🔙 Quay lại trang tải sách pdf ebook Chuyển Mạch Mèm Và Ứng Dụng Trong Mạng Viễn Thông Thế Hệ Sau Ebooks Nhóm Zalo ThS. DUONG VAN THANH NHA XUAT BAN Bl/U OIEN CHUYEN MACH MEM VA tfNG DUNG TRONG MANG VIEN THONG THE Hg SAU ThS. DUONG VAN THANH CHUYEN MACH MEM m VA ffNG DUNG TRONG MANG VI6n THONG THfi Hfi SAU ^ r~ I NHA XUAT BAN BLfU OI$N Ha Noi - 2006 Ma so: HV 02 HM 06 LCJINOIDAU Hien nay, xu hu&ng hoi tu mang vien thong, mang truyen du lieu vd mang may li'nh Jang dien ra manh me tren the gi&i. Mang vien thong the he sau (NG N) ra dan de dap ibig xu huang do. T rai tim " cua NG N chinh la chuyen mach mem. Chuyen mach mem dap ung cho cung cap dich vu da phucmg tien bang rong, co cac ibig dung chinh huang tong ddi qua giang goi (Packet Tandem), tong dai noi hat, VoIP, mang thong tin di dong; co the chuyen tai IP quay sd' ra khoi mang dien tlioai chuyen mach cong cong (PSTN); truyen tin hieu thoai qua chuyen mach goi; cung cap cac dich vu thuan IP; ung dung da phucmg tien cho thue bao IP, co the cung cap cho khach hang cac dich vu n hu M M phone C - khi co cuoc goi den; dich vu da phucmg tien cho phep dien thoai co dinli, di dong, may tinh... co the cung dam thoai; dich vu vi(a truy nhap Internet vua dam thoai tren mot duang day dien thoai; dich vu nhdn tin thong nhat cho phep chuyen cac cuoc goi... Co the noi cong nghe chuyen mach mem la mot trong nhung van de thdi su hien nay. Vcri muc dich gi&i thieu cu the ve chuyen mach mem, Nha xuat ban Buu dien xucit ban cuon sach "Chuyen mach mem vd ung dung trong mang vien thong the he sau ” cua tac gia ThS. Ducrng Van Thanh, Hoc vien Cong nghe Bifu chinh Vien thong. Cuon sach dupe trinh bay vcri 8 chuang, 2 chuang dau gi&i thieu ve hien trang, xu huang phdt trien cua mang vien thong va cong nghe thong tin; khai niem co ban ve NG N va chuyen mach mem. Cac chucmg cdn lai cuon sach se de cap cu the ve chuyen mach mem nhu: mo hinh tliam chieu chuyen mach mem (cac mat phang, thuc the chuc nang), cac giao thuc cua chuyen mach mem (giao thuc khai tao phien, giao thuc cong pliuang tien MEGACO/H.248, giao thuc truyen tai bao hieu SIGTRAN va mot so ung dung ve chuyen mach mem). Cuon sach se Id tai lieu than: khdo huu ich cho cac cdn bo vd ky thuat vien cong tdc trong ITnh vuc vien thong; cac nha hoach dinh phdt trien mang lu&i; cac giao vien, hoc sinh nghien cun ve chuyen mach mem, mang the he sau tai cac tru&ng ddo too chuyen nganh Vien thong. Nha xuat ban Buu dien mong nhan dupe y kien dong gop cua quy vi vd ban doc de nang cao chat lucrng trong cac Ian xuat ban tiep theo. Y kien gop y xin gin ve Nha xuat ban Buu dien -18 Nguyen Du, Ha Noi. Tran trong cam cm./. Ha N6i, thang 5 nam 2006 NHA XUAT BAN BUU DIEN Chirong 1 TO NG Q UAN v f i HIEN TRANG VA XU H U tiN G PH AT TR IEN CUA VlfcN TH O N G VA CONG N G H E TH O N G TIN 1.1 S I/P H A T TRIEN CUA KY THUAT V l£ N THONG VA MAY TINH 1.1.1 Vi6n thong Uoc mo truyen tin di xa da co tCr co xua, song chi thuc sir bit dau phat trien manh me vao khoang cuoi the ky 18 dau the ky 19. Ta hay diem qua nhung moc lich sir quan trong nhat cua qua trinh phat trien ky thuat vi6n thong: - Vao khoang nhung nam cuoi the ky 18 dau the ky 19 xuat hien dien bao quang hoc (Co hieu) o chau Au d6 truyen tin di xa toi hang tram km/gid. Cho toi khoang nam 1840 hau het cac nude chau Au su dung cac he thong tren nh^m muc dich truyln tin phuc vu cho quan su va chinh phu. - Sau khi Michael Faraday phat minh ra cac hien tuong ve dien tu, voi nhung tmh chat rat quf bau cua dong dien khi truyen c}an trong cac moi truong truydn, cac ky su da co gilng tim cach ung dung cac hieu ung dien tu de’ truyen tin thay cho phucmg phap quang hoc. Nguoi dau tien dua ra y tuoiig va da thuc hien thanh cong viec ap dung cac hien tuong dien de truyen tin la William Sturgeon nguoi Anh dung nam cham dien (Electromagnet). - Nam 1822 Francis Ronald da trinh didn “Dien bao” dua tren y tuong cua William Sturgeon. Tuy nhien y tuong nay cua Francis Ronald khong duoc nha cam quyen Anh quoc luc do bao tro v'l khi do mang dien bao quang hoc dang rat thinh hanh tai Anh quoc. - Nam 1824 tai Niu-ooc giao su Samuel Finley Breese Moorse bat dau quan tarn toi lTnh vuc dien tu va thong tin dien tren co so y tuong cua Francis Ronald. - Nam 1831 Joseph Henry (My) sang che chuong dien tu xa va do chinh la tien than cua dien bao sau nay. - Nam 1837 dua tren nguyen ly chuong tu xa Moorse da trinh dien thanh cone nguyen tac cua dien bao Mooc tren co so do mang dien bao phat trien rat manh me va thirc sir bfit dau danh dau ky nguyen vian thong. 8 Cliuyen mach mem va Ung clung trong mang vien tliong the he sau - Sir kien rat thu vi la vao khoang nam 1866 mot nguoi My la Joshua Coppersmit tin rang co the lam ra cai ma ong ta goi la “Telephone” tuong tu nha dien bao nhung dd truy6n tieng noi di xa va ong ta da rat nhiet huy£t truyen ba y tudng cua minh. Tuy v&y Joshua Coppersmit khong bao giothuc hien duoc y tuong tuyet voi nay. - Nam 1876 Alecxand Graham Bell da sang che va hoan thien dien bao nhieu kenh va sau do sang che may dien thoai thuc hien y tuong huy6n thoai cua Joshua Coppersmit la truydn tieng noi di xa. Sang che may dien thoai cua Alecxand Graham Bell co y nghla vo cung trong dai va sau sac doi voi xa hoi hien dai, mo ra ky nguydn phat trien manh me cua nganh Vien thong. - Nam 1925 John Logie Baird da thanh cong truyen bufc anh truyen hinh den trang dau tien va khoang 1928 nguyen ly truydn hinh mau da duoc phat minh ... Tiep theo sau sang che cua Alecxand Graham Bell va John Logie Baird la mdt loat cac sir ki6n quan trong danh d£u thoi ky phat trien manh me cua ky thuat thong tin hien dai. - Nam 1877: May dien thoai tai nha rieng dau tien dugc dua vao su dung. - Nam 1879: Tong dai nhan cong dau tien duoc dua vao su dung. - Nam 1881: Cuoc goi dien thoai duong dai ddu tien duoc thuc hien. - Nam 1889: Hai anh em nha Strowger sang che tong dai tu dong he tirng nac. - Nam 1895: Phat minh Vo tuyen dien. - Nam 1915: Cuoc goi dien thoai xuyen luc dia dau tien. - Nam 1925: Phat minh ghep kenh theo tan so FDM. - Nam 1925: Phat minh vo tuyen truy6n hinh. - Nam 1929: Phat minh PCM. - Nam 1947: Phat minh Transistor. - Nam 1960: Thu nghiem thong tin ve tinh. - Nam 1960: Thu nghiem trudng chuy6n mach dien tu dau tien. - Nam 1963: Sang che may dien thoai an phun. - Nam 1965: Tong dai dien tu SPC dau tien ESS Noi (My). - Nam 1970: Tong dai dien tu so dau tien E10A (Phap). - Nam 1971: Sang che Microprocessor (vi xu ly). - Nam 1976: Tong dai dien tu so hoan toan dau tien DMS100 (Ca-na-da). Chirong I: Tung quan ve hien trang va xu hifcrng phdt trien cua vien thong. 9 - Nam 1977: Sang che Internet - Nam 1977: Sang che cap sgi quang - Nam 1977: Sang che th6ng tin di d6ng - Nam 1987: Phat minh mang thong minh - Nam 1988: Phat minh ATM va B-ISDN, mo dau cho c6ng nghe “Mang the he sau” NGN (Next Generation Network) - Nam 1989: Cap sgi quang den nha rieng. - Nam 1996: Chuyen mach IP - Nam 1997: Chuyd’n mach m£m - Nam 2001: Cac hang bat d£u ung dung VoIP - Nam 2002: Bat d£u irng dung cac dich vu NGN ... H inh 1.1: Can trite phan cap m ang dien thoai cong cong Cho toi ngay nay, trong ky thuat vi<§n thong thi dich vu dien thoai co ty trong Ion va quan trong nhat do vay mang dien thoai cong cong PSTN la mang duoc quan tam 10 Cluiyen mach mem va img dung trong mang vien thong the he sau hang cMu. Cac dich vu khac nhu dien bao, truyen sd lieu, phat thanh, truyen hinh v.v... thudng duoc ghep “ky sinh” tren mang dien thoai c6ng cdng. Hinh 1.1 minh hoa cau true tong quan cua mang PSTN hien dai dien hinh. Doi voi cac quoc gia co dien tfch lanh tho Ion, ca'u true mang vien thong thudng duoc chia thanh 5 cap voi cac tong dai chuc nang tucrng ung tai trung tarn nut mang. Mot tong dai cu the co the hoat dong ket hop m6t so chuc nang, vf du nhu tdng dai noi hat (tong dai cap 5) co the ket hop cung voi tdng dai chuy6n tiep (transit) noi hat de tao thanh tong dai hon hop va duoc xSy lap tai mot mat bang trong mdt nha chung. Tdng dai cap 5 co the ket noi qua tong dai chuy6n tiep noi hat hay true tiep voi tdng dai trung tarn tinh (cap 4). Cac tdng dai trung tarn (ca'p 4 trd len) ket noi vdi cac tdng dai cap cao hon qua dudng trung ke, hieu suat su dung cao neu nhu giua chung thuc su co nhu cau lien lac ldn. Trong nhung trudng hop nay thi trudc het tdng dai thu dinh tuyen cho cac cuoc goi theo dudng su dung cao, neu khong cdn dudng rdi trong hudng nay thi mdi dinh tuyen theo hudng true tiep tdi tdng dai cap cao hon. Luu y rang ngay nay, vdi xu hudng su dung tdng dai SPC (Stored Programme Control - Dieu khien theo chuong trinh) trinh do cong nghe cao va cau true phan tan nen so lugng cap mang co the giam xuong 2-3 muc. Vf du chien luge phat trien mang viin thong cua nganh Buu chinh Vien thong da hoach dinh den nam 2005 mang vi6n thong nude ta co ban chuyen sang irmng NGN (Next Generation Network - Mang the he sau) co cau true 2 muc. Mang PSTN (Public Switched Telephone Network - Mang dien thoai chuy6n mach cong cong) dugc thiet ke va xay dung tdi uu cho viec dap ung cac dac trung luu lugng cua dich vu dien thoai. Trong boi canh hien nay nhieu hinh loai dich vu mdi phat trien rat manh me vf du nhu dich vu so lieu, Internet, video v.v... va nhieu dong luc kinh doanh cua nSn kinh te thi trudng toan cau hoa, mang PSTN truyen thong da boc lo nhieu nhuoc diem do do doi hoi phai chuyen doi mang PSTN hien co sang mang the he mdi co kha nang dap ung tot moi yeu cau cung cap va ung dung dich vu. Dudi day liet ke mot so nhugc diem can ban nhat: • Dich vu so lieu vdi cac dac trung luu lugng rat khac so vdi cac dac trung luu luong dich vu dien thoai, vf du nhu: bang thong su dung, toe do truyen bit, tinh thdi gian thuc, chat luong dich vu v.v... se phat trien nhanh va vugt troi trong tuong lai gin. • Mang PSTN khong thd tao va cung cap cac tinh nang dich vu mdi mot each nhanh chong, hieu qua cho ngudi dung. Vdi sir canh tranh gay gat cua nen kinh te thi trudng ngay cang tang doi hoi viec tao cac dich vu mdi phai thuc hien nhanh chong. Chuong 1: Tong quan ve hien trang vd xu hudng phdt trien cita vien tliong. 