Chu Yen Macht Rong Wan 1

5/19/2018 Chu Yen Macht Rong Wan 1

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BIN SON: NGUYN DUY NHT VIN

K THUT CHUYN MCHTRONG MNG DIN RNG

nng, 2006.

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Destination I/P Port I/P Label O/P Label O/P Port

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Destination I/P Port I/P Label

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TA

Cun sch ny c bin son phc v cho cc sinh vin chuyn ngnh int, Vin thng v Cng ngh thng tin. Ni dung cun sch xoay quanh cc k thut

chuyn mch v c ch bn trong mng din rng WAN (wide area network) m cpht trin h tr cc ng dng truyn thng thoi, video, d liu v multimedia quacc mng ng di. Cu trc ca sch nh sau:

Chng 1: Tng quan.Cung cp cc khi nim tng quan, lch s pht

trin v gii thiu cc phng thc chuyn mch trong mng vin thng.

Chng 2: Chuyn mch knh.Gii thiu mng chuyn mch v trnh

by cc c trng chnh trong mng chuyn mch knh.

Chng 3: Chuyn mch gi.Gii thiu v nguyn l chuyn mch gi,cc hot ng bn trong mng, cc ni dung chuyn mch o v datagram,cc k thut chnh ca nh tuyn v iu khin tc nghn v giao thc

X.25 l giao tip chun gia thit b u cui v mng chuyn mch gi. Chng 4: ISDN.Trnh by nguyn l c bn, cc mc tiu v cc dch

v, cc knh v giao tip ca ISDN, truy cp ngi s dng v cc giaothc trong ISDN.

Chng 5: Frame relay.Gii thiu v frame relay, kin trc giao thc,

iu khin cuc gi, truyn d liu v iu khin tc nghn bn trongframe relay.

Chng 6: ATM.Tho lun v s ATM, t bo, cc ni dung quantrng ca lp thch ng ATM AAL (ATM Adaptation Layer) v iukhin lu lng v iu khin tc nghn ca ATM.

Chng 7: Internet. Chng ny trnh by khi nim v Internet, mhnh, nh tuyn, cc giao thc nh tuyn v cc kiu truy cp Internet.

Chng 8: MPLS.Trnh by cc khi nim tng quan v MPLS, sau l cc cu trc d liu, giao thc phn phi nhn v cc c ch k thutlu lng trong MPLS.

Trong , cc chng 2, 3, 4, 5 v 6 c bin son ch yu t cun sch Dataand Computer Communication ca William Stallings, cc chng cn li da trnnhng ti liu tham kho khc. Ngoi ra, cng do nh hng bi ti liu ca W.Stallings,nn cui mi chng, lun c mc gii thiu ti liu v cc website tham kho b ch chobn c.

Trong qu trnh bin son, khng trnh khi nhng thiu st, mong s phn hi tpha c gi. Xin chn thnh cm n!

NGUYN DUY NHT VIN


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C LC

. TNG QUAN ...........................................................................................................

. TNG QUAN ............................................................................................................10Khi nim ...................................................................................................................10Dch v vin thng .....................................................................................................11Cc dch v vin thng cho ngi s dng:...............................................................12Cc yu cu mng v thit b .....................................................................................12Mng vin thng.........................................................................................................12Chuyn mch..............................................................................................................13

2. LCH S PHT TRIN............................................................................................14Cc h thng chuyn mch nhn cng.......................................................................14Cc h thng chuyn mch in t ............................................................................15Cc h thng s v iu khin my tnh.....................................................................15Cc node chuyn mch cho thng tin d liu ............................................................16

Cc node cho N-ISDN................................................................................................17Cc node cho B-ISDN................................................................................................18Chuyn mch quang...................................................................................................18

3. CC PHNG THC CHUYN MCH...............................................................18Chuyn mch knh.....................................................................................................18Chuyn mch tin.........................................................................................................18Chuyn mch gi........................................................................................................19Chuyn mch khung...................................................................................................20Chuyn mch t bo ...................................................................................................21Chuyn mch nhn a giao thc ................................................................................22Chuyn mch quang...................................................................................................22

4. GII THIU TI LIU THAM KHO ...................................................................23

Cc trang web:............................................................................................................23

2. CHUYN MCH KNH........................................................................................241. MNG CHUYN MCH.........................................................................................242. CC MNG CHUYN MCH KNH....................................................................253. NI DUNG CHUYN MCH..................................................................................28

Chuyn mch phn chia khng gian (Space Division Switching) .............................28Chuyn mch phn chia theo thi gian (Time Division Switching) ..........................31

4.NH TUYN CHO CC MNG CHUYN MCH KNH..................................33nh tuyn lun phin: ...............................................................................................34nh tuyn thch nghi .................................................................................................35

5. BO HIU.................................................................................................................37Cc chc nng bo hiu .............................................................................................37Vng bo hiu ............................................................................................................39Bo hiu knh chung ..................................................................................................39


3. CHUYN MCH GI ............................................................................................441. NGUYN L CHUYN MCH GI......................................................................44

K thut chuyn mch................................................................................................46


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Kch thc gi............................................................................................................48So snh chuyn mch knh vi chuyn mch gi......................................................48Thc hin....................................................................................................................48Cc c trng khc.....................................................................................................49Hot ng bn trong v bn ngoi .............................................................................50Cc loi thit k bn trong v bn ngoi: ...................................................................52

2. NH TUYN ...........................................................................................................53Cc c trng: ............................................................................................................53Tiu ch thc hin.......................................................................................................54Thi im v ni quyt nh ......................................................................................54

Ngun thng tin mng v thi gian cp nht .............................................................55Cc chin lc nh tuyn..........................................................................................56nh tuyn c nh (fixed) .........................................................................................56nh tuyn lan trn (flooding)....................................................................................57nh tuyn ngu nhin (random) ...............................................................................58nh tuyn thch nghi .................................................................................................59Cc thut ton chi ph ti thiu...................................................................................61Thut ton Dijkstra.....................................................................................................61

Gii thut Bellman-Ford.............................................................................................62V d cho c hai thut ton Dijkstra v Bellman-Ford...............................................62So snh .......................................................................................................................63

3. IU KHIN LU LNG ....................................................................................64Phm vi v mc iu khin lu lng .......................................................................65iu khin lung........................................................................................................65iu khin lung dng v ch ...................................................................................66iu khin lung ca s trt ....................................................................................67iu khin tc nghn..................................................................................................69Kim sot kha cht (deadlock) .................................................................................72

Nguyn nhn kha cht..............................................................................................73

Phng n kim sot kha cht:.................................................................................744. X.25 ............................................................................................................................74Dch v knh o..........................................................................................................75Dng gi .....................................................................................................................77Ghp knh ..................................................................................................................79iu khin lung v iu khin li ............................................................................80Chui gi ....................................................................................................................80


4. INTEGRATED SERVICE DIGITAL NETWORK .............................................821. TNG QUAN V ISDN............................................................................................82

Nguyn l c s ca ISDN.........................................................................................82

Giao tip ngi s dng .............................................................................................84Mc tiu......................................................................................................................85Kin trc.....................................................................................................................85Cc tiu chun ............................................................................................................86Series I.100 Cc ni dung tng quan.......................................................................86Series I.200 Kh nng phc v................................................................................87Series I.300 Cc kha cnh mng ............................................................................87Series I.400 Cc giao tip ngi s dng mng...................................................87Series I.500 Cc giao tip lin mng.......................................................................87


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Sies I.600 Nguyn l vn hnh ............................................................................872. CC KNH ISDN .....................................................................................................873. TRUY CP NGI S DNG ...............................................................................904. CC GIAO THC ISDN ..........................................................................................92

Kin trc giao thc ISDN...........................................................................................92Cc ni kt ISDN .......................................................................................................93

Cc cuc gi chuyn mch knh................................................................................93Cc ni kt bn vnh vin...........................................................................................93Cc cuc gi chuyn mch gi qua knh B ...............................................................94Cc cuc gi chuyn mch gi qua knh D ...............................................................96Bo hiu knh chung giao tip ngi s dng v mng ISDN...............................96LAPD .........................................................................................................................99Cc dch v LAPD ...................................................................................................100Giao thc LAPD.......................................................................................................100C.............................................................................................................................101a ch ......................................................................................................................101iu khin ................................................................................................................102Thng tin ..................................................................................................................102

Dy kim tra khung ..................................................................................................102Lp vt l .................................................................................................................102

5. GII THIU TI LIU THAM KHO .................................................................103Gii thiu cc trang web: .........................................................................................103

5. FRAME RELAY ....................................................................................................1041. NN TNG..............................................................................................................1042. KIN TRC GIAO THC FRAME RELAY ........................................................106

Mt phng iu khin...............................................................................................106Mt phng ngi s dng ........................................................................................107So snh vi X.25 ......................................................................................................108

3. IU KHIN CUC GI FRAME RELAY .........................................................110Ni kt FRAME RELAY.........................................................................................111Ni kt truy cp........................................................................................................112

4. TRUYN D LIU NGI S DNG................................................................1135. CHC NNG MNG.............................................................................................1156. IU KHIN TC NGHN...................................................................................116

Cc phng php iu khin tc nghn cho frame relay .........................................116Qun l tc lu lng..........................................................................................118Trnh nghn vi bo hiu tng minh .....................................................................121Gii phng nghn vi bo hiu ngm nh. .............................................................123

7. GII THIU TI LIU THAM KHO .................................................................123Cc trang web:..........................................................................................................124

6. ASYNCHRONOUS TRANSFER MODE............................................................1251. KIN TRC GIAO THC .....................................................................................1252. CC NI KT LOGIC ATM..................................................................................126

S dng ni kt knh o...........................................................................................128Cc c trng ng o/knh o..............................................................................129Bo hiu....................................................................................................................130

3. CC T BO ATM ................................................................................................130


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ng header..............................................................................................................131iu khin li header ...............................................................................................132

4. TRUYN CC T BO ATM ...............................................................................134Lp vt l c s t bo .............................................................................................134Lp vt l trn c s SDH........................................................................................136

5. LP THCH NG ATM .........................................................................................137

Cc dch v AAL......................................................................................................137Cc giao thc AAL ..................................................................................................138

6. IU KHIN LU LNG V IU KHIN TC NGHN ...........................142Cc khuyn ngh iu khin lu lng v nghn cho ATM ....................................142Bin i tr t bo ....................................................................................................143Phn b mng vi s thay i tr t bo..................................................................144S thay i tr t bo ti UNI ..................................................................................145C ch iu khin lu lng v tc nghn...............................................................146iu khin lu lng................................................................................................147Qun l ti nguyn mng .........................................................................................147iu khin chp nhn ni kt...................................................................................149iu khin tham s s dng.....................................................................................150

iu khin u tin ...............................................................................................151Qun l ti nguyn nhanh.........................................................................................152iu khin tc nghn................................................................................................152Hy t bo c chn lc .............................................................................................152Ch th iu khin tc nghn tng minh hng i..................................................152

7. GII THIU TI LIU THAM KHO .................................................................152Gii thiu cc trang web: .........................................................................................153

7. INTERNET PROTOCOL.....................................................................................1541. KHI NIM V INTERNET..................................................................................154

Ngun gc ................................................................................................................154

