CHNG 1GII THIU CHUNG V VoIP

VoIP c xem nh l cng ngh truyn thoi qua mi trng mng da trn giao thc IP. Tuy nhin, nu hiu theo ngha rng th mng VoIP khng ch h tr truyn thoi m cn cho php cung cp cc dnh v khc nh video v d liu. Chng ny gii thiu khi qut v s pht trin ca cng ngh truyn thoi qua mng IP, cc u nhc im ca VoIP, cc loi hnh dch v cng nh m hnh trin khai dch v VoIP cho khch hng u cui v doanh nghip.Ni dung chng bao gm: S ra i v pht trin ca VoIP. u nhc im ca VoIP so vi in thoi thng thng. Cc loi hnh dch v VoIP. Cc m hnh trin khai dch v VoIP.THOI QUA GIAO THC INTERNET

Advanced Network Applications

16

Nhm hc vin K29: Nguyn Quang Phng Nguyn Khnh Bo V Hong

Nhm hc vin K29: Nguyn Quang Phng Nguyn Khnh Bo V Hong 14

1.1 S RA I V PHT TRIN CA VoIPNm 1995 hng Vocaltec thc hin truyn thoi qua Internet. Lc , phc v kt ni ch cn my tnh c nhn PC vi cc thit b ngoi vi thng thng nh card m thanh, tai nghe (headphone), micro, ng dy in thoi, modem, ... Phn mm thc hin nn tn hiu thoi v chuyn i thng tin thnh cc gi tin IP truyn dn qua mi trng Internet. C th ni chnh l mc nh du s ra i ca mt loi hnh dch v vin thng mi: thoi qua IP hay VoIP.Chng ta c th nhn nhn VoIP nh l kh nng thit lp cc cuc gi in thoi qua mng d liu IP vi cht lng dch v thch hp v cc ph thp. Tai u pht, tin hiu thoai c ma hoa, sau o thay vi truyn trn mang PSTN qua cac tng i chuyn mach knh, chung c nen xung tc thp, ong goi va truyn trn mang IP. Tai u thu, cac goi tin nay c giai nen, gii m khi phc li tin hiu thoai ban u. S khac nhau chinh gia VoIP v in thoi truyn thng la mang truyn dn va khun dang thng tin dung truyn dn. Mc d cht lng ca in thoi IP ban u cha c tt nhng chi ph thp hn nhiu so vi in thoi truyn thng tr thnh yu t cnh tranh gip n tn ti. Hin nay, cht lng cc cuc gi thoi qua mng IP ang ngy mt tng ln, v VoIP tr thnh mt trong nhng bc tin quan trng hi t cc cng ngh truyn thng d liu, video v ting ni. S thnh cng ca vic truyn m thanh v nhng bn tin bo hiu cuc gi qua Internet c kim nghim, nhng vic phn chia nhng sn phm thng mi cht lng cao, thit lp nhng dch v cng cng, thuyt phc ngi dng s dng sn phm th cn cn phi c trin khai rng ri hn.S thnh cng ca VoIP mang li mt c hi ln cho cc nh sn xut thit b v cung cp dch v vin thng. Tuy nhin, vic thc thi VoIP trn thc t cn ph thuc vo rt nhiu yu t khc nhau nh cng ngh, c s h tng, phn mm, h thng qun l, v.v. Do c im ca mng gi l tn dng ti a vic s dng bng thng m t quan tm ti thi gian tr lan truyn v x l trn mng, trong khi tn hiu thoi li l dng thi gian thc, cho nn ngi ta phi b sung vo mng nhng phn t mi v thit k cc giao thc ph hp c th m bo cht lng dch v cho ngi dng. S ra i v pht trin nhanh ca VoIP l ng lc cc t chc chun ho lin quan nh ITU-T hay IETF hon thin cc chun ca mnh. C rt nhiu chun h tr VoIP nh H.225, H.245 (cho qun l); H.261, H.263 (cho m ho video); G.711, G.723, G.729 (cho m ho thoi). bo hiu c hai chun c bn l H.323 ca ITU-T v SIP ca IETF. 1.2 U NHC IM CA VoIP SO VI IN THOI THNG THNGCc u imin thoi IP ra i nhm khai thc tnh hiu qu ca cc mng truyn s liu v tnh linh hot trong vic pht trin cc ng dng mi ca giao thc IP v lm cho kh nng cc dch v c cung cp trn mt mng thng nht ton cu tr thnh hin thc. VoIP c cc u im chnh so vi thoi truyn thng nh sau: Gim cc dch v in thoi ng di; Cho php thc hin nhiu cuc gi hn, gim rng bng thng cho mi kt ni; H tr thm nhiu dch v b sung khc v gip trin khai cc dch v mi nhanh chng, d dng v t ng; S dng hiu qu nht nhng u th ca giao thc IP l tnh mm do v d dng tng thch;u im ni bt ca dch v VoIP i vi khch hng l gi cc r hn nhiu so vi thoi truyn thng do cc cuc gi VoIP s dng lng bng thng rt t. Trong khi thoi truyn thng s dng k thut s ho PCM theo chun G.711 vi lng bng thng c nh cho mt knh thoi l 64 kb/s th VoIP s dng kiu m ho ngun nh CS-CELP theo chun G.729 yu cu tc 8 kb/s, hay G.723 ch yu cu 6.3 kb/s hoc 5.3 kb/s. Nh vy, r rng l lng bng thng s dng gim c mt cch ng k. Ngoi ra, do VoIP s dng c ch trit khong lng nn c th tit kim thm lng bng thng khong lng ny truyn cc dng thng tin khc. l mt u im ln ca VoIP so vi in thoi chuyn mch knh truyn thng. Thng thng, bng thng truyn dn cn thit cho mt cuc gi PSTN c th s dng cho 4 n 6, thm ch 8 cuc gi VoIP.Nu chi ph cho cuc gi theo tng pht ta s thy lng tin tit kim c qu l khng nh. Tuy nhin, vic tit kim chi ph cn tu thuc vo vng a l v khong cch. i vi cc cuc gi ni ht th vic tit kim ny c v khng quan trng, nhng i vi cc cuc gi ng di, nht l cuc gi quc t th n tht s l ng k. iu ny c th hin gi cc m cc nh cung cp dch v a ra, thng thng gim cn 1/10 i vi cc cuc gi quc t.u im tip theo l kh nng qun l bng thng. Trong mng in thoi s dng cng ngh chuyn mch knh, ti nguyn bng thng cung cp cho mt cuc gi l c nh. Trong mng IP ti nguyn cung cp cho mt cuc gi mm do v linh hot hn nhiu. Khi ngi s dng cn ti nguyn thc hin mt cuc gi, nu lu lng ca mng thp, bng thng dnh cho cuc gi s cho cht lng tt nht. Vo thi gian cao im, mng s hn ch bng thng ca tng cuc gi mc chp nhn c nhm phc v cng mt lc nhiu ngi nht.u im na ca VoIP l kh nng d dng kt hp cc loi dch v thoi, d liu v video. Thoi v fax ch l cc ng dng khi u cho VoIP, cc ng dng mong i trong tng lai l a phng tin v a dch v. Trong khi tin hnh m thoi, ngi s dng c th va ni chuyn va s dng cc dch v khc nh truyn file, chia s d liu hay xem hnh nh ca ngi bn kia.Mng Internet ang bng n trn ton th gii v ngy cng c nhiu ng dng c pht trin trn nn giao thc IP. Vic trin khai VoIP khng i hi nng cp c s h tng mng mt cch phc tp, cc thit b b sung tng i r v vic ci t, bo dng cng n gin. a s cc hng vin thng ln trn th gii nh Cisco, Juniper, Alcatel, Siemens, u cung cp cc gii php c phn cng v phn mm h tr cho VoIP. Cc gii php ny c th tng thch vi hu ht cc chun giao thc hin nay.Cc nhc imBn cnh cc u im, VoIP cng c nhng nhc im c trng ca thoi gi nh:Giao thc IP l khng tin cy v khng h tr QoS;Thi gian tr truyn trn mng c th vt qu gii hn cho php lm nh hng n cht lng thoi; tr khng ng nht gia cc gi tin gy ra hin tng Jitter (bin ng tr);Nhc im c bn ca VoIP so vi thoi truyn thng l cht lng dch v. Nguyn nhn chnh gy ra hn ch v cht lng dch v l do mng IP hot ng theo nguyn tc c gng ti a v khng tin cy, tc l n khng m bo cht lng dch v cho cc ng dng. Mc phc tp ca mng cng nh cht lng cc kt ni mng cng l yu t lm gim cht lng dch v. Mt yu t na cng nh hng ti cht lng dch v VoIP l do n phi chia ng truyn cng lc vi nhiu dch v khc trn mng m khng c mt c trng ring bit no cc b nh tuyn c th nhn bit v x l u tin hn. Tuy trong phn tiu ca gi IP cng c cc trng ch mc u tin, cc yu cu v tr, s lng, an ton nhng do vn cn c s khng thng nht gia cc nh cung cp dch v v mt s vn nn IP h tr mc u tin khng ng nht v khng c giao thc nh tuyn tham s dch v. Cng nh cc giao thc truyn s liu khc, thit k ban u ca giao thc IP khng phi truyn cc thng tin thi gian thc. Vic truyn tn hiu thi gian thc trn mng chuyn mch gi mt cch lin tc vi tc khng i l rt kh thc hin do cc hin tng nh mt gi hay tr khng c nh. K thut truyn li cc gi b mt hay b li l khng c ngha i vi cc dch v thi gian thc. Tt c cc ISP u c gng ti thiu ha thi gian truyn gi theo kh nng ca mnh m khng quan tm n nng lc ca cc ISP khc. V vy, nu cc im cui ca cuc gi VoIP c phc v bi cc ISP khc nhau th rt c th xy ra hin tng tr chiu i v chiu v l khc nhau, hay khng i xng. Ngoi ra, c ch nh tuyn ca IP c th gy ra cc vng nh tuyn dn n thi gian tr qu ln i vi mt cuc gi thoi, v gi tin mc d n ni nhng cng khng cn ngha na. cho cht lng dch v chp nhn c, cn phi c mt k thut nn tn hiu vi t s nn ln, kh nng ti to cc gi b tht lc, v c ch b m nhn cc gi pha thu gii quyt vn tr ni tip ca cc gi trong qu trnh truyn lan. Tc x l ca cc b m ha/gii m phi nhanh cuc gi khng b gin on. ng thi c s h tng mng cng phi c nng cp ln cc cng ngh mi v phi c c ch kim sot cht lng dch v.1.3 CC LOI HNH DCH V VoIPSau y la nhng dich vu ma thoai IP co kha nng cung cp. Thoi thng minhH thng in thoi ngy cng tr nn hu hiu do gi r, ph bin, d s dng v c ng, nhng n ch c mt s phm iu khin. Trong nhng nm gn y, ngi ta c gng to ra thoi thng minh, song mi c gng u tht bi do nhng tn ti ca cc h thng c sn. K t khi Internet ph khp ton cu, n c s dng tng thm tnh thng minh cho mng in thoi. Gia mng my tnh v mng in thoi c 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 WebWorld Wide Web to ra mt cuc cch mng trong giao dch vi khch hng ca cc doanh nghip. in thoi Web hay "click to dial" cho php cc nh doanh nghip c th a cc phm bm ln trang web kt ni ti h thng in thoi ca h. Dch v bm s l cch d dng v an ton nht a thm cc knh trc tip t trang Web vo h thng in thoi. Truy nhp cc trung tm tr li in thoiKh nng truy nhp n cc trung tm phc v khch hng qua mng Internet l ng lc thc y mnh m thng mi in t. Dch v ny s cho php khch hng c cu hi v mt sn phm no nhn c cu tr li trc tuyn t cc nhn vin ca cng ty mt cch tc th. Dch v fax qua IPNu bn gi nhiu fax t PC, c bit l gi ra nc ngoi th vic s dng dch v fax qua Internet s gip bn tit kim c tin, cn nh khai thc th tit kim c knh thoi. Dch v ny s chuyn bn fax trc tip t PC ca bn qua kt ni Internet thay vi qua mang PSTN. Dich vu tinh cc cho thu bao bi goiThoai qua Internet giup cac nha khai thac co kha nng cung cp dich vu tinh cc cho thu bao bi goi i vi khach hang nc ngoai cung nh khach hang trong nc. 1.4 CC M HNH TRIN KHAI DCH V VOIPHin nay, vic trin khai cc dch v VoIP khng cn l thch thc kh khn nh nhng nm trc. VoIP c th c thc hin trn c s mng phng, gm cc my ch, thit b nh tuyn, my tnh c nhn hay in thoi IP; hoc trn c s mng phn cp, bao gm cc chuyn mch PSTN, my ch iu khin, Gateway, h thng bo hiu, in thoi IP/POTS/PC. Phn ny gii thiu cc m hnh trin khai VoIP, bao gm c kt ni vi mng PSTN v mng truyn thng my tnh, cc kch bn cung cp dch v VoIP cho khch hng c nhn v doanh nghip. VoIP cho khch hng l ngi dng u cuiTrong mng truyn thng PSTN, cc thnh phn mng c t chc theo m hnh phn cp. Vic ci t VoIP khng hp l s ph hy ton b h thng chuyn mch sn c. Do vy, cn phi ngh n gii php phn tn cc chc nng kim sot cuc gi, dch v v truyn thng tin. Nhng dch v lu trong cc tng i c th c chuyn sang nhng my ch v s c cung cp ti ngi s dng vi gi r.Hnh 1.1 m t s thc hin truyn thoi qua mng IP i vi dch v ng di trong nc. Ti y, truy nhp mng t thit b u cui vn c cung cp bi cc tng i kt ni vi thu bao, nhng s truyn tn hiu thoi c gii quyt bi mng IP. Cu trc ny yu cu cc cng VoIP (Gateway) bin i khun dng tn hiu TDM thnh cc gi tin IP ti u vo v ngc li u ra.

