báo cáo tt2

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Em xin cam oan ni dung ca n ny khng phi l bn sao chp ca bt c

n hoc cng trnh c t trc.

Nng, thng 5 nm 2007

Sinh vin thc hin

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Mc lc

CHNG 1..............................................................................................................1

TNG QUAN V H THNG THNG TIN QUANG......................................11.1. Gii thiu chng..............................................................................................1

1.2.2. Nhng u im ca h thng thng tin quang............................................21.2.3. Cu trc v cc thnh phn chnh ca h thng thng tin quang ...............4

1.4. Kt lun chng ...............................................................................................6CHNG 2..............................................................................................................7GII THIU MNG WDM...................................................................................7

2.1. Gii thiu chng..............................................................................................72.2. Nguyn l hot ng ca h thng WDM ........................................................9

2.3. u im ca h thng WDM...........................................................................10

2.4. Vn tn ti ca h thng WDM v hng gii quyt trong tng lai.........112.5. Chuyn mch quang.........................................................................................112.6. Cc thnh phn chnh ca h thng WDM.......................................................13

2.6.1. Thit b u cui OLT...............................................................................132.6.2. B ghp knh xen/rt quang OADM........................................................142.6.3. B khuch i quang.................................................................................192.6.4. Gii thiu v b kt ni cho quang OXC................................................21

2.6.4.1. Chc nng OXC.................................................................................212.6.4.2. Phn loi OXC ..................................................................................25

2.7. S chuyn i bc sng ................................................................................272.8. Kt lun chng...............................................................................................29

CHNG 3............................................................................................................30NH TUYN V GN BC SNG..............................................................30

3.1. Gii thiu chng............................................................................................303.2. Gii thiu v nh tuyn v gn bc sng (Routing and WavelengthAssignment - RWA)................................................................................................303.3. nh tuyn bc sng......................................................................................323.4. nh tuyn (Routing).......................................................................................33

3.4.1. Gii thiu...................................................................................................343.4.2. Phn loi nh tuyn..................................................................................35

3.6. S thit lp ng o (Virtual path) ..............................................................363.7. Phn loi mng quang WDM...........................................................................37

3.7.1. Mng single- hop.......................................................................................373.7.2. Mng Multi- hop.......................................................................................38

3.9. Kt lun chng...............................................................................................38

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APD Avalanche Photodiode Diod tch sng quang thc l

AS Autonomous System H thng c lp

ATM Asynchronous Transfer Mode Kiu truyn bt ng b

A

B

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BGP Border Gateway Protocol Giao thc nh tuyn vng bin

CDM Code Division Multiplexing Ghp knh phn chia theo m

DVA Distance Vector Algorithm Thut ton Vector khong cch

DWDM Dense WDM WDM mt cao

EDFA Erbium Doped Fiber Amplifier B khuch i quang si c pha tp

Erbium

EIGRP Enhanced IGRP Giao thc IGRP nng cp

IGRP Interior Gateway Routing Protocol Giao thc nh tuyn bn trongISDN Itegrated Servise Digital Network Mng s tch hp dch v

LD Diod Laser

LED Light Emitting Diode Diod pht quang

LP Lightpath ng i nh sng

LSA Link State Algorithm Thut ton trng thi lin kt

OADM Optical Add/Drop Multipler B ghp knh xen/rt quang

OLT Optical Line Terminator Thit b u cui quang

OXC Optical Cross Connect B kt ni cho quang

P

O

L

I

E

D

C

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PIN Positive Intrinsic Negative

RIP Routing Information Protocol Giao thc thng tin nh tuyn

RWA Routing & Wavelength Assignment nh tuyn v gn bc sng

SOA Semiconductor Optical Amplifier B khuch i quang bn dn

TDM Time Division Multiplexing Ghp knh phn chia theo thi gian

WDM Wavelength Division Multiplexing Ghp knh phn chia theo bc

sng

H thng thng tin quang ra i cng vi nhng u im vt tri ca n v

ang p dng rng ri trn mng li thng tin ton cu. Hin nay, cc h thng

thng tin quang truyn dn tt c cc tn hiu dch v bng hp, bng rng p ng

yu cu ca mng s tch hp dch v ISDN. V th, h thng thng tin quang s l

mi t ph v tc truyn dn v cu hnh linh hot cho cc dch v vin thng

cp cao.

i vi h thng thng tin quang, mi trng truyn dn chnh l si quang, n

thc hin truyn nh sng mang tn hiu thng tin t pha pht ti pha thu. nh

tuyn v gn bc sng tr thnh chc nng khng th thiu c trong mng quang

R

T

W

S

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WDM. Vn t ra l nh tuyn ng i cho nh sng v gn bc sng cho n

trn mi tuyn nh th no t c mt mng ti u.

Trong n k thut thng tin ny, em xin trnh by v ti nh tuyn v gn

bc sng trong mng WDM (Routing and Wavelength Assignment). n c

chia thnh bn chng:

Chng 2: Gii thiu v h thng WDM.

Chng 3: nh tuyn v gn bc sng trong mng WDM.

ti nh tuyn v gn bc sng trong mng WDM ca n ny phn

tch s cn thit ca chc nng nh tuyn v gn bc sng trong mng quangWDM, tr thnh chc nng khng th thiu trong vic iu hnh mng quang.

Phng php nghin cu ca ti: da vo chc nng ca nh tuyn v gn

bc sng trong WDM, thc hin m phng chc nng nh tuyn trong mng. nh

sng i trong si quang phi i qua nhiu node mng trung gian ti node ch, tc

l qua cc tuyn trung gian. Vic nh tuyn vi tiu ch ti u hm mc tiu l cc

tham s quen thuc nh bng thng, tr, chi ph tuyn,... V th dng thut ton

tm ng ngn nht Dijkstra thc hin m phng nh tuyn ti u mng.Em xin chn thnh cm n thy gio Nguyn Vn Phng tn tnh hng dn,

cung cp ti liu, ng thi ng vin trong thi gian em nghin cu ti ny. Em

xin cm n tt c cc thy c gio trong khoa in T Vin Thng nhit tnh dy

d, cung cp trang b cho em nhng kin thc qu bu, cm n gia nh ng vin

em trong sut thi gian va qua, cm n cc bn gp nhng kin chn thnh gp

phn gip em hon thnh n.

Trong thi gian thc hin n kh ngn n, mc d c nhiu c gng nhng

n khng khi trnh nhng thiu st. Knh mong cc thy c gio trong khoa cng

cc bn tn tnh ch bo v gp kin n c hon thin hn. Em xin chn

thnh cm n.

Nng, ngy...thng...nm 2007

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Chng 1: Tng quan v h thng thng tin quang

CHNG 1

TNG QUAN V H THNG THNG TIN QUANG.

1.1. Gii thiu chng

Lng thng tin trao i trong cc h thng thng tin ngy nay tng ln rt nhanh.

Bn cnh gia tng v s lng, dng lu lng truyn thng trn mng cng thay i.

Dng d liu ch yu l lu lng Internet. S ngi s dng truy cp Internet ngy

cng tng v thi gian mi ln truy cp thung ko di gp nhiu ln cuc ni chuyn

in thoi. Chng ta ang hng ti mt x hi m vic truy cp thng tin c th

c p ng mi lc, mi ni chng ta cn. Mng internet v ATM ngy nay

khng dung lng p ng cho nhu cu bng thng trong tng lai.

Hnh 1.1: S gia tng lu lng d liu v ting ni qua cc nm.

K thut thng tin quang c th c xem l v cu tinh ca chng ta trong vic

gii quyt vn trn. Bi v h thng thng tin quang ra i vi nhng kh nng

vt tri ca n: bng thng khng l (gn 50Tbps), suy gim tn hiu thp (khong

0.2dB/km), mo tn hiu thp, i hi nng lng cung cp thp, khng b nh hng

ca nhiu in t, kh nng bo mt cao V vy thng tin quang c xem l k

thut cho h thng thng tin bng rng. Cc h thng thng tin quang khng ch c

bit ph hp vi cc tuyn thng tin ng di, trung k m cn c tim nng to ln

trong vic thc hin cc chc nng ca mng ni ht v p ng mi loi hnh dch

v hin ti v trong tng lai.

1.2. Gii thiu v thng tin quang

1

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Khc vi thng tin hu tuyn hay v tuyn - cc loi thng tin s dng cc mi

trng truyn dn tng ng l dy dn v khng gian nh hnh 1.2 - th thng tin

quang l h thng truyn tin qua si quang nh hnh 1.3. iu c ngha l thng

tin c chuyn thnh nh sng v sau nh sng c truyn qua si quang. Ti

ni nhn, n li c bin i thnh thng tin ban u.

