Modeling and understanding TCP incast in data center networks

Recently, TCP incast problem attracts increasing attention since the receiver suffers drastic goodput drop when it simultaneously strips data over multiple servers. Lots of attempts have been made to address the problem through experiments and simulations. However, to the best of our knowledge, few solutions can solve it fundamentally at low cost. In this paper, a goodput model of TCP incast is built to understand why goodput collapse occurs. We conclude that TCP incast goodput deterioration is mainly caused by two types of timeouts, one happens at the tail of a data block and dominates the goodput when the number of senders is small, while the other one at the head of a data block and governs the goodput when the number of senders is large. The proposed model describes the causes of these two types of timeouts which are related to the incast communication pattern, block size, bottleneck buffer and so on. We validate the proposed model by comparing with simulation data, finding that it can well characterize the features of TCP incast. We also discuss the impact of most parameters on the goodput of TCP incast.