“All links are error-prone and no link with errors can be made error-free.” Carefully explain whether it is true or false based on what you have learned regarding the link layer, the physical layer and strategies employed for error correction.
Try an answer before revealing the guidance below.
Key Concepts
- Bit errors
- Error detection
- Forward error correction
- Retransmission
- Residual error rate
Answer Approach
- Separate the two claims in the statement.
- Consider whether any physical medium is perfectly error-free.
- Consider what detection, correction, and retransmission can achieve.
- Decide whether “error-free” means perfect or effectively reliable.
Full Answer
Answer status: Draft answer (unofficial). Revision notes, not an official marking scheme.
The first part is essentially true: every physical medium suffers noise, interference, attenuation and fading, so bit errors can occur on any link (fibre far less than wireless). The second part is false in practice: the link layer can make the link appear error-free to higher layers by combining error detection (parity, checksums, CRC), forward error correction, and acknowledgement/retransmission of damaged frames. Strictly, no scheme gives a zero residual error probability, because some error patterns can go undetected, but that probability can be made extremely small.
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