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Chapter 2Application Layer

2: Application Layer 1

Computer Networking:A Top Down Approach,5th edition.

Jim Kurose, Keith RossAddison-Wesley, April2009.

A note on the use of these ppt slides:Were making these slides freely available to all (faculty, students, readers).Theyre in PowerPoint form so you can add, modify, and delete slides(including this one) and slide content to suit your needs. They obviouslyrepresent a lotof work on our part. In return for use, we only ask thefollowing: If you use these slides (e.g., in a class) in substantially unaltered form,

that you mention their source (after all, wed like people to use our book!) If you post any slides in substantially unaltered form on a www site, that

you note that they are adapted from (or perhaps identical to) our slides, andnote our copyright of this material.

Thanks and enjoy! JFK/KWR

All material copyright 1996-2009J.F Kurose and K.W. Ross, All Rights Reserved


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Chapter 2: Application layer 2.1 Principles of

network applications 2.2 Web and HTTP 2.3 FTP

2.6 P2P applications

2.7 Socket programmingwith UDP 2.8 Socket programming


. ec ron c a SMTP, POP3, IMAP 2.5 DNS


4/120

Chapter 2: Application LayerOur goals: conceptual,

implementationaspects of networkapplication protocols

learn about protocolsby examining popular

application-levelprotocols HTTP


transport-layerservice models client-server

paradigm peer-to-peer

paradigm

FTP SMTP / POP3 / IMAP DNS

programming network

applications socket API


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Some network apps e-mail

web instant messaging remote login

social networks

voice over IP real-time video

conferencing


P2P file sharing multi-user network

games

streaming stored videoclips

gr compu ng


6/120

To ra mt ng dng mng, ngha l:vit chng trnh sao cho:

C th chy trn cc host khc

nhau. C th truyn thng vi nhau qua

mng

applicationtransportnetworkdata linkphysical


. .,

communicates with browsersoftware

khng cn phi vit cc phnmm chy trn thit b mng(router, switch, ) Cc thit b mng ko chy cc

apps do ngui dng vit

Li ny cho php pht trin nhanhcc apps chy trn cc host.

applicationtransportnetworkdata link

physical

applicationtransportnetworkdata linkphysical


7/120






. ec ron c a SMTP, POP3, IMAP 2.5 DNS


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Application architectures Kin trc ng dng l yu t phi quyt nh

trc tin khi xy dng ng dng mng Client-server

Including data centers / cloud computing


Peer-to-peer (P2P) Hybrid of client-server and P2P

Kin trc ng dng kin trc mng (VDInternet c kin trc phn tng!)


9/120

Client-server architectureserver:

always-on host a ch IP c nh S dng server farms khi ti

ln


c en s: Truyn thng vi server C th kt ni khng lin

tc

C th s dng a ch IPng Khng truyn thng trc

tip vi nhau.

client/server


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Google Data Centers Chi ph c tnh ca data center: $600M Google tiu $2.4B trong 2007 cho 1 data

center mi Mi data center c cng sut 50-100


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Pure P2P architecture Ko dng server

Cc host truyn thngtrc tip vi nhau Cc peer c th kt ni

peer-peer


ch IP

VD: Gnutella ng dngngun m cho php chia

s file

C tnh m rng cao nhng

kh qun l.


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Hybrid of client-server and P2PSkype L ng dng truyn m trn mng IP (VoIP)

Server trung tm:tm a ch ca bn th 3 Kt ni client-client l trc tip, ko qua Server

Instant messaging


Dch v centralized service: pht hin/nh v shin din/v tr ca client

User ng k a ch IP ca n vi server trungtm mi khi online

User lin lc vi server trung tm tm a chIP ca bn chat.


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Processes communicatingTin trnh (process):

chng trnh chy trn 1host.

Trn cng host, 2 tintrnh tru n thn vi

Tin trnh client : tin trnhkhi to truyn thng

Tin trnh server: tintrnh ch i c linlc


nhau s dng inter-process communication(c h iu hnh nhngha ).

Cc tin trnh trn cchost khc nhau truynthng nhau bng trao i

thng ip (messages)

Lu : cc ng dng P2P

c c tin trnh client lntin trnh server.


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Sockets Cc tin trnh gi/nhn cc

thng ip n/tsocketca n

Tin trnh~ ngi nh =>~

process

socket

host or

server

process

socket

host or

server

controlled by

app developer


Tin trnh y thng ip ra

ca. H tng vn chuyn bn

ngoi ca chuyn giao thng

ip ti socket ca tin trnhbn nhn.

TCP withbuffers,

variables

TCP withbuffers,

variables

Internet

controlled

by OS

API: (1) choice of transport protocol; (2) ability to fix

a few parameters (lots more on this later)


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Addressing processes

nhn thng ip, tintrnh phi c nh danh

(identifier)

Cc host u c 1 a ch

Q:liu a ch IP ca hostm process ang chy trn, c xc nh tin

trnh? A:Khng , v c c

nhiutin trnh c th


, .

Bi tp: dng lnhipconfig t console, ly

a ch IP trn my tnhWindows.

