MBone

The MBONE will make the Internet a hotbed of real-time multimedia communications. In essence, it will become a brand of interactive boardroom, classroom, television, cinema, video game, and edutainment of the kind only dreamed of in the hype about the information superhighway. The MBONE will make it possible, eventually, for all of us to start our own Internet-based TV shows, if we want to, without so much as an FCC license or a transmitter. Or teach in an on-line classroom with students from ten different states. Or hold an important meeting with researchers from around the globe.

The Internet has traditionally been built to send information to one person (or computer) at a time. The information being transmitted has a specific destination in mind, such as an e-mail message that tries to reach a specific (single) colleague. A request for a Web page is transmitted to a single host, and the host sends back the requested information to the single recipient. Although computers can handle hundreds (or thousands, or millions) of these requests every second, the information being moved around is still one-to-one: one computer is sending the information, and only one is receiving it.

This arrangement seems perfectly fine until you consider what happens when you want to send information simultaneously to more than one person. As an example, consider an e-mail message to which you've attached a graphics file. If you send that message to your friend in England, you'll chew up a certain amount of bandwidth. Now, as any seasoned Internaut knows, you can address an e-mail message to 2, 3, or 20 people at the same time. If you send this file to 20 people, you create 20 times as much Internet traffic. So if a band such as R.E.M. wanted to transmit a live concert across the Internet to 150,000 of their closest friends, well, you can easily imagine how quickly the Net would clog up.

The next generation of groundbreaking tools on the Internet will be IP multicast programs. MBONE (multicast backbone) programs are today's implementation of IP (Internet Protocol) multicast. IP multicast programs change the rules of the road by enabling users to "broadcast" packets of information to anyone who is "listening," rather than to a single specific individual or computer. The packets aren't sent individually to each recipient; instead, only one packet is sent, but it ends up at all the specified destinations at (more or less) the same time.

Why is that interesting? Because IP multicasting lends itself to a whole new way to publish information on the Internet. Instead of the electronic equivalent of a one-on-one chat, you use a megaphone to broadcast to everyone who cares to listen. And the people who do the listening can send something right back, not just to you, but to everyone else as well.

As the MBONE gathers steam, it promises a thorough and irrevocable shift in how the world communicates. It promises, in others words, a revolution of its very own.

You can use the MBONE to do the following:

Collaborate with colleagues in real time by using a shared virtual "whiteboard"
Hear and see live lectures from famous professors or scientists, and even ask them questions
Listen to radio stations that "broadcast" on the Internet
Start your own radio show
See live pictures of spacebound NASA astronauts on the space shuttle
Attend a virtual poetry reading where you hear the words in the author's own voice
See and hear rehearsals of Silicon Valley garage bands
Attend an Internet Engineering Task Force meeting without leaving your office

In the future, the MBONE may make it possible for you to do the following:

Watch a customized version of CNN from your computer's desktop
Engage 5,000 other people in a huge intercontinental computer game
See reruns of "Gilligan's Island" and share your snide comments in real time with faraway friends
Put your own garage band's rehearsals online for all to see (and hear)
Automatically download and install authorized upgrades and bug-fixes to your computer software, without your intervention
"Chat" in real time with 20 other users (as you can with Internet Relay Chat, except that you'll use your voice instead of your overworked fingers)
Do plenty of other things that haven't been thought of yet

What Is Multicasting?

Multicasting is a technical term that means that you can send a piece of data (a packet) to multiple sites at the same time. (How big a packet is depends on the protocols involved-it may range from a few bytes to a few thousand.) The usual way of moving information around the Internet is by using unicast protocols -- tools that send packets to one site at a time.

You can think of multicasting as the Internet's version of broadcasting. A site that multicasts information is similar in many ways to a television station that broadcasts its signal. The signal originates from one source, but it can reach everyone in the station's signal area. The signal takes up some of the finite available bandwidth, and anyone who has the right equipment can tune in. The information passes on by those who don't want to catch the signal or don't have the right equipment.

On a multicast network, you can send a single packet of information from one computer for distribution to several other computers, instead of having to send that packet once for every destination. Because 5, 10, or 100 machines can receive the same packet, bandwidth is conserved. Also, when you use multicasting to send a packet, you don't need to know the address of everyone who wants to receive the multicast; instead, you simply "broadcast" it for anyone who is interested. (In addition, you can find out who is receiving the multicast -- something television executives undoubtedly wish they had the capability to do.)

How Is the MBONE Different from Multicasting?

Unfortunately, the majority of the routers on the Internet today don't know how to handle multicasting. Most routers are set up to move traditional Internet Protocol (IP) unicast packets -- information that has a single, specific destination. Although the number of routers that know how to deal with multicast are growing, those products are still in the minority.

