ASP.NET AJAX controls overview
The ASP.NET AJAX controls enable you to create rich client behavior with little or no client script, such as partial-page updating (refreshing selected parts of the page instead of refreshing the whole page with a postback) and displaying update progress during asynchronous postbacks. Asynchronous partial-page updates avoid the overhead of full-page postbacks.
ScriptManager control Manages client script for AJAX-enabled ASP.NET web pages.
ScriptManagerProxy control Enables nested components such as content pages and user controls to add script and service references to pages when a ScriptManager control is already defined in a parent element.
Timer control Performs postbacks at defined intervals. If you use the Timer control with an UpdatePanel control, you can enable partial-page updates at a defined interval. You can also use the Timer control to post the whole page.
UpdatePanel control Enables you to build rich, client-centric web applications. By using UpdatePanel controls, you can perform a partial-page update.
UpdateProgress control Provides status information about partial-page updates in UpdatePanel controls.
All of the ASP.NET AJAX controls require specific settings in a web.config file in order to function correctly. If you try to work with one of these controls, and your website doesn't contain the required web.config file, errors appear in the Design view of the page where the control would have appeared. In Design view, if you click a control that is in that state, Microsoft Expression Web will give you the option to create a new web.config file or update your existing web.config file.
In order for your ASP.NET AJAX controls to display correctly from your web server, your web server must support the .NET Framework version 3.5 or a later version.