§  You might take for granted that when you retrieve a file of information or send an e-mail message across the internet it will always reach its destination.

§  But sometimes it does not, because the process for sending information is extremely complex.

§  In orser for the Internet to work in connecting many different types of computers, software and files together, standardized rules called protocols must be used, that define how computers communicate.

§  A good example of an early communications protocol was Morse code.

§  The Protocol for the Morse code used standardized dots and dashes to communicate over telegraph lines by transmitting electrical impulses.

§  Internet Connections are made with a series of protocols called TCP/IP.

§  The TCP/IP (Transfer Control Protocol/Internet Protocol) defines the Internet as a Packet – Switched Network.

§  With a packet-switched Connection, There is no single, unbroken connection between sender and receiver, like there is with the telephone system.

§  The Telephone System is a connection-oriented, circuit – switched network.

§  When you make a telephone call, the switches at the telephone company set up a dedicated line between you and the person you call, for the duration of the call.

§  While you are using the line, no one else can; and if there is a problem on the network, you lose your connection.

§  A packet-switched network does not require two computers to establish a dedicated, unbroken connection for data transfer.

§  It instead breaks the data into small units or packets and transfers the packets over any phone or data lines that are currently available.

§  When you ask your browser to go to a specific Internet Address, or When you click on a hyperlink, the sending computer breaks the data you have asked for into packets.

§  Each Packet contains a piece of the data. Each packet is labelled with the addressed of the sending and receiving computers along with some instructions on how to put the data back together again once it has reached its destination.

§  The data in these small packets is transferred over phone lines or data lines.

§  The packets take different routes through a complex series of routers.

§  Each router examines the destination address and decides the best way to get the packets to their destination.

§  The packets eventually all reach their destination, your computer, and are put back together again, using the instructions they have been labelled with.

§  That is why it sometimes takes a while to load the data, before information appears on your screen.

§  Of Course, the speed of the data transfer depends on the type of network connection or modem you use.

§  All Internet Functions depend on protocols, which standardized how the data for those functions are transferred.

§  Such protocols include HTTP, FTP, Gopher and telnet etc.

§  They are being chosen according to their desired access and mode of the data transfer from one computer to another.

o    HTTP: HTTP stands for Hyper Text Transfer Protocol. This protocol is used for accessing World Wide Web Documents.

o    FTP: FTP stands for File Transfer Protocol. This protocol is used for transferring files from one computer to another.

o    Gopher: This protocol is used for accessing documents via Gopher Menus.

o    Telnet: This protocol allows the users to logon to a remote computer.

§  The World Wide Web uses HTTP to transfer data. The HTTP protocol contains commands that allow you to jump another hypertext document and retrieve the information in that document.

§  When you enter a URL in your browser window or click on a link, this sends an HTTP command to the web server described in the URL, and directs the server to send the requested file.

§  The computer language used to create hypertext documents is referred to as HTML.

§  HTML uses tags to format documents so that a web browser can read and display them.

§  Tags donate such features as headings, paragraphs, fonts, images, and hypertext links.

§  The HTML code behind any web document may be displayed in a browser window by selecting “Page Resource” on the “View” menu, or by right clicking the mouse and choosing “View Source”.

§  FTP developed in 1985, is a standard method of moving files from one computer to another on the Internet.

§  The transfer of files using FTP can work in either direction.

§  You may retrieve files from a remote server, or transfer files to a remote server, if you have been granted access to that server.


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