Giao Trinh He Thong Thong Tin Quang

"Don't study, don't know - Studying you will know!"

NGUYEN TRUNG HOA

H THNG THNG TIN QUANG V TUYN 1

I. H THNG THNG TIN QUANG

1.1 THNG TIN QUANG

Khc vi thng tin hu tuyn v v tuyn - cc loi thng tin s dng ccmi trng truyn dn tng ng l dy dn v khng gian - thng tinquang l mt h thng truyn tin thng qua si quang. iu c nghal thng tin c chuyn thnh nh sng v sau nh sng c truynqua si quang. Ti ni nhn, n li c bin i tr li thnh thng tinban u. Hnh 1.1. Gii thiu mt h thng truyn dn si quang digitalc s dng rng ri nht hin nay. Trong phn ny chng ta s xem xtcc giai on pht trin ca h thng ny v so snh cc c tnh ca nvi cc c tnh ca nhng h thng ang tn ti. Cui cng, chng ta sgii thch cc tnh cht ca nh sng.

Hnh 1.1. H thng truyn dn si quang digital

1.1.1. S PHT TRIN CA THNG TIN QUANG

Cc phng tin s khai ca thng tin quang l kh nng nhn bit cacon ngi v chuyn ng, hnh dng v mu sc ca s vt thng quai mt. Tip , mt h thng thng tin iu ch n gin xut hinbng cch s dng cc n hi ng cc n hiu. Sau , nm 1791,VC.Chape pht minh ra mt my in bo quang.

Thit b ny s dng kh quyn nh l mt mi trng truyn dn v do chu nh hng ca cc iu kin v thi tit. gii quyt hn ch


ny, Marconi sng ch ra my in bo v tuyn c kh nng thchin thng tin gia nhng ngi gi v ngi nhn xa nhau.

u nm 1980, A.G.Bell - ngi pht sinh ra h thng in thoi - ngh ra mt thit b quang thoi c kh nng bin i dao ng ca myht thnh nh sng. Tuy nhin, s pht trin tip theo ca h thng ny b b b do s xut hin h thng v tuyn.

( Bng 1.1) Cc giai on pht trin ca thng tin cp si quang

Nm Ngun quang Cp si quang

1960 Trin khai my laser Ruby(HUGHES)

1962 My laser Ga As 1965 My laser Co2 (BL)1966 Kh nng s dng ng truyn

dn cp quang (ST, tn tht1000dB/km)

1970 My laser GaAIAS to dao nglin tc (BL, Nga, NEC)

Trin khai thnh cng si spquang s dng abaston (Corning,20 dB/km)

1973 Phng php sn xut si quang c tn tht thp (MCVD, BL, 1dB/km)

1976 My laser GalnAsP dao ng lintc (MIT, KDD, TIT, NTT)

xut kh nng sn xut siquang florua (France, Lucas).

1977 My laser GaAIAs c tui th clng l 100 nm (BL, NTT)

1979 My laser GalnAsP 1,55 um(KDD, BL, TIT) dao ng lin tc

Ch to si quang c Abastoes c tn tht ti thiu (NTT, 0.18dB/km (1.55um))

1980 Cu trc laser ging lng t cch to (Bell Lab).

Ch to si quang Flo (NRL) tn tht 1000 dB/km

1981 GalnAsP LD (1.6 um) ContinuousOscillation (TIT)

1982 LD Array High Power(2.5 W ContinuousOsciltation)

1983 Single Mode, Single FrequencyLD

(KDD, Bel Lab.)

Si quang fluor c tn tht thp(NRT, NTT) tn tht 10 dB/km

1986 Single Mode, Single Frequency Si quang fluor c tn tht thp,


LDCommercialization (NEC,Hitachi etc.)

tn tht 1dB/km (khong2.5 um)

1989 GaAI/AIGa Laser Develoment

S nghin cu hin i v thng tin quang c bt u bng s phtminh thnh cng ca Laser nm 1960 v bng khuyn ngh ca Kao vHockham nm 1966 v vic ch to si quang c tn tht thp. 4 nmsau, Kapron c th ch to cc si quang trong sut c suy haotruyn dn khong 20 dB/km. c c v bi thnh cng ny, cc nhkhoa hc v k s trn khp th gii bt u tin hnh cc hot ngnghin cu v pht trin v kt qu l cc cng ngh mi v gim suy haotruyn dn, v tng gii thng v cc Laser bn dn ... c pht trinthnh cng trong nhng nm 70. Nh c ch ra trong , tn tht ca si quang c gim n 0,18 dB/km. Hn na, trongnhng nm 70 Laser bn dn c kh nng thc hin dao ng lin tc nhit khai thc c ch to. Tui th ca n c c lng hn100 nm. Da trn cc cng ngh si quang v Laser bn dn gi y c th gi mt khi lng ln cc tn hiu m thanh / d liu n cc aim cch xa hng 100 km bng mt si quang c dy nh mt sitc, khng cn n cc b ti to. Hin nay, cc hot ng nghin cunghim chnh ang c tin hnh trong lnh vc c gi l photon hc- l mt lnh vc ti quan trng i vi tt c cc h thng thng tinquang, c kh nng pht hin, x l, trao i v truyn dn thng tin bngphng tin nh sng. Photon hc c kh nng s c ng dng rng ritrong lnh v in t v vin thng trong th k 21.

1.1.2. Cc c tnh ca thng tin quang

Trong thng tin si quang, cc u im sau ca si quang c s dngmt cch hiu qu: suy hao truyn dn thp v bng thng ln. Thmvo , chng c th s dng thit lp cc ng truyn dn nh vmng (nh), khng c xuyn m vi cc ng si quang bn cnh vkhng chu nh hng ca nhim cm ng sng in t. Trong thc t siquang l phng tin truyn dn thng tin hiu qu v kinh t nht angc hin nay

Trc ht, v c bng thng ln nn n c th truyn mt khi lngthng tin ln nh cc tn hiu m thanh, d liu, v cc tn hiu hn hpthng qua mt h thng c c ly n 100 GHz-km. Tng ng, bng cchs dng si quang, mt khi lng ln cc tn hiu m thanh v hnh nh


c th c truyn n nhng a im cch xa hng 100 km m khngcn n cc b ti to.

Th hai, si quang nh nh v khng c xuyn m. Do vy, chng c thc lp t d dng cc thnh ph, tu thu, my bay v cc to nhcao tng khng cn phi lp thm cc ng ng v cng cp.

Th ba, v si quang c ch to t cc cht in mi ph dn nn chngkhng chu nh hng bi can nhiu ca sng in t v ca xung int. V vy, chng c th s dng truyn dn m khng c ting n.iu c ngha l n c th lp t cng vi cp in lc v c th sdng trong mi trng phn ng ht nhn.

Th t, do nguyn liu ch yu sn xut si quang l ct v cht do -l nhng th r hn ng nhiu - nn n kinh t hn cp ng trc nhiu.Gi thnh ca si quang s gim nhanh mt khi cng ngh mi c ara. Ngoi ra, nh cp trn, do c trng l c tn tht thp githnh lp t ban u cng nh gi thnh bo dng v sa cha thp biv chng cn t cc b ti to hn.

Ngoi nhng u im nu trn, si quang c an ton, bo mt cao,tui th di v c kh nng khng mi trng ln. N cng d bodng, sa cha v c tin cy cao. Hn na, n khng b r r tn hiuv d ko di khi cn v c th ch to vi gi thnh thp. Trong bng1.2, chng ta tng hp cc u im trn. Nh nhng u im ny, siquang c s dng cho cc mng li in thoi, s liu/ my tnh, vpht thanh truyn hnh (dch v bng rng) v s c s dng choISDN, in lc, cc ng dng y t v qun s, cng nh cc thit b o.

Bng 1.2 Cc u nhc im ca si quang

c tnh u im Nhc im

tn tht thp C ly ti to xa chiph thit b ngdy dn

Di thng ln Truyn dn dung lngln

Gim kch thc ngtruyn dn

D lp t v bo dngGim chi ph lp tcng

Kh u ni

Phi dn Ngn nga xuyn mThng tin an ton

Cn c cc ng dyCp ngun cho tippht

Ngun - ct Nguyn liu phong ph Cn c cc phng thc


Chi ph sn xut r chnh li mi (cp)

nh gi Dng truyn dn tuytvi

C th gii quyt bngcc tin b cng nghmi

1.2 CP SI QUANG

Si quang l nhng dy nh v do truyn cc nh sng nhn thy cv cc tia hng ngoi. Nh c trnh by trong hnh 1.4, chng c li gia v c phn bao bc xung quanh li. nh sng c th phn xmt cch hon ton trong li th chit sut ca li ln hn chit sut cao mt cht.

V bc pha ngoi o bo v si quang khi b m v n mn, ng thichng xuyn m vi cc si i bn cnh v lm cho si quang d x l. bc ngoi ta dng cc nguyn liu mm v tn tht nng lngquang ln.

Hnh 1.4. Cu trc cp si quang

Li v o c lm bng thu tinh hay cht do (Silica), cht do, kimloi, fluor, si quang kt tinh). Ngoi ra chng c phn loi thnh ccloi si quang n mode v a mode tng ng vi s lng mode canh sng truyn qua si quang. Ngoi ra chng cn c phn loi thnhsi qaung c ch s bc v ch s lp tu theo hnh dng v chit sutca cc phn ca li si quang. Cc vn ny s c trnh by t m mc 1.2.2

1.3. H THNG CP QUANG

Nh kt qu ca cc hot ng nghn cu v pht trin cng caotrong nhng nm 1970, hin nay cng ngh thng tin quang a modeang c s dng rng ri trn ton th gii. Cng ng nh vy i vih thng thng tin quang n mode. Da trn k thut c pht trin,ngy cng nhiu cp quang c s dng trong nhiu lnh vc. Trongphn ny, cc c tnh chung ca cp quang c gii thch v tip ,


chng ti s gii thiu vict hit k mt h thng s v tng t cng nhcng ngh ghp knh phn chia bc sng.

1.3.1. Tng quan v h thng thng tin quang

1. Cu hnh ca h thng thng tin quang.

thit lp mt h thng truyn dn hp l, vic la chn mi trngtruyn dn, phng php truyn dn v phng php iu ch/ ghp knhphi c xem xt trc tin. Cho n nay th khng gian c s dngmt cch rng ri cho thng tin v tuyn, cn cp i xng v cp ngtrc cho thng tin hu tuyn. Trong phn di y, chng ti ch bn ncc phng php truyn dn hin ang sn c da trn vic s dng cpquang. S iu ch sng mang quang ca h thng truyn dn quang hinnay c thc hin vi s iu ch theo mt v cc nguyn nhn sau:

(1) Sng mang quang, nhn c t cc phn t pht quang hin c,khng d n nh pht thng tin sau khi c s thay i v pha v khuych i v phn ln khng phi l cc sng mang n tn.c bit cc it pht quang u khng phi l nht qun v v vyc th coi nh sng i loi nh ting n thay v sng mang. Do ,ch c nng lng l cng nh sng tc thi c s dng.

(2) Hin nay, cc Laser bn dn c ch to c tnh nht quntuyt vi v do c kh nng cung cp sng mang quang n nh.Tuy nhin, cng ngh to phch - Mt cng ngh bin i tn s cnthit iu ch pha - cn cha c pht trin y .

(3) Nu mt sng mang n tn c tn s cao c pht i theo cpquang a mode - iu m c th x l mt cch d dng - th cc ctnh truyn dn thay i tng i phc tp v cp quang b dao ngdo s giao thoa gy ra bi s bin i mode hoc do phn x trongkhi truyn dn v kt qu l rt kh sn xut mt h thng truyn dnn nh. V vy, trong nhiu ng dng, vic s dng phng phpiu ch mt c kh nng s c tip tc.

i vi trng hp u ch quang theo mt (IM) c rt nhiu phngphp bin i tn hiu quang thng qua vic iu ch v ghp knh cctn hiu cn pht. Mt trong nhng v d in hnh c trnh by tronghnh 1.19


Hnh 1.19. Qu trnh ghp knh in

Phng php phn chia theo thi gian (TDM) c s dng mt cchrng ri khi ghp knh cc tn hiu nh s liu, m thanh iu ch xungm PCM (64kb/s) v s liu video digital. Tuy nhin, trong truyn dn cly ngn, ca cc tn hiu video bng rng ri cng c th s dng phngphp truyn dn analog. Phng php iu ch mt s DIM - phngphp truyn cc knh tn hiu video bng IM - v phng php thc hiniu ch tn s (FM) v iu ch tn s xung (PFM) sm tng c lytruyn dn c th c s dng cho mc tiu ny.

Ngoi TDM v FDM, phng php phn chia theo bc sng (WDM) -phng php iu ch mt s sng mang quang c cc bc sng khcnhau thnh cc tn hiu in khc nhau v sau c th truyn chng quamt si cp quang - cng ang c s dng. Hn na, khi truyn nhiuknh thng qua cp quang, mt s lng ln cc d liu c th c gii nh gia tng s li cp sau khi ghp cc knh trn. Phng phpny c gi l ghp knh SDM. H thng truyn dn quang c th cthit lp bng cch s dng hn hp TDM/FDM, WDM v SDM. Chngta c th thy rng h thng truyn dn quang cng tng t nh phngphp truyn dn cp i v cp ng trc truyn thng, ch c khc l nbin i cc tn hiu in thnh tn hiu quang v ngc li ti u thu.Hnh 1.20 trnh by cu hnh ca h thng truyn dn cp quang.


Hnh 1.20. Cu hnh ca h thng truyn dn cp quang

Phng php truyn dn analog c th c tin hnh ch vi mt bkhuych i to iu kin pha thu nhn c mc ra theo yu cubng cch bin i cc tn hiu in thnh cc tn hiu quang v ngcli. Khi s dng phng php iu ch PCM th mi chc nng gii iuch tng ng vi n cn c gn cho pha thu. Cho ti y, chng ta m t cc chc nng c bn ca h thng truyn dn quang. Ngoinhng phn trnh by trn h thng hot ng thc t cn c thmmt mch n nh u ra ca cc tn hiu quang cn pht, mt mch AGC duy tr tnh ng nht ca u ra tn hiu in pha thu v mt mch gim st mi pha.2. Nhng thnh phn c bn ca h thng truyn dn quang.H thng truyn dn quang bao gm cc phn t pht x nh sng (ngunsng), cc si quang (mi trng truyn dn) v cc phn t thu nhnnh sng truyn qua si quang.

