LTvienthong

8/8/2019 LTvienthong

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L thuy t vin thng1. H thng vin thng in t

1.1 H thng vin thng in t ng y nay

Cng ngh vin thng in t tip tc tin b nhanh chng k t khi c phtminh h thng in tn v in thoi n mc n cch mng ho cc ph ngtin thng tin truyn thng khong mt th k tr c y. Ngy nay, h thng vinthng in t c xem nh cc ph ng tin kinh t nht c c trao i tintc v cc s liu. Ngoi ra song song vi tng tr ng v x hi kinh t, vic h nhthnh cc ph ng tin cn thit cho vin thng in t tr nn phc tp h n vc khuynh hng k thut cao nhm p ng nhu cu ang tng v cc dch v ccht lng cao v dch v vin thng tin tin h n; mc d vy cc thit b c th c h nh thnh theo cc cch khc nhau v c cc mc phc tp khc nhautheo cc yu cu ca ngi s dng.

V c bn chng c m phng nh sau (din gii) :

Hnh 1.1. Cu to ca mng li vin thng.

a. Ngu n thng tin: Con ngi hay my pht ra thng tin cn truyn i. Thngtin pht ra c phn loi thnh ting ni, m, v hnhnh (k t, k hiu vhnhnh).

b. Thi t b truyn: B phn hay thit b chuyn thng tin pht ra thnh cc tnhiu c truyn i qua ng truyn dn.

c. ng truyn dn: Mt ph ng tin truyn cc tn hiu t thit b truyn nthit b nhn. Cc loi cp ng trc, cp quang, khng gian, v cc hng sng


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cho php thc hin cc dch v phi in thoi ang c lp t v vn hnh, angcch mng ho cuc sng ca chng ta.

Dch v phi inthoi c a ra hin nay yu cu cc thit b v ph ng tin

vin thng tin tin v chuyn mn ho cao.Thc t ny cng tr nn r rngh n khi chng ta kim tra cc loi tn s hin ang dng; khng ging nh ccph ng tin ph thng ch yu cu cc dng tn hiu 4 KHz cho cc loi dch v,cc di tn 1-4 MHz, 12-240 KHz, v 12-240 KHz ang c s dng, mt ccht ngng cho Video, cc s liu tc va v cao, truyn fax p ng cc ctnh dch v ca chng; ng thi khi cung cp mt dch v, cc tn s khc nhauc th c s dng c kt qu ti u. Theo , vic thit lp nhiu mng livin thng khc nhau, s dng cc di tn khc nhau v cc dch v khc nhau liu khng thc t v khng kinh t. Do vy mt nhu cu cp bch l pht trincng ngh cc mng li vin thng vi dung lng c th giao tip vi nhau, c

kh nng x l cc loi dch v khc nhau c th a ra s dng trong t ng laign. Vi mc ch ny, cc nh nghin cu v k s tham gia vo l nh vc ny ang c gng kt hp cc mng li vin thng hin nay mt cch c h thng vc hiu qu.

Th nh , xu hng gn y c c im l tng nhu cu i vi mng li s. Tkhi pht hin ra cc nguyn l v in thoi t vic chuyn nng lng m thanhthnh nng lng in truyn i ting ni cho n khi pht sinh ra ph ng phptruyn bng ghp knh in thoi, cc dch v in thoi a ra s dng cc hthng chuyn mch phn chia khng gian thng qua cc ng truyn t ng t. iu ny cng da vo cng ngh t ng t. Vo u nhng nm 1960, ph ngphp PCM-24 c th ng mi ho mt cch thnh cng v vy chng minhrng ph ng php truyn dn s l kinh t h n nhiu so vi ph ng php truyndn t ng t. k t , cc h thng tng i s s dng hthng truyn dn s c lp t v vn hnh mt cch rng r i.

Nhng u im ca cc mng li vin thng s l: Khi s dng h thng tng it ng t v ng truyn dn s, b m ho v b gii m c s dng cho ccdch v thoi bin i cctn hiu ngc li thnh ting ni ti thi im chuynmch; Khi s dng h thng s v ng truyn dn s, ch cn c mt thit b ucui vi kh nng thc hin chc nng n gin v cc tn hiu s dc u ni


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mc ghp knh. Mt u im khc ca vic s dng h tng i s l n lmtng cht lng truyn dn. Trong mng li in thoi s, cc tn hin cm ho ti tng i ch gi c gii m, sau c m ho ti tng i trungchuyn v cui cng c gi n tng i b gi.

Theo , bng cch s dng ph ng php ny, c th trnh c vic tng lngting n pht ra khi chuyn cc tn hiu t ng t thnh cc tn hiu s. Ngoi ra, do ng truyn dn s tri qua t thay i v mc h n l ng truyn dn t ng t,hin tng mt ng truyn s c th t nh h n. thc hin mc ch ny,nu s dng mt ng truyn s gia hai tng i, th s mt ng truyn cth c gim bt t 10 dB xung cn 6dB.ng thi, trong mng in thoi s,i vi mt ng in thoi, 64 kbps c dng nh tc bt c s; cc s liu,

fax, v thng tin video c tc nh h

n mc bt ny c th

c gi i mt ccht ng i d dng h n thng qua mng in thoi s. Nh trnh by, cc thit bc th c chia s theo cc yu cu dch vv v th c th c s dng mtcch linh hot ng dng cho cc loi dch v hin ang tn ti cng nh ccdch v mi.

Hnh 1.3. Ti n tr nh trong s ho

Cc nh nghin cu v k s cc nc tin tin ang c gng pht trin loimng truyn thng s ny. Tin b thc hin c trong cng ngh s c giithch s dng m h nh H nh 1.3. Mt ng truyn s dc s dng gia haitng i trong mng li s tch hp c m phng trong s . ng thi mngISDN (mng a dch v s) cng c pht trin trong cc dch v tch hp


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c cung cp vi cc thit b u cui c s ho. Ngoi ra, do cc loi dch vvin thng c a ra ngy cng tr nn phong ph, mt phm vi rng ln ccloi thit b u cui, mt trong 3 phn quan trng mng li vin thng, ch yu l,cc thit b u cui, ng truyn dn v cc thit b tng i, hin nay c s

dng rng r i. Hu ht cc thit b u cui cng cng hin nay u c thit k vn hnh cng d dng cng tt, tuy nhin mt s cc thit b u cui ny gil cc thit b u cui tch hp, c trang b vi cc tnh nng tin tin dng chocc dch v c bit. T , vic s dng truyn thngs tr nn a dng ho h n,v vic c gng pht trin cng ngh ph hp cho cc mc ch cng s cthc hin.

1.2 L ch s pht trin cng ngh vin thng in t

Trong sut lch s ca loi ngi, vic pht minh ra ngn ng l cuc cch mngtruyn thng ln nht u tin. Sau t lu con ngi pht sinh ra tn hiu bngla c kh nng truyn t cc thng tin c hiu qu v nhanh chng ti cc vngxa. Cu truyn lch s cho thy vo khong nm 1000 tr c cng nguyn, cc iqun Hy Lp s dngph ng php ny thng bo cc chin thng ca h chocc cng dn ang nng lng ca Hy Lp. Trong mt thi gian di, ph ng phpny c s dng mt cch rng r i p ng cc nhu cu v truyn thng.Mt cuc cch mng thng tin khc na ln h n xy ta khi con ngi bit clm th no ghi li ngh v t tng ca m nh bng cch d ng cch dng ccch vit. Vi kh nng ny, con ngi c kh nng truyn thng tin m khng bgii hn bi thi gian v khng gian.ng thi, vic pht minh ny a ta ccdch v a th v thng bo. Hong R-ma c th truyn i thng tin cnthit n cc vng xa n 160 km cch xa thnh Rm trong mt ngy bngh thng(mng li) ng b h xy dng nn trong ton quc. Vic pht minh ta cngngh in thc y h n na vic pht trin cc ph ng tin truyn tin v cho conngi c kh nng thng tin vi nhiu ngi h n v vi cc khu vc cch xanhau.

T cui th k 18 n 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 h nh c pht minh v thi gian ny lm thayi th gii chng ta rt nhiu. Trongphn tip theo, cc pht minh ln khc v nhng pht hin lin quan n cng


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ngh thng tin in t xy ra trong sut 160 nm qua cng nh xu hng phttrin ca chng t ng lai c tho lun mt cch ngn gn. Nm 1820,Georgo Ohm a ta cng thc ph ng trnh ton hc gii thch cc tn hiu in chy qua mt dy dn rt thnh cng. V nm 1830, Michall Faraday tm ta nh lut dn in t tr ng. Nm 1850, i s Boolean ca George Boolers tota nn mng cho lgc hc v pht trin cc r -le in. Chnh vo khong thi gianny khi cc ng cp u tin xuyn quai Ty D ng nh in tn clp t. James Clerk Maxwell a ra hc thuyt in t tr ng bng cc cngthc ton hc nm 1870. Cn c vo hc thuyt ny, Henrich Hertz truyn i vnhn c sng v tuyn thnh cng bng cch dng in tr ng ln u tintrong lch s. Tng i in thoi u tin c thit lp u tin nm 1876 ngaysau khi Alexander Graham Bell pht minh ra in thoi. 5 nm sau, Bell bt u

dch v gi in thoi ng di gia New York v Chicago v Guglieno Mareconica Italia lp t mt trm pht sng v tuyn pht cc tn hin in tn.Trong th k 21 vic pht trin v p dng c tnh thc t v cng ngh lin quan ang tip tc pht trin nhanh chng v trong qu trnh , cch mng ho th giichng ta. Nm 1900, Einstein, mt nh vt l ni ting v hc thuyt t ng i, vit rt nhiu ti liu quan trng v vt l cht rn, thng k hc, in t tr ng, vc hc lng t. Vo khong thi gian ny phng th nghim Bell ca M phtminh v sng ch ra ng phng in cc cho cc knh thin vn xoay c v Le

de Forest tr thnh ngi khi xng trong lnh vc vi mch in t thng quapht minh ca ng ta v mt ng chn khng ba cc. Vic ny c tip theo bngpht minh mt h thng tng i t ng t t ng ckh nng hot ng khngcn c bng chuyn mch. Nm 1910, Erwin Schrodinger thit lp nn tng choc hc lng t thng qua cng b ca ng ta v cn bng sng gii thch cuto nguyn t v cc c im ca nguyn t v R.H Goddard ch to thnhcng tn la bay bng phn lc cht lng, v my t-l-tp c pht minh. ng thi, vo khong thi gian ny, pht thanh cng cng c bt u bng

cch pht sng. Nm 1920, Ha rold S. Black ca phng th nghim nghin cu Bell pht minh ra mt my khuch i phn hi m bn m ngy nay vn cn dngtrong l nh vc vin thng v cng ngh my in ton. V.K. Zworykin ca RCA, M pht minh ra n hnh bng in cho v tuyn truyn h nh, v cc cpng trc,ph ng tin truyn dn c hiu quh n cc loi dy ng b nh thng, csn xut. Nm 1939, dch v pht sng truyn h nh thng xuyn c bt u ln


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u tin trong lch s v nm 1930, Claude Schannon ca phng th nghim Bell,bng cch s dng cc cng thc ton hc tin tin thnh cng trong vic t rahc thuyt thng tin dng xc nh lng thng tin ti a m mt h thng vinthng c th x l vo mt thi im nh. Hc thuyt ny c pht trin

thnh hc thuyt truyn thng s. ng thi, ra- a c pht minh trong thi kny. Nm 1940, phng th nghim Bell t nn mng cho cc cht bn dn c tch hp cao ngy nay qua vic pht minh ra n ba cc v Howard Aiken cai hc Harvrd, cng cng tc vi IBM, thnh cng trong vic lp t mt my in u tin c kch thc l 50feet v 8feet. Sau t lu, J. Presper Ecker vJohn W. Mauchly ca i hc Pennsylvania ln u tin pht trin my in tonphn tch gi l ENIAC. Von Neuman da vo my ny, pht trin thnh cngsau my in ton c l u gi ch ng trnh. PCBs c a ra vo nhng nm

50, lm cho vic tch hp cc mch in t c th thc hin c. Cng trongnm , RCA phng thnh cng v tinh nhn to vo khng trung v la-re dngcho truyn thng quang hc c pht minh. Vo nhng nm 60, cc loi LSIs,cc my in ton mini c b nh kiu bong bng, cp quang, v my phn chiathi gian c pht trin v th ng mi ho mt cch thnh cng vo cc nm 70,cc loi CATVs hai hng, a Video, my in ton ho, truyn nh qua vtinh, v cc h thng tng i in t ho ton b c a ra.

2. Cng ngh chuyn mch

2.1 Khi qut chung

2.1.1 Nhu c u i vi h thng chuyn mch

My in tn c Samuel F.B Morse pht minh nm 1837, ln u tin trong lchs, cc tn hiu in c s dng truyn tin; cc s liu c m ho cdng nh mt ph ng tin truyn dn. Vic truyn ting ni tr thnh c th thc

hin c khi Alexander Graham Bell pht minh ra in thoi nm 1876. Nichung, vic truyn thngtin cp n qu tr nh chuyn thng tin t ngi phtthng tinn ngi s dng. Thng tin c xc nh l cc t tng v cc sliu cn thit cho ngi s dng. ng thi, mt s ph ng tin truyn tin cs dng trong sut lch s loi ngi. Loi tn hiu la c dng rng khptrong qu kh l mt v d in h nh. Tuy nhin, v nhu cu v cc dch v truyn


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thng cht lng cao v ng tin cy cng tng ln, con ngi bt u dng inthay cho la lm ph ng tin truyn thng quan trng nht. Trong t ng laign, ngi ta d nh l nh sng s thay th in lm ph ng tin chnh. Hthng truyn thng cp n mt s thit b hay cc b phn s dng cho

php ngi cp tin chuyn thng tin cho ngi s dng; cc b phn ny hay thitb c phn loi thnh cc h thng truyn tin phn tn v h thng truyn thngtng i nh ghi H nh 2.1. Trong trng hp u, ngi cp tin ch cp thng tintrong ngi s dng ch nhn c thng tin truyn i. Mt trong cc v d r rng cho cc loi ny bao gm c i pht thanh v v tuyn truyn h nh.

H truyn thng

H truyn thng phn tn i v v tuyn, truyn h nh v.v.

H truyn thng tng iMng li truyn thng in thoiv.v.

Hnh 2.1. Phn lo i cc h thng truyn thng.

