Tm hiu cng ngh Voice IP v xy dng ng dng hi thoi trc tuyn

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TM HIU CNG NGH VOICE IP V XY DNG NG DNG HI THOI TRC TUYN

SVTH : NGUYN VN PHC-08T1-13A NGUYN HU THIN-08T2-12AGVHD : THS. MAI VN H

Nng: 06/2013NHN XT CA GIO VIN HNG DN

Tm hiu cng ngh Voice IP v xy dng ng dng hi thoi trc tuyn

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MC LCTNG QUAN V TI6Chng 1.C S L THUYT71.1.Tng quan v cng ngh Voice IP71.1.1.Gii thiu chung71.1.1.1.Gii thiu71.1.1.2.Cc dch v ca Voice IP71.1.1.3.u, nhc im ca cng ngh Voice IP81.1.1.3.1.u im81.1.1.3.2.Nhc im91.1.2.Cu trc phn lp ca h thng voice IP101.1.3.Cc m hnh truyn thoi Voice IP111.1.3.1.M hnh truyn thoi PC - PC111.1.3.2.M hnh truyn thoi PC - Phone121.1.3.3.M hnh truyn thoi Phone - Phone131.1.4.Mng IP131.1.5.Qu trnh thit lp cuc gi qua mng Voice IP141.1.6.Cch thc hot ng ca mng Voice IP161.1.6.1.S ha tn hiu analog161.1.6.2.Ly mu171.1.6.3.Lng t ha (Quantization)181.1.6.4.M ha (Encoding)191.1.6.5.Nn ging ni (Voice Compression)191.1.7.Cc yu t nh hng n cht lng dch v Voice IP211.1.7.1.S tr211.1.7.1.1.Tr thut ton (Codec delay)211.1.7.1.2.Tr do to gi (Paketization delay)221.1.7.1.3.Tr do lan truyn (Propagation delay)221.1.7.1.4.Tr chuyn pht gi (Serialization delay)221.1.7.1.5.Tr hng i (Queuing delay)231.1.7.2.S bin thin tr (Jitter)231.1.7.3.Mt gi241.1.7.3.1.nh hng ca mt gi241.1.7.3.2.Phng php x l mt gi241.2.Cc giao thc s dng trong h thng truyn thoi Voice IP251.2.1.Cc giao thc lp truyn ti251.2.1.1.Giao thc TCP (Transmission Control Protocol)251.2.1.2.Giao thc UDP (User Data Protocol)301.2.1.3.Giao thc thi gian thc RTP (Real Time Protocol)311.2.2.Cc giao thc lp mng331.2.2.1.Giao thc Internet (Internet Protocol IP)331.2.2.2.Cc giao thc nh tuyn361.2.2.2.1.nh tuyn IP (Routing)361.2.2.2.2.Cc giao thc nh tuyn371.3.Giao thc khi u phin SIP Secsion Initation Protocol401.3.1.Khi qut v SIP401.3.2.Cc thnh phn ca SIP411.3.2.1.User Agent (UA)411.3.2.2.My ch mng (Network Server)421.3.3.nh a ch v t tn431.4.H.323 v h thng bo hiu trong Voice IP441.4.1.Chng giao thc H.323451.4.2.Cc thnh phn trong h thng H.323461.4.2.1.Thit b u cui H.323471.4.2.2.H.323 gateway471.4.2.3.Gatekeeper481.4.2.4.n v iu khin lin kt a im MCU491.4.3.Cc bc thc hin cuc gi491.4.3.1.Thit lp cuc gi491.4.3.2.Thit lp knh iu khin501.4.3.3.Thit lp knh truyn thng501.4.3.4.Dch v cuc gi501.4.3.5.Kt thc cuc gi50Chng 2.THIT K V XY DNG NG DNG522.1.M t ng dng522.2.Phn tch chc nng522.2.1.Yu cu chc nng522.2.2.Yu cu phi chc nng522.3.Cu trc chng trnh522.3.1.Lp ChatServer522.3.2.Lp ChatHandler532.3.3.Lp ChatClient532.3.4.Lp CommonSoundClass532.3.5.Lp Queue532.3.6.Lp Playback532.3.7.Lp Recoder532.4.Thit k giao din ng dng542.4.1.Giao din Client542.4.2.Giao din Server54Chng 3.TRIN KHAI V NH GI KT QU553.1.Mi trng trin khai553.1.1.Phn cng553.1.2.Phn mm553.2.Kt qu demo ca chng trnh553.3.nh gi v nhn xt593.3.1.Kt qu lm c593.3.2.Hn ch593.3.3.Hng pht trin60

DANH MC BNG BIUBng 1. Tr thut ton ca mt s tiu chun m ha22Bng 2. Cu trc mt TCP header26Bng 3. Cu trc Header UDP31Bng 4. Cu trc RTP header32Bng 5. Cu trc mt bo co RTCP t pha pht33Bng 6. Subnet trong lp B34Bng 7. Cu trc IP header35Bng 8. Cu trc bn tin ICMP39Bng 9. Cc loi s c m t trong bn tin ICMP40Bng 10. Bng phn loi cc bn tin yu cu ca SIP44

DANH MC HNH VHnh 1. M hnh truyn thoi PC to PC12Hnh 2. M hnh truyn thoi PC to Phone13Hnh 3. M hnh truyn thoi Phone to Phone13Hnh 4. Ly mu18Hnh 5. Lng t ha19Hnh 6. Packetizing voice20Hnh 7. Quy trnh thit lp kt ni TCP29Hnh 8. Gii ta kt ni TCP30Hnh 9. a ch lp IP34Hnh 10. Giao thc SIP trong m hnh TCP/IP40Hnh 11. Khun dng bn tin SIP41Hnh 12. Cu trc ca SIP41Hnh 13. S User Agent42Hnh 14. Mi tng quan gia m hnh phn lp OSI v tp cc giao thc s dng trong h thng H.32345Hnh 15. Chng giao thc H.32346Hnh 16. Cu trc h thng H.32347Hnh 17. M phng giao din Client54Hnh 18. M hnh giao din Server54Hnh 19. Kt qu khi khi ng Client55Hnh 20. Kt qu chy khi khng kt ni c vi Server56Hnh 21. Kt qu khi kt ni vi Server thnh cng56Hnh 22. Kt qu sau khi user: nguyenvanphuc vo phng57Hnh 23. Kt qu chy khi thot Server57Hnh 24. Kt qu sau khi user: nguyenhuuthien vo phng58Hnh 25. Kt qu demo khi thc hin chc nng chat gia user: nguyenvanphuc v user: nguyenhuuthien58Hnh 26. Kt qu demo khi thc hin chc nng Talk gia user: nguyenvanphuc v user: nguyenhuuthien59Hnh 27. Kt qu khi chy Server59

