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CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO How the WWW & the Internet Work Instructor: Joseph DiVerdi, Ph. D. Copyright © XTR Systems, LLC How the Internet Works CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The Internet is a communications medium through which information is transferred between computers • Many different services use the Internet for transferring information • They most often use TCP/IP to transfer data – Transmission Control protocol/Internet Protocol • The telephone network is also a communications medium but with very different characteristics Copyright © XTR Systems, LLC How the WWW Works CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The World Wide Web is an information service that uses the Internet as its communication medium • It is based on the technology called hypertext • Hypertext is a method of presenting information • Selected words in a text can be "expanded" – to provide other information about the word – These words are called links to other documents, e.g., text, files, pictures, etc. Copyright © XTR Systems, LLC How the Internet Works CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The Internet is a packet switched network • When data leaves the source computer it is broken up into packets (small chunks of data) and transmitted through larger and larger networks (usually 1-1,500 bytes long) • The packets are routed through the many networks • When the packets arrive at the destination computer they are reassembled into the original message Copyright © XTR Systems, LLC How the Internet Works CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • Breaking the data up into small packets increases the efficiency of the whole network • The exact path taken from the same source to the same destination is often different • The path depends on the instantaneous load on each of the routers and networks • The packet data is identified by the Internet Addresses of the source and destination computers Copyright © XTR Systems, LLC Network Analogies CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The telephone network is a circuit switched network • When a telephone call is made a piece of the network is dedicated to that call • Even if it isn't being used, e.g., being on hold, that piece of the network is unavailable for use by others • Inefficient utilization of Network Resources Copyright © XTR Systems, LLC Network Analogies CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The US postal Service is a packet switched network • No user receives a dedicated piece of the network • Routers are equivalent to Postal substations • Mail sent from Milford, CT to Loveland, CO does not use a reserved plane or truck - it is pooled at a substation and sent to a series of substations • Efficient utilization of Network Resources Copyright © XTR Systems, LLC Internet Addresses CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • An IP address uniquely identifies a computer • IP addresses follow dotted decimal notation – – – – Four decimal numbers Each ranging from 0 to 255 Each number separated by a period The following are unique IP addresses and corresponding to unique computers: • 206.168.235.2 • 192.122.36.5 • 128.174.5.6 • IP addresses are registered and allocated Copyright © XTR Systems, LLC Domain Name System CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • A Host Name is assigned to each computer only for the convenience of human users – Computers are quite happy to refer to each other by IP addresses • Host Names use a hierarchical Domain structure • right-to-left <--> most-to-least significant • Each domain is separated by a period • Host Names are registered and allocated Copyright © XTR Systems, LLC Host & Domain Names CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The following are unique host names corresponding to unique computers: – – – – – – – woody.xtrsystems.com lamar.colostate.edu holly.colostate.edu nic.ddn.mil whitehouse.gov uxc.cso.uiuc.edu ux1.cso.uiuc.edu • One computer may have several host names Copyright © XTR Systems, LLC Original High-level Domains CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO Domain Usage com Commercial organizations edu Educational organizations gov Non-military government organizations mil Military organizations org Other organizations net Network resources Copyright © XTR Systems, LLC CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO Country Domains • The Internet is a world-wide network • Foreign (relative to the USA) countries have responsibility for their own names • Country codes are a set of two letter highestlevel country domains • About 300 country codes exist BO - Bolivia CA - Canada FR - France US - USA BR - Brazil TD - Chad DE - Germany TO - Tonga IR - Iran IQ - Iraq UK - UK TW - Taiwan Copyright © XTR Systems, LLC Domain Name Lookup CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • Convert a Domain Name into an IP address • Use DNS servers – computers whose sole purpose is to maintain lists of IP addresses and domain names • Local DNS servers know local addresses • DNS servers also cache recently requested addresses • Local DNS servers also know addresses of more-significant-domain name servers Copyright © XTR Systems, LLC How Intranets Work • • • • • • CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO An intranet is a private network It uses the same components as the Internet It is unconnected to the Internet It is limited by physical boundaries It is for the sole use of certain members Those members exist within those boundaries Copyright © XTR Systems, LLC How Extranets Work CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • An extranet is a private network • It uses the same components as the Internet • Its members are connected through the Internet • It is not limited by physical boundaries • It is limited by logical boundaries – special (secret) protocols or encryption • It is for the sole use of certain members • Those members exist anywhere Copyright © XTR Systems, LLC Country Domains CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • The following are unique host names corresponding to unique computers: – – – – hockey.guelph.ca alpha.psd.k12.co.us ci.fort-collins.co.us uxc.urbana.il.us • Host Names are registered and allocated Copyright © XTR Systems, LLC non-WWW Internet Services CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • Other services which use the Internet as a communications medium • Nothing to do with the WWW • Telnet provides Login to remote computers • FTP provides inter-computer File Transfer • email provides jokes for everyone • Newsgroups provide Bulletin Boards • Internet Relay Chat (IRC) provides chat rooms Copyright © XTR Systems, LLC Telephone Services CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO • Voice transmission • Fax Transmission Copyright © XTR Systems, LLC