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ĐẠI HỌC THÁI NGUYÊN TRƯỜNG ĐẠI HỌC CÔNG NGHỆ THÔNG TIN VÀ TRUYỀN THÔNG ...................................... BÀI GIẢNG ĐO LƯỜNG TRONG HỆ THỐNG VIỄN THÔNG Biên soạn: Ths. Mạc Thị Phượng 1

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I HC THI NGUYNTRNG I HC CNG NGH THNG TIN V TRUYN THNG......................................

BI GINGO LNG TRONG H THNG VIN THNG

Bin son: Ths. Mc Th Phng

Thi Nguyn, nm 2013

MC LCCHNG 1 TNG QUAN V MNG VIN THNG V CC PHP O TRONG VIN THNG31.1. Tng quan v mng vin thng31.1.1. Cc thnh phn c bn ca mng vin thng31.2. Cc yu t nh hng n cht lng mng vin thng91.3. Cc php o trong mng vin thng141.4 Cc quy trnh o cn dng khi no?15CHNG 2: O LI BIT172.1. nh ngha v cc thut ng172.2. Cc tiu chun v li bit182.2.1. Phn b ch tiu cho knh truyn dn 64kb/s182.2.2. Phn b ch tiu cho m hnh on s phn cp tc 2048 kb/s192.2.3. Tiu chun li bit cho cc lung c s hoc ln hn192.2.4. Tiu chun li bit cho cc lung s tc cao202.2.5. Xc nh li i vi cc lung s PDH212.2.6. Xc nh ch tiu li i vi lung SDH222.3. Nguyn nhn v nh hng ca li bt232.3.1 Nhng ngun gy li bn trong h thng242.3.2 Mt s nguyn nhn bn ngoi gy ra nhiu242.3.3nh hng ca li bit242.4 Nguyn l hot ng my o li bit262.5 Li cm hay trt bit?272.6 My o li bit phn ng li nh th no?272.7. Phng php o li bit302.7.1. Cc php o lung 2Mb/s khi ang cung cp dch v322.7.2. Cc php o khi h thng khng cung cp dch v tc 2 Mb/s392.7.3Cc php o trong mng SDH45CHNG 3: O TRT BIT573.1 nh ngha v cc thut ng573.2. Nguyn nhn gy ra hin tng trt bit613.3. nh hng ca hin tng trt bit683.4. Tiu chun o trt bit713.4.1. Tiu chun rung pha i vi giao din PDH713.4.2. Gii hn cho php i vi mc rung pha v tri pha vo giao din PDH733.4.3. Tiu chun rung pha v tri pha vi giao din SDH743.5. Phng php o753.5.1 Yu cu753.5.2 Cu trc thit b773.5.3.Nguyn l o dung sai793.5.4 Mt s v d v o dung sai jitter80CHNG 4: O KIM MNG CP NG904.1. Gii thiu chung v mng cp ng904.1.1Cu trc mng ngoi vi904.1.2Nguyn tc t chc mng cp924.1.3Nguyn tc xc nh dung lng mng cp ng.964.1.4 Phng thc gim khong cch cp ng n nh thu bao974.2. Yu cu chung v cc tham s o cht lng mng cp ng984.2.1 Yu cu chung v mng cp ng v phn loi cp984.2.2 Mc ch o kim994.2.3 Cc ch tiu k thut phc v o kim994.3 Phng php o1034.3.1 o in tr cch in1034.3.2o in tr mt chiu1044.3.3 o mt cn bng in tr i dy (li dn)1054.3.4 o in dung cng tc ca i dy1064.3.5 o in dung khng cn bng1064.3.6 o suy hao truyn dn (suy hao xen)1074.3.7 o suy hao xuyn m u gn1084.3.8 o suy hao xuyn m u xa109CHNG 5: O KIM TRA NG DY THU BAO S xDSL1105.1. Gii thiu chung v mng xDSL1105.1.1 Khi nim chung1105.1.2 Cu trc tng th mng xDSL1125.2. Cc tham s cn o kim trong trin khai dch v xDSL1135.2.1 Vai tr ca o kim trong trin khai dch v xDSL1135.2.2 Cc tham s cn o kim trong trin khai dch v xDSL1145.3 Phng php o1165.3.1 S dng my o o cc tn hiu lp di v kh nng kt ni lp IP1165.3.2Phn tch kt qu o thc t119CHNG 6: O KIM TRA MNG CP QUANG1216.1. Gii thiu chung1216.2. Yu cu chung v cc tham s cht lng mng cp quang1226.2.1 Yu cu chung v mng cp quang1226.2.2 Mc ch o kim1226.2.3. Ch tiu k thut ca cc php o1236.3. Cc php o1286.3.1. Cc php o dng my o cng sut quang1286.3.2. Cc php o quang s dng my o phn x quang OTDR134

THUT NG VIT TT

CHNG 1 TNG QUAN V MNG VIN THNG V CC PHP O TRONG VIN THNG1.1. Tng quan v mng vin thng1.1.1. Cc thnh phn c bn ca mng vin thng* Khi nim v mng vin thng: Mng vin thng l mng thc hin truyn a thng tin t u pht ti u thu nhm cung cp cc dch v vin thng cho khch hng.Mng vin thng bao gm cc thnh phn chnh: thit b chuyn mch, thit b truyn dn, mi trng truyn v thit b u cui.S khi cc thnh phn ca h thng vin thng, hnh 1.1 * Thit b u cui: Thit b u cui gip cho vic giao tip gia mng v con ngi hoc my, bao gm c cc my tnh. Thit b u cui chuyn thng tin thnh cc tn hiu in v trao i cc tn hiu iu khin vi mng.Cc thit b u cui gm c: my in thoi, my fax, my in bo, my tnh in t, my in thoi di ng v cc thit b ph tr SIM- Subcriber Interface Module: M un giao tip thu bao)* Thit b chuyn mch:Chuyn mch c ngha l thit lp mt ng truyn gia bt c cc thu bao (u cui) no. Chc nng ca cc thit b chuyn mch l thit lp cc ng truyn ny. Vi thit b chuyn mch nh vy, ng truyn c chia x v c th c trin khai mt cch kinh t. Tng i ng vai tr cc nt trong mng vin thng, c cc chc nng c bn sau:- Xc nh thu bao- Kt ni vi thu bao b gi- Phc hi h thng khi cuc gi kt thc.- Tnh cc cuc gi thc hin chc nng trn tng i c nhim v sau:- Bo hiu: l nhim v trao i vi cc thit b bn ngoi tng i gm cc mch in v cc ng dy thu bao, cc trung k u ni n thu bao hay n tng i khc.- X l thng tin bo hiu v iu khin thao tc chuyn mch: thit b iu khin chuyn mch s nhn thng tin bo hiu t ng dy thu bao v trung k, x l cc thng tin ny v a cc thng tin iu khin cp tn hiu n ng dy thu bao, trung k v cc thit b ngoi vi khc iu khin thc hin cng vic chuyn mch, thng bo u ni, gim st v gii phng kt ni.- Tnh cc: tng i phi to ra cc s liu cc ph hp vi tng cuc gi ngay sau khi cuc gi kt thc, s liu cc ny s c x l thnh cc bn tin cc phc v cng tc thanh ton. Gi tr cc phi c tnh ton theo khong cch v thi gian cuc gi.

u cui d liuFaxThit b u cuiu cui d liuin thoiFaxThit b v tuynThit b chuyn mchThit b chuyn mchCc phng tin truyn dnHnh 1.1. Cc thnh phn ca mng vin thngV tinh truyn thngin thoi* Thit b truyn dn: Thit b truyn dn c s dng ni cc thit b u cui hay gia cc tng i vi nhau v truyn cc tn hiu mt cch nhanh chng v chnh xc.Thit b truyn dn c th phn loi thnh thit b truyn thu bao, ni thit b u cui vi mt tng i ni ht, v thit b truyn dn chuyn tip ni gia cc tng i. Da vo mi trng truyn dn, thit b truyn dn c th phn loi s lc thnh thit b truyn dn tuyn s dng cp kim loi, cp si quang v thit b truyn dn radio s dng sng radio.- Thit b truyn dn thu bao: Thit b truyn dn thu bao c th s dng cp kim loi hoc radio. Cp si quang s c s dng cho cc ng thu ring v mng s lin kt a dch v (ISDN), yu cu dung lng truyn dn ln.- Cc thit b truyn dn chuyn tip:Thit b truyn dn chuyn tip s dng cc h thng cp si quang, h thng vi ba, h thng v tinh v.vTrong thit b truyn dn chuyn tip, cc tn hiu v thng tin c truyn qua mt tuyn truyn dn n vi hiu sut kinh t cao.

My pht thuMy pht thuTng iMUX &DEMUXMUX &DEMUXTngiCp quangMi trng truyn dn......Hnh 1.2. Cu hnh h thng truyn dnVi ba1.1.2. Cu trc mng phc v cho cc dch v thng tin nh thoi, s liu, fax, telex v cc dch v khc nh in thoi di ng, nhn tin, nn nc ta hin nay ngoi mng chuyn mch cng cng cn c cc mng ca mt s dch v khc. Ring mng Telex khng kt ni vi mng thoi ca VNPT, cn cc mng khc u c kt ni vo mng ca VNPT thng qua cc knh trung k hoc cc b MSU (Main Switch Unit), mt s khc li truy nhp vo mng PSTN qua cc knh thu bao bnh thng, s dng k thut DLC (Digital Loop Carrier), k thut truy nhp v tuyn...V cu trc mng, mng vin thng ca VNPT hin nay c chia thnh 3 cp: cp quc t, cp quc gia, cp ni tnh/ thnh ph.Xt v kha cnh chc nng ca cc h thng thit b trn mng th mng vin thng bao gm: Mng chuyn mch, mng truy nhp, mng truyn dn, v cc mng chc nng.a. Mng chuyn mchMng chuyn mch c 4 cp (da trn cc cp tng i chuyn mch): qu giang quc t, qu giang ng di, ni tnh v ni ht. Ring ti thnh ph H Ch Minh c thm cp qu giang ni ht.Hin nay mng ca VNPT c cc trung tm chuyn mch quc t v chuyn mch quc gia H Ni, Nng, Thnh ph H Ch Minh. Mng ca cc bu in tnh cng ang pht trin v m rng. Nhiu tnh, thnh ph xut hin cc cu trc mng vi nhiu tng i Host, cc thnh ph ln nh H Ni, Thnh ph H Ch Minh v ang trin khai cc tandem ni ht.Mng vin thng ca VNPT hin ti c chia thnh 5 cp, trong tng lai s c gim t 5 cp xung 4 cp.Mng ny do cc thnh vin ca VNPT iu hnh: l VTI, VTN v cc Bu in tnh. VTI qun l cc tng i chuyn mch qu giang quc t. VTN qun l cc tng i chuyn mch qu giang ng di ti 3 trung tm H ni, Nng v Tp H Ch Minh. Phn cn li do cc bu in tnh qun l.

Cc loi tng i c trn mng vin thng Vit Nam: A1000E10 ca Alcatel, NEAX 61 ca NEC, AXE10 ca Ercsson, EWSD ca Siemens.Cc cng ngh chuyn mch c s dng: chuyn mch knh (PSTN), X.25 relay, ATM (s liu)Nhn chung mng chuyn mch ti Vit Nam cn nhiu cp v vic iu khin b phn tn trong mng (iu khin nm ti cc tng i).b. Mng truy nhpVi tng mng cung cp dch v khc nhau m c mng truy nhp tng ng. Mng truy nhp l mng nm gia ngi s dng dch v vin thng v im dch v ca mng (tng i).Mng truy nhp hin nay gm cc loi sau:- Mng cp kim loi, cp chn, cp treo, cp cng.- Mng cp quang.- Mng v tuyn.- H thng VISAT (Very Small Aperture Terminal).c. Mng truyn dn Cc h thng thit b truyn dn trn mng vin thng ca VNPT hin nay ch yu s dng hai loi cng ngh l: cp quang SDH v vi ba PDH.- Cp quang SDH: Thit b ny do nhiu hng khc nhau cung cp l :Northern Telecom, Siemens, Fujitsu, Alcatel, Lucent, NEC, Nortel. Cc thit b c dung lng ln nh 155Mb/s, 622Mb/s, 2,5Gb/s, 10Gb/s.- Vi ba PDH: thit b ny cng c ngun gc t nhiu hng cung cp khc nhau nh Siemens, Fujitsu, Alcatel, SIS, SAT, NOKIA, AWA. Dung lng 140Mb/s, 34Mb/s, v n.2Mb/s. Cng ngh vi ba SDH c s dng hn ch vi s lng t.Mng truyn dn c 2 cp: mng truyn dn lin tnh v mng truyn dn ni tnh.* Mng truyn dn lin tnh Bao gm cc h thng truyn dn bng cp quang, bng v tuyn.Mng truyn dn lin tnh bng cp quang:Mng truyn dn ng trc quc gia ni gia H Ni v Tp H Ch Minh di 4000 km, s dng STM -16/ 2F BSHR, c chia thnh 4 vng ring ti H Tnh, Nng, Quy Nhn v thnh ph H Ch Minh.- Vng 1: H Ni H Tnh (884Km).- Vng 2: H Tnh - nng (834Km).- Vng 3: Nng Quy Nhn ( 817Km).- Vng 4: Quy Nhn Tp H Ch Minh (1424Km).Cc ng truyn dn khc: H Ni Hi Phng, H Ni Ho Bnh, Tp HCM - Vng tu, H Ni Ph L Nam nh, Nng Tam k. Cc tuyn truyn dn lin tnh ny dng STM- 4. Ring tuyn H Ni Nam nh, nng -Tam K vn cn s dng PDH, trong tng lai s thay th bng SDH.Mng truyn dn lin tnh bng v tuyn:Dng h thng vi ba SDH (STM-1, dung lng 155Mb/s: tuyn Bi Chy Hn Gai), h thng vi ba PDH (dung lng 4Mb/s, 8Mb/s, 34Mb/s, 140Mb/s) trn cc truyn khc.* Mng truyn dn ni tnh Khong 88% cc tuyn truyn dn ni tnh s dng h thng vi ba v h thng truyn dn quang.d. Mng bo hiuHin nay trn mng vin thng Vit nam s dng c hai loi bo hiu R2 v SS7. Mng bo hiu s 7 (SS7) c a vo khai thc ti Vit nam theo chin lc trin khai t trn xung di theo tiu chun ca ITU ( khai thc th nghim t nm 1995 ti VTN v VTI). Cho n nay, mng bo hiu s 7 hnh thnh vi mt cp STP (im chuyn mch bo hiu) ti 3 trung tm (H Ni, nng, H Ch Minh) ca 3 khu vc (Bc, Trung, Nam) v phc v kh hiu qu.Bo hiu cho PSTN ta c R2 v SS7, i vi mng truyn s liu qua IP c H.323, i vi ISDN c bo hiu knh D.Q.931.e. Mng ng bMng ng b ca Vit nam thc hin xy dng giai on 1 v giai on 2 vi 3 ng h ch PRC ti H Ni, Nng, thnh ph H Ch Minh v mt ng h th cp SSU. Mng ng b Vit nam hot ng theo nguyn tc ch t c d phng, bao gm 4 cp, hai loi giao din chuyn giao tn hiu ng b ch yu l 2MHz v 2Mb/s.Cc cp ca mng ng b c phn chia thnh 4 cp nh sau:1. Cp 0: cp ng h ch.2. Cp 1: cp nt quc t v nt quc gia.3. Cp 2: cp nt chuyn tip ni ht.4. Cp 3. cp nt ni ht.Mng c phn thnh 3 vng c lp, mi vng c 2 ng h mu: mt ng h chnh (Cesium) v mt ng h d phng (GPS). Cc ng h ny c t ti trung tm 3 vng v c iu chnh theo phng thc cn ng b.Cc tng i quc t v toll trong vng c iu khin bi ng h ch theo phng php ch t.Cc tng i tandem v host ti cc tnh hot ng bm theo cc tng i toll theo phng php ch t. Cc tng i huyn (RSS) cng hot ng bm theo cc host theo phng php ch t.1.2. Cc yu t nh hng n cht lng mng vin thngTrong cc h thng lin lc ta thy cc tn hiu khi nhn c c s khc bit vi tn hiu khi pht. i vi tn hiu lin tc (analog) s suy yu dn n gim cht lng ca tn hiu, vi tn hiu s, dn n lm sai s v bit. Mt bit c gi tr 1 c th tr thnh bit gi tr 0 v ngc li. Mt tn hiu trn ng truyn s chu cc nh hng sau: B suy gim v dn n mo dng. B lm chm. B nhiu. a. S lm suy gim v mo dng Khi truyn trong mi trng, cng sut ca tn hiu s suy gim. i vi mi trng nh hng s suy gim thng thng theo logarit, thng thng n l gi tr c nh theo khong cch. i vi mi trng khng nh hng s suy gim l mt hm phc tp ph thuc vo khong cch v p sut khng kh. S suy gim s dn n: Tn hiu thu c khng mnh khi phc li tn hiu ban u b phn thu. Tn hiu thu c khng ln bo m t s (t s tn hiu trn tp m) d sinh ra sai s. S suy gim s l hm ca tn s.b. S lm tr tn hiu Tn hiu truyn lan trn mi trng dn bao gi cng b lm tr. i vi mt tn hiu c bng thng gii hn, s lm tr ph thuc vo tn s ca tn hiu. Vi tn hiu c tn s khc nhau n s n b thu thi gian khc nhau. Hin tng ta gi l tn hiu b lm chm trn ng truyn, c bit vi tn hiu s hin tng lm tr cng r rng hn. c. Nhiu Khi truyn, thng thng tn hiu nhn c b thu bao gi cng bao gm tn hiu pht v mt tn hiu ta khng h mong mun c thm vo gia b pht v b thu. Tn hiu ta khng mong mun gi l nhiu. Nhiu s lm hn ch kt qu h thng lin lc ca ta. Nhiu thng c chia lm 4 loi sau: Nhiu nhit . Tp m ni b. Xuyn m. Nhiu xung. Nhiu nhit to ra do s vn chuyn in t trong vt liu, n tn ti trong tr c cc thit b in t, trong mi trng v n l hm ca nhit . Nhiu nhit c nh hng trn tt c dy tn ph nn c tn gi l nhiu trng.Nhiu nhit khng th trnh c. N c tnh:No = kTNo : nhy ngun nhiu.K : Hng s Boltzman = 1,3803 x 10-23 J/kT : Nhit KelvinNhiu cng khng ph thuc vo tn s. Do n c tnh bng watt trong ton bng thng w.N = kTWhoc tnh bng decibel - wattsN = 10logk + 10 log T + 10logW = -228,6 dbW + 10logT + 10logWNhiu do phch tn s bn trong Khi tn hiu vi cc tn s khc nhau truyn trn mi trng c th s sinh ra nhiu ni b. Kt qu ca nhiu ni b c th sinh ra tn s l cng hoc tr 2 tn hiu gc hoc l nhn ca tn hiu . V d s trn cc tn hiu c tn s f1, f2 c th sinh ra tn s f1+f2 v n s lm tng cho tn hiu tn s f1+f2 sn c.Nhiu do hin tng phch sinh ra do hin tng khng tuyn tnh trong cc thit b pht, thu, h thng truyn ... Thng h thng khng tuyn tnh, tn hiu u ra l hm phc tp ca tn hiu u vo.

