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DATA COMMUNICATION

Satish Chandrasatish0402.weebly.com

INTRODUCTION

•• TheThe termterm telecommunicationtelecommunication meansmeans communicationcommunicationatat aa distancedistance..

•• TheThe wordword datadata refersrefers toto informationinformation presentedpresented ininwhateverwhatever formform isis agreedagreed uponupon byby thethe partiesparties creatingcreatingandand usingusing thethe datadata..

•• TheThe datadata communicationscommunications areare thethe exchangeexchange ofof datadatabetweenbetween twotwo devicesdevices viavia somesome formform ofof transmissiontransmissionmediummedium suchsuch asas aa wirewire cablecable..

TELECOMMUNICATIONS

• Tele (Far) + Communications• Early telecommunications 

– smoke signals and drums – visual telegraphy (or semaphore in 1792) 

• Telegraph and telephone– Telegraph (1839)– Telephone  (1876)

• Radio and television • Telephony 

– Voice and Data

SYSTEM COMPONENTS

Simplified Communications Model Simplified Communications Model

The key elements of this model are:

• Source ‐ generates data to be transmitted

• Transmitter ‐ converts data into transmittable signals

• Transmission System ‐ carries data from source to destination

• Receiver ‐ converts received signal into data

• Destination ‐ takes incoming data

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Simplified Data Communications Model

Simplified Data Communications Model

Assume a PC user wants to send an email message m to another user.  The process is modeled as follows:

• User keys in message m comprising bits g buffered in source PC memory.

• Input data is transferred to I/O device (transmitter) as sequence of bits p qg(t) using voltage shifts.

• Transmitter converts these into a signal s(t) suitable for transmission media being used.

• Whilst transiting media signal may be impaired so received signal r(t) may differ from s(t).

• Receiver decodes signal recovering g’(t) as estimate of original g(t).

• Which is buffered in destination PC memory as bits g’ being the received message m’.

Communication Systems COMMUNICATIONS COMPONENTS

• Basic components of a communication system

– Communication technologies– Communication devices 

– Communication channels– Communication channels

– Communication software

Communication Technology Applications

voice mail Twitter

instant messaginge‐mail

instant messagingchat rooms

newsgroups telephony videoconferencing

collaboration groupware global positioning system (GPS)

Communication Channels

• A channel is a path between two communication devices

• Channel capacity: How much data can be passed through the channel (bit/sec) 

– Also called channel bandwidth

Th ll h i h l d f !– The smaller the pipe the slower data transfer!

• Consists of one or more transmission media

– Materials carrying the signal

– Two types: 

• Physical: wire cable 

• Wireless: Air destination network server

T1 lines

T1 lines

T1 lines

T3 lines

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Physical Transmission Media

• A tangible media– Examples: Twisted‐pair cable, coaxial cable, Fiber‐optics, etc.

• Twisted‐pair cable: – One or more twisted wires bundled together M d f– Made of copper

• Coaxial‐Cable:– Consists of single copper wire surrounded by three layers of insulating and metal materials 

– Typically used for cable TV • Fiber‐optics: 

– Strands of glass or plastic used to transmit light – Very high capacity, low noise, small size, less suitable to natural disturbances 

Physical Transmission Media

woven or braided metal copper wire

twisted‐pair cable twisted‐pair wire

plastic outer coating

insulating material

protective coating

glass cladding

optical fiber core

Wireless Transmission Media

• Broadcast Radio – Distribute signals through the air over long distance 

– Uses an antenna – Typically for stationary locations C b h– Can be short range 

• Cellular Radio– A form of broadcast radio used for mobile communication 

– High frequency radio waves to transmit voice or data 

– Utilizes frequency‐reuse 

Wireless Transmission Media

• Microwaves – Radio waves providing high speed transmission 

– They are point‐to‐point (can’t be obstructed) Used for satellite communication– Used for satellite communication

• Infrared (IR) – Wireless transmission media that sends signals using infrared light‐waves

• Communication Satellite– Geo‐stationary orbit– Transponder 

• C band (Downlink/Uplink 4/6 GHz)• Ku band (Downlink/Uplink 11/14 GHz)

– VSAT – Earth Station

Physical Transmission Media Wireless Transmission Media

Wireless channel capacity: 

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DATA FLOW

Simplex: One direction only

Simplex Transmission

Half Duplex Transmission

half duplex: Both directions but only one direction at a time

Full Duplex Transmission

full duplex: send and receive both directions at once

NETWORK

•• AA networknetwork isis aa setset ofof devicesdevices (often(often referredreferred toto asasnodesnodes)) connectedconnected byby communicationcommunication linkslinks..

