Communication and Network Concepts

CHAPTER 14

WHAT’S A NETWORK?WHAT’S A NETWORK?

a network defined as ‘an interconnected collection of autonomous computers’. AUTONOMOUS: Central to this definition is that all computers are autonomous i.e. no computer on a network can start, stop or control another.

INTERCONNECTED : Two or more computers are interconnected if they can exchange information.

NEED FOR NETWORKINGNEED FOR NETWORKING

Resource Sharing: The aim is to make all resource available to anyone or everyone connected.

Reliability: The idea is –if one crashes other can carry on.e.g. if one file is deleted from a system it’s safely stored on an another on the network.

Cost Factor: PCs’ve better performance ratio than micro computers. So better to have 1 pc/user with data stored on 1 shared file server machine.

Communication Medium: the changes at one end can suddenly be sent to the other & vice-versa. It brings faster and better co-operation.

APPLICATION OF NETWORKSAPPLICATION OF NETWORKS

1.PERIPHERALS 2.INFORMATION 3.SHARING PROCESSING

EVOLUTION OF NETWORKINGEVOLUTION OF NETWORKING

networking started way back in 1969 and has evolved since .

The important stages are listed below:-

1.ARPANET

2.THE INTERNET

3.THE INTERSPACE

ARPANETARPANET

Advanced Research Projects Agency NETwork.Way back in 1969 it began sponsored by US Dept. of defense with the goal of linking computers at universities and US defense. Soon the systems began exchanging data & info.It had handful of components but expanded a lot. Another event was creation of another highly (better than ARPANET)capable network by National science Foundation namely-Nsfnet.But nsfnet allowed didn’t allow any private business so private companies built their own networks later joined with arpanet & nsfnet to form internet.

THE INTERNETTHE INTERNET

The internet is a worlwide network of computer networks.

It’s a super network. The common use is that users can communicate with any other user on a different network.

To accomplish these exchanges certain rules (called protocols) must be followed. The internet uses a set of protocols called as TCP/IP (transmission control protocol/internet protocol) .

HOW DOES INTERNET HOW DOES INTERNET WORKWORK

All the computers are not directly connected to internet. Rather they connect to a small network which connect to the internet BACKBONE through GATEWAYS.

Gateway:-Device connecting dissimilar networks.

Backbone:-Central interconnecting structures in which other networks are plugged. (imagine the trunk of any tree from which branches emerge or a human backbone).

FUNCTIONINGFUNCTIONINGAt the source computer, the message/file is divided into very small parts called packets.

Packet has a serial number.

All packets are sent to the destination computer.

The destination computer receives these packets (not surely serially). If a packet is garbled or lost\,it is demanded again.

The message is arranged serially to get back the message/file.

INTERNET FUNCTIONINGINTERNET FUNCTIONING

The reason that internet works at all is that every linked computer uses the same set of rules for communication.

A SET OF RULES IS CALLED PROTOCOL.

TCP/IP is responsible for division and reassembling of packets.

Ip is responsible for guiding the packets to the proper destination.

The future of the internet is interspace.

THE INTERSPACETHE INTERSPACE

Interspace is a client/server software program that allows multiple users to communicate online with real-time audio, video and text-chat in a dynamic 3D environments.

As the internet is a protocol eenvironment for interconnecting networks to transmit data similarly interspace is an application envirom-nment for interconnecting spaces to manipulate information.

SWITCHING TECHNIQUESSWITCHING TECHNIQUES

switching techniques are used to transmit data across networks.

There are various techniques :-

Ways to send a message across a network

CIRCUIT SWITCHINGCIRCUIT SWITCHING

The complete physical connection is established before any data can be exchanged.

Since circuits are switched it gets it’s name.

Telephone is a good example of this technique.

Earlier switching was done manually. There was an operator who would reside in switching office and plug a jumper connecting input & output sockets. Now switching is done automatically.

PACKET SWITCHINGPACKET SWITCHING

The method is same as message switching.

The difference lies in the way of storing and transmitting data.

Block size of data has an upper limit (that requires transfer of chunks of data under the limit called as packets).

The storage is in the main memory instead of on the hard disk.

MESSAGE SWITCHINGMESSAGE SWITCHING

No physical copper path is established in advance between the sender and the receiver as in circuit switching.Instead, the sent data is first stored in the first switching office and then forwarded later, one hop at a time.Each block is received entirely, inspected for errors, and then retransmitted. This procedure continues until message reaches its destination. Owing to its working principle, it is also known as store and forward.

