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The Header#

As with TCP we'll look at the UDP header as well. You'll see just how simple UDP is compared to TCP:

UDP Header

UDP Header
(Devarshi at English Wikibooks, CC BY-SA 3.0, via Wikimedia Commons)

The amount of information in a single datagram compared to a TCP packet is pretty crazy. A UDP datagram is essentially as minimal as you can get with only five fields compared to TCP's 10 mandatory fields. This is why UDP doesn't offer the same guarantees as TCP: it's literally not designed to offer them.