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C huong 6 GIAO THLfC DIEU KHIEN CONG PHUONG TIEN - MEGACO/H.248 6.1 G l 6 l THI$U CHUNG vfi GIAO THtfC Bltu KHlfhs c6 n G PHUONG TlfN Dfiu nam 1998 nhidu nha nghien curu cung nhu cac nha dieu hanh m ang da dua ra mdt so giao thirc didu khien cong phuang tidn khac nhau (M GCP cua IETF, M DCP cua ITU-T...)- M ac du nhu c5u ve m dt giao thurc didu khidn cdng phuang tidn ia r&l ro rang nhung khdng co giao thurc nao nhan duac su ung hd hoan toan. Tdi cud'i nam 1998, IETF thanh lap nhom nghien cun v i giao thurc di6u khien cdng phuang tidn M EGACO (M Egaco GAteway Control working group) vdi nhidm vu xay dung m dt tidu chuan md trdn co sd IP dua trdn nguydn ly. chu/td de’ di6u khien cac cdng phuang tidn, Nortel Network la td chuc dung ddu nhom nay. Nhom nghien curu da lira chon cac uu diem cua hai giao thurc tidn than M GCP va MDCP, ddng thdi bo sung cac tfnh nang tang cudng, tdi thang 3 nam 1999, Nortel Network chinh thurc cdng bd ve m dt giao thurc dieu khien c6ng phuang tien mdi MEGACO. Song song vdi cac nd luc cua IETF trong viec xay dung giao thurc M EGACO, vao thang 5 nam 1999 nhom nghien curu 16 (S G I6 - study group 16) cua ITU -T cung khdi xudng mdt du an xay dung giao thurc dieu khien cdng phuang tidn GCP, sau nay la giao thurc H.248. Cung vao m ua he nam dd, hiep dinh ve vide xay dung m dt chu£n quoc td' M EGACO/H.248 cung duac ky ket giua hai td churc nay. Tdi thang 6 nam 2000, M EGACO/H.248 chinh thuc dugc phe chuan bdi hai td chuc IETF va ITU-T. Trong qua trinh xay dung M EG A C O /H .248, nhung ngudi ung ho M GCP van yeu cau IETF dua ra m ot RFC ve giao thuc MGCP. V ao thang 10 nam 1999, van ban nay dugc ban hanh nhung day khdng phai la tidu chuan chinh thuc cua IETF, RFC nay cung khdng dugc S G I6 cua ITU -T thira nhan mac dii hidn nay ISC ung hd MGCP. Vao thdi diem hidn nay M EG A CO la giao thurc chuan qudc td' duy nhat danh cho dieu khien moi loai cdng phuang tien theo c a che' chu/td. M EGACO se tiep tuc dugc cai tien va phat trien han nua nhd nd luc khong ngimg cua IETF, ITU-SG16 va cac td chuc tieu chuan hoa khac. Chuong 6: Giao thiic dieu khien tdng phucmg tien M EGACO/H.248 - 99 6.2 G IA O THCTC M EG A C O /H .248 6.2.1 Tdng quan ve giao thurc M EG AC O/H .248 M EGACO la giao thurc didu khidn cdng phucmg tien noi chung, bao gdm cdng noi hat, trung k£ trong mang PSTN, giao didn ATM , giao didn thoai va ducmg day tuong tu, didn thoai IP, cac loai may chu... Vdi tfnh nang hd trp rdng rai cac urng dung mdt cach mdm deo, don gian va hidu qua d mure chi phi hop ly, M EGACO se la chuan dupe su dung trong mang thd' hd sau NGN. M EGACO khdng bi rang budc vdi ba't ky mdt giao thurc didu khidn cudc gpi ngang ca'p nao (vf du nhu SIP hay H.323) va hoan toan tuy thudc v&o thid't kd' cua ngudi quan tri mang. Kid'n true cua M EGACO dua trdn 3 ldp: ldp MGC, ldp M G Vci ldp M EGA CO (Hinh 6.1). • Ldp M GC chura tat ca cac phdn mdm didu khidn, xu ly cudc gpi. Ldp nay thuc hidn cac dac didm d mure cudc gpi nhu phat tridn cudc gpi, chuydn cudc gpi, hdi thoai hay giS cudc gpi. Ldp M GC cQng thuc hidn giao ti£p vdi cac MGC cung nhu cac thuc thd ngang ca'p hay cap dudi khac, MGC quan ly moi thuoc tinh trong qua trinh giao tid'p. • Ldp M G thuc hidn cac kd't ndi luu lupng di va tdi cac m ang khac, tuong tac vdi cac ludng luu lupng nay qua urng dung