CN101895935A - Method and device for dynamic caching of wireless local area network switching - Google Patents

Abstract

The invention discloses a method and a device for dynamic caching of wireless local area network switching. The method comprises the following steps of: during establishing and maintaining a Cache used for the wireless local area network switching, searching an access point (AP) by a Station initiatively, and updating the Cache according to an initiative search result; and if the Station judges that a newly discovered access point (AP) has better performance than the AP on the same channel in the cache according to the search result, replacing the AP on the same channel in the Cache by using the newly discovered AP. The method and the device can overcome the defect that a static Cache has lower usability, so the method and the device increase the authentication and association success probabilities with the AP in the Cache during the switching, and greatly reduce the switching delay.

Description

A kind of method and apparatus that is used for the dynamic buffering of WLAN (wireless local area network) switching

Technical field

The present invention relates to the communications field, relate in particular to a kind of method and apparatus that is used for the dynamic buffering of WLAN (wireless local area network) switching.

Background technology

Development along with Radio Transmission Technology, wireless lan (wlan) based on IEEE 802.11 agreements has obtained large-scale deployment, the WLAN of infrastructure (Infrastructure) pattern mainly contains two parts and constitutes: set of basic (Basic Service Set, abbreviate BSS as) and distributed system (Distribution System abbreviates DS as) that BSS is coupled together.

As Fig. 1, BSS is by an access point (Access Point, abbreviate AP as) and associated some stations (Station) formation of this AP, its size is by the signal cover decision of AP, the station is the user terminal among the WLAN, must related with a certain AP (Association) just can with other main-machine communications in the network, for example the set of basic of AP1 correspondence is made of with two Stations related with AP1 AP1 among Fig. 1.DS links together the BSS that disperses, and makes that the Station between the different B SS can communicate by letter each other, thereby has constituted complete WLAN.Because the signal cover of AP is restricted, when Station is mobile in WLAN, enter another BSS by a BSS, can switch, disconnect with current related AP, related with new AP, move along track shown in the arrow as the STA1 among Fig. 1 (standing 1), coverage and the current associated AP of having left AP3 are that AP3 disconnects, with new AP is that AP2 is related, carries out one time handoff procedure.Station also may switch between the BSS that does not belong to same WLAN, and this relates to the switching between the subnet, does not belong to the scope that this paper discusses, and switching mentioned in this article is refered in particular between BSS among the same WLAN and switched.

Application in real time is that a typical case on the WLAN uses, as real-time video and real-time voice application etc.Use in real time service parameters such as propagation delay time and shakes relatively more responsively, and BSS switches the losing and shake of increase, packet that the handover delay that is brought can cause propagation delay time among the WLAN, and this has had a strong impact on the performance of real-time application.Optimize the BSS handoff procedure, reducing handover delay is to be applied in the important prerequisite that is able to large scale deployment under the WLAN environment in real time.

When Station was mobile between BSS, away from the AP of current association, the wireless link condition between AP and the Station descended thereupon gradually, and when link circuit condition can't satisfy the specific criteria of Station definition, Station triggered BSS and switches.802.11 the handoff procedure (seeing accompanying drawing 2) of the BSS of agreement regulation is as follows:

1) finds that (Scan) closes on available AP,, need to find AP2 for the station among Fig. 11.Two kinds of modes of finding AP are arranged: active and passive.Active mode is to send the request of seeking (ProbeRequest) (201), receives to seek and replys (Probe Response) (202); Passive mode is the beacon frame (Beacon) that receives the AP periodic broadcast, and this dual mode can obtain to close on the information of AP, and Station selects an AP according to certain strategy from seek the result then;

2) authenticate (Authentication) to AP.Send authentication request (203), receive authentication response (204);

3) carry out related with AP.Send related request (205), receive association and reply (206), be successfully associated back BSS handoff procedure and finish.

The summation of above-mentioned three phases time delay is exactly the overall delay that BSS switches, and finds that wherein time delay is generally 100 to the hundreds of millisecond, authentication and interconnect-delay be several milliseconds (if complicated authentication modes such as employing 802.1x, the time to postpone a meeting or conference with the second be the order of magnitude.Use time delay responsive relatively in real time, certification level higher when switching is also infeasible, and some are used in real time as based on Session Initiation Protocol (Session InitiationProtocol, session initiation protocol) VoWLAN (Voice Over WLAN, voice on the WLAN) use, Session Initiation Protocol has built-in authentication mechanism, so application authorization mechanism can be simple relatively in real time).

