Adjusting Packet Size to Mitigate TCP Incast in Data Center Networks with COTS Switches

In data center networks, a large number of concurrent TCP connections suffer the TCP Incast throughput collapse due to packet drops in shallow-buffered Ethernet switches. In this work, we first reveal theoretically and empirically that controlling the IP packet size is much more effective in avoiding Incast than cutting congestion window under severe congestion. We further design a general supporting scheme Packet Slicing, which adjusts the IP packet on widely used commodity switches. The design uses standard ICMP signaling, which makes no modification on TCP protocols and can be transparently utilized by various TCP protocols. To alleviate the impact of micro-burst caused by high flow concurrency, we utilize the TCP Pacing scheme to disperse packets over the round trip time, helping Packet Slicing to support more concurrent TCP flows. We integrate Packet Slicing with three state-of-the-art data center TCP protocols on NS2 simulation and a physical testbed. The experimental results show that Packet Slicing broadly improves the goodput of different data center TCP protocols by average 26x, while having almost no effect on the I/O performance of switches and end hosts.