Hnh 1.1 Cu hnh mng h tr VoIP ng dii vi dch v VoIP quc t, cu trc tng t c th c m rng s dng. Khi cc cng VoIP v u cui c t ti nhng quc gia khc nhau. Lu rng mi quc gia c th pht trin v s dng cc loi m ho, c ch nn, ... khc nhau. Nhng chi tit ny cn c xem xt cn thn khi thit k mng.VoIP cho khch hng doanh nghipCc doanh nghip hay t chc thng c mt s mng truyn thng d liu phc v cho cng vic kinh doanh hay hot ng ca mnh. Nhng mng ny c th s dng cc cng ngh X.25, Frame Relay hay ATM. Tuy nhin, gn y hu ht cc mng doanh nghip u c xu hng chuyn sang s dng cng ngh da trn IP, v c cc ng truyn kt ni vi mng Internet. Mt khc, cc doanh nghip vn phi trang b tng i PBX cho cc dch v thoi truyn thng, v h s dng kt ni vt l T1/E1 n cc nh cung cp dch v PSTN. Nh vy, trong mi doanh nghip tn ti hai h thng mng ring bit, kt ni vi hai nh cung cp dch v khc nhau. M hnh phn chia thnh mng thoi v mng s liu ring c ch ra trn hnh 1.2. i vi m hnh ny cn s dng hai hnh thc qun tr mng khc nhau. ng thi, mi cng vic lin quan n ng k s dng dch v hay thanh ton chi ph kt ni cng cn thc hin ring nn gy nhiu bt tin cho doanh nghip.

Hnh 1.2 Mng doanh nghip truyn thngGii php ti u khc phc nhng hn ch v bt tin ca m hnh mng doanh nghip truyn thng l s dng cng ngh gi cho c hai loi hnh dch v thoi v s liu. Trong mt mi trng tch hp, khi VoIP c trin khai, th kt ni T1/E1 hoc DSL ti mng ca nh cung cp dch v c th c s dng cho c truyn d liu v ting ni. Kin trc mng tch hp nh vy c m t trn hnh 1.3. Khi , doanh nghip ch cn kt ni vi mt nh cung cp dch v, s dng mt phng thc thanh ton. Vic qun tr mng cng tr nn n gin hn do giao thc x l l thun nht v cc thit b tng thch vi nhau d dng.

Hnh 1.3 Mng doanh nghip tch hpVic trin khai VoIP c th nhiu mc . m bo truyn thng trong ton phm vi logic ca doanh nghip hay t chc, VoIP c th thc hin trong mt to nh, c khu nh hay thm ch c trong v ngoi nc. i vi cc vn phng nh, ch cn ng dy in thoi cht lng tt hay cp truyn hnh l . VoIP s dng trn ng dy thu bao s (DSL) hay cp ng trc c th d dng p ng nhng yu cu dch v v k thut cho vn phng nh v gia nh (SOHO). iu ny m ra c hi kinh doanh mi cho c cc nh cung cp dch v truyn hnh cp v vin thng.Mt kch bn cho h thng mng ca doanh nghip s dng c IP v nhng cng ngh DSL khc cho truyn thng thoi, d liu v hnh nh c ch ra trn hnh 1.4.

Hnh 1.4 Mng doanh nghip s dng DSL v IP h tr truyn thng i vi cc doanh nghip ln c mng li vn phng, chi nhnh khp c nc v doanh nghip c cc vn phng trn th gii, vic trin khai VoIP cng thch hp hn bi v trong nhng cng ty thng tn ti cc mng IP rng ln. Dch v VoIP thm vo cc mng nh vy ch yu cu u t thm khng nhiu v c kh nng tit kim ng k chi ph cho vic thu ng dy in thoi truyn thng. Nh vy, c th thy vic thc thi VoIP t c mc thnh thc, cho php chuyn dch d dng t m hnh th nghim mu n trin khai trn c mng ngi dng v mng doanh nghip. 1.5 KT CHNGMng in thoi chuyn mch knh truyn thng bc l r nhc im l s dng lng ph ngun ti nguyn bng thng c coi l v gi. Cng vi s ph bin ngy cng rng ri ca cc mng trn nn IP, cng ngh VoIP ra i gii quyt c bi ton v hiu sut s dng bng thng, ng thi vn m bo cht lng m thoi. Thay v s dng mt knh logic c nh mang thng tin thoi th VoIP ct chng thnh cc gi tin v chuyn qua mng IP, nh vy bng thng ca knh logic c chia s vi cc dng d liu khc, v gi thnh chi ph cho mt cuc gi s nh hn nhiu so vi in thoi truyn thng. Chng ny gii thiu nhng nt khi qut v s ra i v pht trin ca cng ngh VoIP, cc u nhc im ca VoIP so vi in thoi truyn thng, cc loi hnh dch v VoIP cng nh l cc m hnh trin khai dch v VoIP cho khch hng u cui v doanh nghip. C th ni, cuc cch mng v truyn thng, my tnh v Internet thay i cch sng v lm vic ca con ngi. Cng ngh VoIP ang dn chim lnh th trng v thm nhp vo mi ni, t khu vc gia nh, cc vn phng nh cho n cc cng ty ln a quc gia. Rt nhiu t chc quc t ang tch cc lm vic tin ti vic chun ha cc giao din, giao thc v cng ngh nhm h tr cho vic trin khai rng ri VoIP. V d v cc t chc ny nh din n chuyn mch mm quc t ISC, cc nhm SIGTRAN, PINT, SPIRITS trong IETF, SG11 trong ITU-T, ... Nhiu website cng cp nhp thng xuyn cc thng tin mi nht v s pht trin ca in thoi IP nh trang web ca IP-Tel (www.iptel.org).

