TCP-Protocol

The Transmission Control Protocol (TCP) is one of the most important protocols within the TCP/IP protocol suite and is used when reliable, connection-oriented data transmission is required. Just as two people first check whether they are listening and have understood what was said before an intense conversation, two computers behave the same way when communicating over TCP.

Before any data can be transferred, the two communication partners establish a connection – the so-called three-way handshake. The first computer sends a SYN packet (a kind of "Hello, I want to talk"), after which the other sends back a SYN-ACK packet ("I heard you and I want to talk too"). Finally, the first computer confirms receipt with an ACK packet – only then does the actual data transfer begin.

What's special about 
TCP is that it guarantees that data arrives at the receiver in the correct order and without any loss. If a packet is lost, it is resent. TCP therefore independently takes care of error correction, flow control, and congestion avoidance – all without the user even noticing. It is used, for example, in websites, emails, or file transfers – wherever reliability is paramount.