EC4: ECN and Credit-Reservation Converged Congestion Control
Zihao Wei, Dezun Dong, Shan Guo Huang, Liquan Xiao · 2019
Bursty traffic and thousands of concurrent flows incur inevitable congestion in data center networks (DCNs) and then affect the overall performance. Various transport protocols are developed to mitigate the network congestion, including reactive and proactive protocols. Reactive schemes to handling congestion after congestion arises are common to current DCNs. However, with the growth of scale and link speed, reactive schemes such as DCTCP encounter the significant problem of slow responding to congestion. On the contrary, proactive protocols are designed to avoid congestion, and they have the advantages of zero data loss, fast convergence and low buffer occupancy (e.g., credit-reservation protocols). But in actual deployment scenario, it is hard to guarantee one protocol to be deployed in every server at one time. When credit-reservation protocol is deployed to DCNs step-by-step, the network is converted to multi-protocol state and faces the following fundamental challenges: (i) unfairness, (ii) high bu er occupancy, and (iii) heavy tail delay. Therefore, we propose EC4, which is for converging ECN-based and credit-reservation protocols with minimal modification. To the best of our knowledge, EC4is the first to address how to harmonize proactive and reactive congestion control. Targeting the common ECN-based protocol-DCTCP, EC4leverages the Forward Explicit Congestion Notification (FECN) to deliver realtime congestion information and redefines feedback control. After evaluation, the results show that EC4e ectively addresses the unfair link allocation. Furthermore, even workloads at 0.6 does not cause buffer overflow, thus largely eliminating the timeouts problem.