The IEEE 802.11 Active ProbingMechanism: Analysisand Enhancements

TheActive Probing mechanism isacritical function oftheIEEE802.11 protocol. Active probing isusedforaccess points discovery, roaming between different access points, andre- cently inWLAN-based location determination systems toachieve reliable signal strength measurements. The802.11standard leaves itopenformanufacturers toimplement theActive Probing mechanism. Inthispaper, weanalyze theperformance ofthe Active Probing mechanism ofthe802.11 protocol. Ouranalysis showsthatthecurrent implementations oftheActive Probing mechanism areinefficient andleadtodecreased capacity. We identify twomainfactors contributing tothis negative effect on thecapacity. Thesefactors areobserved withcards fromdifferent manufacturers andleadtoincreasing theprobing cycle time andunnecessary retransmission. Wepropose different techniques toenhance theefficiency oftheActive Probing mechanism. Theproposed techniques require noorminimal changes tothe wireless cards' drivers andhenceallow incremental deployment.