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Tiu lun Mng My tnh Nng cao Peer-to-Peer Networks

Hunh Ngc Sn - Lp K3MCS - H Duy Tn Page 1

B GIO DC O TO

TRNG I HC DUY TN

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TIU LUNMn:MNG MY TNH NNG CAO

ti:

Peer-to-peer networks

GV hng dn : TS L Trng Vnh

Hc vin : Hunh Ngc Sn

Chuyn ngnh : Thc s Khoa Hc My Tnh

Kha : 3

NNG, 07/2011


2/23


Li ni u

Mng ngang hng (Peer-to-Peer P2P) bt u xut hin t 1999 v thu ht s quan

tm trong nhng nm gn y. c bit vic p dng cc m hnh P2P trong vic xy dngnhng ngdng chia s tp (file), video, in thoi trn nn Internet (Internet-based telephony) t c nhiu thnh cng. Hin nay cc ng dng P2P chim khong 50% (thm ch75%)bngthng trnInternet.

Cc mng ngang hng Peer-to-Peer (P2P) cung cp mt nn tng tt chia s d liu,phn phi ni dung cng vi ccngdng truyn thng a hng mc ng dng phm virng. Cc mng P2P c kh nng cung cp mt kin trc nh tuyn hiu qu c tnhcht t tchc trn din rng, kt hp vi kh nng chu ng li, cn bng ti v quan im v v trrrng.

Tiu lun gm 4 phn chnh:Phn 1: Tng quan.Phn 2: Cc lnh vc ng dng P2P, phn loi P2P.Phn 3: Cc vn v nh tuyn trong P2P.Phn 4: Kt lun.

Em xin chn thnh cm n thy TS. L Trng Vnh hng dn em hon thnh tiu lunny.

Hc vin thc hin

Hunh Ngc Sn



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Phn 1: Tng quan v Mng ngang hng

I. nh ngha mng ngang hng:

1. Gii thiu:

Mng ngang hng (Peer-to-Peer P2P) bt u xut hin t 1999 v thu ht s quantm ca gii CNTT trong nhng nm gn y. c bit vic p dng cc m hnh P2P trong vicxy dng nhng ng dng chia s file (file sharing), in thoi trn nn Internet (Internet-basedtelephony) t c nhiu thnh cng.

Hin nay cc ng dng P2P chim khong 50% (thm ch 75%) bng thng trn Internet.

2. nh ngha P2P:

Mng ngang hng l mt kiu mng c thit k cho cc thit b trong c chc nngv kh nng ca cc thit b l nh nhau.

nh ngha ca Oram v ng nghip: [A Peer-to-Peer system is] a self-organizing system ofequal, autonomous entities (peers) [which] aims for the shared usage of distributed resources in a

networked environment avoiding central services.

+ Mng P2P khng c khi nim my trm (client) hay my ch (server), m ch c khinim cc nt (peers) ng vai tr nh c client v server.

M hnh Client/Server M hnh P2P

II. Mng P2P (P2P Networks) v phn mm ng dng P2P (P2P softwares).1. Home P2P Networks:

Hu ht cc mng my tnh gia nh hin nay l mng P2P.

+ Ngi dng cu hnh cc my tnh theo workgroup cho php cc my c th chia s files,my in v cc ti nguyn, thit b khc.



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+ C mng c dy v khng dy trong gia nh u c th s dng thit lp mng P2P.

2. Mng chia s file P2P:

L mng P2P ph bin v ni ting nht trn Internet hin nay.

+ Chc nng ch yu ca mng l cho php tm kim v truyn d liu da trn giao thcIP (Internet Protocol).

+ truy cp vo mng P2P ny, ngi dng ch cn download v ci t phn mm ngdng ph hp cho my tnh ca mnh.

+ C nhiu mng P2P v phn mm ng dng P2P tn ti hin nay. Mt s phn mm chs dng c cho 1 mng P2P nht nh, mt s hot ng c vi nhiu mng P2P khc nhau.

+ Mt s mng P2P ni ting trn Internet gm: eDonkey, BitTorent, Gnutella.

3. Phn mm ng dng P2P.

Cc phn mm ng dng P2P cn t c 7 tiu ch cn bn sau:

1. Giao din ngi dng khng nm trong trnh duyt (web browser).

2. Cc my tnh trong h thng c th ng vai tr nh c my trm v my ch.

3. Phn mm d s dng v c tch hp nhiu tnh nng tt.

4. ng dng h tr ngi dng to ni dung v thm chc nng.

5. ng dng cho php to kt ni n ngi dng khc.

6. ng dng c nt mi v th v.7. Phn mm ng dng h tr a giao thc trn mng.

Mt s phn mm ng dng P2P ni ting hin nay bao gm: Kazza, eMule, Bittorent,Limewire .

