TTQUANG CHVTK21.1

CHVTK21.1

1. H thng thng tin quang 1.1 Thng tin quangKhc vi thng tin hu tuyn v v tuyn - cc loi thng tin s dng cc mi trng truyn dn tng ng l dy dn v khng gian - thng tin quang l mt h thng truyn tin thng qua si quang. 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 tr li thnh thng tin ban u. Hnh 1.1. Gii thiu mt h thng truyn dn si quang digital c s dng rng ri nht hin nay. Trong phn ny chng ta s xem xt cc giai on pht trin ca h thng ny v so snh cc c tnh ca n vi cc c tnh ca nhng h thng ang tn ti. Cui cng, chng ta s gii thch cc tnh cht ca nh sng.

Hnh 1.1. H thng truyn dn si quang digital1.1.1. S pht trin ca thng tin quang Cc phng tin s khai ca thng tin quang l kh nng nhn bit ca con ngi v chuyn ng, hnh dng v mu sc ca s vt thng qua i mt. Tip , mt h thng thng tin iu ch n gin xut hin bng 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 thc hin 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 my ht 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

1960Trin khai my laser Ruby (HUGHES)

1962 My laser Ga As

1965 My laser Co2 (BL)

1966Kh nng s dng ng truyn dn cp quang (ST, tn tht 1000dB/km)

1970My laser GaAIAS to dao ng lin tc (BL, Nga, NEC)Trin khai thnh cng si sp quang s dng abaston (Corning, 20 dB/km)

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

1976My laser GalnAsP dao ng lin tc (MIT, KDD, TIT, NTT) xut kh nng sn xut si quang florua (France, Lucas).

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

1979My laser GalnAsP 1,55 um (KDD, BL, TIT) dao ng lin tc Ch to si quang c Abastoes c tn tht ti thiu (NTT, 0.18 dB/km (1.55um))

1980Cu trc laser ging lng t c ch to (Bell Lab).Ch to si quang Flo (NRL) tn tht 1000 dB/km

1981GalnAsP LD (1.6 um) Continuous

Oscillation (TIT)

1982LD Array High Power

(2.5 W Continuous Osciltation)

1983Single Mode, Single Frequency LD (KDD, Bel Lab.)Si quang fluor c tn tht thp (NRT, NTT) tn tht 10 dB/km

1986Single Mode, Single Frequency LD

Commercialization (NEC, Hitachi etc.)Si quang fluor c tn tht thp,

tn tht 1dB/km (khong 2.5 um)

1989GaAI/AIGa Laser Develoment

S nghin cu hin i v thng tin quang c bt u bng s pht minh thnh cng ca Laser nm 1960 v bng khuyn ngh ca Kao v Hockham nm 1966 v vic ch to si quang c tn tht thp. 4 nm sau, Kapron c th ch to cc si quang trong sut c suy hao truyn dn khong 20 dB/km. c c v bi thnh cng ny, cc nh khoa hc v k s trn khp th gii bt u tin hnh cc hot ng nghin cu v pht trin v kt qu l cc cng ngh mi v gim suy hao truyn dn, v tng gii thng v cc Laser bn dn ... c pht trin thnh cng trong nhng nm 70. Nh c ch ra trong , tn tht ca si quang c gim n 0,18 dB/km. Hn na, trong nhng 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 hn 100 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 a im cch xa hng 100 km bng mt si quang c dy nh mt si tc, khng cn n cc b ti to. Hin nay, cc hot ng nghin cu nghim 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 tin quang, c kh nng pht hin, x l, trao i v truyn dn thng tin bng phng tin nh sng. Photon hc c kh nng s c ng dng rng ri trong 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 dng mt cch hiu qu: suy hao truyn dn thp v bng thng ln. Thm vo , chng c th s dng thit lp cc ng truyn dn nh v mng (nh), khng c xuyn m vi cc ng si quang bn cnh v khng chu nh hng ca nhim cm ng sng in t. Trong thc t si quang l phng tin truyn dn thng tin hiu qu v kinh t nht ang c hin nay Trc ht, v c bng thng ln nn n c th truyn mt khi lng thng tin ln nh cc tn hiu m thanh, d liu, v cc tn hiu hn hp thng qua mt h thng c c ly n 100 GHz-km. Tng ng, bng cch s 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 khng cn n cc b ti to.Th hai, si quang nh nh v khng c xuyn m. Do vy, chng c th c lp t d dng cc thnh ph, tu thu, my bay v cc to nh cao 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 chng khng chu nh hng bi can nhiu ca sng in t v ca xung in t. 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 s dng 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 a ra. Ngoi ra, nh cp trn, do c trng l c tn tht thp gi thnh lp t ban u cng nh gi thnh bo dng v sa cha thp bi v 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 bo dng, sa cha v c tin cy cao. Hn na, n khng b r r tn hiu v d ko di khi cn v c th ch to vi gi thnh thp. Trong bng 1.2, chng ta tng hp cc u im trn. Nh nhng u im ny, si quang c s dng cho cc mng li in thoi, s liu/ my tnh, v pht thanh truyn hnh (dch v bng rng) v s c s dng cho ISDN, 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 quangc tnhu im Nhc im

tn tht thp C ly ti to xa chi ph thit b ng dy dn

Di thng ln Truyn dn dung lng ln

Gim kch thc ng truyn dnD lp t v bo dng

Gim chi ph lp t cngKh u ni

Phi dnNgn nga xuyn m Thng tin an ton Cn c cc ng dy Cp ngun cho tip pht

Ngun - ct Nguyn liu phong ph Chi ph sn xut rCn c cc phng thc chnh li mi (cp)

nh gi Dng truyn dn tuyt vi C th gii quyt bng cc tin b cng ngh mi

1.2 Cp si quang Si quang l nhng dy nh v do truyn cc nh sng nhn thy c v 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 x mt cch hon ton trong li th chit sut ca li ln hn chit sut ca o mt cht.V bc pha ngoi o bo v si quang khi b m v n mn, ng thi chng 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 lng quang ln.

Hnh 1.4. Cu trc cp si quang Li v o c lm bng thu tinh hay cht do (Silica), cht do, kim loi, fluor, si quang kt tinh). Ngoi ra chng c phn loi thnh cc loi si quang n mode v a mode tng ng vi s lng mode ca nh sng truyn qua si quang. Ngoi ra chng cn c phn loi thnh si qaung c ch s bc v ch s lp tu theo hnh dng v chit sut ca cc phn ca li si quang. Cc vn ny s c trnh by t m mc 1.2.21.3. H thng cp quang Nh kt qu ca cc hot ng nghn cu v pht trin cng cao trong nhng nm 1970, hin nay cng ngh thng tin quang a mode ang c s dng rng ri trn ton th gii. Cng ng nh vy i vi h 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. Trong phn 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 nh cng 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 trng truyn dn, phng php truyn dn v phng php iu ch/ ghp knh phi c xem xt trc tin. Cho n nay th khng gian c s dng mt cch rng ri cho thng tin v tuyn, cn cp i xng v cp ng trc cho thng tin hu tuyn. Trong phn di y, chng ti ch bn n cc phng php truyn dn hin ang sn c da trn vic s dng cp quang. S iu ch sng mang quang ca h thng truyn dn quang hin nay 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 vy c 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 qun tuyt 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 cn thit iu ch pha - cn cha c pht trin y .(3) Nu mt sng mang n tn c tn s cao c pht i theo cp quang a mode - iu m c th x l mt cch d dng - th cc c tnh truyn dn thay i tng i phc tp v cp quang b dao ng do s giao thoa gy ra bi s bin i mode hoc do phn x trong khi truyn dn v kt qu l rt kh sn xut mt h thng truyn dn n nh. V vy, trong nhiu ng dng, vic s dng phng php iu ch mt c kh nng s c tip tc.i vi trng hp u ch quang theo mt (IM) c rt nhiu phng php bin i tn hiu quang thng qua vic iu ch v ghp knh cc tn hiu cn pht. Mt trong nhng v d in hnh c trnh by trong hnh 1.19

