r implementations on correspondent hosts. This means users who are not mobile must install transport implementations to communicate with mobile users. Transport-layer mobility solutions are also transport-specific. Thus, TCP-oriented solutions are appropriate for TCP- based applications, but provide no mobility solution for UDP-based and RTP- based applications. 17.3.4 Application Layer Most of the transport- and network-layer mobility solutions entail consider- able changes in the MHs operating system. This is one of the primary rea- sons behind their low acceptance and deployment. Application-layer mobility management schemes overcome such drawbacks. As the mobility protocol is implemented in the application layer, the scope of operation is not limited to only network boundaries; this solution, like transport-layer mobility, also achieves the true end-to-end semantics. The overhead associated with these solutions is the delay involved with the application layer processing of longer protocol messages. Moreover, lower-layer support in detecting network change is also required. Thus, the main motivation behind an application-layer mobility protocol has been to alleviate the major drawbacks of lower-layer solutions, such as suboptimal routing [7], network architecture change, and host operating sys- tem change, while providing a way to make an MH always reachable for packet forwarding. However, such a protocol incurs considerable (and unacceptable) delay for real-time services due to application-level processing. © 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evaluation Because these mobility protocols operate at the application layer, they cannot maintain a transport layer connection. Hence, they are somewhat decoupled from the actual applications, which work on the basis of a trans- port level connection (e.g., a TCP/IP application communicates over a TCP connection). We believe that application-specific mobility mechanisms may be suffi- cient for the wireless Internet of 