*. Gii thiu Kazaa:

+ Download:www. kazaa. com

+ S dng P2P technology (ngi dng c th kt ni trc tip vi ngi dng khc).

+ Kazaa cho php: Tm v download cc files c chia s bi nhng nh cung cpchuyn nghip v ngi dng.

+ Kazza c s dng nhng kt ni nhanh vi cc SuperNodes: Mi SuperNode cha danhsch cc files chia s bi ngi dng v ni lu tr file.

Super Nodes

http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/http://www.kazaa.com/


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*. Gii thiu Emule:

+ Download:www. emule. com

+ Mt trong nhng phn mm chia s file P2P ln nht gia cc Clients trn Internet.

+ Verson mi nht: eMule 0.49b.

+ C th s dng eMule chia s v download tt c cc loi files trn Internet.

*. Gii thiu Skype:

+ Download:www. skype. com

+ L phn mm P2P VoIP pht trin bi nhng ngi lm Kazaa.

+ Skype cho php ngi dng m thoi v gi message ti ngi dng Skype khc.

+ y l mt overlay network, c 2 loi nodes: Original Host (OH) v Super nodes (SN).

+ OH l mt phn mm ng dng cho php s dng m thoi v gi message.

+ Nhng node c a ch IP tnh, CPU, memory, bng thng mnh th c th c xemxt chn lm super node.

Skype Login

Server

Message exchange

during login

Super Nodes

+ OH kt ni vi mt SN v phi ng k vi Skype login server login thnh cng.

http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.emule.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.skype.com/http://www.emule.com/http://www.skype.com/


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- Dng cng ngh Global Index ca n tm user.

- Firewall traversal: First UDP, second TCP, third TCP port 80 (HTTP), fourth TCPport 443 (HTTPS).

- Tn hiu thng xuyn c mang i trong TCP.

III. So snh m hnh P2P vi m hnh truyn thng Client/Server:

P2P Client/Server

- Mt mng ngang hng cho php cc node(PCs) ng gp, chia s ngun ti nguyn vinhau. Ti nguyn ring r ca cc node (cng, CD-ROM, my in . Cc ngun tinguyn ny c th c truy cp t bt c nodeno trong mng.

- Cc node ng vai tr nh c Client (truy vnthng tin) v Server (cung cp thngtin).

- D liu c lu tr mt Server trung tm,tc cao (Tc truy cp thng ln hn sovi mng P2P).

- Khi mt my client yu cu ly thng tin vthi gian n s phi gi mt yu cu theo mttiu chun do server nh ra, nu yu cu cchp nhn th my server s tr v thng tin mclient yu cu.



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* u, nhc im ca mng P2P, Client/Server:

P2P Client/Server

+ u im:

- Khng cn server ring, cc client chias ti nguyn. Khi mng cng c mrng th kh nng hot ng ca hthng cng tt.

- R.

- D ci t v bo tr.

- Thun li cho vic chia s file, my in,CD-ROM v.v

+ u im:

- Tc truy cp nhanh.- Kh nng m rng cao.

- Hot ng vi bt k loi ng dng no.

- S dng c vi cc ng dng chia sCSDL.

- ng tin cy hn (c server ring).

- Mc an ton cao nht.

+ Nhc im:

- Chm.

- Khng tt cho cc ng dng CSDL.

- Km tin cy.

+ Nhc im:

- Cn server ring (nghn c chai).

- t.

- Phc tp trong vic bo tr, duy tr hotng ca mng.

IV. Lch s pht trin ca P2P:

- Lch s ra i v pht trin ca P2P gn lin vi phn mm ng dng Napster.

+ Nm 1999, Shawn Fanning mt sinh vin i hc 18 tui ri b trng i hc bt u xy dng phn mm mang tn Napster (do bc xc vi vic rt kh khn trong vica v chia s cc file nhc online trn Internet mc d mi ngi u c ngun ti nguyn


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trong a cng ca mnh).

+ Napster c xy dng thnh cng v tr thnh cch chia s file chnh (min ph), n lm thay i cch download file nhc v dung lng cng ln hn nhiu so vi ccchng trnh chia s file trc .

+ Download phn mm, bn c th chia s files t my tnh ca mnh vi tt c mi

ngitrn th gii.

+ 60 triu ngi trn th gii s dng (1 triu ngi Nht) vo thi im . Tuynhin, do c qu ng ngi dng v vn bn quyn m nhc nn cng ty Napster bcm hot ng, phn mm khng cn c s dng na (2003).

- Sau Napster, rt nhiu cc chng trnh khc nh Gnutella, KaZaa and WinMP xut hin. V P2P chuyn sang vic chia s file, chia s processor power ri ca cc nodesch khng phi l chia s cc file m nhc MP3 na.

- Sau s ra i ca Napster, cng ngh P2P pht trin mt cch nhanh chng. Hin ticc ng dng P2P chim khong 50% (thm ch 75%) bng thng trn Internet.

