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Transcript of Network Concepts and Communications
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Network Concepts and
Communications
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Network Concepts
and Communication
In this chapter:
What can be done online?
How are computers connected? What are the physical properties of networks?
How does a computer know how to
communicate with a network?
Can all computers talk to each other?
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Introduction: Everything is
Connected to Everything
Going online: Connecting to a collection of
interconnected computers on a network. Do banking.
Pay bills. Buy groceries.
Book vacation travel.
Send messages.
Participate in discussions. Do research.
Play games.
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Introduction: Everything is
Connected to Everything
Network: A collection of computers, display terminals,
printers, and other devices linked either by physical or
wireless means.
Seeds of Networking 1966: ARPA (Advanced Research Projects Agency)
State Defense Departments research organization.
Focused major development effort on computer networking.
ARPAs Goal: To promote research in advanced future
technologies by funding university and industry research
proposals.
Result: Thousands of databases became available to the
public.
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Client Server Network
Division of labour client program handles user interface and
light processing chores
server program handles heavy work, likedatabase retrieval, and accessing centralised
resources
Client Machine Server
Client ProgramServer
Program
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Computer 1
Computer 3Computer 4
Computer 2
Server
Printer
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The Internet: A Network of
NetworksComputer Networking
Internet: A world-wide networkconnecting millions of computer networks
for the purpose of exchanging data andcommunications using special rules ofcommunication.
The Internetis an interconnected network
of thousands of networks linking academic,research, government, and commercialinstitutions.
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Communication Basics
of Networks
Types of connections of computers intonetworks: Physical versus Wirelessconnections
The first type: The Physical Connection.Physically connect computers together.
Use of wires or optical cables.
The connections are called network links.
Three most common physical links:Twisted pair
Coaxial cable
Fiber-optic cable
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Communication Basics
of Networks
Twisted pair
Two wires twisted together.
A physical communications channel that uses
strands of copper wire twisted together in pairs,acting like an antenna and picking up radio
frequency information or appliance noise.
Telephone company uses twisted-pair copper
wires to link telephones.
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Communication Basics
of Networks
Coaxial cable
Also two wires:
One of the wires is woven of fine strands of copper
forming a tube. The wire mesh surrounds a solid copper wire that
runs down the center.
Space between has a non-conducting material.
Makes them more impervious to outside noise.
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Communication Basics
of Networks
Fiber-optic cable
Light is electromagnetic.
Can transmit more information
down a single strand. It can send a wider set of
frequencies.
Each cable can send several
thousand phone conversations
or computer communications.
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Communication Basics
of Networks
Second type of connections of computersinto networks: Wireless connections
The link is made using electromagnetic
energy that goes through space instead ofalong wires or cables.
Three types of wireless communicationscommonly used in networking:
InfraredRadio frequency
Microwave
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Communication Basics
of Networks
Infrared
Commonly used in TV and
VCR remote controls.
Use infrared frequencies ofelectromagnetic radiation that
behave much like visible light.
Must be in the line of sight.
Often used to connectkeyboards, mice,
and printers.
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Communication Basics
of Networks
Radio frequency
Uses radio frequencies.
Function even though line of sight is interrupted.
Not commonly used because of the possibleinterference from other sources of
electromagnetic radiation such as old electric
drills and furnace motors.
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Microwave Often used to
communicate withdistant locations.
Must be line of sight.
Satellitecommunications usemicrowaves.
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Communication Basics
of NetworksProperties of Transmission
Five basic properties of both the physical and wirelesslinks:
1. Type of signal communicated (analog or digital).
2. The speed at which the signal is transmitted (howfast the data travels).
3. The type of data movement allowed on the channel(one-way, two-way taking turns, two-waysimultaneously).
4. The method used to transport the data(asynchronous or synchronous transmission).
5. Single channel (baseband) and multichannel(broadband) transmission.
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Communication Basics
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Type of signal communicated (analog ordigital).
Analog:Those signals that vary with smooth
continuous changes.A continuously changing signal similar to that
found on the speaker wires of a high-fidelity stereosystem.
