(without using the XMLHttpRequest object of the browser!) which gets the data from an HttpHandler [as you can see in your web.config: <add path="Telerik.ReportViewer.axd" verb="*" type="Telerik.ReportViewer.WebForms.HttpHandler, Telerik.ReportViewer.WebForms, Version=126.96.36.199, Culture=neutral, PublicKeyToken=a9d7983dfcc261be" validate="true"/>]. the report viewer gets the data on the server side only one time with the first request, since you can disconnect from your database (in my case sql server) and still browse through the reports. so i suppose the report data or the pre-generated content - depending what telerik decided to use - is sittin' in the session state on the server and waitin' ... or it's temporarily written as a file on the server harddisk and waitin' there (what i don't think).
telerik, feel free to correct me.
anyways, some pages (like wikipedia.org) consider this approach as ajax, too.
ReportViewer.prototype.NavigateToPage = function(pageIndex)
var input = document.getElementById(this.currentPageID);
input.value = pageIndex;
var url = this.baseReportUrl + "&PageIndex=" + pageIndex;
var reportFrame = document.getElementById(this.reportFrameID);
reportFrame.src = url;