Cable telephony is a form of digital telephony

Digital telephony

Digital telephony is the use of digital electronics in the provision of digital telephone services and systems. Since the 1960s a digital core network has almost entirely replaced the old analog system, and much of the access network has also been digitized...

 over cable TV 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

Public switched telephone network

The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...

 (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.

Emergency calls

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

Emergency Call

Emergency Call is a British film released in 1952 by Nettlefold Films. The film was directed by Lewis Gilbert and stars Jack Warner in a familiar role playing a policeman, Anthony Steel, Joy Shelton and Sid James as a dubious boxing promoter....

s. PacketCable

PacketCable

PacketCable is an industry consortium founded by CableLabs with the goal of defining standards for the cable television modem access industry....

, 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

The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

 demands of traditional analog telephone service

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....

.

Advantage

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

Digital cable

Digital cable is a generic term for any type of cable television distribution using digital video compression or distribution. The technology was originally developed by Motorola.-Background:...

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

Broadband Internet access

Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....

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

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

.

Disadvantage

The biggest disadvantage to digital cable telephone service is similar to the disadvantage of cable Internet access, namely that the medium is shared, resulting in occasional delays and drops when high volumes of bandwidth are used or in some cases shared with entire neighborhoods. These outages are typical during the "prime time" parts of the day, when heavy Internet usage on top of HD viewing and Internet streaming devices can make telephone calls on this system difficult.

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 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

Phantom power, in the context of professional audio equipment, is a method for transmitting DC electric power through microphone cables to operate microphones that contain active electronic circuitry....

over the communication wires and therefore keep attached devices operational.