1.2.2. Nhng u im ca h thng thng tin quang

Thng tin si quang c nhng u im vt tri. Trong phn ny, em a nhng

u im th hin tnh vt tri ca n:

Bng thng khng l y tim nng: tn s sng mang quang trong

khong1013 n 1016 Hz (thng gn vng hng ngoi quanh gi tr 1014 Hz),

cung cp bng thng truyn ln hn nhiu so vi h thng cp kim loi (bng

thng ca cp ng trc khong 500Mhz). Hin ti, gi tr bng thng ca h

thng si quang cha s dng ht nhng vic mt vi GHz qua khong cch

vi km v hng trm Mhz qua khong cch hng chc Km m khng cn s

can thip v in (dng b lp) l c th. V th, dung lng mang thng tin

ca h thng thng tin quang ln hn nhiu so vi h thng cp ng tt nht.

Do suy hao ln bng thng rng, h thng cp ng trc gii hn khong

cch truyn vi ch mt vi km bng thng trn 100Mhz.

Si quang kch thc nh v nh: si quang c bn knh rt nh, thng

bn knh ny khng ln hn bn knh si tc con ngi. V th, thm ch khi si

2

Hnh 1.2: Thng tin hu tuyn

Hnh 1.3: Thng tin quang

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quang c ph thm nhng lp bo v th chng vn nh v nh hn nhiu so vi

cp ng.

S cch li v in: si quang c ch to t thu tinh hoc i lc l cht

do, l nhng cht cch in, v th khng ging vi dy dn kim loi, n khng

cho thy nhng trc trc c bn. Hn na, c tnh ny lm cho vic truyn thng tin

ca si quang tr nn ph hp mt cch l tng cho s thng tin trong nhng mi

trng mo him v in.

Khng b nh hng bi nhiu v xuyn m: si quang c ch to t

cc cht in mi phi dn nn chng khng b nh hng bi nhiu in t, cc xung

in t, nhiu tn s v tuyn. V th hot ng ca h thng thng tin quang khng

b nh hng khi truyn qua mi trng nhiu in. iu c ngha l n c th lp

t cung ng vi cp in lc v c th s dng trong mi trng phn ng ht nhn.

Bo mt thng tin: nh sng t si quang b bc x mt cch khng ng k

nn chng c tnh bo mt tn hiu cao. c tnh ny thu ht i vi qun i, ngn

hng v cc ng dng truyn d liu.

Suy hao thp: s pht trin ca si quang qua nhiu nm t c kt qutrong vic ch to ra si quang c suy hao rt thp. Si quang c ch to vi

suy hao 0.2dB/km v c tnh ny tr thnh li th chnh ca thng tin quang. iu

ny thun li cho vic t b khuch i cho mi khong cch trn ng truyn m

khng cn chuyn sang tn hiu in bc trung gian, do gim c c gi thnh

v c phc tp ca h thng.

Tnh linh hot: mc d cc lp bo v l cn thit, si quang c ch to

vi sc cng cao, bn knh rt nh. Vi li th v kch thc v trng lng, si

quang ni chung l tt hn trong vic lu tr, chuyn ch, x l v lp t d hn h

thng cp ng.

tin cy ca h thng v d bo dng: do c tnh suy hao thp ca si

quang nn c th gim c yu cu s b lp trung gian hoc s b khuch i trn

ng truyn. V th, vi mt vi b lp th tin cy ca h thng c th c nng

3

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cao hn hn h thng dn in. Hn na, tin cy ca cc thit b quang khng cn

l vn , cc thit b quang c tui th rt cao, khong 20-30 nm.

Gi thnh thp y tim nng: thy tinh cung cp cho thng tin quang c

ly t ct, khng phi l ngun ti nguyn khan him. V th, si quang em li gi

thnh thp.

Thng tin quang cng cho php truyn ng thi cc tn hiu c bc sng khc

nhau. c tnh ny cng vi kh nng truyn dn bng thng rng ca si quang sn

c lm cho dung lng truyn dn ca tuyn tr nn rt ln.

1.2.3. Cu trc v cc thnh phn chnh ca h thng thng tin quang

Cc thnh phn ca tuyn truyn dn quang bao gm: phn pht quang, cp si

quang v phn thu quang.-Phn pht quang: c cu to t ngun pht tn hiu quang v cc mch iu

khin lin kt vi nhau. Phn t pht x nh sng c th l: Diod Laser (LD), Diod

pht quang (LED: Light Emitting Diode). LED dng ph hp cho h thng thng tin

quang c tc bit khng qu 200Mbps s dng si a mode. LED pht x t pht,

nh sng khng nh hng nn s dng LED tt trong h thng thng tin quang

th n phi c cng sut bc x cao, thi gian p ng nhanh. LD khc phc nhc

im ca LED, thng s dng LD cho truyn dn tc cao. LD c nhiu u im

hn so vi LED: ph pht x ca LD rt hp (khong t 1 n 4nm nn gim c

tn sc cht liu), gc pht quang hp (5- 100), hiu sut ghp nh sng vo si cao.

- Cp si quang: gm cc si dn quang v cc lp v bc xung quanh bo v

khi tc ng c hi t mi trng bn ngoi. C th chn cc loi si sau: si quang

a mode chit sut nhy bc, si quang a mode chit sut gim dn, si quang n

mode.

4

Mho

Giim

Pht ThuSiquang

Thit bpht

quang Siquang

Blp

Thitb thuquang

Hnh 1.4: Cu trc ca h thng thng tin quang

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- Phn thu quang: do b tch sng quang v cc mch khuch i, ti to tn

hiu hp thnh. Trong h thng thng tin quang, ngi ta quan tm nht i vi cc

b tch sng quang l cc diod quang PIN v diod quang kiu thc APD c ch to

t cc bn dn c bn Si, Ge, InP.

Ngoi cc thnh phn ch yu ny, tuyn thng tin quang cn c cc b ni

quang, cc mi hn, cc b chia quang v cc trm lp. Tt c to nn mt tuyn

thng tin hon chnh.

Tng t nh cp ng, cp si quang c khai thc vi iu kin lp t khc

nhau, c th c treo ngoi tri, chn trc tip di t hoc t di bin,tu

thuc vo cc iu kin lp t khc nhau m ch to ca cp cng khc nhau v

cc mi hn s kt ni cc di cp thnh di tng cng ca tuyn c lp t.

Tham s quan trng nht ca cp si quang tham gia quyt nh di tuyn l suy

hao si quang theo bc sng.

Ngun pht quang thit b pht c th s dng LED hoc laser bn dn. C hai

ngun pht ny u ph hp cho cc h thng thng tin quang, vi tn hiu quang u

ra c tham s bin i tng ng vi s thay i ca dng iu bin. Bc sng lmvic ca ngun pht quang c bn ph thuc vo vt liu ch to, on si quang ra

ca ngun pht quang phi ph hp vi si dn quang khai thc trn tuyn.

Tn hiu nh sng c iu ch ti ngun pht quang s uc lan truyn dc

theo si quang ti phn thu quang. Khi truyn trn si dn quang, tn hiu thng

b suy hao v mo do cc yu t hp th, tn x, tn sc gy nn. B tch sng quang

phn thu thc hin tip nhn nh sng v tch ly tn hiu t hng pht ti. Tn

hiu quang c bin i tr li thnh tn hiu in. Cc Photodiod PIN v Photodiod

thc APD u c th s dng lm cc b tch sng quang trong cc h thng thng

tin quang. c tnh quan trng nht ca thit b thu quang l nhy thu quang.

Khi khong cch truyn dn kh di, ti mt c ly no , tn hiu quang trong

si b suy hao kh nhiu th cn thit phi c cc trm lp quang t trn tuyn.

Nhng nm gn y, cc b khuch i quang c s dng thay th cho cc

5

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1.4. Kt lun chng

Qua chng ny, chng ta tm hiu tng quan v h thng thng tin quang vi

nhng u nhc im ca n. H thng thng tin quang da vo nhng u im vt

tri ca mnh ang pht trin mnh m p ng nhu cu thng tin bng rng hin

nay.

6

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CHNG 2

GII THIU MNG WDM.2.1. Gii thiu chng

K thut mng ghp knh phn chia theo bc sng WDM (Wavelength Division

Mutiplexing) c coi l cuc cch mng v bng thng trong mng xng sng

Internet v hn th na. Nhu cu bng thng ang gia tng mt cch nhanh chng vi

nhiu ng dng mi phong ph, chng hn nh thng mi in t, video theo yu

cu, cc cng vic i hi hot ng ng b trn ton cu. Mng quang WDM a ra ha hn ht sc ngha cho nhu cu bc thit trn.

