i i G I A I PHAP
• I P T V NGANG HANG
1. G i a i THIEU CHUNG
Trong md hlrta cUent/server thi mdt may khach (cUent) se ket ndi vdi mdt may chu thdng qua mdt giao thuc rtaat dmh, nen mgi xu ly se nam tren server va do dd se trarta eho cUents nhimg tinh toan nang ne. Tuy rtaien, md hlrta cUent/server bdc Id mot rtaugc diem quan trgng: khi sd lugng cUents tang den mdt mue do nao dd thi nhu cau ve tai va bang thdng tang len dan den viec may ehu khdng cd kha nang cung cap dich vu cho cae may khach them vao. De glal quyet van de tren, cdng nghe mang ngang hang P2P (peer to peer technology) dugc tin tudng se la Idi giai eho eac van de tren.
Dieu Idiieii cung cap npi dung
Nauoii npi duns
Dieu l^hien cung cap dicli"\'u
EPG
C'liiis Clip iioi (lung va dich \ i i
TS. Le Nhat Thang, Du'dng Ha Thu
2. CAU TRUC HE THONG I P T V P2P Hlrta 1 mtah hga cau tnic he thdng IPTV P2P, gdm 3 phan chinh: cung cap ndi dung va dich vu, dieu khien phan phdi trayen thdng P2P va mang thue bao. Ndi dung va he thdng eung cap dich vu bao gdm 4 bd phan chQc nang chirta:
+ Ngudn ndi dung: ndi dung IPTV, ddng trayen thdng dugc luu trir, dugc dinh dang, ma hda va trayen di tdi dich vu trayen thdng xa hon.
+ Dieu khien cung cap ndi dung: quan ly thdng tta ndi dung IPTV, cae tham sd ddng... va chuyen thdng tta tdi EPG.
May chu huyen thong He thons dau cuoi
May chii huyen tliong
He tiions dau cuoi
He thons dau cuoi
May chii hniyen thong He thons dau cuoi
Dien kliien phan phoi truyen thong P2P Mang thue bao
Hinh 1: Cau true he thong IPTV P2P
TAP CHI CNTT&TT KY 1 ( 8 . 2 0 0 9 ) 1 7
CONG NGHE V I E N THONG
Dieu khien cung cap dich vu: san xuat dich vu IPTV theo ehinh sach dugc dua ra bdi eac rtaa cung cap dich vu IPTV hoae tii rtaitag yeu eau eua eac thue bao.
EPG: su tuong tae glQa eac thue bao IPTV va dieu khien cung cap ndi dung de xu ly cac yeu eau va hien thi ndi dung thdng tta
He thdng dieu khien phan phdi trayen thdng bao gdm: dleh vu trayen thdng va mien quan ly dich vu trayen thdng ma chap itaan cdng nghe P2P de thue hien chQc nang phan phdi ndi dung IPTV nhu: ndi dung luu trir, phan phdi, dirta tuyen, bao dudng.
He thdng mang thue bao bao gdm: he thdng dau cudi (vi du nhu PC cUent, STB) ma cd ndi dung IPTV tii he thdng dieu khien phan phdi tmyen thdng P2P hoae tii thue bao.
3. MOT SO MO H I N H HE THONG IPTV NGANG HANG
3.1. He thong ngang hang thuan tuy (Pure Peer-to-peer Systems)
Trong he thdng nay, tat ca cac may deu dugc ndi vdi nhau. Mdi may trong he thdng dugc ggi la mdt nut mang (peer), chimg cd vai trd rtau rtaau. Trong toan bd he thdng, khdng cd mdt may nao giu vai trd dieu khien. Hoat ddng cua he thdng dua tren cae trao ddi true tiep giua cac peer nhd nhimg Uen ket dugc thiet lap giQa cac peer tuong Qng.
Uu diem eua he thdng ngang hang thuan tiiy la
Peer
kha nang ma rdng dugc, bat ky nQt nao cung cd the tham gia vao mang va sau dd cd the trayen du Ueu vdi cac nut khae. Tuy rihien, he thdng nay lai bdc Id rtaugc diem: trong mdt he thdng, cd qua rihieu Uen ket dugc thiet lap, mdi mdt peer se ndi vdi (N-1) peer edn lai (vdi N la sd may trong mang). Trong tradng hgp tai ciing mdt thdi diem, mdt peer A nao dd nhan dugc cae yeu eau eua tat ea (N-1) peer cdn lai, hien tugng qua tai se xay ra, dieu nay edn the lam cho mang gap sir ed.
