ki thuat chuyen mach

8/9/2019 Ki Thuat Chuyen Mach

1/302

hc vin k thut qun sb mn thng tin - khoa v tuyn in t

mai vn qu, nguyn hu kin, nguyn vn gio

k thut chuyn mch(Dng cho chuyn ngnh in t vin thng)

l-u hnh ni b

h ni 2003

www.4tech.com.vn
http://www.4tech.com.vn/


2/302

mc lc TrangMc lc 1

li ni u 6chng 1. Cc thnh phn ca mng vin thng 8

1.1 Khi qut chung 8

1.1.1 Khi qut v thng tin vin thng 81.1.2 Cc thnh phn ca mng vin thng. 91.1.3 T chc mng vin thng 151.1.4 Cc thnh phn thit yu khc ca mng vin thng. 17

1.2.Chuyn mch knh, chuyn mch tin, chuyn mch gi. 191.2.1 Khi nim v chuyn mch knh (Circuit Switching). 191.2.2 Khi nim v chuyn mch bn tin (Message Switching). 201.2.3 Khi nim v chuyn mch gi. 20

1.2.4 Khi nim v cng ngh atm (Cng ngh chuyn giaokhng ng basynchronous Transfer Mode)

21

1.2.5 lnh vc ng dng ca cc phng thc chuyn mch 241.3. Khi qut v tng i iu khin theo chng trnh ghi sn SPC

(Stored Program Control)25

1.3.1 S pht trin ca cng ngh chuyn mch v phng thciu khin.

25

1.3.2 Tng quan v tng i iu khin theo chng trnh lu trSPC

28

1.3.3 S khi tng qut ca tng i SPC 311.3.4 S khi tng qut ca tng i s SPC (DSSDigital

Switching Systems)34

Chng 2. Chuyn mch knh (Circuit switching) 392.1.Phn loi chuyn mch knh 392.2 Chuyn mch khng gian tng t 41

2.2.1 Khi qut v chuyn mch khng gian tng t 412.2.2 Cu to v nguyn l hot ng ca b chuyn mch khng

gian c bn

42

2.2.3 Xy dng cc trng chuyn mch khng gian tng t trnc s b chuyn mch c bn

46

www.4tech.com.vn


3/302

2.3. iu ch bin xung (PAM-Pulse Amplitude Modulation) vchuyn mch thi gian i vi tn hiu ri rc

57

2.3.1 Nguyn l iu bin xung v u th phn knh theo thigian

57

2.3.2 Chuyn mch PAM 4 dy dng trung k m tn 592.3.3 Chuyn mch PAM 4 dy khng dng trung k m tn

632.3.4 So snh nguyn l chuyn mch PAM 4 dy dng trung km tn v nguyn l chuyn mch PAM 4 dy khng dngtrung k m tn

65

2.3.5 Chuyn mch PAM 2 dy 662.4. Khi qut chung v cng ngh PCM v k thut chuyn mch s 68

2.4.1 Nhng li th c bn ca s kt hp gia truyn dn s vchuyn mch s

68

2.4.2 Khi qut v cng ngh PCM, chc nng ca CODEC 71

2.4.3 Tuyn PCM c s v t chc cc tuyn bc cao trong cctng i s 742.4.4 Khi nim chuyn mch PCM 75

2.5. Cc b chuyn mch thi gian s c bn 792.5.1 Khi qut v chc nng ca cc b chuyn mch thi gian

s79

2.5.2 B chuyn mch thi gian s kiu ghi tun t-c ngunhin

80

2.5.3 B chuyn mch thi gian s kiu ghi ngu nhin-c tun

t

85

2.5.4 B chuyn mch thi gian s kiu c ghi v c u ngunhin

87

2.5.5 Kh nng p dng ca cc b chuyn mch thi gian s. 902.6. Cc b chuyn mch khng gian s c bn 91

2.6.1 Khi qu t v chc nng ca cc b chuyn mch khng gian s 912.6.2 B chuyn mch khng gian s iu khin theo u ra 932.6.3 B chuyn mch khng gian s iu khin theo u vo 952.6.4 Cc c im chung ca b chuyn mch khng gian s 97

2.6.5 Dng c bit ca chuyn mch khng gian s 972.7. Cc cu trc trng chuyn mch s 100

www.4tech.com.vn


4/302

2.7.1 Cu trc mt b chuyn mch thi gian (Cu trc T) 1012.7.2 Cu trc chuyn mch hai tng (Cu trc T-S, S-T) 1032.7.3 Cu trc chuyn mch ba tng (Cu trc T-S-T, S-T-S) 1092.7.4 Cu trc chuyn mch T-S-S-T 117

2.8. iu khin chuyn mch s. 120

2.8.1 Hot ng chuyn mch khi phc v mt cuc gi. 1202.8.2 iu khin khi chuyn mch 121

chng 3. T chc cc phn h trong tng i SPC 1283.1 Phn h ng dng (Application Subsystem) 128

3.1.1 Kt cui cc ng thu bao. 128a. Tng quan v kt cui c c ng thu bao. 128b. Kt cui cc ng thu bao tng t (Analog line) 129c. Kt cui thu bao s 135

d. T chc cc kt cui thu bao 1373.1.2 Kt cui trung k 140

a. Khi qut chung 140b. Kt cui trung k tng t ATTU 141c. Kt cui cc ng trung k s DTI 142d. T chc nhm kt cui trung k 144

3.1.3 Cc b tp trung thu bao xa RLU v chuyn mch thu baoxa RSU

146

3.2 Phn h chuyn mch nhm1503.2.1 Cu to chuyn mch nhm 150

3.2.2 Kt cui ti phn h chuyn mch. 1513.2.3 Cc thit b quan trng khc ca phn h chuyn mch 153

3.3 H thng iu khin 1543.3.1 Khi qut chung 1543.3.2 T chc h thng x l iu khin ca mt tng i 1563.3.3 Phn mm tng i 162

3.4 Phn h bo hiu SiGS 1663.4.1 Khi qut chung 1663.4.2 Tin trnh thc hin mt cuc gi 169

www.4tech.com.vn


5/302

3.4.3 Cu trc mt s thit b bo hiu 1733.5 Phn h ngoi vi iu khin PCS 178

3.5.1 Khi qut chung 1783.5.2 Cu trc ca mt s thit b ngoi vi iu khin 179

Chng 4: tng quan v h thng bo hiu 183

4.1. Khi qut 1834.2 Bo hiu ng dy thu bao 1834.3 Bo hiu lin tng i 184

4.3.1 Bo hiu knh lin kt (Channel Associated Signalling) 186

4.3.2 Bo hiu knh chung (Common Channel Signalling) 187

4.4. Cc chc nng ca bo hiu 188

4.4.1 Chc nng gim st 188

4.4.2 Chc nng tm chn 189

4.4.3 Chc nng vn hnh v qun l mng 189

Chng 5: H thng bo hiu m R2 190

5.1 Khi qut 190

5.2 Phng thc truyn tn hiu ca bo hiu R2 190

5.3. Phn loi bo hiu ca R2 191

5.3.1 Bo hiu ng dy 191

5.3.2 Bo hiu thanh ghi 195

5.3.3 Cc phng php truyn tn hiu bo hiu thanh ghi 201Chng 6: H thng bo hiu knh chung s 7 204

6.1 Khi qut 204

6.2 Cc khi nim c bn 204

6.2.1 im bo hiu SP (Signalling Point) 204

6.2.2 im truyn bo hiu STP (Signalling Transfer Point) 205

6.2.3 Lin kt bo hiu SL (Signalling Link) v chm lin kt bohiu (Link Set)

205

6.2.4 Cc phng thc bo hiu (Signalling Mode) 2066.2.5 Tuyn bo hiu (Signalling Route) v chm tuyn bo hiu 206

www.4tech.com.vn


6/302

(Signalling Route Set)

6.2.6 M im bo hiu SPC (Signalling Point Code) 2076.3 Cu trc ca h thng bo hiu s 7 2086.3.1 M hnh chun h thng m OSI 2086.3.2 Cu trc phn lp ca h thng bo hiu s 7 209

6.3.3 Cc khi chc nng ca h thng bo hiu s 7 2111. Phn chuyn giao bn tin MTP (Message Transfer Part) 2112. Phn ngi s dng in thoi TUP (Telephone User Part) 2253. Phn ngi s dng mng s lin kt a dch v (ISDN

User Part)231

4. Phn iu khin kt ni bo hiu SCCP 2355. Phn ng dng kh nng giao dch TCAP 241

chng 7: c s l thuyt x l cuc gi v phng

php tnh ton thit b mng vin thng.

248

7.1 Mc tiu ca l thuyt x l cuc gi 2487.2 Ti v cng ti 2487.3 Dng cc bo gi v thi gian chim 2517.4 Cc h thng phc v cuc gi 2597.5 Cc phng php tnh ton s thit b phc v 2637.6 Tnh ton s thit b phc v lm vic vi tn tht hin nhin

khng gi lp.265

7.7 Tnh s thit b phc v hot ng vi tn tht hin nhin v vicc bo gi lp li

282

7.8 Tnh ton s thit b phc v lm vic vi cc tn tht hnh thc 2857.9 s dng trung bnh cc knh (ng) ca cc chm 2897.10 Phc v nhiu pha 292

Ti liu tham kho 297

www.4tech.com.vn


7/302

li gii thiu

K thut chuyn mch l mt lnh vc tm hiu, nghin cu cc phngthc chuyn mch, nh hng thng tin t ngun tin n ch nhn tin mt cchchnh xc, hiu qu, nhm m bo cht lng dch v cao, to c s t chcmng vin thng linh hot, a nng v to nhiu tin ch cho ngi s dng.

Trong qu trnh lch s pht trin ca lnh vc k thut truyn v chuynmch cc dng thng tin in nhiu cng ngh chuyn mch c p dngnh cc th h chuyn mch nhn cng, cc loi tng i chuyn mch h cin, cc tng i chun in t, cc tng i in t vi cc loi phn t chuynmch khc nhau nh ma trn chuyn mch tng t, cc chuyn mch s . Ccnguyn l chuyn mch khc nhau cng ln lt thay th nhau v kt hp vinhau trong cc trung tm chuyn mch ca cc mng vin thng nh nguyn lphn knh khng gian, nguyn l chuyn mch thi gian tng t (chuyn mchPAM), chuyn mch s i vi cc tn hiu iu ch xung m ghp knh ng b

(chuyn mch PCM), chuyn mch i vi cc thng tin s dng giK thut chuyn mch thng kt hp vi cc lnh vc k thut cng ngh

khc trong mt cu trc thit b hoc h thng cc thit b hon chnh nh kthut iu khin, k thut x l cc qu trnh ngu nhin, k thut in-in tv ch to linh kin, k thut truyn dn, bo hiu v x l bo hiu . Nhnchung, mi trung tm chuyn mch l mt h thng hon chnh, rt phc tp v ls kt hp ca nhiu lnh vc k thut m trong k thut chuyn mch l nntng.

Mc d trong cc mng vin thng hin nay ph bin s dng cc tng i

chuyn mch s iu khin theo chng trnh ghi sn, nhng trong ti liu nyvn cp n cc nguyn l chuyn mch khc nh cc chuyn mch khnggian tng t, chuyn mch PAM, hoc mt s c ch chuyn mch s liu khcvi mc ch cung cp cc kin thc c bn v k thut chuyn mch, to khnng ng dng cc k thut chuyn mch ny khng ch trong lnh vc vinthng m cn trong cc ng dng mang tnh c th khc nh lnh vc iu khinhoc trong cc h thng cng ngh chuyn dng. Mt l do khc cn nghin cu,tm hiu cc k thut chuyn mch trc y l tnh lun phin ca cc cngngh ny. V d trong cc chuyn mch tc cao c xu hng p dng cc phnt chuyn mch khng gian n gin nht vi iu khin phn tn c c tc chuyn mch cao.

Ti liu ny gm 2 tp.

www.4tech.com.vn


8/302

Ni dung ca tp 1 c chia thnh 5 chng. Chng 1: Cc thnh phnca mng vin thng- Gii thiu khi qut cc thnh phn ca mng vin thng,v tr, chc nng ca tng thnh phn; Cc phng thc chuyn mch v iukhin chuyn mch; S khi tng qut ca tng i SPC. Chng 2: Chuynmch knh- Gii thiu cc cng ngh chuyn mch knh; Nguyn l chuynmch khng gian tng t; Cu trc chuyn mch khng gian mt khu v nhiu

khu; Nguyn l iu ch bin xung v chuyn mch PAM; Cc s chuynmch PAM c bn 4 dy v 2 dy; Khi qut chung v cng ngh PCM vchuyn mch s; Nguyn l phn knh thi gian; Cc b chuyn mch thi gians v chuyn mch khng gian s c bn; Cc cu trc chuyn mch T, TS, ST ,TST, STS, TSST; Phng php iu khin cc chuyn mch s. Chng 3: Tchc cc phn h trong tng i SPC- cp n cu trc ca cc phn h ngdng, phn h chuyn mch, phn h x l iu khin, phn h ngoi vi iukhin, phn h bo hiu. Chng 4- Tng quan v bo hiu v cc h thng bohiu: Gii thiu v cc khi nim bo hiu thu bao, bo hiu trung k, cc h

thng bo hiu knh kt hp v bo hiu knh chung. Chng 5- Gii thiu hthng bo hiu R2 . Chng 6- Gii thiu h thng bo hiu s 7 . Chng 7: Lthuyt x l cuc gi v phng php tnh ton thit b mng vin thng- a racc khi nim v x l cuc gi, ti v cng ti, cc khi nim v phngthc phc v vi tn tht hin nhin, phc v theo hng i v cc phng phptnh ton thit b theo tng phng thc phc v v x l cuc gi.

