4.2 Architectures
4.2.1 Hub and spoke architectures
There are two main types of bus architectures. These are hub and spoke architectures and multicast bus architectures. Figure 4 shows a typical hub and spoke architecture.
It consists of a central hub object which carries out the transmission of data to listener objects. Each listener responds to the event of objects being dispatched to the hub object from a transmitter object which produces the objects to be broadcast. In such an architecture there might be one hub object per channel or a single master object serving all the channels.
This type of architecture is one of the easiest to implement since it can be developed using base technologies such as RMI or 
and 
objects. It also has the advantage that since all objects pass through the hub object, accounting and management functions can be centralised on this object. The main disadvantage of this approach, as compared with the multicast bus architecture approach, is that it can generate large amounts of traffic. There is also a reliability problem in that when the server containing the hub malfunctions the whole system goes down.