Khi nim .................................................................................................................1552. M HNH TCP/IP ...................................................................................................155

Khung dng gi tin Ipv4: .......................................................................................158a ch IPv4..............................................................................................................159Mng con..................................................................................................................160IPv6 (IPng) ...............................................................................................................161TCP (Transmission Control Protocol .......................................................................163).................................................................................................................................163UDP (User Datagram Protocol) ...............................................................................164

3. CC PHNG THC TRUY CP INTERNET ..................................................164Truy cp Dial-up ......................................................................................................165ISDN.........................................................................................................................169

Truy cp bng rng ..................................................................................................170Cc mng truyn hnh cp........................................................................................172Truy cp khng dy..................................................................................................173Truy cp cp si .......................................................................................................174Cc ni kt ring v cc mng din rng WAN.......................................................174

4. NH TUYN .........................................................................................................175Khi nim .................................................................................................................175Hot ng nh tuyn ca Router.............................................................................175Tm ng - Cc gii thut tm ng.....................................................................175


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Chuyn gi tin theo l trnh chn ........................................................................177Cc gii thut tm ng..........................................................................................177Tm ng tnh v ng...........................................................................................178ng n v a ng...........................................................................................179

Ngang hng v c th bc........................................................................................179My trm thng minh v Router thng minh...........................................................179

Intradomain v Interdomain .....................................................................................179Trng thi lin kt v vector di..........................................................................179Cc metric nh tuyn ..............................................................................................180So snh cc giao thc nh tuyn .............................................................................181

5. MT S GIAO THC NH TUYN ..................................................................182Cc loi giao thc nh tuyn...................................................................................182nh tuyn vector khong cch: ...............................................................................182nh tuyn trng thi lin kt:..................................................................................183nh tuyn lai ghp ..................................................................................................184Mt s giao thc dng trong hot ng nh tuyn: ................................................184RIP (Router Information Protocol): .........................................................................186IGRP (Interior Gateway Routing Protocol): ............................................................186

OSPF (Open Shortest Path First): ............................................................................186EIGRP (Enhanced Interior Gateway Routing Protocol): .........................................187

6. GII THIU TI LIU THAM KHO .................................................................187

8. MULTIPROTOCOL LABEL SWITCHING......................................................1891. TNG QUAN V MPLS ........................................................................................1892. CC KHI NIM C BN TRONG MPLS .........................................................190

Cc thnh phn v cc c ch LDP:.........................................................................191Router chuyn mch nhn ........................................................................................192Router nhn bin .....................................................................................................192ng dn chuyn mch nhn.................................................................................192

Cc lp chuyn tip tng ng FEC....................................................................193Nhn .........................................................................................................................193Khng gian nhn ......................................................................................................194Stack nhn ................................................................................................................195Cc ng gi nhn....................................................................................................195ng hm...............................................................................................................195Cc LSR ngc dng (upstream) v xui dng (downstream)................................196

3. CC CU TRC D LIU ...................................................................................196Mc chuyn tip nhn chng tip theo.....................................................................196FEC to NHLFE (FTN) .............................................................................................197nh x nhn a n................................................................................................197Chuyn i nhn.......................................................................................................197

3. GIAO THC PHN PHI NHN.........................................................................198Cc nh danh LDP v cc a ch chng tip theo ..................................................198Pht hin LDP: .........................................................................................................198Phin v thit lp LDP .............................................................................................199Duy tr cc Hello ln cn..........................................................................................201Duy tr cc phin LDP..............................................................................................201Cc thng ip LDP .................................................................................................201Cc kiu cng b nhn .............................................................................................202Cc kiu iu khin LSP ..........................................................................................203


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Cc kiu duy tr nhn ...............................................................................................204nh tuyn................................................................................................................205

5. CC C CH K THUT LU LNG CA MPLS .......................................208TE-RSVP..................................................................................................................209CR-LDP....................................................................................................................209So snh gia hai k thut lu lng s dng trong MPLS ......................................210

Thit lp v duy tr CR-LDP....................................................................................211Thit lp mt CR-LSP h tr cc ng dng nhy cm suy hao ..........................213Thit lp CR-LSR h tr cc ng dng khng nhy vi suy hao .......................213

6. GII THIU TI LIU THAM KHO .................................................................213

TI LIU THAM KHO .............................................................................................214


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K THUT CHUYN MCH TRONG MNG DIN RNG

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1. TNG QUANTrong mng vin thng, vi kin trc phc tp, bi ton c t ra l lm th no

chuyn thng tin n ch mt cch an ton, hiu qu v nhanh chng, ng thi thamn nhu cu dch v ca ngi s dng. gii quyt iu ny, cc k thut chuynmch ln lt ra i, p dng cho cc mng v cc dch v t n gin n cc k phctp, chnh l ni dung trong ti liu ny. Trong chng ny, ngi c s c cungcp kin thc tng quan v lch s pht trin cc phng thc chuyn mch trong mngvin thng.

1. TNG QUAN

Khi nim

Trc tin, chng ta s xt khi nim v truyn thng, vin thng ri sau lnhng khi nim v dch v vin thng, mng vin thng v chuyn mch.

Truyn thng (Communication) l tt c s trao i, vn chuyn thng tin bnghnh thc ny hoc hnh thc khc.

V d: Bn ang c ti liu ny, t bo c sng nay, chuyn tu ch bn i tTp H Ch Minh n Th H ni, bn ang ly thng tin t Internet, bn ang xemtivi, bn ang gi in

Vin thng l 3 v d sau, vy, vin thng (Telecommunication) l s truynthng qua khong cch a l.

T mt thnh ph A, bn mun trao i thng tin vi mt ngi thnh ph B thc cc hnh thc nh trong Hnh 1-1.

Nu bn s dng in thoi, tc l bn s dng dch v vin thng, tele c nghal t xa, biu th mt s bc cu cho mt khong cch a l, ngha l s trao i thngtin t xa.

Vin thng l mt trong nhng lnh vc c ng dng rng ri trong cuc snghin i, cc cng ngh mi lin tc pht trin v lun tm c ng dng trong cc thitb, h thng k thut trong mng vin thng.

Hnh 1-1 S trao i thng tin gia hai thnh ph.

Vt mang dch v: L cc trang thit b c s dng h tr cho dch v . Vd, cp in thoi, my in thoi, tng i l nhng vt mang cho dch v thoi. Tuy


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nhin, khng phi vt mang cho dch v no th ch c th mang cho chnh dch v mcn c th mang cc dch v khc, v d cp in thoi c th mang c cc dch v nhthoi, internet, facsimile.

Hnh 1-2 Vt mang ca dch v thoi.

Dch v vin thng

Trn quan im iu hnh mng, dch v vin thng gm: Dch v c s:L cc dch v c bn c cung cp bi mng vin thng.

Dch v gi tr gia tng:L cc dch v m rng ca dch v c s, khi

ngi s dng dng dch v ny s phi np mt mc ph c th. V dtheo di t gi th trng qua mt s in thoi no , dch v hng dn,chuyn i ngn ng.

Dch v b sung phn b:L cc dch v c xy dng trn dch v

vin thng c s. V d chuyn tip cuc gi v iu kin, ch cuc gi,dch v bo thc.

Dch v b sung tp trung (dch v mng thng minh IN): IN

(Interligent Network) c thc hin trong mt mng cung cp nh v tptrung thng minh, cho php iu khin nh tuyn, tnh cc linh hot. Vd in thoi tr tin trc, in thoi bnh chn

Mt s dch v c s kt hp ca dch v mng thng minh vi dch v gi tr giatng.

Hnh 1-3 Dch v vin thng.


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Cc dch v vin thng cho ngi s dng:

Cc dng chnh ca dch v vin thng l:

Thoi.

S liu.

Video. Mutimedia.

Cc dng trn cn c chia thnh bn nhm khc nhau da vo cch thc cadch v c iu khin vi cm nhn ca ngi s dng.

Hnh 1-4 Cc nhm dch v vin thng theo cm nhn ca ngi s dng.

Dch v tng tc: bao gm cc dch v cho php truyn thng tin theo

hai hng.

Dch v nhn tin:bao gm cc dch v da trn c s lu tr thng tinm c th nghe hoc c c bi ngi nhn. Hp th thoi l mt trongnhng dch v nhn tin.

Dch v tm kim (retrieval):l cc dch v c cung cp truy cp

thng tin c lu tr trong c s d liu. Cc c quan, doanh nghipcung cp dch v thoi cho khch hng ca mnh truy cp thng tinsng qua mt s in thoi. Gi c th trng, t gi trao i, qungcol nhng dch v ca dch v thu nhn.

Dch v phn b:C hai dng dch v phn b, l thng tin mt chiu

n mt ngi nhn hoc thng tin 1 chiu n nhiu ngi nhn.

Cc yu cu mng v thit b

Thoi, d liu v video yu cu khc nhau v mng v cc thit b ca n. Thngtin quan trng trong cc yu cu l:

Bng thng.

T l li bit.

tr.

Mng vin thng

Mng vin thng l tt c cc trang thit b k thut c s dng trao ithng tin gia cc i tng s dng trong mng.

Cc thnh phn mng vin thng:


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Thit b u cui: Chuyn i tn hiu thn thuc vi con ngi thnh tnhiu c chuyn ti trong mng tu thuc li hnh dch v.

Node chuyn mch: Cung cp ni kt cho cc i tng theo yu cu, thc

hin cc chc nng:

o X l thng tin: x l, cung cp thng tin.

o

Chuyn mch.

Phng tin truyn dn: Lin kt hai thnh phn trn. tu thuc mi

trng, a hnh s dng h thng truyn dn thch hp nh cp ng, viba, v tinh, quang

Phn mm: H tr cc thnh phn trn hot ng c hiu qu.

Hnh 1-5 Cc thnh phn mng vin thng.

Chuyn mch

ITU-T nh ngha chuyn mch nh sau: Chuyn mch l s thit lp ni kttheo yu cu truyn thng tin t ng vo yu cu n ng ra c yu cu trong mttp ng vo v ng ra.

Mc ch ca chuyn mch l thit lp ng truyn thng tin qua mng theo cutrc c nh hoc bin ng. Trong mng vin thng, ty theo cch thc thit lp ni ktm ta c cc phng thc chuyn mch khc nhau.

Hnh 1-6 Chuyn mch v mng vin thng.

Thit bu cui Thit b

u cui

Nodechuynmch

Phngtin

truyndn

Phnmm


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Ngy nay, thng tin khng ch biu th ting ni m c th nghe c bi nginhn in thoi m n cn bao hm tt c cc dng thng tin ca dch v vin thng.

Trc y, chuyn mch c ngha l mt ngi iu hnh ni kt cho hai thu baoni chuyn vi nhau cn by gi th thit b chuyn mch phi c kh nng iu khinnhiu hn trc bao gm tnh a dng v cht lng ca thng tin m chuyn mch phcv. Ngoi ra, chuyn mch cn c nhng thng tin nm ngoi thng tin ca dch v ngis dng. V d thng tin c s dng bi mng gi l thng tin bo hiu cng cchuyn mch.

Cc k thut chuyn mch c pht trin trong nhng nm gn y, t ban u,chng ta c chuyn mch knh, rt ph hp vi cc dch v thi gian thc. V sau, ccthu bao yu cu cht lng tt hn, bng thng ln hn, tn dng dung lng truyn dntt hn nn cc k thut khc c ra i.

