Thank you for your question.
These are all methods that can be used for data communications and transmissions.
a) Time division multiplexing (TDM) gives each host or signal a
certain amount of transmission time. The available transmission time
is divided into quanta. Each flow has access to the data link in a
The limitation of this technique, is that hosts that don't have
anything to transmit (which is usually the case) will tie up the link
for nothing and block their share that could instead be used by other
hosts. Therefore TDM is usually very inefficient.
Time division multiplexing
b) Frequency division multiplexing (FDM) works in a slightly different
way. Each flow of data is sent simultaneously over the link at
different frequencies (analogue TV and radio are examples of FDM).
The signals are modulated at the transmission end and demodulated at
the receiving end.
The disadvantage is that the number of flows is fixed. Resizing quanta
or adding frequencies is not practical.
Frequency division multiplexing
c) Wave division multiplexing (WDM) or wavelength division
multiplexing multiplexes several optical carrier signals onto a single
optical fiber. Each signal is transmitted at different wavelengths by
using laser light.
A multiplexor combines the signal together to be transmitted over the
cable, and a demultiplexor separates them once then reach the other
The great advantage that WDM has over the other two technologies, is
that the bandwidth can be increased without changing the transmission
medium or cable. By upgrading the multiplexors and demultiplexors,
bandwidth can be increased.
The disadvantage of this system is that the hardware is expensive.
Wavelength division multiplexing
To sum up, TDM is simple but inefficient. FDM allows maximum
transmission link usage but cannot evolve easily. WDM is fast and
evolutive but is expensive.
I hope this answers your question. If something is unclear, if you
require any more help or you require any clarifications, please do not
hesitate to ask.
"wave division multiplexing" definition