Fast Handoff Scheme for VoIP over WLANs

Abstract

IEEE 802.11 wireless local area networks (WLAN) have been widely deployed, and many applications are implemented on WLAN. As one of the interesting wireless services, wireless voice over internet protocol (VoIP) can provide low-cost real-time voice service to mobile users. But the IEEE 802.11 wireless network cannot satisfy the QoS of VoIP. The delay during handoff process can last up to 1 second. Applications with delay restraint like VoIP will drop the call when the delay is more than 50 ms. Therefore this paper analyzed the delay made by handoff process, and proposed a fast handoff scheme. This fast handoff scheme is based on selective scanning and caching. It can reduce the handoff delay to about 30ms and avoid necessary handoff. Simulations are implemented and the results show the proposed fast handoff scheme is useful and economical. Keywords-IEEE 802.11; handoff; VoIP; QoS; scanning