CN117200859A - Reliable data distribution method based on segment confirmation mechanism in star-ground fusion network - Google Patents

Abstract

The invention provides a reliable data distribution method based on a segment confirmation mechanism in a satellite-ground fusion network, and belongs to the field of satellite mobile communication. The invention designs a reliable GTP-U module by adding an expansion function module in a GTP-U tunnel protocol module of a satellite-borne gNB and UPF. By expanding the GTP-U tunnel protocol, the buffer, timeout retransmission and confirmation mechanism of the mobile service data message are realized, so that the mobile service can monitor the receiving state of the data message on the physical link of satellite communication in real time in a segmented manner, and the packet loss and retransmission can be rapidly found by taking the link section as granularity, thereby greatly improving the bandwidth utilization rate of the satellite communication.

Description

Reliable data distribution method based on segment confirmation mechanism in star-ground fusion network

Technical Field

The invention belongs to the field of satellite mobile communication, and particularly relates to a reliable data distribution method based on a segment confirmation mechanism in a satellite-ground fusion network.

Background

The satellite mobile communication network and the ground mobile communication network have achieved splendid achievement through more than 30 years of independent development, but have respective limitations. The satellite mobile communication network can realize global all-weather coverage, but is relatively closed, and the construction and operation costs are high; the ground mobile communication system has high standardization degree and developed global industry chain, but has limited globalization coverage capacity, and only covers less than 6% of the earth surface area at present. With the appearance of new application scenes and diversity services, the situation that a satellite network and a ground network are independently developed is broken, and the deep fusion and the complementary advantages of the satellite network are realized.

The international standardization organization and related alliance have conducted preliminary exploration of star-to-ground converged network architecture designs and key technologies, but some significant technical challenges still remain. One of the hot topics is how to meet the service quality requirements of various mobile services under the condition of long-time delay and high-error code link of satellites. When the service data passes through the satellite link, a TCP end-to-end retransmission mechanism with good performance in the ground network can cause serious performance degradation due to overlarge RTT (Round Trip Time). Existing research has added PEP nodes (Protocol Enhancing Proxy, protocol enhanced proxy) between the satellite and the earth to perform TCP spoofing, dividing an end-to-end TCP connection into several segments of TCP connections. However, this approach is not applicable to a star-to-ground converged network for the following reasons: 1) The ground mobile communication system (such as 5G) uses a GTP-U (GPRS Tunneling Protocol-User Plane) tunnel to realize an N3 interface between a base station and a UPF (User Plane Function ) network element and an N9/N19 interface between UPFs, user data (including TCP messages) are encapsulated in a GTP-U packet, and an intermediate node of the GTP-U tunnel cannot see an inner TCP message; 2) If the inner layer TCP message is required to be analyzed in the GTP-U tunnel, the processing complexity is greatly increased, and potential safety hazards exist.

GTP-U uses the UDP protocol at the transport layer, whereas UDP has no mechanism to acknowledge retransmissions. In the ground network, the problem of performance does not exist, and because the ground network has good link quality and low time delay, the TCP retransmission mechanism of the end node can also be utilized to obtain good performance. However, if the GTP-U protocol is used directly on-board, there is a problem in that TCP performance is degraded under the condition of long RTT.

In order to realize satellite-ground fusion by using the technical standard of a ground mobile communication system, the GTP-U protocol needs to be modified, a confirmation retransmission mechanism is added, reliable transmission of inter-satellite and satellite-ground segment confirmation retransmission is realized, and the performance problem of TCP end-to-end retransmission is solved.

In view of the above analysis, it is necessary to implement a reliable satellite transmission mechanism based on GTP-U to satisfy the quality of service guarantee of diverse services in a star-earth fusion network.

Disclosure of Invention

In order to meet the service quality requirement of mobile service in a satellite communication network, the invention provides a reliable data distribution method based on a segment confirmation mechanism in a star-ground fusion network. The method can realize reliable data distribution based on a segment confirmation mechanism under the scene of combining the satellite with the ground mobile communication system.

