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From: kentrox!ktxc5!brent@uunet.uu.net (Brent Capps)
Newsgroups: comp.dcom.telecom
Subject: Re: 16 Buttons -- Not 12?
Message-ID: <12659@accuvax.nwu.edu>
Date: 26 Sep 90 18:01:51 GMT
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X-Telecom-Digest: Volume 10, Issue 683, Message 9 of 11

> An odd thought sprang upon me recently while talking to a friend.  Do
> telephones actually use sixteen tones rather than just twelve normally
> available?

The extra tones are used in the AUTOVON/SCOPEDIAL system for
precedence dialling.  The only phone I've ever seen that uses them is
a very peculiar device known as a "4-wire set".  A 4W set is
essentially a trunk-line combination that consists of a trunk with a
special phone set terminating one end, and is used by the military to
run direct connections from AUTOVON COs out to missle silos in the
middle of God-knows-where.  4W sets use all 16 keys.  The numeric keys
and the * key are the same as on a 2500 set, but the # key is called
A, and the right-hand row of keys are called (top to bottom) FO, F, I,
and P.  

These keys are used for precedence dialling: A stands for Automatic
(lowest), P for Priority, I for Immediate, F for Flash, and FO for
Flash Override (the highest precedence level).  The highest allowed
precedence level associated with a particular set is datafilled at the
CO; there are only a handful of FO 4W sets in the country.  4W sets
are extremely strange beasts; their charms include off-hook ringing
(the phone can physically ring while you are off-hook talking to
someone else).  This can be somewhat disconcerting to the uninitiated.

4W sets are a pain to design CO software for, mainly because of their
hybrid nature (ever try to apply staggered dialtone to a trunk?  It's
not easy) and since there is little that a 4W set can do that a normal
2W set cannot, the CO mfgs have been pushing the military to phase
them out.


Brent Capps