Vs, while cables passed about 96% of house units [12]. TV cables and telephone lines constituted the two most common fixed-line telecommunications services into an American home. The cable TV architecture consisted of a cable headend, which receives the TV programmes from terrestrial as well as satellite broadcasts, uses a frequency division multiplexing to transmit up to 500 TV channels on a single medium and feeds it to cables (coaxial or optical fibre) which carry the signals to distribution hubs (Figure 9.17). Each hub can connect to 500-2000 subscribers' homes located within a radius of several hundred meters, using a coaxial cable. A set-top box at the receiving home demodulates the desired channel to the baseband and shows it on TV. The useful frequency spectrum of a coaxial cable is divided into downstream (50 MHz-1 GHz and above) for TV signals and upstream (2-45 MHz) for signalling purposes such as facilitating subscriber pay-per-view channel selection. The frequency allocation is shown in Figure 9.18. The upstream channels can be as narrow as 200 kHz to 3.2 MHz and 6.4 MHz (in later standard releases.) The downstream bandwidth corresponds to the TV channel bandwidth and is 6 MHz in North America and 8 MHz in Europe. With the growth of the internet in the late 1990s, cable TV operators also moved into internet service provision over their infrastructure. The data communications standards were developed through CableLabs, a research and development body established by a global consortium of cable operating companies. The standards are known as Data Over Cable Service Interface Specification (DOCSIS). DOCSIS standards work within the cable TV upstream and downstream frequencies and use one or more of these carriers for data communications. In the downstream the data packets are time division multiplexed and sent to all cable modems connected to the headend. Since the packets are intended for one IP address, only the intended receiver is capable of detecting Distribution Cable Distribution headend Amplifie