OBS Official

7/31/2019 OBS Official

1/57

Chuy n m ch Burst quang OBS

1

LI NI U

Hin nay, truy n thng quang ang pht tri n ngy cng m nh m v tng lai s vn ln chi m v tr hng u trong cc cng ngh truy n thng c dy.Tuy v y, hi n nay truy n thng quang v n ch yu c ng d ng cc m ngli, m ng ng tr c l chnh. Hi n nay trong truy n thng quang, c ba phng php chuy n mch ang c ng d ng, l chuy n mch knh quang(Optical circuit switch), chuy n mch gi quang (Optical packet switch) vchuy n mch burst quang (Optical burst switch). Ba phng php ny u ci m mnh v i m yu ring, trong chuy n mch burst quang hi n nay ang c nghin c u nhi u b i v n r t thch h p trin khai trong i u kintruy n thng quang hi n nay, kh c ph c c nhng i m y u ca hai phng

php chuy n mch cn l i. OBS cho php ta t n d ng c t c truy n t inhanh c a mng truy n t i quang m khng chi m d ng nhi u ti nguyn nh chuy n mch knh quang ng th i cng hn ch nh ng vn g p ph i v b m hay chuy n mch g p ph i trong chuy n mch gi quang.

V i nhng u i m k trn c a OBS cng nh xu h ng nghin c u OBS trnth gi i, nhm sinh vin D08VT1 quy t nh ch n ti Nghin c u vchuy n

m ch burst quang OBS th c hin nghin c u trong mn chuyn v

chuy n mch. M c ch ca ti ny l nh m c c ci nhn t ng qut v cng ngh

OBS, v m t s c i m ca n.Tuy nhin th i gian cng nh kh nng c hn,nn chng em ch chn mt s vn v OBS nghin c u. N i dung chuyn gm cc ph n nh sau:

Chng I : Gi i thi u vOBS

Chng II: K thu t v ki n trc OBS

Chng III: S p x p cc gi tin vo burst trong OBS

Chng IV: K thu t bo hi u trong OBS

Chng em xin chn thnh c m n T hs Hong Tr ng Minh tn tnh gip chng ti trong qu trnh h c t p cng nh lm chuyn ny.


2/57


2

Mc Lc

LI NI U ..........................................................................................................

Mc Lc ................................................................................................................... Danh mc hnh v...................................................................................................... T vit tt v thut ng.............................................................................................. 5 ChngI: Gi i thiu ..................................................................................................

1.1. Chuyn mch knh quang................................................................................................ 9

1.2. Chuyn mch gi quang................................................................................................. 10

1.3. Chuyn mch burst quang.............................................................................................. 12

Chng II: Kthut v kin trc .............................................................................15 2.1 Kin trc mng chuyn mch burst quang.......................................................................... 15

2.2 Cng ngh lin quan............................................................................................................ 19

2.2.1 Cng nghchuyn mch quang.................................................................................... 19

2.2.2 Burst mode receiver...................................................................................................... 20

2.2.3 Chuyn i b c sng.................................................................................................. 21

2.3 Vn tng vt l................................................................................................................ 21

2.3.1 Suy hao......................................................................................................................... 22

2.3.2 Tn sc.......................................................................................................................... 22

2.3.3 Hiu ng phi tuyn ....................................................................................................... 23

Ch ng III: Sp xp Burst .......................................................................................2 3.1 Qu trnh la chn nh thi v ng ng ............................................................................. 26

3.2 Tc ng ca nhm burst theo c tnh lu l ng.............................................................. 28

3.3 K thut c l ng nhm burst da trn ng ng............................................................... 29

3.3.1 K thut nhm burst da trn ng ng.......................................................................... 29

3.3.2 Cc kt qum phng.................................................................................................. 31

Chng IV Bo hiu trong OBS ..............................................................................3 4.1 Phn loi cc phng thc bo hiu.................................................................................... 38


3/57


3

4.1.1 Mt chiu, hai chiu hoc lai ghp............................................................................... 38

4.1.2 Ginh tr c ti nguyn kh i to t ngun, kh i to t ch, hoc kh i to t nodetrung gian............................................................................................................................... 40

4.1.3 Kin tr hoc khng kin tr.......................................................................................... 41

4.1.4 Ginh tr c ti nguyn ngay tc th i hoc ginh tr c c tr..................................... 41

4.1.5 Gii phng r rng hoc gii phng khng r rng...................................................... 42

4.1.6 Tp trung hoc phn tn............................................................................................... 42

4.2 K thut Just-Enough-Time (JET)....................................................................................... 43

4.3 K thut Tell-and-Wait (TAW)........................................................................................... 45

4.4 Bo hiu kh i to t node trung gian (INI)......................................................................... 46

4.4.1 K thut bo hiu kh i to t node trung gian (INI)..................................................... 47

4.4.2 K thut bo hiu kh i to t node trung gian phn bit .............................................. 50

4.5 M hnh phn tch tr.......................................................................................................... 51

4.6 Kt qu c th...................................................................................................................... 53

Kt Lu n .................................................................................................................56 Ti li u tham kh o .................................................................................................57


4/57


4

Danh m c hnh v

Hnh 1.1 Cc phng php truyn dn quang .................................................................... 7Hnh 1.2 Kin trc ca mt chuyn mch gi quang ....................................................... 10Hnh 1.3 S dng th i gian chnh lch trong OBS .......................................................... 12Hnh 2.4 Kin trc mng chuyn burst quang .................................................................. 15Hnh 2.5 S chc nng OBS........................................................................................ 16Hnh 2.6 Kin trc router li ........................................................................................... Hnh 2.7 Kin trc router bin .......................................................................................... Hnh 2.8 chuyn mch MEMS ......................................................................................... 1Hnh 2.9 chuyn mch SOA ............................................................................................. 2Hnh 3. 10nh h ng ca ti trng da trnnh th i v da trnng ng trong cccng nghnhm .................................................................................................................Hnh 3.11 Mng NSF v i 12 node (km) ........................................................................... 3Hnh 3.12th DP v SDP vi ngng v khng c u tin burst trong mng ...... 32Hnh 3.13th SDP n ngng v hai u tin burst trong mng. T lmt gi trnti v i nhng gi tr ng ng khc nhau ............................................................................. 3Hnh 3.14 th SDP v i mt ngng v hai u tin burst trong mng. T lmt gi ivi ng ng cho c hai l p gi tin ti 0,5 Erlang. ........................................................... 35Hnh 3.15 th SDP vi hai ngng v khng c u tin burst trong mng. T lmtgi trn chai gi tr ng ng khc nhau cho c hai u tin ......................................... 36Hnh 3.16th SDP vi hai ngng v hai u tin burst trong mng. T lmt giso v i cc gi tr ng ng khc nhau vi hai u tin..................................................... 37Hnh 4.17 Phn loi k thut bo hiu ............................................................................... 39Hnh 4.18 C ch ginh tr c v gii phng trong OBS .................................................. 41Hnh 4.19 K thut bo hiu Just-Enough-Time (JET) ..................................................... 44Hnh 4.20 So snh gia k thut bo hiu JET (a) v JIT (b) ............................................ 45Hnh 4.21 K thut bo hiu Tell-and-Wait (TAW) ......................................................... 45Hnh 4.22 K thut bo hiu kh i to t node trung gian (INI) ......................................... 48Hnh 4.23 Topo mng ng trc gm 14 im (khong cch tnh bng km) ................. 50Hnh 4.24 (a) T lmt gi so v i ti ................................................................................ 54Hnh 4.25 (a) T lmt gi so v i ti ............................................................................... 55


5/57


5

T vit t t v thu t ng

Vit t t Ch gi i Ti ngAnh

Ch gi i Ti ng Vi t

BHP Burst Packet Header Gi mo u burstDIR Destination Initiated

ReservationGii phng kh i to t ch

DLE Dynamic LightpathEstablishment

Kh i to tuyn quangng

DP Drop Policy Chnh sch loi b FDL Fiber Delay Lines Dy quang tr FWM Four Wave Mixing Hiu ng trn 4 sngINI Intermediate Node

InitiatedK thut bo hiu kh i tot node trung gian

ISI IntersymbolInterference

Nhiu lin k t

JET Just Enough Time K thut bo hiu va--th i-gian

JIT Just In Time K thut bo hiu va-ng-lc

MEMS Micro ElectroMechanical System

H thng vi in c kh

OBS Optical BurstSwitching

Chuyn mch burst quang

OSPF Open Shortest PathFirst

nh tuyn theo ngngn nht tr c

OT Offset Time Th i gian chnh lchOXC Optical Cross

ConnectionKt ni cho quang

RWA Routing andWavelengthAssignment

nh tuyn v phn b b c sng

SBS Stimulated BrillouinScattering

Hiu ng tn xkch thchBrillouin

SCU Switch Control Unit n v iu khin chuynmch

SDP Segmentation andDrop Policy

Chnh sch phn mnh vloi b


6/57


6

SIR Source InitiatedReservation

Gii phng kh i to t ngun

SLE Static InitiatedReservation

Kh i to tuyn quang tnh

SOA SemiconductorOptical Amplifier

Khuych i quang s dng bn dn

TAG Tell And Go K thut bo hiu gi-v-i

TAW Tell And Wait K thut bo hiu gi-v- i

WADM Wavelength Add-Drop Multiplexer

Bghp knh thm b t b c sng

WDM WavelengthDivisionMultiplexing

Ghp knh phn chia theo b c sng

WR-OBS WavelengthRouting OpticalBurst Switching

Chuyn mch burst quangnh tuyn theo b c sng


7/57


7

Ch ng I: Gi i thi u

Trong thp nin va qua, lnh vc networking c spht trin tc rt cao. S phcp mnh mca internet v yu cu ngy cng tng vthng tina phng tin kim chng mt cch nghim ngt gi i hn ca my tnh hinnay cng nh mng vin thng. C mt nhu cu tc th cho s pht trin camng mi c dung l ng cao c kh nng htr nhng yu cu v tng tr ng bng thng. gpnhng nhu cu tng trng , h thng quang WDM c trin khai trong nhiu mng vin thng ng trc. Trong h thng WDM,

mi cp mang nhiu knh truyn thng, mi knh hot ng trn mt b c sngkhc nhau. H thng truyn ti quang nh vt c kh nng cung cp trn 50 Tb/strn 1 cp n.

Hnh 1.1 Cc phng php truy n d n quang

Hnh 1.1 ch ra s pht trin ca nhng phng php truyn ti quang khcnhau.Th h kin trc mng quang u tin gm c nhng lin kt im-imWDM. Mt mng nh vy bao gm mt vi lin kt im-im m lu l ngn node b b, chuyn i t quang sang in, x l tn hiu in, v chuyn t in sang quang tr c khi r i node. Vic thm v b lu l ng ti mi node


8/57


8

trong mng phi chu nhng thit hi nghim trng- s phc tp ca chuynmch v ci gi phi tr ca x l tn hiu in, c bit nu a phn lu l ngtrong mng l lu lng i thng qua.gim thiu gi ca mng, nhng thitb ton quang c th c s dng.

