软件定义网络中TCP伪拥塞问题探究

发布时间：2019-01-20 11:45

【摘要】：软件定义网络(software-defined networking,SDN)将控制平面与转发平面分离,通过控制器配置交换机流表项来实现网络的灵活控制,极大地提高了网络带宽利用率.随着SDN的蓬勃发展,越来越多的高校和公司开始部署SDN.同时SDN也面临着一些传统IP网络中不存在的问题,如一些原本在IP网络中运行良好的协议在SDN网络中性能却受到了严重的影响,TCP协议就是其中之一.从SDN的工作机制出发,通过3个场景阐明了SDN在proactive工作模式下依然存在Packet-In短时间内高速并发的可能性.总结并实验验证了高速并发的Packet-In以及流表更新时旧表项需重排列的特性都会使数据包在SDN网络中产生较大时延.实验结果表明,当TCAM支持4 000个流表项时,最坏情况下仅由新插入流表项优先级原因导致已有流表项的重排列就能使单次传输时延达到10s,并发的高速Packet-In则会使时延加大.以实验为基础,揭示了由于SDN网络特性造成的伪拥塞现象,即传统TCP在SDN网络中面临两大问题:1)TCP建立连接困难;2)TCP协议传输低效.最后通过对实验现象进行分析,提出了解决SDN网络中TCP低效问题可能的工作方向.
[Abstract]:The software defined network (software-defined networking,SDN) separates the control plane from the forwarding plane, and realizes the flexible control of the network by configuring the switch flow table items by the controller, which greatly improves the bandwidth utilization of the network. With the rapid development of SDN, more and more universities and companies begin to deploy SDN. At the same time, SDN also faces some problems that do not exist in traditional IP networks. For example, some protocols that originally run well in IP networks have been seriously affected in the performance of SDN networks. TCP protocol is one of them. Based on the working mechanism of SDN, the possibility of high speed concurrency of Packet-In in proactive mode is explained in three scenarios. It is concluded and verified by experiments that the high speed concurrent Packet-In and the rearrangement of the old table items when the stream table is updated will result in a large delay of data packets in the SDN network. The experimental results show that when TCAM supports 4 000 stream table items, in the worst case, the rearrangement of existing stream table items caused only by the priority of newly inserted stream table items can make the single transmission delay reach 10 s, while concurrent high speed Packet-In can make the delay increase. Based on the experiments, the pseudo congestion phenomenon caused by the characteristics of SDN network is revealed, that is, the traditional TCP faces two major problems in SDN network: 1) the difficulty of establishing TCP connection, 2) the inefficient transmission of TCP protocol. Finally, through the analysis of the experimental phenomena, the possible work direction to solve the low efficiency problem of TCP in SDN network is put forward.
【作者单位】：清华大学计算机科学与技术系;
【基金】：国家自然科学基金重点项目(61432009)~~
【分类号】：TP393.0

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