Router manufacturers have been reluctant to create equipment that can do multicasting until there is a proven need for such equipment. But, as you might expect, it's difficult for users to try out a technology until they have a way to use it. Without the right routers, there's no multicasting. Without multicasting, there won't be the right routers. Catch-22.

What is a router?
A router is a device that connects a local area network -- such as an inter-office LAN -- to a wide area network -- such as the Internet. The router's job is to move information between the two networks.
Most routers today are unicast routers: They are designed to move information from a specific place to another specific place. However, routers that include multicasting capabilities are becoming more common.

In 1992, some bright fellows on the Internet Engineering Task Force (IETF) decided that what no one would do in hardware, they could do in software. So they created a "virtual network" -- a network that runs on top of the Internet -- and wrote software that allows multicast packets to traverse the Net. Armed with the custom software, these folks could send data to not just one Internet node, but to 2, 10, or 100 nodes. Thus, the MBONE was born.

The MBONE is called a virtual network because it shares the same physical media -- wires, routers and other equipment -- as the Internet.

The MBONE allows multicast packets to travel through routers that are set up to handle only unicast traffic. Software that utilizes the MBONE hides the multicast packets in traditional unicast packets so that unicast routers can handle the information.

The scheme of moving multicast packets by putting them in regular unicast packets is called tunneling. In the future, most commercial routers will support multicasting, eliminating the headaches of tunneling information through unicast routers.

When the multicast packets that are hidden in unicast packets reach a router that understands multicast packets, or a workstation that's running the right software, the packets are recognized and processed as the multicast packets they really are. Machines (workstations or routers) that are equipped to support multicast IP are called mrouters (multicast routers). Mrouters are either commercial routers that can handle multicasting or (more commonly) dedicated workstations running special software that works in conjunction with standard routers.

So, what's the difference between multicasting and the MBONE? Multicasting is a network routing facility -- a method of sending packets to more than one site at a time. The MBONE is a loose confederation of sites that currently implement IP multicasting.

The MBONE -- or multicast backbone -- is a fancy kludge, a hack. It is at best a temporary utility that will eventually become obsolete when multicasting is a standard feature in Internet routers. By then there will be an established base of MBONE users (which should make the router manufacturers happy). The utilities and programs that work on today's MBONE will undoubtedly work on the multicast backbone of tomorrow.

Pavel Curtis, a researcher at Xerox PARC (Palo Alto Research Center) says, "I believe that IP multicast is very likely to remain an important part of the Internet for quite a long time, and that it will be the primary audio/video transmission medium on the Net."

"On the other hand," he continues, "I think that the MBONE as an identifiable subset of machines on the Net is already beginning to fade away, as more and more router and computer vendors supply IP multicast support in their products; when multicast support is ubiquitous, the MBONE ceases to be identifiable as something other than the Net as a whole."

What's on the MBONE?

Today, multicasting is used for videoconferencing, audioconferencing, shared collaborative workspaces, and more. Conference multicasts generally involve three types of media: audio, video, and a whiteboard -- a virtual note board that participants can share.

Perhaps the most sought-after function that the MBONE provides is videoconferencing. The MBONE originated from the Internet Engineering Task Force's attempts to multicast its meetings as Internet videoconferences. MBONE video is nowhere close to television quality, but at a few frames a second, video quality is good enough for many purposes. In the spirit of the IETF's early technically-oriented offerings, many of the MBONE events that take place are technical conferences, ranging from the SIGGraph '94 conference in Orlando, Florida, to the International Conference on High Energy Physics in Glasgow, Scotland, to the Second International Conference on Intelligent Systems for Molecular Biology from Stanford University. Users also were able to tune into the MBONE to see astronauts on the space shuttle Endeavor repairing the Hubble space telescope and panel discussions at the 1995 annual meeting of the Congress of Neurological Surgeons.

What is the IETF?
The Internet Engineering Task Force is the branch of the Internet Architecture Board that addresses the immediate technical problems and challenges of the Internet. The IETF is a voluntary committee of technical people such as network operators, engineers, and telecommunications equipment vendors.
The IETF's parent organization, the Internet Architecture Board, concerns itself with the technical challenges facing the Internet, now and in the long term. Such challenges include how to effectively handle the continued burgeoning growth of the Internet, how to keep the Net operational even when each of us can pump 2 megabits per second through the fiber-optic cable that will one day be plugged into our computers, and how to help the network better handle the demands of real-time audio and video.

The MBONE's capability to carry remote audio and video makes it a wonderful tool for seminars, lectures, and other forms of "distance education." Imagine sitting in on a lecture that's being given live thousands of miles away and even asking questions or contributing to a panel discussion. According to Navy Lt. Tracey Emswiler, whose experiments with the MBONE are the basis for her master's thesis in information technology management, "Some people believe that teaching over the MBONE can't be done. We've proven that you can send regular live-broadcast lectures over the MBONE." An average of 10 to 12 universities and labs tune into each distance education lecture that is sent over the MBONE, including institutions in the United States, France, Great Britain, Japan and Germany.