DATA COMMUNICATION DATA COMMUNICATION TERMINOLIGIESTERMINOLIGIES

TERMSTERMSData channel : a medium used to carry information or data from one point to another.Baud : unit of measurement for the inforamtion carrying capacity of a communication channel. (syn: bps-bits per second)Other units are : Bps, kbps, Kbps, mbps (in capitals b means byte and otherwise bit)Bandwidth : technically, it is the difference between the highest & the lowest frequencies of a transmission channel or the width of allocated band of frequencies to a channel.People generally use it to mean the amount of information/data travelling through a single channel at a time. High bandwidth channels are called broadband and low bandwidth channels narrowband channels.

MOREMOREIn digital systems it is expressed in terms of bps like if a modem works @ 57,600 bps and another @28,800 bps ,then the first modem has twice as bandwidth as the second one.In analog systems it’s expressed in terms of the highest & the lowest signal component. Frequency is measured in terms of cycles/second i.e. hertz. 1 kHZ = thousand cycles/second, 1mHZ=103 1 gHZ =103mHZ 1 tHZ = 103 gHZ.Data transfer rates: amount of data transferred by a communication channel per second or a computing or storage device.Measured in bps, Bps, or baud.

TRANSMISSION MEDIATRANSMISSION MEDIA

TRANSMISSION MEDIATRANSMISSION MEDIA

Transmission media or communication channels of network is nothing but the cable/media which provides the link.

There are numerous media which can be divided into :-

1. Guided media (includes wires/cables)

2. Unguided media (includes any form of wave media)

Transmission MediaTransmission Media

IntroductionIntroduction Guided MediaGuided Media Twisted PairTwisted Pair Coaxial CableCoaxial Cable Optical FiberOptical Fiber Unguided MediaUnguided Media Radiowaves TransmissionRadiowaves Transmission Microwave TransmissionMicrowave Transmission Infrared TransmissionInfrared Transmission Laser TransmissionLaser Transmission Satellite TransmissionSatellite Transmission

TWISTED PAIR CABLETWISTED PAIR CABLEIt is the most common form of wiring in data communication applications.General Form : two identical wires wrapped together in a double helix.The bleeding of a signal from one wire to another and which can corrupt signal and cause network errors. This form of signal interference is called crosstalk. To reduce crosstalk wires are twisted in pair in twisted pair cables.

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Figure 7.3 Figure 7.3 Twisted-pair cableTwisted-pair cable

PROS-N-CONSPROS-N-CONS

Advantages: simple, flexible physically, easy to install and maintain, easily connected, very inexpensive.Disadvantages: incapable in long range transmission without repeaters due to high attenuation (reduction, decrease), low bandwidth, supports merely data rates of 1Mbps &10 Mbps (with conditioning).

TYPESTYPESTypes of twisted pair cable:Unshielded twisted pair: UTP cabling is

used for variety of electronic communications. Available in 5 categories

Type descriptionCAT1:Voice Grade communication only; no

data transmissionCAT2: Data Grade Tx up to 4MbpsCAT3: DGT up to 10 MbpsCAT4: DGT up to meters.CAT5 : DGT up to 1000Mbps16MbpsThe UTP cables can have

maximum segment length of 100

SHIELDED TWISTED PAIRSHIELDED TWISTED PAIRSHIELDED TWISTED PAIR(STP): THIS TYPE OF CABLE COMES WITH

SHIELDIING OF THE INDIVIDUAL PAIRS OF WIRES, WHICH FURTHER PROTECTS IT FROM EXTERNAL INTERFERRENCE. ONLY ADVANTAHGE OVER THE UTP IS GREATER PROTECTION FROM CROSSTALK & INTERFERRENCE. HOWEVER, IT’S HEAVIER & COSTLIER & REQUIRES PROPER GROUNDING AT BOTH ENDS. THE MAX SEGMENT LENGTH IS SAME AS UTP.

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Figure 7.4 Figure 7.4 UTP and STP cablesUTP and STP cables

COAXIAL CABLECOAXIAL CABLE

It consists of a solid wire core surrounded by one or more foil or wire shields, each separated by some kind of plastic insulator. The inner core carries the signal, and the shield provides the ground, has high electrical properties & is suitable for high speed communication used for TV signals.Its data transmission characteristics are considerably higher & so it’s used as the basis for a shared cable network, with part of the bandwidth being used for data traffic.Advantages: greater speed, can be used as a basis for a shared cable network.Can be used for broadband transmission.Bandwidth up to 400 MBPS.Disadvantages: expensive, not compatible with twisted pair cablesTypes of coaxial cables:Thicknet: This is thicker than thinnet. Its segments can be up to 500 meters.Thinnet: this form of coaxial cable is thinner and it can have max. length of 185 meters.

