1 Network Introduction

8/14/2019 1 Network Introduction

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Introduction 1-1

Chapter 1

Computer Networksand the Internet


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Introduction 1-2

Chapter 1: IntroductionOverview:

whats the Internetwhats a protocol?network edgenetwork coreaccess net, physical mediaInternet/ISP structure

performance: loss, delayprotocol layers, service modelshistory


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Introduction 1-3

Chapter 1: roadmap

1.1 What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History


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Introduction 1-4

Whats the Internet: nuts and bolts view

millions of connectedcomputing devices: hosts,end-systems

r PCs workstations, serversr PDAs phonesrunning network apps

communication links r fiber, copper, radio,

satelliter transmission rate =

bandwidth

routers: forward packets(chunks of data)

local ISP

companynetwork

regional ISP

router workstationserver

mobile


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Introduction 1-5

Whats the Internet: nuts and bolts view

protocols control sending,receiving of msgs

r e.g., TCP, IP, HTTP, FTP, PPPInternet: network of

networksr loosely hierarchicalr public Internet versus

private intranet

Internet standardsr RFC: Request for commentsr IETF: Internet Engineering

Task Force

local ISP

companynetwork

regional ISP

router workstationserver

mobile


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Introduction 1-6

Whats the Internet: a service view

communicationinfrastructure enablesdistributed applications:

r Web, email, games, e-commerce, database.,voting, file (MP3) sharing

communication servicesprovided to apps:

r connectionlessr

connection-orientedcyberspace [Gibson]:a consensual hallucination experienced daily by

billions of operators, in every nation, ...."


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Introduction 1-7

Whats a protocol?human protocols:

whats the time?I have a questionintroductions

specific msgs sent specific actions taken

when msgs received,or other events

network protocols:machines rather thanhumansall communicationactivity in Internetgoverned by protocols

protocols define format,order of msgs sent and received among network

entities, and actions taken on msg

transmission, receipt


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Introduction 1-8

Whats a protocol?a human protocol and a computer network protocol:

Hi

HiGot thetime?2:00

TCP connection

reqTCP connectionresponseGet http://www.awl.com/kurose-ross

time


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Introduction 1-10

Chapter 1: roadmap

1.1What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History


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Introduction 1-11

The network edge:end systems (hosts):

r run application programsr e.g. Web, emailr at edge of network

client/server modelr client host requests, receives

service from always-on serverr e.g. Web browser/server;

email client/serverpeer-peer model:r minimal (or no) use of

dedicated serversr e.g. Gnutella, KaZaA


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Introduction 1-12

Network edge: connection-oriented service

Goal: data transferbetween end systemshandshaking: setup

(prepare for) datatransfer ahead of timer Hello, hello back human

protocolr set up state in two

communicating hostsTCP - TransmissionControl Protocol

r Internets connection-

oriented service

TCP service reliable, in-order byte-stream data transfer

r

loss: acknowledgementsand retransmissionsflow control:

r sender wont overwhelmreceiver

congestion control: r senders slow down sending

rate when networkcongested


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Introduction 1-13

Network edge: connectionless service

Goal: data transferbetween end systems

r same as before!

UDP- User DatagramProtocol : Internetsconnectionless service

r unreliable datatransfer

r no flow controlr no congestion control

Apps using TCP: HTTP (Web), FTP (filetransfer), Telnet

(remote login), SMTP(email)

Apps using UDP:streaming media,teleconferencing, DNS,Internet telephony


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Introduction 1-14

Chapter 1: roadmap



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Introduction 1-15

The Network Core

mesh of interconnectedroutersthe fundamentalquestion: how is datatransferred through net?

r circuit switching: dedicated circuit percall: telephone net

r packet-switching: datasent thru net indiscrete chunks


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Introduction 1-16

Network Core: Circuit Switching

End-end resourcesreserved for calllink bandwidth, switch

capacitydedicated resources:no sharingcircuit-like

(guaranteed)performancecall setup required


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Introduction 1-17

Network Core: Circuit Switching

network resources(e.g., bandwidth)divided into piecespieces allocated to callsresource piece idle ifnot used by owning call(no sharing)

dividing link bandwidthinto pieces

r frequency divisionr time division


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Introduction 1-18

Circuit Switching: FDMAand TDMA

FDMA

frequency

time

TDMA

frequency

time

4 usersExample:


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Introduction 1-19

Network Core: Packet Switching

each end-end data streamdivided into packets user A, B packets share network resources

each packet uses full linkbandwidthresources used as needed

resource contention: aggregate resourcedemand can exceedamount available

congestion: packetsqueue, wait for link usestore and forward:packets move one hop

at a timer transmit over linkr wait turn at next

link

Bandwidth division into piecesDedicated allocationResource reservation


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Introduction 1-20

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixedpattern statistical multiplexing .

