US Robotics COURIER User Manual page 103

COURIER HIGH SPEED MODEMS
they shift up again to 12K bps, 14.4K bps, and again to 16.SK
bps; or they fall back to 7200 bps and again to 4SOO bps, if the
remote modem is operating at one of those lower speeds.
Initially, the high-speed channel is allocated to the an-
swering modem, the 450-bps channel to the calling modem.
This allocation reverses if the calling modem has more data
to transmit than the answering modem.
Specialized High-Speed Connect
It's possible for two modems in HST mode to connect directly at
9600, 12K, 14.4K or 16.SK bps, without 2400-bps handshaking.
However, this is only recommended for faster connections in
specialized installations where the computer and software
manage error control. The reason is that there can be no error
control because HST modems negotiate error control during
2400 bps handshaking.
Both modems must be set as follows. High speed handshaking
requires a fixed link rate: the modem only connects if the remote
modem is operating at the same link rate-9600 (&N6), 12K
(&N7), 14.4K bps (&NS), or 16.SK bps (&N9).
Serial port rate: 57.6K/3S.4K/19.2K/9600 bps (57.6K, 3S.4K, or
19.2K required for 16.SK or 14.4K connections)
Modem settings: Bl, &Bl, &Hl
I
&H2/ &H3, &MO,
&N6/ &N7
I
&NS/ &N9
HST Mode, Error Control Disabled
If error control is disabled-that is, the Courier HST is set to
&MO or the remote modem isn't set for error control and the
Courier HST reverts to &MO-the Courier operates in one of the
following ways.
1.
If set to &NO, it only connects at 2400 bps or lower. This
ensures that there will not be data transfer at high speeds
unless the call is protected by error control.
Courier HST modems negotiate error control during 2400
bps handshaking. If they cannot connect under error
control, they stay at 2400 bps. Or, if the remote modem is
operating at a lower rate, the Courier HST switches to the
lower rate.
A-2 Link Negotiation and Error Control
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-