Kuliah_03 - Application Layer (HTTP, FTP)

7/24/2019 Kuliah_03 - Application Layer (HTTP, FTP)

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Application Layer 2-1

Chapter 2

ApplicationLayer

ComputerNetworking: ATop Down

Approach

6th

editionJim Kurose, KeithRossAddison-WesleyMarch 2012

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Chapter 2 outline

2!1 principles o"net#or$applications

2!2 We% and &''(2!) *'(

2!+ electronic mail

M'(, ((),.MA(

2!/

2.6 P2P applications

2.7 socket programming

with UDP and TCP


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Application Layer 2-)

Chapter 2 applicationlayer

our oals conceptual,

implementationaspects o" net#or$

applicationprotocols

transport-layerser3ice models

client-ser3erparadim

peer-to-peerparadim

learn about protocols byexamining popular

applicationle!el

protocols

&''( *'(

M'( 4 (() 4 .MA(

creating network

applications

soc$et A(.


4/47

Application Layer 2-+

ome net#or$ apps

e-mail #e% te5t messain

remote loin (2( le sharin multi-user net#or$

ames

streamin stored3ideo 78ou'u%e, &ulu,et9i5:

!oice o!er "P #e.g.$ %kype&

realtime !ideo con'erencing

social networking

search

(

(


5/47

Application Layer 2-/

Creatin a net#or$ app

#rite prorams that run on 7di;erent: end

systems communicate o3er

net#or$

e!!, #e% ser3erso"t#are communicates#ith %ro#ser so"t#are

no need to #rite so"t#are

"or net#or$-corede3ices net#or$-core de3ices

do not run userapplications

applications on ends stems allo#s "or

application

transport

net!ork

data link

physical

application

transport

net!ork

data link

physical

application

transport

net!ork

data link

physical


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Application architectures

possi%le structure o" applications client-ser3er peer-to-peer 7(2(:


7/47Application Layer 2-uest ser3ice

"rom other peers,

pro3ide ser3ice inreturn to other peers

self scalability?ne# peers %rin

ne# ser3icecapacity, as #ell asne# ser3icedemands

peers are

intermittently

peerpeer


9/47Application Layer 2-@

(rocesses communicatin

process:proramrunnin #ithin ahost

#ithin same host, t#oprocessescommunicate usininter-processcommunication7dened %y :

processes in di;erenthosts communicate%y e5chanin

messaes

client process:process thatinitiates communication

server process:processthat waits to be contacted

aside applications

#ith (2( architecturesha3e client processes ser3er processes

clients, ser3ers


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oc$ets

process sends4recei3es messaes to4"rom itssoc$et soc$et analoous to door

sendin process sho3es messae out door

sendin process relies on transportin"rastructure on other side o" door to deli3ermessae to soc$et at recei3in process

#nternet

controlled

by 12

controlled byapp developer

transport

application

physical

lin$

net#or$

process

transport

application

physical

lin$

net#or$

processsocket


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Addressin processes

to recei!e messages$ processmust ha!e identifier

host de!ice has uni*ue +2bit

"P address

Q:does "P address o' host onwhich process runs su''ice

'or identi'ying the process,

identierincludes %oth.( addressand portnum%ersassociated#ith process on host!

e5ample port num%ers &''( ser3er =0

mail ser3er 2/

to send &''( messaeto aia!cs!umass!edu#e% ser3er .( address

12=!11@!2+/!12

port num%er=0

more shortlyB

A:no, manyprocesses can %e

runnin on samehost


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App-layer protocol denes

types o" messaese5chaned,

e!!, re>uest,response

messae synta5 #hat elds in

messaes ho#elds are

delineated messae semantics

meanin o"in"ormation in

elds

open protocols)de'ined in -Cs

allows 'or interoperability

e.g.$ /TTP$ %0TP

proprietary protocols)e.g.$ %kype


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Application Layer 2-1)