bao hidu va sir kidn. Ldp MG cung dieu khien 100 Chuyen mach mem va itng dung trong mang vien thdng the he sau cac thudc tinh thia't bi cua c<5ng phuang tidn (vf du nhu giao didn vdi ngudi dung). Ldp nay khdng he biet gi vd viec di£u khi&i cac thudc tfnh cudc gpi va hoat ddng theo su didu khien ciia ldp MGC. • Ldp M EGACO/H.248 quy djnh c£ch thurc m a ldp MGC didu khidn ldp MG. 6.2.2 Churc nang cua giao thurc M E G A C O /H .248 Giao thurc M EG A CO/H .248 dinh nghTa giao didn didu khi£n cua M GC ddi vdi MG. M EGACO cung ca'p cac churc nang sau: Trung ke MEGACO M . EC?AC° MEGACO Q.931/Q.SIG RGW RGW CO: Tong dai trung tam SG: Cong bao hieu AGW: Cdng truy nhapi MGC: Bo dieu khien cdng phi/ong tien TGW: Cdng trung ke RGW: Cdng tam tru H inh 6.2: V i tri va chuc nang cua giao thuc M E G A C O IH .248 D ilu khien cac loai M G khac nhau (TGW , RG W , A GW , M S...) Hd trp dam phan quyd't djnh cac thudc tfnh cudc goi Cd kha nang xu ly cudc gpi da ngudi dung Hd trp QoS va do ludng luu lupng (cac thdng tin thdng kd sau mdi kd't ndi) Thdng bao ldi giao thuc, m ang, hay cac thudc tfnh cudc gpi 6.2.3 Vi tri cua giao thurc M E G A C O /H .248 trong m o hinh OSI N hu chi ra trong hinh 6.3 giao thuc M EGACO thue hidn churc nang cua m inh d 3 ldp tren cung trong m d hinh OSI: ldp urng dung, ldp trinh dien va ldp phidn. Chuang 6: Giao thUc dieu khien cSng phucmg tien MEGACO/H.248 - 101 6.2.4 Cac kh£i niem trong giao thurc M EG A C O /H .248 Cac loai cong (G ateW ay): GW co dia chi IP va sd cdng UDP mac dinh cua MGC quan ly no - TGW (Trunking G ateW ay) la cdng ndi giua cac tdng dai trung kd' m ang PSTN va m ang IP. - AGW (Access GateW ay) la cdng ndi giua mang ISDN, tdng dai PBX va mang IP. - RGW (R esidential GateW ay) lk cdng ndi giua m dt nhom cac may dien thoai (ndi true tiep vao cdng nay) va mang IP. - NAS (N etw ork Access Server) cung ca'p kha nang truy nhap Internet. - IVR (Interactive Voice Respone) duoc MGC didu khid’n de? thu cac sd va gui FA X ... Mdi loai G W cd kha nang hd trp cac gdi tin khac nhau. Thiet bj dau cudi (Term ination): MGC coi GW la dai dien cho m dt nhom cac term ination, trong dd mdi term ination chiu trach nhidm xu ly cho mdt loai luu lupng. Mdi term ination dupe GW khdi gan m dt ID tai thdi diem nd dupe tao ra. Cd hai loai term ination la: - Term ination co dinh (cac giao didn vat ly, kdnh TDM). Ddi vdi loai term ination nay vide su dung cac lenh “A dd” hay “Subtract” chi don gian la viec lay chung ra hay them vao Null context. - Term ination tam thdi hay term ination Id-gi'c (cdng RTP ndi cdng ndi vdi m ang, chi tdn tai khi sir dung). Loai termination nay dupe tao ra bdi lenh “A dd” va bi xoa di bdi ldnh “ Subtract”. Chuyen mach mem va ifng dung trong mang vien thong the h i sau 102 GW duac MGC coi nhu term ination gd'c, didu nay c6 y nghTa khi MGC m udn lam viec vdi chmh GW (vf du khi tuyen bd GW la “in” hay “out” mdt dich vu nao do). Giao thurc M EGACO co kha nang lam viec vdi mdt s6 luong Idn c£c term ination la do term ination co cac thudc tfnh lira chon (event, signal, statistic). Cac thudc tfnh nay duoc dua vao cac gdi va M GC cd the’ chi dinh term ination la nd chi tie'p nhan nhung gdi nao. Tai mdi thdi didm, term ination cung duac didu khidn d m dt ch£ dd xac dinh (ch£ dd chi nhan, chi gui hoac vua nhan vira gui). Term ination la noi di va d£n eua cac ludng luu luong hay