In order to reduce handover delay, can introduce buffer memory (Cache) mechanism, set up Cache according to the result who seeks, preserve the information of the several A P that Station may switch among the Cache.When BSS switch to take place, Station at first utilized the AP among the Cache, promptly selected AP authentication, association from Cache, if success then do not need to restart the AP discovery procedure has reduced handover delay greatly.But the hit rate of Cache is closely related with its availability, and this just requires Station not only will preserve AP information in Cache, will carry out updating maintenance to these information simultaneously, improves its availability.

The method that existing Cache safeguards is that Station takes out an AP from Cache, switches on the channel of this AP correspondence, initiatively to seek mode AP information is upgraded.This maintenance mode can be referred to as static Cache, and promptly the combination of AP does not change among the Cache, renewal be the attribute information of specific AP.

But, static Cache mechanism can not change the combination of AP among the Cache in maintenance process, and Station can leave the signal cover of some AP when mobile, this moment, these AP were unavailable, close joint conference's failure with them, all related failures of AP among the worst situation and the Cache must be carried out the discovery procedure of seeking of AP again, make handover delay very big, have a strong impact on the performance of real-time application.

Summary of the invention

The technical problem to be solved in the present invention is exactly to propose a kind of method and apparatus that is used for the dynamic buffering of WLAN (wireless local area network) switching, overcomes the lower problem of static Cache availability.

In order to solve the problems of the technologies described above, the invention provides a kind of method that is used for the dynamic buffering of WLAN (wireless local area network) switching, comprising:

When setting up and safeguard the buffer memory Cache that is used for the WLAN (wireless local area network) switching, the Station that stands initiatively seeks AP, upgrades Cache according to initiatively seeking the result;

Wherein, if Station judges that according to initiatively seeking the result newfound access point AP is better than AP performance on the same channel among the Cache, then replace the AP on the same channel among the Cache with described newfound AP.

Further, said method also can have following characteristics:

Station safeguards two channel sets: continue channel set P_chan_set and dynamic channel set D_chan_set,

Described P_chan_set comprises 1,6,11 channels in the 802.11b/g agreement;

Described D_chan_set comprises in the 802.11b/g agreement except that 1,6,11 outer all the other channels;

Initiatively seeking in the process, Station safeguards that channel number remains unchanged among the P_chan_set; Station is provided with the dynamic change as a result that channel quantity is sought along with active among the D_chan_set.

Further, said method also can have following characteristics:

In the process of initiatively seeking, Station at first seeks the channel among the P_chan_set, seeks the channel among the D_chan_set then.

Further, said method also can have following characteristics:

Station is provided with the D_chan_set channel quantity along with the dynamic change as a result of initiatively seeking specifically comprises:

If in initiatively seeking a channel procedure, do not find AP, this channel belongs to the D_chan_set set, and then Station is with the deletion from the D_chan_set set of this channel;

If in seeking process, in current P_chan_set and D_chan_set, all do not find AP, the D_chan_set that then resets set is about to it and reverts to 802.11b/g except that 1,6,11 outer all the other channels.

Further, said method also can have following characteristics:

Describedly upgrade Cache and specifically be meant according to initiatively seeking the result:

In initiatively seeking a channel procedure, according to the selection strategy that sets in advance, the best AP of the performance of selecting this channel to seek is as newfound AP;

If do not have AP to exist among the Cache on this channel, then described newfound AP deposited among the Cache;

If have AP to exist among the Cache on this channel, and judge that the AP that exists among described newfound AP and the Cache is same, then use the information of the AP that exists among the described Cache of information updating of newfound AP;

If there is AP to exist among the Cache on this channel, and judge that the AP that exists among described newfound AP and the Cache is not same, and judge whether newfound AP is better than AP performance on the same channel among the Cache, then replace the AP on the same channel among the Cache with described newfound AP.

