基于直接拥塞通告的数据中心无损网络传输控制机制

A Transmission Control Mechanism for Lossless Datacenter Network Based on Direct Congestion Notification

数据中心网络广泛采用基于优先级的流量控制(Priority-based Flow Control,PFC)机制来避免因缓存溢出而丢包.然而,PFC机制在保证无损传输的同时带来了队头阻塞和拥塞扩散等负面影响.近年来,一些具备端到端拥塞感知能力的传输控制协议被提出来,有效缓解了网络拥塞,减少了PFC的触发.但是在突发流量造成的瞬时拥塞场景下,这些研究工作仍会使得PFC频繁触发而导致严重的队头阻塞和拥塞扩散.针对该问题,在端到端拥塞控制基础上,提出了一种实现于交换机上的直接拥塞通告解决方案(Direct COngestion Notification,DCON),该方案在突发拥塞场景下能及时识别出与非拥塞流(与造成拥塞无关的流)共享入端口的拥塞流(真正造成拥塞的流),并从交换机直接通告发送端对该拥塞流精确地降速.实验结果表明,相比于现有的端到端拥塞控制传输协议,DCON有效避免了PFC的队头阻塞和拥塞扩散,平均流完成时间的最大降幅达到55%.

Priority-based flow control(PFC)mechanism is widely deployed in data center network to avoid packet loss due to buffer overflow.Although PFC mechanism guarantees lossless transmission,it brings negative impacts such as head-of-line blocking and congestion spreading,etc.In recent years,many end-to-end congestion aware transport protocols have been proposed to effectively alleviate network congestion and reduce the triggering of PFC.However,in the case of transient congestion due to burst traffic,PFC is still triggered frequently even if the above end-to-end transport protocols are deployed,resulting in serious head-of-line blocking and congestion spreading.Therefore,on the basis of end-to-end congestion control,this paper proposes a direct congestion notification(DCON)solution implemented on the switches.DCON can timely identify the congested flows(really responsible for congestion)sharing the ingress port with the non-congested flows(not responsible for congestion).Meanwhile,DCON directly sends the congestion notification message to the corresponding senders from the switch and accurately sets the target rate for the identified congested flows at the sender.Compared to the existing end-to-end transmission control protocols,the experimental results show that DCON effectively avoids the head-of-line blocking and congestion spreading of PFC,and reduces the average flow completion time by up to 55%.