CN104052745A - Contention window adjusting method taking 802.11e VoIP application as orientation - Google Patents

Abstract

The invention discloses a contention window adjusting method taking an 802.11e VoIP application as orientation. The method includes the steps that (1) the optimal network access probability TauAPopt of a wireless AP is calculated according to an access MAC layer parameter and a VoIP coding mode; (2) the optimal value CWminAP of the size of the minimum contention window and the optimal value CWmaxAP of the size of the maximum contention window of the AP are calculated according to the TauAPopt; (3) the average collision rate favgj in the jth period at the AP is calculated, and then the network access probability TauSTA of a site STA is adjusted according to the relation of the favgj and the threshold value fopt; (4) the maximum contention window and the minimum contention window of the site are calculated by the AP according to the TauSTA; the maximum contention window and the minimum contention window of the site are broadcasted by the AP by using a periodic Beacon frame. By means of the contention window adjusting method taking the 802.11e VoIP application as orientation, the effective availability of a wireless channel can be improved, the network throughput is improved, and the VoIP capacity is improved as well.

Description

Towards the competition window method of adjustment of 802.11e VoIP application

Technical field

The present invention relates to a kind of competition window method of adjustment towards 802.11e VoIP application.

Background technology

Along with developing rapidly of (VoIP) technology of the voice based on Internet Protocol and WLAN (wireless local area network) (WLAN) technology, the VoIP based on WLAN has obtained fast in recent years, application widely.IEEE802.11 distributed coordination function (DCF) media access controls (MAC) agreement becomes the WLAN MAC agreement of current main flow with its simplification and robustness, to be Carrier Sense Multiple Access (CSMA) avoid (CA) with conflicting to its basic thought.The business that IEEE802.11DCF agreement is mainly supported as it to transmit non real-time property data flow, in order to strengthen the support to real time business such as VoIP, IEEE makes and strengthens distributed channel access mechanism (EDCA, Enhanced Distributed Channel Access).EDCA carries out QoS and supports expansion on the basis of DCF mechanism, the mechanism of different Business Streams being carried out to prioritization is provided, improve the priority of the real time business such as the interior VoIP of WLAN (wireless local area network) (WLAN) with respect to other Business Streams, thereby ensured to a certain extent its qos requirement.But EDCA MAC layer parameter uses fixed value, cannot carry out self adaptation adjusting according to network condition, can not make systematic function realize optimum, a lot of research shows, under high load condition, owing to there being higher collision rate in network, the performance of EDCA shows and is not so good as people's will; In addition, EDCA does not carry out the differentiation of priority to website (Stations, STAs) and access node (AP) in WLAN, causes the imbalance of AP place up-downgoing service traffics, and causes bottleneck effect, has limited VoIP capacity.

(1) static parameter causes collision rate higher in high-load network

CSMA/CA mechanism is in the time working in basic access way, and its workflow is: node is detecting that idle time of channel exceedes rear transmission of DIFS (distributed inter frame space) and divides into groups; If channel busy, node will select one to keep out of the way time delay (keeping out of the way time slot value) and start and keep out of the way timer waiting at random after channel idle DIFS, wait for when this is kept out of the way and delay just and send and divide into groups.Keep out of the way timer successively decreases in time in the time of channel idle; When channel busy, will hang up, until idle time of channel just recovers to successively decrease after exceeding DIFS; In the time keeping out of the way timer and be kept to 0, node starts to send grouping.Keep out of the way time slot value interior by being uniformly distributed random selection at discrete segment [0, CW].CW is called again competition window, and competition window initial value is CW _min, sending unsuccessfully at every turn, competition window all doubles, and restarts said process contention access channel, until send successfully or reach maximum contention window CW _max.Source node is sending after grouping, wait for that destination node sends the ACK frame of confirming reception; And destination node receives after correct grouping, to after wait channel idle SIFS, send ACK frame to source node, the grouping receiving is confirmed.

