Patent ID: 8023433

Claim:
A relay device transmitting a user data packet, containing a content to be distributed to a mobile terminal, in which to set information indicative of a multicast group associated with the content, to a plurality of base stations managed in the way of being grouped into zones, the relay device comprising: a storing unit to store first information indicative of the multicast group in which the mobile terminal participates, second information indicative of a base station performing wireless communications with the mobile terminal and third information indicative of a zone to which the base station belongs, the first information, the second information and the third information forming a set by being associated with each other; a controller, when receiving a LEAVE packet of a request for leaving the multicast group from the mobile terminal via any one of the plurality of base stations, to determine whether or not to transmit a query packet for checking existence of the mobile terminal continuing the participation in a leave target multicast group associated with the LEAVE packet by comparing stored second information associated with the leave target multicast group and the base station that relays the received LEAVE packet; and an interface unit to transmit the user data packet containing the query packet to each of the base stations belonging to the zone associated with the leave target multicast group on the basis of a result of the determination made by the controller.