Multiplexing is the one of the important topics in Networks

1. PRESENTED BY :
MAHIDHAR . D
MSc. STATISTICS AND APPLIED MATHEMATICS-1
Prepared & Submitted By
N. Sai Kumar
K. Venkatesh
P. Revanth Reddy
K. Sangeetha
L. Vijetha
Submitted to
Dr. Nandini Madam

2. History of Multiplexing
◈ The concept of Multiplexing was originated in telegraphy in
the 1870s. Nowadays, it is widely used in communications.
◈ Later in 1874, Thomas Edison invented diplexing to transmit
two individual messages over one line at the same time
◈ George Owen Squier is called the father of Multiplexing in
telephony. He was credited for the development of
telephone carrier multiplexing .
◈ Later in 1894 and the 1930s, time-division multiplexing
(TDM) and frequency division multiplexing (FDM) came into
existence.
2

3. No Multiplexing VS Multiplexing
3
● Suppose there are 4 users at one end and another 4 users at other end.
Note that each user requires one cable to transmit their information. If
the distances are small, the cost of the wire can be tolerated.
Imagine a person communicating from India to US . If the persons are
separated geographically long, the cost of the channels will be high.
❖ This is where multiplexing is used, where one single wire (channel) is
used to establish communication among all the users.

4. ◈ Whenever the bandwidth of a medium linking two devices
is greater than the bandwidth needs of the devices, the link
can be shared.
◈ In a multiplexed system, n lines share the bandwidth of one
link.
4

5. Sharing Medium
◈ A link is divided into channels
5
M
U
X
D
E
M
U
X
n signals
(input)
n signals
(output)
1 link, n channels
Multiplexer Demultiplexer

6. Multiplexing
◈ A Multiplexer (MUX) is a device that combines
several signals into a single signal.
◈ A Demultiplexer (DEMUX) is a device that
performs the inverse operation.
6

7. Multiplexing
◈ Multiplexing is a technique, which allows many users to share a single
communication channel (wire, cable, radio link, fiber optic cable,
satellite) simultaneously. So a number of information sources share the
same communication channel.
◈ Information transmitted can be either voice (telephone signals) or data
(computer signal, images, video etc). Well-known application of
multiplexing is telephone communication system.
◈ It is divided into 3 types
7

8. Types of Multiplexing
8

9. Frequency Division
Multiplexing

10. Wave Length DM
10
WD
M
WD
M
λ1
λ2
λ3
λ1
λ2
λ3
λ1+λ2+λ3

11. Time Division Multiplexing
11
2
3 1
M
U
X
1
2
3
2
3 1
2
3 1
1
2
3
D
E
M
U
X
Data flow

12. Frequency Division Multiplexing (FDM)
◈ Medium BW > Channel BW
◈ Each signal is modulated to a different carrier frequency
◈ E.g., broadcast radio
◈ Channel allocated even if no data
12
An analog multiplexing technique to combine
signals

13. Conceptual View of FDM
13
Channel
3
Channel
2
Channel
1
f1
f2
f3

14. FDM: Multiplexing Process
14

15. FDM: Demultiplexing Process
15

16. Guard Bands
◈ Strips of unused bandwidth to prevent signals from
overlapping
16
FDM
3 kHz
f
FDM
(no guard band)
FDM
(with guard band)
f
3 kHz 3 kHz 3 kHz
f
3 kHz 3 kHz 3 kHz
f
3 kHz
f
3 kHz 3 kHz 3 kHz

17. FDM: Example 1
17
Five voice channels, each with 3-kHz
bandwidth, are to be multiplexed together.
If there is a need for a guard band of 1.5 kHz,
what is the minimum bandwidth of the link?
f
3 kHz 3 kHz 3 kHz 3 kHz 3 kHz
1.5 kHz 1.5 kHz 1.5 kHz 1.5 kHz
21 kHz

18. Analog Hierarchy
◈ Used by AT&T
18
F
D
M F
D
M
F
D
M
F
D
M
5
groups
…
10
supergropus
6
master
groups
group
supergroup
master
group
Jumbo
group
4 kHz
4 kHz
4 kHz
…
12
voice
channels
48 kHz
12 voice channels
240 kHz
60 voice channels
2.52 MHz
600 voice channels
16.984 MHz
3600 voice channels

19. Frequency Division Multiplexing
Other Applications of FDM
◈ AM uses special band from 530 to 1700 kHz. each AM station
needs 10kHz of bandwidth.
◈ FM has a wider band of 88 to 108 MHz . each station needs a
bandwidth of 200 kHz
◈ television broadcasting. Each TV channel has its own
bandwidth of 6 MHz
◈ The first generation of cellular telephones (still in operation)
also uses FDM. Each user is assigned two 30-kHz channels,
one for sending voice and the other for receiving.
� The voice signal, which has a bandwidth of 3 kHz (from 300 to
3300 Hz), is modulated by using FM. Remember that an FM
signal has a bandwidth 10 times that of the modulating signal.
19

