Section 2 Dnp3 Overview; Dnp3 Standard - ABB 620 Series Manual

1MAC459571-IB C
Section 2
2.1
620 series ANSI
Communication Protocol Manual
DNP3 overview

DNP3 standard

The DNP3 protocol was developed by Westronic based on the early versions of the IEC
60870-5 standard telecontrol protocol specifications. Now the protocol specification is
controlled by the DNP Users Group at www.dnp.org.
The ISO/OSI based model supported by this protocol specifies physical, data link and
application layers only. This reduced protocol stack is referred to as EPA. However, to
support advanced RTU functions and messages larger than the maximum frame length as
defined by the IEC document 60870-5-1, the DNP3 data link is intended to be used with
a transport pseudo-layer. As a minimum, this transport layer implements message
assembly and disassembly services.
Physical layer
There are two specified physical layer modes; serial and Ethernet.
Additional information on the DNP3 physical layer is available at the
DNP Users Group at www.dnp.org.
Data link layer
The DNP3 data link layer is designed to operate with connection-oriented and
connectionless asynchronous or synchronous bit serial physical layers. Fully balanced
transmission procedures were adopted to support spontaneous transmissions from
outstations.
Data link functions:
• Performing message data link retransmissions.
• Synchronizing and handling the FCB in the control octet.
• Setting and clearing the DFC bit based on buffer availability.
• Packing user data into the defined frame format, include CRC checksums and
transmitting the data to the physical layer.
• Unpacking the data link frame received from the physical layer into user data, check
and remove CRC checksums.
Section 2
DNP3 overview
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