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