Hybrid fiber-coaxial (HFC) is a
telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than tha ...
industry term for a
broadband
In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...
network
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematics ...
that combines
optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparency and translucency, transparent fiber made by Drawing (manufacturing), drawing glass (silica) or plastic to a diameter slightly thicker than that of a Hair ...
and
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a ...
. It has been commonly employed globally by
cable television
Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with bro ...
operators since the early 1990s.
In a hybrid fiber-coaxial cable system, the television channels are sent from the cable system's distribution facility, the
headend, to local communities through
optical fiber
An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparency and translucency, transparent fiber made by Drawing (manufacturing), drawing glass (silica) or plastic to a diameter slightly thicker than that of a Hair ...
subscriber lines. At the local community, a box called an
optical node
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultra ...
translates the signal from a light beam to
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the uppe ...
(RF), and sends it over
coaxial cable
Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a ...
lines for distribution to subscriber residences. The fiberoptic trunk lines provide adequate bandwidth to allow future expansion and new bandwidth-intensive services such as internet access through
DOCSIS
Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-bandwidth data transfer to an existing cable television (CATV) system. It is used by many cable televisio ...
.
Description
The fiber optic network extends from the cable operators' master
headend, sometimes to regional headends, and out to a neighborhood's hubsite, and finally to a coaxial cable node which serves anywhere from 25 to 2000 homes. A master headend will usually have
satellite dish
A satellite dish is a dish-shaped type of parabolic antenna designed to receive or transmit information by radio waves to or from a communication satellite. The term most commonly means a dish which receives direct-broadcast satellite televisi ...
es for reception of distant video signals as well as
IP aggregation
routers. Some master headends also house
telephony
Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...
equipment (such as automatic
telephone exchange
telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...
s) for providing telecommunications services to the community.
A regional or area headend/hub will receive the video signal from the master headend and add to it the
public, educational, and government access
Public-access television is traditionally a form of non-commercial mass media where the general public can create content television programming which is narrowcast through cable television specialty channels. Public-access television was cre ...
(PEG)
cable TV
Cable television is a system of delivering television programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This contrasts with bro ...
channels as required by local franchising authorities or insert targeted advertising that would appeal to a local area. The various services are encoded,
modulated
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...
and upconverted onto RF
carriers, combined onto a single electrical signal and inserted into a broadband optical transmitter.
This optical transmitter converts the electrical signal to a downstream optically modulated signal that is sent to the nodes. Fiber optic cables connect the headend or hub to optical nodes in a
point-to-point or
star
A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
topology
In mathematics, topology (from the Greek words , and ) is concerned with the properties of a geometric object that are preserved under continuous deformations, such as stretching, twisting, crumpling, and bending; that is, without closing ho ...
, or in some cases, in a protected
ring topology.
Fiber optic nodes
A fiber optic node has a broadband optical receiver, which converts the downstream optically modulated signal coming from the headend or hub to an electrical signal going to the customers. the downstream signal is a RF modulated signal that typically begins at 50 MHz and ranges from 550–1000 MHz on the upper end. The fiber optic node also contains a reverse- or return-path transmitter that sends communication from customers back to the headend. In North America, this reverse signal is a modulated RF ranging from 5–42 MHz while in other parts of the world, the range is 5–65 MHz. This electrical signal is then outputted through coaxial cable to form a coaxial trunk.
The optical portion of the network provides a large amount of flexibility. If there are not many fiber-optic cables to the node,
wavelength division multiplexing
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This techniq ...
can be used to combine multiple optical signals onto the same fiber. Optical filters are used to combine and split optical wavelengths onto the single fiber. For example, the downstream signal could be on a wavelength at 1490 nm and the return signal could be on a wavelength at 1310 nm.
Final connection to customers
The coaxial trunk portion of the network connects 25–2000 homes (500 is typical) in a tree-and-branch configuration off of the node. RF
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost th ...
s are used at intervals to overcome cable attenuation and passive losses of the electrical signals caused by splitting or "tapping" the coaxial cable.
