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User Datagram Protocol (UDP)

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  • Difficulty Level : Medium
  • Last Updated : 01 Nov, 2022
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User Datagram Protocol (UDP) is a Transport Layer protocol. UDP is a part of the Internet Protocol suite, referred to as UDP/IP suite. Unlike TCP, it is an unreliable and connectionless protocol. So, there is no need to establish a connection prior to data transfer. The UDP helps to establish low-latency and loss-tolerating connections establish over the network.The UDP enables process to process communication.

Though Transmission Control Protocol (TCP) is the dominant transport layer protocol used with most of the Internet services; provides assured delivery, reliability, and much more but all these services cost us additional overhead and latency. Here, UDP comes into the picture. For real-time services like computer gaming, voice or video communication, live conferences; we need UDP. Since high performance is needed, UDP permits packets to be dropped instead of processing delayed packets. There is no error checking in UDP, so it also saves bandwidth. 
User Datagram Protocol (UDP) is more efficient in terms of both latency and bandwidth. 

UDP Header – 

UDP header is an 8-bytes fixed and simple header, while for TCP it may vary from 20 bytes to 60 bytes. The first 8 Bytes contains all necessary header information and the remaining part consist of data. UDP port number fields are each 16 bits long, therefore the range for port numbers is defined from 0 to 65535; port number 0 is reserved. Port numbers help to distinguish different user requests or processes. 



  1. Source Port: Source Port is a 2 Byte long field used to identify the port number of the source.
  2. Destination Port: It is a 2 Byte long field, used to identify the port of the destined packet.
  3. Length: Length is the length of UDP including the header and the data. It is a 16-bits field.
  4. Checksum: Checksum is 2 Bytes long field. It is the 16-bit one’s complement of the one’s complement sum of the UDP header, the pseudo-header of information from the IP header, and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets.

Notes – Unlike TCP, the Checksum calculation is not mandatory in UDP. No Error control or flow control is provided by UDP. Hence UDP depends on IP and ICMP for error reporting. Also UDP provides port numbers so that is can differentiate between users requests.

Applications of UDP: 

  • Used for simple request-response communication when the size of data is less and hence there is lesser concern about flow and error control.
  • It is a suitable protocol for multicasting as UDP supports packet switching.
  • UDP is used for some routing update protocols like RIP(Routing Information Protocol).
  • Normally used for real-time applications which can not tolerate uneven delays between sections of a received message.
  • Following implementations uses UDP as a transport layer protocol: 
    • NTP (Network Time Protocol)
    • DNS (Domain Name Service)
    • BOOTP, DHCP.
    • NNP (Network News Protocol)
    • Quote of the day protocol
    • TFTP, RTSP, RIP.
  • The application layer can do some of the tasks through UDP- 
    • Trace Route
    • Record Route
    • Timestamp
  • UDP takes a datagram from Network Layer, attaches its header, and sends it to the user. So, it works fast.
  • Actually, UDP is a null protocol if you remove the checksum field.
    1. Reduce the requirement of computer resources.
    2. When using the Multicast or Broadcast to transfer.
    3. The transmission of Real-time packets, mainly in multimedia applications.
  1. GATE CS 2013, Question 12
  2. GATE CS 2012, Question 65
  3. GATE CS 2007, Question 20
  4. GATE CS 2005, Question 23
  5. GATE IT 2008, Question 66
  6. GATE Mock 2015, Question 5
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