Our telephone exchange has 1000 wire-based connections. You dial a number, you get connected to the exchange and they put you through.
Yesterday, vandals broke in and disconnected all the wires. Your job is to reconnect them.
You can phone any number, and you get a conversation such as:
Hello, is this 123456?
No, this is 654321.
Or maybe a positive result!
How quickly can you restore our telephone exchange?