CN1324862C - Method for regulating congest window in communication network - Google Patents

Abstract

The present invention relates to a method for regulating congestion windows in a communication network. In the method of the present invention, the length of the cache queue of a switching node is calculated, and the reasons for the generation of packet loss are determined according to the length of the cache queue, so that the limiting values of the enabling gate and the congestion window of the switching node are correspondingly regulated by adopting different control strategies in view of different reasons. The present invention not can reserve the advantages when a TCP Reno processes the network congestion situation, and meanwhile, can set appropriate thresholds and congestion control windows by using the bandwidth estimation as for the packet loss resulting from the link properties, so that the network bandwidth is effectively utilized and the throughput of the system is enhanced. In addition, the present invention also calculates the length of the cache queue on the switching node and judges the network congestion situation through the length of the queue so as to process packet loss in time and shorten waiting time for queuing simultaneously.

Description

Adjust the method for congestion window in the communication network

Technical field

The present invention relates to network communications technology field, relate in particular to the method for transport layer adjustment congestion window in a kind of communication network.

Background technology

Internet (the Internet) is a kind of network that the service of doing one's best is provided, TCP (TransportControl Protocol, transmission control protocol) is a kind of reliable transport layer protocol on it, is widely used in the application such as Email, file transfer, Voice ﹠ Video data flow and Web (World Wide Web).According to statistics, the tcp data flow will account among the Internet more than 95%, so Transmission Control Protocol is a kind of prevailing host-host protocol end to end among the Internet, the reliability and stability of current Internet are all inseparable with the congestion control mechanism of Transmission Control Protocol.

The most general TCP realizes it being TCP Reno on the Internet at present, and TCP Reno is a kind of end-to-end transport layer protocol, has adopted the window of AIMD (Additive Increase MultiplicativeDecrease, additivity increases multiplier and subtracts) to adjust mechanism.

In TCP Reno, the actual send window size of transmitting terminal is: MIN (RCVWND, CWDN+NDUP), promptly in " RCVWND " and " CWDN+NDUP " value a less value as actual send window size; Wherein RCVWND refers to the window that the recipient notifies, CWDN refers to the transmitting terminal congestion window, NDUP receives repeat ACK (confirmation) at transmitting terminal number less than tcprexmtthresh (tcprexmtthresh makes TCP start the repeat ACK number of quick retransmission mechanism) before, equal 0, be the number of the repeat ACK received again afterwards.If do not consider flow control, then send window equals CWDN+NDUP.

The congestion control policy of Reno is described below:

If 1. receive non-repeat ACK message, then:

If w＜ssthresh, set w=w+1; If current congestion window w then whenever receives an ACK less than slow enabling gate limit value ssthresh, just window is increased the size of a TCP section, and this process is referred to as slow start-up course;

Otherwise,, just window is increased inverse/one of current window, and this process is referred to as congestion avoidance procedure if current congestion window less than notification window, is whenever received an ACK greater than slow enabling gate limit value;

If the repeat ACK message of 2. receiving, and the ACK message number＞tcprexmtthresh that receives, then:

Retranmit " next expected " segment; Retransmit the message segment of the needs re-transmission that illustrates in the repeat ACK confirmatory message, i.e. grouping;

Seasonal together slow enabling gate limit value equals half of current window; Then set w=ssthresh; The slow enabling gate limit value that congestion window equals to upgrade;

If 3. retransmit timer expired, then enter SlowStart (starting slowly):

Slow enabling gate limit value equals half of current window;

Set w=1; Congestion window equals a message segment;

Yet the above-mentioned TCP Reno that is initially cable environment design is unsatisfactory in the performance that has on the Radio Link of burst error.TCP Reno thinks that all packet loss all are because congested generation, so because link property changes the random packet loss that causes all is used as congestion loss and handles, directly window is reduced to half of packet loss front window.Reducing by half of this window is unnecessary often, causes systematic function to descend, and causes waste of network resources.

