wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

58-4 Industrial Communication Systems
in the market as an open standard promoted its adoption and it has
now been ratified as IEEE Standard 1815.
The heritage of the protocols and the dependencies in the
documentation are illustrated in Figure 58.1.
The elements that are common to both IEC 60870-5-101/-104
and DNP3 include the following:
IEC 60870-5-4
IEC 60870-5-1
IEC 60870-5-2
IEC 60870-5-3
DNP3
• T101/T104 and DNP3 adopt the “Enhanced Performance
Architecture” (EPA) reference model described in IEC 60870-
5-3 that uses only the Physical, Data Link, and Application
IEC 60870-5-5
IEC 60870-5-101
layers of the ISO 7-Layer reference model and dispenses with
the Network, Transport, Session and Presentation layers. IEC 60870-5-104
DNP3 then extends the EPA model with a transport “function”
(a pseudo-layer) that permits assembly of messages
larger than a single data link frame.
FIGURE 58.1
specifications.
Dependencies of the
• T101 and DNP3 use data link frame formats and data link frame handling rules defined in IEC 60870-
5-1 and IEC 60870-5-2. These provide for good message efficiency with good error detection and
rejection, meeting the basic electric power SCADA requirements for message integrity and efficiency.
• T101/T104 and DNP3 are based on the “Report by Exception” (or RBE) paradigm where, in normal
operation, only changes are reported and data that has not changed is not reported. This meets
the basic electric power SCADA requirement for efficiency of message reporting (by eliminating
the unnecessary reporting of unchanged data) and also addresses the requirements to return SOE
information (changes sent in sequence and with time-stamping). The RBE mechanism requires
the initial collection of all data from a field device through an “integrity poll” and the subsequent
reporting of all changes in the correct chronological time sequence. If this is done correctly with
no loss of SOE data, then the resulting data image in the receiving station is always correct.
• Control command procedures include a “Select Before Operate” or “Select/Execute” mechanism
also called a “two-pass control.” This mechanism provides control commands with significantly
enhanced security against random data errors introduced, for example, by induced noise interference
in the communication system. This supports the electric power SCADA requirement for high
integrity validation of control commands.
• Data objects include quality flags that provide extra information to qualify or validate the data
that is being reported.
• Time stamps on change data that indicate the time of measurement of the reported data.
• Data and function types supported by both IEC 60870-5-101/-104 and DNP3 include
• Reporting of single-bit binary status objects
• Reporting of double-bit binary status objects
• Reporting of integer analog measurands
• Reporting of floating-point analog measurands
• Reporting of counters (also called accumulators or integrated totals)
• Control commands to binary outputs (on/off or trip/close commands)
• Control commands to integer or floating-point setpoint outputs
• Control commands to freeze counters/accumulators
• Ability to read and write files to or from field devices
• Ability to set the time and date (clock and calendar) in the field devices, including correcting
for the communication system propagation delay
• Ability to reset remote devices
• Commands to perform an “integrity poll” (collect a refreshed data image of all data from
a field device)
• Commands to collect specific subsets of data from a field device
© 2011 by Taylor and Francis Group, LLC