In TDM each host gets same slot in revolving TDM

frame.

A

B

C10 MbsEthernet

1.5 Mbs

D E

statistical multiplexing

queue of packetswaiting for outputlink


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Introduction 1-21

Packet-switching: store-and-forward

Takes L/R seconds totransmit (push out)packet of L bits on tolink or R bpsEntire packet mustarrive at router beforeit can be transmittedon next link: store and forward delay = 3L/R

Example:L = 7.5 MbitsR = 1.5 Mbpsdelay = 15 sec

R R RL


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Introduction 1-22

Packet-switched networks: forwarding

Goal: move packets through routers from source todestinationr well study several path selection (i.e. routing)algorithms

(chapter 4)

datagram network: r destination address in packet determines next hopr routes may change during sessionr analogy: driving, asking directions

virtual circuit network: r each packet carries tag (virtual circuit ID), tag

determines next hopr fixed path determined at call setup time , remains fixed

thru callr

routers maintain per-call state


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Introduction 1-23

Network TaxonomyTelecommunication

networks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

Datagram network is not either connection-orientedor connectionless. Internet provides both connection-oriented (TCP) andconnectionless services (UDP) to apps.


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Introduction 1-24

Chapter 1: roadmap



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Introduction 1-25

Access networks and physical media

Q: How to connect end systems to edge router? residential access netsinstitutional accessnetworks (school,company)mobile access networks

Keep in mind:

bandwidth (bits persecond) of accessnetwork?shared or dedicated?


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Introduction 1-26

Residential access: point to point access

Dialup via modemr up to 56Kbps direct access to

router (often less)r

Cant surf and phone at sametime: cant be always on

ADSL: asymmetric digital subscriber liner up to 1 Mbps upstream (today typically < 256 kbps)r up to 8 Mbps downstream (today typically < 1 Mbps)r FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream

0 kHz - 4 kHz for ordinary telephone


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Introduction 1-27

Residential access: cable modems

HFC: hybrid fiber coaxr asymmetric: up to 10Mbps upstream, 1 Mbps

downstream

network of cable and fiber attaches homes toISP routerr shared access to router among homesr major issue: congestion

deployment: available via cable companies, e.g.,MediaOne


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Introduction 1-28

Residential access: cable modems


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Introduction 1-29

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes


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Introduction 1-30


home

cable headend

cable distributionnetwork (simplified)


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Introduction 1-31


home

cable headend

cable distributionnetwork

server(s)


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Introduction 1-32


home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM:


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Introduction 1-33

Company access: local area networks

company/univ local areanetwork (LAN) connectsend system to edge routerEthernet:

r shared or dedicated linkconnects end systemand router

r 10 Mbs, 100Mbps,

Gigabit Ethernetdeployment: institutions,home LANs happening nowLANs: chapter 5


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Introduction 1-34

Wireless access networks

shared wireless accessnetwork connects end systemto router

r via base station aka accesspoint

wireless LANs:r 802.11b (WiFi): 11 Mbps

wider-area wireless accessr provided by telco operatorr 3G ~ 384 kbps

basestation

mobilehosts

router


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Introduction 1-35

Home networks

Typical home network components:ADSL or cable modemrouter/firewall/NAT Ethernet

wireless accesspoint

wirelessaccesspoint

wirelesslaptops

router/firewall

cablemodem

to/fromcableheadend

Ethernet(switched)


