ls, respectively. Using the expression for delay model in Equation 17.2, the delays corre- sponding to the GPRS attach and the PDP context activation procedures can be determined as: DAttach = 8D' and DPDP = 4D'. This is because, as shown in Figure 17.5 and Figure 17.6, GPRS attach and PDP context acti- vation procedures requires eight and four message exchanges, respectively. Transport delay without RLP (for WLAN): In this case, there is no RLP retransmission. Instead, due to packet loss, retransmission may be done by upper-layer protocols like TCP or DHCP until there is a successful transmission. Let Nm be the number of such retransmissions. The DHCP packet loss rate in this case is q = 1-(1-p)k The average delay for successfully transmitting a TCP or DHCP packet with no more than Nm retransmissions is given as, (17.3) Note that the DHCP messages have a maximum length of 548 bytes. Also the IEEE 802.11 standard specifies that the WLAN frame duration is 3.5 ms. So, using similar calculations as for the case with RLP, we get k = 1 for both 2 Mbps and 11 Mbps WLAN. Also the end-to-end transmission delay, D, of the wireless channel = 0.27 ms and 0.049 ms for 2 Mbps and 11 Mbps channel, respectively. The interframe time, T = 0.001 secs, is independent of the bit C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security rate. Now, the delay due to DHCP registration is given by DDHCP = 4D", since it is shown in Figure 17.8 that DHCP registration requires four message exchanges. 1) Handoff delay to UMTS network from another UMTS or WLAN network: Since SIP is an application-layer protocol, the processing of SIP messages in the intermediate and destination servers may take considerable time due to the queuing of messages that need to be accounted for. Rough estimates of the queuing delays can be obtained using the classical queueing theory-based waiting time formulas. The major delays occur in the MH, the P-CSCF, I-CSCF, S-CSCF and the destination server due to the queuing of the SIP messag