Editing Wavelength-division multiplexing (section)

===Reconfigurable optical add-drop multiplexer (ROADM)===
{{Main|Reconfigurable optical add-drop multiplexer}}
As mentioned above, intermediate optical amplification sites in DWDM systems may allow for the dropping and adding of certain wavelength channels. In most systems deployed as of August 2006 this is done infrequently, because adding or dropping wavelengths requires manually inserting or replacing wavelength-selective cards. This is costly, and in some systems requires that all active traffic be removed from the DWDM system because inserting or removing the wavelength-specific cards interrupts the multi-wavelength optical signal.

With a ROADM, network operators can remotely reconfigure the multiplexer by sending soft commands. The architecture of the ROADM is such that dropping or adding wavelengths does not interrupt the ''pass-through'' channels. Numerous technological approaches are utilized for various commercial ROADMs, the tradeoff being between cost, optical power, and flexibility.