Wavelength Division Multiplexing (WDM)

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Code Division Multiplexing (CDM)

In Code Division Multiplexing (CDM), transmissions from different stations are multiplexed by different channel codes and sent on a common channel. The different transmissions use the same frequency. Each user is separated by a code. The receivers of them transmissions have their respective transmitters code word. At the receiving end, these data codes are removed (using the code word) from the desired signal. For the receiver, the signals of all other users appear as noise.

   Wavelength Division Multiplexing (WDM)

WDM is the technology for achieving extremely high data rates over fiber-optic cabling. Also known as Dense Wavelength Division Multiplexing  (DWDM), Wavelength Division Multiplexing is likely to replace Time Division Multiplexing (TDM) as the standard transmission method for high-speed fiber-optic backbones in the next few years.

How WDM Works ?

WDM modulates multiple data channels into optical signals that have different frequencies and then multiplexes these signals into a single stream of light that is sent over a fibe-optic cable. Each optical signal has its own frequency, so up to 80 data streams can be transmitted simultaneously over the fiber using only eight different light wavelengths. In addition, each data stream can employ its own transmission format or protocol. This means that, using WDM, you can combine Synchronous Optical Network (SONET), Asynchronous Transfer Mode (ATM), TCP/IP, and other transmissions and send them simultaneously over a single fiber. At the other end, a multiplexer de-multiplexes the signals and distributes them to their various data channels.

o   Devices that support WDM are more costly because they use laser light sources for generating signals over fiber which must be highly stable.