11 m6m dco de kip thdi cung cap cho thi trudng, chong su doc quyen va phu thuoc vao nha san xuat. • Cac dich vu so lieu/dien thoai/video rat kho, tham chi khong the hoi tu trong mang PSTN hien co. • Kien true ha tang mang PSTN dua tren co so cong nghe TDM (Time Divison Mutiplexing - Ghep kenh theo thdi gian) va chuyen mach kenh khong mem deo va khong hieu qua cho viec truyen so lieu va cac dich vu da phucmg tien (multimedia). Mang NGN duoc xay dung tren co so cong nghe chuyen mach goi va IP (Internet Protocol - Giao thuc Internet) nen co ban da khac phuc duoc nhung nhuoc diem neu tren cua mang PSTN va co cac dac di£m vuot trdi ve su dung bang thong, hieu nang cua mang v.v... 1.1.2 May tinh Co tdi hang tram kieu may tinh dien tu so da duoc thiet ke va thu nghiem trong qua trinh phat trien de dat toi trinh do may tinh hien dai. Mot so ldn da bi lang quen theo thori gian, nhung mot so it con lai da co anh hudng quan trong dac biet tdi tien trinh phat trien cua ITnh virc nay. May tinh hien dai da dat tdi nhung thanh tuu dinh cao cua tri tue con ngudi va trong mang vi£n thong hien dai khong the thieu vai tro cua may tinh. Dudi day nhde lai mot so thanh tuu dien hinh. Thuy td cua ky thuat may tinh phai noi tdi nha toan hoc ldi lac ngudi Phap Blaire Pascal, ngudi ma hau the da dat ten cho mdt ngon ngu lap trinh bac cao ndi tieng Pascal de to long ton kinh. Khoang nam 1642 Pascal da thiet ke may tinh co hoc co kha nang thuc hien hai phep tfnh cong va trir. 30 nam sau, nha bac hoc ngudi Due Leibniz da hoan thien may tinh cua Pascal de thuc hien ca bon phep tfnh so hoc. Trong suot vai tram nam sau may tfnh khong co gi thay doi dang ke. Mai tdi khoang nam 1834 Charier Babbage - giao su truong dai hoc tdng hop Cambriger sang che may tfnh so dau tien va ong dat ten cho may tfnh nay la “Analotical Engine”. Do la may tfnh co hoc da nang va dieu khien bang phan mem do Ada Lovelace (con gai cua dai thi hao Lord Bairown) lap trinh va do vay ma mot ngon ngu lap trinh hien dai co ten goi la Ada de ky niem su kien do. - Nam 1943: Sang che may tfnh dien tu so dau tien COLOSSUS. - Nam 1946: Sang che may tfnh dien tu so ENT AC (Electronic Numerical Integrator And Computer) mo dau cho giai doan phat trien manh me cua nganh may tfnh dien tu so'. ENT AC chua tdi 18000 den dien tu, 1500 role, khoi luong tdi 30 tan va tieu thu dien nane deii 140 kW. 12 Chuyen mach mem va ifng dung trong mang vien thong the he sau - Nam 1949: Wilkes sang che may tfnh dien tir sd SPC dSu tien mang ten EDSAC. Cung trong khoang thdi gian nay, John Von Neumann ra't quan tam ITnh vuc may tinh dien tir sd, 6ng da de xuat y tudng tap trung hoa chuong trinh bieu di6n dudi dang s6 nhi phan trong bo nhd cua may tinh cung vdi sd lieu. Y tudng nay duoc su dung trong EDSAC nam 1949 va ngay nay hau het cac may tinh dien tir sd duoc xay dung theo ca'u true cua EDSAC. Trong giai doan tiep theo may tinh dien tir sd SPC phat trien rat manh me va dat duoc cac thanh tuu to ldn. Nam 1963, lan dau tien xuat hien tren thi trudng may tinh lam viec vdi ngdn ngu bac cao. Nam 1980 may tinh ca nhan (PC) dau tien da duoc ung dung. Trong khoang nhung nam 1940-1950 may tinh dien tir sd ra ddi va phat trien manh me, tuy nhien do la cac may tinh don le vi khi do gia thanh ciia mot may tfnh didn tir sd la rat dat. Den khoang nhung nam 1960 nham dap ung y£u cau tang nhanh cac ung dung may tinh dien tir sd cua ngudi dung trong di6u kien gia thanh cua may tinh dien tir sd cdn ra't dat quan diem “chia thdi gian” (Time Sharing) bat dau phat trien nhanh, nhd do mdt may tinh co the chia se cho nhieu ngudi cung sir dung ddng thdi. Hinh 1.2 md ta he thong may tinh ung dung nguyen ly chia thdi gian, nhd do chi sir dung mdt may tinh nhung ddng thdi co kha nang thuc hien nhieu nhiem vu khac nhau, phuc vu cho nhi^u ngudi sir dung. H inh 1.2: H e thong m ay tinh “chia thdi gian " Den nhung nam dau cua thap nien 1970, vi mach LSI/VLSI/Microprocessor ra ddi va phat trien nhanh, nhd do may tinh ca nhan PC (Personal Computer) ra ddi va bat dau phat trien rat manh me. Sau do chung co nhu cau ket ndi mang de chia se chung ngudn tai nguyen, luc dau theo cau hinh tap trung va sau do theo ca'u hinh phan tan nhu minh hoa tren hinh 1.3. Chuong I: Tdng quan ve liien trang vd xu lutdng phdt trien cua vien thong. 13 a. Cciu hinh tap trung Chu giai: HQ-Head Quater: Trung tam; SWT-Service Work-Station: Tram cong tac H inh 1.3: Cau hinh m ay tinh tap trung vd phan tan D5u nhung nam 1980 ky thuat may tfnh phat trien rat manh me va duoc ung dung rdng rai trong nhieu lTnh vuc cua khoa hoc va doi song xa hoi, nhu cau ket noi mang gia tang do do xuat hien cac mang may tfnh cuc bo LAN (Local Area Network). Co hai kieu ca'u hmh co ban mang LAN - Ca'u hinh BUS va cau hinh mach vong. Mang may tinh phat trien rat nhanh va duoc ung dung rong rai do vay cong nghe LAN phat trien nhanh trong giai doan nay, nhu cau lien ket cac mang LAN de md rong pham vi ung dung. Cac mang LAN co the lien ket voi nhau qua mang dien thoai cong cong PSTN nhu minh hoa tren hinh 1.4. LAN (Dich) Hinh 1.4: Cac can true mang L A N Tdng quat, ngav nay viec lien ket mang may tinh ndi chung co the’ thuc hien theo bon kieu kien true mang thirdng gap gom: • Ca'u hinh BUS • Ca'u hinh mach vong 14 Chuyen mach mem vd Ung dung trong mang vien thong the lie sau • Cau hinh phan manh • Cau hinh chuydn mach Su ra dai va phat tridn cua ky thuSt va cong nghe ban dan vao nhung nam d^u cua thap nien 1960 da thuc day mot cach mang manh me nhidu nganh kinh te va khoa hoc ky thuat, trong do co nganh Vidn thong va Cong nghe thong tin. Tuy nhien do co su khac biet tuong doi vd ban chat cua tin hieu su dung cho cac dich vu dien thoai. dien bao, truydn thdng so lieu... va cac han che vd ky thuat luc do ma cac mang vidn thong va xu ly tin duoc xily dung va hoat dong mdt cach tuong ddi doc lap vcri nhau (hinh 1.5). Trong tien trinh phat trien khdng ngirng cua cdng nghe vidn th6ng va cdng nghe xtr ly tin, dac biet la sir phat trid’n va kha nang ung dung tuyet voi cua cong nghe sd bao g6m ky thuat ban dan va vi mach, ky thu&t so va ky thu&t vi xir ly da lam xuat hien va thuc day manh me kha nang ket hop cac dich vu thdng tin khac nhau vao mot mang thdng nhat - Mang vidn thong sd da dich vu tich hop ISDN vdi tdc do kenh co sd la 64 kbit/s (kenh B) sir dung cho dich vu dien thoai, truydn sd lieu,... hay 16 kbit/s (kenh D) sir dung cho bao hieu DSS1 tren cung doan thud bao, CCS7 trdn mang trung ke va truydn sd lieu chuyd’n mach goi, 384, 1536 hay 1920 kbit/s (kenh H) dung cho cac dich vu tdc do cao. Cac kieu kenh co ban neu tren duoc nhom lai dudi dang cac cau true kdnh 2B+D, 23B+D, 30B+D vdi cac tdc do ddng bit 144, 1544 va 2048 kbit/s tuong ung. Sir dung cac kenh co ban va cac cau true nhom kenh nhu mo ta trdn day, mang thong tin da dich vu ISDN bang hep da dap ung duoc nhidu hinh loai dich vu thdng tin truydn thdng dang duoc ung dung kha phd bien trong cac nude co nen kinh te phat trien. 1.2 XU H irdN G H 01 TU CONG NGHE VA TICH HOP DICH VU Tien trinh phat tridn ciia ky thuat vidn thdng va ky thuat xir ly tin duoc bidu didn va mo ta sinh ddng nhu tren hinh 1.5. Tir bon nhom dich vu truydn thdng don le (Hinh 1.5a, qua khur) phat tridn xuat hien nhu cau tich hop va hoi tu dich vu va cdng nghd. Trinh do ket hop tir don gian timg cap mure thap (hinh 1.5b, hien tai) ti£n tdi tich hop va hoi tu toan phan (hinh 1.5c, tuong lai). Tuy nhien, sir phat tridn manh me cua cdng nghe thdng tin va nhu c£u trao ddi thdng tin ngay cang tang nhanh va da dang hoa cua xa hoi ddi hoi phai b6 sung cap bach cac dich vu truyen anh bao gom ca anh tinh va anh dong chat luong cao va truydn so lieu, truyen tep tin tdc do sieu cao ma chung yeu cau tdc do bit tdi vai tram Mbit/s, tham chi tdi hang chuc Gbit/s. Ndi chung mang ISDN bang hep khdng the dap ung thoa man duoc cac yeu cau bo sung neu tren. Mot mang vien thong thong nhat dap ung tat ca cac hinh loai dich vu vien thdng va xir lv tin vdi tdc do yeu c v Vi du cua hinh loai dich vu nay la videography (Anh dd hoa) kenh quang ba. Bang 7.5: Dich vu Phan phoi Kieu tin Vi du dich vu l/ng dung A. Cac dich vu khong dieu khien video - Van ban, do hoa, so lieu So lieu NTSC, PAL, SECAM TV EDTV, HDTV TV Tra tien ngay khi xem Cac dich vu phan phoi tai lieu Phan phoi tin toe do cao Cac chuong trinh truyen hinh Cac chuong trinh truyen hinh Cac chuong trinh truyen hinh Bao chi dien tCr, xuat ban dien tCr Phan phoi so lieu khong han che - Anh dong va am thanh Video, am thanh Phan phoi video - am thanh B. Cac dich vu dieu khien duoc van ban, do hoa, am thanh, anh tinh Kenh video do hoa quang ba Dao tao tCr xa, phan mem ti/ xa, mua hang tUxa, quang cao ti/x a , bao chi dien tir phuc hoi Ngoai cach phan loai dich vu nhu da trinh bay tren day co the cdn co nhieu cach phan loai khac. Vi du mot cach chia dich vu thanh ba nhom nhu sau: 1. Cac dich vu thdng tin: Thoai, am thanh, hinh anh, ban tin, hoi nghi, mang rieng... 