g IP tunneling to a unified IP routing infrastructure. Under MIP, it is assumed that the MH has a home network from which it obtains its statically allocated IP address and that the MH roams from the home network among various foreign networks. Typically, an MH is a host or router that changes its point of attachment from one network to another while keeping its IP address constant. An entity, called the home agent (HA), maintains reachability infor- mation for the MH and forwards the datagram sent to the MH through an IP tunnel to any other visited foreign network. The foreign agent (FA) acts as a router at the visited network, and cooperates with the HA to forward datagrams to any visiting MHs. MIP consists of three important functions: (1) Mobile agent discovery (2) Registration with HA (3) Delivery of datagrams using tunneling The mobility agents make themselves known by sending advertisement mes- sages. On receiving agent advertisements, the MHs get to know whether they are in the home network or in a foreign network. When the MH moves to a foreign network, it obtains a care-of address (CoA) on the foreign net- work by either listening to the advertisement from the FA or contacting a © 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evaluation local DHCP server or Point-to-Point Protocol (PPP) access server. The MH then registers its new CoA with the HA. The datagrams sent by the corre- spondent host (CH), destined for the MH, are intercepted by the HA and forwarded to the MH after encapsulation using a tunnel, with the endpoint at either the FA or the MH itself. The encapsulated datagrams are decap- sulated and delivered to the MH. Mobile IP works fairly well, except when the distance between the visited foreign network and the home network of the MH is sufficiently large, thereby inducing large signaling delay for these registrations. After an MH roams into a new network, no CH traffic will reach the MH until the MH updates its HA. This outage may be noticeable to appl