basic networking knowledge

8/2/2019 Basic Networking Knowledge

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TOPICS

# I NTRODUCTI ON# COMPUTI NG MODELS# NETWORK CLASSI FI CATI ON# NETWORK SERVI CES# TRANSMI SSI ON MEDI A# PHYSI CAL LAYER# NETWORK TOPOLOGI ES# NETWORKI NG PROTOCOLS# NETWORKI NG HARDWARE


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Define Computer Networking

Networking is the sharing ofinformation and services. Computer

networking provides thecommunication tools to allowcomputers to share information and

abilities.

Network

By a computer network we mean an interconnected set of

autonomous computers. By autonomous we mean each of them can

function independent of the others.


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A network consists of two or more computersthat are linked in order to share resources

(such as printers and CD-ROMs), exchange

files, or allow electronic communications.The computers on a network may be linked

through cables, telephone lines, radiowaves, satellites, or infrared light beams.

Network


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Computer networking are based on the following

computing models :-

Distributed computing

Collaborative computing

Computing Models and Network

Development


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The following computing models are usedto categorize the way networking servicesare provided:

Client/Server

Client/Network

Computing models


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In the centralized computing model, largecentralized computers, called mainframes, areused to store and organize data. People enter

data on mainframes using local devicescalled terminals.

In centralized computing, the mainframeprovides all the data storage andcomputational abilities; the terminal is simplya remote input/output device.

Centralized Computing


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Collaborative computing (also called

cooperative processing) is a type of

distributed computing using networked

computers that collaborate by sharing

processing abilities .

Collaborative Computing


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Collaborative computing allows computers to

request processing resources from othercomputers as needed.

Collaborative computing is a form ofdistributed computing.

Collaborative computing allows tasks to be

shared by computers as needed.

Distributed computing assigns each task to asingle computer.

Both use networked computers withprocessing capabilities; and both divide

applications into tasks.


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In the client/server computing model, several clients

(PCs) are connected to a server (PC)...

In the client/server model :-

Processing capabilities are distributed across multiple,machines .

Clients request services from servers.

The server performs some of the processing for theclient.

Applications used in a client/server network can besplit into a front end that runs on the client and a backend that runs on the server.

Client/Server Computing


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Standalone (non-networked) applications such as a

spreadsheet program or a word processing programthat runs on the client but saves its data on the server.

A database application that provides a clientinterface for requests and a search engine on the

server that locates records stored on one or moreservers

Programs, such as an email system, that use the

server to share information

In Client/server model, the following can be us


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Local Area Network (LAN)

Metropolitan Area Networks

(Man) Wide Area Networks (WAN)

Computer Network Classifications


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These are privately-owned communication

systems that cover a short distance i,.E ABUILDING OR A CAMPUS OF BUILDINGS.

Variety of devices including computers,

terminals, peripheral devices and sensors are

used to link using a LAN. LANs OPERATE AT

A HIGH SPEED (i.E 10 mbps OR MORE ANDHAVE A VERY LOW ERROR RATE (1:1011).

LANs


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Local Area Network (LAN)

A LAN is normally contained within abuilding or campus and typically usescommunication links that are owned

and maintained by the group whosedata the LAN carries .

LAN transmission speeds are oftenmeasured in megabits per second(mbps ).


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These can be considered as a bigger version of a

LAN, typically covering a city. It can be eitherpublic or privately owned. Although LAN

technology can be used in man, it has been

distinguished as a separate type of network,

because of the specific standard known as

distributed queue double bus (DQDB) that hasbeen adopted for man. The DQDB comprises of

two unidirectional buses for connecting

computers

MAN


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Wan encompasses a large geographical area, often acountry or a sub-continent, or the entire globe.

Communication is usually done through public

communication systems such as telephone network.

As a consequence, data transfer rate in WAN is low

(several kb/s). Error rate is much higher (1000 times

that of lan), which requires use of suitable error

handling technique.

Wan


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A wide area network (WAN) comprises multipleLANs.

WANs interconnect LANs that can be atopposite sides of a country or located around the

world. WANs often use telephone or satellitecommunication .

Access to WAN links is often leased from a

WAN services vendor who is responsible formaintaining the communication equipment.

For most WAN links, the transmission speedattainable over the available bandwidth ismeasured in kilobits er second kb s .