Phn 2: Cc lnh vc ng dng ca P2P

S ra i ca mng ngang hng to ra cch thc qun l mi cho hng lot cc lnh vcng dng. Bi ny a ra mt cch nhn tng qut cho vn cc lnh vc ng dng ca mngngang hng nh: giao tip (communication), chia s file (file sharing), bng thng(bandwidth), vn lu tr (storage), cc chu trnh x l (processor cycles).

3.1. Giao tip(communication):


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+ ng mt vai tr quan trng trong cc ng dng mng nganghng.

+ L nhn t quyt nh trong cc mng ngang hng v n cung cp thng tin v cc Peers vcc ngun ti nguyn no l sn sng trn mng.

+ To ra kh nng cho cc Peer kt ni trc tip vi cc Peer khc v yu cu cc ngun ti

nguyn.+ Mt v d in hnh v ng dng mng ngang hng trong giao tip l h thng chuyn tinnhntrc tip (instantmessaging).

*. Instant messaging:

- Thng thng, server trung tm lu tr thng tin v danh sch ngi dng ngk.

- Khi c s giao tip gia cc node, vic tm kim ngi dng (node khc) c thc hintrn server.

- Trong trng hp ngi dng khng online, h thng s phi lu tr cc tin nhncho n khi ngi dng ny online.

- Cc dch v in hnh: Napster, ICQ, Jabber.

3.2. Chia s Files (File sharing)

- C th ni ng dng c s dng nhiu nht ca mng ngang hng l chia sfile.

- Theo c tnh khong 70% lu lng mng trn Internet c cho l trao i cc filec bit l cc file m nhc (hn 1 t cc file m nhc c download mitun).

- c im ca vn chia s file l cc Peer c cc file c download vi vai tr l mtClient lm cho chng lun sn sng vi cc Peer khc trong vai tr ca mt Server.

- Vn ch yu cho mng ngang hng ni chung v cho vn chia s file n ring l vn tm kim. Trong ng cnh ca h thng chia s file, c ba m hnh khc nhau c pht trin:m hnh f loo d e d r e qu e s t , m hnh t h mc trung t m v m hnh h n g t i li u . Cc m hnh

ny c minh ho qua cc ng dng thc ca mng ngang hng sau: Gnutella, Naspter vFreeNet.

- Trong h thng Gnutella, khng c s tp trung ho, cc file c lu tr trn cc Peer cahthng, khi c yu cu tm kim mt file my tnh s gi yu cu ny ti tt c cc peer llngging ca n cho ti khi tm thy my cha file cn tm. Tip theo l qu trnh trao i filetrc


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tip gia hai my tnh trongmng.

- Trong h thng Naspter, c s tp trung ho. Khi mt my tham gia vo mng, danh mccc file s c ng k v lu tr trn Server trung tm, khi c yu cu tm kim, my tnhs hi Server trung tm v v tr ca file. Sau vic trao i file c thc hin gia hai mytnh vi nhau.

- Trong h thng Freenet, trong file khng c lu tr trn a cng ca cc peer cung cpchng m c lu tr cc v tr khc trong mng. Mc ch ca vic pht trin mngFreenet l lm cho thng tin c lu tr v truy cp m khng cn bit nh danh. Vi cc tchc nh vy, ch s hu ca mt node mng cng khng bit c ti liu g c lu trtrn a cng ca my anh ta. V l do ny m cc Peer v cc file c cung cp cc s nhdanh khc nhau. Khi mt file c to, n c truyn qua cc peer lng ring ti cc peer cs nh danh gn vi s nh danh ca file nht v c lu tr .

3.3. Bng thng (Bandwidth)

Do yu cu v kh nng truyn dn ca cc mng ngy cng i hi cao c bit l khi mts lng ln d liu a phng tin tng nhanh, hiu qu ca vic s dng bng thng ngycng tr nn quan trng. Hin nay, hng tip cn tp trung trong cc file c lu trtrn mt Server v c truyn t ti my khch yu cu ang c s dng ch yu.Trong trng hp ny khi s lng cc yu cu tng nhanh s dn ti tnh trng nt c chai. Vihng tip cn theo mng ngang hng vn c n b ng t i s t c s ti u nht v n tndng ti a c cc hng truyn dn trong h thng mng.

- Tng cng kh nng cn bng ti trong mng: Khc vi kin trc Client/Server cc mngngang hng lai c th nhn c s cn bng ti tt hn. Vi m hnh Client/Server th c

yu cu truy vn thng tin v vic truyn d liu u c thc hin gia my ch v mykhch, s lm mt s cn bng ti khi c nhiu yu cu kt ni ti my ch. Trong m hnhmng ngang hng, ch c yu cu truy vn c thc hin gia my tnh tham gia mng vimy ch, cn vn truyn file c thc hin gia hai my tnh tham gia mng vi nhau,iu ny dn n vic phn b ti u trn h thng mng.

