A Mechanism for ECN Path Probing and Fallback
Mirja Kühlewind, Brian Trammell · 2013
Explicit Congestion Notification (ECN) is a TCP/IP extension that is widely implemented but hardly used due to the perceived unusablilty of ECN on many paths through the Internet caused by ECN-ignorant routers and middleboxes. This document specifies an ECN probing and fall-back mechanism in case ECN has be successfully negotiated between two connection endpoints, but might not be usable on the path.