•• AA nodenode cancan bebe aa computer,computer, printer,printer, oror anyany otherotherdevicedevice capablecapable ofof sendingsending and/orand/or receivingreceiving datadatapp gg gggeneratedgenerated byby otherother nodesnodes onon thethe networknetwork..

•• AA linklink cancan bebe aa cable,cable, air,air, opticaloptical fiber,fiber, oror anyanymediummedium whichwhich cancan transporttransport aa signalsignal carryingcarryinginformationinformation..

TYPE OF CONNECTION

Point to Point - single transmitter and receiverMultipoint - multiple recipients of single transmission

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NETWORK TOPOLOGIESpersonal computer

personal computer

personal computer

personal computer

personal computer

host computer

printerfile server

personal computer

personal computer

personal computer

personal computer

NETWORK TOPOLOGIES

• CATEGORY OF TOPOLOGY

NETWORK TOPOLOGIES

• Mesh Topology

NETWORK TOPOLOGIES

• Star Topology

NETWORK TOPOLOGIES

• Bus Topology

NETWORK TOPOLOGIES

• Ring Topology

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NETWORK TOPOLOGIES

• Hybrid Topology:

NETWORKS

• growth of number & power of computers is driving need for interconnection

• also seeing rapid integration of voice, data,  image & video technologiesg g

• three broad categories of communications networks:– Local Area Network (LAN)– Wide Area Network (WAN)– Metropolitan Area Network (MAN)

Categories of Networks

• Local Area Networks (LANs)– Short distances– Designed to provide local interconnectivity

• Wide Area Networks (WANs)• Wide Area Networks (WANs)– Long distances– Provide connectivity over very large areas

• Metropolitan Area Networks (MANs)– Provide connectivity over areas such as a city, a

campus

Local Area Networks

• smaller scope– Building or small campus

• usually owned by same organization as attached devicesattached devices

• data rates much higher

• switched LANs, eg Ethernet

• wireless LANs

Local Area Networks (LAN)

• An isolated LAN connecting 12 computers to a hub in a closet

Wide Area Networks

• span a large geographical area

• cross public rights of way

• rely in part on common carrier circuits

• alternative technologies used include:– circuit switching

– packet switching

– frame relay

– Asynchronous Transfer Mode (ATM)

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Wide Area Networks Metropolitan Area Networks

• MAN

• middle ground between LAN and WAN

• private or public network

• high speed

• large area

A heterogeneous network made of four WANs and two LANs

THE INTERNET

• Internet evolved from ARPANET– first operational packet network– applied to tactical radio & satellite nets also– had a need for interoperabilityp y– led to standardized TCP/IP protocols

THE INTERNET

•• TheThe InternetInternet hashas revolutionizedrevolutionized manymany aspectsaspects ofof ourourdailydaily liveslives..

•• ItIt hashas affectedaffected thethe wayway wewe dodo businessbusiness asas wellwell asas thethewayway wewe spendspend ourour leisureleisure timetime..yy pp

•• TheThe InternetInternet isis aa communicationcommunication systemsystem thatthat hashasbroughtbrought aa wealthwealth ofof informationinformation toto ourour fingertipsfingertips andandorganizedorganized itit forfor ourour useuse..

Hierarchical organization of the Internet

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Internet Elements Internet Architecture

Example Configuration MULTIPLEXING

• Bandwidth utilization is the wise use ofavailable bandwidth to achievespecific goals.

• Efficiency can be achieved by multiplexing; i.e.,sharing of the bandwidth between multiple users.

MULTIPLEXING

• Whenever the bandwidth of a medium linking twodevices is greater than the bandwidth needs of thedevices, the link can be shared.

