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Versions: 00 draft-grimes-tcpm-tcpsce

TCP Maintenance and Minor Extensions                         R.W. Grimes
Internet-Draft                                                  P. Heist
Intended status: Standards Track                             8 July 2019
Expires: 9 January 2020


                   Some Congestion Experienced in TCP
                     draft-grimes-tcpmwg-tcpsce-00

Abstract

   This memo classifies a TCP code point ESCE ("Echo Some Congestion
   Experienced") for use in feedback of IP code point SCE ("Some
   Congestion Experienced").

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 9 January 2020.

Copyright Notice

   Copyright (c) 2019 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 (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.






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Table of Contents

   1.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  TCP Receiver  . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Single ACK implementation . . . . . . . . . . . . . . . .   3
     4.2.  Simple Delayed ACK implementation . . . . . . . . . . . .   3
     4.3.  Dithered Delayed ACK implementation . . . . . . . . . . .   3
   5.  TCP Sender  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Related Work  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   4
   11. Informative References  . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] and [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Introduction

   This memo reclassifies the former TCP NS ("Nonce Sum") codepoint as
   ESCE.

   This memo limits its scope to the redefinition of the TCP NS
   codepoint as ESCE, with a few brief illustrations of how it may be
   used.

   SCE provides early and proportional feedback to the CC (congestion
   control) algorithms for transport protocols, including but not
   limited to TCP.  The [sce-repo] is a Linux kernel modified to support
   SCE, including:

   *  Enhancements to Linux's Cake (Common Applications Kept Enhanced)
      AQM to support SCE signaling

   *  Modifications to the TCP receive path to reflect SCE signals back
      to the sender

   *  The addition of three new TCP CC algorithms that modify the




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      originals to add SCE support: Reno-SCE, DCTCP-SCE and Cubic-SCE
      (work in progress as of this writing)

3.  Background

   [I-D.morton-tsvwg-sce] defines the SCE codepoint and [RFC8311]
   (section 3) obsoletes the NS codepoint making it avaliable valiable
   for use.

4.  TCP Receiver

   The mechanism defined to feed back SCE signals to the sender
   explicitly makes use of the ESCE ("Echo Some Congestion Experienced")
   code point in the TCP header.

4.1.  Single ACK implementation

   Upon receipt of a packet an ACK is immediatly generated, the SCE
   codepoint is copied into the ESCE codepoint of the ACK.  This keeps
   the count of bytes SCE marked or not marked properly reflected in the
   ACK packet(s).  This valid implementation has the downside of
   increasing ACK traffic.  This implementation is NOT RECOMMENDED, but
   useful for experimental work.

4.2.  Simple Delayed ACK implementation

   Upon receipt of a packet without an SCE codepoint traditional delayed
   ACK processing is performed.  Upon receipt of a packet with an SCE
   codepoint immediate ACK processing SHOULD be done, this allows some
   delaying of ACK's, but creates earlier feedback of the congested
   state.  This has the negative effect of over signalling ESCE.

4.3.  Dithered Delayed ACK implementation

   Upon receipt of a packet the SCE codepoint is stored in the TCP
   state.  Multiple packets state may be stored.  Upon generation of an
   ACK, normal or delayed, the stored SCE state is used to set the state
   of ESCE.  If no SCE state is in the TCP state, then the ESCE code
   point MUST NOT be set.  If all of the packets to be ACKed have SCE
   state set then the ESCE code point MUST be set in the ACK.  If some
   of the packets to be ACKed have SCE state set then some proportional
   number of ACK packets SHOULD be sent with the ESCE code point set.
   The goal is to have the same number of bytes marked with ESCE as
   arrived with SCE.







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5.  TCP Sender

   The recommended response to each single segment marked with ESCE is
   to reduce cwnd by an amortised 1/sqrt(cwnd) segments.  Other
   responses, such as the 1/cwnd from DCTCP, are also acceptable but may
   perform less well.

   This is still an area of continued investigation.

6.  Related Work

   TBD

7.  IANA Considerations

   There are no IANA considerations.

8.  Security Considerations

   There are no Security considerations.

9.  Acknowledgements

   TBD

10.  Normative References

   [I-D.morton-tsvwg-sce]
              Morton, J. and R. Grimes, "The Some Congestion Experienced
              ECN Codepoint", draft-morton-tsvwg-sce-00 (work in
              progress), 2 July 2019,
              <https://www.ietf.org/archive/id/draft-morton-tsvwg-sce-
              00>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8311]  Black, D., "Relaxing Restrictions on Explicit Congestion
              Notification (ECN) Experimentation", RFC 8311,
              DOI 10.17487/RFC8311, January 2018,
              <https://www.rfc-editor.org/info/rfc8311>.




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11.  Informative References

   [sce-repo] "Some Congestion Experienced Reference Implementation
              GitHub Repository", July 2019,
              <https://github.com/chromi/sce/>.

Authors' Addresses

   Rodney W. Grimes
   Redacted
   Portland, OR 97217
   United States

   Email: rgrimes@freebsd.org


   Peter G. Heist
   Redacted
   463 11 Liberec 30
   Czech Republic

   Email: pete@heistp.net





























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