RFC 3168 (rfc3168) - Page 1 of 63

The Addition of Explicit Congestion Notification (ECN) to IP

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