DOCSIS: internet over the TV cable

In short: DOCSIS is the standard cable providers use to deliver internet over the television cable (coaxial cable).

In more detail: All households of a street share one segment of the cable. The device and the distribution point (“CMTS”) divide the bandwidth into channels.

In Depth

• Sharing: The cable is a shared medium. In the evening with many users, speed may drop, unlike with a dedicated line.
• Versions: DOCSIS 3.0 with bonded channels (up to about 1 Gbit/s download), 3.1 with more efficient modulation (up to 10 Gbit/s), 4.0 for symmetric rates.
• Asymmetry: Upload is often much lower than download because less frequency range remains for it.
• Device: The cable modem (often built into the router) reports channels, levels and noise margin. See SNR and decibel.
• Faults: Bad in-house wiring, loose connectors or splitters worsen the values. The provider sees them and can measure.
• Comparison: Faster than DSL, but a shared medium. Fibre is independent of the neighbour.

See also: reading a speed test properly