Analysis of internal ROADM protection

Reconfigurable optical add/drop multiplexers (ROADMs) are a key component in most carrier networks. One common ROADM design utilizes a set of wavelength-selective switches (WSSs) in a broadcast-and-select architecture. All traffic at the node passes through at least one WSS. If a WSS fails, the affected traffic can be routed over spare network capacity, similar to a link failure. Alternatively, WSS redundancy can be provided internal to the ROADM. We discuss the advantages of internal ROADM protection, and analyze two architectures for providing protection for the WSSs.