20. Frequency Division Multiplexing
Other Applications of FDM
◈ The Advanced Mobile Phone System (AMPS) uses
two bands.
� The first band of 824 to 849 MHz is used for
sending, and 869 to 894 MHz is used for receiving
(Each band is 25 MHz).
� Each user has a bandwidth of 30 kHz in each
direction.
� If we divide 25 MHz by 30 kHz, we get 833.33. In
reality, the band is divided into 832 channels.
� Of these, 42 channels are used for control, which
means only 790 channels are available for cellular
phone users.
20

21. Frequency Division Multiplexing
Implementation
◈ In radio and television broadcasting, there is no
physical multiplexer or demultiplexer. the stations
agree to send their broadcasts to the air using
different carrier frequencies.
◈ In cellular telephone system, a base station needs
to assign a carrier frequency to the telephone user.
� When a user hangs up, her or his bandwidth is
assigned to another caller
21

22. Example
22
The Advanced Mobile Phone System (AMPS) uses two
bands. The first band of 824 to 849 MHz is used for
sending, and 869 to 894 MHz is used for receiving.
Each user has a bandwidth of 30 kHz in each direction.
How many people can use their cellular phones
simultaneously?
Solution
Each band is 25 MHz. If we divide 25 MHz by 30 kHz, we
get 833.33. In reality, the band is divided into 832
channels. Of these, 42 channels are used for control,
which means only 790 channels are available for cellular
phone users.

23. Wavelength Division
Multiplexing

24. WDM
● Wavelength Division Multiplexing is similar to
Frequency Division Multiplexing except for the
fact that optical signals are delivered over fibre
optic cable.
● WDM is a technique used in fibre optics to enhance
the capacity of a single fibre.
● It is utilised to take advantage of the high data
rate capabilities of fibre optic cable.
● It is a technique for analogue multiplexing.

25. ● With the aid of a multiplexer, optical signals from several
sources are merged to produce a broader spectrum of light.
● The signals are separated at the receiving end by a
demultiplexer before being sent to their respective
destinations.
● A prism can be used to do multiplexing and demultiplexing.
● Prism can function as a multiplexer by mixing several optical
signals to produce a composite signal, which is then sent
through a fibre optical connection.

27. ● Prism also does a reverse process, which is signal
demultiplexing.
● Dense wavelength division multiplexing merges a large number
of channels (30, 40, 50, or more) onto a single fibre. DWDM
channels have a very high capacity that is constantly
improving.
● Only a few wavelengths are combined using coarse wavelength
division multiplexing. This has more widely spread channels
and is a less expensive variant of DWDM.

30. Advantages of WDM
● Full-duplex transmission is achievable with the aid of WDM.
● WDM is simple to reconfigure.
● With the aid of WDM, several signals may be sent at the same
time.
● This method is less costly, and system expansion is simple.
● This method is highly secure.
● Because optical fibre is used in WDM, optical components are
more dependable and provide more bandwidth.

31. Disadvantages of WDM
● Because optical equipment is used, the cost
rises.
● Because of poor bandwidth use, wavelength
adjustment might be challenging.
● This technique’s major issue is scalability.

32. TIME DIVISION
MULTIPLEXING

33. TIME DIVISION MULTIPLEXING
●The Time Division Multiplexing (TDM) is a digital procedure.
●TDM is a technique used for transmitting several message signals over a single
communication channel by dividing the time frame into slots, one slot for each
message signal
●Example: Television Broadcast.

34. TDM

35. TYPES OF TDM

36. Synchronous TDM
●In STDM, the multiplexer assigns an equal time slot to every device at all times.
●Each time is assigned a time slot and it shows up.
●The time slots are consolidated into frames.
●Every frame includes one or more time slots committed to each sending device.

37. STDM

38. INTERLEAVING
●Synchronous Time Division Multiplexing (TDM) can be distinguished to a high-
speed rotating switch.
●As the switch is free in front of a device, that device can transmit a particular
record of data onto the direction.
●The switch transfers from device to device at a fixed price and in a permanent
order.

39. STDM

40. MULTIPLEXER

41. DEMULTIPLEXER

42. Asynchronous TDM
●An asynchronous TDM is also called as a Statistical TDM.
●Designed to solve the problem of the synchronous TDM.
●In ATDM, if there are n input lines, then each slot can contain m frames, where m
is less than n.

43. ●In ATDM, the multiplexer scans all the input lines and accepts the portions of
data till the frame is filled.
●When the frame is filled, it is sent across the link.
●If the senders don't have enough data to fill the frame, it is transmitted as
partially filled.

44. ●In ATDM, all sending devices can send data in all slots.
● As the slots are variable the receiver cannot identify the characters by
counting them.
●An efficient addressing mechanism is required, which should supply a unique
address to each time slot.
●These addresses are temporary and discarded by demultiplexer after reading
them correctly.

46. Difference B/W ATDM & STDM
Synchronous
●Few slots are unused.
●multiplexers can have
many input/output (I/O)
lines with a buffer related
to each of them.
Asynchronous
●Slots are entirely used.
●It firmly assigns the time
slots on demand to free
the input channels. Hence
the channel size can be
stored.

47. THANK YOU