Re: [tcpm] Introduce RFC 6937 bis (Proportional Rate Reduction) as a tcpm work item? INPUT NEEDED

["Scharf, Michael" <[e-mail]>]

The TCPM charter would allow TCPM to specify a TCP mechanism including minor adaptations needed for QUIC. The TCPM charter explicitly states:

“TCP's congestion control algorithms are the model followed by
other IETF transports (e.g., SCTP or DCCP), which are standardized in
other working groups, such as the Transport Area WG (tsvwg). In the
past, the IETF has worked on several documents about algorithms that
are specified for multiple protocols (e.g., TCP and SCTP) in the
same document. Which WG shepherds such documents will be determined
on a case-by-case basis. In any case, the TCPM WG will remain in
close contact with other relevant WGs working on these protocols to
ensure openness and stringent review from all angles.”

(This was written before QUIC standardization started.)

Having one document for TCP and QUIC would thus be allowed by the TCPM charter. In that case, the document would probably be last called also in the QUIC working group – at least this is what we have done in similar cases with TSVWG in the past.

I think the formal details could be figured out if there is consensus to have one document only. It is up to the TCPM and QUIC community to decide…

Michael


From: tcpm <[e-mail]> On Behalf Of Ian Swett
Sent: Thursday, November 19, 2020 3:21 PM
To: Scheffenegger, Richard <[e-mail]>
Cc: [e-mail] Extensions <[e-mail]>
Subject: Re: [tcpm] Introduce RFC 6937 bis (Proportional Rate Reduction) as a tcpm work item? INPUT NEEDED

I support this work.

One question for authors and the group.  This specification could be applied to QUIC, but my memory is that there are some small changes to adapt it correctly.  Would noting those changes be in scope for this document, a separate document in QUIC, or an exercise left to the reader?  I'd be happy to contribute any QUIC specific text if that's helpful.

Thanks, Ian

On Thu, Nov 19, 2020 at 2:43 AM Scheffenegger, Richard <[e-mail]<mailto:[e-mail]>> wrote:
As the heuristic is the one major improvement over RFC6937, that is the
one area I am especially interested in. Currently working to have PRR in
FreeBSD, it would be the best time window to add this heuristig instead
of switching between the two variants in a static fashion.

I support this and will certainly be reviewing the documents and provide
feedback!

Richard


Am 19.11.2020 um 04:56 schrieb Matt Mathis:
> The authors of PRR would like to update PRR to Proposed Standard
> status.  This entails introducing a new document as an tcpm work item.
>
> *Please indicate (non) support and/or comment.*
>
> For more details see the tcpm meeting materials from IETF 109
> minutes:
> https://datatracker.ietf.org/meeting/109/materials/minutes-109-tcpm-00
> slides: https://tools.ietf.org/html/draft-mathis-tcpm-rfc6937bis-00
>
> There were about four "I support this work" remarks at the mic (not
> recorded in the minutes), and about as many in the Meetecho chat.
>
> Abridged IETF/tcpm/PRRbis slides:
> --
> PRR  recap (RFC6937 experimental)
> PRR is a special congestion control effective only during fast recovery
>
>   * When inflight >= ssthresh, send at loss_beta*rate_before_loss (e.g.
>     loss_beta = 0.5 for Reno (aka rate-halving), 0.7 for Cubic)
>   * When inflight < ssthresh, send at the same or twice the
>     delivery_rate (more later)
>   * Used by all congestion control modules in Linux during fast recovery
>       o Can be more dominant than the actual C.C. for lossy flows
>         that’re in fast recovery constantly (e.g. video streaming
>         through policers)
>
> --
> Current Status
>
>   *
>
>     PRR is widely deployed
>
>       o
>
>         At least three major OSs: Linux, Windows, (NetFlix) BSD
>
>       o
>
>         Vast majority of Web traffic for years
>
>   *
>
>     No changes to algorithms published in RFC 6937
>
>       o
>
>         PRR-CRB - Conservative Reduction Bound - strict packet
>         conversion during loss recovery
>
>       o
>
>         PRR-SSRB - Slowstart Reduction Bound - one extra segment per ACK
>         during loss recovery
>
>   *
>
>     2015 Heuristic to dynamically select which reduction bound
>
>       o
>
>         Only use PRR-SSRB when making good forward progress
>
>           +
>
>             ACKs that advanced snd.una and report no new losses
>
>       o
>
>         Resolves some pathological cases with token bucket policers
>
>           +
>
>             CC estimates ssthresh before it can possibly measure the
>             token rate
>
>           +
>
>             The heuristic makes the best of a bad situation
>
> --
> Tentative path forward
>
>   *
>
>     Adopt as a tcpm work item
>
>   *
>
>     Update the text
>
>       o
>
>         Normative RFC 2119 language
>
>       o
>
>         Add MAY use the heuristic...
>
>       o
>
>         Trim redundant and obsolete language
>
>           +
>
>             RFC 6937 repeats itself and is much longer than necessary
>
>           +
>
>             Focus on what an implementer needs to know
>
>           +
>
>             Use non-normative references to RFC 6937 for prior
>             measurement work, etc
>
> Thanks,
> --MM--
> The best way to predict the future is to create it.  - Alan Kay
>
> We must not tolerate intolerance;
>         however our response must be carefully measured:
>              too strong would be hypocritical and risks spiraling out of
> control;
>              too weak risks being mistaken for tacit approval.
>
> _______________________________________________
> tcpm mailing list
> [e-mail]<mailto:[e-mail]>
> https://www.ietf.org/mailman/listinfo/tcpm
>

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