RFC - 2481

A Proposal to add Explicit Congestion Notification (ECN) to IP

Original:	ftp://ftp.isi.edu/in-notes/rfc2481.txt
Authors:	K. Ramakrishnan [AT&T Labs Research], S. Floyd [LBNL]
Date:	January 1999
Category:	Informational
This specification has been !!! obsoleted !!!

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Obsoleted by:
RFC-3168prop	The Addition of Explicit Congestion Notification (ECN) to IP

Referred by:	23 RFC
Refers to:	12 RFC

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Status

This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

This note describes a proposed addition of ECN (Explicit Congestion Notification) to IP. TCP is currently the dominant transport protocol used in the Internet. We begin by describing TCP's use of packet drops as an indication of congestion. Next we argue that with the addition of active queue management (e.g., RED) to the Internet infrastructure, where routers detect congestion before the queue overflows, routers are no longer limited to packet drops as an indication of congestion. Routers could instead set a Congestion Experienced (CE) bit in the packet header of packets from ECN-capable transport protocols. We describe when the CE bit would be set in the routers, and describe what modifications would be needed to TCP to make it ECN-capable. Modifications to other transport protocols (e.g., unreliable unicast or multicast, reliable multicast, other reliable unicast transport protocols) could be considered as those protocols are developed and advance through the standards process.

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