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Introduction 1-36

Physical Media

Bit: propagates betweentransmitter/receiverpairsphysical link: what liesbetween transmitter &receiverguided media:

r signals propagate in solidmedia: copper, fiber, coax

unguided media: r signals propagate freely,

e.g., radio

Twisted Pair (TP)two insulated copperwires

r Category 3: traditionalphone wires, 10 MbpsEthernet

r Category 5 TP:100Mbps Ethernet


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Introduction 1-37

Physical Media: coax, fiber

Coaxial cable:two concentric copperconductorsbidirectionalbaseband:

r single channel on cabler legacy Ethernet

broadband:r multiple channel on cabler HFC

Fiber optic cable:glass fiber carrying lightpulses, each pulse a bithigh-speed operation:

r

high-speed point-to-pointtransmission (e.g., 5 Gps)low error rate: repeatersspaced far apart ; immuneto electromagnetic noise


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Introduction 1-38

Physical media: radio

signal carried inelectromagneticspectrumno physical wire

bidirectionalpropagationenvironment effects:

r reflectionr

obstruction by objectsr interference

Radio link types:terrestrial microwaver e.g. up to 45 Mbps channels

LAN(e.g., WaveLAN)r

2Mbps, 11Mbpswide-area (e.g., cellular)

r e.g. 3G: hundreds of kbpssatellite

r

up to 50Mbps channel (ormultiple smaller channels)r 270 msec end-end delayr geosynchronous versus

LEOS


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Introduction 1-39

Chapter 1: roadmap

1.1What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History


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Introduction 1-40

Internet structure: network of networks

roughly hierarchicalat center: tier-1 ISPs (e.g., UUNet, BBN/Genuity,Sprint, AT&T), national/international coverage

r treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1providersinterconnect

(peer)privately

NAP

Tier-1 providersalso interconnectat public networkaccess points(NAPs)


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Introduction 1-41

Tier-1 ISP: e.g., Sprint

Sprint US backbone network


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Introduction 1-42


Tier-2 ISPs: smaller (often regional) ISPsr Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP paystier-1 ISP forconnectivity torest of Internet

tier-2 ISP iscustomer oftier-1 provider

Tier-2 ISPs also peerprivately witheach other,interconnectat NAP


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Introduction 1-43


Tier-3 ISPs and local ISPsr last hop (access) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

local

ISPlocalISP

localISP

local

ISP

localISP Tier 3

ISP

local

ISP

local

ISP

localISP

Local and tier-3 ISPs arecustomers ofhigher tierISPsconnectingthem to restof Internet


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Introduction 1-44


a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

local

ISPlocalISP

localISP

local

ISP

localISP Tier 3

ISP

local

ISP

local

ISP

localISP


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Introduction 1-45

Chapter 1: roadmap



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Introduction 1-46

How do loss and delay occur?

packets queue in router buffers packet arrival rate to link exceeds output link capacitypackets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)free (available) buffers: arriving packets

dropped ( loss) if no free buffers


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Introduction 1-47

Four sources of packet delay

1. nodal processing: r check bit errorsr determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. queueingr time waiting at output

link for transmissionr depends on congestion

level of router


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Introduction 1-48

Delay in packet-switched networks

3. Transmission delay:R=link bandwidth (bps)L=packet length (bits)time to send bits intolink = L/R

4. Propagation delay:d = length of physical links = propagation speed inmedium

propagation delay = d/s

A

B

propagation

transmission

nodal

processing queueing


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Introduction 1-49

Packet loss

queue (aka buffer) preceding link in bufferhas finite capacitywhen packet arrives to full queue, packet is

dropped (aka lost)lost packet may be retransmitted byprevious node, by source end system, or notretransmitted at all


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Introduction 1-50

Chapter 1: roadmap

1.1What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 Internet structure and ISPs1.6 Delay & loss in packet-switched networks1.7 Protocol layers, service models1.8 History


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Introduction 1-51

Protocol Layers

Networks are complex!many pieces:

r hostsr routersr links of various

mediar applicationsr protocolsr hardware,

software


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Introduction 1-52

Organization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing


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Introduction 1-53

Organization of air travel : a different view

Layers: each layer implements a servicer via its own internal-layer actionsr relying on services provided by layer below

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing


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Introduction 1-54

Layered air travel: services

Counter-to-counter delivery of person+bags

baggage-claim-to-baggage-claim delivery

people transfer: loading gate to arrival gate

runway-to-runway delivery of plane

airplane routing from source to destination


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Introduction 1-55

Distributed implementation of layer functionality

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

D e p a r

t i n g a

i r p o r t

a r r

i v i n g a

i r p o r

t

intermediate air traffic sitesairplane routing airplane routing


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Introduction 1-56

Why layering?