TNG QUAN V TI1. Tn tiTm hiu cng ngh Voice IP v xy dng ng dng hi thoi trc tuyn.2. Tm quan trng ca tiCc dch v vin thng rt phong ph v a dng bao gm cc dch v truyn thng v cc dch v mi. C s cho s pht trin ca chng chnh nh vo s pht trin ca cc cng ngh in t v cng ngh mng. Mt cch c th hn c th ni rng s a dng c c l nh vo cc k thut truyn dn, k thut chuyn mch, k thut phn mn Do s xut hin cc cng ngh mi s mng li nhng bc t ph cho cc dch v vin thng phc v cuc sng tt hn.Chng ta c th phn chia cc dch v vin thng theo mt quan im no tuy nhin vic phn loi theo cc cng ngh chuyn mch t ra trc quan nht. Chng ta s dng 3 cng ngh chuyn mch l: chuyn mch knh, chuyn mch gi v chuyn mch thng bo. Mi Loi chuhyn mch c c trng ring do i km vi n l cc dch v vin thng xc nh.Tuy nhin, vi xu hng a dch v ho i hi chng ta phi gii quyt cc loi dch v trn mt c s h tng mng. p ng yu cu cc nh pht trin vin thng khng ngng khng ngng nghin cu cc gii php mi c tnh kh thi v t c mt s kt qu kh quan. C th l vi mt s dch v truyn thng vn i hi kht khe v thi gian thc cng nh cht lng m trc y ch ph hp vi cng ngh chuyn mch knh th by gi vi s h tr ca cc k thut mi cho php chng ta thc hin chng trn chuyn mch gi bi v ch c chuyn mch gi mi c th p ng c yu cu ca a dch v. Mt trong nhng gii php l vic truyn tn hiu thoi trn giao thc internet (Voice Over IP). Do ti v cng ngh Voice IP s gip chng ta tm hiu cng ngh mi gip cho vic tch hp dch v thoi truyn thng vo mng a dch v v c bit hu ch i vi nhng snh vin sp bc vo thc t cng ngh. 3. Mc ch chn ti Tm hiu v Cng ngh Voice IP. Xy dng mt ng dng truyn thoi demo v Voice IP.C S L THUYTTng quan v cng ngh Voice IP1.1.1. Gii thiu chung1.1.1.1. Gii thiuVoice IP vit tt bi Voice Over Internet Protocol l dch v ng dng cho php truyn ti cc cuc m thoi s dng h tng mng IP.Nguyn tc Voice IP gm vic s ho tn hiu ging ni, nn tn hiu s ho, chia tn hiu thnh cc gi v truyn nhng gi s liu ny trn nn IP. n ni nhn, cc gi s liu c ghp li, gii m ra tn hiu analog phc hi m thanh ban u.Voice IP c th va thc hin mi loi cuc gi nh trn mng in thoi knh truyn thng (PSTN) ng thi truyn d liu trn c s mng truyn d liu. Do cc u im v gi thnh dch v v s tch hp nhiu loi hnh dch v nn Voice IP hin nay c trin khai mt cc rng ri.Cc cuc gi trong Voice IP da trn c s s dng kt hp c chuyn mch knh v chuyn mch gi. Trong mi loi chuyn mch trn u c u, nhc im ring ca n. Trong k thut chuyn mch knh ginh ring cho hai thit b u cui thng qua cc node chuyn mch trung gian. Trong chuyn mch knh tc truyn dn lun lun c nh (ngha l bng thng khng i), vi mng in thoi PSTN tc ny l 64kbps, truyn dn trong chuyn mch knh c tr nh.Trong chuyn mch gi cc bn tin c chia thnh cc gi nh gi l cc gi, nguyn tc hot ng ca n l s dng h thng lu tr v chuyn tip cc gi tin trong nt mng. i vi chuyn mch gi khng tn ti khi nim knh ring, bng thng khng c nh c ngha l c th thay i tc truyn, k thut chuyn mch gi phi chu tr ln v trong chuyn mch gi khng quy nh thi gian cho mi gi d liu ti ch, mi gi c th i bng nhiu con ng khc nhau ti ch, chuyn mch gi thch hp cho vic truyn d liu v trong mng truyn d liu khng i hi v thi gian thc nh thoi, s dng u im ca mi loi chuyn mch trn th trong Voice IP kt hp s dng c hai loi chuyn mch knh v chuyn mch gi.1.1.1.2. Cc dch v ca Voice IPHin nay trn th trng c rt nhiu hng cung cp cc sn phm phn cng ln phn mm phc v cho cng ngh Voice IP nh INTEL, RAD, DIALOGIC, SISCO, VOCALTEC iu ny lm cho cht lng Voice IP ngy cng c ci thin. Cc dch v ca Voice IP bao gm: Thoi thng minh: in thoi truyn thng ch bao gm 12 phm iu khin. K t khi internet ph khp ton cu th in thoi c tng thm tnh thng minh. internet cung cp cc tin ch iu khin thoi mt cch hiu qu hn v to ra nhiu ng dng mi cho thoi. Dch v tnh cc cho b gi (Toll free): Thoi qua internet cho php thc hin vic tnh cc cho ngi b gi. Dch v callback Web: dch v ny cho php bn to cc trang Web vi cc phm thc hin cc cuc gi trn . Dch v FAX qua IP: cho php ngi gi FAX s dng dch v internet faxing s tit kim c c v cc ph ln knh thoi. Mt trong nhng dch v fax c a chung l comfax. Dch v Call Center: gateway call center vi cng ngh thoi qua internet cn cho cc nh kim duyt trang Web vi cc PC trang b multimedial kt ni vi cc b phn phi cc cuc gi t ng (ACD). Mt u im ca thoi IP l kh nng kt hp c thoi v d liu trn cng mt knh.1.1.1.3. u, nhc im ca cng ngh Voice IP 1.1.1.3.1. u imMc d cht lng ca mng Voice IP cha p ng c yu cu theo ng cc tiu chun cho mng thoi truyn thng PSTN do nh hng ca mt s cc thng s nu trn. Tuy nhin Voice IP cng th hin c nhng u im vt tri ca n: Gim gi thnh dch vu im vt tri ca Voice IP so vi mng PSTN l gi thnh dch v ca chng, c bit l chi ph cho cc cuc gi ng di. Trc y cc cuc gi ng di i hi cp pht cp pht ring mt knh kt ni, nn chi ph chi ph cho vic s dng ti nguyn mng ca cc cuc gi l rt ln. Vi vic s dng Voice IP, cc cuc gi ng di chia s bng thng vi cc dch v khc trn ng kt ni IP. Cuc gi ch s dng ti nguyn mng khi tht s c thng tin thoi cn truyn i gia cc thu bao. Qu trnh tch d tn hiu thoi c thc hin nh vo cc b tch d tn hiu thoi (VAD Voice Activity Detector) c trang b trn cc b m ho. Chi ph ca cc cuc gi ng di qua ng IP c th ch c tnh cho cc kt ni t thu bao n cc im cung cp dch v. n gin ho cu hnh mngVi vic s dng m hnh truyn thoi Voice IP, cho php qu trnh truyn thoi v d liu trn cng mt mng. Do vy m gim c cc chi ph cho vic lp t thit b cng nh vn hnh hai mng ring bit. Thm vo nh s dng mt cu hnh mng duy nht cho vic cung cp tt c cc loi hnh dch v nn lm n gin ho cu hnh mng, gim s lng thit b trn mng. m bo tin cy v tnh bo mt cho cc dch v thoi tin cy ca mng phn nh kh nng p ng ca mng trong cc trng hp c h hng xy ra i vi cc ng truyn hay thit b trn mng. S dng cc giao thc nh tuyn c kh nng d cc sai hng trn ng truyn v vic tm kim mt ng truyn khc thay th cho cc ng truyn c s c cng l mt phng php m bo tnh tin cy ca mng. i vi mng Voice IP vi vic s dng cc thnh phn qun l mng c kh nng kim tra trng thi ca thit b kt ni trc tip n n, cho php mng Voice IP c kh nng pht hin h hng tc thi v c cch x l thch hp.Bn cnh vic m bo tin cy cho mng Voice IP th vic m bo tnh an ton v bo mt cho cc cuc m thoi cng ht sc quan trng. m bo c tnh an ton v bo mt cho cc gi qua mng, h thng Voice IP s dng cc giao thc bo mt nh RADIUS hay SSH. Bn cnh vic s dng c ch nh a ch ring hay cc phng thc lc gi cng cho php m bo c tnh bo mt ca mng thoi Voice IP.1.1.1.3.2. Nhc im Cht lng dch v cha caoCc 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 khng c m bo trong trng hp mng xy ra tc nghn hoc c tr ln. Tnh thi gian thc ca tn hiu thoi i hi cht lng truyn d liu cao v n nh. Mt yu t lm gim cht 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. Vn ting vngNu nh trong mng thoi, tr thp nn ting vng khng nh hng nhiu th trong mng IP, do tr ln nn ting vng nh hng nhiu n cht lng thoi. K thut phc tpTruyn tn hiu theo thi gian thc trn mng chuyn mch gi l rt kh thc hin do mt gi trong mng l khng th trnh c v tr khng c nh ca cc gi thng tin khi truyn trn mng. c c mt dch v thoi chp nhn c, cn thit phi c mt k thut nn tn hiu t c nhng yu cu kht khe: t s nn ln ( gim c tc bit xung), c kh nng suy on v to li thng tin ca cc gi b tht lc Tc x l ca cc b Codec (Coder and Decoder) phi nhanh khng lm cuc m thoi b gin on. ng thi c s h tng ca mng cng cn c nng cp c tc cao hn hoc phi c mt c ch thc hin chc nng QoS (Quality of Service). Tt c cc iu ny lm cho k thut thc hin in thoi IP tr nn phc tp.1.1.2. Cu trc phn lp ca h thng voice IPVoice IP l h thng truyn thoi s dng h giao thc TCP/IP. Trong Voice IP, cc b x l s tn hiu (digital signal processer DSP) c chc nng m ho, phn on tn hiu thoi thnh cc khung, sau thc thi qu trnh ng gi thit lp cc gi thoi c kh nng vn chuyn trn mng thng qua vic s dng cc giao thc thuc h TCP/IP.Nh vy Voice IP l trnh ng dng c xy dng trn c s h tng ca h thng mng TCP/IP. Mt tp cc giao thc bo hiu c thit lp phc v cho qu trnh thit lp kt ni v iu khin cuc m thoi. Cc giao thc bo hiu qui nh cu trc mng Voice IP v tp cc giao thc c s dng trong mng, ty theo mi giao thc bo hiu khc nhau m ta c cc cu trc mng khc nhau cng nh qu trnh bo hiu, thit lp kt ni khc nhau. Tuy nhin cc mng Voice IP u ging nhau qu trnh m ha v gi ha cc tn hiu thoi cng nh qu trnh truyn cc gi thoi trong mng IP. Cc tn hiu thoi sau khi c m ho v ng gi c chuyn vn gia cc u cui s dng giao thc thi gian thc RTP (Realtime Transport Protocol). RTP l giao thc cung cp cc phng thc phc v cho qu trnh truyn thng cc tn hiu thi gian thc qua mng. RTP s dng UDP l phng tin truyn ti cho cc gi tin ca n.Cc lp di l c s h tng ca mng IP, l phng tin cho cc qu trnh trao i thng tin gia cc u cui trn mng.

Cc thnh phn c bn ca Voice IPCc thnh c bn ca mt mng Voice IP ph thuc vo loi giao thc bo hiu m n s dng. Tuy vy cc thnh phn ny u c thit lp trn mt nguyn tc chung. Nhn chung mt mng Voice IP gm ba thnh phn chnh sau y: Cc u cui: l thnh phn giao tip vi ngi s dng, l phng tin cung cp cc dch v thoi trc tip n ngi s dng. Cng giao tip: thc hin chc nng giao tip gia mng thoi truyn thng PSTN v mng Voice IP. Cc chc nng ca n bao gm: m ho tn hiu, chuyn i nh dng s, chuyn i giao thc bo hiu Thnh phn qun l: thc hin chc nng qun l cc thnh phn thit b hin din trn mngi vi cc h thng Voice IP c thit lp theo chun H.323, cc thnh phn trn tng ng vi cc u cui_terminal (c th l in thoi IP, hay PC trang b phn mm truyn thoi), gateway v gatekeeper.Trn c s s dng linh hot cc thnh phn ny trong mng, h thng Voice IP c th cung cp cc phng thc thc hin cuc gi trong mng khc nhau.1.1.3. Cc m hnh truyn thoi Voice IP1.1.3.1. M hnh truyn thoi PC - PCy l m hnh pht trin u tin ca cc h thng truyn thoi qua mng IP. H thng ny c thc hin trn c s s dng cc phn mm c pht trin ring cho vic truyn thoi gia cc my tnh. Cc phn mm ny c cc tnh nng gi ho cc tn hiu thoi c th truyn qua h thng mng IP n my ch. Qu trnh x l ngc li s c thc hin ti my ch nhm chuyn i cc gi thoi tr v dng tn hiu thoi ban u truyn n tai ngi nghe.M hnh ny thng c p dng trong phm vi t chc hay cng ty nhm p ng cc nhu cu lin lc m khng cn phi trang b thm h thng tng i ni b.Hin nay vi s pht trin nhanh chng ca h thng Internet cng vi cht lng c s h tng mng IP khng ngng c ci thin. Nhiu dch v s dng m hnh ny c ph bin nh: NetMeeting, VoiceChat,

Hnh 1. M hnh truyn thoi PC to PC1.1.3.2. M hnh truyn thoi PC - PhoneVic pht trin m hnh truyn thoi PC to PC cho thy kh nng pht trin h thng Voice IP trn din rng l rt kh khn v khng cung cp vic tch hp vi mng thoi hin c ng thi khng thn thuc vi ngi s dng nh mng PSTN. p ng nhu cu tch hp vi mng thoi PSTN, m hnh truyn thoi PC to Phone ra i. H thng ny cung cp c ch giao tip vi mng PSTN cng nh vic chuyn i a ch IP sang s in thoi thng thng s dng trn mng PSTN. Vi m hnh ny cho php thit lp cuc gi t mt my tnh c trang b phn mm truyn thoi trn mng n bt k mt my in thoi no trn mng PSTN thng qua ng lin kt IP. thc hin cuc gi qua mng nh trn, h thng phi trang b cc gateway l thnh phn giao tip gia mng PSTN truyn thng vi mng Voice IP. Theo gateway s thc hin chc nng chuyn i s IP sang s in thoi tng ng v ngc li, cng nh thc hin cc c ch chuyn i giao thc bo hiu gia hai mng IP v PSTN.