. nh danhbao gm c a

ch IP v s hiu cng (portnumber) c lin kt vi

tin trnh trn host. V d v cc port number:

HTTP server: 80

Mail server: 25


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App-layer protocol defines Cc kiu thng ip c

trao i, e.g., request, response K php thng ip:

Cc giao thc cng hu:

c nh ngha RFCs HTTP: RFC 2616

Cho php lm vic phi


v m t ca tng field. Ng ngha thng ip

ngha ca thng tin trntng field

Cc quy tc v thi imv cch thc cc tintrnh gi v phn hi li

cc thng ip.

. e.g., HTTP, SMTP,

BitTorrentCc giao thc t hu: e.g., Skype, ppstream


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What transport service does an app need?

Mt d liu Mt s ng dng (VD audio)

c th chp nhn mt d

liu. Cc ng dng khc (e.g., file

transfer, telnet) i hi phi

Bng thng Vi ng dng (e.g.,

multimedia) cn bngthng ti thiu t hiuqu.

Cc n d n khc


tuyt i

Kp thi Mt s ng dng (e.g.,

Internet telephony,interactive games) ihi tr thp mcchp nhn c.

(elastic apps) c th thchnghi vi bng thng hinc (VD email, truyn file,)

An ton M ha, ton vn d liu,


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Transport service requirements of common apps

Loi ng dng

file transfere-mail

Web documents

Mt d liu

no lossno lossno loss

Bng thng

elasticelasticelastic

Kp thi

nonono


-

stored audio/videointeractive gamesinstant messaging

oss- o eran

loss-tolerantloss-tolerantno loss

au o: ps- ps

video:10kbps-5Mbpssame as abovefew kbps upelastic

,

yes, few secsyes, 100s msecyes and no


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Internet transport protocols servicesTCP service: connection-oriented:cn qu trnh

thit lp kt ni ( handshake)gia cc tin trnh server v client

Vn chuyn bo m (reliabletransport) gia 2 tin trnh gi v

UDP service: Vn chuyn thng (ko bo

m) gia cc tin trnh giv nhn.

Ko bo m: qu trnh thit


ng ni dung, ko mt gi tin, ko trnggi tin

ng th t

flow control:bn gi ko gi qu

nhanh, lm trn d liu bn nhn congestion control:iu tit tc

gi d liu khi mng qu ti (kohn tt!).

Ko bo m: tnh kp thi, bngthng ti thiu, an ninh

p ng s , v n c uy nm bo, flow control,congestion control, kp thi,bo m bng thng tithiu hay, an ninh

Q: why bother? Why is therea UDP?


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Internet apps: application, transport protocols

ng dng

e-mailremote terminal access

Web

Giao thc tngng dng

SMTP [RFC 2821]Telnet [RFC 854]HTTP [RFC 2616]

Giao thcvn chuyn

TCPTCPTCP


e trans erstreaming multimedia

Internet telephony

HTTP (eg Youtube),RTP [RFC 1889]SIP, RTP, proprietary(e.g., Skype)

TCP or UDP

typically UDP


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. ec ron c a SMTP, POP3, IMAP

2.5 DNS


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Web and HTTPFirst some jargon

Trang Web bao gm cc i tng (objects) i tng c th l file HTML, nh JPEG, Java applet,

file m thanh,


u rang e ao g m e c s aseHTML file) v nhiu i tung c tham chiu

Mi mt i tung c nh v bng mt URL VD URL:

www.someschool.edu/someDept/pic.gif

host name path name


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HTTP overviewHTTP: hypertext transfer

protocol L giao thc tng ng dngca Web

HTTP/1.0 (RFC 1945)

PC runningExplorer


HTTP/1.1 (RFC 2616) M hnh client/server

client:l trnh duyt(browser) cho php yu cu

(request), nhn v hin thcc i tng Web. server:Web server gi cc

i tng n client p

ng cc yu cu tng ngt client.

Serverrunning

Apache Webserver

Mac runningNavigator


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HTTP overview (continued)Uses TCP: Client khi to kt ni TCP

(to socket) server, port 80. Server chp nht kt ni TCP

t pha client

HTTP is stateless Server khng lu li bt k

thng tin no v ccrequest t pha client


Trnh duyt v Web Servertrao i cc HTTP messages(chnh l cc message cagiao thc tng ng dng)

Kt ni TCP c ng.

Protocols that maintain stateare complex! Thng tin qu kh phi

c qun l

Nu lin kt server/client b b, thng tin v trngthi ca 2 pha c th konht qun, cn c iuchnh.


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HTTP connections

Nonpersistent HTTP Persistent HTTP

HTTP s dng c 2 cch: nonpersistent connectionhoc persistent connection (mc nh)


Ti a mt object cgi qua kt ni TCP. Nhiu i tng c thc gi qua 1 kt ni

TCP duy nht giaclient v server


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Nonpersistent HTTPGi s user nhp vo chui URLURL www.someSchool.edu/someDepartment/home.index

1a. HTTP client khi to kt ni TCPn HTTP server (process) tiwww.someSchool.edu trn port80

1b. HTTP server ti hostwww.someSchool.edu ch ikt ni TCP connection port

(trang ny gmtext, tham chiun 10 nh jpeg)


2. HTTP client gi HTTP requestmessage(cha URL) vo socketca kt ni. Message ny ch thrng client mun i tngsomeDepartment/home.index

80. chp nhn kt ni, bocho client

3. HTTP server nhn crequest message, hnh thnhnn response messagechacc i tng c yu cu, vgi message no vo socket can.

time


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Nonpersistent HTTP (cont.)

