CN110505533B - Method for error code retransmission control in TCP video transmission - Google Patents
Method for error code retransmission control in TCP video transmission Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client
- H04N21/63—Control signaling related to video distribution between client, server and network components; Network processes for video distribution between server and clients or between remote clients, e.g. transmitting basic layer and enhancement layers over different transmission paths, setting up a peer-to-peer communication via Internet between remote STB's; Communication protocols; Addressing
- H04N21/643—Communication protocols
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client
- H04N21/63—Control signaling related to video distribution between client, server and network components; Network processes for video distribution between server and clients or between remote clients, e.g. transmitting basic layer and enhancement layers over different transmission paths, setting up a peer-to-peer communication via Internet between remote STB's; Communication protocols; Addressing
- H04N21/647—Control signaling between network components and server or clients; Network processes for video distribution between server and clients, e.g. controlling the quality of the video stream, by dropping packets, protecting content from unauthorised alteration within the network, monitoring of network load, bridging between two different networks, e.g. between IP and wireless
- H04N21/64723—Monitoring of network processes or resources, e.g. monitoring of network load
- H04N21/64738—Monitoring network characteristics, e.g. bandwidth, congestion level
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/60—Network structure or processes for video distribution between server and client or between remote clients; Control signalling between clients, server and network components; Transmission of management data between server and client, e.g. sending from server to client commands for recording incoming content stream; Communication details between server and client
- H04N21/63—Control signaling related to video distribution between client, server and network components; Network processes for video distribution between server and clients or between remote clients, e.g. transmitting basic layer and enhancement layers over different transmission paths, setting up a peer-to-peer communication via Internet between remote STB's; Communication protocols; Addressing
- H04N21/647—Control signaling between network components and server or clients; Network processes for video distribution between server and clients, e.g. controlling the quality of the video stream, by dropping packets, protecting content from unauthorised alteration within the network, monitoring of network load, bridging between two different networks, e.g. between IP and wireless
- H04N21/64784—Data processing by the network
- H04N21/64792—Controlling the complexity of the content stream, e.g. by dropping packets
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- Computer Security & Cryptography (AREA)
- Communication Control (AREA)
- Detection And Prevention Of Errors In Transmission (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
Abstract
The invention discloses a method for error code retransmission control in TCP video transmission. The existing mechanism can cause the transmission speed to be reduced, and a large amount of video stream data messages can be delayed to arrive. The method of the invention judges whether the packet is lost and detects the error code after the receiving party receives the message, and if the error code occurs, the packet loss rate and the error code rate of the message are calculated. The receiver respectively processes according to the packet loss and the error code condition: if the packet loss rate is 0 or less than the threshold value, continuing normal transmission; if the packet loss rate is greater than or equal to the threshold and the error rate is less than the threshold, carrying out no error code retransmission notification processing, and starting a congestion avoidance mechanism and a slow start mechanism; and (3) observing the packet loss rate and the error rate which are both larger than or equal to the threshold, processing according to different conditions after a period of time, if the packet loss is not aggravated, continuing normal acceleration, otherwise, indicating that the congestion phenomenon exists at the same time, and decelerating according to a TCP (transmission control protocol) rule. The method of the invention can greatly reduce the triggering network congestion and smooth the network environment.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to an error code retransmission control method for optimizing packet loss retransmission caused by error codes in a video transmission process adopting a TCP (transmission control protocol).