Trong h truyn thng tng i, ngi cp thng tin v dng thng tin ch a cxc nh v h thng s dng c kh nng cung cp v s dng thng tin vo cngmt thi gian. V d cho vic ny l h thng truyn thng in thoi. H truynthng tng i cp n qu tr nh chn la chn nhng ngi ang cch xanhau hoc gia cc my t cch bit nhau v sau giao tip vi nhau bng tingni hoc bng cc s liu. phn tch mt cch c hiu qu, th cc iu kin sau y phi c p ng.

Trc ht, chn mt bn nhn thng tin v sau chn ng giao tip, mt htng i c dng cho mc ch ny. Cc loi h tng i hin c th c truyn

tin bao gm cc h tng i in t ch yu dng cho cc dch v in thoi v cch chuynmch s liu dng truyn s liu.

Th hai, cc h truyn dn c dng truyn thng tin cc mc cht lng cth chp nhn c khng k n khong cch cn phi c m bo. Hin vaycc h thng truyn dn bng dy nh cc loi cp cn bng, cp ng trc, si


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quang v cc h thng truyn dn khng dy (v tuyn) s dng cc sng ccngn ang c dng rng r i.

Th ba, cc mng li truyn tin phi c thit lp c xem xt n vic b tr h

tng i v ng truyn dn, cht lng giao dintng th, v duy tr cht lngtruyn dn, ngoi ra, mng li tuyn c lp ra, phn phi s mt ng truyn,k hoch nh s, cc vn lin quan n tnh cc phi c thit k theo nhucu ca ngi s dng. Cc h thng truyn thng tng i tip tc c nngcp mt cch nhanh chng k t khi pht minh ra h thng in thoi cch y gn100 nm. V c bn, tt c cc h thng u cn my in thoi chuyn cctn hiu ting ni thnh tn hiu in v ngc li cng nh cc h truyndn truyn cc tn hiu in. Mt mng li truyn tin c th c xy dng bng cch

ni trc tip cc thu bao cung cp v nhn thng tin qua mng l

i khi s l

ngthu bao ny ch a phi nhiu qu. V d, c minh ho (a) ca h nh 2.2,8C2=28 ng l cn thit trong tr ng hp ch c 8 thu bao c ng ktrong h thng. Tuy nhin, khi s dng h tng i vi chc nng giao tip giacc thu bao nh trnh by (b) h nh 2.2 s cc ng in thoi cn thit phibng vi s thu bao ng k trong h thng. Nh trnh by, iu quan trngthit lp cc mng li thng tin mt cch kinh t v c hiu qu.

Hnh 2.2. Cc ph ng php c a mng chuy n mch cho 8 thu bao

2.1.2 Pht tri n cng ngh chuyn mch


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H tng i dng nhn cng gi l loi dng in t c xy dng New Havenca M nm 1878 l tng i th ng mi thnh cng u tin trn th gii. png yu cu ngy cng tng v cc dch v in thoi mt cch tho ng v kt ni nhanh cn cuc ni chuyn v v mc ch an ton cho cc cuc gi, h

tng i t ng khng cn c nhn cng c A.B Strowger ca M pht minh1889. Version ci tin ca m h nh ny, gi l h tng i kiu Strowger tr thnhph bin vo cc nm 20. Trong h tng i Strowger, cc cuc gi c kt nilin tip tu theo cc s in thoi trong h thp phn v do c gi l hthng gi theo tng bc. EMD (Edelmatall-Drehwahler) do cng ty Siemens ca c pht trin cng thuc loi ny; h thng ny cn c gi l h tng i c vcc chuyn mch ca n c vn hnh theo nguyn tc c in.

Doi chin th gii th II bng n, s c gng lp nn cc h tng i mi b tmthi nh ch. Sau chin tranh, nhu cu v cc h tng i c kh nng x l cc

cuc gi ng di t ng v nhanh chng tng ln. Pht trin loi h tng iny yu cu phi c s tip cn mi hon ton bi v cn phi gii quyt cc vn phc tp v tnh cc v vic truyn cuc gi ti sinh yu cu phi c x lnhiu khu. Ericsson ca Thu in c kh nng x l vn ny bng cchpht trin thnh cng h tng i c cc thanh che (Cross bar). H tng i c ccthanh cho c c im ho bi vic tch hon ton vic chuyn mch cuc go

v cc mch iu khin

c pht trin ng thi M. i vi mch chuynmch cho, loi thanh cho kiu m /ng c s dng; bng cch s dng loichuyn mch ny c mt b phn m/ng vi im tip xc c gip vng, ccc tnh ca cuc gi c ci tin rt nhiu. H n na, mt h iu khin chung iu khin mt s cc chuyn mch vo cng mt thi im c s dng. lcc xung quay s c dn li vo cc mch nh v sau c xc nh kt hptrn c s ca cc s quay c ghi li la chn mch ti sinh.

Nm 1965, Mt h tng i in t th ng mi c dung lng ln gi l h ESS s1 c th ng mi ho thnh cng M do vy m ra mt k nguyn mi chocc h tng i in t. Khng ging vicc h tng i thng thng s dng ccchuyn mch c , h thng ESS s 1 l h tng i s dng cc mch in t. Vicnghin cu loi h tng i ny c khi u t u nhng nm 40 v cxc tin nhanh sau khi c pht minh ra n ba cc vo nhng nm 50. H tng i in t mi c pht trin khc v c bn vi cc h thng thng im l


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trong khi h sau ny s dng mch iu khin chuyn mch dng cc l-gc kiudy th h tr c y dng cc thao tc logic bng cc ph ng tin phn mm lpt trong h thng. Ngoi ra, h tng i in t mi trin khai to c s iukhin mt cch linh hot bng cch thay th phn mm cho php ngi s dng c

dch v mi. ng thi, vn hnh v bo dng tt h n, tng i ny ctrang b chc nngr chn on. Tm quan trng vic trao i thng tin v s liumt cch kp thi v c hiu qu ang tr nn quan trng h n khi x hi tin nth k 21. p ng y mt phm vi rng cc nhu cu ca con ngi sngtrong giai on u ca k nguyn thng tin, cc dch v mi nh dch v truyn sliu, dch v truyn h nh bao gm c dch v in thoi truyn h nh, cc dch vtruyn thng di ng ang c pht trin v thc hin. Nhm thc hin c hiuqu cc dch v ny, IDN (mng li s tch hp) c kh nng kt hp cng ngh

chuyn mch v truyn dn thng qua qui tr nh s l s l mt iu kin tin quyt.Ngoi ra, vic iu ch xung m (PCM) c dng trong cc h thng truyn dn c p dng cho cc h thng chuyn mch thc hin vic chuyn mchs. Da vo cng ngh PCM ny, mt mng a dch v s (ISDN) c th x lnhiu lung vi cc dch v khc nhau ang c pht trin hin nay.

2.1.3 Cc ch c nng ca h thng tng i

Mc d cc h thng tng i c nng cp rt nhiu t khi n c phtminh ra, cc chc nng c bn ca n nh xc nh cc cuc gi ca thu bao, ktni vi thu bao b gi v sau tin hnh vic phc hi li khi cc cuc gi hon thnh, hu nh vn nh c. H tng i dng nhn cng tin hnh cc qutrnh ny bng tay trong khi h tng di t ng tin hnh cc vic ny bng ccthit b in.

Trong trng hp u, khi mt thu bao gi i mt tn hiu thoi ti mt tng i,nhn vin cm nt tr li ca ng dy b gi vo cm ca dy ch gi thit

lp cuc gi vi pha bn kia. Khi cuc gi hon thnh, ngi vn hnh rt dyni ra v qa n v trng thi ban u. H tng i nhn cng c phn loithnh lloi in t v h dng c-qui chung.i vi loi dng in t, th thu baolp thm cho mi c-qui mt ngun cp in. Cc tn hiu gi v tn hiu honthnh cuc gi c gi n ngi thao tc vin bng cch s dng t tr ng. ivi h dngc qui chung, ngun in c cung cp chung v cc tn hiu gi v


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tn hiu hon thnh cuc gi c n gin chuyn n ngi thao tc vin thngqua cc n. i vi h tng i t ng, cc cuc gi c pht ra v hon thnhthng qua cc bc sau:

1) Nh n dng thu bao ch gi : Xc nh khi thu bao nhc ng nghe v sau cuc gi c ni vi mch iu khin.

2) Ti p nhn s c quay : Khi c ni vi mch iu khin, thu bao ch gibt u nghe thy tn hiu mi quay s v sau chuyn s in thoi ca thubao b gi. h tng i thc hin cc chc nng ny.

3) K t ni cuc gi : Khi cc s quay c ghi li, thu bao b gi c xc nh,th h tng i s chn mt b cc ng trung k n tng i ca thu bao b gi

v sau chn mt ng ri trong s . Khi thu bao b gi nm trong tng ini ht, th mt ng gi ni ht c s dng.

4) Chuy n thng tin iu khin: Khi c ni n tng i ca thu bao b gi haytng i trung chuyn, c hai tng i traoi vi nhau cc thng tin cn thit nhs thu bao b gi.

5) K t ni trung chuyn: Trong trng hp tng i c ni n l tng i trungchuyn, mc 3) v 4) trn y c nhc li ni vi trm cui v sau thngtin nh s thu bao b gi c truyn i.

6) K t ni ti trm cui : Khi trm cui c nh gi l trm ni ht da tr n s cathu bao b gi c truyn i, th b iu khin trng thi my bn ca thu bao bgi c tin hnh. Nu my khng trng thi bn, th mt ng ni c nivi cc ng trung k c chn kt ni cuc gi.

7) Truy n tn hiu chung : kt ni cuc gitn hiu chung c truyn v ch

cho n khi c tr li t thu bao b gi. Khi tr li, tn hiu chung b ngt v trngthi c chuyn thnh trng thi my bn.

8) Tnh c c : Tng i ch gi xc nh cu tr li ca thu bao b gi v nu cnthit,bt u tnh ton gi tr cc phi tr theo khong cch gi v theo thi giangi.


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9) Truy n tn hiu bo bn: Khi tt c cc ng trung k u b chim theo ccbc tr n y hoc thu bao b gi bn, th tn hiu bn c truyn n cho thubao ch gi.

10) H i phc h thng : Trng thi ny c xc nh khi cuc gi kt thc. Sau ,tt c cc ng ni u c gii phng.

Nh vy, cc bc c bn do h thng tng i tin hnh x l cc cuc gi dc tr nh by ngn gn. Trong h thng tng i in t, nhiu c tnh dch vmi c thm vo cng vi cc chc nng tr n. Nhng iu ny s c bnthm sau ny.

Cc im c bn sau y phi c xem xt khi thit k cc chc nng ny.

1) Tiu chu n truyn dn: mc ch u tin ca vic u ni in thoi l truynting ni v theo l mt ch tiu ca vic truyn dn p ng cht lng giphi c xc nh bng cch xem xt s mt mt khi truyn, rng di tn struyn dn, v tp m.

2) Tiu chu n kt ni : iu ny lin quann vn duy tr dch v u ni cho ccthu bao. Ngh a l, l ch tiu v cc yu cu i vi cc thit b tng i v scc ng truyn dn nhm bo m cht lng kt ni tt. Nhm mc ch ny,mt nng li tuyn linh hot c kh nng x l ng thng c hiu qu vi t lcuc gi b mt t nht phi c lp ra.

3) tin cy : cc thao tc iu khin phi c tin hnh ph hp, c bit cc lixut hin trong h thng vi cc chc nng iu khin tp trung c th gp phihu qu nghim trng trong thao tc h thng. Theo , h thng phi c cchc nng sa cha v bo dng hu hiu bao gm vic chn on li, t m vsa cha.

4) linh hot : s lng cc cuc gi c th x l thng qua cc h thng tng i tng ln rt nhiu v nhu cu nng cp cc chc nng hin nay tng ln. Do , h thng phi linh hot m rng v sa i c.


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5) Tnh kinh t : Do cc h tng i in thoi l c s cho vic truyn thng ichng, chng phi c hiu qu v chi ph v c kh nng cung cp cc dch vthoi cht lng cao. Cn c vo cc xem xt trn y, mt s loi tng i tng c trin khai v lp t k t khi n c a vo ln u tin.

2.2 Chuy n mch cuc gi

2.2.1 Phn lo i chuyn mch cuc gi

C nhiu loi chuyn mchcuc gi bao gm cc chuyn mch loi c in v in t c s dng trong cc tng i. Chng c th c phn loi rng lnthnh cc loi chuyn mch phn chia khng gian v cc loi chuyn mch ghp.

Hnh 2.4. Chuy n mch xoay kiu ng.


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A. Lo i chuyn mch phn chia khng gian

Cc chuyn mch phn chia khng gian thc hin vic chuyn mch bng cchm/ng cc cng in t hoc cc im tip xc c b tr theo cch qung

nhau nh cc chuyn mch xoay v cc chuyn mch c thanh cho. Loi chuynmch ny c cu to bi cc b phn sau:

1) Chuy n mch c ki u chuyn ng truyn

1. Chuyn mch c kiu m/ng2. Chuyn mch c kiu r -le in t3. Chuyn mch in t kiu chia khng gian

Nh c tr nh by h nh 2.3 v 2.4, loi chuyn mch c kiu chuyn ngtruyn l loi chuyn mch thc hin vic vn hnh c t ng t nh chuyn mchxoay. Chuyn mch la chn dy ri trong qu tr nh dn truyn v tinhnh chcnng iu khin mc nht nh. Do tnh n gin ca n, n c s dng rngri trong cc h thng tng i t ng u tin pht trin. Tuy nhin, do tc thc hin chm, s mn cc im tip xc, v thay i cc hng mc tip xc gyra do vic rung ng c hc, ngy nay n t c s dng. Loi chuyn mch ckiu m/ng c pht trin ci tin yu im ca cng tc c kiu chuyn

ng truyn bng cch n gin ho thao tc c hc thnh thao tc m/ng. Loichuyn mch ny khng c chc nng iu khin la chn v c thc hin theogi thuyt l mch gi v mch iu khin l hon ton tch ring nhau. Nh vy,vi kh nng cung cp iu khin linh hot, n c dng rng r i hin nay v c coi l chuyn mch tiu chun, v loi c s dng nhiu nht l loichuyn mch thanh cho.

