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User Datagram Protocol (UDP) explained

User Datagram Protocol (UDP) explained

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User Datagram Protocol (UDP) is an optional communications protocol for data transmission. It is used mostly for establishing low-latency and loss tolerating connections between applications on the internet. The IP address is working both with TCP and UDP and some time referred to as TCP/IP and UDP/IP. Both TCP and UDP send short packets of data, called datagram.

User Datagram Protocol (UDP) Low Overhead vs Reliability

User Datagram Protocol provides the basic transport layer functions. It sends the packets, with lower bandwidth overhead and latency than TCP. User Datagram Protocol (UDP) is not a connection-oriented protocol so it does not offer the sophisticated retransmission, flow control and sequencing mechanism for lost and out of order packets. So User Datagram Protocol (UDP) is not providing a reliability like TCP. But this does not mean that application that uses User Datagram Protocol (UDP) are forever unreliable and substandard. It only means that these functions are not provided by the transport layer protocol and must be implemented in a different place if required.

Because of low overhead, UDP is the best protocol for network applications in which apparent latency is critical such as gaming, voice and video communications, which can bear some data loss without badly disturbing apparent quality. Like TCP, UDP does not set up a connection before sending data, it just starts sending data when required.

UDP Datagram reassemble

UDP datagram is arriving at the destination using different routes, and these datagrams arrive in the wrong order. The UDP does not follow sequence numbers just like TCP. It has no mechanism to reorder the datagram into their transmission order. So, the UDP reassembles the data in the exact order. If the sequence is important to the application; the application should identify the right sequence number and decide how the data should be processed.

UDP Server Processes and Requests

UDP-based server applications assign well-known or registered port numbers just like TCP When these applications and processes are running on a server; they accept the data matched with the assigned port number. When UDP receives a datagram destined for one of these ports; it forwards the application data to the proper application based on its port number.

UDP Client Processes

The client application will ask a server process to start communication between the server and the client. The UDP client process selects a port number from the range of port numbers randomly. The destination port on the server is generally the well-known or registered port number assigned to the server process. Once the client selects the source and destination ports, the header of all datagram uses this selected pair of ports. For returning the data from the server to the client the destination and source port; are reserved for the datagram header.

TCP and UDP

TCP and UDP

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The TCP and UDP transport layer protocols handle data communications between terminals in an IP network. The TCP is a connection-oriented protocol, and UDP is a connectionless protocol.

TCP

Transmission Control Protocol (TCP) tracked the packet transmission from source to destination. For example, sending a software file to someone or downloading software from a website ensures it is 100% delivered or downloaded. WhatsApp is another example of TCP, it is used TCP as transmission control protocol. It informs the user about the receipt of the messages and if those messages have been seen and reproduced. The TCP has three basic operations:-

  • Numbering and tracking segments transmitted to a specific destination from a particular application
  • Acknowledging received data
  • Retransmitting any unacknowledged data after a certain period

Understanding the difference between UDP and TCP is very important. Understanding the work procedure of each protocol, the implementation of reliability features, and how they track the conversation.

Establishing a Session

TCP is a connection-oriented protocol which negotiates and establishes a permanent session between the source and destination devices before forwarding any data. Throughout the session establishment, the devices check for the amount of traffic that can be sent at a specified time, and the communication data between the two can be closely managed.

Reliable Delivery

A segment can become corrupted or lost as transmitted over the network. The reliability ensures each sending segment must arrive at the destination.

Same-Order Delivery

Data can arrive in the wrong order due to multiple routes on the network with different transmission rates and speeds. Using numbering and sequencing, TCP ensures the segments are back in the correct order.

Flow Control

The TCP provides flow control between the source and destination host. The flow control ensures the data rate at which a sender is transmitting. It ensures the data-sending speed according to the speed of the receiver’s receiving capabilities. It is used to manage the flow of data/packets among two different nodes, especially in cases where the sending device can send data faster than the receiver can take in.

UDP

User Datagram Protocol (UDP) is a connectionless and unreliable protocol. It is not guaranteed to reach its destination. Sending someone a non-registered letter or postcard is an example of User Datagram Protocol, where you put it in the postbox. Now, you have no information about the letter’s status or postcard because you don’t know about the receiver’s availability to receive the letter. The chances are good that it will get where it’s supposed to go, but there is no guarantee.

There is a possibility of loss in the way. The post office is not responsible for tracking the letter or informing the sender if the letter does not arrive at the destination. The User Datagram Protocol works Just like the above example.

The User Datagram Protocol provides essential functions for delivering data segments between suitable applications with tiny overhead and data checking. However, the User Datagram Protocol does not acknowledge the receiving data at the destination.

No transport layer processes inform the sender of a successful delivery using UDP. While the TCP reliability functions allow more dynamic communication among applications, they also incur extra overhead and possible transmission delays.

UDP Features

UDP is a best-effort, lightweight transport protocol that offers the same data segmentation and reassembles as TCP but with no TCP reliability and flow control. The features of UDP are as follows:-
No Ordered Data Reconstruction – Data is reconstructed according to its receiving order.
Unreliable Delivery – Any lost segments, like TCP, have not been resent in this protocol.
Connectionless – No session established with the source and destination.
No Flow Control – Does not inform the sender about the resource availability.

UDP Header

UDP does not inform the source and destination about the packets it receives. It also provides any state of the communication session to the client and server. The UDP application is responsible for reliability and can accept some loss of data during transmission over the network, but delays in transmission are unacceptable.

The UDP application required less network overhead than the UDP protocol. It is preferable for streaming live audio, live video, and Voice over IP. The UDP header is called a datagram, as shown in the figure below. The transport layer protocol sent these datagrams as best-effort.

UDP