File transmission method based on 5G SBA and satellite-ground collaborative transmission system

Abstract

The present invention belongs to the technical field of satellite communication and terrestrial communication coordinated transmission, and specifically discloses a file transmission method based on 5G SBA and a satellite-ground coordinated transmission system. The method obtains the Http video stream file request initiated by the user, and the VNF in the MEC server receives the file request instruction and parses it; the VNF controls the MEC server to obtain the file list from the source and parse it. The MEC server establishes multiple parallel TCP connections with the source site and downloads the file fragments according to the content of the file list, and caches them locally; if the file fragment requested by the user is already stored in the MEC server, the file fragment will be immediately provided to the user; otherwise, the VNF forwards the content request to the source site and retrieves it. The technical solution is adopted, satellite communication is used as the backhaul of the 5G network, and VNF technology is introduced in the edge test MEC server of the network architecture, which effectively alleviates the high delay and insufficient coverage faced by global video live broadcast.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite communication and terrestrial communication coordinated transmission, and relates to a file transmission method based on 5G SBA and a satellite-ground coordinated transmission system. Background Art

[0002] In recent years, with the gradual promotion of 5G networks around the world, live streaming based on HTTP (Hyper Text Transfer Protocol) has become more and more popular, and more and more users have begun to generate 4K live streaming through social media such as TikTok, Facebook, and YouTube. These applications require faster and smoother data transmission to support a better immersive experience.

[0003] Currently, most video streaming applications, such as MPEG-DASH or Apple HTTP Live Streaming - HLS, follow the Hypertext Transfer Protocol (HTTP), which divides the video sequence into multiple segments and transmits them in the format of sequence files as required. Usually, such files are transmitted through the TCP (Transmission Control Protocol) underlying protocol.

[0004] According to the traditional technical solution, video streaming files are transmitted through unicast serial transmission. However, in recent years, with the development of 5G edge side, users can pre-extract the requested hot streaming media content from the video source through the parallel transmission control protocol, and pre-load the content with the help of the cache function on the edge side to ensure the user's QoE. Considering that the live broadcast destination users may be distributed in other parts of the world far away from the live broadcast source, the conventional terrestrial communication means can no longer meet the needs of the cross-ocean / continental live broadcast industry in terms of latency.

[0005] In view of the rapid development of low-orbit satellite Internet in recent years, it is considered that low-orbit satellite communications can be used as a backhaul network with the characteristics of low latency and wide coverage to achieve efficient distribution of streaming media content. It is also considered that the slow start and retransmission mechanism of the TCP transmission protocol are not suitable for satellite high-dynamic packet data transmission. Therefore, there is an urgent need for a mechanism that can make up for the defects of TCP transmission in the satellite-ground collaborative network. In addition, the 5G service-based architecture (SBA) has been standardized, which will help the new context-aware content solution adopted in the present invention and use satellite links to provide QoE guarantees to users in the live broadcast industry. Summary of the invention

[0006] The purpose of the present invention is to provide a file transmission method based on 5G SBA and a satellite-ground coordinated transmission system, which can effectively alleviate the problems of high delay and insufficient coverage during global video live broadcast.

[0007] In order to achieve the above object, the basic scheme of the present invention is: a file transmission method based on 5G SBA, comprising the following steps:

[0008] Obtaining a request for an Http video streaming file initiated by a user, the work scope covers the VNF in the MEC server of the user receiving the file request instruction and parsing the request;

[0009] The VNF acts as a reverse file proxy, controlling the MEC server to obtain the file list from the source and parse it;

[0010] According to the contents of the file list, the MEC server establishes multiple parallel TCP connections with the source site and downloads the file segments, which are then cached locally;

[0011] If the file segment requested by the user is already stored in the MEC server, the file segment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it.

[0012] The working principle and beneficial effects of this basic solution are as follows: This solution uses satellite communication as the backhaul of the 5G network and introduces VNF technology in the edge MEC server of the network architecture as a relay resource pool in the transmission path of video content from the source site to the user.

[0013] Using low-orbit satellite communications as the backhaul can effectively alleviate the high latency and insufficient coverage faced by global video live broadcasts. The use of VNF combined with MEC server technology can effectively alleviate the heavy load pressure on satellite links caused by repeated requests for the same video stream during the transmission process, thereby saving bandwidth for satellite links and effectively supporting 4K video streaming live broadcast services with QoE guarantees.