Cc phn t sau y c chn s dng:

1. Phn t pht x nh snga. it Laser (LD)b. it pht quang (LED)c. Laser bn dn

2. Si quanga. Si quang a mode ch s bcb. Si quang a mode ch s lpc. Si quang n mode

3. Phn t thu nh snga. it quang kiu thc (APD)b. it quang PIN (PIN - PD)


1.4. PHNG PHP TRUYN DN NG B E

1.4.1. C s ca tiu chun ho

Trc khi phng php truyn dn ng b c c dng thc cao cpca cc c trng n nht, Metrobus v SONET c nhng ng gpto ln. Metrobus l h thng thng tin quang ng b ni ti m bellCommunications Research ca AT & T Hp chng quc Hoa Knghin cu v pht trin. Cn SONET l tiu chun kt ni ca h thngthng tin quang m sau Bell communications reseach (Bellcore) xut v ri c u ban T1 chp nhn s dng v pht trin cho tiuchun Bc M. Metrobus chng li quan im ca thng tin quang cin, s dng s ghp tng u tin, chp nhn s dng khi nimcontainer (cng ten), s dng Overhead (mo u) mt cch hiu quv thit lp khi nim h thng thng tin quang ng b ni ti, hthng ny coi tn hiu cp 150 Mbit/s lm cp tiu chun. Do vy, trn cs cp 50 Mbit/s, SONET b sung quan nim v cu trc phn cp vphng php ng b nh con tr h thng ho on mo u v sau m ra chn tri mi cho thng tin ton cu. Da trn nhng ci ,chnh phn cp ca ng b (SDH) hin nay ly tn hiu cp 150Mbit/s lm tiu chun, k c phn cp s kiu Chu u, v c ph cpho m ra kh nng thng tin ton cu.

1. Metrobus

Metrobus l mt h thng thng tin quang do J.D.Spalink, mt nhnghin cu ti Bellcore ca AT & T, xut nm 1982. N c trinkhai theo quy m y vo u nm 1984, c cng b vo thng chnnm 1985 v c th nghim thng mi ho vo u nm 1987.Chnh sch c bn ca Metrobus l pht trin h thng thng tin quangti u nht, c cn nhc n kha cnh tc cao, dung lng ln, vn lc trng ca mt h thng thng tin quang, phng hng tin trin camng thng tin, qu trnh pht trin ca cng ngh ct yu v xu hngi mi dch v. Tn gi ca Metrobus c ngun gc t mc tiu ngdng ca n nhm vo vng thnh ph ln (metropolitan). Trong qutrnh R&D cho ng dng ni ln mt s khi nim. in hnh lkhi nim v mng thng tin quang im - a im, khi nim v hthng ng b ni ti, tm nhn ca DS-O, khi nim ghp knh tng utin, iu chnh ng thi nhng tn hiu nhiu cp bng vic iu khins hiu cng ten, thit lp tn hiu tiu chun ni ti 150Mbit/s v sdng mo u.

Do tt c cc h thng thng tin quang trc y u c xuttrong bi cnh ca cc h thng im - ni im, cho nn khi nim cathng tin quang c xem nh mt khi nim c tnh cht cch mng.


Nhng khi nim khc ng vai tr khng th thiu c th hinkhi nim ny. Vi vic cn nhc n di thng v hn m thng tinquang cung cp, ta thy n bo m khong trng cho mo u, vbng vic s dng n cng nh bng vic hnh thnh knh truyn thngmo u, cho php ng dng lin kt ca ton b cc tuyn thng tinquang. Tuy nhin, do t l ca mo u vt qu 4,5% ca ton b,cho nn khi nim ny kh c th c chp nhn trong bi cnh .

Vic la chn 150 Mbit/s (c th l 146,432, Mbit/s) lm tn hiu ni bca mng thc s l mt quan im tin phong. S d nh vy l vnhng iu sau y c d kin : khi c xem xt theo kha cnh phnlp tn hiu digital, tc bt m tt c cc tn hiu c th bao gm l 150Mbit/s; theo kha cnh dch v, tn hiu thoi, s liu v video (k c tnhiu HDTV c nn) hin ti u c th c s dng trong cp 150Mbit/sny; v kha cnh cng ngh bn dn c bn, cng ngh CMOS c thc s dng trong phm vi 150 Mbit/s chng kh khn g. Ngoi ra, vkha cnh thu bao th cn c mt s li th: vi cp phn t 150 Mbit/s,cc nh sng c th c s dng nh s kt hp vi it LED v PIN rtin, v cp si quang c th to iu kin cho s kt hp hiu qu nynh vic s dng si quang a mode c ch s tng dn thay cho nmode.

Khi nim ghp knh tng u tin cng l mt khi nim mang tnh cchmng. N cho php ghp knh trc tip tn hiu DS -1 thnh tn hiu tiuchun150 Mbit/s m khng cn chuyn qua tn hiu DS-2 hoc DS-3 iukhng th c trong h thng ghp knh khng ng b trc y. N trthnh nn tng thc hin kt ni tch/nhp v ni kt cho l nhngni kt thng thy trong mng thng tin quang.

c gii thiu nh mt phng tin thc hin ghp knh tng th nht,khi nim ny gip cho vic ghp knh tn hiu phn cp bng vic iukhin s hiu ca cc cng ten. Ngha l, bng vic xc nh cc ckch thc c nh, lm cho cc tn hiu DS -1. DS -1C, DS-2, DS-3v.v...lp y vo cc tng ng ca cc khi 1, cc khi 2, cc khi 4,cc khi 28 trong cng mt n v thi gian. Nh vy, kt ni tch nhpv kt ni cho rt tin li, bi v tt c cc tn hiu u c x l vin v ca s hiu .

Tn hiu tiu chun ni b bao gm 13Wx88 (1W=16 bt) nh trong hnh1.37. Tc bit l 146,432 Mbit/s (13x88x16x8 kbit/s). 88 n v ca tm (thuc v 88 ) xut hin trong 125m s/13, trong d 4 n v c sdng cho mo u v mi tn hiu DS-n chim s hiu tng ng ca .


Hnh 1.37. Cu trc khung ca Metrobus

Vic gii thiu khi nim ng b ni ti cng l mt tin chomng thng tin ng b. C ngha l, do phm vi mc tiu ch cgii hn cho khu vc thnh ph, da trn tiu chun ni b ca mng,bin php i ph trong trng hp vt qu gii hn cn ng b khng c chun b cht no. Trong trng hp ny tn hiu nh thi ss dng tn s chun ng b ho c bn BSRF v cng c th s dngtn hiu nh thi c n nhn t b dao ng ni v t tn hiu thuc.

nhn r ca tn hiu DS-O c to ra vi n v 125 m s. Khi vicchuyn t mi tn hiu phn cp sang cng ten cng c thc hin vin v 125 m s, th cc tn hiu DS-O nhn c qua ly mu 8 kbit/s cth xut hin mt cch trong sut ngay ti tn hiu phn cp mc cao.

Theo cch nh vy, vic phn tch knh DS-O 64 kbit/s khi tn hiu tiuchun ni b 150 Mbit/s c th c thc hin mt cch d dng.

Hnh 1.38 biu din cu trc ca h thng Metrobus. Phn c trnh bynh bus ni b trong hnh v tng ng vi tn hiu tiu chun ni b146,432 Mbit/s. Tn hiu c to ra t DS-1 n DS-3 qua PMB (bngghp knh c th lp trnh). Thng tin quang 146 Mbit/s c th phi hptrc tip vi tn hiu ny, v i qua thit b truyn dn sng quang LTE-Lightwave Transmission Equipment). c th to nn thng tin quang 876Mbit/s hoc 1,7 Gbit/s bng vic a 6 hoc 12 n v ca tn hiu nyvo WIM (ghp knh xen t m - Word Interleaved Multiplexing), ri sau a qua LTE. Nhng qu trnh ny c m t trong hnh v. Ngoira, h thng PCCS (h thng kt ni cho c th lp trnh) thc hin chcnng ni kt cho qua cc cng ten do tiu chun ca tc bit DS-1to ra bng cch a vo tn hiu 146 Mbit/s.


Hnh 1.38. Cu trc ca h thng Metrobus

2. SONET

Sonet l mt t vit tt ca Synchronous Optical Network (mng quangng b). N c R.J.Boehm v Y.J.Ching vin nghin cu truynthng Bell trnh ln u ban T1- t chc tiu chun truyn thng caBc M - vo cui nm 1984 nh mt n tiu chun v u ni hthng thng tin quang. Vo thi gian , khung c xut c dng3x8x33B nh trong hnh 1.39, v tc bit l 50,688 Mbit/s (=3x8x33x8kbit/s). Tn hiu ny c gi l STS-1 (Synchronous Transport Signal -1 - Tn hiu chuyn giao ng b - 1) v DS - 3 hoc SYNTRAN DS-3,m n c chp nhn nh tn hiu phn cp c bn v c n nha vo qu trnh ghp knh xen byte qua STS-1.

Tng u tin ca SONET c ngh cho mc ch "gp g giachng" v quan im nghi ng v tnh kh thi ca n chim u th.Kt qu l vic tiu chun ho n hu nh khng c tin hnh trongkhong mt nm, sau khi khi nim SONET c gii thiu. Tuynhin, vic tiu chun ho bng nhin c a ra cng vi thng boca Metrobus vo thng chn nm 1985, v khi nim v h thng phncp v k thut ng b ho bng con tr c cc thnh vin ca uban T1 xut thm. Nhng ngi xut SONET pht trin v hthng ho cu trc khung ca tng u tin v a ra cng thc (28+L)(24+M) (8+N). iu ny d tnh tn mo u ca mc DS-3 ln kchthc DS-1 ca L n v; mo u ca mc DS-1 ln kch thc DS-Oca M n v v mo u ca mc DS-O ln Nbit. Tng gia ca khungSONET c cu trc 26Bx30 v 49,92 Mbit/s (30x26x8x8 kbit/s) ciu chnh vi L=2, M=2 N=0 da trn cng thc miu t trong hnh1.39. Vo khong thi gian vin nghin cu truyn thng Bell caAT&T ngh rng tn hiu tiu chun ni b ca Metrobus (c cu trc26x88W v 146,432 Mbit/s) cn c chp nhn l tn hiu tiu chun.Tn hiu ny c biu th bng cng thc ca Vin Nghin cu truynthng Bell s l: J+K (28+L) (24+M), (8+N), J=1, K=3; L=1, M=2; N=0;v L, M v N trong s c cng mt ngha nh c xc nh trc,


K c ngha l s hiu ca tn hiu mc DS-3, cn J l kch thc ca DS-1 i din cho mo u gn vo ton b chng.

Hnh 1.39. Cu trc khung ca SONET

Mc d u ban T1 xem xt k nhng cuc tho lun lin quan n haid n ny, n vn khng th phn quyt c tnh u vit theo kt qui chiu v kim nghim. im bn ci si ni nht l trong nh gigia 150Mbit/s v 50 Mbit/s th tc bit no u vit hn.

Tuy nhin, do s cnh tranh v phn chia th trng vin thng v vai trgia cc cng ty, u nm 1986, u ban T1 i ti mt quyt nh l tnhiu tiu chun STS -1 s l 49,92 Mbit/s. Trong khi ITU - T cng anghot ng nhm tiu chun ho bng knh rng vo cng thi gian thu ban T1 quyt nh ngh ly 149,976 Mbit/s lm d n ca Bc M,n gp ba ln 49,92 Mbit/s; c ngha l u ban T1, ngi quyt nhchn cp 50 Mbit/s, tha nhn v mt k thut tnh thch hp ca 150Mbit/s. Sau , nhng hot ng tiu chun ho SONRT c tin hnhmt cch sun s, ch yu nh u ban ngang cp T1X1, v i n mt


tho thun v mt tiu chun thm ch kh chi tit. Mc d n tinhnh hot ng phi hp ngay tc khc mang tnh cht b mgoi, viITU-T v vn tiu chun kt ni NNI ca B-ISDN, song c rtnhiu mt hn ch trong vic iu tit vi cc tn hiu digital kiu Chuu, bi v 13Bx60 v 49,92 Mbit/s (hoc 146,976 Mbit/s) ch ch yuph hp vi cc tn hiu digital ca Bc M.

Do vy, cu trc 9Bx270 v tc 155,520 Mbit/s, ci c tng ln baln cu trc khung v tc bt ca SONET chnh l phn cp ng b sm n c quy nh nh khuyn ngh G.707-G.709 ca ITU-T.

3. Phn cp s ng b

ITU-T thit lp cc knh H1, H2, H3, H4 nh i vi knh tc caoca khch hng trong qu trnh tiu chun ho ISDN vo u nm 1980.Trong s , knh H1, c tiu chun ho bng vic phn chia nhthnh knh H11 ca 1,536 Mbit/s da trn c s tn hiu DS-1 kiu BcM, v knh H12 ca 1,920 Mbit/s da trn c s tn hiu DS-1 kiuchu u. Mi ang ch c nhng nt i cng mang tnh cht khi nimtng ng vi phn cp s hin c lin quan n cc knh H2, H3, H4, n bt u cp n tiu chun ca mt knh bng rng da trn ccknh . u tin n nghin cu cc tc bit 30-40, 45, 60-70 Mbit/s,sau n 149,976 Mbit/s c a ra, da trn tiu chun SONETca u ban T1.

Trong khi , ITU-T bt u hot ng tiu chun ho phn cp ngb s cho NNI (giao din nt mng) vo thng by nm 1986, khc bitvi UNI (giao din khch hng - mng) ca ISDN. iu ny bt umt giai on tiu chun ho ch thc hng ti phn cp s ng b vITU-T cng u ban T1 duy tr mi quan h hp tc cht ch cho mcch , Hoa k chnh thc a ra cp 50 Mbit/s da trn tn hiuSTS-1 ang c s dng ca SONET ti hi ngh Brazin vo thngHai nm 1987 cn CEPT tm cch chng minh s cn thit ca cp tc 150Mbit/s v n c th thch hp vi c hai h phn cp s kiu Bc Mv kiu Chu u.

Kt qu l, n ca M c thay i thnh 149,976 Mbit/s ca cutrc 13Bx180, da trn tn hiu STS-3, ti Hi ngh Hamburg vo thng7 cng nm , cn CEPT xut tn hiu 155,520 Mbit/s ca 9Bx270i lp vi ca M. Ngi ta tranh ci sut mt thi gian di v haicu trc ny v im tranh ci si ni nht l s chung ho gia tn hiuDS-2 ca 8,448 Mbit/s v DS-3E ca 34,368 Mbit/s tho thun cui cngqua hi ngh Seoul vo thng Hai nm 1988 l cu trc 9Bx270. Tiuchun NNI c tho thun l tiu chun trong cc khuyn ngh G-707 -G.709 ca ITU-T v phn cp s ng b, tp trung trn tn hiu STM-1


ca cu trc khung 9Bx270 v tc bt 155,520Mbit/s, c chnhthc ho.

