TCP congestion control in shared satellite environments

This paper describes the use of a transparent TCP gateway to improve the performance of applications operating in a shared secure satellite environment. Typically, a satellite gateway is installed at each end of the satellite link, and the gateways process all traffic traversing the link. With the proliferation of virtual private network (VPN) technologies, multiple encrypted tunnels can be established over a satellite link. If transparent TCP gateways are used to optimize application performance, a pair of gateways are required at the egress points of each tunnel. Many TCP gateways perform poorly in this situation because they do not implement congestion control on their 'satellite' sides, resulting in network congestion between the sending gateways and the satellite uplink. Our approach is to use Space Communications Protocol Standards (SCPS) transparent transport layer gateways, which are capable of implementing a variety of congestion control schemes on their terrestrial and satellite sides. By using a variant of the TCP Vegas congestion control algorithm, the gateways can communicate indirectly (by detecting changes in packet round-trip times) to efficiently share the satellite bandwidth. Results show that this improves performance over end-to-end TCP without congesting the network between the gateways and the uplink as would pure rate-control.