IEC 60870-5-104 (also known as IEC 870-5-104) is an international
standard, released in 2000 by the IEC (International Electrotechnical
The IEC Technical Committee 57 ( Working Group 03) has developed a protocol
standard for telecontrol, teleprotection, and associated
telecommunications for electric power systems. The result of this work
is IEC 60870-5. Five documents specify the base IEC 60870-5. The
IEC 60870-5-1 Transmission Frame Formats
IEC 60870-5-2 Data Link Transmission Services
IEC 60870-5-3 General Structure of Application Data
IEC 60870-5-4 Definition and coding of Information Elements
IEC 60870-5-5 Basic Application Functions
IEC Technical Committee 57 have also generated a companion
standard IEC 60870-5-104 especially for remote controlled units
RTU, connected to a Controlling Station either via TCP/IP
networking. The IEC 60870-5-104 is based on the five documents IEC
60870-5-1 - 5 and IEC60870-5-101.
As can be seen from the standard's full designation 'Network access
for IEC 60870-5-101 using standard transport profiles', its
application layer is based on IEC 60870-5-101.
IEC 60870-5-104 enables communication between control station and
substation via a standard TCP/IP network. The TCP protocol is used
for connection-oriented secure data transmission.
IEC 60870-5-104 limits the information types and configuration
parameters defined in IEC 60870-5-101, which means that not all
functions available in IEC 60870-5-101 are supported by IEC
60870-5-104. For instance IEC 60870-5-104 does not support short
time stamps (3-byte format), the length of the various address
elements is set to defined maximum values. But in practice, vendors
very often combine the IEC 60870-5-101 application layer with the
IEC 60870-5-104transport profile, without paying attention to these
restrictions. This might then lead to problems, if a device strictly
applies the standard.
Interoperability between devices by different vendors is ensured by
the interoperability list, which is defined by the standard. In the
list, the function range is defined for each device by marking the
applicable functions. The common denominator between different
vendor lists defines the possible function range.
IEC 104 is the European cousin of DNP3. It is more complex than
Modbus, but a good bit simpler than DNP3. It consists of two layers:
APCI - Application Protocol Control Information
used to denote frame types for 104's network mode.
ASDU - Application Service Data Unit that contains
application layer frames. This is the same for 101 and 104.
The application layer defines a number of Type Ids which can be
thought of as function codes. They define the format of the data that
follows. Unlike in DNP3, 104 ASDUs can only contain one type of data.