He Thong Thong Tin Quang Vo Tuyen 360

5/21/2018 He Thong Thong Tin Quang Vo Tuyen 360

1/78

HTHNGTHNG TIN QUANG V TUYN 1

I. HTHNG THNG TIN QUANG

1.1 THNG TIN QUANG

Khc vi thng tin hu tuyn v v tuyn - cc loi thng tin sdng ccmi trng truyn dn tng ng l dy dn v khng gian - thng tinquang l mt hthng 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 trli thnh thng tin

ban u. Hnh 1.1. Gii thiu mt h thng truyn dn si quang digital

c sdng rng ri nht hin nay. Trong phn ny chng ta sxem xtcc giai on pht trin ca hthng ny v so snh cc c tnh ca nvi cc c tnh ca nhng hthng ang tn ti. Cui cng, chng ta sgii thch cc tnh cht ca nh sng.

Hnh 1.1. Hthng truyn dn si quang digital

1.1.1. SPHT TRIN CA THNG TIN QUANG

Cc phng tin skhai ca thng tin quang l khnng nhn bit cacon ngi vchuyn ng, hnh dng v mu sc ca svt thng quai 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 bny sdng kh quyn nhl mt mi trng truyn dn v do chu nh hng ca cc iu kin v thi tit. gii quyt hn ch


2/78


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 - nghra mt thit bquang thoi c khnng bin i dao ng ca myht thnh nh sng. Tuy nhin, spht trin tip theo ca hthng ny

bbbdo sxut hin hthng 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 Khnng sdng ng truyndn cp quang (ST, tn tht1000dB/km)

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

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

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

1976 My laser GalnAsP dao ng lin

tc (MIT, KDD, TIT, NTT)

xut khnng sn xut si

quang florua (France, Lucas).1977 My laser GaAIAs c tui thc

lng l 100 nm (BL, NTT)

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

Chto si quang c Abastoes ctn tht ti thiu (NTT, 0.18dB/km (1.55um))

1980 Cu trc laser ging lng tcchto (Bell Lab).

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

1981 GalnAsP LD (1.6 um) Continuous

Oscillation (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,


3/78


LD

Commercialization (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 nghca Kao vHockham nm 1966 vvic chto 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 cvbi thnh cng ny, cc nhkhoa hc v kstrn khp thgii bt u tin hnh cc hot ngnghin cu v pht trin v kt qul cc cng nghmi vgim suy haotruyn dn, vtng gii thng vcc Laser bn dn ... c pht trinthnh cng trong nhng nm 70. Nhc chra trong ,

tn tht ca si quang c gim n 0,18 dB/km. Hn na, trongnhng nm 70 Laser bn dn c khnng thc hin dao ng lin tc nhit khai thc c chto. Tui thca n c c lng hn100 nm. Da trn cc cng nghsi quang v Laser bn dn giy c thgi mt khi lng ln cc tn hiu m thanh / dliu n cc aim cch xa hng 100 km bng mt si quang c dy nhmt 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 tin

quang, c khnng pht hin, xl, trao i v truyn dn thng tin bngphng tin nh sng. Photon hc c khnng sc ng dng rng ritrong lnh vin tv vin thng trong thk21.

1.1.2. Cc c tnh ca thng tin quang

Trong thng tin si quang, cc u im sau ca si quang c sdngmt cch hiu qu: suy hao truyn dn thp v bng thng ln. Thmvo , chng c th sdng thit lp cc ng truyn dn nhvmng (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 tsiquang l phng tin truyn dn thng tin hiu quv kinh tnht angc hin nay

Trc ht, v c bng thng ln nn n c th truyn mt khi lngthng tin ln nhcc tn hiu m thanh, dliu, v cc tn hiu hn hpthng qua mt hthng c cly n 100 GHz-km. Tng ng, bng cchsdng si quang, mt khi lng ln cc tn hiu m thanh v hnh nh


4/78


c thc truyn n nhng a im cch xa hng 100 km m khngcn n cc bti to.

Thhai, si quang nhnhv khng c xuyn m. Do vy, chng c thc lp t ddng cc thnh ph, tu thu, my bay v cc to nhcao tng khng cn phi lp thm cc ng ng v cng cp.

Thba, v si quang c chto tcc cht in mi ph dn nn chngkhng chu nh hng bi can nhiu ca sng in tv ca xung int. V vy, chng c th sdng truyn dn m khng c ting n.iu c ngha l n c thlp t cng vi cp in lc v c thsdng trong mi trng phn ng ht nhn.

Tht, do nguyn liu chyu sn xut si quang l ct v cht do -l nhng thrhn ng nhiu - nn n kinh thn cp ng trc nhiu.Gi thnh ca si quang sgim nhanh mt khi cng nghmi c ara. Ngoi ra, nh cp trn, do c trng l c tn tht thp githnh lp t ban u cng nhgi thnh bo dng v sa cha thp biv chng cn t cc bti to hn.

Ngoi nhng u im nu trn, si quang c an ton, bo mt cao,tui thdi v c kh nng khng mi trng ln. N cng d bodng, sa cha v c tin cy cao. Hn na, n khng br rtn hiuv dko di khi cn v c thch to vi gi thnh thp. Trong bng1.2, chng ta tng hp cc u im trn. Nh nhng u im ny, siquang c sdng cho cc mng li in thoi, s liu/ my tnh, v

pht thanh truyn hnh (dch v bng rng) v s c s dng choISDN, in lc, cc ng dng y tv qun s, cng nhcc thit bo.

Bng 1.2 Cc u nhc im ca si quang

c tnh u im Nhc im

tn tht thp Cly ti to xa chiph thit bngdy dn

Di thng ln Truyn dn dung lng

ln

Gim kch thc ng

truyn dn

Dlp t v bo dng

Gim chi ph lp tcng

Kh u ni

Phi dn Ngn nga xuyn m

Thng tin an ton

Cn c cc ng dy

Cp ngun cho tippht

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


5/78


Chi ph sn xut r chnh li mi (cp)

nh gi Dng truyn dn tuytvi

C thgii quyt bngcc tin bcng nghmi

1.2 CP SI QUANG

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

Vbc pha ngoi o bo vsi quang khi bm v n mn, ng thichng xuyn m vi cc si i bn cnh v lm cho si quang dxl.

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 chsbc v chs lp tu theo hnh dng v chit sutca cc phn ca li si quang. Cc vn ny sc trnh by tmmc 1.2.2

1.3. HTHNG 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 sdng rng ri trn ton thgii. Cng ng nhvy i vihthng thng tin quang n mode. Da trn kthut c pht trin,ngy cng nhiu cp quang c sdng trong nhiu lnh vc. Trong

phn ny, cc c tnh chung ca cp quang c gii thch v tip ,


6/78


chng ti sgii thiu vict hit kmt hthng sv tng tcng nhcng nghghp knh phn chia bc sng.

1.3.1. Tng quan vhthng thng tin quang

1. Cu hnh ca hthng 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 sdngmt 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 chbn ncc phng php truyn dn hin ang sn c da trn vic sdng cpquang. Siu chsng mang quang ca hthng truyn dn quang hinnay c thc hin vi siu chtheo mt v cc nguyn nhn sau:

(1) Sng mang quang, nhn c tcc phn tpht quang hin c,

khng dn nh pht thng tin sau khi c sthay i vpha 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 thcoi nh sng i loi nhting n thay v sng mang. Do ,chc nng lng l cng nh sng tc thi c sdng.

(2) Hin nay, cc Laser bn dn c ch to c tnh nht quntuyt vi v do c khnng cung cp sng mang quang n nh.Tuy nhin, cng nghto phch - Mt cng nghbin i tn scnthit iu chpha - cn cha c pht trin y .

(3) Nu mt sng mang n tn c tn scao c pht i theo cpquang a mode - iu m c thxl mt cch ddng - th cc ctnh truyn dn thay i tng i phc tp v cp quang bdao ngdo sgiao thoa gy ra bi sbin i mode hoc do phn x trongkhi truyn dn v kt qul rt kh sn xut mt hthng truyn dnn nh. V vy, trong nhiu ng dng, vic s dng phng phpiu chmt c khnng sc tip tc.

i vi trng hp u chquang theo mt (IM) c rt nhiu phng

php bin i tn hiu quang thng qua vic iu chv ghp knh cctn hiu cn pht. Mt trong nhng v din hnh c trnh by tronghnh 1.19


7/78


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 nhsliu, m thanh iu chxungm PCM (64kb/s) v sliu video digital. Tuy nhin, trong truyn dn cly ngn, ca cc tn hiu video bng rng ri cng c thsdng phng

php truyn dn analog. Phng php iu chmt sDIM - phngphp truyn cc knh tn hiu video bng IM - v phng php thc hiniu ch tn s (FM) v iu ch tn sxung (PFM) sm tng c lytruyn dn c thc sdng cho mc tiu ny.

