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A pair gain system consists of Concentrator s or Multiplexer 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 be as simple as providing two telephone connections 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 or Dial-up internet connection. A larger analog pair gain system made by Anaconda 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 s or metal Cabinet s typically resembling small apartment-sized Refrigerator s alongside or near roadways that overlie communications rights-of-way. DACS (Digital Access Carrier System) was a form of pair gain used in the United Kingdom . It uses a form of time division multiple access called ISDN . Analog pair gain has come into disfavor in recent years, as it is detrimental to high speed dial-up modem connections, does not support 56k and is incompatible with Digital Subscriber Line (DSL) systems. More recent digital pair gain systems take the concept even further, however, restoring 56k and DSL capabilities by performing the functions of a DSLAM 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. SEE ALSO |
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