The invention adopts the technical scheme that:

a reliable data distribution method based on a segment confirmation mechanism in a star-ground fusion network comprises the following steps:

step 1: according to the planned network topology of the satellite mobile communication system, starting a reliable GTP-U expansion function for gNB and UPF needing reliable tunneling during network deployment;

step 2: judging whether to initiate reliable tunnel transmission according to the data conditions received by gNB and UPF, if so, turning to step 3, otherwise, continuing to receive data, and repeating step 2;

step 3: the gNB or UPF is used as a GTP-U reliable transmission sending end, when the GTP-U/UDP/IP protocol head is packaged, a PDU session container type extension head used for carrying QoS flow identification is constructed, a reliable GTP-U container extension head is constructed and used for carrying reliable transmission information of a data packet, then the data packet is cached into a service flow retransmission queue of the corresponding QoS flow identification, a retransmission timeout timer is started, if the timer expires and ACK acknowledgement information is not received, the data packet is retransmitted, if the ACK acknowledgement information is received, the retransmission timer is stopped for the data packet which is confirmed to be received, and the data packet is deleted from the service flow retransmission queue; in the data packet transmission process, gNB or UPF detects whether the reliable GTP-U container extension head has a newly defined reliable GTP-U container, if so, the GTP-U data packet carrying the selection ACK information is replied, and the GTP-U sending end is informed of which data packets have been received.

Further, in step 2, it is determined whether to initiate reliable tunnel transmission, which is classified into the following three cases:

1) For the uplink data packet sent by the user terminal is received by the gNB air interface, if the gNB has enabled the reliable GTP-U expansion function, the QoS of the service flow is determined through a packet filtering rule, and if the reliability is required, the gNB initiates the reliable transmission of the tunnel;

2) For the N6 interface of UPF to receive the downlink data packet from DN network, if UPF has enabled reliable GTP-U expansion function, determining the QoS of service flow through packet filtering rule, if there is a requirement for reliability, UPF initiates reliable transmission of tunnel;

3) For a GTP-U data packet received by the UPF at an N9/N19 interface, if the UPF enables a reliable GTP-U expansion function, detecting whether a GTP-U expansion head has a newly defined reliable GTP-U container, and if so, initiating the tunnel reliable transmission of a new section of satellite link again after the reliable transmission of a previous section of satellite link is terminated by the UPF; otherwise, after stripping off GTP-U/UDP/IP protocol head, UPF determines whether QoS of the service flow has requirement for reliability through packet filtering rule, if so, UPF initiates reliable transmission of tunnel.

Further, in step 3, the specific manner of replying the GTP-U packet carrying the selective ACK information is:

setting a selective ACK delay transmission time, and checking whether a selective ACK packet needs to be transmitted or not at intervals of the delay transmission time through a fixed timer; when the selective ACK packet needs to be sent, if the receiving end has QoS stream data packets with the same QoS stream identification to be sent, the selective ACK information needing to be sent is carried on the sending data packet, otherwise, the GTP-U data packet only carrying the selective ACK information is sent independently.

The invention has the beneficial effects that:

1. the invention designs a reliable GTP-U module by adding an expansion function module in a GTP-U tunnel protocol module of a satellite-borne gNB and UPF. By expanding the GTP-U tunnel protocol, the buffer, timeout retransmission and confirmation mechanism of the mobile service data message are realized, so that the mobile service can monitor the receiving state of the data message in real time and sectionally on the physical links (the satellite-to-ground link GSL and the inter-satellite link ISL) of satellite communication, and quickly find out and retransmit the lost packet with the link section as granularity. Reliable route forwarding based on segmentation on the satellite greatly improves the utilization rate of satellite communication bandwidth.

2. The present invention allows for backward compatibility without enabling a reliable GTP-U module when traffic data is transmitted entirely over the terrestrial network in order to reduce processing overhead. Using a switch to enable reliable GTP-U functionality, closing the extended functionality for the case of full use of terrestrial network transmissions; and for a satellite mobile communication system using satellite segment links, the reliable GTP-U expansion function can be started according to the network topology planning on gNB and UPF which need reliable transmission for the physical links of satellite communication. By supporting the selectivity of reliable GTP-U function switching, the flexibility of network deployment can be greatly increased.

