Francis Group, LLC SIP Mobility Technologies and the Use of Persistent Identifiers TABLE 10.1 Average Registration Delays with and without H-SIP Registration Delays [ms] hdomain: virginia H-SIP hdomain: panana H-SIP 84, 260 Note: As shown in Figure 10.5; n = 1000, transport = UDP. 2y is expensive. Our real-time measurements are listed in Table 10.1. Clearly, our measurements show that Equation 10.1a and Equation 10.2a hold for an a ~ 39 ms. We see here that t A is approximately 5tc or 7t for the Virginia and Panama cases respectively. Obviously, the H-SIP approach outperforms the traditional approach as long as Y is significant, which is often the case for roaming subscribers. The value of a directly depends on the implementation of the SIP server, which is the JAIN-SIP Proxy server [36] in this case. Besides, x is random and it directly depends on the location of the local handle server (LHS) [11] storing the particular handle. 10.4.3.2 Call Establishment In comparing the call establishment time given by Equation 10.3d and Equa- tion 10.4d, we are interested in computing the performance enhancement or degradation Al = 1 - X'. We consider the following variables to verify our model: T1 = =tr((hdomain,ruser) - rt(fdomain,r_user) (10.5a) T2 rt(cdomain.hdomain) -rt(cdomain.fdomain) (10.5b) o=T1+T2>1 (10.5c) where o is the difference in the cumulative round-trip delay between the no H- SIP case and the H-SIP case, respectively. Equation 10.5a is true in general due to the presumably large geographical separation between the roaming user and his home server versus using a local server. We also argue that Equation 10.5c holds in general based on our model. i.e., the cumulative round-trip delays for c_user to reach ruser is smaller in the H-SIP scenario. However, T2 in 10.5b can be positive or negative since it directly depends on the cdomain-hdomain separation versus that of cdomain-fdomain. For our particular setup, T2 > 0. It follows from Equation 1.3 and Equation 1.4 that, (10.6a) (10.6b) Al~10 - X (10.6c) C 2009 by