g sessions between different devices, and personal mobility, which is the ability to identify a user with the same address across different devices. After realizing the essential differences of these two protocols, we discuss and analyze the differences of applying SIP and Mobile IP to the network mobility problem on the perspectives of: (1) signaling overhead, (2) header overhead, (3) involved entities, (4) transmission route, (5) handoff latency, and (6) nesting impact. Table 4.2 depicts the summary between the SIP- based network mobility (SIP-NEMO) and the Mobile IPv6-based network mobility (MIPv6-NEMO). 4.3.6 Signaling Overhead Since SIP is a control protocol for signaling, the SIP-NEMO adopts off- plane signaling, i.e., signaling messages are independent from data packets. Thus, the signaling overhead of the SIP-NEMO includes a burst of signaling messages during the re-invitation operation. According to the studies about wireless links, the quality of wireless links is easily affected by a large num- ber of small-sized packets. In order to improve the quality, the SIP-NEMO aggregates a lot of small-size INVITE requests into a URI list. On the other hand, the MIPv6-NEMO adopts in-plane signaling, i.e., signaling messages are embedded into data packets. That is, the signaling overhead of the MIPv6- NEMO is distributed into every data packet. Besides, the MIP V6-NEMO only needs to send a BU back to the corresponding HA while roaming in the Inter- net. Therefore, the signaling overhead of the MIP V6-NEMO is lighter than the one of the SIP-NEMO. 4.3.7 Header Overhead Building on the previous description, the SIP-NEMO has no IP header over- head problem because the signaling of the SIP-NEMO is off-plane. Furthermore, C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security the SIP-NEMO utilizes the header translation to resolve the nesting issue, i.e., adding the RECORD-ROUTE fields. The size increase of a SIP header is slight and not proportional to the nesting level. On the contra