Ngay c sau khi khuyn ngh ca ITU-T c n nh th cc hotng nghin cu v i mi v phn cp s ng b vn c tip tc.Vo thi im khi tiu chun phn cp s ng b ln u tin c quynh, h thng ghp knh ng b c mt cu trc hon chnh nhhnh 1.40. Tuy nhin, khi nhng khuyn ngh G.781 - 784 v G.957 - 958(u da trn c s phn cp s ng b) c tiu chun ho honchnh trong qu trnh nghin cu hai nm sau , th h thng ghp knhng b c n gin ho nh cu trc trong hnh 1.41. C th thyc rng cc ng ghp knh phn cp kiu chu u tng ng mtcch ng k vi cc ng ghp knh phn cp kiu M, v rng bsung cc khi nim mi, chng hn nh AUG, TUG-3. Hiu theo ngngha ca n th phm vi m Metrobus ng gp cho vic tiu chun hoSONET v SONET ng gp cho vic tiu chun ho phn cp s ngb l cc k to ln. Rt nhiu c trng ca phn cp ng b c ngungc t tiu chun ca h thng Metrobus, chng hn nh quan im vmng thng tin quang, khi nim v h thng ng b (mt cch ni ti), r ca DS-O qua khung 125m s, khi nim v ghp knh tng thnht, phi hp tn hiu tc ghp knh bng vic iu khin s hiu cacng ten, thit lp tn hiu cp 150 Mbit/s tiu chun, v nng cao linh hot v tin cy ca h thng nh s dng mo u mt cch hiuqu. Cng nh vy, cu trc h thng phn cp, h thng ho cu trcmo u, ng b ho bng con tr, v kh nng cu trc mng thng tinlin tc a, u xut pht t tiu chun kt ni ca SONET. Da trnnhng c s , tiu chun phn cp s ng b l tiu chun cho phpcu trc nn mng thng tin ton cu qua vic iu chnh kt hp hai kiuphn cp s ca Bc M v ca Chu u.


Hnh 1.40 Cu trc ghp knh ng b s giai on u tin

Hnh 1.41. Cu trc ghp knh ng b

Mt khc, phn cp s ng b vn c khi u v mc ch tiu chunho NNI ca B-ISDN, c nh hng rt ln n tiu chun UNI caB-ISDN. Trc ht, nh hng trc tip ca NNI ca B-ISDN l quy


nh 155,520 Mbit/s cho tc bt tiu chun ca NNI ca B-ISDN vtrong s quy nh tc bt trng tin thp hn 149,760 Mbt/s. Ngoi ra,nh hng c tnh cht c bn khc na l n c cc t bo ATM cnh x trong ng bao ca trng tin VC-4 pht i c s phn cp sng b ca UNI ca B-ISDN. Ni mt cch chnh xc, phn cp s ngb ng mt vai tr ch cht trong vic hnh thnh khi nim B-ISDNcng nh i ti mt phng php truyn dn ng b mi.

1.4.2. SHD v SONET

Nh trn gii thch v qu trnh tiu chun ho phng thc truyndn ng b, SDH v SONET, c mt mi quan h ht sc mt thit. chnh l: hot ng tiu chun ho SONET to iu kin thun tin chotiu chun SDH v n cng m rng SONET SONET c s dngcho thng tin hon cu. Do vy cn phi hiu rng gii thch SDH l bao hm c vic gii thch SONET. Tuy nhin vn c mt s khc bitnh gia SDH v SONET. Nu nhng s khc bit tiu biu gia chngta c th m trn u ngn tay th im bt u c bn ca SDH l cp150Mbt/s, trong khi SONET l cp 50Mbt/s. C ngha l, trong khiSDH kt hp DS-4E vi tn hiu mc thp thnh tn hiu cp cao nht thSONET c DS-3 nh tn hiu cp cao nht. Do c mt khi nim v giaodin, cho nn, ng nhin, y chng phi l mt s khc bit ng k.C ngha l nu ba ln ca tn hiu STS-1 (Tn hiu chuyn giao ng bcp 1) l 51,840 Mbt/s tn hiu truyn dn c bn ca SONET - cphi ghp to thnh STS-3C th n cng c th bng vi tn hiu STM-1-155,520 Mbt/s ca SDH, SDH v SONET c s khc bit no vcc loi tc truyn dn. STM (155,520 Mbt/s, l mt khi c bn,STM - 4 (622,080 Mbt/s), gp bn ln ca STM-1 v STM-16(2.488,320 Mbt/s), gp bn ln ca STM-4, l nhng i tng quan tmchnh trong SDH. Trong khi , trng hp SONET, STS-1 (51,840Mbt/s) l tc c bn, STS-3 (155,520 Mbt/s) STS-9, STS-12(622,080 Mbt/s)STS-18, STS-24, STS-36, STS-36, STS-48 (2.488,320Mbt/s) l cc i tng quan tm (tham kho bng 1.9); khi , nichung, tn hiu STM-n bng vi tn hiu STS-3n trong tc truyn dn :

Bng 1.9 Tc truyn dn ca SDH v ca SONET

SDH SONET

N STM - N N STS - N

1 51.840 Mbps

1 155.520 Mbps 3 155.520 Mbps


9 466.560 Mbps

4 622.080 Mbps 12 622.080 Mbps

18 933.120 Mbps

24 1,244.160 Mbps

36 1,866.240 Mbps

16 2,488.320 Mbps 48 2,488.320 Mbps

V mt cu trc khung, SONET gim i ba ln so vi SDH. Nu SDH lSTM-1, n c cu trc 9x270B v STS-1 ca SONET c cu trc 9x90B,bng mt phn ba kch thc ca SDH. Cng nh vy, mo u on caSTM-1 trong dng 9x9B c b tr hng u ca khung STM - 1, mou on ca STS-1 di dng 9x3B c b tr hng u ca khungSTS-1. Sau , trong c hai trng hp, hng th t c dnh ring chocon tr (pointer). C th l, vic la chn hng th nht, th t v th byca mo u on trong STS-1 tng ng vi mo u on ca STS-1v vic s dng cc thnh phn ny l nh nhau trong c hai trng hp.

SDH v SONET c mt s khc bit trong khi tn hiu cu thnh. Gcgc ca vn nh vy l v STM-1 l cp 155Mbt/s v STS - 1 l cp50Mbt/s. Do , trong trng hp STM - 1 cn phi ghp knh mt cchc h thng tt c cc tn hiu phn cp t DS-1 n DS-4E, trong khi , trng hp STS-1 ch cn thit ghp knh c hiu qu nm loi tn hiuphn cp l DS-1, DS-1E, DS-1C (3,152Mbt/s), DS-2 v DS-3. Do vy,trong trng hp STM-1, cc khi tn hiu gia, chng hn nh C, VC,TU, TUG, AU, AUG v.v.... s c thit lp v th tc ghp knh ngb ton b h thng nh trong hnh 1.41 l cn thit. Ngc li, trongtrng hp STS-1 ch c mt khi tn hiu trung gian, gi l mt nhnho (VT-virtual tributary) l s c thit lp. VT nayf tng ng vi VCca SDH. Cc VT tng ng vi VC-11, VC-12 VC-2 c gi tngng l VT 1,5, VT2 v VT6, cn VT3 c b sung cho DS-1C.

V n v tn hiu trung gian lin quan c khc nhau, cho nn SDH vSONET cng khc nhau v cu trc ghp knh. Trong trng hp SDHcu trc thng k h thng nh trong hnh 1.41 l cn thit , trong nni kt C, VC, TU, TUG, AU, AUG ATM-n vi nhau, cn trong trnghp SONET, ch cn n mt th tc ghp knh n gin l u ni DS-m, VT v STS-1. Sau , phng php nh x cc tn hiu phn cpthnh VT-1,5 VT 2 v VT 6 cng ging nh phng php nh x mi tnhiu phn cp thnh VC-11, VC-12 v VC-2, v phng php nh x DS-1C thnh VT3 s s dng php nh x tun theo cn chnh dng, khng


v m. Phng php dng ghp knh cc VT ny thnh ng baotrng tin STS-1, tc l SPE (Synchronous Payload Envelope - ngbao trng tin ng b) cng ging nh phng php ghp knh VC linquan thnh VC-3 qua TUG-2. Trong trng hp th hai, vic nh x DS-3 thnh SPE cng ging nh phng php nh x DS-3 thanh VC-3,nhng php nh x SYNTRAN DS-3 th c cung cp ph thm.

V phng din thut ng, khi mi quan h tng ng gia SONET vSTM c tm lc, th VT 1,5 VT2, VT6 ln lt tng ng vi VC-11, VC-12, VC-2, STS-1SPE tng ng vi VC-3 v STS-3C vi STM-1. Khi cc thut ng lin quan n phn cp cn i snh, phng tin vtl, on ti to, on ghp knh v lp ng truyn c t ra trongSDH s c gi l lp quang, lp on, lp ng dy v lp ngtruyn trong SONET. Cc thut ng xc nh khc lin quan n nh x,ghp knh, mo u v ng b ho th hu nh ging nhau.

SONET cng nh SDH u da trn khi nim phn cp, s dng khung125 m s, dng mo u h thng, v c tc truyn dn c bn gingnhau. Nhng n c iu tit nh s lin kt tt c cc tn hiu phn cps Bc M k c tn hiu DS-1E kiu Chu u, v n cha ng c thtc ghp knh tng th nht.

Ngoi ra, SONET s dng ng b ho lin quan ti phng php contr, ging nh ca SDH, cho nn c th kt ni ton b nc M bngmng truyn dn ng b.

1.4.3 Phn cp s cn ng b so vi ng b

Lp (mc) s hin c bao gm cc tn hiu DS-1-DS-4 ca h thngChu u/ Bc M, c b phn tiu chun ho vin thng ca ITUv Bell System quy nh. Trong s , cc tn hiu ca h thng Bc M c u ban T1 ca Bc M tha nhn tr li nh tiu chun Bc M,ng thi, tiu chun cng c bit n nh l tiu chun do BellSystem thit lp li.

phn bit lp s ny vi phn cp s ng b c thc thi gn y,n c gi l phn cp s cn ng b.

Phn cp s cn ng b, mt h phn cp s tiu chun ang c sdng, c phn loi thnh h thng Chu u v h thng Bc M nh(a) v (b) trong Hnh 1.42 Phn cp s cn ng b ca Bc M chnh thnh t DS-1 (1,544 Mbt/s), DS-1C (3,152 Mbt/s), DS-2 (6,312Mbt/s) v DS-3 (44,736 Mbt/s), DS-4E (139,264 Mbt/s). Phn cp scn ng b Chu u bao gm DS-1E (2,048 Mbt/s), DS-2E (8,448


Mbt/s), DS03E (34,368 Mbt/s) v DS-4E (139,264 Mbt/s), DS-5E(564,992 Mbt/s).

Ghp knh theo mi giai on l ghp knh cn ng b v n c ngb ho nh cn chnh dng - l mt loi nhi bt.

Phn cp s ng b, nh c trnh by trong (c) ca hnh 1.42, chnh thnh t cc tn hiu STM-n. ng thi, n l mt s nguyn ln, m1,4 v 16 l cc s c quan tm ch yu. Cc tc bt tng ng vicc s ny l 155,520 Mbt/s, 622,080 Mbt/s v 2.488,320 Mbt/s. Mttn hiu STM-n c hnh thnh thng qua ghp knh ng b t cc tnhiu phn cp DS-1, DS-2, DS-3 v DS-4E, DS3E, DS-2E, DS-1E. ngthi, cc tn hiu DS-1C hoc DS-5E khng c s dng. Tn hiuSTM-n c cu thnh t n ln cc tn hiu STM-1 m n l s ghpknh xen byte (BIM).

Tuy nhin, cu trc mo u ca n c tin hnh mt cch hi khc.

Khi so snh (a), (b) trong Hnh 1.42 vi (c) trong cng hnh chng tac th d dng nhn thy rng phn cp s ng b c mt cu trc ngin hn nhiu so vi cu trc ca phn cp s cn ng b.

C ngha l, tt c cc tn hiu phn cp ca h thng Bc M v Chuu ch c mt giai on ghp knh. Trong mt h thng phn cp s cung b vic ghp knh khng ng b c thc hin khi tn hiu trongmt cp c ghp knh thnh cp ca giai on k sau. Trong mt hthng phn cp ng b, vic ghp knh ng b c thc hin khi tnhiu phn cp c ghp thnh tn hiu STM-n. V li, trong phn cp scn ng b tn hiu DS-m thuc v cp ca giai on k sau ca tn hiuDS-(m-1); nhng tt c cc tn hiu ny c mi quan h ngang bng trongphn cp s ng b.

(a) Phn cp khng ng b (Bc M)

(b) Phn cp khng ng b (Chu u)

(c) Phn cp khng ng b


Hnh 1.42. Phn cp s

1.4.4. Khi nim phn cp v mo u

Ni chung, cc tn hiu s c gi i qua ng truyn, on ti to,on ghp knh v mi trng vt l nh c minh ho trong hnh 1.43.Khi p dng cc khi nim phn cp cho qu trnh truyn dn s thng truyn dn c th c phn chia thnh mt lp, ng truyn,mt lp on ghp knh, mt lp on ti to v mt lp mi trng vtl (hoc lp quang hc).

Cu trc ca ghp knh ng b c mt s sp xp theo khng gian c hthng ph hp vi cc khi nim phn lp. Trong Hnh 1.44, khungSTM-n c phn loi theo chc nng; mo u ca on ghp knhc p dng trn lp ca on ti to v trn lp ca on ghp knh.Hn na, mo u ng truyn c p dng cho lp ng truyn vcc mo u cho bt k cc ng c mc thp hn no khc th hindin trong hnh bao trng tin bn trong STM.

Cc mo u c s dng trong ghp knh ng b c phn chiathnh mo u on (SOH-Section overhead) v mo u ng truyn(POH - Path Over-head), da trn nhng khi nim phn cp nh m t


trn. Trong s chng, SOH bao gm mt mo u on ng trc vu on ghp knh.

Hnh 1.43. ng truyn dn (mt ng) v khi nim phn lpca tn hiu s

Mo u on ti toCon tr

Mo u on ti to

Mo u ng truynca lp c mc cao

Mo u ng truyn calp c mc thp

Hnh 1.44. Cu trc khung v cc khi nim phn lp ca STM-n

SOH c chn vo trong giai on cui cng khi tn hiu STM-n chnh thnh cn POH c chn vo bt k khi no tn hiu cng ten oc to thnh.

