Tuesday, August 6, 2013

Internet And Its Features

Web

It is an abstraction(concept) and common set of services on top of the Internet.
It is a set of protocols and tools that let us share information with each other.

World Wide Web

It is a collection of linked documents, or pages, stored on millions of computers and spread over the entire Internet.
The term “World Wide Web” comes from the belief that individual nodes of information are linked with hypertext, and this creates a “web” of information.
The documents on the web are written in HTML-that defines their appearance and layout, and creates the links to other documents. These links are known as hypertext link or hyperlink.
In 1989, Tim-Berners-Lee of European Particle Physics Lab(CERN) in Switzerland has developed WWW.
The purpose of WWW is to provides a network of interactive documents and the software to access them.
It is based on documents called pages that combine text, pictures, forms, sound, animation and hypertext links

Features of WWW

The ability to easily deliver information in any format, to/from a wide range of computing platforms.
Simplified access to the Internet.
The easy availability of extensive information on a wide range of topics.
The Web is interactive.

Uses of WWW

Education Tool
Search Tool
Business Tool

Web Browser

Web Browser is an application that uses information stored at locations around the World Wide Web.
Browser is a piece of software that acts as an interface between the user and the inner-workings of the

Internet.

It is also referred to as Web clients or universal clients.

- Functions:

Contact a web server and sends request for information.
Receives the information and then displays it on the user’s computer.
Browser fetches the requested page, interprets the text and formatting commands that it contains, and displays the page properly formatted on the screen.
Voice based browsers are also being developed.
When given the URL of a document, the browser becomes a client that contacts a Web server on the computer specified in the URL to request the documents.
Browser consists of set of clients, a set of interpreters and a controller to manage them.
The controller forms a central piece of browser.
When a browser interacts with a web server, two programs follow the HTTP.
HTTP allows a browser to request a specific item, which the server then returns.

How to access the WWW : Web Browsers?

Graphical
Text

Web Server

Computers that are connected to the Internet and that contain files that their owners have made publicly available are called web servers.
Any computer can be turned into a Web server by installing web server software and connecting the machine to the Internet.

Ex:

Apache

Microsoft IIS (Internet Information Server)

A server is a member of a class of programs in a modern software architecture called client/server software architecture, in which all applications have two components:

The client component

The server component.

Server

A server is on large Computer
Server is passive
Runs continuously waiting for requests
Runs in background and interfaces only with other software(Clients) and rarely interfaces directly with users.
Server must runs multiple tasks concurrently
Responsible for transmitting the document

Client

A Client is on small computer & runs a multiple instance
Client is active
Runs only on-demand
Client is invoked by a user and takes commands from the user
A Client usually works for one person and does one thing after another in sequence
Responsible for displaying document

Web Pages and Web Sites

Web page is a page containing information and instructions.
The information can be text, images,audio or video.
The instructions are specified in HTML.
A Web site is a collection of related Web Pages(files) stored on a Web Server.
Web sites are hosted on Web Servers.

FORM

Form on a web page allows user to enter data that is sent to a server for further processing
An HTML FORM is a section of document containing normal text, markup and some special elements.
That special elements is known as “Controls”.
FORM tag tells the browser where the form starts and ends.
You can add all kinds of HTML tags between the <FORM> and </FORM>.
The purpose of form element is to present a fill out form to be used for an actions such as registration, queries etc.

HTML defines the following control types:

Buttons

Submit

Reset

Push

Checkboxes

Radio Button

Menus

Text

Files

Hidden Controls

Object Controls

Form Attributes

Action

This attribute specifies a form processing agent

EncType

This attribute specifies the content type used to submit the form to the server

Name

Specifies the FORM name

Method

This attribute specifies which HTTP method will be used to submit the form data set.

GET

While Using Back button, GET request is re-executed
GET method pages can be bookmarked
Page can be hacked
Page can be cached
since form data is in the URL and URL length is restricted
GET is less secure compared to POST
Values will be displayed in the browser's address bar
GET method should not be used for sending sensitive information
It can't be more than 255 characters long.

