CEI EN 61158-3-22

General

This part of IEC 61158 provides common elements for basic
time-critical messaging communications between devices in an
automation environment. 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.

This standard defines in an abstract way the externally visible
service provided by the Type 22 fieldbus data-link layer in terms
of:

a) the primitive actions and events of the service;

b) the parameters associated with each primitive action and
event, and the form which they take; and

c) the interrelationship between these actions and events, and
their valid sequences.

The purpose of this standard is to define the services provided
to:

• the Type 22 fieldbus application layer at the boundary between
the application and datalink layers of the fieldbus reference
model; and

• systems management at the boundary between the data-link layer
and systems management of the fieldbus reference model.

Specifications

The principal objective of this standard is to specify the
characteristics of conceptual data-link layer services suitable for
time-critical communications, and thus supplement the OSI Basic
Reference Model in guiding the development of data-link protocols
for time-critical communications. A secondary objective is to
provide migration paths from previously-existing industrial
communications protocols.

This specification may be used as the basis for formal
DL-Programming-Interfaces. Nevertheless, it is not a formal
programming interface, and any such interface will need to address
implementation issues not covered by this specification,
including:

a) the sizes and octet ordering of various multi-octet service
parameters; and

b) the correlation of paired request and confirm, or indication
and response, primitives.

Conformance

This standard does not specify individual implementations or
products, nor do they constrain the implementations of data-link
entities within industrial automation systems.

There is no conformance of equipment to this data-link layer
service definition standard. Instead, conformance is achieved
through implementation of the corresponding data-link protocol that
fulfils the Type 22 data-link layer services defined in this
standard.