2. LCH S PHT TRIN

Cc h thng chuyn mch nhn cng

Trc y, cc h thng chuyn mch c xy dng bi cc thit b chuynmch hot ng nhn cng. H thng chuyn mch u tin c thit lp New Haven,M, nm 1878. in thoi vin nhn cuc gi v chuyn mch chng n thu bao b gibng tay. in thoi vin thit lp mt knh dn gia hai thu bao, do gi l chuynmch knh. Khi cuc gi kt thc, in thoi vin s gii phng ni kt. Chng ta c thgi in thoi vin l mt h thng iu khin.

Hnh 1-7 Chuyn mch nhn cng.

Chuyn mch nhn cng ny c nhc im l thi gian ni kt cuc gi kh lu,hiu qu chuyn mch km.

Cc h thng chuyn mch in t

Hthng chuyn mch xoayCc nm sau , cc h thng chuyn mch nhn cng c thay th bi cc h

thng chuyn mch in t. Cc h thng ny cung cp lu lng ln hn vi chi phthp hn, chun b cho s bng n ca mng vin thng trong nhng nm tip theo. Cch thng mi cn c kh nng phn b lu lng, nh tuyn tt hn qua mng truyndn, lm gim dung lng cp.


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Nm 1889, Almon B. Strowger, Kansas City, USA xy dng h thng tng i tng u tin, y l h thng tng i tng bc. Tng i ny c cc chuyn mchxoay v cc chuyn mch ny s c x l theo tng ch s a ch nhn c.

Sau l s pht trin ca h thng tng i thanh ghi, cc ch s c x ltrong thanh ghi, khng x l trc tip) nn thch hp vi dung lng tng i ln hn. uim ca iu khin thanh ghi l kh nng chn ng dn thay th, v vy, mng truyndn c th c s dng mt cch hiu qu hn.

Cc h thng ny s dng cc chuyn mch c kiu xoay v ng truyn, sau c thay th bng chuyn mch thanh cho (1937) cho dung lng cao hn, vi thigian chuyn mch nhanh hn, chnh xc hn.

Hthng chuyn mch thanh cho

Nm 1937, h thng chuyn mch thanh cho ra i. Chuyn mch thanh chochuyn thao tc xoay thnh thao tc n nn c nhng u im sau:

Thi gian chuyn mch nhanh, t li, n gin.

L c s pht trin cc h thng chuyn mch sau ny.

Cc h thng s v iu khin my tnh

Nm 1960, tng i iu khin s u tin c xy dng M Chu u lnm 1968.

H tng i ny cn c gi l tng i iu khin bng chng trnh ghi snSPC (Stored Program Control).

K thut truyn dn v chuyn mch pht trin lin tc, lm cho gi thnh thit bgim xung r rt. FDM c xut cho truyn dn thng tin ng di, k thut nyc pht minh khong nm 1910 nhng mi n nm 1950 mi c ng dng, thiim ny, 1000 knh c th c truyn trong cng mt cp ng trc.

Hnh 1-8 Tng i SPC.

Ghp knh s da trn tn hiu PCM c gii thiu khong 1970 lm cho mngtruyn dn tr nn r hn vi cng cht lng truyn dn. Gi thnh c gim hn nakhi cc chuyn mch nhm s c kt hp vi cc h thng truyn dn s. Lc ny, cch thng ny b hn ch bi cc b chuyn i tng t-s t tin. Sau , cc h thngiu khin l cc h thng my tnh, vy cc tng i by gi hon ton l thit b s.Tng i s u tin iu khin bng my tnh c a vo s dng vo nm 1960 M, cc tng i s chu u c hot ng vo nm 1968.


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Cc node chuyn mch cho thng tin d liu

Vic s dng my tnh trong vn phng, cng s cng nh trong gia nh, c nhn tr nn ph bin. Nhu cu s dng v trao i thng tin d liu pht trin mnh, dnn s phn bit gia mng chuyn mch knh v d liu. Lc ny, ngoi mng chuynmch knh ang tn ti, mt mng chuyn mch gi cng c trin khai song song,phc v cho s trao i thng tin d liu gia cc my tnh. Phng thc chuyn mch cbn l chuyn mch gi, cc bn tin ca ngi s dng c chia thnh cc gi nh richuyn i, khi n ch s c sp xp li thnh bn tin nh ban u. u im ni trica chuyn mch gi chnh l kh nng dng chung ng truyn dn.

Hnh 1-9 Chuyn mch d liu.

Cc node cho N-ISDN

Hnh 1-10 Cc node chuyn mch ISDN.

Ngi s dng cn c mt mng c th cung cp cho h c nhiu dng dch vkhc nhau (thoi ln d liu) trong khi , nh cung cp dch v cng mun c mt c sh tng chung cho cc loi hnh dch v, gim chi ph phn cng, gim chi ph bo dng,iu hnh T y bt u hnh thnh khi nim mng hi t, hi t v thit b, hi t v

cng ngh, hi t v dch v, hi t v gi cPht trin cho cc mng tch hp dch v, N-ISDN c th c xem l s kt hp

gia tng i in thoi vi chuyn mch d liu.

Cc node cho B-ISDN

Cc h thng chuyn mch trc ch p ng c mt trong hai iu kin: bngthng, thi gian thc. Trong khi , nhu cu v nhng ng dng multimedia ngy cngcao, va yu cu v bng thng rng, tr b, thay i tr b. Lc ny, B-ISDN c


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Chng 1....OVERVIEW

Trang 17

xut cung cp cc dch v yu cu bng thng v thi gian thc. C nhiu gii phpang c tiu chun ho (ATM, MPLS).

Hnh 1-11 Nhu cu bng thng.

Chuyn mch quang

Hnh 1-12 S pht tri

n ca cc h thng chuyn mch.

Kh khn ca chuyn mch l bng thng b hn ch. Ngy nay, chng ta cnhu cu trao i thng tin vi tc bit rt cao (hng Gbps) trn h thng truyn dnquang, tuy nhin, trong thit b chuyn mch th chng ta phi chuyn i qua tn hiuin m th tc bit l kh thp.


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Sau , s dng chuyn mch quang vi iu khin chuyn mch in t l mtbc qu tin ti mt h thng chuyn mch ton quang.

3. CC PHNG THC CHUYN MCH

Chuyn mch knhL loi chuyn mch phc v s trao i thng tin bng cch cp knh dn trctip gia cc i tng s dng.

Hnh 1-13 Chuyn mch knh.

X l cuc gi tin hnh qua 3 giai on:

Thit lp ng dn da vo nh cu trao i thng tin.

Duy tr knh dn trong sut thi gian trao i thng tin.

Gii phng knh dn khi i tng s dng ht nhu cu trao i.

c im:

Thc hin trao i thng tin gia cc user trn trc thi gian thc.

Cc user lm ch knh dn tng sut qa trnh trao i.

Hiu sut thp.

Yu cu chnh xc thng tin khng cao.

Ni dung trao i khng mang thng tin a ch.

Ph hp vi dch v thoi.

Khi lu lng tng n ngng no th cuc gi mi c th b kho,

mng t chi mi yu cu kt ni mi n khi c th.

Chuyn mch tin

L loi chuyn mch phc v s trao i thng tin gia cc bn tin nh in tn,th in t, file

Thit b u cui gi n node chuyn mch bn tin mang thng tin a ch ch.

Ti y, bn tin c thu nhn, x l (chn ng) ri sp hng ch truyn i.Phng php ny gi l store and forward.

Trong phng php store and forward ny, lun c tr khi chuyn gi ti ch.Thi gian tr ti mt node:


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Chng 1....OVERVIEW

Trang 19

tdelay=tnhn+tx l+tsp hng.

Hnh 1-14 Chuyn mch tin.

c im:

Khng c mi lin h thi gian thc gia cc user.

Knh dn khng dnh ring cho cc user (dng chung ng truyn).

Hiu sut cao.

Yu cu chnh xc.

Ni dung c a ch.

p dng cho s liu.

Vn chp nhn cuc gi mi trong khi lu lng mng ang cao.

Chuyn mch gi

Hnh 1-15 Chuyn mch gi.

Trong cc mng chuyn mch gi, thng tin c truyn cho cc gi vi kchthc khc nhau. Vy, nhim v ca cc nodes l phn b cc gi n ni thu. Mi nodesc trng a ch ca mi gi v nh tuyn gi n tuyn thch hp.

a ch

Bn tinngi s

dng

Thit bu cui Thit b

u cui

Node chuynmch

a ch

Bn ti

nngi s

dng

Thit bu cui Thit b

u cui

Node chuy nmch

Gi


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Mi gi i qua cc node c tin hnh theo phng php store and forward nhchuyn mch tin.

Ti u thu tin hnh sp xp cc gi tr li.

c im:

Trao i thng tin khng theo thi gian thc nhng nhanh hn chuyn

mch tin.

i tng s dng khng lm ch knh dn.

Hiu sut cao.

Thch hp truyn s liu.

Vic kim tra li tng chng l m bo gi truyn khng li nhng lilm gim tc truyn gi qua mng.

Bng thng thp, tc thp.

Ph hp vi mng truyn dn cht lng thp.

Trong cc gi lun c trng kim tra m bo gi truyn khng liqua tng chng.

Chuyn mch khung

Hnh 1-16 Chuyn mch gi v chuyn mch khung trong cng mt mng


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Trang 21

Frame Relay l k thut chuyn mch c pht trin vi tng kt hp cachia x bng thng ging nh chuyn mch gi nhng vi tc cao hn v tr t hnnh trong chuyn mch knh.

Tc ca frame relay cao hn l nh vo phng thc iu khin n gin,khng ch tm n vic iu khin li.

Nh vo iu ny, lu lng c iu khin nhanh hn, Frame Relay chuyntip qua node nhanh hn chuyn mch gi khong 2ms. Mt s l gii khc ca tc cao ca Frame Relay l chuyn mch c b tr rng hn trong mi nodes.

Mng Frame Relay c th c xy dng theo nhiu cch, thng thng l ni ktvnh vin gi l knh o vnh vin (PVC Permanent Virtual Circuit). Cc knh o chuynmch (SVC Switched Virtual Circuit) cng cng c th c ni chung trong tng lai.Frame Relay cn c th thc hin mt mng chuyn mch gi ring.

c im:

Hn ch chc nng kim tra li v iu khin lung.

Tc truyn dn c ci thin ng k so vi chuyn mch gi.

Hot ng ch yu lp 2, vi mc ch ln nht l to mng ring oVPN (Virtual Private Network) cho khch hng.

Bng thng khng c nh cho user m c phn phi mt cch linh hot.

Phc tp do tc bit thay i.

Kh nng n 40Mbps so vi 2Mbps ca chuyn mch gi.

Chuyn mch t bo

Khi yu cu bng thng v thi gian thc ca mt s dch v c nng cao thcc loi chuyn mch k trn khng p ng c. gii quyt vn ny c nhiu giiphp c xut. Mt trong nhng gii php ni tri, l chuyn mch t bo.

