Bandwidth utilization techniques allow multiple signals to be transmitted simultaneously over a single data link. Multiplexing divides the bandwidth into channels that can be assigned to different signals. There are two primary multiplexing techniques: frequency-division multiplexing (FDM) and time-division multiplexing (TDM). FDM is an analog technique that combines signals by assigning each to a different frequency band. TDM is a digital technique that combines signals by assigning each short time slots in a repeating sequence. TDM makes more efficient use of the available bandwidth than FDM.

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2. Note
Bandwidth utilization is the wise use of
available bandwidth to achieve
specific goals.
Efficiency can be achieved by
multiplexing; i.e., sharing of the
bandwidth between multiple users.
6.2

3. 6-1 MULTIPLEXING
Whenever the bandwidth of a medium linking two
devices is greater than the bandwidth needs of the
devices, the link can be shared. Multiplexing is the set
of techniques that allows the (simultaneous)
transmission of multiple signals across a single data
link. As data and telecommunications use increases,
so does traffic.
Topics discussed in this section:
 Frequency-Division Multiplexing
 Synchronous Time-Division Multiplexing
6.3

4. Figure 6.1 Dividing a link into channels
6.4

5. Note
FDM is an analog multiplexing technique
that combines analog signals.
It uses the concept of modulation
6.5

6. Figure 6.4 FDM process
6.6

7. Figure 6.5 FDM demultiplexing example
6.7

8. Figure 6.12 Time Division Multiplexing (TDM)
6.8

9. Note
TDM is a digital multiplexing technique
for combining several low-rate digital
channels into one high-rate one.
6.9

10. Figure 6.13 Synchronous time-division multiplexing
6.
10

11. INTERLEAVING
The process of taking a group
of bits from each input line
for multiplexing is called
interleaving .
6.11

12. Figure 6.15 Interleaving
6.
12

13. FREQUENCY DIVISION MULTIPLEX
Separation of spectrum into smaller
frequency bands
Channel gets band of the spectrum for the Channels
ki
whole time
Advantages: k 3 k 4 k5 k6
no dynamic coordination needed
works also for analog signals
Disadvantages:
waste of bandwidth
if traffic distributed unevenly
inflexible
guard spaces
t

15. 6.15

16. WHY FDM IS FOR ANALOG SIGNALS AND
TDM IS FOR DIGITAL SIGNALS?
FDM stnds for frequency division
multiplexing and it is used only in case of
analog signals because analog signals are
continuous in nature and the signal have
frequency.
TDM-stands for time division multiplexing
and it is used only in case of digital
signals because digital signals are
discrete in nature and are in the form of 0
and 1s. and are time dependent.
6.16

17. ADVANTAGES & DISADVANTAGES OF
TDM & FDM
In TDM, different users share the same channel based on
time slots alloted to them. Each user or source is given a
particular time slot to send its information.
1. The entire channel BW is available for a particular time
interval unlike in FDM where the channel BW is split into
smaller segments. This enables higher data rates.
2. All users share the same frequency, so spectrum
efficieny is increased. Available channel BW is no more a
constraint.
6.17

18. 18
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