Combining RTT and ECN for RoCEv2 Protocol

Remote direct memory access (RDMA) has the advantages of direct user-level access to HW, asynchronous communication, etc. RoCEv2 protocol enables RDMA technology to be used in large-scale data centers over Ethernet. It provides high throughput and low latency for data center, but it faces the problem of network congestion caused by RoCEv2 data flow. Efficient congestion control strategy plays an important role in the performance of RoCEv2 based data center network. At present, the network congestion control algorithms for RoCEv2 protocol are mainly based on ECN marked DCQCN and RTT based TIMELY. ECN and RTT have different characteristics and advantages. ECN is more effective to prevent packet losses; whereas RTT controls end-to-end queuing delay better. In this paper, a new algorithm RTT_DCQCN is presented for congestion control which is based on DCQCN. In RTT_DCQCN, the CNP generation mechanism and rate adjustment strategy are optimized; and the scheme of introducing RTT signal into DCQCN is proposed, in which the congestion degree is judged by using ECN and RTT together. The RoCEv2 protocol is implemented on ns-3 network simulation platform. The simulation experiment on ns-3 proved that RTT_DCQCN is valid for the aim of improving stability, fairness and throughput of the RoCEv2 data flows.