1. Field of the Invention
The present invention relates to a composite communication network of a hierarchical structure including a subnetwork, and more particularly, to a composite communication network in which a message set up in a packet and having a destination node indicated therein is transmitted within the communication network.
2. Description of the Related Art
In a conventional communication network, routing protocols of a network layer level such as RIP (routing message protocol) or IS--IS have been employed for routing control messages. In the case of these protocols, routing table messages have been changed periodically or for occasional requests for change, and hence a routing table for each node has been updated and routing of each node has been carried out based on the thus-renewed routing table.
The conventional routing protocol for control messages described above has a problem in that, for example, the RIP protocol is not applicable to a large-scale network because the transmission range of the routing message is limited to only 16 nodes, while with the IS--IS protocol, although its application is not restricted by a network size, the size of the routing message to be communicated between nodes or the size of a routing table to be held by each node is excessively expanded, resulting in an extended time used for routing, because routing of a whole network is controlled by each node. Further, these protocols are prepared without particular consideration to the physical characteristics of a ring type network, that is, a network of a ring type.