Web applications work on the underlying Http protocol and Http is stateless by nature. It uses the Request – Response pattern between the client and the server, to process the logic at the server and present the information in HTML to the client browser. In the case of long running applications, it would be helpful to the end user to see some status on the browser when the application is processing some complex logic on the server. This article shows a convenient way of showing status information in such cases. The sample demos show how to achieve this in .NET 2.0 using the CallBack infrastructure provided in the framework and also a means to achieve the same effect using the .NET 1.1 framework.

ref: http://www.c-sharpcorner.com/UploadFile/deepakvraghavan/AjaxProgressBars09082006171908PM/AjaxProgressBars.aspx