TCP vs. UDP: Understanding the key differences and best use cases

Every time you browse the web, stream a video or send a file, your device uses either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) to transfer data. Most of the time, you don’t have to think about which one is being used—it happens automatically. But some applications, like VPNs, let you choose between the two. 

So how do you know which one is right for your needs? Understanding the differences between TCP vs. UDP can help you make better decisions for speed, reliability, and security. Let’s break down how they work, their strengths and weaknesses, and when to use each one. 

What is TCP vs. UDP?

What is TCP?

TCP is one of the most commonly used protocol suites on the internet and with good reason. It’s nonproprietary, which means it works on almost any network or operating system (OS). TCP is also built into most OSs as a default protocol because it’s an extremely reliable form of data transfer. 

The protocol establishes a connection before sending packets, delivers the packers in the same order they were sent, and ensures they arrive at the destination undamaged. TCP does require more system resources than some protocols, but it’s also highly scalable. That means you can adapt TCP to your system to reduce the strain on your computer or network resources.

What is UDP?

UDP is another communication transfer protocol used to transmit data over networks. It doesn’t require a pre-established connection or perform any error checking past the basic checksum. Even if the checksum returns an error, UDP will not attempt to resend packets. You’ll simply receive the data packets that don’t contain errors. 

The lack of a preestablished connection and advanced error checking make UDP a fast and efficient protocol for time-sensitive transmissions where lag or buffering could impact user activities. Unfortunately, it also means packets are easily corrupted or lost in transit – leaving you open to cyber threats like DDoS attacks. These attacks overwhelm a network with traffic, making it more susceptible to cyber threats.

TCP vs. UDP: How do they work?

How TCP works

TCP is a connection-orientated protocol. This means before any data is even exchanged, a secure connection must be created between the sender and receiver to ensure both parties are ready for the transfer. Once completed, TCP breaks larger data packets into smaller, more manageable bits, providing sequencing, error checking, and delivery confirmation.

If packets are lost or corrupted during transmission, TCP submits a retransmit request to ensure all data packets arrive in order and complete. It also handles data flow to prevent congestion during transmission. The sender and receiver are disconnected once all data packets are successfully delivered.

The precision used in TCP makes it an excellent protocol for connecting to cloud and file-sharing services, secure email, and other applications where accuracy is more important than speed. 

Applications of TCP

World Wide Web (WWW)

If data packets required to download content online don’t arrive intact the content may not display properly. TCP helps ensure that web pages, images, and prerecorded videos load correctly.

Email

Email services use TCP to create a secure connection to the email server before sending the message. This ensures the sender’s full message is delivered to the correct inbox on the email server. 

File Transfer Protocol (FTP)

When uploading and downloading files to the cloud or file-sharing services, TCP helps ensure each file arrives complete. The protocol also checks for errors and resends packets if necessary, contributing to data accuracy. 

Secure Shell (SSH)

 SSH uses TCP to establish an encrypted connection between the client and server. This allows for reliable and secure network communications, as TCP guarantees data delivery and provides a stable connection that enhances SSH’s existing security features. SSH and TCP pair well for transmitting command data, login credentials, and other secure applications.

How UDP works

UDP provides direct data exchange between the sending and receiving devices without a pre-established connection. It simply uses port numbers to identify applications on the receiving device. No advanced error checking, delivery guarantee, resending of lost packets, or receipt confirmation – data packets undergo a basic error check and are delivered to the receiver. This makes UDP fast and efficient, but not as reliable or secure.

Unlike TCP, however, UDP works for real-time applications like online gaming or video conferencing. Even if datagrams arrive out of order or some are lost, these applications can often adapt by prioritizing the most recent data. For instance, imagine you’re watching a live stream,  the slight glitch UDP may cause is less disruptive than extensive buffering.

Applications of UDP

Voice over Internet Protocol (VoIP) 

VoIP applications leverage UDP to minimize delays, including services like Skype, FaceTime, and WhatsApp. This ensures voice chats are smoother, with slight quality reductions as opposed to the potential lag TCP may cause.

Live video or audio streaming

TCP isn’t compatible with live video or audio streaming, but UDP is. UDP’s straightforward approach makes it easier to distribute multimedia content or send network commands to multiple receivers simultaneously. This means the lightweight protocol is perfect for radio and news broadcasting.