3. The data flows with diversified mobile services correspond to different QoS requirements. Route forwarding for QoS guarantees is typically based on predefined policies from different dimensions (e.g., user level, traffic type, traffic content, etc.). Therefore, reliable transmission on the satellite supported by the satellite mobile communication system also needs to consider service awareness, namely, the satellite-borne gNB and UPF only perform reliable route forwarding on service flows with reliability requirements. On one hand, the gNB can sense the service QoS, and on the other hand, the gNB can dynamically determine whether to carry out on-board reliable transmission on the service flow according to the result of service QoS sensing on the uplink data flow sent from the user terminal, and on the other hand, the UPF supports 3/4/7 layer service identification, and on the other hand, the gNB can dynamically determine whether to carry out on-board reliable transmission on the service flow according to the service QoS result obtained after the UPF carries out service identification on the downlink data flow sent from the DN side. In this way, the satellite mobile communications system can provide service aware on-board reliable route forwarding.

Drawings

Fig. 1 is a schematic diagram of an application scenario of a satellite mobile communication system based on an acknowledgement mechanism.

Fig. 2 is a schematic diagram of an acknowledgment mechanism extension protocol message definition based on GTP-U.

Detailed Description

The current 3GPP standard satellite mobile communication system architecture has proposed that a base station gNB performs star-up and UPF performs star-up, an N3 interface between gNB and UPF and an N9/N19 interface between UPF perform encapsulation and bearing of mobile service original Data messages by adopting GTP-U tunnel protocol, thereby shielding user terminals IP and DN (Data Network) service IP and providing a unified route forwarding entry for the satellite mobile service Data messages. However, neither the GTP-U nor the underlying UDP or IP protocols provide any reliable transmission guarantee, and no retransmission of lost packets is performed. If the transmission of the encapsulated original data message is a protocol for connection-oriented reliable transmission, such as TCP, the retransmission of the lost packet can be performed only at the end node. For mobile service data messages, performance problems are caused in long-distance satellite-to-ground transmission, namely, the end-to-end reliable transmission perception is too slow, TCP congestion control is easy to deteriorate because the satellite communication network loses packets more seriously than the ground mobile communication network, a large number of end-to-end retransmission causes the transmission window to be basically in stagnation, and the transmission performance is poor.

Therefore, based on the urgent need of satellite reliable transmission capability of satellite mobile communication system to improve end-to-end service performance, the invention designs a reliable GTP-U module by adding an extended function module in GTP-U tunneling protocol modules of satellite gNB and UPF. By expanding the GTP-U tunnel protocol, the buffer, timeout retransmission and confirmation mechanism of the mobile service data message are realized, so that the mobile service can monitor the receiving state of the data message in real time and sectionally on the physical links (the satellite-to-ground link GSL and the inter-satellite link ISL) of satellite communication, and quickly find out and retransmit the lost packet with the link section as granularity. Reliable route forwarding based on segmentation on the satellite greatly improves the utilization rate of satellite communication bandwidth.

In view of backward compatibility, there is no need to enable a reliable GTP-U module when traffic data is transmitted entirely over the terrestrial network in order to reduce processing overhead. Using a switch to enable reliable GTP-U functionality, closing the extended functionality for the case of full use of terrestrial network transmissions; and for a satellite mobile communication system using satellite segment links, the reliable GTP-U expansion function can be started according to the network topology planning on gNB and UPF which need reliable transmission for the physical links of satellite communication. By supporting the selectivity of reliable GTP-U function switching, the flexibility of network deployment can be greatly increased.

The data flows with diversified mobile services correspond to different QoS requirements. Route forwarding for QoS guarantees is typically based on predefined policies from different dimensions (e.g., user level, traffic type, traffic content, etc.). Therefore, reliable transmission on the satellite supported by the satellite mobile communication system also needs to consider service awareness, namely, the satellite-borne gNB and UPF only perform reliable route forwarding on service flows with reliability requirements. On one hand, the gNB can sense the service QoS, and on the other hand, the gNB can dynamically determine whether to carry out on-board reliable transmission on the service flow according to the result of service QoS sensing on the uplink data flow sent from the user terminal, and on the other hand, the UPF supports 3/4/7 layer service identification, and on the other hand, the gNB can dynamically determine whether to carry out on-board reliable transmission on the service flow according to the service QoS result obtained after the UPF carries out service identification on the downlink data flow sent from the DN side. In this way, the satellite mobile communications system can provide service aware on-board reliable route forwarding.