2. Cac dich vu noi dung: Audio/Video, ban tin... truyen don hudng tdi ngudi dung. 3. Dich vu giao dich (Transactional services): Cac giao dich tai chinh, buon ban le, thuong mai dien tir. trinh duyet Web... Churomg 2 TO N G Q U A N VE M ANG TH E HE SAU VA C H U Y EN M A C H M EM 2.1 CAU HINH TONG QUAN MANG THE HE SAU 2.1.1 Sir ra doi cua mang the he sau Nhu c^u trao doi thong tin phan anh trinh do phat trien cua xa hdi. Khi th6ng tin duoc thira nhan nhu mot nguon tai nguyen quy gia, nhu cau ve trao doi thong tin cua con nguoi ngay cang doi hoi cao vd chat luong, da dang ve loai hinh thong tin va chung loai dich vu. Didu nay tao ra nhung co hdi ve doanh thu cho nhung nha cung ca'p dich vu vidn thong, nhung cung dat ra khong it nhung kho khan ve mat cong nghe. Truoc day, luu luong chu yeu la tin hieu thoai, mot ha t£ng co so vidn thdng theo mang dien thoai cong cong PSTN cung du dap ung nhu cau khach hang. Mang PSTN hoat dong tren co so chuyen giao theo che' do kdnh (Circuit Mode) voi nhung tong dai chuyen mach kdnh cho phep chuyen mach tin hieu thoai voi do tin cay cao, dam bao rat tot tinh thdi gian thuc. Ngay nay do sir tac dong cua hai yeu to: su gia tang nhu cau cua khach hang va sir ra ddi cua nhung cdng nghe mdi, ha tang vidn thdng cua mdi nude dang dung truoc nhung birdc ngoat. Sir gia tang nhanh nhu cau cua khach hang ve loai hinh dich vu, khdng chi don thuan dich vu dien thoai ma cdn co nhieu dich vu mdi, bao gom ca hinh anh, du lieu va cac dich vu da phuong tien... Neu nhu luu luong thoai duoc dap ung rat tot bdi mang PSTN truyen thdng thi vdi nhung loai luu luong cdn lai nhung mang PSTN lai to ra co rat nhieu nhuoc diem: • Sir dung bang tan khdng linh hoat • Lang phi tai nguyen he thong • Khdng co co che phat hien va sira Idi • Hieu nang sir dung mang thap • Kho hoi tu va tich hop dich vu /R cap quang) S/I iRouter Mang thue bao PSTN. xDSL ! RMG DSLAM Mang IP AMG Access Media Gateway Cong phuong tien truy nhap AS Application Server May chu i/ng dung MGC Media Gateway Controller Dieu khien cong phirong tien MMG Mobile Media Gateway Cong phuong tien di dong MG Media Gateway Cong phuong tien RMG Residential Media Gateway Cong phuang tien noi hat TMG Trunk Media Gateway Cdng phuong tien trung ke SS7 Signalling System No7 Bao hieu so 7 FR Frame Relay Chuyen tiep khung FRS Frame Relay Switch Chuyen mach chuyen tiep khung MS Mobile Switch System He thong chuyen mach di ddng LS Local System He thong noi hat DSLAM Digital Subscriber Line Access Multip. Ghep kenh truy nhap dudng day thue bac IP Internet Protocol Giao thuc Internet SIR Switch/ Router Chuyen mach/Bo dinh tuyen Hinh 2.1: M d hinh m ang N G N vdi cdng nghe chuyen m ach mem Chuang 2: Tdng quan ve mang the he sau va c huyen much mem 25 Mang didu khidn la mang lien kd't cac may chu urng dung (AS) va cac tong dai cdng MGC. AS dd didu khidn v& cung ca'p cac urng dung va dich vu cho ngudi dung con MGC dd didu khidn cac cdng MG va cac tai nguydn mang khac. MGC con co cac ten goi khac la chuydn mach mdm (Softswitch), may chu xu ly cuoc goi hoac Call Agent. Chuyen mach mdm la hd thdng phfin mdm didu khien phan tan dam bao kha nang dieu khidn cudc goi va xu ly bao hidu cho mang thd' hd sau. Tai mure co ban nhat, chuyen mach mdm phai cung ca'p cac tinh nang didu khidn cudc goi lien quan tdi thiet lap va giai phong cudc ndi, dinh tuyen cudc goi, lira chon cac thudc tfnh dich vu bao gom dich vu dien thoai, video, Internet, dich vu da phuong tien..., xac dinh tham quydn cuoc goi, quan ly tdi uu ngudn tai nguydn va chat lugng dich vu theo yeu ciu. Hien nay chuydn mach mdm chu trong thuc hien cac tinh nang chu yd'u sau: - Didu khidn phan tan va thdng minh cac cuoc ket n6'i tai cac cdng MG, dam bao tinh ddc lap va tfnh chuyen ddi thi'ch urng cao ddi vdri cac phuong tien ky thuat sir dung cu thi khac nhau nhu ATM, IP, TDM, SCN (mang chuydn mach kdnh) va PDN (mang s6 lieu goi). - Dinh tuyen cuoc goi trong pham vi mang dua trdn co so bao hieu va cac thong tin trong co so du lidu cua thud bao. - Co kha nang chon cac tid'n trinh ap dung cho xir ly cuoc gpi cua cac hinh loai dich vu khac nhau bao gom dien thoai, am thanh - hinh anh, Internet/Web va da phuong tien. Hd trg da giao thurc dieu khidn va bao hieu, cac chuc nang quan ly nhu xu ly ldi, tfnh cudc v.v... - Co kha nang chuydn dieu khien cuoc goi cho cac thanh phan cua mang khac. Tuong tac lidn mang mdm deo va hieu nang cao. - Giao didn va hd trg cac churc nang ma hoa - giai ma, nen - Giai nen tin hieu dich vu nham giam bang thdng va tdi uu hoa sir dung tai nguydn mang, dap urng chat lugng dich vu QoS (Quality of Service) theo yeu cau cua khach hang va hieu nang cua mang. Cac giai phap cdng nghd va kidn true ha tang mang NGN mdi dua tren co so mang chuydn mach gdi tdc dd cao, cdng nghe SDH/SONET, IP/ATM/MPLS va phan mdm dieu khien phan tan tao didu kien cho sir hoi tu cac giao thurc truyen thdng, chuydn mach, dinh tuyen va xu ly tin hieu dich vu dam bao su tich hgp cac dich vu vidn thong bao gdm didn thoai, am thanh, video, sd lieu, Internet... vdi chat luong dich vu QoS theo yeu cClu cua ngudi sir dung la nhung van de dang dugc quan tam, nghien cuu de ung dung vao thuc tidn. 26 Cliuyen mach mem va inig dung trong mang vien tliong the he sau Trong mot vai nam gan day tren pham vi the gidi cdng nghe chuyen mach mdm bat dau duoc dac biet quan tam nghien curu va da dat duoc cac thanh tuu ap dung vao mang cac tong dai trung ke dat ket qua tot. 2.2 CAC KHAI NIEM VE CHUYEN MACH MEM Cac y kien khac nhau ve chuyen mach mdm cung xuS't phat tu goc do nhin nhan khac nhau ve kien true, chuc nang va cac dac trung cua mang. Truoc khi di toi mot khai niem chung, co the tham khao mot so quan diem ve chuyen mach mem cua mot s6 hang khac nhau. CoinmWorks: (w w w .com m w orks.com ). Chuyen mach mem (Softswitch) bao gom cac mo-dun phan mem tieu chuan, co chuc nang didu khien cuoc goi, bao hieu, co giao thuc lien ket va kha nang thich ung voi cac dich vu mdi trong mang hoi tu. Them vao do, chuyen mach mem thuc hien chuyen mach cuoc goi ma khong phu thuoc vao phuong thuc truyen dan cung nhu cach truy nhap mang, cac dang luu luong khac nhau duoc xu ly trong suot. Thong qua mang IP, chuyen mach mem cung cap cac dich vu IP voi cac yeu cau ngay cang cao cua khach hang. M obileIN: (w w w .m obileIN .com ). Chuyen mach mem la khai niem trong do bao ham viec tach phan cung mang ra khoi phan mem mang. Trong mang chuyen mach kenh truyen thong, phan cung va phan mem cua he thdng chuyen mach khong doc lap voi nhau ma la thuc the toan ven cua mot nha cung cap. Mang chuyen mach kenh dua tren nhung thiet bi chuyen dung cho viec ket noi va duoc thiet ke voi muc dich phuc vu thong tin thoai. Nhung mang chuyen mach goi voi hieu nang cao hon se sir dung giao thurc IP de dinh tuyen thong tin thoai va so lieu qua cac tuyen kha dung va cac thiet bi dung chung. A lcatel: (w w w .alcatel.com ) voi san pham 5424Softswitch su dung de giam tai Internet va chay cac ung dung VoIP H.323, he thong 1000 Softswitch ung dung lam tdng dai chuyen tiep goi. Chuyen mach mem la trung tam dieu khien trong cau true mang vidn thong. No cung cap kha nang chuyen tai thong tin mot cach mem deo, an toan va dap ung cac dac tfnh mong doi khac cua mang. Do la cac san pham co chuc nang quan ly dich vu, dieu khien cuoc goi gatekeeper, the hien d viec hoi tu cac cong nghe IP, ATM, TDM tren nen co so ha tang sa~n co. Hon nua, 1000 softswitch con co kha nang tuong thich giua chuc nang didu khien cuoc goi va cac chuc nang mdi se phat trien sau. Nlur vay, tuy thuoc vao thi trudng cua minh, cac nha cung cap khac nhau co quan diem khac nhau ve chuyen mach mem, tuy nhien cac quan diem do bd sung cho nhau Chiumg 2: Tdng quan ve mang the he sau vd chuyen macli mem 27 tie hinh thanh mot dinh nghTa chung vd chuyen mach mem. Chuyen mach mem la he thong chuydn mach thuc hien day du chuc nang cua chuyen mach truyen thong, co kha nang ket hop nhieu loai dich vu, co the dap ung nhieu loai liru luong, kha nang ket noi vai nhieu loai mang, nhieu loai thiet bi, de dang nang cap cung nhu tuong thich vai cac dich vu mdi va cac dich vu trong tuong lai. To chuc chuyen mach mem quoc te ISC (International Softswitch Consortium) va Nhom dac trach ky thuat Internet IETF (Internet Enginerring Task Force) deu hudng tdi chuyen mach mem vdi kien true mang phan tan vdi cac thanh phan chuc nang hoan toan doc lap nhau - cac thanh phan chuc nang bao gom truyen tai, chuyen mach, didu khien mang va cac lo-gfc dich vu. Loi ich mang lai la mang nay khong gap phai su gidi han ve phan cung nhu trong mang truyen thdng (do la sir can thiet giuta chuyen mach kdnh va truyen tai, giua cac dich vu mang thong minh vdi co che va lo-gic dich vu). He thdng chuyen mach mem hoan toan la chuydn mach trong do cac thuc thd chuc nang ton tai trong cac thiet bi thanh phan vat ly khac nhau va phan tan. Hien nay chuc nang truyen dan dang bat dau chuyen cho cac thanh phan mang trdn co sd cong nghe IP/ATM/MPLS. Trong tuong lai, chuc nang dieu khien mang, lo-gic dich vu cung se tach rdi khoi chuc nang chuyen mach. Viec phan bd cac thuc the chuc pang se cho phep dd dang phat trien cac thuoc tinh tien tien va chuydn giao vdi chi phi thap. Nd luc tach cac thuc thd chuc nang ra khoi chuyen mach lam cho chuc nang chuydn mach trd nen don gian hon, hieu qua hon va re hon. Cac lo-gic dich vu phan bd cung lam cho viec phat trien cac ung dung khong bi han che bdi cac dich vu chuydn giao, dieu khien va mdi truong tao dich vu tap trung. Mang NGN (Hinh 2.1) duoc xay dung trdn co sd ung dung giai phap cong nghe chuyen mach mem se co cau hinh mang loi la cac thiet bi chuydn mach-dinh tuyen SR tdc do cao, dung luong Ion va chung dugc lien ket bang mang chuyen mach goi tren co sd cac cong nghe IP, ATM/ MPLS. Mang truyen tai goi la cac thiet bi chuydn mach MG. Mang truyen tai giao tiep vdi cac mang ngoai thong qua cac MG hoat dong dudi su dieu khien cua MGC. Phan mang truy cap la cac nut truy nhap bang rong va thiet bi truy nhap tich hgp I AD. Chuomg 3 MO HINH TH AM CH IEU C H U Y EN M ACH De co mot khai niem toan dien va thong nhat ve chuyen mach mdm, to chuc chuydn mach mdm quoc te ISC (International Softswitch Consortium) da dua ra mo hinh tham khao cua chuyen mach mem vai cac thirc the va mat phang chuc nang. 3.1 CAC MAT PHANG CHUC NANG Cac mat phang chuc nang dugc dua ra theo nghTa chung nhat nham phan biet cac thuc the churc nang trong kien true chuyen mach mdm. ISC dua ra 4 mat phang chuc nang: mat phang truyen tai (Transport plane); mat phang dieu khidn va bao hidu (Call control and Signaling plane); mat phang urng dung va dich vu (Service and Application plane); mat phang quan ly (Management plane). 