Path: utzoo!attcan!uunet!decwrl!hayes.ims.alaska.edu!accuvax.nwu.edu!nucsrl!telecom-request
From: vances@xenitec.on.ca (Vance Shipley)
Newsgroups: comp.dcom.telecom
Subject: Re: A/A1 Control For Key Telephone Systems
Message-ID: <14049@accuvax.nwu.edu>
Date: 26 Oct 90 14:01:57 GMT
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Reply-To: vances@ltg.UUCP (Vance Shipley)
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In article <13966@accuvax.nwu.edu> drears@pica.army.mil (Dennis G.
Rears (FSAC)) writes:

>  Can anybody tell me what is meant by A/A1 control for key telephone
>systems?  Also what is a 1A2 key system?  A reference would aalso be
>good.

When you say "key telephone systems" I assume you mean "electronic key
telephones" (EKT).  The predecessor to todays EKT's was the 1A2 key.

The 1A2 key telephone system can be recognized (and spotted nearly
everywhere) by the familiar 500/2500 type desk set with a larger base
and six buttons at the front.  One button is red and the others are
clear.  The red button is the hold and the others are line appearances
or even intercom.  The line cord for these sets is a 25-pair cable
(sometimes 16-pair).  Each line appearance uses 3-pair (although two
wires used as return grounds could be skipped, using a common ground
for return).  The six wires are T/R,A/A1,LG,L.  These are; Tip and
Ring of the CO line, A and A1 control (wired to the button in the set,
a normally open contact which is closed when the line button is
depressed), Lamp Ground and Lamp (the power to light the lamp in the
button).

  When a line appearance button is depressed at a set the A1 lead
signals the KSU that it is in use. The KSU lights the lamps for all
other appearances of that line (with the L lead). Note that the actual
CO line is always available at every set, it is only neccesary to
signal the KSU to light the lamps.  Now the hold key would be the
subject of another lengthy article!

  The application of A/A1 control in an EKT system allows the
integration of EKT and 1A2 on the same lines.  When a user on the 1A2
grabs a line the LED associated with that line on the EKT's will
light.

  But before you think that this is a useless feature in today's
telecom world think of the other uses to put it to.  Most hayes
compatable modems include A/A1 control!  You can use your modem on a
line that is on the EKT system and other users will not be able to
break in, their LED's will be lit.  How about those credit
verification terminals, fax machines and TDD's?  If you don't have an
A/A1 control pair on your terminal you can run down to Radio Shack and
buy a cheap little box which senses when the CO line is in use and
trips a relay providing A/A1.  (I hope these are still available).

  For a reference you might try Radio Shack for a book called
"Understanding Telephone Electronics".  This is actually a very good
reference on the history and operation of telephones and the network.


Vance Shipley
SwitchView - The Linton Technology Group
(519)746-4460
vances@ltg   or   ... uunet!watmath!xenitec!ltg!vances