Diameter
Read this article about the history of Diameter and why it was developed. What preceded Diameter as an authentication protocol? While you do not need to understand how Diameter authenticates, you should have a general idea of its authentication process.
6.Diameter Client API
6.3.Startsession API
StartSession API is used for the session establishment between the connected
DIAMETER client and DIAMETER server which deals with the creation sessions and
filling details.