What is User Datagram Protocol (UDP)? TCP vs UDP: What’s the Difference

What is User Datagram Protocol (UDP)?

The User Datagram Protocol (UDP), is a protocol that is used in the transmission layer of the internet protocol suite. It is specifically to enable the communication of data among devices on different networks without connection.

While TCP is connection oriented and offers mechanisms for guaranteeing the accurate and timely delivery of data, UDP is connectionless.

They focus on the fact that UDP transmits the data packets it calls datagrams to the recipient without necessarily establishing a connection with the recipient or ensuring that all received data is okay.

Therefore, UDP is exceedingly faster and more efficient than TCP but it does not incorporate features like error checking and correction.

Key Features of UDP

Connectionless Protocol

UDP is a connectionless oriented protocol, and this implies that before transmitting data, there is no way through which it will first establish a connection with the receiver.

In contrast to TCP, the use of which implies a handshake before connecting and disconnecting from another party, UDP sends packets referred to as datagrams directly to the addressee.

This connectionless nature makes UDP faster since there is no overhead of having to establish a connection and be informed when the other side is ready to receive data or even if the destination side exists at the address specified, but the flip side is that the sending side has no way of knowing this.

Best-effort Delivery

Unlike other upper-layer protocols, such as the Transmission Control Protocol (TCP), UDP employs the best-effort delivery system, which does not offer a ‘guarantee’ of the delivery of the data packets (datagrams) to their intended recipients.

There is no indication from the receiving end and UDP is not a protocol that resends lost packets. In other words, UDP delivers messages under the assumption that they will be delivered but does not endeavor to affirm this delivery.

Finally, UDP does not have a means for getting back the data should it be lost or corrupted during the transmission process, but this would be the responsibility of the application layer in case of such incidents.

No Guarantee of Delivery or Order

Another important feature of UDP is the total lack of orientation as to delivery and receipt of packets at the destination.

Since UDP does not open a connection and does not possess the facilities to check on the status of delivery of each of the packets in the datagram it is possible to receive these datagrams in a disorderly fashion, receive duplicate datagrams and apply to missing datagrams.

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Although, due to the absence of this feature along with other features of error recovery, UDP is much less dependable than TCP; but where timely delivery is valued over definitive delivery then it may be used for the real-time applications such as voice, video and interactive games.

Error-Checking and Correction

Although UDP has only a simple checksum for error detection of the header information to ensure that data has not been corrupted in transit, it does not have an error control.

The checksum is a rudimentary approach for detecting errors in the transmitted data, but if an error is detected, UDP simply throws away the packet, it never attempts to reassure the packet.

This is different from TCP since it offers enhanced checks for error and recovers any lost or damaged data packet and transmits it repeatedly.

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Hence, applications using UDP have to incorporate some mechanisms to correct the errors or else have to bear with errors in the data.

Fast Transmission Speed

A major strength of the UDP is its ability to ensure high transmission rates. Because of how it works, UDP thus being a connectionless protocol that does not involve a handshake and has low protocol overhead, UDP can deliver data at a very high speed.

This makes UDP suitable for applications that need high performance and for cases when data delivery is more beneficial to be done on time rather than being reliable.

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Some examples of interactive multimedia applications are real-time video broadcasting, VoIP, real-time games and others.

The advantage here is the high transmission speed and ease of implementation where error checking and correction are handled at the application level.

How UDP Works?

UDP Packet Structure

The packet structure in a UDP is important when it comes to the understanding of the transfer of data in the context of this protocol.

A UDP packet, also known as a datagram, is composed of two main parts: specifically the header and the data that is to be transmitted in the payload.

The header contains information required for the routing and processing of the data and the payload section has the data that is being transferred.

• Header: The UDP header is small in size, occupying only 8 bytes (64 bits) of memory space. This simplicity is one of the benefits of UDP – this way, its overhead and speed are kept relatively low.
• Data Payload: This part of the packet contains the actual application data that is being transmitted. The length of the payload may be of any length based on the size of data required to be transmitted by the application.

UDP Header Format

The UDP header is quite concise and consists of only four fields, all of which are 2 bytes (16 bits) in length

• Source Port: This field specifies the port number of the sender’s side through which the datagram is transmitted.

It enables the receiving application to understand the location from where the data was received, especially in situations where the latter requires forwarding a response.

• Destination Port: This matter determines the port number on the side of the receiver and specifies which application or service should receive the data.

These ports are crucial in ensuring that the datagram is properly forwarded to the right process in the receiving computer.

• Length: The length field indicates the overall size of the UDP datagram including the header part as well as the data part.

This will enable the receiving device to know where the packet is and especially when the packet size varies depending on the payload.

• Checksum: The checksum is used to ensure data integrity of the data stored in the file. It confirms that the datagram has not been tampered with by using checksum algorithm on the delivered data.

If the checksum fails to tally with the data received, it is in most cases the datagram is discarded.

UDP Port Numbers

Destination UDP port numbers are necessary to figure out which process or application the datagram must be delivered to.

As in a door through which people use to enter into a house, Ports are like doors that data packets employ to access various services within a computer. Every service or the application that transmits data through the network employs a particular port number.

• Well-Known Ports (0-1023): These are assigned to system or well-known services such as DNS, DHCP among others using port number 53 and 67/68 respectively. They are well-known and associated with conventional standards of a network.
• Registered Ports (1024-49151): These ports are counted for the particular usage by the user applications and services which are not so popular or frequently used as compared to those using well-known ports.
• Dynamic/Private Ports (49152-65535): These ports are often used for short time and for private connections; they may be assigned dynamically by the operating system for the client side connections.