CSMA/CA mechanism conflict backoff algorithm is avoided conflict next time by expanding competition window, but cannot determine and can successfully avoid, and perhaps can could send successfully through backoff procedure repeatedly.Much research shows, in high-load network, a packet will experience after repeatedly conflict conventionally, could successfully be sent.Guarantee to QoS such as delay, shakes when this mode is difficult to ensure VoIP transmission.CW in EDCA _minwith CW _maxstatic state setting, cause in high-load network most packets at identical discrete segment [0, CW _max] in select, increased the weight of the probability of conflict.Channel resource has been wasted in the increase of conflict greatly, and throughput is declined rapidly, cannot realize the optimum of systematic function.

(2) the bottleneck effect restricting VoIP capacity of AP

In WLAN (wireless local area network), access node AP (Access Point) is positioned at the joint portion of cable network and wireless network, transmits downstream from cable network to wireless network and the upstream from wireless network to cable network simultaneously.VoIP communication process carries out conventionally between wired website of wireless site and AP outside or wireless site.In supposing the system, only have VoIP data flow, each website has been set up a two-way VoIP communication process by AP and external site.In the time there is N website, there is the up transmission link competitive channel of N bar, and need complete by AP the access of channel from the reciprocal voice call process of external site.Comparatively speaking, the transmission load in AP is N times that each website sends load.According to the principle of CSMA/CA mechanism, AP has identical access channel probability with each website, is all the access that completes wireless medium by fair play.When VoIP talking link capacity increases, when system reaches capacity, AP due to the overweight generation stack overflow of load affect from wired to wireless parties to transfer of data, produce the loss of VoP, the increase of time delay.The increase of these packet loss and time delay has affected the VoIP communication process that all websites are initiated, and has limited the increase of power system capacity.

To sum up, be necessary to design a kind of new self-adapting regulation method, protocol parameter self adaptation is adjusted to ensure the protocol capabilities under heterogeneous networks loading condition; Can carry out prioritization to website and AP, the restriction of the bottleneck effect of reduction AP to VoIP capacity, promotes VoIP capacity simultaneously.

Summary of the invention

Technical problem to be solved by this invention is to provide a kind of competition window method of adjustment towards 802.11e VoIP application, should can promote wireless channel effective rate of utilization towards the competition window method of adjustment of 802.11e VoIP application, improve network throughput, promote VoIP capacity.

The technical solution of invention is as follows:

Towards a competition window method of adjustment for 802.11e VoIP application,

1) be the optimal network access probability of AP according to the MAC layer parameter of access and VoIP coded system calculating WAP (wireless access point)

Described MAC layer parameter comprises slot time, SIFS, DIFS and transmission rate; Slot time represents off time; SIFS (Short Interframe Space) is short frame period; DIFS is distributed coordination frame period (DCF Interframe Space);

2) basis calculate the minimum of AP, the optimal value of maximum contention window size

3) the average collision rate in calculating j cycle of AP place basis again with threshold value f ^optrelation adjust website (STA) network insertion probability τ _sTA:

When time, reduce the network insertion probability τ of website _sTAto adapt to offered load;

When time, the network insertion probability τ of increase website _sTAto adapt to offered load;

4) AP is according to τ _sTAcalculate maximum, the minimum competition window of website; Maximum, the minimum competition window of the Beacon frame broadcast station of AP periodic.

Step 1) in computational methods as follows:

${\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}=\sqrt{\frac{\mathrm{\δ}}{T_{\mathrm{data}}+\mathrm{SIFS}+T_{\mathrm{ack}}+\mathrm{DIFS}}}$

Wherein δ is slot time; T _dataand T _ackit is respectively the time of transmitting a VoIP packet and transmitting corresponding ACK; [being limited to the transmission rate of wireless network and the VoIP encoding mechanism of selection].

Step 2) in with computational methods as follows:

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{AP}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}}-1){(1+(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{AP}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{AP}}\end{array}$

Wherein m is that maximum is kept out of the way number of times, and value is 3.

