Hybrid fibre-coaxial
Encyclopedia
Hybrid fiber-coaxial is a telecommunications industry term for a broadband
network
which combines optical fibre
and coaxial cable
. It was commonly employed globally by cable television
operators since the early 1990s.
, sometimes to regional headends, and out to a neighbourhood's hubsite, and finally to a fiber optic node which serves anywhere from 25 to 2000 homes. A master headend will usually have satellite dishes for reception of distant video signals as well as IP
aggregation routers. Some master headends also house telephony equipment 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
(PEG) cable TV channels as required by local franchising authorities or insert targeted advertising that would appeal to a local area. The various services are encoded, modulated 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. Fibre optic cables connect the headend or hub to optical nodes in a point-to-point or star topology
, or in some cases, in a protected ring topology.
A fibre optic node has a broadband optical receiver which converts the downstream optically modulated signal coming from the headend/hub to an electrical signal going to the homes. Today, the downstream signal is a radio frequency modulated signal that typically begins at 50 MHz and ranges from 550 MHz to 1000 MHz on the upper end. The fibre optic node also contains a reverse/return path transmitter that sends communication from the home back to the headend. In North America, this reverse signal is a modulated radio frequency ranging from 5 to 42 MHz while in other parts of the world, the range is 5 to 65 MHz.
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 can be utilised 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 1310nm and the return signal could be on a wavelength at 1550nm. There are also techniques to put multiple downstream and upstream signals on a single fiber by putting them at different wavelengths.
The coaxial portion of the network connects 25 to 2000 homes (500 is typical) in a tree-and-branch configuration off of the node. Radio frequency
amplifier
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 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 individual, 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. 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 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. If too many splitters are used to connect multiple TVs, the signal levels will decrease, and picture quality on analog channels of TVs past those splitters will go down requiring the use of a "drop" or "house" amplifier.
, telephony
, and high-speed data. Services on these systems are carried on Radio Frequency
(RF) signals in the 5 MHz to 1000 MHz frequency band.
The HFC network can be 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 data. The return-path or upstream
signals carry information 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 cable in both directions between the optical node and the home. In order 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 MHz to 1000 MHz for forward-path signals, and 5 MHz to 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 instead of upstream communication.
Traditionally, since video content was sent only to the home, the HFC network was structured to be non-symmetrical: 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
and telephony, the return-path is being utilised more.
Multiple 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 analogue TV channels which is similar to the method used for transmission of over-the-air broadcast. See broadcast television system
for more information. One analogue TV channel occupies a 6 MHz-wide frequency band in NTSC-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
(CPE), e.g. digital televisions, computers, or set-top box
es, are required to convert the RF signals to signals that are compatible with display devices such as analogue televisions or computer monitors. The 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 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 analogue network. Note that a digital tuner (i.e. TV set-top box) is not required for standard analogue TV channels since most televisions have integrated analogue tuners that can decode the signal, unless some type of scrambling is used.
(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
competes very well with HFC networks in delivering broadcast video services. Interactive satellite system
s are less competitive in urban environments because of their large round-trip delay time
s, but are attractive in rural areas and other environments with insufficient or no deployed terrestrial infrastructure.
Analogous to HFC, Fiber In The Loop
technology is used by telephone local exchange carrier
s to provide advanced services to telephone customers over the POTS
local loop
.
In the 2000s, telecom companies started significant deployments of Fiber to the x such as passive optical network
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.
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
network
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...
which combines optical fibre
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
and coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
. It was commonly employed globally by cable television
Cable television
Cable television is a system of providing television programs to consumers via radio frequency signals transmitted to televisions through coaxial cables or digital light pulses through fixed optical fibers located on the subscriber's property, much like the over-the-air method used in traditional...
operators since the early 1990s.
Description
The fiber optic network extends from the cable operators' master headendCable television headend
A cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. The headend facility is normally unstaffed and surrounded by some type of security fencing and is typically a building or large shed housing electronic...
