Session Initiation Protocol (SIP) has been selected by the Third Generation Partnership Project (3GPP) as the official end-to-end IP signalling protocol for establishing multimedia sessions in the IP-based Universal Mobile Telecommunication Systems (UMTS) network. Since a satellite component has been identified as part of the roll out of UMTS to provide an 'anytime, anyway' communication, there is a need to support SIPbased session establishment over Satellite-UMTS (S-UMTS) as well. Thus this paper aims at evaluating the performance of SIP-based session setup over the S-UMTS, taking into account the larger propagation delay over the satellite as well as the impact of the UMTS radio interface under different channel conditions. This paper presents a possible architecture for a seamless integration of an IP-based terrestrial/satellite network and describes how SIP-based sessions are established. The issue of incorporating a link layer retransmission based on the Radio Link Control acknowledgement mode (RLC-AM) mechanisms is also addressed and its implications on the SIP session establishment performance are examined.