TCP vs. UDP: Protocols Comparison

When transmitting data over a network, two major protocols come into play: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Both TCP and UDP are transport-layer protocols responsible for managing bidirectional data transmission between devices on a network, with TCP emphasizing reliability and UDP prioritizing speed. They play a key role in determining how smoothly you can stream a movie on Netflix, how likely you're to experience lag during online gaming, and how secure your emails are. While both protocols manage how your data is transferred, they each work differently.

This guide breaks down their key differences, advantages, and ideal use cases to help you choose the right protocol for your needs.

What are TCP and UDP?

A network application must decide on how it wants to transmit its data. That decision typically comes down to a simple question: Do I want to send it reliably but slower, or unreliably but quicker? Both methods have their benefits and drawbacks.

TCP and UDP are two different protocols for transferring data over the internet that tell how data should be formatted and sent over a network.

TCP (Transmission Control Protocol) creates a secure communication line to ensure the reliable transmission of all data. Once a message is sent, the receipt is verified to ensure all the data was transferred and no packets were lost along the way.

UDP (User Datagram Protocol) doesn't establish a reliable connection when sending data. Instead, it sends data without confirming the receipt or checking for errors. This runs the small risk that some data may be lost during transmission, but it does this so that it can be faster and send out larger volumes of data with minimal delay.

In short, TCP guarantees delivery at the cost of speed, while UDP prioritizes speed at the risk of occasional packet loss. Which one you choose depends on whether your application values accuracy (TCP) or performance (UDP).

Transmission Control Protocol (TCP)

The first thing to understand is that when we send data, for example, a file, the entire file isn't sent all at once. It's sent in lots of different packets of data, which TCP calls segments. The receiving computer collects these segments, assembles them, and outputs the file.

But what happens if some of the data gets lost along the way? The receiver will not be able to reassemble the data completely, and the file will be corrupted.

This is why we need a way to reliably send data, and this is exactly what TCP does.

TCP is the most widely chosen option for transmitting data, because it can reliably send and receive data.

Suppose there's a temporary network blip and some segments are lost along the way. In that case, TCP can recover them, so the user experience wouldn't be compromised by half-loaded websites or corrupted documents.

Functionality

TCP is a slower communication protocol than UDP, but it's more reliable thanks to features like sequencing, flow control, and error checking. Since every received packet is acknowledged by the server, it becomes extremely difficult for information to go missing. 

You might have noticed this behaviour on instant messaging apps like WhatsApp or iMessage, where message order and delivery records are strictly maintained.

For instance, after the sender transmits the first packet to the server, it receives it and sends a confirmation back to the sender (called an acknowledgement). Once the sender receives the confirmation, it sends the next packet. This continues until all packets are successfully delivered.

Now, let's say a network error occurs and the second packet isn't delivered, the server still sends a response indicating that it only received (and acknowledged) the first packet. The device understands that the second packet failed, and resends it.

It's important to note that TCP doesn't always send packets in chronological order. Packets can be mixed up in transit, but the receiver reassembles them in the correct sequence before processing the data.

Because of these features, TCP is mainly used for data security and in applications requiring integrity and reliability. Common examples include web browsing (HTTP/HTTPS), email (SMTP), and file transfers (FTP).

User Datagram Protocol

A more lax form of communication is the UDP (User Datagram Protocol). It lacks TCP's error handling, sequencing, and reliability. UDP is a communication protocol for time-sensitive tasks like online gaming or media streaming. It simply sends data to the server without waiting for an acknowledgement.

So why would we ever consider using UDP if it's so unreliable? While TCP offers strong reliability, it all comes at a price of resources and latency. Conversely, UDP results in faster communication because it doesn't spend time forming a reliable connection with the server before transferring the data.

UDP chunks are technically called datagrams. With UDP, you send a single request, and the server sends all the chunks in rapid succession without verifying their accuracy. Your data arrives as quickly as possible, but it's usually out of order. The server doesn't care about missing chunks or data integrity.

Where UDP becomes useful is in situations that require live, real-time connections. For example, voice calls, video calls, and gaming all need fast, real-time updates. People can handle a small amount of lost voice data because a bit of jitter in a call isn't a big issue.

