But you don't know how they communicate! the "Asynchrone communication procces" it's hidden of you and you want Understand it!
I will show you ;)
+Create a Aspx Page like this:
-each time you write something in inputText the keyup Event raise a callBack to Server .
+ in Aspx Page Code behind:
The Page must implement ICallbackEventHandler to Catch CallBack Event from Client!
- RaiseCallbackEvent: Catch a CallBack event from Client.
- GetCallbackResult: return a CallBack result to Client.
Now your page is Fully Ajax => Run & Test!