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HC VIN CNG NGH BU CHNH VIN THNG
---------------------------------------------------
BI GING:
TRUYN THNG A PHNG TIN
(Dng cho cc sinh vin ngnh in-in t)
BIN SON: TS. NGUYN QU S
H NI, 12/2009
ii
Mc lc
THUT NG VA CH VIT TT ............................................................................................ v
LI M U ................................................................................................................................ 1
CHNG I TRUYN THNG A PHNG TIN .............................................................. 3
1.1. Gii thiu............................................................................................................................... 3
1.2. S pht trin v hi t ......................................................................................................... 4
1.2.1. S hi t ca vin thng v tin hc ......................................................................... 5 1.2.2. Kin trc ca cc dch v ni mng ........................................................................ 6 1.2.3. Lin kt .................................................................................................................... 7 1.2.4. S tnh ton c th truyn ti c .......................................................................... 8
1.3. Khung c s cng ngh ........................................................................................................ 8
1.3.1. Cc cng ngh a phng tin ................................................................................ 9 1.3.2. Kt ni mang a phng tin ................................................................................ 13 1.3.3. Hi ngh a phng tin ........................................................................................ 14 1.3.4. Multicasting ........................................................................................................... 16 1.3.5. Cc cng ngh cho ni dung in t (e-Content) .................................................. 17
1.4. Khung c s tiu chun hoa .............................................................................................. 19
1.4.1. Cc tiu chun m thanh/hinh nh s v cng nghip a phng tin .................. 20 1.4.2. Cc tiu chun ca ITU-T cho cac h thng truyn thng nghe nhin . .................. 21 1.4.3. Cc tiu chun ma ha hinh nh ............................................................................ 22 1.4.4. Cc tiu chun ma ha m thanh ........................................................................... 24 1.4.5. Cc tiu chun ng b v ghep a phng tin ................................................... 24 1.4.6. Cc tiu chun MPEG trong truyn thng a phng tin ................................... 25
1.5. Kt lun ............................................................................................................................... 29
CHNG II KHUNG C S TIU CHUN HOA MULTIMEDIA ............................ 30
2.1. Gii thiu............................................................................................................................. 30
2.2. Cc hot ng tiu chun ha. .......................................................................................... 31
2.2.1. Nhng l do tim kim mt tiu chun. .............................................................. 32 2.2.2. Nhng giao din c tiu chun ha. .................................................................. 32 2.2.3. Thi gian tiu chun ha................................................................................... 34 2.2.4. S chun ha s din ra nh th no ?................................................................... 35 2.2.5. Ai s qun l cc hot ng chun ha? ................................................................ 36 2.2.6. S chun ha c s dng nhng ni no ? ........................................................ 36 2.2.7. Chu trinh cng ngh v sn phm hoc dch v s c chun ha. .................... 37
2.3. Cc tiu chun xy dng mt c s h tng thng tin ton cu mi ....................... 38
2.3.1. Khi nim .............................................................................................................. 40 2.3.2. Mc ch thc hin ................................................................................................ 41 2.3.3. M hinh chc nng ................................................................................................ 44 2.3.4. M hinh thc thi .................................................................................................... 45 2.3.5. Cch tip cn theo kich ban (Scenarios Approach ) .............................................. 47 2.3.6. Cc n lc tiu chun ha ...................................................................................... 48 2.3.7. Chng trinh nghin cu cua cc nhm tiu chun hoa ca ITU-T cho GII ........ 50 2.3.8. Cc nh hng cho tng lai ............................................................................... 53
2.4. Tiu chun ha cc qu trnh truyn thng a phng tin .......................................... 53
iii
2.4.1. Chin lc ca ITU-T ........................................................................................... 53 2.4.2. nh hng ca ISO/IEC JTC1 trong nhng tiu chun a phng tin ............. 55 2.4.3. Cc tiu chun IETF .............................................................................................. 60 2.4.4. D n chun ha ca ETSI i vi cc ng dng, phn Middleware v mng .... 61 2.4.5. Cc hot ng lin quan ti GII ............................................................................ 63
2.5. ISO/IEC MPEG-21 ............................................................................................................ 63
2.5.1. M hinh ngi s dng (User Model) ................................................................... 65 2.5.2. Cc phn t s (Digital Items) ............................................................................... 65 2.5.3. K hoch thc hin (Work Plan) ........................................................................... 66 2.5.4. Cc kch bn s dng MPEG-21 ........................................................................... 67 2.5.5. Cc yu cu cua ngi s dung ............................................................................. 68
2.6. Cc tiu chun internet v a phng tin cua IETF ..................................................... 70
2.7. Din n v lin doanh cng nghip ................................................................................. 71
2.8. Kt lun ............................................................................................................................... 85
CHNG III LP NG DUNG ............................................................................................... 86
3.1. Cc ng dng ca H.323 cho truyn thng a phng tin ........................................... 86
3.1.1. Cc giao thc s dng trong H.323 ....................................................................... 86 3.1.2. Cc thnh phn ca H.323 ..................................................................................... 87 3.1.3. Qu trinh kt ni .................................................................................................... 87
3.2. ng dng H.264 v MPEG-4 trong nen truyn hinh s ................................................. 88
3.2.1. ng dng MPEG-4 ................................................................................................ 88 3.2.2. ng dng H.264 .................................................................................................... 91
3.3. Cc ng dng MPEG-2 trong truyn tai IPTV ............................................................... 97
3.4. Cc ng dng qung b s ................................................................................................ 99
3.4.1. Hi tu vin thng va quang ba ............................................................................... 99 3.4.2. Dch v pht thanh/truyn hinh s-DAB/DMB ................................................... 100 3.4.3. Cc dch v tng tc trong truyn hinh s ......................................................... 106
3.5. Kt lun ............................................................................................................................. 107
CHNG IV LP MIDDLEWARE ...................................................................................... 108
4.1. Gii thiu........................................................................................................................... 108
4.2. Middleware cho a phng tin ..................................................................................... 109
4.3. Ma ha thng tin .............................................................................................................. 109
4.3.1. Biu din ni dung thng tin ............................................................................... 110 4.3.2. Cc cng ngh nen ct loi ................................................................................... 112 4.3.3. Cc kin trc v cng ngh chuyn ma ............................................................... 115
4.4. To dong thng tin ........................................................................................................... 119
4.4.1. To dong video qua Internet ................................................................................ 120 4.4.2. Nhng thach thc truyn tai video thi gian thc qua Internet ...................... 130 4.4.3. Kin truc end-to-end cho truyn tai video MPEG-4 qua Internet ....................... 131 4.4.4. Truy cp bng rng .............................................................................................. 132 4.4.5. C s cua cht lng dich vu .............................................................................. 133
4.5. An ninh cua cac h thng a phng tin...................................................................... 133
4.5.1. H thng truy cp co iu kin (CA) ................................................................... 133 4.5.2. H thng quan ly ban quyn s DRM-Ky thut Watermarking .......................... 136
iv
4.6. Kt lun ............................................................................................................................. 143
CHNG V LP MANG ........................................................................................................ 144
5.1. Gii thiu........................................................................................................................... 144
5.2. Cc chc nng mng ........................................................................................................ 145
5.2.1. M hinh tham chiu OSI ..................................................................................... 145 5.2.2. Bo hiu trong cc mng truyn thng ................................................................ 149 5.2.3. Th tc nh tuyn cho truyn thng a phng tin .......................................... 150
5.3. Phn tich lu lng mng ............................................................................................... 150
5.4. Cht lng dich vu trong cac h thng a phng tin ni mang .............................. 151
5.4.1. nh ngha QoS ................................................................................................... 152 5.4.2. Cc m hnh QoS ................................................................................................. 152 5.4.3. Cc tham s cht lng dch v .......................................................................... 156
5.5. Mng vin thng th h sau NGN ................................................................................... 158
5.5.1. M hinh kin trc chc nng NGN ..................................................................... 158 5.5.2. M hinh phn lp NGN ....................................................................................... 162 5.5.3. Phn h a phng tin IP (IMS) ........................................................................ 164 5.5.4. Xu hng pht trin NGN ................................................................................... 168
5.6. Cc mng truy cp bng rng ......................................................................................... 169
5.6.1. Cng ngh truy nhp xDSL ................................................................................. 169 5.6.2. Mng cp quang .................................................................................................. 185 5.6.3. Cc mng v tuyn bng rng-Wimax ................................................................ 189
5.7. Mng phn phi ni dung (CDN) ................................................................................... 191
5.7.1. Mng s dng Caching Proxies ........................................................................... 192 5.7.2. Mng s dng Server Farms ................................................................................ 194 5.7.3. Mng phn phi ni dung .................................................................................... 195 5.7.4. H thng inh tuyn yu cu ............................................................................... 198
5.8. Kt lun ............................................................................................................................. 199
TI LIU THAM KHO ......................................................................................................... 200
v
THUT NG VA CH VIT TT
Ch vit
tt T ting Anh Nghia ting Vit
AAA Authentication, Authorization and
Accouting Xc thc, Cp phep, K ton
AES Advanced Encryption Standard Tiu chun mt ma ha tin tin
AK Authorization Key Kha cp phep
ASI Asynchronous Serial Interface Giao din s ni tip bt ng b
ATSC Advanced Television Systems
Committee
y ban cc h thng truyn hinh
tin tin
AVC Advanced Video Coding M ha Video tin tin
CA Conditional Access Truy cp c iu kin
CBC Cipher Block Chaining Chui khi mt ma
CEK Content Encryption Key Kha ma ha ni dung
CI Common Interface Giao din chung
CMLA Content Management License
Administrator
Qun tr giy phep qun l ni
dung
COFDM Coded OFDM Ghep knh phn chia theo tn s
trc giao c ma ha sa li
CRL Certificate Revocation List Danh sch hy b chng nhn
CSA Common Scrambling Algorithm Thut ton trn chung
DAB Digital Audio Broadcasting Pht thanh qung b k thut s
DCF DRM Content Format Khun dng ni dung DRM
DEA Data Encryption Algorithm Thut ton ma ha d liu
DES Data Encryption Standard Tiu chun mt ma ha d liu
DLDRM Download and DRM Ti v v DRM
DMB Digital Multimedia Broadcasting Pht qung b a phng tin s
DRM Digital Rights Management Qun l bn quyn k thut s
DTH Direct To Home Ti tn nh
DTTB Digital Terrestrial Television
Broadcasting
Truyn hinh qung b mt t k
thut s
DTV Digital TV Truyn hinh s
DVB Digital Video Broadcasting Pht qung b video s
DVB-
CBMS
DVB-Convergence
of Broadcast and Mobile Services
Hi t cc dch v qung b v di
ng-DVB
DVB-H DVB-Handheld DVB cho thit b cm tay
vi
Ch vit
tt T ting Anh Nghia ting Vit
DVB-T DVB-Terrestrial DVB pht mt t
ESG Electronic Service Guide Hng dn dch v in t
ETSI European Telecommunication
Standards Institute Vin tiu chun Chu u
FDM Frequency Division Multiplexing Ghep knh phn chia theo tn s
FEC Forward Error Correction Sa li trc
FLUTE FLUTE ng dng truyn file c dng
trong cc mng n hng
GPS Global Positioning System H thng nh v ton cu
H.264 Tiu chun nen video ca ITU
HSDPA High-Speed Downlink Packet Access Truy cp gi ng xung tc
cao
ICI Inter Carrier Interference Can nhiu gia cc sng mang
IMT2000 The ITUs framework for 3G
services
C cu ca ITU cho cc dch v
3G
IPDC IP Datacasting Qung b IP
IPE IP Encapsulator ng gi IP
IPsec IP security Bo mt IP
ISDB-T Integrated Services Digital
Broadcasting Terrestrial
Tch hp dch v s pht qung
b mt t
ISI Inter Symbol Interference Can nhiu gia cc k hiu iu
ch
ITU International Telecommunication
Union Hip hi Vin thng quc t
LTE Long-Term Evolution Pht trin di hn
MBMS Multimedia Broadcasting and
Multicasting Services
Dch v pht qung b v a
hng a phng tin
MediaFLO Media Forward Link Only Cng ngh qung b a phng
tin ca Qualcomm
MPE Multi-Protocol Encapsulation ng gi a giao thc
MPEG Motion Pictures Expert Group Nhm chuyn gia v hinh nh
ng
NOC National Ops Center Trung tm iu hnh quc gia
OFDM Orthogonal FDM Ghep knh phn chia theo tn s
vii
Ch vit
tt T ting Anh Nghia ting Vit
trc giao
OFDM Orthogonal FDM Ghep knh phn chia theo tn s
trc giao
OMA Open Mobile Alliance Lin on di ng m
OMA
BCAST OMA Standard for Broadcasting
Tiu chun OMA cho pht qung
b
PKI Public Key Infrastructure H tng kha cng khai
Podcasting
The broadcasting of multimedia
programs available on the Internet
in multimedia format.
