_(14754023254).jpg)
Atelephone line ortelephone circuit (or justline orcircuit industrywide) is a single-usercircuit on a telephonecommunication system.[1] It is designed to reproduce speech of a quality that is understandable.[citation needed] It is the physicalwire or other signaling medium connecting the user's telephone apparatus to thetelecommunications network, and usually also implies a single telephone number forbilling purposes reserved for that user.
Telephone lines are used to deliver consistentlandline telephone service and digital subscriber line (DSL) phone cable service to the premises.[2] Telephone overhead lines are connected to the public switched telephone network.[3][4] Thevoltage 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, theBell Telephone Company began using two-wire circuits, called thelocal loop, from each user's telephone toend offices, which performed any necessary electrical switching to allow voice signals to be transmitted to more distant telephones.
These wires were typicallycopper, althoughaluminium has also been used, and were carried inbalanced pairs of open wire, separated by about 25 cm (10″) onpoles above the ground, and later astwisted pair cables. Modern lines may run underground and may carry analog or digital signals to the exchange. They may also havea device that converts theanalog signal to digital fortransmission on acarrier system. Often, the customer end of that wire pair is connected to adata access arrangement,and the telephone company end of that wire pair is connected to atelephone hybrid.
In most cases, twocopper wires (tip and ring) for each telephone line run from a home or other small building to a localtelephone exchange. There is a centraljunction box for the building where the wires that go to telephone jacks throughout the building and wires that go to the exchange meet and can be connected in different configurations depending upon the subscribed telephone service. The wires between the junction box and the exchange are known as thelocal loop, and the network of wires going to an exchange is known as theaccess network.
The vast majority of houses in the U.S. are wired with 6-positionmodular jacks with fourconductors (6P4C) wired to the house's junction box with copper wires. Those copper wires may be connected back to two telephone overhead lines at the localtelephone exchange, thus making those jacksRJ14 jacks. More often, only two of the wires are connected to the exchange as one telephone line, and the others are unconnected. In that case, the jacks in the house areRJ11.
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.Inside the walls of the house—between the house's outside junction box and the interiorwall jacks—the most common telephone cable in new houses isCategory 5 cable—4 pairs of 24 AWG (0.205 mm2) solid copper.[5]
Inside large buildings, and in the outdoor cables that run to the telephone companyPOP, many telephone lines are bundled together in a single cable using the25-pair color code.[6] Outside plant cables can have up to 3,600 or 3,800 pairs, used at the entrances of telephone exchanges.[7][8]
Media related toTelephone lines at Wikimedia Commons