On Transient-Constrained Wavelength Assignment

In a network with Reconfigurable Optical Add/drop Multiplexers (ROADMs), transient effects from network failures trigger sudden power changes to channels, even on spans (ROADM-to-ROADM links) upstream/downstream from the failure. Some ROADMs rely on restrictive wavelength assignment rules, called field-of-use (FOU), to insure surviving channels meet performance objectives. Drop depth (DD) (ratio of surviving channels) and span overlap count (SOC) (length of spans of overlapping lightpaths) are two parameters defined for FOU guidelines. For a given DD, FOU guidelines specify a corresponding maximum SOC for each wavelength. Generally, a wavelength can support a longer span overlap count under a smaller drop depth restriction. However, the measured drop-depth changes as wavelengths are assigned. We propose methods to optimize transient-constrained wavelength assignment in commercial ROADM networks. Our solutions have been shown to provide 40% more channels than with typical FOU guidelines.