Service providers are transferring their static optical transport networks from semipermanent connections to agile automatic switched optical networks (ASON) with dynamic optical connection provisioning and restoration. To achieve this goal, service providers are looking for flexible optical network ROADMs with CDC capabilities. Although many contention scenarios during network connection provisioning and restoration have been illustrated, surprisingly academic simulations have showed that the blocking probability improvement of CDC ROADM comparing with CD ROADM is not significant. This is good news for service providers since most deployed optical networks are only CD ROADM capable, instead of CDC ROADM capable. How to make use of existing CD ROADMs to achieve network automation becomes an urgent challenge. In this paper, we present two research results to attack this challenge: (1) first, we built an analytical mode to estimate the CD ROADM contention blocking probability and show that when a CD ROADM add/drop local direction capacity occupation ratio is low or moderate, the contention blocking probability is not significant. From this model, we estimate that one can use a CD add/drop local direction capacity occupation ratio up to 75% before installing another CD ROADM add/drop local direction or installing a CDC add/drop local direction when available. Simulation results on real network topologies and traffic matrices verified our recommendation; (2) second, we observed that most deployed optical networks are usually providing 100G or 200G per wavelength while majority applications are still requesting much smaller bandwidths and service providers often provide OTN (Optical Transport Network) over ROADM architecture for transport services. Since OTN provides electronic switching capability, in this paper, we present a new algorithm and methodology to make use of both OTN switch and CD ROADM to avoid service contention without using CDC ROADM.
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