INTRODUCTION
TO NETWORKS AND INTERNET
A computer network is a
communication system where a group of computers and other devices like printers
are connected by cables and other hardware. The data is shared between two
computers. A network, besides facilitating data communication, allows resources
to be shared among all the systems connected to the network. Thus users in the
second floor of a building can use the printer on the sixth floor if their
computer and the printer are connected to the network.
This
concept of connected computers sharing resources is called networking.
Computers that are connected
in a network can share:
¨ Data
¨ Messages
¨ Printers
¨ Hard Disks
¨ CD-ROMs
¨ Modems
¨ Other hardware resources
ADVANTAGES OF NETWORKING
¨ Network allows efficient management
of resources. For example, multiple users can share a single high-quality
printer, rather than having multiple, possibly lower quality printers on
individual desktops.
¨ Networks keep information
reliable and up-to-date. A well managed, centralized data storage system allows
multiple users to access data from different locations.
¨ Transferring files across a
network is always faster than other, non-network means of sharing files.
Networks help speed up data sharing.
¨ Networks provide the
services like electronic-mail,
which allow much more efficient communication among individuals.
TYPES OF NETWORKING
Networks can be classified
as follows :
Local Area Network (LAN)
If a network is confined to
a single location, typically one building or complex, it is called a Local Area Network (LAN). The
communication on LAN takes place through a physical connection, such as a
cable.
Wide Area Network (WAN)
LANs could not adequately
support needs of large business, with offices spread over wide area. This led
to the development of Wide Area Networks
(WAN). Thus, when a network is spread over wide areas, such as across cities,
states or countries, it is called as a Wide
Area Network (WAN). Communication on a WAN takes place via telephone
lines, satellites or microwave links, rather than through a physical cable.
Metropolitan Area Network (MAN)
In between LAN and WAN is
the Metropolitan Area Network
(MAN). A MAN is a network that covers entire city, but uses LAN technology.
Cable television networks are the examples of MANs distributing television
signals.
Let us see the benefits
offered by LAN to the employee in an organization.
Resources Sharing: Using a LAN, expensive resources like printers,
modems, graphic devices and data storage units can be shared. This enables
several users to access these resources at the same time.
Communication: Another use of a LAN is that it can help you make
the computer do the job of an intercom. You can use the computer to flash the
messages on the screen of other computers in the office, thus saving employees
the time they would spend in going to someone in other department, on some
other floor to deliver a message or a memo. This also reduces the need for
face-to-face meetings and the need to circulate memos among employees.
Hardware Components Of LAN:
¨ Workstations: The term workstations
refers to the computers that are attached to the LAN. On a LAN, there can be
PCs that do not have either hard disk or floppy disk drives. Such PCs are
called diskless workstations.
Such workstations cannot store any data or software. They access them directly
from the LAN server.
¨ Server: A server
is a computer that provides the data, software and hardware resources like
printers that are shared on LAN. A LAN can have more than one server. Each server
has a unique name and all the LAN users identify the server by its name.
File
Server: A file server stores files
that LAN workstations can access. It also decides on the rights and
restrictions that the users need to have while accessing files on the LAN. The
file server also allows LAN users to store the files on their own hard disks.
The file server regulates the amount of space allowed for each user.
Printer
Server: A printer server takes
care of the printing requirements of a number of workstations. In a LAN with
a large number of workstations, several
users could give requests for printing in intervals of just a few minutes. The
printer server typically stores the files to be printed on its disk, and then executes
these requests on a first-in-first-out basis.
Modem
Server: A modem server allows LAN
users to use a modem to transmit long distance messages. Typically, in an
organization, only a few users would need to use the modem. A single modem
server attached to one or two modems would serve the purpose.
¨ Network Interface Unit (NIC)
The
Network Interface Unit (NIC)
is a device that is attached to each of the workstations and the server. The node address of a workstation
means the address of the NIC that is attached to the workstation.
¨ Communication Channel
In
a LAN, the word communication channel
means connecting cable. The quality
and performance of the LAN cables has improved over time with the improvement
in technology.
Some
Of The Communication Channels:
Twisted-pair
Cables
The
oldest and least expensive type of cables used for LANs are the twisted-pair cables. These cables
consists of two insulated copper wires twisted around each other. These cables
are also used for short and medium range telephone communication.
Co-axial
Cable
A co-axial
cable consists of one or more small cables in a protective covering
as shown in the figure. These are
more expensive than twisted-pair cables but
perform better.
Fiber-optic Cables
Fiber-optic cables are made of plastic or glass and are
as thin as a human
hair.
These cables are highly durable and offer excellent performance. Their
speed of transmission is very high.
THE NETWORK OPERATING SYSTEM
We have seen the typical
hardware components of the LAN. There is another very essential element of the
LAN, namely its operating system
(OS). A LAN or any other type of network also needs an operating system. DOS is
an example of single-user operating system. DOS concerns itself with the
operations of a single PC. A network operating system has to concern itself
with the management of the network as a whole. Some of the most popular network
operating systems in use are Novell Netware from Novell Inc., Windows NT Server
from Microsoft.
Some of the functions of a
network operating system
¨ Access
to disk storage space: Network users
can save files in a common location, i.e. the server hard disk. It is necessary
to ensure that every user gets a share of disk space on the server disk.