Trunk coaxial cables are connected to the optical node and form 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 60 or 90 V by a power supply (with a lead acid backup battery inside) and a power inserter. The power is added to the cable line so that optical nodes, trunk and distribution amplifiers do not need an individual, external power source. The power supply might have a
power meter next to it depending on local power company regulations. Trunk cables may have trunk amplifiers.
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. If needed, line extenders, which are smaller distribution amplifiers, boost the signals to keep the power of the television signal at a level that the TV can accept. 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 unless there are telephony devices that need the back-up power reliability provided by the coax power system. The tap terminates into a small coaxial drop using a standard screw type connector known as an
F connector
The F connector (also F-type connector) is a coaxial RF connector commonly used for "over the air" terrestrial television, cable television and universally for satellite television and cable modems, usually with RG-6/U cable or with RG-59/U ...
.
The drop is then connected to the house where a ground block protects the system from stray voltages. Depending on the design of the network, the signal can then be passed through a splitter to multiple TVs or to multiple set top boxes (cable boxes) which may then be connected to a TV. If too many splitters are used to connect multiple TVs, the signal levels will decrease, and picture quality on analog channels will decrease. The signal in TVs past those splitters will lose quality and require the use of a "drop" or "house" amplifier to restore the signal.
Transport over HFC network
By using
frequency-division multiplexing
In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate ...
, a HFC network may carry a variety of services, including analog TV, digital TV (
SDTV
Standard-definition television (SDTV, SD, often shortened to standard definition) is a television system which uses a resolution that is not considered to be either high or enhanced definition. "Standard" refers to it being the prevailing spe ...
or
HDTV
High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the ...
),
video on demand
Video on demand (VOD) is a media distribution system that allows users to access videos without a traditional video playback device and the constraints of a typical static broadcasting schedule. In the 20th century, broadcasting in the form of ...
, telephony, and internet traffic. Services on these systems are carried on RF signals in the 5 MHz to 1000 MHz frequency band.
The HFC network is typically operated bi-directionally, meaning that signals are carried in 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 traffic. The very first HFC networks, and very old unupgraded HFC networks, are only one-way systems. Equipment for one-way systems may use
POTS
Pot may refer to:
Containers
* Flowerpot, a container in which plants are cultivated
* Pottery, ceramic ware made by potters
* A type of cookware
Places
* Ken Jones Aerodrome, IATA airport code POT
* Palestinian Occupied Territories, the We ...
or radio networks to communicate to the headend.
The ''return-path'' or ''
upstream
Upstream may refer to:
* Upstream (bioprocess)
* ''Upstream'' (film), a 1927 film by John Ford
* Upstream (networking)
* ''Upstream'' (newspaper), a newspaper covering the oil and gas industry
* Upstream (petroleum industry)
* Upstream (software ...
'' signals carry information from the home to the headend/hub office, such as control signals to order a movie or internet upstream traffic. The forward-path and the return-path are carried over the same coaxial cable in both directions between the optical node and the home.
To prevent interference of signals, the frequency band is divided into two sections. In countries that have traditionally used
NTSC System M, the sections are 52–1000 MHz for forward-path signals, and 5–42 MHz for return-path signals. Other countries use different band sizes, but are similar in that there is much more bandwidth for downstream communication than for upstream communication.
Traditionally, since video content was sent only to the home, the HFC network was structured to be ''asymmetrical'': one direction has much more data-carrying capacity than the other direction. The return path was originally 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 access
Internet access is the ability of individuals and organizations to connect to the Internet using computer terminals, computers, and other devices; and to access services such as email and the World Wide Web. Internet access is sold by Internet ...
and telephony, the return path is being utilised more.
