CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the WWW & the Internet Work Instructor: Joseph DiVerdi, Ph. D.

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the Internet Works 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the WWW Works 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.

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the Internet Works 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the Internet Works 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Network Analogies 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Network Analogies 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Internet Addresses 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: IP addresses are registered and allocated

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Domain Name System 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Host & Domain Names 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Original High-level Domains DomainUsage comCommercial organizations eduEducational organizations govNon-military government organizations milMilitary organizations orgOther organizations netNetwork resources

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC 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 highest- level country domains About 300 country codes exist BO - BoliviaBR - BrazilIR - Iran CA - CanadaTD - ChadIQ - Iraq FR - FranceDE - GermanyUK - UK US - USATO - TongaTW - Taiwan

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Domain Name Lookup 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How Intranets Work 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How Extranets Work 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Country Domains 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

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC non-WWW Internet Services 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 provides jokes for everyone Newsgroups provide Bulletin Boards Internet Relay Chat (IRC) provides chat rooms

CSU - DCE Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC Telephone Services Voice transmission Fax Transmission