Hnh 2. M hnh truyn thoi PC to Phone1.1.3.3. M hnh truyn thoi Phone - PhoneM hnh truyn thoi Voice IP c s dng ph bin nht hin nay l Phone to Phone. M hnh ny thit lp cc giao tip hai chiu gia mng PSTN v mng gi IP, cung cp cc c ch chuyn i giao thc truyn thoi cng nh bo hiu gia mng thoi PSTN vi mng thoi qua IP.M hnh ny gy c s ch cho cng ngh truyn thoi qua IP v n tip cn c vi mi tng lp ngi s dng vi vic s dng my in thoi v cch quay s thng thng thc hin cuc gi qua mng IP.Trong m hnh ny ngi s dng dng mt m s c bit gi l gi tr cng kt ni gia PSTN v mng IP ri nhn s in thoi cn gi. Qu trnh chuyn i giao thc gia mng thoi v mng IP s c thc hin ti gateway.

Hnh 3. M hnh truyn thoi Phone to Phone1.1.4. Mng IPMng Voice IP c th c xem nh mt h thng tng i cung cp cc phng tin thc hin cuc gi gia cc u cui. H thng ny mang tnh phn tn, ngha l n gm nhiu b phn, thnh phn c lp t nhiu v tr khc nhau. kt ni cc thnh phn ny vi nhau mng IP c s dng v ng vai tr l tuyn mng trc trong vic phn phi thng tin gia cc thnh phn trong h thng Voice IP. thc hin chc nng l tuyn trc trong h thng Voice IP, mng IP phi m bo cho vic phn phi cc gi thoi cng nh cc gi bo hiu n cc thnh phn ca h thng Voice IP. Do s khc nhau v tnh cht ca cc gi bo hiu v cc gi thoi m mng IP phi c cch x l chng khc nhau. Bn cnh mng IP cn thc hin chc nng c bn ca n l truyn d liu. Do vy m mng IP cn phi xc lp c ch u tin cho tng loi lu lng truyn trn mng cng nh cc phng thc chia s ti nguyn mng cho tng loi dch v khc nhau.Do Voice IP s dng IP l phng tin truyn ti thng tin thoi, do n th hin s khc bit c bn trong phng thc truyn thoi vi cc h thng chuyn mch knh. Mng chuyn mch knh l mng s dng c ch ghp knh phn chia theo thi gian TDM (Time Division Multiplexing) cung cp mt knh thng tin v ton b bng thng ca knh cho cuc gi c thit lp qua mng, bt k c tn hiu thoi truyn trn knh hay khng. IP khc mng chuyn mch knh ch n da trn nn tng chuyn mch gi, vi vic thit lp cc knh o thc hin vic truyn thoi gia cc u cui, cc knh thoi c th cng chia s bng thng ca ng truyn. Mng IP ch cp bng thng cho cuc gi khi tht s c thng tin cn gi i nu khng n s dnh bng thng cho cc dch v khc.Cc lp dch v (class of service) trn mng IP s m bo rng cc gi ca mt ng dng bt k s c cp pht mt mc u tin no cho vic truyn ti cc tn hiu trn mng. Vic phn nh cc mc u tin nhm xc nh cc phn ng ca mng i vi cc gi d liu ca mt loi dch v nht nh trong cc trng hp xy ra s c trn mng. S xc nh cc mc u tin ny l cn thit cho ng dng truyn thoi qua mng IP v n m bo rng cc dch v thoi s khng b nh hng bi cc dng lu lng d liu cng c chuyn vn trn mng.Nh vy c th coi IP l phn li ca h thng truyn thoi qua IP v n cung cp tt c cc phng tin cho vic chuyn vn cc gi thoi qua mng. Mng IP khng quan tm n ni dung thng tin ca cc gi thoi cng nh ca cc gi d liu c chuyn vn qua n. M n ch da vo vic phn nh loi dch v cn cung cp c cc c ch thch hp trong vic thit lp u tin cho cc gi thoi m bo tnh cht thi gian thc ca thng tin thoi.1.1.5. Qu trnh thit lp cuc gi qua mng Voice IPVic thit lp cuc gi qua mng d liu i hi vic thc thi cc qu trnh tng t mng thoi truyn thng nh cung cp m hiu quay s, cc m hiu hi m chung cng nh vic cung cp tn hiu chung cho cc tn hiu u cui trn mng thng bo c cuc gi n, Qu trnh x l cuc gi trong mng Voice IP thng qua s dng cc giao thc c thit lp trn cu trc phn lp ca h thng c m t bng cc tin trnh sau: Khi ngi s dng nhc my, thng tin v trng thi nhc my c gi n phn ng dng bo hiu ca h thng Voice IP c thit lp lp phin. p ng cho yu cu gi n, cc ng dng lp phin s pht m hiu mi quay s ng thi ch thu bao quay s. Thu bao quay s in thoi cn gi, cc s ny c tng hp v lu tr trong ng dng lp phin ca Voice IP. Sau khi nhn s ph hp vi cc thng s c cu hnh cho cc u cui trn mng, s in thoi c chuyn i sang a ch IP ca mt u cui tng ng trn mng thng qua bng c s d liu c thit lp trong h thng. u cui ny c cc kt ni n thu bao b gi hay n cc tng i c kh nng hon thnh qu trnh thit lp cuc gi n thu bao b gi. Lp phin sau s thc thi mt trong s cc giao thc bo hiu nh H.323, SIP, thit lp mt knh pht v mt knh thu cho mi hng thng qua mng IP. Nu cc cuc gi c gi n tng i x l th tng i c chc nng chuyn tip cuc gi n thu bao b gi. Nu mng c cu hnh s dng giao thc RSVP (Resource Reservation Protocol) th giao thc ny s c chc nng qun l cc ti nguyn trn mng m bo cht lng ca cc dch v trn mng. C ch m ho v gii m tn hiu c thc thi lp trnh din ci t trn hai u cui thc thi qu trnh gi ho tn hiu thoi c truyn qua mng. Cc thng tin c m ho ca cuc hi thoi s c truyn qua mng s dng tp giao thc RTP, UDP v IP. Voice IP s dng h thng bo hiu trong bng, theo tt c cc ch th cho tin trnh ca cuc gi cng nh cc thng tin bo hiu khc phc v cho tin trnh thit lp kt ni gia hai u cui u c truyn qua cc ng thoi ngay khi knh thoi c thit lp gia hai u cui. Cc thng tin bo hiu c nhn bit qua cc cng thoi v c x l lp phin ti cc u cui. Khi bt k mt u cui no gc my ch th rng cuc hi thoi kt thc, vic qun l ti nguyn cp pht cho cuc gi ca RSVP c xo b v phin lin lc kt thc. Cc u cui li tr v trng thi ri, sn sng cho cc cuc gi tip theo.1.1.6. Cch thc hot ng ca mng Voice IP1.1.6.1. S ha tn hiu analogBiu din tn hiu tng t (analog) thnh dng s (digital) l cng vic kh khn. V bn thn dng m thanh nh ging ni con ngi dng analog do cn mt s lng ln cc gi tr digital biu din bin (amplitude), tn s (frequency) v pha (phase), chuyn i nhng gi tr thnh dng s nh phn (zero v one) l rt kh khn. Cn thit cn c c ch dng thc hin s chuyn i ny v kt qu ca s pht trin ny l s ra i ca nhng thit b c gi l codec (coder-decoder) hay l thit b m v gii m. Tn hiu n thoi analog (ging ni con ngi) c t vo u vo ca thit b codec v c chuyn i thnh chui s nh phn u ra. Sau qu trnh ny thc hin tr li bng cch chuyn chui s thnh dng analog u cui, vi cng qui trnh codec.C 4 bc lin quan n qu trnh s ha (digitizing) mt tn hiu tng t (analog): Ly mu (Sampling) Lng t ha (Quantization) M ha (Encoding) Nn ging ni (Voice Compression)Multiplexing: Ghp knh l qui trnh chuyn mt s tn hiu dng thi qua mt phng tin truyn dn.PAM (pulse-amplitude modulation)- iu ch bin xungTDM (Time Division Multiplexing)-Ghp knh phn chia theo thi gian: Phn phi khong thi gian xc nh vo mi knh, mi knh chim ng truyn cao tc trong sut mt khang thi gian theo nh k.FDM (Frequency Division Multiplexing)-Ghp knh phn chia theo tn s: Mi knh c phn phi theo mt bng tn xc nh, thng thng c b rng 4Khz cho dch v thoi.PCM (Pulse code modulation)- iu ch theo m: l phng php thng dng nht chuyn i cc tn hiu analog sang dng digital ( v ngc li) c th vn chuyn qua mt h thng truyn dn s hay cc qu trnh x l s. S bin i ny bao gm 3 tin trnh chnh: Ly mu Lng t ho M ho. Tin trnh ny hot ng nh sau:Giai on u tin cu PCM l ly mu cc tn hiu nhp (tn hiu i vo thit b s ho), n to ra mt tun t cc mu analog di dng chui PAM. Cc mu PAM c di bin ni tip nhau, sau phn chia di bin ny thnh mt s gii hn cc khong. Tt c cc mu vi cc bin no nu mu no ri vo mt khong c bit no th c gn cng mc gi tr cu khong . Cng vic ny c gi l lng t ho. Cui cng trong b m ho, ln ca cc mu c lng t ho c biu din bi cc m nh phn.1.1.6.2. Ly muChng 1. 1.1. 1.2. 1.3. 1.4.

