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a human analogy

3.1 A Human Analogy

A good analogy of Ethernet technology is a group of people talking in
a small, completely dark room. In this analogy, the physical network
medium is sound waves on air in the room instead of electrical
signals on a coaxial cable.

Each person can hear the words when another is talking (Carrier
Sense). Everyone in the room has equal capability to talk (Multiple
Access), but none of them give lengthy speeches because they are
polite. If a person is impolite, he is asked to leave the room
(i.e., thrown off the net).

No one talks while another is speaking. But if two people start
speaking at the same instant, each of them know this because each
hears something they haven't said (Collision Detection). When these
two people notice this condition, they wait for a moment, then one
begins talking. The other hears the talking and waits for the first
to finish before beginning his own speech.

Each person has an unique name (unique Ethernet address) to avoid
confusion. Every time one of them talks, he prefaces the message
with the name of the person he is talking to and with his own name
(Ethernet destination and source address, respectively), i.e., "Hello
Jane, this is Jack, ..blah blah blah...". If the sender wants to
talk to everyone he might say "everyone" (broadcast address), i.e.,
"Hello Everyone, this is Jack, ..blah blah blah...".

from:
rfc1180

[rfc = Request For Comments]

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