Wide Area Networks (WAN)


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Enterprise and Global Networks

A global network is to cover the entire globe, but

they cross multiple nations that span the earth.

Global networks might not boundaries and caninclude the networks of several organizations

The Internet is a good example of a globalnetwork


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Enterprise and Global

Networks


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INTERNET IS NOT A SEPARATE KIND OF NETWORK,

BUT IT IS A COLLECTION OF NETWORKS OR AANETWORK OF NETWORKSNETWORK OF NETWORKS. ONE PRIMARY GOAL OF

INTERNET IS TO CONNECT VARIOUS NETWORKS IN

A SEAMLESS MANNER. THE GLUE WHICH HOLD

VARIOUS NETWORKS TOGETHER IS THE TCP-IP,

THAT ALLOWS HOSTS TO COMMUNICATE FREELY

ACROSS NETWORK BOUNDARIES. INTERNET

ALLOWS VARIOUS APPLICATIONS SUCH AS E-MAIL,FILE TRANSFER, REMOTE LOGIN AS IN NEWS,

WORLD WIDE WEB, MULTIMEDIA, ETC.

INTERNET


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ADVANTAGES

Speed. Networks provide a very rapid method for sharing and

transferring files.

Lower Cost. A network of low-cost computers gives much better

cost/performance than a single costly mainframe computer..Besides monetary savings, sharing a program on a network

allows for easier upgrading of the program

Security. Files and programs on a network can be designated as

"copy inhibit," Also, passwords can be established for specific

directories to restrict access to authorized users

NEED OF COMPUTER NETWORKING

Centralized Software Management All of the software can be


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Centralized Software Management. All of the software can be

loaded on one computer (the file server). This eliminates

that need to spend time and energy installing updates and

tracking files on independent computers throughout the

building

Communication medium: It offers a powerful communicating

medium among a group of people widely separated.

Resource sharing: Most organisations cannot afford enough

laser printers, fax machines, modems, scanners, and CD-

ROM players for each computer. However, resources likedata, program, costly peripherals or equipments located at

distant places can be shared through network.

El t i M il Th f t k id th


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Electronic Mail. The presence of a network provides the

hardware necessary to install an e-mail system. Electronic

mail on a LAN can enable users to communicate with each

other. If the LAN is connected to the Internet, users can

communicate with others throughout the world

Higher reliablility: A computer network offers higher

reliability than a centralised computing environment

because of the redundancy that can be incorporated both interms of hardware and software. in the event of failure of

one computer, its work-load can be taken over by other

computer.

Higher flexibility: Computer networks allow communication

among heterogeneous systems, which give users betterflexibility

DISADVANTAGES


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Expensive to Install. Although a network will generally

save money over time, the initial costs of installation can

be prohibitive. Cables, network cards, and software are

expensive, and the installation may require the services of

a technician.

Requires Administrative Time. Proper maintenance of anetwork requires considerable time and expertise.

File Server May Fail. Although a file server is no more

susceptible to failure than any other computer, when the

files server "goes down," the entire network may come to

a halt.

DISADVANTAGES


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Cables May Break. Some of the configurations aredesigned to minimize the inconvenience of a broken

cable; with other configurations, one broken cable can

stop the entire network.

No Privacy As programs and data are shared by many

users, this raises the problem of data integrity, securityand privacy.

No ControlIn a distributed system there is certain

amount of loss of control. It is difficult to enforce

standards for software and data.


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Network Services


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Network services are the capabilities that

networked computers share.

Network services are provided by numerouscombinations of computer hardware and

software. Depending upon the task, networkservices require data, input/output resources,

and processing power to accomplish their

Network Services


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ServersServers are classified as service providers.They only provide services.

ClientsClients are classified as service requesters.They only request services.

PeersPeers can be classified as both a servicerequester or provider. They provide and

request services.

The three types of service providers andrequesters:

Network Operating Systems


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Computer networks are often classifiedas one of the following types:

Peer-to-peer Server-centric

Network Operating Systems

Network operating systems (NOS) coordinate theactivities of multiple computers across a network. The

network operating system acts as a director to keepthe network running smoothly. The two major types ofnetwork operating systems are:


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Peer-to-peer networksallow any entity to both

request and provide networkservices.

Peer-to-peer networksoftware is designed so that

peers perform the same orsimilar functions for each

Peer-to-Peer Networks


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Advantages & Disadvantages

Less initial expense - No

need for a dedicated server.

