Before revision: The hop-constrained Steiner tree problem is a generalization of the classical Steiner tree problem , and asks for  minimum cost subtree that spans some specified nodes of a given graph, such that the number of edges between each node of the tree and its root respects a given hop limit.
After revision: The hop-constrained Steiner tree problem is a generalization of the classical Steiner tree problem and asks for minimum cost subtree that spans some specified nodes of a given graph, such that the number of edges between each node of the tree and its root respects a given hop limit.