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An Introduction to the Internet and the Web Frank McCown COMP 250 – Internet Development Harding University.

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Presentation on theme: "An Introduction to the Internet and the Web Frank McCown COMP 250 – Internet Development Harding University."— Presentation transcript:

1 An Introduction to the Internet and the Web Frank McCown COMP 250 – Internet Development Harding University

2 What is the Internet? A “series of tubes” Senator Ted Stevens (June 28, 2006)series of tubes How many internets are there?internets “I hear there’s rumors on the internets that we’re going to have a draft.” - George Bush (Oct 4, 2008) Slide inspiration: Marty SteppMarty Stepp

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

4 “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/Internetcomputer networksInternet Protocol Suite http://en.wikipedia.org/wiki/Internet Internet Computer 1Computer 2 255.254.253.2521.2.3.4

5 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: Common port numbers 22 – ssh 23 – telnet 25 – email 80 – Web

6

7 Web VoIP email IM Streaming video Internet != Web The Internet File transfer

8 Overview of the Web Internet Client – Web BrowserWeb Server 255.254.253.2521.2.3.4 World Wide Web: The system of interlinked hypertext documents accessed over the Internet using the HTTP protocol.

9 http://en.wikipedia.org/wiki/Usage_share_of_web_browsers Web Browser Software that runs on the client used to access and display web content.

10 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. Apache : 54.9% Microsoft IIS: 25.9% Google: 7.7% ngnix: 5.6% Market Share for Top Servers Across All Domains, Aug 1995 - Aug 2010 http://news.netcraft.com/archives/2010/08/11/august-2010-web-server-survey-4.html#more-2752

11 Hypertext Transfer Protocol (HTTP) HTTP is the set of rules that govern communication between web browsers and web servers. Client Request GET /comp/ HTTP/1.1 Host: www.harding.edu 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Example request for http://www.harding.edu/comp/ http://www.harding.edu/comp/

12 Uniform Resource Locator (URL) A URL identifies the location of a resource on the Web. http://www.foo.org/abc/bar.html schemehostnamepath local hostname domain name TLD

13 Domain Name System (DNS) DNSDNS is a hierarchical look-up service that converts a given hostname into its equivalent IP address www.google.comwww.google.com  1.4.5.8 www.cnn.comwww.cnn.com  4.6.2.8 www.hulu.comwww.hulu.com  6.7.8.9 Etc... DNS Server www.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 poisoningDNS cache poisoning

14 Example: Web Page Request http://foo.org/bar.html Client / Web BrowserWeb 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 imageN Potentially many requests DNS (2) foo.org (3) 1.2.3.4

15 Dissecting the Request GET /comp/ HTTP/1.1 Host: www.harding.edu User-Agent: Mozilla/5.0 Firefox/3.6.8 Request type

16 Dissecting the Request GET /comp/ HTTP/1.1 Host: www.harding.edu User-Agent: Mozilla/5.0 Firefox/3.6.8 Relative URL

17 Dissecting the Request GET /comp/ HTTP/1.1 Host: www.harding.edu User-Agent: Mozilla/5.0 Firefox/3.6.8 HTTP version

18 Dissecting the Request GET /comp/ HTTP/1.1 Host: www.harding.edu User-Agent: Mozilla/5.0 Firefox/3.6.8 Hostname

19 Dissecting the Request GET /comp/ HTTP/1.1 Host: www.harding.edu User-Agent: Mozilla/5.0 Firefox/3.6.8 Identify client

20 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body HTTP version Status code & phrase

21 Status Line HTTP/1.1 200 OK Popular status codesPopular status codes: 200Successful 301 Moved permanently 302 Found under different temporary URI 403Forbidden – you don’t have permission 404Not found 500Internal server error HTTP version Status code & phrase

22 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body Number of bytes in response

23 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body MIME type

24 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

25 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body URI for resource

26 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body When the file was last modified on the server

27 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body Web server software

28 Dissecting the 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 2010 18:49:40 GMT Server: Microsoft-IIS/6.0 Harding University - Computer Science Etc... Header Message body HTML displayed in the browser

29 How can I see the HTTP headers? FireFox Add-on: Live HTTP HeadersLive HTTP Headers

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