didu khidn. C o n tex t: Lk khai niem m ang tfnh ddt ph£ cua M EGACO so vdi c ic giao thirc cung loai trudc nd. Khai niem nay cho ph6p tao ra cac phien lien lac da didm. Mdi d£u cudi cd thd tham gia nhidu context khac nhau vdi cac loai luu lupng khac nhau (vf du khi d£u cudi tham gia m dt phidn truydn thdng da phuong tien). D ay la mdt phien k£t ndi bao gdm nhieu term ination. Mdi context dupe GW tao ra ban dau chi cd mdt term ination, cac term ination ke't ndi vdi term ination ddu tien se 15n lupt dupe them vao context nay. Context se bj xoa bd khi term ination cudi cung dupe giai phdng. Sd lupng term ination tdi da trong m dt context phu thudc vao kha nang cua GW (nhirng GW chi hd trp liSn lac didm - didm se chi cd tdi da 2 term ination trong m dt context). Context dupe MG gan m dt sd nhan dang ID bao gdm 32 bit (ID la duy nha't ddi vdi m dt MG). Ta't ca cac term ination khdng tham gia vao mdt kd't ndi nao se nam trong Null Context. Hien nay Context cd 3 thuoc tfnh: topology descriptor (md ta topo phien ke't ndi), priority flag (cd uu tien, hudng dan GW phan b6 tai nguydn trong trudng hop khan hi£m), em ergency flag (cd khan, chi ra context nao se dupe luu lai va khdi phuc trong trudng hop cd sir cd). Cac thudc tfnh khac cua context cd thd dupe bd sung trong tuong lai. T ra n s a c tio n : La m dt chuydn giao, m di transaction gdm transaction hoi (Request) va transaction tra ldi (Reply). Transaction Pending dupe sir dung dd thdng bao rin g transaction v5n dang duoc xir ly (sir dung khi transaction nao dd bi tim eout). Mdi transaction cd m dt sd nhan dang ID. Sd nhan dang ID cd gi£ tri tir 1 tdi 99999. Thdng tin trao ddi giua M GC va cac GW dudi dang cac chuydn giao (chua c£c lenh va cac ban tin thdng bao su kien, tra ldi...), cac lenh trong mdi chuydn giao se duoc xir ly theo thu tir da chi ra. E v en t: La cac sir kien cua ddu cudi (nhu onhook (nha'c m ay), offhook (dat m ay)...). Cac sir kien nay dupe MG phat hien va bao cao tdi MGC. M GC se xem xet chi cac sir kien ma 110 quan tam d ba't ky thdi didm nao (dupe chi ra bdi event descriptor). Chuang 6: Giao thuc dieu khien cdng phucntg tien - MEGACO/H.248 103 Signal: La bao hidu tao ra cac am bao hay hidn thi hinh anh o dau cuoi. Thai gian ton tai cua bao hidu co thd do MGC quy dinh hoac co the t6n tai cho tai khi bi loai bo. No se bi loai bo bat cu khi nao mot su kien dugc phat hien a dau cuoi tru khi co su can thiep cua MGC. Term ination descriptor (mieu ta cac ket cuoi): Cac thuoc tinh cua termination dugc nhom lai thanh cac descriptor bao g6m: - Term ination state descriptor: Cac thudc tinh cua termination (test, co quyen hay bi cam sir dung mot dich vu...) - M edia descriptor: Bang m6 ta cac lu6ng luu lugng (thoai, dat may,...) - Event descriptor: Mo ta cac sir kien dugc phat hien bdi GW va hanh dong dap lai sir kien do - Signal descriptor: M o ta cac bao hidu co thd xay ra d termination - Stream descriptor: Bang cac descriptor cua remote, local, local control doi vai m ot luong liru lugng xac dinh. - Local control descriptor: Chua cac thuoc tinh can quan tam giiifa GW va MGC (che do cua term ination, cac xu ly cua GW khi nhan dugc local hay remote descriptor). - Local descriptor: Chua cac thuoc tinh chi ra luong liru lugng ma GW nhan tu thuc the dau xa. - Rem ote descriptor: Chiia cac thuoc tmh chi ra lu6ng liru lugng ma GW gui tai thuc