Lecture 04

Basic Definitions

Web client- machine that initiates internet request

Web server – machine that services internet request

Browser - software at the client side to interact with web data

Intranet – an internal network of computers confined to a single place

Extranet – when two or more intranets are connected with each other, they form an Extranet –
e.g, Virtual Private Network

Internet – a global network of networks is defined as internet

Internet presents a two-way client server communication model as shown in figure below:

What is Network?

A computer network, or simply a network, is a collection of computers and other hardware

There are two very common types of network available.

1. Local Area Network (LAN)

Local Area Network

A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally
limited to a geographic area such as a writing lab, school, or building.

Computers connected to a network are broadly categorized as servers or workstations. Servers tend
to be more powerful than workstations. Servers are generally not used by humans directly, but
rather run continuously to provide "services" to the other computers (and their human users) on
the network. Services provided can include printing and faxing, software hosting, file storage and
sharing, messaging, data storage and retrieval, complete access control (security) for the network's
resources, and many others.

Workstations are called such because they typically do have a human user which interacts with the
network through them. Workstations were traditionally considered a desktop, consisting of a
computer, keyboard, display, and mouse, or a laptop, with integrated keyboard, display, and
touchpad. With the advent of the tablet computer, and the touch screen devices such as iPad and
iPhone, our definition of workstation is quickly evolving to include those devices, because of their
ability to interact with the network and utilize network services.

Wide Area Network

A Wide Area Network (WAN) is a network that covers a broad area (i.e., any telecommunications
network that links across metropolitan, regional, or national boundaries) using private or public
network transports. Business and government entities utilize WANs to relay data among
employees, clients, buyers, and suppliers from various geographical locations.

Why networking computers?

We network our computers to share resources and communicate. We can do networking for:

1. File sharing
2. Hardware sharing – printer sharing, for example
3. Program sharing
4. User communication through a machine called e-mail server
What is WEB?

The Web is a protocol that uses the internet as the communication structure. It links documents
stored in computers that communicate on the internet. It is based on Hypertext Transfer Protocol
(HTTP) – native protocol of WWW designed for making web page requests.

What is Internet?

The Internet (or internet) is a global system of interconnected computer networks that use the
standard Internet protocol suite (TCP/IP) to serve billions of users worldwide. It is a network of
networks that consists of millions of private, public, academic, business, and government
networks, of local to global scope, that are linked by a broad array of electronic, wireless and
optical networking technologies.

It is a mean to connect different computers worldwide for sending and receiving all kind of
information including text, graphics, videos, and programs.

What is WWW?

The World Wide Web (abbreviated as WWW or W3 commonly known as the Web), is a system
of interlinked hypertext documents accessed via the Internet. With a web browser, one can view
web pages that may contain text, images, videos, and other multimedia, and navigate between them
via hyperlinks.

WWW vs. Internet

It is alw ays mistaken said that the internet and the World Wide Web are both the same
terms, or are synonymous. Actually there is a very significant difference between the two which
has to be clear to understand both the terms. The internet and World Wide Web are both the
networks yet; the internet is the network of the several different computers which are connected
through the linkage of the accessories like the copper wires, the fiber optics and even the latest
wireless connections. However, the World Wide Web consists of the interlinked collection of the
information and documents which are taken as the resource by the general public. These are then
linked by the website URLs and the hyperlinks. Therefore World Wide Web is one of the services
offered by the whole complicated and huge network of the internet.

What is HTTP?

HTTP short for Hyper Text Transfer Protocol is an underlying protocol used by the World Wide
Web to transfer data. HTTP comprises the rules by which the web browsers and servers exchange
information. HTTP defines how messages are formatted and transmitted, and what actions Web
Servers and Browsers should take in response to various commands.

HTTP is called a stateless protocol because each command is executed independently, without any
knowledge of the commands that came before it. Server breaks the connections once request is
complete. We can say, therefore:
  Each operation or transaction makes a new connection
 Each operation is unaware of any other connection
 Each click is a new connection

This is the main reason that it is difficult to implement Web sites that react intelligently to user
input. This shortcoming of HTTP is being addressed in a number of new technologies, including
ActiveX, Java, JavaScript and cookies.

How HTTP works

HTTP is a four step process per transaction

1. Client
 Makes an HTTP request for web page
 Makes a TCP/IP connection
2. Server Accepts request
 Sends page as HTTP
3. Client downloads the page
4. Server breaks the connection

Side Effect of HTTP Transfers

A record is left of all web transaction in a file that resides at the server called common log file.
Good news is that some user data (record of his visits to the web sites) is recorded in a particular
format in the log files. Bad news is that user privacy is not maintained.

What can you do with this data?

 Rearrange your site by knowing which portions of your web site are popularly accessed
and which are ignored by the users
 Change your marketing strategy – e.g., you can introduce some promotional scheme for
boosting the sale of ignored items
 Make a mailing list – you can trace the location from where customers are visiting and
prepare a mailing list for marketing purposes