4.2.2 Multicast bus architectures
This form of technology, like the hub and spoke approach, allows the broadcasting of messages to a number of receivers. Some of the implementations of bus architectures are rooted in multicasting, a technique which allows data to be broadcast to a number of clients. However, some, like the industrial example iBus detailed later in this course, are a sort of software implementation of an Ethernet, where objects are sent down a bus and only processed by any receiver that requires the object; if it isn't required it is passed on to the next receiver.
Multicasting can be thought of as a primitive form of broadcasting of packets. It is carried out using Unreliable Datagram packets (UDP) that are broadcast out on a multicast IP address. Because it is based on UDP, multicasting will suffer from loss of packets when a network is congested. In Java multicasting is based on the class which is an extension of the class.
The architecture of a simple multicast bus architecture is shown in Figure 5. It consists of a transmitter object which sends objects along a multicast bus; attached to the bus are a number of listener objects which are activated when the event corresponding to the dispatch of the object occurs.