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

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 mainte ...

") In

telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

, a network interface device (NID; also known by several other names) is a device that serves as the

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 mainte ...

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 co ...

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 applications.

Wiring termination

The simplest NIDs are essentially just a specialized set of wiring terminals. 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 oth ...

from the

telephone company A telecommunications company is a kind of electronic communications service provider, more precisely a telecommunications service provider (TSP), that provides telecommunications services such as telephony and data communications access. Many t ...

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 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) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists o ...

and allows the customer to plug a "known good"

telephone A telephone, colloquially referred to as a phone, is a telecommunications device that enables 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 ...

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 protector A surge protector, spike suppressor, surge suppressor, surge diverter, surge protection device (SPD), transient voltage suppressor (TVS) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect Electronics, ele ...

s for a telephone line. They protect customer wiring, equipment, and personnel from any transient

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

on the line, such as from a

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

strike to a

utility pole A utility pole, commonly referred to as a transmission pole, telephone pole, telecommunication pole, power pole, hydro pole, telegraph pole, or telegraph post, is a column or post used to support overhead power lines and various other public util ...

. Simple NIDs are "dumb" devices, as they contain no

digital logic A logic gate is a device that performs a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has, for ...

. 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 publicly offered telephone service, is basic Voice band, voice-grade telephone service. Historically, POTS has been delivered by Analog signal, analog signal transmission over copper loops, but the term also d ...

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 called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

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. Some ...

does. Smartjacks also typically provide diagnostic capabilities. A very common capability provided by a smartjack is loopback, 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 A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

, 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

optical fiber An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...

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, an

ITU-T The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

term), also known as an optical network unit (ONU, an

IEEE The Institute of Electrical and Electronics Engineers (IEEE) is an American 501(c)(3) organization, 501(c)(3) public charity professional organization for electrical engineering, electronics engineering, and other related disciplines. The IEEE ...

term), is used to terminate the optical fiber line, demultiplex the signal into its component parts (voice

television Television (TV) is a telecommunication medium for transmitting moving images and sound. Additionally, the term can refer to a physical television set rather than the medium of transmission. Television is a mass medium for advertising, ...

, and

Internet access Internet access is a facility or service that provides connectivity for a computer, a computer network, or other network device to the Internet, and for individuals or organizations to access or use applications such as email and the World Wide ...

), and provide power to customer telephones. If the device combines all these services into one it is known as an IAD. As the ONT must derive its power from the customer premises electrical supply, many ONTs have the option for a battery backup in order to maintain service in the event of a

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

or it will go in alarm mode if disconnected and customer may be notified of this. These terminals are used in both active optical networks and

passive optical network A passive optical network (PON) is a fiber-optic telecommunications network that uses only ''unpowered'' devices to carry signals, as opposed to electronic equipment. In practice, PONs are typically used for the '' last mile'' between Internet ...

s. Typically, an ONT connects via a fiber-optic cable to an OLT to complete a connection. An ONT can work in Single Family Unit/SFU mode (modem/bridge) or Home Gateway Unit/HGU mode (router). In passive optical networks, Management is provided by the OLT via OMCI, in case of a

GPON ITU-T G.984 is the series of standards for implementing a gigabit-capable passive optical network (GPON). It is commonly used to implement the link to the customer (the ''last kilometre'', or ''last mile'') of fibre-to-the-premises ( FTTP) serv ...

connection, and OAM in case of a EPON connection. Authentication and encryption is done via LOID for EPON and PLOAM password, GPON serial number or others for

Environmental conditions

According to

Telcordia iconectiv supplies communications providers with network planning and management services. The company’s cloud-based information as a service network and operations management and numbering solutions span trusted communications, digital identi ...

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