The present invention relates to a method of synchronisation between communication networks exchanging information by frame of informations, each communication network having clock and the number of clock pulses is monitored by a counter. The synchronisation is made by reading information representing the counted clock pulses of the clock of the first network at the appearance of a reference event, inserting at least said information or calculated information on the basis of said information into the frame of information as the synchronisation information, transferring said frame of information from the first to the second network, reading information representing the number of counted clock pulse of the clock of the second network at the appearance of reference event, reading synchronisation information inserted in received frame of information from the first network, calculating a difference between information and synchronising the second network.