Plain old telephone service
Encyclopedia
Plain old telephone service (POTS) 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.
The name is a retronym
, and is a reflection of the telephone service still available after the advent of more advanced forms of telephony such as ISDN, mobile phone
s and VoIP. POTS has been available almost since the introduction of the public telephone system in the late 19th century, in a form mostly unchanged to the normal user despite the introduction of Touch-Tone dialing, electronic telephone exchange
s and fiber-optic communication
into the public switched telephone network
(PSTN).
The system was originally known as the Post Office Telephone Service/System in many countries. The term was dropped as telephone services were removed from the control of national post office
s.
POTS includes:
In the United States, the pair of wires
from the central switch office to a subscriber's home is called a subscriber loop. It is typically powered by −48V
direct current (DC) and backed up by a large bank of batteries (connected in series) in the central office, resulting in continuation of service during most commercial power outages. The subscriber loop typically carries a "load" of about 300 ohm
s, and does not pose a threat of electrocution to human beings (although shorting the loop can be felt as an unpleasant sensation).
Many calling features became available to POTS subscribers after computerization of telephone exchanges during the 1970s and 1980s. The services include:
The communications circuits of the PSTN continue to be modernized by advances in digital communications; however, other than improving sound quality, these changes have been mainly transparent to the POTS customer. In most cases, the function of the POTS local loop
presented to the customer for connection to telephone equipment is practically unchanged and remains compatible with old Pulse dialing
telephones, even ones dating back to the early 20th century.
Due to the wide availability of POTS, new forms of communications devices such as modem
s and facsimile machines are designed to use POTS to transmit digital information.
capabilities, it provides greater reliability than other telephony systems (mobile phone, VoIP, etc.). Many telephone service providers attempt to achieve "dial-tone availability" more than 99.999%
of the time the telephone is taken off-hook
. This is an often cited benchmark in marketing and systems-engineering comparisons, called the "five nines
" reliability standard. It is equivalent to having a dial-tone available for all but less than five minutes each year.
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world.
The name is a retronym
Retronym
A retronym is a type of neologism that provides a new name for an object or concept to differentiate the original form or version of it from a more recent form or version. The original name is most often augmented with an adjective to account for later developments of the object or concept itself...
, and is a reflection of the telephone service still available after the advent of more advanced forms of telephony such as ISDN, mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
s and VoIP. POTS has been available almost since the introduction of the public telephone system in the late 19th century, in a form mostly unchanged to the normal user despite the introduction of Touch-Tone dialing, electronic telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
s and fiber-optic communication
Fiber-optic communication
Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information...
into 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).
The system was originally known as the Post Office Telephone Service/System in many countries. The term was dropped as telephone services were removed from the control of national post office
Post office
A post office is a facility forming part of a postal system for the posting, receipt, sorting, handling, transmission or delivery of mail.Post offices offer mail-related services such as post office boxes, postage and packaging supplies...
s.
POTS includes:
- bi-directional, or full duplexDuplex (telecommunications)A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
, voicebandVoicebandIn electronics, voiceband means the typical human hearing frequency range that is from 20 Hz to 20 kHz. In telephony, it means the frequency range normally transmitted by a telephone line, generally about 200–3600 Hz. Frequency-division multiplexing in telephony normally uses...
path with limited frequency range of 300 to 3400 Hz: in other words, a signal to carry the sound of the human voice both ways at once; - call-progress toneCall-progress toneIn telephony, call progress tones are audible tones sent from the public switched telephone network central office or a private branch exchange to calling parties to indicate the status of phone calls....
s, such as dial toneDial toneA dial tone is a telephony signal used to indicate that the telephone exchange is working, has recognized an off-hook, and is ready to accept a call. The tone stops when the first numeral is dialed...
and ringing signal; - subscriber dialing;
- operator services, such as directory assistanceDirectory assistanceIn telecommunications, directory assistance or directory enquiries is a phone service used to find out a specific telephone number and/or address of a residence, business, or government entity.-Technology:...
, long distance calling, and conference callConference callA conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party...
ing assistance; - a standards compliant analog telephone interface including BORSCHTBORSCHTBORSCHT is an acronym for:Battery supply to subscriber lineOvervoltage protectionRinging current supplySupervision of subscriber terminalCoder and decoderHybrid, 2 wire to 4 wire conversionTesting...
functions
In the United States, the pair of wires
Tip and ring
"Tip" and "Ring" are common terms in the telephone service industry referring to the two wires or sides of an ordinary telephone line. Tip is the ground side and Ring is the battery side of a phone circuit. In the UK these are referred to as the 'A' and 'B' wires...
from the central switch office to a subscriber's home is called a subscriber loop. It is typically powered by −48V
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
direct current (DC) and backed up by a large bank of batteries (connected in series) in the central office, resulting in continuation of service during most commercial power outages. The subscriber loop typically carries a "load" of about 300 ohm
Ohm
The ohm is the SI unit of electrical resistance, named after German physicist Georg Simon Ohm.- Definition :The ohm is defined as a resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere,...
s, and does not pose a threat of electrocution to human beings (although shorting the loop can be felt as an unpleasant sensation).
