The invention is related to transmission network system, specially is related to digital transmission network system combined with protocol network higher than third layer relevant to model of OSI seven layers closely or loosely. The invention includes module of media content provider, conversion gateway of digital video broadcast-Internet protocol, content distribution platform, service router, media server, and intelligent broadband gateway as well as super adapter of user network interface in use for dispatching resources of transmission network. Through super adapter, the system is connected to transmission network. Features are: function of authentication from one point, mechanism for buffering content in three levels, limiting network flow, and network load in certain range to lighten load of network. The invention takes full advantage of characters of layered structure of network.