Khi si quang c s dng truyn thng tin th thch thc c t ra i vi

chng ta trong giai on mi trc nhu cu thng tin ngy cng tng mnh m ca

con ngi. Khi m ngy cng c nhiu ngi bt u s dng cc mng d liu v c

mi ln s dng cng chim mt bng thng ng k trong cc ng dng thng

tin ca h chng hn nh c lt thng tin trn cc trang web, cc ng dng s

dng Java, hi ngh truyn hnh, T cho thy nhu cu thng tin bng rng t

ra ht sc bc thit, v nhu cu ny cn vt xa hn na trong tng lai. Hnh 2.1

cho thy s gia tng bng thng ca cc mng khc nhau qua cc nm. S pht trin

mnh m ny ch yu l do s trin khai cc h thng thng tin quang.

Hnh 2.1: S gia tng bng thng ca cc mng khc nhau qua cc nm

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Chng 2: Gii thiu mng WDM

thch ng vi s pht trin khng ngng v tho mn yu cu tnh linh hot

v thay i mng, cc cng ngh truyn dn khc nhau c nghin cu, trin

khai th nghim v a vo ng dng nh k thut TDM, CDM. Cng ngh ghp

knh phn chia theo bc sng WDM c a chung hn c. iu ny l do cng

ngh TDM c chi ph k thut v thit b lp t h thng tng i cao, c bit

trong TDM gy lng ph mt s knh thng tin khi mi khe thi gian c d tr

ngay c khi khng c d liu gi v pha thu kh khn khi phn bit cc khe thi

gian thuc v knh no gii ghp knh tn hiu. Bn cnh , ghp knh phn chia

theo m CDM cn tn ti nhng hn ch v k thut nh tc iu ch v suy hao

trong m ho cng nh gii m cao. WDM l tin b rt ln trong cng ngh truyn

thng quang, n cho php tng dung lng knh m khng cn tng tc bit ng

truyn cng nh khng cn dng thm si dn quang.

Vi WDM, mi knh vi mt bc sng khc nhau v cc bc sng nh sng

ny khng nh hng ln nhau bi v chu k dao ng ca cc cc knh khc nhau l

hon ton c lp nhau. Khc vi h thng TDM, mi phn t knh WDM c th

hot ng tc bt k v mi knh cng c th mang y dung lng ca mi

bc sng. Chng ny s trnh by r nguyn l hot ng ca h thng WDM v

cc thnh phn ca n.

8

Hnh 2.2: H thng TDM

Hnh 2.3: H thng WDM

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2.2. Nguyn l hot ng ca h thng WDM

Ngy nay, nhu cu ca con ngi v cc dch v thng tin bng rng ngy mt

tng ln, th mng ghp knh a bc sng WDM tho mn c nhu cu .

Theo k thut ny, cc lung nh sng vi cc bc sng khc nhau c truyn trn

cng mt si quang. Mi bc sng mang mt dung lng in hnh, thung l

2.5Gbps.

Nguyn l c bn ca ghp knh theo bc sng l ghp tt c cc bc sng khc

nhau ca ngun pht quang vo cng mt si dn quang nh b ghp knh MUX v

truyn dn cc bc sng ny trn cng si quang. Khi n u thu, b tch knh

quang s phn tch thu nhn li cc bc sng .

Vi cng mt nguyn l hot ng c hai loi truyn dn trong WDM, l:

truyn dn mt chiu v truyn dn hai chiu mt si. H thng WDM mt chiu: c ngha l tt c cc knh cng trn mt si

quang truyn dn theo cng mt chiu.

H thng WDM hai chiu: c ngha l knh quang trn mi si quang truyn

dn theo hai hng khc nhau, dng cc bc sng tch ri nhau thng tin hai

chiu.

9

Hnh 2.4: Nguyn l ghp knh phn chia theo bc sng

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So vi h thng WDM mt chiu, h thng WDM hai chiu gim c s lng

b khuch i v ng dy. Tuy nhin, h thng WDM hai chiu thng b can

nhiu nhiu knh, nh hng phn x quang, vn cch li gia cc knh hai chiu,

tr s v loi hnh xuyn m, ng thi phi s dng b khuch i quang haichiu.

2.3. u im ca h thng WDM

C kh nng to dung lng ln ch trn mt si quang, v c th t

dung lng ln hn khi s dng k thut DWDM (Dense WDM: ghp knh phn chia

theo bc sng mt cao).

10

(b)

Ngun 1

Thu 2

Thit bWDM

Knh vo

Knh ra

Thit bWDM

Ngun 2

Knh vo

Knh raThu

1Mt siquang

1

2

(a)

Ngun 1

Knh 1

Thit bWDM

mt si

quangquang

n ,...,,

21

Knh 2

Ngun 2

Knh n

Ngun n

Knh 1Thu

1

Thu 2

Knh 2

Thu n

Knh n

Thit bWDM

Hnh 2.5: H thng WDM theo mt hng (a) v hai hng (b)

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H thng WDM thun tin khi cho php truyn dn ng thi tn hiu khng

ng nht.

C kh nng truyn dn tn hiu hai chiu.

2.4. Vn tn ti ca h thng WDM v hng gii quyt trong tng lai

Vi h thng WDM, si quang cung cp cho chng ta tc truyn mong mun

nhng bng thng mng li b gii hn bi tc x l cc nt, do tc x l

cc nt c thc hin bng in t, m tc in t li thp hn rt nhiu so vi

tc thng tin truyn trong si quang (khong vi Gbps). Nh vy, tn hiu quang

trn si khi n nt s c chuyn thnh tn hiu in thc hin x l in t (s

chuyn i quang- in O/E), sau c chuyn li thnh tn quang truyn i.

iu ny lm gim tc mng, gii php t ra l xy dng mng m trong

tn hiu c x l hon ton trong min quang, gi l mng ton quang.

Trong mng ton quang, d liu i t ngun n ch hon ton di dng quang

m khng cn bt c s chuyn i quang- in no trn ng i, vic iu khin

x l chuyn mch cng c thc hin di dng quang. Tuy nhin, mng ton

quang hin ti vn cha c tin hnh thnh cng bi nhng tn ti ca n. Ccthit b logic hon ton trong min quang kh thc hin hn nhiu so vi cc thit b

logic in t. Bi v, khc vi cc electron th cc photon khng tng tc nh hng

ln nhau, thng th cc thit b logic phc tp u c to ra bng cch s dng

cng ngh in t. Bn cnh , cc trm lp bng quang cng rt kh thc hin hn

nhiu so vi cc trm lp in t mc d cc trm lp trong mng ton quang c

t nhng khong cch nh k rt xa nhau.

2.5. Chuyn mch quang

Hu ht cc thit b mng ngy nay u da trn tn hiu in, iu c ngha

tn hiu quang cn chuyn i sang tn hiu in c khuch i, ti to hoc

chuyn mch v sau c chuyn i tr li tn hiu quang. iu ny ni n s

chuyn i optical-to-electronic-to-optical (O-E-O) v l cng vic ct li ht sc c

ngha trong vic truyn tn hiu. S lng ln tn hiu i qua mng quang cn c

chuyn mch qua cc im khc nhau, c gi l cc node. Thng tin n node s

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c chuyn v pha trc theo hng n ni m n c gi ti qua ng tt

nht c th, con ng ny c th xc nh bi cc yu t nh khong cch, chi ph,

tin cy,bng thng ca tuyn . Cch chuyn i tn hiu thc hin chuyn

mch l tch nh sng t nhng u vo si quang, chuyn i n sang tn hiu

in v sau chuyn i tr li tn hiu nh sng laser, tn hiu ny c gi i

trong si quang.

Vn c bn ca chuyn mch quang l thay th s tn ti ca chuyn mch

mng in bng mng ton quang, s cn thit ca vic chuyn i O-E-O c loi

b. Nhng thun li ca kh nng ny khi trnh c vic chuyn i O-E-O l iu

ht sc ngha. u tin chuyn mch quang c th r hn bi v khng cn nhiu

tn hiu in tc cao t tin.

Cc b chuyn mch quang cho nhiu ng dng trong mng quang. Mi ng

dng yu cu thi gian chuyn mch v s cng chuyn mch khc nhau. Mt ng

dng ca chuyn mch quang l cung cp cc lightpath. Vi ng dng ny, chuyn

mch c s dng bn trong b kt ni cho nhm cu hnh li chng cung cp

cc lightpath mi. Mt phn mm c thm vo qun l mng t u cui nu cui. V th vi ng dng ny, cc b chuyn mch vi thi gian chuyn mch

ms c th chp nhn, nhng cc b chuyn mch y i hi phi c kch thc

ln.