Dealing with complex systems:explicit structure allows identification,relationship of complex systems pieces

r layered reference model for discussion

modularization eases maintenance, updating ofsystem

r change of implementation of layers servicetransparent to rest of system

r e.g., change in gate procedure doesnt affectrest of system


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Introduction 1-57

Internet protocol stack

application: supporting networkapplicationsr FTP, SMTP, STTP

transport: host-host data transferr

TCP, UDPnetwork: routing of datagrams fromsource to destination

r IP, routing protocols

link: data transfer betweenneighboring network elementsr PPP, Ethernet

physical: bits on the wire

application

transport

network

link

physical


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Introduction 1-58

Layering: logical communication

applicationtransportnetwork

linkphysical


linkphysical application

transportnetworklink

physical

application


physical

networklink

physical

Each layer:distributedentitiesimplement

layer functionsat each nodeentitiesperform

actions,exchangemessages withpeers


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Introduction 1-59

Layering: logical communication


linkphysical


linkphysical application


physical

application


physical

networklink

physical

data

data

E.g.: transporttake data from appadd addressing,reliability checkinfo to formdatagramsend datagram topeerwait for peer toack receiptanalogy: postoffice

data

transport

transport

ack


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Introduction 1-60

Layering: physical communication


linkphysical


linkphysical


linkphysical


linkphysical

networklink

physical

data

data


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Introduction 1-61

Protocol layering and data

Each layer takes data from aboveadds header information to create new data unitpasses new data unit to layer below


linkphysical


linkphysical

source destinationMMMM

t

tn

tnl

MMMM

t

tn

tnl

messagesegmentdatagramframe


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Introduction 1-62

Chapter 1: roadmap

1.1What is the Internet?1.2 Network edge1.3 Network core1.4 Network access and physical media1.5 ISPs and Internet backbones1.6 Delay & loss in packet-switched networks

1.7 Internet structure and ISPs1.8 History


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Introduction 1-63

Internet History

1961: Kleinrock - queueingtheory showseffectiveness of packet-switching

1964: Baran - packet-switching in military nets1967: ARPAnet conceivedby Advanced ResearchProjects Agency

1969: first ARPAnet nodeoperational

1972: r ARPAnet demonstrated

publiclyr NCP (Network Control

Protocol) first host-host protocol

r first e-mail programr ARPAnet has 15 nodes

1961-1972: Early packet-switching principles


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Introduction 1-64

Internet History

1970: ALOHAnet satellitenetwork in Hawaii1973: Metcalfes PhD thesisproposes Ethernet

1974: Cerf and Kahn -architecture forinterconnecting networkslate70s: proprietaryarchitectures: DECnet, SNA,

XNAlate 70s: switching fixedlength packets (ATMprecursor)1979: ARPAnet has 200 nodes

Cerf and Kahnsinternetworking principles:

r minimalism, autonomy -no internal changes

required tointerconnect networksr best effort service

modelr stateless routersr decentralized control

define todays Internetarchitecture

1972-1980: Internetworking, new and proprietary nets


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Introduction 1-65

Internet History

1983: deployment ofTCP/IP1982: SMTP e-mail

protocol defined1983: DNS definedfor name-to-IP-address translation

1985: FTP protocoldefined1988: TCP congestioncontrol

new national networks:Csnet, BITnet,NSFnet, Minitel

100,000 hostsconnected toconfederation ofnetworks

1980-1990: new protocols, a proliferation of networks


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Internet History

Early 1990s: ARPAnetdecommissioned1991: NSF lifts restrictions oncommercial use of NSFnet

(decommissioned, 1995)early 1990s: Web

r hypertext [Bush 1945, Nelson1960s]

r HTML, HTTP: Berners-Leer 1994: Mosaic, later Netscaper late 1990s:

commercialization of the Web

Late 1990s 2000s:more killer apps: instantmessaging, peer2peerfile sharing (e.g.,Naptser)network security toforefrontest. 50 million host, 100million+ usersbackbone links runningat Gbps

1990, 2000s: commercialization, the Web, new apps

Documents

1 Network Introduction