A communication system includes transfer node 200 receiving a registration request signal from mobile node 100 and server 300 receiving the registration request signal from transfer node 200. Transfer node 200 determines, depending on the type of a transmission trigger for the registration request signal occurred, whether or not the number of mobile nodes which will be registered or which will have registration expiry time postponed are a plurality. If the plurality of mobile nodes are not to be processed, transfer node 200 transmits a registration request signal for one mobile node to server 300. If the plurality of mobile nodes are to be processed, transfer node 200 transmits an aggregation registration request signal concerning the plurality of mobile nodes, to server 300. Server 300 executes a process of registering or postponing the mobile node or the plurality of mobile nodes according to signal received from transfer node 200.