DWDM architectures for video on demand transport and distribution

We present our study of VoD service optical network using 16-channel DWDM. One approach is a VoD architecture where all video server equipment is centralized and located in the headend. Another option is to deploy servers in several hubs where each has the capability of providing digital VoD service but on a smaller scale. A centralized video server maybe more attractive as it reduces operating cost. DWDM provides a perfect solution for this application because of the high data transport capacity. In a typical DWDM VoD system video programs are stored in MPEG-II format and transported using 64 or 256-QAM modulation. One VoD server in the headend can provide service to several hubs on a fiber ring by allocating wavelengths to these hubs. The number of dropped wavelengths at a particular location depends on the local demand. VoD programs are routed by wavelength to the appropriate hub location. Each wavelength can carry multiple QAM channels. The frequency allocation of these QAM channels depends on the system design. Usually the QAM is inserted in a frequency band above the traditional 50 MHz to 550 MHz broadcast channels. Since QAM signal can be readily decoded by the set top box in customer home, there is no RF conversion required if this QAM signal band originating at the headend matches the set-top box tuner frequency range. At the hubs, the VoD signal can be combined with local channels and the broadcast channels in RF domain and retransmitted for distribution.