MBONE: Multicasting Tomorrow's Internet
Naval Postgraduate School
Reprinted with permission of the authors and IEEE Computer magazine.
"MBONE Provides Audio and Video Across the Internet" Michael R. Macedonia and Donald P. Brutzman IEEE COMPUTER, vol. 27 no. 4, pp. 30-36, April 1994.
The joy of science is in the discovery. In March 1993, our group at the Naval Postgraduate School heard that the Jason Project, an underwater exploration and educational program supported by Woods Hole Oceanographic Institution in Massachusetts, was showing live video over the Internet from an underwater robot in waters off Baja, Mexico. We worked furiously to figure out how to receive that video signal, laboring diligently to gather the right equipment, contact the appropriate network managers, and obtain hardware permissions from local bureaucrats. After several days of effort, we learned that a satellite antenna uplink cable on the Jason support ship had become flooded with seawater a few hours before we became operational.
Despite this disappointment, we remained enthusiastic because, during our efforts, we discovered how to use the Internet's most unique network, MBONE. Short for Multicast Backbone , MBONE is a virtual network that has been in existence since early 1992. It was named by Steve Casner  of the University of Southern California Information Sciences Institute and originated from an effort to multicast audio and video from meetings of the Internet Engineering Task Force. Today, hundreds of researchers use MBONE to develop protocols and applications for group communication. Multicast provides one-to-many and many-to-many network delivery services for applications such as videoconferencing and audio where several hosts need to communicate simultaneously.
This article describes the network concepts underlying MBONE, the importance of bandwidth considerations, various application tools, MBONE events, interesting MBONE uses (see the two sidebars), and provides guidance on how to connect your Internet site to the MBONE.
MBONE is augmented by "tunneling," a scheme to forward multicast packets among the islands of MBONE subnets through Internet IP routers that (typically) do not support IP multicast. This is done by encapsulating the multicast packets inside regular IP packets. As installed commercial hardware is upgraded to support multicast traffic, this mixed system of specially dedicated mrouters and tunnels will no longer be necessary. We expect that most commercial routers will support multicast in the near future, eliminating the inefficiencies and management headaches of duplicate routers and tunnels.
MBONE can control multicast packet distribution across the Internet in two ways:
These issues can have a major impact on network performance. For example, a default video stream consumes about 128 Kbps of bandwidth, or nearly 10 percent of a T1 line (a common site-to-site link on the Internet). Several simultaneous high-bandwidth sessions might easily saturate network links and routers. This problem is compounded by the fact that general-purpose workstation routers that MBONE typically uses are normally not as fast or robust as the dedicated hardware routers used in most of the Internet.
MBONE is small enough that this technique is not a problem. However, some researchers speculate that, for a larger network with frequently changing group memberships, these routing techniques will be computationally inefficient. Research efforts on these issues are ongoing, since every bottleneck conquered results in a new bottleneck revealed.
Scheduling MBONE events is handled similarly. Special programs are announced in advance on an MBONE event electronic mail list (for example, email@example.com for messages and firstname.lastname@example.org for subscription requests) (see Tables 1 and 2). Advance announcements usually prevent overloaded scheduling of Internet-wide events and alert potential participants.
Cooperation is key. Many people are surprised to learn that no single person or entity is "in charge" of either local topology changes or event scheduling.
The key network concepts that make MBONE possible are IP multicast and real-time stream delivery via adaptive receivers. For example, in addition to the multicast protocols, many MBONE applications are using the draft Real-Time Protocol on top of the User Datagram Protocol and Internet Protocol. RTP , being developed by the Audio-Video Transport Working Group of the Internet Engineering Task Force, provides timing and sequencing services, permitting the application to adapt and smooth out network-induced latencies and errors.
Related real-time delivery schemes are also being evaluated. The end result is that even with a time-critical application such as an audio tool, participants normally perceive conversations as if they are in real time. This is because there is actually a small buffering delay to synchronize and resequence the arriving voice packets. Protocol development continues. Although operation is usually acceptable in practice, many aspects of MBONE are still considered experimental.