Tp 2 ca ti liu ny tp trung vo cc k thut chuyn mch thng tin sliu trong tp trung vo cc phng thc chuyn mch thng tin dng gi nhth tc X25, Frame Relay, SMDS v ATM. Ni dung s c gii thiu khi qut

u tp 2.Trong ti liu ny c th cn nhng sai st, rt mong nhn c kinng gp ca bn c.

www.4tech.com.vn


9/302

Chng 1

Cc thnh phn ca mng vin thng1.1 Khi qut chung

1.1.1 Khi qut v thng tin vin thng

Trao i thng tin l mt nhu cu thit yu trong i sng hng ngy. Khicc mi quan h kinh t - x hi cng pht trin th nhu cu ngy cng tngcao. Cc thng tin c trao i rt a dng v hnh thc nh thoi, vn bn, sliu, hnh nh v rt phong ph v cch thc trao i; chng c th c trao itrc tip qua giao tip, i thoi v cng c th c thc hin mt cch gin tipqua th t, in thoi, in tn . Thng tin vin thng trn ngha rng c thhiu l hnh thc trao i thng tin t xa, bao gm c bu chnh, in tn v inbo v c cc hnh thc thng tin i chng qung b. Tuy nhin, t trc tinay khi nim v thng tin vin thng khng bao hm cc hnh thc trao i

thng tin phi in tn (khng dng tn hiu in), ng thi li gn lin vi hnhthc trao i thng tin qua mt mng no . Do , thng tin vin thng chiu l hnh thc trao i thng tin t xa, m trong tin tc cn truyn cbin i thnh tn hiu in u pht v c truyn qua cc thit b ca mngvin thng (bao gm cc thit b u cui, cc tuyn truyn dn, cc trung tmchuyn mch); u thu tn hiu nhn c s c chuyn i ngc li thnhtin tc cho ngi s dng. Ni cch khc truyn tin qua mng vin thng l hnhthc truyn thng tin t ni ny ti ni khc bng cch s dng tn hiu in,in t, quang in thng qua cc thit b mng.

Thit bu cui

Tn hiuin

Thit bu cui

Tn hiuin

Tin tc Tin tcMngvin thng

Hnh 1.1 : Nguyn l truyn tin qua mng vin thng

www.4tech.com.vn


10/302

1.1.2 Cc thnh phn ca mng vin thng.

a. Thit b u cui.

Tin tc cn truyn, nh ting ni, vn bn, s liu, hnh nh, phi cbin i thnh dng tn hiu in ph hp c th truyn qua mng vin thng.Cc bin i c thc hin bi thit b pht t ti u pht (ni truyn tin).

Sau khi truyn qua mng, tn hiu c thu ti ni nhn, n phi c bin i trli t dng tn hiu in thnh dng tin tc ban u hoc dng tin tc khc nhngc th hiu c cho ngi s dng. Php bin i ny c thc hin bi thit bthu ti u cui nhn tin. Nh vy, c th c cc thit b u ca mng (t ti nipht) v cc thit b cui ca mng (t ti ni thu). Tuy nhin, ti cc im traoi thng tin thng c nhu cu thng tin hai chiu, ngha l va c kh nngtruyn thng tin i va c kh nng nhn thng tin v. V vy, ti cc im nythng s dng loi thit b va thc hin c chc nng pht li va thc hinc chc nng thu, hay va l thit b u ca mng va l thit b cui camng. thng nht, cc thit b thc hin chc nng truyn thng tin vo mngvin thng hoc thit b nhn thng tin t mng hoc loi thit b thc hin c haichc nng trn u c tn gi chung l thit b u cui vin thng. T , thitb u cui ca mng vin thng c th c hiu l thit b giao tip giangi s dng vi mng m nh thit b ny ngi s dng c th truyn tin tcqua mng ti ngi s dng khc ca mng v nhn cc tin tc ca cc ngi sdng khc gi ti. Nhng iu trn y mi ch cp ti kha cnh bin i tntc; ngoi chc nng chnh ny cc thit b u cui cn tham gia vo qu trnhthit lp, duy tr v gii to tuyn truyn tin t n ti cc thit b u cui khckhi tham gia cc cuc lin lc qua mng. Cc chc nng loi ny bao gm thng

bo cho mng khi c nhu cu gi i, gi thng tin chn a ch, nhn cc tn hiuthng bo v tnh trng ca mng hoc tnh trng ca thit b u cui cn linlc. Chng c tn chung l bo hiu thu bao. Mi thit b u cui thng cni vi mng bng mt i dy c gi l ng dy thu bao. Tng ng ming dy thu bao s l mt mch in bn trong mt thit b no ca mng.Mch in c gi l mch in giao tip ng dy thu bao SLIC

(Subscribers Line Interface Circuit). Mch in ny cho php thit b u cuica ngi s dng, qua i dy dn (ng dy thu bao), giao tip c vi ccthit b bn trong mng .

www.4tech.com.vn


11/302

Hnh 1.2 : Chc nng cc thit b u cuiNh vy thit b u cui, i dy thu bao v mch in giao tip i dy

thu bao trong mng cho php mi ngi s dng c quan h thu bao vi mng.Ngi s dng vi t cch l thu bao ca mng c th thc hin cc thao tciu khin tin trnh tin hnh cuc lin lc qua mng v trao i tin tc vi ccthu bao khc qua mng.

b. Trung tm chuyn mch

Qui m ca mt mng c th t rt n gin n cc k phc tp. C th

ly mng in thoi lm v d in hnh. Vi bn cht ng dng t nhin camnh v vi cc loi hnh dch v ngy cng phong ph, mng in thoi mang ngha tng qut ca mng vin thng v l mt i tng nghin cu ch yutrong lnh vc vin thng.

Mt mng in thoi n gin c th ch bao gm cc cp my in thoiu ni trc tip vi nhau qua mt i dy nh hnh 1.3

Theo phng thc ny, phc v lin lc gia mi cp im cn t mtcp my in thoi v ni chng bng mt i dy. Nh vy, nu c n im cnlin lc cho hon ton vi nhau th ti mi im cn c (n-1) my thoi ni

ti cc im cn li, do tng s my in thoi phi dng l n(n-1) my, tngng cn n(n-1)/2 i dy ni chng thnh tng cp.

Thit bu cui

Thit bu cui

SLIC

SLIC

Thit bu cuiSLIC

Bo hi uTin tc Mng

www.4tech.com.vn


12/302

Hnh 1.3 : Mng in thoi t chc theo kiu u ni trc tip tng cp

Phng thc t chc mng kiu ny ch c mt u im duy nht lm bo s c lp gia cc cuc lin lc. V d : Khi A lin lc vi B th ti A

dng my s 1, c lp hon ton vi mng lin lc gia A vi cc im cn lihoc gia cc im cn li vi nhau. T to kh nng t chc mng rt linhhot, d dng thm bt cc mi lin lc, d trin khai thu hi .

Tuy nhin phng thc ny c rt nhiu nhc im nh:

- Phc tp trong s dng: ta hnh dung trn bn lm vic ca gim c cti 4, 5 my in thoi lin lc ti tng phn xng. Khi mun lm vicvi mt phn xng c th th cn chn ng my in thoi ni ti phn xng, hoc c khi tn hiu gi ti t mt phn xng th phi nghe, phi quan s t xc nh cuc gi ang bo trn my no. Rt kh hnh dung nu s im lin

lc ln ti hng trm, hng ngn, thm ch ln ti hng triu thu bao, khng rkhi ngi s dng s xoay s ra sao vi n1 chic my in thoi trn bnlm vic ca mnh.

- Hiu qu s dng thit b u cui v ng dy thp do mi thit b ucui v i dy tng ng ch dng lin lc vi mt i tc duy nht nnchng rt t c dng n.

- Phc tp v tn km trong m rng mng. Gi s mng hin hnh c nim c kh nng ni cho hon ton, nu thm im th n + 1 th cn b xung2n thit b u cui v n i dy ni gia im mi b xung vi n im ban

u. Mt phng n kh d khc l ti mi im cn lin lc ch cn t mtthit b u cui v mt b chuyn mch ng dy ring. Khi cn ni ti mt

AB

CD

www.4tech.com.vn


13/302

im c th no th ngi s dng ch vic dng chuyn mch ring chnng dy ni ti im nh m t trn hnh 1. 4

Hnh 1.4 :Phng n dng chuyn mch ng dy ring

Theo cch ny to thun li cho ngi s dng v gim c s thit bu cui. Tuy nhin, s i dy ni cho gia cc im vn khng gim, bncnh , mi khi thay i s v tr s ko theo t chc li cc i dy v thay idung lng ca chuyn mch ring ti mi thu bao.

Mc d vy, phng n t chc mng theo cch ny cng to ra nhhng cho s ra i ca phng n t chc mng mi m n c s dng cho tingy nay, l, tp trung ton b cc chuyn mch ring vo mt thit bdng chung gi l trung tm chuyn mch hay cn gi l tng i. Khi ti miv tr ngi s dng s ch cn li mt thit b u cui. Thit b u cui nyc ni vi tng i ch bng mt i dy gi l ng dy thu bao. Cc bchuyn mch ring m trc y t ti tng v tr ngi s dng th nay c tptrung c vo trong tng i. Chc nng ca tng i l to ra tuyn ni gia ccng dy ca hai thu bao khi chng cn lin lc vi nhau. Ngha l, khi thu

bao A cn lin lc vi thu bao B th tng i s s dng thit b chuyn mchbn trong n ni mch in ng dy thu bao A n mch in ng dy

A

B C

D

E

www.4tech.com.vn


14/302

thu bao B, duy tr tuyn ni khi hai thu bao lin lc (trao i thng tin)vi nhau, gii phng tuyn ni khi cc thu bao ny kt thc cuc lin lc.Nh vy, chc nng chnh ca cc trung tm chuyn mch (tng i) l to tuyntruyn thng tin t thu bao ny ti thu bao khc khi chng cn lin lc vinhau. thc hin c chc nng ny cn trang b cc thit b chuyn mch phhp trong tng i v phi c kh nng trao i thng tin iu khin gia cc

thit b u cui v thit b iu khin chuyn mch ca tng i. n y ta cth hnh dung rng, tng i l thit b dng chung cho cc thu bao, cc thit bu cui ca cc thu bao c ni ti tng i bng cc ng dy thu bao; bntrong tng i s c cc mch in giao tip ng dy thu bao tng ng vitng ng dy thu bao; thit b chuyn mch dng kt ni cc ng dythu bao, v c phn iu khin iu khin cc kt ni .

Trung tm chuyn mch (tng i) l thit b mng dng to ra tuynthng tin gia cc thit b u cui ca cng tng i vi nhau (cuc gi ni ht),hoc gia thit b u cui ca tng i ny vi thit b u cui ca tng i

khc qua ng trung k (cuc gi lin tng i, cuc gi ng di), hoc giacc trung k vi nhau (cuc gi qu giang).

Hnh 1. 5 :Phng thc lin lc qua tng i

SLICSLIC

SLIC

SLIC

SLICSLIC SLIC

ThiT Bchuyn mch

iu khinchuyn mch

Tng i

ng dythu bao

TICng dy

trung k

www.4tech.com.vn


15/302

Cc nhm chc nng ca Trung tm chuyn mch bao gm:

- Nhm chc nng chuyn mch : To tuyn ni, duy tr, gii phng tuynni i vi tng cuc gi.

- Nhm chc nng bo hiu : Cung cp v x l cc bo hiu thu bao vbo hiu trung k phc v chc nng chuyn mch.

Ngoi ra cc trung tm chuyn mch cn thc hin cc nhm chc nngmng quan trng khc nh t chc, qun l mng (vai tr node mng, qun ltrng thi ca cc u cui v tuyn truyn dn), cung cp giao tip v cc dchv thu bao, phi hp truyn dn( t chc ngn hng knh, dng, mc tn hiu...)bin i v t chc thng tin bn trong trung tm chuyn mch...

Trong t chc mng th cc trung tm chuyn mch l cc node mng, cth dng phc v kt ni gia cc thu bao vi nhau (chuyn mch ni ht)hoc gia node ny vi node khc (chuyn mch kt ni, chuyn tip, ng di,trung tm ca quc t).

c. Cc tuyn truyn dnPhm vi phc v ca mt tng i thng b gii hn v dung lng v v

phn b a l. Thng thng, dn c tp trung thnh cc khu vc. Do titrung tm ca tng vng dn c ngi ta t mt tng i c dung lng ph hp phc v nhu cu lin lc ca dn c trong vng. Gia cc tng i ny c thc cc ng trung k trc tip, cc tuyn truyn dn ti cc tng i ca ccvng ln cn phc v cc cuc lc gia thu bao ca tng i ny vi thu baoca tng i khc. Nhn chung, cc tuyn truyn dn thng c lp t giacc tng i m lu lng thng tin cn trao i ln hoc gia cc trung tmthng tin. l cc tuyn thng tin nhiu knh, trn c s dng k thut ghpknh v cc gii php k thut cho vic truyn tn hiu i xa. Nh vic p dngcc k thut m c th t chc mng vin thng ton cu.

Trong thnh phn mng vin thng cc tuyn truyn dn ni cc trung tmchuyn mch vi nhau, cho php cc cuc gi c th tin hnh qua nhiu nodemng. V vy, chc nng chnh ca chng l to ra lin kt mng gia cc trungtm chuyn mch. Mng vin thng thng c t chc theo kiu phn cp,phn vng. Tn hiu qua cc thit b truyn dn c bin i, c t chc ghptch knh, c ti to v khuch i b nng lng sau tng chng truync i xa, v nh c th t chc mng ln (mng ton cu).

www.4tech.com.vn


16/302

1.1.3 T chc mng vin thng

a. Mng hp ni

Nh trnh by phn trn , mi tng i cc b phc v cc thu baotrong mt vng. Cc vng ny khng c ranh gii r rng, chng c th an xennhau. Gia cc tng i cc b c th l cc trung k trc tip hoc cc tuyn

truyn dn. Tuy nhin, nu s dng cc trung k v cc tuyn truyn dn trc tip to ra mng ni cho gia cc tng i cc b th cu trc mng s rt phctp. Cng tng t nh vic dng i ni ht gim cc ng dy trc tipgia cc thu bao, y cng c th dng tng i kt ni trung gian gia cctng i ni ht gim cc trung k v cc tuyn truyn dn trc tip. Nh vycc trung k trc tip v cc tuyn truyn dn trc tip ch c t gia cc tngi ni ht gn k nhau v ch phc v phn no lu lng thng tin gia chng,phn cn li ch yu c phc v qua tng i hp ni trung gian nh hnh 1.6.