Step 3) in, be taken as current period collision rate with historical collision rate eWMA, that is:

$f_{\mathrm{avg}}^j=(1-\mathrm{\α})*f_{\mathrm{curr}}^j+\mathrm{\α}*f_{\mathrm{avg}}^{j-1};$

Wherein, α is smoothing factor, and value is 0.875; it is the average collision rate in j-1 cycle; be the collision rate in j cycle, determined by following formula:

wherein, E (data_collisions _j) be the number of data packets of conflict in the j cycle, E (data_sent _j) be the number of data packets sending in the j cycle.

Step 3) in, the network insertion probability τ of website _sTApressing following formula determines:

${\mathrm{\τ}}_{\mathrm{STA}}=\left\{\begin{array}{c}{\mathrm{\β\τ}}_{\mathrm{STA}},f_{\mathrm{avg}}^j>f^{\mathrm{opt}}\\ {\mathrm{\τ}}_{\mathrm{STA}}+\mathrm{\ϵ},f_{\mathrm{avg}}^j\≤f^{\mathrm{opt}}\end{array}\right.;$

Wherein, ε is the linear factor that increases, ε=0.1/n, and wherein n is that network access station is counted out; β is that ratio reduces the factor, and β value is 5/6; f ^optvalue be 0.1.This linear adjustment mode that increases the property taken advantage of minimizing (AIMD) can be in the time that network load be lighter, the efficient resource in use network faster; But heavier when network load, when collision rate is higher, can reduce comparatively sharp again the access probability of website, alleviate network conflict rate.

Step 4) in, the minimum contention window size of website with maximum contention window size computing formula as follows:

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{STA}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{STA}}}-1){(1+p_{\mathrm{STA}}\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2p_{\mathrm{STA}}\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{STA}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{STA}}\end{array}$

Wherein, m is that maximum is kept out of the way number of times, value 3; The branch hazard probability of website $p_{\mathrm{STA}}=1-{(1-{\mathrm{\τ}}_{\mathrm{STA}})}^{n-1}(1-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}),$ N is that network access station is counted out.

Beneficial effect:

Competition window method of adjustment towards 802.11e VoIP application of the present invention, be set to optimum constant by the competition window of WAP (wireless access point), regulate the mode of website competition window to promote the VoIP capacity of 802.11e network by WAP (wireless access point) according to network conflict rate self adaptation simultaneously.The competition window of WAP (wireless access point) is one and determined by MAC layer parameter (comprising slot time, SIFS, DIFS and transmission rate) and VoIP coded system, with the network access station irrelevant constant of counting out.The competition window of website carries out self adaptation adjusting by WAP (wireless access point) according to network conflict rate.If WAP (wireless access point) detects collision rate and is greater than given threshold value, will be according to actual conflict rate value, the mode that uses the property taken advantage of to reduce is calculated the access probability that adapts to current network load; If the collision rate detecting is less than or equal to given threshold value, will be according to actual conflict rate value, use linear increase mode to calculate the access probability that adapts to current network load.Last according to the relation of access probability and competition window, calculate the minimax competition window of website.The present invention can ensure the fairness of wireless network up-downgoing stream, and the bottleneck effect of alleviating AP is held quantitative limitation to VoIP, can be according to network load situation, self adaptation regulates contention window value, promotes wireless channel effective rate of utilization, improves network throughput, reduce network delay, improve VoIP capacity.

This competition window self-adapting regulation method that is used for 802.11e wireless network environment VoIP application is according to the feature of VoIP application, the access probability of optimizing AP is doubly (N is the number of access website in network) of N of website access probability, derive by theory, the competition window that draws AP be one only relevant with VoIP coded system to MAC layer parameter, with the irrelevant constant expression of competition website number; In addition, can be according to network load situation, self adaptation regulates website contention window value.This method of adjustment has promoted AP priority, realizes the fair competition of AP place up-downgoing flow, the restriction of the bottleneck effect of reduction AP to VoIP capacity;

The present invention uses the minimax competition window of periodic Beacon frame real-time update website in 802.11e network, need not modify to website, is convenient to actual deployment.