Hnh 1.19. Qu trnh ghp knh in Phng php phn chia theo thi gian (TDM) c s dng mt cch rng ri khi ghp knh cc tn hiu nh s liu, m thanh iu ch xung m PCM (64kb/s) v s liu video digital. Tuy nhin, trong truyn dn c ly ngn, ca cc tn hiu video bng rng ri cng c th s dng phng php truyn dn analog. Phng php iu ch mt s DIM - phng php truyn cc knh tn hiu video bng IM - v phng php thc hin iu ch tn s (FM) v iu ch tn s xung (PFM) sm tng c ly truyn 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 khc nhau thnh cc tn hiu in khc nhau v sau c th truyn chng qua mt si cp quang - cng ang c s dng. Hn na, khi truyn nhiu knh thng qua cp quang, mt s lng ln cc d liu c th c gi i nh gia tng s li cp sau khi ghp cc knh trn. Phng php ny c gi l ghp knh SDM. H thng truyn dn quang c th c thit lp bng cch s dng hn hp TDM/FDM, WDM v SDM. Chng ta c th thy rng h thng truyn dn quang cng tng t nh phng php truyn dn cp i v cp ng trc truyn thng, ch c khc l n bin 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 b khuych i to iu kin pha thu nhn c mc ra theo yu cu bng cch bin i cc tn hiu in thnh cc tn hiu quang v ngc li. Khi s dng phng php iu ch PCM th mi chc nng gii iu ch 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. Ngoi nhng phn trnh by trn h thng hot ng thc t cn c thm mt 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 (ngun sng), cc si quang (mi trng truyn dn) v cc phn t thu nhn nh sng truyn qua si quang.Cc phn t sau y c chn s dng:1. Phn t pht x nh sng a. it Laser (LD)b. it pht quang (LED)c. Laser bn dn 2. Si quang a. Si quang a mode ch s bc b. 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 1.4.1. C s ca tiu chun ho Trc khi phng php truyn dn ng b c c dng thc cao cp ca cc c trng n nht, Metrobus v SONET c nhng ng gp to ln. Metrobus l h thng thng tin quang ng b ni ti m bell Communications Research ca AT & T Hp chng quc Hoa K nghin cu v pht trin. Cn SONET l tiu chun kt ni ca h thng thng tin quang m sau Bell communications reseach (Bellcore) xut v ri c u ban T1 chp nhn s dng v pht trin cho tiu chun Bc M. Metrobus chng li quan im ca thng tin quang c in, s dng s ghp tng u tin, chp nhn s dng khi nim container (cng ten), s dng Overhead (mo u) mt cch hiu qu v thit lp khi nim h thng thng tin quang ng b ni ti, h thng ny coi tn hiu cp 150 Mbit/s lm cp tiu chun. Do vy, trn c s cp 50 Mbit/s, SONET b sung quan nim v cu trc phn cp v phng 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 150 Mbit/s lm tiu chun, k c phn cp s kiu Chu u, v c ph cp ho m ra kh nng thng tin ton cu.1. MetrobusMetrobus l mt h thng thng tin quang do J.D.Spalink, mt nh nghin cu ti Bellcore ca AT & T, xut nm 1982. N c trin khai theo quy m y vo u nm 1984, c cng b vo thng chn nm 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 quang ti u nht, c cn nhc n kha cnh tc cao, dung lng ln, vn l c trng ca mt h thng thng tin quang, phng hng tin trin ca mng thng tin, qu trnh pht trin ca cng ngh ct yu v xu hng i mi dch v. Tn gi ca Metrobus c ngun gc t mc tiu ng dng ca n nhm vo vng thnh ph ln (metropolitan). Trong qu trnh R&D cho ng dng ni ln mt s khi nim. in hnh l khi nim v mng thng tin quang im - a im, khi nim v h thng ng b ni ti, tm nhn ca DS-O, khi nim ghp knh tng u tin, iu chnh ng thi nhng tn hiu nhiu cp bng vic iu khin s hiu cng ten, thit lp tn hiu tiu chun ni ti 150Mbit/s v s dng mo u.Do tt c cc h thng thng tin quang trc y u c xut trong bi cnh ca cc h thng im - ni im, cho nn khi nim ca thng 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 hin khi nim ny. Vi vic cn nhc n di thng v hn m thng tin quang cung cp, ta thy n bo m khong trng cho mo u, v bng vic s dng n cng nh bng vic hnh thnh knh truyn thng mo u, cho php ng dng lin kt ca ton b cc tuyn thng tin quang. 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 b ca mng thc s l mt quan im tin phong. S d nh vy l v nhng iu sau y c d kin : khi c xem xt theo kha cnh phn lp tn hiu digital, tc bt m tt c cc tn hiu c th bao gm l 150 Mbit/s; theo kha cnh dch v, tn hiu thoi, s liu v video (k c tn hiu HDTV c nn) hin ti u c th c s dng trong cp 150Mbit/s ny; v kha cnh cng ngh bn dn c bn, cng ngh CMOS c th c s dng trong phm vi 150 Mbit/s chng kh khn g. Ngoi ra, v kha 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 r tin, v cp si quang c th to iu kin cho s kt hp hiu qu ny nh vic s dng si quang a mode c ch s tng dn thay cho n mode.Khi nim ghp knh tng u tin cng l mt khi nim mang tnh cch mng. N cho php ghp knh trc tip tn hiu DS -1 thnh tn hiu tiu chun150 Mbit/s m khng cn chuyn qua tn hiu DS-2 hoc DS-3 iu khng th c trong h thng ghp knh khng ng b trc y. N tr thnh nn tng thc hin kt ni tch/nhp v ni kt cho l nhng ni 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 iu khin s hiu ca cc cng ten. Ngha l, bng vic xc nh cc c kch thc c nh, lm cho cc tn hiu DS -1. DS -1C, DS-2, DS-3 v.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 nhp v kt ni cho rt tin li, bi v tt c cc tn hiu u c x l vi n v ca s hiu . Tn hiu tiu chun ni b bao gm 13Wx88 (1W=16 bt) nh trong hnh 1.37. Tc bit l 146,432 Mbit/s (13x88x16x8 kbit/s). 88 n v ca t m (thuc v 88 ) xut hin trong 125m s/13, trong d 4 n v c s dng cho mo u v mi tn hiu DS-n chim s hiu tng ng ca .

Hnh 1.37. Cu trc khung ca MetrobusVic gii thiu khi nim ng b ni ti cng l mt tin cho mng thng tin ng b. C ngha l, do phm vi mc tiu ch c gii 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 s s dng tn s chun ng b ho c bn BSRF v cng c th s dng tn hiu nh thi c n nhn t b dao ng ni v t tn hiu thu c. nhn r ca tn hiu DS-O c to ra vi n v 125 m s. Khi vic chuyn t mi tn hiu phn cp sang cng ten cng c thc hin vi n v 125 m s, th cc tn hiu DS-O nhn c qua ly mu 8 kbit/s c th 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 tiu chun 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 by nh bus ni b trong hnh v tng ng vi tn hiu tiu chun ni b 146,432 Mbit/s. Tn hiu c to ra t DS-1 n DS-3 qua PMB (bng ghp knh c th lp trnh). Thng tin quang 146 Mbit/s c th phi hp trc 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 876 Mbit/s hoc 1,7 Gbit/s bng vic a 6 hoc 12 n v ca tn hiu ny vo WIM (ghp knh xen t m - Word Interleaved Multiplexing), ri sau a qua LTE. Nhng qu trnh ny c m t trong hnh v. Ngoi ra, h thng PCCS (h thng kt ni cho c th lp trnh) thc hin chc nng ni kt cho qua cc cng ten do tiu chun ca tc bit DS-1 to ra bng cch a vo tn hiu 146 Mbit/s.

Hnh 1.38. Cu trc ca h thng Metrobus2. SONETSonet l mt t vit tt ca Synchronous Optical Network (mng quang ng b). N c R.J.Boehm v Y.J.Ching vin nghin cu truyn thng Bell trnh ln u ban T1- t chc tiu chun truyn thng ca Bc M - vo cui nm 1984 nh mt n tiu chun v u ni h thng thng tin quang. Vo thi gian , khung c xut c dng 3x8x33B nh trong hnh 1.39, v tc bit l 50,688 Mbit/s (=3x8x33x8 kbit/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 nh a vo qu trnh ghp knh xen byte qua STS-1.Tng u tin ca SONET c ngh cho mc ch "gp g gia chng" 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 trong khong mt nm, sau khi khi nim SONET c gii thiu. Tuy nhin, vic tiu chun ho bng nhin c a ra cng vi thng bo ca Metrobus vo thng chn nm 1985, v khi nim v h thng phn cp v k thut ng b ho bng con tr c cc thnh vin ca u ban T1 xut thm. Nhng ngi xut SONET pht trin v h thng 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 kch thc DS-1 ca L n v; mo u ca mc DS-1 ln kch thc DS-O ca M n v v mo u ca mc DS-O ln Nbit. Tng gia ca khung SONET c cu trc 26Bx30 v 49,92 Mbit/s (30x26x8x8 kbit/s) c iu chnh vi L=2, M=2 N=0 da trn cng thc miu t trong hnh 1.39. Vo khong thi gian vin nghin cu truyn thng Bell ca AT&T ngh rng tn hiu tiu chun ni b ca Metrobus (c cu trc 26x88W 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 truyn thng 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 SONETMc d u ban T1 xem xt k nhng cuc tho lun lin quan n hai d n ny, n vn khng th phn quyt c tnh u vit theo kt qu i chiu v kim nghim. im bn ci si ni nht l trong nh gi gia 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 tr gia cc cng ty, u nm 1986, u ban T1 i ti mt quyt nh l tn hiu tiu chun STS -1 s l 49,92 Mbit/s. Trong khi ITU - T cng ang hot ng nhm tiu chun ho bng knh rng vo cng thi gian th u 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 nh chn cp 50 Mbit/s, tha nhn v mt k thut tnh thch hp ca 150 Mbit/s. Sau , nhng hot ng tiu chun ho SONRT c tin hnh mt 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 tin hnh hot ng phi hp ngay tc khc mang tnh cht b mgoi, vi ITU-T v vn tiu chun kt ni NNI ca B-ISDN, song c rt nhiu mt hn ch trong vic iu tit vi cc tn hiu digital kiu Chu u, bi v 13Bx60 v 49,92 Mbit/s (hoc 146,976 Mbit/s) ch ch yu ph hp vi cc tn hiu digital ca Bc M.Do vy, cu trc 9Bx270 v tc 155,520 Mbit/s, ci c tng ln ba ln cu trc khung v tc bt ca SONET chnh l phn cp ng b s m 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 cao ca 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 nh thnh knh H11 ca 1,536 Mbit/s da trn c s tn hiu DS-1 kiu Bc M, v knh H12 ca 1,920 Mbit/s da trn c s tn hiu DS-1 kiu chu u. Mi ang ch c nhng nt i cng mang tnh cht khi nim tng 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 cc knh . 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 SONET ca u ban T1.Trong khi , ITU-T bt u hot ng tiu chun ho phn cp ng b s cho NNI (giao din nt mng) vo thng by nm 1986, khc bit vi UNI (giao din khch hng - mng) ca ISDN. iu ny bt u mt giai on tiu chun ho ch thc hng ti phn cp s ng b v ITU-T cng u ban T1 duy tr mi quan h hp tc cht ch cho mc ch , Hoa k chnh thc a ra cp 50 Mbit/s da trn tn hiu STS-1 ang c s dng ca SONET ti hi ngh Brazin vo thng Hai 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 M v kiu Chu u.Kt qu l, n ca M c thay i thnh 149,976 Mbit/s ca cu trc 13Bx180, da trn tn hiu STS-3, ti Hi ngh Hamburg vo thng 7 cng nm , cn CEPT xut tn hiu 155,520 Mbit/s ca 9Bx270 i lp vi ca M. Ngi ta tranh ci sut mt thi gian di v hai cu trc ny v im tranh ci si ni nht l s chung ho gia tn hiu DS-2 ca 8,448 Mbit/s v DS-3E ca 34,368 Mbit/s tho thun cui cng qua hi ngh Seoul vo thng Hai nm 1988 l cu trc 9Bx270. Tiu chun 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 chnh thc ho. Ngay c sau khi khuyn ngh ca ITU-T c n nh th cc hot ng 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 quy nh, h thng ghp knh ng b c mt cu trc hon chnh nh hnh 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 hon chnh trong qu trnh nghin cu hai nm sau , th h thng ghp knh ng b c n gin ho nh cu trc trong hnh 1.41. C th thy c rng cc ng ghp knh phn cp kiu chu u tng ng mt cch ng k vi cc ng ghp knh phn cp kiu M, v rng b sung cc khi nim mi, chng hn nh AUG, TUG-3. Hiu theo ng ngha ca n th phm vi m Metrobus ng gp cho vic tiu chun ho SONET v SONET ng gp cho vic tiu chun ho phn cp s ng b l cc k to ln. Rt nhiu c trng ca phn cp ng b c ngun gc t tiu chun ca h thng Metrobus, chng hn nh quan im v mng 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 th nht, phi hp tn hiu tc ghp knh bng vic iu khin s hiu ca cng 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 hiu qu. Cng nh vy, cu trc h thng phn cp, h thng ho cu trc mo u, ng b ho bng con tr, v kh nng cu trc mng thng tin lin tc a, u xut pht t tiu chun kt ni ca SONET. Da trn nhng c s , tiu chun phn cp s ng b l tiu chun cho php cu trc nn mng thng tin ton cu qua vic iu chnh kt hp hai kiu phn 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 chun ho NNI ca B-ISDN, c nh hng rt ln n tiu chun UNI ca B-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 v trong 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 c nh x trong ng bao ca trng tin VC-4 pht i c s phn cp s ng b ca UNI ca B-ISDN. Ni mt cch chnh xc, phn cp s ng b ng mt vai tr ch cht trong vic hnh thnh khi nim B-ISDN cng 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 truyn dn 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 cho tiu chun SDH v n cng m rng SONET SONET c s dng cho 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 bit nh gia SDH v SONET. Nu nhng s khc bit tiu biu gia chng ta c th m trn u ngn tay th im bt u c bn ca SDH l cp 150Mbt/s, trong khi SONET l cp 50Mbt/s. C ngha l, trong khi SDH kt hp DS-4E vi tn hiu mc thp thnh tn hiu cp cao nht th SONET c DS-3 nh tn hiu cp cao nht. Do c mt khi nim v giao din, 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 b cp 1) l 51,840 Mbt/s tn hiu truyn dn c bn ca SONET - c phi 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 v cc 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 tm chnh trong SDH. Trong khi , trng hp SONET, STS-1 (51,840 Mbt/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 (2.488,320 Mbt/s) l cc i tng quan tm (tham kho bng 1.9); khi , ni chung, tn hiu STM-n bng vi tn hiu STS-3n trong tc truyn dn : Bng 1.9 Tc truyn dn ca SDH v ca SONETSDHSONET