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Figure 7.7 Figure 7.7 Coaxial cableCoaxial cable

OPTICAL FIBREOPTICAL FIBRE

Advantages: immune to electrical & magnetic interference.Highly suitable for harsh industrial environment.Secure transmission & high transmission capacity.Can be Used for broadband transmission.Disadvantage: inst6allation problem. Are fragile & may need special care to provide the robustness required for office environment.Connecting two fibers together or a light source

To a fiber is difficult

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Figure 7.10 Fiber optics: Figure 7.10 Fiber optics: Bending of light rayBending of light ray

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Figure 7.11 Figure 7.11 Optical fiberOptical fiber

OPTICAL FIBREOPTICAL FIBRE

• More expensive• Difficult to solder

Types of Fiber Optic Cables

Fiber Optic cables can be either • Single Node that supports segment length of

upto 2 Kms and bandwidth of upto 100 Mbps• Multinode with segment length of upto

100Kms and bandwidth of 2Gbps.

COMPARISON COMPARISON Type Type Sub

typeMaximum Segment Length

Bandwidth Supported

Installation Cost Interference

Twisted Pair Cable

UTPSTP

100 Mtrs100 Mtrs

200 Mbps500 Mbps

EasyModerate

Cheapest Moderate

HighModerate

Coaxial Cable ThinnetThicknet

185 Mtrs500 Mtrs

10 Mbps10 Mbps

EasyHard

CheapModerate

ModerateLow

Fiber Optic Cable

MultinodeSinglenode

2 Kms100 Kms

100 Mbps2 Gbps

Very Hard

Expensive NoneNone

Radio waves TransmissionRadio waves Transmission•The Radio waves have frequencies between 3khz and1GhzThe Radio waves have frequencies between 3khz and1Ghz•Radio waves can penetrate buildings easily, so that are widely use for Radio waves can penetrate buildings easily, so that are widely use for communication both indoors outdoors.communication both indoors outdoors.•They also absorbed by rainsThey also absorbed by rains•At high frequency, radio wave tends to travel in straight line and bounces off At high frequency, radio wave tends to travel in straight line and bounces off the obstacles.the obstacles.

Micro Wave Micro Wave

Micro wave signals are used to transmit a data without cables.

Micro waves electromagnetic waves having frequency between 1 GHZ and 300 GHZ.The microwave signals are similar to radio and television signals .

It consist of,

1. Transmitter

2. Receiver

3. Atmosphere

• There are two types of micro waves data communication system : terrestrial and satellite

• Micro waves are widely used for one to one communication between sender and receiver, cellular phone, satellite networks and in wireless LANs.

Advantages of Microwave

i) It is cheaper than digging trenches for laying cables and maintaining repeaters and cables. If cables get broken by variety of causes.

ii) It offers from land acquisition

SATELLITESATELLITE

Satellites accept data/signals from the earth station, amplify them and retransmit them to another earth station.

Advantage:

Large area of coverage

Better than laying intercontinental cables.

Disadvantage:

High investment

Technological limitations preventing deployment of large high gain antennas on satellite platform.

Infrared WavesInfrared Waves•Electromagnetic waves having frequencies from 300 GHz to 400 THz are Electromagnetic waves having frequencies from 300 GHz to 400 THz are called IR waves or Infrared waves.called IR waves or Infrared waves.•IR waves are used for short range communication and use line of sight IR waves are used for short range communication and use line of sight propagation.propagation.•Infrared waves cannot pass through solid objects, like walls and be easily Infrared waves cannot pass through solid objects, like walls and be easily contained in a room.contained in a room.•They are cheap, easy to build and do not require any government license to They are cheap, easy to build and do not require any government license to use them.use them.•IR waves offer very bandwidth for useIR waves offer very bandwidth for use. ExampleT.V remoteT.V remote

Laser TransmissionLaser Transmission•This type of transmission use thin laser to transfer data up to few kilometers.This type of transmission use thin laser to transfer data up to few kilometers.•Laser beams are unidirectional, therefore this type of transmission system use Laser beams are unidirectional, therefore this type of transmission system use line of sight propagation.line of sight propagation.•In such a transmission system, a photo detector and laser is set on both In such a transmission system, a photo detector and laser is set on both sender and receiver side.sender and receiver side.•Such a system offer very high band width at a very low cost.Such a system offer very high band width at a very low cost.•Other disadvantage is that on hot sunny days these waves are affected by hot Other disadvantage is that on hot sunny days these waves are affected by hot turbulent air and miss the detector.turbulent air and miss the detector.•The major problem in this transmission system is that laser beams cannot The major problem in this transmission system is that laser beams cannot penetrate rain or thick fog.penetrate rain or thick fog.

