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  • July 5, 2026

Difference between TCP and UDP Explained

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Industrial Networking · Ethernet · TCP · UDP · Protocols

TCP and UDP: 4 Fatal Mistakes Engineers Make When Choosing a Protocol

Both ride on the same IP network, yet TCP and UDP behave like two completely different philosophies of communication. This guide explains TCP and UDP in plain terms, including a video walkthrough and a live packet overhead calculator.

Connection Oriented vs Connectionless Reliability vs Speed Industrial Protocol Examples Live Packet Overhead Calculator

Two Very Different Philosophies of Communication

TCP and UDP are both transport layer protocols that ride on top of IP, but they take opposite approaches to getting data from one point to another. TCP treats delivery like registered mail, confirming every step, resending anything lost, and guaranteeing the correct order. UDP treats delivery like dropping a postcard in the mail, sending it and moving on, with no guarantee it ever arrives.

This distinction matters just as much in industrial networks as it does on the wider internet, and it sits right alongside decisions like subnet and VLAN segmentation when designing a reliable plant network.

4 Fatal Mistakes Engineers Make Choosing Between TCP and UDP

1
Assuming UDP is always faster in practiceUDP has lower overhead per packet, but if an application built on UDP has to implement its own retry logic, the real world speed advantage can shrink considerably.
2
Using TCP where retransmission delay itself is unacceptableTCP's automatic retransmission is a strength for file transfer but can introduce unacceptable delay for hard real time control loops that need the newest value, not a resend of an old one.
3
Ignoring that some industrial protocols use both togetherProtocols such as EtherNet/IP commonly use TCP for configuration and explicit messaging, while using UDP for the time critical, cyclic implicit data itself.
4
Forgetting UDP has no built in retransmission at allIf an application needs guaranteed delivery over UDP, that logic has to be built into the application itself, since UDP will not do it automatically.
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TCP and UDP Side by Side

🔵 TCP

Establishes a connection through a three way handshake before sending data, confirming each segment and resending anything lost.

Priority: reliability and correct order over raw speed.

Connection oriented
🟢 UDP

Sends data immediately without establishing a connection first, and does not wait for confirmation or resend anything automatically.

Priority: speed and low overhead over guaranteed delivery.

Connectionless
🟠 Three Way Handshake

The SYN, SYN ACK, ACK sequence TCP uses to establish a session before any actual data is exchanged.

Only used by: TCP, never by UDP.

TCP exclusive mechanism
🟣 Application Layer Retries

When an application built on UDP needs reliability, it must implement its own retry and acknowledgment logic, since UDP will not do this itself.

Common in: real time protocols that need reliability without full TCP overhead.

Custom, application specific

Header Overhead: TCP vs UDP

Minimum Header Size Comparison (Bytes)
UDP header 8 bytesTCP header (minimum) 20 bytesTCP header (with common options) Up to 60 bytes
Both headers ride on top of a 20 byte IP header, so a small UDP packet can be lighter overall than the equivalent TCP packet, especially once TCP's handshake and acknowledgment traffic is counted too. Every Byte of Overhead Matters at High Message Rates
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Watch: TCP vs UDP Comparison

This animated video compares both protocols side by side.

TCP vs UDP Core Differences

FeatureTCPUDP
Connection typeConnection orientedConnectionless
ReliabilityGuaranteed, with retransmissionNot guaranteed
OrderingData arrives in orderNo ordering guarantee
Typical useWeb pages, email, file transferStreaming, DNS, real time control

Where Each Protocol Is Typically Used

🌐
Web Browsing (HTTP)

TCP ensures every part of a webpage loads correctly and in order.

✉
Email (SMTP)

Reliable delivery matters more than speed for message transfer.

📹
Video Streaming and VoIP

UDP tolerates minor loss to keep latency low for live audio and video.

🔍
DNS Lookups

Small, fast UDP queries suit the quick request and response pattern.

🏭
Modbus TCP and SCADA Polling

TCP provides reliable delivery for configuration and supervisory traffic.

⚙
Real Time Industrial Control

Time critical cyclic data often rides on UDP for minimal latency.

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Choosing Between TCP and UDP Correctly

✅ Do
  • Choose TCP when guaranteed, ordered delivery matters most: such as configuration data or file transfer.
  • Choose UDP when the newest data matters more than a resend of old data: such as real time control values.
  • Check exactly what your industrial protocol actually uses: many use both protocols for different message types.
  • Test timeout and retry behavior explicitly: when building reliability into a UDP based application.
⚠ Don't
  • Don't assume UDP guarantees any delivery at all: lost packets are simply lost unless the application handles it.
  • Don't use TCP where its retransmission delay is itself the problem: in tightly timed control loops.
  • Don't ignore firewall and port implications: each protocol's traffic is filtered separately by most firewalls.
  • Don't forget UDP checksum can be optional in IPv4: so corrupted data can occasionally pass through undetected.

Packet Overhead Calculator

Enter your payload size to compare total packet size and overhead percentage for TCP versus UDP.

📦
Packet Overhead Comparison
Payload size to total packet size and overhead percentage
example 100
bytes
✔ Result
TCP total packet
UDP total packet

Quick FAQs: TCP and UDP

Why is UDP used for DNS but TCP for HTTP?
DNS queries are small and simple, so a fast, connectionless UDP exchange works well, and a failed query can just be retried quickly. HTTP typically transfers larger, multi part content where guaranteed, ordered delivery genuinely matters.
Does UDP have any reliability features at all?
UDP includes an optional checksum for basic error detection, but it has no acknowledgment, retransmission, or ordering mechanism. Any reliability beyond that must be built into the application itself.
Can a single application use both protocols?
Yes, this is common in industrial protocols, where TCP handles configuration and less time sensitive messaging while UDP carries the time critical, cyclic data.
Why is TCP generally considered slower than UDP?
TCP's handshake, acknowledgments, and retransmission logic add both processing overhead and potential delay, all in service of guaranteeing reliable, ordered delivery that UDP does not attempt to provide.
Which industrial protocols use TCP versus UDP?
Modbus TCP runs entirely over TCP, while protocols like EtherNet/IP commonly use TCP for explicit messaging and configuration and UDP for real time, cyclic implicit data exchange.
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External References

What we learn today

  • TCP and UDP take opposite approaches, TCP guarantees reliable, ordered delivery, while UDP prioritizes speed and low overhead.
  • TCP uses a three way handshake and automatic retransmission, while UDP sends data immediately with no built in reliability.
  • Many industrial protocols use both together, TCP for configuration and UDP for time critical, cyclic control data.
  • Choosing between them depends on whether guaranteed delivery or minimal latency matters more for that specific data.
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