In view of this, a reliable data distribution method based on a segment acknowledgement mechanism in a star-ground fusion network is provided, and the method comprises the following steps:

step 1: and starting a reliable GTP-U expansion function for gNB and UPF requiring reliable tunneling in network deployment according to the well planned network topology of the satellite mobile communication system.

Step 2: gNB or UPF initiates traffic aware on-board reliable route forwarding in three cases:

1) For the uplink data packet sent by the ue received by the gNB air interface, if the gNB already enables the reliable GTP-U extension function, the QoS of the traffic flow needs to be determined by a packet filtering rule (e.g. 3/4/7 layer traffic identification). If there is a requirement for reliability, the gNB initiates the tunnel reliable transmission.

2) For the N6 interface of the UPF to receive the downlink data packet sent from the DN network, if the UPF has enabled the reliable GTP-U extension function, the packet filtering rule (e.g., 3/4/7 layer service identification) needs to determine the QoS of the service flow, and if the reliability is required, the UPF initiates reliable tunnel transmission.

3) For a UPF to receive a GTP-U data packet at the N9/N19 interface, if the UPF already enables the reliable GTP-U extension function, it needs to detect whether the GTP-U extension header has a newly defined reliable GTP-U container. If the reliable information exists, the UPF initiates the tunnel reliable transmission of the new section of satellite link again after the reliable transmission of the previous section of satellite link is terminated. Otherwise, after stripping off the GTP-U/UDP/IP protocol header, the UPF needs to determine whether the QoS of the service flow has a requirement on reliability through a packet filtering rule (such as 3/4/7 layer service identification), and if the QoS needs to be reliably transmitted, the UPF initiates reliable transmission of the tunnel.

Step 3: gNB or UPF is used as a GTP-U reliable transmission sender, and the basic functions of buffering, overtime retransmission and carrying reliable transmission information are required to be realized:

the data packets are buffered to corresponding traffic Flow retransmission queues of QFI (QoS Flow ID, qoS Flow identification).

And starting a retransmission timeout timer, and retransmitting the data packet if the timer expires without receiving a SACK (optional ACK, selection ACK) acknowledgement.

When the GTP-U/UDP/IP protocol header is packaged, a PDU session container type extension header used for carrying QFI is constructed, and a newly defined extension header reliable GTP-U container is also required to be constructed for carrying reliable transmission information such as Packet Number and Packet Offset of a data Packet.

The gNB or UPF is used as a GTP-U reliable transmission receiving end, and whether a GTP-U expansion head has a newly defined reliable GTP-U container or not needs to be detected. If the reliable information exists, the GTP-U data packet carrying SACK information needs to be replied, and the GTP-U sending end is informed of which data packets are received. Considering reducing network traffic, the SACK does not send SACK to the sender immediately after receiving GTP-U data packets, but adopts a delay confirmation mechanism, for example, the SACK delay sending time is set to be 100ms, but the 100ms is not the time needing delay after receiving data packets, and the system has a fixed timer to check whether the SACK packets need to be sent every 100ms, so that the SACK can perform merging confirmation on the received data packets. Meanwhile, if the receiving end has the same QFI QoS stream data packet to be sent, SACK information can be carried in the sending data packet, and of course, care needs to be taken to ensure that the data packet length does not exceed MTU, namely the data packet is not fragmented, otherwise, the GTP-U data packet only carrying the SACK information is sent independently.

As the GTP-U reliably transmits the gNB or UPF of the sender, it is also necessary to process the SACK acknowledgement information, stop the retransmission timer for the data packet acknowledged to be received, and delete the data packet from the buffer queue.