5. HTTP client nhn c responeemessage cha file HTML , hinth HTML. Phn tch HTML file,tm ra 10 nh jpeg

4. HTTP server ng kt ni TCP


6. Bc 1-5 lp li cho mi itng nh jpeg.

time


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Non-Persistent HTTP: Response timeinh ngha RTT(Round triptime): l thi gian 1 gi

tin nh i t client nserver v quay tr v.

Response time: Cn 1 RTT khi to kt

initiate TCPconnection

RTT


Cn 1 RTT client gi

request HTTP v vi byteca HTTP respons tr v

Thi gian truyn filetotal = 2RTT+transmit time

time totransmitfile

reques

fileRTT

filereceived

time time


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Persistent HTTP

Nonpersistent HTTP issues: Cn 2 RTT cho mi i tng

Tn chi ph x l ca HHcho tng kt ni TCP Trnh duyt thng phi m

nhiu kt ni TCP n thi

Persistent HTTP Server vn duy tr kt ni

sau khi gi cc phn hi. Cc HTTP message sau

gia client v server lm victrn cng kt ni ang m.


ti cc i tng Web

Client gi request ngay khin gp cc i tng. Tn mt RTT cho tt c cc

i tng c ti.


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HTTP request message Hai kiu thng ip HTTP : request, response

Thng ip HTTP request: ASCII (human-readable format)

Dn re uest, m 1


GET /somedir/page.html HTTP/1.1Host: www.someschool.edu

User-agent: Mozilla/4.0

Connection: close

Accept-language:fr

(extra carriage return,

line feed)

trong cc lnh(GET, POST,HEAD)

Cc dngheader

Xung hng,Vu dng

Chth cui thng ip

Host: ni cha trang webUser-agent: loi browser pht ra

requestConnection: close=>nonpersistent connectionAccept language: Fr =>cho bituser mun nhn phin bn Phpng ca i tng


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HTTP request message: general format



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Uploading form inputPOST method:

Trang Web thng baogm cc form input Phn d liu ngui

URL method: S dng GET method


,

gn vo phn thn(entity body) ca thngip request v gi v

cho server

n u ngudng nhp vo, cgn vo trong field URL dng request

www.somesite.com/animalsearch?monkeys&banana


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Method typesHTTP/1.0

GET POST HEAD

HTTP/1.1

GET, POST, HEAD PUT

Upload file c ni dung


Dng cho mc chdebug

Yu cu server ko cngi i tng v clienttrong thng ip

response

ca thng ip request,n ni c ch ra URL field.

DELETE Xa file c ch ra trong

URL field


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HTTP response message

HTTP/1.1 200 OK

Connection closeDate: Thu, 06 Aug 1998 12:00:15 GMT

Server: Apache/1.3.0 (Unix)

-

Dng trng thi(protocol

status codestatus phrase)

cc dng


, ...

Content-Length: 6821Content-Type: text/html

data data data data data ...

header

d liu, e.g.,requestedHTML file


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HTTP response status codes

200 OK

request succeeded, requested object later in this message

Nm trn dng u tin ca thng ip phn hi t serverMt vi m trng thi:


requested object moved, new location specified later in thismessage (Location:)

400 Bad Request

request message not understood by server

404 Not Found

requested document not found on this server

505 HTTP Version Not Supported


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Trying out HTTP (client side) for yourself

1. Telnet to your favorite Web server:

Opens TCP connection to port 80(default HTTP server port) at cis.poly.edu.Anything typed in sentto port 80 at cis.poly.edu

telnet cis.poly.edu 80


2. Type in a GET HTTP request:

GET /~ross/ HTTP/1.1

Host: cis.poly.edu

By typing this in (hit carriagereturn twice), you sendthis minimal (but complete)

GET request to HTTP server

3. Look at response message sent by HTTP server!


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User-server state: cookiesMany major Web sites use

cookies

Four components:1) cookie header line of

HTTP responsemessage

Example: Susan lun truy cp

Internet t my PC Ln u gh thm site e-

commerce, c sd cookies


coo e ea er ne n

HTTP requestmessage3) cookie file kept on

users host, managed byusers browser

4) back-end database atWeb site

Khi e-commnerce serverln u nhn c 1HTTP requests, n to ra: ID duy nht cho Susan

t my PC. 1 dng trong backend

database ng vi ID


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Cookies: keeping state (cont.)

client server

cookie file

ebay 8734

usual http request msg Amazon servercreates ID

1678 for user createentry

usual http responseSet-cookie: 1678

ebay 8734


usual http response msg

usual http response msg

Mt tun sau:

usual http request msgcookie: 1678 cookie-specificaction

access

amazon

usual http request msgcookie: 1678 cookie-

spectificaction

accessebay 8734amazon 1678

backenddatabase


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Cookies (continued)What cookies can bring: authorization shopping carts recommendations

Cookies and privacy: cookies permit sites to

learn a lot about you you may supply name

and e-mail to sites

aside


e-mail)

How to keep state: protocol endpoints: maintain state at

sender/receiver over multipletransactions

cookies: http messages carry state


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Web caches (proxy server)

User thit lp trnhduyt: truy cp Webthng qua cache

Goal: satisfy client request without involving origin server

Proxyserver

origin

server


cc HTTP requests ticache Nu c i tng trong

cache: cache tr v i

tng cho trnh duyt Ngc li, cache

request i tng tserver gc, sau mi

tr v cho trnh duyt.

client

clientoriginserver


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More about Web caching

Cache hnh x nhclient v nh server

Thng thng, cachec ISP (trng H,

Why Web caching?

