How The Internet Works 3n5h3q

How the Internet Works 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.

Components of the Internet 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 • Telnet • 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 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, 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 Common Errors with Browsers – Server Does Not Have A DNS Entry – 503 Service Unavailable – 403.9 Access Forbidden – Too Many s 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.

File Transfer Protocol (FTP) One of the most popular uses of the internet is to / 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 & • anonymous FTP sites (anonymous & email address as s) or automatic logon • Private FTP Sites ( number & ) – 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 number (or name) and

• 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 • ing opens a second link – data connection link (two modes ASCII mode or Binary mode) – Data Connection link closed auotmatically after data has been ed • File compression used for large file

Electronic Mail (E-mail) • Email uses the T/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 – T/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

Email: Advantages and Disadvantages Advantages • Convenience • Speed • Inexpensive • Printable • Reliable • Global • Generality

Disadvantages • Misdirection

• Interception • Forgery • Overload • Junk

• No response

Email Addresses Basic form of an email address is [email protected]

E-Mail Discussion Groups 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 ) – Unmoderated (wide open list) s must subscribe to a mailing list to , 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.

TELNET What is Telnet The Telnet protocol is often thought of as simply providing a facility for remote s 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 of a PC to to a host computer at another site on the Internet. The '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 (name and ). – 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''

Newsgroups 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 decides which newsgroup to carry – Special software to participate in newsgroups. – Moderated & Unmoderated Newsgroups • Moderated – human • Unmoderated – automatically posted to everyone – Subscribe \ Unsubscribe \ Read – Pictures and multimedia files can be posted – files must be specially encoded and then ed and unencode to view them.

HTTP (Hypertext Transfer Protocol) HTTP is a set of rules, or protocols which governs the transfer of hypertext between two or more computers.

The World Wide Web encomes 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 selects a hypertext link, the client program on their computer uses HTTP to 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.

Chat & Instant Messenging 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.) s must choose a nickname. The most popular form of IM is AOL Instant Messenger. AOL IM allows anyone who s 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 the person directly.

•No two people with AOL IM or AOL can have the same screen name. •AOL IM is free to 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 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.

3. • •

•

•

IRC - Internet Relay Chat Unlike AOL IM and ICQ, IRC (Internet Relay Chat) is not owned by any company. To use IRC, you need an IRC client program. IRC has many networks that are completely separate from one another. Some popular networks include The Undernet, EFnet, and DALnet. If you want to chat with someone on IRC, you need to make sure that both of you are on the same network (you can set it and change it each time your start your IRC program.) IRC has very few rules. You are allowed to say pretty much anything to want to pretty much anyone you want. For example, if you are on AOL, and someone keeps bothering you, you could report that screen name to the AOL company. There is no high authority on IRC, but there is still an ignore option to use if someone annoys you. Once you connect to an IRC network with an IRC client program, there are often thousands of rooms (they are called channels) on nearly any topic, and tens of thousands of different people to chat with.