Indeed, much of what happens today on the MBONE is of a technical nature, information that most of us would find dull. However, the nerds don't get to keep the MBONE to themselves. Besides esoteric engineering events, the MBONE is home to more exciting fare, such as multicasts of concerts, a do-it-yourself-radio station, and even poetry readings.

The Seattle-based techno-ambient band Sky Cries Mary performed the first live rock concert on the MBONE, and the Rolling Stones multicasted 20 minutes of their November 18, 1994, Dallas Cotton Bowl concert as a promotion for a subsequent pay-per-view TV special.

Radio broadcasts, in part because of their lesser bandwidth requirements, have become common on the MBONE. Some examples include episodes of "The Cyberspace Report" (a public-affairs show from KUCI 88.9 FM in Irvine, California), Internet Talk Radio, and Radio Free vat.

Some MBONE users are experimenting with distributing Usenet news via the MBONE instead of with NNTP (Net News Transport Protocol). NNTP has been used to pass netnews traffic around since the early days of Usenet, but sending Usenet traffic via multicasting could significantly reduce the total amount of bandwidth used to transmit netnews. Rather than having thousands of copies of a message travel from site to site, each message could be broadcast on the MBONE only once and grabbed by each site as it passes through.

For more discussion about what's on the MBONE, see Chapter 6.

How Large Is the MBONE?

Today, about 1,700 networks (in about 20 countries) are on the MBONE (see Figure 3-1), making the MBONE approximately the size that the entire Internet was in 1990. Unfortunately, there is no way to know how many people within each of the 1,700 networks can access the MBONE.

Figure 3-1: Topology of the MBONE.

The size of the MBONE, compared to the Internet as a whole, is relatively small. As of February 1995, the Internet was home to 48,500 subnetworks, so the MBONE was available on roughly 3.5 percent of the Internet.

Pavel Curtis estimates that by 1996 or 1997, multicasting will be broadly supported in routers. When that happens, and upgraded routers are installed in place of unicast routers, the MBONE and the Internet will effectively be one entity. (See Figure 3-2.)

Figure 3-2: Growth of the MBONE.

Who operates the MBONE?

You may be surprised to learn that no one is actually in charge of the MBONE's topography of event scheduling. Much like the Internet itself, the MBONE's growth has been based on mutual cooperation between network service providers and users. The MBONE community is active and open. Work on tools, protocols, standards, applications, and events is a cooperative international effort. Cooperation is essential due to limited bandwidth on many networks (for example, on intercontinental links).

How do TTLs limit the life of MBONE packets?

An infinitely loud megaphone, one that could be heard anywhere in the world, would be a bad thing: once a few dozen of us had them, we wouldn't be able to get useful information from the din. The MBONE is no exception. Broadcast packets need to have a finite life lest they bounce around the network forever. The MBONE includes procedures for limiting how far multicast packets may travel, to prevent them from saturating the entire Internet. Each packet has a time to live (TTL) value, a counter that is decremented every time the packet passes through an mrouter. Because of TTLs, each multicast packet is a ticking time bomb.

If an MBONE broadcast were a TV station (as in the analogy at the beginning of this chapter), TTLs would be the station's signal area -- the limitation of how far the information can travel before petering out.

Those multicasting something that's of little interest to the outside world (for example, a company board meeting) might produce a packet that had a small time to live (perhaps 10). As the packet moved around the company's internal network, its TTL would be notched down every time it passed through an mrouter. When the packet's TTL reached 0, the packet would die and not be passed further. With careful planning, those multicasting can keep their multicast packets on their internal networks or within their state or country.

Events of interest to the world at large are generally multicast with long TTLs -- perhaps 200 -- to guarantee that the information will reach around the world.

Summary

The key to the MBONE's existence is convergence. Communications concepts and technologies are added to broadcast concepts and technologies, and then are mixed with multimedia concepts and technologies, with the final result being nothing less than an interdependent joining of all three. Unfortunately, like most media convergences, the result often receives less credit than it should, because it seems like such a natural idea in the first place. The MBONE, a technology that is remarkable for existing at all, will almost certainly become a technology that Internet users -- especially those who join during the next few years -- will take entirely for granted.

But then, that's what happens to all successful technologies. Ask most 20-year olds if they're in awe of television's ability to bring live video and audio signals into their house from somewhere half-way around the globe, and you're likely to be greeted with stares of incomprehension. For that matter, try to explain to them how truly wonderful it is that your PC plays the video introduction to Wing Commander III without burping even once; the incomprehension continues. Then turn around and wax eloquently about how amazing it feels to be talking on the phone with someone three time zones away, or that you're listening to a baseball game in another city, or that you turn the key in your ignition and the car seems to start by itself.