Summary of the invention

Problem in view of above-mentioned prior art existence, the purpose of this invention is to provide the method for adjusting congestion window in a kind of communication network, the reason that this method can be distinguished the packet loss generation is random loss or congestion loss, and according to the definite adjustment strategy at window of the reason of grouping generation.

The objective of the invention is to be achieved through the following technical solutions:

Adjust the method for congestion window in described a kind of communication network, comprising:

The length of the buffer queue of switching node in A, the computing network;

B, determine to cause the reason that packet loss produces in the network, and adopt corresponding control strategies that the congestion window of switching node is adjusted respectively at different reasons according to the length of described buffer queue.

Described steps A comprises:

A1, determine the bandwidth of network according to the message that transmits in the network;

A2, according to the length of the buffer queue at the bandwidth calculation switching node place of network;

Described steps A 1 comprises:

ACK (confirmation) message length of receiving according to sending node in the network that message confirmed and the bandwidth of determining network blanking time of adjacent two ACK messages.

Described steps A 1 further comprises:

The ACK that receives with sending node (confirmation) message length that message was confirmed is divided by the blanking time of this ACK message and previous ACK message respectively, and the result of acquisition conduct is based on the sampled value of the network bandwidth of this ACK message;

The a plurality of network bandwidth sampled values that obtain are carried out smoothing processing, obtain the bandwidth of network.

Described steps A 2 comprises:

Bandwidth value, the size of grouping, the network bandwidth of current expectation and the length of calculating the buffer queue at switching node place minimum two-way time between sending node and receiving node according to the network that obtains.

Described steps A 1 specifically comprises:

Network bandwidth sampled value sample_BWE[k] be:

sample_BWE[k]＝(ACKed*seg_size*8)/now～lastACKtime，

Wherein, ACKed represents the message segment number that ACK confirmed received by this, seg_size represents the contained byte of message segment, and now～lastACKtime represents that this is received and receives the time interval of ACK ACK and last time that K was the sequence number of this message of receiving that ACK confirmed;

Network bandwidth sampled value is carried out smoothing processing, estimates to determine network bandwidth BWE[k] be:

$\mathrm{BWE}\left[k\right]=\left(\frac{19}{21}\right)*\mathrm{BWE}[k-1]+\left(\frac{1}{21}\right)*(\mathrm{sample}\_\mathrm{BWE}[k]+\mathrm{sample}\_\mathrm{BWE}[k-1\left]\right);$

And described steps A 2 specifically comprises:

The length of buffer queue N at switching node place is:

$\stackrel{\‾}{N}=(\mathrm{Expected}-\frac{\mathrm{BWE}}{\mathrm{seg}\_\mathrm{size}})*\mathrm{BaseRTT},$

Wherein, $\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}}$ It is the expected rate of current time, cwnd represents the size of congestion window, BaseRtt is the minimum two-way time of message between switching node, and for being the message segment size, BWE is the estimated value BWE[k of the current time network bandwidth of above-mentioned steps A1 acquisition to seg_size as previously mentioned].

Described steps A comprises:

Calculate the length of buffer queue of switching node according to the round minimum time of message between expected rate, actual speed rate and the switching node of current network.

Described steps A further comprises:

Calculation expectation speed Expected and actual speed rate Actual:

$\mathrm{Expected}=\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}},\mathrm{Actual}=\frac{\mathrm{cwnd}}{\mathrm{Rtt}};$

Wherein, cwnd represents congestion window size, and BaseRtt represents the minimum two-way time of message between switching node, and RTT represents the actual two-way time of message between switching node;

Calculating the length of buffer queue N that determines switching node is:

N＝Actual*(RTT-BaseRTT)＝Diff*BaseRTT，

Wherein, Diff=Expected-Actual is the difference of expected rate Expected and actual speed rate Actual.

