CN101895886A - Method and device for selecting access point - Google Patents

Abstract

The invention discloses a method and a device for selecting an access point (AP). The method for selecting the AP during a basic service set (BSS) switching process comprises the following steps that: a Station selects the AP with the minimum search delay from a Cache and performs authentication and association when performing BBS switch, wherein the search delay is a time interval value starting from the time when a search request is sent by the Station to the time when a search response frame is received from the AP. Through the method and the device, the condition of a wireless link is taken into comprehensive consideration and the load imbalance of the AP is effectively avoided; moreover, in the method, a 802.11 protocol does not need to be modified and the method has high deployability.

Description

A kind of method and apparatus of selecting access point

Technical field

The present invention relates to the communications field, relate in particular to a kind of method and apparatus of selecting access point.

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 Cache (buffer memory) mechanism, Cache sets up according to the result that seeks, preserves the information of the several A P that Station may switch to.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.

As mentioned above, when BSS switches, need select a new AP to authenticate with related from Cache, AP is as the relay point of Station communication, and the network performance that its ability and Station obtain is directly related.In order to obtain the better service performance, Station need select the AP that seeks discovery.The standard of existing selection has two classes:

One class is the signal strength values size according to AP, and the best AP of signal is selected; But this method can make most Station concentrate on the AP of a signal " best ", and this makes that the interior user of BSS of AP correspondence is more, and Radio Link influences the network performance that the user obtains near saturation condition;

Another kind of is the AP assist mode, promptly expands the beacon frame of AP and seeks acknowledgement frame, provides some new fields (field is represented the particular network parameter) to select AP to use for Station; This method has been revised 802.11 agreements, has destroyed the consistency of agreement.This machine-processed interoperability is very poor simultaneously, is difficult to transplant, and is difficult to apply it to the existing WLAN that has disposed in a large number and gets on

In sum, prior art selects the method for access point can cause the load of AP unbalanced, perhaps destroys the consistency of agreement.

Summary of the invention

The technical problem to be solved in the present invention is exactly to propose a kind of method and apparatus of selecting access point, overcomes prior art because the problem that the unreasonable load that brings of AP choice mechanism is unbalanced, extensibility is relatively poor.

In order to solve the problems of the technologies described above, the invention provides the method for selecting access point in a kind of set of basic BSS handoff procedure, comprising:

Stand Station when carrying out the BSS switching, from buffer memory Cache, select the access point AP that seeks the time delay minimum to authenticate with related;

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

Further, said method also can have following characteristics:

Described seek time delay be by Station when setting up and safeguarding Cache, initiatively seek in the process of AP seek claim frame by broadcasting and receive that AP replys seek the acknowledgement frame acquisition,

Wherein, 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:

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

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.

In order to solve the problems of the technologies described above, the invention provides the method for selecting access point in a kind of set of basic handoff procedure, comprising:

Station is when carrying out the BSS switching, if Cache is empty, perhaps, the all related failure of the AP that Station obtains from Cache, then Station initiates initiatively to seek the process of AP, seek claim frame and receive the acknowledgement frame of seeking that AP replys by broadcasting, obtain to seek the AP of time delay minimum, and authenticate with this AP and related;

Wherein, seeking time delay is to send from Station to seek claim frame, 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:

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

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.

In order to solve the problems of the technologies described above, the invention provides and a kind ofly setting up and safeguarding the method for selecting access point in the Cache process, comprising:

Setting up and safeguarding in the Cache process, Station initiates initiatively to seek the process of AP, seeks claim frame and receives the acknowledgement frame of seeking that AP replys by broadcasting, obtains the time delay of seeking of AP, and seeks the little AP of time delay on the selection same channel and deposit among the Cache;

Wherein, seeking time delay is to send from Station to seek claim frame, 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:

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

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.

Further, said method also can have following characteristics:

Station selects the AP that seeks the time delay minimum to authenticate with related from Cache when carrying out the BSS switching.

In order to solve the problems of the technologies described above, the invention provides a kind of device of selecting access point, be applied to it is characterized in that among the Station, comprise and seek module and select module;

The described module of seeking is used for initiatively seeking AP, and seeks claim frame and receive the acknowledgement frame of seeking that AP replys by broadcasting, obtain the time delay of seeking of AP, and the time delay of seeking that will obtain is informed the selection module;

Described selection module is used for selecting to seek on the same channel the little AP of time delay and deposits Cache in;

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

Further, said apparatus also can have following characteristics:

The described module of seeking also is used for when from a plurality of time delays of seeking of a certain AP acquisition, and what this AP then was set seeks time delay T _{Probe_delay}For:

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

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

The present invention is directed to the quick switching problem of WLAN (wireless local area network) under the real-time application scenarios, a kind of method based on the selection AP that seeks time delay has been proposed, the method has been taken all factors into consideration wireless link condition, can effectively avoid the unbalanced problem of AP load, and this method does not need to revise 802.11 agreements, and very strong deployable is arranged.

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 that the time delay of seeking of AP defines schematic diagram;

Fig. 5 is the device schematic diagram of the embodiment of the invention.

Embodiment

Basic design of the present invention is: Station selects the AP that seeks the time delay minimum to authenticate with related when carrying out the BSS switching.

Wherein, seeking time delay is that Station initiates initiatively to seek in the process of AP, seeking claim frame by broadcasting and obtain with the acknowledgement frame of seeking that reception AP replys, is to send from Station to seek claim frame, to the time interval value of seeking acknowledgement frame of receiving that AP replys.

