TCP vs UDP: When to Use What, and How TCP Relates to HTTP

Lets first understand why internet need the rules to transport data from one computer to another.

When you open a website an watch some live video or sending a text message to another computer (or we can say client). But the internet have so many problems exists:

• Unreliable (cannot be trustable)

• Distributed

• Congested (full of traffic)

• So many devices connected

To solve this problems, we need some rules which can solve “how to send the data”, “how to receive the data”, “how to know if the data is lost” and “how to identify and recover the lost data”. Those rules are called protocols.

There are two protocols in networking transport:

• TCP - Transmission Control Protocol

• UDP - User Datagram Protocol

Both have some advantage and disadvantage. Let’s deep dive into these protocols.

TCP (Transmission Control Protocol)

TCP is reliable, ordered and works on three way handshake process which is the guaranteed way to send data.

It have following characteristics:

• Trustable

• Less data loss

• Fast data transfer

• Congestion control

• Slightly slower

TCP ensure that:

• Data Arrives

• Data Arrives in correct order

• Lost data can be recovered

• Sender and Receiver should be connected.

UDP (User Datagram Protocol)

UDP is a protocol which is used to send data fast and works based on send and forgot process without an acknowledgement.

It has following characteristics:

• Connectionless

• Unreliable

• Fast

• No delivery or order guarantee

UDP cannot ensures:

• Does the data arrives

• Does the order of data in correct order

• Does not maintain data

• Does not maintain the connection between the sender and receiver

When to use which protocol?

Use TCP, when there is a need of

• no data loss

• order must be preserved

• Accuracy is more important than the speed.

Examples: Email, Website content (HTTP/HTTPS), File downloads, Payments related, Authentications. Messaging.

Use UDP, when there is a need of

• Speed is important more than the accuracy

• Minor data loss can be acceptable

Examples: Online games, Video streaming, Voice calls, Broadcasts.

What is HTTP?

HTTP stands for Hypertext Transfer Protocol. It is an application level protocol. It defines the request and response format, request headers, and methods for the request (GET, PUT, POST, etc.).

It decides what to send (Application Layer) instead of how to send (Transport Layer).

Application Layer:   HTTP
Transport Layer:     TCP / UDP
Network Layer:       IP

Relation between HTTP and TCP?

HTTP uses the TCP to actually transfers the data. Flow when you open a website:

1. When a website is requested, browser create an HTTP request.

2. HTTP gives it to the TCP

3. TCP break it into packets and send them safely

4. Server receives and respond back via TCP

5. Browser receives and rebuilds HTTP response

Conclusion

Mental Model:

• TCP → Safe and efficiently data transfer system

• UDP → Fast data transfer system

• HTTP → Data with some set of rules

The internet does not just send the data, it actually gives a choice to use different type of rules to transfer the data based on the system requirements.