User`s manual

U.S. Robotics I-modem Command Reference
Controlling Data Rates • Page 7-2
&Bn Set the serial port rate as variable or Þxed.
&B0 Variable rates. Allows the I-modem to change its serial port rate to match
the connection rate.
&B1 Fixed rate. The I-modem always communicates with an attached device at
the rate at which you have set the terminal or software, regardless of the
connection rate.
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.
Note The serial port rate must be equal to or higher than the &Nn rate.
&B2 Set the serial port rate as Þxed for ARQ calls and variable for non-ARQ
calls (see Chapter 11, Handshaking, Data Compression, and Error Control
,
for more information about ARQ) when answering only. When the
I-modem connects in ARQ mode, it shifts its serial port rate to a rate that
you specify using your communications software (for example, 38.4
Kbps). If the connection is not under error control, I-modems behave as if
they were set to &B0 and switch their serial port rates to match the connec-
tion rate of each call.