1. Field of the Invention
The present invention relates to a wireless local area network (WLAN) and, more particularly, to a system for balancing load on an access points (AP) over a WLAN and a method therefor.
2. Description of Related Art
The existing IEEE 802.11 standard for WLANs was published in 1997. In the IEEE 802.11 standard, physical layer (PHY) and medium access control (MAC) operations are defined. As shown in the WLAN system of
Load imbalance often occurs in a crowded area. For example, many people attend an exhibition or sports event and carry a mobile communication device (i.e., mobile station). As such, connections to a small number of APs (e.g., APs B and D) are possible. That is, such APs have a heavy load. This is because, as stated above, a mobile station is adapted to automatically connect to an AP having the strongest signal intensity (e.g., one AP nearest the mobile station). The overloaded APs are thus unable to connect to any mobile stations, thus causing a bottleneck. Moreover, such an overload can lower quality of service.
The prior art thus suffered from several disadvantages. For example, load imbalance tends to occur if a free connection of a mobile station to an AP having the strongest signal intensity is allowed. In turn, load imbalance will lower availability of ESS and thus AP resources are wasted. Even worse, overload (i.e., load concentrated on a small number of APs) may limit flow, resulting in a lowering of quality of service. Hence, a need for improvement exists.
An object of the present invention is to provide a system for load balance on APs over a WLAN and method therefor such that the load can be evenly carried on all available APs, thereby effectively utilizing AP resources, increasing availability of ESS, and thus increasing quality of service.
One aspect of the present invention is to provide a system for load balance over a WLAN comprising a WLAN switch having an ESS; a plurality of APs in the ESS, each AP having a BSS wherein at least two BSSs overlap; and a plurality of mobile stations in the BSSs wherein each of the mobile stations located in the overlaid BSSs is adapted to choose one AP for connection from the APs capable of connecting thereto, wherein each mobile station is adapted to detect each connected AP and record the same, in response to connecting to the AP the mobile station is adapted to report information about the connected AP to the WLAN switch via the connected AP, and the WLAN switch is adapted to cause any two APs to have a substantially equal number of the connected mobile stations by adjustment.
Another aspect of the present invention is to provide, in a WLAN system including a WLAN switch having an ESS, a plurality of APs in the ESS, each AP having a BSS wherein at least two BSSs overlap, and a plurality of mobile stations in the BSSs wherein each of the mobile stations located in the overlaid BSSs is adapted to choose one AP for connection from the APs capable of connecting thereto, a method for load balance on the APs, comprising (a) causing each mobile station to detect each connected AP and record the same; (b) in response to connecting to the AP causing the mobile station to report information about the connected AP to the connected AP; (c) causing the connected AP to send the report information to the WLAN switch; and (d) causing the WLAN switch to command any two APs to have a substantially equal number of the connected mobile stations by adjustment.
Other objects, advantages, and novel features of the invention will become more apparent from the detailed description when taken in conjunction with the accompanying drawings.
With reference to
First, each one of mobile stations 1 to 8 is adapted to detect a connected AP (i.e., one capable of receiving signal transmitted from the mobile station) and record the same. It is assumed that mobile stations 1, 2 and 3 are in the BSS of AP A, mobile stations 2, 3 and 4 are in the BSS of AP B, mobile stations 4, 5 and 6 are in the BSS of AP C, and mobile stations 6, 7 and 8 are in the BSS of AP D. Thus, it is recorded that mobile station 1 is adapted to connect to AP A, mobile station 2 is adapted to connect to APs A and B, mobile station 3 is adapted to connect to APs A, B, and C, mobile station 4 is adapted to connect to APs B and C, mobile station 5 is adapted to connect to AP C, mobile station 6 is adapted to connect to APs C and D, mobile station 7 is adapted to connect to AP D, and mobile station 8 is adapted to connect to AP D.
In the existing 802.11 standard, initially a mobile station may try to connect to the nearest AP having the strongest signal intensity by association. As shown, mobile station 1 is connected to AP A, mobile stations 2, 3, and 4 are connected to AP B, mobile station 5 is connected to AP C, and mobile stations 6, 7, and 8 are connected to AP D. It is seen that the load on the APs is not balanced. Preferably, two mobile stations are connected to one AP, i.e., eight mobile stations are averagely carried on four APs.
After connection, an AP table is created based on the recorded AP by one of mobile stations 1 to 8 connected to the AP and the table is reported to the AP. For example, mobile station 1 reports to AP A that {A} is contained in its AP table, mobile station 2 reports to AP B that {A,B} is contained in its AP table, mobile station 3 reports to AP B that {A,B,C} is contained in its AP table, mobile station 4 reports to AP B that {B,C} is contained in its AP table, mobile station 5 reports to AP C that {C} is contained in its AP table, mobile station 6 reports to AP D that {C,D} is contained in its AP table, mobile station 7 reports to AP D that {D} is contained in its AP table, and mobile station 8 reports to AP D that {D} is contained in its AP table.
After collecting the AP tables, each of APs A, B, C, and D arranges them prior to reporting to WLAN switch 21. In a report to WLAN switch 21 prepared by AP A, one {A} is listed. In a report to WLAN switch 21 prepared by AP B, one {A,B}, one {B,C}, and one {A,B,C} are listed. In a report to WLAN switch 21 prepared by AP C, one {C} is listed. In a report to WLAN switch 21 prepared by AP D, one {C,D} and two {D} are listed.
WLAN switch 21 then arranges the reports and obtains a result of mobile stations connected to APs. In the embodiment, WLAN switch finds that there is one connected {A}, one connected {AB}, one connected {BC}, one connected {ABC}, one connected {C}, one connected {CD}, and two connected {D}s. Based on the result the WLAN switch adjusts the mobile stations connected to an AP in which each of the APs having the number of connected mobile stations larger than an average (i.e., larger than an integral portion of a value obtained by dividing the number of total mobile stations by the number of total APs) is required to disconnect the excess mobile station(s) (i.e., obtained by subtracting the average from the number of mobile stations connected to the AP) and the disconnected one(s) is (are) adapted to connect to a corresponding one of the APs having the number of connected mobile stations less than the average. Next, each AP having excess connected mobile stations issues an associate.request to a corresponding AP such that an adjustment can be made immediately. As a result, load balance is obtained.
For obtaining an optimum load balance, the WLAN switch converts the result into a network flow graph as shown in
A result obtained by the maximum flow algorithm is a new association as shown in
In brief, the invention comprises the steps of reporting information about APs connected to mobile stations to the WLAN switch, and enabling the WLAN switch to adjust the number of mobile stations connected to the APs by utilizing the information. As an end, a balance load is obtained. The invention thus has the following advantages. The AP resource can be effectively utilized. The availability of the WLAN system can be increased since a load balance is obtained. Finally, a load is averagely carried on all available APs (i.e., no flow concentration), thus increasing quality of service.
While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims.
Number | Date | Country | Kind |
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093135969 | Nov 2004 | TW | national |