The document discusses the history and development of computer networking and the Internet, including early networks using signal fires, semaphores, and electrical telegraphs, the development of packet switching and protocols that enabled the Internet, and some of the key people and organizations involved in creating the early ARPANET that served as the foundation for today's Internet. It also compares the first transmission of data packets on the ARPANET in 1969 to the live video transmitted from the moon landing just 3 months prior.

1. Lecture 38: The Internet
Netcraft.com:
November 2011 survey
of 500+ million web
sites
cs1120 Fall 2011
David Evans
http://www.cs.virginia.edu/evans

2. Reminders
My office hours today are cancelled. I will have office
hours tomorrow or email for appointment.
Exam 2: Due Wednesday, beginning of class
Problem Set 8:
J Option: due next Monday (7:59pm)
C/W Option:
In-class presentation option (next Monday)
Submission by posting
If you want to present in class, send me an email by 5pm Friday.
Request how much time you want/need and what you want to do.

3. Plan
Type Checking
Most important difference between
Python/Scheme and Java
The Internet
Latency/Bandwidth
Packet switching
Web applications
3

4. Types
Numbers Strings
programs that halt
Colors
Beatle’s Songs that don’t end on the Tonic
lists of lists of lists of anything
Type is a (possibly infinite) set of values
You can do some things with some types, but
not others

5. Why have types?
Detecting programming errors: (usually) better
to notice error than report incorrect result
Make programs easier to read, understand and
maintain: thinking about types can help
understand code
Verification: types make it easier to prove
properties about programs
Security: can use types to constrain the behavior
of programs

6. Types of Types
Does regular Scheme have types?
> (car 3)
car: expects argument of type <pair>; given 3
> (+ (cons 1 2))
+: expects argument of type <number>; given (1 . 2)
Yes, without types (car 3) would produce some silly result.
Because of types, it produces a type error.

7. Types in Python?
>>> "1" + 2
Traceback (most recent call last):
File "<pyshell#17>", line 1, in <module>
"1" + 2
TypeError: cannot concatenate 'str' and 'int' objects
>>> 1 + "2"
Principle of Least Astonishment.
Traceback (most recent call last):
“a programmer should try to think of
File "<pyshell#18>", line 1, in <module>
1 + "2"
the behavior that will least surprise
someone who uses the
TypeError: unsupported operand type(s) for +: 'int' and 'str‘
program, rather than that behavior
>>> 1 + True that is natural from knowing the
2 inner workings of the program.”
7

8. Scheme/Python/Charme Java/Taazda
Scheme, Python: Latent, Dynamically-checked
Don’t see explicit types when you look at code
Checked when an expression is evaluated
Java, Taazda: Manifest, Statically-checked types
Type declarations must be included in code
Types are checked statically before running the
program

9. Java Example The parameter
must be a String
The result class Test {
is an integer
int tester (String s)
> javac types.java
{
The place x
types.java:5: Incompatible type int x; holds an integer
for =. Can't convert
java.lang.String to int. x = s;
x = s; return "okay";
^
types.java:6: Incompatible type }
for return. Can't convert
java.lang.String to int.
}
return "okay"; javac compiles (and type checks) the program. It
^ does not execute it. In Eclipse compilation happens
2 errors automatically in the background.

10. Complex Types
public static void listReverse(ArrayList<Object> p) {
for (int i = 0; i < p.size() / 2; i++) {
Object pi = p.get(i);
p.set(i, p.get(p.size() - i - 1)); ArrayList<String> a = new ArrayList<String>();
p.set(p.size() - i - 1, pi); a.add("one");
} a.add("two");
} a.add("three");
a.add("four");
Subtyping: (similar to Python) listReverse(a);
String is a subtype of Object: The method listReverse(ArrayList<Object>)
(class String extends Object) in the type Main is not applicable for the
type rules allow String where Object arguments (ArrayList<String>)
everything you can do with an Object,
you can do with a String
Generic Types: (type parameters)
ArrayList<S> is not a subtype of
ArrayList<T>
10

11. Parameterized Types
public static <T> void listReverse(ArrayList<T> p) {
for (int i = 0; i < p.size() / 2; i++) {
T pi = p.get(i);
p.set(i, p.get(p.size() - i - 1));
p.set(p.size() - i - 1, pi);
}
}
This works on both ArrayList<String> and
ArrayList<Object>.
11

