Subject: Re: TCP versus real-time apps in an int-serv internet

From: [email-masked] (Fred Baker)
Date: Thu, 10 Nov 1994 11:01:09 -0800

At 6:51 PM 11/9/94, Curtis Villamizar wrote:
>The two acceptable minimalist approaches for real-time are:
>  1) FIFO queue with RSVP queued ahead of elastic --or--
>  2) have enough bandwidth that it doesn't matter
>If you don't do at least one of the two, RSVP (real time) won't work well.

It seems to me that there is a little more to think about here. Among
predictive flows, not all have the same deadline pressure, but all can
generate traffic in a bursty fashion. It seems that you want to use a fair
queuing algorithm among the predictive flows much as you want to among the
elastic flows.

*and*, you want to guarantee that if the predictive flows go berserk, the
elastic traffic will still get some percentage of its traffic through.
Reserved traffic is only protected up to the amount it reserves.

Which leads m to wonder whether what you really want is a WFQ algorithm
which scales traffic schedules for elastic and guaranteed real time
traffic, and which uses the same queuing algorithm with a different
weighting algorithm for predictive traffic. The two would use the same
queue, and by vagaries of weighting puts real time traffic near the head of
the queue.

I've been told I'm all wet before, feel free to dump on me. What am I
missing here?

=============================================================================
        If you're not living on the edge, you're taking up too much room!

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From: Curtis Villamizar <[email-masked]>
Date: Thu, 10 Nov 1994 15:25:49 -0500

> queuing algorithm among the predictive flows much as you want to among the

I fully agree.  I did say minimalist.  I would not expect the WG ot
stop at the bare minimum.

> Reserved traffic is only protected up to the amount it reserves.

I did mention advisory policing (Van will say nasty things about you
when you trash the mbone :) is the current norm and could be
considered rock bottom minimal, but queueing enforced policing of
reserved traffic would better insure elastic didn't get trashed.

> queue, and by vagaries of weighting puts real time traffic near the head of

You are pondering a solution here.  Which is good.  What the WG needs
is to state the requirements we are trying to meet, provide some means
to quantify how well the requirements are met, and probably also
provide an existance proof, that demonstrates that the requirements
can be met with a scalable algorithm.  The existance proof is not part
of the requirements.

> I've been told I'm all wet before, feel free to dump on me. What am I

I just agreed with everything you said.  I hope we are making sense to
others on this list.

Curtis