Access Point Array Load Balancer
With the enormous economies of scale of Wireless LAN (WLAN) hardware, the price of commodity WLAN access points has dropped to the level that is even cheaper than some WLAN adapters. This project proposes to put together an array of off-the-shelf access points, each operating at a different radio frequency, to build a super access point that can both scale up the overall sustained throughput and improve the robustness of WLAN connectivity in the presence of failures and denial-of-service attacks. Just like the idea of RAID (Redundant Arrays of Inexpensive Disks), which puts a set of commodity disks to improve the overall performance and reliability of a disk subsystem, a WLAN access point array is a set of commodity APs that are collocated in the same physical location and coordinate among themselves to improve the network's overall throughput and robustness.
An access point array load balancer is designed to achieve the following goals:
l To improve an access network's aggregate throughput by dynamically adjusting the association between wireless stations and access points so as to balance the traffic load among the array's channels.
l To improve an access network's robustness by tolerating hard and soft AP failures as well as misbehaving stations.
Although conceptually simple, implementing an access point array load balancer is surprisingly challenging for issues such as:
l How to accurately measure the real-time traffic load of each AP and STA?
l Even if real-time traffic load measurements are possible, how to distribute STAs among APs?
l Once load balancing decisions are available, how to convince a particular STA to associate with the AP that we designate?
We have successfully developed such a load balancing scheme and used it to build a working access point array prototype. Measurements on this prototype show that the proposed load balancing scheme can indeed improve the overall throughput and mitigate performance impacts due to misbehaving stations. In addition, the prototype requires no modification to either the access points or the wireless stations, making it a technology readily applicable to existing wireless LAN environments.
l Fanglu Guo and Tzi-cker Chiueh, ``Scalable and Robust WLAN Connectivity Using Access Point Array,'' in Proceedings of 2005 International Conference on Dependable Systems and Networks (DSN 2005), June 2005
l Commercial load balancing products
n Cisco, Data Sheet: Cisco Aironet 350 Series Access Points
n Proxim Wireless Networks, Data Sheet: ORiNOCO AP-600 Access Point
l Academia
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Hot-Spot
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WMCSA 2002
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