What transport ser3ice does anapp needdata interity some apps 7e!!, le

trans"er, #e%transactions: re>uire100D relia%le data

trans"er other apps 7e!!, audio:

can tolerate some losstimingsome apps #e.g.$ "nternet

telephony$ interacti!egames& re*uire low delayto be 1e''ecti!e

throuhput some apps 7e!!,

multimedia: re>uireminimum amount o"throuhput to %eEe;ecti3eF

other apps 7EelasticappsF: ma$e use o"#hate3er throuhputthey et

security encryption, data

interity, B


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Application Layer 2-1+

'ransport ser3ice re>uirementscommon apps

application

file transfer

email

Web documentsrealtime audiovideo

stored audiovideo

interactive games

te3t messaging

data loss

no loss

no loss

no losslosstolerant

losstolerant

losstolerant

no loss

throughput

elastic

elastic

elasticaudio: 4kbps+5bps

video:+0kbps45bps

same as above

fe! kbps up

elastic

time sensitive

no

no

noyes, +00s msec

yes, fe! secs

yes, +00s msec

yes and no


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Application Layer 2-1/

.nternet transport protocolsser3ices

TCP service: reliable transport

%et#een sendin andrecei3in process

ow control:sender#onGt o3er#helmrecei3er

congestion control:throttle sender #hennet#or$ o3erloaded

does not provide:timin, minimumthrouhput uarantee,security

connection!oriented:setup re>uired%et#een client and

UDP service:unreliable data transfer

between sending and

recei!ing process

does not provide:reliability$'low control$ congestion

control$ timing$

throughput guarantee$

security$ or connectionsetup$

3)why bother, 4hy is

there a UDP,


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.nternet apps application, transportprotocols

application

email

remote terminal access

Webfile transfer

streaming multimedia

#nternet telephony

applicationlayer protocol

25T 6*'7 /8/+9

Telnet 6*'7 849

;TT 6*'7 /-+-9'T 6*'7 49

;TT (e.g.,


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ecurin 'C(

'C( H( no encryption clearte5t pass#ds

sent into soc$ettra3erse .nternetin clearte5t

L pro3ides

encrypted 'C(connection

data interity

%%5 is at app layer

pps use %%5 libraries$

which 1talk to TCP

%%5 socket P" clearte5t pass#ds

sent into soc$ettra3erse .nternet

encrypted ee Chapter uest messae AC.. 7human-reada%le "ormat:

re?uest line(@T, 12T,

;A> commands:

header

lines

carriage return,

line feed at start

of line indicates

end of header lines

GET /index.html HTTP/1.1\r\nHost: www-net.cs.umass.edu\r\nser-!"ent: #ire$ox/%.&.1'\r\n!ccept: text/html(application/xhtml)xml\r\n!ccept-*an"ua"e: en-us(en+,'.\r\n

!ccept-Encodin": "ip(de$late\r\n!ccept-0harset: S2-334-1(ut$-3+,'.5\r\n6eep-!li7e: 11\r\n0onnection: 8eep-ali7e\r\n\r\n

carriage return character

linefeed character


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Application Layer 2-2=

&''( re>uest messae eneral"ormat

re?uestline

header

lines

body

method sp sp cr lfversion=*B

cr lfvalueheader field name

cr lfvalueheader field name

CC CC

cr lf

entity bodyCC CC


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Application Layer 2-2@

Hploadin "orm input

(' method #e% pae o"ten

includes "orm input input is uploaded to

ser3er in entity %odyU-5 method)uses =>T method

input is uploaded in U-5

'ield o' re*uest line)www.somesite.com/animalsearch9mon8es;


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Application Layer 2-)0

Methodtypes&''(41!0 ' ('

&A as$s ser3er to

lea3e re>uestedo%Iect out o"

response

/TTPT$ P?%T$ />D

PUT

uploads le inentity %ody topath specied inHRL eld

D>5>T>

deletes lespecied in theHRL eld


31/47


&''( response messae

status line(protocol

status code

status phrase)

header

lines

data, e.g.,

re?uested

;T5B file

HTTP/1.1 ='' 26\r\nDate: Sun( =& Sep ='1' =':'4:=' G>T\r\nSer7er: !pache/=.'.= ?0ent2S@\r\n*ast->odi$ied: Tue( %' 2ct =''5 15:'':'=