Ngoi TDM v FDM, phng php phn chia theo bc sng (WDM) -phng php iu chmt ssng mang quang c cc bc sng khcnhau thnh cc tn hiu in khc nhau v sau c thtruyn chng quamt si cp quang - cng ang c sdng. Hn na, khi truyn nhiuknh thng qua cp quang, mt slng ln cc dliu c thc gi

i nhgia tng s li cp sau khi ghp cc knh trn. Phng phpny c gi l ghp knh SDM. Hthng truyn dn quang c thcthit lp bng cch sdng hn hp TDM/FDM, WDM v SDM. Chngta c ththy rng hthng truyn dn quang cng tng tnhphng

php truyn dn cp i v cp ng trc truyn thng, chc 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 hthng truyn dn cp quang.


8/78


Hnh 1.20. Cu hnh ca hthng 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 cu

bng cch bin i cc tn hiu in thnh cc tn hiu quang v ngc

li. Khi sdng phng php iu chPCM th mi chc nng gii iuchtng 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 tcn c thmmt mch n nh u ra ca cc tn hiu quang cn pht, mt mch AGCduy tr tnh ng nht ca u ra tn hiu in pha thu v mt mchgim st mi pha.

2. Nhng thnh phn cbn ca hthng truyn dn quang.

Hthng truyn dn quang bao gm cc phn tpht xnh sng (ngunsng), cc si quang (mi trng truyn dn) v cc phn tthu nhnnh sng truyn qua si quang.

Cc phn tsau y c chn sdng:

1. Phn tpht xnh snga. it Laser (LD)

b. it pht quang (LED)c. Laser bn dn

2. Si quanga. Si quang a mode chsbcb. Si quang a mode chslpc. Si quang n mode

3. Phn tthu nh snga. it quang kiu thc (APD)

b. it quang PIN (PIN - PD)


9/78


1.4. PHNG PHP TRUYN DN NG BE

1.4.1. Csca tiu chun ho

Trc khi phng php truyn dn ng bc 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 bell

Communications Research ca AT & T Hp chng quc Hoa Knghin cu v pht trin. Cn SONET l tiu chun kt ni ca hthngthng 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, sdng sghp tng u tin, chp nhn sdng khi nimcontainer (cng ten), sdng 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 c

s cp 50 Mbit/s, SONET b sung quan nim v cu trc phn cp vphng php ng bnhcon trhthng 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, kcphn cp skiu Chu u, v c phcpho mra khnng thng tin ton cu.

1. Metrobus

Metrobus 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 trinkhai theo quy m y vo u nm 1984, c cng bvo thng chnnm 1985 v c th nghim thng mi ho vo u nm 1987.Chnh sch cbn 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 hthng thng tin quang, phng hng tin trin camng thng tin, qu trnh pht trin ca cng nghct 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 skhi nim. in hnh l

khi nim v mng thng tin quang im - a im, khi nim v hthng ng bni 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 hthng im - ni im, cho nn khi nim cathng tin quang c xem nhmt khi nim c tnh cht cch mng.


10/78


Nhng khi nim khc ng vai tr khng ththiu c thhinkhi 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, v

bng vic sdng n cng nhbng vic hnh thnh knh truyn thngmo u, cho php ng dng lin kt ca ton b cc tuyn thng tinquang. Tuy nhin, do t lca mo u vt qu 4,5% ca ton b,

cho nn khi nim ny kh c thc chp nhn trong bi cnh .Vic la chn 150 Mbit/s (cthl 146,432, Mbit/s) lm tn hiu ni bca mng thc s l mt quan im tin phong. Sdnhvy l vnhng iu sau y c dkin : khi c xem xt theo kha cnh phnlp tn hiu digital, tc bt m tt ccc tn hiu c thbao gm l 150Mbit/s; theo kha cnh dch v, tn hiu thoi, sliu v video (kctnhiu HDTV c nn) hin ti u c thc sdng trong cp 150Mbit/sny; vkha cnh cng nghbn dn cbn, cng nghCMOS c thc sdng trong phm vi 150 Mbit/s chng kh khn g. Ngoi ra, v

kha cnh thu bao th cn c mt sli th: vi cp phn t150 Mbit/s,cc nh sng c thc sdng nhskt hp vi it LED v PIN rtin, v cp si quang c th to iu kin cho skt hp hiu qunynh 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 thc trong hthng ghp knh khng ng btrc 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 nhmt phng tin thc hin ghp knh tng thnht,khi nim ny gip cho vic ghp knh tn hiu phn cp bng vic iukhin shiu 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 vthi gian. Nhvy, kt ni tch nhpv kt ni cho rt tin li, bi v tt ccc tn hiu u c xl vin vca shiu .

Tn hiu tiu chun ni bbao gm 13Wx88 (1W=16 bt) nhtrong hnh1.37. Tc bit l 146,432 Mbit/s (13x88x16x8 kbit/s). 88 n vca tm (thuc v88 ) xut hin trong 125m s/13, trong d 4 n vc sdng cho mo u v mi tn hiu DS-n chim shiu tng ng ca .


11/78


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 chcgii 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 bcht no. Trong trng hp ny tn hiu nh thi s

sdng tn schun ng bho cbn BSRF v cng c thsdngtn hiu nh thi c n nhn tbdao ng ni v t tn hiu thuc.

nhn r ca tn hiu DS-O c to ra vi n v125 m s. Khi vicchuyn tmi tn hiu phn cp sang cng tencng c thc hin vin v125 m s, th cc tn hiu DS-O nhn c qua ly mu 8 kbit/s cthxut hin mt cch trong sut ngay ti tn hiu phn cp mc cao.

Theo cch nhvy, vic phn tch knh DS-O 64 kbit/s khi tn hiu tiu

chun ni b150 Mbit/s c thc thc hin mt cch ddng.Hnh 1.38 biu din cu trc ca hthng Metrobus. Phn c trnh bynhbus ni b trong hnh v tng ng vi tn hiu tiu chun ni b146,432 Mbit/s. Tn hiu c to ra tDS-1 n DS-3 qua PMB (bngghp knh c thlp trnh). Thng tin quang 146 Mbit/s c thphi hptrc tip vi tn hiu ny, v i qua thit btruyn dn sng quang LTE-Lightwave Transmission Equipment). c thto nn thng tin quang 876Mbit/s hoc 1,7 Gbit/s bng vic a 6 hoc 12 n vca tn hiu nyvo WIM (ghp knh xen tm - Word Interleaved Multiplexing), ri sau

a qua LTE. Nhng qu trnh ny c m ttrong hnh v. Ngoira, hthng PCCS (hthng kt ni cho c thlp trnh) thc hin chcnng ni kt cho qua cc cng tendo tiu chun ca tc bit DS-1to ra bng cch a vo tn hiu 146 Mbit/s.


12/78


Hnh 1.38. Cu trc ca hthng Metrobus

2. SONET

Sonet l mt tvit tt ca Synchronous Optical Network (mng quangng b). N c R.J.Boehm v Y.J.Ching vin nghin cu truynthng Bell trnh ln uban T1- tchc tiu chun truyn thng ca

Bc 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 nhtrong 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 nhtn hiu phn cp cbn v c n nha vo qu trnh ghp knh xen byte qua STS-1.

Tng u tin ca SONET c nghcho mc ch "gp ggiachng" v quan im nghi ngv tnh kh thi ca n chim u th.Kt qu l vic tiu chun ho n hu nhkhng 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 vh thng phncp v kthut ng bho bng con tr c cc thnh vin ca u

ban 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-O

ca M n vv 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 nghrng tn hiu tiu chun ni bca Metrobus (c cu trc26x88W v 146,432 Mbit/s) cn c chp nhn l tn hiu tiu chun.Tn hiu ny c biu thbng cng thc ca Vin Nghin cu truynthng Bell sl: 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 nhc xc nh trc,


13/78


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

Hnh 1.39. Cu trc khung ca SONET

Mc d uban T1 xem xt knhng cuc tho lun lin quan n haidn ny, n vn khng thphn 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 scnh tranh v phn chia thtrng vin thng v vai tr

gia cc cng ty, u nm 1986, uban T1 i ti mt quyt nh l tnhiu tiu chun STS -1 sl 49,92 Mbit/s. Trong khi ITU - T cng anghot ng nhm tiu chun ho bng knh rng vo cng thi gian thuban T1 quyt nh nghly 149,976 Mbit/s lm dn ca Bc M,n gp ba ln 49,92 Mbit/s; c ngha l uban T1, ngi quyt nhchn cp 50 Mbit/s, tha nhn vmt kthut tnh thch hp ca 150Mbit/s. Sau , nhng hot ng tiu chun ho SONRT c tin hnhmt cch sun s, chyu nhuban ngang cp T1X1, v i n mt


14/78


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 chtrong 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 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 baln cu trc khung v tc bt ca SONET chnh l phn cp ng bsm n c quy nh nhkhuyn nghG.707-G.709 ca ITU-T.

3. Phn cp sng b

ITU-T thit lp cc knh H1, H2, H3, H4 nhi 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 cstn 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 chc nhng nt i cng mang tnh cht khi nimtng ng vi phn cp shin 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 uban T1.

Trong khi , ITU-T bt u hot ng tiu chun ho phn cp ng

bscho 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 sng bvITU-T cng uban T1 duy tr mi quan hhp tc cht chcho mcch , Hoa k chnh thc a ra cp 50 Mbit/s da trn tn hiuSTS-1 ang c sdng ca SONET ti hi nghBrazin vo thngHai nm 1987 cn CEPT tm cch chng minh scn thit ca cp tc 150Mbit/s v n c ththch hp vi chai hphn cp skiu Bc Mv kiu Chu u.

