More Accurate ECN Feedback in TCP
draft-ietf-tcpm-accurate-ecn-03

Document Type Active Internet-Draft (tcpm WG)
Last updated 2017-05-30
Replaces draft-kuehlewind-tcpm-accurate-ecn
Stream IETF
Intended RFC status Experimental
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Stream WG state WG Document (wg milestone: Aug 2016 - Submit specification... )
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TCP Maintenance & Minor Extensions (tcpm)                     B. Briscoe
Internet-Draft                                Simula Research Laboratory
Intended status: Experimental                              M. Kuehlewind
Expires: December 1, 2017                                     ETH Zurich
                                                        R. Scheffenegger
                                                            May 30, 2017

                   More Accurate ECN Feedback in TCP
                    draft-ietf-tcpm-accurate-ecn-03

Abstract

   Explicit Congestion Notification (ECN) is a mechanism where network
   nodes can mark IP packets instead of dropping them to indicate
   incipient congestion to the end-points.  Receivers with an ECN-
   capable transport protocol feed back this information to the sender.
   ECN is specified for TCP in such a way that only one feedback signal
   can be transmitted per Round-Trip Time (RTT).  Recently, new TCP
   mechanisms like Congestion Exposure (ConEx) or Data Center TCP
   (DCTCP) need more accurate ECN feedback information whenever more
   than one marking is received in one RTT.  This document specifies an
   experimental scheme to provide more than one feedback signal per RTT
   in the TCP header.  Given TCP header space is scarce, it overloads
   the three existing ECN-related flags in the TCP header and provides
   additional information in a new TCP option.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 1, 2017.

Briscoe, et al.         Expires December 1, 2017                [Page 1]
Internet-Draft          Accurate TCP-ECN Feedback               May 2017

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Document Roadmap  . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Experiment Goals  . . . . . . . . . . . . . . . . . . . .   5
     1.4.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   6
     1.5.  Recap of Existing ECN feedback in IP/TCP  . . . . . . . .   6
   2.  AccECN Protocol Overview and Rationale  . . . . . . . . . . .   7
     2.1.  Capability Negotiation  . . . . . . . . . . . . . . . . .   8
     2.2.  Feedback Mechanism  . . . . . . . . . . . . . . . . . . .   9
     2.3.  Delayed ACKs and Resilience Against ACK Loss  . . . . . .   9
     2.4.  Feedback Metrics  . . . . . . . . . . . . . . . . . . . .  10
     2.5.  Generic (Dumb) Reflector  . . . . . . . . . . . . . . . .  10
   3.  AccECN Protocol Specification . . . . . . . . . . . . . . . .  11
     3.1.  Negotiating to use AccECN . . . . . . . . . . . . . . . .  11
       3.1.1.  Negotiation during the TCP handshake  . . . . . . . .  11
       3.1.2.  Retransmission of the SYN . . . . . . . . . . . . . .  14
     3.2.  AccECN Feedback . . . . . . . . . . . . . . . . . . . . .  15
       3.2.1.  The ACE Field . . . . . . . . . . . . . . . . . . . .  15
       3.2.2.  Testing for Zeroing of the ACE Field  . . . . . . . .  16
       3.2.3.  Safety against Ambiguity of the ACE Field . . . . . .  17
       3.2.4.  The AccECN Option . . . . . . . . . . . . . . . . . .  17
       3.2.5.  Path Traversal of the AccECN Option . . . . . . . . .  19
       3.2.6.  Usage of the AccECN TCP Option  . . . . . . . . . . .  22
     3.3.  AccECN Compliance by TCP Proxies, Offload Engines and
           other Middleboxes . . . . . . . . . . . . . . . . . . . .  23
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