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 ...

, pair gain is the transmitting of multiple POTS signals over the

twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted b ...

s traditionally used for a single traditional subscriber line in

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

systems. Pair gain has the effect of creating additional subscriber lines. This is typically used as an expedient way to solve subscriber line shortage problems by using existing wiring, instead of installing new wires from the central office to the customer premises. The term was invented in the middle 20th century by analogy with earlier use of gain to extend telephone

local loop In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the commo ...

s far from the

telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

. A pair gain system consists of

concentrator In the evolution of modern telecommunications systems there was a requirement to connect large numbers of low-speed access devices with large telephone company 'central office' switches over common paths. During the first generations of digital netw ...

s or

multiplexer In electronics, a multiplexer (or mux; spelled sometimes as multiplexor), also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The sel ...

s which combine the separate signals into a single signal which is transmitted through the existing copper cable pair. The signals are then separated into individual subscriber lines at the customer premises. The pair gain unit which performs the multiplexing can simply provide a second telephone connection over a single subscriber line (called an Analog Multi-Line Carrier or AML) in circumstances where a customer wants to add a new phone line for a

fax machine Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer o ...

dial-up Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network (PSTN) to establish a connection to an Internet service provider (ISP) by dialing a telephone number on a conventional telepho ...

internet connection. A larger analog pair gain system made by

Anaconda Anacondas or water boas are a group of large snakes of the genus '' Eunectes''. They are found in tropical South America. Four species are currently recognized. Description Although the name applies to a group of snakes, it is often used t ...

in the 1960s provided seven lines. Some pair gain units can expand the number of subscriber lines available over a single copper pair to as many as sixty. Large pair gain units are stored in

serving area interface The serving area interface or service area interface (SAI) is an outdoor enclosure or metal box that allows access to telecommunications wiring. Alternate names *Access point (AP) *Cabinet (cab) *B-box (breakout box) *Cross box *Cross-connect b ...

s or metal cabinets typically resembling small apartment-sized

refrigerator A refrigerator, colloquially fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so th ...

s alongside or near roadways that overlie communications rights-of-way.

DACS (Digital Access Carrier System) Digital access carrier system (DACS) is the name used by British Telecom (BT Group plc) in the United Kingdom for a 0+2 pair gain system. Usage For almost as long as telephones have been a common feature in homes and offices, telecommunication ...

is a form of pair gain used in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...

. It uses a form of

time-division multiple access Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession ...

called

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

. Analog pair gain came into disfavor in the 21st century, as it is detrimental to high speed dial-up modem connections, does not support

56k A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carr ...

and is incompatible with

digital subscriber line Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric dig ...

(DSL) systems. 20th century Subscriber Loop Carrier systems had similar problems. More recent digital pair gain systems, however, restore 56k and DSL capabilities by performing the functions of a

DSLAM A digital subscriber line access multiplexer (DSLAM, often pronounced ''DEE-slam'') is a network device, often located in telephone exchanges, that connects multiple customer digital subscriber line (DSL) interfaces to a high-speed digital co ...

at the pair gain device. More recently, the term pair gain has been used to refer to ''any'' multiplex/demultiplex unit used between the central office and end users, not just equipment used with copper twisted pair. Where digital loop carrier (called Remote Integrated Multiplexer in Australia) is installed,

broadband Internet In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...

subscribers may be disappointed when informed that although initial line checks were successful, high speed connections such as

ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...

are unavailable due to infrastructure issues. The problem is that pair gain lines cannot carry high speed data.Pair Gain or RIM Failures
/ref>

References

Local loop Multiplexing {{telephony-stub

See also

References