Introduction
The TCP 3-Way Handshake is a fundamental process that establishes a reliable connection between two devices over a TCP/IP network. It involves three steps: SYN (Synchronize), SYN-ACK (Synchronize-Acknowledge), and ACK (Acknowledge). During the handshake, the client and server exchange initial sequence numbers and confirm the connection establishment.
What is TCP 3-Way Handshake?
The TCP 3-way handshake is a three-step process used to establish a connection between a client and a server before data transmission begins. It ensures that both devices are ready to communicate and agree on initial sequence numbers for the data exchange. The handshake is designed to synchronize the sequence numbers and other parameters, ensuring a reliable connection.
How does the TCP 3-Way Handshake work?
Let’s break down each step of the handshake in detail:
Step 1: SYN (Synchronize)
The client initiates the connection by sending a TCP segment with the SYN flag set to 1. This segment includes an initial sequence number (ISN) chosen by the client. The sequence number is a random value that helps track the order of data packets.
The purpose of this step is to inform the server that the client wants to establish a connection and to synchronize sequence numbers.
Step 2: SYN-ACK (Synchronize-Acknowledge)
Upon receiving the SYN segment, the server responds with its own TCP segment. This segment has both the SYN and ACK flags set to 1.
The server acknowledges the client’s SYN by sending an acknowledgment number, which is the client’s initial sequence number incremented by 1.
The server also includes its own initial sequence number for the client to use.
This step confirms that the server has received the client’s request and is willing to establish a connection.
Step 3: ACK (Acknowledge)
Finally, the client sends an acknowledgment back to the server. This segment has the ACK flag set to 1.
The acknowledgment number is the server’s initial sequence number incremented by 1.
At this point, the connection is established, and both devices can begin exchanging data.
Why is the TCP 3-Way handshake Important?
The TCP 3-way handshake serves several critical purposes in network communication:
Connection Establishment: It ensures that both the client and server are ready to communicate and agree on the initial sequence numbers for data transmission.
Reliability: By synchronizing sequence numbers, TCP ensures that data packets are delivered in the correct order and that no packets are lost or duplicated.
Security: The handshake helps prevent unauthorized or malicious connections by ensuring that both parties actively participate in the connection setup.
Flow Control: The handshake allows both devices to agree on parameters like window size, which controls the amount of data that can be sent before an acknowledgment is required.
Conclusion
The TCP 3-Way Handshake is a critical mechanism for establishing a secure connection between a client and a server over a TCP/IP network. It consists of three important steps: the client initiates the connection by sending an SYN packet, the server responds with a SYN-ACK message to acknowledge the client’s request and synchronize sequence numbers, and the client sends an ACK packet to complete the connection. This handshake ensures that both sides are in sync and prepared for dependable data transmission, making it an essential mechanism for stable and secure communication in TCP/IP networks.