Evaluation of the characteristics of a multimedia interactive satellite communications system

In order to realize a flexible but economical communication system with which users can access multimedia information anytime and anywhere, Tokai University and NTT are currently conducting studies and experiments on a multimedia interactive satellite communications system which uses a satellite circuit for downlinks and a terrestrial network for uplinks. We are presently involved in a field trial of the system applied to tele-education. The fundamental characteristics of the system, round-trip times and throughputs of point-to-point data transmission by TCP and network broadcasting by UDP, have been measured and evaluated. The round-trip rime of actual TCP/IP applications is estimated from the round-trip time measured by using pings (ICMP echo) from clients. The measured TCP throughput is consistent with the throughput estimated from the measured round-trip time and shows that the system is capable of high-speed file transfer, The UDP network broadcasting throughput is 6 Mbps, which is equal to the bandwidth of the leased line in the system. It is confirmed that a higher throughput is possible with a larger window size and a broader-bandwidth leased line. (C) 1998 Scripta Technica.