Hnh 1. 6 :T chc mng kiu hp ni

ng dythu bao

ng dythu bao

Tng ihp ni

Tng ihp ni

Tng ihp ni

ng dythu bao

ng dythu bao

ng dythu bao

Vng 1 Vng 2

Vng 3

Ghi ch

Tng i ni ht

Trung k trc tip

Trung k hp ni

Tuyn truyn dn

www.4tech.com.vn


17/302

Trong phng php t chc mng kiu ny cc tng i hp ni ng vaitr nh tng i ca cc tng i, chng thc hin chc nng kt ni gia cctng i trong tng vng vi nhau v gia vng ny vi vng khc, t chophp gim cc trung k trc tip, m rng phm vi dch v cho cc thu bao vto iu kin t chc mng linh hot hn.

b.Mng phn cp

Khi xy dng mng quc gia cn hoch nh cc cp chuyn mch. Numng khng c phn cp th vic phc v cc cuc gi ng di s gp khkhn do tuyn ng di khng c hoch nh trc, cuc ni s phi quanhiu tng i, thi gian thit lp lu, gi thnh cao, s dng cc thit b kmhiu qu, cht lng phc v thp... Mng phn cp cho php khc phc c ccnhc im cp trn y lm cho cc cuc gi ng di c tin hnhnhanh chng, thun tin v cht lng cao. Vic phn cp i i vi vic hochnh chin lc nh tuyn cho cc loi cuc gi gia hai thu bao bt k. Cccuc gi ng di c nh tuyn theo cc tiu chun ti u. M hnh mng

phn cp c m t trn hnh 1.7. Nhn chung vic x l nh tuyn c thchin trn c s phn tch hng cuc gi v trng thi ca cc ng lin kt giacc trung tm chuyn mch. Khi pht sinh mt cuc gi th hng trc tip sc chn trc tin. Nu hng trc tip khng c kh nng phc v th cucgi s c tin hnh trn mt trong cc hng thay th qua trung tm chuynmch cp cao hn.

Trung tm quc t

Trung tm lin tnh

Trung tm vng

Tng i ni ht

Hngtrc tip

Hngthay th

nh 1.7 :M hnh t chc mng kiu phn cp

www.4tech.com.vn


18/302

1.1.4 Cc thnh phn thit yu khc ca mng vin thng.

a. H thng bo hiu

cc thnh phn chnh trong mng vin thng nh cc thit b u cui,cc trung tm chuyn mch, cc tuyn truyn dn hot ng phi hp nhp nhngvi nhau th gia chng cn c nhng thng tin iu khin. Cc thng tin iu

khin dng trao i gia c c thnh phn chnh trong mng phc v cho ccqu trnh thit lp, duy tr, gii to cuc gi c gi chung l bo hiu.

hiu c vai tr ca bo hiu ta xem xt qu trnh thc hin cuc gigia mt thu bao ca tng i A vi mt thu bao ca tng i B. Hnh1.8 thhin nhng tn hiu bo hiu c trao i gia cc thu bao vi cc tng i vgia cc tng i vi nhau trong cc qu trnh thit lp, duy tr v gii phng ktni.

Hnh 1. 8 : Qu trnh tin hnh cuc gi qua tng i

Qu trnh thc hin mt cuc gi trn thc t c th xy ra nhiu kh nng

khc nhau tu thuc vo l cuc gi ni ht hay ng di, cuc gi c thchin trn vn hay b kt thc gia chng, nguyn nhn cuc gi khng thnhcng, m t s c cc loi tn hiu bo hiu khc nhau c trao i gia cc

Tng iA

Tng iB

ng dythu bao

ng dythu bao

Trung k

hc t hp

Tn hiu "Mi chn s"

Chn cc ch s a ch

Yu cu chim trung k

Chp nhn chimYu cu gi cc thng tin a ch

Cc ch s a ch

Tn hiu chungTn hiu "Hi m chung"

Tr li Tn hiu nhc t hp

Trao i thng tin

Kt thc cuc gi Yu cu gii to cuc gi

Chp nhn gii to Kt thc

Bo hiu ng dythu bao b gi

Bo hiu lin tng iBo hiu ng dy

thu bao gi

www.4tech.com.vn


19/302

thnh phn trong mng . Cc tn hiu bo hiu c th chia thnh bo hiu thubao (bao gm bo hiu ng thu bao gi, bo hiu ng thu bao b gi) vbo hiu trung k (hay bo hiu lin tng i) tu thuc vo tng tn hiu bohiu c s dng trn cung on no ca mng. V cc n v tn hiu bohiu c th v ngha ca chng s c cp trong chng ring ca ti liuny.

b. H thng qun l, iu hnh v bo dng

Cc th h tng i c in trc y cng bt u hnh thnh c squn l v bo dng, tuy nhin ch tp trung vo cng vic tnh cc n gin vcnh bo li th s. Cc th h tng i hin i iu khin theo chng trnh ghisn (SPC- Stored Program Control) cho php lu tr chng trnh iu hnh hotng ca tng i, c s d liu thu bao v d liu trung k, cc chng trnhqun l mng v chn tuyn ti u, cc chng trnh chun on hng hc chophp qun l tp trung cc tng i trong phm vi no v thc hin cc quytrnh bo hnh, bo dng t xa.

c. ng b mng

Cc trung tm chuyn mch hin nay hu ht l cc tng i chuyn mchs, do yu cu s ng b cht ch gia cc tng i. ng b c ngha htsc quan trng, mang tnh sng cn ca mng s ho, n nh hng trc tip ncht lng phc v QoS ca h thng. Ngy cng nhiu loi hnh thng tin ckt hp vi nhau c phc v qua mng vin thng, c nhng loi hnh thng tinrt nhy cm vi hin tng trt v lp, v d nh thng tin s liu, v vy sai stnh trong ng b s dn ti trt v lp thng tin, nh hng ti cht lng phcv v c th gy gin on lin lc bi vy cn p dng cc gii php k thut

m bo ng b mng thng tin s. Chi tit v vn ny s c cp ccchng sau.

www.4tech.com.vn


20/302

1.2 Chuyn mch knh, chuyn mch tin, chuyn mch

gi.

1.2.1 Khi nim v chuyn mch knh (Circuit Switching).

Chuyn mch knh c hiu l mt phng thc chuyn mch m khiphc v mi cuc gi gia mt cp thit b u cui no th knh truyn gia

cc mch in giao tip ca hai thit b u cui c thit lp v dnh ringcho vic trao i thng tin gia hai thu bao ny. Cc cuc gi ng thi gia cccp thu bao khc nhau c tin hnh trn cc knh truyn khc nhau, c lpnhau.

Knh truyn ny c th c hiu l tp hp cc on mch do cc thit bchuyn mch v cc knh c phn phi trn cc tuyn truyn dn to ra mttuyn truyn tn hiu ni tip nhau t mch in ca thu bao ch gi ti mchin ca thu bao b gi.

c im ca chuyn mch knh l :

-Thit lp knh truyn ri mi truyn thng tin trn knh c thit lp.-H thng chuyn mch khng kim sot thng tin trn knh thit lp.

-Thng tin khng b tr hoc b tr khng ng k v khng gy ra rung pha(Tr u cho mi thnh phn tn hiu ca mi cuc gi) do ph hp vidch v thi gian thc.

M hnh ca phng thc chuyn mch knh c ch ra trn hnh 1.9

Hnh 1.9 : M hnh chuyn mch knhCc thit b chuyn mch knh c th l cc b chuyn mch khng gian

(S-Switch) truyn tn hiu lin tc, cc b chuyn mch thi gian (T-Switch) cho

TS1 TS2 TS4 TS5 TS1 TS2 TS4 TS5

S-Switch S-SwitchT-Switch T-Switch

www.4tech.com.vn


21/302

tn hiu pam hoc l cc b chuyn mch s cho tn hiu PCM hay ch n ginl cc b ni dy.

1.2.2 Khi nim v chuyn mch bn tin (Message Switching).

Trong thc t khng c mng chuyn mch chuyn dng cho chuynmch bn tin nhng chng ta vn thng nhn c cc thng tin di dng bn

tin. C th hnh dung nguyn l chuyn mch bn tin nh sau: Tin tc cn truynl bn tin s c gi n node gc km theo a ch ngun v a ch ch. Nodegc lu bn tin trong b nh ca n, lp k hoch chn tuyn ti ch v gi yucu ti node k tip theo k hoch chn tuyn, khi node k tip sn sng tipnhn bn tin th hai node tin hnh trao i bn tin cho nhau, c nh vy bn tins c truyn ti ch. Cng c th truyn bn tin theo cc thut truyn khcnhau, min sao bn tin ti c ch.

Hnh 1.10 :M hnh mng chuyn mch bn tin

c im ca phng thc chuyn mch bn tin:

- Bn tin c kch khng xc nh v vy phi c b nh ln ti cc node tip nhn v lu tr bn tin.

- Thi gian truyn ti tin ln, d gy tc nghn.

- Tr bn tin trong cc node v trong mng khng xc nh.

- p dng cc bin php pht hin v sa li.

1.2.3 Khi nim v chuyn mch gi.

Bn tin c chia thnh cc gi v c truyn cng cc tip u v tip

a

b

c

d

e

f

g

h

i

dte

dte

www.4tech.com.vn


22/302

cui ca gi, cc tip u v tip cui l cc trng iu khin hng dncc node ca mng a cc gi ti ch, kim sot li v iu khin lu lng.Mt bn tin c th gm nhiu gi, chng c th c truyn ti ch theo phngthc hng lin kt (Connection-oriented) hoc theo phng thc phi kt ni(Connectionless). Nh th cc gi ca mt bn tin c th c truyn theo cngmt tuyn qua cc nt mng hoc cng c th c truyn trn cc tuyn khc

nhau. Thm vo , trong qu trnh truyn cc gi c th c li, mt vi gi phitruyn li v do cc gi c th n ch khng theo th t, cc thit b mng vthit b u cui phi c kh nng kim sot v sp xp li cc gi khi phcli bn tin ti u cui thu.

c im ca phng thc chuyn mch gi:

- Gim c tr ti cc node v trong mng

- X l li v sa li hoc truyn li gi nhanh hn so vi chuyn mchbn tin do gim c lng thng tin cn truyn li, gim tc nghnv tng tc truyn tin cng nh kh nng phc v ca mng.

- C th nh tuyn cho tng gi hoc cho tt c cc gi ca cuc githeo cc th tc khc nhau.

Hnh 1.11M hnh nguyn l chuyn mch gi

1.2.4 Khi nim v cng ngh atm (Cng ngh chuyn giao khng

ng basynchronous Transfer Mode)

atm l cng ngh bao gm c kha cnh truyn dn v kha cnh chuynmch, y cng l dng chuyn mch gi c bit. V kha cnh truyn dn c

a

b

c

d

e

f

g

h

i

dte

dte

www.4tech.com.vn


23/302

th coi atm nh mt phng thc ghp knh khng ng b (cn gi l ghpknh thng k), ngha l ng truyn c phn chia mt cch linh hot cho cct bo t cc ngun tin khc nhau, khng cn tun theo mt trt t nghim ngt.Cc t bo ging nh cc gi tin c bit c kch thc c nh (53byte) tc hiu qu truyn dn v chuyn mch cao, gim tr trong mng v trnh tcnghn. Cc trng th tc trong mi t bo c ti thiu ho, n gin thao tcx l t bo ti cc node mng, nh th s tng c tc chuyn mch p ngc cc dch v tc cao. V chuyn mch p dng phng thc chuyn mcha ch th hin trong nhn dng knh o (VCI) v nhn dng ng o (VPI) t n gin ho chc nng chuyn mch, nng cao kh nng chuyn mch, kthp bo hiu knh chung to kh nng s dng VCI, VPI linh ng, d dng tchc mng ton cu.

a. Ch truyn ng b v ch truyn khng ng b

Trn hnh 1.12a minh ho nguyn l ghp knh thi gian ng b(Synchronous Time Division Multiplexing) hay cn gi l phng thc truynng b (Synchronous Transfer Mode). Cc knh c t chc thnh khung vc sp xp theo th t mt cch cht ch. Vic xc nh thng tin ca tngknh phc v cho vic phn phi chng cng nh thc hin cc thao tcchuyn mch phi bt u bng vic xc nh ng b a khung, ng b khung(Frame). Mt hoc thu sai ng b khung cng lm mt thng tin ca cc knh.Do bng thng c phn phi u cho cc knh nn nhng knh khng c thngtin truyn cng chim khe thi gian dnh cho n v cc knh khc c nhu cutruyn tin khng th tn dng c. u im c bn ca phng thc ny l tc truyn n nh do vy rt ph hp vi cc dch v c tc bt c nh v ccdch v yu cu tr khng i cho cc dch v nhy cm vi thi gian thc nh

Framin

Framing Channel1

Channel2

Channeln

Framin

Framing Channel1

Channel2

Channeln

Framin

Framing Channel1

Channel2

Channeln

Framin

Framing Channel1

Time Slot

Periodic Frame

H Channel1

H Channel1

H UnusedChannel

H Channel5

H Channel3

H Channel7

H Channel1

H Channel5

H Channel5

H Channel4

H Channel7

OccupiedTime Slot

IdleTime Slot

a. Ch truyn ng b STM

b. Ch truyn khng ng b ATM

Hnh1.12Minh ho cc ch ghp knh ng b v khng ng b

www.4tech.com.vn


24/302

tn hiu thoi hoc hnh nh.

Trn hnh 1.12b minh ho nguyn l ghp knh thi gian khng ng bATDM (Asynchronous Time Division Multiplexing) hay cn gi l phng thcchuyn giao khng ng b ATM(Asynchronous Transfer Mode). Bng thngc phn pht cho cc knh theo nhu cu (ghp knh thng k - StatisticalMultiplexing) v khng cn tun theo mt th t cht ch nh trong phng thctruyn ng b. Thng tin ca tng knh c truyn cng vi phn tip u H(Header-Overhead) ca n to thnh cc gi. Phn Header cha cc thng tiniu khin gip cho cc thit b mng xc nh c thng tin ca tng knh thc hin cc thao tc nh tuyn, chuyn mch v sp xp li bn tin. Nh cphn Header nn vic ghp v tch knh c tin hnh rt thun tin, bngthng c phn phi mt cch linh hot cho cc knh. Cng nh phn Headerm c th p dng c cu chuyn mch tng i n gin, l nguyn lchuyn mch a ch (Address Switching) hay cn gi l chuyn mch nhn(Label Switching) m chng ta s im qua di y.

