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An Introduction to the Internet and the Web

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1 An Introduction to the Internet and the Web
Frank McCown COMP 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

2 “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

3 ARPANET goes online with 4 nodes (1969)
Dec 1969 June 1970 Dec 1970 Sept 1971 Aug 1972 June 1975

4

5 Created from Alexa web browser toolbar
Created from Alexa web browser toolbar. “Every site is a circle on the map, and its size is determined by website traffic, the larger the amount of traffic, the bigger the circle. Users’ switching between websites forms links, and the stronger the link, the closer the websites tend to arrange themselves to each other.”

6 “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.” Internet Computer 1 Computer 2

7 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 – 80 – Web

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9 Internet ≠ Web The Internet File transfer Web IM VoIP email
Streaming video BitTorrent – accounts for about half of all Internet traffic The Internet

10 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) This NeXT Computer was used by Berners-Lee at CERN and became the world's first Web server. Images:

11 Overview of the Web Internet
Client – Web Browser Web Server World Wide Web: The system of interlinked hypertext documents accessed over the Internet using the HTTP protocol

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

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

14 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 – Dec 2017 Apache : 26% Microsoft IIS: 31% ngnix: 23% Other: 20%

15 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: Server Response HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: nginx <!DOCTYPE html> <html> <meta content="IE=edge" http-equiv="X-UA-Compatible"> <head> Example request for

16 Uniform Resource Locator (URL)
A URL identifies the location of a resource on the Web. local hostname domain name TLD scheme hostname path

17 Domain Name System (DNS)
DNS is a hierarchical look-up service that converts a given hostname into its equivalent IP address DNS Server Etc ... DNS servers contact parent servers for missing entries Authoritative name servers are responsible for specific domains Warning: DNS cache poisoning

18 Example: Web Page Request
DNS (2) foo.org (1) Enter URL (3) (4) HTTP GET bar.html (5) Locate the resource (6) HTTP Response (7) Parse HTML & display (8) HTTP GET image1 (N) HTTP GET imageX Potentially many requests & responses Client (Web Browser) Web Server

19 Dissecting the Request
Request type GET /comp HTTP/1.1 Host: User-Agent: Mozilla/5.0 Firefox/3.6.8

20 Dissecting the Request
Path GET /comp HTTP/1.1 Host: User-Agent: Mozilla/5.0 Firefox/3.6.8

21 Dissecting the Request
HTTP version GET /comp HTTP/1.1 Host: User-Agent: Mozilla/5.0 Firefox/3.6.8

22 Dissecting the Request
Hostname GET /comp HTTP/1.1 Host: User-Agent: Mozilla/5.0 Firefox/3.6.8

23 Dissecting the Request
Identify client GET /comp HTTP/1.1 Host: User-Agent: Mozilla/5.0 Firefox/3.6.8

24 Dissecting the Response
HTTP version Status code & phrase HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body

25 Status Line Status code & phrase HTTP/1.1 200 OK HTTP version
Popular status codes: 200 OK 301 Moved permanently 302 Found under different temporary URI 304 Not modified 403 Forbidden 404 Not found 500 Internal server error

26 Dissecting the Response
Number of bytes in response HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body

27 Dissecting the Response
MIME type HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body

28 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

29 Dissecting the Response
URI for resource HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body

30 Dissecting the Response
When the file was last modified on the server HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body

31 Dissecting the Response
HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Web server software Header Message body

32 Dissecting the Response
HTTP/ OK Content-Length: 6018 Content-Type: text/html Content-Location: Last-Modified: Mon, 05 Jul :49:40 GMT Server: Microsoft-IIS/6.0 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" " <html> <head> <title>Harding University - Computer Science</title> Etc... Header Message body HTML displayed in the browser

33 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

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