Define whether the Queue Parameter is Available

You can use the Server Configuration Tool’s Allow Certain Requests to Optionally be Queued setting to control the availability of the Queue parameter on certain types of request. The Queue parameter is designed for use with PSTN outstations and Direct ‘On Demand’ outstations and allows users to postpone various types of request, including controls, Off Scan, On Scan, Configuration Download, and Tune Alarm Limits.

When you use the Queue parameter on a request, the request is saved on the ClearSCADA server and the relevant driver. Instead of being executed immediately, the request is queued so that it can be executed later as part of a ‘batch’ of queued requests (the queued requests will be executed the next time the outstation communicates with ClearSCADA). For example, using the Queue parameter may be useful when there is a cost involved with establishing connections to PSTN or Direct On Demand outstations—it may be less expensive to execute the requests as a group rather than establish a connection for each individual request.

The availability of the Queue parameter is controlled by the Allow Certain Requests to Optionally be Queued setting on the Server Configuration Tool. By default, the Allow Certain Requests to Optionally be Queued check box is clear (the option is disabled), and so the Queue parameter is unavailable in ViewX and WebX.

To define whether the Queue parameter is available:

1. Access the ClearSCADA Server Configuration Tool (see Accessing the ClearSCADA Server Configuration Tool).
2. Expand the Global Parameters branch of the tree-structure.
3. Select Drivers to display the Drivers section.
4. Use the Allow Certain Requests to Optionally be Queued check box to control the availability of the Queue Request feature:
5. 
   • If you have PSTN outstations or Direct ‘On Demand’ outstations and need to be able to delay requests, you should select the Allow Certain Requests to Optionally be Queued check box. This will mean that the Queue parameter is available; users will be able to queue certain types of requests.
   • If you do not have PSTN outstations or Direct ‘On Demand’ outstations, or have no need to stop requests from being executed immediately, you can disable the Allow Certain Requests to Optionally be Queued setting. This will mean that the Queue parameter is unavailable to users and so they cannot queue requests.
6. Right-click on the system icon in the tree-structure, and select the Apply Changes option to apply the changes.