Int@ Out@ Port

a m 1

b n *

Int@ Out@ Port

c o 2

Port1

Port1

ba

c

Int@ Out@ Port

M a 1

n b 2

Int@ O ut@ Port

o e 2

Port1

Port1

m n

o

Int@ Out@ Port

d p 2

e 0 1

Int@ Out@ Port

c o 2

Port1

Port1

ed

c

Int@ Out@ Port

o c 2

n b 1

n b 2

Int@ O ut@ Port

o c 2

p d 1

Port1

Port1

no

po

a

b e

bc

c

db

nh 1.13 Nguyn l chuyn mch a ch

www.4tech.com.vn


25/302

b. Chuyn mch a ch (Address Switching)

Trn hnh 1.13 minh ho nguyn l chuyn mch a ch. Mi b chuynmch c 2 u vo v 2 cng ra. Trn mi u vo c mt bng nh tuyn dng nh tuyn cho cc gi d liu. Mi gi d liu c gn mt nhn nh tuyn(nh cc ch s nhn dng trong header). Nhn s c so snh vi cc nhnca ct In@. B chuyn mch s chuyn i nhn thnh nhn u ra tngng nh trong ct Out@ v c chuyn ra cng u ra nh trc bi ct Port.Nh vy cc gi s ln lt qua cc b chuyn mch i t mt u vo no ti u ra ca Node chuyn mch. Cc bng nh tuyn s thay i mi khi btu hoc kt thc mt cuc lin lc no di s h tr ca h thng bo hiu.Nh th thao tc ca b chuyn mch bao gm x l nhn u vo, phin dchthnh nhn u ra v hng gi ti cng ra cn thit. V d gi u vo c nhnA s c chuyn thnh nhn M v chuyn ra cng vt l Port1. Ti mi cng ravt l c b nh m tm thi lu tr cc gi khi c nhiu gi cng c nhhng n mt cng ra vt l. B nh m ny lm vic theo nguyn l FIFO

(Vo trc, ra trc - First In First Out).1.2.5 lnh vc ng dng ca cc phng thc chuyn mch

Cc thng tin c ngun gc khc nhau thng c th hin bng ccdng tn hiu khc nhau. V d thng tin thoi hoc truyn hnh thng l dngthng tin lin tc c th hin bng chui tn hiu s tc bit khng i(CBR-Constant Bit Rate), trong khi thng tin my tnh, s liu li thng mangtnh gin on v di dng tn hiu s c tc bt thay i (VBR-Variable BitRate) v v th mi loi thng tin thch ng vi mt cng ngh truyn dn vchuyn mch. Nhng thng tin c tc bit khng i v nhy cm vi tr

thng chn hnh thc truyn ng b v chuyn mch knh. Truyn dn kiung b p ng tc truyn khng i v tr truyn dn l nh nhau cho tt ccc t hp tn hiu ca cng mt cuc gi. Chuyn mch knh thit lp knhdnh ring cho mi cuc gi trc khi truyn thng tin ca cuc gi v mbo tt c cc t hp tn hiu ca cng mt cuc gi s c truyn theo cngmt tuyn c thit lp dnh ring v v th khng lm thay i th t cacc t hp tn hiu , ng thi do c truyn theo cng mt tuyn nn cc thp tn hiu ny s c cng tr nh nhau lm cho tn hiu sau khi phc khngb mo pha, p ng c cc dch v nhy cm vi tr. i vi loi thng tin

c t chc thnh cc gi hoc cc t bo cho php s dng phng thc ghpknh thng k nng cao hiu qu s dng cc thit b mng, ng thi p dngnguyn l chuyn mch a ch n gin ho cc thit b chuyn mch ng

www.4tech.com.vn
mailto:[email protected]:In@.


26/302

thi thch ng vi nhiu loi hnh dch v vi nhiu tc khc nhau. i vinhu cu pht trin mng vin thng a dch v bng rng, cng vi nhng tin bvt bc trong lnh vc quang dn th cng ngh ATM l mt la chn c th png c nhng yu cu ca mt mng vin thng hin i.

1.3 Khi qut v tng i iu khin theo chngtrnh ghi sn SPC (Stored Program Control)

1.3.1 S pht trin ca cng ngh chuyn mch v phng thc iu

khin.

Trong phn ny ch cp ti cng ngh chuyn mch v phng thciu khin c p dng trong lnh vc chuyn mch knh.

Cng vi s pht trin ca cng ngh chuyn mch th cc phng thciu khin p dng trong cc th h tng i cng c pht trin, lun phinthay th ln nhau.

Nh trnh by mc 1.2, khi cc my in thoi c pht minh thu tin, t chc lin lc, n gin chng ni c tng cp trc tip vi nhaum khng qua mt loi tng i no c. Sau l vic p dng cc loi tng inhn cng kiu t thch hoc in chung. Thc cht cc tng i ny l cc thitb ni dy nhn cng, dng cc cp dy phch ni mch in ng dy cathu bao gi vi ng dy ca thu bao b gi. Trong cc tng i nhn cng,hu nh khng c h thng iu khin, cc tn hiu bo hiu cng ht sc ngin. Cc thng tin a ch c trao i bng li yu cu ca thu bao ti nhnvin tng i hoc nhn vin tng i pha ch gi ti nhn vin tng i pha b

gi. Nhn vin tng i thc hin chc nng ca h thng iu khin trong tngi, bao gm quan st, pht hin yu cu gi trao i nhn a ch thu bao bgi, pht tn hiu gi chung ti thu bao b gi, thit lp ni gia thu bao b giv thu bao gi, gim st cuc gi pht hin yu cu kt thc, gii to cuc gikhi c yu cu kt thc cuc gi.

Trong th h tng i t ng dng cc b chn nhy nc vic to tuynni gia mch in ng dy thu bao gi vi mch in ng dy thu bao bgi c thc hin mt cch t ng di s iu khin ca cc chm xung quays c to t a quay s ca thit b u cui thu bao gi. Cc tn hiu bo

hiu bt u phc tp ph hp vi bc pht trin vt bc v cng ngh, tchuyn mch nhn cng sang chuyn mch t ng. Cc tn hiu bo hiu tithiu p ng vic t ng ho qu trnh chuyn mch: Dng mch vng

www.4tech.com.vn


27/302

(bo hiu gim st), chn s dng xung (bo hiu a ch), cc m phc v (bobn, hi m chung, mi quay s), dng chung. Cha hnh thnh h thng iukhin. Mi thit b chuyn mch c b phn iu khin ring, hnh thnh phngthc iu khin c lp - trc tip - ni tip. c lp c ngha l mi b chn cbiu khin ring ca n, trc tip ngha l chm xung quay s iu khin trctip hot ng ca tng b chn, cn ni tip c hiu l mch iu khin ca

b chn c hnh thnh mt cch ni tip theo tin trnh thit lp tuyn ni (xemhnh 1.14)

Nhc im ca phng thc iu khin c lp-trc tip l thit b iukhin phn tn theo cc b chn lm hiu sut s dng thp, kch thc chn bcng knh, tc thit lp tuyn ni chm, khng cho php p dng cc phngphp nh tuyn, d b chn vo ng ct. Tuy nhin, phng thc iu khin nycng c mt vi u th nh nguyn l iu khin rt n gin, li iu khin camt thit b khng gy nh hng nghim trng, khc phc s c nhanh chng

Ngy nay, mt s h thng thng tin s cn chuyn mch tc cao cngc su hng p dng phng thc iu khin c lp, tuy nhin thao tc iu

khin chuyn mch ca n da trn vic x l nhn nh trong chuyn mch ach.

K

K

K

K

K

K

K

K

K

K

KCp chn

s bCp chnnhm 1

Cp chnnhm 2

Cp chnng dy

Hnh 1.14M hnh iu khin c lp-trc tip trong tng i nhy nc

www.4tech.com.vn


28/302

Th h tng i t ng dng b ni dy to (ngang dc) to ranhng tin b ng k. Kh nng ni dy ca cc b ni loi ny tng nhiu sovi loi b chn nhy nc, mi khi dc ca b ni dy ta tng ng mtb chn nhy nc n, t cho php gim ng k th tch thit b chuyn mchca tng i. Nguyn l ni dy theo kiu tip im p nn gim c s mimn. c bit, cho php p dng phng thc iu khingin tip-tp trung.

Nguyn l iu khin gin tip c th hin: Trc tin tn hiu chn s

t thu bao gi c thu v nh thanh ghi a ch, sau mi chuyn ti cc biu khin ca cc cp chn v t phn phi ti tng b ni dy. Nh vy,thit b iu khin cng bt u c tp trung, nng cao c hiu sut sdng ca cc thit b iu khin dng chung, tng kh nng iu khin v chophp chn tuyn theo mt s phng n nh trc, vic chn tuyn mang tnhbao qut trong phm vi mt tng i.

C hai loi tng i c in (nhy nc v to ) c c im chung lkch thc ln, chi ph khai thc kh cao, tiu th nng lng ln, dch v nghonn, cht lng dch v thp. Tuy nhin chng cng phc v trong khong thi

gian hng vi thp k (gn th k).Na cui th k 20 cng ngh ch to cc linh kin bn dn pht trin

mnh, k thut x l tn hiu v k thut vi x l to iu kin cho ngnh cng

B dy phchB iu khin cp chnng dy khu AB

Thanh ghi

a ch

B iu khincp chn thanh ghi

B iu khincp chn nhm

Giao tiptrung k

B iu khin cp chn

ng dy khu CD

A B

C D

A B

nh 1.15Phng thc iu khin gin tip trong tng i to

www.4tech.com.vn


29/302

ngh in t pht trin, trong c lnh vc k thut chuyn mch. Hng lotthit k, pht minh mi trong lnh vc truyn dn nh phn knh theo thi gian,quang dn thc y cc pht kin mi trong lnh vc chuyn mch.

Cc tng i in t c c im chung l thit b chuyn mch c chto trn c s linh kin in t, bn dn, vi mch c kch thc nh, tc ngnhanh, tiu th ngun thp, c kh nng tch hp cao v c bit l thch ng vicc k thut truyn dn tc cao. Phng thc iu khin trong cc tng iin t cng chuyn dn theo hng thay th cc mch logic ri rc trong cckhi, cc b iu khin bng cc phm mn cng cc b x l chuyn dng. Vnh th lm xut hin th h tng i iu khin theo chng trnh lu tr SPC(Stored Program Control). Phn mm iu khin cc tng i cng c dn citin v cng ngy cng cho php ngi s dng c thm nhiu tnh nng dch vtu t chn. Cc tng i iu khin theo chng trnh lu tr SPC cng vi cngngh truyn dn hin i v chuyn mch s nhanh chng thay th cc tng ic in. Phng thc bo hiu cng cn c hon thin lm cho hot ng ca

mng vin thng ngy cng linh hot, hiu qu, thng minh hn. Cc dch vthoi v phi thoi ngy cng xch li gn nhau hn trn c s chuyn mch s viu khin theo chng trnh lu tr. Cng ngh truyn dn v chuyn mch

atm m ra trin vng to ln cho cc dch v ca mng vin thng.

1.3.2. Tng quan v tng i iu khin theo chng trnh lu tr SPC

Trong qu trnh iu khin cc thit b chuyn mch cn phi thc hin rtnhiu php tnh logic, kt qu ca chng li cn c nh iu khin cc phnt chuyn mch. Trc y cc php tnh v cc chc nng nh c thc hintrn cc linh kin ri, n l, kh nng tnh ton chm. Ngy nay, nh vo thnh

tu ca k thut vi x l cho php kt hp cc chc nng x l ny trao chocc b vi x l chuyn dng. Cc php tnh logc trong x l cuc gi, cc qutrnh x l v phn phi bo hiu, chn tuyn, to cc bn tin iu khin chuynmch v cc thit b ngoi vi, kim sot cc mch giao tip c x l bi cc bvi x l trn c s cc phn mm c lu tr nh m gim ng k cclinh kin, nng cao cht lng v tc phc v ca cc tng i.

Vic kt hp iu khin theo chng trnh lu tr vi k thut chuynmch s cng nng cao u th ca cc tng i SPC. Mt s u im ca tng iSPC c th lit k di y:

-Tnh linh hot: Cc tng i SPC c tnh linh hot mc cao th hin kha cnh tc dng lu di v tc dng trc tip. Trc tin xem xt kha cnh tcdng lu di. Trong tng giai on pht trin ca h thng chuyn mch, mt lot

www.4tech.com.vn


30/302

chng trnh c th to ra cho php h tr cc nhu cu dch v v qun l. Shiu chnh phn mm p ng ngy cng da dng v dch v lm cho h thngkhng tr thnh lc hu theo thi gian. Nh vy, cc phn mm c bn m bocho h thng hot ng p ng cc dch v truyn thng v nhu cu hin ti, cxem xt kh nng thay i khi cn nng cp ch cn ci tin i cht v phnmm hoc a thm cc th tc mi m khng cn thay i cu trc phn cng.

Ngha l cu trc phn cng ca tng i SPC cng vi phn mm iu khin banu ca n c thit k theo khuynh hng module ho ph hp vi chin lcm rng c v dung lng v kh nng dch v.

Kha cnh hiu qu trc tip th hin kh nng thay i nhanh chngbng c s d liu c th thch ng vi iu kin thay i trng thi ca mng,ngha l kh nng thch nghi ca h thng vi tng trng thi mng khi c ccbin c, v d khi c mt tc nghn ti mt node mng no hoc trn tuyntruyn dn c c cc php chn tuyn ti u. Hoc i vi thu bao d dngthay i dch v ca tng thu bao bng vic thay i c s d liu ca n theo

yu cu ca ngi s dng.-Cc tin ch cho thu bao: Cc tng i SPC cung cp cho thu bao

nhiu tin ch hn, d dng v r hn trong cc tng i khc. Cc tin ch nyc phn phi bi h thng qun l v theo tnh nng tu chn ca thu bao.Cc tin ch bao gm:

+ Shortcode dialling (dch v quay s tt t b nh ca tng i): Cc ach thng gi c nh trc vo b nh ca tng i vi m tng ngno . Khi cn gi, thu bao ch vic chn m rt gn th a ch nh s t ng c gi ra.

+ Call transfer (dch v chuyn cuc gi): Chuyn cuc gi ti a ch khcmt cch t ng (call forward).

