L thuyt vin thng 1. H thng vin thng in t

1.1 H thng vin thng in t ngy nay

Cng ngh vin thng in t tip tc tin b nhanh chng k t khi c pht minh h thng in tn v in thoi n mc n cch mng ho cc phng tin thng tin truyn thng khong mt th k trc y. Ngy nay, h thng vin thng in t c xem nh cc phng tin kinh t nht c c trao i tin tc v cc s liu. Ngoi ra song song vi tng trng v x hi kinh t, vic hnh thnh cc phng tin cn thit cho vin thng in t tr nn phc tp hn v c khuynh hng k thut cao nhm p ng nhu cu ang tng v cc dch v c cht lng cao v dch v vin thng tin tin hn; mc d vy cc thit b c th c hnh thnh theo cc cch khc nhau v c cc mc phc tp khc nhau theo 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. Ngun thng tin: Con ngi hay my pht ra thng tin cn truyn i. Thng tin pht ra c phn loi thnh ting ni, m, v hnh nh (k t, k hiu v hnh nh).

b. Thit b truyn: B phn hay thit b chuyn thng tin pht ra thnh cc tn hiu c truyn i qua ng truyn dn.

c. ng truyn dn: Mt phng tin truyn cc tn hiu t thit b truyn n thit b nhn. Cc loi cp ng trc, cp quang, khng gian, v cc hng sng c dng rng ri cho mc ch ny. Cc tn hiu c gi i qua ng truyn b nhiu bi cc yu t nh ting n.

d. Thit b nhn: L mt b phn hay thit b dng bin i cc tn hiu nhn c thnh cc tn hiu ban u.

e. Ngi s dng: L con ngi hay my nhn thng tin c phc hi t thit b nhn. H thng vin thng in t c s dng ph bin nht l h thng thng tin in thoi trong con ngi l ngun thng tin cng li l ngi s dng, cn my in thoi dng lm thit b truyn thit b nhn. Hin nay loi my (bng) dch v thng bo thng tin trong my hot ng nh ngun thng tin v con ngi nh l ngi s dng c nh cu cao. Ngoi ra, vic giao tip gia my vi my nh vic trao i s liu hin cng ang hot ng. Nh trnh by hnh 1.2, cc qu trnh trao i c tin hnh thng qua giao din gia ngi vi my, v gia my vi my, nh trong trng hp cc phng php thng thng, s tr nn ngy cng thng dng hn.

Hnh 1.2. Truyn, nhn thng tin

Xu th pht trin cc mng li vin thng hin nay c m t ngn gn phn sau. Trc ht, l gii thch v vic a dng ho cc dch v vin thng v cc phng tin.

Cng vi cc dch v vin thng in t thng dng da trn c s cc h thng in thoi v in tn hot ng mt cch c lp thng qua vic s dng mng li thu bao in thoi, mng li chuyn mch r-le in tn, v mng li thu bao in tn, mt s cc phng tin c phc tp cao v rt mnh cng tng ln nh cc cc phng tin truyn s liu v hnh nh truyn thng tin cc loi v cho php thc hin cc dch v phi in thoi ang c lp t v vn hnh, ang cch mng ho cuc sng ca chng ta.

Dch v phi in thoi c a ra hin nay yu cu cc thit b v phng tin vin thng tin tin v chuyn mn ho cao .Thc t ny cng tr nn r rng hn khi chng ta kim tra cc loi tn s hin ang dng; khng ging nh cc phng 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 cch tng ng cho Video, cc s liu tc va v cao, truyn fax p ng cc c tnh dch v ca chng; ng thi khi cung cp mt dch v, cc tn s khc nhau c th c s dng c kt qu ti u. Theo , vic thit lp nhiu mng li vin thng khc nhau, s dng cc di tn khc nhau v cc dch v khc nhau l iu khng thc t v khng kinh t. Do vy mt nhu cu cp bch l pht trin cng 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 tng lai gn. Vi mc ch ny, cc nh nghin cu v k s tham gia vo lnh vc ny ang c gng kt hp cc mng li vin thng hin nay mt cch c h thng v c hiu qu.

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

Nhng u im ca cc mng li vin thng s l: Khi s dng h thng tng i tng t v ng truyn dn s, b m ho v b gii m c s dng cho cc dch v thoi bin i cc tn hiu ngc li thnh ting ni ti thi im chuyn mch; Khi s dng h thng s v ng truyn dn s, ch cn c mt thit b u cui vi kh nng thc hin chc nng n gin v cc tn hiu s dc u ni mc ghp knh. Mt u im khc ca vic s dng h tng i s l n lm tng cht lng truyn dn. Trong mng

li in thoi s, cc tn hin c m ho ti tng i ch gi c gii m, sau c m ho ti tng i trung chuyn v cui cng c gi n tng i b gi.

Theo , bng cch s dng phng php ny, c th trnh c vic tng lng ting n pht ra khi chuyn cc tn hiu tng t thnh cc tn hiu s. Ngoi ra, do ng truyn dn s tri qua t thay i v mc hn l ng truyn dn tng t, hin tng mt ng truyn s c th t nh hn. thc hin mc ch ny, nu s dng mt ng truyn s gia hai tng i, th s mt ng truyn c th 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 hn mc bt ny c th c gi i mt cch tng i d dng hn thng qua mng in thoi s. Nh trnh by, cc thit b c th c chia s theo cc yu cu dch v v v th c th c s dng mt cch linh hot ng dng cho cc loi dch v hin ang tn ti cng nh cc dch v mi.

Hnh 1.3. Tin trnh trong s ho

Cc nh nghin cu v k s cc nc tin tin ang c gng pht trin loi mng truyn thng s ny. Tin b thc hin c trong cng ngh s c gii thch s dng m hnh Hnh 1.3. Mt ng truyn s dc s dng gia hai tng i trong mng li s tch hp c m phng trong s . ng thi mng ISDN (mng a dch v s) cng c pht trin trong cc dch v tch hp c cung cp vi cc thit b u cui c s ho. Ngoi ra, do cc loi dch v vin thng c a ra ngy cng tr nn phong ph, mt phm vi rng ln cc loi 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 ri. 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 gi l cc thit b u cui tch hp, c trang b vi cc tnh nng tin tin dng cho cc dch v c bit. T , vic s dng truyn thng s tr nn a dng ho hn, v vic c gng pht trin cng ngh ph hp cho cc mc ch cng s c thc hin.

1.2 Lch 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 mng truyn thng ln nht u tin. Sau t lu con ngi pht sinh ra tn hiu bng la c kh nng truyn t cc thng tin c hiu qu v nhanh chng ti cc vng xa. Cu truyn lch s cho thy vo khong nm 1000 trc cng nguyn, cc i qun Hy Lp s dng phng php ny thng bo cc chin thng ca h cho cc cng dn ang nng lng ca Hy Lp. Trong mt thi gian di, phng php ny c s dng mt cch rng ri p ng cc nhu cu v truyn thng. Mt cuc cch mng thng tin khc na ln hn xy ta khi

con ngi bit c lm th no ghi li ngh v t tng ca mnh bng cch dng cch dng cc ch vit. Vi kh nng ny, con ngi c kh nng truyn thng tin m khng b gii hn bi thi gian v khng gian. ng thi, vic pht minh ny a ta cc dch v a th v thng bo. Hong R-ma c th truyn i thng tin cn thit 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 cng ngh in thc y hn na vic pht trin cc phng tin truyn tin v cho con ngi c kh nng thng tin vi nhiu ngi hn v vi cc khu vc cch xa nhau.

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 hnh c pht minh v thi gian ny lm thay i th gii chng ta rt nhiu. Trong phn tip theo, cc pht minh ln khc v nhng pht hin lin quan n cng ngh thng tin in t xy ra trong sut 160 nm qua cng nh xu hng pht trin ca chng tng lai c tho lun mt cch ngn gn. Nm 1820, Georgo Ohm a ta cng thc phng 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 trng. Nm 1850, i s Boolean ca George Boolers to ta nn mng cho lgc hc v pht trin cc r-le in. Chnh vo khong thi gian ny khi cc ng cp u tin xuyn qua i Ty Dng nh in tn c lp t. James Clerk Maxwell a ra hc thuyt in t trng bng cc cng thc ton hc nm 1870. Cn c vo hc thuyt ny, Henrich Hertz truyn i v nhn c sng v tuyn thnh cng bng cch dng in trng ln u tin trong lch s. Tng i in thoi u tin c thit lp u tin nm 1876 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 New York v Chicago v Guglieno Mareconi ca 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 gii chng ta. Nm 1900, Einstein, mt nh vt l ni ting v hc thuyt tng i, vit rt nhiu ti liu quan trng v vt l cht rn, thng k hc, in t trng, v c hc lng t. Vo khong thi gian ny phng th nghim Bell ca M pht minh 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 qua pht minh ca ng ta v mt ng chn khng ba cc. Vic ny c tip theo bng pht minh mt h thng tng i tng t t ng c kh nng hot ng khng cn c bng chuyn mch. Nm 1910, Erwin Schrodinger thit lp nn tng cho c hc lng t thng qua cng b ca ng ta v cn bng sng gii thch cu to nguyn t v cc c im ca nguyn t v R.H Goddard ch to thnh cng 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 dng trong lnh 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 hnh, v cc cp ng trc, phng tin truyn dn c hiu qu hn cc loi dy ng bnh thng, c sn xut. Nm 1939, dch v pht sng truyn hnh thng xuyn c bt u ln 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 ra hc thuyt thng tin dng xc nh lng thng tin ti a m mt h thng vin thng 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 k ny. 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 ca i 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 v John W. Mauchly ca i hc Pennsylvania ln u tin pht trin my in ton phn tch gi l ENIAC. Von Neuman da vo my ny, pht trin thnh cng sau my in ton c lu gi chng trnh. PCBs c a ra vo nhng nm 50, lm cho vic tch hp cc mch in t c th thc hin c. Cng trong nm , RCA phng thnh cng v tinh nhn

to vo khng trung v la-re dng cho 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 chia thi gian c pht trin v thng mi ho mt cch thnh cng vo cc nm 70, cc loi CATVs hai hng, a Video, my in ton ho, truyn nh qua v tinh, 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 cu i vi h thng chuyn mch

My in tn c Samuel F.B Morse pht minh nm 1837, ln u tin trong lch s, cc tn hiu in c s dng truyn tin; cc s liu c m ho c dng nh mt phng 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. Ni chung, vic truyn thng tin cp n qu trnh chuyn thng tin t ngi pht thng tin n ngi s dng. Thng tin c xc nh l cc t tng v cc s liu cn thit cho ngi s dng. ng thi, mt s phng tin truyn tin c s dng trong sut lch s loi ngi. Loi tn hiu la c dng rng khp trong qu kh l mt v d in hnh. Tuy nhin, v nhu cu v cc dch v truyn thng cht lng cao v ng tin cy cng tng ln, con ngi bt u dng in thay cho la lm phng tin truyn thng quan trng nht. Trong tng lai gn, ngi ta d nh l nh sng s thay th in lm phng tin chnh. H thng 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 thit b c phn loi thnh cc h thng truyn tin phn tn v h thng truyn thng tng i nh ghi Hnh 2.1. Trong trng hp u, ngi cp tin ch cp thng tin trong 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 hnh.

