Networks and Internet

8/7/2019 Networks and Internet

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NETWORKS

Fundamentals ofnetworking

The history of the Internet


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Introducing networks A network is an interconnection of agroup of computers that cancommunicate and share resources

The need for connecting computers toform computer networks arose due to

an increase in the businessrequiremenet for sharing, processingand distributing information


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Advantages of Networks

1. Sharing information over the network

2. Optimum utilization of hardware

resources

3. Centralization of data management


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Before installing a network, the

layout, architecture and type of

network need to be decided. In order

to have a good ground for these

decisions, we need to understand thefollowing:

Network topology Network category

Network model


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Network TopologyNetwork topology is a schematic layout

or map of the arrangement of nodes

over a network

This layout also determines the manner

in which information is exchanged withinthe network


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Types of Topologies

Some of the different types of topologies

widely used to setup a network are:

Bus

Star

Ring

Mesh

Cellular


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Bus Topology

The bus topology connects all the nodesto a main cable called bus.

Information is sent to all the nodes on the

network. Each node compares thedestination address with its own address.If they match, the node reads the data.Otherwise, it ignores the message.


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ADVANTAGES

Easy installation

Relativelyinexpensive

DISADVANTAGES

Low fault tolerance

Inability to handle

high network traffic

Lower scalability

Difficulty introubleshooting andmaintenance


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Star Topology

The star topology connects nodes over anetwork using a central control unit calledthe hub

The number of nodes depends on the

capacity of the hub

All the information in the network passes thruthe hub


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ADVANTAGES

Higher scalability

Easy introubleshooting and

maintenance

DISADVANTAGES

High cost of

installation

Single point of

failure


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Ring Topology

The ring topology connects the nodes ona network through a point-to-point

connection

The information is passed from node to

node until it reaches its destination


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ADVANTAGES

Prevention of

collisions

Ease in

troubleshooting and

maintenance

DISADVANTAGES

High risk of network

failure

Expensive setup and

installation


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Mesh Topology

The mesh topology involves point-to-point between all the nodes on the

network

The higher the number of nodes, the

more compex the design is


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ADVANTAGES

High reliability

High suitability forWide Area Networks

DISADVANTAGES

Expensive

installation

Difficult to maintain

and manage

Complex physical

layout


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Cellular Topology

Cellular topology is a wireless topology, wheregeographical area is divided in cells or regions.

Each cell has an main individual node in thecenter. All secondary nodes from one cell can

move to another cell

There are no physical links in the cellulartopology


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ADVANTAGES

Independent of

cabling media

Easy installation

High flexibility

High mobility among

users

DISADVANTAGES

Expensive

installation

Central point of

failure


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Network Categories

The network category refers to the way in whichthe network processes the information. Thecategories are:

Server-Centric Networks: One or more serversprocess the requests centrally

Peer-to-Peer Networks: No specific distinctionexists between a client and a server


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Server-Centric Networks

The server processes client requests basedon the priority associated with the request

It is highly reliable, but if a failure occurs atthe server end, a complete loss of data may

occur


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Peer-to-Peer Networks

Any node can provide a service as well as requesta service from another node on the network

Each node on the network has full control over thenetwork resources.However, each user can onlyaccess resources for which access privilegeshave been granted to the user


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Network Computing

ModelsCentralized: Clients use the resources ofhigh-capacity servers to process the

information

Distributed: Allows all network computers totake part in the processing , but at theirrespective ends, separately

Collaborative: Is an advanced distributedcomputing model. In this model, nodes alsoshare processing capabilities


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Centralized Network

Computing Model


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ADVANTAGES

Centralized data

management

High level of security

Cost effectiveness

DISADVANTAGES

Low performance

and network speed

Central point of

failure


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Distributed Network

Computing Model


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ADVANTAGES

Faster data access

High reliability

Customized network

setup

Optimized use of

resources

DISADVANTAGES

Higher cost of

installation than in

the centralized

model


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Collaborative Network

Computing Model


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ADVANTAGES

Increased

processing speed

DISADVANTAGES

Higher cost of

installation than in

the centralized

model


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Transmission Media

The physical channel that connects networkcomponents is known as the transmissionmedium

This medium determines the speed andconnectivity, as well as the overall performanceand the investments required

The transmission media include:Cables, which connect the network over relativelyshort distances

Wireless carriers, which connect mobilecomputers


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Cables

These are the conventional media that areused to setup networks. When deciding thetype of cable to be used, you need to

consider factors such as the environment inwhich the cabling is going to beimplemented and the overall speedrequirements of the network


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Twisted Pairs Cables

These are the most commonly used cables for

setting up networks. They could be shielded or

unshielded

The maximum recommended length of these cables

is not more than 100 meters. There might be electro

magnetic interference if they are unshielded

UNSHIELDED

SHIELDED


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Coaxial Cables

The structure of the coaxial cable consists of acenter conductor responsible for transmitting data.

The outer conductor or shield protects this centerconductor from EMI, ensuring that data transmissionis not disrupted.

A plastic jacket covers the cable and protects it from

damage


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Coaxial cables are easy to install,

support higher transmission rates (10

Mbps and higher), suffer lower

attenuation rates, and are less sensitive

to EMI than twisted pair cables

They are hard to reconfigure and

reinstall because of the hard covering.