CHNG 2CC GIAO THC S DNG TRONG VoIP

Trong chng trc trnh by v cc k thut h tr cho VoIP. Ni dung ca chng ny s gii thiu v cc giao thc s dng trong mng VoIP. Khi qut v mt s giao thc c bn, vi cch tip cn l tp trung vo nhng kha cnh lin quan n vn h tr thc thi VoIP trn mng.Ni dung chng bao gm: Tng quan v cc giao thc h tr truyn thoi qua mng IP. H thng VoIP da trn H.323. H thng VoIP da trn SIP. H thng VoIP s dng bo hiu lai ghp. ENUM v vn nh s trong VoIP.

Chng trnh bi dng kin thc IP v NGN cho k s TVT ca VNPT

36 Nhm hc vin K29: Nguyn Quang Phng Nguyn Khnh Bo V HongTNG QUAN V CC GIAO THC H TR TRUYN THOI QUA MNG IP0. Cc loi giao thc s dng trong VoIPGiao thc trc tin cn nhc n hin nhin phi l IP. Chun IETF v IPv4 c m t trong RFC 791. IP h tr c hai phng thc truyn dn gi tin cy v khng tin cy. Mc d IPv4 l phin bn c s dng rng ri trn ton th gii, IETF pht trin phin bn tip theo l IPv6 (RFC 1883). Ngi ta mong i IPv6 s gii quyt tt hn vn bo mt, nhn thc cng nh l khc phc c gii hn khng gian a ch ca IPv4. Nhm giao thc th hai l cc giao thc lp vn chuyn TCP v UDP. TCP (RFC 793) s dng c ch ca s iu khin lung v c ch bo nhn t c tnh tin cy cho vic truyn tin. UDP (RFC 768) l giao thc vn chuyn khng tin cy. Khng c c ch phn hi cho vic truyn tin trong UDP.TCP c th s dng cho bo hiu, tha thun tham s, thit lp ng truyn, iu khin kt ni thi gian thc nh VoIP. V d, cc giao thc H.225, H.245 ca ITU-T v DNS ca IETF s dng TCP lm giao thc vn chuyn. UDP c th thch hp cho vic truyn lu lng t cc ngun to thng tin thi gian thc. V d, H.225, DNS, RTP v RTCP u c th s dng UDP lm giao thc vn chuyn.Nhm th ba l cc giao thc h tr vic truyn ti cc gi tin theo thi gian thc RTP/RTCP. Chun H.323 ca ITU-T s dng RTP cho truyn phng tin hoc lu lng mang t pha gi n pha nghe v ngc li trn mt kt ni. RTP l giao thc tng ng dng cho lin lc t u cui n u cui v khng m bo v QoS truyn dn. Giao thc RTCP c th s dng cng vi RTP ch nh ngi dng trong mt phin giao dch. RTCP cng cho php cc bo co (report) ca u thu, u gi v m t ngun c gi trong cng mt gi. Bo co pha u thu cha thng tin v cht lng thng tin nhn c pha u gi c th thay i mt cch thch ng tc truyn dn hay s m ha trong sut phin giao dch. iu ny cho php gim c xc sut nghn lu lng lp phin trong mng.Nhm th t l cc giao thc v chun h tr cho vic iu khin v bo hiu VoIP. Cc giao thc bo hiu v iu khin chnh s dng trong mng VoIP l H.323, SIP, SIGTRAN, MGCP, H.248/Megaco, BICC, ... Cc giao thc ny c hai t chc khc nhau xy dng v pht trin l IETF v ITU-T. C th phn chng thnh hai loi l: giao thc ngang cp (H.323, SIP) v giao thc ch/t (MGCP, H.248/Megaco). Tng giao thc c vai tr khc nhau trong vic thit lp kt ni, chng cng c nhng th mnh v im yu khc nhau.Cc giao thc thuc nhm th nht, th hai v th ba l nhng giao thc rt c bn, c trnh by nhiu trong cc ti liu v mng IP v Internet. Trong ti liu ny s ch tp trung vo nghin cu cc c im v kh nng ng dng ca cc giao thc thuc nhm th t trong h thng VoIP.S pht trin ca cc giao thc bo hiu v iu khin trong VoIPDo tnh cht quan trng v s a dng ca cc giao thc bo hiu v iu khin trong VoIP, phn ny s dnh ring gii thiu v s pht trin cng nh l mi lin h gia cc giao thc thuc nhm ny. Phin bn u tin ca giao thc iu khin truyn thng v bo hiu trong VoIP nh H.225/H.245 c nh ngha trong b giao thc H.323 ca ITU-T vo nm 1996. Cc giao thc ny c s dng cho dch v VoIP thi gian thc trn mng LAN, v c nhng thnh phn h tr lin kt vi mng PSTN (nh l h tr bn tin ISUP cho iu khin cuc gi). C nhiu hot ng tch cc trong lnh vc mng h tr cc dch v VoIP trong mng LAN hoc trong cc doanh nghip cung cp truyn thng VoIP ng di hay quc t. Tuy nhin, cc nh cung cp dch v nhn thy c hai vn hn ch vi phin bn 1 ca giao thc H.323, l: Nhiu dch v v c im cuc gi tin tin trong mng PSTN khng c trin khai d dng khi s dng H.323v1 v giao thc ny thiu tnh m; Vic trin khai rng ri s khng kh thi v hiu qu v kinh t v giao thc ny cn cc proxy y trng thi (state full proxy).Nhng vn ny l ng lc ITU-T pht hnh phin bn 2 ca H.323 vo nm 1998. Thit lp cuc gi trong H.323v2 nhanh v n gin hn, s dng UDP thay v nhiu phin TCP cho mt cuc gi. Nhiu c im quan trng trong H.323 phin bn 1 l khng bt buc i vi phin bn 2. H.323v2 c nh gi v nhn c s h tr ca nhiu nh sn xut. n nm 1999, IETF a ra phin bn u tin ca giao thc SIP cho iu khin cuc gi, to dch v v qun l trong VoIP. SIP c cu trc gn ging HTTP, h tr proxy phi trng thi v cho php truyn d liu trng thi cuc gi qua nhiu proxy. iu ny khin cho vic trin khai rng ri VoIP mang tnh kh thi hn so vi H.323.Qu trnh pht trin vn tip tc, ITU-T thng bo v phin bn H.323v3 nh l s thay i nh ca H.323v2 v chng nhn H.323v4 vo nm 2000. Ngoi ra, cn c phin bn H.323v5 ang trong qu trnh hon thin. IETF cng nghin cu m rng c im nh tuyn cuc gi, bo mt, to dch v trong giao thc SIP. Cng trong cng thi gian, cp n nhng hot ng lin quan n H.323v2 v SIPv2, cc nh nghin cu ti Cisco, Level 3 Communication v Telcordia pht trin kin trc iu khin cuc gi/phng tin cho mng NGN, h tr c in thoi IP v s tin ha t PSTN theo hng x l cuc gi phn tn. Kin trc ny tch bit phn vt l ca iu khin cuc gi thng minh (vn thuc v MGC) ra khi MG. H cng khuyn ngh s dng giao thc MGCP (l s kt hp ca SGCP v IPDC). MGCP h tr s tin ha PSTN bng vic cho php lin kt vi cc thit b (in thoi POTS tng t hay s) v mng chuyn mch knh thng qua nhng im cui xc nh trc. cung cp hot ng lin mng ca qu trnh iu khin dch v v cuc gi gia mng PSTN v mng NGN, MGC cn trao i cc bn tin iu khin tin cy v an ton n mng SS7 qua SG (SG c th s dng giao thc SCTP). Chng ta nh li rng trong mng PSTN, iu khin cuc gi v bo hiu thuc v mng SS7, v cc bn tin c s dng l ISUP v TCAP. C IETF v nhm nghin cu s 9 ca ITU-T ang xem xt vic chp thun nhng m rng ca MGCP (MGCPv2). MGCP cng l tin pht trin khuyn ngh H.248 ca ITU-T v Megaco ca IETF.Vi nhng dch v VoIP da trn thit b chuyn mch, vic lin kt vi nhng tng i, mng v thit b u cui PSTN c l iu cn thit. Trong trng hp ny, cc giao thc bo hiu v iu khin cuc gi H.225 v H.245 trong b giao thc H.323 hot ng rt tt. Giao thc H.248/Megaco ha hn c th kt hp H.323 v SIP khi SIP/H.323 c s dng cho truyn thng gia cc u cui hay gia u cui v Gateway.Vi nhng dch v VoIP c cung cp bi my ch, mng s bao gm my ch v cc b nh tuyn. Trong trng hp ny, SIP v nhiu phin bn ca n l rt ph hp. Vi mt mng ln, IETF khuyn ngh s dng giao thc TRIP (nh tuyn thoi qua IP) nh v my ch m cuc gi nh tuyn n. nh tuyn cuc gi t in thoi SIP hay IP n u cui PSTN (tng t hoc s) th phi s dng Gateway IP-PSTN, b iu khin cuc gi v my ch ENUM. ENUM nh x s in thoi E.164 thnh a ch IP v ngc li H THNG VoIP DA TRN H.323Cc c im ca H.323Mc d c nhiu giao thc v chun cho bo hiu v iu khin cuc gi VoIP thi gian thc, khuyn ngh ITU-T H.22x v H.32x c trin khai rng ri nht trong th h cc giao thc VoIP u tin, c bit l cho cuc gi quc t. H.320 nh ngha u cui v h thng thoi video bng hp. H.321 nh ngha u cui thoi video qua mng ATM. H.322 nh ngha u cui thoi video qua mng LAN c m bo QoS. H.323 nh ngha h thng truyn thng a phng tin da trn gi qua mng khng m bo QoS. H.324 nh ngha truyn thng a phng tin tc bit thp s dng u cui PSTN. H.325 nh ngha c ch bo mt v m ha cho php m bo tnh c nhn v thm quyn ca thit b u cui a phng tin dng H. Chun H.323 cung cp nn tng cho vic truyn thng thoi, video v d liu qua cc mng da trn IP khng m bo cht lng dch v, bao gm c Internet. H.323 cung cp nhiu loi hnh dch v nh: ch c audio (IP telephony), audio v video (video telephony), audio v d liu hay tch hp c audio, video v d liu. N h tr truyn thng a im v c th dng trong nhiu lnh vc vi cc c cu mng khc nhau. Cc thnh phn mng hot ng vi giao thc H.323 l thit b cng GW (Gateway), b iu khin cuc gi GK (Gatekeeper), khi iu khin a im MCU (Multipoint Control Unit) v thit b u cui TE (Terminal Equipment). Cc phn t ny c kt ni thnh vng nh ch ra trn hnh 3.1, s dng mi trng mng cc b LAN.

