Q. On Modems and Baud rate
vr...@silcom.com
I'm running a 28,800 ATT KIT modem.......but my "Chameleon"
connection to my local provider only goes up to 19,000 Baud. I'm under
the impression that baud is the rate in which the computor talks to
the modem......and have been told that with data compression it should
at least equal my modem speed.
Does this mean I'm getting less than half of the advantage of my
modems speed? What Baud rate should I be useing?
Thanks all, in advance. Steve Schwartz
Sir Topham Hatt
:
: I'm running a 28,800 ATT KIT modem.......but my "Chameleon"
: connection to my local provider only goes up to 19,000 Baud. I'm under
: the impression that baud is the rate in which the computor talks to
: the modem......and have been told that with data compression it should
: at least equal my modem speed.
First, off your use of the terminology is so confused here, that it's
hard to say what you are trying to say.
Generallly,
The V.34 modems will try to run the line as fast as possible. You may
not get 28.8 though depending on line conditions.
The number of bits actually pushed through the modem may exceed this
due to compression as you say.
The speed of the host <-> modem connection is independent of the
transfer speed between the two modems, but obviously, if it is set
to low, it may be come a limitting factor in your overall throughput.
As a result, you generally want to set the host speed as fast as
possible, in order to not have your commuications speed limiited because
it couldn't get data from the modem to the host.
However to exceed (I think) 38K on Windoze requires a different
(high speed) comm driver than the default one. One came with
my 28.8 modem, no doublt they're probably freelly avaiable
somewhere.
-Ron
TorJohnson
BAUD - is an old term that means the number of signaling changes that can
occur on a circuit in a unit of time. On a regular telephone line, the
absolute speed limit seems to be 2400 BAUD or 2400 signal changes in a
second.
What people often mistake for BAUD is bits per second or bps. By using
multiplexing techniques, we are able to get many mores bps than BAUD over
a circuit. Current standards on a regular phone line allow for 28,800 bps
or 28.8kbps. In some isolated cases you can get 38.4kbps but you need
usually need to have to identical modems to do it.
Chris Strawser
>I'm running a 28,800 ATT KIT modem.......but my "Chameleon"
>connection to my local provider only goes up to 19,000 Baud. I'm under
>the impression that baud is the rate in which the computor talks to
>the modem......and have been told that with data compression it should
>at least equal my modem speed.
>
>Does this mean I'm getting less than half of the advantage of my
>modems speed? What Baud rate should I be useing?
There are three speeds in a modem connection:
1 - speed between your computer and your modem
2 - speed between the two modems
3 - speed between the remote modem and it's associated computer
Speeds 1 and 3 are called the DTE (data terminal equipment) speeds.
Baud rate is an appropriate term here. Speed 2 is called the DCE
(data communications equipment) speed. Baud is *not* an appropriate
term to use when referring to DCE speed. Bits/Sec is the appropriate
term.
"Baud rate" is usually misunderstood. A 9600 "baud" modem is really a
2400 "baud" modem. Baud means how many signal transactions occur is a
time period. Modern modems encode many bits into a baud. A V.32
modem (9600) is a 2400 baud modem that encodes 4 bits into each baud.
It's better to refer to a V.32 modem as a 9600 bit per second modem.
Use "Bits/Sec" not "BPS" to abbreviate bits per second. "BPS" may be
taken to mean "bytes per second". There's no such thing as a 9600
*baud* modem.
In practice, you should set the DTE speeds as fast as possible. If
you have a 28800 modem, you want your DTE rate set to 38600 or
greater. This is because modern modems compress data, so it's
possible that the DCE *throughput* will exceed the DCE connection
rate. If the data is compressible, your 28800 modem may be able
transmit at 32K, which would necessitate that your DTE can feed your
modem at 32K.
If you connect to your ISP at only 19200, there are four are you need
to look at:
1 - Your DTE rate is set to 19200. This would force the modem to
connect at 19200 or less.
2 - Poor phone line quality prevents your 28800 modem from connecting
at 28000. Modern modems will lower their DCE speed in response to
poor phone line conditions.
3 - The ISP only has 19200 Bits/Sec modems (v.32 terbo).
4 - The ISP has a 28000 modem, but the DTE speed set to 19200.
A long answer to a short question, but there's a lot to know. Good
luck!
For more modem info, see:
http://users.aimnet.com/~jnavas/modem/faq.html