The World Wide Web is the mostpopular part of the Internet by far.The Web allows rich and diversecommunication by displaying text,graphics, animation, photos, soundand video. The Web physicallyconsists of your personal computer,web browser software, aconnection to an Internet ServiceProvider, computers called serversthat host digital data, and routersand switches to direct the flow ofinformation.
The 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 Usenet News HTTP Chat & Instant Messenging
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 betext, file, pictures etc., Links can be identified by highlighted(underlined) and coloured 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. Entire suites built around browsers including modules for reading newgroups, for sending/receiving e-mail Multimedia files – helper applications (plug-ins)
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 browser Google ChromeCommon Errors with Browsers 503 Service Unavailable 403.9 Access Forbidden – Too Many Users are Connected Spinning Hourglass 404 Not Found 401 Unauthorised and 402 Forbidden
Search Engine Lycos & Alta Vista (index based engines) Yahoo (directory based search engine) Google (index based) Ask Jeeves (natural language search engine)Index based search Engines built by computer robot programs (“Spiders") -- not by human selection NOT organized by subject categories -- all pages are ranked by a computer algorithm contain full-text (every word) of the web pages they link to -- you find pages by matching words in the pages you want huge and often retrieve a lot of information -- for complex searches use ones that allow you to search within results (sub searching)
Meta Search Engines Metacrawler copernicUtilities that search more than one search engine and/or subjectdirectory at once and then compile the results in a consolidating uniformformat and listing. Some offer added value features like the ability torefine searches, customize which search engines or directories arequeried.
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 Logon & 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.
FTP Daemon runs on FTP Server handling all FTP transactions, the deamon will ask for an account number (or username) and password Connection command link is opened between your computer and the FTP server when you logon to a FTP site and remains open until explictly closed by user Downloading opens a second link – data connection link (two modes ASCII mode or Binary mode) Data Connection link closed auotmatically after data has been downloaded File compression used for large file
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
Encryption for E-Mail Privacy Public & Private Keys most common form of encryption How E-Mail Spam Works Spam is Unsolicitied Junk E-mail Blocking Spam Write back to Spammer and asked to be removed E-mail Software filters e-mail addresses ISP like AOL block spammers from sending bulk mail to subscribers Ensure that your email address isn’t added to spam list Notify e-mail directories to remove your e-mail address When posting to usenet newsgroups edit your header so that it doesn’t contain your e- mail address
Advantages Disadvantages Convenience • Misdirection Speed • Interception Inexpensive • Forgery Printable • Overload Reliable Global • Junk Generality • No responseEmail AddressesBasic form of an email address is email@example.com
Mailing Lists are a way for groups of people to have publicDiscussions via e-mail.Mailing lists can be moderated or unmoderated. Moderated (screened by the list moderator) Unmoderated (wide open list)Users must subscribe to a mailing list to join, this is achieved bysending a subscribe message to the computer known as a listserver (Listserv). It reads your e-mail and automatically subscribesyou to the list. You can unsubscribe from the list in the same way.The Mailing List is a database of e-mail addresses who havesubscribed.
What 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 on your own PC (the client) touse the resources of a distant Server Computer (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 attachedto the remote host. To use telnet you need to know the internet addressof the host whose resources you want to use.Some practical uses of Telnet include: Telnet is a Protocol that lets you use the power of the Internet to connect you to databases, library catalogs, and other information resources around the world. Telnet lets you connect directly to another computer on the Internet and run programs on the computer (provided you have access permission (Username and Password). Theoretically you have a lot of power at your fingertips. Your dumb terminal or very old PC can run programs on the worlds most powerful computers.
Telnet may have a few practical drawbacks also Telnet is old. It is text based only. You have to know how to run programs at the other end. Different Computer Systems Different Commands, Directory Structures Different Language -- Programming and ``spoken
USENET 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 Special software to participate in newsgroups. 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 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.
When a user selects a hypertext link, the client program on theircomputer uses HTTP to contact the server, identify a resource, andask the server to respond with an action. The server accepts therequest, and then uses HTTP to respond to or perform the action.For example, when you select a hypertext link, you are identifying aparticular resource, and asking the server to send it back to yourcomputer in a format that your computer can display.
There are three commonly used types of chat. They are Instant Messaging, ICQ, and IRC.1. Instant 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.) Users must choose a nickname. The most popular form of IM is AOL Instant Messenger. AOL IM allows anyone who downloads their free software to choose a nick(name) (AOL calls their nicks Screen names) and chat with anyone else with AOL IM or the America Online Service itself. Nearly everyone with America Online is reachable by AOL IM. If you see an AOL e-mail address, you can often cut off the @aol.com to get the IM screen name to contact the person directly.
No two people with AOL IM or AOL can have the same screenname.AOL IM is free to download from: http://www.aim.com/index.adp The software and web site have detailed instructions on how to getstarted.2. ICQ ("I seek you")ICQ is an extremely useful communication program. It allows you tosend messages (chat), send files, send URLs, and more to anyoneelse with ICQ. When you download ICQ (which is free) you are assigned an ICQ number. Two or more people using ICQ can have the same nickname, but no two people can have the same ICQ number.
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