UDP Datagram Transmission and Reception

The UDP datagrams transmission and reception process presents simple, easy to implement mechanisms.

• Transmission: When the application wants to send data it constructs a datagram and gives it to the UDP layer.

The UDP layer then appends a header to the data which contains the source and destination ports, total length of the datagram and a checksum field for the purposes of error detection.

After that, the datagram is passed to the IP layer for routing it to the required network in the path of communication to the destination.

• Reception: On the receiving end, the IP layer transmits the datagram to the UDP layer of the application software.

To prevent data corruption, UDP analyzes datagram’s checksum field. If the datagram is still sound then UDP copies the destination port number and forwards the data to the appropriate application.

Sometimes, when there is a problem with the datagram, for example when it is impossible to verify the checksum, it sends the checksum zero and UDP may discard it, and it’s the application which has to deal with such problems.

TCP vs UDP: What’s the Difference

Feature	TCP (Transmission Control Protocol)	UDP (User Datagram Protocol)
Connection	Connection-oriented	Connectionless
Guarantee of Delivery	Guaranteed delivery	Best-effort delivery (no guarantee)
Error-Checking	Error-checking and correction	Error-checking, but no correction
Packet Order	Ensures packet order	No guarantee of packet order
Speed	Slower due to error-checking and correction	Faster due to minimal error-checking
Latency	Higher latency due to error-checking and correction	Lower latency due to minimal error-checking
Reliability	High reliability, suitable for critical applications	Low reliability, suitable for non-critical applications
Use Cases	File transfers, email, web browsing, remote access, database connections	Online gaming, video streaming, VoIP, DNS lookups, online video conferencing
Header Size	20 bytes (minimum)	8 bytes (minimum)
Packet Size	Variable, up to 65,535 bytes	Variable, up to 65,535 bytes
Connection Establishment	Three-way handshake (SYN, SYN-ACK, ACK)	No connection establishment
Resource Usage	Higher resource usage due to error-checking and correction	Lower resource usage due to minimal error-checking

Advantages of UDP

Low Latency:

UDP offers a lower latency as compared to TCP given the fact that it does not have an initial connection before data transfer occurs.

This makes it suitable for use in applications where fast delivery of data is necessary for instance in gaming and video streaming.

Reduced Overhead:

As you will recall, UDP has very little overhead in terms of protocols or other factors.

Unlike TCP, there are no extra control mechanisms such as connection establishment, flow and error control mechanisms adding to the congestion control consequently leading to small headers and less processing.

Faster Data Transmission:

In its operation, UDP does not check for errors very thoroughly or transmit packets that may have been lost in the networks hence making it faster.

There is preference in circumstances where speed is paramount before accuracy such as in the Transcription of real-time communications.

Simple Protocol:

The design UDP is simple compared to the TCP.

Due to the absence of complex details in the specifications of the protocol, implementing it is relatively slighted and it is best suited for applications that do not demand full TCP functionality.

Multicast and Broadcast Support:

UDP can operate in a multicast and broadcast model of communication whereby a single data packet can be transmitted to numerous receivers all at once.

This is especially important for traffic such as video conferences and live streams in which the same information has to be transmitted to different clients.

Disadvantages of UDP

No Guaranteed Delivery:

It is clear that in the case of UDP there is no guarantee that the packets will arrive at the intended destination.

There is no way of knowing whether the data was received or not hence the occurrence of packet loss particularly in unreliable networks.

No Error Recovery:

One of the main drawbacks is that UDP does not contain integrated error detection and correction systems like TCP contains.

This is because UDP doesn’t require re transmission of data: if, for instance, a packet is lost or corrupted during transmission, then there is no way to request that the data in the lost packet be resent.

No Acknowledgement of Receipt:

One other limitation of UDP that should be mentioned is that it does not send any acknowledgments for the received packets.

There is no response from the receiver to be able to know whether the data got through successfully, or even if it got there at all.

No Flow Control:

One of the important features of UDP that is missing is flow control, this entailing that there are no restrictions applied towards the rate at which data is transmitted between these two entities.

This can result in a situation where a receiver is overpowered by the number of inputs he receives.

Out-of-Order Delivery:

UDP is connectionless and therefore packets sent using this protocol may arrive in any order.

Some protocols use the packet size option to achieve their goals, while others use checksum to verify the delivered data; as for the latter option, given that UDP does not guarantee packet sequencing, it falls on the application layer to reassemble the packets, if needed.

Use Cases for UDP

IoT (Internet of Things) Devices:

Most IoT devices employ UDP for communication because of the low overheads that come with it.

For example, sensors along with smart home devices may utilize UDP for transmission of small data chunks over to a server or gateway.

Tunneling Protocols:

Tunneling is strongly associated with the use of UDP since for instance in the use of VPNs, that is virtual private networks, it is used for transport of encapsulated data in a network.

Testing and Diagnostics:

For various test and diagnostic purposes network administrators employ UDP. It is therefore possible that tools such as ping or traceroute, as an example, utilize UDP in determining network connectivity performance.

Dynamic Data Updates:

Applications where data has to be transmitted frequently while not much stress is given to accuracy of the data use UDP to pass real-time information.

Some examples include automated and self-service systems such as financial trading platforms where the latest prices and available stock updates have to be provided immediately.

Simpler Protocols:

Some of the possible implementations of UDP are given below:

UDP is used in protocols that are straightforward and do not incorporate elaborate error handling mechanisms and are implemented in a context that is inherently simple.

This is in the form of light weight data protocols of interconnecting internal systems or applications.

Conclusion

TCP and UDP are both protocols that run on top of IP. TCP is more reliable whereas UDP is more secure.

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