12. The Internet

13. What is a Network?
Neural Network
http://flowingdata.com/2008/03/12/17-ways-to-visualize-the-twitter-universe/

14. What is a Network?
A group of three or more connected
communicating entities.

15. Beacon Chain Networking
Thus, 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.

16. Pony Express
April 1860 – October 1861
Missouri to California
10 days; 10-15 miles per horse, ~100 miles per rider
400 horses total

17. Chappe’s Semaphore Network
First Line (Paris to Lille), 1794 Mobile Semaphore Telegraph
Used in the Crimean War 1853-1856

18. Measuring Networks
Latency
Time from sending a bit until it arrives
seconds (or seconds per geographic distance)
Bandwidth
Rate at which can you transmit
bits per second

19. Latency and Bandwidth
Napoleon’s Network: Paris to Toulon, 475 miles
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 about 9 days to get ps7.zip

20. Improving Latency
Less transfer points
Longer distances between transfer points
Semaphores: how far can you see clearly
Curvature of Earth is hard to overcome
Use wires (electrical telegraphs, 1837)
Faster transfers
Replace humans with machines
Faster travel between transfers
Hard to beat speed of light (semaphore network)
Electrons in copper: about 1/3rd speed of light

21. How many network transfer points
between here and California?

22. > traceroute www.cs.berkeley.edu
traceroute to web2.EECS.berkeley.edu (128.32.244.172), 30 hops max, 40 byte packets
1 128.143.69.1 (128.143.69.1) 0.869 ms 0.852 ms 1.092 ms
2 internet-2-x.misc.Virginia.EDU (128.143.222.95) 200.639 ms 1.623 ms 5.590 ms
3 nwv-nlrl3.misc.Virginia.EDU (192.35.48.30) 4.207 ms 4.163 ms 4.221 ms
4 nlrl3-router.networkvirginia.net (192.70.138.110) 6.575 ms 4.167 ms 4.218 ms
5 vlan-55.rale.layer2.nlr.net.nlr.net (216.24.186.90) 74.475 ms 74.497 ms 74.356 ms
6 vlan-54.atla.layer2.nlr.net.nlr.net (216.24.186.52) 74.468 ms 74.684 ms 74.849 ms
7 vlan-53.jack.layer2.nlr.net.nlr.net (216.24.186.55) 74.592 ms 74.675 ms 74.487 ms
8 vlan-51.hous.layer2.nlr.net.nlr.net (216.24.186.78) 74.559 ms 74.552 ms 74.352 ms
9 vlan-47.elpa.layer2.nlr.net.nlr.net (216.24.186.74) 74.601 ms 74.425 ms 74.480 ms
10 vlan-43.losa.layer2.nlr.net.nlr.net (216.24.186.73) 74.439 ms 74.428 ms 74.483 ms
11 hpr-lax-hpr2--nlr-pn.cenic.net (137.164.26.25) 74.343 ms 74.302 ms 74.479 ms
12 svl-hpr2--lax-hpr2-10g.cenic.net (137.164.25.38) 82.384 ms 82.457 ms 82.467 ms
13 hpr-ucb--svl-hpr2.cenic.net (137.164.27.130) 84.326 ms 84.412 ms 84.463 ms
14 t1-3.inr-201-sut.Berkeley.EDU (128.32.0.65) 84.575 ms 84.417 ms 84.555 ms
15 evans-eecs-br-10GE.EECS.Berkeley.EDU (128.32.255.54) 87.600 ms 86.131 ms 86.092 ms
16 * * *
17 * * *
18 * * *
Unix: traceroute
19 * * *
Windows: tracert
22

23. >>> cvilleberkeley = 3813 # kilometers
>>> seconds = 84.0/1000
>>> speed = cvilleberkeley / seconds
>>> speed
45392.857142857138
>>> light = 299792.458 # km/s
>>> speed / light
0.15141427321316114
Packets are traveling average at 15% of the speed of
light (includes transfer time through 15 routers)

