From: grima@iphase.com (Gary Rima)
Subject: Re: CDDI interoperability status
Organization: Interphase Corporation, Dallas Texas
Date: Tue, 12 Jan 1993 20:59:16 GMT

In article <up79aqc@sgi.sgi.com> rpw3@rigden.wpd.sgi.com (Rob Warnock) writes:
>vhalkka@klaava.Helsinki.FI (Vesa Halkka) writes:
>+---------------
>| Quite many vendors are selling CDDI stuff, and there is a standard, but
>+---------------
>
>But the standard isn't completely settled yet.
>

How true, unfortunately!

>
>vjs@rhyolite.wpd.sgi.com (Vernon Schryver) writes:
>+---------------
>| For now, given that few others besides Crescendo are building CDDI
>| concentrators, it seems likely that CDDI interoperability is not a problem.
>+---------------
>
>Well, there's what Crescendo has *now* [same as what we were showing at
>Interop in Fall '92], and what the X3T9.5 standards committee is going
>to agree on. Already there have been changes. The "scrambler" coding
>recently agreed on by the committee is incompatible with the existing
>Crescendo implementation [which caused a lot of semiconductor manufacturers
>to have to re-spin their chips]; the final standards for "equalization"
>(filtering), wiring, and connectors have yet to be settled.
>
>Since some people seem to be deploying the existing Crescendo stuff, I expect
>that we'll end up with at least two versions: the existing Crescendo stuff
>and the "ANSI Standard" version. Fortunately, since most uses of CDDI are
>for SAS configurations (i.e., station to concentrator), you should be able
>to intermix the two in the same ring (possibly even in the same concentrator,
>if Crescendo makes their CDDI modules pluggable).
>
	Unfortunately, its a bit more complicated than that.  What Crescendo
"has" now and showed at fall Interop is NOT what they've been widely shipping
under the CDDI banner!  What has been shipping is actually NRZI, and therefore
is totally different than the MLT-3 based system which will ultimately come
out of ANSI.  So there's much more involved than just the scrambler.  Now, that
doesn't mean that what's been shipped can't still be upgraded to ANSI standard
at some point in time - I believe Crescendo does promise that.  What we've seen
in the field doesn't appear to be "field (plug)" replaceable, though, so
adapters and concentrators may need to be returned to Crescendo for the upgrade.

	Also, note that although Crescendo has trademarked the term "CDDI" to
refer to its product, others are using the term in data sheets to refer to
products which do NOT interoperate with Crescendo (either NRZI or MLT-3!).  So
it's buyer beware at this point.

	The one copper solution which is available today with interoperability
among multiple vendors is the "SDDI" shielded twisted pair implementation.
There are at least 12-15 vendors offering compatible SDDI using off-the-shelf
commercial parts from Technitrol and others.  Interphase has chosen to support
SDDI to offer customers an interoperable solution in advance of the final ANSI
standard.  We will be offering an upgrade from SDDI to ANSI UTP similar to the
Crescendo approach from their proprietary offerings to ANSI.

	Caveat:  As an employee of a major industry FDDI supplier, I don't claim
to be totally unbiased about this topic.  The above comments should be
considered in that light.

Regards,

-Gary-

-- 
Gary L. Rima						Interphase Corp.
PP-ASEL-IA						(214) 919-9226
Centurion N7358E					garyr@iphase.com
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Newsgroups: comp.dcom.lans.fddi