The Mbone: Can't You Hear It Knocking?

Two songs into the Dallas stop in the Rolling Stones' ""Voodoo Lounge'' concert tour earlier last month, Mick Jagger paid an unusual tribute: ""I want to say a special welcome to everyone that's climbed into the Internet tonight, and has got into the MBone, and I hope it doesn't all collapse!'' The crowd went wild.

The crowd out there in cyberspace, that is. In addition to the 50,000 people at the Dallas Cotton Bowl, the concert was carried to some 200 workstations around the world that were hooked to the Internet, where Stones fans from Osaka to Oslo gathered around computer screens to watch a bit of rock-and-roll history in the making.

The 20 minutes of the Stones concert carried on the Internet brought worldwide recognition to one of the Net's more intriguing outposts -- the MBone, short for Multicast Backbone. The brainchild of a small group of computer scientists, the MBone is a subset of the Internet capable of ""multicasting.'' That is, rather than ""unicasting'' one packet to one destination, the network copies each packet of information from the source for delivery to each destination that has requested it.

Unlike traditional broadcast methods, the MBone is entirely interactive. It carries audio, video and a ""white board'' feature that enables participants to share text, images and sketches. (""Do larger lips require more bandwidth?'' quipped one fan on the white board during the Stones concert.) The MBone started as ""a wild idea'' in March 1992, when Allison Mankin, a researcher involved with the Internet Engineering Task Force, was too far along in her pregnancy to travel to San Diego for an IETF meeting. Mankin suggested extending an experimental multicasting technology so that an audio feed of the meeting could be transmitted to her and others who couldn't attend. Steve Casner, a computer researcher at the University of Southern California Information Sciences Institute, and Steve Deering, a computer scientist at Xerox Corp.'s Palo Alto Research Center who developed the idea of multicasting, spent weeks setting up a multicast facility.

Since then, more than 100 events have been sent over the MBone. Scientific symposiums and workshops are now commonplace. NASA regularly broadcasts its space-shuttle missions over the MBone. Bill Clinton, Al Gore and the Swedish prime minister have all appeared on it. To say nothing of Severe Tire Damage and Deth Specula, two lesser known rock bands who beat Mick to the MBone.

Connecting to the MBone isn't easy. It requires a powerful workstation and a very high-speed communications line. For that reason, most MBone use is confined to universities and computer-research labs. But for those who do have connections, broadcasts over the MBone are free. And connecting to the MBone allows audio and video to be carried without installing dedicated transmission lines.

The MBone is far from perfect, and its inventors still consider it experimental. For one thing, it's a notorious glutton of bandwidth, or network capacity. Broadcasts sent over the MBone can slow down the entire Internet. And the video and audio quality isn't particularly good. Mick Jagger appeared as a tiny screen inset, and the concert more closely resembled a slide show than a full-motion video. And listening to the Stones on the MBone was like listening to Neil Armstrong speak from the moon.

The Stones concert may have brought the MBone a lot of attention, but its creators have their sights set on more serious applications. Van Jacobson, a scientist at Lawrence Berkeley Laboratory who developed much of the MBone's software, points to a recent surgeons' conference at the University College London. A hundred or so doctors in London and Sweden watched as a surgeon in San Francisco performed a complex liver opera-tion. As he worked, viewers asked questions about the procedure. Ph.D. candidates defend their dissertations to far-flung committees over the MBone. And the Minnesota state government is looking into running town meetings over the MBone during the winter months, when a rural population has difficulty getting to a central meeting place.

In the meantime, the MBone's most pressing need is for more bandwidth, which is already on its way for the Internet at large. When that happens, in the next five or 10 years, say optimists like Deering, Jacobson and Casner, the MBone will lose its novelty and become an entrenched aspect of the Internet. It's just a shot away.