基于ExtendSim的FTP服务系统建模与仿真

FTP serving system modeling and simulation based on ExtendSim

FTP服务仍然是校园网络主要服务之一。它通过文件传输协议FTP(File Transfer Proto-col)与用户共享文件。FTP服务系统是一个随机服务系统,但它的数据传输进程(服务台)之间是相互影响的,服务时间不是相互独立的,所以经典的排队模型M/M/c/N无法准确描述它。所建立的这个模型,克服了经典排队模型的局限性,能更准确地表达FTP服务系统,并通过Ex-tendSim软件对模型进行仿真分析,得到了服务质量(QoS)的重要参数——平均呼损率与系统容量之间的关系。

FTP service is still one of the most important services on campus network.It shares the files with clients through FTP（file transfer protocol）.FTP serving system is a stochastic serving system,but its data-transfer-processes interact and serving time is not independent,so conventional queue model M/M/c/N can not describe it precisely.The model built up in this paper overcomes the localization of M/M/c/N queue model,and can express the FTP serving system more precisely.Finally,we obtain the relation between the average call blocking probability（CBP）— the primary parameter of QoS,and system capacity is obtained through simulating analysis of model based on ExtendSim.