Data link
In telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

 a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver (two pieces of data terminal equipment
Data terminal equipment
Data Terminal Equipment is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment...

) and the interconnecting data telecommunication circuit
Telecommunication circuit
A telecommunication circuit is any line, conductor, or other conduit by which information is transmitted.A dedicated circuit, private circuit, or leased line is a line that is dedicated to only one use...

. These are governed by a link protocol
Link protocol
In communications, a link protocol is a method and specification for transmission of data from one node on a local network or network link to another node on the same link...

 enabling digital data to be transferred from a data source to a data sink
Sink (disambiguation)
A sink is a bowl-shaped fixture used for washing hands or small objects.Sink may also refer to:*Sink, a flow network node that has more incoming flow than outgoing flow...


There are at least three types of basic data-link configurations that can be conceived of and used:
  • Simplex communication
    Simplex communication
    Simplex communication refers to communication that occurs in one direction only. Two definitions have arisen over time: a common definition, which is used in ANSI standard and elsewhere, and an ITU-T definition...

    s, most commonly meaning all communications in one direction only.
  • Half-duplex communications, meaning communications in both directions, but not both ways simultaneously.
  • Duplex communications
    Duplex (telecommunications)
    A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....

    , communications in both directions simultaneously.

In civil aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, a data-link system (known as Controller Pilot Data Link Communications
Controller Pilot Data Link Communications
Controller Pilot Data Link Communications , also referred to as Controller Pilot Data Link , is a method by which air traffic controllers can communicate with pilots over a datalink system.-Necessity:...

) is used to send information between aircraft and air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...

lers when an aircraft is too far from the ATC to make voice radio communication and radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 observations possible. Such systems are used for aircraft crossing the Atlantic and Pacific oceans. One such system, used by NavCanada and NATS
Nats or NATS can refer to:* Nat , a unit of information* National Air Traffic Services, the United Kingdom's main Air Navigation Service Provider * National Association of Teachers of Singing* Naval Air Transport Service...

 over the North Atlantic uses a five-digit data link sequence number which is confirmed between air traffic control and the pilots of the aircraft before the aircraft proceeds to cross the ocean. This system uses the aircraft's flight management computer
Flight management system
A flight management system is a fundamental part of a modern airliner's avionics. An FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern aircraft no longer carry flight engineers or navigators. A...

 to send location, speed and altitude information about the aircraft to the ATC. ATC can then send messages to the aircraft regarding any necessary change of course.

In military aviation, the meaning of data-link is somewhat different – it carries weapons targeting information, and it can also carry information to help warplanes land on aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...


In unmanned aircraft, land vehicles, boats, and spacecraft, a two-way (full-duplex or half-duplex) data-link is used to send control signals
Control system
A control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...

, and to receive telemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...


See also

  • Tactical Data Links
  • Space probe
    Space probe
    A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...

  • Deep Space Network
    Deep Space Network
    The Deep Space Network, or DSN, is a world-wide network of large antennas and communication facilities that supports interplanetary spacecraft missions. It also performs radio and radar astronomy observations for the exploration of the solar system and the universe, and supports selected...

  • Unmanned Aircraft System
  • Terminal (telecommunication)
    Terminal (telecommunication)
    In the context of telecommunications, a terminal is a device which is capable of communicating over a line. Examples of terminals are telephones, fax machines, and network devices - printers and workstations....

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