Hinh 1.5. nh hng nhiu trn tn hiu s.Nhiu xuyn m Nhiu xuyn m l nhiu ta khng mong mun trong khi truyn. V d trong h thng in thoi ta c th nghe c cuc ni chuyn ca ngi khc. N sinh ra do s ghp in t gia cc cp cp xon i, hay trong cp ng trc ng thi truyn nhiu knh, cng c khi do cc ng ten vi ba to ra cc bp sng nh hng.Nhiu giao thoa gia cc k t (ISI) l mt hu qu khng th trnh khi ca c hai h thng truyn thng c dy v khng dy. Morse u tin nhn thy n trn dy cp in bo xuyn truyn ti thng ip bng cch s dng du chm v du gch ngang v t lc n khng i. N c x l bng cch lm chm li vic truyn ti.Trong nhng n lc truyn i, iu c ch l cc tn hiu nhn c c xu hng di ra v chng ln vo nhau. Mt xung ngn i din cho mt du chm nhn c ging nh nhng phin bn gm nhiu du chm ging nhau gy nho tn hiu. Vn xut hin c lin quan n cc thuc tnh ca cc phng tin c s dng v khong cch ca qu trnh truyn tn hiu. chng li tc dng khng mong mun ny, trm lp c thnh lp v cch thc c a ra gim s nho nhot tn hiu.

(b)

Hnh 1.6. (a) Tn hiu c gi i, (b) tn hiu nhn cLm th no iu ny thc s nh hng n chng ngay by gi? Hnh 1.7 cho thy mt chui d liu, 1,0,1,1,0,1 m chng ti mun gi. Trnh t ny l hnh thc xung vung. Xung vung l tt p, nhng trn thc t n rt kh to ra v cng yu cu bng thng kh ln. V vy, chng ta nh hnh nh th hin trong cc ng chm chm. Phin bn hnh c bn trng ging nh mt xung vung v chng ti nhanh chng c th cho bit nhng g c gi thm ch trc quan. Li th (ty ) hnh thnh vo thi im ny l n lm gim yu cu bng thng v thc s c th c to ra bi phn cng.

Hnh 1.7. Hnh 1.8 cho thy mi k hiu khi nhn c. Chng ta c th thy nhng g cc phng tin truyn dn to ra mt ci ui ca nng lng ko di nhiu thi gian hn d nh. Nng lng t cc k hiu 1 v 2 i tt c cc v tr k hiu 3. Mi k hiu can thip vi mt hoc nhiu trong nhng k hiu tip theo. Cc khu vc quanh khu vc nhiu ln.

Hnh 1.8. Mi k hiu nhn c b tri rng raCc tn hiu lan rng v bi nho nh vy m nng lng t mt hiu ng biu tng ca nhng ngi tip theo trong mt cch m cc tn hiu nhn c c mt xc sut cao hn c gii thch khng chnh xc c gi l Inter Symbol Interference hay ISI.Nhiu xung Nhiu xung l loi nhiu khng lin tc, khng quy lut nhiu khi n l nhng t bin bin ln, trong thi gian nh. Nhiu sinh ra do nhiu nguyn nhn khc nhau nh t bin in t trng, nh sng, tt bt h thng my ...Tuy nhin, nhiu xung l nguyn nhn trc tin gy sai s trong khi truyn tn hiu s.Hnh v 1.8 cho ta v d cch nhn tng quan v nh hng ca nhiu n tn hiu truyn.

1.3. Cc php o trong mng vin thngTrong h thng vin thng thc hin qun l mng v cht lng dch v mng i vi khch hng v mc nh hng ca cc sng tn hiu, ngi ta thc hin cc phng php o kim khc nhau. Cc qui trinh o c s dng cho cc lnh vc sau: m bo tnh nng ca h thng ph hp vi nhng khuyn ngh ph hp ca ITU-T; o th tnh ph hp ca mng; Gim st cht lng ca cc dch v cung cp; Ti u ha vic lp qui hoch mng v m rng mng; Khc phc cc ng dy b s c; Chy th nhng h thng mi lp t; Kim tra nhng ng dy mi c cu hnh; Nhng php o sc cng, nhng php o ti; Phn tch thng k; m bo truyn cc thng tin bo hiu khng b li; Phn tch cc th tc truyn thng; M phng phn ng thc t ca mng v nhng li c th khi truyn thng; Kim tra ng cp bng cc php o; Thm nh tnh chu li; Pht hin sm cc vn ca truyn thng; o th kh nng chu trt v phn ng khi c trt; Xc nh v tr xy ra s c trc khi nhng s c ny nh hng n ngi s dng; iu tra v gii quyt nhng vn v tnh tng thch; Ngc li, nhng nhim v chnh ca qun l mng l: Lp cu hnh mi cho cc phn t mng bng cch iu khin t xa; Cung cp nhanh chng cc dch v khc nhau; nh tuyn d phng t ng; Qun l cc h thng do cc nh sn xut khc nhau cung cp; Qun l cc phn t mng phn b v mt a l; Thch ng linh hot vi s thay i cc cu trc hot ng (iu hnh); Gim st cht lng cc kt n (thng k li); S dng ng cch v hiu qu dung lng mng; Ghi vo h s v cc s c.1.4 Cc quy trnh o cn dng khi no?Cc giai on hot ng khc nhau trong sut thi gian sng ca nhiu khi thit b c s dng trn cc mng s t ra cc nhu cu khc nhau v cc qui trnh o. Di y lit k tm tt nhng cng vic cn n cc qui trnh o: Cc php o th cho pht trin /tch hp/hp chun:Cc php o mc rng, tng tc gia phn cng v phn mm, cc php o th ti.Nhng yu cu v qui trnh o: Linh hot, x l cc tc bit v cc m cha c tiu chun ha v.v.., m phng v phn tch ton din, k c ti mc giao thc. Sn xut:Cc php o th bng mch, linh kin, nh gi kt qu o th thnh cng qua hay tht bi) ti mc thng lng ti a.Nhng yu cu v qui trnh o: Tc o c ti a ha, so snh nhanh cc gi tr danh nh v gi tr thc t, iu khin t xa, tch hp vo cc h thng o th t ng. Lp t:Phn tch lc u v phn tch trong thi gian di.Nhng yu cu v qui trnh o: Cc php o c thc hin khi thit b khng cung cp dch v, cc qui trnh/tin trnh o c nh trc, lu tr kt qu o, phn tch lu di, d dng s dng, c th mang i c v mnh. Khc phc s c, bo dng:Pht hin, xc nh v tr v khc phc s c, to li cu hnh, ti u ha hot ng ca mng, cc o c cht lng dch v.Nhng yu cu v qui trnh o: Cc php o khi thit b ang cung cp dch v (in-service) hoc khng cung cp dch v (out-ofservice), gim st ng dy v thuc tnh, m phng li v cc cnh bo, o c ng thi, chi ph thp v c th mang i c, mi th ch cn thong qua l bit, iu khin t xa, nh gi cht lng r rng. Sa cha/Xc nh qui m:Xc nh v tr s c mc bng mch in, m phng cc iu kin hot ng.Nhng yu cu v qui trnh o: Ti liu hng dn y , thc hin thit lp o th.

CHNG 2: O LI BIT2.1. nh ngha v cc thut nga. Li bit: L s thu sai bit do qu trnh truyn dn tn hiu s trong mng s gy rab. T l li bit(BER: Bit Error Rate): L t s gia s bit b li trn tng s bit pht i. Thng s ny c trng cho cht lng truyn dn ca tuyn.c. Li khi (EB: Error Block): L li mt hay nhiu bit trong mt khi bit. Trong , khi bit l tp hp cc bit lin tip trong mt lung vi s lng xc nh.d. Thi gian kh dng: L thi gian trong h thng c coi l c kh nng thc hin cc chc nng quy nhe. Thi gian khng kh dng: L thi gian trong h thng c coi l khng c kh nng lm vic. Khong thi gian mt giy c tnh l khong thi gian n v xem xt t l li bitf. Giy b li (ES: Errored Second): Mt giy trong khong thi gian kh dng c t l li bit nm trong khong t 0 n 10-3.g. Giy b li nghim trng(SES: Severely Errored Second): Mt giy trong khong thi gian kh dng c t l li bit ln hn 10-3 hoc c tn hiu ch th cnh bo AISh. Giy b li theo khi (BES: Block Errored Second): Trong khong thi gian mt giy c t nht mt khi b lii. Giy b li nghim trng theo khi (SBES: Severely Block Errored Second): Trong khong thi gian mt giy c nhiu hn 30% khi b li hoc c t nht mt ch th cnh bo AISj. Li khi nn (BBE: Background Block Error): Mt khi b li khng thuc trong giy li nghim trngk. T l li khi nn (BBER: Background Block Error Rate): L t s gia li khi nn v tng s khi o c trong khong thi gian kh dng.

2.2. Cc tiu chun v li bit 2.2.1. Phn b ch tiu cho knh truyn dn 64kb/sTheo khuyn ngh ITU-T-G821, nh gi cht lng mt tuyn truyn dn, ngi ta da trn m hnh tuyn s gi nh chun. Tuyn ny c di tng cng l 27500km vi thi gian o cc thng s li l mt thng.

Hnh 2.1. M hnh tuyn s gi nh chun

Ton b tuyn c phn thnh 3 cp: - Cp ni ht: l phn ca tuyn nm gia thu bao v tng i ni ht-Cp trung bnh: : l phn ca tuyn nm gia tng i ni ht v trung tm chuyn mch quc t- Cp cao: l phn ca tuyn nm gia cc trung tm chuyn mch quc t

Bng 2 m t ch tiu v giy b li (ES) v pht suy gim cht lng (DM) cho cc cp cp mch.

Bng 3 m t ch tiu v phn b li nghim trng (SES) cho cc cp mch.2.2.2. Phn b ch tiu cho m hnh on s phn cp tc 2048 kb/sTheo khuyn ngh G921 a ra m hnh on s vi cc di thc t l 50 hoc 280 km. Mt on s bao gm hai thit b u cui v mi trng truyn dn gia chng. Phn b ch tiu li cho cc on truyn dn s nh trong bng 4.