NSTM - NNSTS - N

151.840 Mbps

1155.520 Mbps3155.520 Mbps

9466.560 Mbps

4622.080 Mbps12622.080 Mbps

18933.120 Mbps

241,244.160 Mbps

361,866.240 Mbps

162,488.320 Mbps482,488.320 Mbps

V mt cu trc khung, SONET gim i ba ln so vi SDH. Nu SDH l STM-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 ca STM-1 trong dng 9x9B c b tr hng u ca khung STM - 1, mo u on ca STS-1 di dng 9x3B c b tr hng u ca khung STS-1. Sau , trong c hai trng hp, hng th t c dnh ring cho con tr (pointer). C th l, vic la chn hng th nht, th t v th by ca mo u on trong STS-1 tng ng vi mo u on ca STS-1 v 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. Gc gc ca vn nh vy l v STM-1 l cp 155Mbt/s v STS - 1 l cp 50Mbt/s. Do , trong trng hp STM - 1 cn phi ghp knh mt cch c 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 hiu phn 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 ng b ton b h thng nh trong hnh 1.41 l cn thit. Ngc li, trong trng hp STS-1 ch c mt khi tn hiu trung gian, gi l mt nhnh o (VT-virtual tributary) l s c thit lp. VT nayf tng ng vi VC ca SDH. Cc VT tng ng vi VC-11, VC-12 VC-2 c gi tng ng 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 v SONET cng khc nhau v cu trc ghp knh. Trong trng hp SDH cu trc thng k h thng nh trong hnh 1.41 l cn thit , trong n ni kt C, VC, TU, TUG, AU, AUG ATM-n vi nhau, cn trong trng hp 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 cp thnh VT-1,5 VT 2 v VT 6 cng ging nh phng php nh x mi tn hiu 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 bao trng tin STS-1, tc l SPE (Synchronous Payload Envelope - ng bao trng tin ng b) cng ging nh phng php ghp knh VC lin quan 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 v STM 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 vt l, on ti to, on ghp knh v lp ng truyn c t ra trong SDH s c gi l lp quang, lp on, lp ng dy v lp ng truyn 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 khung 125 m s, dng mo u h thng, v c tc truyn dn c bn ging nhau. Nhng n c iu tit nh s lin kt tt c cc tn hiu phn cp s Bc M k c tn hiu DS-1E kiu Chu u, v n cha ng c th tc ghp knh tng th nht.Ngoi ra, SONET s dng ng b ho lin quan ti phng php con tr, ging nh ca SDH, cho nn c th kt ni ton b nc M bng mng truyn dn ng b1.4.3 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 thng Chu u/ Bc M, c b phn tiu chun ho vin thng ca ITU v 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 Bell System 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 s dng, 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 c hnh thnh t DS-1 (1,544 Mbt/s), DS-1C (3,152 Mbt/s), DS-2 (6,312 Mbt/s) v DS-3 (44,736 Mbt/s), DS-4E (139,264 Mbt/s). Phn cp s cn 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 ng b 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, c hnh thnh t cc tn hiu STM-n. ng thi, n l mt s nguyn ln, m 1,4 v 16 l cc s c quan tm ch yu. Cc tc bt tng ng vi cc s ny l 155,520 Mbt/s, 622,080 Mbt/s v 2.488,320 Mbt/s. Mt tn hiu STM-n c hnh thnh thng qua ghp knh ng b t cc tn hiu phn cp DS-1, DS-2, DS-3 v DS-4E, DS3E, DS-2E, DS-1E. ng thi, cc tn hiu DS-1C hoc DS-5E khng c s dng. Tn hiu STM-n c cu thnh t n ln cc tn hiu STM-1 m n l s ghp knh 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 ta c th d dng nhn thy rng phn cp s ng b c mt cu trc n gin 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 Chu u ch c mt giai on ghp knh. Trong mt h thng phn cp s cu ng b vic ghp knh khng ng b c thc hin khi tn hiu trong mt cp c ghp knh thnh cp ca giai on k sau. Trong mt h thng phn cp ng b, vic ghp knh ng b c thc hin khi tn hiu phn cp c ghp thnh tn hiu STM-n. V li, trong phn cp s cn ng b tn hiu DS-m thuc v cp ca giai on k sau ca tn hiu DS-(m-1); nhng tt c cc tn hiu ny c mi quan h ngang bng trong phn 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 uNi 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 th ng 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 vt l (hoc lp quang hc).Cu trc ca ghp knh ng b c mt s sp xp theo khng gian c h thng ph hp vi cc khi nim phn lp. Trong Hnh 1.44, khung STM-n c phn loi theo chc nng; mo u ca on ghp knh c 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 v cc mo u cho bt k cc ng c mc thp hn no khc th hin din trong hnh bao trng tin bn trong STM.Cc mo u c s dng trong ghp knh ng b c phn chia thnh 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 v u on ghp knh.

Hnh 1.43. ng truyn dn (mt ng) v khi nim phn lp ca tn hiu s Mo u on ti toMo u ng truyn ca lp c mc caoMo u ng truyn ca lp c mc thp

Con tr

Mo u on ti to

Hnh 1.44. Cu trc khung v cc khi nim phn lp ca STM-nSOH c chn vo trong giai on cui cng khi tn hiu STM-n c hnh thnh cn POH c chn vo bt k khi no tn hiu cng ten o c to thnh. SOH c chn vo v c tch ra trong on ti to hoc on ghp knh ch th hiu nng truyn dn cng nh hot ng v bo dng tn hiu STM-n. Nh c minh ho trong hnh 1.44, cc SOH nm bn trn v bn di ca con tr c s dng tng ng cho on ti to v on 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 tnh ton li trong mi b ti to.Tuy nhin, ba byte ca B2-SOH cho BIP-24- c b tr phn pha di 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-12 v VC-3. Trong bt k trng hp no POH cng c s dngcho truyn thng u cui - ti - u cui gia nhng im, ni cc VC tng ng c hnh thnh v gii to. gii thch cu trc ca mo u on v mo u ng hy xem khung STM-1 trong hnh 1.45, (a), (b). Vic s dng mi loi mo u trong hnh ny nh sau: A1, A2 dng cho bt sp xp khung; B1, B2; B3 dng kim tra ngang bng chn l, C1, C2 dng cho s lng tn hiu v D1-D12 dng cho knh truyn s liu, cn E1 v E2 dng cho knh nghip v; F1, F2 dng cho knh khch hng; G1 l kim tra trng thi ng truyn, H4 dng ch th a khung; J1 dng ghi du tch ng truyn; K1, K2 dng cho chuyn mch bo v t ng; Z1~ Z5 l cc mo u d phng cho cc mc ch khc.123456789J1

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

2B1E1F1XXC2

3D1D2D3G1

4con trF2

5B2B2B2K1K2H4

6D4D5D6Z3

7D7D8D9Z4

8D10D11D12Z5

9Z1Z1Z1Z2Z2Z2E2XX

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-nKhung STM-n c mt cu hnh nh c trnh by trong hnh 1.46, da trn c s cc khi nim phn lp nh ngha trong phn trc. Do cu trc 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 8 kbit/s). Trong , 9B x n x 9 c phn b cho vng mo u SOH v con tr AU (Khi qun l) v phn cn li ca 9B x n x 261 c phn b 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 kch thc l 9B x 270. Cng nh vy, 9B x 9 trong s l cng ca mo u on v con tr AU, v cng chng y 9B x 261 l ng bao trng tin, v tc bt tr thnh 155,520 Mbt/s.Theo quan im cu trc khung STM-1, SOH c to thnh t hai khu vc 3 x 9B v 5 x 9B, con tr AUPTR bao gm khu vc 1 x 9B v cu hnh ca n nh c trnh by trong hnh 1.45. Mt VC-4 c nh x trong 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-4 v VC-3 u bao gm hnh bao trng tin v vng POH c kch thc 9 x 1B c b tr trc mi hnh bao trng tin. ng thi, cu hnh bn trong ca POH nh trong (b) ca hnh 1.45. VC-4 hoc VC-3 m c gn con tr AUPTR th c gi l AU-4 hoc AU-3.