Set-up - An operating

system (such as Windows95) already in place may

only need to be

reconfigured for peer-to-peer operations.

Decentralized - No

central control for filesand applications.

Security - Does notprovide the security

available on a

client/server network.

S C t i N t k


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@ Client/server network operating systems allow the network

to centralize functions and applications in one or more

dedicated file servers. The File servers provide access toresources and providing security.

@ Individual workstations (clients) have access to the

resources available on the file servers

@ The network operating system provides the mechanism to

integrate all the components of the network and allow multiple

users to simultaneously share the same resources irrespective

of physical location.

@ Novell Netware and Windows NT Server are examples of

client/server network operating systems.

Server-Centric Networks

Ad & Di d


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Centralized - Resources and datasecurity are controlled through the

server.Scalability - Any or all elementscan be replaced individually asneeds increase.

Flexibility - New technology can beeasily integrated into system.

Interoperability - All components(client/network/server) work

together.Accessibility - Server can beaccessed remotely and acrossmultiple platforms.

Expense - Requiresinitial investment in

dedicated server.

Maintenance - Largenetworks will require

staff to ensure efficientoperation.

Dependence - Whenserver goes down,operations will ceaseacross the network.


Online Nearline and


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Online, Nearline, and

Offline Storage Media

Computers store data on a variety ofComputers store data on a variety of


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Computers store data on a variety ofComputers store data on a variety of

magneticmagnetic

and optic disks, diskettes, and tapes.and optic disks, diskettes, and tapes.

Online storage media, such as hard disks,

areimmediately available to the computer.

Nearline storage media, such as tapecarousels,

CD jukeboxes, and so on, are not

immediatelyavailable to the computer, but do not require

human intervention .

Offline storage media, such as removable


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File Update Synchronization


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File Update Synchronization


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Typically, only two or threecomputers can be directly connected

to each printer.

On the other hand, network

print services allow numerous clients

to be serviced

by a single printer.

Network Printing

Advantages of network printing


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Reducing the total number of printers cansave your organization a substantial amount of

money. Having fewer printers reduces thenumber of devices to buy, maintain, and

manage.

Advantages of network printing


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Network Printing

Network Message Services


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Message services include storing,

accessing,and delivering text, binary, graphic,digitized

video, and audio data.

Message services deal withcommunication

between computer users, user

applications,


Network message services help


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Network message services help

you Exchange computer-generated notes

and files Integrate electronic mail with voice

mail systems Route and share data using workflow

and linked object documentapplications

Organize and maintain user anddevice information directories


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In this subsection types of message-

enabled

applications:

Electronic mail

Integrated electronic mail and voicemail

Workgroup applications



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D b R li i


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Data can be retrieved much more rapidly

from local databases than from remote

databases .Therefore, it is often more

efficient for users to work on a local copy

of the data .

Replication creates and synchronizes

multiple copies of a database over the

Database Replication

Distributed Database Replication


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Distributed Database Replication

Methods


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DATA COMMUNICATION CONCEPTS


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The primary concern of a computer network is to facilitate

exchange of information between any pair of nodes in thenetwork. That involves sending of data in the form of signal

from source node to the destination node through A

communication channel. The key issues are:The nature of data

Physical means used to transfer data

Processing of data for efficient communication.

CO UN C ON CONC S

BLOCK DIAGRAM OF TYPICAL COMMUNICATION SYSTEM


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SOURCE

NODE

DESTINATION

NODE

SIGNAL INPUT

TRANSMITTER

TRANSMISSION

CHANNEL

RECEIVER

SIGNAL OUTPUT

COMMUNICATION SYSTEM


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TRANSMISSION MEDIA

In a network of computers, the transmission

media provide the physical path for communicationamong the nodes and the manner in which the nodes

are geometrically interconnected is known as its

topology.

Examples for guided transmission media are twisted-

pair of wires, co-axial cables and optical fiber

Pathway for Communication


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Pathway for Communication

Transmission Media


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Computer transmission media includescable

and wireless technologies that allownetworked

devices to contact one another.

Transmission media cannot guarantee that

other network devices will understand a

message.

It can, however, guarantee a message

C bl M di


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Cable media are wires or fibers that conductelectricity or light.

The following examples are covered in this section:

Twisted pair cable

Coaxial cable

Fiber optic cable

Cable Media

Twisted pair cable


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Twisted pair (TP) cable uses copper wire astelecommunication cable.