- Chia s vic s dng bng thng: Mng ngang hng c th lm tng kh nng downloadv truyn cc file do c ch tn dng ng truyn ti cc peer tham gia mng. Mt file d liuln c chia thnh cc khi d liu nh c lp nhau, cc khi d liu ny c chuyn ngthi n cc peer khc nhau v cui cng n peer yu cu chng. Ti peer yu cu cc khid liu c ghp li thnh file d liu ban u. Cc phn mm in hnh ca vic chia s bngthng l cc phn mm download file, chng hn nh: BitTorrent, FlashGet

3.4. Khng gian lu tr (Storage Space);

Hin nay vi cc h thng cn c yu cu v mt lu tr d liu cao ngi ta thng lachncc gii php lu tr nh:


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+ DAS (Direct Attached Storage): lu tr trc tip tham chiu mt cch trc tip n mt hthng lu tr s gn vi mt server hoc mt trm, m khng cn n mt mng li lu tr giachng. Ta gi l r e tr o n y m, thng c dng gia cc khng gian lu tr phi mng li tSAN v NAS.

+ NAS (Network Attached Storage): lu tr gn vi mng l khng g i an l u t r dl i u nm t ng ca my t nh c k t n i t i mt mng my t nh d l i ut ruy cp t i mng my khch khng ng nht .

+ SAN (Storage Area Networks): vng mng lu tr l mt cu trc kt ni cc thit b lu trca cc my tnh xa (nh l d is k a rr a y s, t a pe li b r a r ie s v o p t ica l juk e b o x e s) ti cc se rverthe o c ch n o , t i h i u h n h , cc thit b xut hin nh c gn kt cc b.Mc d chi ph v phc tp gim, nh nm 2007, SAN vn khng c ph bin ra ngoicc doanh nghip ln.

Bn cnh nhng u im cc gii php cng tn ti mt s nhc imnh:

+ Km hiu qu trong vic s dng h thng lu tr sn c.

+ Phi tng cng vic sao lu d liu.

+ Tng ti trong mng ca cng ty.

Tuy nhin, bng thng mng ngy cng c ci thin cao, tnh kt ni lin thng ngy mtd dng cho php thay i cch thc qun l vn lu tr d liu, gii quyt mt cch hiuqu vn lu tr v khng i hi nhiu v vn qun tr h thng. Vi mng lu tr nganghng ni chung n c gi thit rng ch c mt phn khng gian sn c trn my tnh PCc s dng. Mng lu tr ngang hng l mt cm cc my tnh c xy dng trn mt nnmng my tnh tn ti, chia s tt c cc lu tr sn c trn mng


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3.5 Cc chu trnh x l (ProcessorCycles):

C th nhn thy rng trong cc ng dng i hi cn phi c sc mnh tnh ton ngi tathng tm cchxy dng cc my tnh mnh, t tin ch cha ch trng vo vic tn dngkh nng tnh ton ca cc my tnh c ni mng. Ngy nay do nhng yu cu i hi tnhton hiu nng cao nh cc thao tc tnh ton trong tin sinh hc, trong ti chnh, trong o

lng m nhiu nghin cu ng dng mng ngang hng vo x l tnh ton c a ra.Bng vic s dng cc ng dng mng ngang hng b cm cc chu trnh x l c th nhnc kh nng tnh ton ngang bng vi mt siu my tnh t tin. Trong mt mng mi mytnh l trong sut vi cc my tnh khc v tt c cc node c kt ni mng s to thnh mtmy tnh logic.

3.6. Phn loi mng ngang hng:

- Mng ngang hng c th c phn loi theo mc ch s dng, v d:

Chia s file (file sharing)

in thoi VoIP (telephony)

a phng tin media streaming (audio, video)

Din n tho lun (Discussion forums)

- Mng ngang hng c th c phn loi theo mc tp trung ca mng (i vi P2P overlaynetworks).

P2P

Unstructured P2P Structured P2P

1st Generation 2nd Generation

Centralized Pure Hybrid DHT based


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* Mng ngang hng khng cu trc (unstructured):

o Ni lu tr ni dung (files) hon ton khng lin quan g n overlay topology(cu trc hnh hc ca mng).

o K thut tm kim ch yu l s dng flooding vi cc gii thut tm kim u

tin theo chiu rng (breadth first), hoc u tin theo chiu su (depth-first)cho n khi ni dung c tm thy. Cc k thut khc phc tp hn gm bc

nhy ngunhin (random walk) v ch s routing (routing indices).

o Cc h thng khng cu trc thng ph hp trong trng hp cc node ra vomng thng xuyn, ty y.

3.6.1. c im h thng mng ngang hng tp trung(Centralized):

y l mng ngang hng th h th nht, c im l vn cn da trn mt my ch tmkim trung tm, chnhv vy n cn c gi l mang ngang hng tp trung (centralized Peer-

to-Peer networks). Cu trc Overlay ca mng ngang hng tp trung c th c m t nhmt mng hnh sao (hnh v 2).

