Thursday, November 29, 2012


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.

 

INSULATION

CONDUCTOR
 


 

 

 

 

 

 

 

 

 

 


           

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.

 

 

 

 

 

 

 

INSULATOR

CONDUCTOR
 


 

 

 


WIRE MESH
           


OUTER SHIELD









            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.

MENU BAR
 



TOOLBAR

BROWSER WINDOW


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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