3.2. He thong ngang hang lai (Hybrid Peer- to-peer System)
Trong he thdng nay, moi may deu dugc noi vdi tat ea cac may khae tren mang, each ndi nay mang dae diem cua he thdng ngang hang thuan tiiy. Tuy nhien, van ed mdt may ddng vai trd Server trung tam. Server nay dieu khien hoat ddng cua mang rtau mdt phan tii cd the kiem soat toan bg cae may khae, dam bao ttah chat che cua thdng tm tren mang, day la dac diem eua he thdng tap trang. Tat ca cac ludng dQ Ueu thdng thudng deu dugc trayen true tiep giQa cae peer, chi eac ludng thdng tta dieu khien mdi dugc trayen qua Server trung tam.
Nhimg rtaugc diem cua viec quan ly dieu khien tap trung van tdn tai trong he thdng nay. Neu Server trung tam gap loi, he thdng se mat kha nang tac ddng tdi nhQng thay doi trong ludng du Ueu. Tuy nhien, rtaung Qng dung dang cd se khdng chiu arta hudng eua loi server trung tam vl ludng dQ Ueu giua eac peer van tiep tuc dugc trayen ma khdng quan
Hinh 2: He thong ngang hang thuan tuy
Hlnh 3: He thong ngang hang lal
1 8 I TAP CHI CNTT&TT KY 1 ( 8 . 2 0 0 9 )
tam tdi Ueu Server trung tam cd dang lam viec hay khdng. Viee dinh tuyen du Ueu ngang hang (peer to peer) eho phep he thdng lal dua ra kha nang md rdng tdt hon so vdi he thdng tap trung, tuy nhien, he thdng lai van ban che trong cac van de ve tinh ma rdng ddi vdi thdng tta dieu khien qua cac nQt.
Trong khi he thdng lal dang duac su dung ed hieu qua cho mdt sd Qng dung, phuang phap nay vin bi gidi ban trong pham vl giai quyet rtaQng van de d quy md rtad.
3 . 3 . He t h o n g sieu ngang hang ( S u p e r - p e e r A r c h i t e c t u r e )
3.3.1. Khai niem
Mdi loai he thdng ngang hang cd mQc do tap trang khac rtaau. Doi vdi he thdng ngang hang thuan tiiy, tat ca eac peer deu cd vai trd va trach nhiem rtau rtaau. Trong he thdng ngang hang lai, qua trlrta tim kiem lal dugc thue hien tai ttaimg thu muc tap trang. Khac vdi rtaitag he thdng ndi tren, mang sieu ngang hang lal ed cau tnic tmng gian.
Moi super-peer (nut sieu ngang hang) la mdt nQt mang boat ddng gidng rtau Sever ddi vdi mdt tap con cae CUent. Hlrta 4 mtah hga md hlnh eua mdt he thdng sieu ngang hang.
Trong he thdng nay, moi Super-peer cd vai trd rtau mdt Server, quan 1;^ cae CUent thude rtadm cnia nd. Chang han, trong hlrta Super-peer A giu vai trd
Super PeerB
Client
Server va quan ly eac CUent AI, A2, A3. Tuang tir rtau the ddi vdi cac Super-peer B va C.
3.3.2. Mo ta hoat dpng
Htah S md ta hoat ddng cua he thdng sieu ngang hang qua viec tUn kiem mdt file. Viec tim kiem dien ra rtau sau:
- Nut mang A can tUn kiem file 15, A gui tray van tdi Server quan ly nd la Hub 1
- Hub 1 gui cae tray van tdi cac Hub 2 va Hub 3 - Hub 2, Hub 3 chuyen tiep tray van nay tdi cae cUent do mlnh quan l^
- Tai Hub 3, sau khi gid tray van di, ed cac cUent C va B gui dap Qng trd lal la cd file 15
- Ndi dung tra Idi tmy van dugc gui nguge lal, tii CUent C, CUent B ve tdi Hub 3, qua Hub 1 va tdi noi yeu cau la Client A. Qua trlnh tim kiem ket thQc.
