1

History and Infrastructure

Computer Science 01iIntroduction to the Internet

Brian Cooper23 January 2001

2

Some web statistics

• More than 1 billion pages• Web languages

86.55% English 2.36% French 0.54% Dutch

• http://www.inktomi.com/webmap/

• Today: 1,326,920,000 web pages indexed by Google (http://www.google.com)

3

1,000,000,000?!

from a 1964 book about a near-infinite library that contained all the 500 page books that could be generated by permuting the alphabet:

“The certitude that any book exists on the shelves of the library first led to elation, but soon the realization that it was unlikely to be found converted the feelings to a great depression.” [Luis Borges: The Infinite Library]

4

Today’s Outline

• Quick look at some terms• Infrastructure

LANs and WANs Packets and Ethernet Routing, IP, and Standards

• HTML Introduction?• Today’s Project!

5

Some “Terms”

• http:// vs. www.

• When and why does one use slash, dot, tilde, etc?

• Why do some addresses have ”.html" at the end and others do not?

• Example: http://www-db.stanford.edu/~nsample/cs01/

6

Some “Terms” (continued)

• Who assigns the .com, .edu, .org, .gov., .x and can you choose? .com = commercial .gov = government .edu = educational .ie = Ireland New

domains: .aero, .biz, .coop, .info, .museum, .name, .pro

• How are names registered? www.InterNIC.net, www.icann.org for more information

7

What is the internet anyway?

• Good question

• The internet is not just the “world wide web” anymore than UPS is the interstate highway system.

• But, we will focus on services available on the ‘Net such as the world wide web.

8

So? What is it?!

The internet is a collection of local area networks combined into one extremely large wide area network.

9

Local Area Networks (LANs)

• A small network of computers in close proximity to each other.

• Roughly a single building’s worth of computers connected together

• Usually via ethernet, but other ways are possible (token ring, local talk, etc.)

10

Circuit Switching

• Classic phone system• Even when no information is

exchanged, a connection still ties up the system

• Inefficient use of bandwidth even when information is exchanged

• Absolutely guarantees a minimum amount of bandwidth and latency very good for interactivity

11

Packet Switching

• Messages are broken into small pieces and then transmitted one at a time. Packets on the internet are usually 0.5-1.5

kilobytes Each packet must have an address and

some error correction information-its “header”

• Can interleave one message with another

12

Ethernet

• Original design in 1973 by Bob Metcalf, Xerox PARC

• How can I get bits from one computer to another cheaply, easily, and above all, quickly?

• Could have phone system style setup

13

Ethernet Design

• Each computer has a unique address• All computers are connected to a

single wire (but can be any medium, like radio)

• All computers listen to every message• Wait until the line is free to broadcast• If there is a collision, wait a random

period of time then try again. This is the breakthrough.

14

Wide Area Networks (WANs)

• Connect physically distant computers• Often connect physically distant LANs• Usually involve phone companies• There are a wide variety of ways to do

this, but some significant companies include: Cisco Systems and 3Com (build

hardware) AT&T and Sprint (own the pipes)

15

WAN Design

• Probably very high bandwidth

• Probably fairly low latency

• Pre-Internet, WANS were more or less all proprietary

16

Why make the distinction?

• Because the issues are very different You have full control over the wires on a

LAN You probably have a contract with a phone

company on a WAN

• LANs are relatively cheap to grow• WANs are expensive to grow

What does it take to run a cable from one side of the street to the other?

17

Routers

• Connect two physically different networks an ethernet and a token-ring network a modem connection and an ethernet a LAN and a fiber optic cable

• Translate electrical requirements• Translate between the two

addresses

18

How Routers Work

• Look to other computers like just another machine on the LAN

• Looks at all packets on the LAN and forwards those destined for the outside world

• You often need the IP address of your local router when configuring your internet connection (the gateway)

19

The internet is a giant WAN

• Many computers of various… Types: Intel, Sun, Palm Pilots, Atari, Apple,

embedded systems, etc. Operating Systems: Windows 3.11, 95, 98,

NT, 2000, UNIX, Linux, MacOS’s, etc. Sophistication: Space Shuttle to PCs Speeds: 16MHz 8086’s to 1 GHz machines

• How do I get all of them talking together?

