Why Do You Need Multicasting?
“Necessity is the mother of all invention,” a saying derived from Plato’s Republic, holds very true
in the world of technology. In the late 1980s, Dr. Steve Deering was working on a project that
required him to send a message from one computer to a group of computers across a Layer 3
network. After studying several routing protocols, Dr. Deering concluded that the functionality of
the routing protocols could be extended to support “Layer 3 multicasting.” This concept led to
more research, and in 1991, Dr. Deering published his doctoral thesis, “Multicast Routing in a
Datagram Network,” in which he defined the components required for IP multicasting, their
functions, and their relationships with each other.
The most basic definition of IP multicasting is as follows:
Sending a message from a single source to selected multiple destinations across a
Layer 3 network in one data stream.
If you want to send a message from one source to one destination, you could send a unicast
message. If you want to send a message from one source to all the destinations on a local network,
you could send a broadcast message. However, if you want to send a message from one source to
selected multiple destinations spread across a routed network in one data stream, the most efficient
method is IP multicasting.
Demand for multicast applications is increasing with the advent of such applications as audio and
video web content; broadcasting TV programs, radio programs, and concerts over the Internet;
communicating stock quotes to brokers; transmitting a corporate message to employees; and
transmitting data from a centralized warehouse to a chain of retail stores. Success of one-to-many
multicast applications has created a demand for the second generation of multicast applications
that are referred to as “many-to-many” and “many-to-few,” in which there are many sources of
multicast traffic. Examples of these types of applications include playing games on an intranet or
the Internet and conducting interactive audio and video meetings. The primary focus of this
chapter and the next chapter is to help you understand concepts and technologies required for
implementing one-to-many multicast applications.