Cisco Systems RJ-45-to-AUX manual Multicast, Want to Join the Military?, 139

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.

Want to Join the Military?

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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