Broadcasting in Cycle Preex Digraphs ?

Cycle preex digraphs are directed Cayley coset graphs that have been proposed as a model of interconnection networks for parallel architectures. In this paper we present new details concerning their structure that are used to design a communication scheme leading to upper bounds on their broadcast time. When the diameter is two, the digraphs are Kautz di-graphs and in this case our algorithm improves the known upper bounds for their broadcast time and is indeed optimal for small values of the degree.