Local loop

In telephony, the local loop (also referred to as a subscriber line) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network.

At the edge of the carrier access network in a traditional PSTN (public switched telephone network) scenario, the local loop terminates in a circuit switch housed in an incumbent local exchange carrier telephone exchange.

Infrastructure

Traditionally, the local loop was an electrical circuit carried by a single twisted pair of wires which connected the telephone on the customer's premises to the local telephone exchange. In older systems, where the number of local loops was restricted, different customers could share the same loop, known as a party line.

Modern implementations may include a digital loop carrier system segment or fiber optic transmission system known as fiber-in-the-loop. The local loop may terminate at a circuit switch owned by a competitive local exchange carrier and housed in a point of presence (POP), which typically is either an incumbent local exchange carrier telephone exchange or a "carrier hotel". A local loop may be provisioned to support data communications applications, or combined voice and data:

• analog voice and signaling used in traditional POTS
• Integrated Services Digital Network (ISDN)
• variants of Digital Subscriber Line (DSL)

Many owners of local loops are public utilities that hold a natural monopoly. To prevent the owner from using this natural monopoly to monopolize other fields of trade, some jurisdictions require utilities to unbundle the local loop, that is, make the local loop available to their competitors.

The term "local loop" is sometimes used for any "last mile" connection to the customer, regardless of technology or intended purpose. Hence the phrase "wireless local loop". Local loop connections in this sense include:

• Electric power line local loop: PLT or PLC
• Optical local loop: Fiber Optics services such as FiOS
• Satellite local loop: communications satellite and cosmos Internet connections of satellite television (DVB-S)
• Cable local loop: Cablemodem
• Wireless local loop (WLL): LMDS, WiMAX, GPRS, HSDPA, DECT

See also

• Access network
• Local loop unbundling
• Metallic Path Facilities
• Sub-loop unbundling
• The local loop is an example of outside plant
• Serving area interface
• Telephone line