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Chng 4: H thng thng tin in thoi

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Chng 4

H THNG THNG TIN IN THOI

4.1. Gii thiu v mng in thoi T cui th k 18 n u th k 19, cng ngh pht thanh v truyn thng bng in

c pht trin v bt u c dng rng khp. i pht thanh v truyn hnh c pht minh vo thi gian ny lm thay i th gii chng ta rt nhiu. Nm 1820, GEORGO OHM a ra cng thc phng trnh ton hc gii thch cc tn hiu in chy qua mt u dy dn rt thnh cng. Vo nm 1830, MICHALL FARADAY tm ra nh lut dn in t trng. Nm 1850, i s BOOLEAN ca GEORGE BOOLERS to ra nn mng cho logic hc v cc R-LE in. Chnh vo khong thi gian ny khi cc ng cp u tin xuyn qua i Ty Dng nh in tn lp t. JAME CLERK MAXWELL a ra hc thuyt in t trng bng cc cng thc ton hc vo nm 1870. Cn c vo hc thuyt ny, HENRICH HERT truyn i v nhn c sng v tuyn thnh cng bng cch dng in trng ln u tin trong lch s.

Vo nm 1876, tng i in thoi u tin c thit lp ngay sau khi ALEXANDER GRAHAM BELL pht minh ra in thoi. 5 nm sau BELL bt u dch v gi in thoi ng di gia NEWYORK v CHICAGO. Nm 1878, h thng tng i dng nhn cng gi l loi dng in t xy dng NEW HAVEN ca M, y l tng i thng mi thnh cng u tin trn th gii. Trong tng i ny vic nh hng thng tin c thc hin bng con ngi, ni cch khc vic kt ni thoi cho cc thu bao c thc hin bng cc thao tc trc tip ca con ngi (in thoi vin). Vi tng i nhn cng th thi gian kt ni lu, d b nhm ln.

Theo thi gian cng vi s pht trin ca khoa k thut cc loi tng tng i c pht trin v khng ngng c ci tin. T tng i nhn cng, tng i c, tng i c in, v hin gi l thi k ca tng i in t. 4.1.1. Tng i nhn cng

Tng i nhn cng ra i t khi mi bt u h thng thng tin in thoi. c im ca loi tng i ny l vic nh hng, thng tin u c thc hin bng sc ngi, ni cch khc l vic kt ni thng tin cho cc thu bao c thc hin trc tip bng cc thao tc ca con ngi

Nhim v c th ca ngi in thoi vin trong tng i bao gm: Nhn bit tn hiu (nhu cu gi) ca cc thu bao bng neon bo, chung, ng

thi nh v c thu bao gi Trc tip hi nhu cu kt ni ca thu bao


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Trc tip rung chung cho thu bao c gi Trng hp thu bao c gi bn th in thoi vin trc tip bo cho thu bao gi Khi thu bao c gi nhc my ,in thoi vin nhn bit iu ny v ngt dng

chung ng thi kt ni cho 2 thu bao thng thoi Cng vic tip theo ca in thoi vin l Nu mt trong 2 thu bao gc my in thoi vin nhn bit iu ny, ngt kt ni v

bo cho thu bao cn li bit cuc m thoi kt thc Nhc im: Vi dung lng ln ,kt cu v thit b ca tng i tr nn phc tp, kch thc ln

v cn c nhiu in thoi vin lm vic cng lc mi m bo thng thoi cho cc thu bao. Khi s long thu bao ln n hng trm th iu ny khng th thc hin c.

p lc cng vic ca ngi in thoi vin ln nn xc sut nhm ln cao 4.1.2. Tng i c in

khc phc nhng hn ch v nhc im ca cc loi tng i in thoi nhn cng ,cc nh ch to tng i cho ra ra i cc loi tng i t ng c in v tng bc ci thin chng .Tng i t ng tng nc u tin iu khin trc tip c ch to vo nm 1982 .Mc d c hon thin trn c s nhim v tng i nhn cng nhng n cn rt nhiu nhc im nh cha rt nhiu cc b phn c kh, kch thc qu cng knh

Hnh 4.1. Tng i c in

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Trong tng i c in hot ng thit lp cuc gi c t ng ho nh vo cc

mch iu khin bng in t cng vi b chuyn mch bng c kh: Chuyn mch quay trn (rotary) Chuyn mch tng nc (step-by-step) Chuyn mch ngang dc (cross-bar)

So vi tng i nhn cng c mt s u im: Thi gian kt ni nhanh chng hn ,chnh xc hn C th gia tng dung lng Gim nh c cng vic ca in thoi vin

Nhc im:

Khi s lng thu bao tng th dn n h thng, thit b cng knh, tiu th nhiu nng lng, iu khin kt ni phc tp

S hao mn c kh qua thi gian, dn n cc kt ni km chnh xc v cht lng cuc gi gim

4.1.3. Tng i in t

Nm1965 tng i in t u tin theo nguyn l chuyn mch khng gian tng t a vo khai thc bang NewJery nc M, y l tng i iu khin ni ht theo nguyn l SPC(Stored Program Control). Tng i in thoi loi nay cn cho mi cuc gi mt tuyn vt l(ng dy ) ring. Do vy cng khng th ch to tng i c kh nng tip thng hon ton. V th ngay sau ngi ta hng cng vic nghin cu vo phng thc chuyn mch phn knh theo thi gian (gi tt l chuyn mch thi gian TDM).

Nm 1970, tng i din thoi s u tin c sn xut v lp t a vo khai thc Php. Vo nhng nm u ca thp k 70 hng Bell Laboratory M quyt nh hon thin mt s tng i s dng cho lin lc chuyn tip, vi mc tiu dt ra l truyn dn gia cc tng i nh phng thc s. Thng 1/1976, tng i chuyn tip theo phng thc chuyn mch s mang tnh cht thng mi u tin trn th gii dc lp t khai thc.