Hnh 1.46. Cu trc ca khung STM-nDo vy, trong cu trc ca khung STM-1, AU-4 l t hp ca vng trng tin STM-1 v vng con tr AU, v cu trc cui cng ca STM-1 c th t c khi cc vng SOH tng ng c t ln lt vo phn pha 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 hiu phn cp s mt cch ngang bng v n s thit lp nn cc tn hiu STM-n. Trong hnh 1.41, s tng th ca cu trc ghp knh ng b trn cc tn hiu phn cp c a ra.Trong hnh ny, cc con s nm trong ngoc ch r s lng tn hiu cn thit cho qa trnh ghp knh tng ng. Qua trnh ghp knh ng b nm 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 cho qu trnh ghp knh khng ng b m trong cc tn hiu phn cp c hn thnh.Ti bc u tin ca qu trnh ghp knh ng b, cc tn hiu ca mi cp c nh x sang cc cng ten tng ng. ng thi, phng php chn 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 thm POH vo cngten, v mt TU (khi phn nhnh) c hnh thnh nu gn thm PTR vo n. Tuy nhin, nh trong trng hp VC-4, VC-3, TU s tr thnh AU (Khi qun l) nu tn hiu c nh x thng sang STM-1 m khng qua cc VC khc. Khi , s m (m=1, 2, 3, 4) gn cho mi khi tn hiu s ch th rng mi tc bt ca khi tn hiu lin quan s tng ng vi cp DS-m. Khi m=1, n c chia nh thnh 11 v 12 v chng biu th tng ng cho tc bt ca h thng Bc M DS-1 v h 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/sTrng hp TU-1 (TU - 11 hoc TU-12) n c ghp knh thnh VC-3 v VC-4 thnh kiu TUG (nhm ca khi phn nhnh) sau khi c gp li thnh bn. TU-2 c th c xem nh tng ng vi TUG-2. Ngoi ra, TU-3 c th c xem nh bng vi TUG-3. VC-3 c th c ghp knh thnh VC-4 sau khi c nh tuyn vi TU-3, hoc n c th c 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-n khi 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 1.47 l 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 cc ng k m trong Hnh 1.41. Nh c trnh by trong hnh 1.47, tn hiu DS-1 c nh x trc ht thnh C-11 v sau VC-11 POH c np vo bin i n thnh VC-11. t c TUG-2 khi TU-11 PTR c gn ti VC-11, v sau n c ghp thnh bn. Ngay i vi cc tn hiu TUG-2 chng ta c th thy rng cc con tr TU-11 PTR ca cc TU-11 c gp li vi nhau v c a ra ngoi. Ngoi ra, TUG-3 t c nh ghp knh mt TUG-2 thnh 7 TUG-2 v sau , gn FOH vo u ca chng. TUG-3 li c ghp thnh 3 TUG-3 v cc FOH cng cc 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 ghp TUG-2 thnh 21 TUG v sau gn VC-4 POH v FOH vo pha trc chng.Khi kim tra cc kt qu ghp knh chng ta c th bit rng mi mt trong 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 chnh kch thc.C th thu c AU-4 nh gn AU-4 PTR vo VC-4 v n cng ging nh tn hiu AUG. Cui cng c th thu c tn hiu STM-n khi mt AUG c ghp thnh n AUG v sau . mt mo u on c gn trn chng.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 hiu phn cp s mt cch ngang bng v n s thit lp nn cc tn hiu STM-n. Trong hnh 1.41, s tng th ca cu trc ghp knh ng b trn cc tn hiu phn cp c a ra.Trong hnh ny, cc con s nm trong ngoc ch r s lng tn hiu cn thit cho qa trnh ghp knh tng ng. Qua trnh ghp knh ng b nm 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 cho qu trnh ghp knh khng ng b m trong cc tn hiu phn cp c hn thnh.Ti bc u tin ca qu trnh ghp knh ng b, cc tn hiu ca mi cp c nh x sang cc cng ten tng ng. ng thi, phng php chn 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 thm POH vo cngten, v mt TU (khi phn nhnh) c hnh thnh nu gn thm PTR vo n. Tuy nhin, nh trong trng hp VC-4, VC-3, TU s tr thnh AU (Khi qun l) nu tn hiu c nh x thng sang STM-1 m khng qua cc VC khc. Khi , s m (m=1, 2, 3, 4) gn cho mi khi tn hiu s ch th rng mi tc bt ca khi tn hiu lin quan s tng ng vi cp DS-m. Khi m=1, n c chia nh thnh 11 v 12 v chng biu th tng ng cho tc bt ca h thng Bc M DS-1 v h 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/sTrng hp TU-1 (TU - 11 hoc TU-12) n c ghp knh thnh VC-3 v VC-4 thnh kiu TUG (nhm ca khi phn nhnh) sau khi c gp li thnh bn. TU-2 c th c xem nh tng ng vi TUG-2. Ngoi ra, TU-3 c th c xem nh bng vi TUG-3. VC-3 c th c ghp knh thnh VC-4 sau khi c nh tuyn vi TU-3, hoc n c th c 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-n khi 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 1.47 l 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 cc ng k m trong Hnh 1.41. Nh c trnh by trong hnh 1.47, tn hiu DS-1 c nh x trc ht thnh C-11 v sau VC-11 POH c np vo bin i n thnh VC-11. t c TUG-2 khi TU-11 PTR c gn ti VC-11, v sau n c ghp thnh bn. Ngay i vi cc tn hiu TUG-2 chng ta c th thy rng cc con tr TU-11 PTR ca cc TU-11 c gp li vi nhau v c a ra ngoi. Ngoi ra, TUG-3 t c nh ghp knh mt TUG-2 thnh 7 TUG-2 v sau , gn FOH vo u ca chng. TUG-3 li c ghp thnh 3 TUG-3 v cc FOH cng cc 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 ghp TUG-2 thnh 21 TUG v sau gn VC-4 POH v FOH vo pha trc chng.Khi kim tra cc kt qu ghp knh chng ta c th bit rng mi mt trong 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 chnh kch thc.C th thu c AU-4 nh gn AU-4 PTR vo VC-4 v n cng ging nh tn hiu AUG. Cui cng c th thu c tn hiu STM-n khi mt AUG c ghp thnh n AUG v sau . mt mo u on c gn trn chng.1.4.7 Con tr v ng b ho Trong SDH, k thut con tr c s dng ng b ho. Con tr ny c s dng ch th s thay i mi quan h khi VC c ng chnh theo tn hiu TU hoc AU v khi VC ch th a ch xut pht trong mt khung 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-4 PTR, AU-3 PTR, TU-3 PTR, v TU-11 PTR, TU-2 PTR, TU-12 PTR v.v.... Trong s AU-4 PTR, AU-3 PTR xut hin trn v tr ca AU PTR c ch r trong hnh 1.46 v TU-3 PTR c b tr trn nh ca hng u tin trong phm vi khung TU-3.Cc con tr ca lp c mc cao ni trn c nh du vi H1, H2 v H3. cc con tr ca lp c mc thp, chng hn nh TU-11 PTR, TU-2 PTR v TU-12 PTR c nh du bng V1, V2 v V3. Cc con tr ca lp mc thp ny c cu trc nh sau: ba trong s cc byte u tin ca mi on s t c nh phn chia TU tng ng thnh mt on 125 m s. Trong s , vic ng dng cc on m ba byte u tin ca chng l cc con tr V1, V2 v V3, cn byte th t l V4, th cn cha c xc nh. ng thi, vng trng tin ca mi TU s b tr cc a ch trn byte 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 r phi xc nh cch s dng ba byte ny nh th no. Bn bt ca c hiu s liu mi (NDF-New Data Flag) ch th trng thi ca s liu mi, cn bt SS c s dng phn nh loi ca TU hoc AU tng ng. a ch bt u ca VC tng ng c ghi trn 10 bt sau . 10 bt ny c 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 mi khi a ch ca im xut pht c gia tng v bt D b hu b mi khi a ch ca im xut pht gim i. Cui cng, byte H3 (hoc V3) c s dng np cc s liu hp l khi thc hin vic chn m.

Hnh 1.48. Cu hnh v chc nng ca con trKhi thc hin mt ghp chn dng, cc s liu hp l c pht i bng cch np ti cho byte ng ngay ng sau H3 (V3). Khi xy ra s khc nhau v tn s gia khung TU v AU hoc gia cc VC (l cc trng tin ca 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 VC tng ng bt u ln hn so vi khung TU/AU th trng tin cn pht s c gia tng. ng thi, i cho ti khi tng s cc d liu c tch t do 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 hp VC-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 dng cc phng php tng t tin hnh chn m khi tn s ca VC tng ng bt u thp hn so vi khung TU/AU. Tuy nhin, khi cc bt I s b hu b v cc s liu khng hp l s c np sang byte tip sau ca H3 hoc V3 v a ch s c gia tng 1.1.4.8 Cc c im ca Phng php Truyn dn ng bNh phn tch cho ti lc ny, khi c so snh vi truyn dn khng ng b c mt s c im ni bt. Trong phn sau y s gii thch c im ny.1. Khung 125 sC th thy c im u tin ca truyn dn ng b trong cu trc khung 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 hiu phn cp mc cao ti cc tn hiu phn cp mc thp; c bit l xung ti 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 khng ng b hin ti. Do m bin ng (jitter) thi gian i tr nn nng n. 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 , cc vn lin quan n jitter c th c gii quyt.2. S hp nht cc phn cp sCu trc ghp knh ng b c kh nng ho hp cc tn hiu s Bc M v Chu u. C ngha l, cc tn hiu STM-n c cng hnh dng b ngoi c th c hnh thnh qua th tc ghp knh ng b ngay c khi c gn bt k tn hiu no trong s cc DS-1, DS-2, DS-3 ca Bc M v cc DS-1E, DS-2E, DS-3E, v DS-4E ca Chu u. Ngoi ra, cc tn hiu Bc M c th kt hp c vi cc tn hiu Chu u trong qu trnh ghp knh ng b, v ngc li. Trc y, khng th thc hin c iu ny. Ghp knh tt c cc ng l phi thc t v kh nng s dng phng thc cn phi c xc nh chun b cho s lin kt mng ton cu.

