TCP vs UDP: Key Differences Explained for Beginners

TCP vs UDP: Key Differences Explained for Beginners

TCP vs UDP is one of the first topics every networking beginner learns. Both protocols send data across a network, but they handle it differently. TCP provides reliable, ordered delivery, while UDP has less built-in overhead and does not guarantee delivery.

In this guide, you will learn how each protocol works, the main differences, and when to use each one.

TCP vs UDP in One Minute

TCP: Provides reliable data delivery and keeps data in the correct order.
UDP: Sends data without guaranteeing delivery or order, making it useful for applications that need low delay.
Both: Operate at the Transport Layer (Layer 4) of the TCP/IP networking process.

Not sure what the Transport Layer means? Read our guide on OSI Model vs. TCP/IP Model.

What Is TCP?

TCP stands for Transmission Control Protocol. It is a connection-oriented protocol, which means devices establish a connection before exchanging data.

TCP provides several important features:

Reliable delivery: Lost data can be retransmitted.
Correct order: Data is delivered to the application in the correct sequence.
Error detection: TCP detects corrupted data.
Flow control: Helps prevent the sender from overwhelming the receiver.
Congestion control: Adjusts data transmission to help manage network congestion.

These features make TCP suitable for applications where accurate and complete data delivery is important.

The TCP Three-Way Handshake

Before normal data transfer begins, TCP establishes a connection using three steps:

SYN: The client requests a connection.
SYN-ACK: The server acknowledges the request and responds.
ACK: The client acknowledges the response.

After the handshake, the devices can exchange data.

What Is UDP?

UDP stands for User Datagram Protocol. It is a connectionless protocol, meaning it does not establish a connection through a handshake before sending data.

UDP does not guarantee that packets will arrive, arrive in order, or be retransmitted if lost. Applications can implement their own recovery mechanisms when needed.

UDP has a smaller header and fewer built-in reliability mechanisms than TCP. This can reduce overhead and help applications achieve low latency.

UDP is commonly used when waiting for retransmission could cause unwanted delays, such as during voice calls, online gaming, and live communication.

TCP vs UDP: Comparison Table

Feature	TCP	UDP
Connection setup	Yes	No
Handshake	Yes	No
Delivery guarantee	Yes	No
Packet order	Kept	Not kept
Retransmission	Yes	No
Header size	20+ bytes	8 bytes
Overhead	Higher	Lower
Used for	Web, email, files	Calls, gaming, DNS

Important: UDP is not always faster than TCP in every situation. Its main advantage is lower protocol overhead and the ability to send data without waiting for TCP’s built-in acknowledgments and retransmissions.

A Simple Example

Think of TCP as sending a registered letter. The delivery process helps confirm receipt, and missing data can be sent again.

UDP is more like making a live announcement. You send the message immediately, but you do not automatically know whether everyone received it.

This is why TCP is useful for reliable data transfer, while UDP can be useful for real-time applications.

When Should You Use TCP?

TCP is commonly used when reliable and ordered data delivery is important.

Examples include:

Web browsing: HTTP/1.1 and HTTP/2 commonly use TCP.
Secure websites: HTTPS using HTTP/1.1 or HTTP/2 commonly runs over TCP.
Email: Protocols such as SMTP and IMAP use TCP.
File transfers: FTP and SFTP use TCP.
Remote access: SSH uses TCP.

TCP helps ensure that the data received by the application is complete and in the correct order.

Note: HTTP/3 is different. It uses QUIC, a transport protocol built on UDP, rather than TCP.

When Should You Use UDP?

UDP is often chosen when low latency and minimal protocol overhead are important.

Examples include:

Voice and video calls: Help reduce delays during real-time communication.
Online gaming: Supports time-sensitive updates.
DNS queries: Many standard DNS queries use UDP.
DHCP: Uses UDP to help devices obtain IP configuration.
Live streaming: Some streaming and real-time communication technologies use UDP.

For example, during a video call, a missing packet might cause a brief glitch. Waiting for that packet to be retransmitted could create a noticeable delay.

However, UDP itself does not guarantee low latency or prevent packet loss. The network conditions and application design also matter.

Common TCP and UDP Ports

Service	Port	Protocol
HTTP	80	TCP
HTTPS	443	TCP, UDP
SSH	22	TCP
DNS	53	UDP, TCP
DHCP	67, 68	UDP

Note: HTTP/3 uses QUIC over UDP, typically on port 443. DNS uses TCP as well as UDP, including for zone transfers and certain other situations—not only when a response is too large.

How to View TCP and UDP Information on Windows

You can use the Windows Command Prompt to view network connection information.

Open Command Prompt.
Enter the following command and press Enter:

netstat -ano

The output displays TCP connections and UDP endpoints, along with local and remote addresses where applicable. The -o option also displays the process ID (PID), which can help you identify the application associated with a connection.

TCP entries may show states such as ESTABLISHED or LISTENING. UDP entries do not use the same connection states because UDP is connectionless.

Frequently Asked Questions

Is TCP better than UDP?

Neither protocol is always better. TCP is designed for reliable, ordered delivery, while UDP is useful when low delay and less protocol overhead are priorities. The right choice depends on the application.

Why does DNS use UDP?

Many DNS queries use UDP because it has low overhead and works well for typical request-and-response messages. DNS also uses TCP in situations such as zone transfers and when required by the size or handling of a response.

Can a device use TCP and UDP at the same time?

Yes. A computer can use TCP for one application and UDP for another at the same time, such as browsing a website while participating in a voice call.

Are TCP and UDP important for the CCNA exam?

Yes. Understanding TCP and UDP, their differences, common port numbers, and the TCP three-way handshake is useful for networking fundamentals and CCNA preparation.

Conclusion

TCP and UDP both operate at the Transport Layer, but they serve different needs.

TCP provides reliable, ordered delivery with additional protocol mechanisms. UDP has less built-in overhead and does not guarantee delivery or ordering, making it useful for many real-time applications.

Understanding these differences will help you learn networking fundamentals, troubleshoot connections, and understand how applications communicate across networks.

Leave a comment if you have any questions!

TCP vs UDP: Key Differences Explained for Beginners