Gim thi gian p ngcho cc request t client Gim lu lng ng truy


,

phng) thit lp.

Internet dense with

caches: enables poorcontent providers to

effectively deliver content(but so does P2P filesharing)


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Caching exampleGi nh Kch thc bnh qun ca 1 i

tng web = 1,000,000 bits

S lng request trung bnh t trnhduyt ca t chc gi n originservers = 15 ln/giy

originservers

public

Internet


,

n origin server v quay v lirouter = 2 giy

H qu Mc s dng Web trn LAN = 15% Mc s dng Web trn access link =

100% tr tng cng = Internet delay +

access delay + LAN delay

= 2 sec + minutes + milliseconds

institutionalnetwork 100 Mbps LAN

ps

access link

institutionalcache


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Caching example (cont)

Gii php 1 Tng bng thng access link

(ng truyn t router ca tchc ra router ca Internet) ln100 Mbps

originservers

public

Internet


Mc s dng Web trn LAN =15% = (15 ln/sec * 1000000bits/ln)/100Mbps=15%

Mc s dng Web trn accesslink= 15%

tr tng cng= Internet delay +access delay + LAN delay

= 2 sec + msecs + msecs Chi ph nng cp ng truyn rt

t

institutionalnetwork 100 Mbps LAN

ps

access link

institutionalcache


44/120

Caching example (cont)Gii php kh thi: dng cache Gi s t l p ng ca cache (hit

rate) l 0.4

H qu C 40% request s c p ng

gn nh tc th. C 60% re uest s c ori in

originservers

public

Internet


server p ng.

Mc s dng Web trn accesslink gim xung cn 60%, dn n tr khng ng k ( khong 10msec trn ng truyn 15 Mbps)

tr tng cng = Internet delay+ access delay + LAN delay =.6*(2.01) secs + .4*milliseconds p ng chm

1 DNS Server ko th gntt c cc client => lm gia

tng cc kt ni ng din DNS => tt nghn. Bo tr 1 DNS cho ton cu!

,

t b danh cho mailserver Phn b ti

replicated Web servers:s dng nhiu a ch IPng vi mt tn chnhthc.

Distributed, Hierarchical Database


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Root DNS Servers

com DNS servers org DNS servers edu DNS servers

poly.eduDNS servers

umass.eduDNS servers

yahoo.comDNS servers

amazon.com

pbs.orgDNS servers


Client wants IP for www.amazon.com; 1st approx: Client hi root server tm DNS Server ph trch tn

min com.

Client li hi tip DNS Server ph trch tn min com, tm DNS Server ph trch tn min amazon.com

Client li hi DNS Server ph trch tn min

amazon.com, ly a ch IP cho www.amazon.com

DNS: Root name servers


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DNS: Root name servers Khi cc local name server khng th phn gii tn min (do ko lutrong DB), n s lin lc vi root name server root name server:

Lin lc vi cc authoritative name server v yu cu server ny lo

dm Nhn kt qu phn gii t authoritative name server Tr kt qu phn gii v local name server

Recursivequery


13 root nameservers worldwide

b USC-ISI Marina del Rey, CAl ICANN Los Angeles, CA

e NASA Mt View, CAf Internet Software C. Palo Alto,CA (and 36 other locations)

i Autonomica, Stockholm (plus28 other locations)

k RIPE London (also 16 other locations)

m WIDE Tokyo (also Seoul,Paris, SF)

a Verisign, Dulles, VAc Cogent, Herndon, VA (also LA)

d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MDj Verisign, ( 21 locations)

TLD and Authoritative Servers


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TLD and Authoritative Servers

Top-level domain (TLD) servers: Chu trch nhim i vi cc tn com, org, net,

edu, v tt c cc tn min quc gia mc 1 nh uk,fr, ca, vn,

Network Solutions qun l cc servers dnh cho TLD com


Educause qun l cc servers dnh cho TLD edu

Authoritative DNS servers: DNS server ca cc t chc, cung cp tt c cc nh

x tn-a ch IP ca cc server ca t chc (e.g

Web, mail) Cc DNS Server ny c chnh cc t chc hoc

nh cung cp dch v qun l.

Local Name Server


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Local Name Server

Khng hon ton thuc v H thng DNSc t chc theo cu trc phn cp.

Mi ISP (ISP a phng, cng ty, trng ihc) u c.