2.2.3. Tiu chun li bit cho cc lung c s hoc ln hna. Giy b li

b. Pht suy gim cht lng

c. Giy b li nghim trng (SES)T l phn trm giy b li nghim trng quy chun v u ni ti tc 64kb/s c th c tnh t php o ti tc bit cn o nh sau:SES= Y% + Z%Y: l phn giy b li nghim trng ti tc bit cn oZ: Phn giy khng b li nghim trng nhng cha mt hoc nhiu s mt ng b ti tc bit cn o2.2.4. Tiu chun li bit cho cc lung s tc caoM hnh tuyn s gi nh chun c di tng cng l 27500km vi thi gian o cc thng s li l mt thng. Cc ch tiu li cho lung s tc cao nh bng 5:

2.2.5. Xc nh li i vi cc lung s PDHa. Cc bt bnh thnga1: Mt tn hiu ng b khung b lia2: Mt khi b li (EB) c ch th bi m pht hin li (EDC)d1: Mt khung (LOF)d2: Tn hiu ch th cnh bo (AIS)d3: Mt ng b khung b. Cc thng s v tiu chun o lung PDH Cc thng s v tiu chun o lung PDH c ch th trong bng 7, bng 8:Bng 7: Ch th cc thng s tiu chun v giy b li nghim trng i vi lung PDH

Bng 8 : cc thng s v tiu chun o cc lung PDH

2.2.6. Xc nh ch tiu li i vi lung SDHa. Cc bt thnga1: Mt khi b li qua kim tra ca m pht hin li (EDC)Cc sai hng c trnh by trong bng 9Bng 9: Cc sai hng dn n SES

b. Cc thng s v tiu chun o lung SDHES: Mt giy b li quan st c khi trong mt giy t nht c mt bt bnh thng a1 hoc mt sai hng trong bng 9SES: Mt giy b li nghim trng quan st c khi trong mt giy t nht c x khi b li hoc mt sai hng trong bng 9BBE: Mt li khi nn quan st c khi mt bt bnh thng a1 xy ra trong mt khi nhng khng thuc giy b li nghim trng2.3. Nguyn nhn v nh hng ca li bt u im chnh ca truyn thng s l cht lng tryn dn khng ph thuc vo khong cch truyn thng. Theo Fourier, mi tn hiu s' u c th c m t bi mt s ln cc tn hiu hnh sin chng ln nhau. V th nhng yu t gy nhiu i vi cc tn hiu tng t nh suy hao, xuyn m hay mo v th cng tc ng n truyn dn tn hiu s (hnh 2.2).Cc yu t gy nhiu c phn loi theo loi ngun gy nhiu (cc ngun bn trong hoc bn ngoi h thng) hoc theo nh hng ca chng (li n, li kp).2.3.1 Nhng ngun gy li bn trong h thng Ngun li ch yu l: Tnh khng n nh ca ng h nhp; ng h nhp b tri; Tnh khng n nh do s lo ha ca cc linh kin; S cn bng khng ng i vi suy hao ng dy ph thuc vo tn s (chng hn trong mt b ti to);2.3.2 Mt s nguyn nhn bn ngoi gy ra nhiu Xuyn m (t cc ng dy bn cnh); Trt (tch ly) trong khi truyn dn; Nhiu in t (cc my mc, st,...); Bin ng in p ngun cung cp (chng hn do cc t st gy ra); Nhiu xung (bin nh 5 - 20 mV) ; Nhng bin ng c kh, cc mi tip xc km; S suy gim cc c tnh ca phng tin truyn dn; S c ton b h thng do ng dy b t.2.3.3 nh hng ca li bitKhi c mt in p nhiu tc ng nh th cc trng thi bit ca mt tn hiu s s khng thay i, nu tn hiu nh nh hn mt na chnh lch ca cc mc in p hin th s dn n thay i trng thi bit. Nu tn hiu gy nhiu vt qu mc ngng ny, s gy ra s suy gim ngay lp tc cht lng truyn S sai lch d ch mt bit trong mt ngn bit (t l li bit 10-3) u dn n cht lng truyn dn khng th chp nhn c i vi cc tn hiu m ha theo lut -A, l nhng tn hiu khng c nn thm. Nu vt qu mc ngng ny, t nht l h thng s khng cung cp dch v c na. i vi cc tn hiu thoi c truyn i dng tn hiu nn mc cao th h thng t l li bit cho php thp hn th nhiu (nh trong thng tin di ng).Cc li phn b ngu nhin l kt qu ca mt t s tn hiu trn nhiu km. Trong truyn dn thoi n thun, s phn b li ngu nhin c th ch lm suy gim rt t cht lng m thanh. Nhng i vi truyn thng s liu th li khc. Nu xy ra mt li, thit b u cui s dng phng thc kim tra li trong giao thc truyn thng bo cho u cng cp s liu rng khi s liu b li phi c truyn li. Vic lp li ca cc khi d liu b li c th dn n thng lng d liu thp khng th chp nhn c, lm tng thi gian v chi ph truyn dn.Hnh 2.2 Cc yu t in hnh nh hng n cht lng truyn dnVic nh gi mt cch chi tit s phn b li trn ng truyn cho php phn tch s dng cc phng php c tiu chun ha. Nhng phng php ny c cp chi tit trong phn sauVi vic s dng thng thng mt kt ni 2 Mbit/s cho 30 knh thoi s xut hin thi thong nhng ting lch tch xy ra v nhiu khng mong mun, song khng gy nhiu qu nhiu i vi kt ni ny. Nu kt ni 2 Mbit/s c s dng trong truy nhp ISDN tc s cp cho cc tn hiu thoi v s liu hoc cho truyn cc tn hiu thoi c nn mc cao trong mt h thg thng tin v tuyn, th nhng hu qu ca nhiu c th mc cao hn.Cch thc m nhiu nh hng n cht lng truyn dn c bn c xc nh bi cc tham s sau y: Loi thng tin c truyn dn: Thoi, s liu, video, a phng tin Phng thc truyn dn v kiu m ha c s dng v mc d tha trong tn hiu S li mc phi hay t l li Phn b li: cc li n hay cc chm li Ngun gy nhiu: trong h thng hay cc ngun bn ngoiT l li cho php ca phng thc truyn dn s dng (nh nhy cm vi pha, mc nn). T l li cho php ca cc h thng truyn thng (nh n nh ca ng h nhp, t l trt cho php s sai lch cho php ca nhp ng h).2.4 Nguyn l hot ng my o li bit

Hnh 2.3 Gim st ng b ca my o li bitTt c cc my o li bit u s dng cng mt nguyn l: mt dng chui bit o bit trc (chng hn mt PRBS) c so snh theo kiu bit vi bit vi mt dng chui bit so snh my thu. Nhng s khc nhau c ghi l cc li v c nh gi thm. My thu ng b vi tn hiu u vo ti thi im bt u php o. ng b, mt thanh ghi dch tham chiu c np cho n khi y lung bit tun t v mt dng chui bit so snh c to ra. Tip n my o chuyn sang o t ng. Cc dng chui bit ny c dch theo pha, dn n to ra mt s ln cc xung li. S ng b t c bng vic dng hot ng ca ng h nhp dng to ra dng chui bit so snh mi ln to ra mt xung li. C mt khong thi giani thch hp cho mt s chu k tun t.bit m bo rng trng thi ng b c th khng phi do cc li truyn dn ngu nhin to ra (hnh 2.3).Mt b m tng/gim thng c s dng gim st s ng b ny. N m ln mi ln pht hin c mt li v m xung bt c khi no khng c li xy ra. ng b c th b mt khi gi tr m c t n mt mc ngng (v d do cc cm b li).2.5 Li cm hay trt bit?Cc li truyn dn c th dng cc li n hoc cc cm li. Mt cm li c th do hin tng pha-inh ca sng mang trong truyn dn v tuyn gy ra hoc do nhiu in t ngn (nh chuyn mch) gy ra.Cc nguyn nhn gy li khc, nh trn b m trong tng i s hay cc vn v ng h nhp ti cc thit b cng c th dn n mt i nhng on nht nh ca dng bit hon chnh hoc cc trng thi bit c truyn i hai ln. Vic trt bit dn n mt s dch pha gia cc dng chui bit pht i v thu c theo quan im ca my o li bit.2.6 My o li bit phn ng li nh th no?Nu xy ra mt s dch pha gia cc dng chui bit thu c v tham chiu, s cc li bit o c s l v hn. V trong trng hp ny, mt trng thi ko di (cm li) b ly ra bi mt li n (trt bit), nn php o phi c ngng li v my o li bit phi thc hin ng b li.Tuy nhin mt li chm c th b gy ra bi mt tnh hung dn ti mt s ln cc li bit xy ra trong mt thi gian ngn (v d do tip xc km).Trong cc phng php gim st ng b hay dng c nhc im l mt li chm xut hin s dn ti mt ng b. Thit b o khng th xc nh c liu cc xung li ti u ra ca b so snh c phi l kt qu ca nhng li bit thc hay do mt s dch pha gy ra. V l do ny nhiu thit b o b mt ng b khi li t n mc ngng (chng hn 30%). Qui trnh ny lm sai lch ng k kt qu o, v s cc li bit c xc nh khng ng v nguyn nhn gy ra cc li ny cng khng c pht hin.Mt gii php cho vn phn bit gia vic trt bit v li chm c mt s t cc nh sn xut cc thit b a ra. Gii php ny da trn vic thm vo hai chui gi ngu nhin c dch pha lin quan vi nhau to ra mt chui gi ngu nhin khc. Vic trin khai gii php ny trn thc t c trnh by trong hnh 2.4. Tn hiu ra khi b so snh (2) s chnh l mt PRBS nu c mt s dch pha gia chui thu c v chui tham chiu. Thanh ghi (3) c np lin tc trong khi o v cho php phn bit hai tnh hung: C hai dng chui (chui thu c v chui tham chiu) ging ht nhau nhng dch pha so vi nhau: Cc li bit thc l khng c, m xy ra mt s trt bit. C hai dng chui cng pha nhau, c cc li bit thc.Trong trng hp u, mt s trt bit c pht hin v c nh gi. Khi xy ra li cm, ng b c duy tr nh trong trng hp tn hiu b ngt qung trong thi gian ngn (cc ngt v cng nh). Vic gim st ng b c bit ny m bo rng kt qu thu c cui php o l s cc li thc, v n khng b nh hng bi thit b o. N cn a ra nhng kt lun v nguyn nhn gy li. y l mt u im v n lm n gin vic tm nguyn nhn ca li.Nu mt cnh bo (v d cnh bo mt tn hiu) xy ra trong khi ang o, mt s ln cc li thm vo s c m cho n khi trng thi cnh bo c thit b o khng ch. Nhng li bit thm vo ny c th lm cho cht lng ng truyn km i, trong khi trn thc t th ng truyn li khng c li g c.Qui trnh o ng n s phi t ng loi b, nhng li bit thm vo do mt cnh bo gy ra trong kt qa o, m iu ny c th c thc hin nu bit c thi gian phn ng ca kh pht hin nguyn nhn cho tng tc bit.S khi c n gin ha m t hai pha pht v thu ca mt my o 2 Mbit/s. Dng thc o c to ra s dng mt thanh ghi dch c phn b trn n khe thi gian c th chn la (n = 1 n 31), trong khi nhng khe thi gian cn li c in vo mt tn hiu knh ri. Thng tin bo hiu (khe thi gian 16) v thng tin ng b v gim st li (khe thi gian 0) c thm vo. Mt chip m ha bin i m NRZ thnh m ng dy HDB-3. Tn hiu u vo l tn hiu c th b suyhao mt 40 dB, trc tin c khuch i v c ti to li trong khi thu. Sau khi bin i thnh m NRZ, im bt u khung tn hiu (khe thi gian 0), khe thi gian 16 v cc knh thng tin ca ngi s dng cha mu o c tch ra v c gim st ring r pht hin li v cc cnh bo. Thng tin bo hiu c ghi li v c dch ra. Mt khe thi gian c la chn c th c a n mt b bin i D - A, cho php gim st t m thc v vic nh gi cht lng truyn dn v mt m thanh. Hai khi u vo c thc hin trong cc my o 2 Mbit/s, l nhng my o c th gim st c hai hung truyn dn.

Hnh 2.4 S khi my o lung 2Mb/sDo thng khng th bit trc c nhng tnh hung s c no c kh nng xy ra, b thit b o cn phi c kh nng bt c tt c cc li v cc cnh bo ng thi. Nhng khng phi thit b o no cng p ng c yu cu ny Vic chn v tr o nh hng trc tip n tn hiu th (o) yu cu. Mt chui bit qui nh khng c bt k cu trc khung no l cho ng dng trnh by trong hnh 2.4. Vic thit lp ban u cc ng truyn thng 2 Mbit/s c th c thc hin bng vic s dng hoc khng s dng mt mch vng u xaTiu chun cht lng hin nay l i vi cc kt ni 2 Mbit/s, t l li bit nh hn 10-6. c c cht lng tt hn, chng hn mt kt ni c t l li bit c bo m mc tt hn 10-7, ta phi tr mt gi cao hn nhiu.2.5. Phng php o li bit C th s dng cc phng php o c bn sau: H thng/ng truyn ngng cung cp dch v: S dng cc php o v khc phc s c ng dy trn cc b ghp knh hoc cc thit b ng dy. H thng/ng truyn ang cung cp dch v: S dng kim tra nhm xc nh v tr li v xc nh hiu nng hot ng ca h thng/ng truyn trong thi gian di.

Hnh 2.3. Cc phng php o kim tra li bit trn h thngVic so snh tng bit gia tn hiu thu v tn hiu pht ch c th thc hin c khi h thng ngng cung cp dch v. i vi cc php o trong khi h thng ang hot ng, cc kt lun v cc li trong phn cn li ca lung d liu c suy ra t biu hin ca cc tin trnh tng b phn trong lung d liu .C th kt hp hai phng thc o ny bng cch t trc mt phn dung lng knh cho mc ch o c. Cc php o khi h thng ngng cung cp dch v c th c thc hin s dng bt k phng thc no trong ba phng thc trnh by trong hnh

Hnh 2.4 Cc nguyn l o cho cc phn t ca h thng v ng truyn

Hnh 2.5. S o li bit lung 2Mb/s trong iu kin h thng ang khai thc

Hnh 2.6. S o li bit lung 2Mb/s t u cui ti u cui trong iu kin h thng ngng khai thc

Hnh 2.6. S o li bit trong trng hp u vng2.4.1. Cc php o lung 2Mb/s khi ang cung cp dch vCc php o s dng cc dng chui bit o bit b hn ch rt mnh khi h thng ang cung cp dch v. Thc t cng c th rt kh u ni vt l my o vi ng dy hoc phn t cn o hoc nhn c mt bin tn hiu cao mt khi kt ni c thc hin.iu ny c th do nhng nguyn nhn sau: Cc tn hiu b mo v b suy hao mnh: Vn y l vic chn im o khng ph hp (chng hn ngay trc b ti to tn hiu - regenerator) hoc cc ng cp o di ni ti my o. Suy hao trn ng dy ph thuc tn s l mt vn ch yu dn ti my o khng c kh nng ti to c tn hiu. V vy s cn bng tn hiu y l rt quan trng. S l rt hay nu my phn tch c s dng c th cung cp s cn bng trn ng dy mt cch t ng. Truyn thng quang: Mt b chia cng sut quang c th c cung cp h tr trong nhng trng hp sau: tn hiu c cp qua b chia v mt mt phn nh c trch ra thc hin php o.Nhc im: Knh truyn phi b ngt trong mt khong thi gianngn a b chia vo. Mt cch khc l c th s dng thm mt b bin i quang in. Cc in p ngun cp cho b ti to c t ln trn cng: c bit, vi s c mt trn th trng ca nhng thit b u ni r tin dng cch ly u vo ca my o khi cc in p cao. Nu bin tn hiu ln, mt gii php n gin l s dng mt my o thm d. Nu c th, v l do an ton, php o s c thc hin ti hoc ngay trc thit b kt cui ng dy (LTE: Line Terminating Equipment).Khng c im gim st trn phn t cn o: Hu ht cc nh sn xut u lm cho cc thit b ghp knh ca h va kht vi cc im gim st c bo v cung cp mt tn hiu o c cch ly khi tn hiu ng dy v c lm suy hao i 20 dB. Nu khng c im gim st no, mt im gim st nhn to c th c to ra vi s tr gip ca mt b bin i nh c chc nng tch v lm suy hao tn hi.Cc php o trong khi ang cung cp dch v phi c tin hnh theo cch thc sao cho tn hiu c o khng b nh hng theo bt k cch no bi thit b o2.4.1.1 Cc php o li trn tn hiu ng chnh khungPhn c nh ca tn hiu ng chnh khung di 7 bit (bit u dnh cho so snh CRC) v c truyn i cc khung th hai. Cc php o ny p dng cho mt dung lng truyn dn l 28 kbit/s. Nu cc php o li c thc hin trn tn hiu ng chnh khung, li c th c pht hin m khng cn t trc thm dung lng truyn dn cho php o, cho d tng li thnh phn trong cc knh ca ngi s dng khng c pht hin. Tuy nhin, nhng nguyn nhn gy li in hnh, nh tip xc km; hay ngun cung cp khng n nh, thng c mt trong t nht vi mini giy, v vy tn hiu ng chnh khung cng c nhiu kh nng b nh hng. V l do ny, khng th rt ra nhng kt lun trc tip v t l li ca mt knh 64 kbit/s t vic bit c t l li ca FAS.Chc nng gim st li ca h thng s phn ng khi t l li ca FAS vt qu gi tr ngng qui nh (chng hn 10-6 hoc 10-3).2.4.1.2 Phn tch li CRC v cc li bit EMt my o c th d dng pht hin c CRC n gin bng cch kim tra tng kim tra CRC. Tuy nhin php o ny khng cho bit c bao nhiu li CRC c mt khi mt s c xy ra. My o gi nh rng mt li truyn dn xy ra trong mi khi kim tra b li. Nu c nhiu li xy ra, c mt c may nh l mt s t hp nht nh ca cc li s tr li mt tng kim tra ng.Khi o cc li CRC, cng cn lu rng mt s phn t h thng c th khng trong sut i vi CRC. iu ny c th dn ti tnh hung khng th o c cc li CRC cho d ng truyn b li nghim trng, v c th dn ti nhng kt lun sai v biu hin ca ton b h thng.Cc bit E cung cp thng tin v nhng s c trn ng tr v. Nu c mt li CRC c pht hin trn ng truyn i, bit E c thit lp trn ng tr v trong khong thi gian ca mt a khung CRC. iu ny c ngha l thng tin v ng tr v c th thu c t mt im o duy nht c nh l ch mt tn hiu 2 Mbit/s c gim st.2.4.1.3 Gim st cc li mu im ch yu ca vic gim st nhng li m l ch cc li truyn dn c th c pht hin theo cch ny m khng cn bit cu trc khung ca tn hiu hoc ni dung d liu ca ngi s dng. Tnh d tha c hu trong m c s dng pht hin li cho ton b tn hiu. Nhc im ca vic gim st ny l ch vic gim st li ch c th trn mt on ng truyn trong sut i vi m tn hiu v khng lin quan n vic m ha tn hiu. Trn thc t, vn ny thng khng c ch ti hoc b b qua.Cc li m xy ra khi mt s c trn ng truyn dn lm mo tn hiu c m ha hoc do bn thn b m ha b s c' (trng hp ny him xy ra hn). Cc li m thiig dn ti cc li bit, ty thuc vo loi li v loi m c s dng. Nh chng ta thy, cc quyt nh ca b gi m i vi mt s'm ng dy ph thuc vo trng thi ca s qu bit trc (v d 3 bit cui cng trong m ng dy HDB-3). Nu mt trong nhng s qu ny b sai trong khi truyn dn, n c th dn ti nhng li khng mong mun ngoi li bit thc c pht hin (hin tng nhn li)S ti to ra cc li gy bi cc li phn b mt cch ngu nhin cn c lu n khi s dng mt my o to ra cc li bit v phn tch cc li m.

