Internet Lesson

Slides are at: http://laughton.com/obrien/sjsu/cse/workshop/lesson_internet.html

Download the lesson at: http://laughton.com/obrien/sjsu/cse/workshop/internet_html.zip

adapted from a lecture by Cay Horstmann

What Is The Internet?

• The Internet
  • A newwork connecting computers
  • The communication lines connecting more than 3 billion computers.
• Developed by DARPA for sharing computer resources
  • stands for Defense Advanced Research Projects Agency
  • part of the Department of Defense

  • 

The Internet

• First used by the US government and large universities
• Became popular because of email
• Exploded with the advent of the Web

The Internet - IP Address

• Every computer on the Internet has a number
  • IP address (Internet Protocol address)
    • Google's IP address: 74.125.239.49
    • San Jose State's IP address 130.65.10.101
    • IP address of my domain (laughton.com:) 216.71.185.45
  • think of an IP address like a phone number
• Computers use IP addresses to communicate to each other
• Try entering the number 74.125.239.49 in the address bar of your browser

The Internet - Domain Name

• Numbers are hard for people to remember
• Every computer also has a name cLled the domain name
  • Most people use domain name mostly for the Web
    • www.google.com
    • www.sjsu.edu
• When you type www.google.com into your Web browser:
  • the request goes first to a Domain Name Server - DNS
  • it looks up the ip address of www.google.com (74.125.239.49)
  • sends it back to your computr
  • then the request is sent to that ip address

Domain Name Server in Action

*from http://computer.howstuffworks.com/

Domain Names

Common top level domain names

• COM -- commercial Web sites, though open to everyone
• NET -- network Web sites, though open to everyone
• ORG -- non-profit organization Web sites, though open to everyone
• EDU -- restricted to schools and educational organizations
• MIL -- restricted to the U.S. military
• GOV -- restricted to the U.S. government
• LY, UK, RU and other two-letter country codes

 

Difference between Internet and Web

• Many people used the words "Internet" and "Web" interchangeably
• But there is a difference
• The Internet is the pathway
• The Web is a system of interlinked hypertext documents
  • These documents can be access over the Internet pathways

Internet Analogy

• Think of the Internet as a highway system
• A highway system by itself is just a bunch of paths
• But many different types of vehichles can travel the highway system
  • cars, trucks, motorcylces, bicycles
• Similarly, the Internet is just a pathway
• Many different services ride the Internet
• Only one is the World Wide Web

Some Services That Ride the Internet

• World Wide Web (the most familiar)
• Email service (not web-based)
• FTP - File Transfer Protocol
• Fax over IP
• Voice over IP
• Instant Messaging

Client / Server Architecture

• The services on the Internet are based on communicate between a client and a server.
  • called client/server architecture

    

• A clent requests a service and a server provides the service.
• The client and the server communticate using a specific protocol
• Many protocols on the Internet

What is a "protocol"

• A set of rules by which two computers communicate
• Determines how data is transmitted in telecommunications and computer networking
• Email -
  • POP3 - receiving mail. Post Office Protocol
  • SMTP - sending mail, Simple Mail Transfer Protocol
• FTP
  • File Transfer Protocol
  • Requires an FTP client on user's computer
  • Look at add-on to Chrome
• World Wide Web
  • uses HTTP - Hyper Text Transfer Protocol

Sending data on the Internet

• Packet Switching
  • The process by which stuff is sent from one computer to another
• A message is broken into small chunks and numbered by the sender
• The packets are sent on their way (according to the protocol)
• The packets are passed from node to node
• All packets usually take the same route to reach its destination
  • but if there is a problem, an alternate route is used
  • this keeps the Internet running even when there are local outages
• When all packets are received, the message is reassembled

Sending data on the Internet

• Packet switching is part of TCP/IP communications protocol
  • decentralized
  • increases network efficiency
  • makes a more robust network
    • A packet can be sent from one machine to another over many paths
    • This was praticularly important to the Department of Defense at the inception of the Internet
• Activity - packet switching

Traceroute

• A diagnostic tool for showing the route and measuring the time taken to access a remote node (computer, router, etc)
• Shows each node the packet takes from client to server.
• traceroute to laughton.com from my house

  

Using traceroute

• Mac OSX
  • open Network Utilities.app
    • up through 10.8 in /Applications/Utilities/
    • from 10.9 in /System/Library/CoreServices/Applications/
      • easies to search in Spotlight
  • click Traceroute tab
  • enter the domain name in the textbox
    • i.e. www.laughton.com
• Windows
  • open a command prompt
    • up through Windows : click Start -> All Programs-> Accessories -> Command Prompt
    • from Windows 8 on: from the Start screen type command prompt and press enter
  • type: tracert [domain name]
    • i.e. tracert www.laughton.com
    • notice the spelling

