Research On Marking Policy For Fairness Among TCP Flows In DiffServ

With the increasing development of the Internet, "Best Effort" service can not satisfy requirements of various applications any more. So IETF had proposed Integrated Services (IntServ) Model and Differentiated Services (DiffServ) Model in succession. As IntServ do not have a good scalability, therefore single IntServ Model can't widely used in the Internet. But DiffServ avoids the complexity, provides a good scalability of the QoS solution, and easy to achieve in the backbone network. So DiffServ become a hotspot in the network research recently.Many studies have pointed out that there are unfair problems of bandwidth allocation in DiffServ, these unfairness mainly embodied in two aspects:(1)The fairness of the shared bandwidth between the TCP flow and non-response flow (such as UDP flow); (2) the fairness of the shared bandwidth among heterogeneous TCP flows. Researchers have proposed various algorithms to improve the fairness among TCP flows, which had a certain effect, but they didn't consider the Round Trip Time (RTT), Committed Information Rate (CIR), Retransmission Timeout (RTO) factors on the impact of TCP flows at the same time. This thesis made a research on the model of Diffserv and improved the packet marking policy on the edge routers, improved the fairness among the TCP flows. In summarize, this paper includes following outcomes.Firstly, this thesis made a summarization of the concept of QoS, and pointed out the research actuality and hotspots of IP QoS, then gave the introduction with emphasis on the architecture of QoS, the types of service, and other basic theory of the DiffServ.Secondly, this thesis researched the important factors,that affected the fair sharing of bandwidth among TCP flows, and discussed the research results and problems of realization of the basic packet marking strategy of the IP QoS control in Diffserv. Aim at the unfairness problem of the bandwidth allocation among TCP flows, this thesis proposed a CIR,RTT,RTO aware three color marker(CRRTCM) on the basis of the time sliding windows three color marker(TSWTCM). The basic idea of the marking policy is to change the distribution of bandwidth through changing the marking probability with different colors of package. This marking policy gets the RTT and RTO parameters of various TCP flows from the edge node firstly, and then distribute these parameters to the marker to dispose, the CRRTCM marking algorithm marks packets according to these parameters, it used marking probability of different colors' packets which related to CIR, RTT, RTO parameters to reduce the effect of RTT and RTO. Simultaneous it guaranteed the distribution of bandwidth proportionable and fairly based on the CIR among the TCP flows.Finally, we use the NS2 simulation software which compares the performance of the improved algorithm and the TSWTCM. The simulation results showed that compared to TSWTCM,the marking algorithm guaranteed acquisition of the target rate of various TCP flows and could obtain a reasonable allocation of the remaining bandwidth, the algorithm increased the fairness among the TCP flows.