hat the tar- geted destination is SIP-NMS 1, it would add the RECORD-ROUTE field and then re-route the request to the current contact address of the SIP-NMS 1. 5. Once SIP-NMS 1 receives the INVITE request and detects that the tar- geted node is not registered, the RECORD-ROUTE field indicates the next hop is SIP-NMS 2. SIP-NMS 1 would forward the INVITE request to SIP-NMS 2. 6. When SIP-NMS 2 receives the INVITE request and determines that the destination is a registered node, SIP-NMS 2 forwards the request to the corresponding MN. 7. Once the MN accepts the invitation, it would respond with an OK mes- sage back to the CN. The response is translated by SIP-NMS 2 and C 2009 by Taylor & Francis Group, LLC SIP Mobility Management SIP-NMS 1 in sequence. Since SIP-NMS 1 is the root-SIP-NMS, the con- tact address finally indicates the current location of SIP-NMS 1 when the CN receives the response. The steps above explain how data can be exchanged directly from a CN to an MN via only corresponding SIP-NMSs using the designed header translation. Protocol Analysis Regarding the host mobility issue, many measurements have studied the com- parison between SIP and Mobile IP (Kwon et al. 2002; Nakajima et al. 2003). In this n, we first survey the essential differences between SIP and Mobile IP. Next, we analyze the differences between the SIP-based network mobility (SIP-NEMO) and the Mobile IPv6-based network mobility (MIPv6-NEMO) in advance. Five essential differences between SIP and Mobile IP are: (1) protocol layer, (2) involved address, (3) handoff operation, (4) data delivery, and (5) mobility support. Table 4.1 depicts the comparison summary. 4.3.1 Protocol Layer SIP and Mobile IP belong to different protocol layers. Mobile IP is a network- layer protocol. Thus, Mobile IP can hide IP mobility from upper layers and reduce the development complexity of applications. However, Mobile IP requires changing the existing network-layer protocol stack. A node can possess TABLE 4.1 SIP VS. Mobile IP Session Initiation Protocol (