Cc chng trinh qung b nh
dng a phng tin trn Internet
PPV Pay Per View Xem phim tr tin
PRG Pseudo Random Generator B to gi ngu nhin
QAM Quadrature Amplitude Modulation iu ch bin pha vung gc
QCIF Quarter Common Interface Format
nh dng giao din mn hinh
(176x120 NTSC v 176x144
PAL).
QPSK Quadrature Phase Shift Keying iu ch kha dch pha vung
gc
RI Rights Issuer B pht hnh quyn
RS Reed-Solomon code M Reed-Solomon
SAS Subscriber Authorization System H thng cp phep thu bao
S-DMB Satellite-DMB Ch pht DMB v tinh
TPS Transmission Parameter Signalling Bo hiu tham s truyn dn
TV Television Truyn hinh
VOD Video on Demand Video theo nhu cu
LI M U
Truyn thng a phng tin a ni ln l mt lnh vc nghin cu pht trin ch
o. C th cc my tnh a phng tin m ra nhiu kh nng kt hp cc dng thng
tin s khc nhau nh vn bn, ha, m thanh v phim nh. Vi s lng ngi s
dng a phng tin ngy cng tng nn nhu cu sch v cc h thng v truyn thng
a phng tin rt ln.
Bi ging Truyn thng a phng tin ny s cung cp cac kin thc sinh
vin hiu truyn thng a phng tin trong 3 lnh vc: ng dng, phn nhng v kt
ni mng. Nh gip ch cho sinh vin thc hin nghin cu v pht trin trong lnh
vc h thng cc thng tin giao thc cn thit h tr a dng dch v a phng
tin.
Bi ging ny s gip cho sinh vin hc c cc cng ngh truyn thng a
phng tin ct loi. Mc tiu ca cun bi ging ny l cung cp:
Ngun thng tin v cc ch quan trng trong truyn thng a phng tin.
Cc tng, phng php phn tch, thit k v thc hin cc h thng truyn
thng a phng tin.
T chc ca bi ging nh sau:
Chng I: Bt u bng gii thiu s hi t ca truyn thng v my tnh i
vi cc ng dng v dch v a phng tin. Tip gii thiu v cc cng
ngh truyn thng a phng tin, cc c s d liu a phng tin v nh
hng cng tc tiu chun ha a phng tin.
Chng II: Gii thiu cc nn tng tiu chun ha a phng tin, gii thiu
cc khun kh tiu chun ha ca ITU, IETF, ETSI....
Chng III dnh cho lp ng dng, phn ny trinh by v cc ng dng ca
ITU, cc ng dng ISO MPEG, cc ng dng a phng tin IETF qua IP,
phn tch cc ng dng qung b.
Chng IV gii thiu tng quan lp nhng, m t ma ha v chuyn i thng
tin, v xy dng kin trc giao thc a phng tin, bn v cc m hinh h
thng cho cc dch v a phng tin cng vi cht lng dch v v hot
ng end-to-end trong cc h thng a phng tin, cc kh nng truy cp h
thng v dch v a phng tin, an ninh h thng. Chng ny s kt lun
bng phn nhng lung thng tin.
Chng V tp trung vo lp mng (phn pht/vn chuyn), bao gm nhiu vn
lin quan ti cht lng dch v v hot ng mng, phn tch lu lng v
qun l lu lng, m hinh ha ngun video v lu lng mng, phn tch
qun l lu lng cng vi cc th tc nh tuyn trong truyn thng a
2
phng tin. ng thi phn ny cng cp ti bo hiu trong cc mng a
phng tin. Chng ny s m ra cho sinh vin s pht trin tng lai ca
truyn thng a phng tin v hiu ro hn tim nng ca truyn thng thng
a phng tin trong tng lai.
Tuy a rt c gng v cn thn trong qu trinh bin son nhng chc rng khng
trnh khi nhng thiu sot, tc gi mong nhn c nhiu kin ng gp ca cc
ng nghip cng nh ca cc em sinh vin bi ging ngy cng hon thin hn.
Th gp xin gi v:
- TS. Nguyn Qu Sy
- Khoa ky thut in t 1, Hc vin Cng ngh Bu chnh Vin
thng
- Email: [email protected]
H ni, ngy 06/2010
Tc gi
TS. Nguyn Qu S
3
CHNG I
TRUYN THNG A PHNG TIN
a phng tin-mt s biu din ca ging ni, m thanh, hinh nh, ha v vn
bn a tr thnh ch chnh trong cng ngh thng tin ngy nay. Cc cng ngh
thng tin ny hp nht truyn thng, tin hc v x l thng tin. Trong vi nm gn
y, c mt s lng hot ng ng k trong lnh vc truyn thng a phng tin
nh cc ng dng, phn nhng v kt ni mng. Nhiu ky thut khc nhau t cc
nguyn l cc nhau nh x l nh tnh v phim, th gic my tnh, qu trinh x l ting
ni v m thanh, nhn dng mu thng k, l thuyt hc v cc nghin cu da trn d
liu a v ang c khai thc.
Bi ging ny s cp ti:
Xu hng tng lai trong lnh vc s ha
S tng trng ca cc mng s v c bit l Internet
Nng lc tnh ton ngy cng cao ca cc my tnh c nhn v my xch tay,
PDA v cc in thoi di ng
S hi t ca nhiu cng ngh khc nhau, trong c truyn thng, qung b,
cng ngh thng tin v in t gia inh
S ni ln ca cc dch v v ng dng mi do s pht trin ca Internet v
cc cng ngh v tuyn
S hi t ca cc cc mng tc cao, cht lng cao, xa hi s yu cu cc
ng dng a phng tin thi gian thc nh l mt s m rng ca cc h
thng n phng tin ang c.
Hot ng end-to-end ca cc h thng v dch v a phng tin theo tiu
chun ca ITU...
1.1. Gii thiu
Truyn thng a phng tin ni mng c bt ngun t s hp li ca 2 xu
hng cng ngh:
Th nht l s pht trin ca tnh ton a phng tin
Th hai l s tin b trong kt ni mng cho phep vn chuyn tin cy d liu
s mc bng thng cao.
Cng nhn rng cc bn tin khc nhau c vn chuyn tt nht bng nhiu
phng tin khc nhau, nhng nhng ngi pht trin tnh ton a phng tin mong
mun b sung thm s phong ph ca cc m thanh v hinh nh ca th gii thc, t
dn ti vic m rng phm vi ca cc ng dng v cng a cc ng dng ny ti
nhng ngi s dng. My tnh c nhn tr thnh mt nt truyn thng trung tm thay
4
th mt s lng ln cc thit b v h thng khc bao gm my thu hinh, my ch,
my fax, in thoi v chuyn th. Tuy th ng lc thc y kt ni cc thit b
khch hng ti mng a phng tin vn con li. Ni mng cho phep truyn thng
gia mi ngi vi nhau v cn cho khch hng tri nghim cuc sng, cc s kin
xa. Cc ng dng cho cuc sng, truy cp t xa bao gm hi ngh, gio dc, gii tr v
gim st cc vng t xa.
Truyn thng a phng tin ang c khuyn khch bi cc nh hng sau
trong mng truyn thng:
Chuyn tip khng gin on t iu khin mng tp trung ti iu khin phn
tn
Kt ni khng gin on cc mng khc nhau vi chi ph hp l (chi tr c)
Truyn dn hp nht khng gin on ca a phng tin vi nhiu mc QoS
(bao gm c multicast)
Cc dch v truyn thng a phng (multicast) c k vng tr thnh mt trong
nhng ng dng ph thng nht, xut bn hng ny, phn phi phn mm, ti to c
s d liu v tip tc trong cc mng truyn thng a phng tin tng lai. cung
cp cc dch v truyn thng a phng trong cc mi trng truyn thng khng
ng nht, cn thit phi pht trin mt c ch m bo QoS m c th cung cp QoS
hp l cho mi ma ch theo bng thng v ti nguyn c th s dng.
s dng ti nguyn mng hiu qu, multicast theo thi gian thc v khng theo
thi gian thc u rt quan trng. Trong trng hp ny, s cn ti h tr nhiu lp
QoS v kh nng cho t trc bng thng ng.
Chng ny bt u vi m hinh truyn thng a phng tin. Sau cung cp s
hi t ca vin thng, tnh ton my tnh v in t dn dng, cng vi m t cc cng
ngh cho truyn thng thng a phng tin. Cc ni dung nghin cu, tiu chun ha,
cc chnh sch truyn thng a phng tin cng c nhn mnh. Nhng net chnh
ca cc tiu chun ma ha hinh nh/m thanh s v vai tro ca n trong truyn thng
a phng tin cng c cp ti trong chng ny.
1.2. S pht trin v hi t
a phng tin t n a chng t c thao tc kt hp ca cc d liu thng tin
lin tc v c cc d liu thng tin ri rc. Cc thao tc ny bao gm bt gi, x l,
truyn thng, trinh din v/hoc lu tr. Cc d liu thng tin lin tc l d liu ph
thuc vo thi gian (nh d liu m thanh v hinh nh) trong cc h thng a phng
tin. Ngoi ra truyn thng a phng tin con lin quan ti chuyn giao, cc giao
thc, cc dch v v cc c ch cho cc thng tin lin tc v ri rc qua cc mng s.
S truyn dn d liu hinh nh s qua mng phn phi TV chuyn dng khng phi
mng a phng tin khng cho phep chuyn mt s dng d liu thng tin ri rc.
5
Trong cc ng dng a phng tin ni mng, nhiu thc th khc nhau cng hp
tc cung cp nhng s bo m thi gian thc, vi vy cho phep d liu trinh din
c giao din ca khch hng. Nhng yu cu ny thng ch yu c xc nh
di dng cht lng dch v (QoS). Chng ta phn bit 4 lp QoS:
QoS khch hng (ngi s dng): Cc tham s QoS m t cc yu cu trn cc
dch v ng dng v c th xc ng di dng cht lng thng tin (nh tr
end-to-end) v cc quan h thng tin (nh ng b lung gia cc lung hoc
trong mt lung)
QoS ng dng
QoS h thng: m t cc yu cu trn dch v truyn thng theo QoS ca ng
dng. Chng c th c xc nh theo cc tiu ch nh lng (nh s
bit/giy, thi gian x l cng vic) v cht lng (nh multicast, ng b gia
cc lung, khi phc li hoc vn chuyn d liu theo th t)
QoS mng: m t cc yu cu trn dch v mng (nh ti mng hoc cht
lng mng). Cc ng dng a phng tin m phn QoS mong mun trong
sut giai on thit lp kt ni cng vi lp h thng hoc c th trc tip vi
lp mng, nu nh h thng khng th cung cp QoS cho ng dng.
1.2.1. S hi t ca vin thng v tin hc
Hin nay quan h gia vin thng v tin hc a phong ph hn rt nhiu so vi
trc. Cc quan h ny s tr nn d phn bit hn trong tng lai rt gn. S hi t
ny a v s tip tc tc ng mnh ti cng ngh, cng nghip v xa hi.
d hiu chng ta s chp nhn mt m hinh 3 mc cho mt mng thng tin v
cc dch v, ng dng ca truyn thng a phng tin.
Hnh I-1 M hnh 3 mc cho mt mng truyn thng a phng tin
Mt ng dng l mt tp hp chc nng cung cp cho ngi s dng. Chng ta
quan tm y l cc ng dng c ni mng, chng c phn phi qua cc mi
trng vin thng v tnh ton phn tn. Cc v d ca cc ng dng ni mng l th
in t, in thoi, truy cp c s d liu, truyn file, duyt Web v hi ngh truyn
hnh. Cc v d ca dch v c th l truyn ti m thanh, hinh nh, qun l h thng
file, in, cc c ch thanh ton in t, ma ha v phn phi kha v vn chuyn d liu
tin cy. Hai loi ng dng ni mng lin quan l:
6
ng dng khch hng-khch hng, trong hai hoc nhiu ngi s dng
tham gia vo mt s mi trng dng chung
ng dng khch hng-my ch thng tin, trong mt khch hng tng tc
vi mt h thng t xa, nhn hoc tng tc vi thng tin lu tr trong h
thng.
