Effectiveness of TCP SACK, TCP HACK and TCP Trunk over satellite links

This paper reports a study on the performance enhancements of two extensions to the standard TCP implementation - Selective Acknowledgement (SACK) and Header Checksum (HACK) - over satellite links that are characterized by high latency and high bit error rate. We also examine the effectiveness of TCP Trunk, an edge-to-edge aggregation and congestion control mechanism, over the satellite link. Our study on the effect of varying the TCP window size over a long latency link for New Reno, SACK, HACK and TCP Trunk implementations show that increasing window size does improve the performance, but only up to a certain value of the window size, and a further increase actually reduces the performance. Other interesting observations from our experimental study are: SACK enabled TCP Trunk across the satellite link edge routers can improve the throughput regardless of the end host TCP implementation; disabling the link layer CRC and instead implementing the HACK extension to the TCP (and of course HACK+ SACK) can improve the throughput further.