location information of multiple first terminal devices.

[0024] In a possible implementation, the method further includes: when the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends second indication information to the serving gateway, where the second indication information is used to instruct deletion of the downlink data.

[0025] Based on this solution, when the downlink data cannot be cached in the first access network device, the transmission of the downlink data can be terminated.

[0026] In a second aspect, a communication method is provided. The method can be executed by a mobility management network element, or by a component of the mobility management network element (e.g., a processor, chip, or chip system), or by a logic module or software that implements all or part of the functions of the mobility management network element. The method is described below using a mobility management network element as an example. The method includes: the mobility management network element receiving a first notification message, the first notification message being used to indicate receipt of downlink data from a first terminal device. The mobility management network element sending a first paging message to one or more access network devices located on a satellite, the first paging message being used to request paging the first terminal device. The one or more access network devices include a first access network device. The mobility management network element receives a first request message from the first access network device, the first request message being used to request the mobility management network element to establish a data transmission channel with the first access network device. If the mobility management network element determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable and that the downlink data can be cached on the first access network device, the mobility management network element obtains the downlink data and sends the downlink data to the first access network device.

[0027] Based on the communication method provided in the embodiment of the present application, the mobile management network element can, based on the request of the first access network device, first send downlink data to the first access network device when it is determined that the communication connection between the first access network device and the first terminal device is unavailable and the downlink data can be cached in the first access network device. Thus, after the communication connection between the first access network device and the first terminal device is restored, the first access network device can immediately send the cached data to the first terminal device after paging the first terminal device. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time to complete a data transmission will not be very long.

[0028] In one possible implementation, the mobility management network element determines that downlink data can be cached in the first access network device, including at least one of the following: the mobility management network element determines that the first access network device supports a first function, and the first function includes a storage and forwarding function; or, the mobility management network element determines that the downlink data supports transmission through storage and forwarding operations.

[0029] In this solution, the mobility management network element may consider multiple factors: whether the first access network device supports store and forward, and / or whether the data supports store and forward, to determine whether the downlink data can be cached in the first access network device.

[0030] In one possible implementation, the mobile management network element determines that downlink data supports transmission through storage and forwarding operations, including: the mobile management network element determines that downlink data supports transmission through storage and forwarding operations based on one or more of the following: subscription information of the first terminal device, latency requirements of the downlink data, or the context of the first terminal device.

[0031] This solution provides multiple pieces of information that can be used to determine whether downlink data supports transmission through the store and forward operation.

[0032] In one possible implementation, the mobility management network element determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable, including: the mobility management network element determining that the first request message includes third indication information, where the third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable. Alternatively, the mobility management network element determines that the first request message does not include service request information, where the service request message is used to indicate that the first terminal device requests to establish a connection with the core network.

[0033] This solution provides multiple implementations of determining that the communication connection between the first access network device and the first terminal device is unavailable based on the first request message.

[0034] In a possible implementation, the method further includes: when the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends fourth indication information to the first access network device, and the fourth indication information indicates that establishment of a data transmission channel is rejected.

[0035] Based on this solution, when the downlink data cannot be cached in the first access network device, the transmission of the downlink data can be terminated.

[0036] In a possible implementation, the method further includes: when the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends second indication information to the serving gateway, where the second indication information is used to instruct deletion of the downlink data.

[0037] Based on this solution, when the downlink data cannot be cached in the first access network device, the transmission of the downlink data can be terminated.

[0038] In a third aspect, a communication method is provided, which can be executed by a first access network device, or by a component of the first access network device (such as a processor, a chip, or a chip system, etc.), or by a logic module or software that can implement all or part of the functions of the first access network device. The following is an illustration of the method using the first access network device as the execution subject, and the method includes: the first access network device receives a first paging message from a mobility management network element; wherein the first paging message is used to request paging of a first terminal device. Before the first access network device pages the first terminal device, the first access network device sends a first request message to the mobility management network element, and the first request message is used to request the mobility management network element to establish a data transmission channel with the first access network device; wherein the communication connection between the first access network device located on the satellite and the first terminal device is unavailable. The first access network device receives and caches downlink data from the mobility management network element, or the first access network device receives fourth indication information from the mobility management network element, and the fourth indication information indicates that the establishment of the data transmission channel is rejected.

[0039] Based on the communication method provided in the embodiment of the present application, if the communication connection between the first access network device and the first terminal device is unavailable, the first access network device may first request downlink data from the mobile management network element before paging the first terminal device. If the first access network device receives downlink data, it may cache the downlink data locally. Thus, after the communication connection between the first access network device and the first terminal device is restored, the first access network device may immediately send the cached data to the first terminal device after paging the first terminal device. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time to complete a data transmission will not be very long. In addition, the first access network device may also terminate the transmission of downlink data based on the fourth indication information indicating a refusal to establish a data transmission channel.

[0040] In a possible implementation, the first paging message includes first indication information, where the first indication information is used to instruct the first access network device to cache downlink data of the first terminal device.

[0041] In this solution, the first access network device can determine that it needs to receive and cache the downlink data of the first terminal device based on the indication of the first indication information.

[0042] In a possible implementation, the first request message is also used by the mobility management network element to determine that the communication connection between the first access network device and the first terminal device is unavailable.

[0043] In this solution, the first access network device may determine that the communication connection between the first access network device and the first terminal device is unavailable, and indicate this to the mobility management network element through a first request message.

[0044] In a possible implementation, the first request message includes third indication information, where the third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable.

[0045] Based on this solution, the first access network device can indicate to the mobility management network element that the communication connection between the first access network device and the first terminal device is unavailable by carrying the third indication information in the first request message.

[0046] In one possible implementation, when the first access network device receives and caches downlink data from the mobility management network element, the method further includes: when the communication connection with the first terminal device is restored, the first access network device sends a second paging message to the first terminal device; the second paging message is used to page the first terminal device. The first access network device receives a radio resource control (RRC) connection request message from the first terminal device. Afterwards, the first access network device sends an RRC connection establishment message to the first terminal device. Afterwards, the first access network device receives an RRC connection establishment completion message from the first terminal device. Afterwards, the first access network device sends downlink data to the first terminal device.

[0047] Based on this solution, when the communication connection between the first access network device and the first terminal device is restored, the first access network device can send downlink data to the first terminal device through the RRC connection established with the first terminal device, thereby completing the transmission of data from the core network to the first terminal device.

[0048] In a possible implementation, the second paging message includes fifth indication information, where the fifth indication information is used to instruct the first terminal device to receive downlink data cached in the first access network device.

[0049] Based on this solution, the first access network device can indicate to the first terminal device through the fifth indication information that there is downlink data cached locally in the first access network.

[0050] In a possible implementation, the method further includes: the first access network device determines that the RRC connection request message does not include service request information, and the service request information is used to indicate that the first terminal device requests to establish a connection with the core network.

[0051] Based on this solution, since the first access network device locally caches the downlink data of the first terminal device, there is no need to request downlink data from the core network. Therefore, the RRC connection request message may not include service request information for indicating that the first terminal device requests to establish a connection with the core network.

[0052] In a possible implementation, the method further includes: the first access network device determining that the RRC connection request message includes service request information, where the service request information is used to indicate that the first terminal device requests to establish a connection with the core network; and the first access network device discarding the service request information.

[0053] Based on this solution, since the first access network device locally caches the downlink data of the first terminal device and no longer needs to request downlink data from the core network, the first access network device can discard the service request information used to indicate that the first terminal device requests to establish a connection with the core network.

[0054] In a fourth aspect, a communication method is provided, which can be executed by a first terminal device, or by a component of the first terminal device (such as a processor, a chip, or a chip system, etc.), or by a logic module or software that can realize all or part of the functions of the first terminal device. The following is an illustration of the method using the first terminal device as an example of the execution subject, the method comprising: the first terminal device receives a second paging message from the first access network device; wherein the second paging message is used to page the first terminal device, the second paging message includes fifth indication information, and the fifth indication information is used to instruct the first terminal device to receive downlink data cached in the first access network device. The first terminal device establishes an RRC connection with the first access network device. The first terminal device receives downlink data from the first access network device.

[0055] Based on the communication method provided in the embodiment of the present application, the first access network device can first cache the downlink data of the first terminal device locally, and indicate it to the first terminal device through the indication information in the paging message. Therefore, after the first terminal device receives the paging message and establishes an RRC connection with the first access network device, it can immediately receive the downlink data cached locally in the first access network, without the need for the first access network device to request downlink data from the core network. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time to complete a data transmission will not be very long.

[0056] In one possible implementation, a first terminal device establishes an RRC connection with a first access network device, including: the first terminal device determines to generate an RRC connection request message that does not include service request information based on fifth indication information, where the service request information is used to indicate that the first terminal device requests to establish a connection with the core network. The first terminal device sends an RRC connection request message to the first access network device. Thereafter, the first terminal device receives an RRC connection establishment message from the first access network device. Thereafter, the first terminal device sends an RRC connection establishment completion message to the first access network device.

[0057] Based on this solution, since the first access network device locally caches the downlink data of the first terminal device, there is no need to request downlink data from the core network. Therefore, the RRC connection request message generated by the first terminal device may not include service request information for indicating that the first terminal device requests to establish a connection with the core network.

[0058] In the fifth aspect, a communication method is provided, which can be executed by a service gateway, or by a component of the service gateway (such as a processor, chip, or chip system, etc.), or by a logic module or software that can realize all or part of the service gateway function. The following is an illustration of the method using the service gateway as the execution subject, and the method includes: the service gateway obtains downlink data that needs to be transmitted to the first terminal device, and determines that the mobile management network element serving the first terminal device is located on the satellite. When the service gateway determines that the communication connection between the access network device located on the satellite and the first terminal device is unavailable, the service gateway sends a first notification message to the mobile management network element, and the first notification message is used to indicate the reception of downlink data of the first terminal device. The first notification message includes a second request message, and the second request message is used to request the mobile management network element to cache the downlink data.

[0059] Based on the communication method provided in the embodiment of the present application, when the service gateway determines that the communication connection between the access network device and the first terminal device is unavailable, it can request the mobility management network element to first receive and cache the downlink data through a second request message. Thus, after the communication connection between the access network device and the first terminal device is restored, the first access network device can immediately obtain the cached downlink data from the mobility management network element. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time to complete a data transmission will not be very long.

[0060] In a possible implementation, the method further includes: the serving gateway receiving a response message from the mobility management network element to the first notification message, the response message being used to instruct the serving gateway to send downlink data. The serving gateway sends the downlink data to the mobility management network element.

[0061] Based on this solution, the serving gateway can determine, based on the response message, that the mobility management network element agrees to cache the data, and then send the downlink data to the mobility management network element.

[0062] In a possible implementation manner, the method further includes: the serving gateway receiving sixth indication information from the mobility management network element, where the sixth indication information is used to instruct the serving gateway to delete the downlink data.

[0063] Based on this solution, the serving gateway may terminate the transmission of downlink data based on the sixth indication information.

[0064] In one possible implementation, the method further includes: the serving gateway determining one or more access network devices with available communication connections to the serving gateway. The serving gateway determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that no access network device currently has coverage that includes the first terminal device. The satellite coverage information of the access network device includes a mapping relationship between the coverage of the access network device and time.

[0065] This solution provides a method for determining whether a communication connection between an access network device and a terminal device is available.

[0066] In one possible implementation, the service gateway determines that the mobile management network element serving the first terminal device is located on the satellite, including: the service gateway determines that the mobile management network element serving the first terminal device is located on the satellite based on a mapping relationship between the identification information of the satellite and the identification information of the mobile management network element.

[0067] This solution provides a method for determining whether a mobility management network element is located on a satellite.

[0068] In the sixth aspect, a communication method is provided, which can be executed by a service gateway, or by a component of the service gateway (such as a processor, chip, or chip system, etc.), or by a logic module or software that can realize all or part of the service gateway function. The following is an illustration of the method using the service gateway as the execution subject, and the method includes: the service gateway obtains downlink data that needs to be transmitted to the first terminal device, and determines that the mobile management network element serving the first terminal device is located on the satellite. Based on the satellite coverage availability information corresponding to the mobile management network element, the service gateway sends a first notification message to the mobile management network element when it determines that the communication connection between the service gateway and the mobile management network element is available. The first notification message is used to notify the arrival of downlink data. The satellite coverage availability information corresponding to the mobile management network element includes a mapping relationship between the coverage range corresponding to the mobile management network element and time.

[0069] Based on the communication method provided in the embodiment of the present application, the service gateway can determine whether the communication connection between the mobile management network element and the service gateway is available based on the satellite coverage availability information, thereby avoiding sending a first notification message to the mobile management network element when the communication connection is unavailable, causing unnecessary signaling overhead.

[0070] In one possible implementation, the method further includes: the serving gateway receiving a response message from the mobility management network element to the first notification message, the response message being used to instruct the serving gateway to send the downlink data. Alternatively, the response message includes sixth indication information, the sixth indication information being used to instruct the serving gateway to delete the downlink data.

[0071] Based on this solution, the serving gateway can send downlink data or terminate the transmission of downlink data based on the message fed back by the mobility management network element.

[0072] In one possible implementation, the service gateway determines that the mobile management network element serving the first terminal device is located on the satellite, including: the service gateway determines that the mobile management network element serving the first terminal device is located on the satellite based on a mapping relationship between the identification information of the satellite and the identification information of the mobile management network element.

[0073] This solution provides a method for determining whether a mobility management network element is located on a satellite.

[0074] In the seventh aspect, a communication method is provided, which can be executed by a mobile management network element located on a satellite, or by a component of the mobile management network element (such as a processor, a chip, or a chip system, etc.), or by a logic module or software that can implement all or part of the functions of the mobile management network element. Among them, the mobile management network element is located on a satellite. The following is an illustration of the method using the mobile management network element as the execution subject, and the method includes: the mobile management network element receives a first notification message from a service gateway, and the first notification message is used to indicate the reception of downlink data of the first terminal device. When the mobile management network element determines that the communication connection between the second access network device located on the satellite and the first terminal device is unavailable, and the downlink data can be cached in the mobile management network element, the mobile management network element sends a response message to the service gateway for the first notification message. The mobile management network element receives the downlink data from the service gateway, and caches the downlink data until a third paging message is sent to the second access network device, and the third paging message is used to request paging of the first terminal device.

[0075] Based on the communication method provided in the embodiment of the present application, when the mobile management network element determines that the communication connection between the access network device and the first terminal device is unavailable and the downlink data can be cached in the mobile management network element, it can first request the service gateway to send downlink data. After receiving the downlink data, the mobile management network element can cache the downlink data until the communication connection between the second access network device and the first terminal device is restored, and then request the second access network device to page the first terminal device. Thus, after the second access network device successfully pages the first terminal device, it can immediately obtain the cached downlink data from the mobile management network element. Therefore, based on the communication method provided in the embodiment of the present application, not only can data be transmitted from the core network to the terminal device in a scenario where the feeder link is discontinuous, but the time to complete a data transmission will not be very long.

[0076] In a possible implementation, the first notification message includes second request information, where the second request information is used to request the mobility management network element to receive and buffer the downlink data.

[0077] Based on this solution, the mobility management network element can determine the need to receive and buffer downlink data based on the instruction of the serving gateway.

[0078] In one possible implementation, the mobility management network element determines that downlink data can be cached in the mobility management network element, including: the mobility management network element determines that the mobility management network element supports a first function, the first function including a store and forward function. Alternatively, the mobility management network element determines that the downlink data supports transmission via a store and forward operation.

[0079] In this solution, the mobility management network element may consider multiple factors: whether the mobility management network element supports store and forward, and / or whether the data supports store and forward, to determine whether the downlink data can be cached in the mobility management network element.

[0080] In one possible implementation, the mobile management network element determines that downlink data supports transmission through storage and forwarding operations, including: the mobile management network element determines that downlink data supports transmission through storage and forwarding operations based on one or more of the following: subscription information of the first terminal device, latency requirements of the downlink data, or the context of the first terminal device.

[0081] This solution provides multiple pieces of information that can be used to determine whether downlink data supports transmission through the store and forward operation.

[0082] In one possible implementation, the method further includes: the mobility management network element determines whether the first terminal device is within the coverage range corresponding to the second access network device based on the satellite coverage availability information corresponding to the second access network device and the location information of the first terminal device; wherein the satellite coverage information of the second access network device includes a mapping relationship between the coverage range corresponding to the second access network device and time. If the first terminal device is within the coverage range, the mobility management network element determines that the communication connection between the second access network device and the first terminal device is available. Alternatively, if the first terminal device is not within the coverage range, the mobility management network element determines that the communication connection between the second access network device and the first terminal device is unavailable.

