Chuyển mạch burst quang - Nhóm 10- Hưng-Giang-Hoàn

8/3/2019 Chuyn mch burst quang - Nhm 10- Hng-Giang-Hon

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Chuyn thng tin quang CHUYN MCH BURST QUANG

MC LC

MC LC .................................................................................................................1DANH MC THUT NG V T VIT TT .....................................................3

DANH MC HNH V ............................................................................................4

LI M U ...........................................................................................................5

Chng 1: .................................................................................................................7

Gii thiu v chuyn mch burst quang .....................................................................7

1.1 Chuyn mch knh quang ....................................................................................7

1.2 Chuyn mch gi quang ......................................................................................8

1.3 Chuyn mch burst quang .................................................................................10

1.4 So snh cc cng ngh chuyn mch quang ......................................................11

Chng 2 : ..............................................................................................................12

Cc kha cnh c bn ca chuyn mch burst quang ...............................................13

2.1 Kin trc mng OBS ..........................................................................................13

2.1.1 Cu to nt bin ...........................................................................................14

2.1.2 Cu to nt li .............................................................................................15

2.2 T hp burst ......................................................................................................172.2.1 T hp burst da trn b nh thi ...............................................................17

2.2.2 T hp burst da trn mc ngng ..............................................................18

2.3 Cc c ch bo hiu ...........................................................................................19

2.3.1 C ch bo hiu Just Enough Time (JET) ..............................................20

2.3.2 C ch bo hiu Just In Time (JIT) ........................................................23

2.3.3 C ch bo hiu Tell And Go (TAG) .....................................................25

2.3.4 C ch bo hiu Tell And Wait (TAW) ..................................................26

2.4 Cc thut ton sp xp knh ..............................................................................272.4.1 Knh ri ph hp u tin (FFUC) ...............................................................28

2.4.2 Knh ri vi LAUT gn nht (LAUC) .........................................................29

2.4.3 Knh ri ph hp u tin thc hin lp khong trng (FFUC-VF) ..........30

2.4.4 Knh ri vi LAUT gn nht - thc hin lp khong trng (LAUC-VF) . .31

2.4.5 Khong trng kt thc ti thiu (Min-EV) ...................................................31

2.5 Phn gii tranh chp ..........................................................................................31

2.5.1 B m quang ..............................................................................................31

2.5.2 Chuyn i bc sng ..................................................................................33

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2.5.3 nh tuyn chuyn hng ............................................................................34

2.5.3.1 Gii thiu .................................................................................................34

2.5.3.2 Phng php nh tuyn chuyn hng ....................................................35

2.5.4 Phn on burst ............................................................................................36

KT LUN .............................................................................................................40

TI LIU THAM KHO .......................................................................................42

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DANH MC THUT NG V T VIT TT

Vit tt Ting Anh Ting Vit

ACK Acknowledgement packet Gi tin bo nhn

BA Burst Assembler B t hp burst

ATM Asynchronous Transfer Mode Ch truyn ti khng ng b

BHP Burst Header Packet Gi tiu burst

FDL Fiber Delay Line ng dy tr quang

FFUC First Fit Unscheduled Channel Knh ri ph hp u tin

FFUC-VF First Fit Unscheduled Channel-

Void Filling

Knh ri ph hp u tin-thc

hin lp khong trng

FIFO First In First Out B m vo trc ra trc

IP Internet Protocol Giao thc Internet

JET Just Enough Time (Tn giao thc)

JIT Just In Time (Tn giao thc)

LAUC Latest Available Unscheduled

Channel

Knh ri vi LAUT gn nht

LAUC- VF Latest Available Unscheduled

Channel Void Filling

Knh ri vi LAUT gn nht-thc

hin lp khong trng

MEMS Microelectromechanical System H thng vi c in

Min EV Minimum End Void Khong trng kt thc ti thiu

NAK Negative Acknowledgment Bn tin bo nhn ph nh

OBS Optical Burst Switching Chuyn mch burst quang

OCS Optical Circuit Switching Chuyn mch knh quang

OPS Optical Packet Switching Chuyn mch gi quang

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OXC Optical Cross Connect Thit b ni cho quang

REL Release packet Gi tin gii phng knh

RM Routing Module B nh tuyn

RWA Routing and Wavelength

Assignment

nh tuyn v gn bc sng

S Scheduler B lp lch

SCU Switching Control Unit n v iu khin chuyn mch

SONET Synchronous Optical Network Mng quang ng b

TAG Tell And Go (Tn giao thc)TAW Tell And Wait (Tn giao thc)

WDM Wavelength Division Multiplexing Ghp knh phn chia bc sng

DANH MC HNH V

Hnh 1.1: Mng nh tuyn bc sng......................................................................8

Hnh 1.2: Mng chuyn mch gi quang OPS...........................................................9

Hnh 1.3: Nt chuyn mch trong mng chuyn mch gi quang...........................10Hnh 1.4: S dng thi gian offset trong OBS.........................................................10

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Hnh 2.1: Kin trc mng OBS................................................................................13

Hnh 2.2: S khi chc nng ca mng OBS.....................................................14

Hnh 2.3: Cu to nt bin.......................................................................................15

Hnh 2.4: Cu to nt li.........................................................................................16

Hnh 2.5: T hp burst da trn b nh thi..........................................................18

Hnh 2.6: T hp burst da trn mc ngng.........................................................18

Hnh 2.7: C ch bo hiu Just Enough Time....................................................21

Hnh 2.8: Li ch ca DR........................................................................................23

Hnh 2.9: C ch bo hiu Just In Time.............................................................24

Hnh 2.10: So snh c ch bo hiu JET (trn) v JIT (di)..................................24

Hnh 2.11: C ch bo hiu Tell-And-Go................................................................26

Hnh 2.12: C ch bo hiu Tell And Wait.......................................................27Hnh 2.13: Thut ton FFUC v LAUC...................................................................29

Hnh 2.14: Thut ton FFUC-VF v LAUC-VF......................................................30

Hnh 2.15: M t gii quyt xung t bng b m.................................................32

Hnh 2.16: Dy tr FDL cng vi b khuch i v chuyn mch to thnh mt

vng lp tr..............................................................................................................32

Hnh 2.17: Gii quyt tranh chp bng b chuyn i bc sng...........................33

Hnh 2.18: Cu trc ca mng OBS vi k thut lm lch hng i.......................35

Hnh 2.19: Phng php nh tuyn chuyn hng.................................................36Hnh 2.20: M t gii quyt xung t bng phn on burst...................................37

Hnh 2.21: Cu trc ca burst c ng kiu phn on.......................................38

Hnh 2.22: Xung t lm chng ln cc on ln nhau...........................................39

LI M U

Nhng nm gn y din ra s bng n lu lng thng tin trn ton cu. Yu

cu v bng thng i vi cc dch v vin thng ngy cng gia tng. Mt trong

nhng xu hng pht trin ca mng vin thng hin nay l quang ha t mng li

cho n tn mng truy nhp ca khch hng. Cng ngh ghp knh phn chia theo

bc sng WDM v ang c trin khai trong cc h thng thng tin quang

hin ti cho php tc truyn dn cc ln v kh nng h tr cc lu lng khcnhau nh IP, Ethernet, SONET/SDH. Mt vn t ra cho mng quang WDM l

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la chn c cng ngh chuyn mch thch hp c th s dng mt cch ti u

bng thng ca si quang v gim thiu tr x l ti cc thit b chuyn mch. Ba

cng ngh chuyn mch quang c nghin cu s dng trong mng WDM l:

chuyn mch knh quang, chuyn mch gi quang v chuyn mch burst quang.

Trong ba cng ngh ny, chuyn mch burst quang ra i nhm p ng s bng n

d liu, gii quyt c nhc im ca chuyn mch knh quang v l bc trung

gian trc khi tin ti chuyn mch gi quang trong khi cng ngh cha cho php

c mng truyn ti ton quang. Xut pht t thc t trn nhm chng em chn

hng nghin cu v chuyn mch burst quang. Chuyn Chuyn mch burst

quang trnh by nhng vn c bn nht v chuyn mch burst quang. Ni dung

chuyn bao gm:

Chng 1: Gii thiu v chuyn mch burst quang. Chng ny s gii thiuv cc cng ngh chuyn mch quang chnh l chuyn mch knh quang, chuyn

mch burst quang v chuyn mch gi quang.