Mt ng dng quan trng khc l chuyn mch bo v. y cc chuyn mch

c s dng chuyn cc lung lu lng t si chnh sang si khc trong trng

hp si chnh gp s c. Ton b hot ng nh thi gian tm ra li, thng tin li n

cc phn t mng iu khin vic chuyn mch v qu trnh chuyn mch thc s i

hi phi hon thnh trong thi gian rt ngn. C th c nhiu dng chuyn mch bo

v khc nhau, ph thuc vo phng php c s dng, s cc cng chuyn mch

cn thit c th thay i t hng trm n hng ngn cng khi s dng trong cc b

kt ni cho bc sng.

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2.6. Cc thnh phn chnh ca h thng WDM

Cu trc ca mng WDM gm c cc thnh phn: thit b u cui OLT, cc b

ghp knh xen/rt quang OADM, cc b kt ni cho quang OXC lin kt vi nhau

qua cc kt ni si quang. Ngoi ra cn c b khuch i b suy hao trn ng

truyn.

2.6.1. Thit b u cui OLT

Thit b u cui OLT (Optical Line Terminator) l thit b c dng u cui

ca mt lin kt im ni im ghp v phn knh cc bc sng. Thit b u

cui gm c ba phn t: b tip sng (transponder), b ghp knh cc bc sng

(wavelength multiplexer) v b khuch i (optical amplifier).

B tip sng lm nhim v thch ng tn hiu i vo t mt ngi s dng mng

thnh mt tn hiu ph hp s dng trong mng. V hng ngc li n lm thch

ng tn hiu t mng quang thnh tn hiu ph hp vi ngi s dng. Giao din gia

ngi s dng v b tip sng c th thay i da vo ngi s dng, tc bt v

khong cch hoc suy hao gia ngi dng v b chuyn tip. Giao din ph bin

nht l giao din SONET/SDH.

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Hnh 2.6: OLT

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S thch ng bao gm nhiu chc nng, tn hiu c th c chuyn i thnh

bc sng thch hp trong mng quang, n cng c th thm vo cc phn u header

nhm qun l mng. B tip sng cng c th gim st t l li bit ca tn hiu im

i vo v i ra trong mng. V nhng l do ny nn b chuyn tip thc hin chuyn

i quang- in- quang.

hnh trn, s lm thch ng ch cho theo hng i vo v bc sng hng

ngc li c gi trc tip n hng ngi dng. Trong mt s trng hp, ta c

th trnh s dng b tip sng bng cch thc hin chc nng thch ng bn trong

thit b ngi dng, nh phn t mng SONET nh hnh trn, iu ny lm gim

c chi ph ng k.

Tn hiu ra khi b tip sng c ghp knh vi cc tn hiu khc cc bc

sng khc nhau s dng b ghp knh theo bc sng trn mt si quang. Thm vo

b khuch i c th c dng khuch i cng sut ln nu cn thit trc

khi chng c a n b phn knh. Nhng bc sng ny li c kt thc trong

mt b tip sng nu c hoc kt thc trc tip trong thit b ngi s dng.

Cui cng OLT cng kt thc mt knh gim st quang (OSC). OSC c mangbc sng ring l, khc vi cc bc sng mang lu lng thc s. N dng

gim st vic thc hin ca cc b khuch i dc theo lin kt cng nh cho cc

chc nng qun l khc.

2.6.2. B ghp knh xen/rt quang OADM

B ghp knh xen/rt quang cung cp mt phng tin iu khin lu lng

trong mng. OADM c th c dng cc v tr khuch i trong cc mng ng

di nhng cng c th s dng nhng phn t mng c lp. hiu c li ch

ca b xen/rt quang, ta xt mt mng gia ba node A, B v C nh hnh v di, lu

lng mng gia A v C i qua node B, gi thit cc tuyn lin kt hon ton song

cng.

Gi s yu cu lu lng nh sau: mt bc sng gia A v B, mt bc sng

gia B v C, ba bc sng gia A v C. By gi trin khai cc h thng WDM im

ni im cung cp nhu cu lu lng ny. Vi gii php trong hnh (a), hai h

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thng im ni im c trin khai, mt gia A v B, mt gia B v C. Mi lin kt

im ni im s dng mt OLT cui lin kt. Node B c hai OLT, mi OLT kt

thc bn bc sng, v th cn yu cu bn b tip sng. Tuy nhin ch c mt trong

bn bc sng l dnh cho node B, cc b tip sng cn li dng cung cp lu

lng gia A v C. V th su trong tm b tip sng node B c dng iu

khin lu lng. y l vic rt tn km.

Vi gii php trong hnh (b), thay v s dng cc h thng WDM im ni im,

ta trin khai mt mng nh tuyn bc sng. Mng s dng mt OLT node A v

C, mt OADM node B. OADM rt mt trong bn bc sng, sau kt thc cc

transponder. Ba bc sng cn li i xuyn qua trong min quang m khng cn kt

thc trong cc transponder. iu ny thy c hiu qu l ch s dng hai

transponder thay v s dng n tm transponder nh gii php (a), do gim c

chi ph ng k.

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Cu hi t ra l ti sao cc b tip sng cn thit gii php (a) iu khin

lu lng i qua. Ni cch khc l ti sao chng ta khng n gin loi b cc b

tip sng v thc hin kt ni trc tip cc b ghp knh v tch knh WDM gia hai

b tip sng node B nh trong hnh (b), hn l thit k mt OADM ring bit. iu

ny l c th, cc OLT c thit k h tr kh nng ny. Lp vt l c xy

dng trong cc mng phc tp hn nhiu cc h thng im ni im.

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Hnh 2.7: Vai tr ca OADM trong mng

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C nhiu kin trc xy dng nn OADM, cc kin trc ny in hnh s dng

cc b ghp/b lc. Ta xt OADM nh mt hp en c hai cng mang mt tp hp

cc bc sng v mt s cng ni b. Cc thuc tnh chnh ca OADM gm c:

Tng s bc sng c th cung cp c l bao nhiu.

S bc sng ln nht c th xen/ rt l bao nhiu.

C rng buc trn mt bc sng no c xen/rt. Mt kin trc ch cho

php mt s bc sng xc nh no c xen/ rt ch khng phi bt k bc

sng tu no cng c.

C d dng xen/ rt cc knh thm vo. C cn thit ph v mt knh angtn ti xen/ rt cc knh thm vo.

Tnh n chi ph.

Tnh phc tp ca vic thit k OADM lp vt l v khi thm vo cc knh

mi th nh hng n vic thit k ny nh th no.

Hnh di y cho ta thy cc kin trc ca OADM:

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hnh 2.8(a), mt s knh c chn c th c tch ra v nhng knh khcc i qua. V th khng c s rng buc trn cc knh c rt v xen. V vy cu

trc ny p t nhng rng buc nh nht trong vic thit lp cc lightpath trong

mng. Ngoi ra suy hao qua OADM c nh, c lp vi s knh c rt v xen l

bao nhiu. Tuy nhin kin trc ny li khng hiu qu v chi ph trong vic iu

khin mt s nh cc knh c rt, v bt k bao nhiu knh c rt, tt c cc

knh u cn phi c tch v ghp li vi nhau. Do ta phi tn chi ph cho vic

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Hnh 2.8: Cc kin trc OADM

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tch v ghp cho tt c nhng knh i vo. iu ny cng dn n suy hao cao hn.

Tuy nhin khi mt s lng ln s knh c rt v linh hot trong vic thm vo

hoc ly ra bt c knh no th cu trc ny cng cho ta hiu qu kinh t.

Hnh 2.8(b) l s ci tin ca hnh 2.8(a) nhm gim chi ph thit k trn, vic

ghp v tch knh c thc hin qua hai giai on. Giai on th nht tch ring cc

bc sng thnh nhng di (bands), giai on th hai tch nhng di thnh cc bc

sng ring l. V d nh h thng 16 knh, c th thc hin s dng bn di, mi di

gm bn knh. Nu ch c bn knh c rt mt v tr, th 12 knh c th gi

nguyn trong cc di, thay v phi tch xung thnh tng knh ring l. iu ny cho

thy ta tit kim c chi ph cho b MUX v DEMUX. Ngoi ra, vic s dng

cc di cho php tn hiu c i qua vi suy hao quang thp hn. Khi mng c s

knh ln th cu trc hnh 2.8(b) ghp knh nhiu giai on tr nn cn thit.

Trong cu trc hnh 2.8(c), mt knh ring l c tch v ghp t mt tp cc

knh i vo. Ta gi thit b ny l b xen rt n knh (SC - OADM). tch v

ghp nhiu knh th cc SC - OADM c ni lin tip nhau. Kin trc ny b sung

cho kin trc ca hnh 2.8(a). Vic tch v ghp knh nh hung n cc knh angtn ti, nn nhm gim ti thiu nh hng ny th ln k hoch tp bc sng no

cn c ly ra tng v tr. Tuy nhin nu s knh cn c tch ra l ln th kin

trc ny khng cn ph hp na, do chng ta phi s dng nhiu thit b ring l ni

li vi nhau. iu cho thy n khng hiu qu v kinh t. Ngoi ra suy hao cng

gia tng theo.

