Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

310 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
On the other hand, it has been noted that T101 can have more low-level aspects
that require configuration, which can increase difficulties during system integration. Also,
although DNP3 is in a number of ways more complex, not all of the features have to be
implemented. The minimum implementation sub-sets for DNP3 confine themselves to
limited numbers of functions and addressing modes.
Efficiency
Some of the features of T101 such as the fixed frame length option, single character
application acknowledgments, and less rigorous error checking can result in smaller
messages. However, T101 may require a large number of messages to send information, so
some of the benefit of reduced message overhead is lost. Without knowledge and analysis
of the specific data to be predominantly carried on a system it is probably difficult to make
any conclusions as to whether one or other protocol will operate more efficiently.
Where either protocol is to be carried over networks the message length will have a
bearing on efficiency, because the message will be encapsulated within additional data. In
this case the smaller messages of T101 could lead to a loss of efficiency in this situation.
Support for protocol
IEC 60870-5-101 is dominant in Europe compared to DNP3, but is confined to the
electrical utility industry. DNP3 is at the same time becoming more recognized in Europe
in the utility industry. An example of this is the use of IEEE Std 1379 ‘Recommended
Practice for Data Communications Between Intelligent Electronic Devices and Remote
Terminal Units in a Substation’. This recommended practice recognizes both DNP3 and
T101 for use in this application. T101 and DNP3 are used to similar degrees in Asia, and
DNP3 is dominant in Australia. T101 is supported by a number of major manufacturers as
for DNP3.
In summary, it is clear that both protocols have substantial support, but that this varies
with industry and geographic location.
Summary
Both IEC 60870-5-101 and DNP3 are open protocols that have been designed specifically
for the telecontrol applications. They have been developed to meet common needs, have a
common point of origin, and have emerged over a similar period of time. Both have also
been developed to meet the needs of the electrical utility industry, although DNP3 has
more data types that are weighted to general SCADA usage than for electrical utility
usage particularly.
Comparison of the features of each has shown each has differences that may translate to
benefits in some situations, and drawbacks in others. In a number of ways IEC appears to
be a simpler protocol, but this will not necessarily translate to mean simpler implementation.
DNP’s implementation sub-set levels, defined test procedures and certification
authorities together provide a sound basis for assuring interoperability of products from
different manufacturers.
The choice between IEC 60870-5-101 or DNP3 for an organization will depend on
many factors. In functional terms both achieve similar results. For the product developer,
clearly the protocol supported will depend on the needs of customers, which will be
derived from their industry and location. For many products support of both protocols will
be essential.