Re: 56 kbps modems

[mpd@netcom.com (Mike Duvos)]

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.                      $