Chuyn mch kiu r -le in t l loi chuyn mch c r -le in t mi im ctca chuyn mch loi thanh cho. i vi chuyn mch c loi m/ng c mt tr n y, th thao tc m/ng c thc hin nh vic nh im ct thng quathao tc c hc theo chiu ng/chiu ngang trong khi chuyn mch kiu r -le int, th im ct c th c la chn theo hng ca lung in trong cun dyca r -le.


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V vy v nguyn tc cc thao tc c hc cng nh vic m/ng ca cc im tpxc th c tin hnh nhanh chng h n.

Chuyn mch in t hiu phn chia khng gian c mt cng in t mi im

ct ca chuyn mch c thanh ct cho. N c nhng bt li sau y so vi loichuyn mch im tip xc; khng t ng thch vi ph ng php c do c s khcnhau v mc tn hiu hoc chi ph v cc c im thoi kh xu bao gm chin tng mt cuc gi v xuyn m.

Theo , tr tr ng hp c bit, n ch a lc s dng rng r i. Tuy nhin, docc mch in t nh cc ICs hay cc LSIs tr nn tch hp h n, d kin chng c s dng nhiu h n trong t ng lai gn y.

B. Chuy n mch ghp

Cc loi chuyn mch ghp c vn hnh trn c s cng ngh truyn ti tptrung c s dng rng r i trong h thng truyn dn. Cc chuyn mch ny ccng chung mt cng c hiu qu v kinh r cao h n. C cc loi chuyn mchghp phn chia thi gian ghp cc cuc gi da vo thi gian v chuyn mchghp phn chia tn s ghp cc cuc gi tr n c s tn s.

Nguyn l s dng cho loi chuyn mch phn chia thi gian l n tch nhp thngtin c pha nh bng cch s dng ma trn nhp c pha thay i trong khinguyn l dng cho ph ng php phn chia tn s l tch cc tn hiu c cc tns cn thitbng cch s dng b lc c th thay i. Ph ng php chia tn s c bit l c cc vn k thut nh l vic pht sinh cc loi tn s khc nhauv vic cung cp v ngt cc tn s ny c ng nh b lc c th thay i. ng thin khng kinh t. Theo , ph ng php ny c nghin cu rng r i trong thik u ca s pht trin h thng tng i in t nh ng ch a c vo s dngcho h tng i phn ti. Mt khc, ph ng php phn chia thi gian c nghvo thi k u pht trin h tng i in t v n ang c nghin cu tipngy nay. Ph ng php iu ch ny c phn loi thm thnh iu ch theobin xung (PAM) tin hnh bng chuyn mch PAM v iu ch xung m cthc hin nh chuyn mch PCM. Mi chuyn mch c phn loi thm nh sau.


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Hnh 2.5. Phn lo i chuyn mch ghp.

mt nhiu thi gian pht trin thnh cng chuyn mch PAM. Khi c ara, do thit k n gin ca n, chuyn mch PAM c s dng cho h tng ic dung lng loi va. V d c th ca n l ESS kiu 101, mt loi PBX iukhin t xa c dng M cho cc mc ch c bit v n ch a ph hp cho cc

h thng tng i dung l

ng ln vi nhng vn ca n v cc c im thoinh tp m v xuyn m.ng thi, v n l loi t ng t, t ng lai ca n lkhng r rng. Chuyn mch PCM c d kin l mt trong cc thnh phn chnhca IDN hay ISDN x l nhiu loi thng tin cng mt lc bao gm cs liu.

Mng s tch hp kt hp h truyn dn v h chuyn mch thng qua s dngcng ngh PCM. Do ph ng php ny s dng mch s, n c d nh c vimch ho trc tip trong t ng lai gn y. Khi s dng loi chuyn mch ny,vic chuyn mch c tin hnh trong giai on dn knh theo cc c tnh thoin nh ca PCM. Do vy, bi v chuyn mch r -le nhiu mc c th thc hin c nh s dng chuyn mch ny, mt mng li truyn thng mi c th cthit lp d dng thng qua vic dng loi chuyn mch nay. Nh c tr nhby, ph ng php ny s c s dng rng r i trong t ng lai.

2.2.2 Chuy n mch PCM.


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Chuyn mch PCM l loi chuyn mch ghp hot ng da vo cng ngh dnknh chia thi gian v iu ch xung m. PCM l ph ng php truyn bin caPAM sau khi lng ho n v sau bin i n thnh ra m nh phn. Theo , vic ti m ho c th c tin hnh d dng v n c th d dng phn bit c vi cc tn hiu ngay c khi c tp m v xuyn m trong ng truyn dn.Ngoi ra, thc hin chuyn mch phn chia thi gian c th dng, cc chuynmch thi gian trao i khe thi gian v chuyn mch phn chia thi gian trao i theo khng gian cc khe thi gian c phn chia theo thi gian.

A. Chuy n mch T

Cc s liu a vo c np vo cc khe thi gian trong mt khung (frame). kt ni mt ng thoi, thng tin cc khe thi gian c gi t bn u vo camch chuyn mch n pha u ra. Mi mt ng thoi c nh h nh vi mtkhe thi gian c thtrong mt lung s liu c th. Theo mch chuyn mchthay i mt khe thi gian ca mt lung s liu c th n khe thi gian ca mtlung s liu khc. Qu tr nh ny c gi l qu trnh traoi cc khe thi gian. hnh 2.6 m t qui tr nh chuynmch cc khe thi gian. Khe thi gian a vo c ghi li tm thi trong b nh m. Nh th hin tr n hnh v, cc khe thigian a vo c l u gi a ch 1 (address 1) n ch x (address x) ca khungth hin lung u vo. S liu ca khe thi gian 1, khe thi gian 2, v khe thigian X c l u gi li cc t th nht, th hai v th X t ngng. Vo lc ny,s lii ca mi frame c thay th bi s liu mi mt ln.

Chc nng chuyn mch khe thi gian lin quan n vic chuyn mch t mtkhethi gian c a vo n khe thi gian c la chn ngu nhin c a ra.V d, nu chuyn t khe thi gian 7 ca lung u vo n khe thi gian 2 calung u ra, thng tin t thu bao c ghi khe thi gian a vo s 7 c gin thu bao c ch th bng khe thi gian s 2 u ra.


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Hnh 2.6. Qui trnh chuy n mch theo khe thi gian.

C sn cho loi qui tr nh ny l ph ng php c ngu nhin theo dy ghi ln lt(SWRR) trong cc s liu c ghi ln lt t pha u vo v c c mtcch ngu nhin t pha u ra. Ph ng php c ln lt ghi ngu nhin (RWSR)l ph ng php ghi cc s liu mt cch ngu nhin t pha u vo v c chngtheo trnh t pha u ra, cn ph ng php ghi ngu nhin c ngu nhin(RWRR) l vit v c cc s liu mt cch ngu nhin.

B. Chuy n mch khng gian

Chc nng chuyn i khe thi gian gia cc khe thi gian u vo/ u ra cgii thch phn tr n chu trch nhim cho chc nng chuyn mch hon thin ivi tt c cc khe thi gian. By gi, nu mch chuyn mch x l thu bao M nhl mt im cui ca khe thi gian n, th cn c b nh c s "M" c to bi

cc t c dng tc thch hp. V d, trong tr ng hp tn s mu l 8 KHz,th h thng c 128 khe thi gian c th c kh nng vit v c cc s liu vo bnh mi 125 u giy/128=976 nano giy (nsec.). Tuy nhin, nu h thng tr nnln h n, th cc yu cu v b nh v tc truy nhp c th khng p ng nivi cng ngh ang c hin nay. V d nh , h thng vi 16.384 khe thi gian ckh nng vit v c cc s liu cho mi 76,3 nano giy (125u giy/16.384). Do vy


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tng hiu sut ca h thng, mt ph ng php m rng dung lng s dngcc b phn tiu chun l cn thit. Mt trong cc ph ng php c sn cho mc ch ny l vic i cc khe thi gian trong mt lung khe thi gian ti cc khe thigian ca mt lung khc bng cch u ni qua li cc nhm chuyn mch khe

thi gian vi cng lgc. Cng ngh ny c gi l chuyn mch phn chia khnggian - thi gian s dng cc thanh u cho theo khng gian. y, thanh ucho theo khng gian t ng t nh thanh qut s dng cc tip im r -le trtrng hp yu cu mt cng logic vn hnh tc cao. Mt thanh qut cm phng vi bn u vo ca trc ng v bn u ra ca trc nm ngang. Mtcng lgic c dng im ct cho ca trc ng v trc nm ngang. S tipxc ph hp c tin hnh thng qua vic kch hot cng lgic t ngng trongthi hn ca khe thi gian v nh thng tin c truyn i t bn u vo n

pha u ra.

Hnh 2.7. Thanh c t cho khng giantrong chuy n mch phn chia thi gian.

V d, mt khe thi gian trong lung u vo lin tc c "K" cc t PCM khc nhaukch hot mt cng thch hp thc hin vic chuyn mch ti trc nm ngangmong mun. u vo ca trc ng cn li cth c ni vi u ra ca trcnm ngang bng cch kch hot mt cch ph hp cc cng t ng ng. ng thi, khe thi gian tip theo, mt ng dn hon ton khc vi ng tr c cth c lp ra.


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y ch l cc khe thi gian ca trc ng v trc nm ngang c pht sinhmt cch t ngng trong cng mt thi im v v vy thanh qut, vic chuynkhe thi gian khng c thc hin. Nh trong trng hp chuyn i khe thigian, mt b nh iu khin c thng tin kch hot cc cng ti cc khe thi gian

mong mun l cn thit. H thng c th c "m" cc u vo v "n" ccu ra c m t h nh 2.7. "m" v "n" c th l ging nhau hoc khc nhau tu thucvo cu h nh ca h thc hin vic tp trung, phn phi, v cc chc nng mrng.

V vy, i vi mng chuyn mch khng gian, mt thanh qut nhiu mc c th c s dng. Khi mun gi cc tn hiu t u vo 1 n u ra 2, cng S21 phi c kch hot trong thi hn ca khe thi gian mong mun. Nu Sm1 c kch

hot vo cng thi gian,

u vo "m"

c gi n u ra 1. Nh

gii thch,mt vi thanh qut c th c kch hot ng thi trong thi hn ca khe thi gian

nht nh v v vy s cc ng ni ng thi c th c l mt trong hai s "m"hoc "n" tu theo s no l nh h n.

2.2.3 Ph ng php thi t lp mng chuyn mch kiu phn chia thi gian

Mt mng li c th c lp nn bng cc s dng mt trong cc chuyn mchT, chuyn mch S, hay phi hp c hai, theo mng li c th c thit lp

nh sau:

Chuyn mch T nChuyn mch S nChuyn mch T-SChuyn mch S-TChuyn mch T-S-TChuyn mch S-T-S

S phi hp phc tp h n ca S v T

A. T-S-T

Cu h nh ny cho php h thng x l cc cuc gi mt cch khng b ngt qungdo b kho nh h nh 2.8. Trong vic iu khin mng, vic la chn khe thi gian u vo/ u ra v khe thi gian chuyn mch khng gian l khng lin quan


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n nhau. Ngha l trong trng hp ca T-S-T, th khe thi gian u vo c th c u ni vi khe thi gian u ra bng cch dng khe thi gian trong ngcho ca chuyn mch khng gian. Trong tr ng hp khe thi gian 3 ca u vo c xc nh vi cc cuc gi phi u ni vi khe thi gian 17 ca u ta mong

mun gii thch vic kha trong mng li s v u cui khng gian c th cp ng ni t chiu di u vo n chiu rng u ra, khe thi gian 3 v 17 phi c trao i vi nhau. Nh th, vic u ni t c khi khe thi gian 3 ca uvo v khe thi gian 17 ca u ra cn ri. Vo lc ny ch c th c c mt ng thng, nu khe thi gian 3 c dng, khe thi gian 17 c th c sdng nh ng vo lc ny cc cuc gi b kho.

Trong trng hp mng T-S-T, b bin i khe thi gian u vo c th chon mt

trong cc khe thi gian s dng. Nu h thng c 128 khe thi gian, khe thigian u vo 3 c th c ni vi mt khe thi gian bt k ca khng gian tr khethi gian u vo 3. Theo trong trng hp ca T-S-T iu quan trng phi t mkim ng dy ri cng nh cc khe thi gian s s dng. Trong hu ht cctrng hp, mng li c th cung cp t nht mt hay nhiu ng ni cc khethi gian u vo/ u ra.

Hnh 2.8. C u trc mng T-S-T.

S-T-S

Trong trng hp ca S-T-S, qu trnh t ng t nh T-S-T c tin hnh. Trnhnh 2.9, mt mng S-T-S c m t. Vic la chn khe thi gian u vo/ u ra c xc nh bng ng giao tip theo yu cu. Do b bin i khe thi gian cth c thay i bng cch dng hai chuyn mch khng gian, linh hot cau ni c ci thin. V d, nu khe thi gian 7 cn phi c ni n khe thi


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0 : C t n ti x : Khng c hi n nay tr cc tr ng hp c bit

Bng 2.1 Phn loi ph ng php iu khin chuyn mch.

Ph ng php iu khin c lp cn c gi l ph ng php iu khin nchic; y l ph ng php la chn cc ng nikhi mi chuyn mch tin hnhmt cch c lp vic iu khin la chn v mi chuyn mch c trang b bngmt mch iu khin. Bi v tnh n gin ca mi mch ph ng php ny cs dng rng r i cng vi ph ng php tng bc trong cc h tng i u tin c pht trin. Tuy nhin, vic la chn ng c hiu qu cho ton b h thngl kh khn bi v phm vi la chn ca mi mch iu khin phn no b giihn. Ph ng php iu khin thng thng l ph ng php tp trung cc mch iu khinvo mi ch v sau theo di trng thi u ni ca ton mch lachn cc ng ni. Khi s dng ph ng php ny, cc mch iu khin c tptrung chia s s lng ln cc cuc gi cho nn kh nng ca cc mch iukhin l rt ln. ng thicc chc nng phc tp c th c tin hnh mt cchkinh t. Hu ht cc h tng i kiu c hc phn chia khng gian bao gm c htng i thanh cho cng s dng ph ng php ny. Ph ng php iu khin theoch ng trnh c l u gi l mt trong cc loi ph ng php iu khin chung;chng c tp trung kh cao v chc nng v nh l thit b x l thng tin anng, n tin hnh mt s iu khin u ni. Hu ht cc h tng i in t angdng hin nay u p dng ph ng php ny. Ccu vo iu khin trc tip chomt h tng i l cc xung quay s dc gi n t cc my in thoi. Cc c im x l u ni thay i rt ln tu thuc vo vic s dng cc loi u vo ny.Ph ng php iu khin trc tip l ph ng php trong cc xung nhn ctrc tip kch hot cc mch iu khin nhm chn cc ng ni mt cch lintip. Khi p dng ph ng php ny, vic vn hnh c th c tin hnh mt cch n gin tuy nhin cu h nh mng li tuyn v s quay, l ng ni, phi c miquan h t ng ng 1-1. Theo , cu h nh mng l t linh hot v kh nng thph n. Do , ph ng php ny l khng ph hp vi h tng i c dung lng lnc kh nng x l cc cuc gi ng di.

