TCP vs UDP

TCP vs UDP is one of the most asked Computer Networks interview questions because it checks whether you understand reliability, speed, and transport layer behavior.

What is TCP?

TCP stands for Transmission Control Protocol.

Main features:

• connection oriented
• reliable
• ordered delivery
• error checking
• flow control
• congestion control

What is UDP?

UDP stands for User Datagram Protocol.

Main features:

• connectionless
• faster
• lower overhead
• no guaranteed delivery
• no ordered delivery guarantee

TCP vs UDP Table

| Feature | TCP | UDP | | --- | --- | --- | | Connection type | Connection oriented | Connectionless | | Reliability | Reliable | Not guaranteed | | Speed | Slower | Faster | | Delivery order | Ordered | Not guaranteed | | Overhead | Higher | Lower | | Error recovery | Yes | Minimal |

Where TCP is used

• web browsing
• email
• file transfer
• banking systems

TCP is used when data correctness matters more than speed.

Where UDP is used

• live streaming
• online games
• voice calls
• video calls

UDP is used when low latency matters more than perfect delivery.

Simple Interview Answer

TCP is reliable, ordered, and connection oriented, while UDP is faster, connectionless, and does not guarantee delivery. TCP is preferred when accuracy matters; UDP is preferred when speed and low delay matter.

Why TCP is slower

TCP is slower because it:

• establishes a connection
• acknowledges packets
• retransmits lost packets
• maintains delivery order

Why UDP is faster

UDP is faster because it:

• does not establish a connection
• sends packets with less overhead
• does not wait for acknowledgements

Real-world example

If you are downloading a PDF, TCP is better because you need complete and correct data.

If you are in a live game or video call, UDP is often better because slight packet loss is acceptable but delay feels worse.

Quick Revision Points

• TCP = reliable and connection oriented
• UDP = fast and connectionless
• TCP used for correctness
• UDP used for real-time performance
• TCP has more overhead
• UDP has less overhead

Viva Questions

1. What is TCP?
2. What is UDP?
3. What is the difference between TCP and UDP?
4. Why is TCP reliable?
5. Why is UDP faster?
6. Give one use case of TCP and one of UDP.

Final Tip

In interviews, do not stop at the definition. Always mention one practical use case for each protocol. That makes the answer sound much stronger.