CN1226844C - Adaptive jamming control method suitable of mixed wired/radio network - Google Patents

Abstract

The present invention relates to the technical field of congestion control of a computer network transmission control protocol (TCP), particularly to a self-adaptive TCP congestion control method capable of distinguishing different packet loss reasons on the basis of wired and wireless hybrid networks. The present invention comprises the following steps: a relative one-way delay is calculated; the variation tendency of the relative one-way delay is estimated; the packet loss reason is distinguished; restoring measures are taken. The present invention is characterized in that the situations of links and congestion are judged according to the variation tendency of the relative one-way delay of the acknowledgement packet ACK so as to distinguish whether the link congestion or the wireless errors result in the packet loss and take different recovery mechanisms according to different packet loss reasons in a self-adaptive mode. The present invention only modifies a small part of the TCP of the transmitting end without changing the TCP in the middle node, and the modification only relates to the transmitting layer and is irrelevant to the protocols on other layers. The present invention maintains integrity of transmission protocol semanteme and end-to-end semanteme in the existing wired network.

Description

A kind of adaptive congestion control method of suitable wire/wireless hybrid network

Technical field

The present invention relates to the computer network transmission technique field, particularly a kind of adaptive congestion control method of suitable wire/wireless hybrid network, be the jamming control method of transmission control protocol TCP, the especially a kind of self adaptation TCP jamming control method that can distinguish the different packet loss reason based on the wire/wireless hybrid network.

Background technology

Transmission control protocol (TCP) has experienced after the improvement from TCP Tahoe to many versions of current widely used TCPNewReno, and its jamming control method of continuing to optimize has guaranteed data flow transmission service reliably end to end.The initial congestion control mechanism of realizing in TCP Tahoe comprises two parts: start slowly and Congestion Avoidance.TCP Reno has further introduced quick re-transmission and fast restoration algorithm, can conclude data-bag lost according to the duplicate acknowledgment that transmit leg is received, needn't need wait for as TCP Tahoe that the retransmission timer of lost data packets is overtime.Newreno replenishes again on the Reno basis, makes that transmit leg can more effectively carry out congested control under the situation that continuous packet loss takes place.

This a series of optimization is all at cable network.Duplicate acknowledgment, the overtime data-bag lost that identifies all are interpreted as network congestion, carry out flow control by starting congestion control mechanism: strengthen the retransmission interval, dwindle send window and adapt to network congestion.This method is suitable for the good cable environment of link-quality.

Yet congested in wireless network no longer is the sole cause of loss of data.The high bit-error of Radio Link cause most of packet loss all since link make mistakes and cause.If it must be the principle that is caused by congested that TCP still follows packet loss, blindly reduce transmission rate, just certainly will reduce bandwidth availability ratio, cause the TCP mis-behave.

Have now and mainly can be divided three classes for improving TCP improving one's methods of performance under wireless environment:

(1) end-to-end scheme (End-to-End): only revise the agreement that TCP connects two ends, and do not need the support of intermediate node, guarantee the integrality that connects from transmit leg to recipient TCP.This type of research has TCP Westwood, TCP-Real etc.That performance is best in these agreements is TCPWestwood, and this agreement is estimated the available bandwidth of link by a filter, adjusts threshold value and the congestion window that starts slowly in real time, thereby significantly improves the ability that TCP utilizes bandwidth.When its weak point is with the coexistence of traditional Transmission Control Protocol, will forcibly occupy other protocol streams bandwidth, destroy the friendly (friendliness) between the different agreement stream.

(2) segmentation connectivity scenario (Split Connection): different with end-to-end scheme, transport layer is connected the base station and is divided into two sections, and the TCP transmit leg has been shielded Radio Link fully.Wireless portion can use other congested control technology such as SACK etc. in addition.This class scheme all will be made an amendment the TCP software of mobile host and intermediate node and the TCP that needn't change transmitting terminal realizes.But it has destroyed end-to-end TCP and has connected semanteme, because before data reality is not sent to the recipient, the affirmation of forgery just is fed to transmit leg.

(3) link-local layered scheme (Localized Link Layer): between end-to-end and segmentation connect, thereby it uses the reliable link layer protocol to retransmit the transmitting terminal shielding packet loss relevant with link at link layer.But because link layer protocol and upper-layer protocol all have independently error control function, these functions have certain repeatability, therefore the result that vies each other of the retransmitting function of link layer and transport layer can reduce the effective rate of utilization of wireless channel, causes end-to-end throughput to descend.

