ENGS 4 - Lecture 6 Technology of Cyberspace Winter 2004 Thayer School of Engineering Dartmouth College

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ENGS 4 - Lecture 6Technology of Cyberspace
Winter 2004Thayer School of EngineeringDartmouth
College

• Instructor George Cybenko, x6-3843
• gvc_at_dartmouth.edu
• Assistant Sharon Cooper (Shay), x6-3546
• Course webpage www.whoopis.com/engs4

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Todays Class

• Wrap-up of rule-based systems
• Jons mini-lecture
• Html tables and formatting
• Internet routing basics
• Break
• Bellman-Ford Routing Algorithm
• Abbys mini-lecture
• State-based methods for Predicting the Future

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Jons Mini-lecture
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Basic HTML tables

• ltTABLEgt ... lt/TABLEgt defines a table in HTML. If
  the BORDER attribute is present, your browser
  displays the table with a border.
• ltTRgt ... lt/TRgt specifies a table row within a
  table. You may define default attributes for
  the entire row.
• ltTDgt ... lt/TDgt 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 width30 determines percentage of
  the table a column uses.
• Attribute width30 determines how many pixels
  column uses.

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Basic HTML tables

• ALIGN LEFT, CENTER, RIGHT
• VALIGNTOP, MIDDLE, BOTTOM
• ltTHgt ... lt/THgt 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.

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Basic HTML lists

• ltolgt lt/olgt delimits an ordered list (ie
  numbered)
• ltulgt lt/ulgt delimits an unordered list (ie
  bullets)
• In each case, ltligt denotes a list item.
• Example
• ltolgt
• ltligt Monday
• ltligt Tuesday
• ltligt Wednesday
• lt/olgt

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Internet Routing Basics
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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.

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Circuit Switching
Reserve a circuit and that guarantees
services for each user Requires significant
setup time
Good for telephones, bad for web browsing!!!!
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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!!!!
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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

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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.
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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.edus 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.
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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
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Break
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Bellman-Ford Routing
Computer/host
4
E
D
8
2
A
F
1
1
1
C
B
3
Distance/cost/delay between hosts
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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
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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
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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
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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
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
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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
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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
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Abbys Mini-lecture
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Predicting the Future

• Newtonian revolution (late 1600s) Fma
• Concept of state introduced
• The state of a system is all that is needed to
  predict its future states.
• Having additional information about the systems
  past states does not help to predict its future.
• This defines the notion of state.

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Example

• A cannonball shot from a canon.
• Where will it fall?

position momentum of the canonball is the
state
???
???
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State-based Prediction

• What are examples of state-based prediction?
• Astronomy
• Chemistry
• Biology
• Medicine
• Others?