Upgrading SONET rings with WDM instead of TDM: an economic analysis

We compare a time-division multiplexed (TDM) upgrade of a legacy SONET ring to a single higher speed ring, versus a wavelength-division multiplexed (WDM) upgrade path, in which it is possible to retain the legacy ring and add additional "virtual rings" at different wavelengths and lower speeds. The paper makes the case that the WDM option can be economically compelling.