A 10/7 + $ \epsilon$ Approximation for Minimizing the Number of ADMs in SONET Rings

SONET add/drop multiplexers (ADMs) are dominant cost factors in WDM SONET rings. Whereas most previous papers on the topic concentrated on the number of wavelengths assigned to a given set of lightpaths, more recent papers argue that the number of ADMs is a more realistic cost measure. Some of these works discuss various heuristic algorithms for this problem, and the best known result is a 3/2 approximation in Calinescu and Wan, 2002. Through the study of the relation between this problem and the problem of finding maximum disjoint rings in a given set of lightpaths we manage to shed more light onto this problem and to develop a 10/7 + epsi approximation for it.