H truyn thng

H truyn thng phn tn i v v tuyn, truyn hnh v.v. H truyn thng tng i Mng li truyn thng in thoi v.v.

Hnh 2.1. Phn loi cc h thng truyn thng.

Trong h truyn thng tng i, ngi cp thng tin v dng thng tin cha c xc nh v h thng s dng c kh nng cung cp v s dng thng tin vo cng mt thi gian. V d cho vic ny l h thng truyn thng in thoi. H truyn thng tng i cp n qu trnh chn la chn nhng ngi ang cch xa nhau hoc gia cc my t cch bit nhau v sau giao tip vi nhau bng ting ni 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 h tng 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 cc h chuyn mch s liu dng truyn s liu.

Th hai, cc h truyn dn c dng truyn thng tin cc mc cht lng c th chp nhn c khng k n khong cch cn phi c m bo. Hin vay cc h thng

truyn dn bng dy nh cc loi cp cn bng, cp ng trc, si quang v cc h thng truyn dn khng dy (v tuyn) s dng cc sng cc ngn ang c dng rng ri.

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 din tng th, v duy tr cht lng truyn 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 nhu cu ca ngi s dng. Cc h thng truyn thng tng i tip tc c nng cp mt cch nhanh chng k t khi pht minh ra h thng in thoi cch y gn 100 nm. V c bn, tt c cc h thng u cn my in thoi chuyn cc tn hiu ting ni thnh tn hiu in v ngc li cng nh cc h truyn dn 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 li khi s lng thu bao ny cha phi nhiu qu. V d, c minh ho (a) ca hnh 2.2, 8C2=28 ng l cn thit trong trng hp ch c 8 thu bao c ng k trong h thng. Tuy nhin, khi s dng h tng i vi chc nng giao tip gia cc thu bao nh trnh by (b) hnh 2.2 s cc ng in thoi cn thit phi bng vi s thu bao ng k trong h thng. Nh trnh by, iu quan trng thit lp cc mng li thng tin mt cch kinh t v c hiu qu.

Hnh 2.2. Cc phng php ca mng chuyn mch cho 8 thu bao

2.1.2 Pht trin cng ngh chuyn mch

H tng i dng nhn cng gi l loi dng in t c xy dng New Haven ca M nm 1878 l tng i thng mi thnh cng u tin trn th gii. p ng 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 minh 1889. Version ci tin ca m hnh ny, gi l h tng i kiu Strowger tr thnh ph bin vo cc nm 20. Trong h tng i Strowger, cc cuc gi c kt ni lin tip tu theo cc s in thoi trong h thp phn v do c gi l h thng 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 v cc chuyn mch ca n c vn hnh theo nguyn tc c in.

Do i chin th gii th II bng n, s c gng lp nn cc h tng i mi b tm thi 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 i ny 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 l nhiu khu. Ericsson ca Thu in c kh nng x l vn ny bng cch pht trin thnh cng h tng i c cc thanh che (Cross bar). H tng i c cc thanh 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 chuyn mch cho, loi thanh cho kiu m /ng c s dng; bng cch s dng loi chuyn mch ny c mt b phn m/ng vi im tip xc c gip vng, cc c tnh ca cuc gi c ci tin rt nhiu. Hn na, mt h iu khin chung iu khin mt s cc chuyn mch vo cng mt thi im c s dng. l cc xung quay s c dn li vo cc mch nh v sau c xc nh kt hp trn c s ca cc s quay c ghi li la chn mch ti sinh.

Nm 1965, Mt h tng i in t thng mi c dung lng ln gi l h ESS s 1 c thng mi ho thnh cng M do vy m ra mt k nguyn mi cho cc h tng i in t. Khng ging vi cc h tng i thng thng s dng cc chuyn mch c, h thng ESS s 1 l h tng i s dng cc mch in t. Vic nghin cu loi h tng i ny c khi u t u nhng nm 40 v c xc 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 trong khi h sau ny s dng mch iu khin chuyn mch dng cc l-gc kiu dy th h trc y dng cc thao tc logic bng cc phng tin phn mm lp t trong h thng. Ngoi ra, h tng i in t mi trin khai to c s iu khin 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 hn, tng i ny c trang b chc nng r chn on. Tm quan trng vic trao i thng tin v s liu mt cch kp thi v c hiu qu ang tr nn quan trng hn khi x hi tin n th k 21. p ng y mt phm vi rng cc nhu cu ca con ngi sng trong giai on u ca k nguyn thng tin, cc dch v mi nh dch v truyn s liu, dch v truyn hnh bao gm c dch v in thoi truyn hnh, cc dch v truyn thng di ng ang c pht trin v thc hin. Nhm thc hin c hiu qu 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 trnh 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 mch s. Da vo cng ngh PCM ny, mt mng a dch v s (ISDN) c th x l nhiu lung vi cc dch v khc nhau ang c pht trin hin nay.

2.1.3 Cc chc nng ca h thng tng i

Mc d cc h thng tng i c nng cp rt nhiu t khi n c pht minh ra, cc chc nng c bn ca n nh xc nh cc cuc gi ca thu bao, kt ni 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 qu trnh ny bng tay trong khi h tng di t ng tin hnh cc vic ny bng cc thit 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 dy ni ra v qa n v trng thi ban u. H tng i nhn cng c phn loi thnh lloi in t v h dng c-qui chung. i vi loi dng in t, th thu bao lp thm cho mi c-qui mt ngun cp in. Cc tn hiu gi v tn hiu hon thnh cuc gi c gi n ngi thao tc vin bng cch s dng t trng. i vi h dng c qui chung, ngun in c cung cp chung v cc tn hiu gi v tn hiu hon thnh cuc gi c n gin chuyn n ngi thao tc vin thng qua cc n. i vi h tng i t ng, cc cuc gi c pht ra v hon thnh thng qua cc bc sau:

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

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

3) Kt 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 i ni ht, th mt ng gi ni ht c s dng.

4) Chuyn thng tin iu khin: Khi c ni n tng i ca thu bao b gi hay tng i trung chuyn, c hai tng i trao i vi nhau cc thng tin cn thit nh s thu bao b gi.

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

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

7) Truyn tn hiu chung: kt ni cuc gi tn 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 trng thi c chuyn thnh trng thi my bn.

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

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

10) Hi 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 trnh by ngn gn. Trong h thng tng i in t, nhiu c tnh dch v mi c thm vo cng vi cc chc nng trn. Nhng iu ny s c bn thm sau ny.

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

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

2) Tiu chun kt ni: iu ny lin quan n vn duy tr dch v u ni cho cc thu bao. Ngha l, l ch tiu v cc yu cu i vi cc thit b tng i v s cc 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 l cuc 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 li xut hin trong h thng vi cc chc nng iu khin tp trung c th gp phi hu qu nghim

trng trong thao tc h thng. Theo , h thng phi c c chc nng sa cha v bo dng hu hiu bao gm vic chn on li, tm v sa 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.

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

2.2 Chuyn mch cuc gi

2.2.1 Phn loi chuyn mch cuc gi

C nhiu loi chuyn mch cuc 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 ln thnh cc loi chuyn mch phn chia khng gian v cc loi chuyn mch ghp.

Hnh 2.4. Chuyn mch xoay kiu ng.

A. Loi chuyn mch phn chia khng gian

Cc chuyn mch phn chia khng gian thc hin vic chuyn mch bng cch m/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 chuyn mch ny c cu to bi cc b phn sau:

1) Chuyn mch c kiu chuyn ng truyn

1. Chuyn mch c kiu m/ng 2. Chuyn mch c kiu r-le in t 3. Chuyn mch in t kiu chia khng gian

Nh c trnh by hnh 2.3 v 2.4, loi chuyn mch c kiu chuyn ng truyn l loi chuyn mch thc hin vic vn hnh c tng t nh chuyn mch xoay. Chuyn mch la chn dy ri trong qu trnh dn truyn v tin hnh chc nng iu khin mc nht nh. Do tnh n gin ca n, n c s dng rng ri 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 gy ra do vic rung ng c hc, ngy nay n t c s dng. Loi chuyn mch c kiu 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. Loi chuyn mch ny khng c chc nng iu khin la chn v c thc hin theo gi 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 ri hin nay v c coi l chuyn mch tiu chun, v loi c s dng nhiu nht l loi chuyn mch thanh cho.

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

V vy v nguyn tc cc thao tc c hc cng nh vic m/ng ca cc im tp xc th c tin hnh nhanh chng hn.

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 loi chuyn mch im tip xc; khng tng thch vi phng php c do c s khc nhau v mc tn hiu hoc chi ph v cc c im thoi kh xu bao gm c hin tng mt cuc gi v xuyn m.

Theo , tr trng hp c bit, n cha lc s dng rng ri. Tuy nhin, do cc mch in t nh cc ICs hay cc LSIs tr nn tch hp hn, d kin chng c s dng nhiu hn trong tng lai gn y.

B. Chuyn mch ghp

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

Nguyn l s dng cho loi chuyn mch phn chia thi gian l n tch nhp thng tin c pha nh bng cch s dng ma trn nhp c pha thay i trong khi nguyn l dng cho phng php phn chia tn s l tch cc tn hiu c cc tn s cn thit bng cch s dng b lc c th thay i. Phng php chia tn s c bit l c cc vn k thut nh l vic pht sinh cc loi tn s khc nhau v vic cung cp v ngt cc tn s ny cng nh b lc c th thay i. ng thi n khng kinh t. Theo , phng php ny c nghin cu rng ri trong thi k u ca s pht trin h thng tng i in t nhng cha c vo s dng cho h tng i phn ti. Mt khc, phng php phn chia thi gian c ngh vo thi k u pht trin h tng i in t v n ang c nghin cu tip ngy nay. Phng php iu ch ny c phn loi thm thnh iu ch theo bin xung (PAM) tin hnh bng chuyn mch PAM v iu ch xung m c thc hin nh chuyn mch PCM. Mi chuyn mch c phn loi thm nh sau.