Nhu vay, vdi kien tnie sieu ngang hang, rat khd xay ra tlrta trang mang gap loi nghiem trgng, tuc la loi khi tat ca cae server deu khdng boat ddng dugc do qua tai. Sa dl cd dugc dieu nay la do mang sieu ngang hang dugc to chuc theo timg nhdm, ggi la eac rtadm sieu ngang hang. Moi rtadm nay deu cd mdt Server quan ly boat ddng cua cae CUent trong vQng eua nd. Tuy nhien, vol mang ed quy md Idn, trong dd mdi Server quan ly rihieu CUent trong mdt rtadm sieu ngang hang, hien tugng qua tai van cd the xay
Super Peer C Hlnh 4: He thong sieu ngang hang
o
Hlnh 5: Hoat dpng ciJa mang sieu ngang hang
MjdcC Re 15
TAP CHI CNTT&TT KY 1 ( 8 . 2 0 0 9 ) 1 9
CONG NGHE V I E N THONG
ra. De khac phue dieu nay, ngudi ta dua ra mdt khai niem mdi, dd la khai niem he thdng sieu ngang hang cd du phdng (Super-peer Redundancy).
3.4. He thong sieu ngang hang c6 du* phong ( S u p e r - p e e r Redundancy)
Super PeerB
Super Pc^rC
Hinh 6: Mang sieu ngang hang co duphijng cap 2
Mdt he thdng sieu ngang hang ed du phdng cap k neu nhu ed k nut mang cQng chia se tai tai diem sieu ngang hang. Hinh 6 md ta mdt he thdng mang sieu ngang hang cd du phdng cap 2, trong mang nay, tai mdi super-peer, ed 2 nQt thue hien viec dieu harta tai cua mang, do dO, ggi la mang sieu ngang hang cd du phdng cap 2. Day la mdt eai tien eua mang sieu ngang hang thdng thudng, kien trQc mang theo kieu sieu ngang hang cd du phdng cap k dap Qng dieu kien yeu
cau phat trien eua he thdng mang ed quy md Idn.
Uu diem eua he thdng la cd su can bang tai tai cac super- peer do dd
mang cd do tta cay eao hon so vdi md htah sieu ngang hang thdng thudng. cac cUent se giii tray van tdi mdt trong k nQt thude super-peer, dieu nay da giai quyet dugc van de Idl tram trpng eua mang sieu ngang hang.
4. KET LUAN
He thdng IPTV eo ban su dung md hlrta cUent/
server (C/S) de cung cap dich vu IPTV, tuy rtaien bi gidi han cua dich vu tmyen thdng rtau li gidi han bang thdng, dung lugng luu trir, nang lue xit ly...
va ehi cd kha nang phue vu tdt eho mdt sd lugng rtaat dinh thue bao. Cho nen. Men nay giai phap P2P dang dugc xem xet rtau la mdt giai phap tdt de xay dung mang vdi rtaitag uu the rieng cua nd qua viec glQp ngudi su dung chia se dich vu ngang hang de dang va thuan lgi hon trong viec md rdng thue bao. Tharta cdng Idn cua cac he thdng P2P cho mue dich chia se du Ueu ma ra eon dudng dan tdi mdt Qng dung hoan hao tren tatemet la video true tuyen P2P. Mae du nd giai quyet van de ve quy md, rtaung cac van de thu nghiem ma cdng nghe P2P gap phai la thdi gian bat dau kha dai va su khdng on dirta ed the gay ra rtaimg arta huong Idn tdi eac khach hang tiem nang. Hon nua, cae giai phap ky thuat va md htah kinh doanh cho viec quan ly IPTV P2P van cdn dang dugc tiep tue nghien cim. Nhimg ed gang Idn vin dang dugc thuc hien nham giai quyet cho nhimg yeu cau ddi vdi trayen htah bang thdng rdng chat lugng eao ve ma rdng quy md, gia ca hgp ly va ndi dung phu hgp...
Tai lieu t h a m l<hao
[1]. YANG XIAO, XIAOJIANG DU, JINGYUAN ZHANG, FEI HU, and GUIZANI, S. , Intemet Protocol Television (IPTV): The Killer Application for the Next-Generation Intemet, IEEE Communications Magazine, Vol. 4 5 , No. 1 1 , p. 126-134, November 2007.
