Nối tiếp nội dung của phần 1 cuốn sách "Công nghệ VoIP và các giải pháp nâng cao chất lượng dịch vụ", phần 2 giới thiệu tới người đọc các nội dung: Các giao thức điều khiển, QoS và các yếu tố chính ảnh hưởng đến chất lượng thoại IP, các giải pháp nâng cao chất lượng thoại. Mời các bạn cùng tham khảo.
ChiTdng IV C A C G IA O TH lTC D IE U K H IE N 4.1 GlCrt THIEU So vai thoai truyen thong, thoai IP hoat dong mot moi trudng mdi, hien da co mot sd cac giao thuc lap ung dung phat trien cho thoai Internet Mot diem quan de co mot tang ca sd goi dua tren tieu chuan la kha nang co cac tieu chuan md cho cac lap dieu khien cuoc goi N chuan m a duac cung cap bdi cac giao thuc nhu H.323, MGCP SIP va cac giao dien m d dugc phat trien rong khap qua c a sd tang dong goi Mot cac cong viec cua giao thuc dieu khien cuoc goi la chi cho cac dong RTP bat dau d dau va ket thuc d dau Giao thuc dieu khien cuoc goi hoan tat nhiem vu bang viec bien dich giua cac dia chi IP va cac sd dien thoai Hien chung ta chua the thay the hoan toan mang dien thoai chuyen mach cong cong (PSTN) bang cong nghe VoIP bai nhieu dieu phirc tap ben cac giao thirc mdi chay tren nen tang ciia IP Tuy nhien, gan day cac giao thirc cho bao hieu cuoc goi va dieu khien thiet bi dang dugc chuan hoa chung ta dang gdn dat den mot mdi trudng co tinh lien ket hoat dong cao Giao thirc dieu khien truyen thong (M GCP) hien da trd tieu chuan chinh thirc, cac cai tien dugc thira Chut m g IV: Cac giao Ihire dieu khien 139 nhan gan day phien han cua H.323 da tao dieu kien thuan lgi ket hgp voi cac giao thirc khac de tao cac giai phap cho lie thong truyen thoai hoan chinh va dac tinh ket noi ngang cap cho cac mang goi Giao thirc khai tao phic’n (SIP) dang dirge xem nhu giao thirc bao hieu chinh he thong chuyen mach mem (softsvvitch) Hinh 4.1 dudi day la mo ta chong giao thirc sir dung cho VoIP Hinh 1: Chong giao (hire VoIP Giao thirc H.323 phien ban va ho trg H.245 tren nen TCP, Q.93 tren nen TCP va RAS tren nen UDP Cac phien ban va cua H.323 ho trg them H.245 va Q.931 tren nen UDP Giao thirc SIP ho trg ca TCP va UDP Trong mang NGN cac cuoc goi thoai deu la cac cuoc goi VoIP Chinh vi the phan tilp theo se dc tien (Media Control) Bo codec am (Audio Codecs) G 711, G.722, G.723.1 G 728 G 729 Bo codec vi-de-o (Video Codecs) H.261,H 263 Chia se du li$u (Data Sharing) T 120 T ruyln tai phuang tien (Media RTP/RTCP Transport) Cac phan co ban ciia he thong mang H.323 dugc nio ta hinh 4.2 dudi day Bao gom cac dau cuoi, cong ket ndi thiet bi dieu khien cong ndi (gatekeeper) va khoi dieu khien da diem (MCU) Chuang IV: Cdc giao Ihue dieu khien 141 Dien thoai Hinh 4.2: Cdc phan mang H.323 4.2.1 Thiet bi dau cuoi Dau cuoi cung cap thong tin diem - diem va da diem vai cac ddu cuoi khac Dau cuoi H.323 gom cac khoi nhu dieu khien he thdng, khdi truyen tai p h u an g tien ma hoa audio va giao dien voi mang IP Phan thiet bi chon co the la ma hoa video va thiet bi truyen du lieu 4.2.2 Cong ket noi Cong ket ndi cung cap giao dien giua hai mang khac Cdng k it ndi H.323 ket noi mang H.323 