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Hidn nay, eie img dung ludng phuong tidn ngang hing-P2P dang phit tridn nhanh chdng (P2P-TV,

video streaming,...). Trong eie iing dung niy, bii toin lap lich ddng vai trd quan trong trong vide tim kiem ludng. Bii viet sau dayse 00 thidu tdng quan

ve de thuit toin lap lich duge sU dung trong cic hd thdng truyen hinh ngang hing P2P-TV nhu lip lich chunk, lip lich eie nut ngang hing, lap lich chunk trudc vi lip lich eie nut ngang hing trudc.

1. GIOI THIEU

Xu hudng ehuydn ddi cac may tinh PC thanh cae thiet bi ddu cudi da nang eung cdp ede djch vvi nhu thogi, kdt ndi mgng xa hdi, choi game, thuong mgi didn tu da trd thanh hidn thuc va kha phd bidn hidn nay. Didu nay cho thdy dich vu truydn ddn truydn hinh true tuydn qua Intemet hidn nay Id mdt trong nhftng dich vu hdp ddn vd trong thue td cftng da cd rat nhidu hd thdng duge tridn khai nhu: PPLive, PPStream, SOPeast, TVAnts,... vdi hang nghin, thdm ehi hang tram nghin ngudi truy nhap cimg mdt luc.

TS. Le Nh^t Thdng, Th.S NguySn Thu Hien

Dd dap img duge ydu edu vd kha nang md rdng Cling nhu vdn dd kidm sodt tdi nguydn vd cac co chd eua Intemet, hdu hdt nhung hd thdng phdn phdi tmydn hinh nay ddu dua trdn co chd ngang hang

|P2P) (ede hd thdng P2P-TV). Vdi co chd nay. ngudi su dung (eae nut ngang hang - peer) cua hd thdng se ddng gdp vao vide phan phdi video qua vide gui di nhftng ndi dung ma hg ed tdi eae cac mit ngang hang khac. Dd lam dugc didu nay, cac mit ngang hang phdi lidn kdt vdi nhau tgo thdnh mdt mgng xdp chdng. Khi hai cae mit ngang hdng cd thd trao ddi thdng tin vdi nhau, chimg se Id cdc nut hdng xdm cua nhau (neighbor). Ddi vdi cdc hd thdng td chue theo sd ddng, se cd mdt niit dac bidt gpi la niit ngudn (source) thuc hidn vide chia ludng video thanh cac dogn dft Udu nhd (chunk) phdn phdi ridng bidt va ddc ldp trdn mgng xdp chdng. Vd ca ban, mdi chunk dugc gui tdi cdc ede nut ngang hdng theo edu tnic hinh cdy.

Myc tidu thidt kd ehinh eua cdc hd thdng P2P-TV qudng bd true tuydn Id: gui tdt ea ede chunk tdi tat ca cae ede nut ngang hdng (dam bao dugc chdt lugng)

4 4 I TAP CHI CNTT&TT KY 1 (4.2012)

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CONG NGHE VIEN THONG

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vd trd phdn phat cang nhd cang tdt. Trong thue td, vide thidt kd hd thdng P2P-TV edn phai giai quydt hai vdn dd sau: 1) lua chpn edu tnic mgng xdp chdng;

2) cdch thue phdn phdi eae chunk gifta cac eae nut ngang hang hang

xdm. Trong bai bao nay se chii ydu ban vd vdn dd thu hai trdn mgng xdp chdng khdng edu tnic (kidu ludi). Vdi hd thdng P2P-TV kidu ludi, nguydn tde xay dung mgng rdt don gidn nhu sau: Khi gia nhap hd thdng, mdt cae nut ngang hang A bdt ky se lidn lgc vdi mit quan ly tnmg tdm (ngudn thdng tin video) de ydu edu mdt danh sdch ede nut hang xdm (la ban danh sach vd eae cac nut ngang hang ma cac nut ngang hang A se gui hoac nhan chunk).

