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TP ON BU CHNH VIN THNG VIT NAM

HC VIN CNG NGH BU CHNH VIN THNG

BI GING

MNGVINTHNG

(Lu hnh ni b)

Bin son: TS. Nguyn Tin Ban (ch bin)

ThS. Nguyn Th Thu Hng

H ni, 2010

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Mc lc

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MC LC

MC LC........................................................................................................................3

DANH MC HNH V...................................................................................................7

DANH MC BNG......................................................................................................13

THUT NGVIT TT ............................................................................................. 14

LI NI U ...............................................................................................................18

CHNG 1. GII THIU CHUNG V CC MNG VIN THNG ...................19

1.1 Mng in thoi .............................................................................................. 19

1.1.1 Cu trc chung ............................................................................................ 191.1.2 Nguyn lnh s .......................................................................................26

1.1.3 Cc t chc chun ha v iu phi ...........................................................27

1.2 Mng truyn s liu ........................................................................................29

1.2.1 Cc h thng my tnh v m hnh Client/Server....................................... 29

1.2.2 M hnh tham chiu OSI............................................................................. 31

1.2.3 Mt s v d v cc mng truyn s liu .................................................... 36

1.3 Mng Internet.................................................................................................. 38

1.3.1 S ra i v pht trin.................................................................................38

1.3.2 Cc thnh phn v cu trc mng ...............................................................39

1.3.3 Cc phng thc truy nhp mng............................................................... 41

1.3.4 Cc dch v Internet.................................................................................... 44

1.4 Xu hng hi t ca cc mng vin thng ..................................................... 45

1.4.1 S hi t gia cc mng cc b v din rng............................................. 46

1.4.2 S hi t gia cc mng thoi v s liu .................................................... 47

1.4.3 S hi t gia cc mng cnh v di ng............................................... 47

1.5 Tng kt ..........................................................................................................47

1.6 Cu hi n tp ................................................................................................. 48

CHNG 2. CC NGUYN L XY DNG MNG............................................49

2.1 Lp Vt l ........................................................................................................49

2.1.1 Truyn tn hiu lp Vt l ........................................................................ 49

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2.1.2 ng b v nh thi...................................................................................56

2.1.3 Cc giao thc v c t lp Vt l ...............................................................59

2.2 Lp Lin kt d liu........................................................................................62

2.2.1 Cc chc nng ca lp lin kt d liu .......................................................62

2.2.2 nh khung..................................................................................................64

2.2.3 Kim sot li ...............................................................................................67

2.2.4 iu khin lung .........................................................................................67

2.3 Lp Mng........................................................................................................68

2.3.1 Chc nng ca lp mng v bi ton nh tuyn ........................................68

2.3.2 Cc khi nim cbn vnh tuyn ...........................................................682.3.3 Phn loi kthut nh tuyn.......................................................................72

2.3.4 nh tuyn tnh v nh tuyn ng............................................................74

2.3.5 nh tuyn vectkhong cch ....................................................................77

2.3.6 nh tuyn trng thi lin kt......................................................................83

2.3.7 nh tuyn lai ghp .....................................................................................88

2.4 Tng kt...........................................................................................................89

2.5 Cu hi n tp..................................................................................................90

CHNG 3. CC MNG CHUYN MCH KNH...............................................91

3.1 Mng in thoi chuyn mch cng cng (PSTN)..........................................91

3.1.1 H thng truyn dn ....................................................................................92

3.1.2 H thng chuyn mch..............................................................................108

3.2 Bo hiu trong cc mng chuyn mch knh ................................................119

3.2.1 Gii thiu...................................................................................................119

3.2.2 Bo hiu knh kt hp...............................................................................122

3.2.3 Bo hiu knh chung .................................................................................124

3.2.4 Mng thng minh ......................................................................................129

3.3 Mng s tch hp a dch v (ISDN) ............................................................133

3.3.1 Tin xy dng ISDN........................................................................133

3.3.2 Cu hnh tham chiu..................................................................................134

3.3.3 Cc loi knh v giao din ........................................................................135

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3.3.4 Bo hiu trong ISDN ................................................................................139

3.4 Cc mng in thoi v tuyn.......................................................................141

3.4.1 Mng v tuyn t bo................................................................................141

3.4.2 Mng v tuyn v tinh ..............................................................................142

3.4.3 Xu hng pht trin cc mng v tuyn...................................................143

3.5 Tng kt ........................................................................................................144

3.6 Cu hi n tp...............................................................................................146

CHNG 4. CC MNG CHUYN GI .............................................................148

4.1 Mng cc b (LAN)......................................................................................148

4.1.1 Cc thnh phn mng................................................................................1484.1.2 Kin trc mng..........................................................................................149

4.1.3 iu khin truy nhp ng truyn ..........................................................150

4.1.4 Cc chun LAN ........................................................................................152

4.1.5 Cng ngh Ethernet ..................................................................................155

4.1.6 Cc thit b mng......................................................................................160

4.2 Mng din rng (WAN)................................................................................164

4.2.1 Gii thiu .................................................................................................. 164

4.2.2 Giao thc PPP ...........................................................................................166

4.2.3 X.25...........................................................................................................167

4.2.4 Frame Relay.............................................................................................. 170

4.2.5 ATM..........................................................................................................172

4.3 Tng kt ........................................................................................................175

4.4 Cu hi n tp...............................................................................................175

CHNG 5. MNG IP............................................................................................177

5.1 Kin trc giao thc TCP/IP...........................................................................177

5.1.1 Gii thiu .................................................................................................. 177

5.1.2 Tng Truy nhp mng...............................................................................178

5.1.3 Tng Lin mng........................................................................................178

5.1.4 Tng giao vn............................................................................................178

5.1.5 Tng ng dng..........................................................................................179

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5.2 Cc giao thc tng Lin mng.......................................................................180

5.2.1 Giao thc IP ..............................................................................................180

5.2.2 Giao thc ICMP ........................................................................................198

5.2.3 Giao thc ARP v RARP ..........................................................................201

5.3 Cc giao thc tng Giao vn .........................................................................203

5.3.1 Giao thc TCP...........................................................................................203

5.3.2 Giao thc UDP..........................................................................................214

5.4 nh tuyn trong mng IP .............................................................................216

5.4.1 Giao thc nh tuyn RIP..........................................................................216

5.4.2 Giao thc nh tuyn OSPF ......................................................................2285.4.3 Giao thc nh tuyn BGP ........................................................................243

5.4.4 Thit bnh tuyn IP................................................................................256

5.5 Tng kt.........................................................................................................259

5.6 Cu hi n tp................................................................................................260

TI LIU THAM KHO ............................................................................................261

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Danh mc hnh v

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DANH MC HNH V

Hnh 1.1: Cc thnh phn cbn ca mng in thoi chuyn mch knh..................20Hnh 1.2: Mng tng i ni ht....................................................................................23Hnh 1.3: Cu trc s E.164 quc t theo vng a l...................................................27Hnh 1.4: Cc t chc chun ha trn th gii ..............................................................27Hnh 1.5: M hnh khch ch (client/server).................................................................30Hnh 1.6: M hnh tham chiu OSI ...............................................................................32Hnh 1.7: Cc kiu kin trc mng................................................................................40

Hnh 1.8: Cu trc lin mng ........................................................................................41

Hnh 2.1: Sng hnh sin .................................................................................................49Hnh 2.2: Bin , tn s v pha ca sng hnh sin ......................................................50Hnh 2.3: M dch pha ...................................................................................................51Hnh 2.4: Sng vung....................................................................................................52Hnh 2.5: Ccu truyn tn hiu sng s ......................................................................52Hnh 2.6: Tn hiu s v tng t vi tn hiu tng t v s ......................................53Hnh 2.7: Cc giao din song song v ni tip..............................................................56Hnh 2.8: Khun dng k t truyn d b.......................................................................57Hnh 2.9: Chun lp vt l EIA-232-E ..........................................................................60Hnh 2.10: Khuyn ngh X.21 ca ITU .........................................................................61Hnh 2.11: Cc gi c ng khung lp lin kt d liu .........................................62Hnh 2.12: ng truyn thng o v ng truyn thc s gia hai trm.................63 Hnh 2.13: Lp lin kt d liu truyn gi tin cho lp mng........................................63Hnh 2.14: nh khung bng cch m k t.................................................................64Hnh 2.15: nh khung s dng byte cvi kthut byte stuffing...............................65Hnh 2.16: Kthut bit stuffing .....................................................................................66Hnh 2.17: Bnh tuyn s dng phn a ch mng nh tuyn d liu...............69Hnh 2.18: Lin mng c chia thnh nhiu h t tr..................................................71Hnh 2.19: Tuyn tnh trnh c cp nht nh tuyn qua lin kt WAN ..................75

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Hnh 2.20: Kh nng thay th tuyn hng ca nh tuyn ng...................................76Hnh 2.21: Cc giao thc nh tuyn duy tr v phn phi thng tin nh tuyn..........76Hnh 2.22: Giao thc vctkhong cch gi nh k cc bn sao ca bng nh tuyn

v tch lu cc vctkhong cch.................................................................................78Hnh 2.23: Cc Bnh tuyn vct khong cch khm ph ng i tt nht n

ch t cc hng xm.....................................................................................................78Hnh 2.24: Cp nht nh tuyn tin hnh tng bc, t bnh tuyn ny ti bnh

tuyn khc......................................................................................................................79Hnh 2.25: Bnh tuyn A cp nht bng nh tuyn phn nh s bc nhy mi

nhng khng ng.........................................................................................................79Hnh 2.26: Vng lp nh tuyn tng vctkhong cch .............................................80Hnh 2.27: Gii hn khong cch ti a........................................................................81Hnh 2.28: Khi nim phn chia ranh gii (split horizon) ............................................82Hnh 2.29: Gii thut trng thi lin kt cp nht thng tin tp ca tt c cc bnh

tuyn khc......................................................................................................................83Hnh 2.30: Trong nh tuyn trng thi lin kt, tt c cc bnh tuyn cng tnh

ton ng i ngn nht ti ch...................................................................................84Hnh 2.31: Tin trnh cp nht trng thi lin kt .........................................................85Hnh 2.32: Cp nht khng ng b v ng i khng nht qun dn n s khng

th ti c mng..........................................................................................................86Hnh 2.33: Giao thc nh tuyn lai chia s cc thuc tnh ca nh tuyn vct

khong cch v trng thi lin kt .................................................................................88

Hnh 3.1: Mng PSTN vi tng i s, trung k s v truy nhp tng t ..................92

Hnh 3.2: V d v ghp knh .......................................................................................93Hnh 3.3: Chc nng ca b lp v b khuch i........................................................96Hnh 3.4: Hot ng ca Codec ....................................................................................96Hnh 3.5: B ghp knh PCM-30..................................................................................99Hnh 3.6: Nguyn tc ghp cn ng b .....................................................................101Hnh 3.7: Cc mc truyn dn PDH ...........................................................................103Hnh 3.8: Tin trnh ghp knh phn chia theo bc sng .........................................107