POST

The browser usually alerts the user that data will need to be re-submitted.
POST method pages cannot be bookmarked.
Page never hacked
Page not cached
No restrictions
POST is safer than GET
POST method variables are not displayed in the URL
POST method can be used for sending sensitive information
Whereas no such maximum length limitation holds for the POST request.

<INPUT> ELEMENT

This tag is used to obtain user input in a variety of ways.
It tells the server the type of data to be submitted by the form.

Attributes:

Type
Name
Value
Size
Maxlength
Checked
Src
Align

<TYPE> ATTRIBUTE

It determines which control will be created on the form.
It can take any of the following values:

Text
Password
Checkbox
Radio
Image
Hidden
Submit
Reset
Button
File

<INPUT Type=“TEXT”>

It is used to create a single line text input field.

<INPUT Type=“PASSWORD”>

In this type the input text is rendered in a way to hide the characters.
This control is used for sensitive input such as password.

<INPUT Type=“CHECK BOX”>

Creates an on-screen checkbox for users to make multiple selections.
Checkbox is an on or off switch.
When the switch is checked the value is “yes” else “no”.
This allows user to select more than one value for a given property.
<INPUT type=“CHECKBOX” NAME=“CH1” VALUE=“A” Checked>

<INPUT Type=“RADIO”>

Creates an on-screen radio button for user to make a single selection.
It is also an on or off switch.
The radio button value is only submitted with the form when the switch is on.
<INPUT type=“RADIO” NAME=“RD1” VALUE=“Yes” Checked”>

<INPUT Type=“IMAGE”>

Creates a graphical submit button.
The image value of the type attribute has only one difference from the submit attribute.
<INPUT TYPE=“IMAGE” SRC=“submit_image.gif”>

<INPUT Type=“HIDDEN”>

Creates an element that is not visible by the user.
<INPUT TYPE=“HIDDEN” value=“lotus”>

<INPUT Type=“SUBMIT”>

Creates a submit button.
When this button is activated by the user, the form is submitted to the location specified by the action attribute of the form element.
<INPUT TYPE=“SUBMIT” value=“Submit the Form”>

<INPUT Type=“RESET”>

Creates a reset button.
When this button is activated by the user, all of the form’s controls have their values reset to the initial values specified in the controls on the form.
<INPUT TYPE=“RESET” VALUE=“Reset the Form”>

<INPUT Type=“BUTTON”>

Creates a generalized button.
Unlike the submit or reset buttons, it has no predetermined action.
<INPUT TYPE=“BUTTON” Value=“Click me”>

<INPUT Type=“FILE”>

Creates a control which is used for file uploading.
The field consists of a text entry box for a filename as well as a button immediately to the right of the field, which is usually labeled BROWSE.
Pressing the Browse….. Button allows the user to browse the local system to find a file to specify for upload.
<INPUT TYPE=“FILE”>

<SELECT>

The SELECT element is used to create a list of choices either as a dropdown menu or a list box.
Each of the choices in the list is an OPTION element.
There are two tags involved in creating select lists, the <SELECT> tag and the <OPTION> tag.
The <SELECT> tag offsets the lists .

Attributes:

Name

Assigns a name to the element.

Size

Numbers of rows in the list that should be visible on the form.

Multiple

This boolean attributes allow multiple selections.

Disabled

Locks the field where user can’t change the value. Even user cant select option, cant copy text and the field is not even sent if the form is submitted.

<OPTION>

Used along with <SELECT> to create select lists.
The <OPTION> is used to list the possible values. It has only two attributes.
Selected

When set this boolean attribute specifies that this option is pre-selected.

Value

This attribute specifies the value to be submitted for this choice, if the choice is selected,when the form is submitted.

>Eg:

<SELECT NAME=“listname”>
<OPTION value=“LIST1”>ITEM1
<OPTION value=“LIST2”>ITEM2
<OPTION value=“LIST3”>ITEM3
<OPTION value=“LIST4”>ITEM4
</SELECT>

<TEXTAREA>
The TEXTAREA element is similar to the INPUT element’s text type.
Instead of single line text box, a multi-line text input control is created.
Because there are many lines of text within the <TEXTAREA> element, it is not possible to set the default text for the textarea using the VALUE attribute.
The default text is placed between the <TEXTAREA> …………</TEXTAREA> tags.