Thugt toan lap lich eae nut ngang hang/chunk (lua chpn eae nut ngang hang va chunk) duge su dung de trayen dan chunk 0fta hai cae nut ngang hdng bdt ky se quydt dinh den hieu ndng eua eae hd thdng P2P-TV kieu ludi nay. Nhftng thuat toan nay thdng thudng duge phan thanh hai logi: day (push) hoac keo (pull) tuy theo vide nut gui hay nut nhgn thue hidn vide lua chpn. Cae co chd day thich hpp hon ddi vdi cdc he thdng rang budc ve bang thdng tai len (cae eae nut ngang hang duge kdt ndi qua ADSL hoac cap), do dd vide phdn phdi chunk se duge didu chinh bdi nut giii. Ngugc lgi, cac ca chd keo thich hgp hon ddi vdi eae he thdng rang bude vd bang thdng tai xudng, vi vdy tde dd eua cae ydu edu chunk se thich nghi vtii kha nang tai xudng cua mdi eae nut ngang hang.

Bdt cu khi nao mdt cae nut ngang hdng bat ky mudn gm mdt chunk, nd se phai thuc hidn vide lua chpn cdc nut ngang hdng ilieh trong tap cac cae

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nut ngang hang hang xdm cua nd. Vol bd lap lich chunk X hoac cac mit ngang hang Y cho tmde, ed thd ed bd lap lich chunk tmde (bd lap lich X/Y) hoac bd lap lich cac nut ngang hdng tmde (bd lap lich Y/X). Vdi bd lap lich chunk tmde, thuat toan lap lich se chpn C trudc, sau dd chpn eae nut ngang hang dich i ^ yeu cau chunk C nay. Tuong tu nhu vgy vdi bd lap lich eae nut ngang hang tmde. Sau day, se la nhftng ndi dung dd cdp chi tidt ve cae thugt toan nay.

2. CAC THUAT TOAN LAP LICH TRONG HE THONG P2P-TV

2.1 Cac thuat toan lap ljch chunl(

Lap lich RUc (Random Useful)

Cae mit ngang hang P. lua chpn ngau nhien mpt chunk CjeC(P.,t) (trong dd C{P„t) la tap cac chunk ma cac nut ngang hang P. cd tgi thdi diem f) dugc yeu cau bdi mdt sd ede nut ngang hang trong tap cae eae nut ngang hang hang xdm cua nd.

Hinh 1 the hidn thogt ddng eua thugt toan RUe.

cae nut ngang hang 1 ed cac cae nut ngang hang hang xdm la cac cac nut ngang hang 2, cae nut ngang hang 3, cac nut ngang hang 4, cac nut ngang hang 5. Cac nut ngang hang 1 ed cac chunk 1, 2,3, 5, 6 trong bd ddm cua minh. Cdc nut ngang hang 2 gui ydu cdu ede chunk 1, 2, 3; cdc nut ngang hang 3 gui yeu edu ede chunk 3,5; cac nut ngang hang 4 gui ydu edu chunk 5; vd cae nut ngang hang 5 gui ydu edu eae chunk 1,3. Liic nay, cdc nut ngang hang 1 lua chpn bat ki mdt trong cdc chunk dupe yeu edu (eae chunk 1, 2, 3, 5) de gui di.

TAP CHI CNTT&TT KY 1 (4.2012) 4 5

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Hinh 2: L4ip Hch LUc

Ldp Uch LUe (Latest Useful)

cae nut ngang hang P^ lua chpn chunk ed ehi sd cao nhdt trong tdp ede chunk ydu cdu C^ e C ( /), /) dugc ydu edu bdi mdt sd ede mit ngang hdng trong tdp ede ede nut ngang hdng hdng xdm eiia nd.

Hinh 2 la vi du minh hpa thudt todn ldp lich LUe, trong dd ede nut ngang hang 2 thidu ede chunk 2, 3; ede nut ngang hdng 3 thidu chunk 5, ede nut ngang hdng 4 thidu chunk 3. Cae nut ngang hdng gui yeu cdu tdi cdc nut ngang hdng 1, luc ndy cae nut ngang hdng 1 se lua chpn chunk 5 dd gui, do chunk 5 la chunk ed chi sd cao nhat trong tap eae chunk yeu edu.

Lip lich DLc (Deadline-based scheduler): Cdc nut ngang hdng P. lua chpn chunk C. 6 C (/).,/) ed thdi hgn lap lich ngdn nhdt duge ydu cdu bdi mdt sd ede nut ngang hdng trong tdp ede ede nut ngang hdng hdng xdm eiia nd. Cdc thdi hgn ldp lich duge

gdn eho cdc chunk khdc nhau trong hd thdng, vd mdi thdi hgn ldp Uch duge tri hodn mdt lugng thdi gian nhdt djnh khi gui mdt chunk.

2.2 Cdc thu$t todn l|p ljch cdc nut ngang hdng

L$p Uch RUp (Random Useful de nut ngang hing)

Cdc nut ngang hang P. lua chgn ngdu nhidn mdt cae nut ngang hang P. trong tap eae eae mit ngang hang hang xdm cua nd cdn chunk da chpn.

Vi du trong Hinh 3 eho thdy, Cdc mit ngang hdng 1 cd cdc nut ngang hdng hdng xdm Id cdc cdc nut ngang hdng 2, 3, 4, 5 ed cdc ydu cdu chunk gui tdi ede nut ngang hdng 1. Cdc nut ngang hdng 1 se lua chpn ngdu nhidn mdt cae mit ngang hdng bdt ky (cdc nut ngang hdng 5). vd gui cho cdc mit ngang hdng dd chunk dugc ydu cdu (chunk 3).

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Hinh 4: L ^ ljch MDp

Lip lich MDp (Most deprived eie nut ngang hang)

Cdc nut ngang hdng P. lua chpn cdc nut ngang hang Pj trong tdp ede cdc nut ngang hdng hdng xdm eua nd ed sd chunk nhd nhdt gidng vdi sd chunk md cae mit ngang hdng P^ ed tgi thdi didm dd .

Hinh 4 thd hidn hogt ddng eua ldp Ueh MDp.

Trong dd. cac nut ngang hang 1 sd hftu cac chunk 1. 2, 3. 5. 6. cae niit ngang hang 2 ehi sd hiru ed 2 chunk trimg vdi cac nut ngang hang 1 la chunk 5. 6; cac nut ngang hang 3 la 3 chunk (chunk 1, 2, 6); eae nut ngang hang 4 la 4 chunk (chunk 1, 2.3.

6). Luc nay cac nut ngang hang 1 se lua chpn cac nut ngang hang 2 do sd^lugng ehimk gidng nhau la nhd nhat.

Lip lich ELp (Earliest-Latest)

cae mit ngang hang P^ lua chpn cae nut ngang hang P^ trong tap eae cac nut ngang hang hang xdm eua nd ed ehi sd chunk ldn nhdt trong tap eae

chunk cua eae niit ngang hang Pj vk chunk nay cd chi sd nhd nhdt trong cdc chunk ma cdc eae nut ngang hang hang xdm hidn ed.

Hinh 5 eho thdy Cae nut ngang hang Pj se lira chpn eae nut ngang hang 1, do cae nut ngang hang 1 ed chi sd chunk Id 33 ldn nhdt trong sd cae chunk ma ede nut ngang hang 1 ed vd la ehi sd nhd nhdt so vdi ehi sd cua ede chunk cd trong cae ede nut ngang hang hang xdm eua cae nut ngang hang Pj.

Lip lich BAwp (Bandwidth Aware): Cdc nut ngang hang P. lua chpn ngau nhien cac nut ngang hang dich PJ trong tap cae eae nut ngang hang hang xdm cua nd (nhu trong RUp); xac suat lua chpn P. ti Id vdi bang thdng dau ra cua P..

2.3 Cac t h u a t toan lap ljch chunk trUdc

- LUc/MDp, LUc/RUp, LUc/Elp, LUc/BAwp

Trong cae thuat toan nay, cac nut ngang hang p. lira chpn chunk ed ehi sd cao nhdt trong tap eae chunk yeu cdu Cj eC(i^.,/) duge ydu cau bdi mdt

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TAP CHI CNTT&TT KY 1 (4.2012) | 4 7

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m CC CONG NGHE VIEN THONG

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Hinh 6: L$p lich

sd ede nut ngang hdng trong tdp ede cdc nut ngang hdng hang xdm ciia nd. Sau dd, cae nut ngang hang /) gui chunk ddn cae nut ngang hang Pj, la cae nut ngang hang ed sd chunk nhd nhdt gidng vdi sd chunk md cdc nut ngang hang P. ed tgi thdi didm dd (LUe/MDp). Cdn ndu ede nut ngang hdng P^ gui chunk den mdt cae nut ngang hang P ngdu nhidn trong tap eae cac nut ngang hang hang xdm eua nd thi ta ed thuat toan LUe/RUp. Hay cae nut ngang hang P. gui chunk den cac nut ngang hang P, ed etii sd chunk ldn nhdt trong tap cac chunk eua nd ddng thdi la chi sd nhd nhdt trong cdc chunk md cdc ede nut ngang hdng hdng xdm hidn ed thi dd Id thuat toan LUc/ELp. Hoac se la thudt toan LUe/

BAwp, ndu ede nut ngang hdng fj gui chunk ddn cae nut ngang hang dich P,. theo ti Id vdi bang

RUc/MDp

LUc/MDp V^LUC/RLP

thdng ddu ra eua Py.

Hinh 6 minh hpa ede thudt todn LUe/MDp vd LUe/

RUp. Ndu su dung thudt todn LUc/RUp, chunk 5 Id chunk duge gui tdi eae nut ngang hang 3. Cdn ndu su dung thudt todn LUe/MDp, chunk 5 dugc gui tdi ede niit ngang hdng 2.

- RUc/RUp, RUc/MDp

Minh hga ede thudt todn ndy duge thd hidn trong Hinh 7, tdp cdc chunk ydu cdu Id chunk 2. 3, 5. Cdc nut ngang hdng P, lira chpn ngdu nhidn mdt chunk (chunk 3) dd gui di. Ndu su dung thudt todn RUc/

RUp, trong ede cdc nut ngang hdng hdng xdm ehi ed ede nut ngang hdng 1 vd cdc niit ngang hdng 4 la cd ydu edu chunk 3, do dd cdc niit ngang hdng eung

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4 8 I TAP CHI CNTT&TT KY 1 (4.2012)

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CONG NGHE V I E N THONG

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cap lua chpn ngdu nhidn mdt cdc nut ngang hdng (ede nut ngang hdng 4) dd gui. Chunk 3 cftng cd thd duge gui ddn cdc nut ngang hdng 1 trong tmdng hgp su dung thudt todn RUc/MDp.

Cac t h u a t t o a n l | p ljch cac nut ngang hang tri/dc

Tuong tu nhu lap Uch chunk tmde, chimg ta cung ed the ed eae thuat toan lap Ueh eae nut ngang hang tixrdc nhu sau: RUp/RUc, RUp/LUe, RUp/DLc; MDp/

RUc, MDp/LUe, MDp/DLe; ELp/RUc, ELp/LUc, ELp/DLp, BAwp/RUe. BAwp/LUe. BAwp/DLc. Cu the mdt sd thugt toan lap Uch cae nut ngang hang tmde nhu sau:

Cic thuat toin ELp/RUc, ELp/LUc

Hinh 8 minh hpa thuat toan lap Uch ELp/RUc, eae mit ngang hang 1 duge lua chgn la eae mit ngang hang dich ed ehi sd chunk ldn nhdt trong tap cac chunk cua eae nut ngang hang 1 la 33 va la chi sd chunk nhd nhdt trong sd ede ede nut ngang hang hdng xdm. Cae chunk 31 hoac 32 se duge gui tdi

tmi

eae niit ngang hang 1 tirdn co sd lua chpn chunk ngdu nhidn.

Tuong tu ddi vdi thudt toan ELp/LUc (Hmh 9), eae nut ngang hang 1 se duge lua chpn va duge gui tdi chunk 32, la chunk ed ehi sd ldn nhdt trong tap eae chunk dugc ydu cdu.

Cic thuit toin lap lich RUp/LUe, MDp/LUe, MDp/

RUc

Cae thugt toan lap Ueh nay duge the hien d Hinh 10. Trong dd, eae nut ngang hang 1 ddng vai trd la eae nut ngang hang gui, cae eae nut ngang hang 2, 3, 4 la cac cac nut ngang hang hang xdm cua eae nut ngang hang 1.

Thugt toan RUp/LUe nhu the hien d Hinh lO.a, cac mit ngang hang 1 gui chunk ed ehi sd ldn nhdt (chunk 6) tdi ede nut ngang hdng 4 dugc lua chpn ngdu nhien. Hinh lO.b la thugt toan MDp/LUe, trong dd eae nut ngang hang 1 lira chpn cae nut ngang hang 2 la cac nut ngang hang dich va gui di chunk

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TAP CHI CNTT&TT KY 1 ( 4 . 2 0 1 2 ) | 4 9

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CONG NGHE V I I N THONG

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Hinh 10: cac thuat toan l$p ljch cac nut ngang hang trubc

3 cd chi sd ldn nhdt tdi ede nut ngang hdng 2. Cdn vdi thudt todn MDp/RUc (Hmh lO.c), cdc nut ngang hang 1 lira chpn ngdu nhidn mdt chunk (chunk 2) de gui tdi ede nut ngang hdng 2.

3. KET LUAN

Bdi bdo da trinh bay tdng quan eae thudt todn lap Ueh trong ede hd thdng P2P-TV kidu ludi nhu lap Ueh chunk, lap lich cac mit ngang hang, lap Ueh chunk tmde, Idp Ueh cae nut ngang hdng tmde.

Qua dd eung eho thdy rdt nhidu hudng nghidn ciru

mdi ddi vdi bdi todn ldp Ueh nhu ddnh 0d hidu ndng hd thdng qua ede thudt todn ldp Uch dd cd hodc dugc phdt tridn thdm, hode ed thd dua ra ede thudt todn ldp Uch eho hd thdng cd xem xdt ddn cdc cdng nghd md hda ludng video mdi, cftng nhu ede thudt todn ldp Ueh trong mdi tmdng vd tuydn, hay bdo mdt ndi dung...

Tdi l i f u t h a m khdo

[1]. ALESSANDRO RUSSO, RENATO LO CIGNO (2009), Push/Pull Protocols for streaming In P2P systems, NAPA-Wine Project, Uliiversity of Trento.

[2]. CSABA KIR/U.Y, RENATO LO OGNO, LUCAABENI(2009), Deadline-basedOifferentiatkx) in P2P streaming. University of Trento.

[31. JONNATHAN S K CHAN, VICTOR 0 K U, KING SAN LU, Perfonvance comparison of scheduling algorithms for Cic nut ngang har^-to- Cac nut ngang hang collaborative file distribution.

[4]. HAIDAR NOAH (2009), Inplementann of a cic nut ngang hing todcnut ngang har^ live streaming appTication, Master's D^ree Project, Stockholm, Sweden.

[5]. LUCA ABENI. CSABA KIRALY, RENATO LO CIGNO (2009), Scheduling P2P Multimedia stream. Can

we achieve performance and robustness? Proc. of the 3-rcl IEEE Intemational Conference on Intemet Multimedia Systems Architecture and Applications (IMSAA-09), Bangalore, India, Dec.

9-11,2009.

[6]. LUCAABENI, ALBERTO MONTRESOR (2007), Scheduling in P2P streaming: from algorithm Protocols, NAPA-WINE Project.

[7]. LUCA ABENI, CSABA KIRALY, RENATO LO CIGNO (2009), Achiving perfonvance and rotxistness in P2P streaming systems. University of Trento, Italy, Tech. Rep. TR-DISI-09-041.

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5 0 I TAP CHI CNTT&TT KY 1 (4.2012)