Data distribution system

A videoconferencing system comprising a first control device, a second control device, and a plurality of processing devices, all mutually connected by a packet-based transport network, wherein:

• the first control device and the second control device are configured to advertise a same external network address to videoconferencing terminals on at least one external network;
• each of the first control device and the second control device is configured to receive a videoconferencing session initiation request from a respective videoconferencing terminal on the at least one external network and to designate a respective processing device of the plurality of processing devices to receive data from the respective videoconferencing terminal during a respective videoconferencing session;
• each processing device of the plurality of processing devices is configured to:
• receive data packets for a videoconferencing session;
• process the data packets;
• and send the processed data packets across the packet-based transport network to other processing devices of the plurality of processing devices participating in the same videoconferencing session;
• and
• the videoconferencing system further comprises a session manager configured to manage a videoconferencing session by (i) associating two or more processing devices of the plurality of processing devices with a multicast group on the packet-based transport network, and (ii) configuring the packet-based transport network and/or the two or more processing devices so that data output to the multicast group by any one processing device of the plurality of processing devices in the multicast group is received by all other processing devices in the multicast group, wherein each processing device of the two or more processing devices is arranged to receive data from a respective videoconferencing terminal located on the at least one external network and to send the received data, or data derived therefrom, over the packet-based transport network to the multicast group, and is further arranged to receive further data over the packet-based transport network destined for the respective videoconferencing terminal and to send this further data, or data derived therefrom, to the respective videoconferencing terminal.