Introduction to Internet Development

An Introduction to the Internet and the Web

Frank McCown

COMP 250 – Internet Development

Harding University

Photos were obtained from the Web, and copyright is held by the respective owners.

Short History of Computing by Frank McCown is licensed under a Creative Commons

Attribution-NonCommercial 3.0 Unported License

http://www.opte.org/maps/

http://internet-map.net/

“The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide.” http://en.wikipedia.org/wiki/Internet

Internet

Computer 1

255.254.253.252

Computer 2

1.2.3.4

Internet Protocol Suite

• Internet Protocol (IP): directs packets to a specific computer using an IP address

• Transmission Control Protocol (TCP): directs packets to a specific application on a computer using a port number.

– Common port numbers :

• 22 – ssh

• 23 – telnet

• 25 – email

• 80 – Web

Internet ≠ Web

Web

Streaming video

VoIP

File transfer email

IM

The Internet

Overview of the Web

Internet

Client – Web Browser

255.254.253.252

Web Server

1.2.3.4

World Wide Web: The system of interlinked hypertext documents accessed over the Internet using the HTTP protocol

Web Browser

Software that runs on the client used to access and display web content http://gs.statcounter.com/?#browser-ww-monthly-200807-201408

Mobile Web Browser

Mobile browsers account for 18% of web access in Aug 2013 http://gs.statcounter.com/#mobile_browser-ww-monthly-200812-201408

Web Server

A computer (or software running on a computer) on the

Internet that listens for HTTP requests, typically on port 80, and responds with HTTP responses

Market Share for Top

Servers Across All

Domains, Aug 1995 –

July 2014

Microsoft IIS: 38%

Apache : 35% ngnix: 14%

Google: 2% http://news.netcraft.com/archives/category/web-server-survey/

Hypertext Transfer Protocol (HTTP)

Protocol that runs over TCP/IP and governs communication between web browsers and web servers

Client Request

GET /comp HTTP/1.1

Host: www.harding.edu

Example request for http://www.harding.edu/comp

Server Response

HTTP/1.1 200 OK

Content-Length: 6018

Content-Type: text/html

Content-Location: http://www.harding.edu/comp

Last-Modified: Mon, 05 Jul 2014 18:49:40 GMT

Server: nginx

<!DOCTYPE html>

<html>

<meta content="IE=edge" http-equiv="X-UA-Compatible">

<head>

Uniform Resource Locator (URL)

A URL identifies the location of a resource on the

Web.

local hostname domain name TLD http://www.foo.org/abc/bar.html

scheme hostname path

Domain Name System (DNS)

DNS is a hierarchical look-up service that converts a given hostname into its equivalent IP address www.harding.edu

DNS Server www.google.com

 1.4.5.8

www.cnn.com

 4.6.2.8

www.hulu.com

 6.7.8.9

Etc ...

128.82.4.20

• DNS servers contact parent servers for missing entries

• Authoritative name servers are responsible for specific domains

• Warning: DNS cache poisoning

Example: Web Page Request

(1) Enter URL

(2) foo.org

DNS

(3) 1.2.3.4

http://foo.org/bar.html

(4) HTTP GET bar.html

(6) HTTP Response

(7) Parse HTML

& display

(8) HTTP GET image1

(N) HTTP GET imageX

Client (Web Browser)

Potentially many requests & responses

(5) Locate the resource

Web Server

Dissecting the Request

Request type

GET /comp HTTP/1.1


User-Agent: Mozilla/5.0 Firefox/3.6.8


Path

GET /comp HTTP/1.1




HTTP version

GET /comp HTTP/1.1




Hostname

GET /comp HTTP/1.1




GET /comp HTTP/1.1


Identify client


HTTP version

Dissecting the Response

Status code & phrase

Header

HTTP/1.1 200 OK



Content-Location: http://www.harding.edu/comp/


Server: Microsoft-IIS/6.0

Message body

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"

"http://www.w3.org/TR/html4/strict.dtd"> <html> <head>

<title>Harding University - Computer Science</title>

Etc...

Status Line

Status code & phrase

HTTP/1.1 200 OK

HTTP version

Popular status codes :

200 Successful

301 Moved permanently

302 Found under different temporary URI

304 Not modified

403 Forbidden

404 Not found

500 Internal server error

Header

Message body


HTTP/1.1 200 OK


Number of bytes in response








Etc...


Header

Message body

HTTP/1.1 200 OK


MIME type








Etc...

Popular MIME types

• text/html

• text/plain

• application/pdf

• application/msword

• application/vnd.ms-excel

• image/jpeg

• image/gif

• image/png

• video/quicktime

IANA list of MIME types


Header

Message body

HTTP/1.1 200 OK


URI for resource








Etc...

Header

Message body


When the file was last

HTTP/1.1 200 OK

Content-Length: 6018 modified on the server








Etc...


Header

Message body

HTTP/1.1 200 OK


Web server software








Etc...


Header

Message body

HTTP/1.1 200 OK









Etc...

HTML displayed in the browser

How can I see the HTTP headers?

• Chrome

– Ctrl-Shift-I  Developer Tools

– “Network” button

• Firefox

– Ctrl-Shift-K  Web Console

– “Net” button should be down

• Internet Explorer

– F12  Developer Tools

– “Network” tab

Introduction to Internet Development

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