Low-delay retransmission method for high-speed rail communication

Abstract

The invention discloses a high-speed rail communication-oriented low-delay retransmission method, which comprises the following steps of: performing multi-stream redundant transmission of a high-speed rail train control and train dispatching service by adopting an MPTCP, selecting at least two sub-streams to transmit the same data, and when a certain sub-stream is output in a staggered manner, selecting a retransmission strategy through a retransmission judgment mode, namely whether the error sub-stream is immediately retransmitted or not. Or waiting for arrival of data packets transmitted by other substreams in a redundant manner; if the subsequent data transmission of other substreams succeeds, after the other substreams receive the ACK containing the acknowledgement number of the target data packet, the sender sends a new data packet at the same time when the substreams with error transmission and the other substreams; and if the data transmission of the other sub-streams fails, the sender retransmits the data packet when the error sub-stream is transmitted and the other sub-streams are transmitted under the condition that the other sub-streams receive three repeated ACKs (Acknowledgement Characters) or are overtime. The method is applied to a scene that a plurality of paths are adopted for redundant data transmission in coexistence of a multi-system network, and the low-delay requirement of high-speed rail train control and train dispatching services is guaranteed by selecting a proper retransmission judgment mode.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology, and in particular relates to a low-latency retransmission method for high-speed rail communication. Background Technology

[0002] With the Ministry of Industry and Information Technology approving the test frequencies for the next-generation railway mobile communication system (5G for Railway, 5G-R) based on 5G (the Fifth Generation of Mobile Communication) technology, the railway mobile communication system has entered a transitional period where multiple communication modes coexist, including GSM-R (Global System for Mobile Communication-Railway), 5G-R, and the 400MHz digital wireless train dispatching system. Deep integration of 5G-R, GSM-R, and the 400MHz digital wireless train dispatching system will form a multi-mode, multi-band collaborative onboard integrated wireless access architecture, further improving the transmission reliability of railway train control and dispatching services, thereby ensuring the safety of railway transportation. High-speed rail train control and dispatching services play a crucial role in maintaining the safe and efficient operation of trains. These services require highly reliable, low-latency data transmission capabilities to support reliable real-time data interaction between the train and the ground control system. To improve the reliable transmission of high-speed rail train control and dispatching business data, this invention proposes a low-latency retransmission method for high-speed rail communication based on the railway multi-mode cooperative mobile communication network architecture using the Multipath Transmission Control Protocol (MPTCP), so as to achieve highly reliable and low-latency transmission of high-speed rail train control business data. Summary of the Invention

[0003] This invention provides a low-latency retransmission method for high-speed rail communication under the multi-mode fusion and collaborative onboard integrated wireless access architecture of 5G-R, GSM-R and railway 400MHz digital wireless train dispatching system based on MPTCP mechanism.

[0004] This invention provides a low-latency retransmission method for high-speed rail communication, which uses multipath transmission control protocol (MPTCP) multi-stream redundancy transmission technology to reliably transmit high-speed rail train control and dispatching services. Specifically, it includes the following steps:

[0005] During the MPTCP substream establishment phase, the sender and receiver exchange initialization information through SYN, SYN / ACK, and ACK packets.

[0006] During the data transmission phase, the sender selects at least two sub-streams to transmit data packets and starts a delayed retransmission timer. The sender updates the round-trip time (RTT) value of each sub-stream in real time and periodically updates the packet loss rate. When a sub-stream successfully sends a data packet and receives an ACK, it calculates a new RTT value based on the time difference between sending and receiving, and uses a weighted average method to smooth it to obtain a smoothed RTT. At the same time, the delayed retransmission timer is adjusted to ensure that its initial value is the largest RTT value among all sub-streams. For the packet loss rate, the sender records the number of data packets sent and lost. When the total number of data packets sent reaches the threshold of the total number of data packets sent, the sender calculates the current packet loss rate and uses a weighted average method to obtain a smoothed packet loss rate to improve the stability of performance evaluation.

[0007] During the retransmission judgment phase, when the delayed retransmission timer has not expired and a certain substream receives three duplicate ACKs (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet), two retransmission judgment methods are selected: Method 1: judge whether to retransmit immediately based on RTT and packet loss rate; Method 2: judge whether to retransmit immediately based on path transmission quality factor.

[0008] Method 1 is as follows:

[0009] If the RTT value of the erroneous substream is less than or equal to the difference between the RTT of the other substream, the data packet is immediately retransmitted on the erroneous substream; if it is greater than the difference between the RTT of the other substream, it is further determined whether the packet loss rate of the erroneous substream is greater than the packet loss rate of the other substream.

