Verifying synchronisation of time sources for inter-device communication

A network communication method is provided, the network comprising first and second nodes. The method comprises: transmitting a message from the first node to the second node, wherein the message comprises a data content portion and an identifying portion, wherein said identifying portion includes a first unique identifier corresponding to a time source which controls a time value at the first node; receiving the transmitted message at the second node; comparing the first unique identifier to a second unique identifier, wherein said second unique identifier corresponds to a time source which controls a time value at the second node; and if the result of said comparison is positive, accepting the message for processing at the second node. May be used for communications between a drive 102, 104 and programmable logic controller (PLC) 100.