Background
TCP (Transmission Control Protocol) is a connection-oriented, reliable transport layer communication Protocol based on byte stream, is the main transport Control Protocol for video Transmission in the current Internet environment, and provides reliable and sequential Transmission service between hosts. TCP congestion control is an important reason for its successful application, i.e. as long as the terminal detects data loss, it is considered that the data loss is caused by network congestion, and then a congestion control mechanism is invoked, which is suitable for a wired environment with good link quality. Congestion refers to the phenomenon that a router is forced to discard data information because it cannot handle high-rate arriving traffic. Congestion control refers to preventing excessive data injection into the network so that routers or links in the network are not overloaded. The slow start means that the network condition is detected when the sender host starts sending the datagram, and if the network condition is good, the sender can correctly receive the acknowledgement message segment of the other party every time the sender sends the message segment. The size of the congestion window, i.e. the size of the send window, is increased from small to large. Congestion avoidance refers to a slow increase, rather than a doubling, of the congestion window (cwnd), which increases by 1 rather than doubling every round trip time that elapses, thus causing the cwnd to increase slowly. As long as the congestion of the network is judged, the slow start threshold (ssthresh) is set to be half (more than or equal to 2) of the sending window, cwnd is set to be 1, and then a slow start algorithm is used, so that the data transmission from the host to the network can be rapidly reduced, and the router with the congestion can finish processing the packets accumulated in the queue.
In video transmission based on a wireless environment, because the wireless environment generally has higher Bit Error Rate (BER), variable bandwidth, large delay and frequent mobility characteristics compared with a wired environment, when a conventional TCP technology designed based on the wired environment is applied to the wireless environment, a large performance degradation is caused. This is because, in a wireless environment, packet loss is not necessarily caused by congestion, and most of the packet loss is caused by non-ideal characteristics of the channel itself, such as signal interference, multipath fading, etc., or caused by mobility and handover, TCP treats packet loss caused by error codes as congestion, and obviously, it is not suitable to reduce the packet sending rate. Therefore, how to effectively distinguish the reasons of packet loss in the wireless network and make a correct response becomes a key for improving the performance of transmitting the video stream by the wireless network line TCP.
When the congestion packet is lost, calling a congestion control algorithm to reduce the sending rate of the data packet; and when the wireless packet loss occurs, explicit retransmission is adopted, and the original sending rate is kept.
The impact of high bit error rate on TCP performance includes the following two:
(1) effect of random bit errors on TCP: if the number is small, the recovery can be realized by using an error correcting code; excessive errors may cause the message to be discarded before reaching the transport layer; initiating a fast retransmission; window reduction and throughput rate reduction;
(2) impact of burst errors on TCP performance: a timeout may be triggered; slow start, throughput rate reduction; the fast retransmission results in the retransmission of lost messages, the reduction of congestion windows and the reduction of throughput rate.
The error code is a phenomenon that a transmitted signal is distorted due to external interference of a digital signal in a wireless transmission process and the quality of a route switching device is not ideal enough, or the signal is distorted due to insufficient channel bandwidth, so that a receiving end cannot normally receive a correct message and is discarded.
Explicit Congestion Notification (ECN) in TCP protocol (RFC 3168) discloses a mechanism for router reporting and host responses. When congestion occurs, the sending hosts must still reduce their sending rate. However, by avoiding packet loss, the sending host does not need to enter the retransmission process, nor is the loss sensitive packet flow significantly affected by congestion. IP and TCP use unused fields in the header to support ECN.
At the network layer (IP), a sending host must be able to indicate that it is ECN capable and a router must be able to indicate that it is experiencing congestion while forwarding.
At the transport layer (TCP), the TCP end must indicate to the peer that it is ECN capable. The receiver must be able to inform the sender that it received a congestion advertisement from the router. The sender must be able to inform the receiver that it is being advertised from the receiver and that the sending rate has decreased.
Also, most importantly, this inability to configure the acceptable level of bit errors does not accommodate the presence of an acceptable bit error rate in video streaming, which can reduce the load placed on the network by the large number of bit error retransmissions. It is impossible to judge that error retransmission control must be applied even when there are a large number of errors.
