TCP Connection Establishment and Termination: The 3-Way and 4-Way Handshakes

Understand the three-way handshake for TCP connection establishment and the four-way handshake for connection termination. This guide explains how these processes ensure reliable data transmission using TCP, a connection-oriented protocol.

TCP Connection Establishment and Termination: The 3-Way and 4-Way Handshakes

Introduction to TCP

TCP (Transmission Control Protocol) is a connection-oriented protocol—meaning it establishes a dedicated connection between two devices before sending data. This approach ensures reliable, ordered data transmission, making TCP ideal for applications requiring data integrity (web browsing, email, file transfer). TCP operates at the transport layer of the network model, working with IP (Internet Protocol) for addressing and routing data packets.

TCP Connection Establishment: The 3-Way Handshake

A TCP connection begins with a three-way handshake to ensure both the client and server are ready to communicate:

Steps:

  1. SYN (Synchronize): The client sends a SYN segment to the server, proposing a connection and including its initial sequence number.
  2. SYN-ACK (Synchronize-Acknowledge): The server responds with a SYN-ACK segment, acknowledging the client's request and providing its own sequence number.
  3. ACK (Acknowledge): The client sends an ACK segment, acknowledging the server's response. The connection is now established.

(A simple diagram showing the three-way handshake would be beneficial here.)

TCP Connection Termination: The 4-Way Handshake

Closing a TCP connection uses a four-way handshake to ensure a graceful shutdown, preventing data loss:

Steps:

  1. FIN (Finish): The client sends a FIN segment, requesting to close its side of the connection.
  2. ACK: The server acknowledges the client's FIN.
  3. FIN: The server sends a FIN segment, requesting to close its side of the connection.
  4. ACK: The client acknowledges the server's FIN. The connection is now closed.

(A simple diagram showing the four-way handshake would be beneficial here.)

Conclusion

The three-way handshake for connection establishment and the four-way handshake for termination are fundamental to how TCP ensures reliable data transmission. Understanding these processes helps to understand how TCP handles data integrity and manages connections across networks.