engs4 2004 lecture 6 engs 4 - lecture 6 technology of cyberspace winter 2004 thayer school of...
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ENGS4 2004 Lecture 6
ENGS 4 - Lecture 6Technology of Cyberspace
Winter 2004Thayer School of Engineering
Dartmouth College
Instructor: George Cybenko, x6-3843
Assistant: Sharon Cooper (“Shay”), x6-3546
Course webpage: www.whoopis.com/engs4
ENGS4 2004 Lecture 6
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
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
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
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
Internet Routing Basics
ENGS4 2004 Lecture 6
“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
Circuit SwitchingReserve a “circuit” and that “guarantees” services for each user
Requires significant “setup time”
Good for telephones, bad for web browsing!!!!
ENGS4 2004 Lecture 6
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
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
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
ENGS4 2004 Lecture 6
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.
?
ENGS4 2004 Lecture 6
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
ENGS4 2004 Lecture 6
Bellman-Ford Routing
A
E
C
D
B
F2
1
3
1
4
1
8
Computer/host
Distance/cost/delaybetween hosts
ENGS4 2004 Lecture 6
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.
ENGS4 2004 Lecture 6
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
ENGS4 2004 Lecture 6
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!!!
ENGS4 2004 Lecture 6
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.
ENGS4 2004 Lecture 6
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
ENGS4 2004 Lecture 6
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
ENGS4 2004 Lecture 6
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
ENGS4 2004 Lecture 6
“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
Example
• A cannonball shot from a canon.
• Where will it fall?
??????position +momentum of the canonballis the “state”