wireless delay models for our case study. Transmission delay with RLP (for GPRS radio access): The analysis considers the following parameters: P = Probability of an RLP frame being in error in the air link k = Number of frames in a packet transmitted over the air D = End-to-end frame propagation delay over the air link (typical values of the order of 100 ms). T = Interframe time of RLP (typical values of the order of 20 ms for GPRS). The effective packet loss Pf seen at the transport layer, with RLP operating underneath, is given as: (17.1) 1-p(p(2-p)) where n is the maximum number of RLP retransmission trials and Cij (repre- senting the first frame received correctly at the destination) is the ith retrans- mission frame at the jth retransmission trial. The number of trials (n) is usually less than four. We assume three trials in our analysis. For n = 3 (typical value), the packet loss rate with RLP for packets with k frames is given as: q=1-(1-p(p(2-p))9y C 2009 by Taylor & Francis Group, LLC SIP-Based Mobility Management and Its Performance Evaluation Considering the RLP retransmissions, the transport delay in transmitting a packet over the RLP is given by: (17.2) Interested readers can find further details on the derivations of these expres- sions in [27]. Next, we determine the value of k corresponding to different types of mes- sages involved in the GPRS attach and PDP context activation procedures. The maximum size of the messages exchanged in the GPRS Attach procedure is 43 bytes [28]. Now, for a 9.6 Kbps channel, there are 9.6x103 20 x 10 - 3 x 1 = 24 bytes in each frame. Therefore, the number of frames (k) to be transferred for a single message in the attach procedure is 43/24 22 2. Similarly, for a 19.2 Kbps or higher bandwidth (e.g., 128 Kbps) channel, the number of frames per message is k = 1. On the other hand, the maximum size for the PDP context activation messages is 537 bytes [28]. So the number of frames for PDP messages are k = 537/24 22 23, 12 and 2 for 9.6 Kbps, 19.2 Kbps and 128 Kbps channe