Encodings for audio include Pulse Coded Modulation and Group Speciale Mobile (the name of the standardization group for the European digital cellular telephony standard). Besides concerns for real-time delivery, audio is a difficult media for both MBONE and teleconferencing in general. This is because of the need to balance signal levels for all parties, who may have different audio processing hardware (for example, different microphones and amplifiers). Audio also generates lots of relatively small packets, which are the bane of network routers.
Figure 8-1: MBONE session at the Monterey Bay Aquarium Research Institute showing application tools nv (network video), vat (visual audio tool), wb (whiteboard), and sd (session directory).
Video, audio, and a shared drawing whiteboard are the principal MBONE applications, provided by software packages called nv (net video), vat (visual audio tool), and wb (whiteboard). The principal authors of these tools are Ron Frederick of Xerox Palo Alto Research Center for nv, and McCanne and Jacobson for vat and wb. Each program is available in executable form without charge from various anonymous File-Transfer Protocol sites on the Internet. Working versions are available for Sun, Silicon Graphics, DEC, and Hewlett-Packard architectures, with ports in progress for Macintosh. No DOS, OS-2, Amiga, or Windows versions are available, although ported tools can be found for 386 boxes running the (free) 386BSD Unix. Pointers to all public application tools are included in the Frequently Asked Questions (FAQ) document . Mirror FTP sites are available overseas.
Additional tools are also available or under development. Winston Dang of the University of Hawaii has created imm (Image Multicaster Client), a low-bandwidth image server. It typically provides live images of Earth from various geostationary satellites at half-hour intervals in either visible or infrared spectra. Henning Schulzrinne of AT&T/Bell Laboratories developed nevot, a network voice terminal providing multiple party conferences with a choice of transport protocols. Eve Schooler of the Information Sciences Institute is part of a team developing mmcc, a session orchestration tool and multimedia conference control program. Mike Macedonia of the Naval Postgraduate School, coauthor of this article, has created a multicast version of NPSNET , a 3D distributed virtual environment that uses the IEEE Distributed Interactive Simulation (DIS) application protocol . Stephen Lau of SRI International is experimenting with using graphics workstation windows as image drivers. Kurt Lidl of UUnet Technologies, Falls Church, Virginia, is working on a network news distribution application that uses multicast to reduce overall Internet loading and expedite news delivery. (Their goal is 120 ms total propagation coast to coast @md which is amazing since light takes about 16 ms to make that trip.)
Conferences on supercomputing, the Internet Engineering Task Force, scientific visualization, and many other topics have appeared @md often accompanied by directions on how to download PostScript copies of presented papers and slides from anonymous FTP sites. Radio Free VAT is a community radio station whose DJs sign up for air time via an automated server (email@example.com). Xerox PARC occasionally broadcasts lectures by distinguished speakers. Internet Talk Radio (Carl Malamud, firstname.lastname@example.org) has presented talks by US Vice President Al Gore, talk-show host Larry King, and others. Another new area is remote learning, which can use MBONE to bring expertise over long distances and multiply training benefits. Finally, default MBONE audio and video channels are provided so that new users can experiment and get advice from more experienced users.
Cooperation is essential due to the limited bandwidth of many networks @md in particular, transoceanic links. So far, no hierarchical scheme has been necessary for resolving potentially contentious issues such as topology changes or event scheduling. Interestingly, distributed problem solving and decision making has worked on a human level just as successfully as on the network protocol level. We hope this decentralized approach will continue to be successful, even with the rapid addition of new users.
We found that bandwidth capacities lower than T1 are generally unsuitable for MBONE video, although some users @md sometimes entire countries! @md on specially configured networks have managed to make the tools work at 56 and 64 Kbps.
Given adequate network bandwidth, you next need a designated MBONE network administrator. Working part-time, it typically takes one to three weeks for a network-knowledgeable person to establish MBONE at a new site. Setup is not for the faint of heart, but all the tools are documented, and help is available from the MBONE list.
You should read the Frequently Asked Questions a few times, ensure that software tools and multicast-compatible kernels are available for your target workstations, and subscribe to the mail list in advance to enable you to ask questions and receive answers. Table 1 shows the various worldwide MBONE list subscription request addresses. After subscribing, review the FAQ.