Chng 2: Cc kha cnh c bn ca chuyn mch burst quang. Ni dung

chng 2 gm c:

+Kin trc mng OBS

+T hp burst: theo ngng v da trn b nh thi

+Cc c ch bo hiu: JET,JIT,TAG,TAW

+Cc thut ton sp xp knh: vi thut ton hng ngang (Hoziron) v lp

khong trng (Void Filling)

+Cc gii php gii quyt tranh chp: b m quang, chuyn i bc sng ,

nh tuyn chuyn hng, phn on burst.

Do gii hn v mt thi gian v kin thc nn chuyn khng trnh khi thiu

st. Rt mong nhn c nhng ng gp t thy c v cc bn chuyn canhm c hon thin hn.

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Chng 1:Gii thiu v chuyn mch burst quang

Ni dung chnh ca chng s cp n ba loi chuyn mch quang chnh l :

chuyn mch knh quang, chuyn mch gi quang v chuyn mch burst quang.

1.1 Chuyn mch knh quang

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Mng WDM nh tuyn bc sng bao gm cc thit b ni cho quang OXC

(Optical Cross Connect) c kt ni vi nhau bng cc lin kt WDM trong mt

tp mng hnh li ty . Phng php chuyn mch trong mng nh tuyn bc

sng l chuyn mch knh quang. Chuyn mch knh quang l chuyn mch hng

kt ni (connection oriented). Kt ni t mt nt ngun gi thng tin n mt nt

ch nhn thng tin phi c thit lp trc khi thng tin c truyn i. Trong

mng nh tuyn bc sng th kt ni t ngun ti ch ny c gi l ng

quang (lightpath). ng quang tng ng vi mt tuyn v bc sng c gn

cho tuyn . S thit lp cc ng quang bao gm mt s bc thc hin. Nhng

bc ny bao gm tm ra ti nguyn v tp mng, nh tuyn, gn bc sng, bo

hiu v d tr ti nguyn.

Hnh 1.1: Mng nh tuyn bc sng

1.2 Chuyn mch gi quang

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Hnh 1.2: Mng chuyn mch gi quang OPS

Mng chuyn mch gi quang OPS bao gm cc OXC c ni vi nhau bng

cc lin kt WDM trong mt cu hnh mesh ty . Mng chuyn mch gi quang

bao gm phn li c kh nng truyn ti tc cao v phn bin giao din vi phn

t ca cc mng IP, SONET/SDH, Ethernet.

Cc gi tin truyn trong mng chuyn mch gi quang c phn tiu v phn

ti tin. Tiu c cha thng tin nh tuyn cng nh thng tin iu khin v c

truyn trong bng cng vi ti tin. Khi gi tin truyn ti OXC, tiu s c tch

ra v c x l trong min in (sau khi bin i quang in quang) cn ti tin

s c chuyn mch trong min quang. V phn tiu cn mt thi gian x l

nn phn ti tin c lm tr i bng cch lu m bi ng dy tr quang. Vnguyn l, chuyn mch gi quang mong mun truyn thng tin v x l thng tin

iu khin hon ton trong min quang. Nhng do hn ch v mt cng ngh hin

nay nn phn thng tin iu khin ch c th x l trong min in m thi. Trong

chuyn mch gi quang, tiu c so snh vi mt bng nh tuyn, ti tin s

c chuyn ra cng u ra tng ng trn mt si quang v mt bc sng mi.

Nu khng c bc sng mi no kh dng, gi tin s b hy hoc phi b tr i

ch bc sng kh dng mi.

Thnh phn chnh ca nt OXC l c cu chuyn mch quang v khi iu khin

chuyn mch. Khi iu khin chuyn mch duy tr thng tin v t p mng, duy tr

bng nh tuyn, x l tiu gi tin, iu khin vic lu m, lp lch v chuyn

tip cc gi tin, iu khin c cu chuyn mch chuyn mch gi tin ng thi gian

nh, pht hin tranh chp v phn gii khi tranh chp xy ra gia cc gi tin. C

cu chuyn mch thc hin to kt ni t cng u vo n cng u ra tng ng

theo yu cu ca khi iu khin chuyn mch.

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Hnh 1.3: Nt chuyn mch trong mng chuyn mch gi quang

1.3 Chuyn mch burst quangChuyn mch burst quang ra i nhm t c s cn bng gia chuyn mch

knh quang v chuyn mch gi quang. Cc gi tin lp trn s c tp hp li

thnh cc burst truyn ti trong mng OBS . Cc burst c di khng c nh

gm c hai phn: gi tin iu khin (control packet) hay cn c gi l gi tiu

burst Burst Header Packet (BHP) v phn thng tin d liu cn c gi l data

burst. OBS thc hin vic truyn c lp gi tin iu khin v burst d liu trn

cc knh bc sng khc nhau. Thng tin trong gi tin iu khin gm c chiu diburst, thi im pht burst, cc thng tin nh tuyn. Gi tin iu khin c truyn

i trc burst d liu mt khong thi gian c gi l offset time cu hnh cc

chuyn mch trong sut ng i t ngun ti ch. Thi gian offset time ny bng

tr x l tng cng ca gi tin iu khin ti tt c cc nt trung gian.

Hnh 1.4: S dng thi gian offset trong OBS

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y l mt trong nhng khc bit c bn gia chuyn mch burst quang so vi

chuyn mch gi quang. Khong thi gian ny cho php thng tin iu khin c

x l ti mi nt chuyn mch v cc nt sp xp ti nguyn knh bc sng cho

vic truyn burst d liu da trn thng tin trong gi tin iu khin. Vi OBS khng

yu cu phi x l gi tin iu khin trong min quang. OBS s dng cc m hnh

d tr knh v bo hiu d tr ti nguyn knh bc sng.

1.4 So snh cc cng ngh chuyn mch quang

Nh nu trn, ta c th thy chuyn mch knh quang ch chuyn mch cho

mt bc sng trn mt ng quang nn khng cn thch hp cho mng WDM

hin nay. Nhng n cng c nhng u im ring ca n, ni bt nht l tin

cy. Bn cnh nhc im chnh l tr ln v lng ph bng thng.

Chuyn mch gi quang l loi chuyn mch hng ti trong mng ton quang

vi tc x l nhanh nht trong cc loi nu. Nhng gii hn ca n l ch

s hn ch v cng ngh hin ti khng p ng c cc yu cu cho mt mng

ton quang.

Trong khi lu lng cng ngy cng bng n. Ta c th thy chuyn mch

burst quang p ng c s bng n nh th no. Vi vic t hp cc gi cng

ch n dng chung mt gi iu khin lm gim thiu ti a vic x l thng tin

iu khin. Cc burst d liu hon ton truyn i trn min quang. V tc v kh

nng s dng bng tn hn hn chuyn mch knh quang. Trong thi im hin ti

vi cng ngh nh hin nay th chuyn mch tng gi mt vi vic x l tng y

tiu trong chuyn mch gi quang s khng th p ng c lu lng nh

chuyn mch burst quang. Tuy nhin, ci g cng c hai mt ca n, chuyn mch

burst quang p ng c yu cu v bng n lu lng nhng n vn cha phi l

chuyn mch ton quang, tr t hp burst, vic thay th thit b hay ch l cn thay

th module. l vn trade off trong vin thng.

Nhm 10 H09VT7 11


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Cng ngh

chuyn mch

quang

Hiu qu s

dng bng

thng

Thi gian

chuyn mch

yu cu

X l headerKh nng thch

ng lu lng

Chuyn mchknh quang

Thp Chm Thp Thp

Chuyn mch

gi quangCao Nhanh Cao Cao

Chuyn mch

burst quangCao Trung bnh Thp Cao

Bng 1.1 So snh cc cng ngh chuyn mch quang khc nhau

Chng 2 :

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Cc kha cnh c bn ca chuyn mch burst

quang

2.1 Kin trc mng OBSNh cp chng 1, tng ca chuyn mch burst quang l phn chia

mt bng d liu v mt bng iu khin v thc hin bo hiu ngoi bng cho

php truyn ti d liu trong min quang mt cch hiu qu hn. n v d liu

truyn ti trong mng OBS l cc burst gm c gi tin iu khin v burst d liu.

