Abstract
With the rapid development of the Internet, new technologies and applications are emerging. One of the important applications is voice over IP. Satellites, which have played an important role in telephony communication and TV broadcasting services, are also playing an important role to provide VoIP services with their global coverage and on-board processing ability over IP networks. Satellite network environment, generally characterized by large delay, limited bandwidth and erroneous link, has significant impact on VoIP. The performance of VoIP is adversely influenced by such characteristics because the original VoIP design is intended for terrestrial network environment. Thus, the satellite environment necessitates the need for VoIP to be efficient in both terrestrial and satellite networks. VoIP is characterized by the performance metrics of signaling, bandwidth, delay, jitter and packet loss. Signaling plays a key role in call establishment and rest of the parameters signifies the quality of service (QoS). Rather than a complete redesign, the existing VoIP protocols should be customized to counteract negative impacts posed by satellite network. In this way, the modification of the basic mechanisms should be kept at the minimal level for the end-to-end compatibility assurance. In this thesis, the performance related issues of SIP-based VoIP over satellites is studied. A comparative analysis of network layer protocols, current IPv4 and future IPv6 is performed. Detailed investigation is conducted by both analytical computation and experimentation on the satellite network testbed through emulation. The study shows that delay, jitter and packet loss are quite comparable for both IPv4 and IPv6 over satellites. The call setup time is quite large in both, IPv4 and IPv6. SIP signaling involves several timers and retransmission algorithms for SIP messages. A novel algorithm and new timer values are proposed to reduce the redundant retransmissions. These have reduced the call setup latency, in addition to the bandwidth consumed by SIP messages. Finally, SIP signaling over TCP is also investigated in the IPv6 DVB-RCS satellite environment to categorize the impact of TCP on VoIP in satellites.