Network polling policies
Some driver networks use a single polling mechanism (a poll component, named “Poll Service” or “Poll Scheduler”) adjusted at the network level in the station. Regardless of driver type, the Poll Service provides a “poll scheduler” that scans four polling-rate categories to service pollable items, as follows:
- The Poll Scheduler allocates three rate categories (for example: Slow, Normal, Fast). Pollable items (mainly proxy points) are associated with one of these three rate groups. The rates are assigned by choosing a Tuning Policy in each point's proxy extension (BacnetNetwork and SnmpNetwork) or by using a Poll Frequency setting (drivers other than BacNet and Snmp).
- A fourth “dibs stack” category is allocated for pollable items that transition to a subscribed state. This may be a “temporary subscription,” such as results when viewing unlinked proxy points (without alarm or history extensions) in workbench or a browser. Or, it may occur when a permanently subscribed point is first polled (thereafter, it is no longer “dibs stack-polled”).
Figure 4-8 Polling scheduler
For more information about polling and the priority of polling by the scheduler, refer to the NiagaraAX User Guide.