RFC 2481 (rfc2481) - Page 1 of 25
A Proposal to add Explicit Congestion Notification (ECN) to IP
Alternative Format: Original Text Document
Network Working Group K. Ramakrishnan
Request for Comments: 2481 AT&T Labs Research
Category: Experimental S. Floyd
LBNL
January 1999
A Proposal to add Explicit Congestion Notification (ECN) to IP
Status of this Memo
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.
1. Conventions and Acronyms
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [B97].
Ramakrishnan & Floyd Experimental