Webcasting is a combination of push and smart-pull technologies that lets users subscribe to individual Web pages or entire Web sites. It also allows for the broadcast delivery of multimedia information. Subscriptions and Multicast Subscriptions are the simplest method for monitoring changes to Web pages. Once registered, IE 4.0 will periodically check the pages for updates, notify the user when updates have occurred, and optionally download the updated pages for offline viewing. This process may be refined further in the released version of IE 4.0.
Subscriptions are useful when a user wants a particular set of Web pages kept up to date.
One disadvantage is that only known URLs or pages linked to those URLs can be monitored. Another disadvantage is that there is no way of knowing when or how often a Web author will update pages. Updates may go undetected for long periods or an unnecessary amount of overhead may be used checking for updates more frequently than necessary. While the smart-pull technologies in IE 4.0 will satisfy the needs of many users, sometimes servers truly need to push information to clients. IE 4.0 supports multicast and other true push technologies through an open architecture that provides hooks for third-party extensions.