Internet Concepts

1
Internet Concepts

• CIS 100 Introduction to Computers
• Mr. A. Craig Dixon
• Spring 2006

2
Networks and the Internet

• In order for two computers to communicate with
  each other, they must be connected in an
  arrangement called a network.
• The Internet is really just a network of networks.

3
Connecting to a Network

• Connecting to a network requires that special
  hardware be installed in your computer.
• There are two common connection devices.
• Modem short for modulator / demodulator
  connects computers using a standard telephone
  line
• Network interface card (NIC) connects computers
  using a special type of network cabling
• NICs are not synonymous with Ethernet cards. An
  Ethernet card is a particular type of NIC, and is
  the most popular in personal computers (PCs).
• Most of the time, these devices are internal
  hardware, although they are available as
  peripherals.

4
Communicating on a Network

• In order to communicate with another computer
  over a network, you must
• Use the set of rules governing communication over
  the network, called a protocol. Your computer
  will generally handle this.
• Know the address of the computer you want to
  communicate with.
• There are two types of network addresses
• Medium access control (MAC) address used inside
  a single network
• Internet protocol (IP) address used on the
  Internet
• There are protocols for finding these addresses
  (discussed later).

5
Internet Service Providers (ISPs)

• Most commonly, people connect to the Internet
  through an Internet Service Provider (ISP).
• ISPs charge a fee and provide the following
  services
• Adding your computer to the ISPs network,
  allowing you to communicate with other computers
  on the Internet
• Giving your computer an IP address, allowing
  other computers on the Internet to communicate
  with you
• Providing you access to a DNS server (discussed
  later)
• Many ISPs provide other services like email and
  web hosting as part of their service, but these
  are not required to access the Internet

6
Types of Internet Connections
7
Finding a Computer on the Internet

• So now that youre connected to the Internet, how
  do you find the computer you want to communicate
  with?
• You may think you have the computers address,
  (e.g. www.yahoo.com) but what you actually have
  is its uniform resource locator (URL).
• To understand how to get an IP address from a
  URL, we need to understand the basic structure of
  the Internet.

8
The Structure of the Internet

• Every computer connected to the Internet is in a
  zone.
• Zones are divided into domains and subdomains,
  making them hierarchical.
• At the top of the hierarchy is the root. All the
  computers on the Internet are in roots zone.
• Roots zone is divided into top-level domains
  (TLDs). You may recognize their names.
• TLDs com, net, org, edu, gov, mil, and others
• Each TLD is divided into subdomains. You may also
  recognize some of these.
• TLD subdomains yahoo, google, kctcs, ebay, and
  many others
• Subdomains can be further divided until they
  reach a server, the main computer in a given
  network.

9
Internet Structure Visualized
Root zone
root
Com zone
Yahoo zone
WWW server
com
org
net
edu
bellsouth
yahoo
w3c
hypercon
kctcs
uky
www
www
mail
www
10
Uniform Resource Locators (URLs)

• Now you are probably beginning to see how a URL
  is constructed, but lets take a closer look.
• Consider the URL for our classs website
• http//www.madisonville.kctcs.edu/facstaf/cdixon/c
  is100/index.html

• http stands for hypertext transfer protocol, the
  protocol for retrieving web pages
• www is the name of the server
• madisonville is a subdomain of kctcs
• kctcs is the subdomain of edu
• edu is the top level domain
• /facstaf/cdixon/cis100 is the name of the folder
  (or directory) on the server where the page is
  stored. This part of the URL is called the path.
• index.html is the name of the file we want to see

11
The Domain Name System (DNS)

• As mentioned earlier, your ISP gives you access
  to one or more DNS servers.
• When you try to find a web page using a URL, you
  must first submit the URL to a DNS server so it
  can resolve the URL into an IP address.

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DNS An Example

• Suppose your ISP is BellSouth (www.bellsouth.com).
  