>ATTRIBUTES

NAME:

Assigns a name to the element.

ROWS:

Specifies the number of visible text lines.

COLS:

Specifies the visible width in a average character widths.

>Eg:

<TEXTAREA NAME=“ADDRESS”ROWS=“2” COLS=“20”>……….
</TEXTAREA>

<FIELDSET> ELEMENT

It defines a group of form elements as being logically related.
The browser draws a box around the set of fields to indicate that they are related.
<FIELDSET> is a block level element, so there is no need to use <P> tag between fieldsets

>Example:

<FIELDSET>
<INPUT TYPE=“Checkbox” name=“sports”>Sports
<INPUT TYPE=“Checkbox” name=“Shopping”>Shopping
<INPUT TYPE=“Checkbox” name=“Music”>Music
<INPUT TYPE=“Checkbox” name=“Dancing”>Dancing
</FIELDSET>

<LEGEND> ELEMENT

It is used with <FIELDSET>to give a title to each set of fields.

<FIELDSET>
<LEGEND>Hobbies</LEGEND>
<INPUT TYPE=“Checkbox” name=“sports”>Sports
<INPUT TYPE=“Checkbox” name=“Shopping”>Shopping
<INPUT TYPE=“Checkbox” name=“Music”>Music
<INPUT TYPE=“Checkbox” name=“Dancing”>Dancing
</FIELDSET>

Frame Element(HTML)

FRAME

Frame allows you to divide the page into several rectangular areas and to display a separate document in each rectangle.
Each of those rectangle is known as “Frame”.
Using frames, you can display multiple HTML document in the same browser window.
Each HTML document is called a frame, and each frame is independent of the others.

FRAMESET

The frameset element holds one or more <FRAMESET> or <FRAME> elements. Each frame element can hold a separate document.

Example:

<frameset cols="25%,50%,25%">
<frame src="frame_a.htm" />
<frame src="frame_b.htm" />
<frame src="frame_c.htm" />
</frameset>

NOFRAME

The <noframes> tag is used for browsers that do not handle frames.
The noframes element can contain all the elements that you can find inside the body element of a normal HTML page.
The noframes element is most used to link to a non-frameset version of the web site or to display a message to users that frames are required.
The noframes element goes inside the frameset element.

ROWS

“pixels|percents” defines the row height of each row(vertical) within the frameset. The value of each row height is a comma separated list of sizes

COLS

“pixels|percents” defines the column width of each column(horizontal) within the frameset.The value of each column width is a comma separated list of sizes

ONLOAD

“script” to specify client-side scripting actions to perform when the frame is loaded.

ONUNLOAD

“script” to specify client-side scripting actions to perform when the frame is removed

FRAMEBORDER

To give border around all frames

BORDER

Controls width of all borders

BORDERCOLOR

To change the color of the frame borders

<FRAME> ELEMENT

Defines a frame.
Each frame must contained within a Frameset document that defines the dimension of the frame.

ATTRIBUTE

SRC
Name
NoResize
Scrolling-value(Yes,no or auto)
Marginheight
MarginWidth
FrameBorder-Value(0 or 1),Specifies whether or not to display a border around a frame

Introduction to HTML

HTML

HTML stands for Hyper Text Markup Language.(The markup is the instructions for displaying or printing the text.)
HTML is not a programming languages but it is a markup language.
A markup language is a set of markup tags.
HTML uses markup tags to describe web pages.
It is a descriptive markup language that describes the structure and behavior of a web documents.
HTML was created by Tim Berners-Lee
HTML is a set of code that can be embedded in text to add formatting and linking information.
It allows these different kinds of data to be displayed together.
HTML is nothing more than a plain text file that allows for the inclusion of two kinds of text:

The Content

Text or information to be displayed or played back on the client’s screen.

