Developing IP Multicast Networks, Volume I
Author: Beau Williamson
Publisher: Cisco Press (53)
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.
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
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.
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.
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.
One of the primary architects of OpenCable, Michael
Adams, explains the key concepts of this initiative in his book
Broadband, Second Edition
by George Abe
Introduces the topics surrounding high-speed networks
to the home. It is written for anyone seeking a broad-based familiarity
with the issues of residential broadband (RBB) including product
developers, engineers, network designers, business people, professionals
in legal and regulatory positions, and industry analysts.