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Tm tt--Ngy nay, cng vi s pht trin mnh m vrng khp ca dch v a phng tin i hi bng thng vcht lng dch v cao, cp quang ang c s dng ngycng rng ri nht l trong mng trc th. c nhiutc gi nghin cu a ra nhng gii php nhm thit ktopology mng cp quang m bo yu cu lu lng vichi ph ti thiu. Bi bo ny xut mt gii php thit ktopology vt lcho mng quang trc thvi mc tiu (i)m bo yu cu lu lng gia cc nt mng, (ii) ti thiuha chi ph, bn cnh (iii) mng cn c kh nng chu li.

T kha-- nh tuyn v gn bc sng, kh nng chuli, mng ton quang, thit k topology vt l.

1.GIITHIU

Mng cp quang Wavelength Division Multiplexing (WDM)c th cung cp bng thng rt ln. Tuy nhin, chi ph trinkhai mt mng ton quang ln hn nhiu so vi trin khai mtmng cp ng. Hn na, thit k mng cp quang cn yu cuphi gii quyt bi ton nh tuyn v gn bc sng cho ccyu cu lu lng gia cc nt mng, y l mt bi ton khngn gin.

Mng quang WDM s dng cc bc sng ti cc yu cukt ni gia cc nt mng. Mt yu cu s dng mt bc sngdc theo ng i t u n cui, v ng i ny c gi llightpath.

Vn thit k topology vt l mng quang trc th: mtmng quang thng c thit k tha mn mt ma trnthng lng cc yu cu cho trc. Ma trn ny m t bngthng yu cu gia cc cp nt mng. Mng c cho l thamn ma trn thng lng nu mi yu cu u c nh tuynthnh cc lightpath tha mn cc iu kin l:

iu kin tnh lin tc bc sng: mt lightpath phi sdng chung mt bc sng trn ttc cc link dc theong i ca n t ngun n ch.

iu kin tnh ring bit v bc sng: tt c cclightpath s dng cng mt link (fiber) phi c gn

cc bc sng ring bit.Bi ton thit k topology vt l mng cp quang trc th

c pht biu nh sau:u vo:

Nguyn Vit Hnh, sinh vin lp Truyn thng v mng my tnh, kha 52,Vin Cng ngh thng tin v Truyn thng, trng i hc Bch Khoa H Ni(in thoi: 0943899968, e-mail: hanhicthut@gmail.com).

VinCng ngh thng tin v Truyn thng, trng ihc Bch Khoa H Ni.

Cho trc cc nt mng vi ta ca chng.Cho trc ma trn yu cu v lu lng gia cc cp nt

trong mng di dng: ngun, ch, bng thng yu cu.S bc sng trn mi lin kt trc tip gia hai nt

mng l c nh.Mc tiu:Kt ni cc nt mng thnh mt topology vt l p ng

c yu cu v lu lng gia cc cp nt trong ma trnyu cu.

Ch ph ng i cp l nh nht.Mng c kh nng chu li.

c nhiu nghin cu a ra gii php thit ktopology vtl mng nh: Link Deficit Algorithm [1], Cut SaturationAlgorithm [2] nhng nhng gii thut ny mi gii quytbiton thit k mng khng ton quang (tc l mng cp nghoc mng cp ng kt hp cp quang vi cc thit b chuyni quang in). Mt snghin cu a ra gii php thit kmng cp quang nh Two-Stage Cut Saturation Algorithm vBenchmark Algorithm [3]. Tuy nhin, nhng gii php ny migii quyt bi ton vi mc tiu ti thiu ha chi ph v m bokh nng p ng ca mng khi mng hot ng n nh mchaquan tm ti kh nng sng st ca mng khi c li xy ra.

Trong bi bo ny, ti xut mt gii php thit k topologyvt lcho mng ton quang vi mc tiu p ng ma trn yu

cuvi chi ph ti thiuv ng i cpv c kh nng sng stkhi mng gp li.

