Giao Thuc Iptv 2762

7/31/2019 Giao Thuc Iptv 2762

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GIAO THC IPTV


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M u

S pht trin ca mng Internet ton cu ni ring v cng ngh thng

tin ni chung em li tin b v pht trin vt bc ca khoa hc k thut.

Internet khng nhng rt ngn khong cch v khng gian, thi gian mcn mng li cho mi ngi, mi quc gia v c th gii nhng li ch to ln.

Tc pht trin nhanh chng ca cng ngh thng tin l mt trong nhng li

ch to ln, c vai tr quan trng v tm nh hng rng khp.

Vi s pht trin nhanh chng ca mng Internet bng rng c n lm

thay i c v ni dung v k thut truyn hnh. Hin nay truyn hnh c nhiu

dng khc nhau: truyn hnh s, truyn hnh v tinh, truyn hnh cp, truyn

hnh Internet v IPTV. IPTV ang l cp cao nht v l cng ngh truyn

hnh ca tng lai. S vt tri trong k thut truyn hnh ca IPTV l tnh

nng tng tc gia h thng vi ngi xem, cho php ngi xem ch ngv thi gian v kh nng trin khai nhiu dch v gi tr gia tng tin ch khc

trn h thng nhm p ng nhu cu ca ngi s dng.

Hin nay trn th gii c mt s quc gia trin khai thnh cng IPTV.

Theo cc chuyn gia d bo th tc pht trin thu bao IPTV s tng theo

cp s nhn theo tng nm. Vit Nam hin nay, mt s nh cung cp ang

th nghim dch v IPTV trn mng bng rng ADSL.


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CHNG 1 TNG QUAN V IPTV

1.1 Gii thiu v truyn hnh s theo giao thc IP:

IPTV l tn vit tt ca cm t Internet Protocol Television _ truyn hnh

qua giao thc Internet.ITPV theo nh ngha chnh thc nh sau: IPTV c nh ngha l cc

dch v a phng tin nh truyn hnh nh, tin ni, vn bn, d liu c

phn phi qua cc mng da trn IP m c quan l cung cp cc cp

cht lng dch v, bo mt, tnh tng tc, tnh tin cy theo yu cu. (theo

ITU T FG IPTV)

Nh vy IPTV ng vai tr phn phi cc d liu, k c hnh nh, m

thanh, vn bn qua mng s dng giao thc Internet. iu ny nhn mnh

vo vic Internet khng ng vai tr chnh trong vic truyn ti thng tin truyn

hnh hay bt k loi ni dung truyn hnh no khc. Thay vo , IPTV sdng IP l c ch phn phi m theo c th s dng Internet, i din cho

mng cng cng da trn IP, hay c th s dng mng ring da trn IP.

C th thy, IPTV l mt dch v s m c kh nng cung cp nhng

tnh nng vt tri hn kh nng ca bt k c ch phn phi truyn hnh no

khc. V d, set top box IPTV c th thng qua phn mm cho php xem

ng thi 4 chng trnh truyn hnh trn mn hin th, hay c th nhn tin

nhn sms, e mail.

Tim nng ca IPTV l rt ln. D on rng, nm 2008 s c khong20 triu gia nh s dng dch v IPTV. Nu chng ta tr ph 50$ mi thng

cho dch v IPTV, c mt set top box, th ngn sch s thu v khong 12

t $ mt nm trong vi nm.

1.2 Mt s c tnh IPTV:

- H tr truyn hnh tng tc: Kh nng hai chiu ca h thng

IPTV cho php nh cung cp dch v phn phi ton b cc ng dng TV

tng tc. Cc loi dch v c truyn ti thng qua mt dch v IPTV c th

bao gm TV trc tip chun, TV cht lng cao (HDTV), tr chi tng tc,

v kh nng duyt Internet tc cao.


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- S dch thi gian: IPTV kt hp vi mt my ghi video k thut s

cho php dch thi gian ni dung chng trnh mt c ch cho vic ghi v

lu tr ni dung IPTV xem sau.

- C nhn ha: Mt th thng IPTV t kt cui n kt cui h tr

truyn thng tin hai chiu v cho php ngi dng kt cui c nhn hanhng thi quen xem TV ca h bng cch cho php h quyt nh nhng g

h mun xem v khi no h mun xem.

- Yu cu v bng thng thp: Thay v phn phi trn mi knh

ti mi ngi dng, cng ngh IPTV cho php nh cung cp dch v ch

truyn trn mt knh m ngi dng yu cu. c im hp dn ny cho

php nh iu hnh mng c th tit kim bng thng ca mng.

- C th truy xut qua nhiu thit b: Vic xem ni dung IPTV by

gi khng ch gii hn vic s dng TV. Ngi dng c th s dng my

PC hay thit b di ng truy xut vo cc dch v IPTV.

1.3 S khc bit gia IPTV v truyn hnh Internet:

Do u c truyn trn mng da trn giao thc IP, ngi ta i lc hay

nhm IPTV l truyn hnh Internet. Tuy nhin, 2 dch v ny c nhiu im khc

nhau:

Cc nn khc nhau:

Truyn hnh Internet s dng mng Internet cng cng phn pht cc nidung video ti ngi s dng cui.

IPTV s dng mng ring bo mt truyn cc ni dung video n khch

hng. Cc mng ring ny thng c t chc v vn hnh bi nh cung cp

dch v IPTV.

V mt a l

Cc mng do nh cung cp dch v vin thng s hu v iu khin khng cho

php ngi s dng Internet truy cp. Cc mng ny ch gii hn trong cc khu vc a

l c nh.

Trong khi, mng Internet khng c gii hn v mt a l, ngi dng Interet no

cng c th xem truyn hnh Internet bt k u trn th gii.

Quyn s hu h tng mng

Khi ni dung video c gi qua mng Internet cng cng, cc gi s

dng giao thc Internet mng ni dung video c th b tr hoc mt khi n di


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chuyn trong cc mng khc nhau to nn mng Internet cng cng. Do , nh

cung cp cc dch v truyn nhnh nh qua mng Internet khng m bo cht

lng truyn hnh nh vi truyn hnh mt t, truyn hnh cp hay truyn hnh

v tinh. Thc t l cc ni dung video truyn qua mng Internet khi hin th trn

mn hnh TV c th b git v cht lng hnh nh thp.Trong khi, IPTV ch c phn phi qua mt h tng mng ca nh cung

cp dch v. Do ngi vn hnh mng c th iu chnh c th cung cp

hnh nh vi cht lng cao.

C ch truy cp

Mt set-top box s thng c s dng truy cp v gii m ni j dung

viedeo c phn pht qua h thng IPTV , trong khi PC thng c s dng

truy cp cc dch v Internet. Cc loi phn mm c s dng trong PC thng

ph thuc vo loi ni dung truyn hnh Internet. V d nh, download ccchng trnh TV t trn mng Internet, i khi cn phi ci t cc phn mm

media cn thit xem c ni dung . Hay h thng qun l bn quyn cng

cn h tr c ch truy cp.

Gi thnh

Phn trm ni dung chng trnh c phn pht qua mng Internet cng

cng t do thay i. iu ny khin cc cng ty truyn thng a ra cc loi dch

v da trn mc gi thnh. Gi thnh cc loi dch v IPTV cng gn ging vi

mc ph hng thng ca truyn hnh truyn thng. Cc nh phn tch mong rngtruyn hnh Internet v IPTV c th hp li thnh 1 loi hnh dch v gii tr.

1.4 C s h tng mt mng IPTV


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Hnh 1.1 S khi n gin ca mt h thng IPTV

Trung tm d liu IPTV:

Cng c bit n l u cui_headend. Trung tm d liu IPTV

nhn ni dung t nhiu ngun khc nhau, bao gm truyn hnh a phng,cc nh tp hp ni dung, nh sn xut, qua ng cp, trm s mt t hay

v tinh. Ngay khi nhn c ni dung, mt s cc thnh phn phn cng khc

nhau t thit b m ha v cc my ch video ti b nh tuyn IP v thit b

bo mt ginh ring c s dng chun b ni dung video cho vic phn

phi qua mng da trn IP. Thm vo , h thng qun l thu bao c

yu cu qun l v h s v ph thu bao ca nhng ngi s dng. Ch

rng, a im thc ca trung tm d liu IPTV c yu cu bi h tng c

s mng c s dng bi nh cung cp dch v.

Mng truyn dn bng thng rng:

Vic truyn dn dch v IPTV yu cu kt ni im im. Trong trng

hp trin khai IPTV trn din rng, s lng cc kt ni im im tng

ng k v yu cu rng bng thng ca c s h tng kh rng. S tin

b trong cng ngh mng trong nhng nm qua cho php nhng nh cung

cp vin thng tha mn mt lng ln yu cu rng bng thng mng. H

tng truyn hnh cp da trn cp ng trc lai cp quang v cc mng vin

thng da trn cp quang rt ph hp truyn ti ni dung IPTV.

Thit b ngi dng IPTV:Thit b ngi dng IPTV (IPTVCD) l thnh phn quan trng trong vic

cho php mi ngi c th truy xut vo cc dch v IPTV. Thit b ny kt ni

vo mng bng rng v c nhim v gii m v x l d liu video da trn IP

gi n. Thit b ngi dng h tr cng ngh tin tin c th ti thiu ha

hay loi b hon ton nh hng ca li, s c mng khi ang x l ni dung

IPTV.

Mng gia nh:

Mng gia nh kt ni vi mt s thit b k thut s bn trong mt dintch nh. N ci tin vic truyn thng v cho php chia s ti nguyn (cc

thit b) k thut s t tin gia cc thnh vin trong gia nh. Mc ch ca

mng gia nh l cung cp vic truy cp thng tin, nh l ting ni, m

thanh, d liu, gii tr, gia nhng thit b khc nhau trong nh. Vi mng gia

nh, ngi dng c th tit kim tin v thi gian bi v cc thit b ngoi vi


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nh l my in v my scan, cng nh kt ni Internet bng rng, c th c

chia s mt cch d dng.

1.5 u im ca IP v s la chn IP cho IPTV:

Truyn hnh s c nh thi mt cch chnh xc, l dng d liu lintc c tc bit khng i, thng hot ng trn cc mng m mi tn hiu

c truyn u phc v cho mc ch truyn hnh. Tri vi truyn hnh,

mng IP truyn nhng loi d liu khc nhau t rt nhiu ngun trn mt knh

chung, bao gm th in t, trang web, tn nhn trc tip, ting ni qua IP

(VoIP) m nhiu loi d liu khc. truyn ng thi nhng d liu ny,

Mng Internet phn thng tin thnh cc gi. Nh vy, r rng l IP v truyn

hnh khng phi l mt s kt hp hon ho (l tng) v cng ngh.

Mc d khng tng thch v cn bn, nhng th trng IPTV vn bng

n. Vy l do ti sao li chn cc mng da trn IP truyn tn hiu truynhnh? Cu tr li cho cu hi ny c th tm tt thnh nm im sau:

- Mng IP bng rng vn ti rt nhiu gia nh nhiu nc,

cc nh cung cp dch v truyn hnh c th s dng nhng mng ny

pht cc dch v truyn hnh m khng cn xy dng h thng mng ring ca

h.

- IP c th n gin cng vic pht cc dch v truyn hnh mi,

nh l chng trnh tng tc, truyn hnh theo yu cu

- Gi thnh ca mng IP tip tc gim do s thit b c sn xutmi nm rt ln v s tn ti ca cc chun trn ton th gii.

