How the Internet Says “Hello”: Understanding the TCP 3-Way Handshake

Every time you open a website, send a message, or make a video call — your computer says “hello” to another computer on the internet.

But how does this greeting work?

It happens through something called the TCP 3-Way Handshake — a small but powerful process that helps establish a secure and reliable connection between two machines.

What is TCP?

TCP (Transmission Control Protocol) is one of the main protocols of the internet.
Its job is to:

• Make sure data is sent and received correctly

• Handle packet loss

• Maintain order

• And ensure a reliable connection

Before data is transferred, TCP needs to establish a connection between client and server — this is where the 3-way handshake comes in.

What is the TCP 3-Way Handshake?

The TCP 3-way handshake is the process of establishing a connection between two computers over a network.

It’s called “3-way” because it involves three steps:

1. SYN – Client says: “Hey, I want to connect”

2. SYN-ACK – Server replies: “Sure, I’m ready. You ready?”

3. ACK – Client confirms: “Yep, let’s go!”

Only after this handshake is complete, data can be safely exchanged.

Why is the Handshake Important?

• ✅ Ensures both sides are ready before data transfer

• ✅ Allows devices to exchange initial info (like sequence numbers)

• ✅ Helps in avoiding data loss or duplication

• ✅ Sets up a reliable connection before any real data is sent

How TCP Makes the Connection Reliable

🔢 1. Sequence Numbers

• Every byte of data has a unique sequence number

• Helps receiver know the order of packets

✅ 2. Acknowledgements (ACKs)

• When receiver gets a packet, it sends back an ACK with the next expected sequence number

• Ensures sender knows the data arrived correctly

🔄 3. Retransmission

• If ACK is not received, TCP retransmits the data