io, like MPEG-1, MPEG-2, and MPEG-4. It uses XML to store metadata and can be attached to timecodes in order to tag particular events, or, for example, to synchronize lyrics to a song. MPEG-21-Today, many elements are involved in building an infrastruc- ture for the delivery and consumption of multimedia content. However, there is no big picture to describe how these elements relate to each other. MPEG-21 was created to provide a framework for the all-electronic cre- ation, production, delivery, and trade of content. Within the framework, we can use the other MPEG standards, where appropriate. The basic architec- tural concept in MPEG-21 is the digital item. Digital items are structured digital objects, including a standard representation and identification, as well as metadata. Basically, a digital item is a combination of resources (e.g., videos, audio tracks, images), metadata (such as MPEG-7 descriptors), and structure (describing the relationship between resources). MPEG-1, MPEG-2, and MPEG-4 are primarily concerned with the coding of audio/ visual content, whereas MPEG-7 is concerned with providing descriptions of mul- Multimedia Networking Requirements timedia content, and MPEG-21 enables content to be created, produced, delivered, and traded entirely electronically. Faster compression techniques using fractal geometry and artificial intelli- gence are being developed and could theoretically achieve compression ratios of 2,500:1. Implemented in silicon, this would enable full-screen, NTSC-quality video that could be deliverable not only over a LAN but also over the traditional PSTN as well as wireless networks. Until better compression schemes are developed, we have standardized on MPEG-2, which takes advantage of how the eye perceives color variations and motion. Inside each frame, an MPEG-2 encoder records just enough detail to make it look like nothing is missing. The encoder also compares adjacent frames and records only the sections of the picture that have moved or changed. If only a small section of