Multiplexing

It is the process of combining a number of individual channels into a common frequency band or into a common bit stream for transmission.

Different multiplexing techniques are:
• Frequency Division Multiplexing (FDM)
• Time Division Multiplexing (TDM)
• Wavelength Division Multiplexing (WDM)

Frequency Division Multiplexing
FDM is a process in which the bandwidth is divided in frequency domain, or in other words each of the input signals is transmitted at a different frequency (Carrier) but simultaneously (or in the same time slot).  FDM is a multiplexing technique used for analog signals.

Time division multiplexing
TDM is a type of multiplexing in which different signals are multiplexed in different time slots. In TDM each time slots is fixed for different signals sequentially. TDM uses full bandwidth for every channel, but not at the same time so that every channel gets its time slot in the shared line.

Wavelength division multiplexing
It is a type of multiplexing in which different signals are multiplexed at different wavelengths for full time slots. When each wavelength is multiplexed from different TDM signals then the multiplexing is called TDM over WDM. WDM is widely used for the following reasons:

• Better utilization of fiber
• Low unit cost of bandwidth in high capacity systems

• Easily integrated with existing equipment in the network

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