- Mng IP c mt trn ton th gii, v s ngi dng mng

Internet tc cao tip tc tng rt nhanh.

- IP l cng ngh hon ho cho nhiu ng dng khc nhau, bao

gm s trao i d liu, mng cc b, chia s tp tin, lt web v nhiu nhiu

na

IP cung cp c ch nh hng truyn gi gia cc thit b c lin

kt trong mng. IP l mt giao thc ph bin c s dng khp cc mng

Internet v hng triu cc mng khc c s dng IP. Khng c IP, mi vic s

hn lon bi v khng c cch no mt thit b gi d liu mt cch ring

bit ti mt thit b khc.

Vi vic s dng cc mng IP truyn dn tn hiu truyn hnh, vic

xem truyn hnh hin i s rt khc so vi xem truyn hnh trc y. Cc tn


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hiu truyn hnh by gi khng khc g nhng d liu khc. Nh , ngoi

cc knh truyn hnh qung b truyn thng, chng ta s c thm nhng knh

truyn hnh ring bit, tng tc tha mn nhu cu ca tng ngi.

1.6 Nhu cu thc t ca IPTV

Theo nhm nghin cu a phng tin (MRG ) trong D on IPTV

ton cu nm 2005-2009: tc pht trin IPTV rt cao: gn 1000%. Th

trng IPTV trn th gii pht trin mc tng kp hng nm 78% ln ti

36.9 triu ngi s dng vo nm 2009. Doanh thu dch v cn tng nhanh

hn trong cng thi k, t 880 triu USD ti 9.9 t USD.

Theo Informa: tc pht trin IPTV tng nhanh vo 5 nm ti v t

25.9 triu thu bao IPTV vo cui nm 2010.

Theo nguyn cu TDG: Doanh thu IPTV ton cu s t trn 17 t USDvo nm 2010.

V trn thc t, dch v IPTV c trin khai v t dc thnh cng

nhiu nh Italy ( Fast Web), Hng Kng (PCCW), Canada ( Manitoba) v

Japan (Yahoo BB).

Ti th trng Trung Quc, IPTV bt u c trin khai t nm 2004

vi 2 nh cung cp hng u l CHINA Telecom v ZTE cng vi nhng nh

cung cp khc.

S lng thu bao c th tng ln ti 3-6 triu vo nm 2010.IPTV c trin khai vi bng thng 2M vi k thut nn MPEG-4 part

10 cho TV thng v 6M i vi HDTV.

Cc dch v trin khai trn IPTV n vi ngi dng:

+ LiveTV: truyn hnh trc tuyn

+ VoD: truyn hnh theo yu cu

+ RoD: Dch v ghi hnh theo yu cu

+ NVoD: Xem chng trnh theo lch pht sng


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CHNG 2:CHUN NN S DNG TRONG IPTV

Nn cho php cc nh cung cp dch v truyn cc knh hnh v ting vi

cht lng cao qua mng IP bng rng. Do mt ngi ko th phn bit c

ton b cc phn ca hnh nh. Do vic nn s lm gim ln ca tn hiuban u bng cch b bt cc phn ca hnh nh.

2.1 Nn MPEG:

MPEG l 1 chun nn c s dng rng ri trong thng tin v tinh,

truyn hnh cp v trong cc h thng truyn hnh mt t. MPEG (moving

pictures exert group) c thnh lp nhm pht trin cc k thut nn cho ph

hp vi vic truyn hnh nh. T khi c thnh lp, MPEG a ra cc chunnn nh: MPEG-1, MPEG-2, MPEG4-( Part 2 v part 10), MPEG-7, v MPEG-21.

Trong cc chun ny, MPEG-2 v MPEG-4 Part 10 c s dng rng ri trong IPTV.

2.2 Chun MPEG-2:

MPEG 2 l 1 cng ngh t c thnh cng ln v l 1 chun nn c u

th vt tri dnh cho truyn hnh s c truyn qua nhiu mng truyn thng

bng rng. Chun nn MPEG-2 c chia thnh 2 loi nn hnh v nn ting.

Nn hnh: Video dng c bn l 1 chui cc nh lin tc. 1 frame cnh ngha vi 1 chui bit header. Mt ngi thng thy thoi mi khi xem TV

vi tc 25 hnh/s. S khng c li nu pht vi tc nhanh hn v ngi xem

khng th nhn ra s khc bit. do c th dung lng ca nhng hnh nh

bng cch nn chng li. Cc b nn hnh c s dng vi mi frame m vn

gi cht lng hnh nh cao.

2.2.1 Qu trnh nn MPEG:

Phn u tin ca nn bao gm 1 qu trnh tin ng b. Qu trnh ny c

bn bao gm vic lm gim kch thc ca cc frame. Lm gim kch thc ca

cc frame chnh l lm gim s lng bit , iu ny cng gip gim bng thng

cn thit truyn tn hiu. Tuy nhin, qu trnh ny khng phi ko c tr ngi. V


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d, s gim kch thc ca khung c th thng xuyn gy ra nhng li t s

cnh (ging nh sai t l 4/3 hay 16/9) khi c th hin trn mn hnh TV c

phn gii thp.

Phn 2 ca qu trnh nn tin hiu l chia 1 frame nh ra thnh cc block ckch thc 8 nhn 8 pixelkhi m ha nh nht trong gii thut ca MPEG. C 3

loi block; chi Y, thnh phn mu Cr hoc xanh Cb. Cc loi block thnh

phn mu mang thng tin v nhng mu khc nhau ca hnh nhtrg khi chi

mang thng tin v nhng phn mu en hoc trng ca hnh nh.

Khi hon thnh 2 phn trn, MPEG s thc hin 1 hm ton c gi l

bin i cosin ri rc i vi mi block ring bit. Kt qu thu c l mt ma trn

h s 8*8. DCT s bin i s khc nhau v khng gian thnh cc tn s khcnhau, nhng khng lm thay i cc thng tin trong block, cc blcok ban u s

c ti to li 1 cch chnh xc s dng bin i ngc. Nguyn tc thc hin

hm ny bao gm vic chia cc block thnh cc phn ty theo mc quan

trng. Nhng phn quan trng s c gi nguyn cho ti bc tip theo trong

khi cc phn cn li s b gim bt. iu ny s m bo rng mt ngi khng

ch ti vic nhng phn khng quan trng ca block b b bt khi tc bt b hn

ch.

Bc tip theo trong MPEG l qu trnh lng t ha. Qu trnh lng t

ha d liu s l qu trnh lm gim s lng bt ca cc block. Mc lng t i

vi mi tn hiu video l rt quan trng.

Khi tt c cc block trong frame u c nn li, MPEG s ngt cc frame

thnh 1 dng mi gm nhiu block gi l macro block. Mi macro block c kch

th c 16 nhn 16 cha cc block chi v block thnh phn mu. Nu c s

khc bit gia frame cui cng v frame hin ti, cc thit b nn MPEG s chuyn

nhng block mi ny ti 1 v tr mi trn frame hin ti. iu ny gip khng phi

gi i nhng hnh nh mi hon ton, do c th tch kim bng thng. C 2

cch thc hin iu :


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Nn theo khng gianl lm gim cc bt trn tng frame ring bit. iu ny

c th t c do cc pixel lun ng cnh nhau trong cc frame thng c gi

tr ging nhau. Do thay v m ha tng pixel ring bit. K thut nn theo

khng gian ny m ha s khc bit gia cc pixel cnh nhau. S lng bt cn

thit m ha nhng khc bit ny t hn s lng bt cn thit m ha tng

pixel ring bit.

Nn theo thi gian l lm gim cc bit gia cc frame lin tc. Trong qu

trnh sn xut video c nhng thng tin c lp li gia nhng frame lin tip.

VD: nu trn hnh c 1 bc tng , bc tng vn xut hin lin tc trong 30 hnh

tip theo, m khng thay i ( bc tng khng thay i trong vng 1s) . thay

v m ha 30 ln lin tc trong 1s, nn thi gian ch gi i cc thng tin d on

chuyn ng gia nhng frame hnh, trong trng hp ca bc tng trong VD

trn, d on chuyn ng c t = 0.

C nhiu phung thc khc nhau nn 1 frame hnh. VD nh vi 1 frame

hnh c phc tp cao th cn phng php nn c yu t nn theo khng gian

thp bi v ch c 1 phn rt nh cc pixel c lp li. Nu tc bit c s thay

i ln th kh c th truyn i trong mng IP, v th nhiu b m ha bao gm c

chc nng m c th iu khin v qun l tc chung m ti cc bit ctruyn i ti tng tip theo ca h thng sn xut video.

Bc tip theo ca qu trnh nn MPEG l m ha cc macroblock thnh

cc slice. Slice l 1 chui nh t nm ngang cnh nhau t tri sang phi. Nhiu

slice kt hp vi nhau to thnh 1 hnh. Mi slice c m ha c lp vi nhau

hn ch li.

2.2.2 Cc nh trong chun nn MPEG:

Chun nn MPEG nh ngha 3 loi nh:

Intra-frame (I-frame)---- frame c m ha ring bit khng ph thuc cc

frame trc hoc tip theo.M ha theo h thng c s dng gn ging nh


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nn JPEG. y l frame c lp v c s dng to ra cc loi frame khc.

P-frame ( forward predicted frame)---- khung d on nh tip theo l

khung d on nh da trn cc frame I trc . MPEG khng thc s m ha

nh m cha cc thng tin v chuyn ng cho php IPTVCD c th ti to liframe. P-frame yu cu t bng thng hn I-frame, iu ny l yu t quan trng

i vi mng da trn IPTV.

B-frame (Bi-directional predicted frame )---- frame d on hng: B-

frame l frame c to thnh t vic kt hp cc thng tin t c I-frame v P-

frame. M ha B-frame th tng t vi P-frame, ngoi tr cc vecto chuyn

ng ph thuc vo cc vng trong cc khung tham kho sau . B-frame

chim t dung lng hn l I-frame va P-frame. V th dng Mpeg video gm

nhiu B-frame th chim dung lng thp hn so vi dng cha cc frame Iva P. Thm ch, B-frame gip lm ti thiu bng thng cn thit i vi cc

dng MPEG video. Tuy nhin, B-frame cng c hn ch l tr. Do

IPTVCD phi kim tra 2 khung trc v sau trc khi to ra B-frame.

3 loi nh trn kt hp vi nhau to thnh 1 chui cc frame c gi l nhm

nh (GOP ). Mi nhm nh bt u bng mt frame I v c mt s cc frame B v

P, Mi nhm nh MPEG c cu trc nh sau:

[I B B B P B B B P B B B P B B B P]

Mi nhm nh cn bt u vi mt khung I, mc d kch thc ca mi

nhm nh l khc nhau, nhng trung bnh mi nhm nh trong IPTV c khong

12 n 15 frame. Mi cu trc ca mt nhm nh thng thng c th c miu

t bi 2 thng s: N, s nh trong mt nhm v M, khong cch gia cc frame.

Cc nhm nh c chia thnh 2 loi: nhm ng v nhm m. Vi nhm ng,

khung B cui cng khng yu cu khung I u tin cho nhm nh tip theo gii

m, trong khi vi nhm m cn yu cu khung I cho nhm nh tip theo. Cc

nhm nh sau c kt hp vi nhau to thnh dng video. Mi dng

video bt u bit mt on m, theo sau l mt header v kt thc vi mt

m duy nht.


