 Table 22.10 and Table 22.11 provide the basic procedure/scenarios which are: 1. SIP call setup with no authentication, where the proxy server is stateless and always uses UDP communication. 2. SIP authentication which corresponds exactly to the call flow has been considered in order to see the difference between the use of UDP or TCP between the proxy and tester UAS. The motivation for considering TCP- based SIP communication is to obtain an incremental analysis toward a TLS-based SIP communication setup. Scenarios (5 through to 8) repli- cate (1 through to 4) as far as authentication and UDP/TCP/TLS are employed, by considering a call stateful proxy server. Table 22.10 reports the call throughput for the procedure/scenario (1) for different numbers of active threads. Starting from two threads in parallel, the capacity of the server is saturated: each of the N threads takes 1/N of the server capacity, SO the server throughput is 1/N of the maximum throughput. In Table 22.11 the results of the evaluation by Salsano [21] are reported. The third column reports the theoretical maximum throughput in terms of calls per second that the proxy server can accommodate. This includes all the processing that the proxy performs for a call from its setup to its termination or tear down. The two rightmost columns are the most important ones and report the throughput values converted into relative processing cost. In the © 2009 by Taylor & Francis Group, LLC SIP Security and Quality of Service Performance TABLE 22.11 Experimental Results Total Relative Procedure/scenario throughput (s-1) processing cost 1 No authentication, stateless server, UDP 2 Authentication, stateless server, 3 Authentication, stateless server, 4 Authentication, stateless server, 5 No authentication, call stateful server, UDP 6 Authentication, call stateful server, UDP 7 Authentication, call stateful server, TCP 8 Authentication, call stateful server, TLS Source: From Salsano, S., Veltri, L., and Papalilo, D. SIP security issues: The SIP authentication proc