Terminal output: parity, etc. (C - (nf)

[rpw3 at fortune.UUCP]

#R:wu1:-26700:fortune:11600078:000:1710
fortune!rpw3    Mar 28 20:04:00 1984

If you're going to be pedantic, at least get it right!

A "baud" is the reciprocal of the smallest signaling interval. For
equi-spaced signaling alphabets, the baud rate equals the symbol rate.
For binary signalling with no overhead, bits/sec equals baud.

True, a Bell 209 modem operates at 2400 baud ON THE TELEPHONE LINE SIDE,
where QAM modulation is employed and 4 bits/baud are achieved. But on the
digital (RS-232) side, WHICH IS THE ONLY SIDE USERS NORMALLY SEE, binary
signalling is used, wherein 9600 bits/sec = 9600 baud.

Moreover, on async ports (the vast majority of UNIX connections, no?), the
common use of the term "baud" is actually CORRECT, and using "bits" would
be WRONG! A Bell 212A, on the RS-232 side, handling async with one start
bit and one stop bit and 8 data bits, is 1200 BAUD, but only 960 BITS/sec.
Likewise, the hardwired connection I am using to type this message is
9600 BAUD (104.2 microsecond/symbol), but since I use async with 1 start
bit and one stop bit, I achieve but 7680 bits/second (if you count a char
as 8 data bits, and 6720 bits/sec if you call it 7 bits + parity).
No matter how you count it, though, it comes out to 960 characters/second.

By using synchronous transmission on a 1200 baud modem (which can be
done with either Bell 212A's or Vadic's), one can actually get 1200 BITS
per second, or 150 8-bit bytes/sec (instead of 120 bytes/sec). I have used
stat muxes over Vadic's in this mode, with 4 1200-baud (1S+8D+1S async)
(120 8-bit byte/sec) terminals sharing the line quite nicely.

Rob Warnock

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