The Cisco ONS 15216 optical add/drop multiplexers (OADMs) allow service providers to deliver wavelengths to the building in single-channel increments, and to combine wavelengths from the Cisco ONS 15454, ONS 15252, ONS 15201, and ONS 15540 platforms.The Cisco ONS 15216 offers three OADMs: A one-channel, two-path OADM that allows service providers to add and drop one protected channel (one in each direction east and west) at any point in a DWDM ring; a two-channel, two-path OADM that allows service providers to add and drop two protected channels; and a four-channel, two-path OADM that allows service providers to add and drop four protected channels. The 1 and 2 Channel OADMs are packaged in a compact, 1-RU 19- or 23-inch rack-mounted shelf. The 4 Channel OADM is packaged in a compact, 2-RU 19- or 23-inch rack-mounted shelf. Software-controlled variable optical attenuators are available at the add ports of the units to attenuate the power level of the added channel to match the express stream. This enables the user to ensure the channel being added does not negatively impact the uniformity of the spectrum. This is particularly important for amplified applications where the flatness response of the C-band erbium doped fiber amplifier (EDFA) is directly linked to the uniformity of the input stream. Two output monitor tap ports are also provided in the same chassis to monitor the outgoing signals in east and west directions.