Routing in Turn-Prohibition Based Feed-Forward Networks

The application of queuing theory to communications systems often requires that the respective networks are of a feed-forward nature, that is they have to be free of cyclic dependencies. An effective way to ensure this property is to identify a certain set of critical turns and to prohibit their use. A turn is a concatenation of two adjacent, consecutive links. Unfortunately, current routing algorithms are usually not equipped to handle forbidden turns and the required extensions are nontrivial. We discuss the relevant issues for the example of the widely deployed Dijkstra algorithm. Then, we address the general case and introduce the Turnnet concept, which supports arbitrary combinations of routing algorithms with turn-prohibiting feed-forward mechanisms.