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

4. S dng mt cch h thng cc mo uTrong cc tn hiu STM-1, mo u on v con tr chim mt khng gian 9x9B. Mo u thc t s tng ln khi cc mo u v con tr ca ng ang xt b vt qu trn mt s cc tng. Chng ta c th bit rng cc mo u trong STM-1 vt qu 105 khi tc bo hiu DS-4E l 139,264 Mbit/s. y l mt iu ci tin to ln so vi mng phn cp s khng ng b hin nay. Cc mo u c s dng y sau khi c phn loi thnh SOH, POH v PTR. Chng c s dng to iu kin d dng cho cng tc qun l iu hnh v sa cha mng thng tin.5. ng b ho bng con tr.Trong qu trnh ghp knh ng b, mng thng tin c ng b ho nh vic thnh thong gi vo cc con tr. C ngha l s x dch tn s gia ng h h thng v cc tn hiu thu c th c x l ph hp vi con tr v chn dng/khng/m. Thng qua vic s dng b nh c ng, phng php ng b ho kiu ny to iu kin kh thi cho ng b ho bng rng nh vic a ra kh nng quan h vi mi trng cn ng b. Phng php ng b ho bng con tr tng ng vi vic nhi byte, nu chng ta nghin cu n trong bi cnh ca ng b ho nhi bit. V l do , phng php ng b ho con tr to ra jitter tn s thp v jitter bin cao. Mt trong nhng vn quan trng l phi gii quyt jitter ny.6. Ghp knh mt bcTrong qu trnh ghp knh ng b, cc ng truyn trn cc tn hiu TUG-2 c nh x trc tip thnh cc tn hiu VC-4, hoc cc tn hiu AU-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 nim ny khng h c ng dng i vi qu trnh ghp knh khng ng b ang c s dng.Ngoi ra, khi p dng trn mt mng thng tin, ni mt s lng ln cc tn hiu c gi i nh tin hnh mt s qu trnh ghp knh, khi nim ny to iu kin d dng v kinh t cho kt ni phn chia v kt ni cho. Ghp knh mt bc tr nn kh thi nh da vo khi nim cngten.7. Khi nim Mng thng tin.Phng php truyn dn ng b c thit lp da trn c s ca khi 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 s khng c hiu qu khi thc hin cc kt ni tch/nhp hoc ni kt cho thng 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 cc h thng thng tin quang c s dng ngy mt nhiu th cc h thng v cc tiu chun da trn khi nim ca mng quang tr nn cn thit v khi nim ghp knh mt bc c p dng. Hn na, v mt cc mo 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 vic khai 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 c s khi nim thng tin ton cu. Vic ng b ho c tin hnh mt s ln qua vic s dng cc con tr l yu t cho php mng truyn dn ng 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 cc mo u t bn ngoi v cu trc ghp knh c s dng u da trn khi nim ny ca mng thng tin th mng thng tin ton cu c th tr thnh hin thc.1.6.6 Cc mch vng t hn gn (SHR)1. Li ch ca vic s dng cc SHRCc mng hin ti vi cng ngh cp si quang ang s dng phng php nh tuyn bo v phn tp t ng v tm hng kp bo v mng trong nhng trng hp t cp hoc h hng cc trung tm chnh. Nhng mng nh vy c th c pht trin thnh cc vng SHR nu nh SHR chng t c l kinh t hn. Mt mng mch vng 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 song cng. Mt SHR l mt mng mch vng cung cp di thng v hoc thit b mng d phng sao cho cc dch v b gin on c th c phc hi mt cch t ng sau s c mng. Cc thit b ghp knh dng trong cc cu trc vng l cc thit b ADM c nhim v xen v r 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 t mng bo v phn tp sang mch vng. Hnh 1.68(a) miu t mt mng cp quang hng tm vi ba CO v trung tm phc v ca chng. Cc ng truyn thng gia mt CO v trung tm ca n c i qua chng cp quang u tin im - ni - im, chng ny c bo v nh chng cp quang phn tp vt l do h thng APS iu khin. Cc b ghp knh u cui c s dng trong mng cp quang hng tm ny c th c pht trin thnh mt h thng ADMS tc cao, trong cc ADM ny bt u c hiu lc v khi nim mch vng chng minh c l c hiu qu kinh t. Khi so snh vi i tc hng tm ca n, mch vng c th s cn n cc ADM tc cao hn, bi v n s dng chung khng ch cc phng tin cp quang m cn thit b ghp knh.

Hnh 1.68 Pht trin ca cu trc mch vngNh c m t trong hnh 1.68, cu trc mch vng c nhng u im sau y so vi cu trc hng tm 1:1/DP: (1) gim bt cc si quang v cc thit b quang/in t v cc b ti to; v (2) kh nng sinh tn y trong khi t cp quang v hng nt mng (tr nt b hng). i vi th d trnh by trong hnh 1.68(a), mng hng tm 1:1/Dp yu cu 12 b OLTM, cn mng mch vng trnh by trong hnh 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 th khng nht thit chng t rng cc chi ph u t l thp hn. Nu ta nghin cu mt trng hp trong c hai mng vng v hng tm u s dng cng mt tc ng dy, v chi ph ca mt OLTM vo 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 vi i tc hng tm ca n. By gi chng ta nghin cu mt trng hp khc, trong mng hng tm 1:1/DP s dng h thng 565 Mbit/s v mng vng s dng h thng 2,40 Gbit/s. Gi thit rng gi thnh tng i ca mt thit b kt cui 565 - Mbit/s l 1 v chi ph ca thit b 2,40 Gbit/s gp ba ln gi thnh ny. Mng vng ang nghin cu y cn n bn b ADM 2,4 cobit/s, iu ny dn n mt gi thnh tng i l 12 (1 x 3 x 4 = 12), trong khi mng hng tm 1:1/DP cn n 12 b OLTM 565 Mbit/s, iu ny dn n mt gi thnh tng i l 9,6 (1 x 0,8 x 12 = 9,6). Do vy, trong th d c trng ny, mng hng tm 1:1/DP dng nh t t hn mng vng. Tuy nhin, c th phi cn n cc b ti to cho cc chng bo v phn tp di hn trong cc mng hng tm cp quang rng hn v c th iu chnh nhng li th ca vic s dng cc OLTM tc thp. Khi s lng cc nt trong mng vng tng ln ti tm hoc ln hn, mng 1:1/DP s bt u t hp dn hn so vi mch vng.Lu rng tho lun y ch ch n gi thnh ca tht b ghp knh, bi v n l yu t ni tri nht ca ton b gi thnh h thng chuyn ti bng cp quang i vi cc mng "intra LATA".Trong nhiu trng hp, mng vng c cc u im v kinh t so vi i tc hng tm ca n, tuy nhin, n c th gp kh khn hn hoc t hn nng cp h thng khi dung lng mch vng cn kit. Mch vng cng c th cn n mt h thng iu khin mng phc tp hn so vi i tc nh tm ca n, bi v rng tt c cc nt s tng tc vi nhau khi cc tnh hung s c xy ra hoc c yu cu ti cu hnh. Tuy nhin, vn cn kit ca dung lng mch vng c th c gim bt hoc c gii quyt nh quy hoch mng cn thn hoc trin khai ADM tc cao hn nhiu (chng hn, tnh kh dng ca cc ADM 9,6 Gbit/s). V li (xem mc 4.5), h thng iu khin dng cho mng vng c th c n gin ho khi thit b SONET c trin khai. Bng 1.17 tng kt ho mt s so snh tng i gia cc cu trc mng vng v nh tm vi mng bo v phn tp (Hub/DP).Bng 1.17. So snh gia nh tuyn bo v phn tp v cu trc SHRCc thuc tnhHub/DPSHR/ADM

