1 TCP Performance over Satellite Links

Over the past few years, we have reported on the performance issues faced by TCP/IP based applications on satellite links. Performance is limited by the delay inherent in geosynchronous systems and the probability of bit errors found in any wireless system, including satellite systems. These limitations are becoming more important as new satellite systems o er much higher data transmission rates than those available in the past. While high e ciency on fast satellite links may eventually require new protocol modi cations, our previous studies indicate that full link utilization may be achievable using the TCP performance enhancements that have already been approved or that are currently in the standards process. Of particular interest in the satellite environment are performance enhancements for scaled windows and timestamps (RFC 1323), fast retransmit and recovery (RFC 2001), and selective acknowledgement (RFC 2018). The paper describes each of these performance enhancements and explains how they can increase TCP's performance over satellite links. We present the results of a comprehensive performance study of these TCP protocol enhancements in the satellite environment over error free links. We show results over networks both with and without congestion loss. Finally, we examine TCP's performance on realistic satellite links with a non-zero probability of bit errors, where the e ectiveness of selective acknowledgments is examined and compared to the performance of traditional TCP implementations.