Data over Cable Services
Although Cable TV was known to be a one way system for broadcasting TV programs, nowadays a two way communication across the Cable networks is possible, and this step helps in delivering new services to the users across the cable networks, for example DOCSIS, Interactive TV, Pay Per View (PPV) … etc.
A cable modem is a 64/256 QAM RF receiver capable of delivering up from 30 - 40 Mbps of data in one downstream cable channel. The data in the upstream direction is modulated using a QPSK/16 QAM transmitter with data rates from 320 kbps up to 10 Mbps. This upstream and downstream bandwidth is shared by the active data subscribers connected to a given cable network segment, typically 500 to 2,000 homes on a modern HFC network.
From a user perspective, an individual cable modem may experience access speeds from 500 Kbps to 1.5 Mbps or even more than that-- depending on the network architecture and traffic load -- blazing performance compared to dial-up alternatives.
Frequency Plan Modern Hybrid Fiber/Coax (HFC) systems are operating with 700 MHz of capacity, the operating range is from 50 MHz up to 750 MHz. The 5 MHz - 42 MHz portion of the spectrum is usually reserved for upstream communications from subscribers' homes.
Each standard television channel occupies 6 MHz [USA] of RF spectrum or 8 MHz [Europe]. Thus a modern HFC system with 700 MHz of downstream bandwidth has the capacity for some 110 channels.
To deliver data services over a cable network, one television channel (in the 50 - 750 MHz range) is typically allocated for downstream traffic to homes, this downstream channel is shared among users available per each distribution node, while another upstream channels (in the 5 - 42 MHz band) are used to carry upstream signals.