2.6.3. B khuch i quang

Nhm b li s suy hao tn hiu trn ng truyn si quang cng nh ti cc

thit b (nh cc b ghp knh) th cc b khuch i c t gia cc kt ni si

quang nhng khong cch nh k. Trc khi cc b khuch i quang ra i th

la chn duy nht l ti to li tn hiu, ngha l nhn tn hiu v sau pht li n.

Qu trnh ny c thc hin bng cc b lp ti sinh. Mt b lp chuyn tn hiu

quang thnh tn hiu in, khi phc sau chuyn li thnh tn hiu quang truyn

tip. iu ny hn ch tnh trong sut v tng chi ph bo tr ca h thng.

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K thut khuch i quang chim u th hn nhiu cc b lp. B khuch i

quang khng ph thuc vo tc bit v cc nh dng tn hiu. Mt h thng s

dng khuch i quang c th d nng cp hn nhiu, v d n mt tc bit cao

hn m khng cn phi thay th b khuch i. Hn na cc b khuch i quang c

bng thng ln nn c th c dng khuch i ng thi nhiu tn hiu WDM.

Nu khng vi mi bc sng ta phi s dng mt b lp.

Loi khuch i quang in hnh l b khuch i quang si EDFA (Erbium

Doped Fiber Amplifier - khuch i quang si c pha tp Erbium).

B EDFA thc cht l si quang c pha tp c chc nng khuch i c tn

hiu nh sng, chng c th thay i cc c tnh vt l ca si theo nhit , p sut

v chng c tnh cht bc x nh sng. c im ca si ny l chng c kh nng t

khuch i hoc ti to tn hiu khi c kch thch ph hp.

Theo hnh v th nh sng bm vo t laser c kt hp vi tn hiu vo nh s

dng b ghp WDM trn h thng s dng mt b ghp. nh sng bm ny ctruyn dc theo si c pha Eribium v tn hiu bm ny kch thch cc cc ion

Eribium ln mc nng lng cao hn. S dch chuyn mc nng lng ca in t t

cao xung thp s pht ra photon, c gi l bc x t pht nu khng c bt c tc

ng no t pha bn ngoi, cn gi l bc x kch thch khi do s c mt cc photon

cha nng lng bng nng lng dch chuyn. Khi tn hiu d liu c truyn n

EDFA, tn hiu d liu ny n gp cc ion Er3+ c kch thch mc nng

lng cao. Qu trnh ny lm cho cc ion nhy t trng thi nng lng cao xung

20

Hnh 2.9: EDFA

u vo

B cch li

WDMEDF

B cch li

u ra

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mc trng thi nng lng thp nn pht ra photon, do s khuch i cng sut tn

hiu ln ri truyn i tip trong si quang.

Thng thng, mt b cch li c dng trc ng vo hoc ng ra ca b

khuch i tn hiu EDFA ngn s phn x vo trong b khuch i ny.

EDFA cho h s khuch i ln, cng sut ra ln v nhiu thp, n lm vic

bc sng 1550nm. Trong cc h thng thng tin quang, cho cc EDFA hot ng

th cn c ngun bm. Cc ngun bm thc t l cc diod laser bn dn cng sut cao

dng cung cp ngun nh sng cho EDFA.

EDFA c cc c im sau:

Khng c mch ti to thi gian, mch phc hi (b chuyn i O/E v

E/O).Do mch s tr nn linh hoc hn.

Cng sut ngun nui nh nn khi p dng cho cc tuyn thng tin vt bin,

cp s c cu trc nh v nh hn cp thng.

Gi thnh ca h thng thp do cu trc ca EDFA n gin, trng lng nh,

khong lp v dung lng truyn dn c nng cao.

Ngoi ra do EDFA c kh nng khuch i nhiu bc sng trong cng mt sinn n c kh nng tng dung lng tc ln n 20Gbps hoc cao hn khi s

dng k thut WDM.

Ngoi loi khuch i EDFA cn c dng khuch i SOA (Semiconductor

Optical Amplifiers- b khuch i quang bn dn). V c bn, SOA l mt mi ni

P-N. Lp gia c hnh thnh mi ni hot ng nh l mt vng tch cc. nh

sng c khuch i do s pht x kch thch khi n lan truyn qua vng tch cc

ny. i vi mt b khuch i, hai u cui ca vng tch cc c ph mt lp

khng phn x loi b gn sng trong li b khuch i.

2.6.4. Gii thiu v b kt ni cho quang OXC

2.6.4.1. Chc nng OXC

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Trong mng nh tuyn bc sng WDM, hnh trn gm c hai loi node l:

OXC v Edge node. OXC l node m ng vai tr kt ni cc si quang trong mng.

Edge node ng vai tr cung cp giao din gia nhng h thng kt cui phi quang

(nh l cc IP Router, chuyn mch ATM, hay cc siu my tnh) vi li quang. Cc

Edge node thng nm u cui ca h thng v cc lightpath c thit lp giahai edge node qua cc node trung gian nh hnh trn. y c mong i mang li

cu trc ca mng ton quang, thng tin truyn i trn lightpath khng cn s chuyn

i no t tn hiu in sang quang hoc ngc li t quang sang tn hiu in.

OXC cung cp chc nng chuyn mch v nh tuyn h tr cc lin kt logic

gia hai Edge. Mt OXC lm nhim v truyn thng tin trn mi bc sng mt

u vo v n c th chuyn mch n mt cng ra ring bit. Mt OXC vi N cng

vo- N cng ra m cc cng ny c kh nng x l W bc sng trn mi cng OXC

( optical cross connect) l thnh phn dng iu khin cc cu trc mt li phc

tp v mt s lng ln cc bc sng. OXC l thnh phn mng chnh cho php cu

hnh li mng quang, m cc lightpath c th thit lp v kt thc khi cn thit

m khng phi c cung cp c nh. OXC c cu trc vi mch tch hp rt ln

v kh nng ni kt hng ngn u vo vi hng ngn u ra to nn chc nng

chuyn mch v nh tuyn. Trong thng tin quang, bn mi knh quang c th

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Hnh 2.10: Mng WDM nh tuyn bc sng

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c truyn i trong mt si n, OXC l thit b cn thit c th tip nhn nhiu

bc sng khc nhau cc u vo v nh tuyn cc bc sng ny n cc u ra

thch hp trong mng. thc hin iu ny, OXC cn thit xy dng cc khi chc

nng:

Chuyn mch si: kh nng nh tuyn tt c cc bc sng trn mt si

quang u vo ti mt si quang khc ng ra.

Chuyn mch bc sng: kh nng chuyn mch cc bc sng c th t mt

si quang u vo ti nhiu si quang khc u ra.

Chuyn i bc sng: kh nng nhn cc bc sng u vo v chuyn ichng thnh tn s quang khc ng ra, iu ny l cn thit tho mn cc kin trc

bt ng khi khi s dng chuyn mch bc sng.

Mt OXC c cc chc nng sau:

Cung cp dch v: Mt OXC c th dng cung cp cc lightpath trong mtmng ln mt cch t ng, m khng phi thao tc bng tay. Kh nng ny tr nn

quan trng khi gii quyt s bc sng ln trong mt nt hoc vi s nt trong mng

ln. N cng quan trng khi cc lightpath trong mng cn cu hnh li p ng vi

s thay i lu lng ca mng.

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Hnh 2.11: Cc khi chc nng ca OXC

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Bo v: Chc nng quan trng ca b kt ni cho l bo v cc lightpath khi

si b t hoc thit b gp s c trong mng. B OXC l phn t mng thng minh

m n c th pht hin s c trong mng v nhanh chng nh tuyn li cc lightpath.

Trong sut i vi tc bit: kh nng chuyn mch cc tn hiu vi tc

bit.

Gim st thc hin, nh v li: OXC cho thy tham s ca mt tn hiu

nhng nt trung gian, OXC cho php kim tra thit b v gim st cc tn hiu i

xuyn qua n.

Chuyn i bc sng: ngoi kh nng chuyn tn hiu t cng ny sang cngkhc, OXC cn kh nng c th chuyn i bc sng bn trong.

Ghp knh: cc OXC iu khin cc tn hiu ng vo v ng ra tc

ng dy quang, tuy nhin n c kh nng ghp knh chuyn mch lu lng

ni ti.