Chuyn mch t bo th chia bn tin thnh cc t bo (cell) c kch thc nh vc nh. Cc t bo ny c nh tuyn ngun v nh vy, khi n i qua cc node trongmng th ch tin hnh tra bng ri chuyn tip. ng dn t ngun n ch cxc nh bi node chuyn mch u vo. Vic xc nh ng dn ny c th da trnmt s tham s yu cu ca khch hng.

Hnh 1-17 C s chuyn mch ATM

Trong mt chuyn mch ATM, cc t bo c chuyn t mt knh logic ng von mt hoc nhiu knh logic ng ra. Mt knh logic c ch th bng s kt hp cahai nh danh:

S tuyn vt l.


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nh danh knh - nh danh ng dn o (VPI) v nh danh knh o(VCI) trn mt tuyn vt l.

Chuyn mch cc t bo qua mt node ATM yu cu s kt hp cht ch gia ccnh danh ca cc knh logic ng vo v ng ra.

Trong mng ATM, cc nh danh ca cc knh logic tng ng vi cc khe thi

gian. nh danh kt hp hai gi tr vo trong header ca t bo, l trng VPI v VCI xc nh mt knh logic.

u im:

X l nhanh.

Chuyn tip nhanh.

Tc t n 600Mbps.

Kh nng phc v cc dch v tc bit thay i v c nh.

Tnh thi gian thc hng n chuyn mch knh.

Chuyn mch nhn a giao thcInternet ang pht trin rt mnh v l iu khng th thiu trong cuc sng hin

ti. T , cc dch v mi a s u p dng trn IP (Internet Protocol). Tuy nhin,Internet ang gp tr ngi v thi gian thc v bng thng, kh khn trong vic m boQoS cho ngi s dng. Gii php IP over ATM c xut nhng cng gp kh khntrong k thut.

Chuyn mch nhn a giao thc MPLS (Multiple Protocol Label Switching) ngin ho vic chuyn tip cho cc router bn trong. Cng nh ATM, chuyn mch nhna giao thc c s dng nh tuyn ngun, cc router bin thc hin nh tuyn v ccrouter trung tm ch thc hin chuyn mch, ng thi c kh nng kt hp vi mi giaothc lp mng hin nay cng nh cc giao thc lp thp hn. u im ca MPLS:

Tc nh ATM.

Gi thnh r.

n gin.

Chuyn mch quang

Chuyn mch knh ln chuyn mch gi u c s dng trong cc mngthng tin quang. Do nh ngha trc cu hnh chuyn mch trong chuyn mch knh nniu khin chuyn mch c th c n gin ha v khng cn thit phi x l theo thigian thc. Do , chuyn mch knh l s la chn hng u trong truyn thng quang,trong , cc tc truyn dn l rt cao.

Mt khc, trong chuyn mch gi, khi cc tc truyn dn cng cao th thi giangi n cng ngn. Nh vy, yu cu thay i trong cu hnh chuyn mch cng tr nnkh khn. V d, khi chuyn mch ln th tc chuyn mch s b gii hn bi dunglng bus ni.

Khi xt chuyn mch photon, b m gi trong chuyn mch gi li ny sinh mtvn na. Bi v cc photon khng th c lu nh cc electron (ngha l photonkhng c khi lng tnh) nn kh khn trong vic m cc photon nhiu hn l cho quacc ng dy tr. Nh vy, nhiu thit k chuyn mch gi m s dng b m gimxc sut nghn l khng th d dng trin khai trong chuyn mch photon.


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Chng 1....OVERVIEW

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Hnh 1-18 Chuyn mch photon WDM 4x4.

Xt chuyn mch photon ghp knh phn chia bc sng WDM (wavelengthdivision multiplexing) s dng b ghp ni sao (star coupler) nh Hnh 1-18. Mt bghp ni sao l mt thit b quang nhiu cng m ghp mt s tn hiu ng vo, trnchng mt cch ng nht v phn b chng n tt c cc u ra. Trong kin trc ny,b lc quang c s dng chn lc mt trong cc tn hiu ng vo c bc sng i.

Trong phng thc ny, tn hiu c chuyn mch theo bc sng ca n. Nuta mun tng kch thc chuyn mch th ta ch tng s knh bc sng. Bi v b lcng ra c th chn bt k ng vo nn chuyn mch WDM ny khng xy ra nghn niv gn ging nh chuyn mch thanh cho.

Hai nhc im chnh l suy hao cng sut khi kch thc chuyn mch tng vcn cc ngun sng v cc b lc c kh nng thay i.

4. GII THIU TI LIU THAM KHO [JOHN79] John Bellamy.Digital Telephony. John Wiley and Sons, 1979.

[MAX96] Max Ming Kang Liu. Principles and applicaions of optical

communications. McGraw-Hill Companies, Inc., 1996

Cc trang web:

http://www.shore.net/~ws/DCC5e.html

http://www.soc.hawaii.edu/conlcom-resources.html

http://www.internic.net/ds/dspgol.html

http://www.ericsson.com/support/telecom/book-index/index.shtml


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2. CHUYN MCH KNHT khi pht minh ra my in thoi, chuyn mch knh tr thnh mt k thut ni

tri trong vic truyn thng thoi v n vn cn rt hu hiu trong k nguyn mng stch hp hin nay. Chng ny trc ht gii thiu mng chuyn mch v sau trnhby cc c trng chnh trong mng chuyn mch knh.

1. MNG CHUYN MCH

truyn d liu n mt ni no , th thng tin phi c truyn t ngun nch qua mng vi cc node chuyn mch trung gian, vic thit k cc mng chuyn mchnh vy thng c s dng trong cc mng LAN hoc MAN. Cc node chuyn mchkhng quan tm n ni dung ca d liu, m mc ch ca chng l cung cp mt

phng tin chuyn mch m chuyn d liu t node ny sang node khc cho n khi tich. Hnh 2-1 m t mt mng chuyn mch n gin. Cc thit b u cui mun truynthng c xt nh cc trm. Cc trm c th l cc my tnh, cc thit b u cui hoccc in thoi hoc cc thit b truyn thng khc. Ta s xt cc thit b chuyn mch vimc ch cung cp kh nng truyn thng nh cc node ni vi cc tuyn truyn dn theomt hnh nht nh. Mi trm cng vi cc node v tng hp cc node c xem nhl mt mng chuyn mch.

Hnh 2-1 V d mt mng n gin

1

2

3

6 5

4

A

G

B

C

D

ETrm u

cui

Node chuynmch

Tuyntruyn dn


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Dng thc ca cc mng ny c trnh by trong chng ny v cc chng tiptheo gi l cc mng truyn thng chuyn mch. D liu a vo mng t mt trm ucui c ni n ch bi cc chuyn mch t node ny n node khc. V d nh trongHnh 2-1, d liu t trm A n trm D bng cch gi n node 1 ri c th n node 3ri node 4 n trm D. Ta thy rng:

1. C nhng node ch ni vi node khc, v d node 5, nhim v cachng l chuyn mch qu giang (chuyn mch bn trong trong mng) cho dliu.Cc node khc c mt hoc nhiu trm c ni vi chng, ngoi chc nngchuyn mch ca chng cn thu nhn v pht i d liu n cc trm c ni.

2. Cc tuyn ni gia node ny vi node khc thng c ghpknh, s dng k thut ghp knh phn chia theo tn s FDM hoc ghp knh

phn chia theo thi gian TDM.

3. Thng thng, mng khng c ni kt hon ton, ngha l khngthc hin vic ni trc tip tng i mt gia cc node vi nhau. Tuy nhin,chng thng c nhiu hn mt ng dn c th qua mng, iu ny tng cng tin cy ca mng.

Hai k thut khc nhau c s dng trong cc mng din rng l chuyn mchknh v chuyn mch gi. Hai k thut ny khc nhau v cch thc chuyn mch thngtin t tuyn ny n tuyn khc t ngun n ch. Chng ny, chng ta s ni nchuyn mch knh, chng tip theo l chuyn mch gi v cc chng sau na s bnn cc phng thc pht trin khc ca chuyn mch gi nh Frame Relay, ATM

2. CC MNG CHUYN MCH KNH

Vic truyn thng qua mng chuyn mch knh ng mt s n nh ng dnthng tin gia hai trm u cui. ng dn ny lin quan n mt chui cc tuyn lintc gia cc node khc nhau. Trn mi tuyn vt l, cc knh logic c n nh cho mt

ni kt. Vic truyn thng qua mng chuyn mch knh bao gm 3 giai an:1. Thit lp knh dn: Trc khi tn hiu c th c truyn, knh dn t u

cui n u cui phi c thit lp. V d trong Hnh 2-1, trm A giyu cu n node 1 yu cu mt ni kt n trm D. Lc ny, gia A v1 c dnh ring mt ng dn, node 1 tm n node cui l node 4, lnode ni vi trm D, da vo thng tin nh tuyn vi cc tham s nh chi

ph, di l trnh, node 1 s chn ng dn n node 3 phn bmt knh ri (s dng ghp knh phn chia theo tn s FDM hoc ghpknh phn chia theo thi gian TDM) trn tuyn gi thng ip yu cun trm D. Nh vy, ng dn dnh ring phi c thit lp t A qua 1n 3, v node 3 s n nh mt knh n node 4, node 4 ni vi trm Dto thnh mt ni kt. Ni kt hon thnh vi mt s kim tra trng thica trm D l bn hay sn sng cho vic trao i.

2. Truyn d liu: Thng tin by gi c th c truyn t A qua mng nD. D liu c th l tng t hoc s ty theo mi trng mng. Khi ccvt mang l cc mng s tch hp th vic s dng truyn dn s cho ccdch v thoi cng nh d liu l u im. ng dn gia A vi 1 gi ltuyn, ng dn gia 1 n 3, 3 n 4 gi l knh v t 4 n D gi ltuyn. Trong trng hp tng quan th cc ni kt u l song cng.


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3. Gii phng knh dn: Sau giai an truyn d liu, ni kt c kt thcbi mt trong hai trm u cui, tn hiu c truyn trn ng dn gii phng b nhng ti nguyn c n nh.

Ch rng ng dn phi c thit lp trc khi truyn d liu. Nh vy, dunglng knh phi c d tr gia cc cp node ca ng dn v mi node phi c khnng chuyn mch chuyn tip x l ni kt yu cu. Chuyn mch phi c tnh thngminh phn b v sp xp ng dn qua mng.

Chuyn mch knh c hiu qu km, dung lng knh c phn b trong sutthi gian hot ng ca ni kt, thm ch l khi khng c d liu c tryn. Vi mt nikt cho thoi, s dng c th rt cao nhng vn khng th t c 100%. Vi ni ktn my tnh, dung lng c th ri trong hu ht thi gian kt ni, vi s phn b dunglng nh trn l khng hiu qu. Trong khi hot ng, c nhng khong thi gian trtrong vic truyn bo hiu thit lp ni kt, nhng n khi ni kt c thit lp thmng l trong sut i vi ngi s dng. Thng tin c truyn tc c nh vkhng tr hn trn truyn dn qua cc tuyn, tr ti cc node l khng ng k.

