DOCSIS 3.0 (sometimes DOCSIS 3) is a standard developed by CableLabs to upgrade Hybrid Fiber Coax (HFC) networks to deliver high bandwidth broadband Internet service. It is used by MSOs (cable TV companies) to compete against Telcos using FTTH and FTTN/FTTC with VDSL2. DOCSIS 3 is estimated to cost approximately $70 per subscriber in addition to the cost of a new DOCSIS 3 compliant cable modem required on the subscriber premises, which is inline with the cost of installing DSL in an existing OutSide Plant (OSP) cabinet. What DOCSIS avoids is drastic upgrades to an HFC network, and this is its fundamental appeal. Cable companies can deliver very high Internet access bandwidth for very little additional investment with the various DOCSIS standards, especially DOCSIS 3.
The most important thing about DOCSIS 3.0 is bonding cable TV channels for more bandwidth. Previous versions of DOCSIS only used a single channel and were limited in their throughput. With 4 channels, rates of about 160/120Mbps are possible. With 8 channels, rates of 320/120Mbps are possible. Of course, the cable companies with have to give up these analog video channels to devote them to DOCSIS 3.0, but this can be done incrementally, and it does not have to be done throughout the network all at once.
The equipment required to deliver DOCSIS 3.0 services is the Cable Modem Termination System (CMTS) and the DOCSIS 3.0 cable modems on each subscriber premises. Both must be upgraded to support DOCSIS 3.0 over an existing HFC network, shown below before an upgrade. Note that the HFC network is unchanged with the upgrade to DOCSIS 3.0. The only change is in equipment that is installed in the headend and on the subscriber premises.
Source: fttxtra