voi mang khong phai H.323 nhu PSTN Cong ket noi chuyen ddi giua audio (am thanh) video va cac dinh dang truyen du lieu cung nhu cac giao thuc va he thong thong tin Cong ket ndi chi can thiet Cong nghe VoIP vd cdc giai phap 142 phai ket noi vai mang phi 11.323, do khong can thiet ket noi giua hai thiet hi dau cuoi H.323 4.2.3 Thiet bj dieu khien cong noi Thiet bi dieu khien cong noi la chon, co the sir dung hoac khong Thiet bi dieu khien cong noi cung cap cac djch vu truac dien cuoc goi va dich vu dieu khien cuoc goi cho cac diem cuoi H.323 Tuy nhien, neu thiet bi dieu khien cong noi co mat mang no se co nhiem vu: bien dich dja chi, dieu khien chap nhan, dieu khien bang thong va quan ly viing Cac chirc nang chon ciia thiet bi dieu khien cong noi bao gom: bao hieu dieu khien cuoc goi, xac thuc cuoc goi, quan ly bang thong, quan ly cuoc goi 4.2.4 Khoi dieu khien da diem (MCU) Khoi dieu khien da diem la diem cuoi (endpoint) ho trg hoi nghi giua vien hoac nhieu han MCU dien hinh bao gom bo dieu khien da diem (MC) va mot hoac nhieu bo xir ly da diem (MP) MC xir ly dieu khien va bao hieu de ho trg hoi nghj MP nhan d u lieu audio, video va luong du lieu, xir ly va / r * r phan bo chung den cac diem cuoi vien hoi nghi da diem Bo giao thuc H.323 bao gom nhieu giao thirc Bo giao thuc ho trg chap nhan cuoc goi, thiet lap, trang thai, giai phong luong p h uang tien va cac ban tin he thong H.323 Cac giao thirc dugc ho trg ca c a che truyen dua goi tin cay va khong tin cay qua mang IP nhu minh hoa hinh 4.3 143 Chuang IV Cdc giao thuc dieu khien Truyen tai TCP tin c$y Truyen tai UDP khong tin cay Du lieu audio/video H 225 Dieu khien cuoc goi H 245 RAS RTP RTCP UDP TCP IP Lap vat ly va lien ket du lieu Hinh 4.3: Cdc lap ciia bo giao thuc H.323 Bo giao thirc H.323 bao gom ba viing dieu khien: - Bao hieu dang ky, thira nhan va trang thai (RAS): Bao hieu RAS cung cap dieu khien truac cuoc goi mang thiet bi dieu khien cong noi H.323 - Bao hieu dieu khien cuoc goi (H.225): dua tren khuyen nghi H.225 ciia ITU-T ma no chi viec sir dung cac ban tin ban hieu Q.931 Kenh dieu khien cuoc goi tin cay TCP dugc tao tren mang IP vai ma cong la 1720 - Dieu kh iln va truyen tai thong tin Media (H.245 va RTP/RTCP): H.245 xir ly cac ban tin dieu khien tir dau den cuoi giua cac diem cuoi H.323 Thu tuc giao thirc H.245 thiet lap kenh cho truyen audio, video dir lieu va thong tin kenh dieu khiln T ru y ln da p h uan g tien H.323 dugc cung cap bai RTP va RTCP 4.2.5 Trinh tu thiet lap cuoc goi N£u xem xet mot cach chi tiet thi cuoc goi giua hai dau cuoi H.323 dugc thilt lap nhu hinh 4.4 duai day Cong nglw VoIP va cdc giai phap 144 □ [L IT ! Dau cuoi A Thiet bi dieu khien cong noi O^u cuoi B A R Q -2 ACF -■3 S ETUP4 Call Proceeding ARQ ACF Alerting I Connect H.245 Messages I RTP Media Path -RAS messages •Call Signaling Messages Hinh 4.4: Thiet lap cuoc goi H.323 - Trudc het ca phai da dugc dang ky tai thiet hi dieu khien cong noi - Dau cuoi A gui yeu cau tdi thiet bi dieu khien cong ndi de nghi thiet lap cuoc goi - Thiet bi dieu khien cong ndi