Given edge weighted undirected graph the problem asks to output a spanning tree $T$ of minimum weight such that the path between any two vertices in the tree $T$ is bounded by the input $k$. One of the related paper is at http://www.sciencedirect.com/science/article/pii/S0166218X99001110 .
However i could not find other relevant results which improvised over it in general case. Can anyone please refer me the state of the art in this problem. I am also looking for results on unweighted undirected graphs which i couldn't get. I tried to google out and follow the citations but couldn't get what i wanted.