The Benefits of Using Explicit Congestion Notification (ECN)
RFC 8087

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Internet Engineering Task Force (IETF)                      G. Fairhurst
Request for Comments: 8087                        University of Aberdeen
Category: Informational                                         M. Welzl
ISSN: 2070-1721                                       University of Oslo
                                                              March 2017

      The Benefits of Using Explicit Congestion Notification (ECN)

Abstract

   The goal of this document is to describe the potential benefits of
   applications using a transport that enables Explicit Congestion
   Notification (ECN).  The document outlines the principal gains in
   terms of increased throughput, reduced delay, and other benefits when
   ECN is used over a network path that includes equipment that supports
   Congestion Experienced (CE) marking.  It also discusses challenges
   for successful deployment of ECN.  It does not propose new algorithms
   to use ECN nor does it describe the details of implementation of ECN
   in endpoint devices (Internet hosts), routers, or other network
   devices.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8087.

Fairhurst & Welzl             Informational                     [Page 1]
RFC 8087                     Benefits of ECN                  March 2017

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Benefit of Using ECN to Avoid Congestion Loss . . . . . . . .   5
     2.1.  Improved Throughput . . . . . . . . . . . . . . . . . . .   5
     2.2.  Reduced Head-of-Line Blocking . . . . . . . . . . . . . .   6
     2.3.  Reduced Probability of RTO Expiry . . . . . . . . . . . .   6
     2.4.  Applications That Do Not Retransmit Lost Packets  . . . .   7
     2.5.  Making Incipient Congestion Visible . . . . . . . . . . .   8
     2.6.  Opportunities for New Transport Mechanisms  . . . . . . .   8
   3.  Network Support for ECN . . . . . . . . . . . . . . . . . . .   9
     3.1.  The ECN Field . . . . . . . . . . . . . . . . . . . . . .  10
     3.2.  Forwarding ECN-Capable IP Packets . . . . . . . . . . . .  10
     3.3.  Enabling ECN in Network Devices . . . . . . . . . . . . .  11
     3.4.  Coexistence of ECN and Non-ECN Flows  . . . . . . . . . .  11
     3.5.  Bleaching and Middlebox Requirements to Deploy ECN  . . .  11
     3.6.  Tunneling ECN and the Use of ECN by Lower-Layer Networks   12
   4.  Using ECN across the Internet . . . . . . . . . . . . . . . .  12
     4.1.  Partial Deployment  . . . . . . . . . . . . . . . . . . .  13
     4.2.  Detecting Whether a Path Really Supports ECN  . . . . . .  13
     4.3.  Detecting ECN-Receiver Feedback Cheating  . . . . . . . .  14
   5.  Summary: Enabling ECN in Network Devices and Hosts  . . . . .  14
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

Fairhurst & Welzl             Informational                     [Page 2]
RFC 8087                     Benefits of ECN                  March 2017

1.  Introduction

   Internet transports (such as TCP and Stream Control Transmission
   Protocol (SCTP)) are implemented in endpoints (Internet hosts) and
   are designed to detect and react to network congestion.  Congestion