Specifications

Configuring Modem Signals
11-12
Specifying ALTERNATE SPEED
Description
The ALTERNATE SPEED characteristic is only used with full MODEM
CONTROL access servers.
Two speeds for a modem port can be defined in the access server database:
primary and alternate (or fallback). The primary speed is defined with the speed
characteristic; the ALTERNATE SPEED is defined with the ALTERNATE SPEED
characteristic. You normally set up the primary speed as the high speed and the
ALTERNATE SPEED as the low speed. For ALTERNATE SPEED to work, you
must specify a single input/output speed for the speed characteristic.
If an ALTERNATE SPEED is specified, the access server asserts the DSRS signal
along with DTR and RTS when receiving a connection. DSRS indicates that the
higher primary speed should be used.
The access server monitors the SMI signal to determine whether to use the higher
or lower speed. When SMI is asserted, the access server selects the higher speed;
when SMI is deasserted, the communications selects the lower speed. The modem
connected to the access server must support the SMI signal in order for
ALTERNATE SPEED to work; otherwise, erroneous data transmission can occur.
To determine whether the modem supports the SMI signal, refer to your modem’s
documentation.
The ALTERNATE SPEED feature can be used with dial-out (sends calls) modems.
For dial-in (receives calls) modems, you should enable autobaud and disable
ALTERNATE SPEED. This allows you to configure the dial-in modem to any
speed supported by both the modem and the access server.