3Com 56K Your software may use terms such as locked serial port (fixed rate) or autobaud (variable rate)., The serial port rate MUST be equal to or higher than the Connection rate (&Nn).

8-2 CHAPTER 8: CONTROLLING DATA RATES
Your software may use terms such as locked serial port (fixed rate) or
autobaud (variable rate).
The serial port rate MUST be equal to or higher than the Connection rate
(&Nn).
To allow your modem Set the serial port
rate as Command
To change its serial port rate to match the
connection rate. Variable AT&B0
To always communicate with an attached
device at the rate at which you have set
the terminal or software, regardless of
the connection rate.
Fixed AT&B1 (Default)
For the greatest throughput, set the serial
port to 115200, 57600, or 38400 bps for
high-speed calls, and to at least 9600 bps
for 2400-bps calls.
To shift its serial port rate to a rate that
you specify using your communications
software (for example, 38.4 Kbps) when
the Business Modem connects in ARQ
mode.
If the connection is not under error
control, the Business Modem behaves as
if it was set to &B0 and switches its serial
port rates to match the connection rate
of each call.
Fixed for ARQ calls
and
AT&B2
To implement this feature, first set your
software to the desired rate. Then send
AT&B2&W to the modem.
The Business Modem stores the rate of
the command in NVRAM along with the
current settings. The Business Modem
checks NVRAM for the specified serial
port rate each time it makes an ARQ
connection.
When saving subsequent configurations
to NVRAM, be sure your software is set to
your selected serial port rate so the
correct rate is maintained.
Variable for non-ARQ calls when
answering only.
See Chapter 13, Handshaking, Data
Compression, and Error Control, for
more information about ARQ