Friday, February 15, 2013

The Internet

It is a system with billions of users worldwide. It permits communication and sharing of all types of information between any two or more computers connected through a large and complex network. It was started in 1960’s and opened for public use in 1990’s. With the passage of time it has witnessed tremendous growth and it is still expanding its reach. Its applications include

(i) E mail – It permits exchange of text/graphic material using email software. We can write a letter and send it to the recipient through ISP’s (Internet Service Providers) who work like the dispatching and receiving post offices.

(ii) File transfer – A FTP (File Transfer Programmes) allows transfer of files/software from one computer to another connected to the Internet.

(iii) World Wide Web (WWW) – Computers that store specific information for sharing with others provide websites either directly or through web service providers. Government departments, companies, NGO’s (Non-Government Organisations) and individuals can post information about their activities for restricted or free use on their websites. This information becomes accessible to the users. Several search engines like Google, Yahoo! etc. help us in finding information by listing the related websites. Hypertext is a powerful feature of the web that automatically links relevant information from one page on the web to another using HTML (hypertext markup language).

(iv) E-commerce – Use of the Internet to promote business using electronic means such as using credit cards is called E-commerce. Customers view images and receive all the information about various products or services of companies through their websites. They can do on-line shopping from home/office. Goods are dispatched or services are provided by the company through mail/courier.

(v) Chat – Real time conversation among people with common interests through typed
messages is called chat. Everyone belonging to the chat group gets the message
instantaneously and can respond rapidly.

Facsimile (FAX)
It scans the contents of a document (as an image, not text) to create electronic signals. These signals are then sent to the destination (another FAX machine) in an orderly manner using telephone lines. At the destination, the signals are reconverted into a replica of the original document. Note that FAX provides image of a static document unlike the image provided by television of objects that might be dynamic.

Mobile telephony
The concept of mobile telephony was developed first in 1970’s and it was fully implemented in the following decade. The central concept of this system is to divide the service area into a suitable number of cells centred on an office called MTSO (Mobile Telephone Switching Office). Each cell contains a low-power transmitter called a base station and caters to a large number of mobile receivers (popularly called cell phones). Each cell could have a service area of a few square kilometers or even less depending upon the number of customers. When a mobile receiver crosses the coverage area of one base station, it is necessary for the mobile user to be transferred to another base station. This procedure is called handover or handoff. This process is carried out very rapidly, to the extent that the consumer does not even notice it. Mobile telephones operate typically in the UHF range of frequencies (about 800-950 MHz).