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Hnh 3.9: Mt chng WDM/DWDM n gin ...........................................................108Hnh 3.10: Mt TSI h tr6 ng vo v ra .............................................................114Hnh 3.11: Cc cp tng i trong mng PSTN..........................................................117Hnh 3.12: Cu trc phn cp mng PSTN ca VNPT - Vit Nam ............................118Hnh 3.13: Cc loi bo hiu trong mng chuyn mch knh.....................................120Hnh 3.14: Bo hiu ng dy thu bao trong PSTN................................................121Hnh 3.15: Bo hiu lin i trong PSTN....................................................................122Hnh 3.16: : Bo hiu knh kt hp.............................................................................123Hnh 3.17: Cc bc thc hin ca bo hiu knh kt hp.........................................124Hnh 3.18: Cc phn t trong mng bo hiu s 7......................................................125Hnh 3.19: M hnh tham chiu cho SS7 ....................................................................126Hnh 3.20: Cu trc mt khi tn hiu bo hiu ..........................................................128Hnh 3.21: Kim tra thu pht bn tin qua cc trng thng tin...................................128Hnh 3.22: M hnh khi nim IN (INCM) .................................................................132Hnh 3.23: Kin trc mng IN.....................................................................................133Hnh 3.24: Cu hnh ISDN ..........................................................................................134Hnh 3.25: M hnh tham chiu trn knh B v 2B ....................................................136Hnh 3.26: M gi tam phn ........................................................................................138Hnh 3.27: Cu trc khung LAPD...............................................................................138Hnh 3.28: Bo hiu ISUP...........................................................................................140Hnh 3.29: Cu hnh h thng GSM............................................................................142Hnh 3.30: Phm vi ca thng tin v tinh....................................................................142Hnh 3.31: Cc dch v Vinasat 1 cung cp ................................................................143Hnh 3.32: Lch s pht trin di ng ti 3G ..............................................................144Hnh 4.1: Cc kiu kin trc LAN...............................................................................149Hnh 4.2: Th tc truyn khung trong CSMA/CD ......................................................151Hnh 4.3: Cc chun LAN ph bin ............................................................................153Hnh 4.4: M hnh phn lp Ethernet v quan h vi OSI..........................................156

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Hnh 4.5: Cu trc khung Ethernet..............................................................................157Hnh 4.6: Kt ni gia 2 trm trong mng 10Base-T .................................................158Hnh 4.7: Mng 100Base-TX ......................................................................................159Hnh 4.8: B lp hot ng ti tng vt l trong m hnh OSI ...................................160Hnh 4.9:Cu ni hot ng ti hai tng thp nht trong m hnh OSI .....................161Hnh 4.10: Bnh tuyn hot ng ti 3 tng thp nht trong m hnh OSI ............163Hnh 4.11: Cng ni hot ng c 7 tng trong m hnh OSI .................................164Hnh 4.12: ng gi d liu PPP................................................................................167Hnh 4.13: Mng X.25.................................................................................................168Hnh 4.14: S kt ni DTE-DCE trong X.25.........................................................168Hnh 4.15: M hnh giao thc X.25 ............................................................................168Hnh 4.16: Mng Frame Relay....................................................................................170Hnh 4.17: Cu trc khung Frame Relay.....................................................................171Hnh 4.18: T bo ATM..............................................................................................172Hnh 4.19: ng gi d liu vo cc t bo ti nt mng ATM.................................173Hnh 4.20: M hnh phn tng ATM...........................................................................173Hnh 4.21: Tiu t bo UNI v NNI .......................................................................174Hnh 5.1: M hnh phn tng TCP/IP .........................................................................177Hnh 5.2: Tiu IP datagram ....................................................................................180Hnh 5.3: V d v phn mnh ....................................................................................185Hnh 5.4: Gi tr ca cc trng khi datagram c phn mnh................................186Hnh 5.5: nh dng tng qut ca mt ty chn trong tiu IP .............................186Hnh 5.6: Biu din thp phn du chm ....................................................................188Hnh 5.7: Cc lp a ch IP ........................................................................................189Hnh 5.8: Mng vi hai mc phn cp (cha phn mng con)...................................193Hnh 5.9: Mng vi ba mc phn cp (phn mng con) .............................................194Hnh 5.10: Hot ng ca ARP...................................................................................202Hnh 5.11: Hot ng ca RARP................................................................................203

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Hnh 5.12: Cu trc tiu TCP .................................................................................206Hnh 5.13: Ca s trt ...............................................................................................208Hnh 5.14: Qun l ca s ...........................................................................................209Hnh 5.15: Th tc bt tay ba bc .............................................................................212Hnh 5.16: Th tc gii phng kt ni bn bc.........................................................213Hnh 5.17: nh dng ca UDP datagram...................................................................215Hnh 5.18: V d cc bng nh tuyn RIP ban u....................................................218Hnh 5.19: V d cc bng nh tuyn RIP cp nht cui cng ..................................218Hnh 5.20: nh dng bn tin RIP ...............................................................................219Hnh 5.21: Bn tin RIP yu cu...................................................................................220Hnh 5.22: Bn tin RIP tr li......................................................................................220Hnh 5.23: Bnh tuyn a thng tin v cc mng kt ni trc tip vo bng nh

tuyn, metric ti mng mng ny l 0 .........................................................................222Hnh 5.24: Bnh tuyn nhn thng tin t hng xm v cp nht bng nh tuyn.222Hnh 5.25: nh dng gi RIPv2.................................................................................224Hnh 5.26: Mc u tin ca gi RIPv2 c s dng cho chng thc .....................226Hnh 5.27: Tuyn thay th ch c khi cp nht xong nh tuyn.................................227Hnh 5.28: m v hn xy ra nu c vng lp nh tuyn........................................227Hnh 5.29: S bc nhy ti a l 15 ..........................................................................228Hnh 5.30: H thng thut ng OSPF .........................................................................230Hnh 5.31: Cc kiu mng OSPF ................................................................................234Hnh 5.32: Bnh tuyn chnh v chnh d phng ...........................................234Hnh 5.33: Tiu gi OSPF ......................................................................................235Hnh 5.34: nh dng dng gi Hello .........................................................................236Hnh 5.35: Cc bnh tuyn thit lp mi quan h gn k .......................................238Hnh 5.36: Qu trnh bu DR v BDR chc thc hin trn mng a truy nhp...239Hnh 5.37: Cc bc trao i n c trng thi Full ..........................................240Hnh 5.38: Tuyn tt nht c chn v a vo bng nh tuyn ............................241

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Hnh 5.39: H t tr .....................................................................................................243Hnh 5.40: H t trn kt ni ..................................................................................244Hnh 5.41: H t tra kt ni khng chuyn tip......................................................245Hnh 5.42: H t tra kt ni chuyn tip.................................................................246Hnh 5.43: Ch s dng BGP khi chnh sch nh tuyn khc vi ISP.......................247Hnh 5.44: ng i AS .............................................................................................248Hnh 5.45: Thit lp phin hng xm..........................................................................248Hnh 5.46: Cp nht nh tuyn ch cha nhng thay i...........................................249Hnh 5.47: Rt li tuyn khng hp l ........................................................................249Hnh 5.48: Tiu BGP..............................................................................................250Hnh 5.49: nh dng gi Open ..................................................................................250Hnh 5.50: nh dng gi Update ...............................................................................251Hnh 5.51: nh dng gi Keepalive...........................................................................252Hnh 5.52: nh dng gi Notification.......................................................................252Hnh 5.53: My hu hn trng thi BGP ....................................................................253Hnh 5.54: Thng tin cu hnh bnh tuyn c thn t nhiu ngun...................257Hnh 5.55: Cc thnh phn cu hnh bn trong bnh tuyn....................................257

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Danh mc bng

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DANH MC BNG

Bng 2.1: So snh nh tuyn trng thi lin kt v vctkhong cch.......................87

Bng 5.1: Gi tr MTU i vi cc mng khc nhau ..................................................183

Bng 5.2: Cc a chc bit .....................................................................................191

Bng 5.3: Tin t CIDR v s lng lp C tng ng ...........................................198

Bng 5.4: Cc cng TCP thng dng ..........................................................................205

Bng 5.5: Cc cng UDP thng dng .........................................................................214

Bng 5.6: Bng nh tuyn vectkhong cch ...........................................................216

Bng 5.7: 5 loi gi OSPF...........................................................................................231Bng 5.8: Mt s thuc tnh ng i hin ang s dng ..........................................256

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Thut ng vit tt

14

THUT NGVIT TT

Tvit tt Ty Ngha ting Vit3G Third Generation Th h th3

AAL ATM Adaptation Layer Lp thch ng ATM

API Application ProgrammingInterface

Giao din lp trnh ng dng

ARP Address Resolution Protocol Giao thc phn gii a ch

ATM Asynchronous Transfer

Mode

Phng thc truyn d b

BER Bit Error Rate T l li bit

BGP Border Gateway Protocol Giao thc nh tuyn cng bin

B-ISDN Broadband ISDN ISDN bng rng

BOOTP Bootstrap Protocol Giao thc Bootstrap

CCS7 Common ChannelSignalling Number 7

Bo hiu knh chung s 7

CIR Committed Information

Rate

T l thng tin cam kt

DCLI Datalink ConnectionIdentifier

Nhn dng kt ni lin kt dliu

DNS Domain Name System H thng tn min

EIR Excess Information Rate T l thng tin vt qu

ETC Cng ty vin thng in lc

F Flag C

FCS Frame Check Sequence Trnh t kim tra khungFR Frame Relay Chuyn tip khung

FTP File Transfer Protocol Giao thc truyn file

GK Gate Keeper B gicng

GPRS General Package Radio

Service

Dch v v tuyn gi chung

GW Gateway Cng

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Thut ng vit tt

15

HSPA High-Speed Packet Access Cng ngh truy nhp gi tc

cao

HSDPA High-Speed Downlink

Packet Access

Cng ngh truy nhp gi ng

xung tc cao

IAB Internet ArchitecturalBoard

Hi ng kin trc Internet

ICMP Internet Control MessageProtocol

Giao thc thng ip iu khinInternet

IDN Intergrated Digital Network Mng s tch hp

IETF Internet Engineering Task

Force

Lc lng c trch k thut

InternetIGMP Internet Group Protocol Giao thc

IN Intelligent Network Mng thng minh

IP Internet Protocol Giao thc Internet

IPv4 IP version 4 Giao thc Internet phin bn 4

IPv6 IP version 6 Giao thc Internet phin bn 6

ISDN Integrated Service DigitalNetwork

Mng sa dch v

ISO International Organizationfor Standardization

T chc chun ha quc t

ISP Internet Service Provider Nh cung cp dch v Internet

ISUP ISDN User Part Phn ngi dng ISDN

ITU-T ITU-TelecommunicationSector

Tiu ban vin thng Hip hivin thng quc t

LAN Local Area Network Mng ni htLCN Logical Channel Number S knh logic

M2PAMTP L2 Peer-to-Peer

AdapterB chuyn i bn tin lp 2

ngang hng

M2UA MTP2 User AdapterB chuyn i ngi dng

MTP2

M3UA MTP3 User AdapterB chuyn i ngi dng

MTP3

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Thut ng vit tt

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MG Media Gateway Cng phng tin

MGC Media Gateway Controller Biu khin cng phng tin

MTP Message Tranfer Part Phn chuyn giao bn tin

NGN Next Generation Network Mng th h sau (k tip)N-ISDN Narrowband ISDN ISDN bng hp

OSI Open SystemsInterconnection

Kt ni cc h thng m

OSPF Open Shortest Path First Tm ng ngn nht

PCM Pulse Code Modulation iu xung m

PSTN Public Switch TelephoneNetwork

Mng in thoi chuyn mchcng cng

QoS Quality of Service Cht lng dch v

RARP Reverse AddressResolution Protocol

Giao thc phn gii a chngc

RAS Register Admission StatusBo hiu ng k, cp php,

thng tin trng thi

RIP Routing InformationProtocol

Giao thc thng tin nh tuyn

RSVP Resource ReservationProtocol

Giao thc dnh sn (d tr) tinguyn

RTCP Real Time Control ProtocolGiao thc iu khin thi gian

thc

RTPReal-time Transport

ProtocolGiao thc truyn thi gian thc

SCCP Signaling ConnectionControl Part

Phn iu khin kt ni bohiu

SCP Service Control Point im iu khin dch v

SG Signalling Gateway Cng bo hiu

SIP Session Initiation Protocol Giao thc khi to phin

SMTP Simple Message/MailTransfer Protocol

Giao thc chuyn thn gin

SNMP Simple NetworkManagement Protocol

Giao thc qun l mng ngin

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Thut ng vit tt

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SS Soft Switch Chuyn mch mm

SS7 Signalling System Number 7 Mng bo hiu s 7

SSP Service Switching Point im chuyn mch dch v(hoc chuyn mch trung tm)

STP Signalling Transfer Point im chuyn tip bo hiu

TCP Transmission ControlProtocol

Giao thc iu khin truyndn

TDMA Time division multiple

access

a truy nhp phn chia theo

thi gian

UA User Agent Tc nhn ngi sdng

UDP User Datagram Protocol Giao thc d liu ngi sdng

VNPT Vietnam Posts andTelecommunications Corp.

