Graduation Year

2005

Document Type

Thesis

Degree

M.S.C.S.

Degree Granting Department

Computer Science

Major Professor

Miguel A. Labrador, Ph.D.

Committee Member

Kenneth J. Christensen, Ph.D.

Committee Member

Dewey J. Rundus, Ph.D.

Keywords

Fuzzy inference system, Congestion collapse, Tcp friendliness, Udp, Voice and video applications

Abstract

The stability of the Internet is at risk if the amount of voice and video traffic continues to increase at the current pace. While current transport layer protocols do work well for most applications, they still present some problems. TCP is reliable, tracks the state of some network conditions and reacts drastically to an indication of congestion. TCP serves data-oriented applications very well but it can lead to unacceptably low quality for streaming applications by multiplicatively reducing the congestion window upon a sign of congestion. The other main transport layer protocol, UDP, provides good service for streaming applications but is not friendly to TCP and can cause the well-known existing congestion collapse problem in the Internet.

This thesis proposes a new protocol to provide a good service for voice and video applications while being friendly to TCP and solving the congestion collapse problem. The protocol utilizes a fuzzy logic controller that considers network related information to govern the applications sending rate while satisfying the users needs. Using network information such as the available bandwidth, Packet Loss Rates (PLR), and Round Trip Times (RTT) a fuzzy inference system optimizes the applications send rate to meet the requested rate in a smooth manner without wasting network resources unnecessarily.

The fuzzy logic controller is designed and its performance evaluated using MATLAB model simulations. The results indicate that the fuzzy controller solves the congestion collapse problem by reducing the number of undelivered packets into the network by nearly 100%. It provides smooth transition changes as demonstrated by the controlled UDP flow utilizing an estimated 44% more of the available bandwidth to smooth the send rate than the TCP flow in a highly varying bandwidth environment. The controller also remains friendly with TCP which was demonstrated to share the bandwidth at nearly 50% with one other competing controlled UDP flow.

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