the dau xa. - Digitm ap descriptor: Dinh nghia mdt day tap hgp cac su kien (ve quay so) co the co (theo ke hoach danh so). Day nay dugc gui tai GW dd thu cac chu so quay bai khach hang va gui tdi MGC dudi dang cac gdi hoan chinh (toan bo sd bi ggi). Vi du ve mot “digitm ap”: (01 0 0 l[ 1 - 7 ] x x x I8 x x x x x x x I F x x x x x x x I E x x I 9 1 x x x x x x x x x x I9 0 1 l x . ) Trong dd: 0 Local operator (Nha khai thac noi hat) 00 Long-distance operator (Nha khai thac dudng dai) xxxx Local extension num ber (starts with 8xxxxxxx Local num ber (sd ndi hat) #xxxxxxx O ff-site extension 1 - 7) 104 Chuyen mach mem xa ung dung trong mang viin thdng the he sau *xx Star services 91xxxxxxxxxx Long-distance num ber (Sd dudng dai) 9011 + 15 so di quoc te - Observed event descriptor: Mo ta cac sir kien quan sat duoc (co trong Idnh “N o tify” hay “A u d it Value") - Package descriptor: Trong lenh “A u d it V a lu e”, dung da tra lai bang cac goi tin gui di tu termination. - Service change descriptor: Ly do dua ra lenh “ Service change ”. - Statistic descriptor: Trong lenh “A u d it” hay “Su b tra ct”, de bao cao cac thdng kd d termination. - Topology descriptor: Chi ra topo (cau hinh) cua context. - Audit descriptor: Trong lenh “A u d it”, xac nhan thdng tin ydu cau - Error descriptor: Chua ma ldi va m a ldi van ban (tuy chon) trong ldnh “ Notify ” (hdi va tra ldi). - Event Buffer descriptor: Md ta su kien vira dupe GW phat hien khi kfch hoat event buffering. 6.2.5 Truyen d^n cac ban tin cua giao thurc M EG A C O /H .248 C a che truyen d in su dung can phai dam bao tinh tin cay, cac lenh dang giri di va chd xac nhan tu phfa nhan se dupe luu giu m ot cach ddc lap. Cac ban tin M EGACO cd the dupe truydn d in qua ldp U D P/IP hoac TCP/IP. Cac GW va cac MGC se dupe gan cac dia chi IP, cac ludng luu lupng di va den se qua cac cdng UDP hay TCP dupe chi ra. Vf du nhu cong danh cho lenh “ Service Change request" la 2944 khi sir dung ma hoa van ban va 2945 khi su dung m a hoa nhi phan (ddi vdi ca UDP va TCP), cac cong nay cung dupe sir dung khi khdng cd cdng nao dupe chi ra. Cac transaction Reply se dupe gui tdi cung vdi cdng m a transaction request dupe gui di. Trong qua trinh truyen d in cac ban tin M EGACO cung dat ra mdt van dd ve do trd cua cac ban tin, d in tdi do trd cua cac lenh va tfnh “hop thdi” cua cac xir ly tai GWr hay MGC. De giai quyet van de nay RFC 3525 cung dua ra mdt sd quy tic trong vide xir ly cac ban tin M EGACO tai MGC. Chuong 6: Giao thuc dieu khien cSng phuong tien - MEGACO/H.248 105 6.2.6 Cac lenh cua giao thurc M EG ACO/H.248 Giao thurc M EGACO sii dung 8 lenh trong giao dien di£u khien giua MGC va GW. Bao g6m: - Add: Duoc sir dung d6 them mdt term ination vao context, cung co the de tao mdt context (ne'u dd la term ination d£u tien trong context nay). - M odify: Sir dung de’ thay ddi thuoc tinh, sir kien hay cac bao hieu d mdt termination. - Subtract: Su dung de xoa mdt term ination khdi context, cung cd the la xoa ludn ca context (ne'u dd la term ination cudi cung trong context nay). - Move: Chuyen m ot term ination tir m dt context nay sang m dt context khac. - Audit Value: Tra lai trang thai hien tai cua term ination (M o hieu, sir kien, thudc tfnh, sd lieu thong ke). - Audit Capability: Tra lai t&'t ca cac gia tri cd the cd cua term ination (bao hieu, sir kien, thudc tfnh, sd lieu