3.1.1 Mat phdng truyen tai Mat phang truydn tai thuc hidn churc nang van chuydn cac ban tin giura cac thuc thd trong toan mang. Cac ban tin co thd’ la ban tin bao hieu cu6c goi, ban tin thiet lap cuoc ggi hay luu lugng can truydn. Ca che' truydn tai cac ban tin nay co thd dua trdn bat ky mot cong nghe truyen d in nao, midn la no dap urng cac yeu cau cua viec truyen dan loai luu lugng do. Mat phang truydn tai cung dua ra cac diem truy nhap danh cho viec lien ket vai cac mang khac nham muc dich bao hieu hay truyen tai luu lugng giura chung. Cac thuc the va churc nang cua mat phang nay dugc dieu khien bai cac churc nang trong mat phang bao hieu va dieu khien cuoc goi. Mat phang truyen tai cung co thd dugc chia nho thanh 3 midn: • Mien truyen tai IP: Midn nay cung cap he thong loi va chuyen mach, dinh tuyen cho viec truyen tai cac ban tin qua mang IP. Mien truyen tai IP bao gom cac thiet bi: dinh tuyen, chuydn mach, thiet bi cung cap ca che' giam sat chat lugng dich vu hay cac chinh sach truyen tai. • Mien lien ket mang: Mien nay dam nhan churc nang chuyen doi cac dang luu luong va bao hieu giura cac mang khac nhau nham dam bao sir tuong thich giua chung. 30 Chuyen mach mem va ifng dung trong mang vien thong the he sau bao gom cac thiet bi: cong bao hieu (Signaling Gateway), cong phuong tien (Media Gateway), cong lien ket mang (Interworking Gateway). • Mien truy nhap khong IP: Mien nay nham h6 tro viec truyen dan giura mang IP va cac dau cuoi khong IP hay mang vo tuyen. Vung nay bao gom cac thiet bi: cong truy nhap (Access Gateway) hay cac cong noi hat (Residential Gateway), dau cuoi ISDN, thiet bi truy nhap ti'ch hop IAD, cac cong phuong tien cho cac mang di dong hay mang truy nhap vo tuyen... Mat phang ting dung va dich vu Mat phang quan ly Bao irng riieu dung May chu img dung/chifc nang IN/AIN i Cac API md (Parlav, Jain, CAMEL, SIP, AIN/INAP) Cung cS'p thue bao va djch vu; Mat phang dieu khien} va bao hieu Call Agent, MGC, chuyen mach mem, GK SIP/SIP-T H 323. Chuyen mach> lien mane ho trd van hanh Bao hieu (ISUP, MAP, RANAP, MGCP, Megaco, SIP) va bao dU3ng mang; ho tro tinh cu6c May chu phuong tien Mat phang truyen tai Mien truyen tai IP: Mang loi IP, dinh tuyen, chuyen mach, BG, QoS Mien lien ket mang: TG (NG), SG, ‘ tuong tac GW SS7 1 TDM /ATM 4 ------- \ X ■ \ i \ PST/SS7/N ATM J Mien truy nhap phi IP: Truy nhap khong day (AG) • \ 1 w i f Mang Truy nhap di dong (RAN AG) Truy nhap bang rong (IAD) I MGCP) dau cuoi COau cuoi IP/ " X Dien thoai IP i V 1 ^ VoIP ) (H 323, SIP Mang di dong H inh 3.1: M d hinh tham chieu chuyen m a d i m em ISC 3.1.2 Mat phing bao hieu va dieu khien cuoc goi Mat phang nay dieu khien hau het cac thuc the cua mang, dac biet la cac thuc the thuoc mat phang truyen tai. Cac thiet bi va chuc nang trong mat phang nay tien hanh dieu khien cuoc goi dura tren cac ban tin bao hieu nhan duoc tu mat phang truyen tai. no cung thuc hien viec thiet lap va giai phong cuoc goi tren co so didu khien cac thiet bi thuoc mat phang truyen tai. Mat phang nay bao gom cac thiet bj nhu: bo dieu khien cdng phuong tien (Media Gateway Controller), Gatekeeper (thiet bi dieu khien cOng ket ndi), may chu LDAP. Chuong 3: Mu hinh ilium chieu chuyen mach mem 31 3.1.3 Mat phdng ung dung va dich vu Mat phang nay cung cap cac lo-gic dich vu hay kich ban cua cac dich vu va ung dung tren mang. Cac thiet bi trong mat phang se dieu khien timg budc cuoc goi dua tren cac lo-gfc co san thong qua viec giao tiep vdi cac thiet bi trong mat phang bao hieu va dieu khien cuoc goi. Mat phang nay bao gom cac thiet bi nhu may chu ung dung (Application Servers), may chu chuc nang (Feature Servers). 3.1.4 Mat phang quan ly va bao dudng mang Mat phang nay thuc hien cac chuc nang quan ly nhu tinh cudc, h6 tro van hanh, cac xu ly lien quan tdi thue bao hay cung ca'p dich vu tdi khach hang. Mat phang quan ly co the tuong tac vdi 3 mat phang tren th6ng qua cac giao dien chuan hay giao dien lap trinh md. 3.2 CAC THUC THE CHUC NANG Kien true cua mang khi trien khai chuyen mach mem co the duoc tham khao qua hinh 3.2. Moi khdi clurc nang tren co the thuc hien mot chuc nang nhung cung co the ket hop cung thuc hien mot chuc nang. Theo do cac thuc the’ churc nang thuoc cac mat phang chuc nang khac nhau. H inh 3.2: Cac thirc the chuc nang chuyen m ach mem 32 Cliuyen mach mem va ung dung trong mang vien tlidng the he sau 3.2.1 Churc nang dieu khien cong phuang tien (M GC-F) Chdc nang nay thudng dugc thuc hien bdi thuc the’ vat ly MGC (Media Gateway Controller). Day la mot trong nhung thiet bi quan trgng nha't va dugc biet tai vai nhi£u ten nhu Call Agent, Call controller hay chuyen mach mem. Churc nang MGC-F cung ca'p lo-gic dich vu va bao hieu dieu khidn cuoc goi cho MG. MGC-F co cac dac diem: - Duy tri trang thai cuoc goi doi vai moi cudc ggi MG - Dieu khien giao tiep giua cac MG cung nhu giua MG vai cac thiet bi dau cudi - Dong vai tro la trung gian thoa thuan cac tham so ket noi giua cac dau cudi thuoc cac MG - Tiep nhan va khai tao cac ban tin bao hieu di va tdi cac didm ket cuoi va cac mang ben ngoai - Tuong tac vdi may chu urng dung nham cung ca'p cac dich vu toi khach hang - Quan ly mot so tai nguyen mang nhu: cac cong MG, bang thdng... - Giao tiep vdi cac chuc nang dinh tuyen va tfnh cuoc de hd trg cho viec tinh cudc, nhan thuc va dinh tuyen - Co the tham gia vao nhiem vu quan ly trong mdi trudng mang di dong - Chuc nang nay gom cac giao thuc urng dung Megaco/H.248 va MGCP Chuc nang Call Agent (CA-F) va Internetworking (IW-F) la cac churc nang thanh phan cua MGC-F. CA-F the hien khi MGC xu ly dieu khien cudc goi hay quan ly trang thai cuoc goi. IW-F the hien khi MGC thuc hien churc nang bao hieu giua cac mang bao hieu khac nhau (vi du nhu SS7 va SIP). 3.2.2 Chuc nang djnh tuyen cuoc goi va tinh cudc (R-F, A-F) R-F cung cap cac thdng tin dinh tuyen cuoc goi cho MGC-F, A-F thu thap cac thdng tin phuc vu cho viec tfnh cudc. R-F va A-F co dac diem: - Cung cap chuc nang dinh tuyen cho viec dinh tuyen cuoc ggi lien mang - Cung cap kha nang quan ly phien va di dong - Cap nhat cac thdng tin dinh tuyen tu cac nguon ben ngoai - Tuong tac vdi AS-F nham cung cap cac dich vu hay ung dung tdi khach hang - R-F va A-F la thanh phan cua SPS-F va thudng dugc tich hgp trong chuc nang dieu khien cdng MGC-F. Chucrng 3: Mo hinh tham thieu chuyen much mem 33 3.2.3 Churc nang cong bao hieu va bao hieu cong truy nhap (SG-F/AGS-F) SG-F cung ca'p c6ng phuong tien cho vide bao hieu giura mang IP va PLMN, PSTN (thudng la bao hidu sd' 7). Vai tro chinh cua SG-F la dong goi va truydn cac ban tin bao hien sd 7 cua PSTN (ISUP hoac INAP) hay PLMN (MAP hoac CAP) qua mang IP. AGS-F cung cap cdng phuang tien cho viec bao hieu giua mang IP va mang truy cap dua trdn chuydn mach kdnh. Vai tro chinh cua AGS-F la dong goi va truyen cac ban tin bao hieu V5 hay ISDN, BSSAP, RANAP qua mang IP. Cac dac did’m cua SG-F: - Dong goi va truyen cac ban tin bao hieu cua mang PSTN (SS7) (sir dung giao thuc SIGTRAN) tdi cac MGC-F hay mdt SG-F khac - Mdt SG-F co thd’ phuc vu nhidu MGC-F - Khi SG-F va MGC-F kh6ng dugc cai dat chung, SG-F se thuc hien churc nang giao dien giao thuc (vf du nhu SIGTRAN) - Cac giao thurc urng dung cua churc nang nay bao gom: SIGTRAN, TUA, SUA hay M3UA trdn SCTP Cac dac diem cua AGS-F: - Dong goi va truydn cac ban tin bao hieu V5 hoac ISDN (vf du nhu SS7) toi MGC-F - Mot MGC-F co the’ phuc vu nhieu AGS-F - Khi AGS-F va MGC-F khong dugc cai dat chung, AGS-F se thuc hien chuc nang giao thuc giao dien (vf du nhu SIGTRAN) - Cac giao thirc ung dung cua churc nang nay bao gom: SIGTRAN, IUA, V5UA hay M3UA trdn SCTP. 3.2.4 Churc nang may chu umg dung (AS-F) Chuc nang chinh cua AS la cung cap cac lo-gic dich vu urng dung. Cac dac diem cua AS-F bao gom: - Co the yeu cau MGC ket thuc cuoc goi hay phien lien lac de phuc vu cho mot urng dung nao do, vf du nhu thu thoai, lap cau hoi nghi... - Co the’ yeu cau MGC khdi tao lai cac dac trung cuoc goi vf du nhu tinh nang chuydn cuoc ggi, chung thuc the goi tra trudc... - Co the thay ddi cac md ta luu lugng thdng qua giao thurc SDP. 34 Cliuyen mach mem va Ung dung trong mang vien thdng the lie sau - Co the didu khien MS-F nham chuc nang xir ly luu luong. - Co the ket noi toi cac ung dung Web va co cac giao dien Web. - Co giao dien lap trinh urng dung cho viec tao cac dich vu mdi. - Giao tiep voi MGC-F hay MS-F. - Co the su dung cac dich vu cua MGC-F de dieu khien cac nguon tai nguydn ben ngoai. - Cac giao thuc ung dung bao g6m: SIP, MGCP, MEGACO/H248, LDAP, HTTP, CPL, XML. - Cac giao dien lap trinh ung dung mo bao g6m: JAIN va Parlay. Thong thudng, su ket hop giua AS-F va MGC-F se tao ra cac nang lire didu khi£n cac dich vu tang cudng nhu: dien thoai hoi nghj, chd cu6c goi... Cac nha khai thac se khong sir dung mot giao dien giua AS va MGC, thay vao do la mdt giao dien lap trinh urng dung API giua MGC va AS. Khi a'y AS con co ten goi khac la may chu chuc nang. Chuc nang dieu khien dich vu SC-F (Service Control Function) xuat hien khi AS-F dieu khien lo-gic dich vu. SC-F gom INAP, CAP, MAP, giao dien API md. 3.2.5 Churc nang cong phiromg tien (MG-F) MG giao tiep voi mang IP bang cac dudng didm truy nhap hay trung ke' mang. Noi khac di, MG-F hoat dong nhu mot cong giao tiep giua mang IP va cac mang ben ngoai, do co the la mang PSTN hay PLMN v.v... MG-F co the curTg cap cac cong giao tiep giura mang IP va mang chuyen mach kdnh hay giua cac mang chuyen mach goi voi nhau (IP va 3G hay ATM). Vai tro co ban cua MG-F la: chuydn liru luong tu mot khung dang truyen dan nay sang mot khung dang truyen dan khac, thudng la giua chuyen mach kdnh va chuyen mach goi, giua goi ATM va goi IP, hoac giua cac kenh tuong tu/ ISDN va cac goi giong nhu trong cdng phuang tien noi hat. Cac dac diem chinh cua MG-F: . - Luon ludn co mdi quan he chu/td