User Datagram Protocol (UDP)

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 before data transfer. The UDP helps to establish low-latency and loss-tolerating connections over the network. The UDP enables process-to-process communication.

What is User Datagram Protocol?

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, and 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. 

UDP Header

UDP header is an 8-byte fixed and simple header, while for TCP it may vary from 20 bytes to 60 bytes. The first 8 Bytes contain all necessary header information and the remaining part consists 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. 

UDP Header

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.
• UDP is widely used in online gaming, where low latency and high-speed communication is essential for a good gaming experience. Game servers often send small, frequent packets of data to clients, and UDP is well suited for this type of communication as it is fast and lightweight.
• Streaming media applications, such as IPTV, online radio, and video conferencing, use UDP to transmit real-time audio and video data. The loss of some packets can be tolerated in these applications, as the data is continuously flowing and does not require retransmission.
• VoIP (Voice over Internet Protocol) services, such as Skype and WhatsApp, use UDP for real-time voice communication. The delay in voice communication can be noticeable if packets are delayed due to congestion control, so UDP is used to ensure fast and efficient data transmission.
• DNS (Domain Name System) also uses UDP for its query/response messages. DNS queries are typically small and require a quick response time, making UDP a suitable protocol for this application.
• DHCP (Dynamic Host Configuration Protocol) uses UDP to dynamically assign IP addresses to devices on a network. DHCP messages are typically small, and the delay caused by packet loss or retransmission is generally not critical for this application.
• 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.

Advantages of UDP

• Speed: UDP is faster than TCP because it does not have the overhead of establishing a connection and ensuring reliable data delivery.
• Lower latency: Since there is no connection establishment, there is lower latency and faster response time.
• Simplicity: UDP has a simpler protocol design than TCP, making it easier to implement and manage.
• Broadcast support: UDP supports broadcasting to multiple recipients, making it useful for applications such as video streaming and online gaming.
• Smaller packet size: UDP uses smaller packet sizes than TCP, which can reduce network congestion and improve overall network performance.
• User Datagram Protocol (UDP) is more efficient in terms of both latency and bandwidth.

Disadvantages of UDP

• No reliability: UDP does not guarantee delivery of packets or order of delivery, which can lead to missing or duplicate data.
• No congestion control: UDP does not have congestion control, which means that it can send packets at a rate that can cause network congestion.
• No flow control: UDP does not have flow control, which means that it can overwhelm the receiver with packets that it cannot handle.
• Vulnerable to attacks: UDP is vulnerable to denial-of-service attacks, where an attacker can flood a network with UDP packets, overwhelming the network and causing it to crash.
• Limited use cases: UDP is not suitable for applications that require reliable data delivery, such as email or file transfers, and is better suited for applications that can tolerate some data loss, such as video streaming or online gaming.

UDP Pseudo Header

• The purpose of using a pseudo-header is to verify that the UDP packet has reached its correct destination
• The correct destination consist of a specific machine and a specific protocol port number within that machine

UDP pseudo header

UDP Pseudo Header Details

• The UDP header itself specify only protocol port number.thus , to verify the destination UDP on the sending machine computes a checksum that covers the destination IP address as well as the UDP packet.
• At the ultimate destination, UDP software verifies the checksum using the destination IP address obtained from the header of the IP packet that carried the UDP message.
• If the checksum agrees, then it must be true that the packet has reached the intended destination host as well as the correct protocol port within that host.

User Interface

A user interface should allow the creation of new receive ports, receive operations on the receive ports that returns the data octets and an indication of source port and source address, and an operation that allows a datagram to be sent, specifying the data, source and destination ports and address to be sent.

IP Interface

• The UDP module must be able to determine the source and destination internet address and the protocol field from internet header 
• One possible UDP/IP interface would return the whole internet datagram including the entire internet header in response to a receive operation
• Such an interface would also allow the UDP to pass a full internet datagram complete with header to the IP to send. the IP would verify certain fields for consistency and compute the internet header checksum.
• The IP interface allows the UDP module to interact with the network layer of the protocol stack, which is responsible for routing and delivering data across the network.
• The IP interface provides a mechanism for the UDP module to communicate with other hosts on the network by providing access to the underlying IP protocol.
• The IP interface can be used by the UDP module to send and receive data packets over the network, with the help of IP routing and addressing mechanisms.
• The IP interface provides a level of abstraction that allows the UDP module to interact with the network layer without having to deal with the complexities of IP routing and addressing directly.
• The IP interface also handles fragmentation and reassembly of IP packets, which is important for large data transmissions that may exceed the maximum packet size allowed by the network.
• The IP interface may also provide additional services, such as support for Quality of Service (QoS) parameters and security mechanisms such as IPsec.
• The IP interface is a critical component of the Internet Protocol Suite, as it enables communication between hosts on the internet and allows for the seamless transmission of data packets across the network.

GATE Questions for Practice

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

Frequently Asked Questions on UDP – FAQs

1. Name the protocols that uses UDP?

The protocol that uses UDP Model are:

• Domain Name System(DNS)
• Simple Network Management Protocol(SMTP)
• Routing Information Protocol(RIP)

2. Which is faster: TCP or UDP?

UDP is faster than TCP.