Communication networks and television studios are rapidly changing from analog to digital environments. Ultimately, digital studios will be interconnected via digital facilities. The interface between the broadcaster and the carrier will likely be defined for a number of different grades of service (at various rates of tariff). High-bit-rate high-quality transmission will preserve the program producers' ability to process the signal. Lower bit rates will be used for distribution purposes. Still less capacity will be required for services such as electronic news gathering. The system issues to be resolved include encoding, transcoding, bit rate availability, transmission performance, etc. Meanwhile, composite video may have to be digitized. To accomplish this a number of auxiliary signals will be multiplexed with the video. These signals include audio, test signals, captioning, teletext, etc. The combined bit stream must fit inside a standard transmission hierarchical rate. In addition, the system to be implemented must accommodate the characteristics of both the network (performance, availability, surveillance) and the input signal (S/N).