Hon Wai Leong, NUS(UIT2201, Networks) Page 1

Copyright © 2007 by Leong Hon Wai

Networks, Internet & WWW

Reading Materials:Ch 7 of [SG3]Additional Notes: (from web-site)

Contents:Motivation for NetworksTypes of Networks and Their StructureCommunication Protocols – routing infoNetwork Services / Applications Internet and WWW

Hon Wai Leong, NUS(UIT2201, Networks) Page 2

Copyright © 2007 by Leong Hon Wai

Objectives

In this chapter, you will learn aboutBasic networking conceptsCommunication protocolsNetwork services and benefits A brief history of the Internet and the

WWW

OutlineOutline

What is the Internet?What is the Internet? Where did it come from?Where did it come from? What are we going to discuss in What are we going to discuss in

cs193i?cs193i? BreakBreak Networking basicsNetworking basics Physical InfrastructurePhysical Infrastructure

The Ever-changing The Ever-changing InternetInternet

Different colors based on IP addressDifferent colors based on IP addresshttp://research.lumeta.com/ches/maphttp://research.lumeta.com/ches/map

What is the Internet?What is the Internet?

WWWWWW Video conferencingVideo conferencing ftpftp telnettelnet EmailEmail Instant messagingInstant messaging ……

What is the Internet?What is the Internet?

WWWWWW Video conferencingVideo conferencing ftpftp telnettelnet EmailEmail Instant messagingInstant messaging ……

A communication infrastructureA communication infrastructure

Usefulness is in exchanging informationUsefulness is in exchanging information

“On-line interactive communities... will be

communities not of common location, but of common

interest.... the total number of users...will be large

enough to support extensive general purpose

[computers]. All of these will be interconnected by

telecommunications channels... [to] constitute a labile

network of networks--ever changing in both content

and configuration.”

J. C. R. Licklider

Where Did It Come Where Did It Come From?From?

It was invented by Al Gore. It was invented by Al Gore. JUST KIDDING!JUST KIDDING! Early 1960’s - DARPA (ARPA in 1960’s) project Early 1960’s - DARPA (ARPA in 1960’s) project

headed by Lickliderheaded by Licklider Late 1960’s - ARPANET & research on packet Late 1960’s - ARPANET & research on packet

switching by Robertsswitching by Roberts First node installed by BBN at UCLA in September 1969First node installed by BBN at UCLA in September 1969 1969 - Four host computers (UCLA, SRI, UCSB, University 1969 - Four host computers (UCLA, SRI, UCSB, University

of Utah)of Utah)

Get more info at:http://www.isoc.org/internet/history/http://www.packet.cc/internet.html

ARPANET, 1980ARPANET, 1980

http://mappa.mundi.net/maps/maps_001/

History of the InternetHistory of the Internet 1969 - RFCs begun by S. Crocker 1969 - RFCs begun by S. Crocker

(http://rfc.sunsite.dk/)(http://rfc.sunsite.dk/) 1972 - Email by Ray Tomlinson & Larry Roberts1972 - Email by Ray Tomlinson & Larry Roberts 1970’s - TCP by Vint Cerf & Bob Kahn1970’s - TCP by Vint Cerf & Bob Kahn

Evolved into TCP/IP, and UDPEvolved into TCP/IP, and UDP 1980s – Hardware Explosion (LANs, PCs, and 1980s – Hardware Explosion (LANs, PCs, and

workstations)workstations) 1983 – Ethernet by Metcalfe1983 – Ethernet by Metcalfe

DNS – Distributed and scalable mechanism for DNS – Distributed and scalable mechanism for resolving host names into IP addressesresolving host names into IP addresses

UC Berkeley implements TCP/IP into Unix BSDUC Berkeley implements TCP/IP into Unix BSD 1985 – Internet used by researchers and 1985 – Internet used by researchers and

developersdevelopers

History of the InternetHistory of the Internet

Tim Berners-Lee at CERN in 1989Tim Berners-Lee at CERN in 1989 Proposal for WWW in 1990Proposal for WWW in 1990 First web page on November 13, 1990First web page on November 13, 1990

Hypertext - Text that contains Hypertext - Text that contains linkslinks to to other text.other text. Ted Nelson’s XanaduTed Nelson’s Xanadu Vannevar Bush’s MemexVannevar Bush’s Memex

(http://www.theatlantic.com/unbound/flashbks/computer/(http://www.theatlantic.com/unbound/flashbks/computer/bushf.htm)bushf.htm)

W3CW3CGet more info at:http://www.isoc.org/internet/history/

Communicating Via the Communicating Via the InternetInternet

Network

MSN Messenger

mar@cs.washington.edu

kashaw@cs.stanford.edu

How’s theweather inSeattle, Mar?