Digital: Those signals that vary in steps orjumps from value to value. They are usually inthe form of pulses of electrical energy(represent 0s or 1s).
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Communication Basics
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The speed at which the signal is transmitted(how fast the data travels).
In digital systems: Speed is measured in...
Bits per second(bps).
The number of bits (0s and 1s) that travel
down the channel per second.
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Need for Modem
The computer
communicates
with digital signals
The telephone system
was designed to transmitvoice signals which are
analog
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Communication Basics
of Networks
MODEM- MOdulatorDEModulator
Outgoing: Converts binary data
from computer (digital) intotelephone compatible signals(analog).
Incoming: Converts telephone
signal (analog) into binary datafor the computer (digital).
Can be an external or internaldevice (usually a card).
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Communication Basics
of Networks
The type of data movement allowed on thechannel.
Simplex transmission - One way transmission.
Half-duplextransmission - Flows only one
way at a time.
Full-duplextransmission - Two-way
transmission at the same time.
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Communication Basics
of Networks
The method used to transport the data.
Two types of data transmission, each requiring
a different modem.
Asynchronous transmission-
Information is sent byte by byte.
Cheaper and more commonly used.
Synchronous transmission-
Data is sent in large blocks rather than in smallpieces.
Preceded by special information, concerning error
detection and block size.
These modems are expensive but very fast.
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Communication Basics
of Networks
Single channel versus multichanneltransmission
Channel- A path of a signal.
Single channel- Capable of onlysending/receiving one signal at a time.
Phone line: Single line = single phone call at a
time.
Multichannel - Capable of more than onechannel at a time.
Fiber-optic cable, microwaves, Satellite
transmissions.
C i ti B i
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Communication Basics
of Networks
How is it possible to measure the capacity
of communications links? Bandwidth: DigitalNumber of bits per second (bps) that can be sent
over a link.
The wider the bandwidth, the more diverse kinds of
information can be sent.Simplest is voice, most sophisticated is moving
videos.
Bandwidth: Analog The difference between the highest and lowest
frequencies that can be sent over an analog link(like phone lines).
Measurement is given in hertz (Hz).
For both:The wider the bandwidth, the moreinformation can flow over the channel.
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Typical cable bandwidths used in local area networks.
Cable: Typical Bandwidth:Twisted Pair 10 to 100 Mbps
Coaxial Cable 10 to 100 Mbps
Fiber-optic cable 100 to 200 Mbps
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The Physical Organization
of Networks
Two parts to connect computers to networks
The hardware needed to connect the
computer to the network.
The software needed to control the hardware.
(Software standards will be discussed in the next
section.)
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The Physical Organization
of Networks
Node: The generic name given to all deviceshooked up to a network.
Each node must have a unique address assigned to
them by the network.
Networks are either direct-connected or those that arenot directly linked.
Direct-connected network: Those whose nodes have
direct connections through either physical or wireless
links. Point-to-point: Simplest version of direct-connected
network. Connecting two computing systems.
Example of point to point: Home to ISP.
Example of a network that is not directly linked: Internet.
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The Physical Organization
of Networks
The bus network- A continuous coaxial cable to
which all the devices areattached.
All nodes can detect all
messages sent along the bus.
The ring network- Nodes linked together to form a
circle.
A message sent out from onenode is passed along to eachnode in between until the targetnode receives the message.
Linking nodes:
Th Ph i l O i ti
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The Physical Organization
of Networks
The star network- Each node is linked to a
central node.
All messages are routed
through the central node,who delivers it to the
proper node.
Linking nodes:
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The Physical Organization
of Networks
The fully connected network
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All nodes are connected to all
other nodes.
Internetworking -
Connecting together any numberof direct-connected networks.
The largest: Internet.
Linking nodes:
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The Physical Organization
of Networks
There are two general types of computer
networks:
LAN
(Local Area
Network)
WAN
(Wide Area Network)
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The Physical Organization
of Networks
LAN(Local Area Network)A collection of nodes within a small area.
The nodes are linked in a bus, ring, star, tree,or fully connected topology network
configuration.
Benefits of LANs:Sharing of hardware resources.
Sharing of software and data.Consolidated wiring/cabling.
