M i nhHT PTIT [ Pi ck t he dat e] Bi ging C s k thut chuyn mch

Bin son: Hong Trng Minh, Nguyn Thanh Tr H ni: 2009 HC VIN CNG NGH BU CHNH VIN THNG 1 LI NI U Kthutchuynmchlmttrongnhngkthutmuchtnhttrongcc mng truyn thng. S pht trin mnh m ca h tng truyn thng trong mt s nm gnytoracccuccchmngvkhoahccngnghvkthutchuyn mch l mt phn ca s pht trin . Mc tiu ca cun bi ging l cung cp cho sinh vin chuyn ngnh Vin thng cc kin thc nn tng ca lnh vc chuyn mch, hthnghakinthcchosinhvintipcnccgiiphpkthutvcngngh chuynmchmimtcchtt nht.T lmnntngchoccmn hctiptheo. Ni dung chnh ca cc chng gm: Chngthnhtaracckhinimvlthuytnntngcalnhvc chuyn mch, mt s bi ton v m hnh ng dng trong k thut chuyn mch c trnh by vn tt l c s pht trin v tnh ton cho mt s vn s cp trong cc chng tip theo. Chng th hai tm tt cc vn ct li ca k thut chuyn mch knh bao gm cc nguyn l chuyn mch c bn, cc hnh thi kt ni trng chuyn mch v iu khin kt ni thng tin qua trng chuyn mch. Chngthbatipcnkthutchuynmchgitccvncbnnh nguyntc, phng phpxl gitintrong mngvtrongtrngchuynmchti cc vn phc tp nh cc k thut nh tuyn, cc giao thc nh tuyn v bo hiu m bo cht lng dch v. Chng ny cn a ra mt s vn m v xu hng pht trin ca k thut chuyn mch gi. Chngthttptrungvogiiphpcngnghchuynmchtintinbao gm cc gii php cng ngh mng c nh nh cng ngh MPLS, GMPLS v vn nh tuyn ca cc cng ngh ny. Mng khng dy vi tng lai c ng dng rng ri cng c tm tt trong chng ny vi nhng kin thc v nh tuyn. Tip cn chuyn mch mm vi mt s m hnh ng dng cng c a ra trong chng cui nhmgipSinhvintipcnticcgiiphpcngnghthctintrnmngvin thng. Kthutchuynmchlmtlnhvcrngvlinquantirtnhiulnhvc khc trong mi trng mng truyn thng. V vy, nhm bin son rt mong mun c c s gp chn thnh ca ng nghip v ngi c. H ni, ngy 25 thng 12nm 2009 2 Mc lc LI NI U ............................................................................................................. 1 Mc lc ....................................................................................................................... 2 CHNG 1: GII THIU CHUNG V K THUT CHUYN MCH ...................................... 10 1.1 NHP MN K THUT CHUYN MCH ............................................. 10 1.1.1Gii thiu chung ........................................................................................ 10 1.1.2Mt s khi nim c s .............................................................................. 11 1.1.3Cc m hnh ton hc ng dng trong lnh vc chuyn mch .................... 14 1.1.4Cc l thuyt lin quan .............................................................................. 18 1.2 QU TRNH PHT TRIN CA K THUT CHUYN MCH .............. 22 1.2.1 Lch s v xu hng pht trin cng ngh mng ......................................... 22 1.2.2 Chuyn mch mm v hng tip cn my ch cuc gi CS. ..................... 25 1.2.3 Hng tip cn phn h a phng tin IP (IMS) ....................................... 26 1.3 CC T CHC TIU CHUN ................................................................... 27 1.4 KT LUN CHNG ................................................................................. 30 CHNG 2: K THUT CHUYN MCH KNH ..................................................................... 31 2.1 C S K THUT CHUYN MCH KNH ........................................... 31 2.2 KIN TRC TRNG CHUYN MCH KNH ....................................... 34 2.2.1 Trng chuyn mch khng gian s ........................................................... 34 2.2.2 Trng chuyn mch thi gian s ............................................................... 36 2.2.3 Trng chuyn mch ghp TST ................................................................. 38 2.3 NH TUYN TRONG CHUYN MCH KNH ...................................... 41 2.3.1 Phn loi cc k thut nh tuyn ............................................................... 41 2.3.2Phng php nh s trong mng PSTN ................................................... 44 2.3.3Mng bo hiu PSTN ................................................................................ 46 2.3.4 X l nh tuyn cuc gi trong node mng chuyn mch knh ................. 47 2.4KT LUN CHNG ................................................................................ 48 CHNG 3: K THUT CHUYN MCH GI ......................................................................... 49 3 3.1.C S K THUT CHUYN MCH GI............................................... 49 3.1.1 M hnh kt ni h thng m OSI ............................................................. 50 3.1.2Nguyn tc c bn ca chuyn mch gi ................................................... 51 3.2KIN TRC CA B NH TUYN ........................................................ 53 3.2.1Cc chc nng c bn ca b nh tuyn ................................................... 53 3.2.2 Tin trnh chuyn tip gi tin ...................................................................... 54 3.2.3Cc thut ton tm kim thng tin trong bng nh tuyn ........................... 56 3.3.KIN TRC TRNG CHUYN MCH GI ......................................... 62 3.3.1Phn loi kin trc trng chuyn mch gi ............................................ 62 3.3.2Chuyn mch phn chia thi gian .............................................................. 62 3.3.3Chuyn mch phn chia khng gian .......................................................... 65 3.4 CC KIU B TR HNG I ................................................................ 70 3.4.1Cc kiu kiu b tr hng i c bn .......................................................... 70 3.4.2 Cc phng php x l hng i ................................................................ 77 3.4.3 Mng hng i ........................................................................................... 78 3.5. K THUT NH TUYN TRONG MNG CHUYN MCH GI ........ 82 3.5.1. Cc thut ton tm ng ngn nht........................................................... 84 3.5.2. Cc giao thc nh tuyn in hnh. ........................................................... 87 3.5.3 Mt s gii php ci thin hiu nng k thut nh tuyn .......................... 92 3.6 KT LUN CHNG ................................................................................. 96 CHNG 4: CNG NGH CHUYN MCH TIN TIN .......................................................... 97 4.1. GII THIU CHUNG ................................................................................. 97 4.1.1M hnh hi t cng ngh mng ................................................................ 97 4.1.2Cc gii php ghp hp cng ngh ............................................................ 98 4.1.3 Cng ngh MPLS/GMPLS ......................................................................... 99 4.2K THUT NH TUYN TRONG MPLS/GMPLS ............................... 103 4.2.1 Giao thc nh tuyn v phn phi nhn ................................................... 103 4.2.2 K thut nh tuyn h tr cht lng dch v trong MPLS/GMPLS ........ 106 4.3 NH TUYN TRONG MNG KHNG DY ......................................... 110 4.3.1 Phn loi cc giao thc nh tuyn............................................................ 110 4.3.2 K thut nh tuyn xuyn lp .................................................................. 113 4 4.4 GIIPHP CHUYN MCH MM ........................................................ 114 4.4.1 M hnh kin trc chuyn mch mm ....................................................... 115 4.4.2 Cc giao thc iu khin ca chuyn mch mm ...................................... 117 4.4.3 Cc ng dng ca chuyn mch mm ..................................................... 123 4.5KT LUN CHNG .............................................................................. 130 Ti liu tham kho. ............................................................................................ 132 5 DANH MC THUT NG V T VIT TT 3GThirth Generation Th h th 3 3GPPThirth Generation Partnership ProjectD n cho cc i tc mng th h 3 AAAAuthentification, Authorization, Accounting Nhn thc, cp php, tnh cc AALATM Adaptation LayerLp tng thch dch vADMAdd/Drop MultiplexingB ghp tch lung ADSLAsymetric Digital SubscriberLineng dy thu bao s khng i xng AFAddress FilterB lc a ch A-FAcounting FunctionChc nng tnh cc AMGAccess Media GatewayCng phng tin truy nhpAPIApplication Programable InterfaceGiao din lp trnh ng dng ASAutonomous SystemH thng t tr ASApplication ServerServer ng dng ASGAccess Signalling GatewayCng bo hiu truy nhp ATCAAdvanced Telecom Computing ArchitectureKin trc tnh ton vin thng tin tin ATMAsynchorous Transfer ModePhng thc truyn ti khng ng b AuCAuthentification CentreTrung tm nhn thc BANBroadband Access NodeNt truy nhp bng rng BGCFBorder Gateway Control FunctionChc nng iu khin cng ng bin BGPBorder Gateway ProtocolGiao thc cng ng bin BICCBearer Independent Call Controliu khin cuc gi c lp knh mang B-ISDN BroadbandIntergratedServiceDigital Network Mng s tch hp dch v bng rng CACall AgentAgent cuc gi CAP CAMEL Application Part Phn ng dng CAMEL CBR Constraint Bit RateTc bit rng buc CCF Charging Collector FunctionChc nng tp hp thng tin ccCBRConstant Bit RateTc bit c nh CBSCommitted Burst SizeKch thc burst cam kt CLPCell Loss Priorityu tin tn tht t bo COPSCommon Open Policy ServiceDch v chnh sch m chung CoSClass of ServiceLp dch v CQClass-based QueuingHng i theo lp CR-LDP Constraint-BasedRouting-labelDistribution Protocol Giaothcphnbnhnnhtuynrng buc CSCall ServerMy ch cuc gi CS (IMS)Circuit SwitchedChuyn mch knh CSCFCall Session Control FunctionChc nng iu khin phin cuc giCSPFConstraint Shorted Path Firstnh tuyn rng buc tm ng ngn nht DGDataGramD liu 6 DSLDigital Subscriber Lineng dy thu bao s DSLAMDigital Subcriber Line Acess MultiplexerB ghp knh truy nhp DSL DTLDesignated Transit ListDanh sch ng i nh sn DTMF Dual Tone Multi Frequencya tn m kp DVADistance Vector AlgorithmThut ton vect khong cch EGPExterior Gateway Protocol Giao thc nh tuyn min ngoi ECNExplicit Congestion NotificationThng bo tc nghn hin FECForward Equivelent ClassLp chuyn tip tng ng FIBForward Information BaseC s thng tin chuyn tip FIFOFirst In First OutVo trc ra trc FLCFible Line ConcentratorB tp trung quang FRFrame RelayChuyn tip khung FTPFile Transfer Protocol Giao thc truyn file GFCGeneral Flow Controliu khin lung chung GMPLSGeneralized MultiProtocol Label SwitchMPLS m rng GPRS General Packet Radio ServiceDch v v tuyn gi chung GSM Global System for Mobile CommunicationH thng ton cu cho thng tin di ng HDB3 High-Density Bipolar 3 M lng cc mt cao HDLC High level Data Link Control protocolGiao thc iu khin ng d liu mc cao HLR Home Location RegistorB ng k nhHOLHead Of LineNghn u dng HSSHome Subscriber ServerServer thu bao nh HTTPHyper Text Transfer ProtocolGiao thc chuyn giao siu vn bn IADIntegrated Access DeviceThit b truy nhp tch hp ICMPInternet Control Message Protocol Giao thc bn tin iu khin Internet IFMPIpsilon Flow Management Protocol Giao thc qun tr lung ca Ipsilon IGPInterior Gateway ProtocolGiao thc nh tuyn min trong IM CNIMS- Core NetworkIMS- mng liIMSIP Multimedia SubsystemPhn h a phng tin IP IMS-CSIMS- Circuit SwitchingIMS- chuyn mch knh IM-SSFIMS- Service Switching Function Chc nng chuyn mch dch v IMS INInteligent Network Mng thng minh IOTInteroperability TestingKim tra lin iu hnh IPInternet ProtocolGiao thc Internet IPCPIP Control Pointim iu khin IP I-PNNIIntergated PNNIPNNI tch hp IPXInternetwork Packet ExchangeGiao thc trao i gi lin mng ISCIMS Service Controliu khin dch v IMS