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