Hnh 3.1 Vng mng H.323 v cc phn tH thng H.323 bao gm cc chun v giao thc nh H.225, H.245, RTP/RTCP v cc b m ho/gii m thoi, video, d liu. Chc nng ca H.225 l iu khin cuc gi. H.225 nh ngha giao thc Q.931 v RAS. Q.931 qun l v iu khin vic thit lp/kt thc cuc gi c bn, cn RAS (Registration, Admission, and Status) qun l vic ng k, chp nhn v trng thi, dng truyn bn tin t GW hoc thit b u cui n GK. Bn tin RAS c truyn trong gi tin UDP, gi tin ny cha s bn tin gi yu cu/tr li (xc nhn hoc t chi) trao i gia TE/GW v GK. TE c th s dng RAS tm GK hoc ng k/hy ng k vi GK. GK s dng RAS iu khin im cui trong vng v qun l ti nguyn.Chc nng ca H.245 l tho lun v vic s dng knh v kh nng ca cc bn tham gia phin truyn thng. H.245 nh ngha cc giao thc iu khin cuc gi hi ngh v truyn thng trong bng trao i v tha thun tham s cuc gi. Nhng tham s ny gm ch hin th, knh, tc bit, s tch hp d liu, thi gian tr, Chng cung cp mt tp cc chc nng iu khin cho hi ngh truyn thng nhiu bn tham gia v c th quyt nh quan h ch/t gia cc bn tham gia m/ng knh logic gia cc im cui. RTP (Real-Time Transfer Protocol) l giao thc vn chuyn thi gian thc, cung cp cc chc nng vn chuyn ph hp cho cc ng dng truyn d liu thi gian thc nh audio, video, hay d liu m phng qua cc dch v mng n hng (unicast) hoc a hng (multicast). N c b sung vo d liu UDP trong H.323.RTCP (Real-Time Transfer Control Protocol) l giao thc iu khin vic vn chuyn thi gian thc, n cho php gim st lung lu lng phn tn trong mng v thc hin cc chc nng iu khin lung, nhn dng lung cho cc lu lng thi gian thc.H.323 cung cp nhiu loi hnh dch v t thoi n video v d liu, thng tin a phng tin. Cc b m ho/gii m thoi (audio) l G.711, G.722, G.723.1, G.728, G.729; cho video l H.261 v H.263; cho d liu l T.12x. Cc dng thng tin d liu c truyn trn giao thc RTP/RTCP. RTP mang thng tin thoi thi gian thc, cn RTCP mang thng tin iu khin v trng thi. Thng tin bo hiu (ngoi tr RAS) c truyn tin cy trn giao thc TCP. Hnh 3.2 minh ho cc giao thc H.323 khi so snh vi m hnh OSI.

Hnh 3.2 M hnh giao thc H.323 trong mi tng quan vi OSICc khuyn ngh v giao thc khc hot ng cng H.323 bao gm: H.235: c t tnh bo mt v m ho cho cc u cui theo H.323 v H.245. H.450: c t khung cng vic cho cc dch v b sung nh chuyn cuc gi, gi cuc gi, dng cuc gi, i cuc gi, ch dn c tin nhn ch, nhn dng tn, kt thc cuc gi, v.v. H.246: c t lin mng gia cc u cui H.323 v u cui chuyn mch knh.Cc thnh phn ca h thng H.323Nh gii thiu trn (hnh 3.1), cc thnh phn c bn cu thnh mt vng mng VoIP da trn giao thc H.323 gm c: thit b u cui, Gatekeeper, Gateway v MCU. Sau y trnh by chc nng v nhng c im quan trng nht ca cc phn t ny. Thit b u cui H.323 Thit b u cui H.323 l cc im cui pha khch hng, cung cp giao din trc tip gia ngi dng v mng. Mng VoIP s cung cp cc kh nng truyn thng thi gian thc hai chiu gia mt u cui vi u cui khc, Gateway hay MCU trao i cc tn hiu iu khin, m thanh, hnh nh ng hay d liu gia hai thit b.Hnh 3.3 m t cc khi chc nng ca mt u cui H.323 trong trng hp tng qut, bao gm giao din thit b ngi dng, cc b m ho audio v video, lp H.225.0, khi iu khin h thng v giao din vi mng gi. Tt c cc u cui H.323 u h tr thoi v ti thiu phi c mt khi iu khin h thng, lp H.225.0, giao din mng v b m ho thoi.

Hnh 3.3 Thit b u cui H.323Khi iu khin h thng cung cp cc tn hiu iu khin cho mc ch vn hnh u cui H.323, n m bo cc chc nng nh iu khin cuc gi, thay i bng tn theo yu cu, to cc bn tin thu pht, m t v m cc knh logic.Lp H.225.0 thc hin chc nng nh dng thoi, thit lp v m cc knh logic, chuyn i thng tin lung d liu vo cc bn tin iu khin bo hiu. Giao din mng c chc nng chuyn i dng bn tin H.323 thnh dng thch hp trong mng IP s dng cc dch v TCP, UDP. Nh vy n phi h tr: Giao thc bo hiu cuc gi H.225; Giao thc bo hiu knh iu khin H.245; Cc giao thc RTP/RTCP cho cc gi phng tin.Cc b m ho/gii m thoi l phn t bt buc trong thit b u cui H.323. Cc chun m ho thng gp l G.711, G.728 v G.723.1. Cc b m ho/gii m video l khng bt buc trong thit b u cui H.323. Chng c chc nng m ho tn hiu video t ngun truyn i v gii m tn hiu video nhn c a ti thit b hin th. Cc chun m ho video thng dng l H.261 v H.263. Gateway H.323Gateway H.323 cho php kt ni mng VoIP vi cc mng khc. N l im cui trong mng thc hin cc chc nng chuyn i bo hiu v d liu, cho php cc mng hot ng trn giao thc khc nhau c th phi hp vi nhau. N cung cp kh nng truyn thng thi gian thc v song hng gia cc u cui H.323 trong mng gi vi cc u cui trong mng khc hay vi cc Gateway khc. Trong khuyn ngh H.323, Gateway l mt phn t tu chn v c s dng nh l mt cu ni gia u cui H.323 vi cc u cui H.310 (B-ISDN), H.320 (ISDN), H.321 (ATM) v H.324M (Mobile).Chc nng chnh ca Gateway l phin dch gia cc thc th trong mng chuyn gi (v d IP) vi mng chuyn mch knh (v d PSTN). Cc Gateway c th phin dch khun dng truyn dn, cc tin trnh truyn thng, cc b m ho/gii m hoc m bo tng thch gia u cui H.323 v cc u cui khng theo chun ny. Ngoi ra, n cn tham gia vo vic thit lp v hu b cuc gi. Gatekeeper H.323Gatekeeper l mt thc th tu chn trong mng H.323 cung cp cc chc nng bin dch a ch v iu khin truy nhp mng cho cc thit b u cui H.323, Gateway v MCU. Ngoi ra, Gatekeeper cng c th cung cp cc dch v khc cho cc phn t mng trn nh qun l bng thng hay nh v cc Gateway. Mng H.323 c th c cu trc phn cp, khi cc Gatekeeper cng c phn cp tng ng theo, v d nh s c Gatekeeper quc gia, khu vc hay cc b (hnh 3.4). V mt logic, Gatekeeper l mt thit b c lp nhng trong thc t n thng c tch hp vi cc phn t mng khc trong cng mt thit b vt l. Mi Gatekeeper qun l mt vng mng. Nu trong mng c mt Gatekeeper th cc im cui phi ng k v s dng cc dch v do n cung cp. Mt vng mng H.323 c hiu nh mt tp hp cc nt u cui, Gateway hay MCU, c ng k vi mt Gatekeeper v c qun l bi Gatekeeper ny.