Nguyn tc hot ng:

o Mi client lu tr files nh chia s vi cc node khc trong mng.

o Mt bng lu tr thng tin kt ni ca ngi dng ng k (a ch IP, bng thngkt ni .).

o Mt bng lit k danh sch cc files m mi ngi dng nh chia s (tn file,


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dung lng, thi gian to file .)

o Mi my tnh tham gia mng c kt ni vi my ch tm kim trung tm, cc

yu cu tm kim c gi ti my ch trung tm phn tch, nu yu cu cgii quyt my ch s gi tr li a ch IP ca my cha ti nguyn trong mngv qu trnh truyn file c thc hin theo ng c ch ca mng ngang hng,gia cc host vi nhau m khng cn quan tm my ch trung tm.

u im:

o D xy dng.

o Tm kim file nhanh v hiu qu.

Nhc im:

o Vn lut php, bn quyn.

o D b tn cng.

o Cn qun tr (central server).

Napster l mng ngang hng c trng cho h thng mng ngang hng ca th h th nht,chng c dng cho vic chia s cc file gia cc ngi dng Internet, c s dng rngri, tuy nhin nhanh chng b mt th trng bi yu t v lut php. Khi nim v kin trc caNapster vn cn c s dng trong cc ng dng khc nh: Audiogalaxy, WinMX.

Filedownload query

Mng ngang hng tp trung th h th nht (Napster)

Vi Napster, vic tm kim file b tht bi khi bng tm kim trn my ch v l do no khng thc hin c. Ch c cc file truy vn v vic lu tr c phn tn, v vy my ch

ng vai tr l mt nt c chai. Kh nng tnh ton v lu tr ca my ch tm kim phitng xng vi s nt mng trong h thng, do kh nng m rng mng b hn ch rt nhiu.

3.6.2. Cc mng ngang hng thun ty(Pure)

Mng ngang hng thun ty l mt dng khc ca th h th nht trong h thng cc mngngang hng. Khng cn my ch tm kim tp trung nh trong mng Napster, n khc phcc vn nt c chai trong m hnh tp trung. Tuy nhin vn tm kim trong mng ngang


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hng thun ty li s dng c ch Flooding, yu cu tm kim c gi cho tt c cc nodemng l lng ging vi n, iu ny lm tng ng k lu lng trong mng. y l mt yuim ca cc mng ngang hng thun ty. Cc phn mm tiu biu cho mng ngang hngdng ny l Gnutella 4.0, FreeNet.

u im:Mng ngang hng thun ty (Gnutella 4.0, FreeNet)


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o D xy dng.o m bo tnh phn tn hon ton cho cc node tham gia mng, cc node

tham gia v ri khi mng mt cch ty m khng nh hng n cu trc ca mng.Nhc im:

o Tn bng thng.

o

Phc tp trong tm kim.o Cc node c kh nng khc nhau (ngun CPU, bng thng, lu tr) u c thphi chu ti (load) nh nhau.

3.6.3. Cc mng ngang hng lai(Hybrid)

khc phc nhc im ca mng ngang hng thun ty, mt m hnh mng ngang hngmi c pht trinvi tn gi l mng ngang hng lai. y c gi l mng ngang hng thh 2. Phn mm tiu biu cho mng ngang hng kiu ny l Gnutella 0.6 v JXTA (Juxtapose).JXTA c bt u pht trin bi SUN t 2001 (y l giao thc P2P m ngun m). JXTA

c s dng cho PCs, m a in f r a m e s, c e ll p h o n e s, P D A s giao tip theo cch khng tptrung. Skype cng c xy dng da trn cu trc ny.

- Trong m hnh mng ngang hng lai tn ti mt trt t phn cp bng vic nh ngha ccSuperPeers.

- Cc SupperPeer to thnh mt mng khng cu trc, c s khc nhau gia SupperPeers vClientPeers trong mng, mi SupperPeer c nhiu kt ni n cc ClientPeers.

- Mi SupperPeer cha mt danh sch cc file c cung cp bi cc ClientPeer v a ch IPca chng v vy n c th tr li ngay lp tc cc yu cu truy vn t cc ClientPeer gi ti.

u im:

o Hn ch vic Flooding cc query, lm gim lu lng trong mng, nhng vntrnh c hin tng nt c chai (do c nhiu SuperPeers).

o Khc phc c nhc im v s khc nhau v CPU power, bandwidth

mng ngang hng thun ty, cc SuperPeer s chu ti chnh, cc node khc


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chu ti nh.

