Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: 10BaseT operation, spec?
Summary: It's repeater based
Message-ID: <29786@bu-cs.BU.EDU>
Date: 18 Apr 89 22:07:50 GMT
References: <1627@Portia.Stanford.EDU>
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston U. Information Technology
Lines: 76

In article <1627@Portia.Stanford.EDU> 
morgan@jessica.stanford.edu (RL "Bob" Morgan) writes:
>
>I'm puzzled by various references I've seen recently, in this forum
>and elsewhere, to the operation of the proposed 10BaseT Ethernet.  Is
>the draft spec available from anywhere, either on paper or (better)
>on-line?  Is there some nice, descriptive article somewhere that talks
>about 10BaseT operation and terminology?
>
	I have some of the slide presentations from some of the
meetings from last year when the spec was still very much up in the
air.  Nothing of late, but they are arguing about "link state" and
type of equalization at this point.  Actually, I understand that there
has been another meeting and the 10BaseT has a proposal for 802 to
consider, so all those issues are resolved by now.  They probably
ended up by leveling the playing field (ie, break all existing
implementations :-)  But, hey, I don't want to step on any mines here. 

>When the battle to define the standard was going on last year, I
>thought there was a clear split between the "3Com approach" and the
>"Lattisnet approach."  

	Well, it was more like the DEC/3Com camp versus the
"concentrator" camp, of which LattisNet was but one approach.  Two
main camps with subcamps if you will.   :-)

>The 3Com method involves simply modifying the
>standard Ethernet transmission to work acceptably over twisted pair,
>more or less like a Balun does for other coax-to-TP purposes.  In this
>case the TP is really just an Ethernet cable, the transceiver
>functions are performed at the station, and the machinery in the
>wiring closet is just a multiport repeater with one Balun per port.

	That's right, but with attendant loss of capability.  Ethernet
was not designed for unshielded media like TP.  The committee decided
not to go with an inferior technology, nor to cop out and adopt both
standards.  Good for them.  (My opinion, no flames.)

>The Lattisnet method, on the other hand, uses the TP as an extension
>of the transceiver cable, so that most (some? all?) transceiver
>functions are performed by the wiring-closet machinery, which is
>more-or-less a multiport transceiver.  The device at the station is
>required to multiplex the signals that are normally carried on the
>multiple-conductor transceiver cable so they'll fit on the TP, but
>isn't really a transceiver in the normal sense.  There is no repeater
>in the normal sense (auto-partitioning, retiming, etc) at all.  
>

	LattisNet is kinda like a transceiver, but the "other"
approach is very much a repeater approach.  The twisted pair are
basically transmit and receive pairs, with the concentrator and the
transceiver doing the collision detect and CD signalling.  The
repeater approach makes 10BaseT more consistent with other IEEE media
and gives you some of the fault isolation of IEEE-spec bit-level
repeaters.  Again, the right choice in my opinion.

>Of course, the Lattisnet approach "won" the standards battle.  

	No, I think they lost.  The "repeater camp" won.

>Now,
>I've seen people referring to the 10BaseT wiring closet device as a
>repeater.  Is this just loose terminology or is my understanding of
>10BaseT/Lattisnet wrong?
>
	Just a little dated, I think.  Of course, LattisNet still
works and Synoptics may go ahead and build a 10BaseT option.

	The real test of the 10BaseT is when we have some vendor
interoperability.  A little more time required.

	Disclaimer:  I am an interested party, but my information may
be incorrect or dated in details.  Please don't take my opinion
comments as fact.  Vendors welcome to speak for themselves.

	--Kent England, Boston U