Further, said method also can have following characteristics:

The described selection strategy that sets in advance specifically is meant:

Selection is sought the AP of time delay minimum as the best AP of performance;

The described time delay of seeking is to seek claim frame from Station broadcasting, to the time interval value of seeking acknowledgement frame of receiving that AP replys.

Further, said method also can have following characteristics:

This AP's seek time delay T if Station from a plurality of time delays of seeking of a certain AP acquisition, then makes _{Probe_delay}For:

$T_{\mathrm{probe}\_\mathrm{delay}}=T_1+\frac{\underset{i=2}{\overset{N}{\mathrm{\Σ}}}(T_i-T_{i-1})}{N-1}$

Wherein, T wherein _iBe i and seek time delay, i ∈ [1, N] is integer, and N is the number of seeking acknowledgement frame that Station receives from this AP.

Further, said method also can have following characteristics:

Station is provided with that the AP on the same channel only keeps one among the Cache, if the channel of two AP work is identical, selects to seek the less AP of time delay and adds Cache, and another one is deleted from Cache.

In order to solve the problems of the technologies described above, the present invention also provides a kind of device that is used for the dynamic buffering of WLAN (wireless local area network) switching, is applied among the Station, and comprise and seek module and update module,

The described module of seeking is used for initiatively seeking AP, and informing update module with initiatively seeking the result when setting up and safeguard the Cache that is used for the WLAN (wireless local area network) switching;

Described update module is used for upgrading Cache according to initiatively seeking the result, wherein, if judge that according to initiatively seeking the result newfound AP is better than AP performance on the same channel among the Cache, then replaces the AP on the same channel among the Cache with described newfound AP.

Further, said apparatus also can have following characteristics:

Described device also comprises the channel set maintenance module,

Described channel set maintenance module is used to safeguard two channel set: P_chan_set and D_chan_set; Initiatively seeking in the process, the channel set maintenance module is used for safeguarding that the P_chan_set channel number remains unchanged, and according to from seeking the result that active that module knows is sought, channel quantity dynamic change among the D_chan_set is set;

Wherein, described P_chan_set comprises 1,6,11 channels in the 802.11b/g agreement; Described D_chan_set comprises in the 802.11b/g agreement except that 1,6,11 outer all the other channels.

The present invention is directed to the quick switching problem of WLAN (wireless local area network) under the real-time application scenarios, having proposed dynamic Cache sets up and maintenance mechanism, can overcome the lower shortcoming of static Cache availability, thereby when switching generation, with the authentication of AP among the Cache, be successfully associated probability and increase, reduced handover delay greatly.

Description of drawings

Fig. 1 is the network structure of the WLAN of infrastructure mode;

Fig. 2 is the general handoff procedure that the use of 802.11 agreements regulation is initiatively sought;

Fig. 3 is the process of initiatively seeking;

Fig. 4 is the flow chart of the embodiment of the invention;

Fig. 5 is that the time delay of seeking of the AP of the embodiment of the invention defines schematic diagram;

Fig. 6 is the device schematic diagram of the embodiment of the invention;

Fig. 7 is a kind of handoff scenario of the dynamic Cache maintenance mechanism and the static Cache maintenance mechanism contrast performance of handoffs of the embodiment of the invention.

Embodiment

Be to improve the availability of Cache, the present invention uses dynamic Cache maintenance mechanism, and Cache is according to initiatively seeking result's foundation, and after Station and AP were successfully associated, the method according to this invention was safeguarded dynamically; When switching the maintenance that stops Cache when taking place.

When setting up and safeguarding Cache, the combination dynamic change of AP among the Cache if the new AP that finds is than AP performance on the same channel among the Cache better (it is littler to seek time delay), is then replaced the AP on the same channel among the Cache with new AP.

When Station added network or BSS switching generation for the first time, when selecting AP from Cache, Cache should be non-NULL (having at least one AP information to exist); If Cache is empty, then to find AP initiatively to seek mode, set up Cache.

Before switching generation, being combined in of AP is not unalterable in the maintenance process among the Cache, but along with safeguarding (initiatively seeking) dynamic change.

The information that in Cache, only keeps an AP on a certain channel.

The present invention is described in detail below in conjunction with drawings and the specific embodiments.

