INFORMATION TECHNOLOGY IN BUSINESS AND SOCIETYSESSION 6 – HOW COMPUTERS AND THE WEB WORK

SEAN J. TAYLOR

ADMINISTRATIVIA

• Facebook Experiment: See Beibei Li in 8-186 Friday 2pm-4pm to receive payment

• Varun’s office hours on Monday: 2-4pm in 8th floor tutoring area

• Assignment 1• My office hours: moved to 3:30-5:30pm on

FRIDAY (temporarily)

LEARNING OBJECTIVES

1. Understand basic computer architecture and how it has been enabled by layering platforms and Moore’s law.

2. Be able to explain how the Internet functions at a high level.

WHY WE CARE?

“We’re in an engineering culture. You couldn’t put a [Rupert] Murdoch or a [Michael] Eisner in charge of a company [like Google]. It’s been tried. Terry Semel led Yahoo. I just spent some time with Google engineers. I couldn’t understand a thing they were saying. I don’t think [Semel] understood the engineers’ language, so he couldn’t challenge them. I suspect that’s one reason he didn’t last”

Ken Auletta, SIIA keynote, 1/30/2008

BASIC COMPUTER ARCHITECTURE:INFORMATION REPRESENTATION• Numbers

• Text

• Pictures

• Audio

42 00101010

IT 01001010 01010100

.gif, .jpeg, .bmp,…

AU-Sun, WAV-MS, AIF-Apple, MP3

Understanding Binary:ASCII coding scheme

FROM ANALOG TO DIGITAL DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011

FROM ANALOG TO DIGITAL DATA000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011

000000000000000111111000001100001100001000000100010010010010010000000010010000000010001011110100001100001100000111111000000000000011000000000011

BASIC COMPUTER ARCHITECTURE

UBIQUITOUS COMPUTING

COMPUTER BASICS: HARDWARE• Central processing unit (CPU): the actual hardware that

interprets and executes software instructions and coordinates how all the other hardware devices work together.• Intel: 286386486Pentium I,II,III,IV, AMD Athlon, IBM

PowerPC, Sun SPARC, MIPS• Random Access Memory (RAM): The place to keep the data

and applications while the computer is running• Storage: A tool you use to store information for use at a later

time• floppy disks, CD, DVD, Hard Disks, tape

TELLING COMPUTERS WHAT TO DO

THE INTERNET

WHAT IS THE INTERNET?

• A very large network of computers that “speak” IP (and usually TCP as well)• All connected to each other (hence a “network”)• Information exchanged between two computers may pass through several other

computers

HOW IT BEGAN: THE INTERNET IN 1969

Interface Message Processors (IMPs) – packet switching nodes used to connect to ARPANET

ARPANET 1971

ARPANET 1980

SIMPLIFIED STRUCTURE OF THE INTERNETHierarchy of privately-owned networks• Backbone network: High speed, city-to-city, with network access

points, owned by large service providers (AT&T, Sprint, Level3)• ISP networks: Connect from backbone to local areas (typically

providing access to consumers)• Local access networks: Access to individual computers

Internet:• No single authority• No single control source • No single entry point • No single type of application

INTERNET BACKBONE• Set of interconnected Wide Area Networks (WANs)

• Similar to the Interstate Highway network

• WAN owners (backbone providers) compete with each other• Several connections converge at a Network Access Point

(NAP). Each NAP has at least one intelligent device – transitional data communication facilities.

• Backbone providers own and maintain devices at NAPs

Internet Backbone

Carriers

ISPISP

THE INTERNET

THE INTERNET

LAYERS

WHY IS INTERNET STRUCTURE STRATEGIC?

Resilient. One node goes down, others don’t.Intelligence is at the edges.Content agnostic.Application agnostic.No single authority controls it.Extensible – Can always add more.

PACKET-SWITCHED NETWORKSData is sent as a sequence of ‘packets’• Packet Switched vs. Circuit Switched Networks• It isn’t cost effective to have telephone-like connections

between different communicating computers • This is primarily because data transmission is ‘bursty’

Packetize, transmit, reassemble.

……..

01101010101000010101011100

01101010101000010101011100

01101010101000010101011100

Packets0110110111101111101111101010110111……….01110

Message

Network

PROTOCOLS AND TCP/IPEffective communication requires rules

• Protocol: A set of rules for transmitting data between computers

• Example: TCP/IPThe ‘rules’ in a protocol answer questions like:

• How do I write down the address of the computer I want to send my packet to?

• Where do I send the next packet I get?• How do I detect the beginning of a new packet?• How do I figure out an error in transmission?

IP address

• 32-bit number given to each device connected to the Internet

OSI 7 LAYER MODEL

Coaxial Cable, Twisted Pair

EthernetIPTCP

HTTPSSL

INTERNET PROTOCOLEach Internet computer (host) has an IP address

• String of 32 ones and zeros (IPv4 -> IPv6)• Usually represented by four number segments separated by dots: dotted

decimal notation, e.g., 128.171.17.13• IP names (e.g., www2.nyu.edu) correspond to IP addresses

Routers

• Connect the Internet’s individual networks (subnets)• Cooperate to give an end-to-end route for each packet• Need to be very fast• Who is the world’s leading

seller of routers?

127.18.47.145 127.47.17.47

From:

128.122.199.131

To:

216.115.102.78 IPXpressInternet Delivery Envelope

seanjtaylor.com

www.yahoo.com

TCP OVER IP

IP and TCP protocols allow any two computers on the Internet to exchange data

TRANSMISSION CONTROL PROTOCOL

DNS: UNDERSTANDING DOMAINSDNS is the Internet’s “directory assistance” linking IP names to IP addresses

A computer’s IP name tells you a lot; e.g., the type of organization supporting the Web site

Top-level domain: the last part of IP names, e.g.,• com – commercial or for-profit business• edu – educational institution• gov – U.S. government agency• mil – U.S. military organization• net – Internet administrative organization• org – professional or non-profit organization• biz – business• pro – accountants, doctors, and lawyers, to start

How do you get a domain name?

HTTP: HYPERTEXT TRANSFER PROTOCOL

HTTP IN ACTION

“THE ELEMENTS OF COMPUTING SYSTEMS”“WEAVING THE WEB” (TIM BERNERS-LEE)

NEXT CLASS:COMPUTERS AND THE WEB II

• HTML tutorial