DirecPCtm'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 satellite links for downstream data delivery and public telephone networks at the 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. Our principle object is to lower cost and efficiently provide high bandwidth access to Internet services such as file transfer, the World Wide Web, and the MBONE. In the initial protocol implementation, we achieved four times higher throughput than that of Today's high-speed modems (28.8 Kbps) alone2. 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. Furthermore, we are investigating how to extend IP multicast services to such hybrid networks. The broadcast nature of Satellite communication makes it an efficient way for high- bandwidth multicast transmission.

A revised version of this technical report has been published in
Proceedings of the AIAA: 16th International Communications Satellite Systems Conference and Exhibit, Part 1, pp. 476-482, Washington, D.C., February 25-29, 1996.