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MBone--The Internet's Multicast Backbone


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Introduction to IP Multicast



A Brief History of IP Multicast



The Pros of IP Multicast



The Cons of IP Multicast



Multicast Applications



MBone--The Internet's Multicast Backbone




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Developing IP Multicast Networks, Volume I

From: Developing IP Multicast Networks, Volume I
Author: Beau Williamson
Publisher: Cisco Press (53)
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MBone—The Internet's Multicast Backbone

The Internet's Multicast Backbone (MBone) is the small subset of Internet routers and hosts that are interconnected and capable of forwarding IP multicast traffic.


Note that I said “small subset,” which is to say that IP multicast traffic does not flow to every point in the Internet (yet). Newcomers to IP multicasting often mistakenly think that if they are connected to the Internet they can receive IP multicast traffic. They believe that by just turning on IP multicast routing on their Internet gateway router or by adding some special application to their PC, they can receive MBone multimedia sessions via their dialup Internet service provider. Unfortunately, this is not the case, as you will learn in the following sections.

The next few sections describe various MBone session examples, a history of the MBone, and the MBone architecture of today and tomorrow.

MBone Sessions

One of the most popular sessions on the MBone is the audio/video multicast of NASA's shuttle missions. Other interesting and sometimes rather bizarre multimedia content is often broadcast over the MBone. For example, individuals have set up pet-cams to broadcast video of their pets. On one occasion, an engineer set up a cat-cam at home and kept the workstation at his office tuned in to this video multicast so he could monitor the cat's recovery from its recent surgery.

On another occasion, someone broadcast the live CNN feed of the O. J. Simpson verdict. This multimedia multicast had over 350 members tuned in at one point. Other media events have been multicast over the MBone. In 1994, a Rolling Stones concert was multicast over the MBone from the DEC Systems Research Center. The interesting thing was that about a half-hour before the concert began, the rock group Severe Tire Damage (several members of which were Internet engineers) began transmitting audio and video of their band performing live music. The band timed their show so that they finished as the Rolling Stones concert was beginning, thereby “opening” for the Rolling Stones via the MBone.

Besides the popular NASA shuttle missions and the occasional rock concert, sessions from various conventions and seminars are frequently multicast over the MBone. During a period when I was unable to travel (while I was recovering from minor knee surgery), I tuned in to the Internet Engineering Task Force (IETF) audio and video multicast from my home by way of my Cisco 1600 router and ISDN line that connects me to Cisco's corporate network. This allowed me to keep up with some of the key IETF sessions (which just happened to have to do with IP multicasting) that I was interested in attending.

These sorts of events have been largely responsible for the growing demand for MBone connectivity by more and more Internet users. Although some of the examples that I have given are more for fun than anything else (would you believe that at one time someone was multicasting video of several different lava lamps), commercial and private multicasting over the MBone is rapidly becoming part of the new Internet experience.

History of the MBone

In the early 1990s, several members of the research community complained to the Defense Advanced Research Projects Agency (DARPA)—the governing body of the Internet at that time—that the Internet had become a production network and was therefore no longer available for research and experimentation with new network technologies. As a result, the U.S. government formed the DARPA Testbed Network (DARTNet) to give the researchers a playground network on which they could test and evaluate new tools and technologies without affecting the production Internet.

DARTNet was initially composed of T1 lines connecting various sites including Xerox PARC, Lawrence Berkley Labs, SRI, ISI, BBN, MIT, and the University of Delaware. These sites used Sun SPARCstations running routed as the unicast routing daemon as well as mrouted as the DVMRP multicast routing daemon. Therefore, DARTNet had native IP multicast support between all sites. Weekly audio conferences between researchers located at the various DARTNet sites around the United States were soon normal practice.

In early 1992, the IETF made plans to hold their next meeting in March in San Diego, California. Unfortunately, one of the D