Improving the IEEE 802.11 MAC Layer Handoff Latency to Support Multimedia Traffic

Multimedia applications can be offered to mobile users on the IEEE 802.11 WLAN, if their bandwidth, delay and jitter requirements are met, even in the presence of handoffs. Applications such as VoIP require a delay of less than 150 msecs and packet loss less than 3%. Studies have shown that the latencies achieved by existing handoff implementations can exceed 200 ms and packet loss can exceed 10%. Thus, there is a need for fast handoff solutions, that can meet multimedia traffic requirements. We propose a mechanism for layer-2 fast handoff with the help of background scanning, restricted channel set and preauthentication which does not require any code modification at the access points. The mechanism has been implemented in the MadWiFi wireless open source Linux drivers and tested in an indoor wireless environment. Results have shown that our mechanism achieves latency of less than 10 msec with negligible packet loss even in the presence of handoffs. Thus our mechanism makes mobile multimedia applications possible in IEEE 802.11 WLANs.