How Does the Internet Work

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Chapter 11

• How Does the Internet Work?

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How Important is this Chapter to Understanding
How to Use a Computer?

• 7 or 8 on a scale of 1 to 10

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How Important is this Chapter to understanding
how a computer works?

• 7 or 8 on a scale of 1 to 10

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What is the Internet?

• The Internet involves millions of computers
  connected in a complex way to a maze of local and
  regional networks.
• NOTE that when referring to THE internet, you
  should capitalize the first letter. When
  referring to a network that is configured
  similarly the word internet is not capitalized.

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Origins of the Internet

• 1969
• Department of Defense established, ARPANET, an
  experimental network connecting 4 research
  computers.
• 1980s
• National Science Foundation
• Only scientific, research and academic
  institutions
• NO commercial traffic
• Late 1990s
• Commercialization of the Internet.

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Other Developments

• 1989
• E-mail via CompuServe and MCI Mail
• 1991
• ISPs - Internet Service Providers (AOL, and
  others)
• NAPs - National Access Points
• National and International standards organizations

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Standards for the Internet

• Internet Society (ISOC)
• Internet Engineering Task Force (IETF)
• Internet Architecture Board (IAB)
• Internet Corporation for Assigning Names and
  Numbers (ICANN)

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Ownership and Operation

• No one owns the Internet.
• Revenue is required to offset the hardware,
  software, and maintenance costs.
• The cost must be covered by users.
• Organizations (ex. U of S)
• Individuals (ex. I pay for my connection at home)

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Whats the difference between the Internet and
the World Wide Web?

• Intuitive difference
• WWW is the multimedia portion of the net.
• Images, sounds, videos, animation, etc.
• Technical difference
• Web is the part of the Internet that contains Web
  Servers and Web sites.

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Internet Addresses

• Two designations
• Internet Protocol Address (IP number)
• 32 bit address consisting of 4 parts represented
  decimally.
• 134.198.168.8 is an example
• Each of the 4 numbers has a range from 0 to 255.
• These numbers are assigned by outside agency.
• E.g. Everything at the U of S starts 134.198
• Domain Name
• Descriptive name for IP address
• www.cil.cs.scranton.edu
• Also assigned by outside agency
• Specifically scranton.edu was assigned to the
  Universitys Web site. The rest was chosen by
  the University.
• Upper level domains (.edu in this example) are
  restricted in their use.

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More Addresses

• Ethernet Address (or Media Access Control
  Address)
• 48 bit address (6 bytes) that uniquely identifies
  each networking component in your computer.
• For example, my computer has both a wired and a
  wireless network connection, so it has two MAC
  addresses, one for each device.
• Each MAC address refers to a specific piece of
  hardware.
• Theoretically no two pieces of hardware have the
  same MAC address. BUT, its rumored that certain
  government agencies have special hardware that
  can change MAC addresses to fool communication.

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How does your computer go to the correct Web site?

• EXAMPLE at the U
• Browsers must use IP addresses not domain
  addresses. So the first step is to translate the
  domain address to an IP address.
• You type in www.cil.cs.scranton.edu into your
  browser.
• The browser goes to the Universitys Domain Name
  Server to look up the name.
• Since the name ends in scranton.edu, the name
  server knows that you are seeking a Web server on
  campus. So IT looks up the IP address and sends
  your browser that info and your browser goes to
  that site.

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How does your browser go the correct Web site
(continued)?

• Example at the U (continued)
• You type into your browser www.amazon.com.
• Your browser goes to the Universitys DNS to look
  up the name. It recognizes that the name does
  NOT end in scranton.edu and so it knows that that
  site in NOT on campus.
• So the Us DNS sends the request up the line to a
  higher level DNS which recognizes the location
  and sends back the IP addresss.

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IP Addresses

• Two types Dynamic and Static
• Static IP addresses remain the same. So a
  particular IP address will be associated with a
  particular domain name always.
• Dynamic IP addresses change. Each time you turn
  your computer on it will get a new IP address
  from a list of available addresses.
• Its sort of like a parking permit. The permit
  doesnt guarantee you a particular parking space
  just the right to park in a particular general
  area.
• The Dynamic IP address is obtained from a program
  called DHCP (dynamic host configuration protocol)
  which is located on the computer that you hook to
  when you connect to the Internet.

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What Browser should I use?

• There are many choices
• Internet Explorer
• Firefox, Mozilla, Netscape
• Opera
• The above three are all available in Windows and
  except for IE all are also available on mac and
  unix.
• Safari is the built in browser for macintosh
• Galeon and Konqueror are standards for unix.
• Which one should you use?
• Which ever one you like, but if you have a
  windows computer you should keep IE available
  since lots of Web programmers build sites that
  are not compatible with other browsers.

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How do Browsers work?

• They transfer documents according to hypertext
  transfer protocol (HTTP) or one of its
  derivatives.
• The pages are written in a programming language
  called HTML (HyperText Markup Language).
• Youre familiar with this from your Web page
  creation.
• There are other newer versions of HTML which can
  also be used.
• Scripting languages such as JavaScript can run on
  your browser to make a page interactive.
• PHP is a scripting language that runs on the
  server.

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Scripting Languages (continued)

• Client side processing (using JavaScript or the
  equivalent) lets your computer do the work and
  therefore is faster to use than sending things to
  Web sites and having the work done there and sent
  back.
• Its also more dangerous since it can be used to
  attack your computer.
• Its typically used for mouseovers and similar
  effects.
• Server side processing (such as PHP and ASP) is
  typically used for transmitting forms.

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Summary

• Every computer on the Internet has an address.
• This address can be given in two ways IP address
  and perhaps domain address.
• Computers must use IP addresses to communicate
  and typically for people domain addresses are
  more convenient so there has to be a way to
  translate from domain to IP. This is done using
  Domain Name Servers.
• IP addresses are assigned by external
  organizations. So are domain names. Some of the
  addresses can be chosen locally.

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Summary (continuted)

• Network hardware also has an address which is
  unique to each device.
• Web sites are downloaded using HTTP protocol
• Web sites are created using HTML or equivalent
  languages with client side interactivity using
  JavaScript or equivalent and server side
  programming using several different languages.
• There are many browsers available. But there are
  also many incompetent Web programmers, so you
  need to have access to Internet Explorer for at
  least some Web sites.

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Terminology

• Backbone
• Bandwidth
• Client-Side processing
• Domain Address
• Dynamic IP address
• DHCP
• DNS
• HTML

• ISP
• IP address
• MAC address
• NAP
• Node
• Server-side processing
• Static IP address
• Top-level domain