[0014] Furthermore, the VNF performs context awareness based on the file fragments distributed to the user and instructs the MEC server to search and preload subsequent files at the source site.

[0015] By adopting context-aware instantaneous content holding technology, continuous distribution of data from the source to the destination is achieved.

[0016] Furthermore, the MEC server acts as a processing forwarder to split the end-to-end content transmission path into RAN and satellite backhaul network, using low-orbit satellite communication as the backhaul.

[0017] This reduces the initial startup delay problem faced by the TCP protocol and also provides better content delivery performance.

[0018] Furthermore, each MEC server monitors the real-time live service sessions of all clients within its coverage area, and the MEC server aggregates all session requests for the same live data stream within its coverage area;

[0019] The core UPF (UPF in the 5G core network) monitors the popularity of its live video stream and dynamically adjusts the transmission strategy of the live stream from the source server to the user-side MEC server; if the video content is popular, the ground gateway instructs the satellite to use the multicast protocol to distribute the video stream file to multiple MEC servers;

[0020] If the popularity of the video stream decreases, the core UPF can perform a switch from the multicast protocol to the unicast protocol for data transmission from the source to the user-side MEC server.

[0021] The structure is simple and easy to use.

[0022] The present invention also provides a 5G SBA satellite-to-ground coordinated transmission system based on the method of the present invention, comprising a user, a user-side MEC server and a satellite, wherein the satellite channel is used as a backhaul link, the user utilizes partially virtualized computing and storage resources of the MEC server, and containerizes and deploys VNF to perform caching and transient segment content storage operations, and the user's signal output end is connected to the input end of the MEC server;

[0023] The VNF in the MEC server receives and parses the file request instructions initiated by the user; the VNF acts as a reverse file proxy, controlling the MEC server to obtain the file list from the source and parse it; the VNF controls the MEC server to download the file fragments from the source site according to the content of the file list and cache them locally; if the file fragment requested by the user is already stored in the MEC server, the file fragment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it.

[0024] The system combines the SBA-based 5G core network and satellite backhaul to support live streaming applications, expand communication coverage, and reduce the data transmission delay of live streaming. Compared with existing transmission methods, it is more conducive to global data sharing of live streaming services. VNF technology is introduced in the edge MEC server of the network architecture as a relay resource pool in the transmission path of video content from the source site to the user, enabling users to deploy their own VNFs on the MEC server at the 5G mobile edge, which can not only perform content operations such as instantaneous time holding, but also realize multicast at the application layer. By adopting context-aware instantaneous time content holding technology, continuous distribution of data from the source to the destination is achieved, ensuring the quality of user video streaming content reception.

[0025] Furthermore, the 5G mobile network operator leases satellite channels from the satellite network operator as backhaul links, and the 5G mobile network operator controls the MEC server, which is used by the 5G mobile network operator to provide mobility services;

[0026] The 5G mobile network operator includes a terrestrial core network, a terrestrial bearer network and a wireless access network, and the terrestrial bearer network is used to connect the terrestrial core network and the wireless access network.

[0027] 5G mobile network operators can provide mobility services including core network access and mobility management functions, session management, user layer functions, authentication services, policy control functions, unified data services, application functions and data network functions.

[0028] Further, the ground core network includes PCF network elements, SMF network elements, AF network elements, NEF network elements and AMF network elements, and the PCF network element converts instructions in other control plane network elements into instructions that can be interpreted by the VNF corresponding to the user;

[0029] The SMF network element receives the transmission strategy from the PCF network element and passes it to the VNF for execution by the VNF; the SMF network element processes the context-aware information update and monitoring feedback from the VNF and sends it to the AF network element to facilitate the update of the strategy;

[0030] The AF network element provides context information for identifying the video stream of each video content provider to the 5G mobile network operator; the AF network element processes the context information monitoring report uploaded by the MEC server through the SMF network element, and can adjust the video content operation. The AF network element sends the updated transmission strategy to the PCF network element, and the PCF network element reformats the transmission strategy and sends it to the SMF network element for transmission and execution;

[0031] The NEF network element connects the AF network element and other control plane network elements, and the AMF network element controls the authentication, authorization and user mobility management of the plane.

[0032] The control plane is composed of network elements for easy operation.

