CN102711172A - Modified TCPW congestion control method in wireless network - Google Patents

Abstract

The invention discloses a modified TCPW congestion control method in a wireless network. After a specified data receiving terminal receives a data packet each time, a timestamp is stamped in a reply packet corresponding to the data packet, after a data sending terminal receives the reply packet, the arrive time of the current reply packet is not recorded, but the timestamp on the reply packet is extracted, so as to obtain the timestamp difference, namely the sending time of the last data packet on the sending route, in the next arrived reply packet, the size of the arrived data packet and the sending time of the data packet on the sending route are respectively subjected to averaging at the sending terminal, and then a bandwidth sampling value is obtained according to the specific value of average values. Finally a bandwidth estimated value is smoothly obtained through an exponential weighting moving average filter according to the obtained bandwidth sampling value. The method is more accurate to estimate a current practical available bandwidth value and effectively improves network QoS.

Description

Improved TCPW jamming control method in a kind of wireless network

Technical field

The present invention relates to the congested control of Wi-Fi field, especially a kind of TCPW jamming control method.

Background technology

At present, the congestion control in wireless networks technology is faced with many difficulties.Because wireless network has the self characteristics of terminal mobility, wireless connections; Make that the reliability of link is not high; And want to postpone at high bit-error, greatly and the frequent mobile wireless network in terminal in the existing Transmission Control Protocol of operation; Become difficult relatively, transfer of data has its unsteadiness, and congestion phenomenon also occurs than being easier to.Therefore, want to make Transmission Control Protocol stably to operate in the wireless network, network throughput is preferably arranged, and have good robustness and extensibility, just must carry out corresponding modification original protocol.

TCPW is a kind of congestion avoidance algorithm end to end, meets the design criterion of Transmission Control Protocol fully.In the data transmission procedure of wireless network, it has been eliminated to a certain extent because the negative effect that the data random loss brings for network bandwidth utilance.The algorithm of TCPW is a kind of algorithm based on bandwidth estimation; It mainly is an available bandwidth value of estimating current network through the historical information on the wireless network links, and this historical information generally comprises the stream information of replying that message segment information and the recipient of transmission receive.TCPW checks that through transmit leg the stream information of replying in the historical information comes the message transmission rate of current connection is estimated, thereby the current network available bandwidth is estimated.It estimates the transmission present situation of the adjustment network that resulting available bandwidth value can be real-time; When appearance in the network is congested; Can adjust congestion window cwnd and begin threshold value ssthresh slowly through the available bandwidth value that estimates; The algorithm adjustment that last employing again and formula increase long-pending formula minimizing sends to the grouping size in the network, thereby reaches the purpose of controlling congestion phenomenon, improves the performance of TCP.

TCPW has adopted the thought that the network bandwidth is estimated in real time, and promptly the time interval of the echo reply stream that sends through continuous calculating recipient of transmit leg is estimated the available bandwidth on the link.Adopt ABSE (Adaptive Bandwidth Share Estimation) filtering mechanism to make it comparatively accurate to the estimation of bandwidth.

The TCPW basic idea is; In slow incipient stage and congestion avoidance phase; TCPW is the same with TCP, and the method for adjustment of send window does not change, when generation in the network is congested; Dedicated bandwidth estimated value BWE comes dynamically to adjust congestion window value cwnd and begins threshold value ssthresh slowly, and congestion control mechanism is AIAD.

(1) when transmitting terminal receives three repeat ACKs, makes ssthresh=(BWE*RTT _Min)/seg_size (and being not the ssthresh=cwnd/2 of Reno).Wherein, if cwnd>ssthresh, then cwnd=ssthresh;

(2) when timer generation RTO is overtime, make ssthresh=(BWE*RTT _Min)/seg_size, (and being not ssthresh=cwnd/2), cwnd=1.

Above congestion control mechanism all is based on the basis of bandwidth estimation, and the bandwidth estimation algorithm also becomes the key of this congestion control mechanism.