In the process of setting up Cache or Cache maintenance, all need to adopt the mode of initiatively seeking to obtain AP information.The understanding of present embodiment for convenience, the process that the first active of simply introducing 802.11 agreements regulation is sought, specifically as Fig. 3: Station sequentially is done as follows for passage 1-N:

A) Station visits wireless channel (301,305,307,309) by the mode of CSMA/CA (Carrier Sensing MultipleAccess/Collision Avoidance, csma/conflict is avoided) on a certain channel;

B) Station broadcasts on this channel and seeks claim frame (302,306,308,310);

C) Station starts minimum channel time (minChannelTime) and maximum channel time (maxChannelTime) timer, intercepts to have or not the arrival of seeking acknowledgement frame;

D) if the minimum channel time timer is overtime and do not receive any acknowledgement frame of seeking, switch to next channel, turn to steps A to continue to carry out; If received before the minimum channel time timer is overtime and sought acknowledgement frame (303), remaining seeks acknowledgement frame to continue to stop reception so on channel, up to maximum channel time timer overtime (304), then handles the acknowledgement frame of receiving of seeking;

F) switch next channel, repeat the process of A.

Above-mentioned is the idiographic flow of initiatively seeking, wherein in order to improve the efficient of initiatively seeking, make that seeking process can find as much as possible that AP is (if wait for the minimum channel timer expiry on certain channel at every turn, still do not receive that any seeking reply, then this channel is sought and do not had more meaning, because do not find any available AP on this channel, the channel 2 among Fig. 3 just belongs to this channel).

In the 802.11b/g agreement, the non-intersect folded channel of WLAN is 1,6,11, and generally speaking, the channel of the AP of actual deployment work is usually at 1,6,11 these three channels.

The embodiment of the invention is distinguished 802.11b/g WLAN channel, is divided into two channel sets:

● Persistent Channel Set: continue channel set, abbreviate P_chan_set as, comprise 1 among the 802.11b/g, 6,11 channels;

● Dynamic Channel Set: the dynamic channel set, abbreviate D_chan_set as, comprise and remove 1,6,11 outer all the other channels among the 802.11b/g.

Initiatively seeking in the process, the embodiment of the invention is to these two distinguishing processing of channel set, and channel number remains unchanged among the P_chan_set; The D_chan_set channel quantity can be along with the dynamic change as a result of initiatively seeking, and is specific as follows:

● in the process of initiatively seeking, at first seek the channel among the P_chan_set, seek the channel among the D_chan_set then.

If ● minimum channel timer expiry and do not receive that seek acknowledgement frame and this channel of any AP belong to the D_chan_set set, then with the deletion from set of this channel.

If ● in seeking process, all do not find AP in current P_chan_set and D_chan_set, the D_chan_set that then will reset is about to it and reverts to 802.11b/g except that 1,6,11 outer all the other channels, continues initiatively to seek process.

By classification and differentiating and processing to 802.11b/g WLAN channel, can guarantee on the channel of being sought, to have AP to exist as much as possible, avoided being wasted in the time on the channel of no AP existence.On this basis, according to Fig. 4, specifically describe the dynamic Cache mechanism of the embodiment of the invention:

Step 401:Station begins to start and initiatively seeks process, and whether judge that this is initiatively sought needs initialization Cache, if forward 402 execution to; Otherwise, forward 403 to and carry out;

When Cache is sky, need initialization Cache, do not find any AP in the process such as setting up initiatively to seek Cache (Station adds network for the first time) or last time, it is empty causing Cache;

Step 402: the channel set that initialization need be sought;

Channel set among the D_chan_set is reset, promptly recover it and remove 1,6,11 all the other outer channels among 802.11b/g for comprising;

Step 403: select first channel among the P_chan_set;

Step 404: the mode of following CSMA/CA is competed wireless channel, and after the right to use of acquisition channel, claim frame is sought in broadcasting, starts minimum channel time timer and maximum channel time timer, the arrival that acknowledgement frame is sought in detecting;

Step 405:, change step 415 and carry out if the minimum channel time timer is overtime and do not receive any acknowledgement frame of seeking on this channel; If having received to seek before the minimum channel time timer is overtime replys, change step 406 and carry out;