Kin trc mng thh th hai da trn WADM (ghp knh thm- b t theo bc sng), khim lu l ng c th c thm vo hoc bt iti cc a imWADM. WADM c th cho php nhng knh bc sng c chn trn cp b chn, trong khi nhng b c sng khc li c i qua hon ton. Ni chung,lng lu lng i qua trong mng ln hn nhiu so vi lng lu l ng b drop ti mt node no ; do , nh s dng WADM, ta c thgim gi tngca ton mng, iu ny k vng s c trin khai ti th tr ng mng th.

xy dng mng l i gm nhiu kt ni quang a b c sng, thit b ktni cp l rt cn thit.Kin trc mng quang thh th 3 da trn nhng thit b kt ni ton quang. Nhng thit b ny ri vo 3 loi: coupler sao b ng(passive star), router b ng (passive router) v switch ch ng (active switch).Passive star l thit b qung b.Mt tn hiu n trn mt bc sng cho tr ctrn cng cp u vo ca coupler hnh sao, cng sut ca n s c chia u racc port u ra ca coupler sao.Mt passive router c th nh tuyn ring bitmt vi bc sng n trn mt cpu vo n cng b c sng cp ura.Passive router l thit b tnh; v thcu hnh nh tuyn l c nh. Mt activeswitch cng nh tuyn b c sng t cp u vo n cpu ra v c thh tr kt ni ln l t. Khng ging nh passive router, active switch c thti cuhnh thay i dng kt ni ca bc sng n v bc sng i. Trng nhngmng quang thh3 ny, d liu c cho php qua nhng node trung gian mkhng cn chuyn i sang in, v vy gim c gi ca vic cung cp chcnng chuyn mch in c dung l ng cao v kh nng nh tuyn ti mi node.

H thng m i tonquang c hi vng s cung cp kt ni chuyn mchknh, hoc tuyn quang, gia cc router bin qua mt mng quang li; tuy nhin,do nhng kt ni chuyn mch knh l tnh, chng khng c kh nng iu

tit dung l ng qu l n, bng n ca mng internet. Mt cch l tng, cungcp s vn hnh tt nht c th trong li quang, cc node cn cung cp chuynmch gi ti mc quang. Chuyn mch gi ton quang nh vt dng nh khngkh thi trong tng lai gn do nhng gi i hn vcng ngh.

Mt s thay th tng tcho chuyn mch knh ton quang v chuynmch gi ton quang l chuyn mch burst quang. Trong chuyn mch burst


9/57


9

quang, cc gi tin tip ni nhauvo trong cc n vgiao vn c gi l cc burst. Cc burst sau c chuyn mch qua mng quang li theo ci cch caton quang. Mng chuyn mch burst quang cho php mt mc cao hnca ghp knh thng k v ph h p cho vic x l lu l ng bng n hn so v i

chuyn mch knh quang. Cng lc , mng chuyn mch burst quang khngc nhiu hn ch nh mng chuyn mch gi ton quang. ch r im khcbit gia chuyn mch knh quang, chuyn mch gi quang v chuyn mchburst quang, chng ta s bn k vmi vn sau.

1.1. Chuy n m ch knh quang

Mng nh tuyn b c sng quang s dng chuyn mch knh quang, mcc tuyn quang c kh i to gia cp cc node. S kh i to ca ng i nhsng km theo mt vi cng vic. Nhng cng vic ny bao gm topology vkhm ph ti nguyn, nh tuyn b c sng, v bo hiu v chim gi tinguyn.

Topology v khm ph ti nguyn sc km theo thng tin trng thi phnphi v bo tr ca mng. Thng th ng, thng tin ny s km theo thng tintrn topo mng vt l v trng thi ca lin kt trong mng. Trong mng nhtuyn b c sng WDM, thng tin ny c th km theo ri ca b c sngtrn mt lin kt cho tr c trong mng. Mt giao thc chung cho duy tr thngtin trng thi lin kt trng mng l giao thc OSPF.

Vn tm tuyn ng v phn b b c sng cho tuyn quang tngng v i vic nh tuyn v phn b b c sng (vit tt l RWA).Thngth ng, yu cu kt ni c 2 loi tnh v ng.Trong kh i to tuyn quang tnh(SLE), ton b cc kt ni u c bit tr c, vn l to tuyn quang chonhng kt ni ny trong khi ti thiu ha ti nguyn mng nh s b c sng, s cp ca mng.V i kh i to tuyn quang ng (DLE) mt tuyn quang c tora cho mi yu cu kt ni khi yu cu n, v tuyn quang c ngt sau mtkhong thi gian no .Vn trong tr ng hp lu lng ng l to tuynquang v phn b b c sng trong khi ti thiu ha l ng kt ni b chn hocti a s l ng kt ni c kh i to trong mng ti bt c thi im no.C rtnhiu nghin cu gii quyt cc vn ca RLE v DLE.

Kt ni tuyn quang c nh tuyn bc sng l kh tnh v khng th ph h p vi lu l ng internet bin i v bng n nh ngy nay.Rt r tngrng nu lu l ng rt bin ng, th gi lu l ng quang tuyn quang tnh s


10/57


10

gy ra s khng hiu qu v bng thng. Mt khc nu ta tip cn to ra tuynquang theo cch ng, th thng tin vtrng thi ca mng thay i lin tc,lm cho vic giu thng tin trng thi mng tr nn kh khn. V vy khi lul ng tr nn ngy cng ng v bng n, mt cch tip cn thay th l cn thit

truyn d liu qua mng.1.2. Chuy n m ch gi quang

Khi cng ngh chuyn mch quang c nng cao, chng ta cui cng thy c s xut hin ca mng chuyn mch gi quang m trong cc gi c chuyn mch v nh tuyn c lp qua mng, hon ton trong min quangm khng cn chuyn i tr li sang in ti mi node. Mt mng nh vy chophp mc cao hn ca ghp knh tnh trn cp quang v ph hp hn x l lu l ng bng nso v i chuyn mch knh quang.

Mt v d ca kin trc chuyn mch gi quang c bn c biu dintrong hnh 1.2. Mt node cha c cu chuyn mch quang c kh nng cu hnhl da trn nn tng tng gi mt.C cu chuyn mch c cu hnh li datrn thng tin cha trong tiu ca mi gi tin. Tiu t n c x l in,v c th c mng in-band vi packet, c mng trn mt tn s sng mangcon ; hoc c mang i out-of-band trn mt knh hon ton khc. V mt mtkhong thi gian tiu c x l v cho chuyn mch c cu hnh li,gi tin c thb lm trnh gi n quan mt ng trquang.

Hnh 1.2 Ki n trc c a m t chuy n m ch gi quang

chuyn mch gi quang c thc t, th i gian chuyn mch nhanh lcn thit. Thng th ng, th i gian chuyn mch cho MEM- based switch cyu cu t 1 n 10 ms, trong khi chuyn mch da trn khuch i quang bndn c th i gian chuyn mch di 1ns. Nhc im ca chuyn mch khuch


11/57


11

i bn dn quang l chng c gi t v kin trc chuyn mch yu cu tn hiuphi i qua bcoupler-iu ny lm gim cng sut. Trong khi tc chuynmch c k vng s tng tr ong th i gian gn, cng ngh hin ti cha trng thnh h tr chuyn mch gi quang.

Mt thch thc na trong chuyn mch gi quang l vn ng b.Trongmng chuyn mch gi quang vi cc gi c di khng i, ng b gi tiu vo switch thng c ti thiu xung t. D ng b thng kh t c, mt vi k thut ng b c nghin cu ti nhiu vin khoa hc.

V ti nguyn mng khng c t tr c trong chuyn mch gi quang,gi c thb xung t. Xung t xy ra khi 2 hay nhiu gi c xu h ng ra cngcng u ra ti cng thi im. Thng thng, xung t trong mng chuynmch gi in truyn thng c x l nh b m; tuy nhin trong min quang,rt kh vn hnh b m, do khng c thit b quang tng c v i RAM.Thayvo , b m quang c th c c nh dng b ng cptr. Nh c ng tr ny, ta c th gi gi tin tr i trng mt khong th i gian. Ch rng trong mi kin trc b m quang, kch c b m l c gi i hn, khng ch l do vn cht l ng tn hiu, cn l do gi i hn vkhng gian vt l.lmtrmt gi tin trong 5 micro giy i hi phi c 1 km cp. V gi i hn kch c ca b m, mt node c th khng kh nng x l lng lu l ng ln nhiu kin mng hin nay.

Mt cch tip cn khc gii quyt xung t l nh tuyn gi tin b xungt n cng u ra khc v i cng u ra d nh ban u. Cch tip cn ny c hiu nh chuyn hng nh tuyn hay nh tuyn hot-potato. Trong khinh tuyn chuyn hng thng khng c a dng trong mng chuyn mchgi in do nguy c lp vng v chuyn gi out-of-sequence. Dng chuynh ng quang s l cn thit trong mng chuyn mch gi quang-ni m dungl ng b m l gi i hn v duy tr c mc mt gi h p l. Tuy nhin,tr c khi trin khai n, nhng nghin cu s cn phi i trc tm ra nhng phng n v t qua gi i hn ca chuyn h ng quang.


12/57


12

1.3. Chuy n m ch burst quang

Hnh 1.3 S d ng th i gian chnh l ch trong OBS

Chuyn mch burst quang c s dng t c s cn bng giachuyn mch gi quang v chuyn mch knh quang. Trong mng chuyn mchburst quang, mt burst d liu cha nhiu gi tin IP c chuyn mch quamng ton quang. Mt gi tin iu khin c truyn i trc burst cu hnhcc switch trn tuyn ng ca burst. Th i gian chnh lch (hnh v) cho phpgi tin iu khin c x l v switch c ci t trc khi burst n nodetrung gian; v th, khng cn b m in hay quang no ti cc node trung gian

trong khi gi tin iu khin c x l. Gi tin iu khin c th ch r khongth i gian ca burst cho node bit khi no n cn cu hnh li switch ca ncho burst n tip theo.

Bng 1.1 So snh gi a cc cng ngh ton-quang khc nhau


13/57


13

Bng cch t tr c ti nguyn cho mt khong th i gian nht nh hn lt tr c ti nguyn cho mt khong thi gian khng xc nh, ti nguyn c th c phn bmt cch hiu qu v mc ghp knh cao hn c th t c.V th, chuyn mch burst quang c kh nng v t qua mt sgi i hn ca phn

b bng thng tnh trong chuyn mch knh quang. Hn na, v d liu ctruyn trong cc burst l n, chuyn mch burst quang lm gim cng ngh yucu cho chuyn mch quang nhanh-iu ny cn thit cho chuyn mch giquang.

