Hubs
A hub is typically the least expensive, least intelligent, and least complicated of the three. Its job is very simple – anything that comes in one port is sent out to the others.
If a message1 comes in for computer “A”, that message is sent out all the other ports, regardless of which one computer “A” is on:
And when computer “A” responds, its response also goes out to every other port on the hub:
Every computer connected to the hub “sees” everything that every other computer on the hub sees. The computers themselves decide if they are the targeted recipient of the message and when a message should be paid attention to or not.
The hub itself is blissfully ignorant of the data being transmitted. For years, simple hubs have been quick and easy ways to connect computers in small networks.