What is the request lifecycle for asynchronous (ajax) ASP.NET method calls?

What is the timeline for application / processing events for an asynchronous request generated by a page method in a web form? Looking for a canonical answer or resource.

Note. This is a request for information about how ASP.NET AJAX handles incoming requests made to web services that are exposed to the client script as described here under "Calling Static Methods on an ASP.NET Web Page". This should not be confused with the page lifecycle. It should also be noted that [WebMethod]

both [ScriptMethod]

are ASP.NET AJAX functions, not XML Web services, as one might infer from reading certain MSDN documentation, examples of which can be found here and here .