Hnh trn tng kt s khc bit trong mng chuyn mch ton quang ca 3cng ngh. T hnh v, ta c thddng nhn thy, chuyn mch burst quang cu im ca c chuyn mch gi quang v chuyn mch knh quang trong khitrnh c nhng thiu st ca chng.

Mc d chuyn mch burst quang xut hin cung cp nhng u imhn chuynmch gi quang v chuyn mch knh quang, mt vi vn vnphi xem xt tr c khi chuyn mch burst quang c th trin khai trong mng.C th, nhng vn ny bao gm lp rp burst, k hoch bo hiu, gii quytxung t, lp lch burst v cht l ng dch v.

Lp rp burst c yu cu quyt nh xem bao nhiu gi tin c rprp vo cc burst. Vn km theo l khi no lp rp vo mt burst,bao nhiugi tin cn lp trong 1 burst, loi gi tin no c km theo trong burst. Lp rp

burst s nh hng n di burst cng nh khong th i gian m mt gi tinphi i trc khi c truyn i.

M hnh bo hiu l cn thit cho vic t tr c ti nguyn v cu hnhswitch cho burst n. M hnh bo hiu thng thng t tr c ti nguyntrong OBS l tell-and-go (TAG), tell-and-wait (TAW) v just-enough-time(JET). Trong m hnh TAG, node ngun gi mt bn tin iu khin ti chthch v i cc node dowstream l burst sp n. Tip , node ngun lp tc giburst d liu theo sau bn tin iu khin m khng cn i c bo nhn(ACK). c th i gian x l bn tin iu khin cng nh cu hnh switch ticc node, burst c th cn c qua b m ti mi node. Trong m hnhTAW,pha ngun gi mt bn tin iu khin t tr c ti nguyn cho bursttrn ton tuyn ng. Tip , pha ngun i bo nhn (ACK) rng qu trnht trc ti nguyn thnh cng. Sau khi nhn ack ny, pha ngun s giburst. Nu khng, node ngun s phi tip cn li lm li qu trnh t tr cti nguyn ny. Trong JET, c mt tr gia truyn gi tin iu khin v


14/57


14

truyn burst d liu. trny c th c t ln hn tng th i gian x l gitin iu khin trn c tuyn ng. Do , khi burst n mi node trung gian,gi tin iu khin c x l v knh trn cng u ra cng c phnphi. V vy, khng cn b m burst ti mi node. iu ny l c im rt

quan trng trong m hnh JET.Trong m hnh TAG v JET, pha ngun khng cn phi i xc nhn

tr c khi truyn burst. V vy, rt c th vic t tr c ti nguyn khng thnhcng ti mt node no trn tuyn. Trong tr ng h p ny, mt burst angtruyn s b xung t. Xung t xy ra khi c hn mt burst tranh ginh cngmt ti nguyn ti cng mt thi im. Xung t c thgii quyt bng rt nhiucch. Mt trong nhng cch l lu trmt trong s cc burst n khi tinguyn thch hp ri. Mt cch khc l chuyn h ng mt trong cc burst n cng u ra khc. Mt cch khc na l chuyn mt trong cc burstsang bc sng khc trn cp u ra. Khi cc k thut gii quyt xung t khngthnh cng, burst sb hy b.

Khi chuyn i bc sng c s dng, vn quyt nh b c sng noph h p cho mt burst trn lin kt u ra c gi l lp lch knh.


15/57


15

Chng II: Kthu t v ki n trc

S pht trin ca chuyn mch burst quang da vo s pht trin thnhcng ca mt vi cng ngh ct li, bao gmchuyn mch ton quang,thit b nhn mode burst, chuyn i b c sng quang. Trong khi s pht trin trongnhng lnh vc ny c nhng s pht trin trong vi nm va qua, cng cnthm mt s i hi khc tr c khi nhng cng nghny c th sn sng cho h thng thc t. D loi cng ngh no s c s dng, th ng i thit kmngvn phi quan tm n nhng hn ch tng vt l i v i cc thit b v thnh

phn cng ngh ny. Chng ny sgi i thiu mt ci nhn chung nht v kintrc ca node chuyn mch burst quang, tp trung vo cc thnh phn chnh cnthit cho chuyn mch burst quang. Tip , sgi i thiu mt vi cng nghh tr kin trc chuyn mch burst quang v bn v cc vn tng vt l c th nh hng n hiu nng ca mng chuyn mch burst quang.

2.1 Ki n trc m ng chuy n m ch burst quang Mt mng chuyn mch burst quang bao gm cc node c kt ni v i

nhau qua cc cp. Mi cp c kh nng phc v nhiu knh b c sng s dngghp knh phn chia theo b c sng WDM. Cc node trong mng OBS c th lnode bin hay node li nh trong hnh 2.4. Node bin c trch nhim lp rp ccgi tin vo cc burst, v lp lch cho burst truyn trn knh b c sng. Node lic chc nng chnh l chuyn mch burst t cng u vo t i cng u ra datrn gi tin tiu burst v x l xung t burst.

Hnh 2.4 Ki n trc m ng chuy n burst quang


16/57


16

Node bin u vo lp rp cc gi tin n t u cui khch hng vo trong burst. Burst c lp rp xong c truyn i (ton quang) qua cc router lim khng cn lu trti cc node trung gian. Node bin u ra sau khi nhn c burst, s tch cc burst thnh cc gi tin v chuyn chng ti u cui

ngi dng ch.Trong hnh 2.5, m t nhng chc nng khc nhau trong mng chuyn

mch burst quang. Node bin u vo c trch nhim lp rp burst, nh tuyn,phn b b c sng v lp lch cho burst ti bin. Node li c trch nhim bohiu, lp lch burst ti cc lin kt li v gii quyt xung t. Node bin u rac trch nhim tho cc burst v chuyn gi tin t i tng mng cao hn

Hnh 2.5 S chc nng OBS

Trong kin trc mng, c th gi nh rng mi node c th h tr c lulng vo cng nh lu lng i qua ton quang. V vy mi node gm crouter li v router bin nh trong hnh 2.6 v 2.7.

Router li (hnh 2.6) gm c cc OXC( kt ni cho quang) v SCU(nv iu khin chuyn mch). SCU to ra v duy tr mt bng chuyn tip(forwarding table) v c trch nhim cu hnh OXC. Khi SCU nhn mt gi tintiu burst, n nhn dng cng u ra d tnh ca gi tin. Nu cng u ra d tnh ban u ny ri khi burst d liu n, SCU cu hnh OXC cho burstd liu i qua. Nu cngu ra bn,vic OXC s c cu hnh nh thno dahon ton vo chnh sach gii quyt xung t p dng cho mng. Ni chung,SCU c chc nng gii thch tiu ( bin dch), lp lch, pht hin xung t vgii quyt n, tra bng chuyn tip (forwarding table), iu khin ma trn


17/57


17

chuyn mch, vit li tiu ,v iu khin chuyn i bc sng. Trong tr ngh p burst d liu voOXC trc gi tin iu khin ca n, burst sb hy b.

Router bin (hnh 2.7) c chc nng tin phn loi gi tin, b m gi tin,ghp ni gi tin vo burst, v tho r i gi tin ra khi burst. Nhng chnh schghp burst khc nhau, nh chnh sch ng ng hoc c ch nh th i c th cs dng tp h p cc gi tin d liu l n vo mt burst quang v gi cc burstquang vo mng. Kin trc ca router bin gm c module nh tuyn, mt b sp xp burst, mt b lp lch. Module nh tuyn chn cng u ra ph h p v imi gi tin v gi mi gi tin n module lp rp tng ng. Mi module lprp burst gm c cc gi tin c hng n router bin u ra c th. Trongmodule lp rp burst, c nhiu loi hng i gi tin khc nhau cho mi mc lu l ng. B lp lch to ra mt burst da trn k thut lp rp burst v truynburst qua cng u ra. Ti router u ra,mt module tho r i burst thnh cc gitin v gi gi tin n tng mng pha trn.

Hnh 2.6 Ki n trc router li

Mt vi nh khoa hc xut mt kin trc OBS tp trung hn :WR -OBS (chuyn mch burst quang nh tuyn b c sng). Mt mng WR-OBS kth p nhng chc nng ca OBS v i chuyn mch knh nhanh bng cch phn b


18/57


18

ng v gii phng tuyn quang c nh tuyn b c song qua mt li quangkhng c m.

Hnh 2.7 Ki n trc router bin

u im ca kin trc ny so snh vi OBS thng th ng l c QoS rrng c tnh d phng. So v i mng nh tuyn bc sng quang tnh, th WR -

OBS c u im thchng nhanh vi lu l ng bng n, lin tc thay i trnmng quang v vn hnh hiu qu hn trn mi knh b c sng.

Trong mng WR-OBS, mi request server tp trung ha c trch nhimginhtr c ti nguyn cho cc yu cukt ni trn ton mng.Mi node u vogi yu cu kt ni ca chng ti request server, ni m cc yu cu c xphng da vo node u ra ch v mc QoS.Server c tp trung ha c kh nng phn bti nguyn da vo nhng kin thc ton cc ca n v trng thica mi b c sng trn mi lin kt trong ton mng. Request server tp trungha c trch nhim x l mi yu cu kt ni n l, tnh ton tuyn ng t ngun ti ch tng ng v t tr c request number ca b c sng trn milin kt trn ton tuyn kt ni. Router bin u vo bt u truyn d liu ch sau khi n nhn c mt bn tin xc nhn t request server. WR-OBS c th nng cao throughput ca mng, nhng chnh bn cht tp trung ha ca n rtkh c th m rng c.


19/57


20/57


20

Mt cng ngh chuyn mch cung cp th i gian chuyn mch nhanh lchuyn mch cng SOA (SOA- khuch i quang bn dn). Lc ca mtchuyn mch SOA c bn c ch r trong hnh 2.6. Tia sng n mt u vochotrc c broadcast(qung b) t i nhiu SOA s dng coupler quang. SOA

hot ng nh mt cng m c th bt hoc tt i. Nu SOA c bt ln, tnhiu n c chuyn tip, cho qua n u ra, nu khng tn hiu b chn li.u im ca chuyn mch SOA bao gm th i gian chuyn mch nhanh -khong 1ns, v kh nng multicasting mt tn hiu t i nhiu u ra. Mt nh cim ca chuyn mch da trn SOA l coupler gy ra s gim v cng sut tnhiu, dn n gim khong cch truyn dn ti a ca tn hiu. ng th i SOAcng c gi kh t v c nhy phn cc cao.

