Internet DRAFT - draft-grimes-tcpmwg-tcpsce
draft-grimes-tcpmwg-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.
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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
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Please review these documents carefully, as they describe your rights
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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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