Rate Change Estimation Based Three Colour Marker In Differentiated Service

Due to the explosive development of network technologies, more and more multimedia applications are appearing over the Internet, such as IP telephone, video conference, distance learning, the network is unprecedented complex and diversified."Best Effort"service can not satisfy different network traffic quality requirements of different application any more, while the goal of Quality of Service (QoS) is to provide priority including dedicated band width, latency, controlled jitter loss characteristics. Therefore the research on QoS has become a hot issue.Differentiate Service (DiffServ) which put forward by IETF is one of the solutions for Internet QoS. In DiffServ networks, edge node classify each packet based on its traffic profile and mark its DiffServ codepoint (DSCP), then packets with the same value of DSCP belong to an aggregate. Core nodes choose the particular Per-Hop-Behavior (PHB) for the packet according to its DSCP. It is by separating the implementation mechanism from its PHB that Diffserv possesses good scalability.Researchers found unfairness problem in DiffServ, especially for TCP flow which is a kind of adaptive flow and sensitive to network environment. This paper first introduces the standard congestion control algorithms of TCP. Different TCP implementations adopt different congestion control mechanisms, their performances when suffer packets loss is compared. No matter which implementation adopted yet, the congestion window size would changed undoubtedly when the TCP flow experiences congestion.Basing on above cognitions, combined with the study on the packet marking policies supporting DiffServ, this paper improves the Time Sliding Window Three Colour Marker (TSWTCM) which is the recommended marker, puts forward the Rate change estimation based Three Color Marker (RTCM). RTCM traces flow's rate change, estimates the characteristic of the flow, protects the TCP flow by adjusting the threshold. Simulation experiment results show improvement in TCP performance when competing with UDP, at the same time it heighten the link utilization, ensured the fair bandwidth allocation effectively.Research of this paper is accomplished mainly on a large amount of simulation experiments using Network Simulation (NS). NS is one of the most powerful and widespread tools for network simulation. This paper emphasizes on the DiffServ model in NS, also demonstrate the whole process of writing scripts, obtaining and analyzing experimental data by a practical example.