The UDP Protocol: Characteristics & Structure

Instructor: Brandon Bass

Brandon has taught Masters and Bachelors courses in Computer Science, Security and Programming. He as a Ph.D in Digital Systems Security and Computer Science.

UDP is a protocol that is heavily used in today's world. Sites like YouTube, Netflix, and Amazon make use of UDP's speed of transmission. This lesson will give a history of UDP, highlight its use and problems and discuss its structure and future use.

UDP: History

UDP (user datagram protocol) internet protocol was officially demarcated by David Reed with the RFC 768 under internet standards. The creation of this protocol was revolutionary because it didn't require a connection for communication. UDP was connectionless and could send packets and communication between network endpoints without a prior arrangement.


UDP's use is not for reliability. Applications that use this protocol have to be set to allow for loss, errors, and duplication. Otherwise, they will fail. Loss of packets in protocols like Voice over Internet Protocol, streaming media, 'Massive Multiplayer Online games' or real-time multiplayer games can withstand the loss of a few packets and still function appropriately. Domain Name Service also makes use of UDP because the queries for DNS are incredibly quick. They only use a single request and a single reply.

Other networking protocols that make use of UDP are Routing Information Protocol used in simple routing, Simple Network Management Protocol used in network management and Dynamic Host Configuration Protocol used in assigning IP addresses to systems so they can communicate on the internet. Again, the idea being that these function on a much more rapid order than with a connection-oriented protocol, like TCP (transmission control protocol).

A quick breakdown of UDP's process is that it is for simple message based functions that do not require a connection-oriented protocol. Because there is no single dedication to end-to-end connectivity, the communication process is sped up considerably and data can be transmitted in a single direction from source to destination without being encumbered with verification on the receiver's readiness state. This is the reason UDP wins the speed war with TCP is because of the SYN, SYN\ACK, ACK (part of a required three-way handshake) packet that is used by TCP just to begin establishing communication. When packets are lost, TCP will receive re-transmit orders and have to start the process all over again. UDP does not care if things are missing, lost or out of order. So, it functions much more independently and somewhat haphazardly.

UDP Packet Structure

A breakdown of the fields within a packet is of importance so that you can understand what UDP is sending. The use of a 'pseudo header' or UDP header contains the source and destination addresses, the protocol being used and the length of the UDP packet. Here is a breakdown of how a UDP packet looks in encapsulation before it is sent.

UDP Packet
UDP Packet

That way, any system that receives a misrouted datagram can be protected. The UDP module is required to be able to determine the destination and source addresses from the field and header. With this in place in the datagram, the IP can verify consistency and checksums allowing for UDP to pass complete datagrams with headers to the IP. The real drawback, besides loss or misrouting of packets, is congestion. In networks, congestion can lead to deteriorated services, slow speeds, queuing delays and complete loss of packets and responses. If unchecked, it could lead to a network congestion collapse. So, it is important that applications have control mechanisms to assist with congestion in sending UDP. That, or it is necessary that routers are capable of dropping packets if critical levels are seen.

Quick Facts

For a more directed understanding of UDP, here's a short list of UDP's facts:

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