The Markup

Text or information to control the display or to point to other information items in need of display .

HTML TAGS

Tags are the instructions that are embedded directly into the text of the document.
An HTML tag is a signal to the browser that it should do something other than just throw text up on the screen.
By conventional all HTML tags begin with an open an angle bracket(<) and end with close angle bracket(>).
HTML is specified as TAGs in an HTML document(i.e. Web Page)
There are two types of HTML tags:

Paired Tags
Singular Tags( stand-alone tags/ unpaired tags)

Paired Tags

A tag is said to be a paired tag if the text is placed between a tag and its companion tag.
In paired tags, the first tag is referred to as opening tag and the second tag is referred to as closing tag.

Example:

<i>Welcome</i>
Here, <i> is called opening tag and </i> is called a closing tag

Here are some more examples

<html>
<head>
<title>
<body>
<p>
<h#>
<address>
<nobr>
<center>
<block quote>
<pre>
<font>
<strike>
<b>
<i>
<big>
<small>
<sub>
<sup>
<u>
<lists>
<div>
<strong>

Singular tag

A Singular tag does not have a companion tag.
Singular tags are also known as unpaired tags or Stand-Alone tags.

Example:

<br>
<hr>

This tags does not require any companion tag.

<doctype>
<br>
<hr>
<basefont>
<meta>

HTML Tag

Some HTML tags require additional information to be supplied to them.

For example:-

When a picture is placed on the screen, information like the height and the width of the picture can be specified.

Additional information supplied to an HTML tag is known as Attributes of a Tag.
Attributes are written immediately following the tag, separated by a space.

<table border="1">

Multiple attributes can be associated with a tag, also separated by space.

HTML document

An HTML document contains two distinct parts:
The head
The body.
The head contains information about the document that is not displayed on the screen.
The body contains everything else that is displayed as part of the web of page

<HTML>

<HEAD>

…………..

<!-- header information & it is not displayed on the page

</HEAD>

<BODY>

…………..

<!-- all the HTML for display>

</BODY>

</HTML>

Head Eement

<HEAD> contains general information, or meta-information, about the document.
The head of the HTML document is an unordered collection of information about the document.
The main head element is a <TITLE> tag.
The contents of the <HEAD> are not displayed as part of the document text
It is just written after the <HTML> tag.

<TITLE>
<BASE>
<ISINDEX>
<NEXTID>
<LINK>
<META>
<STYLE>
<SCRIPT>

Title Element

The title of a document is specified by the TITLE element.
The TITLE element should occur in the HEAD of the document.
There may be only one title in any document.
It should identify the content of the document.
The <TITLE> element is not part of the body text, it is displayed in the window title.
It may not contain anchors, paragraph or any highlighting or other HTML Tag.
The title may be used to identify the node in a history list.
Your title should be descriptive but short, less than 64 characters.

Body Element

It specifies the main content of the document.
Body tag is placed immediately after the closing head tag(</Head>) and before any image or text included in the document.
The body of the HTML document contains all the text and images that make up the page together with all the HTML elements that provide the control or formatting of the page.
It is possible to control the document color scheme and background by specifying certain attributes in the <BODY ….> declaration.

Attributes are

used to point to an image file
BgColor: allow settings of background color
Text: used to change the text color

For Additional Quarries Please put Your Valuable Comment (!)

Electronic Journal

ELECTRONIC JOURNAL

Define as the journal that may take two different forms:
Journal that published in print form or digital form
Electronic –only journal, which is produced, published and distributed via electronic medium.

Advantages

Instant access
Issues can be unbundled.
Issues are directly loadable into an electronic database.
Proofreading can be done by authors
Electronic storage is more efficient than that for print volumes.
Paperless, but it has to be recognized that readers may want a printout of the articles they are interested in.

