The invention relates to a method of data-packet transmission from a first network to a second network, one of the networks being a communications bus transporting data packets of isochronous and asynchronous types, characterised in that, with the other network being a packet-switching network, the said method includes, performed within a communications device connected to the communications bus and forming part of the packet-switching network, a step of reserving resources adapted to the types of data packets intended for the second network.