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Slide No. 1

Data Communications

TelecommunicationsTelecommunications LANs, WANs and IntranetsLANs, WANs and Intranets

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Telecommunications

HardwareHardware SoftwareSoftware

ImpactImpact

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Telecommunications

Two computers linked together through Two computers linked together through the telephone systemthe telephone system

in a computer network computers are in a computer network computers are linked together with high-speed cableslinked together with high-speed cables

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Telephone System

very extensivevery extensive most every household has a telephone or the most every household has a telephone or the

very least a line a few hundred feet awayvery least a line a few hundred feet away cheapcheap used for voice transferused for voice transfer voice is a continuous series of analog signals voice is a continuous series of analog signals

(electrical representations of sound)(electrical representations of sound)

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Slide No. 5

Computers

use digital parallel transmissionuse digital parallel transmission a bunch of bits (8) move around a oncea bunch of bits (8) move around a once

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Translation

for computer data to transmitted over an for computer data to transmitted over an analog telephone line - must be analog telephone line - must be converted form digital data to analog converted form digital data to analog signalssignals

the device that allows computer to the device that allows computer to connect to telephones is a modemconnect to telephones is a modem

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Slide No. 7

Modem

modulation/demodulationmodulation/demodulation modulation-transfer the data from modulation-transfer the data from

computer buses in parallel fashion to computer buses in parallel fashion to serial form so that one binary digit at a serial form so that one binary digit at a time can be released to the phone linetime can be released to the phone line

demodulation-accepts the serial data demodulation-accepts the serial data from the phone line and transforms from the phone line and transforms them back into parallel formthem back into parallel form

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Slide No. 8

Rate of Transmission

or transmission speed of a modemor transmission speed of a modem measured in bits per second (bps)measured in bits per second (bps) early modems - 300 bpsearly modems - 300 bps newer models - 14,400 or 28,800 bpsnewer models - 14,400 or 28,800 bps a text of type page is about 2800 chars a text of type page is about 2800 chars

- at 14,400 can send a full page of text - at 14,400 can send a full page of text in 2 secondsin 2 seconds

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Slide No. 9

Data Transfer Rates Compared

Data transfer rate Data transfer rate (bps)(bps)

1,2001,200 2,4002,400 9,6009,600 14,40014,400 28,80028,800

Time to send a 20 Time to send a 20 page wp documentpage wp document

10 min.10 min. 5 min.5 min. 1.25 min.1.25 min. 50 sec.50 sec. 25 sec.25 sec.

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Slide No. 10

Types of Modems internal/externalinternal/external fax modem - the sending fax machine fax modem - the sending fax machine

makes a digital image (pixels) of the makes a digital image (pixels) of the document and converts it to analog - the document and converts it to analog - the receiving fax converts the analog to digitalreceiving fax converts the analog to digital

when received the document is just a when received the document is just a bunch of black and white dots to the bunch of black and white dots to the computer - need OCR software computer - need OCR software

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Slide No. 11

Protocols

how to behave - standardshow to behave - standards modulation protocols - specifies all the modulation protocols - specifies all the

details for communicationdetails for communication set by international standards org.set by international standards org. one example is the rate at which they one example is the rate at which they

exchange dataexchange data V.34 - regulates the 24,400V.34 - regulates the 24,400 V.32bis - regulates the 14,400V.32bis - regulates the 14,400

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Slide No. 12

Protocols

modems can communicate only if both modems can communicate only if both follow the same protocolfollow the same protocol

fall back - two modems communicate fall back - two modems communicate and establish a protocol they both share and establish a protocol they both share - so they can fall back to slower rate - so they can fall back to slower rate

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Voice Mail messaging system with many of the features messaging system with many of the features

of an electronic mail systemof an electronic mail system responses are recorded and placed in voice responses are recorded and placed in voice

mailmail user can dial the number plus some id or user can dial the number plus some id or

password and listen, respond, forward copies password and listen, respond, forward copies to others and delete messagesto others and delete messages

cannot edit message or attach to other cannot edit message or attach to other computer documentscomputer documents

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Video Teleconferencing

allows people to communicate face to allows people to communicate face to face over long distances by combining face over long distances by combining video and computer technologyvideo and computer technology

need video camera, microphone and need video camera, microphone and television monitortelevision monitor

specially equipped computers allow specially equipped computers allow callers to see each other on their callers to see each other on their computer networkscomputer networks

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Slide No. 15

Channels

communication channel - the physical communication channel - the physical link between two computerlink between two computer

two important characteristics aretwo important characteristics are transmission mediumtransmission medium transmission modetransmission mode

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Transmission Media

wire mediawire media wireless mediawireless media

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Wire Media

Twisted pair - simple, inexpensive, but Twisted pair - simple, inexpensive, but slow and susceptible to errorsslow and susceptible to errors

Coaxial Cable - faster and stronger , Coaxial Cable - faster and stronger , more expensivemore expensive

Fiber-Optic - glass fibers smaller than a Fiber-Optic - glass fibers smaller than a human hair are used - light pulses human hair are used - light pulses rather than electrical signals are sentrather than electrical signals are sent