T khi cng ngh bn dn ra i da tng i in t sang mt bc pht trin mi. Trong tng i in in t cc b phn chuyn mch bng bn dn thay th cho cc b phn chuyn mch bng c kh ca tng i c in, lm cho kt cu ca tng i gn i rt nhiu, thi gian kt ni cuc gi nhanh hn, nng lng tiu th t hn. i cng vi s pht trin ca cng ngh bn dn theo thi gian, kch thc ca cc linh kin bn dn


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ngy cng c thu nh dn n cc h thng chuyn mch c tch hp rt nhiu tip im trn mt chip.

u im: Tnh linh hot:

H tr vic tnh cc cc cuc gi C kh nng nng cp khi s lng thu bao tng Kt cu h thng n gin, gn nh

chnh xc v bn cao, do s dng cc b chuyn mch bng bn dn. Thi gian thc hin kt ni nhanh. Cht lng cuc gi tt hn. H tr thu bao thng qua cc dch v tin ch

Quay s nhanh (short-code dailling) Chuyn hng cuc gi (call- transfer) Bo thc ( automatic alam call) Hn ch cuc gi n v i ((Out going comming barring),

4.2. Cu trc ca mng in thoi 4.2.1. Khi nim

Mng in thoi c cu to dng ph h Mng c hnh li pha trn nh h thng Mng c hnh sao pha y h thng

Mng ph thuc vo tng quc gia. C 4 thit b chnh trong 1 mng: Thit b u cui v trm ni b ng ni n thu bao Cc trm chuyn mch ( Tng i ) Thit b ng truyn ( Viba , v tinh , si quang )


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4.2.2. Cc m hnh mng in thoi a. M hnh mng in thoi (mng c nh) quc gia

Hnh 4.2. M hnh mng in thoi quc gia

Cc mng c xy dng lm mt vic duy nht l truyn dn cc tn hiu thng tin t ni ny n ni khc. Cc thnh phn ca mt mng vin thng bao gm, cc trung tm chuyn mch v cc lin kt truyn dn. phc tp ca mt mng vin thng ph thuc vo lu lng thng tinh cn chuyn ti. Do , quy m ca mt mng c th t rt n gin n cc k phc tp. S tng qut ca mt mng in thoi quc gia nh hnh di.

Do s lng thu bao trong mt mng quc gia rt ln nn nu trung tm chuyn mch t ti mt tng i l iu khng th thc hin c. Hn na, v mt v tr a l th u tp trung cc line thu bao vo mt tng i li cng khng th lm c.


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Do vy h thng thng phn cp mng theo vng a l v theo mt dn s cho hp l.

Thng mt h thng mng in thoi quc gia c chia lm nm cp:

Tng i

Tng i

Tng i

Tng i

Tng i x A

Tng i x F

Tng i phng A

Tng i phng

LE LE Thu bao

Tng i ni b(cng s)

Tng i quc gia

Tng i khu vc 1

Tng i ] khu vc M

Tng i cp tnh 1

Tng i cp tnh 1

Tng i cp thnh ph N

Gateway Quc t

Hnh 4.3. Cc cp tng i


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Cp phng, x: Gm mt tng i dung lng khong vi ngn s v h thng cp line u cui v n thu bao. Loi tng i ny va thc hin kt ni trc tip vi thu bao v thc hin chc nng chuyn mch trc tip cho cc thu bao ni i. Cp qun: Gm cc tng i cp qun vi dung lng hng chc ngn s, v mng

lin kt trung k theo v tr a l cho nhng qun gn nhau. Loi tng i ny khng kt ni trc tip vi thu bao m ch thc hin chc nng chuyn mch cho cc thu bao ni vng v kt ni trung gian cho cc thu bao ngoi vng. Cp tnh: Gm cc tng i cp tnh vi dung lng hng trm ngn s, v mng lin

kt trung k theo v tr a l cho nhng tnh gn nhau. Loi tng i ny cng khng kt ni trc tip vi thu bao m ch thc hin chc nng chuyn mch cho cc thu bao ni vng v kt ni trung gian cho cc thu bao ngoi vng. Cp khu vc: Gm cc tng i cp khu vc vi dung lng hng trm ngn s, v

mng lin kt trung k theo v tr a l cho nhng khu vc gn nhau. Loi tng i ny cng khng kt ni trc tip vi thu bao m ch thc hin chc nng chuyn mch cho cc thu bao ni vng v kt ni trung gian cho cc thu bao ngoi vng. Cp quc gia: Gm cc tng i cp quc gia vi dung lng hng trm ngn s, v

mng lin kt trung k theo v tr a l cho nhng tng i cp khu vc gn n, ngoi ra n cn c cc trung k ca ng ra quc t. Loi tng i ny ch thc hin chc nng chuyn mch cho cc thu bao gi vo v ra quc t. b. Mng ni b:

Tng i ni b (PABX Private Automatic Branch Exchange) dng cho cc cng s, nh my. y chng thc hin vic kt ni trc tip cc cuc ni b

Tng i ni b PABX

DTE DTEThu bao A

Thu bao B


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Tn gi quc t ca mt cc loi tng i sau : Tng i c quan PABX: c s dng trong cc c quan, khch sn v thng s

dng trung k CO-Line (central office). Tng i nng thn (Rural Exchange): c s dng cc x, khu dn c ng, ch

v c th s dng tt c cc loi trung k. Tng i ni ht LE (Local Exchange): c t trung tm huyn tnh v s dng

tt c cc loi trung k. Tng i ng di TE (Toll Exchange): dng kt ni cc tng i ni ht cc

tnh vi nhau, chuyn mch cc cuc gi ng di trong nc. Tng i ca ng quc t (Gateway Exchange): tng i ny dng chn hng v

chuyn mch cc cuc gi vo mng quc t ni cc quc gia vi nhau, c th chuyn ti cuc gi qu giang.

4.2.3. Mng truyn dn

Hnh 4.4. Kt ni gia thu bao vi tng i

Mng cp thu bao, kt ni t cc tng i u cui v n cc thu bao thoi. Loi cp c dng l ng dy i, c xon li vi nhau gim nhiu k sinh. Khong cch ti a thng khong 1Km

Cable ng trc, Cable i xng, phm vi hot ng ph thuc vo mt ca ngi s dng trong mng, kch thc ca mng v v tr a l ca ni vng. Ni chung, chiu di trung bnh ca ng dy trong mng t 1.5km n 2km, chiu di ln nht khng qu 10km.

Cp quang, cho php ng truyn vi dung lng ln hng GB. nc ta, h thng mng cp quang c tri rng khp c nc. Trc cp i qua cc bu in trung tm ca cc thnh ph, qun, huyn.


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Mng cng cng quc gia ( mng lin tnh ) , thng thng c ni bng vi ba, si quang , v tinh

Mng quc t , thng thng c ni bng si quang , v tinh . Kt ni v tinh trong mng quc t . Thng thng theo 2 cch sau:

Gn c nh: phng php ny thch hp cho cc quc gia c nhu cu thng tin ln

Gn theo yu cu: phng php ny cho php s dng mm do knh thng tin , nht l i vi cc nc nh , c lu lng thng tin thp , c cc gi cao im lch nhau nhiu a. ng ni thu bao v tng i

Khi thu bao nhc my tin hnh cuc gi, thu bao ny lm ng tip chuyn mch gy ra mt dng in chy trong vng thu bao. Thit b i cui nhn bit trng thi chuyn mch (off hook), b chn ng dy kt ni chuyn mch vi thu bao cung cp mt chui xung mi quay s (dial tone) v sn sng nhn cc xung quay s. Sau , thit b chuyn mch phi kt ni thu bao vi ng dy c a ch l s in thoi quay.