Mi ngi s dng trong mt ng dng ni mng tng tc vi mt thit b u
cui ni b, thit b ny li trao i thng tin vi cc my tnh hoc thit b u cui
xa qua mng. Chng ta cng c th tch cc ng dng ni mng thnh hai lp tng
ng vi quan h tng tc ca ngi s dng vi mt m ch hoc vi mt ngi s
dng khc:
Ngay lp tc: mt ngi s dng tng tc vi mt my ch hoc mt ngi
s dng khc theo thi gian thc, dch v ny yu cu v tr v khong lng
ln nht.
Tri hoan c: Mt ngi s dng tng tc vi mt ngi s dng khc hoc
mt my ch vi quan h khng c nh v tr khng quan trng.
1.2.2. Kin trc ca cc dch v ni mng
Cc ng dng ni mng c thc hin bi cc nt thit b u cui hoc cc thit
b b u cui c kt ni vi nhau. V chc nng c hai kin trc c bn c th t
dng cho cc dch v ni mng (Hinh I-2):
Peer-to-Peer: Ngang hng
V Client-Server
Hnh I-2 Kin trc ngang hng v Client-Server
Trong cu trc ngang hng, hai hoc nhiu thit b u cui, mi thit b gn vi
mt ngi s dng, trao i thng tin qua mt knh cung cp mt ng dng ni
mng gia nhng ngi s dng. Thnh phn truyn thng ni mng gia cc cp
ngang hng thng l i xng v chc nng v ti nguyn knh.
Con trong cu trc Client-Server, mt thit b u cui Client ca ngi s dng
trao i thng tin vi my tnh ch, khng lin quan trc tip ti ngi s dng nhng
thc hin chc nng my ch thng tin. Chc nng ny thng khng i xng, trong
khi my ch thc hin chc nng chnh hoc truy cp c s d liu thi thit b u cui
7
client tp trung vo giao din ngi s dng. Cc thnh phn truyn thng thng l
khng i xng vi hng t my ch v client (knh hng v) thng yu cu bng
thng ln hn.
Hnh I-3 Mt ng dng gia hai ngi s dng
c thc hin bng kin trc ngang hng hoc client-server
1.2.3. Lin kt
Hnh I-4 Hai m hnh ca cc dch v ni mng: dc v ngang
C 2 m hinh kin trc cho cc ng dng ni mng nh (Hinh I-4): Lin kt ngang
v lin kt dc. Trong hu ht cc lin kt dc, mt h tng chuyn dng c s dng
thc hin tng ng dng, ngc li m hinh lin kt ngang c cc c im sau:
Mt hoc nhiu knh truyn ti d liu lin kt v lung thng tin nh m
thanh v hinh nh c cc tham s QoS c th cu hinh c
Mt tp hp cc dch v nh cc dch v phn nhng (th vin. chuyn tin
in t, qun l kha.v.v.) v cc dch v thng tin (m thanh, hinh nh...)
lun sn sng cho tt c cc ng dng.
Mt tp cc ng dng a dng sn sng cho ngi s dng
8
u im chnh ca m hinh ngang l cho php lin kt cc thng tin khc nhau
trong mi ng dng, cng nh cc lin kt cc ng dng khc nhau trong knh. Hin
nay trong vin thng, cc mng ch yu l mng a dch v.
Mt s khc bit khc gia cc mng l chng l cc mng hiu bit ni dung v
khng hiu bit ni dung hoc hiu bit ng dng hoc khng hiu bit ng dng.
Cc mng lin kt dc thng l hiu bit ni dung, c ngha chng nhn dng c
cc ng dng m chng vn chuyn (chng hn nh hi ngh truyn hinh, truyn file,
truyn hinh theo yu cu-VoD). Trong khi cc mng lin kt ngang thng l m ng
dng (chng hn nh Internet).
Mt c im quan trng ca lin kt ngang l giao din m vi nhng c im
ring. Chng c mt b ch tiu ky thut c th s dng t do v cho phep nhiu thc
thi khc nhau t b ch tiu ny. Mt c im ring mong mun khc l kh nng
thm mi hoc ng chc nng. Chng ta c th nh ngha chc nng ng khi khng
mun xut bn hoc cho t chc khc m rng. Chc nng ring ny c th c pht
hnh v m rng nhng phi chu bo v quyn s hu tr tu.
Mt mc ch ca cc giao din ngang m l ng gp cc m un tho ri nh
s c lp ca ng dng vi c s nn tng.
1.2.4. S tinh ton c th truyn ti c
S tnh ton c th truyn ti c a ra 4 u im chnh:
Kh nng m rng: Cho phep c b nh (tm thi v c nh) v tnh ton t
c trn bt k my tnh hoc thit b u cui no thun tin nht. V d,
trong mt ng dng client-server, cho phep s tnh ton c dch chuyn t
my ch xung cc client ca n, nh vy trnh c qu ti trn my ch
Khong lng: Thi gian thi hnh chng trinh loi b c khong lng do tr
truyn ti trn mng.
Truy cp d liu ni b: Mt chng trinh truyn ti c c th truy cp v
thay i s liu lu tr trn bt k my tnh no m n c th chuyn n.
S lin kt: Nu cc chng trinh lin quan ti mt ng dng phn tn to ra
t mt ngun chung, c th ni rng chng lin kt vi nhau theo s iu phi
hot ng ring.
1.3. Khung c s cng ngh
a phng tin v truyn thng a phng tin c nhin nhn tng th nh l
mt h thng phn cp. Cc ng dng v phn mm a phng tin cung cp mt mi
trng tng tc cho cc i tng s dng. Khi mt my tnh yu cu thng tin t
cc my tnh hoc my ch xa, thng tin a phng tin phi vn chuyn qua mng
my tnh. Vi s lng thng tin truyn dn hinh nh v m thanh c th rt ln, nn
gim tr truyn thng thng tin a phng tin ph c nen trc khi truyn qua
9
mng. Cc rng buc nh l gii hn tr v bin thin tr c s dng m bo
c cc hiu ng m thanh v hinh nh pha thu. Do cc mng truyn thng
ang thc hin nng cp lin tc nng cao kh nng truyn thng a phng tin.
Cc mng ni b c s dng kt ni cc my tnh ni b vi cc thit b khc.
Mng vng rng (WAN) v Internet ni vi mng ni b (LAN). Cc tiu chun mi
hn v tt hn lin tc c pht trin cung cp mt xa l thng tin ton cu, m
qua thng tin a phng tin s c chuyn qua.
1.3.1. Cc cng ngh a phng tin
C mt s lng ln cc cng ngh v sn phm a phng tin a c chp
thun rng rai nh QuickTime v Video for Windows.
C mt tiu chun ISO vi tiu MHEG (Multimedia Hypermedia Information
Coding Expert Group)-tiu chun ny l ISO/IEC JTC1/SC29 WG12 dnh cho cc lp
i tng iu khin trinh din thng tin a phng tin v siu thng tin. MPEG-5 l
tiu chun h tr phn phi cc ng dng a phng tin tng tc trong mi trng
client/server a nh cung cp thit b. Cc nh pht trin s dng cc tiu chun ny
pht trin ca\cs ng dng, bi vi s trinh din thng tin l c th thay th cho nhau
trong cc kh nng m t ti liu ca HTML (Hyper Text Markup Language). MHEG
cung cp cc kh nng gim st a phng tin b sung . Tiu chun Abstract Syntax
Notation (ASN.1) ca ISO c s dng miu t gia cc nn tng my tnh khc
nhau, cc ngn ng v h iu hnh khc nhau. Tiu chun s dng khng gian (ta
3 chiu) v thi gian ng b biu din.
a/ SONET (Synchronous Optical Network)
SONET a c Bellcore pht trin cho kt ni mng vng rng ANSI v c s
dng nhiu nc trn th gii, ban u l My v Canada. Tng t Chu u, SDH
(Synchronous Digital Hierarchy) l mt tiu chun ca ITU-T. SONET v SDH v c
bn tng thch vi nhau tn hiu truyn ti ng b (STS 3C 155,52Mbps) v n
ub truyn ti ng b (STM-1). SONET s dng mt khung vn chuyn thng tin
tc thp hn (cc nhnh: m thanh, hinh nh v d liu). Bng thng cho mi
nhnh c bo m. SONET s dng ghep ng b (SMUX) v cc b ghep
add/drop (ADM) chn mt tin hiu t ngun v tch tn hiu pha thu.
b/ Cc mng my tinh
Mng my tnh l cc phng tin truyn ti a phng tin. Mt s c im
chnh ca cc mng my tnh:
Cc mng ni b (LAN) 802.x: Tiu chun 802.x do IEEE nh ngha cha
cc tiu chun sau:
o 802.1bao gm quan h gia 802.X v m hinh tham chiu lin kt h
thng m kt ni 802.x bng cc cu v qun l mng
10
o 802.2iu khin knh logic nh a ch cc im a dch v cho nhiu
ng dng ng thi v cho cc hot ng nh hng kt ni, phi kt ni
v xc nhn.
o 802.3Tiu chun Ethernet
o 802.4Giao thc tiu chun token
o 802.5 Tiu chun token ring
o 802.12Tiu chun 100VG-AnyLAN.
Ethernet l LAN c trin khai rng rai nht v mi hn l tiu chun Fast-
Ethernet. Token Bus c trin khai rt hn ch vi vn sn xut.
Token Ring s dng cc trm theo mt vong tron v s dng mt token trnh
tranh chp.
Fast Ethernet v 100VG-AnyLAN: Ethernet ban u c thit k ni cc
my trm bng cp ng trc, sau c pht trin ln cc i dy xon
ni cc my trm ti mt hub. Tc truyn ti l 10Mbps. nng cao tc
, fast Ethernet a c pht trin cung cp 100 Mbps v phi s dng
mt Hub kt ni cc my trm. 100VG-AnyLan a c thit k gim
st truyn thng a phng tin thng qua mt phng thc nhu cu yu tin.
N n nh u tin cao cho a phng tin, tri vi Ethernet s dng a truy
nhp cm ng sng mang vi pht hin xung t (CSMA/CD). Ethernet khng
th n nh u tin cao cho lu lng thi gian thc nh d liu m thanh v
hinh nh. Cc Hub ca mt 100VG-AnyLAN c th c kt ni theo hinh
sao phn cp vi ln nht 3 lp, v LAN token ring c th c kt ni nh l
mt phn ca mng. Cp s dng trong fast Ethernet c th dng trong
100VG-AnyLAN.
Cc LAN c chuyn mch: Mt mi trnghf dng chung trong LAN a
trinh by trn s c cc vn v kh nng m rng. Khi s lng cc my
trm tng ln, bng thng hiu dng ca mi trm b gim xung. Vn ny
c th c lm nh bt nh s dng mt LAN c chuyn mch, LAN ny
kt ni cc my trm qua mt hub chuyn mch. Truyn thng khng th b
chn nu khng c tranh chp i vi cng ch n. Hn na hot ng ca
mng c th m rng c. B chuyn mch c th hiu v tr mt my trm
LAN thng qua iu khin truy cp mi trng (MAC) v a ch trong mt
my trm LAN phm vi tng t nh s dng cu ni.
o B chuyn mch lp 2 thc hin lp 2 ca m hinh tham chiu OSI v
x l nh mt cu ni. N c th kt ni nhiu LAN v my trm. B
chuyn mch lp 2 nhanh hn cu ni bi vi n s dng cc mch tch
hp chuyn dng (ASIC) chuyn mch lu lng.
11
o B chuyn mch lp 3 c thit k nng cao hot ng v gim chi
ph router, router dng kt ni mng lp 3 ca m hinh tham chiu
OSI. Mt router thc hin 2 chc nng: (1) to ra bng nh tuyn cho
chng tip theo nh thu thp thng tin ca cc router ln cn cng nh
(2) chuyn mch khung ti cng ra thch hp da trn bng nh tuyn.
B chuyn mch lp 3 c thit k thc hin chc nng th hai bng
ASIC. Bng nh tuyn c th c c t mt my ch nh tuyn (c
thit k thc hin chc nng u tin). Mt s b chuyn mch c th
dng chung mt tuyn gim chi ph v ASIC c th chuyn mch
nhanh hm l mt router da trn RISC.
c/ Asynchronous Transfer Mode (ATM)-Sinh vin t nghin cu tm hiu
d/ TV cht lng cao (HDTV).
The Federal Communications Commission (FCC) a thu ht v a nhn c cc
xut vo nm 1988 cho HDTV. Hip hi Grand bao gm General Instruments,
Philips, David Sarnoff Research Center, Thomson Consumer Products, AT&T, v
Zenith a c thnh lp nm 1993. Hip hi Grand a chn MPEG-2 Main Profile v
High Level ma ha v truyn ti hinh nh, v AC-3 do Dolby Labs pht trin cho
ma ha m thanh, trong khi s dng MPEG-2 TS cho ng gi v ghep knh. Bng
thng ca knh truyn l 6MHz, tc d liu 19,4 Mbps, trong khi cc gi MPEG
c trn v b sung thm cc thng tin sa li.
e/ Cable TV (CATV)
Cc dch v mi t CATV bao gm in thoi, fax, video theo nhu cu v truy cp
my tnh ti Internet. Mt modem cp phi c s dng kt ni Internet c ni
gia cp dn v cc card giao din mng Ethernet. Bng thng ca cp c dng
chung cho tt c cc khch hng trn cng cp CATV nh l Ethernet.