Summary of the invention

The objective of the invention is to propose a kind of adaptive congestion control method of suitable wire/wireless hybrid network, be suitable for the transport layer jamming control method.It can be distinguished the different reasons of packet loss, and take corresponding recovery measure adaptively according to link circuit condition.The host-host protocol meaning of one's words and the end-to-end semantic integrity that keep the existing wired network simultaneously promptly only carry out a spot of modification to the Transmission Control Protocol of transmit leg, and do not change the Transmission Control Protocol of intermediate node, and revise and only relate to transport layer, and be irrelevant with other layer protocol.

Technical scheme

A kind of adaptive jamming control method of suitable wire/wireless hybrid network, judge according to the relative one-way delay variation tendency of confirming bag (Acknowledgments below is abbreviated as ACK) congestion condition of link to it is characterized in that key step is as follows:

Step 1: calculate relative one-way delay;

Step 2: estimating variation trend of relative single-way delay;

Step 3: distinguish the packet loss reason; If relative one-way delay ROD is increase trend, then three repeat ACKs or the overtime packet drop that reflects since link congestion cause, otherwise packet loss because Radio Link make mistakes and cause;

Step 4: carry out link-recovery according to above-mentioned packet loss reason.

Technical solution of the present invention provides a kind ofly can distinguish the jamming control method for the treatment of the different packet loss reason.Basic thought is to judge the congestion condition of link according to the delay variation tendency of bag, so distinguish packet loss be because link congestion cause or because wireless makeing mistakes causes, take different Restoration Mechanism according to different packet loss reasons adaptively.Key point wherein is the congestion condition how delay of bag reflects link.

The delay that wraps in the network can be divided into four parts: the queueing delay of medium access delay, propagation delay, transmission delay and each intermediate router inside.Wherein medium access postpones to depend on the characteristic of the network media; Propagation delay refers to that the signal of telecommunication propagates into the needed time of the other end from an end of link, is generally 5us/1km; Transmission delay depends on that each connects the bandwidth of being distributed; Queueing delay refers to wrap in the delay of lining up and being caused in the router, and it is comparatively relevant with the characteristic of router itself, link congestion situation etc.For the wire/wireless heterogeneous network of an actual motion, propagation delay and medium access postpone mainly to have reflected the physical features in path itself, promptly form the length, medium of each bar link in path etc., are that the constant part of end-to-end delay is collectively referred to as inherent delay; Transmission delay and queueing delay are formed the variable part that postpones, and are collectively referred to as dynamic deferredly, and it is mainly caused by bandwidth and the queuing in the forwarded node that every connection is seized, and has reflected the busy extent of network.Therefore we can also be the congestion situation that dynamic deferred variation tendency is estimated network according to postponing variation.

The packet that partly receives when network bottleneck has surpassed its treatable capacity, and newly to packet will constantly insert in the buffer queue owing to can not send, and cause the growth of queue length, and the delay of packet will be increase trend.If queue length has exceeded the buffer memory ability of bottleneck router, grouping will be dropped.As seen postponing to increase is the congested notable feature that causes packet loss.If for no other reason than that the sudden link of Radio Link makes mistakes and make packet loss, and data flow does not cause the link overload, does not just have ever-increasing backlog queue yet, delayed sequence just can not show obvious increase trend yet.Another kind of inevitably situation is: if network slight congested in Radio Link make mistakes and cause packet loss, we may be congestion packet loss with its erroneous judgement according to the variation that postpones, but this erroneous judgement is an acceptable, and the load that this moment, end system was exported to network has approached the limit of Internet resources capacity and disposal ability after all.In a word, thus we can judge that link circuit condition takes more effective congestion control mechanism according to the variation that postpones.

The present invention is based on ACK that transmit leg receives wraps and calculates relative one-way delay.Whenever receive an ACK bag, transmit leg is noted current timestamp clock a _i, in this ACK bag, also carrying the recipient and sending its timestamp s _iAccording to a _iAnd s _iThese two times, can obtain the relative delay (ROD:Relative One-way Delay) that each ACK wraps i: D _i=a _i-s _i, D _iThe absolute delay that is actually from the transmit leg to recipient adds/deducts a side-play amount θ, and θ is two clock jitters between end system.Because only pay close attention to the relative quantity that postpones in next step statistical analysis, therefore this method of measurement does not need to carry out clock synchronization.

