Multicast - Cisco RJ-45-to-AUX Brochure

Figure 7.2: Unicast traffic flow.

Multicast

Multicast is a combination of broadcast and unicast. It sends one copy of the packet to many hosts that
requested it, thereby using less bandwidth. It also saves bandwidth by not sending the packet to the portion of
the network whose hosts didn't request the transmission. Multicast accomplishes this task by transmitting to
an identified group, called a multicast group, rather than to an individual host. Each interface/host can be a
member of multiple multicast groups. The membership is dynamic; a host can leave and join any time it
wants. The traffic is also not limited by any boundary; it can reach the farthest point of the Internet.
Figure 7.3 illustrates multicast traffic flow.
Figure 7.3: Multicast traffic flow.
The characteristics of multicast enable it to take three different forms:
One−to−many—One−to−many is the most common form of multicast traffic. Examples include
database updates, live concerts, news, music/audio broadcasts, announcements, lectures, and many
more.
Many−to−one—Many−to−one multicasts are less common; they include data collection, auctions,
and polling.
Many−to−many—Many−to−many multicasts are rare, but they are gaining popularity as
programmers begin to utilize multicast in some imaginative ways. Chat groups, multimedia
conferencing, concurrent processing, interactive music sessions, and collaboration are examples of
many−to−many multicasts. But don't forget the rising star (and my favorite): interactive multiplayer
games.
The U.S. military has one of the largest interactive multicast−based war−game simulations I've heard of. The
battlefield is divided into map grids, and each grid square is a multicast group. Individuals communicate with
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