The Internet and World Wide Web

CSE 190 M (Web Programming), Spring 2007

University of Washington

Reading: Sebesta Ch. 1 sections 1.1 - 1.5.2, 1.7 - 1.8.5, 1.8.8, 1.9

What is the Internet?

A "series of tubes" (1, 2)

How many internets are there, anyway?

The Internet

Wikipedia: http://en.wikipedia.org/wiki/Internet
a connection of computer networks using the Internet Protocol (IP)
What's the difference between the Internet and the World Wide Web (WWW)?

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)

Transmission Control Protocol (TCP)

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

Domain Name System (DNS)

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

People and organizations

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

Web Server

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)

Web Browser

Firefox web browser

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

Hypertext Transport Protocol (HTTP)

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>
...

HTTP error codes

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
complete list of 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

Uniform Resource Locator (URL)

an identifier for the location of a document on a web site

a basic URL:

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

More advanced URLs

anchor: jumps to a given section of a web page
```
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
```
query string: a set of parameters passed to a web program
```
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)

Web programming technologies

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