gui cho dau cuoi A thong tin can thiet ve dau cuoi B Chuang IV Cdc giao Ihire dieu khien 145 - Dau cuoi A giri ban tin SETUP tai dau cuoi B - Dau cuoi B tra ldi bang ban tin Call Proceeding va dong thdi lien lac vdi thiet bi dieu khien cong noi de xac nhan quyen thiet lap cuoc goi f * * j * r v • & / i - Dau cuoi B giri ban tin canh bao va ket ndi (Alerting and Connect) - Hai dau cuoi trao ddi mot sd ban tin H.245 de xac dinh chii/td, kha nang xir ly ciia dau cuoi va thiet lap ke ndi RTP Day la trudng hop cuoc goi diem-diem don gian nhat, ma bao hieu cuoc goi khong duoc dinh tuyen tdi thiet bi dieu khien cong ndi H.323 hd tro nhieu kich ban thiet lap cuoc goi phirc tap khac H.323 la he thong ghep lai duoc xay dung tir cac thiet bi tap trung thong minh nhu: thiet bi dieu khien cong ndi MCU, cong ket ndi va diem cuoi Mac dii chuan H.323 phien ban gan day nhat co phdn hoan thien hon song van de van sinh nhu thdi gian thidt lap cuoc goi dai, qua nhieu chirc nang thiet bj dieu khidn cdng ndi phai thuc hien va kha nang m d rong sir dung ki£u bao hieu cuoc goi djnh tuyen qua thiet bi dieu khien cdng ndi (GKRCS) Khi cdn sir dung cdng ket ndi dung luong ldn de ket ndi mang PSTN, ngudi ta se sir dung giao thirc dieu khien cdng don gian (SGCP: Simple Gateway Control Protocol) va Giao thuc didu khidn cdng p h u a n g tien (MGCP: Media Gateway Control Protocol) dd thay thd giao thirc cho cdng ket ndi H.323 Cac he thdng didu khien cuoc goi co ve hieu qua hon dap img nhu cau cua cac nha cung cap cd ldn Cdng nghe VoIP vd cdc giai phap 146 Cung vay, giao thuc khoi tao phien SIP (Session Initiation Protocol) co the giai quyet mot so ton tai cua H.323 va no kha nang sc thay the H.323 4.3 GIAO THU’C KHOI TAO PHIEN (SIP) SIP la giao thuc dieu khien bao hieu thuoc lap ung dung, duoc phat trien nhu la mot chuan m a RFC 2543 cua ILTF Khac voi H.323, no dua tren nguon goc Web (HTTP) va co thiet ke kieu mo-dun, dem gian va de dang m a rong vai cac ung dung thoai SIP SIP la mot giao thuc bao hieu de thiet lap, tri va ket thuc cac phien da phuang tien nhu: thoai IP, hoi nghi va cac ung dung tuang tu khac lien quan den viec truyen thong tin da phuang tiyn Uu diem chinh cua SIP so vai cac giao thuc bao hieu khac la cung cap mot su mem deo No dirge thiet ke nhanh va dan gian Giao thuc SIP cung cap cac chuc n in g sau: - Djnh vi nguai dung thong qua dia chi tuang tu nhu email - Nang luc nguai dung: cac tham so phien co the thuang lugng giua hai phia - Lgi l'ch ngucri dung: Xac dinh dua tren kieu ben bi gpi muon tien hanh truyen thong Giao thuc SIP bao gom hai phan: dai ly tram cua ngudi su dung (user agent) va may chii mang (network server) User agent la mot ling dung ket cuoi he thong ma no bao gom ca user agent client (UAC) khdi tao cuoc gQi va user agent server (UAS) no se tra ldi cuoc goi Kien true cua SIP cho phep thong tin ngang cap sir dung giao thuc may khach/may chii Network servers bao gom bon kieu la: Proxy server (may chu liy quyen) Location server (may chu cuc bo; Redirect Chuang IV: Cdc giao thuc dieu khien 147 server (may chu ch uy ln tidp) va Register server (may chu dang ky) ITU-T khong phai la to chuc tieu chuan nhat dua ke hoach thiet lap ket noi thoai IP va dong goi audio Hem han hat ky mot to chuc quan ly cac chuan muc Internet, IETF cung co nhung yeu cau cua rieng minh doi voi nhung he thong VoIP va dugc goi la "Giao thuc dieu khien phien" - SIP Nhung nguai de xuat SIP cho rang H.323 dang xuat hien bao hieu ATM va ISDN, la khong thich hgp cho dieu khien he thong VoIP noi chung va thoai Internet noi rieng Yeu cau khang dinh la H.323 von di rat phuc tap ho trg cac chuc nang phan 1cm la khong can thiet cho thoai IP do doi hoi chi phi cao va khong hieu qua Vi du H.323 xac djnh phucmg phap khac dc phoi hgp hoat dong giua H.225 va H.245, vai cac ket noi khac nhau, H.245 ngang qua ket noi H.225 va tien hanh phuang phap "ket noi nhanh" cua giao thuc tich hgp Mac du hau het cac kha nang thuc hien chi ho trg cho cac ket noi nhanh, tinh tuang thich H.323 lien quan den yeu cau ho trg cua ca phuang phap Ddng thai, nhung ng uai ung ho SIP cung cho rang H.323 khong co kha nang m d rong yeu cau ddi vdi giao thirc bao hieu cho cdng nghe chang han nhu VoIP, la nhung cdng nghe chac chin se phat triln va hd trg cac dich vu va dac tinh mdi Kinh nghiem sir dung cac giao thirc Internet mail (SMTP) da cung cap rdt nhieu triet ly phat trien SIP, tap trung vao kha nang thich img ciia bao hieu tuang lai 271 ( h u a n g V I: G ia i p h a p n dn g cao ch at lu g n g th o a i co the xac dinh dugc PHB Viec cho phep truy cap vao va khoi DS la cac bo djnh tuyln dugc biet den nhu nhung nut ranh gioi DS, nhung nut "phan loai" luu lugng vao vung dua tren mot dac ti'nh luu lugng cua cac nha quan ly mang Viec luu lugng thich hgp voi mot dac tinh cu the co the co mot gia tri CP nhSt dinh Gia tri chi rang mot PHB nhat dinh se dugc ke tiep theo boi nhirng bo dinh tuyen a viing Gia tri co the co hoac khong co y nghTa tuong tu (hoac bat ky) voi nhung bo dinh tuyen d ngoai viing DS Cau true dich vu phan biet tiiy thuoc vao su hieu biet noi chung ve nhung quy tac PHB va ve viec chiing co lien quan nhu the nao den mot QoS cu the se co dugc tir mang De dat dugc muc tieu nay, DiffServ cho rang luu lugng qua ranh gioi viing DS se phai dugc tinh den nhirng thoa thuan Vi du nhung thoa thuan ve mire dich vu (SLA) va nhirng thoa thuan ve dieu kien luu lugng (TCA) Trong mot so PHB se dugc tieu chuan hoa boi IANA va an toan (chang han nhu PHB "mac dinh" tuong tu luu lugng Internet "thudng le"), nhirng nha cung cap se dugc tu thoai mai viec xac dinh nhung di§m ma ciia ho va PHB de dua nhirng mire dich vu ciia ho 6.4.3 Danh gia cac mo hinh Mang Internet hien nhu chiing ta biet khong dugc th ilt f t > > , ke de truyen cac luong thong tin da phuong tien chat lugng cao va dir lieu thdi gian thuc No la mang phi ket noi, khong co su dam bao ve chat lugng va chia se binh dang tai nguyen mang ddi vdi moi ngudi sir dung Do do, mang Internet hien goi la C o n g nghe I o IP va cu c g iu i p p 272 mang co gang toi da (best effort) va khong the cung cap QoS Hien IETF dang