Chuyn mch knh c pht trin kim sot lu lng thoi, nhng n thi

im by gi, chng cn c s dng truyn d liu. V d thng dng ca chuynmch knh l mng chuyn mch thoi cng cng (Hnh 2-2), l s chn la ca ccmng quc gia ni vi cc dch v quc t. Mc d mong mun c bn l thc hin chocc thu bao dch v thoi tng t, nhng mng cn kim sot nhiu lu lng d liuqua modem v ln dn sang mng s. ng dng ph dng ca chuyn mch knh l cctng i nhnh ring PBX (Private Branch Exchange), PBX c s dng ni ktccmy in thoi trong mt ta nh hay mt cng s. Chuyn mch knh cn c sdng trong cc mng ring, ni cc chi nhnh hoc cc t chc li vi nhau, chngthng gm cc h thng PBX ti mi ni v c ni vi nhau bi cc ng thu knhring (leased line) qua mt hoc nhiu nhcung cp dch v nh AT&T. V d cui cngv ng dng ca chuyn mch knh l chuyn mch d liu. Chuyn mch d liutng t nh PBX nhng c thit k ni kt cc thit b x l d liu s vi nhau

nh cc thit b kt cui hay cc my tnh.

Hnh 2-2 Mng chuyn mch in thoi cng cng

Mng vin thng cng cng c th c m t vi bn thnh phn mng nh sau: Cc thu bao: L cc thit b c gn vi mng, cc thu bao thng l

cc my in thoi tng t nhng t l phn trm s tng theo tng nmsang cc thu bao d liu s.

Mch vng ni ht (local loop): L tuyn ni gia thu bao v mng,chng cn c gi l mch vng thu bao. Cc mch vng ni ht thngs dng cp xon ng trc, di khong vi km n vi chc km.


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Cc tng i: L cc trung tm chuyn mch trong mng. Mt trung tmchuyn mch m h tr trc tip cho cc thu bao gi l tng i ni ht(tng i cui), mt tng i ni ht c th h tr cho hng ngn thu baotrong khu vc. M c hn 19000 tng i ni ht v nh vy, ngha lkhng thc t khi ta ni trc tip t tng i ni ht ny n tng i niht kia v s ng trung k l khong 2.108ng dy l rt ln. Lc ny,

cc tng i qu giang c s dng. Cc ng trung k: Ni gia cc tng i vi nhau. Trung k mang nhiu

knh thoi c ghp vi nhau theo tn s FDM hoc thi gian TDM.

Cc thu bao ni trc tip n cc tng i ni ht, cc tng i ni ht c nhimv chuyn mch lu lng gia cc thu bao hoc gia thu bao vi cc tng i khc.Cc tng i ny thc hin vic nh tuyn v chuyn mch cho cc tng i vi nhau. ni kt cho hai thu bao ca cng mt tng i th mt knh dn c thit lp giachng v nu hai thu bao thuc hai tng i khc nhau th knh dn gia chng bao gmmt chui cc knh dn qua mt hoc nhiu tng i trung gian. Nh trong Hnh 2-3, nikt c thit lp gia ng a v ng b qua tng i ni ht. Ni kt cho ng c vng d th phc tp hn nhiu. Trong tng i ni ht ca c, mt ni kt c thit lp

gia c v mt knh trn ng trung k TDM n tng i trung gian. y, knh nyli c ni vi mt knh khc thuc ng trung k ni vi tng i ni ht ca thubao d. Tng i ni ht ca thu bao d s ni knh ny vi ng dy.

Hnh 2-3 Thit lp knh dn.

K thut chuyn mch knh c xut pht t nhng ng dng thoi. Mt trongnhng yu cu chnh ca lu lng thoi l phi thc s khng c truyn dn v mbo khng c s thay i tr (trt). Mt tc truyn dn tn hiu khng i phic duy tr v bn thu cng nh bn pht phi c cng mt tc truyn dn. Cc yu

cu ny l cn thit cho php m thoi ca con ngi. Hn na, cht lng tn hiuthu nhn phi c th hiu c mc ti thiu.

Chuyn mch knh tr nn rng ri, ph bin bi v n thch hp vi victruyn dn tn hiu thoi tng t. Trong thi i s hin nay, th chuyn mch knh rrng khng th p ng v thiu hiu qu. Mc d chuyn mch knh l thiu hiu qunhng n vn l s chn la cho cc mng cc b cng nh cc mng din rng. Mttrong nhng th mnh ca chuyn mch knh chnh l tnh trong sut, l khi mt nikt c thit lp th n l mt ng ni trc tip t hai trm u cui hon ton vtl.

Tng ini hat

Tng ini hat

Tng i

qu giang

a

b

c

d

Trung k

Trung k


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3. NI DUNG CHUYN MCH

Cng ngh chuyn mch knh c tip cn tt nht bng vic xem xt hot ngca mt node chuyn mch n. Mng c xy dng xung quanh mt node chuynmch n gm mt tp hp cc trm gn vi mt n v chuyn mch trung tm. Chuynmch trung tm thit lp ng dn phn b gia hai thit b bt k mun trao i thng

tin. Hnh 2-4 m t cc thnh phn chnh ca mng mt node chuyn mch. Cc nggch t bn trong chuyn mch biu th cc ni kt hin hnh.

.

Hnh 2-4 Cc thnh phn ca mt node chuyn mchTri tim ca mt h thng hin i chnh l chuyn mch s. Chc nng ca

chuyn mch s l cung cp mt ng dn tn hiu trong sut gia cc cp thit b ucui. ng dn l trong sut bi v ni kt ni trc tip gia hai thit b. Thng thng,cc ni kt ny l song cng.

Thnh phn giao tip mng i din cho cc chc nng ca phn cng cn thit ni cho cc thit b s nh cc thit b x l d liu hoc cc my in thoi s vi mng.Cc in thoi tng t cth c ni vi mng nu giao tip mng c cha b chuyni tn hiu tng t sang tn hiu s. Cc ng trung k n cc chuyn mch s khccung cp cc tuyn ghp knh cu thnh mng.

Chuyn mch phn chia khng gian (Space Division Switching)

n v iu khin tin hnh 3 chc nng chnh, u tin, chnh l chc nng thitlp ni kt, y chnh l chc nng hot ng theo yu cu ca thit b c ni vi tngi. thit lp c ni kt, n v iu khin phi c kh nng kim sot v pht hinc nhu cu, xc nh ng dn qua chuyn mch ti ch nu u cui l ri. Chcnng th hai l n v iu khin phi duy tr ni kt. Bi v chuyn mch s s dngnguyn l ghp knh phn chia thi gian v iu ny c th yu cu thao tc lin tc lnchuyn mch nhng cc bits truyn thng phi c chuyn mt cch trong sut. Chc

n v iu khin

Chuyn mch s

Giaotimn

Cctuynn

isongcngnccthitb


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nng th ba l gii phng ni kt, ni kt s c gii phng khi n v iu khin xcnh nhu cu t mt trong hai thit b u cui tham gia vo cuc trao i.

Hnh 2-5Chuyn mch phn chia khng gian.

c trng quan trng ca thit b chuyn mch knh l nghn hay khng nghn.Nghn xut hin khi mng l khng th ni kt cho hai trm vi l do l tt c cc ngdn u ang c s dng. Mng nghn l mng nm trong kh nng ni trn, do ,mng khng nghn cho php tt c cc trm c th ni tng i n tt c cc trm khc

theo yu cu min l cc trm ang ri. Khi mng ch h tr cho lu lng thoi thcu hnh nghn l c th chp nhn v cc cuc gi c thi gian chim gi kh ngn nnch c th nghn trong mt thi im no . Tuy nhin, vi cc thit b x l d liu thc th lkhng ph hp. Trong trng hp ny, mng c cu hnh khng nghn hocgn khng nghn c th tha mn c cht lng dch v yu cu.

Ta tr li xem xt hot ng chuyn mch knh trn mt node chuyn mch n.

Chuyn mch phn chia theo khng gian l dng chuyn mch c pht trin tnguyn bn cho mi trng tng t c thc hin sang lnh vc s. Nguyn l c bnl ging nhau, trong , chuyn mch c s dng mang tn hiu tng t hoc s.

Nh tn gi ca n, chuyn mch phn chia theo khng gian c nhng ng dn tn hiuc phn chia mt mt cch vt l (phn chia khng gian). Mi ni kt yu cu thit lp

ng dn vt l qua chuyn mch c n nh ring truyn dn tn hiu gia haiim cui. Cu trc c s ca chuyn mch l im thng bng kim loi hay cng in tm c th cho php hoc khng cho php tn hiu i qua c iu khin bi n v iukhin.

Hnh 2-5 cho ta mt ma trn chuyn mch n gin vi 10 ng I/O song cng.Ma trn c 10 ng vo v 10 ng ra, mi trm c ni vi ma trn qua mt ng vo vmt ng ra. Ni kt c thc hin qua im thng thch hp, trong ma trn ny yu cu100 im thng.


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Hnh 2-6 Chuyn mch 3 tng.

Chuyn mch thanh cho c mt s gii hn sau:

S im thng nhiu (nhiu nht l bng tch s ng vo v ng ra) th chi

ph chuyn mch ln.

Suy hao ti im thng khin gia hai thit b gn vi hai ng giao nhauti im thng c ni kt km.

Cc im thng c hiu qu s dng km, thm ch khi tt c cc thit b

u cui l hot ng th ch mt phn nh cc im thng l m. khc phc iu ny, cc chuyn mch nhiu tng c p dng. Hnh 2-6 biu

din mt chuyn mch 3 tng. Vic phn chia chuyn mch thnh nhiu tng mang linhiu li im hn so vi chuyn mch n tng:

S im thng gim, tng hiu qu s dng thanh cho. Trong trng hp

ny, s im thng ni cho 10 trm t 100 gim xung cn 48.

C nhiu ng dn qua mng ni vi hai im cui hn so vi chuyn

mch n tng, iu ny lm tng tin cy.

Tt nhin l chuyn mch a tng yu cu s iu khin phc tp hn. thitlp mt ng dn trong chuyn mch n th n ch cn m mt im thng no , cn

trong chuyn mch a tng th ng dn thng qua cc tng phi c xc nh v nhiucng tng ng phi c m.

Nghn c th xy ra trong chuyn mch nhiu tng, ta c th thy rng chuynmch nh trong Hnh 2-5 l loi chuyn mch khng nghn, ngha l ng dn lun cth ni gia bt k ng vo no n ng ra no. Cn i vi chuyn mch nhiu tng nhtrong Hnh 2-6 th gi s vi cc ng nt m biu th trng thi ang hot ng cacc ng vo v cc ng ra th ng vo 10 khng th ni vi cc ng ra 3, 4, 5 v thm chn nhng ng ra khc. Chuyn mch a tng c th lm cho khng nghn bng cch


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tng kch thc hoc s lng cc tng chuyn mch trung gian, nhng iu ny nggnha vi vic tng chi ph.

Chuyn mch phn chia theo thi gian (Time Division Switching)

Cng ngh chuyn mch c lch s pht trin kh l lu i, hu ht cc cngngh xut pht t k nguyn ca tn hiu tng t. Khi k thut s ha tn hiu thoi v

ghp knh phn chia theo thi gian pht trin th c d liu ln thoi u c truyn dng tn hiu s, iu ny dn n s thay i nguyn l trong thit k v cng ngh cacc h thng chuyn mch. Thay v s dng cc h thng phn chia khng gian th cc hthng s thay bng cc thnh phn phn chia theo khng gian v thi gian.

