ist4060 telecommunications and networks - lesson 1.ppt

7/30/2019 IST4060 Telecommunications and Networks - Lesson 1.ppt

1/49

IST4060

Telecommunications and Networks

(a). Introductory Concepts;

(b). Physical Layer Issues Transmission Media


2/49


3/49

Information

Information might be:

a page of w ri t ten text(data communication);

a conversat ion(voice communication);

a TV pic tu re..

Question: Different types of information place dif ferent

demands on the telecommunication system.

Explain how a page of written text and a voice

conversation differ in their demands?


4/49

Information (Contd)

Information usually requires conversion into an

electrical signal in order to be conveyed by

telecommunication means:

Convert at sourc e;

Re-convert at dest inat ion

Question: What information does your mobile phone

convert?


5/49

Duplex Communication

Transport mechanismTransmitter Receiver

Information flow

F ig. 1. Basic physical elements of a telecommunication systemDuplex Operation

Receiver Transmitter

Question: In human conversation, must we have full

duplex operation?


6/49

Simplex Operation

Transport mechanism

Transmitter Receiver

Information flow

F ig. 2. Basic physical elements of a telecommunication systemSimplex Operation

Question: Give examples of simplex systems


7/49

Transport Mechanism

The transport mechanism is not just a single

line; rather, it is a complex switchandl ine

arrangement.

Question: Why the switch? Why the line?


8/49

The Switching Network

1

2

3

4

5

6

7

A

B

C

D

E

F

= communication network node = End station

Question: Analyze the switching fabr ic cr itical ly


9/49

Ful l-Mesh Switching Network

Question:

If a switching network has Ncommunication nodes(switches) and is full-mesh connected, determine the

total number of cables required.


10/49

The Public Switched

Telephone Network (PSTN)

P: Public

S: SwitchedT: Telephone

N: Network

Question: What are the key features of this network?


11/49

The PSTN

PC&

Modem

PC&

Modem

Exchange(s)

Local

loop

PSTN

The Public Switched Telephone Network


12/49

The PSTN Structure

Telephone

set

End

office

Toll

office

Intermediate

switching

office

Telephone

set

Toll

office

End

office

Local

loop Toll

Connecting

trunk

Very high

Bandwidth

Inter-toll trunks

The PSTN

Question: How is it different f rom cellular network?


13/49

I nternational Telephone Numbering Scheme

international

prefix

(00)

country

code

(CC)

national significant number

NSN

trunk area code + subscriber number

maximum 15 digits

Recommended Format of international telephone numbers

Questions: (i). How is it diff erent for cel lular network?

(i i ). How do now dial an international cal l?

(i i i). How do you do an trunk call?

(iv). How do you do a local call?

(v). What is the NSN size in Kenya?


14/49

00 CC Area Code Customer local number

International

prefixCountry

code

National number

Digits

dialled,

in sequence

Example00 44 71 234 5678

UK LondonExchange Customer

General structure of an i nternational number call and example


15/49

0 71 234 5678

General structure of trunk and local calls

234 5678

Area code Customer numberTrunk prefix

Trunk dialed

number

local dialed number

Questions: (i). What determines the length of thecustomer number? Give local examples

(i i ). What determines the length of the

area code? Give local examples

(i i i ). Explain the need for hierarchy.


16/49

Summary

Telecommunications is L ife I tself !


17/49

Physical Layer I ssues

(Transmission Media)

Concept of Bandwidth

Transmission Media Types (Wired/Wireless);

Multiplexing Techniques;


18/49

Concept of Bandwidth

time

Signalstrength(V)

I nformation Signal

F(t)


19/49

Bandwidth (Contd)

Consider an information signalF(t), given by:

F(t) = F0(t) + F1(t) + .. + Fn(t)Fourier ser ies

Transmission media transmits signals

No transmission facility can transmit signals without power loss

[attenuation]

Different signal components diminished by different amounts

[distortion]


20/49

Bandwidth (Contd)

Bandwidth= Width of a frequency band

The range of frequenciestransmitted without

beingstrongly attenuated

Higher

Bandwidth

More information

transmitted


21/49

Analog Signal to Digital Signal

time

Signal

strength(V)

Sampling an analog signal

Sample

Signal frequency= signal repetitions per second

Analog signal


22/49

Key Question 1

How many samples per second?Sampling

rate

Nyquist Sampling Theorem

Sample at the rate oftwice the highest f requency


23/49

4000 cycles / second

x 2 samples/ cycles

8000 samples / second

Maximum frequency (voice)

Nyquist multiplier

Nyquist sampling theorem calculations

Example: Human Voice


24/49

Key Question 2

Each sample has a magnitude; convert each sample

magnitudes to bits

How many bits per sample?

