Design & implementation of a hybrid handover protocol for multi-media wireless LANs

Abstract

Handovers for multi-media Wireless LANs (WLANs) have special requirements, unlike those in the public wireless networks. In this paper, the problems and challenges faced in a multi-media WLAN environment are presented and a multi-tier wireless cell clustering architecture is introduced. New design issues for multi-media handovers are specified and a fast, continuous and efficient hybrid handover protocol is proposed. A prototype of the proposed handover protocol is implemented into a Cambridge Fairisle ATM switch and the results are evaluated. We found that implementing transport mobility for a Wireless ATM environment is not practical as the cell re-routing function is not scalable to increasing cell rate and to the number of mobile connections. It also changes the characteristics of the traffic. Instead, the data link layer mobility implementation is found to work well. The protocol provides symmetric data disruption to traffic flows in both directions and up to seventy five intra-cluster handovers can be supported in a second. Throughout the experiment, cells arrive in sequence with no cell loss observed during the handover, up to the capacity limit of the ATM switch.