Hnh 2.5. Phn loi chuyn mch ghp.

mt nhiu thi gian pht trin thnh cng chuyn mch PAM. Khi c a ra, do thit k n gin ca n, chuyn mch PAM c s dng cho h tng i c dung lng loi va. V d c th ca n l ESS kiu 101, mt loi PBX iu khin t xa c dng M cho cc mc ch c bit v n cha ph hp cho cc h thng tng i dung lng ln vi nhng vn ca n v cc c im thoi nh tp m v xuyn m. ng thi, v n l loi tng t, tng lai ca n l khng r rng. Chuyn mch PCM c d kin l mt trong cc thnh phn chnh ca IDN hay ISDN x l nhiu loi thng tin cng mt lc bao gm c s liu.

Mng s tch hp kt hp h truyn dn v h chuyn mch thng qua s dng cng ngh PCM. Do phng php ny s dng mch s, n c d nh c vi mch ho trc tip trong tng 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 thoi n 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 c thit lp d dng thng qua vic dng loi chuyn mch nay. Nh c trnh by, phng php ny s c s dng rng ri trong tng lai.

2.2.2 Chuyn mch PCM.

Chuyn mch PCM l loi chuyn mch ghp hot ng da vo cng ngh dn knh chia thi gian v iu ch xung m. PCM l phng php truyn bin ca PAM 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 chuyn mch 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. Chuyn 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 ca mch chuyn mch n pha u ra. Mi mt ng thoi c nh hnh vi mt khe thi gian c th trong mt lung s liu c th. Theo mch chuyn mch thay i mt khe thi gian ca mt lung s liu c th n khe thi gian ca mt lung s liu khc. Qu trnh ny c gi l qu trnh trao i cc khe thi gian. hnh 2.6 m t qui trnh chuyn mch cc khe thi gian. Khe thi gian a vo c ghi li tm thi trong b nh m. Nh th hin trn hnh v, cc khe thi gian a vo c lu gi a ch 1 (address 1) n ch x (address x) ca khung th hin lung u vo. S liu ca khe thi gian 1, khe thi gian 2, v khe thi gian X c lu gi li cc t th nht, th hai v th X tng ng. 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 mt khe thi 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 ca lung u ra, thng tin t thu bao c ghi khe thi gian a vo s 7 c gi n thu bao c ch th bng khe thi gian s 2 u ra.

Hnh 2.6. Qui trnh chuyn mch theo khe thi gian.

C sn cho loi qui trnh ny l phng 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 mt cch ngu nhin t pha u ra. Phng php c ln lt ghi ngu nhin (RWSR) l phng php ghi cc s liu mt cch ngu nhin t pha u vo v c chng theo trnh t pha u ra, cn phng php ghi ngu nhin c ngu nhin (RWRR) l vit v c cc s liu mt cch ngu nhin.

B. Chuyn mch khng gian

Chc nng chuyn i khe thi gian gia cc khe thi gian u vo/u ra c gii thch phn trn chu trch nhim cho chc nng chuyn mch hon thin i vi tt c cc khe thi gian. By gi, nu mch chuyn mch x l thu bao M nh l 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 trng 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 b nh mi 125 u giy/128=976 nano giy (nsec.). Tuy nhin, nu h thng tr nn ln hn, th cc yu cu v b nh v tc truy nhp c th khng p ng ni vi cng ngh ang c hin nay. V d nh, h thng vi 16.384 khe thi gian c kh nng vit v c cc s liu cho mi 76,3 nano giy (125u giy/16.384). Do vy tng hiu sut ca h thng, mt phng php m rng dung lng s dng cc b phn tiu chun l cn thit. Mt trong cc phng php c sn cho mc ch ny l vic i cc khe thi gian trong mt lung khe thi gian ti cc khe thi gian 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 khng gian - thi gian s dng cc thanh u cho theo khng gian. y, thanh u cho theo khng gian tng t nh thanh qut s dng cc tip im r-le tr trng hp yu cu mt cng logic vn hnh tc cao. Mt thanh qut c m phng vi bn u vo ca trc ng v bn u ra ca trc nm ngang. Mt cng lgic c dng im ct cho ca trc ng v trc nm ngang. S tip xc ph hp c tin hnh thng qua vic kch hot cng lgic tng ng trong thi hn ca khe thi gian v nh thng tin c truyn i t bn u vo n pha u ra.

Hnh 2.7. Thanh ct cho khng gian trong chuyn mch phn chia thi gian.

V d, mt khe thi gian trong lung u vo lin tc c "K" cc t PCM khc nhau kch hot mt cng thch hp thc hin vic chuyn mch ti trc nm ngang mong mun. u vo ca trc ng cn li c th c ni vi u ra ca trc nm ngang bng cch kch

hot mt cch ph hp cc cng tng ng. ng thi, khe thi gian tip theo, mt ng dn hon ton khc vi ng trc c th c lp ra.

y ch l cc khe thi gian ca trc ng v trc nm ngang c pht sinh mt cch tng ng trong cng mt thi im v v vy thanh qut, vic chuyn khe thi gian khng c thc hin. Nh trong trng hp chuyn i khe thi gian, 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" cc u ra c m t hnh 2.7. "m" v "n" c th l ging nhau hoc khc nhau tu thuc vo cu hnh ca h thc hin vic tp trung, phn phi, v cc chc nng m rng.

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 hn.

2.2.3 Phng php thit 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 mch T, chuyn mch S, hay phi hp c hai, theo mng li c th c thit lp nh sau:

Chuyn mch T n Chuyn mch S n Chuyn mch T-S Chuyn mch S-T Chuyn mch T-S-T Chuyn mch S-T-S S phi hp phc tp hn ca S v T

A. T-S-T

Cu hnh ny cho php h thng x l cc cuc gi mt cch khng b ngt qung do b kho nh hnh 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 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 ng cho ca chuyn mch khng gian. Trong trng 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 u vo 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 s dng nhng 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 thi gian u vo 3 c th c ni vi mt khe thi gian bt k ca khng gian tr khe thi gian u vo 3. Theo trong trng hp ca T-S-T iu quan trng phi tm kim ng dy ri cng nh cc khe thi gian s s dng. Trong hu ht cc trng hp, mng li c th cung cp t nht mt hay nhiu ng ni cc khe thi gian u vo/u ra.

Hnh 2.8. Cu trc mng T-S-T.

S-T-S

Trong trng hp ca S-T-S, qu trnh tng t nh T-S-T c tin hnh. Trn hnh 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 c th c thay i bng cch dng hai chuyn mch khng gian, linh hot ca u ni c ci thin. V d, nu khe thi gian 7 cn phi c ni n khe thi gian 16, th ch c mt yu cu duy nht l khe thi gian phi c kh nng trao i khe thi gian 7 v 16.

iu ny c th t c bng cch s dng mt trong cc s "n" bt k ca thi gian. Cc mng li T-S-T v S-T-S c th c thit k c cng kh nng kt ni cuc gi v t l kho cuc gi. Vic ny chng t l t l phn b 1:1 c tin hnh gia vic phn chia thi gian v phn chia khng gian.

Hnh 2.9. Cu trc mng S-T-S.

2.3 Phng php iu khin

2.2.1 Phn loi phng php iu khin

Mc d c nhiu loi h thng tng i ang c hin nay, tt c cc h thng c th c phn loi nh c ghi Bng 2.1. u tin chng c th c phn loi theo phng php iu khin m/ng ca chuyn mch cuc gi thnh phng php iu khin c lp, phng php iu khin chung, v phng php iu khin theo chng trnh lu gi.

Cc phng php Qu trnh u ni iu khinc lp

iu khinchung

iu khin bng chng trnh

c lu gi

Loi iu khin trc tip 0 x x

Loi iu khin gin tip 0 0 0

0 : C tn ti x : Khng c hin nay tr cc trng hp c bit

Bng 2.1 Phn loi phng php iu khin chuyn mch.

Phng php iu khin c lp cn c gi l phng php iu khin n chic; y l phng php la chn cc ng ni khi mi chuyn mch tin hnh mt cch c lp vic iu khin la chn v mi chuyn mch c trang b bng mt mch iu khin. Bi v tnh n gin ca mi mch phng php ny c s dng rng ri cng vi phng 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 thng l kh khn bi v phm vi la chn ca mi mch iu khin phn no b gii hn. Phng php iu khin thng thng l phng php tp trung cc mch iu khin vo mi ch v sau theo di trng thi u ni ca ton mch la chn cc ng ni. Khi s dng phng php ny, cc mch iu khin c tp trung chia s s lng ln cc cuc gi cho nn kh nng ca cc mch iu khin l rt ln. ng thi cc chc nng phc tp c th c tin hnh mt cch kinh t. Hu ht cc h tng i kiu c hc phn chia khng gian bao gm c h tng i thanh cho cng s dng phng php ny. Phng php iu khin theo chng trnh c lu gi l mt trong cc loi phng php iu khin chung; chng c tp trung kh cao v chc nng v nh l thit b x l thng tin a nng, n tin hnh mt s iu khin u ni. Hu ht cc h tng i in t ang dng hin nay u p dng phng php ny. Cc u vo iu khin trc tip cho mt 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. Phng php iu khin trc tip l phng php trong cc xung nhn c trc tip kch hot cc mch iu khin nhm chn cc ng ni mt cch lin tip. Khi p dng phng php ny, vic vn hnh c th c tin hnh mt cch n gin tuy nhin cu hnh mng li tuyn v s quay, l ng ni, phi c mi quan h tng ng 1-1. Theo , cu hnh mng l t linh hot v kh nng thp hn. Do , phng php ny l khng ph hp vi h tng i c dung lng ln c kh nng x l cc cuc gi ng di.

Phng php iu khin gin tip l phng php tp trung cc xung quay s vo mch nh, c tt c cc s v sau la chn cc ng ni cuc gi thng qua vic nh gi tng hp. Theo vi phng php ny c c tnh ho bi dung lng x l ng thng cao v c kh nng bin i cc s gi, tng ng, cc s gi v cc ng ni c th c xc nh c lp lp nn mng li tuyn 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 cc phng php iu khin chung v iu khin theo chng trnh lu gi l nhanh hn nhiu so vi thao tc quay s. Theo cc s oc quay c tp hp li trong mt mch nh tch bit tm thi nhm s dng mch iu khin tch hp cao v sau chng c c vi tc cc k nhanh iu khin ton b chng ngay lp tc. V l do ny, hu ht cc h tng di s dng phng php iu khin chung v iu khin theo chng trnh lu gi u dng phng php iu khin gin tip loi tr mt s trng hp trong thi k ban u cu qu trnh pht trin.

