chapter- 1_introduction to www

7/30/2019 Chapter- 1_Introduction to WWW

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Introduction

1.1.1 History of WWW WWW was introduced by Sir Tim Berners-Lee the contractor at the

European Organization for Nuclear Research(CERN) Switzerland in1980.

In 1990 Berners-Lee introduced tools Hypertext Transfer Protocol,Hypertext Markup Language and web browser.

During 1992-1995 HTTP protocol a new protocol named Gopher

protocol came up which provided access to content through hypermenus presented as a file system. In 1993 a new web browser with graphical user interface Mosaic got

introduced. In 1994 the World Wide Web Consortium was founded by Berners-Lee

at the MIT with a support from the Defense Advanced Research

Projects Agency. This organization was built for creating standards toimprove the quality of the Web. During 1996-1998, trade marketing started using WWW. The term E-

commerce got introduced during this period only.


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Introduction

During 1999-2000, many entrepreneurs started selling their ideas usingthe dotcom boom.

2002-till date, the WWW has got an evolving nature due to variousdevelopment such as online-booking, efficient search engines andagent based technologies, Fac

1. The internet and WWW

Is a collection of computer and other devices connected together. WWW is a collections of s/w and corresponding protocols used to

access the resources over the n/w. www contains huge amount of documents, images and other resources

which can be accessed using the hyperlinks.

e book, social networking sites and so on.


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Introduction

1.2 Concept of internet Internet is a linking of many computers all over the world. Using such

linking user can share the information or communicate with eachother.

Internet service providers (ISP) to whom we pay for getting theinternet services .

Set up required for the getting the internetworking at your place. Modem

Modulating and demodulating device.

It sends the data into a signal that is compatible with the phone lineand receiving modem demodulates the signal back into digital data.

Speed: - Bits per second (BPS)

LAN and WAN


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Introduction

HUB Single network segment.

A hub receives incoming packets, regenerates the electrical signal andbroadcasts these packets out to all other on the network.

ROUTER To connect two or more computers.

This allows several computers to communicate with each other and tothe internet.

SWITCH Connect the computer to the network. Switch manages the bandwidth of the network.


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Internet service provider (ISP)

Any company that provides individuals or companieswith access to the Internet

Thousands of providers including largecommunications companies

Need an account with the ISP and software that linkswith TCP/IP

Internet protocol datagrams, dial-up, cable, modem,wireless or dedicated high-speed interconnects.

Introduction


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ISP ExamplesInternet Service Provider Web Address

AT&T WorldNet Service www.att.com

Digex, Inc. www.digex.net

GTE Internetworking www.gte.net

IBM Internet Connection www.ibm.net

MCI Internet www.mci2000.com

NetCom On-Line CommunicationServices

www.netcom.com

PSINet, Inc. www.psinet.com

Sprint Internet Services www.sprint.net

Uunet Technologies, Inc. www.us.uu.net


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What is Computer Network ? Network can be defined as a group of computers and other devices

connected together in order to send receive data.

Each of these devices in the computer network is called node.Terminology which is commonly used in computer network and i.e.host.

Network Interface Card (an electronic circuit card that resides insideyour computer popularly called as NIC) so you have a place to plug inthe cable.

Node in the network has some unique address. These addresses help toidentify the computer quickly.

Example:- 192.168.0.165 Network address is made of 4 bytes separated by dots for example

131.108.2.1. first three bytes correspond to network address andremaining three bytes are used for host machine.

Introduction


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NIC NIC provides the hardware interface between a computer and a network. Network adapter hardware.

Ethernet supports data transfers at the rate of 10 Megabits per second .Ethernet cables to a computer, use a network interface card (NIC).

Packet Switching Computer network the data is transferred using packet switching. Messages are broken into units called packets, and sent from one computer

to the other.

The communication among the computers due to packet switching networkis error free and there is no conversion overhead or transformation error.

Network Layers Seven layers

TCP / IP Model

Introduction


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IP Addressing

Each host on a TCP/IP network is assigned a unique 32-bit logicaladdress that is divided into two main parts: network number and hostnumber.

This address is called IP address.

The IP address is grouped four into 8-bits separated by dots.

IP address is divided in two categories network number and hostnumber.

The IP protocol makes use of this address for communication betweentwo computers.

Domain Names System(DNS)

Names which are used to identify computer within a network are calleddomain names.

Uniquely identify your computer the name be referred using DNShierarchy.

E.g com,gov,edu,net,int,org,in,uk,jp

Introduction


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Domain Names System(DNS)

The domain Name space is used to locate the computer uniquely. The internet logically arranges the domain names in an hierarchical

form.

Top level DNS such as com,org,mil,net,uk,in

Each domain name is divided into sub-domains then sub-sub-domains

E.g. the complete path for http://www.cse.tec.ac.in can be uniquelytraced out with the help of domain name space.

Working of DNS Two tasks that can be carried out by DNS servers

1.Accepting and then requesting the programs to convert domain names to

IP address. 2.Accepting and then requesting the other DNS servers to convert domain

names to IP addresses.

The DNS server maintains huge database of domain names.

Introduction


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Protocols and Programs

When the communication between two parties occur:

1.What kind of interface(Port) is used for communication between the twoparties?

2. How does the communication take place?

3. What rules and regulation involved in this communication?

The rules and regulations used for establishing such communication iscalled protocol.

The osi-iso model consists of 7 layers and each layer one or more

protocols are used to handle the transmission of data.

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Introduced Protocols 1. Files: Transferring files from one machine to another can be done

in using protocol is called FTP.

It used port 21 for the transfer of files.

When user wants to download a file from the server FTP is used.

FTP uses two connections between client and server.