Many calling features became available to POTS subscribers after computerization of telephone exchanges during the 1970s and 1980s. The services include:
- VoicemailVoicemailVoicemail is a computer based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to individuals, organizations, products and services, using an ordinary telephone...
- Caller IDCaller IDCaller ID , also called calling line identification or calling number identification or Calling Line Identification Presentation , is a telephone service, available in analog and digital phone systems and most Voice over Internet Protocol applications, that transmits a caller's number to...
- Call waitingCall waitingCall waiting , in telephony, is a feature on some telephone networks. If a calling party places a call to a called party which is otherwise engaged, and the called party has the call waiting feature enabled, the called party is able to suspend the current telephone call and switch to the new...
- Speed dialingAbbreviated dialingAbbreviated dialing is the use of a very short telephone number to reach public services. Typically these are two or three digits, and are most commonly known as being emergency telephone numbers like 9-9-9, 1-1-2 and 9-1-1. Other services may also be available this way, such as the N11 codes in...
- Conference callConference callA conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party...
(three-way calling) - Enhanced 911Enhanced 911Enhanced 911, E-911 or E911 in North America is one example of the modern evolution of telecommunications based system meant as an easy way to link people experiencing an emergency with the public resources that can help. The dial-three-digits concept first originated in the United Kingdom in 1937....
- CentrexCentrexCentrex is a portmanteau of central exchange, a kind of telephone exchange.In the United Kingdom, British Telecom markets this service as FeatureLine .-Use of Centrex:...
- and other services.
The communications circuits of the PSTN continue to be modernized by advances in digital communications; however, other than improving sound quality, these changes have been mainly transparent to the POTS customer. In most cases, the function of the POTS 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...
presented to the customer for connection to telephone equipment is practically unchanged and remains compatible with old Pulse dialing
Pulse dialing
Pulse dialing, dial pulse, or loop disconnect dialing, also called rotary or decadic dialling in the United Kingdom , is pulsing in which a direct-current pulse train is produced by interrupting a steady signal according to a fixed or formatted code for each digit and at a standard pulse repetition...
telephones, even ones dating back to the early 20th century.
Due to the wide availability of POTS, new forms of communications devices such as modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s and facsimile machines are designed to use POTS to transmit digital information.
Reliability
While POTS provides limited features, low bandwidth and no mobileMobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
capabilities, it provides greater reliability than other telephony systems (mobile phone, VoIP, etc.). Many telephone service providers attempt to achieve "dial-tone availability" more than 99.999%
High availability
High availability is a system design approach and associated service implementation that ensures a prearranged level of operational performance will be met during a contractual measurement period....
of the time the telephone is taken off-hook
Off-hook
In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...
. This is an often cited benchmark in marketing and systems-engineering comparisons, called the "five nines
Uptime
Uptime is a measure of the time a machine has been up without any downtime.It is often used as a measure of computer operating system reliability or stability, in that this time represents the time a computer can be left unattended without crashing, or needing to be rebooted for administrative or...
" reliability standard. It is equivalent to having a dial-tone available for all but less than five minutes each year.
See also
- Public switched telephone networkPublic switched telephone networkThe 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...
- Managed Facility Voice NetworkManaged Facility Voice NetworkA managed facilities-based voice network, or MFVN, is a physical network owned and operated by a voice service provider that delivers traditional telephone service via a loop start analog telephone interface. MFVNs are interconnected with the public switched telephone network and provide dialtone...
- RJ11 - the type of telephone jack common in most of the world for single line POTS telephones
- DTMF - the tones used for pushbutton dialing
- Local telephone serviceLocal telephone serviceLocal telephone service is the provision of telecommunications networks and services within a limited geographic region.Traditionally, local telephone service was provided by small companies based in given cities and towns as opposed to larger, national or international companies...
- Category 1 cableCategory 1 cableCategory 1 cable a.k.a. voice-grade copper is a misnomer, probably adopted by those who assumed that TIA set up "Categories" for all types of cables originally defined by Anixter International, the distributor, under the grades called "Levels." Cat 1 cable is used in earlier times...
- Twisted pairTwisted pairTwisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
- 25-pair color code25-pair color codeThe 25-pair color code is a color code used to identify individual conductors in a kind of electrical telecommunication wiring for indoor use, known as twisted pair cables . The colors are applied to the insulation that covers each conductor...
- Foreign exchange office (FXO)
- Foreign exchange station (FXS)
- Network interface deviceNetwork interface deviceIn telecommunications, a Network Interface Device is a device that serves as the demarcation point between the carrier's local loop and the customer's premises wiring....