Mng OBS thc hin vic bo hiu ngoi bng: gi tin iu khin c truyn trn

mt knh bc sng khc vi burst d liu cu hnh cc chuyn mch t ngun

ti ch. Gi tin iu khin mang thng tin v chiu di burst, thi im bursttruyn cng nh cc thng tin nh tuyn khc. Mt khi ti nguyn c d tr

cc burst s c pht i. lm c iu ngi ta xut xy dng mt

mng OBS vi kin trc nh hnh 2.1

Hnh 2.1: Kin trc mng OBS

Mng OBS v bn cht l mt mng WDM trn n thc hin cng ngh

chuyn mch OBS. Mng OBS bao gm cc nt bin (edge node) v cc nt li

(core node) c kt ni vi nhau bng cc lin kt WDM.

Nt bin mng OBS thc hin giao din vi mng khc nh mng IP,

SONET/SDH hay Ethernet. Nt bin v th c kh nng giao tip c trong min

in v min quang v c kh nng bin i in quang cng nh chuyn i bcsng tng thch vi tn hiu truyn trn cc lin kt quang WDM. Nt bin trn

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c s truyn ti burst c th phn thnh nt bin u vo v nt bin u ra. Nt

u vo pha pht vo thc hin t hp cc gi tin t cc u cui thnh cc burst

v to cc gi tin iu khin, nh tuyn v sp xp bc sng truyn cc burst

d liu vo mng li OBS. Nt u ra pha thu thc hin gii t hp cc burst

thnh cc gi tin v gi ti cc mng ch. Nu mt nt bin thc hin thng tin hai

chiu th n s ng vai tr va l nt u vo va l nt u ra.

Nt li c nhim v c bn l chuyn tip burst t cc cng u vo ti cc

cng u ra tng ng, d tr cc knh bc sng cho cc burst d liu da trn

thng tin trong cc gi tin iu khin v gii quyt tranh chp. Hnh 2.2 m t cc

thnh phn ca mng OBS vi cc chc nng khc nhau.

nh tuyn

T hp Burst

Lp lch v spxp bc sng

Bo hiu

Lp lch

Gii quyttranh chp

Gii t hpBurst

Chuyn tipgi

Lu lng raLu lng vo

Nt bin u vo Node li Node bin u ra

Hnh 2.2: S khi chc nng ca mng OBS

2.1.1 Cu to nt bin

Cc nt bin l cc router bin c kh nng giao din in v quang, thc hin

chc nng phn loi gi tin, lu m cc gi tin, t hp cc gi tin thnh cc burst

v gii t hp burst thnh cc gi tin cu thnh. Cc phng php t hp burst khc

nhau nh da trn thi gian ca b nh thi hoc da trn kch thc cc gi tin c

th c s dng t hp cc gi tin d liu thnh cc burst v gi vo trong

mng li OBS. Cu to ca mt router bin bao gm mt b nh tuyn RM

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(Routing Module), cc b t hp burst BA (Burst Assembler) v cc b lp lch

knh S (Scheduler).

B nhtuyn

Lp l chknh

C l a s s0

C l a s s m

C l a s s0

C l a s s m

L ulngv o

L ulng

rat i

nodel i

n node b in1

n node b in N

T h p burst N

T hp bu r s t1

Lp l chknh

Hnh 2.3: Cu to nt bin

B nh tuyn kim tra thng tin nh tuyn ca tng gi tin, chn la cc cng

ra thch hp cho tng gi tin v gi n n b t hp burst thch hp. Mi b t

hp burst to ra cc burst cha cc gi d liu n cng mt ch ti (cng mtrouter bin u ra). Trong mi b t hp burst cn c hng i khc nhau cho cc

loi gi tin ng vi cc dch v khc nhau. B lp lch knh d tr knh bc sng

cho cc burst d liu v chuyn cc burst d liu ti cc cng u ra tng ng.

nt bin u ra, b gii t hp burst s tin hnh tch cc gi tin t cc burst ny v

chuyn tip ln cc lp trn.

2.1.2 Cu to nt li

Nt li gm c OXC v mt n v iu khin chuyn mch SCU (SwitchingControl Unit), cc b chuyn i quang in quang, cc b ghp knh, phn

knh. Ta xt hai phn t chnh l OXC v SCU. SCU to v duy tr mt bng

chuyn tip v chu trch nhim cu hnh cho OXC. Khi gi tin iu khin ti nt

li n s c bin i t min quang vo min in v i n SCU. SCU c

thng tin trong gi xc nh ch n ca gi ny v burst d liu theo sau, k tra

cu thng tin trong bng chuyn tip a n quyt nh chuyn tip d liu n

cng ra no ca OXC. ng thi SCU cng chu trch nhim d tr knh bc

sng cho burst d liu u ra. Gi tin iu khin sau s c cp nht thmthng tin iu khin nu nh nt hin ti cha phi l ch cui cng ca n v

Nhm 10 H09VT7 15


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c bin i in quang v truyn ra knh bc sng u ra tng ng. Trc khi

burst d liu i n router li, SCU s iu khin OXC thit lp kt ni t cng u

vo n u ra tng ng cho burst d liu . Ti nt li c nhiu kch bn c th

xy ra. Nu gi tin iu khin khng thnh cng trong vic d tr ti nguyn cho

burst d liu th c gi tin iu khin v burst d liu s b hy b. Hoc khi cc

burst d liu ti cc u vo cng mun n mt cng u ra ca OXC, khi

tranh chp s xy ra v SCU s c nhim v pht hin v gii quyt tranh chp ny

theo cc chnh sch gii quyt tranh chp m mng s dng. C hai phng php

gii quyt tranh chp m phn 2.5 ca chuyn cp n l s dng cc ng

dy tr quang v chuyn i bc sng. thc hin c cc phng php ny

i hi nt li mng OBS phi trang b thm ng dy tr quang v cc b chuyn

i bc sng.

Hnh 2.4: Cu to nt liTa c th thy cc gi tin khi i vo cc node bin s c nh tuyn chuyn

ri mi chuyn n cc b t hp v sau c lp lch v sp xp trn bc sng

u ra tng ng. Ti cc node li s ch c trch nhim chuyn tip gi tin i nh

x l cc thng tin bo hiu v lp lch. Ti node bin u ra s burst s c gii t

hp v phn phi n a ch.Trong mng OBS x dng cc giao thc nh tuyn

OSPF v GMPLS. C th thy tuyn c la chn ti node bin, cc node ch

ch vic chuyn tip. Nu i thm v cc giao thc trn th chuyn s qu di v

khng tp trung vo c im ring chnh ca OBS nn nhm s khng trnh by c

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th v cc giao thc nh tuyn trn. Mc tip theo s cp n qu trnh t hp

burst l mt trong nhng c im ni bt ca OBS.

2.2 T hp burst

T hp burst l tin trnh tp hp v ng cc gi router nt bin u vo tcc lp cao hn thnh cc burst truyn ti vo mng OBS. Khi cc gi tin i n

t lp cao hn, chng c lu m trong cc b nh m in v c phn loi

theo a ch v loi dch v. Vic t hp burst s quyt nh khi no to ra mt burst

v gi burst vo mng OBS. Hai phng php t hp burst ph bin nht l t

hp burst da trn b nh thi v t hp burst da trn mc ngng.

2.2.1 T hp burst da trn b nh thi

Nh trnh by trong phn 2.1.1, cc router bin c cu to gm c b nhtuyn, cc b t hp burst v cc b lp lch knh. Khi cc gi tin n router bin,

b nh tuyn s cn c vo a ch ch ca cc gi tin chuyn cc gi tin ny

n b t hp burst thch hp. Cc gi tin ny s c lu m tm thi trong cc

hng i khc nhau nm trong b t hp burst. Trong phng php t hp burst da

trn b nh thi, mi b t hp burt s tham chiu thi gian ca mt b nh thi

cc b nm trn mt hng i quyt nh vic t hp cc gi tin thnh cc burst.

Thi im b nh thi bt u m thi gian c th l ngay sau khi mt burst trc

c lp lch truyn i hoc ngay sau khi gi tin u tin n hng i sau

khi hng i trng. Sau mt khong thi gian Tc cu hnh t trc, cc gi tin

trong hng i s c t hp thnh mt burst v lp lch truyn i. Phng

php t hp burst ny s to ra cc burst c chiu di ngu nhin. Lu lng vo

mng thay i phn ln s quyt nh chiu di ca burst. Lu lng vo mng ln,

burst s c kch thc ln, lu lng vo mng nh, burst s c kch thc nh.

Tuy nhin, thi gian ca b nh thi cng l mt nhn t quyt nh kch thc cc

burst.