Tp on Bu chnh vinthng Vit Nam

VoIP Voice over IP Truyn thoi qua IP

WAN Wide Area Network Mng din rng

WCDMA Wideband Code Division

Multiple Access

a truy nhp phn chia theo m

bng rng

WDM Wave Division Multiplexing Ghp knh quang theo bcsng

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Li ni u

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LI NI U

Vin thng l qu trnh trao i thng tin hay qung b thng tin gia cc itng (ngi vi ngi, ngi vi my mc hay vi cc h thng thng tin, ) cc

dng khc nhau nh ting ni, hnh nh, d liu ... v cc v tr khng gian khcnhau. Cng ngh vin thng hin ti t ti mc m trong giy lt chng ta c thtrao i thng tin vi nhau t hai im bt k trn tri t. Vic trao i thng tin nyc thc hin nhvo cc h thng truyn thng qua cc mng cng cng nh mngin thoi, mng pht thanh truyn hnh hay mng my tnh. Nh vy, c th ni csh tng thng tin c hnh thnh da trn cc thit b kt ni vi nhau thng quamng vin thng.

Ti liu ny trnh by nhng kin thc c bn v cc mng vin thng nh

mng in thoi, mng truyn d liu hay mng my tnh. Mi mi trng mng cnhng c tnh ring vi nhng yu cu khc nhau v thit k v vn hnh. Ty voc im v tnh cht ca dch v cung cp m mt mng vin thng c th s dngcng ngh ny hay cng ngh khc thc hin vic trao i thng tin. Song d sdng cng ngh no th mc ch cui cng ca mng vin thng l cung cp dch vvin thng cho khch hng vi cht lng cao nht v gi thnh r nht.

Mng vin thng c thc phn loi theo nhiu quan im: phm vi a l,cng ngh v phng thc chuyn giao thng tin, loi hnh dch v cung cp, cc giao

thc s dng, ... Trc y mi mng vin thng c thit k cung cp mt hocmt vi loi dch vc trng cho mng. Tuy nhin, hin nay cc mng vin thng cxu hng hi t c th truyn c nhiu loi hnh thng tin trn mt nn mngduy nht v d dng cung cp cc dch v vin thng phong ph, a dng n ngi sdng. Bm theo xu hng pht trin v hi t ca cc mng vin thng, ni dung tiliu c thit k gm 5 chng vi nhng ni dung chnh nh sau.

Chng 1 gii thiu khi qut v cc mng vin thng hin nay nh mng in

thoi, mng truyn s liu, mng Internet. Chng 2 trnh by cc nguyn l xy dng

mng vi cch tip cn da trn m hnh phn lp OSI, trong tp trung vo 3 lpdi l lp Vt l, lp Lin kt d liu v lp Mng. Chng 3 trnh by v cc mng

chuyn mch knh, c im k thut v cc cng ngh s dng trong chuyn mch

knh. Chng 4 trnh by v cc mng chuyn gi, cc chun v giao thc lin quan

n cng nghng gi v vn chuyn gi tin qua mng. Chng 5 tp trung vo gii

thiu v mng IP, kin trc TCP/IP v cc giao thc in hnh cng nh l nhng vn

lin quan n bi ton nh tuyn trong mng IP.

Ti liu c bin son trong thi gian tng i ngn nn khng trnh khi cnnhiu thiu st. Tc gi rt mong nhn c nhiu kin ng gp t pha c gi v

cc ng nghip.

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Chng 1. Gii thiu chung v cc mng vin thng

19

CHNG 1. GII THIU CHUNG V

CC MNG VIN THNG

1.1 Mng in thoi

Mng in thoi l mng vin thng cbn nht. Hot ng ca mng in thoi

truyn thng c hiu mt cch n gin l thc hin chc nng truyn m thanh

(thng l thoi) qua khong cch. Ngun pht ra m thanh c th l dy thanh m,

thit b m nhc, gi v hng triu ngun khc. C hai loi mng thoi hin ang c

s dng ph bin l mng in thoi truyn thng (c nh) v mng in thoi di

ng.

Mng in thoi truyn thng (in thoi cng cng) c xy dng t cui th

k 19 vi mc ch ch yu l truyn ting ni ca con ngi. Mng in thoi di

ng ra i sau (cui th k 20 mi c a vo s dng rng ri trn th gii) song

n ang pht trin rt mnh v mang li rt nhiu tin ch cho ngi s dng.

Mc d l mng vin thng cng cng lu i nht song cho ti nay mng in

thoi vn tn ti v pht trin, hn na n cn c s lng ngi s dng nhiu nht

trn th gii so vi cc mng vin thng khc (tnh n thng 2 nm 2010 c khong 6

t thu bao in thoi (4,6 t thu bao in thoi di ng), ring Vit Nam ti 2/2010

c khong hn 135 triu thu bao in thoi /90 triu dn).

1.1.1 Cu trc chung

C th to ra mng in thoi n gin bng cch ni bt k hai my in thoi

bng mt i dy. Trong thi ku ca cc mng in thoi, khi ch c rt t my

in thoi th vic kt ni c thc hin trc tip gia cc my in thoi v s lng

ng dy nh v d dng qun l c. Tuy nhin khi s lng ngi s dng in

thoi tng ln th sng kt ni trc tip gia cc my in thoi s gia tng rt

nhanh v vic kt ni trc tip gia cc my in thoi trnn lng ph. V th cn c

mt mng chuyn mch cc knh thoi, gi tt l mng chuyn knh (switched

network). Khi mi my in thoi ch cn c mt i dy kt ni ti trung tm

chuyn mch. Chuyn mch ny s cung cp cc kt ni trong khong thi gian m hai

my in thoi gi cho nhau v khi ngi s dng khng m thoi na th thit bchuyn mch s ct b kt ni .

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Mng chuyn knh cho php ngi s dng dng chung thit b mng v v th

chi ph cho mng s gim i rt nhiu. Lng thit b dng chung ny c tnh ton

p ng mt cp cht lng dch v nht nh vi gi thnh hp l nht. Vic

tnh ton thit k mng da trn c im l khng c nhiu ngi gi in thoi ng

thi cng lc, v th c th s dng mt kt ni chung cho rt nhiu ngi s dng.

Hnh 1.1 ch ra cc thnh phn ca mng chuyn knh. ng kt ni trc tip

t mi my in thoi ti chuyn mch ni ht (local switch) c gi l mch vng

ni ht (local loop), trong trng hp n gin nht l mt i dy. Thng thng,

mi thu bao c mt i dy dnh ring kt ni vo mng.

Hnh 1.1: Cc thnh phn cbn ca mng in thoi chuyn mch knh

Hu ht cc mng in thoi yu cu c mt chuyn mch cung cp kt ni

gia cc ng dy ca bt k hai thu bao no kt ni ti chuyn mch . V c

nhiu cng ng khch hng c mt chuyn mch phc v nn c nhiu cui githc hin l ni ht (t thu bao ny n thu bao khc trong cng khu vc qun l ca

mt chuyn mch). Tuy nhin, nu hai thu bao c yu cu kt ni li ni vi hai thit

b chuyn mch khc nhau th yu cu kt ni phi thng qua hai chuyn mch mi

thc hin c. Kt ni gia chuyn mch vi chuyn mch y c gi l trung

k (trunk).

Nu c 10 ng trung k kt ni trm A v B th ch c th c 10 cuc gi c

thc hin ng thi gia cc thu bao ca A vi thu bao ca B. Song ngay khi c mt

cuc gi kt thc th trung k s trthnh ri v li tip tc phc v cho mt cuc

gi khc. V th cc trung k dng chung ny c thc huy ng lin tip cho nhiu

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ngi dng. Cc k s nghin cu v lu lng chu trch nhim tnh ton chnh xc

s lng trung k cn thit kt ni gia cc chuyn mch sao cho ti u nht.

1.1.1.1Mch vng ni htMch vng ni ht l ng kt ni gia thu bao v trm chuyn mch trung

tm (CO - Central Office). L ng dy truy nhp ca khch hng ni ti mng,

mch vng ni ht c dnh ring cho mt thu bao. Nh vy, mi khi khch hng

gi in thoi th mch vng hot ng.

Mch vng ny thng l mch hai dy. N cho php nh cung cp dch v

mng, hay cn gi l nh cung cp tng i ni ht (LEC - Local Exchange Carrier),

trang bng truyn dn cht lng hp l vi gi thnh thp. Trn vng ni ht hai

dy ny vic truyn dn bng dng in phi thc hin c hai hng (hng truyntn hiu tin thoi n chuyn mch v ngc li).

i vi mi trng hi thoi th thng mt ngi tham gia cuc thoi ni trong

khi ngi kia nghe (bn song cng - half duplex) v ngi ni th him khi nghe ti

thi im mnh ni. Tuy nhin cc ng dng d liu thng cn truyn hai chiu ng

thi (song cng - full duplex). c im ny ca d liu yu cu nhng c tnh k

thut c th truyn dn d liu song cng trn mch vng ni ht. y chnh l mt

trong nhng vn gp phi khi ngi ta c gng chuyn d liu trn mng c xy

dng truyn lu lng thoi.

1.1.1.2Trm chuyn mch trung tmTrm chuyn mch trung tm (CO) l thnh phn ct li dng thit lp nhng

kt ni tm thi gia cc thu bao. thc hin c iu ny, chuyn mch CO phi

t cui cc ng dy thu bao v cc ng trung k lin trm. thu bao thc

hin mt cuc gi v c cung cp cc ch dn cho cc th tc gi, cc mch dch v

cng phi kt cui chuyn mch.

T nhng nm 1950 n 1960 cc chuyn mch l cin, t nhng nm 70 n

80 l chuyn mch in t v t nhng nm 90 trli y th chuyn mch da trn

cng ngh s.

Phn tiu khin l phn rt quan trng trong vic iu khin v gim st vic

thit lp cuc gi v tin hnh cuc gi. Chc nng ca n c th phn tn cc phn

t chuyn mch hay c tp hp thit b trung tm. Chc nng iu khin c th

c thc hin bi cc rle cin hay cc my tnh k thut s. Mt chc nng phn

tiu khin thng c thc hin khc l tnh cc v gim st lng s dng.

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C mt thnh phn chnh na ca trm CO song li khng thuc v chuyn

mch, l trung tm u dy (wire center). Trung tm ny cha c chuyn mch in

thoi v cc thit b cp ngun, thit b ca nh cung cp, cc khung u cui cho cc

ng dy dnh ring v cc bng th nghim. Nhng b phn trong trung tm ny l

thnh phn bt buc trm CO c th vn hnh c.