Wherein, the time interval of the ACK of sampling bandwidth and corresponding arrival:

b _k=d _k/Δ _k （7）

Δ _k=t _k-t _k-1 （8）

t _kRepresent that one is replied stream ACK at t _kConstantly arrive source end, Δ _kExpression t _K-1To t _kThe time interval, d _kBe illustrated in Δ _kThe time interval in, the data character stream joint number that the TCP receiving terminal is received, b _kBe Δ _kSampling bandwidth in the time interval, adopt the EWMA technique computes to estimate the current bandwidth value that obtains again:

${\mathrm{BWE}}_k={\mathrm{\βBWE}}_{K-1}+(1-\mathrm{\β})\left(\frac{b_k+b_{k-1}}{2}\right)---\left(9\right)$

β=(2τ-Δ _k)/(2τ+Δ _k) （10）

Wherein, BWE _kBe t _kThe estimation of available bandwidth value of filtering constantly, 1/ τ is the cut-off frequency of the low pass filter in the index filter, β is for filtering weights (general value 19/21).

When packet loss took place, TCP Reno reset to 1 with cwnd, when receiving three ACK streams, cwnd was reduced by half.And for fear of when receiving three repeat ACK streams; The excessive atrophy of cwnd; TCP Westwood has introduced a kind of mechanism of fast quick-recovery; It calculates threshold value ssthresh through estimating the estimation of available bandwidth value in the current connection of TCP, makes network take place when congested, and threshold value can be adjusted with available bandwidth synchronously.This congestion control policy based on estimation of available bandwidth has obtained good checking in the congested test of wireless network.But this algorithm also exists defective, and the network bandwidth value that it generally estimates is all high than the actual available bandwidth value of network, when having ACK compressive flow etc. to take place in the network, the estimation of bandwidth is also become very unstable.Simultaneously and since its too high estimation the available bandwidth of network, make transmit leg send to packet on the Radio Link, the congestion phenomenon on the contrary can emphasis network in fact greater than the available bandwidth of network.

2002; After TCPW is proposed first; On this basis; Increasing researcher begins one's study based on the congestion avoidance algorithm of bandwidth estimation, and has proposed a lot of improved algorithms, and wherein topmost improvement algorithm has following four kinds: TCPW BE (Bandwidth Estimation), TCPW RE (Rate Estimation), TCPW CRB (Combined Rate and Bandwidth) and TCPW ABE (Adaptive Bandwidth Estimation).

（1）TCPW?RE(Rate?Estimation)

The difference of it and early stage TCPW algorithm is exactly on the sampling mode of bandwidth.This algorithm will extend to T sample time, get interior all received ACK of TCP transmitting terminal of the T time interval and reply stream.Make that like this sampling bandwidth value of trying to achieve is an average on time interval T.To a certain extent, eliminated the problem of the too high estimation actual available bandwidth of TCPW.Specific algorithm is following:

$b_k=\underset{t_j>t_k-T}{\mathrm{\Σ}}{d}_j/T---\left(11\right)$

${\mathrm{BWE}}_k=\mathrm{\β}{\mathrm{BWE}}_{K-1}+(1-\mathrm{\β})\left(\frac{b_k+b_{k-1}}{2}\right)---\left(12\right)$

β=(2τ-Δ _k)/(2τ+Δ _k) （13）

Wherein, the bandwidth sampling mode in the formula (11) is different, and it will extend to T sample time, and the T default value of this moment is RTT, and other parameters are the same.

In the wireless network environment, if congested only just because the data packet loss causes that the performance of TCPRE algorithm is better than TCPW.

（2）TCP?CRB(Combined?Rate?and?Bandwidth)

The main thought of TCP CRB algorithm is: under wireless network environment; Because TCP RE is relatively more effective in the network of the congested data-bag lost that causes; And that TCPW shows in the network of the packet loss that random error causes is better, and their boths can not adapt to all network environments.Based on this, TCP CBR has combined the advantage of TCPW and TCP RE, and at first (cwnd/ (BWERTTmin)/seg_size) judges network condition, and then selects to use which kind of mode to obtain the bandwidth value of sampling according to congestion detection mechanism.When (cwnd/ (BWERTTmin)/seg_size)>during θ (θ=1.4), use the congestion control mechanism of TCP BE, on the contrary then use the congestion control mechanism of TCP RE.This algorithm has used existing TCP RE and TCPW algorithm more flexibly, and the scope of application is wider than TCPW and two kinds of algorithms of TCP RE.

