Network Architecture - Physical Layer

8/9/2019 Network Architecture - Physical Layer

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Slide 1

The Physical Layer

Chapter 2


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Slide 2The Theoretical Basis for Data

Communication

Fourier Analysis

Bandwidth-Limited Signals

Maximum Data Rate of a Channel


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Slide 3Bandwidth-Limited Signals

A binary signal and its root-mean-square Fourier amplitudes.

(b) (c) Successive approximations to the original signal.

1/T

1/T 1/2T


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Slide 4Bandwidth-Limited Signals (2)

(d) (e) Successive approximations to the original signal.

1/T 1/2T

1/3T 1/4T


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Slide 5Bandwidth-Limited Signals (3)

Relation between data rate and harmonics.

If there is a limitation

to 3000 Hztelephone voice grade line

1/T

Time it takes totransmit 8 bit

(see slide 3) 1/T, 1/2T, 1/NT < 3000


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Slide 6Guided Transmission Data

Magnetic Media

Twisted Pair

Coaxial Cable

Fiber Optics


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Slide 7Twisted Pair

(a) Category 3 UTP.

(b) Category 5 UTP.


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Slide 8Coaxial Cable

A coaxial cable.

Radio-grade flexible coaxial cable.

A: outer plastic sheath

B: copper screen

C: inner dielectric insulator

D: copper core


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Slide 9Fiber Optics

(a) Three examples of a light ray from inside a silica fiber impinging

on the air/silica boundary at different angles.

(b) Light trapped by total internal reflection.


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Slide 10Transmission of Light through Fiber

Attenuation of light through fiber in the infrared region.


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Slide 11Fiber Cables

(a) Side view of a single fiber.

(b) End view of a sheath with three fibers.


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Slide 12Fiber Cables (2)

A comparison of semiconductor diodes and LEDs as light sources.

Monday Sept 28th, 2009


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Slide 13Fiber Optic Networks

A fiber optic ring with active repeaters.


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Slide 14Fiber Optic Networks (2)

A passive star connection in a fiber optics network.


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Slide 15Wireless Transmission

The Electromagnetic Spectrum

Radio Transmission

Microwave Transmission Infrared and Millimeter Waves

Lightwave Transmission

Thursday Oct 1st, 2009 and Oct 5th, 2009


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Slide 16The Electromagnetic Spectrum

The electromagnetic spectrum and its uses for communication.

LF Low Frequency

MF Medium Frequency

HF High Frequency

VHF Very High Frequency

UHF Ultra High Frequency

SHF Super High Frequency

EHF Extremely High F.

THF Tremendously High F.

WIFI


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Slide 17Radio Transmission

(a) In the VLF, LF, and MF bands, radio waves follow the

curvature of the earth.

(b) In the HF band, they bounce off the ionosphere.


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Slide 19Lightwave Transmission

Convection currents can interfere with laser communication systems.

A bidirectional system with two lasers is pictured here.


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Slide 20Communication Satellites

Geostationary Satellites

Medium-Earth Orbit Satellites

Low-Earth Orbit Satellites Satellites versus Fiber


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Communication satellites and some of their properties,

including altitude above the earth, round-trip delay time

and number of satellites needed for global coverage.

Area with highly charged particles

would destroy satellites

Geostationary

Medium-Earth Orbit

Low-Earth Orbit


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First telecom satellite :Telstar July 10, 1962

15 hours for the satellite to get in view.

8 km/s, 4,800 km above the earth

Signal amplified it 10 billion times

Antennas: 49 m high, 64 m wide, 30 tons. Andover Pleumeur bodou Antenna (near Perros Guirec)

http://www.leradome.com/new/article.php3?id_article=37


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Slide 23Communication Satellites (2)

The principal satellite bands.Allows for 1degree

geostationary

spacing


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Slide 24Communication Satellites (3)

VSATs using a hub.

VSAT :

Very Small Aperture Terminals

L E th O bit S t llit


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Slide 25

Low-Earth Orbit Satellites

Iridium

(a) The Iridium satellites from six necklaces around the earth.