Disadvantages

Hardware and software are required
Training
Peer review is less common
Graphics are problematic
Copyright is undecided.
Archives(records) are hard to maintain

Types of Electronic Journal

Types of electronic journal may be classified in various way such as:

By location
By products
By Availability of print products
By Types of Technology Applied
By Price
By Peer Review

Characteristics

Limited Cost
Global Distribution
Very Satisfactory Quality of Reproduction of Image
Electronic subscription and sending in of articles
Personalized Subscription
Possibility of reliable analysis of readership
Use of hypertext
Digital Storage
Good Communication between the author and reader
Commercial Independence

LISTSERVE || NEWSGROUPS || TELNET || GOPHER || VERONICA || WAIS

LISTSERVE

First electronic mailing list software application, consisting of a set of email addresses for a group in which the sender can send one email and it will reach a variety of people.
Also called “distribution lists” or “discussion forums”
Lists of users hold a discussion about a particular subject.
Distribution lists are free and very satisfactory
This system is one of those with easiest access via the Internet, since it only requires the ability to send e-mail.
There are two types of distribution lists:

Moderated-The lists maintained by a single person, whose active participation is necessary for maintaining the list. This type is sometimes called a mailing list. The owner may edit the message in this type.
Unmoderated- The lists that do not require the intervention of anybody, to be maintained, since all the messages are managed by software, which does all the work. This type is called Listserve.

Advantages Of Listserve

Information exchange
Does not require full access to the Internet.
Great independence to the user.

There are major four listservers which provides distribution lists:

ListServe
Listprocessor
Majordomo
Mailbase

NEWSGROUPS

Worldwide system for the electronic exchange of news and views on a particular topic.
Also referred to as Usenet News.
Usenet is a discussion forum similar to distribution lists.
On the Usenet the messages are stored on notice board rather than distribution.
You do not need to subscribe to a newsgroup.
To participate in global distributed discussion system you must have the following facilities:
Your Internet provider must offer a “news feed” service
You must have a client on your computer that can interpret data sent from an NNTP server. This will take the form of a dedicated newsreader, or your web browser if it has been “news enabled

TELNET(TELETYPE NETWORK)

Telnet is a protocol that is most commonly used to log into a remote computer.
Telnet act as a terminal emulator.
Telnet is the protocol that enables one computer to connect to other computer. This process is also referred to as remote login.
The user’s computer which initiates the connection is referred to as the local computer.
The machine being connected to which accepts the connection is referred to as remote or host computer.
Once connected, the user’s computer emulates the remote computer. When the user types in commands, they are executed on the remote computer.
Telnet environment is based on text, as it does not support the graphical interface.
To get access via Telnet, you need an access code

#Using Telnet, you can

Send email
Download source code from websites
Send unexpected input to web servers that can give you amazing and illegal results.
Give arbitrary(random) input to many other services on Internet host computers
Probe the services offered by servers, routers and even people’s home computers.

#There are two ways of using the Telnet tool:

The input mode

Input mode allows you to establish the connection and use the remote computer

The command mode

Command mode is used to set the parameters to Telnet

GOPHER

It is a hierarchical menu-based system for exploring the Internet.
Gopher is a protocol designed to search, retrieve and display documents from remote sites on the Internet.
Originally Gopher had text based interface then it has evolved greatly, becoming a tool for obtaining multimedia data.
You can access Gopher by means of Telnet, although the menu options cannot be selected with the mouse.
Information accessible via gopher is stored on many coputers all over the Internet. These computers are called gopher servers.
Servers do not just contain a files, directories and searchable databases, they can also contain references to other servers.
To retrieve and search this information, you need to run a gopher client application on your computer.
Information stored on many kinds of non-gopher servers is also available via special gopher servers that act as gateways.
Gopher was created as a piece of software to utilize some of the services that were becoming available on the Internet.
It was designed to work with a variety of different Internet stand alone services.

Characteristics

Ease of use with user interface based on menus
It offers the possibility of discovering sources of information on the Internet without needing to know their location.
Gopher server automatically directs the search to the address, where what you want to see is stored.

