Transcript Lecture 10 - ODU Computer Science

CS149D Elements of Computer
Science
Ayman Abdel-Hamid
Department of Computer Science
Old Dominion University
Lecture 10: 9/26/2002
Lecture 10: 9/26/2002
CS149D Fall 2002
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Outline
•Skip section 3.4
•Networks
Network classification
The Internet
World Wide Web
Should cover section 3.5
Lecture 10: 9/26/2002
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Network classification1/3
Two broad categories
•LAN (Local area network)  University campus
•WAN (Wide area network)  Satellite links
Ownership (public domain, private)
•Public domain  open network (Internet)
•Private  proprietary network
Network configuration (pattern in which machines are connected)
Ring, bus, star, irregular
Lecture 10: 9/26/2002
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Network classification2/3
Copyright © 2003 Pearson Education, Inc.
Lecture 10: 9/26/2002
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Network classification3/3
Copyright © 2003 Pearson Education, Inc.
Lecture 10: 9/26/2002
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The Internet
•A network of networks  internet
•An example of an internet is the Internet
•Originated from a research program initiated in 1973 by the
Defense Advanced Research Projects Agency (DARPA)
•Internet is a combination of WANs and LANs involving maybe
millions of machines
•Each network connected to the other by a special machine called a
router
•Router is a machine belonging to 2 networks that allows messages
in one network to be transferred to the other network
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Internet Addressing
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Internet  collection of network clusters known as domains
Domain
Domain
Domain
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Internet Addressing
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•Address of a machine in the Internet is 32 bits
•IP address  IP is Internet Protocol
•Consists of 2 parts
identify the domain (network identifier)
identify the particular machine within the domain (host address)
•Network identifier assigned by InterNIC (Internet Network Information
Center) at time of domain establishment and registration (guarantee uniqueness
of network identifier)
•ODU machine addresses example
128.82.8.42
128.82.8.60
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Internet Addressing
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•InterNIC assigns each domain a unique mnemonic address known as
domain name
•odu.edu
cs.odu.edu
pitfall.cs.odu.edu
(edu, gov, org, com, .. first-level domains)
•Break domain into subdomains
cs.odu.edu
ece.odu.edu
•We need a mapping between numeric addresses and mnemonic addresses
(Each local authority maintains such directory)
•Directory is implemented within the domain in the form of a server called a
name server
(DNS  Domain Name System)
•Name server provides lookup for mnemonic addresses to obtain the
corresponding numeric addresses
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Internet Addressing4/4
Organization to become part of Internet
•Become part of an existing domain
•Establish a new domain (need to register with InterNic)
Individual obtains access to Internet
•Through membership in an organization with a domain
•Through an ISP (Internet Service Provider)
•Dialup, Cable Modem, DSL
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World Wide Web
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Hypertext
Text containing words, phrases, or images that are linked to other
documents (a link to my home page)
When hypertext contains sounds, and video, it is called hypermedia
•Reader of hypertext documents can explore related documents
•A web of related information is formed
•Web that has evolved on the Internet spans the entire globe and is known
as World Wide Web
Request
Netscape
Internet
Explorer
Client machine
Browser
Server machine
Serves web pages
Reply
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World Wide Web
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•Each document is identified by a unique address
•This unique address is called a URL (Uniform Resource Locator)
•The URL allows to identify the server, the protocol in use, and a desired
document
•Sometimes a URL does not explicitly identify a document, in such case a
predetermined document is often returned (usually a home page)
http://www.cs.odu.edu/~hamid/cs149/hw3.html
Document name
Protocol required to
access document
(Hypertext transfer
protocol)
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Mnemonic of host
holding the document
Directory path indicating the
location of the document
within the host’s file system
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World Wide Web
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•A hypertext document contains special markers that describe
 How the document should appear within the browser
Which items within the document are to be linked to other documents
•Systems of markers known as Hypertext Markup Language (HTML)
•Finding information on the WWW  Search Engines
How the Internet Infrastructure works?
(from howstuffworks.com)
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