3.6.4. Mng ngang hng c cu trc(Structured)

o Topo mng c kim sot cht ch.

o Files (hoc con tr tr ti files) c t mt v tr xc nh.

o iu quan trng i vi nhng h thng c cu trc l cung cp s lin kt

(mapping) gia ni dung (v d: id ca file) v v tr node (v d: a chnode). Vic ny thng da trn mt cu trc d liu bng bm phn tn(Distributed Hash Table).

- Da trn cu trc bng bm phn tn c nhiu nghin cu v xut ra cc m hnhmng ngang hng c cu trc, in hnh l cu trc dng vng (nh trong hnh v m t):Chord, Pastry, v cu trc khng gian a chiu: CAN, Viceroy.


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u im:

o Kh nng m rng h thng mng trong m hnh khng cu trc thng b hn

ch bi cc k thut trong vic xy dng mng chng hn nh: M hnh tptrung dn ti vic tht nt c chai khi m rng, k thut Flooding dn ti victng lu lng mng khi m rng mng. Trong khi kh nng m rng vim hnh mng c cu trc c nng cao r rt.

Nhc im:

o Vic qun l cu trc ca topo mng gp kh khn, c bit trong trong trng hpt l vo/ra mng ca cc nodes cao.

Vn cn bng ti


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Phn 3: Cc vn v nh tuyn trong mng ngang hng

Hu nh cc thut ton hin ti ng dng trong mng ngang hng th h mi (mng ccu trc) u nh tuyn da trn key. N nhn mt key, v hi p, chng nh tuyn

mt bn tin ti node ctrch nhim vi key y. Cc key l cc chui s c mt di noy. Cc node l cc b nhn dng, ly t cng khng gian vi cc key (c ngha l cngs lng digits). Mi node lu gi mt bng nh tuyn bao gm mt tp nh cc nodetrong h thng. Cc thut ton nh tuyn u c gng nh tuyn ti node c key ph hpv qua t s hop nht. Di y l mt s thut ton nh tuynhinti:

- nh tuyn da vo tin t (Prefix routing) - PRR: y l thut ton u tin cho victm kim v nh tuyn ca mng ngang hng. Bng cch nh x nhn dng i tngthnh khng gian a ch ca cc peers, PRR nh tuyn da trn key v c th tr gip ccthao tc: c, chn v xa i tng lu tr trong mng chng ph. Nguyn l ca thutton ny l nn tng cho cc thit k DHT sauny. PRR l nh tuyn da trn hu t, ltrng hp i xng ca nh tuyn tin t. nh tuyn hu t v tin t u da trn s

ging nhau tng v tr ca a ch ch ti mi hop dc theo ng cho n khi ch tti. Thit k PPR da trn tp cc node tnh; khng quan tm ti thnh vin l cc nodeng, khng c k thut cp nht bng nh tuyn khi node ra nhp hoc ri mng. Phin bn n gin ca PRR c gi l SPRR c a ra bi Li and Paxton. Mt s ccthut ton Tapestry, Pastry, P-Grid, Cycloid, and Z-Grid. Plaxton, Rajaraman u da trnPRR.

- Plaxon et al [3]: Plaxon et al l mt phin bn ca PRR, y l thut ton u tin cs dng trn quy m ln bi cc DHT, nhng khng cung cp vic nh tuyn tm kim hiuqu. Thut ton ca Plaxton ban u c to ra nh tuyn cc truy vn Web ti cccache ln cn, v n nh hng n thit k ca Pastry, Tapestry v Chord. Phng php

Plaxton c phc tp tham gia/ri b theo hm loga. Plaxton m bo cc truy vn khngbao gi i xa hn trong khong cch mng so vi peerm lu gi key. Tuy nhin, Plaxtoncng c mt s nhc im: yu cu hiu bit ton b xy dng mng chng; peer gcca i tng l im li n; khng c s chn thm hoc xo b peer; khngc s trnhcc im tc nghn nng. i vi mt h thng n node, mi node c O(log n) ln cn, di ng nh tuyn O(log n)bc nhy

-Tapetry [1]: S dng mt bin th ca thut ton Plaxon et al [3] v thm vo tnhnng ng cho cc pees trong mng chng. S dng nh tuyn da trn tin t, Tapestry

s dng thut ton SHA-1 bm a ch cc node thnh cc ID biu din theo h c s 2b.

Mi node lu gi mt bng nh tuyn gm log2

b(N) hng v 2b-1 ct. Hng th nhttrong bng nh tuyn cha cc node c ID khc vi ID ca node ch s th nht.Hng th hai trong bng nh tuyn cha cc node c ID ging vi ID ca node ch sth nht nhng khc ch s th hai. Cc hng cn li ca bng nh tuyn cng c tchc tng t. Qu trnh tm kim c thc hin bng cch so snh ln lt cc ch stin t ca ID v d 4*** => 42** => 422* => 4227, qu trnh ny gi l nh x ln cn.

