Digital data communications for measurement and control Fieldbus for use in industrial control systems Part 3: Data link service definition
|Publication Date:||1 May 2003|
|ICS Code (IT applications in industry):||35.240.50|
|ICS Code (Industrial automation systems):||25.040|
|ICS Code (Open systems interconnection (OSI)):||35.100|
Scope and object
This part of IEC 61158 provides 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 part of IEC 61158 defines in an abstract way the externally visible service provided by the 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 part of IEC 61158 is to define the services provided to
1) the various types of Fieldbus Application Layer at the boundary between the Application and Data Link Layers of the Fieldbus Reference Model, and
2) Systems Management at the boundary between the Data Link Layer and Systems Management of the Fieldbus Reference Model.
Seven distinct types of services are defined in this part of IEC 61158; each has a corresponding protocol in IEC 61158-4. The seven distinct types of DL-service are:
Type 1 - A DL-service which provides a superset of those services expected of OSI Data Link Protocols as specified in ISO/IEC 8886.
Type 2 - A DL-service which provides both a connected and a connectionless subset of those services specified in ISO/IEC 8886.
Type 3 - A DL-service which provides a connectionless subset of those services specified in ISO/IEC 8886.
Type 4 - A DL-service which provides a connectionless subset of those services specified in ISO/IEC 8886.
NOTE 1 This part of IEC 61158 does not define a Type 5 Data Link service. Other parts of IEC 61158 define a Type 5 Application Layer service and protocol. The designation Type 5 is reserved in this part of IEC 61158 to maintain numbering consistency with the other parts of IEC 61158.
Type 6 - A DL-service which provides both a connected and a connectionless subset of those services provided by OSI Data Link Protocols as specified in ISO/IEC 8886.
Type 7 - A DL-service which provides both a connected and a connectionless subset of those services provided by OSI Data Link Protocols as specified in ISO/IEC 8886.
Type 8 - A DL-service which provides a connection-oriented subset of those services specified in ISO/IEC 8886.
NOTE 2 Many of these Types of service are suitable for use with multiple higher-layer protocols. In addition to the potential ability of these types of Data Link service to support unrelated Types of Fieldbus Application Layer protocol, some of these Types of Data Link service also may be able to support:
a) the OSI Network Layer at the boundary between the Network and Data Link Layers of the OSI Basic Reference Model
b) the IETF (IP) Network Layer
c) the Smart Transducer Interface for Sensors and Actuators as defined in IEEE 1451.2.
Where the scope of addressing is adequate, some of these Types of Data Link service also may be able to support
d) an OSI Transport Layer Protocol.
NOTE 3 Use of some of these protocol types is restricted by their copyright holders. In all cases a particular Data Link protocol Type can be used without restriction when coupled with the same Type Physical Layer and Application Layer protocols, or with other combinations as specified in IEC 61784. Use of the various protocol Types in other combinations may require permission of their respective copyright holders.
The principal objective of this part of IEC 61158 is to specify the characteristics of conceptual Data Link 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. It is this latter objective which gives rise to the diversity of services standardized in this part of IEC 61158, and the corresponding protocols standardized in IEC 61158-4.
This specification may be used as the basis for formal DL-Programming-Inter
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.
This part of IEC 61158 does not specify individual implementations or products, nor does it constrain the implementations of Data Link entities within industrial automation systems.
There is no conformance of equipment to this Data Link Service definition standard. Instead, conformance is achieved through implementation of conforming Data Link protocols that fulfill any given Type of Data Link Services as defined in this part of IEC 61158.
Scope of type-specific clauses and subclauses
The different Types of Data Link services defined by this standard are each presumed self-consistent, but in general are unrelated to the other Types of service.
Where a clause or subclause heading explicitly designated one or more Types, that clause or subclause applies only to that (those) Type(s) and all references within that clause or subclause are with respect to that (those) Type(s).
Where a clause does not explicitly designate specific Types, or neither a subclause nor its containing clause explicitly designate specific Types, then that material is presumed to apply to multiple Types.