TCP is transmission control protocol. It is a fundamental part of the internet - at layer 4 of the OSI stack - sitting above the Internet Protocols (aka IPv4 and IPv6); In other words it is not application content like web pages (HTML) or Video Streaming - rather it is a transport mechanism for that content. A metaphor would be railway freight cars - the freight car + track is transport without knowing/caring what is inside the freight car. In Mobile Telecoms TCP accounts for 50-55% of the transmitted traffic.