There is also a scheme that employs congestion avoidance and slow start mechanism, when the network is congested because a large number of datagrams cannot be received normally (whether due to error codes or packet loss), TCP will immediately start the congestion avoidance mechanism, reduce the sending window, and then employ slow start. The congestion can be smoothly and controllably reduced by enabling the congestion mechanism if the congestion occurs in the network due to a large amount of delay and packet loss. However, in a wireless communication environment, packet loss (in a small amount) caused by video transmission errors is only an image blocking phenomenon or a partial mosaic phenomenon which momentarily affects video stream transmission, at this time, if normal congestion control is performed, a slow start threshold (ssthresh) is immediately set to be half of a sending window, cwnd is set to be 1, and then a slow start algorithm is used, so that although data injection into a network by a host can be rapidly reduced, a router with congestion can finish processing packets accumulated in a queue, due to the connection-oriented characteristic of TCP, a great reduction of the transmission speed of a certain video connection by a congestion control strategy can cause a large amount of video stream data messages to arrive in a delayed manner, thereby causing serious video delay, even heavy blocking, and possibly getting worse, gradually or even rushing.
In the existing TCP, both the slow start mechanism and the congestion avoidance mechanism are slow and fast sending, and when packet loss occurs, the speed is reduced by half. Especially in the wireless environment, the reason that the correct message may not be received is only error code, not congestion. Therefore, the improvement point is that the receiver finds out the packet loss and measures the quality of the wireless channel in real time: if the packet loss rate is lower than a certain threshold A and the video quality is tolerable, the feedback confirmation message indicates that retransmission is not needed, bandwidth waste caused by retransmission is avoided, and error code information is prompted in the feedback confirmation message; if the packet loss rate is higher than the threshold A and the error rate is higher than the threshold B, the packet loss is probably caused by the error code, the TCP is not decelerated and is not accelerated, a period of time is observed, if the packet loss is not accelerated, the TCP is continuously accelerated, otherwise, the TCP is decelerated according to the TCP rule, and the congestion phenomenon is caused at the same time; if the packet loss rate is higher than the threshold A and the error rate is lower than the threshold B, it is shown that the packet loss is probably caused by congestion, and the speed is reduced normally according to the TCP rule.
Disclosure of Invention
The invention aims to provide a method for error code retransmission control of TCP video transmission.
TCP based video transmission establishes a connection and enters normal data exchange. Due to the continuity of video streaming, the connection is maintained continuously after the connection is established unless the connection is actively interrupted or the network is disconnected. At a certain point, due to the interference, change, switching and other reasons of the wireless network environment, some packets sent by the sender have error code messages, and the error code messages may be individual or continuous message error codes. This occurs and error retransmission is required. The specific control method of error code retransmission is as follows:
(1) continuously sending messages by a sender, judging whether packet loss occurs and detecting error codes when a receiver receives messages with the sequence number of M1, accumulating the number of error code messages in a time window t if the error codes occur, recording the number as S, and calculating the packet loss rate PLR and the error code rate SER of the messages;
t is the calculation time period of the time window and is set to be 1 second; s is the accumulated number of the error codes, if the error codes appear in the time period t, S is added with 1, and S is a four-digit numerical value.
(2) The receiving party judges the packet loss and error code conditions and performs the following processing:
a, plr is 0, which indicates that no packet loss occurs and the current transmission state is maintained, normal transmission is continued, error code retransmission notification processing is not performed, and the 6-bit reserved field of the TCP acknowledgment packet header sent by the receiver is set to 0; when the sender receives the TCP acknowledgement message and the first 2 bits in the reserved field of 6 bits in the header of the acknowledgement message are 00, the sender determines that retransmission is not needed.
PLR < tau 1, which indicates that a small amount of message error codes occur, can accept the influence on the video stream, keeps the current transmission state, continues normal transmission, and does not perform error code retransmission notification processing. The first 2 position 0 in the 6 bits reserved field of the TCP confirmation message header sent by the receiver indicates that retransmission is not needed, the last 4 bits are S value, and the error code accumulated number S carries out accumulation of the error code message number according to the t time window. τ 1 is the set packet loss rate threshold value of 5 × 10-4～5×10-3. When the sender receives the TCP acknowledgement message and the first 2 bits in the reserved field of 6 bits in the header of the acknowledgement message are 00, the sender determines that retransmission is not needed.
