CN103825689B - Delay determinacy message retransmission method with local cache - Google Patents

Abstract

The invention provides a delay determinacy message retransmission method with a local cache. A receiving end requests data which needs retransmitted from a sending end unequivocally, and information of more than one lost data section is included in a request. The local cache is arranged, lost messages can be subjected to local retransmission, and accordingly the phenomenon of packet loss of a reverse link ACK can be avoided. The method is a strategy through which loss restoring is carried out quickly with limited bandwidth, on a channel with large delay and error rate and asymmetric link bandwidth, the frequency and the amount of message retransmission are reduced, and the problem of channel efficiency lowering during packet loss caused by reverse channel bandwidth limiting on the channel is avoided. By arranging the local cache, the problem that channel transmission efficiency is low due to large delay when reverse ACK messages are lost can be solved. According to the method, satellite link message retransmission efficiency can be greatly improved, and satellite channel using rate is greatly improved.

Description

Delayed deterministic packet retransmission method with local cache

technical field

The invention relates to a delayed and deterministic message retransmission method with local cache.

Background technique

Because satellite links have the characteristics of extended propagation time, large bandwidth and delay product, and high bit error rate, the performance of the widely used TCP protocol in the Internet is greatly affected when it is applied to satellite links, which seriously limits the performance of satellite links. Resource utilization and transmission efficiency cannot meet various business needs. The TCP protocol, Transmission Control Protocol, is a protocol for feedback and response. The receiving end will return the data reception status to the sending end through an ACK message, especially when the message is lost due to link error or network congestion. ACK information understands packet loss and triggers packet retransmission. In the satellite link, the large delay makes the above retransmission efficiency very low, because the traditional ACK information can only contain one error in one transmission window, if the TCP packet has multiple errors in one window , then we have to send multiple ACK messages to notify the sender, which is undoubtedly very unfavorable for asymmetric channels where the uplink channel is strictly limited and the uplink-downlink capacity ratio is between 1:10 and 1:1000.

Aiming at the above problems, a delayed deterministic packet retransmission method with local cache is proposed.

Contents of the invention

The purpose of the present invention is to provide a delayed and deterministic message retransmission method with local cache to solve the problem in the prior art that in the satellite link, the large time delay makes the retransmission efficiency after the message is lost is very low, Because the traditionally used ACK information can only contain one error within a transmission window, if multiple errors occur in a TCP packet within a window, then we have to send multiple ACK information to notify the sender, which is strictly restricted for the uplink channel. Undoubtedly, it is a very unfavorable problem for an asymmetric channel whose uplink and downlink capacity ratio is between 1:10 and 1:1000.

The invention provides a delay-deterministic message retransmission method with local cache, which solves the problems of low message retransmission efficiency and serious waste of channel resources caused by the long time delay of the satellite link.

Technical solution of the present invention is:

A delayed deterministic packet retransmission method with local cache,

Record the specific packet loss of message transmission. When packet loss occurs, the receiving end sends a deterministic retransmission request to the sending end to request the transmission of the lost message. The request carries information about one or more lost messages;

Set the retransmission delay for the newly lost message. When a new message is lost, after the retransmission delay, the receiving end sends a request to the sending end to transmit the newly lost message;

A local buffer is set at the satellite link receiving gateway, and when the reverse link ACK transmission sent by the receiving node is lost, the receiving gateway resends the message.

Preferably, the deterministic retransmission request option is activated through the TCP connection establishment process, the deterministic retransmission request option is located in the option field of the TCP header, and the deterministic retransmission is activated through the negotiation between the sending and receiving ends when the TCP connection is established request options;

If both ends of the TCP connection use the deterministic retransmission request option in the SYN segment of the TCP header, the deterministic retransmission request option will be activated. If either end of the TCP connection does not support deterministic retransmission request, then a regular ACK or a delayed ACK will be used.

Preferably, the receiving data queue records whether the message is correct, and the receiving end uses a bit vector to represent the information of multiple missing messages in an ACK message;

In the receiving data queue of the data receiving end, the information of whether the data is received correctly or incorrectly is recorded. When there is an error message in the queue, the receiving end uses a bit vector to represent the information of multiple missing messages, and sends it to the data sender by responding with an ACK message. end.

Preferably, when a new message is lost, a retransmission delay is set, and the response message ACK is not sent immediately, but after a delay for a period of time, all packet loss situations that occur during this period are marked in the bit vector and returned to the Data sender.