Multiple-system operators
Multi-system operators (MSOs) developed methods of sending the various services over RF signals on the fiber optic and coaxial copper cables. The original method to transport video over the HFC network and, still the most widely used method, is by modulation of standard analog TV channels which is similar to the method used for transmission of over-the-air broadcast.
One analog TV channel occupies a 6-MHz-wide frequency band in
NTSC
The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...
-based systems, or an 8-MHz-wide frequency band in PAL or SECAM-based systems. Each channel is centred on a specific frequency carrier so that there is no interference with adjacent or harmonic channels. To be able to view a digitally modulated channel, home, or
customer-premises equipment
In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation po ...
(CPE), e.g. digital televisions, computers, or
set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of si ...
es, are required to convert the RF signals to signals that are compatible with display devices such as analog televisions or computer monitors. The US Federal Communication Commission (FCC) has ruled that consumers can obtain a cable card from their local MSO to authorize viewing digital channels.
By using digital video compression techniques, multiple standard and high-definition TV channels can be carried on one 6 or 8 MHz frequency carrier, thus increasing the channel carrying capacity of the HFC network by 10 times or more versus an all-analog network.
Comparison to competing network technologies
Digital subscriber line
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric d ...
(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 and data speeds can be range-limited by line lengths and quality.
Satellite television
Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location. The signals are received via an outdoor parabolic antenna commo ...
competes very well with HFC networks in delivering broadcast video services.
Interactive satellite systems are less competitive in urban environments because of their large
round-trip delay time
In telecommunications, round-trip delay (RTD) or round-trip time (RTT) is the amount of time it takes for a signal to be sent ''plus'' the amount of time it takes for acknowledgement of that signal having been received. This time delay includes p ...
s, but are attractive in rural areas and other environments with insufficient or no deployed terrestrial infrastructure.
Analogous to HFC,
fiber in the loop (FITL) technology is used by telephone
local exchange carriers to provide advanced services to telephone customers over the
plain old telephone service
Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from ...
(POTS)
local loop
In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the comm ...
.
In the 2000s, telecom companies started significant deployments of
fiber to the x
Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic ...
(FTTX) such as
passive optical network
A passive optical network (PON) is a fiber-optic telecommunications technology for delivering broadband network access to end-customers. Its architecture implements a point-to-multipoint topology in which a single optical fiber serves multiple e ...
solutions to deliver video, data and voice to compete with cable operators. These can be costly to deploy but they can provide large bandwidth capacity especially for data services.
See also
*
Access network
An access network is a type of telecommunications network which connects subscribers to their immediate service provider. It is contrasted with the core network, which connects local providers to one another. The access network may be furth ...
*
Backbone network
A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, ...
*
Cable modem
*
Cable modem termination system (CMTS)
*
DOCSIS
Data Over Cable Service Interface Specification (DOCSIS) is an international telecommunications standard that permits the addition of high-bandwidth data transfer to an existing cable television (CATV) system. It is used by many cable televisio ...
*
FTTLA
*
Multimedia over Coax Alliance
*
National Cable & Telecommunications Association
NCTA – The Internet & Television Association (formerly the National Cable & Telecommunications Association, and commonly known as the NCTA) is the principal trade association for the U.S. broadband and pay television industries. It represents ...
(NCTA – US)
*
Network service provider
Network Service Provider (NSP) is one of the roles defined in the National Information Infrastructure (NII) plan, which governed the transition of the Internet from US federal control to private-sector governance, with an accompanying shift from th ...
*
Radio frequency over glass (RFoG)
*
Quadrature amplitude modulation
Quadrature amplitude modulation (QAM) is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message sig ...
*
MPEG-2
MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods, w ...
*
Society of Cable Television Engineers
The Society of Cable Telecommunications Engineers or SCTE is a non-profit professional association for the advancement of technology, standards and workforce education related to cable telecommunications engineering. Founded in 1969 as The Societ ...
(SCTE – US)
References
External links
Information on HFC networks in Australia{{telecommunications
Broadband
Fiber-optic communications
Digital cable