Kt qul, n ca M c thay i thnh 149,976 Mbit/s ca cutrc 13Bx180, da trn tn hiu STS-3, ti Hi nghHamburg 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 vhaicu trc ny v im tranh ci si ni nht l schung ho gia tn hiuDS-2 ca 8,448 Mbit/s v DS-3E ca 34,368 Mbit/s thothun cui cngqua hi nghSeoul vo thng Hai nm 1988 l cu trc 9Bx270. Tiuchun NNI c thothun l tiu chun trong cc khuyn nghG-707 -G.709 ca ITU-T v phn cp sng b, tp trung trn tn hiu STM-1


15/78


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 vphn cp sng bvn c tip tc.Vo thi im khi tiu chun phn cp sng bln u tin c quy

nh, h thng ghp knh ng b c mt cu trc hon chnh nhhnh 1.40. Tuy nhin, khi nhng khuyn nghG.781 - 784 v G.957 - 958(u da trn csphn cp sng b) c tiu chun ho honchnh trong qu trnh nghin cu hai nm sau , th hthng ghp knhng b c n gin ho nhcu trc trong hnh 1.41. C ththyc rng cc ng ghp knh phn cp kiu chu u tng ng mtcch ng kvi cc ng ghp knh phn cp kiu M, v rng bsung cc khi nim mi, chng hn nhAUG, 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 sng

bl cc kto ln. Rt nhiu c trng ca phn cp ng bc ngungc t tiu chun ca h thng Metrobus, chng hn nhquan im vmng thng tin quang, khi nim vhthng 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 shiu cacng ten, thit lp tn hiu cp 150 Mbit/s tiu chun, v nng cao linh hot v tin cy ca hthng nhsdng mo u mt cch hiuqu. Cng nh vy, cu trc h thng phn cp, h thng ho cu trcmo u, ng bho bng con tr, v khnng cu trc mng thng tin

lin tc a, u xut pht t tiu chun kt ni ca SONET. Da trnnhng cs, tiu chun phn cp sng bl tiu chun cho phpcu trc nn mng thng tin ton cu qua vic iu chnh kt hp hai kiu

phn cp sca Bc Mv ca Chu u.


16/78


Hnh 1.40 Cu trc ghp knh ng bsgiai on u tin

Hnh 1.41. Cu trc ghp knh ng b

Mt khc, phn cp sng bvn 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


17/78


nh 155,520 Mbit/s cho tc bt tiu chun ca NNI ca B-ISDN vtrong squy nh tc bt trng tin thp hn 149,760 Mbt/s. Ngoi ra,nh hng c tnh cht cbn khc na l n c cc tbo ATM cnh xtrong ng bao ca trng tin VC-4 pht i csphn cp sng bca UNI ca B-ISDN. Ni mt cch chnh xc, phn cp sng

b ng mt vai tr chcht trong vic hnh thnh khi nim B-ISDN

cng nhi ti mt phng php truyn dn ng bmi.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 hht 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 sdngcho thng tin hon cu. Do vy cn phi hiu rng gii thch SDH l

bao hm cvic gii thch SONET. Tuy nhin vn c mt skhc bit

nhgia SDH v SONET. Nu nhng skhc bit tiu biu gia chngta c thm trn u ngn tay th im bt u cbn 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 nhtn hiu cp cao nht. Do c mt khi nim vgiaodin, cho nn, ng nhin, y chng phi l mt skhc 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 - c

phi ghp to thnh STS-3C th n cng c thbng vi tn hiu STM-1-155,520 Mbt/s ca SDH, SDH v SONET c skhc 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


18/78


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

Vmt 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 nhvy, mo u on caSTM-1 trong dng 9x9B c btr hng u ca khung STM - 1, mou on ca STS-1 di dng 9x3B c b tr hng u ca khung

STS-1. Sau , trong chai trng hp, hng thtc dnh ring chocon tr(pointer). Cthl, vic la chn hng thnht, thtv thbyca mo u on trong STS-1 tng ng vi mo u on ca STS-1v vic sdng cc thnh phn ny l nhnhau trong chai trng hp.

SDH v SONET c mt skhc bit trong khi tn hiu cu thnh. Gcgc ca vn nhvy 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 hthng tt ccc tn hiu phn cp tDS-1 n DS-4E, trong khi ,trng hp STS-1 chcn thit ghp knh c hiu qunm 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 nhC, VC,TU, TUG, AU, AUG v.v.... sc thit lp v thtc ghp knh ng

b ton b h thng nh trong hnh 1.41 l cn thit. Ngc li, trongtrng hp STS-1 chc mt khi tn hiu trung gian, gi l mt nhnho (VT-virtual tributary) l sc 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 bsung cho DS-1C.

V n v tn hiu trung gian lin quan c khc nhau, cho nn SDH vSONET cng khc nhau vcu trc ghp knh. Trong trng hp SDHcu trc thng k hthng nhtrong hnh 1.41 l cn thit , trong nni kt C, VC, TU, TUG, AU, AUG ATM-n vi nhau, cn trong trnghp SONET, chcn n mt thtc 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 nhphng php nh xmi tnhiu phn cp thnh VC-11, VC-12 v VC-2, v phng php nh xDS-1C thnh VT3 ssdng php nh xtun theo cn chnh dng, khng


19/78


v m. Phng php dng ghp knh cc VT ny thnh ng baotrng tin STS-1, tc l SPE (Synchronous Payload Envelope - ng

bao trng tin ng b) cng ging nhphng php ghp knh VC linquan thnh VC-3 qua TUG-2. Trong trng hp thhai, vic nh xDS-3 thnh SPE cng ging nh phng php nh x DS-3 thanh VC-3,nhng php nh xSYNTRAN DS-3 th c cung cp phthm.

Vphng 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 nglin quan n phn cp cn i snh, phng tin vtl, on ti to, on ghp knh v lp ng truyn c t ra trongSDH sc gi l lp quang, lp on, lp ng dy v lp ngtruyn trong SONET. Cc thut ngxc nh khc lin quan n nh x,ghp knh, mo u v ng bho th hu nhging nhau.

SONET cng nhSDH u da trn khi nim phn cp, sdng khung125 m s, dng mo u h thng, v c tc truyn dn cbn gingnhau. Nhng n c iu tit nhslin kt tt ccc tn hiu phn cpsBc Mkctn hiu DS-1E kiu Chu u, v n cha ng cthtc ghp knh tng thnht.

Ngoi ra, SONET sdng ng bho lin quan ti phng php contr, ging nhca SDH, cho nn c thkt ni ton bnc Mbngmng truyn dn ng b.

1.4.3 Phn cp scn ng bso vi ng bLp (mc) s hin c bao gm cc tn hiu DS-1-DS-4 ca h thngChu u/ Bc M, c bphn tiu chun ho vin thng ca ITUv Bell System quy nh. Trong s, cc tn hiu ca hthng Bc M c uban T1 ca Bc Mtha nhn trli nhtiu chun Bc M,ng thi, tiu chun cng c bit n nh l tiu chun do BellSystem thit lp li.

phn bit lp sny vi phn cp sng bc thc thi gn y,n c gi l phn cp scn ng b.

Phn cp scn ng b, mt hphn cp s tiu chun ang c sdng, c phn loi thnh hthng Chu u v h thng Bc Mnh(a) v (b) trong Hnh 1.42 Phn cp s cn ng b ca Bc M chnh thnh tDS-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


20/78


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 bv n c ngbho nhcn chnh dng - l mt loi nhi bt.

Phn cp sng b, nhc trnh by trong (c) ca hnh 1.42, c

hnh thnh tcc tn hiu STM-n. ng thi, n l mt snguyn ln, m1,4 v 16 l cc sc quan tm chyu. Cc tc bt tng ng vicc sny 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 btcc 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 tn ln cc tn hiu STM-1 m n l sghpknh 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 thddng nhn thy rng phn cp sng bc mt cu trc ngin hn nhiu so vi cu trc ca phn cp scn ng b.

C ngha l, tt ccc tn hiu phn cp ca h thng Bc Mv Chuu chc mt giai on ghp knh. Trong mt hthng phn cp scung bvic ghp knh khng ng bc 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 bc thc hin khi tn

hiu phn cp c ghp thnh tn hiu STM-n. Vli, trong phn cp scn ng btn hiu DS-m thuc vcp ca giai on ksau ca tn hiuDS-(m-1); nhng tt ccc tn hiu ny c mi quan hngang bng trong

phn cp sng b.

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

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

(c) Phn cp khng ng b


21/78


Hnh 1.42. Phn cp s

1.4.4. Khi nim phn cp v mo u

Ni chung, cc tn hiu sc gi i qua ng truyn, on ti to,on ghp knh v mi trng vt l nhc minh hotrong 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 bc mt ssp xp theo khng gian c hthng 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 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 nhm t


22/78


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 to

Con 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 kkhi no tn hiu cng teno

c to thnh.SOH c chn vo v c tch ra trong on ti to hoc on ghpknh ch thhiu nng truyn dn cng nhhot ng v bo dngtn hiu STM-n. Nhc minh hotrong hnh 1.44, cc SOH nm bntrn v bn di ca con trc sdng 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 bti to.

