Cable telephony is a form of

digital 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 ...

over

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 broa ...

networks. A telephone interface installed at the customer's premises converts analog signals from the customer's in-home wiring to a digital signal, which is then sent over the cable connection to the company's switching center. The signal is then sent on to the

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

(PSTN). Cable telephone provides another revenue stream for cable television system operators and gives the consumer the convenience of a single bill for combined television, internet and telephone services. Richard Grigonis (ed) ''Cable Telephony'' in ''Computer Telephony Encyclopedia'', Focal Press, 2000 pp.68-69

Emergency calls

The biggest obstacle to cable telephone service is the need for nearly 100% reliable service for

emergency call Most public switched telephone networks have a single emergency telephone number (sometimes known as the universal emergency telephone number or the emergency services number) that allows a caller to contact local emergency services for assista ...

PacketCable PacketCable network is a technology specification defined by the industry consortium CableLabs for using Internet Protocol (IP) networks to deliver multimedia services, such as IP telephony, conferencing, and interactive gaming on a cable televisi ...

, one of the emerging standards being developed for digital cable telephony, seems to be the most promising and able to work with the

quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

demands of traditional analog telephone service.

Advantage

The biggest advantage to digital cable telephone service is similar to the advantage of

digital cable Digital cable is the distribution of cable television using digital data and video compression. The technology was first developed by General Instrument. By 2000, most cable companies offered digital features, eventually replacing their previ ...

television, namely that data can be compressed, resulting in much less bandwidth used than a dedicated analog circuit-switched service. Other advantages include better voice quality and perhaps future integration to a

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

network providing cheap or unlimited nationwide and international calling. In most cases, digital cable telephone service is separate from

broadband 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 Inte ...

service being offered by many cable companies and does not rely on IP traffic or the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

Disadvantage

One possible disadvantage to digital cable telephone service is similar to a disadvantage of

cable Internet access In telecommunications, cable Internet access, shortened to cable Internet, is a form of broadband Internet access which uses the same infrastructure as a cable television. Like digital subscriber line and fiber to the premises services, cable In ...

, namely that the medium is shared, which could result in occasional delays and drops when high volumes of bandwidth are used or in some cases shared with entire neighborhoods. These delays could be experienced during the "prime time" parts of the day, when heavy Internet usage and Internet streaming devices can make telephone calls on this system difficult. However, by utilizing Cable Lab's Packet Cable interface specifications, cable operators are able to diminish the effects of heavy internet usage on call quality. This is done by way of QoS provisions present in the Packet Cable specifications.
PacketCable™ Dynamic Quality-of-Service Specification. The second disadvantage it that this service requires power at the subscriber's end. In an emergency, if mains power is lost and without the

battery backup An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power syste ...

unit provided at an additional cost by the cable provider, this telephone service ceases to function. Traditional landline service from phone companies supply

phantom power Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry. It is best known as a convenient power source for con ...

over the communication wires and therefore keep attached devices operational.

References

{{Telecommunications Telephony Cable television technology