[0083] This solution provides a method for determining whether a communication connection between an access network device and a terminal device is available.

[0084] In a possible implementation, the method further includes: the mobile management network element determines one or more access network devices that are available for communication connection with the mobile management network element. The mobile management network element determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that there is no access network device whose current coverage includes the first terminal device among the one or more access network devices. The satellite coverage information of the access network device includes a mapping relationship between the coverage corresponding to the access network device and time. The mobile management network element determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that the access network device whose earliest coverage is expected to include the first terminal device among the one or more access network devices is the second access network device.

[0085] Based on this solution, the mobile management network element can determine the access network device that is expected to restore the communication connection with the first terminal device earliest as the second access network device, so as to minimize the time required for the mobile management network element to cache the downlink data after receiving the downlink data until paging the second access network device.

[0086] In one possible implementation, the location information of the first terminal device includes information about the tracking area where the first terminal device is located when entering the idle state, or information about the updated tracking area obtained according to the tracking area update process of the first terminal device.

[0087] This solution provides location information of multiple first terminal devices.

[0088] In one possible implementation, before the mobility management network element receives downlink data from the serving gateway, the method further includes: the mobility management network element sending a third request message to the serving gateway, where the third request message is used to request the serving gateway to establish a data transmission channel between the mobility management network element and the mobility management network element; and the mobility management network element receiving a response message from the serving gateway to the third request message.

[0089] Based on this solution, the mobility management network element can instruct the serving gateway to send downlink data through the third request message.

[0090] In a possible implementation, the method further includes: when the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends sixth indication information to the serving gateway, where the sixth indication information is used to instruct deletion of the downlink data.

[0091] Based on this solution, when the downlink data cannot be cached in the mobility management network element, the transmission of the downlink data can be terminated.

[0092] In an eighth aspect, a communication device is provided for implementing the various methods described above. The communication device includes modules, units, or means corresponding to the methods described above. The modules, units, or means may be implemented in hardware, software, or by hardware executing corresponding software implementations. The hardware or software includes one or more modules or units corresponding to the functions described above.

[0093] In some possible designs, the communication device may include a transceiver module and a processing module. The transceiver module, which may also be referred to as a transceiver unit, is configured to implement the sending and / or receiving functions of the method of any one of the first to seventh aspects and any possible implementation thereof. The transceiver module may be composed of a transceiver circuit, a transceiver, a transceiver, or a communication interface. The processing module may be configured to implement the processing functions of the method of any one of the first to seventh aspects and any possible implementation thereof.

[0094] In some possible designs, the transceiver module includes a sending module and a receiving module, which are respectively used to implement the sending and receiving functions of the method of any one of the first to seventh aspects above and any possible implementation methods thereof.

[0095] In the ninth aspect, a communication device is provided, comprising: a processor and a communication interface; the communication interface is used to communicate with a module outside the communication device; the processor is used to execute a computer program or instruction so that the communication device executes any of the methods described above.

[0096] In a tenth aspect, a communication device is provided, comprising: at least one processor; the processor is configured to execute a computer program or instruction stored in a memory, so that the communication device performs the method of any of the above aspects. In one possible implementation, the memory may be coupled to the processor, or may be independent of the processor. In another possible implementation, the communication device further includes the memory. Optionally, the memory and the processor are integrated.

[0097] In aspects 8 to 10, the communication device may be the mobility management network element in the first aspect, any implementation of the first aspect, the second aspect, any implementation of the second aspect, the seventh aspect, or any implementation of the seventh aspect, or a device including the mobility management network element, or a device included in the mobility management network element, such as a chip or a chip system. Alternatively, the communication device may be the first access network device in the third aspect, or any implementation of the third aspect, or a device including the first access network device, or a device included in the first access network device, such as a chip or a chip system. Alternatively, the communication device may be the first terminal device in the fourth aspect, or any implementation of the fourth aspect, or a device including the first terminal device, or a device included in the first terminal device, such as a chip or a chip system. Alternatively, the communication device may be the service gateway in the fifth aspect, any implementation of the fifth aspect, the sixth aspect, or any implementation of the sixth aspect, or a device including the service gateway, or a device included in the service gateway, such as a chip or a chip system.

[0098] In the eleventh aspect, a communication device is provided (for example, the communication device may be a chip or a chip system), which includes a processor for implementing the functions involved in any of the above aspects or any of its implementation methods.

[0099] In some possible designs, the communication device includes a memory for storing necessary program instructions and data.

[0100] In some possible designs, when the device is a chip system, it can be composed of a chip, or it can also include a chip and other discrete devices.

[0101] It can be understood that when the communication device provided in any one of the eighth to eleventh aspects is a chip, the above-mentioned sending action / function can be understood as output, and the above-mentioned receiving action / function can be understood as input.

[0102] In the twelfth aspect, a computer-readable storage medium is provided, which stores a computer program or instruction. When the computer program or instruction is run on a communication device, the communication device can execute any of the above aspects or any of its implementation methods.

[0103] In a thirteenth aspect, a computer program product comprising instructions is provided, which, when executed on a communication device, enables the communication device to execute the method of any of the above aspects or any of its implementation methods.

[0104] Among them, the technical effects brought about by any implementation method in the eighth to thirteenth aspects can refer to the technical effects brought about by the corresponding implementation methods in the first to seventh aspects, and will not be repeated here.

[0105] It should be noted that various possible implementations of any of the above aspects can be combined under the premise that there is no contradiction between the solutions.

[0106] In a fourteenth aspect, a communication system is provided, comprising a mobility management network element and a first access network device. The mobility management network element is configured to perform the method of the first aspect, any implementation of the first aspect, the second aspect, or any implementation of the second aspect. The first access network device is configured to perform the method of the third aspect, or any implementation of the third aspect.

[0107] In some possible designs, the communication system further includes a first terminal device, wherein the first terminal device is configured to execute the method of the fourth aspect or any implementation method of the fourth aspect.

[0108] In a fifteenth aspect, a communication system is provided, comprising a serving gateway and a mobility management network element. The serving gateway is configured to execute the method of the fifth aspect, any implementation of the fifth aspect, the sixth aspect, or any implementation of the sixth aspect. The mobility management network element is configured to execute the method of the seventh aspect, or any implementation of the seventh aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] FIG1 is a schematic diagram of a flow chart of data transmission based on a control plane;

[0110] FIG2 is a schematic diagram of the architecture of a communication system provided in an embodiment of the present application;

[0111] FIG3 is a schematic diagram of an application scenario provided by an embodiment of the present application;

[0112] FIG4 is a schematic diagram of a communication method provided in an embodiment of the present application;

[0113] FIG5 is a schematic diagram of another communication method provided in an embodiment of the present application;

[0114] FIG6 is a schematic diagram of a possible process provided by an embodiment of the present application;

[0115] FIG7 is a schematic diagram of another possible process provided by an embodiment of the present application;

[0116] FIG8 is a schematic diagram of another communication method provided in an embodiment of the present application;

[0117] FIG9 is a schematic diagram of another communication method provided in an embodiment of the present application;

[0118] FIG10 is a schematic diagram of another possible process provided by an embodiment of the present application;

[0119] FIG11 is a schematic diagram of another possible process provided by an embodiment of the present application;

[0120] FIG12 is a schematic diagram of the composition of a communication device provided in an embodiment of the present application;

[0121] FIG13 is a schematic diagram of the hardware structure of a communication device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0122] In order to facilitate understanding of the technical solutions of the embodiments of the present application, a brief introduction to the relevant technologies of the present application is first given as follows.

[0123] 1. Data transmission based on the control plane in CIoT on the ground:

[0124] Taking the fourth generation (4G) mobile communication system as an example, in the terrestrial CIoT, a downlink data transmission process based on the control plane is shown in Figure 1 and includes the following steps:

[0125] 0. User Equipment (UE) is attached to the evolved packet system (EPS) and is in the idle state.

[0126] 1. When the S-GW receives downlink data / signaling to be sent to the UE from the packet data network gateway (P-GW), the S-GW buffers the downlink data and identifies which mobile management entity (MME) is serving the UE.

[0127] 2. The S-GW sends a downlink data notification message to the MME, notifying it of the arrival of downlink data. Correspondingly, upon receiving the downlink data notification message, the MME sends a downlink data notification ack message (acknowledgement message, ACK) to the S-GW, notifying the S-GW that the downlink data notification message has been received.

[0128] 3. The MME sends a paging message to each evolved node B (eNodeB / eNB) in the tracking area (TA) where the UE is registered, requesting the eNodeB to page the UE over the air interface.

[0129] 4. After receiving the paging message from the MME, the eNodeB pages the UE.

[0130] 5. Since the UE is in the idle state, upon receiving the paging message, the UE establishes an RRC connection with the eNodeB. Specifically, the UE sends an RRC connection request to the eNodeB. After receiving the RRC connection request, the eNodeB sends an RRC connection establishment message to the UE. After receiving the RRC connection establishment message, the UE sends an RRC connection establishment complete message to the eNodeB. At this point, the RRC connection is considered complete. The RRC connection request message includes a non-access stratum (NAS) control plane service request.

[0131] 6. Optionally, if CIoT is narrowband internet of things (NB-IoT), the eNodeB can retrieve the EPS negotiated quality of service (QoS) profile from the MME based on the configuration.

[0132] 7. The eNodeB sends the UE's NAS control plane service request to the MME via an S1 access protocol (AP) initial message. Based on the NAS control plane service request, the MME determines that the UE paging is successful and can send downlink data to the UE.

[0133] 8. If the S11-U channel is not established between the MME and the S-GW at this time, the MME sends a modify bearer request message to the S-GW to request the establishment of the S11-U channel.

[0134] 9. If the MME sends a modify bearer request message to the S-GW in step 8, the S-GW sends a modify bearer response to the MME as a response to the request message.

[0135] 10. The S-GW sends the cached downlink data to the MME.

[0136] 11-12. The MME performs data encryption and integrity protection on the downlink data and sends the downlink data to the eNodeB that successfully pages the UE via the NAS PDU carried in the downlink S1-AP message. In the case of CIoT EPS optimization for the control plane, the NAS control plane service request sent by the eNodeB to the MME in step 7 does not trigger the MME to establish a data radio bearer. The MME can immediately send the received downlink data to the eNodeB via a NAS protocol data unit (PDU).

[0137] 13. The eNodeB sends the NAS PDU containing the downlink data to the UE via an RRC downlink message.

[0138] It can be understood that Figure 1 is a schematic diagram of the process when it is applied to the 4G system. If the process shown in Figure 1 is applied to the fifth generation (5G) mobile communication system or other communication systems, the names of the devices in the above text can also be replaced with the names in the 5G system or other communication systems.

[0139] In some scenarios, such as when there is no terrestrial mobile communication network or the signal of the terrestrial mobile communication network is poor, CIoT data can be transmitted through NTN. In this case, consider applying the data transmission process shown in Figure 1 to the NTN scenario. Since in the NTN scenario, the satellite is connected to the ground station on the network side through a feeder link, and is connected to the terminal equipment on the ground through a service link, for the case where the eNodeB is located on the satellite, the core network elements such as MME and S-GW are located on the ground, and the UE is also located on the ground, the above process can be divided into four stages based on whether the signaling / data involving the eNodeB is transmitted through the feeder link or the service link. The four stages of the above process are specifically shown in Figure 1. For example, since step 3 is the interaction between the eNodeB and the MME based on the feeder link, the stage before step 3 can be divided into the feeder link stage, and steps 4 to 5 are the interaction between the UE and the eNodeB based on the service link, which can be divided into the service link stage.

[0140] However, in NTN scenarios, there are discontinuous feeder links. If the process shown in Figure 1 is applied in NTN scenarios, the following defects may occur:

[0141] If a satellite base station needs to interact with ground-based devices via a feeder link or service link at a certain stage, and the required link is unavailable at that time, the base station cannot complete the corresponding interaction. If the base station abandons the interaction attempt, the process cannot continue, and data cannot be sent from the core network to the terminal device. If the base station decides to wait until the corresponding link is restored to continue the process, since the process is divided into four stages, after the base station waits for the link to be restored to complete the process in that stage, the link required for the next stage may be unavailable at this time, and the base station must continue to wait until the link is restored. In this case, the time required to complete the data transmission from the core network to the terminal device will be very long, and the data transmission efficiency will be very low.

[0142] Therefore, in scenarios where the feeder link is discontinuous, how to send data from the core network to the terminal device is an urgent problem to be solved. Based on this problem, the present application provides a communication method, device, and system that can send data from the core network to the terminal device in scenarios where the feeder link is discontinuous, and can improve the efficiency of data transmission compared to the process shown in Figure 1.

[0143] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Among them, in the description of the present application, unless otherwise specified, " / " indicates that the objects associated before and after are in an "or" relationship. For example, A / B can represent A or B; "and / or" in the present application is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. In addition, in the description of the present application, unless otherwise specified, "multiple" refers to two or more than two. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, c can be single or multiple. In addition, in order to facilitate the clear description of the technical solutions of the embodiments of the present application, in the embodiments of the present application, words such as "first" and "second" are used to distinguish between identical or similar items with substantially the same functions and effects. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit differences. At the same time, in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or design schemes. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a concrete way for easy understanding.

[0144] In the embodiment of the present application, "indication" may include direct indication and indirect indication, and may also include explicit indication and implicit indication. The information indicated by a certain information (such as the first indication information or the second indication information below) is called information to be indicated. In the specific implementation process, there are many ways to indicate the information to be indicated, such as but not limited to, the information to be indicated can be directly indicated, such as the information to be indicated itself or the index of the information to be indicated. The information to be indicated can also be indirectly indicated by indicating other information, wherein the other information and the information to be indicated have an association relationship. It is also possible to indicate only a part of the information to be indicated, while the other parts of the information to be indicated are known or agreed in advance. For example, the indication of specific information can be achieved by means of the arrangement order of each piece of information agreed in advance (such as specified in the protocol), thereby reducing the indication overhead to a certain extent. At the same time, the common parts of each piece of information can also be identified and indicated uniformly to reduce the indication overhead caused by indicating the same information separately.

[0145] In addition, the specific indication method can also be various existing indication methods, such as but not limited to the above-mentioned indication methods and various combinations thereof. The specific details of the various indication methods can be referred to the prior art and will not be repeated herein. As can be seen from the above, for example, when it is necessary to indicate multiple information of the same type, there may be a situation where the indication methods for different information are different. In the specific implementation process, the required indication method can be selected according to specific needs. The embodiment of the present application does not limit the selected indication method. In this way, the indication method involved in the embodiment of the present application should be understood to cover various methods that can enable the party to be indicated to obtain the information to be indicated.

[0146] It should be understood that the information to be indicated can be sent as a whole or divided into multiple sub-information and sent separately, and the sending period and / or sending time of these sub-information can be the same or different. The specific sending method is not limited in the embodiments of this application. The sending period and / or sending time of these sub-information can be predefined, for example, predefined according to a protocol, or can be configured by the transmitting device by sending configuration information to the receiving device.

[0147] In an embodiment of the present application, "pre-definition", "pre-defined", "pre-configured" or "pre-configured" can be implemented by pre-saving corresponding codes, tables or other methods that can be used to indicate relevant information in the device. For example, it can be burned into the device when the device leaves the factory. The embodiment of the present application does not limit its specific implementation method. Among them, "saving" can mean saving in one or more memories. The one or more memories can be set separately or integrated in an encoder or decoder, a processor, or a communication device. The one or more memories can also be partially set separately and partially integrated in a decoder, a processor, or a communication device. The type of memory can be any form of storage medium, which is not limited by the embodiment of the present application.

[0148] The "protocol" involved in the embodiments of the present application may refer to a protocol family in the communication field, a standard protocol with a similar protocol family frame structure, or a related protocol used in future communication systems. The embodiments of the present application do not make specific limitations on this.

[0149] In the embodiments of the present application, descriptions such as "when...", "in the case of...", "if" and "if" all mean that the device will perform corresponding processing under certain objective circumstances. It does not limit the time, nor does it require the device to perform judgment actions when implemented, nor does it mean that there are other limitations.

[0150] In the embodiment of the present application, "sending information to... (taking a terminal device as an example)" can be understood as the destination end of the information being the terminal device. This can include sending information directly or indirectly to an anchor network element. "Receiving information from... (taking a mobile management network element as an example)" can be understood as the source end of the information being a mobile management network element, which can include receiving information directly or indirectly from a mobile management network element. The information may be processed as necessary between the source and destination ends of the information transmission, such as format changes, but the destination end can understand the valid information from the source end. Similar expressions in this application can be understood similarly and will not be repeated here.

