CCMA: A Dynamical Concurrent-Connection Management Agent to Mitigate TCP Incast in Datacenters

While aggregator applications with many-to-one TCP traffic pattern prevail in datacenter networks, they often suffer from catastrophic goodput degradation due to their highly bursty traffic overwhelming a single bottleneck link, which is known as the TCP Incast issue. In this paper, we first derive three analytical results that mitigate Incast via managing connections, i.e., equalizing the in-flight packet amounts of concurrent connections, closing all the connections with higher timeout possibilities, and closing some of the connections with identical timeout possibilities. Afterward, we design an Incast mitigation application, i.e., concurrent-connection management agent (CCMA). Unlike previous Incast solutions, CCMA is an application-layer agent on the receiver, which manages concurrent TCP connections on behalf of aggregator applications. CCMA requires no modification to existing communication hardware or software. For multiple coexisting aggregators, CCMA sequentially schedules them to avoid traffic collision. For each aggregator, CCMA dynamically adjusts the advertised window sizes and the concurrency number of each aggregator following our analytical results to achieve low Incast probability and high goodput. The extensive real-world experiments and NS3 simulations show that CCMA maintains zero Incast probability while greatly improving the goodput of TCP by 7.8–13.5 times.