Re: 56 kbps modems

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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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I personally, am not much for this, I am just one with various ideas, and 
questiosn and such, so here goes.

On Mon, 16 Sep 1996, Remo Pini wrote:

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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

Ok, I agree with those.

> 
> 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?

> 
> 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?

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..

> 
> 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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> 



Erp

On Mon, 16 Sep 1996, Jay Gairson wrote:

> 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?

No problem here. My ISDN bill is a small fraction of my regular phone bill.

--Lucky

Jay Gairson <erp@digiforest.com> writes:

 > 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.

Baud denotes the number of state changes made by the modem on the
line per second.  The possible states generally form some sort of
regular pattern in frequency/phase space, with each state being
maintained long enough to reliably determine it on the other end.

Before the advent of V32 and V32.bis modems, the underlying
symbol rate was substantially lower than it is now.  Then it was
determined that it was possible to overdrive the line cards on
digital switches to equalize them over a wider range of
frequencies, without smoking them down.  The newer modems take
advantage of this kludge.

Since the underlying digital data stream is eight thousand 8-bit
u-law samples per second, there are genuine theoretical limits in
terms of symbols per second which cannot be crossed.

 > 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.

Don't confuse "baud" in terms of characters per second through
your modem with the low level symbol rate of the modem's analog
output into the phone line.  The "baud" you see is a function not
only of the low level symbol rate, but of framing, the V.42
compression/error correction process, and other factors.

 > 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?

The price of ISDN is a function of phone company marketing, not
the cost of providing the service.  Domestic US service is almost
entirely digital now, and moving the subscriber line interface to
the consumer end, so the digital aspects of the network may be
fully exploited, is not a conceptually expensive process.

(Yes I know the software upgrade to ESS for ISDN costs a
bundle.)

--
     Mike Duvos         $    PGP 2.6 Public Key available     $
     mpd@netcom.com     $    via Finger.                      $

>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?

As I write this message I'm in the last day of my ISDN service for now.
When I was doing independent consulting work I installed ISDN at my office.
This was to facilitate connectivity to work in California from Minnesota.
After taking a job working for a company locally in Minneapolis I succumbed
to the temptation of installing ISDN at my home and moved my Combinet
router home. I won't deny that I'll be giving up considerable convenience
since the ISDN connection has the ability to come up quickly and
automatically as I send packets to external destinations (that's in theory,
your mileage can vary considerably). But the price per month is ridiculous
for the marginal improvement in connectivity I get over my U of M account
that only costs me about $100 per year. For the price I'm paying for ISDN
Internet connectivity I could buy 32 meg of memory or a gigabyte drive
every month.

The driving force in my decision is the continuing improvement in modem
speeds. When I started with ISDN, my modem speed was 9600 and plenty
finicky at that. Now you can get 33.6 modems for less than $200.

_________________
Steve Bryan
sbryan@gofast.net