Phn cn li ca bi bo c t chc nh sau. Phn 2 giithiu gii php thit k mng c a ra trc y thutton Benchmark [3]. Gii php xut c a ra phn 3.Phn 4 cung cp mt s kt qu th nghim, chng minh giithut xut l tt hn gii thut c. Kt lun c a ratrong phn 5.

2.GIITHUTBENCHMARK.

Gii thut Benchmarkthc hin thit k topology vt l chomng ton quang. Gii thut thc hin a dn cc link vo

topology mng cho n khi mng c th p ng tt c cclighpath trong ma trn yu cu (ma trn thng lng). tng ca gii thut nh sau. Bi v mng c Nnt nn c thc N(N-1)/2 link trc tip. Cc link ny c k hiu l

2121 ,,, NNlll . Sp xp cc link vi chi ph theo th t tng

dn.i. R rng s link yu cu nh nht l 0 v ln nht l

N(N-1)/2, gi s link yu cu nh nht l LB, s link yucu ln nht l UB thLB=0 v UB=N(N-1)/2.

ii. Tnh mid = 2UBLB .

Thit k topology vt l mng cp quang trc thc kh nng chu li

Nguyn Vit Hnh

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iii. Vi cc link t l1 n lmid thc hin phng php nhtuyn v gn bc sng (Routing and Wavelengthassignment) xc nh liu rng mng ny c th cungcp ttc cc lightpath c th trong ma trn yu cu, nu cth th UB = mid, ngc li LB = mid.

Nu UBLB > 1 th tr li bc iii)ngc li chi ph camng bng tng chi ph ca l1, l2,, lUBv dng li.

Bi ton nh tuyn v gn bc sng c chia thnh hai bi

ton con l bi ton nh tuyn v bi ton gn bc sng.nhtuyn l tm ng i t nt ngun ti nt ch cho mi yu cutrong ma trn thng lng. Gn bc sng l tm bc sng cnri ging nhau trn tt c cc link m ng nh tuyn i qua,ngnh tuyn tr thnh lightpath, bc sng tm c sc dng ti yu cu trn lightpath.

nhtuyn theo ng i ngn nht (Shortest path) s dngthut ton Dijkstra. Trong trng hp khng tm c ng it nt ngun ti nt ch (v topology hin ti khng lin thng)th Benchmark thc hin thm vo topology hin ti nhng linkmi v thchin nh tuyn li trn topology mi ny.Khi tt ccc yu cu c nh tuyn, cc ng ingn nht gia

mi cp nt c lu li, v sau s c gn bc sng.Sau khi thc hin xong bi ton nh tuyn cho cc yu cu,Benchmark gii quyt bi ton gn bc sng cho cc path c nh tuyn s dng chin lc First-Fit.

Chin lc First-Fit stm v gn nhng bc sng theo mttrnh tcnh. Tt ccc bc sng c nh stthp ncao v cc bc sng c chn gn cng theo chstthpn cao, tc l bc sng u tin c chn l bc sng cchsnhnht trong sbc sng ri v gn cho yu cu. Vimi yu cu, First-Fit thc hin kim tra xem trn tt c cclinkm yu cu c nh tuyn qua cn nhng bc sng noging nhau v cha c gn, bc sng chung cn ri c ch snh nht s c chn gn.Nu First-Fit khng th gn bcsng cho mt lightpath bt k no th Benchmark s thchin thm vo topology hin ti nhng link mi v thc hinnh tuyn v gn bc sng li cho cc yu cu trong ma trnthng lng.

Nu tt c cc yu cu u c nh tuyn v gn bc sngthnh cng th topology hin ti l topology cn thit k, giithut kt thc.

Gii thut Benchmark bt u bng cch khi to mttopology vi khong mt na s link gia cc nt mng, iuny dn ti chi ph ng i cp ca topology khi to l ln.Hn na, gii thut Benchmark cha t ra mc tiu thit ktopology mng c kh nng chu li.