[0151] The technical solution provided in this application can be used in various communication systems, which may be a third generation partnership project (3GPP) communication system, for example, a 4G mobile communication system, a long term evolution (LTE) system, a 5G mobile communication system and its evolution system, an NTN system, a multiple-input multiple-output (MIMO) system, a vehicle to everything (V2X) system, a system of hybrid networking of LTE and new radio (NR), or a device-to-device (D2D) system, a machine to machine (M2M) communication system, IoT (such as CIoT), and other communication systems, such as future communication systems. In addition, the term "system" and "network" can be used interchangeably.

[0152] It should be noted that the network architecture and business scenarios described in the embodiments of the present application are intended to more clearly illustrate the technical solutions of the embodiments of the present application, and do not constitute a limitation on the technical solutions provided in the embodiments of the present application. Ordinary technicians in this field can know that with the evolution of network architecture and the emergence of new business scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0153] FIG2 is a schematic diagram of a possible, non-limiting communication system applicable to embodiments of the present application. As shown in FIG2 , the communication system 10 includes a radio access network (RAN) 100. The RAN 100 includes at least one access network device 110 and at least one terminal device (e.g., 120a-120c in FIG2 , collectively referred to as 120). The RAN 100 may also include other devices, such as wireless relay devices and / or wireless backhaul devices (not shown in FIG2 ). The terminal device 120 is wirelessly connected to the access network device 110.

[0154] As shown in FIG2 , the communication system 10 also includes a core network (CN 200 in FIG2 ). Access network equipment 110 can be wirelessly connected to CN 200. The core network equipment in CN 200 and the access network equipment 110 in RAN 100 can be different physical devices, or they can be the same physical device that integrates core network logical functions and radio access network logical functions.

[0155] If the communication system 10 is applied in an NTN scenario, 3a and 3b in FIG3 are schematic diagrams of possible, non-limiting application scenarios provided by embodiments of the present application. In the application scenario shown in 3a, access network equipment is deployed on a satellite, and no inter-satellite links (i.e., communication links between satellites) exist between satellites. In the application scenario shown in 3b, access network equipment is deployed on a satellite, and inter-satellite links exist between satellites. In the application scenarios shown in 3a and 3b, the access network equipment on the satellite can communicate with a gateway on the ground via a feeder link, thereby further communicating with the core network on the ground. The access network equipment on the satellite can also communicate with terminal equipment on the ground via a service link.

[0156] Among them, if the embodiment of the present application is applied in an IoT system, the terminal devices in 3a and 3b in Figure 3 can also be called IoT devices.

[0157] Optionally, if the communication system 10 is used in an NTN scenario, while the access network equipment is located on a satellite, some core network elements may also be located on the satellite. The satellite on which some core network elements are located and the satellite on which the access network equipment is located may be the same satellite or different satellites. If some core network elements and the access network equipment are located on different satellites, some core network elements may communicate with the access network equipment via inter-satellite links.

[0158] For example, if the embodiment of the present application is applied to a 4G mobile communication system, the MME may be located on a satellite. If the embodiment of the present application is applied to a 5G mobile communication system, the access and mobility management function (AMF) may be located on a satellite.

[0159] The access network device in the embodiment of the present application refers to a RAN node (or device) that connects a terminal device to a wireless network. In some network architectures, the access network device may be a base station. Currently, examples of some access network devices include: the next generation Node B (gNB), a transmission reception point (TRP), an eNodeB, a radio network controller (RNC), a Node B (NB), a base station controller (BSC), a base transceiver station (BTS), a home evolved NodeB (HNB), a base band unit (BBU), or a wireless fidelity (Wifi) access point (AP).

[0160] In addition, in a network structure, multiple access network devices collaborate to assist terminal devices in achieving wireless access, and different access network devices respectively implement part of the functions of the base station. For example, the access network device can be a centralized unit (CU), a distributed unit (DU), a CU-control plane (CP), a CU-user plane (UP), or a radio unit (RU). The CU and DU can be set separately, or they can be included in the same network element, such as a baseband unit (BBU). The RU can be included in a radio frequency device or radio frequency unit, such as a remote radio unit (RRU), an active antenna unit (AAU), or a remote radio head (RRH).

[0161] In different systems, CU (or CU-CP and CU-UP), DU or RU may also have different names, but those skilled in the art can understand their meanings. For example, in an open access network (open RAN, O-RAN or ORAN), CU may also be called O-CU (open CU), DU may also be called O-DU, CU-CP may also be called O-CU-CP, CU-UP may also be called O-CU-UP, and RU may also be called O-RU. For the convenience of description, this application uses CU, CU-CP, CU-UP, DU and RU as examples for description. Any unit of CU (or CU-CP, CU-UP), DU and RU in this application can be implemented by a software module, a hardware module, or a combination of a software module and a hardware module.

[0162] All or part of the functions of the access network device in this application may also be implemented through software functions running on hardware, or through virtualization functions instantiated on a platform (such as a cloud platform). The access network device in this application may also be a logical node, logical module, or software that can implement all or part of the functions of the access network device.

[0163] The terminal device in the embodiments of the present application may also be referred to as a terminal, UE, mobile station (MS), mobile terminal, etc., and is a device with wireless transceiver capabilities. The terminal device can be widely used in various scenarios, such as vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality (VR), augmented reality (AR), industrial control, self-driving, remote medical surgery, smart grid, smart home, smart office, smart bracelet, smart city, etc. Currently, some examples of terminal devices include: mobile phones, tablets, computers with wireless transceiver capabilities, wearable devices, vehicles, drones, helicopters, airplanes, ships, robots, robotic arms, smart home devices, etc. The embodiments of the present application do not limit the device form of the terminal device.

[0164] In the embodiments of this application, core network elements / core network devices refer to devices in the core network that provide service support for terminal devices. Currently, some examples of core network elements include MME elements and AMF elements, which are not listed here. Among them, MME elements can be responsible for access and mobility management of terminal devices in 4G systems. AMF elements can be responsible for access and mobility management of terminal devices in 5G systems.

[0165] In the embodiment of the present application, a network element may also be referred to as an entity or a functional entity. For example, an MME network element may also be referred to as an MME entity or an MME functional entity.

[0166] The communication method provided in the embodiment of the present application will be described in detail below with reference to Figures 2 to 3.

[0167] It should be noted that the message names between network elements or the names of parameters in the messages in the following embodiments of the present application are only examples, and other names may be used in specific implementations. The embodiments of the present application do not specifically limit this.

[0168] It should be noted that, in the embodiments of the present application, “cache” and “store” are the same concept and can be used interchangeably.

[0169] It is understood that in the embodiments of the present application, each network element may perform some or all of the steps in the embodiments of the present application. These steps or operations are merely examples, and the embodiments of the present application may also perform other operations or variations of various operations. In addition, the steps may be performed in a different order than those presented in the embodiments of the present application, and it is possible that not all operations in the embodiments of the present application need to be performed.

[0170] As shown in Figure 4, a communication method is provided for an embodiment of the present application. Figure 4 illustrates the method by taking the mobile management network element and the first access network device as the execution subjects of the interaction diagram as an example, but the present application does not limit the execution subjects of the interaction diagram. For example, the mobile management network element in Figure 4 can also be a module such as a chip, a chip system, or a processor applied to the mobile management network element, and can also be a logical node, a logical module, or software that can realize all or part of the functions of the mobile management network element; the first access network device in Figure 4 can also be a module such as a chip, a chip system, or a processor applied to the first access network device, and can also be a logical node, a logical module, or software that can realize all or part of the functions of the first access network device.

[0171] The mobility management network element in the embodiments of the present application can perform mobility management on the terminal device. It can have different names in different communication systems, and the embodiments of the present application are not limited to this. For example, in a 4G communication system, the mobility management network element can be an MME network element. In a 5G communication system, the mobility management network element can be an AMF network element. In other communication systems, the mobility management network element can also have other names, which does not affect the application of the communication method of the embodiments of the present application.

[0172] As shown in FIG4 , the communication method includes steps S401 to S404:

[0173] S401. A mobility management network element receives a first notification message, where the first notification message is used to indicate receiving downlink data of a first terminal device.

[0174] S402: When the mobility management network element determines that the communication connection between the first access network device located on the satellite and the first terminal device is unavailable and that downlink data can be cached in the first access network device, the mobility management network element sends first indication information to the first access network device, where the first indication information is used to instruct the first access network device to cache the downlink data. In response, the first access network device receives the first indication information from the mobility management network element.

[0175] S403: Before the first access network device pages the first terminal device, the first access network device sends a first request message to the mobility management network element, where the first request message is used to request the mobility management network element to establish a data transmission channel with the first access network device. Accordingly, the mobility management network element receives the first request message.

[0176] S404: The mobility management network element sends the downlink data of the first terminal device to the first access network device. Correspondingly, the first access network device receives and buffers the downlink data of the first terminal device.

[0177] The communication method shown in Figure 4 can be applied to the NTN scenario. In which, the access network device (such as the first access network device) is located on the satellite, and the mobility management network element and the first terminal device are located on the ground. The mobility management network element and the first access network device can execute the communication method shown in Figure 4. When the communication connection between the first access network device and the first terminal device is unavailable and the downlink data can be cached in the first access network device, the first access network device can obtain the data from the mobility management network element in advance and cache the data based on the instruction of the mobility management network element. Thus, after the communication connection between the first access network device and the first terminal device is restored, the first access network device can immediately send the cached data to the first terminal device after paging the first terminal device. Therefore, compared to applying the existing process to the NTN scenario, in the embodiment of the present application, the first access network device does not need to wait for the communication connection between the first access network device and the mobility management network element to be restored after paging the first terminal device, and then request data from the mobility management network element, thereby saving the time for data to be transmitted from the core network to the terminal device.

[0178] The following is an introduction to S401-S404 respectively.

[0179] In S401, the mobility management network element may receive a first notification message from another core network element. The mobility management network element may determine, based on the first notification message, that it needs to receive downlink data from the first terminal device and transmit the downlink data to the first terminal device.

[0180] Exemplarily, the first notification message may be a downlink data notification. In this case, the first notification message may notify the mobility management network element that downlink data of the first terminal device has arrived at the core network and needs to be transmitted to the first terminal device.

[0181] The embodiment of the present application does not limit the core network element that sends the first notification message to the mobility management network element. For example, the serving gateway may send the first notification message to the mobility management network element.

[0182] The core network element that sends the first notification message to the mobility management network element may obtain downlink data of the first terminal device and cache the downlink data before S401. The core network element may determine the mobility management network element serving the first terminal device and send the first notification message to the mobility management network element.

[0183] In S401, the first terminal device is in an idle state and is attached to the core network. For example, if the embodiment of the present application is applied to a 4G communication system, the first terminal device is attached to the EPS. After receiving the first notification message, the mobility management network element can determine that the first terminal device is in an idle state based on the information of the first terminal device carried therein, and further determine that the first terminal device needs to be paged.

[0184] In S402, after receiving the first notification message, the mobility management network element may determine whether there is an access network device that has both an available communication connection with the mobility management network element and an available communication connection with the first terminal device. If not, the mobility management network element may determine an access network device that has an available communication connection with the mobility management network element and an unavailable communication connection with the first terminal device. This access network device may be referred to as the first access network device.

[0185] In addition, if there is currently an access network device that has an available communication connection with the mobility management network element and an available communication connection with the first terminal device, the mobility management network element may not determine the first access network device. Optionally, in this case, the mobility management network element may page the terminal device through an access network device that has an available communication connection with the mobility management network element and an available communication connection with the first terminal device. In this case, the specific process of data from the core network to the first terminal device can refer to the above description of the process shown in Figure 1.

[0186] The embodiments of the present application do not limit the specific implementation method of the mobility management network element determining whether the connection between the access network device and the terminal device is available. The following uses the example of determining whether the connection between the first access network device and the first terminal device is available to introduce a possible implementation method provided by the embodiments of the present application.

[0187] The mobility management network element determines whether the first terminal device is within the coverage range corresponding to the first access network device (which may be the coverage range of the satellite where the first access network device is located, or the coverage range of the first access network device, hereinafter referred to as the coverage range) based on the satellite coverage availability information corresponding to the first access network device and the location information of the first terminal device. When the first terminal device is within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is available. When the first terminal device is not within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is unavailable.

[0188] The location information of the first terminal device may include information indicating the area where the first terminal device is located. For example, the location information of the first terminal device may include identification information of the tracking area (TA) where the first terminal device is located. For another example, the location information may include a tracking area list (TA list) where the tracking area where the first terminal device is located is located. Alternatively, the location information of the first terminal device may also be information such as the latitude and longitude information of the first terminal device.

[0189] The embodiments of the present application do not limit the specific manner in which the mobile management network element obtains the location information of the first terminal device. For example, the mobile management network element may obtain information about the tracking area in which the first terminal device is located when the first terminal device enters an idle state. For another example, the mobile management network element may obtain information about the updated tracking area based on the tracking area update (TAU) process of the first terminal device. The mobile management network element may use the obtained at least one item of tracking area information as the location information of the first terminal device.

[0190] The satellite coverage availability information corresponding to the first access network device may include a mapping relationship between the coverage range of the satellite where the first access network device is located and time. For example, the satellite coverage availability information corresponding to the first access network device may include the following mapping relationship: at 12:00, the coverage range of the satellite where the first access network device is located is area 1; at 13:00, the coverage range of the satellite where the first access network device is located is area 2, and so on.

[0191] Optionally, if the first access network device and one or more other access network devices are located on the same satellite, the satellite coverage availability information corresponding to the first access network device may include a mapping relationship between the coverage range of each access network device on the satellite and time. Alternatively, it may also include a mapping relationship between the coverage range of the first access network device and time.

[0192] The embodiments of the present application do not limit the specific manner in which the mobility management network element obtains the satellite coverage availability information corresponding to the first access network device. For example, the mobility management network element may pre-configure the satellite coverage availability information corresponding to the first access network device. In another example, the mobility management network element may calculate the satellite coverage availability information corresponding to the first access network device based on the ephemeris information of the first access network device.

[0193] In one possible scenario, for determining the first access network device, if there are currently multiple access network devices whose communication connections with the mobility management network element are available and whose communication connections with the first terminal device are unavailable, the mobility management network element can select one access network device from among them as the first access network device. The embodiment of the present application does not limit the specific manner in which the mobility management network element selects the first access network device. For example, the mobility management network element can randomly select one access network device from among them as the first access network device. The following describes a possible implementation method provided by an embodiment of the present application.

[0194] The mobility management network element determines one or more access network devices that are available for communication with the mobility management network element. If the mobility management network element determines, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that there is no access network device whose current coverage includes the first terminal device among the one or more access network devices, the mobility management network element selects, from the one or more access network devices, an access network device whose coverage is expected to include the first terminal device the earliest, as the first access network device, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices.

[0195] Among them, the satellite coverage available information corresponding to the access network device can be specifically referred to the above introduction to the satellite coverage available information corresponding to the first access network device, which will not be elaborated here.

[0196] The embodiments of the present application do not limit how to determine the one or more access network devices determined by the mobility management network element to be capable of a communication connection with the mobility management network element. For example, the mobility management network element may determine, based on the acquired satellite coverage availability information corresponding to the access network device, whether the coverage range of the access network device includes the mobility management network element, thereby determining whether a communication connection between the access network device and the mobility management network element is available.

[0197] The above describes how the mobile management network element determines the first access network device. In S402, when the mobile management network element determines the first access network device, the mobile management network element can further determine whether the downlink data of the first terminal device can be cached in the first access network device. If the mobile management network element determines that the downlink data of the first terminal device can be cached in the first access network device, the mobile management network element can send a first indication message to the first access network device to instruct the first access network device to cache the downlink data of the first terminal device.

[0198] Exemplarily, the first indication information may be carried in a first paging message sent by the mobility management network element to the first access network device. In other words, the first indication information is transmitted via the first paging message, wherein the first paging message may be used to request paging of the first terminal device.

[0199] Regarding determining whether downlink data of the first terminal device can be cached in the first access network device, in one possible implementation, the mobility management network element may determine at least one of the following:

[0200] Whether the first access network device supports a first function, where the first function includes a store and forward function. Alternatively, whether the downlink data of the first terminal device supports transmission via a store and forward operation. If at least one of the above is determined to be supported, the mobility management network element may determine that the downlink data of the first terminal device can be cached in the first access network device.

