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Definition

The User Datagram Protocol is an OSI layer 4 transport protocol.

Header Structure

The header has a fixed size of 8 bytes. The maximum size of the payload is $2^{16} - 1$

0      7 8     15 16    23 24      31
+--------+--------+--------+--------+
|     Source      |   Destination   |
|      Port       |      Port       |
+--------+--------+--------+--------+
|                 |                 |
|     Length      |    Checksum     |
+--------+--------+--------+--------+
|
|          data octets ...
+---------------- ...

In contrast to TCP, UDP does not provide sequence numbers to detect the order of the packets.

References

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