Effect of different marking strategies on explicit congestion notification (ECN) performance

The congestion control mechanisms built into the transmission control protocol (TCP) use packet drops as a means to detect congestion occurring in the network. Unnecessary packet drops lead to poor performance for low-bandwidth delay-sensitive applications. Explicit congestion notification (ECN) is proposed as a mechanism to provide feedback to the sources about impending congestion in the routers without the need to drop packets. This requires the ECN bit of the IP packet to be marked at the router based on mechanisms like random early detection (RED) to identify congestion. We examine three different marking strategies, viz., mark-tail, mark-front and mark-random. The throughput performance of ECN flows and the unfairness among the ECN flows are examined. We also study the interaction between ECN and non-ECN flows