SOH c chn vo v c tch ra trong on ti to hoc on ghpknh ch th hiu nng truyn dn cng nh hot ng v bo dngtn hiu STM-n. Nh c minh ho trong hnh 1.44, cc SOH nm bntrn v bn di ca con tr c s dng tng ng cho on ti to von ghp knh. C ngha l B1, SOH cho BIP-8 (Bit Interleaved Parity-8) c b tr trn phn pha trn ca PTR v n c kim tra v tnhton li trong mi b ti to.

Tuy nhin, ba byte ca B2-SOH cho BIP-24- c b tr phn phadi ca PTR v chng ch c kim tra cui ng dy. Nh cp trn, POH c phn chia thnh POH ca lp c mc cao cho VC-4 hoc VC-3 v POH ca lp c mc thp hn dng cho VC-11, VC-12v VC-3. Trong bt k trng hp no POH cng c s dngchotruyn thng u cui - ti - u cui gia nhng im, ni cc VC tngng c hnh thnh v gii to.


gii thch cu trc ca mo u on v mo u ng hy xemkhung STM-1 trong hnh 1.45, (a), (b). Vic s dng mi loi mo utrong hnh ny nh sau: A1, A2 dng cho bt sp xp khung; B1, B2; B3dng kim tra ngang bng chn l, C1, C2 dng cho s lng tn hiuv D1-D12 dng cho knh truyn s liu, cn E1 v E2 dng cho knhnghip v; F1, F2 dng cho knh khch hng; G1 l kim tra trng thing truyn, H4 dng ch th a khung; J1 dng ghi du tchng truyn; K1, K2 dng cho chuyn mch bo v t ng; Z1~ Z5 lcc mo u d phng cho cc mc ch khc.

1 2 3 4 5 6 7 8 9 J1

1 A1* A1* A1* A2* A2* A2* C1* X* X* B3

2 B1 E1 F1 X X C2

3 D1 D2 D3 G1

4 con tr F2

5 B2 B2 B2 K1 K2 H4

6 D4 D5 D6 Z3

7 D7 D8 D9 Z4

8 D10 D11 D12 Z5

9 Z1 Z1 Z1 Z2 Z2 Z2 E2 X X

Hnh 1.45. Cu trc mo u

* Cc byte khng c pha trn(a) Mo u on (b) Mo u ng truyn

1.4.5. Cu trc ca khung STM-n

Khung STM-n c mt cu hnh nh c trnh by trong hnh 1.46, datrn c s cc khi nim phn lp nh ngha trong phn trc. Do cutrc ny chim mt vng 9Bxnx270 (B=Byte) trong vng 125 m s, cho


nn n c mt tc bt l n x 155,520 Mbt/s (=9 x n x 270 x 8 x 8kbit/s). Trong , 9B x n x 9 c phn b cho vng mo u SOH vcon tr AU (Khi qun l) v phn cn li ca 9B x n x 261 c phnb cho ng bao trng tin ca STM-1.

Do vy, STM-1, mt tn hiu c bn ca phn cp s ng b, s c kchthc l 9B x 270. Cng nh vy, 9B x 9 trong s l cng ca mou on v con tr AU, v cng chng y 9B x 261 l ng bao trngtin, v tc bt tr thnh 155,520 Mbt/s.

Theo quan im cu trc khung STM-1, SOH c to thnh t hai khuvc 3 x 9B v 5 x 9B, con tr AUPTR bao gm khu vc 1 x 9B v cuhnh ca n nh c trnh by trong hnh 1.45. Mt VC-4 c nh xtrong vng cn li, hoc ba tn hiu VC-3 c th c nh x sang vng cng vi mo u c nh (FOH-Fixed Overhead). Cc tn hiu VC-4v VC-3 u bao gm hnh bao trng tin v vng POH c kch thc 9x 1B c b tr trc mi hnh bao trng tin. ng thi, cu hnh bntrong ca POH nh trong (b) ca hnh 1.45. VC-4 hoc VC-3 m cgn con tr AUPTR th c gi l AU-4 hoc AU-3.

Hnh 1.46. Cu trc ca khung STM-n

Do vy, trong cu trc ca khung STM-1, AU-4 l t hp ca vngtrng tin STM-1 v vng con tr AU, v cu trc cui cng ca STM-1c th t c khi cc vng SOH tng ng c t ln lt vo phnpha trn/ pha di ca AU-4.

1.4.6 Cu trc ghp knh ng b

Nh c m t, qu trnh ghp knh ng b x l tt c cc tn hiuphn cp s mt cch ngang bng v n s thit lp nn cc tn hiuSTM-n. Trong hnh 1.41, s tng th ca cu trc ghp knh ng btrn cc tn hiu phn cp c a ra.


Trong hnh ny, cc con s nm trong ngoc ch r s lng tn hiu cnthit cho qa trnh ghp knh tng ng. Qua trnh ghp knh ng bnm trong hnh ch nht in chm (c ch th bng ch SM), trong khi, hnh ch nht pha bn tri c ch th bng ch AM, biu th choqu trnh ghp knh khng ng b m trong cc tn hiu phn cpc hn thnh.

Ti bc u tin ca qu trnh ghp knh ng b, cc tn hiu ca micp c nh x sang cc cng ten tng ng. ng thi, phng phpchn dng/khng/m hoc ch chn dng trong khi bt c s dng ng b ho. Mt VC (Cng ten) c hnh thnh nu a thmPOH vo cngten, v mt TU (khi phn nhnh) c hnh thnh nugn thm PTR vo n. Tuy nhin, nh trong trng hp VC-4, VC-3, TUs tr thnh AU (Khi qun l) nu tn hiu c nh x thng sangSTM-1 m khng qua cc VC khc. Khi , s m (m=1, 2, 3, 4) gn chomi khi tn hiu s ch th rng mi tc bt ca khi tn hiu lin quans tng ng vi cp DS-m. Khi m=1, n c chia nh thnh 11 v 12v chng biu th tng ng cho tc bt ca h thng Bc M DS-1 vh thng Chu u DS-1E.

Hnh 1.47. Qa trnh ghp knh trn ng truyn

Tuy nhin, trong trng hp STM-n, tc bt gp n ln 155,520 Mbt/s

Trng hp TU-1 (TU - 11 hoc TU-12) n c ghp knh thnh VC-3v VC-4 thnh kiu TUG (nhm ca khi phn nhnh) sau khi c gpli thnh bn. TU-2 c th c xem nh tng ng vi TUG-2. Ngoira, TU-3 c th c xem nh bng vi TUG-3. VC-3 c th c ghpknh thnh VC-4 sau khi c nh tuyn vi TU-3, hoc n c thc ghp thng vo AU (khi qun l - Administrative Unit) nh nh


tuyn cho AU-3. Nhm n v qun l AUG- Administrative Unit Group)c th c xem nh tng ng vi AU-4. S t c tn hiu STM-nkhi gn mo u on (SOH) vo n nhm AUG c ghp knh.

Ghp knh ng b c a ra nh mt trong cc th d trong hnh 1.47l qu trnh ghp knh trn cc ng truyn ca DS-1\C-11\VC-11\TU-11\TUG-2\TUG-3\VC-4\TU-4\AUG\STM-n, c ch dn bng ccng k m trong Hnh 1.41. Nh c trnh by trong hnh 1.47, tnhiu DS-1 c nh x trc ht thnh C-11 v sau VC-11 POH cnp vo bin i n thnh VC-11. t c TUG-2 khi TU-11 PTRc gn ti VC-11, v sau n c ghp thnh bn. Ngay i vi cctn hiu TUG-2 chng ta c th thy rng cc con tr TU-11 PTR ca ccTU-11 c gp li vi nhau v c a ra ngoi. Ngoi ra, TUG-3 tc nh ghp knh mt TUG-2 thnh 7 TUG-2 v sau , gn FOH vou ca chng. TUG-3 li c ghp thnh 3 TUG-3 v cc FOH cngcc VC-4 POH s c gn vo pha trc chng t c VC-4.

Theo b ngoi, tn hiu VC-4 cng ging nh tn hiu thu c nh ghpTUG-2 thnh 21 TUG v sau gn VC-4 POH v FOH vo pha trcchng.

Khi kim tra cc kt qu ghp knh chng ta c th bit rng mi mttrong 84 tn hiu TU-11 c th c truy nhp trn VC-4. ng thi,FOH ch c s dng nh mt mo u c in tm iu chnhkch thc.

C th thu c AU-4 nh gn AU-4 PTR vo VC-4 v n cng gingnh tn hiu AUG. Cui cng c th thu c tn hiu STM-n khi mtAUG c ghp thnh n AUG v sau . mt mo u on c gntrn chng.

1.4.7 Con tr v ng b ho

Trong SDH, k thut con tr c s dng ng b ho. Con tr nyc s dng ch th s thay i mi quan h khi VC c ng chnhtheo tn hiu TU hoc AU v khi VC ch th a ch xut pht trong mtkhung TU hoc AU v im xut pht ca n b thay i.

Nh c trnh by trong hnh 1.41 cc loi con tr kh dng l AU-4PTR, AU-3 PTR, TU-3 PTR, v TU-11 PTR, TU-2 PTR, TU-12 PTRv.v.... Trong s AU-4 PTR, AU-3 PTR xut hin trn v tr ca AUPTR c ch r trong hnh 1.46 v TU-3 PTR c b tr trn nh cahng u tin trong phm vi khung TU-3.


Cc con tr ca lp c mc cao ni trn c nh du vi H1, H2 vH3. cc con tr ca lp c mc thp, chng hn nh TU-11 PTR, TU-2PTR v TU-12 PTR c nh du bng V1, V2 v V3. Cc con tr calp mc thp ny c cu trc nh sau: ba trong s cc byte u tin cami on s t c nh phn chia TU tng ng thnh mt on 125m s. Trong s , vic ng dng cc on m ba byte u tin ca chngl cc con tr V1, V2 v V3, cn byte th t l V4, th cn cha c xcnh. ng thi, vng trng tin ca mi TU s b tr cc a ch trnbyte ng ngay ng sau V2 v sau , theo trnh t 0, 1, 2 ....

Cc con tr H1, H2, H3 v V1, V2, V3 c cng mt chc nng nh nhau,trong khi chng c dnh du mt cch khc nhau. Hnh 1.48 ch rphi xc nh cch s dng ba byte ny nh th no. Bn bt ca c hius liu mi (NDF-New Data Flag) ch th trng thi ca s liu mi, cnbt SS c s dng phn nh loi ca TU hoc AU tng ng. ach bt u ca VC tng ng c ghi trn 10 bt sau . 10 bt nyc phn chia thnh 5 bt I (Increment - gia tng) v 5 bt D (Decrement- gim) nh c trnh by trong hnh. Trong s , bt I s b hu b mikhi a ch ca im xut pht c gia tng v bt D b hu b mi khia ch ca im xut pht gim i. Cui cng, byte H3 (hoc V3) cs dng np cc s liu hp l khi thc hin vic chn m.

Hnh 1.48. Cu hnh v chc nng ca con tr

Khi thc hin mt ghp chn dng, cc s liu hp l c pht i bngcch np ti cho byte ng ngay ng sau H3 (V3). Khi xy ra s khcnhau v tn s gia khung TU v AU hoc gia cc VC (l cc trng tinca chng) th cc byte con tr c th c s dng gii quyt cc vn ny nh s dng php chn dng/ khng/m. Nu tn s ca VCtng ng bt u ln hn so vi khung TU/AU th trng tin cn pht sc gia tng. ng thi, i cho ti khi tng s cc d liu c tch tdo s khc bit tn s tr nn bng 1 byte (trong trng hp VC-4 l ba


byte), ri khi np chng cho mt byte H3 hoc V3 (trong trng hpVC-4 l 3 byte), ng thi hu b cc bt D. Khi , trn khung k sau,ghi li a ch mi m n c gim i 1 tng ng vi a ch c ghi trc trn mt con tr 10 bt tin hnh chn m. S dngcc phng php tng t tin hnh chn m khi tn s ca VC tngng bt u thp hn so vi khung TU/AU. Tuy nhin, khi cc bt I sb hu b v cc s liu khng hp l s c np sang byte tip sau caH3 hoc V3 v a ch s c gia tng 1.

1.4.8 Cc c im ca Phng php Truyn dn ng b

Nh phn tch cho ti lc ny, khi c so snh vi truyn dn khngng b c mt s c im ni bt. Trong phn sau y s gii thch cim ny.

1. Khung 125 s

C th thy c im u tin ca truyn dn ng b trong cu trckhung ca n; l cu trc khung c hnh thnh bng cc khi 125.c im ny khng c trong phn cp s khng ng b hin dng.Trong phn cp s ng b n cho php vic truy nhp t cc tn hiuphn cp mc cao ti cc tn hiu phn cp mc thp; c bit l xungti tn hiu DS-O c thc hin mt cch d dng. Bng c im ny,ton b qu trnh x l s liu c th c thc hin nh mt n v byte.Tuy nhin c im ny lm ny sinh vn trong phn cp s khngng b hin ti. Do m bin ng (jitter) thi gian i tr nn nngn. C ngha l vic chn dng/khng/m l cn thit khi cc tn hiu C-1 v C-2 c hnh thnh t cc tn hiu s DS-1 v DS-2. Nh , ccvn lin quan n jitter c th c gii quyt.

2. S hp nht cc phn cp s

Cu trc ghp knh ng b c kh nng ho hp cc tn hiu s Bc Mv Chu u. C ngha l, cc tn hiu STM-n c cng hnh dng b ngoic th c hnh thnh qua th tc ghp knh ng b ngay c khi cgn bt k tn hiu no trong s cc DS-1, DS-2, DS-3 ca Bc M v ccDS-1E, DS-2E, DS-3E, v DS-4E ca Chu u. Ngoi ra, cc tn hiuBc M c th kt hp c vi cc tn hiu Chu u trong qu trnhghp knh ng b, v ngc li. Trc y, khng th thc hin ciu ny. Ghp knh tt c cc ng l phi thc t v kh nng s dngphng thc cn phi c xc nh chun b cho s lin kt mngton cu.

3. Cu trc phn lp


Mt trong nhng c im ni bt ca truyn dn ng b l n c ththo hip cc khi nim phn lp khc nhau. Da trn khi nim ny, ccmo u c phn loi thnh SOH v POH trong cu trc khung. Cngha l mng thng tin ch yu c phn lp thnh cc ng v ccon. Cc mo u cn thit cho cc ng s khng c x l ti ccon m chng c truyn i mt cch trong sut. Cc SOH nm phnpha trn hoc phn pha di ca con tr s c phn loi theo chcnng - chng c gn tng ng vi chc nng on ti to v chcnng on ghp knh. C ngha l cc on li c phn lp mt lnna thnh cc on ghp knh mc cao v cc on ti to mc thp.