Hnh 2.9 Chuy n m ch SOA

2.2.2 Burst mode receiver Thit b thu truyn thng s dng trong h thng truyn dn quang nh

SONET th ng khng ph h p v i chuyn mch burst quang. Mt thit b thunh vy mc nh pha v cng sut khng i cho tn hiu n v cng mc nhrng tn hiu lun lun hin hu trn ng truyn. Trong mng OBS,cc burstn mt thit b thu cho tr cc th c pha v cng sut khc nhau,v burst cth n t nhiu ngun khc nhau v c th i qua nhiu tuyn trong mng. Hnna, do bn cht ca burst, mt tn hiu ch hin din trn ng truyn trongkhong th i gian ca mt burst.

Burst mode receiver l thit b thu c thit k thchng v i pha vcng sut bin thin ca burst n. Mt c tnh khc ca Burst mode receiver lthi gian t xung ng h nhanh. Burst mode receiver c kh nng phc hixung ng hca tn hiu 2 GB/s trong 24ns.


21/57


21

2.2.3 Chuy n i b c sng Trong mng chuyn mch burst quang vn hnh WDM, rt l t ng khi c

th c kh nng chuyn i b c sng ti mi node gim xung t. C mtcch quen thuc nht chuyn i tn hiu t mt b c sng ti b c sng

khc l chuyn i tn hiu quang thnh tn hiu in v s dng tn hiu in iu ch tn hiu quang trn bc sng u ra mong mun. Phng php nykh n gin v c th chuyn i tn hiuvn hnh tc ln t i 10 Gb/s; tuynhin, cch tip cn ny l khng trong sut v i hi tn hiu quang c nhdng iu chnht nh v mt tc nht nh.

Mt cch tip cn v i vn hnh chuyn i bc sng ton quang liu ch cross-gain. Trong iu ch cross-gain, d liu c gi qua mtSOAcng v i mt tn hiu sng bm lin tc (CW- continuous wave) trn mt b c sng khc. Khi tn hiu d liu cao, sng mang trong vng tng ca soa tr tnn cn kit, v SOA tr nn bo ha. Kt qu l, s khuch i ca CW gim.Khi tn hiu d liu thp, tn hiu CW nhn c ton b s khuch i. V th,mt bn sao chp ng c ca d liu s c t vo tn hiu u ra. K thutny c kh nng chuyn tn hiu hot ng tc 10 Gb/s. Gi i hn cachuyn i da trn iu ch cross-gian l nhng k thut ny i hi cngsut u ra cao cho tn hiu d liu, v tn hiu u ra c t l extinction thp (t lcng sut cho mt bit khng chia cho cng sut cho mt bit 1). iu ny l dokc khi SOA bo ha, tn hiu CW vn nhn mt vi s khuch i.

Mt phng php khc cung cp chuyn i bc sngquang l s dng trn bn sng. Trn bn sng l hiu ng phi tuyn m khi c tn hiu ctn s f1 v f2 tng tc to ra nhng thnh phn tn sm i 2f1-f2 v 2f2-f1.Nu tn hiu d liu hot ng tn s f1 v tn hiu bm CW hot ng tns f2, khi dliu s b p t lm vic ti tn s 2f1-f2 v 2f2-f1. Tn hiumi c to ra c cng sut nh hn tn hiu u vo, v th kh nng chuyni ca k thut ny l khng tht hiu qu. Hn na hiu qu cn b gim dos sai khc gia bc sng bm v tn hiu bc sng u ra tng.

2.3 V n tng v t l Khi thit kmt mng chuyn mch burst quang, nhng hn ch vt l lrt ng quang tm. Cth nh suy hao,tn sc, hiu ng phi tuyn. Trongnhng vn ny, nhiu ci xut hin trong mng quang thng th ng, mtvi ci khc xut hin nh mt vn c bit trong chuyn mch burst quang.


22/57


22

2.3.1 Suy hao Khi tn hiu quang i trn cp, cng sut tn hiu suy gim do suy hao. Suy

hao l do s hp th v tn x rayleigh. Hp th l do nh sng b hp th trncc phn t silica hoc tp cht. hu ht cc cp, l ng hp th cho khong

b c sng hu ch(0.8-1.6 micromet) l khng ng k. Tn x rayleigh ldo bin thin nhca chit sut ca cp lm tn x nh sng.

Trong mng chuyn mch burst quang, suy hao lm gim khong cch tia m burst c th i c. Trong hu ht cc tr ng h p, khuch i quang cth s dng khc phc iu ny; tuy nhin khuch i quang cng c thgyra nhiu.

2.3.2 Tn s c Nu tn hiu quang gm c hiu thnh phn b c sng, th s khc bit

gia cc thnh phn ca tn hiu s i v i vn tc khc nhau gy ra s tri rngca tn hiu trong min th i gian. Hiu ng ny l tn sc. Cc dng ca tn scbao gm c tn sc mode v tn sc chromatic.

Tn sc mode l do nhiu mode ca cng mt tn hiu lan truyn ti nhngvn tc khc nhau trn cp. Tn sc mode c th kh bng cch ta s dng cpn mode. Cp n mode c ng knh li nh, ch c th mang i duy nhtmt mode ca tn hiu truyn lan.

Tn sc chromatic l do vn tc nh sng l mt hm ca b c sng. V th nu tn hiu gm nhiu hn mt thnh phn b c sng, dn n thnh phn nylan truyn nhanh hn thnh phn kia, gy ra s tri rng trn min th i gian catn hiu. Loi tn sc chromatic ny bao gm tn sc vt liu- m chit sut cas i bin i nh mt hm ca b c sng (chit sut s i v i cc thnh phn tiasng khc nhau l khc nhau) v tn sc ng dn sng-chit sut cho mt b csng nht nh da vo phn cng sut i trong li v phn cng sut i ngoi v ca s i.

Trong tr ng h p m tn hiugm mt xung biu din mt bit n l, tnsc gy ra dn xung khi n lan truyn qua s i. Khi xung b dn ra, n c thdnra nhiu gy ra nhiu v i xung bn cnh, gy ra ISI. Suy hao s lm gi ihn khng gian bit v tc truyn dn trong knh quang.

Ti b c sng 1300nm, tn sc vt liu trong cp n mode thng th nggn nh bng khng. Rt may mn l y cng chnh l mt ca s suy hao thptrong quang. Qua nhng k thut nng cao nh dch tn sc, c th to ra s i v i


23/57


23

tn sc bng 0 ti mt bc sng no t1300nm t i 1700nm. Trong s i dchtn sc, li v v c thit k sao cho tn sc ng dn sng l m, v th khicng v i tn sc vt liu s cho tn sc tng v khng. Tuy nhin, tn sc ch bng khng cho mt bc sng n.

Cng v i vn v ISI, suy hao cng c thgy ra vn v ng b trong mng chuyn mch burst quang. Trong mt mng chuyn mch burstquang, tiu burst thng c gi n b c sng khc vi b c sng caburst. Mi bc sng trong cc bc sng stri qua cc mc tn sc khcnhau, gy ra hin tng burst v tiu c th tri li gn hay raxa nhau hntrong min th i gian. Nu khong cch vt l ca mi lin kt v suy hao cacp l bit tr c, c th b li tn sc bng cch iu chnh cho ph h poffset ca node ngun.

2.3.3 Hi u ng phi tuy n Hiu ng phi tuyn trong cp th ng cnh hng n: tc truyn dn,

s knh, khong cch knh, cng sut tn hiu. Mt vi v d v hiu ng phituyn: trn 4 sng, t iu ch pha, iu ch pha cho, tn x kch thch raman,tn x kch thch brillouin.

Trn bn sng (FWM) xy ra khi 2 b c sng hot ng ti 2 tn s f1, f2s trng vo nhau to ra tn hiu 2f1-f2 v 2f2-f1. Nhng tn hiu to ra sau nygi l sideband, c th gy nhiu nu chng trng v i tn s s dng truyn d

liu. Cng nh vy, trn c th xy ra gia s kt h p ca 3 hay nhiu hn cc b c sng.Hiu ng trn 4 sng trong WDM c th c lm gim nh s dngknh c khong cch khng u.

T iu ch pha l do thay i v cng ca tn hiu, gy ra s thay iv pha ca tn hiu.S bin i tc th i v pha ca tn hiu c th to ra thnhphn tn s ph thm trong tn hiu. Nhng thnh phn tn s ny kt h p v ihiu ng ca tn sc, sgy ra s tri rng hoc nnli ca xung trong min th igian.

iu ch pha cho l s dch v pha ca 1 tn hiu gy ra do s thay icng ca 1 tn hiu lan truyn ti b c sng khc. Gn v i t iu ch pha,s dch v pha c th to ra thnh phn tn s vi, gy ra tng tn sc. Mc diu ch pha cho c th gi i hn hiu nng ca h thngquang, n cng cnhngng dng tch cc ca n. S dng iu chpha cho, mt tn hiu mt


24/57


25/57


25

Chng III: Sp xp Burst

Nhm burst l qu trnh tp h p d liu n t l p cao vo trong burst tili vo node bin ca mng OBS. Khi cc gi tin n t lp cao hn, chngc lu trong cc bnh in ty thuc vo lp v ch ca chng. Khi c ch nhm burst phi thay th nhng gi tin ny da trn mt vi chnh schnhm.

Thng s kha trong nhm burst l tiu chun ban u c tnh quyt nhkhi to ra mt burst v gi burst vo mng. Tiu chun ban u cho vic tothnh mt burst l rt quan trng, n iu khin cc c tnh ca burst i votrong mng li OBS. C mt vi nhm burst c thng qua trong cc ti liuOBS hin nay. im chung ca hu ht cc cng ngh nhm burst l da trnnh th i (timer-based) v da trn ng ng (threshold-based).

Trong phngphp tip cn da trn nh th i, mt burst c to ra vgi vo mng quang ti khong thi gian nh k. Sp xp da trn nh th i c s dng cung cp khong th i gian chun gia cc burst lin tip t cng ng vo ca node n mng li. y, di ca burst cng thay i ty

theo s thay i ca ti.Trong phng php tip cn da trn ng ng trong nhm burst, mt gi i

hn c t l gi tr l n nht ca s gi c cha trong mi burst. V th, ccburst kch c c nh s c to ra ti bin ca mng. Cch tip cn v ng ngtrong nhm burst s to ra cc burst khng c thi gian theo nh k.

Cch tip cn v nh thi v ngng l tng ng, ti mt tc n c nh, mt gi tr ng ng c th c nh x n mt gi tr timeout v ng c li,nguyn nhn l cc burst c di tng tnhau cho mi tr ng h p.