Hnh 3.4 Mng H.323 phn cp v m hnh qun l ca cc GK Khi iu khin a im MCUMCU l mt im cui trong mng cung cp kh nng truyn thng cho ba hay nhiu thit b u cui v Gateway tham gia hi ngh a im. N cng c th kt ni hai thit b u cui trong mt hi ngh im-im sau pht trin thnh mt hi ngh a im. MCU bao gm hai phn: b iu khin a im MC (Multipoint Controller) v b x l a im MP (Multipoint Processor).MC l phn t bt buc, cung cp cc chc nng iu khin h tr cc hi ngh a im. N thc hin vic trao i kh nng vi mi im cui trong mt hi ngh. MC gi mt tp kh nng ti cc im cui ch th m hnh hot ng m chng c th s dng. MC cng c th sa li tp cc kh nng gi ti cc thit b u cui khi chng tham gia hay ra khi hi ngh hay v mt l do no khc.MP l phn t tu chn, nhn cc dng audio, video v d liu t cc im cui trong mt hi ngh a im. N s x l tp trung cc lung phng tin ny v tr li chng cho cc im cui. N c th thc hin cc chc nng nh trn, chuyn mch hay cc x l khc di s iu khin ca MC. MP c th x l mt lung phng tin n l hay nhiu lung phng tin ph thuc vo kiu ca hi ngh c h tr.Thit lp kt ni trong H.323H thng H.323 c th kt ni vi cc mng khc nh PSTN, ISDN, mng di ng hay cc mng doanh nghip cung cp dch v thoi lin mng. Thit b ca ng kt ni cc mng khc nhau ny chnh l cc Gateway (hnh 3.5). Kh nng kt ni ny lm cho H.323 tr thnh mt gii php ph bin cung cp dch v VoIP ng di hay quc t vi gi r.

Hnh 3.5 Kt ni h thng H.323 vi cc mng khcC th s dng H.323 thc hin nhiu m hnh cung cp dch v VoIP ng di khc nhau. Hot ng kt ni ph thuc vo m hnh s dng v c th khc nhau cht t ty vo tng trng hp c th. V d trn hnh 3.6 cho thy trnh t thit lp phin truyn thng thoi H.323 thi gian thc t mt in thoi PSTN n mt in thoi khc qua mng IP.

Hnh 3.6 Thit lp phin VoIP H.323 gia hai in thoi PSTN qua mng IPT hnh v c th thy th tc thit lp cuc gi VoIP gia hai in thoi PSTN c thc hin trong 10 bc. Sau khi kt ni xong, lu lng thoi s c chuyn qua mng IP, c th l Internet hay Intranet. Lu rng trong hnh ny, ARQ (Admission Request) l yu cu kt ni, ACF (Admission Confirm) l xc nhn yu cu kt ni, LRQ (Location Request) l yu cu nh v, v LCF (Location Confirm) l xc nhn nh v. Cc cng vo v ra c ch nh bi IGW (Ingress Gateway) v EGW (Egress Gateway), cn cc GK vo v ra tng ng vi IGK (Ingress GK) v EGK (Egress GK). H THNG VoIP DA TRN SIPCc c im ca SIPGiao thc khi to phin SIP (Session Initiation Protocol) l giao thc iu khin bo hiu thuc lp ng dng c s dng thit lp, duy tr v kt thc cc phin a phng tin hay cc cuc gi qua mng IP. SIP lin kt vi cc giao thc IETF khc nh thng bo phin SAP (Session Announcement Protocol) v m t phin SDP (Session Description Protocol) cung cp mt s lng ln cc dch v VoIP. Tng t nh HTTP, SIP l giao thc client/server, bao gm tp hp cc yu cu c gi t ng dng khch (SIP client) ti my ch (SIP server). My ch x l cc yu cu ny v tr li ng dng khch. Mt bn tin tr li cng vi cc bn tin lin kt vi n gi l mt giao dch (SIP transaction). SIP s dng mt s kiu bn tin v trng mo u ging HTTP, xc nh thng tin theo mo u c th ging nh giao thc s dng trn Web.SDP bao gm cc thng tin v lung phng tin, thuc tnh kh nng ca bn nhn, a ch ch cho unicast hoc multicast, cng UDP, kiu ti tin, ... Kh nng ca bn nhn c th gm danh sch cc b m m ngi gi s dng trong sut phin. Nhng thuc tnh ny c th thng lng li t ng trong sut phin gim xc sut tc nghn. Nhng c im ca SDP gn ging vi nhng c im ca giao thc H.245.SAP c dng vi SDP thng bo cc m t phin ti ngi dng (qua gi tin UDP).SIP h tr vic nh a ch mt cch linh hot. a ch u b gi c th l a ch email, URL, hoc s in thoi E.164 ca ITU-T. Vic thit lp phin truyn thng c thc hin n gin v SIP cung cp dch v nh v, qun l ngi gi, thit lp cuc gi nhng khng dnh sn ti nguyn cho knh truyn thng tin. Nhng c im ny ca SIP ging vi H.225. Mt s phin bn khc nhau ca SIP c s dng trong vi nm gn y, trong SIP-T l phin bn c nhiu tnh nng nht, h tr kt ni vi mng PSTN. SIP-T l s m rng ca SIP cho php kt cui cuc gi vi mng PSTN. N ng gi bn tin SS7 ISUP, Q.931 ISDN hay bo hiu CAS nh l phn nh km MIME gn vo bn tin SIP. SIP-T c kh nng mang thng tin bo hiu v cuc gi PSTN-PSTN qua mng IP. M ha trong MIME cho php thng tin bo hiu c truyn theo kiu ng hm gia cc MGC. Ngoi ra, SIP-T c y cc chc nng ca SIP.Giao din lp trnh SIP bao gm ngn ng x l cuc gi CPL (Call Processing Language), SIP-CGI (Common Gateway Interface) v SIP-serverlet (server based applet).CPL (RFC 2824) l ngn ng kch bn da trn XML m t dch v cuc gi. CPL c kh nng to quyt nh da trn thuc tnh cuc gi v to dch v ngi dng qua GUI. CPL nhanh, n gin v tnh m rng.SIP-CGI tng t nh HTTP CGI, l giao din to cc dch v SIP s dng ngn ng lp trnh. Vic to dch v ging nh pht trin cc trang web ng. SIP-CGI linh ng hn CPL nhng khng c tnh m rng bng, v cng nhiu ri ro hn khi thc hin. N cn c bo v chng li nhng script c hi. SIP serverlet c nguyn l ging HTTP serverlet. N cng ging CGI nhng hot ng trong my o Java (JVM) my ch. Serverlet khng phc tp nh CGI v qu trnh thc thi c bo v trong cu trc Java sandbox. Do , n linh hot hn, c tnh m rng v bo mt hn CPL.Trn hnh 3.7 l cc lp giao thc h tr cho dch v VoIP s dng bo hiu SIP. ng dngiu khin cuc gi v bo hiu

Trnh dinTrnh din(Truyn phng tin)

nh a chDTMFM ha (G.7xx)nh a ch

PhinDNSCc bn tin bo hiu SIP

[Register, Ack, Options,Cancel,Bye, ]RTP(RFC 1889)[nh s trnh t, kiu gi, timestamp]RTCP(RFC 1890)[quan trc QoS]TRIP(RFC 2871)

[u cui s dng nh v my ch]

DNS(RFC 2065, 2136/37)[u cui s dng pht hin a ch IP]

Giao vnTCP (tin cy),RFC 793UDP (khng tin cy),RFC 768

Hnh 3.7 Cc lp giao thc h tr cho VoIP da trn SIP SIP h tr 5 dch v trong vic thit lp v kt thc cc phin truyn thng: nh v ngi dng (xc nh v tr ca ngi dng tin hnh hi thoi); Xc nh nng lc ngi dng (cc phng thc v tham s tng ng trong hi thoi); Xc nh nhng ngi sn sng tham gia hi thoi; Thit lp cc tham s cn thit cho cuc gi; iu khin cuc gi (bao gm c qu trnh truyn v kt thc cuc gi).Cc thnh phn ca h thng SIPKin trc h thng SIP (hnh 3.8) bao gm cc thnh phn: Tc nhn gi (User Agent); Cc my ch mng, gm Proxy Server, Location Server, Redirect Server v Registrar Server; Cc Gateway. Hnh 3.8 Cc thnh phn ca h thng SIP u cui SIP User Agent (UA) l thit b u cui trong mng SIP, c th l mt my in thoi SIP hay my tnh chy phn mm SIP. Cc thnh phn ng dng lin quan bao gm: UAC (User Agent Client) l mt ng dng khch pha ngi gi, n khi u v gi bn tin yu cu SIP; UAS (User Agent Server) l mt ng dng ch, n nhn v tr li cc yu cu SIP, nhn danh cc my ch chp nhn, chuyn hoc t chi cuc gi.Thit b cui trong SIP bao gm c chc nng client v server, do bn tham gia cuc gi c th to yu cu hoc nhn yu cu. C UAC v UAS u c th kt thc cuc gi. Cc my ch SIPCc my ch SIP thc hin cc chc nng ca h thng SIP trong mng nh iu khin v qun l cuc gi, trng thi ngi dng. Proxy Server l phn mm trung gian hot ng c nh Server v Client thc hin cc yu cu thay mt cc u cui khc. Tt c cc yu cu c x l ti ch bi Proxy Server nu c th, hoc c chuyn cho cc my ch khc. Trong trng hp Proxy Server khng trc tip p ng cc yu cu ny th n s thc hin khu chuyn i hoc dch sang khun dng thch hp trc khi chuyn i. Mt yu cu SIP c th truyn qua nhiu Proxy Sever trc khi n UAS ch. Location Server l phn mm nh v thu bao, cung cp thng tin v nhng v tr c th ca pha b gi cho cc phn mm Proxy Server v Redirect Server.Redirect Server l phn mm nhn yu cu SIP, chuyn i a ch SIP sang mt s a ch khc v gi li cho u cui. Khng ging nh Proxy Server, Redirect Server khng bao gi hot ng nh mt u cui, tc l khng gi i bt c yu cu no. Redirect Server thng bo cho client v server k tip client c th lin lc vi n trc tip. Redirect Server cng khng nhn hoc hu b cuc gi. Registrar Server l phn mm nhn cc yu cu ng k REGISTER. Trong nhiu trng hp Registrar Server m nhim lun mt s chc nng an ninh nh xc nhn ngi s dng. Thng thng Registrar Server c ci t cng vi Proxy Server hoc Redirect Server hoc cung cp dch v nh v thu bao. Mi ln u cui c bt ln (in thoi hoc phn mm SIP) th u cui li ng k vi Server. Nu u cui cn thng bo cho Server 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. SIP GatewayCc Gateway thc hin chc nng kt ni (internetworking) gia h thng SIP vi cc mng khc.Thit lp kt ni trong SIPHnh 3.9 m t vic truyn cc bn tin thit lp cuc gi SIP. C th nhn thy rng s lng bn tin cn thit thit lp cuc gi SIP t hn so vi H.323. Bn tin yu cu ca SIP l INVITE (mi tham gia phin kt ni), cn bn tin tr li 200 OK c ngha l yu cu kt ni c chp nhn. Bn tin yu cu cha phn mo u mang thng tin cuc gi. Sau phn mo u l thn bn tin cha m t v phin s c thit lp.