VERONICA

Veronica is a tool which simplifies the search for resources in Gopher.
Veronica comes from “Very Easy Rodent Oriented Networked Index of Computerized Archives”
Veronica starts the search on the Gopher menus, from which you select “GOPHER-space search” or the name veronica, by keying in a keyword.
It gives you Gopher addresses with the keyword on their menus.
You can choose which of these sources in order to enter them.
While searching following things must be in consideration:
Search is not case sensitive
Veronica does not carry out searches in the complete text of the resources available on the Internet.

Types of Search Using VERONICA

Searching GOPHER space by keywords in titles- This type locates all types of resources that have title containing the keyword.
Searching GOPHER directories only for keywords in titles- It searches only for directories in which the keyword is contained in the title.
Simplified Veronica- When you select the option, veronica asks you for the keyword or words you want, together with additional information to control the search:

Simple search
Search by more than one keyword
Search for word roots
Search by types of Gopher
Specification of the number of resources analyzed

WAIS(WIDE AREA INFORMATION SERVERS)

It is a tool designed to search for information on the Internet by means of the keyword and provide as a result a list of the resources related to the keyword, ordering them according to the number of times the keyword appears in the document.
WAIS searches for the keyword , selected by the user in the text of the files stored on the network.
It is a system of searching in the complete text, not just on the menus or in the names of files.
WAIS uses Natural Query Language
The query is put into the system in natural language and WAIS discounts the irrelevant words and starts to search for the keywords

Searching For Documents With WAIS

You can gain access to WAIS in various ways:
Using a client program
Making a connection with quake.think.com and login as wais
Entering WAIS via WWW .

Domain Name Service && IP Address

Domain Name Service

Domain name is a way to identify and locate computers connected to the Internet.
No two organizations can have the same domain name.
A domain name always contains two or more components separated by periods, called dots(“.”)
Once a domain name has been established , ”Sub domains "can be created within the domain.

#The structure for this is:

Hostname.subdomain.second-leveldomain.top-leveldomain
DNS as a whole consists of a network of servers that map Internet domain names like www.google.co.in to a local IP addresses.
DNS enables domain names to stay constant while the underlying network topology and IP address change.
Each domain name corresponds to numeric IP addresses.
The Internet uses the numeric IP address to send data.

#For instance,

You may be connecting to a World Wide Web server with the domain name www.microsoft.com”, but as far as network is concerned, you are connecting to the web server with the IP address associated with that domain name.
E.g. IP address for www.microsoft.com is 192.11.1.1
Domain Name System completes the task of matching the domain names to IP addresses.
Domain names and their corresponding IP addresses, must be unique.
Domain Name System is a collection of databases that contain information about domain names and their corresponding IP addressing
Domain Name Servers are computers that translate domain names to IP addresses.
This system allows the Internet users to deal with the more sensitive domain names, rather than having to remember a series of numbers.
Domain name space is a hierarchical ,tree structured name space, starting at an unnamed root used for all DNS operations.
In DNS name space, each node and leaf in the domain name space tree represents a named domain.Each domain can have additional child domains.

#There are three components of DNS:

Resolver
Name server
Database of resource records(RRs)

Web Hosting || Virtual Private Network || Voice Over Network

WEB HOSTING

It is a type of Internet hosting service that allows individuals and organizations to make their own website accessible via world wide web.
To put your web site on the Internet you need three things:

Domain name is an identification label that identify IP resources such as web sites.
E.g. www.google.com
Web host account is the account hosting companies
Web site is a site created by the user.

VIRTUAL PRIVATE NETWORK

It is a group of computer systems, connected to a private network.
It is secure way of connecting to a private LAN at a remote location using Internet.
VPN’s include encryption, strong authentication of remote users or hosts, and mechanisms for hiding or masking information about the private network topology from potential attackers on the public network.

VOICE OVER INTERNET

Internet telephony is the new technology, where phone calls can be made in any part of the world through the internet.
There are various web sites offering Net Telephony services like Net2phone, Vocal tec, net meeting.
Family of internet technologies, communications protocols and transmission technologies for delivery of voice communications and multimedia sessions over IP networks, such as Internet.

Listening the word Internet Concepts the first Question stuck to the mind is....

What is Internet..?

