TCP Alternative Backoff with ECN (ABE)
RFC 8511

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Internet Engineering Task Force (IETF)                        N. Khademi
Request for Comments: 8511                                      M. Welzl
Category: Experimental                                University of Oslo
ISSN: 2070-1721                                              G. Armitage
                                                                 Netflix
                                                            G. Fairhurst
                                                  University of Aberdeen
                                                           December 2018

                 TCP Alternative Backoff with ECN (ABE)

Abstract

   Active Queue Management (AQM) mechanisms allow for burst tolerance
   while enforcing short queues to minimise the time that packets spend
   enqueued at a bottleneck.  This can cause noticeable performance
   degradation for TCP connections traversing such a bottleneck,
   especially if there are only a few flows or their bandwidth-delay
   product (BDP) is large.  The reception of a Congestion Experienced
   (CE) Explicit Congestion Notification (ECN) mark indicates that an
   AQM mechanism is used at the bottleneck, and the bottleneck network
   queue is therefore likely to be short.  Feedback of this signal
   allows the TCP sender-side ECN reaction in congestion avoidance to
   reduce the Congestion Window (cwnd) by a smaller amount than the
   congestion control algorithm's reaction to inferred packet loss.
   Therefore, this specification defines an experimental change to the
   TCP reaction specified in RFC 3168, as permitted by RFC 8311.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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 candidates 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
   https://www.rfc-editor.org/info/rfc8511.

Khademi, et al.               Experimental                      [Page 1]
RFC 8511                           ABE                     December 2018

Copyright Notice

   Copyright (c) 2018 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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Choice of ABE Multiplier  . . . . . . . . . . . . . . . .   4
   4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Rationale for Using ECN to Vary the Degree of Backoff . .   6
     4.2.  An RTT-Based Response to Indicated Congestion . . . . . .   7
   5.  ABE Deployment Requirements . . . . . . . . . . . . . . . . .   7
   6.  ABE Experiment Goals  . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

Khademi, et al.               Experimental                      [Page 2]
RFC 8511                           ABE                     December 2018

1.  Introduction

   Explicit Congestion Notification (ECN) [RFC3168] makes it possible
   for an Active Queue Management (AQM) mechanism to signal the presence
   of incipient congestion without necessarily incurring packet loss.
   This lets the network deliver some packets to an application that
   would have been dropped if the application or transport did not
   support ECN.  This packet loss reduction is the most obvious benefit