Based On Differentiated Services (diffserv) Ip Qos Control Strategy

As the increasing of real time applications such as IP telephone, video conference, distance learning, the Internet is required to provide a good QoS support. However, current IP network can only provide "Best Effort" service and can't satisfy different network traffic quality requirements of multimedia applications or all kinds of users. IP QoS control mechanisms have become one of the research hotspots on IP networks in recent years.This thesis analyzes the Differentiated Service architecture and studies its control mechanisms of realizing IP QoS, including packet marking policy, queue scheduling algorithm and packet dropping mechanism etc. After that a DiffServ simulation platform is built using the improved DiffServ model in NS2 (Network Simulation 2) developed by U.C. Berkeley and simulations have been done on it, which shows that the platform ,can service different traffic flows and provide a better solution for realizing point-to-point IP QoS.This thesis studies the control mechanisms of realizing IP QoS in DiffServ and does research work as below:Firstly, this thesis studies the packet marking policies. In order to solve the problem of unfairness of the bandwidth allocation between aggregates, the srTCM packet marking algorithm is improved. The simulation results show that the algorithm can improve the fairness of the bandwidth allocation between aggregates.Secondly, studies the queue scheduling algorithms supporting DiffServ and proposes an improved queue scheduling algorithm DWRR, the simulation results show that the algorithm can provide accurate bandwidth distribution to the traffic flows on the output port according to its queue weight.Thirdly, studies the congestion packet dropping mechanisms. The calculation of the packet dropping probability of the dsRED model in NS's DiffServ model is ameliorated, which makes it change more gentle and improves the stability of thealgorithm.Finally, based on the studies in the previous parts, this thesis improves the DiffServ model in NS-2.1b9a under Linux environment and builds a DiffServ simulation platform. The simulation results show that the platform can service different traffic flows with different QoS requirements.