engs4 2004 lecture 6 engs 4 - lecture 6 technology of cyberspace winter 2004 thayer school of...

ENGS4 2004 Lecture 6

ENGS 4 - Lecture 6Technology of Cyberspace

Winter 2004Thayer School of Engineering

Dartmouth College

Instructor: George Cybenko, x6-3843

[email protected]

Assistant: Sharon Cooper (“Shay”), x6-3546

Course webpage: www.whoopis.com/engs4

http://www.whoopis.com/engs4


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”


Jon’s Mini-lecture


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.


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.


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>


Internet Routing Basics

http://www.danheller.com/images/Cuba/Streets/streets-a-big.jpg


“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.


Circuit SwitchingReserve a “circuit” and that “guarantees” services for each user

Requires significant “setup time”

Good for telephones, bad for web browsing!!!!


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!!!!


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


Resolving internet addresses

Your computer LAN

DHCP Server

DNS Server

1. Can I get an IPaddress, etc?

2. Here is a temporaryaddress andother information.

3. What is the address ofwww.cnn.com?

4. www.cnn.com is207.25.71.82

Rest ofthe world

Bridge or gateway or router or switch


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?

Router

Network 1

Network 2

A router can be a dedicated piece of hardware or a computerwith several network interfaces. Cisco, 3Com, etc sell routers.

?


Network routing

Routing table in a router looks like.....

Pattern Next node on path

129.170.*.* host 1125.*.*.* host 2105.121.5.21 host 3default host 4


Break


Bellman-Ford Routing

A

E

C

D

B

F2

1

3

1

4

1

8

Computer/host

Distance/cost/delaybetween hosts


A

E

C

D

B

F2

1

3

1

4

1

8

A 0B 1C *D 2E *F *

A 2B *C 1D 0E 4F *

A 1B 0C 3D *E *F *

A *B 3C 0D 1E *F 1

A *B *C 1D *E 8F 0

A *B *C *D 4E 0F 8

Initial table hasdistance to each host one hop awayand * otherwise.


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 0B 1 1C * 4D 2 2E * 6F * *

A 2 2B * 3C 1 1D 0 0E 4 4F * 2

A 1 1B 0 0C 3 3D * 3E * *F * 4

A * 3B 3 3C 0 0D 1 1E * 5F 1 1

A * *B * 4C 1 1D * 2E 8 8F 0 0

A * 6B * *C * 5D 4 4E 0 0F 8 8

newdistance to X = min( distance toneighbor + distancefrom neighbor to X)where min is over allneighbors


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 0 0B 1 1 1C * 4 3 D 2 2 2E * 6 6F * * 4

A 2 2 2B * 3 3C 1 1 1D 0 0 0E 4 4 4F * 2 2

A 1 1 1B 0 0 0C 3 3 3D * 3 3E * * 7F * 4 4

A * 3 3B 3 3 3C 0 0 0D 1 1 1E * 5 5F 1 1 1

A * * 4B * 4 4C 1 1 1D * 2 2E 8 8 6F 0 0 0

A * 6 6 B * * 7 C * 5 5 D 4 4 4 E 0 0 0 F 8 8 6

Repeat it!!!


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 0 0 0B 1 1 1 1C * 4 3 3D 2 2 2 2E * 6 6 6F * * 4 4

A 2 2 2 2B * 3 3 3C 1 1 1 1D 0 0 0 0E 4 4 4 4F * 2 2 2

A 1 1 1 1B 0 0 0 0C 3 3 3 3D * 3 3 3E * * 7 7F * 4 4 4

A * 3 3 3B 3 3 3 3C 0 0 0 0D 1 1 1 1E * 5 5 5F 1 1 1 1

A * * 4 4B * 4 4 4C 1 1 1 1D * 2 2 2E 8 8 6 6F 0 0 0 0

A * 6 6 6 B * * 7 7C * 5 5 5D 4 4 4 4E 0 0 0 0F 8 8 6 6

Repeat it...stopwhen the tabledoes not change.


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 0 0 0 AB 1 1 1 1 BC * 4 3 3 DD 2 2 2 2 DE * 6 6 6 DF * * 4 4 D

A 2 2 2 2 AB * 3 3 3 AC 1 1 1 1 CD 0 0 0 0 DE 4 4 4 4 EF * 2 2 2 C

A 1 1 1 1 AB 0 0 0 0 BC 3 3 3 3 CD * 3 3 3 AE * * 7 7 AF * 4 4 4 C

A * 3 3 3 DB 3 3 3 3 BC 0 0 0 0 CD 1 1 1 1 DE * 5 5 5 DF 1 1 1 1 F

A * * 4 4 CB * 4 4 4 CC 1 1 1 1 CD * 2 2 2 CE 8 8 6 6 CF 0 0 0 0 F

A * 6 6 6 D B * * 7 7 DC * 5 5 5 DD 4 4 4 4 DE 0 0 0 0 EF 8 8 6 6 D

The min neighbordetermines thepaths


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 AB 1 BC 3 DD 2 DE 6 DF 4 D

A 2 AB 3 AC 1 CD 0 DE 4 EF 2 C

A 1 AB 0 BC 3 CD 3 AE 7 AF 4 C

A 3 DB 3 BC 0 CD 1 DE 5 DF 1 F

A 4 CB 4 CC 1 CD 2 CE 6 CF 0 F

A 6 D B 7 DC 5 DD 4 DE 0 EF 6 D

Only need thetotal distancesand the next neighbor


A

E

C

D

B

F2

1

3

1

4

1

8

A 0 AB 1 BC 3 DD 2 DE 6 DF 4 D

A 2 AB 3 AC 1 CD 0 DE 4 EF 2 C

A 1 AB 0 BC 3 CD 3 AE 7 AF 4 C

A 3 DB 3 BC 0 CD 1 DE 5 DF 1 F

A 4 CB 4 CC 1 CD 2 CE 6 CF 0 F

A 6 D B 7 DC 5 DD 4 DE 0 EF 6 D

Ooops...what if thenetwork changes??

2

Have enough informationto keep updating the tableuntil it stops changing


Abby’s Mini-lecture


“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”.


Example

• A cannonball shot from a canon.

• Where will it fall?

??????position +momentum of the canonballis the “state”


State-based Prediction

• What are examples of state-based prediction?

• Astronomy

• Chemistry

• Biology

• Medicine

• Others?

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