An Overview of Communication

Engineering

(Wired)

Dr. Akmal Chaudhary

Assistant Professor

Department of Electrical Engineering

Ajman University of Science & Technology

Ajman, 2013

What is Communication?

2

• What does communication means?

The term communication means the transfer of some form of

information from one place to another place.

• What is telecommunication?

In telecommunications, sender transmits a signal through a

transmission medium such as air/cable.

• Importance of Communications!Teleconferencing, teleshopping, telebanking, internet,

computer networks, mobile,...etc

What is Communication?

3

Communications

Telecommunications

Sender Receiver

Signal

Transmission

Medium(air)

Sender

Receiver

Signal

Transmission

medium (wire)

Basics - What is Signal?

4

• To be transmitted, data must be transformed to

electromagnetic signals.

• Data can be analog or digital. Analog data are

continuous and take continuous values. Digital data

have discrete states and take on discrete values.

• Signals can be analog or digital. Analog signals can

have an infinite number of values in a range; digital

signals can have only a limited number of values.

• In communication, we commonly use periodic analog

signals and nonperiodic digital signals.

• Both analog and digital signals have amplitude and

frequency.

Basics - Analog and Digital Signal

Digital SignalDigital Signal

tt

A A

5

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Basics - Importance of Modulation

• In modulation, a message signal, which contains the

information is impressed onto the carrier.

• Modulation is used because data signals are not

always suitable for direct transmission.

• There are three basic types of modulation: Amplitude

modulation, Frequency modulation, and Phase

modulation

• Telecommunications: electronic transmission of

signals for communications, via telephone, radio,

television, etc.

• Data communications: subset of telecommunications

that refers to the electronic collection, processing, and

distribution of data, typically between computer

system hardware devices.

• Telecommunications medium: anything that carries

an electronic signal and interfaces between a sending

device and a receiving device.

Telecommunications

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Elements of Telecommunications System

8

Signal [2]

Signal [2]

Sending Computer

System and

Equipment[1]

Medium[4]Telecommunications

Device[3]Receiving Computer

System and

Equipment[6]

Telecommunications

Device[5]

Medium[4]

Signal [2]

Medium[4]

• Examples of Today’s Communication Methods:

Satellite (Telephone, TV, Radio, Internet, … )

Microwave (Telephone, TV, Mobile, …)

Optical Fibers (TV, Internet, Telephone, … )

Copper Cables (Telephone lines, Cable TV, …………)

Types of Communication Systems

�Simplex

• Unidirectional

• As on a one-way street

�Half-duplex

• Both transmit and receive possible, but not at the same time

• Like a one-lane road with two-directional traffic

• Walkie-talkie, radio broadcast

�Full-duplex

• Transmit and receive simultaneously

• Like a two-way street, telephone network

• Channel capacity must be divided between two directions

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Communication Technology Applications

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Voice mail Twitter/Facebook

E-mailInstant

messaging Chat rooms

Newsgroups TelephonyVideo

conferencing

Collaboration Groupware Global Positioning

System (GPS)

• There are two types of transmission media: guided and

unguided.

Types of Transmission Media

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Twisted-pair

cableFree Space

Coaxial

cableFiber-optic

cable

Transmission

media

Guided

(wired)

Unguided

(wireless)

Twisted Pairs - Guided Media

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• Twisted pairs of copper wire, shielded or unshielded

are used for telephone service.

Insulator Conductors

Plastic cover Plastic cover

Metal Shield

Twisted Pairs - Guided Media

• Cumulative effect of noise is equal on both sides of

twisted pair.

• Twisting does not always eliminate the noise, but does

significantly reduce it

• The use of twisted pairs is limited by the distance.

Transmission speed and data rates are too low.

13

Coaxial Cable- Guided Media

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• Carries signals of higher frequency ranges than those

in twisted-pair cable.

Plastic cover

Outer conductor

(shield)

Insulator

Inner conductor

• Optical fiber is made of glass. It transmits signals in

the form of light.

