Error Control refers to the techniques and mechanisms used to detect and correct errors that occur during data transmission across a communication network.
- It ensures reliable communication by identifying and resolving issues caused by noise, interference, or other factors that may corrupt the transmitted data.
Sources of Errors
Errors during transmission can occur due to various physical and environmental factors, including:
- Interference: Electromagnetic disturbances from external sources, such as nearby devices or radio waves.
- Attenuation: Weakening of the signal strength over long distances.
- Crosstalk: Overlapping of signals from adjacent transmission lines.
- Impulse Noise: Sudden bursts of electrical noise caused by power surges or lightning.
Error Prevention
Preventative measures reduce the likelihood of errors in data transmission:
- Quality Media: Using high-quality cables and connectors to minimize interference and attenuation.
- Shielding: Protecting cables from external electromagnetic interference.
- Signal Conditioning: Amplifying and shaping signals to maintain clarity over long distances.
Error Detection
Error detection techniques identify whether data has been corrupted during transmission. Common methods include:
- Parity Check: Adds an extra bit to the data to indicate whether the number of 1s is even or odd.
- Cyclic Redundancy Check (CRC): Computes a checksum based on the data and appends it to the frame. The receiver recalculates the checksum to verify data integrity.
- Checksum: Adds all the data units to detect errors during packet delivery.
Error Correction via Retransmission
When errors are detected, retransmission ensures correct data delivery:
ARQ (Automatic Repeat Request):
- The receiver detects errors and requests the sender to resend the data.
Types of ARQ:
- Stop-and-Wait ARQ: The sender waits for acknowledgment after sending each frame.
- Go-Back-N ARQ: The sender retransmits the frame causing the error and all subsequent frames.
- Selective Repeat ARQ: Only erroneous frames are retransmitted
Forward Error Correction (FEC)
FEC adds redundant data to enable error correction without retransmission:
How It Works:
- The sender encodes the data with extra bits based on mathematical algorithms.
- The receiver uses the redundant bits to detect and correct errors.
Applications:
- Real-time applications like video streaming and voice communication where retransmission is impractical.
Error Control in Practice
Real-world error control mechanisms combine detection and correction techniques:
- Ethernet uses CRC for error detection.
- Wi-Fi employs advanced error correction mechanisms like FEC and retransmission.
- Satellite and deep-space communication rely heavily on FEC due to long delays in retransmission.
