ASP.NET AJAX is not just a JavaScript wrapper library of the “Ajax” technology. It spans both the client and server. Server-side controls let you use Ajax even without using a single JavaScript code. Client-side library provides a lot more functionalities beside Ajax. 

1.  ASP.NET AJAX Architecture

– Client Side –

The client-side library is called “Microsoft Ajax Library” or  “Core Library“.

• Type System
• Components: DOM, JSON, Network, Services
• Application

– Server Side –

The server-side Ajax support is called “ASP.NET AJAX Server Extensions“.

• Server Controls
• Web Services Bridge
• Application Services Bridge

2. Client-side Framework

– Type System –

The “Type System” of the “Microsoft Ajax Library” is to introduce object-oriented programming concepts (classes, inheritance, event-handling …)  to JavaScript. This is the foundation layer for other types in the library.

– Components –

Built on top of the “Type System“, “Components” provides resuable modules and controls.

– Application –

The “Application” layer provides  an event-driven programming model that you can use to work with DOM or Components. In an AJAX-enabled page, an “Application” object manages the client lifecycle of a web page. It hosts all client components.

3.  Server-side Framework

– Server Controls –

ASP.NET provides server controls to let you create an Ajax-enabled page even without using JavaScript.

• ScriptManager
• UpdatePanel

– Web Services Bridge –

You can create a gateway to call external web services from client-side script.

–  Application Services Bridge –

You can create an interface to access some of the application services (Authentication and Profile) from client-side script.

4. Microsoft Ajax Library

The Microsoft Ajax Library is organized in client classes contained in namespaces. The root namespace is “Sys“.

• {Global}: Extension to JavaScript itself; All shared members and types; Array, Boolean, Date, Error, Object, Number, String and Type
• Sys: Root name space of AJAX library for base runtime classes; Application, Component and Debug
• Sys.Net: Classes for Network layer; Asynchronous service calls  between client-side JavaScript and server-side Web services; WebServiceProxy, WebRequest, WebRequestManager, WebServiceError, and XMLHttpExecutor
• Sys.Serialization: Classes for JSON(JavaScript Object Notation) serialization/deserialization; JavaScriptSerializer
• Sys.Services: Classes for accessing ASP.NET services (authentication, profile)
• Sys.UI: Classes for Components and DOM; Behavior, Control, DomElement, and DomEvent
• Sys.WebForms: Classes related to partial page update; PageRequestManager