Schweitzer Engineering Laboratories SEL-751 - Table D.4 TCP;UDP Selection Guidelines; Table D.5 DNP3 Access Methods; DNP3 in the SEL-751

D.6
SEL-751 Relay Instruction Manual Date Code 20170927
DNP3 Communications
DNP3 in the SEL-751
DNP3 in the SEL-751
The SEL-751 is a DNP3 Level 2 remote (outstation) device without dual end
point.
Data Access
Table D.5 lists DNP3 data access methods along with corresponding SEL-751
settings. You must select a data access method and configure each DNP3
master for polling as specified.
The SEL-751 is an outstation device without dual end point. For a TCP
connection, the relay sends out unsolicited messages only if a DNP3 master
has already established a session and enabled unsoliticed messaging for that
session. However, for a serial/modem/UDP connection, the relay
automatically dials out and sends unsolicited messages as defined by the
settings.
In both the unsolicited report-by-exception and quiescent polling methods
shown in Table D.5, you must make a selection for the PUNSOLn setting.
This setting enables or disables unsolicited data reporting at power up. If your
DNP3 master can send a message to enable unsolicited reporting on the
SEL-751, you should set PUNSOLn to No.
Table D.4 TCP/UDP Selection Guidelines
Use in the case of… TCP UDP
Most situations X
Non-broadcast or multicast X
Mesh Topology WAN X
Broadcast X
Multicast X
High-reliability single-segment LAN X
Pay-per-byte, non-mesh WAN, for example, Cellular Digital Packet Data
(CDPD)
X
Low priority data, for example, data monitor or configuration information X
Table D.5 DNP3 Access Methods
Access Method Master Polling SEL-751 Settings
Polled static Class 0 Set ECLASSBn, ECLASSCn,
ECLASSAn to 0; UNSOLn to No
Polled report-
by-exception
Class 0 occasionally,
Class 1, 2, 3 frequently
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event class;
UNSOLn to No
Unsolicited report-
by-exception
Class 0 occasionally,
optional Class 1, 2, 3 less
frequently; mainly relies
on unsolicited messages
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event class;
set UNSOLn to Yes and PUNSOLn to
Yes or No
Quiescent Class 0, 1, 2, 3 never;
relies completely on
unsolicited messages
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event class;
set UNSOLn and PUNSOLn to Yes.
NOTE: Because unsolicited
messaging is problematic in most
circumstances, SEL recommends
using the polled report-by-exception
access method to maximize
performance and minimize risk of
configuration problems.
NOTE: In the settings in Table D.5,
the suffix n represents the DNP3
session number from 1 to 5. All
settings with the same numerical
suffix comprise the complete DNP3
session configuration.