ing model. The transmission delay over a wireless channel is determined by the size of the transmitted message as well as the bandwidth (data rate) of the wireless channel. The delay over the Internet is mostly caused by congestion over the Internet. For intra-domain messages, the delay on the Internet should be replaced by the transmission delay between the BS and the local server, which can be assumed to be negligible. Therefore, we can get: PBs+QBs+AI+QCN (11.2) DMN,AAA/DHCP + PBS + QBS + PAAA/DHCP + QAAA/DHCP (11.3) where Bwireless is the bandwidth of the wireless links and P and Qi respec- tively denote the processing delay and queuing delay in node i. LSIP, LAAA and LDHCP indicate the length of SIP messages, authentication messages, and DHCP application messages, respectively. Similarly, we can also get the value of DCN,MN and DAAA/DHCP,MN. Substituting (11.2) and (11.3) into (11.1), we have: 5LSIP+2LAAA+4LDHCP + 11PBS + 6PMN + 2PCN Bwireless + PAAA + 2PDHCP + 5AI + 11QMN + 11QBS + 5Q CN + 2QAAA + - QQ DHCP (11.4) 11.3.3 Handoff Initiation Based on User Mobility An active MN should attach to the network offering the best service. However, when it moves out of the radio coverage of the current domain, it should switch to a less desirable access network to maintain communications connectivity. Ideally, a handoff should complete right after the MN moves out of the current domain, which means that the best handoff initiation time is Dhandoff before it moves out of current network coverage area. The remaining dwelling period of the MN in the current network can be predicted by two factors: the coverage area C of the network and mobility pattern of the MN. We define C as the area where the RSS of the network is strong enough to be detected by the MN's radio. It may not be exactly circular due to refraction and reflection of radio signals around/by obstacles such as buildings. With the advancement of radio tracking technologies, it is very likely that a future-generation MN will be equipped with a global positioni