+Ring back when free (camp on): Cuc gi n mt thu bao ang bn schung li khi thu bao cn gi gii phng tr li.

+Automatic alarm call : Tng i t ng pht tn hiu cnh bo ti thi im

t trc (bo gi).

+Outgoing and Incoming call barring: Hn ch gi ti v gi i. Cho phpch thu bao hn ch cc cuc gi n v cc cuc gi i (gi ng di)

+Itemized billing: Cung cp ho n tnh cc chi tit cc cuc gi.+ Malicious call tracing : Thu bao hoc c quan c quyn c bit vngun gc ca cuc gi quy ri.

www.4tech.com.vn


31/302

Nhiu tin ch trn i hi tng cng kh nng bo hiu thu bao, v dyu cu s dng tnh nng chn m bng bo hiu a tn (DTMF Dual ToneMultifrequency). Mt s tin ch yu cu h thng bo hiu lin i thch hp.

- u im trong qun tr : Cc tng i SPC cung cp rt nhiu cc tinch qun l nh : iu khin cc tin ch ca thu bao, thay i nh tuyn, thay

i s liu thu bao v trung k, xut cc thng tin thng k qun l tng i, ccs liu phc v bo tr , chun on d bo hng hc.

Vic kt hp k thut s cng a li cc u im ni bt: K thut sc p dng cho khu chuyn mch v iu khin to thnh tng i s hohon ton, kt hp vi truyn dn s lm cho mng vin thng s cng th hinth mnh ca mnh.

Tc thit lp cuc gi c ci thin ng k do c s tng thch vdng v p gia phn iu khin v phn t chuyn mch, cng vi c tnhkhng nghn mch (non-blocking) ca cc chuyn mch s cho php thit kmng chuyn mch gn nh, tit kim v kh thng cao. Ngoi ra, nu cuc giang tin hnh b gin on bi mt l do no th c gng ti thit lp cucgi c th c thc hin m khng gy ra s cm nhn cho ngi s dng.

- Tit kim khng gian: Cc chuyn mch s c kch thc rt nh nhng

do tch hp rt cao nn kh nng chuyn mch rt ln li p dng k thutghp knh theo thi gian nn hiu xut s dng rt cao t gim c khnggian ca phn thit b chuyn mch v kch thc chung ca tng i.

- tin cy rt cao v rt d dng bo tr: Do khng c cc phn t c

in nn trong hot ng ca tng i loi tr c cc hng hc, sai st c kh.

Kch thc ca cc linh kin li gn nh nn cho php p dng cc bin php dphng m bo thay th t ng khi c sai st, s c. Cc mch chc nng cch to di dng module c kim sot bng cc chng trnh chun on,cnh bo hng hc, cung cp kh nng t bo hnh v cung cp thng tin y cho vic sa cha, bo tr. Ngoi ra cc tng i SPC cn cung cp kh nng qunl v bo dng t xa.

- Cht lng cuc ni: kt hp chuyn mch s v truyn dn s cho phpci thin rt c bn cht lng cuc ni bi cc l do: Truyn dn s trnh csuy hao tn gc, loi tr cc tn hiu nhiu, tp m, trnh c tp m tch lu. T cht lng cc cuc gi ng di v cuc gi ni ht khng c s khc bit.

www.4tech.com.vn


32/302

-Kh nng kt hp cc dch v phi thoi : Cc loi dch v phi thoi nhvideo, fax, telex, s liu ... c s ho c th c truyn v chuyn mch trongcng mng vi tn hiu thoi.

Mt mi trng s ho hon ton (tr mng thu bao) gm chuyn mchs, truyn dn s, iu khin theo chng trnh lu tr SPC, kt hp vi bo hiuknh chung s to nn mt mng vin thng hon chnh trong giai on hin nay Hon chnh vi ngha mnh cung cp v bo m cc dch v a dngp ng nhu cu ngy cng tng v cng cao ca ngi s dng. Bo hiu knhchung cung cp kh nng lin lc nhanh chng gia cc h thng iu khin cacc tng i, cung cp kh nng bao qut tnh trng ca cc node mng v cctuyn truyn dn, t c th chn tuyn nhanh, hiu qu v ti u hn. Ngoira bo hiu knh chung cn cho php m rng mt s dch v xuyn qua mng,iu hnh v bo dng tp trung.

1.3.3. S khi tng qut ca tng i SPC

Nhn chung cc tng i SPC c th l tng i Analog hoc tng iDigital dung lng v kt cu ca chng rt a dng. Hnh 1.16 ch a ra s khi tng qut ca tng i SPC. C th chia cu trc ca cc tng i SPC thnhhai h thng chnh : H thng thoi v H thng x l iu khin.

H thng thoi li c th chia thnh cc phn h : Phn h thu bao v

bo hiu thu bao, phn h trung k v bo hiu trung k, phn h chuyn mch.

Phn h thu bao v bo hiu thu bao gm cc mch kt ni ng dy thu

bao thc hin cc chc nng BOCHTRS (B- Battery feedcp ngun, O-Over-voltage protection chng qu p, C- Codec (coder and decoder) m ho v giim, H-Hybridbin i 2dy/4 dy, T-Testkim tra o th, R-Ring rung chung,S-Supervision gim st trng thi). Cc thit b u cui thu bao c th l loitng t (analog) hoc loi s (digital). i vi loi analog tt c cc chc nngtrn c thc hin ti mch kt cui ng thu bao SLIC (Subscribers lineInterface circuit). i vi loi thu bao s ISDN (Integrated Services digitalNetwork) mt s chc nng trn c thc hin ngay ti thit b u cui. Ngoicc mch giao tip ng dy thu bao, trong phn h ny cn c cc khichuyn mch tp trung thu bao dng tp trung ti thu bao. Chng c thitk theo tng nhm mch kt cui ng dy thu bao. Chc nng ca cc b tptrung ti thu bao l phn phi cc knh thoi a vo mng chuyn mch cho

cc mch kt cui ng dy thu bao khi thu bao tham gia mt cuc gi no v gii phng knh thoi khi thu bao kt thc cuc gi.

www.4tech.com.vn


33/302

iu ny rt quan trng, v cng ti ca mi thu bao ch khong 0,02Erlang. B chuyn mch tp trung ti thu bao s tp trung cc ti ca cc thubao trong tng nhm ti chm knh chuyn mch dng chung; ni cch khc ccb tp trung ti thu bao to kh nng dng chung mt s lng knh chuynmch cho s ng thu bao ca mt nhm sao cho hiu sut s dng knh chuynmch gn bng 1 vi mc gi ht cho trc. Ngoi ra b chuyn mch tp trungti thu bao cn lm nhim v ni mch in thu bao ti cc b to cc tn hiu

m tn Tone Gen., cp cc tn hiu Mi quay s, Bo bn, Hi mchung; hoc ti b thu m a tn MFR-MultiFrequency Receivertu thucvo tng giai on khi thu bao thit lp hoc kt thc mt cuc gi no . Biu khin giao tip LOC-Local controllerthc hin cc chc nng: phn phicc tn hiu bo hiu ng dy thu bao qua b chuyn mch tp trung ti thubao v phn phi knh thoi qua b chuyn mch , qun l trng thi thu bao,iu khin phn phi tn hiu bo hiu v cc tn hiu nh thi, lp cc bn tiniu khin truyn ti phn h x l iu khin, nhn v x l cc bn tin iukhin t phn h x l iu khin v to cc tn hiu iu khin b chuyn mch

tp trung ti thu bao v cc mch kt cui.Phn h chuyn mch nhm thng bao gm mng chuyn mch nhm,

b iu khin chuyn mch v mt s khi chc nng tu thuc vo tng loi

slic

slic

Khichuynmchtp

trung

thubao

Khi iu khin giao tipLOC

mfr

ToneGen.

Mngchuynmchnhm

atic

dtic

An Cas ccs

LOC

LOCiu khinchuyn mch

B x ltrung tm

B nhchnh

Thit b giaotip ngi-my

B nhchung

Thit bkim tra

Thit bcnh bo

Phn h thu bao v bo hiu thu bao Phn h chuyn mch nhm Phnhtrungkv

bohiutrungk

Phn h x l v phn phi bo hiu

Phn h x l trung tmPhn h qun l v bo dng

Hnh 1.16S khi tng qut ca tng i SPC

System BusBus controller

www.4tech.com.vn


34/302

tng i. Mng chuyn mch ca chng c th khc nhau c v mt cng ngh,c v cu trc v dung lng. C th l chuyn mch analog hoc chuyn mchdigital, c th c cu trc mt cp hoc nhiu cp tu thuc vo loi tng i vdung lng. B iu khin chuyn mch thc hin cc chc nng nh : Nhn ccbn tin iu khin chuyn mch t phn h x l trung tm; x l cc bn tin v chuyn chng thnh cc s liu iu khin tng ng sau a n cc b

chuyn mch c th; thc hin chc nng chn tuyn theo yu cu ca bn tiniu khin; hoc gii to tuyn ni theo bn tin gii phng cuc gi. Ngoi ra,cc b iu khin chuyn mch cn c th thc hin mt s chc nng lin quanti vic chn v tch cc bn tin iu khin qua mng chuyn mch. Cc thit bkhc thuc phn h chuyn mch thng bao gm thit b to cc tn hiu nhthi trong cc tng i chuyn mch s ng b mng chuyn mch v ccthit b ngoi vi chuyn mch; ngoi ra, chng cn c th l cc thit b dngchung nh b nh cc bn ghi t ng tr li, b nh cc a ch thng gi, thitb chuyn mch nhiu ng...

Phn h trung k v bo hiu trung kbao gm cc mch giao tip ccloi trung k tng t ATIC-Analog trunk interface circuit, trung k s (DTIC-Digital trunk Interface), x l tn hiu trung k s, x l bo hiu trung k vcc b iu khin km theo. Tu theo tng loi trung k c cc mch in giaotip trung k khc nhau. i vi trung k analog c th c loi 2 dy v 4 dy.Nhn chung cc mch giao tip ny c cc chc nng ging giao tip thu baotng t, tuy nhin c mt vi chc nng khc bit v bo hiu v cp ngun.iu ny s c cp chng ring. Cc mch giao tip trung k s thchin cc chc nng GAPZACHO (G-Generation of frame to khung, A-

Alignment of frame ng chnh khung, P- Polar conversion o cc, Z-Zerostring compression nn chui bt 0 lin tip, A-Alarm cnh bo, C-Clockrecovery ti to nhp, H- Hunt during reframe ti ng b, O-office signalingbo hiu lin i). Ngoi ra, phn h ny cn c b phn ghp v tch knh, ccb iu khin nhm trung k LOC phi hp vi h thng x l iu khin.

H thng x l iu khin c chia thnh cc phn h: phn h x l v

phn phi bo hiu, phn h x l trung tm, phn h qun l v bo dng.

Phn h x l v phn phi bo hiu thng bao gm cc thit b thu,

pht bo hiu, x l v phn phi bo hiu cung cp kt qu x l cho cc b iu

khin chuyn mch v x l cuc gi. Tu thuc tng loi tng i c th c ccthit b bo hiu CAS-Channel Associated Signaling hoc bo hiu CCS-Common Channel Signaling. a s cc tng i chuyn mch s hin i u

www.4tech.com.vn


35/302

xem xt ng dng CCS thch ng vi s pht trin ca mng vin thng trongtng lai. Tuy nhin, cng cn c thit b CAS lin kt vi cc h thng hinhnh.

Phn h x l trung tm iu hnh hot ng ca ton b tng i thng

qua cc b iu khin cp thp hn nh cc b iu khin giao tip LOC trongcc phn h ca h thng thoi. Cc b iu khin LOC trao i thng tin iukhin vi b x l trung tm thng qua Bus h thng (System Bus) di dng ccbn tin iu khin. B x l trung tm x l cc thng tin iu khin nhn ct cc b iu khin LOC trong qu trnh x l cuc gi v to ra cc bn tin iukhin gi li cc b iu khin iu hnh cc qu trnh phc v cuc gi.B nh chnh MM-Main Memory cha chng trnh iu hnh hot ng ca bx l v cc thng tin cn thit trong qu trnh x l. B nh chung cha chngtrnh gc ca tng i v cc d liu thu bao, d liu trung k v d liu chungca tng i. B x l trung tm v cc b iu khin khc c th truy cp b nhchung s dng cc c s d liu .

Phn h qun l v bo dng thc hin chc nng qun l hot ngca ton b tng i thng qua vic gim st hot ng ca cc b iu khinLOC, b x l trung tm v thng qua cc thit b kim tra, o th. N s a racc tn hiu hoc bn tin cnh bo, cc hng dn tng ng theo mi trng thica h thng. Thit b giao tip Ngi-my gip cho nhn vin vn hnh v cnb k thut c th theo di hot ng ca h thng v c kh nng giao tip vih thng thay i cc tham s v ch hot ng ca cc khi chc nng catng i.

Nhn chung cc tng i SPC dung lng nh thng xy dng h thng

x l iu khin tp trung a x l a chc nng. Cc tng i SPC dung lngthng ln t chc theo cu hnh nhiu b x l chuyn dng, phn cp, phndung lng .

1.3.4 S khi tng qut ca tng i s SPC (DSSDigital Switching

Systems)

Cc tng i SPC chuyn mch s gi chung l H thng chuyn mch sDSS ra i vo na cui th k 20. Ngy nay trn mng vin thng nc ta vnhiu nc khc c cc DSS ca nhiu hng sn xut nh NEC, Fujitsu Nht bn,Siemems c, Eriscon Thy in, Northern telecom Canaa, AT&T M, Alcatel

Php, L-G Hn Quc Ti Vit nam, ngnh bu chnh vin thng tin hnhnghin cu ch to v a vo s dng trn mng mt s DSS, ng thi cng

www.4tech.com.vn


36/302

cc bn lin doanh xy dng mt s c s sn xut ch to cc loi tng i DSSp ng nhu cu trong nc v hnh thnh cc c s nghin cu chuyn ngnh.

