As an example multiprocessor, we will consider a machine that uses a
ring-structured interconnection network. Such networks are found
in the KSR-1 multiprocessor [3] and the experimental
Hector machine [4]. In order to provide a small
enough model for effective experimentation through simulation,
we have chosen the single-ring structure shown in figure 
.
The system consists of nodes connected by a unidirectional bit-parallel
slotted ring. Each node has one processing module connected to it,
comprising a processor, a cache, and a local memory.
Figure: Multiprocessor under study
The communications protocol is that of the Hector multiprocessor. Every processor can access the memory on any node, but there is a disparity between the access time to the processor's local memory and the access time to another processor's memory. A processor never has two outstanding requests at the same time.
Information is transferred in packets. The width of the ring is large enough to hold either a full request message or 8 bytes of data in a single slot, as well as overhead such as the addresses of the destination and source nodes. There is one slot per node and packets are transferred from one node to the next in a single clock cycle.