Khaled: Probably you want to know the difference between Colored and Non-Colored (Black and White) Interfaces. DWDM Multiplexer receives "n" number of Signals of different wavelengths as per ITU Grid.

The client may be SDH/SONET, Router with Ethernet Interfaces (eg 1G/10G/etc), or other signals. By default, the output signal is 1310 nm or 1550 nm. For feeding this signal into DWDM Mux, it needs to be converted into specific wavelength. This job is typically done by the OTU (Transponder). In this case, the Client Signal is non-colored (1310/1550nm) which is converted into colored signal (specific lambda) by the OTU.

In the above scenario, two cards are used: Line Card of the Client Equipment and the OTU. To save the cost, and probably due to a few other reasons, the above functionality can be combined into one card. In that case, the Line Signal of the Client Equipment is called Colored Signal.

So the main difference between colored and non-colored signal is that non-colored in 1310/1550nm while the colored signal is lambda-specific (anywhere in the C-Band or any other band used in DWDM). C-Band ranges from 1530-1560 nm (sometimes upto 1565 nm).

Hope it explains all.

The transponder converts the gray interface of the client (i.e. 1310 or 1550 nm) into specific DWDM wavelength (i.e. C-Band) when they have exactly The same bandwidth (e.g. 10G client to 10G DWDM lambda or 40G client to 40G DWDM lambda).

If you however have various client interfaces with different rates, (e.g. SDH/SONET, 1GbE, 10GbE), then a Muxponder shall/can be used instead of Transponder to multiplex these clients efficiently (assuming they are intended to the same direction).

Another way to do it more efficiently is by using OTN cross-connection/switch, wherein you will need to have Client/Tributary Cards for your client interface, Line Cards on your DWDM side and the OTN Cross-connect/switch in the middle to carry out the efficient cross-connection/mapping/grooming/switching between them on an ODUn level...

Hope this also add more details.