rong thi gian va qua - 8 tun thc tp Trung tm vin thng IP ca Cng ty SPT - Cng ty C Phn Dch v Bu chnh Vin thng Si Gn, mt qung thi gian khng dimcngkhngqungn,emthcshiubitnhiuthmvcngtyvtica mnh. Em nhn c s gip tn tnh ca thy Bi Cng Trng v cc anh ch trong phng K thut nghip v, mi ngi to iu kin rt tt em c th hon thnh tt k thc tp ca mnh. cbit em rt cm n Thy Bi Cng Trng quan tm vgip em rt nhiu trong qu trnh tm v x l ti liu. Em xin thnh tht cm n! EmkhngbitnighnbnglngcmnchnthnhsuscnTS.TrnCng Hng.TrongsutthigianquaThyhngdnrttntnhvytrchnhimtocho bn em cm gic rt thn thin v gn gi mt mi trng rt tt lm vic. Thy nhn xt bi lm tng t ca chng em v cho nhng li khuyn rt hu ch chng em rt kinh nghim v c c kt qu tt nht! Em xin chn thnh cm n Thy! Sut bn nm hc va qua, cc thy c trong Hc vin dy d v ch bo tn tnh chochngem,tochochngemmtcinnvngchccthttinvngbckhira trng. Vi s quan tm ca Hc vin, chng em thcs c mt mi trng trong sng, lnh mnh v y hiu qu gip chng em cng ngy cng trng thnh hn. Em xin cm n rt nhiu!Em cng xin cm n cc bn lp D02THA1, cc bn gip em rt nhiu, hc hi v trao i c mt ci nhn ton din hn v cc vn cn quan tm. Mi li ni ch thay bng li cm n chn thnh v su sc t tri tim mnh! Sinh vin : Nguyn Th Ngc H LI NHN XT TI NI THC TP . . . . . . . . . . . . . . . . . . . . . . . . . . TP. HCM, ngy .. thng .. nm 2006 Ngi hng dn k tn NHN XT CA GIO VIN HNG DN .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. TP. HCM, ngy .. thng .. nm 2006 Gio vin hng dn k tn Thi gian thc tp : t 03/07/2006 n 25/08/2006+Ngy 03/07 : Nhn nhim v thc tp ti Trung tm Vin thng IP ca SPT +Tun 1 (T 03/07 n 09/07) : Tm hiu v cng ty SPT +Tun 2 v 3 (T 10/07 n 22/07) : Nghin cu VoIP v cc m hnh c bn +Tun 4 v 5 (T 23/07 n 06/08) : Nghin cu cc phng thc truyn v m hnh x l cuc gi +Tun 6 v 7 (T 07/08 n 19/08) : Nghin cuccgiao thc truyn vhot ng ca chng trn IP. +Tun 8 (T 20/08 n 25/08) : Tng kt v vit bi bo co thc tp +Ngy 21/08 : Np bo co cho thy hng dn c duyt +T ngy 22 /08 n ngy 25/08 : Chnh sa bo co ln cui +Ngy 25/08 : Kt thc thc tp v bo co +Ngy 26/08 n 28/08 : In n v np cun bo co thc tp cho Khoa CNTT rong s hi nhp v pht trin ca thi i, cng ngh l mt trong nhng sn phm khngththiu,gpphnquantrngtrongisngcamimtchngta.Vcngngh VoIPcngrainhth!VoIPvangckhaithctrittimnngcth phc v tt nht nhu cu cho mi ngi. Trong nhng nm va qua, do bit c u nhc im ca cng ngh VoIP m cc nh cung cp dch v khai thc v ng dng n to nn bc t ph trong vic h gi cc vin thng, em li ngun li ln cho khch hng. H tr giao tip thoi s dng giao thc Internet (IP), hay VoIP tr nn rt hp dn v n cungcpmtgiccthp,nghng.Thct,gicccucgitrnIPangtrthnh mt trong nhng yu t bn l dn ti s hp nht ca cng ngh truyn thng thoi, video v d liu. S kh thi trong vic truyn thoi v cc tn hiu cuc gi trn mng Internet c chngthcnhngvicmangliccsnphmchtlngcao,thitlpccdchvcng cng, cng nh thuyt phc ngi s dng dng chng th mi ch bt u. VoIP c th c nh ngha l kh nng gi in thoi v gi FAX trn mng d liu nn IP vi mt cht lng dch v (QoS) ph hp v mt gi cc r hn. Cc nh sn xut thit b nhn thy VoIP mt c hi mi i mi v cnh tranh. S thch thc vi h l bin kh nng ny tr thnh hin thc bng cch pht trin cc thit b h tr VoIP. Vi cc ISP, kh nng gii thiu dch v mi ng thi tng cng hiu sut s dng ng truyn lrt hp dn. Vi ngi s dng, h s c hng li t cc ng dng kt hp thoi/d liu cng nh cc li ch kinh t. Ni dung bn bo co thc tp l Nghin cu m hnh x l cucgi v ccgiao thc truyn thoi trn mng. y l mt phn trong ti tt nghip ca em Vit chng trnh m hnh x l cuc gi PC to Phone trn giao thc H.323. Trong bn bo co ny em s i su tm hiu hn v m hnh x l cuc gi PC to Phone v giao thc truyn thoi H.323 lm tin cho vic hon thnh lun vn tt nghip sau ny. Bn bo co thc tp m bo ba ni dung chnh sau: 1.t vn +Gii thiu ti +u nhc im ca cng ngh VoIP +Hng pht trin VoIP 2.Cc ni dung thc hin +Nghin cu k M hnh x l cuc gi +Cc giao thc truyn thoi trn mng v hot ng ca chng 3.Kt lun Trong thi gian hon thnh bo co khng trnhkhi nhng sai st, em mong Qu thy c v cc bn thng cm v cho em nhng li khuyn b ch. Sinh vin : Nguyn Th Ngc H LI GII THIUTM HIU V CNG TY SPT PHN A - T VN Chng 1: TNG QUAN V IN THOI INTERNET .............................................. 1 1.1.Gii thiu chung ....................................................................................................... 1 1.2. Mt s c im ni bt ca VoIP ........................................................................... 2 1.2.1.ng dng VoIP............2 1.2.2.u nhc im ca VoIP... 3 1.2.2.1.u im:...................................................................................................... 3 1.2.2.2.Nhc im: ............................................................................................. 5 1.2Cc nhn t nh hng n cht lng thoi ................................................... 5 1.3S pht trin ca dch v VoIP ........................................................................... 6 1.4.1Kh nng trin khai6 1.4.2Yu cu pht trin6 1.4.3Nhng kh khn khi trin khai dch v6 1.4.4Xu hng pht trin 7 PHN B NGHIN CU V M HNH X L CUC GI Chng 2: QUY TRNH THC HIN CUCGI IN THOI IP ........................ 8 2.1.Mt s giao thc h tr mng in thoi IP .......................................................... 8 2.1.1.Kin trc TCP/IP8 2.1.2.Giao thc Internet (IP)8 2.1.3.Giao thc TCP10 2.1.3.1.TCP Header ............................................................................................ 10 2.1.3.2.Kt ni TCP-TCP connection ................................................................. 12 2.1.4.UDP User Datagram Protocol12 2.1.4.1.UDP datagram ........................................................................................ 12 2.1.4.2.Thoi qua UDP Voice over UDP, not TCP ....................................... 14 2.1.5.Giao thc chuyn vn thi gian thc Real Time Transport Protocol14 2.1.5.1.nh dng vng ti ca RTP-RTP Payload Formats ........................... 14 2.1.5.2.RTP header ............................................................................................... 14 2.1.6.Giao thc RTCP RTP Control Protocol16 2.2.Qu trnh x l trong in thoi thngthng .................................................. 16 2.3.Qu trnh truyn dn VoIP ................................................................................... 17 2.3.1.Cc bc thc hin cuc gi IP.18 2.3.2.Mt s chc nng cn thc hin trn quy trnh x l cuc gi IP..19 Chng 3: M HNH C BN X L CUC GI QUA INTERNET .................... 20 3.1.M hnh c bn ....................................................................................................... 20 3.2Hot ng ca mt s m hnh cn bn ................................................................ 25 3.2.1 M hnh Gateway bo hiu...25 3.2.2M hnh Phone to Phone26 3.2.3M hnh PC to Phone.27 3.2.4M hnh PC to PC...28 3.2.5Cuc gi t in thoi n PC...28 3.3. Kt lun .................................................................................................................... 28 PHN C CC GIAO THC TRUYN THOI TRN MNG Chng4:CCGIAOTHCTRUYNTHOITRNMNGVHOTNG CA CHNG ..................................................................................................................... 29 4.1. Tng quan gii thiu cc giao thc truyn ........................................................... 29 4.2.1. H.323..31 4.2.1.1. Tiu chun H.323 ...................................................................................... 31 4.2.1.2.Cc giao thc trong H.323 ..................................................................... 32 4.2.1.2.1.Giao thc H.225 RAS (Registration/Admission/Status): ............. 33 4.2.1.2.2.Giao thc bo hiu cuc gi H.225 ................................................ 34 4.2.1.2.3.Giao thc iu khin cuc gi H.245 ............................................. 35 4.2.1.3.Cc th tc kt ni ................................................................................... 35 4.2.1.4.Hot ng ca H323: ............................................................................. 39 4.2.1.4.1. Cc knh thng tin trong H.323 ........................................................ 39 4.2.1.4.2.Trnh t thit lp mt cuc gi trong H.323 ................................. 43 4.2.1.5.Mt s hot ng in hnh ca H.323 ................................................. 44 4.2.1.5.2.Hot ng pht hin gatekeeper: .................................................... 45 4.2.1.5.3.Hot ng ng k vi Gatekeeper: ................................................ 45 4.2.1.5.4.Hot ng thit lp knh truyn thng: .......................................... 46 4.2.1.5.5.Hot ng thay i bng thng: ...................................................... 47 4.2.1.5.6.Ngt kt ni gia hai u cui H.323 lin vng: ........................... 48 4.2.1.6. Bo hiu thit lp cuc gi VoIP .............................................................. 48 4.2.2.MGCP...52 4.2.2.1.Kt ni MGCP .......................................................................................... 53 4.2.2.2. Cc lnh ca MGCP.................................................................................. 58 4.2.2.3. Cc thng s ca MGCP........................................................................... 59 4.2.2.4.Cc s kin, bo hiu, cc gi MGCP .................................................... 60 4.2.3. Giao thc khi to phin SIP (Session Initiation Protocol)..61 4.2.3.1. Cc thnh phn chnh trong SIP ............................................................. 62 4.2.3.2.Hot ng chnh ca SIP ......................................................................... 62 4.2.3.2.1.Hot ng ca Proxy server ............................................................. 62 4.2.3.2.2. Hot ng ca Redirect server.......................................................... 63 4.2.3.3. Thit lp mt cuc hi m bng SIP ..................................................... 65 4.2.4.MEGACO.68 4.2.4.1. Cu trc ca Megaco ................................................................................ 69 4.2.4.1.1. Cu trc ca Gateway trong Megaco ............................................... 70 4.2.4.1.2. Context ................................................................................................ 71 4.2.4.1.3. To, xo v sa i Context .............................................................. 71 4.2.4.1.4. Termination ........................................................................................ 71 4.2.4.2. Mt s lnh Megaco .................................................................................. 72 4.2.4.3.Hot ng ca Megaco............................................................................. 72 4.2.5.Bo hiu trong mng chuyn mch cng cng (PSTN) - SS7.75 4.2.5.1.B giao thc SS7 ..................................................................................... 76 4.2.5.2.Cc lin kt bo hiu .............................................................................. 76 4.2.5.3.Cc im bo hiu .................................................................................. 