Ty theo nh cung cp thit b modem cp, tc hng v t Headend ti gia
inh t 4-27Mbps v hng i t gia inh ti headend l 96Kbps-27Mbps. CATV
thc hin cc dch v thoi thong qua SONET ni Headend vi mng in thoi
chuyn mch cng cng PSTN.
f/ Mch vong (ng dy) thu bao s (DSL).
cnh tranh vi CATV i vi cc dch v VoD v Internet, cc cng ty in
thoi ang trin khai DSL. DSL bao gm:
ISDN
Mch vong thu bao s khng i xng (ADSL)
DSL tc d liu cao (HDSL)
DSL n ng (SDSL)
DSL tc d liu rt cao (VDSL)
12
DSL h tr in thoi tng t cng nh giao din tc c s ca ISDN (BRI)
(2 knh d liu B 64Kbps v 1 knh iu khin D 16Kbps, v c 384kbps cho hi ngh
truyn hinh. DSL c th trin khai cho nhiu khch hng. Cng ngh DSL p ng
c truyn thong a phng tin. Bng thng DSL chuyn dng cho 1 khch hng
trong khi bng thng ca cp dng chung cho tt c cc khch hng (b chia s).
g/ Internet.
Internet a pht trin t mng d liu cng ng ng thnh mt h tng xa hi
thng tin ton cu. Cc khch hng ang tin tng vo Internet trong kinh doanh,
khng ch cc dch v World Wide Web v cc ng dng truyn thng nh truyn
Email, truyn file m con ang ngy cng tng cc ng dng thi gian thc nh m
thanh, hinh nh thi gian thc v cc ng dng dng chung.
Mc tiu thit k ban u ca Internet l lm mng d liu c kh nng chu li
cao cho quc phong. thc hin c, s lng d liu dng chung trong mng v
cc h thng u cui l ti thiu, l thng tin tnh ton tp hp cc tuyn.
Trc y cc routerr s dng hng i FIFO (vo trc ra trc) cho tt c cc lu
lng vi thc hin n n gin. Nhng sau mt thi gian ngy cng tng nhu cu thc
hin qun l cho cc dng khc nhau, cho cc khch hng khc nhau v cho cc mng
qu ti.
Cc giai on pht trin giao thc v thc hin mng Internet nh sau:
Giai on u nh ngha dch v v tng chuyn kiu dch v c
xut. Cc router phn bit lu lng hoc bng kim tra cc bit c bit trong
giao thc IP hoc bng giao thc ng dng. Tt c cc giao thc truyn file
(FTP) v giao thc ng dng World Wide Web, giao thc truyn siu vn bn
hot ng qua giao thc iu khin truyn dn (TCP), giao thc ny m rng
t giao thc IP khng tin cy cung cp vn chuyn ng dng tin cy v
trinh t.
Tc dng ca nh tuyn kiu dch v v iu khin tc ngn TCP l mng
cung cp dng chung cng bng cho cc khch hng. Bi vi tt c cc khch
hng TCP c chung mt dung lng mi lc, nn thi gian s dng b thay i
ph thuc vo s lng ngi s dng hin ti. Mt h thng truy cp thu
ring a c cc nh khai thc Internet a vo khai thc.
Truyn thng nhm rt hu ch cho cc ng dng lin quan ti nhiu thit b
thu v pht ng thi. ng trc multicast l mt chng ph o trn mng
Internet hin ti cung cp dch multicast, nh gim c ng k ti trn
mng cho cc ng dng nh vy. Ban u ngi ta hy vong co th s dung no
cho cac giao dich thay th , nhng thiu cac giao thc truyn tai (end-to-end)
h tr chng. Multicast a c trin khai nhanh chong hn cho ho cac ng
13
dng da trn UDP , cho cc chng trinh hi ngh truyn hinh v m thanh .
Cc ng dng in hinh da trn UDP cung cp tc gi gn nh c inh ti
mng. h tr s lng ty khch hng s dng cc ng dng ny m
khng bi qua tai, Internet a phai m rng bng mt s cach nh :
o t trc ti nguyn : c th lm vic vi mt lp ln cc ng dng
nhng se lun lun la mt s ng dung chim phn ln dung lng
mng
o Tnh cc da trn s dng: phng thc nay a nhn c s quan tm
tronng nghin cu phat trin tiu chun
1.3.2. Kt ni mang a phng tin
Nhiu ng dung nh th in t , hi nghi truyn hinh , v cc h thng lm vic
cng tac yu cu a phng tin c ni mng. Trong cac ng dung nay , cc i
tng a phng tin c lu tai mt may chu (server) v c chi li (play back)
cc my khch (Clients). Cc ng dng nh vy c th yu cu qung b d liu ti
cc v tr xa khac nhau hoc truy cp nhng ni tr cac tai nguyn a phng tin
ln. Cc mng a phng tin yu cu tc hoc bng thng rt ln , thm chi ngay
c khi d liu a c nen . Cc mng truyn thng c dng cung c p cc truyn
dn li t do (error-free). Tuy nhin hu ht cac ng dng a phng tin co th chiu
dng li truyn dn do s hong hoc tn tht goi ma khng cn truyn lai hoc sa li .
Trong mt s trng hp , tha man cac yu cu vn chuyn thi gian thc hoc co
c ng b , mt s goi thm chi bi bo i . Chng ta c th p dng cc giao thc
truyn dn trong s thp cho cac mang a phng tin . Cc giao thc ny khng th
chp nhn pht li bi vi chng c th gy ra tr khng chp nhn c .
Cc mng a phng tin cung cp khong lng thp cn thit cho hot ng
tng tac. Vi d liu a phng tin phai c ng b khi no ti ich , cc mng nn
cung cp truyn dn ng b co dich thp (jitter).
Trong cc mng a phng tin, hu ht cc trao i thng tin l a im tri vi
truyn thng truyn thng. V d nh cc hi ngh lin quan ti nhiu hn 2 thnh vin
tham gia cn phn phi thng tin bng cc thit b khc nhau ti tng thnh vin khc.
Cc mng hi ngh s dng cc phng php phn phi multicast v ni cu. Multicast
ti to mt tn hiu vo duy nht v vn chuyn n ti nhiu ch. Cu ni kt hp
nhiu tn hiu u vo thnh mt hoc nhiu tn hiu ra, sau vn chuyn cc tn hiu
ti ti cc thnh vin.
Cc mng truyn thng Ethernet khng ph hp vi a phng tin v n ch cung
cp 10Mbps, thi gian truy cp khng b gii hn, cn khong lng v dch khng
th d on c. Cc mng token-ring cung cp 16Mbps, chng c th gim stv a
phng, tuy nhin khong lng truy cp c th rt cao.
14
Mt mng FDDI (Giao din d liu phn phi trn cp quang) cung cp bng
thng 10Mbps, cho a phng ti. ch ng b, FDDI c khong lng truy
cp nh v dch nh. N cng m bo tr truy cp b gii hn v bng thng trung
bnh d bo c i vi lu lng ng b. Tuy nhin do chi ph cao, cc mng
FDDI c s dng ch yu lm mng ng trc nhiu hn l mng cho cc my
trm.
Cc la chn tn kem hn l cc mng truyn thng m rng:
Fast Ethernet cung cp ln ti 100Mbps
Token ring u tin: lu lng a phng tin c tch ring khi lu lng
thng thng theo u tin. Hinh I-5 ch ra mt tokenring u tin. B qun
l bng thng ng vai tro chnh nh cc phin theo doi, xc nh u tin v
ng k phin a phng tin.
Hnh I-5 Token ring u tin
Chng c 3 phng thc vng u tin cho cc ng dng hi ngh truyn hnh:
u tin nh nhau i vi video v cc gi khng ng b
u tin cao c nh cho cc gi video v u tin thp c nh cho cc gi
khng ng b
u tin cao c iu chnh theo thi gian cho cc gi video v u tin thp c
nh cho cc gi khng ng b
Phng thc th nht oi hi cnh tranh trc tip gia hi ngh truyn hnh v cc
trm ng b v phng thc ny t c tr mng nh nht cho cc khung khng
ng b. Tuy nhin n lm gim cht lng hi ngh truyn hnh.
Phng thc th hai, trong cc trm hi ngh truyn hinh c u tin cao c nh
s khng b suy gim cht lng hi ngh nhng lm tng tr mng khng ng b.
Cui cng h thng u tin c iu chnh thi gian cung cp s cn bng gia hai
phng thc trn. Cht lng ca hi ngh truyn hnh tt hn phng thc th nht
trong khi tr mng khng ng b cng ngn hn phng thc th hai.
1.3.3. Hi ngh a phng tin
15
Hi ngh a phng tin cho phep s lng ln cc thnh vin trao i thng tin
a phng tin qua cc mng thoi v d liu. Mi thnh vin c mt my trm a
phng tin kt ni vi cc my trm khc qua cc mng tc cao. Mi thnh vin
c th gi hoc nhn hinh nh, m thanh v d liu; ng thi c th thc hin cc
hot ng cng tc nht nh. Hi ngh a phng tin s dng khi nim khng gian
lm vic o dng chung, khng gian ny m t mt phn mn hinh c ti to li
mi my trm.
Thch thc ln nht trong hi ngh a phng tin xy ra khi cc thnh vin hi
ngh lin tc pht i cc dong hinh nh v m thanh. Cc nghin cu tp trung vo kt
hp cc dong ny vi nhau to thnh mt dong ghep. Ngi ta a a ra nhiu cng
ngh v giao thc cho nh s phng tin v kin trc truyn thng ti u.
Cc h thng hi ngh a phng tin phi cung cp nhiu chc nng nh thit lp
nhiu cuc gi ng thi, truyn dn tinh trng hi ngh , iu khin m thanh va hinh
nh theo thi gian thc , phn b ng tai nguyn mang , truyn d liu a im , ng
b khng gian dung chung v iu chnh h thng di cc iu kin li .
Cc kin trc h thng hi ngh c th c phn bit bng v tr ca cc chc
nng tng hp m thanh va cac cu hinh kt ni cua chung . Do vy c 2 lp kin truc
c tn gi l Tp trung v Phn tn , ngoi ra lp th ba l lp lai . Cc h thng t cc
h ny c th c nh gi di dng cht lng , kh nng m rng , kh nng m
rng, kh nng tng thch vi cc tiu chun hin ti v thc t.
a/ Kin truc hi nghi tp trung
Hi nghi thoai t xa a c cung cp bng cac cu ni hi nghi tp trung , nhng
ngi tham d quay s ti mt trung tm vao mt thi im a chun b trc . Cc
im cui thit lp kt ni mt -mt (tng i mt ) v cc kt ni bo hiu . Cc cu
ni thit lp cac ng dn d liu gia cac im cui nh tng hp cac tin hiu u
vo vi nhau v tr li tn hiu a tng hp cho cac hi nghi . tranh ting vong ,
nhng ngi tham d nhn mt tin hiu m thanh ro rng bao gm tt c m thanh ca
nhng ngi tham d tr ting noi cua ho . Cu ni lam giam nhiu nn va kha n ng
xy ra ting vng nh ch tng hp M trong N ngi ni .
b/ Cc kin trc hi ngh phn tn
Trong mt hi nghi phn tan , cc thit b trao i vi nhau gia cc im cui m
khng s dung cu tp trung . Cht lng m th anh c tng ln nh loai bo c
chuyn tip cua cac cu . Tuy nhin cac im cui phai co kha nng nhn va tng hp
nhiu dong ng thi . S phn tan chc nng x ly m thanh qua cac im cui dn
ti khng yu cu tin h toan nhiu nh cac cu ni thng thng . Hi nghi phn tan
c biu din bng cac m hinh full -mesh va m hinh hi nghi multicast (a
phng).
16
Trong hi nghi full -mesh (N thanh vin ), mt kt ni phng tin full -duplex
c thit lp gia tt ca cac cac thanh vin tao ra cac kt ni mesh . Mi im
cui phat mt ban sao dong d liu cua no ti N-1 im cui khac va nhn N -
1 dong v. Mi cp u cui co th trao i thng tin vi nhau bng mt kiu
CODEC bt ky. iu khin bao hiu cua cac im cui co th tp trung may
ch, sao trang thai cho hi nghi c duy tri , trong o trang thai hi nghi co
th bao gm cac thanh vin hi nghi hoc cac yu cu dch v m thanh b
sung.