PLR is more than or equal to tau 1 and SER is less than tau 2, which indicates that packet loss is probably caused by congestion, normal deceleration is carried out according to a TCP congestion avoidance mechanism, and error code retransmission notification processing is not carried out; the first 2 position 01 in the 6 bits of the TCP acknowledgement message header reservation field sent by the receiver represents the congestion deceleration, and the last 4 bits are S value. When the sender receives a TCP acknowledgement message and the first 2 bits in a reserved field of 6 bits of an acknowledgement message header are 01, a congestion avoidance mechanism and a slow start mechanism are started. τ 2 is a set bit error rate threshold of 5 × 10-5～5×10-4。
And D, PLR is more than or equal to tau 1, SER is more than or equal to tau 2, which indicates that error codes exist at the moment and approaches the error code allowable limit, the processing method adopts the steps of firstly not accelerating and not decelerating, observing a period of time k, if packet loss is not intensified, continuing normal acceleration, otherwise, indicating that congestion exists at the same time, and decelerating according to TCP rules. k is an observation time window and is set to be 0.5-2 seconds. The specific error retransmission notification processing is as follows:
a. when PLR is larger than or equal to tau 1 and SER is larger than or equal to tau 2 for the first time, the front 2 position 10 in the reserved field of 6 bits of the TCP confirmation message header sent by the receiving party represents error code observation, the rear 4 bits are S values, and simultaneously error code observation timing is started; after receiving the confirmation message, the sender does not retransmit or decelerate and continues normal transmission.
b. After k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, but PLR is not increased, it shows that there is no aggravation of packet loss, the front 2 position 10 in 6 bits of reserved field of TCP acknowledgement message header sent by receiver shows error code observation, the back 4 bits are S value, and at the same time, error code observation timing is started; after receiving the confirmation message, the sender continues to perform normal transmission without retransmission or deceleration.
c. After k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, PLR is increased, but SER is not increased, which indicates that congestion is aggravated, the former 2 position 01 in 6 bit reserved field of TCP acknowledgement message header sent by receiver indicates congestion deceleration, the latter 4 position is S value, and error code observation timing is started at the same time; when the sender confirms that the first 2 bits in the 6-bit reserved field of the message header are 01, a congestion avoidance mechanism and a slow start mechanism are started.
d. After k time period, the PLR is still more than or equal to tau 1 and the SER is more than or equal to tau 2, the PLR is increased and the SER is increased, which indicates that the error code is aggravated, and error code retransmission is needed because the error code exceeds the threshold value to influence the actual use. The front 2 position 11 in the 6 bit reserved field of the TCP acknowledgement message header sent by the receiver represents deceleration and retransmission, the rear 4 bit is S value, and error code observation timing is started at the same time. When the sender confirms that the first 2 bits in the 6-bit reserved field of the message header are 11, a congestion avoidance mechanism and a slow start mechanism are started, error code retransmission is carried out simultaneously, and the number of retransmitted messages is 0.5 times of the S value.
The method can accept a small amount of error codes, and error code packet loss retransmission is not started, so that the triggering network congestion can be greatly reduced; the reserved message field is used for transmitting the error code severity and the speed reduction + retransmission instruction, and no extra overhead is needed; in the environment of wireless transmission of video streams, the retransmission of each video stream is double impact on the network, and the retransmission is started as required, so that the network environment can be smoothed.
Detailed Description
The video stream receiver finds out the packet loss, and the wireless channel quality is measured in real time: if the packet loss rate is higher than the set threshold, the error rate is also higher than the set threshold, which indicates that the packet loss is probably caused by the error code, the TCP is not decelerated and is not accelerated, a period of time is observed, if the packet loss is not aggravated, the TCP is continuously accelerated, otherwise, the TCP is decelerated according to the TCP rule, and the congestion phenomenon is continuously generated; if the packet loss rate is higher than the set threshold and the error rate is lower than the set threshold, it is indicated that the packet loss is probably caused by congestion, and the speed is reduced normally according to the TCP rule.