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Wireless Transmission

Cellular telephone system -Cellular telephone system - microwave transmission - longer microwave transmission - longer

distances, straight-line transmission - distances, straight-line transmission - cannot pass through buildings or cannot pass through buildings or mountainsmountains

satellite transmission - uses satellites in satellite transmission - uses satellites in spacespace

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Bandwidth

relates to the data transfer capacity of relates to the data transfer capacity of the mediumthe medium

measured in kilobits per second (Kbps), measured in kilobits per second (Kbps), megabits per second (Mbps) or gigabits megabits per second (Mbps) or gigabits per second (gbps) per second (gbps)

from slow to fast - twisted pair, coax from slow to fast - twisted pair, coax then fiber opticthen fiber optic

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Slide No. 20

Transmission Mode

enables the receiving computer to know enables the receiving computer to know where one byte ends and next byte where one byte ends and next byte begins.begins.

Synchronous/asynchronous Synchronous/asynchronous transmissiontransmission

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Slide No. 21

Synchronous

the computer are synchronized - there the computer are synchronized - there is a set unit of time to relay a unit of is a set unit of time to relay a unit of datadata

more complex to implementmore complex to implement used mainly in networksused mainly in networks

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Asynchronous

each byte is marked with a start and each byte is marked with a start and stop bitstop bit

more data to be sent - thus 20% slower more data to be sent - thus 20% slower than synchronous (2/10)than synchronous (2/10)

simpler to implementsimpler to implement modemsmodems

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Digital Telephony

most of the long distance telephone service is most of the long distance telephone service is already digitalalready digital

local service is still analoglocal service is still analog ISDN - Integrated Service Digital Network - ISDN - Integrated Service Digital Network -

interim solution - can transmit digital over interim solution - can transmit digital over twisted pair - no conversion necessary - twisted pair - no conversion necessary - ( digital modem)( digital modem)

you can have this service but costs extrayou can have this service but costs extra

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Telecommunications Software

Telecommunications software is Telecommunications software is software that transforms a computer software that transforms a computer into a terminal capable of connecting to into a terminal capable of connecting to a multi-user computer system by means a multi-user computer system by means of the telephoneof the telephone

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Slide No. 25

Features of Communications Program

directs the modem to dial the telephone directs the modem to dial the telephone numbernumber

choose the communications settingschoose the communications settings emulate many computer terminalsemulate many computer terminals enable user to store and print received enable user to store and print received

datadata

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Uses of Telecommunications

Telecommuting (5.5 million people)Telecommuting (5.5 million people) E-mailE-mail BBSs - bulletin board systemsBBSs - bulletin board systems on-line information serviceson-line information services teleconferencingteleconferencing

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LANs, WANs and Intranets

Local Area NetworksLocal Area Networks Wide Area NetworksWide Area Networks

Networks within CompanyNetworks within Company

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Computer Network

Computer Networks need direct, high-Computer Networks need direct, high-speed connectionsspeed connections

These connections have more much These connections have more much more bandwidth than a standard more bandwidth than a standard telephone linetelephone line

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LANs

Local Area NetworkLocal Area Network direction connectionsdirection connections doesn’t use wires owned by telephone doesn’t use wires owned by telephone

companycompany can connect from two to hundreds of can connect from two to hundreds of

computerscomputers

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Slide No. 30

LAN Hardware

Cable - twisted pair, coaxial and fiber Cable - twisted pair, coaxial and fiber optic cablesoptic cables

NIC card (Network Interface Card)NIC card (Network Interface Card) Hub or Cable Interface Unit - sends and Hub or Cable Interface Unit - sends and

receives signals on the network cablereceives signals on the network cable can connect LANs together by using a can connect LANs together by using a

bridge, router or gateway.bridge, router or gateway.

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Network Topology

The physical layoutThe physical layout starstar ring ring busbus

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Network Models

Client/server (CS network)Client/server (CS network) peer-to-peerpeer-to-peer

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WANs

Wide Area Networks - distance is more Wide Area Networks - distance is more than a mile and as much as half the than a mile and as much as half the globeglobe

require special media (normally require special media (normally provided by telephone companies)provided by telephone companies)

require special hardwarerequire special hardware

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WAN Hardware

Special-purpose telephone wires, fiber-optic Special-purpose telephone wires, fiber-optic cables, microwaves, or satellitescables, microwaves, or satellites

dedicated, private, or leased linededicated, private, or leased line multiplexors - combines computers signals multiplexors - combines computers signals

and passes them on and one on the other and passes them on and one on the other end takes them apart and sends them directlyend takes them apart and sends them directly

routers- sends data the right wayrouters- sends data the right way front-end processorsfront-end processors

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Slide No. 35

Intranets

Network within an organizationNetwork within an organization ““private” webprivate” web keeps the learning curve low when keeps the learning curve low when

moving either back to the “real” web or if moving either back to the “real” web or if you move from the “real” web to an you move from the “real” web to an intranetintranet