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A Proposal to add Explicit Congestion Notification (ECN) to IP (RFC2481)

IP.com Disclosure Number: IPCOM000003061D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 20 page(s) / 60K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

K. Ramakrishnan: AUTHOR [+2]

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.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 5% of the total text.

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].

2. Introduction

TCP's congestion control and avoidance algorithms are based on the

notion that the network is a black-box [Jacobson88, Jacobson90]. The

network's state of congestion or otherwise is determined by end-

systems probing for the network state, by gradually increasing the

load on the network (by increasing the window of packets that are

outstanding in the network) until the network becomes congested and a

packet is lost. Treating the network as a "black-box" and treating

loss as an indication of congestion in the network is appropriate for

pure best-effort data carried by TCP which has little or no

...