Re: [RTG-DIR] [Detnet] Rtgdir last call review of draft-ietf-detnet-mpls-04

["Andrew G. Malis" <[e-mail]>]

I also agree with Carlos and Balázs regarding documenting the CW word
divergence from the SHOULD in RFC 4385. We've done that in the past, for
example with the ATM PW.

Cheers,
Andy


On Mon, Jan 27, 2020 at 1:22 PM Carlos Pignataro (cpignata) <
[e-mail]> wrote:

>
>
> > 2020/01/27 午前11:59、Lou Berger <[e-mail]>のメール:
> >
> > okay, will leave it -
>
> Sounds good —
>
> > but we generally don't provide the motivation for every tradeoff /
> design decision in IETF standards.
> >
>
> though this is not what was asked :-)
>
> RFC 4385 says:
>
>    To provide consistency between the
>    designs of different types of PW, it SHOULD also use the following
>    preferred format:
>
> So explaining why not following a SHOULD from the relevant PS seems
> appropriate.
>
> I agree, it would be counterproductive to provide the motivation for every
> tradeoff or design decision made. Please do not. The CW format, though, was
> asked a couple times.
>
> Carlos.
>
> > Lou
> >
> > On 1/27/2020 10:08 AM, Carlos Pignataro (cpignata) wrote:
> >> Hi, Lou,
> >>
> >>> 2020/01/27 午前9:41、Lou Berger <[e-mail]>のメール:
> >>>
> >>> Hi,
> >>>
> >>> Balázs thank you for the clarification -- see below for one comment.
> >>>
> >>> On 1/10/2020 8:56 AM, Balázs Varga A wrote:
> >>>> Yes, but why not the Preferred CW?
> >>>>
> >>>> <Balazs>/<Stewart> Sum of mailing + proposed fixing:
> >>>> The PCW only supports a 16bit sequence number and it has the skip
> zero auto-signaling of active S/N feature.
> >>>> This was a problem for DetNet because:
> >>>> - We were worried about S/N rollover frequency in some applications
> and so we wanted the option of a larger S/N.
> >>>> - We wanted to have the option to propagate the S/N from the payload
> to the transport to simplify the implementation
> >>>> in some cases. These applications have a non-skip zero S/N. Skip zero
> is an irritation to implement and we should probably
> >>>> have signaled in in PWs.
> >>>> As you note in is only a preferred design for PWs, DetNet is not
> constrained by that and there were good reasons to adopt
> >>>> this alternate approach.
> >>>> We assume to fix this with adding above information to the text.
> >>>> NEW text to be added in section 4.2.1:
> >>>>     "This format of the d-CW was created in order (1) to allow larger
> S/N space to
> >>>>     avoid S/N rollover frequency in some applications and (2) to
> allow non-skip
> >>>>     zero S/N what simplifies implementation."
> >>> While I completely agree with the rational and validity of the good
> question, I don't think such motivation belongs in the document.  We
> generally don't document every design decision in a specification.  I don't
> feel strongly about this so if others do, I'll defer to their opinion...
> >>>
> >>> Balázs, Carlos, Do you think it should stay?
> >>>
> >> I have no strong feelings either way, but I believe if this is a
> departure from a “preferred” format from a BCP, then a one-liner
> explanation would not hurt. I’d leave this one in.
> >>
> >> Thanks,
> >>
> >> Carlos.
> >>
> >>> Thanks,
> >>>
> >>> Lou (as contributor)
> >>>
>
>