Hybrid fiber-coaxial
Hybrid fiber-coaxial (HFC) is a broadband telecommunications network that combines optical fiber and coaxial cable.
At the local community, an optical node translates the signal from a light beam to radio frequency (RF), and sends it over coaxial cable lines for distribution to subscriber residences.
[2] The fiber optic trunk lines provide enough bandwidth to allow additional bandwidth-intensive services such as cable internet access through DOCSIS.
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 (such as automatic telephone exchanges) for providing telecommunications services to the community.
A regional or area headend/hub will receive the video signal from the master headend[6] 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, along with internet from a CMTS (an Integrated CMTS, which includes all parts required for operation), or a CCAP which provides both internet and video.
[9][10] CCAPs aim to replace the conventional, integrated CMTS which only provides data and Edge QAMs used for video which are separate pieces of equipment.
The various services from CMTSs, CCAPs, Edge QAMs and QAM modulators are combined onto a single RF electrical signal using headend RF management modules such as splitters and combiners[17][18][19] and the resulting signals are inserted into a broadband optical transmitter which in practice is a transmitter module in an "optics platform" or headend platform such as an Arris CH3000, Scientific Atlanta Prisma, or a Cisco Prisma II.
The fiber optic node also contains a reverse- or return-path transmitter that sends communication from customers back to the headend.
If there are not many fiber-optic cables to the node, wavelength division multiplexing can be used to combine multiple optical signals onto the same fiber.
[55][56] The first amplifiers in outdoor housings with hinges and seals, for installation between utility poles hanging from messenger wires, were offered in 1965.
[58][59] Supertrunks made of coaxial cable with FM modulated video signals,[60][56] fiber optics or microwave links were used to connect headends to hubs.
[70] To cope with needs for increased digital bandwidth such as for DOCSIS internet, cable operators have implemented expansions in the RF spectrum in HFC networks beyond 1 GHz to 1.2 GHz,[71][72] have transitioned to only handling IP traffic in the network thus eliminating dedicated video RF channels, used digital transport adapters (DTAs) for transmitting normally analog signals, or used Switched Digital Video (SDV)[73][74] which allows the number of television channels in coaxial cables to be reduced without reducing the number of channels that are offered.
[85][87] Distributed Access Architecture (DAA) covers Remote PHY and Remote MACPHY and has as the goal, moving functions closer to end customers, allowing for easier capacity expansions as centralized facilities for equipment are downsized or potentially eliminated, and newer DOCSIS versions beyond DOCSIS 3.1 with higher speeds.
[98] Full duplex (FDX) DOCSIS allows upstream and downstream signals to simultaneously occupy a single frequency range without time division multiplexing.
The forward-path or downstream signals carry information from the headend/hub office to the home, such as video content, voice and Internet traffic.
As additional services have been added to the HFC network, such as Internet access and telephony, the return path is being utilised more.
Multi-system operators (MSOs) developed methods of sending the various services over RF signals on the fiber optic and coaxial copper cables.
To be able to view a digitally modulated channel, home, or customer-premises equipment (CPE), e.g. digital televisions, computers, or set-top boxes, 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 Communications Commission (FCC) has ruled that consumers can obtain a cable card from their local MSO to authorize viewing digital channels.
In the 2000s, telecom companies started significant deployments of fiber to the x (FTTX) such as passive optical network solutions to deliver video, data and voice to compete with cable operators.