Vng ni b ca thu bao l mt ng hai dy cn bng , tr khng c tnh khong 500 n1000 (thng l 600 ).

Mt ngun chung ca i cui cung cp ngun 48 VDC cho mi vng thu bao. Hai dy dn c ni vi tip v ring- thut ng dng m t jack in thoi. Hnh 4.5 minh ha vng ni b v jack cm in thoi. ng ring c in th 48 VDC i vi tip. Tip c ni t (ch i vi DC) i cui.

Hnh 4.5. ng ni thu bao v tng i

Khi thu bao cha nhc my (on-hook) in th DC ri trn ng dy gia tip v ring khong -48V thit b u cui ca thu bao in thoi.


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Khi thu bao nhc my (off-hook) lm ng tip im chuyn mch, to nn mt dng in xp x 20 mADC chy trong vng thu bao, in th DC ri trn ng dy gia tip v ring gim

Tn hiu thoi m tn c truyn trn mi hng ca ng dy khi c s thay i nh ca dng in vng. S thay i ca dng in gm tn hiu AC chng chp vi dng in vng DC.

in thoi ca thu bao ch chung, mt tn hiu cp dng chung c bin d xp x 90 Vrms (tn s 20 Hz) c ly t i cui a ti ng dy. b. Ting di (echo)

Nghe ting di ging ni ca chnh mnh trong khi s dng in thoi s rt kh chu. Ting di l kt qu ca s phn x tn hiu xy ra ti nhng im khng phi hp tr khng dc theo mng in thoi.

Ni chung, thi gian tr ca ting di di hn v tn hiu ting di mnh hn s lm nhiu lon n ngi ni nhiu hn.

S phi tr khng trn ng truyn thng xu nht trn cc vng thu bao v ti ni giao tip vi u cui. y vic phi hp tr khng rt kh iu khin v chiu di ca vng thu bao v cc thit b thu bao qu khc nhau.

Ting di nghe c bi ngi ni b suy gim hai ln: t ngi ni n im phn x v ngc li.

Trn cc ng truyn di ngi ta phi s dng cc b trit ting di c bit, hay thm vo cc b suy hao lm gim mc ting di.

B trit ting i c s dng trong cc mch truyn tin khi thi gian tr ca mt vng tn hiu vt qu 45 ms. V d, s lan truyn thi gian tr trn cc ng thng tin v tinh c th vi trm ms, nn ta phi s dng b trit ting di.

Cc b trit ting di c v hiu ho trong khi truyn d liu cc cuc gi. 4.3. Cc tiu chun truyn dn ca mng in thoi

ITU (international Telecomunication Union) Hip hi vin thng quc t thuc lin hip quc vch nh cc tiu chun trong h thng vin thng quc t

ITU gm 4 n v thng trc

Ban th k

CCITT ban khuyn ngh quc t v in thoi v in bo

CCIR ban khuyn ngh quc t v thng tin v tuyn

CIEF Ban qun l di tn


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Bao gm cc tiu chun sau: i. Tiu chun truyn dn suy hao knh truyn

Thi gian tr knh truyn

Bng thng knh truyn

nh hng ca nhiu (Noise , crosstalk)

c tnh ca h khi mo dng ii. Tiu chun chuyn mch Xc sut mng kt ni b bn

Hot ng ca h khi c kt ni bn

Thi gian ch cho 1 kt ni

Xc sut kt ni nhm

S chnh xc khi tnh cc iii. tin cy ca h thng : Xc sut h 1 phn hay ton phn

Kh nng t sa ca h thng

Hu qu khi h hng

Hot ng ca h khi h

4.3.1. Tiu chun truyn dn: suy hao knh truyn Gi Pin v Pout l cng sut vo v ra ca mng hai ca Nu Pin> Pout mng suy hao; Pin


5

4.3.2. suy hao chun. CIITT khuyn ngh : Suy hao mng quc gia ni pht 3400Hz, BW =3100Hz

Tn s 800 Hz c suy hao 0dB

Tn s 300hz v 3400 Hz c suy hao 8,7 dB Di thng ca mng in thoi xp x 300 Hz-3400 Hz. Di tn s ny tng ng vi

ph ca tn hiu ting ni. Mt p tuyn tn s tiu biu c trnh by trong hnh sau

7


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Hnh 4.7. Bng thng knh truyn

4.3.6. Nhiu nn v nhiu xuyn knh Nhiu l tn hiu khng mong mun tn ti hay xm nhp vo trong knh Nhiu nn (Background noise) tn ti ngay c khi khng c tn hiu thng tin Nhiu xuyn knh (Crosstalk) do nh hng t cc knh ln cn T s tn hiu trn nhiu S/N c nh ngha l S/N = Psignal /Pnoise Thng thng c tnh theo dB S/N [dB] = 10 lg(Psignal /Pnoise ) [dB]

4.3.7. Mo phi tuyn Tn hiu tn s f qua knh truyn pht sinh nhiu tn s hi bc cao gy ra mo phi tuyn. Nu khng c lc b , cc thnh phn tn s ny cng tr ln nhau trn knh truyn to thnh nhiu trn tn ( Intermodulation noise) suy hao ph thuc vo tn s

4.3.8. Cht lng chuyn mch nh gi bi kh nng phc v , khng nghn mch

4.3.9. tin cy Xc nh bng xc sut hot ng ca thit b hon thnh 1 nhim v t trc ,

trong iu kin v thi gian nh trc

t tin cy cao , cn

S dng linh kin cht lng cao mc tin

S dng cu trc c an ton cao , nh hot ng song song tn nhiu v s lng

Cn dung ho gia tin cy v gi thnh h thng


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4.4. Bo hiu trong tng i 4.4.1. Gii thiu chung

Bo hiu c coi nh l mt phng tin trao i thng tin v cc lnh t im ny n im khc, cc thng tin v cc lnh ny lin quan n qu trnh thit lp, gim st v gii phng cuc gi. Phn loi h thng bo hiu

Thng thng h thng bo hiu c chia lm 2 loi l:

Bo hiu thu bao: l bo hiu gia thit b u cui vi tng i, thng thit b u cui l my in thoi.

