We’ve already had some permutation of the phrase “data is king” drummed into our heads for the past few years. Yes, data is knowledge, knowledge is power, and we live in the age of Big Data. Great! However, that data still needs to move from Point A to Point B.

That’s where data transfer protocols enter the picture. There are several different methods of moving data from one party to another, and we’re about to take a close look at two. But, first, we're tackling TCP vs UDP, including what they are, how they work, and how they compare.

But before answering the question “What are TCP and UDP,” let's talk about OSI network models.

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OSI Model's Seven Layers

The International Organization for Standardization created a conceptual model to allow different communication systems to talk using a standard protocol. That model is called the Open Systems Interconnection model, or OSI for short. Think of OSI as a universal language that lets computers of all kinds swap information.

OSI has seven layers, and each of them serves as a guide for how information is exchanged. The layers are:

  1. Physical layer
  2. Data link layer
  3. Network layer
  4. Transport layer
  5. Session layer
  6. Presentation layer
  7. Application layer

TCP and UDP are Internet Protocols (IP), and IPs exist in the OSI’s network layer. Internet Protocols let you send emails to friends, download cat videos, or check your bank balance online. Consider IPs the FedEx or UPS of the Internet, delivering data packages to recipients.

What are TCP and UDP?

TCP stands for Transmission Control Protocol. TCP is a connection-oriented protocol, meaning that it requires an established connection before data can be transmitted between two locations. In addition, TCP features built-in systems that look for errors and guarantee that data gets delivered in the same order it’s sent.

However, TCP eats up bandwidth, a price you pay for sending and receiving web pages, images, and data files.

On the other hand, UDP stands for User Datagram Protocol, a more straightforward, connectionless Internet protocol that doesn't need error-checking and recovery services. UDP has no overhead for opening, maintaining, or terminating a connection. UDP continuously sends data to the recipient, regardless of whether they get it or not.

Although UDP isn’t the best choice for sending an e-mail, looking at a webpage, or downloading files, it’s great for real-time communications such as broadcast or multitasked network transmissions.

Let’s take a closer look at the differences between TCP and UDP while we answer the question “what are TCP and UDP.” We will see how the two protocols stack up in speed, bandwidth usage, error checking, and security.

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What is the Difference Between TCP and UDP?

This convenient table shows you the differences between TCP and UDP at a quick glance:

 

TCP

UDP

Service/Connection Type

TCP is connection-oriented, meaning it needs an established connection.

UDP is connectionless, requiring no opening, maintaining, or ending a connection.

Data Transfer Method

Data units are called packets. TCP reads data as byte streams and transmits messages to segment boundaries.

UDP uses individually sent packets (also called datagrams) with defined boundaries and checks for integrity on receipt.

Speed

TCP is comparatively slower than UDP.

UDP is faster than TCP.

Error Checking

TCP has a robust error-checking mechanism.

UDP offers a basic error-checking mechanism using checksums.

Priority

Data integrity, completeness, and reliability.

Speed

Does it Guarantee Delivery?

Yes, TCP guarantees data delivery to the destination.

No, UDP cannot guarantee delivery.

Broadcasting

TCP does not support broadcasting.

UDP supports broadcasting.

Retransmission

TCP can retransmit lost packets

UDP has no lost packet retransmission capability

Handshake

Uses handshakes like SYN, ACK, SYN-ACK

Since it’s a connectionless protocol, there’s no handshake

Stream Type

Byte stream

Message stream

Weight

TCP is heavy-weight, requiring three packets to set up a socket connection before sending data.

UDP is lightweight, with no tracking connections, ordering of messages, etc.

Overhead

Low, though higher than UDP

Extremely low

Best User For

Reliable data transfers. Used by FTP, HTTPS, HTTP, POP, SMTP, etc.

Fast real-time data transmissions. Video conferencing, DNS, streaming, VoIP, etc.

 

Consider this analogy. You have two houses (A and B) separated by a deep trench filled with red-hot magma. You have a package of vital medicine that needs to go from House A to House B. There are two ways you can get the critical supplies across:

  • Take the time and energy to construct a steel bridge carefully over the chasm and walk across
  • Tie the package to a brick and throw it across the chasm.

That first option guarantees the medicine will absolutely find its way into the hands of House B’s occupants. It just takes a little longer, relatively speaking. However, the second option takes no time to tie the package to a rock and throw it, but the missile may fall short and land in the magma. Perhaps some of the medication may fall out in transit. Or someone else might pick the package up. So yes, the second method is faster, but it’s less reliable.

What are TCP and UDP: Speed Comparison

We’ve hinted at how TCP and UDP compare in speed, but let’s look closer. UDP is faster than TCP because it supports a continuous stream of packets and dispenses with 'acknowledgment.' TCP always acknowledges packet sets, so it must retransmit every negative acknowledgment, which is needed when data packets get lost.

Since UDP avoids the unnecessary TCP transport overheads, it uses bandwidth more efficiently and makes fewer demands of poor-performing networks.

How the IP Works to Transfer Data

The process of moving data across the Internet is called "routing." Each source and destination have an IP address analogous to your home's address. A standard IPv4 address has a 32-bit number consisting of subnets, defined as segments of numbers divided by periods. Each subnet has up to three digits, for up to 12 digits or 15 characters if you include the periods.

The IP breaks down your data into smaller PDUs known as packets if using TCP or datagrams when using UDP. First, each bundle receives a label (header) that indicates the destination and source. Then, the data gets transferred through routers or gateways, containing information lists for different IP addresses and their respective domains across the Internet. The information moves from one gateway to the next until one of them eventually recognizes the package's destination.

What are TCP and UDP: Which is Better for Video Conferencing?

TCP flow controls are dependable but can’t recover missing data fast enough to be useful for real-time video conferences. After all, speed is essential. That’s why UPD is far better suited for video conferencing.

TCP vs. UDP Applications: When Is One Method Better Than the Other?

Here is a breakdown of the situations where one protocol is best used over the other.

  • If you’re heavily using multimedia or Voice Over Internet Protocol (VoIP), you should use UDP.
  • It would be best if you used TCP sockets when both the client and server send packets independently at the same time. This choice will result in an occasional delay, but it's a minor inconvenience.
  • You should UCP when both the client and server send packets separately, but random delays aren’t acceptable. For instance, online multiplayer games.
  • Bottom line, if you value reliability over speed, go with TCP. The TCP protocol guarantees that the destination receives the information precisely as it was sent. You must contend with its speed issues and the occasional retry due to a connection refusal. But if you want speed and don't care about the precise nature of the received data or missing packets, go with UDP.
  • If you're concerned about Internet security, you're better off using TCP. For example, you send request packets to a server if you're using TCP to access a web page. The server then responds by sending more data packets, each labeled with the sender and recipient information, and an expectation that it will be acknowledged. Packets get checked for corruption and tracked for completeness. If there are any errors or missing acknowledgments, the server is prompted to resend the packet.
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About the Author

John TerraJohn Terra

John Terra lives in Nashua, New Hampshire and has been writing freelance since 1986. Besides his volume of work in the gaming industry, he has written articles for Inc.Magazine and Computer Shopper, as well as software reviews for ZDNet. More recently, he has done extensive work as a professional blogger. His hobbies include running, gaming, and consuming craft beers. His refrigerator is Wi-Fi compliant.

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