Colorless, partially directionless, and contentionless architecture for high-degree ROADMs

With the rapid growth of Internet traffic, there can be multiple pairs of bi-directional fibers on a network link. This leads to the need for high-degree reconfigurable optical add/drop multiplexers (ROADMs) in an optical network. However, this high-degree requirement poses new challenges to ROADMs since it is challenging and expensive for a wavelength selective switch (WSS), a key switching component in a ROADM, to expand its size. Therefore, a common strategy is to use small-size WSSs to build a high-degree ROADM. In this paper, we design a novel colorless, partially directionless, and contentionless (CpDC) ROADM architecture, in which the sizes of WSSs can be significantly reduced by partially sacrificing the directionless feature of a ROADM. The partially directionless feature may degrade the switching performance of a ROADM. Thus, to tackle this issue, we also propose an interconnection pattern for the ROADM backplane to effectively connect fiber links and add/drop modules. An analytical model is developed to evaluate the lightpath blocking performance of a single CpDC ROADM. Efficient routing, fiber, wavelength, and add/drop port assignment (RFWPA) algorithms (i.e., the shortest-path-based and waveplane-based algorithms) are also developed for lightpath establishment in an optical network made up of CpDC ROADMs, in which two wavelength selection strategies [i.e., non-interconnection aware (NIA) and interconnection aware (IA)] are further proposed. Simulation studies show that, while these achieve almost the same lightpath blocking performance as conventional CDC ROADMs, CpDC ROADMs are more effective from considerations of cost, insertion loss, and node volume. The waveplane-based RFWPA algorithm with the IA strategy is also found to be the most effective for lightpath provisioning in an optical network made up of CpDC ROADMs.