TRANSPORT
One packet is lost.
Only one notices.
BOTH RUN ON THE SAME NETWORK
Both hand your data to a network that drops things. Then they differ.
TCP ACKNOWLEDGED
SENDER
waits for it
NETWORK
drops one
RECEIVER
acks it
Nothing came back, so the timer fires and TCP sends it again.
UDP FIRE AND FORGET
SENDER
not told
NETWORK
drops one
RECEIVER
silent
Nothing comes back at all, so the loss is never noticed by anyone.
TCP — every packet is acknowledged.
A lost one is sent again.
UDP — nothing is acknowledged.
A lost one is simply gone.
One packet is lost.
Only one notices.
You'll want this one
in the interview.