Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!mcvax!dfk
From: dfk@cwi.nl (Daniel Karrenberg)
Newsgroups: comp.dcom.lans
Subject: Re: Thin ethernet questions
Message-ID: <851@sering.cwi.nl>
Date: 29 Mar 89 10:54:05 GMT
References: <724@m3.mfci.UUCP> <170@usna.MIL>
Organization: CWI, Amsterdam
Lines: 50

In article <170@usna.MIL> tsmith@cad.usna.mil.UUCP (Tim G. Smith) writes:
>
>All of the MPRs to do this were not cheap but in my opinion they were
>well worth the money. If you use MPRs you can save a lot of network
>debugging time- you just look for the faulted segment and then deal
>with it. The whole net does not come crashing done due to one fault.
>They are really great for making life easier on the network managers.
>They also keep one person from screwing up the net by pulling the
>network apart or taking of his terminator. If someone screws with the
>parts of the net accessible in his office he only takes himslf and
>maybe his officemate off the net. No one else gets affected. That is a
>real nice feature when you have a lot of naive users.

I agree most emphatically. We use similar setup and in the beginning 
it looked really expensive. But it's sure worth the ease in debugging.
Of course it is essential that your MPRs indicate a faulty segment and
it's very nice if they reconnect it once the fault goes away. We had
early verions of the DEMPR that didn't do that so you had to go in an push
the reset button. We are now using ISOLAN MPRs. They work OK and are
quite dependable. We have 24 of them (one was DOA).

It might also be helpful if the users could see the lights on the MPRs
to find out whether their segment is broken. This might eliminate some
of the calls on the network support. We don't have this however and
the load is still bearable.

>Wiring each office individually also makes it easier when people move
>from one subnet to another (USNA subnets by departments and every
>summer offices get shuffled among departments). 

We didn't do that because it's too expensive for us. But locating a fault 
in a string of say 5 offices is still quite possible and certainly better 
than having everything or even a complete floor stop.

We also use connector boxes with 2 BNCs per connection in each office.
They automatically bridge the segment at the box unless there are
two BNC connectors plugged (screwed ?) in. The boxes are placed
right under the ceiling out of reach of cleaning personnell and user's feets.
This eliminates some faults but we had a good deal of problems with faulty 
microswitches in these connector boxes to start with :-).

Recommendation: Use MPRs and make the segments as small as possible down
to the office level if you can afford it. Keep cheapernet cables and
connectors out of reach of users and other people likely to tamper.
Select your MPRs carefully (indicator lights, auto reconnect, MTBF).

-- 
Daniel Karrenberg                    Future Net:  <dfk@cwi.nl>
CWI, Amsterdam                        Oldie Net:  mcvax!dfk
The Netherlands          Because It's There Net:  DFK@MCVAX