This part of IEC 61158 specifies the requirements for fieldbus component parts. It also specifies the media and network configuration requirements necessary to ensure agreed levels of a) data integrity before data-link layer error checking; b) interoperability between devices at the physical layer. The fieldbus physical layer conforms to layer 1 of the OSI 7-layer model as defined by ISO 7498 with the exception that@ for some types@ frame delimiters are in the physical layer while for other types they are in the data-link layer.