[0201] Among them, store and forward (S&F) can be understood as, in the scenario where the feeder link of the NTN network is discontinuous, the data is first cached in the access network equipment located on the satellite, and then forwarded between the terminal device and the core network through the access network equipment.

[0202] In one possible implementation, the mobility management network element may determine whether the downlink data of the first terminal device supports transmission via a store-and-forward operation based on one or more of the following: subscription information of the first terminal device, latency requirements of the downlink data, or the context of the first terminal device. Optionally, the mobility management network element may also determine whether the downlink data of the first terminal device supports transmission via a store-and-forward operation based on other information, which is not specifically limited in this embodiment of the present application.

[0203] For example, the subscription information of the first terminal device or information in the context of the first terminal device may indicate whether the downlink data of the first terminal device supports transmission through a store-and-forward operation. For another example, if the latency requirement for the downlink data of the first terminal device is high, the mobility management network element may deem that the downlink data does not support transmission through a store-and-forward operation. If the latency requirement for the downlink data of the first terminal device is low, the mobility management network element may deem that the downlink data supports transmission through a store-and-forward operation.

[0204] In one possible implementation, the mobility management network element may determine whether the downlink data of the first terminal device supports transmission through a store-and-forward operation based on whether the service (which may be referred to as the first service) corresponding to the downlink data of the first terminal device supports transmission through a store-and-forward operation. If the first service supports it, the downlink data of the first terminal device also supports it. If the first service does not support it, the downlink data of the first terminal device also does not support it.

[0205] In this implementation, the mobility management network element may determine whether the first service supports transmission via a store-and-forward operation based on one or more of the following: subscription information of the first terminal device, latency requirements of the first service, or context of the first terminal device. Optionally, the mobility management network element may also determine whether the first service supports transmission via a store-and-forward operation based on other information, which is not specifically limited in this embodiment of the present application.

[0206] For example, the subscription information or context of the first terminal device may include information indicating whether the first service supports transmission via a store-and-forward operation. For another example, if the first service has a high latency requirement, the mobility management network element may determine that the first service does not support transmission via a store-and-forward operation. If the first service has a low latency requirement, the mobility management network element may determine that the first service supports transmission via a store-and-forward operation.

[0207] In addition, if the mobility management network element determines that the downlink data of the first terminal device cannot be cached in the first access network device, the mobility management network element does not need to send the first indication information to the first access network device. Optionally, in this case, the mobility management network element can send a second indication information to the core network network element that sends the first notification message, such as a service gateway. The second indication information is used to instruct the deletion (or discarding) of the downlink data of the first terminal device. After receiving the second indication information, the core network network element can delete the downlink data of the first terminal device based on the instruction of the second indication information.

[0208] In one possible case, the second indication information may be carried in a response message to the first notification message.

[0209] Optionally, if the mobility management network element sends the second indication information, the mobility management network element may also send a first information element. The first information element may indicate a reason for deleting the downlink data of the first terminal device. In this case, the reason for deleting the downlink data of the first terminal device indicated by the first information element may be: the communication connection between the first access network device and the first terminal device is unavailable, and the downlink data of the first terminal device cannot be cached in the first access network device.

[0210] In one possible case, the second indication information and the first information element may be carried in the same message.

[0211] In S403, after receiving the first indication information, the first access network device can determine, based on the first indication information, that it needs to first receive and cache the downlink data of the first terminal device. At this time, the first access network device can first send a first request message to the mobility management network element (indicating that the first terminal device is not paged yet, but the first request message is sent first) to request the establishment of a data transmission channel between the first access network device and the mobility management network element (which can also be understood as requesting the mobility management network element to send data). Correspondingly, the mobility management network element receives the first request message.

[0212] Exemplarily, the first request message may be an S1-AP message.

[0213] Optionally, the first request message may include an indication that the first access network device has not yet paged the first terminal device. Alternatively, the first request message may not include a service request message, where the service request message is used to indicate that the first terminal device is requesting to establish a connection with the core network. For example, the service request message may be the control plane service request in the process shown in Figure 1.

[0214] Optionally, before the first access network device sends the first request message to the mobility management network element, the first access network device may retrieve the context of the first terminal device from the mobility management network element.

[0215] In S404, the mobility management network element may obtain the downlink data of the first terminal device, and then send the downlink data of the first terminal device to the first access network device.

[0216] Optionally, the mobility management network element may obtain the downlink data of the first terminal device from the core network element that sends the first notification message, for example, may obtain the downlink data of the first terminal device from the serving gateway.

[0217] In a possible implementation of obtaining the downlink data of the first terminal device from the service gateway, the mobile management network element can send a third request message to the service gateway, and the third request message is used to request the service gateway to establish a data transmission channel with the mobile management network element. After receiving the third request message, the service gateway sends a response message to the mobile management network element for the third request message, and sends the downlink data of the first terminal device to the mobile management network element. In one possible case, the third request message can also be understood as a request to modify the bearer between the service gateway and the mobile management network element. In this case, the process of the mobile management network element obtaining data from the service gateway can be specifically referred to steps 8-10 in the process shown in Figure 1.

[0218] Optionally, after the mobility management network element obtains the downlink data of the first terminal device, it can encrypt and integrity protect the downlink data of the first terminal device.

[0219] Furthermore, after receiving the downlink data from the first terminal device, the first access network device may cache the downlink data locally and wait for the communication connection between the first access network device and the first terminal device to be restored.

[0220] As shown in Figure 5, another communication method is provided for an embodiment of the present application. Figure 5 takes the mobile management network element and the first access network device as an example of the execution subject of the interaction diagram to illustrate the method, but the present application does not limit the execution subject of the interaction diagram. For example, the mobile management network element in Figure 5 can also be a module such as a chip, a chip system, or a processor applied to the mobile management network element, and can also be a logical node, a logical module or software that can realize all or part of the functions of the mobile management network element; the first access network device in Figure 5 can also be a module such as a chip, a chip system, or a processor applied to the first access network device, and can also be a logical node, a logical module or software that can realize all or part of the functions of the first access network device.

[0221] As shown in FIG5 , the communication method includes steps S501 to S504:

[0222] S501. A mobility management network element receives a first notification message, where the first notification message is used to indicate receiving downlink data of a first terminal device.

[0223] S502: A mobility management network element sends a first paging message to one or more access network devices located on a satellite. The first paging message is used to request paging of a first terminal device. In response, the one or more access network devices receive the first paging message. The one or more access network devices include the first access network device.

[0224] S503: If the communication connection between the first access network device and the first terminal device is unavailable, the first access network device sends a first request message to the mobility management network element. In response, the mobility management network element receives the first request message from the first access network device. The first request message is used to request the mobility management network element to establish a data transmission channel with the first access network device.

[0225] S504: When the mobility management network element determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable and that the downlink data can be cached on the first access network device, the mobility management network element sends the downlink data to the first access network device. Accordingly, the first access network device receives and caches the downlink data of the first terminal device.

[0226] The communication method shown in Figure 5 can be applied to the NTN scenario. In which, the access network device (such as the first access network device) is located on the satellite, and the mobile management network element and the first terminal device are located on the ground. The mobile management network element and the first access network device can execute the communication method shown in Figure 5. After the first access network device receives the first request message from the mobile management network element, if the communication connection between the first access network device and the first terminal device is unavailable, the first access network device can request data from the mobile management network element before paging the first terminal device. The mobile management network element can then, based on the request of the first access network device, send the data to the first access network device when it is determined that the downlink data can be cached in the first terminal device, so that the first access network device can cache the data. Thus, after the communication connection between the first access network device and the first terminal device is restored, the first access network device can immediately send the cached data to the first terminal device after paging the first terminal device. Therefore, compared to applying the existing process to the NTN scenario, in the embodiment of the present application, the first access network device does not need to wait for the communication connection with the mobile management network element to be restored after paging the first terminal device, and then request data from the mobile management network element, thereby saving the time for data to be transmitted from the core network to the terminal device.

[0227] The following is an introduction to S501-S504 respectively.

[0228] For details of S501, please refer to the above introduction to S401, which will not be elaborated here.

[0229] In S502, the embodiment of the present application does not limit how the one or more access network devices that receive the first paging message are specifically determined. For example, the mobility management network element may send the first paging message to access network devices whose satellite coverage overlaps with the tracking area registered by the terminal device, based on the tracking area registered by the terminal device. For another example, the mobility management network element may send the first paging message to any access network device that has an available communication connection with the mobility management network element.

[0230] In the following, one of the one or more access network devices that receive the first paging message is referred to as a first access network device to introduce the following embodiments.

[0231] In S503, the first access network device may determine whether the communication connection between the first access network device and the first terminal device is available. If not, the first access network device may first send a first request message to the mobility management network element (indicating that the first terminal device is not paged yet, but the first request message is sent first) to request establishment of a data transmission channel between the first access network device and the mobility management network element (which can also be understood as requesting the mobility management network element to send data).

[0232] Exemplarily, the first request message may be an S1-AP message.

[0233] Additionally, if the first access network device determines that the communication connection between the first access network device and the first terminal device is available, the first access network device may first page the first terminal device. If the paging of the first terminal device is successful, the first access network device may establish an RRC connection with the first terminal device and then request the first terminal device's data from the mobility management network element. In this case, the specific flow of data from the core network to the first terminal device can be found in steps 4-13 of the process shown in Figure 1.

[0234] The embodiment of the present application does not limit the specific implementation method of the first access network device determining whether the communication connection between the first access network device and the first terminal device is available. For example, the first paging message received by the first access network device may carry the location information of the first terminal device. The first access network device may determine whether the first access network device is within the coverage of the first access network device based on the location information of the first terminal device and the coverage of the first access network device. If it is within the coverage, it can be determined that the communication connection between the first access network device and the first terminal device is available. If it is not within the coverage, it can be determined that the communication connection between the first access network device and the first terminal device is unavailable. Among them, the location information of the first terminal device can be specifically referred to the above introduction to the location information of the first terminal device in S402, which will not be expanded here.

[0235] Optionally, before the first access network device sends the first request message to the mobility management network element, the first access network device may retrieve the context of the first terminal device from the mobility management network element.

[0236] In S504, the mobility management network element may determine, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable.

[0237] In one possible implementation, the first request message may include third indication information. The third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable. The mobility management network element may determine, based on the third indication information, that the communication connection between the first access network device and the first terminal device is unavailable.

[0238] In another possible implementation, the first request message may not include a service request message, where the service request message is used to indicate that the first terminal device is requesting to establish a connection with the core network. For example, the service request message may be the control plane service request in the process shown in Figure 1. If the mobility management network element determines that the first request message does not include a service request message, it may determine that the communication connection between the first access network device and the first terminal device is unavailable.

[0239] Furthermore, if the mobility management network element determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable, the mobility management network element may further determine whether the downlink data of the first terminal device can be cached in the first access network device. If the downlink data can be cached in the first access network device, the mobility management network element may obtain the downlink data of the first terminal device and then send the downlink data of the first terminal device to the first access network device.

[0240] Among them, the embodiment of the present application does not limit how the mobile management network element determines whether the downlink data of the first terminal device can be cached in the first access network device. For details, please refer to the above introduction to S402, which will not be elaborated here.

[0241] How the mobility management network element obtains the downlink data of the first terminal device can be referred to the above introduction to S404 and will not be elaborated here.

[0242] In addition, if the mobility management network element determines that the downlink data of the first terminal device cannot be cached in the first access network device, the mobility management network element may not send the downlink data of the first terminal device to the first access network device. Optionally, in this case, the mobility management network element may send fourth indication information to the first access network device, where the fourth indication information indicates that establishment of a data transmission channel is refused. The first access network device may determine, based on the fourth indication information, that the mobility management network element refuses to send the downlink data of the first terminal device.

[0243] In one possible case, the fourth indication information may be carried in a response message to the first request message. Exemplarily, the response message to the first request message may be an S1-AP message.

[0244] Optionally, if the mobility management network element sends the fourth indication information to the first access network device, the mobility management network element may also send a second information element to the first access network device. The second information element may indicate a reason for refusing to establish the data transmission channel. In this case, the reason for refusing to establish the data transmission channel indicated by the second information element may be: the downlink data of the first terminal device cannot be cached in the first access network device.

[0245] In one possible case, the fourth indication information and the second information element may be carried in the same message.

[0246] Optionally, if the mobile management network element determines that the downlink data of the first terminal device cannot be cached in the first access network device, the mobile management network element may send a second indication message to the core network element that sends the first notification message, such as the service gateway. The second indication message is used to indicate the deletion (or discarding) of the downlink data of the first terminal device. Optionally, if the mobile management network element sends the second indication message, the mobile management network element may also send a first information element. The first information element may indicate the reason for deleting the downlink data of the first terminal device. For details of the second indication information and the first information element, please refer to the above introduction to S402 and will not be expanded here.

[0247] Furthermore, after receiving the downlink data from the first terminal device, the first access network device may cache the downlink data locally and wait for the communication connection between the first access network device and the first terminal device to be restored.

[0248] Optionally, based on the embodiment shown in Figure 4 or Figure 5, after the first access network device receives and caches the downlink data of the first terminal device, the following subsequent process may also exist: when the communication connection between the first access network device and the first terminal device is restored, the first access network device pages the first terminal device, and after the paging is successful, establishes an RRC connection with the first terminal device. After the first access network device establishes the RRC connection with the first terminal device, the first access network device sends the downlink data of the first terminal device to the first terminal device. The subsequent process may include the following steps:

[0249] When the communication connection between the first access network device and the first terminal device is restored, the first access network device sends a second paging message to the first terminal device, wherein the second paging message is used to page the first terminal device. Accordingly, the first terminal device receives the second paging message. After the first terminal device determines that the network is paging the first terminal device based on the second paging message, it sends an RRC connection request message to the first access network device, requesting to establish an RRC connection. Accordingly, the first access network device receives the RRC connection request message. Then, the first access network device sends an RRC connection establishment message to the first terminal device. Accordingly, the first terminal device receives the RRC connection establishment message. Then, the first terminal device sends an RRC connection establishment completion message to the first access network device. Accordingly, the first access network device receives the RRC connection establishment completion message from the first terminal device. At this point, it can be considered that the RRC connection establishment is complete.

[0250] After the RRC connection is established, the first access network device sends the downlink data of the first terminal device cached in the first access network device to the first terminal device.

[0251] In a possible implementation, the subsequent process may specifically refer to steps 4-5 and step 13 in the process shown in Figure 1. In addition, the embodiment of the present application also provides several possible implementations, which are introduced below.

[0252] In one possible implementation, the second paging message may include fifth indication information, where the fifth indication information is used to instruct the first terminal device to receive downlink data cached on the first access network device. Based on the fifth indication information, the first terminal device may determine that the first access network device has locally cached the downlink data of the first terminal device.

[0253] Optionally, in this implementation, the RRC connection request message may include indication information indicating the reason for requesting the RRC connection, and the reason indicated by the indication information may be: receiving downlink data cached in the first access network device.

[0254] Optionally, in this implementation, the first terminal device may generate an RRC connection request message that does not include service request information based on the fifth indication information, where the service request information is used to indicate that the first terminal device is requesting to establish a connection with the core network. Accordingly, after receiving the RRC connection request message, the first access network device may determine that the RRC connection request message does not include service request information. For example, the service request information may be the control plane service request in the process shown in Figure 1.

[0255] In another possible implementation, the RRC connection request message received by the first access network device includes service request information. After receiving the RRC connection request message, the first access network device can determine whether the downlink data of the first terminal device is cached locally. If the downlink data of the first terminal device is cached locally, the first access network device can discard the service request information. In one possible case, the first access network device can discard the service request information after sending the cached downlink data to the first terminal device.

[0256] Alternatively, if there is downlink data of the first terminal device cached locally, the first access network device may also cache the service request information locally, and send the service request information to the mobile management network element when the communication connection between the first access network device and the mobile management network element is available.

[0257] In addition, if the first access network device determines that there is no locally cached downlink data for the first terminal device, the first access network device may cache the service request information locally and send the service request information to the mobility management network element when the communication connection between the first access network device and the mobility management network element is available. Optionally, if the mobility management network element receives the service request information, it may trigger the mobility management network element to send the downlink data of the first terminal device to the first terminal device.

[0258] Exemplarily, in the above possible implementation, after the first access network device establishes an RRC connection with the first terminal device, the first access network device can send a NAS PDU to the first terminal device through a downlink RRC message, wherein the NAS PDU includes downlink data of the first terminal device.

[0259] Optionally, when the RRC connection between the first access network device and the first terminal device is still maintained, the first terminal device or the first access network device may use NAS PDU to continue transmitting uplink or downlink data.