Ph ng php iu khin gin tip l ph ng php tp trungcc xung quay s vomch nh, c tt c cc s v sau la chn cc ng ni cuc gi thng qua


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vic nh gi tng hp. Theo vi ph ng php ny c c tnh ho bi dunglng x l ng thng cao v c kh nng bin i cc s gi, t ng ng,cc s gi v cc ng ni c th c xc nh c lp lp nn mng lituyn linh hot. c bit, chc nng ny l cn thit c th s dng mt cch c

hiu qu cc tuyn gi ng di. Tc vn hnh ca mch iu khin trong ccph ng php iu khin chung v iu khin theo ch ng trnh l u gi l nhanhh n nhiu so vi thao tc quay s. Theo cc s oc quay c tp hp litrong mt mch nh tch bit tm thi nhm s dng mch iu khin tch hpcao v sau chng c c vi tc cc k nhanh iu khin ton bchng ngay lp tc. V l do ny, hu ht cc h tng di s dng ph ng php iu khin chung v iu khin theo ch ng trnh l u gi u dng ph ng php iu khin gin tip loi tr mt s tr ng hp trong thi k ban u cu qu tr nh

pht trin.

2.3.2 Ph ng php iu khin c lp

Cc h tng i theo tng bc nh ca Strowger hoc h tng i EMD s dngph ng php iu khin c lp trong tng mch iu khin ring c b trkm theo cho mi chuyn mch. Mc d c, y vn l v d tt ca ci gi l iu khin phn tn; n tin hnh vic iu khin chuyn mch mt cch thngnht bng cch kch hot mt cch c lp cc iu khin chuyn mch phn tn.Mch phn tn c bt li l n lm gim kh nng chuyn mch hoc cc chcnng chuyn mch. Tuy nhin, v h thng c trang b loi mch ny c kh nngc lp cc li mt cch c hiu qu, h ny c th c thay i hoc c mrng d dng. c bit, ph ng php ny rt c th c dng rng r i khi cngngh thit b mi bao gm tch hp cao ca mch in t tr nn php trinh n. Ph ng php iu khin c lp oc phn loi thm thnh cc loi iukhin trc tip v iu khin gin tip. phn tip theo, chng c xem xt chitit h n.

A. Ki u iu khin trc tip

Nh m t phn tr c y, cc xung sinh ra khi thu bao quay s c avo trc tip, tip n c x l mt cch lin tc la chn ng ni. Theo , mt chuyn mch chn ng c nh ra bng s quay nhn c v


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sau chn ng dy ri trong s . H thng c to nn bi mt nhm ccchuyn mch nh vy.

Hai loi chuyn mch hin c l loi chuyn mch c hc kiu chuyn ng n

chn cc ng ra thng qua vic dch chuyn nhiu chiu n nh dch chuynquay v chuyn theo ng thng v mt loi chuyn mch c hc kiu chuyn 2cp phi hp hai cch chuyn nhiu chiu nh chuyn theo chiu ng. Cnhiu ph ng php kch hot cc chuyn ng c ni tr c y; mt ph ngphp quay bnh rng ng h s dng cc ph ng tin in t hoc ng c cbit v mt h thng ngun chuyn ng dch chuyn tng chuyn mch bng cchlp t mt my pht in chung mt s chuyn mch hoc thng qua cc bnhrng hoc cc phi hp phc tp khc.

B. Ki u i u khin gin tip

Ph ng php iu khin trc tip c th c s dng cho cc h tng i dunglng nh mt cch khng kh khn. Tuy nhin, khi s dng cho h thng c dunglng ln, cu h nh mng tr nn phc tp v khi lp t mt ng trung k giacc tng i c l u lng nh, th hiu qu ca n b gim xung ng k. giiquyt cc vn ny, ph ng php iu khin gin tip c pht trin. Ngha lmch nh s gi c lp t trong h tng i c cc s gi c l u gi.

Khi tng i b gi c xc nh, vic chuyn i s phi c tin hnh tu theovic thit lp mng li dy cng nh vic thc hin nhn s lin tc v thm ccs c quay. Ph ng php ny c gi l ph ng php iu khin gin tip hayph ng php chuyn i c l u gi. Hng ca ng trung k c th c chnbng cch quay mt s thp phn gii hn n 10; v vy khi dng ph ng php iu khin c lp cu h nh mng li tuyn phn no b hn ch trong khi i viph ng php iu khin gin tip th ng truyn dn c th hot ng vi hiuqa cao v cu h nh mng li tuyn khng quan h trc tip vi cc s c

quay. Nh trnh by tr n, ph ng php iu khin c lp l v d c bitca iu khin phn tn. C th phn b cc chc nng chuynmch (xc nhcuc gi, nhn s c quay, xc nh ng trung k, chn ng dy ri, cp in, truyn/nhn mt s tn hiu, gi li, xc nh thi im kt thc gi, hi phcv cc chc nng khc) cho cc loi mch khc nhau u ni cc nhnh. Mi


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mch c kt cu n gin v mt vi chuyn mch c tp hp thnh nhmhnh thnh h tng i.

2.3.3 Ph ng php iu khin chung

H iu khin chung l ph ng php tch gia mch chuyn mch gi ca h tng i v mch iu khin v phn chia mt snh cc mch iu khin thnh nhiu iu khin u ni t hiu qu cao h n. iu khin u ni c tin hnhthng qua cc qu trnh sau: giai on tp trung ng khi cc cuc gi pht sinht cc thu bao c tp hp li sau c ni vi mng chuyn mch gi, giai on phn b trong cc cuc gi tp hp c phn loi theo cc hng,thi k ti pht sinh trong cc cuc gi t pha tng i i din c ti pht liv sau c chuyn n tng i bn kia, v mt on chn cui cng khi cccuc gi n c ni vi pha b gi. Ph ng php iu khin chung tng phnhay l h thng nh du theo giai on l ph ng php chia cc chc nng tr n y thnh cc thi k khc nhau v sau phn b chng cho mt s loi ccmch iu khin chung. Mt khc h nh du chung l ph ng php cho phpmch iu khin chung iu khin cc u ni thng qua mng chuyn mch gica mt tng i.

Khi s dng ph ng php iu khin chung tng phn, h tng i c th c

tch ra thnh cc ngn v theo khi no cn thit, c th b sung cc ngn mtcch d dng m rng h thng. Tuy vy, nhng bt li sau y thng gp khis dng ph ng php ny: vic x l thng tin iu khin gia mi ngn l khkhn, s ln cc thit b trung k c a vo thng qua khong trng trong ccmch gi tch ring, dung lng x l ng thng b gim ng k do ton b hthng khng c tch hp hon ton v cc chc nng phc tp. Do vy, hinnay h nh du chung c dng rng r i h n. H tng i s 5 ca M l v d in h nh s dng ph ng php nh du theo giai on v h tng i kiu C45

ca Nht dng h nh du thng thng.

A. H nh du thng th ng


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Nh trnh by phn tr c y, h nh du thng thng l ph ng php iu khin ton bvn hnh ca vic u ni chn lc tr n mng thng qua vic sdng chuyn mch cuc gi.

iu ny khng c ngh a l ch c mt mch iu khin hoc mt h tng i cs dng. Thay v , n c ngh a l mt mch iu khin iu khin ton b h thngthoi. Trong trng hp i vi h tng i thanh cho, cch thc hin chung lvic iu khin cc cuc gi c thc hin thng qua vic s dng cc mch iukhin chung khc nhau tu thuc vo tc iu khin yu cu. V vy, i khi c 2thit b thc hin cc chc nng khc nhau c lp t cnh k nhau. Khi sdng ph ng php ny, chuyn mch gi ton b c kim tra u tin v sau thng tin ch a c chim gi ca mi phn c tp hp li chn ng ni.

V vy, hin t

ng kho

ng thng, pht sinh do tnh trng my bn, c th c gi mc ti thiu c hiu qu cao h n. Do c cc l do ny, nn hu htcc h tng i c pht trin gn y s dng h nh du chung. Tr n hnh2.10, ng ni cuc gi ca h tng i s 5 c th hin.

Hnh 2.10. ng ni cuc gi ca h tng i s 5.

Thao tc ni cuc gi ca h thng chuyn mch thc hin nh

sau:

(1) Ni m: t lc thu bao nhc ng ni cho n khi truyn tn hiu mi quay s.(2) Tip nhn xung quay s: s c ghi vo thanh ghi khi my thu bao ch giquay s.


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(3) Ni cuc gi i: Da vo s nhn c trong thanh ghi ch gi ng ra catng i trung chuyn ni vi my thu bao b gi c xc nh(4) Ni trong ni b tng i: Nu my thu bao b gi nm trong tng i ni ht,th ng gi trong tng i ni ht c la chn.

(5) Ni cuc gi n: Khi cuc gi n t mt tng i khc, thanh ghiu vo bchim bi mt ng trung k vo.(6) Ni trung chuyn: Nu h thng chuyn mch l trung chuyn, th cuc gin c chuyn ti tng i xa hoc tng i cui.

kim tra xem nhng chc nng tr n c thc hin b nh thng khng, h thngchuyn mch thng c trang b thm chc nng qun l, vn hnh v bodng ca b iu khin t ng, chc nng pht hin li, v tr, thi gian gy li v

thit b ghi.

B. Ph ng php i u khin chung tng phn

Vic iu khin u ni ca h thng chuyn mch c thc hin qua nhng qutrnh sau: giai on tp trung ng theo l u lng cn x l sau khi xc nh ctn hiu gi, giai on phn phi cc cuc gi cho cc a ch da tr n s quay,giai on thc hin ni r -le, v cui cng l giai on la chn cui cng khi cccuc gi c ni ti cc thu bao b gi. Theo nh trn, mi giai on c s iu

khin khc nhu, H thng nh du giai on l ph ng php phn chia s iukhin thnh nhiu nhm v sau phn loi phm vi iu khin u ni t ngng phn phi.

H thng ny khc vi h thng nh du chung ch phm vi gim st ca mtmch iu khin chung l mt b phn ca mng chuyn mch cuc gi nh ch r trong hnh 2.11


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dch v ny. ESS hot ng theo ph ng php iu khin bng ch ng trnh l utr ny.

A. Nguyn t c mch logic l u tr

Trc ht, n khc vi cc mch logic ni dy thng thng nhng im sau.Hnh 2.12 minh ho mt mch tun t s dng logic ni dy gm cc cng logicnh V, Hoc v Khng, nhng mch logic kthp bng ni dy p ng ccnhu cu ca mch im tip xc v mch nh l u tr cc bn tin v thao tc qua v sau ch th trng thi thao tc. Hot ng ca mch logic ni dy cxc nh thng qua vic thc hin ni dy. Qu tr nh ny t ng t nh vic vnhnh ca cng nhn lnh ngh.Ngha l, mch ny x l nhng cng vic thngl n gin lin quan ti trng thi dng in v thng tin a vo. Do n c ththc hin nhng cng vic c bit nh ng khng thc s linh hot. Mch logicl utr c bit lc th hin trong h nh 2.13. Ch ng trnh l u tr trong mch nh lmt b lnh th hin mc thao tc. Mt khc n th hin chc nng ph hp vi n v mch logic kt hp ca mch logic dy dn. Mch x l s hc logic dingii cc mnh ln c c v ch nh a ch b nh ca lnh c c tip . Phn ln nhng thng tin trong a ch ny c ghi li khi nhp lnh. Mch xl s hc logic qua nh gi a ch tng phn v thng tin u vo ti thi im xc nh a ch y ca mnh lnh s c x l tip theo. Khi hon tt mtlot cc thao tc bng cch thc hin cc lnh mt cch tun t nh bn ti, vsau i ti nhng lnh th hin kt qu iu khin l u ta v sau c.

B. Ph ng php chuy n mch i u khin bng ch ng trnh l u tr

Vic iu khin bng ch ng trnh l u tr ca h thng tng i in t c mt bnh c nh ghi nh cc ch ng trnh v mt b nh tm thi vit v c ccd liu mt cch t do. Trong b nh c nh, cc lnh thao tc chuyn mch, s

in thoi, s ca thit b u cui, thng tin chn ng trong mng, loi dch vu cui, v cc loi thng tin dch s c l u tr c nh. Mt khc, b nh tmthi c dng nh trng thi ca tng thit b u cui v cc cuc gi c iu khin, cc giai on


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(1) Vit cc ch ng trnh hiu qu(2) Dung lng ln v mch nh tit kim(3) iu khin tc cao(4) tin cy cao

(5) Dch v mi d thch ng(6) Mch c tiu chun ho(7) Chc nng t chn on v sa cha

C. Cc lo i dich v chuyn mch cuc gi

C 2 loi dch v trong h thng chuyn mch chung: thng tin v dch v chuynmch cuc gi v truyn v x l d liu.Trong phn sau y s m t vn tt ccdch v thoi trong h thng chuyn mch chung:

(1) Quay s tt: Cc s ca my thu bao thng gi tt bng 2 hay 3 s cbit(2) Gi ch: Nu my thu bao b gi bn, th cuc gi ti thu bao c tng thc hin li khi thu bao c gii phng bng cch quay mt s c bit(3)n nh cuc gi t ng: Mt cuc gi c th thit lp gia bn ch gi vbn c gi vo thi gian nh tr c.(4) Hn ch gi: Hn ch gi i (PBX v loi khc )

(5) Gi vng mt: Bn tin ghi c kch hot khi thu bao b gi vng mt(6) Hn ch gi n : Cn gi l vn hnh i ngu. Ch nhng thu bao dc bitmi c php gi.(7) Chuyn thoi: Mt cuc gi n s c chuyn ti mt my in thoi khc(8) T ng chuyn ti s mi: Dng khi thayi s in thoi(9) Chn la s i din: S i din c th la chn t do(10) Ni s i din ph: Mt cuc gi c t ng chuyn ti s tip theo khikhng c tr li ca s i din quay

(11) Bo c cuc gi n khi ang bn: Khi nhn c cc cuc gi khc tronglc ang bn(12) Ch cuc gi: Nhn c cuc gi t bn th ba khi ang bn th c tht t ng cuc gi vi bn th ba(13) Gi cho thao tc vin khi bn : Gi cho in bo vin khi bn(14) Thoi 3 ng: 3 Thu bao c th gi cng lc


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Hnh 2.15. K t cu ca h thng chuyn mch s chung.

