Editing Plain old telephone service

{{short description|Traditional analog land line telephone service}}
'''Plain old telephone service''' ('''POTS'''), or '''publicly offered telephone service''', is basic [[Voice band|voice-grade telephone service]]. Historically, POTS has been delivered by [[Analog signal|analog signal transmission]] over copper loops, but the term also describes [[Backward compatibility|backward-compatible]] analog connections offered by digital telephone systems.<ref>{{Cite web |title=AnyMediaTM Access System: Software Release Description for Software Release 1.0.0.0" (PDF). Lucent Technologies. September 28, 1998. Retrieved February 28, 2020. |url=https://documentation.nokia.com/cgi-bin/dbaccessfilename.cgi/363211104_V1_AnyMedia%20Access%20System%20Release%201.0.0.0%20Software%20Release%20Description.pdf}}</ref>  

Copper loop POTS was the standard service offering from telephone companies in the United States from 1876 until 1988,<ref>{{Cite web |title=I.430 : Basic user-network interface – Layer 1 specification". International Telecommunication Union. 2010-08-23. Retrieved 2015-05-07. |url=https://www.itu.int/rec/T-REC-I.430-198811-S/en}}</ref> when the [[Integrated Services Digital Network]] (ISDN) Basic Rate Interface (BRI) was introduced, followed by the development of [[mobile phone|cellular telephone]] systems and [[voice over internet protocol]] (VoIP).

Despite the advent of these technologies, copper loop POTS remains a basic form of residential and small business connection to the [[telephone network]] in many parts of the world. The term encapsulates a technology that has been available since the introduction of the public telephone system in the late 19th century, remaining largely unchanged despite the introduction of innovations such as [[Touch-Tone]] dialing, electronic [[telephone exchange]]s and [[fiber-optic communication]] into the [[public switched telephone network]] (PSTN).

==Characteristics==
Modern, automated POTS is characterized by several aspects:<ref>{{cite book|last1=Coll|first1=Eric|title=Telecom 101|date=2008|publisher=Teracom Training Institute|isbn=978-1894887014|url=http://www.telecom101.com}}</ref>
*Bi-directional ([[Duplex (telecommunications)|full duplex]]) communications.
*Using balanced signaling of voltage analogs of sound pressure waves on a two-wire copper loop
*Restricted to a narrow frequency range of 300–3,300&nbsp;Hz, called the [[voiceband]], which is much less than the human hearing range of 20–20,000&nbsp;Hz
*[[Call-progress tone]]s, such as [[dial tone]] and [[ringing tone]]
*[[Pulse dialing]] and [[dual-tone multi-frequency signaling]] (DTMF)
*[[BORSCHT]] functions:  battery feed (B), over-voltage protection (O), [[Ringing (telephony)|ringing]] (R), [[Signaling (telecommunications)|signaling]] (S), coding (C), hybrid (H), and test (T)
*Loop start, ground start and [[E and M signaling|E&M signalling]]

The [[Tip and ring| pair of wires]] from the central office switch to a subscriber's home is called a [[local loop|subscriber loop]]. It carries a direct current (DC) [[volt]]age at a nominal voltage of −48V when the receiver is on-hook, supplied by a power conversion system in the central office.  This power conversion system is backed up with a bank of batteries, resulting in continuation of service during interruption of power to the customer supplied by their electrical utility.

The maximum resistance of the loop is 1,700{{nbsp}}[[ohm]]s, which translates into a maximum loop length of {{convert|18,000|ft|km|disp=or|abbr=out|0}} using standard 24-[[American wire gauge| gauge wire]]. (Longer loops are often constructed with larger, lower-resistance 19-gauge wire and/or specialized central office equipment called a ''loop extender''. They may be {{convert|50,000|ft|km|disp=sqbr}} or more.)

Many [[calling feature]]s became available to telephone subscribers after computerization of telephone exchanges during the 1980s in the United States. The services include [[voicemail]], [[caller ID]], [[call waiting]], [[Abbreviated dialing|speed dialing]], [[conference call]]s (three-way calling), [[enhanced 911]], and [[Centrex]] services.

The communication circuits of the [[public switched telephone network]] continue to be modernized by advances in digital communications; however, other than improving sound quality, these changes have been mainly transparent to customers. In most cases, the function of the [[local loop]] presented to the customer for connection to telephone equipment is practically unchanged and remains compatible with [[pulse dialing]] telephones.

Due to the wide availability of traditional telephone services, new types of communications devices, such as [[modem]]s and [[Fax|fax machines]], were initially designed to use traditional analog telephony to transmit digital information.

==Historical services==
[[File:Manhole Cover - Post Office Copper Telephone Cable Pit.jpg|thumb|In many countries, the post office originally operated telephony systems: hence ubiquitous "PO" markings on historical telephone infrastructure in many countries]]
In countries where telephone systems were originally operated by the postal service administrations, the systems were known as ''post office telephone service'' as early as 1912<ref>{{cite book
|last=Bennett
|first=Edward
|year=1912
|title=The Post Office And Its Story
|url=
|page=194
}}</ref><ref>The British General Post Office (GPO) Guide of 1914 specifically mentions subscribers of the "Post Office Telephone Service"</ref><ref>''Join the Post Office Telephone Service!'' [Advertisement] Te Ao Hou, December 1958, p. 65.</ref> In Australia, New Zealand, and the United Kingdom the telephone system was a government service, under Post Office control, until privatisation in the 1970s and 1980s.

==See also==
{{Portal|Telephones}}
* [[25-pair color code]]
* [[Basic exchange telecommunications radio service]]
* [[Category 1 cable]]
* [[Dual-tone multi-frequency signaling]]
* [[Local telephone service]]
* [[Managed facilities-based voice network]]
* [[Network interface device]]
* [[Publicly Available Telephone Services]]
* [[Registered jack]] – the type of telephone jack common in most of the world for single-line POTS telephones
* [[Twisted pair]], used as cabling in POTS

==References==
{{Reflist}}
{{Telecommunications}}
 
[[Category:Telephone services]]