4. S dng mt cch h thng cc mo u

Trong cc tn hiu STM-1, mo u on v con tr chim mt khnggian 9x9B. Mo u thc t s tng ln khi cc mo u v con tr cang ang xt b vt qu trn mt s cc tng. Chng ta c th bitrng cc mo u trong STM-1 vt qu 105 khi tc bo hiu DS-4El 139,264 Mbit/s. y l mt iu ci tin to ln so vi mng phn cps khng ng b hin nay. Cc mo u c s dng y sau khic phn loi thnh SOH, POH v PTR. Chng c s dng toiu kin d dng cho cng tc qun l iu hnh v sa cha mngthng tin.

5. ng b ho bng con tr.

Trong qu trnh ghp knh ng b, mng thng tin c ng b honh vic thnh thong gi vo cc con tr. C ngha l s x dch tn sgia ng h h thng v cc tn hiu thu c th c x l ph hp vicon tr v chn dng/khng/m. Thng qua vic s dng b nh cng, phng php ng b ho kiu ny to iu kin kh thi cho ngb ho bng rng nh vic a ra kh nng quan h vi mi trng cnng b. Phng php ng b ho bng con tr tng ng vi vic nhibyte, nu chng ta nghin cu n trong bi cnh ca ng b ho nhibit. V l do , phng php ng b ho con tr to ra jitter tn s thpv jitter bin cao. Mt trong nhng vn quan trng l phi giiquyt jitter ny.

6. Ghp knh mt bc

Trong qu trnh ghp knh ng b, cc ng truyn trn cc tn hiuTUG-2 c nh x trc tip thnh cc tn hiu VC-4, hoc cc tn hiuAU-3 c nh x trc tip thnh cc tn hiu. Ci gi l ghp knh


mt bc; tng trung gian b b qua trong qu trnh ghp knh. Khi nimny khng h c ng dng i vi qu trnh ghp knh khng ng bang c s dng.

Ngoi ra, khi p dng trn mt mng thng tin, ni mt s lng ln cctn hiu c gi i nh tin hnh mt s qu trnh ghp knh, khi nimny to iu kin d dng v kinh t cho kt ni phn chia v kt nicho. Ghp knh mt bc tr nn kh thi nh da vo khi nimcngten.

7. Khi nim Mng thng tin.

Phng php truyn dn ng b c thit lp da trn c s cakhi nim mng thng tin. Do bi cc h thng thng tin quang hin nay c thit k da trn quan nim truyn dn im ni im cho nn skhng c hiu qu khi thc hin cc kt ni tch/nhp hoc ni kt chothng xuyn xy ra i vi cc tn hiu c to ra trn cc nt gia, sau khi hnh thnh mng truyn thng. Tuy nhin, khi s lng cch thng thng tin quang c s dng ngy mt nhiu th cc h thngv cc tiu chun da trn khi nim ca mng quang tr nn cn thitv khi nim ghp knh mt bc c p dng. Hn na, v mt ccmo u th cc SOH cn cho cc on v POhH cn cho cc ng c phn loi v mt vi loi mo u trong s c gn cho vickhai thc v bo dng mng thng tin c hiu qu.

8. Mng thng tin ton cuMt c im khc ca mng truyn dn ng b l n c da trn cs khi nim thng tin ton cu. Vic ng b ho c tin hnh mt sln qua vic s dng cc con tr l yu t cho php mng truyn dnng b c ng b ho vi mng thng tin ton cu. V mc ch ,phn cp s ca Bc M v ca Chu u kt ni vi nhau. Nu ccmo u t bn ngoi v cu trc ghp knh c s dng u da trnkhi nim ny ca mng thng tin th mng thng tin ton cu c th trthnh hin thc.

1.6.6 Cc mch vng t hn gn (SHR)

1. Li ch ca vic s dng cc SHR

Cc mng hin ti vi cng ngh cp si quang ang s dng phngphp nh tuyn bo v phn tp t ng v tm hng kp bo vmng trong nhng trng hp t cp hoc h hng cc trung tmchnh. Nhng mng nh vy c th c pht trin thnh cc vngSHR nu nh SHR chng t c l kinh t hn. Mt mng mchvng l mt tp hp cc nt hnh thnh nn mt vng khp kn, trong


mi nt c kt ni qua mt phng tin truyn thng songcng. Mt SHR l mt mng mch vng cung cp di thng v hocthit b mng d phng sao cho cc dch v b gin on c th cphc hi mt cch t ng sau s c mng. Cc thit b ghp knhdng trong cc cu trc vng l cc thit b ADM c nhim v xen vr cc knh ti ch v chuyn tip xuyn sut cc knh qu giang.Hnh 1.68 miu t mt th d v mt kch bn pht trin mng tmng bo v phn tp sang mch vng. Hnh 1.68(a) miu t mtmng cp quang hng tm vi ba CO v trung tm phc v cachng. Cc ng truyn thng gia mt CO v trung tm ca nc i qua chng cp quang u tin im - ni - im, chng nyc bo v nh chng cp quang phn tp vt l do h thng APSiu khin. Cc b ghp knh u cui c s dng trong mng cpquang hng tm ny c th c pht trin thnh mt h thngADMS tc cao, trong cc ADM ny bt u c hiu lc v khinim mch vng chng minh c l c hiu qu kinh t. Khi so snhvi i tc hng tm ca n, mch vng c th s cn n cc ADMtc cao hn, bi v n s dng chung khng ch cc phng tincp quang m cn thit b ghp knh.

Hnh 1.68 Pht trin ca cu trc mch vng

Nh c m t trong hnh 1.68, cu trc mch vng c nhng uim sau y so vi cu trc hng tm 1:1/DP: (1) gim bt cc siquang v cc thit b quang/in t v cc b ti to; v (2) kh nngsinh tn y trong khi t cp quang v hng nt mng (tr nt bhng). i vi th d trnh by trong hnh 1.68(a), mng hng tm1:1/Dp yu cu 12 b OLTM, cn mng mch vng trnh by tronghnh 1.68(b) ch i hi c 4 b ADM. Ph thuc vo cc tc ng dy c dng, mt s ADM t hn cho mch vng c thkhng nht thit chng t rng cc chi ph u t l thp hn. Nu tanghin cu mt trng hp trong c hai mng vng v hng tmu s dng cng mt tc ng dy, v chi ph ca mt OLTMvo khong 80% chi ph ca mt ADM (ti cng mt tc ng


dy) th mng vng c th tit kim dc 58% chi ph u t so vii tc hng tm ca n. By gi chng ta nghin cu mt trnghp khc, trong mng hng tm 1:1/DP s dng h thng 565Mbit/s v mng vng s dng h thng 2,40 Gbit/s. Gi thit rng githnh tng i ca mt thit b kt cui 565 - Mbit/s l 1 v chi phca thit b 2,40 Gbit/s gp ba ln gi thnh ny. Mng vng angnghin cu y cn n bn b ADM 2,4 cobit/s, iu ny dn nmt gi thnh tng i l 12 (1 x 3 x 4 = 12), trong khi mnghng tm 1:1/DP cn n 12 b OLTM 565 Mbit/s, iu ny dnn mt gi thnh tng i l 9,6 (1 x 0,8 x 12 = 9,6). Do vy, trongth d c trng ny, mng hng tm 1:1/DP dng nh t t hnmng vng. Tuy nhin, c th phi cn n cc b ti to cho ccchng bo v phn tp di hn trong cc mng hng tm cp quangrng hn v c th iu chnh nhng li th ca vic s dng ccOLTM tc thp. Khi s lng cc nt trong mng vng tng lnti tm hoc ln hn, mng 1:1/DP s bt u t hp dn hn so vimch vng.

Lu rng tho lun y ch ch n gi thnh ca tht b ghpknh, bi v n l yu t ni tri nht ca ton b gi thnh h thngchuyn ti bng cp quang i vi cc mng "intra LATA".

Trong nhiu trng hp, mng vng c cc u im v kinh t so vii tc hng tm ca n, tuy nhin, n c th gp kh khn hnhoc t hn nng cp h thng khi dung lng mch vng cn kit. Mch vng cng c th cn n mt h thng iu khinmng phc tp hn so vi i tc nh tm ca n, bi v rng tt ccc nt s tng tc vi nhau khi cc tnh hung s c xy ra hoc cyu cu ti cu hnh. Tuy nhin, vn cn kit ca dung lng mchvng c th c gim bt hoc c gii quyt nh quy hoch mngcn thn hoc trin khai ADM tc cao hn nhiu (chng hn, tnhkh dng ca cc ADM 9,6 Gbit/s). V li (xem mc 4.5), h thngiu khin dng cho mng vng c th c n gin ho khi thit bSONET c trin khai. Bng 1.17 tng kt ho mt s so snhtng i gia cc cu trc mng vng v nh tm vi mng bo vphn tp (Hub/DP).

Bng 1.17. So snh gia nh tuyn bo v phn tp v cu trc SHR

Cc thuc tnh Hub/DP SHR/ADM

Kh nng nng cp D dng Kh khn - tTng s cp quang Nhiu hn t hnTng s u cui Nhiu hn t hnTc u cui Thp hn Cao hn


Kh nng sinh tn ca cp si quang 100% * 100%Kh nng sinh tn ca trung tm ** Ngho Tt hn

* Ph thuc vo cp bo v 1:1 hay 1: N

** Gi thit ton b to nh trung tm b h hng.

2. SHR ca SONET

SHR l mt mng ng vng cung cp di thng hoc v thit bmng d tha, sao cho cc dch v b gin on c th c khiphc mt cch t ng. Gii php chung bo m mt kh nng thn gn l cung cp mt vng truyn thng th hai song song vivng lm vic th nht. Trong trng hp ny, mt s c trn vngc th c b qua nh chuyn cc cuc truyn thng sang vng thhai; ni chung n c coi nh mt chc nng chuyn mch ngdy (hoc chuyn mch bo v). Hn na, nu vng th hai pht theohng ngc li so vi vng th nht th mt s ngt trong c haivng gia hai nt k lin nhau c th c cu vn nh cc nt trnmt trong hai pha b ngt bng vic u vng cc cuc lin lc ngctr li sang vng th hai. N c gi mt cch thng dng l chcnng u vng ngc. Hnh 1.69 miu t cc th d v chuyn mchng dy v mch vng ngc phc hi.

Ch rng mt s kt hp cc chc nng vng ngc v chuynmch ng dy (trn mt trong hai pha b ngt) c th c sdng phc hi dch v b gin on. Do vy, mt thuc tnh quantrng ca SHR l: nu vng b "gy" ti bt k mt im no , thhng truyn dn i vi cc tn hiu c th c o li nhm trnhvic mt dch v.

Cc SHR ca SONET c th c phn chia thnh hai loi ph binl n hng v song hng theo hng ca lung lu lng dicc iu kin bnh thng. Cu trc ca SHR thuc v mt trong hailoi ph bin ny c th khc nhau v c ch iu khin bo v cns dng phc hi cc dch v b gin on.

SHR n hng

Trong SHR n hng (USHR) lu lng lm vic c chuynquanh mng vng ch theo mt hng (chng hn ngc chiu kimng h). Hy tham kho hnh 1.70(a). Lu lng t bt k mt ntno c nh tuyn theo cc ng truyn thng lm vic t Nt1 ti Nt 3 (tc l ng 1-2-3). Lu lng quay v tip tc i theovng t Nt 3 quay v Nt 1 theo cng mt chiu nh t Nt 1 nNt 3, s dng phn cn li ca vng lm vic (tc l ng 3-4-1).


Do vy, lu lng i ti ti Nt 1 v Nt 3 theo cc con ng khcnhau. Do qu trnh truyn dn ca lu lng lm vic bnh thngtrn USHR ny l ch i theo mt chiu cho nn dung lng ca vngc xc nh bi tng nhu cu gia cc nt. Cc USHR i khic gi l "cc vng quay ngc" l bi v vng truyn thng thhai (ch bo v) c pht i theo chiu ngc vi vng th nht(vng lm vic).

Hnh 1.69. Chuyn mch ng dy so vi u vng ngc dung phc hi ng vng.

V cc knh phc v c nh tuyn mt cch n hng, cho nncn phi c mt cp quang vn chuyn chng. USHR ny c thc ci t theo khi nim bo v 1:1 hoc 1 + 1. USHR s dngmt vng ring bit lm vng bo v m n khng vn chuyn nhucu dch v trong trng thi bnh thng v n trn (u vng) ccknh b gin on sang vng bo v t pha vng lm vic khi thnhphn ca mng b hng. Cu trc 1:1/USHR ny cng c gi lmt SHR n hng trn (USHR/L). Tng phn li, USHR 1 + 1phn chia cc tn hiu sang c hai vng lm vic v bo v ti ntpha pht ny (c ngha l bc cu u cui), cn nt pha thu s lachn tn hiu tt nht trong hai tn hiu nh nhau da trn tiu chunchuyn mch bo v. Cu hnh USHR 1 + 1 ny i khi c gi lmt ng n hng SHR (USHR/P). Lu rng cc USHR 1:1 cth c cu hnh nh cc USHR 1:N, c ngha l mt vng truynthng bo v c cho N vng truyn thng lm vic dng chung:tuy vy cc USHR 1:N khng phi l loi t hn gn c ton b.


Hnh 1.70. Cc nh ngha v cc SHR n hng v song hng

SHR song hng

Nh c trnh by trong hnh 1.70(b), trng hp SHR songhng (BSHR), lu lng lm vic i theo c hai hng trn mtng duy nht; ng ny s dng hai ng truyn thng songsong vi nhau (hng hot ng v hng ngc li) gia cc ntca vng (chng hn gia Nt 1 v Nt 3). Th d, trong iu kinbnh thng, cc tn hiu t Nt 1 n Nt 3 c nh tuyn quang 1-2-3, cn cc tn hiu quay v t Nt 3 ti Nt 1 c nhtuyn qua cng mt ng nh vy (ng 3-2-1). V lu lng cnh tuyn trn mt ng duy nht gia cc nt m dung lng dtha quanh mt vng c th c dng chung trn c s tng tuynkt ni v n khng c dnh ring cho tng yu cu trn vng (nh i vi trng hp USHR). Do cc knh nghip v c nhtuyn song hng ti hai nt, cho nn cn n hai cp quang vnchuyn cc knh nghip v ny.

