ondent DHCP Server DHCP DISCOVER (1) DHCP OFFER (2) DHCP REQUEST (3) DHCP ACK (4) SIP INVITE (5) SIP OK (6) FIGURE 17.8 DHCP registration procedure. The MH, on receiving this OFFER message, sends a DHCP REQUEST message (3) to the DHCP server to confirm the offer made. The DHCP server then sends the MH DHCP ACK message (4) with the new IP address to be assigned to the MH. The SIP message exchange to re-establish the connection is similar to that for UMTS networks, where the MH, after acquiring the new IP address, re-invites the CH to its new address by sending a SIP INVITE message (messages 5, 6, and 7). 17.5.3 Handoff Delay Analysis In this section, we derive the handoff delay introduced due to the wireless link in the UMTS and WLAN access networks and the queueing delay in the different servers in the signaling path. We show that the handoff delay due to the wireless access is beyond the maximum tolerable limit for streaming media in low-bandwidth UMTS networks and not in WLANs. Let D Handoff denote the handoff delay during the mid-call terminal mobility, which can be divided into two parts: (1) the delay occurred during the attachment procedure and (2) the delay due to location update using the SIP INVITE message. During each of these procedures, messages are transported over the wireless access link, which introduces major delays in comparison with the queuing and transmission delay introduced by the high-speed backbone networks. To compute the delay for transmitting messages over the wireless links in the access networks, we have used the delay models for frame and packet © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security transmission over a wireless link under various link error conditions, as pro- posed in [27]. The outdoor operation of GPRS radio access networks makes it more vulnerable to noise, thus increasing the bit error rate (BER) for the wireless channel. To improve the BER performance for transmission of control packets over wireless links, a semi-reliable link