, sometimes to regional headends, and out to a neighbourhood's hubsite, and finally to a fiber optic node which serves anywhere from 25 to 2000 homes. A master headend will usually have satellite dishes for reception of distant video signals as well as IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
aggregation routers. Some master headends also house telephony equipment 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, educational, and government access
Public, educational, and government access television, refers to three different cable television specialty channels...
(PEG) cable TV channels as required by local franchising authorities or insert targeted advertising that would appeal to a local area. The various services are encoded, modulated and upconverted onto RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
carriers
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
, 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. Fibre optic cables connect the headend or hub to optical nodes in a point-to-point or star topology
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
, or in some cases, in a protected ring topology.
A fibre optic node has a broadband optical receiver which converts the downstream optically modulated signal coming from the headend/hub to an electrical signal going to the homes. Today, the downstream signal is a radio frequency modulated signal that typically begins at 50 MHz and ranges from 550 MHz to 1000 MHz on the upper end. The fibre optic node also contains a reverse/return path transmitter that sends communication from the home back to the headend. In North America, this reverse signal is a modulated radio frequency ranging from 5 to 42 MHz while in other parts of the world, the range is 5 to 65 MHz.
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 can be utilised 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 1310nm and the return signal could be on a wavelength at 1550nm. There are also techniques to put multiple downstream and upstream signals on a single fiber by putting them at different wavelengths.
The coaxial portion of the network connects 25 to 2000 homes (500 is typical) in a tree-and-branch configuration off of the node. Radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
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 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 individual, 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. 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
F connector
The F connector is a type of 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, in older installations, with RG-59/U cable. It was invented by Eric E...
. 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. If too many splitters are used to connect multiple TVs, the signal levels will decrease, and picture quality on analog channels of TVs past those splitters will go down requiring the use of a "drop" or "house" amplifier.
Transport over HFC network
By using frequency division multiplexing, an HFC network may carry a variety of services, including analogue TV, digital TV (SDTV or HDTV), Video on demandVideo on demand
Video on Demand or Audio and Video On Demand are systems which allow users to select and watch/listen to video or audio content on demand...
, telephony
Telephony
In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....
, and high-speed data. Services on these systems are carried on Radio Frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) signals in the 5 MHz to 1000 MHz frequency band.
The HFC network can be 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 data. The return-path or upstream
Upstream (networking)
In computer networking, upstream refers to the direction in which data can be transferred from the client to the server . This differs greatly from downstream not only in theory and usage, but also in that upstream speeds are usually at a premium...
signals carry information 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 cable in both directions between the optical node and the home. In order 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 MHz to 1000 MHz for forward-path signals, and 5 MHz to 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 instead of upstream communication.
Traditionally, since video content was sent only to the home, the HFC network was structured to be non-symmetrical: 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
Many technologies and service plans for Internet access allow customers to connect to the Internet.Consumer use first became popular through dial-up connections in the 20th century....
and telephony, the return-path is being utilised more.
Multiple System Operators
Multi system operator
A Multiple System Operator or Multi System Operator is an operator of multiple cable television systems. A cable system in the United States, by Federal Communications Commission definition, is a facility serving a single community or a distinct governmental entity, each with its own franchise...
(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 analogue TV channels which is similar to the method used for transmission of over-the-air broadcast. See broadcast television system
Broadcast television system
Broadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television signals. There are three main analog television systems in current use around the world: NTSC, PAL, and SECAM...
for more information. One analogue TV channel occupies a 6 MHz-wide frequency band in NTSC-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
Customer-premises equipment
Customer-premises equipment or customer-provided equipment is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication channel at the demarcation point...
(CPE), e.g. digital televisions, computers, or set-top box
Set-top box
A set-top box or set-top unit is an information appliance device that generally contains a tuner and connects to a television set and an external source of signal, turning the signal into content which is then displayed on the television screen or other display device.-History:Before the...
es, are required to convert the RF signals to signals that are compatible with display devices such as analogue televisions or computer monitors. The 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 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 analogue network. Note that a digital tuner (i.e. TV set-top box) is not required for standard analogue TV channels since most televisions have integrated analogue tuners that can decode the signal, unless some type of scrambling is used.