Hnh 2.7 ti to cc li m trong mt tn hiu c m ho HDB32.4.1.4 nh gi cc cnh bo v cc s c truyn dnH thng t pht hin nhng cnh bo v nhng s c ln v hot ng ca n trong khi ang hot ng v gi nhng thng tin ny ti h thng qun l mng hoc bo cho nhn vin iu hnh bit c s c xy ra bng cc tn hiu cnh bo quang hoc m thanh.Cc qui trnh o nh gi cht lng v pht hin li ch yu s dng tn hiu ng chnh khung, CRC v cc li mPhn tch d liu ca ngi s dngMy o phi c kh nng pht hin v nh gi cc giao thc mng c truyn i trong cc khe thi giann x 64 kbit/s. Vic m s cc khi lp li c th c s dng xc nh thng lng d liu. Ngun gy li thng c th c xc nh t loi li xy ra trong giao thc truyn dn. Theo cch ny, nhng li c tnh h thng trong nhiu trng hp c th c o theo n tn nhng thit lp khng ng i vi cc thit b u cui.

Hnh 2.8 Nhng tnh hung li v cnh bo quan trngCc bn tin cnh bo: AIS cnh bo khn Cp/cnh bo khng khn cpMt AIS l c th xy ra khi mt tn hiu ton bit "1" trn ng dy hoc trong mt khung tn hiu. Tn hiu ng chnh khung ca mt AIS c phn khung l ng, nhng tt c cc khe thi gian khc c thit lp l mt tn hiu ton bit "1". Bn tin cnh bo AIS c th hin th ngun gy li. Trong trng ny, c mt s c pha u vo ca b ghp knh (cc lung thnh phn i vo b ghp knh). Mt AIS khng phn khung c truyn i nu b ghp knh khng nhn c bt k khung tn hiu no t u xa.Cc bn tin li bit SAVic s dng cc bit SA c gii thch chi tit trong mc sau. ngha ca cc t hp bit SA theo qui nh ca tng nc. iu ny cn c ghi nh khi gim st lu lng quc t. Cc bit SA i khi cng c s dng truyn i cc giao thc bo hiu tc 4 kbit/s. sai lch tn s tn hiuPhp o ny ch c ngha nu ngun ng h nhp bn trong ca thit b o n nh hn nhiu so vi ngun ng h nhp ca cc phn t h thng. Trn thc t, gi tr chnh xc ca nhp ng h ca c hai u c cp s' m (cc ng h thch anh), sao cho vic o tc bit nhn c ch cho nhng kt qu c ngha khi sai lch tn s tn hiu l cc ln. Tnh hung s khc i nu my o c trang b hai b thu 2 Mbit/s v c th o khc nhau gia cc ng h hng i v hng tr v. Nhng sai lch nhp ng h qu ln dn ti trn b m, gy ra hin tng trt bit.Cc dch pha ca cc chui bit o (trt bit)Trt bit xy ra khi mt hai nhiu bit thng tin b lp li hoc b ri trong khi truyn dn. Cc vn v nh thi xy ra khi cc mng ca cc nh cung cp khc nhau c n vi nhau l nguyn nhn chnh gy ra trt bit. Vic pht hin s trt bt i hi mt knh ri c th c in vo mt chui bt o. Gim st cc t m nh (truyn dn thoai)Phn b b m, c ngha l phn khc nhau gia cc t m nh dng v m, cn xp x bng khng. Nhng sai lch ln c th biu th trng thi bo ha hoc cc vn khc v mc tn hiu.2.4.1.5 Cc v d v vic gim st li khi h thng ang cung cp dch vMt ngi s dng truyn d liu tc 64 kbit/s trn mt ng dy thu ring 2 Mbit/s phn nn v thi gian p ng cho kt ni qu lu.Cu hi u tin cn c tr li l: Ch c ngi s dng b nh hng hay nhng ngi khc cng b nhng c th v h kin nhn hn hoc t hn nn h cha phn nn? cn phi lm s c l xy ra do ngn hn hoc n ch xy ra nhng thi im c th. S c ny c th do cc giao din hoc do vic trin khai khng ng cc giao thc truyn thng ti thit b u cui ca ngi s dng.Vic gim st ng thi FAS v tng kim tra CRC trn c hai hng cho ta mt s khng nh chc chn rng s c do nhiu bn ngoi gy ra: Li xy ra ti cng thi im v vi cng tn s trn c hai hng. Do cc li FAS cng c mt, nn c nhiu kh nng cc knh 64 kbit/s khc cng b nh hng.

Hnh 2.9 Gim st phn b ca b m hoTrong v d ny, mt php o ko di vi gi c tin hnh v cc kt qu c hin th dng biu . Chc nng phng to - thu nh (zoom) cho php phn tch chi tit s phn b li trong khong thi gian vi giy. V d ny cho thy r rng rng cc li xy ra theo kiu dn cm, ch yu trong gi hnh chnh bnh thng. Nhiu t mc cao nht vo lc bt u ngy lm vic. Cc trng nhiu in t b nghi l th phm. iu ny c xc nhn: mt cp truyn dn di trong dy ko ca mt thang my b trt ra khi ray dn cp.Ngi s dng mt mng dng ring phn nn rng, cc tn hiu d liu s c mt PBX truyn i ng nhng cc kt ni thoi trn chnh PBX lin tc c s c.Hai t m v phn b ca b m ha t m s c gim st bng mt my o c kh nng gii m cc tn hiu ting ni c s ha cc khe thi gian c chn la. Kt qu l r rng: Gi tr b ca b m ha qu cao (hnh 2.9). Nguyn nhn nhanh chng c pht hin: B m ha trn card tng t b qu ti. Vn ny c th c loi b bng cch so snh ph hp mc tn hiu (s dng mt in tr kt cui).2.4.1.6 Cc php o tch v chnC nhiu vn truyn thng khng th gii quyt c khi s dng cc phng php o trnh by, hoc c th ch c gii quyt phn no vi rt nhiu n lc v thi gian. Vic kim tra cht lng truyn dn tha thun gia nh cung cp mng v ngi s dng l vn quan trng, c bit vi nhng ng dy thu ring 2 Mbit/s.L do l v nh cung cp mng lp t mt phn t h thng (NTPM: Network Termination Primary Multiplexer - B ghp knh s cp kt cui mng) c th hin th r rng bt k li no pha ngi s dng (cc bit Sa) nhng n ch cung cp thng tin rt hn ch v ng tr v (t mng n ngi s dng). Thm ch nu cc s c xc nh xy ra trn ng tryn, dn ti cc li FAS v CRC, th vic to li phn mo u ca khung truyn dn c ngha l c mt tn hiu khng b li khe thi gian 0 u ra pha ngi s dng ca kt cu mng (NT). Cc NT l trong sut v mt bit i vi tt c cc khe thi gian t khe s 0. Trong nhng trng hp ngoi l, khe thi gian 0 c th cng c truyn i trong sut qua NT bng cch thit lp li mt b chuyn mch, cho php gim st tn hiu. Cc nh cung cp mng thng khng cho php ngi s dng thc hin vic ny.Lm th no mt ngi s dng thay v thc hin vic nu trn m tin hnh xc nh xem trong kh hot ng bnh thng liu cc s c c xy ra pha mng hay khng? Kh nng duy nht l thc hin mt php o s dng cc knh ri trong mt kt ni. Php o ny c trnh by trong hnh 2.10, c chn in vo cc knh ri ca mt kt ni cc chui bit o. ch tch v chn, my o tch hoc trch ra nhng ni dung ca mt hoc mt s khe thi gian (n X 64 kbit/s) c chn v chn vo mt chui bit o c chn vo ch cng khe hoc nhng khe c tch ra. iu ny cho php trnh by mt cch c th cht lng truyn dn ca mt knh n pha 2 Mbit/s, bt k cc phn t h thng c lp t c truyn khe thi gian trong sut hay khng hay n c to ra trn c hai hng truyn dn Nhc im ca php o ny l kt ni phi c ngt trong thi gian ngn chn thit b o vo v ch kt ni s b mt nu my o hng.Kiu o ny cn c gi l ch tch v chn. N biu th c mt gp nhau gia cc php o trong khi h thng ang cung cp dch v v cc php o khi h thng khng cung cp dch v. Ch tch v chn c nhng u im ni bt so vi vic s dng cc tn hiu o nhn to hon ton c my o to ra, c bit trong nhng tnh hung xy ra nhng vn rc ri. Mt s m phng chnh xc cc iu kin hot ng thc l c th thc hin c nu my o c th m phng cc cm li hoc cc li n lp li mt cch c th trong mt knh c chn (n = 1 + 31) trong ch thng. Nu my o c mt u vo ring chn li, mt b to tp m c th c ni vi n m phng cc li phn b ngu nhin.Kiu o ny cn c th c s dng nh l mt s thay th tm thi nu khng c cc m-un ca b ghp knh dng cc card tn hiu s ring r. Bn thn my o cung cp giao din d liu v chn d liu o vo mt hoc mt s khe thi gian c chn (trong trng hp n X 64 kbit/s).

Hnh 2.10 Phn tch tn hiu trong ch truyn qua2.4.2. Cc php o khi h thng khng cung cp dch v tc 2 Mb/s2.4.2.1 o cc thit b ghp knhNu vic khc phc s c cho thy rng c mt phn t ca h thng lin quan n tuyn truyn dn c th l nguyn ngn gy ra s c, th cc php o trc tip trn bn thn thnh phn h thng l cn thit.

Hnh 2.11 o mc knh sPhp o cc b ghp knh bao gm nhng ng dng sau: Thit b o c ni vi pha u vo ca b ghp knh. y ch cn s dng mt php o vi cc tn hiu khng cu trc khung. Mt mch vng c to nn ti pha u ra ca thit b ghp knh. Thit b o c ni vi pha u ra ca b ghp knh. Mt mch vng c to nn pha vo ca b ghp knh. Cc php o mch vng c thc hin t pha 2 Mbit/s (pha u ra ca b ghp knh) lun yu cu mt tn hiu c cu trc khung. Mt s thit b c o (nh NTPM) yu cu cc tn hiu c cu trc khung pha u vo cng nh pha u ra ca b ghp knh. Thit b o thc hin mt php o na knh s (digital). u ra ca thit b o m phng lung hoc u ra ca b ghp knh, ty thuc vo cch n c u ni nh th no. ng dng ny cung cp phng tin cho vic o hot ng ca cc card giao din c s dng ni vi mng truyn dn.2.4.2.2 Cc php o s dng cc tn hiu n X 64 kbit/sMt ng dng u ni ban u (line-up) tn hiu phn khung in hnh cho mt b ghp knh s cp kt cui mng (NTPM) c trnh by trong hnh 2.12. y thit b o pht i v phn tch mt chui bit gi ngu nhin (PRBS: Pseudo Random Bit Sequence) c phn b trn tt c cc khe thi gian(n X 64 kbit/s). y l mt s m phng thc t ca mt tn hiu 2 Mbit/s vi tt c cc khe thi gian u c nhi cc bit.

Hnh 2.12 u ni thit b o trn mng

Hnh 2.13 Cc php o s dng tn hiu n x 64Kb/sHnh 2.13 trnh by vic thip lp u ni ban u mt giao din b ghp knh n X 64 kbit/s (n = 3). Loi truy nhp tc ca ny c yu cu cho nhng thit b u cui c th hot ng c cc tc bit n X 64 kbit/s. Cc knh n X 64 kbit/s thng khng c b ghp knh phn b cc khe thi gian k tip nhau, v vy thit b o phi chn li v loi b nhng khong cch gia cc khe thi gian trong khung 2 Mbit/s (bng mt b cha m) v lp rp li cc on n X 8 bit thnh mt tn hiu o lin tc.Nhng kt qu tin cy m hu nh c gi tr thng tin nh nhng kt qu thu c t mt php o li bit thc c th thu c bng cch phn tch ng thi chui PRBS, tn hiu ng chnh khung (FAS), tn hiu ng chnh khng khung (NFAS) v php kim tra tng CRC (Cyclic Redundancy Check: Kim tra d tha theo chu k).Php o trc tip vi cc knh n X 64 kbit/s (n = 1 + 31) cng cn cho vic u ni ban u cc lung d liu thnh phn (cc lung i vo b ghp knh) nh my tnh, video, in thoi thy hnh, pht thanh v tuyn s vi dung lng t 64 kbit/s (n = 1) cho n 1984 kbit/s (n = 31).2.4.2.3 Kim tra kh nng chu ng ca h thng i vi s sai lch ca nhp ng hMt h thng truyn thng 2 Mbit/s vn phi hot ng ng khi nhp ng h sai lch ti 50 10-6. Cc nh sn xut o kim cc sn phm ca h nhng gi tr cn cao hn na, bi v s lo ha ca thit b v nhng khim khuyt ca vic u ni dy c th dn n gim cc gi tr ti a v kh nng chu ng ca h thng.

