Networking Kid → expert

Collision Domains at 3 Levels

Explain collisions to a 5-year-old, a student and a professor

Lesson notes

Key points

If two kids shout across a room at once, nobody understands, so both wait a moment and try again.
On shared Ethernet, a collision domain is every device whose frames can collide; a hub makes one big domain, while each switch port is its own.
Half-duplex Ethernet uses CSMA/CD: sense the carrier, detect the collision, send a jam signal, then wait a random binary exponential backoff.

Takeaway: Hubs share one collision domain; every switch port is its own.

Quick check: How many collision domains does a 24-port hub create?

24
12
1

A hub repeats bits to all ports, so every device shares one domain.

Talking over each otherCollision domainCSMA/CD backoff

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