Described step B comprises:

If the length of the described buffer queue of B1 is greater than the queue length threshold value of setting, determine that then the network bandwidth is saturated, and the packet loss that produces in the network is because of congested causing, and carries out the adjustment of the window and the enabling gate limit value of this switching node according to corresponding congestion control policy;

If the length of the described buffer queue of B2 is less than the queue length threshold value of setting, then determine network bandwidth unsaturation, and the packet loss that produces in the network causes for changing because of link property, and carries out the adjustment of the window and the enabling gate limit value of this switching node according to the control strategy that changes based on link property.

Adjust in the described communication network in the method for congestion window, the described basis of step B2 is carried out the window of this switching node and being adjusted into of enabling gate limit value based on the control strategy that link property changes:

If receive the ACK message of three repetitions, adjustment starts thresholding slowly and equals estimated bandwidth and the product of minimum two-way time and the ratio of TCP message segment size, and, if the current congestion window then makes congestion window equal to start slowly thresholding greater than slow enabling gate limit value;

If the re-transmission timer expired then makes congestion window equal 1, order starts thresholding slowly and equals estimated bandwidth and the product of minimum two-way time and the ratio of TCP message segment size, and if start thresholding less than 2 slowly, then makes starting thresholding slowly and equaling 2.

TCP Reno is by congestion window being reduced by half, can effectively reduce the buffer memory team leader, handle the network congestion situation timely when handling network congestion, and the performance of this algorithm has obtained good confirmation in cable network.As seen from the above technical solution provided by the invention, the present invention not only can keep the above-mentioned advantage of TCP Reno when handling network congestion, simultaneously for the packet loss that causes because of link property, also realized utilizing bandwidth estimation to set suitable thresholding and congested control window, the network bandwidth is effectively utilized, improve the throughput of system.

In a word, the present invention can effectively distinguish the reason that packet loss produces, improving the throughput performance of TCP on the Radio Link as the case may be, and can be according to the congestion condition of network, self adaptation is adjusted window, to strengthen the stability of Transmission Control Protocol.In addition, the present invention also calculates the length of buffer queue at switching node place, and judges the network congestion situation by formation is long, so that reduce queue waiting time when in time handling packet loss.

Description of drawings

Fig. 1 is the flow chart of method of the present invention.

Embodiment

The core concept of method of the present invention is the length by the buffer queue that calculates switching node, then, determine in the network to produce the reason of packet loss according to the length of buffer queue, and adopt different control strategies that the congestion window and the enabling gate limit value of switching node are adjusted accordingly at different reasons.One aspect of the present invention can utilize the number of receiving grouping that the ack msg stream that returns confirmed and two adjacent ACK blanking time estimation network bandwidth, utilize this bandwidth information of estimating to calculate the size of the length of buffer queue N at switching node place again; The size of the length of buffer queue N that can also determine switching node according to the expected rate and the actual speed rate value of current network on the other hand.

After having obtained the size of length N of buffer queue of corresponding switching node, just can judge the congestion condition of network according to the N value.Promptly when packet loss takes place, judge the reason of packet loss according to the congestion condition of network, if when packet loss takes place, N thinks that greater than the queue length threshold value of setting packet loss is that network congestion causes; When if packet loss takes place, N is less than the queue length threshold value of setting, think that then packet loss is because the influence that link property changes produces, and at the packet loss that causes based on different reasons, just can take different control strategies to carry out the adjustment of congestion window and enabling gate limit value.

For the present invention there being further understanding, existing in conjunction with the accompanying drawings, and with the length value that calculates the buffer queue of switching node according to the network bandwidth be example the invention will be further described, referring to Fig. 1, specifically comprise following processing procedure:

Step 1: to network bandwidth value sample_BWE[k] sample;

sample_BWE[k]＝(ACKed*seg_size*8)/now～lastACKtime，

Wherein, ACKed represents the message segment number that ACK confirmed received by this, seg_size represents the contained byte of message segment, now～lastACKtime represents that this is received and receives the time interval of ACK ACK and last time, K is the sequence number of this message of receiving that ACK confirmed, described ACKed value and seg_size value can obtain according to the feature of network, now～lastACKtime value then can root by the actual monitoring acquisition of the time of reception of ACK message.

