Differences between TCP and UDP: Complete Guide to Network Protocols

In the world of computer networks, there are two protocols that reign at the transport layer: TCP and UDP. Although both are used to send data between connected devices, their approaches are very different. Therefore, understanding the details of what makes each one unique is an advantage for any user, developer, or system administrator looking for an efficient, secure connection tailored to their needs.

While TCP ensures that data arrives intact and in order, UDP compromises on speed and efficiency at the expense of reliability. This crucial difference determines when and where it's best to use one or the other. Throughout this comprehensive guide, we'll explore the features, uses, advantages, disadvantages, inner workings, and real-world use cases of both protocols.

What is TCP?

TCP, or Transmission Control Protocol, is a connection-oriented transport protocol. Before any data is sent, a reliable connection is established between the devices involved by means of a so-called Three-Way Handshake which ensures that both sides are prepared to communicate.

This process includes three packet exchanges:

• The client sends a packet with the SYN (synchronize) flag.
• The server responds with a SYN-ACK (synchronize-acknowledge) packet.
• Finally, the client returns an ACK to confirm the connection.

Once the connection is established, all data is delivered in an orderly and error-free manner. TCP is responsible for:

• Number each package.
• Verify correct reception with acknowledgments (ACK).
• Resend those that are lost or arrive damaged.

Thanks to these measures, TCP is ideal for applications that require precision and reliability, such as emails, web browsing, file transfers or connections SSH. If you want to know more about how network servers work, you can visit our article on NTP servers.

Key Features of TCP

• Total reliability: With TCP, data will always arrive, even if some parts must be retransmitted multiple times.
• Delivery in order: Segment numbering ensures that everything is reassembled as shipped.
• Duplicate Detection: If a packet arrives repeated, the protocol automatically discards it.
• Flow control: TCP adapts to the receiver load to avoid overloads. This capability is similar to what is considered fix ping spikes in online games.
• Congestion control: Adjusts sending speed based on network conditions.
• Multiplexing Capability: Allows sending and receiving data simultaneously (Full-Duplex mode).
• Advanced algorithms: Protocols such as TCP Reno, Tahoe, Vegas, or Cubic help optimize data transfer on modern networks.

TCP header and its structure

The TCP header is at least 20 bytes long and may include optional fields that increase its size. It contains:

• Port of origin and port of destination.
• Sequence number and ACK number.
• Flags like SYN, ACK, FIN, RST, URG.
• Reception window size (which defines how much the receiver can receive).
• Checksum to verify errors.

This richness ensures robust connections, but also adds complexity and additional resource consumption.

What is UDP?

UDP, or User Datagram Protocol, is a connectionless protocol characterized by its speed and simplicity. There's no pre-handshake, no follow-up, no exhaustive checks. Each datagram is sent separately, as if they were independent messages.

UDP is ideal for applications where low latency is more important than reliability, as video games online, live video streaming, VoIP or DNS services.

Because of its minimal header of only 8 bytes, UDP can transmit more useful data in each packet. This makes it a lightweight and efficient solution for fast communications.

Key features of UDP

Without connection: No pre-link is established, so each datagram is sent separately.

Does not guarantee delivery: Packages can be lost, duplicated, or arrive out of order.

No flow control or congestion: The receiver receives everything as is, without the ability to regulate.

Minimum latency: Fewer steps and a lightweight header allow data to be sent in record time.

Ideal for multicast or broadcast: You can transmit to multiple recipients without creating individual connections like TCP.

UDP Header Structure

UDP only requires 8 bytes per datagram, making it incredibly efficient. Its fields are:

• Port of origin.
• Port of destination.
• Total length of the datagram.
• Checksum for basic error control.

There is no numbering or acknowledgments, so the protocol does not interfere with transmission speed.

Fundamental differences between TCP and UDP

• Connection-oriented: TCP establishes a pre-channel, UDP does not.
• Guaranteed delivery: TCP guarantees that everything arrives, UDP does not.
• Order: TCP reorders packets, UDP delivers them as they fall.
• Header: TCP uses a minimum of 20 bytes, UDP only 8.
• Speed: UDP is much faster.
• Reliability: TCP is the most reliable.
• Broadcast/Multicast: UDP allows it, TCP does not.

When to choose TCP or UDP?

The choice should be made according to the type of application and the priority objectives:

Ideal cases for TCP

• Web navegation: HTTP, HTTPS.
• Emails: SMTP, POP3, IMAP.
• File transfer: FTP, SFTP.
• secure connections: SSH.
• Instant messaging where every message counts.

Ideal cases for UDP

• Online games: Speed ​​is more essential than losing a package.
• Streaming video or audio: Real-time services such as YouTube or Twitch.
• VoIP: Voice calls or video calls.
• DNS and DHCP: Quick queries that don't require confirmations.
• Broadcast or multicast services.

Proven performance differences

Studies such as those of Top10VPN They measured download speeds, efficiency, and data usage across both protocols. According to their tests with NordVPN and ExpressVPN:

• UDP was up to 94% faster than TCP when connecting between distant locations such as the US and Australia.
• TCP can consume up to 20% more data than UDP.

This is because TCP requires more auxiliary communications, such as ACK packets, and retransmits if there are errors. In this sense, learning how to properly configure TCP VPN servers can make a difference in terms of connection efficiency.

What role do TCP and UDP play in VPNs?

Virtual private networks allow you to choose between TCP and UDP, and depending on the use, one option may be better than the other.

OpenVPN, for example, supports both protocols. It is recommended to use UDP for:

• Streaming
• Online games
• VoIP connections

While TCP is ideal for:

• Secure emails
• Web navegation
• Delicate transfers

By default, NordVPN uses UDP, but you can switch to TCP if connection or security issues are detected.

Latest protocols and evolution

To overcome limitations of TCP or UDP, new protocols have emerged such as:

• QUIC: It uses UDP but with advantages such as multiplexing, mandatory encryption (TLS 1.3), and lower latency. It is used in HTTP/3.
• SCTP: Combination of UDP and TCP features with multiple flows between points.
• DCCP: UDP variant with congestion control, ideal for multimedia.
• WireGuard: VPN modern that only uses UDP for its speed and ease of reestablishing connections (VPN roaming).

TCP and UDP continue to dominate due to their universal compatibility and mass adoption. Each has its strengths: TCP provides complete reliability when sending information, while UDP focuses on efficiency in situations where every millisecond counts. Knowing how to differentiate between them and applying them correctly makes a difference in the performance and stability of any connection or application on the network.