Hnh 2.14 o kim phn thu ca mt b ghp knhMt v d thc t: Sau khi c nhng phn nn t mt s khch hng, nh cung cp tin hnh o kim mt kt ni 2 Mbit/s. ng truyn dn biu th mt s phn b,li mc cao lin tc. Mt phn t ca h thng b nghi ng l nguyn nhn gy li cho ng truyn v ng truyn b li b ngng cung cp dch v. ng dng trnh by trong hnh 2.14 cho php o nhng chc nng quan trng nht ca b ghp knh. Trong v d ny, ta s nhanh chng nhn thy khi tc bit truyn dn ca thit b o c b bng cc bc 1 ppm cho n khi b ghp knh khng cn hot ng ng na v b mt ng b nhng sai lch rt nh so vi tc bit danh nh. B ghp knh hng ny c thay th v gi tr li nh sn xut sa cha cng vi h s cc kt qu m my o cung cp.Cc b cm bin cnh bo lp trong thit b ghp knh cng c th c kim tra d dng theo kiu ny. B ghp knh s mt ng b nu c nhiu hn ba tn hiu ng chnh khung lin tip hoc c hn 913 php so snh CRC trong mt giy l khng ng. kim tra chc nng ny, PDH m phng cc t FAS v CRC bit li dng cc cm li (FAS) hoc bng mt s c th thay i cc li trong mt giy (CRC).2.4.2.4 o tr tn hiuCht lng ca truyn dn tn hiu s' bng v tuyn hoc v tinh cng c qui nh bi tr truyn lan ca tn hiu. Nhng khuyn ngh ca ITU-T qui nh cc gi tr ti a i vi tr tn hiu. Tr tn hiu gy bi cc tng i chuyn mch s v cc thit b ni cho c th dn ti nhng mc tr tch lu cao khng th chp nhn c khi vic nh tuyn ng truyn khng ph hp.

Hnh 2.15 Php o thi gian trCc php o tr c thc hin s dng mt chui bit gi ngu nhin (PRBS). Phn to tn hiu ca thit b o gi mt xung ti phn thu ca my o khi c mt chui bit o xc nh (chng hn chui di nht cc bit 0) c truyn i. B thu (ca my o) gim st chui PRBS n. B thu ny cng to ra mt xung khng pht hin ra chui bit xc nh trong tn hiu n. Tr tn hiu c tnh ra t s khc nhau v thi gian gia hai xung ny.Nhc im ca php o ny l thi gian tr ca h thng c th di hn khong thi gian (chu k) ca chui bit s dng cho php o. V vy ta nn thc hin mt d on bng l thuyt thi gian tr c th xy ra v chn di ca chui bit o tng ng, nu khng cc kt qu thu c c th khng r rng khi o c thi gian tr di. phn gii biu th kt ca php o tr cn t nht mc mt micr giy. Tc bit cng cao, khong thi gian(chu k) ca mt chui bit o cho trc cng ngn, sao cho thi giantr ti a c th o c gim xung cc tc bit cao.Nguyn l o c gii thch trong hnh 2.15. Tr ch c th o c vi phng php ny khi thit lp mt mch vng ti u xa ca ng truyn. Thi gian tr c th xc nh c bng cch khc nh vic ng b mt cch chnh xc hai my o cch xa nhau. Vic ny c th c thc hin bng cch s dng h thng nh v ton cu (GPS: Global Positioning System) bng v tinh, l h thng cung cp thng tin nh thi c chnh xe cao dng m ha.2.4.2.5 S dng tn hiu ng chnh khng khung (cc bit SA) gim st liCc nh cung cp mng cnh tranh nhau ch xoay quanh s tranh ci lin quan n vic nh cung cp mng no chu trch nhim trong trng hp c s c mng v ai c bn phn cho nhng tn tht do s c" v truyn thng mng gy ra. Vic s dng cc bit SA hin th li cho php lm r nhng vn ny, bng cch thit lp cc mch vng o v bng vic gim tn hiu n. Cc bit SA gip cho ngi k s nhanh chng lm r mt bn tin bo li v xc nh c v tr a l ni xy ra s c.Nh cp n phn bn v cc nguyn l c bn, cc bit SA c s dng mt cu trc theo phng thng ng trong cc NFAS k tip nhau. Chng c tc 4 kbit/s v cho php thc hin cc chc nng o v nh v li gia cc tng i chuyn mch v cc thit b u cui. ngha ca bit ny ty thuc vo hng truyn v c trnh by trong bng 2.1.Bng 2.1 M ho cc bit SA

Mt tiu chun ETSI c pht hnh nm 1995 (ETS 300233) qui nh vic s dng cc tnh nng ca bit SA trong vic khc phc s c v kim tra nhng truy cp b ghp knh s cp. Vic s dng cc bit SA cho php cnh bo tnh trng thc ca s c kt cui mng v thc hin u chuyn cc mch vng o. Sau nhn vin dch v c th tn dng nhng nh gi v trng thi li tm ra trong tng i s2.4.3 Cc php o trong mng SDHGim st li trong cc phn t SDH c ci thin rt nhiu so vi PDH. V vy cc thit b c s dng ch yu trong khi lp t, chy th v khc phc s c hn l dng gim st trong khi h thng ang cung cp dch v. iu ny dn ti s phn loi cc nhim v o kim cho lp t v khc phc s c nh sau:o kim tnh nng: Cc php o thit b cng: Truyn i cc tn hiu cn ng b (ng b) v phn tch cc tn hiu u ra ng b (cn ng b); Trin khai cc bin th nh x khc nhau; o kim m bo cc chc nng phn knh v nh x ca cc giao din ni cho hot ng ng.o kim cc b cm bin pht hin li c lp sn trong my: Cc phng tin m phng v phn tch li truyn dn, cnh bo v cc s c tnh nng; Truy cp o li v phn tch giao thc i vi cc knh truyn dn dng cho gim st h thng v iu khin nt mng; Gim st hiu nng hot ng ca h thng.o th kim tra s ng b v nh thi ca mng Phn tch trt v tri nh gi hot ng ca con tr.Di y l mt s phng php truy nhp vo tn hiu cn o trong khi iu hnh h thng:u ni vi cc im gim st cc c tnh in: cc tn hiu thng b suy hao 20 dB. Nhiu nh sn xut b qua c im ny v th ngi khc khng th gim st c mch.Cc php o s dng my phn tch SDH ch thng mch vng: My o cho tn hiu in hoc tn hiu quang i qua m khng b thay i g, gim st li v cc bn tin bo li. Nhc im: Trc tin phi ngt mch ni my phn tch v tn hiu ca h thng s b nh hng khi mv phn tch hot ng khng chun.S dng mt b chia cng sut quang: B chia quang ly ra mt phn nh cng sut tn hiu quang, phn cn li c cho qua m khng b thay i g. u im: Hot ng khng chun hay s c ca my phn tch khng nh hng n tn hiu ca h thng. Trc tin mch phi c ngt ra chn b chia cng sut quang vo. S l tt hn nu b chia cng sut quang l mt b phn ca my o c s dng.Chc nng l b phn b ca mt thit b ni cho c th c s dng chuyn mt bn sao ca tn hiu cn qua ti u ra ca mt card giao din cha s dng trong thit b ni cho ny my o SDH c th ni trc tip vi n.2.4.3.1 Cu trc thit b o SDHHnh 2.16 trnh by cu trc c bn ca mt my o SDH c trang b cc chc nng. Vic trin khai ng thi cc chc nng SDH, SONET v ATM m bo rng my o c th lin tc theo kp s pht trin ca mng li. Vic bao gm c hai chun PDH (tiu chun chu u 2/8/34/140 Mbit/s v tiu chun Bc M 1,5/6/45 Mbit/s) v cc qui trnh nh x tng ng cho php thc hin cc php o trn nhng kt ni quc t v cho php s dng c my o bt c u trn th gii. y l yu t quan trng i vi nhng nc s dng cc h thng pha trn ca nhiu chun truyn dn, hoc cc b phn pht trin, tch hp, sn xut v dch v ca cc nh sn xut thit b vin thng quc t.Kinh nghim thu c vi vic trin khai cc h thng SDH ban u ch ra rng trong nhiu trng hdp vic khi ng v o th cc giao din STM-4 v STM-16 bng cch ni vng tr v v o pha STM-1 l khng . Nhiu nh cung cp mng yu cu c nhng bng chng bng o c m bo hot ng ca STM l khng c vn g. My phn tch cn phi da trn cc nguyn l iu khin v x l tiu chun v iu ny to cho ta nhng u im to ln trong vic n gin ha cc qui trnh vn hnh v x l kt qu o. Nu b thit b my o c km theo mt my tnh c nhn, th c th chy cc qui trnh o th t ng v c th iu khin c thm nhng thit b khc nh cc my qut im o nh s dng cc phm mm iu khin thit b tiu chun (nh LabWindows).Cc phng tin iu khin t xa hin c chun trn th trng. Nu b thit b o bao gm mt my tnh c nhn (PC) th c th thc hin c nhng chc nng b sung nh s dng cc card PCMCIA, chng hn iu khin qua ISDN hoc kt hp vi mt mng LAN trong mi trng sn xut.

Hnh 2.16 Cu trc my o SDH2.4.3.2 Phn tch nh xS trnh by trong hnh 2.17 l o kim chc nng nh x ca SDH (v d C-12, C-3, C-4 tng ng vi cc tc 2, 34 v 140 Mbit/s).My o gi i mt tn hiu 2, 34 hoc 140 Mbit/s v phn tch tn hiu ny t tn hiu ra STM-1 ca thit b ni cho. thc hin php o na knh ny, my phn tch phi gi i mt tn hiu phn khung hoc khng phn khung ty thuc vo cu hnh card cng. Trong trng hp nh x khng ng b cc tn hiu 2 Mbit/s, vic b tn s ca tn hiu 2 Mbit/s dn n s nhi bit b thay i trong cng-ten-n. Cc bit ng b sp xp vo cng-ten-n p li vic b trong tn hiu 2 Mbit/s thnh phn bng nhng di chuyn ca con tr. My phn tch s dng s so snh chui bit o o li bit trong phn t tin chui bit gi ngu nhin (PRBS) v nh gi nhng di chuyn ca con tr ca TU-12 v AU-4. ng thi, thng tin v tnh chn l (cn bng), xc nhn li, cnh bo v phn b cng-ten-n cha trong phn mo u ca cc cng-ten-n VC-3/4 v VC-12 (byte V5) cng c phn tch

Hnh 2.17 S o phn tch nh x (C12, C3, C4)Trong s trnh by trn, phn t mng p ng bng cc bn tin cnh bo nu khng c tn hiu ti u vo A trong khi o na knh t B n C. V vy my phn tch cn cung cp mt tn hiu ra th hai. Thng s l nu cc giao in in v quang ca my o cng hot ng. Mt u vo/ra bn ngoi t vo my o cho php bt k mt tn hiu 2 Mbit/s no u c chn vo hoc tch ra m-un truyn ti ng b (STM) ny2.4.3.3 Khi ng cc giao din cngLm th no c th bit c cc giao din cng 2 Mbit/s c c u n ng hay khng? Trong s hnh 2.18, cc mch vng bn trong c thit lp tt c cc giao din u vo 2 Mbit/s ca nt mng bng mt lnh chuyn mch thch hp. My o SDH truyn i mt tn hiu STM-1 cha 63 cng-ten-n, mi cng-ten-n mang mt tn hiu 2 Mbit/s. My thu kim tra tn hiu STM-1 ny v phn tch tng tn hiu thnh phn (cc tn hiu 2 Mbit/s). Nu thc hin php o nhn cng y s tiu tn nhiu thi gian v phi t li s knh cho mi ln o.Hnh 2.18 trnh by mt phng php khc, gim c ng k thi gian o yu cu. My phn tch truyn i mt cu trc khung STM-1 cha 63 cng-ten-n. Mi cng-ten-n c np vo mt chui bit PRBS tun t mt cch t ng v c kim tra xem c li cnh bo no khng bng mt php o th nhanh pha thu (ch qut).Trc khi a h thng trng thi trc tuyn (on-line), phi m bo c c cu hnh ng cho cc ngng ca b cm bin. thc hin vic ny, my phn tch m phng cc li ca tn hiu ng chnh khung hoc cc li bit chn l bng s phn b chn la c (lin tc hoc theo cm li). Nu t l li c chnh tt, c th tin dn ti ngng ca b cm bin v kim chng c hot ng tt ca n.

Hnh 2.18 Khi ng STM 1 vi vng lp 2Mb/s2.4.3.4 Cc php o s dng tn hiu th c cu trcS trnh by trong hnh 2.19 l mt trong nhng php o c bn trn cc b ni cho ng b. B ni cho ny nh x tn hiu trng hp, bn thn mt tn hiu 140 Mbit/s li c to nn t vic ghp cc tn hiu 34, 8 v 2 Mbit/s hoc 64 kbit/s. Trong trng hp ny, b ni cho thc hin phn knh khung 140 Mbit/s v cc tn hiu thnh phn 2 Mbit/s c ng gi vo khi truyn ti STM-1 tng ng theo s iu khin ca b iu khin nt mng.S hot ng ng i vi cc tn hiu c cu trc (phn khung) ca b ni cho ch c th kim tra c nu my phn tch c th m phng mt tn hiu 140 Mbit/s cha 04 tn hiu thnh phn 34 Mbit/s, m mi tn hiu thnh phn ny li bao gm 16 tn hiu 2 Mbit/s c cu trc hoc khng c cu trc.

Hnh 2.19 Php o s dng tn hiu c cu trc kim tra tnh nng chuyn mch thng, b to tn hiu o ca b thit b o np vo mt knh o tc 64 kbit/s, 2, 8 hc 34 Mbit/s (c hoc khng c cu trc) mt kiu chui bit o (PRBS) v ghp tn hiu ny ln ti tc ti a l 140 Mbit/s. Tn hiu ghp knh ny cn c th c nh x vo khung STM-1. B phn tch phn gii tn hiu ra (STM-1) ca b ni cho v thc hin mt php o li bit trn chui bit o ti mt mc phn cp c chn la. My phn tch thc hin phn knh tn hiu 140 Mbit/s hin ti cng ra thnh cc tn hiu 2 Mbit/s hoc 64 kbit/s. Mt lot cc b ghp knh hoc phn knh thng thng c thc hin bi cc s phn tng cc thit b ghp knh cn ng b. My o SDH cn c kh nng chn nhng li c th v cc cnh bo vo ng ghp knh c la chn.2.4.3.5 o kim hot ng chuyn mch cc dch v phn b

Hnh 2.20 o kim hot ng chuyn mch ca b ni choMt lnh chuyn mch c th c s dng phn b mt knh 2 Mbit/s dnh cho ngi s dng ca mt giao din b ni cho STM-1 trn n knh (n =1 n 63) ca mt tuyn ra. B ni cho thc hin vic ti to v phn b cc chc nng trong trng hp ny.Trong ng dng trnh by trong hnh 2.20, my phn tch s dng mt chui bit PRBS m phng mt knh ca ngi s dng c ni vi u vo ca b ni cho. Tt c cc knh ti giao din ra m cha chui bit o c pht hin mt cch t ng. Kiu o ny cn c th c s dng xc nh cc mch vng pha 2 Mbit/s ca b n cho.2.4.3.6 Php o trn cc b xen/rCc b ghp knh xen/r (ADM: Add/Drop Multiplexer) l nhng nt mng nh c nhng tnh nng hn ch. Chng ang ngy cng tr nn quan trng, lm phng tin truy nhp ph cp ca ngi s dng l cc cng kt ni gia th gii cn ng b v ng b. Cu hnh chung nht cho cc mng ng b ni vng l mt vng gm cc ADM Hnh 2.21 trnh by hai cu hnh o n gin cho cc php o na knh v c knh. y, cng vy, vic qut t ng cc cng-ten-n thnh phn l rt hu ch. My phn tch phi cung cp mt tn hiu STM-N ngoi tn hiu cn ng b kh cc bn tin cnh bo khi ADM.