1.1.1.3Trung kTrung k l thit b truyn dn gia cc chuyn mch. Thng thng trung k l

cc ng truyn s ghp knh tc cao (kim loi hoc cp quang). Cc ng trung

k c th di hng trm kilomt v c nhiu khch hng dng chung. Nu khng

ng trung k trc tip p ng nhu cu kt ni (v d khi cc ng trung k

c s dng ht) th cuc gi c th kt ni trn nhiu trung k xuyn qua nhiu

chuyn mch.

Mng in thoi ca AT&T (M) t nhng nm 1970 c thit k hnh thp 5

cp. Ngy nay mng in thoi cc quc gia c t cp hn, thng l 3 hoc 4 cp (

Vit Nam l 3 cp). Trong s phn cp ny th cp thp nht l trm CO. Nu

khng tm c trung k kt ni trc tip gia cc trm CO th cuc gi c chuyn

tip ln cp tip theo. Cp chuyn mch tip theo ny li tm kt ni trc tip, nu

khng tm c, n s chuyn cuc gi ln cp cao hn na. Khi cuc gi ti nh

phn cp th lng thit b chim dng cng gia tng. Vic tnh ton lu lngtrong mng ny l vn sng cn v n phi m bo gim thiu chi ph cho vic

nh tuyn mt cuc gi.

V trung k thng kh di v c s lng t hn so vi cc mch vng ni ht

nn n rt quan trng v cn phi iu chnh mt cch kinh t cung cp c cht

lng ng truyn tt hn so vi mch vng ni ht. V th, cc trung k thng l

cc ng truyn 4 dy s nu l dy ng hoc ngy nay th ngi ta hay dng trung

k quang.Snh i gia chi ph dch v v cht lng l vn ph cp trong mng

in thoi cng cng. Mc ch ca n l cp c dch v r ti khch hng v

em li li nhun hp l cho nh cung cp vin thng. Snh i ny lin quan ti

cht lng truyn dn. N hu ch cho vic chi tr nhiu hn cho s t trung k cht

lng cao. Cn v pha ngi s dng, vi s lng mch vng thu bao rt ln th

lng u t cng s rt ln.

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1.1.1.4Mng tng i ni htHnh 1.2 m t mng tng i ni ht (mng LEC). y hai trm CO cung cp

ng truyn cho khch hng v trung k ti cc trm khc. Ch phn bit gia cc

nhm trung k c mt s dng cao (high-usage trunk) vi nhm trung k cui(final-trunk) qua cch thc truy nhp.

Hnh 1.2: Mng tng i ni ht

Nhm mt s dng cao l nhng trung k khng kh nng chuyn ti

ton b lu lng. Cc cuc gi gia hai chuyn mch c kt ni bng nhm trung

k c mt s dng cao trc tin c nh tuyn ti chnh nhm trung k ny. Nu

khng cn trung k ri th cuc gi sc nh tuyn sang nhm trung k cui v

cuc gi c th s chuyn ti mt chuyn mch CO khc. Cc chuyn mch CO ny

c gi l chuyn mch chuyn tip (tandem). Trc y cc chuyn mch tandem

l chuyn mch lp 4 v chuyn mch CO l chuyn mch lp 5. Chng c phn

lp theo cu trc hnh thp (mng AT&T trc 1983). Chuyn mch tandem c th

c cu hnh ch kt cui cc trung k hoc c kt cui trung k v ng dy ca

khch hng.

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1.1.1.5Cc mng ringNgoi cc mng cng cng c gii thiu, hin nay vn tn ti kh nhiu

mng ring. Mt s mng do cc n v v cng ty xy dng c lp hoc thu mt

phn phng tin ca cng ty in thoi. Cc thnh phn trong mng ring cng tngt nh mng cng cng, ch c s khc bit v tn ca cc phn t trong mng.

1.1.1.6Tng i nhnh ringTng i nhnh ring - PBX (Private Branch Exchange) l mt chuyn mch

in thoi do khch hng shu v nm pha khch hng. Tng i PBX thit lp

kt ni gia cc trm ca n theo cch tng t nh cc chuyn mch CO. N cng

cung cp kt ni ti mng cng cng hay ti cc mng ring ln hn. Cc PBX thng

c k hoch nh s ring khc bit vi mng cng cng. truy nhp ra s cngcng, thng th ngi s dng phi quay thm u s, v d nh bng vic quay s 9

trc khi bt u quay mt sin thoi cng cng, ngi s dng c php truy

nhp vo mng cng cng. Khi PBX thit lp mt ng truyn ti chuyn mch

CO v sau tn hiu mi gi c CO cp cho ng dy thu bao ny, tip

ngi s dng s quay sin thoi cng cng cn gi.

Cc ng dy v trung k PBX c thc cng ty ring iu hnh v thit lp

hoc c th thu t nh cung cp mng ni ht. Cc ng dy ny c thi qua trung

tm u dy v ni ti mt PBX khc.

Ngoi PBX, cc cng ty mun c mng in thoi dnh ring c th la chn

gii php Centrex. y l tn thng dng cho cc dch v ging nh PBX c nh

cung cp dch vin thoi cng cng cp t chuyn mch CO. Dch v ny c th

bao gm k hoch nh s ring, la chn loi dch v, gi cuc gi, chuyn tip cuc

gi hay cc c tnh khc.

Khi la chn gia dch v Centrex v PBX cc cng ty cn xem xt hai yu t:

kh nng ci t, vn hnh v bo dng csh tng chuyn mch ring v kh nngqun l, gim st v bo dng mi trng iu khin m bo vn hnh chuyn

mch hiu qu. Yu t th hai ny c th rt kh khn vi nhng khch hng truyn

thng mi, t kinh nghim.

1.1.1.7in thoi truyn thng v in thoi IPNh vy, chng ta gii thiu c cc thnh phn v vic vn hnh ca mt

mng in thoi chuyn mch knh in hnh. Sau y l m t tnh hung in hnh

vi cuc gi in thoi ng di trn mng chuyn mch knh truyn thng. Khinhc in thoi, bn c kt ni ti chuyn mch CO ca nh cung cp dch vin

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thoi ni ht (LEC). Chuyn mch ny s cung cp m mi quay s ch cho bn bit

l bn c kt ni v hy bm s. in thoi ca bn c mt ng truyn i v

v dnh ring ni ti chuyn mch LEC, chnh l ng truyn m bn phi tr ph

thu hng thng.

Khi thc hin cuc gi ng di, chuyn mch pha ch gi chim gi mt

trung k ni ti tng i chuyn tip (IEC) v chuyn s thu bao b gi ti tng i

chuyn tip ny. IEC snh tuyn cuc gi ti mt LEC ca thu bao b gi v IEC

snh tuyn cuc gi ti im hin din (POP) ch thch hp v chim gi trung k

ti chuyn mch LEC ch . Chuyn mch ch s c gng hon thnh cuc gi

bng cch gi chung ti in thoi b gi. Khi bn b gi nhc my th vic thit lp

cuc gi xong. Cuc gi ny c thc hin kt ni theo phng thc knh (circuit

mode): ch gi ni ti chuyn mch LEC, LEC chuyn ti POP ca IEC, POP ca IECni ti POP ca IEC bn kia (b gi), POP IEC bn b gi li ni ti chuyn mch LEC

b gi (ch) v chuyn mch LEC ni ti bn b gi. Vic tnh cc c bt u khi

bn b gi tr li cuc gi (hon thnh kt ni mch). Khi mt trong hai bn h my,

mch ny b ct v cc thit b dng chung (trung k) c gii phng.

Mt xu hng mi ang xut hin trong vin thng l vic s dng cng ngh

chuyn mch gi truyn lu lng thoi. Giao thc chuyn mch gi c la chn

ngy nay chnh l giao thc Internet (IP). u im ca chuyn mch gi so vi chuynmch knh chnh l chi ph. S lng cuc gi dng chung trung kmng gi c th

nhiu hn s lng cuc gi dng trong mng knh. Nguyn nhn l v tnh thng k

t nhin trong vic ghp mng chuyn gi. Khi ngi s dng mun m thoi th

mng s cung cp bng thng cho ngi . Khi ngi s dng ri (khng ni) th

khng cn cung cp bng thng.

Trong mng chuyn knh th mng cn cp bng thng cho cuc gi trong sut

thi gian m thoi m khng xt n vic ngi s dng c ni hay khng. V d,

bn gi in thoi cho ai trong 10 pht. Trong mng knh bn phi s dng gp hai

ln bng thng (2 chiu) trong 10 pht ngha l tng ng vi 20 pht bng thng.

Trong khi mng gi, c ti 50 phn trm thi gian bn dng nghe, khi

khng cn bng thng, v 30 phn trm thi gian trong khi bn ni l khong lng

(con s ny c th thay i theo c tnh ting ni ca mi ngi). Nh vy tng

ng vi 20 pht bng thng trn mng knh th mng gi ch cn 7 pht, hay l bn

tit kim c 2/3 lng bng thng cho mi cuc gi.

Sau y l m t mt cuc gi thoi IP s dng in thoi chun truyn thng.Cuc gi bt u ging nh cc cuc gi khc, khi ngi s dng A nhc in thoi v

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c kt ni ti LEC ca ngi . Tuy nhin, ngi A gi ti cng VoIP v l cuc

gi ni ht. Cng ny s tr li v yu cu ID ngi s dng c nhp qua bn phm

in thoi. Nu c php, mt m mi quay s th hai sc gi cho ngi gi v

ngi gi s bm sin thoi b gi. Sau , cng pha ch gi phi tm cng pha b

gi. Trong nhiu trng hp, nh vn hnh cng s bo cho nhau s hin din ca

mnh v gi csd liu cc a ch cng IP lin quan ti cc sin thoi. i li,

cng pha ch gi s c tha gi IP (multicast) xc nh cng pha b gi. Mt

khi xc nh c cng b gi, cng pha ch gi s gi cho b gi mt lot gi IP

yu cu thit lp kt ni ti ch. Nu yu cu c chp nhn, cng pha b gi s

kt ni ti u cui b gi.

Mt khi ngi s dng B tr li cuc gi, th kt ni chuyn mch xut hin

gia A v cng pha ch gi v gia cng pha b gi v B. Tn hiu thoi sc giqua mng thnh dng cc gi IP ti cng ch. Vic truyn dn thoi gia card ng

dy trn chuyn mch LEC v cng tng ng s dng tc lung s PCM truyn

thng l 64 kb/s. Tuy nhin, vic truyn gi IP s dng ccu nn bng thng mi

thp hn nhiu (v d 8 kb/s), v th cc cng s thc hin nhng chuyn i cn thit.

in thoi IP v cc nh cung cp dch v thoi Internet (ITSP) l phn ang gia

tng trong nn cng nghip in thoi vi ngy cng nhiu nh cung cp. Nhiu nh

cung cp dch vin thoi ng di ang vn chuyn lu lng thoi trn nn giIP vi cht lng ngy cng tng.

1.1.2 Nguyn lnh s

E.164 l tn quy hoch nh s in thoi quc t c Ban chun ha vin

thng ca Hip hi vin thng quc t (ITU-T) a ra v qun l. N ch r nh dng,

cu trc cng nh vic phn cp qun l cc sin thoi. E.164 ng l ti liu

ca ITU m t v cu trc h thng cc sin thoi. ITU a ra v quy nh cc m

quc gia, nhng vic qun l cc sin thoi trong mi quc gia li c chnh phu quyn cho mt cquan vin thng thuc quc gia nm gi. V d, m quc gia

cho Canada l 1, c l 49, Nht l 81, Vit Nam l 84, ... Cc ch s cn li ca s

in thoi c mi quc gia gn theo k hoch nh s ca mnh v c gi l s

quc gia (NSN).