G>T\r\nETa": A15dc&-ac-


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&''( response status codes

='' 26

re>uest succeeded, re>uested o%Iect later in this ms%'1 >o7ed Permanentl

re>uested o%Iect mo3ed, ne# location specied later inthis ms 7Location:

C'' ad Be,uest

re>uest ms not understood %y ser3erC'C ot #ound

re>uested document not "ound on this ser3er

' HTTP Fersion ot Supported

status code appears in +st line in servertoclient response message.

some sample codes:

' i &''( 7 li id : "


33/47

Application Layer 2-))

'ryin out &''( 7client side: "oryoursel"

1! 'elnet to your "a3orite We% ser3er

opens T7 connection to port 80

(default ;TT server port) at cis.poly.edu.

anything typed in sent

to port 80 at cis.poly.edu

telnet cis.pol.edu 3'

/. type in a @T ;TT re?uest:

GET /ross/ HTTP/1.1

Host: cis.pol.edu

by typing this in (hit carriage

return t!ice), you send

this minimal (but complete)@T re?uest to ;TT server

D. look at response message sent by ;TT server$

se Wireshar$ to loo$ at captured &''( re>uest4response:


34/47

Application Layer 2-)+

Hser-ser3er state coo$ies

many We% sites usecoo$ies

four components:

1: coo$ie header line

o" &''( responsemessae

2: coo$ie headerline in ne5t &''(re+uestmessae

): coo$ie le $epton userGs host,manaed %yuserGs %ro#ser

+: %ac$-end

data%ase at We%

example)%usan always access "nternet

'rom PC

!isits speci'ic ecommerce site

'or 'irst time

when initial /TTP re*uests

arri!es at site$ site creates)

uni>ue .

entry in %ac$enddata%ase "or .


35/47

Application Layer 2-)/

Coo$ies $eepin EstateF 7cont!:

client server

usual http response msg

usual http response msg

cookie file

one !eek later:

usual http re?uest msgcookie: 1678

cookie

specific

action

access

ebay 8734usual http re?uest msg AmaEon server

creates #>

+-F8 for user create

entry

usual http responseset-cookie: 1678

ebay 8734amazon 1678

usual http re?uest msgcookie: 1678 cookie

specific

action

access

ebay 8734

amazon 1678

backend

database


36/47


Coo$ies 7continued:

what cookies canbe used for: authoriOation shoppin carts recommendations user session state

7We% e-mail:

cookies and privacy: coo$ies permit sites

to learn a lot a%outyou

you may supplyname and e-mail tosites

aside

how to keep ,state-: protocol endpoints maintain

state at sender4recei3er o3ermultiple transactions

coo$ies http messaes carrystate


37/47

Application Layer 2-)uests tocache

o%Iect in cache

cache returnso%Iect

else cachere>uests o%Iect

"rom oriin ser3er,

goal:satis"y client re>uest #ithout in3ol3inoriin ser3er

client

pro3y

server

client

;TT

re?ue

st

;TTrespo

nse

;TTre?uest ;TT

re?uest

origin

server

origin

server

;TTresponse ;TTre

sponse


38/47

Application Layer 2-)=

More a%out We% cachin

cache acts as%oth client andser3er

ser3er "or oriinalre>uestin client

client to oriin ser3er

typically cache isinstalled %y .(7uni3ersity,company,residential .(:

why Web caching

reduce response time 'or

client re*uest

reduce tra''ic on aninstitution@s access link

"nternet dense with caches)

enables 1poor content

pro!iders to e''ecti!elydeli!er content #so too

does P2P 'ile sharing&


39/47

Application Layer 2-)@

Cachin e5ample

origin

serverspublic

#nternet

institutional

net!ork

+ @bps BAG

+.4 5bps

access link

assumptions: a3 o%Iect siOe 100K %its a3 re>uest rate "rom

%ro#sers to oriinser3ers1/4sec

a3 data rate to %ro#sers1!/0 M%ps

R'' "rom institutional routerto any oriin ser3er 2 sec

access lin$ rate 1!/+ M%ps

conse+uences: LA utiliOation 1/D access lin$ utiliOation @@D total delay .nternet delay

N access delay N LA delay

2 sec N minutes N usecs

problem!

