2.3.2 Packets

If there is an error in a message, how is it detected and rectified?

1. Compute a checksum over the message
2. send the checksum with the message
3. Calculate a new checksum over the received message
4. Compare the checksums - if different, then message is in error
5. Ask for the message to be resent

Probability of error rises with length of message,

Thus message sent in separate lumps with maximum number of bits per lump, known as packets.

If the message fits in one packet, good. Otherwise message is in many packets.