Brief description of the drawings

Fig. 1 is flow chart of the present invention.

Fig. 2 is test environment topological diagram of the present invention.

Fig. 3 is throughput with the network access station variation diagram (G.711,802.11b) of counting.

Fig. 4 is that throughput is with different coding mechanism variation diagram (10STAs, 802.11b).

Fig. 5 is the ratio (G.711,10STAs, 802.11b) of up-downgoing stream throughput.

Fig. 6 is the VoIP capacity (G.711) of algorithms of different.

Fig. 7 is the CDF distribution map (G.711,50STAs, 802.11g) of packet loss.

Fig. 8 is the CDF distribution map (G.711,50STAs, 802.11g) of network delay.

Fig. 9 is that in hybrid network environment, DATA stream throughput is counted variation diagram (G.711,802.11b) with VoIP speech channel.

Figure 10 is VoIP flow network time delay figure (G.711,802.11b) in hybrid network environment.

Figure 11 is VoIP stream packet loss figure (G.711,802.11b) in hybrid network environment.

Embodiment

Below with reference to the drawings and specific embodiments, the present invention is described in further details:

Embodiment 1:

Referring to Fig. 1, it is flow chart of the present invention.It is the method realizing on AP, and process is as follows:

According to MAC layer parameter corresponding to 802.11 mechanism of access and corresponding VoIP coding method, calculate the optimal value of AP access probability, use variable storage:

${\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}=\sqrt{\frac{\mathrm{\δ}}{T_{\mathrm{data}}+\mathrm{SIFS}+T_{\mathrm{ack}}+\mathrm{DIFS}}}$

Wherein δ is slot time; T _dataand T _ackbe respectively a VoIP packet of transmission and time of transmitting corresponding ACK, computational methods are that the length of DATA or ACK bag is divided by physical transmission rate.For VoIP application, the length of DATA bag is the packet size of VoIP.

Based on what calculate according to formula

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{AP}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}}-1){(1+(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{AP}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{AP}}\end{array}$

Calculate the optimum contention window parameter of AP with wherein m is that maximum is kept out of the way number of times, value 3.Based on this numerical value, AP upgrades respectively the minimax contention window value of AC_VO (VoIP rank data flow) in updateCWMin (), updateCWMax () function.

VoIP application needs symmetrical up-downgoing flow, and for the VoIP data flow of N website, the load capacity that AP need to transmit is N times of each website load capacity.Therefore, need the access probability of preferential AP, alleviate the restriction that AP causes VoIP capacity as bottleneck node.The present invention is set to N times of website access probability by the access probability of AP, strictly shifts onto through a series of, obtains the expression formula of the optimum access probability of AP.This expression formula be one with network access station count out irrelevant, the constant only being determined by MAC parameter and VoIP coded system.

For website competition window adaptive updates, implementation procedure is as follows:

Defined variable DATAFailureCount, DATATotalCount was respectively used to add up in each cycle, the DATA data packet number retransmitting and the DATA data packet number of transmission, the ratio of the two is as current period (j cycle) the collision rate factor, and uses variable storage, that is:

$f_{\mathrm{curr}}^j=\frac{E(\mathrm{data}\_{\mathrm{collisions}}_j)}{E(\mathrm{data}\_{\mathrm{sent}}_j)}$

For reducing the deviation of instantaneous conflict, the average collision rate factor is proposed make its dynamic calculation within a update cycle, to reflect the average collision rate in j update cycle, its computing formula is as follows:

$f_{\mathrm{avg}}^j=(1-\mathrm{\α})*f_{\mathrm{curr}}^j+\mathrm{\α}*f_{\mathrm{avg}}^{j-1}$

Wherein, α is collision smoothing factor, and value is 0.875.