8 bits per sample


25/49

4000 cycles / second

x 2 samples/ cycles

8000 samples / second

Maximum frequency (voice)

Nyquist multiplier

Example: Human Voice

8000 samples / second 8 bits per sampleX

64,000 bits per second = 64000 bps = 64 kbps

Data requi red needed to transport voice signal = 64 kbps


26/49

Review Question

Determine the data rate needed to transport

10 voice cal lssimultaneously

What happens if10 voice callsare required at

the same time yet the available data rate

can only support8 callssimultaneously


27/49

Guided Transmission Media;

Unguided Transmission Media;

Transmission Media Types


28/49

1. Transmission Media - I ntroduction

Transport a raw bit stream from one machine to another

Various media available, different in the following ways:

Bandwidth; Delay; Cost;

Ease of installation & Maintenance

Guided MediaMagnetic tape, copper wire, fiber optics;

Unguided Mediaradio waves


29/49

(i). Magnetic Media

Industry standard tape 200 gigabytes

Box full of 1000 tapes 200 x 103 gigabytes

Courier company can deliver in 24 hours

Effective data rate = (200 x 103 x 1012 x 8 bits)/(86,400 secs)

= 19 Gbps

Example

Removable Mediarecordable DVDs

Physically transport the data from one machine to another

Very Cost-effective

Backup

Tapes

Delay


30/49

(i i ). Twisted Pair Copper

For many applications, we need an on-l ine connection

Very widely used: Adequate performance;

Low cost

Twisting helps minimize interference

CAT 310 Mbps;

CAT 5100 Mbps;

CAT 61000 Mbps

I ncreasing twists

per cm of cable length

UTP

{Unshielded

Twisted

Pair}


31/49

(i i i). Coaxial Cable

Has better shieldingthan twisted pair cable:

H igher bandwidth;

Can span long distances

Consists ofsti ff coppersurrounded byinsulating mater ial

H igher bandwidth;

Good noise immuni ty 800 Mbps

Cable TV & Metropoli tan networksUses


32/49

(i i i). F iber Optics

Uses light, not electricity, to transmit information.

Pulse of l ight: 1 bit;

Absence of l ight: 0 bit.

Components of the cable:

L ight sourcesuch as a light emitting diode (LED);

Transmission Mediumthin glass of fiber;

Detectorgenerates an electrical pulse when light falls on it


33/49

Fiber Optics (Contd)

Immune to electrical interference

High data rates 2 Gbps to 28 Gbps

Applications: Long distance phone lines;

Computer Networks


34/49

Copper vs. F iber

Fiber has the following advantages:

Much higher bandwidths;

Low attenuation;

Not affected by corrosive chemicals;

No electromagnetic interference;

Thin and lightweightlower installation cost;

Di ff icul t to tapgood secur ity


35/49

Copper vs. Fiber (Contd)

Copper has the following advantages:

Excellent resale valueto copper ref iners;

More familiar technology;

Cheaper interfacesnetwork inter face cards.

The Future is F iberespecially long distances;

Copper is to the desktop


36/49

Wireless (Unguided) Transmission

Laptop;

Notebook;

Palmtop;

Wristwatch

WirelessTransmission

Media

Mobile devices

Desktops;Telephones;

Faxes, etc F ixed (non-mobile) devices

Wired

Transmission


37/49

Wireless Transmission

Wireless transmission suits:

Mountaineous areas;

Costly r ight of way;

Mobil i ty requi rements


38/49

Electromagnetic Spectrum

100 102 104 106 108 1010 1012 1014 1016 1018 1020 1022 1024

Radio Microwave Infrared

Visible

light

UV X-ray Gamma ray

Frequency in HZ

time

Signa

lstreng

th(V)

= wavelength f = frequency


39/49

Wavelength

All the waves travel at the speed

of light (approximately)

Speed of light

FrequencyWavelength =

Speed of light 3 x 108 meters/sec


40/49

Wavelength (Contd)

Frequency(Hz)

Wavelength(meters)

102

104

106

108

1010

1012

3 x 106

3 x 104

3 x 102

3

0.03

0.0003

Low

frequency

High

frequency


41/49

Radio Waves

Radio transmissions (88 MHz to 110 MHz);

TV Transmissions (300 MHz to 3 GHZ), UHF broadcasts


42/49

Microwaves

Transmissions occur between two ground stations;

Microwaves travel in straight lines;

Atmospheric conditions and solid objects interfere with them

Features

Applications:Mobile phones;

Television distr ibution;

Long distance telephone communications


43/49

Satellite

Basically,

This is microwave transmission where one

of the stations is a satellite orbiting the earth.

Applications:

Telephone;

Television;

News Services;Weather reporting

M il itary Use


44/49

1m 10m 100m 1km 10km 100km 1000km

Infrared

Bluetooth

WLANs

WLL,

Cellular

FM, MW,SW Radio

Satellite

Range of Wireless Systems


45/49

Satell i te vs. Fiber

2. Fiber is a fixed line technologyno use for mobility

3. Satellite provides potential for broadcast, not fiber.

4. Satellite good where the terrain is hostile.

5. Satellite good where right-of-way is expensive

6. Satellite good where rapid deployment is keymilitary.


46/49

Satel l i te vs. F iber

But:

F iber offers more bandwidth than satel l i te;

Satell i tes cost more than f iber

F iber and satel l i te wil lcoexist for years to come

M di S


47/49

Media: Summary

MediaData Rate

(Mbps)

Repeater Spacing

(km)

Copper 10 - 100

Fiber 2000

Wireless

10 - 100

1 - 10

12 - 274

Transmission band dependent

Why is Bandwidth so Crucial?


48/49

Despite the great promise, the following are the key limitations

associated with wireless systems:

Scarce spectrumlow data rates;

Reliabilityhigh loss rates;

Powermobility brings about battery operation;

Securitymedium is broadcast.

Broad I ssues With Wireless


49/49

Summary

Media transports data (in analog or digital form);

Media types wil l coexist for years to come.

ist4060 telecommunications and networks - lesson 1.ppt

Documents