Hi nghi multicast la ng nghia vi hi nghi vung rng qua MBone . Trong
mt hi nghi multicast , mi im cui phat mt ban sao duy nht cua dong d
liu ti ia chi multicast v nhn N -1 dong v. i vi pha thu , khng co gi
thay i so vi kich ban cua full -mesh tr cac dong v trn 1 cng. Hi nghi
multicast la mt dang khac cua hi nghi tp trung. Thay vi kt ni ti mt cu
hi nghi cac im cui tham gia hi nghi bng ng ky ti mt ia chi
multicast cua hi nghi . ia chi nay co th c quang cao bi mt trong
nhng im cui hoc bi mt may chu trung tm hoc c phn phat ti cac
thnh vin tham d trc khi hi ngh.
c/ Lp lai (gia phn tan va tp trung)
Kin truc hi nghi khng co chuyn tip la mt kin truc lai gia cac tip cn kin
trc tp trung v phn tn truyn thng . M hinh nay s dung mt cu ni khng co
trung gian (cu ni hi nghi chon -v-chuyn tip cho nhiu ngi noi ng thi ). Cu
ny chn M ngi ni hin ti chuyn cc tn hiu a nen ca h ti N -M im cui ,
ti chng c gii ma v kt hp li . Nu M=2, ngi noi th nht nhn tin hiu
ca ngi ni th hai v ngc li.
Kin truc hi nghi khng co chuyn tip nay co mt s c im cn quan tm . H
thng loai bo c chuyn tip , hot ng c lp vi CODEC m thanh v gim yu
cu tinh toan cua cu . Nhc im lag cac m rng cua giao thc cn phai mang d
liu cua hi nghi, trong khi cac im cui phai h tr thit bi u cui va kt hp nhiu
dong d liu ng thi.
1.3.4. Multicasting
Internet a chng kin mt s tng trng phi thng cung vi s phat trin cua
nhiu ng dung mi hn , tinh vi hn oi hoi mang phai co cac chc nng phong phu
hn. Vic lam chu s tin b cua cac cng ngh bng rng , v tuyn va Web hon
ton c th thit k va thc hin cac mang hn hp c ln co th h tr phn phi
ni dung, hi thi thoai, dong m thanh, hc t xa, khng gian lam vic cng tac va cac
dng y . Theo inh hng nay, multicast a tr thanh mt cng ngh cho phep va
ong vai tro quan trong trong thit k , pht trin v khai thc nhiu ng dng , dch v
17
hin nay va tng lai da trn vn chuyn goi hiu qua ti nhiu ich ng t hi. Mc
d khi nim ca multicast c v nh rt hp dn bn ngoi nhng thc ra l rt kh
khn thc hin trong mi trng nhiu nha cung cp dich vu Internet .
Vi nhng tin b trong cng ngh hinh anh s , dch v video theo nhu cu a
trin khai trong thc t mt vai nm gn y . H thng VoS ln cn lu tr vai trm
b phim va h tr hang nghin khach hang.
phat trin mt giai phap tit kim chi phi , nhiu nha nghin cu a ngh in cu
trn nhiu tai nguyn khac nhau , cc chnh sch phn chia s dng kh nng multicast
ca cc mng truyn thng tin tin . Trong mt mt nm gn y , cc phng thc
qun b khc nhau nh pyramid (kim t thap ), harmonic (i u hoa ), skyscraper
(chc tri ) a c xut lam giam tr khi tao va yu cu bng thng
nh s dung b m thu .
Ngoi qung b , phng thc multicast cung c s dung phuc vu mt nhom
cc khch hng ti thiu yu cu h thng . Khc vi phng thc qung b c bng
thng bi gii han, yu cu bng thng cho phng thc multicast c lp vi tc ti
ca cc phim video . Gia nhiu cach tip cn nhom khac nhau trong h thng
multicast nay thi qua thi gian nhom (batching-by-timeout) v kch thc nhm l hai
cch tip cn ph thng nht s dng cc chnh sch n gin . Mt s phng thc
nhm mi nh mang thch ng v nhm thch ng a c xut cho cac dich vu
theo yu cu thi gian . Ro rng, truyn dn quang ba se la hiu qua nht nu video la
rt ph bin . Tuy nhin nu tc ti cho video khng u thi mt s tai nguyn se bi
b ph v phng thc nhm se hiu qua hn.
1.3.5. Cc cng ngh cho ni dung in t (e-Content)
Mt cng ngh mi co hiu lc co nghia la mt cu thuc cua nganh cng nghip .
C thc ca thi i chng ta l kt qu ca hiu ng kt hp 3 cng ngh chnh:
X ly tin hiu: chuyn i cac tin hiu tng t thanh cac tin hiu s ;
Cng ngh thng tin: cho phep x l d liu dng s
Vin thng: cho phep truyn d liu s n/t bt ky ch nao trn th gii .
Ni dung s ti c cac khach hang cui goi la ni dung in t .
a/ X ly tin hiu s
Vo thp ky 80, Philips va Sony a gii thiu mt loai ia m nhac mi - Compact
Disc hoc CD hoc CD -Audio. Loi a ny s dng cc cng ng h quang-in t
cung cp m thanh cht lng trng quay ma khng thay i cht lng theo thi
gian. CD a la mt thit bi thanh cng va s lng u ia CD trn th gii a ln ti
hng trm triu b . Khng ging vi casset, cc khch hng thng thng khng th
copy tng bit cua CD ma chi co th sao chep u ra tng t .
18
Vo u nhng nm 1990, CD-ROM-mt thit bi ngoai vi cua may tinh khai thac
ky thut s tng t CD a tr thnh mt thit bi ph bin lu tr d liu may tinh
v cc chng trinh. Ti gia nhng nm 90, CD-ROM a tr thanh mt thit bi ngoai
vi tiu chun cho may tinh PC va sau o la cac CD co th ghi c , khi o hang triu
ngi s dung co th sao chep cac ia CD cua ho . ng thi cc cng ngh nen m
thanh-hinh nh a t c hon thin v c tiu chun ha . Hng triu CD video
c th xem phim hng gi trn mt a nh CD , cc u thu truy n hinh s va DVD -
mt th h mi cua CD co th lu tr cac b phim 2 gi cht lng cao . Cc thit b
ny a tha man c khch hng , cung cp cho khach hang cac thit bi ngay cang
nh hn vi nhiu chc nng hn v nhiu hinh anh, m thanh hn.
b/ Cc mng k thut s
Vo gia nhng nm 90, Internet a at c mc s dung m rng ti mi
trng giao duc/nghin cu/quc phong. Ngn ng HTML-mt tiu chun khun dang
trang vi kha nng i nh nghia ng dn a tao ra World Wide Web vi hang triu
trang vn ban vi hoa c siu lin kt va s dung may tinh co th truy cp c
bng cac trinh duyt . Mt s cng ty a b sung them mt s thng tin khac nh hinh
nh v m thanh . Tuy nhin tc bit thp co th s dung cho phn ln khach hang
(vi chc kbps) a lam giam cht lng m thanh va hinh anh .
c/ Chui gia tri
Cc m hinh kinh doanh ang pht trin khng ngng , i luc cho phep va i luc
biu hin s phat trin cua cng ngh . S dung in hinh hin nay cua WEB la
qung b sn phm hoc dch v.
Hinh I-6 m ta cac nhn t trong chui gia tri . Trung tm cua hinh ch ro 3 nhn t
chnh: nh cung cp ni dung , ngi ban le va thit bi cua ngi tiu dung . Ngoi ra
con c 4 nhn t na:
Cc dch v ti chnh: gii quyt cc giao dch gia 2 khi bt ky
Cc dch v th vin : cung cp thng tin ni dung va h tr khach hang tim
kim ni dung quan tm
Cc dch v cng ngh: yu cu biu din, s gn kt, phn phi, tiu dung ni
dung hoc d liu v ni dung
Cc dch v vn chuyn: chuyn ni dung gia nhng ngi s dung
19
Hnh I-6 Chui gia tri
Ni chung , c th ni rng c gia 2 khi co mt lung ni dung va d liu lin
quan ti ni dung : mt lung cac quyn s du ng, mt lung cac quyn cng ngh cho
phep mang v tiu th ni dung v mt lung ti chnh gii quyt chuyn giao cc
quyn ni dung va lin quan . Hn na , lut phap ong mt vai tro quan trong trong
cho phep va huy bo mt s chc nng cua mt s khi.
Ngoi ra con mt s cng ngh khc :
Biu din thng tin: MPEG-1, MPEG-2 v MPEG-4
M ta, nhn dang va bao v ni dung
1.4. Khung c s tiu chun hoa
Khi cac cng ngh mi a ra cac chc nng va hot ng tt hn thi nhu cu i
vi cac tiu chun ngay cang tr nn quan trong . Khng co cac tiu chun , cc dch v
thi gian thc se bi anh hng vi cac b ma hoa va giai ma khng th trao i thng
tin vi nhau. Cc dch v khng theo thi gian thc s dng cc dong bit lu tr cng
c th bt li hoc bi vi s khng sn sng ca cc nh cung cp dch v trong ma
ha ni dung ca h theo nhiu khun dng tha ma cc kh n ng ca khch hng
hoc bi vi s min cng cua khach hang khi phai cai t s lng ln cac b giai
ma.
S tiu chun hoa cac h thng truyn thng trc y c tao ra bi cac nganh
cng nghip theo s kt hp do c. a phng tin kt hp cac dang truyn thng khac
nhau yu cu mt cach tip cn mi -ngang hoc theo lp - pht trin cc tiu chun .
iu o co nghia mt s thay i cn ban v cach ma cac tiu chun c tao ra . S
tng cng bng thng cho cac khach hang cui cung gy ra s thay i v vai tro cua
quyn lc cng cng trong iu chinh s dung cng ngh cung cp dich vu .
C nhiu nh ngha v tiu chun ha . Chng ta c th nh ngh a l qu trinh
cc c nhn nhn bit c u im ca cng vic ang lm nhng th xc nh theo
mt cach ng thun va soan thanh lut l rng thoa thun bng mt hp ng . Ngc
li chng ta tha hip gia ci chng ta mun lm v ci ngi khc mun lm . Mc
20
d n rng buc t do ca chng ta , nhng chung ta vn thng tham gia vao nh mt
tha thun bi vi cc u im vt tri cc nhc im .
Cc bc thc t sau y nn c thc hin co kt qua mong mun:
Chn cc ng dng mc tiu
Lit k cac chc nng cn thit cho tng ng dung
Chia nho cac chc nng thanh cac thanh phn co phc giam xung u
c th nhn dng trong cc ng dng khc
Nhn dang cac thanh phn chung trong h thng quan tm
Kim tra cac cng cu nay co th c s dung lp rap cac h thng muc
tiu va cung cp cac chc nng mong mun .
1.4.1. Cc tiu chun m thanh/hnh nh s v cng nghip a phng tin
Cc dch v nghe nhin cung cp truyn thng thi gian thc ca m thanh cng
vi thng tin hinh anh gia hai hoc nhiu khach hang cui . Thng tin nhin la cac anh
chuyn ng thng hng , nhng co th la anh tinh , hoa hoc dang bt ky khac .
ITU-T SG15 a tiu chun hoa cac h thng truyn thng nghe nhin trong nhiu mi
trng mang khac nhau.
B tiu chun u tin la cac khuyn nghi cua ITU -T a c thit lp chnh thc
vo thng 12/1990 cho ISDN bng hep:
Knh B: 64kbps
Knh H0: 384 kbps
V knh H11/H12: 1536/1920kbps
Khuyn nghi H.320 m ta toam b h thng va quy inh mt s khuyn nghi khac
cho cac thanh phn tng ng cua h thng cn tun thu nh:
Ma ha m thanh
Ma ha hinh nh
Ghep a phng tin
iu khin h thng
Cc ng dng mc tiu chnh l hi ngh truyn hinh , in thoai co hinh , sau o
m rng an ninh va kt ni a im cho h thng ISDN bng hep a c nghin cu.
Song song vi hoat ng tiu chun hoa nay , cc hot ng tiu chun ha mi a
c bt u vao thang 7/1990 cho bng rng va cac h thng nghe nhin cht lng
cao. Cng vic nghin cu a thanh cng vi khuyn nghi H .261. Nhm nghin cu
mi nay ban u co trach nhim vi ma hoa video cho ch chuyn giao ng b
(ATM) v hp tc vi ISO/IEC JTC/SC29/WG1 (MPEG).
