Hybrid fibre-coaxial

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Hybrid fiber-coaxial (HFC) is a telecommunications industry term for a network which incorporates both optical fiber along with coaxial cable to create a broadband network. It has been commonly employed by cable TV operators since the 1990s. See diagram below for a typical architecture for an HFC Network.

The fiber optic network extends from the cable operators central office, to the area's headend, out to a neighbourhood's hubsite, and finally to a fiber optic node which services any number of homes ranging from 1 to 2000 homes.

A fiber optic node converts optical signals to electronic and vice versa. It is a "dumb" device in that it does not demodulate or otherwise interpret the signals. Fiber optic cables connect the optical node to a distant headend or hub.

The coaxial portion of the network connects 100 to 2000 homes (500 is typical) in a tree-and-branch configuration. Radio frequency amplifiers are used at intervals to overcome cable attenuation and splitting losses. Trunk coaxial cables are connected to the optical node and form essentially a coaxial backbone to which smaller distribution cables connect. Trunk cables also carry AC power which is added to the cable line at usually either 60V or 90V by a power supply and a power inserter. The power is added to the cable line so that trunk and distribution amplifiers do not need an external power source. From the trunk cables, smaller distribution cables are connected to a port of the trunk amplifier to carry the RF signal and the AC power down individual streets along side customer homes going through line extenders (which are distribution amplifiers that are substantially smaller than trunk amplifiers.) The distribution line is then "tapped" into and used to connect the individual drops to customer homes. These taps pass the RF signal and block the AC power. The tap terminates into a small RG11 or RG6 coaxial connector which then is connected to the house and either to a main splitter (ground block) inside the house, or to a main panel or DT on a building with multiple suites.

[edit] Transport over HFC Network

By using frequency division multiplexing, an HFC network may carry a variety of services, including analog TV, digital TV (standard definition and HDTV), Video on demand, telephony, and high-speed data. from the home to the headend/hub office, such as control signals to order a movie or internet data to send an email. The forward-path and the return-path are actually carried over the same coaxial cablein both directions on the same network from the headend/hub office to the home, and from the home to the headend/hub office. The forward-path or downstream signals carry information from the headend/hub office to the home, such as video content, voice and internet data. The return-path or upstream signals carry information from the home to the , so the HFC network is structured to be non-symmetrical, meaning that one direction has much more data-carrying capacity than the other direction. Years ago, the return-path was only used for some control signals to order movies, etc., which required very little bandwidth. As additional services have been added to the HFC network, such as internet data and telephony, the return-path is being utilized more.

Cable Multiple System Operators (MSOs) developed methods of sending the various services over RF signals on the fiber optic and coaxial cables. The original method to transport video, and still widely used method, over the HFC network is on standard analog TV channels which is the same method used as over-the-air broadcast television channels.(See Broadcast television system for more information.) One analog TV channel occupies an entire 6 MHz-wide frequency channel or frequency carrier (i.e. channel 2 is centered on frequency carrier 55.25 MHz), which is very bandwidth inefficient. Digital TV channels offer a more-efficient way to transport video by using MPEG-2 or MPEG-4 coding over Quadrature amplitude modulation (QAM) channels. Using this method, multiple home, or consumer premise equipment (CPE), are required to convert the RF signals to signals that are compatible with television sets, computers and telephones. Examples of these devices are television Set-top boxes, information.) One analog TV channel occupies an entire 6 MHz-wide frequency channel or frequency carrier (i.e. channel 2 is centered on frequency carrier 55.25 MHz), which is very bandwidth inefficient. Digital TV channels offer a more-efficient way to transport video by using MPEG-2 or MPEG-4 coding over Quadrature amplitude modulation (QAM) channels. Using this method, multiple standard digital TV channels (up to 10 channels) can be carried on one frequency carrier thus increasing the carrying-capacity of a frequency carrier by 10 times. HDTV utilizes the forward path signals and convert them to usable signals in the home. These same devices also generate the return-path signals to communicate back to the headend/hub office. Note that a CPE (i.e. TV set-top box) probably is not required for standard analog TV channels since most televisions have integrated analog tuners that can decode the signal, unless some type of scrambling is used.

[edit] Competitive Network Technologies

Digital subscriber line (DSL) is a technology used by traditional telephone companies to deliver advanced services (high-speed data and sometimes video) over twisted pair copper telephone wires. It typically has lower data carrying capacity than HFC networks.

Satellite television competes very well with HFC networks in delivering broadcast video services. It usually does not compete well in delivering internet data, telephony and interactive services (i.e. VOD) because it does not have a good method to transport return-path information.

Analogous to HFC, Fiber In The Loop technology is used by telephone local exchange carriers to provide advanced services to telephone customers over the POTS local loop.

Starting in the 2000’s, Fiber-to-the-Home networks (FTTH), also called Fiber-to-the-Premise, began to widely roll out to compete with HFC networks. Passive optical networks are a specific type of FTTH network being significantly deployed in the United States and other countries.