COMMUNICATIONS NETWORK

A communications network that can determine for itself its own network topology, that is the identity and interconnection of nodes comprising the network is described. The network comprises a plurality of nodes (A to E) ea ch having at least one port (A1 to E1), the ports being interconnected (7 to 13 ) in accordance with the network topology and in which communication traffic i s conveyed over the network via the interconnected ports. Each port is arrange d to transmit first information (h to u) within the communication traffic including the identity of the port (Section trace identity) from which the communication traffic originates. Means are provided which are arranged to transmit second information between nodes identifying which first informatio n identity relates to which node and which port; and processing means arranged for determining for each node from the first and second information, the identity of adjacent node/s and the identity of the port/s to which its port s are connected.