Transport A, Transport B

The Advanced Television Enhancement Forum is a non-profit coalition formed to promote html-based enhanced television standards and deployment. The foundation for ATVEF content is existing web standards.

Triggers to activate content may arrive via text channel 2 of line 21. The content cache can be loaded by broadcast data if available, or upon demand over the Internet. The "TV:" URL is added to reference television channels and may be used anywhere that a URL may reference an image.

Content Level 1.0 requires support for HTML 4.0, CSS 1, ECMAScript and DOM 0. (However, some receivers claiming ATVEF compliance do not support all features of HTML 4.0) (ECMAScript + DOM 0 = JavaScript 1.1) Receivers are required to provide 1MB for content caching and 1KB for session cookies. Six MIME types must be supported: text/html (HTML 4.0), text/plain, text/css (CSS1 only), image/png, image/jpg (no progressive encoding) and audio/basic.

Possible directions for future content levels include Dynamic HTML, synchronized multimedia, 3-D rendering, tuning, XML, Java, and higher-quality audio among others.

(Related ETVCookBook pages: ATFEF Transport A - ATVEF Transport B - Localize ATVEF)

Advanced Television Enhancement Forum

Nomenclature used in the ATVEF specification to denote the means by which the enhanced content is delivered to the set-top-box. Transport A denotes delivery of the enhanced content via the Internet, either via a traditional modem or broadband connection. Transport B denotes delivery of enhanced content via a data broadcast. Even though the number of users with broadband connections to the Internet is growing, it is presumed that servers will not be able to handle the potential millions of simultaneous clicks on popular enhanced content for popular shows. Instead, by sending the content in the data-broadcast to every user cache in advance of the trigger, no excessive demands are placed upon the server. Enhanced content can use a mix of both transports; Transport A for a wide array of less popular content that would exceed the data-broadcast bandwidth and cache size, and Transport B for a smaller amount (1MB in ATVEF) of highly popular content. In either case, triggers are presumed to arrive via the broadcast. (Related ETVCookBook pages: ATVEF Transport A - ATVEF Transport B)