Telephone line or telephone circuit (or just line or circuit within the industry) is a single-user circuit on a telephone communication system. Typically this refers to 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.
In 1876 the earliest lines were single electrically conducting metal wires directly connecting one telephone to another with the Earth forming the return circuit. Later in 1878 the Bell Telephone Company began to use 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.
These wires were typically copper, although aluminum has also been used, and were carried in balanced pairs separated by about 25 cm (10") on poles above the ground, and later as twisted pair cables. Modern lines may run underground, and may carry analog or digital signals to the exchange, or may have a device that converts the analog signal to digital for transmission on a carrier system.
Leased Line - A permanent telephone connection between two points set up by a telecommunications common carrier. Not a dedicated cable, a leased line is actually a reserved circuit between two points. Leased lines can span short or long distances. They maintain a single open circuit at all times, as opposed to traditional telephone services that reuse the same lines for many different conversations through a process called "switching."
Leased lines most commonly are rented by businesses to connect branch offices, because these lines guarantee bandwidth for network traffic. So-called T1 leased lines are common and offer the same data rate as symmetric DSL (1.544 Mbps). Individuals can theoretically also rent leased lines for high-speed Internet access, but their high cost (often more than $1000 USD per month) deters most. Fractional T1 lines, starting at 128 Kbps, reduce this cost somewhat and can be found in some apartment buildings and hotels.
Virtual Private Networks (VPNs) are an alternative technology to leased lines.
Also Known As: dedicated line
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