Hnh 2.15 minh ho cu h nh ca h thng chuyn mch s in h nh. Cc ngunthng tin v thu bao t ng t gm cc in thoi dn dng, th ng mi v cngcng. Modem d liu c th dng lm ngun thng tin t ng t. V modem dnggi thng tin s s dng mch t ng t. Mch trung k dng giao tip vi cch chuyn mch khc, vi in thoi vin v mch dch v cng nm trong s ny.Thng tin t ng t c ni vi h chuyn mch s qua mt gi phi tuyn MDF.MDF trang b vi cc b phnhn ch vt th in do b st hay cc ngun cao

th khc, cung cp cc a im tin li cho vic ni h chuyn mch vi ccngun bn ngoi. Thit b bo v s cp ny cng vi thit b bo v th cp, cdng bo v cc b phn in t trong h thng chuyn mch s.

2.4.2 Thi t b giao tip t ng t

Cc chc nng c bn ca mch thu bao t ng t c th tm tt bng t"BORSCHT" gm ch u, ca tng chc nng, l:

Ngun c qui (B)Bo v in p cao (O)Bo chung (R)Bo hiu hoc gim st (S)B lp/gii m (C)Hybrid (chuyn i 2 dy/4 dy) H


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o th (T)

A. B np c qui

B ny dng cung cp in gi cho tng my in thoi thu bao v ng thidng truyn cc tn hiu nh nhc my hoc xung quay s.

B. B o v in p cao

Cc b phn in t nhy cm ca h thng chuyn mch cn phi c bo vmt cch y chng khng b vt qu in p do chp hoc in th ngmi khng n nh. Nh vy cn phi lp t sn cc phn t bo v trong hthng chuyn mch d cho h thng ny c th chng li c tc ng v dng

do in p qu cao sinh ra. Mt khc dng in ny c th a vo c 2 u cuica hai dy in thoi hoc gia mt trong hai dy v t (GND).

C. Chuy n tn hiu gi

Chc nng ny dng chuyn cc tn hiugi thng bo rng cuc ni chuynca khch hng sp b chm dt. Bi v tn hiu cao th xoay chiu c dng lmtn hiu gi, h thng ny c kh nng x l hin tng phng in trong qu tr nhtruyn v c trang b cc ph ng tin ngn cn thaotc sai trn mch. H thngny cng cn phi c trang b qut gi.

D. Xc nh tn hiu

Chc nng ny dng d pht hin cc tn hiu nhc my/t my pht sinh t thubao hoc cc tn hiu xung quay s. Mch ny phi c tin cy cao.

M ha, gi i m

Chc nng ny dng m ho cc tn hiu ting ni t ng t thnh cc tn hiuting ni s v ngc li.

Hybrid


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Chc nng chnh ca hybrid l chc nng chuyn i 2 dy thnh 4 dy. Nh ccchc nng ph, vic chm dt, cch in v cc chc nng chuyni t cn isang khng cni cho cc tn hiu xoay chiu c sn.

o th

Cc ng dy thu bao thng b hng do b ngp nc, chp mch vi ngdy in hoc b t dy. Ngi ta nghin cu ta mt li thit b kim tra tng pht hin tr c cc loi li ny bng cch theo di cc ng dy thubao mt cch thng xuyn theo chu k. Thit b ny c ni vo ng dytrong ph ng php analog kim tra v o th.

Nh vy, thit b giao tip analog ca h thng chuyn mch s thng c mt bus

test-in ( o th u vo) v test - out ( o th u ra)cho cc loi giao tip ny. Nichung, thc hin chc nng o th vo v o th ra ngi ta dng mt r -le.

2.4.3 Thi t b giao tip s

Mt trong nhng u im quan trng ca h thng chuyn mch s l n c th sdng cc tn hiu truyn dn s m khng phi thay i chng. Nh vy cngh a l cc dng bt PCM (ghp knh chia thi gian) s dng trong h thngchuyn mch cng ging nh cc dng bt s dng trong hu ht cc thit b truyndn. Kt qu l ngi ta c th s dng cc mch t ng i n gin giao tipgia cc h thng chuyn mch v thit b truyn dn v tit kim h n. H thngphn cp s l t hp cc thit b truyn dn s chy vi nhiu loi tc bit. Minc nh r a tc bit cho cc h thng ca h. Trong tr ng hp nc M, thitb ng truyn dn s c gi l thit b ti T v h thng c s dng rng r inht l cc thit b ti T. T1 truyn dng bit tc 2 hng 1,544 Mbps (mega bitesper second). Cc thit b ti T khc c l T1C, T2, T3 v T4. Vic s dng chng c xc nh theo cc kiu ghp knh. V 1.544 Mbps l tc bit c s, nn huht cc h thng chuyn mch s c cc mch giao tip vi tc bit ny. Ccnc Chu u s dng 2.048Mbps l tc bit c s. Hai iu kin di yphi c p ng giao tip mt cch c hiu qu gia h thng chuyn mchs v thit b truyn dn s.


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1) Yu c u v in: lin quann in p, xung in, dng sng, tr khng v tc bit. c ng dng cho tt c cc h thng chuyn mch v cc thit b truyndn.

2) Yu c u v loi bit : Xc nh r cc bit ny l ting ni cc d liu, s nh dngkhung, s nh dng tn hiu hay l cc s liu bo dng v sa cha. Ngoi trvi trng hp t i, cc bit ny khng lin quan trc tip n cc thit b truyn dnv chng ch c ng dng cho cc h thng chuyn mch.

Hai iu kin tr n y xc nh 1 cch y cc tn hiu c truyn qua ccthit b truyn dn. DS1 (tn hiu s 1) l tn hiu c s dng rng r i nht. Tnhiu ny nh r yu cu v in cho cc tn hiu c truyn thng qua vic sdng thit b truyn dn T1 v gi tr ca tng bit c dng bit. V vy, cc loi knhnh D1, D2, D3 v D4 m p ng c cc c im kthut ca DS1 (tnhiu s 1) c kh nng hot ng cng vi thit b truyn dn. Ngoi ra, cc yucu cho cc thit b giao tip s c lin quan n gi tr bit ca dng bit nh sau.

Dng bit ny c xc nh cho mt 1, c s dng ly thng tinngb t thit b ti T. Mt dng bit phi c t nht l 1, trong s 12,5% hay h n Oss khng c pht ra lin tc. cc nc s dng lut m , dng bit c to thnh t cc khung bao gm 193

bit trong 1 khung (frame). Mt khung bao gm 1 bit khungv 24 knh, v miknh c 8 bit. Cc bit khung c s dng gi thng tin tn hiu v xc nh v tr ca mi mu tin.Thng tin tn hiu (nhc my, t my) ca mi knh c a vo trong LSB(bit t quan trng nht ) ca mi knh ca mi khung th 6. Bit ny c gi lbit dch chuyn.

Ngoi cc yu cu v tn hiu s 1 k tr n (DS1), h thng chuyn mch s cn

thc hin cc chc nng sau:

Cc m knh c chn ph hp phi c gi n tt c cc ng trungk cn ri. Cc m ny phi png t trng 1 v chng phi c gii mthnh hu nh l in 1 chiu 0 volt. Thng thng, chng c truyn thngqua vic lp 01111111.


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Thng thng, "0" c thm vo kt thc khng gi i cc t m cc bit can l 0. iu c ngha l nu m s 00000000 c a ra hin th, n s c thay th bng 00000010. Qu tr nh ny c thc hin trong khung cngvi bit dch chuyn. Do nu vic thm "0" v s dch chuyn xy ra cng 1 lc

m knh ch c s dng cho vic truyn d liu, th ch c 6 bit trong mi knh c dng v tc bit lc by gi s l 48 Kbps. gii quyt vn ny,ngi ta ang mong i 1 qui lut DS1 mi cm bit dch chuyn v vic thm"0", s c a ra trong t ng lai gn.

Thm ch nu cc dng bit a vo c ng b ho, pha c th c thayi. Do , mi dng bit phi c kh nng chm li mi lin h pha thch hp c thnh lp tr c khi thc hin vic chuyn mch.

Vic giao tip DS1 phi c kh nng bo m c vic bo dng sa chav cc chc nng bo co v cnh bo.

Ngoi cc chc nng tr n, thit b giao tip s phi c trang b cc chc nngbo li 2 cc, pht ra s ln nh khung li v trt qu . y thng l nhngln c ni n nh "GAZPACHO", 1 t da theo cc k t u tin ca michc nng. l

Vic pht ra m khungVic xp hng khungNn dy 0 (Zero)i ccX l cnh boKhi phc li ng hTm trong khi nh li khungBo hiu gia cc tng i

2.5 Mng l i truyn thng cng cng

2.5.1 Mng l i truyn thng v iu kin kt cu

Mng li truyn thng c th c nh ngha i khi l mt h thng chuynthng tin. Cc mng li truyn thng in hin nay ang c s dng x l


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cc loi thng tin khc nhau bao gm mng li in thoi, mng li in tn, vmng li truyn s liu. Ngoi ra, ISDN l mt mng li c kh nng x l tchhp cc loi thng tin tr n. V kha cnh loi cuc gi v cc dch v, cc mngli truyn thng c th c phn chia thnh mng truyn thng cng cng,

mng truyn thng chuyn dng v mng truyn thng di ng. Da vo phm vicc dch v truyn thng c a vo hot ng, cc mng truyn thng c th c phn loi tip thnh mng truyn thng ni b, mng truyn thng ni ht,mng truyn thng lin tnh, mng truyn thng quc t. Nu chng ta phn loichng v x l chuyn mch, ta c th c mng truyn thng tc thi v mngtruyn thng nhanh (dash). Nh ni trn, cc mng truyn thng c th cphn ra nhiu h n na tu theo nhu cu v i hi ca ngi s dng. V cn bn,mng truyn thng bao gm mt h thng chuyn mch nh r ng ni cuc

gi theo yu cu ca thu bao v mt h thng truyn dn truyn thng tin gin ngi nhn. V cn bn, n phi p ng nhng iu kin sau y.

1. C kh nng kt ni cc cuc gi c gi i t tt c cc thu bao ch gi c ng k trong h thng n thu bao b gi vo bt c lc no hoc vo thigian nh tr c.

2. C kh nng p ng cc yu cu v nhng c tnh ca truyn dn.3. S ca thu bao b gi phi c tiu chun ho.

4. C kh nng thc hin vic truyn tin mt cch cn thn v

tin cy cao.5. Cn c mt h thng ghi ho n hp l.6. Hot ng ca n cn phi va tit kim va linh hot.

thc hin c nhng iu tr n, mng tng i phi c thit k, sau avo hot ng mt cch ng n bng cch xem xt cht lng cuc gi, khnng x l cuc gi, chi ph lp t v chi ph vn hnh, mi lin h gia h thngtruyn dn v h thng chuyn mch. Cc mc c nu ra trn y c th ctng hp thnh s kt ni cuc gi v tiu chun truyn dn, k hoch nh s, tin cy v h thng ghi ho n.

2.5.2 Mng chuyn mch v in thoi

V cc thu bao ng k trong h thng ri rc, nn v cn bn m ni th hthng ny phi c kh nng x l tt c cuc gi ca h mt cch tit kim, tin cy


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Bt c mng li no c cp tr c y c th c lp t p ngnhng nhu cu v yu cu ca thu bao. Trong trng hp c mt vng rng lncn nhiu h thng chuyn mch, thng thng th mng mc theo h nh li cthit lp. i vi nhng vng nng thn hoc nhng vng xa xi nh nng tri hoc

cc lng chi c mt gi thp, ngi ta s dng mng h nh sao. Cc ph ngphp ni mng c th dng cho cc mng li ng dy c phn no phc tph n. Thng thng vic ni mng c thc hin theo 4 mc nh c minh hotrong hnh 2.17; trung tm ni ht, trung tm lin tnh, trung tm khu vc, trung tmvng. Trong mng li phn cp c cc mc nh trn, vic to hng thay th baogm cc hng c mc s dng cao v cc hng thay th c s dng. Nu 1cuc gi c pht sinh, hng c mc s dng cao s c t mu tin. Cucgi ny c ni vi bn b gi thng qua hng thay th ca tng i mc cao

k tip.

2.5.3 Mng d liu chuy n mch tuyn

p ng mt cch thch ng nhu cu ngy cng tng ca vic truyn s liu vcc dch v thoi mi, cc dch v chuyn mch s liu c pht trin v cthc hin bng cch s dng mng d liu chuyn mch tuyn v mng d liuchuyn mch gi.

A. M ng d liu chuyn mch tuyn :

Mng d liu chuyn mch l mt ph ng php ni cc ng dy thng tin t ccbn gi n cc bn nhn v sau thc hin vic trao i thng tin gia cc bnvi nhau. Mng li in thoi l mt v d in hnh. Mng li in thoi clp ra thc hin vic trao i thng tin ting ni, cn mng d liu chuyn mchtuyn c lp t trao i d liu. N biu th cc iu kin giao tip ca mngv cung cp cc thit b u cui cn thit cho cc dch v truyn m s nh cc

thng tin d liu, fax bng s; dch v telex. Vi mng li ny, cc d liu c th c truyn i nhanh h n, tin cy h n v tit kim h n l s dng mng li inthoi hin c hay mng li thu bao cho cc dch v in thoi s. Thi gian ihi kt ni cng ngn h n nhiu. Mng d liu chuyn mch gi ( y ang nin l "mng chuyn mch gi") thit lp ng trao i thng tin nh trong trnghp mng li in thoi thng thng, v sau trao i thng tin. Mtkhi cuc


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gi c thit lp, mt ng mch c lp gia 2 ngi s dng c lp ra saocho s dng mch ny nh mt ng dy chuyn dng cho n khi chm dtcuc gi. Bi v h thng chuyn mch khng lin quan trc tip vi thng tin angtruyn qua ng dn, n khng gy bt c hn ch no v cc kiu thng tin, cc

m thng tin v trt t iu khin truyn dn. Ngoi ra, khng c s chm tr trongtruyn dn do thi gian x l trong h thng chuyn mch. Ngha l, c th ni rngmng chuyn mch gi c mt thng sut cao trong mng li. Mng li inthoi cng cng (PSTN) c dng cho vic trao i thng tin ting ni v n ctrang b cc h thng chuyn mch v truyn dn cn thit. Trong bng 2.2 c ghicc h thng chuyn mch ang dng hin nay v c tnh ca chng.