2.3.2 Phng php iu khin c lp

Cc h tng i theo tng bc nh ca Strowger hoc h tng i EMD s dng phng php iu khin c lp trong tng mch iu khin ring c b tr km 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 thng nht 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 chc nng chuyn mch. Tuy nhin, v h thng c trang b loi mch ny c kh nng c lp cc li mt cch c hiu qu, h ny c th c thay i hoc c m rng d dng. c bit, phng php ny rt c th c dng rng ri khi cng ngh thit b mi bao gm tch hp cao ca mch in t tr nn php trin hn. Phng php iu khin c lp oc phn loi thm thnh cc loi iu khin trc tip v iu khin gin tip. phn tip theo, chng c xem xt chi tit hn.

A. Kiu iu khin trc tip

Nh m t phn trc y, cc xung sinh ra khi thu bao quay s c a vo 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 sau chn ng dy ri trong s . H thng c to nn bi mt nhm cc chuyn 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 chuyn quay v chuyn theo ng thng v mt loi chuyn mch c hc kiu chuyn 2 cp phi hp hai cch chuyn nhiu chiu nh chuyn theo chiu ng. C nhiu phng php kch hot cc chuyn ng c ni trc y; mt phng php quay bnh rng ng h s dng cc phng tin in t hoc ng c c bit v mt h thng ngun chuyn ng dch chuyn tng chuyn mch bng cch lp t mt my pht in chung mt s chuyn mch hoc thng qua cc bnh rng hoc cc phi hp phc tp khc.

B. Kiu iu khin gin tip

Phng php iu khin trc tip c th c s dng cho cc h tng i dung lng nh mt cch khng kh khn. Tuy nhin, khi s dng cho h thng c dung lng ln, cu hnh mng tr nn phc tp v khi lp t mt ng trung k gia cc tng i c lu lng nh, th hiu qu ca n b gim xung ng k. gii quyt cc vn ny, phng php iu khin gin tip c pht trin. Ngha l mch nh s gi c lp t trong h tng i c cc s gi c lu gi. Khi tng i b gi c xc nh, vic chuyn i s phi c tin hnh tu theo vic thit lp mng li dy cng nh vic thc hin nhn s lin tc v thm cc s c quay. Phng php ny c gi l phng php iu khin gin tip hay phng php chuyn i c lu gi. Hng ca ng trung k c th c chn bng cch quay mt s thp phn gii hn n 10; v vy khi dng phng php iu khin c lp cu hnh mng li tuyn phn no b hn ch trong khi i vi phng php iu khin gin tip th ng truyn dn c th hot ng vi hiu qa cao v cu hnh mng li tuyn khng quan h trc tip vi cc s c quay. Nh trnh by trn, phng php iu khin c lp l v d c bit ca iu khin phn tn. C th phn b cc chc nng chuyn mch (xc nh cuc 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 phc v cc chc nng khc) cho cc loi mch khc nhau u ni cc nhnh. Mi mch c kt cu n gin v mt vi chuyn mch c tp hp thnh nhm hnh thnh h tng i.

2.3.3 Phng php iu khin chung

H iu khin chung l phng php tch gia mch chuyn mch gi ca h tng i v mch iu khin v phn chia mt s nh cc mch iu khin thnh nhiu iu khin u ni t hiu qu cao hn. iu khin u ni c tin hnh thng qua cc qu trnh sau: giai on tp trung ng khi cc cuc gi pht sinh t 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 li v sau c chuyn n tng i bn kia, v mt on chn cui cng khi cc cuc gi n c ni vi pha b gi. Phng php iu khin chung tng phn hay l h thng nh du theo giai on l phng php chia cc chc nng trn y thnh cc thi k khc nhau v sau phn b chng cho mt s loi cc mch iu khin chung. Mt khc h nh du chung l phng php cho php mch iu khin chung iu khin cc u ni thng qua mng chuyn mch gi ca mt tng i.

Khi s dng phng 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 mt cch d dng m rng h thng. Tuy vy, nhng bt li sau y thng gp khi s dng phng php ny: vic x l thng tin iu khin gia mi ngn l kh khn, s ln cc thit b trung k c a vo thng qua khong trng trong cc mch gi tch ring, dung lng x l ng thng b gim ng k do ton b h thng khng c tch hp hon ton v cc chc nng phc tp. Do vy, hin nay h nh du chung c dng rng ri hn. H tng i s 5 ca M l v d in hnh s dng phng 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 thng

Nh trnh by phn trc y, h nh du thng thng l phng php iu khin ton b vn hnh ca vic u ni chn lc trn mng thng qua vic s dng chuyn mch cuc gi.

iu ny khng c ngha l ch c mt mch iu khin hoc mt h tng i c s dng. Thay v, n c ngha l mt mch iu khin iu khin ton b h thng thoi. Trong trng hp i vi h tng i thanh cho, cch thc hin chung l vic iu khin cc cuc gi c thc hin thng qua vic s dng cc mch iu khin chung khc nhau tu thuc vo tc iu khin yu cu. V vy, i khi c 2 thit b thc hin cc chc nng khc nhau c lp t cnh k nhau. Khi s dng phng php ny, chuyn mch gi ton b c kim tra u tin v sau thng tin cha c chim gi ca mi phn c tp hp li chn ng ni. V vy, hin tng kho ng thng, pht sinh do tnh trng my bn, c th c gi mc ti thiu c hiu qu cao hn. Do c cc l do ny, nn hu ht cc h tng i c pht trin gn y s dng h nh du chung. Trn hnh 2.10, 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 gi quay

s. (3) Ni cuc gi i: Da vo s nhn c trong thanh ghi ch gi ng ra ca tng 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 ghi u vo b chim

bi mt ng trung k vo. (6) Ni trung chuyn: Nu h thng chuyn mch l trung chuyn, th cuc gi n c

chuyn ti tng i xa hoc tng i cui.

kim tra xem nhng chc nng trn c thc hin bnh thng khng, h thng chuyn mch thng c trang b thm chc nng qun l, vn hnh v bo dng ca b iu khin t ng, chc nng pht hin li, v tr, thi gian gy li v thit b ghi.

B. Phng php iu khin chung tng phn

Vic iu khin u ni ca h thng chuyn mch c thc hin qua nhng qu trnh sau: giai on tp trung ng theo lu lng cn x l sau khi xc nh c tn hiu gi, giai on phn phi cc cuc gi cho cc a ch da trn s quay, giai on thc hin ni r-le, v cui cng l giai on la chn cui cng khi cc cuc 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 phng php phn chia s iu khin thnh nhiu nhm v sau phn loi phm vi iu khin u ni tng ng phn phi.

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

Hnh 2.11. Phng php iu khin chung tng phn.

Phng php ny c c im nh sau:

(1) Phm vi mng chuyn mch gi do mt mch iu khin nh (2) H thng chuyn mch c th phn chia v xp t li bng cch kt hp cc b

phn mt cch khc nhau linh hot hn.

(3) Vn hnh mng tuyn c th thc hin linh hot tu theo yu cu v ng thng. (4) Nhng li xy ra ch c nh hng t nht i vi ton h thng v cc mch iu

khin c m-un ho. (5) Kh nng ca mng chuyn mch gi b gim bt r rt. (6) Hiu qu ca ng trung k gim xung nhiu (7) Cn c nhng ng trung k d phng gia cc mng chuyn mch phn phi (8) Thng tin v iu khin phi truyn gia cc mch iu khin chung

Nh trn, phng php iu khin chung tng phn thit k n gin c s dng rng ri trong cc m hnh h thng tng i c ng ni cho trc y.

2.3.4 Phng php iu khin bng chng trnh lu tr

Vic iu khin c lp v iu khin chung c phn loi trong kha cnh s ca h thng iu khin. Tri li, nu chng ta xem xt h thng t kha cnh php tnh x l cc bin i logic th mch iu khinr ca h thng chuyn mch c th phn loi tip thnh mch logic dy v mch logic lu tr. Ni chung mch iu khin s c thc hin vi nhng php tnh logic nh (AND), (OR), v (NOT), v kt hp vi thao tc b nh xc nh trng thi tip theo sau khi lu tr phn ghi trc . Vi mc ch , c 2 phng php thao tc: logic dy l phng php kt hp cc r-le, mch im tip xc hay cng in t v sau ni cc thao tc logic cn thit thit lp h thng. Thao tc iu khin c xc nh bng phng php ni dy. Nhng mch iu khin ca phn ln cc h thng chuyn mch k c h thng chuyn mch thanh che pht trin trc y u c thc hin theo phng php ny.

Mch logic lu tr l phng php thc hin cc php tnh logic theo ch th trn mch nh bng cch s dng mt my tnh in t a nng. Th d, CPU ca my tnh in t ch gm c mt mch cng v mch logic c s.Nhng php tnh v thao tc phc tp c th thc hin bng cch dng mch c s nhiu ln theo thng tin nh ghi li trong chng trnh. Cc loi thao tc ny c xc nh bi cc mch dy c nh (hardware: phn cng) v cc chng trnh a vo b nh (phn mm) quyt nh, v cc thao tc c gi l nhng php logic lu tr. Phng php iu khin dng cc mch logic lu tr gi l iu khin bng chng trnh lu tr (SPC). Mch ni dy ton phn dng cho cc thao tc chuyn mch nht nh nh xc nh thu bao ch gi, chn ng, h s xung quay s khng c trong CPU thc hin iu khin chung trong phng php ny. Nh trong trng hp my tnh in t tng hp, h thng ch c cc mch c bn c chc nng logic v s hc. Trnh t thc hin thao tc chuyn mch c lu trong mch nh di dng nhng lnh chng trnh v sau theo cc lnh thc hin thao tc chuyn mch bng cch kch hot cc mch c s nhiu ln. Phng php ny i hi s bin i logic tc cp v mch nh c dung lng ln. Do n c s dng rng ri vi s xut hin ca mch in t vn hnh n gin.

Li th ng k nht ca phng php iu khin bng chng trnh lu tr l iu khin rt linh hot. Trc y, cc h thng truyn thng ch yu s dng truyn ting ni 1:1. Tuy nhn ngy nay cc h thng chuyn mch phi c kh nng x l nhng dch v truyn thng mi nh truyn ting ni/hnh nh v cc loi trao i s liu v dch v chuyn mch in thoi nh quay s tt v in thoi hi ngh, iu i hi phi c tnh linh hot, tnh c th m rng v tnh sn sng. h thng tng i in t (ESS) c pht minh phc v nhng loi dch v ny. ESS hot ng theo phng php iu khin bng chng trnh lu tr ny.

