 PACKETS. (From Choudhary, U., Perl, E., and Sidhu, D. Using T.38 and SIP for real-time fax transmission over IP net- works. 26th Annual IEEE Conference on Local Computer Networks (LCN'01), 74, IEEE November 2001. With permission.) T.38 G/W IP Router SIP Proxy SIP Proxy T.38 G/W IP Router SIP messages Fax data packets FIGURE 22.12 Separate paths for SIP messages and fax images. (From Choudhary, U., Perl, E., and Sidhu, D. Using T.38 and SIP for real-time fax transmission over IP networks. 26th Annual IEEE Conference on Local Computer Networks (LCN'01), 74, IEEE November 2001. With permission.) networks where the Signaling System #7 (SS7) links are distinct from the trunks. Figure 22.12 gives a view of this model. 3. Network Model 3 uses the same network as network model 2. However, not all SIP messages travel between the SIP proxy servers in this case. In general, all SIP terminals are configured to know their network's SIP proxy server. Hence, to set up a SIP call, they contact their SIP proxy server first not having to know themselves the entire route to a receiver. They only need to know how to route SIP calls they initiate to their designated SIP proxy servers. The SIP proxy server then handles all the signaling for the rest of the call. The AUXL link is used for fax data packets as is in network model 2. Table 22.9 shows the performance measures recorded by Choudhary [11]. In terms of link utilization values on IPSL, network model 3 is the most suitable. In terms of just link utilization values on AUXL, network model 2 is only marginally better. In terms of end-to-end fax data packet delay, network models 2 and 3 are on average equally good. When just packet end-to-end delay is considered, network model 3 is the best. The average SIP call setup time and average fax call setup for network model 3 is the best. © 2009 by Taylor & Francis Group, LLC SIP Security and Quality of Service Performance TABLE 22.9 Experiment Results Model 1 Model 2 Model 3 Average link utilization of IPSL (Mbps) 77.50 9.223 0.9546 Aver