Hnh 2.22 Php o trn cc b ghp knh xen r2.4.3.7 Cc php o li bit DCC/ECCDDC/ECC l t vit tt ca Data Communications Channel/ Embedded Control Communications Channel (Knh thng tin s liu/Knh thng tin gn lin) Cc knh s liu Dl n D3 trong SOH cung cp mt kt ni d liu nhanh tc 192 kbit/s dng cho vic trao i cc giao thc gia cc phn t mng v qun l mng. Hot ng ca nhng knh s liu ny phi c kim tra khi tin hnh o th nghim , thu hoc khi c s c xy ra phn qun l mng. Cc my phn tch c trn th trng hin nay u cho php try nhp vo cc knh t D1 n D3 thng qua mt giao din bn ngoi. Mt chui bit o c a n v c khi phc t gio din ny phc v cho vic phn tch. Chui bit gi ngu nhin ny m phng cc d liu m s c truyn i khi h thng trng thi trc tuyn (on-line). Nu my o SDH c th np mt chui bit gi ngu nhin (PRBS) vo cc knh t D1 n D3 v D4 n D12 th s rt hu dng. Nh th khng cn phi c thm thit b o c no na.2.4.3.8 o trCc nh cung cp mng lun n lc gim thiu tr tn hiu trn cc mng vin thng ca mnh. Cc t chc tiu chun ha ang t ra nhng gii hn i vi tr tn hiu (ITU-T G782). Tr c o bng cch s dng cc chui bit gi ngu nhin trong cc cng-ten-n ca SDH. Kt qu ca php o tr phi c phn gii mc micrgiy, sao cho c th o c tr ti a cho php trong mt nt mng l 125s 2.4.3.9 Kim tra chc nng chuyn mch bo v t ngCc qui trnh chuyn mch bo v t ng (APS: Automatic Protection Switching) trong trng hp c s c c trnh by chi tit trong cc Khuyn ngh G. 783 (Chuyn mch tuyn tnh) v G.841 (Chuyn mch vng). APS c thc hin nh s dng cc byte Kl v K2. Hin nay, cc byte K3 v K4 trong VC-3/4 hoc VC-11/12/2 cng c chun ha cho mc ch ny.Khi pht hin c li xy ra (nh t l li qu cao, mt tn hiu hoc mt ng b khung), phn t mng u tin pht hin ra s c ny s dng cc byte K bo cho tt c cc phn t mng khc c lin quan bit chuyn sang ch chuyn mch bo v. Vic chuyn sang ng truyn d phng cn din ra trong mt vi miligiy, thc t c th coi khng c s ngt qung ca truyn thng, sao cho ngi s dng khng th nhn bit c c s chuyn i ng truyn ny. bo m cho hai phn t mng s hot ng tin cy vi nhau cho d c li xy ra, mi phn t phi c o kim ring r.Ta phi tr li nhng cu hi sau khi kim tra hot ng ca APS (chc nng chuyn mch bo v t ng): Tt c cc phn t mng c s dng cng mt giao thc khng? Nhim v ca php o kim: M phng v din gii giao thc APS bng ch.

Hnh 2.23 Kim tra chc nng chuyn mch bo v t ngPhi mt bao lu chuyn sang ng truyn d phng? Nhim v ca php o kim: o thi gian chuyn mch bo v t ng.Trong hnh 2.23, my o SDH c s dng m phng cc trng thi khc nhau ca cc byte K1 v K2. php o ny n gin nht mc c th v khng cn phi c kin thc su v SDH, cc lnh v cnh bo chuyn mch c chun ha phi c th c thit lp c dng k t n gin trn my o SDH. Mt cch khc l to ra cc trng thi thnh phn bng cch son tng byte mt th kh thc hin v lm nh vy rt d mc liThi gian tri qua gia s m phng lnh chuyn sang mch d phng v ln thc hin chuyn mch thnh cng trc c o bng my o v c so snh vi mt gi tr ngng c th chn la c.Giao thc APS c nh gi bng vic s dng cc trig ghi li cc trng thi bit trong cc byte Kl v K2 trong cc khung k tip nhau. Sau nhng thng tin ny c hin th km theo cc mc thi gianv nhng din gii v cc m APS2.4.3.9 M phng hot ng ca con trMng s phn ng li nh th no nu n b dn p bi cc cm con tr gy ra do nhng thay i t ngt ca tn hiu xung nhp (chng hn khi chuyn sang mt on ng truyn khc?). ITU-T nh ra cc chui con tr trong Khuyn ngh G.783, l khuyn ngh c th c dng kim tra xem mng c gi n nh trong nhng trng hp nh vy khng. kim tra cc ch tiu hot ng ca mng i vi nhng tn hiu quan trng, th phi m phng nhng tn hiu ny tin hnh o c. Cc t chc tiu chun ha qui nh nhng chui o kim thch hp (ITU-T G.783, ANSI Tl.105.03 v Bellcore GR-253) m phng nhiu bc tng v gim t ngt ca con tr (hnh 2.24).

Hnh 2.24 m t cc chui con tr i vi chun G.783

Hnh 2.25 Cc hot ng con tr m phng cc bc tng gim, thay i t ngtLng tng 87/3, hay cn gi l 87/3 INC (INC vit tt ca t Increment) c ngha l mt khong m trong cc con tr gia khng thay i sau mt chui 87 bc tng trong gi tr con tr. C kh nng pht hin c nhng nh hng trn ti tin nu c th m phng c cc con tr v nh gi c cc con tr AU v TU mt cch ng thi. Qui trnh m phng cc hot ng ca con tr c tiu chun ha trong Khuyn ngh G.783 ca ITU-T nh trnh by trong hnh 2.25. cn phi c kh nng chuyn mch cho ti tin i qua m khng c li bt k hot ng m phng con tr nh th no.

CHNG 3: O TRT BIT3.1 nh ngha v cc thut ngRung pha v tri pha l nhng bin i pha ca tn hiu s thu c so vi v tr l tng ca chng. Nhng bin i pha ln hn hoc bng 10Hz gi l rung pha (Jitter)Nhng bin i pha nh hn hoc bng 10Hz gi l tri pha (wander)

Hnh 3.1. Hm jitter ca mt tn hiu sKhi jitter xut hin thi im chuyn mc ca mt xung s s sm hn hoc tr hn so vi tn hiu chun, cc sai lch ny l ngu nhin v lin tc. Bin ng ny dng thi gian hay pha.

Hnh 3.2. Tn hiu s c jitter v ng h chunDng sng jitter c th c biu din bng 1 hm lin tc theo thi gian v c lp vi tn hiu s b nh hng. Hnh 3.1 minh ha nh hng ca jitter vo mt tn hiu nh thi gian .* n v o jiiterJitter c c trng bi bin v tn s. Bin jitter l gi tr nh - nh ca hm jitter theo thi gian cn tn s l s ln dao ng quanh thi im c trng trong mt giy.Bin ca jitter c o bng khong n v - UI (interval unit). Khong n v UI c th hiu n gin l rng ca mt bit Do xung ng h ca tn hiu NRZ v RZ l nh nhau nn UI s khng ph thuc vo dng tn hiu s. Ngoi ra, UI cn khng ph thuc vo tc bit v n c ly chun da trn chu k ca mt xung ng h chun. Nhng thun li ny lm cho UI tr thnh mt tham s danh nh, cho php so snh bin jitter o cc tc bit khc nhau ca mt phn cp s

Hnh 3.3. Khi nim khong n vV d: Bin tc thi ca jitter o c l 1 s trong dng sng vung 100khz, v chu k ca dng sng 100 khz l 10 s do khong thi gian c ngha i vi dng sng ny l 5 s. Nh vy khong UI l 5 s v bin jitter l 1:5 = 0,2 UI.* Sai s khong thi gian (Time Interval Error -TIE).Sai s thi gian hay sai khong thi gian, sai s ny tch ly khi mt ngun tn s c s dng nh mt ng h. Tn s ti thi im bt k t l:

Vi fD l tn s danh nh. Nh vy s sai bit thi gian gia thi gian ng h biu kin v thi gian ng l:

Sai S Khong Thi Gian (TIE) c nh ngha l lch pha gia tn hiu c o vi tn hiu ng h tham chiu (chun). TIE thng c tnh theo ns bng cch chia lch pha ny vi tn s danh nh ca ng h chun. thun tin chn TIE = 0 ti thi im bt u ca chu k o T. Do TIE hin th s thay i pha ngay t khi php o bt u. Php o TIE l nn tng cho cc php tnh khc (MTIE, TDEV).3.2. Nguyn nhn gy ra hin tng trt bitJitter (bin ng chp chn nhanh) c th xut hin t cc nguyn nhn khc nhau trong mt h thng truyn dn s, tuy vy ch yu cc nguyn nhn ny c th phn thnh cc loi sau:a. Jitter do cc phn t nh thi gy raJitter ny c bin v tn s tng i thp tc l wander, n xut hin do cc nguyn nhn sau : Tp m pha trong cc mch dao ng lm ng h trong ton h thng cng nh trong cc mch logic do s khng hon thin ca cc linh kin mch. nh hng ca nhit ln cc b ao ng ni dng thch anh lm thay i tn s ca n. S khng n nh do nhit thng rt ln, do cc b cng hng thng phi t trong cc b tn nhit m bo chnh xc ca nhit bn trong l 0. lc khi nhit phng my thay i t 0 ti 60c S bin i chm trong cc ngun cung cp, s bin i in p offset nh hng n mc ngng kch thch trong cc mch logicHnh 3.4 minh ha thnh phn jitter c to ra do s khng n nh ca vng chuyn tip trong mch logic. Thnh phn jitter ny t c nh hng ln cht lng truyn dn.

Hnh 3.4. Jitter do s khng n nh ca vng chuyn tip trong mch logic.b.Jitter do s thay i thi gian tr truyn dnBt c s thay i no trong thi gian tr ca tn hiu trn ng truyn dn u a n s bin ng v pha ca tn hiu tng ng. Thng th s thay i ny l do s bin i chm v nhit ni t cp gy ra. Jitter trong trng hp ny c tn s thp v thng c coi l wander.c. Jitter do giao thoa gia cc k tKnh truyn dn c c tnh bin v pha khng l tng. V th, chui tn hiu khi truyn qua knh truyn dn s b mt tnh trc giao. ng ra knh truyn dn, cc k t s b ko di v chng ln ln nhau to ra hin tng giao thoa gia cc tn hiu. Do , thi im ly mu ti u ti to li tn hiu ban u cng b lch i gy ra jitter (hnh 3.5). Jitter ny gi l jitter mu ph thuc.

Hnh 3.5 Jitter do giao thoa gia cc k td. Jitter do hiu chnhTrong k thut ghp knh cn ng b PDH, ng h ca cc tn hiu lung s chy t do (free-running). iu ny c ngha l c s khc bit gia ng h ca cc tn hiu lung s v ng h ghp knh so vi ng h danh nh. m bo s ng b trong qu trnh tch/ghp knh, cc b ghp knh s dng k thut thch nghi ng h nh sau: b ghp knh lun c ng h ln hn mt cht so vi cc ng h ca cc lung s v s khc bit gia hai ng h s c khc phc bng hiu chnh.Hiu chnh l mt qu trnh trong cc bit c u n chn vo cc lung bit n nng tc bit ln n tc m thit b ghp knh yu cu. u cui xa nh c tn hiu iu khin hiu chnh, cc bit c chn thm vo trc b ly ra khi phc tn hiu thng tin tr li gi tr danh nh ca n. Vic loi b bit hiu chnh u cui lm cho tn hiu s c nhng khong trng (khe thi gian). Tn hiu bt thng ny ngoi vic i vo b lu tr n hi cn c a n u vo mch PLL (phase locked loop), mch ny tch c tn hiu nh thi t tc trung bnh ca tn hiu bt thng. Tn hiu nh thi tng hp c s dng c tn hiu n ra khi b nh n hi (n hp thu s bt thng ny). B ghp knh pha pht c b nh m n hi (elastic store) bao gm cc t bo nh mt bit m c th c ghi vo, c ra mt cch c lp vi nhau (tc l ti mt thi im c th va ghi vo mt t bo, va c ra t mt t bo khc). Tn hiu i n c ghi vo cc t bo mt cch tun hon nh ng h c khi phc t tn hiu n vng kha pha TR. Cc bt nh c c ra nh xung nhp ca ng h ca b ghp knh c tn s cao hn nn a ch c ra tin dn n a ch ghi vo. S khc nhau gia a ch ghi vo v a ch c ra c gim st bi b so snh a ch (AC). Khi m s sai lch gia a ch c ra vi a ch ghi vo nh hn ba t bo b nh, b iu khin chn (logic) s kim ch c v qu trnh chn bt u: Nu v tr bit iu khin chn (justification service bit) trong khung xut hin , bit s c gi tn 1. Khi v tr bit iu khin chn xut hin th a ch c s c gi li mt chu k ng h v t bo nh hin ti s c c thm mt ln na, y l bit chn v bit ny s b loi ra u thu. Bi v a ch c c gi li 1 chu k ng h nn s khc nhau gia a ch c v a ch ghi tng ln.Chu trnh trn s c lp i lp li v th tn s ng h ca cc lung cn ng b s tng thch vi tn s ca ng h b ghp knh.Khong thi gian gia thi im bt u qu trnh chn v thi im thc hin c th ko di vi chu k khung. Trong thi gian ny a ch c cng tin gn a ch ghi hn na. V th qu trnh chn cn c khi ng ngay khi khong cch gia hai a ch nh hn 3 trnh tnh trng cn b nh.Do bit chn khng th a vo lp tc sau khi t ti ngng chn v ch c a vo v tr dnh cho n trong khung k tip. Nh vy c mt thnh phn jitter thi gian ch i (waiting time jitter) xut hin, u thu cng c b nh n hi. Tn hiu iu khin chn s ngn cn vic ghi cc bit ti v tr chn hay iu khin chn vo b nh Vic xa chn gy ra gin on trong tn hiu ng h thu - tn hiu ng b khong h (gap timing) ti cc v tr chn. Tn hiu ng b khong h c a n ng vo mch PLL, mch ny tch c tn hiu nh thi (ng b lin tc) t tc trung bnh ca tn hiu ng b khong h. Tn hiu nh thi c s dng c tn hiu ra khi b nh n hi. Nh vy tn hiu c c ra vi s ng b lin tc, c ngha l tn hiu xut hin ng ra mt cch u n. lm c iu ny s t bin v pha ng vo b so pha (phase comparator) c bin i thnh s dch chuyn in p. S dch chuyn ny c lm phng bi b lc thng thp. Tn hiu ng ra ca b lc thng thp c dng iu khin b dao ng c iu khin bng in p (VCO) to ra tn hiu ng h lin tc t tc trung bnh ca tn hiu ng b khong h.Do tnh khng l tng ca b lc thng thp, s dch chuyn in p khng bao gi c lm phng mt cch hon ho. l l do khin tn s ca tn hiu nh thi c lm phng bin thin theo tn hiu ng ra ca b so pha, tc l jitter c pht sinh, jitter ny gi l jitter do chn (pulse stuffing jitter).

Hnh 3.6. S khi ca mt b m mm do (pha ghp knh)

e. Jitter do hot ng ca b ti to xung ng hCc thit b truyn dn cn ng b hin nay u s dng nguyn l t nh thi, tc l ng h cn thit cho cc mc ch ng b c khi phc t lung tn hiu s thu c.