3.GIITHUTXUT.

Gii thut xutmc tiu thit k topology vt l mngquang trc th p ng c yu cu v lu lng gia ccnt mng, c kh nng chu li v ti thiu ha chi phng icp. Gii thut xut cgi l gii thut Survival. tngca giithut c m t trong Hnh 1.

Chi tit v gii thut Survival nh sau: Bc 1:

Khi to topology: ni cc nt to thnh vng khpkn c chu vi nh nht theo cc bc nh sau:

oBt u t mt nt bt k, loi b nt ny ra khitp nt, tm nt gn n nht trong nhng nt cnli ca tp nt, kt np nt ny v cnh ni hai nt vo vng v ntny c loi khi tp nt.

oT nt mi kt np, ta li tm nt gn n nht, ktnp nt ny v cnh ni hai nt vo vng v loib nt mi c kt np vo vng khi tp nt.Qu trnh tip tc n khi tt c cc nt ca vo vng.

oThm link gia ntbt u v nt cui cng cxt trong tp nt, ta c mt ring i qua tt c ccnt trong tp nt cho.

Hnh 1. Lu thut ton Survival

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Topology dng vngc chn bi v n l cu trc dng 2 connected n gin nht, c kh nng cung cp c ch backupkhi mng gp li.

Bc 2:Thc hin nh tuyn v gn bc sng cho cc yu cutrong ma trn thng lngtrn topology va to:

nh tuyn: tm hai ng i ngn nht v khng ctnhau (ta gi hai ng ny l shortest path v alternateshortest path) cho mi cp ngun-ch (source-destination) trong ma trn yu cu. i vi mi cpngun ch, ng shortest path l ng i ngn nhtc tm bng gii thut Dijkstra. Sau , tm ngalternative shortest path ta loi b mi link ca ngshortest path ra khi topology v thc hin Dijkstra lnna.

Gn bc sng: Ti s dng chin lc First Fit gn bc sng cho cc lightpath c nh tuyn.Lightpath c di ln s c u tin gn bc sng

trc.

Vi mi lightpath: thc hin gn bc sng trn shortest pathtrc, xy ra ba trng hp 1) gn bc sng thnh cng; 2) trncc link m shortest path i qua cn cc bc sng ri nhngkhng tm c bc sng ri ging nhau; 3) trn cc link mshortest path i qua tm c bc sng ri ging nhau nhngs bc sng tm c nh hn bng thng yu cu.Vi trnghp 2) v 3)th kim tra xem topology hin ti l th y haycha, nu cha th thm mt link c chi ph ng i cpnh nht vo topology v thc hin nh tuyn v gn bc sngli, thc hin cng vic ny cho n khi shortest path c gn

bc sng thnh cng. Nu gn bc sng trn shostest paththnh cng th tip tc gn bc sng trn alternate shortest paththeo cch tng t vi shortest path. Nu khng tha mn thtng t nh trn ta lithm mt link c chi ph nh nht trongs nhng link cn li gia cc nt (khi topology cha l thy ) v thc hin nh tuyn v gn bc sng li trntopology mi ny. Lm tng t cho tt c cc lightpath trongma trn yu cu. Gii thut dng li khi png c tt c ccyu cu trong ma trn yucu hoc khi topology tr thnh thy .

4. KT QUTH NGHIMV THO LUN

Gii thut Benchmark v gii thut Survival c ci tv th nghimvi u vo ging nhau.Cc tp d liu csinh theo nguyn tcnh sau:

N nt c sinh vi ta ngu nhin trong khong[0;800],

S yu cu (S phn t ca ma trn yu cu) c nhpvo nm trong khong N n N(N-1)/2.

Bng thngyu cugia cc cp nt trong ma trn yucu l mt gi tr nguyn c sinh ngu nhin nm trongkhong [1;5].

S bc sng trn mi link l ging nhau.

Kt qu thc nghim trong Hnh 2 v Hnh 3 cho thy rng,gii thut Benchmark chy tt trong trng hp mng c t nt.Khi s nt tng ln th Benchmark cho kt qu l mt mng vichi ph ngy cng tng. C hai gii thut Benchmark v Survivalu ph thuc rt nhiu vo ma trn yu cu. Tuy nhin, t haihnh trn c th thy rng, vi mt tp nt, khi s yu cu trongma trn yu cu tng ln th gii thut Benchmark cho kt qukhng i, tc l mng c d tha cao. Trong khi , gii

thut Survival li cho kt qu l cc mng vi chi ph thay ikhi s yu cu trong ma trn yu cu l thay i. Vi mi mtma trn yu cu, gii thut Survival tnh ton a ra mttopology c kh nng p ng c cc yu cu v c kh nngchu li vi d tha thp.

Hnh 2. di ng i cp ca mng c thit k bi haigii thut trong trng hp mi link c 64 bc sng

Hnh 3. di ng i cp ca mng c thit k bihai gii thut trong trng hp mi link c 128 bc sng

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Nguyn nhn ca s khc bit ny l: gii thut Benchmarkngay tu thm khong mt na s link c th c trongmng. V th, khi s nt trong mng tng ln th ngay khi bt ugii thut Benchmark khi to mt topology mng kh dyc vi chi ph rt ln. Topology ny bn thn n c th png c mt ma trn lu lng ln hn ma trn u vo nhiuln.

Ngc li, khi bt u, gii thut Survival thc hin kt nicc nt mng li thnh mt vng. Vi topology khi to nhvy, th khi s nt mng tng ln th chi ph khi to topologycng tng ln khng nhiu. Hn na, topology vng m borng s lun tm c hai ng i khng giao nhau cho mi cpngun ch trong ma trn yu cu, y l iu kin cn quantrng mng c khnng sng st khi gp li.Vi topologydng vngva khi to ny, gii thut Survival thc hin nhtuyn v gn bc sng cho mi cp ngun ch trong ma trnyu cu.Nu qu trnh nh tuyn v gn bc sng kt thckhng thnh cng th Survival ch thm dn tng link votopology (ch khng phi mt na s link nh Benchmark)vli th nh tuyn v gn bc sng li ln na. Vic thm link

vo ring topology s chia nh ring ny ra thnh cc ring nhhn, khi nh tuyn v gn bc sng li th mt s yu cu sc nh tuyn qua cc path mi v vic gn bc sng c ths c thc hin, Survival s dng li khi m c va s link.

Trong cc th nghim trn c th thy rng, ty theo mi matrn yu cu m gii thut Survival cho ra cc mng vi chi phkhc nhau, trong khi Benchmark cho ra cng mt kt qu vicc ma trn yu cu khc nhau. iu ny chng t rng, giithut Survival a ra gii php thit k mng p ng yu cuvi d tha t, cn Benchmark lun thit k mt mng vi d tha l ln. Nhng phi chng trong mi trng hp,Benchmark u cho ra mt topology ging nhau cho cc ma trnyu cu khc nhau? Hai gii thut c th nghim trongtrng hp s nt mng l 20 nt, cc ma trn yu cu ln ltc s yu cu l 20, 60, 100, 140 v 180 yu cu, nhng vi sbc sng trn link khc nhau trong mi ln th nghim vi cctp d liu trn. Kt qu thu c c th hin trong Hnh 4.

Hnh 4 cho thy, khng phi trong mi trng hpBenchmark u cho ra mt topology ging nhau cho cc ma trnthng lngkhc nhau. Gii thch iu ny l, trong hnh 2 sbc sng trn mi link l64 bc sng, nn Benchmarkc thnh tuyn v gn bc sng cho tt c cc yu cu trong ma trnthng lngtrn topology khi to; trong khi Hnh 4, s bcsng trn mi link khng Benchmark thc hin nh tuynv gn bc sng cho tt c cc yu cutrn topology khi to

nn n thc hin thm vo topology nhng link mi nhtuyn v gn bc sng li.

Trong Hnh 4, chi ph mng kt qu ca gii thut Survivaltrong mt s trng hp l cao hn so vi mng kt qu ca giithut Benchmark, thm ch c trng hp gii thut Benchmarkc th cho kt qu cn Survival th khng (trng hp mng l th y ). C iu ny l v, gii thut Survival thc hinnh tuyn v gn bc sng trn hai ng cho mi yu cutrong ma trn thng lng ( mng c kh nng chu li), trongkhi vi mi yu cu, Benchmark ch thc hin tm v gn bcsng trn mt ng. D dng thy rng, gii thut Survival cmng kt qu tt hnkhi tng s bc sng trn mi link ln,

trong khi Benhmark cho kt qu gn nh khng i, khi s bcsng trn link tng n mt ngng nht nh th gii thutSurvival cho kt qu tt hn so vi Benchmark. y cng l mtu im ca gii thut Survival so vi Benchmark.

5. KT LUN

Bi bo ny xut gii php thit k topology vt lcho mng ton quang, ci t v thc nghim vi nhiu tpdliu. T c s lthuyt, kt qu thc nghimgii thutv c so snh vi gii thut Benchmark, c th kt lun rng: (i)giiphp xutl kh thi, c th p dng cho nhiu m hnhmng khc nhau; (ii) gii thut Survival c th thit k hiu qu

cho mng ton quang vi chi ph thp; (iii) thm vo Survivalcho php thit k topology vt l mng ton quang c kh nngsng st khi gp li.

6. LI TRI N

Ti xin chn thnh cm n TS. Trng Th Diu Linh tntnh hng dn, ch bo v cho ti nhng gp qubu tithc hin ti mt cch tt nht.

7. TI LIU THAM KHO

[1] Kamalesh V.N, S K Srivatsa, Topological Design ofMinimum Cost Survivable Computer Communication

Networks: Bipartite Graph Method, (IJCSIS) InternationalJournal of Computer Science and Information Security,

Vol. 3, No. 1, 2009.

[2] Kris T. Newport, Pramod K. Varshney, Design ofSurvivable Communications Networks under Performance

Constraints, IEEE TRANSACTIONS ON

RELIABILITY, VOL. 40, NO. 4, 1991 OCTOBER.

[3] Gaoxi Xiao, Yiu-Wing Leung, Kwok-Wah Hung,Two-Stage Cut Saturation Algorithm for Designing

All-Optical Networks, IEEE TRANSACTIONS ON

COMMUNICATIONS, VOL. 49, NO. 6, JUNE 2001.

Hnh 4. di ng i cpca Benchmark v Survivalkhi thay i s bc sng trn mi link

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[4] Rajiv Ramaswami, Kumar N. Sivarajan, Galen H. Sasaki,Optical Networks - A Practical Perspective, 3rd Edition,

2010.

[5] Huan Liu, Fouad A. Tobagi, Physical topo design forall-optical networks.

[6] Tony Kenyon, High-performance data network design,2002.

[7] Debasis Mandal, Satyajit Nath, Bivas Mitra, SurvivableRouting in WDM Weighted Networks, In Proceedings ofthe 2ndIEEE International conference on COMmunication

System softWAre and MiddlewaRE (COMSWARE

2007), Bangalore, India, 7-12 January 2007.

[8] Amit Wason, R.S. Kaler, Survivable routing andwavelength assignment algorithm for multiple link failures

in wavelength-routed all-optical WDM networks, 10 June

2010.

[9] Rajneesh Randhawa, J.S. Sohal, Static and dynamicrouting and wavelength assignment algorithms for future

transport networks, 20 November 2008.

[10] Imrich Chlamtac, Aura Ganz, Gadi Karmi, LightpathCommunications: An Approach to High BandwidthOptical WANs, IEEE TRANSACTIONS ONCOMMUNICATIONS, VOL. 40, NO. 7, JULY 1992.