Communication among interconnected subnetworks.

A composite communication network of a hierarchical structure including a subnetwork at least in part thereof has a gateway (GW) node having a control message communication medium which comprises three or more routes. Routing of the network layer level is performed between GW nodes and routing of the data link layer level is conducted in the ring subnetwork. Each node in the ring has an NE address to be distinguished in the ring and a routing table which shows a routing direction corresponding to a destination node. When the GW node in the ring including a target of a control message receives a message, the GW node sets an NE address of the target node in the packet of the message as a destination address, and processes the packet for transmitting to the control message communication medium indicated in the routing table. The node that receives the packet carries out mapping of the destination NE address of the packet and NE address of its own node by means of a routing application protocol of the data link layer level. When the two addresses coincide, the node transmits the packet to the internal message processor, but when they do not coincide, the node transmits the packet to a neighboring node and routing of the control message is performed with reference to the data link layer level in the ring subnetwork.