Cc tham s chnh ca nhm burst c xem xt l gi tr nh thi, T, di burst b nht, Bmin, v di burst l n nht, Bmax, Bmin c th c tnh tonda trn th i gian x l tiu burst ti mi node v t l ca cc knh iukhin so v i sknh d liu trong s i quang.


26/57


27/57


28/57


28

trn tc lu lng n. S dng cc d on chiu di burst, BHP c th c gi vo mng li tr c khi to ra burst thc t, dnh ring ngun lctrong mng li OBS; do , tit kim c trnhm burst. Gi tr d on c th c s dng thit lp t ng gi tr ng ng (hoc gi tr nh th i) cho

burst tip theo. Cc hc gi a ra mt m hnh d on tuyn tnh d ondi burst tip theo da trn s tng quan ca lu l ng. L i th ca nhmda trn d on l tn hiu bo hiu v nhm c th c thc hin song song,do hn ch c trnhm.

3.2 Tc ng c a nhm burst t heo c tnh lu l ng Trong khi nhm burst, cc gi tin n t lp cao c lu trong hng i

da theo a ch ch ca chng v l p QoS. Sau khi cc tiu ch ca vic to cc burst c tha mn, burst tng ng c to ra v gi vo mng li. Do ,chng ta c th thy rng cc c im ca gi tin n v vic phn b di gitinnh h ng mnh m n cc c im ca gi tin n tng ng v vic phnb di burst. c nhiu tranh lun v tc ng ca nhm burst voburstiness ca lu l ng gi n. Ng i ta tin rng nhm burst lm gim mc t tng ng ca lu l ng gi vo (hiu ng lm mn). Lu rng lu l ngc xem xt c xem l t tng ng nu qu trnh n l bursty ti bt k quy m thi gian cho trc.Lu l ng Poisson truyn thng cho thy burstinessch quy m th i gian nh hn, nhng cch tip cn tc n l c nh khixem xt v i quy m th i gian rt di hoc l v cng. Ni chung, rt d dng

x l lu l ng mt cch tri chy hn (Poisson) so vi lu l ng bursty (t tng ng). Phn [10-12] khng nh rng nhm burst ch thay i phm vingn ty thuc vo lu lng gi tin n, nhng cc c tnh phm vi di tronglu l ng gi vn khng thay i. Kt qu ny mu thun v i kt qu c ch ra trc trong [13], y ngi ta khm ph phng php tip cn da trnnh thi cho nhm burst d i dng t tng ng ca gi tin mu i n v ch ra rng c chnhm burst lm gim cc c tnh t tng ng ca lu l ngtrn mng ng trc quang.

Trong [10-12], ngi ta khng nh rng, cho mt k hoch nhm datrn nh th i v i mt s phn b burst n c nh (t), s phn b di burstl Gausian. Ngoi ra, khi cho mt k hoch nhm da trn ng ng v i mt s phn b di burst c nh th s phn b burst n cng l Gaussian. Tuynhin, ngi ta cng cp rng mc d s ph thuc phm vi ngn c tc dnglm m t, cc cng ngh tp h p burst da trn nh thi v ng ng khng th gim s ph thuc phm vi l n trong mt lung lu l ng. Thng qua m


29/57


29

phng, [10,11] ch ra rng s tng quan kin trc mng l n quy m th i gianv hn vn khng thay i.

3.3 K thu t c l ng nhm burst d a trn ng ng Nghin cu trong phn [14] l k thut nhm burst da trn ng ng vnh

h ng ca chng trong vn mt gi trong mt mng chuyn mch burstquang (OBS). N cng nghin cu nh h ng ca nhm burst trong vic cungcp h tr QoS trong mt mng OBS.

Trong nghin cu ny, cc gi c nhm li vo trong cc burst da trna ch ch ca chng v l p QoS, v mi loi burst c nhm s dng mt gitr ng ng duy nht. Cc gi n c th thuc mt lp c bit, thhin yu cuvQoS ca cc gi tin. Nu khng mt tnh tng qut, chng ta gi s rng c 2lp lu lng i vo, v i tn l Class 0 v Class 1, y lu lng Class 0 c utin cao hn Class 1. Mc tiu l tm c khong ng ng ti u ti thiuha mt mt gi ca Class 0 cho mt mng d i ti nht nh. Ngoi ra, ta cng c php gi nh rng cc burst c gi tin Class 0 c phn b mt utin burst 0, v cc burst c gi tin Class 1 c phn bgi tr u tin burst1.

Mt mng OBS s dng k thut bo hiu JET v i phn mnh burst cxem xt. Cc burst c th nhn c s i x khc nhau trong mng li OBSda trn u tin burst. Mt mng khng th cung cp cc ng tr quang.Trong chng ny, chng ta xem xt nhiu k thut nhm burst da trn ng ng

v ch ra nh h ng ca cc cng ngh trong trong vic mt gi.3.3.1 K thu t nhm burst d a trn ng ng

nhm burst, mt ngng c s dng nh mt tham shn ch xcnh khi no to ra mt burst v gi burst vo mng li quang. Ngng xc nhr s gi c nhm vo trong burst. Cho n khi iu kin v ngng c png, cc gi tin n s c lu trong cc hng i gi u tin ti cc node truynhp. Mt khi t n ng ng, mt burst c to ra v s c gi vo mngquang. Do chnh sch ng ng, tt c cc burst s c cng s gi tin khi i votrong mng; tuy vy, khi mt burst i qua mng li,di ca burst c th thayi ty theo cc chnh sch gii quyt xung t, chng hn nh vic phn mnhburst, ty thuc mng li.

Nh c tho lun phn 3.1, c mt s nh i gia s l ng tranhchp v s trung bnh cc gi tin mt trn xung t, v k vng rng c mtkhong ti u ca gi tr ng ng s ti thiu ha xc sut mt gi. Mc tiu


30/57


30

chnh ca chng ta l tm c khong ng ng ti u v i mt ti cho tr c trongmng.

Vi tr ng h p c nhiu l p gi tin, mt gi tr ngng n c th c pdng cho tt c cc gi tin khng ph thuc vo lp, cc ng ng khc nhau cth c p dng mi l p gi tin.C nhiu ng ng c th l cn thit thamn tr QoS v m bo mt gi ca mi lp.Trong tr ng h p ny, mc tiu l tm ra ng ng ti u cho mi lp gi tin yu cu v QoS c p ng.

Trong mng li quang c ththm phn khc nhau gia cc burst c chacc l p gi tin khc nhau bng vic phn b u tin cho mi burst v p dngcc chnh sch u tin gii quyt tranh chp. Bng cch kt hp cc ng ng datrn l p v nhiu gi tr u tin, chng ta c thc mc ln hn ca s khcbit cho mi l p khc nhau ca lu l ng.

Vic thc hin cc k hoch ngng khc nhau c so snh d i chunv chnh sch loi b (DP) v chnh sch phn mnh (SDP) cho vic gii quyttranh chp. Trong chun DP, cc burst n tr hn bloi bnu n xung t v i burst khc. Trong chnh sch SDP, cc on chng cho ca burst n sm hnb loi b khi cc burst n chm hn xung t v i n.

Chng ta bt u bng vic xem xt mt l p ca lu l ng d liu, v sau m rng cho 2 l p, ch ra QoS c cung cp trong mi tr ng hp nh th no:

- Ngng n m khng c u tin burst: Trong chnh sch ny, mtngng n c s dng cho tt c d liu burst. Chng ta theo di xc sutmt gi v tng s xung t c phn tch cho nhiu ti v ng ng. Chng ta hivng s hin din ca gi tr ng ng ti u v i mt phm vi ti cho tr c v imng nht nh, m xc sut mt gi scc tiu.

- Ngng n vi 2 u tin burst: Trong chnh sch ny, chng ta gi s rng mng c 2 lp lu l ng khc nhau v chng ta c mt ng ng vi di burst duy nht cho tt c lu lng. Chng ta nh gi xc sut mt gi v s xung t cho nhiu ti v ng ng. Hai u tin burst l 0 v 1. Gi tr 0 c u tin cao hn.

- Hai ngng m khng c u tin burst: Trong chnh sch ny, chng tagi s rng mng c mt lp lu lng. Chng ta c 2 ng ng khc nhau trongmng, nh gi nh h ng ca 2 ngng c di burst khc nhau vo xcsut mt gi v s lng xung t.


31/57


31

- Hai ng ng vi 2 u tin burst: Trong chnh sch ny, chng ta gi s rng mng c 2 lp lu l ng v chng ta c mt ng ng vi di burstduy nht cho mi lp lu lng. Chng ta nh gi xc sut mt gi v sxungt cho nhiu ti v ngng. C 2 u tin burst l 0 v 1. Gi tr 0 l c u

tin cao hn.

Hnh 3.11M ng NSF v i 12 node (km)

3.3.2 Cc k t qu m ph ng nh gi hiu nng ca k thut nhm burst, chng ti pht trin mt

m hnh m phng. Sau y l cc gi nh c c kt qu:

- Gi tin n l phn bPoisson v i tc - di gi tin l c nh 1250 byte- Truyn tc 10 Gb/s- Th i gian chuyn mch 10 s- Lu l ng vo phn b u qua tt c cp nhn-ginh tuyn ng ngn nht c s dng tm ng gia 2 node

Hnh 3.2 cho thy 14 node mng NSF m chng trnh m phng thc

thi. Chng ti kim tra cc khoch ng ng khc nhau m t v i mng NSFtrn. Kt qu m phng chy cho n khi mt shu hn cc gi c nhnti cc ch.

Ngng n m khng u tin burst

Trong tr ng h p mt lp n cc gi tin v mt mc u tin burst n


32/57


32

th mt ngng n c s dng. Xc sut mt gi v tng s xung t cphn tch v i nhiu gi tr ti v ng ng. T kt qu ca ngng n, chng titheo di mt gi tr ng ng ti u v i mt mng v i ti cho trc, cho xcsut mt gi l nhnht. Hnh 3.3(a) v (b) cho thy kh nng mt gi v i DP v

SDP nh l chnh sch giquyt tranh chp ti li.

