Design and Implementation of TCP-Friendly Meters in P4 Switches

Abstract

Metering the traffic of a flow and dropping the portion of traffic that exceeds the target rate set by the meter is very important to provide quality of service (QoS) in a network. Most existing switches on the market provide the meter function. Although these meters regulate the traffic of a UDP flow very well, according to our tests, they are not TCP-friendly. For example, we found that a TCP flow passing the meter of a commercial switch can only achieve about 10% of the target rate. Based on our studies, we found that this poor performance is due to the bad interactions between the TCP congestion control and the meter function. In this paper, we design and implement a TCP-friendly meter in the packet processing pipelines of a P4 switch. Experimental results show that our meter regulates a TCP flow very well and can maintain its achieved rate within 5% of the target rate. Compared with the meters in several hardware switches, our meter improves the achieved rate of a TCP flow by almost 85% of the target rate.