Bng nh tuyn ca mt node X c chia thnh nhiu mc (log2b(N)), mi mc i bao

gm cc lin kt (2b-1) n cc node c tin t ging n ch s th i-1 vi ID ca X. Khimt node nh tuyn n node ch n s i theo ng n node c ID gn ging vi IDch nht (da theo bng nh tuyn). Sau mi chng node tip theo s c mc cao hn t


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nht l 1, v vy sau nhiu nht l log2b(N) chng qu trnh tm kim s kt thc. Trong

iu kin bnh thng phc tp tm kim ca Tapestry l O(log2b (N)).

-Pastry: Trong Pastry vic nh tuyn bao gm vic chuyn truy vn ti node ln cn ctin t c chia s di nht vi key (v, trong trng hp cht ch, th ti node c b nhndng gn nht v s i vi key). Pastry c O(log n) ln cn v nh tuyn trong vngO(log n)bc nhy.

-Chord: Chord s dng mt khng gian ID vng trn kch thc N. Mt node Chord viID l u c mt con tr ti node u tin ng sau n trong khng gian ID theo chiu kimng h, k hiu l Succ(u) v mt con tr ti node ng trc n trong khng gian ID,k hiu l Pred(u). Cc node to thnh mt danh sch lin kt hai chiu. Bn cnh , mtnode Chord lu M=log2(N) con tr gi l cc finger. Tp cc finger ca node ID u c xcnh nh sau F(u)={Succ(u+2i-1)}, 1 i M. Vi cch la chn finger th ny, trongmng Chord, cc node quan st khng gian ID ca vng trn bt u t ID ca chng.ng thi vi cch la chn finger ca Chord, khng gian ID s c chia i, na thnht cng c chia i, ri phn t th nht li c chia i Qu trnh tm kim lkt qu t nhin theo cch chia khng gian ID da trn vic tm ID successor. Trong iukin thng thng, phc tp ca thut ton l O(log2(N)).

-CAN: CAN c mt hiu nng nh tuyn O(d.Nd ) v trng thi nh tuyn trong bin2.d. CAN chn cc key ca n t mt khng gian d chiu. Mi node c gn vi mtmin lp phng ca khng gian key ny, v cc ln cn ca n l nhng node s hu cckhi lp phng k cn. nh tuyn bao gm chuyn ti ln cn gn key hn. CAN ctnh cht v hiu nng khc cc thut ton khc, cc node c O(d) ln cn v chiu di

ng dn l O ( dn d) hops. Tuy nhin, khi d = log n, CAN c O(log n) ln cn v chiu ding dn O(log n), ging vi cc thut ton khc.

Mt s nhn xt v nh tuyn trong mng ngang hng c cu trc

Mng c cu trc, thng gi l cc mng P2P th h mi, thng s dng m hnh nhtuyn da trn bng bm phn tn DHT lm gim chi ph nh tuyn v cung cp mtgii hn cho sbc nhy c yu cu trong vic tm kim mt mc d liu. Cc h thngnh vy c cc u im nh: tnh phn tn, kh nng m rng, tnh sn sng, khong cchnh tuyn ngn, sc chu ng li. nh tuyn DHT da trn khi nim nh tuyn trn cs tin t, ban u c gii thiu bi Plaxton h tr s tham gia/ ri b ng ca ccpeer v cung cp cc c ch khi phc khi gp li. Ni cch khc, cc mng P2P c cutrc c ngha l t p mng P2P c iu khin cht ch v cc cc i tng d liu ct ti cc v tr c th sao cho t c hiu nng truy vn tt hn. V d cho cc mngnh vy l Plaxton, Pastry, Tapestry, Chord v CAN, ang trin khai cc thut ton nh

tuyn DHT khc nhau [5]. Cc c tnh l thuyt th c s dng xc nh v cithin hiu nng ca cc h thng nh vy. Thng thng, cc th nh th thng cng knh (logn ) v(logn ) mc ti mi node, n l s peers trong h thng.

Mt vn quan trng ca cc h thng c cu trc lin quan n tnh n nh (churn) nnh hng nghim trng n hiu nng mng. Cc nhc im khc l mo u cao, thiuh tr cho truy tm keyword v cc truy vn phc tp. Tuy nhin, cc n lc gn y hngn vic pht trin ca mt nn tng thng nht cho cc h thng DHT khc nhau, llm cho cc mng c cu trc ngy cng hp dn hn. Mt nn tng nh vy c mongi l s cung cp mt API trn c s KBR (nh tuyn trn c s Key), kt hp vi mt


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m hnh dch v DHT c bn trin khai cc ng dng DHT mt cch d dng.

Mt vn quan trng khc l cc k thut nh tuyn tm kim s dng trong cc hthng P2P v cc cch ti u chng. Mt k thut nh tuyn m bo tnh hiu qu v QOSt u vo ngi dng. Thch thc t ra l vic pht trin cc m hnh nh tuyn ti umi cho cc mng ln t vi nghn n vi chc nghn server v hng triu khch hng.

