Enhancing the radio link protocol for VoIP session establishment signalling over satellite-UMTS

Session initiation protocol (SIP) is an application layer signalling protocol used in the IP-based UMTS network for establishing multimedia sessions. With a satellite component identified to play an integral role in UMTS, there is a need to support SIP-based session establishment over satellite-UMTS (S-UMTS) as well. Due to the inherent characteristics of SIP, the transport of SIP over an unreliable wireless link with a larger propagation delay is inefficient. To improve the session setup performance, a link layer retransmission, based on radio link control acknowledgement mode (RLC-AM) mechanisms, is utilised. However, the current UMTS RLC-AM procedure is found to cause undesirable redundant retransmission when applied over satellite. As such, the paper proposes an enhancement to the RLC protocol through a timer-based retransmission scheme. Simulation results reveal that not only can the system capacity be improved through this redundant retransmission avoidance scheme, but also better system performances, in terms of session setup delay and failure, are gained.