[0010] If the packet loss rate of the erroneous substream is less than or equal to the packet loss rate of the other substream, the data packet is immediately retransmitted on the erroneous substream; if the packet loss rate of the erroneous substream is greater than or equal to the packet loss rate of the other substream, the system waits for the redundant data packet from the other substream to arrive.

[0011] Method two is as follows:

[0012] First, calculate the transmission quality factor for each path. If the quality factor of the faulty sub-stream is less than or equal to that of another sub-stream, it indicates that the link quality of the faulty sub-stream is good, and the data packet is immediately retransmitted on the faulty sub-stream. If the quality factor of the faulty sub-stream is greater than that of another sub-stream, it indicates that the link quality of the faulty sub-stream is poor, and the system waits for the redundant transmission of the data packet from the other sub-stream to arrive.

[0013] Furthermore, the delayed retransmission timer is set to the maximum value of the RTT for each sub-stream; the sender sends a data packet and starts the delayed retransmission timer; when a data packet fails to be transmitted on a certain sub-stream, i.e. the sender receives multiple duplicate ACKs, if the delayed retransmission timer is not 0, a retransmission judgment is triggered; when the sender does not receive an ACK containing the acknowledgment number of the target data packet and the delayed retransmission timer times out, it indicates that the sender has waited enough time without receiving the expected data packet acknowledgment from other sub-streams, and the sender immediately retransmits the data packet simultaneously on multiple sub-streams.

[0014] Furthermore, the sender and receiver exchange information during the MPTCP three-way handshake to establish connections for multiple substreams.

[0015] During the first handshake, the sender needs to send a SYN packet with an improved MP_JOIN option field to inform the receiver that the current transmitted service is a high-speed rail train control and dispatch service, which requires multi-stream redundant transmission, as well as the retransmission judgment method selected by the sender for high-speed rail train control and dispatch services.

[0016] During the second handshake, the receiver needs to respond by sending a SYN / ACK packet with an improved MP_JOIN option field to acknowledge receipt of the information from the sender.

[0017] During the third handshake, the sender needs to send an ACK packet with an improved MP_JOIN option field to the receiver, informing them of the total number of packets to be sent threshold information.

[0018] The transmission system of the low-latency retransmission method for high-speed rail communication of the present invention includes, but is not limited to, a transmitting end device and a receiving end device, for realizing low-latency transmission of high-speed rail train control and dispatch services.

[0019] The sending end serves as both the initialization initiator and the redundant data packet transmission initiator. The initialization initiator is responsible for sending initialization-related information to the receiving end to establish an MPTCP connection and configure sub-streams. The redundant data packet transmission initiator is responsible for simultaneously sending the same data packets on at least two sub-streams and deciding whether to retransmit immediately or wait for redundant data packets to arrive on other sub-streams based on the retransmission judgment method.

[0020] The receiving end acts as both the initialization receiver and the redundant data packet receiver. The initialization receiver needs to immediately send back an acknowledgment frame after receiving the initialization information to ensure the reliability of data transmission. The redundant data packet receiver is responsible for receiving data packets from different substreams and notifying the sending end of the status of the data packets through the ACK mechanism (for example, sending three duplicate ACKs to the sending end indicates that the target data packet has not been received).

[0021] The entire system is based on the MPTCP multipath transmission protocol and uses multiple substreams to perform redundant transmission of high-speed rail train control and dispatching business data, thereby ensuring high reliability of high-speed rail train control and dispatching business data transmission.

[0022] The beneficial technical effects of this invention are as follows:

[0023] (1) The present invention adopts the MPTCP mechanism to redundantly transmit train control and dispatch services. When a link fails to transmit, the sender dynamically determines whether to retransmit immediately or wait for other links to transmit redundant data to arrive, ensuring that data transmission can be restored in time even in poor network conditions, thus ensuring the reliability of high-speed rail train control and dispatch services in the mobile communication system and ensuring the safety of railway transportation.

[0024] (2) This invention reduces retransmissions by designing a delayed retransmission timer and making retransmission decisions based on RTT and packet loss rate or path quality factor. By avoiding frequent retransmissions on unreliable substreams, it reduces the long communication delay caused by repeated transmissions, thus meeting the low latency requirements of high-speed rail train control services.

[0025] (3) By sacrificing certain computing resources to obtain more efficient and reliable data transmission services, this invention enhances the system's adaptability to changes in network conditions and reduces retransmissions. Compared with existing mechanisms based on single substream retransmission, it not only reduces network load but also improves the overall efficiency of data transmission, providing strong support for ensuring the safe operation of high-speed rail. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the signaling interaction process during the MPTCP sub-stream connection establishment phase of this invention.