T T TTh i gian

L1 L2 L3

Nhm 10 H09VT7 17


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Hnh 2.5: T hp burst da trn b nh thi

2.2.2 T hp burst da trn mc ngng

Trong phng php t hp burst da trn mc ngng, s lng cc burst b

gii hn hay chiu di ca cc burst l bng nhau. C th l khi khi kch thc cacc gi tin trong hng i t n mt gi tr ngng L, cc gi tin c t hp

thnh burst v lp lch truyn i. Phng php t hp burst ny khng m bo

v thi gian tr t hp burst.

X1 X2 X3Thi gian

L L L

Hnh 2.6: T hp burst da trn mc ngng

Mt vn t ra cho vic t hp burst l lm sao tm ra gi tr ca b nh thi

v kch thc ngng ti thiu ha xc sut mt gi trong mng OBS. Nu nh

mc ngng qu thp dn n kch thc burst nh, s lng burst truyn trong

mng s nhiu dn n xc sut xy ra xung t cc router li cao, nhng s

lng gi trung bnh b mt do xung t li nh. Tuy nhin, s lng burst nhiu slm tng p lc ln mt bng iu khin do phi x l nhiu cc gi tin iu khin

ca mi burst d liu. Nu thi gian cu hnh cho mi nt chuyn mch khng c

b qua, cc burst ngn s khin cho vic s dng ti nguyn mt cch km hiu qu

do phi mt nhiu thi gian chuyn mch. Ngc li, khi mc ngng ln dn n

kch thc burt ln, s lng burst vo mng s nh, do xc sut xy ra xung t

s nh nhng s lng gi trung bnh b mt do xung t s ln.

V th, cn c mt s cn bng gia s lng xung t v s lng gi mt

trung bnh ti mi ln xung t. Do , hot ng ca mng OBS s c ci thin

khi cc gi n c t hp thnh burst vi mt kch thc ti u. Tng t,

phng php t hp burst da trn b nh thi cng cn gi tr ti u v mt thi

gian.

Vic la chn phng php t hp burst ty thuc vo loi lu lng c

truyn i. Phng php t hp burst da trn b nh thi thch hp vi cc lu

lng b gii hn v mt thi gian nh cc dch v thi gian thc nh thoi, truyn

ti video v thi gian tr t hp burst b gii hn. Nu khng c gii hn v tr,phng php t hp burst da trn mc ngng ph hp cho cc dch v khng yu

Nhm 10 H09VT7 18


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cu thi gian thc nh truyn s liu, v cho php iu khin c s lng gi b

mt trong mi ln xung t.

Vic s dng c hai loi phng php da trn b nh thi v da trn mc

ngng l la chn tt nht v vic t hp burst s linh hot hn l ch dng mttrong hai phng php k trn. Bng cch tnh ton gi tr mc ngng ti u v s

dng gi tr ca b nh thi da trn tr gi cho php, ta c th chc rng s

lng mt gi l nh nht trong khi vn m bo tr cho php.

Sau khi mt burst c to ra s dng cc phng php c ni trn, burt

c lu m trong hng i trong mt khong thi gian trc khi truyn i sao

cho gi tin iu khin ca burst c thi gian d tr ti nguyn. Trong thi

gian ny, cc gi tin khc c th tip tc n router nt bin. Vic thm cc gi tin

ny vo burst l khng chp nhn c v ti nguyn cho burst lc u c d tr

cn c vo chiu di ca burst c trong gi tin iu khin. cc gi tin ny cho

cc burst ng sau c kh nng tng tr trung bnh trong trng hp lu lng

ln. Trong [4], theo Yang Chen, Chunming Quiao v Xiang Yu, mt cch gim

thiu tr l thc hin d on chiu di burst: Gi tin iu khin s mang thng tin

v chiu di burst l L + f(t) thay v l L vi L l chiu di chnh xc ca burst khi

gi tin iu khin c gi i, f(t) l chiu di d on ca cc gi tin i n trong

khong thi gian offset v c tnh ton da trn tc trung bnh ca lu lngti. Gi s chiu di thc s ca cc gi tin i n l l(t). Nu f(t) > l(t), chiu di

ca burst khi truyn vo nt li l L + l(t), ti nguyn d tr cho burst s b lng

ph. Nu f(t) < l(t), chiu di ca burst khi truyn vo nt li l L + f(t). Mt phn

gi tin c chiu di l(t) f(t) s c ghp vo truyn trn cc burst pha sau.

Nu f(t) = l(t) l trng hp l tng nht khi vic d tr ti nguyn cho burst s

l ti u v khng tng tr.

2.3 Cc c ch bo hiu

Khi burst c truyn vo mng li OBS, mt c ch bo hiu phi c thc

hin nhm mc ch phn b ti nguyn v cu hnh trng chuyn mch cho tng

burst ti mi nt thng qua cc gi tin tiu burst BHP hay gi tin iu khin.

OBS s dng bo hiu ngoi bng: Gi tin BHP c truyn trn mt bc sng

Nhm 10 H09VT7 19


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khc vi burst d liu. Tuy nhin, BHP c truyn trn cng mt ng i t

ngun ti ch nh burst d liu thng bo cho cc nt chuyn mch d tr ti

nguyn v cu hnh trng chuyn mch cho burst d liu tng ng.

Di y ta xt bn c ch bo hiu c bn trong OBS l Just Enough Time,Just In Time, Tell And Go v Tell And Wait. Trong ba c ch bo

hiu u l ba c ch bo hiu mt chiu: Nt ngun gi gi tin iu khin d

tr ti nguyn v thc hin truyn burst d liu m khng cn i nt ch thng

bo vic d tr ti nguyn t ngun ti ch c thnh cng hay khng. C ch bo

hiu Tell And Wait l c ch bo hiu hai chiu: nt ngun s ch truyn burst

d liu khi c xc nhn knh truyn c thit lp hon ton t ngun ti

ch.

2.3.1 C ch bo hiu Just Enough Time (JET)

Trong phng thc JET, c mt tr gia vic truyn dn gi tiu burst v

burst d liu. tr ny ln hn tng thi gian x l gi iu khin dc theo tuyn.

Mc ch l sao cho khi burst n mi nt chuyn mch trung gian th gi tiu

burst c x l xong v mt knh trn cng u ra c ch nh. Do

khng cn ng dy tr quang lm tr burst d liu mi nt. y l mt c

tnh quan trng ca JET v ng dy tr quang tn km v c nhiu hn ch (v d

nh ch cho tr c nh, chiu di ln). C ch bo hiu Just Enough Timec m t trn hnh 2.7, node ngun u tin gi mt gi tiu bust (Burst

Header Packet BHP) trn mt knh iu khin ti node ch. BHP c x l ti

mi node tip theo vi yu cu thit lp ng d liu ton quang cho burst d liu

tng ng. Nu qu trnh d tr ti nguyn thnh cng, chuyn mch s c cu

hnh cho burst d liu i qua. Trong lc , burst s i ti ngun trong min in.

Sau mt khong thi gian offsetime xc nh trc, burst c gi trong min

quang trn bc sng c chn.

Nhm 10 H09VT7 20


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TRANSMISSION

&RELEASE PHASE

Time

Source Intermediate nodes Destination

BHP

SETUP &

CONFIRM

PHASE

ST

Burst

Hnh 2.7: C ch bo hiu Just Enough Time

Offset time c tnh ton c bn da trn s nt chuyn mch trung gian t

ngun ti ch v thi gian chuyn mch ca node ch. Offset time c tnh l[1]:

OT = h. + ST

y: h l s nt chuyn mch trung gian gia ngun v ch.

l thi gian x l tiu burst trn mt nt trung gian.

ST l thi gian cu hnh li chuyn mch nt ch.

Gi tiu burst cha thng tin v offset time v chiu di burst. V khi qua mtnt trung gian th gi tr offset time s phi c cp nht li v gi tr offset time s

gim i mt lng ng bng thi gian x l gi tin tiu burst. Khi qu trnh d

tr ti nguyn thnh cng, knh bc sng ti mt nt s ch c n nh hon

ton cho burst khi bit u tin ca burst d liu truyn ti nt. Tc l trong khong

thi gian offset time, knh khng b chim hay ri cho d ng k ti nguyn

thnh cng. Knh c th gn cho burst d liu khc min sao cho vic truyn cc

burst d liu khng b chng ln nhau. Kiu d tr ti nguyn ca JET gi l d tr

ti nguyn tr (Delayed Reservation). Sau khi truyn xong burst d liu knh bc

Nhm 10 H09VT7 21


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sng s t ng c gii phng m khng cn phi c bn tin gii phng knh

c gi t ngun ti ch. V th mt c im khc ca JET l gii phng ti

nguyn khng r rng (Implicit Release).