Hnh 3.9 Thit lp phin VoIP gia hai u cui SIP qua mng IPHin nay, c phn mm v phn cng SIP h tr in thoi IP u c sn. nh tuyn cuc gi qua mng IP, SIP s dng giao thc TRIP (RFC 2871) cung cp kh nng nh v my ch m cuc gi nh tuyn n. nh tuyn cuc gi n u cui PSTN (in thoi POTS) th cn s dng ENUM (RFC 3761). ENUM nh x s in thoi E.164 thnh a ch SIP v ngc li.SIP cng c th kt hp vi cc giao thc bo hiu v thit lp cuc gi khc. Theo cch , mt u cui dng SIP xc nh a ch hp l ca mt h thng v giao thc t a ch gi n l giao thc c lp. V d, c th dng SIP ch ra rng ngi tham gia thng qua H.323, cng H.245, xc nh a ch ngi dng ri s dng H.245 thit lp cuc gi. Vn lin kt mng SIP v H.323 ang thu ht c s ch ca nhiu nh nghin cu. Hin ti c hai gii php vn c h tr v trin khai bi cc nh cung cp sn phm phn mm cng nh phn cng. So sanh SIP va H.323 Nh tnh n gin, linh hot v c kin trc module nn SIP c xem l giao thc thay th cho giao thc bo hiu H.225 (s dng trong H.323). C H.323 v SIP s dng RTP cho lung phng tin. Bi v SIP s dng nh dng bn tin HTTP v a ch URL nn d dng tch hp vi web, email hoc nhng dch v v ng dng trn IP khc (v d, nhn tin tc th). SIP h tr nhiu c im cuc gi nng cao trong POTS nh nhn dng ngi gi, dch v bin i tn/s ngi gi, i cuc gi, chuyn cuc gi, ch cuc gi, phn phi cuc gi t ng, nh v ngi s dng, dch v follow-me, ...SIP cho php s dng cc proxy phi trng thi hot ng nhanh trong mng li, v cc proxy trng thi y ti bin mng, do SIP c tnh m rng hn H.323. Tuy nhin, nu nh s dng GK ch h tr RAS trong mng li v GK nh tuyn y bin th H.323 cng c th t c kh nng m rng tng t.Cc u im chnh ca SIP so vi H.323 l: SIP co rt it ban tin, khng co chc nng tha nhng co th s dung thit lp nhng phin kt ni phc tap nh hi nghi. n gian, gon nhe v da trn khun dang text, SIP la giao thc ra i sau nn a khc phuc c nhng im yu cua cac giao thc trc y. Cac phn mm may chu Proxy, may chu Registrar, may chu Redirect, dich vu inh vi, ... co th chay trn cac may chu khac nhau va vic cai t thm may chu hoan toan khng anh hng n cac may chu a co. Chinh vi vy h thng chuyn mach SIP d dang m rng va nng cp SIP h tr ti a kha nng di ng cua u cui. Nh cc may chu Proxy, Registrar va Redirect nn h thng lun nm c cac vi tri chinh xac cua thu bao. Mt thu bao co ia chi co th nhn c cuc goi thoai hay ban tin t bt ky ia im nao, thng qua bt ky thit bi u cui nao h tr SIP nh may tinh ban, may tinh xach tay, SIP phone, ... La giao thc khi tao phin trong mang chuyn mach goi, SIP cho phep tao ra nhng tinh nng mi hay dich vu mi mt cach d dang v nhanh chong. CPL va CGI la mt s cng cu h tr thc hin iu nay SIP co th tich hp vi cac giao thc a co cua IETF nh RSVP, RTP, RCTP, SAP, MIME, HTTP, SDP, ... xy dng thanh cac ng dung hoan chinh.Nh vy, c th thy SIP c xem l giao thc iu khin v bo hiu y ha hn cho dch v VoIP. Nhiu nh cung cp vit phn mm SIP vi mc ch thc hin n trn nhng my tnh hay my ch. Mt s nh cung cp dch v nng cp nhng c im my ch SIP c chc nng chuyn mch mm. Cc chuyn mch mm s c chc nng ca b iu khin cuc gi.Bng 3.1 tng kt mt s so snh c im ca hai giao thc H.323 va SIP.Bng 3.1 So snh cc c im ca SIP v H.323Chi tiu so sanhSIPH.323

T chc chun haIETFITU

Quan h kt niNgang cpNgang cp

Thit bi u cuiu cui thng minh SIPu cui thng minh H.323

Cac may chuProxy, Redirect, RegistrarGatekeeper

Khun dang ban tinText, UTF-8Nhi phn ASN.1 PER

Tr thit lp cuc goi1,5 RTT6-7 RTT hoc hn

ia chiDang URLCac alias, s in thoai E.164

Giam sat trang thai cuc goiTuy chon: giam sat trong thi gian thit lp cuc goi hoc trong toan b thi gian cuc goiGK lun giam sat trang thai cuc goi

Cht lng dich vuS dung cac giao thc khac nhau nh RSVP, OPS, OSP am bao QoS.GK iu khin bng thng am bao QoS. S dung RSVP dnh trc tai nguyn

Bao mtng ky tai Registrar Server, co xac nhn u cui va ma hoang ky vi GK, co xac nhn u cui va ma hoa theo H.235.

Tao tinh nng va dich vu miD dangKho

Kha nng m rngD dangHan ch

Tich hp vi WebTtKem

Tinh hinh chun hoa hin nayang tip tuc c hoan thin. Cac nha cung cp thit bi a tich hp SIP vao san phm.a c chun hoa chi tit. H.323 ang c s dung rng rai.

H THNG VoIP S DNG BO HIU LAI GHPS dng MGCP v H.248/Megaco Ngoi H.323 v SIP, cc giao thc iu khin bo hiu khc h tr cho VoIP phi k n l MGCP (RFC 2805) v H.248/Megaco (RFC 3015). MGCP c to ra bi s hp nht gia SGCP v phn iu khin phng tin ca giao thc iu khin thit b IP lp 3 (IPDC). MGCP cung cp c ch phn tch cc Gateway thnh hai phn: bo hiu (hay iu khin cuc gi) v x l phng tin c iu khin, trong vic iu khin c thc hin tp trung i vi cc Gateway phn tn. MGCP coi h thng phn tn cc Gateway bao ph ton b cc thnh phn mng nh b iu khin cuc gi CC, MGC hay CA, cc MG v SG.MG chuyn lu lng chuyn mch knh vo min gi (IP, ATM, ...). N c chc nng bin i m chp nhn lu lng thoi truyn trong vng PSTN vi m ha G.711 hay phn phi m ha thoi G.723 hoc G.729 vo min gi. Vi tnh nng cao cp ca MG nh h tr trit ting vng da trn phn cng, cc k thut m gi phc tp v FEC (sa li) nng cao cht lng thoi.CC hay MGC, hoc CA l thit b cha phn iu khin cuc gi thng minh. Trong H.323 n c gi l GK hay b iu khin cuc gi, trong MGCP l CA v trong H.248/Megaco l MGC. Chc nng chnh ca MGC l iu khin cuc gi v nh tuyn cuc gi mt cch thng minh. N iu khin nhiu MG v SG.SG lin kt gia CC mng gi (v d, H.323 GK) vi mng SS7, bin dch iu khin cuc gi v phn phi dch v. Giao din ca n vi mng SS7 s dng lin kt loi A hay F, vi CC s dng lin kt IP.Nguyn l chuyn mch mm c ngun gc t s pht trin ca MGCP. Chuyn mch mm nhiu lc c coi l s tp hp cc phn mm l cc thc th trong my tnh/my ch. Nhng thc th ny gip to, qun l, iu khin, tnh cc v gii phng cuc gi. Do tp hp cc my ch, nh H.323 GK, SIP server, MGC, CA v SS7 SG, c th c xem l chuyn mch mm. Ging nh MGCP, H.248/Megaco tch phn iu khin bo hiu khi MG. Chc nng iu khin c x l bi MGC. H.248/Megaco c xem l s m rng ca MGCP, n h tr thm vic iu khin phng tin gia mng TDM v ATM cng nh l mt vi tnh nng linh hot v c im mi. H.248/Megaco c th hot ng trn c UDP hoc TCP. Hin nay, bn cnh h tr SIP, nhiu din n cng nghip lin quan n VoIP v cc nh cung cp ang tp trung n H.248/Megaco. MGCP c th lin kt hot ng vi ng dng khch H.323, nhng chc nng chnh ca n l kt ni PSTN-PSTN qua mng IP. H.248/Megaco khng h tr QoS v khng tng thch vi MGCP. N cng khng gii quyt vn giao thc MGC-MGC. Cc giao thc SIP, SCTP hay BICC s gii quyt tt hn vn lin kt mng.Hnh 3.10 m t cc lp giao thc h tr cho VoIP da trn MGCP v H.248/Megaco. ng dngBo hiu cuc gi/iu khin nh tuyn v Gateway

