Subject: Re: re-chartering L2TP

From: James Carlson <[email-masked]>
Date: Thu, 18 Jan 2001 12:43:42 -0500 (EST)

Danny McPherson writes:
> > MPLS runs over many things, including PPP.  If the circuit emulation
> > protocols are written to run over MPLS, then nothing special needs to
> > be done for L2TP, because CES/MPLS/PPP/L2TP will work.  Again, one
> > mechanism and one specification are better than many.
> 
> One small observation -- this requires that MPLS be 
> deployed ubiquitously throughout the *Internet* (read:
> inter-provider as well).  I assure you, it won't be
> any time soon.  

No, it doesn't necessarily require that at all.  It may require some
mechanisms for tunneling over the non-MPLS portions of the path.  Such
as, for instance, MPLS/PPP/L2TP.  But, then again, it may not.

Who is currently buying CES that crosses provider boundaries?  Why
would we think it's so much more likely to occur with CES over (pick
an IETF protocol)?

I think operational considerations -- such as being able to hold a
single provider to a contracted set of performance parameters -- will
be likely to trump any "ubiquity" argument.  (Besides, the point here
is to displace equipment that happens to carry legacy CES services,
*not* to invent new reasons and ways to carry CES.)

In all of the cases that I know of where real CES is used -- AAL-1
with fancy clock adjustment deltas to carry async timing across the
network -- it's a kludge (such as voice over TDM rather than voice
over IP) that may well disappear in the future.  Finding extended uses
for it seems like a poor optimization.  (Note that frames != circuits,
and tunneling AAL-5 or Frame Relay may be another matter entirely,
although the contractual issues are likely similar.)

> Folks that I see supporting IP-based CES (e.g., ATM, FR & 
> even TDM) can [typically] easily support MPLS-based models.  
> However, folks don't necessarily want solutions that require
> MPLS today.

Can you flesh out the service model that has interprovider CES over IP
as an integral component?  Frankly, I can't say that I've talked to
any carrier that was interested in anything like that, and it's a
little surprising to hear it as a fundamental requirement.  Perhaps I
wasn't paying enough attention during one of those presentations (or
perhaps the answer is proprietary), but I'd still like to know.

-- 
James Carlson, Internet Engineering       <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757   42.497N   Fax +1 781 442 1677
Second Edition now available - http://people.ne.mediaone.net/carlson/ppp

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From: Danny McPherson <[email-masked]>
Date: Thu, 18 Jan 2001 10:02:21 -0700

-danny