Thnh cng ca MPEG da trn s ln g cac phn t ng thi . Quan trong nht
l c th nh thi im thit lp . MPEG a xut hin vao thi im khi cac thut toan
m thanh va hinh anh a at ti tim cn , v kh nng ca x l tn hiu s a thoa
21
man phc tap cua thut toan . MPEG cung thanh cng trong gianh c cac thanh
vin tham gia la tt ca cac nha cng nghip , nhng ngi ang oi hoi hi tu . Nh s
quan tm cua cac nha cng nghip i vi MPEG trong cac ng dung m thanh va
hinh nh s, MPEG tham gia vao lp trinh din nghe nhin va hoan toan c lp vi lp
truyn tai . Mt thanh phn cui cung thanh cng la cac b giai ma thay cho cach tip
cn b ma hoa -b giai ma thng th ng. Do o , MPEG co th cung cp giai phap
chun cho nhng ngi tham gia chinh , h a xem xet vic s dng ma ha m thanh
v hinh nh s cho cc sn phm ca th trng mi rng ln .
i vi cng nghip a phng tin c 2 t chc tiu chun chinh la ITU va ISO .
Cc tiu chun ma ha hinh nh hin nay a c 2 t chc nay inh nghia . Cc tiu
chun nay khac nhau chu yu tc bit theo cac ng dung . Tt ca cac tiu chun co
th c s dng ch yu cho cc ng dng c khong tc bit ln . Theo cac thut
ton ma ha, tt ca cac tiu chun u theo mt khung c s tng t nhau .
1.4.2. Cc tiu chun ca ITU-T cho cac h thng truyn thng nghe nhin.
H thng PSTN a c mt nhom chuyn gia cua nghin cu ma hoa tc bit
thp. H a a ra khng ch khuyn ngh H .324 cho toan b h thng , m c khuyn
ngh ma ha video H .263, khuyn nghi ma hoa m thanh G .723.1 v nh ngha
phng thc ghep knh trong khuyn nghi H .223. Mt m hinh ngn xp giao thc
chung cua cac thit bi u cui nghe nhin theo Seri H c chi ra trong Hinh I-7.
Hnh I-7 Ngn xp giao thc chung cua cac thit bi u cui nghe nhin
a/ Tiu chun ITU-T H.320
Theo tt ca cac tiu chun cua ITU , lin kt theo tiu chun H .320 l bt buc .
Lin kt nay co c qua mt gateway . Trong mt s trng hp, gateway phai thc
hin cac giao dich gia cac giao thc bao hiu khac nhau , cc tiu chun nen khc
22
nhau va cac phng thc ghep khac nhau . Nhng bin i cua bao hiu , nen v ghep
knh la do cac c im kh c nhau ca cc mng c s m mi tiu chun p dng .
Tiu chun H .320 inh nghia mt may chu hi nghi trung tm goi la MCU (Khi iu
khin a im) cho phep nhiu cuc goi ng thi.
b/ Tiu chun ITU-T H.310 v H.321
Hai khuyn nghi nay cho cac h thng nghe nhin trong mi trng ATM :
H.321-Thch ng cc thit b u cui in thoi c hinh H .320 vi mi
trng ISDN bng rng.
H.310-Cc h thng truyn thng nghe nhin bng rng .
c/ Tiu chun ITU-T H.322
Khuyn nghi nay bao trum lp t cac mang LAn va cac thit bi hi nghi in
thoi c hinh v thit b hi ngh truyn hinh , tng ng nh khuyn nghi H .320
cho NISDN.
d/ Tiu chun ITU-T H.323 Standard.
Khuyn nghi na y xac inh thit bi va cac h thng cho in thoai c hinh trn
mng LAN c QoS khng c m bo.
Cc xem xet thit k trong pht trin ca H.323 nh sau:
Lin kt, c bit vi NISDN va H.320
iu khin truy cp LAN trnh tc ngn
Cc m hinh a cuc gi
Kh nng m rng t cc mng nh ti cc mng c kch thc trung binh
1.4.3. Cc tiu chun ma ha hnh nh
C 2 cch tip cn hiu cc tiu chun ma ha hinh nh (H.261, H.263 v
H.26L)
Mt cach tip cn la tp trung vao cu truc dong bit va cn nm c mi
lp cu truc biu din cai gi va mi bit trong dong bit chi thi cai gi . Cch tip
cn nay rt quan trong i vi cac nha san xut vi cc sn phm ca h phi
tun thu tiu chun.
Cch tip cn khc l tp trung vo cc thut ton ma ha c th s dng
to ra cc dong bit tun th tiu chun v cn nm c thnh phn no khng
xc nh cc th ut toan ma hoa . Cch tip cn ny cung cp hiu bit su hn
v cac ky thut ma hoa hinh anh .
a/ Tiu chun ITU-T H.261
Tiu chun nay inh nghia cac ng dung hi nghi truyn hinh va in thoai co
hinh. H.261 nhn manh c c tc bt thp v tr ma ha thp . Thut toan ma hoa s
dng trong H .261 c ban la mt lai ghep cua bu chuyn ng loai bo cac d tha
23
tm thi v chuyn i ma ha gim d tha khong trng . Do o H .261 c nh
hng rt quan trong ti cac tiu chun ma hoa ang co va ang phat trin .
b/ Tiu chun ITU-T H.263
Trong sut qua trinh phat trin cua H.263:
Mc tiu ngn han l m rng H.261 s dng khung chung
Mc tiu di hn l thit k mt tiu chun ma ha hinh nh c th khc c
bn vi H.261 c c hiu qu ma ha cao hn .
Vi cc hot ng tiu chun ha din ra rt di , nhng n lc ngn han tao ra
H.263 v H .263 version 2, trong khi n lc dai han c xem nh la H .26L/H.264.
Thc cht H .263 kt hp cac yu t cua H .261 cng vi MPEG v c ti u cc
tc bit rt thp.
Thc t, H.263 cung cp hiu qua ma hoa cao hn so vi H .261 tt c cc tc
bit. Vi H.263 a c xy dng trn H .261 nn cu truc chinh cua 2 tiu chun thc
cht tng t nhau. Cc khc bit chnh bao gm:
H.263 h tr nhiu khun dang anh hn
H.263 s dung bu chuyn ng na im nh (half-pel), nhng khng s dung
lc nh trong H.261.
H.263 s dung 3D VLC cho h s ma hoa DCT ngoai thut toan ma hoa c
bn, 4 la chon trong H .263 l m phn gia b ma ha v gii ma cung
cp cht lng cao hn.
H.263 cho phep kich thc bc lng t thay i mi khi ln
(Macroblock-MB) vi tiu nho.
Mt khac bit chinh gia H .261 v H.263 l d bo na im nh trong b chuyn
ng. Khi nim ny cng c s dng trong MPEG.
c/ Tiu chun H.264/AVC
Mc du H.264 c da trn khung c s chuyn i d bao bu chuyn ng theo
khi thng thng trong H .261, H.262, H.263, nhng nhng thay i quan trong nh
lc vong , chuyn i nguyn (4x4) v chuyn i ngc , d bao khng gian hng
cho d bao bu chuyn ng anh tham chiu ma ha trong anh , nhiu anh (ln ti 5),
ma ha di thay i
H.264 c hng ti mt dai rng tc bit rng (64kbps n 240Mbps), di
rng cc mc cht lng v cc phn gii theo thi gian thc , tr end-to-end thp
cho nhiu dang ngun khac nhau . Tiu chun nay co th c ap dung cho dong
video, truyn hinh quang ba , cc dch v i thoi Tt c cc y u t ny v li
ma ha l chi ph ca phc tp ngy cng tng . Trong khi ma hoa chinh (dong bit
c ma hoa thc s ) a c tiu chun hoa , cc phn khc nh cc dong bit tun
24
th, phn mm tham chiu , khun dang 4:4:4, su bit tng cng (ln ti 12bpp),
kim tra, giy phep s hu ang c phat trin nhng giai oan khac nhau .
1.4.4. Cc tiu chun ma ha m thanh
ITU a tiu chun hoa 3 b ma hoa 3 tiu chun m thanh c th p d ng cho
truyn thng a phng tin tc thp .
Khuyn nghi G .729 8 kbps CD -ACELP co tr b codec thut toan 15ms va
cung cap m thanh cht lng mang . B ma hoa nay c thits k cho cac
ng dng v tuyn nhng cng c th p dung cho truyn thng a phng
tin.
Khuyn nghi G .723.1: b ma hoa m thanh 6,3 v 5,3 kbps cho truyn thng
a phng tin a c thit k cho in thoai co hinh tc bit thp . Kch
thc khung 30ms va tr codec thut t on 1 chiu 37,5ms cho phep giam tc
bit so vi G.729.
1.4.5. Cc tiu chun ng b v ghep a phng tin
Cc dong s cp theo khuyn ngh ITU -T H.222 nh m thanh , hinh nh, d liu,
iu khin ng b khung hinh anh va cac ti n hiu chi thi , mi loai co th c tiu
chun hoa quc t hoc tiu chun ring . Cc dong s cp ny c ghep thnh mt
dong gi ni tip theo cc chc nng ca H .222.0, H.222.1/H.222.1. Cc chc nng
ny bao gm khi p hc c s thi gian ghep , ng b thit bi , loi b dch (trt),
qun l b m , an ninh va iu khin truy cp , bo hiu knh con v cc ch
trick (mo) l cc c ch h tr chc nng iu khin tng t ghi hinh . Khuyn
ngh H.222.1 xc nh cc phn t v cc th tc t H .222.0 s dng chng trong
cc mi trng ATM v cng xc nh cc im ma v th tc cheo cc dong s cp
theo inh nghia cua ITU -T. H.222.1 cho phep s d ng c hai dong chng trinh
H.222.0 v dong truyn ti H .222.
a/ Khuyn nghi H.221 ca ITU-T
Khuyn nghi nay quy inh cu truc khung knh 64-1920kbps trong cac dich vu
nghe nhin. H.221 l giao thc ghep v ni cho cc thit b u cui H.320. C th ghep
ti 30 knh B tao thanh mt siu knh vi tc bit la nx 64 kbps. Cc knh thng
tin cho thng tin m thanh va hinh anh khng thc hin iu khin li m da hoan
ton vo kh nng sa li ca ma ha thng tin.
b/ Khuyn nghi ITU-T H.223.
Khuyn nghi nay quy inh giao thc ghep dung cho truyn thng a phng tin
tc bit thp . C th s dng 3 kiu lp thich ng (AL), cc lp khc nhau tnh cht
xc sut li v tr. AL1 v AL2 phc v cc nhim v khc nhau con AL 3 c thit
k s dung ma hoa video.
25
c/ Khuyn nghi ITU-T H.225.
Khuyn nghi H .225.0 m ta cac phng tin kt hp , ma ha v ng gi m
thanh, hinh nh , d liu v iu khin truyn ti gia cc thit b u cui H .323
trn cac LAN khng am bao QoS , hoc gia cac thit bi u cui H .323 v cc
gateways H .323. Cc gateway H .323 c th kt ni ti cc thit b u cui H .320,
H.324 hoc H .310/H.321 trn cac mang tng ng NISDN , PSTN hoc BISDN . Cu
hinh thit b u cui gateway ny v cc th tc c m t trong H .323 v H .225
bao trum cac giao thc va khun dang ban tin . Phm vi ca truyn thng H .225 l gia
cc thit b u cui H .323 v cc gateway H .323 trn cung LAN bng cung giao thc
truyn tai.
d/ Giao thc iu khin chung H.245.
Khuyn nghi nay inh nghia cac ban tin va cac thu tuc trao i thng tin iu
khin gia cac thit bi u cui a phng tin . H.245 xc nh bo hiu thit b u
cui-ti-thit bi u cui xac inh cac kha nng ma hoa va giai ma cua thit bi u
cui xa sau khi thit lp kt ni mang va iu phi n nh v gii phng cc ti
nguyn thit bi u cui qua cuc goi .
H.245 a c inh nghia nh la cac khuyn nghi chung phu hp vi s dung cho
mt dai cac ng dung thit bi u cui a phng tin . H.245 a c cu truc bng 3
phn chinh : c phep , ng nghia va cac thu tuc (syntax, semantics, and procedures ).
Tng tac gia cac thc th giao thc khac nhau chi qua truyn thng vi ngi s
dng H.245. H.245 cung cp nhiu dch v khc nhau cho ngi s dng H .245. Mt
s dich vu la trao i kha nng , cc th tc bo hiu knh logic , cc tn hiu iu
khin va chi thi.
