Performance Analysis Of High Speed Transport Protocol XCP And Its Internetworking With Traditional TCP

With the deployment of new technology such as fiber communications, the bandwidth capacity grows rapidly, and the traditional TCP cannot fully utilize the available bandwidth because of its conservative congestion control mechanism. Therefore, high speed transport protocols have been a hot topic in recent years, among them some famous ones are HSTCP, STCP, BIC, FAST TCP and XCP. Because of its prominent performance such as rapid convergence, excellent fairness and very small queueing delay, XCP has attracted much attention from researchers. However, because the congestion control of XCP is quite different from that of traditional TCP, and as a result, it is difficult to connect XCP with traditional TCP. To address this problem, some schemes such as TCP-friendly XCP, XCP-based CSFQ and XCP-i have been proposed by researchers. However, these schemes do not deal in-depth with the possible flows appears in the hybrid networks during the upgrade process, and the TCP compatibility and feasibility of these schemes are poor.Why the proposals cannot study in-depth is because little knowledge is known about the time-scale characteristics of XCP. To address this problem, the author investigates deeply into the time-domain performance of XCP, and derives the time-domain sending rate of XCP, based on this point, the response function of XCP is also provided. Based on this knowledge, an XCP-TCP gateway based scheme is further proposed by the author, analysis and simulations validate the proposal. The original work of this paper can be concluded as follows.By analyzing the relationship between feedback and input traffic rate, the author derived that the input traffic rate of an XCP bottleneck converges to its bandwidth capacity in exponential rate. Under a single bottleneck model, by concentrating on the throughput ratio, its time-domain expression was first derived. The expression showes the throughput ratio converges to the flow number ratio in exponential rate. Secondly, the time-domain sending rate of an XCP flow is also given. These results not only validate the previous conclusion about XCP performance such as fairness and bandwidth utilization, but also provide more intuitive view about XCP congestion control.Based on the previous studies, five indexes are proposed to evaluate the high speed transport protocols. As one of the most important index, scalability can be described by the reponse function. Under a periodic drop event model, the author first derived the response functions of FAST TCP and XCP. Different from other response functions, the average throughput of XCP is related not only to the drop event rate, but also the per-flow bandwidth. Thus it proved that the scalability of XCP is better than other ones.Based on the comparison of the previous schemes about XCP interconnecting with traditional TCP, the author proposed an XCP-TCP gateway based scheme. The scheme first extensively investigated the work status of possible flows appear in the upgrading process, and derived the analytical fairness between these flows. Results show that these flows can coexist well with each other. Secondly, the author also analyzed the bandwidth utilization, converge time and queueing delay of an XCP bottleneck. Results show that the bandwidth utilization of the bottleneck is not less than 80% when in equilibrium, and that the queueing delay is better than that of a traditional FIFO router.