Cng c gi l default name server Khi mt host truy vn DNS, cu hi c gi

n cho local DNS Server

Lm vic nh 1 my i din (proxy), chuyn tiptruy vn DNS n h thng phn cp DNS.

root DNS serverDNS name


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local DNS server

23

4

5

TLD DNS server

resolution example Mt host

cis.poly.edu mun bita ch IP address cagaia.cs.umass.edu


requesting hostcis.poly.edu

gaia.cs.umass.edu

dns.poly.edu

1 6

authoritative DNS serverdns.cs.umass.edu

78 iterated query: Server c hi s tr

li l tn ca servercn hi k tip

I dont know thisname, but ask thisserver

root DNS server

DNS name


70/120

root DNS server

2

67TLD DNS server

3recursive query: t trch nhim phn

gii tn min honton ln cc serverc hi.

resolution example


requesting hostcis.poly.edu

gaia.cs.umass.edu

local DNS server

dns.poly.edu

1

45

authoritative DNS server

dns.cs.umass.edu

8

heavy load?

DNS: caching and updating records


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DNS: caching and updating records

Mi khi name server c c mapping, n s lucache li mapping ny

Cc mc cache s ht thi hiu (bin mt) saumt thi gian. TLD Server thn c lu cache t i cc local


name servers Do cc root name server t khi c ving thm.

C ch cp nht/bo tin uc thc hin theo thitk ca IETF RFC 2136 http://www.ietf.org/html.charters/dnsind-charter.html

DNS records


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DNS: CSDL phn b, lu cc resource records (RR)

RR format: (name, value, type, ttl)

Type=A name l hostname

Type=CNAME name is b danh ca vi tn


Type=NS name l domain (VD

foo.com)

value l hostname caauthoritative name serverdnh cho domain ny

value l IP address

chnh thc (canonical name)

www.ibm.com l b danh caservereast.backup2.ibm.com

value l tn chnh thc(canonical name)

Type=MX value l tn ca mailserver

uc lin kt vi name

DNS protocol, messages


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p , g

DNS protocol : quy nh cc query msg v reply msg,c hai c cng nh dng message

Phn msg header identification: 16 bit #

for uer , re l to uer


uses same #

flags: query or reply

recursion desired

recursion available reply is authoritative

DNS protocol, messages


74/120

p , g

Name, type fieldsfor a query

RRs in responseto uer


records forauthoritative servers

additional helpful

info that may be used

Inserting records into DNS


75/120

g

example: new startup Network Utopia register name networkuptopia.com at DNSregistrar

(e.g., Network Solutions) provide names, IP addresses of authoritative name server(primary and secondary)

re istrar inserts two RRs into com TLD server:


(networkutopia.com, dns1.networkutopia.com, NS)(dns1.networkutopia.com, 212.212.212.1, A)

create authoritative server Type A record for

www.networkuptopia.com; Type MX record fornetworkutopia.com How do people get IP address of your Web site?

Chapter 2: Application layer


76/120

p pp y

2.1 Principles ofnetwork applications

2.2 Web and HTTP 2.3 FTP

2.6 P2P applications 2.7 Socket programming

with UDP 2.8 Socket programming



2.5 DNS

Pure P2P architecture


77/120

Khng c server ch phc v. Cc host truyn thng trc

tip Cc peers kt ni nhau khng

peer-peer


3 trng hp: Phn phi file Tm thng tin Case Study: Skype

File Distribution: Server-Client vs P2P


78/120

Cu hi: Truyn 1 file t 1 server n N peer mtbao lu?

Serverus:server uploadbandwidth

ui:peer i upload


us

u2d1d2

u1

uN

dNNetwork (with

abundant bandwidth)

File, size Fbits

bandwidth

di:peer i downloadbandwidth

File distribution time: server-client


79/120

us

u2d1 d2u1

u

dN

Server

Network (withabundant bandwidth)

F Server ln lt giN bn sao ca file: htNF/us giy

Client i ti 1 bn sao


mt F/di giy

Tng tuyn tnh theo N

(vi N ln)

= dcs = max { NF/us, F/min(di)}i

Thi gian chuyn fileF ti N clients s dng cch ti p cnclient/server

File distribution time: P2P


80/120

us

u2d1 d2u1

u

dN

Server

Network (withabundant bandwidth)

F Server phi gi 1 bn sao

ca file: ht F/usgiy client i ti file ht F/di giy Tng cng c NF bits


Tc upload (ca ton h thng) nhanhnht c th: us + ui

dP2P = max { F/us, F/min(di), NF/(us + ui) }i

Server-client vs. P2P: example


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2.5

3

3.5

tionTime P2P

Client-Server

Client upload rate = u, F/u = 1 hour, us = 10u, dmin us


0

0.5

1

1.5

2

0 5 10 15 20 25 30 35

N

MinimumD

istribu

File distribution: BitTorrent


82/120

tracker: theo di cc peers

ang tham gia vo torrent

torrent:nhm cc

peers ang trao icc phn mnh file(chunk of file)

P2P file distribution


Ly danh sch cc peer

tradingchunks

peer


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BitTorrent (1) file c chia thnh cc mnh (chunks)256KB. peer ang tham gia vo torrent:

cha c mnh no, nhng s tch ly cc chunks


trong sut qu trnh ghi danh vi tracker ( thu danh sch cc peers),

kt ni ti mt tp con cc peers (lng ging) Trong khi ang download file, peer cng upload cc

chunks (m n c v c yu cu) cho cc peer khc. peers c th tham gia vo torrent v rt lui. Khi peer c c file, n c th ri torrent (ch k) hoc

li torrent (v tha)