The video stream receiver finds out the packet loss, and the wireless channel quality is measured in real time: if the packet loss rate is lower than a certain threshold value and the video quality is tolerable, the feedback confirmation message indicates that retransmission is not needed, bandwidth waste caused by retransmission is avoided, and error code information is prompted in the feedback confirmation message; filling the received maximum fragment sequence number by the confirmed sequence number; if the packet loss is higher than the packet loss threshold value, marking a mark of 'unnecessary retransmission' is not marked, and the confirmed sequence number fills the received sequence number of the lost fragment;
if the receiver finds that the error rate is higher than the threshold value, alarm information is filled in reserved bits of the confirmation message; and the sender receives the confirmation message for analysis, identifies error code warning information, and immediately takes measures to adjust the quality of the wireless channel if the error code rate is higher than a threshold value, wherein the measures comprise measures of automatically adjusting the orientation of an antenna, the sending power and the like.
The method for judging the error rate utilizes a method for feeding back 'unnecessary retransmission' or the error rate by reserved bits of the confirmation message.
TCP based video transmission establishes a connection and enters normal data exchange. Due to the continuity of video streaming, the connection is maintained continuously after the connection is established unless the connection is actively interrupted or the network is disconnected. At a certain point, due to the interference, change, switching and other reasons of the wireless network environment, some packets sent by the sender have error code messages, and the error code messages may be individual or continuous message error codes. This occurs and error retransmission is required. The method for error code retransmission control in TCP video transmission specifically comprises the following steps:
(1) continuously sending messages by a sender, judging whether packet loss occurs and detecting error codes when a receiver receives messages with the sequence number of M1, accumulating the number of error code messages in a time window t if the error codes occur, recording the number as S, and calculating the packet loss rate PLR and the error code rate SER of the messages;
t is the calculation time period of the time window and is set to be 1 second; s is the accumulated number of the error codes, if the error codes appear in the time period t, S is added with 1, and S is a four-digit numerical value.
(2) The receiving party judges the packet loss and error code conditions and performs the following processing:
a, plr is 0, which indicates that no packet loss occurs and the current transmission state is maintained, normal transmission is continued, error code retransmission notification processing is not performed, and the 6-bit reserved field of the TCP acknowledgment packet header sent by the receiver is set to 0; when the sender receives the TCP acknowledgement message and the first 2 bits in the reserved field of 6 bits in the header of the acknowledgement message are 00, the sender determines that retransmission is not needed.
PLR < tau 1, which indicates that a small amount of message error codes occur, can accept the influence on the video stream, keeps the current transmission state, continues normal transmission, and does not perform error code retransmission notification processing. The first 2 position 0 in the 6 bits reserved field of the TCP confirmation message header sent by the receiver indicates that retransmission is not needed, the last 4 bits are S value, and the error code accumulated number S carries out accumulation of the error code message number according to the t time window. τ 1 is the set packet loss rate threshold value of 5 × 10-4～5×10-3In this embodiment, τ 1 is 0.001. When the sender receives the TCP acknowledgement message and the first 2 bits in the reserved field of 6 bits in the header of the acknowledgement message are 00, the sender determines that retransmission is not needed.