thdng ke). Cac lenh tren duoc su dung bdi MGC. - Notify: GW sir dung de bao cao cac sir kien ma nd phat hien duoc tdi MGC. - Service Change: Lenh nay dupe sir dung bdi: + GW , de’ thdng bao vdi MGC rin g mdt nhom term ination cd y dinh rdi khdi hay tham gia m dt dich vu nao dd. + GW , de dang ky vdi M GC nd khdi ddng. + MGC, d£ tuyen bo m ot chuyen giao tdi GW + M GC, de lenh cho MG nao dd dua mot nhom term ination hay mot term ination tham gia hoac ra khdi mdt dich vu. 6.2.7 Ma hoa lenh cua giao thurc M EG A C O /H .248 Cac ban tin M EGACO cd the dupe m a hoa bang hai cach: m a hoa nhi phan (binary encoding) va ma hoa van ban (text encoding). Trong phuong phap ma hoa nhi phan, tieu chuan ISO/ITU ASN.l dupe sir dung. ASN. 1 la ngdn ngiir dinh nghTa cach giri du lieu giua cac he thong khdng gidng nhau, nd dinh nghTa d cac he thdng cung mdt cu phap dur lieu (trong cac giao thuc tang urng dung). ASN. 1 dupe viet bang cac ngdn ngu: khac nhau trong timg he thdng, phu hop vdi 106 Chuyen much mem vd ifng dung trong mang vien tltong the he sau tung hd thdng. Khi mot he thdng mud'n giri du: lidu, hd thdng dd se ma hoa dur lidu cin giri theo A S N .l, sau dd gui di, he thdng nhan se ti£n hanh giai ma theo chuan dinh sin A SN .l. Cac luat m a hoa theo chuan A SN .l bao gdm: BER (Basic Encoding Rule), CER (Canonial Encoding Rule), PER (Package Encoding Rule), DER (Distinguished Encoding Rule). Vide su dung luat ma hoa nao la tuy ngudi thid't k£. Trong phuang phap m a hoa van ban, chu£n ABNF duac sir dung (RFC2234). C6 th£ sir dung 2 dinh dang: rut gon (com pact text) va d£y du (pretty text). Chung duoc md ta nhu sau: Rut gon !/1 [124.124.124.222] T = 9998 {C = -{SC = ROOT {SV {MT = RS. AD = 55555, PF = ResGW/1 , RE = "901 MG Cold B oor})}} D a y du M E G A C O /1 [124.124 124.222] Transaction = 9998 { Context = - { ServiceChange = ROOT { Services { Method = Restart, ServiceChangeAddress = 55555, Profile = ResGW/ 1, Reason = "901 MG Cold Boot" } } } } Ca hai dinh dang d6u cd uu va nhuoc di£m cua minh, dinh dang rut gon cho ban tin cd kfch thudc nho han, thdi gian m a hoa ngan han tuy nhidn dd tin cay khdng cao bkng djnh dang ddy du. 6.2.8 Cu phap lenh cua giao thurc M EG A C O /H .248 Dd’ tidn phan tich ta cd thd’ la'y m dt ldnh d£ m inh hoa, day la ldnh tir M GC tdi GW. MGC to RGW 2: MEGACO/1 [216.33.33.61]: 27000 Transaction = 1240 { Context = 2 { Modify = TermB { Signals {cg/bt} Media { LocalControl { Chuong 6: Giao thtic dieu khien cSng phuong tien - MEGACO/H.248 Mode = recvonly} } }. Modify = EphB { Media { LocalControl { Mode = recvonly} } } } } } Ldnh trong vf du trdn bao g6m cac phdn sau: - D ia chi IP cua noi gui (M GC hay GW) 216.33.33.61 (IPv4) - S6' c6ng nai gui 2700 - S6 nhSn dang transaction 1240 + Context ID + C ontext ID... M 6i C ontext se c6 nhi6u ldnh: o N otify 0 A udit O M odify Trong mdi ldnh lai g6m: • Term ination ID — TermB • Local Term ination State • Cac descriptor 107 Chuyen mcich mem va ung dung trong mang vien thdng the he sau 108 T ra ns ac ti on x A c ti on 1 +--------------+ +--------------- + +--------------- + | C om mand I 1 | | C ommand I I 2 + ------------------- + | | | C om man d | 3 +-------------- + | | + -------------------- + + ---------------------+ + ----------------- + + --------------- - + | Co m m a n d | 4 | | + -------------------- + A c ti on 2 +------------ | Command I 1 A c ti on 3 + ---------------- + | C om man d | | C o mm an d | | C o mm an d | I I I | | | 1 2 +-------------- + +--------------- + 3 +---------------+ Ta co the thay: mdi transaction g6m nhidu action (m6i action cho 1 context), m6i action g6m nhieu lenh, m6i lenh se co cac descriptor. 