Telemetry Channels are the communication lines through which information is passed between the ClearSCADA server and the outstations on your system.
ClearSCADA commonly uses two types of telemetry channel, depending on types of communication supported by the outstations on your system:
- Direct—Direct channels are used by outstations that are permanently connected to the ClearSCADA server (for example, via a cable, network, or a continuous radio signal).
You need to add and configure a suitable Direct channel for each uninterrupted communications connection between the ClearSCADA server and the Direct outstations in your system.
- PSTN—PSTN (Public Switched Telephone Network) channels are used by outstations that communicate with the server using dial-up modems. ClearSCADA uses PSTN channels to represent telephone line connections between the ClearSCADA server and PSTN outstations.
Some types of outstation use PSTN channels as the primary means of communication with the ClearSCADA server. For outstations that use a Direct connection to the server, but that also have access to a suitable dial-up modem, PSTN can be used as a ‘fallback’ means of communicating with the server, should the permanent channel(s) become unavailable.
If your system uses PSTN outstations, you need to configure one PSTN Channel to represent each telephone line that is available for use by the ClearSCADA server and/or the PSTN outstations on your system.
If your system uses Direct outstations that are able to use PSTN as a fallback means of communication, you need to configure one PSTN Channel to represent each telephone line that is available for use by the ClearSCADA server and / or the PSTN and PSTN fallback outstations on your system.
Unlike permanent connections, PSTN connections are only established when required. The telephone call is usually terminated as soon as any data has been transmitted.
When a ClearSCADA server dials out to an outstation, it selects any channel that has the same Connection Type as the outstation, provided that the channel is available for use and has valid configuration, with Dial Out configured.
A system administrator can specify which channels the server should use if several are available (see Define how a PSTN Channel is Selected for Communications in the ClearSCADA Guide to Server Administration).
When an outstation dials in to the server, it only ever uses the line or lines that it is configured to use (see Define Dial In Line Properties on a PSTN Outstation). The channels it uses have to be configured to allow outstations to Dial In to the server.
Refer to the driver-specific documentation for the types of channel that an individual driver supports.
Use the fields on the appropriate Channel Form to configure the channels on your system. The Form has several tabs (see Tabs on Channel Forms).