ISDNIntegrated Service Digital Network Mng s a dch v tch hp IS-ISIntermediate System to Intermediate SystemGiao thc nh tuyn lin mng ISPInternet Service ProviderNh cung cp dch v Internet ISRIP Switching RouterB nh tuyn chuyn mch IP 7 ISUPISDN User PartPhn ngi dng ISDN ITU-T InternationalTelecommunicationUnion sector T Lin minh vin thng quc t IW-FInternetWorking FunctionChc nng kt ni lin mng LANLocal Area Network Mng ni ht LDPLabel Distribution Protocol Giao thc phn phi nhn LERLabel Edge RouterB nh tuyn bin (LSR bin) LGNLogical Group NodeNt i din nhm logic LOCLOcal ControlerB iu khin ni b LSALink State AlgorithmThut ton trng thi ng LSP Label Switched Pathng chuyn mch nhn LSRLabel Switching RouterB nh tuyn chuyn mch nhn M3UAMTP3 User Adaptation LayerLp tng thch ngi dng MTP3MAPMobile Application PartPhn ng dng di ng MGMedia Gateway Cng phng tin MGCMedia Gateway Controleriu khin cng phng tin MGCPMedia Gateway Control Protocol Giao thc iu khin cng phng tin MHA Min Hop AlgorithmThut ton bc nhy ti thiu MIRA Min Interference Routing AlgorithmThut ton nh tuyn nhiu ti thiu MMASMulti Media Application ServerServer ng dng a phng tin MMCSMulti Media Call ServerServer gi a phng tin MMGMobile Media GatewayCng phng tin cho mng di ng MMPP Markov Modulete Poisson ProcessTin trnh Poisson m phng MarkovMNOMobile Network OperatorNh iu hnh mng di ng MoSMean of ServiceThang im nh gi trung bnh MPLSMultiProtocol Label SwitchChuyn mch nhn a giao thc MPOAMultiProtocol over ATMa giao thc qua ATM MRFCMedia Resource Function Control iu khin chc nng ti nguyn a phng tin MRFPMedia Resource Function Processor Bxlchcnngtinguynaphng tin MSFMultiService ForumDin n a dch vMTUMaximum Transfer Unitn v truyn bn tin ln nht NGNNext Generation NetworkMng th h k tip NHCNext Hop ClientTrm con bc k tip NHRPNext Hop Resolution Protocol Giao thc gii bc k tip NHSNext Hop ServerTrm ch bc k tip OMAOpen Mobile AllianceLin minh dch v di ng m OSAOpen Service Architecture Kin trc dch v m OSPFOpen Shortest Path FirstGiao thc ng ngn nht trc tin OXC Optical Cross-ConnectB u ni cho quang PAMPulse Amplitude Modulation iu bin xung 8 PARPNNI Augmented Routingnh tuyn PNNI m rng PCMPulse Code Modulationiu xung m P-CSCFProxy- CSCFCSCF i din PDFPolicy Decicion FunctionChc nng quyt nh chnh sch PDUProtocol Data Unitn v d liu giao thcPGPeer Group Nhm ngang hng PGLPeer Group LeaderTrng nhm trong nhm cng cp PLMNPublic Land Mobile NetworkMng di ng mt t PMPhysic MediumMi trng vt l PNNIPrivate Network to Network InterfaceGiao din mng - mng ringPPPPoint to Point Protocol Giao thc im ti im PQPriority QueuingHng i u tin PSTNPublic Switched Telephone NetworkMng chuyn mch in thoi cng cng PTPayload TypeKiu ti tin PTSEPNNI Topology State ElementPhn t trng thi cu hnh PNNI PTSPPNNI Topology State Packet Gi tin trng thi cu hnh PNNI QoSQuality of ServiceCht lng dch v RANAPRadio Access Network Application PartPhn ng dng mng truy nhp v tuynRASRegistration Admistion and Status ProtocolGiao thc trng thi, qun l v ng k R-FRouting FunctionChc nng nh tuyn RIPRouted Information Protocol Giao thc thng tin nh tuyn RMGRemote Media GatewayCng phng tin xa RSVP Resource Reservation Protocol Giao thc dnh trc ti nguyn RSVP-TE RSVP Traffic EngineeringRSVP cho k thut lu lng RTCPRealtime Transport Protocol Giaothctruyntiiukhinthigian thc RTPRealtime Transport ProtocolGiao thc truyn ti thi gian thcSAPService Access Pointim truy nhp dch vSARSegmentation Reassembly SublayerPhn lp ct mnh to gi SCP System Control Pointim iu khin h thng SCIMService Capability Interaction ManagementQun tr tng tc kh nng dch v SCS Service Capability ServerServer kh nng phc v S-CSCFServiced-CSCFCSCF phc v SCTPStream Control Transport ProtocolGiao thc truyn ti iu khin lung SDHSynchronous Digital HierarchyPhn cp s ng b SDSSpace Division SwitchingChuyn mch phn chia khng gian SGSignalling GatewayCng bo hiu SIGTRANSignalling TransportGiao thc truyn ti bo hiuSINShip - in - the - NightChuyn hng SIPSession Initiation ProtocolGiao thc khi to phin 9 SMTPSimple Message Transfer Protocol Giao thc truyn th n gin SNMPSimple Network Management ProtocolGiao thc qun tr mng n gin SPCStored Program Controliu khin theo chng trnh ghi sn SSFService Switching FunctionChc nng chuyn mch dch v SPVCSoft Permanent Virtual ChanelKnh o c nh mm SUASCCP User Adaptation layerLp tng thch ngi dng SCCP SVCSwitched Virtual ChanelKnh o chuyn mchSWPA Shortest Widest Path Algorithm Thuttontmngrngnhtvngn nht TCTransmision ConvergenceHi t truyn dn TCPTransport Control ProtocolGiao thc iu khin truyn ti TDMTime Division MultiplexingGhp knh phn chia theo thi gian TDSTime Division SwitchingChuyn mch phn chia thi gian TE Traffic EngineeringK thut lu lng TLTotal LengthTng di TLVType/ Length/ ValueCc tham s kiu/ di/gi tr TMGTrunk Media GatewayCng phng tin trung k TOSType Of ServiceKiu phc v TTLTime to LiveThi gian sng TUATCAP User Adaptation Layer Lp tng thch ngi dng TCAP UACommon Signalling User Adaptation LayerLp tng thch ngi dng bo hiu CCS UDPUser Datagram Protocol Giao thc d liu ngi dngUEUser EquipmentThit b ngi dng UMTS UniversalMobileTelecommunication SystemH thng vin thng di ng ton cu UNIUser-Network InterfaceGiao din ngi dng - mng VBRVariable Bit RateTc bit thay i VCVirtual ChanelKnh o VCCVirtual Chanel ConnectionKt ni knh o VCIVirtual Chanel IdentifierNhn dng knh o VoIPVoice over IPThoi qua IP VPIVirtual Path IndentifierNhn dng lung o WAPWireless Application ProtocolGiao thc ng dng khng dy WCDMA R4 WirelessCodeDivisionMultipleAccess Release 4 atruynhp phnchia theom phin bn 4 WDMWavelength Division MultiplexingGhp knh phn chia theo bc sng WFQ Weighted Fair QueuingHng i cn bng trng s WLANWireless LANMng ni ht khng dy WSPA Widest Shortest Path Algorithm Thuttontmngngnnhtvrng nht 10 Chng 1 GII THIU CHUNG V K THUT CHUYN MCH 1.1 NHP MN K THUT CHUYN MCH 1.1.1Gii thiu chung Vin thng l mt phn ca khi nim thng tin - mt dng thc chuyn giao thng tin. Mng vin thng c coi l h tng c s ca x hi s dng k thut in, in t v cc cng ngh khc chuyn giao thng tin. Mng vin thng di gc n ginnhtcnhn nhngmtphpccntmng,cc ngtruyndnktni gia hai hay nhiu im xc nh v cc thit b u cui thc hin trao i thng tin gia ngi s dng. Mt cch khi qut chng ta c th coi tt c cc trang thit b, phng tin c s dng cung cp dch v vin thng to thnh mng vin thng. Thit b u cui l cc trang thit b ca ngi s dng giao tip vi mng cung cp dch v. Thit b chuyn mch l cc nt ca mng vin thng c chc nng thit lp vgiiphng ngtruynthnggiaccccthitbucui.Thit btruyn dn c s dng ni cc thit b u cui hay gia cc nt vi nhau thc hin truyncctn hiu mt cch nhanhchngv chnhxc.Cc phntv phngtin ca mng truyn thng cu trc thnh h tng truyn thng nhm cung cp cc dch v cho ngi s dng.Tythucvoccdchvchchtmccgiiphpcngnghcxydng, phngphptipcnnyvangtntitronghtngmngtruynthnghin nay.Trong mt s nm gn y, cng vi s pht trin ca cng ngh tin tin l xu hng hi t c v cng ngh v dch v mng truyn thng gia mng c nh, mng di ng v mng internet sang mng th h k tip NGN (Next Generation Network). H tng mng vin thng thay i khng ngng nhm p ng cc yu cu ngy cng cao ca ngi s dng, s tc ng ny lin quan v nh hng ti rt nhiu lnh vc trn ccyu t khoa hc cng ngh v khoa hc k thut, trong bao gm k thut chuyn mch. Mt xu hng mi c hnh thnh trn c s hi t v tch hp h tng cng ngh nhmxydng mt htngtruynthngchungchocc mitrngkin todchvlpcao.Chnhvvy,mtlotccgiiphpkthutvcngngh chuyn mch mi v ang c a ra v trin khai. h tr sinh vin v ngi c tip cn cc vn chuyn su ca lnh vc ny, bi ging c s k thut chuyn mch tip cn cc vn nn tng k thut, cc gii php cng ngh v xu hng pht trin nhmgip ngi c nhn thctng quancckhacnhkthutlin quanti lnh vc ny. 11 Trong cc phn u tin ca ti liu s gii thiu cc khi nim c s lin quan ti lnh vc chuyn mch, nht l cc c s ton hc v l thuyt lin quan. Tip sau l cckthutvnguyntchotngcaccmngchuynmchknhvchuyn mchgicngviccvn lin quan nh nhtuyn, nhsvchtlngdch v. Cc k thut chuyn mch mi trong h tng tch hp cng ngh ctrnh by trongccchngcuilskthpgiaccgiiphpcngnghvgiiphpk thut, nhm th hin m hnh tng th ca cc cng ngh tin tin ang ng dng v trin khai trn mng vin thng hin nay.1.1.2Mt s khi nim c s tipcnccvn mangtnhcthcakthutchuynmch, phn nys gii thiu mt s cc thut ng v khi nim c s lin quan ti cc chng tip theo ca bi ging tron lnh vc chuyn mch. i, nh ngha chuyn mch Chuyn mch l mt qu trnh thc hin u ni v chuyn thng tin cho ngi s dng thng qua h tng mng vin thng. Ni cch khc, chuyn mch trong mng vinthngbaogmchcnngnhtuynchothngtinvchcnngchuyntip thng tin. Nh vy, theo kha cnh thng thng khi nim chuyn mch gn lin vi lpmngvlplinktdliutrong mhnhOSI(OpenSystemInterconnection) ca T chc tiu chun quc t ISO (International Organization for Standardization). i vi mt s trng hp m rng, khi nim chuyn mch cn c hnh thnh theo m hnh phn lp v tri di t lp 2 ti lp 7 trong m hnh OSI. ii, H thng chuyn mch Qutrnhchuynmchcthchinticcntmng,trongmngchuyn mch knh cc nt mng thng gi l h thng chuyn mch (Tng i), trong mng chuyn mch gi thng c gi l thit b nh tuyn (B nh tuyn). Trong mt s mng c bit, phn t thc hin nhim v chuyn mch c th va ng vai tr thit bucuivangvaitrchuynmchvchuyntipthngtin.ivi mts kin trc mng c bit v d nh mng ty bin (Ad-hoc), cc thit b u cui cn c th ng vai tr nh mt ni cp v nhn ngun lu lng trong mng, ng thi m nhim chc nng chuyn tip cc thng tin cho cc phn t khc trong mng.iii, Phn loi chuyn mch Cc h thng chuyn mch cu thnh mng chuyn mch, ta c hai dng mng chuyn mch c bn: Mng chuyn mch knh v mng chuyn mch gi. Tuy nhin, di gc truynvx lthngtin,chuyn mchcncth nhn nhn thnh bn 12 kiu:chuynmchknh,chuynmch bntin,chuynmchgi vchuynmcht bo. Mng chuyn mch knh thit lp cc mch (knh) ch nh ring cho kt ni trc khi qu trnh truyn thng thc hin. Nh vy, qu trnh chuyn mch c chia thnh 3 giai on phn bit: thit lp, truyn v gii phng. thit lp, gii phng v iu khinktni,mngchuynmchknhsdngcckthutbohiuthchin nh mt thnh phn bt buc.i ngc vi mng chuyn mch knh l mng chuyn mch gi, da trn nguyn tcphnchiacc lulng dliuthnhcc gitinvtruynitrn mngchias, migitinlmtthcthclpchaccthngtincnthitchoqutrnhxl thngtin trnmng.Ccgiaionthitlp, truynvgiiphngs cthchin ng thi trong mt khong thi gian v quyt nh ng i c xc lp bi thng tin trong tiu gi tin. Knh thng tin c hnh thnh gia cc thit b mng khng phthuctheologicthigianmchc nghakhi clulngchuynquac gilccknho,ccknhoccngmtsctnhcghpthnhlungo. Cc nt mng c th thc hin chuyn mch cho tng knh o hoc c lung o thay v cho tng gi tin ring bit, tip cn ny cho php nng cao hiu nng truyn thng ton mng nh gim bt mt s quy trnh x l. iv, K thut lu lng TE K thut lu lng TE (TrafficEngineering) c coi l mt trong nhng vn quan trng nht trong khung lm vic ca h tng mng vin thng. Mc ch ca k thutlulnglcithinhiunngvtincycacchotngcamng bngccgiiphptiunguntinguynmngvlulngmngcngnhca ngisdng.Mtcchchitithn,kthutlulngcnhnnhnnhmt cng c s dng ti u ti nguyn s dng ca mng bng phng php k thut nh hngcclunglulng ph hpviccthamsrng buctnh hoc ng. Cc tham s y bao gm c tham s mng v tham s yu cu ca ngi s dng. Nh vy, mc tiu c bn ca k thut lu lng l hng ti cn bng v ti u cc iu khin ca ti v ti nguyn mng thng qua cc thut ton v gii php k thut. i vi cc nh thit k v khai thc mng, k thut lu lng ng vai tr quyt nh trong cc bi ton lin quan ti hiu nng mng. Do s bin ng ca ccyu cu t pha ngis dng,cclulngyu cuvkh nng phcvca hthng mng lun cn c cc gii php ti u. V vy, k thut lu lng lun c coi l vn c phc tp cao nht l trong cc cng ngh mng chng ln v t hp. 13 v, Bo hiu