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Re: 56 kbps modems


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To: [email protected], [email protected]
Date: Tue Sep 17 08:20:07 1996
Argh, criticism!!!!! :-0

> > 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)
> Personally, by saying that no transmission on a standard phoneline can 
> have more than 3100 baud, is a statement saying that technology and 
> science, shall never advance, to a point where things are possible.
> If you remember right, just 10 or so years ago, we stated that 2400 baud
> was the highest possible baud, and we would never go over.  My modem, 
> running on a standard phone line, is a 28.8 USRobotics modem, with 
> the software, and hardware upgrades to a 3400 baud, I get on an average
> day anywhere from 3500 to 3600 baud for send/receive.  On a bad day, I 
> only get 3100 to 3200.  SO I would say, that my phone lines, are cleaner
> than most eh?  And Yes, I am in the US.
> Speaking of ISDN, how many people, can afford to have a personal ISDN 
> line in there house?  And then afford to connect to something/someone 
> else on a next to permanent basis monthly?

Well, if your modems says to "hell with the switch", you can do a lot of 
things with frequencies. And since the filters in the switch are not that 
accurate, you *might* get away with 3400 hz, which I doubt. Now if your 
phonecompany for what reason ever supports more bandwidth, thats good for 
you, but try to get your 3600 baud = 3600 hz modem to be accepted by the 
FCC will pose a problem, since it states in the regulations, that a modem 
has to stick to the 300-3400 hz band limits.

> > 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.

> What about new ways of splitting the steps and baud more so that it
> shows less at a higher level....  Just a question..  Ahh well, I'm
> getting a page so I shall finish this now...  Answer appreciated..


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