76 4.2.5.4.Cc loi lin kt bo hiu SS7: .............................................................. 77 4.2.5.5.SS7 over IP .............................................................................................. 78 4.2.5.5.1.Gii thiu.......................................................................................... 78 4.2.5.5.2.Tin trnh thit lp cuc gi SS7-H323-SS7 .................................. 78 PHN D - KT LUN Chng 5 : KT LUN ..................................................................................................... 80 e^ PhlcA-CCKTHUTCBNXYDNGNGDNGTRUYNTHOI TRN MNG GI PhlcB-YUCUCHTLNGDCHVTRONGCCNGDNG TRUYN THOI TRN MNG GI Cc thut ng vit tt Ti liu tham kho Hnh 1.1:M hnh s dng dch v IP .................................................................................. 2 Hnh 2.1 : So snh m hnh kin trc TCP/IP v m hnh tham chiu OSI. ...................... 8 Hnh 2.2 : Khun dng ca IP datagram ............................................................................... 9 Hnh 2.3 : S tng ng gia Datagram v Frame .............................................................. 9 Hnh 2.4 : Khun dng ca TCP datagram ......................................................................... 10 Hnh 2.5 : Kt ni TCP .......................................................................................................... 12 Hnh 2.6 : Khun dng ca UDP datagram ......................................................................... 13 Hnh 2.7 : Khun dng ca RTP .......................................................................................... 15 Hnh 2.8 :Qu trnh x l trong in thoi thng thng ................................................ 17 Hnh 2.9 : in thoi IP ....................................................................................................... 18 Hnh 2.10 : C ch truyn thoi ............................................................................................ 19 Hnh 3.1 : M hnh thit b H.323 ....................................................................................... 20 Hnh 3.2: Min H.323 ............................................................................................................. 21 Hnh 3.3 : Thit b u cui H.323 ........................................................................................ 22 Hnh 3.4: M hnh tng qut VoIP ....................................................................................... 25 Hnh 3.5:Gateway bo hiu thc hin nh x m hiu sang gi ...................................... 26 Hnh 3.6: M hnh Phone to Phone ...................................................................................... 27 Hnh 3.7: M hnh PC to Phone ............................................................................................ 27 Hnh 3.8 : M hnh PC to PC ................................................................................................ 28 Hnh 4.1: Chng giao thc ca H.323, MGCP v SIP ........................................................ 29 Hnh 4.2: Chng giao thc H.323 ......................................................................................... 32 Hnh 4.3 : Kin trc phn tng giao thc ............................................................................ 33 Hnh 4.4 : Thit lp cuc gi ................................................................................................. 36 Hnh 4.5 : iu khin lung bo hiu ................................................................................... 37 Hnh 4.6 : Lung truyn thng v iu khin truyn thng .............................................. 38 Hnh 4.7 : Kt thc cuc gi .................................................................................................. 38 Hnh 4.8 : Qu trnh thit lp cuc gi H.323 ...................................................................... 42 Hnh 4.9: S thit lp cuc gi Gatekeeper H.323 ni vng ......................................... 43 Hnh 4.10: S thit lp cuc gi Gatekeeper H.323 lin vng ...................................... 44 Hnh 4.11 :Cc giai on chnh ca H.323 ........................................................................... 44 Hnh 4.12 :Hot ng pht hin Gatekeeper ....................................................................... 45 Hnh 4.13 :Hot ng ng k vi Gatekeeper ................................................................... 46 Hnh 4.14: Hat ng thit lp knh truyn thng ............................................................. 46 Hnh 4.15: Hot ng thay i bng thng .......................................................................... 47 Hnh 4.16: Ngt kt ni gia hai u cui H.323 lin vng ................................................ 48 Hnh 4.17: Thit lp cuc gi ................................................................................................ 48 Hnh 4.18:ng k vi Gatekeeper .................................................................................... 49 Hnh 4.19: Thit lp knh iu khin cho cuc gi c bn khng c Gatekeeper ........... 49 Hnh 4.20: Yu cu thay i rng bng tn Thay i thng s truyn ..................... 50 Hnh 4.21: Yu cu thay i rng bng tn thay i thng s nhn ......................... 51 Hnh 4.22: Kt thc cuc gi ................................................................................................. 52 Hnh 4.23: M hnh MGCP ................................................................................................... 53 Hnh 4.24: Lung giao thc MGCP (a) ................................................................................ 55 Hnh 4.25: Lung giao thc MGCP (b) ................................................................................ 57 Hnh 4.26: Cc thnh phn SIP, s c ni r trong phn k tip. ................................. 61 Hnh 4.27: Hot ng ca Proxy Server .............................................................................. 63 Hnh 4.28: Hot ng ca Redirect server .......................................................................... 64 Hnh 4.29: iu khin cuc gi SIP ...................................................................................... 66 Hnh 4.30: M hnh MEGACO ............................................................................................. 69 Hnh 4.31: Cu trc Megaco ................................................................................................. 70 Hnh 4.32: Cu trc Gateway trong Megaco ....................................................................... 70 Hnh 4.33: Lung giao thc Megaco (a) ............................................................................... 73 Hnh 4.34: Lung giao thc Megaco (b) ............................................................................... 74 Hnh 4.35: B giao thc SS7 .................................................................................................. 76 Hnh 4.36: Cc im bo hiu ............................................................................................... 77 Hnh 4.37: Cc loi lin kt bo hiu SS7 ............................................................................ 77 Hnh 4.38: Cuc gi SS7-H.323-SS7 ..................................................................................... 79 Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp1 Chng 1: TNG QUAN V IN THOI INTERNET 1.1 . Gii thiu chung Cm t "Internet telephony" thng gi ln hnh nh nhng tay ham m my tnh cm bo mch m thanh vo PC ca h c th tr chuyn "min ph" vi cc ng minh trn ton th gii vo nhnggi rnh ri. Haynh nhngk v li tranh th cccucgi in thoi quctrtincthchinmmnquaInternet.Hyloibnhngtngrakhi u v chng c xa ri! in thoi Internet ang ni ln nh mt cng c truyn ti ting ni v fax trn th gii vi cc ph r. V khng ch c th, cc hng cn nhn thy nhiu li ch khc t nhng ng dng kt hp ting ni v d liu truyn qua cc mng dng giao thc Internet (IP- Internet Protocol), cho php h h tr cc trung tm in m dng Web, v t chc hi m trao i c ting ni ln d liu trn bng ng (live whiteboard).Nhiu nh sn xut, t Lucent Technologies Inc., Micom Communications Corp., cho n ArrayTelecomInc.anghngncccnginthoiInternetvphnmmchomi trngtruynthngvcngtc,ainthoivfaxngnviInternet.Mtshng truyn thng v cc nh cung cp dch v Internet (ISP - Internet Service Provider) nh ang tn dng nhng c tnh ca cc sn phm ny cung ng cc dch v fax v in m qua Internet.H tr giao tip thoi s dng giao thc Internet (IP), hay VoIP tr nn rt hp dn v n cungcpmtgiccthp,nghng.Thct,gicccucgitrnIPangtrthnh mt trong nhng yu t bn l dn ti s hp nht ca cng ngh truyn thng thoi, video v d liu. S kh thi trong vic truyn thoi v cc tn hiu cuc gi trn mng Internet c chngthcnhngvicmangliccsnphmchtlngcao,thitlpccdchvcng cng, cng nh thuyt phc ngi s dng dng chng th mi ch bt u. VoIP c th c nh ngha l kh nng gi in thoi v gi FAX trn mng d liu nn IP vi mt cht lng dch v (QoS) ph hp v mt gi cc r hn. Cc nh sn xut thit b nhn thy VoIP mt c hi mi i mi v cnh tranh. S thch thc vi h l bin kh nng ny tr thnh hin thc bng cch pht trin cc thit b h tr VoIP. Vi cc ISP, kh nng gii thiu dch v mi ng thi tng cng hiu sut s dng ng truyn l rt hp dn. Vi ngi s dng, h s c hng li t cc ng dng kt hp thoi/d liu cng nh cc li ch kinh t. Sau y l mt m hnh s dng rng ri dch v VoIP chng ta c mt ci nhn tng quan hn v loi hnh dch v ny. Qua y cng c th a ra nhng nh gi v u nhc im ca VoIP v li ch khi s dng. Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp2 Hnh 1.1:M hnh s dng dch v IP 1.2 . Mt s c im ni bt ca VoIP 1.2.1. ng dng VoIP VoIP c th c p dng cho gn nh moi yu cu ca giao tip thoi, t mt cuc m thoinginchonmtcuchinghnhiungisdngphctp.Chtlngm thanh c truyn cng c th bin i ty theo ng dng. Gateway S lin kt ca mng Internet vi PSTN c th c hon thnh nh gateway, hoc kh nng ny c tch hp vo mt PBX hoc c cung cp nh mt thit b c lp. in thoi truy cp Internet in thoi thng thng (c nh hay di ng) c th c b sung phc v nh mt thit b truy cp Internet trong khi vn cung cp nhng tnh nng thoi thng thng. Trung k vn phng trn mng Intranet S thay th cc ng trung k gia cc PBX ca cc cng ty s dng lin kt Intranet s gip tng cng quy m v hp nht cc phng tin mng. Truy cp t xa (t mt chi nhnh hay nh ring) Mt vn phng nh t xa c th truy cp cc dch v thoi, d liu v fax ca cng ty s dng mng Intranet ca cng ty . iu ny hu ch cho cc nhn vin lm vic ti nh c th x l cng vic c quan vo ban m, ngy ngh hoc i cng tc ni xa. Gi in t mt my tnh qua mng Internet Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp3 ChcncmtPCvmicrophonenimngInternet.iunyrtthunlichovic gi v nhn in thoi t my tnh xch tay. Truy cp cc trung tm tr li in thoi Truy cp ti cc trung tm phc v khch hng qua Internet s thc y mnh m ng dng thng mi in t. Dch v ny s cho php mt khch hng c cu hi v mt sn phmcchohngquamngInternetcccnhnvincngtyhngdntrc tuyn. Truyn fax thi gian thc thao tc trn mng chuyn mchgi, mt n vgiao din fax phichuyn i d liu thnh dng gi, x l chuyn i tn hiu v iu khin giao thc (cc chun T.30 v T.4) v m bo hon thnh vic chuyn cc d liu qut theo ng th t. Vi ng dng ny, vn mtgi v tr u cui tr nn nghim trnghn trong ngdng thoi nn cn c kim sot cht ch. Thoi thng minh Hthnginthoingycngtrnnhuhiu:r,phbin,dsdng,cng. Nhng n hon ton ng ngn. N ch c mt s phm iu khin. Trong nhng nm gn y, ngi ta c gng to ra thoi thng minh, u tin l cc thoi bn, sau l n cc server. Nhng mi c gng u tht bi do s tn ti ca cc h thng c sn. Internet s thay i iu ny. K t khi Internet ph khp ton cu, n c s dng tngthmtnhthngminhchomnginthoitoncu.Giamngmytnhv mng in thoi tn ti mt mi lin h. Internet cung cp cch gim st v iu khin cc cuc thoi mt cch tin li hn. Chng ta c th thy c kh nng kim sot v iu khin cc cuc thoi thng qua mng Internet. Dch v in thoi Web WorldWideWeblmcuccchmngtrongcchgiaodchvikhchhngca cc doanh nghip. inthoi Web hay bm s (click to dial) cho phpcc nh doanh nghip c th a thm cc phm bm ln trang web kt ni ti h thng in thoi ca h.Dchvbmslcchdnhtvantonnhtathmccknhtrctipt trang Web ca bn vo h thng in thoi. Dch v fax qua IP NubnginhiufaxtPC,cbitlgirancngoithvicsdngdchv Internet faxing s gip bn tit kim c tin v c knh thoi. Phn ln cc ng dng VoIP s l cc hot ng thi gian thc. Tuy nhin mt s dch v thoi s c lu v truyn i bng cch s dng VoIP. Chng hn cc bn tin thoi c th c chun b t mt my in thoi v s c chuyn n mt hp th thoi -> d liu tch hp s dng dch v qua Internet hay Intranet. Phn ln cc ng dng VoIP s l cc hot ng thi gian thc. Tuy nhin, cc dch v thoiluritruyncngcthihnhbngcchsdngVoIP.Chnghn,ccthng ipthoicthcchunbtmtmyinthoivcchuyntimthpth thoi/d liu tch hp dng dch v Internet hay Intranet. 1.2.2.u nhc im ca VoIP 1.2.2.1.u im: Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp4 Gim cc ph dch v in thoi ng di: do s dng cc tiu chun nn thoi t tc 64 Kbit/s nn cc ph ca VoIP bao gi cng r hn rt nhiu so vi cc ph ca cuc gi qua mng in thoi PSTN. MtgiccchungcththchincvimngInternetvdotitkim ng k cho dch v thoi v FAX. Ngi ta c tnh c khon 70% cc cuc gi n ChulgiFAX,phnlntrongsc thcthaybiVoIP.Schias chi ph thit b v thao tc gia nhng ngi s dng thoi v d liu cng tng cng hiu qu ca mng bi l s d tha bng tn trn mng ca ngi ny c th c s dng bi mt ngi khc, do mang li hiu qu cao hn. Nhiu cuc gi hn vi bng thng nh hn v s dng bng thng hiu qu hn: kthutchuynmchknhtruynthngcaPSTNyucumtmchgiachuyn mch ca cng ty in thoi v thit b khch hng c m v n chim trong sut thi gian cuc gi, bt chp lng thng tin c c truyn i hay khng (ngi gi vngibgiukhngnichuyn),dnnhaophdithngmtcchvch. Trongkhi,VoIPvikthutmhann,tritkhonglng(thngkckhong 50%thigianimlnggiacccucithoi),gihavsdngkthutghp knh phn chia theo thi gian thng k STDM (tc l s dng di thng khi cn n), tt c ni dung nh thoi, vn bn, video, cc chng trnh my tnh hoc dng thng tin khc, truyn qua mng di dng gi c nh trc tip ti ch bi cc l trnh khc nhau, chia s ti nguyn mt cch hiu qu. C s h tng kt hp ny c th h tr vic ti u ha bng tn ng thng nht. V conngilnhntquantrngnhngcngdsailmnhttrongmtmngvin thng, mi c hi hp nht cc thao tc, loi b cc im sai st, v thng nht cc h thng thanh ton s rt c ch. Trong cc t chc kinh doanh, s qun l trn c s SNMP c th ccung cpcho c dch v thoi v d liu s dng VoIP. Vic s dng thng nht giao thc IP cho tt c ng dng ha hn gim bt phc tp v tng cng tnh mm do. Cc phng tin lin quan nhiu dch v danh b v dch v an ninh c th c chia s d dng hn. H tr tt hn cc dch v b sung: mt thun li khc ca VoIP so vi PSTN l n chophptoralpdchvmibngcchkthpctnhtruynthngthoithi gian thc v s x l d liu nh l cc trang web tch hp in thoi, truyn thng a phng tin, dy hc t xa, ... Ngoi cc dch v thng thng ta cn thm cc dch v gia tng nh ICW (Internet Call Waiting) cho php khch hng nhn c bn tin thng bo trn mn hnh my PC, lc khch hng c th x l bng cch cho nhn vo hp th thoi, tr li bng phn mm trn PC hay tr li bng thoi, hay dch v V2L (Virtual Second Line) cho php user nhn cuc gi thng qua nh cung cp dch v Internet (ISP) ca h. S kt hp ny cng vi hiu qu ca my tnh m ra mt thi i thng tin mi. S hin din ph bin ca IP: ngy nay tt c cc my tnh c nhn v my ch trong Internet,WebusdnggiaothcIP.VtrnycaIPlmchontrthnhmt nntngthunliphttrinlulngthoi.HnnaIPhotngtrongmng cc b ln mng din rng. IP cng chng minh tnh thch ng ca n i vi cc i tng s dng phi d liu. V vy, cc nh khai thc s dng IP truyn thoi, l s tch hp ca mng d liu v mng in thoi. Titkim:Titkimtrongchiphutthitbvtitkimchiphchocucgi. Vi mng PSTN, xy dng mt tng i cn phi c nhiu thit b phn cng, cc h iu hnh, phn mm ng dng phc tp, ngoi ra cn cn cc chi ph cho v tr t tngi,chiphvnhnhbodngdogithnhcao.CnivimngVoIP, ngoi mt s cc thit b phn cng chuyn bit th computer l thnh phn chnh yu Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp5 trong mng m computer l thit b c sn xut hng lot, gi thnh khng cao. Chi ph cho cuc gi thoi IP ng di thp, y l mt yu t quan trng thc y VoIP pht trin. 1.2.2.2. Nhc im: Cht lng dch v l nhc im chnh ca in thoi IP. Cc mng s liu vn d khng phi xy dng vi mc ch truyn thoi thi gian thc, v vy khi truyn thoi qua mng s liu cho cht lng cuc gi thp v khng th xc nh trc c. S d nh vy l v gi tin truyn trong mng c tr thay i trong phm vi ln, kh nng mtmtthngtintrongmnghontoncthxyra.Mtyutlmgimcht lng thoi na l k thut nn tit kim ng truyn. Nu nn xung dung lng cng thp th k thut nn cng phc tp, cho cht lng khng cao v c bit l thi gian x l s lu, gy tr. Vntingvng:Nunhtrongmngthoi,dotrtnntingvngkhngnh hngnhiuthtrongmngIP,dotrlnnntingvngnhhngnhiuncht lng thoi. V vy, ting vng l mt vn cn phi gii quyt trong in thoi IP. Nhng vi s pht trin ca cng ngh k thut theo tc hin nay th tt c nhng nhc im trn u nm trong kh nng khc phc c. 1.2Cc nhn t nh hng n cht lng thoi Cht lng ca m thanh c khi phc qua mng in thoi l mc tiu c bn ca dch v, mc d cc tiu chun c ITU pht trin.C 3 nhn t c th nh hng su sc ti cht lng ca dch v thoi: +Tr: Hai vn gy ra bi s tr u cui trong mt mng thoi l ting vang v chng ting. Ting vang tr thnh vn khi tr vt qu 50ms. y l mt vn chtlngngknncchthngVoIPphikimsotvcungcpcc phng tin loi b ting vang. Hin tng chng ting (ging ngi ny gi ln gingngikia)trnnngknutrmtchiu(one-waydelay)lnhn 250ms. +S bin thin tr (Jitter): Jitter l s bin thin thi gian tr gy nn bi s tr ng truyn khc nhautrn mng.Loi b jitter i hi thu thp cc gi v gi chng lu cho php cc gi chm nht n c pht li ng th t, lm cho s tr tng ln.+Mtgi:MngIPkhngthcungcpmtsbomrngccgitinsc chuyn ti ch ht. Cc gi s b loi b khi qu ti v trong thi gian tc nghn. Truyn thoi rt nhy cm vi vic mt gi, tuy nhin vic truyn li gi ca TCP thngkhngphhp.Cccchtipcncsdngbliccgimtl thm vo cuc ni chuyn bng cch pht (play) li gi cui cng v gi i thng tin . Tuy th, s tn tht gi trn 10% ni chung l khng chp nhn c. S duy tr cht lng thoi chp nhn c bt chp s thay i trong hot ng ca mng(nhtcnghnhaymtktni)tcnhnhngkthutnhnnting,trit khong lng v cc mng h tr QoS. Mt s s pht trin trong nhng nm 90, nht l trong x l tn hiu s, cc chuyn mch mng cht lng cao, v cc giao thc c s QoS, c phi hp h tr v khuyn khch cng ngh thoi trn mng d liu. Qu trnh tin x l bng phn mm ca cuc in m cng c th c s dng ti u ha cht lng m thanh. Mt k thut, c gi l trit khong lng s xc nh mi khi c mt khong trng trong li thoi v loi b s truyn cc khong ngh, hi th v cc khongimlngkhc.iucthlnti50-60%thigiancamtcucgi,giptit Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp6 kim bng tn ng k.Bi l s thiuccgi c hiu l s im lng hon ton u ra, mt chc nng khc c yu cu u nhn b sung cc ting ng u ra.1.3S pht trin ca dch v VoIP1.4.1 Kh nng trin khaiVoIP hin hnh thnh dch v nhng iu khin n tr thnh mt phn chnh yu ca th trng thoi tch hp hay ch l mt dch v thiu s ph thuc nhiu vo s pht trin ca mngInternetngynay.Thiimchuyntmngchuynmchknhsangmngchuyn mch gi l mt yu t quyt nh s thnh bi ca nh cung cp dch v v vai tr r rt ca VoIP trong tng lai.Ph bin dch v VoIP nm gia hai kh nng: Khnngth1:ChtlngdchvcamngInternettiptckhngnnh, cc in thoi truyn thng gim mnh (loi b kh nng h gi thoi Internet ) th lc VoIP vn ch l mt dch v chim thiu s. Kh nng th2 : Hiu qu v tng trng ca cc dch v VoIP v mng tch hp khin khch hng chuyn sang dng mng Internet lm cho hiu qu kinh t tng cng vi s tng trng ca lu lng. 1.4.2Yu cu pht trinMc tiu cho cc nh pht trin kh n gin: b sung kh nng gi in thoi (c truyn thoilnbohiu)choccmngnnIPvktnichngvimnginthoicngcng cng nh cc mng in thoi c nhn duy tr cc chun thoi hin thi cng nh cc c tnh m mi ngi mong i mt my in thoi. Thch thc cho cc nh pht trin sn phm pht sinh trong 5 khu vc: ChtlngthoiphitngngviPSTN,btchpccmngccccp QoS khc nhau. MngIPphitcnhngtiuchuncnthitbaogmgimthiucc cucgi b tchi, s tr trn mng, mtgi vt lin kt. iu ny c ihingaytrongctnhtrngttnghnhaykhinhiungisdngphi chia s cc ti nguyn mng. iukhincucgi(bohiu)philmchoqutrnhgitrnntrongsut khinngigikhngcnbitkthutnocsdngthchindch v. Lin kt dch v PSTN/VoIP bao gm cc gateway gia cc mi trng mng thoi v d liu. Qunlhthng,anton,achhav thanhtonphiccungcp,tt nht l c hp nht vi cc h thng h tr hot ng PSTN (OSS). CucchyuatoraccsnphmVoIPphhpvimtdirngcccuhnhca ngi s dng mi ch bt u. Cc chun phi c thng qua v thc thi, cc gateway cung cp giao din IP v PSTN dung lng cao phi c trin khai, cc mng sn c cn c h tr QoS v cc dch v cng cng ton cu cn c thit lp. 1.4.3Nhng kh khn khi trin khai dch vC 3 kh khn chnh : Vntiuchun:DotiuchunquctcainthoiIPcnangkhng ngng pht trin v hon thin, c bit l tiu chun thng tin gia cc min Chng 1: TNG QUAN V IN THOI INTERNET ___________________________________________________________________________ Bo co thc tp7 khc nhau, gia cc mng khc nhau vv... cn ang trong thi gian tranh lun nh hng trc tip n s tng thch gia cc sn phm in thoi IP ca cc nh cung cp khc nhau. Ngoi ra vn chuyn mch ca thu bao cc minkhcnhau,vnltrnhvvntngthchdchv,vnthanh tonccphgiaccnhcungcpdchvkhcnhaucnangchc gii quyt. Vnmngtruynti:inthoiIPdatrnInternet,mgaiothcca InternetlTCP/IPcthitkchyunhmchodchvdliuphithi gian thc. Trc mt cha c th thc hin qun l rng di thng, khng ch lu lng cho nn khng th cung cp cc dch v QoS. Lu lng truyn dn trong mng Internet l khng th xc nh trc c v lung thay i, v vy nh hng nghim trng n cht lng thng thoi. Cn c vo tnh hnh k thut hin nay c th ni Internet i vi thng tin in thoi thi gian thc yu cu cht lng cao cn tn ti nhiu khim khuyt. Vn dung lng thit b: Cc nh sn xut thit b tip nhn Internet v cc nh sn xut thit b cng mng u ang c gng pht trin vi quy m ln, t vi ca ra E1 cho n hn 100 ca ra E1. Tuy nhin dung lng ca thit b hin nay cn cch xa so vi cc sn phm ca vin thng. 1.4.4Xu hng pht trin HinnaymnhthahnchoVoIPlccmngdoanhnghipIntranetvmng Extranet thng mi. C s h tng da trn IP cho php iu khin qun l vic s dng cc dch v, cho php hay khng cho php truy nhp cc dch v. Cc sn phm in thoi trn mng Internet cha th p ng cc yu cu cht lng dch v nh in thoi thng thng. Bi vy, pht trin VoIP trn Intranet, Extranet l hng pht trin trc mt. Mt khc cc nh khai thc vin thng ang trin khai u t xy dng cc cng ni gia mng IP v mng thoi (cc VoIP Gateway). Nhng Gateway ny xy dng t nn tng PC tr thnh cc h thng mnh c kh nng iu khin hng trm cuc gi ng thi. Bi vy cc doanh nghip s pht trin mt lng ln cc Gateway trong n lc gim cc chi ph lin quan n lu lng thoi, fax v video hi ngh. Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp8 Chng 2: QUY TRNH THC HIN CUCGI IN THOI IP 2.1.Mt s giao thc h tr mng in thoi IP 2.1.1. Kin trc TCP/IP Hu ht my khch (client) v my ch (server) trong mng Internet s dng giao thc TCP/IP(TransmissionControlProtocol/InternetProtocol).TCP/IPthcchtlmthgiao thc cng lm vic vi nhau cung cp phng tin truyn thng lin mng. Hnh sau m t v so snh kin trc TCP/IP v m hnh tham chiu OSI. Hnh 2.1 : So snh m hnh kin trc TCP/IP v m hnh tham chiu OSI. 2.1.2.Giao thc Internet (IP) IP (Internet Protocol) l giao thc nn tng cho nh tuyn cc gi qua Internet v cc mng khc da trn TCP/IP. Trong phm vi ca nhng mng th h mi,IP quan trng bi nhiu nguyn nhn, n l giao thc hp nht gia my tnh v vin thng. N cung cp mt gii php cho vic hp nht cng ngh mi trn nguyn tc k tha h tng c s c. N a ranhngphngthchiuquvtitkimhnhpnhtthoivsliutrnmtnn chung, thm ch n cn cho php to ra nhng ng dng mi nh khng gian dng chung, ng dng ny cho php ngi ta cng tc vi nhau nhng d n m ch s dng mt trnh duyt web. IP cn cung cp s hp nht gia cc mng c dy v khng dy. Mc d tn ti nhiugiaothckhcnhphngthctruynkhngngb(ATM)nhngkhngcgiao thc no c th so snh c vi IP v kinh t, hiu qu v phm vi hot ng ton cu ca n. MngdngchungIPhiuquhnmngchuynmchknhPSTNtrncscc knh chuyn dng thit lp gia cc im cui. Cc kt ni ny phn nhiu thi gian l ri. i vi cc cuc gi thng thng c n 40% thi gian b lng ph bi nhng khong lng Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp9 (khngnichuyn).TrongmngIP,ccgichcgiquamngkhicthngipcn truyn i. iu ny cho php mng c th truyn c mt lu lng nhiu hn qua rng bng thng sn c. C ch ng gi cho php mng x l bt k t hp no ca thoi v s liu trong cng mt thi gian qua cng mt knh.Khi cuc gi c thit lp bng a ch IP hoc email, ngi s dng mi u cui ni vo microphone c kt ni vo cc card m thanh trong cc my tnh ring ca h. Phn mm thoi ly mu ting ni, s ho v nn thng ip m thanh, sau truyn cc gi theo ng TCP/IP thng qua Internet ti bn u cui xa. u cui cc gi s c thu v ghp li cho ng th t. m thanh s c gin ra v gi n loa ca card m thanh cho bn nghe. Thut ton nn s b nhiu cho tr vn c ca Internet. Khi cc gi c gin v thng ip m thanh c pht ra th cc gi c nn li tip tc chuyn n. Vic x l ny gn nh t n thi gian hi thoi thc. Giao thc IP thc hin truyn thng tin di dng cc n v d liu gi l datagram. Mt datagram (Ipv4) bao gm hai phn chnh l header v data vi khun dng chi tit c m t trong hnh sau Hnh 2.2 : Khun dng ca IP datagram Khi gi cc datagram trn ng truyn vt l, cc datagram phi c ng gi di dng cc frame do ng truyn vt l khng xc nh c cc datagram. Ton b datagram s nm trong vng d liu ca frame nh hnh sau: Frame HeaderFrame Data Hnh 2.3 : S tng ng gia Datagram v Frame Trongtrnghptiu,mtIPdatagramvakhpvi mtframevtl,nhngtrn thc t do kch thccc datagram rt khc nhau, do rt kh c th xc nh kch thc lnnhtcadatagramsaochophhpvimtframe,hnnamimngutntimt n v truyn dn cc i MTU (Max Transfer Unit), n v ny biu th kch thc ti a m mt n v d liu c th c truyn qua. Do khi mt datagram c kch thc vt qu kchthcchophpcaframetrongmng,ncnphicphnon,mionckch Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp10 thc cho php ca frame trong mng, n cn phi c phn on, mi on c kch thc nh hn kch thc cho php. QutrnhphnonthngdinraticcgatewaynigiahaimngcMTUkhc nhautrnngtruyndliu.Cconsaukhicphnchiavngmhaithnhphn: phn header c cu trc ging vi phn header ca datagram ban u ngoi tr cc bit ch th trongphnflagsvphndatalthnhphncaphndliubanu.Kchthctngth caconngnhinphinhhnthamsMTUcamnghinthi.Khidliu c gi ti trm ch, da vo cc tham s flags v fragment offset m d liu s c tp hp li nh ban u.2.1.3.Giao thc TCP L giao thc hng kt ni, c chc nng kt hp cc cng vi cc kt ni, thit lp cc kt ni theo kiu bt tay ba bc (threeway handshake), phn on d liu, nh s th t cho ccgi d liu, bonhn v truyn li ccgi tin v iu khincctrm lp, tnh ton checksum, iu khin lung d liu vi cc phng php ca s gi v ca s nhn, giao tip viccngdngtngtrn,kimsotlivsa li,iukhin tcnghntrnmngvkt thc hay hu b mt kt ni. Giao thc TCP (Transmission Control Protocol) l giao thc kt nivitincycaogiahaihostcamngchuynmchgihinnay.Trongngdng VoIP, giao thc TCP c s dng lm giao thc bo hiu ch khng phi truyn s liu v gi TCP c nhiu header gy ra thi gian tr cao khng p ng yu cu v thi gian thc ca thoi. DoccphngthchotngcaTCPcbonhnvphtliccgihnghoc thiu nn khng kh thi khi dng TCP cho c ch mang thoi trong mt cuc gi VoIP. Vi VoIP, mt gi khng quan trng hn tr. 2.1.3.1.TCP Header Hnh 2.4 : Khun dng ca TCP datagram MttintrnhngdngtrongmthosttruynhpvoccdchvcaTCPcungcp thngquamtcng(port).MtcngkthpvimtachIPtothnhmtsocketduy nhttronglinmng.DchvTCPccungcpnhmtlinktlogicgiamtcp socket. Mt socket c th thamgia nhiu lin kt vi cc socket xa khc nhau. Trc khi Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp11 truyn d liu gia 2 trm cn phi thit lp mt lin kt TCP gia chng v khi khng cn nhu cu truyn d liu th lin kt s c gii phng. Source port: 16 bit l s hiu cng trm ngun Destination port: 16 bit l s hiu cng ca trm chSequence number: 32 bit - s th t ca octet u tin trong on ny Acknowledgment Number: 32 bit - nu bit kim tra ACK c bt ln th trng ny cha gi tr s th t ca on k tip cn nhn. Data offset: 4 bit, ch s lng t trong TCP header, mi t 32 bit Reserved: 6 bit d tr thng t gi tr bng 0 Checksum: 16 bit, m kim sot li theo phng php CRC cho ton b on. Urgent Pointer: 16 bit tr ti s hiu tun t ca byte i theo sau d liu khn, cho bit di ca d liu khn. Vng ny ch c hiu lc khi bit URG c thit lp. Control bit: phn mm TCP s dng xc nh mc ch v ni dung ca cc segment, 6 bit ch cc trng khc nhau theo th t sau: URG: con tr ch du hiu khn cp ACK: trng pht tn hiu ACK EOL: tn hiu kt thc tn hiu gi RST: thit lp li kt ni SYN: ng b cc s tun t FIN: bo hiu khng cn d liu gi Window: 16 bit, kim sot lung d liu theo c ch ca s Option: c di thay i, c 3 tu chn ca TCP: 0 - Kt thc danh sch tu chn 1 Khng hot ng 2 Kch c ln ti a ca segment Padding:cdithayi,phnchnthmvoheadermbophnheaderlunkt thc mt mc 32 bit, phn thm vo ny ton l s 0. TCP data: cha d liu ca tng trn c di ti a l 65,535 bit. Mt cng kt hp vi mt a chIP to thnh mt socket duynht trong lin mng.Giao thc nynm trn lp chuyn vn trn lpIP,vi chc nng m bocho ccgi c phn phi n ng achmkhngclikhchnviIP,gicthbmt.TCPrailmtnlc nhm khc phc yu im ca IP - mt giao thc khng tin cy. Ti y, TCP s phn lungdliuthnhtngongilsegment.SaugnchomisegmentmtTCP header,headergmcmtssequencenumberbitccvsgic truynivcuicngncgnthmphnheaderIPtruynitrnlpvtl. Qu trnh ngc li s xy ra ti u thu. TCP port number: tri hn vi tn gi, trng ny khng ch bt c mt knh vt l hay phn cng no c m thc cht dng phn bit cc trnh ng dng ang chy. Bt c khi nomttrnhngdng(Telnet,SimpleMailTransferProtocol(SMTP),)munbt u phin lm vic TCP, mt port duy nht s c gn cho phin truyn thng ny. S port do t chc IANA (Internet Assigned Numbers Authority) cp. Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp12 SequencenumbervAcknowledgementnumber:Sequencenumberdngphnbitcc segmentkhcnhautronglungdliu,thcchtndngmsoctetctrong ondliu,vdoncssequencenumberl100,di150octetthon segment k s c Sequence number l 250. Acknowledgement number dng yu cu s segment k tip, v d nh trn sau khi truyn i on 100 th u thu s tr li gi tip on 250. 2.1.3.2.Kt ni TCP-TCP connection Sau y chng ta s xt n qu trnh bt tay 3 bc ca TCP: Hnh 2.5 : Kt ni TCP Phaclientcntraoidliuvichngtrnhngdngcaserversaukhigicc thngskhitophintruynthng:sportngun,portch,sngunhinSequence number (vd 2000), c ca s, c on segment ln nht c th. Bn server cng tr li v a ra thng s tng t, sau mi bn tun t tr li v yu cu gi mi cng vi tng gi tr Sequence number, ACK ln mt. 2.1.4.UDP User Datagram Protocol 2.1.4.1.UDP datagram Lgiaothckhngktni,khngtincydokhngtruynligitin,khngiu khin lung, khng iu khin tc nghn mng. Do t chc nng phc tp nn UDP c xu th hot ng nhanh hn TCP nn n thng dng trong cc ng dng khng i hi tin cy cao trong giao vn.ClientServer SYN Seq = 2000 Window size SYN Seq= 4000 ACK = 2001 Window size MSS Seq = 2001 ACK = 4001 MSS = Maximum segment size Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp13 Hnh 2.6 : Khun dng ca UDP datagram SourcePort:16bittuchn.Khicchn,gitrcatrngnychnhportngun pha thu c th gi hi p cho pha gi trong trng hp cn thit. Khi khng s dng c gi tr bng 0.Destination Port: 16 bit, a ch port ch Length:16bit,chiuditrongccoctetcadatagram.MtgiUDPcchiuditial 65535 trong 65527 octet dng cho data. Checksum: 16 bitTrong VoIP, thoi ch yu c truyn qua UDP ch khng phi TCP v bn cht ca thoi l mang tnh thigian thc. Do vic mt mt vi gi tin bn thu khng nh hng nhiu n cht lng thoi. Kh nng cho php mt gi tt hn l tr trong vic truyn thoi. Giaothcthchinrtngin:UDPtiniphtchnginlchuyndliu cnhtuynnch.Ngcli,tininhnUDPchvicchuynginhncln lp cao hn. Khng ging TCP, UDP khng c chc nng kim tra hay xc nhn u pht bit mt gi nhn ng a ch hay khng. Th th ti sao ngi ta thch s dng UDP hn l TCP, mt giao thc rt ng tin cy??? Ch n gin l do c rt nhiu chng trnh i hi cn phi truyn d liu nhanh, p ng ca h thng n gin, v d i vi h thng qun l tnmin(DomainNameSystem-DNS),nimclientgitnminn serverqunltn minccachIPtngng.Sthchinstrnnrcrinuphithitlpv hu b cc kt ni TCP ch truyn hai gi thng tin m thi.iu g s xy ra nu gi UDP b mt? Khi chng trnh ch gi tip theo m khng thy tr li khi qu thi gian time-out th t ng gi gi yu cu tip theo. Nh vy xy ra trng hp ti u thu s nhn n hai gi. Cch gii quyt l chng trnh s c gn thm chc nng thng minh: gn phn nhn din yu cu vo trong d liu nhm pht hin thu hai ln. Chc nng truyn li c ch nh trong tu chn gi tr cho source port:Nu cn tr li th gn gi tr cho source port Nu khng th source port c gi tr zero Ch rng port TCP v port UDP mc d c cng gi tr nhng vn l hai port phn bit nhau trnh tnh xung t d liu khi c haichng trnh s dng hai port ny. R rng Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp14 header UDP n gin hn TCP rt nhiu, cng thm trng chiu di (length) gip xc nh c tng chiu di gi (header + data).2.1.4.2. Thoi qua UDP Voice over UDP, not TCP Do c im thoi cho php phc hi vic mt gi bng cc thut ton m ho v gii m nn UDP mc d vn l giao thc khng tin cy nhng li c chn truyn thoi. Mt khc, thoi rt nhy cm vi vn tr nn TCP khng th p ng c iu ny. Hn na, khimtgi,TCPstngtruynlikhiquthigiantimeoutmchathytrli ACK ca pha nhn.iu dn n tr qu ln khng th chp nhn c. i vi thoi, mt gi khong 5% l c th chp nhn c. Cng vi mt vi im yu ca UDP, RTP ra i nh mt k thut nhm h tr cho cc ng dng thi gian thc nh thoi hay video. 