et, the SIP-NMS should re-invite the on-going sessions as the mid-call operation of the SIP-based host mobility. Thus, a burst of INVITE requests are produced. In order to avoid congestion over wireless links, the SIP-NMS would send an INVITE request with a URI list to a local SIP-FS. Once SIP-FS receives this kind of INVITE requests, it would re-produce similar requests based on the embedded URI list and then forward the reproduced requests to all targeted CNs. 4.2.2 Re-Registration Operation Like the SIP-based host mobility, if each SIP-NMS changes its location, it needs reregister its new contact address to the corresponding SIP-HS using the pre-call operation. Once a SIP-NMS updates its new contact address, the carried mobile network can recover its reachability. However, when an MN moves into a mobile network and is attached to a SIP-NMS, the MN needs to re-register its new location to the corresponding SIP server for redirecting its sessions to the newly-attached mobile network. In order to achieve this goal, the SIP-NMS would do some header translation. In other words, the SIP-NMS would replace some fields in the SIP header in order to re-route packets destined to the MN to the correct mobile network. Figure 4.4 depicts the SIP-NEMO re-registration operation. An MN is supposed to locate in its home network. The detailed steps are as follows: 1. The MN must register itself to the SIP server in its home network. 2. The MN roams into a mobile network and acquires a new contact address. 3. The MN must re-register its new contact address to the corresponding SIP server in its home network. © 2009 by Taylor & Francis Group, LLC SIP Mobility Management MN's home network SIP-NMS's home network 5. Invite 7. Invite 6. Moved temporarily SIP-HS server 8. Invite 4. Re-register ((p)) 1. Register 3. Re-register SIP-NMS 9. Invite 2. Move Mobile network FIGURE 4.4 The SIP-NEMO re-registration operation. 4. The SIP-NMS, which is the gateway of this mobile network, would trans- late the REGISTER request, i.e., use the SIP-NM