RFC 3168 (rfc3168) - Page 1 of 63
The Addition of Explicit Congestion Notification (ECN) to IP
Alternative Format: Original Text Document
Network Working Group K. Ramakrishnan
Request for Comments: 3168 TeraOptic Networks
Updates: 2474, 2401, 793 S. Floyd
Obsoletes: 2481 ACIRI
Category: Standards Track D. Black
EMC
September 2001
The Addition of Explicit Congestion Notification (ECN) to IP
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
This memo specifies the incorporation of ECN (Explicit Congestion
Notification) to TCP and IP, including ECN's use of two bits in the
IP header.
Table of Contents
1. Introduction.................................................. 3
2. Conventions and Acronyms...................................... 5
3. Assumptions and General Principles............................ 5
4. Active Queue Management (AQM)................................. 6
5. Explicit Congestion Notification in IP........................ 6
5.1. ECN as an Indication of Persistent Congestion............... 10
5.2. Dropped or Corrupted Packets................................ 11
5.3. Fragmentation............................................... 11
6. Support from the Transport Protocol........................... 12
6.1. TCP......................................................... 13
6.1.1 TCP Initialization......................................... 14
6.1.1.1. Middlebox Issues........................................ 16
6.1.1.2. Robust TCP Initialization with an Echoed Reserved Field. 17
6.1.2. The TCP Sender............................................ 18
6.1.3. The TCP Receiver.......................................... 19
6.1.4. Congestion on the ACK-path................................ 20
6.1.5. Retransmitted TCP packets................................. 20
Ramakrishnan, et al. Standards Track