• The DNS server provided by BellSouth is
  authoritative for any computer in the zone
  bellsouth. This means it knows the IP address of
  any server in the domain bellsouth or any of
  bellsouths subdomains.
• If you try to reach www.kctcs.edu, BellSouths
  DNS server does not know how to reach this server
  (i.e. it is unauthoritative) because kctcs is not
  in zone bellsouth.
• BellSouths DNS server must ask the server above
  it (i.e. coms DNS server) to help. But kctcs is
  not in zone com either. (It is in zone edu.)
  Therefore, com must ask the server above it
  (root).
• Every computer is in zone root, but root cannot
  store all of the IP addresses on the Internet. It
  can, however, point coms DNS server to edus DNS
  server, which it does.
• Now your request passes through edus DNS to
  kctcss DNS, which returns to you the IP address
  of the requested server (www).

13
DNS Example Visualized
root
com
org
net
edu
bellsouth
yahoo
w3c
hypercon
kctcs
uky
you
www
your request
14
The Client-Server Relationship

• Once you have located the computer you wish to
  communicate with (the remote host), your computer
  (the local host) will attempt to establish a
  channel of communication between the two.
• In most cases, the local host is requesting
  information (such as the content of a web page)
  from the remote host.
• We call the requesting computer the client and
  the responding computer the server therefore,
  this type of relationship between the hosts is
  called a client-server relationship.

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What is a Web Page?

• Now youve got the page you want. So, what is it?
• Web pages, by and large, are constructed using a
  special language called hypertext markup language
  (HTML).
• HTML is text-only. So how are you able to see
  colors, links, and graphics?

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Browsers

• Web pages are viewed using a program called a
  browser.
• The most common browser by far is Microsofts
  Internet Explorer, which commands approximately
  86 of the market.
• Released in November 2004, Mozilla Firefox has
  made rapid gains in popularity, garnering almost
  a 10 market share at last check. (Its also my
  personal favorite.)
• Apple Macintoshs Safari browser is also making
  gains, and figures to rise even more prominently
  with Microsofts announcement that it will no
  longer develop a version of Internet Explorer for
  Apple Macintosh computers.
• Another player in the browser market figures to
  be the Opera browser, especially if the rumored
  purchase of Opera by search engine Google comes
  to fruition.
• The once-dominant Netscape Navigator browser has
  been steadily losing popularity many experts
  consider it a dead browser, despite AOLs attempt
  to resurrect it.
• A browser is a program that renders the HTML
  page. This means it interprets the HTML text to
  determine how text, graphics, etc. should be
  displayed.

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HTML An Example
What the browser sees
What you see

• Hello, World!
• 
  
• This text is red.
• 
  
• Go to kctcs.edu.

Hello, World! This text is red. Go to kctcs.edu.
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More on Browsers

• Because it is up to the browser to decide how the
  HTML should be rendered, some pages look
  differently when viewed with different browsers.
• Some parts of HTML work in one browser, but not
  in another.
• The World Wide Web Consortium (W3C) has tried to
  establish standards for HTML that all browsers
  should support, although browser makers
  (especially Microsoft) have bucked this trend.
• A good web page designer will test his or her
  page in several browsers before publishing it.
• As web content grows to include Flash animations,
  Java Applets, CGI scripts, and the like, these
  differences are likely to widen.

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Anatomy of a Browser
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Hyperlinks

• The true power of HTML lies in the use of
  hyperlinks.
• Any text or graphic can be enhanced with a
  hyperlink. When a hyperlinked object is clicked,
  the browser requests another resource (web page,
  Word document, etc.) either from the same server
  or from a completely different one.
• This allows quick and easy navigation between web
  pages.
• There are three ways to recognize a hyperlinked
  object.
• Most browsers render hyperlinked text in blue and
  underline it. Hyperlinked graphics have a blue
  border.
• The browsers status bar shows the URL of the
  resource linked to by the hyperlink.
• The browser changes the cursor, usually to a
  hand.
• All three of these behaviors can be overridden by
  the pages author, but at least one usually isnt
  so the user can clearly tell which objects are
  hyperlinked.

