A control system, comprising: a first control apparatus including: a controller configured to obtain information regarding a plurality of relay devices (30xx, 30yy) for relaying content data in a session to be established among a plurality of communication terminals (10aa, 10bb), and determine one of the plurality of relay devices (30xx, 30yy) as a representative relay device to manage a relay destination of content data in the session to be established; and a transmitter configured to transmit relay device identification information for identifying the representative relay device to the plurality of communication terminals (10aa, 10bb) subject for participation in the session; and a second control apparatus including: a receiver configured to receive, from a first communication terminal of the plurality of communication terminals (10aa, 10bb) subject for participation in the session, a request for starting relay of content data including the relay device identification information of the representative relay device; and a transmitter configured to transmit, with a request for starting relay of content data, the relay device identification information of the representative relay device to a first relay device connected to the first communication terminal, to cause the first relay device to further transmit the request for starting relay of content data to the representative relay device identified with the relay device identification information of the representative relay device. a controller configured to obtain information regarding a plurality of relay devices (30xx, 30yy) for relaying content data in a session to be established among a plurality of communication terminals (10aa, 10bb), and determine one of the plurality of relay devices (30xx, 30yy) as a representative relay device to manage a relay destination of content data in the session to be established; and a transmitter configured to transmit relay device identification information for identifying the representative relay device to the plurality of communication terminals (10aa, 10bb) subject for participation in the session; and a second control apparatus including: a receiver configured to receive, from a first communication terminal of the plurality of communication terminals (10aa, 10bb) subject for participation in the session, a request for starting relay of content data including the relay device identification information of the representative relay device; and a transmitter configured to transmit, with a request for starting relay of content data, the relay device identification information of the representative relay device to a first relay device connected to the first communication terminal, to cause the first relay device to further transmit the request for starting relay of content data to the representative relay device identified with the relay device identification information of the representative relay device. a receiver configured to receive, from a first communication terminal of the plurality of communication terminals (10aa, 10bb) subject for participation in the session, a request for starting relay of content data including the relay device identification information of the representative relay device; and a transmitter configured to transmit, with a request for starting relay of content data, the relay device identification information of the representative relay device to a first relay device connected to the first communication terminal, to cause the first relay device to further transmit the request for starting relay of content data to the representative relay device identified with the relay device identification information of the representative relay device.