[0027] Figure 2 This is a schematic diagram of the low-latency retransmission method for high-speed rail communication according to the present invention.

[0028] Figure 3 , Figure 4 This is a flowchart illustrating the low-latency retransmission method for high-speed rail communication according to the present invention.

[0029] Figure 5 , Figure 6 This is a schematic diagram illustrating the format of the MP_JOIN option field in the SYN data packet of an embodiment of the present invention.

[0030] Figure 7 , Figure 8 This is a schematic diagram illustrating the format of the MP_JOIN option field in the SYN / ACK data packet according to an embodiment of the present invention.

[0031] Figure 9 , Figure 10This is a schematic diagram of the format of the MP_JOIN option field in the ACK data packet of an embodiment of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0033] This invention discloses a low-latency retransmission method for high-speed rail communication. The core of this method is the use of MPTCP for multi-stream redundant transmission of high-speed rail train control and dispatch services to improve transmission reliability and ensure railway transportation safety. Specifically, at least two sub-streams are selected to transmit the same data. When an error occurs in one sub-stream, a retransmission strategy is selected based on a retransmission judgment method: whether to immediately retransmit in the erroneous sub-stream or wait for the arrival of data packets from other redundant sub-streams. If subsequent data transmission in other sub-streams is successful, the sender, upon receiving an ACK containing the target data packet acknowledgment number (i.e., the sequence number in the ACK packet is greater than the target data packet sequence number) in other sub-streams, simultaneously sends new data packets in the erroneous sub-stream and other sub-streams. If data transmission in other sub-streams fails, the sender, upon receiving three duplicate ACKs (i.e., the sequence number in the ACK packet is not greater than the target data packet sequence number) or a timeout occurs in other sub-streams, simultaneously retransmits data packets in the erroneous sub-stream and other sub-streams, thereby solving the problems of excessive retransmissions and long data transmission delays in existing technologies.

[0034] There are two methods for determining whether to immediately retransmit: Method 1: Based on RTT and packet loss rate. If the RTT of the erroneous substream is greater than the difference between its RTT and those of other substreams, and the packet loss rate of the erroneous substream is greater than that of other substreams, then wait for the arrival of redundant data packets from other substreams. Otherwise, retransmit the erroneous substream immediately. Method 2: Based on path quality factor. The path quality factor is derived by weighting RTT and packet loss rate. If the path quality factor of the erroneous substream is greater than that of other substreams, then wait for the arrival of redundant data packets from other substreams. Otherwise, retransmit the erroneous substream immediately.

[0035] This invention designs a delayed retransmission timer, initially set to the maximum RTT (Round-Trip Time) of a substream for redundant data packets. The sender starts this timer while transmitting data packets on multiple substreams. The function of this delayed retransmission timer is: when a data packet fails to transmit on a substream and the delayed retransmission timer is not zero, the retransmission judgment of this invention is initiated to determine whether to retransmit immediately or wait for the arrival of redundant data packets on another link, thus utilizing the advantages of multi-path transmission to reduce immediate retransmissions. When the delayed retransmission timer expires, indicating that the sender has waited sufficient time without receiving the expected data packet acknowledgment from other substreams, the sender immediately retransmits the data packet simultaneously on multiple substreams. The existence of the delayed retransmission timer helps to implement a retransmission judgment method based on RTT and packet loss rate. For example, before the delayed retransmission timer expires, if a specific condition is met (i.e., the sender has not received an ACK containing the target data packet acknowledgment number and has received multiple duplicate ACKs), a retransmission judgment will be triggered; otherwise, if the sender has not received an ACK containing the target data packet acknowledgment number and the delayed retransmission timer expires, the sender immediately retransmits the data packet simultaneously on multiple substreams.