Because copper is such a good conductor of electrons,copper wires do not constrain electromagnetic signals

well. Twisted pair can be used for both Analog and Digitalcommunication

Twisting the copper wires reduces cross talk and signalemissions.

Each intertwined strand conducts a current whoseemitted waves are cancelled out by the other wires

Twisted Pair


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Twisted Pair


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TWISTED-PAIRCharacteristics:-Twisted pair can be used for both analog

and digital communication. The data rate that can be

supported over a twisted pair is inversely proportional tothe square of the line length. Maximum transmission

distance of 1km can be achieved for data rates up to

1mb/s. For digital signal, repeaters are needed for about2km. To reduce interference, the twisted pair can be

shielded with metallic braid. This type of wire is known as

shielded twisted pair(STP) and the other is known asunshielded twisted pair(UTP).

The Electrical Industries Association (EIA)popularized a category labeling scheme for five


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popularized a category labeling scheme for five

different qualities of twisted pair cable:

Category 1 and 2: Voice and low-speed data (lessthan or equal to 4 Mbps)

Category 3: Data (typically 10-16 Mbps, although100 Mbps is possible)

Category 4: Data (less than or equal to 20 Mbps)Category 5: High-speed data (less than or equal to100 Mbps)

Category 3 and Category 5 UTP are commonly usedin computer networking. Category 3 is suitable formost computer networks.


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The two types of TP cable are :

Unshielded

Shielded

Unshielded Twisted Pair Cable


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Unshielded Twisted Pair Cable


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UTP is commonly used in telephone systems. It

is widely available and has been largely standardized.

The standard connector for

unshielded twisted pair

cabling is an RJ-45

connector. This is a plasticconnector that looks like a

large telephone-style

connector

A Common Unshielded Twisted PairInstallation


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Installation

Shielded Twisted Pair Cable


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A disadvantage of UTP is that it may be

susceptible to radio and electrical frequencyinterference. Shielded twisted pair (STP) is

suitable for environments with electrical

interference; however, the extra shielding

can make the cables quite bulky. Shielded

twisted pair is often used on networks usingToken Ring topology.



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Today, most TP cable is unshielded, but some

forms of shielded twisted pair(STP) still exist.

STP is insulated cable that includes bundledpairs wrapped in a foil shielding. Various

transmission media specifications from Apple

Computer and IBM use STP cable.

Shielded Twisted Pair


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Shielded Twisted Pair Installation


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Coaxial Cable


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Coaxial cable (commonly called coax) is made of twoconductors that share a common axis, hence the name

(co, axis).

Typically, the center of the cable is a relatively stiffsolid copper wire or stranded wire encased in

insulating plastic foam.

The foam is surrounded by the second conductor, awire mesh tube (some include conductive foil wrap),which serves as a shield from interference and signalcapture.

A tough, insulating plastic tube forms the cover of thecable.

Coaxial Cable


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Coaxial cable standards are

used in computer networking


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The most common types meet one of the following ohmand size standards (ohms are a measurement of the

cables resistance to direct or alternating electriccurrents):

75 ohm RG-6 (used for Satellite TV)

50 ohm RG-8 and RG-11 (used in thick Ethernetspecifications discussed later)

50 ohm RG-58 (used in thin Ethernet specificationsdescribed later)

75 ohm RG-59 (used for cable TV and cable modems)

93 ohm RG-62 (used for ARC net specifications)

Common Coaxial Cable Installation


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Fiber Optic Cable


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Fiber optic cables can be composed of a singlejacketed strand, but often multiple strands are bundled

in the center of a cable. Some fiber optic cables alsoprovide an additional metallic, or fiberglass wire toincrease cable strength.

Optical fibers can be multimode or single mode innature. Single-mode fiber has been optimized to allowonly one light path; multimode fiber allows various

light paths.

Single-mode fiber has a higher capacity but costsmore to produce and use than multimode fiber.

Fiber Optic Cable


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Type of Fiber-Optic Cable


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Single-Mode and

Multimedia Propagation


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Cable Transmission MediaComparison


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p


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RADIO WAVERADIO WAVE

MICROWAVEMICROWAVE

INFRARED LIGHTINFRARED LIGHT

Radio Wave


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The portion of the electromagnetic spectrum that isusually considered radio frequency (RF) resides

between 10 KHz and 1 GHz. This range of radiofrequencies includes broadcast bands for :

Shortwave radio

Very high frequency (VHF) television and FM radio

Ultra-high frequency (UHF) radio and television

Radio frequencies are divided between regulatedand unregulated bandwidths.

