The server sends multicast messages over a multicast channel. Each multicast-enabled topic is associated with a channel. The channel determines the multicast port and multicast group address to which the server sends messages.
The multicast message is received by a multicast daemon running on the same computer with the message consumer. When an EMS client subscribes to a multicast-enabled topic, it automatically connects to the multicast daemon. The multicast daemon begins listening on the channel associated with that topic, receives any broadcast messages, and delivers them to subscribed clients.
Figure 18 shows the communication flow between a multicast message consumer, EMS server, and multicast daemon.
Figure 19 shows how using multicast can reduce the amount of bandwidth used to send a message. Where publish and subscribe messaging creates a copy of a published message for each message consumer, multicast broadcasts the message only once. Multiple multicast daemons listening on the channel receive the same broadcast.