CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the...

CSU - DCE 0723 - Advanced PerlWWW Overview - Fort Collins, CO

Copyright © XTR Systems, LLC

How the WWW& the Internet

Work

Instructor: Joseph DiVerdi, Ph. D.



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



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.




• 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




• 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



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



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 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



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



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



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



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



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



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



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



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



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



Telephone Services

• Voice transmission• Fax Transmission

CSU - DCE 0723 - Advanced Perl WWW Overview - Fort Collins, CO Copyright © XTR Systems, LLC How the...

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