HELP!Baud rate

[Ho]

What is baud-rate ? I am quite confused about the setting.
How to determine ? (according to serial port chip, modem or line?)
What does it affect ? (accuracy, tranfer speed ?)
Many thanks in advance.

[Cor Speelman]

[posted to comp.dcom.modems]

Ho <ko...@singnet.com.sg> wrote in article
<5elv9j$g...@lantana.singnet.com.sg>:

People often use the term "baud" when they actually mean bps (bits per
second). The baud-rate is the number of high/low shifts made on a line per
second. You can consider it as the signal frequency that is used on the
telephone line. Modern high-speed modems are capable of transmitting 9
data bits per baud, so for instance with a 28800 bps connection the
baud-rate is 28800/9 = 3200 baud. To avoid confusion it is better to speak
about bits per second.
All 28k8 modems that I know of are capable of V42bis data compression. In
theory the maximum compression factor is 4 but in practice the factor
seldom exceeds 2 (for compressed files like zip files the factor is about
1). So for a 28800 bps modem the serial port speed should be at least
57600 bps, and if possible 115200 bps. For a 115200 bps serial port you
need a "16650 compatible UART" as serial port chip.
In practice it is best to set the serial port to a fixed speed of 57600 or
115200 bps, and to let your modem report the DCE (modem to modem) speed,
which is much more informative than the DTE (serial port) speed.

If you have questions on modems, I can recommend the following websites:
A good FAQ on modems for beginners is "Curt's High Speed Modem Page"
(http://www.teleport.com/~curt/modems.html).
More comprehensive and with more technical details is "Navas 28800 modem
FAQ" (http://www.aimnet.com/~jnavas/modem/faq.html).

Regards,
Cor Speelman

[R. Collins]

Ho wrote:
>
> What is baud-rate ? I am quite confused about the setting.
> How to determine ? (according to serial port chip, modem or line?)
> What does it affect ? (accuracy, tranfer speed ?)
> Many thanks in advance.

The first thing to do is forget about the term "Baud rate". You don't
need to worry about it.

Remember, there are _two_ connections you're worried about: the Pc to
modem connection (called the DTE link) and the modem to modem connection
(the DCE link). Each link can run at different speeds.

The DCE (modem to modem) speed is negotiated by the modems - you have no
real control over it. The speed you _do_ control is the DTE speed, and
this you should set _higher_ than the highest speed to expect to connect
at. For a 33.6kbps modem, set the port (DTE) speed to 57,600 or
115,200bps in your comm program.

Rick