[0260] Optionally, if the first access network device receives uplink data from the first terminal device, and the first access network device determines that the current communication connection between the first access network device and the mobile management network element is unavailable, the first access network device can wait until the communication connection between the first access network device and the mobile management network element is restored before sending the uplink data of the first terminal device to the mobile management network element.

[0261] Exemplarily, the first access network device may send a NAS PDU carrying uplink data of the first terminal device to the mobility management network element via an uplink S1-AP message.

[0262] Optionally, after receiving the uplink data of the first terminal device, the mobility management network element may check the integrity of the uplink data and decrypt the data. Further, the first access network device may send the uplink data of the first terminal device to the packet data network gateway via the serving gateway.

[0263] For example, it is assumed that the communication method provided in the embodiment of the present application is applied to a 4G communication system, the mobile management network element is the MME, the core network element that sends the first notification message to the MME is the S-GW, the S-GW obtains downlink data from the P-GW, the first access network device is the eNodeB, and the first terminal device is the UE. Among them, the eNodeB is located on the satellite, and the UE, MME, S-GW and P-GW are located on the ground. In one possible scenario, if the process shown in Figure 4 is combined with a possible subsequent process described above, a possible process for data from the core network to the first terminal device can be shown in Figure 6, including the following steps:

[0264] S601. The P-GW sends downlink data of the UE to the S-GW.

[0265] S602. The S-GW sends a first notification message to the MME. The first notification message is used to notify the UE of the arrival of downlink data.

[0266] S603. If the MME determines that the communication connection between the eNodeB and the UE is unavailable, it further determines whether the UE's downlink data can be cached in the eNodeB. If it can be cached in the eNodeB, the MME sends a first paging message to the eNodeB, the first paging message including first indication information, and sends a response message to the first notification message (i.e., an ACK for the first notification message) to the S-GW, indicating that the first notification message has been received.

[0267] S604: The eNodeB sends a first request message to the MME, requesting to establish a data transmission channel between the eNodeB and the MME.

[0268] Optionally, before S604 , the eNodeB may retrieve the UE context from the MME.

[0269] S605: A data transmission channel is established between the S-GW and the MME, and the MME receives the downlink data of the UE from the S-GW.

[0270] Optionally, the MME may send a third request message to the S-GW to request bearer modification. Accordingly, the S-GW feeds back a bearer modification response to the MME. At this point, the data transmission channel is established.

[0271] Optionally, after receiving the downlink data from the UE, the MME may encrypt and integrity protect the data.

[0272] S606: The MME sends the UE's downlink data to the eNodeB.

[0273] S607 : The eNodeB buffers the downlink data of the UE and waits for the communication connection with the UE to be restored.

[0274] S608: When the communication connection between the eNodeB and the UE is restored, the eNodeB sends a second paging message to the UE.

[0275] Optionally, the second paging message may include fifth indication information, and the fifth indication information is used to instruct the first terminal device to receive downlink data cached in the first access network device.

[0276] S609: The eNodeB establishes an RRC connection with the UE.

[0277] Optionally, when establishing the RRC connection, the RRC connection request message sent by the UE to the eNodeB does not include the service request information, or may include the service request information.

[0278] Optionally, if the RRC connection request message includes service request information, the eNodeB may discard the service request information, or may cache the service request information.

[0279] S610: The eNodeB sends downlink data to the UE.

[0280] Assume that the communication method provided in the embodiment of the present application is applied to a 4G communication system, the mobile management network element is the MME, the core network element that sends the first notification message to the MME is the S-GW, the S-GW obtains downlink data from the P-GW, the first access network device is the eNodeB, and the first terminal device is the UE. Among them, the eNodeB is located on the satellite, and the UE, MME, S-GW, and P-GW are located on the ground. In another possible scenario, if the process shown in Figure 5 is combined with a possible subsequent process described above, another possible process for data from the core network to the first terminal device can be shown in Figure 7, including the following steps:

[0281] S701. The P-GW sends downlink data of the UE to the S-GW.

[0282] S702. The S-GW sends a first notification message to the MME. The first notification message is used to notify the UE of the arrival of downlink data.

[0283] S703. The MME sends a first paging message to one or more eNodeBs, where the first paging message is used to request the eNodeB to page the first terminal device.

[0284] S704: The eNodeB determines whether the communication connection between itself and the UE is available. If not, the eNodeB sends a first request message to the MME to request establishment of a data transmission channel between the eNodeB and the MME. The first request message includes the third indication information, or the first request message does not include a service request message.

[0285] Optionally, before S704 , the eNodeB may retrieve the UE context from the MME.

[0286] S705: The MME determines, based on the first request message, that the communication connection between the eNodeB and the UE is unavailable, and further determines whether the UE's downlink data can be cached in the eNodeB. If it can be cached in the eNodeB, the MME sends a response message (i.e., an ACK for the first notification message) to the S-GW, indicating that the first notification message has been received.

[0287] S706: A data transmission channel is established between the S-GW and the MME, and the MME receives the downlink data of the UE from the S-GW.

[0288] Optionally, the MME may send a third request message to the S-GW to request bearer modification. Accordingly, the S-GW feeds back a bearer modification response to the MME. At this point, the data transmission channel is established.

[0289] Optionally, after receiving the downlink data from the UE, the MME may encrypt and integrity protect the data.

[0290] S707 : The MME sends the UE's downlink data to the eNodeB.

[0291] S708 : The eNodeB buffers the downlink data of the UE and waits for the communication connection with the UE to be restored.

[0292] S709 : When the communication connection between the eNodeB and the UE is restored, the eNodeB sends a second paging message to the UE.

[0293] Optionally, the second paging message may include fifth indication information, and the fifth indication information is used to instruct the first terminal device to receive downlink data cached in the first access network device.

[0294] S710: The eNodeB establishes an RRC connection with the UE.

[0295] Optionally, when establishing the RRC connection, the RRC connection request message sent by the UE to the eNodeB does not include the service request information, or may include the service request information.

[0296] Optionally, if the RRC connection request message includes service request information, the eNodeB may discard the service request information, or may cache the service request information.

[0297] S711. The eNodeB sends downlink data to the UE.

[0298] As shown in Figure 8, another communication method is provided for an embodiment of the present application. Figure 8 illustrates the method by taking the service gateway and the mobile management network element as the execution subjects of the interaction diagram as an example, but the present application does not limit the execution subjects of the interaction diagram. For example, the mobile management network element in Figure 8 can also be a module such as a chip, a chip system, or a processor applied to the mobile management network element, or a logical node, a logical module, or software that can realize all or part of the functions of the mobile management network element; the service gateway in Figure 8 can also be a module such as a chip, a chip system, or a processor applied to the service gateway, or a logical node, a logical module, or software that can realize all or part of the functions of the service gateway.

[0299] As shown in FIG8 , the communication method includes steps S801 to S804:

[0300] S801. The serving gateway obtains downlink data to be transmitted to the first terminal device, and determines that the mobility management network element serving the first terminal device is located on the satellite.

[0301] S802: When the serving gateway determines that the communication connection between the access network device located on the satellite and the first terminal device is unavailable, the serving gateway sends a first notification message to the mobility management network element, where the first notification message is used to instruct the mobility management network element to receive downlink data from the first terminal device. The first notification message includes second request information, where the second request information is used to request the mobility management network element to receive and cache the downlink data. In response, the mobility management network element receives the first notification message from the serving gateway.

[0302] S803: When the mobility management network element determines that the communication connection between the second access network device located on the satellite and the first terminal device is unavailable and the downlink data can be cached in the mobility management network element, the mobility management network element sends a response message to the serving gateway in response to the first notification message. Accordingly, the serving gateway receives the response message to the first notification message.

[0303] S804: The serving gateway sends downlink data of the first terminal device to the mobility management network element. Accordingly, the mobility management network element receives the downlink data of the first terminal device and buffers the downlink data of the first terminal device until a third paging message is sent to the second access network device, where the third paging message is used to request paging of the first terminal device.

[0304] The communication method shown in Figure 8 can be applied to an NTN scenario. In this case, an access network device (such as a second access network device) and a mobility management network element serving a first terminal device are located on a satellite, and a serving gateway and the first terminal device are located on the ground. The mobility management network element and the serving gateway can execute the communication method shown in Figure 8. If the serving gateway determines that the communication connection between the access network device located on the satellite and the first terminal device is unavailable, it can request the mobility management network element to cache the downlink data of the first terminal device in the mobility management network element.

[0305] The mobile management network element can, based on the request of the service gateway, first obtain the data from the service gateway and cache the data when it determines that the downlink data can be cached in the first terminal device, and then request the second access network device to page the first terminal device when the communication connection between the second access network device and the first terminal device is restored. Thus, after the second access network device pages the first terminal device, it can immediately obtain the downlink data of the first terminal device from the mobile management network element. Therefore, compared to applying the existing process to the NTN scenario, in the embodiment of the present application, after the second access network device pages the first terminal device, the mobile management network element no longer needs to wait for the communication connection between the second access network device and the service gateway to be restored before requesting data from the service gateway, thereby saving the time for data to be transmitted from the core network to the terminal device.

[0306] The following is an introduction to S801-S804 respectively.

[0307] In S801, the serving gateway may obtain downlink data of the first terminal device from other core network elements. Exemplarily, the serving gateway may receive downlink data of the first terminal device from a packet data gateway.

[0308] In S801, the first terminal device is in an idle state and is attached to the core network. For example, if the embodiment of the present application is applied to a 4G communication system, the first terminal device is attached to the EPS.

[0309] After acquiring the downlink data of the first terminal device, the serving gateway determines the mobility management network element serving the first terminal device. Further, the serving gateway determines that the mobility management network element is located on a satellite.

[0310] The embodiments of the present application do not limit how the service gateway determines whether the mobile management network element is located on a satellite. In one possible implementation, the service gateway may pre-acquire a mapping relationship that characterizes whether the mobile management network element is located on a satellite. Exemplarily, the mapping relationship may include the identification information of one or more satellites and the corresponding relationship between the identification information of one or more mobile management network elements. After the service gateway determines the mobile management network element serving the first terminal device, it searches the mapping relationship to see whether there is a satellite corresponding to the mobile management network element. If there is a satellite corresponding to the mobile management network element, it can be determined that the mobile management network element is located on a satellite. If there is no satellite corresponding to the mobile management network element, it can be determined that the mobile management network element is not located on a satellite.

[0311] In S802, the serving gateway may determine whether there is an access network device with which a connection to the first terminal device is available when the communication connection between the serving gateway and the mobility management network element is available. If not (i.e., when the communication connection between the access network device and the first terminal device is unavailable), the serving gateway may carry a second request message in the first notification message sent to the mobility management network element to request the mobility management network element to receive and cache the downlink data of the first terminal device.

[0312] In addition, if there is an access network device with an available connection to the first terminal device, the serving gateway may send a first notification message to the mobility management network element that does not include the second request message. In this case, the specific flow of data from the serving gateway to the first terminal device can refer to steps 2-13 in the process shown in Figure 1.

[0313] The embodiments of the present application do not limit how the service gateway determines whether the communication connection between the service gateway and the mobility management network element is available, and how to determine whether the connection between the access network device and the terminal device is available.

[0314] Regarding the availability of the communication connection between the service gateway and the mobile management network element, in one possible implementation, the service gateway can obtain the satellite coverage availability information corresponding to the mobile management network element, and determine whether the coverage range corresponding to the mobile management network element (which can be the coverage range of the satellite where the mobile management network element is located, or the coverage range of the mobile management network element) includes the gateway station connected to the service gateway based on the satellite coverage availability information corresponding to the mobile management network element. In the case that the coverage range corresponding to the mobile management network element includes the gateway station connected to the service gateway, the service gateway can determine that the communication connection between the service gateway and the mobile management network element is available. In the case that the coverage range corresponding to the mobile management network element does not include the gateway station connected to the service gateway, the service gateway can determine that the communication connection between the service gateway and the mobile management network element is unavailable. Among them, the satellite coverage availability information can be specifically referred to the introduction to S402 above, which will not be expanded here.

[0315] With respect to determining whether the connection between an access network device and a terminal device is available, in one possible implementation, the service gateway may determine one or more access network devices with which a communication connection is available with the service gateway, and determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, whether there is an access network device whose current coverage includes the first terminal device among the one or more access network devices. If not, the service gateway may determine that there is no access network device with which a connection is available with the first terminal device. If there is an access network device whose current coverage includes the first terminal device, the service gateway may determine that a connection between the access network device and the first terminal device is available. The implementation may be specifically described in the above introduction to S402 and will not be expanded upon here.

[0316] Among them, for one or more access network devices that are determined to have an available communication connection with the serving gateway, since the access network devices communicate with the serving gateway through a mobility management network element, when the access network device and the mobility management network element are located on the same satellite, if it is determined that the communication connection between the mobility management network element and the serving gateway is available, it is also determined that the communication connection between the access network device and the serving gateway is available. When the access network device and the mobility management network element are located on different satellites, if it is determined that the intersatellite link between the satellite on which the mobility management network element is located and the satellite on which the access network device is located is available, and the communication connection between the mobility management network element and the serving gateway is available, it can be determined that the communication connection between the access network device and the serving gateway is available.

[0317] In S803, after receiving the first notification message, the mobility management network element can determine that the first terminal device is in an idle state based on the information of the first terminal device carried therein, and further determine that the first terminal device needs to be paged.

[0318] The mobility management network element may determine, based on the second request message included in the first notification message, that there is currently no access network device with which a communication connection with the first terminal device is available. Furthermore, the mobility management network element may determine whether the downlink data of the first terminal device can be cached in the mobility management network element. If so, the mobility management network element may send a response message to the serving gateway in response to the first notification message. In this case, the response message may instruct the serving gateway to send the downlink data of the first terminal device.

[0319] The embodiments of the present application do not restrict how the mobility management network element determines whether the downlink data of the first terminal device can be cached in the mobility management network element. In one possible implementation, the mobility management network element can determine whether the downlink data of the first terminal device supports transmission via a store and forward operation. If so, the mobility management network element can determine that the downlink data of the first terminal device can be cached in the mobility management network element.

[0320] Among them, storage and forwarding can be understood as, in the scenario where the feeder link of the NTN network is discontinuous, the data is first cached in the mobile management network element located on the satellite, and then forwarded between the terminal device and the ground core network through the mobile management network element.

[0321] Among them, for determining whether the downlink data of the first terminal device supports transmission through the storage and forwarding operation, please refer to the above introduction to S402, which will not be elaborated here.

[0322] In addition, optionally, if the mobile management network element determines that the downlink data of the first terminal device cannot be cached in the mobile management network element, the mobile management network element may send a response message to the service gateway for the first notification message. In this case, the response message may instruct the mobile management network element to refuse to receive the downlink data of the first terminal device.

[0323] Optionally, if the mobility management network element determines that the downlink data of the first terminal device cannot be cached in the mobility management network element, the mobility management network element may send a sixth indication message to the serving gateway, where the sixth indication message is used to instruct the deletion (or discarding) of the downlink data of the first terminal device. After receiving the sixth indication message, the serving gateway may delete (or discard) the downlink data of the first terminal device according to the instruction of the sixth indication message.

[0324] Optionally, if the mobility management network element sends the sixth indication information to the serving gateway, the mobility management network element may also send a third information element to the serving gateway, where the third information element may indicate the reason for deleting the downlink data of the first terminal device. In this case, the reason indicated by the third information element may be that the downlink data of the first terminal device cannot be cached in the mobility management network element.

[0325] In S804, after receiving the response message to the first notification message, the serving gateway can determine, based on the response message, that the mobility management network element agrees to receive and cache the downlink data of the first terminal device. Further, the serving gateway sends the downlink data of the first terminal device to the mobility management network element.

[0326] Optionally, before the service gateway sends the downlink data of the first terminal device to the mobility management network element, the mobility management network element may send a third request message to the service gateway, where the third request message is used to request the service gateway to establish a data transmission channel with the mobility management network element. After receiving the third request message, the service gateway sends a response message to the mobility management network element for the third request message. Accordingly, the mobility management network element receives a response message to the third request message from the service gateway. In one possible case, the third request message can also be understood as a request to modify the bearer between the service gateway and the mobility management network element.

[0327] In S804, after receiving the downlink data from the first terminal device, the mobility management network element caches the downlink data from the first terminal device until the mobility management network element determines that the communication connection between the second access network device and the first terminal device is available. At this time, the mobility management network element sends a third paging message to the second access network device, where the third paging message is used to request paging of the first terminal device.

