Proxy Mechanism of Multiplexing TCP Connections over Satellite Internet

Since a satellite link provided by GEO (Geostationary Earth Orbit) Satellites has a large propagation delay, TCP performance is known to be degraded when the TCP connection is utilized between sender and receiver hosts interconnected via the satellite link. It is mainly because the window size of the TCP connection increases slowly due to the large propagation delay on the satellite link, and because the satellite network has a very large bandwidth-delay product. Ironically, this tendency becomes remarkable as the link capacity gets large. In this thesis, we propose a novel architecture of a proxy mechanism for multiple TCP connections on the Satellite Internet, to overcome the problems. The proposed architecture splits the TCP connection between the sender and receiver hosts into three connections, which are a terrestrial connection from the sender host to the sender-side ground station, a satellite connection between the sender-side and receiver-side ground stations, and another terrestrial connection between the receiver-side ground station and the receiver host. It makes us possible to configure each TCP connection according to the characteristics on each network, by which it is expected to improve the overall throughput of the data transfer. Furthermore, to avoid the throughput degradation of terrestrial connections due to the low throughput of the satellite connection, we adopt SCTP (Stream 1 Control Transmission Protocol) as a transport-layer protocol to multiplex TCP connections on the satellite link, to effectively use the capacity of the satellite link. We further propose the congestion control mechanisms adopted to the satellite SCTP connection. It is based on the congestion control mechanism of TCP Vegas, which can well match the characteristics of the satellite connection, since TCP Vegas can provide a stable available bandwidth-delay product. Additionally, we discuss the method to deal with the difference of the available bandwidth between the terrestrial connections and the satellite connection and to improve the fairness among the multiplexed TCP connections. We evaluate the performance of the proposed mechanism through numerical results of simulation experiments, and confirm that the proposed mechanism can improve the utilization of the satellite link and the fairness among multiplexed TCP connections, when compared with the traditional mechanisms.