The Internet Protocol (IP) is expected to become the main carrier of traffic to mobile and wireless nodes. This includes ordinary data traffic like http, ftp and email as well as voice, video and other time sensitive data. To support mobile nodes, basic IP has been extended with protocols (Mobile IP) to support intercepting and forwarding of packets to a mobile and possibly roaming node. Seamless roaming requires that users and applications do not experience loss of connectivity or any noticeable hick-ups in traffic. This thesis proposes improvements to the Mobile IPv6 protocol.
In this thesis we focus on handoff initiation in Mobile IPv6. We have investigated two existing handoff initiation strategies, the Eager Cell Switching strategy and the Lazy Cell Switching strategy. To determine the handoff latency as a function of the configuration of essential protocol parameters, for each handoff initiation strategy we have proposed a mathematical model describing handoff performance.
To bridge the gap between theory and practice we have setup a testbed running FreeBSD 4.1 and installed it with KAME Mobile IPv6 software. Using this testbed we have studied the handoff latency experienced by an actual roaming mobile node using either of the two handoff initiation strategies. From an extensive empirical study using this testbed we conclude, that the proposed theoretical models are in excellent conformance with empirical results.
Using the mathematical models for the Eager Cell Switching strategy and the Lazy Cell Switching strategy we have proposed a new protocol configuration resulting in improved handoff performance for both strategies but without increasing network load. This theoretical performance improvement was also confirmed in experiments conducted in the testbed.
As both Lazy Cell Switching and Eager Cell Switching were found to have serious performance lacks we have proposed an advanced handoff initiation strategy (Parametric Cell Switching) which utilizes link layer information. A novelty of Parametric Cell Switching is that it can be configured to use many different criteria in a handoff decision. A particular instance of Parametric Cell Switching, implemented as a prototype and merged into the KAME software, showed much improved performance to both of the existing handoff initiation strategies.
We conclude that we have been successful in reducing the handoff latency for the existing handoff initiation strategies, but that in order to experience seamless roaming a mobile node must use link layer information in a handoff decision. Our prototype implementation seems promising, as in an informal building wide experiment using Wireless LAN as the link media, it was able to roam between three base stations serving three different networks without losing packets.