An automatic repeat request is a form of a message displayed in case of an error. It’s prominent in the two-way communication system—a plethora or group of error control protocols. The protocols exist in the data link layer and transport layer of the OSI (Open system interconnection) model.
How does the ARQ work?
This protocol’s core purpose is to ensure the acknowledgment of receiving the receiver’s message before the time out occurs. Time out refers to the period before which the message must be sent to the sender to confirm its delivery. In case the timeout condition arises, the receiver will not receive the confirmation. Also, this will prompt the sender to send the message again. The process continues until the non-corrupted, and the whole packet is transmitted across the network.
Applications of the ARQ Protocol
The protocol works in the shortwave radio for reliable delivery of signals. Various applications of ARQ are:
- Specific service orientation protocol
- High-level data link protocol
- X-modem file transfer protocol
- A binary synchronous communication protocol
- Service orientation protocol
Types of ARQ Protocol
- Stop and wait for automatic repeat request
stop and wait for ARQ is an alternating protocol for managing the transmission over the networks. It is useful in two-way communication systems. The protocol enables acknowledgment when a message is finally delivered to the sender. If the message is not sent or not received at the other end, then the acknowledgment message won’t be sent. This enables the continuation of sending the packets until it finally reaches the safe destination. Timeout plays a crucial role in this protocol. The sender’s action depends upon the Timeout and various other factors.
- Go-Back-NARQ
Go back to n automatic repeat request type – the receiver’s acknowledgment is completely eradicated, and several frames or packets are sent continuously without prompting anything to the sender or receiver. The time took less, and the process is relatively straightforward. The sender sends the sequence number along with acknowledgment to make sure the transmission occurs smoothly. The only fault in this system is that the frames can be transmitted more than once, and if one sequence is corrupted, everything needs to be re-considered.
- Selective ARQ
This one is similar to Go Back N-ARQ, but the sending continues even when the frame is corrupt. The receiver keeps track of the sequence number of the frames. If a frame is not received at the receiver’s end, the sender will continue sending the frames until the full window is empty. Unlike the previous one, this does not send the packet multiple times.
Merits – ARQ
- Detecting errors is simple as compared to other existing techniques.
- Decoding is easy, and simple techniques can be used to process.
D-Merits – ARQ
- A medium having a high error rate might cause transmission of the multiple frames.
- A high error rate might cause a loss of productivity and efficiency of the system.
automatic repeat request error management mechanism is provided by
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