Tuy nhin, ba byte ca B2-SOH cho BIP-24- c b tr phn phadi ca PTR v chng chc 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.


23/78


gii thch cu trc ca mo u on v mo u ng hy xemkhung STM-1 trong hnh 1.45, (a), (b). Vic sdng mi loi mo utrong hnh ny nhsau: A1, A2 dng cho bt sp xp khung; B1, B2; B3dng kim tra ngang bng chn l, C1, C2 dng cho slng 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 thi

ng truyn, H4 dng ch th a khung; J1 dng ghi du tchng truyn; K1, K2 dng cho chuyn mch bo vtng; Z1~ Z5 lcc mo u dphng cho cc mc ch khc.

1 2 3 4 5 6 7 8 9 J1

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

2B1 E1 F1 X X C2

3D1 D2 D3 G1

4 con tr F2

5B2 B2 B2 K1 K2 H4

6D4 D5 D6 Z3

7D7 D8 D9 Z4

8D10 D11 D12 Z5

9Z1 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 nhc trnh by trong hnh 1.46, datrn c scc khi nim phn lp nh ngha trong phn trc. Do cutrc ny chim mt vng 9Bxnx270 (B=Byte) trong vng 125 m s, cho


24/78


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 bcho vng mo u SOH vcon trAU (Khi qun l) v phn cn li ca 9B x n x 261 c phn

bcho ng bao trng tin ca STM-1.

Do vy, STM-1, mt tn hiu cbn ca phn cp sng b, sc kch

thc l 9B x 270. Cng nhvy, 9B x 9 trong s l cng ca mou on v con trAU, v cng chng y 9B x 261 l ng bao trngtin, v tc bt trthnh 155,520 Mbt/s.

Theo quan im cu trc khung STM-1, SOH c to thnh thai khuvc 3 x 9B v 5 x 9B, con trAUPTR bao gm khu vc 1 x 9B v cuhnh ca n nhc trnh by trong hnh 1.45. Mt VC-4 c nh xtrong vng cn li, hoc ba tn hiu VC-3 c thc nh xsang vng cng vi mo u cnh (FOH-Fixed Overhead). Cc tn hiu VC-4v VC-3 u bao gm hnh bao trng tin v vng POH c kch thc 9

x 1B c btr 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 trAUPTR 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 trAU, v cu trc cui cng ca STM-1c tht 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 bxl tt ccc tn hiuphn cp s mt cch ngang bng v n s thit lp nn cc tn hiuSTM-n. Trong hnh 1.41, stng thca cu trc ghp knh ng btrn cc tn hiu phn cp c a ra.


25/78


Trong hnh ny, cc con snm trong ngoc chr slng tn hiu cnthit cho qa trnh ghp knh tng ng. Qua trnh ghp knh ng bnm trong hnh chnht in chm (c chthbng chSM), trong khi, hnh chnht pha bn tri c ch thbng chAM, biu thchoqu trnh ghp knh khng ng bm 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 xsang cc cng tentng ng. ng thi, phng phpchn dng/khng/m hoc chchn dng trong khi bt c sdng 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, nhtrong 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 , sm (m=1, 2, 3, 4) gn chomi khi tn hiu schthrng mi tc bt ca khi tn hiu lin quan

stng ng vi cp DS-m. Khi m=1, n c chia nhthnh 11 v 12v chng biu thtng ng cho tc bt ca hthng Bc MDS-1 vhthng 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 thc xem nhtng ng vi TUG-2. Ngoira, TU-3 c thc xem nhbng vi TUG-3. VC-3 c thc 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) nhnh


26/78


tuyn cho AU-3. Nhm n vqun l AUG- Administrative Unit Group)c thc xem nhtng ng vi AU-4. St c tn hiu STM-nkhi gn mo u on (SOH) vo n nhm AUG c ghp knh.

Ghp knh ng bc a ra nhmt trong cc th dtrong 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 km trong Hnh 1.41. Nhc trnh by trong hnh 1.47, tnhiu DS-1 c nh xtrc 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 ththy rng cc con trTU-11 PTR ca ccTU-11 c gp li vi nhau v c a ra ngoi. Ngoi ra, TUG-3 tc nhghp 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 sc gn vo pha trc chng t c VC-4.

Theo bngoi, tn hiu VC-4 cng ging nhtn hiu thu c nhghpTUG-2 thnh 21 TUG v sau gn VC-4 POH v FOH vo pha trcchng.

Khi kim tra cc kt qughp 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 chc sdng nhmt mo u c in tm iu chnhkch thc.

C th thu c AU-4 nhgn 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 trv ng bho

Trong SDH, kthut con trc sdng ng bho. Con trny

c sdng chthsthay i mi quan hkhi VC c ng chnh

theo tn hiu TU hoc AU v khi VC chtha chxut pht trong mtkhung TU hoc AU v im xut pht ca n bthay i.

Nhc trnh by trong hnh 1.41 cc loi con tr khdng 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 chr trong hnh 1.46 v TU-3 PTR c btr trn nh ca

hng u tin trong phm vi khung TU-3.


27/78


Cc con trca lp c mc cao ni trn c nh du vi H1, H2 v

H3. cc con trca lp c mc thp, chng hn nhTU-11 PTR, TU-2

PTR v TU-12 PTR c nh du bng V1, V2 v V3. Cc con trca

lp mc thp ny c cu trc nhsau: ba trong scc byte u tin ca

mi on st c nhphn 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 trV1, V2 v V3, cn byte thtl 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 t0, 1, 2 ....

Cc con trH1, H2, H3 v V1, V2, V3 c cng mt chc nng nhnhau,

trong khi chng c dnh du mt cch khc nhau. Hnh 1.48 ch r

phi xc nh cch sdng ba byte ny nhthno. Bn bt ca chiu

sliu mi (NDF-New Data Flag) chthtrng thi ca sliu mi, cnbt SS c sdng 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) nhc trnh by trong hnh. Trong s, bt I sbhubmi

khi a chca im xut pht c gia tng v bt D bhubmi khi

a chca im xut pht gim i. Cui cng, byte H3 (hoc V3) c

s

d

ng

np cc s

li

u h

p l

khi th

c hi

n vi

c chn m.

Hnh 1.48. Cu hnh v chc nng ca con tr

Khi thc hin mt ghp chn dng, cc sliu hp lc pht i bngcch np ti cho byte ng ngay ng sau H3 (V3). Khi xy ra skhcnhau vtn sgia khung TU v AU hoc gia cc VC (l cc trng tinca chng) th cc byte con trc thc sdng 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 scc dliu c tch tdo skhc bit tn strnn bng 1 byte (trong trng hp VC-4 l ba


28/78


byte), ri khi np chng cho mt byte H3 hoc V3 (trong trng hpVC-4 l 3 byte), ng thi hubcc bt D. Khi , trn khung ksau,ghi li a ch mi m n c gim i 1 tng ng vi a chc ghi trc trn mt con tr10 bt tin hnh chn m. Sdngcc phng php tng ttin hnh chn m khi tn sca VC tngng bt u thp hn so vi khung TU/AU. Tuy nhin, khi cc bt I s

bhubv cc sliu khng hp lsc np sang byte tip sau caH3 hoc V3 v a chsc 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 bc mt sc im ni bt. Trong phn sau y sgii thch cim ny.

1. Khung 125s

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 sng bn cho php vic truy nhp t cc tn hiu

phn cp mc cao ti cc tn hiu phn cp mc thp; c bit l xungti tn hiu DS-O c thc hin mt cch ddng. Bng c im ny,ton bqu trnh xl sliu c thc thc hin nhmt n vbyte.Tuy nhin c im ny lm ny sinh vn trong phn cp skhngng bhin ti. Do m bin ng (jitter) thi gian i trnn 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 tcc tn hiu sDS-1 v DS-2. Nh, ccvn lin quan n jitter c thc gii quyt.

2. Shp nht cc phn cp s

Cu trc ghp knh ng bc khnng ho hp cc tn hiu sBc Mv Chu u. C ngha l, cc tn hiu STM-n c cng hnh dng bngoic thc hnh thnh qua thtc ghp knh ng bngay ckhi cgn bt ktn hiu no trong scc DS-1, DS-2, DS-3 ca Bc Mv 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 ccc ng l phi thc tv khnng sdng

phng thc cn phi c xc nh chun bcho slin kt mngton cu.

3. Cu trc phn lp


29/78


Mt trong nhng c im ni bt ca truyn dn ng b l n c ththohip 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 chyu c phn lp thnh cc ng v ccon. Cc mo u cn thit cho cc ng skhng c xl ti ccon m chng c truyn i mt cch trong sut. Cc SOH nm phn

pha trn hoc phn pha di ca con tr sc 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. Sdng mt cch hthng cc mo u

Trong cc tn hiu STM-1, mo u on v con tr chim mt khnggian 9x9B. Mo u thc ts tng ln khi cc mo u v con trcang 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-4El 139,264 Mbit/s. y l mt iu ci tin to ln so vi mng phn cpskhng ng bhin nay. Cc mo u c sdng 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 bho bng con tr.

