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1MRK 511 391-UUS A
670 series 2.2 ANSI
Communication protocol manual
Link-layer confirm usage is not recommended and the implementation is optional. The
IED does not request data-link layer confirmations for TCP/IP communication.
See the DNP technical bulletin TB1998-0402, section 3 for details at
www.dnp.org.
Transport pseudo-layer
To support advanced RTU functions and messages exceeding the maximum data link
frame length, a transport pseudo-layer which implements message assembly and
disassembly services was adopted.
Transport functions:
•
Fragmenting user data into one or more data link frames and transmitting the data
to the data link layer
•
Assembling the data link frames received from the data link layer into user data
•
Controlling all aspects of the data link excluding data link configuration
Transport responsibilities:
•
Exchange of SDUs between peer DNP3 transport pseudo layers
•
Error notification to transport users
•
Sequencing of SDUs
Application layer
The application layer is responsible for performing operations on data objects defined
by the device or on the device itself. These operations include returning actual values
(read function), assigning new values (write function) if the object represents control
points, arming and energizing the output point (select, operate or direct operate
functions) and if counters are used, reading actual values and clearing the counters.
DNP3 uses the term point to identify an entity, and these entities can be categorized
into point-types, such as analogs or binaries. Points are addressed by giving them an
index number and an object is a formatted representation of data from a point. These
objects can be assigned to classes in order to organize events and current values into
categories. The DNP3 protocol defines four data classes to organize data reporting.
Communication modes
The IED supports four DNP3 communication modes.
Section 2
DNP3 overview
13
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