Competitive network technologies
Digital subscriber lineDigital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric 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 and data speeds can be range-limited by line lengths and quality.
Satellite television
Satellite television
Satellite television is television programming delivered by the means of communications satellite and received by an outdoor antenna, usually a parabolic mirror generally referred to as a satellite dish, and as far as household usage is concerned, a satellite receiver either in the form of an...
competes very well with HFC networks in delivering broadcast video services. Interactive satellite system
Satellite Internet access
Satellite Internet access is Internet access provided through satellites. The service can be provided to users world-wide through low Earth orbit satellites. Geostationary satellites can offer higher data speeds, but their signals can not reach some polar regions of the world...
s are less competitive in urban environments because of their large round-trip delay time
Round-trip delay time
In telecommunications, the round-trip delay time or round-trip time is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received...
s, but are attractive in rural areas and other environments with insufficient or no deployed terrestrial infrastructure.
Analogous to HFC, Fiber In The Loop
Fiber in the loop
Fiber In The Loop is a system implementing or upgrading portions of the POTS local loop with fiber optic technology from the central office of a telephone carrier to a remote Serving area interface located in a neighborhood or to an Optical Network Unit located at the customer premises...
technology is used by telephone local exchange carrier
Local exchange carrier
Local Exchange Carrier is a regulatory term in telecommunications for the local telephone company.In the United States, wireline telephone companies are divided into two large categories: long distance and local...
s to provide advanced services to telephone customers over the POTS
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
local loop
Local loop
In telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...
.
In the 2000s, telecom companies started significant deployments of Fiber to the x such as passive optical network
Passive optical network
A passive optical network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal at the service provider's central...
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
- Broadcast television systemBroadcast television systemBroadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television signals. There are three main analog television systems in current use around the world: NTSC, PAL, and SECAM...
- Cable modemCable modemA cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high...
- DOCSISDOCSISData Over Cable Service Interface Specification is an international telecommunications standard that permits the addition of high-speed data transfer to an existing cable TV system...
- FTTLAFTTLAFTTLA refers to "Fibre To The Last Amplifier". Classic analogue cable television trunks used several amplifiers at intervals in cascade, each of which degrades the signal. FTTLA replaces the coaxial cable all along the line to the last amplifier with optical fibre...
- National Television System(s) CommitteeNTSCNTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
- National Cable & Telecommunications AssociationNational Cable & Telecommunications AssociationThe National Cable & Telecommunications Association is the principal trade association for the U.S. cable TV industry, representing cable operators serving more than 90 percent of the nation’s cable households and more than 200 cable program networks, as well as equipment suppliers and providers...
(NCTA) - Radio FrequencyRadio frequencyRadio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
(RF) - Quadrature amplitude modulationQuadrature amplitude modulationQuadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
- MPEG-2MPEG-2MPEG-2 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 which permit storage and transmission of movies using currently available storage media and transmission...
- Society of Cable Television EngineersSCTEThe Society of Cable Telecommunications Engineers or SCTE is a non-profit professional association for the advancement of technology related to cable telecommunications engineering. Founded in 1969, SCTE has a current membership of over 12,000 individuals.- Publications :SCTE offers several...
(SCTE) - Passive optical networkPassive optical networkA passive optical network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal at the service provider's central...
- Video on demandVideo on demandVideo on Demand or Audio and Video On Demand are systems which allow users to select and watch/listen to video or audio content on demand...
- RMS CommunicationsRMS CommunicationsRMS Communications Inc. is a manufacture/supplier of CATV passives for the Cable TV industry.-History:Founded in 1943, RMS Communications is engaged in the import, assembly and sale of electronic devices and components for various segments of the communications industry...