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Th t cc khung c truyn i trn mng bng rng th khc vi th t

cc khung trong chui bit u vo ca b m ha. Bi v b gii m trong IPTVCD

cn x l cc frame I v P trc khi to ra khung B. Mi quan h tng th gia

cc chui nh, nh, cc slice, cc khi macro, cc khi v cc im nh c

minh ha hnh sau:

Hnh 2.1 Cu trc dng MPEG video

Mc d MPEG-2 c s dng trong truyn hnh cp v v tinh, nhng

MPEG-2 c nhng hn ch i vi cc mng c bng thng gii hn.Do mt

cng ngh nn mi vi nhiu tnh nng c pht trin trong nhng nm gn

y vi mc ch truyn video qua mng bng thng gii hn. MPEG-4 part 10

c s dng trong h tng mng IPTV.

2.3 MPEG-4:

Chun MPEG-4 thnh cng hn so vi chun MPEG-2. Thm vo ,MPEG-4 a ra 1 h thng hon chnh vi cc c im h tr cc nh dngd liu. Mpeg-4 bao gm rt nhiu phn c th thc hin cng nhau hoc ringbit.

Phn1:Systems; Phn2:Visual;


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Phn3:Audio; Phn 4: Conformance xc nh vic trin khai mt MPEG-4 s nh th no; Phn 5: Cc phn mm tham chiu, a ra mt nhm cc phn mm thamchiu quan trng, c s dng trin khai MPEG-4 v phc v nh mt vd demo v cc bc phi thc hin khi trin khai; Phn 6: Khung chun cung cp truyn thng a phng tin tch hpDMIF (Delivery Multimedia Integration Framework), xc nh mt giao dingia cc ng dng v mng/lu tr; Phn 7: Cc c tnh ca mt b m ho video ti u (b xung cho ccphn mm tham chiu, nhng khng phi l cc trin khai ti thiu cn thit). Cc phn mi b xung tip cho chun MPEG-4 sau ny l: Phn 8: Giao vn (v nguyn tc khng c xc nh trong chun, nhngphn 8 xc nh cn nh x nh th no cc dng MPEG-4 vo giao vn IP); Phn 9: M t phn cng tham chiu (Reference Hardware Description); Phn 10: MPEG-4 Advanced Video Coding /H.264 l thnh tu mi nhtv nn video, trn c s ng b vi kh nng tnh ton v dung lng bnh ca cc my tnh PC hin nay, ng dng cc phng php m ho phctp hn nhiu cc phng php trc v c th thc hin c trong mitrng phn mm v phn cng, do nhm chuyn gia MPEG hp tc vinhm IUT Study Group pht trin v c nhiu kh nng s tr thnh chun mho video qui m ton cu, duy nht ca ITU v ISO; Phn 11: M t khung hnh (Scene Description - c tch ra t phn 1); Phn 12: nh dng file truyn thng ISO (ISO Media File Format); Phn 13: Qun l bn quyn ni dung IPMP (Intellectual PropertyManagement and Protection Extensions); Phn 14:nh dng fille MP4 (trn c s phn 12); Phn 15: nh dng file AVC (cng trn c s phn 12);

Phn 16: AFX (Animation Framwork eXtensions) v MuW (Multi-userWorlds).

Cng ngh m ho video trong MPEG-4.

Chun MPEG-4 l mt chun ng d thay i: vi MPEG-4, cc itng khc nhau trong mt khung hnh c th c m t, m ho v truyni mt cch ring bit n b gii m trong cc dng c bn ES (ElementaryStream) khc nhau. Cng nh xc nh, tch v s l ring cc i tng(nh nhc nn, m thanh xa gn, vt, i tng nh video nh con ngi

hay ng vt, nn khung hnh), nn ngi s dng c th loi b ring tngi tng khi khun hnh. S t hp li thnh khung hnh ch c thc hinsau khi gii m cc i tng ny.

Trn Hnh 2.2 th hin mt trng hp in hnh ca t hp khun hnhMPEG-4, cho thy nhiu i tng (bn, qu cu, bng en, ngi hngdn v audio) c t vo mt h thng to khng gian 3 chiu (3-D) i


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vi v tr ngi xem gi nh. Cc thit b m ho v gii m video u pdng s m ho nh nhau cho mi i tng video VO (Video Object)ring bit (hnh 2), nh vy ngi s dng c th thc hin cc hot ngtng tc ring vi tng i tng (thay i t l, di chuyn, kt ni, loi b,b xung cc i tng) ngay ti v tr gii m hay m ho.

Hnh 2.2 T hp khung hnh trong MPEG-4


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Hnh 2.3 Cu trc b m ha v gii m MPEG-4

Cc b phn chc nng chnh trong cc thit b MPEG-4 bao gm: B m ho hnh dng ngoi Shape Coder dng nn on thng tin, gipxc nh khu vc v ng vin bao quanh i tng trong khung hnhscene. B d on v tng hp ng gim thng tin d tha theo thi gian. B m kt cu mt ngoi Texture coder dng x l d liu bn trong vcc d liu cn li sau khi b chuyn ng.

Hnh 2.4 l mt v d v m ho v tng hp khung hnh video s dngtrong MPEG-4. Nhiu i tng, nh ngi, xe t, nh ca, c tch rakhi video u vo. Mi i tng video sau c m ho bi b m hoi tng video VO (video object) v sau c truyn i trn mng. Ti vtr thu, nhng i tng ny c gii m ring r nh b gii m VO v gin b t hp compositor. Ngi s dng c th tng tc vi thit b cutrc li khung hnh gc (a), hay x l cc i tng to ra mt khung hnhkhc (b). Ngoi ra, ngi s dng c th download cc i tng khc t ccth vin c s d liu (c sn trn thit b hay t xa thng qua mng LAN,WAN hay Internet) chn thm vo hay thay th cc i tng c trongkhun hnh gc (c).

Hnh2.4 M ha v tng hp khung hnh trong MPEG-4


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c th thc hin vic t hp khung hnh, MPEG-4 s dng mt ngnng m t khung hnh ring, c gi l nh dng nh phn cho cc khunghnh BiFS (Binary Format for Scenes). BiFS khng ch m t u v khi nocc i tng xut hin trong khung hnh, n cng m t cch thc hot ngca i tng (lm cho mt i tng xoay trn hay chng m hai itngln nhau) v c iu kin hot ng i tng v to cho MPEG-4 c khnng tng tc. Trong MPEG-4, tt c cc i tng c th c m ho vis m ho ti u ring ca n video c m ho theo kiu video, textc m ho theo kiu text, cc ho c m ho theo kiu ho - thayv vic x l tt c cc phn t nh pixels nh l m ho video nh ng. Docc qu trnh m ho c ti u ho cho tng loi d liu thch hp, nnchun MPEG-4 s cho php m ho vi hiu qu cao tn hiu nh video,audio v c cc ni dung tng hp nh cc b mt v c th hot hnh.

2.4 Tng quan v MPEG-4 Part 10

u nm 1998, 2 t chc ITU-T v VCEG cng a ra mt chun nnmi H.26L nhm tng gp i hiu sut nn . Do chun nn ny s m ranhiu ng dng mi nh truyn hnh qua mng Internet, truyn hnh di ng vpht trin cc ng dng hin c.

Cui nm 2001, VCEG v MPEG thnh lp JVT ( Joint Video Team) cnhim v hon thnh chun nn mi v chnh thc c thng qua vi tn gi lMPEG-4 Part 10 hoc H.264/AVC vo thng 3 nm 2003.

2.4.1 Cu trc phn lp ca H.264/AVC

Vi s gia tng cc ng dng v dch v trn nhiu mng th cu hi t

ra l lm th no qun l c cc ng dng . Do vy, chun H.264/AVCphi c linh hot cao v c th ng dng trn nhiu mng khc nhau. Do, chun H.264/AVC c thit k theo phn lp m ha video VCL ( VideoCoding Layer) v lp NAL lm nhim v tng thch vi mi trng mngkhc nhau.


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Hnh 2.5: Cu trc phn lp ca H.264

a) Lp mng NAL ( Network Abstration Layer)

NAL c kh nng nh x t lp VCL n lp truyn ti:+ RTP/IP cho dch v thi gian thc qua mng Internet (conversational

v streaming).+ nh dng file: ISO MP4 cho lu tr v truyng ti MMS.+ H32x cho cc dch v m thoi c dy v khng dy.+ Dng truyn ti MPEG-2 cho cc dch v qung b.

Gi NAL: d liu video c m ha c t chc trong mt n vNAL( hay gi NAL). Mi gi c di tnh theo byte. Byte u tin ca mi giNAL l byte mo u, n ch r loi d liu c cha trong NAL, cc bytecn li cha d liu.

Phn d liu ca NAL c ghp xen.Cu trc ca n v NAL c nh dng chung cho vic s dng truyn

trong h thng hng bit v hng gi.

b) Lp m ha video:

Lp m ha video ca H.264/AVC th tng t vi cc tiu chun khcnh MPEG-2 video. N l s kt hp d on theo thi gian v theo khnggian,vvi m chuyn v.

nh c tch thnh cc khi. nh u tin ca dy hoc im truy

nhp ngu nhin th c m ha Intra, c ngha l khng dng thng tinno ngoi thng tin cha trong bn thn nh. Mi mu ca mt khi trong mtframe Intra c d on nh dng cc mu khng gian bn cnh ca cckhi m ha trc . i vi tt c cc nh cn li ca dy hoc gia ccim truy cp ngu nhin, m ha Inter c s dng, dng d on bchuyn ng t cc nh c m ha trc.

c) Khi nim v nh, khung, bn nh, macroblock

Tn hiu video c m ha trong H.264 bao gm tp hp cc nhc m ha c trt t. Mt nh c th biu din bng c mt khung hoc

mt bn nh. Nhn chung, mt khung gm c hai bn nh xen k nhau: bnnh trn v bn nh di. Bn nh trn gm cc dng chn 0, 2, 4, , H/2 -1,vi H l tng s dng trong mt khung. Bn nh di gm cc dng l v btu t dng th 2.


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Hnh 2.6: Cc bn nh trong mt khung

Cc macroblock:Mi nh video, frame hoc field, c chia thnh ccmacroblock c kch thc c nh bao trm mt din tch nh hnh ch nhtgm 16 x 16 mu thnh phn luma v 8 x 8 mu cho mi mt trong hai thnhphn chroma. Tt c cc mu macroblock luma hoc chroma c d ontheo khng gian hoc thi gian, v d on ti ch hp thnh c truyn inh dng m chuyn v. Do vy mi thnh phn mu d on ti ch cchia nh thnh cc khi. Mi khi c bin i nh dng bin i nguyn (aninteger transform), v cc h s bin i c lng t ha v c truyn ibngphng php m ha entropy.

Cc macroblock c t chc thnh cc slice, biu din cc tp con canh cho v c th c gii m c lp. Th t truyn cc macroblocktrong dng bit ph thuc vo bn phn phi Macroblock (MacroblockAllocation Map) v khng nht thit phi theo th t qut. H.264 / AVC h trnm dng m ha slice khc nhau.n gin nht l slice I (Intra), trong ttc macroblock c m ha khng c tham chiu ti cc nh khc trong dyvideo. Tip theo l cc slice P v B, vic m ha c tham chiu ti ccnh trc n (slice P) hoc c nh trc ln nh sau (slice B). Hai dng slicecn li l SP (switching P) v SI (switching I), c xc nh cho chuyn mchhiu qu gia cc dng bit c m ha cc tc bit khc nhau.

2.4.1 H.264 CODEC

Ging nh cc tiu chun nn trc y ( v d nh MPEG-1, MPEG-2 v MPEG-4),H.264 khng c nh ngha l b CODEC ( mt cpencoder v decoder) m H.264 nh ngha cc c php ca lung nn video.Trong thc t, b m ha v gii m bao gm cc thnh phn c bn nhtrong hnh 2.8 v hnh 2.9. So vi cc chun nn trc bao gm cc thnh


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phn nh b d on, bin i, lng t, m ha entropy, H.264 CODECcn bao gm b lc deblocking v c nhiu thay i quan trng trong cc chitit v chc nng ca cc thit b.

B m ha (hnh 2.8) bao gm 2 dng d liu , dng forward (t trisang phi) v dng ti to (t phi sang tri). Dng d liu trong b gii mc truyn t phi sang tri trong hnh 2.9.

Hnh 2.7: S b m ha H.264.

B m ha dng forward

Mt khung hoc trng li vo Fn c x l trong cc khi ca mtmacroblock ( p ng cho 16x16 pixel trong mt hnh bnh thng). Mimacroblock c m ha ch trong nh hoc lin nh, vi tng block trongmacroblock. Mt d don PRED (k hiu l P trong hnh 2.8) c nh dngda trn cc mu nh c ti to li.

Trong ch nn lin nh, PRED c hnh thnh t slice hin thi vac m ha, gii m v ti to li (uFn trong hnh, ch rng cc mu khngc lc c s dng to nn PRED)

Trong ch nn trong nh, PRED c hnh thnh bng cch d onb chuyn ng t mt hoc hai nh tham kho c. Trong hnh 2.8, nh thamkho l nh Fn 1 va c m ha. Nhng, d on tham chiu i vi mimacroblock c th c chn t cc hnh nh trong qu kh hoc trong tnglai va c m ha, ti to v lc ( theo th t hin th) .

D on PRED tr vi block hin ti er tm ra s khc bit , c bini v lng t ha thu c h s lng t X s c sp xp li v m


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ha entropy. H s c m ha entropy cng vi thng tin v cnh c mha trong mi block trong macroblock (ch d on, mc lng t, thng tinv vector chuyn ng, ) nh dng nn cc dng bit truyn ti lp mngtru tng truyn hoc lu tr.

Hnh 2.8: B m ha

B m ha dng ti to

Bn cnh vic m ha v truyn ti cc block trong macroblock, b mha cn gii m ( ti to) chng lm tham kho cho cc d on trong tnglai. H s X c gii lng t (Q1 ) v bin i ngc (T1 ) thu c skhc bit block Dn . Block d on PRED c cng vo to thnh block

ti to uFn

. B lc c ng dng gim nh hng ca mo v cc nhtham kho d on c to t 1 chui cc block Fn.

Mc ch chnh ca b gii m dng ti to trong b m ha l chcchn rng c b m ha v gii m u s dng cc tham s khung xc nh to ra d on P. Nu khng c cc tham s ny, d bo P b m ha vgii m s khng c xc nh, dn n li gia b m ha v gii m.

Hnh 2.9 B gii m


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B gii m

B gii m nhn c cc dng bit c nn t NAL. Cc thnh phnd liu c gii m entropy tm ra h s lng t X. S dng gii lngt v bin i ngc thu c Dn. S dng cc thng tin header c gii

m t cc dng bit, b m ha to ra block d on, ging ht vi PRED cto ra b m ha. PRED c cng vi Dn to ra uFn , sau clc to ra cc block Fn.

2.4.3 Cc c im chnh ca MPEG-4 Part 10:

a) Kch thc block nh c th thay i c:Thnh phn chi ca macroblock (16*16 mu) c th c chia theo 4

cch: mt macro block 16 *16 phn macroblock, hai macroblock 16*8 phn, hai8* 16 phn hoc bn macroblock 8*8 phn. Nu kiu 8*8 phn c chn, mibn 8*8 sub-macroblock trong mt macro block c th c chia theo 4 cch:mt phn sub-macro block 8*8, hai phn sub-macroblock 4*8, hai phn sub-macroblock 8*4 hoc bn phn sub-macroblock 4*4 . Cc phn ny v cc sub-macroblock to ra nhiu cch kt hp gia trong mi macroblock.

Trong thc t, phn c kchthc ln ph hp vi nhng v tr khng chitit, v phn kch thc nh ph hp vi cc v tr c chi tit cao.

Hinh 2.10: B chuyn ng

b) chnh xc ca vector b chuyn ng cao:


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Mi phn hay mi phn sub-macroblock trong mt macro c m ha

trong nh c d on t mt vng c cng kch thc trong nh tham kho.hu ht cc chun nn trc ch t c chnh xc ca vector bchuyn ng, nhng vi H.264 c th t c ti .

c) Tham chiu nhiu nh b chuyn ng:

nh P trong MPEG-2 l nh d on c tham chiu t mt nh trc, cn nh B l nh d on 2 chiu c tham chiu t nhiu nh I ho Ptrc v sau n.

Trong chun nn H.264, nh hin ti c th tham chiu bi nhiu nh,iu ny cho php tng hiu sut nn. Mt lng ln cc nh c gii nn vlu trong b gii nn.

Trong cc chun nn trc , th t cc nh dng cho mc ch thamchiu b chuyn ng v th t cc nh th hin c mi quan h cht ch vinhau. Tuy nhin, chun nn H.264 khc phc nhc im ny bng cchcho php b gii nn la chn th t cc nh tham chiu.

Hnh 2.11: Tham chiu a nhd) D on trong nh:

Cc mu ca mt macroblock c d on bng cch ch s dng phnthng tin ca macroblock c truyn i trong mt nh.

Trong chun nn H.264/AVC, c hai loai d on trong nh cho thnh


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phn chi Y. Loi th nht l intra 4x4 v loi th 2 l intra 16x16. Trong INTRA4x4, cc phn t nh c kch thc 16x16 c chia thnh 16 phn c kchthc 4x4, vic d on c thc hin vi tng phn ring bit. C 9 mode don ty chn i vi cc block thnh phn chi Y kch thc 4x4, 4 mode ivi thnh phn chi Y kch thc 16x16, 4 mode cho thnh phn mu Cr, Cb. Bnn s la chn mode d on sao cho s khc bit gia P v block c mha l nh nht.

c mode d on thnh phn chi Y 4x4C 9 mode d on thnh phn chi Y kch thc 4x4, l:

Mode 0: d on theo chiu dcMode 1: d on theo chiu ngangMode CD: d on da trn trung bnh tt c cc mu xung quanh t bn

tri v t trn ca khi d liu hin ti.Mode 3: d on d trn cc mu c nghing 45 t phi sang tri.Mode 4: d on d trn cc mu c nghing 45 t tri sang phi.Mode 5 : s dng php ngoi suy vi gc c nghing 26.6 so vi

chiu dc.Mode 6: s dng php ngoi suy vi gc c nghing 26.6 so vi

chiu ngangMode 7: s dng php ngoi suy vi gc c nghing 26.6 so vi

chiu dc bn phiMode 8: s dng php ngoi suy vi gc c nghing 26.6 t so vi

chiu ngang.

Hnh 2.12: Mode d on thnh phn chi Y kch thc 4x4

Hnh 2.13: Mode d on 16x16 lin nh


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Cc mode d on thnh phn chi Y 16x16

Nh d ni trnh by trn, mt mode d on c p dng cho tonb mt macro thnh phn chi kch thc 16x16. C 4 mode d on l don theo chiu dc, d on theo chiu ngang, d on phng. i vi mode

d on phng, mt hm tuyn tnh c s dng gia cc mu t bn tri vt trn xung so vi mu d on hin ti. Mode ny hot ng hiu qu giacc vng c chi lin tc thay i. Cc mode hot ng ging nh i vithnh phn chi kch thc 4x4, ch khc l chng hot ng i vi ton bmacroblock thay v vi 16 phn kch thc 4x4.

Cc mode d on cc thnh phn mu Cr v Cb:

D on trong nh i vi cc thnh phn mu ca mt macroblocktng t nh i vi thnh phn chi Y c kch thc 16x16. Bi v tn hiumu c s thay i lin tc trong hu ht cc trng hp. N lun p dng chocc khi 8x8 s dng d on ngang, dc, DC v s on phng.

Hnh 2.14: D on nh I

e) loi b d tha khng gian:

Bin i Cosine ri rc DCT hai chiu trong cc chun MPEG-1, MPEG-2nhm mc ch loi b phn d tha khng gian. DCT c p dng cho cckhi 8x8. trong H.264/AVC, DCT c p dng vi h s nguyn. Kch thckhi thay i, c th l 16x16, 4x4, hoc trong trng hp c bit c th dngkhi kch thc 2x2. Vic s dng khi c kch thc nh hn so vi cc chun


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nn trc cho php b m ha tng thch tt hn vi bin ca cc itng chuyn ng.

Hnh 2.15: Loi b d tha khng gian

C 3 loi bin i khc nhau c s dng trong MPEG-4 Part 10, l;

Mt bin i Hadamard p dng cho mng 2 chiu kch thc 4x4

cc h s 1 chiu DC ca thnh phn chi Y trong mode 16x16. Mt bin i Hadamard p dng cho mng 2 chiu kch thc 2x2

cc h s 1 chiu DC ca thnh phn mu Cr, Cb.

Mt bin i da trn DCT p dng cho tt c cc block kch thc4x4.

D liu trong 1 macroblock c truyn di theo th t nh trong hnh sau:Nu macroblock c m ha s dng mode Intra 16x16, th block s

c dn nhn l -1, v bao gm cc h s mt chiu c bin i trong miblock chi 4x4, v c truyn i u tin. Sau , cc block chi t 0-15c truyn i theo trt t nh trong hnh v(cc h s mt chiu trong mt

macroblock c m ha s dng mode Intra 16x16 khng c gi i). Block16 v 17 c gi i,bao gm 2 mng kch thc 2x2 cc h s mt chiu ccthnh phn mu Cr, Cb. Cui cng l cc block t 18-25(khng c cc h s mtchiu).


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Hnh 2.16: Th t truyn cc block trong mt macroblock

f) M ha Entropy:

Hnh 2.17: M ha Entropy

M ho s hc nh phn thch nghi vi ng cnh (Context-adaptive

binary arithmetic coding - CABAC)


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M ho c di t m thay i thch nghi vi ng cnh (Context-

adaptive variable-length coding - CAVLC)

M ho c di t m thay i (Common variable-length coding -

VLC)

g) B lc deblocking:

Cu trc khi c bn ca H.264 l 4x4 cho bin i v b chuyn ng.Do vy, nh s hnh thnh cc ng bin gia cc khi. B lc s trit tiu ccbin ny hnh nh c t nhin hn.

Mt b lc c s dng cho mi macroblock c m ha nhm lmgim mo. B lc deblocking c s dng sau bin i ngc b m ha(trc khi ti to li v lu tr ) v ngc li i vi b gii m. B lc gip cithin cht lng hnh nh. Hnh nh c lc s s dng lm d on bchuyn ng cho cc hnh nh trong tng lai v iu ny c th gip ci thin

cht lng nn bi v nhng hnh nh c lc chn thc hn so vi cc nhkhng c lc.

h) Th t macroblock mm do:

cung cp cc phng php che giu hiu qu trong cc knh ckhuynh hng b li vi cc ng dng tr thp, H.264 / AVC h tr mt cim gi l th t macroblock mm do (FMO Flexible MacroblockOrdering). FMO nh r mt gin (pattern) n nh cc macroblock trongnh vo mt hoc vi nhm slice. Mi nhm slice c truyn ring bit. Numt nhm slice b mt, cc mu trong cc macroblock bn cnh v mt khng

gian, thuc v cc nhm slice c thu ng, c th c s dng cho chedu hiu qu li.

2.4.4 u im ca H.264/AVC:

Cht lng hnh nh tt: H.264 l chun nn s dng cng ngh mthanh, hnh nh mi kh nng nn tt hn so vi cc chun nn trc .Do , chun nn cung cp dch v phn pht hnh nh cht lng caoqua mng bng thng gii hn.

Yu cu bng thng thp: Cht lng hnh nh ca H.264 gn gingvi MPEG-2 nhng H.264 cn t bng thng truyn ti tn hiu vi cngcht lng. im ny rt ph hp s dng trong h thng IPTV.

C kh nng kt hp vi cc thit b x l video c sn nh MPEG -2v h tng mng da trn IP c sn .

H tr truyn hnh phn gii cao: Khi s dng ti u chun nnth lm c th lm tng kh nng truyn d liu ca mng. Do cc nh


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cung cp dch v truyn thng c th s dng chun nn ny cung cpchng trnh video phn gii cao qua mng sn c.

H tr nhiu ng dng:Chun nnH.264 c s dng trong nhiu ngdng, vi nn khc nhau th c nhng yu cu ring. V d, ng dng truyn aim trong IPTV yu cu phi hin th hnh nh dng chun truyn hnh, trongkhi, i vi cc ng dng gii tr di ng, hnh nh phi hin th c trn ccthit b di ng. ph hp vi mi ng dng, chun nn H.264 c rt nhiuprofile v level.c im ca profile v level l tc bit v kch thc nh.

C th truyn c lp: Chun nn H.264 c th truyn qua nhiu giaothc nh ATM, RTP,UDP, TCP v cc dong MPEG-2.

D dng thch nghi vi cc mng cht lng km nh c ch sa li .

2.4.5 Cc ng dng ca H.264/AVC

Chun nn ny c thit k cho cc ng dng sau:

+Truyn hnh qung b qua qua v tinh, cp, mt t+Truyn hnh tng tc, video theo yu cu (VoD).

+Lu tr a quang, bng t, DVD.

+Tch hp dch v qua ISDN, LAN, DSL, mng khng dy, mng di ng,

modem.

+Nhn tin a phng tin MMS qua ISDN, DSL, LAN mng di ng.

Cn nhiu ng dng khc c pht trin trn mng hin ti nh video

phone, v mng tng lai.

Kt lun:

T nhng c im v u im ca MPEG-4 AVC nh du mt bc ngottrong lnh vc nn video, p dng cc k thut tin tin nhm mc ch sdng bng thng hiu qu hn v em li cht lng nh cao hn. Vi cc kthut ny, MPEG-4 AVC c th gim tc bit xung hn 50% so vi chunMPEG-2. Do , MPEG-4 Part 10 c la chn ng dng trong IPTV.


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CHNG 3: NG GI NI DUNG VIDEO

Vic ng gi cc chng trnh video bao gm vic chn v t chc cc dliu video thnh cc gi ring bit.

3.1 Tng quan v m hnh truyn thng IPTV (IPTVCD)M hnh truyn thng trong IPTV c 7 lp(v mt lp ty chn) c xpchng ln nhau.

Cc d liu video pha thit b gi c truyn t lp cao xung lp thptrong m hnh IPTV, v c truyn i trong mng bng rng bng cc giao thcca lp vt l. thit b nhn, d liu nhn c chuyn t lp thp nht n lptrn cng trong m hnh IPTV.

Hnh3.1: m hnh truyn thng IPTV

Do , nu 1 b m ha gi chng trnh video n 1 thit b IPTV cakhch hng, th phi chuyn qua cc lp trong m hnh IPTV c pha thit bnhn v thit b gi. Mi lp trong m hnh IPTV c lp vi nhau v c chcnng ring. Khi chc nng ny c thc hin , d liu j video c chuyn nlp tip theo trong m hnh IPTV. Mi lp s thm vo hoc b i phn thng tin

iu khin ca cc gi video trong quad trnh x l. Thng tin iu khin cha ccthng tin gip thit b c th s dng gi d liu ng chcnng ca n, vthng c nh dng nh cc header hoc trailer. Bn cnh vic truyn thnggia cc lp, cn c cc lin kt o gia cc tng cng mc. 7 lp v 1 lp bsung trong m hnh IPTV c th c chia lm 2 loi: cc lp cao v lp thp.cc tng cao hn th quan tm nhiu hn ti cc ng dng ca IPTV v cc nhdng file, trong khi cc tng thp hn th quan tm ti vic truyn ti cc ni dung.


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3.2 M hnh IPTV v truyn ti cc ni dung MPEG

Hnh 3.2 cho ta ci nhn r hn v vic cc ni dung video c nn quacc lp nh th no khi s dng h thng MPEG khi chuyn t lp trn xung lpdi.

Hnh 3.2ng gi cc lp trong m hnh IPTV

3.2.1 Lp m ha video:

Qu trnh truyn thng bt u lp m ha, cc tn hiu tng t hoc sc nn. Tn hiu li ra ca b nn l cc dng Mpeg c bn. cc dng MPEG cbn c nh ngha l cc tn hiu s lin tc thi gian thc. C nhiu loi dngc bn. VD, m thanh c m ha s dng MPEG c gi l dng c bn mthanh. Mt dng c bn thc ra ch l tn hiu ra th t b m ha. Cc dng dliu c t chc thnh cc khung ti lp ny. Cc thng tin cha trong mt dngc bn c th bao gm:

Loi khung v tc

V tr ca nhng block d liu trn mn hnh

T s cnh

Cc dng c bn l nn tng to nn cc dng MPEG.

iu quan trng phi ch l lp ny c chia thnh 2 lp ph theo c tnhca chun H.264/AVC: lp m ha video(VCL) v lp tru tng(NAL). Lp phVCL quan tm ti vic nn cc ni dung video. Tn hiu u ra ca lp ny l chui


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cc slice nh. Dng bit lp NAL c t chc thnh cc gi ri rc c gi l cckhi NAL. nh dng ca cc khi NAL c m t trong hnh 3.3(=3.6)

Cc khi trong hnh 3.3 m t 1 khi NAL vi phn payload ni dung video.N c th cha cc loi payload khc trong phn ny nh thng tin iu khin.Nhng khi nh th c xp vo loi khng phi khi VCL (non-VCL unit). Cc

khi NAL c kt hp vi nhau thnh chui, nh dng nn khi truy cp. ch rng khi NAL c to nn t chun H.264/AVC c th h tr cho c cu trcmng da trn giao thc IP v cc mng khng da trn giao thc IP.

Hnh 3.3 Cu trc ca khi NAL

3.2.2 Lp ng gi Video:

truyn cc dng c bn m thanh, d liu v hnh nh qua mng s, mi dngc bn ny phi c chuyn i sang mt dng c chn ca gi PES c nhdu thi gian (PES- parketized Element Stream ). Mt dng PES ch bao gm 1 loid liu t 1 ngun. Mt gi PES c th c kch thc khi c nh hoc thay i,c th ln ti 65536 byte/gi. Bao gm 6 byte header, v s byte cn li cha nidung chng trnh.nh dng ca 1 PES header c minh ha trong hnh 3.4 vgii thich trong bng 3.4.


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Hnh 3.4nh dng gi MPEG PES

Bng 3.1 Cu trc ca mt gi MPEG PESTn trng Chc nng

Tin t m btu gi Gi PES bt u vi tin t 0x000001

Nhn dngdng(1 byte)

Trng ny nhn dng loi payload trong gi.Mt mu bit 111x xxxx cho bit l gi audio,cn mu bit 1110 xxxx cho bit rng l givideo. Gi tr "X" c s dng biu th ccs ca cc dng MPEG

di gi PES Trng di 2 byte ch th di gi

M ng b Trng c dng ng b ni dung videov audio

C header PES

Trng 14 bit cha cc b ch th PES khcnhau hay cc c, cung cp phn cng hayphn mm b gii m ca set - top box IP vithng tin thm vo. Cc loi c gm:

iu khin tranh chp PES: C ny bo cho b

gii m gi c c bo m hay khng thngqua x l tranh chp

u tin PES: C ny cung cp cho b giim thng tin v mc u tin ca gi PESB ch th sp xp d liu: B ch th ny quytnh Payload ca PES bt u vi bit video hayaudio


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Thng tin bn quyn: Khi bit ny c thit t,ni dung video c bo v bi bn quynBn gc hay bn sao: C ny ch ra ni dungny l bn gc hay bn sao

di d liuheader caPES

Trng ny nhn ch ra tng s byte b chimbi cc trng header khc nhau

Trng headerca PES Trng ny cha mt s cc bt ty chn

Payload caPES

Payload ca PES gm cc dng audio hay dliu video

Do bn cht ca mng, th t hay chui cc khung video t li ra ca trung tmd liu IPTV c th khc th t cc khung do cc thit b ca ngi dng nhn c. do, gip qu trnh ng b, cc h thng da trn MPEG thng dn nhn ccgi PES khc nhau trong chui video.

C 2 loi nhn thi gian c s dng i vi mi gi PES: nhn thi giantrnh din(PTS), v nhn thi gian gii m(DTS):

PTS---- nhn thi gian trnh din c gi tr thi gian 33 bit, c t trongtrng PES header. Mc ch ca vic s dng PTS cho mi gi l xc nh xemkhi no v theo trt t no th gi c xem (bi ngi xem).

.DTS---nhn gii m s dng gip b gii m thit b ca ngi sdng bit khi no x l gi .

Khi nim ng dng nhng nhn thi gian khc nhau i vi mi gi PEStrong dng m ha MPEG c minh ha trong hnh 3.5.

Nh ch ra trn, th t cc gi c truyn i qua mng khc vi tht cc gi nhn c thit b ca ngi s dng. Thit b ngi s dng IPTV sdng cc nhn PTS v DTS ti to li ni dung video gc. bn cnh vic gi icc ni dung nn MPEG-2, PES cn c kh nng truyn ti cc khi H.264/AVCqua mng IPTV. Cc chi tit qu trnh nh x c m t hnh 3.6.

3.2.3 Lp cu trc dng truyn ti:


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Lp tip theo trong m hnh truyn thng IPTV lm nhim v to nn dng truynti, bao gm 1 dng lin tip cc gi. Nhng gi ny thng c gi l cc gi TS,c to ra bng cch ngt cc gi PES thnh cc gi TS c kch thc c nh l 188bytec lp vi thi gian. S dng thi gian c lp ny lm gim kh nng mt gi tintrong qu trnh truyn v gim n. Mi gi TS bao gm 1 trong 3 nh dng truynthng: d liu, m thanh, hnh nh. Do , cc gi TS mang c nh 1 loi hnh truynthng. Mi gi TS bao gm 184 byte payload v 4 byte header. Cc thnh phn caTS header c m t trong hnh 3.7 v gii thch trong bng 3.2

Hnh 3.5 nh dng gi MPEG TS


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Hnh 3.6 nh x gi truy cp AVC sang gi MPEG PES

Hnh 3.7 ng dng nhn thi gian vi cc gi MPEG PES

Bng 3.2 Cu trc gi MPEG TS

Tn trng Chc nng

Trng ngb

Phn header thng bt u bng cc bit ngb (8 bit), thng l cc bit 0. Trng nydng xc nh im bt u ca 1gi IPTV.

Trng ch thli bit c ny s ch ra 1 li (nu c) lin quan ndng truyn ti

Trng ch thim bt ukhi truyn ti

bit c ny s ch ra 1 im bt u ca khitruyn ti

Mc u tintruyn ti

Khi t c ny s ch ra mc u tin khipayload

ID chng trnh

Trng quan trng nht trong phn header l13bit xc nh IDchng trnh. N s ch ra gi

no thuc dng no.Cc gi thuc dng noth s c cng ID chng trnh.B phn knhtrong b ca ngi s dng dng thng tin phn bit cc loi gi khc nhau.ch rng ccgi null c ID chng trnh = 8191. Cc gikhng c ID chng trnh th s b thit b nhn


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IPTV loi b

iu khin vic

tranh chp cctruyn ti

2 bit ca trng ny s cho bit trng thi mha ca phn payload gi truyn ti.

Trng iukhin thch nghi

trng 2 bit ny s cho bit liu header ca gid liu c lin quan ti dng truyn ti c baogm trng thch nghi v payload khng

B m tin

B m tin s m tng ln 1 khi 1 gi dngtruyn ti vi cng mt ID chng trnh. Nh c th xc nh c nu c mt hoc b lpgi. iu ny c th nh hng hnh nh.

Trng thchnghi

Trng ny c th c hoc khng c trongphn header.Trng thch nghi ny bao gm nhiu thng tinkhc nhau c s dng nh thi v iukhin, bao gm c PCR. PCR c s dng ng b ng h IPTVCD vi ng h b mha. Gi tr PCR c di 42 bit v c tngtheo tc ng h chun, 27MHz. Ngay saukhi ng b, vic gii m MPEG - 2 IPTV ctin hnh

Trng thchnghi

Trng ny c th c hoc khng c trongphn header.Trng thch nghi ny bao gm nhiu thng tinkhc nhau c s dng nh thi v iukhin, bao gm c PCR. PCR c s dng ng b ng h IPTVCD vi ng h b mha. Gi tr PCR c di 42 bit v c tngTheo tc ng h chun, 27MHz. Ngay saukhi ng b, vic gii m MPEG - 2 IPTV ctin hnh.

Lp ny cng cung cp chc nng to ra cc dng chng trnh. Mt dngchng trnh l mt gi PES cha 1 vi dng c bn c m hoasuwr dng cngng h ch, hoc ng h h thng. Cc kiu dng ny c pht trin cho nhngng dng nh lu tr ni dng video trn cc a quang hoc a cng.

Bn cnh cc ni dung hnh nh v m thanh c nn, dng truyn ti bao


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gm nhiu thng tin c trng ca chng trnh hoc metadata m t cc dng bit.Thng tin ny c cha trong 4 bng PSI.

(1) Bng chng trnh kt hp (PAT)- Vic truyn cc bng PAT l bt buc vl im vo cc bng PSI. Bng chng trnh kt hp lun c ID chng trnh l 0.Bng ny a ra cc lin kt gia ch s chng trnh v ID ca chng trnh

(2) Bng nh x chng trnh: Bng nh x chng trnh cng l bt bucv mang co thng tin v mt chng trnh c th. Bng nh x chng trnh litk cc ID chng trnh cho cc gi mang cc thnh phn ca 1 chng trnh cth (m thanh, hnh nh, d liu, v cc thng tin PCR).Hnh 3.8 m t 1 v d vmi quan h gia bng chng trnh kt hp (PAT) v bng chng trnh nh x(PMT).

V th khi 1 thit b ngi dng(IPTVCD) yu cu 1 chng trnh, bngchng trnh kt hp s c kim tra, sau s kim tra bng chng trnh nhx nh ngha cc IP chng trnh v gi m thanh, hnh nh v d liu lin ktvi chng trnh . Trong v d ny, thu bao la chn chng trnh1 v thit b

IPTV ca ngi s dng nh v ton b cc gi truyn ti vi ID chng trnh l 36i vi phn hnh nh ca chng trnh v cc gi vi ID chng trnh l 3 vi ccphn m thanh ca chng trnh. Nu d liu l qung b vi chng trnh, thbng nh x chng trnh s bao gm cc chi tit trn xc nh cc gi d liutruyn ti.


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Hnh 3.8 Mi lin h gia PMT v PAT

(3) Bng iu kin truy cp(CAT)- bng iu kin truy cp l 1 bng tychn PSI bao gm cc ID chng trnh ca EMMs (cc tin qun l quyn truy cp).

Tin qun l quyn truy cp bao gm cc thng tin v mc cho php i vi h thngtruy cp. bng iu kin truy cp(CAT) thng c cha trong 1 gi gi vi IDchng trnh l 1.

(4) Bng thng tin mng (NIT)- Bng thng tin mng NIT l 1 bng tychn lu tr cc thng tin nh tn s knh v s dng truyn ti. Set top box s sdng thng tin ny chnh sng ti cc chng trnh c th.

Khi TS c cu trc v nh dng, n s c chuyn xung lp truyn titrc tip hoc ti lp s dng giao thc truyn ti thi gian thc (RTP).

3.2.4 Lp giao thc truyn ti thi gian thc( ty chn):Lp ty chn ny c s dng rng ri trong nhiu ng dng khc nhau. Lp

ny hot ng nh 1 lp trung gian gia cc ni dung c nn MPEG-2, H.264/AVC lp cao hn v c lp thp hn trong m hnh IPTV. Giao thc RTP chnh l li calp ny v thngl block c s h tr truyn dng ni dung theo thi gian thc quamng IP.


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Giao thc truyn ti thi gian thc phn pht cc dng m thanh v hnh nhbng cch ng gi cc ni dung ny trong mt nh dng ring bit c gi gi.Migi bao gm phn header v payload(d liu IPTV). s dng hiu qu bng thng,phn payload thng bao gm nhiu hn 1 gi MPEG-TS.

Phn header bao gm cc chc nng ct yu cc th truyn thnh cng

cc d liu thi gian thc qua mng. header ca RTP c th nhn bit vi headerca UDP c gi tr l 5004, v bao gm rt nhiu trng.Chi tit v cc trngkhc nhau c minh ha trong hnh 3.9 v bng 3.3

C 1 iu ng ch , l giao thc thi gian thc khng c trng ditrong phn header bi v n ph thuc vo giao thc truyn ti c bn cung cploi thng tin ny. Nh miu t trong bng 3.6, li ch chnh ca vic chn ccn dung video c nn v trong cc gi RTP l:

(1) Thm s chui vo gi gip c b gii m pha nh cung cp vthit b ngi dng c th sp xp li cc gi nhn c t mng IP.

(2) Trng nhn thi gian gip khc phc cc vn nh jitter v mtng b gia ngun v ch.

Hnh 3.9nh dng RTP header

Khi header truyn ti thi gian thc c thm vo payload video, gi truyn tithi gian thc c gi ti giao thc TCP hoc UDP tip tc x l.

nh dng phn payload ca RTPcho vic ng gi dng bit nn MPEG-2: thayv s dng UDP mang cc gi TS MPEG-2 th mt vi h thng IPTV s dng lpRTP thm vo lp UDP truyn cc gi. Vic nh x cc gi MPEG-TS sang ccgiRTP l kh n gin. Cu trc bao gm phn hader v payload ca gi MPEG-2 TS.Mi gi c di 188 byte. Hnh 3.10 m t cu trc truyn ti ni dung DVB da trnMPEG-2 qua mng IP.


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nh dng payload RTP cho vic nggi dng bitc nn dng chunH.264/AVC: RFC 3984 cung cp khuyn ngh v gii php truyn cc ni dungH264/AVC v nh ngha 3 c ch chn cc khi NAL vo RTP payload:

(1) Mt gi NAL ring bit: k thut ny nh ngha s nh x gi NAL

sang tng payload RTP. Cu trc ca tng gi NAL c m t trong hnh 3.11.(2) Gi NAL tp hp: K thut ny nh ngha s nh x nhiu gi NAL

sang 1 gi RTP. Cu trc ca gi NAL tp hp c m t trong hnh 3.12.

Bng 3.3: Cu trc ca gi IPTV da trn RTP

Tn trng Chc nng

Phin bn (V) Trng ny xc nh phin bn RTP c dng tronggi IPTV

Phn m (P) Trng ny xc nh c byte m trong gi RTP haykhng

Phn m rng(X)

Nu bit ny c t bng 1 th phn m rng theo ngaysau tiu c nh

Tng s ngungp (CSRC)

Trng ny cha thng tin s b nhn din CSRC ctrong gi

Bit du Chc nng ca n c xc nh bi m t RTP.Thng c s dng xc nh ranh gii khung

Loi Payload(PT)

Trng ny ch thng tin v nh dng payload caIPTV. V d, gi tr 34 ch ra ni dung video c m has dng H.263

S th t gi

Trng ny gip tm ra c nhng gi b mt, li. Gipcho IPTVCD sp xp li cc gi c gi ti khng theoth t, xc nh ng knh thc gi khng ng v chra gi b lp. Gi tr trong trng c tng ln mt mi

ln mt gi RTP c gi qua mng. Khi dng IPTV btu, mt gi tr bt k c gn cho trng ny gimri ro b hacker tn cng

Du thi gianTrng ny gi du thi gian ca gi, c khi to tmt ng h ng tin cy. Trng ny c sd thmvo trong cc gi m thanh v hnh nh ng theo th t


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thi gian ca dng IPTV

Ngun ng b

(SSRC)

Mc ch ca trng ny ch ra ngun ng b trongmng IPTV. Trng ny thng c s dng kt hp

vi trng s th t gi sa nhng vn xy ratrong chui IPTV

Danh schCSRC

Mc ch ca trng 32 bit ny ch ra nhng ngunvideo v audio gp vo payload IPTV

Hnh 3.10 Cc gi MPEG TS

Hnh 3.11 nh x ni dung H264/AVC ( tng khi NAL ring bit ) sang RTPpayload


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Hnh 3.12 nh x ni dung H264/AVC ( nhiu khi NAL ring bit ) sang mt RTPpayload

Hnh 3.13 nh x ni dung mt H264/AVC NAL sang nhiu RTP payload


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Khi NAL tp hp c nh ngha xc nh dung lng gi ln nht i vimi mng. VD, vi mang Ethernet kch thc gi ln nht l 1500 byte, cn vi mngATM kch thc gi ln nht l 54 byte. Dng cc gi NAL tp hp nh x nhiu giNAL sang 1 phn payload RTP khng cn phi chuyn m v thm nhiu tiu gikhi trin khai IPTv trn cc nn.

(3) Gi NAL phn tch: y l k thut nh x 1 khi NAL ring r ra khinhiu phn payload RTP. Cu trc ca mt gi Nal phn tch c m t nh tronghnh 3.13).

im ng ch l gi phn tch NAL phi c gi qua mng theo 1 trtt lin tip. iu ny l c th khi s dng cc s tng dn trong header caRTP.K thut ny em li 2 li ch cho nh cung cp dch v. Th 1, iu ny giptruyn lng ln chng trnh c phn gii cao da trn IP. Th 2 l gip tngkh nng sa li.

Ch rng, k thut RTP thng c trin khai trong cc mng khng m

bo cht lng dch v QoS truyn cc dch v IPTV. Mc d RTP gip lm tngkh nng cc dng ti ch trong trt t ng, nhng khng c thit k m bocc mc cht lng dch v. Do , trch nhim ca nh cung cp dch v l n bovideo lun c u tin khi chng c truyn i trong h tng mng.

3.2.5 Lp truyn ti:

Thng thng cc gi RTP l dng u vo ca lp truyn ti. iu ngch l c th nh x trc tip cc gi MPEG-TS sang payload giao thc ca lptruyn ti.

Lp truyn ti IPTV c thit k m bo cc kt ni u cui l tin cy.Nu d liu ti thit b ngi nhn ng. Lp truyn ti s truyn li. Lp truyn tithng bo vi lp trn c cc thng tin chnh xc hn.

TCP v UDP l 2 giao thc quan trong nht c s dng lp ny.

a) S dng TCP nh tuyn cc gi IPTV :

TCP l giao thc ct li ca b giao thc internet v c xp vo loi nhhng kt ni. iu ny c bn c ngha l kt ni c thit lp gia u cuinh cung cp v thit b IPTV cua ngi s dng truyn cc chng trnh qua

mng.TCP c kh nng iu khin li xy ra trong qu trnh truyn cc chngtrnh qua mng. Cc li nh mt gi, mt trt t gi,hoc lp gi thng gp trongm trng truyn IPTV. x l cc tnh hung ny, TCP s dng h thng cc slin tc cho php thit b gi c th gi li cc d liu hnh nh b mt hochng. H thng s lin tc ny l trng c di 32 bit trong cu trc gi. trngu tin cha chui s bt u ca d liu trong gi v trng th hai cha gi tr


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ca chui s tip theo m video server ang i (mong) nhn tr li t IPTVCD

Hnh 3.14 C ch iu khin lung ca TCP

Bn cnh vic sa cc li c th xy ra trong qu trnh truyn ni dung video quamng IP bng rng, TCP cn c iu khin lung d liu. iu ny c th t cbng cch s dng trng kch thc ca s, vi thut ton c gi l ca s trt.Gi tr trong trng ny xc nh s cc byte c th truyn i qua mng trc khi nhnc xc nhn t pha thit b nhn.

Trong mi trng IPTV, gi tr trng kch thc ca s chnh l kch thcvng m trong IPTVCD tr i lng ni dung c trong vng m ti mt thi im.D liu ny s c gi cho ti khi bn tin thng bo nhn c gi v t IPTVCD.

Khi gi tr ca trng ny bng 0, IPTVCD pha u thu s khng kh

nng x l cc d liu IPTV tc ln. khi , TCP s ch th cho video serverdng hoc lm chm li tc gi cc gi d liu ti IPTVCD. iu ny s m borng IPTVCD s khng b trn cc gi d liu ti. Khi IPTVCD x l xong cc ccgi d liu trong vng mv video server bit c iu th gi tr ti vng ms tng ln, v video server s bt u truyn tip cc ni dung. Trong mi trngIPTV l tng, s ca ca s c bo v t IPTVCD s bo cho server bit khnggian vng m cn trng chnh la tc m ti cc ni dung video c gi i t


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video server.

Cc cng TCP v Socket: Mi im cui ca 1 lin kt IPTV th c 1 a chIP v 1 gi tr cng lin quan. V th mi lin kt c 4 thnh phn khc nhau:

(1) a ch IP ca video server(2) S ca cng ca video server

(3) a ch IP ca IPTVCD

(4) S ca cng ca IPTVCD

Vic kt hp a ch IP v s ca cng cho php 1 tin trnh trn IPTVCD c thlin lc trc tip vi tin trnh ang chy trn mt trong cc my server c t trungtm d liu IPTV. Mt cng gm 16 bit nh ngha hng truyn cc thng bogia cc lp mng. C 2 loi cng :

Cng well known c gi tr t 1 n 1023. Loi cng ny thng c ccserver s dng v c qun l bi IANA

Cng Ephemeral c thiu lp bi IPTVCD trng thi tm thi khi lin lcvi IPTV server. Cc cng thng c nh trong ngn xp phn mm IP. Cc gi trny thng ln hn 1024 v nh hn65535. Cng ny khng chu s qun l ca IANA.

Socket cng l mt thnh phn quan trng khc trong m hnh truyn thng IP.Mt socket v c bn l 1 giao din ng dng chng trnh (API), c s dng

lm cho lm vic lin lc gia cc tin trnh ang chy trn 1 thit b IP. Mt socketc thit t bng cch kt hp a ch IP vi s ca cng.

Hnh 3.15 Qu trnh truyn thng trong mng IPTV


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hiu hn v mi lin h gia a ch IP v socket xt cc bc thit lp 1knh truyn thng gia 1 tin trnh chy trn IPTVCD v 1 tin trnh chy trn trungtm cung cp d liu IPTV. Bc c m t nh sau:

(1) Chun b d liu: Tin trnh gi chy trn h thng server dong IPTV chunb ni dung v gi module truyn thng TCP/IP truyn cc d liu ti 1 tin trnh ang

chy trn mt IPTVCD. Cc tin trnh truyn thng bt u v thng tin header cthm vo ni dung khi truyn qua cc lp trong IPTVCM.

(2) Thit lp kt ni logic TCP: C 2 u kt ni u c nh ngha bi1 a ch IP v 1 s cng. kt hp gia a ch IP v s cng gi l socket.H thnga ch i vi lin kt truyn thng bao gm cc thnh phn sau:

Giao thc

a ch IP ca my ch IPTV

ID ca tin trnh chy trn my ch IPTV

a ch IP ca IPTVCD

ID ca tin trnh chy trn IPTVCD

(3) Truyn d liu: Truyn thng bt u thng qua socket gia 2 tin trnh tpha IPTV server n IPTVCD

(4) Qun l cc dng ni dung IPTV: giao thc TCP qun l cc dngIPTV trong khi kt ni c thit lp

(5) Hy b kt ni: Khi hon thnh vic truyn cc ni dung IPTV,IPTVCD hoc trung tm d liu s hy b socket v kt ni mng

Header: Thng tin ny gip cho segment c truyn i t ngun nch. Header mang thng tin chnh l s cng ca ngun v ch, s chui casegment v kim tra tng. Cc s tng m bo rng d liu c th ti v tr vt ng cc tin trnh ang chy trn mi thit b IP. S chui gip TCP c thhiu c bng cch no a d liu v dng trc khi b gt thnh ccsegment.

D liu video:

Bng 3.4nh dng ca TCP segment

Tn trng Chc nngCa ngun Trng 16 bit. Ch ra s ca cng ngunCng ch Trng 16 bit. Ch ra s ca cng ch

Ch s dyCh ra ch s dy ca on TCP. iu ny gipTCP theo c vt ca mi gi IPTVchuyn qua mng


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Ch s chpnhn

cha ch s dy tip theo m thit b gi mongmun nhn c. Trng ny ch cha gi tr nynu bt iu khin ACK c thit lp

di d liu trng ngn ny ch ra v tr trong on m d liu

video bt uc ttrc

Trng ny c t trc s dng sau ny vc gi tr bng 0

Cc bit iukhin

Trng ny gm c 6bt iu khin:URG: Urgent pointerACK: AcknowledgmentPSH: PushRST: Reset (t li lin kt)SYN: Synchronize (ng b ch s dy)FIN: khng c thm d liu t bn gi

Ca sCh ra kch thc ca s cho d liu phn phigia nhng ln nhn

Checksum Kim tra li bo v d liu c gi qua mngcon tr khncp

Ch c dch khi trng con tr khn cp ccho php

Cc ty chnv m

Cc ty chn l cc bi s 8 bit c sn v c thcha cc kiu bin khc nhau. Cc ty chn cla chn s quyt nh di ca on TCP. ml phn cui cng ca tiu v to thnh bi ccs 0

TCP nh x segment sang giao thc IP sau khi chn cc thng tin cn thit

vo trong phn header.Nh m t trn, TCP cung cp ton b cc chcnng truyn ti cc d liu qua mng IP.

b) S dng UDP nh hng cc gi IPTV:

UDP l giao thc thuc v b giao thc Internet. UDP cho php my ch kt nivi mng bng rng gi ti cc IPTVCD dch v truyn hnh qung b c cht lnghi lng ngi dng. UDP ging vi TCP nhng l phin bn s lc hn, a ra chos lng ti thiu cc dch v truyn ti. UDP l giao thc khng lin kt, iu cngha l kt ni gia video server v IPTVCD ko cn phi thit lp trc khi d liu ctruyn i. Video server dn gin ch thm vo a ch IP ch v s cng vo datagramv gi ti c s mng phn pht ti a ch IP ch.Khi trn mng, UDP sd cch tt

nht c gng thu c d liu v im ch ca n. Ch rng UDP s dng cckhi d liu c gi l cc datagram truyn ni dung qua mng.

UDP datagram: UDP datagram bao gm 8 byte header v d liu video. Ccthnh phn c bn ca 1 UDP datagram c m t trong hnh 3.16 v bng 3.5

u im v nhc im ca UDP:

u im ca UDP:


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Khng c ngt trong qu trnh truyn ni dng video: khng c tr trongqu trnh phn phi ngay c khi trong mng c cc gi b tr hoc b hng. Ngcli, khi s dng TCP, c th xy ra s ngt qung khi phi ch cc gi b tr v cckhung hnh ti hoc phi ch cc gi b hng c thay th.

Dung lng thp: Kch thc header ca UDP ch bao gm c 8 byte

trong khi TCP header chim ti 20 byte. Tc thit lp kt ni: thi gian thit lp v hy b kt ni gia IPTVCD

v cc thit b trung tm d liu IPTV ngn. Do , vic phn phi cc gi sdng giao thc UDP thng nhanh hn so vi s dng giao thc TCP.

H tr truyn 1 chiu: UDP khng yu cu ng v, do cho php cccng ty s dng v tinh c th truyn ni dung IPTV truyn a im ti khch hngca mnh.

Nhc im ca UDP:

Mc d UDP l nhanh chng v hiu qu i vi cc ng dng cn thigian, v s l khng hiu qu trong trng hp:

Tnh ton vn ca d liu: Tnh ton vn ca d liu khi s dng UDP lkhng c bo m khi UDP ch cung cp 1 dch v duy nht l kim tra tng vmultiplexing thng qua s cng. bt k vn no cng c th xy ra trong qutrnh truyn thng ti u cui no cn c iu khin c lp vi cc ngdng. Cc vn thng gp nh l pht li, ng gi v lp rp li, truyn li ccgi b mt, s tc nghn, v iu khin lung nm ngoi kh nng sa li caUDP.

Kh khn trong vic vt qua cc tng la: Nhiu loi tng la trnmng chn cc thng tin UDP gy ra cc li trong qu trnh truyn thng. ykhng phi l vn ln i vi cc nh cung cp dch v IPTV, tuy nhin n cngnh hng ti cc cng ty cung cp dch v Internet TV.


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Hnh 3.16nh dng datagram da trn UDP

Bng 3.5 Cu trc datagram IPTV da trn UDP

Tn trng Chc nng

Ca ngunch ra ch s ca ca qu trnh gi datagram. Nl ca ty chn v nu khng cdng th s c in y bng cc s 0

Ca chCh ra ch s ca ca qu trnh ch ang chytrn IPTVCD

di

Gip cho IPTVCD xc nh di v kch thc

ca datagram UDP ang n. Trng di bao gm mt gi tr h 8, bao gm c tiu v d liu video thc s.

Checksum

Trng ny di 2 byte cha s c nh trc,cho php mt IPTVCD kim li tnhnguyn vn ca UDP ang n da trndatagram IPTV.

