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Educational Computing
Computer Networks David Goldschmidt, Ph.D. Computer Science The College of Saint Rose
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No single point of failure!
Networks Root node Hierarchical Networks: Nodes are not equal Nodes interconnect in strict pattern Single point of failure Heterarchical Networks: Nodes interconnected at random No node is more important than another Leaf nodes No single point of failure!
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The Internet The Internet is a global decentralized heterarchical network made up of many smaller networks “Information Superhighway” Originally developed in 1960s as ARPANET Advanced Research Projects Agency NETwork Continued linked computer availability in case of nuclear attack Use in academia led to , file transfer, Web, etc.
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Internet Backbone Network
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Internet Service Providers
Internet Service Providers (ISPs) have direct connections to (or are part of ) the Internet ISPs sell temporary Internet access Time Warner Cable Digital Subscriber Line (DSL) Wireless 3G and 4G Networks Tethered connections Leased line (e.g. T1, T3) through telephone company Satellite Telephone access numbers
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Internet Service Providers
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Local Area Networks Local Area Network (LAN) is a network of machines covering a limited geographical area Metropolitan Area Network (MAN) covers more densely populated area
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Wide Area Networks Wide Area Network (WAN) covers multiple locations
Each location consists of a LAN or MAN LANs and WANs are often connected via private networks
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The Internet as Global WAN
The Internet is the world’s largest network Links millions of businesses, governments, educational institutions, and individuals
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How the Internet Works
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Internet Protocols What is a protocol ?
A protocol describes how communication should take place e.g. Robert’s Rules of Orders Transmit data over the Internet using 2 protocols: Transmission Control Protocol (TCP), which provides error handling, packet resubmission, etc. Internet Protocol (IP), which provides “low-level” packet-based communications
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Internet Addresses An Internet Addresses identifies machines on the Internet Numeric addresses e.g , Non-numeric addresses e.g. IP addresses Domain names
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Internet Addresses
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Billions and Billions Served....
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Voice Over IP Internet telephony using Voice Over IP (VOIP) Vonage
Skype magicJack etc.
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File Transfer Protocol (FTP)
FTP is a communications protocol for transferring files between computers e.g. Publishing a Web site FTP sites on the Internet contain documents, software, images, video, audio, etc. ftp://ibiblio.org/pub/docs/books/gutenberg/
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World Wide Web World Wide Web (WWW) Building blocks of the Web:
Invented by Tim Berners-Lee in early 1990s while at CERN Web is decentralized and runs on top of the Internet Building blocks of the Web: Uniform Resource Locator (URL) HyperText Transfer Protocol (HTTP) HyperText Markup Language (HTML)
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Uniform Resource Locators
A Uniform Resource Locator (URL) identifies the protocol, domain (machine) name, and file path of the resource being requested Protocol Domain name (a.k.a ) Resource name and path (location of HTML file)
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Domain Name Registration
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HyperText Markup Language
HyperText Markup Language (HTML) defines page layout, fonts, links, text, etc. HTML tags describe how Web browsers should display text, images, etc. <html> <title>Welcome to My Web Site</title> <body style="background-color: gray;"> <img src="people.gif" width="184" height="119"> <p>Welcome to my cool new Web site. <a href=" here for news.</a> </p>
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Search Engines A search engine is an online software application that enables users to electronically locate and retrieve Web pages Keyword-based search How does a search engine “know” about all those Web pages?
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Crawling the Web How does a search engine “know” about all those Web pages? Search engine software crawls the Web Records everything it sees in giant index How do search requests return results so quickly? Redundancy LOTS of redundant data on redundant hardware distributed across the world
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Browsing the Web We browse the Web using Web browser software:
Internet Explorer, Firefox, Safari (Mac), etc.
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Multimedia on the Web Web pages incorporate graphics, animation, audio, video, etc.
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Graphics on the Web Images are available on the Web in many different formats: Graphics { Photographs
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Right-click and select “View Picture”
Graphics on the Web Images are embedded in Web pages using HTML Right-click and select “View Picture”
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Audio on the Web Audio on the Web may be downloaded or streamed
Formats include MP3, WAV, WMV
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Video on the Web Like audio, video on the Web may be downloaded or streamed
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Searching for Audio and Video
Search for audio or video clips using Google:
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Searching for Audio and Video
Search for audio using Altavista:
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Searching for Audio and Video
Search for video using YouTube:
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Saving Audio and Video Clips
To save an audio or video clip: Right-click on the URL link to clip Select “Save Target As...” or “Save Link As...” Streaming audio and video might not save to your own computer If not, add URL link as a bookmark or favorite
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Saving a Web Page Saving a Web page is tricky because there are usually multiple files (HTML, GIF, JPG, etc.) Save options: Save entire Web page Save HTML only Save text only
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