A. Nguyn tc mch logic lu 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 logic nh V, Hoc v Khng, nhng mch logic kt hp bng ni dy p ng cc nhu cu ca mch im tip xc v mch nh lu tr cc bn tin v thao tc qua v sau ch th trng thi thao tc. Hot ng ca mch logic ni dy c xc nh thng qua vic thc hin ni dy. Qu trnh ny tng t nh vic vn hnh ca cng nhn lnh ngh.Ngha l, mch ny x l nhng cng vic thng l n gin lin quan ti trng thi dng in v thng tin a vo. Do n c th thc hin nhng cng vic c bit nhng khng thc s linh hot. Mch logic lu tr c bit lc th hin trong hnh 2.13. Chng trnh lu tr trong mch nh l mt 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 din gii 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 x l 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 mt lot cc thao tc bng cch thc hin cc lnh mt cch tun t nh bn ti, v sau i ti nhng lnh th hin kt qu iu khin l u ta v sau c.

B. Phng php chuyn mch iu khin bng chng trnh lu tr

Vic iu khin bng chng trnh lu tr ca h thng tng i in t c mt b nh c nh ghi nh cc chng trnh v mt b nh tm thi vit v c cc d 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 v u cui, v cc loi thng tin dch s c lu tr c nh. Mt khc, b nh tm thi c dng nh trng thi ca tng thit b u cui v cc cuc gi c iu khin, cc giai on

Hnh 2.12. Mch logic dy dn.

Hnh 2.13. Mch logic lu tr.

iu khin, v kt qu tn thi ca cc php tnh s hc ang thc hin. Trong hnh 2.14, cu hnh ca h thng tng i in t s dng iu khin bng chng trnh lu tr c

minh ho. Mng chuyn mch cuc gi thc hin ni v ct cc cuc gi. B qut c s dng xc nh trng thi ca tng trm u cui ca mch gi, nh cc mch ng thu bao, ng trung k, v thit b nhn xung quay s; n qut trng thi bt-tt theo chu k v sau gi thng tin u vo cho mch iu khin trung tm. Mch iu khin trung tm, mt mch iu khin in t gm mt mch iu khin v tng thanh ghi, qun l v vn hnh ton b h thng iu khin.

N cng c dng cho thit b thao tc s hc ca my tnh in t tng hp. N hot ng theo chng trnh lu tr trong mch nh c nh. Bng cch truyn cc trng thi ghi trong mch nh tm thi mt cch tun t theo thng tin u vo, n thc hin iu khin cuc gi bng cch s dng phng php phn chia thi gian. Mch b nh c nh l mt b lu tr chng trnh s dng ch yu nh cc chng trnh v mch nh tm thi c dng nh trng thi x l cuc gi v do gi l b lu tr cuc gi. B x l trung tm gm 2 b phn .

Chc nng iu khin mng chuyn mch c dng thc hin m/ng chuyn mch gi, iu khin ng trung k hoc cc php kim tra c lin quan vi cc ng gi. Mch iu khin trung tm, da vo kt qu cc giai on lnh thc hin, ghi ra danh sch cc lnh c lin quan ti trnh t thao tc ca mch chuyn mch gi trong mch nh tn thi: Danh sch lnh hon tt c gi n mch kch hot chuyn mch ch th phng php thao tc cho mch chuyn mch gi.

H thng tng i in t, cng vi cc mch c bn ni trc y, ni chung c mt bn vn hnh v bo dng cho cc dch v sa cha. H thng ny cng thc hin mt chng trnh sa cha phc hi nhng li xy ra trong h thng v t ng chn on cc v tr li. Kt qu thc hin

Hnh 2.14. Thit lp h thng tng i in t.

nhng chc nng ny c in ra qua my in. Nhn vin sa cha cn c vo cc bn bo co , thay cc bng li sa cha. Ngoi ra bn bo dng v sa cha c dng thay cc s quay, ng r- le v cc chc nng dch v. Ngi qun tr c th thc hin vic ny bng cch thay i thng tin din gii tng ng hoc cc chng trnh. Ni

chung, nhng iu kin sau y phi c p ng cho hot ng thch hp ca h thng tng i in t s dng phng php iu khin bng chng trnh lu tr.

(1) Vit cc chng 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 loi dich v chuyn mch cuc gi

C 2 loi dch v trong h thng chuyn mch chung: thng tin v dch v chuyn mch cuc gi v truyn v x l d liu. Trong phn sau y s m t vn tt cc dch 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 c bit (2) Gi ch: Nu my thu bao b gi bn, th cuc gi ti thu bao c t ng

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 v bn c

gi vo thi gian nh trc. (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 bit mi

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 thay i 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 khi khng c

tr li ca s i din quay (11) Bo c cuc gi n khi ang bn: Khi nhn c cc cuc gi khc trong lc ang

bn (12) Ch cuc gi: Nhn c cuc gi t bn th ba khi ang bn th c th t 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 (15) Gi hi ngh: 3 hay nhiu hn my thu bao c th tham gia gi cng lc (16) Gi my: Thu bao c th gi cho bn th ba sau khi gi my vi ngi ang ni (17) t gi tt c: Tt c hay mt s in thoi trong tng i c gi cng lc

thng bo (18) Tnh cc tc th: C th tnh cc ngay lp tc (19) Dch c tnh cc chi tit: C chi tit v cc cho cc cuc gi (20) Bo thc: Tn hiu bo thc vo gi nh trc (21) Tm cuc gi xu: C th t ng tm ra s ca my ch gi

Mt trong s cc chc nng ni trn ang c a vo h thng chuyn mch dng thanh cho. Tuy vy, h thng tng i in t s dng mch nh dung lng ln v phng php iu khin bng chng trnh lu tr c tnh linh hot c th cung cp dch v mt cch tit kim v hiu qu hn.

2.4 Thit b ngoi vi

2.4.1 Tng qut

Cc h thng chuyn mch s hin nay ang thay th h thng chuyn mch tng t l nhng h thng chuyn mch ln ang hot ng. Nh vy cc h thng chuyn mch s cn phi c trang b kh nng giao tip vi mng tng t hin tn ti. Cc h thng chuyn mch s trn mng in thoi cng cng phi lm nhiu hn l vic p ng cc in thoi s. Ngha l, cc h thng chuyn mch s phi c kh nng x l nhiu loi in thoi khc nhau k c loi tng t. Do cc mch giao tip tng t nh mch thu bao tng t hay mch ng trung k tng t (analog) l phn chnh ca cc h chuyn mch s. Mt s cc thit b giao tip analog trong h thng l mt trong nhng nhn t quan trng nht xc nh nhng tham s nh gi c, kch thc, mc tiu th in. Gi ca nhng mch thu bao tng t chim khong 80% hoc hn trong gi thnh sn xut ton b h thng. V vy cc nh sn xut h chuyn mch dng mch VLSI thay th cho mch giao tip analog gim gi thnh ca mch thu bao analog

Hnh 2.15. Kt cu ca h thng chuyn mch s chung.

Hnh 2.15 minh ho cu hnh ca h thng chuyn mch s in hnh. Cc ngun thng tin v thu bao tng t gm cc in thoi dn dng, thng mi v cng cng. Modem d liu c th dng lm ngun thng tin tng t. V modem dng gi thng tin s s dng mch tng t. Mch trung k dng giao tip vi cc h chuyn mch khc, vi in thoi vin v mch dch v cng nm trong s ny. Thng tin tng t c ni vi h chuyn mch s qua mt gi phi tuyn MDF. MDF trang b vi cc b phn hn 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 cc ngun bn ngoi. Thit b bo v s cp ny cng vi thit b bo v th cp, c dng bo v cc b phn in t trong h thng chuyn mch s.

2.4.2 Thit b giao tip tng t

Cc chc nng c bn ca mch thu bao tng 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 o th (T)

A. B np c qui

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

B. Bo v in p cao

Cc b phn in t nhy cm ca h thng chuyn mch cn phi c bo v mt cch y chng khng b vt qu in p do chp hoc in thng mi khng n nh. Nh vy cn phi lp t sn cc phn t bo v trong h thng 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 cui ca hai dy in thoi hoc gia mt trong hai dy v t (GND).

C. Chuyn tn hiu gi

Chc nng ny dng chuyn cc tn hiu gi thng bo rng cuc ni chuyn ca khch hng sp b chm dt. Bi v tn hiu cao th xoay chiu c dng lm tn hiu gi, h thng ny c kh nng x l hin tng phng in trong qu trnh truyn v c trang b cc phng tin ngn cn thao tc sai trn mch. H thng ny 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 thu bao hoc cc tn hiu xung quay s. Mch ny phi c tin cy cao.

M ha, gii m

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

Hybrid

Chc nng chnh ca hybrid l chc nng chuyn i 2 dy thnh 4 dy. Nh cc chc nng ph, vic chm dt, cch in v cc chc nng chuyn i t cn i sang khng cn i 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 ng dy in hoc b t dy. Ngi ta nghin cu ta mt li thit b kim tra t ng pht hin trc cc loi li ny bng cch theo di cc ng dy thu bao mt cch thng xuyn theo chu k. Thit b ny c ni vo ng dy trong phng 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. Ni chung, thc hin chc nng o th vo v o th ra ngi ta dng mt r-le.

2.4.3 Thit b giao tip s

Mt trong nhng u im quan trng ca h thng chuyn mch s l n c th s dng cc tn hiu truyn dn s m khng phi thay i chng. Nh vy c ngha l cc dng bt PCM (ghp knh chia thi gian) s dng trong h thng chuyn mch cng ging nh cc dng bt s dng trong hu ht cc thit b truyn dn. Kt qu l ngi ta c th s dng cc mch tng i n gin giao tip gia cc h thng chuyn mch v thit b truyn dn v tit kim hn. H thng phn cp s l t hp cc thit b truyn dn s chy vi nhiu loi tc bit. Mi nc nh ra tc bit cho cc h thng ca h. Trong trng hp nc M, thit b ng truyn dn s c gi l thit b ti T v h thng c s dng rng ri nht l cc thit b ti T. T1 truyn dng bit tc 2 hng 1,544 Mbps (mega bites per 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 hu ht cc h thng chuyn mch s c cc mch giao tip vi tc bit ny. Cc nc Chu u s dng 2.048 Mbps l tc bit c s. Hai iu kin di y phi c p ng giao tip mt cch c hiu qu gia h thng chuyn mch s v thit b truyn dn s.

1) Yu cu v in: lin quan n 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 truyn dn.

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

Hai iu kin trn y xc nh 1 cch y cc tn hiu c truyn qua cc thit b truyn dn. DS1 (tn hiu s 1) l tn hiu c s dng rng ri nht. Tn hiu ny nh r yu cu v in cho cc tn hiu c truyn thng qua vic s dng thit b truyn dn T1 v gi tr ca tng bit c dng bit. V vy, cc loi knh nh D1, D2, D3 v D4 m p ng c cc c im k thut ca DS1 (tn hiu s 1) c kh nng hot ng cng vi thit b truyn dn. Ngoi ra, cc yu cu 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 tin ng b t thit b ti T. Mt dng bit phi c t nht l 1, trong s 12,5% hay hn Os s 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 khung v 24 knh, v mi knh 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 l bit dch chuyn.

