Par avion · New letter
Send a message by pigeon.
It is cut into packets and flown across a small internet to your friend.
Real networks never send a message whole. They cut it into packets: small pieces that travel separately and are put back together at the other end.
Par avion
Cutting your letter into packets
Each envelope carries a header, the label on the outside: its number (3/8), who it is from, who it is for, and a checksum, a short code worked out from the contents so the receiver can tell if anything was damaged.
The link
Par avion
A letter
Two layers worked together. IP moved each packet hop by hop, with no idea of the whole. TCP, at each end, numbered the packets, checked them, asked again for lost ones and put them back in order.
Return to sender
This letter got torn.
The link looks incomplete. Ask your friend to copy it again.
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