Star, Bus and Trees

Star topology (or single-level tree [BGMR96], or a hub) is a convenient model not only from the hardware point of view, but can also represent a master-slave paradigm of parallel applications. We assume that the originator is located in the center of the star (or in the root of the single-level tree) which is $P_1$. All the communications are performed by the originator which distributes data to the PEs consecutively, and then collects the results (if any). $P_i$ is connected with the originator via link $i$ with parameters $S_i, C_i$. In the (single) bus interconnection the bus is a resource which cannot be shared by the communications, and must be accessed sequentially. Hence, the originator activates other PEs one by one as in the case of the star topology. Therefore, the bus and the star can be analyzed in the same way. Below we refer to the star terminology.