david evans cs200: computer science university of virginia computer science class 28: networks, the...
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David Evanshttp://www.cs.virginia.edu/evans
CS200: Computer ScienceUniversity of VirginiaComputer Science
Class 28: Networks,The Internet,and the World Wide Web
Memex MachineVannevar Bush, As We May Think,
LIFE 19:11 (1945)
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29 March 2004 CS 200 Spring 2004 2
This Week in CS200
• Today: Networking and the Internet
• Wednesday: – How to make a dynamic web site using HTML,
SQL, PHP
• Friday: Models of Computation
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29 March 2004 CS 200 Spring 2004 3
College CS Program• Not a Major – must still have a CLAS Major
• Advantages:– Priority registration for CS classes– Certificate and metaphorical “goldstar” on your
transcript (if you take enough courses)
• Disadvantages:– Applications due Tuesday, 6 April– Have to write a 1 page essay
• If you have received at least one gold star, I will write a letter of support for you
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29 March 2004 CS 200 Spring 2004 4
Who Invented the Internet?
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29 March 2004 CS 200 Spring 2004 5
Who Invented Networking?
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29 March 2004 CS 200 Spring 2004 6
What is a Network?
A group of three or more connected communicating entities
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29 March 2004 CS 200 Spring 2004 7
Beacon Chain NetworkingThus, from some far-away beleaguered island, where all day long the men have fought a desperate battle from their city walls, the smoke goes up to heaven; but no sooner has the sun gone down than the light from the line of beacons blazes up and shoots into the sky to warn the neighboring islanders and bring them to the rescue in their ships. Iliad, Homer, 700 BC
Chain of beacon’s signaled Agammemnon’s return (~1200BC), spread on Greek peaks over 600km.
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29 March 2004 CS 200 Spring 2004 8
Pony Express
• April 1860 – October 1861
• Missouri to California– 10 days– 10-15 miles per horse, ~100 miles per rider
• 400 horses total (not per station like Kahn’s)
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29 March 2004 CS 200 Spring 2004 9
Chappe’s Semaphore Network
Mobile Semaphore Telegraph Used in the Crimean War 1853-1856
First Line (Paris to Lille), 1794
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29 March 2004 CS 200 Spring 2004 10
Measuring Networks• Latency
Time from sending a bit until it arrives
seconds (or seconds per geographic distance)
• Bandwidth
How much information can you transmit per time unit
bits per second
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29 March 2004 CS 200 Spring 2004 11
Latency and Bandwidth• Napoleon’s Network: Paris to Toulon, 475 mi• Latency: 13 minutes (1.6s per mile)
– What is the delay at each signaling station, how many stations to reach destination
– At this rate, it would take ~1 hour to get a bit from California
• Bandwidth: 2 symbols per minute (98 possible symbols, so that is ~13 bits per minute– How fast can signalers make symbols– At this rate, it would take you about 9 days to get
ps7.zip
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29 March 2004 CS 200 Spring 2004 12
Improving Latency• Less transfer points
– Longer distances between transfer points– Semaphores: how far can you see clearly
• Telescopes can help, but curvature of Earth is hard to overcome
– Use wires (electrical telegraphs, 1837)
• Faster travel– Hard to beat speed of light (semaphore network)– Electrons in copper travel about 1/3rd speed of light
• Faster transfers– Replace humans with machines
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29 March 2004 CS 200 Spring 2004 13
How many transfer points between here and California?
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29 March 2004 CS 200 Spring 2004 14
] tracert cs.berkeley.eduTracing route to cs.berkeley.edu [169.229.60.28]over a maximum of 30 hops:
1 <10 ms <10 ms <10 ms router137.cs.Virginia.EDU [128.143.137.1] 2 <10 ms <10 ms <10 ms carruthers-6509a-x.misc.Virginia.EDU [128.143.222.46] 3 <10 ms <10 ms <10 ms uva-internet.acc.Virginia.EDU [128.143.222.93] 4 <10 ms <10 ms <10 ms 192.35.48.42 5 <10 ms <10 ms 10 ms 192.70.138.22 6 <10 ms 10 ms 10 ms nycm-wash.abilene.ucaid.edu [198.32.8.46] 7 20 ms 20 ms 20 ms clev-nycm.abilene.ucaid.edu [198.32.8.29] 8 21 ms 30 ms 30 ms ipls-clev.abilene.ucaid.edu [198.32.8.25] 9 30 ms 40 ms 30 ms kscy-ipls.abilene.ucaid.edu [198.32.8.5] 10 40 ms 50 ms 40 ms dnvr-kscy.abilene.ucaid.edu [198.32.8.13] 11 70 ms 70 ms * snva-dnvr.abilene.ucaid.edu [198.32.8.1] 12 70 ms 70 ms 70 ms 198.32.249.161 13 70 ms 70 ms 71 ms BERK--SUNV.POS.calren2.net [198.32.249.13] 14 70 ms 70 ms 70 ms pos1-0.inr-000-eva.Berkeley.EDU [128.32.0.89] 15 70 ms 70 ms 70 ms vlan199.inr-202-doecev.Berkeley.EDU [128.32.0.203] 16 * * * Request timed out. 17 70 ms 100 ms 70 ms relay2.EECS.Berkeley.EDU [169.229.60.28]
Trace complete.
> (define meters-to-berkeley (* 1600 3000)) ;; 3000 miles * 1600 meters/mi> (define seconds-to-berkeley 0.070)> (define speed-to-berkeley (/ meters-to-berkeley seconds-to-berkeley))> speed-to-berkeley ;;; meters per second68571428.57142857> (define speed-of-light 300000000) ;;; 300 000 000 meters per second> (/ speed-of-light speed-to-berkeley)4.375The Internet latency today is about ¼ the best physically possible!