trong mng vin thng Bohiulmtphncacchiukhinmngsdngcctnhiuiu khin truyn thng, trong mng vin thng bo hiu l s trao i thng tin gia cc phn t trong mng lin quan ti cc vn nh: iu khin, thit lp cc kt ni v thc hin qun l mng. Trong mng chuyn mch knh, bo hiu l mt thnh phn c bn ca qu trnh kt ni, nh c chc nng bo hiu m h thng chuyn mch c th thc hin c nhim v chuyn mch, thng qua thng tin bo hiu t nt mng ti cc thit b u cui ca ngi s dng xc nh cc yu cu v qun l kt ni t ngi s dng ti nt mng, bo hiu mng c thc hin h tr trc tip cho qutrnhnhtuyn,chnknhvqunlktnigiaccntmng.Trongmng chuyn mch gi, h thng bo hiu hng ti mc tiu iu khin thit b v qun l mng nhiu hn l mc tiu gn kt vi quy trnh nh tuyn nhm thit lp knh nh trong mng chuyn mch knh. Cc h thng bo hiu c th phn loi theo c tnh v nguyn tc hot ng gm: bohiutrongbngv bohiungoibng,bohiungvbohiuthanhghi, bo hiu knh lin kt v bo hiu knh chung, bo hiu bt buc, v..v. Cc thng tin bo hiu c truyn di dng tn hiu in, quang hoc bn tin. V d, cc h thng bo hiu trong mng chuyn mch in thoi cng cng PSTNc nh s t No1-No7, trong gm c cc dng bo hiu s, tng t hay bn tin. Trong mng IP hin c rt nhiu giao thc bo hiu c s dng cho cc kt ni v tri rng trn cc lp t lp 2 ti lp 5 trong m hnh OSI. vi, Mng tch hp dch v s bng rng B-ISDN Xuhngphttrincamngvinthnglunhngtimthtngduynht nhmpngttnhtccloi hnhdchv trncsbngthngrng.Mngtch hpdchvsbngrngcnhnghanhsau:Mngtchhpdchvsbng rng c nhim v cung cp cc cuc ni thng qua chuyn mch, cc cuc ni c nhhoc bn c nh, cc cuc ni t im ti im ti im hoc t im ti a im v cungcpccdchvyucu,ccdchvdnhtrchocccdchvyucuc nh. Cuc ni trong B-ISDN phc v cho c cc dch v chuyn mch knh, chuyn mchgitheokiuaphngtin,nphngtin,theokiuhnglinkt (Connection-Oriented) hoc phi lin kt (Connectionless) v theo cu hnh n hng hoc a hng. Hin nay, cng vi vi xu hng tch hp dch v s bng rng l s hi t ca cc min mng khc nhau, B-ISDN c mt lot cc c tnh mi khng ch trongkhacnhkt ni mcntrongcckhacnhkhc nh qunl, iukhinv dch v. V vy, tn gi chung thng c s dng l h tng mng bng rng. 14 1.1.3Cc m hnh ton hc ng dng trong lnh vc chuyn mchM hnh ton hc c mt v tr ti quan trng trong rt nhiu lnh vc, trong c lnh vc chuyn mch.Hng lot cc bi ton thit k, nh gi h thng khng th thc hin trn cc h thng thc v c tin hnh thng qua cc m hnh ng dng. Vi tm quan trng ca m hnh ton hc ng dng trong lnh vc chuyn mch, mc nycabigingaramtscclthuytcslinquantrctiptibiton nh tuyn v chuyn mch gm cc vn xc sut v phc tp thut ton. Thm vo , lu lng trong k thut chuyn mch thng c m t qua cc s kin n ca cc thc th ri rc (yu cu chim knh, gi, t bo, v.v..), n c th m hnh ho bi tin trnh im. C hai dng tin trnh im l tin trnh m v tin trnh gia hai s kin n.Khi nim c s trn s ng vai tr xuyn sut trong cc h thng m phngskinrircvcc biton ti u hthngtrncs m hnh hav m phng. Mt s dng phn b thng ng dng c ch ra di y. i, Phn b Erlang Phn b Erlang l mt phn b xc sut lin tc c gi tr dng cho tt c cc s thc ln hn zero v c a ra bi hai tham s: sc k (s t nhin; Int) v tham stl (sthc;real).Khithamsk=1phnbErlangtrthnhphnbm. PhnbErlangltrnghpcbitcaphnbGammavithamsklst nhin. Trong trng hp tng qut, k trong phn b Gamma l s thc. ii, Qu trnh MarkovQu trnh Markov l mt qu trnh mang tnh ngu nhin (stochastic process) thng s dng mtcc hthng khng nhvictnh nhsau:trngthickti thi im k l mt gi tr trong tp hu hn {1,.,M}. Vi gi thit rng qu trnh ch din ra t thi im 0 n thi im N v trng thi u tin v cui cng l bit, chui trng thi s c biu din bi mt vect hu hn C = (c0,...,cN). Nu P(ck | c0,c1,...,c(k 1)) biu din xc sut (kh nng xy ra) ca trng thi ck ti thi im k khi tri qua mi trng thi cho n thi im k 1. Gi s trong qu trnh th ck ch ph thuc vo trng thi trc ck 1 v c lp vi mi trng thi trc khc. Qu trnh ny c gi l qu trnh Markov bc 1 (first-order Markov process). (a) Chui markov ri rc ChuiMarkovthigianrircbaogmmttphpcctrngthivxcsut chuyn i gia chng ti nhng khong thi gian ri rc nhau. Vi yu cu xc sut chuyn i gia cc trng thi l mt hm ch ph thuc vo trng thi, s chuyn i nykhngcnxuthintinhngkhongthigianxcnhmchtuntheomt quy lut thi gian no . 15 KthutchuiMarkovthigianrircpdngchoccstrngthitu, trong tn ti mi lin kt gia cc i tng khc nhau tun th mt s iu kin. Nu mt s trng thi khng th chuyn n trng thi khc th tin trnh c coi l mc li v iu ny dn ti s phn ha chui ny thnh cc chui ring l. Vic tng s lng trng thi s m t h thng chnh xc hn nhng cng ko theo phc tp tnh ton tng ln. (b) Chui Markov thi gian lin tcChuiMarkovthigianlintcng dngtronglnhvcchuynmchthng mhnhhachohthngangisdngktnitimtbnhtuynhaytruy nhp thit b chuyn mch. M hnh ha cho cc s kin n ca kiu h thng ny l xem cc s kin xy ra ti cc khong thi gian rt nh. Khi gia s thi gian tin ti 0 (At0), gi tr gn ng l c coi l m hnh thi gian lin tc. Tuy nhin, vi bitonny,chngtaphisdngccphptnhviphntonhcthaychonhng phpnhnxcsutngincsdng phntchchuiMarkovthigianri rc.TrnthctmhnhchuiMarkovrtnhiungdngtronglnhvckthut chuyn mch nh: cc bi ton m hnh ho lu lng, tnh ton kh nng tc nghn, cp phc v GoS ca trng chuyn mch v mt s vn iu khin khc. Vi mt lot cc yu cu mi ca mng a dch v v cht lng dch v v tch hp lu lng, vn m hnh ha bi ton lu lng khng dng m hnh Markov m cn cphttrintheomtshngcphctplnhn,vdnhmhnhlu lngttngngsdngtrongbitonmhnhhalulnginternet.Tuy nhin, m hnh chui Markov trong k thut chuyn mch lun ng vai tr c s ca cc tnh ton thit k v qun l h thng chuyn mch. iii, Phn b Poisson Qu trnh Poisson l dng c bit ca qu trnh Markov vi thi gian lin tc. Qu trnhPoisson( ) N t mtqutrnhmslnxuthinmtbincAnocho nthi imt .Vd,nuscucginmttngilmtqutrnhPoisson, micucgichimdngthitbtrongmtkhongthigianno,giscc khong thi gian ny l cc bin ngu nhin c lp cng phn b, khi tng s gi gilmtqutrnhPoissonphchp.CcqutrnhPoissonthigianthunnht (time-homogeneous)cxutphttccqutrnhMarkovthigianlintcthi gian thun nht. iv, Mt s m hnh lu lng thng dng Mt s m hnh lu lng c m t di y thng c s dng m hnh ha lung lu lng trong cc h thng m phng mng vin thng gm: 16 0 1 1{ ( )} ,{A } ,{B }t n n n nN t = = = hoc 1{W }n n= Trong tin trnh hi phc 1{A }n n= l c lp, cc phn b c th c s dng nh biu din trong bng 1.1. M hnh ny n gin nhng thiu tnh thc tin vnkhngckh nngthhinccutrctngquantronglulng thc t. Tin trnh Poisson l tin trnh hi phc vi cc thi gian tng tc 1{A }n n= l hm phn b m vi tham s t l o.Tin trnh ny c th c coi nh l tin trnh m vi 0{N(t)}t= c lp v tnh dng tng theo hm possion. V d,{ ( ) } exp( )( ) / !nP N t n t t n = = Tin trnh Poisson thng c s dng trong l thuyt lu lng thoi v tnh n gin v mt vi c tnh ring ph hp. Cc cuc gi thoi n h thng chuyn mch knh thng c m hnh ha bi tin trnh poission. TintrnhBernulliltintrnhPoissonthigianrirc.Trongmhnhny, xcsutca mtskin n tikhethigian btklp, clpviccs kin khc. S lng cc s kin n ti khe thi gian th k l phn bnh thc.V d,{ ( ) } (1 )n k nkP N t n p pn| |= = |\ . v thi gian gia hai s kin n l phn b hnh hc{ } (1 )jnP A j p p = = . Tin trnh khi phc kiu giai on l lp c bit ca tin trnh khi phc vi thi gian gia cc s kin n phn b kiu giai on (phase-type). l mt lp quan trng v cc m hnh ny c th phn tch c. Ni cch khc, bt k phn b no c th xp x ha bi cc phn b giai on. M hnh lu lng da trn chui Markov a s ph thuc vo cc chui ngu nhinAn.Cutrccamhnhnhsau:GithittintrnhMarkov 0{ ( )}tM M t==vi khng gian trng thi ri rc. M ti trng thi ic thi gian chimgitheophnbhmmvithams i chphthucvoi,chuyn trng thi sang j vi xc sut pij. Mi bc nhy Markov c th hin s kin nvithi giangia haiskin ntuntheo hm m.ylm hnhlu lng Markov n gin nht. TintrnhhiphcMarkovtngquanhntintrnhMarkovvthhin 0{( , )}n n nR M t== cnhnghabichuiMarkov{ }nM vcckhongthi giannhy nt araccrngbucsau:phnbcacccp 1 1( , )n nM t= =ca trng thi bc nhy k tip v thi gian nhy ch ph thuc vo trng thi hin thi Mn , v khng ph thuc vo trng thi pha trc hoc thi gian bc nhy pha trc. 17 Tintrnh nMarkov(MAP MarkovArrivalsProccess) l mtphnlp ca tin trnh hi phc Markov. Trong MAP, thi gian gia cc s kin n l kiu giai on v s kin n l mt tin trnh tc thi ca chui Markov. Tin trnh ny c khi to li vi hm phn b ph thuc votrng thi nht thi ngay khi s kin xy ra. Tin trnh ny rt linh hot trong cc bi ton m hnh ha lu lng. TintrnhbiniuMarkov(MMPMarkovModulatedProccess)lmt chui Markov lin quan ti thi gian v cc iu khin trng thi hin thi ca n.GismttintrnhMarkovthigianlintc 0{M(t)}t=vikhnggian trngthi 1,2, ...m. Vi Mtitrng thik ,xcsutcaccskin n c xc nh qua lut xc sut ti k. Khi M chuyn sang trng thi khc (j) th lut xc sut mi ch c tc dng vi j. Ni cch khc, lut xc sut c p dng cho tng trng thi v bin iu theo chui. TintrnhPoissonbiniutheoMarkov(MMPPMarkovModulated Poisson Proccess) l mt trong cc m hnh ph bin m hnh ha lu lng. Trong m hnh ny, khi tin trnh Markov c bin iu trong trng thi k ca M v s kin n xy ra tun theo tin trnh Poison vi tc k . Trng hp nginnhtcaMMPPlm hnhhaitrngthi(ON/OFF)vitcn Poisson. M hnh ny cn c gi l tin trnh Poisson ngt v c s dng m hnh ha ngun lu lng thoi vi trng thi ON tng ng vi c tn hiuthoivOFFtngngvikhonglng,hocmhnhhachoc tnh bng n lu lng ca lu lng chuyn mch gi. Trong m hnh lu lng Fluid, lu lng c xem xt nh mt dng chy ca cc n v lu lng. y l mt m hnh rt quan trng cho cc h thng chuynmchgi,khiccnvlulngring(gi)quanhrtlnvi khong thi gian chn trc. u im ca m hnh ny l tnh n gin khi so snh vi cc m hnh lu lng khc v n c kh nng nm bt c cu trc caccnvlulngringbit.Kiumhnhnginnhtlkium hnh hai trng thi: ON khi cc lu lng n vi tc khng iv OFF khikhngclulng. phntch m hnh ny,ccchukthigiangia ON v OFF c th gi thit l tun theo phn b hm m. Ni cch khc, l mt dng thay th cho tin trnh hi phc. Da trn cc m hnh lu lng khc nhau ta c th ng dng cc m hnh hoc thpccmhnhchoccngdngringbit.Viclachnngmhnhlu lng s xc nh c cc c tnh quan trng ca lu lng. Trn c s , cc bi ton phn tch v thit k cc nt chuyn mch hoc cc b nh tuyns c c cc kt qu tt nht nhm phn nh ng nht thc t ca mng. 18 1.1.4Cc l thuyt lin quan i, L thuyt hng iL thuyt hng i l mt trong cc cng c ton hc mnh cho vic phn tch c lng trong cc h thng vin thng v cc mng my tnh. L thuyt hng i thng thng c p dng cho cc h thng l tng a ra kt qu gn ng cho mt m hnh thc t. Tnh cht chung ca cc gii php ng dngl thuyt ny l lm r hn cc c trng lu lng, cung cp d bo nhng ranh gii tt hn trn nhng ktqunghincunhtnh,vchngcthrthuchtrongvickimtratnh chnh xc v hp l ca cc gi thit thng k. L thuyt hng i l mt hng pht trincalthuytxcsutnghincuccqutrnhlinquannhngiv cung cp cc phng php phn tch hoc dng thc ng (closed form) trong vi lnh vcnhtnh[3].Lthuythngixcnhvtmccphngntiuh thng phc v tt nht. Ngi ta phn loi cc qu trnh sp hng da vo lut phn b ca qu trnh n, lut phn b phc v, nguyn tc phc v v c cu phc v. M t hng i Kendall D.G.Kendall xut k hiucho cc h thng hng i gm 5 thnh phn theo th t:A/B/X/Y/Z.ThngthngmhnhKendallcxttheonguyntcntrc phcvtrcFCFS(FirstComeFirstServer),nsauphcvtrcLCFS(Last Come First Server), phc v theo th t ngu nhin SIRO (Serial In Random Out) v chia s x l PS (Parallel Proccess). Trong : A: phn b thi gian tin trnh n B: phn b thi gian phc v X: s lng server Y: dung lng tng cng ca h thng Z: s lng cc khch hng NulutphnbcxtdidngtngqutthAhocBlykhiuG(General). i khi ngi ta cn k hiuGI(general independence). Nu qutrnhn l qutrnh Poisson, nghal thigian ntrunggianc phnb m thA c k hiuM(Markovian). Tng t nu thi gian phc v c phn b m thB cng c k hiuM . NuthigianntrunggianhocthigianphcvcphnbErlang-kthA,B c k hiu kE . Nu thi gian n trung gian hoc thi gian phc v l hng s thA hocB c k hiuD (Deterministic). Mt s tham s o hiu nng thng c s dng trong hng i l: 19 qL : dihng itrung bnh ca hng, l kvngca chuithigianlin tc { }0( )qtl t> trong ) (t lq l s khch hng i trong hng ti thi imt . L: di hng i trung bnh ca h thng, l k vng ca chui thi gian lin tc{ }0) (> tt l trong) (t l lskhchhngtronghthngtithiimt .Vy ) ( ) ( t l t lq= + s khch hng ang c phc v. qW :Thi gian i trung bnhca hnglkvng ca qutrnhthigianrirc { } ... , 2 , 1 ; = n qn trong nql khong thi gian m khch hng thnphi i trong hng cho n lc anh ta c nhn phc v. W: Thi gian i trung bnh ca h thng l k vng ca qu trnh thi gian ri rc { } ... , 2 , 1 ; = n wntrong n n ns q w + = lthigiankhchhngthn trongh thng, l thi gian i trong hng v thi gian c phc v. Mt s hng i thng dng c ch ra di y: Hng i M/M/1: Thi gian ca tin trnh n c phn b theo hm m m hay theo tintrnh Poisson(thcchtltintrnhkhngnhhocctnhMarkov)A :=M; B:=M; X:=1. Thi gian n ca cc s kin theo tin trnh Markov Thi gianphc vphn b theo hm m m B := M. H thng ch c 1 server. Hng i c khng gian m l v hn. Hng i G/G/1: H thng c 1 Server, qu trnh n l tng qut nhng cc thi gian ntrunggian nt clp, ccng phn bv ckvngchungl| |1E t .Thigian phcvtrongmichukcngclp,cngphnbvckvngchung| |1E s . Hng i ny c Kendall k hiu l1 / / G G.Hng i M/G/1: Hng i ny c qu trnh n Poisson tc , ngha l qu trnh n trung gian ntc phn b m tc . Qu trnh phc v{ }nsc xt mt cch tng qut nhng gi thit thi gian phc v trong cc chu k l c lp vi nhau v c cnglut phn b.Trng hphng iM/M/1ltrng hp c bit cahng i M/G/1 vi qu trnh n Poisson vi tc n , thi gian phc v c phn b m tc ;1 / / D M : Qu trnh n Poisson vi tc n , thi gian phc v khng itc ;1 / /kE M : Qu trnh n Poisson vi tc n , thi gian phc v ngu nhin c lp c cng phn b Erlang- k vi tc . 