About Telecommunication Network

1. Telecommunication
Networks:
1.1 Evolution of Telecommunications
1.2 Classification of Switching System
Chapter 1

2. The Evolution of
Telecommunications

3. Evolution of Telecommunication
Technology
 Today’s telecommunication
technologies have evolved from fire
signals, drum-beats to instant long-
distance communication using
electrical, radio and electro-optical
signals.

4. Early Signaling and Telegraphy
 Semaphore -method of visual signaling, usually by
means of flags or lights, in which visual on or off stage
represent letters or words.
.

5. Early Signaling and Telegraphy
 Morse code - the transmission of a series of short and
long pulses (dots and dashes) that represented
characters.
 Duplexing - simultaneously transmitting a signal in both
directions along the same wire.
 Multiplexing - simultaneously transmitting an
indeterminate number of multiple signals over one circuit.

6. Early Signaling and Telegraphy
 1856 - Western Union Telegraph Company was founded.
 1861 – Over two thousand telegraph offices operated
across the United States.

7. Telephone Technology

8. Telephone Technology

13. ARPANET: Advanced Research Projects
Agency Network

21. Infrastructure
 Wires criss-crossing cities and states and
terminating in several exchanges or central offices.
 Exchange was also known as a switching point because
the device used to open and close a circuit is known as a
switch.
 Operators would connect the circuits and complete
the call for the subscriber.
 Subscribers refers to a telephone company customer

22. Telephone Switching
 1878- The first telephone exchange opened in New
Haven, Connecticut.
 Connected 21 separate lines.

23. Switching System
Manual Automatic
Electromechanical Electronic
(Stored program control)
Strowger or
Step by Step
Crossbar
Space Division
Switching
Time Division
Switching
Digital Analog
Space Switch Time Switch Combination Switch

24.  In 1889 Almon Strowger developed the
automatic switch called the step-by-step.
 In 1896 he replaced the button-pushing
method with a rotary dialer.

25.  In 1913, N.J. Reynolds, a Western Electric
engineer, developed a better automatic switch,
the crossbar switch. It used a grid of horizontal
and vertical bars, with electromagnets at their
ends. The horizontal bars could rotate up and
down to connect to specific vertical bars and thus
complete circuits.
 Original version could complete 10 simultaneous
connections.
 By the 1970 a single crossbar could connect 35,000
connections.

26.  In the mid-20th
century AT&T integrated
electronics into crossbar switches
 1965 – first electronic switching system was
used
 Handled up to 65,000 two-way voice circuits.
 Until 1970 all telephone switches depended on
a continuous physical connection to complete
and maintain the call.

27.  1976 – New electronic switching device
was put into service.
 Time division switching - a transmission
technique in which samples from multiple
incoming lines are digitized, then each
sample is issued to the same circuit, in a
predetermined sequence, before finally
being transmitted to the correct outbound
line.

28.  Space division switching - manipulating the physical
space between two lines, thereby closing a circuit to
connect a call.
 Local switching center (often called a local office) - a
place where multiple phone lines from homes and
businesses in one geographic area converge and
terminate.
 Tandem switching center - an exchange where lines
from multiple local offices converge and terminate.
 Toll switching center - an exchange where lines from
multiple tandem switching centers converge and
terminate.

29. Telephone Technology

30. Wireless Technology
 Telegraphs and telephones are examples of
wireline, or wire-bound technology, because
they rely on physically connected wires to
transmit and receive signals.
 Wireless technology - relies on the
atmosphere to transmit and receive signals.

31. Wireless Technology
 Examples of wireless technology
 Phones
 Radios
 Televisions
 Satellite communications

32. Wireless Technology
 1894- Italian physicist Guglielmo Marconi a
method of transmitting electromagnetic signals
through the air.
 His invention relied on an induction coil.

33. Wireless Technology
 Induction coil is made by winding wire in a either one or multiple
layers around a metal rod to form a coil then applying a charge
 Charged wire induces an electromagnetic field that generates
voltage
 Marconi connected an induction coil to a telegraph key. Each
time the key was pressed the coil discharged a voltage through
the air between to brass surfaces
 Metal filings in a glass cylinder became charged and cohered.
The length of time they cohered translated into short and long
pulses.
 Pulses were relayed to a Morse code printer.
 Marconi invention used the same type of signals sent and
received by a telegraph.

34. Wireless Technology
 Vacuum tube - a sealed container made of glass, metal,
or ceramic, that contains, in a vacuum, a charged plate
that transmits current to a filament.
 Audion - patented in 1907by DeForest, is a type of
vacuum tube that contains an additional electrode in the
middle of the positive and negative electrodes.
 Boosts or amplifies a signal.
 First instants of signal amplification and it formed the basis
for all subsequent radio and television advances.
 1912- Edwin Armstrong improved the Audion. He
discovered that by feeding the signal back the tube the
power of the Audion could be increased.

35. Wireless Technology
 Continued experimentation resulted in the
invention of Frequency modulation.
 Frequency modulation is technology used in FM
radio and other forms of wireless technology.
 In Frequency modulation one wave containing
the information to be transmitted (for example,
Kantipur FM, Hits FM) is combined with another
wave, called a carrier wave, whose frequency is
constant.
 Frequency is the number of times each second that a
sine wave completes a full cycle.

36. Wireless Technology
 The advent of FM radio afforded the best clarity of
all wireless technologies then available.
 Walkie-Talkies use frequency modulation
 1946- Bell Laboratories connect the first wireless
car phone to the St. Louis network.
 1962- Telstar Satellite successfully transmitted
television and telephone conversation across the
Atlantic for the first time.

37. Wireless Technology
 Geosynchronous - means that satellites orbit
the earth at the same rate as the earth turns.
 Uplink - a broadcast from an earth-based
transmitter to an orbiting satellite.
 At the satellite, a transponder receives the
uplink, then transmits the signals to another
earth-based location in a downlink.

38. Wireless Technology

41. Circuit Switching
A private road all for yourself
Dedicated end to end connection

42. Packet Switching
Divided packets can take different paths and
times
A shared highway