Data communication POV

POV: you are an Ethernet frame on a shared cable

POV: you are a frame trying to cross a shared Ethernet cable

Lesson notes

Key points

Before you leave, your station listens to the cable; it is quiet, so carrier sense says you may transmit.
Halfway along, another station also started sending, and your signals smash together into garbled voltage: a collision.
Your station detects it, sends a jam signal so everyone knows, and stops transmitting you immediately.
Now you wait a random number of slot times, doubling the range after each collision, then try again: binary exponential backoff.

Takeaway: CSMA/CD: listen, send, detect collision, jam, back off randomly.

Quick check: In CSMA/CD, how long does a station wait before retrying after a collision?

A fixed one slot time
A random backoff time
Until the receiver asks

Random backoff makes it unlikely both stations retry at the same moment again.

Carrier senseCollisionJam signalExponential backoff

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