¨ Access
to shared files: In a network,
certain files on the server are accessed by several workstations at the same
time. The network operating system ensures that this takes place smoothly.
¨ The network operating system
takes care of security, ensuring that files of one user are not accessed by
other users.
¨ It manages the sharing of
peripherals like printers among workstations.
INTERNET
The Internet is the world's
largest library i.e., it is a vast network of computers that can store
documents, known as Web pages, linked together by hyperlinks that enable you to
move between pages on the same server, or even different servers. The Web pages
are programmed in HTML (Hyper Text Markup Language), deviced by Tim Berners
Lee.
To view an HTML document, you will need software that
understands the HTML format. These software packages are known as browsers.
These browsers are generally graphical in nature, user friendly and possess
additional features. The popular browsers are Internet Explorer, Netscape
Navigator and Opera. Most features on the different browsers are similar, so it
is easy to use any of them.
Surfing
A browser has a set of buttons on the top, known as
toolbar. There is also a text entry box where you can enter the name of any
site that you want to visit.
Let us consider the address
of the site - www.eyecare.org. This address is a URL (Universal Resource
Locator), originally created by Tim Berners Lee. Type the URL in the browser
window as shown in the figure. Before this, make sure that the Internet
connection is working. The page will start loading. The status bar at the
bottom shows the progress of this operation.
On moving your
mouse to the page, you will notice the arrow turning into a hand over some
parts of the text (generally underlined and in blue) or some images. This
depicts hyperlink to another document. This may be on the same website or on a
totally different website located on a different server.
Toolbar:
Back button: If you want to
revert back to the main page, you could use the Back
button.
It takes you to the previous page that you visited.
Forward button: To revert the above process use the Forward button.
Print button: The Print button
is used to take a printout of the page on an attached
printer.
Stop button: This stops the
browser from loading the HTML document.
Refresh button: This reloads the
HTML document.
Note1: If you want to visit a link without closing the
current page that you are viewing, right click on the link. Now among the
options that you are presented with, choose the option that will allow you to
view the document in a new window. This way you will have two windows of your
browser running. It is possible to open any number of windows, but that would
slow down your browsing speed.
Note2: If you get URL wrong, your browser will indicate
that an error has been made. A URL has no spaces between letters, and always
uses forward slashes.
Note3: In order to make explicitly that you are using
HTML, your URL should look like this - http://www.eyecare.org, where HTTP
stands for Hyper Text Transfer Protocol. Another protocol is known as FTP (File
Transfer Protocol) where you would have to replace the http:// with ftp://.
Some sites have an alternative FTP site, to enhance down loading.
E-mail
E-mail is the common form of
communication on the internet. It is the electronic version of a normal postal
service. On the internet, which spans countries and continents, there is a
uniform scheme of addressing everyone. This address is an e-mail ID. A typical
e-mail ID would read: information@sankaranethralaya.org.
There are three main parts
of this e-mail ID:
Information: the actual
login name, or person's unique identification within the organisation.
sankaranethralaya: the
organisation's name.
Org: the class of
organisation. This category is also known as a top-level domain.
Domain Names
|
.com
|
Commercial site, generally
a company site.
|
|
.org
|
Organisational site,
generally a large organisation that is associated in some way with the site.
|
|
.net
|
Network site, generally a
Network or ISP.
|
|
.edu
|
Educational institution
site, most US
universities and other educational institutions work under this domain.
|
|
.gov
|
US government, most official sites that belong to
the Federal government.
|
|
.mil
|
US military.
|
|
.in
|
Indian domain name,
actually to be used with every site that is based in India.
|
Some additional lower level
domains specific to India
are:
.vsnl.net.in - Old VSNL
domain, now .vsnl.com
.satyam.net.in - Satyam
domain
.ernet.in ERNET - most
educational institutions in India
are on it.
In Web based access, your
e-mail access is via the Web pages of the site offering you the e-mail access.
Therefore, to read, reply or create any message, you need to be connected to
the Internet. Examples include www.mailcity.com, www.netaddress.com etc. To use
web based e-mail, first create an account. Go to the respective site and follow
the instructions for new users. Once this is done, your account will be
created. To check your e-mail, enter the address of the site that you need to
visit in the browser. You may need to enter your e-mail ID and password at the
start.
Some of the sites offering
free Web-based e-mail accounts.
http://www.hotmail.com
http://mail.yahoo.com
http://www.india.com
http://www.netaddress.com
http://www.indiamail.com
http://www.pobox.com
Chats
As with the most internet
applications, IRC (Internet Relay Chat) can be accessed either directly using
the chat client or via a browser. An IRC server is a dedicated server on the
internet, which allows people to access it, and communicate with others using
it. In an effort to organise the conversations, each IRC is divided into
channels. A channel is an area that is devoted to particular topic. People can
therefore choose to enter channels that deal with the subjects of their
interest.
Searching for information:
Finding information on the
internet is much more difficult than it seems. A search engine is a software
that allows you to search the Web for documents of interest to you.
Examples of search engines:
www.yahoo.com
www.altavista.com
www.hotbot.com
www.askjeeves.com
ASSIGNMENT
1. What is
networking?
2. A
_________________ is a network that covers an entire city.
3. What are the
advantages of networking?
4. What are
the three types of Networks? Explain.
5. Write short
notes on a. Network operating system b. Communicational Channels.
6. What can
you do on Internet?
7. Expand: a.
HTTP, b. HTML
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