[0328] The second access network device is one of the one or more access network devices whose communication connection with the first terminal device is unavailable when the communication connection between the serving gateway and the mobility management network element is available. In S804, after receiving the downlink data from the first terminal device, the mobility management network element may wait until the communication connection between the second access network device and the first terminal device is restored. This embodiment of the application does not limit how the mobility management network element determines the second access network device. For example, the mobility management network element may determine any access network device located on a satellite as the second access network device. For another example, the mobility management network element may, based on satellite coverage availability information corresponding to the one or more access network devices and the location information of the first terminal device, determine the access network device among the one or more access network devices whose coverage is expected to include the first terminal device the earliest as the second access network device. This embodiment of the application does not limit how the mobility management network element determines whether the communication connection between the second access network device and the first terminal device is restored. For example, the mobility management network element may determine whether the communication connection between the second access network device and the first terminal device is available based on satellite coverage availability information corresponding to the second access network device. For details, please refer to the description of S402 above.

[0329] As shown in Figure 9, another communication method is provided for an embodiment of the present application. Figure 9 takes the service gateway and the mobile management network element as an example of the execution subject of the interaction diagram to illustrate the method, but the present application does not limit the execution subject of the interaction diagram. For example, the mobile management network element in Figure 9 can also be a module such as a chip, a chip system, or a processor applied to the mobile management network element, and can also be a logical node, a logical module or software that can realize all or part of the functions of the mobile management network element; the service gateway in Figure 9 can also be a module such as a chip, a chip system, or a processor applied to the service gateway, and can also be a logical node, a logical module or software that can realize all or part of the functions of the service gateway.

[0330] As shown in FIG9 , the communication method includes steps S901 to S904:

[0331] S901. The serving gateway obtains downlink data to be transmitted to the first terminal device, and determines that the mobility management network element serving the first terminal device is located on the satellite.

[0332] S902: The serving gateway sends a first notification message to the mobility management network element, where the first notification message is used to indicate receiving downlink data of the first terminal device. Correspondingly, the mobility management network element receives the first notification message.

[0333] S903: When the mobility management network element determines that the communication connection between the second access network device located on the satellite and the first terminal device is unavailable and the downlink data can be cached in the mobility management network element, the mobility management network element sends a response message to the serving gateway in response to the first notification message. Accordingly, the serving gateway receives the response message to the first notification message.

[0334] S904: The serving gateway sends downlink data of the first terminal device to the mobility management network element. Accordingly, the mobility management network element receives the downlink data of the first terminal device and buffers the downlink data of the first terminal device until a third paging message is sent to the second access network device, where the third paging message is used to request paging of the first terminal device.

[0335] The communication method shown in Figure 9 can be applied to an NTN scenario. In this scenario, an access network device (such as a second access network device) and a mobility management network element serving a first terminal device are located on a satellite, while a service gateway and the first terminal device are located on the ground. The mobility management network element and the service gateway can execute the communication method shown in Figure 9. After receiving a notification message from the service gateway, the mobility management network element can, if it determines that the communication connection between the second access network device and the first terminal device is unavailable and that downlink data can be cached on the first terminal device, first obtain data from the service gateway and cache the data. It then requests the second access network device to page the first terminal device when the communication connection between the second access network device and the first terminal device is restored. Thus, after paging the first terminal device, the second access network device can immediately obtain the downlink data of the first terminal device from the mobility management network element. Therefore, compared to applying existing processes to NTN scenarios, in this embodiment of the present application, after the second access network device pages the first terminal device, the mobility management network element can no longer wait for the communication connection with the service gateway to be restored before requesting data from the service gateway, thereby saving the time it takes for data to travel from the core network to the terminal device.

[0336] The following is an introduction to S901-S904 respectively.

[0337] For details about S901, please refer to the above introduction to S801, which will not be elaborated here.

[0338] In S902, after the serving gateway obtains the downlink data of the first terminal device, it can determine the mobility management network element serving the first terminal device. Further, the serving gateway can determine that the mobility management network element is located on the satellite.

[0339] The embodiment of the present application does not limit how the serving gateway determines whether the mobility management network element is located on the satellite.

[0340] In S902 , the serving gateway may send a first notification message to the mobility management network element when determining that the communication connection between the mobility management network element and the serving gateway is available.

[0341] The embodiments of the present application do not limit how the serving gateway determines whether the communication connection between the serving gateway and the mobility management network element is available. In one possible implementation, the serving gateway may determine whether the communication connection between the serving gateway and the mobility management network element is available based on the satellite coverage availability information corresponding to the mobility management network element. For details, please refer to the above description of S802 and will not be elaborated here.

[0342] In S903, after the mobile management network element receives the first notification message, it can determine that the first terminal device is in an idle state based on the information of the first terminal device carried therein, and then determine that the first terminal device needs to be paged. In addition, the first request message can trigger the mobile management network element to determine whether there is an access network device with which a communication connection with the first terminal device is currently available and which has a communication connection with the mobile management network element. If not, the mobile management network element can determine a second access network device with which a communication connection with the mobile management network element is unavailable, and determine whether the downlink data of the first terminal device can be cached in the mobile management network element. If the downlink data of the first terminal device can be cached in the mobile management network element, the mobile management network element can send a response message to the service gateway for the first notification message. In this case, the response message can instruct the service gateway to send the downlink data of the first terminal device.

[0343] The second access network device is one of the one or more access network devices whose communication connection with the first terminal device is unavailable. For details, please refer to the above introduction to S803, which will not be elaborated here.

[0344] The embodiment of the present application does not limit how the mobility management network element determines whether a communication connection with the first terminal device is currently available and whether there is an access network device with a communication connection with the mobility management network element. Furthermore, the embodiment of the present application does not limit how the mobility management network element determines whether the downlink data of the first terminal device can be cached in the mobility management network element. For details, please refer to the above description of S802, which will not be elaborated here.

[0345] In addition, optionally, if the mobile management network element determines that the downlink data of the first terminal device cannot be cached in the mobile management network element, the mobile management network element may send a response message to the service gateway for the first notification message. In this case, the response message may instruct the mobile management network element to refuse to receive the downlink data of the first terminal device.

[0346] Optionally, if the mobility management network element determines that the downlink data of the first terminal device cannot be cached in the mobility management network element, the mobility management network element may send a sixth indication message to the serving gateway, where the sixth indication message is used to instruct the deletion (or discarding) of the downlink data of the first terminal device. After receiving the sixth indication message, the serving gateway may delete (or discard) the downlink data of the first terminal device according to the instruction of the sixth indication message.

[0347] Optionally, if the mobility management network element sends the sixth indication information to the serving gateway, the mobility management network element may also send a third information element to the serving gateway, where the third information element may indicate the reason for deleting the downlink data of the first terminal device. In this case, the reason indicated by the third information element may be that the downlink data of the first terminal device cannot be cached in the mobility management network element.

[0348] In S904, after receiving the response message to the first notification message, the serving gateway can determine, based on the response message, that the mobility management network element agrees to receive and cache the downlink data of the first terminal device. Further, the serving gateway sends the downlink data of the first terminal device to the mobility management network element.

[0349] Optionally, before the serving gateway sends the downlink data of the first terminal device to the mobility management network element, the mobility management network element may send a third request message to the serving gateway. After receiving the third request message, the serving gateway may send a response message to the mobility management network element in response to the third request message. For details, please refer to the above introduction to S804, which will not be elaborated here.

[0350] In S904, after receiving the downlink data of the first terminal device, the mobility management network element caches the downlink data of the first terminal device until the mobility management network element determines that the communication connection between the second access network device and the first terminal device is available. At this time, the mobility management network element sends a third paging message to the second access network device, and the third paging message is used to request paging of the first terminal device.

[0351] Optionally, based on the above-mentioned process shown in Figure 8 or Figure 9, after the mobile management network element sends the third paging message to the second access network device, the following subsequent process may also exist: after the second access network device receives the third paging message, it can page the first terminal device. If the paging of the first terminal device is successful, the second access network device can establish an RRC connection with the first terminal device. Furthermore, after the RRC connection is established, the second access network device can request downlink data from the mobile management network element. For example, the second access network device can send a first request message to the mobile management network element, requesting to establish a data transmission channel between the second access network device and the mobile management network element. Furthermore, the mobile management network element can send the downlink data of the first terminal device to the second access network device based on the request of the second access network device. Accordingly, after the second access network device receives the downlink data of the first terminal device, it can send downlink data to the first terminal device.

[0352] In one possible scenario, the second access network device pages the first terminal device, establishes an RRC connection with the first terminal device, and requests downlink data from the mobility management network element. For details, see steps 4-7 of the process shown in Figure 1. For details, see steps 12-13 of the process shown in Figure 1, where the second access network device receives downlink data from the first terminal device and sends downlink data to the first terminal device.

[0353] For example, it is assumed that the communication method provided in the embodiment of the present application is applied to a 4G communication system, the mobile management network element is MME, the core network element that sends the first notification message to the MME is S-GW, the S-GW obtains downlink data from the P-GW, the second access network device is eNodeB, and the first terminal device is UE. Among them, the eNodeB and MME are located on the satellite, and the UE, S-GW and P-GW are located on the ground. In one possible scenario, if the process shown in Figure 8 is combined with a possible process of data from the mobile management network element to the first terminal device, another possible process of data from the core network to the first terminal device can be shown in Figure 10, including the following steps:

[0354] S1001. The P-GW sends downlink data of the UE to the S-GW.

[0355] S1002: The S-GW determines whether the MME serving the UE is located on a satellite. If so, the S-GW determines whether the communication connection between the eNodeB and the UE is available. If the communication connection between the eNodeB and the UE is unavailable, the S-GW sends a first notification message to the MME, which notifies the UE of the arrival of downlink data. The first notification message includes second request information, which requests the MME to receive and buffer the downlink data. In response, the MME receives the first notification message.

[0356] S1003. The MME determines, based on the second request message, that the communication connection between the eNodeB and the UE is unavailable. The MME determines whether the UE's downlink data can be cached in the MME. If so, the MME sends a response message to the S-GW in response to the first notification message. Accordingly, the S-GW receives the response message to the first notification message (i.e., an ACK for the first notification message).

[0357] S1004: A data transmission channel is established between the S-GW and the MME. The S-GW sends the UE's downlink data to the MME. In response, the MME receives and buffers the UE's downlink data, waiting for the communication connection between the eNodeB and the UE to be restored.

[0358] Optionally, the MME may send a third request message to the S-GW to request bearer modification. Accordingly, the S-GW feeds back a bearer modification response to the MME. At this point, the data transmission channel is established.

[0359] Optionally, after receiving the downlink data from the UE, the MME may encrypt and integrity protect the data.

[0360] S1005 . When the communication connection between the eNodeB and the UE is restored, the MME sends a third paging message to the eNodeB. The third paging message is used to request the eNodeB to page the UE.

[0361] S1006. The eNodeB sends a second paging message to the UE. The second paging message is used to page the UE.

[0362] S1007. The eNodeB establishes an RRC connection with the UE.

[0363] S1008: The eNodeB sends a first request message to the MME, requesting to establish a data transmission channel between the MME and the eNodeB. Correspondingly, the MME receives the first request message.

[0364] Optionally, before S1008 , the eNodeB may retrieve the UE context from the MME.

[0365] S1009. The MME sends the UE's downlink data cached locally in the MME to the eNodeB.

[0366] S1010. The eNodeB sends downlink data to the UE.

[0367] For example, it is assumed that the communication method provided in the embodiment of the present application is applied to a 4G communication system, the mobile management network element is MME, the core network element that sends the first notification message to the MME is S-GW, the S-GW obtains downlink data from the P-GW, the second access network device is eNodeB, and the first terminal device is UE. Among them, the eNodeB and MME are located on the satellite, and the UE, S-GW and P-GW are located on the ground. In another possible scenario, if the process shown in Figure 9 is combined with a possible process of data from the mobile management network element to the first terminal device, another possible process of data from the core network to the first terminal device can be shown in Figure 11, including the following steps:

[0368] S1101. The P-GW sends downlink data of the UE to the S-GW.

[0369] S1102: The S-GW determines whether the MME serving the UE is located on a satellite. If the MME is located on a satellite, the S-GW sends a first notification message to the MME when determining that the communication connection between the S-GW and the MME is available. The first notification message is used to notify the UE of the arrival of downlink data.

[0370] S1103. The MME determines whether the communication connection between the eNodeB and the UE is available. If not, the MME determines whether the UE's downlink data can be cached in the MME. If so, the MME sends a response message to the S-GW regarding the first notification message. Accordingly, the S-GW receives the response message to the first notification message (i.e., an ACK for the first notification message).

[0371] The subsequent process of S1103 is the same as S1004-S1010 and will not be expanded here.

[0372] The above description mainly describes the solutions provided by the embodiments of the present application from the perspective of interaction between various devices. Accordingly, the embodiments of the present application also provide a communication device for implementing the various methods described above. The communication device can be the mobility management network element, first access network device, serving gateway, or first terminal device in the above method embodiments, or a device including the above mobility management network element, first access network device, serving gateway, or first terminal device, or a component that can be used for the above mobility management network element, first access network device, serving gateway, or first terminal device. It will be understood that, in order to implement the above functions, the communication device includes hardware structures and / or software modules corresponding to performing each function. Those skilled in the art will readily appreciate that, in conjunction with the various exemplary units and algorithm steps described in the embodiments disclosed herein, the present application can be implemented in hardware or a combination of hardware and computer software. Whether a function is implemented in hardware or in a hardware-driven manner by computer software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this application.

[0373] In the embodiment of the present application, the communication device can be divided into functional modules according to the above method embodiment. For example, each functional module can be divided according to each function, or two or more functions can be integrated into one processing module. The above integrated modules can be implemented in the form of hardware or in the form of software functional modules. It should be understood that the division of modules in the embodiment of the present application is schematic and is only a logical functional division. In actual implementation, there may be other division methods.

[0374] Figure 12 shows a schematic diagram of the structure of a communication device 1200. The communication device 1200 includes a processing module 1201 and a transceiver module 1202. Optionally, the communication device 1200 may also include a storage module 1203. The transceiver module 1202, also known as a transceiver unit, is used to implement transceiver functions and may be, for example, a transceiver circuit, a transceiver, a transceiver, or a communication interface.

[0375] Taking the communication device 1200 as the mobility management network element in the above embodiment as an example, in a possible implementation manner:

[0376] Transceiver module 1202 is configured to receive a first notification message, the first notification message being used to instruct reception of downlink data from a first terminal device. If processing module 1201 determines that the communication connection between a first access network device located on the satellite and the first terminal device is unavailable and that downlink data can be cached on the first access network device, transceiver module 1202 is further configured to send first indication information to the first access network device, the first indication information being used to instruct the first access network device to cache the downlink data.

[0377] In one possible implementation, the processing module 1201 determines that the downlink data can be cached in the first access network device, including at least one of the following: determining that the first access network device supports the first function, the first function includes a storage and forwarding function; or determining that the downlink data supports transmission through a storage and forwarding operation.

[0378] In one possible implementation, the processing module 1201 determines that the downlink data supports transmission through a store and forward operation, including: determining that the downlink data supports transmission through a store and forward operation based on one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device.

[0379] In one possible implementation, transceiver module 1202 is further configured to receive a first request message from a first access network device, the first request message being used to request establishment of a data transmission channel between communication apparatus 1200 and the first access network device. After acquiring downlink data from the first terminal device, transceiver module 1202 is further configured to send the downlink data to the first access network device.

[0380] In one possible implementation, the processing module 1201 is further configured to determine whether the first terminal device is within the coverage area corresponding to the first access network device based on the satellite coverage availability information corresponding to the first access network device and the location information of the first terminal device; wherein the satellite coverage information of the first access network device includes a mapping relationship between the coverage area corresponding to the first access network device and time. If the first terminal device is within the coverage area, the processing module 1201 determines that the communication connection between the first access network device and the first terminal device is available; alternatively, if the first terminal device is not within the coverage area, the processing module 1201 determines that the communication connection between the first access network device and the first terminal device is unavailable.

[0381] In one possible implementation, the processing module 1201 is further used to determine one or more access network devices that are available for communication connection with the communication apparatus 1200. The processing module 1201 is further used to determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that there is no access network device whose current coverage includes the first terminal device, wherein the satellite coverage information of the access network device includes a mapping relationship between the coverage corresponding to the access network device and time. The processing module 1201 is further used to determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that the access network device whose earliest coverage is expected to include the first terminal device is the first access network device.

[0382] In a possible implementation, when the processing module 1201 determines that the downlink data cannot be cached in the first access network device, the transceiver module 1202 is further configured to send second indication information to the serving gateway, where the second indication information is configured to instruct deletion of the downlink data.

