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If your modem communicates properly with remote users, it is probably in control. It is
recommended that you occasionally change some of the functional settings and then
change them back, just for the to ensure that the modem is communicating, and to
ensure 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 using
appropriate shutdown procedures. Disconnect and reconnect modem power, and power
on the system 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.
The command &D2 is usually successful, but not always. The sample modem
configuration 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 Recovery
v Prevention
Before proceeding with one of these strategies, determine if your server's modem is set
up properly to respond to DTR.
With the remote terminal connected to serial port 1 and defined as the primary console
device, there are two tests you can perform:
1. Will the modem drop the connection after the System initialization complete
message 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 for
this information. The &Dn command appears in three places each in three of the
sample modem configuration files, (see the note on page 224).
2. Will the server's modem disconnect when the power drops? You can make this
observation at the remote terminal by commanding your server to shutdown and
power off. (The AIX command shutdown -F will do this.) Watch for the message NO
CARRIER on your remote terminal.
Appendix G. Modem Configurations
223
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