Robust Congestion Signaling

David Ely, Neil Spring, David Wetherall, Stefan Savage, and Tom Anderson.   Robust Congestion Signaling. Proc. of the Ninth International Conference on Network Protocols, November 2001, pages 332 - 341.


We present an improved Explicit Congestion Notification (ECN) mechanism that enables a router to signal congestion to the sender without trusting the receiver or other network devices along the signaling path.  Without our mechanism, ECN-based transports can be manipulated to undermine congestion control.  Web clients seeking faster downloads, for example, can trivially conceal congestion signals from Web servers.  A misbehaving connection would exceed its fair bandwidth share at the expense of competing traffic by as much as an order of magnitude in our simulations.  Our improved mechanism is robust because it does not depend on correct implementations at locations other than the sender and marking router, and it is practical because it admits an efficient implementation that is backward-compatible with prior ECN and TCP/IP mechanisms.