Note that the SACK acknowledgement includes ACK and NACK functions, which inform the sender of which consecutive and non-consecutive packets have been received, and also implies which packets have not been received by the sender and need to be retransmitted. In the scene of large bandwidth and low delay, the logic of packet loss judgment becomes more important, so the method adopts a SACK confirmation mechanism.

In order to implement the above method, a low-orbit satellite mobile communication system is provided below, which includes devices such as UE (User Equipment), satellite-borne gNB, satellite-borne UPF, ground UPF, 5GC control plane, and ground DN network device.

The UE terminal and DN network equipment (such as FTP server) are service starting point and receiving point; the satellite-borne gNB can realize the protocol processing function of a wireless access network part of the satellite mobile communication system, and transmits service, signaling and test verification data between the 5G core network and the UE terminal; the space-borne UPF and the ground UPF are combined network elements of PSA (PDU Session Anchor ) and I-UPF (relay UPF), which are forwarding nodes of service data, the PSA is PDU session anchor, and the I-UPF is a relay point, which is commonly used for Xn/N2 switching and service diversion.

Fig. 1 is a schematic diagram of an application scenario of the method, in which a network architecture for implementing real-time segmented reliable transmission on satellite communication physical links (inter-satellite links ISL and satellite-to-ground links GSL) in a low-orbit satellite mobile communication system is illustrated. The N3 interface of the satellite-borne gNB and the N3, N9 and N19 interfaces of the satellite-borne/ground UPF all adopt GTP-U/UDP/IP tunnel links, and the inter-satellite links ISL (such as an N3 tunnel link between the satellite 1 satellite-borne gNB and the satellite 5 satellite-borne UPF or an N19 tunnel link between the satellite 4 satellite-borne UPF and the satellite 5 satellite-borne UPF) and the satellite-ground link GSL (such as an N9 tunnel link between the satellite 4 satellite-borne UPF and the ground UPF) realize the reliable transmission of each section of the N3/N9/N19 tunnel by opening the function of the increased reliable GTP-U expansion module, so that the problem of performance degradation caused by the fact that packet loss sensing and retransmission can only be carried out end to end under the condition that no reliable GTP-U expansion module exists is solved.

A low orbit satellite mobile communication system based on confirmation mechanism comprises a UE terminal, a satellite mobile platform, a 5GC control surface, a ground UPF and a service server in DN network; the satellite mobile platform includes a satellite-borne gNB and a satellite-borne UPF. The reliable GTP-U expansion function is started by the satellite-borne gNB and the satellite-borne UPF, the ground UPF is communicated with the satellite-borne UPF through the gateway station, an access point to a DN network is provided, and the reliable GTP-U expansion function is started.

Considering the consumption of bandwidth by ACK, the SACK acknowledgement mechanism adopts a delayed acknowledgement mode, that is, instead of immediately replying after receiving a data packet, the system starts a periodic timer (for example, the interval time is set to 100 ms), detects whether the SACK packet needs to be sent after expiration of the timer, if so, one SACK packet may include multiple packet acknowledgement information, and if there is exactly a data packet to be forwarded at this time, the SACK acknowledgement information may be carried together in a newly defined GTP-U extension header reliable GTP-U container of the forwarding packet without fragmentation.

There are two typical application scenarios: 1) inter-UE interworking, such as data flows (forwarding paths illustrated by short dashed lines) of the interworking between UE1 and UE3 in fig. 1; 2) The UE accesses the DN network device, such as UE2 in fig. 1, to access the data flow (forwarding path indicated by dotted line) of the service server in the DN network.

For the first scenario, communication is performed between UEs. The UE1 selects satellite-borne gNB and satellite-borne UPF transmission mobile services of the satellite 1 and satellite-borne UPF transmission mobile services of the satellite 4, and the UE3 selects satellite-borne gNB and satellite-borne UPF transmission mobile services of the satellite 5, so that a UE1 session anchor point is arranged on the satellite-borne UPF of the satellite 5, a UE3 session anchor point is arranged on the satellite-borne UPF of the satellite 4, and data flows of the UE1 and the UE3 are required to be carried through an N3 interface GTP-U tunnel between the satellite 1-satellite 5 and the satellite 3-satellite 4 and an N19 interface GTP-U tunnel between the satellite 4-satellite 5. By using the reliable GTP-U extension function, packets communicated by UE1 and UE3 may be reliably transmitted in real-time over the inter-satellite link ISL described above.

