How do I Configure Geo SCADA Expert to Optimize the Use of the WITS-DNP3 Protocol?
From version 3.0 of the WITS-DNP3 standard, there is an optimized way to use the protocol. These optimizations can significantly reduce the number of messages that are exchanged between a Master Station and Field Device, particularly when a communications session is first established. These can be particularly beneficial with on-demand battery powered devices, as they help to prolong the life of the battery.
ClearSCADA 2017 R3 (Geo SCADA Expert) onwards supports optimized use of the WITS-DNP3 protocol and communications with WITS Field Devices that themselves support optimized use of the protocol. (Geo SCADA Expert also continues to provide support for communicating with WITS Field Devices that do not support optimized use of the WITS-DNP3 protocol, or are using an earlier version of the protocol.) With WITS 3.0 and above, a device's WITS Device Profile indicates whether that device supports optimized use of the WITS protocol (see WITS Device Profiles). To take advantage of all of the optimizations:
- the Field Device must support the optimized use of the protocol (this is indicated in section 1.12.5 of the device's WITS Device Profile)
- the Outstation database item in Geo SCADA Expert must include some specific configuration (see below).
Some of the optimizations do not require support from the Field Device and so can be used with any Field Device, including those using older versions of the WITS-DNP3 standard.
To configure Geo SCADA Expert to optimize the use of the WITS-DNP3 protocol, you should specify the following settings (none of the settings get downloaded to the Field Device; they purely control some of Geo SCADA Expert's communications startup activities). The properties to which the settings apply are on the DNP3 tab of the DNP3 WITS Outstation Form, and as such the properties are documented in the Geo SCADA Expert Guide to the DNP3 Driver.
- Read Device Attributes—This property is located within the Startup section of the tab. Set to 'Following a Master Station or Outstation Startup' (see Configure the Actions that Occur on Communications Startup in the Geo SCADA Expert Guide to the DNP3 Driver).
- Polling—Only applicable to Field Devices that support and have String points. This property is located within the String Points Polling (Static Data) section of the tab. Set to 'Following a Master Station or Outstation Startup' (see Specify Whether Geo SCADA Expert Polls an Outstation for Static String Point Data in the Geo SCADA Expert Guide to the DNP3 Driver). (For Field Devices that do not have String points, ensure that the property is set to 'Disabled'.)
- Check Clock Drift—This property is located within the Set the Clock section of the tab. Set to 'Integrity Poll' (see Define Whether Geo SCADA Expert Updates the Outstation Clock in the Geo SCADA Expert Guide to the DNP3 Driver).
This property has an associated risk when it is set to 'Integrity Poll' and a combination of other factors apply (including the outstation's clock never having been set). When all of the factors apply, this could result in queued events being discarded due to them having timestamps that are in the distant past. For information about this risk and a list of the factors involved, see Define Whether Geo SCADA Expert Updates the Outstation Clock in the Geo SCADA Expert Guide to the DNP3 Driver.
- Minimum Drift—This property is also located within the Set the Clock section of the tab. The WITS-DNP3 standard states that this should be set to 10 seconds (see Define Whether Geo SCADA Expert Updates the Outstation Clock in the Geo SCADA Expert Guide to the DNP3 Driver).
UNEXPECTED BEHAVIOR OF APPLICATION
In addition to the above, you should also consider further optimization opportunities:
- Is it necessary to use DNP3 Secure Authentication?
The standard recommends that DNP3 security measures are used. However, you might consider turning these off if you have performed a detailed analysis of the perceived security threat, and this demonstrates that you will still be able to meet your organization's security requirements without using DNP3 Secure Authentication.
The physical communications medium may provide adequate security, or you might deem that the type of data being transmitted does not warrant the use of DNP3 Secure Authentication.
DNP3 Secure Authentication can increase the number of message transactions at the start of a communications session by as much as 25%. Additionally, it will also increase the size of some of the messages.
- The number of points for which data is logged and the frequency with which that data is logged
Only configure a Field Device to log (store) data for those points for which there is a genuine need to retain the data historically. For other points, merely retrieving the current data might well be sufficient.
For those points for which you do require data to be logged, be aware that a Field Device can pack the logged data more efficiently if the data for all of the points is logged at the same frequency.