| Mobile Internet is now a hotspot in both the Internet world and the telecommunication world. With Mobile IPv6, a Mobile Node (MN) can transparently roam and handover across different IP subnet, without disturbing upper layer's communication. However, when MN roams across subnets, handover delay is introduced, and some of the data packets could be lost. As more and more real time applications based on IP network are coming into existence, it gets even more critical to minimize the handover delay and packet loss rate for MN handover as well as providing seamlessly IP-based handover and improving QoS. As a cheap technology for providing high-speed wireless services for hotspot areas such as airport, library, etc, WLAN is getting more and more important. However a single WLAN has limited coverage and it supports only link-layer handover. By supporting IP-layer roaming, Mobile IP makes it possible for MN to roam across WLANs with uninterrupted transmission sessions, thus actually enlarge moving area at MN's liberty. Handover purely based on IP Layer has an unavoidable larger delay. By analyzing the conditions that cause this delay and by combining the characteristics of 802.11 networks, this paper tries to realize a fast handover at IP layer by utilizing information of physical layer provided by the 2nd layer. Further, by providing packet caching and forwarding mechanism, seamless handover based on Mobile IP could be realized and this paper implements a model of seamless handover of Mobile IP based on 802.11 network on NS2 simulation platform. This paper is organized as follows: Chapter 1 gives an introduction for Mobile IP, it also gives the research background... |
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