Performance evaluation of voice handovers in real 802.11 networks

In this paper we look at the performance of 802.11 networks for real-time voice communication. In particular, we focus on triggering timely handovers of voice calls from the 802.11 network to the cellular infrastructure. We have devised an algorithm that uses link layer, IP, and application measurements to determine when best to handover an ongoing call. Hence, determining the optimal handover time is the research challenge we face. A unique aspect of this challenge is that either poor algorithmic, or network performance, will be audible as poor voice quality to the end user. Our solution must also be robust and flexible due to the varying environmental conditions and differing hardware types. We look at two typical problem scenarios for 802.11 networks, one is poor coverage situations, and the other is sudden heavy traffic loads. We will show that it is possible to address the coverage problem, but heavy load situations are difficult to solve with a handover solution. We include our experiences whilst designing and evaluating this solution, plus give hints to the software and firmware writers of 802.11 products.