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COURIER HIGH SPEED MODEMS
Additional Operations G-3
The modem uses the U.S. Robotics proprietary HST cellular
protocol to make connections. The call starts at 1200 bps, a V.42
error control connection is negotiated, then the modem switches
to 4800 bps and begins measuring the line conditions.
Depending on line conditions, the modem decreases or
increases its connection rate, to a minimum speed of 300 bps
and a maximum of 12K bps. If a connection terminates before
data transfer is completed, the system tries to re-establish the
link and complete the transfer.
If a large number of blocks are being resent (shown by the ARQ
LED flashing randomly; some software displays the blocks
retransmitted in the file transfer window), you may want to
reduce the packet size by doing the following:
1. Be sure DIP switch 9 is ON so that the modem remains
online if it receives +++.
2. If DIP switch 9 is OFF, switch it to ON and reset the modem
by issuing the ATZ command.
3. Send the modem the escape sequence by typing +++ so that
the transmission is interrupted, and wait 1 second.
4. Type AT S33=1 to reduce the packet size.
5. Then type ATO so that the modem returns online and
continues to transmit.
NOTE: HST cellular connections can only be made with other
U.S. Robotics modems in HST cellular mode. The modem
cannot be used to place a voice or data call to another phone or
modem when it is in this mode.