The DOCSIS Digital Document Library documents are standard reading for any broadband engineer / technician. I have posted this documents in the document library as a quick reference. They are freely available in other sources, but sometimes it is nice to have them all in one location:
This standard describes the framing structure, channel coding, and channel modulation for a digital multi-service television distribution system that is specific to a cable channel. The system can be used transparently with the distribution from a satellite channel, as many cable systems are fed directly from satellite links. The specification covers both 64 and 256 QAM. Most features of both modulation schemes are the same. Where there are differences, the specific details for each modulation scheme is covered.