[0033] Further, the wireless access network includes RAN equipment, edge MEC server and edge UPF network element;

[0034] The RAN equipment includes equipment including a base station system, which is used for access by terminal users;

[0035] The edge MEC server is used for localized service deployment and is close to service deployment based on traditional data centers, data forwarding, network connection, and third-party virtual service support;

[0036] The edge UPF network element is used to respond to the request of the SMF network element, connect the RAN equipment and the external data network, perform protocol encapsulation and decapsulation, packet routing and forwarding, data packet inspection and QoS Flow mapping, and complete the implementation of user plane gating, redirection, and traffic steering policy rules.

[0037] The structure is simple and easy to use.

[0038] Furthermore, the content provided by the user depends on the real-time original information generated in the terminal device, and the original information is uploaded to the cloud service center via RTMP;

[0039] The cloud service center encodes the original information and compresses it into multiple real-time RTSP streams at different bit rates in real time;

[0040] According to the underlying transport protocol, each RTSP stream is periodically packaged into a series of file segments, and its information is stored in a regularly updated manifest file.

[0041] The operation is simple and convenient for data transmission.

[0042] Furthermore, the satellite network operator includes a satellite gateway, a satellite terminal, a network control center and a network management center;

[0043] The satellite gateway and the satellite terminal are interconnected via one or more channels of the satellite, the satellite gateway uses a variety of network topologies, and one satellite gateway can provide access to satellite terminal groups in different logical groups;

[0044] The network control center provides real-time control of the satellite network, and the network management center is used to manage system elements of the satellite network.

[0045] Satellite network operators can maintain, manage, deploy and operate satellite platforms through various devices, which facilitates their use. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a structural schematic diagram of the file transmission method based on 5G SBA of the present invention;

[0047] Figure 2 It is a structural schematic diagram of user content generation of the file transmission method based on 5G SBA of the present invention;

[0048] Figure 3 It is a schematic diagram of the video stream request process session structure of the file transmission method based on 5G SBA of the present invention. DETAILED DESCRIPTION

[0049] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0050] In the description of the present invention, it is necessary to understand that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0051] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0052] The present invention discloses a file transmission method based on 5G SBA, and proposes a satellite-ground network collaborative transmission architecture based on 5G SBA. The architecture uses satellite communication as the backhaul of the 5G network. Considering the high-speed and low-latency transmission required in the real-time live broadcast application scenario, the equipment involved in the satellite-ground collaborative network is diversified, and the network is heterogeneous and complex. VNF technology is introduced in the edge MEC server of the network architecture as a relay resource pool in the transmission path of video content from the source site to the user, and the continuous distribution of data from the source end to the destination side is realized by adopting the instantaneous content holding technology based on context perception. VNF technology separates network functions from proprietary hardware, so that these functions can be run in general commercial servers, switches and storage units, and operators do not have to install new proprietary equipment in the network.

[0053] Compared with the existing technology, the use of low-orbit satellite communication as the backhaul can effectively alleviate the high latency and insufficient coverage faced by global video live broadcast. The use of VNF (virtualized network functions) can realize the functions that can be implemented on physical devices in the form of software. Combined with MEC (multi-access edge computing) technology, it can effectively alleviate the heavy load pressure on the satellite link caused by repeated requests for the same video stream during the transmission process, thereby saving bandwidth for the satellite link. The architecture and method can effectively support 4K video streaming live broadcast services with QoE guarantees.

[0054] like Figure 1 As shown, the file transmission method based on 5G SBA includes the following steps:

[0055] Obtain file requests initiated by users (such as requests for HTTP video streaming files. HTTP file encapsulation and disassembly will become more flexible, simple and fast, and HTTP allows the transmission of any type of data objects, which is conducive to reducing the processing delay of streaming media files on the server). The work scope covers the VNF in the MEC server of the user receiving the file request instruction and parsing the request (specifically, the parsing method of the HTTP protocol can be used); usually, the MEC server is located near the user to ensure low latency during access; the MEC server, as a processing forwarder, divides the transmission path of the end-to-end (E2E) content into RAN and satellite backhaul networks, and uses low-orbit satellite communication as the backhaul, which reduces the initial startup delay problem faced by the TCP protocol and also improves better content delivery performance;

[0056] VNF acts as a reverse file proxy, controlling the MEC server to obtain and parse the file list from the source (the content on the file list is HTTP protocol, which may be just general text. After the MEC server obtains the text list, it indexes the corresponding content on the list to the source according to the list, which can be specifically parsed using the HTTP protocol).

