IP Multicast

A multicast is a single data stream sent from one source to a group of recipients. Examples might be a stock ticker or live video feed. Figure 7-3 shows an example multicast topology, as contrasted to unicast and broadcast.

Multicast Topolgy
Unicast Topolgy
In contrast, a unicast is traffic from one source to one destination (see Figure 7-2).


Broadcasting
A broadcast is traffic from one source to all destinations (see Figure 7-3). Broadcasts are not routed!Some features of multicast traffic are:

• Multicast uses UDP, so reliability must be handled by the end host.
• The sending host does not know the identity of the receiving hosts; it knows just a group IP addresses.
• Group membership is dynamic. Hosts join a group, notify their upstream router, and the router begins forwarding data to them.
• Hosts can belong to more than one group.
• Hosts in a group can be located in many different places.