Telephone line

[2] It is the physical wire or other signaling medium connecting the user's telephone apparatus to the telecommunications network, and usually also implies a single telephone number for billing purposes reserved for that user.

[4][5] The voltage at a subscriber's network interface is typically 48 V between the ring and tip wires, with tip near ground and ring at –48 V. In 1878, the Bell Telephone Company began using two-wire circuits, called the local loop, from each user's telephone to end offices, which performed any necessary electrical switching to allow voice signals to be transmitted to more distant telephones.

Modern lines may run underground and may carry analog or digital signals to the exchange.

They may also have a device that converts the analog signal to digital for transmission on a carrier system.

Older houses often have 4-conductor telephone station cable in the walls color coded with Bell System colors: red, green, yellow, and black as 2-pairs of 22 AWG (0.33 mm2) solid copper; "line 1" uses the red/green pair and "line 2" uses the yellow/black pair.