e length of time over which the node will lose packets when a handoff process is on going. 7. Tovertime = (Hmax - TDHCP): The time difference between Hmax and TDHCP. © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security TABLE 22.6 Disruption Time VS. TmTOn Disruption time (msec) TmTOn MIP-SIP Source: From Jung, J.W., Mudumbai, R., Mont- gomery, D., and Kahng, H.K., Performance evaluation of two layered mobility management using mobile IP and session initiation protocol. Global Telecommuni- cation Conference 2003 (GLOBECOM'03), 3, 1190 1194, IEEE 2003. With permission. Tests were performed by Jung [10] to assess some of these disruption times and the results are reflected in Table 22.6, Table 22.7 and Table 22.8. Three factors are considered. Table 22.6 illustrates the handoff disruption time as the delay, ThTOn increases. Here TmTOc is set at 30 ms. Table 22.7 shows the disruption time as the delay TmTOc increases. Here ThTOn is assumed to be 30 ms. As SIP mobility only depends on the dis- tance between the MN and CN, the disruption time of SIP-mobility increases according to the delay nTOc In Table 22.6, TmTOc and ThTOn, are set at 30 and 100 ms, respectively. Also the Hmax is fixed at 500 ms. Because the handoff in SIP over mobile IP does not need IP renewal time, its disruption time is the same as that in Disruption Time versus ThTOn However as the SIP-based approach always needs a new IP address, its disruption time increases proportional to the rate of increase for Tovertime. Simulation results show that the proposed approach out-performs the existing approach in most cases. This shows that VoIP can be supported over wireless Internet. 22.2.3 Handoff Delay Disruption of SIP in IP Services The performance of SIP in IP services can better be appreciated if we adopt similar metrics and measures for comparing them. One such approach uses the so-called "shadow registration" proposed by Kwon et al. [4]. In shadow registration, the mobile node establishes security association with