Types of networks

• Classification based on geographical spread:– LAN– MAN– WAN

What is a LAN?

• Local Area Network• A group of computers in a single location• Limited by no. of computers and distance covered• Example: Our school network

What is a MAN?

• Metropolitan Area Network :• Networks spread over a city• Example: cable T.V networks spread over a city

What is a WAN?

• Wide Area Network : spread over countries• Separated by large distances•WAN can also be a group of LANs spread across different locations and connected together.• Largest WAN: Internet

What are Topologies?

The physical shape computers and devices create when connected together

The different topologies are:• BUS• STAR• RING• MESH• HYBRIDS

• Bus (not commonly found in LANs anymore)– Needs termination– Adding devices disrupts

the network– Cable failure hard to find

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Bus TopologyBus Topology

BNC T-ConnectorBNC T-Connector

Coaxial Coaxial cablecable

Network CardNetwork Card

• Star (Most common topology)– Requires a hub/switch– Easy to troubleshoot– Requires more wiring

– Star Topology

Topologies

• Ring– No beginning and no end– Uses token passing to communicate

• Mesh– All computers are connected to each other– More Fault tolerant

Variation of Major Topologies(Hybrids)

• Star-Bus– Backbone interconnect two

or more hubs

• Star-Ring– Physical Star, but logical ring– The way the IBM token ring Works.

Network Devices

Modem

• Modulation/demodulation • Used to connect and communicate with other

computers via telephone lines• Digital Analog• Analog Digital

Working of a Modem

TXD: Transmit Data Communication Equipment Data RXD: Receive Terminal DTR: Data Terminal Ready Equipment DSR: Data Set Ready RTS: Request to send CD : Carrier detect CTS: Clear to send

Micro controlled terminal

DTE

MODEM

DCE

MODEM

DCESIMILAR DTE

TXD

RXD

RTSCTS CDDTRDSR

Working of a Modem

1. When powered up, DTE and DCE performs self check and terminal asserts DTR

2. Modem asserts DSR to terminal when ready to transmit data

3. When terminal wants to send data it asserts RTS to modem

4. Modem asserts CD to indicate the establishment of contact with the destination

5. When modem is ready to transmit data it asserts CTS6. Modem unasserts CTS and stop transmitting

Varieties of Modem

• Internal modem• External modem•

RJ-45

• Eight wire connector• Commonly used to connect computers on LAN• Similar to standard telephone connector(RJ-11)• Registered Jack 45.

Ethernet Card• Ethernet- LAN architecture developed by Xerox

Corp• Ethernet cards to be installed in computers

connected in Ethernet• Contains connections for either coaxial or twisted

pair cables• For coaxial cable – BNC (Bayone-Neill-Concelman)• For twisted pair – RJ-45 connector• AUI connector (Attachment Unit Interface) – to

attach coaxial, twisted pair or fiber optics cable

• Hubs• Switches• Routers• Repeaters

Bridges (Switches) Vs. Hubs

A Hub sending a packet form F to C.A Switch sending a packet from F to C

Collision domains in a nonbridged and bridged network

In heavy load, each station has an average effective theoretical bandwidth = 10/12

Each station has an average effective bandwidth equal =10/3

Usually used to connect individual computers not LANs like bridge

A switch when compared to bridge has multiple ports.

Switches can perform error checking before forwarding data, which are very efficient by not forwarding packets that error-end out or forwarding good packets selectively to correct devices only.

