计算机网络自定向下设计课件第三章

Internet

Historyr

1961:

Kleinrock

-queueingtheory

shows

effectiveness

of

packet-switchingr

1964:

Baran

-

packet-switching

in

military

netsr

1967:

ARPAnet

conceivedby

Advanced

ResearchProjects

Agencyr

1969:

first

ARPAnet

nodeoperationalr

1972:ARPAnetdemonstratedpubliclyNCP

(NetworkControl

Protocol)first

host-hostprotocolfirst

e-mailprogramARPAnet

has

15nodes1961-1972:

Early

packet-switching

principlesInternet

Historyr

1970:

ALOHAnet

satellitenetwork

in

Hawaiir

1973:

Metcalfe’s

PhD

thesisproposes

Ethernetr

1974:

Cerf

and

Kahn

-architecture

forinterconnecting

networksr

late70’s:

proprietaryarchitectures:

DECnet,

SNA,XNAr

late

70’s:

switching

fixedlength

packets

(ATMprecursor)r

1979:

ARPAnet

has

200

nodesCerf

andKahn’sinternetworking

principles:minimalism,autonomy

-

nointernal

changesrequired

tointerconnectnetworksbest

effort

servicemodelstateless

routersdecentralizedcontrol1972-1980:

Internetworking,

new

and

proprietary

netsInternet

Historyr

1983:

deploymentof

TCP/IPr

1982:

smtp

e-mailprotocol

definedr

1983:

DNS

definedfor

name-to-IP-address

translationr

1985:

ftp

protocoldefinedr

1988:

TCPcongestion

controlr

new

nationalnetworks:

Csnet,BITnet,

NSFnet,Minitelr

100,000

hostsconnected

toconfederation

ofnetworks1980-1990:

new

protocols,

a

proliferation

of

networksInternet

Historyr

Early

1990’s:

ARPAnetdecommissionedr

1991:

NSF

lifts

restrictionson

commercial

use

of

NSFnet(decommissioned,

1995)r

early

1990s:

WWWhypertext

[Bush1945,

Nelson1960’s]HTML,

http:

Berners-Lee1994:

Mosaic,

laterNetscapelate

1990’s:Late

1990’s:r

est.

50

millioncomputers

on

Internetr

est.

100

million+

usersr

backbone

links

runnningat

1

Gbps1990’s:

commercialization,

the

WWWATM:

Asynchronous

Transfer

Mode

netsInternet:r

today’s

de

factostandard

for

globaldata

networking1980’s:r

telco’s

developATM:

competingnetwork

standardfor

carrying

high-speed

voice/datar

standards

bodies:m

ATM

ForumATM

principles:r

small

(48

byte

payload,

5byte

header)

fixed

lengthcells

(like

packets)fast

switchingsmall

size

good

for

voicer

virtual-circuit

network:switches

maintain

state

foreach

“call”r

well-defined

interfacebetween

“network”

and“user”

(think

oftelephone

company)ATM

layersr

ATM

AdaptationLayer

(AAL):interface

to

upperlayersend-systemsegmentation/reassemblyr

ATM

Layer:

cellswitchingr

Physical

ATMphysicalphysicalphysicalATMphysicalWhere’s

the

application?ATM:

lower

layerfunctionality

onlyIP-over

ATM:

laterapplicationTCP/UDPIPAAL

ATMphysical

applicationTCP/UDPIPAALapplicationTCP/UDPIPAAL

ATMapplicationTCP/UDPIPAAL

ATMSummary

on

IntroductionCovered

a

“ton”

of

material!r

Internet

overviewr

what’s

a

protocol?r

network

edge,core,access

networkr

performance:

loss,

delayr

layering

and

servicemodelsr

backbones,

NAPs,

ISPsr

historyr

ATM

networkYou

now

hopefully

have:r

context,

overview,“feel”

ofnetworkingr

more

depth,

detaillater

in

courseApplication

LayerGoals:r

conceptual

+implementation

aspectsof

network

applicationprotocolsclient

serverparadigmservice

modelsr

learn

about

protocols

byexamining

popularapplication-levelprotocolsMore

goalsr

specific

protocols:httpftpsmtppopdnsr

programmingnetworkapplicationssocketprogrammingApplications

and

application-layer

protocolsApplication:

communicating,distributed

processesrunning

in

networkhosts

in

“userspace”exchange

messages

toimplement

appe.g.,

email,

filetransfer,

the

WebApplication-layer

protocolsone

“piece”

of

anappdefine

messagesexchanged

by

apps

andapplicatio

transport

network

data

link

physicalapplicatiotransport

network

data

linkphysicalapplicatio

transport

network

data

linkphysicalClient-server

paradigmTypical

network

app

has

twopieces:

client

and

server

applicatiotransport

network

data

linkphysicalapplicatio

transport

network

data

linkphysicalClient:initiates

contact

with

server

(“speaksfirst”)typically

requests

service

from

server,e.g.:

request

WWW

page,

send

emailServer:provides

requested

service

to

cliente.g.,

sends

requested

WWW

page,receives/stores

received

emailrequestreplyApplication-layer

protocols

(cont).API:

applicationprogramminginterfacer

defines

interfacebetween

applicationand

transport

layerr

socket:

InternetAPItwo

processescommunicate

bysocket,

readingdata

out

of

socketQ:

how

does

a

process“identify”

theother

process

withwhich

it

wants

tocommunicate?IP

address

of

hostrunning

otherprocess“port

number”

-allows

receivingsending

da…taliontsomore

on

thisholsatetro.determineto

which

localWhat

transport

servicedoes

an

app

need?Data

lossr

some

apps

(e.g.,

audio)

cantolerate

some

lossr

other

apps

(e.g.,

filetransfer,

telnet)

require100%

reliable

data

transferTimingr

some

apps

(e.g.,

Internettelephony,

interactivegames)

require

low

delay

tobe

“effective”Bandwidthsome

apps

(e.g.,

multimedia)require

minimum

amount

ofbandwidth

to

be

“effective”other

apps

(“elastic

apps”)

makeuse

of

whatever

bandwidth

they

getTransport

service

requirements

of

common

appsApplicationfile

transfere-mailWeb

documentsreal-time

audio/videostored

audio/videointeractive

gamesfinancial

appsData

lossnolossnolossnolossloss-tolerantloss-t