[2]. ALEXANDRO SENTINELLI, GUSTAVO MARFIA, MARIO GERiA, and LEONARD KLEINROCK, Will IPTV Ride the Peer-to- Peer Stream?, IEEE Communications Magazine, Vol. 4 5 , No. 6, p.
8 6 - 9 2 , June 2007.
[3]. GERARD O'DRISCOLL, Next Generation IPTV Services and Technologies, A John Wiley & Sons INC, 2007.
2 0 I TAP CHI CNTT&TT KY 1 (8.2009)
•
' ^ afi^>-3: iJO^.-t'^a.sn,V . JohnLaHeiet Mors Now showing: Pojwlar picks 1501 N^t.-r*..-.'"-'*^-
. :}^
^ ^
^ P ^
^4 ^'f rf™
The Corpi^u aridE J.mm/ Carter.,
IHEiiJCREDlBLEi fi iBfe .-^ . • Bii mm
CHIEN LUOC
Ap \\ic dang dat len vai cac nha cung cap djch vu vien thong l<hi trien lihai djch vu video theo nhieu hinh thirc phai s6m hdn, nhanh hdn va tot hdn cac nha canh tranh vdi ho. Bai viet nay giup cac nha cung cap dich vu CO them thong tin cho viec chuan bj tot nhat ha tang cd sd ciia minh va lam the nao de bien Udc md thanh Idi nhuan.
CAC MANG V I D E O : CAU TRUC CQ BAN Cung cap video, mang ndi dung, IPTV, trd choi tay ba... - day mdi chi la mdt sd rat it thuat ngQ thudng hay dimg ngay nay de ndi ve video qua cac mang du Ueu bang rdng. Y ruem cua cac mang video nay dang ngay cang la mdt thach thQc, va eimg gidng rtau hau het eac thach thuc mang, nd dang bi tac ddng bdi cac yeu td cdng nghe, kinh doanh va luat phap.
Video tao ra ba thach thQc chirta cho cac rtaa quy
hoach va cac rtaa khai thac mang. Thu rtaat, video rtau mdt img dung "ddi" bang thdng. Mdt tep video la rat Idn so vdi hau het cac loai thdng tta bat ky nao khac dugc van chuyen qua mdt mang. ThQ hai, ddng video mdt mang thdi gian thuc thich hgp. Hau bet cac Qng dung bang rdng ed dung sai cao vdi cae bien ddng eua do tre va su mat mat gdi, nhung video thudng bi hdng hoan toan chi vl mdt bien ddi rat rtad trong dd tre, va bat ky mdt su mat gdi nao eung cd the pha hoai trai nghiem xem chuong trirta. Cudi cQng, video dugc ngudi dimg nhan thQc la mdt trai nghiem Uen tire, thdi gian dai, va neu mdt phan dang ke nao dd tra nen xau di thi tat yeu se la nhung dieu than phien va rtaimg yeu cau tra lai tien! Khdng gidng rtau mdt cudc ggi bi mat, hay mdt ket ndi xau trong dam thoai, trong dd ngudi dimg ed the khac phue chi don gian bang each ggi lal, ket ndi video la mdt cam ket cua ca hai ben, va bat ky mdt hdng hdc nao eitag chic chan tao ra phan Qng tieu cue cua khach hang.
TAP CHi CNTT&TT KY 1 (8.2009) 2 1
CONG NGHE VIEN THONG
Nhimg yeu td nay arta hudng tdi tat ca cac mang video, rtaimg mQc dd arta hudng phu thude vao md hUta video. Cd ba md hlnh dich vu video bang rdng.
cac md Itirta video bang rdng md phdng hoat ddng eua mdt he thdng cap TV, cung cap eho khach hang xem rihieu kerta. Cae md hlnh video theo yeu cau (VoD) cho phdp khach hang chay video theo thdi gian thuc, rtaung video va thdi gian xem do khach hang chgn lira. Md hlrta "luu lai de xem" (md hlnh download) cho phdp khach hang tai video sang mdt dia tai eho de xem.