PLR is more than or equal to tau 1 and SER is less than tau 2, which indicates that packet loss is probably caused by congestion, normal deceleration is carried out according to a TCP congestion avoidance mechanism, and error code retransmission notification processing is not carried out; the first 2 position 01 in the 6 bits of the TCP acknowledgement message header reservation field sent by the receiver represents the congestion deceleration, and the last 4 bits are S value. When the sender receives a TCP acknowledgement message and the first 2 bits in a reserved field of 6 bits of an acknowledgement message header are 01, a congestion avoidance mechanism and a slow start mechanism are started. τ 2 is a set bit error rate threshold of 5 × 10-5～5×10-4In this embodiment, τ 2 ═0.0001。
And D, PLR is more than or equal to tau 1, SER is more than or equal to tau 2, which indicates that error codes exist at the moment and approaches the error code allowable limit, the processing method adopts the steps of firstly not accelerating and not decelerating, observing a period of time k, if packet loss is not intensified, continuing normal acceleration, otherwise, indicating that congestion exists at the same time, and decelerating according to TCP rules. k is an observation time window, and is set to be 0.5 to 2 seconds, and k is 1s in the embodiment. The specific error retransmission notification processing is as follows:
a. when PLR is larger than or equal to tau 1 and SER is larger than or equal to tau 2 for the first time, the front 2 position 10 in the reserved field of 6 bits of the TCP confirmation message header sent by the receiving party represents error code observation, the rear 4 bits are S values, and simultaneously error code observation timing is started; after receiving the confirmation message, the sender does not retransmit or decelerate and continues normal transmission.
b. After k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, but PLR is not increased, it shows that there is no aggravation of packet loss, the front 2 position 10 in 6 bits of reserved field of TCP acknowledgement message header sent by receiver shows error code observation, the back 4 bits are S value, and at the same time, error code observation timing is started; after receiving the confirmation message, the sender continues to perform normal transmission without retransmission or deceleration.
c. After k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, PLR is increased, but SER is not increased, which indicates that congestion is aggravated, the former 2 position 01 in 6 bit reserved field of TCP acknowledgement message header sent by receiver indicates congestion deceleration, the latter 4 position is S value, and error code observation timing is started at the same time; when the sender confirms that the first 2 bits in the 6-bit reserved field of the message header are 01, a congestion avoidance mechanism and a slow start mechanism are started.
d. After k time period, the PLR is still more than or equal to tau 1 and the SER is more than or equal to tau 2, the PLR is increased and the SER is increased, which indicates that the error code is aggravated, and error code retransmission is needed because the error code exceeds the threshold value to influence the actual use. The front 2 position 11 in the 6 bit reserved field of the TCP acknowledgement message header sent by the receiver represents deceleration and retransmission, the rear 4 bit is S value, and error code observation timing is started at the same time. When the sender confirms that the first 2 bits in the 6-bit reserved field of the message header are 11, a congestion avoidance mechanism and a slow start mechanism are started, error code retransmission is carried out simultaneously, and the number of retransmitted messages is 0.5 times of the S value.
Claims (3)
1. A method for error code retransmission control in TCP video transmission is characterized in that the control method specifically comprises the following steps:
(1) continuously sending messages by a sender, judging whether packet loss occurs and detecting error codes when a receiver receives messages with the sequence number of M1, accumulating the number of error code messages in a time window t if the error codes occur, recording the number as S, and calculating the packet loss rate PLR and the error code rate SER of the messages;
t is the calculation time period of the time window and is set to be 1 second; s is the accumulated number of the error codes, if the error codes appear in the time period t, the S is added with 1, and the S is a four-digit numerical value;
(2) the receiving party judges the packet loss and error code conditions and performs the following processing:
a, plr is 0, which indicates that no packet loss occurs and the current transmission state is maintained, normal transmission is continued, error code retransmission notification processing is not performed, and the 6-bit reserved field of the TCP acknowledgment packet header sent by the receiver is set to 0; when a sender receives a TCP confirmation message and the first 2 bits in a reserved field of 6 bits of a confirmation message header are 00, determining that retransmission is not needed;