Radio Frequencies


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Wireless LANs have gained strongWireless LANs have gained strong

popularity in a number of verticalpopularity in a number of vertical


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the health-care retail

manufacturing

warehousing

academic

markets including :markets including :

Wi h i l LAN h d

Why wireless?


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With wireless LANs, users can access sharedinformation without looking for a place to plug in,and network managers can set up or augmentnetworks without installing or moving wires.

Wireless LANs Technology


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Manufacturers of wireless LANs have arange of technologies to choose from when

designing a wireless LAN solution.

Each technology comes with its own set of

advantages and limitations.

Narrowband Technology


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A narrowband radio system transmits and receives

user information on a specific radio frequency. Narrowband radio keeps the radio signal frequencyas narrow as possible just to pass the information.

Broad Band/Spread Spectrum Technol


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Most wireless LAN systems use spreadspectrum technology, a wideband radiofrequency technique developed by the

military for use in reliable, secure, mission-critical communications systems.

Spread-spectrum is designed to trade offbandwidth efficiency for reliability, integrity,and security.

If a receiver is not turned to the right

freq enc a spread spectr m signal looks


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frequency, a spread-spectrum signal lookslike background noise.

There are two types of spread spectrum

radio:

Frequency hoppingand Direct sequence.

Direct Sequence Spread

Spectrum


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Multiple subsets can be used within any frequencyrange, direct sequence signals can coexist with other

signals.

Unwanted signals are simply ignored or treated as aspurious signal or noise.

Direct sequence signals can be intercepted almostas easily as other RF signals, eavesdropping isineffective because it is quite difficult to determinewhich specific frequencies to monitor, retrieve all thechips, identify valid data, and interpret the signal.

Spectrum

Direct Sequence SpreadSpectrum


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Frequency Hopping Spread

Spectrum


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Frequency hopping quicklyswitches between pre-

determined frequencies.Both transmitter andreceiver must follow the

same pattern and maintaincomplex timing intervals.

Spectrum

FHSS appears to be short-duration impulse noise.

Microwave


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Microwave data communication systems exist in two

forms:

Terrestrial (earth-based) systems

Satellite systems


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Terrestrial microwave


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Terrestrial microwave typically uses directional

parabolic antennas that require an unobstructed

path or line of sight to other units. Terrestrial

microwave signals, commonly in the low GHz

frequency range, are generated by a transceiver.

They are often used to link separate buildings

where cable installation would be Troublesome ormore expensive.

Satellite microwave


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Satellite microwave typically uses low GHz

frequency range microwaves.

They use parabolic antennas located on

earth and orbiting satellites

Infrared Technology


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Infrared (IR) : Systems use very high

frequencies, (100 Ghz-1000Terahertz) just belowvisible light in the electromagnetic spectrum, tocarry data.

Like light, IR cannot penetrate opaque objects,it is either directed (line-of-sight) or diffusetechnology.

Inexpensive directed systems provide verylimited range (3 ft) and typically are used forpersonal area networks but occasionally areused in specific wireless LAN applications.

Infrared links use LEDs, Laser Diodes,Photodiodes to exchange data between stations


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Transmission Media Connectors

T i i di t tt h


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Transmission media connectors attachdirectly to the transmission media and

serve as the physical interface between themedia and computing devices. Everymedium has one or more physical

connectors that you can use.


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Transmission Media ConnectorInstallation


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In 1977, the International Organization for

standardization (ISO) created the Open SystemsInterconnection (OSI) Reference Model.

OSI defines standards by which computerscan communicate together

It describes the architecture, protocols and

services required to achieve this goalThe reference model serves seven OSI layersthey are as follows:-

OSI reference modelOSI reference model


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The OSI reference modelThe OSI reference model


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Headers and the OSI ReferenceHeaders and the OSI Reference

ModeMode


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Each layer adds its own control

information, called a header, whichcontains that layers requests orinformation. This header is read and

processed by the peer layer.