Gi s rng mi chuyn mch knh hin i u s dng k thut phn chia thigian cho vic thit lp v duy tr cc knh. Chuyn mch phn chia theo thi gian baogm cc dng bit tc thp (trong cc khe) kt hp thnh mt dng bit tc cao cchuyn i bi b iu khin logic chuyn d liu t ng vo n ng ra. hiuc chuyn mch phn chia theo thi gian, ta xt chuyn mch bus TDM nh sau.

Chuyn mch bus TDM cc chuyn mch s khc da trn k thut ghp knhphn chia theo thi gian ng b TDM (Time Division Multiplexing). K thut TDM

cho php nhiu dng bit tc thp dng chung mt ng truyn tc cao. Tp hpcc ng vo c ly mu lun phin. Cc mu c sp xp lin tc vo trong cc khethi gian dng khung tun hon ca cc khe vi s khe trn mt khung bng s ngvo. Mt khe c th l 1 bit, 1 byte hoc mt khi di hn. iu quan trng trong TDMng b l ngun v ch d liu phi bit v khe thi gian ca nhau. Do , khng cn

phi xc nh cc bit trong mi khe.

Hnh 2-7 Chuyn mch bus TDM.

Hnh 2-7 biu din n gin v k thut ny. Mi thit b gn vi chuyn mchqua ng dy dn song cng. Cc ng dy ny c ni vi cc cng iu khin n

n v iu khin

Giaotim

n

Cctuynnisongcngnc

cthitb

Chu

nmchs


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bus s tc cao. Mi ng dy c gn mt khe thi gian cho ng vo a n.Trong thi gian ca mt khe thi gian, cng ca ng dy c m, cho php t dliu nh a vo bus. Trong khong thi gian ny, cc cng ca ng dy kia cng cm n ng ra. Nh vy, trong thi gian ca mt khe thi gian, d liu c chuyn tng dy ng vo n ng dy ng ra. Trong nhng khe thi gian khc, chuyn mchcng thc hin cho mt cp ng vo v ng ra khc dng chung bus tc cao.

Xt s thc hin khng nghn nh trong Hnh 2-7. Vi chuyn mch c htr, v d 100 thit b phi c 100 khe thi gian tng ng, mi khe thi gian c gnvi mt ng vo v ng ra. S lp i lp li ca tt c cc khe thi gian gi l khung. Vicgn ng vo c th c nh, ng ra c th thay i theo ni kt. Khi bt u mt khe thigian, ng vo c th chn mt cm d liu vo trn ng dy m n s truyn n ccng ra xc nh.

Nh vy, khe thi gian phi bng thi gian truyn d liu ca ng vo + trtruyn dn qua bus gia ng vo vi ng ra v ng nht cc khe thi gian thchiudi ca khe thi gian c nh ngha bng thi gian truyn dn + tr truyn dn cabus t u cui n u cui.

Tc bus phi ln c th khi phc chnh xc cc khe. V d, xt mt hthng ni kt cho 100 ng dy song cng c tc 19.2kbps. D liu ng vo cm ti cc cng. Mi b m phi c xa bng cch m cng nhanh ngn schng chp. Nh vy, tc d liu trn bus trong v d ny phi ln hn 1.92Mbps. Tc d liu tht ca d liu phi ln tnh ton d phng cho tr truyn dn.

Hnh 2-8 iu khin chuyn mch bus TDM.

Cc xem xt trn xc nh dung lng mang lu lng ca mt chuyn mchnghn, trong , khng c vic gn c nh cc ng dy ng vo vi cc khe thi gian

1

2

3

4

5

6

132546

315264

B nh iukhin

iu khin

logic


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m chng c phn b theo yu cu. Tc d liu trn bus cho bit c cao nhiu nikt c th c tin hnh trong cng mt thi im. Vi mt h thng c 200 thit b tc 19.2kbps v bus c tc l 2Mbps th khong mt na thit b c th c ni mt thi im bt k.

S chuyn mch bus TDM c th cung cp cho cc ng dy vi cc tc d liu khc nhau. V d, nu mt ng dy tc 9600bps ly mt khe ttrn khung thdy 19,2kbps s ly 2 khe trn khung. Tt nhin, ni kt ch c th c thit lp trn ccdy cng tc .

Hnh 2-8 l v d v iu khin chuyn mch bus TDM. Gi thit thi gian truyntrn bus l 0.01s. Thi gian ca mt khung l 30.06s gm 6 khe thi gian, mi khe thigian 5.01s.B nh iu khin ch th cng c m trong thi gian ca khe thi gian.Trog v d ny, b nh gm 6 nh. Chu k iu khin ca b nh l thi gian cakhung (30.06s). Trong khe thi gian th nht, cng vo l 1 v cng ra l 3 c phpm cho d liu i t thit b 1 qua bus n thit b 3. Tng t nh vy, ta c s ni ktcho cc cp 2-5, 3-6, 3-1, 5-2 v 6-4 trong cc khe thi gian tip theo. Nh vy, chuynmch thc hin s trao i thng tin cho cc cng 1-3, 2-5 v 4-6.

4.NH TUYN CHO CC MNG CHUYN MCH KNH

Trong mt mng chuyn mch knh ln, nhiu ni kt s yu cu mt ng dnbao gm nhiu chuyn mch. Khi cuc gi c khi xng, mng phi xc nh mtng ni qua mng t thu bao ch gi n thu bao b gi thng qua vi chuyn mchv cc ng trung k. C hai yu cu chnh cho cu trc ca mng thc hin chin lcnh tuyn l hiu qu v co gin. Yu cu u tin m t vic ti thiu ha thit b(chuyn mch v cc trung k) trong mng kim sot lng ti trong mng. Ti yucu thng c biu din bi thut ng ti lu lng gi bn, l lng ti trung bnhtrong gi bn trong ngy. Trn quan im chc nng, l nhng chc nng thit yu kim sot lng ti, trn quan im gi thnh l vic tithiu ha thit b s dng.Vi

yu cu th hai l tnh co gin, c nhng trng hp mng qu ti mt thi im no, th mng phi c kh nng cung cp lp dch v hp l cc chuyn mch v cctrung k c th vn hot ng c trong trnh trng nh vy trong mt khong thi giannht nh.

tng chnh ca chin lc nh tuyn l xc nh bn cht ca vic cn bnggia tnh hiu qu v tnh co gin. Theo truyn thng, chc nng nh tuyn trong ccmng vin thng cng cng l phi n gin. Mng thng c cu trc cy hoc th bc,mt ng dn c tin hnh bng cch khi u t thu bao ch gi, theo cy ca nodeu tin, sau n cy ca th bao b gi. tng thm tnh n hi ca mng, thngthm vo cc ng trung k c s dng cao i qua cu trc cy ni cc tng i clu lng ln gia chng. Vic thm cc ng trung k c s dng cao cung cp

d phng v dung lng b sung cho mng, tuy nhin, n li lm gim tnh hiu qu vgii hn c n hi. Bi v s nh tuyn ny khng c kh nng thch hp vi cctnh trng thay i, mng phi c thit k tha mn cc yu cu c th. V d l ccgi bn cho lu lng t ng sang ty v lu lng t bc xung nam l khng trngnhau, mi lu lng a yu cu khc nhau vo h thng. iu ny lm cho s phn tchnh hng cacc s thay i ny tr nn kh khn, dn n qu tm, khng gii hn vkhng hiu qu. Trong vn n hi, cu trc th bc c nh vi s b sung cc ngtrung k c th tr nn yu km v d b s c.


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xt cc yu cu pht trin trn cc mng vin thng, cc nh cung cp khngs dng cu trc th bc c nh na m chuyn sang cu trc ng. Phng php nhtuyn ng l mt phng php quyt nh ng dn theo trnh trng lu lng hinhnh. V d cc node chuyn mch knh thng c mi quan h ngang cp hn l thbc, cc node thng c dung lng v thc hin cc chc nng nh nhau. Vi kin trcnh vy, nh tuyn l phc tp v linh hot hn. Phc tp hn bi v cu trc khng

cung cp mt ng dn bn cht trong tp hp cc ng dn nh da trn cu trcth bc nhng n linh hot hn v c nhiu ng dn lun phin hn.

Hai thut tan nh tuyn ng c thc hin l nh tuyn lun phin v nhtuyn thch nghi.

nh tuyn lun phin:

Hnh 2-9 nh tuyn lun phin vi chuyn mch ngun X v chuyn mch ch Y.

Bn cht ca nh tuyn lun phin l cc ng dn c th c s dng gia haitng i l c nh ngha trc. Chuyn mch ngun chu trch nhim chn ng dnthch hp cho mi cuc gi. Mi chuyn mch c xc nh mt tp cc ng dn chin lc trc cho mi ch trong trt t u tin ca n. S chn la u tin l mt nikt trung k trc tip gia hai chuyn mch. Nu ng trung k ny l khng c khnng th la chn th hai c tin hnh th v c nh th. Th t ng dn (th t


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ng dn c th) da vo s phn tch trn cc mu lu lng trong qu trnh trcv c thit k ti u vic s dng ti nguyn mng.

Nu ch c th t ng dn c nh ngha cho mi cp ngun ch th s c gi l s nh tuyn lun phin c nh. S khc bit ca tp hp cc ng dnc lp chin lc trc c s dng trong cc khong thi gian khc nhau lynhng u im ca cc mu lu lng khc nhau trong nhng khong thi gian khcnhau v cc thi im khc nhau trong ngy. Nh vy, vic quyt nh ng dn datrn trng thi lu lng hin hnh (lun phin ng dn nu) v cc mu lu lng c(xc nh th t ng dn c xt).

V d nh trong Hnh 2-9. Chuyn mch ngun X c 4 ng dn c th ni nchuyn mch ch Y. ng dn trc tip (a) lun c xt u tin. Nu trung k ny lkhng sn sng (bn hay khng th phc v) th nhng ng khc s c xt trong mtth t c th ty theo khong thi gian. V d nhng ngy trong tun v bui sng thng dn b c xt tip theo.

Mt dng ca k thut nh tuyn lun phin ng c xy dng bi BellOperating Companies cung cp dch v in thoi ni ht v vng gi l nh tuyn a

lun phin MAR (multialternative routing). Phng php ny cn c s dng biAT&T trong cc mng ng di gi l nh tuyn khng th bc ng DNHR (dynamicnon-hierarchical routing).

nh tuyn thch nghi

S nh tuyn thch nghi c thit k cho php chuyn mch tc ng tis thay i cc mu lu lng trong mng. S nh vy yu cu chi ph qun l lnnh cc chuyn mch trao i thng tin bit cc trng thi ca mng. Tuy nhin, so vis lun phin th s thch nghi c tim nng ti u hn trong vic s dng tinguyn mng.

Qun l lu lng ng DTM (dynamic traffic management) l kh nng nhtuyn c pht trin bi Northern Telecom v c s dng trn cc mng ni ht v

quc gia ca Canada.DTM s dng b iu khin tp trung tm ra ng dn lun phin tt nht

c chn ty theo nghn trong mng. B iu khin trung tm thu thp d liu trngthi t mi chuyn mch trong mng c khon 10 giy mt ln xc nh cc ngdn lun phin chn trc. Mi cuc gi c th u tin trn ng dn trc tip nuc gia cc chuyn mch ngun v ch. Nu cuc gi b kha th n th trn ng dnlun phin th hai.

