In
telecommunicationTelecommunication is transmission over a distance for the purpose of communication. In earlier times, this may have involved the use of smoke signals, drums, semaphore, flags or heliograph. In modern times, telecommunication typically involves the use of electronic devices such as the telephone,...
s, a
network interface device (
NID) is a device that serves as the
demarcation pointIn telephony, the demarcation point is the point at which the telephone company network ends and connects with the wiring at the customer premises...
between the carrier's
local loopIn telephony, the local loop is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider's network...
and the customer's
premises wiringIn telecommunication, on-premises wiring is customer-owned communications transmission lines. It is also called customer premises wiring . The transmission lines can be metallic or optical fiber, and may be installed within or between buildings.Premises wiring may consist of horizontal wiring,...
.
Generically, NIDs may also be called a
network interface unit (
NIU) or
telephone network box. A
smartjack is a type of NID which has 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
terminalsA terminal is a the point at which a conductor from an electrical component, device or network comes to an end and provides a point of connection to external circuits. A terminal may simply be the end of a wire or it may be fitted with a connector or fastener...
. These will typically take the form of a small, weather-proof box, mounted on the outside of the building. The
telephone lineA telephone line or telephone circuit is a single-user circuit on a telephone communications system...
from the
telephone companyA telephone company provides telecommunications services such as telephony and data communications. Most of the largest telcos, whatever their origins, are or were at one time nationalized or state-regulated monopolies...
(telco) 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, the NID separates "telco" from "customer". The telco owns the NID itself, and all wiring up to it. Anything past the NID is the customer's responsibility. To facilitate this, there will typically be a test jack in the NID itself. Attaching to the test jack disconnects the customer premises wiring from the
networkThe public switched telephone network is the network of the world's public circuit-switched telephone networks, in much the same way that the Internet is the network of the world's public IP-based packet-switched networks...
. The customer can plug a "known good"
telephoneThe telephone is a telecommunications device that transmits and receives sound, most commonly the human voice. It is one of the most common household appliances in the developed world, and has long been considered indispensable to business, industry and government...
into the test 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 itself is faulty, and the telco is responsible for repair.
Most NIDs also include "circuit protectors", which are
surge protectorA surge protector is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to regulate the voltage supplied to an electric device by either blocking or by shorting to ground voltages above a safe threshold...
s for a telephone line. They protect customer wiring, equipment, and personnel from any transient
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
on the line, such as from a
lightningLightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
strike to a telephone pole.
Simple NIDs contain no "intelligence" or "logic"; they are "dumb" devices. They have no capabilities beyond wiring termination, circuit protection, and providing a place to connect test equipment.
Smartjacks
Several types of NIDs provide more than just a terminal for the connection of wiring. Such NIDs are colloquially called "smartjacks" 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 linesDigital signal 1 is a T-carrier signaling scheme devised by Bell Labs. DS1 is a widely used standard in telecommunications in North America and Japan to transmit voice and data between devices. E1 is used in place of T1 outside of North America, Japan, and South Korea...
.
Plain old telephone servicePlain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in most parts of the world. The name is a retronym, and is a reflection of the telephone service still available after the...
lines generally cannot be equipped with smartjacks.
Despite the name, most "smartjacks" are much more than a simple
telephone jackTelephone jacks are the sockets that receive the telephone plugs on the manual telephone switchboards....
. One common form for a smartjack is a
circuit boardA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring board...
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 segregation from line transmission — similar to what a
repeaterA repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
does.
Smartjacks also typically provide diagnostic capabilities. A very common capability provided by a smartjack is
loopbackThe term loopback is generally used to describe methods or procedures of routing electronic signals, digital data streams, or other flows of items, from their originating facility quickly back to the same source entity without intentional processing or modification...
, such that the signal from the telco is transmitted back to the telco. This allows the telco to test the line from the central office, without the need to have test equipment at the customer site. The telco 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 signalAlarm indication signal is a signal transmitted by an intermediate element of a multi node transport circuit that is part of a concatenated telecommunications system to alert the receiving end of the circuit that a segment of the end-to-end link has failed at a logical or physical level, even if...
, which reports trouble at one end of the line to the far end. This helps the telco 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 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 ONT (optical network terminal) is used to terminate the fiber optic line,
demultiplexThe multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
the signal into its component parts (voice telephone,
televisionTelevision is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission...
, and Internet), 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
batteryAn electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy. Since the invention of the first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power source for many household and industrial...
backup, to maintain service in the event of a
power outageA power outage is a short- or long-term loss of the electric power to an area.There are many causes of power failures in an electricity network...
.
See also
- 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...
- Point of appearance
Point of appearance is a generic term for any point in a telephone/data circuit from which a technician can test or pull stats. Some appearances are virtual, such as a Digital cross connect system computer terminal. Others are physical, like a punch-down COSMIC frame where a technician can place a...
- Customer premises wiring
- Customer premises equipment
- Local exchange carrier
Local Exchange Carrier is a regulatory term in telecommunications for the local telephone company.In the United States, wireline telephone companies are divided into two large categories: long distance and local...
- CSU/DSU
A CSU/DSU is a digital-interface device used to connect a Data Terminal Equipment device or DTE, such as a router, to a digital circuit ....
- Channel service unit
In telecommunications, a channel service unit is a line bridging device for use with T-carrier that:*is used to perform loopback testing,*may perform bit stuffing,*may also provide a framing and formatting pattern compatible with the network,...
- Data service unit
A data service unit, sometimes called a digital service unit, is a piece of telecommunications circuit terminating equipment that transforms digital data between telephone company lines and local equipment. The device converts bipolar digital signals coming ultimately from a digital circuit and...
- Main distribution frame
In Telephony, a Main Distribution Frame is a signal distribution frame for connecting equipment to cables and subscriber carrier equipment . The MDF is a termination point within the local Telephone exchange where exchange equipment and terminations of local loops are connected by jumper wires...
External links
— Photographs of several simple NIDs, including "inside" and "outside" views