Re: [tsvwg] Review comments on a careful read of the L4S ID (#8. DCTCP)

[Bob Briscoe <[e-mail]>]

Gorry,

Please advise whether the following edits address this concern.

See [BB]

On 06/05/2021 07:52, Gorry Fairhurst wrote:
>
> =================================================================
> *8. Please be clear throughout that the IETF is NOT endorsing DCTCP 
> spec. as an Internet Protocol, even if the underlying basis is 
> important to the L4S transport.*
>
> This text:
> “An example of a scalable congestion control that would enable the L4S
> service is Data Center TCP (DCTCP), _which until now has been_
> applicable solely to controlled environments like data centres
> [RFC8257], because it is too aggressive to co-exist with existing
> TCP-Reno-friendly traffic. “

[BB] PROPOSED:

   L4S relies on 'scalable' congestion controls for these delay
    properties and for preserving low delay as flow rate scales, hence
    the name.  The congestion control used in Data Center TCP (DCTCP) is
    an example of a scalable congestion control, but DCTCP is applicable
    solely to controlled environments like data centres [RFC8257],
    because it is too aggressive to co-exist with existing TCP-Reno-
    friendly traffic.



> and later:
> “Note that a transport such as DCTCP is
> still not safe to deploy on the Internet _unless it satisfies the_
> _requirements listed in Section _4.”

[BB] PROPOSED:

    Note that a scalable congestion
    control is still not safe to deploy on the Internet unless it
    satisfies the requirements listed in Section 4.

> and later still:
> “cause Classic ECN
> congestion controls sharing the same queue to starve themselves,
> which is why they have been confined to private data centres or
> research testbeds_(until now)_.”

[BB] PROPOSED:

    outcompete Classic ECN congestion controls
    sharing the same queue, which is why they have been confined to
    private data centres or research testbeds.


> and
> “It turns out that a congestion control algorithm like DCTCP that
> _solves_ the latency problem also _solves_ the scalability problem of
> Classic congestion controls.”

[BB] PROPOSED:

    It turns out that these scalable congestion control algorithms that
    solve the latency problem also solve the scalability problem of
    Classic congestion controls.


> and
> “The L4S service is
> for more general traffic _than just_ DCTCP--“

[BB] Substituted 'TCP Prague'

> The ID later states:
> “As with all transport behaviours, a detailed specification 
> (probablyan experimental RFC) will need to be defined for each congestion
> control, following the guidelines for specifying new congestion
> control algorithms in [RFC5033].”

[BB] Incidentally, as part of other changes requested by implementers 
during the survey, we've changed the following:
s/will need to be defined/is preferable/

> and Annexe A appears to confirm this.
>
> ⁃This would be significantly improved by replacing references to DCTCP 
> as a protocol with references to the congestion control 
> method/algorithm used by DCTCP: RFC8257 is informational and 
> explicitly explained it is not EXP.To me this text in the ID provides 
> many contradictions about implying DCTCP as a transport for the 
> Internet. That’s something that really grates with me and I much 
> prefer the much later statement in the IDthat “a detailed 
> specification (probablyan experimental RFC) will need to be defined”. 
> If the claim were different, relating to methods based on DCTCP, that 
> might be more acceptable.
>
> Making this a reference DCTCP as a CC method would be good to address 
> my issue.
>
> =================================================================
>

[BB] I certainly sympathize with GF's concerns about causing confusion 
on the status of DCTCP. I thought I'd done well on this, but I can see 
now the concerns that Gorry raises. I hope the above changes are acceptable.

Proposed resolution: See instances above.



Bob

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/