Patent ID: 8799488

Claim:
A relay server configured to communicate with a first relay server connected to a first network, and to function as a second relay server connected to a second network, the relay server comprising: a relay group information creation unit configured to create relay group information indicating that the first relay server and the second relay server constitute a relay group; an inter-relay server sharing unit configured to share relay server information and the relay group information between the first relay server and the second relay server; the relay server information including: first relay server information created by the first relay server, the first relay server information including first relay server activation information indicating an activation state of the first relay server, and first client terminal registration information regarding a first client terminal connected to the first network and registered in the first relay server, the first client terminal registration information includes a connection state between the first relay server and the first client terminal; and second relay server information created by the second relay server, the second relay server information including second relay server activation information indicating an activation state of the second relay server, and second client terminal registration information regarding a second client terminal connected to the second network and registered in the second relay server, the second client terminal registration information includes a connection state between the second relay server and the second client terminal; a client terminal-oriented sharing unit configured to share the relay group information and the relay server information between the second relay server and the second client terminal; and a communication execution unit configured to perform communication relayed by the second relay server, the communication being performed with an addressee selected based on the relay group information and the relay server information; wherein the communication execution unit includes: a transfer destination decision unit configured to, based on the addressee, the relay group information and the relay server information, determine a transfer destination of the communication relayed by the second relay server; a call control establishment unit configured to establish a first session with the transfer destination by using a call control protocol; and a communication route establishment unit configured to, upon having received an establishment request for a communication route from the transfer destination, confirm whether or not an identification information received along with the establishment request matches an identification information included in call control information of the first session, and when the received identification information matches the included identification information, establish a first communication route corresponding to call control of the first session.