Online gaming

Fast-paced, online multi-player games with real-time upgrades and live chat use UDP because it doesn’t require as much bandwidth or processing power. That means gamers experience lower latency and smoother connections.

Domain Name System (DNS) 

Speed and efficiency make UDP better for small, less extensive queries with quick responses. Looking up a domain name (e.g. www.example.com) is a direct request for a specific site, so the advanced checks performed by TCP aren’t as crucial as they are for open browsing. 

Simple Network Management Protocol (SNMP: 

 UDP isn’t concerned with packet order and it’s not connection-oriented, so it’s fast and relatively reliable for rapid communication – which is necessary for managing network devices.

TCP vs. UDP: Key differences explained

Choosing whether to use TCP vs. UDP is about understanding what matters most in a given situation. Do you need reliability, or is speed your priority?

Some applications can’t afford lost data packets, while others function just fine even if some information goes missing. This is where TCP and UDP differ most. Below, we break down how they compare in terms of speed, reliability, and efficiency so you can see when to use each one.

Speed comparison: Which is faster?

UDP is faster because it doesn’t require as much processing power or bandwidth as TCP. This is due to its lack of advanced error-checking and immediate connection to the receiving device. The quick implementation of UDP makes it suitable for live-streaming applications and other instances where real-time communications are necessary.

Data integrity: Which is more reliable?

TCP is more reliable because it performs advanced error-checking, ensures data packet order, integrity, and arrival, and requests a retransmittal of any damaged or lost packets. The timeliness and accuracy make TCP well-suited to any application where data integrity must be precisely maintained. For example, TCP and internet protocol (IP) are frequently used together to determine how online data is exchanged over a network.

Use cases: When to use TCP vs. UDP

Choosing between TCP vs. UDP depends on what matters more—accuracy or speed. TCP ensures data integrity, while UDP prioritizes fast delivery, even if some packets get lost.

When to use TCP

TCP is the right choice when data loss isn’t an option and every packet must arrive intact and in order. It’s best for:

• Long, uninterrupted data transfers: When missing packets would break functionality.
• Situations requiring error correction: When packet loss could cause corruption or failure.
• Reliable, congestion-managed connections: When the network must adjust to varying speeds without dropping packets.
• Multi-step processes that require confirmation: When both sender and receiver need verification before continuing communication.

When to use UDP

UDP is better when low latency is more important than perfect accuracy. It’s ideal for:

• Time-sensitive transmissions: When small delays would ruin the experience.
• One-way data flow: When retransmitting lost packets isn’t necessary.
• High-volume, low-priority traffic: When the goal is speed over reliability.
• Scenarios where the latest data matters most: When older packets can be ignored in favor of new ones.

TCP vs. UDP in VPN Protocols

VPNs rely on TCP and UDP to transmit encrypted data, but the choice of protocol affects speed, reliability, and how well the VPN performs in different network conditions.

• UDP is the default choice for most VPNs because it’s faster and more efficient. It minimizes latency, making it ideal for streaming, gaming, and browsing.
• TCP is slower due to its error-checking and retransmission features, but it provides a more stable connection. This makes it useful when bypassing firewalls or on networks that block or throttle UDP traffic (such as work and school networks).

Some VPNs only offer OpenVPN (TCP/UDP), but others, like ExpressVPN, go beyond OpenVPN to deliver faster, more secure, and more reliable options.

Which protocol does ExpressVPN use?

ExpressVPN supports multiple encryption protocols, including IKEv2, L2TP, OpenVPN, and its own custom Lightway protocol. 

ExpressVPN’s OpenVPN implementation has support for both TCP and UDP, meaning you can switch between them depending on your needs. TCP is used for reliable connections where it’s crucial that all data packets arrive intact and in order, making it ideal for tasks that require high data accuracy like downloading files or loading detailed web pages. UDP, on the other hand, is favored for activities where speed is more important than precision, such as streaming or gaming.

ExpressVPN offers its own Lightway protocol. In addition to running on the UDP protocol, Lightway also supports TCP, which can be slower than UDP but connects better on certain networks. This allows Lightway to be used in a wide range of scenarios.

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