Ngoi cc yu cu v tn hiu s 1 k trn (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 trung k cn ri. Cc m ny phi p ng t trng 1 v chng phi c gii m thnh hu nh l in 1 chiu 0 volt. Thng thng, chng c truyn thng qua vic lp 01111111.

Thng thng, "0" c thm vo kt thc khng gi i cc t m cc bit ca n l 0. iu c ngha l nu m s 00000000 c a ra hin th, n s c thay th bng 00000010. Qu trnh ny c thc hin trong khung cng vi 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 tng lai gn.

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

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

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

Vic pht ra m khung Vic xp hng khung Nn dy 0 (Zero) i cc X l cnh bo Khi phc li ng h Tm trong khi nh li khung Bo hiu gia cc tng i

2.5 Mng li truyn thng cng cng

2.5.1 Mng li truyn thng v iu kin kt cu

Mng li truyn thng c th c nh ngha i khi l mt h thng chuyn thng tin. Cc mng li truyn thng in hin nay ang c s dng x l cc loi thng tin khc nhau bao gm mng li in thoi, mng li in tn, v mng li truyn s liu. Ngoi ra, ISDN l mt mng li c kh nng x l tch hp cc loi thng tin trn. V kha cnh loi cuc gi v cc dch v, cc mng li 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 vi cc 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 loi chng v x l chuyn mch, ta c th c mng truyn thng tc thi v mng truyn thng nhanh (dash). Nh ni trn, cc mng truyn thng c th c phn ra nhiu hn 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 gi n 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 thi gian nh trc.

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 trn, mng tng i phi c thit k, sau a vo hot ng mt cch ng n bng cch xem xt cht lng cuc gi, kh nng x l cuc gi, chi ph lp t v chi ph vn hnh, mi lin h gia h thng truyn dn v h thng chuyn mch. Cc mc c nu ra trn y c th c tng 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 h thng ny phi c kh nng x l tt c cuc gi ca h mt cch tit kim, tin cy v nhanh chng. t c mc ch ny, cc c tnh v nhng yu cu i hi ca thu bao phi c xem xt m bo cc dch v thoi cht lng cao. Mt mng ni ht vi mt hoc hai h thng chuyn mch c th c thit lp nu cn thit. i vi cc thu bao sng trong mt vng ring bit c th ch cn mt h thng tng i. Nhng nu s thu bao trong mt vng ring bit vt qu mt gii hn no , c th lp t nhiu tng i. Ni chung, cc mng li ng dy c th c lp ra nh minh ho trong hnh 2.16. Mng li mc ni tip trong hnh (a) c lp ra bng cch ni tt c cc mng li dy ca tt c cc vng theo kiu ni tip. Tri li, mng li vng trong hnh (b) c thit lp theo kiu trn. Nh c m t trong hnh (c), mng hnh sao c tp trung vo 1 im chuyn mch. Trong hnh (d) trng hp mng c mc theo kiu li cc ng ni cc pha vi nhau c thc hin. Cng vy, nu c yu cu, mng li ghp c th c lp t nh hnh (e).

Hnh 2.16. Cc kiu mng li ng dy

Hnh 2.17. Thit lp mng tng i

Bt c mng li no c cp trc y c th c lp t p ng nhng nhu cu v yu cu ca thu bao. Trong trng hp c mt vng rng ln cn nhiu h thng chuyn mch, thng thng th mng mc theo hnh li c thit 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 hnh sao. Cc phng php ni mng c th dng cho cc mng li ng dy c phn no phc tp hn. Thng thng vic ni mng c thc hin theo 4 mc nh c minh ho trong hnh 2.17; trung tm ni ht, trung tm lin tnh, trung tm khu vc, trung tm vng. Trong mng li phn cp c cc mc nh trn, vic to hng thay th bao gm cc hng c mc s dng cao v cc hng thay th c s dng. Nu 1 cuc gi c pht sinh, hng c mc s dng cao s c tm u tin. Cuc gi 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 chuyn mch tuyn

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

A. Mng d liu chuyn mch tuyn :

Mng d liu chuyn mch l mt phng php ni cc ng dy thng tin t cc bn gi n cc bn nhn v sau thc hin vic trao i thng tin gia cc bn vi nhau. Mng li in thoi l mt v d in hnh. Mng li in thoi c lp ra thc hin vic trao i thng tin ting ni, cn mng d liu chuyn mch tuyn c lp t trao i d liu. N biu th cc iu kin giao tip ca mng v 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 hn, tin cy hn v tit kim hn l s dng mng li in thoi hin c hay mng li thu bao cho cc dch v in thoi s. Thi gian i hi kt ni cng ngn hn nhiu. Mng d liu chuyn mch gi ( y ang ni n l "mng chuyn mch gi") thit lp ng trao i thng tin nh trong trng hp mng li in thoi thng thng, v sau trao i thng tin. Mt khi cuc gi c thit lp, mt ng mch c lp gia 2 ngi s dng c lp ra sao cho s dng mch ny nh mt ng dy chuyn dng cho n khi chm dt cuc gi. Bi v h thng chuyn mch khng lin quan trc tip vi thng tin ang truyn 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 trong truyn dn do thi gian x l trong h thng chuyn mch. Ngha l, c th ni rng mng chuyn mch gi c mt thng sut cao trong mng li. Mng li in thoi cng cng (PSTN) c dng cho vic trao i

thng tin ting ni v n c trang b cc h thng chuyn mch v truyn dn cn thit. Trong bng 2.2 c ghi cc h thng chuyn mch ang dng hin nay v c tnh ca chng.

Phng php chuyn mch

Phng php chuyn mch gi

Phng php chuyn bn tin

Phn b mch trao i thng tin

Cho mi cuc gi Cho mi packet Cho mi bn tin

Phng php phn phi mch trao i thng tin

Ngay tc th Chuyn ngay tc th theo lung

Ngay tc th

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

Mt cht (cuc m thoi vn c th c)

Nhiu

Loi thng tin trao i Khng hn ch Dng gi C th nh dng bn tin

Tnh thng sut ca thi gian *

C Khng Khng

iu khin li trong mng

Khng C C (i vi mt t s khc khng c)

Phm vi cc dch v ph c a vo hot ng

t Trung bnh Nhiu

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

* y l mt c tnh duy tr qung thi gian gia cc tn hiu v vic chuyn chng. c tnh ny phi c p ng trong vic truyn tn hiu dng sng nh ting ni.

Mng chuyn mch gi bao gm cc thit b u cui, thit b mch d liu, cc chuyn mch a phng, b tp trung a phng v my pht li. Cc nguyn tc hot ng ca mng li ny c minh ho trong hnh 2.18. Cc tn hiu s t thu bao u cui c mu ho tu theo tc ca ng h nhn c t DCE v sau gi n ng dy thu bao. B tp trung a phng ghp cc tn hiu ny 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 vic chuyn mch nhng tn hiu ny v sau truyn chng n thu bao mun gi theo trnh t ngc li. Cc ng dy thng tin s dng trong mng chuyn mch gi l loi 4 dy, c th thc hin phng php trao i thng tin i ngu ton b, tuy nhin thu bao u cui kia cng c kh nng thc hin phng php thng tin na 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 dng gi v nhn, dch v kt ni, dch v gi trc tip bt u cc cuc gi m khng cn quay s, dch v nhn dng trm u cui v dch v gi tt.

Hnh 2.18. Nguyn tc hot ng ca mng chuyn mch tuyn.

B. Thit lp mng li

1) Khi nim v thit lp mng li

Mng d liu chuyn mch tuyn nh trong trong hnh 2.19 bao gm phn cp chuyn mc thp, phn t mt trm u cui n LS (chuyn mch a phng) c s dng thu nhp v ghp knh cc d liu chuyn mch v mt phn cp mc cao thc hin chc nng chuyn mch. Thng thng phn cp mc thp ca mng li in thoi, cc b phn tp trung a phng ch c lp t trong cc trm chuyn mch c trang b cc h thng i. Tri li, trong mng chuyn mch gi cc b tp trung a phng m c t ri rc, cc xa h thng chuyn mch, tp trung lu lng gi v mt ni m h thng tng i c lp t.

Tn hiu s c tp trung v c ghp knh nh ni trn c chuyn mch ti h thng chuyn mch phn chia thi gian v sau chuyn ti thu bao u cui b gi.

Hnh 2.19. Phn cp mng chuyn mch

Trong phn cp b tp trung a phng, nhng tn hiu cn thit cho h thng chuyn mch c chuyn thnh cc d liu dn knh / tch knh t trm u cui. Cc thu bao c ni vi cc h tp trung a phng hoc trc tip vi cc trm a phng LS. Trn tuyn truyn dn gia ngi thu bao v h thng chuyn mch, c nhng mch thu bao, b phn phc hi gia cc tng i v mch c nhim. Ngoi ra b phn phn hi khng bao gm trong mch thu bao ca mng in thoi trong khi i vi trng hp mng tuyn, b phn phn hi bao gm trong b phn mch thu bao.

2. Cc thit b mng

1) Phng php R- le

Phng php r - le trong phng php chuyn mch tuyn c minh ho trong hnh 2.20. Thit b dng trong mng chuyn mch gm nhng thit b iu khin thu bao, thit b truyn d liu tc cao, cc b tp trung a phng v mt h thng chuyn mch phn chia thi gian. Cc thit b iu khin thu bao l cc thit b t khu vc t trm u cui n b tp trung a phng. Cc thit b ny bao gm nhng khi dch v d liu, b dn knh 0, dn knh 1 v mt khi iu khin mng (NCU). B dn knh 0 chuyn cc tc dch v khc nhau ca ngi s dng sang 64 Kbps v B dn knh 1 li chuyn cc tn hiu ca nhm 0 t 64 Kbps sang 1,544 Mbps trc khi truyn chng i. Thit b truyn d liu tc cao l mt ng 1,544 Mbps ni t b tp trung a phng n h thng chuyn mch phn chia thi gian. N bao gm mt thit b ng b khung, thit b ng b dng tp trung, thit b cung cp tn hiu ng h s, v b dn knh 1. Gia thit b ng b dng tp trung ca b tp trung a phng v thit b ng b khung ca h thng chuyn mch phn chia thi gian, thng tin v ng b cn thit cho vic nhn dng knh c trao i trong khi bo hiu v truyn dn d liu cao tc. B dn knh 1, trong trng hp l b phn ca thu bao, ghp tc nhm 0 t 64 Kbps thnh nhm s cp 1,544 Mbps hoc ngc li. ng h ng b cn kch hot thit b ny nhn c t thit b cung cp tn hiu ng h s. B tp trung a phng thu nhp nhng tn hiu d liu c ghp thnh nhm 0 vi 64 Kbps t nhng trm u cui khc nhau v ghp chng thnh nhm s cp 1,544 Mbps. Ngoi ra, n cng pht hin ngun ch gi v ngt mch theo yu cu ca tng trm u cui.