Trong qu trnh ghp knh ng b, mng thng tin c ng bhonhvic thnh thong gi vo cc con tr. C ngha l sx dch tn sgia ng hhthng v cc tn hiu thu c thc xl ph hp vicon tr v chn dng/khng/m. Thng qua vic s dng b nh cng, phng php ng bho kiu ny to iu kin khthi cho ng

bho bng rng nhvic a ra khnng quan hvi mi trng cnng b. Phng php ng bho bng con trtng ng vi vic nhi

byte, nu chng ta nghin cu n trong bi cnh ca ng bho nhibit. V l do , phng php ng bho con trto ra jitter tn sthp

v 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 xtrc 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


30/78


mt bc; tng trung gian bbqua trong qu trnh ghp knh. Khi nimny khng hc ng dng i vi qu trnh ghp knh khng ng bang c sdng.

Ngoi ra, khi p dng trn mt mng thng tin, ni mt slng ln cctn hiu c gi i nhtin hnh mt squ trnh ghp knh, khi nim

ny 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 hthng thng tin quang hin nay c thit kda trn quan nim truyn dn im ni im cho nn skhng c hiu qukhi 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 slng cchthng thng tin quang c sdng ngy mt nhiu th cc hthngv cc tiu chun da trn khi nim ca mng quang trnn cn thitv khi nim ghp knh mt bc c p dng. Hn na, vmt 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 cu

Mt c im khc ca mng truyn dn ng bl n c da trn cskhi nim thng tin ton cu. Vic ng bho c tin hnh mt sln qua vic s dng cc con tr l yu t cho php mng truyn dnng bc ng bho vi mng thng tin ton cu. V mc ch ,

phn cp sca Bc Mv ca Chu u kt ni vi nhau. Nu ccmo u tbn ngoi v cu trc ghp knh c sdng u da trnkhi nim ny ca mng thng tin th mng thng tin ton cu c thtrthnh hin thc.

1.6.6 Cc mch vng thn gn (SHR)

1. Li ch ca vic sdng cc SHR

Cc mng hin ti vi cng nghcp si quang ang sdng phngphp nh tuyn bo vphn tp tng v tm hng kp bo vmng trong nhng trng hp t cp hoc h hng cc trung tmchnh. Nhng mng nhvy c thc pht trin thnh cc vngSHR nu nhSHR chng t c l kinh t hn. Mt mng mchvng l mt tp hp cc nt hnh thnh nn mt vng khp kn, trong


31/78


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 bmng dphng sao cho cc dch vbgin on c thc

phc hi mt cch tng sau s cmng. Cc thit bghp knhdng trong cc cu trc vng l cc thit bADM c nhim vxen 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 vnhchng cp quang phn tp vt l do h thng APSiu khin. Cc bghp knh u cui c sdng 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 khini

m m

ch vng ch

ng minh

c l c hi

u qu

kinh t

. Khi so snh

vi i tc hng tm ca n, mch vng c thscn n cc ADMtc cao hn, bi v n sdng chung khng chcc phng tincp quang m cn thit bghp knh.

Hnh 1.68 Pht trin ca cu trc mch vng

Nhc m ttrong 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 bquang/in tv cc bti to; v (2) khnng

sinh tn y trong khi t cp quang v hng nt mng (trnt bhng). i vi th dtrnh by trong hnh 1.68(a), mng hng tm1:1/Dp yu cu 12 bOLTM, 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 trng cc chi ph u tl thp hn. Nu tanghin cu mt trng hp trong chai mng vng v hng tmu sdng cng mt tc ng dy, v chi ph ca mt OLTMvo khong 80% chi ph ca mt ADM (ti cng mt tc ng


32/78


dy) th mng vng c thtit kim dc 58% chi ph u tso vii tc hng tm ca n. By gichng ta nghin cu mt trnghp khc, trong mng hng tm 1:1/DP s dng h thng 565Mbit/s v mng vng sdng hthng 2,40 Gbit/s. Githit rng githnh tng i ca mt thit bkt cui 565 - Mbit/s l 1 v chi phca thit b 2,40 Gbit/s gp ba ln gi thnh ny. Mng vng ang

nghin cu y cn n bn bADM 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 bOLTM 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 dc 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 vphn 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 lnt

i tm hoc l

n h

n, m

ng 1:1/DP s

b

t

u t h

p d

n h

n so v

i

mch vng.

Lu rng tho lun y chch n gi thnh ca tht bghpknh, bi v n l yu tni tri nht ca ton bgi thnh hthngchuyn ti bng cp quang i vi cc mng "intra LATA".

Trong nhiu trng hp, mng vng c cc u im vkinh tso vii tc hng tm ca n, tuy nhin, n c th gp kh khn hnhoc t hn nng cp hthng 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 stng tc vi nhau khi cc tnh hung scxy ra hoc cyu cu ti cu hnh. Tuy nhin, vn cn kit ca dung lng mchvng c thc gim bt hoc c gii quyt nhquy hoch mngcn thn hoc trin khai ADM tc cao hn nhiu (chng hn, tnhkhdng ca cc ADM 9,6 Gbit/s). V li (xem mc 4.5), h thngiu khin dng cho mng vng c thc 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 v

phn tp (Hub/DP).Bng 1.17. So snh gia nh tuyn bo vphn tp v cu trc SHR

Cc thuc tnh Hub/DP SHR/ADM

Khnng nng cp Ddng Kh khn - t

Tng scp quang Nhiu hn t hn

Tng su cui Nhiu hn t hn

Tc u cui Thp hn Cao hn


33/78


Khnng sinh tn ca cp si quang 100% * 100%

Khnng sinh tn ca trung tm ** Ngho Tt hn

* Phthuc vo cp bo v1:1 hay 1: N

** Githit ton bto nh trung tm bhhng.

2. SHR ca SONETSHR 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 khi

phc mt cch tng. Gii php chung bo m mt khnng thn gn l cung cp mt vng truyn thng th hai song song vivng lm vic thnht. Trong trng hp ny, mt sctrn vngc thc bqua nhchuyn cc cuc truyn thng sang vng thhai; ni chung n c coi nhmt chc nng chuyn mch ngdy (hoc chuyn mch bo v). Hn na, nu vng thhai pht theo

hng ngc li so vi vng th nht th mt s ngt trong c haivng gia hai nt klin nhau c thc cu vn nhcc nt trnmt trong hai pha bngt bng vic u vng cc cuc lin lc ngctrli sang vng thhai. N c gi mt cch thng dng l chcnng u vng ngc. Hnh 1.69 miu tcc th dvchuyn 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 vbgin on. Do vy, mt thuc tnh quan

trng ca SHR l: nu vng b"gy" ti bt kmt im no , thhng truyn dn i vi cc tn hiu c thc o li nhm trnhvic mt dch v.

Cc SHR ca SONET c thc phn chia thnh hai loi phbinl n hng v song hng theo hng ca lung lu lng dicc iu kin bnh thng. Cu trc ca SHR thuc vmt trong hailoi phbin ny c thkhc nhau vcchiu khin bo vcnsdng phc hi cc dch vbgin 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 tbt kmt ntno c nh tuyn theo cc ng truyn thng lm vic tNt1 ti Nt 3 (tc l ng 1-2-3). Lu lng quay vtip tc i theovng tNt 3 quay vNt 1 theo cng mt chiu nhtNt 1 n

Nt 3, sdng phn cn li ca vng lm vic (tc l ng 3-4-1).


34/78


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 chi 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 (chbo v) c pht i theo chiu ngc vi vng thnht

(vng lm vic).

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

V cc knh phc vc 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 v1:1 hoc 1 + 1. USHR sdngmt vng ring bit lm vng bo vm n khng vn chuyn nhucu dch v trong trng thi bnh thng v n trn (u vng) ccknh bgin on sang vng bo vtpha vng lm vic khi thnh

phn 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 + 1

phn chia cc tn hiu sang chai vng lm vic v bo v ti ntpha pht ny (c ngha l bc cu u cui), cn nt pha thu slachn tn hiu tt nht trong hai tn hiu nhnhau 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 cthc cu hnh nhcc 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 thn gn c ton b.


35/78


Hnh 1.70. Cc nh ngha vcc 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 kin

bnh thng, cc tn hiu t Nt 1 n Nt 3 c nh tuyn quang 1-2-3, cn cc tn hiu quay v tNt 3 ti Nt 1 c nhtuyn qua cng mt ng nhvy (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 thc dng chung trn cstng tuynkt ni v n khng c dnh ring cho tng yu cu trn vng

(nhi vi trng hp USHR). Do cc knh nghip vc nhtuyn song hng ti hai nt, cho nn cn n hai cp quang vnchuyn cc knh nghip vny.

Mt BSHR c thdng 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 thhai, c lp vi vngthnht, sc cung cp bo v. Cc knh lm vic v bo vssdng cc vng truyn thng khc nhau. Cc BSHR 1:1 cng c thc cu hnh nhcc BSHR 1:N, tc l mt vng truyn thng bo

vdng cho N vng truyn thng lm vic. Nhc cp trn,cc BSHR 1:N khng phi l loi thn gn y , v do vy, trongmc ny skhng tho lun vchng. 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 dphng bo v. cung cpmt 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 mchuyn mch bo v ng dy nh s dng phng php TSI


36/78


ho nhp cc knh lm vic trong cp quang b hng vi cc knhbo v trong cp quang khng bnh hng. Cc USHR v BVSRcn c thc 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 t

ng khi sc.SHR chuyn mch bo vng dy

Mt cu trc SHR chuyn mch bo vng dy sdng tiu ng dy ca SONET (chng hn cc byte K1 v K2) vnchuyn cc tin bo scv xc pht ng tc chuyn mch bov. ng tc chuyn mch bo vchc thc hin ti lp ngdy phc hi khi scv khng lin quan n lp ng truyn.

