How the Internet

8/13/2019 How the Internet

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How the Internet Works

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.


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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 thesecomponents.

World Wide Web (World Wide Web is like an InternetLibrary with millions of books)

FTP

E-mail & E-mail Discussion Groups Telnet Usenet News HTTP Chat & Instant Messenging


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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)


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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.


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URLs (Uniform Resource Locators) are the addresses of the WWW pageshttp://www.computing.dcu.ie/~cgreene/index.html

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

A 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 throughout theInternet 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 Server

A web se rver i s a p rogram tha t runs o n w eb s i t es and i s respons ib lefor replying to a web bro ws ers request for f i les


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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 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 onscreen, they can also display programs, animation, graphics,

video-conferencing, download files etc., Browsers also allowyou 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)


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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 (Microsofts 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 Users are Connected

Spinning Hourglass 404 Not Found 401 Unauthorised and 402 Forbidden


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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 humanselection

NOT organized by subject categories -- all pages are ranked by acomputer algorithm

contain full-text (every word) of the web pages they link to -- youfind pages by matching words in the pages you want

huge and often retrieve a lot of information -- for complex searchesuse ones that allow you to search within results (sub searching)


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Meta Search Engines Metacrawler copernic

Utilities 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.


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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 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 othersoftware programs such as WS_FTP95 are simpler and easierto use.


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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 computerand the FTP server when you logon to a FTP site and remainsopen until explictly closed by user

Downloading opens a second link data connection link (twomodes ASCII mode or Binary mode) Data Connection link closed auotmatically after data has

been downloaded

File compression used for large file


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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 thenext

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


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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 isnt added to spam list

Notify e-mail directories to remove your e-mailaddress When posting to usenet newsgroups edit your header

so that it doesnt contain your e -mail address


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Email: Advantages and Disadvantages

Advantages Convenience Speed Inexpensive Printable Reliable Global Generality

Email AddressesBasic form of an email address is

[email protected]

Disadvantages

Misdirection

Interception

Forgery

Overload

Junk

No response


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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 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 l i s t s erver(Listserv). It reads your e-mail and automatically subscribes you tothe list. You can unsubscribe from the list in the same way.

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


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TELNET

What is Telnet

The Telnet protocol is often thought of as simply providing a facility forremote logins to computer via the Internet. Telnet follows a Client / ServerModel. You run a piece of software on your own PC (the client) to use theresources 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 user's PC then acts as a dumb terminal attached

to 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 dumbterminal or very old PC can run programs on the worlds most powerful

computers.


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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''


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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 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 toview them.


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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 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 aconnection to "computer B" (the server) and make a request.The server accepts the connection initiated by the client andsends back a response.

An HTTP request identifies the resource that the client is

interested in and tells the server what "action" to take on theresource.


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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.


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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.) Users must choose a nickname.The most popular form of IM is AOL Instant Messenger. AOL IMallows anyone who downloads their free software to choose anick(name) (AOL calls their nicks Screen names) and 'chat' withanyone else with AOL IM or the America Online Service itself.

Nearly everyone with America Online is reachable by AOL IM. Ifyou see an AOL e-mail address, you can often cut off [email protected] to get the IM screen name to contact the person directly.


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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 tosend messages (chat), send files, send URLs, and more to anyoneelse with ICQ.

When you download ICQ (which is free) you are assigned anICQ number. Two or more people using ICQ can have thesame nickname, but no two people can have the same ICQnumber.


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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 needto make sure that both of you are on the same network (you canset 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 couldreport that screen name to the AOL company. There is no highauthority on IRC, but there is still an ignore option to use ifsomeone annoys you.

Once you connect to an IRC network with an IRC client program,there are often thousands of rooms (they are called channels) onnearly any topic, and tens of thousands of different people tochat with.

How the Internet

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