Full-Duplex operation

Isolated collision domains

Figure 15.11 Routers connecting independent LANs and WANs

Routers

An Institutional Network Using Hubs, Ethernet Switches, and a Router

Hub

• Connects several computers together• Similar term – concentrator• Concentrator – provides a central connection point

for cables from workstations, servers & peripherals• Hubs are multislot concentrators• Active hubs – amplify signals when it moves from

one connected device to another• Passive hubs – allows signal to pass from one

computer to another without any change

Switch

• Segments network into different subnetworks called subnets

• Segmenting prevents overloading• Receives data, filters it and forwards the packets

between the LAN segments• Switched LANS

Repeater

• Amplifies the signal transmitted on the network• Two types

– Amplifier– Signal repeater

• Amplifier – amplifies all incoming signal including noise

• Repeater – receives the packet and retransmits it

Bridge

• Interconnets two networks with same standard but different cables

• On receiving a packet it examines the physical destination address and then decides whether to allow the packet to cross the bridge

Router

• Can handle different protocols• If destination is unknown to a router it sends

traffic to another router• Router uses logical addresses and bridge uses

physical addresses

Gateways

• Connects dissimilar networks• Node on one network which serves as an

entrance to another network• In enterprises – routes traffic from a

workstation to the outside network– Acts as a proxy server and a firewall

• Home – ISP that connects the user to the internet

LAN Design

• Network design problem consists of:– Environment given

• Location of hosts, servers, terminals and other end nodes; projected traffic for the environment and projected costs

– Performance constraints• Network reliability, traffic throughput, host/client

computer speeds

– Internetworking variables• Network topology, line capacities and packet flow

assignments

General network design process

Access needs and costs

Select topologies and technologies to satisfy needs

Model network workload

Simulate behavior under expected load

Perform sensitivity tests

Rework design as needed

80-20 Rule

• 80 percent of the traffic on a given network segment should be local and not more than 20 percent of the network traffic should need to move across a backbone

• Using repeaters– 5-4-3 Rule

• Maximum path between two stations should not be more than 5 segments with 4 repeaters between those segments

• Using bridges– Used to connect separate segments of a network

When to use hubs/ bridges/ switches/ routers

Connection between two computers Istall NIC in both computers Attach them using a crossover cable

To increase the distance between the computers Use repeaters

Repeater

To connect more than three computersUse hub

Disadvantages Share bandwidth among all devices, cannot filter traffic, broadcast data Solution – to use bridge

HubHub

• Bridge– Ensures traffic goes to the intended segment and

not to all segments

• Switch– Replaces bridges to give dedicated bandwidths to

each lan segment– Disadvantage – network traffic flows to all LAN

segment– Solution – router

• Router– Filter n/w traffic based on IP which tells the router

the LAN segment the network traffic belongs to

For building a small LAN

• Client computers with NIC installed• Server• Hub• Cabling• Networking OS software

For connecting offices and departments

• Clients with NIC installed• Servers• Hubs• Cabling• Networking OS software• Switch• Router for shared internet access

Cabling Max. Length Speed

Thicknet coax 500 m 10 Mbps

Thinnet coax 185m 10 Mbps

Cat 3, 4, 5, 6 Twisted pair 100m 10Mbps

Cat 5,6 Twisted pair 100m 1Gbps

Fiber optic 2Km 200 Mbps

Wireless 150+feet 11/54 Mbps

Infrared Direct of line of sight Up to 16 Mbps

NETWORK PROTOCOLSNETWORK PROTOCOLS

TCP/IP

Application Layer

TCP(reliable tranportation)

IP(routing)

HOST TO NETWORK LAYER(physical + data link)

TCP/IP

• TCP is responsible for keeping track of what is send and retransmits anything that is not send through.

• It also breaks messages to packets.• IP: basic service is to get datagrams to the

destination.

SLIP/PPP• Serial Line IP: First protocol for relying IP

packets over dial up lines• SLIP is largely supplanted by PPP• Point to Point Protocol

IPCP – IP Control Protocol

NCP-Network Control Protocol

LCP-Link Control Protocol

Transport of IP packets over PPP links

Traffic Transportation(flow and error control)

Establish Link

• Direct connection through leased lines too expensive for individual users.

• SLIP/PPP enables the user to access internet via simple modem and telephone lines, that is via an ISP.

WIRELESS/MOBILE COMPUTING

• WIRELESS communication is simply data communication without the use of land lines.

• Eg. satellite communication(computing device is continuously connected to base network)

• Mobile computing means that the computing devices is not continuously connected to the base or central network.

• Eg. Laptop,Smartphones(may communicate with base location with or without wireless connection)

WIRELESS/MOBILE COMPUTING• Technologies and interfaces used.1.GSMGlobal System for Mobile communicationCell-phone works anywhere the standard is

supported.SIM(subscriber Identification Module) GSM users

simply switch SIM cards to connect to specific Service Providers in different countries.

• Uses TDMA: radio frequency divided into time slots

CDMA

• Code Division Multiple Access• Uses Spread spectrum Techniques.• Data send in small pieces over number of

discrete frequencies.• Each users signal is spread over the entire

bandwidth by unique spreading code. The same code used to retrieve the signal at the receiver end.