Step 2: the network bandwidth sampled value of obtaining is carried out smoothing processing ,] with the bandwidth value BWE[k of current network that to estimate;

$\mathrm{BWE}\left[k\right]=\left(\frac{19}{21}\right)*\mathrm{BWE}[k-1]+\left(\frac{1}{21}\right)*(\mathrm{sample}\_\mathrm{BWE}[k]+\mathrm{sample}\_\mathrm{BWE}[k-1\left]\right).$

Step 3: the buffer queue that calculates the switching node place according to the bandwidth value of the current network that obtains;

$\stackrel{\‾}{N}=(\mathrm{Expected}-\frac{\mathrm{BWE}}{\mathrm{seg}\_\mathrm{size}})*\mathrm{BaseRTT};$

Wherein $\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}}$ It is the expected rate of current time, cwnd represents the size of congestion window, BaseRtt is the minimum two-way time of the message that sends of switching node, seg_size is the grouping size that switching node sends message, BWE is the estimated value BWE[k of the current time network bandwidth], described cwnd value is for there being the parameter of application in the Network Transmission, the present invention directly obtains application and gets final product, and described BaseRtt value relatively obtains according to the tracking to RTT.

Step 4: when in the network packet loss taking place, whether the length value N that judges described buffer queue is greater than the queue length threshold value β that sets, if greater than, then execution in step 5, otherwise, execution in step 6, described queue length threshold value β is generally an empirical value, can obtain by network test, can be 3 for this value of present network.

Step 5: the length value N＞β that determines buffer queue, at this moment, think that the network bandwidth is saturated, the reason of the packet loss that produces is based on congestion loss, and carry out the adjustment of congestion window and slow enabling gate limit value according to the congestion control policy in the algorithm of TCP-Reno, that describes in concrete adjustment process and the background technology is identical.

Step 6: the length value N＜β that determines buffer queue, at this moment, it is saturated to think that the network bandwidth does not have, network does not take place congested, the reason of packet loss is likely owing to link property changes and causes, described link property changes, and promptly Radio Link generally includes the influence of Internet protocol capabilities:

1. link error rate: wireless host adopts wireless or the infrared waves transmission communicates, and very easily is subjected to environmental interference, and the BER on the wireless network (bit error rate) is wired 10 times or poorer, as long as a wireless links is arranged, will have influence on the performance of whole network;

2. bandwidth: bandwidth is scarce resource in wireless network, compares to 1000M (even higher) with typical wired ethernet 10M, and the bandwidth of WLAN (wireless local area network) less relatively (2M), and also variation is also bigger;

3. mobility: wireless host frequently moves when communication, causes easily that loss of data even communication are temporary transient to be interrupted.TCP is interpreted as it congested, and excites congestion control mechanism, but this there is no need, because in case move and stop, wireless host begins again to have received data, so just causes the decreased performance of TCP.

For because of link property changes the packet loss that causes, need carry out the adjustment of congestion window and slow enabling gate limit value according to the following control strategy that changes based on link property, concrete processing procedure is;

If switching node is received the ACK message of three repetitions, then carry out following operation:

Ssthresh=(bwe*BaseRTT)/(seg_size); / make the network bandwidth and the product of minimum two-way time and the ratio of TCP message segment size that slow enabling gate limit value equals to estimate;

If (cwnd＞ssthresh); If/current congestion window is greater than slow enabling gate limit value;

Cwnd=ssthresh; / make congestion window equal to start slowly thresholding;

Simultaneously,, then need to carry out again the transmission of corresponding message, and start corresponding timer, when this timer expired, then carry out following operation if switching node is received the ACK message of repetition:

Cwnd=1; / make congestion window equal 1;

Ssthresh=(bwe*BaseRTT)/(seg_size); / order starts thresholding slowly and equals estimated bandwidth and the product of minimum two-way time and the ratio of TCP message segment size;

if(ssthresh＜2)

Ssthresh=2; If/start thresholding slowly less than 2, then order starts thresholding slowly and equals 2.