Mt OXC c phn theo chc nng thnh mt trung tm chuyn mch v mt

khu lin hp cng. Trung tm chuyn mch cha b chuyn mch m n thc hin

chc nng kt ni cho thc s. Khu lin hp cng cha cc card c dng nh cc

giao din lin lc vi cc thit b khc. Cc cng giao tip c th bao gm cc b

chuyn i quang- in, in- quang hoc khng.

Mt phn t kt ni cho c bn 2 x 2 gi cc tn hiu quang t hai ng vo n

hai ng ra v c hai trng thi, l: trng thi cross v trng thi bar. Trong trng

thi cross, tn hiu t cng vo pha trn c gi n cng ra pha di, v tn hiu

t cng vo pha di c gi n ng ra pha trn. Trong trng thi bar, tn hiu t

cng vo pha trn c gi n cng ra pha trn, v tn hiu t cng pha di c

gi ti cng ra bn di.

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2.6.4.2. Phn loi OXC

OXC c chia lm hai loi:- Hybrid OXC (hay OXC khng trong sut): hin ang rt ph bin, n thc hin

chuyn i tn hiu quang sang tn hiu in, thc hin kt ni bng cch s dng k

thut kt ni in t v sau li chuyn i tn hiu in sang tn hiu quang.

- All optical OXC (hay OXC trong sut): l cch kt ni trc tip cc knh quang

trong min photonic. Tn hiu dng photonic trong sut qu trnh chuyn mch m

khng cn thit qu trnh chuyn i O-E-O. OXC ny c th phn thnh cc thnh

phn thit b chuyn mch quang Free Space, thit b quang trng thi rn v cc thit

b gng c in. Trong s cc thit b chuyn mch ph bin nht kt ni nhiu u

vo vi nhiu u ra l WRG. Vi thit b ny, mt bc sng cho trc cng vo

25

Hnh 2.13: Hybrid OXC

Hnh 2.12: Trng thi ca OXC

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bt k s xut hin mt cng ra xc nh nh hnh 2.13. Loi chuyn mch quang

Free Space ny c bit nh l chc nng nh tuyn bc sng.

Cc thit b chuyn mch quang Free Space: n c hiu l lm nhim v

nh tuyn bc sng, mt loi khc th chm laser c chiu mt cch c hc vo

mt trong nhng si quang. Trong trng hp ny, mt ma trn ca cc chm tia trn

n kt hp mt ma trn ca cc si quang, lc mt trong nhng chm tia nng

lng v mt si quang thu s c nh hng chng kt hp vi nhau t

c mt kt ni trong khng gian.

Cc thit b quang trng thi rn: l cc cp thit b bn dn nh hng, cc

thit b ny c th thay i mt trong nhng c tnh quang trn ng i da vo

cc ng dng iu khin tn hiu nh nhit , nh sng, dng in hay in p. Cc

c tnh quang bao gm s phn cc, s truyn nh sng, s hp th, ch s khc x.

H thng vi c in: da vo s phn x nh sng trn mt b mt sng bng

lm thay i tnh nh hng ca nh sng. K thut ny da trn h thng gng c

in (MEMS Micro Electro Mechanical Systems).

Xt mt trung tm cung cp dch v ln, y c th kt thc nhiu kt ni,

mi kt ni mang nhiu bc sng. Mt s bc sng ny khng cn c kt thc

v tr m mun i n node khc. OXC thc hin chc nng ny, n lm vic k

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Hnh 2.14: OXC ton quang WGR

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bn cc phn t mng SONET/ SDH, b nh tuyn IP v cc chuyn mch ATM,

cc thit b u cui WDM v b ghp knh xen/ rt. Mt cch in hnh, mt s

cng OXC c kt ni n cc thit b WDM, cc cng khc c ni n cc thit

b kt cui. V th OXC cung cp dung lng hiu qu hn nhiu.

2.7. S chuyn i bc sng

Chuyn i bc sng l kh nng chuyn tn hiu t bc sng ny( 1 ) trn mt

ng vo sang bc sng khc ti ng ra ( 2 ). B chuyn i rt c ch trong vic

gim xc sut tc nghn mng. Nu cc b chuyn i c tch hp vo trong b kt

ni cho quang trong mng WDM, cc kt ni c th c thit lp gia ngun vch ngay c khi trn tt c cc tuyn ca ng i khng c sn cng mt bc

sng. Cc b chuyn i bc sng gip loi tr s bt buc tnh lin tc v bc

sng.

B chuyn i bc sng y gip cho vic gim xc sut tc nghn tt hn

nhng thc t b chuyn i ny rt kh thc hin bi cc l do v chi ph v gii hn

k thut. Trong mt mng c rt t node mng c trang b b chuyn i bc

sng, do cn phi c s la chn cc node t cc b chuyn i bc sng cc

v tr thch hp sao cho ti u mng, thng t cc b chuyn i bc sng

nhng node m lu lng mng xy ra cc i.

tr--

V d nh hnh trn, mt lightpath c thit lp gia Node A v Node B trn

bc sng 1 , v mt ng lightpath khc c thit lp gia Node B vi Node C

trn bc sng 2 . Nu c mt yu cu Node A n Node C, yu cu khng th

thit lp c v s bt buc tnh lin tc v bc sng. Nu c b chuyn i bc

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1

2

1

2

Node A Node B Node C

Hnh 2.15: S chuyn i bc sng

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sng c t Node B m n c kh nng chuyn i t bc sng 1 sang 2 , th

yu cu c th thc hin thnh cng. R rng cc b chuyn i bc sng c th ci

thin c hiu sut khi cc bc sng ri c sn trn cc tuyn, v mt bc sng

chung th khng c.

Chuyn i bc sng c chia ra lm hai loi:

Chuyn i bc sng quang - in: theo phng php ny, tn hiu trc

tin c chuyn sang tn hiu in s dng b tch sng. Lung bit c lu tr

trong b m. Sau tn hiu in c dng li ng ra ca mt tunable laser

to thnh mt bc sng mong mun ng ra. Phng php ny khng thch hp

cho tc bit cao hn 10Gbps, tiu hao cng sut ln v thc hin phc tp hn cc

phng php khc.

Chuyn i bc sng ton quang: qu trnh chuyn i bc sng c

thc hin hon ton trong min quang. Phng php ny da vo hiu ng trn bc

sng to ra mt bc sng khc.

Kh nng chuyn i bc sng c th thc hin qua nhiu mc khc nhau. Hnh

di y minh ho s khc nhau gia u vo v u ra, trng hp nhiu cng thcng phc tp hn nhng cng tng t. Kh nng chuyn i bc sng hon ton

tc l c th chuyn i mt bc sng ng vo thnh mt bc sng bt k ng

ra. Kh nng chuyn i bc sng gii hn qui nh rng mi bc sng u vo c

th c chuyn i thnh mt s bc sng xc nh trc ng ra. Trng hp

c bit ca chuyn bc sng gii hn l chuyn i bc sng c nh khi m mt

bc sng u vo ch c th chuyn i thnh mt bc sng c nh u ra. Nu

mi bc sng c chuyn i thnh chnh n th chng ta gi khng c s

chuyn i no.

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2.8. Kt lun chng.

Qua chng ny, ta thy c ng lc thc y mng WDM hin nay.

Nhng mng ny cung cp cc lightpath t u cui ny n u cui kia qua cc

node mng trung gian. Mt lightpath gm c mt knh thng tin quang, hoc bc

sng, gia hai node mng m c nh tuyn qua nhng node trung gian. Cc nodemng trung gian c th chuyn mch v chuyn i bc sng. V vy cc mng ny

c xem l cc mng nh tuyn bc sng.

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Hnh 2.16: Cc kh nng chuyn i bc sng

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Chng 3: nh tuyn v gn bc sng

CHNG 3

NH TUYN V GN BC SNG.

3.1. Gii thiu chng

Trong mng quang nh tuyn bc sng, ngi s dng lin lc vi nhau qua cc

knh thng tin quang c gi l cc lightpath. Lightpath l mt ng i ca tn hiu

nh sng t ngun n ch di dng quang thng qua cc kt ni trung gian. Mt

lightpath c th ko di qua nhiu tuyn truyn dn cung cp mt kt ni chuyn

mch mch gia hai node m c th cha mt lung lu lng ln gia chng.

Khi cc lightpath thc hin vic mang thng tin t mt node ngun n mt node

ch no th n cn c nh tuyn v gn bc sng. nh tuyn v gn bc

sng cho lightpath l vn ht sc quan trng v xy ra thng xuyn trong mng.

Chng ny s ni r v vic nh tuyn v gn bc sng cho cc lightpath, cc

thut ton thc hin nh tuyn v cc phng php gn bc sng trong mng WDM.

3.2. Gii thiu v nh tuyn v gn bc sng (Routing and Wavelength

Assignment - RWA).