[0383] Taking the communication device 1200 as the mobility management network element in the above embodiment as an example, in another possible implementation manner:

[0384] The transceiver module 1202 is used to receive a first notification message, where the first notification message is used to indicate the reception of downlink data from the first terminal device. The transceiver module 1202 is also used to send a first paging message to one or more access network devices located on the satellite, where the first paging message is used to request paging of the first terminal device. The one or more access network devices include a first access network device. The transceiver module 1202 is also used to receive a first request message from the first access network device, where the first request message is used to request the communication device 1200 to establish a data transmission channel with the first access network device. When the processing module 1201 determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable and that the downlink data can be cached on the first access network device, the transceiver module 1202 is also used to obtain the downlink data and send the downlink data to the first access network device.

[0385] In one possible implementation, the processing module 1201 determines that the downlink data can be cached in the first access network device, including at least one of the following: determining that the first access network device supports the first function, the first function includes a storage and forwarding function; or determining that the downlink data supports transmission through a storage and forwarding operation.

[0386] In one possible implementation, the processing module 1201 determines that the downlink data supports transmission through a store and forward operation, including: determining that the downlink data supports transmission through a store and forward operation based on one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device.

[0387] In one possible implementation, the processing module 1201 determines, based on the first request message, that the communication connection between the first access network device and the first terminal device is unavailable, including: determining that the first request message includes third indication information, where the third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable. Alternatively, determining that the first request message does not include service request information, where the service request message is used to indicate that the first terminal device requests to establish a connection with the core network.

[0388] In a possible implementation, when the processing module 1201 determines that the downlink data cannot be cached in the first access network device, the transceiver module 1202 is further configured to send fourth indication information to the first access network device, where the fourth indication information indicates that establishment of a data transmission channel is rejected.

[0389] In one possible implementation, the method further includes: when the processing module 1201 determines that the downlink data cannot be cached in the first access network device, the transceiver module 1202 is further used to send a second indication information to the service gateway, and the second indication information is used to indicate the deletion of the downlink data.

[0390] Taking the communication device 1200 as the mobility management network element in the above embodiment as an example, in another possible implementation manner:

[0391] Transceiver module 1202 is configured to receive a first notification message from a serving gateway, the first notification message being used to indicate receipt of downlink data from a first terminal device. If processing module 1201 determines that the communication connection between a second access network device located on the satellite and the first terminal device is unavailable and that downlink data can be cached in communication device 1200, transceiver module 1202 is further configured to send a response message to the serving gateway regarding the first notification message. Transceiver module 1202 is further configured to receive downlink data from the serving gateway and cache the downlink data until a third paging message is sent to the second access network device, the third paging message being used to request paging of the first terminal device.

[0392] In one possible implementation, the processing module 1201 determines that the downlink data can be cached in the mobility management network element, including: determining that the mobility management network element supports a first function, the first function including a store and forward function, or determining that the downlink data supports transmission via a store and forward operation.

[0393] In one possible implementation, the processing module 1201 determines that the downlink data supports transmission through a store and forward operation, including: determining that the downlink data supports transmission through a store and forward operation based on one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device.

[0394] In one possible implementation, the processing module 1201 is further configured to determine whether the first terminal device is within the coverage range corresponding to the second access network device based on the satellite coverage availability information corresponding to the second access network device and the location information of the first terminal device; wherein the satellite coverage information of the second access network device includes a mapping relationship between the coverage range corresponding to the second access network device and time. If the first terminal device is within the coverage range, the processing module 1201 determines that the communication connection between the second access network device and the first terminal device is available. Alternatively, if the first terminal device is not within the coverage range, the processing module 1201 determines that the communication connection between the second access network device and the first terminal device is unavailable.

[0395] In one possible implementation, the processing module 1201 is further used to determine one or more access network devices that are available for communication connection with the mobile management network element. The processing module 1201 is further used to determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that there is no access network device whose current coverage includes the first terminal device. The satellite coverage information of the access network device includes a mapping relationship between the coverage corresponding to the access network device and time. The processing module 1201 is further used to determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that the access network device whose earliest coverage is expected to include the first terminal device is the second access network device.

[0396] In one possible implementation, the transceiver module 1202 is further configured to send a third request message to the serving gateway, where the third request message is used to request the serving gateway to establish a data transmission channel with the communication device 1200. The transceiver module 1202 is further configured to receive a response message to the third request message from the serving gateway.

[0397] In a possible implementation, when the processing module 1201 determines that the downlink data cannot be cached in the first access network device, the transceiver module 1202 is further configured to send sixth indication information to the serving gateway, where the sixth indication information is configured to instruct deletion of the downlink data.

[0398] Taking the communication device 1200 as the first access network device in the above embodiment as an example, in a possible implementation manner:

[0399] The transceiver module 1202 is used to receive a first paging message from a mobile management network element; wherein the first paging message is used to request paging of the first terminal device. Before the communication device 1200 pages the first terminal device, the transceiver module 1202 is also used to send a first request message to the mobile management network element, and the first request message is used to request the mobile management network element to establish a data transmission channel with the communication device 1200; wherein the communication connection between the first access network device located on the satellite and the first terminal device is unavailable. The transceiver module 1202 is also used to receive and cache downlink data from the mobile management network element, or the transceiver module 1202 is also used to receive fourth indication information from the mobile management network element, and the fourth indication information indicates that the establishment of the data transmission channel is rejected.

[0400] In one possible implementation, when transceiver module 1202 receives and buffers downlink data from a mobility management network element, transceiver module 1202 is further configured to send a second paging message to the first terminal device; the second paging message is used to page the first terminal device. Transceiver module 1202 is further configured to receive an RRC connection request message from the first terminal device. Transceiver module 1202 is further configured to send an RRC connection establishment message to the first terminal device. Transceiver module 1202 is further configured to receive an RRC connection establishment completion message from the first terminal device. Transceiver module 1202 is further configured to send downlink data to the first terminal device.

[0401] In a possible implementation, the processing module 1201 is further used to determine that the RRC connection request message does not include service request information, and the service request information is used to indicate that the first terminal device requests to establish a connection with the core network.

[0402] In a possible implementation, the processing module 1201 is further configured to determine that the RRC connection request message includes service request information, where the service request information indicates that the first terminal device requests to establish a connection with the core network. The processing module 1201 is further configured to discard the service request information.

[0403] Taking the communication device 1200 as the first terminal device in the above embodiment as an example, in a possible implementation manner:

[0404] The transceiver module 1202 is configured to receive a second paging message from the first access network device. The second paging message is used to page the communication device 1200 and includes fifth indication information, which instructs the communication device 1200 to receive downlink data buffered in the first access network device. The processing module 1201 is configured to establish an RRC connection between the communication device 1200 and the first access network device. The transceiver module 1202 is also configured to receive downlink data from the first access network device.

[0405] In one possible implementation, a communication device 1200 establishes an RRC connection with a first access network device, including: a processing module 1201, based on fifth indication information, determining to generate an RRC connection request message that does not include service request information, where the service request information is used to instruct the communication device 1200 to request to establish a connection with the core network. A transceiver module 1202 is further configured to send an RRC connection request message to the first access network device. The transceiver module 1202 is further configured to receive an RRC connection establishment message from the first access network device. The transceiver module 1202 is further configured to send an RRC connection establishment complete message to the first access network device.

[0406] Taking the communication device 1200 as the service gateway in the above embodiment as an example, in a possible implementation:

[0407] The transceiver module 1202 is configured to obtain downlink data to be transmitted to the first terminal device. The processing module 1201 is configured to determine that the mobility management network element serving the first terminal device is located on a satellite. When the processing module 1201 determines that the communication connection between the access network device located on the satellite and the first terminal device is unavailable, the transceiver module 1202 is further configured to send a first notification message to the mobility management network element, where the first notification message is used to instruct the reception of downlink data from the first terminal device. The first notification message includes second request information, where the second request information is used to request the mobility management network element to receive and cache the downlink data.

[0408] In one possible implementation, the transceiver module 1202 is further configured to receive a response message to the first notification message from the mobility management network element, the response message being used to instruct the communication device 1200 to send downlink data. The transceiver module 1202 is further configured to send downlink data to the mobility management network element.

[0409] In a possible implementation, the transceiver module 1202 is further configured to receive sixth indication information from the mobility management network element, where the sixth indication information is configured to instruct the communication device 1200 to delete downlink data.

[0410] In one possible implementation, processing module 1201 is further configured to determine one or more access network devices available for communication with communication apparatus 1200. Processing module 1201 is further configured to determine, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that no access network device currently has coverage of the first terminal device. The satellite coverage information of the access network devices includes a mapping relationship between the coverage of the access network devices and time.

[0411] In one possible implementation, the processing module 1201 determines that the mobile management network element serving the first terminal device is located on the satellite, including: determining that the mobile management network element serving the first terminal device is located on the satellite based on a mapping relationship between the identification information of the satellite and the identification information of the mobile management network element.

[0412] Taking the communication device 1200 as the service gateway in the above embodiment as an example, in another possible implementation:

[0413] The transceiver module 1202 is used to obtain downlink data that needs to be transmitted to the first terminal device. The processing module 1201 is used to determine that the mobile management network element serving the first terminal device is located on a satellite. The processing module 1201 is also used to determine whether the communication connection between the communication device 1200 and the mobile management network element is available based on the satellite coverage availability information corresponding to the mobile management network element. In the case that the communication connection between the communication device 1200 and the mobile management network element is available, the transceiver module 1202 is also used to send a first notification message to the mobile management network element, and the first notification message is used to notify the arrival of downlink data. The satellite coverage availability information corresponding to the mobile management network element includes a mapping relationship between the coverage range corresponding to the mobile management network element and time.

[0414] In one possible implementation, the transceiver module 1202 is further configured to receive a response message from the mobility management network element to the first notification message, where the response message is used to instruct the communication device 1200 to send downlink data. Alternatively, the response message includes sixth indication information, where the sixth indication information is used to instruct the communication device 1200 to delete the downlink data.

[0415] In one possible implementation, the processing module 1201 determines that the mobile management network element serving the first terminal device is located on the satellite, including: determining that the mobile management network element serving the first terminal device is located on the satellite based on a mapping relationship between the identification information of the satellite and the identification information of the mobile management network element.

[0416] Among them, all relevant contents of each step involved in the above method embodiment can be referred to the functional description of the corresponding functional module and will not be repeated here.

[0417] Alternatively, the modules in FIG12 may also be referred to as units. For example, the processing module may be referred to as a processing unit, and the transceiver module may be referred to as a transceiver unit. In addition, in the communication device shown in FIG12 , the names of the various units may not be those shown in the figure. For example, the transceiver module may also be referred to as a communication module or a communication unit.

[0418] If the various units in Figure 12 are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the embodiment of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor (processor) to execute all or part of the steps of the method described in each embodiment of the present application. The storage medium for storing computer software products includes: various media that can store program codes, such as a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0419] In the embodiment of the present application, the communication device 1200 is presented in the form of various functional modules divided in an integrated manner. The "module" here can refer to an application-specific integrated circuit (ASIC), a circuit, a processor and memory that executes one or more software or firmware programs, an integrated logic circuit, and / or other devices that can provide the above functions.

[0420] In a simple embodiment, those skilled in the art may appreciate that the communication device 1200 may take the form of the communication device shown in FIG13 .

[0421] As shown in Figure 13, the communication device 1300 includes one or more processors 1301, a communication line 1302, and at least one communication interface (Figure 13 is only an example of including a communication interface 1304 and a processor 1301), and may optionally also include a memory 1303.

[0422] The processor 1301 may be a general-purpose central processing unit (CPU), a microprocessor, an ASIC, or one or more integrated circuits for controlling the execution of the program of the present application.

[0423] The communication line 1302 may include a path for connecting different components.

[0424] Communication interface 1304 may be a transceiver module for communicating with other devices or communication networks, such as Ethernet, RAN, terminals, and wireless local area networks (WLANs). For example, the transceiver module may be a device such as a transceiver or a transceiver. Alternatively, communication interface 1304 may be a transceiver circuit or input / output interface within processor 1301, used to implement signal input and output to the processor.

[0425] The memory 1303 may be a device having a storage function. For example, it may be a read-only memory (ROM) or other types of static storage devices that can store static information and instructions, a random access memory (RAM) or other types of dynamic storage devices that can store information and instructions, or an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, an optical disc storage (including a compact disc, laser disc, optical disc, digital versatile disc, Blu-ray disc, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited thereto. The memory may exist independently and be connected to the processor via a communication line 1302. The memory may also be integrated with the processor.

[0426] The memory 1303 is used to store computer-executable instructions for executing the solution of the present application, and the execution is controlled by the processor 1301. The processor 1301 is used to execute the computer-executable instructions stored in the memory 1303, thereby implementing the communication method provided in the embodiment of the present application.

[0427] Alternatively, optionally, in an embodiment of the present application, the processor 1301 may also perform processing-related functions in the communication method provided in the following embodiments of the present application, and the communication interface 1304 is responsible for communicating with other devices or communication networks, which is not specifically limited in the embodiments of the present application.

[0428] Optionally, the computer-executable instructions in the embodiments of the present application may also be referred to as application code, which is not specifically limited in the embodiments of the present application.

[0429] In a specific implementation, as an embodiment, the processor 1301 may include one or more CPUs, such as CPU0 and CPU1 in FIG13 .

[0430] In a specific implementation, as an embodiment, the communication device 1300 may include multiple processors, such as the processor 1301 and the processor 1307 in FIG13 . Each of these processors may be a single-core processor or a multi-core processor. The processors here may include, but are not limited to, at least one of the following: a CPU, a microprocessor, a digital signal processor (DSP), a microcontroller unit (MCU), or an artificial intelligence processor, and other types of computing devices that run software. Each computing device may include one or more cores for executing software instructions to perform calculations or processing.

[0431] In a specific implementation, as an embodiment, the communication device 1300 may further include an output device 1305 and an input device 1306. The output device 1305 communicates with the processor 1301 and can display information in a variety of ways. For example, the output device 1305 can be a liquid crystal display (LCD), a light emitting diode (LED) display device, a cathode ray tube (CRT) display device, or a projector. The input device 1306 communicates with the processor 1301 and can receive user input in a variety of ways. For example, the input device 1306 can be a mouse, a keyboard, a touch screen device, or a sensor device.

[0432] The above-mentioned communication device 1300 may sometimes also be referred to as a communication device, which can be a general-purpose device or a dedicated device. For example, the communication device 1300 can be the mobility management network element, the first access network device, the first terminal device, the serving gateway, or a device having a similar structure as shown in Figure 13. The embodiments of the present application do not limit the type of the communication device 1300.

[0433] In addition, the composition structure shown in Figure 13 does not constitute a limitation on the communication device. In addition to the components shown in Figure 13, the communication device 1300 may include more or fewer components than shown in the figure, or combine certain components, or arrange the components differently.

[0434] Optionally, the functions / implementation processes of the transceiver module 1202 and the processing module 1201 in FIG12 may be implemented by the processor 1301 in the communication device 1300 shown in FIG13 calling computer-executable instructions stored in the memory 1303. Alternatively, the functions / implementation processes of the processing module 1201 in FIG12 may be implemented by the processor 1301 in the communication device 1300 shown in FIG13 calling computer-executable instructions stored in the memory 1303, and the functions / implementation processes of the transceiver module 1202 in FIG12 may be implemented by the communication interface 1304 in the communication device 1300 shown in FIG13.

[0435] It should be understood that one or more of the above modules or units can be implemented by software, hardware, or a combination of the two. When any of the above modules or units is implemented in software, the software exists in the form of computer program instructions and is stored in a memory, and a processor can be used to execute the program instructions and implement the above method flow. The processor can be built into an SoC or ASIC, or it can be an independent semiconductor chip. In addition to the core used to execute software instructions to perform calculations or processing within the processor, it can further include necessary hardware accelerators, such as FPGAs, programmable logic devices (PLDs), or logic circuits that implement dedicated logic operations.

[0436] When the above modules or units are implemented in hardware, the hardware can be any one or any combination of a CPU, a microprocessor, a DSP chip, an MCU, an artificial intelligence processor, an ASIC, a SoC, an FPGA, a PLD, a dedicated digital circuit, a hardware accelerator or a non-integrated discrete device, which can run the necessary software or not rely on the software to execute the above method flow.

