Historical
DS/EN IEC 61158-4-2:2019
Industrial communication networks - Fieldbus specifications - Part 4-2: Data-link layer protocol specification - Type 2 elements
1.1 General*The data-link layer provides basic time-critical messaging communications between devices in*an automation environment.*This protocol provides communication opportunities to all participating data-link entities,*sequentially and in a cyclic synchronous manner. Foreground scheduled access is available*for time-critical activities together with background unscheduled access for less critical*activities.*Deterministic and synchronized transfers can be provided at cyclic intervals up to 1 ms and*device separations of 25 km. This performance is adjustable dynamically and on-line by reconfiguring*the parameters of the local link whilst normal operation continues. By similar*means, DL connections and new devices may be added or removed during normal operation.*This protocol provides means to maintain clock synchronization across an extended link with*a precision better than 10 s.*This protocol optimizes each access opportunity by concatenating multiple DLSDUs and*associated DLPCI into a single DLPDU, thereby improving data transfer efficiency for datalink*entities that actively source multiple streams of data.*The maximum system size is an unlimited number of links of 99 nodes, each with 255 DLSAPaddresses.*Each link has a maximum of 224 related peer and publisher DLCEPs.*1.2 Specifications*This document specifies*a) procedures for the timely transfer of data and control information from one data-link user*entity to a peer user entity, and among the data-link entities forming the distributed datalink*service provider;*b) the structure of the fieldbus DLPDUs used for the transfer of data and control information*by the protocol of this document, and their representation as physical interface data units.*1.3 Procedures*The procedures are defined in terms of*a) the interactions between peer DL-entities (DLEs) through the exchange of fieldbus*DLPDUs;*b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system*through the exchange of DLS primitives;*c) the interactions between a DLS-provider and a Ph-service provider in the same system*through the exchange of Ph-service primitives.*1.4 Applicability*These procedures are applicable to instances of communication between systems which*support time-critical communications services within the data-link layer of the OSI or fieldbus*reference models, and which require the ability to interconnect in an open systems*interconnection environment.*Profiles provide a simple multi-attribute means of summarizing capabilities of an*implementation, and thus its applicability to various time-critical communications needs.*1.5 Conformance*This document also specifies conformance requirements for systems implementing these*procedures. This document does not contain tests to demonstrate compliance with such*requirements
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