Tat ca cac mang video deu bat dau eimg vdi nhu eau eua khach hang, eho nen budc dau tien de bleu thiet ke mang video la biet cac mang video dimg lai a dau - ngudn ndi dung se la gl. Thuc te la viec trQ ndi dung video trong moi vimg thatta phd Idn cd the dugc tien harta eho cac md htah phat quang ba va tao ddng video theo yeu eau. Viee tru tai chd se tranh dugc rtaimg thay doi chat lugng ma viec chuyen tai qua tatemet mang lai, va hau bet cac chuong triita video du hap dan de dem lai lgi nhuan ehae chan se dugc tieu thu day du trong mdt vung thatta phd de mirta chimg eho gia ea eua viee luu tru tai chd. Dieu nay cd nghia la hau het cac mang video se la cae mang thatta phd. TQ cac ngudn ndi dung, cac mang video phai phan phat video di khip noi, nhung khdng phai tdi "cac khach hang" ma la tdi "cac cdng khach hang". Thuc te, mang video la mdt tap hgp cac ket ndi hlrta sao giQa cac ngudn ndi dung va cac diem cong khach hang nay. Dieu nay ed nghla la, tat ca cac mang video deu ed the dugc nhta rtaan rtau cac cau tnie hai-vimg: phan phat true chirta tdi cac diem cdng va sau dd phan phat tdi eac khach hang tren mang tray rtaap. Hai chu de nay phai dugc xem xet mdt each tach biet.
Trong mdt sd tradng hgp cae rtaa khai thac ed the lam ddi tac vdi cac rtaa cung cap ve tinh quang ba true tiep (DBS - Duect Broadcast SateUite) de ed cac tai Ueu phat quang ba, ma tai Ueu nay khdng dugc tai tren mang video. Nha khai thac se phat
quang ba di dau, giai phap nao dugc su dung de phan phat kerta quang ba tdi khach hang, tiiy thuoc vao phuong tien dugc su dung cho mang tray rtaap khach hang.
Noi khach hang cd cac phuang tien dung lugng rat eao (cap CATV, POOFTTH...), thi nha khai thac cd the su dung de cap eac kerta phat quang ba, chi dan gian la phat quang ba chat Ueu kerta theo mdt khudn dang cap tieu ehuan. Trong tradng hgp nay, chat Ueu phat quang ba tren thue te khdng he do mang video van chuyen. Noi nao viec di day cap ddng dugc su dung (DSL), dung lugng khdng du de tai ngay ca mdt sd lugng tdi thieu cac kerta quang ba theo each ddng gdi ca ban dien hinh, va mdt hlrta thQc arta xa kerta phai dugc su dung. Vdi glal phap nay, ket ndi tray rtaap cua khach hang dugc chia thanh cac "khe" ma cac kerta cd the dugc arta xa vao dd theo yeu eau. Dung lugng eua ket ndi tray rtaap se quyet dinh bao nhieu khe cd the dugc phan bo (khoang 4 Mblt/s eho mdt khe cd do phan giai tieu chuan va khoang 8,S Mbit/s cho do phan giai cao). Khi dieu chirta, khach hang ed the chgn mdt kerta ma khi dd thiet bl eua tdng dai phue vu se arta xa vao mdt khe kerta.
Viec anh xa kenh tao ra mdt tap hgp mdi dang ke cae yeu eau trong mang video, bdi vl eac kenh phat quang ba phai dugc phan bd tdi eac diem cdng theo khudn dang dQ Ueu va sau dd dugc ddng gdi tharta cac ket ndi DSL thich hgp. Hau het cae he thdng hien tai dang su dung giao thQc IP multicast (phat da phuong IP) va giao thQc dang ky (IGMP) cho mue dich nay. Rat can den viec xu ly dac biet de bao dam rang man arta eua khach hang khdng hi "pixelate" khi thay doi eac kerta, mdt van de phd bien neu xuat hien chuyen mach giQa eac "khung chu chdt" ciia video n6n.
VoD cd cae yeu cau mang dd thi (metro) hoan toAn khac. Mdt cdng ddng dien htah gdm 8.000 ngudi dimg tai mdt diem cong ed the cd 300 kerta quang
2 2 I TAP CHI CNTT&TT KY 1 (8.2009)
ba, tao ra mdt tai khoang 1,2 Gblt/s theo do phan giai tieu ehuan neu video gdi-dQ Ueu dugc su dirng.