Ph ng php

chuyn mch

Ph ng php

chuyn mch gi

Ph ng php

chuyn bn tinPhn b mch traoi thng tin

Cho mi cuc gi Cho mi packet Cho mi bn tin

Ph ng php phnphi mch trao ithng tin

Ngay tc th Chuyn ngay tc th theo lung

Ngay tc th

Thi gian tr hon Khng ng k (cuc m thoi c ththc hin c)

Mt cht (cuc mthoi vn c th c)

Nhiu

Loi thng tin traoi

Khng hn ch Dng gi C th nh dngbn tin

Tnh thng sut cathi gian *

C Khng Khng

iu khin li trongmng

Khng C C (i vi mt t skhc khng c)

Phm vi cc dch vph c a vohot ng

t Trung bnh Nhiu

Bng 2.2. Cc c tnh v phn loi h thng chuyn mch


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* y l mt ctnh duy tr qung thi gian gia cc tn hiu v vic chuynchng. c tnh ny phi c p ng trong vic truyn tn hiu dng sng nhting ni.

Mng chuyn mch gi bao gm cc thit b u cui, thit b mch d liu, ccchuyn mch a ph ng, b tp trung a ph ng v my pht li. Cc nguyntc hot ng ca mng li ny c minh ho trong h nh 2.18. Cc tn hiu s tthu bao u cui c mu ho tu theo tc ca ng h nhn c t DCEv sau gi n ng dy thu bao. B tp trung a ph ng ghp cc tn hiuny cng vi cc tn hiu c gi n t cc mch thu bao khc v sau truyn chng n h thng chuyn mch. H thng chuyn mch thc hin vicchuyn mch nhng tn hiu ny v sau truyn chng n thu bao mun gi

theo trnh t ng

c li. Cc

ng dy thng tin s dng trong mng chuyn mchgi l loi 4 dy, c th thc hin ph ng php traoi thng tin i ngu ton b,tuy nhin thu baou cui kia cng c kh nng thc hin ph ng php thng tinna i ngu.

Cc dch v c a vo hot ng trong mng chuyn mch gi bao gm cc ng dy thu bao thng thng cho cc cuc gi i v n, dch v chuyn dnggi v nhn, dch v kt ni, dch v gi trc tip bt u cc cuc gi m khngcn quay s, dch v nhn dng trm u cui v dch v gi tt.

Hnh 2.18. Nguyn t c hot ng ca mng chuyn mch tuyn.

B. Thi t lp mng l i


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1) Khi ni m v thit lp mng l i

Mng d liu chuyn mch tuyn nh trong trong hnh 2.19 bao gm phn cpchuyn mc thp, phn t mt trm u cui n LS (chuyn mch a ph ng)

c s dng thu nhp v ghp knh cc d liu chuyn mch v mt phncp mc cao thc hin chc nng chuyn mch. Thng thng phn cpmc thp ca mng li in thoi, cc b phn tp trung a ph ng ch c lpt trong cc trm chuyn mch c trang b cc h thng i. Tri li, trong mngchuyn mch gi cc btp trung a ph ng m c t ri rc, cc xa hthng chuyn mch, tp trung l u lng gi v mt n i m h thng tng i clp t.

Tn hiu s c tp trung v c ghp knh nh ni tr n c chuynmch ti h thng chuyn mch phn chia thi gian v sau chuyn ti thu baou cui b gi.

Hnh 2.19. Phn c p mng chuyn mch

Trong phn cp b tp trung a ph ng, nhng tn hiu cn thit cho h thngchuyn mch c chuyn thnh cc d liu dn knh / tch knh t trm ucui. Cc thu bao c ni vi cc h tp trung a ph ng hoc trc tip vi cctrm a ph ng LS. Trn tuyn truyn dn gia ngi thu bao v h thngchuyn mch, c nhng mch thu bao, b phn phc hi gia cc tng i v


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Hnh 2.20. Ph ng php r -le ca mng chuyn mch tuyn

2) H thng chuyn mch phn chia thi gian

H thng chuyn mch phn chia thi gian, nh bn ti tr c y, bao gm mtthit b ng thoi phn chia thi gian, thit b x l trung tm v thit b vo ra.Thit b x l trung tm l mt thit b iu khin, mt trong nhng thit b quantrng nht ca h thng chuyn mch. Thit b vo/ra chuyn v nhn thng tin x l chuyn mch giacc thit b x l trung tm v kt qu ca n n v i tbo dng v sa cha. N gm mt thit b a t, thit b bng t, thit b hin thv my in dng. Thit b gi phn chia thi gian l mt thit b trong chuynmch phn chia thi gian c thc hin, thit lp mt ng gi bng cch bini cc khe thi gian tr n ng truyn ghp knh phn chia thi gian ca nhms cp, di s iu khin ca CPU.


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Hnh 2.21. Nguyn t c h thng chuyn mch s phn chia thi gian

Trong hnh 2.21 minh ho h thng chuyn mch s phn chia thi gian gm ccchuyn mch thi gian v khng gian. Nh hnh v, c 2 ng vo v mi ng

c ghp vi 3 knh, v 2 ng ra mi ng c ghp vi 3 knh. ngvo/ra c ghp knh c gi l xa l (ng truyn tc cao- highway).Chuyn mch thi gian thc hin chc nng thay i trt t thi gian ca cc khethi gian tr n highway, cn chuyn mch khng gian b tr cc cng theo cch cbit v thay i cc knh highway vi nhau kt ni. Khi nh kt ni cuc gi Xvo knh th nht ca ng ra 1 vi ng ra 1, th t knh ca X phi thay iv knh th nht ca ng ra 1 b A chim. Nh vyvic bin i khe thi gian c thc hin chuyn mch thi gian v do X ca knh th nht b chuyn

sang knh th 2. Sau , cuc gi X

c ni vo knh th 2 ca

ng ra 1 khicng phn chia thi gian G22 c m/ng trong pha th 2 ca xung P2. Vic ktni c thc hin tr n c s cc th tc tr n. Trong h thng chuyn mch phnchia thi gian, nhng tn hiu c ghp knh c chuyn mch v c an nhng tuyn dn knh theo hng mong mun m khng phi qua qu tr nhm ho v giim.

2.5.4 Mng d liu chuyn mch gi

A. L ch s pht trin

Cng ngh chuyn mch gi do lc lng khng qun M sng to da theo ngh ca Paul Baran nm 1961 p ng nhu cu lp mt h thng truyn thngc tin cy cao. Khng qun M khi u vic nghin cu cng ngh nynhm c c h thng truyn tin cy c th chng li s tn cng bt ng ca k ch. Kt qu ca cuc nghin cu nh sau:

(1) Mng truyn tin phn tn(2) D liu l u tr trong cc khi (gi)(3) Cn phi c chuyn mchl u tr

Cn c vo nhng kt qu nghin cu ny, B Quc phng M k mt hpng pht trin vi cng ty BBN (Bolt Beranek and Newman) v trong nm 1969,cng ty ny sng ch thnh cng mng ARPA (Cc cng tr nh nghin cu tin


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tin). truyn tin,mng ARPA gn vi h thng chuyn mch IMP (b x lthng bo giao tip) v ni vi cc trung tm my tnh ln ca i hc Illinois,U.S.C., v cc n i khc qua mt mng 50 Kbps ni gia cc h thng chuynmch. Tr n c s thnh cng ca mng PRPA v cng ngh chuyn mch gi,

nhiu nc khi xng nghin cu v mng d liu chuyn mch gi v datrn kin ngh chun X.25 cn cho vic tiu chun ho vic giao tip gia mngchuyn mch gi cng cng v trm u cui ca ITU- T, pht trin thnh cng v a vo s dng cc dch v khong nm 1975. Nhng v d in h nh lTYMENET ca Hoa K, GTE TELENET dch v th ng mi ca mng ARPA,DATAPAC ca Canada, TRANSPAC ca Php, PSS ca Anh, DATEX-P ca c,DDX-P ca Nht, v DACOMNET ca Hn Quc.

2) Nh ng nguy n t c:

Mng d liu chuyn mch gi ch s dng nhng u im ca chuyn mch tuynv mng d liu chuyn thng bo; d liu truyn dn c chia thnh cc n vtruyn dn c kch thc nht nh gi l gi (128 bytes hoc 256 bytes) tr c khi a vo mng chuyn mch gi (t y gi l "mng gi"). Mng gi chuyn mchcc n v gi v ri chuyn ti trm u cui nhn gi. Nhng nguyn tc ny c minh ho trong h nh 2.22. D liu do ngi s dng gi i c chia thnhnhng n v gi v sau chuyn theo tr nh t v mng gi.

Do , thng tin ngn c a vo mt gi, trong khi thng tin di ch c gi isau khi b chia thnh nhiu gi. Trong mi gi c a ch ca trm u cui gi l IDca trm. Cc gi chuyn i t trm ch gi c tm thi gi trong h thngchuyn mch gi. H thng chuyn mch gi, da theo a ch ca trm u cuighi trong gi nhn, la chn con ng tt nht ti a ch cho v ri chuyn nvo h thng chuyn mch tip theo. H thng chuyn mch ach n nhn lyv phn phi cho cc trm u cui t ng ng v nh vy truyn ton b thng tin

ca mt gi. Cc th tc (Protocol) truyn tin nh lp ng truyn dn, xo bnhng li trong truyn dn v gi li nhng thng bo truyn dn c thc hinkhi traoi d liu gia trm u cui v h thng chuyn mch v gia cc hthng chuyn mch vi nhau. Cc trm u cui trao i gi li c phn loithnh trm u cui ch gi v trm u cui ch khng gi tu theo ch trao i thng tin, ngh a l c dng cc th tc hay khng. Khc vi cc mng


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cc trm u cui ti cc h thng chuyn mch. H thng tp trung cp thp gmc mt PMX v cc trm u cui. Thit b ghp knh gi phc v cc trm ucui loi chung v loi gi. l mt thit b dng tp hp d liu t cc trmu cui loi chung dng gi,l u tr tm thi d liu t cc trm u cui loi

gi trong thit b v sau ghp knh/tch knh nhng gi tr c khi gi chng i cc h thng chuyn mch. Nhng thit b ghp knh gi ny c thit lp didng h nh sao trong h thng chuyn mchgi nh sau:

Hnh 2.23. Phn c p mng chuyn mch gi

2) Cc ph ng ti n d ng cho m ng chuyn mch gi

(1) Ch r -le

Ch r -le ca h thng chuyn mch gi c ch r trong hnh 2.24. Trmchuyn mch gi gm nhng h thng chuyn mch gi, thit b ghp knh gi vnhng thit b o th iu khin.

Thit b ghp knh gi dng l u tr tm thi thng bo nhn c t nhngtrm u cui loi chung vn hnh theo ch ng b v ri bin i sang dnggi. Nhng gi ny c ghp knh trc khi truyn cho nhng h thng chuynmch gi. Cc thit b u cui c th c dng trong h thng chuyn mch gi c tip tc phn loi thnh cc thit bu cui loi gi v nhng thit b ucui loi chung. Thit b u cui loi gi l nhng thit b hot ng tr n c s


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chun X.25 theo khuyn ngh ca ITU-T. Cc thit b u cui khc c th phn loitheo tc vn hnh v ph ng php ng b c gi l cc thit b u cui loichung. Chng c phn loi ging nh mng chuyn mch tuyn. ng truyndn gia thit b ghp knh gi v h thng chuyn mch cng ging nh ng

truyn dn ca mng chuyn mch tuyn.

(2) H thng chuyn mch gi

H thng chuyn mch gi c th c phn loi thm thnh mt h thng x ltrung tm v iu khin tn hiu cao tc. H thng x l trung tm iu khin thit b iu khin bo hiu cao tc v thit b vo/ra thng qua vic s dng ph ng php iu khin bng ch ng trnh ghi sn. N cng a ra nhng thng tin cn thitqua a t hoc my in dng c ng nh phn tch thng tin trong h thng chuynmch gi v ri truyn nhng mnh lnh chi tit ti tng thit b theo kt qu thu c. Thit b iu khin bo hiu cao tc nhn mt gi c ghp knh t thitb ghp knh gi v traoi nhng tn hiu gia cc h thng chuyn mch gi. Ntruyn/nhn thng tin truyn d liu mt cch chnh xc, kim tra cc dngthng tin lin quan ti cc thit b v cc li. Ngoi ra n cn c th yu cu truynli khi c li.

(3) M ng chuyn mch gi

Mng chuyn mch d liu gi thng c nhng chc nng sau:

(A) i u khin vic nh tuyn

Trong trng hp mt mng gi vi 4 h thng chuyn mch gi nh trong hnh2.25, thu bo s 1 c gn vi mt thu bao duy nht khi n c ng k trongmng.


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Hnh 2.26. Th tc truyn tin gi

Khi nhn c gi ny, mng gi i gi gi u vo trong c knh logic m thubao u cui s dng n cho thu bao s 2. Nu thu bao s 2 dng trong trngthi c th nhn c cuc gi, n gi gi thng tin chp nhn gi cho mng. Mnggi gi thng tinnhn c cho thu bao s 1 nh l mt gi kt ni cuc gi vnh vy lp c ng lin lc logic gia thu bao 1 v 2. Sau vic truyn gid liu c thc hin qua knh logic lc c thit lp. Mt cuc gi o c thit lp thng qua cc th tc tr n. Mt gi yu cu xo c gi i khichm dt lin lc v knh logic ny c gii phng qua vic dng mt gi ch thxo v gi xc nhn xo. Cng nh trong trng hp gi in thoi, cuc gi o lcuc gi thit lp ra mt mch logic chotrao i d liu v sau gi d liu ch qua knh v cui cng xo knh i khi hon tt lin lc.

G i o vnh vin

Gi o vnh vin l ph ng php thit lp ng lin lc logic vnh vin gia 2 thubao v do khng cn phi thit lp hoc xo knh logic nh trong trng hpgi o.


