The telephone system remains as the backbone of low-cost telecommunications services in North
America. An understanding of the telephone system is necessary when considering its use for data
Telephone: invented in 1874 by Alexander Graham Bell and patented in 1876
Single wire: In the beginning, the market was for telephones only. It is the customer who used to
wire them between telephones using single wires and the earth as the ground or the
other conductor to complete the circuit.