Also, they are more expensive than

twisted pair cables


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iber Optic Cables

Fiber optic cables use light rays or lasersrays instead of electricity to transmitdata. This makes these cables a suitablecarrier of data in areas that are prone tohigh levels of EMI or for long-distance

transmissions


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Wireless

The advantage ofthe wireless

technology is that it

helps connectdistant networks,

without needing to

physically set up

cables between the

destination and the

source points


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Radio Transmissions

As a wirelesstechnology, radiowaves are the mostcommonly used

medium ofcommunication. Thispopularity is attributedto the easy generationof radio waves andtheir ability to travelover long distanceswithout significantdistortions


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Microwave Transmissions

Microwavetransmissions aremore expensive thanradio transmissions,

but send data over ahigher bandwidth

They are difficult toinstall because theyrequire extremeprecision. MW are alsosusceptible toatmospheric conditions


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Infrared Transmissions

They use infrared radiation to transmit data

Infrared transmissions are used for datatransmission over short and medium rangedistances of up to 1 kilometer

There are two modes of transmission: line

of sight and scattered


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Network Operating

System(NOS)A Network Operating System (NOS) is an

enhanced version of an Operating System

(OS), with features that allow themanagement and connectivity of nodes

within a network

NOS also allows the sharing of information

and resources based on the accessibility

privileges allocated to each user or node


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Examples of NOS

Windows Server (2003, 2008)

Novell Netware

Unix

Linux Server


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Windows Server

FEATURES

Acti ir ct r ( r r rce

management er ice)

Remote access permissions

Virt al Pri ate Net or s

Terminal ser er Symmetric multiple processing

Remote installation ser ices


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Novell Netware

FEATURES

Novell irectory Services (NDS) TCP/IP encapsulation

Clustering andmultiprocessor support


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Unix

FEATURES

Internet- ased services Compati ility wit differentprotocols

Networ security (levels of access)


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Linux

FEATURES

A Linuxserver can e used to dial outandconect to t e Internet

A Linuxmachinecan e used effectively

on the Internetasa ebserver

Sharing of resources with Windows

machines thru the Sambaserver


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INTERNET

The Internet is a global system of

interconnected computer networks that use

the standard InternetProtocol Suite (TCP/IP)to serve billions of users worldwide.

It is a network of networks that consists of

millions of private, public, academic, business,and government networks, of local to global

scope, that are linked by a broad array of

electronic, wireless and optical networking

technologies.


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The earlier computers used the technologyavailable at the time to allow communicationbetween the central processing unit and remoteterminals.

As the technology evolved new systems were

devised to allow communication over longerdistances (for terminals) or with higher speed(for interconnection of local devices) that werenecessary for the mainframe computer model.

Using these technologies it was possible toexchange data (such as files) between remotecomputers.


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However, the point to point communication modelwas limited, as it did not allow for direct

communication between any two arbitrarysystems; a physical link was necessary.

The technology was also deemed as inherentlyunsafe for strategic and military use, becausethere were no alternative paths for thecommunication in case of an enemy attack.

As a response, several research programs started

to explore and articulate principles ofcommunications between physically separatesystems, leading to the development of the packetswitching model of digital networking


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These research efforts included those of the

laboratories of Vinton G.Cerf atStanford

University, Donald Davies (NPL), Paul Baran(RAND Corporation), and Leonard Kleinrock at

MIT and at UCLA.

The research led to the development of several

packet-switched networking solutions in the

late 1960s and 1970s, including ARPANET,

Telenet, and the X.25 protocols. Additionally,public access and hobbyist networking systems

grew in popularity, including unix-to-unix copy

(UUCP) and FidoNet.


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They were however still disjointed separate

networks, served only by limited gatewaysbetween networks. This led to the application

of packet switching to develop a protocol for

internetworking, where multiple different

networks could be joined together into asuper-framework of networks.

By defining a simple common network system,

the InternetProtocol Suite, the concept of thenetwork could be separated from its physical

implementation.


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This spread of internetworking began to form into

the idea of a global network that would be called

the Internet, based on standardized protocolsofficially implemented in 1982.

Adoption and interconnection occurred quickly

across the advanced telecommunication networksof the western world, and then began to penetrate

into the rest of the world as it became the de-facto

international standard for the global network.

However, the disparity of growth between

advanced nations and the third-world countries led

to a digital divide that is still a concern today.


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Following commercialization and introduction of

privately run Internet service providers in the

1980s, and the Internet's expansion for popular

use in the 1990s, the Internet has had a drasticimpact on culture and commerce. This includes

the rise of near instant communication by

electronic mail (e-mail), text based discussion

forums, and the World Wide Web.

Investor speculation in new markets provided by

these innovations would also lead to the inflation

and subsequent collapse of the Dot-com bubble.But despite this, the Internet continues to grow,

driven by commerce, greater amounts of online

information and knowledge and social networking

known as Web 2.0


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The World Wide Web

The World Wide Web, abbreviated

as WWW and commonly known as the

Web, is a system of

interlinked hypertext documentsaccessed via the Internet.

With a web browser, one can view webpages that may contain text, images,

videos, and other multimedia and

navigate between them via hyperlinks.


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Using concepts from

earlier hypertext

systems, Englishengineer and computer

scientistSir Tim

Berners-Lee, now the

Director of the World

Wide Web Consortium,

wrote a proposal in

March 1989 for whatwould eventually

become the World Wide

Web


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AtCERN in Geneva,

Switzerland, Berners-Lee

and Belgian computerscientist Robert

Cailliau proposed in 1990

to use "HyperText... to

link and access

information of various

kinds as a web of nodes

in which the user canbrowse at will", and

publicly introduced the

project in December.


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"The World-Wide

Web (W3) was

developed to be a

pool of human

knowledge, and

human culture,which would allow

collaborators in

remote sites to

share their ideas

and all aspects of a

common project."


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