R.6.32
SEL-421 Relay Reference Manual Date Code 20111215
DNP3 Communications
DNP LAN/WAN
DNP LAN/WAN
The installation of an Ethernet card in an SEL-421 Relay provides a DNP3
Level 2 Slave interface for direct Ethernet network connections to the relay.
Because of the benefits that local- and wide-area networks provide, they have
become ubiquitous throughout utilities. Networks are now found in control
rooms, substations, and other areas where they were rarely seen until just
recently. In line with this trend, the DNP User’s Group produced an extension
of the DNP3 specification with recommendations for implementing DNP
LAN/WAN networks.
The specification contains several key recommendations about DNP3
operation over LAN and Wide Area Network (WAN) links. The most
significant recommendations are listed below:
➤ DNP3 will use the TCP/IP and UDP/IP protocol suite, also
known as “The Internet Protocol Suite.”
➤ Ethernet is the recommended physical layer, but the
recommended implementation will function over any link
where the TCP/IP and UDP/IP protocol suite is present.
➤ All devices must support messaging through both TCP
(connection oriented) and UDP (connectionless) mechanisms.
➤ The full DNP3 protocol stack is retained. It is supplemented by
the network protocol layers so that major restructuring of
DNP3 is unnecessary.
➤ Link layer confirmations, which are optional but discouraged
for serial DNP, are specifically not allowed for DNP LAN/
WAN. The IP Suite already provides a reliable delivery
mechanism that is backed up by confirmations at the
application layer when required.
DNP LAN/WAN in the SEL-421
See Introduction to DNP3 on page R.6.1 for an introduction to DNP3.
Ethernet Card
Installation of the Ethernet card in an SEL-421 provides a high-performance
network interface that enables the use of industry-standard SCADA network
protocols, including DNP3 Level 2 slave functionality. DNP3 over the
SEL-421 Ethernet port incorporates most Serial DNP3 functions, and includes
event data reporting with direct time tags, customized data maps and session
settings, and operator-initiated control through remote bits.
Configuration and operation of the DNP LAN/WAN interface in the SEL-421
is completely independent of the Serial DNP3 interface, but is just as
integrated. In this section, DNP LAN/WAN is discussed as a function of the
SEL-421, with the implication that this refers to the operation of an Ethernet
card (with the DNP3 option) installed in an SEL-421.
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