ications and hence to end users. To reduce the effect of this outage time, MIP was enhanced to incorporate route optimization and smooth handoff [7] by enabling the MH to directly bind to the CH and keep it updated on its current location. The regional registration scheme [13] has been proposed to reduce the number of signaling messages to the home network, and hence the signaling delay, when an MH moves from one FA to another. This proposal employs a hierarchy of FAs to handle MIP registration updates within a visited network. 2) Micro-mobility Protocols: The limitations of MIP, discussed above, cause severe quality of service (QoS) degradation for the user. Therefore, some kind of localized micro-mobility protocols are needed. These protocols operate in a restricted administrative domain and provide the MHs within that domain with connections to the core network, while keeping signaling cost, packet loss, and handover latency as low as possible. Several micromobility protocols have been proposed, including HAWAII [14], Cellular IP (CIP) [15], Terminal Independent Mobile IP (TIMIP) [16], and Intra Domain Mobility Management Protocol (IDMP) [17]. 17.4.3 Transport-Layer Mobility A TCP connection is uniquely identified by a 4-tuple: <source IP address, source port, destination IP address, destination port> Once an MH changes its point of attachment and acquires a new IP address, any existing TCP con- nection will be interrupted. Transport-layer mobility protocols maintain TCP connectivity, which means a TCP session broken due to the mobility of an MH can be resumed after the MH acquires a new IP address. One solution to this problem is TCP-Migrate [6], which we have chosen as the representative transport layer mobility protocol. TCP-Migrate requires minimal change in the network infrastructure, whereas other solutions [14] require the introduc- tion of an additional network entity such as a proxy, to split up the TCP connection. Introduction of such additional entities is not only costly but also fairly impractical