API

Trnh dinTrnh din(Truyn phng tin)

nh a chDTMFM ha (G.7xx)nh a ch

PhinDNSiu khin giao dchQun lng biu khin lnhRTP(RFC 1889)[nh s trnh t, kiu gi, timestamp]RTCP(RFC 1890)[quan trc QoS]DNS(RFC 2065, 2136/37)[u cui s dng pht hin a ch IP ca thit b]

Giao vnTCP(RFC 793)UDP (in MGCP)TCP/UDP (in H.248/Megaco)UDP (RFC 768)

Hnh 3.10 Cc lp giao thc h tr cho VoIP da trn MGCP v H.248/Megaco S dng SCTP SCTP (RFC 3057 v RFC 2960) l giao thc mi c khuyn ngh bi nhm nghin cu SIGTRAN ca IETF. SCTP cp n truyn ti bn tin bo hiu SS7 nh ISDN (Q.931), ISUP, gia nhiu phn t mng nh SG, MGC v MG qua mng gi IP.SCTP l giao thc truyn gi tin cy (thuc lp vn chuyn). Lp tng thch c s dng truyn bn tin TCAP, ISUP, MTP-2 v MTP-3. SCTP cung cp tnh bo mt, nh thi, tin cy hn nhng c ch hin c da trn TCP/UDP.Cc c im chnh ca SCTP l: Tng thch ngc vi UDP; Truyn ti c bo nhn (ack), khng li v khng trng lp d liu ngi dng; H tr phn on d liu thch ng vi kch thc bn tin MTU trn ng truyn; m bo truyn theo th t d liu ngi dng trong nhiu lung; Cho php ghp nhiu bn tin ca ngi dng vo gi SCTP.SCTP s dng UDP lp giao vn. ph hp vi yu cu ca chun SS7, SCTP c thit k h tr nghim ngt cc yu cu v mt gi, tr mng v bo mt. Do , c th ni SCTP s c chp nhn l mt giao thc truyn ti bo hiu trong mng IP.Hu ht cc hng sn xut SG u h tr SCTP. Nhiu hng th nghim v trin khai thnh cng vic kt ni mng ca cc nh khai thc khc nhau s dng SCTP.S dng BICC Giao thc iu khin cuc gi c lp knh mang BICC (Bearer Independent Call Control) c khuyn ngh bi ITU-T, m bo truyn thng gia cc Server (hay MGC) v cho php cc nh vn hnh mng chuyn c cc dch v in thoi t mng chuyn mch knh sang mng chuyn mch gi. BICC l giao thc bo hiu da trn ISUP, c s dng h tr dch v ISDN bng hp qua mng ng trc bng rng m khng gy phin phc vi cc giao din vi mng hin ti v cc dch v u cui-u cui. BICC c thit k hon ton tng thch vi mng hin c v vi bt k h thng no c kh nng truyn cc bn tin thoi. BICC h tr cc dch v bng hp c lp vi cng ngh truyn ti bn tin cho tn hiu thoi v bo hiu. Cc bn tin BICC cha thng tin iu khin cuc gi v iu khin ti tin. Phin bn u tin ca BICC (CS1) ra i nm 2000, nh ngha hot ng ca giao thc BICC vi bo hiu AAL-2 trong mng ATM. Phin bn th 2 (CS2) hon thnh vo nm 2001, h tr iu khin cuc gi trn mng IP s dng SCTP. ITU-T Q.1901 v Q.765.5 l nhng khuyn ngh tng t nhau v BICC. Vo thng 5 nm 2001, nhm nghin cu 11 ca ITU-T c y thc pht trin nhng c im ging SIP v SCTP trong phin bn CS3 ca BICC. BICC-CS3 h tr giao din mng-mng (NNI) v cho php tng tc vi cc h thng bo hiu H.323 v SIP. Thit lp kt ni trong h thng s dng bo hiu lai ghp i vi mng hi t th h sau, vic trin khai cc dch v da trn cc giao thc bo hiu nh SIP v H.248/Megaco chc chn s mang li nhiu hiu qu. S c hai mng b ng chm n trong tng lai l PSTN da trn chuyn mch knh v VoIP da trn H.323. Xu hng pht trin cc mng hi t a dch v l s dng kin trc tch hp, lai ghp nhiu phng thc bo hiu v iu khin cuc gi ci tin dch v VoIP nhm m bo tnh linh hot v tng thch gia cc h thng.Hnh 3.11 minh ha vic s dng chuyn mch mm vi cc giao thc bo hiu v iu khin khc nhau trong mng th h sau. Kin trc ny h tr cc cuc gi da trn SIP/H.323, MGCP/H.248 v PSTN, cho php nh tuyn cuc gi, dch v truyn thng tin bo hiu t mt vng bo hiu ny sang vng bo hiu khc. Ngi dng cui c th kt ni vo mng qua in thoi POTS, SIP UA, hoc u cui H.323. Nhng thit b u cui ny c th truyn thng di s iu khin ca chuyn mch mm (gm MGC v SG) s dng SS7, SIP/H.323 hay MGCP/H.248.

