History -- why not 20 pulse/sec dials? [telecom]

History -- why not 20 pulse/sec dials? [telecom]
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History -- why not 20 pulse/sec dials? [telecom] hancock4 08-06-2008
Posted by on August 6, 2008, 8:17 pm
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The Panel and Crossbar switches of the Bell System were able to handle
dial pulses coming in at 20 pulses per second, twice as fast as the
standard 10 pulses per second. Some customer PBX switchboards had
fast dials.

Step by Step could be modified to handle 20 pps, but that created
excessive wear on the equipment.

Apparently, modifying a standard rotary dial to go at 20 pps was easy
to do and no CO adjustment was necessary. Way back, someone in high
school figured out how to to do it and a bunch of people secretly
converted their phones; and it worked. (We were served by either
panel or #1 xbar in a large city.

Given that the Sender was the most expensive piece of equipment,
wouldn't have been to the Bell System's advantage to modify dials in
Panel/Crossbar service areas (often large cities serving millions of
lines)? Calls would go through faster and customers would be happy as
well. The Sender would be released for other calls more quickly.

Perhaps I'm not aware of a key technical point that makes this harder
than it seems.

Could anyone familiar with the technology elaborate on this topic?


[Note--while Touch Tone had the same time saving, TT required a more
expensive customer set and frequency interpreters at the CO end which
were not cheap.]


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Posted by Eric Tappert on August 7, 2008, 1:54 am
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On Wed, 6 Aug 2008 20:17:29 -0400 (EDT), hancock4@bbs.cpcn.com wrote:

>The Panel and Crossbar switches of the Bell System were able to handle
>dial pulses coming in at 20 pulses per second, twice as fast as the
>standard 10 pulses per second. Some customer PBX switchboards had
>fast dials.
>
>Step by Step could be modified to handle 20 pps, but that created
>excessive wear on the equipment.
>
>Apparently, modifying a standard rotary dial to go at 20 pps was easy
>to do and no CO adjustment was necessary. Way back, someone in high
>school figured out how to to do it and a bunch of people secretly
>converted their phones; and it worked. (We were served by either
>panel or #1 xbar in a large city.
>
>Given that the Sender was the most expensive piece of equipment,
>wouldn't have been to the Bell System's advantage to modify dials in
>Panel/Crossbar service areas (often large cities serving millions of
>lines)? Calls would go through faster and customers would be happy as
>well. The Sender would be released for other calls more quickly.
>
>Perhaps I'm not aware of a key technical point that makes this harder
>than it seems.
>
>Could anyone familiar with the technology elaborate on this topic?
>
>
>[Note--while Touch Tone had the same time saving, TT required a more
>expensive customer set and frequency interpreters at the CO end which
>were not cheap.]


Toll operators did use 20 pps dials. Of course they were dialing on a
short loop while many customers were dialing on longer, or even very
long loops. The transmission properties of long loops distort dial
pulses, so the "safe" thing to do was to design customer equipment to
avoid problems on any circuit.

E. Tappert


Posted by Geoffrey Welsh on August 7, 2008, 10:51 am
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hancock4@bbs.cpcn.com wrote:
> [Note--while Touch Tone had the same time saving, TT required a more
> expensive customer set and frequency interpreters at the CO end which
> were not cheap.]

If I recall correctly, at one point I owned a modem with hook control but not
touch-tone... dialling was accomplished by setting and clearing a bit on an
I/O port under program control. I don't know how much a DTMF generator would
have added to the cost of the modem, but we really didn't need it either.
And, yes, many terminal programs offered to dial faster than 10 PPS.

--

Geoffrey Welsh <Geoffrey [dot] Welsh [at] bigfoot [dot] com>


.


Posted by on August 8, 2008, 12:59 pm
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> hanco...@bbs.cpcn.com wrote:
> > [Note--while Touch Tone had the same time saving, TT required a more
> > expensive customer set and frequency interpreters at the CO end which
> > were not cheap.]
>
> If I recall correctly, at one point I owned a modem with hook control but
not
> touch-tone... dialling was accomplished by setting and clearing a bit on an
> I/O port under program control.  I don't know how much a DTMF generator
would
> have added to the cost of the modem, but we really didn't need it either.
> And, yes, many terminal programs offered to dial faster than 10 PPS.

By the time modems were cheap enough to be used at home (late 1970s),
the cost of electronics had dropped enough so that frequency
converters were not as expensive. By the late 1970s Touch Tone was
available to the majority of subscribers and gaining in popularity.
Further, Panel was pretty much gone by then and ESS was quickly coming
on-line.

I was thinking more for the 1950s and 1960s.


Posted by on August 8, 2008, 4:40 pm
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On Aug 8, 12:59 pm, hanco...@bbs.cpcn.com wrote:


> I was thinking more for the 1950s and 1960s.

FWIW, when I got my first home computer around 1992 I had rotary
service. The modem was easily set to 20 pps by a AT command string.
(It could also be set to different make/break ratios for use in other
countries). The ESS had no trouble.

I bought an phone with an auto dialer at that time. That dialed pulse
very slowly, I could dial faster on a plain rotary phone, which was
frustrating. It spit out Touch Tone fast.


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other useful resources:
The Federal Communications Commission (FCC)
Telecommunications Industry Association
Electronic and Software Security Products and Services
International Telecommunication Union

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