（3）TCP?ABE(Adaptive?Bandwidth?Estimation)

This algorithm is to time interval T _kValue more flexible; It mainly is in time to adjust according to the congestion state of network to get; The sampling bandwidth value that obtains so also is that the congestion condition according to network carries out in good time adjustment ground; Thereby make algorithm can well estimate, and draw the controlling value that relatively meets network state, help control more the network congestion phenomenon to the state of network.The concrete bandwidth of TCP ABE sampling formula is following:

$b_k=\underset{t_j>t_k-T}{\mathrm{\Σ}}{d}_j/T_k---\left(14\right)$

$T_k=\mathrm{RTT}\·(\frac{\mathrm{cwnd}}{\mathrm{RTT}\min }-{\mathrm{Th}}_k)/\frac{\mathrm{cwnd}}{\mathrm{RTT}\min }---\left(15\right)$

Th _k=εTh _k+(1-ε)Th （16）

$\mathrm{Th}=\frac{\underset{t_j>t_k-\mathrm{RTT}}{\mathrm{\Σ}}{d}_j}{\mathrm{RTT}}---\left(17\right)$

The concrete implication of parameter also has brightly specifically with being arranged in the following formula among the TCPW RE, no longer details here.The tracking network state that TCPABE algorithm ability is real-time is adjusted the parameters in the formula according to network state, thereby can be good at improving the real-time and the accuracy of algorithm.But this algorithm also has apparent in view shortcoming, and the parameter that it relates to is many, calculates more complicated.

Summary of the invention

In order to overcome the defective of the too high estimation network available bandwidth value in the existing TCPW congestion avoidance algorithm; And the network asymmetry is to the influence of network congestion control, and the present invention provides a kind of and more accurately estimates current actual available bandwidth value, effectively improves improved TCPW jamming control method in the wireless network of network QoS.

The technical solution adopted for the present invention to solve the technical problems is:

Improved TCPW jamming control method in a kind of wireless network, said improved TCPW jamming control method may further comprise the steps:

Step 1 after each data receiver receives a packet, is all stamped a timestamp in its corresponding response packet, calculate the difference Δ t of adjacent timestamp then at data sending terminal _i

Step 2, according to the definition of the network bandwidth, Δ t _iThe sampling bandwidth value of network calculates as follows in period:

$b_i=\frac{d_i}{\mathrm{\Δ}{t}_i}---\left(1\right);$

In the formula (1), d _iBe illustrated in time period Δ t _iIn, institute's data packets for transmission size in the network;

Step 3 is asked sliding average

and

to the packet size that the difference and the receiving terminal of timestamp receives respectively in this time period

Step 4 based on step 1-3, can obtain the current sampling bandwidth value in the network:

$b_i=\frac{\stackrel{\‾}{d_i}}{\stackrel{\‾}{{\mathrm{\Δt}}_i}}---\left(2\right)$

Step 5, the available bandwidth value that sampling bandwidth estimated value that utilization obtains and the estimation of available bandwidth value of last time calculate current network carries out level and smooth value with the exponentially weighted moving average (EWMA) filter, and is specific as follows:

$B_i=\mathrm{\β}{B}_{i-1}+(1-\mathrm{\β})\left(\frac{b_i+b_{i-1}}{2}\right)---\left(3\right)$

Wherein, β representes the mean value weights.

Further again, in step 1, after data sending terminal receives response packet, be not the time of advent of the current response packet of record, but extract the timestamp on its response packet, the difference Δ t of the timestamp in the response packet of adjacent arrival _iIn fact be exactly that last data wrap in the transmitting time on the transmit path;

Δt _i=t _i-t _i-1 （4）

In (4) formula, t _iFor after receiving terminal receives i packet, the timestamp of in the echo reply bag, stamping, Δ t _iBeing the difference between two timestamps of adjacent arrival, also is that i data wrap in the transmitting time on the transmit path in the network.

Further; In step 3; During the slip

of difference sliding average that stabs computing time and the packet that receives in this time period size, the employing computing formula:

$\stackrel{\‾}{{\mathrm{\Δt}}_i}=\mathrm{\α}\stackrel{\‾}{t_{i-1}}+(1-\mathrm{\α})\·t_i---\left(5\right)$

$\stackrel{\‾}{d_i}=\mathrm{\α}\stackrel{\‾}{d_{i-1}}+(1-\mathrm{\α})\·d_i---\left(6\right)$

Wherein, α representes the mean value weights, for the transient change of reaction network to sampling bandwidth estimation effect degree, the b of this moment _iBe the bandwidth sampling estimated value of being tried to achieve under the condition of the present invention.