Vi Vit Nam, s quc gia gm hai phn. Phn u l m vng (v d H Ni l

4, T.P H Ch Minh l 8, ) hoc m mng (ca cc nh cung cp khc nhau, v d

Vinaphone l 91, 94, 123 hoc Mobifone l 90, 93, 122). Phn sau l m tng i

(CO) v m thu bao (thng l 4 s t 0000 n 9999). Tuy nhin mt s m quc

gia c dnh ring cho cc dch vc bit v d nh dch v 1800, 1900 hay dch v

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113 (gi cng an), 114 (bo chy), 119 (sa cha in thoi) v.v. Mt s tng i CO

c th phc v hng trm nghn thu bao nn c th c vi m CO. Mt s tng i

khc li ch phc v vi trm hoc vi ngn s. Nh vy mt s E.164 dng y

bao gmm quc gia,m vng hoc thnh phhoc mng cung cp, v cui cng

lsin thoi. Hnh 1.3 l cu trc s E.164 theo vng a l.

Hnh 1.3: Cu trc s E.164 quc t theo vng a l

V d chui s chun y i vi sin thoi H Ni l +84-4-38549352

vi m quc gia l 84, m vng l 4, m tng i l 3854 v m thu bao l 9352.

1.1.3 Cc t chc chun ha v iu phiPhn ny gii thiu mt s t chc chun ha cho trong ngnh vin thng,

gm cc t chc vin thng quc t, khu vc v quc gia (Hnh 1.4).

Hnh 1.4: Cc t chc chun ha trn th gii

Mng in thoi cng cng c cc phn t thit b thuc v nhiu nh cung cp

c th gn vi cc giao din v chun c t cc quy tc t c dch v. Tng

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t, cc chun cng cn vi mng d liu. Sau y gii thiu v mt s t chc chun

ha quan trng trn th gii.

Lin minh vin thng quc t (ITU)

L mt cquan chuyn mn ca Lin hp quc chu trch nhim v vin thng.N bao gm gn 200 nc thnh vin v cng tc chun ho c chia thnh cc phn

chnh: ITU-T (trc y gi l CCITT) v ITU-R (trc y gi l CCIR). T l vit tt

ca Telecommunication (vin thng), cn R l vit tt ca Radio (v tuyn).

ITU-T v ITU-R xut bn ra cc khuyn ngh, thc cht l cc tiu chun chnh

v vin thng. ITU-T xy dng cc tiu chun v cc mng vin thng cng cng (v

d nh PSTN, ISDN, B-ISDN, ), cn ITU-R v v tuyn (v d nh vic s dng

tn s trn th gii v cc c tnh k thut ca cc h thng v tuyn). Rt nhiunhm tham gia vo cng vic ny nhng ch c cc cquan thuc quc gia mi c

quyn b phiu. ITU-T xy dng c hu ht cc tiu chun ton cu cho cc

mng cng cng, v l t chc chun ha c nh hng ln nht n cc chun in

thoi trn th gii. a ch: http://www.itu.int/ITUTELECOM/index.html.

T chc chun ha quc t (ISO)

L t chc quc t to ra cc chun cho cng nghip v thng mi (v d nh

chun v tc phim, ng ren c vt v vin thng). a ch http://www.iso.ch/.

Vin chun ha quc gia M (ANSI)

Nghin cu v n bn cc chun thng qua cc y ban c php nh chun T1

cho vin thng. a ch: http://www.ansi.org/.

Lin minh gii php cng nghip vin thng (ATIS)

c cc nh cung cp vin thng ti tr. Cc nh ti try ban T1 cho vic

pht trin cc chun vin thng. a ch: http://www.atis.org/.

Hip hi cng nghip in t(EIA)

L cquan chun ha ca cc nh sn xut, a ra cc chun nh chun giao

din EIA-232. a ch: http://www.eia.org/.

Vin cc k sin v in t(IEEE)

Nghin cu nhiu chun lin quan n in t v vin thng, trong c y ban

802 pht trin rt nhiu chun cho mng ni ht. a ch: http://www.ieee.org/.

Vin tiu chun vin thng Chu u (ETSI)

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L t chc chun ha i din cho cc cng ty vin thng t 52 nc trong v

ngoi Chu u. a ch: http://www.etsi.org/

1.2 Mng truyn s liu

Truyn s liu l mt loi hnh rt ph bin trong thi i thng tin hin nay.

l mt trong cc loi hnh dch v vin thng v c thc hin trn mt s mng khc

nhau nh: Mng s liu chuyn mch gi, mng s liu chuyn mch knh, mng in

thoi cng cng, hay n gin l cc mng my tnh (LAN, MAN, WAN), cc mng

thu ring, Cc mng truyn s liu c pht trin t rt sm v ngy nay n hin

din rt nhiu kha cnh trong cuc sng con ngi.

Ngoi ra, vic truyn s liu cn c thc hin thng qua mt s mng khc,

trong vic truyn s liu qua mng my tnh, mng Internet ang pht trin rtmnh m. Chng ta s nghin cu v cc mng ny phn sau.

Khi thc hin truyn s liu trn mng, ngi s dng i hi mt s yu cu

nh: cht lng truyn, tc , vn an ton v bo mt thng tin t c

iu ny, d liu truyn phi c m ha v x l tun theo cc th thc nht nh

no .

1.2.1 Cc h thng my tnh v m hnh Client/Server

1.2.1.1Cc hthng my tnhVo nhng nm 1980, my tnh bn ni ln nh mt phng n thay th

gi r cho cc my tnh ln t tin. Mi my tnh bn u c kh nng tch hp

mi thit b ngoi vi v phn mm hon thnh mt s cng vic c th, song vic

chuyn giao d liu gia cc h thng cha c thc hin tng, khi cn trao i

d liu ngi s dng phi dng ti a mm.

Vi pht trin ca cng nghip my tnh, cc nh qun tr mng, chuyn vin

tip th, ngi dng, v thit k vin bt u thy r cc u im ca vic dng chungd liu v phn cng gia mt nhm cc my PC tuy ring l song li mang tnh hp

tc. T mng my tnh ra i, n trthnh mt phng tin truyn b thng

tin. Mun hiu r cc im phc tp ca tin trnh truyn thng d liu v kt ni

mng my tnh, bn phi c mt nn tng khi nim cn bn v mng my tnh.

Mng my tnh (computer network) l mt nhm cc my tnh tng kt chia s

cc dch v thng qua mt kt ni dng chung. Do , yu cu ca mng my tnh l

hai hoc nhiu c nhn c mt ti liu no mun cng nhau chia s. Mt c nhnphi c kh nng cung cp mt ti liu no . Cc h thng ring l phi c kt ni

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vi nhau thng qua mt phng tin vt l. Mi h thng ni vi phng tin vt l

ny phi tun th mt lot cc quy tc truyn thng chung th d liu mi n c

ch chng nh, v do cc h thng gi nhn mi hiu c nhau. Cc quy tc

iu hnh tin trnh truyn thng my tnh c gi l giao thc (protocol).

H thng mng my tnh thng c mt trong hai m hnh sau: khch/ch

(Client/Server) v ngang hng. Nhiu mi trng mng s dng c hai m hnh. V d,

mt cng ty c th dng ng thi cc h iu hnh Netware khch/ch cng vi

Novell v Windows for Workgroup ngang hng ca Microsoft.

1.2.1.2M hnh Client/Server (khch/ch)Mt trong nhng nguyn tc s dng mng l cho php chia s cc ti nguyn.

Vic chia s ny thng c thi hnh bi hai chng trnh ring bit, mi chngtrnh chy trn cc my tnh khc nhau. Mt chng trnh c gi l Server, cung cp

ti nguyn, chng trnh kia c gi l Client, s dng ti nguyn . Cc chng

trnh Server v Client thng l chy trn cc my khc nhau. Mt chng trnh

Server c th cng p ng cho nhiu chng trnh Client trn nhiu my tnh khc

nhau cng mt lc (Hnh 1.5).

Hnh 1.5:M hnh khch ch (client/server)

Di m hnh khch/ch, cc ti nguyn phn cng c thc tp trung trn

cc my ch v cc my khch c thc thit k theo cc cu hnh phn cng ti

thiu. M hnh khch/ch t ra l l tng i vi cc mng ln cn n h thng bo

mt mng. Di m hnh khch/ch, ngi qun tr c th d dng iu khin quyn

truy nhp cc ti nguyn mng.

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Thng thng chng trnh Server chy trn mt my tnh no trong mng,

c kh nng cung cp mt dch v no . Chng trnh Client l chng trnh giao

tip vi ngi s dng, khi nhn yu cu ca ngi s dng, chng trnh Client s

gi cc yu cu n chng trnh Server v chkt qu tr v, chng trnh Server khi

nhn c yu cu, s thi hnh dch v tng ng v tr kt qu v cho chng trnh

Client.

S lin h gia chng trnh Client v Server ch thng qua nhng dng thc

thng ip c qui nh khi lp trnh cn vic x l li Server v hin th ti Client l

c lp nhau. Do chng trnh Client v Server c th thay i thng xuyn m

vn hot ng tt min sao vn tun theo cc giao thc truyn thng gia chng.

1.2.2 M hnh tham chiu OSI

Vo cui thp nin 70 th k 20, t chc tiu chun ho quc t (ISO) lp ra

mt tiu ban nhm pht trin mt khung chun cho kin trc mng my tnh, chnh

l m hnh tham chiu cho vic kt ni cc h thng m(OSI). Mc ch ca m hnh

ny l gim thiu s khng tng thch gia cc h thng my tnh.

Nm 1982, ISO pht hnh bn d tho cc tiu chun quc t mang tn ISO

7498. Ti liu ny cha ra khung chun cho vic thit k cc giao thc truyn thng

ch khng a ra cc c tnh k thut chi tit cn thit cho tnh tng thch. CCITT

v ITU-T pht hnh ti liu ny trn khuyn ngh X.200.

Ban u OSI c thit k cho truyn thng my tnh. Ngy nay d liu v thoi

khng nht thit phi c tch ra thnh cc mng khc nhau. Nhiu khi mng khng

bit v khng quan tm ti vic d liu ang truyn cha thng tin g. ISO v ITU-T

nh r tt c cc h thng v mng mi theo nguyn l phn tng ca OSI. Tuy nhin

c mt vi h thng ton cu khng c thit k theo OSI, tiu biu nht l Internet.

Internet da trn cc chun sn c, nhng khng c ph chun bi ISO hoc ITU-T.

Tn OSI xut pht t mc ch lm cho cc h thng tr thnh m vi hthng khc trong vic truyn thng. Cc nh sn xut c t do s dng cc c tnh

k thut m ny. Tuy nhin vn tn ti nhiu h thng truyn d liu c quyn,

cc c tnh k thut ca h thng ny l c quyn ca nh sn xut. Do vy chng

khng th s dng c cho cc h thng khc.

Trong m hnh OSI, h thng truyn thng c chia thnh 7 tng (Hnh 1.6).

Khi chng ta xem xt n cc chc nng mi tng thc hin, chng ta s nhn thy

cc tng cng thp cng c nhiu chc nng lin quan n cng ngh mng s dng

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cho truyn d liu thc s. Cn cc tng cng cao cng c nhiu chc nng phc v

cho cc ng dng phm mm chy trn cc my ch.

Trong m hnh OSI, tt c cc tng t tng 4 n tng 7 c thc hin ch trong

truyn thng cc my trm, chng khng thc hin qu trnh truyn d liu u-cuithc s. Qu trnh ny thuc v cc tng t 1 n 3. Mc ch ca cc tng cao nht l

trgip cho cc ng dng phn mm, v thc hin c iu ny cc tng cao nht

cung cp cc dch v phc tp hn ch khng ch n gin l mt lung d liu.