2.1.5.Giao thc chuyn vn thi gian thc Real Time Transport Protocol RTP c ch nh trong RFC 1889, b vo cc thiu st ca UDP. RTP hot ng ti lp trn ca UDP b sung nhiu chc nng. V d: mi gi RTP c mt s sequence number trnh ng dng RTP t nht c th pht hin ra s mt gi v m bo pha nhn nhn ng loi gi. Hay gi RTP c thm nhn thi gian (time stamp) cho bit thi gian m gi c ly ra t lung d liu chnh, nh vy trnh ng dng tai pha u nhn d ng b v tnh ton ctr,jitter.Thtra,RTPtnkhngththaythchoTCPhayUDPmphihiu rng RTP nh mt giao thc b sung nhm cung cp thm thng tin cho lp ng dng lp ny c th quyt nh x l gi nh th no l tt nht. Bt c khi no mt phin RTP c m th phin RTCP cng c m. D liu RTP c chuyn ti trn port UDP chn v tng ng cc gi RTCP cng c chuyn ti trn port UDP l k tip. Phn d liu trn gi RTP chuyn d liu thi gian thc. Gi RTCP m nhn phn iu khin gim st cht lng dch v QoS. Audio v video c truyn trn cc phin RTP ring bit. 2.1.5.1.nh dng vng ti ca RTP-RTP Payload Formats D liu gi trong RTP l thoi c s ho to ra RTP payload, sau c gn thmphnmouRTPheader.K,giRTPcngthmphnheaderUDPgiqua giao thc UDP. Xung ti lp IP, gi UDP c gn thm phn header IP to ra gi IP, sau gi IP c nh tuyn n ni nhn qua mng IP. Ti u thu, qu trnh ny xy ra ngc li,tchhtphnheadercatnglpxong,dliucavoccngnxp(stack)ca chng trnh ng dng. Khi bn u thu nhn c gi RTP, vi con s ch ra trong trng loi ti (payload type) s xc nh lut m ho m bn pht dng, do bn thu d dng giim.Trngpayloadtypec2dng:dngtnh(staticpayloadtype)vdngng (dynamicpayloadtype).Thngthng,mtgiRTPcthbaogmnhiumuthoihay video c m ho cng mt cch. Nu gi RTP b mt th c th chng trnh bn thu s lp ch trng ny bngcch chn li gi c trc vo hay mi gi s km theo mt bn sao ca gi trc . Ch l bn sao ny c th c m ho theo mt phng php khc sao cho t tn bng thng nht so vi bn chnh. bit c m ho no c th c p ng, trckhitruyndliuthngquagiaionbohichaibnthngnhtdngmho no m chng c th p ng c. V d, bn A mun truyn thoi theo dng m ho XXX bochobnB.ucuiBngtruyngiRTPmhatheophngphpXXXvi payload type l 120 trc khi bt u cuc gi. Sau khi cuc gi kt thc, payload type 120 ny c th dng ch ra cc dng m ho khc cho cc cuc gi sau. l v d cho dng dynamicpayloadtype,RTPaudio/videoprofilecspayloadtypet96n127cs dng cho dynamic payload type. Dynamic payload type rt hu dng, n cho php pht trin thm nhiu loi m ho ngoi cc chun m ho c quy nh trong series G ca ITU-T. 2.1.5.2.RTP header Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp15 RTP header bao gm thng tin cn thit cho vic phc hi mu thoi ban u ti u thu. RTP c dng format nh sau: Hnh 2.7 : Khun dng ca RTP Version (V): 2 bit - ch ra version hin ti ca RTP. Padding (P): 1 bit bit ny c lp ln 1 ch gi c cha mt hay nhiu octet thm vo cui payload m chng khng thuc phn payload. Extension(X):1bit-chrakhinothphnheadercnhckmtheophnheaderm rng c dng format nh hnh trn. CSRC count (CC): 4 bit - ch ra s lng b nhn dng ngun. Marker(M): 1 bit -gii thch v dng ca payloadc mang theo trong gi. Bit ny c ni n trong RFC 1890 (audio/video profile) cho php chng trnh ng dng ti u thu bit c khng c gi no c gi i trong sut qu trnh im lng (k thut trit khong lng). Bit M s c set 1 trong gi u tin sau qu trnh im lng . PayloadType(PT):audio,videoencodingmethod7bit-dngformatcapayloadRTP. Thng thng gi RTP c m ho trong mt dng format payload duy nht ngoi tr REDprofile(Redudantpayloadtype),cchtrongRFC2198,crtnhiudng payload.Sequence number : 16 bit gi tr ngu nhin khi bt u mt phin trao i do bn thu c th a ra (xem thm qu trnh bt tay ba bc trong giao thc TCP). Nh , bn thu c th a ra ACK i bn pht gi gi k tip, ngoi ra n cn cho php pht hin mt gi hay gi n sai a ch.Timestamp:32bitthigiancamuutintrongpayloadctora,trchratmt ngun xung clock. Do , lp ng dng ti u xa d dng ng b trong vic phc hi d liu c, cng nh tnh ton jitter. Tu theo dng format ca payload s c tn s xung ng h khc nhau, v d: thng thng tn s xung c chn l 8000Hz. Gi tr timestamp s tng tu thuc vo s mu cha trong gi nhiu hay t, v d mt gi cha 10 mu thoi (voice sample) v c timestamp bng 1 th gi k tip phi c timestamp l 11.SSRC Synchronization Source: 32 bit Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp16 CSRClist:Danhschcctinguynphntn0ti15itng,miitng32bit- cha mt gi tr SSRC cho vic phn phi trong mi phin. Trng ny c dng khi lung d liu RTP n t b trn v gip nhn ra ngun ban u trc khi qua b trn. 2.1.6.Giao thc RTCP RTP Control Protocol CngviRTP,giaothcRTCP(RTPControlProtocol)csdngphnhi cht lng truyn thoi trong khi nhng gi thoi tht s c a vo gi RTP. i vi truyn im n im, vic gi RTCP l khng ng k (khong 5s/1gi) v rt c ch. Vi RTCP, c hai pha pht v nhn u bit r vic thu/gi ca mi bn, bit c li gy ra suy gim cht lng (suy hao mng, tr, jitter). T , ngi iu hnh mng c th trc tip thay i hay sa cha t mt u cui xa. RTCP rt cn thit cho vic ng b cc lung thoivvideo.ivivictritkhonglngtrongtruynthoi,RTCPlmchomthoi ging nh hai pha u cui ang i din nhau. Thng tin SDES hu dng cho giao din vi ngi dng. Cc dch v m RTCP cung cp l: Gim st cht lng v iu khin tt nghn y l chc nng c bn ca RTCP. N cung cp thng tin phn hi ti mt ng dng v cht lng phn phi d liu. Thng tin iu khin ny rt hu ch cho cc b pht, b thu v gim st. B pht c th iu chnh cch thc truyn d liu da trn cc thng bo phn hi ca b thu. B thu c th xc nh c tt nghn l cc b, tng phn hay ton b. Ngi qun l mng c th nh gi c hiu sut mng. XcnhngunTrongccgiRTP,ccnguncxcnhbiccsngu nhincdi32bit.CcsnykhngthuntinivingisdngRTCP cung cp thng tin nhn dng ngun c th hn dng vn bn. N c th bao gm tn ngi s dng, s in thoi, a ch email v cc thng tin khc. ng b mi trng Cc thng bo ca b pht RTCP cha thng tin xc nh thi gian v nhn thi gian RTP tng ng. Chng c th c s dng ng b gia m thanh vi hnh nh. iu chnh thng tin iu khin Cc gi RTCP c gi theo chu k gia nhng ngi tham d. Khi s lng ngi tham d tng ln, cn phi cn bng gia vic nhn thong tin iu khin mi nht v hn ch lu lng iu khin. h tr mt nhm ngi s dng ln, RTCP phi cm lu lng iu khin rt ln n t cc ti nguyn khc ca mng. RTP ch cho php ti a 5% lu lng cho iu khin ton b lu lng ca phin lm vic. iu ny c thc hin bng cch iu chnh tc pht ca RTCP theo s lng ngi tham d. 2.2.Qu trnh x l trong in thoi thngthng m thoi trao i qua in thoi trc khi c s ho s c i qua b lc loi b i nhng thnh phn tn s cao. Di m thoi pht ra ca ngi bao gm c nhng thnh phnctnslnn12.000Hz,nhngivinhngngdnginthoi,nhngthnh phn tn s cao ny s b lc v loi i. c bit l, trong mng in thoi truyn thng, cc thit b gii hn knh truyn c thit k vi mc ch loi b cc thnh phn tn s trn 3.3 kHz.Chnhvvy,tnhiuthoiclymuvitns8.000Hztrongccngdngs dng k thut PCM. Chun G.711 l mt chun m ho ca ITU-T p dng k thut PCM v n tr thnh chun m ho ph bin trong h thng in thoi t trc n nay. Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp17 Hnh 2.8 :Qu trnh x l trong in thoi thng thng ividngtingnicaconngi,rngbngtnthngcgiihntrong khong 4.000 Hz, chnh v vy cn tin hnh ly mu 8.000 ln trn mt giy. bin ng catnhiuthoicngvitltnhiutrnnhiuSNR(Signal-to-Noise)squytnhs mclngtcnthit.ivimthoitrongccngdnglinquanninthoi,256 mc lng t c tm ra v bt u p dng t nhng nm 1950. Vi s mc lng t ny th cn 8 bit biu din duy nht cho mi mc. Do vy, cn 64.000 bps m ho ting ni ca ngi trao i qua in thoi sang dng s. K thut iu ch xung theo m PCM khng ihiqutrnh xltnhiuphctp,ylphngphputincpdngvtr thnh mt k thut ph bin c s dng trong cc thit b in thoi ngy nay (PCM c trn khai t nhng nm 1960). PCM cung cp cht lng m ho tt, c s dng trong k thut thu a nhc hin i dng Compact Disc mc d tc ly mu vn cn cao v t m cn di nhm m bo cho tn s 22 kHz. Vn m k thut PCM mc phi l n i hi mt lng bng thng kh cao biu din cho tn hiu thoi. 2.3.Qu trnh truyn dn VoIPThc cht in thoi qua mng IP (VoIP Voice over IP) cng khng hon ton khc hn inthoithngthng.utintnhiuthoicngcshonhngsauthayv truyn trn mng PSTN qua cc trng chuyn mch, chng s c nn xung tc thp, nggivchuyniquamngIP,tibnnhnccgitinnycgiinnthnhcc lungPCM64KBtruynnthubaobgi.Skhcnhauchnhlmngtruyndnv khun dng thng tin dng truyn dn. Sau y l v d v cuc gi VoIP: Gi s thu bao A mun gi thu bao B. Thu bao A quay s in thoi ca thu bao B. Mng PSTN c nhim v phn tch a ch v kt ni n Gateway1. Ti y a ch ca B li c phn tch v Gateway1 xc nh c thu bao B c kim sot bi Gateway2. N s thit lp mt phin lin kt vi Gateway2. Cc thng tin bo hiu m Gateway1 nhn c t PSTN s c chuyn i thch hp sang dng gi v truyn n Gateway2. TiGateway2ccgitinlicchuyningclivtruynsangmngPSTN. Mng PSTN c nhim v nh tuyn cuc gi n thu bao B. Cc thng tin tr li s c chuyningcliquaGateway2nGateway1.Saukhicucgicthitlp,cc Ly mu 8KHz Lng t ha 8bit/mu Chuyn mch0101010111101 64 Kbps Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp18 GatewaycnhimvchuynigiaccgitinthoitrnmngIPvcclungPCM truyn trn mng PSTN. Hnh 2.9 : in thoi IP 2.3.1.Cc bc thc hin cuc gi IP Bc1:tnhiuthoicangigicsha(cthchinbicngtyin thoi, bi nh cung cp dch v Internet hoc bi mt PC) Bc2:sdngthuttonphchp,tnhiuthoiscnnvricphn tch thnh cc gi. Bng cch s dng giao thc Internet, cc gi c nh a ch v c gi qua mng c tng hp li theo ng th t bn thu. iu ny c th thc hin bi cc cng ty in thoi, ISP hoc mt PC. Bc 3: trong qu trnh truyn dn trn Internet, cc gi c th b mt hoc b tr hoc cclicthgythithichoccgi.Kthutsalitruynthngsyucu truynliccgimthocbhhng,nhngnuqutrnhtruyndnlthngtin thi gian thc th k thut ny s khng lm vic, v th cc h thng sa li v pht hin li c s dng to ra m thanh lm y khong trng (qu trnh ny lu tr mt phn tn hiu thoi ca ngi ni v s dng gii thut phc tp on ni dungcaccgiblivtorathngtinthoimilmhiuqutuyntruyn thng). Bc 4: sau khi cc gi c truyn v n bn u thu, cc gi c tp hp li v gii nn phc hi d liu gn ging vi d liu ngun , ti to li tn hiu thoi ban u. IP PSTN Thu bao A Thu bao B Gateway1 Gateway2 PCPC Chng 2 : QUY TRNH THC HIN CUC GI IN THOI IP______________________________________________________________________________________________ Bo co thc tp19 Hnh 2.10 : C ch truyn thoi 2.3.2.Mt s chc nng cn thc hin trn quy trnh x l cuc gi IP Phn tch a ch: Xc nh a ch kt hp sin thoi cgi viGateway c trch nhim vi m vng ca bn b gi. nhtuyn:MngIPphichuynccgibngccphngtinsnc,duytrthi gian tr thp nht khi cn bng lu lng qua mng sao cho kt ni khng b qu ti. m bo cht lng: Cuc gi s cng tn ti vi cc lu lng khc nhau. Vi cc lu lng cng chung kt ni, phi c cch thc tch bit v nhn dng lu lng thoivicclulngkhckhngihithi giantrthpnhtnhiuthoinn thoi c th c u tin tng tc trn ng i ca n v lm cho cuc gi khng b ln lt bi cc cuc gi khc lm mng qu ti, suy gim cht lng cuc gi. Truyn ti d on: Lp truyn ti ca giao thc TCP/IP phi bo m mt mc tincychochuidliu,truyntilintckhngclivthmnhngmbo khc. Trong trng hp lu lng thi gian thc, chc nng quan trng nht ca lp giao vn l bo m vic truyn ti thng tin audio bnh thng, khi khng thc hin vic truyn ti d on (khi khng kt ni c vi IP) th cc Gateway phi gn d liu ng vi mt khong thi gian tng i c th ti thit lp kt ni. Bo hiu cuc gi: Mng cung cp truyn ti in thoi IP khng phi ch truyn ti cucgivongGatewaycanmcnbngcchnophibohiuchocc Gateway c th hiu c lung IP truyn i. Mhothoi:Cucgiscmhodidngchuidliusvitc 64Kbit/s,phnlnuimcainthoiIPsoviinthoitruynthnglkh nng nn chui d liu ny thnh chui ch c tc 32Kbit/s, 16Kbit/s hay thm ch cn nh hn v cc gi IP c dng truyn ti chui ny. X l li: Nu c mt vn pht sinh trong qu trnh thc hin cuc gi chng hn nh li Gateway, sgin on ca dch v mng, th phi c mt s phng thc sa li hon thnh cuc gi. Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp20 Chng 3: M HNH C BN X L CUC GI QUA INTERNET XlcucginichungvxlcucgiquaIPniringslmttrongnhng phng tin h tr cho a dch v. X l cuc gi in thoi lin quan n vi hot ng kh phc tp. Mc tiu ch yu l kt ni mt ngi gi n mt hay nhiu ngi. Trong vi h thng, th tc x l gi gia mt thu bao vi nh cung cp dch v lin quan n vic trao i mt vi tn hiu khc nhau hay truyn v nhn cc tn s tn hiu c bit gi l m hiu. 3.1.M hnh c bn Gateway thc s c cu to t Media Gateway Controller (MGC), Media Gateway (MG) v Signaling Gateway (SG). Ton b Gateway l thc th mng giao tip vi mng IP v mng in thoi PSTN. N phi cung cp giao tip truyn thng thi gian thc, song cng gia mng IP v mng in thoi. Hnh 3.1 : M hnh thit b H.323 Cc thnh phn to nn Gateway +Media GatewayMedia Gateway cung cp chc nng nh x v thng dch gia cc mng IP v mng in thoi. V d n c th thng dch G.711 64 kbit/s sang G.723.1 6,3 kbit/s hay ngc li. Cc hot ng ny c xem nh cn thit cho lung v cng c th bao gm s trit echo nu cn. i vi lu lng xut pht t mng IP, s kt cui ng truyn gi c thc hin v cc gi khng hot ng trn pha mng in thoi. Do , cc gi ny phi c nh x sang knh in thoi (DS0 hay knh B ca ISDN). Cc hot ng theo chiu ngc li din ra khi lu lng pht ra t mng in thoi. Media Gatewaycng c th chu trch nhim h tr cc dch v nh pht thng bo v m hiu khi cn. N theo di lu lng v thng k mc kh dng trn mng. +Signaling GatewaySignalingGatewaychutrchnhimvcchotngbohiucahthng.Vdn thngdchmtthngipSETUPcaH.323ntmtH.323Gatekeeperthnhmt thng ip a ch khi to SS7 ISUP i n mt tng i in thoi. N cng bin dch GatekeeperGatekeeperGatekeeper Media GW Controller Signalling GW Gateway Media GW A B D C G F J N E.a E.b Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp21 ccmhiuinthoianalogthnhccsnhphnchuynquamngsliudi dng mt gi v cng chuyn i cc biu din nhn phn thnh ra cc m hiu in thoi ti u thu. nh x cc m hiu analog sang nh phn tng ng l mt nhim v d dng. Mt cng vic kh khn hn i vi Signaling Gateway l kh nng chp nhn cc lung tn hiuthayitmyinthoi.Vdmtsnginmtphmtrnmyinthoi trong mt thi gian di v i mt thi gian trc khi n phm khc. mt u khc, mt lung ch s quay c nhp vo mt cch t ng t mt my tnh c nhn vi tc quaytonbccchstrongvng2giy.SignalingGatewaykhngchcthchp nhn cc bin i bo hiu ny m cn biu din chng mt cch chnh xc di dng cc thng ip d liu ph hp vi s thng dch ti endpoint kia ca ng dy. S biu din chnh xc ny ng vai tr quan trng trong mc tiu ng b ho vi phn mm v thit b ca h thng in thoi.+Media Gateway Controller MediaGatewayControllerlbiukhintoncccahthng.Niukhin Media Gateway v Signaling Gateway. N phi tng tc vi H.323 Gatekeeper, nh vy n c th x l cc thng ip H.225 v H.245. N cng chu trch nhim cho s xc thc v bo mt mng. N gim st ti nguyn ca ton b h thng v duy tr s kim sot tt c cc kt ni. +Cc thnh phn khc Gatekeeper cng l mt b iu khin v c vi chc nng ging nh Media Gateway Controller. Cng vic ca n l iu khin cc hot ng H.323 trn mng IP. BackendcngcthcdngbiGatewayvGatekeeperthchinccchc nng nh tnh cc, qun l c s d liu, nh tuyn v phn gii a ch. Cc giao tip c nh nhn E l E.a l giao tip cho cc lin kt thu bao in thoi (cc ng dy v trung k), E.b l giao tip cho cc bo hiu SS7. J v N cp n cc giao tip c s hot ng ca Megaco v MGCP. Giao thc iu khin H.323 hot ng qua cc giao tip c k hiu l A, C, D v G. Hnh 3.2: Min H.323 Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp22 Cc thnh phn trong m hnh H.323 Thit b u cui: L thit b u cui giao tip vi ngi s dng (terminal, client). Thit b t im cui ni lung d liu v tn hiu H.323 bt u v kt thc. N c th l my tnh a phng tin hoc thit b c lp nh USB IP Telephony (universal serial bus). Terminal lccucuiclientcungcptnhthigianthc,truynthnghaichiuviccthcth H.323 khc. u cui H.323 phi c 3 chc nng sau: -Bohiuviukhin:H.323phicungcpiukhinbohiuH.245chovic thit lp v bo hiucuc gicng nhgiao thc ng k qun l trngthi c nh ngha trong H.225 cho vic giao tip vi gatekeeper. Giao tip c tnh thi gian thc: u cui H.323 phi cung cp cc giao thc RTP, RTCP cho vic sp xp th t cc gi tin. -Mhovgiim:mhovgiimlnnhnhnhhaymthanhtrckhi truyn v gii nn khi nhn. Tt c u cui H.323 u cung cp chun m ho m thanh G.711. ychnhlnhnghthngucui(haycngilimcui)trnmngccb (xemhnh3.3).Ccthitbucuiphickhnnghtrthigianthc,hithoihai chiu vi cc thnh phn H.323 khc. Ngoi ra cc thit b u cui cn c kh nng h tr c ch m ho m thanh v thoi, c ch bo hiu v khi to cuc gi nh Q.931, H.245 v RAS.Ngoira,ccthitbucuicngcthhtrthmccchcnngtuchnkhc nh c ch m ho hnh nh v truyn d liu (nh hnh thc whiteboarding). Cc chun m homthanhnhG.711,G.723.1,G.728,vccchunmhohnhnhnhH.261v H.263 c nhim v nn v gii nn dng d liu a phng tin. Dng d liu a phng tin sau c truyn ti qua mng bng giao thc RTP/RTCP (RTP chu trch nhim truyn ti d liu tht s trong khi RTCP mang thng tin trng thi v iu khin). RTP/RTCP thc thi trn giao thc UDP, cn cc giao thc bo hiu hot ng tin cy trn nn TCP. RAS h tr cchngk,cpquynvxcnhntrngthi.Q.931mboqutrnhthitlpvkt thc cuc gi. H.245 m nhim qu trnh giao tip hi thoi. Hnh 3.3 : Thit b u cui H.323 Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp23 Thit b gatekeeper: NhtabitachIPtronggiaothcTCP/IPrtkhnh,bttinivikhch hng.Trongtrnghpmyinthoigichomytnhskhngthchincdoin thoi khng th bit c a ch IP hin thi ca PC khi n ng nhp vo mng v ngc liPCmungichointhoiphibitachIPcagatewayqunlsinthoi. iu quan trng na, khi dung lng mng tr nn qu ln, ti nguyn mng s kh qun l sao cho ti u nht. T nhng l do trn, vic s dng gatekeeper tr nn cn thit hn bao giht.ylthitbtuchntrongmhnhhotngH.323(Vdnhhnhthchp trnmngNetmeetingkhngsdnggatekeeper),nhngtrongmtstrnghpthcthi th cn c s c mt ca thit b ny. Mi gatekeeper m nhim mt min H323 (l mt tp hp cc thit b H.323). Thng thng th c mt gatekeeper trn mt min H.323, nhng c thtngslnggatekeepertrongmiminchomcchdphnghaycnbngti. Gatekeeper in hnh thng l nhng ng dng phn mm c thc thi trn my PC, hoc c th c tch hp trn gateway hay trn thit b u cui. Mt s thng ip ca cc giao thctruynquagatekeeper,mtskhctruyntrctipgiahaithitbucui.Cng nhiuthngipctruynthngquagiaccgatekeeperthcngihigatekeeper kh nng chu ti v iu khin. Ch l dng d liu a truyn thng khng bao gi chu tc ng bi cc chc nng ca gatekeeper. GatekeepercthchockhngctronghthngH.323nhnglicnhngchc nng bt buc nu c s dng trong h thng. Gatekeeper thc hin 4 chc nng:-Chuyn i a ch (t a ch nh danh alias hay s in thoi thnh a ch IP hay s cng TCP/UDP),-Bo hiu iu khin cuc gi (Call Control Signaling),-Phn quyn thit lp cuc gi (Call Authorization). Tt c cc u cui phi ng k vi gatekeeper quyn u tin thit lp cuc gi.-Qun l bng thng ( Banwidth Management).Gatekeeper l phn t khng bt buc phi c, c nhim v qun l cc thit b u cui vccgateway.H.323quynhrccchcnngbtbucvkhngbtbuc.Gatekeeper cungcpnhngyutquantrngchomngthoiIP.lnhngchcnngtchhps danh b v nh tuyn bn trong qu trnh thiplp cucgi.Nhng chc nng ny rt cn thitchothoivvideothigianthckhimtinguynchnvccimktniphi ng. Ngoi ra gatekeeper cn c mt s chc nng khc nh: chp nhn cuc gi, iu khin bng thng, gim st ti, sau cng l cc dch v in thoi IP trn cp thng mi. OCc chc nng bt buc ca gatekeeper: -Dch a ch: cho php dch cc quy c, cc k hiu, cc a ch email thnh a ch IP thit lp lin lc IP.-iukhintruynhp:datrnknhRASgiagatekeepervccphntkhc thng qua cc bn tin ARQ/ACF/ARJ. AdmissionRequest(ARQ):ucuigingatekeeperyucuc cho php tham gia vo cuc gi. Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp24 AdmissionConfirm(ACF):gatekeepercpquynthamgiachou cui. AdmissionReject(ARJ):gatekeepertchichoucuithamgia cuc gi. -Qun l bng thng: thng qua cc bn tin BRQ/BCF/BRJ c th chp nhn hoc t chi khi c nhiu cuc gi cng mt lc. BandwidthRequest(BRQ):cthtucuihaygatekeeperyucu thay i di thng. BandwidthConfirm (BCF): xc nh thay i di thng. BandwidthReject (BRJ): do u cui hay gatekeeper tr li t chi vic i di thng . -Kh nng nh tuyn: gatekeeper c th nh tuyn cuc gi trong vng m n qun l (vng H.323). C th hiu vng y l: mt s cc u cui, gateway, khi iu khinaimcqunlbi1gatekeepertothnhmtvng.Cucgini vng s do 1 gatekeeper qun l. Cuc gi ngoi vng s do 2 gatekeeper qun l.Nh cc kh nng ny gatekeeper c th tnh cc v thc hin cc mc ch bo mt. Gatekeeper c th nh tuyn li cuc gi ti mt gateway thch hp da trn kh nng c th cp c di thng l bao nhiu cho cc thit b u cui. OCc chc nng khng bt buc ca gatekeeper: -iu khin bo hiu: gatekeeper c th la chn gia 2 phng thc bo hiu cuc gi trc tip gia 2 thit b u cui hoc bo hiu cuc gi thng qua gatekeeper. -Hn ch truy nhp : gatekeeper c th s dng bo hiu H.250.0 t chi cuc gi ca u cui khi nhn thy c li trong vic ng k. -Gim st cuc gi. -Gim st rng bng tn : gatekeeper c th hn ch cc u cui cng mt lc s dng mng. -Lu gi cc thng tin tnh cc. Vic dng gatekeeper rt c li v a ch IP kh nh, bt tin cho ngi s dng. Ngoi ra, nu khng c gatekeeper th my in thoi khng th gi my tnh c ni mng c, cng thm vic khng th qun l ti nguyn lm cho h thng khng ti u.Khi iu khin a im MCU (Multipoint Control Units): Cc MCU l cc h thng u cui h tr cho hnh thc hi ngh qua mng gia ba hay nhiuimcui.L1imcui(Endpoint)trongmng,MCUcungcpkhnngnhiu Terminal,Gatewaycngthamgiavomtlinktaim.NbaogmmtMC (MultipointController)btbucphicvmtMP(MultipointProcess)cthchoc khng. Nhim v ca MC l iu tit kh nng trao i audio, video, data gia cc Terminal theogiaothcH.245.Tuynhin,MCkhngthaotctrctiptrnccdngdlium nhim v ny c giao cho MP, MP s thc hin vic kt hp, chuyn i, x l cc bit d liu. ThngthkhiiukhinaimbaogmbiukhinaimMC(Multipoint Controller) hay b x l a im MP (Multipoint Processor): Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp25 B iu khin a im MC (Multipoint Controller): H tr c ch iu khin v bo hiu cho hnh thc hi ngh qua mng. B x l a im MP (Multipoint Processor): Nhn cc dng d liu t thit b u cui, x l chng v tr v cho cc u cui khc tham gia trong hi ngh. Khi iu khin a im MCU c th t chc tp trung hay phn tn: Hnh thc tp trung: MCU m nhim c c ch bo hiu ca b iu khin a im MC v x l dng d liu ca b x l a im MP. Hnh thc phn tn: MCU ch m nhim c ch bo hiu, dng d liu truyn trc tip gia cc u cui. Trong trng hp nyMCU khng mang cc chc nng ca b x l a im MP. Hnh 3.4: M hnh tng qut VoIP 3.2Hot ng ca mt s m hnh cn bn +Thit b chnh hnh thnh mng VoIP l: oThit b x l cuc gi (PBX). oThit b u cui: my in thoi, my tnh bn, my tnh xch tay, hoc cc phng tin nghe nhn khc. oMedia/ VoIP Gateway oMng IP 3.2.1 M hnh Gateway bo hiu Gateway bo hiu (Signaling Gateway) lin quan n giao tip vi cc hot ng iu khininthoicauser.Giaotipnyihischpnhncctnhiuinthoi, chng hn nh cc ch s c quay, ch th nhc my, v chuyn i cc tn hiu ny thnh cc bit nh phn (c t vo trong gi s liu). Thng tin ny c Gateway x l theo kiu s liu v c ng vo trong gi IP chuyn i gi s n mt router. Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp26 Biudinnhphnchocctnhiuinthoicthdngmttronghaidng:Gn mt tn ring cho mi m hiu (v d mt tn cho ch s 5) hay m t c tnh m thanh ca tn hiu (v d: 770/1336 DTMF Hz cho ch s 5). D chn la dng no i na th cc biu din nh phn cng phi c chuyn ngc tr li cc m hiu t nhin ti my in thoi c gi. Hnh 3.5 :Gateway bo hiu thc hin nh x m hiu sang gi 3.2.2M hnh Phone to Phone Cuc gi c thc hin t in thoi n in thoi (Phone to Phone): y l mt dchvgiinthoingditrongnchocquctvigiccthp.Cch thchotngcaloihnhdchvnylkthpgiamnginthoivmng Internet: cuc gi t my thc hin cuc gi s c kt ni vi tng i ca nh cung cpdchv,tiytnhiuthoiquamtGatewayschuynthnhtnhiutruyn theo giao thc IP. Ti ni nhn, tn hiu c chuyn ngc li thnh tn hiu thoi v n in thoi ca ngi nghe. -Nhc my, gc my -m hiu quay s -Rung chung -Tp hp k s - Hot ng m thoi Router Gateway Hot ng m thoi -Nhc my, gc my -m hiu quay s -Rung chung -Tp hp k s - Internet m hiu m hiu Gateway Gi Gi Router Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp27 Hnh 3.6 : M hnh Phone to Phone 3.2.3M hnh PC to Phone Cuc gi c thc hin t my PC n in thoi (PC to Phone): y chnh l dch v in thoi Internet. Loi hnh ny c thc hin thng qua nh cung cp dch v, my PC sau khi kt ni vi nh cung cp dch v c th gi in nbt k quc gia no m nh cung cp dch v c h tr. Mi quc gia c th c cc cc ph khc nhau. Loi hnh ny hin nay ch thc hin c theo chiu quc t. Hnh 3.7 : M hnh PC to Phone Chng 3 : M HNH C BN X L CUC GI QUA INTERNET_________________ ___________________________________________________________________________ Bo co thc tp28 3.2.4M hnh PC to PC CucgithchintPCnPC:ychnhlhnhthcVoicechat.Trongtrng hpnytnhiuctruynhontontheogiaothcIPvthngquamtsphn mm m cc nh cung cp dch v h tr nn tn hiu thoi c th truyn c theo giao thc ny. Hnh 3.8 : M hnh PC to PC 3.2.5Cuc gi t in thoi n PC Trongtrnghpnythutintnhiuthoiscbinithnhcctnhiu truyn theo giao thc IP nh cc Gateway, sau da vo a ch IP ca mi my tnh cnimngmtnhiucthnngPCchcngi.Hinnaythloihnh ny cha c php cung cp Vit Nam.

