Years ago, the CCITT started a group of recommendations for individual protocols.
The CCITT is now called the ITU-T, and its data communications recommendations
have not been wildly successful. The best known is probably recommendation X.25,
which still has a large following in some parts of the world. An X.25 package was
available for FreeBSD, but it died for lack of love. If you need it, you’ll need to
invest a lot of work to get it running.