vdi MGC-F thdng qua giao thuc MGCP hay MEGACO/H.248 - Co the thirc hien cac chuc nang xu ly luu luong nhu chuyd’n ma, ddng gdi, loai bd tieng vong, giam sat hien tuong rung pha (Jitter), dua ra cac xu ly khi bi mat gdi tin ... - Co the’ thuc hien cac chuc nang chen luu luong nhu tao am bao tien trinh cu6c goi, tao am DTMF, tao tap am xen... Chuong 3: Mo hinh tham chieu chuyen mach mem 35 - Thuc hidn chuc nang bao hieu va phat hien sir thay ddi trang thai cua cac thiet bi diu cuoi nhu: phat hien DTMF, phat hien sir kien on/off-hook (dat/nhac may), phat hien tfn hieu thoai tich cuc... - Quan va phan bo tai nguyen cho cac chuc nang tren. - Phan tich cac con so nhan duoc tu thid't bi dau cuoi dua tren ke hoach danh s6' va quay so do MGC giri toi. - Cung ca'p co che cho churc nang MGC-F de kiem tra sir thay ddi trang thai va nang lire cua cac diem ket cuoi. MG-F khong yeu cau kha nang quan ly trang thai cac cuoc goi. MG-F chi quan ly trang thai ket noi cua cac cu6c goi ma no h6 tro. - May dien thoai SIP phone ket hop MG-F va MGC-F trong m6t thiet bi. - Cdng urng dung SIP ket hop MG-F va MGC-F trong mot thiet bi. - Cac giao thurc ung dung bao gom RTP/RTCP, TDM, H248, MGCP. 3.2.6 Churc nang may chu phuong tien (MS-F) Chuc nang cua may chu phuong tien la dap ung cac yeu cau cua AS-F va MGC-F de thuc hien viec xu ly luu luong tren cac dong luu luong dong goi. Cac dac trung chinh cua MG-F: - H6 tro nhieu bo ma va chuyen ddi ma - H6 tro cho viec dieu khien bdi nhieu AS-F hay MGC-F - H6 tro cho nhieu tfnh nang dong thdi g6m: o Phat hien so o Tao dong am bao va thong bao o Tao am bao o Ghi, luu trur dong da phuong tien o Nhan dang tieng noi o Tao tieng noi tir van ban o H6 tro tinh nang cuoc goi Hoi nghi o Xir ly Fax o Phat hien thoai tich cuc va khoang trong ... - Cac giao thuc ung dung bao gom SIP, H248, MGCP Tir trinh bay tren day ve m6 hinh va cac thuc the chuc nang cua he thong chuyen mach mem chung ta co the’ khai quat cong nghe chuydn mach mem nhu sau: Chuyen 36 Chuyen mach mem va inig dung trong mang vien thdng the he sau mach mem la he thong phan mdm dam bao kha nang bao hieu va didu khidn cuoc goi trong mang the he mdi NGN. Chuydn mach mem chuyen lo-gic dieu khidn dich vu ra khdi thiet bi chuyen mach tdi co sd du lieu mang hay cac may chu ung dung AS (trong mang PSTN 80% dich vu do cac tong dai chuydn mach kdnh truydn thdng cung cap). Ngay nay, chuyen mach mdm thudng chay trdn he dieu hanh “SU N Solaris". 3.3 SO SANH CHUYEN MACH m £ m VA CHUYEN MACH TRUYDN THONG 3.3.1 Kien true cac he thdng chuyen mach Chuyen mach mem thuc hien cac chuc nang tuong tu chuydn mach kdnh truydn thdng nhung vdi nang lire mem deo va cac tfnh nang iru viet hon. Cac uu diem cua chuyen mach mem mang lai la do d he thdng chuydn mach mem churc nang chuydn mach duoc thuc hien bang phan mem dua trdn cau true phan tan va cac giao dien lap trinh ung dung md. Trdn hinh 3.3 minh hoa mo hinh he thong chuydn mach truyen thdng va he thdng chuyen mach mdm. Tu hinh ve ta thay hai he thdng chuydn mach nay deu gom 3 khdi: phan cung, phan mem dieu khien cuoc goi va phan mem cac dich vu ung dung. He thong chuyen mach truyen thong He thong chuyen mach mem Hinli 3.3: M o hinh cac he thong chuyen mach Tuy nhidn trong chuydn mach truyen thdng tuc he thdng chuydn mach dien thoai sir dung trong mang PSTN, phan cung chuyen mach luon di kern vdi phan mem dieu Chuang 3: Md hinh tliam chieu cliuyen mach mem 37 khien cudc goi va phan mem umg dung cua cung mot nha cung cap. Didu nay lam tang tinh do'c quydn trong viec cung ca'p cac he thdng chuyen mach, kh6ng dam bao mot moi truong tao dich vu mdi do do lam gicfi han kha nang phat trien cac dich vu moi cua cac nha quan tri mang. Khac phuc dieu nay, chuyen mach mdm dua ra giao dien lap trinh ung dung md, co kha nang tuong thi'ch phan mdm didu khien va phan cung cua cac nha cung ca'p khac nhau. Dieu nay cho phep cac nha cung cap phan mem va phan cung co duoc quan diem chung va tap trung vao 17nh vuc cua minh. Vdi cac giao dien lap trinh md, chuyen mach mem co the dd dang nang ca'p, thay the va tuong thich vdi ung dung cua cac nha cung cap khac nhau. Chuyen mach mdm duoc xay dung trdn co sd cong nghe mang IP, xir ly thong tin mot cach trong suot, cho phep dap ung nhidu loai luu luong khac nhau. Duoc xay dung theo cau hinh phan tan, tach cac churc nang dieu khien cuoc goi va ung dung cua he thdng ra khdi chuc nang chuyen mach lam cho nhiem vu chuyen mach tro nen don gian hon va do dd nang luc xu ly manh me hon, linh hoat va hieu qua hon. Dong thdi cong nghe chuyen mach mem lam giam tinh ddc quyen cua cac nha cung cap, gop phin tang tinh canh tranh va do do giam gia thanh cua he thdng chuydn mach. Cac phan tich tren day duoc lam sang to them khi nghien curu cac hinh 3.4 va hinh 3.5 minh hoa so do khoi chuc nang cua tdng dai chuyen mach kdnh truyen thdng va tdng dai chuyen mach mem. H inh 3.4: S o do chi(c nang he thong chuyen m ach kenh 38 Cluiyen much mem vd ifng dung trong mang vien thdng the lie sau Hinh 3.5 dudi day minh hoa so do khoi churc nang cua chuydn mach mdm. MG MG Hinh 3.5: So do chuc nang he thong chuyen m ach mem 3.3.2 Phuong thuc xir ly cuoc goi Tdng dai truydn thong xay dung theo cau true tap trung (hinh 3.5), chuc nang xir ly cuoc goi va chuc nang chuydn mach vat ly luong luu luong deu dugc tap trung trong mot tdng dai. Thiet bi nay dong thdi vira giam sat thud bao, dua ra cac xir ly theo tien trinh cuoc goi vua thirc hien churc nang chuyen mach cac ludng luu lugng. Mang m-- WZ' Giam sat trang thai thue bao DTMF • K h5i7 ' chuyen mach Yeu cau am b£o (chuong bi goi, ■ hoi am chuong...) de thiet lap hay giai phong ket noi ? Giao tiep trung ke Hinh 3.6: H oat ddng cluiyen m ach kenh truyen thong Trong khi do he thdng chuyen mach mem (hinh 3.6) vdi cau true phan tan. churc nang xir ly cuoc goi (Media Gateway Controller) va chuyen mach vat ly cac luong luu luong (Media Gateway) dirge tach rdi nhau. Hai chuc nang nay giao tiep vdi nhau qua cac giao dien lap trinh ung dung vdi cac giao thirc bao hieu va dieu khien nhu MGCP, Chuong 3: Mo hinh tliam chieu cluiyen mach mem 39 MEGACO/H.248. Trong he thong chuyen mach mdm cac Media Gateway MG thirc hien chuc nang giam sat trang thai cac dau cudi, sau do gui thdng tin vd cho Media Gateway Controller MGC xir ly, MGC xir ly cudc goi va didu khien MG chuydn mach vat ly de tao kdnh truyen thong luu luong. Cac ban tin bao hieu so 7 duoc thu va xir ly bdi cong bao hidu SG. Giao ti£p thue bao • chuyin mach kenh hofic goi Giao tiep trung k£ - chuyen m ach------ kenh ho|c g6i / H inh 3.7: H oat ddng cua chuyen mach mem Tom lai, cdng nghe chuyen mach truydn thdng tach biet hai phuong thuc chuyen mach kdnh va chuyen mach gdi, trong khi dd chuyen mach mem ket hop va hoan thien chung trong mang hoi tu va tich hop, do do he thdng chuyen mach mdm dam bao tinh da nang, kinh te, mem deo va hieu qua cao hon so vdi he thdng chuyen mach truyen thdng. 3.3.3 Cac iru diem cua chuyen mach mem Quan diem cua cac nhd quan tri mang Nhin tu phfa nha quan tri mang, co rat nhieu loi fch de’ ho tang tinh canh tranh va giam chi phi dau tu CAPEX cung nhu chi phi dieu hanh mang OPEX (tat ca se dem lai loi fch cho khach hang): - M oi trudng kien tao dich vu moi: Vdi giao dien ung dung lap trinh md cac nha quan tri mang co the’ tu minh dua ra cac ung dung va dich vu tdi cac khach hang cua minh. Dieu nay khien ho hoan toan chu dong trong viec dua ra cac chien luge kinh doanh va phat trien dich vu mot cach lau dai, ft phu thuoc vao cac nha san xuat. - Kha nang van hdnli vd bao dudng tit xa: Cac nha quan trj mang thuc hien van hanh va bao dudng cac thiet bi phan bd ciia minh thdng qua mang vdi cac giao didn true quan. He thdng nay cho phep ho co the truy cap tdi tung tai nguyen thuoc timg cac rieng biet thdng qua mot may chu dat d bat ky noi nao. 40 Chuyen mach mem vd ifng dung trong mang vien thong the he sau - Giam thai gian trien khai dich vu va lie thong: Vi co mdt kien true mo do d6 viec trien khai he thong co the thuc hien bang viec nang ca'p cac thidt bi hien co va lap dat them cac MG, MGC, SG, AS. Dich vu dua ra duoc tridn khai bang phan mdm trdn cac mo-dun API. Tat ca didu do lam giam thdi gian tiep can thi trudng cua nha quan tri, ke tu khi bd von dau tu. Mot dac diem rat quan trong dd la nhd viec urng dung cac giao didn lap trinh ung dung md API nha cung cap dich vu khdng cdn hoan toan bi phu thuoc vao nha san xuat, do do viec tao ra va dua dich vu ma thi trudng co the thuc hidn mot cach nhanh chong, tien ich va hieu qua cao. - Dam bao vd duy tri ca sd ha tdng sdn co: Didu nay la ra't quan trong trong khi khau hao cua ha tang san co chua he't hay van cdn mang lai nhieu loi nhuan. Uu diem nay cho phep cac nha quan tri mang co the’ vua khai thac he thdng cu vua trien khai hd thong mdi, djch vu mdi ngay trdn nen he thdng cu. - Tdi itu lida nang life cua mang theo yeu cau tu phia khdcli lidng: Day la kha nang cho phep cac nha quan tri mang giam thidu chi phi cho vide du phong gia tang khach hang trong tuong lai. Ho chi can dau tu ha tang tuong xirng vdi sd thud bao cua minh, khi md rong thi trudng, cac cac mdi se duoc bo sung dd dang. LTu diem nay cung tao dieu kien kinh doanh cho nhung ngudi co von han che', vdi sd it khach hang va do cung chinh la kha nang chong doc quyen, khuye'n khi'ch phat trien dong thdi tao didu kien cho nhieu ddi tac cung khai thac, dau tu va canh tranh. - Kha nang nang cap he thdng cao, thuc day viec ung dung cac cdng nghe mdi: Vdi kien true md, ha tang mang co the’ dd dang duoc nang cap va viec ung dung cdng nghe mdi khong lam anh hudng tdi ha tang mang san co. Cuoi cung ta co the’ dua ra mot bang so sanh cac thuoc tinh cua chuyen mach mem va chuyen mach kenh truyen thdng. Bang 3.1: So sanh cac thuoc tinh cua chuyen m ach mem vd chuyen m ach kenh truyen thdng Chuyen mach mem Chuyen mach trong tong dai PSTN truyen thong Phuang