In the VS2008 Microsoft include basic and frequently used AJAX server extender in its toolbox under AJAX Extensions tab. It contains both Server side and Client Side code to give Ajax like behaviors.
The server control they included are
1) Script Manager
2) Scrip Manager Proxy
3) Update Panel
4) Update Progress
Script manager must be included before any Ajax Server control or any AJAX client script are include (ie) Partial-page rendering, which enables regions on the page to be independently refreshed without a post back. It manages AJAX Extensions script libraries and script files, partial-page rendering, and client proxy class generation for Web and application services.
SCRIPT MANAGER PROXY
In some situation you have to use more than one Script manager, but per page you can use only one Script Manager at that time you can use Script Manage Proxy.
By using Asp.Net update panel we can update only that particular region instead of refreshing the entire page. This is referred to as performing a partial-page update.
The UpdateProgress control enables you to provide feedback about the progress of partial-page rendering.
The Timer control is to postbacks the page at defined intervals. If we use the Timer control with an UpdatePanel control, we can enable partial-page updates at a defined interval.