Abstract: A method for assigning a predetermined wavelength between two different nodes in a wavelength division multiplexing ring communication network that has an N number of nodes and at least one pair of optical fibers sequentially connecting the N number of nodes is disclosed. A matrix is formed to represent optical-path configuration and wavelength assignment for an N−1 number of nodes. The matrix is extended by adding a column at any position of the matrix. Then X is assigned to the added column. An N/2 number of rows is added in the matrix. Tracking along each row toward the left, from the added column, a firstly encountered numeral is selected, and then the selected numeral is increased by one. Numerals 1, 2 . . . N/2 are assigned sequentially to locations corresponding to the added column in the added rows, and X is assigned to locations next to the numeral-assigned locations, where the number of X-assigned locations is equal to a hop-number corresponding to the assigned numeral.