What is the three-way handshake in TCP?

The TCP three-way handshake is a process used to establish a reliable connection between two devices over a network.

Lazaro

Nov 16, 2024

TCP (Transmission Control Protocol) is a fundamental protocol for reliable data transmission over networks.

Connection Establishment

The three-way handshake consists of three steps:

SYN (Synchronize):
- The client initiates the connection by sending a SYN packet to the server.
- This packet contains a random sequence number chosen by the client.
SYN-ACK (Synchronize-Acknowledge):
- Upon receiving the SYN, the server responds with a SYN-ACK packet.
- This packet acknowledges the client's sequence number and includes the server's own random sequence number.
ACK (Acknowledge):
- The client sends an ACK packet back to the server.
- This packet confirms receipt of the server's sequence number.

After these three steps, the connection is established and data transfer can begin.

Purpose and Benefits

The three-way handshake serves several important purposes:

Synchronization: It allows both parties to agree on initial sequence numbers for tracking packets.
Reliability: It ensures that both sides are ready and able to communicate.
Security: It helps prevent unauthorized access by requiring acknowledgment from both parties.

Key Features

Sequence Numbers: Each side generates a random sequence number to track packets and ensure correct ordering.
Flags: TCP uses specific flags (SYN, ACK) in the packet headers to indicate the purpose of each message.
Resource Allocation: The server allocates necessary resources for the connection during this process.

Connection Termination

A similar process, often called a four-way handshake, is used to gracefully close a TCP connection. This involves exchanging FIN (finish) and ACK packets between the client and server.

The three-way handshake is a fundamental part of TCP's reliability and connection-oriented nature, ensuring that data transmission begins on a stable and synchronized foundation.