21
Browser Cache

• In the interest of speed, most browsers will
  cache web pages the first time they are visited.
• On subsequent visits, if the browser determines
  that the page has not been modified, it displays
  the cached copy instead of requesting the page
  from the server.
• Occasionally, the browser does not detect a
  change that occurred. If you do not believe you
  are seeing the most up-to-date information, click
  your browsers Refresh or Reload button to force
  the browser to request the page from the server.

22
Web Sites That Know You

• Some web sites appear to remember your
  preferences on subsequent visits. This is
  primarily accomplished in one of two ways.
• A server-side database stores your preferences.
  When you visit the site, you enter a username and
  password, and your preferences are loaded from
  the database.
• On your first visit, the site silently places a
  small text file (called a cookie) on your hard
  drive. This file contains your preferences and is
  automatically loaded by the site when you visit
  it again.
• Use of cookies can be turned off in your browser,
  but many sites require that it be turned on in
  order to function.
• Many privacy advocates are opposed to cookies.
• Some browsers and third-party applications offer
  to remember your passwords. This is not tied in
  any way to the web site itself.

23
Search Engines

• With such a vast quantity of information on the
  Internet, how can you find what you are looking
  for?
• There are many sites on the Internet called
  search engines.
• At the minimum, a search engine allows the user
  to type in a word or phrase to search for, then
  returns results that it determines most closely
  match the users request. The users request is
  called a query. Each individual result is called
  a hit.
• Some popular search engines are Yahoo, Google,
  AltaVista, and Ask Jeeves.
• Search engines are constantly updating their
  knowledge of information on the Internet using
  spiders.
• Spiders are programs that crawl the Internet
  (i.e. follow all possible links and reporting the
  information found there back to the search
  engine.)
• Some search engines do not use spiders. Instead,
  they query many other search engines and combine
  the list of hits. These engines are called
  meta-search engines.
• Some popular meta-search engines are Dogpile,
  MetaCrawler, and Excite.

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Search Engine Tips
Many users find that they cannot narrow their
searches enough to find useful results. Below are
some ways to get more relevant hits.

• Use quoted phrases.
• If you are looking for Microsoft Windows, type
  Microsoft Windows (with quotes) instead of
  Microsoft Windows (without quotes.)
• The former searches for pages that contain the
  phrase Microsoft Windows, while the latter
  searches for pages containing both the words
  Microsoft and Windows anywhere in the page.
• Use Boolean operators like OR and NOT
• If you want information about bay windows, you
  may want to search for windows NOT microsoft.
  (Notice the Boolean operator is in all caps some
  search engines require this.)
• Use as many keywords as possible
• You can always reduce the number of keywords
  later if you didnt find what you were looking
  for.

25
Email

• One of the most popular uses for the Internet is
  sending and receiving email.
• To send and receive email, you need an email
  account. This will include at least two things
• An email address of the form username_at_domainname.t
  ld.
• Mail storage where your incoming messages are
  stored.
• While most ISPs provide a small amount of
  storage for email (
  services like Yahoo Mail, Hotmail, and GMail
  allow users 2 GB or more of storage.
• A person may have numerous email accounts.

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Using Email

• There are two ways to access an email account.
• With a mail client like Outlook, Eudora, Mozilla
  Thunderbird, or Zimbra
• Must be configured for each email account
• Downloads messages to your local machine
• Through a web mail interface (if your email
  provider has one)
• Can be accessed from any computer connected to
  the Internet with no extra configuration
• Messages stay on the mail server

27
File Transfer

• Files can be transferred from one computer to
  another over the Internet using the file transfer
  protocol (FTP).
• The process of transferring a file from a remote
  host to your local machine is called downloading.
• The process of transferring a file from your
  local machine is called uploading.
• Most browsers natively support downloading, but
  uploading often requires a special utility called
  an FTP client.

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Downloading with an Internet browser

• Right click the link for the resource you want to
  download.
• A context menu will appear. Choose Save Target
  As (Internet Explorer) or Save Link As
  (Firefox).
• A save dialog will appear. Choose where you want
  to save the file.
• Change the filename if desired, then click Save