[0057] The MEC server establishes multiple parallel TCP connections with the source site according to the file list content and downloads the file fragments and caches them locally. The VNF performs context awareness based on the file fragments distributed to the user, predicts the subsequent file information required by the client, and instructs the MEC server to search and preload the subsequent files at the source site.

[0058] If the file segment requested by the user is already stored in the MEC server, the file segment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it.

[0059] In a preferred embodiment of the present invention, each MEC server monitors the real-time live service sessions (real-time QoE status, such as buffering and video quality, etc.) of all clients under its coverage, and the MEC server performs necessary content operations, such as instantaneous time period holding, etc., so as to provide customized, context-aware QoE guarantees for each user and each session. At the same time, the MEC server can execute transport layer performance enhancement technology to strengthen the QoE guarantee of the application layer. The MEC server aggregates all session requests for the same live data stream under its coverage. Within the coverage of the same MEC server, no matter how many sessions request the same video stream, application layer multicast can be achieved by establishing a stream dialogue between the MEC server and the content source.

[0060] The core UPF monitors the popularity of its live video stream and dynamically adjusts the transmission strategy of the live stream from the source server to the user-side MEC server; if the video content is popular, the ground gateway instructs the satellite to use the multicast protocol to distribute the video stream file to multiple MEC servers. For example, if the core UPF detects that the live video stream is popular in multiple distributed MEC servers, the core UPF can decide that the source uses a multicast protocol, such as the FLUTE protocol, to broadcast the video stream file to multiple MEC servers. If the popularity of the video stream decreases, the core UPF can switch from the multicast protocol to the unicast protocol for data transmission from the source to the user-side MEC server.

[0061] The present invention also provides a 5G SBA satellite-ground collaborative transmission system based on the method of the present invention, including users (i.e., video content providers, Video Content Provider, VCP), user-side MEC servers and satellites, and users include mobile devices such as mobile phones and laptops. The satellite channel is used as a backhaul link, and the satellite backhaul includes a satellite, a satellite link and a ground gateway. The user utilizes the partially virtualized computing and storage resources of the MEC server, and deploys VNF in a containerized manner to perform caching and transient segment content preservation operations, and the user's signal output end is connected to the input end of the MEC server. MEC is generally deployed not far from the end user, where the terminal can be wirelessly covered.

[0062] The VNF in the MEC server receives and parses the file request instructions initiated by the user; the VNF acts as a reverse file proxy, controlling the MEC server to obtain the file list from the source and parse it; the VNF controls the MEC server to download the file fragments from the source site according to the content of the file list and cache them locally; if the file fragment requested by the user is already stored in the MEC server, the file fragment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it.

[0063] In a preferred embodiment of the present invention, a 5G mobile network operator (MNO) rents a satellite channel from a satellite network operator (SNO) as a backhaul link, and the 5G mobile network operator controls the MEC server, which is used by the 5G mobile network operator to provide mobility services. The 5G MNO virtualizes its computing and storage resources and rents them to VCPs, which can deploy virtualized network functions (VNFs) in multi-access edge computing (MEC) servers. The SNO rents its satellite channel bandwidth resources to the 5G MNO, facilitating its use of standard terrestrial backhaul links and using satellite networks as backhaul links.

[0064] More preferably, the 5G mobile network operator includes a terrestrial core network (CN), a terrestrial bearer network and a wireless access network. The terrestrial core network adopts the mechanism of separating the user plane and the control plane in the 5G standard. The terrestrial bearer network is used to connect the terrestrial core network and the wireless access network and is responsible for data transmission. The structure of the terrestrial bearer network itself includes fronthaul, midhaul and backhaul networks. 5G mobile network operators can provide mobility service content including core network access and mobility management functions, session management, user layer functions, authentication services, policy control functions, unified data services, application functions and data network functions.

[0065] The ground core network includes PCF (Policy Control Function) network elements, SMF (Session Management Function) network elements, AF (Application Function) network elements, NEF (Network Open Function) network elements and AMF (Mobility Management Function) network elements. The PCF network element converts the instructions in other control plane network elements (such as SMF network elements and AF network elements) into instructions that can be interpreted by the user's corresponding VNF. All network elements communicate through bus connections. Most control plane network elements are operated by MNOs, but AF network elements are usually controlled by third parties, such as CPs.

[0066] The SMF network element receives the transmission policy from the PCF network element and passes it to the VNF for execution; the SMF network element processes the context-aware information update and monitoring feedback from the VNF and sends it to the AF network element to facilitate the update of its policy (the workflow within the 5G core network).