BitTorrent (2)

M1


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Pulling Chunks Ti 1 thi im nht nh,

cc peer khc nhau ang cc cc chunks khc nhau.

nh k, mt peer (VD Alice)s hi cc lng ging v danh

Sending Chunks: tit-for-tat Alice gi cc chunks ti 4

lng ging m hin thichng ang gi cho Alicecc chunks khc mccao nht.


s ch c c chunks m ch ng

c. Peer ny (Alice) gi yu cu

xin cc chunks m n cn

thiu. u tin xin chunks no m

t lng ging c nht(rarest first)

Sau m i 10s, snh

gi li top 4 ny. Sau mi 30 giy: chn ngu

nhin peer khc, gi chunk

cho peer ny. peer mi c chn c

th tham gia vo top 4

optimistically unchoke

Slide 84

M1 n ming tr mingMVC, 5/1/2010


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BitTorrent: Tit-for-tat


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(1) Alice chn ngu nhin c Bob v gi chunks cho Bob(2) Alice tr thnh mt trong 4 peer gi chunks cho Bobnhiu nht; Bob gi chunks cho Alice p tr.

(3) Bob tr thnh mt trong 4 peer gi chunk cho Alice nhiu nht.


Cng upload vi tc cao,cng c th tm thy ccpeer trao i chunks d hn& nhn c file nhanh hn.

Distributed Hash Table (DHT)


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DHT = CSDL phn tn trn mi trng P2P[distributed P2P database] CSDL cha cc cp (key, value);

key: tn ni dung; value: a ch IP (ni lu ni dung) Peers truy vn CSDL bng cch cung cp tr key

CSDL tr v gi tr ca value khp vi tr key

Peers cn c thchn [insert] cc cp (key,value) mi vo CSDL.

DHT Identifiers


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Mi peer c gn mt s id nh danh, l snguyn nm trong vng [0,2n-1] (n nguyn c nh) Mi id c th c biu din qua chui n bits.

i hi mi tr ke l m t s n u n thu c cnvng [0,2n-1]

thu c tr key nguyn nh i hi trn, sdng hm bm h, h nhn tr key gc v tr v trnguyn trong vng [0,2n-1] eg, key = h(Led Zeppelin IV) y l l do ti sao ta gi n l DHT (distributed hash

table)

Lu cp (key, value) peer no?


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Vn : Lu tr cp (key, value) peer no? Quy tc: Lu ti peer c id=key. Nu khng

c peer nh vy th lu ti peer c id gnnht.

Quy c trong bi ging: id gn nht l idnm lin sau trong danh sch cc id. VD: n=4; peers: 1,3,4,5,8,10,12,14;

key = 13, th peer lin sau l 14 key = 15, th peer lin sau l 1

1

Circular DHT (1)


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1

3

415

5

810

12

Mi peer ch bit peer lin trc v lin sau. Overlay network

Circle DHT (2)


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0001

0011

1111

Ai chu trch nhim

cho key 1110 ?L ti

O(N) messages

on avg to resolve

query, when thereare N peers

0100

0101

10001010

1100

1110

1110

1110

1110

1110

1110

Define closestas closestsuccessor

Circular DHT with Shortcuts1 Ai chu trch nhim(0011)


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13

4

15

Ai chu trch nhimcho key 14 (1110) ?

(1111)

(0011)

Mi peer qun l a ch IP ca peer lin trc, peerlin sau v cc short cuts.

Gim t 6 cn 2 messages. C th thit k shortcuts sao cho s lng ging v

s message khi truy vn u bng O(log N)

5

810

(1000)

Peer Churn1


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3

4

12

15

x l trnh trng cc peer n vi m khng bo trc(peer churn),mi peer cn phi bit cc a chIPca 2 peer lin sau ca n.

Mi peer s ping nh k 2 peer linsau ca n xc nh l chng cn

Peer 5 t ngt ri khi vng. Peer 4 pht hin ra iu ny; nhn peer 8 lm peer lin

sau (th nht); v hi peer 8 peer lin sau ca 8?; sau xem peer lin sau ca 8 l peer k lin sau (thhai)ca n.

Nu peer 13 mun gia nhp vng th sao?

810

.

P2P Case study: SkypeSkype clients (SC)


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Bn cht P2P: cc cpuser c th truyn thng

trc tip. Giao thc tng ng dng

Skype clients (SC)

Supernode

SN

Skypelogin server


.

T chc phn cp, sdng cc Supernode nh x gia username v

a ch IP, c lu phn

b gia cc Supernode.

Peers as relays Vn gp phi khi c 2


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Vn gp phi khi c 2peer (VD Alice v Bob) unm ng sau NAT NAT ngn chn cc peer t

bn ngoi khi to cc kt ni(hay cuc gi) n cc peerbn trong


Gii php: S dng cc supernode ca

Alice v Bob, 1 supernodec chn ra lm relay node(nt chuyn tip)

Tng peer s khi to kt nivi nt chuyn tip. Do cc peer c th truyn

thng cho nhau vt qua NATnh nt chuyn tip.



