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From: brian@casemo.UUCP (Brian Cuthie)
Newsgroups: comp.dcom.telecom
Subject: Re: Subscriber Line Interfaces (SLIC) characteristics ?
Message-ID: <230@casemo.UUCP>
Date: Mon, 26-Oct-87 17:56:02 EST
Article-I.D.: casemo.230
Posted: Mon Oct 26 17:56:02 1987
Date-Received: Sat, 31-Oct-87 15:26:47 EST
References: <159@vema.lamont.LDGO.Columbia.edu>
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Organization: CASE Communications, Columbia, MD
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Keywords: telephone interface help
Approved: telecom@xx.lcs.mit.edu


In article <159@vema.lamont.LDGO.Columbia.edu>, dale@lamont.UUCP (dale chayes) writes:
> 
> I am (reluctantly) doing an interface between a PBX (probably a Mitel SX-20)
> and a Magnavox MX-211 INMARSAT (ship earth station) and am in need of a (the)
> reference that defines (electrikly) a Subscriber Line (SLIC?.)  
> 
> It seems to me that the 'thing to do' is to supply a current source (as if
> there was a 'local office' in my 4 to 2 conversion box, and detect 'off hook'
> by from the current flow.
> 
> Comments, reccomendations, and a reference are welcome.


Dale, you forgot to mention which side of the PBX you would like to interface
to.   If you want to interface on the instrument side (ie. where a phone would
normally go) then you must make something that looks like a phone to the
PBX.  This really isn't too hard.  You just need to have a two wire interface
that has an impedance of about 600 ohms and a DC resistance of about
200 ohms or less.  This is usually done best through a transformer.  To
my knowledge, Mitel uses their MH88500 SLIC as the interface on that end.
(You can get the specs on that part from Mitel. They sell it in the open
market and it's in their data book.  I've used them in my own PBX and they're
quite nice.)

If, rather, you would like to connect to the trunk end of the PBX (the
interface that usually connects to the phone company), then you need
to build something that looks like a phone line.  It should be a 2 or 4
wire interface (depending on the Mitel trunk interface) and it should
be capable of supplying about 24 volts and 30 ma into a 200 ohm DC load.
It should also have an impedance of 600 ohms.  Depending on the 
requirements of the Mitel PBX you could actually use their MH88500 SLIC.

Really, it would be best to get the Mitel data book and look at their SLIC.
It will provide some useful information regardless of which interface you
actually have to build.

Hope this helps...

Cheers,
Brian

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Brian Cuthie
CASE Communications
Columbia, Md 21046
(301) 290 - 7443