Subject: Re: [Diffserv] doubts on draft-ietf-differv-model-06.txt

From: Dan Grossman <[email-masked]>
Date: Tue, 04 Sep 2001 15:06:34 -0400

> 
> > I haven't seen any response to these questions. I'd like to see
> > a response from the authors ASAP so that we are sure we can
> > issue a Last Call at the same time as the MIB.
> 
> > Ashley Shi wrote:
> > >
> > > Can any author clarify the following questions for Appendix A?
> > >
> > > 1) Is the token interval used the same as the token update interval? If
> > > yes, its definition in informal model is not consistent with most
> > > implementations. The token update interval is a preconfigured value for
> > > token bucket meter, which is not directly correlated with B/R, for
> > > example, a implementation may use 2000 updates per sec, anther one may
> > > use 4000 updates per sec.
> 
> This is Fred Baker's text, I believe.  He and I apparently have divergent
> ideas about how token buckets ought to behave, so I don't want to claim
> to speak authoritatively about this part of the text, but I believe that
> the text assumes that the "token interval" == actual token update interval.
> 
> The model you have in mind is more consistent with the model in A.4,
> I think.
> 
> > > 2) The description for strict token bucket on page 50 doesn't match the
> > > mathematical model in A.4.
> > >    The description implies when new tokens to the bucket, the upper
> > > bound B deesn''t hold.
> > >    The mathematical model does bound the number of tokens in the bucket
> > > by bucket size B.
> 
> I believe that you are correct.  I know of at least four implementations
> that behave as described in A.4; I have no doubt that there are
> counterexamples that behave as described in A.2.  The discrepancy has to
> do with how frequently one thinks that tokens are replenished.  A.4 assumes
> that this happens with a granularity that depends on precision with
> which time intervals are calculated.
> 
> I don't know how to reconcile the two models, other than by calling
> A.4 the really really strict token bucket.
> 
> 
> Regards,
> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Steven L. Blake               <[email-masked]>
I'll agree with Steve.  Perhaps Fred can clarify.

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From: Brian E Carpenter <[email-masked]>
Date: Tue, 04 Sep 2001 14:57:07 -0500

At this stage, we need precise proposed change(s) to the text,
or nothing will happen.

   Brian

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From: Fred Baker <[email-masked]>
Date: Tue, 04 Sep 2001 13:26:03 -0700

At 12:06 PM 9/4/2001, Dan Grossman wrote:
>Perhaps Fred can clarify.

there is an extensive discussion in the archives, as well as in your and my 
private mailboxes.

Since the model is now largely irrelevant (it describes *a* way diffserv 
might be implemented, but is mostly OBE, and goes way too far into 
designing a router to be even remotely considered to be the One True Way 
That All Of Us Will Rip Out Our Existing Code And Hardware And Re-implement 
It), I'm personally willing to see the text you're concerned about removed.

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From: Dan Grossman <[email-masked]>
Date: Tue, 04 Sep 2001 17:12:38 -0400

> It), I'm personally willing to see the text you're concerned about removed.
I'm going to have to apolgise here.  My last note was a shoot-from-the-hip 
response, out of context of some subsequent emails.  I was simply wondering 
whether there's a simple clarification to the original question, not to 
relaunch a past battle.  Frankly, I haven't had much time to think about it.

---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 04 Sep 2001 16:05:52 -0500

Fred raises an interesting thought. The informal model has, I think, been
quite useful in developing the MIB and PIB, but it was never intended
to describe any real implementation, and the MIB and PIB are the
standards-track items. There will be a WG Last Call fairly soon for
the MIB, PIB, and model - unless people think that the model is indeed
OBE and should be retired with honour rather than becoming an RFC.
Opinions welcome.

   Brian

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From: Brian E Carpenter <[email-masked]>
Date: Tue, 04 Sep 2001 17:04:23 -0500

Answering my own thought... the PIB at least contains many, many
(non-normative) references to the model draft. It would be a lot
of work to remove them.

Since the model says it "is not intended as a
guide to system implementation nor as a formal modelling description,"
I believe we do not need to insist on every detail, and I don't personally
see a problem with the way Appendix A is now, but if Fred can tell us
exactly what to delete, we can certainly do so.

   Brian

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From: Fred Baker <[email-masked]>
Date: Tue, 04 Sep 2001 22:33:32 -0700

At 03:04 PM 9/4/2001, Brian E Carpenter wrote:
>I don't personally see a problem with the way Appendix A is now, but if 
>Fred can tell us

basically, I'm saying that if the text I contributed is causing a problem 
(Appendix A), rip it out. If it's not, leave it in.

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From: "Andrew Smith" <[email-masked]>
Date: Tue, 4 Sep 2001 23:31:30 -0700

Glad to hear that Fred is nominating the Model draft for a long-overdue New
Year's honour (for long and arduous public service, I assume, not because it
is a famous sporting personality).

I think people should try reading the title of the Model draft as well as
reading its abstract: it's a model for thinking about management of Diffserv
devices, it is not an implementation model. I don't know why some of you are
still confused about that. If there is material in the draft that goes
beyond the advertised scope then that should be pruned. If there are areas
that are not covered then there should be material added (within the
boundaries of time schedules and rough consensus of course). But, Fred,
please don't misrepresent the intended purpose and exaggerate in such a
manner.

[In case you're wondering, that was an opinion in favour of keeping the
draft on track for publication as an informational RFC, sanctioned by this
WG, if not by Fred].

Andrew Smith

-----Original Message-----
From: Brian E Carpenter [mailto:[email-masked]]
Sent: Tuesday, September 04, 2001 2:06 PM
To: Fred Baker
Cc: Dan Grossman; Steve Blake; [email-masked]; [email-masked]
Subject: Re: [Diffserv] doubts on draft-ietf-differv-model-06.txt

   Brian