ARQ Strategies Explained – Error Detection, Parity Bits, Hamming Code & CRC | StudyPalz скачать в хорошем качестве

ARQ Strategies Explained – Error Detection, Parity Bits, Hamming Code & CRC | StudyPalz

ARQ strategies: Error Detection and correction, Parity Bits, Hamming Codes and CRC. DAY 15 – ARQ STRATEGIES, ERROR DETECTION AND CORRECTION 1) ARQ – AUTOMATIC REPEAT REQUEST Definition: ARQ is an error-control technique used in data communication where the receiver detects errors and requests retransmission of corrupted data from the sender. Purpose: Ensure reliable data transmission Detect and recover from transmission errors Basic Working: 1. Sender transmits frame 2. Receiver checks for errors 3. If correct → ACK (Acknowledgment) sent 4. If error → NAK or timeout → retransmission Common ARQ Strategies: Stop-and-Wait ARQ Go-Back-N ARQ Selective Repeat ARQ -------------------------------------------------- 2) STOP-AND-WAIT ARQ Definition: Sender sends one frame at a time and waits for acknowledgment before sending the next frame. Steps: 1. Send frame 2. Wait for ACK 3. If ACK received → send next frame 4. If timeout → resend frame Advantages: Simple implementation Disadvantages: Low efficiency in high-speed networks -------------------------------------------------- 3) GO-BACK-N ARQ Definition: Sender can send multiple frames before receiving acknowledgment, but if an error occurs, it retransmits that frame and all subsequent frames. Characteristics: Sliding window protocol Receiver accepts only correct order frames Advantage: Better efficiency than Stop-and-Wait Disadvantage: More retransmissions if error occurs -------------------------------------------------- 4) SELECTIVE REPEAT ARQ Definition: Only the corrupted or lost frames are retransmitted instead of the entire sequence. Characteristics: Receiver stores out-of-order frames More complex but efficient Advantage: Minimum retransmissions Disadvantage: Higher complexity -------------------------------------------------- 5) ERROR DETECTION AND CORRECTION Error Detection: Technique used to identify whether data has been corrupted during transmission. Error Correction: Technique used to detect and fix errors without retransmission. Examples: Detection → Parity, CRC Correction → Hamming Code -------------------------------------------------- 6) PARITY BITS Definition: A parity bit is an extra bit added to data to detect errors. Types: Even Parity: Total number of 1s becomes even. Odd Parity: Total number of 1s becomes odd. Example: Data: 1011001 Number of 1s = 4 (even) Parity bit (even parity) = 0 Advantage: Simple and fast Disadvantage: Detects only single-bit errors -------------------------------------------------- 7) HAMMING CODE Definition: Hamming code is an error-correcting code that can detect and correct single-bit errors. Key Idea: Extra parity bits are placed at positions that are powers of 2. Positions: 1, 2, 4, 8, 16 … Working: 1. Insert parity bits 2. Calculate parity values 3. Receiver checks parity 4. If error detected → identifies exact bit position Advantage: Can correct single-bit errors Disadvantage: More redundant bits required -------------------------------------------------- 8) CRC – CYCLIC REDUNDANCY CHECK Definition: CRC is an error detection technique that uses polynomial division to detect errors in data. Working: 1. Sender treats data as binary polynomial 2. Divides by generator polynomial 3. Remainder becomes CRC bits 4. Receiver performs same division 5. If remainder = 0 → no error Advantages: Detects burst errors Highly reliable Disadvantages: Only detects errors (does not correct) -------------------------------------------------- 9) SUMMARY TABLE Technique Purpose --------------------------------- Parity Bit Error detection Hamming Code Error correction CRC Error detection ARQ Error recovery (retransmission)