Hnh 3.7. S khi ca mt b tch xung nh thi B to xung nh thi to xung ti nhng thi im m sng cn hi vi tn s nh thi i qua zero. Trong trng hp l tng, nu ngng bt u lm vic ca b to xung nh thi ng bng zero th cc xung nh thi s c hnh thnh ng vo thi im i qua zero ca sng cn hi. Trn thc t b to xung nh thi c mt vng khng cm ng i vi s thay i ca tn hiu vo. Hu qu l cc xung nh thi c th c to ra vo cc thi im ngu nhin trong gii hn ca nhng vng khng cm ng ni trn. ln ca nhng vng ny (hu qu l bin jitter) ph thuc vo bin ca tn hiu. Nh vy s thng ging bin ca sng cn hi (hu qu s giao thoa gia cc tn hiu) bin i thnh s thng ging pha (jitter) ca cc xung nh thi.S giao thoa gia cc tn hiu cn a ti s thng ging v rng v v tr thi gian ca cc xung ng vo ca b khung dao ng. S thng ging ny s lm bin ng thi im chuyn qua zero ca cc tn hiu cn hi a n jitter ca cc xung nh thi tng ng. y mt ln na cn thy r rng do s iu hng khng chnh xc ca khung dao ng tn s ring ca khung s khc vi tn s nh thi. iu ny dn ti s khng n nh ca nhng thi im i qua zero ca tn hiu cn hi v gy ra jitter.Hot ng ca b to xung nh thi ch c hiu qu khi mt ca chui tn hiu vo tng i cao, tc l chui tn hiu vo cha nhiu xung kch thch cho khung cng hng. Trong trng hp tn hiu vo cha cc chui 0 (zero) di th khung cng hng s khng c kch thch mt cch hiu qu. S tt dn ca khung dao ng b ko di. Pha ca tn hiu nh thi v th s b bin ng. S rung pha ny c gi l jitter mu ph thuc

Hnh 3.8. Sng cn hi v cc thi im hnh thnh xung nh thif. Jitter trong mng PDH/SDHHai loi jitter c nh hng rt mnh ln vic truyn tn hiu PDH qua mng SDH. l jitter nh x (mapping jitter) v jitter con tr (pointer jitter).* Jitter nh x truyn cc tn hiu cn ng b trong khung SDH, trc tin cn phi nh x chng vo cc container. K thut chn c s dng cn bng tc gia cc lung s PDH v cc container tng ng. trm u cui xa, cc container c gii nh x tr li thnh tn hiu PDH bng cch xa chn.Do vic chn v xa chn cng nh vic lm phng pha trong qu trnh nh x / gii nh x m cc thnh phn jitter do chn v jitter thi gian ch i c sinh ra. Trong trng hp ny jitter c gi l jitter nh x/ gii nh x. Jitter ny tng ng vi jitter chn v jitter thi gian ch i trong mng PDHJitter nh x c bin thp v tn s tng i cao. Bin jitter nh x thay i khi tc lung PDH dch chuyn so vi VC-N * Jitter con trTrong k thut truyn dn SDH, s khc nhau v ng h ca hai mng hay hai phn t ca mng ( im kt ni cho hay trm ghp knh u cui) c b tr bng cch hiu chnh con tr trong khung tn hiu ng b, tc l thay i v tr thi gian ca cc container ti thng tin trong khung tn hiu c truyn i. iu ny c thc hin bng cch tng hoc gim gi tr ca con tr i mt n v. Cc container o v th s dch i mt byte (trong SONET) hay ba byte (trong SDH), tng ng vi pha tn hiu b dch i 8 hay 24 UI.Do vic hiu chnh con tr ch c th thc hin t nht sau 3 khung tn hiu, u thu, tn hiu ng h thu cng phi c lm phng ging nh trong qu trnh chn bit. Cc thnh phn jitter tng t (jitter do chn v jitter thi gian ch i) c to ra. Trong trng hp ny cc bin ng pha c tn s cao c loi tr, jitter cn li ch cha cc thnh phn tn s thp c bin cao.Nh vy, trong k thut truyn dn ng b, lung tn hiu c khi phc pha thu lun lun cha hai loi jitter l jitter nh x v jitter con tr. Hai thnh phn ny lun lun kt hp vi nhau thnh jitter kt hp.3.3. nh hng ca hin tng trt bit- Jitter lm tng xc sut li a vo trong tn hiu s: jitter lm cho thi im ti to tn hiu s (thi im ly mu tn hiu ) b lch i so vi thi im l tng ca chng khi lch ny vt qu dung sai cho php th li bit xy ra .Tn hiu s qua knh truyn dn thng b mo do giao thoa. Nu ng h ly mu khng c jitter th vic ly mu c thc hin ng thi im t u, do vic quyt nh tn hiu truyn i ( l o hay 1 ) vn c th thc hin chnh xc.Nu c tn hiu s v ng h c cng mt jitter ln , v tr chuyn tip ca ng h so vi v tr ti u ca tn hiu ( gia tn hiu ) khng thay i . Do vic ly mu vn c thc hin chnh xc v li bit khng xy ra. y l trng hp i vi jitter tn s thp m mch khi phc ng h dng PLL c th theo nhng bin thin pha ca tn hiu s.Ti cc tn s jitter cao, mch khi phc ng h khng th bm theo nhng bin i pha nhanh ca tn hiu s. Khi ng h c khi phc dch pha hn 0,5 UI so vi tn hiu s thu c th vic ly mu tn hiu s khng chnh xc v gy ra li bit.

Hnh 3.10. Ly mu ng

Hnh 3.11. Ly mu ng ngay c khi c bin ln

Hnh 3.12. Ly mu sai tn hiu s do jitter- Jitter a cc trt khng iu khin c vo tn hiu s: Khi jitter qu ln, dung lng ca cc b nh m c s dng ht v th gy ra hin tng trn hoc cn b nh. Hiu ng ny gy ra trt, mt hoc nhn i (lp li) cc lung bt trong mt khung s a n SES v cc s c khc.i vi cc dch v thoi, slip (trt) ny c th l nguyn nhn gy ra nhng ting ng nh c th nghe thy. Loi ting ng ny khng xut hin thng xuyn v khng nghim trng. Tuy vy cc dch v thoi vn ra nhng gii hn cho php vi slip.i vi cc dch v khc, slip c th gy ra nhng hu qu nghim trng. Trong truyn fax ch 1 slip cng gy nn nhiu hoc mt i 8 dng trong bn fax. iu ny tng ng vi vic mt 0,08 inch chiu ng (trc tung). Vic mt thng tin s dn n cn phi truyn li (fax li) bn tin cn fax. Vic truyn li ny phi do ngi s dng; khng c thc hin t ng bi thit b.nh hng ca slip i vi truyn s liu l nguyn nhn gy ra cc dy li. di ca cc li ny ph thuc vo tc c s liu v loi modem t 10 mili giy n 1,5 giy.Trong thi gian b li, thit b thu u ni vi modem thu c s liu t qung v kt qu l ngi s dng phi truyn li s liu.Khi slip xy ra trong dch v hi ngh video, cng s dn n vic xy ra cc li v cn phi thit lp li qu trnh.Tc ng ca slip i vi vic truyn s' liu ph thuc vo giao thc truyn dn. Nu s dng giao thc khng c kh nng truyn li s xy ra vic s liu b mt, b lp li, hoc b li. Giao thc truyn li c kh nng pht hin slip v do s khccxcdtds57i ng vic truyn li.i vi vic truyn video s (hi ngh video), cc php kim a ch ra rng slip thng gy nn nhiu tng on ca nh. Mc nghim trng v chiu di ca nhiu ph thuc vo loi m v thit b nn tn hiu c s dng S suy gim l nguy him nht i vi thit b gii m tc bit thp.Slip tc ng mnh ln cc dch v m ha (mt m). Slip dn n vic mt cha kha mt m. Vic ny lm cho vic truyn dn khng th hiu c v do cn phi truyn li cha kha v khi phc li lin lc. Tuy nhin, yu cu truyn li cha kha th khng ph hp vi tnh bo mt- i vi cc ng dng bo mt khng th chp nhn c nhiu hn 1 slip trong 1 ngy.- Jitter lm suy gim cht lng tn hiu tng t c m ha:i vi cc tn hiu tng t c m ha, jitter trong lung s ho s nh hng n tnh ng u gia cc mu ca tn hiu PAM c khi phc. Tn hiu ting ni c m ha PCM c th chu c nh hng ny, nhng i vi tn hiu hnh v cc tn hiu khc th nhy hn nhiu.i vi cc tn hiu truyn hnh s, khi truyn trong khong cch xa c th mo do jitter (dao ng v pha). Mo pha do thay i v tr xung ca cc mu gy ra mo ng bin, cc chi tit nh thay i lin tc theo cc khung.- nh hng ca jitter v wander trong mng SDH:Trong h thng SDH cn quan tm n c jitter v wander. Cc vng kha pha rt nhy cm vi jitter vn c s dng trong mch khi phc ng h. Ngoi ra cn c cc b nh m FIFO (Frist In Frist Out) rt nhy cm vi wander. Cc FIFO hot ng vng m (open loop) ph thuc vo ng h c v ghi. Do mi bin ng pha t 10 Hz n DC (wander) tr thnh 1 tham s ht sc quan trng.Nu jitter ca ti thng tin qu ln, n c th lm trn hoc cn cc b m FIFO. Hu qu cht lng dch v suy gim nghim trng a n mt mt v doanh thu.3.4. Tiu chun o trt bit3.4.1. Tiu chun rung pha i vi giao din PDH

3.4.2. Gii hn cho php i vi mc rung pha v tri pha vo giao din PDH

Hnh 3.14. Gii hn thp nht cho php rung pha v tri pha li vo cc i ca thit b

3.4.3. Tiu chun rung pha v tri pha vi giao din SDH

3.5. Phng php o3.5.1 Yu cu

3.5.2 Cu trc thit b

Hnh 3.15. Cu trc c bn ca thit b o jitter

Hnh 3.16. S khi my phn tch jitter/wanderMt my phn tch jitter c bn gm: mt b bin i mu/ng h (Pattern/clock converter), b to ng h chun (Internal reference clock generator), b o pha (Phase meter hay Phase detecter), cc b lc trng lng (Weighting filters) v b o gi tr nh (Peak value detecter). Hnh 3.16 l s khi ca my phn tch jitter. B bin i mu/ ng h to ra tn hiu ng h t tn hiu s thu c. ng h ny c jitter ging nh jitter trong tn hiu s (tn hiu iu pha xung m PPM). ng h ny c so snh vi ng h chun ong b o pha. Tn hiu ng ra c rng t l vi s thay i jitter theo thi gian (tn hiu iu ch rng xung PDM). Tn hiu ny c a qua cc b lc trng lng gii hn ph tn sjitter. Cc b lc s o cc gi tr m v dng ca tn hiu ny v hin th chng theo n v UIpp . Tn hiu ng ra ca b lc c a ti ng ra b gii iu ch x l tip nu c yu cu. Vic phn tch jitter sau c th thc hin trong min thi gian hoc tn s v d nh c th s dng my hin sng (oscilloscope), my o mc chn hay my phn tch ph. B to ng h chun bo m pha tham chiu bng cch s dng vng kha pha (PLL) hiu chnh s lch pha do jitter. Bng thng ca vng kha pha PLL xc nh tn s gii hn di ca php o jitter.3.5.3.Nguyn l o dung saiHnh 3.17 l m hnh nguyn l o dung sai jitter. B to jitter gm mt ngun ng h, mt ngun jitter v mt b to mu (hnh 3.18) . Ngun jitter thng l tn hiu iu ch sng hi. ng h b iu pha bi cc sng sin ny s iu khin b to mu pht ra chui bit c jitter mong mun. Trong cc phn sau, cc b to jitter s c hiu theo nguyn l trn.PRBS

Hnh 3.17 M hnh o dung sai jitterTi mt tn s cho trc, tng bin jitter cho n khi li bit xut hin ng ra ca thit b cn kim tra. Bin jitter c hin th trn b to jitter chnh l dung sai ca jitter ti tn s ni trn. Ln lt thc hin php o ny vi cc tn s khc nhau theo khuyn ngh ca CCITT. Ni cc im o thu c, ta c ng cong dung sai ca jitter. ng cong ny phi tha mn mt n dung sai jitter tng ng theo cc khuyn ngh nu trn.

Hnh 3.18. S khi b to jitter Hai phng php o dung sai jitter : bt u li (onset of error) v pht BER (Ber penalty). Bt du li (Onset of error):Phng php ny thch hp cho vic kim tra phn ln cc thit b mng. N kim tra c cht lng hot ng ca b m ln mch ti to ng h bn trong phn t mng. Tn hiu kim tra c cp cho thit b cn kim tra v bin jitter c tng ln cho n khi li BER vt qua mt ngng xc nh. Theo khuyn ngh 0.171, ngng li l 2 giy c li (ES) trong khong thi gian o l 30 giy. Quy trnh kim tra c th nh sau :1. Tng bin jitter ti mt tn s cho trc cho n khi li c ghi nhn.2. Gim jitter cho n khi khng c ES trong vng 30 giy.3. Tng dn bin jitter ln cho n khi c 2 ES c ghi nhn trong vng 30 giy.4. Bin jitter ny chnh l dung sai jitter ti tn s thc hin o.5. Lp li cc bc 1-3 i vi cc tn s cn li. Pht BER (BER penalty):Phng php ny thng p dng kim a cc trm lp giao tip quang. Phng php ny ch kim tra c cht lng ca mch ti to ng h bn trong thit b. Quy trnh kim tra nh sau :1. Khi khng c jitter u vo, tng dn suy hao quang cho n BER = 10 102. Gim suy hao i ldB.3. Tng dn bin jitter ti mt tn s cho trc cho n khi BER t li gi tr ban u (BER = 10'10).4. Bin jitter ny chnh l dung sai jitter ti tn s thc hin o.5. Lp li bc trn cho tt c cc tn s cn li (trong di tn theo khuyn ngh G.968 ITU).Lu : Trn thc t, khi s dng mc BER chun 10 -10, thi gian thc hin php o rt lu. Ni chung c th s dng cc mc BER chun khc trong di 10-7 n 10-10 gim thi gian o nu iu ny khng nh hng n kt qu o.3.5.4 Mt s v d v o dung sai jittera) o dung sai jitter ca thit b u cui ng dyHnh 3.19 l nguyn l o dung sai ca thit b u cui ng dy (LTE) 34Mb/s. Tn hiu kim a khng c jitter c a vo pha ghp knh. LTE bin i tn hiu m giao din HDB3 thnh m ng dy 4B 3T. Tn hiu 4B 3T khng c jitter ny c a qua b to jitter ni vng (loop through jitter generator). B to jitter ny a jitter vo tn hiu ng dy thu c v ni vng thng (loop through) LTE.Jitter a vo tn hiu c tng dn ln theo mt quy trnh xc nh trc cho n khi li bit bt u hin th (n my o li bit) pha tch knh. Kt qu thu c chnh l dung sai jitter ca LTE.

Hnh 3.19. o dung sai jitter thit b u cui b) o dung sai pha ghp knhHnh 3.20 l nguyn l o dung sai pha ghp knh ca thit b ghp knh MUX 2/8. Chui tn hiu gi ngu nhin c jitter c a n mt ng vo 2Mb/s. Bin jitter ti mt tn s cho trc c tng dn cho n khi li bit xut hin tn hiu tng 8Mb/s.

Hnh 3.20. o dung sai jitter b ghp knh c)o dung sai pha tch knhHnh 3.21 l nguyn l o dung sai pha tch knh ca thit b tch knh DEMUX 8/2. Tn hiu khung 8 Mb/s c jitter c da n ng vo DEMUX b tch knh hot ng ng b vi khung th cp. Bin jitter ti mt tn s cho trc c tng dn cho n khi li bit xut hin tn hiu 2 Mb/s.