Nu ti nt trung gian no , qu trnh d tr khng thnh cng, burst s b loib.

Mt vn ny sinh trong vic tnh ton gi tr offset cho JET l phi xc nh

c s nt chuyn mch trung gian gia ngun v ch. Trong mng OBS, thng

tin v s lng cc nt chuyn mch trung gian trn mt ng i t ngun ti

ch thng thng l khng sn c. Thm ch khi nhng thng tin ny bng cch

no c bit th do nh hng ca l trnh thay i, n cng khng m bo

tnh hp l khi s dng [5].

Nh vy, cn mt gi tr offset time m khng ph thuc vo ng truyn s

dng v khng yu cu trao i thng tin gia cc node mng vi nhau. Hin nay

vi nhng tin b trong ch to phn cng cho cc giao thc truyn thng, tr x l

ti cc node trung gian l rt ngn trong hu ht cc chc nng chung ca giao thc

bo hiu. Trong trng hp ny, cc dy tr quang c th c s dng mt cch

hp l ti cc node trung gian lm tr mi burst u vo mt lng thi gian cn

bng vi tr x l tiu . Ta c th b qua cc tr ny trong tnh ton. S mi

ny c gi l giao thc ch c tr ch (Only Destination Delay ODD) v gi trtrong biu thc l [5]:

OT = + ST

,ST l cc gi tr tr ti ch.

*D tr tr (DR) trong vic s dng hiu qu bng thng:

D tr tr s em li hiu qu cao trong vic s dng bng thng. Hnh 2.8 minh

ho ti sao d tr tr to nn s dng hiu qu bng thng.

Gi s xt ti node X, mt gi iu khin ti v thc hin dnh trc ti nguyn

ti thi im t1' v thi im bt u tin ca burst th nht n l t1, vi t1> t1' .Ta

c khong thi gian offset time ca burst th nht l: offset time = t1 - t1'.

Cng gi s c mt gi iu khin khc (gi iu khin th 2) n node ang xt

thi im t2', tng t t2 l thi im bt u tin ca burst th 2 n. Ta c thi

gian tr ca burst ny l: offset = t2 - t2'.

Nhm 10 H09VT7 22


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Thi imgiiu khin th

nht ti Burst thnht

Thi imgiiu khin th

hai ti

t1'

t2'

t1

Burst thhai

t2

Trnghp 1

Trng hp 2

t2 + l2 t1+l1

Thi imgi

iu khin thnht ti Burst th 2

Thi imgiiu khin th

hai ti

t1'

t2'

t2

Burst th 1

t1 t1+l1 t2 + l2

Hnh 2.8: Li ch ca DR

xc nh thi im n ca Burst th nht (t1) , khi thi gian x l gi iu

khin c th thay i t node ny n node khc, trong gi iu khin s cho bit

gi tr thi gian tr c s dng ti node k tip. Gi tr ny c th c cp nht

da trn thi gian x l gi iu khin ti node hin ti.

Trong chuyn mch burst quang da trn giao thc JET , vic xc nh thi im

n ca burst t1 l rt quan trng. Trong giao thc JET rng bng c ng k

ti thi im t1 +l1, l1 l khong thi gian tn ti ca burst th 1 , thay v n v

hn. iu ny s lm tng hiu qu s dng bng thng v gim xc sut loi b

burst .

Nh hnh trn, trong c hai trng hp, chng ta s dng giao thc JET v d

tr tr th burst th 2 n vn c phc v nu t1' < t2' < t2+l2 < t1 (trng hp 1)

hay t1' < t2' < t1+l1 < t2 (trng hp 2).

DR lun s dng thi gian tr. tng hiu qu s dng thi gian tr trong JET

v gim tr khi phi truyn li burst, gi iu khin s c truyn i ti thi

im sm nht c th c bng cch c lng di burst. Nu di burst ln

hn di c lng th mt gi iu khin khc s c gi i xo rngbng ng k. Nu di burst nh hn di c lng th phn d liu cn

li c gi i nh mt hay nhiu burst b sung.

2.3.2 C ch bo hiu Just In Time (JIT)

C ch bo hiu Just-In-Time (JIT) tng t nh c ch bo hiu JET, nhng c

ch ny s dng phng thc d tr ti nguyn tc thi (Immediate Reservation) v

gii phng ti nguyn r rng (Explicit Release). Gia burst d liu v gi tiu

Nhm 10 H09VT7 23


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burst c khong thi gian offset time do JIT khng yu cu phi s dng ng

dy tr quang ti cc nt chuyn mch trung gian.

TRANSMISSION

&RELEASE PHASE

Time


BHP

SETUP &

CONFIRM

PHASE

ST

Burst

Hnh 2.9: C ch bo hiu Just In Time

Khi gi tiu burst c gi i d tr ti nguyn, ti mt nt chuyn mchtrung gian, mt bc sng kh dng s c n nh cho burst d liu ngay sau khi

gi tiu burst c x l. Bc sng ny s dnh ring cho burst d liu cho n

khi c mt bn tin gii phng c gi i t node ngun gii phng kt ni. Gi

tiu burst khng cn phi mang thng tin v thi im n ca burst d liu v

di ca burst [3]. Nu qu trnh d tr ti nguyn tht bi, burst d liu s b loi

b.

02 1

0

12

OT 2OT

1

OT 0

HeaderControl

Chanel

Data

chanel

2 1 00

Header Header HeaderREL

0

2 1

Hnh 2.10: So snh c ch bo hiu JET (trn) v JIT (di)

Nhm 10 H09VT7 24


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Hnh 2.10, so snh c ch bo hiu JET v JIT. Trong c ch bo hiu JET s

dng phng thc d tr ti nguyn tr (Delayed Reservation), ngha l bc sng

kh dng ch c n nh khi burst d liu 0 ti c nt nn trong khong thi

gian offset time c th truyn burst d liu 1 trn cng mt bc sng m khng

xy ra tranh chp. Khi burst d liu 0 kt thc truyn, knh truyn s c gii

phng ngay v vy burst d liu 2 c th c gi vo mng OBS ngay khi burst

0 kt thc. Trong c ch bo hiu JIT, do s dng phng thc d tr ti nguyn

tc th nn trong khong thi gian offset time, burst d liu 1 khng th truyn

qua mng OBS trn cng bc sng vi burst d liu 0. V khi burst d liu 0

truyn kt thc th bn tin gii phng s c gi i t node ngun gii phng

knh, trong thi gian gii phng knh th burst d liu 2 khng th truyn qua

mng OBS c. Nh vy c ch bo hiu Just In Time s dng bng thngkhng hiu qu nh Just Enough Time. Trong [4], Jing Teng v George N.

Roukas tin hnh m phng v kt qu cho thy c ch bo hiu JIT cho t l

mt burst cao hn c ch bo hiu JET.

2.3.3 C ch bo hiu Tell And Go (TAG)

y l c ch bo hiu d tr ti nguyn tc th v gii phng ti nguyn r rng.

Trong TAG, gi iu khin c truyn dn trn mt knh iu khin c theo

sau bi mt burst, trn mt knh d liu vi lch bng khng hoc khng ngk. Burst c m bng cch s dng ng dy tr quang (Fiber Delay Line

FDL) trong khi gi tin iu khin c x l ti mi node trung gian. c im ny

ca Tell And Go ging vi chuyn mch gi quang. Nu vic chim dng bc

sng thnh cng th burst c truyn dn dc theo knh chim tri li burst s

b loi b v mt bn tin ph nh bo nhn (NAK Negative Acknowledgment)

c gi tr li ngun. Node ngun s gi mt gi iu khin sau khi truyn dn

burst gii phng ti nguyn b chim dc theo tuyn [2].

Nhc im c bn ca phng php ny l gii hn v mt cng ngh ca

ng dy tr quang FDL. FDL c th lm tr burst trong mt khong thi gian c

nh v khng th thch nghi vi kch thc burst d liu thay i. Cng nh c ch

bo hiu Just In Time, TAG khng tn dng ti nguyn hiu qu do s dng d

tr tc th v gii phng ti nguyn r rng. Khi cha c bn tin Release, knh s

khng c gii phng v trong khong thi gian gii phng knh, knh s khng

c gn cho bt c burst no khc.

