Re: newbie needs advice

[david@uow.edu.au (David Wilson)]

Dennis Fenton <defenton@mbnet.mb.ca> writes:
>In ProTerm's Online Parameters menu there is a Baud Rate box. It only
>allows preprogrammed choices. 14 400 is not one of them. It jumps from 9
>600 to
>19 200. If you choose 9 600 that will be what you connect at and it stays 
>there. If you choose the next setting above the modem's it will try to 
>connect at that rate and then automatically drop to the modem's rated
>speed
>of 14 400 bps(bps is more correct although many people say baud).

>I think this feature is common to all comm programs and modems. I have a
>14 400 in my 486. There the comm program is Hayes Smartcom. It connects at
>57 600 and then drops to 14 400.

With modern modems, the speed at which the computer talks to the modem
(the port speed) need not (and in most cases should not) be the same speed
that the modem talks to the other modem (the line speed). As modern modems
have built in compression, it would be wasteful to send 9600bps data to
a 9600bps modem as there would be no gain from the compression. So with
MNP-5 giving approx 2x compression, a 9600bps modem should be fed at about
19200bps.

Unfortunately, not all data is equally compressible so the modem must be
able to tell the computer to stop sending data when it gets a patch of
less compressible data (ie a .zip file). This is the hardware handshake that
the //c lacks. Equally, when downloading a file to a disk, the //c needs
to tell the modem (which then tells the remote modem and its computer) to stop
sending data while it writes a block to disk).

V42bis can do up to 4x compression so a 33.6kbps modem should have a port
speed of about 134400bps.

P.S. On the connection between the modem and the computer, buad = bps as
pure binary signalling is used. Between the two modems, bps > baud as
more than 1 bit can be sent per signal change (using amplitude and phase
changes to represent the different multibit combinations).
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au