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2. DNP3 Protocol Primer
PXM 4/6/8K DNP3 Ethernet Communications User Manual
MN150005EN January 2017 www.eaton.com
In some multi-drop forms, communications are peer-to-peer.
A station may operate as a master for gathering information
or sending commands to the outstation in another station.
And then, it may change roles to become an outstation to
another station.
The middle row in
Figure 2
shows a hierarchical type sys-
tem where the device in the middle is an outstation to the
master at the left and is a master with respect to the out-
station on the right. The middle device is often termed a
sub-master.
Both lines at the bottom of
Figure 2
show data concentrator
applications and protocol converters. A device may gather
data from multiple outstations on the right side of the figure
and store this data in its database where it is retrievable by
a master station on the left side of the figure. This design is
often seen in substations where the data concentrator col-
lects information from local intelligent devices for transmis-
sion to the master station.
Figure 3. Master and Outstation Relationship – Layering.
2.1.4 TCP/IP
Many vendors offer products that operate using TCP/IP to
transport DNP3 messages in lieu of the media discussed
above. Link layer frames, which we have not talked about
yet, are embedded into TCP/IP packets. This approach has
enabled DNP3 to take advantage of Internet technology and
permitted economical data collection and control between
widely separated devices.
2.1.5 More On Layering
Communication circuits between the devices are often
imperfect. They are susceptible to noise and signal distor-
tion. DNP3 software is layered to provide reliable data
transmission and to affect an organized approach to the
transmission of data and commands.
Figure 3
shows the
layering that was not shown in
Figure 1
.
