The organization that sets many of the standards for the Internet - the Internet Engineering Task Force - http://www.ietf.org
Internetwork Design Guide - A good set of tutorials from Cisco.
Whatis.com - A very good dictionary of computer-related terms.
To get copies of RFCs: http://www.rfc-editor.org/
One relatively minor note: Wide area networks often apply a trailer as well as a header, similar to local area networks.