The World Wide Web

• System of interlinked hypertext documents
• Stored on computers all over the world called web servers
• Accessed through the Internet.
• Using a web browser as the client, you request web pages from the server
• The server returns the requested page to the client
• The page may contain text, images, videos, and other multimedia
• You can navigate between pages using hyperlinks.
• (from wikipedia.org)

The process

• You type www.google.com into your web browser (client)
  • Sends an HTTP request
• The request is routed to Google's web server (server)
  • A web server is software that can serve web pages
  • That means, it can get the requested page and return it to the computer that requested it.
• The web server finds the document requested and
  • sends it back in an HTTP response
• Then the connection is broken

HTTP Process

• Web client (better known as a "browser") communicates with a Web server
  • uses Hyper Text Transfer Protocol (HTTP)
• Client connects to web server (e.g. http://www.sjsu.edu/index.html)
  • Sends a HTTP Request: GET /index.html
• Web server locates the HTML page
  • sends the page back in an HTTP Response
• Client disconnects from web server

HTTP is a stateless protocol

• Treats each request as an independent transaction
• Unrelated to any previous request
• Communication consists of independent pairs of requests and responses.
• Neither side remembers anything about the last transaction

The Problem of Statelessness

• So how does Amazon.com remember you and greet you by name?
• How can it remember all the things you want to buy?
• Stateless protocol makes it hard to implement things like shopping cart
• You tell browser to visit a store page
• Browser connects, gets the page, disconnects, shows the page
• You click on "add to cart" link
• Browser connects again. Server says “Who are you?”
• How can server remember you?
• Cookies!

Cookies

• Little text file a server can ask the browser to store on your computer
• Can contain information about you and the current visit

Cookies

• You tell browser to visit store page
• Server says “Hello stranger, next time you connect, give me this number: 42385”
• Browser gets the page, disconnects, shows page
• You click on "add to cart" link
• Browser connects again and says “Hello server, the number is 42385. Give me this page.”
• Can also be used to remember your name, etc

Look at your cookies

• Chrome
  • Chrome>preferences> Advanced Settings (on Mac)
  • under Privacy, click Content Settings...
  • Click All cookies and site settings

Google Search Engine

• How can it find all those pages so fast?
• It “crawls”the web (web crawler)
  • gets a page and reads its links
  • ...and then gets those pages...
  • ...and follows the links in them.
• It indexes all this information and stores in a massive database using a very large number of computers

• Google Data Centers
  

 

Web pages

• Written using HTML
  • HyperText Markup Language
• Web browsers know how to render the HTML text into a webpage

Crawling the Web

Possible projects

• Create a model of a network
• Create a drawing of a network
• Write a short paper on
  • Domain name server
  • ARPANET
  • TCP/IP

 

Web Lesson

HTML

• Hyper Text Markup Language
• The language of the web
• Plain text, with tags to denote styles, fonts, colors, etc.
  • header <h1> to <h6>
    • <h1>Welcome to my page!</h1> 
  • paragraph <p>
  • other
    • <b>Bold this word</b>
• Most tags have a start and end part
• Besides displaying text, you can have images
  • <img src="http://horstmann.com/sjsu/spring2008/cs40/tower-hall.jpg" />
• Links look like this
  • <a href="http://www.sjsu,edu/index.html">SJSU</a>

HTML

• Hyper Text Markup Language
• The language of the web
• Plain text, with tags to denote styles, fonts, colors, etc.
  • header <h1> to <h6>
    • <h1>Welcome to my page!</h1> 
  • paragraph <p>
  • other
    • <b>Bold this word</b>
• Most tags have a start and end part
• Besides displaying text, you can have images
  • <img src="http://horstmann.com/sjsu/spring2008/cs40/tower-hall.jpg" />
• Links look like this
  • <a href="http://www.sjsu,edu/index.html">SJSU</a>

Your Assignment

• download FileZilla (an FTP client)
  • https://filezilla-project.org/
• go to File/Site Manager
• Click New Site
  • name the site
  • enter this information
  • Host: ftp.laughton.com
  • port: 21
  • Protocol: ftp
  • Encryption: Use plain FTP
  • Logon type: Normal
  • Username: cs40
  • Password: SJSU#cs40#
  • Acount: leave blank
• Click Connect
• In the right-hand side you will see the site I created for the class
• Right click in the right-hand part
• Click New Directory
• Name it your lastname_first name (John Smith's directory would be smith_john)
  • use all lowercase
• download Seamonkey
  • http://www.seamonkey-project.org/

Title