Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

What is webcasting? To see a real working example, point your Web browser at eWeek's webcast site (http://www.eweek.com/webcast). You can choose from a list of news items and hear streaming audio and video presentations. A player is required, either RealPlayer from RealNetworks or Microsoft's Windows Media Player. Depending on the bandwidth available, you may see an actual moving image, rather than a series of changing still images. The audio is usually pretty good, though, and certainly beats reading text on the screen, and live interviews give you the emotion of the person speaking.

The technology behind webcasting is streaming audio and video. That means RTP (Real-time Transport Protocol) over UDP (User Datagram Protocol) in most cases. These technologies are outlined under "Multimedia" along with related technologies.

Webcasting is also called "netcasting," "Internet broadcasting," or "data broadcasting," although webcasting is more associated with streaming video and audio. Data broadcasting is more about sending news, stock quotes, and related information to subscribers using "push" techniques. Push is the opposite of "pull," which is what you do when you access Web site. With push, Web sites automatically send you information. E-mail is a push techniques that people use to send other people information, sometimes without the recipient asking for it. Think of push in terms of low-bandwidth data broadcasting (stocks, news, sports headlines). Think of webcasting as full multimedia broadcasting.

The ultimate webcasting technology is multicasting, which is based on special Internet protocols that deliver content along efficient paths from the sender to multiple receivers. The idea is to send packets only along paths that lead to subscribers of the multicast information, thus cutting down on traffic. See "Multicasting."

The webcasting community even has its own organization called the International Webcasting Association. Its Web site is listed on the related entries page. The IWA serves companies that are active in the delivery of multimedia (audio and video) services to consumers or business customers via the Net and other networks. Another association is DiMA (Digital Media Association).

One thing to keep in mind is the U.S. government's Digital Millennium Copyright Act. Special provisions were added for webcasting in 1998 that cover licensing of Internet radio stations, which is essentially audio webcasting. A good source for legal information on this type of webcasting is a set of articles by Sean Flinn at ZDNet Music. The Web site is listed on the related entries page.

Microsoft has done a lot of work to integrate webcasting into its Windows product line. It defines webcasting as a generic term that refers to any automated delivery of personalized and up-to-date information. Webcasting is made possible through the Windows Active Desktop and Active Channels. The Active Desktop provides a common and customizable user interface for organizing webcast sites and information. A typical Active Desktop might contain a weather chart that is updated constantly. Users subscribe to sites that support Active Desktop. Subscription and updates may be handled by CDF (Channel Definition Format), which provides a format that publishers can use to define elements such as media channels, types of information, schedules, and so on. This information helps users subscribe to and manage content.