This Document Has Been Superseded
A newer publication replaces it: BSI BS EN IEC 61158-4-21
Industrial communication networks. Fieldbus specifications -- Data-link layer protocol specification. Type 21 elements
1.1 General
The DLL provides basic time-critical data communications between devices in an automated environment. Type 21 provides priority-based cyclic and acyclic data communication using an internal collision-free, full-duplex dual-port Ethernet switch technology. For wide application in various automation applications, Type 21 does not restrict the cyclic/acyclic scheduling policy in the DLL.
1.2 Specifications
This standard describes:
1.3 Procedures
The procedures are defined in terms of:
1.4 Applicability
These procedures are applicable to instances of communication between systems that support time-critical communications services in the data link layer of the OSI or fieldbus reference models, and that require the ability to interconnect in an open systems interconnection environment. Profiles provide a simple multi-attribute means of summarizing an implementationβs capabilities, and thus its applicability to various time-deterministic communications needs.
1.5 Conformance
This standard also specifies conformance requirements for systems implementing these procedures. This standard does not contain tests to demonstrate compliance with such requirements.
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