15 Jul
1998
15 Jul
'98
8:15 a.m.
Hey! A great way to bring this thread back on topic! How do those
electronic switches work, and what is the approximate network topology
of the system? Is there a reference guide to it somewhere? I'd love to
take a look.
>From about the 1970s and on (somewhere around
there...about the time
the
first electronic switching systems start appearing)
***snip***
As far as I know, a telephone rings because when it's on hook, any
current on the phone line is connected to the ringer. When someone is
trying to connect, the company sends a periodic AC signal to the phone.
If the caller ID data signal was sent first, it would cause jittering in
mechanical ringers, and a maddening noise in electronic ones. When the
ring is detected, the caller ID can 'pick up' the phone line briefly to
check the data signal, which should be extremely brief. The station
knows to keep ringing the phone if the user has caller ID. This is my
theory.
I don't know the specific reasons that are behind
sending the data
burst
after the first ring. It may have a lot to do with the
caller ID boxes
needing some sort of indicator to let them know a call was coming and
they
should start monitoring for the carrier. I think the
caller ID boxes
could have easily been designed to continually monitor the line for a
carrier and then capture the data that came before the first ring.
Sam Alternate e-mail:
dastar(a)siconic.com
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