[0437] Optionally, an embodiment of the present application further provides a communication device (for example, the communication device may be a chip or a chip system), which includes a processor for implementing the method in any of the above method embodiments. In one possible design, the communication device also includes a memory. The memory is used to store necessary program instructions and data, and the processor can call the program code stored in the memory to instruct the communication device to execute the method in any of the above method embodiments. Of course, the memory may not be in the communication device. When the communication device is a chip system, it may be composed of a chip, or it may include a chip and other discrete devices, which is not specifically limited in the embodiment of the present application.

[0438] Optionally, an embodiment of the present application also provides a computer-readable storage medium, which stores a computer program or instruction. When the computer program or instruction is run on a communication device, the communication device can execute the method described in any of the above method embodiments or any of its implementation methods.

[0439] Optionally, an embodiment of the present application further provides a communication system, which includes the network device described in the above method embodiment and the terminal device described in the above method embodiment.

[0440] In the above embodiments, all or part of the embodiments can be implemented by software, hardware, firmware, or any combination thereof. When implemented using a software program, all or part of the embodiments can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions according to the embodiments of the present application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that includes one or more media integrated therein. The available media may be magnetic media (eg, floppy disks, hard disks, magnetic tapes), optical media (eg, DVDs), or semiconductor media (eg, solid state drives (SSDs)).

[0441] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0442] Although the present application has been described with reference to specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the scope of the present application. Accordingly, this specification and the drawings are merely illustrative of the present application as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present application. Obviously, those skilled in the art may make various modifications and variations to the present application without departing from the scope of the present application. Thus, the present application is intended to encompass such modifications and variations as fall within the scope of the claims of the present application and their equivalents.

Claims

1. A communication method, characterized in that, The method includes: A mobility management network element receives a first notification message, where the first notification message is used to indicate receiving downlink data of a first terminal device. When the mobility management network element determines that the communication connection between a first access network device located on a satellite and the first terminal device is unavailable, and the downlink data can be cached in the first access network device, the mobility management network element sends first indication information to the first access network device, where the first indication information is used to indicate caching the downlink data to the first access network device.

2. The method according to claim 1, wherein The mobility management network element determining that the downlink data can be cached in the first access network device includes at least one of the following: The mobility management network element determines that the first access network device supports a first function, and the first function includes a store-and-forward function; or, The mobility management network element determines that the downlink data supports being transmitted through store-and-forward operations.

3. The method according to claim 2, characterized in that The mobility management network element determining that the downlink data supports being transmitted through store-and-forward operations includes: The mobility management network element determines that the downlink data supports being transmitted through store-and-forward operations according to one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device.

4. The method according to any one of claims 1 to 3, characterized in that, The first indication information is carried in a first paging message, and the first paging message is used to request paging the first terminal device.

5. The method according to any one of claims 1-4, characterized in that, The method further includes: The mobility management network element receives a first request message from the first access network device, where the first request message is used to request the mobility management network element to establish a data transmission channel with the first access network device. The mobility management network element sends the downlink data to the first access network device.

6. The method according to any one of claims 1-5, characterized in that, The method further includes: The mobility management network element determines whether the first terminal device is within the coverage range corresponding to the first access network device according to the satellite coverage availability information corresponding to the first access network device and the location information of the first terminal device; where the satellite coverage availability information corresponding to the first access network device includes the mapping relationship between the coverage range corresponding to the first access network device and time. When the first terminal device is within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is available; or, When the first terminal device is not within the coverage range, the mobility management network element determines that the communication connection between the first access network device and the first terminal device is unavailable.

7. The method according to any one of claims 1 to 6, characterized in that, The method further includes: The mobility management network element determines one or more access network devices with available communication connections to the mobility management network element. The mobility management network element determines that among the one or more access network devices, there is no access network device whose current coverage range includes the first terminal device according to the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices; where the satellite coverage information corresponding to the access network device includes the mapping relationship between the coverage range corresponding to the access network device and time. The mobility management network element determines, according to the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that among the one or more access network devices, the access network device whose expected earliest coverage area includes the first terminal device is the first access network device.

8. The method according to claim 6 or 7, characterized in that, The location information of the first terminal device includes one or more of the following: information on the tracking area where the first terminal device is located when entering the idle state, or information on the updated tracking area obtained according to the tracking area update process of the first terminal device.

9. The method according to any one of claims 1-8, characterized in that, The method further includes: In the case where the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends second indication information to the serving gateway, and the second indication information is used to indicate deletion of the downlink data.

10. A communication method, characterized in that, The method includes: The mobility management network element receives a first notification message, and the first notification message is used to indicate receiving downlink data of a first terminal device; The mobility management network element sends a first paging message to one or more access network devices located on a satellite, and the first paging message is used to request paging the first terminal device; The mobility management network element receives a first request message from the first access network device, and the first request message is used to request the mobility management network element to establish a data transmission channel with the first access network device; the one or more access network devices include the first access network device; In the case where the mobility management network element determines, according to the first request message, that the communication connection between the first access network device and the first terminal device is unavailable and the downlink data can be cached in the first access network device, the mobility management network element sends the downlink data to the first access network device.

11. The method according to claim 10, wherein The mobility management network element determines that the downlink data can be cached in the first access network device, including at least one of the following: The mobility management network element determines that the first access network device supports a first function, and the first function includes a store-and-forward function; or, The mobility management network element determines that the downlink data supports transmission through store-and-forward operations.

12. The method according to claim 11, wherein The mobility management network element determines that the downlink data supports transmission through store-and-forward operations, including: The mobility management network element determines, according to one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device, that the downlink data supports transmission through store-and-forward operations.

13. The method according to any one of claims 10 to 12, characterized in that, The mobility management network element determines, according to the first request message, that the communication connection between the first access network device and the first terminal device is unavailable, including: The mobility management network element determines that the first request message includes third indication information, and the third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable; or, The mobility management network element determines that the first request message does not include a service request message, and the service request message is used to indicate that the first terminal device requests to establish a connection with the core network.

14. The method according to any one of claims 10-13, characterized in that, The method further includes: In the case where the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends fourth indication information to the first access network device, and the fourth indication information indicates rejecting the establishment of the data transmission channel.

15. The method according to any one of claims 10-14, characterized in that, The method further includes: In the case where the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends second indication information to the serving gateway, and the second indication information is used to indicate deleting the downlink data.

16. A communication method, characterized in that, The method includes: A first access network device receives a first paging message from a mobility management network element; wherein, the first paging message is used to request paging a first terminal device. In the case where the communication connection between the first access network device and the first terminal device is unavailable, the first access network device sends a first request message to the mobility management network element, and the first request message is used to request the mobility management network element to establish a data transmission channel between the first access network device and the mobility management network element. The first access network device receives and caches the downlink data from the mobility management network element; or, The first access network device receives fourth indication information from the mobility management network element, and the fourth indication information indicates rejecting the establishment of the data transmission channel.

17. The method according to claim 16, characterized in that, The first paging message includes first indication information, and the first indication information is used to indicate that the first access network device caches the downlink data of the first terminal device.

18. The method according to claim 16, wherein The first request message is further used to determine that the communication connection between the first access network device and the first terminal device is unavailable.

19. The method according to claim 18, wherein The first request message includes third indication information, and the third indication information is used to indicate that the communication connection between the first access network device and the first terminal device is unavailable.

20. The method according to any one of claims 16-19, characterized in that, In the case where the first access network device receives and caches the downlink data from the mobility management network element, the method further includes: In the case where the communication connection with the first terminal device is restored, the first access network device sends a second paging message to the first terminal device; the second paging message is used to page the first terminal device. The first access network device receives a radio resource control (RRC) connection request message from the first terminal device. The first access network device sends an RRC connection establishment message to the first terminal device. The first access network device receives an RRC connection establishment completion message from the first terminal device. The first access network device sends the downlink data to the first terminal device.

21. The method according to claim 20, wherein The second paging message includes fifth indication information, and the fifth indication information is used to indicate that the first terminal device receives the downlink data cached in the first access network device.

22. The method according to claim 21, wherein The method further includes: The first access network device determines that the RRC connection request message does not include service request information, and the service request information is used to indicate that the first terminal device requests to establish a connection with the core network.

23. The method according to claim 21, wherein The method further includes: The first access network device determines that the RRC connection request message includes service request information for indicating that the first terminal device requests to establish a connection with the core network; The first access network device discards the service request information.

24. A communication method, characterized in that, The method includes: The first terminal device receives a second paging message from the first access network device; wherein, the second paging message is used to page the first terminal device, and the second paging message includes fifth indication information for indicating that the first terminal device receives downlink data cached in the first access network device; The first terminal device establishes a data transmission connection with the first access network device; The first terminal device receives the downlink data from the first access network device.

25. The method according to claim 24, wherein The data transmission connection includes a Radio Resource Control (RRC) connection. The data transmission connection established between the first terminal device and the first access network device includes: The first terminal device determines, according to the fifth indication information, to generate an RRC connection request message that does not include service request information for indicating that the first terminal device requests to establish a connection with the core network; The first terminal device sends the RRC connection request message to the first access network device; The first terminal device receives an RRC connection establishment message from the first access network device; The first terminal device sends an RRC connection establishment completion message to the first access network device.

26. A communication method, characterized in that, The method includes: The serving gateway obtains downlink data to be transmitted to the first terminal device and determines that the mobility management network element serving the first terminal device is located on a satellite; When the serving gateway determines that the communication connection between the access network device located on the satellite and the first terminal device is unavailable, the serving gateway sends a first notification message to the mobility management network element. The first notification message is used to notify that the downlink data of the first terminal device has arrived; the first notification message includes second request information for requesting the mobility management network element to cache the downlink data.

27. The method according to claim 26, wherein The method further includes: The serving gateway receives a response message from the mobility management network element for the first notification message. The response message is used to instruct the serving gateway to send the downlink data; The serving gateway sends the downlink data to the mobility management network element.

28. The method according to claim 26, wherein The method further includes: The serving gateway receives sixth indication information from the mobility management network element for instructing the serving gateway to delete the downlink data.

29. The method according to any one of claims 26-28, characterized in that, The method further includes: The serving gateway determines one or more access network devices with which the communication connection between the serving gateways is available; The service gateway determines that among the one or more access network devices, there is no access network device whose current coverage area includes the first terminal device, based on the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices; wherein, the satellite coverage information of the access network device includes the mapping relationship between the coverage area corresponding to the access network device and time.

30. The method according to any one of claims 26-29, characterized in that, The service gateway determines that the mobility management network element serving the first terminal device is located on a satellite, including: The service gateway determines that the mobility management network element serving the first terminal device is located on the satellite based on the mapping relationship between the identification information of the satellite and the identification information of the mobility management network element.

31. A communication method, characterized in that, The method includes: The service gateway obtains the downlink data to be transmitted to the first terminal device and determines that the mobility management network element serving the first terminal device is located on a satellite; Based on the satellite coverage availability information corresponding to the mobility management network element, when determining that the communication connection between the service gateway and the mobility management network element is available, the service gateway sends the first notification message to the mobility management network element, where the first notification message is used to notify that the downlink data of the first terminal device has arrived; wherein, the satellite coverage availability information corresponding to the mobility management network element includes the mapping relationship between the coverage area corresponding to the mobility management network element and time.

32. The method according to claim 31, wherein The method further includes: The service gateway receives a response message from the mobility management network element for the first notification message, where the response message is used to instruct the service gateway to send the downlink data; or, The response message includes sixth indication information, where the sixth indication information is used to instruct the service gateway to delete the downlink data.

33. The method according to claim 31 or 32, characterized in that, The service gateway determines that the mobility management network element serving the first terminal device is located on a satellite, including: The service gateway determines that the mobility management network element serving the first terminal device is located on the satellite based on the mapping relationship between the identification information of the satellite and the identification information of the mobility management network element.

34. A communication method, characterized in that, The method is applied to a mobility management network element located on a satellite, and the method includes: The mobility management network element receives a first notification message from the service gateway, where the first notification message is used to notify that the downlink data of the first terminal device has arrived; When the mobility management network element determines that the communication connection between the second access network device located on the satellite and the first terminal device is unavailable and the downlink data can be cached in the mobility management network element, the mobility management network element sends a response message for the first notification message to the service gateway; The mobility management network element receives the downlink data from the service gateway and caches the downlink data until a third paging message is sent to the second access network device, where the third paging message is used to request paging the first terminal device.

35. The method according to claim 34, wherein The first notification message includes second request information, where the second request information is used to request the mobility management network element to cache the downlink data.

36. The method according to claim 34 or 35, characterized in that, The mobility management network element determines that the downlink data can be cached in the mobility management network element, including: The mobility management network element determines that the mobility management network element supports a first function, where the first function includes a store-and-forward function; or, The mobility management network element determines that the downlink data supports being transmitted through store-and-forward operations.

37. The method according to claim 36, wherein The mobility management network element determines that the downlink data supports being transmitted through store-and-forward operations, including: The mobility management network element determines that the downlink data supports being transmitted through store-and-forward operations based on one or more of the following: the subscription information of the first terminal device, the latency requirement of the downlink data, or the context of the first terminal device.

38. The method according to any one of claims 34 - 37, characterized in that, The method further includes: The mobility management network element determines whether the first terminal device is within the coverage area corresponding to the first access network device according to the satellite coverage availability information corresponding to the second access network device and the location information of the first terminal device; where the satellite coverage availability information corresponding to the first access network device includes the mapping relationship between the coverage area corresponding to the first access network device and time; When the first terminal device is within the coverage area, the mobility management network element determines that the communication connection between the second access network device and the first terminal device is available; Or, when the first terminal device is not within the coverage area, the mobility management network element determines that the communication connection between the second access network device and the first terminal device is unavailable.

39. The method according to any one of claims 34-38, characterized in that, The method further includes: The mobility management network element determines one or more access network devices for which the communication connection with the mobility management network element is available; The mobility management network element determines, according to the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that among the one or more access network devices, there is no access network device whose current coverage area includes the first terminal device; where the satellite coverage availability information corresponding to the access network device includes the mapping relationship between the coverage area corresponding to the access network device and time; The mobility management network element determines, according to the location information of the first terminal device and the satellite coverage availability information corresponding to the one or more access network devices, that among the one or more access network devices, the access network device whose earliest expected coverage area includes the first terminal device is the second access network device.

40. The method according to claim 38 or 39, characterized in that, The location information of the first terminal device includes the information of the tracking area where the first terminal device is located when it enters the idle state, or the updated tracking area information obtained according to the tracking area update process of the first terminal device.

41. The method according to any one of claims 34 - 40, characterized in that, Before the mobility management network element receives the downlink data from the serving gateway, the method further includes: The mobility management network element sends a third request message to the serving gateway, where the third request message is used to request the serving gateway to establish a data transmission channel with the mobility management network element; The mobility management network element receives a response message from the serving gateway for the third request message.

42. The method according to any one of claims 34 to 40, characterized in that The method further includes: When the mobility management network element determines that the downlink data cannot be cached in the first access network device, the mobility management network element sends sixth indication information to the serving gateway, and the sixth indication information is used to indicate deletion of the downlink data.

43. A communication device, characterized in that, The communication device includes a module or unit for performing the method according to any one of claims 1-9, 10-15, 16-23, 24-25, 26-30, 31-33, or 34-42.

44. A communication device, characterized in that, The communication device includes: a processor; the processor is configured to execute computer programs or instructions stored in a memory, so that the communication device performs the method according to any one of claims 1-9, 10-15, 16-23, 24-25, 26-30, 31-33, or 34-42.

45. A chip system, characterized in that, Comprising: a processor and an interface circuit; The interface circuit is configured to receive computer execution instructions and transmit them to the processor; The processor is configured to execute the computer execution instructions, so that the communication device performs the method according to any one of claims 1-9, 10-15, 16-23, 24-25, 26-30, 31-33, or 34-42.

46. A computer-readable storage medium, characterized in that, A computer program or instruction is stored thereon, and when the computer program or instruction is executed by a computer, the computer is caused to execute the method according to any one of claims 1-9, 10-15, 16-23, 24-25, 26-30, 31-33, or 34-42.

47. A communication system, characterized in that, The communication system includes a mobility management network element and a first access network device; wherein, the mobility management network element is configured to perform the method according to any one of claims 1-9 or 10-15, and the first access network device is configured to perform the method according to any one of claims 16-23.

48. The communication system according to claim 47, characterized in that, The communication system further includes a first terminal device; the first terminal device is configured to perform the method according to claim 24 or 25.

49. A communication system, characterized in that, The communication system includes a mobility management network element and a serving gateway; wherein, the serving gateway is configured to perform the method according to any one of claims 26-30 or 31-33, and the mobility management network element is configured to perform the method according to any one of claims 34-42.

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