1.1 Overview
In network communications, as in many fields of engineering, it is a fact that “one size does
not fit all.” Engineering design is about making the right set of trade-offs, and these trade-offs
must balance conflicting requirements such as simplicity, generality, ease of use, richness of
features, performance, memory size and usage, scalability, determinism, and robustness.
These trade-offs must be made in light of the types of information flow (e.g. periodic, one-tomany,
request-reply, events), and the constraints imposed by the application and execution
platforms.
The Type 15 fieldbus provides two major communication mechanisms that complement each
others to satisfy communication requirements in the field of automation: the Client/Server and
the Publish/Subscribe paradigms. They can be used concurrently on the same device.
Type 15 Client/Server operates in a Client/Server relationship. Its application layer service
definitions and protocol specifications are independent of the underlying layers, and have
been implemented on a variety of stacks and communication media, including EIA/TIA-232,
EIA/TIA-422, EIA/TIA-425, HDLC (ISO 13239), fiber, TCP/IP, Wireless LANs and Radios.
Type 15 Publish/Subscribe operates in a Publish/Subscribe relationship. Its application layer
service definitions and protocol specifications are independent of the underlying layers and
can be configured to provide reliable behaviour and support determinism. The most common
stack is UDP/IP.
The fieldbus application layer (FAL) provides user programs with a means to access the
fieldbus communication environment. In this respect, the FAL can be viewed as a “window
between corresponding application programs.”
This part of IEC 61158 provides common elements for basic time-critical and non-time-critical
messaging communications between application programs in an automation environment and
material specific to Type 15 fieldbus. The term “time-critical” is used to represent the
presence of a time-window, within which one or more specified actions are required to be
completed with some defined level of certainty. Failure to complete specified actions within
the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant and possibly human life.
1.2 Specifications
The principal objective of this part of IEC 61158 is to specify the characteristics of conceptual
application layer services suitable for time-critical communications, and thus supplement the
OSI Basic Reference Model in guiding the development of application layer protocols for timecritical communications.
1.3 Conformance
This part of IEC 61158 does not specify individual implementations or products, nor do they
constrain the implementations of application layer entities within industrial automation
systems.
There is no conformance of equipment to this application layer service definition standard.
Instead, conformance is achieved through implementation of conforming application layer
protocols that fulfill the Type 15 application layer services as defined in this part of
IEC 61158.
1.4 Type overview
In network communications, as in many fields of engineering, it is a fact that “one size does
not fit all.” Engineering design is about making the right set of trade-offs, and these trade-offs
must balance conflicting requirements such as simplicity, generality, ease of use, richness of
features, performance, memory size and usage, scalability, determinism, and robustness.
These trade-offs must be made in light of the types of information flow (e.g. periodic, one-to-many, request-reply, events), and the constraints imposed by the application and execution platforms.
IEC 61158-5-15:2007 history
2010IEC 61158-5-15:2010 Industrial communication networks - Fieldbus specifications - Part 5-15: Application layer service definition - Type 15 elements
2007IEC 61158-5-15:2007 Industrial communication networks - Fieldbus specifications - Part 5-15: Application layer service definition - Type 15 elements