20

Protocol

• A way for machines to talk to one another

• Like Korean or ASL or PASCAL• Hundreds of different protocols

operate together to make the internet work properly Each is responsible for a different service Each is built on some protocol below

21

Internet Protocol (IP)

• The most basic protocol of the Internet

• Designed to get a single packet from one computer to another

• Abstracts the physical connection between two machines

22

IP Addresses I

• Every computer on the Internet has one

• Represented by four numbers between 0 and 255 (ie, four bytes) My home machine: 216.132.81.61 My office machine: 171.65.75.234 My office router: 171.64.75.1

23

IP Addresses II

• An IP address is like a phone number A neighborhood like a phone exchange

code:• 171.64.75. = (650) 723-1963

A machine number is like the last four digits• .234 = (650) 723-1963

Not always this straight forward… the “dash” floats

• Move your machine neighborhood and it will need a new IP address

24

More about IP

• IP actually promises to do very little• Try to get a single packet from one computer

to another• Does not guarantee a packet’s

arrival timing error free transmission route

• Has no idea about a packet’s content, but does know its length

25

This is actually very powerful

• Any physical media that can implement IP can get on the internet completely! It is possible to implement IP over radio

waves (ricochet modems) It has even been proposed to implement

IP over carrier pigeon!

26

The problem with IP

• 32 bits long means that the maximum size of the Internet is 4,294,967,296 computers sounds like a lot, but isn’t Ran out of addresses in late 1994 or early 1995 Currently using tricks to circumvent that limit

• A new version called IPv6 is coming to augment the current IPv4 128-bit addresses, other optimizations 2128 vs. 1080 (< 284 = number of particles in the known

universe)

27

Routing Packets

• No router knows how to get from any one computer to any other

• If a router doesn’t know the destination, it passes the packet to another router believed to be closer

• This router repeats the process• So a packet hops from router to

router until it finds the destination

28

More on Routing

• The routing system is extremely flexible and decentralized

• Downside: One bad router in a certain place can really screw up a portion of the Internet This is often what crackers mean when

they talk about “bringing down the internet”

Bring down enough routers to really mess things up (BBNPlanet)

29

Why was IP designed that way?

• A product of the cold-war nuclear threat• The Internet descended from military

research to develop a wide-area network able to withstand a nuclear war: ARPAnet Because a packet’s route, timing, etc. isn’t

guranteed, the Internet is extremely reliable in the face of local catastrophic failure

Problems (other than nuclear war) take down local sections of the internet everyday, but IP adapts automatically

30

Aside: Open Standards

• Every Internet protocol is publicly known Most generated through standards bodies

and research institutions Anyone can implement the standard for free Anyone who does knows it will work with the

entire Internet Contrast to proprietary systems

• industry alone could never make IP successful

31

Transmission Control Protocol (TCP)

• Almost always mentioned in the same breath as IP (TCP/IP)

• Fakes a reliable connection over an unreliable one

• Delivers an entire message to a particular destination How is this different from IP’s guarantees? Why is it nice that TCP is built on top of IP?

32

How TCP Works

• Adds certain information to an IP packet Packet 1 of 10 Time sent Error correction information Destination application (email, web, etc.)

• the “port” number

• The destination computer asks the original computer to resend any missing or corrupted packets

• Resorts the packets into the proper order

33

More TCP/IP

• How does the TCP protocol compare to the IP protocol below it? Low bandwith High latency But reliable!

• Other protocols built directly on top of IP- such as UDP- are often referred to as TCP/IP anyway

34

To capitalize or not

“An internet” vs “The Internet”

For almost everyone in the world, there is only one internet

35

Project: putting the web to work!

• How long will I be around?www.northwesternmutual.com/games/longevity/

index.html

• Calculator Madnessphysics.hallym.ac.kr/education/lecture/SEP/HSG/RefCalculators.html

• Results! nsample@stanford.edu(good site, bad site? A calculation of some sort?)