nghien ciru hai co che co the ho tro QoS mang Internet, la mo hinh djch vu tich hop ( Integrated Services) va dich vu khac biet ( Differentiated Services) Ca hai phuong phap da duoc xem xet va danh gia Trong phuong phap theo mo hinh dich vu tich hop kho lam viec tot mang ldn vi co qua nhieu luu lugng tao su dung giao thirc danh trudc tai nguyen (RSVP) va cac phan mang phai luu giCr cac bang dich vu va trang thai ldn Con phuong phap mo hinh dich vu khac biet thich hgp thi mem deo horn vdi mang ldn va cung dugc ua dung hon Cac goi du lieu dugc phan ldp va dugc gan vao mot cac ldp dich vu boi bo dinh tuyen dau vao mang qua co che danh dau goi Cac bo dinh tuyen loi dem gian chi phai chuyen cac goi theo ldp djch vu ciia chiing Bang So sanh DiffServ vd IntServ IntServ DiffServ Ban c h it cua viec phan chia dich vu Phan chia theo tung luong Phan chia tung lap Ca sa de phan loai luu luong Mot so truang tieu de Truong DS Giao thuc bao hieu C ln thiet phai co (RSVP) Khong yeu cau Pham vi dich vu Tren toan chang tu d lu cuoi Tren tung chang phan chia den d lu cu6i theo Kha nang cung c lp Bi giai han bai so luang luong Bi gioi han boi so luong lap Quan ly mang Tuang tu rihu mang chuyen mach kenh Tuong tu nhu1 mang IP hi^n 273 Thudt ngu vd viet kit THUAT NGU-VA VIET TAT ARP Addresss Resolution Protocol Giao thuc phan giai dia chi AS Autonomous System He th6ng to tri ATM Asynchronous Transfer Mode Phuong thuc truyen tai khong dong bo BA Behavior Aggregate Tap hop hoat dong xu ly BGP Border Gateway Protocol Giao thuc dinh tu y in cong m iin CELP Code Excited Linear Prediction Du bao tuyen tinh kich thich ma COPS Common Open Policy Service Dich vu chinh sach mo chung CIDR Classless InterDomain Routing Dinh tuyen lien vung khong phan lop CSRC Contributing Source Identifier Bo nhan dang tap hop nguon CRC Cyclic Redundancy Check Kiem tra vong du CTI Computer Telephony Integration Tich hop dien thoai may tinh DHCP Dynamic Host Configuration Protocol Giao thuc cau hinh tram dong DLCI Data Link Connection Identifier Nhan dang ket noi lop lien k it du lieu DNS Domain Name System He thong ten vung DS Differentiated Service Dich vu khac biet EGP Edge Gateway Protocol Giao thuc dinh tuyen cong bien ETSI European Telecommunication Standard Institute Vien Tieu chuan V iin thong chau Au FDDI Fiber Distributed Data Interface Giao dien du lieu phan bo quang 274 Cong nghe VoIP va cuc gidi phap FTP File Transfer Protocol Giao thirc truyen tep HDLC High-level Data Link Control D iiu khien hen ket dir lieu mire cao HTTP Hyper Text Transfer Protocol Giao thirc truyen d i/ lieu sieu v3n ban IANA Internet Assigned Numbers Authority Ca quan chi dinh so Internet ICMP Internet Control Message Protocol Giao thi>c ban tin dieu khien Internet IETF International Engineering Task Force To chirc tieu chuan ky thuat quoc te cho Internet IEEE Institute of Electrical and Electronic Engineers Vien ky thuat dien va dien tir IGMP Internet Group Management Protocol Giao thirc quan ly nhom lien mgng IGP Interior Gateway Protocol Giao thirc cong mang nqi b