For the second scenario, the UE accesses a DN network device. The UE2 selects the satellite-borne gNB of the satellite 2, the satellite-borne UPF of the satellite 4 and the ground UPF to transmit the mobile service, and the data flow of the service server in the DN network for the UE2 to access needs to be carried through the N3 interface GTP-U tunnel between the satellite 2 and the satellite 4 and the N9 interface GTP-U tunnel between the satellite 4 and the ground UPF. Packet forwarding for communication between UE2 and the service server may be performed on the above-mentioned inter-satellite link ISL and the satellite-to-earth link GSL between satellite and gateway station.

The on-board gNB on satellite 1/2/3 and the ground UPF both need to initiate the on-board reliable route forwarding of service awareness, the QFI of the service flow is determined through packet filtering detection (such as 3/4/7 layer service identification) and has reliable transmission requirements, and in the GTP-U tunnel protocol encapsulation process, a GTP-U expansion header PDU session container is added for carrying the QFI, and a newly defined GTP-U expansion header is also required to be added.

The satellite-borne UPF on the satellite 4/5 can determine that the service flow needs reliable route forwarding according to a reliable GTP-U container extension header carried in a received GTP-U message, initiate the tunnel reliable transmission of a new section of satellite link again after the reliable transmission of a previous section of satellite link is terminated, and add the reliable GTP-U container extension header for carrying reliable transmission information such as Packet Number (Packet Number), packet Offset (Packet Offset) and the like. After the GTP-U tunnel protocol packet header is packaged, the sending data packet is cached in a retransmission queue marked by QFI, and a retransmission timer is started.

The satellite-borne gNB or UPF on the satellite 1/2/3/4/5 and the ground UPF are required to be used as receiving ends of the reliable transmission of the GTP-U, process the reliable transmission information (such as the number of packets, the packet offset and the like) in the extension head of the reliable GTP-U container and label the packet receiving state information. And after the SACK periodic timer is overtime, sending SACK confirmation information to the sending end.

As the GTP-U reliably transmits the gNB or UPF of the sender, it is also necessary to process the SACK acknowledgement information, stop the retransmission timer for the data packet acknowledged to be received, and delete the data packet from the buffer queue.

The key points of the method are that GTP-U protocol is extended, FIG. 2 is a schematic diagram of GTP-U extension protocol message definition of the method, and the G-PDU protocol stack, GTPv1-U packet head definition, extension head type value, GTP-U extension head format and newly added GTP-U extension head reliable GTP-U container definition for transmitting user plane data are given, and the main thinking is as follows:

(1) The GTPv1-U packet header has optional parameter extension packet header, which is represented by E and Next Extension Header Type, and the value 1 of E represents that the extension packet header is arranged subsequently, so that a new extension header type is added, namely 0x10000110 represents a reliable GTP-U container, and the reliable GTP-U extension header type represents that the extension header can carry information of reliable GTP-U transmission.

(2) Based on the standard GTP-U extension header format, a new Extension Header Content protocol format is defined for the newly added extension header type reliable GTP-U container, and is specifically described as follows:

1) Type (2 bits): GTP-U reliable information type, value 0 (NONE) is defined as no reliable information package, value 1 (PKT) is defined as reliable information package for forwarded data package, value 2 (SACK) is defined as SACK for reliable information package, value 3 (PKT and SACK) is defined as reliable information package for forwarded data package and SACK package at the same time.

2) PKN Length (3 bits): the packet sequence number length, when the Type value is 1 or 3, is a value other than 0.

3) Offset Length (3 bits): the packet sequence number offset length, when the Type value is 1 or 3, is a value other than 0.

4) Packet Number: the packet sequence number is incremented from 1, and the number of the parameter bytes is determined by the value of PKN Length.

5) Offset Number: the packet sequence number Offset is used to identify the original sequence number of the retransmission packet, and the value of the Offset Length determines the byte number of the parameter.