Khi mt lightpath c chn v xc nh, mi lightpath cn c nh tuyn v gn

bc sng cho n. T t ra bi ton nh tuyn v gn bc sng.

nh tuyn l vn tm ng gia hai node bt k trong mng tho mn mt

mc ch no , thut ng gi l ti u hm mc tiu (cost function). Vn ny

rt quen thuc v rt quan trng trong mng. Thng thng nh tuyn trong IP s

dng thut ton tm ng Dijkstra, vi hm mc tiu l cc metric quen thuc nh

bng thng, tr, chi ph tuyn, Trong mng quang, tm ng c hiu theo hai kha cnh, l tm ng vt l

mang c mu lu lng yu cu (Routing) v a ra bc sng ph hp mang

lu lng trn mi link dc path (Wavelength Assignment) trong s cc bc sng cho

php (bi mi path gm mt s fiber, m trn mi fiber ny, bn c th c W sub-

chanels, cng l W bc sng v W la chn cho yu cu kt ni hin ti). Vn ny

c vit tt l RWA. Khi tm c mt path vt l v nh du bc sng trn cc

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link dc theo path , th chng ta c mt ng quang, cn gi l lightpath (LP). Rc

ri t ra i vi bi ton RWA l n a ra hai iu kin sau:

iu kin tnh lin tc bc sng: mt lightpath phi s dng chung mt

bc sng trn tt c cc link dc theo ng i ca n t ngun n ch. iu

kin ny c minh ho nh hnh di bng cch mi lightpath c th hin

bng mt mu nht nh trong sut ng i.

Hnh 3.1: iu kin tnh lin tc bc sng

iu kin tnh ring bit v bc sng: tt c cc lightpath s dng cng mt

link (fiber) phi c gn cc bc sng ring bit. iu kin c minh ho

nh (hnh 2.10) m n c tho mn khi hai lightpath cng chia s cng mt

link c th hin bng hai mu khc nhau (hai bc sng khc nhau).

Vn xy ra khi cc bc sng trn hai link k cn khc nhau, lc cn dngn b chuyn i bc sng, l ti nguyn t ca mng. Cc gii thut lun tm

cch gim thiu chi ph ny.

Bi ton RWA c th a ra nh sau: cho mt s hu hn cc lightpath c thit

lp trn mng v mt s gii hn cc bc sng. Ta phi xc nh ng i cho mi

lightpath v xc nh s bc sng nn c gn cho cho cc lightpath ny t c

s lightpath c th thit lp l ln nht. Mc d nhng lightpath c ng i ngn nht

c v ti u hn, nhng i khi ta nh phi loi b s la chn ny nhiu lightpath

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hn c th thit lp. V th cc gii thut thng cho php nhiu ng i thay phin

nhau i vi mi lightpath c thit lp.

Cc ng i nh sng (lightpath) m khng th c thit lp v nhng rng buc

v ng i v bc sng c gi l nghn, do vy vn ti u mng tng ng

hn ch n mc thp nht xc xut tc nghn ny.

Khi hai lightpath m chng c tuyn truyn dn trng nhau th chng s khng

c gn cng mt bc sng. Thng thng mt ng i nh sng (lightpath) hot

ng vi cng mt bc sng trn nhng si quang m n i qua. Trng hp ny ta

ni rng lightpath tho mn s rng buc v tnh lin tc bc sng. Tuy nhin nu

mt nt chuyn mch/nh tuyn c trang b vi mt b chuyn i bc sng th

iu kin rng buc v tnh lin tc bc sng khng cn na, lightpath ny c th

chuyn sang nhiu bc sng khc nhau trn ng i t ngun n ch ca n.

Mng li c m hnh bng Graph G(E,V) vi E (edge) l tp cc cnh v V l

tp cc nh (vertical). Vi mi cp node bt k S-D trong mng (v tng ng trong

Graph), tn ti mt tp cc ng i (path) vt l c th gia chng (mi path bao gm

mt s fiber hay link, edge trung gian), k hiu: R. Tp cc ng i ny c th tmtheo mt gii thut tm ng ph bin nh Dijkstra, Prim hay Mentor vi mt hm

mc tiu tu chn.

3.3. nh tuyn bc sng

Trong mt mng khng c b chuyn i bc sng, cc lightpath phi s dng

cng mt bc sng t ngun n ch. Khi c nhu cu cho cuc gi, b nh tuyn

bc sng WR phi s dng gii thut c thit lp t trc chn mt cng ra v

bc sng tng ng. S la chn bc sng ng vai tr quan trng i vi ton b

xc sut tc nghn. V vy mt WR phi tm ra ng i cho yu cu thit lp lightpath

v thc hin gn bc sng sao cho ti thiu ho xc sut tc nghn. Chc nng ny c

tm quan trng trong vic thit k cc mng ton quang.

Bi ton RWA c chia lm hai loi nh sau:

RWA dnh cho lu lng mng c nh (static traffic): vi loi ny th cc

yu cu v lightpath c bit trc, tt c mi ng i v bc sng gn cho cc

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lightpath c thit lp c nh t trc ( v d nh yu cu truyn t Router ny

n Router l khng i, tnh theo n v LP, xt trn ton mng ta c ma trn hng

N*N ). Khi c yu cu i n, mt ng i v bc sng ch nh t trc c

gn cho yu cu tng ng . V vy, qui trnh nh tuyn v gn bc sng l c

nh, khng thay i theo thi gian. Vi loi ny, cng vic thc hin khng phc tp,

n n gin l gn mt ng i no cho lightpath. Mc ch ca phng php ny

l tng cc i ton b dung lng ca mng, tc l c th thit lp ng thi s

lightpath l ln nht. y l bi ton trong mng khng c s chuyn i bc sng.

RWA dnh cho lu lng mng thay i (dynamic traffic): trong mng

quang nh tuyn bc sng, cc yu cu v lightpath i n theo mt qui trnh ring

bit v thi gian chim bi cc yu cu ny cng theo mt qui lut ring. Vi dng lu

lng mng thay i th cn c mt gii thut ng nh tuyn cc lightpath qua

nhng ng i khc nhau da vo s tc nghn trn cc tuyn truyn dn. T gii

thut cho bi ton RWA ng c a ra, n da vo trng thi hin thi ca mng

xc nh ng i cho mi yu cu thit lp lightpath. Mt kt ni b nghn nu

khng c ng i no c th dng mang n. Mt trong nhng thch thc giiquyt bi ton nh tuyn v gn bc sng vi lu lng mng thay i l pht trin

cc gii thut v giao thc thit lp cc lightpath, nhm hn ch n mc thp nht

xc sut tc nghn trong mng (tc l s yu cu kt ni s b t chi/ tng s yu cu),

nng cao hiu sut s dng ti nguyn (cng mt lng fiber, node, b chuyn i

bc sng,c th to ra nhiu lightpath nht) v ci thin hiu nng tng th ca

mng (hiu nng = xc sut tc nghn ca mng + phc tp ca gii thut) . Mt

phng php n gin l da vo gii thut tm ng i b nghn t nht thit lp

cc lightpath ng. Trong gii thut ny, mt lightpath c thit lp trn ng i t

b nghn nht t tp cc lightpath khc nhau gia cp ngun - ch. Bc sng c

cp pht l bc sng u tin cn ri gia nhng tuyn lin kt trong ng ny.

Bi ton RWA ( Routing and Wavelength Assignment) c chia lm hai phn:

nh tuyn v gn bc sng.

3.4. nh tuyn (Routing)

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3.4.1. Gii thiu

nh tuyn c coi l thnh phn ct yu ca kin trc mng, thit k mng v

iu hnh mng ca mi mng thng tin, l thnh phn khng th thiu trong mng

vin thng. Cc yu t thc y cho qu trnh thay i v pht trin nh tuyn mng

ch yu do nhu cu ci thin hiu nng mng, cc dch v mi a vo khai thc v s

thay i cng ngh mng, v y cng l mt trong nhng thch thc khi xy dng v

khai thc mng. Hu ht cc mng vin thng truyn thng c xy dng theo m

hnh mng phn cp m hnh ny cho php s dng nh tuyn tnh trn qui m ln.

