TTYs for the deaf

From: Eric Smith <eric_at_brouhaha.com>
Date: Sat Dec 11 18:48:42 2004

Fred wrote:
> the ASR33 TTY is Bell 103 at 300 baud?

Michael wrote:
> That's what I've always thought, anyone who knows otherwise please correct
> me.

The ASR33 TTY does 110 baud. Maybe it can be regeared for other
rates, but I'm reasonably certain that it won't work at 300 baud.

Bell 103 uses FSK, so it will work at any baud rate up to 300 (offically)
or 450 (unofficially; I'm not sure how well that really works).

All of the full-duplex 1200 bps and faster dialup modem protocols starting
with Bell 212 and V.22bis use PSK, QAM, or even fancier techniques which
do synchrnous modulation, so the channel bit rate is firmly tied to the
modulation rate. However, the channel bit rate is NOT equal to the baud
rate, because there are more than two symbols, and thus more than one bit
per baud. For example, Bell 212 and V.22bis are 1200 bps, but only 600
baud using two symbols. V.22bis is 2400 bps at 600 baud using four
symbols.

Eric
Received on Sat Dec 11 2004 - 18:48:42 GMT