Automatic Repeat Request in Computer Networks
Automatic Repeat Request:
In the Data link layer, Automatic Repeat Request (ARQ) means a request for transmission of data in cases of the damaged frame, lost frame, and lost acknowledgement. In Computer Networks, there are mainly two types of Automatic Repeat Requests.
- Stop and Wait ARQ
- Go-back-N ARQ
Stop and Wait ARQ:
In this technique, the sender can send a single frame only at a time to the receiver. On getting acknowledgement from the receiver it can send the next frame. So that’s why it is known as Stop and Wait for ARQ. The sender sends a frame, stops transmission and waits for an acknowledgement.
Go-back-N ARQ method is based on a sliding window flow control mechanism. In this technique, the sender can send a series of frames without getting an acknowledgement up to the window width. At the same time, the sender gets acknowledgement from the receiver and sends more frames to it. If the sender doesn’t receive any acknowledgement from the receiver it stops sending data after sending the window width number of frames.
In case of any error, the sender has to send all frames starting from the damaged frame. The maximum number of frames that can transmit without getting any acknowledgement is known as the window width.