3.3. Kt lun MngInternetcnggiaothcTCP/IPtrthnhmtnglcttthcycccng nghmivkhnngtruynthoithigianthcquaccmngIPchlmttrongnhng ng dng mi nht ca cc cng ngh . C th ni, mng Internet c mt c hi tt thc y vic kt hp dch v, trong cho php thoi v fax c truyn qua cc mng IP.Truyn thng trn cc mng chuyn mch gi nh IP, ATM v Frame Relay tr thnh chinlccachungchoccccngtylnccnhhochnhmngcngcng. Chnh v th, ngy cng nhiu cng ty nhn thy gi tr ca vic truyn voice trn mng IP gimgiccinthoivgiccfaxngthitnnmngchoccngdng multimedia nng cao. Cung cp dch v thoi cht lng cao trn mng IP l mt bc i bn l cho s hp nht thoi, fax, video v cc dch v vin thng khc. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp29 Chng 4: CC GIAO THC TRUYN THOI TRN MNG V HOT NG CA CHNG 4.1. Tng quan gii thiu cc giao thc truyn Nidungcaphnnyhngnmtccgiaothciukhinbohiucs dng trong cng ngh truyn thoi trn mng gi. Bo hiu l mt c ch c vai tr rt quan trng, cho php thit lp cucgi cng nh chophp trin khai caccdch v b sung v nng cp. C ch bo hiu cn thit cho qu trnh thit lp cuc gi trn mng, v hn na n cn cho qu trnh lin tc vi mng in thoi chuyn mch cng cng PSTN. Xut pht t bn cht tng tc ca vic bo hiu nn ngi ta s dng truyn mt s thnh phn ca giao thc H.323 (c bit l giao thc H.245) trn giao thc TCP v trn IP, cnmtsthnhphnkhccaH.323(vdnhthnhphnngk,cpquynvnhn dng trng thi RAS (Registration Admission Status) ca H.225.0) c truyn trn giao thc UDP v trn IP. Hnh 4.1: Chng giao thc ca H.323, MGCP v SIP C ba phng php tip cn khc nhau c xy dng trong vng 5 nm qua lin quan n c ch bo hiu cho cc ng dng thoi trn mng gi VoP (xem hnh minh ho4.1), l: Tt c cc thit b (bao gm thit b mng NE (Network element) v thit b u cui khch hng CPE (Customer Premises Equipment)) u c thit k vi c ch x l thng minh. Trong trng hp ny c th s dng giao thc H.323 ca ITU. Mngcthitkmtcchthngminh,nhngccthitbucuilil ccthitbdumbbnhthng.Trongtrnghpny,bncthtrinkhai Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp30 giaothcMGCP(Mediagatewaycontrolprotocol),MEGACO/H.248(Media gatewaycontroller),Hthngbohiuknhchungs7CCSS7(Common Channel Signaling System 7) Cc thit b u cui l cc thit b thng minh, cn mng thuc loi dumb. Trongtrnghpny,giaothckhitophinSIPlcchtrinkhaiph hp. R rng l, i vi cc nh cung cp dch v vin thng s chn 2 phng php tip cn u tin, trong khi cc doanh nghip li chn cch tip cn cui cng. H.323 vi nhiu phin bn ra i vn ang chim lnh th trng truyn thng cho n by gi. N c ngun gc t ccgiao thc bo hiu ca mng dch v s tch hpISDN, v do vy n c cu trc ging vi m hnh PSTN v cc mi trng lin tc vi mng PSTN. N l mt dng giao thc bo hiu Q.931 ca ITU-T trn TCP/IP. Di y l bng sp xp thi im ra i ca cc thnh phn bo hiu cho m hnh thoi gi VoP. Bng 4.1: Cc chun iu khin bo hiu v thi im chun ho Nhiugiaothcbohiukhcnhaucphttrintrnnhiutrngphikhc nhau p ng cho qu trnh bo hiu phin tng tc thi gian thc trn mng gi. Nhng giaothcnybtnguntccngungcphttrinkhcnhauvinhngkhacnhhtr khc nhau.Giao thc H.323 c pht trin trong cng ng mngLAN doanh nghip nh mtkthuthtrhnhthchinghtruynhnh(videoconferencing),ncnhiuim tng ng vi cc giao thc bo hiu trong ISDN nh Q.931. Giao thc MGCP/MEGACO c ngun gc t cc nh cung cp dch v vin thng, n kt hp vi c ch iu khin ni min ca cc gateway chuyn mch mm. T chc IETF pht trin giao thc SIP, s dng lirtnhiuthnhphntngttrongccgiaothcquenthuctrnInternetnhSMTP (SimpleMailTransferProtocol),hayHTTP(HypertextTransferProtocol),URLs(Uniform ResourceLocators), MIME (MultipurposeInternet Mail Extension) v DNS (Domain Name System).Mcdttculccgiaothcbohiunhngchngkhngnganghnghay Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp31 ng cp m c th cng tn ti d vn cn nhiu tranh lun v iu ny. Bng4.2 s cung cp s so snh gia cc giao thc ny trn nhiu kha cnh khc nhau. Bng 4.2: So snh trn mt s kha cnh gia ba giao thc bo hiu chnh SIPH.323MGCP/MEGACO phc tpThpCaoCao Kh nng m rngTtYuTrung bnh C thu c li nhun t vic trin khai cc dch v mi hay khng? C Khng Khng C ph hp trin khai trn Internet? CKhngKhng Kh nng tng thch vi h thng SS7 KmKmTt Chi ph vn hnh v trin khai ThpCaoTrung bnh 4.2. Cc giao thc v hot ng truyn thoi trn mng4.2.1. H.323 4.2.1.1. Tiu chun H.323 H.323lmtchunquctvhithoitrnmngcarabiHiphiVin thng Quc t ITU (International Telecommunication Union). Chun H.323 ca ITU xc nh cc thnh phn, cc giao thc, cc th tc cho php cung cp dch v truyn d liu thi gian thcaphngtin(multimedia)nhaudio,video,dataquamngchuynmchgi(bao gm c mng IP) m khng quan tm n cht lng dch v. Mt trong nhng ng dng ca H.323 l in thoi IP. Theo khuyn nghcaITU-T,giao thc H.323phin bn 4 m t cc u cui v cc thnh phn khc cung cp cc dch v hi thoi a phng tin thng qua mng chuyn mch gi, nhngc th khng cung cp cch m bo v QoS. Cc thnh phn tronggiao thc H.323 cung cp cc giao tip v thoi v video thi gian thc cng nh truyn s liu. H.323 cn bao gm c chc nng iu khin cuc gi, qun l thng tin a phng tin, qun l bng thng v ng thi cung cp giao din gia mng LAN v cc mng khc. H.323 l mt chun c phm vi hot ng rng ln trong cc lnh vc truyn thng a phng tin trn mng cc b LAN. H.323 nh ngha c ch thit lp v hu b cuc gi cho Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp32 cc ng dng thoi, video v hi ngh a phng tin (cc dch v nh: whiteboarding, data collaboration, videoconferencing). Cc c tnh lin quan n cucgi nhgi cucgi, ch cuc gi, chuyn cuc gi, chuyn tip cuc gi,nh danh ngi gi, chn cuc gi cng c h tr trong H.323.Hnh 4.2 minh ho chng giao thc H.323. Hnh 4.2: Chng giao thc H.323 H.323 nh ngha 04 thnh phn c bn trong h thng l: b kt cui (terminal), thit b kt ni lin mng Gateway, b iu khin Gatekeeper v khi iu khin a im MCU nh trong hnh: Cc thnh phn ca H.323 bao gm: ( trnh by chng 3) Thit b u cui Cc Gateway Cc Gatekeeper Khi iu khin a im MCU (Multipoint control units) Cc thnh phn giao thc bao gm: Thnh phn H.225.0 (RAS) v Q.931 Giao thc H.245 GiaothcthigianthcRTP(Real-TimeProtocol)/Giaothciukhin truyn thi gian thc RTCP (Real-Time Transport Protocol) C ch m ho m thanh v hnh nh. 4.2.1.2.Cc giao thc trong H.323 H.323 l mt b cc tiu chun ca ITU, c a ra cho vic truyn thng multimedia (VD: thoi) qua mngIP m vn m bo chtlngca dich v. H.323 nh ngha nhng tiu chun v nhng thnh phn c s dng qun l mt mng VoIP. l: Cc giao thc c s dng qun l vic thit lp (setup) v kt thc (teardown) cuc gi. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp33 Cc tiu chun nn v gii nn (CODEC) cho vic chuyn tn hiu thoi t tng t thnh tn hiu s. Cc thit b s dng trong mng. Cc giao thc H.323 c s dng iu khin cc ng dng audio, video v data. CcchunH.323baogmchunCODEchovicnnvgiinn,csdng chuyn i tn hiu thoi t tn hiu tng t thnh tn hiu s v ngc li. CcphntH.323baogmccucui(terminal),thitbvccdchvchovic truyn thng multimedia qua LANs, WANs Khuyn ngh H.323 a ra 1 tp cc giao thc phc v cho qu trnh truyn d liu thi gian thc trn mng chuyn mch gi. Kin trc phn tng giao thc c m t nh sau: Hnh 4.3 : Kin trc phn tng giao thc 4.2.1.2.1.Giao thc H.225 RAS (Registration/Admission/Status):Cc bn tin H.225 RAS c truyn trn knh RAS khng tin cy v vy chng c ti i trong gi tin UDP. CcbntinH.225RAScdngtraoigiaccimcui(thitbucui, Gateway,) v Gatekeeper cho cc chc nng nh: -Tm Gatekeeper: l qu trnh im cui tm 1 Gatekeeper n c th ng k. -ng k: c th tham gia vo 1 min do Gatekeeper qun l, cc im cui phi ng k vi Gatekeeper v thng bo a ch giao vn v cc a ch hnh thc ca n. -nh v cc im cui: l tin trnh tm a ch giao vn cho 1 im cui khi bit a ch hnh thc ca n (thng qua Gatekeeper). Mi khi c cuc gi,Gatekeeper nhn cachhnhthccaphabgi,nphithchinthtcnyxcnh c a ch dng truyn tin ca b gi. -Cciukhinkhc:giaothcRAScncdngtrongcccchiukhin khcnhiukhinthunhnhnchsimcuithamgiavomin,iu khin gii phng khi Gatekeeper. Mt s bn tin RAS H.225: -Pht hin Gatekeeper: GRQ (yu cu), GCF (cng nhn), GRJ (t chi). -ng k u cui: RRQ (yu cu ng k), RCF (cng nhn ng k), RRJ (t chi ng k). Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp34 -Hy ng k u cui: BRQ (yu cu hy ng k), BCF (cng nhn hy ng k), BRJ (t chi hy ng k). -Thay i bng thng:BRQ (yu cu thay i bng thng), BCF (chp nhn thay i bng thng), BRJ (t chi thay i bng thng). -yu cu nh v: LRQ (yu cu nh v), LCF (chp nhn nh v), LRJ (t chi nh v). -Cng nhn cuc gi: ARQ (yu cu cng nhn), ACF (chp nhn cng nhn), ARJ (t chi cng nhn). -Ngtktni:DRQ(yucungtktni),DCF(chpnhnngtktni),DRJ(t chi ngt kt ni). -Ch x l: RIP -Truyvntrngthi:IRQ(yucuthngtin),IRR(pngyucuthngtin), IACK (cng nhn yu cu thng tin), INAK (ph nhn yu cu thng tin). 4.2.1.2.2. Giao thc bo hiu cuc gi H.225 Giao thc H.225 dng thit lp lin kt gia cc im cui H.323, qua lin kt cc d liu thi gian thc s c truyn i. Bo hiu cuc gi mng H.323 l trao i cc bn tin ca giao thc H.225 qua 1 knh bo hiu tin cy. Do yu cu tin cy ca bo hiu nn cc thng bo ca H.225 s c truyn i trong gi TCP. Qu trnh bo hiu cuc gi c bt u bi bn tin Setup c gi i trn knh bo hiu tin cy H.225.0. Theo sau bn tin ny s l chui cc bn tin phc v cho qu trnh thit lp cuc gi vi trnh t da trn khuyn ngh H.225 m u tin l bn tin yu cu gim st btbuc.Yucunycngvinhngbntinsaulinquannqutrnhkhaibo/tm kimgiaucuivGatekeepersctruynitrnknhkhngtincyRAS(knh truyn thng tin v khai bo, gim st v trng thi). Qu trnh ny kt thc khi thit b u cui nhn c trong bn tin CONNECT a ch chuyn ti an ton m trn s gi i cc bntiniukhinH.245.BntinbohiuH.225.0skhngbphnonkhiiquacc PDU(ProtocolDatagramUnit)cnnhngbntinctruynitrnknhRASlnhng bn tin khng chun ha. Khi khng c Gatekeeper trn mng th cc bn tin H.225 s c trao i trc tip gia cc im cui. Nu c Gatekeeper trong mng th Gatekeeper s quyt nhvictraoiccbntinH.225giaccimcuiltrctiphayphithngqua Gatekeeper. Mt s bn tin bo hiu cuc gi H.255: -Setup: thng bo yu cu thit lp cuc gi t u cui v mang thng tin v a ch cng nh tn min ca thu bao ch gi. -Call procceding:cho bit u cui ch nhn cyu cu v qu trnh thit lp cuc gi ang c bt u. -Alerting: thng bo tn hiu chung ang cgi ti u cui ch, ch thu bao nhc my. -Connect: l bn tin c gi t u cui ch ngay khi thu bao nhc my, bn tin nycnthngboachucui(gmachcngvachIP)thitlp knh iu khin H.245. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp35 4.2.1.2.3. Giao thc iu khin cuc gi H.245 Giao thc iu khin cuc gi H.245 dng thc hin vic gim st cc hot ng ca ccthcthH.323baogm:traoikhnngccimcui,ng/mknhlogic,iu khin lung, quyt nh ch/t, cc lnh v ch th khc. Knh H.245 c thit lpgia 2 im cui, 1 im cui vi 1 MC hoc 1 im cui vi 1 Gatekeeper. Cc im cui ch thit lp 2 knh H.245 duy nht cho mi cuc gi m n tham gia. -Trao i kh nng: trc khi tin hnh cuc gi a phng tin, mi u cui phi bit c kh nng nhn v gii m tn hiu ca u cui kia. Bit c kh nng nhn ca u cui nhn, u cui truyn s gii hn ni dung ca thng tin m n truyni,ngcli,thngbokhnngtruynschophpucuinhnlc chnchthuphhp.Tphpcckhnngcaucuichonhiulung thng tin c th c truyn i ng thi v u cui c th khai bo li tp hp cc kh nng ca n bt k lc no. Tp hp cc kh nng ca mi u cui c cung cp trong bn tin H.245 TerminalCapabilitySet. -Bo hiu knh logic: 1 knh logic l 1 knh mang thng tin t im cui ny ti im cui khc (trong trng hp hi thoi im-im) hoc n nhiu im cui khc (im-a im). H.245 cung cp cc bn tin ng/m cc knh logic. Sau khi knh logic c m thng tin media mi c truyn i trn cc knh ny. -Xc nh master/slave : th tc ny nhm gii quyt vn xung t gia 2 im cui u c kh nng MC khi cng tham gia vo mt cuc gi hi ngh, hoc gia 2 im cui khi mun m 1 knh thng tin 1 chiu. Mt s bn tin iu khin cuc gi H.245: -TerminalCapacitySet:ylbntinutincgiquaknhH.245dng xc lp kh nng u cui (cc chun m ha m u cui c th h tr). Bn tin ny s c u cui gi i xc nhn cho bn tin TerminalCapacitySet m n nhn c. -OpenLogicalChannel: dng thit lp knh thng tin gia 2 u cui, bn tin ny mangthngtinxcnhsnhndngknhthngtinscthitlpvcc thngskhcnhloidliuctruynti,achcngUDPchoknh RTP, -CloseLogicalChannel: dng yu cu gii ta knh truyn RTP gia 2 u cui, ucuicnlisbonhnchoyucunybngvicgibntin CloseLogicalChannelAck. 4.2.1.3.Cc th tc kt ni y l module m t chi tit tng bc thc hin cuc gi ca H.323, thit lp truyn thng v kt thc cuc gi. y l v d mng c 2 u cui H.323 T1 v T2 kt ni vi nhau thng qua mt gatekeeper - M hnh iu khin bo hiu cuc gi. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp36 +Thit lp cuc gi Hnh 4.4 : Thit lp cuc gi 1.T1 gi thng ip RAS ARQ trn knh RAS n gatekeeper ng k. 2.Gatekeeper xc nhn thng tin t T1 bng cch gi ACF n T1. 3.T1 gi thng ip bo hiu thit lp cuc gi H.225 n T2 yu cu kt ni. 4.T2 hi p vi thng ip call proceeding (bt u cuc gi) H.225 n T1. 5.T2ngkvigatekeeper.NgithngipRASARQngatekeepertrnknh RAS. 6.Gatekeeper xc thc ng k bng cch gi thng ip RAS ACF n T2. 7.T2 cnh bo thit lp kt ni vi T1 bng cch gi thng ip cnh bo alerting. 8.T2 xc thc vic thit lp kt ni bng cch gi thng ip kt ni connect n T1, v cuc gi c thit lp. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp37 +iu khin lung bo hiu Hnh 4.5 : iu khin lung bo hiu 9.KnhiukhinH.245cthitlpgiaT1vT2.T1githngip TerminalCapabilitySet(xclpkhnngucui)nT2traoikhnngca chng. 10. T2thanhnkhnngcaT1bngcchgithngipTerminalCapabilitySetAck xc nhn cho bn tin TerminalCapabilitySet m n nhn c. 11. T2 trao i cc kh nng vi T1 bng thng ip TerminalCapabilitySet12. T1 xc thc cc kh nng ca T2 bng thng ip TerminalCapabilitySetAck 13. T1 m knh truyn thng vi T2 bng thng ip openLogicalChannel.14. T2 chp nhn thit lp knh logic 1 chiu t T1 n T2 thng qua vic gi thng ip openLogicalChannelAck.15. T2mknhtruynthngmediaviT1thngquavicgithngip openLogicalChannel. 16. T1chpnhnthitlpknhlogic1chiutT2nT1bngcchgithngip openLogicalChannelAck. By gi 2 lung truyn thng u c thit lp. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp38 +Lung truyn thng v iu khin truyn thng Hnh 4.6 : Lung truyn thng v iu khin truyn thng 17. T1 gi lung truyn thng ng gi RTP n T2. 18. T2 gi lung truyn thng ng gi RTP n T1 19. T1 gi thng ip RTCP n T2 20. T2 gi thng ip RTCP n T1 +Kt thc cuc gi Hnh 4.7 : Kt thc cuc gi 21. T2 bt u gii phng cuc gi. N gi thng ip EndSessionCommand n T1. 22. T1ngtucuicucgivxcthcngreleasethngquavicgithngip EndSessionCommand n T2. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp39 23. T2honttvicgiithotcucgibngcchgithngipreleasecompleten T1. 24. T1vT2tchriktnivigatekeeperbngcchgithngipRASDRQn gatekeeper. 25. GatekeepertchriktniviT1vT2cxcthcbngcchgithngip DCF n T1 v T2. 4.2.1.4.Hot ng ca H323: H.323 s dng khi nim knh xy dng nn mt cu trc thng tin trao i gia cc thc th. Knh l mt kt ni trong sut c th l n hng hoc hu hng.Trong H.323, c cc knh thng tin sau: 4.2.1.4.1. Cc knh thng tin trong H.323 -Knh bo hiu RAS: Register / Admission / Status Knh truyn thng tin v khai bo, gim st v trng thi. Knh ny c ch ra giao thcbohiuH.225.0,cungcpcchthngtingiamtucuivGatekeeper. Ngoi vic bo hiu trc tip gia hai u cui ch gi v b gi, thu bao ch gi c ththchinthaotcbohiugintipquagatekeeper.NuGatekeeperchpnhn th Gatekeeper s tr v a ch chuyn vn cho knh bo hiu cuc gi ca thu bao b gi. -Knh bo hiu cuc gi: Knhbohiunycvaitrthitlpvhubcucgi.Knhtruynccbntin phcvchoqutrnhthitlpcucgivitrnhtdatrnkhuynnghQ.931 nhngkhnghontonlQ.931.Qutrnhnysktthckhiucuinhnc a ch chuyn ti cho knh iu khin bo hiu H.245. -Knh iu khin bo hiu H.245: Knh thng tin ny thc hin nhiu chc nng nh: -Trao i kh nng ca hai u cui: loi thng tin, ch m ho m hai bn c th cng p ng, tc bit ti a m b pht c th gi. -ng m knh logic: thc hin cc knh logic mt chiu truyn audio v video trong mi trng hi ngh a im v thc hin ng m knh hai chiu truyn data. -iu khin lung: trong trng hp c li xy ra v mt s chc nng khc, v d nh trng hp thay i chun m ho khi mt trong hai thu bao c yu cu.-Knh logic truyn thng tin:Vi mi loi thng tin thoi, audio, video,... chng u c truyn ti trn cc knh ring bit s dng giao thc RTP v RTCP. H.323chrarngknhbohiuRASvknhlogicctruyntrntrnktni khngantonUDP,triliviknhiukhin bohiuH.245cchuyntian ton trn TCP, mt giao thc kh quen thuc trn internet. phin bn 1 v 2, H.323 ch ra rng knh bo hiu cuc gi c a trn giao thc chuyn vn an ton nhng phinbn3triknhnytuchnchuynbnggiaothcantonhockhngan ton. Di y l tm tt trnh t cc bc trong qu trnh thit lp cuc gi: Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp40 Bc 1: Khm ph ra gatekeeper c nhim v qun l v ng k - Thit lp knh RAS. oQu trnh khm ph ra gatekeeper qun l (RAS) theo trnh t: -Khchhnggiigimulticastmangthngtinyucugatekeeper (Ai l gatekeeper qun l ti?) -Gatekeepertrlivigimangthngtinxcnhngatekeeperph hp hay mang thng tin t chi. ong k vi gatekeeper (RAS) theo trnh t cc bc: -Khch hng xc nh ra gatekeeper ca mnh vi a ch v bit hiu i km. -Khch hng gi i yu cu ng k vi gatekeeper ny. -Gatekeeper tr li vi thng tin xc nhn ng hay loi b. -Trongmhnhny,ckhchhngAvBungkvi gatekeeper A. Bc2:nhtuyncucgigiaccimucuithngquaGatekeepers dng c ch bo hiu Q.931 oC ch chp nhn cuc gi (RAS) c tin hnh nh sau: -KhchhngAbtuarayucuchpnhn(Ticthtin hnhcucgi?).Githngtinnycngmangthngtinvlng bng thng ti a c yu cu cho cuc gi. -Gatekeeper tr li vi mt thng ip xc nhn Confirm -Bng thng cho cuc gi cng c xc nhn hay t chi -a ch knh bo hiu cuc gi ca gatekeeper cng c cung cp oCuc gi c thit lp qua gatekeeper (Q.931) thng qua qu trnh: -Khch hng A gi i bn tin khi to cuc gi (Call setup message) cho gatekeeper-Gatekeeper chuyn bn tin ny n pha khch hng B -Nu khch hng B chp nhn th mt yu cu chp nhn s c gi li v pha gatekeeper-Nucucgicgatekeeperchpnhn,khchhngBsgibn tin kt ni (connect message) cho khch hng A ch nh mt knh iukhincucgiphcvchomcchgiaotipgiahaiu cui. Bc3:Btuthitlpgiaotipvtraoithngtin,sdngcchiu khin H.245 Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp41 oQu trnh trao i thng tin s dng giao thc H.245 c thc hin nh sau: -Phakhchhngtraoithngtinvnnglcucuicamnh. Ccthngipnymangthngtinmtkhnngtruyndngd liu a phng tin (kh nng m ho audio/video) ca mi u cui khch hng. -Nu s dng hnh thc hi ngh truyn hnh th qu trnh tho thun hot ng ca b iu khin a im cng c thc hin trong pha hot ng ny. -Sau khi trao i cc thng tin m t v kh nng, khch hng s tho thun phng thc truyn dng d liu a phng tin sao cho tng thchgiaccucuivinhau.Khiccknhgiaotipa phng tin s c m ra. Bc4:Thitlpccdchvchocucgi,cchnhthcgiaotipaphng tin, s dng c ch iu khin cuc gi H.245 oQu trnh thit lp c ch giao tip a phng tin c tin hnh nh sau: -mknhlgictruynccdngdliuaphngtin,pha khchhngthchincucgistruynibntinknhlgicm (Open Logical Channel Message) (s dng H.245). -Phakhchhngnhncucgistrlivibntinxcnhnv knh lgic m ny (Open Logical Channel Acknowledgement) (cng s dng H.245) -Cc dng d liu a phng tin c truyn qua cc knh mang bn chtkhngtincyny.Sutqutrnhny,ccbntiniukhin cng c truyn i nhng trn nhng knh c tin cy cao. Bc5:KtthccucgisdngcchiukhincucgiH.245vcch bo hiu cuc gi Q.931. oQu trnh kt thc cuc gi din ra nh sau: -C hai thnh phn tham gia cuc gi u c quyn kt thc cuc gi. -Gi s khch hng A mun kt thc cuc gi. -KhchhngAhonttqutrnhtruyndliuvngknhlogic dng truyn d liu. -Khch hng A gi lnh kt thc phin lm vic (H.245). -Khch hng B ng knh logic v truyn i lnh kt thc phin lm vic. -Khch hng A ng knh iu khin H.245. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp42 -Nu knh bo hiu cuc gi vn cn m, thng ip hon ton ng Q.931 s c gi gia cc khch hng ng knh ny. Hnh 4.8 sau tm tt li cc bc ca qu trnhthit lp cuc gi. Hnh 4.8 : Qu trnh thit lp cuc gi H.323 Nhiu c tnh mi c thm vo trong phin bn th hai ca H.323, bao gm: H.235: Cung cp c ch bo mt v xc thc, thng qua cn c cc mt m trong qu trnh ng k vi gatekeeper. H.450.x:Cungcpccdchvbsungnhchuyncucgivchuyntip cuc gi. Qu trnh thit lp cuc gi nhanh: oB qua mt s thng ip thit lp. oc khi to bng thng ip Khi to nhanh do Q.931 cung cp c h tr mt s kh nng m rng c bn. C ch ch nh thm gatekeeper cho cc u cui. ThitbgatekeepercthyucuchuyntipthngtinQ.931chophpnh tuyn cuc gi trc tip. TchhpT.120tthn(ylchuntuchnchodngddiu),knhT.120 c m ra cng tng t nh bt k cc knh H.323 khc. Chng 4: CC GIAO THC TRUYN THOI V HOT NG TRN MNG_______ __________________________________________________________________________ Bo co thc tp43 4.2.1.4.2. Trnh t thit lp mt cuc gi trong H.323 Nu mt ngi mun ni chuyn vi mt ngi khc, ngi gi mt yu cu xc nhnngatekeepercabngi.Gatekeeperngvaitrnhthcthqunlcungcp quyn truy cp ti nguyn, iu khin bng thng v nh x tn thnh a ch IP. Gatekeeper tm a ch m bn gi c th xc nhn c bn b gi. Sau bn gi thit lp mt kt ni TCP n a ch IP ca bn b gi. Bn gi gi bn tin SETUP Q.931 v bn b gi phc p bng bn tin CONNECT Q.931. Sau giai on thit lp bo hiu Q.931, qu trnh iu khin bohiuH.245btu.BntinH.245thohipdunglngcaccucuinhkh nng h tr cc chun audio hay video. Th tc H.245 Logical Channel dng m cc knh dliuahngkhcnhau.KnhdliucnhnghalmtcpknhUDP,mtcho RTP v mt cho RTCP. Cc gi tin m thanh v hnh nh c gi trong RTP v gi t u cui ny n u cui khc. Hnh 4.9: S thit lp cuc gi Gatekeeper H.323 ni vng Gatekeeper Gateway AGateway B ng k H.225 (UDP) ng k H.225 (UDP) Thit lp cuc gi H.225 (Q.931) (TCP) iu khin cuc gi