Wherein, if the minimum channel time timer is overtime and do not receive any acknowledgement frame of seeking on this channel, and this channel belongs to D_chan_set, then need delete this channel in D_chan_set;

Step 406: the acknowledgement frame of seeking that receives AP;

Step 407:, then change step 408 and carry out if the maximum channel time timer is overtime; Otherwise changeing step 406 carries out;

Step 408: according to the selection strategy that sets in advance, the AP that the performance of selecting this channel search to arrive is best;

Step 409: judge whether existing AP exists on this channel among the Cache, if, then change step 410 and carry out, otherwise, change step 412 and carry out;

Step 410: judge whether the AP that obtains exists in Cache, if, then change step 411 and carry out, otherwise, change step 413 and carry out;

Whether the MAC Address (hardware address) by the AP on this channel among the AP that relatively obtains and the Cache is identical, can judge whether these two AP are same AP, if MAC Address is identical, then shows it is same AP; Otherwise, be different AP;

Step 411: upgrade the information of this AP, change step 414 and carry out;

The AP that obtains exists in Cache, upgrades the information of this AP, such as seeking time delay, signal strength signal intensity etc.;

Step 412: this AP is deposited among the Cache, change step 414 and carry out;

The working channel of seeking all AP among the AP that find to obtain and the Cache is all different, and this AP is added Cache, and soon the information of AP is kept among the Cache such as information such as seeking time delay;

Step 413: retention property AP preferably in Cache, change step 414 and carry out;

On a certain channel, found new AP (hardware address of all AP among hardware address and the Cache is all different), but there be the AP identical among the Cache with this AP working channel, select according to the selection strategy that sets in advance, retention property is AP preferably, abandons the AP of poor-performing;

Step 414: whether this seeks process and should finish, and if not, then change step 415 over to and carry out, otherwise, finish this and seek process;

The condition that finishes can for:

1) all frequency ranges among P_chan_set and the D_chan_set has all been carried out once seeking the transmission of request and seeking the trial reception of replying;

2) also can define this and seek the moment that must finish,, seek process need and finish as surpassing this constantly;

Step 415: switch to the next channel in the channel set, change step 404 and carry out;

Wherein, initial first channel from P_chan_set begins, and switches successively, till last in switching to D_chan_set.

Different selection strategies can be set, in above-mentioned steps 408 and the step 413, select according to the selection strategy that sets in advance, such as, selection strategy can be the signal strength values size according to AP, the best AP of signal is selected; Passing through of also can proposing according to the present invention sought time delay and selects, and selects to seek the little AP of time delay, thinks that promptly to seek the little AP performance of time delay better.

Specifically, in step 406, receive the acknowledgement frame of seeking of AP, and calculate each and seek the time delay of seeking of replying correspondence; Each is sought time delay and is defined as: seek claim frame from successfully sending, to the time interval between the acknowledgement frame of seeking that receives that AP returns, unit is millisecond (also can be converted into the second is unit), concrete available formula 1 expression.T wherein _i: i (i is 1,2 ..., N) the individual time delay of seeking; T _Recvi: receive i acknowledgement frame of a certain AP constantly; T _Send: Station broadcasts on this channel and seeks claim frame constantly.As shown in Figure 5, first that receive certain AP sought to calculate behind the acknowledgement frame and sought time delay 1 (T ₁), receive that second of this AP seeks to calculate behind the acknowledgement frame to seek time delay 2 (T ₂), so carrying out, the N that receives this AP seeks to calculate behind the acknowledgement frame and seeks time delay N (T _N).Need to prove on a certain channel and may have a plurality of AP, so can receive the acknowledgement frame of seeking of a plurality of AP, each AP seek acknowledgement frame also have a plurality of, so time-delay when calculating each and seek seeking of acknowledgement frame need be write down this and seek time delay corresponding to which AP;

T _i=T _Recvi-T _Send(formula 1)

For a plurality of time delays of seeking that same AP obtains, the present invention assert this AP first to seek time delay the most important, particularly, in step 408,, handle according to formula 2 with the time delay of seeking that obtains.Formula 2 shows, certain AP seeks time delay T _{Probe_delay}Be two parts and, first seeks answer delay T to a part for this AP of receiving ₁Another part is counted for seeking time delay from second, adjacent two seek the time delay difference and arithmetic mean, N is all numbers of receiving of seeking acknowledgement frame of this AP.T _{Probe_delay}Unit be millisecond (also can be converted into second for unit), it is to select AP to carry out related selection foundation from Cache, also be to carry out dynamic Cache upgating object when safeguarding, dynamically among the Cache variation of AP combination also around T _{Probe_delay}Carry out.