With sample value D _iDeposit among the array rod_arr, obviously have only the variation tendency of a nearest N ROD just to reflect the present situation of network, so can array size be set to fixed value N (N gets empirical value 100), make its member pass continuous variation in time.

In case receive the packet loss sign, transmit leg is used as distinguishing the criterion of different packet loss according to the variation tendency of the delayed sequence of sampling before this.Statistical method is as follows

1) preliminary treatment: K sample { D ₁, D ₂..., D _kBe divided into $\mathrm{\Γ}=\sqrt{K}$ Group, every group has Γ continuous sample, obtains every group intermediate value Use following two kinds of statistical methods to detect the variation tendency of data flow then;

2)PCT(Pairwise?Comparison?Test)

$S_{\mathrm{PCT}}=\frac{{\mathrm{\Σ}}_{k=2}^{\mathrm{\Γ}}I\left({\hat{D}}_k{\widehat{>D}}_{k-1}\right)}{\mathrm{\Γ}-1}$

I (X): if X sets up, I (X)=1, otherwise be 0, PCT measures is adjacent two ratios that the sample that is increase trend accounts in all samples, 0≤S _PCT≤ 1, if two samples are incoherent, S so _PCTDesired value be 0.5; If very strong increase trend is arranged, so should be near 1; If S _PCT＞0.66, promptly be judged to increase trend; If S _PCT＜0.54 is judged to and does not increase trend; Otherwise be uncertain trend;

3)PDT(Pairwise?Difference?Test)

$S_{\mathrm{PDT}}=\frac{{\hat{D}}_{\mathrm{\Γ}}-{\hat{D}}_1}{{\mathrm{\Σ}}_{k=2}^{\mathrm{\Γ}}|{\hat{D}}_k-{\hat{D}}_{k-1}|}$

PDT has quantized its degree that changes from beginning to end of absolute change with respect to sample value, wherein-and 1≤S _PDT≤ 1.If sample is incoherent, so S _PDTDesired value be 0; If very strong growth trend is arranged, S _PDTNear 1; If S _PDT, be increase trend at＞0.55 o'clock; If S _PDT＜0.45 is judged to and does not increase trend; Otherwise, be uncertain trend;

4) if one of comprehensive PCT and PDT PCT/PDT are increase trend, another can be judged to ROD so and be increase trend, otherwise ROD does not present tangible increase trend for increasing or uncertain trend.

The criterion of distinguishing packet loss is: according to front PCT and the comprehensive result who judges of PDT, if ROD is increase trend, as can be known three repeat ACKs or the overtime packet drop that reflects since link congestion cause, otherwise packet loss is made mistakes because of Radio Link and is caused.

With this criterion as differentiation packet loss reason, can make suitable recovery policy at the packet loss that different reasons cause: if postpone to be obvious increase trend, can be judged to packet loss is because due to the network congestion, so still, according to the congestion control policy of traditional TCP, reduce the transmission rate that grouping enters network, and the message segment of retransmission of lost; Otherwise packet loss can be thought that Radio Link is made mistakes and cause, only need this moment to retransmit and needn't change transmission rate.

This jamming control method adaptively can directly apply in the TCP realization of wire/wireless hybrid network transmit leg.

Description of drawings

Fig. 1 is the flow chart of adaptive congestion control method of the present invention, mainly comprises the steps:

(1) waits for that the ACK bag arrives; In case ACK wraps arrival, then enter step (2);

In the wait process, do not receive ACK bag else and if retransmission timer is overtime, then forward step (3) to;

(2) calculate the relative one-way delay (ROD) that this ACK wraps: the timestamp clock a of record current sender _i, and the recipient who carries in this ACK bag sends its timestamp s _iAccording to a _iAnd s _iThese two times, can obtain this ACK bag _iRelative delay: D _i=a _i-s _iWith sample value D _iDeposit among the array rod_arr, the big or small N of array rod_arr gets empirical value 100.Transmit leg judges whether this ACK bag is the 3rd repeat ACK bag, if then change step (3) over to, otherwise continues the corresponding operating of traditional Transmission Control Protocol;

