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From: normb@tekred.UUCP (Norm Babcock )
Newsgroups: net.dcom
Subject: re: Direct Connect Modems
Message-ID: <143@tekred.UUCP>
Date: Thu, 1-Nov-84 13:13:32 EST
Article-I.D.: tekred.143
Posted: Thu Nov  1 13:13:32 1984
Date-Received: Sun, 4-Nov-84 04:38:51 EST
Organization: Tektronix, Redmond OR
Lines: 22

Douglas Robinson made a good comment about the inability
of digital PBXs (CBXs) to handle direct connect modems.
One that I'm familar with is the Danray system, (now
Northern Telecom), which uses a six-wire telset. Two for
transmit, two for receive, and two for telset power. The
assumption is that a acoustic modem will work, but in general
doesn't, for the primary reason that the modem tones "mean"
something to the PBX, and the PBX goes off into never-never
land, thinking it's supposed to hold, transfer, or something
else. Some PBX/CBX have a feature called 'OPX', which allows
the attachment of a standard 500 telset. They have to provide
this feature to allow the customer the use of recorders and
answer machines. Some people will refer to an OPX circuit used
for data as a 'featured OPX'. This is in error. Whatcha need
is a non-featured OPX, in which case, the PBX will ignore the
modem tones. Another pitfall: incoming call signaling makes the
modem go belly-up. Also most modems will not answer the double
ring on incoming calls. (Inside calls are single, outside double).

My favorite modem, after evaluating a large number of them,
is the Racal-Vadic Auto Dial VA212PA. A little more expensive,
but worth it. Norm