Bits and BytesBits and Bytes Computer Data is stored in BinaryComputer Data is stored in Binary

Binary Digits (bits) Base 2 representationBinary Digits (bits) Base 2 representation10111000011010101011100001101010

Every 8 bits == 1 ByteEvery 8 bits == 1 Byte10111000 01101010 (2 bytes (once known 10111000 01101010 (2 bytes (once known as octet))as octet))

Hexadecimal == Base 16 representationHexadecimal == Base 16 representation1011 1000 0110 10101011 1000 0110 1010 B 8 6 AB 8 6 A

Decimal == Base 10 (we have 10 fingers)Decimal == Base 10 (we have 10 fingers)0...9, A = 10, B= 11, C = 12, D = 13, E = 0...9, A = 10, B= 11, C = 12, D = 13, E = 14, F = 1514, F = 15

Bits and BytesBits and Bytes

Kilobyte (2^10=1024 Bytes, Kilobyte (2^10=1024 Bytes, 10^3=1000 Bytes in networking)10^3=1000 Bytes in networking)

Megabyte (2^20 Bytes, 10^6 in Megabyte (2^20 Bytes, 10^6 in Networking)Networking)

Gigabyte (2^30 Bytes, 10^9 in Gigabyte (2^30 Bytes, 10^9 in Networking)Networking)

Terabyte (2^40, 10^12)Terabyte (2^40, 10^12) Petabyte (2^50, 10^15)Petabyte (2^50, 10^15)

Latency Latency How long minimum communication takes in How long minimum communication takes in

seconds (s)seconds (s) Round trip vs. single tripRound trip vs. single trip More difficult to overcome than bandwidthMore difficult to overcome than bandwidth

Bandwidth Bandwidth Number of bits per time unit usually seconds (bps)Number of bits per time unit usually seconds (bps)

Performance: Latency Performance: Latency and Bandwidthand Bandwidth

bandwidth

latency

link

Any-to-Any Any-to-Any CommunicationCommunication

nn2 2 Network Effect (Metcalfe’s Law)Network Effect (Metcalfe’s Law) Total utility of system proportional to nTotal utility of system proportional to n22

Think about Orkut, MSN MessengerThink about Orkut, MSN Messenger

BabelBabel Internet consists Internet consists

of many different of many different types of networkstypes of networks EthernetEthernet Token ringToken ring

Different types of Different types of operating systems operating systems and other and other softwaresoftware

How do they work How do they work together?together? StandardsStandards

Token-ring

mar@cs.washington.edu

kashaw@cs.stanford.edu

How’s theweather inSeattle, Mar?

MSN Messenger

Network

Ethernet

Divide Work into LayersDivide Work into Layers

0 1 0 1 0 0101001010

ba

01010 01010

physically encode bits on “wire” physically encode bits on “wire”

connect segments, address connect segments, address (locating points on graph) and (locating points on graph) and route (navigating graph)route (navigating graph)

make network simple and reliablemake network simple and reliable

Link Level

Ethernet, token ring

Network

IP

End-to-End

TCP, UDP

Application

HTTP, SMTP, FTP,TELNET, DNS

Sending Data Along Sending Data Along WiresWires

Connection-orientedConnection-oriented Circuit switchedCircuit switched

Persistent connection set up between sender Persistent connection set up between sender and receiverand receiver

Example: telephone systemExample: telephone system ConnectionlessConnectionless

Packet switchedPacket switched Data partitioned into packets and Data partitioned into packets and

sent individually from sender to receiversent individually from sender to receiver Reassembled at receiverReassembled at receiver

Message

H Data H Data H Data H Data

Comparison of Switching Comparison of Switching TechnologiesTechnologies

Circuit switchedCircuit switched AdvantagesAdvantages

Only route onceOnly route once Latency and Latency and

bandwidth constantbandwidth constant DisadvantagesDisadvantages

Idle resources Idle resources unavailable for other unavailable for other connectionsconnections

Large setup timeLarge setup time Single point of failureSingle point of failure

Distributed stateDistributed state

Packet switchedPacket switched AdvantagesAdvantages

Efficient use of Efficient use of wireswires

Small startup Small startup overheadoverhead

DisadvantagesDisadvantages Route each packetRoute each packet Per packet Per packet

overheadoverhead BurstyBursty

EthernetEthernet Bob Metcalfe at Xerox PARCBob Metcalfe at Xerox PARC Used for local area networks (LANs)Used for local area networks (LANs)

Physically near one anotherPhysically near one another 200 computers within 100 meters200 computers within 100 meters

Broadcast mediumBroadcast medium Single wire connects all computersSingle wire connects all computers

Each computer has unique 48-bit MAC addressEach computer has unique 48-bit MAC address All computers constantly listenAll computers constantly listen

““Carrier Sense, Multiple Access with Carrier Sense, Multiple Access with Collision Detect”Collision Detect” Sender waits until wire unused before sendingSender waits until wire unused before sending If hears collision, stops, waits random time, If hears collision, stops, waits random time,

retransmitsretransmits

EthernetEthernet

Ethernet VariationsEthernet Variations

Ethernet PropertiesEthernet Properties

SharedShared Distributed (not Centralized)Distributed (not Centralized) InsecureInsecure Unpredictable Latency & BandwidthUnpredictable Latency & Bandwidth But it works!But it works!

Under light load (<30%), appears to be Under light load (<30%), appears to be point-to-pointpoint-to-point

Alternative to Ethernet:Alternative to Ethernet:Token RingToken Ring

Alternative introduced by Alternative introduced by IBM (1980s)IBM (1980s)

““Passing the Conch Shell”Passing the Conch Shell”

Hon Wai Leong, NUS(UIT2201, Networks) Page 26

Copyright © 2007 by Leong Hon Wai

Thank you.