Multiplexing techniques such as frequency division multiplexing (FDM), time division multiplexing (TDM), and wavelength division multiplexing (WDM) allow multiple transmission sources to share a common circuit. FDM involves modulating each signal to a different carrier frequency with guard bands between frequencies. TDM involves interleaving digital signals in time slots, which may be allocated even if no data is being sent. WDM transmits multiple beams of light at different wavelengths over an optical fiber, functioning as a form of FDM for optical networks.

1. Unit -3
Multiplexing
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

2. Figure 8-1
Multiplexing vs. No Multiplexing
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

3. Multiplexing
• Enable two or more transmission sources to
share a common circuit
• Most common forms – FDM and TDM
• FDM – associated with analog signal,
simultaneous transmission
• TDM – associated with digital signal (could
also be analog) with time slices
3

4. Multiplexing
4

6. Frequency Division Multiplexing
• Each signal is modulated to a different
carrier frequency
• Carrier frequencies separated so signals do
not overlap (guard bands)
• Channel allocated even if no data
6

7. Frequency Division Multiplexing
Diagram
7

8. Figure 8-3
FDM
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

9. Figure 8-5
Multiplexing, Frequency Domain
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

10. Figure 8-7
Demultiplexing, Frequency Domain
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

11. Figure 8-4
FDM, Time Domain
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

12. Figure 8-6
Demultiplexing, Time Domain
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

13. TDM

14. Synchronous Time Division
Multiplexing
• Multiple digital signals interleaved in time
• May interleave bits, so not necessarily
synchronous transmission
• Time slots pre-assigned to sources and
fixed
• Time slots allocated even if no data
• Time slots do not have to be evenly
distributed amongst sources
14

15. Time Division Multiplexing
15

16. Figure 8-9
Synchronous TDM
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

17. TDM, Multiplexing

18. Figure 8-11
TDM, Demultiplexing
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

19. Framing Bits

20. Figure 8-13
Data Rate
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

21. Figure 8-14
Asynchronous TDM
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

22. Figure 8-15
Frames and Addresses
a. Only three lines sending data
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

23. Figure 8-15-continued
Frames and Addresses
b. Only four lines sending data
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

24. Figure 8-15-continued
Frames and Addresses
c. All five lines sending data
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

25. Wavelength Division
Multiplexing
• Multiple beams of light at different frequency
• Carried by optical fiber
• A form of FDM
• Each colour of light (wavelength) carries separate data
channel
25

26. WDM Operation
• Same general architecture as other FDM
• Number of sources generating laser beams
at different frequencies
• Multiplexer consolidates sources for
transmission over single fiber
• Optical amplifiers amplify all wavelengths
– Typically tens of km apart
• Demux separates channels at the destination
26

27. Figure 8-16
WDM - Wavelength Division Multiplexing
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

28. Figure 8-16
WDM - Wavelength Division Multiplexing
WCB/McGraw-Hill © The McGraw-Hill Companies, Inc., 1998

29. WDM - Wavelength Division Multiplexing