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thng chuyn mch cui cng gn vi ngi thu bao b gi; tr nh t sai s csa li v gi nhn tr ng lp s c loi b. Nhng gi thp h n gi b mt cngb loi b gi i nhng gi ng ti thu bao cui theo ng tr nh t.

V ph ng php biu d liu khng c mt ng lin lc logic nn vic iu khintrnh t c thc hin thu bao u cui ch khng phi tr n mng.

(E) Tr ng thi ng c t

H thng chuyn mch gi l mt h thng chuyn mch l u tr, l u gi tm thicc d liu trong b nh. Nhiu my thu bao c chung mt h thng chuyn mchv v c ca b nh trong h thng c gii hn, nn xy ra t nh trng ch tc dothiu b nh. i khi ch tc c th lan sang cc h thng chuyn mch bn cnh

cho n khi ngng li ton b lung ca cc gi thng tin tr n mng. ch tc c xyra do nhiu vn k c do khc nhau v tc truyn tin gia cc thu bao.

(F) i u khin lung

S lng gi d liu a vo mng cn c gii hn trnh ch tc. Nhngph ng php dng cho mc ch ny gm mt tin tr nh hn ch b m hnch s lng ti a cc gi d liu truyn i, mt tin tr nh gi l ph ng php iukhin ca s truyn i mt s lng nht nh cc gi d liu qua mng ntrm u cui i din v ch tip tc truyn gi d liu tip theo sau khi c s xc nh nhn c cc gi , mt tin tr nh gi l WABT, ph ng php ny gi tnhiu khng sn sng nhn khi thiu b m hn ch u vo, v mt tin tr nhgi l ph ng php trung tm qun l mng, iu khin trng thi ca ng thngtrong mng bng cch to ra mt trung tm qun l mng. Trong thc t, mt stin tr nh m t tr n c ng c s dng cng mt lc trong mng gi.

(G) D ch v b xung

H thng chuyn mch nhm c nhng dch v b sung tho mn mt cch hiuqu h n nhng nhu cu ca ngi s dng.

K t ni khp kn


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Nh minh ho trong h nh 2.28, kt ni khp kn l mt dch v cho php ngi sdng dng mng gi nh l mt mng thu. Vic truyn tin ca kt ni khp kn vmy thu bao chung khc khng th thc hin c.

Hnh 2.28. K t ni khp kn

2.5.5 Ph ng php bo hi u

thc hin vic ni mch, thng tin cn thit iu khin phi c trao igia in thoi v h thng chuyn mch v gia cc h thng chuyn mch vinhau. Ph ng php bo hiu l mt th tc v ph ng php truyn nhng thngtin ny, v d, gia in thoi v h thng chuyn mch, nhng yu cu tip nivphc hi, ch nh la chn bng xung quay s, tr li thng bo bng m ch gihoc m chung trao i vi nhau.Ngoi ra, nhng tn hiu gia cc tng i vinhau nh kch hot, tr li, la chn, kt thc, ngt v thng tin cc c trao igia cc h thng chuyn mch tr n mng in thoi. Trong h nh 2.29 minh holung tn hiu c bn.


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Hnh 2.30. Bo hi u knh k t hp (a) v Bo hi u knh chung (b)

Bo hiu knh kt hp c chia thnh h thng bo hiu trong bng s dng ditn ting ni v h thng bo hiu ngoi bng s dng tn s bo hiu khc vi ditn ting ni. M a tn dng to m bng cch kt hp tn s s dng 2 trongs 6 tn s ca di tn ting ni. l mt v d in h nh v bo hiu trong bng.Xung quanh s hay u vng trc tip l th d v h thng bo hiu ngoi bng.Bo hiu knh chung gip h thng s dng cc thit b bo hiu; nhng ph ngtin phc tp c th c thit lp mt cch kinh t v c th truyn nhiu thng tinhai chiu vi tc cao. Ph ng php bo hiu s 6 / s 7 theo khuyn ngh caITU-T l v d in h nh thuc v ph ng php ny.

A. Ph ng php bo hi u R2 - MFC

y l mt cch bo hiu knh kt hp v mt v d in h nh l ph ng php R2 -MFC. Ph ng php ny c ITU-T tiu chun ho nm 1968. N c th cphn loi thm thnh bo hiu gim st v bo hiu chn lc nh sau:

1/ Bo hi u gim st


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Nhng tn hiu gim st c chuyn ti h thng chuyn mch tu theocc trngthi thayi ca mng xy ra c hai u ca ng gi, v d nh sau:

Ri (Idle): ng trung k sn sng s dng

Chim (Seizure): tn hiu bo rng h thng chuyn mch pha ch gi chim ng trung k i ti h thng chuyn mch phab giChp nhn chim (Seizure acknwledgement): tn hiu thng bo xc nhn tnhiu chim ca h thng chuyn mch pha ch gi.Tr li / Xung o (Answer/meter): tn hiu bo tr li ca my thu bao b gi choh thng chuyn mch pha ch giXung tnh cc / Chp nhn chim (Metering/Seizue acknwledgement): tn hiulin quan ti xung tnh cc ca in thoi cng cng. i khi dng lm tn hiu

bo chim.Xo v (Clear back): tn hiu thng bo ti h thng chuyn mch pha b girng thu bao b gi t my.Xo i (Clear forward): tn hiu thng bo ti h thng chuyn mch pha b girng thu bao ch gi t my.Kho: tn hiu bo rng tn hiu t ngng khng th a ra ngoi c.

2) Tn hi u la chn:

Tn hiu la chn xem xts ca my thu bao b gi. Tr n c s , c th xc nh c v tr ca my thu bao b gi. 15 tn hiu hng i v 15 tn hiu hngv c to ra bng cch s dng kt hp tn s ca 2 trong s 6 tn s trongbng truyn v nhn cc loi thng tin khc nhau.

T n s s dng

Tn hiu hng i: 1,380Hz, 1.500Hz, 1.620Hz, 1.740Hz, 1.860Hz v 1.980Hz

Tn hiu hng v: 540Hz, 660Hz, 780Hz, 900Hz, 1.020Hz v 1.140Hz

Nhiu ngha c ch nh cho tng tn hiu tr n v nhng ngha tn hiu cdin gii khc nhau tu theo v tr ti tn hiu hng v A- 3, A - 5, hoc chui bohiu truyn v nhn s lng ln thng tin.


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Tn hiu hng i

Phn loi vo nhm I, II: I - 1, I - 2,........................................... I 15

II - 1, II - 2,.......................................................II - 15

Tn hiu hng v

Phn loi vo nhm A, B: A - 1, A - 2,........................................ A - 15

B - 1, B - 2,....................................................... B - 15

(1) Tn hi u h ng i

C 15 tn hiu hng i trong nhm I v 15 trong nhm II. Tn hiu nhm I ch yul th hin cc s ca my thu bao b gi. Tn hiu u tin trn chui bo hiupht i c din gii l tn hiu nhm I. Cng nh vy, tn hiu v u tin cdin gii l tn hiu nhm A. S dng tn hiu v c th (A- 3, A - 5) th c th thchin c vic chuyn i t nhm I sang nhm II. Khi c chuyn sang nhmnhm II bng tn hiu v A- 5, th c th chuyn i c sang nhm I. Vicchuyn i t nhm Asang nhm B ch c th thc hin c vi tn hiu v A- 3.Mt khi chuyn sang nhm B th khng th chuyn sang nhm A c.

Tn s Ghi ch

1.980 1.860 1.740 1.620 1.500 1.380 iTn hiu

s540 660 780 900 1.020 1.140 V

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

7 0 0


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I - 4 Ngn ng: Nga Ch s 4

I - 5 Ngn ng: Ty Ban Nha Ch s 5

I - 6 D phng (ngn ng) Ch s 6

I - 7 D phng (ngn ng) Ch s 7I - 8 D phng (ngn ng) Ch s 8

I - 9 D phng (sphn bit) Ch s 9

I - 10 S phn bit Ch s 0

I - 11 Ch th M nc (cn B tritna m di O/G)

Truy nhp ti I/C inbo vin(m II)

I - 12 Ch th M nc ( khng cn b

trit m di )

Truy nhp ti in bo vin tr

hon (m 12) yu cu khng c chp nhn

I - 13 Ch th gi th (gi bng thit b o th t ng)

Truy nhp ti thit b th (M13) khng k ni vi v tinh

I - 14 Ch th M nc (gn b tritna m di O/G)

Cn b trit na m di I/C kc ni vi vtinh

I - 15 D phng Chm dt xung (M 15) chm

dt nhn dng

Bng 2.4. Nhm I tn hiu hng i

Tn hiu I- 11 ~ I - 15

Do cc h thng to ra (khng k cc my thu bao)

Trong h thng chuyn mch r -le quc t, ngha 1 ch c s dng cho tn hiu

u tin, ngh a 2 dng cho cc tn hiu khc.

Tn hiu Ngh a Nhn xt

II - 1 My thu bao khng u tin

II - 2 My thu bao u tin


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II - 3 Thit b bo dng

II - 4 D phng

II - 5 in bo vin

II - 6 Truyn d liuII - 7 My thu bao (hoc in bo vin khng c ph ng tin

chuyn tn hiu i)

II - 8 Truyn d liu

II - 9 My thu bao u tin

II - 10 in bo vin c ph ng tin truyn tn hiu i

II - 11 - 15 D phng cho s dng ca quc gia

Bng 2.5. Nhm II tn hiu hng i cng trung chuyn

Nhm II Tn hi u h ng i

Nhng tn hiu ca nhm II th hin cc cp ca pha ch gi. Bin i t nhm Isang bng tn hiu hng v A- 3 hay A - 5

Tn hiu II- 1 ~ II - 6: Dng cho cc cuc gi trong nc

Tn hiu II - 7 ~ II - 10: Dng cho cc cuc gi quc tTn hiu II- 11 ~ II - 15: D tr cho cc cuc gi trong nc

Tn hiu Ngh a Nhn xt

A - 1 Gi s tip theo (n + 1) ca s bn b gi

A - 2 Gi s p cht (n - 1)

A - 3 nhn a ch y , chuyn sang nhn tn hiu

ca nhm B

A - 4 Tc nghn trong mng quc gia

A - 5 Gi cp my ch gi

A - 6 a ch y , tnh cc, thit lp cc iu kin thoi


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A - 7 Gi s th n- 2

A - 8 Gi s th n- 3

A - 9 D tr cho s dng trong nc

A - 10 D tr cho s dng trong ncA - 11 Yu cu thng tin v s dng B trit m di

A - 12 Gi digit v ngn ng hoc ch s phn bit

A - 13 Gi thng tin v bn cht knh

A- 14 Yu cu thng tin v s dng B trit m di

A - 15 Tc nghn trong tng i quc t hoc ti u ra ca n

Bng 2.6. Nhm A tn hiu hng v

(2) Tn hi u h ng v

Do cc h thng to ra (khng k cc my thu bao)

Nhm A tn hiu hng v

To ra do tn hiu hng i ca Nhm I hoc tn hiu hng i ca Nhm II cho

nhng tr ng hp c bit. Chng th hin nhng yu cu v s thu bao b gi vnhn thng bo y .

Tn hiu Ngh a Nhn xt

B - 1 D tr cho s dng quc gia

B - 2 Pht tone thng tinc bit

B - 3 ng thu bao bn

B - 4 Tc nghn (sau khi chuyn t nhm A sang Nhm B)B - 5 S ch a c gn

B - 6 ng thu bao ri, tnh cc

B - 7 ng thu bao ri, khng tnh cc

B - 8 ng thu bao khng hot ng c


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B - 9 - 15 D tr cho s dng quc gia

Bng 2.7. Nhm B tn hiu hng v

- Nhm B tn hiu hng v

c chuyn i bng tn hiu hng i nhm II hay tn hiu v A-3. Chng thhin thng tin v trng thi ca nhng my thu bao b gi v thit b chuyn mchca cc h thng chuyn mch pha b gi.

B. Bo hi u s 7

H thng bo hiu s 7 (SS No.7) ca ITU-T c thit lp p ng nhng yu

cu pht trin bo hiu ca mng s ho hon ton da tr n knh 64 Kbps. SSNo.7 l mt h thng bo hiu knh chung. Nhng h thng bo hiu SS No.7trc y hot ng 2.400bps v c thc hin tr n nhng knh t ng tchun VF. Chng khng c cng nng y v c ng khng ph hp vi mng shin nay v c bit l vi ISDN. Tuy nhin ngi ta c th thy rng c nhiu imt ng ng trong ho v cu trc thng bo gia CCIS/ITU-T v SS No.7.

Ni mt cch n gin, ITU-T SS No.7 c m t nh l mt h thng bo hiu

knh chunga dng

c tiu chun ho quc t:

Ti u ho vn hnh vi cc mng s c chuyn mch s dng B iu khinch ng trnh l u tr (SPC).C th p ng nhng nhu cu hin nay v t ng lai v chuyn thng tin chonhng b lin x l bin ng vi nhng mng thng tin s iu khin gi, iu khin t xa, s dng v qun l mng d liu c s v bo dng bohiu.Cung cp mt ph ng tin tin cy chuyn thng tin ng tr nh t khng thtlc hoc tr ng lp.

ITU-T SS No.7, trong nhng nm t 1980, c bit n nh mt h thng bohiu cho ISDN. S tht ng nh vy. Khng c c cu h tng SS No. t trongmng s, th khng c ISDN vi s truy nhp khp mi n i. Cn phi lm r mt iu quan trng. ITU-T SS No.7 bn thn n l s la chn bo hiu trong mng


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s PSN (Mng in thoi cng cng- khi khng c ISDN). N c th t ng vngmt m nh trong chc nng ny. SS No.7 l mt h thng truyn d liu thit k chomt mc ch duy nht: bo hiu. N khng phi l mt h thng a nng. Do vychng ta phi nh n nhn SS No.7 nh l (1) mt mng d liu chuyn dng v (2)

mt h thng bo hiu.

