Understanding pbx_dundi.c

Hello friends
I am badly in need of your help.
I was trying to understand pbx_dundi.c :open_mouth:
Trying to understand the way( internals ) of how exactly this dundi protocol works function to function
But it is too tough!!!
So can anybody of you have any good informative source regarding it :question:
Then plz let me know.
Thanking you in advance.