Headers and the OSI Reference ModelHeaders and the OSI Reference Model


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OSI Reference Model as a ConceptualOSI Reference Model as a Conceptual

FrameworkFramework


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Connection Type MethodsConnection Type Methods


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Point-to-point

Multipoint

Connection Type MethodsConnection Type Methods


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Point-to-Point Connections


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A point-to-point connection is a direct link

between two devices. When you attach a personal

computer directly to a printer, you have created a

point-to-point link. Another example is the linkbetween two microwave antennas.

A direct connection between a computer and a

printer is a common example of a point-to-point

connection.

PointPoint--toto--Point ConnectionsPoint Connections


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Multipoint ConnectionsMultipoint Connections


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Network Topologies

In a network of computers the manner in which


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There are two types of topology: physical and logical.

The physical topology of a network refers to theconfiguration or the actual layout of cables,

computers, and other peripherals. Logical topology is

the method used to pass the information betweenworkstations.

In a network of computers, the manner in which

multiple nodes are physically interconnected is referred

to as its topology.

Physical Topology Methods


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Common Physical Topologies


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Physical Topologies


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Linear Bus

Ring

Star

Mesh

Cellular

Linear Bus

A linear bus topology consists of a main long cable called a


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backbone to which network devices are either directly attached

or are attached using short drop cables .

Ethernet and Local Talk networks can use a linear bus topology.


Easy to connect a Entire network shuts down if


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computer or

peripheral to a

linear bus.

Requires less cable

length than a star

topology.

there is a break in the main

cable.

Terminators are required at

both ends of the backbone

cable.

Difficult to identify the problem

if the entire network shuts

down.

Not meant to be used as a

stand-alone solution in a large

building.

Typical Bus Topology LAN


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A physical ring is

Ring


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A physical ring is

a circulartopology. Eachdevice connects

directly to the ringor indirectly

through aninterface deviceand drop cable.

Typical Physical Ring TopologyLAN


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Star

A l


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A star topology uses acentral device with dropcables extending in all

directions. Eachnetworked device is

connected via a point-to-point link to a hub.

Physical Star Topology


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Star


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Easy to install and wire.

N di ti t th

Requires more cable

length than a linear


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No disruptions to the

network whenconnecting or removing

devices.

Easy to detect faults andto remove parts.

length than a linear

topology.

If the hub or

concentrator fails,

nodes attached are

disabled.

More expensive than

linear bus topologies

because of the cost of

the concentrators.

Star-Wired Ring

i d i l


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A star-wired ring topology may appear

(externally) to be the same as a startopology. Internally, the MAU (multi-

station access unit) of a star-wired ringcontains wiring that allows information to

pass from one device to another in a circle

or ring. The Token Ring protocol uses a

star-wired ring topology.

Star-Wired Ring


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Tree

A l bi h i i f


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A tree topology combines characteristics of

linear bus and star topologies. It consists ofgroups of star-configured workstations

connected to a linear bus backbone cableTree topologies allow for the expansion of

an existing network, and enable schools to

configure a network to meet their needs.

Tree


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Point to point O erall length of each


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Point-to-point

wiring forindividual

segments.

Supported by

several hardware

and software

vendors.

Overall length of each

segment is limited by the typeof cabling used.

If the backbone line breaks,

the entire segment goes

down.

More difficult to configureand wire than other

topologies.

A mesh network has point-to-pointi b d i i h

Mesh Topology


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connections between every device in the

network.

Each device requires an interface for every

other device on the network, a true meshtopology is not usually considered practical.

Unless each workstation frequently sendssignals to all other workstations, an excessiveamount of network bandwidth is wasted.

Physical Mesh Topology


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Typical Physical Mesh TopologyLAN


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A cellular topology combines wireless point-to-

Cellular topology


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point and multipoint strategies to divide a

geographic area into cells. Each cell represents the

portion of the total network area in which a specific

connection operates.

Cellular topologies exhibit qualities that are very

different from cable topologies. For example,

devices can roam from cell to cell while maintaininga connection to the network.

Physical Cellular Topology


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As a wireless structure, the topology does not

Physical Cellular TopologyLAN


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depend on the interconnection of cable.

Cellular topology relies on the location of

wireless media hubs.

Devices within the cell communicate with a

central station or hub. Hubs are interconnected

so that they route data across the network and

provide the complete network infrastructure.

Typical Physical Cellular TopologyLAN


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Considerations for Choosing aTopology

Money. A linear bus network may be the least


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y yexpensive way to install a network; you do nothave to purchase concentrators.