$T_{\mathrm{probe}\_\mathrm{delay}}=T_1+\frac{\underset{i=1}{\overset{N}{\mathrm{\Σ}}}(T_i-T_{i-1})}{N-1}$ (formula 2)

After the dynamic Cache of present embodiment safeguards that occurring in Station and AP is successfully associated, can periodically carry out, also can take other similar modes, when BSS switches generation, stop Cache and safeguard, after switching on the new AP, proceed the maintenance of Cache according to set strategy, up to the generation once more of switching, and so forth.

Foregoing description is that dynamic Cache sets up and maintenance process, though certainly BSS to switch Cache when taking place be but that sky or Cache are for empty authenticate from wherein directly obtaining AP, under the situation of related all failures, also can carry out the above-mentioned process of initiatively seeking.

As shown in Figure 6, the device of the dynamic buffering that is used for the WLAN (wireless local area network) switching of the embodiment of the invention comprises and seeks module, update module and channel set maintenance module, seeks module and links to each other with the channel set maintenance module with update module respectively;

The described module of seeking is used for initiatively seeking AP, and informing update module with initiatively seeking the result when setting up and safeguard the Cache that is used for the WLAN (wireless local area network) switching;

Described update module is used for upgrading Cache according to initiatively seeking the result, wherein, if judge that according to initiatively seeking the result newfound AP is better than AP performance on the same channel among the Cache, then replaces the AP on the same channel among the Cache with described newfound AP;

Described channel set maintenance module is used to safeguard two channel sets: continue the set of channel set and dynamic channel; Initiatively seeking in the process, the channel set maintenance module is used for safeguarding that the P_chan_set channel number remains unchanged, and according to from seeking the result that active that module knows is sought, the dynamic change of D_chan_set channel quantity is set.

The specific implementation of each module of device that is used for the dynamic buffering that WLAN (wireless local area network) switches no longer describes in detail referring to the said method flow process herein.

For dynamic Cache maintenance mechanism and this machine-processed advantage among the present invention better is described, in conjunction with above-mentioned embodiment, we specify by handoff scenario shown in Figure 7.

As shown in Figure 7, Station is moved to position B by position A along the diagram track.When the A place, related with AP2, when using present static Cache maintenance mechanism, the information of AP1 and AP3 is arranged in the Cache; Also only upgrade the information of AP1, AP3 when upgrading AP, the combination among the Cache is AP1 and AP3 all the time.But enter the AP4 scope when switching when moving to the AP2 edge, AP1, AP3 have lost validity (the Station present position has exceeded the signal cover of AP1 and AP3 during switching) in the Cache list item, close joint conference's failure with it, must carry out AP (AP4) discovery work again, make handover delay very big.

For scene shown in Figure 7, according to dynamic Cache maintenance mechanism provided by the invention, find to have on three channels AP to exist at the A place, might as well establish 1,6 and 11, there is not mutual interference mutually in AP3 with AP4, and identical working channel (for example channel 1) can be set.Seek above three channels when safeguarding Cache, utilization is sought the result and is dynamically changed Cache according to strategy.On channel 1, can find AP4 when in moving process, upgrading Cache, with the AP3 on its replacement cochannel.When switching generation, AP4 has been arranged among the Cache, so can not produce the situation of Cache failure, improved the efficient of Cache, reduced handover delay.

Certainly; the present invention also can have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.

Claims (10)

1. method that is used for the dynamic buffering that WLAN (wireless local area network) switches comprises:

When setting up and safeguard the buffer memory Cache that is used for the WLAN (wireless local area network) switching, the Station that stands initiatively seeks AP, upgrades Cache according to initiatively seeking the result;

Wherein, if Station judges that according to initiatively seeking the result newfound access point AP is better than AP performance on the same channel among the Cache, then replace the AP on the same channel among the Cache with described newfound AP.