[0036] The specific technical solution of this invention is as follows: When the sender receives three duplicate ACKs (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet) in a certain sub-stream, it determines whether to retransmit immediately based on the retransmission judgment method. The entire process includes a sub-stream connection establishment stage, a data transmission stage, and a retransmission judgment stage. In the sub-stream connection establishment stage, the sender and receiver negotiate and select the retransmission judgment method. In the data transmission stage, the sender and receiver periodically update the packet loss rate of each sub-stream, update the RTT value of each sub-stream in real time, and adjust the initial value of the delayed retransmission timer according to the updated RTT value to ensure that the initial value of the delayed retransmission timer is always the maximum value of the RTT of each sub-stream. In the retransmission judgment stage, it determines whether the sub-stream with transmission errors should be retransmitted immediately or wait for the arrival of redundant data packets from other sub-streams, based on the retransmission judgment method negotiated in the sub-stream establishment stage. The specific steps of each stage are as follows:

[0037] I. MPTCP Multi-Stream Connection Establishment Phase

[0038] In this phase, the MP_JOIN header option field format in the SYN, SYN / ACK, and ACK packets was enhanced. The interaction process between the sender and receiver during the MPTCP multi-substream connection establishment phase is as follows: The sender first sends a SYN packet to the receiver. This SYN packet carries the service type, whether a multi-stream redundancy transmission mode is used, and the retransmission judgment method information. After receiving the SYN packet, the receiver replies with a SYN / ACK packet to confirm receipt of the information from the sender. After receiving the SYN / ACK packet, the sender replies with an ACK packet. This ACK packet carries a threshold for the total number of packets sent. For each packet sent, the sender increments the total number of packets by 1. When the cumulative total exceeds the threshold, the packet loss rate is immediately updated. The specific packet loss rate update method is described in the data transmission phase section below. The sender maintains a delayed retransmission timer based on the RTT value of each substream. The initial value of this timer is set to the maximum value of the RTT of each substream. When the RTT value of a substream is updated, the initial value of the delayed retransmission timer is also updated accordingly.

[0039] Figure 1 This is a flowchart illustrating the signaling interaction during the MPTCP sub-stream connection establishment phase. MPTCP first exchanges the MP_CAPABLE option field to initialize the first sub-stream, and then exchanges the MP_JOIN option field to add the remaining sub-streams to the current connection. See the section describing the sub-stream establishment process later for details.

[0040] II. Data Transmission Stage

[0041] 1. The sender updates the RTT value of each substream in real time.

[0042] For train control and dispatch services, multi-stream redundant transmission is used. The sender selects at least two sub-streams for redundant data transmission and starts a delayed retransmission timer. After a sub-stream successfully transmits a data packet, the receiver sends an ACK to the sender. Upon receiving the ACK, the sender updates the RTT value of the sub-stream. The RTT value update method is as follows: For each sub-stream... , For sub-flow Current RTT value, For sub-flow The smoothed RTT value. The transmission time is recorded when a data packet is sent. When an ACK is received, record the reception time. The round-trip time is then calculated as follows:

[0043]

[0044] To reduce the impact of instantaneous fluctuations and thus obtain a more stable performance estimate, the statistically obtained current RTT value is smoothed to obtain a smoothed RTT. ,initial Setting it to 0 will result in the statistically obtained... and The weighted average was updated. The formula is as follows:

[0045]

[0046] in, Weighting factor ,generally The value is relatively small (e.g., 0.125).

[0047] The sender based on the updated Update the delayed retransmission timer to ensure that the initial value of the delayed retransmission timer is always the maximum value of the RTT of each substream.

[0048] 2. The sender periodically updates the packet loss rate of each substream.

[0049] For each sub-flow , and The initial value is 0, where The total number of data packets sent. This represents the total number of lost data packets. It increments with each data packet sent. , When the total number of data packets sent reaches the threshold, calculate the current packet loss rate. and will The value is incremented again after being set to 0. When the sender receives an ACK, it indicates that the data packet has been received correctly. If a data packet does not receive a corresponding ACK (i.e., timeout or duplicate ACK is received), the data packet is considered lost, and the value is incremented. The packet loss rate is:

[0050]

[0051] To reduce the impact of instantaneous fluctuations and obtain a more stable performance estimate, a weighted average smoothing process is performed on the current packet loss rate LoseRatei and the previous packet loss rate to obtain a smoothed packet loss rate. Update using weighted average :

[0052]

[0053] in, Let be the smooth packet loss rate of the i-th sub-stream, with an initial value of 0. Weighting factor It usually takes a small value (such as 0.1).

[0054] III. Retransmission Judgment Stage

[0055] If the sender does not receive an ACK containing the sequence number of the target data packet (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet), the delayed retransmission timer has not expired, and a certain substream has a transmission error, receiving three duplicate ACKs (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet), indicating that the receiver has not received the target data packet, then the retransmission judgment stage begins. For ease of analysis, assume the substream with the transmission error is substream 1, and the other substream is substream 2.

