L02-Background - Session 2 Background Session 2 Background...

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Session 2 – Background 9/1/2010 1 © Robert Kelly, 2001-2010 Session 2 Background 1 Lecture Objectives Understand how an Internet resource is accessed Understand the high level structure of the “Internet cloud” Understand the high level structure of the TCP/IP protocols Understand how a computer finds the IP address f h t NS © Robert Kelly, 2001-2010 of a host using DNS Know the structure of MIME type standards
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Session 2 – Background 9/1/2010 2 © Robert Kelly, 2001-2010 Reference Mime types http://www.w3schools.com/media/media_mimeref.asp Cyber Security Cyber War by Richard Clarke and Robert Knake, Harper Collins, 2010 © Robert Kelly, 2001-2010 3 What is a URL? A short string that identifies a resource on the Web Stands for Uniform Resource Locator Uniform – varied and new types of resources Resource – Anything that has identity (e.g., image) Reduces the tedium of connecting to a host, selecting a path, selecting a resource, etc. into a © Robert Kelly, 2001-2010 single string that: Can be saved as a bookmark in your browser Can be saved as an object in your Java code
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Session 2 – Background 9/1/2010 3 © Robert Kelly, 2001-2010 URL Example http://www.cs.sunysb.edu Protocol identifier Resource name Protocol Identifier - Indicates the name of the protocol to be used to fetch the resource R th l t dd f th © Robert Kelly, 2001-2010 Resource name is the complete address of the resource Resource name may be appended with a fragment / reference / named anchor (denoted by #) or include a query string (denoted by ?) URL Resource Name For http, the name includes: host name, path name to the file, port number (optional), and location within the resource (optional) The resource is not necessarily a file, it can be generated on the fly A t ili l h ( /) i h th d f Very important concept © Robert Kelly, 2001-2010 A trailing slash (www.sun.com/) is shorthand for the file named /index.html
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Session 2 – Background 9/1/2010 4 © Robert Kelly, 2001-2010 Relative URLs Contains only enough information to reach the resource relative to (in the context of) another URL Used within HTML files <td> <a href=“LectureCode.html“ >Intro</a></td> specified relative to the location of the file in which they are contained URL context = © Robert Kelly, 2001-2010 new URL("http://www.sciam.com/feature_directory.cfm"); URL aURL = new URL( context , "myImage.gif"); Examples of URL Schemes The standard Java library currently provides support for http and ftp Other protocols can be used with some extra coding tel:+358-555-1234567 fax:+358.555.1234567 modem:+3585551234567;type=v32b?7e1;type=v110
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