Demarcation point

In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines who is responsible for installation and maintenance of wiring and equipment—customer/subscriber, or telephone company/provider. The demarcation point varies between countries and has changed over time. In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines who is responsible for installation and maintenance of wiring and equipment—customer/subscriber, or telephone company/provider. The demarcation point varies between countries and has changed over time. Demarcation point is sometimes abbreviated as demarc, DMARC, or similar. The term MPOE (minimum or main point of entry) is synonymous, with the added implication that it occurs as soon as possible upon entering the customer premises. A network interface device often serves as the demarcation point. 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 and Canada. 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. As a result of 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. The demarcation point varies from building type and service level. In its simplest form, the demarcation point is a junction block where telephone extensions join to connect to the network. This junction block usually includes a lightning arrester (which requires a wire to ground). In multi-line installations such as businesses or apartment buildings, the demarcation point may be a punch down block. In most places this hardware existed before deregulation. In the United States, the modern demarcation point is a device defined by FCC rules (47 C.F.R. Part 68) to allow safe connection of third-party telephone customer-premises equipment and wiring to the Public Switched Telephone Network (PSTN). The modern demarcation point is the network interface device (NID) or intelligent network interface device (INID) also known as a 'smartjack'. The NID is the telco's property. The NID may be outdoors (typically, mounted on the building exterior in a weatherproof box) or indoors. The NID is usually placed for easy access by a technician. It also contains a lightning arrestor, fuse 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 accessible RJ-11 jack (a 'test jack' or 'demarcation jack'), which is connected directly to the telephone network, and a small loop of telephone cord connecting to the jack by a modular connector. When the loop is disconnected, the on-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.