Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!mtunh!mkd
From: mkd@mtunh.ATT.COM (Mark Darby)
Newsgroups: comp.dcom.lans
Subject: Re: Starlan/Ethernet compatibility
Message-ID: <670@mtunh.ATT.COM>
Date: 13 Jun 89 17:53:16 GMT
References: <2009@wasatch.utah.edu>
Organization: AT&T ISL Middletown NJ USA
Lines: 90



In <2009@wasatch.utah.edu>, Walt Haas (haas@wasatch.utah.edu) writes:

>We're in the market for Ethernet over twisted pair products.  The
>guys from AT&T want to sell us Starlan-10 (surprise!) but I have a few
>questions about compatibility with Ethernet in general and 10BASET in
>particular:
>
>1) Are there any compatibility issues that arise if I use existing
>   Ethernet interfaces through AT&T's AUI adapters into Starlan hubs?
>
>2) How big are the differences between Starlan and the forthcoming 10BASET,
>   ie. if I buy a Starlan now, how well will it interoperate with the
>   Brand X 10BASET products I buy next year?
>
>Thanks in advance for any information.
>
>Walt Haas    haas@cs.utah.edu    utah-cs!haas

Answer to 1 
-----------
Let me first clarify that the AT&T AUI Adapter is in reality
a TPMAU (TP = Twisted Pair) in IEEE Parlance, or a Twisted Pair
transceiver in Ethernet Parlance.

There shouldn't be any problem using the AT&T AUI Adapter with any
interface card which has an IEEE 802.3/Ethernet Type 2 compliant AUI
interface.  The design guide for the AUI Adapter's AUI connector is
Chapter 7 of the IEEE 802.3 green book.

On the twisted pair side, the only real problem is making sure you have
proper connectivity.  Always make sure an OUT jack is connected to an IN
jack at the other end, or vice versa.

Answer to 2
-----------
The AT&T StarLAN 10 products today meet key technical parameters of the
10BASE-T draft:

           1) Transmit level: the draft specifies 2.5 volts nominal peak
           2) Equalization technique: at the transmitter, not the receiver
           3) distance support: 100 meters on typical installed TP wire
              Greater distance in 25 pair is not feasible.
           4) HUB element: a multiport repeater as specified in Chapter 9
              of the IEEE 802.3 Supplement.  This includes auto-partitioning,
              an option in Chapter 9, but mandatory in 10BASE-T.

The AT&T StarLAN 10 architecture is based on HP's original proposal to
10BASE-T at the beginning of the standard-writing process circa 8/87.
That basic proposal included symmetric transceivers, one at each end of a
wire link, and that the 10BASE-T HUB is a Multi-Port Repeater,
not to be confused with a concentrator.

In fact, AT&T has direct (at the twisted pair interface)
interoperability with HP's StarLAN 10 product, as well as Ungerman Bass's
twisted pair Ethernet product.  That's what standards are all about.

One remaining key technical element exists which neither 
AT&T, HP, nor UB has implemented yet, at least not that I know of.
That is the link integrity function.  10BASE-T proposes
a function to determine the availability of the twisted pair link between
endpoints (e.g. node to repeater).  The function consists of periodic pulses
transmitted on a link by link basis in the absence of true data.  These pulses,
transmitted/received correctly, will have no effect on other network elements.
This function was added to the 10BASE-T draft near the end of the writing
process and was radically changed just before the latest draft,
assuring no one was ""compliant"".

Any vendor with an existing pre-standard embedded base should make available
a migration path to products based upon the final standard, with maintained
interoperability between it's own pre-standard and post-standard products.
AT&T's plan includes the ability of switching on and off the link integrity 
function per link on it's post-standard products to allow full interoperability
with it's pre-standard hardware, along with pre-standard HP and UB products.
Post-standard products from other vendors would need to implement a similar
scheme to interoperate with pre-standard products, or face a forklift upgrade!

As was stated earlier, the issue of link integrity is the only real outage,
other than possibly a trivial nit or two, between the draft
(as it stands now) and current product. The link integrity function has
been changed by the task force just recently before letter ballot, and will
probably change once again because of various holes in the overall function.

The draft has completed letter balloting by the 802.3 Working Group.
The 10BASE-T Task Force will meet later this month to resolve all NO
votes from the balloting.

				Mark Darby
				201-957-2706