Lung d liu ny c tng mng cung cp v c th cha li. Trong trng hp dch

v phc hi li khng c giao thc tng giao vn cung cp th cc nh thit k phn

mm ng dng phi thit k mt lc phc hi li trong ng dng ca mnh.

Application

Presentation

Session

Transport

Network

Data link

Physical

Giao thc tng ng dngng dng

Trnh din

Phin

Giao vn

Mng

Lin kt d liu

Vt l

Phn mmng dng

My ch B

Giao thc tng trnh din

Giao thc tng phin

Giao thc tng giao vn

Network

Data link

Physical

Mng

Lin kt d liu

Vt l

a)

b)

c

a)

b)

c

Mng truyn thng cp di

Mi trng vt la) Giao thc tng mngb) Giao thc tng lin kt d liuc) Giao thc tng vt l

Tng 7

Tng 6

Tng 5

Tng 4

Tng 3

Tng 2

Tng 1

Phn mm

ng dng My ch A

Hnh 1.6: M hnh tham chiu OSI

1.2.2.1Tng vt lTng vt l lin quan n qu trnh truyn dn tn hiu qua mt knh truyn

thng. Vn chnh ca vic thit k l m bo khi mt bn gi bit 1 th bn kiacng phi nhn c bit 1 ch khng phi bit 0. Cc c tnh k thut in hnhca tng vt l gm: tc bit, gi trin p (hoc l cng dng in) c sdng biu din bit 0 v bit 1, s chn cm v loi b ni (connector) s dng.Tng vt l trong cc h thng c thit k gim thiu li khi hot ng. Trongtrng hp c li th cc tng trn s bnh hng.

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Cc c t ca tng vt l lin quan n cc giao din in, cv phng tintruyn dn vt l. Phng tin truyn dn c hiu l di tng vt l, nhng ccc tnh n yu cu c cha trong c t ca tng vt l.

1.2.2.2Tng lin kt dliuTng lin kt d liu c nhim v to lp cc khung, gi chng ti knh truyn

thng vt l thng qua tng vt l; nhn khung, kim tra li v chuyn khung khng cli ln tng mng. Tng lin kt d liu pha nhn gi tn hiu xc nhn cho tng linkt d liu pha truyn. Pha truyn c th truyn li khung nu trong mt khong thigian nht nh pha nhn khng gi tn hiu xc nhn.

ISO nh r tng lin kt d liu cho cc mng LAN v chia cc c t thnh 2

tng con:

- Tng con iu khin truy nhp phng tin (MAC Medium Access Control)- Tng con iu khin lin kt logic (LLC Logical Link Control)

Do tnh cht phc tp ca tng lin kt d liu trong cc mng LAN m s phnchia ny l cn thit. Trong mng LAN, cc my tnh c ni ti cng mt dy cp,chng chia s kh nng truyn dn ca mt knh qung b (a truy nhp hoc truynhp ngu nhin). Tng con MAC lin quan n cc chc nng ph thuc phn cngmng. Hai v d ph bin nht ca cc cng ngh truy nhp mng LAN l CSMA/CD(Ethernet) v Token Ring. Tng con LLC quan tm nht n kha cnh ton vn d

liu nh: truyn li d liu, xc nhn vic nhn d liu. i vi cc lin kt im-imn gin hn th khng cn phi tch tng MAC. Trong trng hp ny, ch mt c tgiao thc tng lin kt d liu cng c th bao ph ton b tng lin kt d liu.

Trong mng LAN, mi my tnh c ring mt a ch MAC (a ch phn cng).a ch ny c s dng xc nh ngun v ch ca mi khung trn knh qungb. Nhc a ch MAC, cc my tnh c th c mt kt ni im-im thng qua mtknh qung b c chia s bi nhiu kt ni im-im. Cn ch rng a ch MACchc s dng bn trong mng LAN ch khng c truyn ti cc mng khc.

1.2.2.3Tng mngCc tng bn di tng mng ch quan tm n cc kt ni im-im gia 2

nt. Tng mng c nhng kin thc v kin trc mng v cng vi tng mng ca ccnt n phc v, cc gi d liu c nh tuyn thng qua mng ti ch. Mi ntc ring mt a ch ton cc (tng mng).

Vn chnh yu l xc nh c bao nhiu gi tin c nh tuyn t imngun ti im ch. Vic nh tuyn c th da trn cc bng nh tuyn cnh titng mng v chng him khi thay i, hoc cc tuyn c th thay i phn nh titrng hin thi ca mng.

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Khi c nhu cu, cc my ch ca mng c th t do gi cc gi tin. Chngthng khng c bit g v mt lu lng ca cc my ch khc hoc ca cc ktni trn mng. Tnh c, nu c nhiu my ch cng trao i thng tin ti mt thiim v c qu nhiu gi c truyn th s to ra cc khu vc d b tc nghn trn

mng. Vic iu khin tc nghn cng thuc v tng mng.Trong cc mng d liu cng cng, chc nng tnh cc thng c xy dng

bn trong tng mng. Phn mm trong tng mng phi m xem c bao nhiu gi tinhoc k t m mi khch hng gi a ra thng tin tnh cc.

Trong mt mng qung b bit lp (chng hn Ethernet) vic nh tuyn ngin n mc c th khng cn n tng mng. a ch MAC c th nhn dng ccmy ch. Tuy nhin nu cc mng ny c ni ti cc mng khc, th bt buc phic cc a ch mng. Ch rng cc a ch MAC s dng trong tng lin kt d liu

l khng quan trng bn ngoi mng LAN.

1.2.2.4Tng giao vnTng giao vn l tng u-cui thc su tin. Cc giao thc t tng giao vn

trln ca cc trm s dng mng nh mt kt ni im-im truyn thng. Thng

ip ngun trn ng i c thc tng mng tch ra v tng phin bn nhn s lni u tin cc gi nh thuc cng mt thng ip gp li nhau.

Tng giao vn hot ng nh mt tng giao din gia cc tng thp (dnh cho

vic kt ni mng) v cc tng cao (dnh cho cc dch vng dng). Nhim v catng ny l m bo thng xuyn vic truyn dn tu cui n u cui khng cli v cc gi tin khng b mt trong qu trnh truyn thng. thc hin iu nytrong tng giao vn c th bao gm cc th tc truyn li hoc th tc xc nhn.

Tng giao vn thng cung cp 2 lp dch v cscho tng phin:

- Truyn cc thng ip v gi d liu ring bit qua mng. Cc thng ip ctruyn c th ti ch theo th t khc nhau v li c th xut hin. V d giaothc UDP User Datagram Protocol ca Internet (khng thuc v cc giao thc

OSI) v giao thc giao vn, lp 1 (TP1) ca OSI (IS 9072).- Knh truyn im-im khng li s chuyn cc thng ip theo cng mt th

t nh khi chng c gi. V d giao thc iu khin truyn thng (TCP) caInternet (khng c trong chun giao thc OSI) v TP4 ca OSI (IS 8072/8073)

1.2.2.5Tng phinTng giao vn m bo cho s thnh cng trong truyn thng u-cui gia cc

my tnh. Thc t, qu trnh truyn thng c thc hin bi 4 tng bn di tngphin. Ba tng cao nht khng cn thit cho qu trnh truyn d liu, nhng chng tos tng thch cho cc ng dng v do vy cc chng trnh ng dng chy trn ccmy c th hiu c nhau.

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Tng phin cho php s dng trn cc my khc nhau thit lp cc phin lmvic vi nhau. V d, n cho php ngi s dng truy nhp vo mt h thng chia sthi gian xa hoc cho php truyn tp gia 2 my tnh.

Tng phin cho php truyn thng cc d liu bnh thng, ging nh tng giao

vn thc hin, nhng n cn cung cp mt s dch v mrng hu ch cho cc ngdng. Chng hn dch v qun liu khin m thoi. Cc phin lm vic c th chophp truyn thng 2 hng hoc 1 hng ti mt thi im. Nu truyn thng mthng c cho php, tng phin c th cho bit hng no ang s dng. Tng phincn cung cp chc nng qun l th bi, v vi s trgip ca chc nng ny ch cmy no nm th bi mi c th thc hin mt thao tc nguy cp.

Mt dch v khc ca tng phin l dch v truyn thnh cng cc tp kchthc ln. Nu khng c dch v ny th ch cn mt li n gin trong qu trnh

truyn thng cng c th ph hy c mt tp v do phi truyn li c tp. hnchiu ny, tng phin cung cp cch chn cc im kim tra vo trong lung dliu, v do vy nu c li th ch cn truyn li d liu tim kim tra cui cng.

1.2.2.6Tng trnh dinNh chng ta thy, cc tng thp ch yu lin quan ti qu trnh truyn c th

t cc bit hoc d liu t ngun n ch. Thay vo , tng trnh din lin quan ndng thng tin c truyn i. Mi my tnh c th c cch biu din d liu ni tiring ca n, do vy nhng tho thun v chuyn i l cn thit cc my tnh cth hiu c nhau.

Nhim v ca tng trnh din l m ha d liu c cu trc theo cc nhdng ca my tnh thnh lung d liu ph hp cho truyn dn. Chng hn nh vicnn d liu. Tng trnh din pha nhn gii m d liu c nn thnh dng biudin c yu cu. Tng trnh din gip c 2 my tnh hiu c ngha ca lung bitnhn c theo cng mt cch.

Cc my tnh khc nhau c cch biu din d liu ni ti khc nhau. Tt c cc

my tnh ln IBM u s dng m trao i thp phn c m ho nh phn mrng(EBCDIC Extended Binary-Coded Decimal Interchange Code), m k t 8 bit; trongkhi thc t tt c cc my khc u s dng m ASCII 7 hoc 8 bit. Cc chp Intelnh s cc byte ca n t phi sang tri, trong khi cc chp Motorola th li nh s ttri qua phi. Do cc hng sn xut my tnh him khi thay i cc quy c ca ringmnh nn cc chun ton cu cho vic biu din d liu ni ti s khng bao gicchp nhn.

Mt gii php m bo tnh tng thch l nh ngha mt chun cho dngbiu din mng ca d liu. Nh vy bt k my tnh no cng c th truyn thngc vi cc my tnh khc nu n chuyn i nhng biu din d liu ni ti thnhdng mng c chun ho ny.

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1.2.2.7Tng ng dngTng ng dng bao hm cc ng dng truyn thng s dng dch v ca cc

tng thp hn. Cc ng dng ca ngi s dng thc hin cc cng vic trn my tnhkhng thuc vo tng ng dng, nhng chng trao i thng tin nhs trgip cagiao thc tng ng dng. Chng trnh x l vn bn l mt v d vng dng cangi s dng.

phc v cc ng dng ngi s dng, cc ng dng truyn thng cn thit

nh truyn tp hoc mt u cui ASCII thng c nh ngha nh cc giao thc

tng ng dng. ng dng truyn thng cung cp cho cc ng dng ngi s dng

nhng dch v khng ph thuc nh sn xut. Cc dch v tng ng dng thng sn

c i vi cc lp trnh vin ging nh cc dch v khc cu hiu hnh. Vi s tr

gip ca cc dch v ny, nh lp trnh phn mm ng dng khng phi lo lng g vqu trnh truyn thng d liu thc t. H c th s dng tt c cc dch v ca chng

giao thc c thc hin trn mi trng pht trin phn mm ca h.