Nhn chung tng i DSS l mt h thng tng hp cng ngh cao, tptrung hi t rt nghiu ngnh cng nghip: Cng nghip in t, vi mch, k

Hnh 1.17 :S tng quan tng i SPC chuyn mch s.

slic

slic

t

sac

dlcd

loc

ATatic

AT atic

u

x

dmux

locmdf

DT

dtg

mfr

dtic

ddf

dtic

dtic

TdsWn

bt

MarkerScannerDistributorCasccs

bc

cc mm

ioc m-mi vdu prtdkumtu

To omcOa&ms

aps Swns

pcs

Sigs

cps

www.4tech.com.vn


37/302

thut vi x l, cng ngh vin thng, cng ngh thng tin, k thut Iu khin, ckh chnh xc C th ni, ngay c nhng tng i DSS dung lng khng lnlm nhng cng l mt h thng tng th rt phc tp trn quan im tng hpca cc ngnh k thut. Do , vi phm vi ca ti liu ny ch xem xt cc DSSdi mc n gin nht.

Hnh1.17 trnh by cu trc tng quan ca H thng chuyn mch s DSSiu khin theo chng trnh lu tr SPC.

Ton b tng i c chia thnh cc phn h chc nng, l : Phn hng dng APS-Application subsystem, phn h chuyn mch SWNS-SwitchingNetwork subsystem, phn h x l trung tm CPS-Central Processing subsystem,phn h bo hiu SiGS-Signaling subsystem, phn h ngoi vi iu khin PCS- Peripheral control subsystem v phn h iu hnh, qun l v bo dngOA&MS-Operation, Administration & Maintenance subsystem.

Phn h ng dng APS bao gm cc mch giao tip ng dy thu bao

SLic ( Subscribers Line Interface Circuit) v cc mch trung k tng t AT(Analog Trunk Interface Circuit). Mi ng thu bao c kt cui ti tng ibng mt mch SLIC ring qua gi phi dy chnh MDF ( Main Distribution

Frame). Cc thu bao c chia thnh tng nhm, mi nhm c iu khin bib iu khin vng LOC ( Local Controller), mt b phn phi cc tn hiu nh

thi TSAC (Time Slot Assignment Circuit) cn gn cc khe thi gian pht, thu

cho tng mch slic phc v chc nng m ha v gii m CODEC. B chuynmch ng dy s DLCD (Digital Line Concentration Device) thc hin chc

nng chuyn mch tp trung ti thu bao v chuyn mch tn hiu phc v t b

to tn hiu m tn dng s DTG (Digital Tone Generator), chuyn mch ngdy ti b thu tn hiu chn s a tn MF (Multi Frequency Receiver).

Mi ng dy trung k tng t cng c kt cui ti tng i bngmch ATIC(Analog Trunk Interface Circuit) chng cng c t chc thnh tngnhm v do b iu khin vng LOC iu khin. Mi nhm c mt b tch vghp knh MUX/ DEMUX ( Multiplexer v Demultiplexer) ghp tn hiu tcc mch ATIC theo hng vo v tch tn hiu theo hng ra a ti tngmch ATIC.

Cc tuyn tn hiu s PCM gia phn h ng dng v phn chuyn mch

c a qua gi phn phi tn hiu s DDF (Digital Distribution Frame), mituyn qua mt mch giao tip truyn dn s DTIC( Digital TrunkInterface

Circuit). Cc giao tip ny thc hin cc chc nng GAPZACHO phc v cho

www.4tech.com.vn


38/302

vic xc nh khung, khe theo hng vo v t chc khung khe theo hng ra,chuyn i m truyn dn ph hp, ti to xung nhp v ng b

Phn h chuyn mch SWNS bao gm cc thit b ca mng chuyn mchSwN- Switching Networkv cc thit b phc v khc. Mng chuyn mch ca

tng i c cu trc ph thuc vo dung lng ca tng loi tng i v thit kring ca tng hng sn sut. Tuy nhin, a s chng l mng chuyn mch phnchia thi gian (Time Division Switching Network), chng thng c cc cu trcT, TS, ST, TST v TSST trong T l k hiu chuyn mch thi gian s Tsw-Time Switch, cn S l k hiu chuyn mch khng gian s SswSpace Switch. Cc

chuyn mch u lm vic theo nguyn l phn khe thi gian v vy mngchuyn mch ca cc tng i s cn c gi l mng phn thi TDNw TimeDivision Network. Ngoi mng chuyn mch, trong phn h ny cn phi cmodule ng h chun BTBase time, thng l b dao ng c n nh caov tn s v cc b chia to cc tn hiu nhp cung cp cho hot ng ca cc bchuyn mch s, cc thit b truyn dn tn hiu s v cc b phn phi thi

gianTSAC ca phn h ng dng.Phn h bo hiu SiGS m nhn chc nng x l v phn phi bo hiu,

iu khin cc qu trnh chn, tch bo hiu. i vi tn hiu bo hiu CAS(Channel Associated Signaling) khi qua chuyn mch s cng c chuyn thnhdng s ging cc tn hiu tin tc khc v c phi hp vi hai pha ca mngchuyn mch bng cc b thch nghi. Bo hiu CCS (Common ChannelSignaling) dng trao i gia cc h thng DSS vi nhau.

Cc bo hiu ng dy thu bao hoc s c thu v x l s b ti phnh ng dng sau mi gi ti phn h ngoi vi iu khin PCS-Peripheral

Control Subsystem hoc l c nhn trc tip ti b qut trng thi (Scanner),cc bn tin iu khin t b x l trung tm c chuyn qua b phn phiDistributor. Nhim v ca b iu khin chuyn mch Marker l m bn tin

iu khin t phn h x l trung tm CPS chuyn thnh nhng s liu iukhin chuyn mch .

Phn h x l trung tm CPS m nhn chc nng iu khin hot ng

ca ton b tng i. Tu thuc vo dung lng v cu hnh tng i m phn hny c cu trc kiu mt b x l hay nhiu b x l. Trong cu trc nhiu b xl thng x l theo kiu phn cp, mt b x l cao nht qun l hot ng ton

b cc b x l cp thp hn, mt s b x l m nhim vic x l cuc gi vphn chia ti theo khu vc. Mi b x l thng c b nh chnh lu chng

www.4tech.com.vn


39/302

trnh v cc kt qu x l v c kh nng truy cp ti b nh chung nhn thmd liu thu bao v bng nh tuyn hoc ti nguyn khi cn thit.

Phn h iu hnh, qun l v bo dng OA&MS thng bao gm

cc thit b t ng theo di hot ng ca h thng, iu khin cc qu trnhchuyn i d phng, cnh bo khi c s c, cc thit b hin th, m thanh cnhbo ngi iu hnh iu khin vn hnh v theo di hot ng ca h thng,mt s ti nguyn lu tr s liu lu di v chng trnh gc. Cung cp khnng iu khin t xa v bo dng t xa tp trung ti trung tm bo dng.

www.4tech.com.vn


40/302

Chng 2

Chuyn mch knh (Circuit switching)2.1.Phn loi chuyn mch knh

Thng tin c trao i qua mng vin thng rt a dng nh thng tin

thoi, thng tin nh, vn bn, s liu. Mi loi c yu cu ring i vi thit btruyn dn v chuyn mch. C loi thng tin rt nhy cm vi tr nh thng tinthoi, thng tin hnh nh; v vy chng yu cu thit b dng truyn dn vchuyn mch chng phi khng gy tr hoc c tr th phi rt nh ngi sdng khng cm nhn c v gi tr thi gian tr phi l hng s trong sutthi gian ca cuc lin lc khng gy mo tn s tn hiu. i vi loi thngtin ny nn dng chuyn mch knh phc vthng tin dch v thi gian thc.

Tn gi chuyn mch knh th hin nguyn l hot ng ca mng. Khiphc v mt cuc lin lc gia hai thit b u cui no th mt knh thng tin(n cng hoc song cng tu thuc hnh thc lin lc) hoc mt tuyn ni c

thit lp xuyn qua mng t mch in ca thit b u cui ny ti mch inca thit b u cui kia. Knh thng tin hoc tuyn ni tn ti dnh ring chocuc lin lc sut t khi bt u ti khi kt thc cuc gi. Cc cuc gi ctin hnh ng thi qua mng phi c phc v trn cc knh c lp nhau.Trong lch s pht trin k thut chuyn mch mt s phng thc chuyn mchknh c p dng trong cc h thng tng i, l: chuyn mch phn knh

T hp

Chuyn mch knh

Chuyn mchkhng gian tng t

Chuyn mch PAM Chuyn mch s

Nhn cng T ng 2 dy 4 dy Tsw ssw

T

thch

in

chung

Nhy

nc

To

Ma

trnnh 2.1Phn loi chuyn mch knh

www.4tech.com.vn


41/302

theo khng gian dng cho tn hiu lin tc, chuyn mch phn knh theo thigian i vi tn hiu ri rc ho (tn hiu iu bin xung PAM-Pulse Amplitude

Modulation), chuyn mch s PCM ( cho tn hiu iu ch xung m pcm-Pulse Code Modulation). Thng k cc loi chuyn mch knh c ch ra trnhnh 2.1.

Trong cc tng i nhn cng, tng i kiu nhy nc, tng i ta hoc tng i dng b ni dy ma trn khi mt cuc gi c tin hnh th ccphn t chuyn mch s to thnh mch ni dy lin tip t mch in ca thitb u cui ny ti mch in ca thit b u cui i thoi vi n. Sau tnhiu trao i gia cc thit b u cui ny s i qua mch ni dy . Nu c cccp thu bao khc cng lm vic ng thi th gia tng cp mch in ca ccthu bao cng c tuyn ni gia chng v cc tuyn ny hon ton c lpnhau v b tr trong khng gian. Khi kt thc mi cuc gi cc phn t chuynmch dng cho cuc gi s c gii phng v cc cuc gi tip tip theogia cc thu bao khc c th s dng li chng to tuyn mi. Cc thit b

chuyn mch khng gian tng t c c im l trn tuyn ni c thit lpgia hai thu bao c th truyn tn hiu theo c hai hng, ngha l c th phc vcuc gi song cng trn hai dy v c th cho qua c tn hiu analog v tn hiudigital, thm ch c tn hiu ri rc PAM.

Nguyn l chuyn mch PAM da trn vic phn chia cc khe thi gian.Mt phn t chuyn mch c th phc v cho nhiu cuc gi c tin hnh ngthi theo nguyn tc cho tn hiu ca cc cuc gi khc nhau qua n trong cckhe thi gian khc nhau theo tng chu k. Tn hiu qua phn t chuyn mch ltn hiu c ri rc ho c chu k lp ca cc xung iu bin bng vi chu k

lp cc khe dnh cho tng mch cho tn hiu ca mi cuc gi i qua. Tuy ccchuyn mch PAM khng c p dng mt cch rng ri do nhiu hn ch cachng, nhng chng cng to nn tng cho cng ngh chuyn mch tin tin hnsau ny m hin ang c s dng rng ri l cc chuyn mch s PCM.

Cc xung iu bin ca tn hiu PAM rt mnh (hp), cng sut tn hiurt nh, v vy trong truyn dn rt d b tc ng ca cc tn hiu khc lm bindng, t , vic khi phc li dng ban u gp nhiu kh khn v k thut PCMkhc phc nhc im ny rt hiu qu. Trong k thut s ho tn hiu PCM, ccxung PAM cn tri qua cc cng on lng t v m ho. Mi xung iu binc m ho bng mt t hp cc bt tng ng v sau chng c truyn

di dng cc t hp bt . Ti u thu, t cc t hp bt thu c s khi phcli dng ca tn hiu c truyn i gn ng vi tn hiu gc. Vic chuyn

www.4tech.com.vn


42/302

mch tn hiu PCM cng c thc hin theo nguyn l phn khe thi gian. Ccc loi b chuyn mch PCM c bn l chuyn mch thi gian s Tsw-Timeswitch v chuyn mch khng gian s Ssw-Space switch, chng khc nhau vcu to v tnh nng. Mng chuyn mch ca tng tng i c xy dng trn cs kt hp cc Tsw v Ssw theo mt trong cc cu hnh T, TS, ST, TST, TSST,STS, ....

2.2. Chuyn mch khng gian tng t

2.2.1 Khi qut v chuyn mch khng gian tng t

Cc tng i thng c thit k cho vic chuyn thng tin hai hng(song cng), v d in thoi thng truyn tn hiu thu v pht trn cng i dy,mc d mt vi im ca tuyn truyn dn cc tn hiu hng pht v hng thuvn c th c tch ring phc v vic khuych i lp, tng c ly truyn,nhng nhn chung cc tn hiu thoi ni ring v cc tn hiu tng t ni chung

vn thng s dng phng thc truyn hai hng trn cng i dy. T ccb chuyn mch khng gian tng t cng phi c kh nng chuyn mch tnhiu hai hng gia mch in ca thu bao no vi mch in ca thu baokhc ang lin lc vi n. Chuyn mch khng gian tng t to ra tuyn nitruyn thng tin hai hng qua cc phn t chuyn mch ni gia mch inca thu bao ny v mch in ca thu bao khc ang lin lc vi n. Cc cuclin lc ng thi qua chuyn mch khng gian tng t phi c tin hnh quacc tuyn ni ring bit xuyn qua mng chuyn mch khng gian , ngha lgia cc tuyn ny khng c cc on mch in dng chung.

12

N

.

.

12

M

.

.

Hnh 2.2 :M hnh chc nng chuyn mch khng gian

C(,)

Ccuvo(I)

Ccura(O)

Cc tn hiu iu khin

www.4tech.com.vn


43/302

Trng chuyn mch khng gian tng t c th c to thnh t mthoc nhiu b chuyn mch khng gian c bn theo cc cu trc ghp khc nhau.S phn t chuyn mch dng to ra mt tuyn ni xuyn qua trng chuynmch ca mt tng i ph thuc vo s cp chn, s khu trong mi cp chn vcch ghp ni cc b chuyn mch. Mi b chuyn mch khng gian c bn ck hiu v c m t chc nng nh trn hnh 2.2

c im chung ca cc chuyn mch loi ny l:- S u vo Input v s u ra output c th ging hoc khc nhau.- Nu c nhiu cuc gi i qua b chuyn mch th phi m bo mt u

vo ch ni vi khng qu mt u ra ngha l cc tn hiu iu khin C(, ) v

C(x, y) tn ti ng thi khi v ch khi x v y.