Wireless in Local Loop

• Serves local area by deploying multiple transmit/receive base stations.

• What is WLL?- WLL is a system that connects subscribers to the local telephone station wirelessly.

• Systems WLL is based on:– Cellular– Satellite (specific and adjunct)

A general WLL setup

GPRS

• General Packet Radio Service: Technology for radio transmission of small packets of data especially between mobile devices and internet.

• 114kbps

1 G 2G 3G

• 1G: • analogue cellular system. • Supported only voice calls• 2G: GSM • digital cellular system• 2.5G: GPRS• Rate 144 kbps

3 G

• It is a broad band, packet based transmission of text, digitized voice, video and multimedia.

• 2Mbps

SMS/ CHAT/VC

1.Short Message Service transmission of short text messages to and from a mobile phone.2.Chatting is online textual talk. , in real time•Protocol used: Internet Relay Chat3.Video Conferencing:•Two way videophone conversation among multiple participants •Protocols: H.323 and SIP(Session Initiation Protocol)

VoIP

• Voice Over Internet Protocol.• Enables voice communication over internet

Voice is compressed into data packets that can be efficiently transmitted over network

• Converted back to voice at receiver end.

Wifi/WiMax

• Wi-Fi: Wireless Fidelity• Lets you connect to internet without direct

line from your PC to ISP• Limited to 30-100m• Hot Spot is the venue that offers Wi fi access.• Wi Max: Range- up to 50km. Wi Max base

station(tower) connected to internet using wired high speed connection

• Connect to users by microwave link.

TELNET

• Internet Utility that lets you to log onto remote systems.

• Run telnet client: startRun command type TELNET

• Connect to Telnet site(by address)• Start browsing• Finally disconnect

NETWORK SECURITY CONCEPTSNETWORK SECURITY CONCEPTS

NETWORK SECURITY ISUUES

• Physical Security holes: unauthorized physical access

• Software security holes: eg. Virus• Inconsistent usage holes. Assembling flaws by

network administrator

Protection Methods

• Authorization: by login id• Authentication: prove to be authenticated by

Password protection• Biometric systems: finger prints• Encrypted smart cards: It generates a new

and different token which cannot be used later even if hacked.

Firewall

• Prevents unauthorized access to and from a private network.

• Packet Filter: user defined rules govern acceptance or rejection of packets

• Application gateway: Applies security mechanisms to specific applications like FTP, TELNET

• Circuit Level: Applies security mechanism when connection is established. Thereafter packets flow without checking.

• Proxy Server: It effectively hides the true network address.

Cookies

• Messages transmitted by the web server to the web browser.

• Browser stores it as text file.• This message is send back to server each time it

requests a page from server.• Purpose: Identify users a provide customised

web pages for them.• Personal information given to website stored as

cookies.

HACKERS/CRACKERS

• HACKERSNo malicious aim. Normally a computer

enthusiast.

• CRACKERS: Malicious programmers who break into secure system

CyberLaw

• A generic term that refers to all the legal and regulatory aspects of the internet and the world wide web.

• Cyber Crimes:Tampering (concealing, destroying, altering)with

computer source documents.Hacking, breach of confidentiality and privacy

etc..

IPR

• Intellectual Property Rights• Product Of intellect that has commercial value• Eg. Patents.

VIRUSESVIRUSESComputer Virus is a malicious program that requires a host & is designed to make a system sick, just like a real virus.Three basic types:-

1. File infectors (attach themselves to a program file)2. Boot sector viruses (installs themselves on beginning tracks

of hard drive )3. Macro viruses (infect data files)

Characteristics of a virus are replicatibility, requirement of host, external activation, replication ability is limited to (virtual)system.DAMAGES:-

1. Can destroy FAT2. Can create bad sectors on disk or duplicate itself 3. Can format entire disk or a specific tracks4. Can destroy specific executable files and alter data files,

causing loss of integrity5. Can hang the system

TROJAN HORSESTROJAN HORSES

A trojan horse is a code hidden in a program such as a game or a spreadsheet that looks safe to run but has hidden side effects.

Trojan horses spread through e-mail, exchange of disks & information exchange. Worms also spread trojans.

It causes damages what a virus can but only difference is its masking effect which hides its operation.