[0056] 1. If retransmission judgment method one is selected, the sender first determines whether the RTT value of substream 1 is greater than the difference between the RTT and substream 2. The RTT of the substream with the transmission error is defined as RTT1, and the RTT of the other substream is defined as RTT2. The difference between the two is... ,Right now:

[0057]

[0058] like If so, the data packet is immediately retransmitted on substream 1; if Then determine if the packet loss rate of subflow 1 is greater than the packet loss rate of subflow 2. Define the packet loss rate of subflow 1 as LossRate1 and the packet loss rate of subflow 2 as LossRate2. If... If so, the data packet is immediately retransmitted on substream 1; if If the data packet in substream 2 is transmitted successfully, and the sender receives an ACK containing the acknowledgment number of the target data packet (i.e., the sequence number in the ACK packet is greater than the sequence number of the target data packet), then substream 1 and substream 2 will transmit new data packets simultaneously. If the data packet in substream 2 is transmitted incorrectly, and the sender receives three duplicate ACKs with the same sequence number (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet) or the delay retransmission timer is 0, then data packets will be retransmitted simultaneously on substream 1 and substream 2.

[0059] 2. If retransmission judgment method two is selected, the sender calculates the sub-stream quality factor for each sub-stream based on the current RTT and packet loss rate. The sub-stream quality factor is obtained by weighting the RTT and packet loss rate.

[0060]

[0061] in, Let be the subflow quality factor of the i-th subflow, and 'a' be the weighting factor. It can be dynamically adjusted. Let be the smoothed RTT value of the i-th subflow. Let be the smooth packet loss rate of the i-th sub-stream. Updated in real time during the aforementioned data transmission phase. The data is updated periodically during the aforementioned data transmission phase.

[0062] The subflow quality factor of subflow 1 is defined as: The subcurrent quality factor of subcurrent 2 is .like If this indicates that the link status of sub-stream 1 is good, then the data packet will be retransmitted immediately on sub-stream 1; if If the condition indicates that the link status of sub-stream 1 is poor, then wait for the redundant transmission data packets of sub-stream 2 to arrive. If the data packet transmission of sub-stream 2 is successful, the sender receives an ACK containing the acknowledgment number of the target data packet, and then sub-stream 1 and sub-stream 2 transmit new data packets simultaneously; if the data packet transmission of sub-stream 2 fails, the sender receives three duplicate ACKs with the same sequence number (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet) or the delay retransmission timer is 0, then the data packet is retransmitted simultaneously on sub-stream 1 and sub-stream 2.

[0063] If the sender does not receive an ACK containing the acknowledgment number of the target data packet and the delayed retransmission timer times out, the sender will retransmit the data packet on the selected substream simultaneously.

[0064] Figure 2 This diagram illustrates a low-latency retransmission method for high-speed rail communication. It assumes a scenario where endpoints A and B need to transmit high-speed rail train control and dispatch services, and an MPTCP connection is established between them. To improve transmission reliability, multi-stream redundancy is implemented based on the MPTCP connection for high-speed rail train control and dispatch services; two links are chosen for redundant transmission. Sending end A is configured with address A1, and receiving end B is configured with two addresses B1 and B2. A1 to B1 constitutes one sub-stream P1, and A1 to B2 constitutes another sub-stream P2. In the MPTCP protocol, each sub-stream has its own sub-stream sequence number (SSN). To ensure correct ordering of data packets spanning multiple sub-streams, a data sequence number (DSN) is introduced. When a data packet is sent through a sub-stream, in addition to the SSN unique to that sub-stream, a DSN is appended. The receiving end can then reassemble the data based on the DSN, ensuring data integrity and order. Figure 2 In this scenario, the sending end simultaneously transmits data packets with DSNs of 13-16 on two substreams. The SSNs on substream P1 are 23-26, and on substream P2 are 11-14. The sending end sends data packets and starts a delayed retransmission timer. The RTT (Round-Trip Time) of substream P1 is defined as less than that of substream P2, so the initial value of the delayed retransmission timer is set to the RTT value of substream P2. If the receiving end does not receive a data packet with DSN 13 on substream P1, it replies with three ACKs with acknowledgment number 13. After receiving three duplicate ACKs on substream P1 (with sequence numbers equal to the target data packet sequence number), the sending end assumes that, based on the retransmission judgment method of this approach, it will wait for redundant data packets to arrive from the other substream. Figure 2 The receiver correctly receives the redundant transmitted data packets in substream P2, and the sender receives four ACKs on substream P2, acknowledging receipt of data packets with DSNs 13-16 respectively, at which point data transmission ends. The sender then simultaneously transmits new data packets in substreams P1 and P2.

