Performance of Satellite Gateway over Geostationary Satellite Links

A significant amount of today´s Internet traffic, including World Wide Web (WWW), file transfer, e-mail and remote access traffic, is carried by the Transmission Control Protocol (TCP) transport protocol. Geostationary satellite links have a number of features that may degrade the performance of the TCP over them. The satellite links have an average round-trip time (RTT) of around 500 ms. The TCP uses a slow-start phase to probe the network at the start of a connection. The time spent in the slow-start phase is directly proportional to the RTT. For a satellite link, it means that the TCP stays in the slow-start phase for a longer time than in the case of a small RTT link. This drastically decreases the throughput of the short-duration TCP connection. Furthermore, when packets are lost, the TCP enters the congestion-avoidance phase. Due to the higher RTT, the TCP remains in the congestion-avoidance phase for a longer time, which reduces the throughput of both short and long-duration TCP connections. Satellite gateways are proven to improve the TCP throughput by 300 -- 800% across high-delay and lossy satellite links.