2.2.2 Cu to v nguyn l hot ng ca b chuyn mch khng gian c

bn

Nhn chung cc b chuyn mch khng gian tng t c cu trc ma trnnh hnh 2.3

Phn ma trn chuyn mch gm cc u vo 1, 2 ... N v cc u ra1,2,3.... M, giao im gia mt u ra vi mi u vo l mt phn t chuynmch . Nh vy mi phn t chuyn mch c dng "ni xuyn" t mt uvo ti mt u ra c th, V d: phn t chuyn mch 31 dng ni u vo I 1vi u ra O3, cn phn t 25 li dng ni u vo I 5 vi u ra O2. Phn iukhin chuyn mch thng l b nh v gii m s liu iu khin a ra tnhiu iu khin tng phn t ca ma trn chuyn mch.

Yu cu i vi cc phn t chuyn mch ca b chuyn mch khng giantng t l khng lm suy hao tn hiu, khng gy xuyn m, khng to ra tp mnn. iu ny c th hiu n gin l khi trng thi m (ni thng) th tr

khng ca phn t chuyn mch phi cc nh (l tng l = 0), nh th skhng lm tn hao tn hiu truyn qua n. Cnkhi trng thi ng(ngt mch,

h mch) phi c tr khng rt ln () tn hiu t mt u vo khng b truynti cc u ra khng mong mun, d ch l rt nh, nh th tn hiu knh thngtin ny khng b xuyn sang cuc ni khc.

V d: Khi phn t 32 m th u vo I2 v u ra O3 c ni thng, tn

hiu t u vo I2 c truyn ti u ra O3 hoc ngc li m khng b suy hao.Khi cc phn t khc trn hng 2 v ct 3 phi ng hon ton trnh d tnhiu ra cc cuc gi ang tin hnh ng thi trn cc u vo v u ra khc.

www.4tech.com.vn


44/302

Gi s phn t 31 b d (tr khng h mch khng ln) th tn hiu cacuc gi trn phn t 32 c th b lt ti cuc gi ang tin hnh gia u vo I1vi u ra no . Hai ch tiu trn c th biu din thng qua iu kin cn caphn t chuyn mch tng t l h s chuyn mch.

Ngoi ra cc phn t chuyn mch khi ni mch phi khng gy ra tp mni (tp m nn). Tp m nn to ra nhng nhiu ro trong tn hiu, cn tr victruyn v thu cc tn hiu hu ch. Cc tp m nn do tip xc ca tip im, chtlng linh kin gy ra.

Cc phn t chuyn mch c th l r le in t, r le ng kn (Heccon),cc loi bn dn nh diode, tranzistor ... Mt vi phn t chuyn mch dng trongcc b chuyn mch khng gian tng t c m t trn hnh 2.4

V thc cht phn t chuyn mch khng gian tng t l phn t dng

ni thng t mch u vo ti mch u ra khi c tn hiu iu khin ni v lmh mch khi c tn hiu ngt mch.

hn iu khin chuyn mch

I1

I2

I3

I4

In

.

.

o1 O2 O3 O4 Om. .

11

12

13

14

1N

21

22

23

24

2N

31

32

3

34

3N

41

42

43

44

4N

51

52

53

54

5N

Cc u ra

Ccuvo

Ma

trn

chuy

nmch

Phnt

chuynmch

nh 2.3 Cu trc b chuyn mch khng gian c bnSlk

H= Tr khng h mchTr khng kn mch 10

8

www.4tech.com.vn


45/302

Cc phn t chuyn mch kiu c in nh r le in t hoc r le ng knthng c h s chuyn mch H tt hn so vi cc linh kin bn dn. Tuy nhinchng c kch thc ln, tiu th nng lng cao hn, iu khin phc tp hn vtc chuyn mch thp. Do yu cu v tr khng thng v tr khng h mchnn ch mt s loi linh kin bn dn c th dng lm phn t chuyn mch,chng tiu th nng lng thp, d phi hp vi phn iu khin logic v cc h

thng iu khin dng vi x l.

Phn iu khin ca b chuyn mch thc hin chc nng phi hp giaphn iu khin chung vi cc phn t chuyn mch. Tu thuc vo tng loi bchuyn mch m phn iu khin ny c th c cu trc v tnh nng khc nhauc v cch thc iu khin, dng tn hiu v mc tn hiu iu khin. Nhn chungphn iu khin ca b chuyn mch nhn s liu iu khin t phn iu khinchung v chuyn n thnh tn hiu iu khin a ti phn t chuyn mch cth ca b chuyn mch, ngha l n thc hin chc nng nh m v gii m sliu iu khin .

Theo nguyn l phn knh khng gian, khi tuyn ni cho mt cuc gi

c thit lp i qua mt b chuyn mch c bn no th phn t chuyn mchc dng thit lp tuyn ni cho cuc gi s b chim t khi bt u thit

Cundy

uvo

ura

u iukhin

Ngun

Phn t chuyn mch bng Rle in t

uvo

ura

u iukhin

Phn t chuyn mch Heccon

Ngun

u vo

ura

iukhin

Phn t chuyn mchdng Tranzistor

u vo u ra

R1

R2

R3

R4L1

D1

iu khin

Phn t chuyn mchdng Diode

Hnh 2.4Mt s phn t chuyn mch dng trong cc b chuyn mch khnggian c bn

+

www.4tech.com.vn


46/302

lp tuyn ni m thoi cho ti khi tuyn ni c gii phng v n cdnh ring cho cuc gi trong sut thi gian tin hnh cuc gi. Cc cuc gic tin hnh ng thi qua b chuyn mch s i qua cc phn t chuynmch c lp cho mi cuc gi. Vic truyn tn hiu cn c tin hnh trn 2hoc nhiu dy, v vy phn ma trn chuyn mch thng gm 2 hoc nhiu lp,phn t chuyn mch ti mi giao im phi c nhiu cp tip im, mi cp

dng cho mt lp v c chung iu khin hoc mi lp c phn t chuyn mchti mi giao im nhng cc phn t ca tng giao im cng tn c u iukhin chung. i vi b chuyn mch khng gian tng t, khi mt phn t trng thi ni th tn hiu truyn qua n nh qua mt im ni dy thng thng,ngha l khng phn bit u vo v u ra, tn hiu c truyn theo hai hngv nh th i vi b chuyn mch khng gian tng t cng khng c khi nimu vo v u ra ca b chuyn mch. Vic gi l u vo v u ra ca bchuyn mch ch tin cho vic gii thch theo tin trnh thit lp tuyn ni chomi cuc gi ch khng c ngha i vi tn hiu truyn qua b chuyn mch.

Cc quy c v khi nim chung*K hiu b chuyn mch khng gian (Xem hnh 2.5)

*Kh thng ca b chuyn mch:

1

2

3

N

1 2 3 M

K hiu kiu ma trn tip im

1

2

3

N

1 2 3 M

K hiu kiu ma trn giao im

1

2

3

N

1

2

3

M

K hiu kiu quy c K hiu kiu b chn

N M

nh 2.5 Cc k hiu ca b chuyn mch khng gian tng t

www.4tech.com.vn


47/302

B chuyn mch tip thng hon ton(ton thng) l b chuyn mch mmi u vo u c kh nng ni ti u ra bt k. i vi loi b chuyn mchny phi c quan h 1:1 gia u vo-phn t chuyn mch-u ra, ngha l trngiao im gia mt u vo bt k vi mt u ra bt k u phi c phn tchuyn mch tng ng (hnh 2.6a)

B chuyn mch khng ton thng (tip thng khng hon ton) loi ny

khc loi trn l mt s giao im ca ma trn chuyn khng c phn t chuynmch. Nh th mt s u vo khng th ni ti mt s u ra no (hnh 2.6b)

B chuyn mch gp : Nu php ni C(i , j) C (j, i) v C (, ) 1 thcc phn t c th tp trung mt pha ca ng cho chnh trn ma

trn chuyn mch v ta c b chuyn mch gp vi n(n-1)/2 phn t chuynmch nh hnh (2.6c)

*Kch thc b chuyn mch

Chuyn mch vung: Khi s u vo v u ra ca b chuyn mch bngnhau v ton thng

Chuyn mch ch nht : Chuyn mch ton thng nhng s u vo vu ra khc nhau.

Ngoi ra tu thuc vo ng dng c th th s lp ca b chuyn mchcng c th khc nhau.

2.2.3 Xy dng cc trng chuyn mch khng gian tng t trn c s

b chuyn mch c bn

a. Khi qut chung v ng dng chuyn mch khng gian tng t

V c bn cc b chuyn mch khng gian tng t c ch to xydng trng chuyn mch ca cc tng i phn knh theo khng gian. Chng

1

2

3

N

1 2 3 M

a. B chuyn mch ton thng

1

2

3

N

1 2 3 M

b. B chuyn ch khng ton thng

1

2

3

5

5 4 3 1

c. B chuyn mch gp

4

2

nh 2.6Minh ho kh thng ca b chuyn mch khng gian

www.4tech.com.vn


48/302

dng ni mch gia mch in ca thu bao ny vi mch in ca thu baokhc to ra tuyn truyn tn hiu thoi gia cc thu bao ny khi phc v cuc gigia tng cp thu bao vi nhau (chuyn mch ni b), chng cng c th cdng to ra cc tuyn ni t cc trung k ti cc thu bao (chuyn mch trungk) hoc cng c th dng ni mch gia mch in thu bao hoc mch intrung k vi cc thit b bo hiu nh cc u tn hiu mi quay s, bo bn, hi

m chung, cc thit b thng bo bng li, cc b thu tn hiu chn s hoc vithit b kim tra o th.

Ngy nay, trong cc tng i chuyn mch s a s cc trng chuynmch nu trn c thay bng chuyn mch s, tuy nhin, mt s khu vnphi s dng cc b chuyn mch khng gian tng t. V d : Cc b chuynmch kim tra, o th khng th dng chuyn mch s thay th m phi dng ccchuyn mch khng gian tng t th mi c th o c cc tham s in. Nhvy, tu thuc vo lnh vc ng dng ngi ta xy dng cc trng chuyn mchkhng gian tng t c cu trc v kch thc (dung lng) khc nhau, theo cc

ch tiu khc nhau. i vi cc loi tn hiu khc nhau th cn chn cc bchuyn mch thch hp v cc ch tiu in nh tr khng ca phn t chuynmch, xuyn m, tp m. i vi cc chuyn mch c cc tnh nng khc nhauth cn xem xt n ch tiu v kh thng ca cu trc chuyn mch. Trong ccmc tip theo chng ta khng cp ti cc ch tiu in (chng c chn theoyu cu c th) m ta ch xem xt cc cu trc ca cc trng chuyn mch, khthng ca chng v lnh vc p dng.

b. Trng chuyn mch mt khu

Cc b chuyn mch khng gian c bn thng c kch thc hn ch (su vo, s u ra khng ln). Khi cn trng chuyn mch c kch thc lnhn, cch n gin nht l ghp cc b chuyn mch c bn li vi nhau theo s mt khu. Theo s mt khu ta c th ni song song ng tn cc u voca b chuyn mch ny vi cc u vo ca b chuyn mch khc tng su ra nh ch ra trn hnh 2.7a hoc v qui c trn hnh 2.7b (tm gi l ghptng u ra). Cng theo cch ny c th tng s u vo, bng cch chn bchuyn mch hoc mt trng chuyn mch mt khu khc, c cng s u ra vcc u ra ny c ni song song ng tn vi nhau th ta c trng chuyn

mch mt khu mi c s u vo c m rng bng tng s u vo ca 2trng chuyn mch mt khu c ( hnh 2.7c,d)

www.4tech.com.vn


49/302

Nh th ta c th ghp cc b chuyn mch c bn vi nhau theo cch mrng c u vo v u ra ta s c trng chuyn mch mt khu c s uvo v u ra theo yu cu.

c im ca trng chuyn mch khng gian mt khu l:-Mi yu cu chuyn mch gia mt u vo vi mt u ra ca trng

chuyn mch ch qua mt phn t chuyn mch. V d (xem hnh 2.7c) : niu vo 1 vi u ra 3 dng phn t chuyn mch 31 ca b chuyn mch phatrn, ni u vo N+2 vi u ra 2, dng phn t 22 ca b chuyn mch pha

di-Lun tn ti tng quan 1:1 gia u vo-phn t chuyn mch-u ra

nu cc b chuyn mch dng trong s mt khu l cc b chuyn mch ton

123

M

123

M'

1

2

3

N

1 2 3 M

1

2

3

N

1 2 3 M'

M+M' u ra

Nu

vo

a.

123

N

NxM

NxM'

1

2

3

N

1 2 3 M

1

2

3

N'

1 2 3 M

N+N'uvo

M u ra

1

3

N

123

M

NxM

N'xM

d.

1

3

N'

c.

nh 2.7 Cc cch ghp c bn xy dng trng chuyn mch mt khu

www.4tech.com.vn


50/302

thng. Ngha l trng chuyn mch mt khu s l ton thng nu cc bchuyn mch c dng trong n l cc b chuyn mch ton thng.

* Cc nhc im c bn ca trng chuyn mch mt khu.-S phn t chuyn mch tng nhanh khi tng s u vo hoc u ra ca

trng chuyn mch. S phn t chuyn mch ca trng chuyn mch bng tch

ca s u vo vi s u ra- Khi ni song song nhiu b chuyn mch tng s u vo v u raca trng chuyn mch s gy ra hin tng d knh (xuyn m gia cc knh)

c. Trng chuyn mch hai khu

i vi nhng trng chuyn mch nhiu u vo, nhiu u ra, nu xydng theo s mt khu s qu tn km do cn nhiu phn t chuyn mch.Thm vo , vic ni song song nhiu b chuyn mch vi nhau dn n lmgim tr khng h mnh trn cc phn t chuyn mch v s dn n d tn hiugia cc u vo v cc u ra vi nhau lm cho tn hiu b suy gim trn cc

ng dn chnh v lm tng thm hin tng xuyn m gia cc knh ln cn. khc phc nhng nhc im trn, cn xy dng cc trng chuyn mchtheo s 2 khu hoc 3 khu.

C rt nhiu nguyn tc u ni s 2 khu, 3 khu. Trong phn ny chxem xt nguyn tc u ni n gin nht, l nguyn tc 1:1, ng tn.

