XMLHttpRequest object receives call and sent it to server. Server retrieves data and sends XML or JSON data back to HMLHttpRequest callback function and data is shown to user on browser. UpdatePanel allows rendering partial page. You can refresh important parts of the page instead of refreshing whole page. UpdateProgress control shows the progress for all partial-page updates on the page. You can use an UpdatePanel control for every UpdateProgress control. ScriptManager control in one page. It registers ajax library scripts for that page. It also creates proxies for asynchronous web service call. ScriptManager control in one page but the page can have multiple ScriptManagerProxy controls. If you have the ScriptManager in master page which will go across all pages, you cannot add another ScriptManager to underlying pages, instead ScriptManagerProxy control would be added to those underlying pages otherwise the page would show error. RIA is browser dependent or require browser plugin or a virtual machine to deliver user application. readyState is a function to be called when the readyState property changes. It holds the status of the XMLHttpRequest. real-time applications include security authentications which can be applied for the AJAX web applications on the server side and client side as well. XML in AJAX is least used whereas the JSON is the most used data format for the exchange of information across different sources. AJAX also provides the feature of fetching resources using Fetch API of XMLHTTPRequest object. HTML_AJAX.replace() and HTML_AJAX.append() in AJAX.Following are the functions :