Mobility Protocols and Handover Optimization: Design, Evaluation and Application

Chapter 5Layer 2 Optimization

With the growth of IEEE 802.11-based wireless LANs, Voice over IP (VoIP) and similar applications are now commonly used over wireless networks. A mobile station performs a handoff whenever it moves out of the range of one access point and tries to connect to a different one. This takes a few hundred milliseconds, causing interruptions in VoIP sessions. This chapter introduces a new handoff procedure that reduces the MAC layer handoff latency, in most cases to a level where VoIP communication becomes seamless. This new handoff procedure reduces the discovery phase using a selective scanning algorithm and a caching mechanism.

5.1 Introduction

IEEE 802.11-based wireless LANs have seen very fast growth in the last few years and VoIP is one of the most promising services to be used in mobile devices over wireless networks. One of the main problems in VoIP communication is the handoff latency introduced when moving from one access point to another. As we will show below, the amount of time needed for a handoff in an 802.11 environment is too large for seamless VoIP communication. We have been able to reduce the handoff latency using a modified handoff procedure, where the modifications are limited to the mobile device and are compatible with standard 802.11 behavior.

In the following, we first briefly discuss the work done in this particular area, followed by a brief description of how we tackled the problem. Then, in Section 5.3, we describe the IEEE ...