• Multiplexing is the set of techniques that allows thep g q(simultaneous) transmission of multiple signalsacross a single data link.

• As data and telecommunications use increases, sodoes traffic.

THE CONCEPT OF MULTIPLEXING

• Multiplexing to refer to the combination ofinformation streams from multiple sources fortransmission over a shared medium– Multiplexor is a mechanism that implements theconceptconcept

• Demultiplexing refers to the separation of acombination back into separate informationstreams– Demultiplexor to refer to a mechanism thatimplements the concept

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Multiplexing and Demultiplexing MULTIPLEXING IN NETWORKS

Main pur

Sharing thpose is ?

e medium

MULTIPLEXING IN NETWORKS

each sender communicates with a single receiverall pairs share a single transmission mediummultiplexor combines information from the sendersfor transmission in such a way that thed l i l h i f i fdemultiplexor can separate the information forreceivers.

MULTIPLEXING

MULTIPLEXER EXAMPLE NETWORK SHARINGNetwork Resources (bandwidth) divided into “pieces”• pieces allocated to calls• resource piece idle if not used by owning call (no sharing)• dividing link bandwidth into “pieces”

– frequency division– time division

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FDM and TDM

FDM

frequency

4 users

Example:

time

TDM

frequency

time

Spectrum

• AM: 535 kHz to 1.7 MHz• TV: 54‐88 (VHF, channels 2‐6) and 174‐220 (UHF, channels 7‐13)• Unlicensed vs. licensed

– cell phone (800 MHz, 1800/1900 MHz)– Wi‐Fi (2.4 GHz, 5 GHz)

Categorization of Multiplexing Frequency Division Multiplexing

• FDM is an analog multiplexing technique that combines analog signals.

FDM: Multiplexing Process FDM: Demultiplexing Process

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FDM: Example

• Assume that a voice channel occupies a bandwidth of 4 kHz.We need to combine three voice channels into a link with abandwidth of 12 kHz, from 20 to 32 kHz. Show theconfiguration, using the frequency domain. Assume thereare no guard bands.g

• Shift (modulate) each of the three voice channels to adifferent bandwidth. We use the 20 to 24 kHz bandwidth forthe first channel, the 24 to 28 kHz bandwidth for the secondchannel, and the 28 to 32 kHz bandwidth for the third oneand then combine them.

FDM: Example

FDM: Bandwidth

• Five channels, each with a 100‐kHz bandwidth, are to bemultiplexed together. What is the minimum bandwidth of thelink if there is a need for a guard band of 10 kHz between thechannels to prevent interference?

Wave Division Multiplexing

• WDM is an analog multiplexing technique to combine optical signals.

WDM: MULTIPLEXING & DEMULIPLEXING TIME DIVISION MULTIPLEXING

• TDM is a digital multiplexing technique forcombining several low‐rate digital channelsinto one high‐rate one.

• In synchronous TDM the data rate of the link• In synchronous TDM, the data rate of the linkis n times faster, and the unit duration is ntimes shorter.

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TDM TDM

TDM TDM

Frequency Division Multiplex• Separation of spectrum into smaller frequency bands•Channel gets band of the spectrum for the whole time Advantages:

no dynamic coordination neededworks also for analog signals

Disadvantages:

Channelski

k3 k4 k5 k6gwaste of bandwidth, if traffic distributed unevenlyinflexibleguard spaces

t

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Why FDM is for analog signals and TDM is for digital signals?

FDM stands for frequency division multiplexing and it isused only in case of analog signals because analog signalsare continuous in nature and the signal have frequency.

TDM‐stands for time division multiplexing and it is used

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p gonly in case of digital signals because digital signals arediscrete in nature and are in the form of 0 and 1s. and aretime dependent.

ADVANTAGES & DISADVANTAGES OF TDM & FDM

In TDM, different users share the same channel based on time slotsallotted to them. Each user or source is given a particular time slot tosend its information.

1. The entire channel BW is available for a particular time intervalunlike in FDM where the channel BW is split into smaller segments.

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unlike in FDM where the channel BW is split into smaller segments.This enables higher data rates.

2. All users share the same frequency, so spectrum efficiency isincreased. Available channel BW is no more a constraint.

ENDS