20 ii, L thuyt phc tp phc tp l thut ng lin quan ti t chc ca h thng v l mt khi nim rng vcnhnnhndinhiugckhcnhau.Tronglnhvcchuynmch, phctpgnlin vikhi nimthngtin, phctp hthng v phc tp tnh ton. L thuyt phc tp c ng dng rt nhiu trong k thut chuyn mch gm mt s vn c bn nh: Tnh ton, phn tch, thit k cu trc trng chuyn mch, thc hin nh tuyn, phn loi lung lu lng v cc thut ton xp hng hoc tm kim thng tin trong cc h thng chuyn mch hoc b nh tuyn. Banukhinimthngtin doShanonaranm1948datrncsxcsut thng k, khi nim thng tin tuyt i do Kolmogorov a ra nm 1973 da trn c sthutton.Thngtinchiunhmtilngcnbnnhnghamtcch nghim ngt c th o lng c ca s vt ging nh nng lng. Thng tin tuyt i cha trong mt i tng hu hn chnh l phc tp Kolmogorov (Kolmogorov complexity) ca i tng . phc tp ca mt i tng hu hn x l di ngn nht ca m t hu hiu ca x, hay di ngn nht ca chng trnh (v s liu ban u), tnh bng x chng hn, sinh ra x. Cho trc x v nu tm ra m hnh hay chng trnh m t x c di bng phc tp Kolmogorov ca x th chnh l m t ngn nht khng th gn hn.Mt kha cnh khc ca phc tp l lin quan ti cu trc ca mt h thng. Mt kthut quantrngtrongton hcs dng mt quan hgiacc phnttrong cu trc ca h thng l th v l thuyt th. V d, mt mng truyn thng c th th hin theo cch t nhin nht qua th gm cc node mng ng vai tr cc nh ca th v cc tuyn lin kt ng vai tr cc cnh ca th. Vic phn tch cc m hnhthng qua thsgiptac ccc giithuttt nhtchocc bitonlin quan ti phc tp ca h thng, nht l cc bi ton tm ng, nh tuyn trong k thut chuyn mch. Nh vy, kt qu ca l thuyt phc tp s l quan h c bit ca s pht trin thut ton ca cc ng dng thc tin.iii, l thuyt th Nhngttngcbncalthuytthc xutlnutinkhinh ton hcLenhardEurlers dngth gii quytbiton 7cycuKronigsbeg (1736).nnay,lthuytthccoilmt nhnhphbincatonhcng dng trong nhiu lnh vc gm ton hc, k thut my tnh v nhiu ngnh khoa hc khc[4].Mtsng dng chyucalthuytthtrongkthutchuynmch lin quanticcvn m hnh ha mng, nhtuyn,phctpvkthutlu lng nhm htrcho bitonti uhthng. Trong mc nystrnh by mts 21 khi nimcsca lthuytthvv dng dnglthuytthcho biton tm ng. Mt s khi nim c s ca l thuyt th th: Theo cch hiu thng thng, mt th m t hnh thi kt ni cho mt tp ccitnggmccnhhocntktnivinhauquacclinktgilcc ng, cnh hoc cung. Trong ton hc, th c nh ngha nh sau: Cho V lmttp huhnc nhnghaE(V)={{u.v}u,veV, uv};tpcon ca V gm hai phn t ring bit (u v v). Mt cp G(E,V) vi E_ E(V) c gi l mt th. Cc phn t V c gi l cc nh (nt) v E l cc cnh (lin kt) ca th. Mt th vi tp li V c gi l th trn V, Mt tp li ca th G c k hiu l VG v cnh k hiu l EG v ta c mt kiu biu din theo G: G=(VG, EG). Cc kiu th c m t di y: th v hng: th v hng hoc th G l mt cp c th t G(E,V) vi cc cnhvhng.Trong,VltpccnhvEltpkhngthtchaccnh phn bit, c gi l cnh. th c hng: Mt th c gi l c hng l mt cp c th t G(E,V) vi cccnhchng.Trong,VltpccnhvEltpcthtchaccnh phn bit, c gi l cnh. Mt cnh e=(x,y) k hiu cho hng t x ti y. thnvath:thnlthmgiahainhchctiamt cnh, a th l th m gia hai nh c th nhiu hn mt cnh. Trong th n v a th u c th c hng hoc v hng. th hn hp:th hnhpl thtrong ccccnhlc hngvv hng. th trng s: L th m trng s (s) c gn cho mi cnh. Cc trng s c th thhincho nhiuthamskhc nhau tythucvo biton.Trngs thl tng cc trng s gn cho tt c cc cnh ca th. Cc th c mt lot cc c tnh v cc c tnh ny rt quan trng trong cc bi ton kho st, so snh gia cc th vi nhau.Hai cnh ca th c gi l lin k, nu chng cng chung cc nh, tng t nh vy i vi cc nh. Mt cnh v tp li trn cnh c gi l lin thuc. th ch c mt nh v khng c cnh c gi l th tm thng, mt th ch c cc nh v khng c cnh c gi l th khng cnh. Mt th khng c nh v cnh c gi l th rng hoc th trng. 22 Mt th G=Kv c gi l th hon chnh trn V nu ton b nh u c ni hay tt c hai nh l lin k : E= E(V). Tt c cc th hon chnh c bc n u ng cu vi cc th khc v c k hiu l Kn. Hai th G v H c gi l ng cu vi nhau khi cc nh ca th H c thay th tn tng ng vi cc nh trong G. Hai th ng cu cng chung cc c tnh l thuyt th. V d v hai th ng cu c trnh by trong hnh 1.1, trong cc yu cu ng cu c ch ra tng ng:v1 1; v2 3; v3 4; v4 2; v5 5. Hnh 1.1: Hai th ng cu v biu din di dng ma trn thcthcbiudindi dngmatrnlinthuc,viV(G)={v1,v2,vn} theotht.MatrnlinkcaGlmatrngm(nxn)phntviccphnt Mij=1 hoc Mij=0 ty thuc vo vivj e E(G) hoc khng. Tt c cc ma trn lin k u l ma trn i xng qua ng cho v mt th c th c nhiu ma trn lin k ph thuc vo bc ca th. Hai th ng cu cng chung mt ma trn lin k, chnh xc hn l c chung mt tp cc ma trn lin k. Trn hnh 1.7 trn y ch ra v d v biu din dng ma trn cho th. 1.2 QU TRNH PHT TRIN CA K THUT CHUYN MCH 1.2.1 Lch s v xu hng pht trin cng ngh mng Vokhongthp nin 60cath k20,ln utinxut hinsn phmtng i in t s l s kt hp gia cng ngh in t vi k thut my tnh. Tng i in t s cng cng u tin ra i c iu khin theo chng trnh ghi sn SPC (Stored Program Control), c gii thiu ti bang Succasunna, Newjersey, USA vo thng 5 nm 1965. Trong nhng nm 70 hng lot cc tng i thng mi in t s ra i. MttrongnhngtngiltngiE10caCITAlcatelcsdngti Lannion (Php). V thng 1 nm 1976 Bell gii thiu tng i in t s cng cng 4ESS.Huhtchongiaionnycctngiintsusdnghthng chuyn mch l s v cc mch giao tip thu bao thng l Analog, cc ng trung k l s. Mt trng hp ngoi l l tng i DMS100 ca Northern Telecoma vo nm1980dngtonbkthutsutintrnthgii.Hthng5ESScahng 23 AT&T c a vo nm 1982 ci tin rt nhiu t h thng chuyn mch 4ESS v cccchcnngtngthchviccdchvmngstchhpdchvISDN (IntegratedServiceDigitalNetwork).Sauhuhtcchthngchuynmchs uaracccuhnhhtrchoccdchvminhISDN,dchvchomng thng minh v cc tnh nng mi tng thch vi s pht trin ca mng li. Khongnm1996khimngInternettrthnhbngntrongthgiicngngh thng tin, n tc ng mnh m n cng nghip vin thng v xu hng hi t cc mng mytnh,truynthng, iukhin.H tng mng vinthng tr thnhtm im quan tm trong vai tr h tng x hi. Mt mng c th truyn bng rng vi cc loi hnh dchvthoiv phithoi, tc caov m bocchtlng dchvQoS(QualityOfService)trthnhcp thittrn nntngca mtkthut mi: KthuttruyntikhngngbATM(AsynchronousTransferMode).Cch thng chuyn mch in t s cng phi dn thay i theo hng ny cng vi cc ch tiukthut,giaothc mi. Mtv d in hnhlcchthngchuyn mchknh khicungcpccdchvInternetsctincykhcsovicccucgithng thng vi thi gian chim dng cuc gi ln hn rt nhiu, v cng nh vy i vi cc bi ton lu lng. S thay i ca h tng mng chuyn i sang mng th h k tipNGN v angtcngrtlnticc hthngchuynmch, di ytrnh by mt s vn lin quan ti mng NGN v cc c im ca qu trnh hi t mng cahtngmngcngcng.MngchuynmchknhcngcngPSTNvIP (Internet Protocol) ang dn hi t ti cng mt mc tiu nhm hng ti mt h tng mng tc cao c kh nng tng thch vi cc ng dng a phng tin tng tc v m bo cht lng dch v. Hnh 1.2 di y ch ra xu hng hi t trong h tng mng cng cng: Hnh 1.2: Xu hng hi t cng ngh mng cng cng Skhcbitnybtutnhngnm 1980,PSTNchuynhngtipcnsang phngthctruyntibtngbATMhtraphngtinvQoS,sau 24 chuyn hng sang cng ngh kt hp vi IP chuyn mch nhn a giao thc hin nay. Trong khi Internet a ra mt tip cn hi khc vi PSTN qua gii php trin khaikintrcphnlpdchvCoS(ClassOfService)vhngtimbocht lngdch v QoS thng qua m hnh tch hp dch v IntServ v phn bit dch v DiffServ,ccchinlccaInternettheo hngtngthchvi IP, mng quangv hngtimngchuynmchnhnagiaothctngqutGMPLS(Generalized MultiProtocol Label Switch). Cng ngh chuyn mch nhn a giao thc MPLS ra i vonm2001lsnlckthphaiphngthcchuynmchhngktni (ATM,FR)vicngnghchuynmchphiktni(IP),cngnghchuynmchnhn a giao thc MPLS nh ngha khi nim nhn (Label) nm trn mt lp gia lp 2vlp 3trong m hnhOSI,vi mctiutn dngti acc uimcachuyn mchphncng(ATM,FR)vsmmdo,linhhotcaccphngphpnh tuyn trong IP. Mt s quc gia c h tng truyn ti cp quang pht trin tt c xu hngs dngcckthutchuynmchquangvsdngcccng nghtrn nn quangnhGMPLS,IPquacngnghghpbcsngquangWDM(Wavelength Division Multiplexing), kin trc chuyn mch trong mng th h k tip NGN. Trong mi trng mng hin nay, s phn cp h thng thit b bin (ni ht), thit b qu giang v thit b li trong mng cung cp cc dch v PSTN vn ang tn ti. Cc mng bao trm nh FR, ATM v Internet ang c trin khai song song v to ra nhu cu kt ni lin mng. Cc truy nhp cng thm gm cp ng, cp quang v truynhpkhngdyangctrinkhailmadngvtngmttruynhpt pha mng truy nhp.S tng trng ca cc dch v truy nhp to nn sc p v t ra 3 vn chnh i vi h thng chuyn mch bng rng a dch v: Truy nhp bng thng rng, s thngminhcathitb bin vtruyndntccaoti mngli.Ccthit btruy nhp bng thng rng bao gm cc thit b h tng mng truyn thng (tng i PSTN niht)vccmoduletruynhpngdysDSLAM(DigitalSubcriberLine Access Mutiplexer) phi truyn ti v nh tuyn mt s lng ln cc lu lng thoi v d liu ti thit b g mng. Cc thit b g mng hin c rt nhiu dng gm VoiP CccngtruynhpchothitbVoiP(VoiceOverIP),cngtrungk,chuynmch ATM, b nh tuyn IP v cc thit b mng quang. Cc thit bbin cn phi h tr ccchcnngnhnthc,cpquynvtikhonAAA(Authentificaton, Authorization v Accounting) cng nh nhn dng cc lung lu lng t pha khch hng, v vy vic qun l v iu hnh thit b binl mt vn rt phc tp. 25 Vi mi trng mng PSTN trc y, cc thit b li mng chu trch nhim chnh trongiu hnh vqunlviu nycthay ichcnngchoccthit bg mng trong mi trng NGN. Cc h thng chuyn mch a dch v cn phi h tr cc chuyn mch lp 3 trong khi vn phi duy tr cc chuyn mch lp 2 nhm h tr cc dch v ATM v FR truyn thng, c tin cy cao v phi tch hp tt vi cc h tng c sn.Hn na, cc h thng chuyn mch phi c mm do ln nhm tng thch v pngccyu cutngtrnglulngt phakhchhng.V vy,cchiu khincchthngchuynmch c phttrintheo hng phnlpv module ho nhm nng cao hiu nng chuyn mch v m bo QoS t u cui ti u cui. HngtipcnmychcucgiCS(CallServer)vhngtrinkhaiphnha dchvIP(IMS) ctrnh bydi ylnhngim mc quantrng nhttrong lch s pht trin k thut chuyn mch trong nhng nm gn y. 1.2.2 Chuyn mch mm v hng tip cn my ch cuc gi CS. Hngtipcnmychcucgi CS c hnhthnhtrong qutrnhchuyn i cchtngmngchuynmchknhsangchuynmchgitrongmngPSTN. thc hin qu trnh chuyn i v truyn thoi trn nn IP, mt gii php c th thc thi l to ra mt thit b lai c th chuyn mch thoi c dng knh v gi vi s tch hp ca phn mm x l cuc gi. iu ny c thc hin bng cch tch ring chc nng x l cuc gi khi chc nng chuyn mch vt l. Thit b B iu khin cng aphngtinMGC(MediaGatewayController)ccoilthnhphnmucht trong gii php k thut chuyn mch mm Softswitch.Bn cht ca khi nim chuyn mch mm nm ti phn mm thc hin chc nng x l cuc gi trong h thng chuyn mch cho php chuyn ti nhiu loi thng tin theo cc giao thc khc nhau (chc nng x l cuc gi bao gm nh tuyn cuc gi v qun l, xc nh v thc thi cc c tnh cuc gi). Theo thut ng chuyn mch mm th chc nng chuyn mch vt l c thc hin bi cng a phng tin MG (Media Gateway), cn x l cuc gi l chc nng ca b iu khin cng a phng tinMGC.Chuynmchmmkhiphttxuhngtchchcnngtruyntiv iu khin trong mi trng mng phc hp, vic tch chc nng nhm c c mt s li im chnh sau: Cho php c mt gii php phn mm chung i vi vic x l cuc gi. Phn mmnyccittrnnhiuloimngkhcnhau,baogmcmng chuyn mch knh v mng gi (p dng c vi cc dng gi v mi trng truyn dn khc nhau). 