Kh nng nng cpD dngKh khn - t

Tng s cp quangNhiu hnt hn

Tng s u cuiNhiu hnt hn

Tc u cuiThp hnCao hn

Kh nng sinh tn ca cp si quang 100% *100%

Kh nng sinh tn ca trung tm **NghoTt 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 SONETSHR l mt mng ng vng cung cp di thng hoc v thit b mng d tha, sao cho cc dch v b gin on c th c khi phc mt cch t ng. Gii php chung bo m mt kh nng t hn gn l cung cp mt vng truyn thng th hai song song vi vng lm vic th nht. Trong trng hp ny, mt s c trn vng c th c b qua nh chuyn cc cuc truyn thng sang vng th hai; ni chung n c coi nh mt chc nng chuyn mch ng dy (hoc chuyn mch bo v). Hn na, nu vng th hai pht theo hng ngc li so vi vng th nht th mt s ngt trong c hai vng gia hai nt k lin nhau c th c cu vn nh cc nt trn mt trong hai pha b ngt bng vic u vng cc cuc lin lc ngc tr li sang vng th hai. N c gi mt cch thng dng l chc nng u vng ngc. Hnh 1.69 miu t cc th d v chuyn mch ng dy v mch vng ngc phc hi. Ch rng mt s kt hp cc chc nng vng ngc v chuyn mch ng dy (trn mt trong hai pha b ngt) c th c s dng phc hi dch v b gin on. Do vy, mt thuc tnh quan trng ca SHR l: nu vng b "gy" ti bt k mt im no , th hng truyn dn i vi cc tn hiu c th c o li nhm trnh vic mt dch v.Cc SHR ca SONET c th c phn chia thnh hai loi ph bin l n hng v song hng theo hng ca lung lu lng di cc iu kin bnh thng. Cu trc ca SHR thuc v mt trong hai loi ph bin ny c th khc nhau v c ch iu khin bo v cn s dng phc hi cc dch v b gin on.SHR n hngTrong SHR n hng (USHR) lu lng lm vic c chuyn quanh mng vng ch theo mt hng (chng hn ngc chiu kim ng h). Hy tham kho hnh 1.70(a). Lu lng t bt k mt nt no c nh tuyn theo cc ng truyn thng lm vic t Nt 1 ti Nt 3 (tc l ng 1-2-3). Lu lng quay v tip tc i theo vng t Nt 3 quay v Nt 1 theo cng mt chiu nh t Nt 1 n Nt 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 khc nhau. Do qu trnh truyn dn ca lu lng lm vic bnh thng trn USHR ny l ch i theo mt chiu cho nn dung lng ca vng c xc nh bi tng nhu cu gia cc nt. Cc USHR i khi c gi l "cc vng quay ngc" l bi v vng truyn thng th hai (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 dng phc hi ng vng.V cc knh phc v c nh tuyn mt cch n hng, cho nn cn phi c mt cp quang vn chuyn chng. USHR ny c th c ci t theo khi nim bo v 1:1 hoc 1 + 1. USHR s dng mt vng ring bit lm vng bo v m n khng vn chuyn nhu cu dch v trong trng thi bnh thng v n trn (u vng) cc knh b gin on sang vng bo v t pha vng lm vic khi thnh phn ca mng b hng. Cu trc 1:1/USHR ny cng c gi l mt SHR n hng trn (USHR/L). Tng phn li, USHR 1 + 1 phn chia cc tn hiu sang c hai vng lm vic v bo v ti nt pha pht ny (c ngha l bc cu u cui), cn nt pha thu s la chn tn hiu tt nht trong hai tn hiu nh nhau da trn tiu chun chuyn mch bo v. Cu hnh USHR 1 + 1 ny i khi c gi l mt ng n hng SHR (USHR/P). Lu rng cc USHR 1:1 c th c cu hnh nh cc USHR 1:N, c ngha l mt vng truyn thng 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 hngSHR song hngNh c trnh by trong hnh 1.70(b), trng hp SHR song hng (BSHR), lu lng lm vic i theo c hai hng trn mt ng duy nht; ng ny s dng hai ng truyn thng song song vi nhau (hng hot ng v hng ngc li) gia cc nt ca vng (chng hn gia Nt 1 v Nt 3). Th d, trong iu kin bnh thng, cc tn hiu t Nt 1 n Nt 3 c nh tuyn qua ng 1-2-3, cn cc tn hiu quay v t Nt 3 ti Nt 1 c nh tuyn qua cng mt ng nh vy (ng 3-2-1). V lu lng c nh tuyn trn mt ng duy nht gia cc nt m dung lng d tha quanh mt vng c th c dng chung trn c s tng tuyn kt 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 nh tuyn song hng ti hai nt, cho nn cn n hai cp quang vn chuyn cc knh nghip v ny.Mt BSHR c th dng hai hoc bn cp quang, tu thuc vo vic b 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 vng th nht, s c cung cp bo v. Cc knh lm vic v bo v s s dng cc vng truyn thng khc nhau. Cc BSHR 1:1 cng c th c cu hnh nh cc BSHR 1:N, tc l mt vng truyn thng bo v 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, trong mc ny s khng tho lun v chng. Trong trng hp ca BSHR hai cp quang, cc knh lm vic v bo v s dng cng mt cp quang vi mt phn di thng c d phng bo v. cung cp mt chc nng t hn gn, thng mt na di thng s c d phng bo v. Vic b tr mng vng nh vy c th bo m chuyn mch bo v ng dy nh s dng phng php TSI ho nhp cc knh lm vic trong cp quang b hng vi cc knh bo v trong cp quang khng b nh hng. Cc USHR v BVSR cn c th c phn loi tip thnh cc SHR chuyn mch bo v ng 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 ng chuyn mch bo v cho php vng c phc hi mt cch t ng khi s c.SHR chuyn mch bo v ng dyMt cu trc SHR chuyn mch bo v ng dy s dng tiu ng dy ca SONET (chng hn cc byte K1 v K2) vn chuyn cc tin bo s c v xc pht ng tc chuyn mch bo v. ng tc chuyn mch bo v ch c thc hin ti lp ng dy 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. Cc cu trc chuyn mch bo v ng dy c xc nh cho c hai loi USHR v BSHR, s dng nguyn tc u vng lu lng sang ng bo v. Khi mt vng b t cn phi c iu khin ti chv iu khin t xa thc hin vic u vng lu lng ti cc nt nm trn hai pha ca ch t. H thng chuyn mch bo v ng dy l mt s la chn t nhin i vi tt c cc BSHR bi v nh tuyn yu 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 bo v ng dy (tc l APS) phc hi cc yu cu nu mt cu kin mng b h hng.SHR chuyn mch bo v ng truynMt cu trc SHR chuyn mch bo v ng truyn s dng tn hiu ca lp ng truyn (chng hn, ng AIS) khi ng chuyn mch bo v. Khc vi h thng chuyn mch bo v ng dy, h thng chuyn mch bo v ng truyn s phc hi mt knh STS hoc VT u cui - ti - u cui. Chuyn mch ng truyn ca mt ng c trng no c lp vi trng thi ca cc ng 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 cc SHR chuyn mch ng truyn. Vi chuyn mch bo v ng truyn, ngi ta xc nh r hai cp ca cc mc mch vng: VT v STS. SHR chuyn mch bo v ng truyn VT c xc nh nh mt vng, trong ng truyn VT c chuyn mch cho cc cuc sp xp li mch vng, v SHR chuyn mch bo v ng STS c xc nh nh mt mch vng trong cc ng truyn STS c chuyn mch ti sp xp mch vng.Cc vng chuyn mch ng truyn STS v VT tng ng c s dng 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 SONET da trn c s nh truyn yu cu v c ch iu khin bo v.

Hnh 1.71.1.7 S tin trin sang BISDNB-ISDN c pht trin iu tit cc th loi khc nhau ca cc tn hiu bng rng, da trn nhng khi nim v tiu chun ISDN v tiu chun 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 lin kt tt c cc tn hiu lin tc theo thi gian thc v cc tn hiu s liu theo nhm c s phn b di tn rng (cn thit cung cp cc dch v bng 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 thoi thy 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 thng ATM (phng thc chuyn giao khng ng b) c xut nh l mt gii php.Cc khi nim v BISDN c pht trin p ng mt cch hiu qu cc nhu cu ang cng ngy cng gia tng v cc th loi dch v bng 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, cn c lin kt vi cc loi dch v phn b, chng hn nh CATV. Ngoi ra, phi c mt chc nng cung cp c cc dch v ch knh, c cc dch v ch gi.Mt khc, li tng c mt i hi v kh nng mng c kh nng cung cp 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 trung bnh/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 khc nhau 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 h thng ATDM (ghp knh khng ng b phn chia theo thi gian) c s dng ghp mt nhm cc t bo ATM; mt h thng truyn thng da trn c s cc t bo ATM v ghp knh ATDM c gi l h thng 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 thng tin ATM ging nh h thng thng tin gi, trong n s dng cc t bo ATM nh mt phng tin truyn dn c bn, trong khi n khc vi chuyn mch gi ch n ng thi c th x l c cc tn hiu thi gian thc v tng ng. Ngoi ra, cc h thng chuyn mch gi ni chung c s dng mt cch cc b trong cc mng LAN, cn i vi h thng ATM th do n c thit k s dng trn cc mng cng cng nh c ln, cho nn n khc phc c nhng kh khn trong vic gn a ch, iu khin kt ni v lu trnh, chuyn mch v truyn dn. Mt khc, so vi h thng thng tin ch knh (phn b knh cho mi dch v ri sau thng qua cc knh ny m chuyn cc tn hiu thng tin i nh mt dy bt lin tc), ATM phn chia cc tn hiu mang thng tin ri sau np chng vo cc t bo ATM chuyn chng i qua cc knh o. Do vy, mt s vn mi lin quan n vic thit 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 nm 1980, t n nay n vn c nghin cu v nng cp. Do vy trong mc sau y s xem xt li cc vn lin quan n chng, da trn cc iu khon thuc v BISDN ca ITU-T.H thng thng tin ATM c pht trin ci t B-ISDN cho nn i khi n c xem l "mng ATM".1.7.1 Cc khi nim c bn ca B-ISDNKhi x hi pht trin, khi cng ngy cng c nhiu cng ty mc ln, th nhu cu v cc dch v a phng tin v cc dch v bng rng khc nhau cng ang gia tng mt cch ng k. By gi cng ngy cng c nhiu ngi s dng cc u cui s liu, cc my tnh c nhn, cc my Fax v cc h thng hi ngh video, v s lng cc cng ty nhn tham gia vo cc dch v CATV cng tng ln.Ngoi ra, nhu cu v cc dch v nh in thoi thy hnh (video), truyn hnh phn gii cao, truyn s liu tc cao, dch v gim st bng video, truy tm bng video, video text bng rng cng ang tip tc gia tng. Nhng dch v k trn bao gm cc dch v giao lu cng nh cc dch v phn phi m mt s trong cc dch v c th cn n cc mng 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 cn phi 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 mng truyn thng chung cho tt c cc dch v lin kt.BISDN - mt mng thng tin s, c kh nng cung cp cc loi hnh dch v bng hp, chng hn nh in thoi, cc u cui s liu, gim st t xa, facximin, teletext, cng nh cc dch v bng rng, chng hn nh in 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-ISDNB-ISDN c nhng mc ch c bn l kt hp tt c cc dch v hin hu vo mt mng truyn thng trong tng lai. Do vy, v c bn n cung cp 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 chnh in 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 liu tc cao, facsimile mu, CATV, phn phi HDTV, m thanh nhy cm cao, th truyn hnh, gim st bng video, truyn chng trnh chiu phim phn gii cao v videotex bng rng.Nhng dch v BISDN ny bao gm tt c cc dch v c nhng c tnh khc nhau. C ngha l, cc dch v tng tc chng hn nh in thoi hoc in thoi thy hnh v cc dch v thng bo chng hn nh bu chnh in t hoc bu chnh bng hnh nh v cc dch v truy tm tra cu bn v v vn bn u c bao gm trong . Cc dch v ny l cc dch v thng tin m tn hiu ca dch v c chuyn giao theo c hai chiu, song bn cnh , chng cn c cc dch v phn phi mt chiu, chng hn nh dch v CATV.Nhng c trng ni bt nht ca cc tn hiu dch v B-ISDN l phm vi phn b di thng ca n rt rng. Trong khi tn hiu cu hnh c bn ca ISDN 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 trn quan im tc truyn dn, cc tn hiu ca dch v chim bng tn rng t vi bit/s ca cc tn hiu gim st t xa ti cc tn hiu video vi vi trm Mbit/s. Ngoi ra, thi gian s dng n trong phm vi t cc s liu 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 nhiu Mbit/s, cn cc tn s m n s dng v phn b thi gian s dng th c phm vi rt rng.c tnh phn b khc ca tn hiu dch v B-ISDN l cc tn hiu lin tc, chng hn nh ting ni v hnh nh, c th cng "sng chung" vi cc tn hiu nhm, chng hn nh s liu u cui. Cc tn hiu ting ni v hnh nh c th tr thnh cc tn hiu tc bt bng nhau nh phng php s ho. Tuy nhin, cc tn hiu s liu khc nhau l cc tn hiu vi tc bt bin i rt rng. Mt khc, cc tn hiu hnh nh v m thanh i hi c x l theo thi gian thc, cn trong trng hp s liu th khng cn nh vy.

