Multicast Messages
A multicast message is any message with many potential recipients. Potential recipients are called subscribers.
The subject name of the message indirectly determines the message’s destination—the set of subscribers that receive the message. Every subscriber to that subject name receives the message; non-subscribers do not receive it. The set of subscribers can change dynamically, depending on which programs are listening for the subject name. If no subscribers exist, then none receive the message (even though it still travels the network). Reliable Multicast Message illustrates this model of message delivery.
Rendezvous applications are free to invent public subject names, constrained only by the syntactic and semantic rules in Subject Names.
Figure 6: Reliable Multicast Message
Multicast messages are like radio broadcasts; the sender picks a frequency, and any listener who tunes to that frequency receives the broadcast. The public subject name is analogous to a radio frequency; any program that listens for a subject receives all messages bearing that subject name.
A multicast message does not imply multicast packet protocols. A multicast message can reach its destination using multicast protocols, broadcast protocols, or even intra-process communications—depending on the transport object that the program uses to send the message. (In contrast, TIBCO Rendezvous documentation uses phrases such as multicast group and multicast addressing to indicate multicast network protocols.)