Technical conceive of the present invention is: after the inventive method specified data receiving terminal receives a packet at every turn; All in its corresponding response packet, stamp a timestamp; Then after data sending terminal receives response packet; Be not the time of advent of the current response packet of record, but extract the timestamp on its response packet, in fact the difference of the timestamp in the response packet of the adjacent arrival that obtains like this is exactly that last data wrap in the transmitting time on the transmit path.Respectively the packet size of confirming to arrive is averaged with the transmitting time of this packet on transmit path at transmitting terminal then, the ratio according to them obtains the bandwidth sampled value again.According to resulting bandwidth sampled value, use the exponentially weighted moving average (EWMA) filter smoothly to obtain the bandwidth estimation value at last.

Beneficial effect of the present invention mainly shows: when having situation such as ACK compression generation, the sudden arrival of message segment, answering delay to take place in the network; The available bandwidth of the estimation network that the meeting of TCPW algorithm is too high; It is unstable that the bandwidth estimation value also can become; TCPW also can take too much bandwidth, the congestion phenomenon of emphasis network.The present invention is through asking for of timestamp and being used of moving average value; Well solved this problem, made the network bandwidth estimated value of trying to achieve well to follow the tracks of the network bandwidth available estimate on the transmit path, avoided the influence of return path and bursts greatly bandwidth estimation; Improved network throughput greatly; Occurring in the congestion phenomenon at network, can effectively adjust the network congestion state, is a kind of method of comparatively desirable raising network QoS.

Description of drawings

Fig. 1 is the timestamp t that transmitting terminal receives _iThe sketch map of the packet size of the correspondence that receives with receiving terminal.

Embodiment

Below in conjunction with accompanying drawing the present invention is further described.

With reference to Fig. 1, though at present the congested control method of multiple network is arranged in wireless network, wherein the TCPW algorithm is more satisfactory aspect congested control, it also strictly observe TCP end to end design criterion design.But when in network, having bursts, delay compressed package etc. to take place, the network jitter under the TCPW is bigger, has influenced the recovery of network state.Method in the present embodiment just is being based on that above analysis result draws.

In the network, the data transmission rate of TCP source end is dynamically to adjust according to the state of network is next.The speed that is exactly according to the response packet that returns of improving one's methods of TCPW among the present invention measures and the current available bandwidth of estimation network, thereby adjusts the data transmission rate of source end.The network source end is according to estimating that the current network available bandwidth value that obtains is provided with congestion window size and starts threshold value slowly.

When the network connection is in slow incipient stage and congestion avoidance phase, there is not congestion phenomenon to take place in the network, this moment, TCPW was the same with TCP, and the method for adjustment of send window does not change.When generation in the network was congested, this moment, TCPW was different to the adjustment scheme and the TCP of network.TCPW dedicated bandwidth estimated value BWE comes dynamically to adjust congestion window value cwnd and begins threshold value ssthresh slowly, and congestion control mechanism is AIAD.

(1) when transmitting terminal receives three repeat ACKs, ssthresh=(BWE*RTT is set _Min)/seg_size, wherein, if cwnd is>Ssthresh then is provided with cwnd=ssthresh;

(2) when timer generation RTO is overtime, ssthresh=(BWE*RTT is set _Min)/seg_size, cwnd=1.

Wherein ssthresh is for start threshold value slowly, and cwnd is a congestion window size, RTT _MinBe minimum round-trip delay value, seg_size is the size of tcp data bag.

Wherein the network availability bandwidth estimated value BWE method that just need use the bandwidth estimation of mentioning among the present invention is estimated to obtain.Shown in accompanying drawing 1, after data sending terminal receives response packet, note the timestamp t that echo reply is wrapped _iBig or small d with the received packet of data receiver _i, calculate the difference Δ t of the timestamp in the response packet of adjacent arrival again _i

Δt _i=t _i-t _i-1 （1）

In (1) formula, t _iFor after receiving terminal receives i packet, the timestamp of in the echo reply bag, stamping, Δ t _iBe the difference between two timestamps of adjacent arrival, and then the packet size that respectively difference and the receiving terminal of timestamp is received is asked sliding average in this time period

With

Adopt computing formula:

$\stackrel{\‾}{{\mathrm{\Δt}}_i}=\mathrm{\α}\stackrel{\‾}{t_{i-1}}+(1-\mathrm{\α})\·t_i---\left(2\right)$

