Mobility Protocols and Handover Optimization: Design, Evaluation and Application

Chapter 10Cooperative Roaming

In a wireless network, mobile nodes (MNs) repeatedly perform tasks such as layer 2 (L2) handoff, layer 3 (L3) handoff, and authentication. These tasks are critical, particularly for real-time applications such as VoIP. We propose a novel approach, namely cooperative roaming (CR), in which MNs can collaborate with each other and share useful information about the network in which they move.

We show how we can achieve seamless L2 and L3 handoffs regardless of the authentication mechanism used and without any changes to either the infrastructure or the protocol. In particular, we provide a working implementation of CR and show how, with CR, MNs can achieve a total L2 + L3 handoff time of less than 16 ms in an open network and of about 21 ms in an IEEE 802.11i network. We consider behaviors typical of IEEE 802.11 networks, although many of the concepts and problems addressed here apply to any kind of mobile network.

10.1 Introduction

Enabling VoIP services in wireless networks presents many challenges, including quality of service (QoS), terminal mobility, and congestion control. In this chapter, we focus on IEEE 802.11 wireless networks and address issues introduced by terminal mobility.

In general, a handoff happens when an MN moves out of the range of one access point (AP) and enters the range of a new one. We have two possible scenarios:

1. If the old and new APs belong to the same subnet, the MN's IP address does not have to change at the new AP. ...