Nhm 10 H09VT7 25


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Time

BHP

Burst


Gi tinNAK

Gi tinRELEASE

Hnh 2.11: C ch bo hiu Tell-And-Go

2.3.4 C ch bo hiu Tell And Wait (TAW)

C ch bo hiu Tell And Wait c m t trn hnh 2.12. Trong phng

thc TAW, node ngun s gi mt gi iu khin d tr ti nguyn cho burst d

liu dc theo tuyn. Sau nt ngun s i mt bn tin xc nhn ACK t nodech thng bo vic d tr ti nguyn thnh cng. Burst d liu s c gi i t

node ngun trn tuyn ng chn. V sau khi burst c truyn n ch s c

mt bn tin gii phng kt ni c gi i gii phng ti nguyn t ngun ti

ch.

Nu qu trnh d tr ti nguyn l khng thnh cng ti mt nt OBS trung gian

no n nt ch th ngay lp tc s c mt bn tin thng bo khng thnh cng

c gi v t nt gii phng ti nguyn c thit lp trn tuyn t nt

ngun n nt v burst s khng c pht i. Nt ngun s phi gi li gi iu

khin d tr ti nguyn t ngun ti ch mt ln na.

Nu chng ta so snh TAW v cc c ch bo hiu mt chiu th nhc im ca

TAW l thi gian cn thit cho thit lp knh; tuy nhin u im ca TAW l t l

mt d liu l rt thp. Do , TAW ph hp cho lu lng yu cu tin cy v t l

mt burst v cc burst c kch thc tng i ln so vi thi gian thit lp knh

truyn t ngun ti ch.

Nhm 10 H09VT7 26


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Hnh 2.12: C ch bo hiu Tell And Wait

2.4 Cc thut ton sp xp knh

Khi mt gi tin tiu burst ti nt li, khi iu khin chuyn mch SCU x lgi tin ny v mt thut ton sp xp knh hay lp lch knh c thc hin gn

burst d liu cho mt knh bc sng thch hp u ra. Khi lp lch knh ly

thi im burst n v chiu di burst t gi tin iu khin. Thut ton c th cn

phi duy tr thi im knh truyn ri gn nht LAUT (Latest Available

Unscheduled Time) hay cn gi l horizon, cc tham s void v gap trn mi

knh d liu u ra. Theo l thuyt, LAUT ca mt knh d liu l thi im gn

nht mt knh d liu c th s dng cho mt burst d liu cha c lp lch hay

c th hiu l thi im kt thc ca mt burst c lp lch trong mt s trng

hp. Gap l khong thi gian c tnh gia thi im n ca mt burst cha

c lp lch v thi im kt thc ca mt burst c lp lch trc . Void

l khong thi gian gia hai burst d liu c lp lch trn mt knh d liu m

trong thi gian khng c burst d liu no khc c lp lch.

Nhng thng tin sau c s dng bi khi lp lch cho hu ht cc thut ton

lp lch knh:

- Lb l chiu di burst.

Nhm 10 H09VT7 27


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29/42


c sp t da trn ch s ca knh (D0, D1, D2, D3), burst d liu i n s c

sp xp trn knh D1 v theo th t knh D1 nm trc knh D2. u im ca thut

ton ny l n gin v tc nhanh. Nhc im ca thut ton ny l t l mt

burst cao v tn dng ti nguyn khng hiu qu.

Hnh 2.13: Thut ton FFUC v LAUC

2.4.2 Knh ri vi LAUT gn nht (LAUC)

Thut ton LAUC v c bn thc hin tng t nh thut ton FFUC, n cng

duy tr gi tr ca LAUT trn tt c cc knh d liu nhng trong qu trnh tm kim

knh d liu thch hp thay v sp xp burst d liu trn knh thch hp u tin tm

c, gii thut ny la chn knh c LAUT gn vi thi im n ca burst d

liu nht. Gii thut LAUC cng c m t trn hnh 2.13. Cc knh d liu D1 vD2 l thch hp v v thi im burst i n nm sau cc LAUT ca hai knh ny.

Nu nh thut ton FFUC c s dng th knh D1 c la chn. Tuy nhin, vi

thut ton LAUC cn quan tm n khong thi gian gia t v LAUT ca mi

knh, n s chn knh no c khong thi gian ny nh nht; iu ny lm tng

hiu qu s dng knh truyn so vi FFUC. Chng ta thy rng Gap 1 > Gap2 do

burst s c sp xp trn knh D2.

Nhm 10 H09VT7 29


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2.4.3 Knh ri ph hp u tin thc hin lp khong trng (FFUC-

VF)

im khc bit ca cc thut ton lp khong trng ni chung l khng lu tr

gi tr LAUT m lu thi im bt u S v kt thc E ca mi burst c lplch trn mi knh d liu. u im ca thut ton ny l tn dng khong trng

gia hai burst d liu c sp xp lm tng hiu sut s dng knh truyn. FFUC-

VF cng ging nh FFUC, n la chn knh truyn theo th t. Knh truyn u

tin vi mt khong cch void thch hp c la chn.

Hnh 2.14: Thut ton FFUC-VF v LAUC-VF

Thut ton FFUC-VF c m t trn hnh 2.14. Da trn Si,j v Ei,j, tt c cc

knh d liu D0, D1, D2, D3 c kh nng p ng cho burst d liu n cha clp lch. Nu cc knh ny c sp t theo ch s ca tng knh, burst d liu mi

n s c lp lch ng ra D0 v n tha mn cc iu kin sau: l knh c s th

t u tin c E0,0 nm trc E0,a, khong trng void ca knh ny ln hn chiu

di ca burst mi n cha c lp lch.

Nhm 10 H09VT7 30


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2.4.4 Knh ri vi LAUT gn nht - thc hin lp khong trng (LAUC-

VF)

Gii thut LAUC-VF cng lu nhng thi im bt u S v kt thc E cho mi

burst d liu c lp lch trn tt c cc knh d liu. u im ca gii thutny l tn dng c khong trng gia hai burst d liu c sp xp. Knh

truyn vi khong trng m khong cch nh nht s c chn. thit lp

LAUC VF, khi iu khin chuyn mch phi lu li thng tin s dng ca tt c

cc knh d liu. iu ny lm cho LAUC VF phc tp hn so vi FFUC v

LAUC. Nhng tn dng ti nguyn hiu qu hn 2 loi trn.

2.4.5 Khong trng kt thc ti thiu (Min-EV)

Mt dng khc ca LAUC VF l Minimum End Void (MinEV). MinEV s xts khc nhau gia thi im bt u ca burst d liu lp lch v thi im kt

thc ca burst d liu n mi trn knh. MinEV chn mt knh c gi tr trc n

nh nht. V vy gii thut ny cn lu thng tin ca cc knh d liu trc

2.5 Phn gii tranh chp

2.5.1 B m quang

Cn s dng b m khi c nhiu hn mt gi vo mun chuyn ti cng mt

u ra. Mt trong nhng c trng c bn ca chuyn mch OBS l khng cn b

m quang: nt trung gian trong mng quang khng yu cu phi c b m quang.

Cc burst i xuyn qua cc nt trung gian m khng c bt k s tr no.

Vic gii quyt xung t mng chuyn mch gi min in truyn thng s

dng cc b nh RAM lu gi tm thi cc gi tin khi xung t xy ra; tuy nhin

mt b m ging nh RAM trong min quang hin nay vn cha c hu hiu.

Trong mng quang, ngi ta xut dng dy tr FDL (Fiber Delay Line) lu

gi cc gi tin trong min quang mt khong thi gian c nh. Yu cu tr thay itrong trng hp nhiu gi cn lm tr v cn x l ti cng mt thi im. Ghp

theo bc sng v theo thi gian u c s dng trnh tranh chp. m quang

c thc hin khi s dng ng dy tr si quang (FDL). Chiu di ca FDL c

th tnh ton c. Chng hn m mt gi IP c 512 byte truyn vi tc 10

Gbit/s cn s dng 82 m si quang. FDL khng th a tn hiu ra ti thi im bt

k; nhng n l mt h thng vo trc ra trc (FIFO) nn cc gi i qua ton b

chiu di ca FDL l c m.

Nhm 10 H09VT7 31


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Bng cch kt ni cc dy tr FDL theo tng hay kt ni song song, b m c

xut ny c th gi cc gi tin trong min quang hay burst d liu trong cc thi

gian khc nhau.

