How the Internet Works

1
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.

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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 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

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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 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.

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• URLs (Uniform Resource Locators) are the address
  of the WWW pages
• http//www.computing.dcu.ie/jkernan/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

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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 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)

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• Web Browsers
• Common Web Browser
• 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 Error 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 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)

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• 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.

10
File Transfer Protocol (FTP)

• 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.

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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
  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

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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
• 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

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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-mail
  address
• 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

• Disadvantages
• Misdirection
• Interception
• Forgery
• Overload
• Junk
• No response

• Advantages
• Convenience
• Speed
• Inexpensive
• Printable
• Reliable
• Global
• Generality
• Email Addresses
• Basic form of an email address is
  username_at_hostname.subdomain.domain

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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 by sending a subscribe message
  to the computer known as a list server
  (Listserv). It reads your e-mail and
  automatically subscribes 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.

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TELNET

• 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.

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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''

18
Newsgroups

• USENET is the worlds biggest electronic
  discussion forum, 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 particiapate 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.

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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 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.

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• 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.

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Chat Instant Messenging

• There are three commonly used types of chat. They
  are Instant Messaging, ICQ, and IRC.
• 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.) User 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
  _at_aol.com 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 http//www.aol.com/aim/
  home.html. The software and web site have
  detailed instructions on how to get started.
• 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.

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• 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.