Station can obtain several from a certain AP and seek time delay (receive several seek acknowledgement frame), and these are sought the average that calculated with mathematical model that time delay defines according to the present invention is sought time delay.

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

The calculating that AP seeks time delay occurs in the process of setting up Cache or Cache maintenance, and both of these case all needs to adopt the mode of initiatively seeking to obtain AP information, particularly calculates the choice criteria of AP: seek time delay.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 embodiments of the present invention, above-mentioned steps D) in,, then calculates each and seek and reply the corresponding time delay of seeking if before the minimum channel time timer is overtime, received and seek acknowledgement frame; 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 accompanying drawing 4, 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, behind the maximum channel timer expired, switching to before the next one seeks on the channel,, handle according to the formula 2 that the present invention proposes 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 is to carry out dynamic Cache emphasis upgating object when safeguarding, dynamically the variation of AP combination also is around T among the Cache _{Probe_delay}Carry out.

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

Delay when calculating the seeking of AP, begin to carry out dynamic Cache maintenance mechanism:

Select the AP that seeks the time delay minimum that current channel seeks as newfound AP;

If it is all different to seek the working channel of all AP among newfound AP and the Cache, this AP is added Cache, soon AP seek time delay and some other information is kept among the Cache;

If there be (have an AP in Cache, the hardware address of this AP is identical with newfound AP) in newfound AP in Cache, then upgrade the time delay information relevant of seeking of this AP with other;

If 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, according to seeking time delay these two identical AP of working channel are accepted or rejected, the size of seeking time delay that compares the two, if it is less that original AP seeks time delay, then newfound AP is abandoned; If it is less that newfound AP seeks time delay, then with the cochannel AP among the newfound AP replacement Cache.

That is: the AP on the same channel only keeps one among the Cache, if two AP working channels are identical, select to seek the less AP of time delay and adds Cache, and another one is deleted from Cache.

When BSS switched generation, the AP that seeks the time delay minimum was selected, and authenticates with related.

In addition, Station is when carrying out the BSS switching, if Cache is empty, perhaps, the all related failure of the AP that Station obtains from Cache, then Station initiates initiatively to seek the process of AP, seeks the acknowledgement frame of seeking that claim frame and reception AP reply by broadcasting, the AP of time delay minimum is sought in acquisition, and authenticates with this AP and related.

As shown in Figure 5, the device of the embodiment of the invention is applied to comprise among the Station: what link to each other seeks module and selects module;

The described module of seeking is used for initiatively seeking AP, and seeks claim frame and receive the acknowledgement frame of seeking that AP replys by broadcasting, obtain the time delay of seeking of AP, and the time delay of seeking that will obtain is informed the selection module;

Described selection module is used for selecting to seek on the same channel the little AP of time delay and deposits Cache in;

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

The described module of seeking also is used for when from a plurality of time delays of seeking of a certain AP acquisition, and what this AP then was set seeks time delay T _{Probe_delay}For:

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

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

In sum, seek time delay and be the standard of selecting AP when switching from Cache, and when safeguarding Cache, AP seeks the foundation that time delay also is AP dynamic change among main upgating object and the Cache.The AP system of selection based on seeking time delay (Probe Delay) that the present invention proposes not only can avoid the AP load unbalanced, and does not need to revise agreement, and extensibility is preferably arranged.

Claims (10)

1. select the method for access point in the set of basic BSS handoff procedure, comprising:

Stand Station when carrying out the BSS switching, from buffer memory Cache, select the access point AP that seeks the time delay minimum to authenticate with related;

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

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

Described seek time delay be by Station when setting up and safeguarding Cache, initiatively seek in the process of AP seek claim frame by broadcasting and receive that AP replys seek the acknowledgement frame acquisition,

Wherein, 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:

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

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.

3. select the method for access point in the set of basic handoff procedure, comprising:

Station is when carrying out the BSS switching, if Cache is empty, perhaps, the all related failure of the AP that Station obtains from Cache, then Station initiates initiatively to seek the process of AP, seek claim frame and receive the acknowledgement frame of seeking that AP replys by broadcasting, obtain to seek the AP of time delay minimum, and authenticate with this AP and related;

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

4. method as claimed in claim 3 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:

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

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.

5. setting up and safeguarding the method for selecting access point in the Cache process for one kind, comprising:

Setting up and safeguarding in the Cache process, Station initiates initiatively to seek the process of AP, seeks claim frame and receives the acknowledgement frame of seeking that AP replys by broadcasting, obtains the time delay of seeking of AP, and seeks the little AP of time delay on the selection same channel and deposit among the Cache;

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

6. method as claimed in claim 5 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:

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

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.

7. method as claimed in claim 5 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.

8. as any described method in the claim 5～7, it is characterized in that,

Station selects the AP that seeks the time delay minimum to authenticate with related from Cache when carrying out the BSS switching.

9. a device of selecting access point is applied to it is characterized in that among the Station, comprises seeking module and selecting module;

The described module of seeking is used for initiatively seeking AP, and seeks claim frame and receive the acknowledgement frame of seeking that AP replys by broadcasting, obtain the time delay of seeking of AP, and the time delay of seeking that will obtain is informed the selection module;

Described selection module is used for selecting to seek on the same channel the little AP of time delay and deposits Cache in;

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

10. device as claimed in claim 9 is characterized in that,

The described module of seeking also is used for when from a plurality of time delays of seeking of a certain AP acquisition, and what this AP then was set seeks time delay T _{Probe_delay}For:

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

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

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