Cisco offers a 4-lambda, 4-channel Coarse Wave Division Multiplexing (CWDM) Optical Add-Drop Module (OADM). The four wavelengths (lambdas) are set to 1470, 1510, 1550, and 1590 nm. The module add/drops these four wavelengths from the network side (network connector) into four separated channels on the equipment side, one wavelength into one channel. All other four wavelengths (1490, 1530, 1570, and 1610 nm) are passed through the module.