(3) estimating variation trend of relative single-way delay: according to the variation tendency of N nearest ROD sample of previously described PCT, PDT statistical method estimation, the criterion as the differentiation packet loss enters step (4);

(4) distinguish the packet loss reason: if ROD is increase trend, three repeat ACKs or the overtime packet drop that reflects cause owing to link congestion as can be known, then execution in step (5.1) on the contrary packet loss make mistakes because of Radio Link and cause, change step (5.2) over to;

(5) recovery measure:

(5.1) if packet loss be congested due to, still reduce the packet of congestion window and retransmission of lost according to the congestion control policy of wired TCP;

(5.2) if packet loss is a Radio Link make mistakes due to, only need the packet of retransmission of lost and needn't reduce congestion window.

Advantage

The present invention can clearly distinguish the packet loss that packet loss that network congestion causes and Radio Link are made mistakes and caused, and the packet loss that different reasons are caused adopts corresponding recovery policy, thereby has avoided traditional Transmission Control Protocol to adjust the blindness of congestion window.Can obviously improve throughput for this jamming control method of wire/wireless hybrid network good fairness and friendly performance are arranged simultaneously.In addition,, and do not change the Transmission Control Protocol of intermediate node, and revise and only relate to transport layer because it has just carried out minor modifications to the Transmission Control Protocol of transmitting terminal, irrelevant with other layer protocol.The host-host protocol meaning of one's words and the end-to-end semantic integrity that have kept the existing wired network.

Claims (4)

1. the adaptive congestion control method of a suitable wire/wireless hybrid network, judge the congestion condition of link according to the relative one-way delay variation tendency of confirming bag ACK: it is characterized in that concrete steps are as follows:

Step 1: calculate relative one-way delay;

Step 2: estimating variation trend of relative single-way delay;

Step 3: distinguish the packet loss reason; If relative one-way delay ROD is increase trend, then three repeat ACKs or the overtime packet drop that reflects since link congestion cause, otherwise packet loss because Radio Link make mistakes and cause;

Step 4: carry out link-recovery according to above-mentioned packet loss reason.

2. adaptive congestion control method according to claim 1 is characterized in that, wherein the relative one-way delay ROD described in the step 1 is the timestamp a that transmitting terminal carries according to the ACK bag of receiving _iCurrent time s with transmitting terminal _iObtain: D _i=a _i-s _i

3. adaptive congestion control method according to claim 1 is characterized in that, the described estimation relative one-way delay of step 2 variation tendency wherein, and the method for employing is as follows:

1) preliminary treatment: K sample { D ₁, D ₂..., D _k) be divided into $\mathrm{\Γ}=\sqrt{K}$ Group, every group has Γ continuous sample, obtains every group intermediate value Use following two kinds of statistical methods to detect the variation tendency of data flow then;

2)PCT

$S_{\mathrm{PCT}}=\frac{{\mathrm{\Σ}}_{k=2}^{\mathrm{\Γ}}I({\hat{D}}_k>{\hat{D}}_{k-1})}{\mathrm{\Γ}-1}$

I (X): if X sets up, I (X)=1, otherwise be 0.If S _PCT＞0.66, promptly be judged to increase trend; If S _PCT＜0.54 is judged to non-increase trend; Otherwise be uncertain trend;

3)PDT

$S_{\mathrm{PDT}}=\frac{{\hat{D}}_{\mathrm{\Γ}}-{\hat{D}}_1}{{\mathrm{\Σ}}_{k=2}^{\mathrm{\Γ}}|{\hat{D}}_k-{\hat{D}}_{k-1}|}$

If S _PDT, be increase trend at＞0.55 o'clock; If S _PDT＜0.45 is judged to non-increase trend; Otherwise, be uncertain trend;

4) if one of comprehensive PCT and PDT PCT/PDT are increase trend, another is an increase/uncertain trend, can be judged to ROD so to be increase trend, otherwise ROD does not present tangible increase trend.

4. adaptive congestion control method according to claim 1 is characterized in that, wherein the recovery measure described in the step 4 is as follows:

1) if packet loss be congested due to, still the congestion control policy according to wired TCP reduces congestion window and retransmission data packet may.

2) if packet loss is a Radio Link make mistakes due to, only need to retransmit and needn't reduce congestion window.