Repeater
Shout to a friend across the playground and they hear you. Shout to someone at the far end of the sports ground and your words fade into the noise. Signals on a cable fade in the same way.
1The problem: signals fade
Data travels along a cable as a signal. The further it goes, the weaker it gets. The cable also picks up a little electrical noise all along its length. Once the signal is weaker than the noise, the 1s and 0s can no longer be told apart.
Make the cable longer and watch the signal fade. Then add a repeater.
A simplified picture, set to the usual rule that an Ethernet cable carries a signal for about 100 metres.
2What a repeater is
Look closely at the wave in the lab after the repeater. It is not the weak, noisy wave made bigger. It is a clean wave again. A repeater works out which 1s and 0s were sent and sends a fresh copy of them, so the noise is left behind.
Think of a relay race
3Where a repeater goes
A repeater goes on any cable run that is longer than the cable can carry. In the exam’s campus case studies, that means: if two buildings are more than about 100 metres apart and joined by Ethernet cable, a repeater is needed between them.
4Check yourself
What does a repeater do?
Two blocks of a campus are 160 m apart and are to be joined by Ethernet cable. What should be added?