However, if we start trying to resend voice data, that would introduce latency and make the entire call difficult to hear. UDP is utilized for critical real-time performance-based applications. It's mostly implemented for Remote Procedure Call (RPC) applications, Domain Name System (DNS), and protocols like Dynamic Host Configuration Protocol (DHCP), Trivial File Transfer Protocol (TFTP), Simple Network Management Protocol (SNMP), and more.

How do TCP and UDP work?

To better understand the differences between these protocols, let's compare how to handle the process of sending data across a network.

How TCP works 

TCP is a connection-oriented protocol, which means the participating devices must establish a connection before they can begin to exchange data. This process is governed by a three-way handshake (SYN → SYN-ACK → ACK).

Once the connection is established, TCP ensures reliability through the following steps:

• Sequencing. Every data packet (segment) has a sequence number attached to identify its order.
• Acknowledgement (ACK). The receiver sends an ACK to the sender to confirm successful receipt of the data.
• Error correction. If the sender doesn't receive an ACK within a timeout period, it assumes the packet was lost and retransmits it.
• Reassembly. The receiver uses the sequence numbers to reassemble the data in the correct order, even if packets arrive out of sequence.

This process continues throughout the session, allowing TCP to detect missing data and ensure the entire message eventually gets delivered intact.

How UDP works

UDP skips the connection setup entirely. There's no handshake, no tracking, and no checking before data is sent. UDP transmission is essentially "send-and-forget."

The process is simpler and faster:

• No handshake. The sender just starts transmitting packets (datagrams) directly to the target address.
• No acknowledgement. The receiver accepts incoming datagrams but doesn't send any ACK back to the sender.
• No retransmission. If a datagram is lost in transit, neither the sender nor receiver will automatically know or try to correct it.
• No ordering. Datagrams may arrive out of order, and UDP doesn't rearrange them (it's up to the application to handle this).

The trade-off is deliberate: UDP sacrifices reliability for speed, and in scenarios where latency kills user experience, that's a worthy exchange.

Difference between TCP and UDP

Now, let's take a look at some key differences between TCP and UDP:

Connection management

TCP is a connection-oriented protocol. A sender and receiver must first establish a connection using the TCP three-way handshake before any data can be transmitted. This ensures both parties are ready for data exchange. 

UDP, on the polar end, doesn't require an explicit connection to send data. This reduces overhead but removes any guarantees about delivery.

Reliability

When you send data via TCP, it's guaranteed to arrive at your intended destination without errors. It uses acknowledgements (ACKs) to confirm receipt and will recover and resend data if it's corrupted or lost in transit. 

UDP doesn't guarantee data delivery. Once a datagram is sent, it doesn't check whether it was received, arrived out of order, or retransmitted if it was lost.

Data transmission and ordering

TCP transmits data as a continuous stream, ensuring that packets are received in the same order as they were sent. If packets arrive out of order, TCP will reorder them using their sequence numbers. 

UDP sends datagrams independently without placing any priority on sequencing.  This means that packets can arrive in the wrong order or not arrive at all.

Speed and overhead

UDP is faster than TCP because it has less work to do. TCP introduces additional overhead because of its connection management, flow control, and error-checking mechanisms. Each TCP packet includes a larger header (20 to 60 bytes) due to the information required for these features.  UDP is more lightweight as it features an 8-byte header, which makes it faster.

Flow and congestion control

TCP has a built-in flow and congestion control mechanism. This prevents a sender from overwhelming a receiver or flooding the network with too much data at once. UDP doesn't offer flow or congestion control, as the packets are sent out at a constant rate regardless of whether the network can keep up. If the network is overloaded, the data packets are simply dropped.

What are the applications of TCP and UDP?

TCP and UDP are used in different situations depending on whether an application needs reliability or speed. Here's a quick overview of where each protocol is typically used:

Wrapping up

Choosing between TCP and UDP comes down to what your application needs. If reliability and data integrity matter most, TCP is the right choice. If you prioritize speed, low latency, and can tolerate occasional data loss, UDP is the way to go.

Decodo supports both TCP and UDP across its proxy lineup. This is super important because different applications rely on different transport protocols. Web browsing, logins, API requests, and most scraping operations use TCP, while streaming, gaming traffic, DNS lookups, VoIP calls, and some automation tools often rely on UDP for faster speeds.

This support extends across all Decodo proxy types, including Residential, ISP, Mobile, and Datacenter proxies, giving you consistent performance whether you need reliability, speed, or both.

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