Length of cable needed. The linear bus networkuses shorter lengths of cable.

Future growth. With a star topology, expanding anetwork is easily done by adding anotherconcentrator.

Cable type. The most common cable in LAN isunshielded twisted pair (Cat. 5), which is mostoften used with star topologies.


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Networking Protocols

The most common protocols are:


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The most common protocols are:

Ethernet

Local Talk

Token Ring FDDI

Ethernet

The Ethernet protocol is by far the most widely used.

Ethernet uses an access method called CSMA/CD (Carrier Sensei A /C i i i )


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Multiple Access/Collision Detection).

This is a system where each computer listens to the cable beforesending anything through the network.

Sometimes, two computers attempt to transmit at the same instant.When this happens a collision occurs. Each computer then backs

off and waits a random amount of time before attempting toretransmit.

With this access method, it is normal to have collisions.

However, the delay caused by collisions and does not normallyeffect the speed of transmission on the network. The Ethernet

protocol allows for linear bus, star, or tree topologies. Data can betransmitted over twisted pair, coaxial, or fiber optic cable at aspeed of 100 Mbps.

Ethernet Cards


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Local Talk

Local Talk is a network protocol that was developed by AppleComputer, Inc. for Macintosh computers. The method used by iscalled CSMA/CA (Carrier Sense Multiple Access with Collision


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called CSMA/CA (Carrier Sense Multiple Access with Collision

Avoidance).It is similar to CSMA/CD except that a computer signals its intentto transmit before it actually does so.

The Macintosh operating system allows the establishment of apeer-to-peer network without the need for additional software.

With the addition of the server version of AppleShare software, aclient/server network can be established.

The Local Talk protocol allows for linear bus, star, or treetopologies using twisted pair cable. A primary disadvantage of

Local Talk is speed. Its speed of transmission is only 230 Kbps.

Token Ring

The Token Ring protocol was developed by IBM in the mid-1980s.

The access method used involves token-passing. In Token Ring,th t t d th t th i l t l d th


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the computers are connected so that the signal travels around the

network from one computer to another in a logical ring.A single electronic token moves around the ring from onecomputer to the next. It simply passes the token on to the nextworkstation till it reaches the computer which wishes to transmitand receives an empty token, it attaches data to the token. Thetoken then proceeds around the ring until it comes to the computerfor which the data is meant.

At this point, the data is captured by the receiving computer. TheToken Ring protocol requires a star-wired ring using twisted pair

or fiber optic cable.It can operate at transmission speeds of 4 Mbps or 16 Mbps.

FDDI

Fiber Distributed Data Interface (FDDI) is a networkprotocol that is used primarily to interconnect two or


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p p y

more local area networks, often over large distances.The access method used by FDDI involves token-passing. FDDI uses a dual ring physical topology.

Transmission normally occurs on one of the rings;however, if a break occurs, the system keepsinformation moving by automatically using portions ofthe second ring to create a new complete ring.

A major advantage of FDDI is speed. It operates overfibre optic cable at 100 Mbps.

Summary Chart:


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Protocol Summary


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RELATIONSHIP BETWEEN

MEDIUM AND TOPOLOGY

The choice of transmission media and topology cannot be

made independently They together decides the reliability


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made independently. They together decides the reliability,

expandability and performance of the network. The topology

used for different media are given by the following table.

MEDIUM TOPOLOGIES

TWISTED-PAIR BUS, RING, STAR

BASEBAND COAXIAL BUS, RING, STAR

BROADBAND COAXIAL BUS, TREE

OPTICAL FIBRE RING, TREE


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Networking Hardware

File Servers

Workstations


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Network Interface Cards Modems

Repeaters

Concentrators/Hubs Transreceivers

Switches

Bridges Multiplexer

Routers

File Servers

A file server stands at the heart of most networks.It is a very fast computer with a large amount of RAM

and storage space, along with a fast network interfacecard


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card.

The network operating system software resides on thiscomputer, along with any software applications and datafiles that need to be shared.

The file server controls the communication of informationbetween the nodes on a network.

For example, it may be asked to send a word processor

program to one workstation, receive a database file fromanother workstation, and store an e-mail message duringthe same time period. This requires a computer that canstore a lot of information and share it very quickly.

Workstations

All of the computers connected to the file serveron a network are called workstations.