Internet is a global network of interconnected computers over world wide web.
It is a global web of computers that allows individuals to communicate with each other.
Internet consists of two types of computers:

Server
Server is a computer or program that fulfils the request of another computer or program.
Client
Client is a computer or program that requests a service of another computer or program.

Applications of Internet

Communicate with other people
Sharing information or resources
Connect to other computer systems

Types of Network

MILNET - Military Network
DARPA - Defense Advanced Research Network
BITNET - Because it’s Time Network
USENET - User Network
NSFNET - National Science Foundation Network.
ARPANET - Advanced Research Projects Agency/Administration Network

History of Internet

In 1969, the Department of Defense (DOD) of the United States (US) started a network using four computers at four separate universities throughout the United States enabling users to share resources and information, which was known as ARPAnet(Advanced Research Projects Administration Network).
In 1972, there were 37 computers connected to ARPANET. In that year, ARPA’s name was changed to DARPA (Defense ARPA).
In order to manage the size and complexity of the network were broken into two parts:
MILNET-for managing Military sites
ARPANET –for managing non-military sites(Network for research and educative purpose)
In 1970’s other networks like BITNET and USENET also come into being.
In 1980’s NSFNET was created. NSFNET allowed universities and research agencies to link up with its super computer.

# How Internet works...?

Internet is a global network of computers, each computer connected to the internet must have a unique address. That address is known as IP address.
Internet includes thousands of host computers(servers) which provides data and services as requested by client system.

Message starts
Message is divided into small chunks known as packets
Each packets are assigned a port number.
Each packets receives its destination address.
Data conversion from analog to digital and vice versa.
The ISPs router examines the destination address in each packet and determines where to send it.

ISP(Internet Service Provider)

When you connect your computer to the internet, you are connecting to a special type of server which is provided & operated by your ISP.
The job of this ISP is to provide the link between your browser & the rest of the internet.
The single ISP server handles the internet connections of many individual browsers.
The main component of providing access to the Internet consists of:
International connectivity, which allows you to connect to the amorphous(unstructured) Internet.
Domestic connectivity, which allows you to connect to the domestic gateway.
There are three ways an ISP can connect to the Internet:

VSNL(Videsh Sanchar Nigam Limited)/DOT(Department of Telecommunications)
STPI(Software Technology Park India)Private Operators
VSNL-VSNL is india’s leading provider of international telecommunications and Internet services.
DOT-DOT is responsible for issuing security clearances.

STPI- STPI is a semi government organization that has authorized to sell international gateway services to companies involved in developing software
Private Operators- Private operators are a private independent companies competing directly with the multi-system operators

Types Of Internet Connections

Connection Types

Dial-up Access
ISDN(Integrated Services Digital Network)
Leased Lines
Cable Internet

Dial-up Access

Also known as narrowband
Least expensive way to get connected with Internet
Speed is too low.
Use the Point-to-Point Protocol.
To use a Dial-up You need a modem.
Doesn't require any special H/W.
Only used for Email & light Web Browsing.

Overview of C Programming Language

Basic Information About C Programming Language

Computer Component

Hardware

Hardware is the equipment, or the devices, associated with a computer.

Software

The instructions that tell the computer what to do are called software or programs.
Program written by programmers

Hardware and software accomplish four major operations:

Input
Processing
Output
Storage.

Types of Language

High – level Language

Language in human readable form are known as high – level language.
E.g. C, C++, Java etc.

Low – level Language

Language in the form of 0s and 1s is known as low level language.
Also known as machine language

Types of Error

Syntax Error

Refers to an error in the syntax of a sequence of characters or tokens for particular programming language.
Syntax error will be display at compile time.

Logical Error

Error occurs because of logic of code is known as logical error.
It will be display at run time.

Compiler and Interpreter

It is one kind of program to convert high level language into low level language.
Interpreter check code line by line if error than display error.
Compiler check whole code and than display list of errors.

Reserve Keywords

Some words are reserved for special purpose which are known as reserve keywords.
Reserve keywords are not used as an name of variable, functions, class etc.
The keywords must be written in lower case only.