phap chuyen mach Tren co so phan mem Tren c0 so cac cau kien dien tCr Kien true Phan tan, theo cac chuan mo Rieng biet cua ti/ng nha san xuat va tap trung cao Kha nang thich hap vai ung dung cua nha cung cap khac Kha nang thay doi mem deo, linh hoat De dang (API mo) Kho khan Co Kho khan Chucrng 3: Md hinh tham t hieu chuyen mat h mem 41 1------------------------------------------ Chuyen mach memChuyen mach trong tdng dai PSTN truyen thdng Gia thanh Re hon, khoang bang mot nCra tdng dai dien tCr truyen thdng Oat hon Kh£ nang nang cap Ra't cao va nhanh Tdt, tuy co han che hon va cham Gia thanh cua cau hinh ca ban Thap, gia thanh thay doi g3n nhu tuyen tinh theo sd luong thu& bao. Cau hinh co b in c6 the sir dung cho mang doanh nghiep Kh3 nang ket ndi dong thdi Vai tram ddn vai trieu ket ndi ddng thdi Dung luong ban d£u nho Co the xay dung tdng dai dung luong vai tram sd Rat cao, tdng dai PSTN khong thich hop cho mang doanh nghiep. vai tram nghin den 1 trieu ket ndi ddng thdi Dung luong ban dau yeu cau rat Idn Truydn thong da phuong tien Co R£t han che Hdi nghi truyen hinh Tdt hon Co, nhung han che Luu lupng Thoai, fax, dOrlieu, video... Chu yeu la thoai va fax Thiet ke cho do dai cuoc goi Khong han che Ng3n (chi vai phut) Tao djch vu mdi De, nhanh va tuiam Kho, cham va phu thuoc vao nha san xuat Quan diem cua khach hang Nhin tu phuang dien khach hang, ho duoc lai vd mat gia ca va su da dang ve dich vu khi trien khai chuyen mach mdm, cu thi la: • NSng cao tien fch su dung nhd sir phat tridn cong nghe va kha nang hoi tu cong nghd va tich hap djch vu. • Giam gia thanh nhd tfnh canh tranh cua thi trudng. • Dap ung moi yeu c•oo. 'O Cong May tram PSTN = Cong phuang tien trung ke /tl ATM trung ke phuang tien duang day H inh 4.1: Phan loai giao thuc bao hieu trong chuyen m ach m em 44 Chuyen mgcli mem va ifng dung trong mang vien thong the he sau Cac giao thurc nay co the phan thanh hai loai: giao thuc ngang cap (H.323, SIP) va giao thirc Chu-td (MGCP, MEGACO/H.248). M6i loai giao thurc co uu diem va nhuoc diem rieng cua minh voi cac churc nang khac nhau, t6n tai trong mang d cac cap khac nhau. Hinh 4.1 minh hoa vi tri va pham vi su dung cac giao thurc trong mang. Vi tri" va vai tro cua timg giao thuc tren co the duoc minh hoa tren hinh 4.2. May chu phuong tien khien c o n q ^ tf Mang IP Cong phuong tien (Media Gateway) Hinh 4.2: Cac giao thuc bao hieu trong m ang chuyen m ach m em • Giao thurc ngang cap H.323, SIP duoc su dung de trao doi thong tin bao hieu va dieu khien giua cac MGC, giua MGC va cac may chu. • Giao thurc chu to MGCP, MEGACO/H.248 la giao thurc bao hieu dieu khien giura MGC va cac cong ket noi (trong do MGC dieu khien cong ket ndi). • Giao thurc SIGTRAN la giao thuc bao hieu giura MGC va cong bao hieu. Churc nang cua giao thuc nay la chuyen doi bao hieu SS7 va IP. Cac giao thurc ngang cap thuc hien churc nang mang d cap cao hon, quy dinh cach thurc giao tiep giua cac thuc the cung cap de cung phoi hop thuc hien cuoc goi hay cac ung dung khac. Trong khi do cac giao thuc chu-td la san pham cua viec phan bd khdng dong deu tri tue mang, phan ldn tri tue mang duoc tap trung trong cac thuc the' chuc nang dieu khien (dong vai tro la chu), thuc the nay se giao tiep (dieu khien) vdi nhieu thuc the khac qua cac giao thuc chu-td nham cung ca'p dich vu. Bang 4.1 so sanh cac thuoc tinh co ban cua hai loai giao thuc mang thudng dung. Chucmg 4: Cue giao thuc ca ban cua chuyen much mem 45 Bang 4.1: Bang so sanh cac giao thuc bao hieu va dieu khien Loai giao thurc Chu-td. Ngang cap ■ - Van hanh-Khai thac Phat trien dich vu Phat trien dich vu (doi vdi nha khai thac) - Cac thiet bi/Cong don gian/it tri tue - Tri tue ting dung chtia trong may chu mang - Phat trien tren co sd may chu. Cong cu chung - Nhanh chong hon dua dich vu mdi ra thi trudng thdng qua cac mang khac nhau. - Chi cap nhat cac dich vu dieu khien - Cac dich vu co the quan ly dupe mot cach dong qua mang - Cac thiet bi/cong phUc tap/thong minh - Tuong tac ngang cap - Cac thiet bi chuyen dung - Co the - Can phai nang cap tat ca cac thiet bi cdng de trien khai cac tinh nang dich vu mdi qua mang Gia thanh - Tdi UU hoa gia thanh cac thiet bi cdng do vay cho phep giam gia thanh cua toan he thdng (dac biet la ddi vdi cac he thdng Idn). - Thdi han cua cac thiet bi cdng dai hon Vi du - MEGACO/H.248 -M G C P - NCS/J.162 (Phien ban cu cua MGCP) - Gia thanh cua cac cdng don khdi cao - Gia thanh he thdng cao (dac biet la doi vdi cac he thdng Idn). - Cac thiet bi cdng co the can phai nang cap phan cting thudng xuyen - SIP -H .323 TCr bang thong ke tren day chung ta thay ro la giao thuc chu-td cho phep tap trung phan tri tue ung dung vao mot sd it cac may chu dieu khidn, do do co the dd nang cao hieu qua cua cac thiet bi cdng ket noi va co the nhanh hon trong viec dua dich vu urng dung mdi vao thi trudng vi chi can cap nhat mdi cho phan tap trung nhu cac may chu. Mang thirc te' thudng ket hop ca hai loai giao thuc bao hieu neu trdn nhu chung ta da thay ro trdn cac hinh 4.1 va hinh 4.2. 4.2 GIAO THUC H.323 Giao thurc H.323 la tieu chudn danh cho truyen thdng da phuang tien tren ca sd mang chuyen mach gdi, do ITU ban hanh. Phien ban dau tien duoc dua ra vao nam 1996 va phien ban 4 la phien ban dang duoc sir dung rong rai duoc ban hanh vao nam 2001. Phien ban 1 va 2 h6 tro H.245 tren ndn TCP. Q.931 tren nen TCP va RAS tren nen UDP. Cac phien ban 3 va 4 co h6 trg them H245 va Q.931 tren nen TCP va UDP. Ban dau H.323 du dinh danh cho X.25 va ATM nhung trong thuc te no lai dugc biet den nhidu han vdi ung dung VoIP. 46 Chuyen macli mem va ifng dung trang mang vien thdng the he sau Ngan xep giao thurc H.323 theo m6 hinh OSI: Ldp lien ket dur lieu Ldp vat 19 Hinh 4.3: N gan xep giao thitc H .323. Tu ngan xep giao thuc H.323 trinh bay tren day ta thay: • H.323 h6 tro cho luu luong thoai qua cac chu&n ma hoa G .711, G.722, G.728, G.729, G.723.1 tren nen giao thurc RTP va RTCP thong qua phuang thuc chuydn tai khong tin cay UDP. Chuang 4: Cac giao thuc ca ban cua chuyen mach mem 47 • H.323 h6 tro luu lixcnmg video qua eae chuin ma hoa H.261, H.263 tren nen cac giao thuc RTP v£ RTCP cung qua phuong thuc truyen tai khdng tin cay (UDP). • H.323 hd tro luu luong du lidu cac giao thuc T.122, T.124, T.125, T.127, T.126 qua phuong thurc truydn tai tin cay (TCP). • H.245 la giao thuc dieu khien kenh (trao ddi cac thudc tfnh cuoc goi giua 2 d^u cuoi). H.225 la giao thirc bao hidu giua d£u cud'i va gatekeeper (thiet bi dieu khidn cdng kd't ndi). Thiet bj dieu khien Thiet bi dieu khien cdng ndi (Gatekeepen) da diem (MCU) Ca'u hinh mang H.323 (hinh 4.4) bao g6m cac thanh phan sau: • Dau cud'i: Thid't bi dau cuoi H.323 bat budc phai hd tro nhung giao thuc: - Bao hieu didu khien cudc goi H.225 - Bao hieu dieu khien kdnh H.245 - Giao thuc RTP/RTCP cho dii lieu - Cac loai bd ma hoa thoai Viec hd tro cac ma hoa video la khdng bat budc ddi vdi cac dau cudi H.323. • Cdng ndi dam nhidm churc nang chuydn ddi giua hai mang, thi du giua mang chuydn mach gdi va mang PSTN. • Gatekeeper co chuc nang chinh la chuydn ddi dia chi va didu khidn bang thdng. Trong mang H.323 khdng nhat thid't phai co Gatekeeper, tuy nhien neu co Gatekeeper thi tat ca cac d5u cudi phai dang ky trudc khi thuc hien cudc goi. 48 Chuyen much mew va ifng dung trong mang vien thong the he sau • H.323 MCU (Multipoint Control Unit - Don vi didu khidn da didm) hd trg cac cudc goi hdi nghi cua 3 hay nhieu hon cac dau cudi cung tham gia trong mot phien lidn lac. Trong MCU co hai md-dun: Bd didu khidn da did’m MC (Multipoint Controller) c6 churc nang didu khidn va bd xu ly da di^m MP (Multipoint Processor) nhan va xir ly cac ludng du lidu thoai, video hoac du lidu khac. 4.3 GIAO THfrC SIP Giao thurc SIP do nhom lam viec MMUSIC (Multiparty Multimedia Session Control) cua IETF phat trien tu tieu chufin RFC 2543. Day la giao thurc bao hieu ldp urng dung co churc nang mo ta viec khdi tao, thay ddi va huy phidn truydn thdng da phucmg tidn giua cac d£u cudi. SIP duoc dua ra trdn co sd nguydn ly giao thurc trao ddi thdng tin cua mang Internet (HTTP). SIP la giao thurc ngang cap, hoat ddng theo nguydn tac hoi/ dap (server/client). Vi tri giao thurc SIP trong md hinh phan ldp hd thdng duoc md ta nhu hinh 4.5. l/ng dung cua may tram SIP API day du API don gian API L/ng dung 1 dac biet I s Agent phan phat M Giao thirc SIP + Md rong EAPI I6p truyen tai Ldp truyen tai (UDP/TCP) Hinh 4.5 Giao thuc SIP trong m o hinh phan lap he thdng TCr hinh 4.5 trdn day chung ta thay rang giao thuc SIP co thd’ chay trdn ndn ca UDP va TCP vdi IPv4 hoac IPv6. SIP duoc thiet ke ddc lap vdi cac giao thurc truyen dan muc thap va co the bd sung cac tinh nang mdi thdng qua vide thay doi cac tham sd hay tieu de cua cac ban tin. Cac thuc the mang cua giao thurc SIP bao gom: • Dau cudi SIP: Co the la may dien thoai SIP hay may tinh chay phan mem SIP. Mdi dau cuoi se duoc gan mot dia chi SIP URL de dinh danh va nhan thuc. • Proxy Server (may chu uy quyen) la dai dien cho mot nhom cac dau cuoi SIP. co nhidm vu dap ung cac yeu cau SIP cua nhom dd hay tu cac proxy khac. Trong trudng hop no khdng dap urng duoc thi yeu cau se duoc chuydn cho mot proxy khac. Chuang 4: Cac giao thuc coban cua chuyen mach mem 49 • Redirect Server (may chu chuyen d6i dia chi): Nhan dia chi SIP va gui lai cho noi hoi duori dang dia chi khac cua proxy kd' tid'p dd lien l&c. • Registrar Server (may chu dang ki): Co chuc nang nhan thuc, bao mat. Ghi lai dia chi SIP va dja chi IP cua d£u cud'i SIP dang ky. Noi each khac la may chu nay thue hien cac churc nang dang ky va quan ly cac dau cuoi (Endpoints) va dia chi cua chung. • Location Server (may chu djnh vj) la phan mem djnh vj dau cudi, cung cap thdng tin ve nhung vi tri co the cua phfa bj goi cho cac phdn mem Proxy Server va Redirect Server. SIP sir dung phuong phap ma hoa kieu van ban vdi ca'u true ban tin theo kieu hoi/dap, bao gdm cac ban tin sau: • Ban tin INVITE - Bat dau thiet lap cudc goi bang cach gui ban tin mdi dau cudi khac tham gia • Ban tin ACK - Ban tin nay khang djnh client (may tram) da nhan duoc ban tin tra ldi ban tin INVITE • Ban tin BYE - Bat dau ket thuc cudc goi • Ban tin CANCEL - Huy yeu cSu dang nam trong hang doi • Ban tin REGISTER - Dau cudi SIP su dung ban tin nay de dang ky vdi Registrar Server • Ban tin OPTIONS - Su dung de xac djnh nang luc cua may chu • Ban tin INFO - Su dung de tai cac thdng tin nhu am bao DTMF Trong phien hoi thoai SIP, mdi ben tham gia duoc gan mdt dja chi SIP, cac user (ngudi su dung) se dang ky vj tri dang nhap vdi may chu SIP. Qua trinh thiet lap mot phien lien lac SIP didn ra nhu sau: 1. Dang kf, khdi tao va djnh vj dau cuoi 2. Md ta phien cua dau cudi duoc mdi tham gia (am thanh, video hay da phuong tien) 3. Xac nhan thai do hudng ung cua dau cuoi duoc mdi 4. Neu dau cuoi duoc mdi co thai do tfch cuc, cuoc goi duoc thid't lap 5. Cac nhiem vu xu ly trong qua trinh cuoc goi 6. Giai phong cudc goi Chi tiet cac qua trinh xu ly thid't lap cua phien lien lac SIP neu tren duoc minh hoa tren hinh 4.6. 