upTwo simple NIDs, carrying six lines each, on the outside of a building upA German copper phone line termination box called '' Abschlusspunkt LinienTechnik'' (APL, " Demarcation point") In

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

s, a network interface device (NID; also known by several other names) is a device that serves as the demarcation point between the carrier's

local loop In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the commo ...

and the customer's premises wiring. Outdoor telephone NIDs also provide the subscriber with access to the station wiring and serve as a convenient test point for verification of loop integrity and of the subscriber's inside wiring.

Naming

Generically, an NID may also be called a network interface unit (NIU), telephone network interface (TNI), system network interface (SNI), or telephone network box. Australia's National Broadband Network uses the term '' network termination device'' or NTD. A smartjack is a type of NID with capabilities beyond simple electrical connection, such as diagnostics. An '' optical network terminal'' (ONT) is a type of NID used with

fiber-to-the-premises Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic ...

applications.

Wiring termination

The simplest NIDs are essentially just a specialized set of wiring

terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output devi ...

s. These will typically take the form of a small, weather-proof box, mounted on the outside of the building. The

telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or ot ...

from the

telephone company A telephone company, also known as a telco, telephone service provider, or telecommunications operator, is a kind of communications service provider (CSP), more precisely a telecommunications service provider (TSP), that provides telecommunicat ...

will enter the NID and be connected to one side. The customer connects their wiring to the other side. A single NID enclosure may contain termination for a single line or multiple lines. In its role as the demarcation point (dividing line), the NID separates the telephone company's equipment from the customer's wiring and equipment. The telephone company owns the NID itself, and all wiring up to it. Anything past the NID is the customer's responsibility. To facilitate this, there is typically a test jack inside the NID. Accessing the test jack disconnects the customer premises wiring from the

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

and allows the customer to plug a "known good"

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

into the jack to isolate trouble. If the telephone works at the test jack, the problem is the customer's wiring, and the customer is responsible for repair. If the telephone does not work, the line is faulty and the telephone company is responsible for repair. Most NIDs also include "circuit protectors", which are surge protectors for a telephone line. They protect customer wiring, equipment, and personnel from any transient

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of ...

on the line, such as from a

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

strike to a

telephone pole A utility pole is a column or post typically made out of wood used to support overhead power lines and various other public utilities, such as electrical cable, fiber optic cable, and related equipment such as transformers and street lights. It ...

. Simple NIDs contain no digital logic; they are "dumb" devices. They have no capabilities beyond wiring termination, circuit protection, and providing a place to connect test equipment.

Smartjack

upThree smartjacks for T-1 circuits, in two shelves; a 66 block is on the left Several types of NIDs provide more than just a terminal for the connection of wiring. Such NIDs are colloquially called ''smartjacks'' or Intelligent Network Interface Devices (INIDs) as an indication of their built-in "intelligence", as opposed to a simple NID, which is just a wiring device. Smartjacks are typically used for more complicated types of telecommunications service, such as T1 lines.

Plain old telephone service Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...

lines generally cannot be equipped with smartjacks. Despite the name, most smartjacks are much more than a simple telephone jack. One common form for a smartjack is a

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich str ...

with a face plate on one edge, mounted in an enclosure. A smartjack may provide signal conversion, converting codes and protocols (e.g. framing types) to the type needed by the customer equipment. It may buffer and/or regenerate the signal, to compensate for signal degradation from line transmission, similar to what a

repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Som ...

does. Smartjacks also typically provide diagnostic capabilities. A very common capability provided by a smartjack is

loopback Loopback (also written loop-back) is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure. There are m ...

, such that the signal from the telephone company is transmitted back to the telephone company. This allows the company to test the line from the central

telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

, without the need to have test equipment at the customer site. The telephone company usually has the ability to remotely activate loopback, without even needing personnel at the customer site. When looped back, the customer equipment is disconnected from the line. Additional smartjack diagnostic capabilities include alarm indication signal, which reports trouble at one end of the line to the far end. This helps the telephone company know if trouble is present in the line, the smartjack, or customer equipment. Indicator lights to show configuration, status, and alarms are also common. Smartjacks typically derive their operating power from the telephone line, rather than relying on premises electrical power, although this is not a universal rule.

Optical network terminals

In fiber-to-the-premises systems, the signal is transmitted to the customer premises using

fiber optic An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...

technologies. Unlike many conventional telephone technologies, this does not provide power for premises equipment, nor is it suitable for direct connection to customer equipment. An optical network terminal (ONT) is used to terminate the fiber optic line, demultiplex the signal into its component parts (voice

television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...

, and

Internet access Internet access is the ability of individuals and organizations to connect to the Internet using computer terminals, computers, and other devices; and to access services such as email and the World Wide Web. Internet access is sold by Interne ...

), and provide power to customer telephones. As the ONT must derive its power from the customer premises electrical supply, many ONTs have the option for a

battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

backup in order to maintain service in the event of a

power outage A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electricity ...

Environmental conditions

According to Telcordia GR-49, requirements for telecommunications NIDs vary based on three categories of environmental conditions: # Normal conditions: This refers to a normal environment that is expected in most areas of any service provider. Temperatures are expected to be in the range of , and humidity is expected to be less than 90% RH. No unusual contamination is expected. # Severe climatic conditions: These cover environments more severe than those of a normal environment (i.e., higher humidity, high lightning activity, exposure to salt-laden atmosphere, and exposure to contaminants). Temperatures are expected to be in the range of , and humidity may exceed 90% RH. Jacks installed in NIDs in such environments are known to become contaminated and develop low insulation resistances and low dielectric breakdown voltages when subjected to high humidity. These problems can cause noisy lines or even service outages. # Flooded conditions: These cover areas of a service provider prone to flooding, such as in coastal or flood plain locations. After a flooding incident, temperature is expected to be in the range of , and humidity may exceed 90% RH. The requirements are not to determine if the NID will function during a flood, but to review the ability of the NID to function after the flood has subsided. Service providers must decide which condition best suits their application.

Citations

General references

* * * * * {{refend Fiber to the premises Local loop Telephony equipment