mobility in SIP. Correspondent Node (CN) Home network (2) 200 OK (1) Re-INVITE SIP server Visited network Mobile Node (MN) FIGURE 22.5 Mid-call mobility in SIP. The second type of mobility is the mid-call mobility. It allows a node to maintain an ongoing session with its peer during handoff as in Figure 22.5 [8]. As shown in Figure 22.5 an MN sends a re-INVITE request with a new IP address to CN (1), and the CN sends packets to MN directly at the new point of attachment to the network (2). C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security Testbed backbone Router A Router B Home network Visited networks 802.11b MN's movement FIGURE 22.6 Experimental test bed for handoff measurement in IPv6 mobile networks. (From Nakajima, N., Dutta, A., Das, S., and Schulzinne, H. Handoff delay analysis and measurement for SIP based mobility in IPv6. International Conference on Communications (ICC'03), 26, 1085-1089, May 2003. With permission.) 22.2.2.3 Handoff Delay Handoff duration is composed of two broad delays, which are link layer estab- lishment and signaling delays. Link layer establishment delay is normally neg- ligible compared with signaling delay. Handoff delay as a result of mobility was measured by Nakajima et al. [8] using a small network test bed of three mobile nodes, one correspondent node, a home network and a visited net- work consisting each of a router within an IPv6 domain. The network used by Nakajima [8] is shown as Figure 22.6. Total handoff delay (T) is defined [8] as the time between detachment from the old access point and establishment of communication with a new corre- spondence node (CN). It consists of three components: 1. The time for switching lower layer medium to access network (T1). 2. The time for detecting a new router and a new link (T2). 3. The time for recovery of communication with a CN after detecting a new link (T3). Therefore T = T1 + T2 + T3. Nakajima [8] concentrated on measuring T3. There are two main factors which contribute to delay T3; Dupl