Thin t (Email) l mt v d v cc giao thc ng dng. Trong v d ny,

ngoi cc chc nng ging vi cc chc nng ca giao thc truyn tp, n cn cung

cp cc chc nng vit sn nh xo, gi v c th. V d, nhng c tnh k thut ca

tng ng dng nh ngha nh dng ca trng a ch v trng thng ip.

phn bit gia chng trnh ng dng v tng ng dng c xc nh bimt giao thc, chng ta hy ly thin t lm v d. Chng ta c th c mt ng

dng chy bn trn tng ng dng. Chng trnh ny c th cung cp 9 mu, mt trnh

son tho thn thin ngi s dng, cc ca snh a ch v nh ni dung thng

ip. N cng c th cung cp mt phng php nh a ch thn thin ngi s dng

chng hn nh khi chng ta nh mt a chch l John th a ch ny sc

phn mm chuyn i thnh dng m tng ng dng hiu c.

Cn ch rng dch v tng ng dng cung cp cho chng ta cc dch v truynthng nhng chng ta c th phi nng cao cc dch v ny cng vi mt phn mmng dng s dng n cho cc mc ch ni b.

1.2.3 Mt s v d v cc mng truyn s liu

Nhu cu truyn s liu c t rt lu v cc mng truyn s liu cng xut

hin t nhng nm 1980. Theo pht trin ca cng ngh mng, vic truyn s liu

cng c thc hin trn cc mng da trn nn cng ngh khc nhau, t nn cng

ngh chuyn knh n cng ngh chuyn gi.

Mng s liu cng cng chuyn mch knh - CSPDN (Circuited Switched Public

Data Network)

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c a vo s dng t nhng nm 1980. y l mng hon ton s v c

thit k ring cho truyn thng s liu. Thng c bn tc truyn cbn l: 600,

2400, 4800 v 9600 b/s, c th la chn mt trong bn tc ny. Knh truyn s

c duy tr trong sut thi gian truyn.

Mng s liu cng cng chuyn mch gi - PSPDN (Packet Switched Public Data

Network)

c s dng khp th gii t nhng nm 1970. Mng ny cho php cc u

cui c tc bit khc nhau v ngi s dng c th thm nhp mt s csd liu

ln trn khp th gii. Hu ht cc mng truyn s liu trn th gii u l mng

chuyn gi.

Mng in thoi cng cng - PSTN (Public Switched Telephone Network)Do cc ng dy in thoi ch dng truyn cc tn hiu m thanh vi di

tn 0,3 3,4 KHz nn mun truyn s liu th phi s dng Modem l cc thit biu

ch v gii iu ch tn hiu truyn d liu thnh tn hiu tng t c di tn ph hp

vi ng dy in thoi v ngc li.

Mng truyn s liu X25

X.25 l mt giao thc c CCITT (Consultative Committee for International

Telegraph and Telephone: Hi ng Tham Vn vin Thoi v in Tn Quc T)cng nhn. Giao thc ny l giao thc rt ph bin c a ra nhm bo m s

nguyn vn ca d liu khi di chuyn trong mng. N nh ngha s kt ni vi nhau

ca nhiu mng dng k thut ni chuyn gi vi cc my tnh lin h hoc cc u ra.

X.25 cho php cc my tnh ca nhiu mng cng cng khc nhau c th lin lc

xuyn qua mt my tnh trung gian tng mng.

Mng Frame Relay (FR)

FR c dng cho vic ni cc thit b trong WAN. Giao thc FR c to ra dng trong mi trng c tc truyn dn cao hn X.25 v kh nng b li t. M,

n h trtc tc T-1 (hay DS1) ln n 1,544 Mb/s. Thc ra, frame relay cbn da

trn giao thc c l X.25. S khc bit l ch frame relay l k thut "gi nhanh"

(fast-packet) v k thut ny s khng tin hnh iu chnh li. Khi tm ra li, n ch

n gin hu b gi c li i. Cc u cui chu trch nhim cho vic pht hin li v

yu cu gi li gi hy b.

Mng my tnh

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Mng LAN, MAN, WAN, Internet, mng a dch v bng rng. Cc mng ny

c trnh by chi tit trong phn 1.3 v trong cc chng 4, 5.

Cc mng ring

Cc mng c s dng ring cho vic truyn dn d liu v c th l ring chotrng hc, doanh nghip, chnh ph hay quc gia.

1.3 Mng Internet

Internet l mt mng thng tin ton cu c thc truy nhp cng cng gm

cc mng my tnh c lin kt vi nhau. Mng ny truyn thng tin theo kiu

chuyn gi d liu da trn mt b giao thc c chun ha (TCP/IP). Mi trng

lin mng ca Internet bao gm hng ngn mng my tnh nh hn ca cc doanh

nghip, cc vin nghin cu v trng i hc, cc chnh ph cng nh l ngi dng

c nhn trn ton cu.

1.3.1 Sra i v pht trin

Nm 1969, mng ARPAnet ca b Quc phng Mc thnh lp. (ARPA l

vit tt ca cm t Advanced Research Projects Agency - Cquan cc d n nghin

cu cao cp) vi mc tiu l:

- L mt mng my tnh c kh nng chu ng cc s c (v d mt s nt mngb tn cng v ph hu nhng mng vn tip tc hot ng).

- Mng cho php mt my tnh bt k trn mng lin lc vi mi my tnh khc.

Nm 1982, b giao thc TCP/IP (Transmission Control Protocol/Internet

Protocol) c a ra. y l giao thc gip cho cc my c th d dng truyn thng

vi nhau v cng chnh l giao thc chun trn Internet cho n ngy nay.

Nm 1983, ARPAnet s dng b giao thc TCP/IP v sau , Qu khoa hc

quc gia ca M (National Science Foundation - NSF) ti trcho vic xy dngNSFnet thay th cho ARPAnet.

Nm 1986 NSFnet lin kt 60 trng i hc M v 3 trng i hc Chu u.

im quan trng ca NSFnet l n cho php mi ngi cng s dng.

Nm 1991, ti trung tm nghin cu nguyn t Chu u CERN, Tim Berners

Lee trin khai thnh cng dch v World Wide Web (WWW). Chnh nhdch v ny

m ngi s dng tm thy mng my tnh ton cu c nhiu iu hp dn.

Nm 1993 NSF lp InterNIC cung cp nhiu dch v mi, khi nim Internet,mng thng tin ton cu c hnh thnh.

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Ngy nay Internet thc s l mng my tnh ca ton cu vi vic cho php mi

ngi u tm thy dch v m mnh cn n

Thng 12 nm 1997, Vit Nam chnh thc tham gia kt ni vo mng li ton

cu Internet. Cho ti 2/2010 c trn 23 triu ngi s dng Internet chim khong27% dn s.

Internet c xy dng trn nn k thut chuyn mch gi, k thut ny ang

c pht trin chp nhn c mc cht lng dch vi vi cc ng dng thi

gian thc nh video v thoi. Chng ta mong i mng Internet sp ng cc ng

dng thng tin thi gian thc vi cht lng tt nh cc dch vang c thc hin

trn cc mng s dng cng ngh chuyn mch knh.

1.3.2

Cc thnh phn v cu trc mng1.3.2.1Cc thnh phn ca mng

Internet l mng ca cc mng, n kt ni cc mng my tnh thng qua thit b

kt ni s dng cc giao thc kt ni. Cc thnh phn ca Internet bao gm:

Cc h thng u cui (end system) kt ni vi nhau to thnh mng, c th l

cc my tnh c nhn, my ch hoc cc thit b khc. Hin nay ngy cng

nhiu cc loi thit b c kh nng kt ni vo mng my tnh nhin thoi di

ng, PDA, TV,...

Mi trng truyn (media) m cc thao tc truyn thng c thc hin qua .

Mi trng truyn c th l cc loi dy dn (cp ng hoc cp quang), sng

in t (i vi cc mng khng dy).

Cc thit b kt ni trong mng: switch c chc nng phn cch cc mng my

tnh thnh cc phn on (segment) ring bit gim hin tng ng ,

gim truyn qung b (broadcast) hay thc hin chc nng bo mt; hub c

chc nng nh mt b lp c nhiu cng, thng tin cng vo sc a titt c cc cng ra, bnh tuyn c chc nng kt ni cc mng my tnh hay

kt ni cc ngi s dng vi mng my tnh cc khong cch xa vi nhau

thng qua cc ng truyn thng nhin thoi, ISDN, T1, X.25,

Giao thc truyn thng (protocol) l cc quy tc quy nh cch trao i d liu

gia cc thc th.

1.3.2.2Kin trc mngMng my tnh c thc phn b trong cc phm vi khc nhau, ngi ta c

th phn ra cc loi mng nh sau:

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LAN (local Area Network) l mng cc b, kt ni cc my tnh trong mt khu

vc bn knh hp, thng th khong vi trm mt. Mi trng truyn thng c

tc kt ni cao, nh cp xon, cp ng trc, cp quang. Mng LAN thng

c s dng trong ni b ca mt cquan, mt t chc. Cc LAN kt ni li

vi nhau thnh mng WAN.

MAN (Metropolitan Area Network) kt ni cc my tnh trong phm vi mt

thnh ph. Kt ni c thc hin thng qua mi trng truyn thng tc

cao (50/100 Mb/s).

WAN (Wide Area Network) l mng din rng, kt ni my tnh trong ni b

quc gia, hay gia cc quc gia trong cng mt chu lc. Thng thng kt ni

ny c thc hin thng qua mng vin thng. Cc WAN kt ni vi nhau

thnh GAN.

GAN (Global Area Network) kt ni my tnh t cc chu lc khc nhau.

Thng thng kt ni ny c thc hin thng qua mng vin thng xuyn lc

a v v tinh.

Mi mng li c kiu kin trc (topology) khc nhau: mng hnh sao (star) - mi

my tnh trn mng sc kt ni vi nhau thng qua mt thit b trung tm nh hub

hay switch, mng hnh li (mesh) - mi my tnh sc kt ni trc tip vi cc

my cn li trong mng, mng hnh cy (tree) - cc my tnh c kt ni theo cu

trc hnh cy c th bc, vng (ring) - mi my tnh trong mng s kt ni vi hai my

gn n nht to thnh hnh vng, xa l (bus) tt c cc my tnh trong mng sc

kt ni ti mt bus chu trnh (loop), (Hnh 1.7).

Hnh sao (star) Chu trnh (loop) Li (mesh) Cy (tree)

Vng (ring) Xa l (bus)

Hnh 1.7: Cc kiu kin trc mng

Trong lin mng c th thy s kt hp ca cc kiu kin trc ny (Hnh 1.8).

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Hnh 1.8: Cu trc lin mng

Regional ISP (Internet Service Provider): Nh cung cp dch v Internet khu vc

POP (Point Of Present): im hin din

1.3.3 Cc phng thc truy nhp mng

1.3.3.1Cc phng thc truy nhp c dyKhi c ci t vo trong mng, cc my trm phi tun theo nhng quy tc

nh trc c th s dng ng truyn, l phng thc truy nhp. Phng thctruy nhp c nh ngha l cc th tc iu hng trm lm vic lm th no v lc

no c th thm nhp vo ng dy cp gi hay nhn cc gi thng tin. Sau y

gii thiu v 3 phng thc truy nhp cbn.

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

Giao thc ny thng dng cho mng c cu trc hnh tuyn, cc my trm cng

chia s mt knh truyn chung, cc trm u c chi thm nhp ng truyn nh

nhau (Multiple Access). Tuy nhin ti mt thi im th ch c mt trm c truyn

d liu m thi. Trc khi truyn d liu, mi trm phi lng nghe ng truyn

chc chn rng ng truyn ri (Carrier Sense). Trong trng hp hai trm thc hin

vic truyn d liu ng thi, xung t d liu s xy ra, cc trm tham gia phi pht

hin c s xung t v thng bo ti cc trm khc gy ra xung t (Collision

Detection), ng thi cc trm phi ngng thm nhp, chi ln sau trong khong

thi gian ngu nhin no ri mi tip tc truyn. Khi lu lng cc gi d liu cn

di chuyn trn mng qu cao, th vic xung t c th xy ra vi s lng ln dn n

lm chm tc truyn tin ca h thng. Phng thc truy nhp CSMA/CD thngdng trong mng c dy.