[0065] Figures 3-4 A flowchart illustrating a low-latency retransmission method for high-speed rail communication is presented, in which... Figure 3 and Figure 4 These represent two retransmission determination methods. The initial setting is to transmit the same data packet simultaneously on two sub-streams and start a delayed retransmission timer; if the sender does not receive an ACK containing the target data packet's acknowledgment number and the delayed retransmission timer has not expired, but a sub-stream receives three duplicate ACKs (the sequence number in the ACK packet is not greater than the target data packet's sequence number):

[0066] In retransmission judgment method one (such as...) Figure 3 First, determine whether the RTT of the sub-stream that received the duplicate ACK is greater than the difference between the RTT of the other sub-stream. If it is less than or equal to the difference, retransmit immediately on the sub-stream that received the duplicate ACK. Otherwise, further determine the packet loss rate. If the packet loss rate of the sub-stream that received the duplicate ACK is less than or equal to that of the other sub-stream, retransmit immediately. Otherwise, wait for the redundant transmission data packets of the other sub-stream to arrive.

[0067] In retransmission judgment method two (such as...) Figure 4 The quality factor of each sub-stream is calculated. If the quality factor of a sub-stream receiving duplicate ACKs is less than or equal to the quality factor of another sub-stream, it is immediately retransmitted; otherwise, it waits for the redundant transmission data packet from the other sub-stream to arrive. If the data packet from the other sub-stream is successfully transmitted, the sender receives the ACK and slides the transmission window, ending the data transmission. If the data packet from the other sub-stream is transmitted incorrectly, and the sender receives three duplicate ACKs on the other sub-stream or the delayed retransmission timer expires, the data packet is retransmitted simultaneously on both sub-streams. If the delayed retransmission timer expires and the sender does not receive an ACK, the sender retransmits the data packet simultaneously on both sub-streams.

[0068] During the sub-stream connection establishment phase, after the MPTCP connection completes the initialization of the first sub-stream, the sender and receiver perform a three-way handshake based on the control information carried in the MP_JOIN header option field of the MPTCP data packet to add other sub-streams to the current connection. During the first handshake, the onboard equipment needs to send a SYN data packet to inform the ground equipment of the current service type, whether a redundant multi-stream transmission mode is used, and the selected retransmission judgment method. During the second handshake, the ground equipment needs to send a SYN / ACK data packet in response. During the third handshake, if the onboard equipment determines that the transmitted service is a high-speed rail train control and dispatch service, the onboard equipment needs to send an ACK data packet to the ground equipment to inform it of the total number of data packets sent threshold information. It should be noted that the MP_JOIN header option field exists in all three handshake SYN, SYN / ACK, and ACK data packets. This field is located between the MPTCP data packet header information and the data content and carries control and management information. Therefore, the format of the MP_JOIN header option field of the data packets used in the above process needs to be specifically designed.

[0069] (1) Format design of the MP_JOIN header option field of the SYN packet during the first handshake

[0070] The format of the MP_JOIN option field in the SYN packet during the first handshake is as follows: Figure 6 As shown, the format of the MP_JOIN option field in the original SYN packet in the RFC6824 file is as follows: Figure 5 As shown, the MP_JOIN option field of the SYN packet in RFC6824 has been improved, mainly by adding the ServiceType, RedundantTransmission, and RetCriteria fields. It should be noted that the optional implementations of the MP_JOIN option field content in the SYN packet include, but are not limited to, […]. Figure 5-6 The scheme is shown below. The functional definitions of each field are explained below:

[0071] a) Kind field

[0072] This field indicates the type of the option field. When the value of this field is 30, it indicates that the header option field is an MPTCP header option field.

[0073] b) Length field

[0074] This field is used to indicate the length of the header options field.

[0075] c) Subtype field

[0076] This field indicates the subtype of the MPTCP option field. When this field is set to 0x1, it indicates that the subtype is the MP_JOIN option field for joining an MPTCP connection.

[0077] d) ServiceType field

[0078] This field indicates the type of service. Compared to the MP_JOIN option field format in the SYN packet of RFC6824, this invention adds a ServiceType field, which is 1 bit long. When this field is set to 1, it indicates that the service type is high-speed rail train control service; when this field is set to 0, it indicates that the service type is other services.

[0079] e) RedundantTransmission field

[0080] This field indicates whether the sender of this option field uses redundant multi-stream transmission of data packets. Compared to the MP_JOIN option field format in the SYN packet of RFC6824, this invention adds a RedundantTransmission field, which is 1 bit long. When the ServiceType field value is 1, this field is set to 1, indicating redundant multi-stream transmission of data packets; when this field is set to 0, it indicates single sub-stream transmission of data packets.

