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Internet & Web OverviewFort Collins, CO
Copyright © XTR Systems, LLC
How the WWW &the Internet Work
or"I didn't know they aren't
the same thing."
Instructor: Joseph DiVerdi, Ph.D., MBA
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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.
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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:• 206.168.235.2• 192.122.36.5• 128.174.5.6
• IP addresses are registered and allocated
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort Collins, CO
Copyright © XTR Systems, LLC
Original High-level Domains
Domain Usage
com Commercial organizations
edu Educational organizations
gov Non-military government organizations
mil Military organizations
org Other organizations
net Network resources
Internet & Web OverviewFort 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 - Bolivia BR - Brazil IR - Iran
CA - Canada TD - Chad IQ - Iraq
FR - France DE - Germany UK - UK
US - USA TO - Tonga TW - Taiwan
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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
Internet & Web OverviewFort 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• email provides jokes for everyone• Newsgroups provide Bulletin Boards• Internet Relay Chat (IRC) provides chat
rooms
Internet & Web OverviewFort Collins, CO
Copyright © XTR Systems, LLC
Telephone Services
• Voice transmission• Fax Transmission
Internet & Web OverviewFort Collins, CO
Copyright © XTR Systems, LLC
A Very Simple Transaction
Internet & Web OverviewFort Collins, CO
Copyright © XTR Systems, LLC
Simple Transaction w/ Image