Multi-rate and multi-hop optical carriers in WDM ring

By means of optical transparency wavelength division multiplexing (WDM) networks with multi-rate transmissions are becoming a reality. The potential advantages of individually selecting the transmission rate for each lightpath are however not yet fully understood. A recent work studied for the first time multi-rate and multi-hop (M&M) networks in which tributary signals are transmitted over a concatenation of lightpaths, each one operating at its own transmission rate. The study revealed that the problem of designing M&M networks is NP-complete and optimal solutions are practically available only for small networks. The paper presents a heuristic algorithm for designing M&M ring networks that yields efficient sub-optimal solutions in polynomial time. The algorithm determines the rate for each lightpath taking into account a number of factors including the node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), single- and multi-hop (constant bit rate) optical networks, are discussed in the paper and documented with numerical results. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals.