UNE-EN IEC 61158-3-2:2023

240 1.1 General

241 This part of IEC 61158 provides common elements for basic time-critical messaging

242 communications between devices in an automation environment. The term time-critical is

243 used to represent the presence of a time-window, within which one or more specified actions

244 are required to be completed with some defined level of certainty. Failure to complete

245 specified actions within the time window risks failure of the applications requesting the

246 actions, with attendant risk to equipment, plant and possibly human life.

247 This standard defines in an abstract way the externally visible service provided by the Type 2

248 fieldbus data-link layer in terms of:

249 a) the primitive actions and events of the service;

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

251 take; and

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

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

254 " the Type 2 fieldbus application layer at the boundary between the application and data-link

255 layers of the fieldbus reference model;

256 " systems management at the boundary between the data-link layer and systems

257 management of the fieldbus reference model.

258 Type 2 DL-service provides both a connected and a connectionless subset of those services

259 specified in ISO/IEC 8886.

260 1.2 Specifications

261 The principal objective of this standard is to specify the characteristics of conceptual data-link

262 layer services suitable for time-critical communications and thus supplement the OSI Basic

263 Reference Model in guiding the development of data-link protocols for time-critical

264 communications. A secondary objective is to provide migration paths from previously-existing

265 industrial communications protocols.

266 This specification may be used as the basis for formal DL-Programming-Interfaces.

267 Nevertheless, it is not a formal programming interface, and any such interface will need to

268 address implementation issues not covered by this specification, including:

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

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

271 1.3 Conformance

272 This standard does not specify individual implementations or products, nor does it constrain

273 the implementations of data-link entities within industrial automation systems.

IEC CDV 61158-3-2 © IEC:2021 20009

274 There is no conformance of equipment to this data-link layer service definition standard.

275 Instead, conformance is achieved through implementation of the corresponding data-link

276 protocol that fulfills the Type 2 data-link layer services defined in this standard.