26 Lnglcchocchiuhnh,ccmitrngmytnhchun,titkim ng k trong vic pht trin v ng dng cc phn mm x l cuc gi. Cho php cc phn mm thng minh ca cc nh cung cp dch v iu khin t xa thit b chuyn mch t ti tr s ca khch hng, mt yu t quan trng trong vic khai thc tim nng ca mng trong tng lai. Chuynmchmmthchinccchcnngtngtchuynmchknhtruyn thngchocccucginhngvinnglcmmdovcctnhnnguvithn. Cc u im ca chuyn mch mm mang li l do vic chuyn mch bng phn mm da trn cu trc phn tn v cc giao din lp trnh ng dng m.Trongchuynmchtruynthng,phncngchuynmchlunikmviphn mm iu khin ca cng mt nh cung cp. iu ny lm tng tnh c quyn trong viccungcpcchthngchuynmch,khngcungcpmtmitrngkinto dchv mi,lmgiihnkhnngphttrinccdchvmicacc nhquntr mng. Khc phc iu ny, chuyn mch mm a ra giao din lp trnh ng dng m API (Application Programable Interface), cho php tng thch phn mm iu khin vphncngcacc nhcung cpkhc nhau.iu nycho phpcc nhcungcp phn mmv phncngc cting nichungvtptrungphttrintheo hng m ti cc vng hot ng ring. Vi cc giao din lp trnh m, chuyn mch mm c th d dng c nng cp, thay th v tng thch vi cc ng dng ca nhiu nh cung cp dch v v thit b khc nhau. Mt s c im chnh ca chuyn mch mmgm:Chuyn mch mm c xy dng trn c s mng IP, x l thng tin mt cch trong sut, cho php p ng nhiu loi lu lng khc nhau.cxydngtheocu hnh phntn,tch ccchc nngkhc khichc nngchuynmchcnglmchonhimvchuynmchtrnnngin hn v do nng lc x l mnh m hn.Cngnghchuynmchmmlmgimtnhcquyncaccnhcung cp,gpphntngtnhcnhtranhvdogimgithnhcahthng chuyn mch mm.Cc vn k thut chi tit ca chuyn mch mm s c trnh by trong chng cui ca ti liu bi ging. 1.2.3 Hng tip cn phn h a phng tin IP (IMS) thc hin hi t gia mng di ng vi mng c nh theo hng IP ho, mng th h k tip NGN ng dng ti mng 3G (Third Generation) trong nhiu cch. Vo 27 nm2000,3GPP(3rdGenerationPartnershipProject)thitlpccctnhca WCDMA R4 (Wireless Code Division Multiple Access Release 4), l ln u tin akhi nimchuynmch mmvotrong hthng mngli di ng.Sthayi ny nh hng tikin trc mng, cc giao din mng, s pht trin ca cc dch v trong h thng thng tin di ng hng s pht trin ca 3G ti NGN. Trong kin trc mng, NGN v 3G u nhm chuyn hng tch bit gia lp iu khin v lp knh mang trong cc giao thc giao tip. 3G v NGN a ra rt nhiu giao thc nh: Giao thc iu khin c lp knh mang BICC,Giao thc khi to phin SIP/SIP-T, giao thciukhinbohiuH.248/Megaco,giaothctruyntibohiutrongnnIP (SIGTRAN), v..v khng ch cung cp cc dch v nh thoi m cn l cc dch v a phng tin thng qua cc giao din dch v m. iu ny to kh nng kin to cc dch v mi cho cc nh cung cp dch v th 3 ng thi trong c vng mng c nh v di ng. Khi kin trc chuyn mch mm c ng dng trong vng NGN 3G, n cgilchuynmchmm di ng.Gii phptch hpvh trcc dchvIP trong di ng c thc hin qua phn h IMS (Internet Multimedia Subsystem) nm ti bin vng mng c nh v di ng. 1.3 CC T CHC TIU CHUN H thng tiu chun lun ng vai tr ct li trong qu trnh pht trin cng ngh. Cctiuchuncho phpcc nhcungcpthit b phttrinccsnphmtheo mt tp c tnh chung v ngi s dng cng nh nh cung cp dch v c th la chn c cc thit b t nhiu nh cung cp.H thng tiu chun c chia thnh hai loi:Tiu chun thc t (de facto) v tiu chun php l (de jure). Tiu chun thc t c pht trin bi mt nh cung cp thit b hoc mt nhm cc nh cung cp c chp thun bi cc t chc tiu chun. Tiu chunphplclpbithathunchunggiacctchctiuchunQucgia hocybantiuchunQuct.Cctiuchunlin quantilnhvcchuyn mch thuc v c hai loi tiu chun trn, nhng tp trung ch yu trong h thng tiu chun php l. Di y l mt s t chc tiu chun v din n chnh.i, Lin minh vin thng Quc t ITU LinminhvinthngQuctITU(InternationalTelecommunicationUnion)l mttchclinchnhphcthnhlpngy01/01/1934gmcccQucgia ThnhvinvThnhvinLnhvc,viquynhnvnghavcxcnhr nhm hptc tc cc mctiu chung caLinminh.Lin minhvinthng QuctITUgm3lnhvcchnh: LnhvcthngtinvtuynITU-R(Radiocommunication);LnhvctiuchunhovinthngITU-T 28 (TelecommunicationStandardization);LnhvcphttrinvinthngITU-D (Development) [6]. MctiucaITU-T nhmtiuchun hatonculnhvcvinthngthng qua cchotngnghincukthut,iuhnh,trliccyucuvaracc khuynngh.ITU-Tcthnhlpvothng03/1993thaythchoybantvn inthoivintnQuctCCITT(InternationalTelegraphandTelephone ConsultativeCommittee).ITU-Tctchcbi15nhmnghincukthutv aracctiuchundidngkhuynngh.CckhuynnghcaITU-Tct chcthnhcc nhm c nhthttheo chciAlphabet. Cckhuynnghca ITU-T trong series Q lin quan ti bo hiu v chuyn mch. V d, Q.2931 m t th tc bohius dng thitlpknho im-imquagiao dinngis dng mng trong mi trng ATM. ii, T chc tiu chun Quc t ISOTchctiuchunQuctISO(InternationalOrganizationforStandardization) c thnh lp vo nm 1947 gm cc y ban tiu chun ca cc Quc gia. Nhim v catchctiuchunQuctISOlxctinvictiuchunhavcchot ng lin quan trn ton cu nhm to iu kin thun tin trong trao i hng ha v dch v, pht trin s hp tc trn nhiu lnh vc. Cc tiu chun ISO a ra cc tiu chun ha bao trm tt c cc lnh vc k thut, trong lnh vc vin thng m hnh h thng kt ni h thng m OSI (Open System Interconnection) l mt tiu chun ph bin ca ISO. ISO hp tc vi y ban in t Quc t IEC (International Electronical Commission) pht trin cc tiu chun trong mng my tnh v lp ra y ban lin ktkthutJCT1(JointTechnicalCommittee1)nm1987phttrincctiu chun trong lnh vc cng ngh thng tin [6]. iii, Vin k thut in v in t IEEEIEEE (Institute of Electrical and Electronics Engineering) l cng ng chuyn gia k thut ln nht trn th gii pht trin cc tiu chun trong lnh vc in-in t v mytnhthngquahiphitiuchunIEEE-SA(StandardsAssociation).IEEE-SA gm Hi ng qun tr v cc y ban tiu chun. Hi ng qun tr chu trch nhim v chnh sch, ti chnh v hng chin lc cho cc y ban tiu chun. y ban tiu chunchutrch nhim phttrinv qunl cctintrnhtiuchun hathng qua cc d n [6]. iv, T chc c nhim k thut InternetIETF IETF (The Internet Engineering Task Force) l mt cng ng m Quc t ca cc nh thit k mng , iu hnh mng, cc nh cung cp thit b v cc nh nghin cu 29 lin quantisphttrincakintrc Internet.Mtsvngchcnngc bnca IETF nh: ng dng, Internet, qun l mng, ccyu cu iu hnh, nh tuyn, bo mt, truyn ti v dch v ngi s dng. Mi mt vng c mt vi nhm lm vic thc thi cc nhim v c th. Cc tiu chun ca IETF c a ra di dng cc yu cu dn gii RFC (Request for Comments) gn vi cc s hiu. V d, RFC 1058 dn gii cc vn lin quan ti giao thc thng tin nh tuyn RIP (Routing Information Protocol)trong mngIP.RFCgm ba dng: RFCtiuchun,RFCbnthov RFC xut. Cc dng RFC bn tho v RFC xut ch c hiu lc trong mt khong thi gian, cc ti liu ny c th c chnh sa, cp nht, thay th hoc loi b khi ht thi hn [6]. v, Vin tiu chun vin thng chu u ETSIETSI (European Telecommunications Standards Institute) l t chc tiu chun ha vin thng, phi li nhun v c lp ca chu u cng nh ca th gii c t chc nm1988.MctiucaETSInhmhtrqutrnhtiuchunhatronglnhvc vin thng, cng ngh thng tin v truyn thng ton cu thng qua cc din n, to iu khin cho cc thnh vin ch cht ng gp kin xy dng cc tiu chun. Cc nhm lm vic c thnh lp thc hin tiu chun ha cc nhim v c th. V d, Nhm WG3 trong d n TIPHON ca ETSI a ra cc tiu chun v bo hiu v iu khincucgitrongmitrngkthpgiaothcIPvihtngmngvinthng. Nhm WG4 a ra cc tiu chun v nh s, tn gi v a ch cho cc thit b ngi s dng u cui. ETSI a ra mt s dng ti liu pht hnh gm: Tiu chun ETSI, bin bn ETSI, c tnh k thut v bo co k thut. Trong dng ti liu tiu chun ETSI v bin bn ETSI c pht hnh sau qu trnh b phiu [6]. vi, Din n chuyn mch a phng tin MSFMSF(TheMultimediaSwitchingForum) cthnhlp nm 1998,cungcpcc tiu chun cho chuyn mch a dch v da trn nn tng ATM, h tr cc kiu dch v gm cc dch v IP v dch v ATM cng nh l cc dch v khc. Cc ti liu tiu chun c xy dng bi ba nhm lm vic:Kin trc: Kin trc giao din v nguyn l giao din;iu khin chuyn mch: Cc giao din iu khin v qun l chuyn mch; Phng tin: M hnh iu khin thoi v cc giao din cng a phng tin. vii, Din n IP/MPLSDin n IP/MPLS c thnh lp vo thng 7/2007 v l mt t chc Quc t phi linhuncacc nhcungcp dch v,cc nhcungcpthit b,cc trung tm o 30 kim v ngi dng x nghip. Mc tiu ca din n tp trung vo cc gii php pht trinvngdngtrnhtngcngnghIP/MPLS.Cctiuchuncadinn IP/MPLShngtischuyndchcacccngnghhinthisanghtng IP/MPLSph hp vi cc tp c tnh ca IETF v ITU-T. Mt trong cc tiu chun cxydngbidinnIP/MPLSkthpviITU-Tllinktbohiu MPLS/PNNI v bo hiu cho thoi qua MPLS [6]. 1.4 KT LUN CHNG Chng 1 tp trung vo gii thiu cc thut ng, nh ngha c bn trong lnh vc k thut chuyn mch. Nhm khi qut cc kin thc v lnh vc lin quan ti k thut chuyn mch, cc khi nim c s v cc l thuyt lin quan ti k thut chuyn mch c a ra. Trong , cc m hnh ton c s c trnh by vn tt l nn tng cacc vn m hnh ha, phntchvtnhtonccthamsmngchuynmch. Qutrnh phttrinvxu hng phttrincng ngh mng ctrnh bytiphn cui ca chng nhm gip sinh vin nhn thc v l trnh v xu hng chuyn i h tng mng vin thng cng nh cc tc ng lin quan ti lnh vc chuyn mch. Cc t chc tiu chun c gii thiu trong chng ny nhm gip sinh vin phn bit v xcnhrcckhacnhtiuchunkthut vcng ngh cp dngtronglnh vc chuyn mch.

31 Chng 2 K THUT CHUYN MCH KNH 2.1 C S K THUT CHUYN MCH KNH Kthutchuynmchknh datrn nguyntcthitlpknh ni dnhring cho cc cuc gi phc v cho qu trnh truyn tin qua mng. K thut chuyn mch knh ng vai tr quan trng trong cc h thng mng vin thng k t mngchuyn mch in thoi cng cng truyn thng PSTN (Public Switched Telephone Network) n cc mng quang hin i. Chng 2 ca cun bi ging nys trnh by cc vn k thut chuyn mch knh c ng dng trong mng in thoi cng cng PSTN v tp trung vo cc nguyn l c bn ca chuyn mch knh tn hiu s.Chuynmchknhtnhiusl qutrnhktni,traoithngtinsgiacc khethigiancghpknhphnchiathigianTDM(TimeDivisionMode). Lulngngidngcchuynittnhiutngtsangtnhiustheo nguyn l PCM (Pulse Code Modulation) v ng thnh cc khung tn hiu PCM theo chunG.704ITU-Trictruynnntmngthchinchuynmchtrn trng chuyn mch. Tiu chun G.704 ITU-T m t cc dng cu trc khung tn hiu PCM ca h thng PCM 24 (T1) v h thng PCM 30/32 (E1) nh sau: i, Cu trc khung v a khung PCM 24 Cu trc khung PCM 24 c m ho theo lut v c mt s c tnh c bn sau: Hnh 2.1: Cu trc a khung PCM 24 Tc truyn 1,544 Kb/s; Mt khung gm 24 DS0 (64 kb/s). di khung l 125 s c 193 bit c nh s t 1- 193; Bit u tin ca mi khung c s dng xp khung, gim st v cung cp lin kt s liu. K thut m ho ng dy : AMI, B8ZS. 32 Cutrcakhunggmhaikhundng:DS4nhm12khung,vkhungm rng EPS nhm 24 khung (hnh 2.1 th hin cu trc a khung 24). Bit bo hiu F s dng xp a khung, lin kt d liu, kim tra v bo hiuc ch nh trong tng khungii, Cu trc khung v a khung PCM 30 Cu trc khung PCM 30 th hin trn hnh 2.2 c m ho theo lutA v c mt s c tnh c bn sau: Tc truyn 2,048 Kb/s; Mt khung gm 32 TS/30 CH. di khung l 125 s cha 256 bit; nh s t 1 n 256. Hnh 2.2: Cu trc khung v a khung PCM 30 K thut m ho ng dy : AMI, HDB3. Cutrcakhungcha16khung.TS0sdngxpkhungvngb, TS16 s dng cho bo hiu. iii, Trao i khe thi gian ni TSI Trong k thut chuyn mch knh, sau khi tn hiu thoi c m ho thnh cc t m nh phn 8 bit, cc knh thng tin c xc lp trn cc khe thi gian cch nhau 125s v c truyn i nh cc h thng truyn dn v chuyn mch.Trn nguyntcs dng chung ti