Think of a situation where two people are talking on the phone line. One person speaks, but the other does not reply. Some words get cut off, some sentences repeat, noise in between, and some never arrive at all. After sometime, the connection breaks down completely.
This is exactly what happens on the internet if the data is sent without rules or protocols.
Networks are not always reliable.
Sometimes networks are noisy.
Data packets can be lost, duplicated, or arrive out of order.
So now the big question is:
“How do computers communicate reliably over the network?”
This is where TCP and UDP come into the picture. They are designed to handle data transmission in different ways, depending on the situation and the level of reliability required.
Two Protocols, Two Different Goals
Let’s look at two simple scenarios:
A user wants to deliver a package to a friend, so he chooses a courier service. He hands over the parcel and receives a tracking number. The courier confirms when the package is picked up and when it is delivered. Everything is delivered in the correct order. If something is lost along the way, it is resent. The delivery might take a little longer, but it is guaranteed.
This is exactly how TCP works.
Imagine a live radio broadcast. The broadcaster sends the message only once. There is no confirmation that every listener received it. If something is missed or lost due to noise or interference, it is gone forever. Nothing is resent, and the broadcast keeps moving forward.
This is how UDP works.
Both approaches solve communication problems but with different goals.
TCP focuses on reliability, ordering, loss detection, retransmission, and correctness, while UDP focuses on speed and real-time delivery.
So, a natural question arises:
“How do TCP and UDP actually send data differently under the hood?”
How do TCP and UDP actually send data differently under the hood?
TCP: “Connection First, Data Later”
Before sending any data, TCP first establishes a connection using the 3-way handshake:
SYN – “Am I audible?”
SYN-ACK – “Yes, I can hear you.”
ACK – “Let’s start.”
Only after this handshake does, TCP begins, sending data and reliability by:
Numbering each packets.
Sending data in ordered format.
Waits for acknowledgements.
Retransmits lost packets.
Controlling speed to avoid congestion.
This makes TCP slow but more reliable.
UDP: “Send and Move on”
UDP is connectionless, there is no handshake, no setup, and no confirmation.
When application sends data using UDP:
The data is sent immediately.
There is no check for the receiver status, is ready than send the data.
There are no acknowledgements.
Lost packets are not retransmitted.
Packets may arrive out of order.
This makes UDP fast but less reliable.
But as developers, we should ask:
“When should we use TCP, and when should we use UDP in real applications?”
Let’s find out.
When should we use TCP, and when should we use UDP in real applications?
Now that we understand how TCP and UDP work, the next question is when should we use each of them in real applications?
When to Use TCP?
Use TCP when:
Data must be delivered in the correct order.
Data must not be lost.
Acknowledgements are required after successful transmission.
Accuracy and reliability are critical.
In these cases, TCP ensures reliable communication.
Real-world examples:
Web browsing
Email
File downloads
APIs
When to Use UDP?
Use UDP when:
Speed matters more than accuracy.
Small data loss is acceptable.
Real-time delivery is more important than perfect reliability.
In these cases, UDP sacrifices reliability for speed.
Real-world examples:
Video streaming
Online gaming
Live broadcasts
Voice and video calls
Now, we are understood both the TCP and UDP, but another question comes to mind:
“What is HTTP, why do we use it, and how is it related to TCP?”
This is where the concept of HTTP comes into the picture.
TCP and HTTP?
We can think like:
TCP ensures data arrives correctly.
HTTP defines what that data represents.
Specifically, HTTP defines:
How requests and responses are structured?
Methods like GET, POST, PUT, DELETE?
Status codes such as 200, 404, 500 and many more.
HTTP does not send data by itself. It relies on lower-level transport protocols to move data across the network, this is where TCP comes in picture.
The Relationship Between TCP and HTTP
HTTP runs on top of TCP.
A simple way to think about this:
TCP makes sure the data arrives safely and in the correct order.
HTTP explains what that data represents and how it should be interpreted.
Why HTTP Does Not Replace TCP?
HTTP cannot replace TCP because it does not handle:
Orderning of packets
Connection management
Reliable delivery
Retransmission
Acknowledgement
Those responsibilities belong entirely to TCP.
HTTP and TCP are not competitors.
You can think like HTTP is a wrapper around TCP.
They are partners, each solving a different part of the communication.
Big Picture
Each protocol has a clear responsibility, and none of them exist by accident.