Whenever you attempt to log in by using a directly connected modem or alphanumeric terminal, ttymon goes to work. First, the SAC process is started by SMF. Then, the SAC automatically starts the port monitors that are designated in its administrative file, /etc/saf/_sactab. After the ttymon port monitor has been started, it monitors the serial port lines for service requests.
When someone attempts to log in by using an alphanumeric terminal or a modem, the serial port driver passes the activity to the operating system. The ttymon port monitor notes the serial port activity, and attempts to establish a communications link. The ttymon port monitor determines which data transfer rate, line discipline, and handshaking protocol are required to communicate with the device.
After the proper parameters for communication with the modem or terminal are established, the ttymon port monitor passes these parameters to the login program and transfers control to it.