Mt BSHR c th dng hai hoc bn cp quang, tu thuc vo vicb tr dung lng d tha. Trong trng hp BSHR bn cp quang(hoc cu hnh 1:1) mt vng truyn thng th hai, c lp vi vngth nht, s c cung cp bo v. Cc knh lm vic v bo v ss dng cc vng truyn thng khc nhau. Cc BSHR 1:1 cng c thc cu hnh nh cc BSHR 1:N, tc l mt vng truyn thng bov dng cho N vng truyn thng lm vic. Nh c cp trn,cc BSHR 1:N khng phi l loi t hn gn y , v do vy, trongmc ny s khng tho lun v chng. Trong trng hp ca BSHRhai cp quang, cc knh lm vic v bo v s dng cng mt cpquang vi mt phn di thng c d phng bo v. cung cpmt chc nng t hn gn, thng mt na di thng s c dphng bo v. Vic b tr mng vng nh vy c th bo mchuyn mch bo v ng dy nh s dng phng php TSI


ho nhp cc knh lm vic trong cp quang b hng vi cc knhbo v trong cp quang khng b nh hng. Cc USHR v BVSRcn c th c phn loi tip thnh cc SHR chuyn mch bo vng dy v ng truyn ph hp vi mc ca SONET dng :(1) vn chuyn cc tin bo gp s c v (2) xc pht hot ngchuyn mch bo v cho php vng c phc hi mt cch tng khi s c.

SHR chuyn mch bo v ng dy

Mt cu trc SHR chuyn mch bo v ng dy s dng tiu ng dy ca SONET (chng hn cc byte K1 v K2) vnchuyn cc tin bo s c v xc pht ng tc chuyn mch bov. ng tc chuyn mch bo v ch c thc hin ti lp ngdy phc hi khi s c v khng lin quan n lp ng truyn.N phc hi yu cu ng dy khi mt phng tin b s c. Cccu trc chuyn mch bo v ng dy c xc nh cho c hailoi USHR v BSHR, s dng nguyn tc u vng lu lng sangng bo v. Khi mt vng b t cn phi c iu khin ti chviu khin t xa thc hin vic u vng lu lng ti cc nt nmtrn hai pha ca ch t. H thng chuyn mch bo v ng dy lmt s la chn t nhin i vi tt c cc BSHR bi v nh tuynyu cu BSHR s dng cng mt nguyn tc nh cc h thng im -ni - im hin nay, l nhng h thng s dng h chuyn mch bov ng dy (tc l APS) phc hi cc yu cu nu mt cu kinmng b h hng.

SHR chuyn mch bo v ng truyn

Mt cu trc SHR chuyn mch bo v ng truyn s dng tnhiu ca lp ng truyn (chng hn, ng AIS) khi ngchuyn mch bo v. Khc vi h thng chuyn mch bo v ngdy, h thng chuyn mch bo v ng truyn s phc hi mtknh STS hoc VT u cui - ti - u cui. Chuyn mch ngtruyn ca mt ng c trng no c lp vi trng thi ca ccng khc. Mc d mt nt no pht hin mt s c ng dy,th chuyn mch vn c thc hin ti lp ng truyn cho ccSHR chuyn mch ng truyn. Vi chuyn mch bo v ngtruyn, ngi ta xc nh r hai cp ca cc mc mch vng: VT vSTS. SHR chuyn mch bo v ng truyn VT c xc nh nhmt vng, trong ng truyn VT c chuyn mch cho cccuc sp xp li mch vng, v SHR chuyn mch bo v ng STSc xc nh nh mt mch vng trong cc ng truyn STSc chuyn mch ti sp xp mch vng.


Cc vng chuyn mch ng truyn STS v VT tng ng c sdng ch yu trong cc mng lin tng i v cc mng u vng.

Hnh 1.71 miu t cc yu cu k thut ca cu trc vng SONETda trn c s nh truyn yu cu v c ch iu khin bo v.

Hnh 1.71.

1.7 S TIN TRIN SANG BISDN

B-ISDN c pht trin iu tit cc th loi khc nhau ca cc tnhiu bng rng, da trn nhng khi nim v tiu chun ISDN v tiuchun thng tin quang ng b, trong khi h thng thng tin ATM c pht trin ci t B-ISDN. Mc tiu ch yu ca BISDN l linkt tt c cc tn hiu lin tc theo thi gian thc v cc tn hiu s liutheo nhm c s phn b di tn rng (cn thit cung cp cc dch vbng hp, pht hin t xa, chng hn nh gim st t xa, u cui s liu,in thoi v fax, v cc dch v bng rng, chng hn nh in thoithy hnh, hi ngh truyn hnh, truyn tn hiu truyn hnh nt cao,truyn s liu tc cao v.v). B-ISDN i hi mt phng php hiu qu c th x l chung tt c cc dch v ni trn. H thng truyn thngATM (phng thc chuyn giao khng ng b) c xut nh lmt gii php.

Cc khi nim v BISDN c pht trin p ng mt cch hiuqu cc nhu cu ang cng ngy cng gia tng v cc th loi dch vbng rng khc nhau. iu tit tt c cc loi tn hiu bng rng ny,cc dch v thng tin, chng hn nh cc th loi in thoi video, cnc lin kt vi cc loi dch v phn b, chng hn nh CATV. Ngoira, phi c mt chc nng cung cp c cc dch v ch knh, c ccdch v ch gi.

Mt khc, li tng c mt i hi v kh nng mng c kh nng cungcp dch v gim st t xa hot ng ti mt tc truyn dn thp (bit/s)cng nh dch v thoi/th tn hot ng tc truyn dn trungbnh/cao (vi chc kbit/s cho thoi v vi trm Mbit/s cho video). Mt


gii php cho vic ny l xut tiu chun ho cc loi tn hiu khcnhau ca cc dch v ng c cc hnh thc b ngoi nh nhau v sau, tch tr chng li ghp knh. Cc t bo ATM c s dng tiu chun ho cc hnh thc b ngoi ca cc tn hiu dch v v hthng ATDM (ghp knh khng ng b phn chia theo thi gian) c s dng ghp mt nhm cc t bo ATM; mt h thng truynthng da trn c s cc t bo ATM v ghp knh ATDM c gi l hthng thng tin ATM.

H thng truyn thng ATM lin kt h thng thng tin digital ch knh ang hot ng vi h thng thng tin ch gi. H thng thngtin ATM ging nh h thng thng tin gi, trong n s dng cc tbo ATM nh mt phng tin truyn dn c bn, trong khi n khcvi chuyn mch gi ch n ng thi c th x l c cc tn hiuthi gian thc v tng ng. Ngoi ra, cc h thng chuyn mch gini chung c s dng mt cch cc b trong cc mng LAN, cni vi h thng ATM th do n c thit k s dng trn ccmng cng cng nh c ln, cho nn n khc phc c nhng kh khntrong vic gn a ch, iu khin kt ni v lu trnh, chuyn mch vtruyn dn. Mt khc, so vi h thng thng tin ch knh (phn bknh cho mi dch v ri sau thng qua cc knh ny m chuyn cctn hiu thng tin i nh mt dy bt lin tc), ATM phn chia cc tnhiu mang thng tin ri sau np chng vo cc t bo ATM chuynchng i qua cc knh o. Do vy, mt s vn mi lin quan n victhit lp ni kt, qu trnh bo hiu, n truyn dn v chuyn mch pht sinh.

B-ISDSN hay h thng thng tin ATM c trin khai vo cui nm1980, t n nay n vn c nghin cu v nng cp. Do vy trongmc sau y s xem xt li cc vn lin quan n chng, da trn cciu khon thuc v BISDN ca ITU-T.

H thng thng tin ATM c pht trin ci t B-ISDN cho nni khi n c xem l "mng ATM".

1.7.1 Cc khi nim c bn ca B-ISDN

Khi x hi pht trin, khi cng ngy cng c nhiu cng ty mc ln, thnhu cu v cc dch v a phng tin v cc dch v bng rng khcnhau cng ang gia tng mt cch ng k. By gi cng ngy cng cnhiu ngi s dng cc u cui s liu, cc my tnh c nhn, cc myFax v cc h thng hi ngh video, v s lng cc cng ty nhn thamgia vo cc dch v CATV cng tng ln.


Ngoi ra, nhu cu v cc dch v nh in thoi thy hnh (video), truynhnh phn gii cao, truyn s liu tc cao, dch v gim st bngvideo, truy tm bng video, video text bng rng cng ang tip tc giatng. Nhng dch v k trn bao gm cc dch v giao lu cng nh ccdch v phn phi m mt s trong cc dch v c th cn n ccmng ring ca mnh (do mt s trong cc dch v l cc dch v ch knh, mt s l cc dch v ch gi). Song lm c iu cnphi u t mnh v s lm cho thng tin tr nn km hiu qu. Do ,hin ang c mt nhu cu lin kt cc dch v ni trn thnh mt mngtruyn thng chung cho tt c cc dch v lin kt.

BISDN - mt mng thng tin s, c kh nng cung cp cc loi hnh dchv bng hp, chng hn nh in thoi, cc u cui s liu, gim st txa, facximin, teletext, cng nh cc dch v bng rng, chng hn nhin thoi thy hnh, hi ngh truyn hnh, truyn dn hnh nh c phn gii cao, truyn s liu tc cao, gim st bng video v CATV...

Do vy, B-ISDN c th c xem nh mt mng thng tin m n c pht trin t mng ISDN bng hp hin ang c s dng.

1.7.2 Cc c trng tn hiu ca dch v B-ISDN

B-ISDN c nhng mc ch c bn l kt hp tt c cc dch v hin huvo mt mng truyn thng trong tng lai. Do vy, v c bn n cungcp cc dch v bng hp, chng hn nh in thoi, u cui s liu,fasimile, son tho vn bn t xa, c s o t xa, videotex, bu chnhin t, teletex. Ngoi ra, n c kh nng cung cp cc dch v bng rng,chng hn nh in thoi thy hnh, hi ngh truyn hnh v truyn s liutc cao, facsimile mu, CATV, phn phi HDTV, m thanh nhy cmcao, th truyn hnh, gim st bng video, truyn chng trnh chiuphim phn gii cao v videotex bng rng.

Nhng dch v BISDN ny bao gm tt c cc dch v c nhng c tnhkhc nhau. C ngha l, cc dch v tng tc chng hn nh in thoihoc in thoi thy hnh v cc dch v thng bo chng hn nh buchnh in t hoc bu chnh bng hnh nh v cc dch v truy tm tracu bn v v vn bn u c bao gm trong . Cc dch v ny lcc dch v thng tin m tn hiu ca dch v c chuyn giao theo chai chiu, song bn cnh , chng cn c cc dch v phn phi mtchiu, chng hn nh dch v CATV.

Nhng c trng ni bt nht ca cc tn hiu dch v B-ISDN l phm viphn b di thng ca n rt rng. Trong khi tn hiu cu hnh c bn caISDN bng hp c phn b quanh tn hiu thoi th vic phn b tc tn hiu ca B-ISDN bao gm cc lp digital khc, cc tn hiu video


khc nhau v cc tn hiu truyn s liu tc cao. Do , ng trnquan im tc truyn dn, cc tn hiu ca dch v chim bng tnrng t vi bit/s ca cc tn hiu gim st t xa ti cc tn hiu video vivi trm Mbit/s. Ngoi ra, thi gian s dng n trong phm vi t cc sliu tc thp, c di vi giy, ti dch v video c di vi gi,cc dch v thoi c di vi ba pht.

Nh m t, B-ISDN c kh nng cung cp dch v bng rng ti nhiuMbit/s, cn cc tn s m n s dng v phn b thi gian s dng th cphm vi rt rng.

c tnh phn b khc ca tn hiu dch v B-ISDN l cc tn hiu lintc, chng hn nh ting ni v hnh nh, c th cng "sng chung" vicc tn hiu nhm, chng hn nh s liu u cui. Cc tn hiu ting niv hnh nh c th tr thnh cc tn hiu tc bt bng nhau nh phngphp s ho. Tuy nhin, cc tn hiu s liu khc nhau l cc tn hiu vitc bt bin i rt rng. Mt khc, cc tn hiu hnh nh v m thanhi hi c x l theo thi gian thc, cn trong trng hp s liu thkhng cn nh vy.

Hnh 1.72. Phn b dch v ca B-ISDN

Do nhng s khc nhau nh vy, chuyn mch v truyn dn cc tn hiudch v B-ISDN tr nn kh m thc hin c. V l do , chuyn


mch gi l l tng i vi tc thp hoc s liu nhm, trong khi ,i vi tn hiu ting ni v hnh nh th chuyn mch knh l thch hphn. Ngoi ra, i vi cc tn hiu thoi, chuyn mch phn chia thi gian pht hin t lu l thch hp hn c, cn i vi cc tn hiu video tc cao l chuyn mch knh phn chia theo khng gian.

V vy, tm c mt h thng truyn dn c kh nng trao i vi nhaucc tn hiu tc thp/cao v cc tn hiu lin tc/ nhm l cc k khkhn.Tc s liu knh1.7.3 Nn tng k thut ca B-ISDN

Nh cp trc y, v cc dch v do B-ISDN cung cp c nhng cim khc nhau, cho nn mt s cng ngh c bn c i hi hinthc ho B-ISDN. Th nht, x l tc cao v cng ngh mi trng,truyn dn bng rng v cng ngh chuyn mch bng rng; chng cyu cu l bi v cc tn hiu ca dch v bng rng v tc cao c sdng rng ri. V li, vic ci thin cng ngh v thit b x l video lcn thit bi v cc dch v chnh ca B-ISDN l cc loi dch v videokhc nhau. Hn na, cng ngh mng thng tin i vi nhng vn trny l cn thit, bi v cc dch v tc thp/tc cao c cung cpv cc dch v ch gi ng tn ti.

Nhng cng ngh c bn ny c pht trin v c nng cp lintc nhm p ng mt cch y nhu cu v cc dch v bng rngcng ngy cng tng. Th nht, cng ngh thng tin quang c nngcao; suy hao ca cp si quang c gim xung thp hn 0,5 dB/Kmv gi c ca cc phn t bc x/thu nh sng st xung kh nhanhchng; Hn na, cng ngh v mch tch hp v cng ngh ch to cccu kin cng rt tin tin. Cc phn t Silc lng cc hoc GaAsc pht trin mt cch thnh cng c kh nng thc hin vic x l tc cao (hng trm Mbit/s hoc Gbit/s) v CMOS c kh nng x l mc150 Mbit/s. Ngoi ra, cng ngh phn mm v m p tin trin mt cchthnh cng to iu kin iu khin tc cao, cng nh hot ng vchuyn mch tc cao tr nn c th c.