50 Chuyen mach mem va ifng dung trong mang vien thdng the he sau SIP UA PROXY SERVER INVITE w/ SDP INVITE w/ SDP 100 Trying 100 Trying 180/183 (Ringing) w/SDP 180/183 (Ringing) w/SDP RTP/RTCP (Optional) 200 OK 200 OK RTP/RTCP ACK ACK BYE BYE 200 OK 200 OK Lifu y: Bao hieu SIP co the chay tren UDP hay TCP Hinh 4.6 Thiet lap va huy cuoc goi SIP Cac ban tin tra lcri cac ban tin SIP ndu tren g6m co: lxx - Cac ban tin chung 2xx - Thanh cong 3xx - Chuyen dia chi 4xx - Yeu c£u khdng duoc dap ung 5xx - Sir co cua may chu 6xx - Su c6 hoa mang Chi tie't cu the ve giao thurc bao hieu SIP se duoc trinh bay trong chuong 5. 4.4 GIAO THUC M GCP-M EGACO/H.248 Mot trong nhung giao thurc quan trong nhat, la ndn tang cua chuydn mach mdm la giao thurc didu khien cong phuong tien MGCP (Media Gateway Control Protocol). Giao thuc nay quy dinh each thurc ma MGC dieu khi£n cac MG trong viec thiet lap ket noi khi ma cac phan mem dieu khidn, xu ly cuoc goi dupe tach khoi cac MG. MGCP dupe phat trien tir hai giao thirc ban dau la: giao thirc didu khidn cong don gian SGCP (Simple Gateway Control Protocol) va giao thurc didu khidn thiet bi Internet IPDC (Internet Protocol Device Control). MGCP la giao thurc dupe thid't ke danh chu yeu de xir ly bao hieu trong mang IP, giao thuc nay it co nang lire xir ly cho vide truydn tai cac goi thoai Clutcnig 4: Cue giao thuc co ban cua chuyen mach mem 51 noi chung, vi du nhu VoATM. Viec ung dung MGCP trong thuc te cung chi ra mot so nhupc diem cua giao thuc nay nhu thieu mot phuong thuc huu hieu de MGC co the thu thap thong tin vd kha nang xu ly cua mot MG nao do. Nhung nhupc diem nay dupe khde phuc bdi mot giao thurc khac vdi cac di£m ke thua tu MGCP va cac tinh nang tang cudng, giao thufc MEGACO (MEdia GAteway COtrol protocol) do IETF phat trien. To churc ITU da phoi hop vdi IETF de phat trien giao thurc tuong tu nhu MEGACO va goi ten la giao thuc H.248. Chuong 6 tiep theo se xem xet chi tie't ve hai giao thuc nay. 4.5 GIAO THUC SIGTRAN Mang NGN la su lien ket mang va hoi tu cua cong nghe thdng tin, mang IP, va internet vao mang vidn thdng. Su hoi tu nay dat ra yeu cdu chuydn tiep giua mang PSTN truyen thong va mang IP. Dieu nay dupe tien hanh nhd giao thurc truyen tai bao hieu SIGTRAN (SIGnaling TRANsport). Hinh 4.7 trinh bay ngan xep giao thurc SIGTRAN ISUP 1 SCCP I MTP3 | TCAP | M3UA | M2UA j SUA | IUA SCTP IP Ethernet IP over ATM H inh 4.7: Ngan xep giao thuc SIG TRAN SIGTRAN la mot giao thuc hd tro cho mang dien thoai IP (VoIP), no cho phep truyen tai cac ban tin bao hieu sd 7 qua mang IP, nhd dd luu lupng cua mang PSTN va ISDN dua tren bao hieu sd 7 co the truyen qua mang IP. Dd lam dupe didu nay, SIGTRAN su dung mot loat cac giao thurc thanh phan va cac mo-dun tuong thich bao gom: Giao thuc truyen tai dieu khien dong SCTP (Stream Control Transport Protocol), mo-dun tuong thich vdi MTP ldp 3 (M3UA), mo-dun tuong thich vdi MTP ldp 2 (M2UA), ldp tuong thich vdi ngudi dung ISDN (IUA). • SCTP co cac churc nang: - Truyen tai cac ban tin bao hieu cua mang PSTN qua mang IP 52 Cluiyen macli mem va ifng dung trong mang vien tliong the he sau - La giao thirc truyen tai tin cay tren ndn mang goi theo che dd khong hudng ket ndi. - Xac nhan khong co ldi va khdng truyen lai du lieu. - Phan manh du lieu (cat mdt ban tin khach hang cua SCTP va dua vao nhieu gdi) - Ddng goi du lieu (gop nhieu ban tin la khach hang vao mdt gdi) • M3UA co cac chute nang: - H6 tro chuyen giao cac ban tin MTP ldp 3 (ISUP, SCCP, TUP...) - Hd tro cho hoat dong cua cac giao thurc ldp MTP3 - Hd tro quan ly ket hop truyen tai SCTP va luu luong giua mdt SG va mot hay nhieu MGC - H6 tro cho MGC hay cac co sd du lieu luu tru chia se luu luong • SUA co cac churc nang: - Hd tro chuyen giao cac ban tin phan ngudi dung SCCP (vi du nhu TCAP, RANAP) - H6 tro cac dich vu khong hudng ket ndi (connectionless oriented) SCCP - H6 tro cac dich vu hudng ket ndi (connection oriented) SCCP - Hd tro quan ly ket hop truyen tai SCTP va luu lupng giua mot SG va mot hay nhieu nut bao hieu IP - Hd tro cho viec thong bao mot cach ddng bo su thay doi trang thai cho cdng tac quan ly. Chi tie't cu the ve giao thurc SIGTRAN se dupe trinh bay trong chuong 7. Chuong 5 GIAO THUC KHCfl TAO PHIEN SIP 5.1 DINH NGHIA VA CAC THANH PHAN CUA H $ THONG SIP 5.1.1 Cac dinh nghTa va khai niem co ban Call: Mdt cudc goi g6m ta't ca cac thanh vidn trong phidn dupe men bdi mdt tai nguyen chung. Mdt cuoc goi SIP dupe nhan biet bdi mot Call-ID (Bd nhan dang cudc goi) duy nhat. Call leg: Dupe nhan bid't bdi su kd't hop cua Call-ID, “To” va “From”. Client: La mot chuong trinh ling dung giri di nhung yeu cau cua SIP. Client co the anh hudng true tiep hoac khdng dd'n ngudi sir dung. Client dupe chura trong cac Proxy va User Agent. Conference: Hdi nghi la mdt phien hdi thoai da phuong. Mot hoi nghi co th£ khdng co hoac co nhieu thanh vien bao gdm cac trudng hop nhu hdi nghj da phuong, hdi nghi nhieu mat ludi (full-mesh), cudc goi hai thanh vien... mdt vai cudc goi co the tao ra mot hoi nghi. D ow nstream : la yeu cau giri true tiep tir phia chu goi den ngudi nghe (tir UAC den UAS). Final Response: la cac dap ung de ket thuc mot phien giao dich SIP, bao gdm cac dap ung sau: 2xx, 3xx, 4xx, 5xx, 6xx. Invitation: La yeu cau khdi tao giri tir User hoac Server dd nghi tham gia vao mot phien hoi thoai. Mot ldi mdi day du gom mot yeu cau INVITE ngay sau mdt yeu cau ACK. Parallel search: Trong mot qua trinh tim kiem song song mdt Proxy dua ra mdt vai ydu c£u tdi ngudi dung hien tai trong khi nhan mdt yeu cau den. Provisional Response: Dap ung tam thdi la dap ung dupe Server thdng bao mdt tien trinh goi nhung chua ket thuc mdt phien giao dich SIP, dap ung lxx la mot dap ung Provisional Response. 54 Chuyen mach mem vd ibig dung trong mang vien thong the he sau Server: La mot chuong trinh ung dung co nhidm vu nhan cac yeu cau hop le tir cac dich vu va gui tra lai cac dap ung. Session: Theo dac ta cua SDP thi mot phien da truyen thong la tap hop nhung nguoi gui va nhan cung voi dong du lieu tir noi gui den noi nhan. No duoc xac dinh bdi chuoi cac ten User, Session ID (chi so phien), kieu mang, kidu dia chi va dia chi cac phan tu trong trudng nguon. Upstream: Dap ung gui true tiep tu UAS den UAC. URL-encoded: La chu6i ky tu ma hoa theo chu^n RFC 1738. Dac tinh cua cac kidu Server khac nhau duoc tdng ket trong bang 5.1: Bang 5.1: D ac tinh cua cac kieu Server Dac tinh Redirect Server Proxy ServerUser Agent Server Registrar Server Hoat dong nhu mot SIP Client Khong Co Khong Khong Tra lai trang thai 1xx Co Co Co Co Tra lai trang thai 2xx Khong Co Co Co Tra lai trang thai 3xx Co Co Co Co Tra lai trang thai 4xx Co Co Co Co Tra lai trang thai 5xx Co Co Co Co Tra lai trang thai 6xx Khong Co Co Co Chen tieu de (Via) Khong Co Khong Khong Chap nhan (ACK) Co Co Co Khong 5.1.2 Cac thanh phan cua kien true SIP Xet tren quan diem Client/Server, cac thanh phan chmh cua mot he thdng SIP dirge mo ta bdi hinh 5.1. Trong hinh 5.1, UA (User Agent) la thiet bi dau cuoi trong mang SIP. no co thd la mot may dien thoai SIP hay mot may tfnh chay phan mem dau cuoi SIP. UA co the khdi tao, thay ddi hay giai phong cuoc goi. Trong do phan biet hai loai UA: UAC (User Agent Client) va UAS (User Agent Server). UAC la mot thuc the thuc hien viec khoi tao mot cuoc goi con UAS la mot thirc thd thirc hien viec nhan cuoc ggi. Nhung ca UAC va UAS deu co the giai phong cuoc goi. Chuong 5: Giao thuc khoi tao phien SIP 55 Proxy Server la phan mdm trung gian hoat ddng vua nhu Server va vua nhu ca Client d£ thue hidn cac ydu c Status-code g6m 3 chCr sd. Chu s6 d 7) Tieu de chap nlian (Accept) Khi khdng chap nhan tieu de hien co tuc la co su xua't hien cua truong Accept, Server se phat di mot gia tri mac dinh cua ung dung sdp. Vi du: accept: application/sdp; lever = 1, application/x-private, text/html 8) Tieu de Accept-encoding Trudng tieu de yeu cau Accept-encoding cung giong nhu tieu de Accept va bieu didn su chap nhan cua dap ung. 9) Tieu de Accept-language Cu phap phan tieu de ngon ngu chap nhan quy dinh ve lenh trong ngon ngu dua vao tham sd ap dung vao SIP tdt nhu the nao. Trudng tieu de yeu cau Accept-language cho phep Client thong bao cho Server ngon ngu no mong muon de nhan reason-phrases, mieu ta phien hay ma trang thai dupe truyen tai bdi than ban tin. Mot Proxy cd the’ su dung trudng nay dd trp giup viec lira chon dich ddi vdi cac cuoc goi. 10) Tieu de cho phep (Allow) Truong tieu de thuc the (entity-header) liet ke tap hop cac chi thi dupe hd trp bdi tai nguyen djnh nghTa bdi yeu cau URI. Muc dich cua trudng nay la thong bao den ngudi nhan cac chi thj gia trj ket hop vdi tai nguyen mot cach chinh xac. Trudng tieu dd Allow co mat trong dap ling 405 va