Hnh 3.11 Kin trc mng VoIP ton cu s dng bo hiu lai ghpMt cch khi qut, th tc thit lp cuc gi s dng lai ghp nhiu giao thc bo hiu v iu khin gia hai thc th mng c thc hin nh sau: MGC (s dng H.248/Megaco) thit lp im cui (H.323 TE, SIP UA, in thoi IP/POTS) tm tn hiu off-hook, v d: ngi s dng nhc my to cuc gi. MG thng bo MGC v tn hiu off-hook. H thng u cui c th s dng SS7, SIP, H.323 lin lc vi MGC. MG t tone cuc gi ln ng dy sau khi nhn lnh t MGC, lng nghe tone DTMF v truyn s tr li MGC. MGC nh tuyn cuc gi. N s dng giao thc bo hiu gia cc MGC nh SIP-T hoc BICC-CSx lin lc vi MGC pha u cui b gi. MGC pha u cui b gi thng bo cho MG tng ng gi m rung chung qua ng dy n thit b u cui tng ng vi s b gi. Khi MG pht hin thit b u cui tng ng vi s b gi l off-hook, c hai MG u c iu khin bi MGC ch tng ng thit lp knh kt ni hai chiu qua mng gi. Knh ny c th l RTP trong trng hp mng IP, knh o qua AAL-2 hoc AAL-5 trong mng ATM.ENUM V VN NH S TRONG VoIPNi chung cc u cui VoIP c th c nh danh bi tn ngi s dng (user name) dng text nh a ch SIP. Cc nh danh ny c dng nh a ch th in t v trong nhiu trng hp c th chnh l a ch email ca ngi dng. Tuy nhin, c s h tng mng hin ti vn ang cung cp dch v thoi cho cc u cui c nh danh bi s thu bao theo chun E.164 ca ITU-T. Do , mt vn c t ra l lm th no cc thu bao c nh danh theo kiu khc nhau ny c th gi c cho nhau, hay ni cch khc l c th tm thy nhau trn mng. Gii php cho vn ny l nh x cc s in thoi dng E.164 sang dng tn min DNS, v chnh l ni dung ca chun ENUM, a ra trong RFC 3761 ca IETF.ENUM (E.164 Number Mapping) l h thng s dng dch v tn min DNS nh x cc s in thoi dng +8448549352 thnh cc gi tr nh danh URI (Uniform Resource Identifier). ENUM cho php s dng h thng qun l phn cp ca DNS. Cc th tc truy vn Internet pht trin m rng ni dung thng tin cha trong cng mt s in thoi, vn vn c coi l duy nht v tng ng i vi mt ch th. Vi mt s in thoi ng vi c nhn no , thng qua cc php truy vn (ging nh tra cu danh b, trang vng) c th tm c rt nhiu cc thng tin lin quan. y ch khc l h thng lu tr thng tin l h thng DNS c sa i, php truy vn l th tc DNS rt pht trin. Vi th mnh ca dch v Internet, cc truy vn da trn DNS c coi l rt d trin khai v ng dng. s dng c ENUM cn dnh cho n mt tn min trong h thng tn min cp 1 trn Internet (ngang hng vi .com; .net, v.v.). Tn min cp 1 c ch nh s dng th l .arpa (Address and Routing Parameter Area), tn min cp 2 l e164.arpa v tip tc cc cp di.Mt cch vn tt, tm c tn min tng ng vi mt s E.164 no , cc bc sau s c thc hin:1. S E.164 phi c vit di dng y theo quy nh ca ITU, bao gm c cc m quc gia v m mng (vng), v d: +8448549352 2. B i du + trc v thm du "." vo gia cc ch s: 8.4.4.8.5.4.9.3.5.2 3. o ngc th t v thm chui "e164.arpa" vo cui: 2.5.3.9.4.5.8.4.4.8.e164.arpaNh vy, s in thoi +8448549352 tr thnh tn min 2.5.3.9.4.5.8.4.4.8.e164.arpa trn Internet. Cch bin i ny vn gi c m in thoi quc gia ca Vit Nam (84), m vng H Ni (4) v s in thoi 8549352 (my tnh x l t phi qua tri). Khch hng c s thoi +8448549352 ny mun s dng cc dch v khc nh mail, web, ... th ch cn ng k thm. Trong phn mm ng dng dch v c cc bn ghi dnh cho a ch SIP, mail, web, ... Trong h thng tn min, ngi ta s dng mt trng d liu c bit l trng NAPTR (Naming Authority Pointer) ch ra cc dch v khc nhau khi kt ni ti mt trm c nh danh no . Ni mt cch khc, n ch ra cc dch v m trm c. Vic x l cc trng NAPTR c thc hin thng qua thut ton NAPTR. u vo ca thut ton ny l chui th hin s E.164 theo nh dng nh trong bc 1 ca qu trnh chuyn i ni trn, tc l chui c dng: "+8448549352". u ra ca thut ton l mt chui nh danh URI trong dng thc tuyt i ca n theo RFC 2396.V d v ng k s dng dch v nh sau:$ORIGIN 2.5.3.9.4.5.8.4.4.8.e164.arpa IN NAPTR 10 100 u E2U+sip !^.*$!sip:kvt@ptit.edu.vn! .IN NAPTR 10 101 u E2U+mailto !^.*$!mailto:kvt@ptit.edu.vn! .IN NAPTR 10 102 u E2U+http !^.*$!http://www.ptit.edu.vn! .IN NAPTR 10 103 u E2U+tel !^.*$!tel:+84-4-8549352! .Mi mt dch v ng k nh trn c gi mt NAPTR resource record. Ngi s dng c th truy vn theo s in thoi v ch r ng dng dch v no mun s dng (in thoi SIP, th in t, web, v.v.).ENUM c th ng dng u cui, tng i hay cc thit b Gateway. T s in thoi, qua truy vn ENUM ng dng s bit c th tc giao tip cn s dng, a ch ti nguyn ch c truy vn v cc thng s khc thc hin kt ni. Mt trong nhng u im chnh ca ENUM l khng cn thit phi quy hoch li vic nh s m c th s dng cu trc nh s sn c. S dng ENUM, mt u cui IP c th d dng kt ni vi u cui in thoi truyn thng. Cc nh cung cp dch v thoi t c nhiu li ch vi vic a cc h thng chuyn mch mm h tr ENUM vo s dng. Trong trng hp ny, vic ng dng ENUM l hon ton trong sut i vi ngi s dng, vic nh tuyn cuc gi trong mng c th c quyt nh bi h thng DNS ENUM ni b, hoc s dng h thng ENUM ton cu.Nh vy, ENUM cho php khch hng ch cn mt s in thoi l c th s dng c tt c cc dch v vin thng trn phm vi ton cu. Xt v mt k thut, cng ngh ny hon ton c th thc hin c. Tuy nhin, s in thoi E.164 ang do ITU-T v chnh ph cc nc thnh vin qun l, cn tn min Internet li c qun l trn nguyn tc t iu tit ca th trng ngi s dng. V vy, vic qun l nh s trong ENUM l mt vn cn gii quyt khi a cng ngh ny vo thc t.KT CHNGChng ny trnh by v cc giao thc h tr cho truyn thoi qua mng IP, trong tp trung vo nhng giao thc thuc nhm bo hiu v iu khin cuc gi VoIP. Trong ni dung ca chng cp n c im giao thc, cc phn t mng cng nh l vn thit lp kt ni trong cc h thng VoIP da trn H.323 v SIP; tho lun v nhng c gng ca cc t chc v giao thc lin quan m bo cho vic lin kt cc dch v trong min IP. Cui cng, m hnh h thng VoIP tch hp s dng bo hiu lai ghp v vn m bo nh s trong h thng VoIP ton cu cng c trnh by.Do h tr tt lin kt vi mng PSTN v c tnh n nh, H.323 vn c xem l mt giao thc ph bin dnh cho VoIP. Phin bn mi ca H.323 c gng lin kt vi mng SIP trong vic cung cp nhng c im v chc nng H.323 c nhiu tnh thn thin vi Internet hn. Vi nhng dch v chuyn mch IP, mt ln na H.323 c xem l t hon thin tha mn yu cu ca ngi s dng. Tuy nhin, khch hng VoIP ang chuyn hng nhanh chng sang SIP bi v SIP l mt giao thc thng minh v linh hot. Cc phn t mng u tin ti h tr hon ho cho vic kt ni s dng SIP v dch chuyn theo hng dch v da trn SIP. Microsoft cng nhanh chng h tr SIP trong h iu hnh Windows XP ca mnh.SIP l giao thc c la chn v n khuyn khch s i mi ti im cui hay thit b cui. N i theo m hnh ca Internet trong vic to cc dch v mi cng nh phn phi v qun l chng. Chiu hng trong nhiu doanh nghip v gia cc nh cung cp l SIP ha H.323 hn l H.323 ha SIP. Thm ch nu H.323 hon ton b SIP ha, SIP vn s l ngi chin thng v n n gin v ging vi kin trc, giao thc ca Internet: im cui l cc thit b thng minh (nh PC), v mng l s kt hp ca cc b nh tuyn v my ch (ch khng phi tng i hay mainframe). SIP gn nh ging vi giao thc H.225, cn SDP c th c so snh vi H.245.Khi cp n giao thc gia MG v MGC, c th thy rng vic s dng H.248/Megaco s pht trin nhanh mc d c th s dng H.323 hay MGCP trong khu vc ny. Lin kt gia SG v MGC s s dng SIP mc d c th dng SCTP. lin kt gia cc MGC th SIP-T, SCTP hoc BICC-CSx c th c s dng. Ngi ta ang xem xt l liu IETF v ITU-T c kt hp cc hot ng ca h v SIP/SCTP v BICC-CSx hay khng. Trong qu kh, hai t chc ny thnh lp cc nhm pht trin c lp cc giao thc iu khin phng tin/cuc gi cng nh kin trc v giao thc truyn ti phng tin. Mt v d l giao thc H.248/Megaco c hon thin bi c hai t chc, thc y s pht trin MGC v kin trc mng da trn chuyn mch mm, h tr s tin ha ca mng PSTN. Ni chung, cc chun tt hn, n nh hn, c tnh m hn s c pht trin nu hai t chc ny lm vic cng nhau t c cng mc ch. Mt lu l ISC v MSF lun theo sau mi s kt hp pht trin hay khuyn ngh ca ITU-T v IETF.i vi vic lin kt dch v vng IP v PSTN, nhm nghin cu SIGTRAN pht trin giao thc SCTP cho truyn dn tin cy v an ton cc bn tin SS7 qua mng IP. Cc nhm lm vic PINT (PSTN and Internet Inter-Networking) v SPIRITS (Service in the PSTN/IN Requesting Internet Service) ca IETF khuyn ngh vic s dng SIP v SCTP to dch v cuc gi in thoi khi ngun t mng IP v ngc li. SIP cho php to nhanh, gi thnh hp l, duy tr, phn phi kt ni v dch v VoIP tin tin, cn SCTP c mong i l giao thc vn chuyn hiu qu bn tin SS7 qua mng IP. Nhng giao thc ha hn nh SIP, TRIP, ENUM, H.248/Megaco, SCTP v BICC s c s dng v ci tin nhm to nhanh, qun l ng v phn phi cc dch v. Giao thc thi gian mng NTP (RFC 1345) rt hu ch cho vic ng b ng h ca nhiu phn t mng VoIP v cung cp dch v thoi thi gian thc qua khu vc a l rng ln. S ng b ny gip nng cao cht lng thoi v tnh tin cy dch v. NTP c th hot ng mt my ch xc nh gi l my ch thi gian mng NTS, v c th phn b thng tin nh thi t mt ngun thi gian c tin cy cao n cc b nh tuyn v MG dng cho dch v VoIP.Kin trc chuyn mch mm da trn cc giao thc bo hiu v iu khin cuc gi cng vi nhiu k thut m bo QoS mi v ang c tip tc pht trin. Khng nghi ng g, chng s khuyn khch s hi t gia mng d liu v mng thoi, v kt qu l s hin din mi ni ca VoIP.

G.711

G.728

G.722

G.723.1

G.729

Tn hiu thoi

H.263

H.261

T.125/T.122

T.124

T.126

T.127

RTP

RAS

RTCP

H.450.1

H.450.3

H.450.2

X.224.0

H.245

H.225

TCP

UDP

H.235

Tn hiu video

D liu

Cc dch v b sung

iu khin

ng dng

Trnh din

Phin

Giao vn

Vt l

Lin kt d liu

Mng

Thit b I/O video

Thit b I/O audio

ng dngd liu ngi dng

M ha video H.261, H.263

M ha audio G.711, G.722 G.723, G.728 G.729

Tr ng thu

LpH.225.0

Giao din mng

iu khin H.245

iu khincuc gi H.245

iu khinRAS H.225

iu khinh thng

Giao din ngi dng iu khin h thng

Data

CP 1

CP 3

CP 2

GK quc gia

GK khu vc 1

GK khu vc 2