TCP stands for Transmission Control Protocol. It is a transport layer protocol.
The main category is for general information about the protocol. Sites about implementations of the standard should go to the Implementations subcategory.
This category is for documents about TCP specifically. Material about TCP/IP should be submitted to Computers/Internet/Protocols.
Both production and experimental TCP implementations and sets of patches to other implementations.
It may be hard to distinguish between an implementation and a piece of research; when in doubt, submit to this category.
If possible, HTTP links to HTML documents are preferable.