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.
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
TCP and UDP Side by Side
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.
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.
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.
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.
Header Overhead: TCP vs UDP
Watch: TCP vs UDP Comparison
This animated video compares both protocols side by side.
TCP vs UDP Core Differences
| Feature | TCP | UDP |
|---|---|---|
| Connection type | Connection oriented | Connectionless |
| Reliability | Guaranteed, with retransmission | Not guaranteed |
| Ordering | Data arrives in order | No ordering guarantee |
| Typical use | Web pages, email, file transfer | Streaming, DNS, real time control |
Where Each Protocol Is Typically Used
TCP ensures every part of a webpage loads correctly and in order.
Reliable delivery matters more than speed for message transfer.
UDP tolerates minor loss to keep latency low for live audio and video.
Small, fast UDP queries suit the quick request and response pattern.
TCP provides reliable delivery for configuration and supervisory traffic.
Time critical cyclic data often rides on UDP for minimal latency.
Choosing Between TCP and UDP Correctly
- 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 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.
Quick FAQs: TCP and UDP
External References
- Wikipedia: Transmission Control Protocol
- Wikipedia: User Datagram Protocol
- RFC 793: Transmission Control Protocol Specification
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.