Hnh 4. Ly muTn hiu m thanh trn mng in thoi c ph nng lng t n 10Khz. Tuy nhin, hu ht nng lng u tp trung phn thp hn trong di ny. Do tit kim bng thng trong cc h thng truyn c ghp knh theo FDM v c TDM. Cc knh in thoi thng gii hn bng tn trong khong t 300 n 3400Hz. Tuy nhin trong thc t s c mt t nng lng nhiu c chuyn qua di dng cc tn s cao hn tn s hiu dng 3400Hz. Do ph tn s c th c m rng n 4Khz, theo l thuyt Nyquist: khi mt tn hiu th c ly mu ng thi mi khong nh k v c tc t nht bng hai ln ph tn s cao nht, sau nhng mu ny s mang thng tin cho php vic ti to li chnh xc tn hiu thit b nhn. Vi ph tn s cao nht cho thoi l 4000Hz hay 8000 mu c ly trong mt giy, khong cch gia mi mu l 125 micro giy.1.1.6.3. Lng t ha (Quantization)

Hnh 5. Lng t haTin trnh k tip ca s ha tn hiu tun t l biu din gi tr chnh xc cho mi mu c ly. Mi mu c th c gn cho mt gi tr s, tng ng vi bin (theo chiu cao) ca mu.Sau khi thc hin gii hn u tin i vi bin tng ng vi di mu, n lt mi mu s c so snh vi mt tp hp cc mc lng t v gn vo mt mc xp x vi n. Qui nh rng tt c cc mu trong cng khong gia hai mc lng t c xem c cng gi tr. Sau gi tr gn c dng trong h thng truyn. S phc hi hnh dng tn hiu ban u i hi thc hin theo hng ngc li.1.1.6.4. M ha (Encoding)Mi mc lng t c ch nh mt gi tr s 8 bit, kt hp 8 bit c 256 mc hay gi tr. Qui c bit u tin dng nh du gi tr m hoc dng cho mu. By bt cn li biu din cho ln; bit u tin ch na trn hay na di ca dy, bit th hai ch phn t trn hay di, bit th 3 ch phn tm trn hay di v c th tip tc.Ba bc tin trnh ny s lp li 8000 ln mi giy cho dch v knh in thoi. Dng bc th t l ty chn nn hay tit kim bng thng. Vi ty chn ny th mt knh c th mang nhiu cuc gi dng thi.1.1.6.5. Nn ging ni (Voice Compression)Mc d k thut m ha PCM 64 Kps hin hnh l phng php c chun ha, nhng c vi phng php m ha khc c s dng trong nhng ng dng c bit. Cc phng php ny thc hin m ha ting ni vi tc nh hn tc ca PCM, nh tn dng c kh nng ca h thng truyn dn s. Chc hn, cc m ha tc thp ny s b hn ch v cht lng, t bit l nhiu v mo tn s.Mt s v d h thng m ha ting ni tc thp:CVSD( Continuously variable slope delta modulaton) K thut ny l mt dn xut ca iu ch delta, trong mt bit n dng m ha mi mu PAM hoc ln hn hoc nh hn mu trc . V khng hn ch bi 8 bit, m ha c th hat ng tc khc nhau vo khang 20 Kps. ADPCM( Adaptive differential PCM): K thut ny l mt dn xut ca PCM chun, s khc bit gia cc mu lin tip nhau c m ha, thay v tt c cc mu iu c m ha, c truyn trn ng dy. CCITT c ngh mt chun ADPCM 32 Kps, 24 Kps, 16Kbs cho m ha ting ni.Chun PCM th cng c bit nh chun ITU G.711Tc G.711: 64 Kps=(2*4 kHz)*8 bit/mTc G.726: 32 Kps=(2*4 kHz)*4 bit/mTc G.726: 24 Kps=(2*4 kHz)*3 bit/mTc G.726: 16 Kps=(2*4 kHz)*2 bit/mu

Hnh 6. Packetizing voiceMi mt khi ging ni c s ho v c nn li, n phi c chia thnh nhng phn nh, t vo gi IP, Voice IP th khng hiu qua cho nhng gi tin nh, trong khi nhng gi tin ln th to ra nhiu tr, do nh hng ca vi loi header m kch thc cu d liu thoi (voice data ) cng s nh hng.V d header cu IP, UDP, RTP l 40 byte, nu gi tin voice cng ch khong 40 byte th hon ton khng hiu qu, kch thc gi tin ln nht c th trong mi trng Ethernet l 1500 byte, dng 40 byte cho header cn li 1460 byte c th s dng cho phn d liu thoi, tng ng vi 1460 mu(samples) khng c nn hay thi gian t phn d liu vo gi tin. Nu gi b mt nhiu hay n ch khng ng th t s lm cho cuc thoi b ngt qung.Thng thng, cn khong 10us n 30 us (trung bnh l 20us) t d liu thoi vo bn trong gi tin, v d phn d liu thoi(voice data) v kch thc 160 byte khng nn cn khong 20us t phn d liu thoi vo bn trong gi tin. S lng d liu thoi bn trong gi tin cn cn bng gia s hiu qu trong s dng bng thng v cht lng ca cuc thoi.1.1.7. Cc yu t nh hng n cht lng dch v Voice IPCht lng ca m thanh c khi phc qua mng in thoi l mc tiu c bn ca dch v, mc d cc ch tiu chun c ITU pht trin. C 3 nhn t c th nh hng su sc ti cht lng ca dch v thoi:1.1.7.1. S tr

Dch v thoi cng nh cc dch v thi gian thc khc c gii hn nghim ngt v tr trong vic truyn ti cc gi thoi gia cc u cui. Nu tr qu ln c th gy ra cc nh hng xu n cht lng ca tn hiu thoi nh ngt qung qu trnh m thoi hay gy ra ting vang (echo).Cc nguyn nhn gy tr trn mng Voice IP:1.1.7.1.1. Tr thut ton (Codec delay)

y l tr do cc b codec to ra v l thi gian thc thi ca cc thut ton m ha. tr m ha ph thuc vo tng loi thut ton m ha. Cc thut ton m ha cng n gin v cho tc bit ln th thi gian thc thi cng ngn, do tr thp.Tiu chun m haGii thut nnTc Kbit/sTr m ha (ms)Tr gii m (ms)

G.711PCM6400

G.729CS_ACELP87.57.5

G.723.1ACELP5.3/6.418.7518.75

Bng 1. Tr thut ton ca mt s tiu chun m ha1.1.7.1.2. Tr do to gi (Paketization delay)Cc loi gi thng bao gm hai hay nhiu mu thoi, do vy m pha pht phi ch trong khong thi gian bng bi s thi gian to mu thoi trc khi c th pht gi i. y l tr gy ra do qu trnh gi ha thoi. Qu trnh ng gi thoi c thc hin nhm gim s hao ph bng thng cho phn tiu c gi km theo cc tn hiu thoi. gim tr, cc gi thoi trong mng Voice IP thng c kch thc nh. Tuy vy nu kch thc ca gi thoi qu nh s lm tng s hao ph bng thng trn mng do phn tiu gi km theo mi gi chim t l ln trn tng kch thc ca mi gi.Chun RFC qui nh rng chu k gi ha ngm nh i vi dch v trn mng Voice IP l 20ms. Tuy vy mt s tiu chun m ha c th c cc qui nh khc, nh tiu chun G.723.1 to cc khung thoi c di 30ms v mi khung s c pht i nh mt gi thoi vi s b sung phn tiu ca knh RTP.1.1.7.1.3. Tr do lan truyn (Propagation delay) tr do lan truyn l thi gian cc tn hiu lan truyn trn ng truyn gia cc u cui. Thng thng tr ny l khng ng k v tc lan truyn ca tn hiu tng i ln. tr ny ch c tnh n trong tr ca ton mng khi c ly ca ng truyn ln.1.1.7.1.4. Tr chuyn pht gi (Serialization delay)Qu trnh chuyn pht gi cng l mt nguyn nhn gy ra tr ln trn mng. N l thi gian cn thit chuyn pht mt gi d liu ln ng truyn vt l t mt nt mng. tr ny ph thuc vo tc giao tip ca cc ng truyn vt l m h thng s dng. Tc ca cc ng vt l cng cao th tr cng thp.Thm vo tr ny cn tng ln theo s nt mng m gi s i qua, v mi nt mng u thc thi qu trnh chuyn pht gi ln ng lin kt gia n vi nt mng ln cn.Mc d tr do chuyn pht gi l khng loi b c nhng nu s dng cc giao tip c tc cao, v hn ch cc ng lin kt m cc gi i qua th c th ti thiu c tr ny.1.1.7.1.5. Tr hng i (Queuing delay) tr hng i l thi gian m cc gi thoi phi nm ch trong cc b m trc khi n c pht i. Thi gian tr ny l mt i lng bin thin c qui nh bi lu lng ti trn mng. Khi lu lng ti qua mng thp, cc gi thoi c th c chuyn pht i ngay m khng cn phi a vo b m. Tuy vy khi lu lng i qua mt nt mng ln, tc x l ca cc nt mng khng p ng c tc lung lu lng n, cc gi phi ch trong cc hng i, tr hng i c th lm cho tng tr trn ton mng ln. m bo tr i vi cc gi thoi l thp nht,mng IP cn xc lp c ch u tin trong vic x l v phn pht gi thoi.1.1.7.2. S bin thin tr (Jitter)Nh cp chng 5, Jitter l chnh lch v khong cch gia cc gi u thu so vi khong cch chun qui nh. Khi cc khung c pht qua mt mng IP, tng thi gian tr m mi khung tri qua c th khc nhau. S d nh vy l v cc gi thoi c x l hon ton c lp nn tng tr hng i, thi gian x l, truyn pht gi c th bin i ty thuc vo ti tng th trong mng cng nh cu trc ca mng. Do mc d cc khung thoi u do cng mt ngun to ra ti cc khong thi gian u n, th pha ch thng vn khng thu c cc khung ny trong cc khong thi gian bng nhau v s chnh lch v tr ca cc gi trong mng.Jitter s lm cho cc u cui thu khng x l kp trong trng hp khong cch gia cc gi thoi qu ngn v ng thi cng c th lm cho pha thu hiu nhm cc gi b mt khi khong cch gia cc gi qu ln.Phng php chung x l i vi jitter l gi cc khung thoi ti b m cho php cc khung chm nht cng ti kp thi c c theo mt th t ng trong nhng khong thi gian xc nh. Lng jitter cng ln th mt s khung cng c gi lu trong b m v s to ra thm thi gian tr. tr ny gi l tr gy ra do b m jitter. gim thiu tr gy ra do b nh m, b nh m jitter thch nghi c s dng. Nguyn tc hot ng ca b nh ny l nu lng jitter trong mng nh th kch thc b m s nh. Nu jitter tng ln do ti ca mng tng th kch thc b m s t ng tng b li.Nh vy, jitter trong mng s lm xu cht lng thoi mc n lm tng tr t u cui ti u cui do c b m. i khi nu jitter qu ln, b nh m c th cho php mt mt s khung duy tr thi gian tr gy ra bi hin tng jitter khng qu ln.1.1.7.3. Mt gi1.1.7.3.1. nh hng ca mt giNh cp phn u, mt gi l hin tng khng th trnh c do c ch phn phi khng kt ni cng nh khng m bo tnh tin cy ca mng IP. Khc vi cc dch v truyn d liu, mt gi c th c khc phc nh cc c ch pht li gi c thit lp lp truyn ti, nh s dng giao thc TCP chng hn. Trong thng tin thoi, do tnh cht thi gian thc ca chng, khng cho php s dng c ch pht li v s lm tng tr ca mng.Trong thng tin thoi, mc d xc sut mt gi c th c chp nhn mt mc nht nh tuy vy mt gi ng ngha vi vic mt i cc mu thoi c th dn n t qung trong qu trnh m thoi. Do vy m cht lng ca mng thoi cn chu nh hng bi cch x l ca cc u cui i vi phn khung b xa.1.1.7.3.2. Phng php x l mt gi