Simultaneous distribution of information.
More efficient person-to-person communication.
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The Physical Organization
of Networks
MAN(Metropolitan Area Network) Consists of many local area networks linked
together.
Span the distance of just a few miles.
WAN(Wide Area Network)
Consists of a number of computer networks includingLANs.
Connected by many types of links.
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Internet Connections
There are many types of Internet
connections
1) DIALUP
2) DSL
3) VSAT
4) ISDN5) DEDICATED LINE
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DIALUP
This is the most basic type of Internet
connection.
This connection is made through a
modem, that uses a telephone line to
connect to the Internet.
The modem must dial the telephone every
time it wants to connect to the Internet,hence the name dial-up connection.
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DSL (Digital Subscriber Line )
An DSL connection uses high-speed transmissions
through telephone lines.
DSL connections are speedy
The only caveat here is that the closer you are to the
main telephone switching station, the faster yourconnection speed will be.
There are two types of DSL such as ADSL and SDSL.
There are two types of DSL internet connection,
namely Asymmetrical Digital Subscriber Line (ADSL)
and Symmetrical Digital Subscriber Line (SDSL). The
difference between the two is their data transfer
speed.
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ISDN
An ISDN (Integrated Services Digital Network)
connection uses high-speed, high-quality digital
telecommunication lines.
The advantage of an ISDN service is that theyare made up of digital circuits.
This special phone line must be installed by a
phone company
ISDN supports data transfer rates of 64 Kbps
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VSAT
VSAT (Very Small Aperture Terminal) is a
satellitecommunications system
A VSAT consists of two parts, a transceiverthat
is placed outdoors in direct line of sight to thesatellite and a device that is placed indoors to
interface the transceiver with the end user's
communications device, such as a PC
VSAT handles transmission rates of up to 56
kilobits per second.
http://searchmobilecomputing.techtarget.com/gDefinition/0,,sid40_gci212939,00.htmlhttp://www.webopedia.com/TERM/V/transceiver.htmlhttp://www.webopedia.com/TERM/V/end_user.htmlhttp://www.webopedia.com/TERM/V/PC.htmlhttp://www.webopedia.com/TERM/V/PC.htmlhttp://www.webopedia.com/TERM/V/end_user.htmlhttp://www.webopedia.com/TERM/V/transceiver.htmlhttp://searchmobilecomputing.techtarget.com/gDefinition/0,,sid40_gci212939,00.html -
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Working of VSAT
The tranceiver receives or sends a signal to asatellite transponderin the sky. The satellitesends and receives signals from an earth stationcomputer that acts as a hubfor the system.
Each end user is interconnected with the hubstation via the satellite in a star topology. Forone end user to communicate with another,each transmission has to first go to the hub
station which retransmits it via the satellite to theother end user's VSAT.
VSAT handles data, voice, and video signals.
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DEDICATED LINE
A telecommunications line that lets your
computer have a direct, permanent
connection to the Internet; in contrast with
a dial-up connection which is only openedfor temporary use.
is not shared in common among multiple
users as dial-up lines are
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Wi Fi stands for Wireless Fidelity and is
used to define any of the wireless
technology
the most common usage of Wi Fi
technology is for laptop users to gain
Internet access in locations such as
airports, coffee shops
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Internet Service Providers (ISPs)
An Internet service provider (ISP) is anorganization that provides Internet accounts,
whether dial-in, DSL, ISDN, cable, satellite, or
wireless. Thousands of ISPs exist in the United States, including dozens of ISPs with
dial-up access phone numbers throughout
the country, and many with phone numbers in
limited regions. For example, EarthLink (www.earthlink.com) has access phone
numbers in all major U.S. cities, whereas
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Intranet
An Intranet is a network based on the internet
TCP/IP open standard. An intranet belongs to an organization, and is
designed to be accessible only by theorganization's members, employees, or others
with authorization. An intranet's Web site looks and act just like
other Web sites, but has a firewall surrounding itto fend off unauthorized users.
Intranets are used to share information. Secureintranets are much less expensive to build andmanage than private, proprietary-standardnetworks.