N phc hi yu cu ng dy khi mt phng tin bsc. Cc

cu trc chuyn mch bo vng dy c xc nh cho chailoi USHR v BSHR, sdng nguyn tc u vng lu lng sangng bo v. Khi mt vng bt cn phi c iu khin ti chviu khin txa thc hin vic u vng lu lng ti cc nt nmtrn hai pha ca cht. Hthng chuyn mch bo vng dy lmt sla chn tnhin i vi tt ccc BSHR bi v nh tuynyu cu BSHR sdng cng mt nguyn tc nhcc hthng im -ni - im hin nay, l nhng hthng sdng hchuyn mch bovng dy (tc l APS) phc hi cc yu cu nu mt cu kinmng bhhng.

SHR chuyn mch bo vng 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 hthng chuyn mch bo vngdy, 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 scng 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 vng 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 vng STSc xc nh nhmt mch vng trong cc ng truyn STSc chuyn mch ti sp xp mch vng.


37/78


Cc vng chuyn mch ng truyn STS v VT tng ng c sdng chyu 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 csnh truyn yu cu v cchiu khin bo v.

Hnh 1.71.

1.7 STIN TRIN SANG BISDN

B-ISDN c pht trin iu tit cc thloi 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 hthng thng tin ATM c pht trin ci t B-ISDN. Mc tiu chyu ca BISDN l linkt tt ccc tn hiu lin tc theo thi gian thc v cc tn hiu s liutheo nhm c sphn bdi tn rng (cn thit cung cp cc dch v

bng hp, pht hin txa, chng hn nhgim st txa, u cui sliu,

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 sliu tc cao v.v). B-ISDN i hi mt phng php hiu quc thxl chung tt ccc dch vni trn. Hthng truyn thngATM (phng thc chuyn giao khng ng b) c xut nhlmt gii php.

Cc khi nim vBISDN c pht trin p ng mt cch hiuqu cc nhu cu ang cng ngy cng gia tng v cc th loi dch v

bng rng khc nhau. iu tit tt ccc 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 vphn b, chng hn nhCATV. Ngoira, phi c mt chc nng cung cp ccc dch vchknh, cccdch vchgi.

Mt khc, li tng c mt i hi vkhnng mng c khnng cungcp dch vgim st txa 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


38/78


gii php cho vic ny l xut tiu chun ho cc loi tn hiu khcnhau ca cc dch vng c cc hnh thc bngoi nhnhau v sau, tch trchng li ghp knh. Cc tbo ATM c sdng 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 sdng ghp mt nhm cc tbo ATM; mt h thng truyn

thng da trn cscc tbo ATM v ghp knh ATDM c gi l hthng thng tin ATM.

Hthng truyn thng ATM lin kt hthng thng tin digital chknh ang hot ng vi h thng thng tin chgi. H thng thngtin ATM ging nhh thng thng tin gi, trong n sdng cc t

bo ATM nhmt phng tin truyn dn cbn, trong khi n khcvi chuyn mch gi chn ng thi c thx l c cc tn hiuthi gian thc v tng ng. Ngoi ra, cc hthng chuyn mch gini chung c sdng mt cch cc b trong cc mng LAN, cn

i vi h thng ATM th do n c thit k s dng trn ccmng cng cng nh cln, 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 vri 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 tbo ATM chuynchng i qua cc knh o. Do vy, mt svn mi lin quan n victhit lp ni kt, qu trnh bo hiu, n truyn dn v chuyn mch

pht sinh.B-ISDSN hay hthng 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 sxem xt li cc vn lin quan n chng, da trn cciu khon thuc vBISDN ca ITU-T.

Hthng 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 cbn 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 gicng ngy cng cnhiu ngi sdng cc u cui sliu, cc my tnh c nhn, cc myFax v cc h thng hi nghvideo, v s lng cc cng ty nhn thamgia vo cc dch vCATV cng tng ln.


39/78


Ngoi ra, nhu cu vcc dch vnhin thoi thy hnh (video), truynhnh phn gii cao, truyn s liu tc cao, dch vgim st bngvideo, truy tm bng video, video text bng rng cng ang tip tc giatng. Nhng dch vktrn bao gm cc dch vgiao lu cng nhccdch v phn phi m mt s trong cc dch v c th cn n ccmng ring ca mnh (do mt strong cc dch v l cc dch vch

knh, mt sl cc dch vchgi). Song lm c iu cnphi u tmnh v slm cho thng tin trnn km hiu qu. Do ,hin ang c mt nhu cu lin kt cc dch vni trn thnh mt mngtruyn thng chung cho tt ccc dch vlin kt.

BISDN - mt mng thng tin s, c khnng cung cp cc loi hnh dchvbng hp, chng hn nhin thoi, cc u cui sliu, 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 sliu 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 tmng ISDN bng hp hin ang c sdng.

1.7.2 Cc c trng tn hiu ca dch vB-ISDN

B-ISDN c nhng mc ch cbn l kt hp tt ccc dch vhin huvo mt mng truyn thng trong tng lai. Do vy, vcbn n cungcp cc dch v bng hp, chng hn nh in thoi, u cui s liu,fasimile, son tho vn bn txa, c so txa, videotex, bu chnh

in t, teletex. Ngoi ra, n c khnng cung cp cc dch vbng rng,chng hn nhin thoi thy hnh, hi nghtruyn hnh v truyn sliutc cao, facsimile mu, CATV, phn phi HDTV, m thanh nhy cmcao, th truyn hnh, gim st bng video, truyn chng trnh chiu

phim phn gii cao v videotex bng rng.

Nhng dch vBISDN ny bao gm tt ccc dch vc nhng c tnhkhc nhau. C ngha l, cc dch vtng tc chng hn nhin thoihoc in thoi thy hnh v cc dch v thng bo chng hn nhbuchnh in thoc bu chnh bng hnh nh v cc dch vtruy tm tra

cu bn vv vn bn u c bao gm trong . Cc dch vny lcc dch vthng tin m tn hiu ca dch vc chuyn giao theo chai chiu, song bn cnh , chng cn c cc dch v phn phi mtchiu, chng hn nhdch vCATV.

Nhng c trng ni bt nht ca cc tn hiu dch vB-ISDN l phm viphn bdi thng ca n rt rng. Trong khi tn hiu cu hnh cbn caISDN bng hp c phn bquanh tn hiu thoi th vic phn btc tn hiu ca B-ISDN bao gm cc lp digital khc, cc tn hiu video


40/78


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 tvi bit/s ca cc tn hiu gim st txa ti cc tn hiu video vivi trm Mbit/s. Ngoi ra, thi gian sdng n trong phm vi tcc sliu tc thp, c di vi giy, ti dch vvideo c di vi gi,cc dch vthoi c di vi ba pht.

Nh m t, B-ISDN c khnng cung cp dch vbng rng ti nhiuMbit/s, cn cc tn sm n sdng v phn bthi gian sdng th c

phm vi rt rng.

c tnh phn bkhc ca tn hiu dch vB-ISDN l cc tn hiu lintc, chng hn nh ting ni v hnh nh, c thcng "sng chung" vicc tn hiu nhm, chng hn nhsliu u cui. Cc tn hiu ting niv hnh nh c thtrthnh cc tn hiu tc bt bng nhau nhphng

php sho. Tuy nhin, cc tn hiu sliu khc nhau l cc tn hiu vi

tc 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 nhvy.

Hnh 1.72. Phn bdch vca B-ISDN

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


41/78


mch gi l l tng i vi tc thp hoc sliu 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 tlu l thch hp hn c, cn i vi cc tn hiu video tccao l chuyn mch knh phn chia theo khng gian.

V vy, tm c mt hthng truyn dn c khnng trao i vi nhaucc tn hiu tc thp/cao v cc tn hiu lin tc/ nhm l cc kkhkhn.

Tc sliu knh

1.7.3 Nn tng kthut ca B-ISDN

Nhcp trc y, v cc dch vdo B-ISDN cung cp c nhng cim khc nhau, cho nn mt scng nghcbn c i hi hinthc ho B-ISDN. Thnht, xl tc cao v cng nghmi trng,truyn dn bng rng v cng nghchuyn mch bng rng; chng cyu cu l bi v cc tn hiu ca dch vbng rng v tc cao c sdng rng ri. Vli, vic ci thin cng nghv thit bxl video lcn thit bi v cc dch vchnh ca B-ISDN l cc loi dch vvideokhc nhau. Hn na, cng nghmng thng tin i vi nhng vn trny l cn thit, bi v cc dch vtc thp/tc cao c cung cpv cc dch vchgi ng tn ti.

