Transmission Control Protocol (TCP) is the most widely used transport protocol for reliable data transfer in the Internet. TCP uses packet drop as an indication of network congestion. Unnecessary packet drops lead to poor performance. This problem also exists when TCP traffic is in a Differentiated Services (DiffServ) enabled network. Moreover, the DiffServ network inherits the problem of TCP that biases against connections with long round trip time (RTT) and leads to unfairness among the connections with different RTTs. Explicit Congestion Notification (ECN) is proposed as a mechanism to avoid packet losses and thus improve the link efficiency. In this thesis, variation of ECN with a new marking strategy called mark-random is proposed to provide better fairness among the connections. S...[ Read more ]

Transmission Control Protocol (TCP) is the most widely used transport protocol for reliable data transfer in the Internet. TCP uses packet drop as an indication of network congestion. Unnecessary packet drops lead to poor performance. This problem also exists when TCP traffic is in a Differentiated Services (DiffServ) enabled network. Moreover, the DiffServ network inherits the problem of TCP that biases against connections with long round trip time (RTT) and leads to unfairness among the connections with different RTTs. Explicit Congestion Notification (ECN) is proposed as a mechanism to avoid packet losses and thus improve the link efficiency. In this thesis, variation of ECN with a new marking strategy called mark-random is proposed to provide better fairness among the connections. Simulation results show that mark-random strategy performs the best in fairness performance compared with the other strategies. Further experiments show that a cooperation problem exists between the ECN mechanism with different marking strategies and DiffServ network. Two additional schemes, called "OUT Marking Scheme" and "Throughput Sustaining Scheme", are proposed to solve the cooperation problem. Experimental results show a great improvement by applying mark-random strategy with "OUT Marking Scheme" in a DiffServ network under different scenarios.