What is User Datagram Protocol (UDP) in Networking?

UDP is an alternative to TCP. It is a communication protocol used for the exchange of data between the devices in a network

What is User Datagram Protocol (UDP) in Networking?

UDP is an alternative to TCP. It is a communication protocol used for the exchange of data between the devices in a network. It is especially meant for the transmission of time-sensitive files. So, it transfers the data faster than TCP but is not as reliable as TCP. 

To enable faster data transfer, it avoids factors like the handshake, doesn’t check whether the data is transmitted properly, and if some data is lost while transmitting, it will not resume it. Hence, it accelerates the speed of transmission but doesn’t guarantee successful data transfer. 

User Datagram Protocol is used for time-bound tasks where it is better to drop the packets of data instead of waiting. Generally, it is preferred for video playbacks, voice traffic, and DNS lookups. 

User Datagram Protocol (UDP) is a communications protocol that is primarily used to establish low-latency and loss-tolerating connections between applications on the internet.

UDP speeds up transmissions by enabling the transfer of data before an agreement is provided by the receiving party. As a result, UDP is beneficial in time-sensitive communications, including voice over IP (VoIP), domain name system (DNS) lookup, and video or audio playback.

TCP is regarded as a trustworthy transport channel since it sends discrete packets. On the other hand, UDP is regarded as a best-effort means of communication and sends packets known as datagrams. This means that UDP doesn't offer any guarantees regarding the delivery of the data or any unique capabilities to retransmit lost or damaged messages.

UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests. It also provides an optional checksum capability to verify that the data arrived intact. 

User Datagram Protocol features

User Datagram Protocol has attributes that make it beneficial for use with applications that can tolerate lost data. Below are some examples:

  • It allows packets to be dropped and received in a different order than they were transmitted, making it suitable for real-time applications where latency might be a concern.
  • It can be used for transaction-based protocols, such as DNS or Network Time Protocol (NTP).
  • It can be used where a large number of clients are connected and where real-time error correction isn't necessary, such as gaming, voice or video conferencing, and streaming media.

UDP header composition

UDP uses headers when packaging message data to transfer over network connections. UDP headers contain a set of parameters -- called fields -- defined by the technical specifications of the protocol.

The User Datagram Protocol header has four fields, each of which is 2 bytes. They are the following:

  • source port number, which is the number of the sender;
  • destination port number, the port to which the datagram is addressed;
  • length, the length in bytes of the UDP header and any encapsulated data; and
  • checksum, which is used in error checking -- its use is required in IPv6 and optional in IPv4.

How UDP works 

To transfer a datagram from one computer to another, UDP requires IP. UDP collects data in a UDP packet and adds its own header data to the packet to carry the data. The source and destination ports for communication, the packet length, and a checksum make up this data. UDP packets are delivered to their destinations after being enclosed in an IP packet.

Unlike TCP, UDP doesn't guarantee the packets will get to the right destinations. This means UDP doesn't connect to the receiving computer directly, which TCP does. Rather, it sends the data out and relies on the devices in between the sending and receiving computers to correctly get the data where it's supposed to go.

Most applications wait for any replies they expect to receive as a result of packets sent using UDP. If an application doesn't receive a reply within a certain time frame, the application sends the packet again, or it stops trying.

UDP uses a simple transmission model that doesn't include handshaking dialogues to provide reliability, ordering or data integrity. Consequently, UDP's service is unreliable. Packets may arrive out of order, appear to have duplicates or disappear without warning.

Although this transmission method doesn't guarantee that the data being sent will reach its destination, it does have low overhead and is popular for services that don't absolutely have to work the first time.  

Applications of UDP

Lossless data transmission

UDP can be used in applications that require lossless data transmission. For example, an application that is configured to manage the process of retransmitting lost packets and correctly arrange received packets might use UDP. This approach can help to improve the data transfer rate of large files compared to TCP.

In the Open Systems Interconnection (OSI) communication model, UDP is in Layer 4, the transport layer. UDP works in conjunction with higher-level protocols to help manage data transmission services, including Trivial File Transfer Protocol (TFTP), Real Time Streaming Protocol (RTSP) and Simple Network Management Protocol (SNMP).

Gaming, voice and video

For network applications where perceived latency is important, including in gaming, audio, and video communications, UDP is the best protocol. These illustrations can experience some data loss without degrading in perceived quality. Although there may be some loss, forward error correcting methods are occasionally used in addition to UDP to enhance audio and video quality.

Services that don't need fixed packet transmission

Applications that require the secure flow of information can also use UDP, but they should have their own ways of responding to packets. These services are advantageous since they are not constrained by predetermined patterns to ensure the accuracy and completeness of the delivered data packets. Users can choose how and when to react to inaccurate or poorly organized information.

Multicasting and routing update protocols

UDP can also be used for multicasting because it supports packet switching. In addition, UDP is used for some routing update protocols, such as Routing Information Protocol (RIP).

Fast applications

UDP can be used in applications where stability is not as important as speed. In a situation when it's acceptable to lose a few data points from a quick acquisition, it might be wise to use UDP.

UDP characteristics include the following:

  • It is a connectionless protocol.
  • It is used for VoIP, video streaming, gaming and live broadcasts.
  • It is faster and needs fewer resources.
  • The packets don't necessarily arrive in order.
  • It allows missing packets -- the sender is unable to know whether a packet has been received.
  • It is better suited for applications that need fast, efficient transmission, such as games.