6) SACK Length (6 bits): and when the Type value is 2 or 3, the SACK block number is not 0, and the SACK block number is 63 at the maximum.

7) Left Edge of Block: sequence number of first packet of continuous/discontinuous block.

8) Right Edge of Block: sequence number of last packet of continuous/discontinuous block.

It should be noted that, because network bandwidth is saved as much as possible, when the reliable GTP-U container extension header format is designed, the method uses the variable-length Packet Number and the Offset Number, and allows one GTP-U Packet to carry both payload information (i.e., T-PDU) and SACK acknowledgement information.

In summary, the invention creates a low orbit satellite mobile communication system based on a confirmation mechanism, and realizes the real-time segmentation reliable transmission on satellite communication physical links (inter-satellite links ISL and satellite-ground links GSL) by enabling the functions of newly added reliable GTP-U expansion modules on satellite gNB, satellite UPF and ground UPF network elements.

Claims (3)

1. The reliable data distribution method based on the segment confirmation mechanism in the star-ground fusion network is characterized by comprising the following steps:

step 1: according to the planned network topology of the satellite mobile communication system, starting a reliable GTP-U expansion function for gNB and UPF needing reliable tunneling during network deployment;

step 2: judging whether to initiate reliable tunnel transmission according to the data conditions received by gNB and UPF, if so, turning to step 3, otherwise, continuing to receive data, and repeating step 2;

step 3: the gNB or UPF is used as a GTP-U reliable transmission sending end, when the GTP-U/UDP/IP protocol head is packaged, a PDU session container type extension head used for carrying QoS flow identification is constructed, a reliable GTP-U container extension head is constructed and used for carrying reliable transmission information of a data packet, then the data packet is cached into a service flow retransmission queue of the corresponding QoS flow identification, a retransmission timeout timer is started, if the timer expires and ACK acknowledgement information is not received, the data packet is retransmitted, if the ACK acknowledgement information is received, the retransmission timer is stopped for the data packet which is confirmed to be received, and the data packet is deleted from the service flow retransmission queue; in the data packet transmission process, gNB or UPF detects whether the reliable GTP-U container extension head has a newly defined reliable GTP-U container, if so, the GTP-U data packet carrying the selection ACK information is replied, and the GTP-U sending end is informed of which data packets have been received.

2. The reliable data distribution method based on the segment acknowledgement mechanism in the star-to-ground fusion network according to claim 1, wherein in step 2, it is determined whether to initiate reliable tunnel transmission, and the method is divided into the following three cases:

1) For the uplink data packet sent by the user terminal is received by the gNB air interface, if the gNB has enabled the reliable GTP-U expansion function, the QoS of the service flow is determined through a packet filtering rule, and if the reliability is required, the gNB initiates the reliable transmission of the tunnel;

2) For the N6 interface of UPF to receive the downlink data packet from DN network, if UPF has enabled reliable GTP-U expansion function, determining the QoS of service flow through packet filtering rule, if there is a requirement for reliability, UPF initiates reliable transmission of tunnel;

3) For a GTP-U data packet received by the UPF at an N9/N19 interface, if the UPF enables a reliable GTP-U expansion function, detecting whether a GTP-U expansion head has a newly defined reliable GTP-U container, and if so, initiating the tunnel reliable transmission of a new section of satellite link again after the reliable transmission of a previous section of satellite link is terminated by the UPF; otherwise, after stripping off GTP-U/UDP/IP protocol head, UPF determines whether QoS of the service flow has requirement for reliability through packet filtering rule, if so, UPF initiates reliable transmission of tunnel.

3. The reliable data distribution method based on the segment acknowledgement mechanism in the star-to-ground fusion network according to claim 1, wherein in step 3, the specific manner of replying to the GTP-U data packet carrying the selective ACK information is as follows:

setting a selective ACK delay transmission time, and checking whether a selective ACK packet needs to be transmitted or not at intervals of the delay transmission time through a fixed timer; when the selective ACK packet needs to be sent, if the receiving end has QoS stream data packets with the same QoS stream identification to be sent, the selective ACK information needing to be sent is carried on the sending data packet, otherwise, the GTP-U data packet only carrying the selective ACK information is sent independently.