Hnh 2.20. Phng 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 trc y, bao gm mt thit 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 quan trng nht ca h thng chuyn mch. Thit b vo/ra chuyn v nhn thng tin x l chuyn mch gia cc thit b x l trung tm v kt qu ca n n v i t bo dng v sa cha. N gm mt thit b a t, thit b bng t, thit b hin th v my in dng. Thit b gi phn chia thi gian l mt thit b trong chuyn mch phn chia thi gian c thc hin, thit lp mt ng gi bng cch bin i cc khe thi gian trn ng truyn ghp knh phn chia thi gian ca nhm s cp, di s iu khin ca CPU.

Hnh 2.21. Nguyn tc 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 cc chuyn 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. ng vo/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 khe thi gian trn highway, cn chuyn mch khng gian b tr cc cng theo cch c bit v thay i cc knh highway vi nhau kt ni. Khi nh kt ni cuc gi X vo knh th nht ca ng ra 1 vi ng ra 1, th t knh ca X phi thay i v knh th nht ca ng ra 1 b A chim. Nh vy vic 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 khi cng phn chia thi gian G22 c m/ng trong pha th 2 ca xung P2. Vic kt ni c thc hin trn c s cc th tc trn. Trong h thng chuyn mch phn chia thi gian, nhng tn hiu c ghp knh c chuyn mch v c a n nhng tuyn dn knh theo hng mong mun m khng phi qua qu trnh m ho v gii m.

2.5.4 Mng d liu chuyn mch gi

A. Lch 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 thng c tin cy cao. Khng qun M khi u vic nghin cu cng ngh ny nhm 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 lu tr trong cc khi (gi) (3) Cn phi c chuyn mch lu tr

Cn c vo nhng kt qu nghin cu ny, B Quc phng M k mt hp ng 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 trnh nghin cu tin tin). truyn tin, mng ARPA gn vi h thng chuyn mch IMP (b x l thng bo giao tip) v ni vi cc trung tm my tnh ln ca i hc Illinois, U.S.C., v cc ni khc qua mt mng 50 Kbps ni gia cc h thng chuyn mch. Trn 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 da trn kin ngh chun X.25 cn cho vic tiu chun ho vic giao tip gia mng chuyn 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 hnh l TYMENET ca Hoa K, GTE TELENET dch v thng 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) Nhng nguyn tc:

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

Do , thng tin ngn c a vo mt gi, trong khi thng tin di ch c gi i sau khi b chia thnh nhiu gi. Trong mi gi c a ch ca trm u cui gi l ID ca trm. Cc gi chuyn i t trm ch gi c tm thi gi trong h thng chuyn mch gi. H thng chuyn mch gi, da theo a ch ca trm u cui ghi trong gi nhn, la chn con ng tt nht ti a ch cho v ri chuyn n vo h thng chuyn mch tip theo. H thng chuyn mch a ch n nhn ly v phn phi cho cc trm u cui tng ng v nh vy truyn ton b thng tin ca mt gi. Cc th tc (Protocol) truyn tin nh lp ng truyn dn, xo b nhng li trong truyn dn v gi li nhng thng bo truyn dn c thc hin khi trao i d liu gia trm u cui v h thng chuyn mch v gia cc h thng chuyn mch vi nhau. Cc trm u cui trao i gi li c phn loi thnh trm u cui ch gi v trm u cui ch khng gi tu theo ch trao i thng tin, ngha l c dng cc th tc hay khng. Khc vi cc mng truyn dn thng sut nh in thoi hin nay hay cc mng chuyn mch, ch chuyn mch gi tr hon vic truyn dn v n thc hin truyn dn lu tr trong mch v hot ng da theo cc th tc truyn tin. Tuy nhin, do nhng l do trn, nhng trm u cui chy theo nhng tc khc nhau v cc m s dng c th trao i vi nhau c th cung cp nhiu dch v hn, c kh nng m rng v cht lng truyn tin cao. Ngoi ra, n khc vi cc mng in thoi hin c l h thng ghi ho n ca n c th tnh cc cc cuc gi theo t l khi lng thng tin c truyn dn.

Hnh 2.22. Nguyn tc chuyn mch gi

3) c im

y l mt mng truyn tin rt tin cy c th chn ng bnh thng khc bng n v gi c th gi thay th ngay c khi h thng chuyn mch v mch ca mng gi c li v c a ch ca i tc trong gi c truyn i.

(1) tin cy cao

y l mt mng truyn tin rt tin cy c th chn ng bnh thng khc bng n v gi, c th gi thay th ngay c khi h thng chuyn mch v mch ca mng gi c li v c a ch ca i tc trong gi c truyn i.

(2) Cht lng cao

V chuyn mch gi hot ng theo ch truyn dn s biu hin bng 0 v 1, cht lng truyn dn ca n l tuyt ho. N cng c th thc hin truyn dn cht lng cao bng cch kim tra xem c li khng trong khi truyn dn gi gia cc h thng chuyn mch v gia thu bao vi mng.

(3) Kinh t

H thng chuyn mch gi dng cc ng truyn tin tc cao ni vi cc h thng chuyn mch nm trong mng nhm ghp knh cc gi ca cc thu bao khc nhau tng tnh kinh t v hiu qu truyn dn ca cc ng truyn dn.

(4) Tin trnh chuyn mch

Do h thng chuyn mch gi, chuyn mch, phi s dng ch chuyn mch lu tr a d liu vo b nh trong h thng chuyn mch bng n v gi, nhng tin trnh ny c th thc hin d dng trong h thng chuyn mch v c th pht trin mt phm vi dch v rng ln. Ngoi ra, h thng ny c th thay i tc truyn tin ca tng thu bao, chuyn i m thu bao v th tc truyn v nhn theo trnh t iu khin truyn dn thu

bao. Ngha l, h thng ny cho php thu bao ng k nhng dng h thng chuyn mch khc nhau hot ng vi cc tc v ch th tc khc nhau lin lc vi nhau.

(5) Cc dch v b sung

H thng chuyn mch gi c th cung cp nhng dch v b sung nh trao i thng bo, th in t v dch v khp kn khi cc gi c lu tr trong h thng chuyn mch. Hn na, mt dch v la chn nhanh chng a d liu vo cc gi yu cu cuc thoi ca thu bao ch gi, quay s tt v cc dch v thay th tip vin c th c thc hin.

B. Thit lp mng

1) Khi nim v thit lp mng

Mng chuyn mch gi nh ch r trong hnh 2.23, gm mt h thng chuyn mch cp cao ni nhng h thng chuyn mch v mt h thng tp trung cp cao t cc trm u cui ti cc h thng chuyn mch. H thng tp trung cp thp gm c mt PMX v cc trm u cui. Thit b ghp knh gi phc v cc trm u cui loi chung v loi gi. l mt thit b dng tp hp d liu t cc trm u cui loi chung dng gi, lu tr tm thi d liu t cc trm u cui loi gi trong thit b v sau ghp knh/tch knh nhng gi trc khi gi chng i cc h thng chuyn mch. Nhng thit b ghp knh gi ny c thit lp di dng hnh sao trong h thng chuyn mch gi nh sau:

Hnh 2.23. Phn cp mng chuyn mch gi

2) Cc phng tin dng cho mng chuyn mch gi

(1) Ch r-le

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

Thit b ghp knh gi dng lu tr tm thi thng bo nhn c t nhng trm u cui loi chung vn hnh theo ch ng b v ri bin i sang dng gi. Nhng gi ny

c ghp knh trc khi truyn cho nhng h thng chuyn mch gi. Cc thit b u cui c th c dng trong h thng chuyn mch gi c tip tc phn loi thnh cc thit b u cui loi gi v nhng thit b u cui loi chung. Thit b u cui loi gi l nhng thit b hot ng trn c s chun X.25 theo khuyn ngh ca ITU-T. Cc thit b u cui khc c th phn loi theo tc vn hnh v phng php ng b c gi l cc thit b u cui loi chung. Chng c phn loi ging nh mng chuyn mch tuyn. ng truyn dn 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 l trung 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 phng php iu khin bng chng trnh ghi sn. N cng a ra nhng thng tin cn thit qua a t hoc my in dng cng nh phn tch thng tin trong h thng chuyn mch 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 thit b ghp knh gi v trao i nhng tn hiu gia cc h thng chuyn mch gi. N truyn/nhn thng tin truyn d liu mt cch chnh xc, kim tra cc dng thng tin lin quan ti cc thit b v cc li. Ngoi ra n cn c th yu cu truyn li khi c li.

(3) Mng chuyn mch gi

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

(A) iu khin vic nh tuyn

Trong trng hp mt mng gi vi 4 h thng chuyn mch gi nh trong hnh 2.25, thu bo s 1 c gn vi mt thu bao duy nht khi n c ng k trong mng.

Hnh 2.24. Phng php phc hi mng chuyn mch gi

Khi thu bao 1 mun truyn cc gi cho thu bao 2, thu bao 1 t mt b nhn dng (s ca thu bao khc/s ca knh logic) xc nh ni n ca gi ghi vo trong gi v ri gi n vo h thng chuyn mch A. H thng chuyn mch gi A xc nh mt h thng chuyn mch m n phi gi gi nhn n. Tin trnh ny gi l iu khin nh tuyn. Nh ch r trong hnh 2.25, gi ca bao 1 c th gi i ti bt k mt con ng no trong s b, c v d. Tuy vy hng d cn phi c chn bo m khong cch ngn nht v hiu qu cao nht. Nu hng d b trc trc hoc lu lng qu ln, gi cn c gi theo b v c. Thc t, h thng chuyn mch hot ng trn c s mt bng l trnh; ni dung ca bng ny c th thay i khi cn tu theo tnh trng ca h thng chuyn mch k cn v s lu thng ca mng. Bng ny cn phi c son tho v s dng theo nhng nguyn tc nh sn nh l thut ton nh tuyn c nh.

Hnh 2.25. V d v mng chuyn mch gi

B) Knh logic

Trong vic truyn d liu, qu trnh truyn tin gia 2 thu bao khng c thc hin mt cch t ng ngay c khi ng thng tin c kt ni bng in. Trong trng hp mt cuc gi in thoi, ch c mt ng lin lc c ni khi pha c gi tr li in thoi. Nh vy ch c knh vt l l c thit lp. Loi knh ny gi l knh logic. Trong mng gi, knh logic ny c phn loi thnh cuc gi o, cuc gi o vnh vin v d liu biu tu theo loi ca chng.

