In IEEE 1588 - 2002 , all PTP messages are sent using multicast messaging .
IEEE 1588 - 2008 introduced an option for devices to negotiate unicast transmission on a port - by - port basis .
In IEEE 1588 - 2002 , all PTP messages are sent using multicast messaging , while IEEE 1588 - 2008 introduced an option for devices to negotiate unicast transmission on a port - by - port basis .