ry, the MIPv6- NEMO embeds signaling messages into the IP header of each data packet. All packets must add a new IP header before entering a tunnel or remove the outer IP header after leaving a tunnel. With the increase of the nesting level, the MIPv6-NEMO that employs the tunneling mechanism to resolve mobility induces the heavy IP header overhead. 4.3.8 Involved Entities When SIP is extended to support network mobility, three back-to-back user agents (B2BUAs), i.e., (1) SIP-HS, (2) SIP-NMS, and (3) SIP-FS, are defined and involved in the SIP-NEMO. The SIP-HS and the SIP-NMS are responsible for header translation and the SIP-FS is used to providing a URI-list service. On the other hand, the MIP V6-NEMO involves two entities: (1) the mobile router (MR) and (2) corresponding HA. These two entities are in charge of maintaining a bi-directional tunnel for data exchange. 4.3.9 Transmission Route As described before, the transmission route of the SIP-NEMO INVITE requests from a CN to an MN can be represented as (CN) (SIPserver) (SIP-HS)n (SIP-NMS)n (MN), in which n is the level number of nesting inside a mobile network. After the session establishment, the trans- mission route is reduced and denoted by (CN) (SIP-NMS)n (MN). However, the MIPv6-NEMO must transmit packets through bi-directional tunnels. Thus, the transmission route is represented as (CN) (HA)n (MR)n (MN). 4.3.10 Handoff Latency Handoff latency is determined on how to recover the originally ongoing sessions after roaming to another point of attachment. For the SIP-NEMO, the SIP- NMS would actively re-invite all corresponding CNs. Thus, the handoff latency of the SIP-NEMO is determined on the route between the SIP-NMS and each CN. On the contrary, the MR recovers the reachability of the carried mobile network by re-register its new CoA to its HA. Then, the HA can tunnel packets to the mobile network. Hence, the handoff latency of the MIP V6-NEMO is determined on the route between the MR and its HA. 4.3.11 Nesting Impact Based on the above analysis, some is