[tcpm] [Errata Held for Document Update] RFC8257 (6697)

RFC Errata System <rfc-editor@rfc-editor.org> Fri, 13 May 2022 21:27 UTC

To: vidhi_goel@apple.com, sbens@microsoft.com, dthaler@microsoft.com, pravb@microsoft.com, lars@netapp.com, glenn.judd@morganstanley.com
From: RFC Errata System <rfc-editor@rfc-editor.org>
Cc: martin.h.duke@gmail.com, iesg@ietf.org, tcpm@ietf.org, rfc-editor@rfc-editor.org
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Date: Fri, 13 May 2022 14:27:18 -0700
Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/pxQzlcY1CRYiwSkF1F0uddegYd8>
Subject: [tcpm] [Errata Held for Document Update] RFC8257 (6697)
Precedence: list

The following errata report has been held for document update
for RFC8257, "Data Center TCP (DCTCP): TCP Congestion Control for Data Centers".

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You may review the report below and at:
https://www.rfc-editor.org/errata/eid6697

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Status: Held for Document Update
Type: Technical

Reported by: Vidhi Goel <vidhi_goel@apple.com>
Date Reported: 2021-09-28
Held by: Martin Duke (IESG)

Section: 3.3

Original Text
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The below pseudocode follows after DCTCP.Alpha is updated on ACK processing. This is wrong as cwnd should only be reduced using DCTCP.Alpha when ECE is received.

9. Rather than always halving the congestion window as described in
[RFC3168], the sender SHOULD update cwnd as follows:

cwnd = cwnd * (1 - DCTCP.Alpha / 2)

Corrected Text
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Instead, a new paragraph for Congestion Response to ECN feedback would be much clearer. First start with RFC 3168's response to ECE and then provide DCTCP's response to ECE.

I am thinking splitting section 3.3 into two sub-sections -
3.3.1 Computation of DCTCP.Alpha
3.3.2 Congestion Response to ECE at sender

Notes
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Although RFC 8257 refers to RFC 3168 congestion window halving at step 9, but it is confusing to put it right after step 8.

Literally interpreted, a window with no congestion marks would reduce the cwnd, which is wrong.

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RFC8257 (draft-ietf-tcpm-dctcp-10)
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Title : Data Center TCP (DCTCP): TCP Congestion Control for Data Centers
Publication Date : October 2017
Author(s) : S. Bensley, D. Thaler, P. Balasubramanian, L. Eggert, G. Judd
Category : INFORMATIONAL
Source : TCP Maintenance and Minor Extensions
Area : Transport
Stream : IETF
Verifying Party : IESG

[tcpm] [Errata Held for Document Update] RFC8257 … RFC Errata System