trong dap ung Options. Allow = “Allow” “ :” l#m ethod 11) Tieu de cho pliep (Authorization) UAS muon xac dinh ban than minh vdi may chu sau khi nhan dupe dap ung 401, no co the lam dieu nay bang cach dua trudng tidu de yeu cau Authorization vao mot ydu cau. Gia trj trudngAuthorization bao gom cac uy nhidm chua thong tin cho phep UASbiet pham vi hoat dong cua tai nguyen da dupe ydu cau. 12) Tieu de Call-ID (chi so cuoc goi) Trudng tieu de chung Call-ID xac dinh mot ldi mdi thanh vien hoac tat ca cac dang ky cua mot Client thanh vien mot cach duy nhat. Chu y rang mot hoi nghj da Chuong 5: Giao thUi khdi tao phien SIP 77 phuong tidn dcm gian co thd’ thdm vai cudc goi vdi cac Call-ID khac nhau, neu ngudi su dung mdi nhidu Idn khac nhau den cung mdt hoi nghi. Ddi vdi mdt ydu cdu INVITE, mdt UAS bi goi khdng nen canh bao vdi ngudi su dung dd nd'u ngudi su dung da dap urng lai Call-ID trong ydu cdu INVITE. Nd'u ngudi su dung da la mot thanh vidn cua hdi nghi va cac tham so cua hdi nghi da dupe chua trong mot mieu ta phidn khdng cd thay doi thi UAS bi goi nay cd the chdp nhan cuoc goi bat cha'p Call-ID. Mot ldi mdi cho Call-ID hoac phidn hien tai cd the thay doi cac tham sd cua hdi nghi. Mot urng dung cua Client cd the dua ra mot chi thi don gian tdi ngudi su dung ve cac tham so cua hdi nghi da dupe thay doi va chap nhan cuoc goi tu dong hoac no cd the’ ydu cdu ngudi sir dung xac nhan. Mot ngudi sir dung cd the dupe mdi den cung mot hdi nghi hoac cudc goi su dung nhidu Call-ID khac nhau. Client cd the loai phat hien nhung ban sao nay bang each no su dung cac nhan dang trong mieu ta phidn. Chi thi Register (dang kf) va Option (tuy chon) su dung gia tri Call-ID de ydu cau dupe gid'ng hoan toan vdi dap ung. Tdt ca cac ydu cdu Register dua ra bdi mdt Client phai cd cung mot Call-ID. Khudn dang: Call-ID = ( “Call-ID’T‘i” )“ :”local-id“@ ”host Local-id = l*uric 13) Tieu de giao dich (Contact) Trudng tidu de chung Contact cd the’ xac nhan trong ydu cau INVITE, ACK, Register va trong dap urng lxx, 2xx, 3xx va 485. No cung ca'p URL dd ngudi sir dung cd the cd cac giao tiep xa hon. Cac ydu cdu INVITE va ACK cd the chua tidu dd Contact de chi ra vj tri khdi tao ydu cau. Dap urng INVITE lxx: Mot UAS gui mot dap urng lxx cd the chen vao tidu de dap urng Contact. No cung cd y nghTa nhu dap urng lxx va dap urng INVITE 2xx. Chu y rang ydu cau CANCEL khdng dupe gui den dja chi dd. Dap urng INVITE 2xx: Mdt Server gui mot dap urng 2xx cd the chen vao mot tieu dd dap ung Contact dd chi ra vj tri SIP trong cung mot Call-ID. Trudng tidu de Contact chua dja chi cua Server hoac Proxy, neu tram d phia sau tudng lira. Gia tri tidu de duoc sao chep vao trudng Request-URI cua ydu cdu tid'p theo cho cuoc goi nay. Neu dap ung khdng chua tidu de Record-route thi dja chi trong trudng tidu de Contact dupe bo sung nhu phdn tur cudi cung trong trudng tidu de route. 78 Chuyen much mem vu Ung dung trong mang vien thong the he sau Yeu cau Register: Yeu cau Register co the chtia trudng tidu dd Contact, no chi ra vi tri ngudi sir dung co the den. Ydu cSu Register dinh nghTa trudng chi duoc sir dung vdi expire “0” de loai bo t&'t ca cac dang ky ngudi sir dung dac biet. Mot lham sd' expire tuy chon chi ra thdi gian ket thuc cua dang ky. Neu Contact nao khdng cd tham sd expire thi trudng tidu dd expire dupe sir dung nhu gia tri mac dinh. Dap ting 2xx Register: Mdt dap ting Register cd the quay vd tat ca cac vi tri ngudi sir dung hien tai cd the dat dd'n. Mot tham sd expire mac dinh chi ra thdi gian kd't thuc cua dang ky. Dap ting 3xx va 485: Trudng tidu dd dap ting Contact cd the’ sir dung chung vdi ma dap ting 3xx va 485 de chi ra mot hoac nhidu dia chi thay the'. No cd the’ xua't hidn trong cac chi thi BYE, INVITE, OPTION. Trudng tieu dd Contact chtia URI dua ra vj tri mdi hoac tdn cua User de thir hoac cd the la cac tham sd truydn bd sung dac bidt. Dap ting 300, 301, 302, 485 chtia trudng Contact vdi dja chi URI mdi. Client sao chep cac phan tir “user”, “password”, “host”, “port” va “user param ” cua URIContact vao URI ydu cfiu djnh hudng ydu cau den dja chi dac ta bdi tham sd “m addr” va “port”, sir dung giao thtic truyen tai trong “transport param”. Mot trudng tidu dd dap ting Contact cd the chtia bat ky URI thich hop de chi ra bj goi nao cd th£ dat dupe, khdng han chd' den SIP-URL. Cac tham sd sau dupe djnh nghTa: - q: gia trj q chi ra uu tidn tuong doi giua vj tri cho trudc (0< q< l), q cang Idn dd uu tidn cang cao. - Action, tham so nay dupe sir dung khi dang ky vdi ydu c5u Register. Neu tham sd nay khdng dupe dac ta thi hoat dong xay ra phu thuoc vao ca'u hinh Server, khi do trong cac dap ting ciia no, cac ban sao nen chi ra che do dupe sir dung. Tham sd nay khdng dupe chu y trong cac ydu cau khac nhau. - Expire: tham sd expire chi ra thdi gian hieu luc cua URI. 14) Tieu de m d hou ndi dung (Content-Encoding) Gia trj ciia trudng tidu de thuc the Content-Encoding chi ra cac m a hoa phu hop dupe ting dung trong phan than ban tin, vi vay co che' giai ma phai dupe ting dung dd dat dupe kieu truyen thdng trong trudng tidu dd Content-Type. Neu nhieu ma hoa dupe dung trong ban tin thi ma hoa phai dupe sdp xep phu hop theo thu tu chung dupe dung. Client cd the dung ma hoa Content va phan than ciia ydu c£u. Neu Server khdng co kha nang ma hoa phan than hoac phan khong the’ nhan biet dupe bat ky gia tri Chifang 5: Giao thuc khdi tao phien SIP 79 Content-Encoding nao, thi no phai guri dap ung 415, liet ke cac ma hoa co the chap nhan trong tieu de Accept-Encoding. Mot Server co the ap dung Content-Encoding vao phan chmh trong cac dap ung. Server chi dupe sir dung cac ma hoa da liet ke trong tieu de Accept-Encoding trong yeu c3u. 15)Tieu de do ddi noi dung (Content-Length) Gia tri trudng tieu de Content-Length chi ra kfch co ph£n chmh cua ban tin. La sd Octet tfnh theo thap phan gui den phia nhan. Cac ung dung nen dung trudng nay de chi ra kfch cd phan chmh cua ban tin da truyen di, ba't ke kidu phuong tien gi cua thuc the. Gia trj Content-Length > 0 deu dupe su dung (gia trj bang khdng khi phan than trong ban tin khdng cd). Neu Server nhan yeu c£u UDP cd trudng Content-Length, ma gia trj ciia no Idn hon kfch cd cua phan than ban tin gui trong yeu cau, thi Client tao ra dap ting 400. Neu cd du lieu bd sung trong goi UDP sau khi byte cudi cung cua than ban tin dupe doc, thi Server phai xu ly phan du lieu nhu ban tin rieng. Dieu nay cho phep nhieu ban tin dupe dat trong cung mdt gdi UDP. 16) Tieu de kieu noi dung (Content-Type) Gia trj truong tieu dd Content-Type chi ra kieu truyen thdng cua than ban tin gui den phfa nhan. 17) Tieu de CSeq CSeq do chinh Client bd sung vao mdi ydu cau. Trudng tieu de CSeq trong than ban tin yeu cau chtia chi thj ydu cau va sd lupng chudi dupe chon theo ydu cau cua Client, vdi mdt gia trj Call-ID. Sd lupng chudi phai la mot sd nguydn khdng dau 32 bit. Gia trj khdi tao cua no la tuy y nhung phai nhd hon 231. Cac yeu cau ACK va CANCEL phai chtia cung gia trj CSeq nhu trong ydu cau INVITE trong khi ydu cau BYE vdi CSeq khdng cao hon se tao ra dap ting 400. Mot Server cua UAS phai nhd sd lupng chudi cao nhat ddi vdi bat ky ydu cau INVITE nao trong cung gia trj vdi Call-ID, Server phai dap lai bat ky ydu cau INVITE nao vdi cung mdt sd lupng chudi thap hon. 18) Tieu de thdi gian (Date) La mdt trudng tieu de chung phan anh thdi gian khi yeu cau hoac dap ting dupe gui di liin dau. Vi vay, cac ban tin truyen dat cd cung gia trj trudng tieu de du lieu nhu ban tin dau tidn. 80 Cliuyen macli mem vd ifng dung trong mang vien thdng the he sau 19) Tieu de m d hoa (Encryption) Truong tieu de ma hoa chung dac ta ndi dung dupe ma hoa. Trudng tieu dd n&y thudng su dung cho cac yeu cdu va cac dap urng end-to-end (ditu cudi toi d&u cudi). Ydu cau dupe ma hoa dua tren khoa cong khai cua thuc the goi la trucmg tidu dd ‘T o ”. Dap u:ng dupe ma hoa dua tren khoa cdng khai truyen trong trucmg tidu dd kh6a dap ting. Chu y rang ban than khoa c6ng khai khong dupe su dung de’ ma hoa. Didu n&y phu thuoc vao tung thuat toan dupe su dung. Doi vdi ba't ky ban tin da dupe ma hoa nao, thi it nha't co ph£n than ban tin va co the cac truong tidu dd khac dupe ma hoa de giai ma than ban tin, sau do thuc hidn ghdp ban tin ban dau den dudng day yeu cau va den cac tidu de cua ban tin ban dau. Tidu dd ban tin trong phan da giai ma thay the hoan toan tidu de ban tin trong phan ban tin ban dau voi cac truong co cung tdn. Ma hoa chi de cung cap su bf mat: phia dich khdng dam bao rang yeu c iu hoac dap ting tir phia gui dupe liet ke trong tieu de ban tin From m a phfa dich chi dam bao rang phfa gui sir dung khoa cong khai ciia phfa dfch. Tuy nhien, cac Proxy khdng co kha nang thay doi ydu cau hay dap ting. Vi cac Proxy co the dira vao sir quy dinh trudc cua chung de ket hop ba't ky trudng tidu de SIP nao nen khong co su dam bao rang cac ydu cau da ma hoaco cac trucmg tidu dd “an” (hide) se cung den dfch nhu cac ydu cau khdng ma hoa dupe dinh danh khac nhau. 20) Tieu de thuc the ( Expires) Trudng tieu de thuc the expire dua ra thdi gian va ngay ma noi dung ban tin se hd't hieu lire. Trudng nay chi dupe dinh nghTa trong chi thi Register va INVITE. Ddi vdi Register: No la trudng tidu de dap ting va yeu cau trong ban tin Register, Client chi ra dang ky gia tri trong bao lau. Trong dap ting Server chi ra thdi gian hd't hieu lire sdm nha't ciia cac dang ky. Server cd the lira chon khoang thdi gian ngan hon trong yeu cau tir Client nhung khong nen lau hon. Ddi vdi INVITE: No la trudng tieu dd dap ting va yeu cau. Trong mdt ydu cdu, chu goi co the han che gia tri ciia yeu cau, vf du Client cd the han che khoang thdi gian tim kie'm mot yeu cau hoi nghi. 21) Tieu de xuat phdt (From) Cac dap ting va ydu cau phai cd trudng tidu dd chung From de chi ra bo khdi dau yeu cau. Server sao chep trudng tieu de From tir ydu cau vao dap ting. Trudng From cd