(b) 1628 moving cells cover the earth.

66 satellites


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Slide 26Globalstar

(a) Relaying in space.

(b) Relaying on the ground.

Globalstar48 satellites

Iridium


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Slide 27Public Switched Telephone System

Structure of the Telephone System The Politics of Telephones

The Local Loop: Modems, ADSL and Wireless

Trunks and Multiplexing

Switching


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Slide 28Structure of the Telephone System

(a) Fully-interconnected network.

(b) Centralized switch.

(c) Two-level hierarchy.


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Slide 29Structure of the Telephone System (2)

A typical circuit route for a medium-distance call.


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Slide 30

Major Components of the

Telephone System

Local loops

Analog twisted pairs going to houses and

businesses

Trunks Digital fiber optics connecting the switching

offices

Switching offices Where calls are moved from one trunk to another


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Slide 31The Politics of Telephones

The relationship of LATAs, LECs, and IXCs. All the

circles are LEC switching offices. Each hexagon

belongs to the IXC whose number is on it.

Geographic organisation :

LATA : Local Access and Transport Area

(164 in the US)Company organisation :

LEC : Local Exchange Carrier

IXC : InterXchange Carrier


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Slide 32

The Local Loop: Modems,

ADSL, and Wireless

The use of both analog and digital transmissions for a computer to

computer call. Conversion is done by the modems and codecs.


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Slide 33Modems

(a) A binary signal

(b) Amplitude modulation

(c) Frequency modulation

(d) Phase modulation

Thursday Oct 8th 2009


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Slide 34Modems (2)

(a) QPSK. 2bits per symbol. 1 sample = 2-bit value

(b) QAM-16. 4 bits per symbol. 1 sample = 4-bit value

(c) QAM-64. 6 bits per symbol. 1 sample = 6-bit value

Amplitude

Phase

Bandwidth

Symbol

Baud

Quadrature Phase Shift KeyingQuadrature Amplitude Modulation


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Slide 35Modems (3)

(a) V32 for 9600 bps. 4 data bit and one parity bit at 2400 baud

(b) V32 bis for 14,400 bps. 6 data bit and one parity bit at 2400 baud

V34 for 28,800 bps. 12 data bit at 2400 baud

V34bis for 33,600 bps. 14 data bit at 2400 baud

V90 for 33,6 kbps upstream and 54 kbps downstream.

V92 for 48 kbps upstream and 54 kbps downstream


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Slide 36Digital Subscriber Lines

Bandwidth versus distanced over category 3 UTP for DSL.

ADSL


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Slide 37Digital Subscriber Lines (2)

Operation of ADSL using DMT (Discrete MultiTone) modulation.

Each channel uses a V34 like scheme


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Slide 38Digital Subscriber Lines (3)

A typical ADSL equipment configuration.DSLAM : Digital Subscriber Line Access Multiplexer

NID : Network Interface Device


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Slide 39Wireless Local Loops

Architecture of an LMDS system.

Or Wimax

802.16


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Slide 40Frequency Division Multiplexing

(a) The original bandwidths.

(b) The bandwidths raised in frequency.

(b) The multiplexed channel.


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Slide 41Wavelength Division Multiplexing

Wavelength division multiplexing

used for fiber optics.


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Slide 42Time Division Multiplexing

US Japan T1 carrier

24 channels (1 for synchronisation). 7 bit data. 193 bit frame or 1.544 Mbps

International E1 carrier

32 channels (2 for signalling). 8 bit data. 256 bit frame or 2.048 Mbps

Used for

Copper Wires

125 microseconds to

allow for 8000 samples

per second (Pulse

code modulation for

voice)


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Slide 43Time Division Multiplexing (2)

Differential Pulse Code Modulation : Delta modulation.

Idea is to transmit the difference. Here delta is stored on 1 bit.


