Using CitectSCADA > Communicating with I/O Devices > Communicating with Remote Devices via Modems > Modems at the I/O server

Modems at the I/O Server

To decide how many modems to use at the I/O Server end, decide what function each modem will perform. A single modem can do any one of the following functions:

Dial-out

Makes calls to remote I/O Devices in response to a CitectSCADA request; for example, scheduled, event-based, operator request, and so on. Also returns calls from remote I/O Devices.

Dial-in

Only receives calls from remote I/O Devices, identifies the caller, then hangs up immediately so it can receive other calls. CitectSCADA then returns the call using a dial-back or dial-out modem.

Dial-back

Only returns calls from remote I/O Devices.

Dial-in and dial-out

Receives calls from remote I/O Devices and makes scheduled calls to remote I/O Devices.

Dial-in and dial-back

Receives and returns calls from remote I/O Devices.

Your modem setup depends on your system requirements. When making your decision, consider the following guidelines:

See Also