From: nason@pa881a.inland.com
Newsgroups: comp.dcom.lans.ethernet
Subject: Re: Max Repeaters/multiport repeater wiring questions
Date: 26 Aug 92 18:00:17 GMT
Organization: Inland Steel Company, East Chicago, IN

In article <1992Aug21.172813.1606@ra.royalroads.ca>, bbaskett@post.RoyalRoads.ca (Bill Baskett) writes:
> 
> These are probably FAQs but I couldn't find a FAQ list.
> There are basic questions, I'm sure, but if I don't ask, I'll
> never know!
> 
> 1) I find conflicting information (mostly from salespersons) about 
>    how many repeaters I can have in my network. One source says
>    2 another says 3 and yet another says 4. Which is correct?
>    (I should say, how many can I have between to communicating
>    systems on the same ethernet (i.e. not broken by a non-repeating
>    apparatus such as a bridge or gateway?)
> 
This is semantics.  DEC used to call it two repeaters but other vendors got a
marketing edge by saying they could use four repearters.  It depends on how you
like to define *one* repeater.  If you define one half of a link as one
repeater than you may have four repeaters in your LAN.  If you define on half
of a link repeater as one-half of a repeater, than you may have two repeaters,
eg. four halves.  A coax to coax repeater is considered (today) as two
repeaters bacause it has two AUI connectors.  A Fiber repeater is considered
one repeater today because is has one AUI connector.  Thin wire and multiport
(both thin and TP) are considered two repeaters.

Also, the rule is not how many repeaters you may have.  Its how many you may
have in the path between two nodes.  "No two node may communicate through more
than two repeaters".  You can have a dozen repeaters or more.     

> 2) Is a repeater effectively two transceivers? If so, then do
>    the thin to fiber converters (one at each end of fiber) count
>    as one repeater?

No, a repetar connects to the transciever.  One MAU (transceiver) per
repeater under the current four repeater terminology.  The second question is
controversial.  I posted an argument some months back claiming that any device
that crosses toplogical media was a repeater.  Ie, thick-thin, thick-fiber,
thin-TP etc...  I got some good arguments.  In general I would call them
repeaters but based on the arguments I received, I would use the vendors design
guidelines in implementing these "converters".

> 
> 3) Which is the correct way to wire a thinnet segment into a 
>    multiport repeater?
>   
>    a)                                  b)
>   
>     .------------.                       .--------------.
>     | mpr box    |                       | mpr box      |
>     `---.--------'                       `----.---------'
>         |                                     |
>     |---T--------------|                      |
>                                               |
>                                               -     <-terminator
>     (two terminators, t-connection        (one terminator, direct bnc
>      to multiport repeater)                connection to multiport repeater)
> 
>     I'm 99% sure it's (b), but I have to resolve this issue to the
>     satisfaction of all. (BTW would (a) be correct for a bridge?)

The answer is b. no ands, ifs, or buts.  The output of the MPR box is the start
of a thinwire segment.  The mpr provides the terminator in most boxes.  If you
use a, you are branching a thinwire segement, illegal.  

> 
> 4) Can a transceiver be plugged directly into the workstation, or
>    is there some reason that you must use the tranceiver cable?

You may plug the transceiver directly in, if it fits mechnically.  We do it all
the time.  The connectors become your AUI.  
> 
> 5) Are thinnet segments supposed to be grounded somewhere?

Yes, once and only once at some convenient point along the segment.  Usually
with an mpr, the grounding for each segment is done at the repeater.  See the
mpr vendors instructions.  
> 
> -- 
My opinions are my own and not those of my company.  
Free advice is worth its cost.  
--- John M. Nason - NA9U ---|--------------------------------------------|
Inland Steel Company        |  -- nason@pa621a.inland.com                |
Process Automation MS 2-464 |  -- Fax:   219-399-7856                    |
3210 Watling Street         |  -- Voice: 219-399-2450                    |
East Chicago IN 46312       |"Ya can't shoot em till they stop sparklin" |
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