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In this lesson, you will learn more about User Datagram Protocol (UDP), User Datagram Protocol (UDP) header and header fields.

User Datagram Protocol (UDP) is a protocol at Transport Layer, which is not reliable when compared with Transmission Control Protocol (TCP). User Datagram Protocol (UDP) is also called as a connection less protocol. UDP is much simpler than TCP, and it doesn't perform any of the complex functions of TCP we discuss before. UDP provides no reliability, flow-control, or error recovery to IP. UDP only serves as a multiplexer/demultiplexer using port numbers. Following are the important characteristics of UDP.

1) User Datagram Protocol (UDP) is a connectionless protocol, which means UDP is not a reliable protocol when compared with Transmission Control Protocol (TCP).

2) User Datagram Protocol (UDP) is capable of performing fundamental error checking. The UDP header includes a checksum field that the destination device can use to check the integrity of the data.

3) User Datagram Protocol (UDP) does not provide sequencing of data. Therefore, the data may arrive at the destination device in a different order from which it was sent. This may happen in large networks, such as the Internet, where the Datagrams might take different paths to the destination and experience delays in different routers. In a LAN, sequencing is not going to create problems. Applications that require sequencing must code their own sequencing mechanism as part of the application.

User Datagram Protocol (UDP) Header

Source Port Number: The first 16 bits of the UDP header contain the port number of the application sending the data.

Destination Port Number: The next 16 bits contain the port number of the application that receives this data.

Length: The next 16 bits identify how long the datagram is in bits.

Checksum: Checksum field of UDP header contains checksum value. UDP uses a concept called as "pseudo header". Pseudo header helps to find transfer bit errors and also to protect against other types of network errors like the possibility of IP datagram reaching a wrong destination. Click the following link to learn the concept of UDP pseudo header.

Important protocols which use UDP as the Transport Layer protocol are Trivial File Transfer Protocol (TFTP), Domain Name System (DNS), Remote Procedure Call (RPC) used by the Network File System (NFS), Simple Network Management Protocol (SNMP) and Lightweight Directory Access Protocol (LDAP).

Visit the following link to know the differences between TCP and UDP.

For a complete list of Well Known port numbers, visit IANA Port Number Assignment web page.

You have learned about User Datagram Protocol (UDP), different fields in User Datagram Protocol (UDP) Header. Click "Next" to continue.