nguyn,thngtinca ngi s dng c chuyn i trn cc knh c phn chia logic theo thi gian. Vic sp xp li ni dung thng tin trn cc khe thi gian trong cng mt khung thng tin c gi l qu trnh 33 trao i khe thi gian ni TSI (Time Slot Interchange). Mt c cu s dng chuyn i khe thi gian ni c minh ho trn hnh 2.3. Hnh 2.3: Nguyn l trao i khe thi gian ni TSI Cc khi thit b chnh gm c:Cc tuyn PCM u vo v u ra c cu trc khung gm n khe thi gian, yu cu chuyn i ni dung thng tin ca mt khe thi gian bt k t u vo ti u ra. Bnhlumtmthihotngtheonguyntctruyxutngunhin (RAM) c dung lng cha ton b thng tin d liu trong mt khung PCM, (S ngn nh: n, dung lng ngn nh: 8 bit).Khi iu khin CM (Control Memory) s dng ghi cc thng tin iu khin chuyn i ni dung khe thi gian trn b nh lu m (S ngn nh: n, dung lng ngn nh: l= log2n). Qu trnh ghi c vo cc b nh c ng b thng qua mt b m khe thi gian TS.C. Khicyucuchuyninidungthngtinvtuthucvongunti nguyn ca h thng, khi x l trung tm s a cc d liu iu khin ti khi iu khinCM nhmspxpvtrchuynicacc khethigian.m botc lung thng tin u vo v u ra, trong mi khe thi gian b nh lu m phi thc hin ng thi hai tc v ghi thng tin vo v c thng tin ra. Theo nguyn tc trao i khe thi gian ni TSI, tr ti a ca thng tin trao i khng vt qu thi gian ca mt khung: Td (max) = (n-1)TS < 125s. 34 2.2 KIN TRC TRNG CHUYN MCH KNH Chuyn mch knh tn hiu s l qu trnh thc hin trao i ni dung thng tin strongcckhe thigiancacctuynPCM uvoti ura.thc hin hiu ququtrnhchuynmch,cctuynPCMthngcghpknhvitccao trc khi a ti trng chuyn mch.Vicb tr s dng cc trng chuyn mch trong h thng chuyn mch ph thuc ch yu vo kin trc iu khin ca h thng. Tuynhin,kintrctrngchuynmchknhcchiathnhhaidngphnchia theonguyntchotng:TrngchuynmchkhnggianS(Space)vtrng chuyn mch thi gian T (Time).Di y s trnh by nguyn l cu trc ca trng chuyn mch khng gian (S), thi gian (T) v kin trc ghp ni cc trng chuyn mch (TST). 2.2.1 Trng chuyn mch khng gian s TrngchuynmchkhnggiansSthchinqutrnhchuynnidung thng tin t cc tuyn PCM u vo ti cc tuyn PCM u ra m khng lm thay i v tr khe thi gian trn trc thi gian. to ra knh truyn thng cho cc cuc gi, cc thng tin c chuyn qua trng chuyn mch khng gian s c chuyn mch nh k vi khong thi gian 125s.Cc trng chuyn mch khng gian (S) c thit k h tr chuyn mch ng thi mt s lng ln cc cuc ni di s iu khin ca cc chng trnh ghi sn. Hnh 2.4 trn y ch ra s nguyn l cu trc ca trng chuyn mch khng gian (S)inhnhtheokiuiukhinuvo.Kiuiukhinuracthchin bng s hon i v tr gn cng u ra ca cc phn t kt ni. Trng chuyn mch khng gian (S) c cu to t hai khi chnh: Khi ma trn chuyn mch v khi iu khin cc b. i, Khi ma trn chuyn mchKhi ma trn chuyn mch c cu trc di dng ma trn hai chiu gm cc cng uvov cccng ura.Trncccnglcctuyn PCMcchukkhung 125s.Cc im nitrong matrnlccphnt logickhng nh(thngthngl ccmchAND).Mt matrn c(N)cng uvov(M)cng uratrthnh ma trn vung khi N=M. 35 Hnh 2.4: Nguyn l chuyn mch khng gian (S) ii, Khi iu khin khu vc Khi iu khin khu vc gm mt s khi thit b nh:B nh iu khin kt ni CMEM (Control MEMory) lu tr cc thng tin iu khin theochngtrnhghisncho matrn chuynmch, ni dungthngtin trongCMEMsthhinvtrtng ngcaimktnicnchuynmch (S ngn nh: n, dung lng ngn nh: l= log2N);B gii m a ch DEC (DECode) chuyn cc tn hiu iu khin m nh phn thnh cc tn hiu iu khin cng cho phn t kt ni AND;B m khe thi gian TS.C (Time Slot Counter) nhn tn hiu ng h t ng hhthngcpccxungngbchobiukhintheongbcacc tuyn PCM vo v tuyn PCM ra;TS.C a tn hiu ng b vo b chn (SEL) ng b qu trnh ghi dch a ch v tc v ghi c ca b nh CMEM. Nguyn tc hot ng ca trng chuyn mch khng gian (S) gm mt s bc c bn sau: 36 Cc tuyn PCM trn cc cng u vo v u ra c ng b ho theo tn hiu ng b. Nh trn hnh 2.4 ch ra mi khi iu khin khu vc LOC m nhim mt cngura,vvysbiukhinLOCsbngngscngura(Mbiu khin). i vi mi mt cuc ni thoi, chu k ng tip im c thc hin tun t theo chu k 125s. Vic ngt cc kt ni c thc hin n gin thng qua qu trnh ghi li d liu trong b nh CMEM. Cc khong thi gian cn li s c thc hin cho cc kt ni khc. Nu ma trn chuyn mch l ma trn vung th tng s knh ti acthktni ngthislCmax= n x N(n:skhethigian trong mt khung PCM; N: s cng u vo chuyn mch (S)). Trng chuyn mch khng gian (S) mang tnh thi gian nu xt v tnh chu k ca qutrnh ng ngttip im.Vchuknylcnhchottccccuc ni quatrngchuynmch.Nhcimluntntitrongcctrngchuynmch khnggian(S)lxyrahintngtc nghnkhic nhiu hn mtyucuchuyn mch ca cc khe thi gian u vo cng ch s cng mun n mt cng u ra. Mt ma trnchuynmchkhngtc nghn hon ton c nh nghal mt matrnc kh nng p ng c cc kt ni t cc u vo bt k ti cc u ra bt k.Hin tng tranh chp cng u ra trong ni b trng chuyn mch c gi lhintngtcnghnni.giiquytvntrn,cctrngchuynmch(S) thng c kt hp vi cc b m gy tr thi gian trnh tranh chp, chnh l cc gii php ghp ni trng chuyn mch (S) vi trng chuyn mch thi gian (T) trong cc h thng chuyn mch thc t.2.2.2 Trng chuyn mch thi gian s Trngchuynmchthigiantnhiusthchinqutrnhchuynini dung thng tin t mt khe thi gian ny sang khe thi gian khc, vi mc ch gy tr cho cc tn hiu. Qu trnh gy tr tn hiu c thc hin theo nguyn tc trao i khe thi gian ni. Hnh 2.5 ch ra s nguyn l cu trc ca trng chuyn mch thi gian(T).Trngchuynmchthigian(T)chaikiuiukhin:iukhinu vo thc hin qu trnh ghi thng tin c iu khin v c ra tun t; iu khin u ra thc hin ghi thng tin tun t v c ra theo iu khin. Trong mc ny ta xem xt nguyn l hot ng ca trng chuyn mch (T) theo kiu iu khin u ra.Trng chuyn mch thi gian (T) c cu to t 2 khi chnh: Khi b nh thoi SMEM (Speech MEMory) v khi iu khin cc b LOC. 37 Hnh 2.5: Nguyn l chuyn mch thi gian (T) KhibnhthoiSMEMlmtthitbghinhtruyxutngunhinRAM (S lng ngn nh: n; dung lng ngn nh: 8 bit). Nh vy, b nh SMEM lu ton b thng tin trong mt khung tn hiu PCM. m bo tc lung thngtin quatrngchuynmch,tc ghiccaCMEMphilngp2 ln tc lung trn tuyn PCM u vo hoc u ra. Khi iu khin khu vc gm mt s khi nh: B nh iu khin CMEM lu tr cc thng tin iu khin SMEM, s th t ca ngn nh v ni dung d liu trongCMEMthhinccchskhethigianTScntraoinidungtin. TS.C nhn tn hiu t ng h h thng iu khin cc b chn SEL1, SEL2 nhm ng b ho qu trnh ghi c thng tin d liu cho CMEM v SMEM. Nguyntchotngcatrngchuynmchthigian(T)trncsca nguyn tc trao i khe thi gian ni. Hnh 2.5 th hin kiu iu khin ghi vo tun t c ra c iu khin SWRR (Sequence Write Random Read). Trng chuyn mch thi gian (T) mang tnh khng gian nu xt trn kha cnh v tr thng tin d liu trong cc ngn nh ca CMEM. Chuyn mch (T) lun gy tr tn hiu v tr ln nht khng vt qu mt khung PCM, Td (max) = (n-1)TS. Do tc ghi c ca b nh yu cu ln gp 2 tc lung PCM nn s lng khe thi gian trong mt khung thng khng vt qu 1024 khe thi gian do gii hn ca cng nghvtliu int. mrng dunglng, ngitalachngii phpghpvi cc trng chuyn mch khng gian (S). 38 2.2.3 Trng chuyn mch ghp TST Di gc h thng, h thng chuyn mch s c coi l h thng tn tht. V vy, vn nng cao hiu nng chuyn mch lun l vn hng u trong thit k chtotrngchuynmch.Trongkthutchuynmchknh,cchintngtc nghn c coi l yu t c bn c tc ng suy gim cht lng h thng v ch yu ri vo cc h thng chuyn mch s dng tng (S). Tc x l v thi gian tr trong trngchuynmch(T)cnglccthamsnhhnglntihiunngtrng chuynmch.Tuynhin,doctnhtnhincachuynmch,vicsdngcc chuyn mch khng gian (S) trong h thng chuyn mch l yu t bt buc. Hn na, chuynmch(S)chnhliukinmuchtpngcdunglngchuyn mch trong thc tin. V vy, cc trng chuyn mch thc tin thng c ghp ni atngv phi hpgiacc kiuchuynmch(T)v(S).Mctiukt niatng chuyn mch khng ch nhm tng dung lng h thng m cn lm gim bt phc tp v s lng thit b trong trng chuyn mch. Kt ni a tng trong chuyn mch knh c chia thnh hai kiu nhm m bo kh nng khng tc nghn hon ton cho trng chuyn mch: Kiu kt ni y v kt ni tng phn.Nguyn tc ghp ni cc trngchuyn mch 3 tng tun ththeo nh l Clos c pht biu nh sau: Matrnchuynmchktni3tngkhngtcnghnkhivchkhisktni trung gian r2 n + m -1. Trng hp c bit khi n=m th r2 2n-1. Tcctngchuynmch(T)v(S)cbncthcnhiukiughpcctng chuynmchtheocc m hnh nh:TS,ST, STS,TSTtytheo dunglngvkin trc iu khin h thng. Do s pht trin rt nhanh ca tc x l m kin trc ghp niTSTthngcsdngnhiunhttrongcchthngchuynmchthng mi. Do vy, trong phn ny ta xem xt cc nguyn tc hot ng ca trng chuyn mch ghp da trn kiu ghp ni TST. Trn thc t, trng chuyn mch ghp TST nhmgii quytbiton mrng dung lngvs dngchocckt ni hai hng trong trng chuyn mch thc t. Theo l thuyt, trng chuyn mch TST c h s tp trung l 1:1 v m bo khng tc nghn khi s lng khe thi gian trn lin kt trung gian tun th theo nh l Clos. Nh mc 2.2.2trnytrnh by,trngchuynmchthigianTcth hot ng theo hai kiu iu khin u vo (RWSR) v iu khin u ra (SWRR), v vykhighp2tngTtasc4phngnghpnitngngvicckiuiu khin tng chuyn mch T1 v T2. 39 Trong v d trn hnh 2.6 ta chn chuyn mch thi gian tng T1 hot ng theo nguyntcSWRRvchuynmchthigiantngT2hotngtheonguyntc RWSR, A truyn v nhn thng tin d liu trn TS#05, B truyn v nhn thng tin d liutrnTS#10,khethigiantrunggiangiaT1-SvS-T2cchnlTS#15, thng tin iu khin ti cc CMEM tng T c vit tt di dng a[b] [a: ch s ngn nh, b: ni dung ngn nh]. Hnh 2.6: Ghp ni trng chuyn mch TST Ni dung thng tin trn cc b nh CMEM c trnh by vn tt nh sau: HngktnitABquaSMEM1(T1)SSMEMN(T2),ccbnh CMEM1(T1) v CMEMN(T2) c ni dung tng ng 15[5] v 15[10]. HngktnitBAquaSMEMN(T1)SSMEM1(T2),ccbnh CMEMN(T1) v CMEM1 (T2) c ni dung tng ng 15[10] v 15[5]. Tnidungcckhiiukhinchuynmch(T)nhtrnhnhv,tanhn thyhaikhiiukhinCMEM1(T1)vCMEM1(T2)hontongingnhau,cng nh vy i vi CMEM N (T1) v CMEM N (T2). tit kim s b iu khin ta c th s dng mt b iu khin s dng iu khin chung thay v hai b iu khin. V trng hp ang xt l trng hp c bit khi ta chn khe thi gian trung gian ging nhau (TS#15), iu ny s khng ng vi 40 trng hptng qutkhiAv Bcng c ktniticng mtkhichuynmch thigiantrongtngT1, hintngtranhchpsxy rakhichaiyu cuuvo TS#05 v TS#10 cng mun ra u ra TS#15. Mt gii php trnh trng hp ny l s dng kt ni th hai (BA) qua tuyn trung gian c khe thi gian l TS#15 + 2n. Lcnynidungbiukhintngngl:CMEM1(T1):=15[5];CMEM1(T2):= (15+2n)[5]; CMEMN(T1):= (15+2n)[10]; CMEMN (T2):= 15[10].Khisdngmtbnhingunhtrn hnh2.6(A*)tahontoncth iukhin chaibiukhinCMEMtihaitngchuynmchbngmtkhi iu khin. Trng hp s dng mt b nh dng chung nh trn hnh 2.6 (B*) khi ta chn chuyn mch tng T1 hot ng theo nguyn tc RWSR v chuyn mch tng T2 hot ng theo nguyn tc SWRR.VnchnkhethigiantrunggiantrongtrngchuynmchTST iu khin kt ni gia cc tng T v S l mt khu quan trng trong qu trnh x l chuyn mch.Phngphptmkimkhethigiantrunggianricthchinmtcch n gin qua vic x l tm kim cc cp bit (bn/ ri) ti u ra tng T1 v u vo tng T2. Phng php c xut tm kim cc cp bit ri ti hai u l phng phptmkimkiumtnchnknh.Ccbittrongthanhghichthtrngthiv thanhghimtnthhinrsbn/ricaccknhthngquabnnhnhx trng thi. Ba thut ton thng c s dng trong cch thc di chuyn mt n gm: Ngu nhin lin tip, c nh- lin tip v phng php th lp.