Download 10/04/04

COMS 161
Introduction to Computing
Title: Local Area Networks
Date: October 4, 2004
Lecture Number: 17
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Announcements
• This material is from chapter 17 in the
book
• Homework 5
– Due next Wednesday 10/06/04
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Review
• Local Area Networks
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Outline
• LANs
– Topology
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Interconnecting LANs
• Different devices available for connecting
LANs together
– Repeaters
– Routers
– Bridges
– Gateways
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Repeater
• Amplifies and repeats all signals
• Used to increase the size of a LAN
• Especially useful when the LAN must extend
to a distance longer than a single cable can
handle
HUB
REPEATER
HUB
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Bridge
• Connects two LANs of similar types
• Only data for the ‘other’ LAN is passed
through
• Lets LANs act together like a larger LAN while
still maintaining their individual autonomy
HUB
BRIDGE
HUB
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Router
• Can connect LANs of similar or different
types
– Specially designed to manage data flow in connected
networks – knows which route to use to most
effectively get the data to the right destination
HUB
ROUTER
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Gateway
• Generally used to connect LANs to WANs
• Very effective at routing Internet traffic
BRIDGE
HUB
HUB
BRIDGE
HUB
The
Internet
ROUTER
HUB
GATEWAY
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Internet(work)
• Collection of
autonomous
networks
• The Internet
• Intranets
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The Internet
• The Internet
– Really just a very loose collection of networks
– No single entity controls the Internet
– Many kinds of information fly through it constantly
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Email, IM (instant messaging)
Web pages
Entertainment – files and streaming media
Commerce and business data
VOIP – Voice over Internet Protocol (telephone)
Etc., etc.
– No one validates this information
– No one directly polices this information
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History of The Internet
• Originally a US military project from the late
60’s: ARPANET
– 1964 — Paul Baran (RAND Corp.) proposes a
loosely-coupled, robust network
– Designed to survive a nuclear attack
– 1969 — ARPANET formed as a four-node network
(UCLA, SRI, UCSB, and U of Utah-Salt Lake City)
• Expanded into academics and research in the
70’s
– 1974 — Kahn and Cerf head TCP/IP project
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History of The Internet
• Separated from MILNET in early 80’s
– 1980 — CSNET added to ARPANET
– 1986 — NSF forms NSFNET
– 1987 — NSFNET “backbone” expands the Internet
worldwide
– 1989 — CERN launches WWW project
• NSF decommissioned ARPANET in 1990
– 1992 —
– 1993 —
– 1995 —
Internet Society formed
NCSA Mosaic GUI for WWW
NSFNET decomissioned
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History of The Internet
• 1998 — Government funds Internet2
• Arpanet was originally allowed only noncommercial uses
– Universities and government laboratories
– Peer-pressure only, since there is no central
control!
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History of The Internet
• The ARPANET in 1971 – 18 sites
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History of The Internet
• The ARPANET in 1980 – about 75 sites
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History of The Internet
• Original top-level domains:
.edu .gov .org .net .mil .com .int
• International domains came later:
.us .uk .jp .de .tv etc.
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The Web
• The World Wide Web (WWW)
– Just one part of the Internet
– Consists of all information on the Internet that has
been made available using a particular method
(HTML & HTTP)
– Your computer is part of the Internet whenever you
are connected
– Information on your computer can become part of
the Web
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Web Browsers
• Web browsers are programs that make it easy for
anyone on the Internet to access information on the
Web
• Many to choose from; they all use common
techniques
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Mozilla (www.mozilla.org)
Netscape Communicator (AOL Time Warner)
Internet Explorer (Microsoft)
Opera (www.opera.com)
MSN TV [formerly WebTV] (Microsoft)
Cell Phones
PDAs (e.g. Palm Pilots)
Lynx (text-only browser)
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History of The World Wide Web
• Invented by Tim Berners-Lee at CERN (1989)
• Originally designed for
distributing scientific
research results
– Text pages that can be
shared among different
computer systems
– Simple, text-based browsers
• Quickly adopted by other organizations
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History of The World Wide Web
• First graphical browser (Mosaic) developed in 1993
by an undergrad at University of Illinois (Marc
Andreesen)
– (only 11 years ago!)
– Distributed freely
– Widely used in academics and government
• Mosaic expanded by Netscape
– Internally called “Mozilla”
– Originally still distributed without charge
• Microsoft’s Internet Explorer came later
• Netscape now commercialized (AOL Time/Warner)
• Mozilla still free (split off from Netscape)
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History of The World Wide Web
• “Ban” on commercial traffic on the Web lifted soon
after Mosaic released
• .com quickly becomes largest domain
• E-commerce explosion starts in the late 90’s
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Amazon.com founded 1994 by Jeff Bezos
IPO 1997 @ $18/share
Each share bought then now worth $540 – 3000% in 10 yrs
First profit 2001; currently $6,000,000,000/yr sales
• New top-level domains recently added to the Internet
due to increased Web activity:
.biz .info .name etc.
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