erlapping coverage regions of the two nodes involved in handover. The time required to acquire DHCP address renewal while in the overlap region can be significant and can cause disruption in calls (VoIP) and silence periods during handoff. To understand the mechanisms that lead to the delays and the performance of mobility management at the network and the application layers, this section summaries and compares the two mobility management schemes. 22.2.2.2.1 Mobility management using mobile IP The well-known mobile IP triangular routing scheme is shown in Figure 22.1. Two agents (routers) are involved. The home agent (HA) is at the home network (subnet A) and the foreign agent (FA) is at the foreign network (subnet B). The corre- spondent node (CN) seeks to establish communication with a mobile terminal originally attached to the HA. In this mobility management scheme, while the mobile node is within the intersecting region of the two neighboring subnets, it must acquire a new address using DHCP from the foreign agent. The FA Agent advertisement Registration request Registration reply Correspondent node Tunneling Foreign agent agent Mobile node Subnet A Subnet B FIGURE 22.1 Mobile IP mobility management scheme. (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.) © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security advertises its availability using an agent advertisement (1) to all the nodes within its coverage region. The mobile node upon hearing this advertisement sends a request for registration message (2) to the FA. This message contains in part the identities of the mobile node and of its HA. If a DHCP address is available, it is issued to the mobile node and it is registered at the subnet B. The FA also informs the HA of the new registration (2). Data sent by