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Truyn th bi (Token Passing)

Giao thc ny c dng trong cc LAN c cu trc vng s dng k thut

chuyn th bi (token) cp pht quyn truy nhp ng truyn (quyn c truyn

d liu). Th bi y l mt n v d liu c bit, c kch thc v ni dung (gmcc thng tin iu khin) c quy nh ring cho mi giao thc. Trong ng cp

lin tc c mt th bi chy quanh trong mng. Phn d liu ca th bi c mt bit

biu din trng thi s dng ca n (bn hoc ri). Trong th bi c cha mt a ch

ch v c lun chuyn ti cc trm theo mt trt t nh trc. i vi cu hnh

mng dng vng th trt t ca s truyn th bi tng ng vi trt t vt l ca cc

trm xung quanh vng.

Mt trm mun truyn d liu th phi i n khi nhn c mt th bi ri.

Khi trm si bit trng thi ca th bi thnh bn, nn gi d liu c km theo a

ch ni nhn vo th bi v truyn i theo chiu ca vng, th bi lc ny tr thnh

khung mang d liu. Trm ch sau khi nhn khung d liu ny, s copy d liu vo

bm ri tip tc truyn khung theo vng nhng thm mt thng tin xc nhn. Trm

ngun nhn li khung ca mnh (theo vng) c nhn ng, i bit bn thnh bit

ri v truyn th bi i. V th bi chy vng quang trong mng kn v ch c mt th

nn vic ng d liu khng th xy ra, do vy hiu sut truyn d liu ca mng

khng thay i.Trong cc giao thc truyn th bi cn gii quyt hai vn c th dn n ph

vh thng. Mt l vic mt th bi lm cho trn vng khng cn th bi lu chuyn

na. Hai l mt th bi bn lu chuyn khng dng trn vng. u im ca giao thc

l vn hot ng tt khi lu lng truyn thng ln. Giao thc truyn th bi tun th

ng s phn chia ca mi trng mng, hot ng da vo s xoay vng ti cc

trm. Vic truyn th bi s khng thc hin c nu vic xoay vng bt on.

Giao thc phi cha cc th tc kim tra th bi cho php khi phc li th bi b

mt hoc thay th trng thi ca th bi v cung cp cc phng tin sa i logic

(thm vo, bt i hoc nh li trt t ca cc trm).

FDDI (Fiber Distributed Data Interface)

FDDI l k thut dng trong cc mng cu trc vng, chuyn th bi tc cao

bng phng tin cp si quang. FDDI s dng h thng chuyn th bi trong cch

vng kp. Lu thng trn mng FDDI bao gm 2 lung ging nhau theo hai hng

ngc nhau. FDDI thng c s dng vi mng trc trn nhng mng LAN

cng sut thp c th ni vo. Cc mng LAN i hi tc truyn d liu cao v di

thng ln cng c th s dng FDDI.

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1.3.3.2Cc phng thc truy nhp khng dyTrn mng khng dy s c nhng phng thc truy nhp ng truyn khc

nh SDMA, FDMA, TDMA, CDMA,... v cc phng thc kt hp.

FDMA (Frequency Division Multiple Access)a truy nhp phn chia theo tn s. Trong phng php truy nhp ng truyn

ny mi ngi s dng trong mt cell sc phn cho mt di tn s (bng tn) nht

nh. Cc bng tn s dng ca cc ngi dng khc nhau (ti mt thi im) s

khng chng ln nhau (non-overlap). Ngi s dng ch s dng bng tn c cp

php v th nhiu ngi trong cng mt cell c th cng truyn mt lc m khng gy

nhiu cho nhau.

Tuy nhin v s lng ngi s dng mng nhiu nn vic s dng li bng tnc th din ra ti cc cell khc nhau. Nu 2 cell A v B gn nhau th vic s dng li

bng tn c th gy nhiu.

TDMA (Time Division Multiple Access)

a truy nhp phn chia theo thi gian. Vi cch truy nhp ng truyn ny mi

ngi dng c phn chia cho mt khong thi gian trong bng tn c gi l cc

time-slot. Tc l trong mi khong thi gian (rt ngn) mt ngi dng sc s

dng ton b bng tn ng truyn.CDMA (Code Division Multiple Access)

a truy nhp phn chia theo m. Trong phng thc truy nhp ny th cc ngi

dng u c truyn trong cng mt thi gian v c th trn cng mt tn s. Mi

ngi s dng c gn cho mt m (code) ring bit v khng c ngi dng no

trong cng t bo dng chung m . M ny c dng m ha d liu trc khi

gi vo knh truyn dng chung. Ti ni thu tn hiu s s dng m ca ngi dng

tng ng lc bt (khng hon ton) nhng tn hiu t ngi dng khc. iu nycng lm tng thm phc tp ca b lc tn hiu ti cc thit b thu tn hiu.

SDMA (Space Division Multiple Access)

a truy nhp phn chia theo khng gian. Phng php ny s dng cc khong

khng gian gia nhiu ngi s dng trong mt cell. Trm gc (Base Station) khng

truyn tn hiu n ton b cell m n s tp trung hng tn hiu vo vng khng gian

ca ngi dng cn phc v v gim cng sut tn hiu ti cc vng ca thu bao

khc. lm c vic ny th yu cu BS phi c h thng Antenna ln v c khnng kh nhiu.

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1.3.3.3Phng thc truy nhp ngu nhin ALOHA/Slotted-ALOHA tng ca ALOHA l trong mng mi khi nt gi c gi d liu cn gi th

ngay lp tc n gi ton b gi tin vo knh truyn dng chung. Nu gi tin c

truyn xung t vi gi tin t nt khc th ngay lp tc nt s truyn li gi tin vi xc sut p. Nu vic tnh xc sut xc nh n khng c truyn th nt i trong

khong thi gian truyn mt gi tin v li truyn tip gi tin vo knh truyn dng

chung vi xc sut p. Li im ca ALOHA l khng cn ng b thi gian ti cc nt

gi.

SLOTTED-ALOHA: tng chnh ca Slotted-Aloha l chia thi gian thnh

cc khong c di bng thi gian truyn mt gi tin. Tt c cc nt c gi tin cn

truyn u ch truyn gi tin ti u mi khong thi gian. Nu c xung t th tt c

cc nt s pht hin xung t ngay trong khong thi gian v mi nt s truyn li

gi tin vi xc sut p hoc chcho ti u khong thi gian sau. Vi phng thc ny

cn phi ng b thi gian gia cc nt trong mng.

1.3.3.4DAMA (Demand Assigned Multiple Access) -a truy nhp theo nhu cuPhng php ny da trn tng chnh l Aloha nhng c khc phc nhc

im gi gi tin bt k lc no c gi tin cn gi ca mt nt bng cch yu cu mt

nt mun gi d liu i th phi t ch trc (reservation time slot). Mi nt trong

mng sng k vi h thng DAMA mt time-slot trong tng lai m n mun gigi tin ca n ti thi im . Khi h thng cp time-slot cho nt tng ng (nu c

nhiu nt cng t mt time-slot th c th da vo u tin cp quyn s dng,

v d First Come First Serve) th ti time-slot xc sut nt tng ng gi thnh

cng gi tin ca n rt cao vi bng thng gn nh ln nht ca knh truyn. Do c

im l mi nt chc truyn trong khong thi gian t trc nn cho d ti

khong thi gian a no nt c quyn s dng khong thi gian khng c gi tin

gi i nhng n vn c cp quyn, trong khi mt nt c gi tin mun gi ikhng c quyn s dng khong thi gian . c im ny lm tng tr trong

mng. H thng DAMA thng s dng cho lin kt vi v tinh (satellite links).

1.3.4 Cc dch v Internet

Cc dch v Internet bao gm dch v truy nhp Internet, dch v kt ni Internet

v dch vng dng Internet. Dch v kt ni Internet l dch v cung cp cho cc c

quan, t chc, doanh nghip cung cp dch v Internet kh nng kt ni vi nhau v

vi Internet quc t. Dch v truy nhp Internet l dch v cung cp cho ngi s dng

kh nng truy nhp Internet. Dch vng dng Internet l dch v s dng Internet

cung cp cc ng dng cho ngi s dng.

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Sau y gii thiu mt s dch v thng dng trn Internet.

WWW (World Wide Web)

Web l s tp hp ca nhng trang d liu HTML cha tt c cc my tnh

trn th gii. WWW bao gm cc trang thng tin c k t, hnh nh v cc hiu ng ...m bn c th xem bng cc trnh duyt web (Web browser), v d nh Microsoft

Internet Explorer (IE) hoc Netscape Navigator.

E-mail (Thin t)

L dch vp ng yu cu trao i thng tin gia nhng ngi s dng Internet

thng qua vic gi, nhn thin t (Electronic Mail). y l mt trong nhng dch

vc s dng nhiu nht trn Internet vi l do tin li, nhanh chng v kinh t.

FTP (File Transfer Protocol)

FTP l mt h thng ch yu chuyn ti file gia cc my vi tnh vo Internet.

File c chuyn ti c dung lng rt ln. FTP hu ht c s dng cho vic

chuyn ti nhng d liu mang tnh c nhn.

IRC (Internet Relay Chat)

Chat gip cho con ngi truyn t thng tin thng qua internet bng cch g

mu tin t bn phm my vi tnh. lm c iu ny bn phi kt ni vi mng

phc v IRC. Mt ln kt ni bn c th tham gia chat vi hng trm ch khc nhau

hoc thm ch to ch ring cho chnh bn.

Telnet

L dch v kt ni chng trnh ca my tnh ngun vi mt my tnh khc xa.

Trong trng hp ny bn cn phi c tn ngi s dng (username) v mt m

(password) cng nh tn ca my , bn cng phi cn bit m h thng my s

dng - h thng tng qut y l UNIX.

1.4 Xu hng hi t ca cc mng vin thng

S hi t thoi, video v d liu cng vi s mrng th trng v xu hng

ton cu ha dn ti vic cnh tranh cc mc khng th lng trc trong th

trng truyn thng. p lc cnh tranh ang ngy cng to ra khi nhiu cng ty ang

s dng hiu qu ca cc mng a dch v chuyn mch gi hay cn gi l cc mng

th h sau (NGN).

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S pht trin mng vin thng c c l da trn s pht trin ca cc cng

ngh trong cc lnh vc tin hc, in t v vin thng cng vi s gia tng v cht

lng v sa dng dch v theo yu cu ca khch hng.

V cng ngh vin thng, xu hng pht trin tp trung vo ba lnh vc cbn: Cng ngh truyn dn: Cng ngh quang ang khng nh c kh nng

c v cht lng truyn dn v bng thng. Mng truyn dn ang c

quang ha p ng tt hn nhu cu ngy cng cao ca khch hng

(phc vc dch v yu cu tc cao, bng thng rng, cht lng...)

Cng ngh chuyn mch: tch hp vi mch, k thut s cng vi cng

ngh thng tin, ATM: vi xu hng kt hp knh v gi, a dch v, a

tc , chuyn mch quang. Cng ngh truy nhp: Kt hp truyn thng v tin hc; phng thc truy

nhp a dng nh quang, cp ng (ADSL, HDSL), v tuyn (WiFi,

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