BSS transition optimizations and analysis for VoIP over WLAN

Abstract

Voice over IP (VoIP) is emerging as a critical application for IEEE 802.11 Wireless Local Area Networks (WLANs). However, the limited range of the IEEE 802.11 radio forces frequent transitions from one access point to another. Moreover, the introduction of IEEE 802.11i security and IEEE 802.11e Quality of Service (QoS) has increased the average transition time from ms to seconds, leaving mobile users with the unenviable dilemma of choosing good security and QoS while sacrificing real-time performance, or gaining acceptable real-time performance at the expense of security and QoS. Thus, optimizations to device transitioning that will provide an acceptable balance of latency, security, and QoS are needed to enable VoIP. This paper analyzes WLANs MAC layer transition procedure and optimizations being considered by IEEE 802.11 Working Group to improve transition times while retaining good security and QoS. The transition time improvements proposed in this paper are achieved through discovery phase optimizations and transition phase optimizations. The selective scanning and smart AP selection algorithms are designed to optimize the discovery phase to enable the mobile device to better exploit its ambient radio resource environment. The transition phase optimization seeks to accelerate device transition without compromising security. The paper then identifies security flaws in the current design and proposes simple corrections. Finally, experiment results for transition optimization are explained that demonstrate a significant increase in transition efficiency.