Thesis (M.Eng.)--Chulalongkorn University, 2004

Mobile internet protocol (Mobile IP) is internet standard-tracking protocol that enhances the existing IP to accommodate mobility. When a mobile node (MN) moves out of current cell and moves into new cell, consequent lost connection causes many lost packets. A mechanism called handoff is needed to continue communication. We describe several handoff implementations based on the IEEE 802.11 standard on a Borland Delphi 7 for network simulation. Performance of the conventional Mobile IP handoff scheme, the positional information based handoff scheme and the proposed scheme are evaluated in terms of packet loss and traffic overhead. In the conventional Mobile IP, handoff occurs when MN receives a new agent advertisement which contains different prefix network from previous one. This causes many lost packets because of high handoff latency. We also implement the positional information based handoff scheme using the position of MN equipped with a global positioning system (GPS) in order to trigger a handoff. The handoff occurs when MN's position exceeds a threshold. We, moreover study the disadvantage of the positional information based scheme such as unorganized handoff mechanism and traffic overhead. The unorganized handoff resulted by fixed threshold can be solved by dynamic threshold handoff mechanism in the proposed method. The proposed scheme implements an improving advertisement message in order to lower handoff latency. The traffic overhead in proposed scheme can be lowered by using a T buffer message which commands a new FA to buffer packets while MN is moving out of previous FA. From the simulation, we obtain low handoff latency and zero lost packets in the proposed method when T[subscript improving] ADV implements the lowest link delay than the current link delay. During handoff, the proposed scheme occur less data forwarded and less number of shortened ADV message than those of the positional information handoff scheme. Finally, the proposedscheme achieves lower handoff latency and minimize packet loss than those of the positional information based handoff and the conventional Mobile IP scheme