Neu oQng mdt cdng ddng dd xem ludng VoD trong mdt gid, thi tai du lieu ed the Idn gap nam den tam lan, tuy thude vao eac thdi gian tning lap cua nguoi dQng rtau the nao. Toan bd tai bien ddi nay phai dugc van chuyen giua cac diem cdng va eac server ndi dung. Dieu nay ed nghia la eac mang video dugc du kien eung cap VoD can dugc thiet ke eho cae tai VoD. Ddi vdi cac nha khai thac, video theo yeu cau chic chan phai la mdt ung dung cap sgi quang dudng true va DWDM. Phan Idn ngudi dung mong dgi video quang ba phai theo thdi gian thue, nhung VoD ed the dugc dem de vugt qua cae bien sd mang rtau dd trd va do tragi trd. Tuy nhien, viee mat gdi thi khd cd the dugc chap rtaan trong cae mang video, eho nen noi nao ed kha nang dem VoD thi cdng viec phd bien la phai ddi dd tre lay mat gdi trong thiet ke. Cdn mdt dieu phd bien nQa la cung cap du thua dung lugng mang de tranh tac nghen ngay tii dau.
Cae mang video la cae mang phan bd chQ khdng phai la eac mang trayen thdng. Phan Idn dugc thiet ke de trarta cho luu lugng khach hang khdi vugt qua tai nguyen video, va do vay, cac ket ndi ddng hang khdng rtaimg la khdng can thiet ma cdn dugc ngan chan mdt each tich cue. Dieu nay cd nghia la cau tnic cua cae mang thiet ke eho video se phai la hlnh sao ChQ khdng phai mang ludi va du phdng se dugc
cung cap theo cae eo che don gian gidng rtau keo den nhieu rtaa (multi-homtag).
CAI DAT V I D E O THEO YEU CAU
Video theo yeu eau cd le la thach thuc Idn nhat eua tat ca cac Qng dung mang. Viec tao ludng video theo thdi gian thuc lam nay sinh eac thach thuc Idn trong viee khdng ehe sir mat gdi, va hien tugng tr6 /jitter, cdn video theo yeu eau tao ra rtaimg chuyen bien rat Idn trong cac yeu eau bang thdng ma nd khdng ehi tac ddng den chat lugng khach hang video ma cdn tac ddng den ca ttah nang cua cac Qng dung mang thanh phd mdt each tong the. Qua trlrta can dugc tien hanh theo ba budc:
1. Suy xet md htah dich vu, cd nghla la ban chat cua ndi dung, khudn dang video, va cac thiet bi ma video dugc phan phat tdi.
2. Suy x§t md hlnh phan phat, ed nghia la cae dac tinh cua mang tmy rtaap khach hang va mang ket ndi dudng true.
3. Suy xdt md hlnh quan ly va trg giup, ed nghla la each thQc ma theo dd video se dugc dat hang, ho trg va tlrta cudc.
Cae md hlrta dich vu video theo yeu cau cd the dugc dae trung theo loai thiet hi ma tren dd video se dugc xem, va ddi khi cdn theo mQc do ma video cd the dugc dem khi giao hang trade khi xem. Cac tuy chgn d day la:
1. Video man hlnh nhd, dugc thiet ke de xem tren may dien thoai di ddng, cac ban dieu khien game, hoae thiet bi xach tay khac. Ndi chung, dang video nay ddi hoi dd phan giai thap hon ngay ca ddi vdi san pham cd do phan giai Ueu chuan, va thudng khdng su dung dp phan giai eao do itaimg han che khi xem. Do vay, chac chan la Ueu thu it bang thdng hon. Ngoai ra, ngudi dimg chac chan chap rtaan rtaimg true trac khi xem vdi loai san pham nay. Tuy nhien, d day viec dem la khdng the ed.
2. Video may tlrta, dugc phan phat tdi may tlrta
TAP CHI CNTT&TT KY 1 (8.2009) 2 3
CONG NGHE VIEN THONG
xach tay hay may tinh de ban, hoae tdi mdt may tlrta "media center". Dang video nay ddi hdi do phan giai eao hon - thue te la eao rtau xem tmyen htah - nhung he thdng may tinh thudng cd the dem dl thich Qng vdi rtaQng bien ddi trong hieu nang mang. NhQng khach hang eua video may tinh tham chi cd the mudn luu tru tu Ueu tai chd de xem nhieu Ian.
3. Xem tmyen hlrta, noi video dugc phan phat tdi mdt "hop dat tren nde" va dugc dan den mdt man anh TV de xem. cac khach hang eua loai video nay cd it chap rtaan cae van de video nhat, va dang video nay yeu cau chat lugng cao rtaat ed the cd.