Trong trng hp n gin nht, cc u cui s b qua cc khe trng trong dng thoi nu mt mu thoi b mt. Ngha l cc ni dung thoi cha trong cc mu thoi b mt s b b qua. iu ny c th chp nhn c nu xc sut mt gi thp v thng tin thoi khng yu cu chnh xc cao.Tuy nhin nu qu nhiu khung b mt, ting ni s b t on vi cc m tit hoc cc t b mt, mt phng php c th c s dng khi phc li cc on thoi b mt l pht li mu thoi ngay trc . Phng php ny lm vic tt nu ch c vi mu b mt trong ton b qu trnh m thoi v khng lin tc. i ph vi cc li nhm, tng ng nhiu mu thoi b mt, ngi ta thng phi dng phng php ni suy. Da vo cc mu thoi trc , b gii m s d on cc khung b mt c th l g. K thut ny c gi l k thut che du s mt gi (Packet Loss Concealment).Cc giao thc s dng trong h thng truyn thoi Voice IPCc giao thc lp truyn tiGiao thc TCP (Transmission Control Protocol)

Giao thc TCP c dng lm giao thc kt ni vi tin cy cao gia hai host trong mng my tnh hin nay. Trong ng dng truyn thoi Voice IP, giao thc TCP c dng lm phng tin vn chuyn cc gi bo hiu nh c tin cy cao. TCP cung cp cc kh nng: C s truyn d liu: TCP c th truyn lin tc cc dng octec theo hng bt k gia hai host trn mng bng cch ng gi cc octec. tin cy: trong trng hp data b mt, b h, b lp li hoc sai th t ban u, data phi c truyn li. Nu u thu nhn ng d liu s gi tn hiu khng nh ACK (Acknowledgment) v u pht. Nu u gi khng nhn c ACK, data s c pht li. Ti u thu, cc octec cng c nh s th t sp xp li cc on n sai trt t v loi b cc on b trng lp. Data b h c th sa sai bng cch thm trng checksum vo mi on pht i v khim tra li ti u thu, nu khng tng hp data s b loi b. Kim tra dng: TCP cung cp cho u thu kh nng kim tra s byte pht i ban u t ngun. Sau mi on d liu nhn c thnh cng, u thu phn hi mt ca s cha dy cc s tun t nh s cc octec nhn c. Phn knh: cho php nhiu qu trnh ng xy ra trong mt host duy nht, TCP kt hp t hp cc a ch kt hp gia a ch mng IP v a ch port to thnh cc a ch socket ring bit cho pha thu v pha pht. Mi cp a ch kt hp xc nh mt kt ni duy nht. Kt ni: Khi c yu cu kt ni t hai pha, hai bn phi hnh thnh kt ni logic trc khi truyn d liu i. Khi hon tt vic truyn thng, kt ni c gii ta tr v trng thi ri tip tc thc hin cc kt ni khc nu c. u tin v tnh bo mt: lp ng dng c th yu cu thm hai c tnh ny bng cch thm mt s trng thch hp vo header ca gi TCP.Source PortDestination Port

Sequence Number

Acknowledgment Number

Data OffsetReservedControl bitsWindow

ChecksumUrgent Pointer

Option + Padding

Data

Bng 2. Cu trc mt TCP header Source Port : 16 bit, cng ngun. Destination Port : 16 bit, cng ch. Sequency Number : 32 bit, s th t ca octec data u tin trong on ny. Acknowlegment Number : 32 bit, nu bit kim tra ACK c bt, trng ny cha s th t ca on k tip cn nhn. Data Offset : 4 bit, s t 32 c s dng trong TCP header nhm xc nh v tr u tin ca d liu trong gi. Reserved : 6 bit, d tr, thng t gi tr 0. Control bits : 8 bit URG : Urgent Pointer field significant, con tr ch du hiu khn cp. ACK : Acknowledgment field significant, trng pht tn hiu ACK. EOL : End of Letter, tn hiu kt thc vn bn gi. RST : Reset the connection, thit lp li kt ni. SYN : synchronize sequency number, ng b cc s tun t. FIN : No more data from sender, bo hiu khng cn data gi. Window : 16 bit, s octec data bt u bng octec c cp trong trng Acknowledgment. Checksum :16 bit, m kim sot li theo phng php CRC cho ton b on. Urgent Pointer : 16 bit, tr ti s tun t ca octec i theo sau d liu khn, cho bn nhn bit di ca on d liu khn. Vng ny ch c hiu lc khi bit URG c bt kn 1. Option : di bit thay i, nm cui TCP header v c di l bi s ca 8 bit. Padding : di thay i, xc nh v tr kt thc vng header. S tun t (sequency number)Mi octec data trong gi TCP gi i u c nh s tun t v c xc nhn ti u thu bng tn hiu ACK. Mi on cng mang mt s ACK l s th t ca octec data k tip s c gi i theo hng ngc li. Khi TCP gi mt on n ng thi chp mt bn sao ca on vo hng ch pht li v khi ng b nh thi, nu nhn c tn hiu ACK t pha thu, bn sao s b loi b khi hng i. Nu cha nhn c tn hiu ACK sau thi gian ti a cho php (time out) bn sao s c pht li.S tun t c nh s trong gii hn t 0 ti 2^32 1 s. S th t nh nht c nh s octec data u tin ngay sau header.Khi mt kt ni mi c thit lp, s th t bt u c cung cp gm 32 bit. Vic khi to gii hn trong chu k 32 bit xung clock trong cc bit thp c tng ln lt sau 4 micro giy. Do chu k khi to c lp li sau 4,55 gi. V cc on d liu khng tn ti trong mng khng qu vi chc pht nn kh nng s tun t b trng lp l khng h c.i vi mi kt ni u c s tun t nhn v gi. Chui s th t gi khi to c nhn bit trong qu trnh khi to kt ni.i vi kt ni c thit lp hoc khi to ban u, c hai TCP thu v pht u phi ng b s th t octec data. C ch bt tay ba bc l cn thit v cc s th t khng gn cng vi xung clock trong mng. Ni nhn tn hiu ng b u tin khng c cch no nhn bit on data c phi l gi c b delay hay khng tr khi n ghi nh s th t cui cng c s dng cho kt ni, do ni nhn yu cu TCP gi phi kim tra li tn hiu ng b SYN. Qui trnh thit lp kt ni TCP C ch bt tay ba chiu c s dng thit lp kt ni cho vic truyn ti thng tin trn giao thc TCP. Th tc ny c bt u bi cc giao thc TCP trn mt h thng v c p ng bi cc th tc tng ng ca giao thc TCP trn mt h thng khc. Tin trnh ny cng c thc hin nu c hai giao thc TCP trn hai h thng ng thi khi to mt tin trnh kt ni.Qu trnh khi to kt ni c bt u bng vic mt trong hai giao thc TCP gi gi d liu c ng nhn SYN n mt u cui khc yu cu thit lp kt ni. Cc tin trnh tip theo trong qu trnh thit lp kt ni gia hai h thng A v B c m t nh hnh:

Hnh 7. Quy trnh thit lp kt ni TCP Gii ta kt ni TCP Kt ni TCP c gii ta khi nhn c thng bo CLOSE bi cc trnh ng dng trn mt trong hai u cui. Thng bo CLOSE c pht i khi xy ra mt trong cc trng hp sau: User ch nh cho TCP ng kt ni. TCP nhn c gi FIN t u cui bn kia. C hai user cng thc thi lnh ng ng thi.Qu trnh gii ta kt ni c m t nh hnh sau:

Hnh 8. Gii ta kt ni TCPGiao thc UDP (User Data Protocol)UDP l mt giao thc truyn ti khng tin cy: UDP thit lp cc cng giao tip vi cc trnh ng dng, qua cc trnh ng dng c th gi d liu n lp UDP x l. Mi trnh ng dng c mt cng giao tip ring truyn d liu xung lp UDP. UDP phn on cc gi, thm header v tm ng gi cc gi UDP n u cui ch. Ty theo tnh trng mng m cc gi c th i bng cc ng khc nhau n ch, do cc gi c th b mt hoc sai th t pha nhn. Phn header ca giao thc UDP c gim ti thiu gim thi gian tr x l cc gi tin, m bo tnh thi gian thc cho d liu. Tuy nhin phn header ngn cng lm cho UDP khng khc phc c tnh trng mt gi cng nh khi phc li th t ca cc gi tin.UDP source portUDP destination port

UDP message lengthUDP checksum

Data

Bng 3. Cu trc Header UDP UDP source port: cng UDP ngun. UDP destination port: cng UDP ch. UDP message length: chiu di bn tin UDP bao gm c header v d liu. UDP checksum: trng kim tra pht hin v sa li.Giao thc thi gian thc RTP (Real Time Protocol)Giao thc RTP cung cp cc chc nng vn chuyn thch hp cho cc ng dng truyn ti thi gian thc nh tn hiu audio, video hay tn hiu m phng qua cc dch v mng a chiu (multicast) hay hai chiu (unicast). RTP khng qun l ti nguyn v cht lng dch v cho dch v thi gian thc. Giao thc iu khin thi gian thc RTP qun l vic cp pht bng thng cho qu trnh m thoi a chiu, ng thi cung cp mt s chc nng iu khin. RTP da vo vic pht nh k cc gi iu khin cho tt c cc thnh phn trong mng trong mt phin, s dng cng mt k thut phn pht gi nh cc gi d liu. RTP v RTCP c thit k chy c lp vi cc lp bn di. Do RTP v RTCP chy c lp vi nhau nn cn phi thit lp hai knh truyn ring bit bng vic s dng hai cng UDP khc nhau. 0 1 2 3 4 5 6 7 VersionPXCSRC Count

MPayload Type

Sequency Number (16 bit)

Timestamp (32 bit)

Synchronization Source Identifier (SSRC) (32 bit)

Contributing Source Identifier (CSRC)

Payload

Bng 4. Cu trc RTP header Version: phin bn giao thc RTP. P: ch nh cc gi tin RTP c c chn thm mt s byte thc hin cn chnh. X: xc nh phn tiu c thm mt s trng m rng hay khng. CSRC Count: xc nh s nhn dng CSRC c xc nh trong phn header. M: c p dng trong cc h thng s dng phng php loi b khong lng. Bit M s c set gi tr 1 ngay sau s xut hin ca khong lng. Payload Type: xc nh loi thng tin c truyn i. Sequency Number: xc nh s th t ca gi thoi c truyn i. Timestamp: xc nh thi im cc gi thoi c pht i. Synchronization source: xc nh lung ng b chung ca lung thng tin RTP trn mng. Cc dng thng tin RTP c cng ngun ng b s c cng mt ngun tham chiu nh thi v chui s th t. Contributing source: khng s dng trong h thng H.323, mang thng tin ng b cho lung RTP c tng hp t nhiu lung RTP khc nhau.