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2.5 DNS

Socket programming

M c tiu: h c cch xy dng ng d ng client/server


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Socket API c gii thiu trong BSD4.1

UNIX, 1981 A application-created,

socket

Mc tiu: hc cch xy dng ng dng client/servertruyn thng vi nhau s dng sockets


c cc ng dng to ra, s

dng v gii phng mt cchtng minh. client/server paradigm C 2 loi dch v vn chuyn

thng qua socket API UDP TCP

-con ro e nter ace

(a door) into whichapplication process canboth send and

receive messages to/fromanother application

process

Socket programming basics


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Server phi angchy trc khi client

c th gi d liu chon.

Socket c th xc nhtrong ni b nh shiu cng(portnumber)

Server phi c 1socket (ca) m nh n c th nhn/gi i cc segment

Tng t, client cngcn c 1 socket

Tng t nh s hiu

cn h trong 1 ta nh Client cn phi bit a

ch IP ca Server v s

hiu cng ca socket.


Socket programming with UDP


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UDP: khng c kt ni giaclient v server

Khng bt tay Bn gi gn a ch IP v s

hiu cng ln tng segment

Quan im ng dng

UDP cun c dch v vn chu n


Server c t tr c xu t a

ch IP v s hiu cng cabn gi t segment nhnc.

datagram khng m bo tin

cy gia client and server

Lu : Thut ng chnh thc gi gi

tin UDP l datagram. Trong lpny chng ta s gi l UDPsegment

Running example


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Client: Ngi s dng g vo mt dng vn bn Chng trnh client gi dng ny n server

Server: Server nhn c dng vn bn Server chuyn thnh ch hoa tt c cc k t Gi dng vn bn c sa i n client

Client: Nhn dng vn bn Hin th


Client/server socket interaction: UDP

Server (running on h tid) Client


101/120

Server (running on hostid)

create socket,

clientSocket =DatagramSocket()

Client

T o data ram vi server IP v

create socket,

port= x.serverSocket =DatagramSocket()


ngclientSocket

c datagram tclientSocket

port=x; gi datagram thng quaclientSocketc datagram t

serverSocket

Son tr li choclient (vi achIP client vs hiu cng),gi thng quaserverSocket

Example: Java client (UDP)

keyboard monitor


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inFromUser

Process

inputstream

Input: receivespacket (recall

Clientprocess


sendPacke

t

to network from network

receivePacke

t

clientSocket

UDPpacket

UDPpacket

UDP

socket

Output: sends

packet (recallthat TCP sentbyte stream)

a rece vebyte stream)

client UDP

socket

Example: Java client (UDP)


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import java.io.*;import java.net.*;

class UDPClient {public static void main(String args[]) throws Exception{

Create


u ere ea er n rom ser =new BufferedReader(new InputStreamReader(System.in));

DatagramSocket clientSocket = new DatagramSocket();

InetAddress IPAddress = InetAddress.getByName("hostname");

byte[] sendData = new byte[1024];byte[] receiveData = new byte[1024];

String sentence = inFromUser.readLine();

sendData = sentence.getBytes();

Createclient socket

Translatehostname to IP

address using DNS

Example: Java client (UDP), cont.

Create datagram


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DatagramPacket sendPacket =new DatagramPacket(sendData, sendData.length, IPAddress, 9876);

clientSocket.send(sendPacket);

DatagramPacket receivePacket =

Create datagramwith data-to-send,

length, IP addr, port

Send datagramto server


, .

clientSocket.receive(receivePacket);

String modifiedSentence =new String(receivePacket.getData());

System.out.println("FROM SERVER:" + modifiedSentence);

clientSocket.close();}

}

Read datagram

from server

Example: Java server (UDP)


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import java.io.*;import java.net.*;

class UDPServer {

public static void main(String args[]) throws Exception{Create

datagram socket


=

byte[] receiveData = new byte[1024];byte[] sendData = new byte[1024];

while(true){

DatagramPacket receivePacket =new DatagramPacket(receiveData, receiveData.length);

serverSocket.receive(receivePacket);

at port 9876

Create space forreceived datagram

Receivedatagram

Example: Java server (UDP), contString sentence = new String(receivePacket getData());


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String sentence = new String(receivePacket.getData());

InetAddress IPAddress = receivePacket.getAddress();

int port = receivePacket.getPort();

String capitalizedSentence = sentence.toUpperCase();

Get IP addrport #, of

sender


sendData = capitalizedSentence.getBytes();

DatagramPacket sendPacket =new DatagramPacket(sendData, sendData.length, IPAddress,

port);

serverSocket.send(sendPacket);

}}

}

Write outdatagram

to socket

End of while loop,loop back and wait foranother datagram

Create datagramto send to client

UDP observations & questions

C client v server u dng DatagramSocket


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C client v server u dng DatagramSocket a ch IP bn nhn v s hiu cng c gn

tng minh vo segment. iu g s xy ra nu thay i c hai clientSocket ,

server oc e n my oc e

Liu client c th gi 1 segment n 1 server mkhng bit n a ch IP ca server v/hoc portnumber?

