ared with the PDD for 5 kbps bandwidth which was approximately 420 ms. PDD decrease with increasing bandwidth. At a bandwidth of 254 kbps, the PDD was around 50 ms. In realistic 3G network configurations, the bearer allocated for signaling is a few kbps [5] requiring very small time. ASD values recorded by Curcio and Lundan [5] were constantly 45 ms for channels of at least 5 kpbs, but increases for very narrow channels (2 kpbs to 166 ms). This could be attributed to mes- sage queuing and congestion at lower channel bandwidths and the possibility of retransmissions [5]. The CRD could not be measured, because the media packets queued up in the simulator and blocked the channel for a long time [5]. Globally, SIP signaling delays are well within the Grade of Service (GoS) bounds proposed by the ETSI TIPHON QoS classes [6]. Losses in the air interface and narrow channels have great impact on the overall SIP call setup time. They result in large call setup times. However, it is expected that UDP/IP header compression and SIP message compres- sion algorithms will reduce the SIP call setup delay over 3GPP networks significantly. 22.2.2.1.2 Message transfer delay Since the INVITE method is con- sidered to be the most important method in SIP, because it is used to establish a session between participants and normally contains the description of the session to be setup, it is interesting to determine its performance in general. This was done by Kueh [3] for message transfer delay at block error rates of 0, 10 and 20%. It was found that the message transfer delay increases as the message size (and hence the session description) increases. This is expected. It is found that the transfer delay of the INVITE request is substantially reduced compared to when no link-layer retransmission is employed; whereby the delay reduction increases as the message size and the block error rates increase. This is because without retransmission at the link-layer, a segment that is lost means that the whole message cannot be recovered at the r