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Instructor: George Cybenko, x6-3843 gvc@dartmouth

ENGS 4 - Lecture 6 Technology of Cyberspace Winter 2004 Thayer School of Engineering Dartmouth College. Instructor: George Cybenko, x6-3843 gvc@dartmouth.edu Assistant: Sharon Cooper (“Shay”), x6-3546 Course webpage: www.whoopis.com/engs4. Today’s Class.

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Instructor: George Cybenko, x6-3843 gvc@dartmouth

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  1. ENGS 4 - Lecture 6Technology of Cyberspace Winter 2004Thayer School of EngineeringDartmouth College Instructor: George Cybenko, x6-3843 gvc@dartmouth.edu Assistant: Sharon Cooper (“Shay”), x6-3546 Course webpage: www.whoopis.com/engs4 ENGS4 2004 Lecture 6

  2. Today’s Class • Wrap-up of rule-based systems • Jon’s mini-lecture • Html tables and formatting • Internet routing basics • Break • Bellman-Ford Routing Algorithm • Abby’s mini-lecture • State-based methods for “Predicting the Future” ENGS4 2004 Lecture 6

  3. Jon’s Mini-lecture ENGS4 2004 Lecture 6

  4. Basic HTML tables <TABLE> ... </TABLE> defines a table in HTML. If the BORDER attribute is present, your browser displays the table with a border. <TR> ... </TR> specifies a table row within a table. You may define default attributes for the entire row. <TD> ... </TD> defines a table data cell. By default the text in this cell is aligned left and centered vertically. Table data cells may contain other attributes to determine the characteristics of the cell and/or its contents. See Table Attributes at the end of this table for more information. Attribute width=“30%” determines percentage of the table a column uses. Attribute width=“30” determines how many pixels column uses. ENGS4 2004 Lecture 6

  5. Basic HTML tables ALIGN =“LEFT”, “CENTER”, “RIGHT” VALIGN=“TOP”, “MIDDLE”, “BOTTOM” <TH> ... </TH> defines a table header cell. By default the text in this cell is bold and centered. Table header cells may contain other attributes to determine the characteristics of the cell and/or its contents. See Table Attributes at the end of this table for more information. Attributes cspan and rspan determine how many columns and rows a cell spans. ENGS4 2004 Lecture 6

  6. Basic HTML lists <ol> </ol> delimits an “ordered” list (ie numbered) <ul> </ul> delimits an “unordered” list (ie bullets) In each case, <li> denotes a list item. Example: <ol> <li> Monday <li> Tuesday <li> Wednesday </ol> ENGS4 2004 Lecture 6

  7. Internet Routing Basics ENGS4 2004 Lecture 6

  8. “Switching” is necessary In the early days of telephones, telephone lines were dedicated to pairs of customers. This very quickly became unscalable. Lines had to be “switched” on demand. ENGS4 2004 Lecture 6

  9. Circuit Switching Reserve a “circuit” and that “guarantees” services for each user Requires significant “setup time” Good for telephones, bad for web browsing!!!! ENGS4 2004 Lecture 6

  10. Packet Switching Send “packets” into the network, routing each packet individually, like the post office. Packets are “routed” through the network, sorted at “switches”. Requires no setup time but no guarantee of service!! Bad for telephones, good for web browsing!!!! ENGS4 2004 Lecture 6

  11. Time vs Frequency Division Multiple Access (TDMA vs FDMA) • TDMA – Divide a communications resource or channel using time slots. Users take turns using the same resource by using it only in their allotted slots. • FDMA – Divide a communications resource or channel using frequency division. Users simultaneously use the channel but at different frequencies. • Examples? • Code Division Multiple Access ENGS4 2004 Lecture 6

  12. Resolving internet addresses Rest of the world Bridge or gateway or router or switch DNS Server LAN 4. www.cnn.com is 207.25.71.82 Your computer 1. Can I get an IP address, etc? DHCP Server 3. What is the address of www.cnn.com? 2. Here is a temporary address and other information. ENGS4 2004 Lecture 6

  13. IP Packets and routing • IP is Internet Protocol (also Intellectual Property sometimes) • IP addresses consist of four numbers between 0 and 255 • What is www.dartmouth.edu’s IP address? Network 1 Router ? Network 2 A router can be a dedicated piece of hardware or a computer with several network interfaces. Cisco, 3Com, etc sell routers. ENGS4 2004 Lecture 6

  14. Network routing Routing table in a router looks like..... Pattern Next node on path 129.170.*.* host 1 125.*.*.* host 2 105.121.5.21 host 3 default host 4 ENGS4 2004 Lecture 6

  15. Break ENGS4 2004 Lecture 6

  16. Bellman-Ford Routing Computer/host 4 E D 8 2 A F 1 1 1 C B 3 Distance/cost/delay between hosts ENGS4 2004 Lecture 6

  17. A * B * C * D 4 E 0 F 8 A 2 B * C 1 D 0 E 4 F * Initial table has distance to each host one hop away and * otherwise. 4 E D 8 2 A 0 B 1 C * D 2 E * F * A F 1 A * B * C 1 D * E 8 F 0 1 1 A 1 B 0 C 3 D * E * F * A * B 3 C 0 D 1 E * F 1 C B 3 ENGS4 2004 Lecture 6

