Implementing Explicit Congestion Notification (ECN) in TCP for IPv6

This paper discusses our design and implementation of Explicit Congestion Notification (ECN) for TCP on IPv6. The first part of the paper describes how ECN marks packets instead of dropping them to signal incipient congestion. Marking packets instead of dropping them carries a number of benefits, such as avoiding costly delays waiting for retransmissions timeouts or dropping packets on flows sensitive to even a single packet loss. The next part of the paper then reviews what changes are required to routers and to hosts to implement an ECN scheme. Our specific implementation is described, including justifications for some of our design decisions. We then explain how we tested our implementation, evaluating both only the router’s behavior and the end-to-end performance of our system. Finally, we analyze our testing results and offer conclusions and other lessons learned from our research.