Rockwell Automation 1758-RTU202 DataSite Software User Manual FRN 1.2 - Manual (Page 235)

Publication 1758-UM002D-EN-P - October 2010
DataSite DNP3 Configuration Utility (DS DNP3) 235
DNP3 Protocol Structure
DNP3 is a layered protocol based on OSI-7 layer protocols.
It supports the following layers:
• Application layer
The application layer sends request information from the master station
to the slave station, or unrequested response information from the slave
station to the master station. Information in this layer can be confirmed
and re-issued.
• Transport layer
The transport layer divides big application layer packets into several
small information packets in order to facilitate transmission by the data
link layer.
• Data link layer
The data link layer sends messages to the physical layer or receives
information from it. To ensure the accuracy of data transmission, every
16 words of information in the data link layer is a data block with an
additional two-byte cyclic redundancy check (CRC) code. Information in
this layer can be confirmed and re-issued.
• Physical layer
The physical layer describes the physical media for DNP
communication, such as a serial port or Ethernet.
DNP3 Data Object Library
DNP3 protocol contains data points with a variety of data types. Data points
are grouped according to their data types, and the groups are called data
objects. Examples of data objects are, binary input object, binary output
object, analog input object, counter object, freeze counter object, string object,
and analog output object. The collection of these data object groups is referred
to as the data object library.
DNP3 data objects can be further defined through object variants, such as the
16-bit analog input, 32-bit floating-point analog input, and binary input, all of
which contain time.