FSQCN: Fast and simple quantized congestion notification in data center ethernet

Abstract

Currently, Quantized Congestion Notification (QCN) has been accepted as the standard layer 2 congestion control protocol in Data Center Ethernet. In this study, we find that QCN has two drawbacks. First, the incomplete binary search of QCN may fail to find the proper sending rate, leading to the complicate supplement mechanisms of QCN. Accordingly, the cost of hardware implementation is increased. Second, in face of unknown network environments, the rate setting of QCN is inconsistent. More specifically, the sending rate is set to be the link rate at initialization, while QCN additively probes for extra bandwidth in face of dynamic network. Consequently, QCN may spend much time on acquiring the spare bandwidth if its sending rate is increased from a low value. To address these problems, we propose the Fast and Simple QCN (FSQCN), following the same framework as QCN. FSQCN complements the binary search and removes other complicate supplement mechanisms in QCN. Thus, FSQCN is much simpler and more efficient than QCN. Moreover, FSQCN resets the sending rate to the link rate explicitly when the switch detects spare bandwidth. Extensive simulation experiments validate that FSQCN controls the queue length well like QCN, and responds faster than QCN, especially in face of the large number of burst short flows in data center networks.