RackCC: Rack-level Congestion Control

Many data center traffic patterns exhibit abundant concurrent connections and high churn. In the face of these characteristics, server-centric congestion control is a poor fit—each connection, no matter how small, must start from scratch testing when and how much to send along a given path. This is despite the fact that there are a large number of flows that may have already probed the exact same path, not just at a server level, but also at a rack level. Thus, we argue for rack-level congestion control in which all connections are tunneled through rack-to-rack JumboFlows. This design allows an entire rack’s connections to cooperate with one another for better fairness and performance, particularly for short flows. In this paper, we examine situations in which JumboFlows might be useful and present a preliminary design of a system (RackCC) that implements JumboFlows.