Bo hiu trung k: l qu trnh bo hiu gia cc tng i vi nhau. Ta c s tng quan v h thng bo hiu nh sau:

Bo hiu trung k gm 2 loi :

Bo hiu knh kt hp CAS (bo hiu knh ring): l h thng bo hiu m trong thng tin bo hiu nm trong knh thoi hoc trong knh c lin quan cht ch vi knh thoi.

Bo hiu knh chung CCS : l h thng bo hiu m trong thng tin bo hiu nm trong mt knh tch bit vi cc knh thoi, knh bo hiu ny c s dng chung bo hiu cho mt s ln cc knh thoi.

Bo hiu

Bo hiu trung k Bo hiu thu bao

Bo hiu knh kt hp CAS

Bo hiu knh chung-- CCS

Hnh 4.8. H thng bo hiu

Cc chc nng ca bo hiu: C th tng qut cc chc nng ca bo hiu nh sau: chc nng gim st, chc nng

tm chn, chc nng khai thc v bo dng mng.


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Chc nng gim st: chc nng ny c s dng nhn bit s thay i v trng thi ca ng dy thu bao hoc ca trung k (bao gm cc tn hiu: nhc my chim, nhc my tr li, trng thi ng dy bn-ri-gii phng). Cc tn hiu gim st c th dng c dng (khng dng) hoc l cc m nh phn c trng cho tng trng thi.

Chc nng tm chn: lin quan cht ch n qu trnh x l cuc gi nh: trao i cc thng tin a ch, c tnh thu bao. Trong qu trnh bo hiu, chc nng tm chn phi c thc hin trong mt khong thi gian xc nh thng c gi l thi gian tr quay s (PDD - Post Delay Dialing), l khong thi gian c xc nh t khi thu bao ch gi pht xong cc con s a ch thu bao b gi cho n khi nhn c hi m chung, yu cu thi gian tr PDD cng nh cng tt. Ngoi ra yu cu i vi h thng bo hiu m c th l chc nng tm chn phi c tin cy cao, tc bo hiu nhanh, hiu qu.

Chc nng khai thc v bo dng mng : phc v cho vic khai thc duy tr s hot ng ca mng li. Cc tn hiu bo hiu thuc chc nng ny gm: - Nhn bit v trao i cc thng tin v trng thi tt nghn ca mng. - Thng bo v trng thi thit b, ng trung k. - Cung cp cc thng tin tnh cc. - Cung cp cc thng tin v li trong qu trnh truyn thng tin bo hiu.

4.5. Kho st tng i in t PABX 4.5.1. Cu trc khi ca tng i ( hnh 4.9 ) 4.5.2. Mch thu bao Cp dng cho thu bao khi m thoi

Cm bin trng thi ca thu bao (nhc my, gc my) nh vo s thay i tng tr ca ng dy.

Cp m hiu cho thu bao

Cp dng chung cho thu bao 4.5.3. Mch trung k Cm bin dng chung gi vo

To ti gi cho thu bao i vi tng i bn ngoi

Quay s ra tng i bn ngoi

C bin p cch ly vi tng i bn ngoi


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K

hi

Thu

B

ao

+ T

rung

K

K

hi

Thu

B

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+ T

rung

K

K

H

I C

HU

YN

M

CH

K

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I/O

K

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iu

kh

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trun

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m

Lin

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Lin

e 2

Lin

e n

Kh

i D

TM

F

Ngu

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cp

Kh

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Kh

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Bus

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Rin

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5V

12V

1

5V

Tra

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Lin

e 3

Tra

ck 1

T

rack

2

Tra

ck 3

Hnh 4.9. S khi tng i ni b


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4.5.4. Khi iu khin trung tm : - Mch x l trung tm iu khin mi hot ng ca tng i, thc hin cc chc

nng ca tng i, cc dch v cho thu bao v trung k. - Mch x l l mt CPU n lm nim v iu khin cc thit b chuyn mch, thit b

ngoi vi, cc chng trnh c lu tr sn trong b nh chng trnh, nh d liu v b nh bin dch.

- B nh chng trnh ghi tt c cc chng trnh h thng v cc chng trnh ng dng phc v cho cc chng trnh x l cuc gi.

- B nh d liu ghi li tm thi cc d liu cn thit phc v cho qu trnh x l cuc gi nh cc ch s a ch, trng thi bn ri ca ng dy thu bao.

- B nh phin dch cha cc thng tin v loi dch v ca thu bao, cc bng m lp tuyn, cc thng tin v tnh cc B nh d liu l b nh tm thi, cn b nh chng trnh v bin dch l b nh bn c nh. Cc s liu trong b nh d liu thay i trong qu trnh thc hin cuc u ni.

CPU

Nh chng trnh

Nh bin dch

Nh d liu B vo ra B vo ra

Hnh 4.10. Cu trc khi iu khin trung tm

4.5.5. Khi chuyn mch

tng i in t, c hai h chuyn mch, chuyn mch khng gian v chuyn mch thi gian. N c chc nng thit lp mch u cho cc cuc gi, truyn dn ting ni v cc tn hiu khc cho thu bao.

H chuyn mch khng gian: h ny cc b phn chuyn mch c thit lp gia u vo v u ra, n s dng ring cho mi cuc gi v duy tr trong sut khong thi gian m thoi. Cc tuyn gi khc hon ton c lp vi nhau.

H chuyn mch thi gian: Trong h thng ny mi mt cuc lin lc c s dng mt phn thi gian ca tuyn . Phn thi gian ny trong tng i in t hin nay c lp li vi chu k 125 us (Tn s 8 KHz) cho mu tin. giai on u ngi ta truyn


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dn trc tip cc tn hiu PAM, nhng cht lng khng m bo do b nh hng ca tp m, nhiu, mo dng. Hin nay cc tng i u s dng nguyn tc chuyn mch PCM nn cht lng thng tin c nng cao.

Tm li khi chuyn mch c chc nng :

Kt ni thng thoi cho thu bao vi thu bao, v thu bao vi trung k.

Cp m hiu cn thit cho thu bao.

Kt ni thu bao vi mch thu DTMF khi thu bao quay s (thu bao s dng dng tone).

Kt ni mch pht tone DTMF vi trung k khi c yu cu quay s ra tng i cng cng (vi trung k ch tone). 4.5.6. Khi m hiu

To cc tn hiu cn thit nh Dial tone, Busy tone, Ring back tone, nhc tin ch, cp cho thu bao.

Sau y l cc tn hiu thng nghe thy trn cc thu bao :

Tn hiu mi quay s: 350 Hz - 440 Hz, pht lin tc.

Tn hiu bo bn: 480 Hz - 620 Hz, pht theo nhp 0.5s ngng 0.5s.