2. the method for claim 1 is characterized in that,

Station safeguards two channel sets: continue channel set P_chan_set and dynamic channel set D_chan_set,

Described P_chan_set comprises 1,6,11 channels in the 802.11b/g agreement;

Described D_chan_set comprises in the 802.11b/g agreement except that 1,6,11 outer all the other channels;

Initiatively seeking in the process, Station safeguards that channel number remains unchanged among the P_chan_set; Station is provided with the dynamic change as a result that channel quantity is sought along with active among the D_chan_set.

3. method as claimed in claim 2 is characterized in that,

In the process of initiatively seeking, Station at first seeks the channel among the P_chan_set, seeks the channel among the D_chan_set then.

4. method as claimed in claim 2 is characterized in that,

Station is provided with the D_chan_set channel quantity along with the dynamic change as a result of initiatively seeking specifically comprises:

If in initiatively seeking a channel procedure, do not find AP, this channel belongs to the D_chan_set set, and then Station is with the deletion from the D_chan_set set of this channel;

If in seeking process, in current P_chan_set and D_chan_set, all do not find AP, the D_chan_set that then resets set is about to it and reverts to 802.11b/g except that 1,6,11 outer all the other channels.

5. the method for claim 1 is characterized in that,

Describedly upgrade Cache and specifically be meant according to initiatively seeking the result:

In initiatively seeking a channel procedure, according to the selection strategy that sets in advance, the best AP of the performance of selecting this channel to seek is as newfound AP;

If do not have AP to exist among the Cache on this channel, then described newfound AP deposited among the Cache;

If have AP to exist among the Cache on this channel, and judge that the AP that exists among described newfound AP and the Cache is same, then use the information of the AP that exists among the described Cache of information updating of newfound AP;

If there is AP to exist among the Cache on this channel, and judge that the AP that exists among described newfound AP and the Cache is not same, and judge whether newfound AP is better than AP performance on the same channel among the Cache, then replace the AP on the same channel among the Cache with described newfound AP.

6. method as claimed in claim 5 is characterized in that,

The described selection strategy that sets in advance specifically is meant:

Selection is sought the AP of time delay minimum as the best AP of performance;

The described time delay of seeking is to seek claim frame from Station broadcasting, to the time interval value of seeking acknowledgement frame of receiving that AP replys.

7. method as claimed in claim 6 is characterized in that,

This AP's seek time delay T if Station from a plurality of time delays of seeking of a certain AP acquisition, then makes _{Probe_delay}For:

$T_{\mathrm{probe}\_\mathrm{delay}}=T_1+\frac{\underset{i=2}{\overset{N}{\mathrm{\Σ}}}(T_i-T_{i-1})}{N-1}$

Wherein, T wherein _iBe i and seek time delay, i ∈ [1, N] is integer, and N is the number of seeking acknowledgement frame that Station receives from this AP.

8. method as claimed in claim 6 is characterized in that,

Station is provided with that the AP on the same channel only keeps one among the Cache, if the channel of two AP work is identical, selects to seek the less AP of time delay and adds Cache, and another one is deleted from Cache.

9. a device that is used for the dynamic buffering of WLAN (wireless local area network) switching is applied to it is characterized in that among the Station, comprise and seek module and update module,

The described module of seeking is used for initiatively seeking AP, and informing update module with initiatively seeking the result when setting up and safeguard the Cache that is used for the WLAN (wireless local area network) switching;

Described update module is used for upgrading Cache according to initiatively seeking the result, wherein, if judge that according to initiatively seeking the result newfound AP is better than AP performance on the same channel among the Cache, then replaces the AP on the same channel among the Cache with described newfound AP.

10. device as claimed in claim 9 is characterized in that described device also comprises the channel set maintenance module,

Described channel set maintenance module is used to safeguard two channel set: P_chan_set and D_chan_set; Initiatively seeking in the process, the channel set maintenance module is used for safeguarding that the P_chan_set channel number remains unchanged, and according to from seeking the result that active that module knows is sought, channel quantity dynamic change among the D_chan_set is set;

Wherein, described P_chan_set comprises 1,6,11 channels in the 802.11b/g agreement; Described D_chan_set comprises in the 802.11b/g agreement except that 1,6,11 outer all the other channels.

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