WORMSWORMS

A worm is a program designed to replicate.Characteristics of a worm: Can replicate No host or is self contained Activated by creating a process (need for a multi-tasking system) If a network worm, will replicate across communication links

How they Spread?Worms are generally found in multitasking & network systems. Worms, they spread autonomously, without needing any other program, user’s action or intervention etc.Damage ?Disrupt or create system management problems.Some scan for passwords and other loopholes then send it to the attacker.Some times they install trojans or viruses that damage our system.

SPAMSPAM

Spam refers to electronic junk mail or junk newsgroup postings. Some people define spam more generally as any unsolicited e-mail.defines spam as unsolicited usually commercial e-mail sent to a large number of addresses.AVOIDING SPAM Creating a filter that finds and does something to e-mail that you suspect is spam.Another escape is not to register yourself with a true id to sign up for things on the net. These places often share that e-mail id with other companies that fills you with spam in exchange of benefits.

VIRUS PREVENTIONVIRUS PREVENTION

It is not an easy task. Needs extra carefulness & adherence to these guidelines:-Never use a foreign disk without scanning for viruses.Scan files downloaded from internet. Always.Never boot computer from a floppy which may contain virus.Write protect your disks.Use licensed software.Password protect your pc to prevent unattended modifications.Make regular backups.Install & use antivirus software.Keep antivirus software up to date.

WEB SERVERSWEB SERVERS

<HTML><HTML>

HYPER TEXT MARKUP LANGUAGEHTML: WHAT IT IS? Document-layout & hyperlink-specification language i.e., a

language used to design the layout of a document & specify the hyperlinks.

Html tells the browser how to display the contents of a hypertext document i.e., a document including text, images & other supported media. It also tells how to make the page interactive by using special hyperlinks.

HTML: WHAT IT IS NOT? First of all it is not a programming language but just a descriptive

language. It’s neither a word processing tool nor a desktop publishing

solution. It’s just a page-layout & hyperlink specification-language.

XMLXMLextensible Markup Language.XML is a markup language for documents containing structured information.Structured information contains both content ( words, images etc.) & indication of what role does that content play content in a footer is different from that of header or content in a caption is different from a title).

∞ (HTML==XML) ??NO. In HTML tags and semantics meaning/role of tags) is fixed unlike in XML.XML permits to define tags and structural relationships between them. Since there’s no predefined tag set there can’t be any pre-established semantics. All the semantics of an XML is either defined by the applications that process them or by the used stylesheets.

DHTMLDHTMLDynamic HTML refers to web content that changes each time it is viewed. e.g. same page could result in a different page depending upon :Geographic location of the readerTime of dayPrevious pages viewed by the readerProfile of the reader

DHTML refers to new HTML extensions that will enable a web page to react to user input without sending requests to the web server.It can be thought of as “animated HTML”. Ex:- a piece of text can change from one color to another upon clicking or after some time.

HTTPHTTPHyper Text Transfer Protocol is an application-level but light & fast protocol.It’s a generic, stateless, object oriented protocol.Another feature is typing of data representation, allowing systems to be built independently of the data being transferred. It has been in use by WWW since 1990.HTTP allows an open-ended set of methods to be used to indicate the purpose of a request.It builds on the discipline of URI (Uniform Resource Identifier), as a location or name, for locating resource on which method is to be applied.Messages are passed to the HTTP in a format same as internet email or MIME (multipurpose internet mail extensions). HTTP is also used as a generic protocol for communication between gateways/proxies etc. to other protocols.

It consists of two fairly distinct items:

1. set of requests from browsers to servers

2. set of responses going the other way.

Though HTTP was designed to work with web but it’s been made more general to accommodate future possibilities of OO applications.

HTTP has different built-in methods to allow users to open a web page, to disconnect an existing connection, to read the header of a webpage, to append to an existing resource or to store a webpage etc.

URL & DOMAIN NAMESURL & DOMAIN NAMES

HTTP uses internet address in a special format called a Uniform Resource Locator or URL.

Typically URLs look like this:

type://address/path

Type:- type of server address (also the protocol they use):- address of the server path:- location of file on the server.

In the address last group of characters (.com, .gov etc.) is domain indicator.

The naming scheme by which servers are identified is known as domain name system.

Another method of addressing (identifying server) is by assigning distinct numbers known as IP addressing method. Such addresses are called as IP addresses.

Lastly, a url specifies a distinct address for each resource on the net. A character based internet address is a domain name.

WEB-BROWSERS & SERVERSWEB-BROWSERS & SERVERS

A web browser is a WWW client that navigates through the World Wide Web and displays web-pages. Example .IE

A web server is a WWW server that responds to the requests made by the web browsers.

