Local Loop Facility Tour


The local loop consists of feeder cables which are used to carry telephone traffic from the phone company's central office, which is also called a wire center, to various service areas established throughout the geographic territory served by that particular central office.

In most cases, local loops are copper (conventional twisted pair).  Inside the central office, the local loop begins at the Main Distribution Frame (MDF).  The MDF is a very large structure where the copper wires which make up a local loop are attached.  Hundreds of these wires are bundled together into a single cable bundle serveral inches thick.  This cable runs through the basement of the central office and out into the phone company's conduit system and then into a neighborhood.  At some point, the cable will come out of the conduit system into an above-ground cabinet.  In this cabinet, each of the individual wires will be attached to a particular location on a small panel.  These individual wires are "cross-connected" at this point with wires running into nearby homes and businesses.

There are also other types of local loops.  Sometime the feeder cables are equipped to act as Subscriber Loop Carrier (SLC) systems.  In the case of copper cables, this is accomplished by installing subscriber digital loop carrier systems.  Alternatively, fiber optic cables can be used to transmit the digital signals optically.  The actual equipment used at the end of the feeder to provide the loop carrier system functionality is typically housed in special above-ground cabinets or in below-ground Controlled Environmental Vaults (CEVs).  The area served by digital carrier feeder cable is classified as a carrier serving area.

Only about 5% of phone company's loops are subscriber digital loop carriers.  The other 95% is still plain old copper.  However, much of todays growth is being implemented through the placement of subscriber loop carrier systems.