What is TCP 3-Way Handshake?
The TCP 3-Way Handshake is a three-step process that is used to make a secured and reliable connection between a client and server before the actual transmission of data. After these three steps and the establishment of the connection between them, data transfer takes place.
A secured and reliable connection of TCP is only possible due to this 3-way handshake process.
TCP 3-Way Handshake Process
The following steps are involved in establishing a connection using the 3-Way Handshake Process.
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. The final acknowledgment from the client (ACK)
- After receiving the SYN from the server, the client sets the ACK flag to 1.
- It sends the expected sequence number (2001) by the server which is equal to the Acknowledgment number received from the server.
- It also sends the Acknowledgment number which is one greater than the sequence number received from the server which denotes the next expected sequence number.
The above three processes are called the TCP 3-Way Handshake. After these three steps, the connection is established between the two. The data can be transmitted between them after the connection establishment.