[0081] f) RetCriteria field

[0082] This field indicates the two optional retransmission determination methods. Compared to the MP_JOIN option field format in the SYN packet of RFC6824, this invention adds a RetCriteria field, which is 1 bit. When the ServiceType field value is 1, this field can be set to 0 or 1. Setting it to 0 indicates selecting retransmission determination method one, and setting it to 1 indicates selecting retransmission determination method two. When the ServiceType field value is 0, this field value is set to 0, indicating that no retransmission determination method is used.

[0083] g)B field

[0084] This field indicates whether the current substream is used as a backup path. When this field is set to 1, it means that the sender of this option field will use the current substream as a backup path if other paths fail; when this field is set to 0, it means that the sender of this option field will not use the current substream as a backup path if other paths fail.

[0085] h) Address ID field

[0086] This field is used to indicate the source address of the current data packet.

[0087] i) Receiver's Token field

[0088] This field is used to indicate the token value of the recipient.

[0089] j) Sender's Random Number field

[0090] This field is used to indicate the random number sent by the sender.

[0091] (2) Format design of the MP_JOIN header option field of the SYN / ACK packet during the second handshake

[0092] The format of the MP_JOIN option field in the SYN / ACK packet is as follows: Figure 8 As shown, the format of the MP_JOIN option field in the original SYN / ACK data packet in the RFC6824 file is as follows: Figure 7 As shown, the design is based on the MP_JOIN option field of the SYN / ACK packet in RFC6824; the main additions are the ServiceType field, the RedundantTransmission field, and the RetCriteria field; the optional implementation schemes for the MP_JOIN option field content of the SYN / ACK packet include, but are not limited to, […]. Figure 7 , Figure 8 The meanings of the newly added fields in the scheme shown are the same as those of the MP_JOIN option field in the SYN packet, and will not be repeated here.

[0093] (3) Format design of the MP_JOIN header option field of the SYN / ACK packet during the third handshake

[0094] The format of the MP_JOIN option field in the ACK packet during the third handshake is as follows: Figure 10 As shown, the format of the MP_JOIN option field in the original ACK packet in the RFC6824 file is as follows: Figure 9 As shown, the design is based on the MP_JOIN option field of the ACK packet in RFC6824; the main difference is that the reserved field has been redefined; the optional implementation schemes for the MP_JOIN option field content of the ACK packet include, but are not limited to, those for... Figure 9 , Figure 10 The following section explains the functional definitions of each field in the scheme shown:

[0095] a) Kind field

[0096] The meaning of this field is the same as that of the MP_JOIN option field in the SYN packet.

[0097] b) Length field

[0098] The meaning of this field is the same as that of the MP_JOIN option field in the SYN packet.

[0099] c) Subtype field

[0100] The meaning of this field is the same as that of the MP_JOIN option field in the SYN packet.

[0101] d) PacketCountThreshold field

[0102] This field indicates the threshold for the total number of data packets sent by a sub-stream. For each data packet sent by a sub-stream, the total number of data packets is incremented by 1. When the total number of data packets reaches the threshold, the packet loss rate is updated, and then the total number of data packets starts accumulating again from 0. Compared to the MP_JOIN option field format of the ACK packet in RFC6824, this invention redefines a PacketCountThreshold field, which is 7 bits, within the original reserved field. When the ServiceType field value is 1, this field is set to 0, indicating that the field is invalid; when the field value is X, it indicates that the threshold for the total number of data packets sent by this sub-stream is X-1.

[0103] e) Sender's HMAC field

[0104] This field is used to indicate the sender's HMAC value.

[0105] The above description is only a partial embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A low-latency retransmission method for high-speed rail communication, characterized in that, To ensure reliable transmission of high-speed rail train control and dispatching services based on MPTCP multi-stream redundancy transmission technology, the following steps are specifically included: During the MPTCP substream establishment phase, the sender and receiver exchange initialization information through SYN, SYN / ACK, and ACK data packets. During the data transmission phase, the sender selects at least two sub-streams to transmit data packets and starts a delayed retransmission timer. The sender updates the round-trip time (RTT) value of each sub-stream in real time and periodically updates the packet loss rate. When a sub-stream successfully sends a data packet and receives an ACK, it calculates a new RTT value based on the time difference between sending and receiving, and uses a weighted average method to smooth it to obtain a smoothed RTT. At the same time, the delayed retransmission timer is adjusted to ensure that its initial value is the largest RTT value among all sub-streams. For the packet loss rate, the sender records the number of data packets sent and lost. When the total number of data packets sent reaches the threshold of the total number of data packets sent, the sender calculates the current packet loss rate and uses a weighted average method to obtain a smoothed packet loss rate to improve the stability of performance evaluation. During the retransmission judgment phase, when the delayed retransmission timer has not expired and a certain substream receives three duplicate ACKs (i.e., the sequence number in the ACK packet is not greater than the sequence number of the target data packet), two retransmission judgment methods are selected: Method 1: judge whether to retransmit immediately based on RTT and packet loss rate; Method 2: judge whether to retransmit immediately based on path transmission quality factor.

