Demarcation point
In telephony, the demarcation point is the point at which the telephone company network ends and connects with the wiring at the customer premises. A demarcation point is also referred to as the demarc, DMARC, MPOE, or minimum point of entry.
History
Prior to the Bell System divestiture on January 1, 1984, American Telephone & Telegraph Company (AT&T) through its Bell System companies held a natural monopoly for telephone service within the United States. AT&T owned the local loop, including the telephone wiring within the customer premises and the customer telephone equipment. A similar arrangement existed with smaller, regional telephone companies such as GTE. After the deregulation of the telephone system, unbundling of the local loop, and lawsuits by companies wishing to sell third-party equipment to connect to the telephone network, there was a need to delineate the portion of the network which was owned by the customer and the portion owned by the telephone company or the common carrier. Where the portions meet is called the demarcation point.
Equipment
The demarcation point varies from building type and service level. In its simplest form, the demarcation point is a junction block where customer telephone extensions join to connect to the network. This junction block usually includes a lightning arrestor (which requires a wire to earth ground.) In multi-line installations such as businesses or apartment buildings, the demarcation point may be a punch-down block. This hardware likely existed before deregulation.
The modern demarcation point is a device defined by FCC rules (47 C.F.R. Part 68) [1] to allow safe connection of third-party telephone equipment and wiring to the Public Switched Telephone Network (PTSN). It is a square, weatherproof housing which contains the wiring junction. It is usually placed for easy access by a technician. It also contains a lightning arrestor, fusible link and test circuitry which allows the carrier to remotely test whether a wiring fault lies in the customer premises or in the carrier wiring, without requiring a technician at the premises. The demarcation point has a user accesible RJ-11 jack and small loop of telephone cord connecting to the jack. When the loop is disconnected, the premises wiring is isolated from the telephone network and the customer may directly connect a telephone to the network via the jack to assist in determining the location of a wiring fault. In most cases, everything from the central office to and including the demarcation point is owned by the carrier and everything past it is owned by the property owner.
As the local loop becomes upgraded, with fiber optic and coaxial cable technologies sometimes replacing the original unshielded twisted pair to the premises, the demarcation point has grown to incorporate the equipment necessary to interface the original POTS wiring and equipment to the new communication channel.