$\stackrel{\‾}{d_i}=\mathrm{\α}\stackrel{\‾}{d_{i-1}}+(1-\mathrm{\α})\·d_i---\left(3\right)$

Wherein, α representes the mean value weights, for the transient change of reaction network to sampling bandwidth estimation effect degree, general value gets 0.9 here greater than 0.5.The b of this moment _iBe the bandwidth sampling estimated value of being tried to achieve under the condition of the present invention

Based on above analysis, can obtain the current sampling bandwidth value in the network:

$b_i=\frac{\stackrel{\‾}{d_i}}{\stackrel{\‾}{{\mathrm{\Δt}}_i}}---\left(4\right)$

Sampling bandwidth estimated value that utilization obtains and the estimation of available bandwidth value of last time calculate the available bandwidth value of current network; The jitter problem that network is caused to bursts; We carry out level and smooth value with the exponentially weighted moving average (EWMA) filter, and are specific as follows:

${\mathrm{BWE}}_i=\mathrm{\β}{\mathrm{BWE}}_{i-1}+(1-\mathrm{\β})\left(\frac{b_i+b_{i-1}}{2}\right)---\left(5\right)$

Wherein β representes the mean value weights, gets 19/21 here, BWE _iThe current available bandwidth value of required exactly network of trying to achieve.

Claims (3)

1. improved TCPW jamming control method in the wireless network, it is characterized in that: said improved TCPW jamming control method may further comprise the steps:

Step 1 after each data receiver receives a packet, is all stamped a timestamp in its corresponding response packet, calculate the difference Δ t of adjacent timestamp then at data sending terminal _i

Step 2, according to the definition of the network bandwidth, Δ t _iThe sampling bandwidth value of network calculates as follows in period:

$b_i=\frac{d_i}{\mathrm{\Δ}{t}_i}---\left(1\right);$

In the formula (1), d _iBe illustrated in time period Δ t _iIn, institute's data packets for transmission size in the network;

Step 3 is asked sliding average

and

to the packet size that the difference and the receiving terminal of timestamp receives respectively in this time period

Step 4 based on step 1-3, can obtain the current sampling bandwidth value in the network:

$b_i=\frac{\stackrel{\‾}{d_i}}{\stackrel{\‾}{{\mathrm{\Δt}}_i}}---\left(2\right)$

Step 5, the available bandwidth value that sampling bandwidth estimated value that utilization obtains and the estimation of available bandwidth value of last time calculate current network carries out level and smooth value with the exponentially weighted moving average (EWMA) filter, and is specific as follows:

$B_i=\mathrm{\β}{B}_{i-1}+(1-\mathrm{\β})\left(\frac{b_i+b_{i-1}}{2}\right)---\left(3\right)$

Wherein, β representes the mean value weights.

2. improved TCPW jamming control method in the wireless network as claimed in claim 1; It is characterized in that: in step 1; After data sending terminal receives response packet; Be not the time of advent of the current response packet of record, but extract the timestamp on its response packet, the difference Δ t of the timestamp in the response packet of adjacent arrival _iIn fact be exactly that last data wrap in the transmitting time on the transmit path;

Δt _i=t _i-t _i-1 （4）

In (4) formula, t _iFor after receiving terminal receives i packet, the timestamp of in the echo reply bag, stamping, Δ t _iBeing the difference between two timestamps of adjacent arrival, also is that i data wrap in the transmitting time on the transmit path in the network.

3. improved TCPW jamming control method in according to claim 1 or claim 2 the wireless network; It is characterized in that: in step 3; During the slip

of difference sliding average that stabs computing time and the packet that receives in this time period size, the employing computing formula:

$\stackrel{\‾}{{\mathrm{\Δt}}_i}=\mathrm{\α}\stackrel{\‾}{t_{i-1}}+(1-\mathrm{\α})\·t_i---\left(5\right)$

$\stackrel{\‾}{d_i}=\mathrm{\α}\stackrel{\‾}{d_{i-1}}+(1-\mathrm{\α})\·d_i---\left(6\right)$

Wherein, α representes the mean value weights, for the transient change of reaction network to sampling bandwidth estimation effect degree, the b of this moment _iBe the bandwidth sampling estimated value of being tried to achieve under the condition of the present invention.

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