TCP
Transmission Control Protocol
Übertragungssteuerungsprotokoll
TCP is the protocol that ensures reliable, ordered data transmission over the otherwise unreliable Internet Protocol (IP). It guarantees that all data packets arrive completely and in the correct order — the basis for the web, e-mail and most applications. Together they form the TCP/IP stack.
History & facts. TCP builds on Internet Protocol (IP) and complements it with connection setup (the well-known three-way handshake), acknowledgements, retransmission of lost packets and order assurance. This reliability has its price in overhead but is indispensable for most applications. Security-relevant are, among other things, attacks that abuse the connection setup (for instance for overload) as well as the fact that TCP itself brings no encryption — a higher layer provides that.
Outlook & recommendation. For practice it is important: which TCP connections a system establishes is a central signal in network observation and forensics — unusual destinations or ports can indicate control traffic (C2) or data outflow. Since TCP is unencrypted, confidentiality must be ensured by an overlying encryption. Understanding TCP connection states is the basis of any well-founded network analysis.