Hnh 2.15: M t gii quyt xung t bng b m

Cch ny c th gim mt d liu nhng li khng m bo gi n ng th

t. Trong mt s kin trc ca b m quang, kch thc ca nhng b m th b

gii hn khng ch xt n yu t v mt tn hiu m c yu t v kch thc vt l.

lm tr mt burst khong 1 ms th cn phi c mt on cp di hn 200 km.

Bi v nhng hn ch ca b m quang nn mt node mng c th khng th png c lu lng ti ln v trong iu kin ti t bin. Nhng b m quang

da trn nh tuyn bc sng v iu khin bc sng trong mt vng khp kn

cng l mt gii php cho b m quang

Hnh 2.16: Dy tr FDL cng vi b khuch i v chuyn mch to thnh

mt vng lp tr

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2.5.2 Chuyn i bc sng

m kt hp vi chuyn i bc sng gii quyt tranh chp cc gi trong

min thi gian. Tranh chp trong min khng gian phi s dng nh tuyn chch

hng. Tuy nhin gii php ny khng th s dng trong mng chuyn mch tonquang do tnh phc tp ca nh tuyn ng. Cn m khi hai gi quang c nh

tuyn ng thi ti cng mt cng ra. Nu c hai gi c cng bc sng th chng

khng th i ti u ra

Trong WDM, nhiu bc sng c ghp cng lc trn mt lin kt kt ni hai

chuyn mch quang. Nhiu bc sng c th gim ti thiu s lng xung t. Gi

s rng c hai burst u i n mt ch v ra cng ng ra ti cng thi im. C

hai burst c th vn cn truyn i tip nu trn hai bc sng khc nhau. Cch

thc ny rt c kh nng trong vic gim thiu xung t, c bit trong lc s

lng bc sng c th ghp trn si quang ngy cng tng ln. Ngi ta c on

trong tng lai c th ghp t 160 n 320 bc sng trn mt si quang. Chuyn

i bc sng l tin trnh chuyn i mt bc sng ng vo thnh mt bc

sng khc ng ra. B chuyn i bc sng l nhng thit b chuyn i bc

sng ng vo thnh mt bc sng khc ng ra, do vy tng kh nng s dng

li bc sng, ngha l cng mt bc sng c th c s dng li mang nhiu

kt ni trn nhng lin kt khc nhau trong mng. Do nhng b chuyn i bcsng cung cp kh nng nng cao hiu sut s dng bc sng

Hnh 2.17: Gii quyt tranh chp bng b chuyn i bc sng

Trong mng chuyn mch burst quang, s lng xung t c th gim xung

bng cch s dng thm kh nng s dng li bc sng cho php nhiu bc sng

cng hot ng trn mt lin kt t node ng vo n node ng ra. Mt burst

n xung t (contenting burst) c th c chuyn ti bt k bc sng no

ng ra ang ri. Hin nay cc b chuyn i bc sng ch c a ra v s dng

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trong cc phng th nghim, cng ngh ny cng cha hon thin v khong bc

sng c kh nng chuyn i cn hn ch. Sau y l mt s loi chuyn i bc

sng:

- Chuyn i ton b (Full conversion): Mt bc sng mi n c thchuyn n bt k bc sng no ng ra; do vy khng c mt bc sng no

xut hin lin tc trn mt kt ni t u cui n u cui.

- Chuyn i c gii hn (Limited conversion): Vic chuyn i bc sng b

gii hn khng phi tt c cc knh ng vo u c th kt ni n tt c cc

knh ng ra. Vic gii hn ny s lm gim chi ph ca chuyn mch trong khi

chp nhn mt s lng xung t.

- Chuyn i c nh (Fixed conversion): y cng l mt dng ca limitedconversion, trong mi knh ng vo c kt ni vi mt hay nhiu knh ng

ra c ch nh trc.

- Chuyn i mt phn (Sparse wavelength conversion): Trong mng c th bao

gm cc node c chuyn i ton b, c gii hn, c nh v khng c b

chuyn i bc sng.

2.5.3 nh tuyn chuyn hng

2.5.3.1 Gii thiu

Lm lch hng i l mt phng php gii quyt nghn bng vic nh tuyn

mt burst tranh chp n mt ng ra khc so vi ng ra theo d kin. Tuy nhin

burst lch hng c th n ch theo mt tuyn di hn. V vy c th xy ra tr

u cui u cui ca mt burst. Lm lch hng i khng c kh thi trong

mng chuyn mch in v kh nng lp v phn tn burst.

Trong khi x l gi iu khin truyn i burst trn tuyn chnh, nu burst

cm thy nghn th mt gi iu khin khc c bt u t nt nghn trung gian

v burst c truyn qua mt tuyn la chn t nt trung gian .C nhiu yu t

quyt nh nh tuyn, trc ht n xc nh c la chn tuyn cho mt burst

c hay khng hay loi b v thc hin gi li t nt ngun.

Trong nh tuyn chuyn hng, xung t c gii quyt bng cch nh

tuyn burst d liu n mt ng ra khc thay v l ng ra nh ban u; tc l k t

node i theo con ng khc n ch ch khng cn i theo con ng

ngn nht ban u.

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Hnh 2.18: Cu trc ca mng OBS vi k thut lm lch hng inh tuyn chuyn hng khng c quan tm i vi mng chuyn mch

gi trong min in; tuy nhin, n li thc s cn thit i vi mng ton quang

trong khi cc b m quang cn hn ch.

2.5.3.2 Phng php nh tuyn chuyn hng

Phng php nh tuyn lch hng i trong OBS bao gm cc bc c miu

t nh trong hnh 2.19

Bc 1: Nt ngun truyn i mt gi iu khin.

Bc 2: Nt trung gian x l gi iu khin v c gng dnh trc mt knh hot

ng cho burst.

Bc 3: Nt ngun truyn i burst sau mt khong offset.

Bc 4: Nu ti mt nt khng c knh ng ra no hiu lc cho burst, trc ht

n kim tra c phi nt hin ti l ngun hay khng. Nu nt hin ti l nt ngun

th nh tuyn chuyn hng khng thc hin. Thay v , sau khi i mt khongthi gian, ngun truyn li gi iu khin ri sau burst c truyn i. Nu nt

hin ti l nt trung gian th chuyn sang bc 5.

Bc 5: Nt hin ti c xem nh l mt nt trung gian. V vy nt hin ti

tnh ton thng s th hin v thc hin kim tra da trn nhng thng s . Do

vy n quyt nh c lm lch hng hay l loi b v thng bo cho ngun thc

hin truyn li. Nu quyt nh l lm lch hng i, th tuyn chn la c chn

trong DRT. Tuy nhin, nu khng c tuyn no c hiu lc trong DRT th nt hin

ti loi b burst v gi bn tin NACK n ngun truyn li t ngun.

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Hnh 2.19: Phng php nh tuyn chuyn hngThut ton a ra gii php iu khin nghn khc phc nhng s c xy ra i

vi mng, t hiu qu cao v chi ph mng tng i thp. Chng ta cng a ra

c mt s kt qu quan trng biu th bn cht ca node bin cng nh node

trung gian. Cc kt qu ny rt c ch trong vic nghin cu s bin thin ca xc

sut burst suy hao khi cc thng s h thng v lu lng thay i.

2.5.4 Phn on burst

Trong cc nghin cu v mng chuyn mch burst quang, khi xung t xy ragia hai burst m khng th gii quyt bng cc phng php trn th mt trong hai

burst b rt ton b, cho d cc phn chng ln ca cc burst ln nhau l rt nh.

Trong cc ng dng yu cu nghim ngt v tr nhng khng quan tm lm n

mt gi th ngi ta mong mun l rt cc gi chng ln hn l rt ton b burst.

ng V. M. Vokkarane a ra phng php cho vic gii quyt xung t bng

cch phn on burst (Burst Segment), lm cho s lng gi mt i gim xung

bng cch ch cho rt phn chng ln ln nhau ca mt trong hai burst. u

im ca phng php ny l c th xem xt n cc mc u tin ca tng burst t

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c th a ra quyt nh rt b mt phn ca burst n xung t (contenting

burst) hay burst b xung t (contented burst) (nh hnh 2.20)

Trong phn on burst, mt burst bao gm nhiu n v truyn ti nh hn gi

l on (segment). Mi on gm bao gm mt header v phn payload ca on.Header ca on bao gm cc trng cho bit ng b, thng tin sa li, thng

tin v ngun v ch n v chiu di ca on trong trng hp cc on c chiu

di khc nhau. Phn payload ca on c th mang nhiu loi d liu, nh gi IP, t

bo ATM hay cc frame Ethernet (Hnh 2.21). Khi hai burst xung t vi nhau

trong mng chuyn mch burst quang, ch c mt s on ca mt burst chng ln

ln burst kia mi b rt, nh hnh 2.22. Nu thi gian chuyn mch khng c b

qua th c thm mt s on c th b rt khi chuyn mch c cu hnh tr li.

