ment scheme for long-term TCP connections. Secondly, disruption can occur during handoff when the mobile node is within the overlap region if the acquisition of the new SIP session is not completed before the node moves out of the overlap region. Because the mobile node must acquire in this case a new address through DHCP, there are delays associated with completing the acquisition of the new IP address. This handoff delay can be significant and is a function of the implementation of SIP and the mobility schemes. Some versions of the DHCP can cause a delay of about 2 sec during address renewal. This delay is reduced to about 0.1 sec if duplicate address detection scheme is removed from the DHCP. Delays in SIP mobility-based communication can further be distinguished and analyzed. C 2009 by Taylor & Francis Group, LLC SIP Security and Quality of Service Performance SIP Re-INVITE SIP OK Correspondent node 3 DATA Re-registrar SIP Server with Registrar Mobile node Subnet A Subnet B FIGURE 22.2 Mobility management scheme using SIP. (From Jung, J.W., Mudumbai, R., Montgomery, D. and Kahng, H.K. Performance evaluation of two layered mobility management using mobile IP and session initiation protocol. Global Telecommunication Conference 2003 (GLOBECOM'03), 3, 1190-1194, IEEE 2003. With permission.) Figure 22.3 shows that in trying to establish sessions, SIP operations lead to delays associated with the signaling. In the scenario described in Figure 22.3, the SIP proxy is assumed to have Anike's location address (host_b.telkom.com) and Johnson therefore invites Anike through it. The sequence of messages sent is as follows. Johnson sends an INVITE message through the proxy server (1), and the proxy server relays the INVITE message to Anike at host_b.telkom.com (2). While Anike is being alerted a 180 Ringing message is sent back to Johnson via the proxy server (3, 4). After Anike has answered to the call, 200 OK response is sent back to John- son to notify him that Anike accepts the call (5, 6). Then Johnson sends an ACK (7