WEB SITES, WEB SITES, ADDRESSESADDRESSES & PAGES & PAGES

A location on a net server is called web sites.

The unique address of each (URL) is called address.

A web page is document or simply a page in a web site.

WEB HOSTINGWEB HOSTINGWeb hosting is a means of hosting web-server application on a computer system through which electronic content on the internet is readily available to any web browser client.Web Hosting Can Be Grouped Under: 1.free hosting:- site hosting for free. You too can put

up own websites for raw fun.2. virtual or shared hosting : virtual hosting is where

one’s site is hosted on the web server of the hosting company along with other web-sites giving 24-hour access& can be updated through a password log-in.

3.dedicated hosting: a dedicated server is rented usually for big websites by companies. Dedicated for large, high traffic, or for those with special needs e.g. e-commerce, security.

WEB SCRIPTING Contd…WEB SCRIPTING Contd…

4. co-location hosting: the company actually owns the server & is responsible for all server administration and the web hosting company provides physical requirements of rack, high speed connection, a regular power supply, and a limited amount of technical support such as data back up or hardware upgrades.

WEB SCRIPTINGWEB SCRIPTING

A script is a list of commands embedded in a web-page. Scripts are interpreted and executed by a certain program or script-engine.

Most common scripting languages are VBScript, ASP(Active Server Pages), JavaScript, PHP(Hypertext Preprocessor), PERL, JSP etc.

Types of scripts:Client-side script : It enables interaction within

the web-page, is downloaded and executed by the browser (is browser-dependent i.e. browser must be enabled to run the script).Applications : To get data from user’s screen or browser, online games, customized web-pages.

Server-side script: It supports execution at server end. Results are sent to the client, is browser independent of browsers. APPLICATIONS : password protection, dynamic addition of content to web-pages.

OPEN SOURCE TERMINOLOGIESOPEN SOURCE TERMINOLOGIES

OPEN SOURCE SOFTWAREOPEN SOURCE SOFTWAREOpen Source Software commonly means software whose licenses do not impose much conditions. Users are free to use, modify & distribute software hassle-free but not certainly free of charge.It has been officially defined by the open source definition at http://www.opensource.org/docs/definition_plain.html. It states that :-Open source doesn’t just mean access to source code. The distribution terms of open-source software must comply with the following criteria :-

1. Free Redistribution2. Source Code(available to download from internet)3. Derived Works(modification allowed)4. Integrity of The Author’s Source Code(derived work should carry

different name and version number)5. No Discrimination Against Persons Or Groups

1.No Discrimination Against Fields Of Endeavor

2.Distribution Of License3.License Must Not Be Specific To A Product4.The License Must Not Restrict Other

Software5.License Must Be Technology Neutral

FREEWAREFREEWARE

The term freeware has no clear definition, but generally refers to free of cost & redistributable software, but no modification & no source code.

It is distributed in binary form(ready to run)

Freeware is often used in marketing situations in order to sell products and gain market advantages.

One example is Microsoft Internet Explorer.

SHAREWARESHAREWARE

Shareware is a software, which is made available with the right to redistribute copies, but it is stipulated that if one intends to use the software, often after a certain period of time, then a license fee must be paid.Source code & modifiability absent.The objective is to increase no. of prospective users.Generally a built-in timed mechanism limits the functionality after a certain period of time.

PROPRIETARY SOFTWAREPROPRIETARY SOFTWARE

Neither open nor free, its use is regulated and further distribution and modification is either forbidden or requires special permission by the supplier or vendor.

Normally the source code is not given to the user.

FLOSSFLOSS

FLOSS refers to Free Livre And Open Source Software or to Free Libre And Open Source Software.

The term is used for software that is both free software and open software.

Here the words libre(a Spanish word) or livre(a Portuguese word) mean freedom.

GNUGNU

GNU is a recursive acronym for GNU’s NOT UNIX.

This project was initiated by richard m. stallman with an objective to create a system compatible with UNIX but not same as UNIX.

It has not only made an OS but the project has grown since its inception and now it creates software of almost all kinds.

The same person founded the Free Software Foundation.

FSFFSF

FSF is Free Software Foundation. It is a non profit organization created to support free software movement in 1985 by Richard M Stallman.

FSF has funded many software developers to write free software.

Now a days, it also works on legal and structural issues for the free software community.

OSIOSI

OSI is Open Source Initiative founded byBruce perens & erics raymond (in feb 1998) .

It specifies the criteria for open source software & properly defines terms and specifications for open source software.

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