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Multiplexing T1 streams into higher carriers. T4 = 6T3 = 6*7T2 = 6*7*4T1

E5 = 4E4 = 16E3 = 64E2 = 256E1

Time Division Multiplexing (4)


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Slide 45

Time Division Multiplexing (4)

SONET/SDH : fiber optics trunks (1985)

Two back-to-back SONET frames.

Synchronous Optical NETwork

Used for

long distance

810 bytes every 125

microseconds

Wednesday Oct 12th 2009


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SONET and SDH multiplex rates.

STS-768 OC-768 STM-256 39,813,120 38,486,016

STS-1536 OC-1536 STM-512 79,626,120 76,972,032

STS-3072 OC-3072 STM-1024 159,252,240 153,944,064 (2007 not manufactured yet)


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Slide 47Circuit Switching

(a) Circuit switching.

(b) Packet switching.


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Slide 48Message Switching

(a) Circuit switching (b) Message switching (c) Packet switching

(b) never used in practice


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Slide 49Packet Switching

A comparison of circuit switched and packet-switched networks.

Packet switch is more fault tolerant

h bil l h


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Slide 50The Mobile Telephone System

First-Generation Mobile Phones:Analog Voice

1946, Car-based system, 1 frequency, 1 channel

1960, 2 frequencies, 23 channels, very limited

Second-Generation Mobile Phones:

Digital Voice

1982, AMPS, cells with different frequencies per

channels Third-Generation Mobile Phones:

Digital Voice and Data

Wednesday Oct 8th 2008

Ad d bil h S


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Slide 51Advanced Mobile Phone System

(a) Frequencies are not reused in adjacent cells.

(b) To add more users, smaller cells can be used.

AMPS : Bell Labs 1982

Ch l C i


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Slide 52Channel Categories

AMPS handles 832 channels, divided into 4 categories:

Control (base to mobile) to manage the system

Paging (base to mobile) to alert users to calls for them

Access (bidirectional) for call setup and channelassignment

Data (bidirectional) for voice, fax, or data

D-AMPS


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Slide 53

D-AMPS

Digital Advanced Mobile Phone System

(a) A D-AMPS channel with three users.

(b) A D-AMPS channel with six users.

GSM


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Slide 54

GSM

Global System for Mobile Communications

GSM uses 124 frequency channels, each of which

uses an eight-slot TDM system

GSM (2)


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Slide 55GSM (2)

A portion of the GSM framing structure.

CDMA C d Di i i M l i l A


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Slide 56

CDMA Code Division Multiple Access

(a) Binary chip sequences for four stations(b) Bipolar chip sequences (notation convention)(c) Six examples of transmissions

(d) Recovery of station Cs signal

They are all

orthogonal

AB = 0 ( aibi/8 = 0)A A = 1 ( aiai/8 = 1)

A transmits 1

B transmits 0

C does not transmit

D does not transmit

1 : C has transmitted 1

0 : C has not transmitted

-1 C has transmitted 0

A is reserved a chip

sequence

00011011 means 1

11100100 means 0

Third-Generation Mobile Phones:


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Slide 57

Third Generation Mobile Phones:

Digital Voice and Data

Basic services an IMT-2000 network should provide

High-quality voice transmission Messaging (replace e-mail, fax, SMS, chat, etc.)

Multimedia (music, videos, films, TV, etc.)

Internet access (web surfing, w/multimedia.)

W-CDMA (Wideband) or UMTS pushed by Ericsson

CDMA2000 pushed by Qualcomm


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C it A t T l i i


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Slide 59Community Antenna Television

An early cable television system.

I t t C bl


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Slide 60Internet over Cable

Cable television HFC : Hybrid Fiber Coax

I t t C bl (2)


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Slide 61Internet over Cable (2)

The fixed telephone system.

Dedicated connection to the home!!

S t All ti


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Slide 62Spectrum Allocation

Frequency allocation in a typical cable TV system

used for Internet access

C bl M d


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Slide 63Cable Modems

Typical details of the upstream and downstream

channels in North America

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Network Architecture - Physical Layer