Lecture 10: 9/26/2002 CS149D Fall 2002 1

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 2

Outline•Skip section 3.4

•Networks

Network classification

The Internet

World Wide Web

Should cover section 3.5

Lecture 10: 9/26/2002 CS149D Fall 2002 3

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 CS149D Fall 2002 4

Network classification2/3

Copyright © 2003 Pearson Education, Inc.

Lecture 10: 9/26/2002 CS149D Fall 2002 5

Network classification3/3

Copyright © 2003 Pearson Education, Inc.

Lecture 10: 9/26/2002 CS149D Fall 2002 6

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

Lecture 10: 9/26/2002 CS149D Fall 2002 7

Internet Addressing1/4

Internet collection of network clusters known as domains

Domain

Domain

Domain

Lecture 10: 9/26/2002 CS149D Fall 2002 8

Internet Addressing2/4

•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

Lecture 10: 9/26/2002 CS149D Fall 2002 9

Internet Addressing3/4

•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

Lecture 10: 9/26/2002 CS149D Fall 2002 10

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

Lecture 10: 9/26/2002 CS149D Fall 2002 11

World Wide Web1/3

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

Client machineBrowser

Server machineServes web pages

Request

Reply

Netscape

Internet Explorer

Lecture 10: 9/26/2002 CS149D Fall 2002 12

World Wide Web2/3

•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

Protocol required to access document (Hypertext transfer protocol)

Mnemonic of host holding the document

Directory path indicating the location of the document within the host’s file system

Document name

Lecture 10: 9/26/2002 CS149D Fall 2002 13

World Wide Web3/3

•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)