Preferably, a local buffer is set to prevent loss of reverse link ACK transmission. Set up a local cache on the G2 gateway to store the packets sent to H2. When the reverse link ACK sent by H2 is lost, G2 will retransmit it locally, saving the time for retransmitting lost packets.

Preferably, if the deterministic retransmission request is lost during transmission, the data receiving end resends the request.

Preferably, the steps of initiating deterministic packet retransmission are described as follows:

Step 1: The sender sets the deterministic message retransmission option in the TCP header option, and initiates a connection request to the receiver, that is, sets the SYN (synchronization) flag in the header;

Step 2: The receiving end receives the connection request, if the protocol stack supports the processing of this option, go to step 3, otherwise go to step 4;

Step 3: The receiving end sets the deterministic message retransmission option in the TCP header option, and initiates a connection response to the sending end, that is, sets the SYN/ACK (synchronization/response) flag in the header, indicating that the use of this option is accepted;

Step 4: The receiving end initiates a connection response to the sending end, that is, sets the SYN/ACK (synchronization/response) flag in the header, indicating that the use of this option is not accepted;

Step five: end.

Preferably, the steps for the receiving end to transmit deterministic message retransmission information to the sending end are described as follows:

Step 1: The receiving end checks the message loss of the receiving queue;

Step 2: The receiving end fills in the header information according to the packet loss situation, and sets the type value in the deterministic packet retransmission option to 21; fills in the length value, the first error offset, the first error length value, and the bit vector;

Step 3: The receiving end sends the response message when the retransmission delay clock times out;

Step 4: End.

Preferably, the processing steps of the receiving end of the deterministic retransmission request are described as follows:

Step 1: Transmit the first error in the deterministic retransmission request;

Step 2: Retransmit in ascending order of the bit vector, that is, the deterministic retransmission request bit vector sequence is shifted to the left until the 1 MSS data segment corresponding to the 0 on the left of the last 1 is retransmitted;

Step three: end.

The present invention provides a message retransmission method on a satellite link, that is, a deterministic retransmission request method (DSACK) with a local cache. In this method, the data receiving end explicitly requests the sending end for data that needs to be retransmitted, and A request may contain information about more than one missing data segment. Set a local cache to retransmit the lost packets locally, thus preventing packet loss in the reverse link ACK. This method is a strategy for faster loss recovery with limited bandwidth, so it is very important for long-latency networks.

The beneficial effects of the present invention are: a delayed and deterministic message retransmission method with local cache in the present invention, the receiving end records the specific packet loss of message transmission, and when packet loss occurs, the receiving end requests the sending end to only transmit Lost packets, and information of multiple lost packets can be carried in one request. This kind of delayed deterministic message retransmission method with local cache can reduce the frequency and quantity of message retransmission on channels with large delay, bit error rate and link bandwidth asymmetry, and avoid Due to the limited bandwidth of the reverse channel, the channel efficiency decreases when the packet is lost. At the same time, by setting a local cache, it can solve the problem of low channel transmission efficiency caused by large delay when the reverse ACK message is lost. The method can greatly improve the retransmission efficiency of the satellite link message, and greatly improve the utilization rate of the satellite channel.

Description of drawings

Fig. 1 is a schematic diagram of a network environment of an embodiment of the present invention;

FIG. 2 is three deterministic retransmission request data segments generated using bit vectors in an embodiment of the present invention;

Fig. 3 is a schematic diagram of a data sequence of a TCP receiving end in an embodiment of the present invention;

Fig. 4 is a flow chart of sending a retransmission response by the receiving end in an embodiment of the present invention.

detailed description

Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

The method described in this embodiment is applied in the network environment shown in FIG. 1 . The connection between users H1 and H2 includes a satellite link, and the satellite link and the ground link are separated by gateway stations G1 and G2. The entire connection is divided into three sections, and different protocol processing methods are adopted. The message retransmission method in this embodiment is applied to the satellite link segment connection 2 .

As shown in Figure 2, the figure shows the data queue where the sequence error occurs at the data receiving end. According to the data segment requirements of the deterministic retransmission request option, a bit vector is used to send a deterministic retransmission request. In Figure 2, there are three errors in the buffer queue at the receiving end. The first error occurs immediately when the previous ACK is received, so its offset is 0 and occupies the length of 2 MSS. The second error occurs The offset from the current ACK where the error occurs is 8, occupying 2 MSS lengths, and the offset of the third error is 12, occupying 1 MSS length.

The deterministic retransmission request data segment generated by the data receiving end is shown in FIG. 3 . It should be noted that the type is constant 21, which specifically refers to the deterministic retransmission request in the TCP header; the length refers to the 6 bytes of the deterministic retransmission request option plus the 2 bytes of its bit vector, a total of 8 words section; the last 1 is filled with five 0s to make up eight bits of a byte.

