Data Carrier Detect handling

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The server uses the Data Carrier Detect (DCD) signal to monitor the true state of a modem.

If the DCD signal on the modem's port is "high," the server believes the modem to be in use. It is therefore important to know which circumstances cause this signal to be forced into a "high" state. The DCD signal can be raised high for the following reasons:

  • The use of clocal in the stty attributes for runtime field on the SMIT TTY Configuration panel.
  • Having the Ignore Carrier Detect field set to enable on the SMIT TTY Configuration panel for ttys connected to a 128-port adapter.
  • The modem forces DCD high with either AT commands or switches.
  • The tty port is already in use by an application.
    Note: When modems make a connection with another modem, the modem raises the CD. Most modem defaults settings set this signal "high" at all times even when the modem is idle. CD should not be forced "high."