We consider optical networks that use path restoration to restore lightpaths in the event of link failures. We present capacity-assignment algorithms and signaling protocols for various design options and evaluate their performance in terms of capacity efficiency, restoration speed, and proportion of connections that can be restored successfully. Results show that, with preplanning, methods that share restoration capacity can provide rapid restoration while providing significant capacity savings (as much as 40%) over methods with dedicated capacity. Methods with failure-dependent (FD) restoration paths and wavelengths provide significant capacity savings over methods with failure-independent (FI) paths and wavelengths. However, this comes at a cost of considerably higher restoration time as well as an increased fault-monitoring requirement. The wavelength-continuity requirement favors methods with preplanning over methods with dynamic wavelength assignment (DWA) after the failure. Increasing capacity does not compensate for lack of preplanning, which makes DWA appropriate only as a secondary restoration mechanism (e.g., best effort). Overall, preplanned FI restoration offers a good compromise between capacity efficiency, failure recovery time, and implementation complexity.
© 2002 Optical Society of AmericaPDF Article