(i) Phng php ngu nhin - lin tip: phng php ny da trn nguyn tc tm kimngunhinmtkhethigianri,nu khethigianutinchnngunhin khng tho mnyu cu, h thng dch chuyn lin tip trong ton di nhm tm khe thigiantho mnyucu. Phng php nytorahiu ngchim dngcc bt cc im xc lp ngu nhin, thi gian tm kim s ko di khi s lng knh b chim tng ln. (ii) Phng php c nh lin tip: Phng php ny ch nh khe thi gian u tinsautmlintiptrnton di.Hiungtridiccknhbchimdngbt utknhcchnvxcsutchnknhtrongphngphpnykhngging nhau. (iii)Phngphpthlp:Phng php nydatrnctnhcalulngyu cuvschimdngngunhincacckhethigian.Qutrnhthlpdatrn 41 theo khong thi gian chim dng khe thi gian. Phng php ny c bit hiu qunu m hnh lu lng u vo c xc nh. 2.3 NH TUYN TRONG CHUYN MCH KNH nh tuyn l mt chc nng then cht trong cc mng truyn thng nhm nh racctuynngchuynlulngtngunnngch.Tytheotiuch cnthitkhixydngcchthng mng mpdngcckthutnhtuynkhc nhau: nh tuyn phn cp, nh tuyn tnh, nh tuyn ngNi dung ch yu ca phnnysxemxtcckthutnhtuyncbncacchthngchuynmch knhdngtrongmngPSTNgnlinvikhochnhsvhotngcant mng chuyn mch knh khi thc hin x l nh tuyn cuc gi.2.3.1 Phn loi cc k thut nh tuynC hai kiu nh tuyn c bn trong k thut chuyn mch knh l : nh tuyn phn cp v cc lc nh tuyn ng da trn mng phn cp.i,nh tuyn phn cp Trn hnh 2.7ch ra mt cu hnh mng n gin gm 2 cp, h thng chuyn mch 1, 4 ti cp thp v h thng chuyn mch (c k hiu l node trn th) 2, 3 ti mc cao. Trn hnh 2.7 (a) mt cuc gi c kt ni trc tip t node 1 ti node 4 nu tn ti lin kt trc tip. nu lin kt 14 bn, cuc gi s trn theo hng 13 v y c coi l cuc gi th, khi lin kt 34 cn ti nguyn cho cuc gi th kt ni thnh cng t 14. Nu lin kt 34 khng cn knh ri cho cuc gi th cuc giccoilkhngthkt ni.Trongtrnghpny,ngktni(134) c gi l hng trn cho hng 14. Tuy nhin, lc ny cn c th cung cp nhtuynlun phin, nucuc gikhngtmthymchritrnlinkt1-4, cuc gi th s chim ng 1-2 nh nhm trung k cui. Hnh 2.7: V d v nh tuyn phn cp Ccnhmtrungktrongmngnhtuynphncpgmc2loi:trungklu lnglnHU(highusage)vtrungkcui(finaltrunk).Nhmtrungklulng 42 ln l nhm trung k thng xuyn c lu lng trn , nhm trung k cui l nhm khng cho php cc nhm khc trn ti nu cuc gi khng tm c knh ri. Trong hnh trn, cc nhm trung k 1-4, 1-3 v 2-4 l trung k lu lng ln v 1-2, 3-4 l nhmtrungkcui.Thtcacccucgithsl14,134,124.Trong m hnh mng trn hnh 2.12 (b) c b sung nhm trung k cui 2-3, th t cucgithsl14,134,124,v1234.Cngtrongmhnh mng ny,cuc gicth bt uti node 2ti node 4, hai ng nhtuyn c sp theo th t sau 24 v 234. Tuyn 214 s khng c xc nh bi c ch nh tuyn phn cp khng cho php nh tuyn ti cc node c cp thp hn. Vi mc tiu trnh lp vng trong qu trnh nh tuyn, mt s lut c p dng cho c ch nh tuyn phn cp nh sau: Mt nodeti mccao hn phic chc nngnhtuynvchuynmchcho cc node cp thp hn. Cuc gi c nh tuyn qua node phn cp trc tip i vi c node ngun v node ch. i vi cc cuc gi t min phn cp ny sang min phn cp khc, cc nhm trungkHUtrong min cha node ngunchuynmchti bccao hntrong min cha node ch. Lut ny c gi l lut nh tuyn u tin. Trong thc t, cc h thng chuyn mch knh c b tr phn cp thnh 5 cp vi cp cao nht c kt ni hnh li y nhm h tr lu lng mc ti a, cc ng nh tuyn lun phin c nh ngha trc, mt s lut c p dng nhm trnhnhtuynvnglpvcccucgicnhtuyntinodeccpcaohn hoc ngang cp. ii,nh tuyn ngMtcimbtlilnnhtcaqutrnhnhtuynphncplkhngth nhtuyncucgiticcnodecbcthphn,trnvdhnh2.9(b)tuyn 214 l khng th xc nh cho kt ni t node 2 sang node 4 mc d c th cn d bngthng.Hn na,trong nhtuynphn cps dngcch iukhin cuc gi ly tin PCC (Progressive Call Control), iu khin cuc gi chuyn t mt node nysangnodekhcchotikhitmcnodechvnukhngthtmthymt trung k ra ti trung k chuyn tip th cuc gi s tn tht. Ni cch khc, iu khin cuc gi khng cho php ti nh tuyn t node ngun. Mt c ch b sung cho qu trnhchuynngciukhincucgitnodetrunggianvnode ngungilc ch crankback, c ch ny cho php node ngun ti nh tuyn. Trn c s mt s lc nh tuyn ng c xy dng cho mng phn cp nhm khc phc cc im 43 hnchcanhtuynphncp.Diystrnhbyslccckthutnh tuyn ng c bn v cc u nhc im ca n v phn loi cc lc nh tuyn ng. nh tuyn ng khng phn cp. nh tuyn ng khng phn cp DNHR (Dynamic Nonhierarchical Routing) l mtkthut nhtuynphthuctheothi gian,cctptuyncthitlptrc theo th t. Ty thuc vo khong thi gian trong ngy, trong tun m cc lu lng ti c chuyn qua cc tuyn. Cn c vo cc mu lu lng thng k m cc tuyn ctnhtontrcv cspxptheo tht. Cccucgithsthc hinln lt trn cc tuyn xc nh v trng hp cui cng l s dng c ch crankback. Nh vy, DNHRcho php nhiu hn 2 lin kt cho mt cuc gi trong mng v lu tr cc ng nh tuyn lun phin ti cc node. nh tuyn iu khin ng. nhtuyniukhinngDCR(DynamicallyControlledRouting)lmtk thut nh tuyn thch ng yu cu cp nht trng thi mng theo chu k. Cn c vo trng thi ca cc lin kt mng, cc tuyn c tnh ton bi mt b x l trung tm. Cchnhtuyniukhinngchophpdphnglnhn2linktchomt cuc gi, tuy nhin nh tuyn iu khin ng khng thc hin c ch crankback. V vy, cuc gi s tn tht nu cc ng lin kt nh ngha trc b nghn do khng m bo thi gian thc hoc h thng tnh ton trung tm li. nh tuyn lun phin ng nhtuynlun phin ngDAR(Dynamic AlternateRouting)llc nh tuynphntnvthch ng.Tngt nhcclc nhtuynngkhc,DAR cng b hn ch bi s lin kt nh tuyn v thiu c ch crankback. i vi mi mt nodenguni,duytrmtngdndphngktrongcachecan.Mtcucgi mi s th lin kt trc tip ij, nu khng cn bng thng trn ng lin kt trc tip,nschuynsangnglunphintrongcache.Khicucgichuynsang ngnhtuynlunphin,nodengunchntipmtngdnmilunphin thngquaqutrnhchnngunhin.Mcdthuttontngingin,nhng DAR cho php cache cc tuyn c lu lng ti thp nht v mi khi lu lng thay i cc ng nh tuyn lun phin s la chn t ng cc ng lun phin c ti thp nht. nh tuyn lun phin ng c th cho php cp nht trng thi lin kt ca mngtnhtonngdnthngquamtqutrnhhcthngtinnhtuynt ng. V vy, DAR cn c coi l c ch nh tuyn theo s kin. nh tuyn mng thi gian thc 44 nhtuynmngthigianthcRTNR(Real-TimeNetworkRouting)cpht trintkthutnhtuynngkhngphncpDNHRvllcnhtuyn tng thch ng. Bng nh tuyn cho cc tuyn lun phin c cp nht theo tng cucgi.Thng quacc bntintruyvn,cctrngthilinktcxcnhtheo tng thi im v xc lp theo kh dng ca lin kt. Mt tp cc tuyn kh dng c lu tr trong bng nh tuyn v l c s cho cc quyt nh chn tuyn. Phn loi cc lc nh tuyn Mt s cc kiu nh tuyn trn y c th c phn loi thnh cc kiu lc nh tuyn nh sau. (1) Tp trung v phn tn. Trong cc h thng tp trung, tnh ton tuyn c thc hin bi mtbx ltnhton.CclcnhtuynnhDNHRvDCR nmtrongloi ny.Trong nhtuynphntncc nodechuynmcht tnh ton ng dn v RTNR v DAR thuc loi ny. (2) Phthucthi gianvtngthch.nhtuyn phthuc thigianlin quan tini dung bngnhtuynbin i theothigian toramttp ng dn kh dng trc. nh tuyn tng thch lin quan ti tn sut cp nht bng nhtuyndatrnlulnghocskin.DNHRthucloithnhtv DCR, RTNR v DAR thuc loi th hai. (3) nh k v theo yu cu. Trong kiu nh tuyn tng thch, cp nht bng nh tuyncthchintheochukhoctheoyucu.DCRllcnh tuyn cp nht theo chu k (10s) v RTNR v DAR c hot ng cp nht theo cuc gi hoc tuyn d phng nghn. (4) Phthuctrngthiv phthucskin.nhtuynphthuctrngthi lin quan ti xem xt trng thi ca mng trong quyt nh nh tuyn. Thng thng, trng thi y c xt l kh dng ca lin kt, v d nh trong hailcnhtuynDCRvRTNR.DARidinchokiuphthucs kin khi n chn ng lun phin trong trng hp c s kin li xy ra.2.3.2Phng php nh s trong mng PSTN i, K hoch nh s ton cu ng dnginhnhcakthutchuynmchknhlmngchuynmchin thoi cng cng PSTN. Nguyn tc chung ca qu trnh nh tuyn cho cc cuc gi trong mng PSTN da trn a ch ch, cc h thng chuyn mch thc hin qu trnh nh tuyn thng qua a ch ch trn c s thng tin bo hiu. Cc phng php nh tuyntrongmngPSTNthctlunthngnhtvikhochnhs,tnhcc, 45 truyndnvbohiu.TchclinminhvinthngquctITU-Tchracc nguyn tc c bn ca k hoch nh s trong mng PSTN nhm m bo 3 yu t:(1)Cung cp nhn dng duy nht trong phm vi quc gia v quc t, (2)p ng c cc yu cu tng trng ca thit b u cui,(3) di cc con s ph hp vi khuyn ngh ca t chc vin thng quc t.Khuyn ngh ITU-T E.164 ra i vo thng 5 nm 1997, thuc vo seri E vi tiu "Hot ng chung ca mng, dch v in thoi, hot ng dch v v cc tc nhn con ngi",quynhcc"Hot ng, nhs, nhtuyn vcc dchv di ng-Hot ng quc t - Quy hoch nh s cho dch v in thoi quc t". Chi tit hn,E.164 quy nh v cc phng php nh s cho cc thit b vin thng hot ng trong mng cng cng.E.164tptrung quynhcutrccons vchc nngcaccss dngtrong vinthngcngcngqucttuntheotheo3dng:Vng,dchvchungvtheo mng. E.164 quy nh c th mi loi tin t cn thit cho tng dng nhm thng nht vicnhstoncuchomiloinhucudchv.Ngoira,E.164cngcungcp ccquycchungnhtuyncucgigiaccconsvnhmstrnton h thng. ivi mngchuynmch inthoicngcng PSTN,E.164 quynhtngdiccconssdngkhngvtqu15 digits,cphncpthnhccvngm gm: m quc gia, m vng, m tng i v cc con s thu bao. Cc h thng m nythng ikmvimtrungkto racctintc nh(prefix).Cchthng chuyn mch da trn cc tin t phn bit cc cuc gi ra trong vng, trong nc hocquct.Cncvoccachtint,hthngbngbin dchcahthng chuyn mch s lu cc nh x a ch logic sang a ch vt l s dng trong qu trnh nh tuyn. Mt v d v h thng nh s theo vng a l nh sau: +84 43 556 9999; Trong : + l tin t cho bit dy a ch c vit theo dng y ; 84 l m quc gia ca Vit nam, 43 l m vng hay cn gi l m trung k, 556 9999 l s thu bao gm 556 l m tng i v 9999 l con s thu bao ni i.ii, a ch trong mng bo hiu s 7 Mngbo hius7 ngmtvaitrquantrngtrongcch nhtuynca mng PSTN v hin l phng php bo hiu ph bin nht hin nay cho mng PSTN. Cc a ch node trong SS7 (Signalling System No7) c gi l cc m im (point code), chng l cc a ch logic v c nhn dng ti lp 3 ca chng giao thc SS7. C hai dng m im c s dng trn th gii hin nay tun theo chun ca ANSI v ITU c m t trn hnh 2.8. 46 Hnh 2.8: M im theo tiu chun ANSI v ITU M im bo hiu theo tiu chun ca ANSI c di 24 bit v c chia thnh 3 trng chc nng 8 bit gm: S hiu mng, m vng v thnh vin. Cch nh a ch theo ANSI tng t nh cch nh a ch IP. Trng 8 bit u tin nhn dng bi nh cung cp mng SS7,trng th hai nhn dng im m bo hiu SSP v trng chc nng th 3 ch ra cc thnh vin kt ni ti im m bo hiu.M im bo hiu theo ITU c di 14 bit v chia thnh 3 trng chc nng: trng th nht gm 3 bit nhn dng vng, trng th hai gm 8 bit nhn dng mng v trng th 3 gm 3 bit l nhn dng im bo hiu. 2.3.3Mng bo hiu PSTN Hnh2.9diymtmtmngSS7inhnhgmcckiunodetrong mngSS7nh:imchuynmchdchvSSP(ServiceSwitchingPoint),im chuyn tip bo hiu STP (Signalling Transfer Point) v im iu khin dch v SCP (Sevice Control Point). Su dng lin kt c nh ngha trong mng SS7 gm: Hnh 2.9: Cu hnh nt v lin kt mng SS7 Lin kt truy nhp (A-link) kt ni cc SSP ti STP, hoc SCP ti STP. Lin kt cu ni (B-link) kt ni cc STP khng cng lp. Lin kt cho (C-link) kt ni cho cc STP cng lp. Lin kt trc giao (D-link) kt ni cc SSP ti cc STP ca vng khc. Lin kt m rng (E-link) s dng kt ni mt SSP ti STP ca vng khc. Lin kt (F-link) s dng kt ni trc tip hai nhm SSP.S hiu mng (8bit)M vng (8bit)Thnh vin (8bit) Nhndngvng (3bit) Nhndngmng (8bit) NhndngSSP (3bit) (a) (b) 47 nhtuynccbntinbohiutrongmngSS7cthchintheo phng php hop-by-hop v da trn mt tp lut nh tuyn di y: Mt bn tin pht ra t SSP ti mt SSP kt ni trc tip s chn ng F-link trc. Nu F-link khng tn ti, bn tin s chn A-link l tuyn ng dn cho bn tin. Mt bn tin t mt SSP ti mt SSP khc c phc v bi mt cp STP c nh tuyn theo ng A-link ti STP ca vng sau mi c chuyn tip. Mt bn tin ti STP ca vng ch la chn A-link kt ni ti SSP ch, nu A-link khng tn ti, bn tin theo ng C-link ti STP cng cp kt ni ti SSP ch. Mt bn tin ti STP ca vng ch c th chn E-link ti SSP ch, nu E-link khng tn ti, bn tin c nh tuyn ti STP ca vng ngun theo B-link. LachntiptheolsdngB-linktivngchthhaicaSSPhocs dng C-link ti cc vng khc c kt ni ti SSP ch. Mt bntint mtSSPti mtSCPthc hin nhtuyntrnF-link nun tn ti, nu F-link khng tn ti, bn tin s c nh tuyn ti STP ngun trn ng A-link kt ni ti SCP. Da trn cc lut trn, mng bo hiu SS7 xy dng mt cu trc d phng cho php nhtuyna nggia hai nodeSS7.Mttuyntrong mngSS7l mttp lin kt tun t nh ngha con ng t SSP ngun ti SSP ch, mt tp hp tuyn gm nhiu tuyn t ngun ti ch c t nht hai tuyn: mt tuyn s cp v mt tuyn th cp, iu ny cho php cung cp ty chn lun phin ti mi node. 2.3.4 X l nh tuyn cuc gi trong node mng chuyn mch knh Nh trnh bytrn nhtuyntrong mngPSTN baogmccth tc tm mt ng i trong mng cho cuc gi gia 2 thu bao. Vi cc trng hp 2 thu bao ny cng kt ni vo mt tng i gi l cuc gi ni b hoc 2 thu bao kt ni vo2tngikhcnhau cgi lcucgilin im s lin kt to nntuyn ng cho cuc gi l khc nhau. Vi mc tiu phn tch qu trnh x l bo hiu v nh tuyn cho cuc gi trong mt node mng mt cch y nn phn ny tp trung vo qu trnh x l cuc gi lin i. Vic thit lp v gii phng ng i trong mng c bt u v kt thc thng qua bo hiu.Trong h thng chuyn mch knh cc kt ni cho cuc gi lin i c thit lp dc theo ng i