Mi chuyn mch i trao i cc thng s o lu lng sau n trung tm iukhin:

Iij: s trung k ri trn tuyn n chuyn mch j cho tt c cc chuyn

mch trong mng. CPUi: s dng VPU ca chuyn mch i.

Oij: thng s lu lng trn c gi t i n j trn ng ni trc tip.

Da trn cc thng tin ny, trung tm iu khin s tr v cho mi chuyn mch imt cch nh k mt ch c th c c ca chuyn mch j.

rij: nh danh ca chuyn mch qua chuyn mch i xc nh cc cuc gi trc tipca n ti j khi tuyn trc tip l y.


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Vic chn rij ty vo vic c tuyn trc tip tn ti gia i v j hay khng. Nutuyn trc tip tn ti th rijxcnh chuyn mch t t gi tr ti a khi:

Max{At*min[Iit-PAit,Ttj-PAtj]}, ti,j.

Nu khng c tuyn trc tip gia i v j th rijxc nh chuyn mch t gi tr tia khi:

Max{At*min[Iit,Ttj]}, ti,j.

Trong , Atl tham s trong phm vi [0,1] m phn nh sn sng ca chuynmch t. N bng 1 khi cc chc nng l bnh thng v nh hn nu chuyn mch t angqu ti, iu ny lm cho cc ng dn lun phin qua cc chuyn mch qu ti t licun hn v t c chn bi b iu khin mng hn.

PAxy: Tham s tha nhn bo v cho lu lng trc tip trn tuyn x-y, iu nyphn tch lu lng ra khi tuyn khi n gn y.

Phng trnh th hai l ging nh phng trnh th nht nhng khng c mt cathanm s tha nhn bo v. L do ca n l: nu khng c tuyn trc tip gia chuynmch i v j th lu lng t i n j khng c tha nhn u tin cho lu lng trc

tip trn cc tuyn trn cc ng dn thay th tim tng.Hnh 2-10 m t qu trnh chn la. Nu tuyn t i n j l bo ha th ng dn

thay th khuyn co l i-y-j. Mc d ng dn i-x-j c dung lng ri nhiu hn nhngn khng c khuyn khch bi v n ang qu ti.

Hnh 2-10 Vic chn ng thch hp trong TDM.

Vic s dng tp cc tham s da vo trng thi mng cho sc mnh ca dunglng mng. Hn na, n tr nn d dng thc hin vi nhiu s thay i ca vic xcnh cc gi tr ca cc tham s v quyt nh hiu qu thc hin ca chng. V d, tham


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s PAxyc th thit lp l mt gi tr c nh trong mng c n nh tng i hoctham s trn Oxyc th c s dng.

5. BO HIU

Trong mt mng chuyn mch knh, cc tn hiu iu khin l phng tin qunl, thit lp, duy tr v gii phng cc cuc gi. Chc nng qun l cuc gi v c chcnng qun l mng yu cu thng tin c trao i ga cc tng i vi thu bao, giacc tng i vi tng i v ga cc tng i vi trung tm qun l mng. Vi mt mngvin thng ln th mt s iu khin bo hiu phc tp tng ng c yu cu. Trong

phn ny, ch gii thiu khi qut cc chc nng bo hiu, sau xem xt k thut datrn cc mng tch hp hin i, l bo hiu knh chung.

Cc chc nng bo hiu

Cc tn hiu iu khin nh hng n nhiu kha cnh hot ng ca mng, baogm cho php cc dch v mng cho cc thu bao ln cc c ch bn trong mng. Lcny, cc mng tr nn phc tp hn, s chc nng c thc hin bi tn hiu iu khin

tng trng tng ng. Cc chc nng sau l cc chc nng quan trng nht:1. Truyn tn hiu c th nghe thy c cho thu bao, bao gm cc m mi

quay s, tn hiu bo bn, hi m chung

2. Truyn cc ch s quay gia cc tng i cathu bao ch gi.

3. Truyn thng tin gia cc chuyn mch ch th rng cuc gi khng th nikt.

4. Truyn thng tin gia cc chuyn mch ch th rng cuc gi l kt thc vng dn c th c gii phng.

5. Tn hiu chung.

6.

Truyn thng tin c s dng vi mc ch tnh cc.7. Truyn thng tin cho bit trng thi ca cc thit b hoc trung k trong

mng. Thng tin ny c th uc s dng vi mc ch nh tuyn v vnhnh.

8. Truyn thng tin c s dng kim tra v cch ly cc s c ca hthng.

9. iu khin thit b c bit, chng hn nh thit b knh v tinh.

v d cho vic s dng tn hiu iu khin ta xt tin trnh gi ca cc thu baocng tng i.

1. Trc khi tin hnh cuc gi, c hai my in thoi l khng s dng (t

my). Cuc gi c bt u khi mt thu bao nhc t hp (nhc my),hot ng ny c bo v tng i mt cch t ng.

2. Chuyn mch tr li bng tn hiu mi quay s, bo hiu rng thu bao cth quay s.

3. Thu bao ch gi quay s ca thu bao b gi, chuyn a ch n tng i.

4. Nu thu bao b gi l khng bn th chuyn mch bo hiu cho thu baony bng tn hiu chung, lm rung chung ca my thu bao b gi.


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5. Tn hiu hi tip c cung cp cho thu bao ch gi.

Nu thu bao b gi khng bn, chuyn mch tr v tn hiu hi mchung cho thu bao ch gi khi chung thu bao b gi.

Nu thu bao b gi bn th chuyn mch gi tn hiu bo bn chothu bao ch gi.

Nu cuc gi khng th tin hnh thng qua chuyn mch thchuyn mch gi mt thng bo n thu bao ch gi.

6. Thu bao b gi chp nhn cuc gi bng cch nhc t hp, trng thi nythng bo v tng i mt cch t ng.

7. Chuyn mch kt thc chung cho thu bao b gi v hi m chungcho thu bao ch gi, ng thi thit lp ni kt gia hai thu bao.

8. Ni kt c gii phng khi mt trong hai thu bao t my.

Khi hai thu bao trao i vi nhau thuc hai tng i khc nhau th cc chc nngbo hiu trn ng trung k gia chuyn mch vi chuyn mch c yu cu:

1.

Chuyn mch ngun chim gi ng trung k trung gian ri, gi tn hiuch th chim dng trn ng trung k, yu cu thanh ghi thu nhn squay ca thng i ch thu nhn a ch c truyn.

2. Chuyn mch ch gi tn hiu xc nhn ch thtng thi sn sng cathanh ghi.

3. Chuyn mch ngun gi cc ch s a ch ca thu bao bi gi.

Hnh 2-11 biu din vic s dng tn hiu iu khin ca ngun v ch. Bo hiuc th c phn thnh cc chc nng khc nhau nh gim st, a ch, thng tin cuc giv qun l mng.

Thut ng gim st c s dng ph bin ch n chc nng iu khin m c

c trng nh phn (true/false, on/off) nh yu cu phc v, tr li, cnh bochng theodi trng thi ca thu bao cng nh nhu cu vti nguyn mng. Cc tn hiu iu khingim st c s dng xc nh nu ti nguyn yu cu l sn sng v chim gi n,chng cn c s dng truyn thng cho cc trng thi ca ti nguyn c yu cu.

Bo hiu a ch nhn dng mt thu bao. Ban u, bo hiu a ch c to rabi thu bao ch gi khi thc hin quay s cho thu bao b gi. a ch c th c truynqua mng h tr cho chc nng nh tuyn v xc nh v chung cho thu baob gi.

Thut ng thng tin cuc gi xt cc tn hiu m cung cp thng tin cho thu baov trng thi cuc gi. iiu ny lm ni bc tn hiu iu khin bn trong gia ccchuyn mch s dng thit lp v kt thc cuc gi. Cc tn hiu bn trong nh vy l

cc thng ip tng t hoc s. Ngoi ra, cc tn hiu thng tin cuc gi l cc m hiuc th nghe thy c bi ngi gi hoc in thoi vin vi mt t hp in thoi thchhp.

Cc tn hiu gim st, a ch v thng tin cuc gi c bao h trong vic thitlp v gii phng cuc gi. Ngoi ra, cc tn hiu qun l mng c s dng vnhnh, x l s c v ton b hot ng ca mng. Cc tn hiu nh vy c th cchuyn trong cc thng ip nh l mt danh sch cc tuyn c chin lc c di


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t trm cp nht cc bng nh tuyn. Cc tn hiu ny bao trm mt phm vi rng vs phn loi c th phi m rng khi tng phc tp ca mng chuyn mch.

Vng bo hiu

Bo hiu c th c xt trong hai ng cnh: Bo hiu gia thu bao v mng vbo hiu bn trong mng. Bo hiu hot ng khc nhau gia hai ng cnh ny.

Bo hiu gia thu bao hoc my in thoi v chuyn mch hay tng i ni vin c xc nh cc c trng ca thit b ca thu bao v cc nhu cu ca ngi sdng. Cc tn hiu trong mng hon ton l gia my tnh vi my tnh. Bo hiu bntrong c xt khng ch l qun l cccuc gi ca thu bao m cn t qun l mng.

Nh vy, vi bo hiu bn trong, cc lnh cc p ng v tp cc tham s phi phc tphn rt nhiu.

Hnh 2-11 o hiu qua mng chuyn mch knh

Vi hai k thut bo hiu khc nhau c s dng, tng i chuyn mch ni htphi cung cp mt nh x gia mi quan h phc tp ca k thut bo hiu c s dngbn trong mng vi k thut bo hiu t phc tp hn nhiu c s dng vi thu bao.

Bo hiu knh chung

Bo hiu truyn thng trong mng chuyn mch knh trn c s tng tuyn trungk hay trong knh. Vi bo hiu trong knh, knh c s dng mang bo hiu lncuc gi m tn hiu bo hiu iu khin. Bo hiu nh vy bt ngun t thu baochh gi theo cng ng dn vi cuc gi n thu bao b gi. u im trong loi bohiu ny l khng tng thm thit b truyn dn tn hiu bo hiu, phng tin truyn dnthoi c dng chung vi bo hiu.

Hai dng ca bo hiu trong knh l trong bng v ngoi bng. Bo hiu trongbng khng ch dng chung ng dn vt l vi cuc gi m n phc v m cn s dng


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cng di tn ca tn hiu thoi. Dng ny ca bo hiu c mt s u im. Cc tn hiuiu khin c cng c trng in t nh tn hiu thoi, chng c th i n bt c nino m tn hiu thoi c th n. Nh vy, chng khng b gii hn trong vic s dngbo hiu trong bng khp ni trong mng, k c nhng vng chuyn i tn hiu ttng t sang s hoc ngc li. Ngoi ra, chng khng th thit lp cuc gi trn mtng truyn thoi cht lng km.

