| With quick emergence of delay/bandwidth sensitive multimedia applications in the Internet, it is evident that Quality of Service should be provided by the Internet to handle these applications. One of the current efforts to add QoS to the Internet is called Differentiated Service (DiffServ ) Network. DiffServ provides service differentiation among traffic aggregates of different users over a long time scale. It pushes sophisticated classifying, marking, policing and shaping operations to the network boundary and keeps the core network more scalable. However, whether DiffServ network can provide the promised services is not clear.; This dissertation focused on evaluating performance of DiffServ and mechanisms to improve the performance of a DiffServ network. First, a new model was proposed to model the performance of a DiffServ with a Token Bucket Marker. The results from simulation and the model showed good correspondence. Second, based on the observations from the modeling work, a new traffic-marking scheme, called ItswTCM, is proposed. This new marker provides strong incentive for users to obey their contract and provides better fairness for different service subscribers under a large scale of network conditions. This helps to solve one of the biggest problems in a DiffServ network—the fairness problem. Third, a modified version of TCP together with the proposed ItswTCM marker is used to further improve the fairness performance of a DiffServ network under combined UDP & TCP traffic. Finally, the issues of running DiffServ over ATM network have been discussed. A priority based early packet discarding (PEPD ) buffer scheme, which can be used in an ATM switch to solve the possible service degradation encountered when running DiffServ over ATM, has been proposed. A simple model analysis is provided for the proposed PEPD scheme and the performance of this scheme is evaluated.; This dissertation provides a solid foundation to evaluate the performance of DiffServ and provides some suggestions to improve the performance of DiffServ. Based on these work, it is concluded that new mechanisms must be added to DiffServ network to provide the promised services. |