Ngoai ra, thudng la khdng the dem dugc tu Ueu nay, va do vay nhung bien ddi trong hieu nang mang chac chan tao ra su keu ca eua khach hang.
Mang phan phat dugc chia tharta hai phan, phan ket ndi bang rdng khach hang thuc su va phan de phan phat video tdi diem tray rtaap hay cdng bang rdng cua khach hang. Ket ndi bang rdng tdi khach hang thiet lap mdt gidi ban bang thdng kha dung eho VoD. Khdng rtaQng bang thdng phai du de xu 1^ video (4-5 Mbit/s cho video do phan giai tieu chuan, het cd man htah va 8-10 Mbit/s cho phan giai cao), ma nd cdn phai du de bao dam rang viee tac nghen tray rtaap khdng lam nay sinh van de ve do tre va mat gdi. Hau het cac dich vu VoD tra-tien va chac chan la tat ea eac dich vu VoD tra tien-mdl- lan-xem deu se can den mdt hlrta thQc quan ly bang thdng nao dd de bao dam rang nhieu ngudi dung video hoae cac Qng dung bang rdng khac khdng arta hudng gl den bleu nang.
Video theo yeu eau Ueu thu mdt sd lugng bang thdng nao dd va tao ra mdt sd bien ddng tiem tang trong tai eua mang, cho nen hau het cac nha khai thac se thiet ke cac mang VoD tach rdi khdi cac Qng dung khae. Do each su dung VoD chiu aita hudng bdi cae xu hudng thi tradng dai chQng (phat hanh mdt bd phim mdi, mdt dgt TV dac biet, mdt budi hoa
nhac v.v...), eho nen can ho trg kha nang tai cau htah bang thdng rtaim dieu Uet rtaQng su tang len ddt bien Uong su dung hoae tao ddng bd khi xem.
Dieu nay dae biet dQng d noi eac dudng dan VoD hd trg eac sir kien tai cho.
Md hlrta quan ly va hd Ua dQng cho video theo yeu cau rat ed the la quan trgng bae rtaat va de bi lang quen rtaat ttong sd tat ca cac van de trong VoD. cac rtaa khai thac da duong dau vdi cac chi phi cham sdc khach hang gia tang deu dan, va bay gid chi mdt rac rdi rtad duy rtaat cung cd the phai tra gia nhieu den mQc mat hang nam trdi xay dung mdi quan he huu ich vdi khach hang mdi khae phuc dugc. Tren thuc te, noi nao VoD dugc eung cap bdi mdt ben thu ba hoae bdi mdt to chuc rieng biet (dae biet la neu td chQc dd tach biet ve mat cau tnic vl rtaimg ly do the che), thi dieu quan trgng la trach nhiem cham sdc khach hang phai dugc xac lap rd rang, khdng chi giua cac td chQc Uen quan eua nha cung cap ma edn vdi nen tang khach hang.
Cham sdc khach hang trong VoD ed the dugc phan loai rtau sau:
1. Ngan chan trade tii mang, noi viec giam sat mang va khic phuc su cd dugc van hanh de bao dam rang cac hdng hdc hoae tae nghen khdng arta hudng den dich vu. Day la mdt loai rat quan trgng vl viec ngan chan rtaimg than phien cua khach hang thudng re hon nhieu so vol viec ddi phd vdi hg.
2. Ngan chan trade tii dich vu, trong dd viec hieu
L I ^ . *^
" "TSSKT'C^
•vqa
1 i->«^-JKjl
2 4 TAP CHI CNTT&TT KY 1 (8.2009)
biet tudng tan mdt tlrta ttang khach hang nao dd cQa dich vu VoD dat dugc tQ ttang thiet bi tai gia khach hang, server ndi dung hoae tii mang. Loai cham sdc nay cd the dugc dat muc Ueu, rtau cham sdc muc mang, vao viec ngan chan rtaimg van de bang viec du doan tac nghen v.v..., hoae nd eimg cd the rtaam vao viec md ra mdt cudc ddi thoai cua khach hang qua kerta xem htah rtaim ngan cam mdt cudc ggi khach hang nao dd.
