IBM RS6000 Service Guide - Page 324

If your modem communicates properly with remote users, it is probably in control. It may be wise to occasionally change some of the functional settings and then change them back, just for the sense of security that the modem is communicating, and to assure it has been initialized recently. Another strategy, particularly if your system is difficult to access physically, is to protect it with an Uninterruptable Power Source (UPS) and a phone-line surge protector. In case recovery becomes necessary, your system should be shut down as gracefully as possible. Disconnect the power cable and press the power button to drain capacitance while power is disconnected. Disconnect and reconnect modem power, then reconnect system power to allow complete reinitialization of your system. Seamless Transfer of a Modem Session There are about as many modem command variations as there are modems. The sample modem configuration files have been written to capture the largest number of workable modem settings. The modem command &Dn (where 'n' is a number) generally sets the modem response to the Data Terminal Ready (DTR) signal from the server's serial port. The desired response is that the modem will hold a connection while DTR is enabled, and drop the connection when DTR is released. This is the mechanism by which the server "hangs up" on a connection under normal conditions. Usually the command &D2 will work, but not always. The sample modem configuration files2 take this high percentage position. You should 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: 1. Recovery 2. Prevention Before proceeding with one of these strategies, you need to determine if your server's modem is set up properly to respond to DTR. D-6 Service Guide