Nhng cng nghcbn ny c pht trin v c nng cp lintc nhm p ng mt cch y nhu cu v cc dch v bng rng

cng ngy cng tng. Thnht, cng nghthng tin quang c nngcao; suy hao ca cp si quang c gim xung thp hn 0,5 dB/Kmv gi c ca cc phn tbc x/thu nh sng st xung kh nhanhchng; Hn na, cng nghvmch tch hp v cng nghch to cccu kin cng rt tin tin. Cc phn t Silc lng cc hoc GaAsc pht trin mt cch thnh cng c khnng thc hin vic xl tccao (hng trm Mbit/s hoc Gbit/s) v CMOS c khnng xl 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 nhhot ng vchuyn mch tc cao trnn c thc.

Vic nn, chuyn i v ti to cc tn hiu dch vkhc nhau trnnddng do pht trin cng nghxl tn hiu. Vli, vic thu thp, thayi v x l cc tn hiu dch v trnn ddng hn nhpht trincng nghmy tnh. Qua vic sdng cng nghni trn, cng vi cngnghVLSI, cc thit bu cui khch hng hiu qu c pht trin.Thm vo , cc thit bu cui B-ISDN c sdng cho cc thit bvideo khc nhau c trin khai mt cch thnh cng v c sdng


42/78


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 vkhc nhau cng nhvic sho mng thng tin v ng gp vo spht trin cng nghthng tin. Da vo nhng vn ni trn, hthng thng tin ATM c khnng cung cp dch vB-ISDN c nhng nt c trng khc nhau. iuny dn n spht trin cng nghlin kt dch vB-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 scp ca

ISDN trong dng knh H11 1,536 Mbit/s v knh H12 1,920 Mbit/s, v vvy hnh thnh c sca ISDN cng vi giao din cbn 2B + D 144kbit/s.

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

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

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 vtiu chun ho NNI, vn c tin hnh di nhiu iu kinkh khn, i n thothun l sdng tiu chun tn hiu STM-1, ccu trc 9B x 270 v c tc bit 155,520 Mbit/s, ti hi ngh Seoulc tchc vo thng Hai nm 1988. Sau , n trthnh phn cp sng b ca cc khuyn nghG.707 - G.709. Mt khc, nhim v tiu

chun 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 nghtrn. 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 vgiao lu v cc dch vphn 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


43/78


kch thc ca tbo 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 chnh l WP8 nhng cng vic tiu chun

ho 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, vkch thc ca tbo ATM, "4+32" byte (u tbo +trng tin) do ngi chu u xut cnh tranh vi "5+64" byte dongi Ma ra. Song cui cng quyt nh l "5+48" byte scsdng cho mc ch ny. Do bnh 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 tbo ATM thun tu. Hn

na, cng c php btr cc tn hiu khc ca G.702. WP8 xcnh r nhng chi tit ca nhng iu khon cn c bn ci nh cckhuyn nghthuc Seri I ti Hi nghMasyama, tchc Nht Bn vothng 11 nm 1990. Nh vy, khun kh tng th v BISDN chon chnh. Mt khc, khi ITU c tchc li vo nm 1993, nhmnghin cu 13 (SG.13) ca ITU-T bt u m trch cc hot ngnghin cu vtiu chun ho BISDN.

1.7.5 Nguyn tc cbn ca BISDN

Nh trnh by trc y, BISDN l mt khi nim c a ra thomn nhu cu vcc dch vbng rng ang cng ngy cng gia tng. Ccmc ch cbn ca BISDN l thit lp mt mng sc khnng linkt v cung cp cc hnh loi dch vbng rng khc nhau thng qua vicsdng 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 vgiao lu v phn phi cng nhcc dch vchknh vchnhm cng c cung cp. Thm vo , cc dch vbng hp vcc dch vbng rng c cung cp mt cch ng thi. t ccc mc ch ni trn, BISDN phi c khnng htrcc ni kt truyn

thng bn cnh cnh cc ni kt im - ni - im a im - ni -im v cc ni kt dnh dng cc du ring/cnh; Nhvy, BISDNcn phi c khnng thng minh mrng v ci tin cc dch vv qun l hot ng, bo dng v iu khin mng mt cch hiu qu.

Cu trc ca B-ISDN phi nh thno sao cho n khng cn trspht trin cng nghhoc spht trin phng php hin thc ho trongtng lai. Ngoi ra, n phi c khnng p ng cc nhu cu ca khchhng hoc spht trin mng m n c thpht sinh mt ln na. Hn


44/78


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 mththng truyn thng phn chia u cc hnh loi dch vkhc nhau, spxp chng vo cc t bo ATM c kch thc nh nhau v cui cng,

chuyn chng i nhcc ATDM. Hn na, n thit lp cc ng o vcc knh o chuyn giao tbo ATM.

Do , thng qua vic sdng ATM, c ththc hin c kt ni mngc linh hot cao v phn bdi 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 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 vB-ISDN cng ging nhca ISDN. Tuy nhin, vic thitlp B-ISDN c thc hin khc vi thit lp ISDN.

Thnht, BISDN l mt mng s lin kt a dch vnh trong trnghp ISDN, nhng n khc vi ISDN chn bo m vic lin kt ccc tn hiu bng rng na. V l do , m hnh cu trc c bn caBISDN cng ging nhca ISDN, ngoi trkhnng xl cc tn hiu

bng rng, ng thi vi cc chc nng ca ISDN bng hp. Vmt thitlp 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 tR, S v T.

Tuy nhin, chng ch tng tnhau vmt khi nim m khng tngthch nhau vmt hot ng thc t. C ngha l BISDN khng thcthc hin chbng vic bsung cc thit bca dch vbng 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 nhcc phn tlin quan ca BISDN chvmt khi nim. Tuynhin n c thphi ghp vi TE1 ca ISDN hoc vi TA qua vic sdng TE2 ca BISDN. Trong hot ng thc tBISDN 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 hthng ni trn ca ISDN.

C ngha l, trong khi ISDN chyu iu tit hthng thng tin knh (hthng thng tin gi cng c iu tit) th BISDN chyu sdng h


45/78


thng thng tin gi, ng thi vn iu tit hthng thng tin knh). Donhng skhc nhau vh 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 Hthng thng tin ATM

ATM l mt hthng truyn thng thc hin BISDN. ATM l mt hthng chuyn giao kiu gi c hnh thc c bit, sdng ATDM. TrongBISDN, thng tin c chuyn i nhmt lung lin tc ci gi c mtkch thc khng i. Cc gi c kch thc cnh ny c gi l cctbo ATM. Do vy thng tin dch vcng c btr vo tbo 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 tbo ATM ca mt s

knh i ti mt cch khng ng b.Nu sdng ATM, dung lng ca knh nghip vcng c tnh theos lng cc tbo ATM. Cho nn svt qu dung lng truyn dnca thng tin c biu thbi slng cc tbo 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 chuyn

giao thng tin dch v. Mi khi mt knh o c thit lp, shiu nhndng ni kt c gn v khi ni kt c gii to, shiu nhn dng nycng c hub. Trnh tsp xp gia cc tbo ATM trong mt knho no do cc chc nng ca lp ATM dkin trc. Thng tin bohiu vthit lp ni kt c chuyn giao cc tbo 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 sdng l lp ATM, lp ng dng ATM (AAL) v lp mccao. Lp AAL nh xcc tn hiu dch vsang khu vc trng tin ca

cc tbo ATM, cn lp ATM thc hin chc nng to u ca tboATM chuyn giao trng tin mt cch trong sut. Lp vt l thc hinchc nng chuyn i cc tbo ATM thnh hng bt v sau , chuynchng i.

Kch thc ca tbo 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 tbo l nhn dng cc tbo thuc vcng mt knh


46/78


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

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

(a) Cu trc ca tbo

(b) Cu trc u trong UNI

(c) Cu trc u trong NNI

Hnh 1.73 Cu trc ca tbo ATM

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

1.7.8. Cu trc chc nng ca BISDN

M hnh cu trc chc nng chung ca ISDN bng rng vcbn gingnhISDN bng hp. C ngha l vmt cu hnh tiu chun, nhm chcnng v im gc, chai cu trc l nhnhau. N chra rng B-ISDNc hnh thnh trn cskhi nim ca ISDN. M hnh cu trc cbnca B-ISDN nhc trnh by trong hnh 1.74. Cu trc ca ISDN bngrng bao gm khnng mc cao v khnng mc thp.


47/78


Khnng mc cao l chc nng lin quan n thit bu cui (TE) vkhnng mc thp bao gm khnng ISDN bng hp da trn khnng

bng rng, 64 bit/s, v khnng bo hiu lin tng i.

Hnh 1.74. M hnh cu trc cbn 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. chthim 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 nhctrnh by trong hnh 1.76. Chc nng ca mt bng qun l c phnchia thnh : qun l mt bng v qun l lp.


48/78


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 nhvy, qun l lp hm lqun 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 cucgi v iu khin kt ni s c qun l. Trn mt bng khch hng,thng tin vkhch 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 nhtrong bng 1.18.

Lp Lp con Chc nng

Lp 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 hubmo u tboChc nng thng dch VPI/NCI ca tboChc nng ghp knh v tch knh cho tbo

Lp vt lHi ttruyndn

Chc nng phn chia tc tboChc nng to ra v khngdnh tn hiu HECChc nng nhn dng tboChc 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 tlp con hi t(CS), lp con phn on vlp rp li (SAR). CS bin i thng tin dch vkhch hng ca lp mccao thnh khi s liu giao thc (PDU) v SAR to nn phn thng tinkhch hng ca tbo ATM bng vic ngn chn PDU.

