How the Internet WorksThe World Wide Web is the mostpopular part of the Internet by far.- Web allows rich and diversecommunication by displaying text,graphics, animation, photos, soundand video.- Web physically consists of yourpersonal computer, web browsersoftware, a connection to anInternet Service Provider, Serverthat hosts data, routers andswitches to direct the flow ofinformation.
Components of the InternetThe Internet is comprised of many components such a Email, FTP andUsenet News. The World Wide Web is simply one of thesecomponents. • World Wide Web (World Wide Web is like an Internet Library with millions of books) • FTP • E-mail & E-mail Discussion Groups • Telnet • Usenet News • HTTP • Chat & Instant Messaging
What is the World Wide Web?One simple definition of the WWW is:The WWW is a Hypertext Information SystemHypertext browsing: •Non-Linear structure (not a book) •You read what you want next •Click on Hypertext links to navigate the WWWFeatures of the WWW are: •Graphical •Easy to use •Cross Platform •Distributed •Dynamic •Interactive (forms, Java)
What is Hypertext?Hypertext is a method of presenting information, where selected wordsin text can be expanded at any time to provide other information aboutthe word.Those words are links to other documents which may be text, file,pictures etc., Links can be identified by highlighted (underlined) andcoloured text.HTML (Hypertext Markup Language) is the language used to createWWW pages and associated links.
URLs (Uniform Resource Locators) are the addresses of the WWWpages http://www.computing.dcu.ie/~cgreene/index.htmlTo view / read the WWW pages you must have a special application i.e. aweb browserA Web browser is an application program that provides a way to look atand interact with all the information on the World Wide Web.Technically, a Web browser is a client program that uses the HypertextTransfer Protocol (HTTP) to make requests of Web servers throughoutthe Internet on behalf of the browser user and then displays web pages byinterpreting the HTML that is used to build thses pages on the web.To publish and deliver information on the web you need a web ServerA web server is a program that runs on web sites and is responsiblefor replying to a web browsers request for files
The Web works on a client / server model in which client software(Browser) runs on a local computer. The Server software runs on aweb host. To use the web you must make an Internet connection andthen launch your web browser. – Type the URL you want to visit – Browser makes a connection to a server using HTTP protocol – The Server then • Accepts the connection • Sends the file contents back to browser, and • Closes the connection – Web browsers interpret the html pages and display them on screen, they can also display programs, animation, graphics, video-conferencing, download files etc., Browsers also allow you to create and publish web pages.
Web BrowsersCommon Web Browsers – Mosaic – first graphical browser – Netscape Navigator (First commercial browser, originally known as Mosaic Navigator as originated from Mosaic) – Internet Explorer (Microsoft’s browser) – Lynx – text only browserCommon Errors with Browsers – Server Does Not Have A DNS Entry – 503 Service Unavailable – 403.9 Access Forbidden – Too Many Users are Connected – Spinning Hourglass – 404 Not Found – 401 Unauthorised and 402 Forbidden
File Transfer Protocol (FTP)One of the most popular uses of the internet is to download/ upload filesthat is transfer files from a computer on the internet to your computerand vise versa. – Various types of files (executable programs, graphics, audio, text) – Different types of FTP Sites all use Login & Password • anonymous FTP sites (anonymous & email address as passwords) or automatic logon • Private FTP Sites (account number & password) – FTP runs on a Client / Server model. • windows has a client command-line FTP program, but other software programs such as WS_FTP95 are simpler and easier to use.
Electronic Mail (E-mail)• Email uses the TCP/IP protocol• SMTP (Simple Mail Transfer Protocol) – File attachments (binary Files) • MIME (Multipurpose Internet Mail Extension) • Uuencode (Unix to unix encoding)• How e-mail is delivered – TCP/IP – Gateways translate email formats from one network to the next – Routers internal / external (firewall)• E-mail Software – Mail Clients – Eudora, MS Exchange • Create folders, search through messages, address books, mailing lists – Most e-mail software reads HTML- based pages (links)• Mail Server
Email: Advantages and DisadvantagesAdvantages Disadvantages• Convenience • Misdirection• Speed • Interception• Inexpensive • Forgery• Printable • Overload• Reliable • Junk• Global • No responseEmail AddressesBasic form of an email address is firstname.lastname@example.org
TELNETWhat is TelnetThe Telnet protocol is often thought of as simply providing a facility forremote logins to computer via the Internet.Telnet follows a Client / Server Model. You run a piece of software onyour own PC (the client) to use the resources of a distant ServerComputer (host computer).Telnet enables the user of a PC to login to a host computer at anothersite on the Internet.The users PC then acts as a dumb terminal attached to the remote host.To use telnet you need to know the internet address of the host whoseresources you want to use.
NewsgroupsUSENET is the worlds biggest electronic discussion forum. Itprovides a way for messages to be sent among computers acrossthe entire Internet. People from all over the world participate indiscussions on thousands of specific areas of interest callednewsgroups – Global bulletin Board and discussion area. – Usenet and all messages are stored on a Usenet Server – Different Hierarchies of Newsgroups exist. • Subcategories – Internet site Administrator decides which newsgroup to carry – Moderated & Unmoderated Newsgroups • Moderated – human moderator • Unmoderated – automatically posted to everyone – Subscribe Unsubscribe Read – Pictures and multimedia files can be posted – files must be specially encoded and then downloaded and unencode to view them.
HTTP (Hypertext Transfer Protocol)HTTP is a set of rules, or protocols which governs the transfer ofhypertext between two or more computers.The World Wide Web encompasses the universe of information thatis available via HTTP. – HTTP is based on the client/server principle. – HTTP allows "computer A" (the client) to establish a connection to "computer B" (the server) and make a request. The server accepts the connection initiated by the client and sends back a response. – An HTTP request identifies the resource that the client is interested in and tells the server what "action" to take on the resource.
Chat & Instant MessagingInstant Messaging Instant messaging (IM) is one of the most popular forms of chat. Most of the time, instant messaging is just between two people, although most IM software can handle group chats (with 3 or more people.)