Tn hiu hi chung: 440 Hz 480 Hz, pht theo nhp 1s ngng 3s. 4.5.7. Khi to chung

To tn hiu chung cp cho thu bao, tn hiu sin c tn s 20 - 25 Hz, pht theo nhp 2s ngng 4s, bin AC P-P t 75 90V. 4.5.8. Khi ngun Cung cp in p cho ton b tng i

Do tng i thit k l tng i ni b c phm vi lm vic nh (chiu di ng dy thu bao khng ln), st p trn ng dy khng nhiu, nn ta chn ngun cp cho thu bao l +24V. Ngoi ra khi ngun cn cung cp in p +5V v +15V cho khi iu khin, khi m hiu, ma trn chuyn mch, khi to tn hiu chung.

Nh vy, khi ngun c nhim v cung cp in p +24V, +15V v +5V cung cp cho tng i.

4.5.9. Khi DTMF Khi DTMF c tc dng gii m cc phm bm ca my in thoi hot ng ch

tone thnh cc bit d liu cn thit CPU nhn bit v x l.

Khi DTMF s dng IC thu DTMF chuyn dng, VD: IC MT8870B.


64

4.5.10. Khi giao tip I/O L mt h thng cc b m vo ra, l mi lin kt ca b vi x l v cc khi

khc trong h thng.

4.6. Cc k thut chuyn mch ca tng i V c bn c phn ra ba loi: chuyn mch mch (Circuit switching) v chuyn

mch d liu (Data switching) v chuyn mch mm (Soft switching).

Chuyn mch mch li c phn ra hai loi: Chuyn mch khng gian (Space Division Multiplexing), chuyn mch thi gian (Time Division Multiplex).

Chuyn mch d liu c phn ra hai loi: Chuyn mch thng ip (Message switching) v chuyn mch gi (Package switching).

Chuyn mch mm l hnh thc chuyn mch linh hot, hiu qu v hin i nht ang c pht trin s dng.

4.6.1 Chuyn mch khng gian SDS (Space Division Switching) a. Khi nim

SDS l hnh thc chuyn mch bng cch thit lp mt ng truyn vt l kt ni hai im thng tin.

C s to nn cc b chuyn mch l cc tip im c kh hay cc cng in t c iu khin.

Dng n gin nht ca chuyn mch khng gian l ma trn tip im nxn (n u vo v n u ra ) Crossbar Switch .

N

1 2

1

N

2

N 1


65

Hnh 4.11. Cu trc khi Chuyn mch khng gian SDM Tuy nhin, n c 1 s nhc im sau:

S tip im rt ln ~ n2 gi thnh cao

Nu mt 1 tip im no th dn n kh khn ni gia 2 thu bao

S tip im s dng thc t rt t ch l n so vi n2

b. Chuyn mch khng gian nhiu cp

Hnh 4.12. Cu trc khi chuyn mch khng gian nhiu cp

Trong thc t , ngi ta s dng chuyn mch nhiu cp

Ngi ta chia N u vo thnh N/n nhm

Mi nhm c n u vo lp thnh cp th 1

Mi nhm c k u ra , li a vo cc u vo ca cp th 2, v c nh th tip tc V d mng trn hnh c 3 cp i xng ( chuyn mch SSS) , Hnh 4.12.

iu kin khng nghn mch k = 2.n -1


6

Hnh 4.13. iu kin khng nghn mch k = 2.n -1

6

SS tthhuu bbaaoo SS ttiipp iimmmmnngg SSSSSS

SS ttiipp iimm mmnngg nn ggiinn

112288 77 668800 1166 338844

551122 6633 448888 226622 114444

33004488 551166 009966 44,,22**110066

88119922 44,,22**110066 66,,77**110077

3322 776688 33,,33**110077 110099

113311 007722 22,,66**110088 11,,77**11001100

Cc u im so vi chuyn mch n gin S cc tip im ma trn t hn C nhiu ng ni thng qua mng kt ni 2 im u cui

Nhc im phn iu khin phc tp hn nhiu Nu chn s cc nhm con khng hp l mng c th b kho khi lu lng tng


6

4.6.2 Chuyn mch khe thi gian TSI (Time Slot Interchange ). H thng chuyn mch TDM (Time Division Multiplex) c s cng kt ni ~ 2N.

Nhn ca b chuyn mch TDM l khi chuyn mch TSI

Multiplexer Demultiplexer

DM

DM

DM

)(1 tx

)(2 tx

)(txN

)(1 nd

)(2 nd

)(ndN

DDM

DDM

DDM

)(1 nd

)(2 nd

)(ndN

)(1 tx

)(2 tx

)(txN

D(n) D(n)

Transmission

TSI Switching

N tn hiu t N thu bao a vo b ghp knh Mux, u ra ca Mux l lung s tc

cao cha cc khung , mi khung c n khe thi gian TimeSlot tng ng vi n thu bao Mi khe c th l 1 bit ( hay 1 byte hay nhiu byte ) V d kt ni khe 2 vi khe 5 , th tn hiu t khe 2 a n u vo TSI c

i sang khe 5 ti u ra ca TSI v a n b gii ghp knh xut ra ti khe 5

7


68

Hnh 4.14. Chuyn mch TDM

Khi s thu bao tng , thi gian tr tng vt mc , ngi ta s dng cu trc nhiu TSI ghp nhau gi l TMS

4.6.3. Chuyn mch TST

Trong thc t , ngi ta s dng cc cu hnh TST hay STS tng hiu qu . Phc tp hn l TSSST , SSTSS , TSTST


69

Hnh 4.15. Gii thch chuyn mch TST

Hnh 4.16. S khi chuyn mch TST


70

4.6.4. Chuyn mch d liu a. Chuyn mch bn tin ( chuyn mch thng ip message)

Ngi ta c th s dng chuyn mch mch in truyn d liu , nhng gp phi nhiu nhc im nh yu cu 2 thu bao phi hot ng cng thi im , hiu sut s dng ng truyn khng cao

Hnh 4.17. Mng chuyn mch bn tin

Mng chuyn mch knh khng thch hp truyn s liu. i vi cc bn tin rt ngn th mng chuyn mch knh li cng khng thch hp v khng c hiu qu.