Identifiers

Identifiers refer to the names of variables, functions and arrays.

Rules for identifiers

Must consists of only letters, digits, or underscore.
First character must be an alphabet (or underscore).
Only first 31 characters are significant.
Cannot use a reserve keyword.
Must not contain white space.

Constants

Constants refer to fixed values that do not change during the execution of program.

Backslash Character Constant

Variables

Variable is a named location of memory that is used to hold a value.
Its value can be modified during the program execution.
We can also say that variable is an identifier that is used to represent a single value.

Data Types

It is a type of data that can be represent in the value of data element.
It defines the type of constant which is going to store into the variable.
Compiler will allocate memory for variable based on data type.

Comments

Sometime we want to write comment in the program which is not an executable part of our source code.

There are two types of comment

Single line comment ( // )

E.g. // This is a single line comment

Multi line comment ( /* ------------ */)

E.g. /* Program name : sum.cpp
Definition : To calculate the sum */

Declaring Variable

Before using the variable, you have to define variable to give information to compiler.
Syntax
Datatype VariableName;
E.g.
int StudentId;
char Name;
float Average;
double SumOfSalary;
Statements used to declare variable is known as declarative statement.
When we declare a variable
Space for a variable is set in memory to hold a value of the specified data type.
That space is associated with the variable name.
That space is associated with a unique address.
E.g. int StudentId;

Variable Initialization

At the time of variable declaration we can assign default value which is known as variable initialization.
E.g. int StudentId = 25;

Assigning value to variable

We can also assign the value to the variable.
The statement which assign value to the variable is known as assignment statement.

C Program Structure

Preprocessor Directive
Global Declaration
User Defined Functions
int main()
{ Local Declaration
Statements }

Output Function : printf()

printf( ) is a function defined in stdio.h header file.
It reads data from the computer’s memory and display it on standard output device.
printf stands for print formatted.
On success, the total number of characters written is returned otherwise return negative number.

Syntax :
printf(“control string”, VariableList);
Ex.
Input Code : printf(“Welcome to home”);
Output is : Welcome to home
Ex.
Input Code : int StudentId = 10;
printf(“%d”, StudentId);
Output is : 10

You can also combine message and value of variable.

Ex.
Input Code : int StudentId = 10;
printf(“Id of student is %d”, StudentId);
Output is : Id of student is 10

You can also specify the width of field.

Syntax :
printf(“%field-width FS”, VariableName);
E.g.
Input Code : int No = 2563;
printf(“%3d”, No);
Output : 256

Input Function : scanf()

It is input formatting function.
It will read data from standard input and stored in given variable.
scanf stands for scan formatted.
Remember that leading white spaces are ignored.
On success, the function returns the number of items successfully read.
In the case of an input failure before any data could be successfully read, EOF is returned

Syntax :
scanf(“Control String”, &VariableList);
E.g.
int No;
scanf(“%d”, &No);
char Str;
scanf(“%c”, &Str);

You can't use message in scanf function.
If you want to display message for user understanding than use printf function.

E.g.
int No;
printf("Enter one number:¨);
scanf("%d", &No);

Width is used to specified that maximum number of characters to be read.
But if the whitespace character found before width, that only many characters are going to be stored.

E.g.
int No;
scanf(“%2d”, &No);

Operator

Unary Operator

Operator which required one operand is known as unary operator.

Binary Operator

Operator which required two operand is known as binary operator.

Ternary Operator

Operator which required three operand is known as ternary operator.

Goto Statement

We can change the normal sequence of execution by transferring control to other part of the program using goto statement.
Syntax: goto label_name;
Here the label name should be valid identifier which may appear in anywhere in the program.

Break Statement

The break statement uses to come out from a loop.
It can be used to force to end the loop before its natural end.
Remember that break statement can only used with loop statements and switch statement.

Continue Statement

The continue statement skip the rest part of the loop and transfer control at the beginning of the loop for next iteration.

Switch Statement

We can choose statements to execute based on some value.
This can be achieve using nested if….else statement. But it is very complex.
C language provide switch statement to avoid this type of complexity.