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


49/78


nhp dch vsau khi thng dch v ghp knh/tch knh cho cc tbo.Bn cnh , n xl cc on PT hoc CLP v thc hin chc nng lto ra v hubmo u tbo ATM.

Lp vt l bao gm lp con hi ttruyn dn v lp con mi trng vtl. Chc nng ca lp con hi ttruyn dn bao gm vic phn chia tc

tbo, to ra v xc nhn byte sa sai u , pht hin im bin giitbo. Ngoi ra, trong trng hp pht theo phn cp sng bn 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 thn bng vic sdng 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) chcho thy rng B-NT c thdung 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 thcu hnh chung ca loi tp trung ho,cn (b) chthcu hnh chung ca loi phn b. Cng nhvy, (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 bphi hp phng tin, cn Wchra im kt ni gia cc MA vi nhau. Ngoi ra, TE* chthTE to racu trc kiu bus v SSB ch thim kt ni gia cc TE* ny. MA lthit bv B l im gc u thuc loi phi tiu chun. B-NT1 thc hinchc nng ca lp 1, chng hn nhim 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 theo

phng php tp trung hoc phng php phn b. Cc chc nng linquan n B-NT2 l bphi hp phng tin (MA), tm kim bin gii t

bo, tp trung ho, nhm. ghp knh, tch knh, gn ngun, xl phi

ghp chc nng AAL vbo 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 bkhc, trn lp 1 vlp c mc cao hn, kcOAM.

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

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


50/78


(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 cbn 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


51/78


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 tha 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 nhthnh 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


52/78


Hnh 1.79. Mi quan hgia 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 tbo hoc mng da trn SDH. Mi quan hgia 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 tbo 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 nhkt 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 tbo lin quan n cng mt VPC sc chuyn giao trn cng

mt 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.


53/78


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 tin

bng sng in t, pha thu nhn sng in tpha pht qua khng gianv tch ly tn hiu gc. Vlch sca thng tin v tuyn, vo u thkny 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 thdng lm vt phn xsng in t.

Nhng yu t mra mt knguyn thng tin v tuyn cao tn iquy m. Gn 40 nm sau Marconi, thng tin v tuyn cao tn l phng

thc thng tin v tuyn duy nht sdng phn xca tng i lu, nhngn hu nhkhng 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 sdng bng tn scc cao (VHF) v c nghin cu lin tc sau chin tranh thgii - tr thnh hin thc nh spht trin cc linh kin in tdng choHF v UHF, chyu l pht trin ngnh Raa. Vi sgia tng khngngng ca lu lng truyn thng, tn sca thng tin v tuyn vnti cc bng tn siu cao (SHF) v cc cao (EHF). Vo nhng nm 1960,

phng php chuyn tip qua vtinh c thc hin v phng phpchuyn tip bng tn xqua tng i lu ca kh quyn xut hin. Donhng c tnh u vit ca mnh, chng hn nhdung lng ln, phm vithu rng, hiu qukinh tcao, thng tin v tuyn c sdng 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 vtinh - vtrv.v... Tuy nhin, can nhiu vi lnh vc thng tin khcl iu khng trnh khi, bi v thng tin v tuyn sdng chung phnkhng gian lm mi trng truyn dn.

i ph vi vn ny, mt lot cc cuc Hi nghv tuyn Quc t c tchc tnm 1906. Tn sv tuyn hin nay c n nhtheo "Quy chthng tin v tuyn (RR) ti Hi nghITU Geneva nm1959. Sau ln lt l Hi nghvphn bli di tn ssng ngn sdng vo nm 1967, Hi nghvbsung quy chtn sv tuyn chothng tin vtrvo nm 1971, v Hi nghvphn bli tn sv tuynca thng tin di ng hng hi cho mc ch kinh doanh vo nm 1974.Ti Hi nghca ITU nm 1979, di tn sv tuyn phn b c m


54/78


rng ti 9kHz - 400 Ghz v xem xt li v bsung cho Quy chthngtin v tuyn in (RR). gim bt can nhiu ca thng tin v tuyn,ITU tip tc nghin cu nhng vn sau y bsung vo ssp 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 sdng phng php iu chchng li can nhiu.

2.2 CC C TNH CA SNG V TUYNTn ssdng cho sng in tnhvai tr sng mng trong thng tinv tuyn c gi ring l "tn sv tuyn" (RF). Tn sny chim mtdi rt rng tVLF (tn scc thp) ti sng milimt. Khng thl giiy sng v tuyn theo l thuyt, bi v n khng chbnh hng

bi tng i lu v tng in ly m cn bi cc thin th, kcmt tri.

Do vy, vic nh gi cc trng thi ca cc hnh tinh, ca tng i luv in ly v vic dbo ng truyn sng v tuyn cng nhkhnng

lin lc da trn nhiu dliu trong qu khl ht sc quan trng. Phnsau y ca chng trnh ny sgip 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 sv tuyn

Trong thng tin v tuyn, cch truyn sng v tuyn v vic sdngthit 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 cchv phng thc sdng sng v tuyn.

Bng 2.1. Phn loi, cchv sdng sng v tuyn

Tn s Phn loibng tn

Cchtruynsng vtuyn

Cly thng tin v lnh vc sdng

3KHz~30 KHz VLF Sng t-in ly

Thng tin o hng qun skhp thgii


55/78


30KHz~300KHz LF Sng t 1500Km o hng v tuyn

300KHz~3MHz MF Sng t(Clyngn)

Sngtri

(Clydi)

Pht thanh cnh

Hng khng, o hng,lin lc nghip d

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

6~30Mhz : Thng tin ding

Thng tin kinh doanh

v nghip d, dn squct

30MHz~300MHz VHF Sng tr i

Sngilu

Thng tin trc thi, VHF, FM

a thng tin

300MHz~3GHz UHF Sng tr i

Sngilu

Raar, a thng tin

Thng tin di ng

3GHz~30GHz SHF, Viba Sng tr i Thng tin vtinh, 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 chcho thy cnc sng phn x tbmt t t ti trm thu, ngoi sng trc tiptheo ng thng.

(a)Trong tm trc thi

(b)Ngoi tm trc thi


56/78


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 trnn khng thc do cong ca bmt trit nh trnh by trong hnh 2.1(b) nhng vn c th c sng vtuyn truyn lan xung mt t do c sng bmt v sng tri, nhhin tng khc x(hnh 2.2). Ni chung, sng bmt, sng trc tipv sng phn x, trsng tri, u c gi l sng t. Sng tri lsng in tbthay i hnh trnh ca mnh ti tng in ly v quaytrvtri t; tng in ly l ni hi tca v sin tch, nh hnh

ti cao 100-400Km. Ngoi sng bmt v sng tri cn c sngtn x- l phn xdo nhng sbin i mnh lit ca tng i luv in ly hoc do sng in tva chm vi cc vt cht, chng hnnh cc sao bng, v b tn x ri t ti u thu. Sng tn xc sdng trong phng php chuyn tip qua tn xi lu.

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

1. Slan truyn ca bng tn sthp

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 ssdng cng cao, sng t cng yu (truyn lantn sthp). Hin tng nhiu xc mi tng quan cht chvi dnin v hng sin mi ca t trong ng lan truyn. V cly 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 so vi chiu cao tbmt tri t lnti tng in ly. Cho nn, mt t v tng in ly ng vai tr nhhai bc


57/78


tng. N c gi l chng dn sng mt t - in ly m nhn,c ththng tin ti ton thgii. Bng tn scc thp c sdng chyu cho thng tin hng hi v thng tin o hng.

2. Struyn lan ca bng tn scao

Thng tin cly xa bng bng tn scao c thc hin nhsphn x

ca sng tri trn tng in ly. Trong phng thc thng tin ny, mt thu sng tri phthuc vo tn sv tuyn v trng thi ca tng in ly,trng thi ny thay i theo thi gian, theo ngy, theo ma v theo iukin thi tit. Cho nn vic dbo trng thi ca tng in ly l v cngquan trng i vi thng tin lin lc sdng sng tri.

(1) Tng in ly

Tng in ly hnh thnh ti cao 100Km - 400Km l do kt qu cavic ion ho trng thi ca tng i lu bng cc tia cc tm v tia X do

mt tri bc x. Tng in ly c phn chia thnh mt vi lp c gi trmt in tcc i. Mi tng c phn chia thnh cc lp D, E, Ftheo cao ca n. Lp F li c phn chia thnh lp F1, F2. Hnh 2.3trnh by mt tnh theo cao ca cc lp ion in hnh.

Hnh 2.3. Mt in t/ion ca tng in ly - theo cao

(2) Truyn sng trong lp Ion

Trong khi tng in ly c thxem nhmt tm dn in phng trong victruyn lan cc tn s thp th lp ion ho ging nhmt tm in mikhng lm hskhc xca n bin i lin tc, v sbin i ca mtion th

He Thong Thong Tin Quang Vo Tuyen 360

Documents

Transcript of He Thong Thong Tin Quang Vo Tuyen 360