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How can pieces rebuild a message?
Device A
NIC send queue
Network
Move
Move routers; their wires stay attached.
Network readyWires cross without joining.
Device B
Sequencewaiting
Header
Payload
Trailer
Packets Routes Accepted Message
Sent at A
Damaged arrival
Received at B
Sent at A
Received at B
All packets and arrival attempts
Routers choose an onward neighbour after reading destination B. Payload units are characters; the checksum is a small teaching example. Coloured packets keep their identity; colour does not mean correct.