Common control properties
Several network control parameters are common to Schedule, History, and other network features provided under station to station communications. The following descriptions may apply to Niagara Network and other drivers.
Enabled
An Enabled property is available at the network level, device (or station) level, and as part of the schedule and history import and export extensions. Setting Enabled to true allows the network, device, or component to operate and communicate. Changing the setting to false disables the network device, or component functions, thereby stopping any related network traffic that they might initiate.
Retry Trigger
By default, device extensions Histories and Schedules contain a “Retry Trigger” component, appearing in the property sheet view but not in any Manager view. The retry trigger can have a significant impact on traffic if there are one or more unsuccessful import or export actions attempted.
Figure 4-9
Retry trigger settings
Upon any unsuccessful execution of a history import or export descriptor or schedule import or export descriptor contained in that same device extension, the Retry Trigger defines subsequent “retries” that will automatically occur upon the interval period defined (default value is 15 minutes). This continues until successful execution occurs. Obviously, a smaller time interval creates more “retry” traffic when communication between the remote and supervisor station is interrupted for an extended period.
Execution Time
By default, import and export descriptors (associated with both Histories and Schedules) contain the Execution Time component. This component provides for flexible timing for executing an import or an export. Options for Execution Time settings are described under the "Trigger Mode" topic.
Figure 4-10
Execution time
If an Execution Time trigger fails, the Retry Trigger settings are invoked. The difference between the Retry Trigger and Execution Time component is that the the Execution Time component fires at the defined “Execution Time(s)” whereas the Retry Trigger fires whenever a subordinate execution fails. It is possible to set an Execution Time to an interval as low as 1 second, thus creating constant import or export traffic. If an unusually low setting (frequent firing) is multiplied over many histories and calendars, it can be a source of excessive network traffic.
Trigger Mode
This property allows you to choose a triggering mode for a "Retry Trigger" or an "Execution Time". Trigger mode options are shown in Figure 4-11 and described in the following list:
Figure 4-11 Trigger modes (shown in Execution Time component)
requires a manual execution action in order to perform the import. No import takes place until a user takes an action to execute it.
allows you to specify a time for import to occur on a once-daily basis.
You may consider scheduling imports at different times across a network–possibly staggering the times if large history files are anticipated.
allows you to specify a frequency and time period when imports occur.
This option allows you the most flexible control options, but also allows you to increase network traffic significantly by decreasing the time interval between imports. It is possible to decrease the interval to as little as 1 second between imports, which is excessive for most applications.