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Abstract : |
In several experiments using NASA's Advanced Communications Technology Satellite (ACTS), investigators have reported disappointing throughput using the TCP/IP protocol suite over 1.536Mbit/sec (T1) satellite circuits. A detailed analysis of FTP file transfers reveals that both the TCP window size, and the TCP "Slow Start " algorithm contribute to the observed limits in throughput. While it is tempting to approach a solution to this issue by raising the TCP window size, there are several issues which can not be addressed in that way: (1) In order to raise the TCP window size sufficiently to allow full utilization of a T1 circuit, the TCP Extended Window Option is required[4]. Commercial implementation of this option in major operating systems has not been completed. (2) The use of very large windows may actually hurt throughput if a moderate bit error rate is present on the satellite channel. (3) A change in the window size does not address the effect of the TCP Slow Start algorithm. We therefore propose an application-layer solution by adding an option to the standard FTP which uses multiple data connections. The use of multiple TCP connections allows the effective utilization of the, |
