Automatic Repeat Requests (ARQ) is a method of error control for data transmission in telecommunications networks. It is a type of Error Detection and Error Control (EDAC) technique. It is mainly used in streaming media, such as audio and video, over the Internet.
In ARQ, if the receiver of a data frame (packet) finds that there is an error in the data, then it will request the sender to resend the data. ARQ increases the reliability of data transfers since the sender resends only those data packets which contain errors instead of resending all the packets. This technique reduces the time required for data delivery as it avoids redundant data transmission and keeps track of transmitted data.
ARQ is implemented using different protocols such as Stop-and-wait, Go-Back-N, and Selective Repeat. In Stop-and-wait, the sender sends a packet and waits for the acknowledgement (ACK) from the receiver indicating successful or unsuccessful reception of data. If ACK is received, the sender sends next packet and so on. If no ACK is received, the sender retransmits the packet.
Go-Back-N and Selective Repeat are variations of Stop-and-Wait. In Go-Back-N, the sender sends N packets at once and waits for corresponding ACKs. If no ACK is received, all the packet is retransmitted. in Selective Repeat, the sender sends packets one by one and waits for an ACK. If an ACK is not received, the packet is retransmitted while other packets ahead of the one that failed are not re-sent.
ARQ is used in data communication networks such as Wi-Fi networks, cellular networks, and DSL services. It is used for reliable transmission of data and to prevent re-transmission of already sent data in case of errors. ARQ is also widely used in satellite communication and other areas where data is transmitted over a large distances.