Cc th in t , cc file truyn trn mng c gi chung l cc bn tin (message). N c truyn qua mng nh l cc d liu s

Mt trong cc dng chuyn mch c chn phc v nhu cu trn l chuyn mch bn tin. N phn tch phn u bn tin tm a ch ni nhn

Thng thng cc node chuyn mch l cc my tnh , m n gi bn tin b nh m . Thi gian tr mi node gm thi gian nhn bn tin vo node v thi gian sp hng ch n lt mnh chuyn ti node khc

Chuyn mch bn tin khng cn thit lp mt ng dn dnh ring gia hai trm u cui m mt bn tin c gi t ni pht ti ni thu c n nh mt l trnh trc bng a ch ni nhn m mi trung tm c th nhn dng chng. Ti mi trung tm chuyn mch (nodes chuyn mch), bn tin c tm lu vo b nh, x l ri truyn sang trung tm khc nu tuyn ny ri. . Kh nng lu li c th trong thi gian di do i x l hay trung tm tip theo cha sn sng nhn.


71

u im so vi chuyn mch mch in ( knh ):

Do bn tin c th tm thi b gi 1 node no nn cao im lu thng s gim , ng dy s dng hiu qu hn

Khng cn trm thu lun sn sng v mng c th tm gi bn tin

Chuyn mch bn tin khng bao gi b bn

Chuyn mch bn tin c th gi ng thi n nhiu ni nhn cng 1 lc

C th thit lp u tin cho 1 bn tin

C th kim tra sai v qun l qu trnh trong mng

Khng cn cng tc truyn gia cc thu bao

Mng c th i dng cc m truyn

H thng Mng nhn bn tin t cc my tnh (Terminal)

H thng phn tch u tin

H thng pht hin li v yu cu truyn li

H thng lu tt c cc bn tin c gi n trong vi gi , vi ngy. C th lu vnh vin bng bng a

Nu c my tnh nhn tm thi khng lm vic th h thng c th ch hay gi bn tin n a ch khc nu c yu cu

My tnh cp s th t cho cc bn tin c gi i , do h thng c th tm li cc bn tin b mt

Khi h thng b tm dng , n thng bo n tt c cc my tnh s th t cui cng cc bn tin m n nhn c

H thng c th cung cp cc s liu thng k v s lu thng qua n

b. K thut chuyn mch gi

Tng quan

Chuyn mch gi s dng u im ca chuyn mch knh v chuyn mch tin, ng thi khc phc c nhc im ca hai loi chuyn mch ny.

Chuyn mch gi gn ging chuyn mch bn tin Ch khc nhau l thay v gi 1 bn tin ln th ngi ta ct bn tin ra thnh nhiu gi

nh hn ( c vi ngn Byte ) v gi cc gi ny i ln ca gi :


72

Nu ct bn tin cng nhiu gi , tn dng kh nng truyn song song ng thi trn mng , s truyn nhanh hn

Nu gi qu nh , do mi gi phi cha thm phn header nn lng thng tin d tha phi truyn cng nhiu hn Mng chuyn mch gi bao gm cc thnh phn c bn sau: trm (station), nt mng

(node) v cc ng truyn dn (link).

Hnh 4.18. Mng chuyn mch gi.

chng li, mng chuyn mch gi s dng phng thc t ng hi li. Qu trnh ny i hi cc trung tm khi nhn c cc gi th xc nh xem gi c li hay khng, nu li th n s pht yu cu pht li cho trung tm pht.

Ph thuc vo ng i cc gi trong cng 1 bn tin m ngi ta chia lm 2 loi l Datagram (dg) , v mch o (Virtual Circuit)

2

4

1

6

5

3

User A

User F

Datagram (dg) (giao thc phi kt ni -Connectionless): Cc gi i theo cc ng c lp ring , phn header ca cc gi cha a ch ca cc node m n i n

Virtual Circuit (VC) (giao thc hng kt ni -Connection Oriented)): Khi c nhu cu gi bn tin, s thit lp mch o qua cc node , cc gi trong cng 1 bn tin s i chung qua mch o ny . Phn header ca cc gi khng cha a ch ca cc node m n i n

Phng php chuyn gi theo kiu Datagram

Cc bc cn thit truyn thng tin i t ngun n ch nh sau:

Bc 1: Phn on gi pha pht.

Bc 2: nh tuyn cc gi .


73

Bc 3: Ti hp gi pha thu. Tu thuc vo giao thc truyn thng m c nhiu mc phn chia bn tin thnh cc

gi vi chiu di khc nhau. Ngoi nhng thng tin c ct t bn tin, gi cn c chn thm cc phn u v ui phc v cho vic nh tuyn qua mng.

u uiD liu

Bn

Gi tin Hnh 4.19. Nguyn l ct mnh v to

gi.


74

Phng php chuyn gi theo kiu mch o

Trc khi gi c chuyn i th c mt gi gi l c hiu, c gi t nt gc, trong c a ch nt gc. C hiu ny s chy qua cc nt, i n u n t hng chim kt ni qua nt . Khi ng i c chim, v d t A qua 5 n B, n gi tn hiu cng nhn chim (ACK) n nt gc. Sau , cc gi s liu c gi mt cch tun t t nt gc n nt ch theo tuyn ng c thit lp.

Hnh 4.20. M hnh h thng chuyn mch o

Tuyn ng chim (v d t A qua 4, 5, 6 n B) c coi nh c nh trong sut thi gian kt ni. Kiu truyn tin ny ging vi chuyn mch knh, v do vy c gi l mch o hay knh o. Trong mi gi, ngoi phn s liu thc cn c thm phn nhn dng lin kt knh o c s dng cho mc ch ch tuyn.

c im chnh ca k thut mch o l tuyn gia cc trm c thit lp chuyn s liu, nhng khng c ngha l ng ny c dnh ring nh trong chuyn mch knh. Mi gi c th c lu tm ti tng nt, sp hng v chuyn ti nt tip theo


75

nu cn. Ti cng mt thi im, mi trm c th c mt hoc nhiu mch o kt ni ti mt hoc nhiu trm khc trong mng.

Th tc truyn thng tin theo kiu mch o gm 3 pha: thit lp kt ni, chuyn thng tin v gii phng kt ni. Do vy, giao thc truyn thng trong trng hp ny cn c gi l giao thc hng kt ni (Connection Oriented).

Ngoi cn c mch o vnh vin, mch o vnh vin l phng thc thit lp mch o c nh gia hai thu bao. V mt logic c th so snh vi ng dy cho thu trong mng chuyn mch knh, v kiu chuyn mch ny khng cn thit lp hay gii phng cuc gi qua mng

So snh gia datagram v mch o

Phng php mch o c nhiu u im hn so vi datagram, nu hai trm d nh trao i s liu trong mt khong thi gian di .

Trong phng php mch o, nt khng phi thc hin nh tuyn cho tng gi, m n ch thc hin nh tuyn mt ln duy nht cho tt c cc gi.

