MobiSys 2004: Second International Conference on Mobile Systems, Applications, and Services, June, 2004, Boston, USA
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Divert: Fine-grained Path Selection for Wireless LANs

Allen Miu, Godfrey Tan, and Hari Balakrishnan, MIT CSAIL; John Apostolopoulos, HP Labs

The performance of Wireless Local Area Networks (WLANs) often suffers from link-layer frame losses caused by noise, interference, multipath, attenuation, and user mobility. We observe that frame losses often occur in bursts and that three of the five main causes of frame losses--multipath, attenuation, mobility--depends on the transmission path traversed between an access point (AP) and a client station.

In a typical WLAN deployment, different transmission paths to a client exist in places where overlapping coverage is provided by a set of neighboring APs. Using experimental measurements and analysis on a 802.11b testbed, we show that fine-grained path selection among a set of neighboring APs can significantly reduce path-dependent losses in WLANs. We design and implement a WLAN distribution system called Divert, which supports fine-grained path selection for downlink communications, on an 802.11b testbed. Divert reduces frame losses without consuming any extra bandwidth in the wireless medium. Our experimental results show that Divert can reduce frame loss rates in realistic scenarios by as much as 26% compared to a fixed-path scheme that uses the best available transmitter.