Abstract: A method of assigning capacity and routing flow in a bi-directional line switched SONET ring based upon ring topology and demand data defines for each pair of links of the ring a two-edge cut. Each two-edge cut divides the ring into two sets of nodes. For each two-edge cut, the capacity assignment method calculates a demand equal to the sum of all demands between nodes on opposite sides of the two-edge cut. The capacity assignment method then determines the maximum demand and sets the capacity of each link equal to one-half the maximum demand plus one-half of one demand unit. The flow routing method of the present invention calculates a cut difference for each two-edge cut. A critical cut is a two-edge cut having a cut difference equal to or less than one. If there is a critical cut with demands greater than zero on the same side of the critical cut, the method performs a first processing routine.