In the above-mentioned processing procedure, step 1 has been described the acquisition process of the length of buffer queue value of switching node to step 3, in TCP Vegas, described length of buffer queue value can also adopt following method to obtain, but, when obtaining the length of buffer queue value, also need to obtain the network bandwidth value in the current network by following method for guaranteeing the realization of follow-up congestion window and enabling gate limit value adjustment mechanism;

The length of buffer queue value that is switching node can also obtain by following computational process:

At first, expected rate Expected that computing network is current and actual speed rate Actual are specially: expected rate $\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}},$ Actual speed rate $\mathrm{Actual}=\frac{\mathrm{cwnd}}{\mathrm{Rtt}};$

Wherein, cwnd represents the size of congestion window, and BaseRtt represents the two-way time of the minimum of the message that switching node sends, and RTT represents the actual two-way time of the message that switching node sends, and RTT obtains by actual monitoring;

The difference Diff of calculation expectation speed Expected and actual speed rate Actual is then: Diff=Expected-Actual;

The computing formula that obtains RTT based on the length N of the buffer queue of switching node is again:

RTT＝BaseRTT+N/Actual；

Can draw according to following formula, the length N of buffer queue is:

N＝Actual*(RTT-BaseRTT)＝Diff*BaseRTT。

Certainly, can also adopt other method to obtain the value of length N of the buffer queue of switching node among the present invention, then, just can carry out the adjustment of congestion window and enabling gate limit value, to adapt to the demand of Network Transmission according to the N value that obtains.

By the description process of the specific implementation of the invention described above as can be seen, the present invention has not only kept the algorithm advantage of TCP Reno when handling network congestion, as by congestion window is reduced by half, can effectively reduce the buffer memory team leader, handle network congestion situation etc. timely, simultaneously, also to change the packet loss that causes owing to link property, effectively utilize the network bandwidth and estimate to set suitable thresholding and congested control window, the network bandwidth is effectively utilized, improve the throughput of system.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claims.

Claims (10)

1, adjust the method for congestion window in a kind of communication network, it is characterized in that comprising:

The length of the buffer queue of switching node in A, the computing network;

B, determine to cause that packet loss produces in the network is former because congested or link characteristics changes according to the length of described buffer queue, and adopt corresponding control strategies that the congestion window of switching node is adjusted respectively at different reasons.

2, adjust the method for congestion window in the communication network according to claim 1, it is characterized in that described steps A comprises:

A1, determine the bandwidth of network according to the message that transmits in the network;

A2, according to the length of the buffer queue at the bandwidth calculation switching node place of network.

3, adjust the method for congestion window in the communication network according to claim 2, it is characterized in that described steps A 1 comprises:

The message length that the ACK message of receiving according to sending node in the network is confirmed and the bandwidth of determining network blanking time of adjacent two ACK messages.

4, according to the method for adjusting congestion window in claim 2 or the 3 described communication networks, it is characterized in that described steps A 1 further comprises:

The message length that confirmed of the ACK message of receiving with sending node is divided by the blanking time of this ACK message and previous ACK message respectively, and the result of acquisition is as the sampled value based on the network bandwidth of this ACK message;

The a plurality of network bandwidth sampled values that obtain are carried out smoothing processing, obtain the bandwidth of network.

5, adjust the method for congestion window in the communication network according to claim 4, it is characterized in that described steps A 2 comprises:

Bandwidth value, the size of grouping, the network bandwidth of current expectation and the length of calculating the buffer queue at switching node place minimum two-way time between sending node and receiving node according to the network that obtains.

