The Complexity of Sorting with Networks of Stacks and Queues

We consider a sorting problem oil networks whose nodes are storage elements of type stack or queue. A railway switchyard could he ail instance of such a network. Given is ail input node where a permutation of items 1 to n is delivered and ail output node where they are expected in sorted order. How many moves, where an item is transfered from one node to an adjacent node, are needed in the worst case for the sorting? Among others we have the following results: A characterization of networks where the sorting complexity is Theta (n log n). A lower bound of Omega(n(2-epsilon)) for the network consisting of only two stacks that call exchange items.