Vic nn, chuyn i v ti to cc tn hiu dch v khc nhau tr nnd dng do pht trin cng ngh x l tn hiu. V li, vic thu thp, thayi v x l cc tn hiu dch v tr nn d dng hn nh pht trincng ngh my tnh. Qua vic s dng cng ngh ni trn, cng vi cngngh VLSI, cc thit b u cui khch hng hiu qu c pht trin.Thm vo , cc thit b u cui B-ISDN c s dng cho cc thit bvideo khc nhau c trin khai mt cch thnh cng v c s dng


vi cc monitor TV cht lng cao, cng vi cc camera video c nhy cao.Mt khc, cc hot ng tiu chun ho ca ISDN, theo sng kin caITU-T trong nhng nm 1980, nh hng n rt nhiu hot ngnghin cu v s lin kt cc loi tn hiu dch v khc nhau cng nhvic s ho mng thng tin v ng gp vo s pht trin cng nghthng tin. Da vo nhng vn ni trn, h thng thng tin ATM c khnng cung cp dch v B-ISDN c nhng nt c trng khc nhau. iuny dn n s pht trin cng ngh lin kt dch v B-ISDN.

1.7.4 Nn tng ca tiu chun ho B-ISDN

Trong qu trnh tiu chun ho B-ISDN tin hnh vo u nhng nm 80,ITU-T quy nh cc knh H1, H2, H3, H4 l cc knh tc cao cakhch hng. Trong s , knh H1 c phi ghp vi nhm s cp caISDN trong dng knh H11 1,536 Mbit/s v knh H12 1,920 Mbit/s, v vvy hnh thnh c s ca ISDN cng vi giao din c bn 2B + D 144kbit/s.

H2, H3 v H4 c quy nh l cc knh bng rng tng ng vi phncp s ang tn ti.

Bt u t nm 1985 ngi ta ch n cc knh bng rng v ktqu l cc tc bit 30 - 40, 45 60 - 70 Mbit/s c xem l tiu chuncho cc knh H2, H3 v H4. Mt khc, u ban T1 a ra mt d n sdng 149,760 Mbit/s da trn c s SONET.

Sau , vo thng By nm 1986, ITU-T bt u tiu chun ho giao dinnt mng (NNI) mt cch c lp vi tiu chun ho giao din khchhng - mng (UNI) ca BISDN.

Nhim v tiu chun ho NNI, vn c tin hnh di nhiu iu kinkh khn, i n tho thun l s dng tiu chun tn hiu STM-1, ccu trc 9B x 270 v c tc bit 155,520 Mbit/s, ti hi ngh Seoulc t chc vo thng Hai nm 1988. Sau , n tr thnh phn cp sng b ca cc khuyn ngh G.707 - G.709. Mt khc, nhim v tiuchun ho UNI ca B-ISDN do BBTG (Broad Band Task Group- Nhmc trch bng rng) thc hin ho nhp vi khuyn ngh I.121 vonm 1988 ti cng hi ngh trn. l nhng vn kin u tin c tkhun kh c bn ca B-ISDN. Nhng vn kin ny quy nh rng B-ISDN phi da vo ATM v cc dch v ca n, phi c phn chiathnh cc dch v giao lu v cc dch v phn b, v rng cu trc chcnng/tiu chun ca B-ISDN phi c thit lp ging nh ca ISDN.Cc vn kin ny cng xc nh r m hnh giao thc cho ATM v


kch thc ca t bo ATM l 30 byte. Ngoi ra, cc vn kin ny phnnh 32,768 Mbit/s cho H21, 43 - 45 Mbit/s cho H22 v 132 - 138, 240Mbit/s cho H4. Thm na, n quy nh UNI l lp 150 Mbit/s v lp 600Mbit/s.

Sau t lu, BBTG c ch nh l WP8 nhng cng vic tiu chunho UNI gp nhng kh khn lin quan n kch thc ca t boATM, n tc bit v cu trc khung trn mt giao tip.

Ngoi ra, v kch thc ca t bo ATM, "4+32" byte (u t bo +trng tin) do ngi chu u xut cnh tranh vi "5+64" byte dongi M a ra. Song cui cng quyt nh l "5+48" byte s cs dng cho mc ch ny. Do b nh hng mnh ca SDH c tiuchun ho trc , tc bt ca mt giao tip c quyt nh l155,520 Mbit/s. Ngoi ra, cu trc khung ca lp vt l quyt nhtun theo cu trc khung STM-1 hoc dng t bo ATM thun tu. Hnna, cng c php b tr cc tn hiu khc ca G.702. WP8 xcnh r nhng chi tit ca nhng iu khon cn c bn ci nh cckhuyn ngh thuc Seri I ti Hi ngh Masyama, t chc Nht Bn vothng 11 nm 1990. Nh vy, khun kh tng th v BISDN chon chnh. Mt khc, khi ITU c t chc li vo nm 1993, nhmnghin cu 13 (SG.13) ca ITU-T bt u m trch cc hot ngnghin cu v tiu chun ho BISDN.

1.7.5 Nguyn tc c bn ca BISDN

Nh trnh by trc y, BISDN l mt khi nim c a ra thomn nhu cu v cc dch v bng rng ang cng ngy cng gia tng. Ccmc ch c bn ca BISDN l thit lp mt mng s c kh nng linkt v cung cp cc hnh loi dch v bng rng khc nhau thng qua vics dng truyn dn tc cao, chuyn mch tc cao, x l tn hiu,my tnh, phn mm v cng ngh cu kin. V li, thng qua BISDN,cc dch v giao lu v phn phi cng nh cc dch v ch knh vch nhm cng c cung cp. Thm vo , cc dch v bng hp vcc dch v bng rng c cung cp mt cch ng thi. t ccc mc ch ni trn, BISDN phi c kh nng h tr cc ni kt truynthng bn c nh c nh cc ni kt im - ni - im a im - ni -im v cc ni kt dnh dng cc du ring/c nh; Nh vy, BISDNcn phi c kh nng thng minh m rng v ci tin cc dch v v qun l hot ng, bo dng v iu khin mng mt cch hiu qu.

Cu trc ca B-ISDN phi nh th no sao cho n khng cn tr spht trin cng ngh hoc s pht trin phng php hin thc ho trongtng lai. Ngoi ra, n phi c kh nng p ng cc nhu cu ca khchhng hoc s pht trin mng m n c th pht sinh mt ln na. Hn


na, da trn cc khi nim ca ISDN, tiu chun giao din phi ghp vgiao thc cng cn phi c thit lp mt cch ph hp.

BISDN dng ATM thc hnh cc chc nng ca mnh. ATM l mth thng truyn thng phn chia u cc hnh loi dch v khc nhau, spxp chng vo cc t bo ATM c kch thc nh nhau v cui cng,chuyn chng i nh cc ATDM. Hn na, n thit lp cc ng o vcc knh o chuyn giao t bo ATM.

Do , thng qua vic s dng ATM, c th thc hin c kt ni mngc linh hot cao v phn b di thng bin i. Cng vi nhng ci, ATM c kh nng chuyn giao thng tin v s liu qua cc loiphng tin vt l v cc mng chuyn ti khc nhau, bi v n c xcnh mt cch c lp vi cc phng tin chuyn ti ca cc lp vt l.

1.7.6. So snh B-ISDN v ISDN

B-ISDN l mt khi nim xut pht t tiu chun ISDN. Do vy, ccquan im v B-ISDN cng ging nh ca ISDN. Tuy nhin, vic thitlp B-ISDN c thc hin khc vi thit lp ISDN.

Th nht, BISDN l mt mng s lin kt a dch v nh trong trnghp ISDN, nhng n khc vi ISDN ch n bo m vic lin kt ccc tn hiu bng rng na. V l do , m hnh cu trc c bn caBISDN cng ging nh ca ISDN, ngoi tr kh nng x l cc tn hiubng rng, ng thi vi cc chc nng ca ISDN bng hp. V mt thitlp cu trc chc nng hay cu hnh tiu chun, BISDN cng ging nhca ISDN. Nhm chc nng ca n bao gm TE1, NT1, NT2 v TA,cng cc im chun c hnh thnh t R, S v T.

Tuy nhin, chng ch tng t nhau v mt khi nim m khng tngthch nhau v mt hot ng thc t. C ngha l BISDN khng th cthc hin ch bng vic b sung cc thit b ca dch v bng rng vomng ISDN hoc TE ca ISDN khng th c u ni ti NT caBISDN. Do , cc nhm chc nng ca ISDN v cc im chun cngging nh cc phn t lin quan ca BISDN ch v mt khi nim. Tuynhin n c th phi ghp vi TE1 ca ISDN hoc vi TA qua vic sdng TE2 ca BISDN. Trong hot ng thc t BISDN khc rt xa viISDN; h thng thng tin ISDN c cc c trng kt hp cc h thngthng tin chuyn mch knh s ang hot ng vi h thng chuynmch gi, trong khi BISDN dng h thng ATM hon ton khc vicc h thng ni trn ca ISDN.

C ngha l, trong khi ISDN ch yu iu tit h thng thng tin knh (hthng thng tin gi cng c iu tit) th BISDN ch yu s dng h


thng thng tin gi, ng thi vn iu tit h thng thng tin knh). Donhng s khc nhau v h thng truyn thng , qu trnh truyn dn,bo hiu v qun l mng ca BISDN cng c tin hnh khc viISDN. Do vy, BISDN cn c coi l khc hn so vi ISDN.

1.7.7 H thng thng tin ATM

ATM l mt h thng truyn thng thc hin BISDN. ATM l mt hthng chuyn giao kiu gi c hnh thc c bit, s dng ATDM. TrongBISDN, thng tin c chuyn i nh mt lung lin tc ci gi c mtkch thc khng i. Cc gi c kch thc c nh ny c gi l cct bo ATM. Do vy thng tin dch v cng c b tr vo t bo ATM,sau c chuyn i theo nhng kch thc khng i. V sau , tnhiu truyn dn ca BISDN c to nn nh ATDM vi cc t boATM. ng thi ATDM l mt phng php ghp knh thng k, thchin vic phn chia theo thi gian ghp cc t bo ATM ca mt sknh i ti mt cch khng ng b.

Nu s dng ATM, dung lng ca knh nghip v cng c tnh theos lng cc t bo ATM. Cho nn s vt qu dung lng truyn dnca thng tin c biu th bi s lng cc t bo ATM. Vic phn phidung lng truyn dn c xc nh theo dung lng yu cu v khnng phn phi c th c thng qua thng lng vi mng thng tintrong qu trnh thit lp cuc gi.

ATM - mt h thng kiu lin kt - s thit lp cc knh o chuyngiao thng tin dch v. Mi khi mt knh o c thit lp, s hiu nhndng ni kt c gn v khi ni kt c gii to, s hiu nhn dng nycng c hu b. Trnh t sp xp gia cc t bo ATM trong mt knho no do cc chc nng ca lp ATM d kin trc. Thng tin bohiu v thit lp ni kt c chuyn giao cc t bo ATM ring bit.

H thng ATM xc nh r m hnh chun ca giao thc phn lp chuyn giao thng tin mt cch c h thng v c ng. Cc lp giaothc c s dng l lp ATM, lp ng dng ATM (AAL) v lp mccao. Lp AAL nh x cc tn hiu dch v sang khu vc trng tin cacc t bo ATM, cn lp ATM thc hin chc nng to u ca t boATM chuyn giao trng tin mt cch trong sut. Lp vt l thc hinchc nng chuyn i cc t bo ATM thnh hng bt v sau , chuynchng i.

Kch thc ca t bo ATM l 53 byte. N c phn chia thnh mou 5 byte v ng bao trng tin 48 byte (hnh 1.73(a). Chc nng chyu ca mo u t bo l nhn dng cc t bo thuc v cng mt knh


o (trong s cc t bo ATM) hin din trong mt lung thng tinATDM.

l chc nng do VPI (phn t nhn dng ng o) v VCI (phn tnhn dng knh o) ch r trong (b) v (c) ca hnh 1.73.

(a) Cu trc ca t bo

(b) Cu trc u trong UNI

(c) Cu trc u trong NNI

Hnh 1.73 Cu trc ca t bo ATM

ng thi, ng o c ngha l mt b cc knh o cng s dng chungcc ng no v mo u t bo cng c phn loi thnh loitrng tin (PT) v ch th thm quyn mt t bo v cung cp kh nngiu khin sa sai ca mo u. N cn cung cp thm chc nng iukhin lung chung cho mo u t bo trong giao din UNI.

1.7.8. Cu trc chc nng ca BISDN

M hnh cu trc chc nng chung ca ISDN bng rng v c bn gingnh ISDN bng hp. C ngha l v mt cu hnh tiu chun, nhm chcnng v im gc, c hai cu trc l nh nhau. N ch ra rng B-ISDNc hnh thnh trn c s khi nim ca ISDN. M hnh cu trc c bnca B-ISDN nh c trnh by trong hnh 1.74. Cu trc ca ISDN bngrng bao gm kh nng mc cao v kh nng mc thp.


Kh nng mc cao l chc nng lin quan n thit b u cui (TE) vkh nng mc thp bao gm kh nng ISDN bng hp da trn kh nngbng rng, 64 bit/s, v kh nng bo hiu lin tng i.

Hnh 1.74. M hnh cu trc c bn ca B-ISDN

Cu hnh tiu chun ca B-ISDN c trnh by trong hnh 1.75

Hnh 1.75. Cu hnh tiu chun ca B-ISDN

im gc l Sb v Tb, nhm chc nng bao gm B-TE1, B-TE2 v B-TA, B-NT1, B-NT2. Trong hnh 1.75, cc thit b u cui (B-TE) ccha B-TE1, B-TE2 v B-TA. Cng nh vy, B-NT2 v B-NT1 tngng nm trong mng B-IDN dnh ring v B-ISDN cng cng. ch thim gc v nhm chc nng ca mnh, B c ngha l B-ISDN.

1.7.9. M hnh chun ca giao thc

M hnh chun giao thc (PRM) ca B-ISDN c hnh thnh t mtbng qun l, mt bng iu khin, v mt bng khch hng nh ctrnh by trong hnh 1.76. Chc nng ca mt bng qun l c phnchia thnh : qun l mt bng v qun l lp.


Hnh 1.76. Cu hnh chun ca B-ISDN

Qun l mt bng trong mt bng qun l ca PRM ca B-ISDN c nghal qun l tng th ton h thng. Cng nh vy, qun l lp hm lqun l ngun tim nng v khch hng lun bin i, v qun l thngtin OAM. Ngoi ra, trn mt bng iu khin, thng tin iu khin cucgi v iu khin kt ni s c qun l. Trn mt bng khch hng,thng tin v khch hng c gim st. Cc giao thc ca mt bng iukhin v mt bng khch hng c phn loi thnh lp mc cao, lpng dng ATM (AAL), cng lp ATM v lp vt l. Chc nng ca milp nh trong bng 1.18.

