Subject: Concerns about exported numbers 12/2 12/26/95 12:00:16

From: "Roch Guerin ((914) 784-7038)" <[email-masked]>
Date: Tue, 26 Dec 95 18:03:32 EST

Reference:  Your note of Tue, 26 Dec 95 12:00:16 PST

Yakov,

Far from me to claim that RC 20250 spells out *in details* how to obtain
these numbers in all configurations, but I believe it takes a decent
crack at spelling one way of getting them in the ATM case.  Now, I'll
certainly grant you that it will be harder to get such numbers from
E/N switches, but then I'm not sure what kind of "guarantees", if any,
you can get from such switches.  It's not even clear you can get the
kind of bandwidth guarantee that Fred was talking about.  In general,
things will very much depend on the kind of QoS support, if any at all,
each vendor will put in, but even then I'm not sure how to really
externalizes that in a standard way for E/N switches.  In the context
of T/R switches, you could take advantage of built-in priority support
as a mechanism to provide some form of guarantees and your question may
make more sense in that environment.  It may still be tricky to provide
any real hard guarantees even then, but I haven't really thought about
it.  With FDDI, which is another environment that may be worth
considering, it's probably easier to figure out the numbers because of
the built in support for isochronous traffic.

This being said, it's also true that the type of guarantees specified in
the Guaranteed Service specs are not necessarily appropriate for all
applications (I know you and many other people, would probably use even
stronger words than that), but that's why we have the controlled load
specs.  In the case of applications whose QoS requirements may warrant
the kind of guarantees that the Guaranteed Service provides, then I'll
argue that it may be more likely that the devices/hosts they'll run on
will be attached to local networks which have some level of native
QoS support, i.e., ATM campus switches.  In that case and assuming we
have support in the routers, we should be able to accumulate the
necessary information end-to-end.

I'm clearly not claiming that Guaranteed Service will be available
everywhere on day one, but its specifications are not inconsistent
with the capabilities of most of the platforms and technologies that
consider providing some form of QoS support.  On the other hand, it is
also clear that it should not be the only spec for providing some
level of QoS guarantees, but I think that is well understood and
agreed upon.

Roch
*************** Referenced Note ***************
To: "Roch Guerin ((914) 784-7038)" <[email-masked]>
cc: [email-masked], [email-masked], [email-masked],
        [email-masked], [email-masked], [email-masked],
        [email-masked]
Subject: Re: Concerns about exported numbers 12/22/95 13:14:20
Date: Tue, 26 Dec 95 12:00:16 PST
From: Yakov Rekhter <yakov at cisco.com>

Roch,

> Some of that stuff is discussed in the other Research report I mentioned
> in my previous note (RC 20250), but the jist of it is that you do need
> some form of numbers from the switches/clouds that do not run RSVP natively,
> and typically it will be available in the form of a D term only.

It is one thing to say that "you do need some form of numbers from the
switches/clouds". But to make this practical one also has to spell out
*in details* how these numbers could be obtained. And as Fred pointed
out, ATM is not the only technology that could pose a problem for getting
these numbers. For example, how would you propose to get these numbers
in the presence of Ethernet switches ?

Yakov.

---

From: Yakov Rekhter <[email-masked]>
Date: Thu, 28 Dec 95 11:44:32 PST

Roch,

> the built in support for isochronous traffic.

Let me see if I can summarize the above.

1. Supporting Guaranteed Delay in the presence of Ethernet switches
is highly problematic

2. Supporting Guaranteed Delay in the presence of Token Ring switches
is problematic (but more thoughts required)

3. Supporting Guaranteed Delay in the presence of FDDI switches may
be less problematic than with Ethernet or Token Ring, but further
investigation is needed

4. Supporting Guaranteed Delay in the presence of ATM switches seems
feasible.

Would you agree with this summary ?

Yakov.