Tiu chun c bn cho vic pht trin cc thut ton nh tuyn DHT hiu qu l cung cp

tradeoff tt nht vi mt tp cc tham s nh: hiu qu nh tuyn, n hi vi node li,nh tuyn cc im nng v hiu nng trn c s th. Cc tham s khc nh tiu tn tinguyn t nht cngquan trng khng km, c bit l trong trng hp cc mng Ad-hocdi ng.

Mt s hng nghin cu v ci thin hiu nng nh tuyn ca h thng P2P c cutrc

nh gi hiu nng ca cc ca cc chin lc nh tuyn trong mng ngang hng P2P ccu trc (P2P-DHT) nhm to c s cho vic a ra cc gii php ci tin hiu nng cachng ng thi gip la chn, s dng cc thut ton hiu qu hn. Mt s hng nghin

cu ca cng ng P2P ang n lc ci thin hiu nng tm kim ca h thng P2P- DHT:- iu chnh cu trc chng ph cnh tranh vi cu trc Internet tng di sao chocc ln cn chng ph l gn v mt vt l do s gim thiu hao ph mi chng.

- Mt phng php khc tng hiu nng tm kim ca h thng DHT l gim s bcnhy n ch hn l gim hao ph cho mi bc nhy. iu ny c thc hin bngcch tng mc kt nica mi peers. Phng php ny gim ng knh mng nhngli yu cu kch thc cc bng nh tuyn ln hn, s l thch thc khi mi trngkhng n nh nh l P2P.

- Cc xut khc kt hp u im ca c hai phng php trn cng c a ra, cho php ccpeers la chn ln cn v ni dung mt cch thng minh v linh ng. Trong

trng hp ny, s ti u chng ph dn n mt cu trc mng khng u, c ngha lcc node khc nhau c th qun l cc phn khng bng nhau ca khng gian bm, c thkt ni vi mt s lng node khc nhau, v cc kt ni c th ch n cc node mt cchngu nhin, khng theo mt quy tc nht nh no c. Ngay c khi khng c s ti umng, th s khng u cng c th xy ra do cc sp xp khng on trc c ca ccnode tham gia v ri b mng.


22/23

Kt lun

Khong mi nm tr li y, th gii chng kin s bng n ca Internet bng thngrng, cng vi n l s pht trin mnh m ca cc ng dng peer-to-peer. Vi nhiu uim ha hn nh tnh hiu qu, linh hot v kh nng m rng cao, cc mng peer-to-peer v ang thu ht c nhiu s quan tm t cng ng nghin cu. Mng peer-to-peer

pht trin qua nhiu th h, th h hin nay l mng c cu trc da trn kh nng lu trv tm kim d liu hiu qu theo c ch Bng bm phn tn (DHT). Vn ct li ca P2Pl cc thut ton nh tuyn, n ng vai tr quyt nh hiu qu hot ng khi thit lp ccdch v h thng nn tng ca mng ngang hng ni ring v mng o trn Internet nichung.


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Ti liu tham kho

[1] Phan Anh & Nguyn nh Ngha HCN - HQGHN, Cc vn hin i trong Cngngh Thng tin:Peer-to-Peer Networks

[2] ThS. V Th Thy H, TS. L Nht Thng, nh tuyn trong mng nganghng th h mi, Cng ty Vin thng Quc t VTI ti tr[3] Z. H. TAN, W. CHENG, G. R. CHANG, X. X. GAO, and H. WANG, A Structured

P2P Overlay Routing Protocol Based on Distributed Selection Algorithm, Journal ofComputer Science, China.Vol. 35, No 4B, pp. 96-98, April 2008.[4] WAN FARIZA BINTI, WAN ABDUL RAHMAN, FARHAT ANWAR,Performance Evaluation on Peer-to-peer (P2P) Distributed Hash Table (DHT) Protocols,Proceedings of the International Conference on Electrical Engineering and Informatics,Bandung, Indonesia, June 17-19,2007.[5]. K. LUA, J. C. MARCELO PIAS, R. SHARMA and S. LIM, A Survey and Comparisonof Peer-to-Peer Overlay Network Schemes, IEEE Communications Survey and Tutorial,Vol. 7, No 2,2005.[6] J. LI, J. STRIBLING, T. M. GIL, R. MORRIS, and M. F. KAASHOEK, Comparingthe Performance of Distributed Hash Tables Under Churn, in 3rd International

Workshop onPeer-to-Peer Systems (IPTPS 04), (San Diego, CA, USA), February 2004.[7]ALEXANDRU POPESCU, DAVID ERMAN, MARKUS FIEDLER and DEMETRESKOUVATSOS, Routing in Content Addressable Networks Algorithms and Performance,20th ITC Specialist Seminar, 18-20. May 2009, Hoi An, Vietnam.

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