VPRCPTLength

Sender

NTP Timestamp (32 bit cao)

NTP Timestamp (32 bit thp)

RTP Timestamp

Senders packet count

Senders octec count

SSRC of first source

Fraction lostCumulative number of packet lost

Extended highest sequency number received

Interarrivel jitter

Last SR

Delay since last SR

SSRC of second source

Profile specific extensions

Bng 5. Cu trc mt bo co RTCP t pha phtCc giao thc lp mngGiao thc Internet (Internet Protocol IP)IP l giao thc hot ng lp mng, l giao thc khng tin cy v khng hng kt ni. Giao thc IP khng iu khin lung v khng bo nhn, thc hin chc nng phn pht cc gi d liu nhn c t lp chuyn ti, phn thnh cc gi c kch thc thch hp, nh a ch ngun, ch v nh tuyn cho cc gi tin truyn trn mng n ch. a ch mng IP phn phi d liu trn mng, IP xc lp c ch phn nh a ch cho cc u cui trn mng. Cc u cui bao gm gateway v cc host.a ch IP gm 32 bit, chia lm hai phn: NetID v HostID.Ty theo s bit phn nh cho phn NetID v HostID m cc a ch IP c chia thnh 5 lp nh hnh v sau:

Hnh 9. a ch lp IPMi lp a ch cho bit kch c ca mng.Trong nhiu trng hp, ty theo cch t chc mng ca tng n v ,mt mng c th chia thnh nhiu mng con (subnet). Khi cn c thm mt vng subnetID nh danh cc mng con . Vng subnet ID s nm trong vng hostID c. Mng con che du t chc bn trong mng vi cc router bn ngoi, vic s dng mng con gip gim kch thc bng nh tuyn cc nt mng.10NetIDSubnetIDHostID

Bng 6. Subnet trong lp BCu trc header ca datagrams lp mng (IP header)

0 16 31

VersionIHLType of serviceTotal length

IdentificationFlagsFragment offset

Time to liveProtocolHeader checksum

Source address

Destination address

OptionPadding

Bng 7. Cu trc IP header Version : 4 bits (version ca mng internet hin nay l version 4) IHL (internet header length) : 4 bits, biu din di ca internet header 32-bit words. Gi tr ti thiu l 5. Trng IHL gii hn chiu di IP header l 60 byte. Type of service : 8 bits, cung cp tham s ch dch v s dng khi truyn gi qua mt mng d0c bit no . Di y l ni dung chi tit cc bit ca trng type of service: Bit 0-2: bit ch th dng gi u tin Bit 3 : 0 = Delay thng; 1 = Delay thp Bit 4 : 0 = Through put thng; 1= Through put cao Bit 5 : 0= Relibility thng; 1= Relibility cao Bit 6-7: bit d tr Total length: 16 bits, xc nh chiu di mt datagram k c header v d liu. Gi tr ti a l 65355 octecs. Thng thng cc host ch c th x l cc gi c chiu di ti a 576 octecs gm 512 octecs d liu v 64 octecs header. Cc host ngun ch c th gi datagram c chiu di hn 576 octecs khi bit chc host ch c kh nng x l gi ny. Identification: 16 bits, gi km trong gi gip ni nhn d dng nhn dng v tp hp gi khi gi. Flag: 3 bits, c xc nh c phn nh gi ra na hay khng Bit 0: d tr t gi tr 0 Bit 1 (DF): 0 = c th phn on; 1 = khng phn on Bit 2 (MF): 0 = phn on ln cui; 1 = phn on tip Fragment offset: 13 bits, xc nh no trong datagram c phn on Fragment offset c tnh bng n v tng 8 octecs (64 bits). Phn on u tin c offset l 0. Time to live: 8 bits, l thi gian tn ti ti a ca gi trong mng, c tnh theo n v giy. Mi ln gi qua mt b nh tuyn gi tr ny gim i 1s ngay c khi thi gian x l gi ny cha ti 1 giy. Khi gi tr ny bng 0, gi b y ra khi mng. Protocols: 8 bits, xc nh giao thc truyn d liu lp k tip (UDP, TCP, ICMP). Header checksum: 16 bits, xc nh tnh hp l ca datagram, c tnh cho header v c s dng bi giao thc lp trn. Source Address: 32 bits, a ch ngun. Destination Address: 32 bits, a ch ch. Options: di bit tu , trng option c th c hoc khng trong datagram v c xc nh bi cc host hoc cc gateway nu c chn la no trong khi truyn cc datagram chng hn gi tr tu chn bo mt.Cc giao thc nh tuynnh tuyn IP (Routing)Thng thng mt h thng mng c cu thnh t vic lin kt nhiu mng ring r vi nhau nn vic phn phi d liu trn mng c phn thnh hai loi l phn phi d liu trc tip v phn phi d liu gin tip.Phn phi d liu trc tip l qu trnh phn phi d liu gia cc host trn cng mt mng.Phn phi d liu gin tip l phn phi d liu gia cc host trn cc mng khc nhau.Khi pht i mt gi bn tin lp mng s quyt nh qu trnh phn phi d liu l gin tip hay trc tip thng qua vic so snh a ch mng c xc nh trong phn ch trn tiu ca gi tin vi a ch ca mng. C hai trng hp xy ra: a ch mng v a ch ca mng trn gi tin ging nhau, qu trnh phn phi d liu trc tip. a ch mng v a ch mng trn gi tin khng ging nhau, qu trnh phn phi d liu gin tip. Cc thit b nh tuyn s quyt nh ng i k tip cho cc gi tin n cc mng khc.Qu trnh phn phi d liu trc tip c thc thi lp 2 trong khi qu trnh phn phi d liu gin tip c thc thi lp 3.Qu trnh phn phi d liu gi l qu trnh nh tuyn c thc thi bi cc giao thc nh tuyn lp mng.Cc giao thc nh tuyn lp mng c th c chia thnh hai loi: Giao thc nh tuyn ni vng : Interior Gateway Protocol (IGP). Cc giao thc nh tuyn thuc nhm IGP bao gm: Routing Information Protocol (RIP). Interior Gateway Routing Protocol (IGRP). Enhanced IGRP. Intermidiate System to Intermidiate System (IS IS). Open Shortest Path First (OSPF). Giao thc nh tuyn lin vng : Exterior Gateway Protocol (EGP). Loi thng dng nht thuc nhm ny l BGP (Border Gateway Protocol).Cc giao thc nh tuynGiao thc RIP (Routing Information Protocol)RIP l mt giao thc nh tuyn c s dng ph bin trong cc mng ni b. RIP l loi giao thc nh tuyn s dng thut ton nh tuyn vector khong cch. Theo phng thc nh tuyn RIP, mi router trn mng s broadcast cc bn tin ca n ln mng sau mi 30s. Bn tin m mi router pht i mang thng tin v bng nh tuyn hin thi ca chng: a ch ch. Khong cch o bng s router m mt gi d liu phi i qua n ch.Cc router cp nht cc bn nh tuyn, tnh ton khong cch v la chn ng dn theo thut ton vector khong cch trnh by trn.Giao thc IGRP (Interior Gateway Routing Protocol) Mc d l mt giao thc nh tuyn n gin nhng RIP cha gii quyt c cc khuyt im ca thut ton vector khong cch. Giao thc IGRP cng l mt giao thc s dng thut ton vector khong cch nhng c ci tin l s dng mt vector metric gm nhiu tham s thay cho s router nh trong RIP.Cc thng s trong vector metric ca IGRP bao gm: Thi gian tr trn ng truyn (Dc). Bng thng khng ti ca ng truyn. chim dng knh ca ng truyn. tin cy ca ng truyn (r). Metric ca mt ng dn c xc nh nh sau:Metric = [(K1/Be)+(K2*Dc)]*r Trong : K1, K2 l hng s ty theo loi hnh dch v. Be = bng thng khng ti * (1 - chim dng knh).nh tuyn Giao thc ICMP (Internet Control Message Protocol) ICMP l giao thc dng kim tra v iu khin cc tin bo cha thng tin v cc tham s cht lng v cc s c xy ra trong mng. Cc gateway v cc host ch dng cc tin bo ICMP bo cho host ngun bit v cc s c xy ra trn mng.Cu trc tin bo ICMP:TypeCodeChecksum

Unused

IP header + IP datagram

Bng 8. Cu trc bn tin ICMPCc loi s c:TypeName of events

0Echo Reply

3Destination

4Unreachable

5Source Quench

8Redirect

11Echo

12Time Exceeded

13Parameter Problem

14Timestamp

15Timestamp Reply

16Information Request

17Address Mask Request

18Address Mask Reply

Bng 9. Cc loi s c m t trong bn tin ICMPGiao thc khi u phin SIP Secsion Initation ProtocolKhi qut v SIP

Giao thc khi to phin (SIP) l mt giao thc bo hiu mi xut hin thc hin iu khin phin cho cc kt ni a dch v. V c bn, hot ng iu khin bao gm khi to, thay i v kt thc mt phin c lin quan n cc phn t a phng tin nh video, thoi, tin nhn, game trc tuynSIP (Session Initiation Protocol) l mt giao thc bo hiu c s dng thit lp cc phin trong mng IP, mt phin c th n gin l mt cuc gi in thoi 2 chiu, mt thng bo danh sch cc tin nhn hoc mt hi ngh s dng truyn thng a chiu

Hnh 10. Giao thc SIP trong m hnh TCP/IP

Hnh 11. Khun dng bn tin SIPCc thnh phn ca SIPGiao thc SIP gm hai thnh phn chnh l: i l trm ngi dng (user agent) My ch mng (Network Server )