n ch c nh sn qua cc bng nh tuyn. Bng nh tuyn c xy dng trn c s nhn cng. Thng thng, mt h thng chuyn mch 48 knh gm mt s bng bin dch, v d nh bng bin dch cho cc tuyn ng nh tuyn quc t, quc gia v ni ht. Cn c vo cc con s m thu bao ch gi gi ti tng i m h thng phn tch s s la chn bng bin dch nh tuyn cho ph hp. Phng php truy nhp bng bin dch trong mt s tng i chuyn mch knh in hnh thng s dng kiu con tr, vi kha l cc tin t. Cn c vo tin t v thng tin ccit snti hthngchuynmchknhmtng itrunggian hockt cui c xc nh. Tin trnh bo hiu tip theo s thc hin vic xc nh tuyn v knh truyn cho cc cuc gi.2.4KT LUN CHNGKthutchuynmchknhlkthutngdngphbinnhttrongccmng chuyn mch in thoi cng cng PSTN. Trong chng 2 trnh by vn tt vcu trckhungtn hiucaktnigiacc nodechuynmchknh.Ccnguynlv nguyntcc bncatrngchuynmchknhtheothigian,khnggianvghp kthpcngctrnhby.Ccphngphpnhtuynthngcsdng trong h thng chuyn mch knh lun gn lin vi cc th tc bo hiu kt ni cuc gi. Cc vn chi tit v bng bin dch v cc tham s c th phc v cho qu trnh nh tuyn cuc gi ph thuc vo kin trc mng chuyn mch knh. 49 Chng 3 K THUT CHUYN MCH GI 3.1.C S K THUT CHUYN MCH GI Kthutchuynmchgidatrnnguyntcchuynthngtinquamngdi dng gi tin. Gi tin l thc th truyn thng hon chnh gm hai phn: Tiu mang ccthngtin iukhinca mnghocca ngis dngvti tinl dliuthc cn chuyn qua mng. Qu trnh chuyn thng tin qua mng chuyn mch gi c th khng cn xc lp ng dnh ring v cc mng chuyn mch gi c coi l mng chia s ti nguyn, cc gi tin s c chuyn giao t cc nt mng ny ti nt mng khc trong mng chuyn mch gi theo nguyn tc lu m v chuyn tip, nn mng chuynmchgicnccoilmngchuyngiaotrongkhimngchuynmch knh c coi l mng trong sut i vi d liu ngi s dng. Trn hng tip cn tng i n gin t kha cnh dch v cung cp, cc dch v ccungcptrnmngvinthngchiathnhdchvthoivdchvphithoi, trong i din cho dch v phi thoi l dch v s liu. Mt cch trc quan, mng chuyn mch in thoi cng cng PSTN c pht trin trn c s k thut chuyn mchknhcungcpccdchvthoitruynthng.Ccmngdliunhcc mngccbLAN(LocalAreaNetwork),mngInternetlmngchuynmchgi da trn k thut chuyn mch gi thc hin chuyn ti thng tin d liu cho ngi s dng. Nh trong chng 2 trnh by, dch v thoi trong mng chuyn mch cng cng PSTNthngsdngkthutiuchPCMvchimdngbngthngcnh 64kb/s, cht lng cuc gi thoi ph thuc ch yu vo k thut iu ch v s dng knh dnh ring cho cc cuc ni. Mt khc, cht lng cc dch v d liu c thc hinquamngchuynmchgiphthucrtlnvolngbngthngcungcp. Mt s ng dng i hi bng thng rt ln v nhiu khi khng c nh, s bin ng bng thng ln theo xu hng tngbt thng c gi l hin tng bng n bng thng. V vy, c ch xc nh knh dnh ring trc trong mng chuyn mch knhkh c th p ng c tiu ch bng n bng thng ca cc dch v d liu. Mt kha cnh khc ca cht lng dch v cng lun c tnh n trong qu trnh chuynthngtinchongisdngltrcaqutrnhtruyntin.Ccdchv thoi i hi thi gian tr thp v n nh, yu cu ny hon ton c tha mn trong mng chuyn mch knh v mng chuyn mch knh s dng knh dnh ring v kt ni c hng cho cc kt ni. Trong khi , cc mng chuyn mch gi ch yu nhm 50 mc ch cung cp dch v truyn d liu c th c xy dng theo hng kt ni v s dng knh o cung cp cc dch vyu cu tr thp v n nh. Tuy nhin, mtkhiyucutrcadchvdliukhngqungtnghothmngdliu thng cxydngtheo mhnh phikt ni nhmgimthiu cc quytrnh iu khin v lu lng iu khin trn mng. 3.1.1 M hnh kt ni h thng m OSI Trong khong gia nhng nm 70, khi cng nghip my tnh bt u pht trin rt mnhkotheonhucuktnithngtincaccmytnhtngtbintrncc h tng mng khc nhau. iu ny thc y mt qu trnh chun ha cc kt ni gia cchtngmngkhcnhauvkintrc.Hthng mrainhmtoracctiu chun ho cho tt c cc u ni gia cc kin trc mng, c gi l m hnh kt ni hthng m OSI(OpenSystemInterconnection)dotchctiuchun quctISO a ra. Hnh 3.1: M hnh phn lp OSI RM Mc tiu ca m hnh kt ni h thng m OSIl m bo rng bt k mt x lngdngnoukhngnhhngtitrngthinguynthuca dchv,hoc cc x l ng dng c th giao tip trc tip vi cc h thngkhc trn cng lp nu cchthng cngc htr theotiuchunca m hnhOSI.M hnhOSIcung cpmtkhunglmvictiuchunchocchthngktnivinhaudatrnm hnh phn lp. M hnh gm c 7 lp chc nng chnh c th phn loi thnh 2 vng chnh.Lpthpcungcpccdchv ucui- ti-ucuip ng phngtin truyn s liu,cc chc nng hng v pha mng t lp 3 ti lp 1. Lpcaocungcpccdchvngdngpngtruynthngtin,ccchc nng hng v ngi s dng t lp 4 ti lp 7. M hnh OSI c th chia thnh ba mi trng iu hnh: 51 Mi trng mng: lin quan ti cc giao thc, trao i cc bn tin v cc tiu chun lin quan ti cc kiu mng truyn thng s liu khc nhau. MitrngOSI:Chophpthmvoccgiaothchngngdngvcctiu chun cho php cc h thng kt cui trao i thng tin ti h thng khc theo hng m. Mitrnghthngthc:XydngtrnmhnhOSIvlinquantictnh dch v v phn mm ca ngi sn xut, n c pht trin thc hin nhim v x l thng tin phn tn trong thc t.Nhng mi trng ny cung cp nhng c tnh sau: Giao tip gia cc lp. Chcnngcacclp,giaothcnhnghatphpcanhngquytcv nhng quy c s dng bi lp giao tip vi mt lp tng ng tng t trong h thng t xa khc. Mi lp cung cp mt tp nh ngha ca nhng dch v ti lp k cn. Mt thc th chuyn thng tin phi i qua tng lp. Cc chc nng chi tit ca cc lp c nh ngha trong tiu chun ISO 7498 v chun X.200 ca ITU-T. 3.1.2Nguyn tc c bn ca chuyn mch gi ccccgitinchuynmch,mt qutrnh phnmnhvotogit d liu ngi s dng c thc hin ti cc lp cao pha ngi s dng. Bn t i n nguy n t hu ( di L bi t )Thng ti n CRCTi u Trng t hng t i n c di (M bi t )Titi n (N bi t)Ti u CRCBtbtu k hung Bt kt t hc khung Hnh 3.2: ng gi d liu theo m hnh OSIQu trnh phn mnh v to gi theo cc lp ca m hnh OSI ch ra trn hnh 3.2 gm m hnh ng gi d liu v khun dng d liu ng dng. T cc lung d liu ngisdng,thngtincctmnhtheoccctnhcahthngtruyndn hocchuynmch, mttrongccthamschnhyucs dng xc nhkch 52 thc gi l tham s tc truyn dn ti a MTU (Maximum Transfer Unit) ca cc linkt.nvdliungisdngcchuynquatnglpvmangtiu thng tin ca tng lp ti khi phn on to gi ti lp 3 ca m hnh OSI. K thut chuyn mch gi cho php kt ni thng tin t u cui ti u cui qua qutrnhchiastinguyn,sdngcctpthtcvcclinktctckhc nhau truyn cc gi tin v c th chuyn gi trn nhiu ng dn khc nhau. C haikiuchuynmchgicbn:chuynmchdatagramvchuynmchknho VC (Virtual Circuit). Trn hnh 3.3 m t s lc 2 kiu chuyn mch ny. Hnh 3.3: Chuyn mch Datagram v chuyn mch knh o i,Chuyn mch Datagram Chuynmchdatagramcungcpchoccdchvkhngyucuthigianthc, vicchuynccgitin phthucvoccgiaothclpcao hocnglinktd liu.Chuynmchkiu datagramkhngcngiaionthitlpktnivrtthch hp ividngdliuclulngthpvthigiantntingn.Chuynmch datagram l chuyn mch kiu n lc ti a (best effort), cc thng tin v tr s khng c m bo cng nh cc hin tng lp gi, mt gi cng d dng xy ra i vi kiu chuyn mch ny. Cc datagram phi cha ton b cc thng tin v a ch ch v cc yu cu ca lp dch v pha trn c th hin trong tiu , v vy tiu ca datagram l kh ln. V u im, chuyn mch datagram cho php la chn cc con ng ti ch nhanh nht p ng cc thay i nhanh ca mng. ii, Chuyn mch knh o Chuyn mch knh o VC yu cu giai on thit lp tuyn gia thit b gi v thit bnhnthngtin,mtknhochnhthnhgiaccthitbtrongngdn chuyn mch; knh o l knh ch c xc nh khi c d liu truyn qua v khng phthucvologicthigian.Chuynmchknhoyucumttuynhinngay trongqutrnhnhtuynvknhoc nhndngthngquatrngnhndng knh o VCI (Virtual Channel Identifier) nm ti tiu gi tin. Trong qu trnh thit lpknho,nhndngknhoVCIctorabiccnodechuynmchch 53 nh cc ngun ti nguyn ca gi tin s chuyn qua (v d: b m, dung lng lin kt).Mt khi knh o c thit lp dc theo tuyn ng t ngun ti ch qua cc lin kt v cc node th knh c s dng truyn cc gi tin. Cc gi c VCI trong tiu c th c s dng nh con tr truy nhp ti cc thng tin lu tr ti cc nt chuyn mch. Cc trng nhn dng knh o cn phi duy nht phn bit cc thng tin ngi s dng v ti s dng, nu s dng cc VCI cho ton b mng th s lng VCI rt ln v khng ngng tng ln theo kch c mng. V vy, ngi ta s dng cc nhn dng knh o theo cc vng cc b, thm ch l trn tng lin kt. Vi cch ny, khi mt VC khi to mi mt nt chuyn mch dc tuyn ng s phi xc lp cc nhn dngknhotrncclinkt uvo vlinkt uraca ntchuynmch . Cc nt phi tho thun vi nhau v nhn dng knh o duy nht trn lin kt gia hai nt cho mt knh o.Nhn dng knh o trn cc lin kt u vo v u ra khng cn thit phi ging nhau,mt s knh o c cng mt c tnh (v d, cng a ch ngun v a ch ch) c th ghp thnh lung o v c th hin qua trng chc nng VPI (Virtual Path Identifier),Thit bchuynmchnhndngthngtinlungovthc hinchuyn mch ton b lung o.3.2KIN TRC CA B NH TUYNTrckhitmhiuccvnlinquanti kintrctrng chuynmchgi,ta xemxtslccccutrcc bnca hthngchuynmchgi hinnay,cch thng chuyn mch gi trong mng internet c cn c gi l cc b nh tuyn. Mc nystrnh byvccthnh phnchcnngv hot ngc bnca b nh tuynquaqutrnhchuyntipgitinvvictmkimthngtintrongbngnh tuyn. 3.2.1Cc chc nng c bn ca b nh tuynHai chc nng, nhim v c bn ca mt b nh tuyn c nhn nhn di gc kthutchuynmchlchcnngnhtuynvchuyntipgitinquabnh tuyn.Trn hnh 3.4th hin mtkintrcchcnng inhnhca b nhtuyncng nhcctuynktnigiacckhichcnng.Mtsnhimvchnhcmt nh sau: Da trn cc thng tin trao i vi cc b nh tuyn ln cn, tin trnh nh tuyn xy dng cu hnh mng v tnh ton ng dn tt nht thng qua c s d liu trongbngnhtuyn.Cuhnhmngphnnhccmngchcthtmkimv nhndngquaccachtintIPvcthhintrongbngnhtuyn.Bng 54 nh tuyn nh x thng tin d liu 1:1 ti mt bng c s d liu mang tnh cc b sdngchuyntipgitinlbngchuyntip. Tintrnhxlchuyntipltin trnh chuyn cc gi tin t cc giao din u vo ti cc giao din u ra thch hp da trn cc thng tin trong bng chuyn tip. Hnh 3.4: Tin trnh x l nh tuyn v chuyn tip trong b nh tuyn 3.2.2 Tin trnh chuyn tip gi tin (i) Cc chc nng chuyn tip c bn chuyn tip mt gi tin IP t mt giao din u vo ti mt giao din u ra, mt b nh tuyn cn phi thc hin cc chc nng c bn sau: XcnhntiuIP:Ttcccgitinti bnhtuynucxcnhn thngtinthng quatiu.Ccgitinctiu khng hpls bloi b ngay lp tc. Cc thng tin cn xc minh nh: phin bn IP, di tiu v tng di gi. iukhinthigiansnggitin:Ccbnhtuynthchingimgitr trng TTL (time to live) trong tiu gi tin IP trnh hin tng lp vng. Gi tr ln nht ca TTL l 255 v s gim i 1 khi mi ln qua b nh tuyn, trng TTL c gi tr = 0 th gi tin s b loi b. Tnhlitngdi:SaukhitrngTTLthayi,tngditiuc cp nht li. Thay v tnh ton li ton b di tiu , b nh tuyn ch tnh ton lchtngca nvTTLlun lungim 1sau mi bc qua b nh tuyn. Tm kim tuyn: a ch ch ca gi tin c s dng tm kim trong bng chuyn tip nhm xc nh cng u ra. Kt qu ca qu trnh tm kim ch ra mt cng u ra (unicast) hoc mt tp cng u ra (multicast). 55 Phnon:Quytrnhphnoncthchinkhinvtruynlnnht MTU ca lin kt cng u ra nh hn MTU ca lin kt cng u vo.X l trng ty chn trong gi tin IP: Trng ty chn ca gi tin IP ch ra cc x l c bit i vi gi tin ti b nh tuyn. (ii) Cc chc nng chuyn tip phc tp Bn cnh nhng chc nng chuyn tip c bn, cc chc nng chuyn tip phc tp cs dng htr mts ctnh c bitca mitrngngdng nh:Bo mt,ccyucululngkhc nhaut ngis dngvcc mcchtlng dch v. Cc vn trn c chuyn thnh cc x l ph tr trong qu trnh chuyn tip gitingmnhndngccyucu,xcnhtinguynvphnbitmcdchv thng qua mt s c ch sau: Phnloigi:phnbitccgitin,bnhtuynkhngchxcnh trng a ch IP ch m cn xc nh mt s trng chc nng khc nh: a ch ngun, a ch ch, cng ngun v cng ch. Tin trnh phn bit gi tin v ng dng cc hot ng cn thit vi gi tin c gi l qu trnh phn loi gi tin. Bin dch gi: Trong mt s kch bn kt ni mng, b nh tuyn ng vai tr nh mt cng kt ni gia mng ring v mng cng cng, trn h tr chc nng bin dch a ch mng NAT (Network Address Translation). Chc nng ny yu cu b nh tuyn duy tr mt danh sch cc host kt ni v a ch cc b chuyn i a ch. Sp xp th t u tin lu lng: B nh tuyn c th c yu cu m bo mt s mc cht lng dch v. V vy, b nh tuyn cn p dng cc mc u tin khc nhau cho cc lung lu lng ph hp vi cc yu cu cung cp cht lng dch v. Qu trnh x l chuyn gi c m t mt cch khi qut qua cc giai on sau : 1. Khi mt gi n Card ng truyn u vo, c ch chuyn tip gi thc hin cc th tc kim tra li c bn khng nh gi v tiu l khng c li. Tnh ton lch (offset) trong bng