6.2.9 Cau true ban tin M EG A C O /H .248 Ban tin giao thuc MEGACO/H.248 Header Transaction Req or Reply Transaction Req or Reply Trans Hdr Action Ctx Properties Transaction Req or Reply Action Command Descnptor H inh 6.4: C an true ban tin M E G A C O Command 109 Chuong 6: Giao thurc dieu khien cong phuong tien - MEGACO/H.248 M6i ban tin M EGA CO bao g6m nhi£u transaction va mdt header. Trong do header chura ckc th6ng tin nhan thuc, bao mat. Mdi transaction g6m nhidu action (cho m6i context) va mdt transaction header (chura transaction ID). M6i context lai gom mot context header, mdt context properties va cac ldnh. Context header chura contextID, context properties chura cac thdng tin v6 ca'u hinh context, thudc tinh, mure iru tien. Mdi ldnh gdm m dt com m and header va cac descriptor cua lenh dd. 6.3 H O AT D0NG CU A G IAO TH tfC M EG A C O /H .248 Khi m dt d iu cudi nko dd nha'c may va dinh thuc hien cudc goi, sir kien nhac may nay se duoc ph£t hidn bdi MG quan ly nd. MG se thdng bao sir kidn nay tdi MGC true thudc, MGC se chi djnh MG nay bang mdt ldnh dd’ gui am bao mdi quay sd tdi dau cudi dd, ddng thdi ban dd sd (digitm ap) cung duac MG nay cap nhat tir MGC, dd’ phuc vu cho vide thu c ic chu sd va giri toan bd sd duac quay vd MGC. Gia su d£u cudi bj goi thudc mdt MG khac nhimg cung duac quan ly bdi MGC trdn. Qua trinh thid't lap lien ke't duac tidn hanh theo 3 budc c a ban sau: OQQ oao OQQ oaa Oien thoai ti/ong ti/ Oien thoai ti/ong tu H inh 6.5: M o td cuoc goi M E G A C O - MGC yeu cau MG thu nha't thid't lap mot ke't ndi tai diem ket cudi thu nhat. MG nay se phan bd tai nguydn cho kd't ndi yeu cau va dap ung lai bang ban tin tra ldi. Ban tin tra ldi se chura cac thdng tin can thiet de’ MG thu hai cd the’ giri cac Chuyen mach mem va ifng dung trong mang viin thdng the he sau 110 ban tin mdt cach tin cay tdi lidn kd't vua thid't lap. Cac th6ng tin nay c6 th£ Ik: dja chi IP, tdn c6ng UDP, TCP hay cac thdng tin ddng goi ban tin. - Tircmg tir, MGC cung ydu cku MG thur hai thid't lap mdt lidn kd't d didm kd't cudi thu hai. MG nay phan bo tai nguydn cho kd't nd'i nay trdn c a sa cac thdng tin trong ban tin dap umg cua MG thu: nha't. Tdi luat, MG thu hai cung d ip umg lai bang ban tin chura cac thdng tin ckn thid't nham dam bao MG thu nh£t cd th£ gui cac ban tin m ot cach tin c$y tdi lidn kd't vira thid't lap bdi MG thu hai. - Cac thong tin trong ban tin dap ung cua MG thu hai se duoc giri tdi MG thur nhat. Khi nay lien ket da duoc thid't lap, qua trinh truydn thdng cd thd didn ra theo hai chidu. Luu lupng dupe truyen tai nhd cac giao thirc RTP hay RTCP. Trong trudng hop hai MG dupe quan ly bdi 2 M GC khac nhau, cac M GC nky se trao ddi cac thdng tin bao hieu thdng qua mot giao thurc bao hieu tir MGC tdi MGC (c6 the la SIP hay H.323) de dam bao viec ddng bd trong vide thiet lap kd't nd'i tdi hai di£m ke't cuoi. Khi lien ke't da dupe thiet lap, cac tham so ciia no dupe giam sat bdi MGC va c6 the dupe thay doi dudi cac lenh ciia M GC (vf du nhu them m dt ke't cudi vao lidn kd't). 