rate at the Server or CH A - Constant Internet Delay FIGURE 17.9 Queuing model for analyzing delay in SIP-based handoff to UMTS network. C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security TABLE 17.2 System Parameters Parameters Symbols SIP message arrival rate at the UE/MH SIP message arrival rate at the CSCF servers Processing delay for each SIP message in the UE/MH Destination and the CSCF server load SIP message arrival rate at the destination Processing delay for each SIP message at the destination Load at the destination for messages other than SIP Arrival rate at the destination for messages other than SIP Processing delay at the destination for messages other than Internet delay in transmitting of SIP messages Queueing delay at the MH Delay in transmitting a packet over an RLP link in UMTS network DP-CSCF Queueing delay at the P-CSCF server DI-CSCF Queueing delay at the I-CSCF server DS-CSCF Queueing delay at the S-CSCF server DDest Queueing delay at the destination (CH) Queueing delay at the P-CSCF server Queueing delay at the gateway to the WLAN Transport delay with RLP Transport delay without RLP a non-preemptive priority-based M/G/1 queue [31]. Since our objective is to estimate the SIP message processing delay, we have considered only those messages having higher priority than SIP messages and ignored other lower priority messages. The derivation of the delay, DRLP, requires us to adopt a transport-layer-based delay model over wireless links. Now, SIP messages work with both TCP and UDP. Since we are dealing with wireless links and TCP is a reliable protocol, the SIP messages are assumed to be sent over TCP. So a delay model for TCP transmission over wireless links is required. According to the model used and the results reported in [27], the delay to transmit a TCP segment consisting of k frames over a radio link with RLP operating over it, is given by k(Pf-(1-p)) (17.8) C 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evalu