Hnh 3.12 th DP v SDP v i ngng v khng c u tin burst trong m ng

(a) T lm t gi so v i t i(b) T lm t gi so v gi tr ng ng


33/57


33

Hnh 3.3(a) cho thy tng xc sut mt gi so v i ti ca cc gi tr ng ngl 100, 400 v 600 gi tin cho c DP v SDP. Chng ta quan st thy ng ng400 gi hot ng tt hn 2 ng ng kia l 100 v 600. V th n l cn thit tm mt khong ng ng ti u sao cho mt gi l nh nht.S cn thit ca

ng ng ti u c th c hiu tt hn bng vic phn tch hnh 3.3(b). ychng ta thy rng vic mt gi bt u gim, khi chm n gi tr nh nht nli bt u tng. Mt gi l nh nht khi gi tr ng ng nm trong khong 280-430 gi tin. Vic mt gi ban u cao c th l do cc gi mt trong khi cu hnhli mt switch trong vic gii quyt xung t. dc ca vic mt gi t l thunv i th i gian chuyn mch. Khi th i gian chuyn mch l khng ng kvi ivi kch th c burst, vic mt gi vn duy trn nh trong khong 300-450 gitin. Khi hn 450 gi, mt gi tng.Chng ta chn 400 gi l gi tr ng ng ti ucho mng NFS d i ti l 0 n 1 Erlang. Ng ng ti u c thkhc nhau ty

theo cp node ca mng, tc burst n, v khong ti ca mng. Ngng n vi u tin burst

Vi tr ng hp 2 u tin burst v mt ngng n, chng ta nh gi xcsut mt gi v s xung t cho cc bin i v ti v ngng. Hai u tin burstl 0 v 1. Gi tr 0 c u tin cao hn.Chng ta sdng gi tr ng ng ti uc c t hnh 3.3(b) nh gi tr ng ng, khi n c mt gi l nh nht. Hnh3.4 v 3.5, cho thy hiu nng cho SDP nh mt chnh sch gii quyt xung ttrong mng li OBS. Chng ta gi nh rng t l d liu u vo ca 2 l p gitin lnh nhau.

Hnh 3.4 cho thy xc sut mt gi so v i ti cho cc ng ng 100, 400 v600 gi tin cho c hai u tin burst. Chng ti quan st thy mt gi l p gi tincao hn l nh hn khng ng kso v i mt gi l p thp hn. Quan st thyrng, thm ch v i s ln xung t l l n, chng ta vn c c mt gi thp hnl cc gi lp cao hn do sphn mnh.

Vic kt h p cc hnh v ca xc sut mt gi cho c cc burst cos utin 0 v 1 c ch ra i lp v i nhiu gi tr ng ng chot rong hnh 3.5. chngta thy rng vic mt gi cc gi lp cao hn l nh hn so v i cc gi l p thphn. Ngoi ra, chng ta c th thy rng mt gi tng ln khi gi tr ngng v tqu 400 gi.


34/57


34

Chng ta quan st thy cc burst c u tin 0 th c mt mt gi l cc tiuti cc gi tr ngng 400 v 600 gi tin, trong khi cc burst c u tin 1 c mtgi cc tiu ti ng ng 400 gi tin.

Hnh 3.13 th SDP n ngng v hai u tin burst trong m ng. T l m t gi trn t i v i nh ng gi tr ng ng khc nhau

Trong phn sau, chng ta snhn thy rng cc gi tr ngng n lkhcnhau cho kt qu mi u tin burst trong khi hot ng tt hn cho c2 l p gitin.


35/57


35

Hai ngng m khng u tin burst

Trong tr ng h p ny c 2 gi tr ngng m khng c u tin trongcc burst, chng ta nh gi xc sut mt gi v s xung t cho nhiu ng ngkhc nhau. Kt qu c ch ra trong hnh 3.6 SDP c gi nh l c pdng trong mng li, v v ta ca mng l 0.5 Erlang.Tc gi n cho milp lu l ng l ging ht nhau.

Trong hnh 3.6 chng ta quan st thy rng xc sut mt gi cho cc gi tr ngng khc nhau. Khi khng c u tin burst no trong mng, khi xung t,di gi tin hot ng nh u tin; do cc burst di c mt gi thp hnburst ngn. Chng ta quan st thy vic mt gi ca cc burst ngn lun lun l nhn mt gi ca cc burst di hn. V vy, c 2 mt bng trong hnh 3.6 khi c hai ng ng cn bng. Khi u tin khng c kt h p vo mng, vic mtgi l i xng cho burst ca chai gi tr ng ng.

Hnh 3.14 th SDP v i mt ng ng v hai u tin burst trong m ng. T l m t gi i vi ng ng cho c hai l p gi tin ti 0,5 Erlang.


36/57


36

Hai ng ng v i u tin burst

Hnh 3.7 cho thy hiu nng mng vi hai u tin burst v hai gi tr ng ng, v vi SDP nh l chnh sch gii quyets xung t trong mng li OBS.Chng ta gi s tc d liu u vo ca c hai lp lu lng l nh nhau. Vquan st s khc bit dch v gia hai l p gi tin khc nhau.

Hnh 3.7 ch cho ta thy xc sut mt gi v i nhiu gi tr ng ng cho haiu tin, v i ti l 0.5 Erlang. Chng ta quan st thy vic mt gi ca l p gi tincao duy tr khng i v i cc gi tr khc nhau ca ng ng 1. Mt gi ca l pgi tin thp gim khi kch thc burst tng do xung t t hn vi cc burst u tin cao hn. Khi ngng tng, mt gi tng do s gia tng ca s l ngtrung bnh gi mt trn xung t.

Hnh 3.15 th SDP v i hai ngng v khng c u tin burst trong m ng. T l m t gi trn c hai gi tr ng ng khc nhau cho c hai u tin


37/57


37

Trong tr ng h p tng qut, ta thy rng xc sut mt gi trung bnh trongmng bt u tng khi tng di ngng burst, v t n cc tiu ti gi tr ng ng ti u. Khi khi n c gi tr ng ng ti u, xc sut mt gi trungbnh bt u tng nhv i s tng ca di ng ng burst. Bng vic m phng,

chng ta quan st thy rng khi m phng cho 10 t gi tin c kch th c c nh,xc sut mt gi trung bnh vn bng phng sau khi t n gi tr ng ng tiu. Do , tt c burst ln hnhoc bng v i gi tr ng ng sc mt gi l cctiu. Mc d tng di ng ng burst, chng ta vn gim c ti trn mt bngiu khin OBS, chng ta cng phi xem xt n tc ng ca s gia tng diburst trong tr gi tin u cui-n-u cui.

Hnh 3.16 th SDP v i hai ngng v hai u tin burst trong m ng.T l m t gi so v i cc gi tr ng ng khc nhau v i hai u tin


38/57


38

Chng IV Bo hiu trong OBS

Khi mt burst truyn dn trn mt li quang, mt phng thc bo hiucn phi c thc hin phn b ti nguyn v cu hnh cc chuyn mchquang cho burst trn mi node quang. Gin bo hiu trong mng chuynmch burst quang s dng cc gi mou burst truyn ngoi di. Trong mt phng thc bo hiu ngoi di, cc mo u c lin kt v i mt burst ctruyn trn mt b c sng khc so vi burst . Cc gi mo u ngoi ditruyn dc theo cng tuyn ng nh burst , bo cho mi node dc theotuyn cu hnh kt ni quang cho ca node thchng vi burst angtruyn t i thi im thch h p.

Trong phn ny, chng ta s nghin cu cc thng s c trng cho ccgiao thc bo hiu OBS khc nhau. Ta sm t c thmt sgiao thc bo hiuOBS nghin cu.4.1 Phn lo i cc phng th c bo hi u

Mt s s thay i ca cc giao thc bo hiu trong chuyn mch burst cth xy ra, ph thuc vo ti nguyn dc mt tuyn c ginh tr c cho mtburst bng cch no v vo lc no.c bit, mt phng thc chuyn mch cth c c trng b i nhng tnh cht sau:

Ginh tr c ti nguyn mt chiu, hai chiu hoc theo phng thc lai; Ginh tr c ti nguyn kh i to t ngun, kh i to t ch, hoc kh i

to t node trung gian; Ginhtr c ti nguyn bn vng hoc khng bn vng; Ginh tr c ti nguyn ngay lp tc hay c th i gian tr; Gii phng ti nguyn r rng hoc timn; Bo hiu tp trung hoc phn tn. Cc tnh cht ny c m t c th hn trong cc phn sau y.

4.1.1 M t chi u, hai chi u ho c lai ghpMt phng thc bo hiu c th hot ng bng cch s dng vic dnh

tr c ti nguyn theo mt hng, hai h ng hoc ginh tr c theo kiu lai ghp.Trong mt phng thc bo hiu theo kiu ginh tr c mt chiu, node ngun s gi i mt gi tin iu khin yu cu mi node trn tuyn phn b ti nguyncn thit cho burst d liu v theo cu hnh cc kt ni cho. Node ngun sau


39/57


39

gi i burst dliu ngay m khng ch i phn hi t cc node trung giancng nh l node ch xem qu trnh ginh tr c ti nguyn mi node thnh

cng hay tht bi.Khi m vic ginh tr c ti nguyn khng c phnhi(mt chiu), c th rng qu trnh ny khng thnh cng v burst sb

loi b. Mt khc, v khng cn ch i xc nhn burst d liu c th c gii nhanh hn, theo gim c tr truyn d liu u-cui.

Hnh 4.17 Phn lo i k thu t bo hi u

Cc k thut bo hiu v i vic ginh tr c ti nguyn hai chiu da trnvic nhn xc nhn. Khi mo u ca burst c gi i tngun n ch ginh tr c ti nguyn cho mt burst, mt bn tin phn hi xc nhn rng tinguyn yu cu c cp pht c gi tr li t ch vngun. Burst d liusch c truyn sau khi nhn c phn hi. Nu bt k mt node trung giantrn tuyn m yu cu b t chi, node sgi mt xc nhn t chi nngun, ch ra vic ginh trc ti nguyn tht bi.Node ny cng sthc hin

cc hnh ng thch hp gii phng tt c cc qu trnh ginhtr c tinguyn ca cc lin kt trc trn tuyn. Ngun c th chn la gia vic c gng yu cu li bng cch gi mt mo u burst m i, hoc n gin l loi b yu cu. Phng thc bo hiu qu trnh ginh tr c ti nguyn c xc nhn (haichiu) c th loi b vic mt cc burst trong li OBS, tuy nhin cng dn ntr truyn u-cui gia tng.


40/57


40

Mt k thut bo hiu lai ghp to ra mt s tha hip gia hai phng thcginh tr c ti nguyn mt chiu v hai chiu l mt k thut mang n vic xcnhn tng phn i vi qu trnh ginh trc ti nguyn. Trong phng thc bohiu lai ghp, qu trnh ginh tr c ti nguyn t ngun n mt vi node trung

gian trn tuyn c xc nhn thng qua cc bn tin phn hi, trong khi qutrnh ny t node trung gian n ch cha c xc nhn. V tr no ca nodekh i to s quyt nh s mt mt v tr cho mt burst. Nu node trung giangn v i ngun, hiu nng tng t nh vic ginh tr c ti nguyn khng c xcnhn, v nu node trung gian gn v i ngun, hiu nng sgn nh l phngthc ginh tr c c xc nhn.4.1.2 Ginh tr c ti nguyn kh i t o t ngu n, kh i to t ch, hoc kh ito t node trung gian

Mt k thut bo hiu c th kh i to qu trnh ginh trci v i cc ti

nguyen yu cu ngun, ch, hoc mt im trung gian. Trong k thutginh tr c kh i to t ngun (SIR), ngun ti nguyn dnh cho burst c ngk trn ng truyn khi mo u burst truyn t ngun n ch. Node ngun,khi nhn c xc nhn v ngun ti nguyn, s truyn i burst vo mng li nhng thi im d kin ( c ln lch).

