Dte Rate Select (&Bn) - US Robotics COURIER User Manual

COURIER HIGH SPEED MODEMS
DTE Rate Select (&Bn)
Use this command to select variable or fixed rates at the DTE
interface. Initially, the modem's DTE interface rate depends on
your terminal or software setting. The modem detects this rate
from the rate at which it receives the AT command. After that,
the DTE rate depends on the modem's &B setting, as follows.
&BO
&Bl
&B2
Variable rates. Default. When the modem switches its
link rate to connect with a modem operating at a different
rate, it also switches its DTE rate. The software or
terminal also switches DTE rates to match the link rate.
This setting requires variable rates on the phone link,
&NO, so that the Courier can switch link rates to match
the rate of the remote modem.
Fixed rate. The modem always communicates with the
DTE at the rate at which you have set the terminal or
software, regardless of the link rate. For the greatest
throughput, set the DTE to 57.6K, 38.4K or 19.2K bps for
high speed calls and to at least 9600 bps for 2400-bps calls.
This setting is not affected by the &N setting. However,
the DTE rate must be equal to or higher than the link rate.
In addition, this setting requires Transmit Data flow
control enabled, preferably hardware control (&Hl), so
that the modem's buffer doesn't overflow.
Fixed for ARQ calls/Variable for non-ARQ calls. Answer
mode only. When the modem goes off hook and connects
in ARQ mode, it shifts its DTE rate up to a user-specified
rate, for example, 19.2K bps. If the connection is not
under error control, the modem behaves as if it were set
to &BO and switches its DTE rate to match the connection
rate of each call.
This option is designed for installations such as Bulletin
Boards that receive calls from a wide variety of modems,
ranging from the very slow to those with the Courier's
advanced design.
4-14 Interface Controls
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