1. Connection is used for actual data transfer

2. For control information (commands).

Introduction

GUI

Control process

Data transferprocess

Control process

Data transferprocess

Control connection

Data transfer connectionClient Server

Fig:-Two connections used in FTP processing


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Introduced Protocols When client makes a request for file download then using the data

transfer connections actual data gets transmitted from server to theclient.

At the same time server keeps track of how much data is sent so far and

how much is remaining.

This tracking can be done using the control transfer connection.

During the file downloading/uploading we can see a message about howmany bytes are getting transferred and how much time is remaining.

Commands used in FTP are

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Introduced Protocols Command Meaning of the command FTP Start the FTP session

User Identifies the User

Get Downloads the file from the server

Put Uploads the file to the server Ls list files

Close close the connection

Open open a new connection

Introduction


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Introduced Protocols

Problems with FTP:

1. Some machine have firewalls that prevent the transfer of files in to andbackward direction.

Firewall is a piece of s/w embedded in your machine.

Its purpose is to block unwanted transfer of the data.

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2.Email:-Mail clients make use of standard protocols for Sending themails SMTP protocol and receiving the mail the POP3 protocol is used.

1. Transfer of Emails to remote server.

Asynchronous protocol because it allows delayed delivery of message.

Use of port 25.

Mail Transfer Agent(MTA) is interface between email system and local emailserver.

User agent(UA) is user interface client such as Microsoft outlook express.

Introduction


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Introduced Protocols 2. Post office protocol version 3(POP3) is used by local email clients.

Use of port 110.

The POP protocol has two parts 1. client POP- receivers POP and a serverPOP-receivers email server.

The client i.e the receiver opens TCP connections with receivers POP server.

The client must be authenticated by user name and password.

Then the client can receive the emails from the mailbox.

Introduction


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3.Instant Messaging:-.

Used to send short messages.

Internet Relay Chat(IRC) is a protocol which is used for groupcommunication but this comm is one to one commu.

User connects to client application and ultimately links to IRC server.

E.g. Bots appli

4.Remote Machine Access

Remote machine can be accessed using the protocol called Telnet.

Used port 23 for the commu.

Doesnt provide any encryption technique so the commu using telnet is notsecured

Secured commusecure shell SSH which is same as telnet

Introduction

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Introduced Protocols 5.Web Pages:-.

How a web page demanded by gets displayed on our browser. 1) Type the website name .Web address is divided into three parts.

Protocol: HTTP Which tells the web browser that user wishes to communicate with web server on port 80.

Port 80 is reserved for communication between web browser and web server.

2)part is the server address.this tells the web browser which server it needs tocontact in order to retrieve the information.

The web browser communicate with a DNS to find the IP add for the website.

3.part of this address denotes the resource user wants to see.

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Introduced Protocols 5.Web Pages:-.

the web server sends the html for this page back to users web browser.

If there are additional files needed in order to show the web page the webbrowser makes additional requests for each of these.

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HTTP Request-Response Message HTTP takes part in web browser and web server communication it is called

a communication protocol.

It is a stateless protocol.i.e. It can not remember the previous usersinformation nor it remembers the number of times the user has visitedparticular website.

HTTP Request Message Structure

Start lineThree part separated by a single space

1. Request method 2.Request-URI 3.HTTP version

In Request method defines the CONNECT method which is used during the webbrowser and server comm.

It is written in Upper case letters.-

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HTTP Request-Response Message

The primary method is GET The GET methods is used 1. when u type a URLin address bar.2. When u click on some hyper links which is present in thedocument.

GET:-Retrieve the information requested by the user.

Retrieve the information from a specified URI and is assumed to be

safe, repeatable operation by browsers. POST:-To send an information collected from a user form.

Request the server for desired web page and the request made isaccepted as a new subordinate of the resource identified

For operations that have side effects and cant be safelyrepeated.e.gtransferring money

PUT:-This method uploads a representation of the specified resource.Typethe website name .Web address is divided into three parts.

Introduction

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HTTP Request-Response MessageRequest URI:

The Uniform Resource Identifier(URI) is a string used to identify the namesor resource on the internet.

Combination of URL and URN(Name)

Web address URL and Specific name of the place or locationURN

HTTP version:

Version information

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HTTP Response-Structure

Status line is similar to the start line in the request message. it consists ofthree fields. 1. HTTP version 2. Status code 3. Reason phrase.

HTTP version represent the version information

Status code is numeric code indicating the type of response

Reason phrase is in the text string form and presents the information aboutthe status code.

E.g HTTP/1.1 200 OK

200 status code OK Reason phrase

In header field in response message is similar to that of request message e.g.Date,Server,Last-Modified

Message bodyresponse message

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Application and Development Tools Various tools are available on the web

Resources on the web are freeware or shareware. FTP use the console window of windows os to transfer the file from one

computer to another.

Graphics or audio conversion tools available using which data in one fileformat can be converted to another.

There are some plug-ins available for developing the web application likeHTML,PHP,PERL

Shareware

Freeware it can be distributed under a different kind of license where,although the code is not available to view or alter, you do not pay a charge forit.

IDE e.g Eclipse IDE for JAVA

Online tools for checking the syntax of their source code.

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Web Browser Web browser is a s/w which is basically used to use resources on the web.

Client and server Various web browsers

Web browser protocol--HTTP protocol

Scripting languages HTML,XML,DHTML,PHPclient side scripting

Server side scripting JSP,ASP

Function defined by web browser

Choices

If you are going to develop applications or even just web pages, which

browser do you choose. The best way to answer this is to ask yourself what you need and probably

more importantly, what your visitors are going to be using.

Introduction

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