Trong khi nh tuyn tnh vn cn tn ti th tnh cht c lp gia ngi s dng

v mng vn mc cao; nh tuyn tnh ch yu da trn mong mun ca ngi s

dng nhiu hn l tnh trng ca mng hin thi. Mng hin i hin nay c xu hng

hi t cc dch v mng, yu cu t ra t pha ngi s dng l rt a dng v phc

tp. Cc phng php nh tuyn ng c s dng nhm nng cao hiu nng mng

ca mng mi ny, tng thm tnh ch ng, mm do p ng tt hn yu cu ngi

s dng dch v.

nh tuyn ch s la chn ng i trn mt kt ni mng thc hin vicgi d liu. nh tuyn ch ra hng, s dch chuyn ca cc gi (d liu) c nh

a ch t mng ngun n ch thng qua cc node trung gian; thit b chuyn dng l

b nh tuyn (router). Tin trnh nh tuyn thng ch hng i da vo bng nh

tuyn, l bng cha cc l trnh tt nht n cc ch khc nhau trn mng. V vy

vic xy dng bng inh tuyn, c t chc trong b nh ca router, tr nn v cng

quan trng cho vic nh tuyn hiu qu.

Khi c nhu cu cho cuc gi n, b nh tuyn xc nh ng i cho yu cu thit

lp lightpath. Nh vy bi ton nh tuyn l xc nh ng i cho mi yu cu thit

lp lightpath. Mi ng i l mt chui cc tuyn truyn dn t im ngun n im

ch. Nhm gim s phc tp trong tnh ton, ng thi bi ton n gin hn, ta s

xt ng i ngn nht gia hai im u cui ny. thc hin iu ny, ta s dng

mt gii thut tm ng i ngn nht da trn gii thut Dijkstra. hiu r v thut

ton dng trong nh tuyn, ta tm hiu v l thuyt th.

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3.4.2. Phn loi nh tuyn

C nhiu cch phn loi nh tuyn, c th a ra mt s loi nh tuyn nh sau:

Da vo chc nng thch nghi vi trng thi hin thi ca mng phn loi

thnh: nh tuyn tnh v nh tuyn ng

nh tuyn tnh: vi nh tuyn tnh, ng dn c chn trc cho mi cp

ngun ch ca cc node trong mng. Cc gii thut nh tuyn chi ph ti thiu c

th c s dng. K hoch nh tuyn tnh c s dng hu ht cc mng truyn

thng, trong k hoch nh tuyn ny ch yu vi mc ch lm gim cc h thng

chuyn mch phi i qua vi yu cu kt ni ng di. K thut nh tuyn tnh bc l

mt s nhc im nh: quyt nh nh tuyn tnh khng da trn s nh gi lu

lng v topo mng hin thi. Cc b nh tuyn khng pht hin ra cc b nh tuyn

mi, chng ch c th chuyn thng tin n ti cc cc b nh tuyn c ch nh

trc ca nh qun l mng.

nh tuyn ng: nh tuyn ng la chn tuyn da trn thng tin trng thi hin

thi ca mng. Thng tin trng thi c th o hoc d on v tuyn ng c th thay

i khi topo mng thay i hoc lu lng mng thay i. nh tuyn ng th hintnh linh hot v d dng m rng mng.

Da vo phm vi nh tuyn, ta phn loi thnh: nh tuyn trong v nh tuyn

ngoi.

nh tuyn trong: nh tuyn xy ra bn trong mt h thng c lp (AS

Autonomous System), cc giao thc thng dng l RIP (Router Information

Protocol), IGRP (Interior Gateway Routing Protocol), OSPF (Open Shortest Path First),

EIGRP (Enhanced IGRP),

nh tuyn ngoi: nh tuyn xy ra gia cc h thng c lp (AS), lin quan ti

dch v ca nh cung cp mng s dng giao thc nh tuyn ngoi rng v phc tp.

Giao thc thng dng l BGP (Border Gateway Protocol).

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3.6. S thit lp ng o (Virtual path)

Mt ng o c xem nh mt ng i ca nh sng t ngun n ch. Khi c

yu cu cuc gi c to ra nt, nt s dng gii thut nh tuyn v gn bc sng

tm ra mt ng i v mt bc sng cho cuc gi . Nt s gn bc sng

c chn cho cuc gi v nh tuyn n n nt k tip. mi nt trung gian ca

ng i, bc sng ca lightpath i ti c kim tra xem c sn c gn v t

c th i tip hay khng. Nu bc sng khng c sn, v nu nt c b

chuyn i bc sng, n c th chuyn sang bc sng khc nh tuyn lightpath.ng i va thit lp c gi l ng o, c thit lp sn trc khi bt k d liu

no c truyn qua.

Mt ng vt l bao gm tt c cc tuyn truyn dn (link) hnh thnh trn l trnh

t ngun n ch, nhng ng o c th cha cc bc sng ging hoc khc nhau

t ngun n ch. Hai yu cu cho cuc gi c cng chung im u cui ch v

ngun c th c cng ng vt l nhng c cc ng o khc nhau. Hnh sau ch ra

s hnh thnh ca mt lightpath. y hai cuc gi c to ra t nt 1 v ng o

cho mi cuc gi to thnh c v ra. i vi cuc gi th nht, nt 1 gn bc sng

1 v gi n n nt 2. Gi s nt 2 c mt b chuyn i bc sng nhng khng c

sn bc sng 1 , v th n chuyn sang bc sng 2 v gi n nt 3. Nt 3 gn tip

2 v n c sn v nh tuyn lightpath n ni. Bng cch ny ng o th nht

c thit lp. Nu cuc gi th hai c to ra nt 1 ngay sau , th mt ng o

th hai c to ra tng t. Ta thy rng ng vt l th ging nhau nhng cc

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ng o th khc nhau. Tng s cc ng o c thit lp t ngun n ch ph

thuc vo s bc sng sn c trn si. S ng o c thit lp tht s ph thuc

vo tc cuc gi i n. Cc b chuyn i bc sng gip thit lp c nhiu

ng o hn.

3.7. Phn loi mng quang WDM

3.7.1. Mng single- hop

Trong mng quang WDM single- hop, mt khi lung d liu c pht i didng nh sng s n c ch trc tip m khng cn phi chuyn sang dng in

nhng node trung gian. truyn dn mt gi, mt trong nhng laser pht ca nt gi

v mt trong nhng b thu ca node nhn phi c chnh n cng mt bc sng

trong khong thi gian truyn dn gi.

Trong cc mng chuyn mch mch, tc iu chnh ca cc b thu pht thng

yu cu thp. Ngc li trong cc mng chuyn mch gi, cc b thu pht cc node

cn c chnh n cc bc sng khc nhau mt cch nhanh chng gi v nhn

cc gi tin khc tip theo. Bn cnh vn k thut ca vic chuyn i bc sng

nhanh, mt thch thc quan trng khc na l pht trin cc giao thc phi hp hiu

qu nhng kt ni cc bc sng khc nhau trong mng.

mt h thng single- hop hot ng hiu qu, bng thng c cp pht gia cc

node ang tranh chp phi c qun l linh ng. Cc h thng ny c th phn thnh

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hai loi: c phi hp trc khi truyn dn v khng yu cu phi hp trc khi truyn

dn.

Cc loi phi hp dng mt knh iu khin n dng chung gia cc node v s

truyn d liu tht s xy ra thng qua mt s cc knh d liu. Cc node ri cn gim

st knh iu khin. Trc khi pht hoc thu gi d liu, mt gi chnh b pht hay bt

thu ca n n knh d liu thch hp. Ngc li trong h thng loi th hai, khng c

s tn ti ca knh iu khin v cc node pht hoc thu t cc knh c nh trc.

3.7.2. Mng Multi- hop

Mng multi- hop khc phc c nhc im ny bng cch trnh s dng b thu

pht iu chnh bc sng. Mi node c trang b mt s cc b thu pht quang c

chnh c nh. Mi b pht trong mng c chnh n mt bc sng khc nhau. Kt

ni trc tip single- hop gia hai node ch c th xy ra khi nu nt n c mt trong

nhng b thu ca n c chnh n mt trong nhng bc sng ca node gi. S kt

ni gia mt cp node bt k trong mng t c bng cch nh tuyn thng qua cc

node trung gian. knh thng tin quang c chuyn thnh dng in, a ch n

ca gi c gii m, sau gi c chuyn mch in v c pht li trn bcsng n node ch hoc n cc node trung gian khc m qu trnh ny c

lp li. V vy, mt gi s tri qua nhiu bc sng thng qua mt s node trung gian

trc khi n c node ch.

3.9. Kt lun chng

Qua chng ny, chng ta tm hiu v phng php nh tuyn v gn bc

sng trong mng WDM, khi c yu cu thit lp lightpath t node ngun n node ch

th b nh tuyn bc sng c nhim v xc nh ng i v gn bc sng cho

lightpath . Trong mng quang WDM, vic s dng thut ton nh tuyn bc sng

t c ti u mng l iu ht sc ngha.

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Thut ton Dijkstra vi vic nh tuyn tm ng ngn nht c nhiu u im

trong mng tp trung nn em s s dng m phng vic nh tuyn trong mng

quang.

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báo cáo tt2

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