Effective Extensions of Internet in Hybrid Satellite-Terrestrial Networks

Direct PCTM's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only VSAT satellite links for downstream data delivery and public telephone networks at modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. In the initial protocol implementation, we achieved four times higher throughput than that of today high-speed modems (28.8 Kbps) alone (Falk 1995). This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques. TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths. A revised version of this report has been published in Proceedings of the 1st Conference of Commercial Development of Space, Part One, pp. 339-344, Albuquerque, New Mexico, January 7-11, 1996.