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What every developer should know about TCP

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The Transmission Control Protocol is one of the main protocols of the Internet protocol suite.

Handshake

Before a client can start sending data to a server, it needs to perform a handshake for TCP and another one for TLS.

TCP uses a three-way handshake to create a new connection.

The sender picks a randomly generated sequence number “x” and sends a SYN packet to the receiver.
The receiver increments “x,” chooses a randomly generated sequence number “y” and sends back a SYN/ACK packet.
The sender increments both sequence numbers and replies with an ACK packet and the first bytes of application data.

Flow control is a backoff mechanism implemented to prevent the sender from overwhelming the receiver.

The receiver stores incoming TCP packets waiting to be processed by the application into a receive buffer.