If your modem communicates properly with remote users, it is probably in control. It isrecommended that you occasionally change some of the functional settings and thenchange them back, just for the to ensure that the modem is communicating, and toensure it has been initialized recently.Another strategy, particularly if your system is difficult to access physically, is to protectit with an Uninterruptable Power Source (UPS) and a phone-line surge protector.In case recovery becomes necessary, your system should be shut down as usingappropriate shutdown procedures. Disconnect and reconnect modem power, and poweron the system to allow complete reinitialization of your system.Seamless Transfer of a Modem SessionThere are about as many modem command variations as there are modems. Thesample modem configuration files have been written to capture the largest number ofworkable modem settings.The modem command &Dn (where n is a number) generally sets the modem responseto the Data Terminal Ready (DTR) signal from the server’s serial port. The desiredresponse is that the modem will hold a connection while DTR is enabled, and drop theconnection when DTR is released. This is the mechanism by which the server ″hangsup″ on a connection under normal conditions.The command &D2 is usually successful, but not always. The sample modemconfiguration files take this high percentage position, (see the note on page 224).Consult your modem’s manual for its specific response scheme for the &Dn command.There are two methods for dealing with the modem’s response to DTR:v Recoveryv PreventionBefore proceeding with one of these strategies, determine if your server’s modem is setup properly to respond to DTR.With the remote terminal connected to serial port 1 and defined as theprimary consoledevice, there are two tests you can perform:1. Will the modem drop the connection after the System initialization completemessage appears at the remote terminal?If yes, the modem is set up correctly.If no, try another &Dn setting for your server’s modem. See your modem manual forthis information. The &Dn command appears in three places each in three of thesample modem configuration files, (see the note on page 224).2. Will the server’s modem disconnect when the power drops? You can make thisobservation at the remote terminal by commanding your server to shutdown andpower off. (The AIX command shutdown -F will do this.) Watch for the message NOCARRIER on your remote terminal.Appendix G. Modem Configurations 223
