Reload cost problems: minimum diameter spanning tree

We examine a network design problem under the reload cost model. Given an undirected edge colored graph, reload costs on a path arise at a node where the path uses consecutive edges of different colors. We consider the problem of finding a spanning tree of minimum diameter with respect to the reload costs. We present lower bounds for the approximability even on graphs with maximum degree 5. On the other hand we provide an exact algorithm for graphs of maximum degree 3.