scope:

The data-link layer provides basic time-critical messaging communications between devices in an automation environment. This protocol provides a means of connecting devices through a partial mesh network, such that most failures of an interconnection between two devices can be circumvented. In common practice the devices are interconnected in a non-redundant hierarchical manner reflecting application needs Specifications. This International Standard 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 standard, and their representation as physical interface data units. 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.