From: craig@cattnts (Craig Campbell)
Subject: Re: Repeaters
Organization: AT&T / NCR Canada Ltd., Toronto, Canada
Date: Mon, 6 Apr 1992 20:10:18 GMT

In article <1992Apr3.031822.1128@news.Hawaii.Edu> whinery@nancy.uhcc.Hawaii.Edu (Alan Whinery) writes:
>In article <1992Apr1.151835.8309@picker.com> SYSNET@engvax.picker.com (Leonard A. Visconti) writes:
>>We are beginning to use 10baseT hubs to extend portions of our network
>>and I am concerned about the number of these devices which can be 
>>daisy-chained.  
>>(...)
>>I've often heard of a 'three repeater rule' which says nodes cannot reliably
>>communicate through three ( or is it more than three?) repeaters. It would

>More than a rule of thumb, that. It is part of the 802.3 spec.

>You're going down a dark dead-end alley here.

>Since most hubs come with a number of 10BaseT connections and one connection
>to another medium (either a BNC for 10Base2 thinnet or an AUI port for 
>a transceiver), you can avoid the whole issue by running coax from hub to 
>hub and not stacking hubs. We have several places on our campus where 
>there are a high concentration of 10BaseT users, and there has never been
>a reason to go more than one hub deep. Just take a thin coax segment, 

I am unclear how this is a) an improvement or b) makes any difference.

If three hubs is the rule (another poster said 4), and each hub has 11 ports,
then you can connect 11*10 = 110 end points without using coax, repeaters or
bridges (allowing respect for cable lengths).

The following is information about AT&T StalLAN (10BaseT) equipment.  How
applicable this is to 10BaseT equipment in general is not known by me and
left as an exercise for the reader.  
This is not a sales blurb, but I do have AT&T hub information available,
(dated May 1991) and it says,

"All the StarLAN Hubs are IEEE mulri-port repeaters (MPR)."

further,

"Every once in a while someone asks if we [AT&T] are violating the IEEE 802.3
 configuration rules that specify a maximum of four repeaters in a path between
 two stations.  After all, StarLAN 10 Hubs are 802.3 multi-port repeaters,
 and we do allow many more than four hubs in a given path.  StarLAN 10 rules
 do not limit the number of repeaters -- only the maximum delay that is applied
 to any combination of devices (such as repeaters and media).  It is true that 
 the IEEE 802.3 spec specifies four repeaters, but this is intended for 
 coax-based networks with 500m media segments and is unnecessarily
 constraining for networks that utilize other media and other topologies, such
 as StarLAN 10 with UTP 100m links.

 AT&T's position is that the IEEE limitation on four repeaters is fine for 
 traditional coax-based ethernet networks, but is unnecessary and too
 restrictive for StarLAN 10 networks.  The important matter for any network
 is that the end-to-end maximum delay contributions from media and devices
 in any given station-to-station path.  Adherence to StarLAN 10 configuration
 rules assures that any network - pure StarLAN 10, pure coax, or a combination
 does just that.

 On the other hand, if the customer feels strongly that the number of repeaters
 should be limited to four, the StarLAN 10 hubs will accomodate that
 restriction.  Up to 100 hubs could be connected to a coax backbone, resulting
 in a two hub delay between any users."

>Probably best to avoid repeaters in series whenever you can.

Or perhaps it makes no difference at all.

>Alan
>whinery@nancy.uhcc.hawaii.edu
>
>--
>D. Alan Whinery, Computer Networks Engineer
>The University of Hawaii at Manoa
>2565 The Mall, Honolulu, HI 96822
>(808)956-6430    FAX (808)956-2412

Note/Disclaimer:  I am offering this information as a possible general guide.
		 I am not speaking for AT&T or NCR.  If you are interested in
		 a specific vendors products, and/or would like guarantees,
		 warranties, or technical assistance, then please contact 
		 that vendor directly.  Do not misconstrue free USENET advice
		 for anything more than free advice, worth what you paid for it.
		 (That should cover me...:-))

-- 
Craig Campbell		|	These opinions are entirely the result of a 
Systems Engineer	|	small butterfly crashing into the far side
NCR Canada,		|	of the planet.  Chaos Rules.
an AT&T Company		|	I speak for no one, except, possibly, myself.
Newsgroups: comp.dcom.lans.ethernet