How TCP works | TCP Three Way Handshake Explained | What is Connection Establishment

The three-way handshake is a process used by TCP to establish a connection between a client and a server. It ensures that both devices agree to establish a reliable communication channel before data transfer begins. The three steps involved in the TCP three-way handshake are.

SYN: The client initiates the handshake by sending a SYN (synchronize) packet to the server. The SYN packet contains a randomly generated sequence number (SYN number) to identify the data segments being sent. The client also chooses an initial sequence number (ISN) that will be used for subsequent data transmission.

SYN-ACK: Upon receiving the SYN packet, the server responds by sending a SYN-ACK (synchronize-acknowledge) packet back to the client. The SYN-ACK packet contains an acknowledgment number that is one more than the client's ISN, indicating the next sequence number the server expects to receive. The server also generates its own ISN for subsequent data transmission.

ACK: Finally, the client acknowledges the server's SYN-ACK packet by sending an ACK (acknowledge) packet. The ACK packet includes the acknowledgment number, which is one more than the server's ISN, indicating the next sequence number the client expects to receive. At this point, the connection is established, and both the client and server can begin exchanging data using the agreed-upon sequence numbers.

The purpose of the three-way handshake is to establish synchronization and agreement between the client and server regarding the sequence numbers used for data transmission. It ensures that both devices are ready to send and receive data on a reliable and ordered connection. This handshake process helps prevent confusion and data loss that could occur if the devices have different initial sequence numbers or are not synchronized properly.