Section 2
DNP3 overview
2.1
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
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.
2.1.1
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
.
2.1.2
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.
1MRS757820 B
Section 2
DNP3 overview
Recloser Protection and Control RER615
7
Communication Protocol Manual
