Hitachi Relion 670 Series Communication Protocol Manual page 16

Section 2
DNP3 overview
DNP3 can also be used over packet-oriented networks such as TCP/IP and UDP in which, for example,
Ethernet may be used. In this case DNP3 can be said to be tunneled over TCP/IP or UDP.
Data link layer
The DNP3 data link layer is designed to operate with asynchronous or synchronous bit serial physical
layers. Fully balanced transmission procedures were adopted to support spontaneous transmissions
from remotes.
Data link functions include:
• Performing message data link retransmissions.
• Packing user data into the defined frame format includes CRC and transmitting the data to the
physical layer.
• Unpacking the data link frame received from the physical layer into user data, checking and
removing CRC.
• Controlling the physical layer.
• In unsolicited reporting mode, performing collision avoidance/detection procedures to ensure reliable
transfer of data across the physical link.
• Responding to all valid frames received from the physical layer.
Data link responsibilities:
• Exchange of Service data units (SDUs) between peer DNP3 data links
• Error notification to data link user
• Sequencing of SDUs
• SDU delivery quality.
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.
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
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Additional information on the DNP3 physical layer is available at the DNP Users Group at
www.dnp.org.
See the DNP technical bulletin TB1998-0402, section 3 for details at www.dnp.org.
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1MRK511391-UUS Rev. L
DNP, 670 series
Communication protocol manual