Hnh 12. Cu trc ca SIPUser Agent (UA)1.2. 1.3. 1.4. 1.4.1. 1.4.2. User Agent ( UA) l mt h thng cui cng hot ng trn nhn danh ca ngi dng, User Agent phi c kh nng thit lp mt session ca phng tin ny vi cc user agent khc. UA bao gm User Agent Client (UAC) khi to cuc gi v User Agent Server (USA) tr li cuc gi.User Agent (UA) c th l my in thoi SIP hoc my tnh chy phn mm u cui SIP Hnh 13. S User AgentMy ch mng (Network Server) My ch mng bao gm:My ch y quyn (Proxy server): l mt chng trnh trung gian, hot ng nh l mt server v mt client cho mc ch to cc yu cu thay mt cho cc client khc. Cc yu cu c phc v bn trong hoc truyn chng n cc server khc. Mt proxy c th dch v nu cn thit c th to li cc bn tin yu cu SIP trc khi chuyn chng n server khc hoc mt UA. Trong trng hp ny trng Via trong bn tin p ng, yu cu ch ra cc proxy trung gian tham gia vo tin trnh x l yu cu.My ch nh v (Location Server) : l phn mm nh v thu bao, cung cp thng tin v nhng v tr c th ca thu bao b gi cho cc phn mm my ch y quyn v my ch chuyn i a ch.My ch chuyn i a ch (Redirect Server): l phn mm nhn yu cu SIP v chuyn i a ch SIP sang mt s a ch khc v gi li cho u cui. Khng ging nh my ch y quyn, my ch chuyn i a ch khng bao gi hot ng nh mt u cui, tc l khng gi i bt c yu cu no. My ch chuyn i a ch cng khng nhn hoc hu cuc gi.My ch ng k (Register Server): l phn mm nhn cc yu cu ng k,trong nhiu trng hp my ch ng k m nhim lun mt s chc nng an ninh nh xc nhn ngi s dng. Thng thng my ch ng k c ci t cng vi my ch y quyn v my ch hay a ch hoc cung cp dch v nh v thu bao. Mi ln u cui c bt ln ( v d my in thoi hoc phn mm SIP) th u cui li ng k vi my ch. Nu u cui cn thng bo cho my ch v a im ca mnh th bn tin REGISTER cng c gi i. Ni chung cc u cui u thc hin vic ng k li mt cch nh k.nh a ch v t tn mi v nhn din pha b gi phi c t tn. T n l dnh chung nht ca a ch ngi s dng trong internet, SIP chn email nh b nhn din ging cc dng useridomain, userihost, useriIP-address, hoc phone-numberigateway. B phn nhn din c th xem nh tn ca mt my ch m nhi s dng ng nhp vo ti thi im, mt da ch email hoc l dch v chuyn i tn ca mt domain c th no . Cc a ch ca dng phone-numberigateway ch r cc s in thoi GSTN c th tip cn theo cc gateway t tn.Hot ng quan trng nht ca SIP l mi cc thnh vin mi vo mt cuc gi. Mt SIP client u tin thu c cc a ch ni cc thnh vin mi lin lc ti, di dng nameidomain. Client sau d tm cch chuyn i a ch domain ny thnh a ch IP d l ni cc server c th tm thy c. S chuyn i ny c lm bng vic th trong mt dy, cc bn ghi dch v DNS, tn hp quy tc CNAME (conomical Name) v cc bn ghi a ch ci cng. Mi ln a ch IP server tm thy, client gi n thng ip INVITE dng mt trong hai UDP hoc TCP.Server dng nhn thng ip l khng phi server i din ngi s dng ni ngi s dng thc t nm trn n, n c th l proxy server hoc server trung gian.Mt tiu VIA d tm tin trnh ca li mi t server n server, cho php tr li tm ng quay li ca n v gip server d ra cc vng lp. Trong mi trng hp nh vy proxy server v server gim tip bng cch ny hay cch khc phi xc nh server bc nhy tip theo. y l mt chc nng xc nh v tr server. Mt s xc nh v tr server l thc th khi SIP (none-SIP) n c thng tin v cc server bc nhy tip theo cho cc ngi s dng khc nhau. Proxy server c th gi ngiu li mi ti cc server ti mt ln, trong cc bc nhy lin lc vi nhi s dng ti mt trong cc v tr. Chng c th gi li mi n cc nhm a pht p,lin lc mt cch hiu qu n nhiu cc bc nhy tip theo theo mt cch hiu qu nht. Mi ln s dng server i l ngi s dng l c lin lc n kt thc mt cch tr li n client. S tr li c mt m tr li v mt thng ip tr li. m bo tin cy ngay c i vi cc giao thc truyn ti khng ng tin cy, server truyn li tr li cui cng cho n khi client xc nhn bng vic gi yu cu ACK n server.Bn tin ngha

INVITEkhi to mt phin ( bt u thit lp cuc gi bng cch gi bn tin mi u cui khc tham gia)

ACKbn tin ny khng nh my trm nhn c bn tin tr li bn tin INVITE

BYEYu cu kt thc phin

CANCELHu yu cu ang nm trong hng i

REGISTERu cui SIP s dng bn tin ny ng k vi my ch ng k

OPTIONSs dng xc nh nng lc ca my ch

INFOs dng ti cc thng tin nh m bo DTMF

Bng 10. Bng phn loi cc bn tin yu cu ca SIPH.323 v h thng bo hiu trong Voice IPChun H323 c ra i vo thng 5/1996 do ITU-T c t. Chun H.323 cung cp nn tng k thut cho truyn thoi, hnh nh v s liu mt cch ng thi qua cc mng IP, bao gm c Internet. Tun theo chun H.323, cc sn phm v cc ng dng a phng tin t nhiu hng khc nhau c th hot ng cng vi nhau, cho php ngi dng c th thng tin qua li m khng phi quan tm ti vn tng thch.H.323 cng cung cp cc tiu chun v tr cho cc tn hiu m thanh, nh ngha mc u tin trong vic chuyn ti cc tn hiu yu cu thi gian thc trong truyn thng Internet.

Hnh 14. Mi tng quan gia m hnh phn lp OSI v tp cc giao thc s dng trong h thng H.323Chng giao thc H.323H323 bao gm cc chun sau: H.245: khuyn ngh v bo hiu iu khin truyn thng multimedia. H.225.0: ng gi v ng b cc dng thng tin a phng tin (thoi, truyn hnh, s liu). Khuyn ngh ny bao gm giao thc RTP/RTCP v cc th tc iu khin cuc gi Q.931 (DSS 1). Cc chun nn tn hiu thoi: G.711 (PCM 64 kbps), G.722, G.723, G.728, G.729. Cc chun nn tn hiu video: H.261, H.263 T.120: Cc chun cho cc ng dng chia s s liu.

Hnh 15. Chng giao thc H.323Cc thnh phn trong h thng H.323H thng H.323 bao gm cc thnh phn: Thit b u cui H.323 (H.323 Terminal): L mt trm cui trong mng LAN, m nhn vic cung cp truyn thng hai chiu theo thi gian thc. H.323 Gateway: Cung cp kh nng truyn thng gia h thng H.323 v cc h thng chuyn mch knh khc (PSTN/ISDN). Gatekeeper: L mt thnh phn khng bt buc. N thc hin cc chc nng qun l hot ng ca h thng. Khi c mt gatekeeper trong h thng, mi thnh phn trong h thng phi thc hin th tc ng k vi gatekeeper. Tt c cc im cui H.323 (terminal, gateway, MCU) ng k vi gatekeeper to thnh mt vng H.323 (H.323 zone) do gatekeeper qun l. n v iu khin lin kt a im (MCU - Multipoint Control Unit): Thc hin chc nng to kt ni a im h tr cc ng dng truyn thng nhiu bn. Thnh phn ny cng l tu chn.

