Distance Limitation and LAN Design

The electrical signals get weaker as they travel through the cable and the delays must be short to enable the CSMA/CS and token passing etc.
But usually, there is a need of extension beyond the normal length limit.

LAN Extension

Most techniques use hardware is used to extend the diameter of the LAN medium.

Fiber Optic Extension

The fiber modems are responsible for conversions between light and digital signals.
The fiber optic spans over kilometers with minimal delay and maximum bandwidth.

Repeaters

As the signals travel, they get weakened.
Therefore, repeaters re-transmit the signal.

As the figure suggests, 1 repeaters doubles the max length meanwhile 2 repeaters triples the max length.

Although infinite length can be achieved but it introduces delay which disturbs the CSMA/CD.
Therefore, the Ethernet standard specifies that no more than 4 repeaters should be used to connect 2 stations.

Disadvantage

repeaters only amplify and re-transmit.
This also includes collision errors etc.

Bridges

These consist of following components: 1. 2 NICs 2. CPU 3. Memory 4. ROM

It runs the code stored in its ROM.
It connects 2 LAN segments, listens to all the traffic and transmits only valid frames unlike repeaters.

Frame Filtering

Most bridges are self learning.
They automatically add addresses of computers to their address list.