6.4 UU DIEM CUA GIAO THUC M EGACO/H.248 SO V 6 l CAC GIAO THttC D ltlJ KHIEN CONG PHUONG TIEN KHAC So vdi giao thurc MGCP, giao thurc M EGACO version 1 (phidn ban 1) co cac uu diem noi troi sau: • Hd trp djch vu da phuang tien, eae djch vu hdi nghj da diem tang cudng. • Cai tien cu phap lenh de viec xir ly ban tin hieu qua hon. • Co kha nang lua chon giao thuc TCP hay UDP. • Chap nhan ca viec ma hoa van ban hay nhj phan. • Cac goi tin ciia M EG A CO chi tie't hon MGCP, han the' nua cac gdi tin mdi co the dupe djnh nghTa dira tren cac goi tin co sd nay. • Dua ra khai niem context, khai niem nay hd trp kd't nd'i da djch vu, da didm. Dudi day se m d ta hoat ddng ciia M GC va MG theo giao thuc M EG A C O trong timg trudng hop cu the. Dudi day se khao sat hoat ddng eua M EGACO hd trp cac djch vu thdng thudng va cac dich vu bd sung. Chiton# 6: Giao thuc dieu khien cdng phuong tien - MEGACO/H.248 111 6.5 K flT N d i GI0A HAI CONG N0I HAT (RGW ) Gia su co hai dau cuoi nguai sir dung duac ket n6i vdi hai RGW. Trong do, hai RGW nay duoc quan ly bai cung m6t MGC nhir bieu didn hinh 6.5. Qua trinh MGC didu khidn cac RGW xir ly cuoc goi didn ra nhu sau: B u o c I : Ban dau MGC giri lenh “M odify” tai tat ca cac RGW de phat hien sir kien offhook (thue bao nhac may). Ban tin cua lenh “M odify" nhu sau: MGC to RGW1: MEGACO/1 [216.33.33.61]: 27000 Transaction = 1234 { Context = - { Modify = TermA { Media { LocalControl { Mode = Receiveonly} }. Events =1111 {at/of} } } } B u o c 2: Cac RG W lan luat tra ldi lenh tren cua MGC bang cac ban tin Reply MG1 to MGC: MEGACO/1 [209.110.59.34]: 25000 Reply = 1234 { Context = - {Modify = TermA} } B u o c 3: Gia sir nguai dung A thuoc RGW l nha'c may tao tin hieu nhac may, sir kien nay se duac RGW l bao cao tai MGC bang lenh "N otify". MG1 to MGC: MEGACO/1 [209.110.59.34J: 25000 Chuyen mach mem va ung dung trong mang vien thdng the he sau 112 Transaction = 2000 { Context = - { Notify = TermA {O bservedEvents =1111 { 20010202T10000000: al/of}} } } B udc 4: M GC giri Reply cua lenh nay cho RG W 1. MGC to MG1: MEGACO/1 [216.33.33.61]: 27000 Reply = 2000 { Context = - {Notify = TermA} } Bu&c 5: MGC se giri lenh “M odify” tdi RG W 1, ldnh nay g6m 3 descriptor: signal descriptor dugc sir dung dd gui am mdi quay sd tdi ngudi dung A, digitm ap descriptor chua md hinh mfiu cac sd co the quay theo kd' hoach danh sd (vf du nhu 29****), event descriptor liet ke cac goi DTMF, goi tin hoan thanh quay sd va gdi tin giam sat trang thai dat may ciia d iu cudi. MGC to MG1: MEGACO/1 [216.33.33.61]: 27000 Transaction = 1235 { Context = - { Modify - TermA { Signals {cg/dt}, DigitMap= D m apl {(29XX)} Events = 1112 { al/on, dd/ce {DigitMap=Dmap1} }. }}} Bu&c 6: RGW l tra ldi M GC bang mot ban tin Reply. RGW1 tien hanh xir ly cac descriptor theo thur tu signal, digitm ap, event descriptor. Dau tidn am mdi quay sd se Chuong 6: Giao thuc dieu khien cong phuctng tien - MEGACO/H.248 1 13 dugc giri tdi term ination A, sau do digitm ap se dugc cap nhat vao ca sa du lieu cua RGW 1, digitm ap dugc kich hoat khi RGW 1 thu dugc sir kien hoan thanh quay sd. termination A sau khi nhan dugc am mdi quay sd se tien hanh quay so. MG1 to MGC: MEGACO/1 [209.110.59.34]: 25000 Reply = 1235 { Context = - {Modify = TermA} } B udc 7: Khi cac con sd dugc RGW l thu day du va hgp le, chung se dugc giri tdi MGC bang lenh “N otify". MG1 to