Transcript internet_and_WWW

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