Trc tin l mng c th cung cp cc dch v lin quan n mch o gm c sp xp v iu khin li. Sp xp cp n vic khi cc gi c chuyn trn cng mt tuyn th chng s n ch theo th t nh khi pht t nt gc. iu khin li l mt dch v bo m rng khng nhng cc gi n ch theo ng th t m cn n chnh xc.

V d nu gi trong th t t nt 4 khi n nt 6 c li th nt 6 s yu cu nt 4 pht li gi . u im na l v s dng mch o nn cc gi c chuyn nhanh hn v khng cn th tc nh tuyn cho tng gi.

u im ca datagram l khng c pha thit lp, do vy khi trm gi s liu ngn th datagram s phn pht nhanh hn. Datagram mm do hn v khi mt phn ca mng c s c th n s t nh tuyn li trnh tc nghn.

Datagram c u im so vi mch o trong trng hp

Khi cc my tnh ch gi 1 vi gi th Datagram nhanh hn

Datagram linh ng hn trong trng hp nghn mch , n s tm ng i khc

VC t tin cy hn trong trng hp c 1 node trong mng b h th cc VC qua node u b hy


76

T chc phn lp ca mng chuyn mch gi.

S dng m hnh 7 lp ISO OSI m t khi nim mng chuyn mch gi v ch yu da trn 3 lp bc thp :

LpHnh thc truyn

Lp 3: lp mng Gi

Lp 2: lp tuyn d liu

Khung

Lp 1: lp vt l Bit

Lp vt l:

Dnh cho tuyn ni vt l gia thit b trong mng. Thng tin trao i di dng bit, bao gm cc thng tin v s liu, bo hiu (iu

khin) dng iu khin thao tc ca tuyn ni v xc nh trng thi c th s dng ca tuyn, xung nhp ghp ni cc tn hiu s liu khi khi phc cu trc tin pht my thu. Cc tn hiu ny dng trao i tin tc cp cao hn gia hai thit b.

Lp tuyn d liu (Data-Link )

Chuyn tin gia cc thit b, theo , yu cu bn tin c chuyn i khng bi li v theo 1 trnh t chnh xc. Pht hin li trong khung tuyn bng phng php ARQ (Automatic Repeatre Quest), bao gm 3 phng thc :

Phng thc dng v ch : Bn pht pht 1 khung v phi ch t pha thu. Nu nhn c s xc nhn l : ACK : Bn pht tip tc pht khung tip theo. NAK : Bn pht pht li khung pht.

Phng thc quay li : Bn pht pht lin tc tng khung, nu nhn c ACK th tip tc pht, nu l NAK

th n s xc nh th t khung li v pht li lin tc khung ny.

Phng thc lp li c chn lc : Pht lin tc cc khung, nu li th pht li khung b li v tip tc cng vic ang d

dang. Mng chuyn mch gi (X.25) thng dng phng thc kch c ca s 7, tc l


77

bn pht pht 7 khung mi cn 1 khung xc nhn t bn thu.

Lp mng

Lp tuyn lm cng vic sa li, iu khin lung theo tuyn gia hai thit b u ni vi nhau. Lp mng to iu kin cho thng tin gia cc thit b m chng khng c u ni trc tip vi nhau (ngha l qua mng).

thit lp tuyn ni lp mng gia hai thit b, th chng cn c kh nng thch ng vi nhau.

Thng thng, mi thit b u ni vo mng c a ch ring, mi thit b c th da vo a ch ca thit b khc m yu cu thit lp thng tin gia chng.

C 2 cch xy dng lp mng : - Mi thit b c mt a ch ring.

- Dng tuyn ni gia 2 thit b xy dng mt a ch.

4.7 Nguyn l hot ng ca tng i Nhn dng thu bao gi nhc my: Tng i nhn dng thu bao gi nhc my

thng qua s thay i tr khng ca ng dy thu bao. Bnh thng khi thu bao gc my in tr ca mch gim t vi chc K xung cn t 150 1500 Ohms. Tng i nhn bit s thay i in tr (tc l thay i trng thi ca thu bao) thng qua b cm bin.

Tng i kim tra xem c cn line trng hay khng, nu cn th cp dial tone cho thu bao. Nu tt c cc line u bn th cp busy tone cho thu bao.

Khi thu bao nhn c dial tone th bt u quay s. Tng i nhn bit thu bao bt u quay s s ct dial tone cho thu bao v bt u nhn bit cc s m thu bao a quay. Tu theo c tnh ca thu bao (s dng ch pulse hay tone) m tng i s nhn bit cc s quay theo phng php khc nhau.

Nu thu s dng ch pulse, tng i s nhn cc xung quay nh cc xung c pht ra t thu bao. Tu theo cc tiu chun m t l gia cc Space v Mark ca cc xung, thi gian ngt gia cc xung s khc nhau v s xung pht ra (vi cng mt phm bm) cng khc nhau

100ms

20mA 300ms

0mA

Next digit


78

Hnh 4.17. S cc xung quay s o Nu thu bao c s dng ch tone, th tng i s nhn bit xung quay

s nh cc tn hiu tn s kp DTMF (Dual Tone multiple Frequency) pht ra t thu bao, nh hnh v di: Mi cp tn s (tone) xut hin ti thiu l 40ms, thi gian ti thiu gia hai s l 60ms.

Hnh 4.18. DTMF (Dual Tone multiple Frequency) Tng i nhn bit cc s thu bao gi n v nhn xt.

Nu s u nm trong tp thu bao ca tng i th tng i s phc v nh cuc gi ni i.

Nu s u khng nm trong tp thu bao ca tng i th tng i phc v nh mt cuc lin i, qua trung k v gi phn nh v quay s sang tng i i phng gii m.

Nu m u l m gi cc chc nng c bit, tng i s thc hin cc chc nng phc v cc yu cu ca thu bao.

Thng thng, tng i c dung lng nh c thm nhiu chc nng c bit lm cho chng trnh phc v cc thu bao thm phong ph, tin li cho ngi s dng lm tng kh nng khai thc v s dng tng i.

Nu vi thu bao rnh, tng i s cp chung cho thu bao vi in p AC t 75 110V, tn s 20 25Hz. Vi chu k nhp 1 giy c, 3 giy khng.

Khi thu bao gi nhc my, tng i nhn bit trng thi nhc my ny, tin hnh ct dng chung cho thu bao c gi mt cch kp thi trnh h hng thu bao.

1

4

7

2

5

8

3

6

9

10 1

1

1

1

1

697 Hz

770 Hz

852 Hz

941 Hz

Mc ch c bit

( sai lch tn s = 1.5%)

1209 Hz

1336 Hz

1477 Hz

1633 Hz


79

ng thi tng i cng ct m hiu ring back tone cho thu bao gi v tin hnh kt ni thng thoi cho hai thu bao.

