A New DCQCN Rate Increase Algorithm with Adaptive Byte Counter

Datacenter networks are constructed of high speed networks, such as 40Gbps Ethernet, and quite severe communication quality, low latency and high throughput, is required from applications. RDMA (Remote Direct Memory Access) is now a hot topic in datacenter networking because it can operate high speed data transmission without TCP/IP protocol overhead. DCQCN (Datacenter Quantized Congestion Notification) has been proposed as congestion control for RDMA over Ethernet. In this paper, we reveal with our preliminary evaluation for DCQCN that 1) byte counter behavior causes fairness issues, 2) parameter setting of small timer for time counter and large byte counter makes time counter a dominant factor in rate increase algorithm, and 3) time counter behavior which is independent of transmission rate resolves fairness issues. And we also show that DCQCN has a technical problem of delaying transition timing to Hyper-Active Increase phase due to large byte counter setting, which causes slow convergence to the desirable transmission rate. We propose a new setting for byte counter in DCQCN so that its interval of counter increment is independent of transmission rate. This algorithm, named Adaptive Byte Counter DCQCN (ABCDCQCN), enables shorter interval of byte counter increment and can resolve both fairness issue and fast convergence of transmission rate.