3. Phan Qng, ttong dd muc dich la ddi phd lai mdt van de dang dugc khach hang khieu nai. Cham sdc phan img se cd hai muc Ueu ehinh: thuyet phuc khach hang tim kiem su hd trg true tuyen thay vl ddi hoi phai kdo theo mdt dai dien dich vu khach hang, va giam bdt thdi gian giai quyet van de bang viec chuan bi eho ddi ngu hd trg khach hang cd du thdng tta can thiet de rtaarta chdng chan doan van de va cung cap each dieu tri cho khach hang.
Video theo yeu eau la su thach thuc Idn rtaat ttong tat ca cac ung dung mang do cac yeu cau bang thdng va cac yeu cau QoS cua nd. Bat chap viec thiet ke can than va thuc ti6n lap dat dugc quan tam thuc su, lgi rtauan tren cac dich vu nay eimg vdi uy tta cua rtaa cung cap dich vu cd the itaarta chdng bi suy giam.
MPLS D I E M - D A D I E M
Vdi yeu cau eao ve bang thdng va dung sai thap ddi vdi do tragi, phan bd video theo thdi gian thue da thuc day sir phat trien cua Chuyen mach Nhan Da giao thuc (MPLS) diem-ndl-da diem, rtaung cdng nghe nay eitag ed the ed lgi eho eac loai du Ueu khac ddi hdi su chuyen tai tin cay va cd kha nang md rdng quy md cao. MPLS diem-da diem ket hgp hieu qua cae giao thuc da diem rtau PM va DVMRP vdi cac kha nang ve do tta cay va chat lugng dich vu (QoS) eua MPLS.
Video thudng dugc phan bd tii mdt ngudn duy rtaat tdi mdt sd lugng rat Idn cac dich. Chang ban.
viec phat quang ba mdt su kien the thao ed the yeu eau eung mdt ludng dQ Ueu duac gm di eimg mdt IQc tdi cac head-end cua he thdng tmyen htah cap dimg cho mgi he thdng cap. Ludng dQ Ueu cd the bao gdm bang thdng len tdi 300 Mbit/s va ddi hdi phan phat ma khdng bi mat du Ueu va khdng cd do tragt Oitter). Trong qua khQ, ATM hoae SONET da timg dugc su dung de dap img eac yeu cau nay. cac mang IP dem lal rtaitag lgi the ve ttah Urta boat va chi phi tuong ddi thap so vdi cac cdng nghe eu nay, rtaung khdng the thoa man cae yeu cau phan bd video trade khi phat trien MPLS diem-da diem.
MPLS eai thien dugc bleu qua cua chuyen tiep gdi IP tmyen thdng. Vdi MPLS, mdi ludng du Ueu dugc gan mdt dudng chuyen mach rtaan (LSP - Label Switched Path) rieng biet. Mdt rtaan nhan dang mdi gdi cau tharta ludng video. Cimg vdi dudng chuyen mach nay, cac bd dinh tuyen su dung nhan de rtaan dang LSP chirta xac va gui chuyen tiep gdi theo nd.
Cac rtaan MPLS deu rat ngan va ed the dugc su dung de ghi chi sd vao mdt bang cua eac LSP mdt each hieu qua hon nhieu so vdi viec su dung mdt dia chi IP ed day du dich den vdi mdt mat na mang con de ttah toan chang ke sau.
Ky thuat luu lugng MPLS cho phdp rtaa quan ly mang an dirta cac dac trung QoS cho mdt LSP. Thi du rtau, mdt LSP cho video cd the dugc tao ra bang viee ehi ra rtaimg Unk va router dap Qng dugc cac yeu cau ve bang thdng kha dung va dd tr§ ed the dugc du bao trade. Mdt dudng du phdng cd the dugc tao ra ddng thdi rtau LSP sao cho luu lugng cd the dugc tai dtah tuyen rtaarta chdng neu cd mdt Unk bi dot hoae bd dirta tuyen bi hdng.
Viec ket hgp hieu qua eiia cac giao thue phat da phuang vdi cac tien ich thiet ke luu lugng trong MPLS hua hen eho phep trien khai cac Qng dung ma tmdc day cac mang IP khdng hd tra dugc. Cac tieu chuan MPLS diem-da die'm sdp dugc hoan tharta bdi Nhdm Cdng tac MPLS ttong IETF.
(Con tiip)
TAP CHI CN ITT&TT KY 1 (8.2009) | 2 5 j