Hnh 1.72. Phn b dch v ca B-ISDNDo nhng s khc nhau nh vy, chuyn mch v truyn dn cc tn hiu dch 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 hp hn. 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 nhau cc tn hiu tc thp/cao v cc tn hiu lin tc/ nhm l cc k kh khn1.7.3 Nn tng k thut ca B-ISDNNh cp trc y, v cc dch v do B-ISDN cung cp c nhng c im khc nhau, cho nn mt s cng ngh c bn c i hi hin thc 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 c yu cu l bi v cc tn hiu ca dch v bng rng v tc cao c s dng rng ri. V li, vic ci thin cng ngh v thit b x l video l cn thit bi v cc dch v chnh ca B-ISDN l cc loi dch v video khc nhau. Hn na, cng ngh mng thng tin i vi nhng vn trn y l cn thit, bi v cc dch v tc thp/tc cao c cung cp v cc dch v ch gi ng tn ti.Nhng cng ngh c bn ny c pht trin v c nng cp lin tc nhm p ng mt cch y nhu cu v cc dch v bng rng cng ngy cng tng. Th nht, cng ngh thng tin quang c nng cao; suy hao ca cp si quang c gim xung thp hn 0,5 dB/Km v gi c ca cc phn t bc x/thu nh sng st xung kh nhanh chng; Hn na, cng ngh v mch tch hp v cng ngh ch to cc cu kin cng rt tin tin. Cc phn t Silc lng cc hoc GaAs c 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 mc 150 Mbit/s. Ngoi ra, cng ngh phn mm v m p tin trin mt cch thnh cng to iu kin iu khin tc cao, cng nh hot ng v chuyn mch tc cao tr nn c th c.Vic nn, chuyn i v ti to cc tn hiu dch v khc nhau tr nn d dng do pht trin cng ngh x l tn hiu. V li, vic thu thp, thay i v x l cc tn hiu dch v tr nn d dng hn nh pht trin cng ngh my tnh. Qua vic s dng cng ngh ni trn, cng vi cng ngh 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 b video 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 ca ITU-T trong nhng nm 1980, nh hng n rt nhiu hot ng nghin cu v s lin kt cc loi tn hiu dch v khc nhau cng nh vic s ho mng thng tin v ng gp vo s pht trin cng ngh thng tin. Da vo nhng vn ni trn, h thng thng tin ATM c kh nng cung cp dch v B-ISDN c nhng nt c trng khc nhau. iu ny dn n s pht trin cng ngh lin kt dch v B-ISDN.1.7.4 Nn tng ca tiu chun ho B-ISDNTrong 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 ca khch hng. Trong s , knh H1 c phi ghp vi nhm s cp ca ISDN trong dng knh H11 1,536 Mbit/s v knh H12 1,920 Mbit/s, v v vy hnh thnh c s ca ISDN cng vi giao din c bn 2B + D 144 kbit/s.H2, H3 v H4 c quy nh l cc knh bng rng tng ng vi phn cp s ang tn ti.Bt u t nm 1985 ngi ta ch n cc knh bng rng v kt qu l cc tc bit 30 - 40, 45 60 - 70 Mbit/s c xem l tiu chun cho cc knh H2, H3 v H4. Mt khc, u ban T1 a ra mt d n s dng 149,760 Mbit/s da trn c s SONET.Sau , vo thng By nm 1986, ITU-T bt u tiu chun ho giao din nt mng (NNI) mt cch c lp vi tiu chun ho giao din khch hng - mng (UNI) ca BISDN.Nhim v tiu chun ho NNI, vn c tin hnh di nhiu iu kin kh khn, i n tho thun l s dng tiu chun tn hiu STM-1, c cu trc 9B x 270 v c tc bit 155,520 Mbit/s, ti hi ngh Seoul c t chc vo thng Hai nm 1988. Sau , n tr thnh phn cp s ng b ca cc khuyn ngh G.707 - G.709. Mt khc, nhim v tiu chun ho UNI ca B-ISDN do BBTG (Broad Band Task Group- Nhm c trch bng rng) thc hin ho nhp vi khuyn ngh I.121 vo nm 1988 ti cng hi ngh trn. l nhng vn kin u tin c t khun 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 chia thnh cc dch v giao lu v cc dch v phn b, v rng cu trc chc nng/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 phn nh 32,768 Mbit/s cho H21, 43 - 45 Mbit/s cho H22 v 132 - 138, 240 Mbit/s cho H4. Thm na, n quy nh UNI l lp 150 Mbit/s v lp 600 Mbit/s.Sau t lu, BBTG c ch nh l WP8 nhng cng vic tiu chun ho UNI gp nhng kh khn lin quan n kch thc ca t bo ATM, 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 do ngi M a ra. Song cui cng quyt nh l "5+48" byte s c s dng cho mc ch ny. Do b nh hng mnh ca SDH c tiu chun ho trc , tc bt ca mt giao tip c quyt nh l 155,520 Mbit/s. Ngoi ra, cu trc khung ca lp vt l quyt nh tun theo cu trc khung STM-1 hoc dng t bo ATM thun tu. Hn na, cng c php b tr cc tn hiu khc ca G.702. WP8 xc nh r nhng chi tit ca nhng iu khon cn c bn ci nh cc khuyn ngh thuc Seri I ti Hi ngh Masyama, t chc Nht Bn vo thng 11 nm 1990. Nh vy, khun kh tng th v BISDN c hon chnh. Mt khc, khi ITU c t chc li vo nm 1993, nhm nghin cu 13 (SG.13) ca ITU-T bt u m trch cc hot ng nghin cu v tiu chun ho BISDN.1.7.5 Nguyn tc c bn ca BISDNNh trnh by trc y, BISDN l mt khi nim c a ra tho mn nhu cu v cc dch v bng rng ang cng ngy cng gia tng. Cc mc ch c bn ca BISDN l thit lp mt mng s c kh nng lin kt v cung cp cc hnh loi dch v bng rng khc nhau thng qua vic s 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 v ch nhm cng c cung cp. Thm vo , cc dch v bng hp v cc dch v bng rng c cung cp mt cch ng thi. t c cc mc ch ni trn, BISDN phi c kh nng h tr cc ni kt truyn thng 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, BISDN cn 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 s pht trin cng ngh hoc s pht trin phng php hin thc ho trong tng lai. Ngoi ra, n phi c kh nng p ng cc nhu cu ca khch hng 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 v giao thc cng cn phi c thit lp mt cch ph hp.BISDN dng ATM thc hnh cc chc nng ca mnh. ATM l mt h thng truyn thng phn chia u cc hnh loi dch v khc nhau, sp xp 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 v cc knh o chuyn giao t bo ATM.Do , thng qua vic s dng ATM, c th thc hin c kt ni mng c 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 loi phng tin vt l v cc mng chuyn ti khc nhau, bi v n c xc nh mt cch c lp vi cc phng tin chuyn ti ca cc lp vt l1.7.6. So snh B-ISDN v ISDNB-ISDN l mt khi nim xut pht t tiu chun ISDN. Do vy, cc quan im v B-ISDN cng ging nh ca ISDN. Tuy nhin, vic thit lp B-ISDN c thc hin khc vi thit lp ISDN.Th nht, BISDN l mt mng s lin kt a dch v nh trong trng hp ISDN, nhng n khc vi ISDN ch n bo m vic lin kt c cc tn hiu bng rng na. V l do , m hnh cu trc c bn ca BISDN cng ging nh ca ISDN, ngoi tr kh nng x l cc tn hiu bng rng, ng thi vi cc chc nng ca ISDN bng hp. V mt thit lp cu trc chc nng hay cu hnh tiu chun, BISDN cng ging nh ca 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 tng thch nhau v mt hot ng thc t. C ngha l BISDN khng th c thc hin ch bng vic b sung cc thit b ca dch v bng rng vo mng ISDN hoc TE ca ISDN khng th c u ni ti NT ca BISDN. Do , cc nhm chc nng ca ISDN v cc im chun cng ging nh cc phn t lin quan ca BISDN ch v mt khi nim. Tuy nhin n c th phi ghp vi TE1 ca ISDN hoc vi TA qua vic s dng TE2 ca BISDN. Trong hot ng thc t BISDN khc rt xa vi ISDN; h thng thng tin ISDN c cc c trng kt hp cc h thng thng tin chuyn mch knh s ang hot ng vi h thng chuyn mch gi, trong khi BISDN dng h thng ATM hon ton khc vi cc h thng ni trn ca ISDN.C ngha l, trong khi ISDN ch yu iu tit h thng thng tin knh (h thng 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). Do nhng 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 vi ISDN. Do vy, BISDN cn c coi l khc hn so vi ISDN1.7.7 H thng thng tin ATMATM l mt h thng truyn thng thc hin BISDN. ATM l mt h thng chuyn giao kiu gi c hnh thc c bit, s dng ATDM. Trong BISDN, thng tin c chuyn i nh mt lung lin tc ci gi c mt kch thc khng i. Cc gi c kch thc c nh ny c gi l cc t 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 , tn hiu truyn dn ca BISDN c to nn nh ATDM vi cc t bo ATM. ng thi ATDM l mt phng php ghp knh thng k, thc hin vic phn chia theo thi gian ghp cc t bo ATM ca mt s knh i ti mt cch khng ng b.Nu s dng ATM, dung lng ca knh nghip v cng c tnh theo s lng cc t bo ATM. Cho nn s vt qu dung lng truyn dn ca thng tin c biu th bi s lng cc t bo ATM. Vic phn phi dung lng truyn dn c xc nh theo dung lng yu cu v kh nng phn phi c th c thng qua thng lng vi mng thng tin trong qu trnh thit lp cuc gi.ATM - mt h thng kiu lin kt - s thit lp cc knh o chuyn giao thng tin dch v. Mi khi mt knh o c thit lp, s hiu nhn dng ni kt c gn v khi ni kt c gii to, s hiu nhn dng ny cng c hu b. Trnh t sp xp gia cc t bo ATM trong mt knh o no do cc chc nng ca lp ATM d kin trc. Thng tin bo hiu 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 giao thc c s dng l lp ATM, lp ng dng ATM (AAL) v lp mc cao. Lp AAL nh x cc tn hiu dch v sang khu vc trng tin ca cc t bo ATM, cn lp ATM thc hin chc nng to u ca t bo ATM chuyn giao trng tin mt cch trong sut. Lp vt l thc hin chc nng chuyn i cc t bo ATM thnh hng bt v sau , chuyn chng i.Kch thc ca t bo ATM l 53 byte. N c phn chia thnh mo u 5 byte v ng bao trng tin 48 byte (hnh 1.73(a). Chc nng ch yu 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 tin ATDM. l chc nng do VPI (phn t nhn dng ng o) v VCI (phn t nhn 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 ATMng thi, ng o c ngha l mt b cc knh o cng s dng chung cc ng no v mo u t bo cng c phn loi thnh loi trng tin (PT) v ch th thm quyn mt t bo v cung cp kh nng iu khin sa sai ca mo u. N cn cung cp thm chc nng iu khin lung chung cho mo u t bo trong giao din UNI.1.7.8. Cu trc chc nng ca BISDNM hnh cu trc chc nng chung ca ISDN bng rng v c bn ging nh ISDN bng hp. C ngha l v mt cu hnh tiu chun, nhm chc nng v im gc, c hai cu trc l nh nhau. N ch ra rng B-ISDN c hnh thnh trn c s khi nim ca ISDN. M hnh cu trc c bn ca B-ISDN nh c trnh by trong hnh 1.74. Cu trc ca ISDN bng rng 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) v kh nng mc thp bao gm kh nng ISDN bng hp da trn kh nng bng rng, 64 bit/s, v kh nng bo hiu lin tng i.