Cuc gi o

Khi mt ng thoi c thit lp trn mng in thoi, knh c dng cho n khi gi xong. iu ny cng ging nh trng hp cuc gi o ca mng gi. Nh trnh by trong hnh 2.26, khi mt thu bao ch bt u gi thu bao ny gi mt gi yu cu gi bao gm s in thoi ca i tc v s knh logic thu bao s dng trn mng.

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 thu bao u cui s dng n cho thu bao s 2. Nu thu bao s 2 dng trong trng thi c th nhn c cuc gi, n gi gi thng tin chp nhn gi cho mng. Mng gi gi thng tin nhn c cho thu bao s 1 nh l mt gi kt ni cuc gi v nh vy lp c ng lin lc logic gia thu bao 1 v 2. Sau vic truyn gi d liu c thc hin qua knh logic lc c thit lp. Mt cuc gi o c thit lp thng qua cc th tc trn. Mt gi yu cu xo c gi i khi chm dt lin lc v knh logic ny c gii phng qua vic dng mt gi ch th xo v gi xc nhn xo. Cng nh trong trng hp gi in thoi, cuc gi o l cuc gi thit lp ra mt mch logic cho trao i d liu v sau gi d liu ch qua knh v cui cng xo knh i khi hon tt lin lc.

Gi o vnh vin

Gi o vnh vin l phng php thit lp ng lin lc logic vnh vin gia 2 thu bao v do khng cn phi thit lp hoc xo knh logic nh trong trng hp gi o.

D liu biu

Khng nh nhng knh logic ni trc y, y l mt phng php khng cn thit lp mt knh logic gia 2 thu bao. Thay vo , thu bao ch gi ch vic gi mt gi c s ca pha i din trong mi gi v da theo s mi gi, mng gi gi ti h thng chuyn mch tip theo. Cc gi s c gi i qua cc loi tuyn khc nhau. Phng php ny c bit cli khi chuyn v nhn nhng thng bo ngn.

(C) Ghp knh gi

Ni chung, mt thu bao c th c nhiu s knh logic ngay khi nu mt ng dy c ni vt l vi mng gi. Nu thit b u cui c th x l d liu t nhiu ngun cng mt lc, mt cuc gi cho nhiu hn 2 thu bao c th thit lp c. y gi l ghp knh gi.

Hnh 2.27. Ghp knh gi

(D) iu khin trnh t

Do cc gi d liu chuyn qua mt knh logic c th chuyn theo nhiu ng khc nhau, trnh t gi d liu c th thay i. Vic iu khin trnh t l mt qu trnh sa cha v ngn nga vic xy ra. Trong mt gi d liu c mt trng th tc truyn v trng th tc nhn; Thu bao truyn gn s th tc truyn khi truyn i mt gi. Trnh t ca gi d liu nhn qua mng c kim tra ti h thng chuyn mch cui cng gn vi ngi thu bao b gi; trnh t sai s c sa li v gi nhn trng lp s c loi b. Nhng gi thp hn gi b mt cng b loi b gi i nhng gi ng ti thu bao cui theo ng trnh t.

V phng php biu d liu khng c mt ng lin lc logic nn vic iu khin trnh t c thc hin thu bao u cui ch khng phi trn mng.

(E) Trng thi ng ct

H thng chuyn mch gi l mt h thng chuyn mch lu tr, lu gi tm thi cc d liu trong b nh. Nhiu my thu bao c chung mt h thng chuyn mch v v c ca b nh trong h thng c gii hn, nn xy ra tnh trng ch tc do thiu 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 trn mng. ch tc c xy ra do nhiu vn k c do khc nhau v tc truyn tin gia cc thu bao.

(F) iu khin lung

S lng gi d liu a vo mng cn c gii hn trnh ch tc. Nhng phng php dng cho mc ch ny gm mt tin trnh hn ch b m hn ch s lng ti a cc gi d liu truyn i, mt tin trnh gi l phng php iu khin ca s truyn i mt s lng nht nh cc gi d liu qua mng n trm 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 trnh gi l WABT, phng php ny gi tn hiu khng sn sng nhn khi thiu b m hn

ch u vo, v mt tin trnh gi l phng php trung tm qun l mng, iu khin trng thi ca ng thng trong mng bng cch to ra mt trung tm qun l mng. Trong thc t, mt s tin trnh m t trn cng c s dng cng mt lc trong mng gi.

(G) Dch v b xung

H thng chuyn mch nhm c nhng dch v b sung tho mn mt cch hiu qu hn nhng nhu cu ca ngi s dng.

Kt ni khp kn

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

Hnh 2.28. Kt ni khp kn

2.5.5 Phng php bo hiu

thc hin vic ni mch, thng tin cn thit iu khin phi c trao i gia in thoi v h thng chuyn mch v gia cc h thng chuyn mch vi nhau. Phng php bo hiu l mt th tc v phng php truyn nhng thng tin ny, v d, gia in thoi v h thng chuyn mch, nhng yu cu tip ni v phc hi, ch nh la chn bng xung quay s, tr li thng bo bng m ch gi hoc m chung trao i vi nhau.Ngoi ra, nhng tn hiu gia cc tng i vi nhau nh kch hot, tr li, la chn, kt thc, ngt v thng tin cc c trao i gia cc h thng chuyn mch trn mng in thoi. Trong hnh 2.29 minh ho lung tn hiu c bn.

Hnh 2.29. Lung tn hiu c bn

Phng php chuyn bo hiu li c phn loi thnh phng php bo hiu knh kt hp v bo hiu knh chung (CCS). Trong h thng chuyn mch thng thng, tn hiu c pht v thu qua mt knh thoi ring l. gi l bo hiu knh kt hp. Trong phng php bo hiu knh chung, nhng knh gi tch bit nhau v do cc tn hiu c thu thp vo nhng knh truyn cao tc c bit trc khi c truyn v nhn. Phng php ny c th chuyn nhiu thng tin theo 2 chiu d cc knh thoi c b bn hay khng. Do n tng cng c hiu qu ca ton b h thng bng cch kim tra ton b mng tuyn v n linh hot p ng nhng dch v mi. V nhng l do , n l iu l tng i vi ISDN. Phng php ny nh trng hp phng php iu khin chng trnh lu tr, ph hp vi h thng chuyn mch in t c cc chc nng tp trung.

Hnh 2.30. Bo hiu knh kt hp (a) v Bo hiu knh chung (b)

Bo hiu knh kt hp c chia thnh h thng bo hiu trong bng s dng di tn ting ni v h thng bo hiu ngoi bng s dng tn s bo hiu khc vi di tn ting ni. M a tn dng to m bng cch kt hp tn s s dng 2 trong s 6 tn s ca di tn ting ni. l mt v d in hnh 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 phng tin phc tp c th c thit lp mt cch kinh t v c th truyn nhiu thng tin hai chiu vi tc cao. Phng php bo hiu s 6 / s 7 theo khuyn ngh ca ITU-T l v d in hnh thuc v phng php ny.

A. Phng php bo hiu R2 - MFC

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

1/ Bo hiu gim st

Nhng tn hiu gim st c chuyn ti h thng chuyn mch tu theo cc trng thi thay i 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 pha b gi Chp nhn chim (Seizure acknwledgement): tn hiu thng bo xc nhn tn hiu 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 cho h

thng chuyn mch pha ch gi

Xung tnh cc / Chp nhn chim (Metering/Seizue acknwledgement): tn hiu lin 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 gi rng thu bao b gi t my.

Xo i (Clear forward): tn hiu thng bo ti h thng chuyn mch pha b gi rng thu bao ch gi t my.

Kho: tn hiu bo rng tn hiu tng ng khng th a ra ngoi c.

2) Tn hiu la chn:

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

Tn 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 trn v nhng ngha tn hiu c din gii khc nhau tu theo v tr ti tn hiu hng v A - 3, A - 5, hoc chui bo hiu truyn v nhn s lng ln thng tin.

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 hiu hng i

C 15 tn hiu hng i trong nhm I v 15 trong nhm II. Tn hiu nhm I ch yu l th hin cc s ca my thu bao b gi. Tn hiu u tin trn chui bo hiu pht i c din gii l tn hiu nhm I. Cng nh vy, tn hiu v u tin c din gii l tn hiu nhm A. S dng tn hiu v c th (A - 3, A - 5) th c th thc hin c vic chuyn i t nhm I sang nhm II. Khi c chuyn sang nhm nhm II bng tn hiu v A - 5, th c th chuyn i c sang nhm I. Vic chuyn i t nhm A sang 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 i

Tn hiu s 540 660 780 900 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 8 0 0 9 0 0 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0

Bng 2.3. a ch tn s bo hiu R2 - MFC

Tn hiu i nhm I

Trong nhm I, c 2 ngha nh trong Bng 2.4

Tn hiu I - 1 ~ I - 10

Ni chung, chng tng ng vi ch s ca s my thu bao b gi

(I - 1 = 1, I - 2 = 2, ....... I - 9 = 9 , I - 10 = 0 )

i vi nhng cuc gi quc t, ngn ng ch s c s dng ni vi in bo vin, c th khi cuc gi quc t kt thc tng i cui ( ngha 1). Nu khng cn ti ngn ng, chng c s dng nh l nhng ch s phn bit th hin nhng tng i cui. Chng ch c truyn i khi h thng chuyn mch r-le quc t yu cu nhng ch s phn bit v ngn ng bng tn hiu hng v A - 12.

Nhm I Nhn xt Tn hiu Ngha 1 Ngha 2

I - 1 Ngn ng: Php Ch s 1

I - 2 Ngn ng: Anh Ch s 2

I- 3 Ngn ng: c Ch s 3

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 7

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

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

I - 10 S phn bit Ch s 0

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

Truy nhp ti I/C in bo 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 (M 13) khng k ni vi v tinh

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

Cn b trit na m di I/C k c ni vi v tinh

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, ngha 2 dng cho cc tn hiu khc.

Tn hiu Ngha Nhn xt II - 1 My thu bao khng u tin

II - 2 My thu bao u tin

II - 3 Thit b bo dng

II - 4 D phng

II - 5 in bo vin

II - 6 Truyn d liu

II - 7 My thu bao (hoc in bo vin khng c phng tin chuyn tn hiu i)

II - 8 Truyn d liu

II - 9 My thu bao u tin

II - 10 in bo vin c phng 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 hiu hng i

Nhng tn hiu ca nhm II th hin cc cp ca pha ch gi. Bin i t nhm I sang 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 t Tn hiu II - 11 ~ II - 15: D tr cho cc cuc gi trong nc

Tn hiu Ngha