Hnh 16. Cu trc h thng H.323Thit b u cui H.323Cc thnh phn chc nng ca mt thit b u cui H.323 c miu t nh hnh v di y: Cc phn giao tip vi ngi s dng. Cc b codec (Audio v video). Phn trao i d liu t xa (telematic). Lp (layer) ng gi (chun H.225.0 cho vic ng gi multimedia). Phn chc nng iu khin h thng V giao din giao tip vi mng LAN.H.323 gatewayGateway mang cc tnh nng phc v cho hot ng tng tc ca cc thit b trong h thng vi cc thit b trong mng chuyn mch knh nh PSTN, ISDN,... H.323 gateway c t gia cc thnh phn trong h thng H.323 vi cc thit b nm trong cc h thng khc (cc mng chuyn mch knh SCN). N phi cung cp tnh nng chuyn i khun dng d liu truyn v chuyn i th tc mt cch thch hp gia mng LAN cc loi mng m gateway kt ni ti, l: Thc hin chuyn i khun dng d liu thoi, video, s liu nu cn. Thc hin chc nng thit lp cuc gi, hu cuc gi i vi c hai pha mng LAN v mng chuyn mch knh (SCN - Switched Circuit Network). Nhn chung, thit b cng c nhim v phn nh c tnh ca mt im cui H.323 trong mng LAN ti mt thit b cui trong mng chuyn mch knh v ngc li nhm to ra tnh trong sut i vi ngi s dng. Cc gateway c th lin kt vi nhau thng qua mng chuyn mch knh cung cp kh nng truyn thng gia cc thit b u cui H.323 khng nm trong cng mt mng LAN. Cu trc ca Gateway bao gm: Khi chc nng ca thit b H.323, khi chc nng ny c th l chc nng u cui ( giao tip vi mt terminal trong h thng H.323) hoc chc nng MCU ( giao tip vi nhiu terminal). Khi chc nng ca thit b chuyn mch knh, mang chc nng giao tip vi mt hay nhiu thit b u cui trong mng chuyn mch knh.Khi chc nng chuyn i, bao gm chuyn i khun dng d liu v chuyn i th tc.GatekeeperGatekeeper cung cp cc dch v iu khin cuc gi cho cc im cui trong h thng H.323. Gatekeeper l tch bit vi cc thit b khc trong h thng v mt logic, tuy nhin trong thc t th n c th c tch hp vi cc thit b khc nh gateway, MCU...Khi c mt trong h thng, gatekeeper phi cung cp cc chc nng sau: Dch a ch: Dch t a ch alias hoc mt s in thoi o ca mt im cui sang a ch IP tng ng. iu khin kt np: iu khin vic cho php hot ng ca cc im cui. iu khin bng thng: iu khin cp hoc t chi cp mt phn bng thng cho cc cuc gi ca cc thit b trong h thng. Qun l vng: Thc hin cc chc nng trn vi cc im cui H.323 ng k vi gatekeeper (mt vng H.323).Ngoi ra, GateKeeper c th cung cp cc chc nng nh bo hiu iu khin cuc gi, iu khin cho php cuc gi, qun l bng thng, qun l cuc gi, tnh cc.n v iu khin lin kt a im MCUMCU h tr vic thc hin cc cuc m thoi hi ngh gia nhiu thit b u cui. Trong chun H.323, MCU bt buc phi c mt b iu khin a im MC (Multipoint Controller) v MP (Multipoint Processor).MC iu khin vic lin kt gia nhiu im cui trong h thng bao gm: X l vic m phn gia cc thit b u cui quyt nh mt kh nng x l dng d liu media chung gia cc thit b u cui. Quyt nh dng d liu no s l dng d liu multicast. MC khng x l trc tip mt dng d liu media no. Vic x l cc dng d liu s do cc MP m nhim. MP s thc hin vic trn, chuyn mch, x l cho tng dng d liu thi gian thc trong cuc hi ngh. Vic truyn thng tin trong mng IP tn ti di ba hnh thc: Unicast, multicast v broadcast. Trong h thng H.323 cuc hi ngh nhiu bn c th c ba loi cu hnh hi ngh sau: Cu hnh tp trung (Centralized Multipoint Conference). Cu hnh phn tn (Decentralized Multipoint Conference). Cu hnh lai (Hybrid Multipoint Conferrence).Cc bc thc hin cuc giThit lp cuc giVic thit lp cuc gi s dng cc bn tin c nh ngha trong khuyn ngh H.225.0. C th xy ra 6 trng hp, l : Cuc gi c bn - C hai thit b u cui u khng ng k. C hai thu bao u ng k ti mt Gatekeeper. Ch c thu bao ch gi c ng k vi Gatekeeper. Ch c thu bao b gi c ng k vi Gatekeeper. Hai thu bao ng k vi hai Gatekeeper khc nhau. Thit lp cuc gi qua Gateway.Thit lp knh iu khinKhi kt thc giai on 1 tc l c ch gi ln b gi hon thnh vic trao i cc bn tin thit lp cuc gi, th cc u cui s thit lp knh iu khin H.245. Bn tin u tin c trao i gia cc u cui l terminalCapabilitySet cc bn thng bo cho nhau kh nng lm vic ca mnh. Mi mt thit b u cui u c c tnh ring ni ln kh nng ch m ho, truyn, nhn v gii m cc tn hiu a dch v. Knh iu khin ny c th do thu bao b gi thit lp sau khi n nhn c bn tin Set-up hoc do thu bao ch gi thit lp khi n nhn c bn tin Alerting hoc Call Proceeding. Trong trng hp khng nhn c bn tin Connect hoc mt u cui gi Release Complete, th knh iu khin H.245 s c gii phng. Thit lp knh truyn thngSau khi trao i kh nng (tc nhn ti a, phng thc m ho..) v xc nh quan h master-slave trong giao tip giai on 2, th tc iu khin knh H.245 s thc hin vic m knh logic truyn s liu. Cc knh ny l knh H.225. Sau khi m knh logic truyn tn hiu l m thanh v hnh nh th mi u cui truyn tn hiu s truyn i mt bn tin h2250 Maximum Skew Indication xc nh thng s truyn.Dch v cuc giC mt s dch v cuc gi c thc hin trn mng H.323 nh: thay i rng bng tn, gim st trng thi hot ng, hi ngh c bit, cc dch v b sung. Kt thc cuc giMt thit b u cui c th kt thc cuc gi theo cc bc ca th tc sau: Dng truyn lung tn hiu video khi kt thc truyn mt nh, sau gii phng tt c cc knh logic phc v truyn video. Dng truyn d liu v ng tt c cc knh logic dng truyn d liu. Dng truyn audio sau ng tt c cc knh logic dng truyn audio. Truyn bn tin H.245 endSessionCommand trn knh iu khin H.245 bo cho thu bao u kia bit n mun kt thc cuc gi. Sau n dng truyn cc bn tin H.245 v ng knh iu khin H.245. N s ch nhn bn tin endSessionCommand t thu bao u kia v s ng knh iu khin H.245 Nu knh bo hiu cuc gi ang m, th n s truyn i bn tin Release Complete sau ng knh bo hiu.N cng c th kt thc cuc gi theo cc th tc sau y: Mt u cui nhn bn tin endSessionCommand m trc n khng truyn i bn tin ny, th n s ln lt thc hin cc bc t 1 n 6 trn ch b qua bc 5. Trong mt cuc gi khng c s tham gia ca Gatekeeper th ch cn thc hin cc bc t 1 n 6. Trong cuc gi c s tham gia ca Gatekeeper th cn c hot ng gii phng bng tn. Th tc ny c th hin trn hnh v. V vy sau khi thc hin cc bc t 1 n 6, mi u cui s truyn i bn tin DRQ (3) ti Gatekeeper. Sau , Gatekeeper s tr li bng bn tin DCF (4). Sau khi gi DRQ, u cui s khng gi bn tin IRR ti Gatekeeper na v khi cuc gi kt thc. Th tc kt thc cuc gi do Gatekeeper thc hin c th hin hnh di. u tin, Gatekeeper gi bn tin DRQ ti u cui. Khi nhn c bn tin ny, u cui s ln lt thc hin cc bc t 1 n 6, sau tr li Gatekeeper bng bn tin DCF. Thu bao u kia khi nhn c bn tin endSessionCommand s thc hin th tc gii phng cuc gi ging trng hp u cui ch ng kt thc cuc gi ( trn). Nu cuc gi l mt hi ngh th Gatekeeper s gi DRQ ti tt c cc u cui tham gia hi ngh.

THIT K V XY DNG NG DNGM t ng dngYu cu phi xy dng c ng dng hi thoi Voice IP trong mng Lan theo kiu kt ni PC to PC bng ngn ng lp trnh Java trn Eclipse.ng dng truyn thoi Voice IP qua mng LAN c xy dng nhm mc ch thit lp mt h thng truyn thoi ni b ti cc c quan, tn dng cc kt ni sn c gia cc u cui PC. Thay v phi xy dng h thng chuyn mch knh nh i vi cc tng i in t hay tng i s thc thi cc tin trnh kt ni thc hin cuc gi, thoi c th c truyn ti qua cc ng kt ni Ethernet vi tc 10Mbit/s cng vi cc thng tin d liu trn mng LAN.Trong m hnh truyn thoi PC to PC, qu trnh m thoi c thc hin ngay trn cc u cui PC c trang b micro v loa. Micro thc hin chc nng chuyn i tn hiu m thanh sang dng tn hiu in a vo soundcard cn loa l thit b pht thanh.Phn tch chc nngYu cu chc nng Chc nng Talk ni chuyn gia cc Client Chc nng chat gia cc Client Chc nng connect kt ni vi Server Chc nng Hands Free - loa ngoiYu cu phi chc nng Giao din ging vi giao din chung cc phn mm Chatvoice ph bin nh Skype, Yahoo Cc chc nng ph cn thit nh exit, trng thi chat m thanh khi truyn t vng v nhiu.Cu trc chng trnhCu trc m ngun xy dng chng trnh gm 7 lp:Lp ChatServer public class ChatServer extends Thread{ }Chc nng: Thit lp mt my ch qun l vo ra ca cc Client Dng kt ni cc ClientLp ChatHandlerpublic class ChatHandler extends Thread {}Chc nng: Cc lung my ch c nhnLp ChatClientpublic class ChatClient extends JFrame implements Runnable, ActionListener {}Chc nng: ng dng ChatvoiceLp CommonSoundClasspublic class CommonSoundClass {}Chc nng: Queue dng cho nhng th khcLp Queuepublic class Queue {}Chc nng: Queue dng chi li m thanhLp Playbackpublic class Playback implements Runnable {}Chc nng: Chi m thanhLp Recoderpublic class Recorder extends Thread {}\Chc nng: Ghi m thanhThit k giao din ng dngGiao din ClientChat Voice-IPExitIP AddressPortConnectMn hnh chatUserInput TextTalkStatus

Hnh 17. M phng giao din ClientGiao din Server

Hnh 18. M hnh giao din Server

Thot Server khi ng

TRIN KHAI V NH GI KT QUMi trng trin khaiPhn cng My tnh: Tng thch Intel Pentium IV 3.0 GHz hoc cao hn B nh: 512MB RAM tr ln a cng: 100MB a trng hoc nhiu hn Mn hnh: SVGA video, phn gii 1024x768 hoc tt hn. Co kt ni mang Lan/InternetPhn mm H iu hnh: Windows 2000/XP/2003/Vista/Window 7/Window 8 B g ting Vit: Unikey (Unicode) May ao Java jdk1.6.u24Kt qu demo ca chng trnh

Hnh 19. Kt qu khi khi ng Client

Hnh 20. Kt qu chy khi khng kt ni c vi Server

Hnh 21. Kt qu khi kt ni vi Server thnh cng

Hnh 22. Kt qu sau khi user: nguyenvanphuc vo phng

Hnh 23. Kt qu chy khi thot Server

Hnh 24. Kt qu sau khi user: nguyenhuuthien vo phng

Hnh 25. Kt qu demo khi thc hin chc nng chat gia user: nguyenvanphuc v user: nguyenhuuthien

Hnh 26. Kt qu demo khi thc hin chc nng Talk gia user: nguyenvanphuc v user: nguyenhuuthien

Hnh 27. Kt qu khi chy Server

nh gi v nhn xtKt qu lm c xy dng c c bn mt chng trnh chatvoice theo yu cu ti Xy dng thm chc nng chat vn bn trong ng dng Chng trnh t c yu cu truyn thoi m thanh bng cng ngh Voice IP, t c th hiu r c c ch truyn thoi trn nn IP, mt cng ngh ang rt c quan tm hin nay.Hn ch Giao din ca ng dng cn nhiu hn ch, kh khan, tnh thm m cha cao. Chc nng th hin trng thi status ca ngi dng cha c xy dng thnh cng. Do thi gian v kin thc v cng ngh cn thiu st nn cha p dng c cc b giao thc nh H.323, SIP vo ng dng.Hng pht trin Tm hiu k hn cng ngh truyn thoi Voice IP v ngn ng lp trnh Java Tip tc hon thin cc chc nng khc ca mt ng dng chatvocieVic xy dng mt ng dng hi thoi trc tuyn vi cng ngh Voice IP i hi thi gian, kin thc phi y v cng ngh mi c th xy dng thnh cng c ng dng. chng trnh c th p dng vo thc t cn c i ng chuyn mn mi thnh cng c.

TI LIU THAM KHO[1] Tham kho cc ti liu v Voice IP trn Internet[2] n tt nghip Cng ngh Voice IP H dn lp Hi Phng[3] M ngun chatvoice http://www.planet-source-code.com/vb/scripts/ShowCode.aspGVHD: THS. MAI VN HPage 2

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SDP

Media coding

SIP

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DHCP

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802.11

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