PLR is less than tau 1, which indicates that a small amount of message error codes occur, the influence on the video stream can be accepted, the current transmission state is kept, normal transmission is continued, and error code retransmission notification processing is not performed; the first 2 position 0 in the 6 bits of reserved field of TCP confirmation message header sent by the receiver represents that retransmission is not needed, the last 4 bits are S value, and the error code accumulated number S carries out accumulation of error code message number according to t time window; τ 1 is a set packet loss rate threshold; when a sender receives a TCP confirmation message and the first 2 bits in a reserved field of 6 bits of a confirmation message header are 00, determining that retransmission is not needed;
PLR is more than or equal to tau 1 and SER is less than tau 2, which indicates that packet loss is probably caused by congestion, normal deceleration is carried out according to a TCP congestion avoidance mechanism, and error code retransmission notification processing is not carried out; the first 2 positions 01 in the 6 bits of the head reserved field of the TCP acknowledgement message sent by the receiver represent congestion and deceleration, and the last 4 bits are S values; when a sender receives a TCP confirmation message and confirms that the first 2 bits in a 6-bit reserved field of a message header are 01, a congestion avoidance mechanism and a slow start mechanism are started; τ 2 is a set bit error rate threshold;
PLR is greater than or equal to tau 1 and SER is greater than or equal to tau 2, which indicates that error codes exist at the moment and approaches the error code allowable limit, the processing method adopts the steps of firstly not accelerating and not decelerating, observing a period of time k, if packet loss is not intensified, continuing normal acceleration, otherwise, indicating that congestion exists at the same time, and decelerating according to TCP rules; k is an observation time window; the specific error retransmission notification processing is as follows:
a. when PLR is larger than or equal to tau 1 and SER is larger than or equal to tau 2 for the first time, the front 2 position 10 in the reserved field of 6 bits of the TCP confirmation message header sent by the receiving party represents error code observation, the rear 4 bits are S values, and simultaneously error code observation timing is started; after receiving the confirmation message, the sender does not retransmit or decelerate and continues normal transmission;
b. after k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, but PLR is not increased, it shows that there is no aggravation of packet loss, the front 2 position 10 in 6 bits of reserved field of TCP acknowledgement message header sent by receiver shows error code observation, the back 4 bits are S value, and at the same time, error code observation timing is started; after receiving the confirmation message, the sender continues to perform normal transmission without retransmission or deceleration;
c. after k time period, still PLR is more than or equal to tau 1 and SER is more than or equal to tau 2, PLR is increased, but SER is not increased, which indicates that congestion is aggravated, the former 2 position 01 in 6 bit reserved field of TCP acknowledgement message header sent by receiver indicates congestion deceleration, the latter 4 position is S value, and error code observation timing is started at the same time; when the sender confirms that the first 2 bits in the reserved field of 6 bits of the message header are 01, a congestion avoidance mechanism and a slow start mechanism are started;
d. after k time period, the PLR is still more than or equal to tau 1 and the SER is more than or equal to tau 2, the PLR is increased and the SER is increased, which indicates that the error code aggravation phenomenon occurs, and error code retransmission is needed because the error code exceeds the threshold value to influence the actual use; the front 2 position 11 in the 6 bit reserved field of the TCP confirmation message header sent by the receiver represents deceleration and retransmission, the rear 4 bit is S value, and error code observation timing is started at the same time;
when the sender confirms that the first 2 bits in the 6-bit reserved field of the message header are 11, a congestion avoidance mechanism and a slow start mechanism are started, error code retransmission is carried out simultaneously, and the number of retransmitted messages is 0.5 times of the S value.
2. The method of claim 1, wherein the method comprises the following steps: τ 1 > τ 2, τ 1 equal to 5 × 10-4～5×10-3τ 2 equal to 5 × 10-5～5×10-4。
3. The method of claim 1, wherein the method comprises the following steps: k is equal to 0.5-2 s.
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| CN112492646B (en) * | 2020-11-27 | 2022-04-08 | 清华大学 | Congestion control method and device based on congestion cause identification |
| CN115603870B (en) * | 2022-09-02 | 2024-05-28 | 杭州航天电子技术有限公司 | Buffer-free bit error rate real-time detection method based on increment number |
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