Data communication
Explainer
Why Ethernet puts a flip in every bit
Send a thousand zeros in a row and the receiver gets lost. Here's why.
Quick check · tap an answer to continue
Lesson notes
Key points
- With simple NRZ encoding, a long run of zeros is a flat line, so the receiver's clock drifts and miscounts bits.
- Manchester encoding fixes this by putting a transition in the middle of every single bit period.
- In the IEEE 802.3 convention, a low-to-high transition means one and high-to-low means zero.
- The cost is bandwidth: up to two transitions per bit, so the signal needs roughly double the baud rate of NRZ.
Definitions
- Manchester encoding
- A line code where every bit has a mid-bit transition; the direction of the transition represents 0 or 1.
Takeaway: Manchester trades double bandwidth for a built-in clock.
Quick check: What does Manchester encoding guarantee in every bit period?
- A voltage transition
- A parity check
- A zero voltage level
The mid-bit transition lets the receiver recover the clock.
NRZ problemMid-bit transitionDirection = bitSelf-clocking cost
Lessons like this, for your syllabus.
Short narrated study videos written for your course, level and exam. Free to start.
Get lessons for your own syllabus