6, adjust the method for congestion window in the communication network according to claim 5, it is characterized in that described steps A 1 specifically comprises:

Network bandwidth sampled value sample_BWE[k] be:

sample_BWE[k]＝(ACKed*seg_size*8)/now～lastACKtime，

Wherein, ACKed represents the message segment number that ACK confirmed received by this, seg_size represents the contained byte of message segment, and now～lastACKtime represents that this is received and receives the time interval of ACK ACK and last time that K was the sequence number of this message of receiving that ACK confirmed;

Network bandwidth sampled value is carried out smoothing processing, estimates to determine network bandwidth BWE[k] be:

$\mathrm{BWE}\left[k\right]=\left(\frac{19}{21}\right)*\mathrm{BWE}[k-1]+\left(\frac{1}{21}\right)*(\mathrm{sample}\_\mathrm{BWE}[k]+\mathrm{sample}\_\mathrm{BWE}[k-1\left]\right);$

And described steps A 2 specifically comprises:

The length of buffer queue N at switching node place is:

$\stackrel{\‾}{N}=(\mathrm{Expected}-\frac{\mathrm{BWE}}{\mathrm{seg}\_\mathrm{size}})*\mathrm{BaseRTT},$

Wherein, $\mathrm{Expected}=\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}}$ It is the expected rate of current time, cwnd represents the size of congestion window, BaseRtt is the minimum two-way time of message between switching node, and for being the message segment size, BWE is the estimated value BWE[k of the current time network bandwidth of above-mentioned steps A1 acquisition to seg_size as previously mentioned].

7, adjust the method for congestion window in the communication network according to claim 1, it is characterized in that described steps A comprises:

Calculate the length of buffer queue of switching node according to the round minimum time of message between expected rate, actual speed rate and the switching node of current network.

8, adjust the method for congestion window in the communication network according to claim 7, it is characterized in that described steps A further comprises:

Calculation expectation speed Expected and actual speed rate Actual:

$\mathrm{Expected}=\frac{\mathrm{cwnd}}{\mathrm{BaseRtt}},$ $\mathrm{Actual}=\frac{\mathrm{cwnd}}{\mathrm{Rtt}};$

Wherein, cwnd represents congestion window size, and BaseRtt represents the minimum two-way time of message between switching node, and RTT represents the actual two-way time of message between switching node;

Calculating the length of buffer queue N that determines switching node is:

N＝Actual*(RTT-BaseRTT)＝Diff*BaseRTT，

Wherein, Diff=Expected-Actual is the difference of expected rate Expected and actual speed rate Actual.

9, according to the method for adjusting congestion window in claim 1,2,3, the 7 or 8 described communication networks, it is characterized in that described step B comprises:

If the length of the described buffer queue of B1 is greater than the queue length threshold value of setting, determine that then the network bandwidth is saturated, and the packet loss that produces in the network is because of congested causing, and carries out the adjustment of the window and the enabling gate limit value of this switching node according to corresponding congestion control policy;

If the length of the described buffer queue of B2 is less than the queue length threshold value of setting, then determine network bandwidth unsaturation, and the packet loss that produces in the network causes for changing because of link property, and carries out the adjustment of the window and the enabling gate limit value of this switching node according to the control strategy that changes based on link property.

10, adjust the method for congestion window in the communication network according to claim 9, it is characterized in that, the described basis of step B2 is carried out the window of this switching node and being adjusted into of enabling gate limit value based on the control strategy that link property changes:

If receive the ACK message of three repetitions, adjustment starts thresholding slowly and equals estimated bandwidth and the product of minimum two-way time and the ratio of TCP message segment size, and, if the current congestion window then makes congestion window equal to start slowly thresholding greater than slow enabling gate limit value;

If the re-transmission timer expired then makes congestion window equal 1, order starts thresholding slowly and equals estimated bandwidth and the product of minimum two-way time and the ratio of TCP message segment size, and if start thresholding less than 2 slowly, then makes starting thresholding slowly and equaling 2.

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