The Turnnet concept: routing in feed-forward networks with prohibited turns

The application of queuing theory to communication systems often requires that the respective networks are of a feed-forward nature, that is they have to be cycle-free. An effective way to ensure this property is to prohibit the use of a certain set of turns, where a turn is a combination of two adjacent, consecutive links. Unfortunately, current routing algorithms are usually not equipped to handle forbidden turns and the required extensions are far from being trivial. In this paper we discuss the relevant issues for the example of the widely deployed Dijkstra algorithm. Then, we address the general case and present our Turnnet concept, which supports arbitrary combinations of routing algorithms with turn-prohibiting feed-forward mechanisms.