  18. A * 6 B * * C * 5 D 4 4 E 0 0 F 8 8 newdistance to X = min( distance to neighbor + distance from neighbor to X) where min is over all neighbors A 2 2 B * 3 C 1 1 D 0 0 E 4 4 F * 2 4 E D 8 2 A 0 0 B 1 1 C * 4 D 2 2 E * 6 F * * A F 1 A * * B * 4 C 1 1 D * 2 E 8 8 F 0 0 1 1 A 1 1 B 0 0 C 3 3 D * 3 E * * F * 4 A * 3 B 3 3 C 0 0 D 1 1 E * 5 F 1 1 C B 3 ENGS4 2004 Lecture 6

  19. A * 6 6 B * * 7 C * 5 5 D 4 4 4 E 0 0 0 F 8 8 6 A 2 2 2 B * 3 3 C 1 1 1 D 0 0 0 E 4 4 4 F * 2 2 Repeat it!!! A 0 0 0 B 1 1 1 C * 4 3 D 2 2 2 E * 6 6 F * * 4 4 E D 8 2 A F 1 A * * 4 B * 4 4 C 1 1 1 D * 2 2 E 8 8 6 F 0 0 0 1 1 A 1 1 1 B 0 0 0 C 3 3 3 D * 3 3 E * * 7 F * 4 4 A * 3 3 B 3 3 3 C 0 0 0 D 1 1 1 E * 5 5 F 1 1 1 C B 3 ENGS4 2004 Lecture 6

  20. A * 6 6 6 B * * 7 7 C * 5 5 5 D 4 4 4 4 E 0 0 0 0 F 8 8 6 6 Repeat it...stop when the table does not change. A 2 2 2 2 B * 3 3 3 C 1 1 1 1 D 0 0 0 0 E 4 4 4 4 F * 2 2 2 A 0 0 0 0 B 1 1 1 1 C * 4 3 3 D 2 2 2 2 E * 6 6 6 F * * 4 4 4 E D 8 2 A F 1 A * * 4 4 B * 4 4 4 C 1 1 1 1 D * 2 2 2 E 8 8 6 6 F 0 0 0 0 1 1 A 1 1 1 1 B 0 0 0 0 C 3 3 3 3 D * 3 3 3 E * * 7 7 F * 4 4 4 A * 3 3 3 B 3 3 3 3 C 0 0 0 0 D 1 1 1 1 E * 5 5 5 F 1 1 1 1 C B 3 ENGS4 2004 Lecture 6

  21. A * 6 6 6 D B * * 7 7 D C * 5 5 5 D D 4 4 4 4 D E 0 0 0 0 E F 8 8 6 6 D A 2 2 2 2 A B * 3 3 3 A C 1 1 1 1 C D 0 0 0 0 D E 4 4 4 4 E F * 2 2 2 C The min neighbor determines the paths A 0 0 0 0 A B 1 1 1 1 B C * 4 3 3 D D 2 2 2 2 D E * 6 6 6 D F * * 4 4 D 4 E D 8 2 A F 1 A * * 4 4 C B * 4 4 4 C C 1 1 1 1 C D * 2 2 2 C E 8 8 6 6 C F 0 0 0 0 F 1 1 A 1 1 1 1 A B 0 0 0 0 B C 3 3 3 3 C D * 3 3 3 A E * * 7 7 A F * 4 4 4 C A * 3 3 3 D B 3 3 3 3 B C 0 0 0 0 C D 1 1 1 1 D E * 5 5 5 D F 1 1 1 1 F C B 3 ENGS4 2004 Lecture 6

  22. A 6 D B 7 D C 5 D D 4 D E 0 E F 6 D Only need the total distances and the next neighbor A 2 A B 3 A C 1 C D 0 D E 4 E F 2 C A 0 A B 1 B C 3 D D 2 D E 6 D F 4 D 4 E D 8 2 A F 1 A 4 C B 4 C C 1 C D 2 C E 6 C F 0 F 1 1 A 1 A B 0 B C 3 C D 3 A E 7 A F 4 C A 3 D B 3 B C 0 C D 1 D E 5 D F 1 F C B 3 ENGS4 2004 Lecture 6

  23. 2 A 6 D B 7 D C 5 D D 4 D E 0 E F 6 D A 2 A B 3 A C 1 C D 0 D E 4 E F 2 C Ooops...what if the network changes?? A 0 A B 1 B C 3 D D 2 D E 6 D F 4 D 4 E D 8 2 A F 1 A 4 C B 4 C C 1 C D 2 C E 6 C F 0 F 1 1 A 1 A B 0 B C 3 C D 3 A E 7 A F 4 C A 3 D B 3 B C 0 C D 1 D E 5 D F 1 F C B 3 Have enough information to keep updating the table until it stops changing ENGS4 2004 Lecture 6

  24. Abby’s Mini-lecture ENGS4 2004 Lecture 6

  25. “Predicting the Future” • Newtonian revolution (late 1600’s) : F=ma • Concept of “state” introduced • The “state” of a system is all that is needed to predict it’s future states. • Having additional information about the system’s past states does not help to predict it’s future. • This defines the notion of “state”. ENGS4 2004 Lecture 6

  26. Example • A cannonball shot from a canon. • Where will it fall? position + momentum of the canonball is the “state” ??? ??? ENGS4 2004 Lecture 6

  27. State-based Prediction • What are examples of state-based prediction? • Astronomy • Chemistry • Biology • Medicine • Others? ENGS4 2004 Lecture 6

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