The World Wide Web is the most popular part of the Internet by far. The Web allows rich and diverse communication by displaying text, graphics, animation, photos, sound and video. The Web physically consists of your personal computer, web browser software, a connection to an Internet Service Provider, computers called servers that host digital data, and routers and switches to direct the flow of information.

The Internet is comprised of many components such a Email, FTP and Usenet News. The World Wide Web is simply one of these components.

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 System

Hypertext browsing:

•Non-Linear structure (not a book)

•You read what you want next

•Click on Hypertext links to navigate the WWW

Features 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 words in text can be expanded at any time to provide other information about the word. Those words are links to other documents which may be text, file, pictures etc., Links can be identified by highlighted (underlined) and coloured text.

HTML (Hypertext Markup Language) is the language used to create WWW pages and associated links.

URLs (Uniform Resource Locators) are the addresses of the WWW pages

http://www.computing.dcu.ie/~cgreene/index.html

To view / read the WWW pages you must have a special application i.e. a web browser

A Web browser is an application program that provides a way to look at and interact with all the information on the World Wide Web.

Technically, a Web browser is a client program that uses the Hypertext Transfer Protocol (HTTP) to make requests of Web servers throughout the Internet on behalf of the browser user and then displays web pages by interpreting the HTML that is used to build thses pages on the web.

To publish and deliver information on the web you need a web Server

A web server is a program that runs on web sites and is responsible for 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 a web host. To use the web you must make an Internet connection and then 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 Browsers

Common 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 Chrome

Common 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 copernic

Utilities that search more than one search engine and/or subject directory at once and then compile the results in a consolidating uniform format and listing. Some offer added value features like the ability to refine searches, customize which search engines or directories are queried.

One of the most popular uses of the internet is to download/ upload files that is transfer files from a computer on the internet to your computer and 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 Convenience Speed Inexpensive Printable Reliable Global Generality

Email Addresses

Basic form of an email address is username@hostname.subdomain.domain

Disadvantages

• Misdirection

• Interception

• Forgery

• Overload

• Junk

• No response

Mailing Lists are a way for groups of people to have public Discussions 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 by sending a subscribe message to the computer known as a list server (Listserv). It reads your e-mail and automatically subscribes you to the list. You can unsubscribe from the list in the same way.

The Mailing List is a database of e-mail addresses who have subscribed.

What is Telnet The Telnet protocol is often thought of as simply providing a facility for remote logins to computer via the Internet. Telnet follows a Client / Server Model. You run a piece of software on your own PC (the client) to use the resources of a distant Server Computer (host computer).Telnet enables the user of a PC to login to a host computer at another site on the Internet. The user's 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 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. It provides a way for messages to be sent among computers across the entire Internet. People from all over the world participate in discussions on thousands of specific areas of interest called newsgroups

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 of hypertext between two or more computers.

The World Wide Web encompasses the universe of information that is 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 their computer uses HTTP to contact the server, identify a resource, and ask the server to respond with an action. The server accepts the request, and then uses HTTP to respond to or perform the action.

For example, when you select a hypertext link, you are identifying a particular resource, and asking the server to send it back to your computer 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 screen name. AOL IM is free to download from: http://www.aim.com/index.adp The software and web site have detailed instructions on how to get started.

2. ICQ ("I seek you")

ICQ is an extremely useful communication program. It allows you to send messages (chat), send files, send URLs, and more to anyone else 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.