See Figure 4 for the process of sending a retransmission response at the receiving end.

Embodiment A delayed deterministic message retransmission method with local cache, by recording the specific packet loss of message transmission, when packet loss occurs, the receiving end sends a deterministic retransmission request to the sending end, requesting transmission of lost message, the request carries information about one or more lost messages; a retransmission delay is set for a newly lost message, and when a new message is lost, the receiving end sends a request to the sending end to transmit a new message after the retransmission delay Lost message: A local buffer is set at the gateway of the receiving end of the satellite link. When the reverse link ACK transmission sent by the receiving node is lost, the gateway of the receiving end resends the message.

The deterministic retransmission request option is activated through the TCP connection establishment process, the deterministic retransmission request option is located in the option field of the TCP header, and is activated through the negotiation between the sending and receiving ends when the TCP connection is established; If both ends of the TCP connection use the deterministic retransmission request option in the SYN segment of the TCP header, the deterministic retransmission request option will be activated. If either end of the TCP connection does not support deterministic retransmission request, then a regular ACK or a delayed ACK will be used.

The receiving data queue records whether the message is correct or not. The receiving end uses a bit vector to represent the information of multiple missing messages in an ACK message; When there is an error message in the queue, the receiving end uses a bit vector to represent the information of multiple missing messages, and sends it to the data sending end by responding with an ACK message;

When a new message is lost, set the retransmission delay, instead of sending the acknowledgment message ACK immediately, but after a period of delay, mark all the packet loss that occurred during this period in the bit vector, and return it to the data sender in a unified manner ;

Set up a local cache on the G2 gateway to store the packets sent to H2. When the reverse link ACK sent by H2 is lost, G2 will retransmit it locally, saving the time for retransmitting lost packets.

If a deterministic retransmission request is lost during transmission, the data receiver resends the request.

The steps for initiating deterministic packet retransmission are described as follows:

Step 1: The sender sets the deterministic message retransmission option in the TCP header option, and initiates a connection request to the receiver, that is, sets the SYN (synchronization) flag in the header;

Step 2: The receiving end receives the connection request, if the protocol stack supports the processing of this option, go to step 3, otherwise go to step 4;

Step 3: The receiving end sets the deterministic message retransmission option in the TCP header option, and initiates a connection response to the sending end, that is, sets the SYN/ACK (synchronization/response) flag in the header, indicating that the use of this option is accepted;

Step 4: The receiving end initiates a connection response to the sending end, that is, sets the SYN/ACK (synchronization/response) flag in the header, indicating that the use of this option is not accepted;

Step five: end.

The steps for the receiving end to transmit deterministic packet retransmission information to the sending end are described as follows:

Step 1: The receiving end checks the message loss of the receiving queue;

Step 2: The receiving end fills in the header information according to the packet loss situation, and sets the type value in the deterministic packet retransmission option to 21; fills in the length value, the first error offset, the first error length value, and the bit vector;

Step 3: The receiving end sends the response message when the retransmission delay clock times out;

Step 4: End.

Preferably, the processing steps of the receiving end of the deterministic retransmission request are described as follows:

Step 1: Transmit the first error in the deterministic retransmission request;

Step 2: Retransmit in ascending order of the bit vector, that is, the deterministic retransmission request bit vector sequence is shifted to the left until the 1 MSS data segment corresponding to the 0 on the left of the last 1 is retransmitted;

Step three: end.

The deterministic retransmission request option is located in the TCP header, and the deterministic retransmission request option includes the following data segments, as shown in Figure 3:

Type: This field is a byte that must be used when using a deterministic retransmission request. It is the first byte of the deterministic retransmission request option, and its value is 21;

Length: It is the second byte of the deterministic retransmission request option, which is the number of bytes occupied by the deterministic retransmission request option, including the bit vector of the deterministic retransmission request. The standard length value is 6 bytes plus bits the length of the vector;

The first error offset: This field occupies two bytes, which is the third and fourth bytes of the deterministic retransmission request option. This value indicates the difference between the first error in the data queue at the receiving end and the currently received The offset between the ACKs. Its unit is MSS (Maximum Segment Size), which can be simply calculated by the following formula.

Error 1 offset = (offset sequence value - ACK value) / (number of bytes contained in 1 MSS)

The length of the first error: This field occupies two bytes, which are the fifth and sixth bytes of the deterministic retransmission request option. This field represents the length of the first transmission error segment mentioned above, and shows how many bytes the error occupies in total, and its unit is MSS. Calculate according to the following formula:

Error 1 length = number of bytes in error 1/number of bytes contained in 1 MSS.

