If the sender does not receive an ACK within a designated time (timeout) or receives a NAK, it retransmits the packet. 3. Types of ARQ Protocols 3.1. Stop-and-Wait ARQ
is a fundamental error-control mechanism used in telecommunications and data link layers to ensure reliable transmission over unreliable communication links. Unlike Forward Error Correction (FEC) , which allows the receiver to correct errors, ARQ relies on the receiver identifying errors and requesting retransmission of data from the sender. This paper covers the primary types of ARQ protocols, their mechanisms, and performance tradeoffs. 2. Fundamental Mechanisms ARQ protocols operate based on two main principles:
An Adaptive Type-I1 hybrid ARQ/FEC Protocol - Clemson University If the sender does not receive an ACK
Requires complex buffering and ordering at the receiver. 4. Performance Considerations
) before needing an ACK. If a frame is lost, the receiver discards all subsequent frames, and the sender must retransmit all frames starting from the lost one. Better utilization than Stop-and-Wait. Cons: High retransmission overhead in poor channels. 3.3. Selective Repeat ARQ (SR) if the error is too great
SR provides the best throughput in high-error rate scenarios.
Only the specific lost or corrupted frame is retransmitted, rather than the entire window. Pros: Highly efficient utilization of bandwidth. a retransmission is requested. This approach
combines traditional ARQ with Forward Error Correction (FEC) . The receiver attempts to correct small errors using error-correcting codes; if the error is too great, a retransmission is requested. This approach, specifically Type-II Hybrid ARQ , provides a more efficient approach in poor radio conditions, optimizing throughput. 6. Conclusion