Trong cc m t sau y, ta gi burst n trc hay burst b xung t gi lcontented burst v burst n sau hay burst n xung gi l contending burst.

t c tnh trong sut th lp quang khng cn phi nhn ra ranh gii thc

s ca cc on v khng cn bit nh dng phn payload ca mi on. Trong

trng hp ny, lp quang ch nhn ra thng tin nh cc node ngun v ch

ca burst, thi gian offset, thi gian ca burst v c th l u tin ca burst.

Tnh trong sut ny c th dn n vic quyt nh ti u nht cho vic gim thiu

mt gi nhng cng c th mt on c th b chia thnh hai phn tch bit do vyc th mt mt gi s tng ln trong trng hp on ny n ch khng c

nhn ra; tuy nhin, bng cch bo m tnh trong sut, lp li quang tr nn n

gin v khng cn thit phi tnh ton li cc gi tr trong gi iu khin cc node

li.

Hnh 2.20: M t gii quyt xung t bng phn on burst

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Nu nh ranh gii ca cc on hon ton trong sut trong mng li ton quang

th cc node bin phi chu trch nhim nh ngha v x l cc on trong min

in. Hn na, node nhn phi c kh nng nhn ra im bt u ca mi on v

xc nh xem th on c cn nguyn vn hay khng; do , mt s header dng

nhn ra li v sa li phi cha trong mi on. Thm vo thng tin v tn

hiu ng h c th cng cn phi c trong mi header ca mi on node nhn

ng ra c th xc nh v phc hi d liu trn mi on. Mt on c th mt

frame Ethernet. Nu mi on bao gm mt frame Ethernet, vic ng b v nhn

ra frame c thc hin bi trng preamble trong header ca frame Ethernet,

trong khi li v cc frame khng cn nguyn vn c th c nhn ra bng cch s

dng trng CRC trong frame Ethernet; do , khng cn thit phi c phn iu

khin cho mi on v mi th c sn trong mt frame Ethernet. Nu cc onkhng c nh ngha nh nhng frame Ethernet, vic chn la chiu di ca

mi on tr thnh mt thng s chnh ca h thng. Mt on c th c chiu

di c nh hay thay i. Khi cc on c chiu di khng i th vic ng b

my thu tr nn d dng; tuy nhin, nhng on c chiu di thay i li c kh

nng cha c nhng gi c chiu di khc nhau. Kch thc ca mi on cn

phi cn nhc gia mt mt trong mt ln xung t v s lng header trong mt

burst. on di s dn n mt nhiu d liu cho mi ln xung t; tuy nhin,

nhng on di cng dn n t overhead v t s gia chiu di header so vichiu di payload s nh theo. Trong chng ny, chng ta gi s rng mi on

l mt frame Ethernet c chiu di c nh v khng cn phi tm kch thc ti u

ca mi on.

Hnh 2.21: Cu trc ca burst c ng kiu phn on

Mt s vn khc trong phn on burst l quyt nh xem on no b rt khi

xung t xy ra gia hai burst. Chng ta t tn cho burst b xung t l

contented burst cn burst xung t l contenting burst. Ch rng chm c

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xem l contented hay contenting burst ph thuc vo th t ca n n chuyn

mch ch khng phi th t ca gi iu khin n trc hay n sau. C hai cch

xc nh xem nhng on no nn rt, c gi l tail-dropping (rt phn

ui) v head-dropping (rt phn u).

Hnh 2.22: Xung t lm chng ln cc on ln nhau

Trong cch rt phn ui tail-dropping th cc on chng ln ca contented

burst s b rt cn trong cch rt phn head-dropping u th cc on ca

contenting burst chng ln s b rt. u im ca vic tail-dropping hn head-

dropping trong vic thay i cc gi sai th t node ch vi gi thuyt rng cc

gi b rt c truyn li sau . Vic head-dropping lm cho cc gi n ch sai

th t; tuy nhin, u im ca head-dropping l n chc chn rng mt khi burst

n mt node khng bt gp mt xung t no v sau cc burst ny tip tc i

n ch m khng ph thuc vo cc burst i sau n c mc u tin no i chng

na.

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KT LUN

Sau mt thi gian su tp, tm hiu ti liu v thc hin chuyn "Chuyn

mch burst quang" gip nhm hiu c mt cch tng quan v nguyn l v

cc vn c bn ca chuyn mch burst quang. Chuyn trnh by nhng nidung:

- Gii thiu v so snh v cc cng ngh chuyn mch quang, nu bt c ngha

quan trng ca vic s dng chuyn mch burst quang trong giai on pht trin

hin ti ca mng truyn ti quang.

- Nhm i su phn tch kin trc mng OBS v hot ng ca mng OBS theo s

khi chc nng ca mng: v cc phng php t hp burst, cc c ch bo hiu

ch yu nh JET, JIT, TAG, TAW, cc thut ton sp xp knh, cc phng phpgii quyt tranh chp.

Qua cc ni dung trnh by nh trn, ta thy rng:

- Chuyn mch OBS c kh nng tn dng ti nguyn hiu qu, ph hp vi cc

cng ngh v phn cng v thit b trong mng WDM hin ti, v kh nng h tr

cho nhiu loi giao thc khc nhau.

- Cc c ch v phng php t hp burst bo hiu, sp xp knh v gii quyt

tranh chp ca OBS a dng v linh hot c th h tr cc lu lng loi dch v

yu cu QoS khc nhau.

- Tuy nhin, OBS l mt cng ngh cha c chun ha v cha c h thng

thng mi thc t no c a vo trin khai. Nhng vn c bn ca chuyn

mch OBS c trnh by trong chuyn ch yu da trn cc cng trnh nghin

cu, cc bi bo khoa hc v cc lun vn ca cc nh nghin cu v cc k s

nc ngoi.

- Vn nghin cu v OBS hin ti v tng lai l tm ra c cc giao thc ti

u cho hot ng ca mng v t c th thit k v ch to cc thit b mng ph

hp.

Do y l mt lnh vc cn kh mi, nn vic tm hiu v chuyn Chuyn

mch burst quang mi ch dng li mc l thuyt tng qut, cha i su vo

phn tch, nh gi c th ht cc vn ( nh vn nh tuyn, QoS..). Nhm rt

mong nhn c s nh gi, ng gp kin ca thy gio v cc bn chuyn

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c hon thin hn na, ng thi c th lm tin tip tc nghin cu,

pht trin cc cng ngh mi hn sau ny.

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TI LIU THAM KHO

[1] Jason P.Jue, Vinod M. Vokkarane, Optical Burst Switched Networks,2005.Chng 1 trang 1 9, chng 2 trang 11 15, chng 3 trang 23 26, chng

4 trang 37 53, chng 5 trang 57 66, chng 6 trang 81 98.

[2] Mrinal Nandi, A technique to minimize contention in Optical Burst

Switching Networks, 2007. Chng 1 trang 1 6, chng 2 trang 10 26,

chng 3 trang 32 - 39 .

[3] Jolyon Ambrose Scoreby White, Modelling and demensioning of Optical

Burst Switching Networks,2007. Chng 2, trang 11 34.[4] Jing Teng, George N.Rouskas, A comparison of the JIT, JET and Horizon

Wavelength Reservation Schemes on a single OBS node,2003.

[5] Lisong Xu, Harry G.Perros, George N.Rouskas, A simulation study of optical

switching and access protocols for WDM ring networks,2002. Trang 143 145

[6] Yang Chen, Chunming Qiao, Xiang Yu, Optical Burst Switching: A new area

in optical networking research,1998. Mc 1 n ht mc 6 trang 1 9.

[7] Mai Th Kim Lin, Nguyn ng Phc Lm, Gii php iu khin nghn

trong mng chuyn mch burst quang bng phng php lch hng i, Bo

co Hi tho sinh vin ngin cu khoa hc i hc Nng, 2010

Documents

Chuyển mạch burst quang - Nhóm 10- Hưng-Giang-Hoàn