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A typical workstation is a computer that isconfigured with a network interface card,networking software, and the appropriate cables.

Workstations do not necessarily need floppy diskdrives or hard drives because files can be saved onthe file server.

Almost any computer can serve as a networkworkstation.

Network Interface Cards

The network interface card (NIC) provides the physical connection between

the network and the computer workstation.

A memory buffer inside the network card grabs massages from the computer


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y g g p

and holds them until the card can send the message through the cable.

Another memory buffer holds messages coming on the network cable until

the computer is ready to read the message

Most NICs are internal, with the card fitting into an expansion slot inside thecomputer.

Network interface cards are a major factor in determining the speed and

performance of a network. It is a good idea to use the fastest network card

available for the type of workstation you are using.

The three most common network interface connections are Ethernet cards,

Local Talk connectors, and Token Ring cards.

Sample Network InterfaceBoards


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Network Interface Board Installations


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Ethernet Cards


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MODEMA modem is a device that converts digital data into analog signal for

transmission over telephone line. It involves modulation at thetransmitting end and demodulation at the receiving end. The same

device can be used to connect remote computers over telephone


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networks.In some instances, modems can take the place of NICs in

connecting a device to a network.

For example, you can dial in to your network from acomputer with a modem, if a modem and phone connection

are available on a device on your network.

The following functions are involved in the management of a modem:-

Dialing

Answering

Disconnecting

Modem Installation


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Repeaters

A repeater is a device that boosts a network'ssignal as it passes through the transmission


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medium by electrically amplifying the signal itreceives and re-broadcasting it.

They are used when the total length of yournetwork cable exceeds the standards set for thetype of cable being used.

Repeater Use


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Repeater Installation


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Concentrators/Hubs

Hubs receive transmissions from connected devices

and transmit the signals to the other connected


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devices. The hub organizes the cables and transmitsincoming signals to the other media segments.

Some network implementations require a centralpoint of connection between media segments. These

central points are referred to as hubs, multiport

repeaters, or concentrators.

Cables from network devices plug in to the ports on

the hub.

An active hub, which connects medium segments

together, regenerates or amplifies signals. Because

they generate signals, active hubs can extend themaximum cable length. All computers connected by

active hubs still receive signals from all other


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computers.

A passive hub, which connects medium segments

together, does not regenerate or amplify signals. It

is not a repeater. The distance limitations on eachsegment connected to a passive hub are different

than those applied to segments connected by active

hubs.

HubInstallation


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Transceivers

A Transceiver is not a repeater . The function of a

i i i l d i h k


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transceiver is to connect a single device to the network.There are four types of transceivers, they are:-

(a)Thick wire transceiver.

(b)Thin co-axial transceiver.

(c)Twisted pair transceiver.

(d)Fibre optic transceiver

Switches

Switches allow you to avoid the congestion

of a shared Ethernet network by permitting


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you to create individual segments. The

improvement in network performance can

be dramatic.


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Bridges

A bridge is a device that allows you to segment a large

network into two smaller, more efficient networks.


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A bridge extends the maximum distance of your

network by connecting separate network segments.

Bridges selectively pass signals from one segment to

another based on the physical location of the

destination device.

Bridge Operations

Bridges receive all signals on

all segments they are attached


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to. Determine the segment

location of the source and

destination devices for each

signal received.

Retransmit signals whose

source and destination devicesare on different segments out

the port connected to the

destination devices segment.

Bridge Installation


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A transmission media that provides morecapacity than a signal can use. To

efficiently use the entire transmission

Multiplexers


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efficiently use the entire transmissionmedia bandwidth, you can installmultiplexers.

A multiplexer combines two or moreseparate signals on a transmission media

segment.


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Routers

A router translates information from one

network to another; it is similar to a super

intelligent bridge


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intelligent bridge.

Routers connect two or more logically

separate networks. Each network isidentified by its network address, a logical

name assigned to it.Each network in an internet work must be

assigned a unique network address.

Router Operations


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Routers are typically much moreprocessing intensive than bridges. As aresult, their processing speeds (generally

measured in packets or blocks of data

Routers


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measured in packets or blocks of data forwarded per second) are not usually ashigh.

Routers are capable of much moresophisticated path selection. The decision

to buy a bridge or a router hinges onspecific requirements and the specificnetwork environment.

Router Installation


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basic networking knowledge

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