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Multicast Applications


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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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Multicast Applications

It's not uncommon for people to think of IP multicasting and video conferencing as almost the same thing. Although the first application to be used on an IP multicast-enabled network is often video conferencing, video is only one of many IP multicast applications that can add value to a company's business model. In fact, after some initial experiments with video conferencing over the IP multicast network, many companies find that for the bandwidth consumed, the talking head in a typical audio/video conference provides little added value to the communication process.

This section looks at some other IP multicast applications that have the potential for improving productivity, including multimedia conferencing, data replication, real-time data multicasts, and gaming and simulation applications.

Multimedia Conferencing

Some excellent IP multicast, multimedia conferencing tools were developed for the UNIX environment for use over the MBone (the next few sections discuss more about the MBone). These tools (many of which have recently been ported to the Windows 95 and NT platforms) permit a many-to-many audio-only or audio/video conference to take place via IP multicast. In addition to the audio and video tools, a UNIX-based Whiteboard tool was developed that permits users to share a common, electronic whiteboard. Besides these MBone freeware tools for multimedia conferencing over IP multicast networks, other companies are now beginning to offer commercial forms of these tools with other value-added features. (Chapter 4, “Multimedia Multicast Applications,” looks at the MBone freeware tools in detail and explains how to download them.)

Many people start with audio/video conferencing because video is a particularly exciting new way to communicate over a network. After the novelty of video wears off and the realities of the bandwidths and workstation horsepower that are consumed by video conferencing (particularly if everyone in the conference is sourcing video at the same time) become apparent, it's not uncommon to see audio-only conferencing become the normal mode. Additionally, if an audio-only conference is coupled with an IP multicast-based, data-sharing application (such as the Whiteboard application previously mentioned) that allows the members of the conference to share graphics information, the result is an extremely powerful form of multimedia conferencing that does not consume much bandwidth.

Data Distribution

Data replication is another IP multicast application area that is rapidly becoming very popular. By using IP multicasting, IS departments are adopting a push model of file and database updates. Applications such as Starburst's MFTP product, as well as work done in the area of reliable multicast by Globalcast, permit the reliable delivery of files and data to groups of nodes in the network. As the name MFTP implies, this product is like a multicast form of FTP. One or more files may be sent simultaneously with FTP to a group of nodes in the network by using IP multicasting.

This sort of technology permits companies to push new information such as price and product information to their remote stores every night so that the stores have up-to-date information the next business day.

Real-Time Data Multicasts

The delivery of real-time data to large groups of hosts is another area where IP multicasting is becoming popular. A good example is the delivery of stock ticker information to workstations on the trading floor. Previously, special applications were built to deliver this time-critical information to traders on the trading floor. More and more financial and investment firms are also investigating the use of IP multicasting to deliver information to their customers as another revenue-generating financial and trading service.

By assigning different financial categories (bonds, transportations, pharmaceuticals, and so forth) to different multicast groups, traders can use their workstations to receive only the real-time financial data for which they are interested.

Gaming and Simulations

IP multicasting is very well suited for use in network gaming or simulation applications. Although numerous PC games and simulations permit groups of networked gamers to battle each other in simulated dogfights or other fantasy environments such as Doom, virtually all these applications make use of unicast, point-to-point connections.

Typically, a gaming or simulation application must learn of the other participants via either manual configuration or some other special participant notification mechanism. When the notification occurs, each PC makes an IP unicast connection to all the other PCs in the game or simulation. Obviously, this is an Order(N2) problem that requires on the order of N2 interconnections between all N PCs and does not scale to large numbers of participants. The upper limit for this sort of game or simulation depends largely on the horsepower of the individual PCs or workstations being used and is usually between 5 and 10 participants.

Another method that is sometimes used in this type of networked environment is to have a central gaming or simulation server to which all participants must connect via an IP unicast connection. This places the burden of distributing the real-time game or simulation data to all of the participants on the server. Again, depending on the horsepower of the server, this solution can typically scale only to 100 or so participants.

IP multicasting can be used to extend gaming and simulations to extremely large numbers of participants. Participating PCs or workstations simply join the IP multicast group and begin sending and receiving gaming and simulation data. Dividing the simulation data into more than one stream and then communicating this information via separate IP multicast groups can further extend this concept. This division of data permits the PCs or workstations to limit the amount of simulation data that they are sending and receiving (and, hence, the number of IP multicast groups they need to join) to what they currently need to participate in a game or simulation situation.

For example, each room in a fantasy battle game could be assigned a separate IP multicast group. Only those PCs or workstations whose participants are in this room need to join this multicast group to send and receive simulation data about what is happening there. When players leave the room and go into another room, they leave the IP multicast group associated with the first room and join the IP multicast group associated with the new room.


The U.S. military has built one of the largest IP multicast-based, war-game simulations that I have ever seen. This simulation divides the battlefield into map grids, each of which corresponds to a multicast group. This results in the use of thousands of IP multicast groups to communicate between the individual participants of the simulation. As each participant, such as a tank or an F-16 fighter, enters the map grid, the simulation application joins the associated IP multicast group in order to receive simulation data about what is happening in the map grid. When the participant leaves the map grid and goes to another, the application leaves the original multicast group and joins the IP multicast group associated with the new map grid.

As more IP networks become multicast enabled, more game and simulation application developers are expected to make use of IP multicasting for large-scale simulations. It's not unthinkable that sometime in the near future, thousands of gamers will be simultaneously battling it out over the Internet in the ultimate Doom game.


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