Protection and restoration in optical networks

Summary form only given. Today's DWDM optical line systems (OLS) carry OC48/OC192 SONET/SDH voice and data, fiber-cut and equipment-failure protected by the SONET/SDH rings. Emergence of new transmission protocols such as IP over fiber or gigabit Ethernet requires protocol independent optical protection implemented in the new transmission layer called an optical network. High cost of 1+1 dedicated protection is reduced with the optical shared ring protection (OSPring) where a single protection wavelength protects against simultaneous failures of non-overlapping paths on several service wavelengths. Simultaneous failures of overlapping paths cannot be protected by OSPring. Optical cross connects interconnect DWDM OLS systems to give the ability to restore traffic from the failed OLS by re-routing it through its inter-connected partners. The required 50 milliseconds protection delay is much shorter than the seconds long restoration.