1) M i li n h ca SS N o.7 v i OSI

ITU-T SS No.7 c lin h vi OSI ti mt mc nht nh. C mt nhm ngi ta tin rng SS No.7 cn c hon ton thchng vi 7 tng ca OSI. Tuy nhin,cc nhm lm vic ITU-T chu trch nhim cho tng v thit k SS No.7 ngnngi v s chm tr hoc l cho ngi s dng s liu, hoc l cho ngi s dng in thoi ca mng s PSN hay ISDN. Vic chm tr trong lc quay s u tin lmt trong nhng bin php vn hnh ch yu ca mt he thng bo hiu. tithiu ho mc tr,7 tng OSI c b bt tng 4. Thc ra, khuyn ngh ITU-TQ.709 qui nh khng nhiu h n 2.2 giycho mc tr quay s ca 95% cc cucgi. hn ch mc tr ny, mt gii hn c t ra cho s lng cc im lmtr, n c gi l STPs, m c th c truyn qua bi mt bn tin bo hiu vmt thit k vn c ca SS No.7 di dng mt h thng 4 tng. H nh 2.31 ch ralin quan gia th tc SS No.7 vi cc tng ca OSI. Chng ta nn ghi ch rngnhng chc nng mng bo hiu SS No.7 tng 3 bao gm cc chc nng x lbn tin bo hiu v cc chc nng qun l mng. H nh 2.32 cho thy cu trc tngqut ca h thng bo hiu SS No.7 Schlanger c nhng nhn xt thch hpnh sau:

:Bo hiu c thc hin mt cch c th to ra mt mng li lin lc phcho ngi s dng u cui mng. Cng nh vy mt s ngi lp lun chorng ton b mu chun ca SS No.7 nh l mt th tc trong h thng lin lc phch cn tn ti tng 3 OSI (tng mng li) v pha di."

H thng lin kt mOSI

H thng bo hiuNo.7 (SS No.7)

7 Tng ng dng

6 Tng gii thiu


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Hnh 2.32 C u trc tng qut cc chc nng ca ITU -T SS No.7

Trch t ITU-T Rec. Q701

2) C u trc h thng bo hiu

Hnh 3.22 minh ho cu trc c bn ca SS No.7 cho thy hai phn ca h thng:phn truyn bn tin (MTP) v cc phn cho ngi s dng. C 3 phn cho ngis dng:

- Cho ngi s dng in thoi (TUP)

- Cho ngi s dng s liu (DUP) v mtb phn "khc" m trong ng cnh nymun ni ti phn ngi s dng ISDN (ISUP). H nh 3.21 v 3.22 cho thy cctng 1, 2 v 3, l cc tng cu thnh MTP. Cc on ch dn k tip m t chc

n

ng ca tng tng ny theo quan

im h thng.

Tng 1 xc nhcc c tnh vt l, in v chc nng ca ng lin kt s liubo hiu v ph ng tin truy nhp n. Trong mi tr ng mng s liu ng s64 Kbps l phn kt ni c bn b nh thng. Phn kt ni bo hiu c th truy


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nhp c bng chc nng chuynmch cung cp kh nng t ng ti to licu h nh lin kt bo hiu.

Tng 2 thc hin chc nng lin kt bo hiu. N xc nh cc chc nng v cc

th tc truyn cc bn tin bo hiu qua mt ng lin kt s liu bo hiu ringl. Mt bn tin bo hiu c truyn qua ng lin kt bo hiu theo cc n vtn hiu c chiu di thayi. Mt n v tn hiu bao gm thng tin iu khintruyn tin thm vo vi ni dung thng tin ca bn tin bo hiu.

Chc nng lin kt bo hiu bao gm:

Gii hn mt n v tn hiu bng cc c.Chng nhm ln c bng vic chn thm cc bit. iu khin li bng cch pht li v iu khin chui n v tn hiu bng dy strong tng n v tn hiu v thng bo xc nhn lin tc mt cch r rng.Pht hin li lin kt bo hiu bng cch kim tra li trong n v tn hiu vphc hi lin kt bo hiu bng cc th tc c bit.

Tng 3 vi chc nng mng bo hiu, v nguyn tc, a ra nh ngha cc chcnng v th tc truyn chung v c lp ca cc lin kt bo hiu ring l. C 2 loichc nng tng 3:

(1) Cc chc nng x l bn tin bo hiu. Trong khi truyn bn tin, nhng chcnng ny hng bn tin ti lin kt bo hiu hoc phn cho ngi s dngt ngng.(2) Cc chc nng qun l mng bo hiu. Chc nng ny iu khin xc nhhng theo thi gian thc, iu khin v ti to li cu h nh mng khi cn thit.

Tng 4 l phn cho ngi s dng. Mi phn cho ngi s dng xc nh ccchc nng v cc th tc c tr ng cho tng ngi s dng ring bit, d l in thoi, s liu hay phn ngi s dng ISDN.

Bn tin bo hiu c nh ngha bi chun ITU-T Reg. Q.701 nh l mt tp hpthng tin, c nh ngha ti tng 2 hay 4, c lin quan ti 1 cuc gi, s qun lv.v. m sau c chuyn i nh mt thc th bi chc nng chuyn bn tin.Mi mt bn tin u cha ng "thng tin dch v" bao gm 1 ch s dch v nhn


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dng phn ngi s dng ngun v c th l xc nh bn tin lin quan ti vicng dng ni a hay quc t ca phn ngi s dng.

Thng tin bo hiu ca bn tin cha ng thng tin ca ngi s dng, nh cc s

liu hoc cc tn hiu iu khin cc cuc gi, thng tin qun l v bo dng,dng v kch c bn tin. N cng bao gm 1 "nhn". Nhn ny gip cho vic nhhng bn tin bi tng 3 qua mng bo hiu ti ch ca n v hng bn tin tiphn ngi s dng hoc tuyn mong mun.

Trong lin kt bo hiu, thng tin bo hiu nh vy c cha trong cc n v tnhiu bn tin (MSUs) m cc n v ny li bao gm cc chc nng iu khintruyn c lin quan ti cc chc nng tng 2.

Trong SS No.7 c mt s thut ng c s dng cn phi hiu tr c khi i tipcc bc sau:

Cc im bo hiu (signalling Points): l nhng nt trong mng c s dng bohiu knh chung.Quan h bo hiu (Signaling Relation) (t ng t vi quan h l u lng): l btc hai im bo hiu no m kh nng lin lc gia cc phn ngi s dngt ngng vi chng tn ti, c gi l c 1 quan h v bo hiu.

Cc lin kt bo hiu (Signaling links) cc lin kt bo hiu chuyn cc bn tinbo hiu gia 2 im bo hiu.Cc im ngun v ch (Originating and Destination Points): l cc v tr cachc nng phn ngi s dng ngun v v tr ca chc nng phn ngi sdng nhn t ngng. im truyn bo hiu (Signaling Transfer Point (STP)): l mt im m trong mt bn tin nhn c tr n mt lin kt bo hiu c truyn i ti mt lin ktkhc.

Nhn tin (Massage Label): mi bn tin c mang theo mt nhn. nhn tiuchun, phn c s dng cho vic nh tuyn c gi l nhn nh tuyn(routing label). Nhn nh tuyn bao gm:

im ch v ngun ca bn tin


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Mt m s dng phn ti, y c th l phn t quan trng nht trong kt cu camt nhn m n nh ra phn giao dch ca ngi s dng tng 4.

Nhn tiu chun nu rng mi mt im bo hiu trong mng bo hiu c gn

cho mt m nhn dng theo s m c thit lp cho mc ch to nhn.

nh tuyn bn tin (Message Routing): l qu trnh la chn cc lin kt bo hiu c s dng cho tng vic nh tuyn bn tin bo hiu tr n c s phn tchnhn nh tuyn ca bn tin kt hp vi cc s liu nh tuyn c nhtrc ti mt im bo hiu c bit no .Phn b bn tin (Messaga Distribution): l qu trnh xc nh phn ngi sdng m mt bn tin s c gi ti. S la chn c thc hin nh s phntch ch s dch v.Phn bit bn tin (Message Discrimination): l qu trnh xc nh s nhn mtbn tin ti mt in bo hiu l im ch cu bn tin. Quyt nh ny da tr ns phn tch m ch ca nhn nh tuyn trong bn tin. Nu im bo hiu l im ch, bn tin c chuyn ti chc nng ch ca bnt tin. Cn nu khng,bn tin s c chuyn ti chc nng nh tuyn chuyn tip tr n ng linkt bo hiu.Qun l mng bo hiu (Signaling Network Management): c thit lp bi 3l nh vc k thut:- Qun l l u lng bo hiu.- Qun l lin kt bo hiu.- Qun l nh tuyn bo hiu.

Cc chc nng qun l l u lng bo hiu l:

iu khin nh tuyn bn tin,k c sa i tuyn bn tin duy tr s kt ni.m bo lung bn tin cng vi cc sa i v nh tuyn bn tin.

Cc thao tc iu khin lung hn ch nh hng ca qu ti.

Cc chc nng qun l lin kt tn hiu iu khin cc b lin kt u ni theo khuvc, bao gm c vic khi phc lin kt. Chc nng ny cung cp cc s liu linkt ca cc lin kt khu vc ti cc chc nng qun l l u lng tn hiu.


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Chc nng qun l nh tuyn bo hiu. Chc nng qun l nh tuyn bo hiu ch c s dng khi lin kt bo hiu hot ng ch gn nh kt hp (quasi -associated). Ch gn nh kt hp lin quan ti nhng lin kt bo hiu m sdng 1 tuyn khc vi tuyn bn tin thng thng. Nhim v qun l tuyn l

truyn thng tin v nhng thay i trong kh nng c th c cc tuyn bo hiutrong mng li bo hiu to iu kin cho cc im bo hiu xa c th ccc tc ng qun l l u lng bo hiu mt cch thch hp.

Mt danh sch cc c tnh k thut v mng li thng tin s c trnh bybng 3.2. Nhng c tnh ny c lit k theo th t m tc gi cho l t ngxng vi tm quan trng ca chng i vi lnh vc in thoi ni chung. Tuy nhintrong ccng dng ring bit khc, s cn nhc no c th cho l t nhiu quan

trng h

n. Chng hn, mc cui cng, s gim bt tnh rc ri kh hiu lc

im ni tri khin mng s c a chung trong qun s.

3) n v bo hiu s 7

C th c 3 dng n v tn hiu cho SS No.7 nh sau; Cu h nh ca mi n v tnhiu c trnh by h nh 2.23

MSU ( n v tn hiu bn tin). Truyn cc s liu gia tng 3 v tng 4.

LSSU ( n v tn hiu trng thi lin kt). Thng tin v trng thi cc lin kt tnhiu chuyn pht s liuFLSU ( nv tn hiu chn thm). c chuyn pht khi MSU v LSSU khng c chuyn pht


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Hnh 2.33. Kch th c ca n v tn hiu SS No.7

(1) Kch th c n v tn hiu s 7

Nh trn cho thy, cc kch thc n v tn hiu dng cho h thng bo hiu SSNo.7 khc vi MSU, LSSU v FISU. Mi tr ng ca n v bo hiu c ngha nhsau

A- Tr ng chung

DF (c d liu). Ch nh im bt u v kt thc ca n v bo hiu.Mu: h7e (0 1 1 1 1 1 1 0)BSN (dy s li). Th hin dy s ca n v tn hiu cui cng thu nhn

c mt cch chnh xc.BIB (bit ch th li). Dng cho yu cu pht li ca cc n v bo hiu khi c lixut hin.FSN (Dy s tin). Th hin dy s ca n v tn hiu s c pht.FIB (Bit ch th tin). Dng ch th vic pht li ca n v bo hiu bng BIBLI (Ch th di)

Ch ra s Octet ca tr ng gia LI v CK (1 octet = 8 bits). H thng chuyn mchu cui b gi thc hin CRC so snh t nh trng li ca n v bo hiu nh gi. Trng ny c s dng cho vic nh gi ny.

B-Tr ng duy nht LSSU

- SF (Trng trng thi). Tr ng ny th hin trng thi ca lin kt bo hiu

C- Tr ng duy nht MSU.

- SIO (Tm bit thng tin dch v). y l mt b tm bit xc nh phn ngi sdng m trong s bao gm thng tin c pht i.

- SIS (Trng thng tin bo hiu). M im ch, m im ngun, m lin kt bohiu, v b tm bit t 2 ~ 272 c th thay i

(2) Phn lo i nhm n v bo hiu


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FAM (Bn tin a ch tin). Cc bn tin s c chuyn tip theo thng tin a ch FSM (Bn tin thit lp tin). Cc bn tin s c chuyn i tip sau cc bn tin a ch. Cc bn tin ny s li c phn loi thnh cc bn tin chung c ccthng tin cn thit cho vicnhn dng cc ng ch gi hoc thit lp cuc gi

v cc bn tin c cc tn hiu lin tc. Nhng bn tin ny c gi ngc li yu cu c thm thng tin cho thit lp cuc gi.SBM (Bn tin thng bo thit lp thnh cng gi v). y l mt nhm bn tin sgi cc thng tin lin quan ti s thnh cng ca vic thit lp cuc gi. C ccbn tin hon thin a ch v bn tin tnh cc.UBM (Bn tin thng bo thit lp khng thnh cng gi v). y l mt nhmbn tin chuyn v cc thng tin v vic thit lp cuc gi khng thnh cng.CSM (Bn tin gim st cuc gi). y l mt nhm bn tin theo di cc cuc

gi c thit lpCCM (Bn tin gim st mch). L nhm bn tin theo di cc nhm ng thubao

2.5.6 Mng truyn thng tch hp

Cc in thoi thng thng ch c s dng ni vi mt pha i din t ngng nhm thit lp mt cuc gi. Trong truyn s liu, cc ng dy chuyn dngdng cho mt s lng hn ch cc thu bao c ng c s dng. Ngoi ra, ccmng li in tn hin nay ang hot ng nh l cc h thng c lp vi cc hthng thng tin khc. Mt khc, tm quan trng ca vic m bo cc ph ng tinthch hp trao i thng tin ngy cng tng khi x hi ngy cng tin gn ti thii thng tin. ng u vi nhng thay i y, cc h thng chuyn mch int ang c tch hp v nhng c im mi c pht trin. Thm na, vicnghin cu cc dch v mi hoang ton p ng cc yu cu ca ngi s dngc ng ang c tin hnh. Mi gn y, cc c gng nhm kt hp cc h nh thckhc nhau ca cc h thng thng tin ang c thc thi nhm to c hiu qucao h n v chi ph t h n. Ni chung, mc tiu c bn ca truyn thng c th c coi nh l qu trnh gi v nhn cc thng tin cn thit qua cc loiph ngtin truyn thng khc nhau. ng thi, s giao tip my-my c s dng xl cc s liu cng nh iu khin cc tn hiu.


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Ngoi ra, chng c th c phn loi theo dng dchv chuyn mch s ccung cp nh sau: x l l u lng tc thi cho in thoi v cc TV, x l l ulng nhanh n i c l

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