# TCP 3-Way Handshake Process

**Transmission Control Protocol (TCP)** provides a secure and reliable connection between two devices using the 3-way handshake process. TCP uses the full-duplex connection to synchronize (SYN) and acknowledge (ACK) each other on both sides. There are three steps for both establishing and closing a connection. They are − SYN, SYN-ACK, and ACK.

![Comparing QUIC and TCP | blabs](https://www.potaroo.net/ispcol/2022-11/quicvtcp-fig1.png align="center")

## **3-Way Handshake Connection Establishment Process**

The following diagram shows how a reliable connection is established using 3-way handshake. It will support communication between a web browser on the client and server sides whenever a user navigates the Internet.

![](https://www.tutorialspoint.com/assets/questions/media/59897/10(a).jpg align="center")

**1\. The client starts the process and sets the SYN flag to 1**

* The client sends the message to the server by setting the SYN flag to 1.
    
* The message contains some other information like sequence numbers(2000), maximum segment size, window size.
    
* A sequence number is a randomly generated 32-bits number.
    
* SYN - It stands for synchronization. It sends the message to the server to synchronize with the received sequence number.
    
* The window size is used for the flow control. It denotes the capacity of the data that can be received.
    
* For example - If the window size is 10000 and the maximum segment size is 1000. Then, the maximum number of data segments that should be transmitted is 10000/1000 = 10.
    

**2\. The server replies with (SYN+ACK)**

* After receiving the synchronization request from the client, the server sends the acknowledgment to the client by setting the ACK flag to 1.
    
* It sends the Acknowledgment number (ACK) to the client which is just 1 greater than the received sequence number from the client. For example - If the sequence number received from the client is 2000 then the acknowledgment sent by the server will be 2001.
    
* It denotes the next sequence expected by the sender.
    
* In addition to this, the server also sends a randomly generated sequence number (suppose 4000 ) and sets the SYN flag to 1.
    
* The server also sends its window size which is the buffer capacity of the server and maximum segment size to the client for flow control.
    
* It is required so that none of the ends need to do the fragmentation of packets.
    

### **3 -Way Handshake Closing Connection Process**

To close a 3-way handshake connection,

* First, the client requests the server to terminate the established connection by sending FIN.
    
* After receiving the client request, the server sends back the FIN and ACK request to the client.
    
* After receiving the FIN + ACK from the server, the client confirms by sending an ACK to the server.
    

![](https://www.tutorialspoint.com/assets/questions/media/59897/10(b).jpg align="center")

### Conclusions:

The TCP 3-Way Handshake is like a polite conversation starter between two computers. Before they exchange any real data, they first greet each other (SYN), acknowledge the greeting (SYN-ACK), and confirm everything is good to go (ACK). This ensures a reliable, secure connection for communication. Likewise, ending the conversation uses a similar back-and-forth to close things gracefully. Understanding this process is essential for anyone diving into how the internet really works under the hood.