Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

154 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
The device profile document also lists many configuration details including default
configurations for confirmations, retries and other details. All of these need to be checked
for compatibility with the planned implementation.
Confirming interoperability:
• Determine DNP3 polling mode to be used
• Determine range of slave devices
• Assemble device profile documents for range of slave devices
• Determine minimum required DNP3 level
• Determine functions above this level that will require support
• Determine data objects above selected base level that will require support
• Examine device profiles for RTUs and establish compatibility with IEDs
• Examine device profiles for master station and establish compatibility
with RTUs
6.3 Implementation rules and recommendations
The following sub-sections summarize rules and recommendations that appear in the subset
definition document DNP3 Subset Definitions, Version 2, Nov 1995. These rules and
recommendations provide information that extends and clarifies that contained in the
Basic Four documents.
6.3.1 Error responses
Error responses are defined to cope with side-effects of having levels. These are the
possibility that a device of one level will be polled for data objects that it cannot provide.
Types:
• Request not valid for its level
• Request not valid for the particular device
These are reported by the internal indications bits 0–2.
Event objects are also a special case, because although they are not tied to a physical
device and they may not exist at a given time, because there may be no new events to
report. In this case the device must provide a null response rather than a ‘requested objects
unknown’ response.