working of telephone system and multiplexing data

1. Telephone System &
Multiplexing
Performed By: 1) Abhishek Gaikwad
2) Ketan more
3) Aditya Shinde
4) Vaibhav Pote

2. Telephone Systems
O Telephone Networks use Circuit
Switching. The telephone network came
into existence in late 1800s.
O The POTS is a old telephone network
which used analog systems and analog
signals to transmit voice.
O During the recent years, the telephone
network has changed a lot. The network is
now digital as well as analog.

3. Components of Telephone
Systems

4. O The figure shows the most basic
telephone network that is made of three
main components:
 Local loop
 Trunks &
 Switching offices
1) Local Loops:
• Local Loop is a twisted pair cable this is used
for connecting a subscribers telephone to the
nearest end office.
• The local loop has a bandwidth of 4 kHz if it is
used for voice communication
2) Trunks:
• Trunks are the transmission media that
handles the communication between offices

5. • The trunks handles hundreds of thousands of
connection simultaneously. The transmission
media used as trunks is usually optical fiber
cables or satellites links
Switching offices:
• Connecting every subscriber permanently
with all the other subscriber using wires will
be an impossible thing.
• Hence the telephone companies use
switches located at the switching offices to
establish a connection as and when required
, between the calling and the called
subscribers.

6. MULTIPLEXING
O It is process of simultaneously transmitting
two or more signals over a single
communication channel.
O Due to multiplexing it is possible to
increase the number of communication
channels so that more information can be
transmitted.
O The typical applications of multiplexing are
in telemetry and telephony or in the
satellite communication.

7. Concept of Multiplexing
O The multiplexer
receives a large
number of different
input signals
O Multiplexer has only
one output which is
connected to single
communication
channel.

8. O The multiplexer combines all input signals
into a single composite signal and
transmits it over the communication
medium.
O Sometimes the composite is used to
modulate a carrier before transmission.
O At the receiving end, of communication
link, a demultiplexer is used to sort out the
signal into their original form.
O A demultiplexer is the circuit which
decomposes the multiplexed signal into
the original signals.

9. Classification
Of Multiplexing
MULTIPLEXING
Analog Multiplexing Digital
Multiplexing
FDM WDM TDM

10. TYPES OF MULTIPLEXING
O There are basically three types of
multiplexing:
1. Frequency Division Multiplexing (FDM)
2. Time Division Multiplexing (TDM)
3. Wavelength Division Multiplexing
(WDM).

11. FDM
O The FDM is based on the concept of
sharing bandwidth of a common
communication channel. The signals
which are to be transmitted
simultaneously will each modulate a
separate carrier.
O The modulation can be AM, SSB, FM or
PM. The modulated signals are then
added together to form a complex signal
which is transmitted over a signal channel.

12. FDM (Block Diagram)

13. Advantages
O A large number of signals can be
transmitted simultaneously .
O Due to slow narrow band fading only a
single channel gets affected.
Disadvantages
O FDM suffers from the problem of
crosstalk.
O All the FDM channels get affected due to
wideband fading.

14. Applications of FDM
O Telephone systems.
O AM(amplitude modulation) and
FM(Frequency modulation) radio
broadcasting
O TV broadcasting.
O First generation of cellular phones used
FDM.

15. WDM(Wavelength Division
Multiplexing)
O WDM is the variation of FDM, for fiber
optic channels.
O As shown in figure, 2 fibers come together
at a prism, each having energy in a
different band. After passing through the
prism, beams are combined onto a single
shared fiber, for transmission to a distant
destination, where they are split again.

16. Fibers and Prism Diagram

17. Applications
O One important
application of WDM
is SONET network
in which multiple
optical fiber lines
are multiplexed and
demultiplexed.

18. TDM(Time Division
Multiplexing)
O In TDM all the signals to be transmitted
are not transmitted simultaneously.
Instead, they are transmitted one by one .
O Thus each signal will be transmitted for a
short time. One cycle or frame is said to
be complete when all the signals are
transmitted once on the transmission
channel. The TM principle is illustrated in
the Figure o the next slide.

19. O As shown in the figure one transmission of
each channel completes one cycle of
operation called as “Frame”.
O The TDM system can be used to multiplex
analog and digital signals, however it is
more suitable for the digital signal
multiplexing.

20. Advantages of TDM
O Intermodulation distortion is absent.
O TDM circuitry is not very complex.
O The problem of crosstalk is not very
severe.
O Full available channel bandwidth can be
utilized for each channel.

21. Disadvantages
O Synchronization is essential for proper
operation.
O Due to slow narrow band fading, all the
TDM channels may get wiped out.
Applications
1) For Multiplexing of digital data.
2) For digital telephony.
3) In the mobile phones.