Re: 56 kbps modems

[Remo Pini <rp@rpini.com>]

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To: cypherpunks@toad.com
Date: Mon Sep 16 15:59:53 1996
I think I have to throw in some words here, too:

1. BAUD is one distingushable signal form.
2. BPS is bits per second

3. NO transmission over a standard phoneline can have more than 3100 baud, 
because the frequency of anything transmitted over that line is band 
limited to 300hz - 3400hz. (If you have ISDN it's not relevant anyway, 
since you are fixed with 8000hz or 64000 bps->in europe :), 56000 bps in 
usa)

4. Most modern transmission schemes work with multiple bits per baud. I.e. 
you transmit 10 bits in one baud if you have a 31000 bps modem. the only 
limitation in transmission speed is the amount of binary values you can 
pack into one baud. that on the other hand is limited by the S/N (signal to 
noise) ratio of your line. If you have a noise of 0.9%, you can't use more 
than 100 steps or you have ambiguous signals. since people talk about 56000 
bps modems (we tried 34000 modems here and they couldn't produce more than 
28800 on a very good connection) that would mean, that you have to transmit 
18 bits = 262144 (!) distinguishable signal forms per baud.

Comments?

Remo Pini
 
- ------< fate favors the prepared mind >------
Remo Pini                        rp@rpini.com
PGP:  http://www.rpini.com/crypto/crypto.html
- ----< words are what reality is made of >----
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