Arrive when the one-period time, complete and comprise DATAFailureCount, DATATotalCount variable is in interior initialization.The deviation of average collision rate of this cycle and given collision rate threshold value relatively simultaneously, adopting linearly increases the mode that the property taken advantage of reduces and adjusts channel access rate τ, is calculated as follows:

$\mathrm{\τ}=\left\{\begin{array}{c}\mathrm{\τ}+\mathrm{\ϵ},f_{\mathrm{avg}}^j\≤f^{\mathrm{opt}}\\ \mathrm{\β\τ},f_{\mathrm{avg}}^j>f^{\mathrm{opt}}\end{array}\right.$

In the time that network conflict rate is greater than given threshold value, show that network load is heavier, higher channel conflict causes the wasting of resources.Therefore, now should, by reducing channel access probability, reduce network conflict rate.Otherwise, in the time that network conflict rate is less than or equal to given threshold value, illustrating that network load is lighter, channel time slot idleness is higher.Therefore, should improve channel access probability, thereby promote channel time slot utilance, promote throughput.

Website access probability based on calculating, utilizes formula:

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{STA}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{STA}}}-1){(1+p_{\mathrm{STA}}\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2p_{\mathrm{STA}}\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{STA}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{STA}}\end{array}$

Wherein, m is that maximum is kept out of the way number of times, value 3; n is that network access station is counted out.Calculate respectively minimum, the maximum contention window of website

Finally, AP uses Beacon frame, periodically site parameter is broadcast to website (100ms).

Test result on NS2 emulation platform shows, compared with the inventive method strengthens machine-processed BDCF with the DCF that gives tacit consent to people's up-to-date propositions in 2013 such as EDCA layer mechanism and Y.Gao, can effectively promote network throughput, balance up-downgoing flow, time delay, packet loss, improve VoIP capacity.

Fig. 2 is the network topological diagram that we test use, comprises an AP, 70 wireless sites and 70 wired nodes.Wireless site is deployed in taking AP as the center of circle, and radius is on the circle of 500 meters.Descending TCP stream sends to wireless receiving node from wired source node, and up TCP stream sends to wired receiving node from radio sources node.The bandwidth of all wire links is 100Mbps, and time delay is 2ms.All wireless sites (comprising AP) use Destination-Sequenced Distance-Vector Routing (DSDV) Routing Protocol, and wireless access mechanism is used the basic access way of 802.11b or 802.11g.Each node receives only or sends a VoIP stream or UDP background stream, and when transmission UDP background stream, data package size is 1000bytes, and data transmission rate is 1Mbps.The feature of the encoding mechanism of using in experiment is as shown in table l.In method, some parameters arrange as follows: α=0.875, m=3, β=5/6.Method of adjustment BEDCA of the present invention changes as shown in Fig. 3-11 with offered load with the performance of acquiescence EDCA mechanism and BDCF.

Table l different coding mechanism characteristic

Can find out in conjunction with Fig. 3 to Fig. 5, along with the increase of offered load (network access station count out increase or VoIP code rate increases) the inventive method BEDCA is compared with traditional E DCA, BDCF, can obtain and approach optimum network throughput, the fairness of energy active balance up-downgoing stream throughput.In addition, can find out from Fig. 6 to Fig. 8, BEDCA energy active balance network delay, packet loss, promote VoIP capacity.Can find out in conjunction with Fig. 9 to Figure 11, in the network environment coexisting at VoIP stream and DATA stream, BEDCA can, in ensureing DATA stream throughput, promote VoIP capacity.BEDCA is for the feature of VoIP application, be doubly (N is the number of the website that participates in the competition) of N of website access probability by the access probability of preferential AP, the access probability of self adaptation Competition adjustment website, effectively reduce network conflict rate, ensure the fairness at aspects such as throughput, packet loss, time delays between up-downgoing stream, elevator system VoIP capacity.

