In optical ring networks, the impact of residual fiber dispersion on the cascadability limit of the optical add-drop systems due to in-band crosstalk is investigated. An experimentally verified re-circulating non-zero dispersion shifted fiber (NZ-DSF) loop model is used to emulate the cascade effect of multiple add-drop nodes. The nodes are implemented based on Wavelength Selective Switches (WSSs) at varying node degrees to support different network configurations. It is shown that 16 node metro rings can be constructed cost effectively using NZ-DSF, at link distances of 75 km, for fiber dispersions as high as 4.6 and 1.2 ps/nm-km at bit rates of 2.5 and 10 Gb/s, respectively, at a 1dB of crosstalk induced penalty. A modular architecture extending to large degree ROADM for mesh networks is also proposed and scalability in terms of crosstalk is reported.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.