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29 March 2004 CS 200 Spring 2004 15
Improving Bandwidth• Faster transmission
– Train signalers to move semaphore flags faster– Use something less physically demanding to transmit
• Bigger pipes– Have multiple signalers transmit every other letter at
the same time
• Better encoding– Figure out how to code more than 98 symbols with
semaphore signal– Morse code (1840s)
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29 March 2004 CS 200 Spring 2004 16
Morse CodeRepresent letters with series ofshort and long electrical pulses
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29 March 2004 CS 200 Spring 2004 17
Circuit Switching
• Reserve a whole path through the network for the whole message transmission
Paris Toulon
Nantes
LyonBourges
Once you start a transmission,know you will have use of the network until it is finished. But,wastes network resources.
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29 March 2004 CS 200 Spring 2004 18
Packet Switching
• Use one link at a time
Paris Toulon
Nantes
LyonBourges
Interleave messages – send whenever the next link is free.
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29 March 2004 CS 200 Spring 2004 19
Circuit and Packet Switching
• (Land) Telephone Network– Circuit: when you dial a number, you have a
reservation on a path through the network until you hang up
• The Internet– Packet: messages are broken into small
packets, that find their way through the network link by link
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29 March 2004 CS 200 Spring 2004 20
internetwork
A collection of multiple networks connected together, so messages can be transmitted between nodes on different networks.
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29 March 2004 CS 200 Spring 2004 21
Okay, so who invented the Internet?
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29 March 2004 CS 200 Spring 2004 22
The First internet• 1800: Sweden and Denmark worried about
Britain invading
• Edelcrantz proposes link across strait separating Sweden and Denmark to connect their (signaling) telegraph networks
• 1801: British attack Copenhagen, network transmit message to Sweden, but they don’t help.
• Denmark signs treaty with Britain, and stops communications with Sweden
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29 March 2004 CS 200 Spring 2004 23
First Use of Internet
• October 1969: First packets on the ARPANet from UCLA to Stanford. Starts to send "LOGIN", but it crashes on the G.
• 20 July 1969:Live video (b/w) and audio transmitted from moon to Earth, and to several hundred televisions worldwide.
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29 March 2004 CS 200 Spring 2004 24
The Modern Internet• Packet Switching: Leonard Kleinrock (UCLA)
thinks he did, Donald Davies and Paul Baran, Edelcrantz’s signalling network (1809) sort of did it
• Internet Protocol: Vint Cerf, Bob Kahn
• Vision, Funding: J.C.R. Licklider, Bob Taylor • Government: Al Gore (first politician to promote
Internet, 1986; act to connect government networks to form “Interagency Network”)
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29 March 2004 CS 200 Spring 2004 25
Government and NetworkingChappe wanted a commercial network
Anyone performing unauthorized transmissions of signals from one place to another, with the aid of telegraphic machines or by any other means, will be punished with an imprisonment of one month to one year, and a fine of 1,000 to 10,000 Francs.
The use of novel methods that modify established habits, often hurts the interests of those who profit the most from the older methods. Few people, with the exception of the inventors, are truly interested in helping projects succeed while their ultimate impact is still uncertain. . . . Those in power will normally make no effort to support a new invention, unless it can help them to augment their power; and even when they do support it, their efforts are usually insufficient to allow the new ideas to be fully exploited. (Claude Chappe, 1824)
French Law passed in 1837 made private networking illegal
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29 March 2004 CS 200 Spring 2004 26
The World Wide Web
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29 March 2004 CS 200 Spring 2004 27
The “Desk Wide Web”
Memex MachineVannevar Bush, As We May Think, LIFE, 1945
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29 March 2004 CS 200 Spring 2004 28
Licklider and Taylor’s VisionAvailable within the network will be functions and services to which you subscribe on a regular basis and others that you call for when you need them. In the former group will be investment guidance, tax counseling, selective dissemination of information in your field of specialization, announcement of cultural, sport, and entertainment events that fit your interests, etc. In the latter group will be dictionaries, encyclopedias, indexes, catalogues, editing programs, teaching programs, testing programs, programming systems, data bases, and – most important – communication, display, and modeling programs. All these will be – at some late date in the history of networking - systematized and coherent; you will be able to get along in one basic language up to the point at which you choose a specialized language for its power or terseness.
J. C. R. Licklider and Robert W. Taylor, The Computer as a Communication Device, April 1968
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29 March 2004 CS 200 Spring 2004 29
The World Wide Web
• Tim Berners-Lee, CERN (Switzerland)
• First web server and client, 1990
• Established a common language for sharing information on computers
• Lots of previous attempts (Gopher, WAIS, Archie, Xanadu, etc.)
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29 March 2004 CS 200 Spring 2004 30
World Wide Web Success
• World Wide Web succeeded because it was simple!– Didn’t attempt to maintain links, just a
common way to name things – Uniform Resource Locators (URL)
http://www.cs.virginia.edu/cs200/index.html
Service Hostname File Path
HyperText Transfer Protocol
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29 March 2004 CS 200 Spring 2004 31
HyperText Transfer Protocol
Client (Browser)
GET /cs200/community/ HTTP/1.0
<html><head>…
Contentsof file
Server
HTML HyperText Markup Language
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29 March 2004 CS 200 Spring 2004 32
Growth of World Wide Web
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29 March 2004 CS 200 Spring 2004 33
PS7 Demo
http://www.cs.virginia.edu/cs200/community/
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29 March 2004 CS 200 Spring 2004 34
Charge
• Try some tracert experiments next time you are on the Internet
• PS7 Due 7 April