What is TCP and why it is needed?

TCP stands for Transmission Control Protocol.
TCP is used to send data safely and reliably over the internet.
It makes sure data reaches the destination correctly and in order.

Problems TCP is designed to solve

Without TCP:

i) Data can be lost

ii) Data can arrive in the wrong order

ii) Sender may not know if data was received

TCP solves these problems by using rules and checks.

What is the TCP 3-Way Handshake?

The 3-Way Handshake is the process TCP uses to start a connection.
It ensures both sides are ready to communicate.

Think of it like saying:

i) “Can I talk?”

ii) “Yes, you can.”

iii) “Okay, let’s talk.”

Step-by-step: SYN, SYN-ACK, ACK

ii) SYN
Client sends a SYN message to request a connection.

ii) SYN-ACK
Server replies with SYN-ACK to accept the request.

iii) ACK
Client sends ACK to confirm.
Connection is established.

How data transfer works in TCP

After connection setup:

i) Data is sent in small packets

ii) Each packet has a sequence number

ii) Receiver sends acknowledgements (ACKs)

This helps TCP track data properly.

How TCP ensures reliability

TCP ensures:

i) Reliability: Resends lost data

ii) Order: Arranges data correctly

iii) Correctness: Uses acknowledgements

If a packet is lost, TCP sends it again.

How a TCP connection is closed

TCP closes the connection gracefully using FIN and ACK messages.
Both sides agree before closing the connection.