Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!bu.edu!telecom-request
From: julian%bongo.UUCP@nosc.mil (Julian Macassey)
Newsgroups: comp.dcom.telecom
Subject: Re: Pulse-Mode Frequencies?
Message-ID: <72215@bu.edu.bu.edu>
Date: 13 Jan 91 15:41:13 GMT
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Reply-To: Julian Macassey <julian@bongo.info.com>
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X-Telecom-Digest: Volume 11, Issue 34, Message 6 of 8


In article <15962@accuvax.nwu.edu> jon_sree@world.std.com (Jon
Sreekanth) writes:
X-Telecom-Digest: Volume 11, Issue 23, Message 6 of 6


>On this topic, why do many voice mail and other phone operated
>services insist on users having DTMF phones ? Is it really hard to
>detect pulse mode digits? I can see that the low numbers might be a
>problem, (can't distinguish it from a noise pulse), but if one saw
>five to ten regularly spaced pulses, isn't that adequate for
>recognition?

	The reason is that the pulse is a DC disconnection at your
phone instrument. This disconnection and therefore interruption of the
DC current extends only to your local CO. The far end will just hear a
click. Hearing the click above line noise is tricky. So yes, at the
far end, these are not "pulses" of 0 - 10V with 300V transients, but
clicks, not quite the same thing. DTMF on the other hand is still DTMF
after it has been down a fiber optic cable and across two satellite
links.

	Touch Tone was invented so subscriber signalling could be
carried over radio (microwave etc) circuits. Pulse dialling will not
work unless you have copper wire carrying DC - yes, subscriber carrier
excepted.

	Voice mail boxes, etc work well with DTMF and miserably trying
to listen for clicks. Then DTMF is also faster than pulse. Plus of
course there is no pulse equivalent for * and # (-:

	In the UK, a bank was offering a dial in interactive account
service.  Because of the dearth of DTMF phones in the UK, part of the
banks deal was a ten pound (money) deposit for a hand held DTMF
generator that you held to the mouthpiece to punch in your account
number etc. 

>I've seen AT&T answering machines which say on the box that they
>work with pulse phones (at the remote end, for checking one's
>messages).  I haven't played with them. Does anyone know how they
>work, or how reliable the detection is? 

	Not too reliable I would guess.

DTMF = Dual Tone Multi Frquency = Touch Tone
CO = Cental Office = Telephone Exchange


Julian Macassey, n6are  julian@bongo.info.com  ucla-an!denwa!bongo!julian
N6ARE@N6YN (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495