2. The low-latency retransmission method for high-speed rail communication according to claim 1, characterized in that, The first method is specifically as follows: If the RTT value of the erroneous substream is less than or equal to the difference between the RTT of the other substream, the data packet is immediately retransmitted on the erroneous substream; if it is greater than the difference between the RTT of the other substream, it is further determined whether the packet loss rate of the erroneous substream is greater than the packet loss rate of the other substream. If the packet loss rate of the erroneous substream is less than or equal to the packet loss rate of the other substream, the data packet is immediately retransmitted on the erroneous substream. If the packet loss rate of the erroneous substream is greater than or equal to the packet loss rate of the other substream, then wait for the redundant transmission data packets of the other substream to arrive.

3. The low-latency retransmission method for high-speed rail communication according to claim 1, characterized in that, The second method is specifically as follows: First, calculate the transmission quality factor for each path. If the quality factor of the faulty sub-stream is less than or equal to the quality factor of another sub-stream, it indicates that the link quality of the faulty sub-stream is good. Then, the data packet is immediately retransmitted on the faulty sub-stream. If the quality factor of the faulty sub-stream is greater than that of another sub-stream, it indicates that the link quality of the faulty sub-stream is poor, and the system waits for the redundant data packets from the other sub-stream to arrive.

4. The low-latency retransmission method for high-speed rail communication according to claim 1, characterized in that, The delayed retransmission timer is set to the maximum value of the RTT of each sub-stream; the sender sends a data packet and starts the delayed retransmission timer; when a data packet fails to be transmitted on a certain sub-stream, that is, the sender receives multiple duplicate ACKs, if the delayed retransmission timer is not 0, a retransmission judgment is triggered; when the sender does not receive an ACK containing the acknowledgment number of the target data packet and the delayed retransmission timer times out, it indicates that the sender has waited enough time without receiving the expected data packet acknowledgment from other sub-streams, and the sender immediately retransmits the data packet simultaneously on multiple sub-streams.

5. A low-latency retransmission method for high-speed rail communication according to claim 1, characterized in that, The sender and receiver exchange information when establishing connections for multiple substreams via the MPTCP three-way handshake. During the first handshake, the sender needs to send a SYN packet with an improved MP_JOIN option field to inform the receiver that the current transmitted service is a high-speed rail train control and dispatch service, which requires multi-stream redundant transmission, as well as the retransmission judgment method selected by the sender for high-speed rail train control and dispatch services. During the second handshake, the receiver needs to send a SYN / ACK packet with an improved MP_JOIN option field to acknowledge receipt of the information from the sender. During the third handshake, the sender needs to send an ACK packet with an improved MP_JOIN option field to the receiver, informing them of the total number of packets to be sent threshold information.

6. A transmission system applicable to the low-latency retransmission method for high-speed rail communication as described in any one of claims 1 to 5, characterized in that, Including but not limited to transmitting devices and receiving devices, used to achieve low-latency transmission of high-speed rail train control and dispatch services; Among them, the sending end is the initiator of initialization and the initiator of redundant data packet transmission; the initiator of initialization is responsible for sending initialization-related information to the receiving end to establish an MPTCP connection and configure sub-streams; the initiator of redundant data packet transmission is responsible for sending the same data packets on at least two sub-streams simultaneously, and deciding whether to retransmit immediately or wait for redundant data packets on other sub-streams to arrive based on the retransmission judgment method. The receiving end acts as both the initialization receiver and the redundant data packet receiver. The initialization receiver needs to immediately send back an acknowledgment frame after receiving the initialization information to ensure the reliability of data transmission. The redundant data packet receiver is responsible for receiving data packets from different substreams and notifying the sending end of the status of the data packets through the ACK mechanism. The entire system is based on the MPTCP multipath transmission protocol and uses multiple substreams to perform redundant transmission of high-speed rail train control and dispatching business data, thereby ensuring high reliability of high-speed rail train control and dispatching business data transmission.

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