Shared Outstations

Shared outstations use a dual channel communications set-up whereby the outstations communicate with the ClearSCADA server via one of two Direct Channels. The outstations are grouped into Shared Outstation Sets. Unless configured otherwise, each outstation may communicate via either of its set’s direct channels—all of the outstations in the set do not have to use the same channel at any given time.

As with a Switched Dual Channel set-up, shared dual channel communications provide a direct ‘backup’ channel. If ClearSCADA detects that one of the direct channels has failed, it continues to communicate with the outstations using the alternate channel.

The main advantage of a shared dual channel set-up over a switched dual channel set-up is that each outstation may use either of the channels. This provides more efficient communications as the load is shared between the two channels rather than the entire data transfer occurring via one channel while the other channel is idle.

If supported by the driver and outstation type, a Shared outstation may also have a dial-up modem to provide PSTN fallback. With PSTN fallback, if ClearSCADA detects that both direct channels have failed, communications between ClearSCADA and the outstation continue via the modem and PSTN channel. For further information, see Direct - PSTN Fallback.

For information on assigning direct channels to a Shared outstation set, see Defining Channel Settings for a Shared Set.

You can configure each outstation in a shared outstation set to:

• Use either channel (see Communications via Either Channel).
• Use a specific channel (see Communications Fixed on Line A or Fixed on Line B).
• Use the same channel as the outstation that has been designated that outstation’s ‘Group Master’ (see Communications Determined by a Group Master).

You configure the required properties using the fields on the Shared tab of the Outstation Form (see Define an Outstation’s Shared Properties).