Lp Lp con Chc nngLp mc cao Chc nng hi tLp ng dng Hi t Chc nng hi t

Phn on vlp rp li Chc nng phn on v chc nng lp rp li

Lp ATM AAL Chc nng iu khin dng chungChc nng to ra v hu b mo u t boChc nng thng dch VPI/NCI ca t boChc nng ghp knh v tch knh cho t bo

Lp vt l Hi t truyndn

Chc nng phn chia tc t boChc nng to ra v khngdnh tn hiu HECChc nng nhn dng t boChc nng to ra v khi phc dn

Mi trng vtlChc nng thng tin thi gian bitChc nng lin quan n mi trng vt l

Bng 1.18. Chc nng ca mi lp trong PRM ca B-ISDN

Lp AAL c hnh thnh t lp con hi t (CS), lp con phn on vlp rp li (SAR). CS bin i thng tin dch v khch hng ca lp mccao thnh khi s liu giao thc (PDU) v SAR to nn phn thng tinkhch hng ca t bo ATM bng vic ngn chn PDU.

Lp ATM iu khin kt ni v dng thng tin trong UNI bng vic sdng on GFC. Cng nh vy, n kt ni VPI/VCI vi cc im truy


nhp dch v sau khi thng dch v ghp knh/tch knh cho cc t bo.Bn cnh , n x l cc on PT hoc CLP v thc hin chc nng lto ra v hu b mo u t bo ATM.

Lp vt l bao gm lp con hi t truyn dn v lp con mi trng vtl. Chc nng ca lp con hi t truyn dn bao gm vic phn chia tc t bo, to ra v xc nhn byte sa sai u , pht hin im bin giit bo. Ngoi ra, trong trng hp pht theo phn cp s ng b n thchin chc nng to ra v khng nh khung truyn dn. Lp con mitrng vt l c ngha l bc truyn dn cui cng qua cp si quanghoc cp ng trc.

1.7.10. Giao din khch hng - mng ca B-ISDN

Cu hnh ca giao din khch hng - mng (UNI) ca B-ISDN c trnhby trong hnh 1.77, trong trng hp ch th n bng vic s dng ccim chc nng Tb, Sb v R v cc nhm chc nng B-NT1, B-NT2, B-TE1, B-TE2, v B-TA. Trong hnh ny, cc trng hp (a), (b), (c), (d),(e), (f), (i), (j) c cu hnh ging nh cu hnh trong ISDN. Cng nhvy, cc trng hp (g), (h) ch cho thy rng B-NT c th dung cp ccim gc S v Sb mt cch ng thi.

Cu hnh vt lca UNI kt ni im c trnh by trong hnh1.78. Trong hnh ny, (a) ch th cu hnh chung ca loi tp trung ho,cn (b) ch th cu hnh chung ca loi phn b. Cng nh vy, (c), (d),(e) ch th ln lt cu trc bus hnh sao, cu trc bus v cu trc vngca loi phn b. MA trong hnh ny l b phi hp phng tin, cn Wch ra im kt ni gia cc MA vi nhau. Ngoi ra, TE* ch th TE to racu trc kiu bus v SSB ch th im kt ni gia cc TE* ny. MA lthit b v B l im gc u thuc loi phi tiu chun. B-NT1 thc hinchc nng ca lp 1, chng hn nh im cui ng dy truyn dn, xl phi ghp truyn dn, vn hnh v bo dng. B-NT2 thc hin chcnng ca lp 1 v lp c mc cao v n c th c cu hnh theophng php tp trung hoc phng php phn b. Cc chc nng linquan n B-NT2 l b phi hp phng tin (MA), tm kim bin gii tbo, tp trung ho, nh m. ghp knh, tch knh, gn ngun, x l phighp chc nng AAL v bo hiu, x l giao thc bo hiu v chuynmch kt ni bn trong. B-TE thc hin truyn thng gia khch hng -vi - khch hng v gia khch hng - vi - my, kt cui phi ghp, xl giao thc bo hiu, x l ni kt trn cc thit b khc, trn lp 1 vlp c mc cao hn, k c OAM.

(a), (b) Trng hp giao din vt l l Sb, v Tb

(c), (d) Trng hp giao din vt l l Sb


(e), (f) Trng hp giao din vt l l Tb

(g), (h) Trng hp S, Sb, Tb l ng tn ti

(i), (j) Trng hp Sb, v Tb l ng nht

Hnh 1.77. Cu hnh vt l c bn ca UNI

(a) Cu hnh chung ca loi B-NT2 tp trung ho (Cu trc hnh sao)

(b) Cu hnh chung ca loi B-NT2 phn b

(c) Cu trc bus hnh sao

(d) Cu trc bus

(e) Cu trc vng


Hnh 1.78. Cu trc tng quan v vt l cho phng tin dng chung.

1.7.11 Giao din mng ca B-ISDN

Nu cn nhc rng BISDN l mng chuyn ti ca ATM, th c th a rakhi nim phn lp ca mng. C ngha l, mng chuyn ti c phnlp thnh mng lp ATM v mng lp vt l. Mng lp ATM li cchia nh thnh lp con ca knh o v lp con ca ng o.

im cui ca lp con tng ng

im ni kt ca lp con tng ng


Hnh 1.79. Mi quan h gia cc mng phn lp ca B-ISDN

Cng nh vy, mng ca lp vt l c chia nh thnh lp con cang truyn dn, lp con ca on digital v lp con ca on ti to.Khi nim cc mng phn lp ny u c p dng trong trng hpmng da trn t bo hoc mng da trn SDH. Mi quan h gia cc lpmng ca B-ISDN c trnh by trn hnh 1.79. Trong lp con ca knho c cung cp kt ni knh o (VCC - Virtual Channel Connection) chuyn giao thng tin gia khch hng - khch hng gia khch hng -mng v gia mng - mng. Do vy VCC c thit lp gia cc imchun Tb hoc Sb v cc t bo lin quan n cng mt kt ni VCC sc chuyn giao qua cng mt knh.

Trong lp con ca ng o c cung cp ni kt ng o (VPC - VirtualPath Connection) chuyn giao thng tin gia khch hng - khch hng,gia khch hng - mng v gia mng - mng. Do vy, VPC c cuhnh nh kt ni lin tc ca cc knh kt ni VP, cn VPC, gia khchhng - khch hng c thit lp gia cc im chun Tb hoc Sb. Ngoira, cc t bo lin quan n cng mt VPC s c chuyn giao trn cngmt ng.

Mng ca lp vt l l mt mng truyn dn ng b, c kt hp vimng ca lp phng tin truyn dn: c ngha l lp con ca ngtruyn dn chnh l ng VC-4 trong trng hp phn lp da trnSDH; lp con ca on digital v lp con ca on ti to tng ng lon ghp knh v on ti to.


2. THNG TIN V TUYN

2.1 NN TNG CA THNG TIN V TUYN

Thng tin v tuyn s dng khong khng gian lm mi trng truyndn. Phng php thng tin l: pha pht bc x cc tn hiu thng tinbng sng in t, pha thu nhn sng in t pha pht qua khng gianv tch ly tn hiu gc. V lch s ca thng tin v tuyn, vo u th kny Marconi thnh cng trong vic lin lc v tuyn qua i Ty dng,Kenelly v Heaviside pht hin mt yu t l tng in ly hin din tng pha trn ca kh quyn c th dng lm vt phn x sng in t.Nhng yu t m ra mt k nguyn thng tin v tuyn cao tn iquy m. Gn 40 nm sau Marconi, thng tin v tuyn cao tn l phngthc thng tin v tuyn duy nht s dng phn x ca tng i lu, nhngn hu nh khng p ng ni nhu cu thng tin ngy cng gia tng.

Chin tranh Th gii ln th hai l mt bc ngot trong thng tin vtuyn. Thng tin tm nhn thng - lnh vc thng tin s dng bng tn scc cao (VHF) v c nghin cu lin tc sau chin tranh th gii - tr thnh hin thc nh s pht trin cc linh kin in t dng choHF v UHF, ch yu l pht trin ngnh Raa. Vi s gia tng khngngng ca lu lng truyn thng, tn s ca thng tin v tuyn vnti cc bng tn siu cao (SHF) v cc cao (EHF). Vo nhng nm 1960,phng php chuyn tip qua v tinh c thc hin v phng phpchuyn tip bng tn x qua tng i lu ca kh quyn xut hin. Donhng c tnh u vit ca mnh, chng hn nh dung lng ln, phm vithu rng, hiu qu kinh t cao, thng tin v tuyn c s dng rt rngri trong pht thanh truyn hnh qung b, v tuyn o hng, hngkhng, qun s, quan st kh tng, lin lc sng ngn nghip d, thngtin v tinh - v tr v.v... Tuy nhin, can nhiu vi lnh vc thng tin khcl iu khng trnh khi, bi v thng tin v tuyn s dng chung phnkhng gian lm mi trng truyn dn.

i ph vi vn ny, mt lot cc cuc Hi ngh v tuyn Quc t c t chc t nm 1906. Tn s v tuyn hin nay c n nhtheo "Quy ch thng tin v tuyn (RR) ti Hi ngh ITU Geneva nm1959. Sau ln lt l Hi ngh v phn b li di tn s sng ngn s dng vo nm 1967, Hi ngh v b sung quy ch tn s v tuyn chothng tin v tr vo nm 1971, v Hi ngh v phn b li tn s v tuynca thng tin di ng hng hi cho mc ch kinh doanh vo nm 1974.Ti Hi ngh ca ITU nm 1979, di tn s v tuyn phn b c m


rng ti 9kHz - 400 Ghz v xem xt li v b sung cho Quy ch thngtin v tuyn in (RR). gim bt can nhiu ca thng tin v tuyn,ITU tip tc nghin cu nhng vn sau y b sung vo s sp xpchnh xc khong cch gia cc sng mang trong Quy ch thng tin vtuyn:

- Dng cch che chn thch hp trong khi la chn trm.

- Ci thin hng tnh ca anten

- Nhn dng bng sng phn cc cho.

- Tng cng ghp knh.

- Chp nhn s dng phng php iu ch chng li can nhiu.

2.2 CC C TNH CA SNG V TUYN

Tn s s dng cho sng in t nh vai tr sng mng trong thng tinv tuyn c gi ring l "tn s v tuyn" (RF). Tn s ny chim mtdi rt rng t VLF (tn s cc thp) ti sng milimt. Khng th l giiy sng v tuyn theo l thuyt, bi v n khng ch b nh hngbi tng i lu v tng in ly m cn bi cc thin th, k c mt tri.

Do vy, vic nh gi cc trng thi ca cc hnh tinh, ca tng i luv in ly v vic d bo ng truyn sng v tuyn cng nh kh nnglin lc da trn nhiu d liu trong qu kh l ht sc quan trng. Phnsau y ca chng trnh ny s gip bn c hiu c c ch truynsng v tuyn theo tn s thng tin v tuyn cng nhng vn khc,lin quan n sng v tuyn.

2.2.1 Phn loi tn s v tuyn

Trong thng tin v tuyn, c ch truyn sng v tuyn v vic s dngthit b truyn thng ph thuc vo tn s v tuyn s dng. Bng 2.1trnh by bng tn s v tuyn c phn loi theo tiu chun quc thin hnh v theo c ch v phng thc s dng sng v tuyn.

Bng 2.1. Phn loi, c ch v s dng sng v tuyn

Tn s Phn loibng tn

C chtruynsng vtuyn

C ly thng tin v lnh vc sdng

3KHz~30 KHz VLF Sng t-in ly

Thng tin o hng qun skhp th gii


30KHz~300KHz LF Sng t 1500Km o hng v tuyn300KHz~3MHz MF Sng t

(C lyngn)

Sngtri(C lydi)

Pht thanh c nhHng khng, o hng,lin lc nghip d

3MHz~30MHz HF Sng tri 3~6MHz : Thng tin lin tca

6~30Mhz : Thng tin ding

Thng tin kinh doanh

v nghip d, dn s quct

30MHz~300MHz VHF Sng triSngilu

Thng tin trc thi, VHF, FMa thng tin

300MHz~3GHz UHF Sng triSngilu

Raar, a thng tinThng tin di ng

3GHz~30GHz SHF, Viba Sng tri Thng tin v tinh, thng tin cnh,

Raar

30GHz~300GH EHF,Milimeter

Sng tri Thng tin cho tng lai

2.2.2 ng truyn lan sng v tuyn

Sng v tuyn khng truyn lan theo dng l tng khi chng trongkhng gian do nh hng ca mt t v tng i lu. Hnh 2.1 m tng truyn sng gia cc u pht T v u thu R v ch cho thy cnc sng phn x t b mt t t ti trm thu, ngoi sng trc tiptheo ng thng.

(a) Trong tm trc thi

(b) Ngoi tm trc thi


Hnh 2.1. ng i ca Sng v tuyn

Khi khong cch gia trm pht v trm thu xa nhau hn, thng tinbng sng i thng tr nn khng th c do cong ca b mt trit nh trnh by trong hnh 2.1(b) nhng vn c th c sng vtuyn truyn lan xung mt t do c sng b mt v sng tri, nhhin tng khc x (hnh 2.2). Ni chung, sng b mt, sng trc tipv sng phn x, tr sng tri, u c gi l sng t. Sng tri lsng in t b thay i hnh trnh ca mnh ti tng in ly v quaytr v tri t; tng in ly l ni hi t ca v s in tch, nh hnhti cao 100-400Km. Ngoi sng b mt v sng tri cn c sngtn x - l phn x do nhng s bin i mnh lit ca tng i luv in ly hoc do sng in t va chm vi cc vt cht, chng hnnh cc sao bng, v b tn x ri t ti u thu. Sng tn xc s dng trong phng php chuyn tip qua tn x i lu.

Hnh 2.2. Hnh trnh ca sng v tuyn i qua ng chn tri

1. S lan truyn ca bng tn s thp

S lan truyn ca bng tn s thp l nh vo sng t. N c thchin nh nhiu x sng in t. Do nhiu x t l nghch vi bcsng cho nn tn s s dng cng cao, sng t cng yu ( truyn lantn s thp). Hin tng nhiu x c mi tng quan cht ch vi dnin v hng s in mi ca t trong ng lan truyn. V c ly truynsng trn mt bin di hn so vi mt t cho nn tn s thp c sdng rng ri trong thng tin v tuyn o hng. Trong trng hp tn scc thp, bc sng ln hn nhiu s

Giao Trinh He Thong Thong Tin Quang

Documents

Transcript of Giao Trinh He Thong Thong Tin Quang