Practical_modern_SCADA_protocols_-_dnp3,_60870-5_and_Related_Systems

180 Practical Modern SCADA Protocols: DNP3, 60870.5 and Related Systems
8.1.5 IEC 60870-5-1 1990
Link transmission procedures
This section represents the four frame formats from IEC 60870-5-1 and then describes the
internal processes in terms of the service primitives and transmission procedures. The
service primitives are the control indications passed between the link layer and its higher
level user, and the transmission procedures describe the sequence of events occurring over
the physical communications link. A control field is described that is transmitted over the
link and is used by the link layer procedures of each side of the link in controlling the
transmission process. The terms unbalanced and balanced transmission are presented and
used to describe whether transmission can be initiated only by a master station, or by any
station. Services and transmission procedures are presented in detail for both unbalanced
and balanced transmissions.
8.1.6 IEC 60870-5-3 1992
General structure of application data
This section presents two models of the structure of data at the application level. The
reference model 2 version shows how application user data, for example point information
to be transmitted, is encapsulated within an application protocol data unit, with or without
application protocol control information added, and then passed to the underlying link
layer for transmission. It also describes a general structure for application data, and rules
for forming application data units in general.
8.1.7 IEC 60870-5-4 1993
Definition and coding of application information elements
This section provides rules for the definition of information elements, and defines a
common set of information elements that may be used for transmission of information in
telecontrol applications. These include generic elements such as signed and unsigned
integers, fixed and floating point numbers, bit-strings, and time elements. The intention of
this section is to provide a set of information building blocks from which a companion
standard, or profile can utilize selectively to build a complete set of application level
information objects. No such set of information objects is selected by this section,
however.
8.1.8 IEC 60870-5-5 1995
Basic application functions
This section describes the highest level functions of the transmission protocol, which are
those application functions above layer 7 of the OSI model. Application service primitives
are the request and response indications passed between the application layer and the
application user. Application functions are described.
A set of basic application functions and associated service primitives, or requests
and indications, are presented. These cover the highest level functions that would be
required to carry out telecontrol operations. They include station initialization, methods of
acquiring data, clock synchronization, transmission of commands, totalizer counts, and file
transfer. Again, it is stated in this section that it would be the role of a specific companion
standard to select from these functions and possibly add to them in defining a complete
working protocol.