Cachin e5ample "atter


40/47

Application Layer 2-+0






conse+uences: LA utiliOation 1/D access lin$ utiliOation @@D total delay .nternet delay N

access delay N LA delay 2 sec N minutes N usecs

Cachin e5ample "atteraccess lin$

origin

servers

+.4 5bps

access link1/+

M%ps+4 5bps

msecs

Cost:increased access link speed (not cheap$)

@!@D

public

#nternet

institutional

net!ork

+ @bps BAG

Cachin e5ample install local


41/47

institutional

net!ork

+ @bps BAG


Cachin e5ample install localcache

origin

servers

+.4 5bps

access link

local !ebcache






conse+uences: LA utiliOation 1/D access lin$ utiliOation 100D total delay .nternet delay N

access delay N LA delay 2 sec N minutes N usecs

HH

&ow to compute linkutili.ation# delay/

Cost:!eb cache (cheap$)

public

#nternet

Cachin e5ample install local


42/47


Cachin e5ample install localcache

Calculating access linkutili.ation# delay withcache:

suppose cache hit rate is0!+ +0D re>uests satised at

cache, 60D re>uestssatised at oriin

origin

servers

+.4 5bps

access link

access lin$ utiliOation 60D o" re>uests use access lin$

data rate to %ro#sers o3eraccess lin$ 0!6P1!/0 M%ps !@ M%ps utiliOation 0!@41!/+ !/=

total delay 0!6 P 7delay "rom oriinser3ers: N0!+ P 7delay #hensatised at cache:

0!6 72!01: N 0!+ 7Qmsecs: Q 1!2 secs less than #ith 1/+ M%ps lin$

7and cheaper too:

public

#nternet

institutional

net!ork

+ @bps BAG

local !ebcache


43/47

Application Layer 2-+)

Conditional '

0oal:donGt sendo%Iect i" cache hasup-to-date cached3ersion no o%Iect

transmission delay

lo#er lin$ utiliOation

cache:speci"y dateo" cached copy in

&''( re>uest$-modi$ied-since:dateI

server:responsecontains no o%Iect i"cached copy is up-

;TT re?uest msgI-modiied-since: !date"

;TT response

#$$%&1'(3(4 )ot *odiied

ob%ect

not

modified

before

IdateJ

;TT re?uest msgI-modiied-since: !date"

;TT response#$$%&1'( +(( ,

!data"

ob%ect

modified

after

IdateJ

client !eb cache

server


44/47

Application Layer 2-++

Chapter 2 outline

2!1 principles o"net#or$applications

app architectures app re>uirements

2!2 We% and &''(

2!) *'(

2!+ electronic mail M'(, ((),

.MA(

2!/

2!6 (2( applications

2!< soc$etprorammin

#ith H( and 'C(


45/47

Application Layer 2-+/

*'( the le trans"er protocol

file transfer

'Tserver

'Tuser

interface

'Tclient

local file

system

remote file

system

user

at host

trans"er le to4"rom remote host client4ser3er model

client:side that initiates trans"er 7eitherto4"rom remote: server:remote host

"tp R*C @/@ "tp ser3er port 21

*'( separate control data


46/47


*'( separate control, dataconnections

*'( client contacts *'(ser3er at port 21, usin

'C( client authoriOed o3er

control connection client %ro#ses remote

directory, sendscommands o3er control

connection #hen ser3er recei3es

le trans"er command,serveropens 1nd'C(data connection 7"or le:to client

'Tclient

'Tserver

TCP control connection,server port 21

TCP data connection,server port 20

ser3er opens another'C( data connection totrans"er another le

control connection,out of band-

*'( ser3er maintainsEstateF currentdirectory, earlierauthentication


47/47

*'( commands, responses

sample commands: sent as AC.. te5t

o3er control channel SEB username

P!SS password *STreturn list o" le

in current directory

BETB $ilenameretrie3es 7ets: le

ST2B $ilenamestores 7puts: le ontoremote host

sa!ple return codesstatus code and phrase #as in

/TTP&

%%1 sername 26(

password re,uired

1= data connection

alread open+

trans$er startin"

C= 0anJt open data

connectionC= Error writin"

$ile

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Kuliah_03 - Application Layer (HTTP, FTP)

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