Making sure line speeds are set correctly

The ttymon process' main function is figuring your line speed, if a constant speed has not been specified. It does so with either the autobaud method or with the rotary method.

With autobaud speed matching, if the incoming line is set to 8 data bits and no parity, ttymon can usually determine your line speed. This is activated by choosing the auto option when setting up a ttymon from the Modem Manager. Otherwise, the rotary method is used, starting at the speed you specified when setting up ttymon for the line.

When a call comes in that uses the rotary method, and the starting baud rate is not correct for the line, pressing the <Break> key on the remote terminal moves ttymon to the next speed in the sequence. Once the correct speed is reached, the login prompt displays on the remote terminal.

Rotary sequences are defined in the file /etc/ttydefs (see ttydefs(4)). Each entry in the file specifies a baud rate in the sequence, and points to the next entry in the sequence. The final entry points back to the first entry in that sequence. Any number of sequences may be defined; the baud rate at which you start in the sequence (and, therefore, the sequence itself) for any particular dialing attempt is the baud rate specified when you started the ttymon process for the line on which the call is coming in.

There are three important sequences in /etc/ttydefs:

• The 9600 sequence is for 7 bit, even parity communications.

• The baudNP sequences (where baud can be any baud rate, such as 9600NP) are for 8 bit, no parity communications. However, the 8th bit is stripped so there are really only 7 data bits.

• The baud_8bit sequences (where baud can be any baud rate, such as 9600_8bit) are for 8 bit, even parity communications.

For most of today's modems you should use the highest speed setting that the modem supports, and not the auto setting. This is because the modem usually maintains a constant speed at the serial line interface and just changes the modem-modem speed on slower speeds. For example, if your modem is 9600 baud, it is recommended that you select a 38400 baud rate for the modem.

ttymon's activities are logged in /var/saf/ttymon/log. Note that this log tends to be terse, and not that helpful to the general user.

Stopping and restarting ttymon

If ttymon appears to be no longer accepting incoming calls, you might try to stop it and restart it. To do this, log in as root and enter:

/usr/sbin/sacadm -k -p ttymonnn
/usr/sbin/sacadm -s -p ttymonnn

where nn identifies the ttymon instance to be stopped and restarted.