Hst Mode - US Robotics COURIER User Manual

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COURIER HIGH SPEED MODEMS
APPENDIX A. LINK NEGOTIATION (HANDSHAKING) AND ERROR
CONTROL
This appendix includes detailed information on how USRobotics
HST and V.32 bis modems negotiate with remote modems for
the rate and other characteristics of each connection. You may
find it helpful if you are having difficulty connecting with
another modem.
In addition, you'll find information on error control and,
especially useful, some statistics and guidelines on using the
modem for the best throughput.
The following text relies on familiarity with two terms used in
this manual, ARQ and DTE. ARQ (automatic repeat request)
designates a connection under error control. DTE (data
terminating equipment) means the computer or terminal to
which the modem is attached. DTE rate is the same as serial port
rate.
LINK NEGOTIA T/ON (HANDSHAKING)
HST Mode
During high-speed link negotiation, timing and procedures
differ for HST or V.32 bis modulation, as follows.
Serial port rate: 57.6K/38.4K/19.2K/9600 bps (57.6K, 38.4K, or
19.2K required for 16.BK or 14.4K connections)
Modem settings: Bl, &Bl, &Hl/ &H2/ &H3, &M4/ &MS, &NO
1. The modems begin handshaking by training (synchronizing)
at 2400 bps and exchanging information on their error
control, data compression, and speed capabilities.
2. Once the modems enable error control, handshaking
proceeds as follows. If the remote modem is operating at
2400 bps or lower, the Courier stays at 2400 bps or falls back
to match the remote modem's slower rate.
If the remote modem is HST-compatible and operating at a
higher speed, both modems shift up and train at 9600 bps.
From there, depending on the speed of the remote modem,
Link Negotiation and Error Control A-1