I'm studying the 802.1.X authentication guidelines and the DIAMETER protcol as successor of RADIUS but i can't figure out what are the main difference between pure 802.1X Port-Based Authentication and DIAMETER. What are their differences?
802.1X provides client-side/front-end port-level authentication (between suplicant and authenticator). RADIUS and Diameter provide back-end authentication (between authenticator and authentication server).
Essentially, they are different things. 802.1X is an application while RADIUS/Diameter can potentially provide authentication for various applications.
Note that Diameter is no acronym like RADIUS, but a play of words - the diameter is twice the radius.