Tunable DWDM OTDR for testing through mux/demux channels to provide complete end-to-end link characterization and troubleshooting of metro Ethernet links and commercial services - For commercial services in fiber-to-the building (FTTB)/fiber-to-the-premises (FTTP) and cellular-backhaul (CBH) deployments that are evolving and migrating from CWDM to DWDM metro Ethernet links.