Hnh 1.74. M hnh cu trc c bn ca B-ISDNCu hnh tiu chun ca B-ISDN c trnh by trong hnh 1.75

Hnh 1.75. Cu hnh tiu chun ca B-ISDNim 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) c cha B-TE1, B-TE2 v B-TA. Cng nh vy, B-NT2 v B-NT1 tng ng nm trong mng B-IDN dnh ring v B-ISDN cng cng. ch th im gc v nhm chc nng ca mnh, B c ngha l B-ISDN.1.7.9. M hnh chun ca giao thcM hnh chun giao thc (PRM) ca B-ISDN c hnh thnh t mt bng qun l, mt bng iu khin, v mt bng khch hng nh c trnh by trong hnh 1.76. Chc nng ca mt bng qun l c phn chia thnh : qun l mt bng v qun l lp.

Hnh 1.76. Cu hnh chun ca B-ISDNQun l mt bng trong mt bng qun l ca PRM ca B-ISDN c ngha l qun l tng th ton h thng. Cng nh vy, qun l lp hm l qun l ngun tim nng v khch hng lun bin i, v qun l thng tin OAM. Ngoi ra, trn mt bng iu khin, thng tin iu khin cuc gi 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 iu khin v mt bng khch hng c phn loi thnh lp mc cao, lp ng dng ATM (AAL), cng lp ATM v lp vt l. Chc nng ca mi lp nh trong bng 1.18.Lp Lp conChc nng

Lp mc caoChc nng hi t

Lp ng dngHi tChc nng hi t

Phn on v lp rp liChc nng phn on v chc nng lp rp li

Lp ATM AALChc 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 lHi t truyn dnChc 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 vt lChc 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-ISDNLp AAL c hnh thnh t lp con hi t (CS), lp con phn on v lp rp li (SAR). CS bin i thng tin dch v khch hng ca lp mc cao thnh khi s liu giao thc (PDU) v SAR to nn phn thng tin khch hng ca t bo ATM bng vic ngn chn PDU.Lp ATM iu khin kt ni v dng thng tin trong UNI bng vic s dng 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 l to 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 vt l. 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 gii t bo. Ngoi ra, trong trng hp pht theo phn cp s ng b n thc hin chc nng to ra v khng nh khung truyn dn. Lp con mi trng vt l c ngha l bc truyn dn cui cng qua cp si quang hoc cp ng trc1.7.10. Giao din khch hng - mng ca B-ISDNCu hnh ca giao din khch hng - mng (UNI) ca B-ISDN c trnh by trong hnh 1.77, trong trng hp ch th n bng vic s dng cc im 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 nh vy, cc trng hp (g), (h) ch cho thy rng B-NT c th dung cp cc im gc S v Sb mt cch ng thi.Cu hnh vt lca UNI kt ni im c trnh by trong hnh 1.78. 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 vng ca loi phn b. MA trong hnh ny l b phi hp phng tin, cn W ch ra im kt ni gia cc MA vi nhau. Ngoi ra, TE* ch th TE to ra cu trc kiu bus v SSB ch th im kt ni gia cc TE* ny. MA l thit b v B l im gc u thuc loi phi tiu chun. B-NT1 thc hin chc nng ca lp 1, chng hn nh im cui ng dy truyn dn, x l phi ghp truyn dn, vn hnh v bo dng. B-NT2 thc hin chc nng ca lp 1 v lp c mc cao v n c th c cu hnh theo phng php tp trung hoc phng php phn b. Cc chc nng lin quan n B-NT2 l b phi hp phng tin (MA), tm kim bin gii t bo, tp trung ho, nh m. ghp knh, tch knh, gn ngun, x l phi ghp chc nng AAL v bo hiu, x l giao thc bo hiu v chuyn mch 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, x l giao thc bo hiu, x l ni kt trn cc thit b khc, trn lp 1 v lp 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-ISDNNu cn nhc rng BISDN l mng chuyn ti ca ATM, th c th a ra khi nim phn lp ca mng. C ngha l, mng chuyn ti c phn lp thnh mng lp ATM v mng lp vt l. Mng lp ATM li c chia nh thnh lp con ca knh o v lp con ca ng o.im cui ca lp con tng ngim ni kt ca lp con tng ng

Hnh 1.79. Mi quan h gia cc mng phn lp ca B-ISDNCng nh vy, mng ca lp vt l c chia nh thnh lp con ca ng 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 hp mng da trn t bo hoc mng da trn SDH. Mi quan h gia cc lp mng ca B-ISDN c trnh by trn hnh 1.79. Trong lp con ca knh o 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 im chun Tb hoc Sb v cc t bo lin quan n cng mt kt ni VCC s c chuyn giao qua cng mt knh.Trong lp con ca ng o c cung cp ni kt ng o (VPC - Virtual Path Connection) chuyn giao thng tin gia khch hng - khch hng, gia khch hng - mng v gia mng - mng. Do vy, VPC c cu hnh nh kt ni lin tc ca cc knh kt ni VP, cn VPC, gia khch hng - khch hng c thit lp gia cc im chun Tb hoc Sb. Ngoi ra, cc t bo lin quan n cng mt VPC s c chuyn giao trn cng mt ng.Mng ca lp vt l l mt mng truyn dn ng b, c kt hp vi mng ca lp phng tin truyn dn: c ngha l lp con ca ng truyn dn chnh l ng VC-4 trong trng hp phn lp da trn SDH; lp con ca on digital v lp con ca on ti to tng ng l on ghp knh v on ti to.Nguyn l c bn ca k thut ghp bc sng quang WDM?

Hi: ngh cho bit nguyn l c bn ca k thut ghp bc sng quang WDM?p: WDM l phng thc ghp knh quang theo bc sng (Wavelength Division Multiplexing). Thng thng trong tuyn thng tin quang im ni im, mi mt si dn quang cho mt tia laser vi mt bc sng nh sng truyn qua, ti u thu, b tch sng quang tng ng s nhn tn hiu t si ny. Mi mt sng laser ny mang mt s tn hiu in vi mt ph nht nh. T nhng nm 1980, cng ngh si quang c nhiu tin b nn phng thc ghp knh quang theo bc sng c ng dng trong mng vin thng ng trc v quc t. y, WDM cho php ta tng dung lng knh m khng cn tng tc bit ca ng truyn v cng khng dng thm si dn quang.

Hnh 1 minh ho cu hnh ca h thng WDM. Trong cc lung tn hiu quang t cc ngun c cc bc sng khc nhau l1, l2,..., ln c ghp li nh b ghp knh MUX. B ghp MUX phi m bo t suy hao v khng cho s xuyn nhiu gia cc lung. Cc lung tn hiu sau khi ghp c truyn trn mt si quang ti pha thu. Trn mt tuyn ng c c ly di th chm sng quang c khuch i nh cc b khuch i.

Hnh 1B chia lung DEM, ti u thu s tch cc lung sng quang l1, l2,..., ln ti cc b thu Rx tng ng ca tng lung. Tip theo cc b tch sng quang trong thit b thu Rx, khi phc li cc tn hiu in ca tng lung tng ng vi pha pht.

Nh ta bit, ghp knh l bin php ghp mt s knh tn hiu in thnh mt lung chung c dung lng thng tin ln hn. Trong nhng nm 1960, ni ti cc h thng thng tin nhiu knh ta quen ni ti cc tn hiu in v c 2 cch ghp l ghp theo tn s FDM (trong h thng truyn dn analog, ta thng quen gi l k thut ti ba) v ghp theo thi gian TDM.

Ti y chng ta hy xem xt gia WDM v FDM c g ging nhau v khc nhau. Ta bit rng bc sng dao ng l ca nh sng l s nghch o ca tn s f nn WDM c phn tng t nh FDM tc l ph tn hiu phn b theo trc tn s. im khc nhau l cc ngun pht quang lm vic bc sng nm (nanomet) tng ng vi tn s rt cao (hn 200.000GHz). Cc sng quang ny b iu ch trc tip bi tn hiu thng tin in. Tn hiu in ny c di ph nht nh, nhng so vi di ph ca ngun pht quang th ch s dng phn rt nh bng tn truyn dn ca si quang. S b ta c th biu din cc lung tn hiu quang nh hnh 1b.

H thng truyn dn WDM theo hai hng c th nh hnh 2, khng quy nh pht mt u v thu mt u. Nh vy, ta c th pht thng tin ti bc sng l1 theo mt lung ng thi cng truyn thng tin theo hng ngc li ti bc sng l2.

Hnh 2Cng vi s pht trin nhanh chng ca h thng thng tin quang, k thut ghp knh quang li xut hin k thut ghp knh quang theo thi gian OTDM (Optical Time Division Multiplexing) c rt nhiu trin vng. Mt k thut ghp knh khc cng c ng dng trong mng thng tin quang l ghp knh quang theo tn s OFDM (Optical Frequency Division Multiplexing). K thut OFDM cho php cc lung c tn s mang khc nhau c ng thi truyn qua v chim mt di ph nht nh trong lung sng nh sng. Cng ngh OFDM ang c trin khai thc nghim, s knh c th ghp trong mt lung quang c th ti hng trm. OFDM c coi nh l bin php ghp quang c mt dy c. Mi mt knh thng tin c tc ln hn 1Gbyte nh ghp knh quang theo tn s OFDM ta c th thit lp c tc truyn dn cao hn 1Tbit/s (1Tera=103Giga). Ghp theo WDM nh hng su sc n cu trc ca h thng thng tin quang. N cho php khai thc mt cch n gin v kinh t lng thng tin vo mt si quang n mode trn c ly di v tng mm do ca cu trc phn phi. Nhng ng truyn dn th nghim t c tc lu lng 160Gbit/s phn phi trn 8 knh ghp theo bc sng.

Hn na, ghp theo WDM khng ch gim bt nh hng ca tn sc m cn chng c tn hao do phn cc. Cc h thng thng tin quang hin i c s dng b khuch i quang ghp nhiu knh theo WDM. Nu vi lu lng l 2,5Gbit/s, ghp theo WDM t 8 n 16 lung th ta thc hin c mt ng thng tin quang vi lu lng l 20Gbit/s n 40Gbit/s trn mt si n mode m vn dng li c cc thit b ghp knh v phn knh hin c. Ni mt cch khc, WDM cho php tng tch s lu lng nhn vi c ly trn mt si quang