24. Busselton, Western Australia, Australia
24

25. > traceroute -q 1 -w 10 www.busselton.wa.gov.au
traceroute to busselton.wa.gov.au (203.41.180.233), 30 hops max, 40 byte packets
1 128.143.69.1 (128.143.69.1) 1.196 ms
2 internet-2-x.misc.Virginia.EDU (128.143.222.95) 0.822 ms
3 192.35.48.26 (192.35.48.26) 4.243 ms
4 xe-9-3-0.edge3.Washington1.Level3.net (4.59.144.65) 4.151 ms
5 vlan60.csw1.Washington1.Level3.net (4.69.149.62) 4.149 ms
6 ae-64-64.ebr4.Washington1.Level3.net (4.69.134.177) 16.255 ms
7 ae-4-4.ebr3.LosAngeles1.Level3.net (4.69.132.81) 69.054 ms
8 ae-63-63.csw1.LosAngeles1.Level3.net (4.69.137.34) 68.423 ms
9 ae-4-90.edge1.LosAngeles6.Level3.net (4.69.144.208) 68.298 ms
10 reach-level3-xe.losangeles.level3.net (4.68.62.10) 68.209 ms
11 i-0-4-2-0.1wlt-core01.bi.reach.com (202.84.251.201) 69.159 ms
12 i-0-6-2-0.sydo-core02.bx.reach.com (202.84.140.221) 208.434 ms
13 TenGigE0-2-0-5.oxf-gw1.Sydney.telstra.net (203.50.13.13) 210.659 ms
14 Bundle-Ether1.ken-core4.Sydney.telstra.net (203.50.6.5) 218.852 ms
15 Bundle-Pos3.win-core1.Melbourne.telstra.net (203.50.11.13) 225.130 ms
16 Pos0-0-0-0.fli-core1.Adelaide.telstra.net (203.50.6.186) 234.263 ms
17 Bundle-Pos2.wel-core3.Perth.telstra.net (203.50.11.19) 269.102 ms
18 GigabitEthernet0-1.wel13.Perth.telstra.net (203.50.115.151) 267.374 ms
19 *
20 *
21 *
25

26. 26

27. Bandwidth
How much data can
you transfer in a given
amount of time?

28. 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)

29. Morse Code
Represent letters with series of
short and long electrical pulses

30. Circuit Switching
Reserve a whole path through the network for
the whole message transmission
Paris Bourges Lyon Toulon
Once you start a transmission,
know you will have use of the
network until it is finished. But,
Nantes wastes network resources.

31. Packet Switching
Use one link at a time
Paris Bourges Lyon Toulon
Interleave messages – send
whenever the next link is free.
Nantes

32. Circuit and Packet Switching
(Land) Telephone Network (back in the old days)
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; software reassembles packets as
received

33. Today’s Internet: Bandwidth
Ethernet:
up to 100 Mbits/sec
My office:
~50 M bits / sec
UVa Wireless:
57 M bits / sec
Cable modem at home:
~ 30 M bits / sec
33

34. internetwork
A collection of multiple networks connected
together, so messages can be transmitted
between nodes on different networks.

35. The First (international) 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

36. The (capital-I) Internet
Packet Switching:
Leonard Kleinrock (UCLA) thinks
he did, Donald Davies and Paul
Baran, Edelcrantz’s signalling
network (1809)
Internet Protocol:
Vint Cerf, Bob Kahn
Vision, Funding (DARPA):
J.C.R. Licklider, Bob Taylor
Government: Al Gore
First politician to promote
Internet, 1986; act to connect
government networks to form Vint Cerf (in the Rotunda, 2010)
“Interagency Network”

37. First Use of the Internet
October 1969: First packets on the ARPANet
from UCLA to Stanford. Starts to send
"LOGIN", but it crashes on the G.
How impressive is this compared to
communications event 3 months earlier?

38. 20 July 1969:
Live b/w video from the moon, transmitted
live to millions of televisions worldwide
38

39. Exam 2 due
Charge Wednesday, beginning of
class
From Tim Berners-Lee’s “Answers for Young People” http://www.w3.org/People/Berners-Lee/Kids.html
I think the main thing to remember is that any really powerful thing can be
used for good or evil. Dynamite can be used to build tunnels or to make
missiles. Engines can be put in ambulances or tanks. Nuclear power can be
used for bombs or for electrical power. So the what is made of the Web is up
to us. You, me, and everyone else.
Here is my hope: The Web is a tool for communicating. With the Web, you
can find out what other people mean. You can find out where they are
coming from. The Web can help people understand each other.
Think about most of the bad things that have happened between people in
your life. Maybe most of them come down to one person not understanding
another. Even wars.
Let’s use the web to create neat new exciting things.
Let’s use the Web to help people understand each other.