The Nature of Light

o The speed of light

• 300,000 Km/sec in a vacuum

• Depends on the density of the medium through which it is

traveling

o Other properties of light

• Refraction, Critical angle, Reflection

Optical Fiber - Guided Media

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Optical Fiber - Guided Media

16

Outer Jacket

Plastic

buffer

Glass or

plastic core

Cladding

Du Pont Kevlar

for strength

Construction of Fiber Optics / Optical Fiber

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Optical Fiber - Guided Media

Bending of Light Ray

I < critical angle,

refraction

I = critical angle,

refraction

I > critical angle,

reflection

Less

dense

Less

dense

Less

dense

More

dense

More

dense

More

dense

Sender Receiver

Cladding

Cladding

Core

Optical Fiber - Guided Media

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o Advantages

�Higher bandwidth

�Less signal attenuation

�Immunity to electromagnetic interference

�Resistance to corrosive materials

�Light weight and greater immunity to tapping

o Disadvantages

�Installation and maintenance

�Unidirectional light propagation

�Cost

Unguided Media - Wireless

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o Broadcast Radio

� Distribute signals through the air over long distance using

an antenna

� Typically for stationary locations and can be short range

o Cellular Radio� High frequency broadcast used for mobile communication

to transmit voice / data and utilizes frequency-reuse

Unguided Media - Wireless

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o Microwaves

� Radio waves providing high speed transmission. They are

point-to-point (can’t be obstructed)

� Microwaves are used for robust / efficient satellite

communication

o Infrared� Wireless transmission media that sends signals using

infrared light- waves - Such as?

�TV remotes, keyboards, printers

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Data Transmission Modes

o The transmission of digital data across a link can be

accomplished in either parallel or serial mode.

Transmission Modes

Parallel Serial

Synchronous Asynchronous

Data Transmission Modes

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o Serial Transmission

� Data is transmitted, on a single channel, one bit at a time

one after another

� Advantage: reduced cost and allows two ways of

transmission: asynchronous, synchronous

o Asynchronous� A gap between two bytes: means asynchronous at byte

level. Uses start bit (0) and stop bits (1s)

o Synchronous

� Special sequence of 1/0 between frames: No gap!

Sender transmitted

101 0 0 1 1 0

Receiver received

101 0 0 1 1 0

Sen

der tran

smitted

1

0

0

1

1

0

0

1 Rec

eiv

er r

ecei

ved

1

0

0

1

1

0

0

1

Data Transmission Modes

o Parallel Transmission� Each bit has it’s own piece of wire along which it travels

- often used to send data to a printer

� Advantage: speed

Transmission Impairments

Impairment

causes

Distortion NoiseAttenuation

• Signals travel through transmission media, which are

not perfect. The imperfection cause impairment in the

signal.

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Attenuation - Transmission Impairments

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• Loss of energy to overcome the resistance of the

medium: heat

Original Attenuated Amplified

Transmission medium Point 2Point 1 Point 3

Amplifier

Distortion - Transmission Impairments

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• The signal changes its form or shape due to resistance

offered by the medium.

At the sender At the receiver

Composite signal

sentComposite signal

received

Components,

in phase

Components,

out of phase

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Noise - Transmission Impairments

• Several types of noises, such as thermal noise, induced

noise, crosstalk, and impulse noise, may corrupt the

signal.

Transmitted Noise Received

Point 1 Point 2Transmission medium

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Telephony – Brief History

Before 1984

● Almost all services are provided by AT&T Bell System

● In 1984, AT&T was broken into

♦ AT&T long Lines

♦ 23 BOCs(Bell Operating Companies)

♦ BOCs are grouped together to several RBOCs

Between 1984 and 1996

● Divided into more than 200 LATAs (Local Access

Transport Areas)

After 1996

● Any companies can provide any services

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A Telephone System

Local

Exchange LocalExchange

LocalExchange

Local loop

Long distance

network

Trunkcircuit

Subscriber line

• Many local telephone exchanges had sprung up and

Bell Telephone acquired them and interconnected

them for long distance.

• This telephone system is called Public Switched

Telephone Network (PSTN)

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Basic Telephone

Ear

T

R

MouthDTMF

Ringer

C

Dial switch

SLIC

Telephone

Subscriber

LineLocal

Exchange

Cradle switchOff-hook

On-hook

Tip(+)

Ring (-)

• Hybrid coil prevents the incoming speaker signal

and the outgoing microphone signal from

interfering with each other

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Telephone System – Circa 1900

Pair of copper wires

“local loop”

Manual routing at local exchange offices

o Analog voltage travels over copper wire end-to-end • Voice signal arrives at destination severely attenuated

o Routing performed manually at exchanges office(s)• Routing is expensive and lengthy operation

• Route is maintained for duration of call

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Multiplexing - PSTN

1900: 25% of telephony revenues went to copper mines

o Standard was 18 gauge, long distance even heavier

o Two wires per loop to combat cross-talk

o Needed method to place multiple conversations on a single trunk

1918: “Carrier system” (FDM)

o 5 conversations on single trunk

o Later extended to 12 (group)

o Still later supergroups, master groups, supermaster groups

1963: T-carrier system (TDM)

o T1 = 24 conversations per trunk

o Later T3 = 28 T1s

o Still later SDH rates with 1000s of conversations per trunk

f

Channels

t

Timeslots

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Signaling - PSTN

• Public Switched Telephone Network (PSTN) with

automatic switching requires signaling.