C th no nhiu client s dng server ny?




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. ec ron c a

SMTP, POP3, IMAP 2.5 DNS

Socket-programming using TCP


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TCP service: reliable transfer ofbytes from one processto another


process

TCP withbuffers,

variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,variables

socket

controlled by

applicationdeveloper

controlled byoperatingsystem

host orserver

internet

Socket programming with TCPClient phi lin lc vi server Khi c client lin lc, server


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Trc tin, tin trnh serverphi ang chy.

Server phi c socket cto sn, ch n cc lin lct pha client.

,TCP to mi mt socket server process lin lc viclient Cho php server trao i

vi nhiu client


Client lin lc vi server bng

cch: To client-local TCP socket Ch nh a ch IP, port

number ca server process Khi client to socket: client

TCP thit lp kt ni nserver TCP

source port numbers c

dng phn bit client(ni r trong Ch. 3)

TCP provides reliable, in-ordertransfer of bytes (pipe)between client and server

Quan im ng dng

Client/server socket interaction: TCP

Server (running on hostid) Client


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wait for incomin

create socket,port=x, for

incoming request:

welcomeSocket =ServerSocket()

create socket,

TCP


connection requestconnectionSocket =

welcomeSocket.accept()

connect to hostid, port=xclientSocket =

Socket()

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

connect on setup

keyboard monitor

Stream jargon

St e m l d k t i


112/120

inFr

omUser

Process

inputstream

Client

process

Stream l dy cc k t ivo hoc ra khi mtprocess

Mt input stream c linkt vi mt vi ngun nhp


outToServer

to network from network

inFromServer

clientSocket

inputstream

outputstream

TCPsocket

client TCPsocket

,bn phm hoc socket.

Mt output stream c linkt vi mt u ra, VD mnhnh hoc socket.

Socket programming with TCP

VD v /dng client-server:


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VD v /dng client server:1) Client c dng t standard

input (inFromUser stream),

gi n server thng quasocket (outToServer stream)

2: Application Layer112

3) Server chuyn i k t trong

dng thnh ch hoa, gi ngcli client.

4) Client c, in ra dng b sa it socket (inFromServer

stream)

Example: Java client (TCP)

import java.io.*;


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p j ;import java.net.*;class TCPClient {

public static void main(String argv[]) throws Exception{

Strin sentence


String modifiedSentence;

BufferedReader inFromUser =new BufferedReader(new InputStreamReader(System.in));

Socket clientSocket = new Socket("hostname", 6789);

DataOutputStream outToServer =new DataOutputStream(clientSocket.getOutputStream());

Createinput stream

Createclient socket,

connect to serverCreate

output streamattached to socket

Example: Java client (TCP), cont.


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BufferedReader inFromServer =new BufferedReader(new

InputStreamReader(clientSocket.getInputStream()));

sentence = inFromUser.readLine();

Createinput stream

attached to socket


outToServer.writeBytes(sentence + '\n');

modifiedSentence = inFromServer.readLine();

System.out.println("FROM SERVER: " + modifiedSentence);

clientSocket.close();

}}

en neto server

Read linefrom server

Example: Java server (TCP)import java.io.*;import java.net.*;


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class TCPServer {

public static void main(String argv[]) throws Exception{

String clientSentence;Strin ca italizedSentence


ServerSocket welcomeSocket = new ServerSocket(6789);

while(true) {

Socket connectionSocket = welcomeSocket.accept();

BufferedReader inFromClient =new BufferedReader(newInputStreamReader(connectionSocket.getInputStream()));

welcoming socket

at port 6789Wait, on welcomingsocket for contact

by client

Create inputstream, attached

to socket

Example: Java server (TCP), cont

C t t t


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DataOutputStream outToClient =

new DataOutputStream(connectionSocket.getOutputStream());

clientSentence = inFromClient.readLine();Read in linefrom socket

Create outputstream, attached

to socket


capitalizedSentence = clientSentence.toUpperCase() + '\n';

outToClient.writeBytes(capitalizedSentence);}

}}

Write out lineto socket

End of while loop,

loop back and wait foranother client connection

TCP observations & questions

Server c 2 kiu socket:


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ServerSocket v Socket

Khi client g vo ca serverSocket, server to raconnectionSocket v hon tt TCP conx.

vo segment tng minh. Liu nhiu clients c th s dng server?.


Chapter 2: Summary

application architecturesour study of network apps now complete!

specific protocols:


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application architectures client-server

P2P hybrid

specific protocols: HTTP

FTP SMTP, POP, IMAP

DNS


requirements: reliability, bandwidth, delay

Internet transport servicemodel connection-oriented,reliable: TCP unreliable, datagrams: UDP

P2P: BitTorrent, Skype

socket programming

Chapter 2: Summary

Most importantly: learned aboutprotocols


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typical request/reply

message exchange: client requests info or

Important themes:

control vs. data msgs

in-band out-of-band


serv ce server responds with

data, status code message formats:

headers: fields giving info

about data data: info being

communicated

centralized vs.

decentralized stateless vs. stateful

reliable vs. unreliable

msg transfer complexity at network

edge

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