TELECOM Digest Editor wrote:
> firstname.lastname@example.org wrote on the topic of Speed Dials:
TELECOM Digest Editor noted in response to Lisa Hancock:
>> [TELECOM Digest Editor's Note: Plus which, on (at least the older) AE
>> rotary dial phones, the dial would return 'faster' when you removed
>> your finger. WE dials pulsed and clicked their way back. PAT]
>> The dial speed is about 10 pulses per second. (A good modem manual
>> will tell you exactly the "contact make/break" times and the settings
>> for outside the U.S. as well).
>> Anyway, I believe panel switching and certainly crossbar and ESS could
>> and would accept 20 pulses per second. Way back in HS a kid figured
>> out on his phone dial an adjustment to make it 20 p/s and it worked
>> (on either #1 xbar or panel). PBX switchboards had 20 p/s dials.
>> However, I think they realized this higher speed was rough on
>> equipment and did not provide it to the general public for that
>> reason. I don't know if SxS could handle it but SxS components had
>> wear issues and certain improvements was rough on SxS unless it was
>> carefully spread out among switches within an office.
> I tried an experiment once with a Hayes modem and tone dialing. I kept
> setting the 'dialing speed' faster and faster on the modem so that
> eventually, instead of getting a faster and faster 'beep, beep, bloop'
> sound as it was 'dialing' or toning out its signal it got to where
> the modem was 'toning out' its signal in just two or three seconds
> total. Central office was still able to keep up with that pace on the
> touchtone speed, but then I set the modem to get it all out in about
> one or two seconds -- just an audible blur, no way for the naked ear
> to make anything out of it -- and then about half the time, my call
> 'could not be completed as dialed'. If I slowed it down just a pinch,
> so that ten digits still reached the central office in about three or
> four seconds, it always heard me and made the right connection. I did
> _not_ think touch tone signals could be interpreted that fast, but on
> ESS I guess they can be.
The original ESS circuits very likely couldn't keep up. But newer and
newer line cards (or whatever they call them) likely at some point
switched to DSP (digital signal processing) chips. This gives each
line the equivalent of a filter tied to a computer program to analyze
the signals coming in and very quickly pick the 2 tones being