Hnh 3.21. o dung sai b tch knhd)o jitter ng ra

Hnh 3.22. M hnh o jitter ni tiM hnh a c p dng cho cc thit b cn kim tra c b to ng h bn trong (b ghp knh PDH ) v khi khng cn tn hiu ng vo. M hnh b dng cho cc thit b cn li. Mt ngun litter ni ti rt thp c th cn phi s dng cho m hnh ny. C th s dng cc b to jitter cht lng cao vi kiu iu ch bt tt (switched off). o jitter ni ti cn phi s dng cc thit b o jitter c jitter ni ti thp. D nhin, jitter ni ti ca thit b o phi nh hn jitter ca thit b cn kim tra.e) o jitter ni ti ca trm lp 34 Mb/sHnh 3.23 l mt v d v o jitter ni ti ca mt trm lp 34 Mb/s theo m hnh b. Trm c ni vi b m phng ng dy thng qua b lc nhnh. M ng dy c s dng l 4B 3T (MMS 43). Bng k thut iu ch ct (modulation switch off ), b to jitter to ra chui gi ngu nhin (2 - 1) khng c jitter, m HDB3. B i m s bin i HDB3 thnh 4B 3T, tc 34 Mb/s gim xung cn 26.7 Mbaud. B m phng ng dy v b lc nhnh c s dng ti to cc iu kin lm vic bnh thng cho trm lp. My o jitter s o trc tip jitter ni ti tc 26.7 Mbaud. Kt qu o c trong di tn t 2 Mhz n 3.6 MHz khng c vt qu 0.034 UIpp .

Hnh 3.23. o jitter ni ti ca mt trm lp 34 Mb/sf)o Jitter nh x

Hnh 3.24. o jitter nh xS o c nh by trn hnh 7.23. My phn tch SDH gi tn hiu cn ng b ti ng vo ca phn t mng (b ghp knh xen-rt ADM). Tn hiu nhnh c nh x vo khung tn hiu ng b. phn thu, tn hiu c gii nh x t khung tn hiu ng b tr li tn hiu PDH ban u. Bng cc b lc trng lng jitter, thit b o s phn tch v hin th gi tr ca jitter nh x trong tn hiu nhnh c khi phc. trnh jitter do hiu chnh con tr, thit b kim tra v phn t mng phi c ng b vi nhau t mt ngun ng h chun.Phng php o:Thay i dch tn s ng h tn hiu PDH trong dung sai cho php (v d 50ppm vi 2 Mb/s), o gi tr nh-nh ca jitter ng ra trong 60 giy v so snh vi cc gii hn tiu chun.Khi dch tn s gia PDH v SDH ln, qu trnh chn trong nh x i vo ng thi n nh vi cc chn nhanh (tc l jitter c cc thnh phn tn sc cao v l cc thnh phn d dng b lc bi b gii nh x).Khi dch tn s nh, jitter tng do qu trnh chn c tn s thp hn. B gii nh x t hiu qu hn trong vic lc cc thnh phn ny.Khi ng h PDH v SDH c cng mt tc jitter s khng xut hin (khng xy ra chn).g) o jitter con tr tng hpS o c trnh by trn hnh 3.25. trnh jitter xut hin do hiu chnh con tr khng iu khin c, thit b o v phn t mng phi c ng b vi nhau t mt ng h chun. My o pht ra cc chui con tr theo cc tiu chun khc nhau tc ng ln mng hay phn t mng. My o s o tc ng ca cc chui con tr ny ln tn hiu lung nhnh thu c. Gi tr jitter thu c khng c vt qa gii hn cho trc trong cc di thng trng lng jitter xc nh. Cc gi tr nh-nh ca jitter c ghi nhn theo chu k 60 giy.

Hnh 3.25. o jitter con tr tng hpKhi thc hin php o ny cn lu 2 im sau: Thi im bt u php o khng th ty m phi ng b vi chui con tr c th c s dng. Chu k o thay i, ph thuc vo mi chui con tr c th c s dng v cng phi c ng b vi chui .Mc ch kim traMc ch ca php o ny l nh gi nh hng ca s thay i gi tr con tr trong SDH. V d, mt hiu chnh con tr ca AU-4 s to ra mt gin on pha 21.5 bit (154 ns) trong ti 140 Mb/s. cn phi nh gi kh nng ca b kh ng b trong vic lm phng s chuyn tip pha ny trong tn hiu 140Mb/s ng ra. Mt vn khc cng cn quan tm l nh hng cua cc con tro TU mc d chng c tm quan trng t hn do t xut hin.Thit b o phi c kh nng to ra cc chui con tr kim tra khc nhau: n (single) - Theo lnh ca ngi s dng. Chm(Burst) - 2-8 ln hiu chnh con tr lin tc m phng mu con tr trong trng hp xu nht: cu hnh li ng b nt mng u xa. Lin tc - c s dng m phng trng hp nt mng u xa b mt ng b. l ng hp nt mng mt ht ngun ng h s cp v hot ng kiu kim gi (holdover). Cc chui kim tra G.783 - s m t trong phn sau.Thc hin kt hp cc loi kim tra ny, ngi vn hnh c th bo m rng jitter trong mng SDH / PDH ca h c hn ch v s khng vt qua cc gii hn mng cho trc d tnh thng k ca hiu chnh con tr l khng xc nh.Chui kim tra con tr (pointer test sequences):Chui kim tra con tr l mu lp li ca cc hiu chnh con tr theo thi gian. Cc chui ny c nh ngha r rng trong khuyn ngh G.783 ITU. Tt c cc chui kim tra con tr u c chung mt nguyn l v cu trc v cc yu cu v o c (xem phn cu trc chui kim tra con tr).Ni chung cc chui con tr chia ra lm hai loi: n/chm (single/burst): (H 3.26) c s dng kim tra p ng ca cc b chnh ng b (desynchronizer) i vi cc s kin con tr ring bit. Cc s kin ny m phng cc ng h c wander qu mc hay s chuyn mch cc ngun ng b chun mt im no trn mng. Cc s kin ny cch bit theo thi gian, thng thy t nht l 10 giy cc b chnh ng b kp phc hi tr li trng thi n inh khi khng c dch chuyn con tr. Hnh 3.27 ch th hin minh ha chuoi kim tra con tr loi ny. Chui ny c th gi l chui chm kp n cc. u n / chu k (regular / periodic) (H3.27) c s dng kim tra p ng ca cc b chnh ng b i vi cc s kin lin tc. Cc s kin ny m phng trng hp c s lch tn s c nh hay mt ng b ti mt im no trn mng. Cc hiu chnh bt bnh thng nh b xung con tr hay kh con tr c xem l mt phn ca chui. Cu trc chui kim tra con tr:Cc chui con tr ni chung u gm 3 giai on (hnh 3.26, 3.27): Giai on khi ng(Lnitialization period): Giai on ny bo m rng cc b nh m ca b x l con tr c lm y (ngha l khng hot ng im gia) do tc ng ca chui con tr mi th hin chnh xc trong kt qu o. Vi tc 1 con /giy (tc ti a l 3 con tr /giy), giai on ny ko di t nht 30 giy Giai on lm ngui (Cool-Down period) Giai on ny bo m rng cc b chnh ng b v ti to ng h thch nghi vi trng thi n nh khi khng c dch chuyn con tr hay trng thi n nh khi hiu chnh con tr u n (chui con tr u n). Giai on ny phi ko di trong mt khong thi gian l mt s nguyn ln cc chui hoan chnh (vi di 60 giy hay mt chui c chu k di hn). Nu trong chui c s bt thng th phi c t nht mt s bt bnh thng trong giai on ny. Giai on o ( Measurement period ) Giai on ny phi ko di cho mt s chu k hon chnh. Mt s chui kim tra c cha cc s bt bnh thng hoc l con tr b xung hoc l con tr b kh. Trong trng hp ny, giai on phi cha t nh't hai s bt bnh thng bo m kt qu o n nh. Trong giai on o, gi tr ti a nh-nh c ghi nhn

Hnh 3.26. Chui kim tra con tr n/trm tng qut

Hnh 3.27. Chui kim tra con tr u n/chu k tng qutCc vn cn lu khi o jitter con tr Tt c 3 giai on: khi ng, lm ngui, o u phi c trong chui kim tra con tr. Cc php o phi c thc hin ng b vi chui kim tra. Tn s ct ca b lc jitter phi c iu khin cht ch. Jitter con tr c bin ln tn s thp nn li trong p ng ca b lc bng cao s lm cho php o khng chnh xc.Cc php o bng y (full-band) vi b lc bng cao 0.1Hz n 10Hz rt c li cho vic xc nh c tnh ca qu trnh chuyn tip pha v c thm cc thng tin cho vic chn on.

CHNG 4: O KIM MNG CP NG4.1. Gii thiu chung v mng cp ng4.1.1Cu trc mng ngoi viMng ngoi vi l mt trong ba thnh phn chnh cu thnh mng vin thng (h thng chuyn mch, h thng truyn dn v h thng mng ngoi vi).4.1.1.1 Mng cp thu baoCu trc tng quan mng cp thu bao c trnh by trong hnh 4.1.

Hnh 4.1 Cu trc mng cp thu baoMng cp thu bao gm: Mng cp ng thu bao l h thng cp thng tin si ng kt ni t nt chuyn mch/im truy nhp n nh thu bao, mng bao gm cc thnh phn nh: gi phi dy chnh (MDF: Main Distribution Frame), mng sng cp, phin ni dy, t cp, hp cp, cp vo nh thu bao v h thng cng b; Mng cp quang thu bao l h thng cp si quang kt ni t nt chuyn mch/im truy nhp n nh thu bao, mng bao gm cc thnh phn nh: gi phn phi cp quang (ODF: Optical Distribution Frames), mng sng quang, t cp, n v mng quang (ONU: Optical Network Unit) v h thng cng b.4.1.1.2 Mng cp quang trung kMng cp quang trung k c chia lm hai cp: Mng trung k cp I l h thng cp quang thuc mng vin thng ng trc quc gia, quc t c s dng kt ni trung k gia cc tng i trung tm - chuyn tip, chuyn tip - chuyn tip, chuyn tip - cng, cng - cng. Mng trung k cp II l h thng cp quang thuc mng vin thng ni tnh, thnh ph, c s dng kt ni trung k gia cc tng i trung tm - trung tm, trung tm - tng i chuyn tip ni ht, trung tm - v tinh/im truy nhp.4.1.1.3 H thng h tr, bo v mng ngoi viH thng h tr, bo v mng ngoi vi bao gm: h thng hm, h, cng cp, ct b tng cp, trang thit b chng st cho mng cp ng v cp quang4.1.2Nguyn tc t chc mng cp 4.1.2.1Mng cp ng thu baoMng cp ng thu bao c qui hoch phn vng da trn cc nguyn tc sau: Mng cp ng thu bao ca mt tnh, thnh ph c phn thnh cc vng mng theo ng vng phc v ca cc tng i ni ht. Trong mt vng mng, mng cp ng thu bao ca mt tng i c phn thnh nhiu vng phc v theo cc tuyn cp chnh nh minh ho trn hnh 4.2. Da vo mt dn c, c im a l ca vng dn c v cc chng ngi t nhin to bi cc ng giao thng ln, ng st, sng ngi, knh rch phn khu vc phc v ca cc tuyn cp chnh thun tin cho vic thi cng, xy dng v qun l mng;Vng phc v ca mt tuyn cp chnh c phn thnh 3 dng sau:Vng phc v trc tip: Trong vng phc v trc tip thu bao c kt ni trc tip vi nt chuyn mch qua mt cp chnh, khu vc A trn hnh 4.2 m t phm vi vng phc v trc tip ca mng cp chnh;

Hnh 4.2 : S phn vng phc v ca mng cp ng ni ht Vng phc v qua mt cp phi cp: Trong vng ny thu bao c kt ni vi nt chuyn mch qua mt cp phi v mt cp chnh, khu vc B trn hnh 1.2 m t phm vi vng phc v ca mt cp chnh. Vng phc v qua hai cp phi cp: Trong vng ny thu bao c kt ni vi nt chuyn mch qua mt cp chnh, mt cp phiCp I v mt cp phi cp II, khu vc c trn hnh 4.2 m t vng phc v ca mt tuyn cp phi cp I;Thc hin nguyn tc gim cp phi cp n mc ti thiu nhm nng cao cht lng mng ngoi vi; khng khuyn khch m hnh phi cp ln hn hai cp tr nhng trng hp trin khai tm thi do nhu cu pht trin nhanh v cha trin khai u t kp.C ba cch phi cp trn mng cp dng thu bao: Phi cp trc tip l cch phi cp m thu bao c ni vi nt chuyn mch ch qua mt hp cp, hnh 1.3 l s cu hnh phi cp trc tip, trong s ny, cp chnh l cp ni t MDF n hp cp, cch phi cp ny thc hin ngay khu vc t tng i v nhng khu vc c mt dn c cao cch tng i khong 500 mt;

Hnh 1.3: S cu hnh phi cp trc tip Phi cp mt cp l cch phi cp m thu bao c ni vi nt chuyn mch ch qua mt hp cp v mt t cp. Hnh 1.4 m t cu hnh phi cp mt cp. Trong cu hnh ny, cp chnh l cp ni t MDF n t cp, cp phi l cp ni t t cp n hp cp, cch phi cp ny thc hin ti cc khu vc th n nh c mt in thoi cao, vng phc v ca tng i n nh v l ni c nhu cu cao v dch v Internet bng rng.

Hnh 4.3 S phi cp trc tipPhi cp hai cp l cch phi cp m thu bao c ni vi MDF qua mt t cp cp I, mt t cp cp n v mt hp cp; hnh 1.5 m t cu hnh phi cp hai cp. Trong cu hnh ny, cp chnh l cp ni t MDF n t cp cp I, cp phi cp mt l cp ni t t cp cp I n t cp cp II, cp phi cp hai l cp ni t t cp cp II n hp cp. Cch phi cp ny c tnh linh ng cao, thng p dng i vi vng dn c ang pht trin hoc vi vng ngoi thnh, khu vc nng thn nng cao hiu sut s dng ca mng cp chnh v cp phi. Khi s pht trin thu bao ti cc cc vng ny n nh th s chuyn sang cu hnh phi cp mt cp bng cch thay t cp cp mt bng mng xng r nhnh cp.

Hnh 4.4: S phi cp mt cp

Hnh 4.5 : S phi cp 2 cp4.1.2.2 Mng cp chnh Cn c vo c im a l v vng phc v ca tng i ni ht, mng cp chnh phi c t chc theo tng tuyn v c phn vng phc v cho tng cp chnh Cp chnh phi c ngm ho ti cc trung tm tnh, thnh ph, huyn l, th trn. S dng mng sng cp trn cc tuyn cp chnh r nhnh cp chnh sang cc tuyn khc nhau vi nhu cu dung lng cp cn dng trn cc tuyn nhnh thp hn, khng c dng t cp r nhnh cp. Mng sng cp phi chu c ngp nc lu ngy. T cp cp I c dung lng t 200 i n 600 i. T cp c t trong vng phc v ca t cp. V tr t t cp c la chn sao cho bo m yu cu s dng ti u dung lng cng b, cng nh thun tin cho vic thi cng cp phi, bo dng, x l v thay th cp. Khng t qua su trong vng phc v ca t cp nhm trnh vic phi chy nhiu cp phi ngc v pha tng i gy tn dung lng cng b. Khng t t cp gn t phn phi in lc. T cp t cao trnh ngp lt theo cc qui nh v phng chng lt bo. Trc khi tuyn cng b b qu ti t nht l 18 thng, phi lp phng n thay cp ng bng cp quang vi thit b truy nhp nhm gii phng l cng b cho pht trin mng trong tng lai. u tin thay trc cc tuyn cp c cht lng xu, c chiu di ln nht v qua nhiu cp phi cp. Cc tuyn cp c cht lng xu do s dng lu nm hoc do s c k thut cn c phng n