The Internet

The Internet+World Wide Web+"Image"

the Web is the collection of web sites and pages around the world; the Internet is larger and also includes other services such as email, chat, online games, etc.

Internet Protocol (IP)

a simple protocol for attempting to send data between two computers
each device has a 32-bit IP address
addresses written as four 8-bit numbers (between 0 and 255)
e.g. 145.10.34.3
find out your internet IP address: whatismyip.com
find out your local IP address:
in a terminal, type: ipconfig (Windows) or ifconfig (Mac/Linux)

adds multiplexing, guaranteed message delivery on top of IP
multiplexing: multiple programs using the same IP address
- port: a number given to each program or service
- port 80: web browser
- port 25: email
- port 22: ssh
- port 5190: AOL Instant Messenger
- more common ports
some programs (games, streaming media programs) use simpler UDP protocol instead of TCP

a set of servers that map written names to IP addresses
- Example: www.cs.washington.edu ? 128.208.3.88
many systems maintain a local cache called a hosts file
- Windows: C:\Windows\system32\drivers\etc\hosts
- Mac: /private/etc/hosts
- Linux: /etc/hosts

World Wide Web Consortium (W3C): web standards
Internet Engineering Task Force (IETF): internet protocol standards
Internet Corporation for Assigned Names and Numbers (ICANN): decides top-level domain names

a computer running web server software that listens for web page requests on TCP port 80
popular web server software:
- Apache: www.apache.org
- Microsoft Internet Information Server (IIS)
  - available as part of Windows XP (directions)

a software application that displays web pages
popular web browser software:
- Mozilla Firefox: getfirefox.com
- Microsoft Internet Explorer (IE): part of Windows
- Apple Safari: part of Mac OS X
- Opera: opera.com

the set of commands understood by a web server and sent from a browser
some HTTP commands (your browser sends these internally):
- GET filename : download
- POST filename : send a web form response
- PUT filename : upload
simulating a browser with a terminal window:

·         $ telnet www.cs.washington.edu 80

·         Trying 128.208.3.88...

·         Connected to 128.208.3.88 (128.208.3.88).

·         Escape character is '^]'.

·         GET /index.html

·         <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 ...">

·         <html>

·         ...

the web server returns a special “error code” number to the browser, possibly followed by an HTML document
common error codes:

Number	Meaning
200	OK
301-303	page has moved (permanently or temporarily)
403	you are forbidden to access this page
404	page not found
500	internal server error

·         http://www.aw-bc.com/info/regesstepp/index.html

·         ~~~~   ~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~

·         protocol    host                path

upon entering this URL into the browser, it would:
- ask the DNS server for the IP address of www.aw-bc.com
- connect to that IP address at port 80
- ask the server to GET /info/regesstepp/index.html
- display the resulting page on the screen

·         http://www.textpad.com/download/index.html#downloads

- the above URL fetches index.html and then jumps downward to a part of the page labeled downloads
port: for web servers on ports other than the default 80

·         http://www.cs.washington.edu:8080/secret/money.txt

·         http://www.google.com/search?q=miserable+failure&start=10

- the above URL asks the server at www.google.com to run the program named search and pass it two parameters:
  - q (set to "miserable+failure")
  - start (set to 10)

Hypertext Markup Language (HTML): used for writing web pages
- XHTML: A newer, more rigidly standardized specification of HTML
Cascading Style Sheets (CSS): supplies stylistic info to web pages
Javascript: allows interactive and programmable web pages
Asynchronous Javascript and XML (AJAX): allows fetching of web documents in the background for enhanced web interaction
Google AJAX Search API: embeds Google services in web pages
PHP Hypertext Processor (PHP): allows the web server to create pages dynamically
Structured Query Language (SQL): interaction with databases