Practical traffic grooming scheme for single-hub SONET/WDM rings

In SONET/WDM networks, one fiber supports multiple wavelengths and each wavelength supports several low rate tributary streams. "Traffic grooming" then is defined as properly using a SONET add/drop multiplexer (ADM) to electronically multiplex and demultiplex the required tributary traffic patterns with minimal resource cost (wavelengths and ADMs). This paper studies the traffic grooming problem in single hub SONET/WDM networks and extends existing results. We analyze the real deployments, generalize their results, and study practical special cases. We prove that a two-fiber bidirectional line-switched ring (BLSR/2) would never be more expensive than a unidirectional path-switched ring (UPSR) under any traffic pattern. We also present the exact minimum costs of uniform traffic in both UPSR and BLSR/2. We give approximation algorithms for optimal grooming of non-uniform traffic. Finally, we consider how to select the line speeds if there are two different line speeds available.