These tools can also work in isolation between workstations on a single LAN without an mrouter. We recommend that you test the application tools locally in advance (before going through the dedicated mrouter effort) to see if they are compatible with your system and match your expectations.
To receive multicast packets on your LAN, you will need to configure an mrouter. This can be either a single workstation on a LAN, or a host dedicated as a parallel mrouter. A nondedicated single workstation can receive and pass multicast to its LAN neighbors, but this arrangement can place double MBONE traffic on that LAN.
A more practical approach is to dedicate an old unused workstation as an mrouter and equip it with two Ethernet cards, which are needed so this mrouter can act independently and in parallel with your standard IP router. (NPS uses both approaches.) After deciding on your mrouter configuration, obtain and load the application software tools. You are now ready to put multicast on your LAN.
Once connected, you should pass along any lessons learned to the tool authors or the MBONE list. When the opportunity presents itself, show your overall network site administrator something spectacular on MBONE (such as a live space walk) and make sure your site is budgeting funds to increase your network bandwidth.
Demands on network bandwidth are significant and getting more critical. You might consider Tengdin's First (and Only) Law of Telecommunications: "The jump from zero to whatever baud rate is the most important jump you can make. After that, everyone always wants to go straight to the speed of light."
On one occasion, an unusual topology change at NPS caused a feedback loop that overrode the NASA Select audio track. Although plenty of people were willing to point out the symptoms of our error, it was not possible for the rest of the network to cut off the offending workstation cleanly. More situations will undoubtedly occur as MBONE developers and users learn more. Unpleasant surprises usually trigger a flurry of discussion and a corresponding improvement in the tools.
Expect to spend some time if you want to be an MBONE user. It is time-consuming because learning and fixing are involved and because it is lots of fun!
It is not every day that someone says to you, "Here is a multimedia television station that you can use to broadcast from your desktop to the world." These are powerful concepts and powerful tools that extend our ability to communicate and collaborate tremendously. They have already changed the way people work and interact on the net.
MBONE and Distance Learning at the Naval Postgraduate SchoolMike McCann, Naval Postgraduate School Visualization Laboratory
In March 1993, the W.R. Church Computer Center at the Naval Postgraduate School dedicated a Sun Sparcstation 2 to act as a Multicast Backbone (MBONE) router for the campus and the Monterey Bay research community. This router and an IP-encapsulated tunnel from Stanford University provides the NPS backbone with real-time audio, video, and other MBONE data feeds.
The MBONE is an excellent tool for those doing research in networks and video teleconferencing technology. Although it is not generally thought of as "ready for prime time" (audio dropouts may be frequent and video, at best, is only 3 frames per second over the Internet), NPS successfully used it to provide training in Cray Fortran optimization from the National Center for Atmospheric Research in Boulder, Colorado.
Five people who would not have been able to afford to travel to Boulder remotely "attended" the three-day training course at the NPS Computer Center's Visualization Laboratory. For the session, students @md including myself @md enjoyed two-way audio and video between the classroom at NCAR and the lab at NPS, and could ask questions of the NCAR instructor over the network. Advance preparation, good audio, and a camera operator in the NCAR classroom gave us a real feeling of presence in Boulder. "It was just like being there," one of my classmates said.
Paul Hyder of NCAR was instrumental in helping set up a direct "backup" tunnel between NPS and NCAR, where the slowest link is the T1 line between NPS and Stanford. During the course, there was only one 30-minute period of broken-up audio. We later determined that this interruption was caused by congestion on NCAR's Ethernet LAN. For much of 1993, the NPS Visualization Lab loaned a Sun Sparcstation 10 to the Monterey Bay Aquarium Research Institute for testing and incorporation into the live audio/video link to the research vessel Point Lobos and the remotely operated vehicle Ventana that explore the Monterey submarine canyon each day (see Figure 8-2). Local researchers in oceanography, virtual reality, and autonomous underwater vehicles continue to take advantage of the collaboration opportunities that this technology makes possible.
It might not be too long before MBONE enables us to videoconference with a classroom or a colleague half way around the world @md directly from our desktop workstations.
The figure shows the sd (session directory) of MBONE events.