1.4.6. Cc tiu chun MPEG trong truyn thng a phng tin
S thanh cng cua MPEG da trn nhiu thanh phn ng thi . Quan trong nht la
thi im ma MPEG a c thit lp . V tn goi MPEG a xut hin vao thi im
khi cac thut toan ma hoa m thanh va hinh anh a at ti cht lng tim cn . MPEG
cng a thnh cng trong quy nh s tham gia cua t t ca cac nganh cng nghip (c
xu hng hi tu trong cac ng dung m thanh va hinh anh ). MPEG a ong gop vao
s chp thun thc t cua lp biu din nghe nhin , lp ny c lp vi h thng vn
chuyn. Thnh phn thnh cng cui cng tp trung trn cc b gii ma thay cho cch
tip cn b ma hoa -b giai ma truyn thng . Do o MPEG co th cung cp giai phap
tiu chun cho nhng ngi chi -l nhng ngi ang cn nhc s dng ma ha s
cho m thanh va hinh anh cho cac san phm i mi co thi phn ln , ng thi MPEG
c th cho phep t c nhanh hn l khng c n .
Mi mt tiu chun MPEG bt u bng nhn dng phm vi v pht hnh mt
Mi tham gia xut (Call for Proposals), sau o i vao 2 giai oan chinh:
26
Giai oan th nht la giai oan canh tranh lin quan ti kim th va anh gia
cc xut sng gi chn ra mt vi xut cao nht , sau o cac thanh
phn cua xut nay la c s bt u cua giai oan 2
Giai oan 2 gm phat trin hp tac cac thanh phn (giai oan 1) qua qua trinh
sng lc tng tc ca m hinh th nghim (m ta ma hoa ). Khun dang cua
d liu biu din c xem nh cu truc va co th da vao xy dng cac
dng khc nhau ca cc dong d liu (dong bit) hp l. Cc quy tc dch d
liu (dong bit) c goi l qu trinh gii ma . Khi a ra nen d liu m thanh
v/hoc hinh anh , mt b ma hoa phai tun theo mt qua trinh cac bc tun
t goi la qua trinh ma hoa . Tuy nhin qua trinh ma hoa nay khng c tiu
chun hoa va thay i vi cac b ma hoa co phc tap khac nhau co th c
s dung cho cac ng dung khac nhau . Ch c rng buc l u ra ca qu trinh
ma ha l dong bit ra chun v cu trc c th dch c theo ng ngh a
gii ma ca cc cc b gii ma tun th tiu chun .
a/ Tiu chun MPEG-1
MPEG-1 l tiu chun lu tr v khi phc cc nahr ng v m thanh trong mi
trng lu tr s . inh hng ban u cho tiu chun MPEG -1 l m thanh v hi nh
nh c cht lng tt khong 1,4Mbps cho ng dung ia CD . Cc yu cu c bn
bao gm:
Ma ha hinh nh vi cht lng tt 1 n 1,5 Mbps va m thanh vi cht
lng tt 128-256 kbps
Truy cp ngu nhin ti mt khung trong thi gian han ch
Kh nng chuyn tip nhanh v o li nhanh , cho phep tim kim va xem xui
ngc mt s ln vi tc thng thng
Mt h thng chi lai (playback) c ng b va truy cp ti d liu nghe
nhin
Bn canh cac yu cu co trc , s lng cac yu cu khac cung tng ln nh h
tr nhiu phn giai anh , s vng chc i vi li , cn bng cht lng ma hoa vi
tr ma hoa (t 150ms n 1s), v kh nng ca cc b ma ha thi gian thc vi chi
ph hp l. Tiu chun MPEG-1 bao gm cac phn sau : H thng, hinh nh, m thanh,
tun thu va phn mm.
Phn m thanh cua tiu chun MPEG -1 a tr thanh thanh phn chinh cho phat
thanh quang b lp 2 m thanh MPEG 1 vi cht lng CD . Lp III a tr thanh
khun mu tiu chun cho phn phi m nhac trn veb . Tiu chun MPEG -1 y u
(Cc h thng m thanh -hinh nh) l khun dng tiu chun cho phn phi cc chi tit
hinh nh chuyn ng qua Web.
27
MPEG-1 a cung cp c hi vng chc u tin cho cng nghip vi in t u
t vao cng ngh hinh anh s . Hin nay cac chip giai ma MPEG -1 c san xut t
nhiu ngun , mt s trong o kt hp vi cac nha in t oc cac bit t CD . Cc
thit bi va s lng ngay cang tng cua cac may tinh ca nhn ang tao ra cac iu kin
ph bin sn xut ni dung a phng tin.
b/ Tiu chun MPEG-2
Tiu chun MPEG -2 a c thit k cung cp kh nng nen , ma ha v pht
cht lng cao , pht cc tn hiu a phng tin a knh qua qung b mt t , phn
phi qua v tinh va cac mang bng rng . Tiu chun MPEG -2 xc nh cc yu cu
i vi ma hoa hinh anh , ma ha m thanh v ma ha cc h thng tng hp m
thanh va hinh anh a ma hoa thanh cac dong d liu ring do ngi s dung inh
ngha, kim tra tun thu kim tra cac dong bit va b gia i ma o co thoa man cac yu
cu hay khng va m phong phn mm cho ma hoa va giai ma ca hai chng trinh va
dong truyn ti. L mt tiu chun truyn dn , MPEG-2 h tr nhiu dang khun dang
gi khc nhau bao gm cc g i ln co dai thay i t 1 n 64 kbp. ng thi
MPEG-2 cng cung cp kh nng sa li ph hp vi truyn dn qua TV cp v cc
knh v tinh. Tiu chun MPEG-2 bao gm cac phn sau:
Cc h thng, hinh nh, m thanh
Tun th, phn mm,
Thit bi, lnh va iu khin lu tr s (DSM-CC)
Ma ha n thanh tin tin (AAC), hinh nh 10 bit, giao din thi gian thc,
Tun thu cua DSM-CC
c/ Tiu chun MPEG-4
MPEG-4 l tiu chun cho cc ng dng a phng t in. Tiu chun nay hng
ti video cho Internet va Intranet , video v tuyn , mua ban tng tac , th in t hinh
nh v ph im anh nha , cc tro chi , m phong va hun luyn cac c s i tng
thng tin. Vi cc vng ng dn g nay co mt s yu cu chinh da trn s h tr cua
cc tiu chun trc y, nn MPEG-4 xc nh cc chc nng sau:
Tng tac da trn ni dung
Kh nng truy cp ton cu
Ci thin nen
Tiu chun MPEG -4 bao gm cac phn sa u: Cc h thng , m thanh , hinh nh ,
tun thu, phn mm va khung c s vn chuyn a phng tin .
Kin truc khai nim cua MPEG -4 bao gm 3 lp: lp nen, lp ng b va lp vn
chuyn:
Lp nen la hiu thng tin va khng hiu vn chuyn
Lp ng b la khng hiu thng tin va khng hiu vn chuyn
28
Lp vn chuyn khng hiu thng tin va hiu vn chuyn
Thit k cua MPEG -4 c tp trung quanh mt khi ni dung c s goi la i
tng nghe nhin (AVO). Mi AVO c biu din tach ring va tr thanh c s cho
mt dong c lp.
d/ Tiu chun MPEG-7
MPEG-7 l tiu chun biu din ni dung cho tim kim , lc, qun l v x l
thng tin a phng tin . Mt muc tiu cua MPEG -7 l cho phep tim kim a
phng tin trn Internet va nng cao trang thai hin tai bng cac giai phep hp ly la
tiu chun hoa mt giao din cho cac b m ta va cac phng thc m ta -cc phng
thc nay kt hp vi ni dung thoa ma tim kim nhanh va hiu qua . Nh vy ni
dung nghe nhin vi metadata MPEG -7 c th d dng c nh ch s v d dng
c tim kim . MPEG-7 hng ti xac inh khng chi tim ni dung quan tm trong
cc ng dng keo (pull application) nh la khi phuc c s d liu ma ca trong cac
ng dng y (push applications) nh la chon va loc trich ni dung quan tm tr0ong
cc knh qung b. Ngi ta ky vong MPEG -7 s lm vic khng ch vi cac ni dung
ma ha theo MPEG m c cc ni dung c ma ha khng phi MPEG .
S lng ln cua cac vung ng dung truyn thng cung nh ang ni ln khai thac
tim kim v khi phc m MPEG-7 c th p dng l:
Cc s kin quan trng-Lch s, chnh tr
Gio dc-khoa hoc, y t va ia ly
Thng mai-t ai, ti chnh, kin truc
Xa hi v gii tr-dch v hng ngy, cc tro chi tng tc
Thi gian ri-Th thao, mua sm, du lich
Lut php-thm tra ti pham va (tim kim ) cc c nhn mt tich
B m ta MPEG -7 m ta cac dang thng tin a phng tin khac nhau . S m ta
ny s c kt hp vi ni dung ca n cho phep tim kim cc chi tit nhanh hn
v hiu qu . Chi tit nghe nhin co d liu MPEG -7 lin quan ti no co th c anh
ch s v tim kim . Chi tit nay nay co th bao gm cac anh tinh , cc ha , cc m
hinh 3D, m thanh, ging ni, hinh nh v thng ti n v cac phn t nay c kt hp
nh th nao trong mt trinh din a phng tin . Cc trng hp c bit ca cc cc
kiu d liu chung co th bao gm ca m ta khun mt va cac c im cua ngi .
Mc du MPEG -7 khng tiu chun hoa vic trich thuc tinh nhng s m ta
MPEG-7 c da trn u ra cua qua trinh trich thuc tinh va mc du MPEG -7
khng tiu chun hoa search engine nhng m ta kt qua c search engine s dung .
e/ Khung c s a phng tin MPEG-21
Cc mc tiu ca MPEG-21 nh sau;
29
Phi hiu c nu cc thnh phn khc nhau ph hp vi nhau v ph hp
nh th nao
Phi bn lun cn thit cc tiu chun mi no , nu cac khoang trng trong ha
tng con tn ti v khi hai im trn a tin ti c
Phi thc hin lin kt cc tiu chun khac nhau
D an MPEG-21 a bt u vi muc tiu cho phep s dung trong sut va s dung
tng them cac ngun a phng tin qua nhiu mng v thit b . Nghin cu a thc
hin uwocj nhn dang mt s cng ngh cn thit at c muc tiu MPEG -21,
bao gm:
Khai bao hang muc s
Biu din ni dung -d liu c biu din nh th nao vi cac thit bi k hc
nhau
Qun l v s dng ni dung -ci ddawtj cc giao din , giao thc cho phep tao
ra, thao tac , tim kim , truy cp , lu tr , vn chuyn va s dung (s dung lai )
ni dung
Qun l v bo v s hu tr tu -phng tin cho phep ni dung c quan ly ,
bo v lin tc v tin cy qua cc mng v dch v khc nhau .
Cc thit b u cui v mng -kh nng cung cp truy cp lin kt v trong
sut ti ni dung qua cac mang va cai t thit b u cui.
Bo co s kin -cc n v v cc giao din cho phep ngi s dugnj hiu
chnh xc hot ng ca tt c cc s kin a bo co trong khung c s .
f/ Cc tiu chun ma ha nh tinh
Cng vi vic s dng ng y cang tng cac h thng truyn thng a phng tin ,
nen nh yu cu cht lng ngy cng cao hn v yu cu nhiu thuc tnh mi . Nen
nh khng ch phi gim c yu cu lu tr v bng thng , m con phi cho phep
trch son tho , x ly va hng ti cac thit bi v ng dng c th . Cc tiu chun
sau y a c quan tm nghin cu la MPEG -4 VTC, JPEG, JPEG-LS, PNG,
JPEG2000.
1.5. Kt lun
Chng I trinh bay tng quan cac vn lin quan ti truyn thng a phng
tin, s hi tu cua vin thng va quang ba la ng lc cho s phat trin truyn thng
a phng tin . Vai tro cua cac t chc tiu chuan quc t trong cac linh vc khac
nhau cua truyn thng a phng tin cung c cp.
30
CHNG II
KHUNG C S TIU CHUN HOA MULTIMEDIA
S tiu chun hoa toan cu ang ngay cang tr nn quan trong hn trong at c
mt ha tng thng tin toan cu (GII). Cc t chc tiu chun ha vin thng v thng
tin nh ITU va ISO /IEC, mi t chc a thanh lp cac nhom c bit tp trung vao
xc nh cc tiu chun cho GII . Chng nay tim kim cac hoat ng cua cac t chc
lin quan ti GII . ng thi tng kt li hi n trng ca cc tiu chun truyn thng a
phng tin. Nhng thanh t chinh hng ti trin khai GII c m ta . IETF la mt
t chc tiu chun tp trung vao phat trin cac giao thc s dung trn mang IP . IETF
bao gm nhi u nhom nghin cu va c quan ly bi nhom Internet Engineering
Steering Group, Internet Architecture Board , v Internet Society . Ni dung chng
cng cp ti qu trinh tiu chun ha ca ETSI i vi ng dng , phn sun va
mng.
