A variation of the channel assignment problem is naturally modeled by L(2, 1)-labelings of graphs. An L(2, 1)-labeling of a graph G is an assignment of labels from {0, 1, . . . , λ} to the vertices of G such that vertices at distance two get different labels and adjacent vertices get labels that are at least two apart and the λ-number λ(G) of G is the minimum value λ such that G admits an L(2, ...