Table 8-1: E-mail Addresses for Requesting Addition to the MBone Mail Lists
Remote Science over the MBONE during the Jason ProjectAndy Maffei, Woods Hole Oceanographic Institution
Jason/Medea is a remotely operated, dual-vehicle system developed by the Woods Hole Oceanographic Institution for underwater science and exploration. The Jason Foundation for Education uses this system as part of an annual Jason Project expedition.
During 1993, more than 600,000 K-12 students were involved in the project via live satellite transmissions. While prime broadcast hours of the expedition focused on the project's educational mission, an intense science program was conducted on a concurrent round-the-clock basis. The EDS Corporation and the University of Texas at Dallas provided a 56-Kbps data circuit for the project. Running on a Sun Workstation, MorningStar PPP software established the Internet connection with research vessel Laney Chouest from which the vehicles were deployed. This Internet connection made a transparent link with the multicast IP-based MBONE. Although the lab experimented with multicast videoconferencing tools such as nv and vat, our primary interest in using the MBONE was to transmit experimental data and to support shore-based models that depicted the positions and movement of the Laney Chouest and the two Jason/Medea vehicles. This technology was used by several investigators collaborating on Jason science projects at different locations throughout the US.
Both 2D and 3D models were developed at the Deep Submergence Laboratory for use on Sun and Silicon Graphics workstations. Software packages to access these models, along with real-time MBONE data, were available to anyone on the MBONE who wanted to try them out. As sonar surveys progressed during the expedition, data was transmitted back to shore, and the detailed models were updated and then distributed over the Internet.
A workstation on board the Laney Chouest generated multicast packets containing navigation and attitude information for the three vehicles. These packets were distributed in real time over the MBONE so users running the modeling software could watch a graphic display of Jason prowling real seafloor features as scientists investigated seamounts, thermal plumes, and the area's unique ecology. In addition to vehicle information, experimental data variables (such as temperatures) were multicast on the MBONE. Scientists and other interested users could write programs to read these experimental values, watch the models evolve, and get immediate feedback on progress being made during different experiments.
From the accounts of participating researchers, MBONE use enhanced the science carried out during the cruise. However, since we spent a lot of time supporting specific experiments, we were unable to spend much time helping other interested MBONE users get models up and running at their own sites. This was the first time we used multicast IP during an experiment, but we nevertheless learned a great deal. Such unique experiments demonstrate the value of other science-based tools, in addition to more generic videoconferencing applications.
For additional information, contact Andy Maffei at Woods Hole Oceanographic Institution, Deep Submergence Laboratory, Woods Hole, MA 02543.
Mail List Mailing List For Subscription Requests Region mbone-eu email@example.com Europe mbone-jp firstname.lastname@example.org Japan mbone-korea email@example.com Korea mbone-na firstname.lastname@example.org North America mbone-nz email@example.com New Zealand mbone-oz firstname.lastname@example.org Australia mbone-sg email@example.com Singapore mbone firstname.lastname@example.org Others rem-conf email@example.com WorldwideTable 8-2: Electronic Mail Addresses for Putting Messages on the Mailing Lists
Mail List Mailing List for Posting Messages Purpose Mbone firstname.lastname@example.org Network configuration and tool development rem-conf email@example.com Conference announcements and general discussion
Baker, S., "Multicasting for Sound and Video," Unix Review, Feb. 1994, pp. 23-29. Casner, S., and S. Deering, "First IETF Internet Audiocast," ACM SIGComm Computer Communications Review, July 1992, pp. 92-97; also as ftp://venera.isi.edu/pub/ietf-audiocast.article.ps
Curtis, P., MBone map, available via anonymous FTP from ftp://parcftp.xerox.com/pub/net-research/mbone-map-big.ps
Deering, S., "MBone: The Multicast Backbone," CERFnet Seminar, Mar. 3, 1993, ftp://parcftp.xerox.com/pub/net-research/cerfnet-seminar-slides.ps.
Don Brutzman, Ph.D., is an Assistant Professor at the Naval Postgraduate School in Monterey, CA. He may be reached at firstname.lastname@example.org or via his Web page, http://www.stl.nps.navy.mil/~brutzman.
This article was published in IEEE COMPUTER magazine, pp. 30-36, April 1994.
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