Trong k thut bo hiu ginh tr c kh i to t ch(DIR), ngun s phti mt bn tin yu cu v ti nguyn n node ch, bn tin yu cu ny thu thpthng tin v cc b c sng kh dng trn tt c cc lin kt dc theo tuyn. Datrn nhng thng tin thu thp c, ch schn mt b c sng kh dng (nu

n tn ti) cho cc khong th i gian ph h p v gui i mt bn tin yu cuginh tr c li cho pha ngun. Bn tin ny s i qua cc node trung gian, ngk cc bc sng c chn cho nhng chu k thch h p. Nguyn nhn chnh gynn tc nghn (hoc mt mt d liu) trong SIR l do thiu ngun ti nguyn ri,trong khi v i DIR, smt mt xy ra do thng tin qu choc qu chm.

Trong k thut ginh tr c ti nguyn kh i to t node trung gian (INI), tinguyn thng c ginh trc tng tkiu DIR t ngun n mt s nodetrung gian, v tng tkiu SIR t node trung gian n ch.

Ni chung, gim mt mt theo yu cu ti cc node theo h ng gi i,SIR da trn k thut c th ginh tr c nhiu hn mt (hoc tt c nu c th)cc bc sng cho n im ch, v gii phng nhng ti nguyn ginh tr ckhng cn thit hng ng c li. Cch tip cn ny c th dn n hiu nngkm b i hin t ng nghn h ng truyn i vthi u ti nguyn. Mt khc, DIRda trn k thut ch thu thp nhng thng tin trng thi c thv tt c cc nodetrung gian v da trn cc thng tin , chn ra mt b c sng. V th, nu


41/57


41

thng tin trng thi n l khng c cp nht, bc sng c chn c th s b chim dng b i cc yu cu khc trong khong th i gian t lc m trng thi c thu thp n lc m tin nhn ginh tr c chuyn n node , cn c gil khong th i gian d tn thng (Vulnerable period ). V th, DIR chu mt mt

do thng tin khng c cp nht trong khong th i gian d tn thng. 4.1.3 Kin tr ho c khng kin trMt trong nhng quyt nh quan trng m mi k thut bo hiu phi

quyt nh l hoc ch i ngun ti nguyn ang c s dng(cho n khin c gii phng) hoc ngay lp tc ch ra rng c xung t v kh i to cc c ch khi kt ni b ngt nh l truyn li, lch h ng, hoc k thut m. Trongcch tip cn theo kiu kin tr, ch i cc ngun ti nguyn ang c s dngv gn cc b c sng dn n vic gim c mt mt, gi s rng cc b mthch hp c chun b sn cc node (mng bin v mng li), do c th

lu tr c cc burst ang n. V i cch tip cn khng kin tr, mc tiu l cmt gi i hn trong tr (ti thiu ha tr vng); do node tuyn b yu cu b t chi nu ti nguyn khng c sn ngay thi im , v thc hin cc k thut gii quyt xung t thch h p.4.1.4 Ginh tr c ti nguyn ngay t c th i ho c ginh tr c c tr

Da trn khong th i gian ca qu trnh ginhtr c ti nguyn trn knh,cc k thut bo hiu c thphn loi thnh ginh tr c ti nguyn tc th i hocginh tr c ti nguyn c tr.Trong k thut ginh tr c ti nguyn tc th i,knh s c ginh tr c ngay lp tc khi m tin nhn setup (BHP) n c

node. Theo cch khc, trong mt k thut ginh tr c c tr, knh s c ginhtr c khi m burst d liu thc s c chuyn n node (hoc kt ni). Theocc yu cu ca k thut ginh tr c c tr, tin nhn BHP phi mang theo khongth i gian chnh lch gia bn thn n v burst d kiu tng ng v i n.

Hnh 4.18 C ch ginh tr c v gi i phng trong OBS

V d, k thut bo hiu just-in-time (JIT) s dng k thut ginh tr cngay lp tc, trong khi just-enough-time (JET) hot ng theo nguyn tc ginhtr c c tr.Thng thng, ginh tr c ngay lp tc n gin thc hin,nhng chu nghn nhiu hn do phn bti nguyn khng hiu qu. Mt khc,


42/57


43/57


44/57


44

gian ny ngun v thm th i gian tr vo khong th i gian chnh lch. Qutrnh trny yu cu s dng s i quang trFDL (Fiber delay line ), bao gm ccvng s i quang. Tr truyn dn FDL bng tng th i gian m burst d liu sb tr.

Hnh 4.19 K thu t bo hi u Just-Enough-Time (JET)

JIT tng t nhJET tr vic JIT hot ng theo kiu ginh tr c ngay lptc v gii phng r rng thay v ginh tr c c trv gii phng khng r rng.Hnh 4.4(a) v (b) so snh mt s bo hiu tng ts dng ring JET vJIT. L i ch chnh ca vic s dng cck thut theo kiu mt chiu l gimthiu tr u cui trong truyn dn d liu trn mng ng trc quang.


45/57


45

V i ci gi phi tr l t lmt gi cao do xung t gia cc burst d liuv ti nguyn trong mng li khng c b m.

Hnh 4.20So snh gi a k thu t bo hi u JET (a) v JIT (b)

4.3 K thut Tell-and-Wait (TAW)

Hnh 4.21 K thu t bo hi u Tell-and-Wait (TAW)


46/57


46

Hnh 4.5 minh ha cho k thut bo hiu TAW. Trong TAW, bn tinSETUP c gi dc theo tuyn truyn ca burst thu thp thng tin tnhkh dng ca knh tt c cc node trn ng truyn. pha ch, mt thutton gn cho knh c thc hin, v thi gian ginh tr c mi kt ni

c xc nh da trn th i gian s m nht knh kh dng i v i tt c ccnode trung gian. Mt bn tin xc nhn CONFIRM c gi theo hng ng cli (t ch vngun), tin nhn ny ng k knh truyn trong khong th i gian yu cu cho mi node trung gian. bt k node no dc theo tuyn truyn,nu knh yu cu bchim dng, mt bn tin gii phng RELEASE cgi t ch gii phng cc ngun ti nguyn c t tr c. Nu giCONFIRM n c ngun thnh cng, th burst s c gi vo mng li.

Bn cnh , do TAW tng t nh mng nh tuyn da trn b c sng,knh c th c ng k theo hng i nh l qu trnh ginh tr c kh i to t

ngun (SIR) hoc theo hng ng c li t ch tr li ngung nh trong qutrnh ginh tr c kh i to t ch (DIR). TAW trong OBS khc v i mng nhtuyn theo b c sng WDM v trong TAW, ti nguyn ch c ginh tr c bt c mt node trong th i gian truyn burst .Mt khc, nu chu k ca burstkt thc trong lc ng k, mt c chgii phng khng r rng shot ng ti a hiu nng bang thng.

Tt c cc giao thc c tho lun pha trn u l k thut bo hiu mtchiu ngoi tr TAW, mt k thut bo hiu hai chiu. Nu chng ta so snhTAW v JET, im bt l i ca TAW l thi gian ci t vng, v d nh lth i

gian cn ci t cho knh, tuy nhin mt mt d liu TAW l cc k thp.Th nn TAW ph h p vi lu lng nhy cm v i mt mt.Mt khc, trongJET, t lmt gi cao, tuy nhin tr u cui thp hn so v i TAW. Trong TAW,cn n 3 ln tr truyn dn t ngun ti ch cho burst c th n c ch,trong khi v i JET, th i gian tr ch l tng ca tr truyn dn mt chiu v th igian chnh lch. Khng c k thut bo hiu no cho php s linh hot tr v t lmt gi.

4.4 Bo hi u kh i to t node trung gian (INI)

Nhiu k thut bo hiu c a ra truyn d liu hon ton theo kiuquang trn mng OBS. ph h p v i cc yu cu ginh trc ti nguyn ng truyn d liu, u tin k thut bo hiu phi tm mt tuyn ng t ngunn ch, sau lp lch cho burst trn mt b c sng ring bit mi nodetrung gian.

K thut bo hiu phn tn c nghin cu nhiu nht l Tell-and-wait(TAW) v Just-enough-time (JET). TAW l mt k thut bo hiu hai chiu, da


47/57


47

trn vic c phn hi, s dng thit lp r rng v tin nhn iu khin giiphng kt ni. JET l k thut bo hiu mt chiu khng cn phn hi s dngthit lp kiu c l ng v gii phng mo u burst. nhm trnh s chuyni sang min in li, tt c cc k thut bo hiu u c mt th i gian chnh

lch gia bn tin mo u burst v d liu tng ng. Bn tin BHP cng c th xc nh khong th i gian ca burst cho php mt node bit khi no n cncu hnh li chuyn mch ca n cho burst tip theo, thm vo l cha ngc th i gian chnh lch. Th i gian chnh lch cho php BHP c x l o minode trun gian trc khi burst n cc node trung gian.

Trong mt mng IP trn nn OBS, chng ta mong mun cung cp s h tr QoS cho ccng dng v i cc yu cu QoS ring bit, nh l cho VoIP, Videotheo yu cu VoD, v hi ngh video. Nhiu gii php c a ra h tr QoS trong mng li OBS. Tuy vy khng c mt k thut n lno c th cho

php s linh hot h tr c lung lu l ng nhy cm v i tr cng nh lul ng nhy cm v i mt mt trong cng mt mng OBS. Cng c cc c ch dnh cho QoS, nh l JET v i th i gian chnh lch b sung cho cc l p khcnhau ca lu l ng, tuy nhin n c t l tc nghn cao. Bn cnh , nodengun cn phi tnh ton th i gian chnh lch nhiu ln h tr cho cc yucu khc nhau ca cc gi tin cc l p khc nhau.

Trong mc ny, chng ta s xem xt mt k thut bo hiu lai ghp gi lbo hiu kh i to t node trung gian (INI), v mt s m rng ca k thut bohiu INI cung cp s bo hiu khc nhau da trn cc yu cu ca ng dng

qua k thut bo hiu kh i to t node trung gian phn bit (DINI). K thutDINI mang n s khc nhau m khng cn phi b sung thm th i gian chnhlch.

