It uses the concept of sliding window, and so is also called sliding window protocol.
Go – Back – N ARQ − Go – Back – N ARQ provides for sending multiple frames before receiving the acknowledgement for the first frame. If a positive acknowledgement is received then the next frame is sent. If the timer expires, the frame is retransmitted. It then waits for a finite time to receive a positive acknowledgement from receiver. The sender keeps a copy of the sent frame. Stop – and – Wait ARQ − Stop – and – wait ARQ provides unidirectional data transmission with flow control and error control mechanisms, appropriate for noisy channels. There are three ARQ protocols in the data link layer. This process is repeated until the correct frame is transmitted. a timeout occurs, the sender understands that the frame has been corrupted or lost during transit. If the sender does not receive the acknowledgement of a transmitted frame before a specified period of time, i.e. In these protocols, the receiver sends an acknowledgement message back to the sender if it receives a frame correctly. They are often used in Global System for Mobile (GSM) communication. ARQ is also called Positive Acknowledgement with Retransmission (PAR).ĪRQs are used to provide reliable transmissions over unreliable upper layer services. They are named so because they provide for automatic retransmission of frames that are corrupted or lost during transmission. These protocols reside in the Data Link Layer and in the Transport Layer of the OSI (Open Systems Interconnection) reference model. Automatic Repeat ReQuest (ARQ) is a group of error – control protocols for transmission of data over noisy or unreliable communication network.
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