Automatic Repeat reQuest (ARQ), also known as Automatic Repeat Query, is an error-control method for data transmission

Data transmission

Data transmission, digital transmission, or digital communications is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media...

 that uses acknowledgement

Acknowledgement (data networks)

In data networking, an acknowledgment is a signal passed between communicating processes or computers to signify acknowledgment, or receipt of response, as part of a communications protocol...

s (messages sent by the receiver indicating that it has correctly received a data frame

Data frame

In computer networking and telecommunication, a frame is a digital data transmission unit or data packet that includes frame synchronization, i.e. a sequence of bits or symbols making it possible for the receiver to detect the beginning and end of the packet in the stream of symbols or bits...

 or packet) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) to achieve reliable data transmission over an unreliable service. If the sender does not receive an acknowledgment before the timeout, it usually re-transmits

Retransmission (data networks)

Retransmission, essentially identical with Automatic repeat request , is the resending of packets which have been either damaged or lost. It is a term that refers to one of the basic mechanisms used by protocols operating over a packet switched computer network to provide reliable communication...

 the frame/packet until the sender receives an acknowledgment or exceeds a predefined number of re-transmissions.

The types of ARQ protocols include

• Stop-and-wait ARQ
  Stop-and-wait ARQ
  Stop-and-wait ARQ is a method used in telecommunications to send information between two connected devices. It ensures that information is not lost due to dropped packets and that packets are received in the correct order. It is the simplest kind of automatic repeat-request method...
  
  
• Go-Back-N ARQ
  Go-Back-N ARQ
  Go-Back-N ARQ is a specific instance of the automatic repeat request protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an acknowledgement packet from the receiver...
  
  
• Selective Repeat ARQ
  Selective Repeat ARQ
  Selective Repeat ARQ / Selective Reject ARQ is a specific instance of the Automatic Repeat-Request protocol used for communications.-Concept:...
  
  

These protocols reside in the Data Link

Data link layer

The data link layer is layer 2 of the seven-layer OSI model of computer networking. It corresponds to, or is part of the link layer of the TCP/IP reference model....

 or Transport Layer

Transport layer

In computer networking, the transport layer or layer 4 provides end-to-end communication services for applications within a layered architecture of network components and protocols...

s of the OSI model

OSI model

The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...

.

Examples

The Transmission Control Protocol

Transmission Control Protocol

The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...

 uses a variant of Go-Back-N ARQ

Go-Back-N ARQ

Go-Back-N ARQ is a specific instance of the automatic repeat request protocol, in which the sending process continues to send a number of frames specified by a window size even without receiving an acknowledgement packet from the receiver...

 to ensure reliable transmission of data over the Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

, which does not provide guaranteed delivery of packets; with Selective Acknowledgement (SACK), it uses Selective Repeat ARQ

Selective Repeat ARQ

Selective Repeat ARQ / Selective Reject ARQ is a specific instance of the Automatic Repeat-Request protocol used for communications.-Concept:...

.

The ITU-T

ITU-T

The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....

 G.hn

G.hn

G.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...

 standard, which provides a way to create a high-speed (up to 1 Gbit/s) local area network

Local area network

A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...

 using existing residential wiring (power lines

Power line communication

Power line communication or power line carrier , also known as power line digital subscriber line , mains communication, power line telecom , power line networking , or broadband over power lines are systems for carrying data on a conductor also used for electric power transmission.A wide range...

, telephone lines, and coaxial cables

Ethernet over coax

Ethernet over Coax is a family of technologies that supports the transmission of Ethernet frames over coaxial cable.- History :The first Ethernet standard, known as 10BASE5 in the family of IEEE 802.3, specified baseband operation over coaxial cable...

), uses Selective Repeat ARQ

Selective Repeat ARQ

Selective Repeat ARQ / Selective Reject ARQ is a specific instance of the Automatic Repeat-Request protocol used for communications.-Concept:...

to ensure reliable transmission over noisy media.