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From: pat@hprnd.HP.COM (Pat Thaler)
Newsgroups: comp.dcom.lans
Subject: Re: Starlan/Ethernet compatibility
Message-ID: <2230006@hprnd.HP.COM>
Date: 16 Jun 89 20:06:46 GMT
References: <2009@wasatch.utah.edu>
Organization: HP Roseville Networks Division
Lines: 72

Bob Morgan writes: 
> 
> Here's a quote from the front page of the 10BASE-T draft dated April
> 7, 1989:
> 
> > This is an unappproved draft which is subject to change and cannot be
> > presumed to reflect the position of Project 802 or the IEEE, Inc.
> > DO NOT SPECIFY OR CLAIM CONFORMANCE TO THIS DOCUMENT.
> 
> To paraphrase Gene Shue, the standard ain't a standard 'til the fat
> lady sings.  If you think you're buying conforming equipment before
> the standard is approved, you're only fooling yourself.
> 
>  - RL "Bob" Morgan
>    Networking Systems
>    Stanford
> ----------

This is something that all purchasers should know.  Vendors and the 
press tend to use the words "conformant" and "compliant" very loosely.
Any draft standard is a moving target and not a good measure of 
compliance.  In buying product now, the important question to ask
the vendor is "How will you support migration to 10BASE-T when the
standard is completed?"

As Mark Darby points out, 10BASE-T is a definition of a new 
MAU/transciever (802.3/Ethernet terminology).  As such, the interface
between the MAU/transceiver and the DTE/station is the AUI.  This
interface is already defined in 802.3 section 7.  Since the interface
is already defined, there should be no interoperation problems 
between well designed pre-standard 10BASE-T-like products and
existing DTEs or repeater.

The 10BASE-T draft defines the interface between the MAUs and 
the behavior of the MAUs.  That interface is where the questions
of interoperability between pre-standard products and 10BASE-T
products arise.  Mark Darby's comments on link test and the 
current status of 10BASE-T draft are accurate.

10BASE-T MAUs support a point-to-point links which are usually
connected together through multi-port repeaters (see section 9
in the 802.3 Supplement, not the original section 9).  If one only
needs to support two stations, two MAUs could be connected with
no repeater.  Make sure the receive pair of one MAU goes to the 
transmit connection of the other.

Because 10BASE-T uses repeaters as the hub of the star, you can
use a coax or fiber-optic backbone to join the stars togeather.
10BASE-T segments can be added to existing networks.  This is
also true for pre-standard products which use repeaters as hubs.  

Products designed to support 100 m of cable reliably will often 
support longer distances if you try one instance.  After all when 
we do the designs we have to allow for variations in MAU components 
and cables.  The problems are: 

  If you install it that way 100 times it may work 9 out of 10.

  It may work fine some days and not others.  Temperature variations
  and noise variations may degrade performance.  Degraded performance
  includes high bit error rate or not working at all.

There are lower attenuation twisted pair cables available if you
want to support more than 100 m.  Or you can put in a repeater.
Or use fiber which supports 1 Km or more.

Pat Thaler
916-785-4538

My comments are my own and do not necessarily represent the opinions
of the 10BASE-T task force.  (So are my spellings.  I was in a hurry
and probably left some typos behind.)