Graduation Year

2006

Document Type

Thesis

Degree

M.S.Cp.E.

Degree Granting Department

Computer Science and Engineering

Major Professor

Miguel A. Labrador, Ph.D.

Co-Major Professor

Ken Christensen, Ph.D.

Committee Member

Adriana Iamnitchi, Ph.D.

Keywords

performance evaluation, TCP modeling, congestion window-based protocols, send rate, Markov regenerative processes.

Abstract

Besides the two classical techniques used to evaluate the performance of a protocol, computer simulation and experimental measurements, mathematical modeling has been used to study the performance of the TCP protocol. This technique gives an elegant way to gain insights when studying the behavior of a protocol, while providing useful information about its performance.

This thesis presents an analytical model for the SF-SACK protocol, a TCP SACK based protocol conceived to be appropriate for data and streaming applications. SF-Sack modifies the multiplicative part of the Additive Increase Multiplicative Decrease of TCP to provide good performance for data and streaming applications, while avoiding the TCP-friendliness problem of the Internet. The modeling of the SF-SACK protocol raises new challenges compared to the classical TCP modeling in two ways: first, the model needs to be adapted to a more complex dynamism of the congestion window, and second, the model needs to incorporate the scheduler that SF-SACK makes use of in order to maintain a periodically updated value of the congestion window. Presented here is a model that is progressively built in order to consider these challenges. The first step is to consider only losses detected by triple-duplicate

acknowledgments, with the restriction that one such loss happens each scheduler interval. The second step is to consider losses detected via triple-duplicate acknowledgments, while eliminating the above restriction. Finally, the third step is to include losses detected via time-outs. The result is an analytical characterization of the steady-state send rate and throughput of a SF-SACK flow as a function of the loss probability, the round-trip time (RTT), the time-out interval, and the scheduler interval.

The send rate and the throughput of SF-SACK were compared against available results for TCP Reno. The obtained graphs showed that SF-SACK presents a better performance than TCP. The analytical model of the SF-SACK follows the trends of the results that are presently available, using both the ns-2 simulator and experimental measurements.

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