An Introduction to the Internet and ... - sites.harding.edu

An Introduction to the Internet and the Web

Frank McCownCOMP 250 – Web 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

“We've all heard that a million monkeys banging on a million typewriters will eventually reproduce the entire works of Shakespeare. Now, thanks to the Internet, we know this is not true.”

‐ Robert Wilensky

ARPANET goes online with 4 nodes (1969)

Dec 1969

Dec 1970

Aug 1972

June 1970

Sept 1971

June 1975

http://www.mappingcyberspace.com/gallery/figure1_2.html

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

nternetI

Computer 1 Computer 2

255.254.253.252 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

Web

VoIP

email

IM

Streaming video

Internet ≠ Web

The Internet

File transfer

Tim Berners‐Lee and others at CERN develop the World Wide Web (WWW), HTML documents transmitted over the Internet by a web server to web browsers using URIs and HTTP (1st web page online on Aug 6, 1991)

Images: http://www.radford.edu/sjennings15/text.htm http://en.wikipedia.org/wiki/Tim_Berners‐Lee

Overview of the Web

nternetI

Client – Web Browser Web Server

255.254.253.252 1.2.3.4

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

http://gs.statcounter.com/#browser‐ww‐monthly‐200807‐201509

Web Browser

Software that runs on the client used to access and display web content

http://gs.statcounter.com/#mobile_browser‐ww‐monthly‐200812‐201509

Mobile Web Browser

Mobile browsers account for 51% of global web access in Jan 2017

Web ServerA computer (or software running on a computer) on the Internet that listens for HTTP requests, typically on port 80, and responds with HTTP responses

Apache : 26%Microsoft IIS: 31%ngnix: 23%Other: 20%

Market Share for Top Servers Across All Domains, Aug 1995 –Dec 2017

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 RequestGET /comp HTTP/1.1Host: www.harding.edu

Server ResponseHTTP/1.1 200 OKContent-Length: 6018Content-Type: text/htmlContent-Location: http://www.harding.edu/compLast-Modified: Mon, 05 Jul 2014 18:49:40 GMTServer: nginx

<!DOCTYPE html><html><meta content="IE=edge" http-equiv="X-UA-Compatible"><head>

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

Uniform Resource Locator (URL)A URL identifies the location of a resource on the Web.

http://www.foo.org/abc/bar.html

scheme hostname path

localhostname

domain name TLD

Domain Name System (DNS)DNS is a hierarchical look‐up service that converts a given hostname into its equivalent IP address

www.google.com 1.4.5.8www.cnn.com 4.6.2.8www.hulu.com 6.7.8.9Etc ...

DNS Serverwww.harding.edu 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

http://foo.org/bar.html

Client (Web Browser) Web Server

(4) HTTP GET bar.html

(1) Enter URL

(6) HTTP Response(5) Locate the

resource

(7) Parse HTML& display

(8) HTTP GET image1

(N) HTTP GET imageX

Potentially many requests & responses

DNS

(2) foo.org(3) 1.2.3.4

Dissecting the Request

GET /comp HTTP/1.1Host: www.harding.eduUser-Agent: Mozilla/5.0 Firefox/3.6.8

Request type



Path



HTTP version



Hostname



Identify client

Dissecting the Response

HTTP/1.1 200 OKContent-Length: 6018Content-Type: text/htmlContent-Location: http://www.harding.edu/comp/Last-Modified: Mon, 05 Jul 2010 18:49:40 GMTServer: Microsoft-IIS/6.0

<!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...

Header

Message body

HTTP versionStatus code & phrase

Status Line

HTTP/1.1 200 OK

Popular status codes:200 OK301 Moved permanently302 Found under different temporary URI304 Not modified403 Forbidden 404 Not found500 Internal server error

HTTP version

Status code & phrase




Header

Message body

Number of bytes in response




Header

Message body

MIME type

Popular MIME types

• text/html• text/plain

• image/jpeg• image/gif• image/png

• application/pdf• application/msword• application/vnd.ms‐excel

• video/quicktime

IANA list of MIME types




Header

Message body

URI for resource




Header

Message body

When the file was last modified on the server




Header

Message body

Web server software




Header

Message body

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

Documents

An Introduction to the Internet and ... - sites.harding.edu