How Multicast IP Travels Along the MBone


How Multicast IP Travels Along the MBone

The MBone (Multicast Backbone) is a high-speed Internet backbone capable of sending live video and audio broadcasts. It's a network of host computers that communicate with one another using a technique called IP (Internet Protocol) Multicast. An MBone multicast begins when a video signal is digitized and compressed so that it can be sent over the Internet. Without compression, the signal would be too large and take too long to deliver.



 


Chapter 40. How Virtual Reality Is Created by VRML

Imagine the Internet as a place where you could walk through three-dimensional worlds, pick up objects, examine them, and go to other Internet locations by flying or walking through doors. Picture home pages that are more than flat, two-dimensional surfaces that you can only read. What if you could be inside them, just like you can walk through a city or a building?

That's the promise of virtual reality (VR) on the Internet. In fact, it's more than just a promiseVR is already here. You'll find many virtual worlds you can explore on the Internet. You can walk through a giant computer, explore bizarre art galleries, visit outer space, go to the sites of what seem like ancient ruins, explore inside the human brain, and much more.

Virtual worlds are created using a computer language called Virtual Reality Modeling Language (VRML). This language instructs computers on how to build 3D geometric objects. Programmers and artists use the language to build complex worlds from these geometric objects. A VRML world is created by an ASCII text file containing VRML language commandsand for greater realism, graphics files can be added to this world as well. Because the virtual world is only an ASCII file, with perhaps a few graphics files, it can be downloaded quickly to your computer from the Internet, although some worlds with many graphics in them can be large.

When a virtual world is created, it is posted on an Internet server. When you want to visit that world, you either type in its URL or click a link to it, just as you do to visit any other location on the World Wide Web. To display the virtual world, you need a program capable of displaying the worldeither a separate virtual reality browser, or more likely, a plug-in player that configures itself to your normal web browser.

The VRML file describing the virtual world downloads to your computer. This can take a few minutes, or well over half an hour, depending on the size of the world and your connection speed. After the file is on your computer, your CPU computes the geometry of the world, based on the VRML commands in the file. Again, depending on the size of the world and the speed of your CPU, this can take only a minute or two, or up to 10 minutes or more. After the world is computed, you can walk through it, fly through it, examine objects, and spin them. You can also visit other virtual worlds or places on the Internet by interacting with the world.

VR on the Internet is being used for far more than just creating virtual worlds people can walk through. For example, it has been used to create views of the brain and of molecules. It has been used by astronomers to show the rotation of molecular gas in a galaxy undergoing active star formation. Finally, as with everything else related to the Internet, VR will be eventually used for things that today none of us can imagine.

Despite all its appeal, one major problem with VR worlds is that they can be very large. Because of that, they can be very slow to load and interact with due to the current limited bandwidth of the Internet. As bandwidth increases, those problems might eventually go away.