Tng i gii to mt s thit b khng cn thit tip tc phc v cho cuc m thoi khc.

4.8 Cc chc nng hot ng ca tng i Mc d hin nay nh s pht trin ca khoa hc cng ngh, Cc tng i c nng

cp rt nhiu ln t khi pht minh ra my in thoi, nhng chc nng c bn ca tng i v x l cc cuc gi ca thu bao, kt ni thu bao vi thu bao b gi hu nh khng thay i chng ch khc nhau v phng thc thc hin. Trong tng i t ng hin nay cc chc nng chnh ca tng i bao gm:

1. Nhn dng s thu bao ch gi: Xc nh khi thu bao nhc ng nghe v cuc gi c ni mch iu khin, tng i cp tn hiu mi quay s hoc tn hiu bo bn cho thu bao gi.

2. Tip nhn cc con s c quay: Sau khi nhn c tn hiu mi gi quay s, thu bao ch gi quay s thu bao b gi. Tng i cn ghi li cc s c quay.

3. Kt ni cuc gi: Sau khi tng i ghi li cc s c quay, tng i phn tch v xc nh s b gi. Sau tng i chn knh ni trong cc nhm ng dy trung k n tng i c thu bao b gi. Nu tng i nm trong thu bao ni ht th ch c mt tng i tham gia vo vic kt ni cuc gi.

4. Chuyn thng tin iu khin: Khi tng i thu bao ch gi c ni vi tng i ca thu bao b gi qua tng i chuyn tip, th hai tng i ny trao i vi nhau cc thng tin cn thit v thu bao ch gi, b gi

5. Kt ni chuyn tip: Trong trng hp tng i c ni n tng i chuyn tip th cc qu trnh 3 v 4 li c lp li trong qu trnh x l cuc gi, sau cc thng tin ca thu bao ch gi v b gi c truyn i.

6. Kt ni ti trm cui: Khi trm cui c nh gi l trm ni ht, da theo s thu bao b gi c truyn i th b iu khin trng thi thu bao ca tng i b gi c tin hnh. Nu thu bao b gi khng trng thi bn th mt knh c thit lp ni vi knh trung k c chn kt ni cuc gi.

7. Truyn tn hiu chung: kt ni cuc gi, tn hiu chung s c pht n thu bao b gi v cho n khi thu bao b gi nhc my tr li. Khi thu bao b gi tr li tn hiu, chung b ngt v thu bao b gi c chuyn sang trng thi m thoi.

8. Tnh cc: Sau khi nhn c tn hiu xc nhn cuc gi hon tt t tng i, thu bao b gi v cho n khi thu bao b gi nhc my tng i ch bt u tnh thi gian gi.


80

9. Truyn bo tn hiu bn: Khi tt c cc ng trung k n tng i ca thu bao gi b chim ht, hoc thu bao ang bn th tn hiu bo bn s c gi ti thu bao ch gi.

10. Hi phc h thng: Sau khi cuc gi kt thc, tt c cc knh ni cho cuc gi u c gii phng. Ngoi ra i vi cc tng i hin i ngy nay cn c thm nhiu chc nng khc h tr cho cng tc khai thc v bo dng.

4.9 Cc phng php iu khin tng i: 1. Phng php iu khin c lp: L phng thc m tng i iu khin cc kt

ni, tng i khng chu chi phi ca bt k tng i ngoi no khc. 2. Phng php iu khin chung: L hnh thc m cc tng i c iu khin v

gim st ca mt trung tm.

Tng i 2

Tng i 1 Tng i 0

Tng i 3

Tng i trung tm

Hnh 4.19. Phng php iu khin chung

3. Phng php iu khin bng chng trnh lu tr:

Tng i 2

Tng i 1 Tng i 0

Tng i 3

D liu trng thi (T1, T2, T4)

D liu trng thi (T1, T0

D liu trng thi (T1, T0) D liu trng thi

(T0, T1, T4)

Hnh 4.20. Phng php iu khin bng chng trnh lu tr


81

Vi phng php ny th mi tng i s thng xuyn lu tr v cp nht trng thi thng tin ca tng i bn v cc ng trung k ni vi chng.

Khi thc hin mt cuc gi ni i th vic iu khin kt ni vn do chnh tng i chnh thc hin.

Khi iu khin mt cuc gi lin i (gi s tng i 2, 4 th ti tng i 2 s xem xt ng i u tin ngn nht ng vi n l1 trng thi ca tng i u tin, xem xt n c ri hay khng v tng i c kh nng kt ni c hay khng).

Nu tng i 4 ri, th tng i ny c kh nng thc hin vic kt ni cuc gi, tng i 2 s truyn s quay v thc hin cc th tc kt ni nh bnh thng.

Nu nh tng i 4 bn hay khng c kh nng kt ni cuc gi th tng i 2 s t ng tm kt ni u tin k tip n tng i ln cn.

4.10 Cc hnh thc thng tin trn mng in thoi Do nhu cu thng tin tch hp trn mt ng dy, cc nh sn xut lin tc pht trin

h thng, t h thng thng tin thoi vi mc ch phc v cho cc cuc gi thoi, cho n cung cp dch Fax, truyn d liu v sau cng l cung cp dch Internet.


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4.11 Qu trnh thit lp, duy tr v kt thc cuc gi ( A gi B)

Thu bao gi A Tng i Thu bao b gi B TH1: Nhc my Nhn trng thi nhc, gc my Cp Dial tone

(B ri, Quay s Ct Dial tone B Ni i) Gii m DTMF Kim tra => B : thuc ni i Kim tra => B c ri khng B ri Cp chung cho B chung Cp Ring back tone cho A Nhn trng thi nhc my B B nhc my Ct chung B Ct Ring back tone A Kt ni thng thoi Gc my Nhn trng thi gc my Hu kt ni thng thoi Cp Ring tone TH2: Kim tra => B :

thuc ni i B bn Kim tra => B c ri khng B bn (ni i) Cp Busy tone


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TH 3 A gi B , B khc tng i vi A , B ri A Tng i ca A Tng i

ngoi ca B B A Nhc my Nhn trng thi nhc my

Cp Dial tone cho A A Quay s Ct Dial tone Gii m DTMF Kim tra=>B l thu bao ngoi Kimtra=>c trung k ri Quay li s ra ngoi Nhn trng thi nhc my Gii m DTMF Kim tra=>B l ni i Kim tra=>B ri Cp chung B Ring back tone A B Nhc my Nhn trng thi nhc my B Thng thoi Thng thoi Hu kt ni thng thoi B gc my Thng thoi Cp Busy tone