[0067] The AF network element provides 5G mobile network operators with context information that identifies the video stream of each video content provider, including the target IP address and port number. The AF network element processes the context information monitoring report uploaded by the MEC server through the SMF network element, and can adjust the video content operation (such as caching or fragment preservation, etc.). The AF network element sends the updated transmission strategy to the PCF network element, and the PCF network element reformats the transmission strategy and sends it to the SMF network element for transmission and execution.

[0068] The NEF network element connects the AF network element with other control plane network elements, and the AMF network element controls the authentication, authorization and user mobility management of the control plane.

[0069] In a preferred embodiment of the present invention, the wireless access network includes RAN (Radio Access Network) equipment, edge MEC servers and edge UPF network elements, and the RAN equipment includes equipment including a base station system for access by terminal users.

[0070] Edge MEC server refers to an IT resource pool device built on a miniaturized hardware platform that provides resources including computing, memory, storage, and network. It is used for localized business deployment and is close to business deployment based on traditional data centers. It has functions such as data forwarding, network connection, and third-party virtual business support.

[0071] The edge UPF network element (User-Plane Function, usually running on the MEC server) is used to respond to the request of the SMF network element, connect the RAN equipment and the external data network, perform protocol encapsulation and decapsulation, packet routing and forwarding, data packet inspection and QoS Flow mapping, and implement policy rules such as user plane gating, redirection, and traffic steering.

[0072] In a preferred embodiment of the present invention, Figure 2 and Figure 3 As shown, the content provided by the user depends on the real-time original information generated in the terminal device (the real-time video original information generated by the APP downloaded in the terminal device, such as Tik Tok, Facebook, YouTube, etc.), and the original information is uploaded to the cloud service center through RTMP (Real-Time Messaging Protocol).

[0073] The cloud service center encodes the original information and compresses it into multiple real-time RTSP (Real-Time Streaming Protocol) streams in real time at different bit rates (the size specified in the RTSP real-time streaming protocol). According to the underlying transport protocol (such as HLS / DASH), each RTSP stream is periodically packaged into a series of file fragments, and its information is stored in a regularly updated manifest file.

[0074] In a preferred embodiment of the present invention, the satellite network operator includes a satellite gateway (Satellite Gateway, SG), a satellite terminal (Satellite Terminal, ST, i.e., a satellite ground station), a network control center (Network Control Center, NCC) and a network management center (Network Manage Center, NMC).

[0075] Satellite gateways and satellite terminals are interconnected through one or more channels of the satellite. Satellite gateways use a variety of network topologies (such as star, multi-star, mesh hybrid star, etc.). A satellite gateway can provide access to satellite terminal groups in different logical groups.

[0076] The network control center provides real-time control of the satellite network (such as connection control, including the signaling required to establish, supervise and release connections), and the network management center is used to manage the system elements of the satellite network (such as configuration, fault, performance and security management).

[0077] This solution introduces context-aware HTTP video stream instant content holding and caching technology. The node is located between the RAN and the backhaul network and can be implemented through the VNF in the MEC server. The MEC will periodically publish a sequence request list based on user needs. The list contains the latest information about the availability of segments on the real-time video source. Because the MEC obtains multiple video segments of a certain user, the terminal will mistakenly believe that there is a large amount of cached content in the MEC and will not request upward. At this time, the MEC can simultaneously process instructions from other users requesting the same video, and can simultaneously download subsequent multiple video segments through the parallel TCP protocol to ensure that users receive real-time high-quality video frames.

[0078] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0079] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A file transmission method based on 5G SBA, characterized in that: The steps include: Obtaining a request for an Http video streaming file initiated by a user, the work scope covers the VNF in the MEC server of the user receiving the file request instruction and parsing the request; The VNF acts as a reverse file proxy, controlling the MEC server to obtain the file list from the source and parse it; According to the contents of the file list, the MEC server establishes multiple parallel TCP connections with the source site and downloads the file segments, which are then cached locally; If the file segment requested by the user is already stored in the MEC server, the file segment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it; Each MEC server monitors the real-time live service sessions of all clients within its coverage area, and the MEC server aggregates all session requests for the same live data stream within its coverage area; The core UPF monitors the popularity of its live video stream and dynamically adjusts the transmission strategy of the live stream from the source server to the user-side MEC server. If the video content is popular, the ground gateway instructs the satellite to use the multicast protocol to distribute the video stream file to multiple MEC servers. If the popularity of the video stream decreases, the core UPF can perform a switch from the multicast protocol to the unicast protocol for data transmission from the source to the user-side MEC server.

