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Narasimhan, PriyaAn Evaluation of Realistic TCP Traffic on Satellite Networks
Master of Science (MS), Ohio University, 2002, Electrical Engineering & Computer Science (Engineering and Technology)

There are many factors governing the performance of TCP-based applications on satellite channels. The end-to-end performance of TCP is known to be degraded by the delay, noise and asymmetry inherent in geosynchronous systems. These results have been based on experiments that evaluate the performance of TCP in single flow tests. Single flow tests are useful for deriving information on the theoretical behavior of TCP and allow for easy diagnosis of problems. However, they do not represent realistic situations and therefore cannot be used to authoritatively comment on performance issues. Our experiments tested TCP's performance in a more dynamic environment with competing traffic flows from hundreds of TCP connections running simultaneously across the satellite channel.

Another aspect investigated was TCP reaction to bit errors on satellite channels. TCP interprets delays and losses as a sign of network congestion. This causes it to cut down its transmission rate leading to poor performance. We allowed the bit error rate on our satellite channel to vary widely and tested the performance of TCP as function of these bit error rates. Our studies show that the average performance of TCP on satellite channels in these realistic conditions is good and establishes the robustness of TCP on satellite channels. Many of our observations contradict commonly held beliefs about the performance of TCP on satellite links.

Committee:

Shawn Ostermann (Advisor)

Keywords:

TCP Performance; Satellite Channels; Performance Degradation; Realistic TCP Traffic

Hayes, ChristopherAnalyzing the performance of new TCP extensions over satellite links
Master of Science (MS), Ohio University, 1997, Electrical Engineering & Computer Science (Engineering and Technology)
It has been shown in Kruse that long delay satellite channels suffer poor throughput using the Transmission Control Protocol, TCP. Performance is limited by the delay inherent in geosynchronous satellites. Several changes have been proposed that could help TCP performance over long delay paths. These changes include big windows and PAWS proposed in RFC 1323, Selective Acknowledgments(SACK), proposed in RFC 2018, Hoe's fast retransmit modifications, and Mathis and Mahdavi's Forward Acknowledgments(FACK). This thesis examines the performance of the new TCP extensions over long delay links. Performance is examined using one, two, and three drop loss events and transfers of various file sizes. This thesis also investigates the performance of the new TCP extensions when encountering varying degrees of bit errors in the satellite channel.

Committee:

Shawn Ostermann (Advisor)

Keywords:

Satellite Channels; Selective Acknowledgments; Geosynchronous Satellites

Allman, MarkImproving TCP performance over satellite channels
Master of Science (MS), Ohio University, 1997, Electrical Engineering & Computer Science (Engineering and Technology)

This thesis outlines performance problems with the Transmission Control Protocol(TCP) in networks containing geosyncronous satellite channels, as well as solutions to these problems. The first solution is a modification of the File Transfer Protocol (FTP). Standard FTP uses one TCP data connection to transfer a single file. However, our modifications allow FTP to employ multiple parallel TCP data connections to transfer a single file. Experiments have shown that this approach allows FTP to utilize the full capacity of the NASA ACTS satellite system. This application-level solution also provided insights into general TCP modifications that will allow all applications to fully utilize the available bandwidth provided by satellite channels. The insights provided by XFTP include the need for larger TCP windows, selective acknowledgments, changes to the slow start and congestion avoidance algorithms and the need for available bandwidth estimation. We altered the slow start algorithm to be more aggressive, as suggested by XFTP. Experiments using these slow start modifications show better utilization of satellite channels. Finally, this paper presents recommendations for which TCP mechanisms should be widely implemented and which mechanisms need further study.

Committee:

Shawn Ostermann (Advisor)

Keywords:

Transmission Control Protocol; Geosyncronous Satellite Channels; File Transfer Protocol