UDP | User Datagram protocol – Explained in detail – 2023

NetUDP stands for User Datagram Protocol. It is a Transport layer protocol of the OSI Model. The protocol number of the User Datagram protocol is 17. It is used in different Application layer protocols. In this article, we will discuss UDP in more detail.


What is the User Datagram Protocol (UDP)?

UDP is a connectionless transport layer protocol, which transmits data without establishing any connection between the sender and receiver. Application layer protocols, encapsulate their headers and send them to the transport layer, where exactly the UDP works. Then, UDP encapsulates its header and thus forms a segment and sends it to the IP protocol at the Network layer.

In UDP, if senders send the data to the recipient, then there is no guarantee that the recipient successfully receives the data. Thus, it is not a reliable protocol. Also, there is nothing like the reliable messages we discussed in TCP. UDP is fast in comparison to TCP.

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The header of User Datagram Protocol (UDP)

The UDP header has less number of fields in comparison to the TCP Header. UDP Header consists of 4 fields, each of which 16 bit. Here, the use of source port and checksum filed is optional in IPv4. In IPv6, the only source field is optional. For more information, you may refer to the below image to know UDP Header:


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  • Source Port number: It is a 16-bit field, which is optional. Usually, this field contains the sender port number.
  • Destination Port Number: It is also a 16-bit field, which is always required. This field identifies as a receiving port. Most of the time, this field contains a port number from well-known ports.
  • Length: The length field specifies the total length of the UDP header in bytes.
  • Checksum: This field is used for error checking and correction. In IPv4, this field is optional but in IPv6 this field is mandatory. Whenever there is no need for this field, then this field has all zeros.
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Application of User Datagram Protocol

Although many application layer protocols, use TCP on transport layer protocol, we still have applications where fast delivery of the data is important, i.e., Audio/Video applications. Such applications use User Datagram Protocol on the Transport layer.

Common examples are DHCP, DNS, SNMP, Routing Information Protocol, etc.

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In this article, we have discussed the User Datagram Protocol in detail. We have also discussed the Header and the variety of applications that used UDP on the transport layer of the OSI Model.

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