DOCSIS

DOCSIS, or Data Over Cable Service Interface Specification, is a telecommunications standard for transmitting data over cable television infrastructure using hybrid fiber-coaxial networks. It enables high-speed Internet, VoIP, and other data services over existing cable TV channels without requiring new local access networks. The specification was developed by CableLabs and first released in 1997; since then multiple versions have been deployed, including DOCSIS 1.x, 2.x, 3.x and 4.x, with the most widespread deployments using DOCSIS 3.0 and 3.1.

DOCSIS defines both the physical (PHY) layer and the media access control (MAC) layer that govern how data is modulated, framed, and accessed over the coax network. Downstream data are typically modulated using QAM on allocated RF channels, while upstream uses time-division multiple access on dedicated channels. A key feature is channel bonding, which combines multiple downstream and upstream channels to increase total throughput. Newer versions introduce orthogonal frequency-division multiplexing (OFDM) for downstream and orthogonal frequency-division multiple access (OFDMA) for upstream, improves efficiency, latency, and spectral use.

In a cable system, the headend houses the Cable Modem Termination System (CMTS) and serves customer premises equipment through cable modems. DOCSIS specifies the interfaces and data encapsulation between CMTS and modems, enabling IP traffic to traverse the network.

DOCSIS has enabled competitive broadband speeds over existing cable infrastructure and continues to evolve, with deployments varying by region and provider. It remains the dominant technology for cable broadband in many markets, supporting residential and business services.