Performance Evaluation and Improvement of the Mobile Internet Protocol: A Study of Hand-offs, Transport Layer Performance and Flow Mobility

Abstract

TCP/IP was originally designed without any considerations for mobile computing. The greatest technical difficulties are encountered in the routing service of the IP layer. Mobile IP is an enhancement to the IP protocol which allows for transparent routing of traffic to mobile nodes in the Internet. In this manner, mobile nodes may vary their point of attachment between Internet administrative domains without having to interrupt active communications.Mobile IP introduces several overheads including extended packet loss during Mobile IP/IP layer hand-offs. Moreover, Mobile IP was designed focusing on mobile nodes equipped with a single access interface, capable of maintaining a single point of attachment to the Internet.This thesis focuses on evaluating and improving the performance of Mobile IP and of other protocols in conjunction with Mobile IP. Different types of Mobile IP hand-offs have been investigated. It was determined that all standardised Mobile IP hand-off techniques introduce a service disruption unacceptable for real time communications such as Internet telephony or for file transfer and WWW. In an effort to accelerate Mobile IP hand-offs, new hand-off types were introduced and proposals were made regarding the hierarchical organisation of Mobile IP infrastructure. It was shown that TCP, the primary and reliable, transport layer protocols of TCP/IP, misinterprets all packet loss experienced during Mobile IP hand-offs as the effect of network congestion and curtails the amount of offered load to the connection every time that a mobile node migrates. New protocol extensions were proposed and evaluated, aiming at resolving the incompatibilities between TCP and Mobile IP.The thesis demonstrates how Mobile IP can be deployed to introduce Internet mobility management facilities to WAP, the industrial de facto standard for Internet access to mobile phones. The demonstration involves a migration scenario between two heterogeneous wireless technologies, i.e. Wireless LANs and GSM. It was shown that Mobile IP inherits the interconnecting property of the Internet Protocol. In this manner, the problem of integrating heterogeneous protocols, above and below it, is reduced into a matter of routing.Considering the ever increasing availability of mobile devices equipped with multiple wireless access interfaces the inability of Mobile IP to take advantage efficiently of this property was considered a major drawback. A significant part of this thesis is devoted to the introduction of flow mobility management facilities that allow for dynamic distribution of flows or parts of a flow (datagrams) between the available interfaces in mid-session. Through extensive experimental evaluation it was shown that both data and telecommunications services can benefit from this approach.