Ngoi cc t chc tiu chun ny , cc din n cng nghip tham gia vao nghin
cu xy dng tiu chun bao gm:
Telecommunication Information Network Architecture (TINA),
International Multimedia Telecommunications Consortium (IMTC),
MPEG-4 Industry Forum (M4IF),
Internet Streaming Media Alliance (ISMA),
Third Generation Part- nership Project (3GPP/3GPP2),
Digital Video Broadcasting (DVB),
Digital Audio
2.1. Gii thiu
Nhiu nm v trc, chun ha trong vin thng l lnh vc hot ng ca cc t
chc chun ha nh lin minh vin thng quc t (ITU), t chc chun ha quc t
(ISO), y ban k thut in quc t (IEC), y ban k thut lin hp 1(JTC1). By gi,
cc hot ng ny cng ang c trin khai bi cc hi ng(nhm) chun ha khu
vc nh vin cc tiu chun vin thng Chu u (ETSI), y ban T1, y ban cng ngh
vin thng (TTC). S phi hp gia cc nhm ny rt quan trng m bo rng cc
ngun ti nguyn khng lang ph trong vic t c mc ch cui cng l cc tiu
chun ton cu.
Nm 1989, cc hot ng phi hp ny c bt u vi s thnh lp ca hi cc
chun vin thng quc t(ITSC). Nm 1994, ITSC c t chc li thnh nhm phi
hp cc tiu chun ton cu (GSC) v tip tc cc cng vic ca minh. Trong cc lnh
vc c quan tm nhiu nh phng thc truyn ti khng ng b (ATM) v a
phng tin, cc din n v cc t chc a c thnh lp v nhanh chng t c
nhng thnh tu trong cc mc tiu ca minh. Do , cc t chc chun ha quc t
31
ang kin thit li chnh minh c th m nhn nhng cng vic mt cch nhanh
chng.
T do trong vin thng a m ra mt th trng cnh tranh trong v ngoi nc
trong nhng nm gia 1980 My, Chu u, v Chu , cng vi cc k thut tin tin
trong truyn thng s, thng tin di ng v cc h thng nh v ton cu a lm thay
i nn kinh t xa hi v cc mi trng k thut. Cc k thut v nn cng nghip vin
thng, thng tin, gii tr, in t dn dng ang hi t thng qua s ha v mang n
cc ng dng a phng tin trong cc lnh vc ny. Trong cc mi trng mi nh
vy thi cc chun ang c pht trin bi cc t chc v cc nhm tr nn ngy cng
quan trng. Thng thng cc chun cng nghip c pht trin rt nhp nhng. Cc
t chc chun ha nh ITU-T, ISO/IEC, v JTC1 oi hi phi hot ng nhanh hn.
C s h tng thng tin ton cu(GII) l im mu cht trong hi t cng ngh v
cc ngnh cng nghip, v s cung cp a dng cc dch v a phng tin. Lin kt
v hp tc ton cu l mt trong nhng tiu ch chnh ca GII v oi hi cc chun
ton cu. Nm 1994, ETSI, y ban T1 v TTC ca Nht Bn a thnh lp mt y ban
c bit cho vic nghin cu cc kha cnh ca cc chun v truyn thng a phng
tin v GII. Nm 1995, ITU-T to ra nhm cc bo co vin lin on trong GII(JRG-
GII). Nm 1996, ISO/IEC, JTC1 a to lp mt nhm hot ng c bit trong GII
(SWG-GII). Cng vi l m a c nhiu nhng hot ng chung lin quan ti cc
chun GII cho vic xc lp nhng vn bao trm v thit lp mi quan h hi hoa
gia cc t chc cho chun quc t, vng v khu vc.
Truyn thng a phng tin bao gm nhiu cc cng ngh vin thng, x l
thng tin, v pht thanh. Cng ngh thng tin gii quyt cc qu trinh nh tng hp,
vn chuyn, thu hi, lu tr, trinh by v bin i tn hiu thnh nhiu dng. Trong
nhng dng ny bao gm thoi, ting ni, video, ha, vn bn, hinh nh, d liu v
s kt hp gia chng, trong khi nhng ngi s dng u cui ti pha thu c th l
ngi s dng, my mc hoc kt hp c hai. Vi th chun ha vin thng v IT cn
phi c m rng xa hn trong tng lai v nhng mi quan tm n vn qun l.
Nhng ngi sn xut c gng cn bng vi nhng chun cn thit bo v th
trng ca h. Cc nh cung cp dch v cng c gng gim gi thnh sn phm a
chun ha. Trong nhng gi sau y chng ta s c gng bao qut nhng kha cnh k
thut v kinh t xa hi ca nhng chun v vic qun l cc chun. Chng ta cng s
miu t nhng quan im v nhng im ni bt trong qu trinh a ra cc chun, lm
cho chng tng thch, ro rng
2.2. Cc hot ng tiu chun ha.
Cc chun nhm duy tri nhng tng thch trong mi trng a phng tin ngy
cng phc tp. Thnh cng trong vic chun ha oi hi s hiu bit v mi trng
32
trong n c tin hnh. S pht trin ca cc h thng thng tin nh in thoi di
ng, internet, multimedia.. oi hi nhng hp ng c bit gia cc bn lin quan:
nh sn xut thit b, vn hnh mng, nh cung cp dch v, ngi s dng u cui.
Nhiu cc h thng mi hng ti s hp nht cc phn t t cc cng ngh vin
thng, x l thng tin v cng ngh pht thanh. Ngy nay, i a s cc chun c
lm trong, thi thong lm trc qu trinh thit k sn phm. Kt qu l khng nhng
c nhiu k thut cn thit m thi gian hon thnh mi sn phm cng nhanh hn.
iu ny trc tin lm gia tng cc nhm chun khu vc v quc gia, sau lm tng
s lng cc congxoocxiom. Tuy nhin, chun ha oi hi thi gian v nhng ti
nguyn hiu nhng ci gi thc s cn c chun ha v lm th no thnh tu
t c phi hi hoa gia cc quyn li i lp. S thnh cng trong vic truyn ti
kin thc t nghin cu cho n qu trinh ng dng vo thc hnh lun lun oi hi
nhng cuc th nghim. Nu chun ni n cc khi nim mi, thi cn phi b i cc
kha cnh khng ro rng lc u.
Nhng nhn t chin lc l nhng l do yu cu mt chun, giao din c
chun ha, v thi gian tiu chun ha. Mt khc, vic xem xet cc chin thut lin
quan ti nhng cu hi sau: chun ha s din ra nh th no? Ai s ch o hot ng
chun ha? V cc chun s c s dng u.
2.2.1. Nhng li do tim kim mt tiu chun .
Chun ha l mt quyt nh kh khn. Trong trng hp nhng cng ngh a
c xem xet cn thn, mt t chc thng mi s chp nhn v s dng cc chun
nu chng gip h m rng th trng. Tuy nhin chun ha cng l cch gip
cc t chc mi trong th trng gm nhng cng ty c u th vt tri hn. Chun
ha cng gip hp php ha cc cng ngh mi v cho phep cc t chc s dng cc
cng ngh ny chim c v tr trung tm. V pha ngi dung, cc chun m
tnh sn c ca ca mt thit b, thnh phn t mt vi ngun, c bit l chng cho
phep ta s dng ln cc sn phm t nhiu nh cung cp.
Quyt nh khng chun ha cng cha 2 n . Nhng nh sn xut c l mun
minh l ngi duy nht iu khin c thi trng . S khn cp tiu chun ha
ngh rng nhng sn phm v nhng ngi tiu dng theo ui s n nh sut thi ki
di. V d, th trng ton cu cho nhng th thng minh trong thng mi in t oi
hi mt chui cc chun cho cc h thng vn hnh, nhu cu, cc giao din..
khuyn khch s pht trin ca cc ng dng.
2.2.2. Nhng giao din c tiu chun ha.
Hinh II-1 minh ha nhng giao din c t chc trong tng lp khun dng.
Chng gm cc chun cho tham chiu, tng ng, tng thch v linh hot. Thm
vo , nhng chun cho thi hnh v cht lng c th tt c cc tng.
33
Nhng chun tham chiu cung cp cc thit b o lng m t nhng thc th
thng thng bng nhng b tham chiu. V d in hinh l nhng chun n v cho
cc n v o lng vt l (Ohm, volt, watt, dBm). V d khc trong lnh vc cng
ngh thng tin v vin thng l b k t ASCII tiu chun ha cc ngn ng my bc
cao, m hinh kt ni cc h thng m, v k hoch a ch ha cho cc dch v thoi
v internet quc t.
Nhng chun tng ng vch ro nhng kha cnh phi ng nht c hai pha
ca ng truyn tin cng nh nhng s thay i hoc dung sai cho phep nu c. S
tng ng cn thit thit lp thnh cng kt ni. Nhng v d gm c nhng tiu
chun thng thng ca cc mc tn hiu, hinh dng nhng xung hin ti, thut ton
ma ha ngun cho ting ni v video tng tc, thut ton mt ma v cc h thng vn
hnh my tnh.
Nhng chun tng thch phi hp cc lung sinh ra bn truyn v bn nhn
pha cui bn kia. Nhng chun ny c lin quan ti cc cu hinh, cc chun chc
nng, cc mu giao din, cc hp ng ngi s dng. Cc cu hinh, chun chc nng,
cc mu giao din xc nh mt tp hp cc la chn c nh thi hnh cc dch v
c a ra. V d nh nhng chun kin trc ch ra nhng cch sp xp c th ca
cc thnh phn v nhng khi kin trc thc hin mt chc nng c bit cc bn
lin quan. Mt v d khc bao gm cc giao thc giao din xc nh cc khi chung
ca bn pht v bn thu phi m bo s thnh cng trong giao tip mc d c hai bn
khng phi ng nht.
Hnh II-1 Cc tiu chun k thut vi kin trc phn lp
34
Nhng tiu chun linh hot ch trng vo s tng thch cc tnh hn tp, kh
nng ca mt bn n so vi cc nhm khc vi nhng h thng khc nhau, v chiu
hng ln xung ca n. V d nh m phn gia cc nh sn xut s dng khuyn
ngh ca ITU-T v modem cho phep s thay i ca d liu ngi dng vi nhng
modem trc thng qua nhng quy tc chung.
2.2.3. Thi gian tiu chun ha
C hai kiu cho vic nh thi cc chun: mt kiu m t v mt kiu d on.
a/ Kiu m t
Kiu m ta miu t mi quan h v thi gian gia chun v chu ki sn xut sn
phm. N gip chng ta hiu mi quan h hu nghim ca chun ti s pht trin th
trng, nhng khng hng dn trong vic a ra cc kt lun v nh thi hoc trinh
by t m v s chun ha. V tr ca chun trong chu ki sn phm c ch ra Hinh
II-2. i vi sn phm ca chu trinh dch v cuc sng, cc chun c th l chun
on trc, hoc p ng. Cc chun on trc l nhng chun cn thit cho s cng
nhn rng rai mt thit b hoc dch v. Chng rt quan trng lin kt cc h thng
thng tin, v iu ny gii thch vi sao li c nhiu cc chun d on trc(V.32
mode, giao din gi X.25, ISDN, TCP/IP, Recomm. H.323 cho thit b u cui a
phng tin, tng bo mt cho thng mi in t-SSL).
Hnh II-2 V tri tiu chun trong chu ky san phm
Cc chun d on trc phi c phm vi v ch th rnh mch v a ra mt tp
nhng kha cnh kich thch th trng. Cc chun participatory theo ui tng bc
vi nhng s b sung kim tra nhng c im k thut trc khi lm theo chng.
Mt vi chun participatory l thut ton ma ha thoi v ting ni trong cc khuyn
ngh ca ITU-T G.726, G.724, G.728 v G.729. Cc ng dng khc nhau ca internet
trn tng TCP c th cng c xem nh l cc chun participatory( MBONE,
MMUSIC).
35
Cc chun p ng h thng ha cc sn phm hoc dch v a c bn, hoc
vch ro cht lng mong i ca mt dch v. Cc chun ny a ra mt cch c h
thng thng tin khoa hc v d liu sn c bn trong cc sn phm k thut hu dng.
Kiu d on lm cho ph hp thi gian ca cc chun vi nhng kh nng thc
cht bn trong cng ngh s dng cng ngh ng cong hinh S. nh thi gia