4.4.1 K thut bo hi u kh i to t node trung gian (INI) c th vt qua c cc gi i hn ca TAW v JET, cc tc gi to

nn k thut bo hiu kh i to t node trung gian.Trong k thut bo hiu INI,mt node gia ngun v ch trn tuyn c la chn nh l node kh i to.Mt node kh i to l mt node trung gian gia ngun v ch m mt

thuth ton ginh tr c knh hot ng xc nh thi im s m nht burstc th c gi t ngun v cc thi im s m nht tng ng m lc ccnode gia ngun v node kh i to c th ln lch nhn burst.node kh i to,qu trnh ginh tr c thc s ca knh bt u trn c hai h ng, t node kh ito n ngun v t node kh i to n ch.Sla chn node kh i to l quytnh trong k thut bo hiu INI.


48/57


48

Hnh 4.6 minh ha cho k thut bo hiu INI. Khi mt burst c to ra node bin, mt bn tin SETUP c gi n ch. Bn tin ny s thu thp chitit vcc knh tt c cc node dc theo tuyn truyn cho n khi n n cnode kh i to. Mt bn tin CONFIRM sau s c gi n node ngun,

bn tin ny ng k tr c cc knh dc theo tuyn truyn t node kh i to nngun. Nu mt knh ang bn bt c node no, mt bn tin RELEASE c gi li cho node kh i to gii phng cc ti nguyn c ginh tr ct trc .Nu gi tin CONFIRM n c ngun, burst s c gi i thi gian c sp lch trc.Node trung gian cng ng th i gi i mt bntin SETUP v pha ch, ng k cc knh truyn gia node trung gian vch. Nu bt k mt node no gia node kh i to v node ch, bn tin nykhng th ng k trc c mt knh no, th burst sb loi b ti node .

Hnh 4.22 K thu t bo hi u kh i t o t node trung gian (INI)


49/57


50/57


50

node 7 nhn burst ang n thi im tng ng. Bn tin BHP gi t nodekh i to ch t tr c cc knh truyn c th c v ch thc hin hng i t node kh i to n ch.

Hnh 4.23 Topo m ng ng tr c gm 14 i m (kho ng cch tnh b ng km)

4.4.2 K thut bo hi u kh i to t node trung gian phn bi tK thut bo hiu INI c th c m rng cung cp QoS l p quang.

C th thc hin nhiu k thut bo hiu trong cng mt mng cung cp ccdch v phn bit, cho php h tr c cc lung lu l ng nhy cm v i mt mtcng nh v i tr, v d ta c th dng TAW cho lu l ng nhy cm v i mtmt, v JET cho lu l ng nhy cm v i tr. Gii php v i mng li c hai k thut bo hiu khc bit ch c th cung cp s bo m QoS mc thp. cung cp cc cp tt hn v i s khc bit vQoS, chng ta cn thay i m

hnh INI.S dng INI, ta c th bo m c yu cu v t lmt gi v tr ca mi

ng dng ring bit bng cch chn mt cch cn thn node kh i to. Ni chung,v i ccng dng yu cu cao v tr ta th ng chn node kh i to gn v inode ngun, nh thtr truyn dn u cui s nh hn so v i yu cu ca ngdng. V i ccng dng c yu cu vmt mt, chng ta chn node kh i to gnvi node ch, chc chn rng trn hu ht tuyn truyn u c s xc nhn 2chiu.

Gi s, chng ta phi h tr ba lp lu l ng khc nhau, gi l P0, P1 vP2, v i P0 nhy cm v i tr, P1 nhy cm v i c tr ln mt mt, v P2 nhycm v i mt mt. Chng ta c th s dng node ngun lm node kh i to choP0, node gia lm node kh i to cho P1, v node ch lm node kh i to cho P2,qua cung cp cc dch vkhc bit trm cng mt mng OBS.


51/57


51

4.5 M hnh phn tch tr Trong mc ny, chng ta s tho lun vmt m hnh phn tch cho php

c lng c tnh tr ca mi k thut bo hiu OBS. Chng ta gi thit rngtuyn c nh ngn nht, Rsd , c tnh ton v i mi cp ngun-ch ring;

khng c b m quang hay b chuyn i b c sng cc node mng li.Khng mt tnh tng qut, ta xem xt mt mng quang v i mt b c sng trnmi s i quang. M hnh ny c th c m rng bng cch tngs b c sngtrn mt s i quang. Do khng c b chuyn i b c sng, nhiu sng mangtrn mi mt s i quang c th coi nh l nhiu l p ca mng, v i mt l p chomi b c sng. Chng ta cn phi so snh tr u cui ca cc k thut bo hiu, l JET. TAW v INI.Chng ta bt u bng cch nh ngha cc gi trsau:

t bhp : trx l gi mo u burst mi node OBS. Chng ta gi s rng tr truyn dn ca cc bn tin bo hiu khc nhau, nh l SETUP, RELEASE,

v CONFIRM, tt c cc node u c xc nh.t sw: th i gian chuyn mch yu cu ti cu hnh cc kt ni cho quang

mi node OBS.t agg : tr tp hp burst, do k thut sp xp hot ng node OBS u vo.t b : th i gian truyn dn burst d liu.t ot : th i gian chnh lch, th i gian kh i to c nh gia tin nhn mo u

burst ngoi bang v burst d liu node u vo.t ij p: th i gian tr truyn dn trn s i quang gia nodei v node j.Gi tr c th ca t ij pl 5 s/km,t bhp c gi tr vi trm ns, vt sw vo

khong vis. u tin chng ta tnh tontr gi trung bnh u cui, T SIG , to ra b i mi

k thut bo hiu. T SIG l khong th i gian t lc gi tin u tin n node uvo cho n lc burst n c ch thnh cng. Xem xt mt tuyn truyn v i nhop n ch.

(a) Just-Enough-Time (JET) ho c Just-In-Time (JIT):Trong k thut Just-Enough-Time (JET) hoc Just-In-Time (JIT), tr u

cui c tnh bng tng ca th i gian tp h p burst, th i gian chnh lch, th igian truyn dn burst, v th i gian lan truyn burst d liu.

T JET = T JIT = t agg + t ot + t b +ij

ijp

sd

n

l R

t

V i,t ot = n t bhp + t sw

Nu ta xem xt n k thut Tell-and-Go (TAG), c mt s khc bit thng s tr, th i gian chnh lch, t ot = 0, v th i gian trb b sung mi hop


52/57


52

FDL,t fdl tng ng v i t bhp + t sw, c to ra bi cc FDL u vo tt c ccknh d liu mi node, b cho trx l mo u iu khin v th i gian tr chuyn mch.

T TAG = t agg + nt fdl + t b + ijij

psd

n

l R

t

(b) Tell-and-Wait (TAW):Trong Tell-and-Wait (TAW), tr u cui c tnh bng tng th i gian

tp h p burst, th i gian thit lp kt ni trn vng, th i gian truyn dn burst, vth i gian lan truyn burst. Th i gin chnh lch b sung l cn thit, nu tngca th i gian x l mo u burst trn mi hop tt c cc node trung gian cngthem th i gian cu hnh li cho chuyn mch ln hn so v i th i gian thit lp

kt ni vng. V th,T TAW = t agg + 3

ij

ijp

sd

n

l R

t + t b+ t ot

V,

t ot = 0nu2ij

ijp

sd

n

l R

t (n + 2 ) t bhp + t sw

(c) Bo hi u kh i to t node trung gian (INI):

Trong INI, tr u cui c tnh bng s kt h p th i gian tr c tnh hai phng php TAW v JET. Tr u cui trong INI cng phthuc vo v tr ca node kh i to, k , th i gian tp h p burst, th i gian truyn dn burst, v th igian lan truyn burst d liu. t l l scc hop gia ngun v node kh i to, vm l shop gia node kh i to v node ch.

T INI = t agg + 2 ijij

sk

n

pl R

t +ij

ijp

sd

n

l R

t + t b+ t ot

Trong ,

t ot = 0 nu ijij

w2sk

n p bhp sl R

sum t mt t v


53/57


54/57


54

Burst d liu s khng truyn trn mng cho n khi ti nguyn gia nodengun v node kh i to c ng k xong.

Hnh 4.24 (a) T l m t gi so v i ti

(b) Tr trung bnh u cu i so v i t i (t rong node kh i t o lngun,node u tin, node th hai, node th ba v ch)

K thut bo hiu INI mang n s linh hot cho vic ginh tr c knhtruyn da trn loi d liu c truyn.T l mt gi ca INI thp hnso v i


55/57


55

JET v tr u cui thp hn so vi TAW. Nh vy, k thut lai INI l mt giiphp linh hot cho php gii quyt nhiu yu cu khc nhau v lu l ng trongmng quang thh tip theo.

Hnh 4.25 (a) T l m t gi so v i ti

(c) Tr trung bnh u cu i so v i t i (trong node kh i t o lngun, node trung gian v ch trong cng mt mng cung c p s khc

bit qua bo hi u)


56/57


56

Kt Lu n

Qua bo co chuyn ny, chng ta c th thy c mt cch tng qutv cng ngh chuyn mch gi quang OBS. Ta c th thy c s u vit cacng ngh OBS trong truyn thng quang hin nay so v i cng ngh chuynmch gi quang (OPS) v chuyn mch knh quang. Cng ngh chuyn mchgi quang gp vn v kh nng x l tiu in hin nay cha p ng kptc truyn dn ca ng quang, ng th i cc cng nghb m trong minquang cng cn kh trin khai, nn kh nng trin khai OPS cha phi l ti u.Trong khi cng nghchuyn mch knh quang th vn mc phi nhc imchu ca chuyn mch knh l khng sdng hiu qu ti nguyn. l ldo cng ngh OBS c quan tm nghin cu nhiu. Trong chuyn ny,nhm chng em ch cp n mt skha cnh ca OBS.

Chng thnht gi i thiu mt cch tng qut nht v OBS trong khi chng thhai trnh by v k thut v kin trc ca OBS. Chng thba ni v qu trnh sp xp gi tin vo burst quang da trn nh th i v da trnng ng.Chng th t nu ln cc gii php bo hiu trong OBS v i mt s cc cngngh tiu biu nh Just-Enough-Time (JET), Tell-And-Wait (TAW) hay

Intermediate-Node-Inititation (INI).Do thi gian cng nh hiu bit c hn, c kh nhiu vn cha c a

vo bo co chuyn ny nh vn gii quyt xung t, lp lch cho bursthay vn vQoS. Hi vng chng em c th tm hiu thm vnhng vn nytrong th i gian t i.

Mt ln na chng em xin chn thnh cm nthy Hong Trng Minh h ng dn chng em hon thnh bo co chuyn ny.

Nhm sinh vin D08VT1


57/57


Ti li u tham kh o

[1] JASON P. JUE, VINOD M. VOKKARANE OPTICAL BURSTSWITCHED NETWORKS, 2005

[2] Internet

OBS Official

Documents

Transcript of OBS Official