2. The file transmission method based on 5G SBA as claimed in claim 1, characterized in that: VNF performs context awareness based on the file fragments distributed to the user and instructs the MEC server to search and preload subsequent files at the source site.

3. The file transmission method based on 5G SBA as claimed in claim 1, characterized in that: The MEC server acts as a processing forwarder to split the end-to-end content transmission path into RAN and satellite backhaul network, using low-orbit satellite communications as the backhaul.

4. A satellite-to-ground coordinated transmission system based on the method according to any one of claims 1 to 3, characterized in that: It includes users, user-side MEC servers and satellites. The satellite channel is used as a backhaul link. Users use some virtualized computing and storage resources of the MEC server and deploy VNFs in a containerized manner to perform cache and transient segment content storage operations. The user's signal output end is connected to the input end of the MEC server. The VNF in the MEC server receives and parses the file request instruction initiated by the user; The VNF acts as a reverse file proxy, controlling the MEC server to obtain the file list from the source and parse it; The VNF controls the MEC server to download file fragments from the source site according to the file list content and cache them locally; If the file segment requested by the user is already stored in the MEC server, the file segment will be provided to the user immediately; otherwise, the VNF forwards the content request to the source site and retrieves it.

5. The satellite-to-ground coordinated transmission system according to claim 4, characterized in that: 5G mobile network operators lease satellite channels from satellite network operators as backhaul links. 5G mobile network operators control MEC servers, which are used by 5G mobile network operators to provide mobility services. The 5G mobile network operator includes a terrestrial core network, a terrestrial bearer network and a wireless access network, and the terrestrial bearer network is used to connect the terrestrial core network and the wireless access network.

6. The satellite-to-ground coordinated transmission system according to claim 5, characterized in that: The ground core network includes PCF network elements, SMF network elements, AF network elements, NEF network elements and AMF network elements. The PCF network element converts instructions in other control plane network elements into instructions that can be interpreted by the VNF corresponding to the user; The SMF network element receives the transmission strategy from the PCF network element and passes it to the VNF for execution by the VNF; the SMF network element processes the context-aware information update and monitoring feedback from the VNF and sends it to the AF network element to facilitate the update of the strategy; The AF network element provides context information identifying the video stream of each video content provider to the 5G mobile network operator; The AF network element processes the context information monitoring report uploaded by the MEC server through the SMF network element and can adjust the video content operation. The AF network element sends the updated transmission strategy to the PCF network element, and the PCF network element reformats the transmission strategy and sends it to the SMF network element for transmission and execution; The NEF network element connects the AF network element and other control plane network elements, and the AMF network element controls the authentication, authorization and user mobility management of the plane.

7. The satellite-to-ground coordinated transmission system according to claim 5, characterized in that: The wireless access network includes RAN equipment, edge MEC server and edge UPF network element; The RAN equipment includes equipment including a base station system, which is used for access by terminal users; The edge MEC server is used for localized service deployment and is close to service deployment based on traditional data centers, data forwarding, network connection, and third-party virtual service support; The edge UPF network element is used to respond to the request of the SMF network element, connect the RAN equipment and the external data network, perform protocol encapsulation and decapsulation, packet routing and forwarding, data packet inspection and QoS Flow mapping, and complete the implementation of user plane gating, redirection, and traffic steering policy rules.

8. The satellite-to-ground coordinated transmission system according to claim 4, characterized in that: The content provided by the user depends on the real-time original information generated in the terminal device, and the original information is uploaded to the cloud service center via RTMP; The cloud service center encodes the original information and compresses it into multiple real-time RTSP streams at different bit rates in real time; According to the underlying transport protocol, each RTSP stream is periodically packaged into a series of file segments, and its information is stored in a regularly updated manifest file.

9. The satellite-to-ground coordinated transmission system according to claim 5, characterized in that: The satellite network operator includes satellite gateways, satellite terminals, network control centers and network management centers; The satellite gateway and the satellite terminals are interconnected via one or more channels of the satellite, and a satellite gateway provides access to satellite terminal groups in different logical groups; The network control center provides real-time control of the satellite network, and the network management center is used to manage system elements of the satellite network.

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