A data communication network comprising a plurality of nodes interconnecting transmission paths (ring 01, ring 10) in a ring structure arranged to propagate data messages between data systems coupled to the network by the nodes in opposite directions around the network ring structure. An executive node (2) having ring interface units (212, 222, 232) interconnecting ones of the transmission paths is arranged to selectively couple a network control processor (3) with various sectors of the transmission paths to enable the network control processor (3) to control the traffic flow of data messages on the data communication network.