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Slide No. 3 Chapter 1, Unit c Telecommunications n Two computers linked together through the telephone system n in a computer network computers are linked together with high-speed cables
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Chapter 1, Unit c Slide No. 1
Data Communications
TelecommunicationsTelecommunications LANs, WANs and IntranetsLANs, WANs and Intranets
Chapter 1, Unit c Slide No. 2
Telecommunications
HardwareHardware SoftwareSoftware
ImpactImpact
Chapter 1, Unit c Slide No. 3
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
Chapter 1, Unit c Slide No. 4
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)
Chapter 1, Unit c 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
Chapter 1, Unit c Slide No. 6
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
Chapter 1, Unit c 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 them from the phone line and transforms them back into parallel formback into parallel form
Chapter 1, Unit c 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
Chapter 1, Unit c 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.
Chapter 1, Unit c 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
Chapter 1, Unit c 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
Chapter 1, Unit c 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
Chapter 1, Unit c Slide No. 13
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
Chapter 1, Unit c Slide No. 14
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
Chapter 1, Unit c Slide No. 15
Transmission Media
wire mediawire media wireless mediawireless media
Chapter 1, Unit c Slide No. 16
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
Chapter 1, Unit c Slide No. 17
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
Chapter 1, Unit c Slide No. 18
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
Chapter 1, Unit c Slide No. 19
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
Chapter 1, Unit c Slide No. 20
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
Chapter 1, Unit c Slide No. 21
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
Chapter 1, Unit c Slide No. 22
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
Chapter 1, Unit c Slide No. 23
Uses of Telecommunications
TelecommutingTelecommuting E-mailE-mail BBSs - bulletin board systemsBBSs - bulletin board systems on-line information serviceson-line information services teleconferencingteleconferencing
Chapter 1, Unit c Slide No. 24
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
Chapter 1, Unit c Slide No. 25
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
Chapter 1, Unit c Slide No. 26
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.
Chapter 1, Unit c Slide No. 27
Network Topology
The physical layoutThe physical layout starstar ring ring busbus
Chapter 1, Unit c Slide No. 28
Network Models
Client/server (CS network)Client/server (CS network) peer-to-peerpeer-to-peer
Chapter 1, Unit c Slide No. 29
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
Chapter 1, Unit c Slide No. 30
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 end and passes them on and one on the other end takes them apart and sends them directlytakes them apart and sends them directly
routers- sends data the right wayrouters- sends data the right way front-end processorsfront-end processors
Chapter 1, Unit c Slide No. 31
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