Nguyn tc 1:1 ngha l gia mt b chuyn mch khu trc vi mi bchuyn mch khu sau ch c duy nht mt dy trung gian. Nguyn tc ng tnngha l cc u ra ca b chuyn mch th i khu trc s c ni ln lt vomi u vo th i ca tng b chuyn mch khu sau. V d (Xem hnh 2.8): Cc

u ra ca b chuyn mch th 1 khu A (k hiu l A1) s c u ti u voth 1 ca tng b chuyn mch khu B theo th t: u ra 1 ca A1 c ni tiu vo 1 ca b chuyn mch B1; u ra 2 ca A1 ni vi u vo 1 ca bchuyn mch B2; u ra 3 ca A1 ni vi u vo 1 ca b chuyn mch B3 ....

u ra ca A1 ni vi u vo 1 ca b chuyn mch B. Tng t nh th, ccu ra ca b chuyn mch th 2 khu A (k hiu l A2) s c u ti u voth 2 ca tng b chuyn mch khu B cng theo th t trn . C nh th cho

ti b chuyn mch cui cng khu A (k hiu l A). Cc u ra ca n s c

u ti u vo th ca tng b chuyn mch khu B. Nh vy, tng s u ra

ca cc b chuyn mch khu A phi bng tng s u vo ca cc b chuynmch khu B. Nu s u ra ca mi b chuyn mch khu A l v s b

chuyn mch khu A l , u ni theo nguyn tc 1:1, ng tn th cn m

www.4tech.com.vn


51/302

bo rng s u vo ca mi b chuyn mch khu B phi l v s b chuyn

mch khu B phi l

Theo nguyn tc ny :

- Mi yu cu ni gia mt u vo v mt u ra ca trng chuynmch phi i qua mt phn t chuyn mch ca mt b chuyn mch khu A,

1

23

4

m

1

23

4

A1

1

23

4

m

1

2

3

4

A2

1

2

3

4

m

1

2

3

4

A3

1

23

4

m

1

23

4

A

1

23

4

1

23

4

n

b1

1

23

4

1

2

3

4

n

b2

1

2

3

4

1

2

3

4

n

B3

1

23

4

1

23

4

n

b

nh 2.8S tng qut trng chuyn mch 2 khu

ab11

ab12

ab13

ab1

ab21

ab22

ab23

ab2

ab31

ab1ab2

ab3

ab

ab3

ab33

ab32

www.4tech.com.vn


52/302

mt dy trung gian gia khu A v khu B, mt phn t chuyn mch ti mt bchuyn mch khu B v ng i l duy nht. V d : ni gia u vo xca b chuyn mch Ap ti u ra y ca b chuyn mch Bq th tuyn ni duy

nht l t u vo x(Ap) phn t chuyn mch qx(Ap) u ra q(Ap) dy

trung gian abpq u vo p(Bq) phn t chuyn mch yp(Bq) u ray(Bq).

- Do mi b chuyn mch khu A vi tng b chuyn mch khu B ch cduy nht mt dy trung gian nn ti mi thi im ch c th phc v khng qumt php ni t mt trong cc u vo ca b chuyn mch khu A vi mttrong cc u ra ca cng mt b chuyn mch khu B. V d : Gia A1 v B2ch c duy nht mt dy trung gian ab12 nn gia cc u vo ca A1 v cc ura ca B2 ti mi thi im ch c th thc hin khng qu mt php ni . Gi skhi dy ab12 phc v cho mt php ni gia u vo 3A1 vi u ra 2B2, nuxut hin mt yu cu ni khc gia u vo 4A1 vi u ra 3B2 th yu cu mi s b t chi do khng cn ng dy trung gian gia A1 v B2 phc v,

mc d cc dy trung gian khc nh ab11, ab13.... ab1 c th vn ri, nhngchng khng dn ti B2. Ngi ta gi hin tng ny l gi htdo thiu ng

trung gian, hay l tn tht ni ca trng chuyn mch .

trnh hin tng gi ht cn phi to ra cc tuyn ni linh ng hngia cc u vo v cc u ra ca trng chuyn mch v iu ny c th thchin c nh cc s nhiu khu. lm r vn ny ta xem xt cc trngchuyn mch khng gian 3 khu.

d. Trng chuyn mch ba khu

Trn hnh 2.9 l trng chuyn mch khng gian 3 khu c xy dngtheo nguyn tc 1:1, ng tn nh trnh by mc trn. Nhn vo s ny tanhn thy rng mi yu cu ni gia mt u vo ca trng chuyn mch vimt u ra ca n phi i qua 3 khu A, B, C v khi qua mi khu phi i qua 1b chuyn mch no . Ngha l, mi yu cu chuyn mch s c thc hinqua 3 b chuyn mch 3 khu v 2 dy trung gian gia khu A ti khu B vgia khu B ti khu C. Tuy nhin, trong trng hp ny ch c b chuyn mchkhu A v khu C c cha u vo v u ra ca yu cu chuyn mch s l nim tuyn ni theo yu cu trn buc phi i qua. Cn bt k b chuyn mch noca khu B cng c th c dng phc v yu cu ni min sao cc dytrung gian ab v bc t b chuyn mch ca khu B ti b chuyn mch uvo khu A v b chuyn mch ra khu C theo yu cu l ang cha b dng

www.4tech.com.vn


53/302

phc v yu cu ni khc. T , mi yu cu chuyn mch c th c thchin theo nhiu tuyn ni khc nhau qua trng chuyn mch 3 khu v cng t gia cc u vo ca mt b chuyn mch khu A no vi cc u ra ca

cng mt b chuyn mch khu C c th phc v ng thi nhiu cuc ni ( )

V d : Nu cuc ni gia u vo 2A1 vi u ra nC2 c thc hin theotuyn 1.

bc11

bc12

bc13

bc1

bc21

bc22

bc23

bc2

bc31

bc1

bc3

bc

bc3

bc33

bc32

nh 2.9S tng qut trng chuyn mch 3 khu

1

23

4

m

1

23

4

A1

1

23

4

m

1

23

4

A2

1

23

4

m

1

2

3

4

A3

1

23

4

m

1

23

4

A

1

23

4

1

23

4

b1

1

23

4

1

23

4

b2

1

23

4

1

2

3

4

B3

1

23

4

1

23

4

b

ab11

ab12

ab13

ab1

ab2

ab22

ab23

ab2

ab31

ab1

ab2

ab3

ab

ab3

ab33

ab32

1

23

4

n

c1

1

23

4

n

c2

1

23

4

n

c3

1

23

4

n

c

1

23

4

1

23

4

1

23

4

1

23

4

bc 2

www.4tech.com.vn


54/302

Tuyn 1 : u vo 2A1u ra 1A1dy trung gian ab11 u vo

1B1u ra 2B1dy trung gian bc12 u vo 1C2 u ra nC2Nu xut hin yu cu ni gia u vo 3A1 vi u ra 1C2 th c th

thc hin theo tuyn 2

Tuyn 2 : u vo 3 A1u ra 2A1dy trung gian ab12 u vo

1B2u ra 2B2dy trung gian bc22 u vo 2C2 u ra 1C2 hoc c thi qua cc b chuyn mch trung gian B3, B4, , B

Tm li:* S 3 khu cho php to tuyn ni linh ng khi cn thc hin mt yu

cu chuyn mch no .* S 3 khu cho php thc hin nhiu yu cu ni ng thi gia mt

nhm u vo khu A vi cc u ra cng nhm khu C. hai c im ny lmcho s 3 khu gim c ng k kh nng gi ht so vi s 2 khu.

Quy tc chung xy dng trng chuyn mch nhiu khu

xy dng trng chuyn mch nhiu khu theo nguyn tc 1:1, ngtn th quan h gia cc b chuyn mch khu trc vi cc b chuyn mchkhu tip sau phi tun theo nguyn tc.

- S u ra ca mi b chuyn mch khu trc phi bng s b chuynmch khu sau.

- S u vo ca cc b chuyn mch khu sau bng s b chuyn mchkhu trc.

V d : Xem hnh 2.9 nu s b chuyn mch khu B l th mi b

chuyn mch khu A phi c u ra, cn mi b chuyn mch khu C phi c

u vo. Khu A c b chuyn mch vy nn mi b chuyn mch khu B

phi c u vo.

T nguyn tc u ni 1:1, ng tn ny c th bin tu thnh nhiunguyn tc u ni c qui lut hoc bt qui lut khc tu thuc vo yu cu thitk. Trong cc tng i, n gin vic chn tuyn, nn p dng cc nguyn tcu ni c qui lut.

Hnh 2.10 cho mt s tham kho ca loi trng chuyn mch c quilut.

www.4tech.com.vn


55/302

Hnh 2.10:Trng chuyn mch 3 khu u cho

* c im ca cc cu trc chuyn mch khng gian tng t v kh nng

ng dng ca tng cu trc

- S mt khu c s phn t chuyn mch ln nht nhng n gin nhtv khng c tn tht ni.

- xy dng trng chuyn mch kch thc cho trc, s 2 khu cndng t phn t chuyn mch nht, tuy nhin tn tht ni cao nht.

- S phn t chuyn mch cn s dng trong s ba khu nhiu hntrong hai khu nhng t hn so vi trong s mt khu cho trng chuynmch cng s u vo v u ra. Tn tht ni gim hn so vi s hai khu.

Tuy nhin, cc nhn xt trn y ch ng trong trng hp s u vo vu ra ca trng chuyn mch ln v c phn nhm hp l, cc trng hpkhc kt qu c th ngc li.

Do tnh cht v kh thng ca mi cu trc chuyn mch l khc nhau nnlnh vc p dng cng khc nhau.

1

2

3

m

a1

1

2

3

m

a2

1

2

3

m

a3

1

2

3

m

a4

1

2

3

n

c1

1

2

3

n

c2

1

2

3

n

c3

1

2

3

n

c4

B1

b2

b3

b4

www.4tech.com.vn


56/302

Loi trng chuyn mch mt khu thng c p dng cp chn ms u vo v s u ra chnh lch nhau nhiu, nh chn thit b kim tra o th(cc u vo l cc mch thu bao, cc u ra l cc thit b o). Cng c th sdng s ny chn trung k gi ra, gi vo (s trung k rt t so vi s thubao) hoc chn cc b thu pht bo hiu ng dy thu bao.

Loi trng chuyn mch hai khu c tn tht ni cao v vy nn s dng

trong cc cp chn mang tnh t do (ch c mt a ch bt buc, mt a ch cth chn t do, v d nu u vo l bt buc th c th chn u ra bt k hocngc li). N thch hp vi cp chn s b hoc cp chn nhm trong cc tngi dung lng ln.

Trng chuyn mch ba khu c tn tht ni c th iu chnh c khithay i h s nn-dn ca cc khu do c th t c cht lng dch vQoS-Quality of service theo yu cu v hiu qu kinh t mong mun, n thngc p dng cc cp chn m c hai a ch u l bt buc (a ch u vo va ch u ra ca trng chuyn mch i vi mi yu cu l cc a ch bt

buc) v d: trong cp chn ng dy thu bao b gi, khi a ch u vo cth l a ch mch in thu bao ch gi hoc knh u vo cn a ch ra lmch in thu bao b gi.

Hnh 2.11 ch ra s cu trc chung cho cc tng i dung lng ln.Dung lng ca tng i c chia thnh cc nhm, mi nhm c t vi chc tivi trm thu bao. Cc cp chn thit b o th, kim tra hoc chn trung k cth dng cc trng chuyn mch mt khu. Cp chn s b, chn nhm c th

Chn

trung k

Ti cc

trung k

Thit bbo hiu

Thit bbo hiu

Thit bkim tra

Thit bkim tra

Chn thu bao b gi

Chn thu bao b gi

Chn nhm

Chns b

Chns b

Chn nhm

Hnh 2.11:S khi cc trng chuyn mch trong tng i phn knhkhng gian

www.4tech.com.vn


57/302

dng trng chuyn mch mt khu hoc hai khu, cn cp chn ng dy dngtrng chuyn mch ba khu. Trong cc tng i dung lng trung bnh v dunglng nh cc cp chn c th kt hp li vi nhau v n gin ho cu trc catng i.

B chn trung k ni thu bao vi trung k trong cc cuc gi vo vgi ra. B chn o th, kim tra ni cc thit b kim tra o th vi cc ng

dy thu bao hoc trung k. Cc b chn ny c s u vo v u ra rt chnhlch nhau, v vy tt nht nn dng cc trng chuyn mch mt khu. Cp chns b t ng ni thu bao ti cc thit b bo hiu nh cc b to m mi quays, hi m chung, bo bn, hoc b thu cc tn hiu chn s. Cc thit b bohiu thng gm mt s loi, mi loi c vi b. Khi c yu cu chn mt loino ni vi mt ng dy th cp chn ny c th chn mt trong s ccb thuc loi yu cu. Ngha l c th chn t do gia mt s u ra ca cpchn, do vy y nn p dng loi trng chuyn mch hai khu t hiuqu cao. Cng tng t nh vy i vi cp chn nhm, cc u ra t mt b

chn nhm thng c mt s u ra cng ti b chn ng dy ca cng mtnhm, do cng c th chn t do mt trong s cc u ra . i vi trngchuyn mch chn ng dy thu bao th c hai a ch u vo v u ra u lbt buc nn ch c th p dng loi trng chuyn mch khng tn tht hoc tntht nh (mt khu hoc ba khu).

Vi s pht trin ca cng ngh in t, kch thc ca cc b chuynmch khng gian tng t ngy cng c thu nh, dung lng c tng cao vtch hp kh nng iu khin mm do, cng vi tc chuyn mch cao chophp ch to cc trng chuyn mch gn nh, tiu th ngun thp v vi cc chtiu k thut tt hn v khng ch p dng trong cc tng i phn knh khnggian m cn c p dng trong mt s khu ca cc tng i hin i v mt slnh vc k thut khc.

www.4tech.com.vn


58/302

2.3 iu ch bin xung (PAM- Pulse Amplitude

Modulation) v chuyn mch thi gian i vi tn

hiu ri rc2.3.1 Nguyn l iu bin xung v u th phn knh theo thi gian

nh lut Kocheniskov pht biu rng : i vi tn hiu lin tc c tn scc i l Fmax th khng cn truyn lin tc tn hiu m ch cn truyn gi trtc thi ca tn hiu ti cc thi im cch u nhau sao cho tn s ri rc holn hn 2Fmax. Ti u thu, c th ti to li tn hiu tng i chnh xc trn cs cc gi tr

ki thuat chuyen mach

Documents