3. Transmission network
It is the communication network of the signal such as transmission video of in order to, frequency, the transmission network that network of special railway line of net of net of satellitic frame relay, ground frame relay, DDN, ISDN and X.25 net can make system of conference of video of type of each other of much hand over item by item. Notable is, of broadband network popularized long-range video conference to bring more vast space, the video conference application that is based on H.323 agreement receives a network to go up to had achieved quite good result in the broadband such as ADSL, FTTB LAN.