• The present PSTN has thousands of features and all

require signaling support

• Examples:

� On-hook / off-hook

� Pulse / Tone dialing

� Receiver off-hook

� Call waiting

� Caller number identification

� Call forwarding

� Hook-flash

� Fax transmission detect

� Inter-CO messaging

� Echo cancellation

� Voice mail

� Conference calls

� Coin-drop

� Billing

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Signaling Methods

Signaling can be performed in many ways

o Analog voltage signaling loop-start, ground-start

o In-band signaling DTMF

o Channel associated signaling (CAS) ABCD bits

o Common channel signaling (CCS) SS7, QSIG

● Trunk Associated CCS

● Separate signaling network CCS

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Telephony Routing

o Circuit switching - route is maintained for duration of call

o Route “set-up” is an expensive operation, just as it was for

manual switching. Today, complex least cost routing

algorithms are used.

o Call duration consists of set-up, voice and tear-down

phases

The PSTN – Circa 1960

Local loop

Subscriber line

Automatic routing through universal telephone network

Trunks circuits

� Analog voltages used throughout, but extensive Frequency

Division Multiplexing

• Voice signal arrives at destination after amplification and

filtering to 4 KHz.

� Automatic routing

• Universal dial-tone with voltage and tone signaling.• Circuit switching (route is maintained for duration of call) 36

The Digitalization of PSTN

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Shannon (Bell Labs) proved

is better than

Therefore, PSTN was digitalized

Better means

�More efficient use of resources (e.g. more channels on trunks)

�Higher voice quality (less noise, less distortion)

�Added features

Digital

Communications

Analog

Communications

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Timing

In addition to voice, the digital PSTN transports timing

� This timing information is essential because of

● The universal use of TDM

● The requirement of accurate playback (especially for

fax/modem)

� Receiving switches can recover the clock of the transmitting

switch

� Every telephony network has an accurate clock called

“stratum 1”

� Clocks synchronized to it are called “stratum 2”, “stratum 3”

and so on

The Present PSTN

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Subscriber line

PSTN Network

Core

backbone

• Analog voltages and copper wire used only in “last mile”,

but core designed to mimic original situation• Voice signal filtered to 4 KHz at input to digital network

• Time Division Multiplexing of digital signals in the network• Extensive use of fiber optic and wireless physical links• T1/E1, PDH and SONET/SDH “synchronous” protocols

• Automatic routing• Circuit switching (route is maintained for duration of call)• Signaling can be trunk associated or via separate network (SS7)

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Nonvoice / Data Services

The PSTN can even be used to transport non-voice signals

such as FAX or DATA

� These services disguise themselves as voice by using a

modem

� Proper timing is essential

� Special signaling is required

PSTN

VoP course

Asymmetrical Digital Subscriber Line

o Asymmetrical Digital Subscriber Line (ADSL) is

an asymmetric communication technology

designed for residential users; it is not suitable for

businesses.

o The existing local loop can handle bandwidths up

to 1.1 MHz

o ADSL is an adaptive technology. The system uses

a data rate based on the condition of the local loop

line.

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Cable Television

o Started to distribute video signals to locations with

poor or no reception in the late 1940s: Unidirectional

o It was called Community Antenna TV

Picking Antenna

Coaxial Cable

Amplifier

Splitter

Tap

Drop Cable

Summery Of Training – (First Session)

Basics of Communication Engineering

Major elements of Communication System

Transmission media types and impairments

Transmission modes and working principles

Telephony Public Switched Telephone Network

Digital over Analog and how digitalization happened!

Services Offered by modern day telephony

Brief explanation of ADSL and cable television43

What Is The Next?

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Wireless Communication Systems

What will you be given training on:

● Brief History of Wireless Communication

● In-depth insight into Mobile Communication

That’s all folks!