MGC: MEGACO/1 [209.110.59.34]: 25000 Transaction = 2001 { Context = - { Notify = TermA {ObservedEvents =1112 { 20010202T10010000:dd/ce {ds="2992", Meth=FM}}} } } B u d c 8: M GC xac nhan lenh tren bang ban tin Reply giri tdi RGW l . M GC sau khi nhan lenh tren se phan tich sd bi goi va biet dau cudi term ination B do thuoc RGW 2 (gia sir dau cudi nay r6i va san sang nhan cuoc goi). MGC tiep tuc di6u khien RGW l . MGC to MG1: MEGACO/1 [216.33.33.61]: 27000 Reply = 2001 { Context = - {Notify = TermA} } B u d c 9: MGC se giri cho RGW l hai lenh. Lenh "Add" de tao mot context va them ngay term ination A vao do. MGC biet rin g term ination B rdi, nd se giri hdi am Chuyen much mem vd ifng dung trong mang vien thdng the he sau chuong cho term ination A. Lenh thu 2 de tao m6t ddu cu6'i 16-gic A va them dau cudi nay vao context vua tao ra. MGC to MG1: MEGACO/1 [216.33.33.61]: 27000 Transaction = 1236 { Context = $ { Add = TermA { Signals {cg/rt} } Add = $ { Media { { LocalControl { Mode = Receiveonly, I Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4 } } } } } B udc 10: RGW1 se giri ban tin Reply cho M GC bao gom contextID( 1), dia chi IP va so cong danh cho liru luong. MG1 to MGC: MEGACO/1 [209.110.59.34]: 25000 Chuong 6: Giao thifc dieu khien cdng phuong lien - MEGACO/H.248 Reply = 1236 { Context = 1 { Add = TermA, Add=EphA{ Media { Local { v=0 c=IN IP4 209.110.59.33 m=audio 30000 RTP/AVP 4 a=recvonly } ; RTP profile for G. 723 is 4 } } } } } B u o c 11: M GC se giri tdi RGW 2 2 lenh. Lenh 1 de tao mot context va them term ination B vao context nay. Bao hieu chuong cung dugc giri tai termination B nha lenh signal descriptor. Lenh thur hai se tao mot dau cudi lo-gic B va them dau cudi nay vao context vira tao ra. Cac thdng tin dia chi IP, sd cong cua term ination A cung dugc gui tdi RGW 2. MGC to MG2: MEGACO/1 [216.33.33.61]:27000 Transaction = 1237 { Context = $ { Add = TermB { Media { LocalControl {Mode = Receiveonly} }, Signals {al/ri} Events= 1234{al/of}, Chuyen much mem va ifng dung trung mang vien tliong the he sau h Add = $ {Media { LocalControl { Mode = Receiveonly, h Local { v=0 c=IN IP4 $ m=audio $ RTP/AVP 4 }, Rem ote { v=0 c=IN IP4 209.110.59.33 m=audio 30000 RTP/AVP 4 } ; RTP profile for G. 723 is 4 } } } } } B u d c 12. RGW 2 sau khi nhan lenh se thirc hien lenh va giri ket qua thuc hien tcri MGC, bao gom contextID (2), dia chi IP va so c6ng danh cho luu lugng. M GC dgi cho term ination B phat tfn hieu nhac may (offhook). MG2 to MGC: 'MEGACO/1 [207.176.47.89]: 26000 Reply = 1237 { Context = 2 { Add = TermB, A d d = EphB{ Media { Local { 117 Chuong 6: Giao thuc dieu khien cdng phucmg tien MEGACO/H.248 - v=0 c=IN IP4 207.176.47.90 m=audio 40000 RTP/AVP 4 } } ; RTP profile for G723 is 4 } B u d c 13: Khi term ination B nha'c may, RGW 2 se bao cao vdi MGC bang ldnh 'Notify”. MG2 to MGC: MEGACO/1 [207.176.47.89]: 26000 User A RGW 2 MGC RGW2 User B Modify to check for OffHook Modify Response User A goes OffHook Notify OffHook Notify Response Modify SD:dialtone DialTcne ED onhook, digcomp DM digitMap Modify Response User A dials digits Notify digits diealed Notify Response Add TermA SD: ringbacktone Add $, Local SDP Info-underspecified RingBack tone Add Resp TermA Add Resp Local SDP (specitied) H inh 6.6a: Luu do cuoc goi giua hai ngudi dung thudc hai RG W duoc quan ly bdi ciing m ot M GC.