What is a Web Telephony Application?

To telephone callers, a Web telephony application is a voice that answers the telephone and guides them through a hierarchy of menus to complete a task or obtain information. A typical application begins by greeting the caller, presenting a list of items, and directing the caller to select an item. The caller responds by pressing the telephone key that corresponds to the desired item or, optionally, by speaking the selection. This process continues until the caller's needs are met or the caller hangs up.

To a developer, a Web telephony application is a Web site designed to be rendered by the Microsoft Web Telephony Engine (WTE). In most respects, a Web telephony application resembles a "regular" Web site because each consists of a set of HTML pages that use scripting and other Web technologies to provide content to the user. The main difference is that a Web telephony application uses HTML extensions, Telephony Application Programming Interface (TAPI), and extensions to the Internet Explorer Object Model to create a Web site that can be rendered to a caller over a telephone line.

Although a Web telephony application is designed to be accessed by telephone, it is also possible to access any Web telephony application through a graphical Web browser. However, making the same application work well in both media requires additional effort, such as hiding parts of the application's HTML from one medium or the other. A Web telephony application designed to also work well while being accessed through a graphical Web browser is called a dual-access application. For more information, see Dual-access Considerations.

The WTE maintains a list of applications that it can run. An application must be added to the list before the engine can run the application. Adding an application allows the engine to associate the application with a particular telephony service provider (TSP) line attached to the computer. When a call comes on a given line, the WTE starts the application associated with that line. An application can be added to the list either by using the WTE administration tool, or by a third-party setup program or administration application.

All applications must have a home page and, optionally, can have a post-call page. The home page is the first HTML page to which the engine navigates when a call comes on the line with which the application is associated. Authors can use the home page to initialize application variables or perform telephony operations. For example, an application might check the caller ID of the incoming call to decide whether to answer the call, transfer it to another extension, and so on.

The post-call page is an HTML page to which the WTE navigates after the call has ended. It is typically the last page in an application, and allows the application to process data collected from the caller during the course of the call.