Claims (6)

1. towards a competition window method of adjustment for 802.11e VoIP application, it is characterized in that:

1) be the optimal network access probability of AP according to the MAC layer parameter of access and VoIP coded system calculating WAP (wireless access point)

Described MAC layer parameter comprises slot time, SIFS, DIFS and transmission rate; Slot time represents off time; SIFS is short frame period; DIFS is distributed coordination frame period;

2) basis calculate the minimum of AP, the optimal value of maximum contention window size

3) the average collision rate in calculating j cycle of AP place basis again with threshold value f ^optrelation adjust website (STA) network insertion probability τ _sTA:

When time, reduce the network insertion probability τ of website _sTAto adapt to offered load;

When time, the network insertion probability τ of increase website _sTAto adapt to offered load;

4) AP is according to τ _sTAcalculate maximum, the minimum competition window of website; Maximum, the minimum competition window of the Beacon frame broadcast station of AP periodic.

2. the competition window method of adjustment towards 802.11e VoIP application according to claim 1, is characterized in that step 1) in computational methods as follows:

${\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}=\sqrt{\frac{\mathrm{\δ}}{T_{\mathrm{data}}+\mathrm{SIFS}+T_{\mathrm{ack}}+\mathrm{DIFS}}}$

Wherein δ is slot time; T _dataand T _ackit is respectively the time of transmitting a VoIP packet and transmitting corresponding ACK.

3. the competition window method of adjustment towards 802.11e VoIP application according to claim 1, is characterized in that step 2) in with computational methods as follows:

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{AP}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}}-1){(1+(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2(1-e^{-{\mathrm{\τ}}_{\mathrm{AP}}^{\mathrm{opt}}})\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{AP}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{AP}}\end{array}$

Wherein m is that maximum is kept out of the way number of times, and value is 3.

4. the competition window method of adjustment towards 802.11e VoIP application according to claim 1, is characterized in that step 3) in, be taken as current period collision rate with historical collision rate eWMA, that is:

$f_{\mathrm{avg}}^j=(1-\mathrm{\α})*f_{\mathrm{curr}}^j+\mathrm{\α}*f_{\mathrm{avg}}^{j-1};$

Wherein, α is smoothing factor, and value is 0.875; it is the average collision rate in j-1 cycle; be the collision rate in j cycle, determined by following formula:

wherein, E (data_collisions _j) be the number of data packets of conflict in the j cycle, E (data_sent _j) be the number of data packets sending in the j cycle.

5. the competition window method of adjustment towards 802.11e VoIP application according to claim 1, is characterized in that step 3) in, the network insertion probability τ of website _sTApressing following formula determines:

${\mathrm{\τ}}_{\mathrm{STA}}=\left\{\begin{array}{c}{\mathrm{\β\τ}}_{\mathrm{STA}},f_{\mathrm{avg}}^j>f^{\mathrm{opt}}\\ {\mathrm{\τ}}_{\mathrm{STA}}+\mathrm{\ϵ},f_{\mathrm{avg}}^j\≤f^{\mathrm{opt}}\end{array}\right.,$

Wherein, ε is the linear factor that increases, ε=0.1/n, and wherein n is that network access station is counted out; β is that ratio reduces the factor, and β value is 5/6; f ^optvalue be 0.1.

6. according to the competition window method of adjustment towards 802.11e VoIP application described in claim 1-5 any one, it is characterized in that step 4) in, the minimum contention window size of website with maximum contention window size computing formula as follows:

$\begin{array}{c}{\mathrm{CW}}_{\min }^{\mathrm{STA}}=(\frac{2}{{\mathrm{\τ}}_{\mathrm{STA}}}-1){(1+p_{\mathrm{STA}}\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}{\left(2p_{\mathrm{STA}}\right)}^i)}^{-1}\\ {\mathrm{CW}}_{\max }^{\mathrm{STA}}=2^m*{\mathrm{CW}}_{\min }^{\mathrm{STA}}\end{array}$

Wherein, m is that maximum is kept out of the way number of times, value 3; The branch hazard probability of website n is that network access station is counted out.