IEC 61158-4-2:2019 specifies 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 data-link service provider and 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. This fourth edition cancels and replaces the third edition published in 2014 and constitutes a technical revision. lt;br /gt;This edition includes the following significant technical changes with respect to the previous edition: lt;br /gt;•clarifications of ControlNet object in 7.2; lt;br /gt;•extensions and clarifications of TCP/IP interface object in 7.5; lt;br /gt;•extensions and clarifications of Ethernet Link object in 7.6; lt;br /gt;•clarifications of DeviceNet object in 7.7; lt;br /gt;•extensions and clarifications of CCO object in 7.8; lt;br /gt;•extensions and clarifications of DLR object in 7.9; lt;br /gt;•extensions and clarifications of Port object in 7.11; lt;br /gt;•addition of PRP/HSR Protocol and PRP/HSR Nodes Table objects in 7.12 and 7.13; lt;br /gt;•extensions and clarifications of DLR protocol in Clause 10; lt;br /gt;•addition of PRP/HSR protocol mapping in Clause 11; lt;br /gt;•update of indicator behaviour in A.2.2 and A.2.4; lt;br /gt;•miscellaneous editorial corrections.