Bo hiu ngoi bng c nhng u im, l tn hiu thoi khng s dng htbng thng 4kHz c phn cho n nn khong trng cn li c s dng truyn bohiu. u im chnh ca phng php ny l cc tn hiu bo hiu c th truyn mcho d c hoc khng truyn tn hiu thoi trn ng dy, iu ny cho php s gim stv lin tc cho cuc gi. Tuy nhin, s bo hiu ngai bng phi cn thm thit b kim sot di tn bo hiu v tc bo hiu l chm hn v tn hiu trong mt di tnhp.

Cc mng chuyn mch vin thng cng cng tr nn phc tp hn v cungcp nhiu dch v phong ph v a dng hn rt nhiu, cc tr ngi ca bo hiu trongknh, cc ngc im, tr ngi ca bo hiu trong knh ngy cng l r. Tc truynthng tin b gii hnbi bo hiu trong knh. Vi bo hiu trong bng, cc knh thoi

c s dng ch c th truyn tn hiu bo hiu khi khng c tn hiu thoi trn mch.Bo hiu ngoi bng th bng thng rt hp cho php tn hiu truyn trn gy kh khntrong vic cung cp, tc ng nhanh cho i tng cho d dng thng ip n ginnht.

Nhc im th hai ca bo hiu trong knh l tr ln t khi thu bao quay sn khi ni kt c thit lp. Yu cu gim tr ny l mt vn kh phc tp chomng.

C hai nhc im ny c th gii quyt bi bo hiu knh chung vi bo hiuc mang trn cc ng dn hon ton c lp vi cc knh thoi. ng dn bo hiuc lp c th mang tn hiu bo hiu cho mt s knh ca thu bao v nh vy c mtknh iu khin chung cho cc knh thu bao ny.

ng 2-1. Cc k thut bo hiu trong cc mng chuyn mch knh

M t Ghi chTrong knh

Trong bng

Ngoi bng

Truyn tn hiu iu khin trangbng tn thoi

Tn hiu iu khin c truyncng phng tin nhng ngoi

bng tn thoi.

L k thut n gin nht. L cn thit cho cctn hiu thng tin cuc gi v c th c sdng cho cc thng tin iu khin khc. Bohiu trong bng c th c s dng nhiudng ng truyn khc nhau.

Khc vi trong bng, ngoi bng cung cp khnng gim st lin tc trong thi gian ni kt

Knh chungTn hiu iu khin c truynqua cc knh bo hiu m cppht tn hiu iu khin dngchung cho cc knh thoi

Gim thi gian thit lp cuc gi so vi knhring. Ngoi ra, cn thch hp vi cc chcnng b sung.

Nguyn l ca bo hiu knh chung c m t v so snh vi bo hiu trongknh nh trong Hnh 2-12. Ta c th thy rng, ng dn bo hiu cho bo hiu knhchung c phn tch ring bit so vi cc ng dn thoi ca cc thu bao. Bo hiuknh chung c th c cu hnh theo yu cu v bng thng mang cc tn hiu iu


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khin cho cc chc nng a dng v phong ph. Nh vy, phng thc bo hiu ln kintrc mng chuyn mch u phc tp hn bo hiu trong knh. Tuy nhin, vi gi thnhmy tnh ngy cng gim khin bo hiu knh chung cng tr nn li cun hn. Cc tnhiu iu khin l cc thng ip m c trao i gia cc chuyn mch cng nh giacc chuyn mch vi trung tm qun l mng. Vy, phn iu khin bo hiu ca mng lmt mng my tnh phn tn chuyn ti cho cc thng ip ngn.

Hnh 2-12 o hiu trong knh v bo hiu knh chung.

Hai kiu hot ng c s dng trong bo hiu knh chung (Hnh 2-13). Trongkiu kt hp, knh bo hiu dc theo cc nhm trung k gia hai chuyn mch v phc vcho cc knh thoi trn cc nhm trung k , cc node chuyn mch l cc im bohiu. Trong kiu khng kt hp, mng c b sung cc node gi l cc im chuyn tipbo hiu. Kiu ny khng gn cc knh bo hiu vi cc knh trong cc nhm trung km y tn ti hai mng ring bit vi cc tuyn ni gia chng phn iu khinmng c th iu khin qua cc node chuyn mch phc v cho cc cuc gi ca cc thubao. Qun l mng thng p dng kiu khng kt hp nh l cc knh bo hiu cth thc hin cc nhim v linh hoat hn. Kiu khng kt hp l kiu c s dng trongISDN.

Vi bo hiu trong knh, cc tn hiu iu khin ca hai chuyn mch c to ra

bi b x l v c chuyn n knh ng ra. bn thu, cc tn hiu iu khin phic chuyn t cc knh thoi n b x l. i vi bo hiu knh chung, cc tn hiuiu khin c truyn trc tip t b x l ny n b x l khc m khng kt hp chtch vi tn hiu thoi, y chnh l th tc n gin hn v l mt trong nhng ng cca bo hiu knh chung l t b nh hng hoc nhiu qua li gia thng tin cu cc thubao v thng tin bo hiu. Mt ng c ct yu na ca bo hiu knh chung chnh lthi gian thit lp cuc gi gim. Xt chui cc s kin cho vic thit lp cuc gi vibo hiu trong knh qua nhiu hn mt chuyn mch. Tn hiu iu khin c gi tchuyn mch ny n chuyn mch khc trn ng dn c sp t. Ti mi chuyn


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mch, tn hiu iu khin khng th truyn qua chuyn mch n chuyn mch tip theotrn ng dn m knh dn phi c thit lp qua chuyn mch ny. Trong bo hiuknh chung, vic chuyn tip thng tin iu khin c th chng chp qua tin trnh thitlp knh dn nn thi gian thit lp cuc gi nhanh hn nhiu.

Hnh 2-13 Kiu kt hp v khng kt hp.

Bo hiu khng kt hp c u im sau: Ta c th xy dng mt hoc nhiu trungtm iu khin, tt c cc thng tin c chuyn qua trung tm iu khin mng, yu cuc x l v gi n cc chuyn mch kim sot lu lng cho cc thu bao tng ng,iu ny c th c x l trn quan im tng th v tnh trng mng hn.

Nhc im ca bo hiu knh chung l phc tp hn v k thut. Tuy nhin, khiphn cng gim gi v s gi tng mt cch t nhin cc thit b s trong mng vinthng lm cho bo hiu knh chung tr thnh mt k thut ph hp.

Trong mt mng n gin th thu bao khng cn truy cp n phn bo hiu knhchung ca mng. Tuy nhin, trong mng s phc tp, bao gm ISDN, th phng thcbo hiu knh chung c trin khai gia thu bao v mng.


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6. GII THIU TI LIU THAM KHO

[BELL91] Bellamy, J.Digital Telephony. New York: Wiley, 1991.

[FREE96] Freeman, R. Telecommunication System Engineering. New

York: Wiley, 1996. [FREE94] Freeman, R. Reference Manual for Telecommunications

Engineering. New York:Wiley, 1994.

[GIRA90] Girard, A. Routing and Dimensioning in Circuit-Switched

Networks. Reading, MA: Addison-Wesley, 1990.

[MART90] Martin, J. Telecommunications and the Computer. EnglewoodCliffs, NJ: Prentice Hall, 1990.


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3. CHUYN MCH GIKhong nm 1970, cc nh nghin cu chuyn sang mt dng kin trc mi cho

vic truyn thng d liu s ng di, chnh l chuyn mch gi. Mc d k thutchuyn mch gi c pht trin thc s t trc thi gian ny nhng n c xcnhn li rng k thut c s ca chuyn mch gi l nn tng cho k thut ngy nay c

pht trin thnh mng u nhng nm 1970 v chuyn mch gi em li mt vi k thuthiu qu cho vic truyn thng d liu ng di.

Chng ny cung cp mt ci nhn tng quan v k thut chuyn mch gi. Xemxt nhng u im ca chuyn mch gi (linh hot, dng chung ti nguyn, kin nh,

p ng nhanh). Mng chuyn mch gi l tp hp phn tn ca cc node chuyn mchgi. Trong l tng th tt c cc node chuyn mch gi u bit c trng thi ca tonmng nhng thc ra, v cc node l phn tn nn lun c thi gian tr gia s thay itrng thi ca cc phn trong mng v s xc nhn v thay i ny. Hn na, lun cthng tin dn ng (overhead) trong thng tin trng thi. Nh vy, mt mng chuynmch gi c th khng bao gi hot ng mt cch hon ho v cc thut ton phc tpc s dng i vi thi gian tr v cc bt li thng tin dn ng ca hot ngmng.

u chng s gii thiu v nguyn l chuyn mch gi, k tip, ta xem xt hotng bn trong mng, gii thiu cc ni dung chuyn mch o v datagram. Sau , cck thut chnh ca nh tuyn v iu khin tc nghn c xem xt. Cui chng gii

thiu v X.25 l giao tip chun gia thit b u cui v mng chuyn mch gi.

1. NGUYN L CHUYN MCH GI

Mng vin thng chuyn mch knh ng di thit k ban u kim sot lulng thoi v a s lu lng trong mng ny l thoi. Cc c trng chnh ca ccmng chuyn mch knh l ti nguyn trong mng c n nh cho cc cuc gi. Vicc ni kt thoi th cc knh c phn trm s dng cao v hu ht cc thi gian, nginy hoc i phng ni chuyn. Tuy nhin, mng chuyn mch knh bt u tng ccni kt d liu th hai thiu st l ra mt cch r rng:

Trong mt ni kt d liu user/host (v d my tnh c nhn ng nhp vo server

c s d liu) th phn ln ng dy l ri. Nh vy, vi cc ni kt d liu th mngchuyn mch knh l khng hiu qu.

Trong mng chuyn mch knh, ni kt cung cp truyn dn vi mt tc dliu khng i. Nh vy, mi thit b u cui phi truyn v pht cng tc vi thit bu cui kia, iu ny hn ch s dng mng trong ni kt vi s a dng ca cc mytnh ch v cc kt cui.

hiu c chuyn mch gi gii quyt bi ton ny nh th no, ta vn tt tngqut hot ng chuyn mch gi. D liu c truyn trong cc gi c kch thc ngn.


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Chng 3....PACKET SWITCHING

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Kch thc gi ti a tiu biu l 1000 octects (bytes). Nu ngun c thng ip di hncn gi th thng ip c chia thnh mt chui cc gi (Hnh 3-1). Mi gi cha mt

phn (hoc ton b vi thng ip ngn) l d liu ca user cng vi thng tin iu khin.Thng tin iu khin ti thiu gm nhng thng tin m mng yu cu c th nhtuyn gi qua mng v phn phi n hng ti ch. Ti mi node, gi c thu nhn,lu gi v chuyn n n node tip theo.

Hnh 3-1 Gi.

Hnh 3-2 V d mt mng chuyn mch gi n gin

Trong Hnh 3-2, gi s cc gi c gi tu trm A n trm D. Cc gi s bao

gm thng tin iu khin chth ch n l E. Gi c gi t A vo node1.Node 1 slu tr gi, xc nh node k tip (l 3), sp hng gi ng ra tuyn (tuyn 1-3). Khituyn l sn sng th gi c chuyn n node 3, ti y, qu trnh din ra tng t chuyn gi n node 4 v cui cng n D. Phng thc ny c nhng thun li so vichuyn mch knh:

Hiu qu ng dy l ln hn v tuyn t node n node c th dngchung cho nhiu

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