Deterministic retransmission request bit vector: After the bit vector error 1 length field, it occupies consecutive bytes, which contains the rest of the detected errors that exist in the receiving queue, so the number of occupied bytes will vary with the number of errors change. The bit vector is composed of 0 and 1. 0 indicates that a data block of the MSS size at this position has been lost, and 1 indicates that it has been successfully received. If there are less than eight bits, add 0 after the last 1 to make up eight bits, and the 0 here does not represent lost data.

Claims (8)

1. A delayed deterministic message retransmission method with local cache, characterized in that: Record the specific packet loss of message transmission. When packet loss occurs, the receiving end sends a deterministic retransmission request to the sending end to request the transmission of the lost message. The request carries information about one or more lost messages; Set the retransmission delay for the newly lost message. When a new message is lost, after the retransmission delay, the receiving end sends a request to the sending end to transmit the newly lost message; Set up a local cache at the satellite link receiving gateway, and when the reverse link ACK transmission sent by the receiving node is lost, the receiving gateway will resend the message; The deterministic retransmission request option is activated through the TCP connection establishment process, the deterministic retransmission request option is located in the option field of the TCP header, and is activated through the negotiation between the sending and receiving ends when the TCP connection is established; If both ends of the TCP connection use the deterministic retransmission request option in the SYN segment of the TCP header, the deterministic retransmission request option will be activated. If either end of the TCP connection does not support deterministic retransmission request, then a regular ACK or a delayed ACK will be used. 2. The delayed deterministic message retransmission method with local cache as claimed in claim 1, characterized in that: the receiving data queue records whether the message is correct, and the receiving end uses a bit vector to represent multiple Information about missing messages; In the receiving data queue of the data receiving end, the information of whether the data is received correctly or incorrectly is recorded. When there is an error message in the queue, the receiving end uses a bit vector to represent the information of multiple missing messages, and sends it to the data sender by responding with an ACK message. end. 3. The delayed deterministic message retransmission method with local cache as claimed in claim 1, characterized in that: when a new message is lost, the retransmission delay is set, and the response message ACK is not sent immediately, but delayed After a period of time, all packet loss situations that occurred during this period are marked in the bit vector and returned to the data sender in a unified manner. 4. The delayed deterministic message retransmission method with local cache as claimed in claim 1, characterized in that: a local cache is set at the G2 gateway to store the message sent to H2, and when the reverse link ACK sent by H2 When lost, G2 performs local retransmission. 5. The delayed deterministic packet retransmission method with local cache according to any one of claims 1-4, wherein if the deterministic retransmission request is lost during transmission, the data receiving end resends the request . 6. The delayed deterministic message retransmission method with local cache according to any one of claims 1-4, characterized in that: the step of initiating deterministic message retransmission is described as follows: Step 1: The sender sets the deterministic message retransmission option in the TCP header option, and initiates a connection request to the receiver, that is, sets the SYN flag in the header; Step 2: The receiving end receives the connection request, if the protocol stack supports the processing of this option, go to step 3, otherwise go to step 4; Step 3: The receiving end sets the deterministic message retransmission option in the TCP header option, and initiates a connection response to the sending end, that is, sets the SYN/ACK flag in the header, indicating that the use of this option is accepted; Step 4: The receiving end initiates a connection response to the sending end, that is, sets the SYN/ACK flag in the header, indicating that the use of this option is not accepted; Step five: end. 7. The delayed deterministic message retransmission method with local cache according to any one of claims 1-4, wherein the step of transmitting deterministic message retransmission information from the receiving end to the sending end is described as follows: Step 1: The receiving end checks the message loss of the receiving queue; Step 2: The receiving end fills in the header information according to the packet loss situation, and sets the type value in the deterministic packet retransmission option to 21; fills in the length value, the first error offset, the first error length value, and the bit vector; Step 3: The receiving end sends the response message when the retransmission delay clock times out; Step 4: End. 8. The delayed deterministic message retransmission method with local cache according to any one of claims 1-4, characterized in that: the steps of deterministic retransmission request receiving end processing are described as follows: Step 1: Transmit the first error in the deterministic retransmission request; Step 2: Retransmit in ascending order of the bit vector, that is, the deterministic retransmission request bit vector sequence is shifted to the left until the 1 MSS data segment corresponding to the 0 on the left of the last 1 is retransmitted; Step three: end.