D liu video

Phn ny ca datagram cha d liu video. Trongtrng hp mi trng IPTV,d liu l mt phn ca datagram UDP c nhdng bi giao thc dng video v

audio m c s dng ti u cui IPTV

i vi IPTV, UDP t ra hu ch khi trung tm d liu cn gi cc nidung video IP ti nhiu IPTVCD v l giao thc mc truyn ti ph bin nht mcc nh cung cp dch v IPTV.


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c) S khc bit gia TCP v UDP:

Khi cc nh cung cp dch v pht cc ni dung IPTV ti cc thu bao, iu quantrng l cc ni dung ny phi n thit b ca ngi dng ng lc v trong dng ng.Ni cch khc, cc gi video phi khng b ngt qung. Do , cc nh cung cp dch vcn chc chn s dng giao thc h tr kh nng phn phi qua h tng mng.

Mc d TCP cung cp cc ng dng vi nhiu c trng v mng so viUDP, nhng cc nh cung cp dch v IPTV khng thng chn TCP l giao thctryn ti.iu ny ch ra 1 thc t rng IPTV l ng dng thi gian thc v khngc tr. TCP c th a ngm vo s phn phi ni dung video IP do thc t rnggiao thc s dng c ch iu khin dng.c im v hn ch cuTCP i viphn phi chng trnh thi gian thc:

Cn bng gia nhy v tr---- IPTV t nhy vi mt hoc ngt gi hnl vi tr. Vic truyn li cc gi nng cao tin cy ca kt ni gia my ch vthit b truy cp IPTV. Tuy nhin, khi vic truyn li din ra nhiu th s lm trtng ln.

TCP l giao thc kt ni lin kt---- Nh trnh by trn TCP yu cuthit lp kt ni logic gia my ch v IPTVCD trc khih truyn cc ni dungIPTV. Khi ngi xem chuyn t knh ny sang knh khc cng s gy ra tri vi mi trng truyn hnh trc tip ca IPTV.

H tr sa li---- TCP cung cp nhiu tnh nng, ng ch l kh nngsa li v iu khin lung. Tuy nhin, vic sa li trong mng IP video c th lmgim cht lng dch v ti khch hng.

c im ca truyn video: video bao gm 1 chui cc nh lin tip, bt ckhi no xy ra ngt vi tc m ti cc hnh nh ny c x l v hin thtrn ITVCD cng lm gim cht lng hnh nh hin th v nh hng ti ngi

s dng. Thi gian x l mi nh ring bit ch mt khong 1 phn ca giy. Nus dng TCP sa li do ngt, c ch sa li nh sau:

(1) IPTVCD s bo gi d liu b li bng vic t c.

(2) Mt bn tin s c gi ti my ch IPTV thng bo cho ng dngbit 1 trong cc gi nhn c b ngt.

(3) Di s qun l ca TCP, my ch cn phi tm ra v gi li gi b ngt.

(5) IPTV CD nhn c gi mi trong vung m v hin th ni dung videotrong gi .

Trong khi TCP thc hin cc bc trn, IPTVCD phi ch gi b li ctruyn li v phi trng lung video hoc b qua gi truyn li khi nhn c,Do k thut sa li ca TCP l khng cn thit.

Mt gi IP----- qu trnh x l mt cc gi IPTV nhiu hay t cng ging nhquad\s trnh sa ngt gi IPTV. Cc gi b mt cng cn c truyn li, gy ra nh


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hng bt li ti dich v phn phi IPTV.

H tr iu khin lung---- Bn cnh vn sa li v thit lp kt ni logic,giao thc TCP cn h tr iu khin tc bit lung d liu gi i, c th gy ra nhiutr ngi trong vic truyn v nhn ni dung IPTV. Tr ngi ny xy ra khi vng m

IPTV bt u trn cc gi IPTV hoc mng b nghn. Khi xy ra trng hp ny, mych nhn c yu cu gim tc gi cc gi tin ln mng. Nu my ch thc hinyu cu gim tc , c 1 kh nng l: khi tc gim xung hnh nh s khngth hin th c. Nu bn tin dng c thc hin, dch v IPTV s b tt hon ton.

Khng h tr a truyn thng---- TCP khng hot ng hiu qu trong mitrng a truyn thng, Do , UDP l la chn tt hn TCP i vi cc dch vtruyn thng nh cc ng dng a truyng thng IPTV v truyn qung b.

y l nhng nguyn nhn chnh TCP t c s dng trong IPTV trc tip.TCP c dng trong cc ng dng khc nh e-mail, download cc chng trnhInternet TV.

Mc d, tin cy v kh nng s li ca UDP khng bng TCP nhngUDP l giao thc c la chn phn pht cc dch v IPTV . UDP c ccnhc im sau: khng c kh nng tm v sa li. Vn ny c khc phcbng cch gn cc hm sa li vo cc ng dng IPTV chy trn cc mng hoctrong chnh cc dng video.

3.2.6 Lp IP:

Sau lp truyn ti l lp IP(cn c gi l lp lin mng ) Nhim v chnh ca lpny l a cc d liu ti cc v tr mng ring bit thng qua nhiu mng c lp c

lin kt vi nhau c gi l lin mng. Lp ny c s dng gi cc d liu thngqua cc ng khc nhau ti ch. IP l giao thc tt nht c s dng trong lp linmng. giao thc ny cung cp dch v phn pht gi c bn cho tt c cc dch v IPTV.Cc loi dch v ny vi h thng truyn n im, ni cc gi c truyn t ngun ti 1IPTVCD ch, khc vi h thng truyn a im ni m cc gi c truyn t my chti nhiu IPTVCD.

IPv4 l giao thc ph bin nht c s dng trong mng IPTV ngy nay.Nhim v chnh ca IP l phn pht cc bit d liu trong cc gi t ngun ti ch. IP sdng k thut c hiu qu cao nht phn pht d liu. Ni cch khc khng c tintrnh no m bo qu trnh phn pht thng tin qua mng. Cc khi c s ca giaothc IP l cc on bit d liu ct trong cc gi v c nh a ch.

Gi IP l n v d liu bao gm d liu video thc v cc thng tin cavic nhn video t trung tm cung cp d liu IPTV ti ch IPTVCD. Thnh phnchnh ca mt giIPv4 c m t trong hnh 3.17 v bng 3.6.


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Cch nh a ch IP: trong mi trng IPTV, a ch IPv4 thng cdng nh ngha IPTVCD v trung tm cung cp d liu. a ch IPv4 l chui 4s c ngn cch vi nhau bng cc du chm nh ngha 1 cch chnh xcv tr vt l ca 1 thit b, v d nh set-top box, trong mng. a ch IPv4 gm 32 bittrong h nh phn. Cc s nh phn ny c chia thnh 4 octet, mi octet 8 bit,mi octet c i din bi 1 s h thp phn nm trong khong t 0 n 255. Mioctet c ngn cch bi 1 du chm trong h thp phn. a ch IP c t chcthnh 2 phn:

(1) a ch mng dng nh ngha mng bng rng m IPTVCD kt niti.

(2) a ch host dng nh ngha cc thit b IPTV.

Hnh 3.17 nh dng gi video IPv4

Bang 3.6: Cu trc gi video IPv4

Tn trng Chc nng

Phin bnCh ra phin bn ca IP c s dng trn mng

_ IPv4 hay IPv6

di Header M t kch thc ca header, gip cho IPTVCDnhn ra payload ca d liu video bt u u


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Loi dch v

Cn c bit l im m phn bit dch v(DSCP_Differentiated services code point).Trng ny kh quan trng cho vic phn phini dung IPTV bi v n cho nh cung cp dch vthit t loi ni dung c mang trong gi dliu. Thng tin ny sau c x l bi b nhtuyn IP trong h thng mng. iu ny cho phpcc b nh tuyn chp nhn v lm cho mc chtlng dch v thch hp vi nhng loi lu lngkhc nhau

Tng chiu diBo cho IPTVCD bit ton b chiu di ca giIPTV. Gi tr ny c di 16bit, c ngha l mtgi c th c kch thc ti a l 65535 byte

th nhn dng

c b nh tuyn s dng phn mt gi lnthnh nhiu mnh nh. Khi c phn mnh, bnh tuyn s dng trng ny phn bit cc

mnh khc nhau ca gi ban u

C

Cc c xc nh cc kiu phn mnh khc nhau,hoc gi l mt mnh, hoc n c cho phpphn mnh, hoc gi l mnh cui cng hay cthm mnh khc.

di camnh

Khi mt gi IPTV c phn mnh v chuyn iqua mng th chc nng ca IPTVCD l tng hpcc mnh theo ng th t. Trng ny nh smi mnh, cho php IPTVCD tng hp li theong th t

Thi gian sng

V mt gi IP chuyn qua mng, trng thi gian

sng s c mi b nh tuyn dc theo ngtruyn kim tra v gi tr bn trong trng ny sc gim dn. Qu trnh ny tip tc cho n khigi tr trng ny gim v 0. Khi iu ny xy rac ngha l gi ny ht hn v s b loi b. Chcnng chnh ca trng ny l loi b cc gitrn mng m khng c kh nng truyn n ch.

iu ny s lm gim tc nghn trn mng. Gi trca trng ny trong khong t 30 n 32.

Giao thc

Trng di 8 bit, ch ra loi giao thc ng gibn trong datagram IP. Nu gi tr l mt th sau

ICMP c dng, l hai tng ng vi IGMP,l 6 c s dng cho lu lng TCP, v 17c s dng cho ng dng UDP

Kim tra tngheader

cho php IPTVCD tch datatgram khi header li.Gi b li thng b IPTVCD loi b hay hy

a ch ngunCha a ch IP ca thit b gi gi IPTV. Trongmi trng IPTV, thit b gi thng l my ch


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VoD hoc l b m ha.

a ch chCha a ch ca thit b nhn c ch nh.Trong mi trng IPTV, a ch ny thng l ach ca IPTVCD

Ty chn v

m

c nh cung cp IPTV s dng cung cp

thm cc c im khcD liu L ni dung video

Mt im ng ch l mt vi bit u tin ca a ch s nh ngha cc bit cnli ca trng a ch s c phn chia th no cho host v mng. thun li chovic s dng v qun l, a ch IP c chia thnh cc lp khc nhau. Chi tit a chcc lp c m t trong bng 3.7.

Trng a ch ca mng v host c m t nh trong hnh 2.18.

Bn cnh vic chia thnh cc lp, mt s a ch IP c dnh ring cho cc

mng t nhn. Cc a ch ny nm trong di:10.0.0.0 to 10.255.255.255

172.16.0.0 to 172.31.255.255192.168.0.0 to 192.168.255.255

Bng 3.7 cc lp a ch IPv4

Lp a ch IP M t

A

M t mt mng s hu s u tin trong a chIP, c gi tr t 0 n 128. Ba s cn li c

dng xc nh mt IPTVCD, my ch, hay thitb mng khc. Do , mt a ch lp A c a chmng 7 bit v a ch host 24 bit. Bit c th t caonht c thit lp bng 0C 126 a ch mng lp A trn th gii v mimng trong s c s a ch IP h trhn 16 thit b mng. Tt c cc a ch IP lp Ac cp php t InterNIC t nhiu nm trc.

B

Mt mng lp B c a ch gm s u tin c gitr t 128 n 191. Gi tr ny tng ng via ch mng 14 bit v mt a ch cc b 16 bit.Gi tr ca 1 v 0 gn cho 2 bit c th t cao nht.C khong 16000 mng lp B trn Internet, mimng c kh nng h tr 64000 thit b mng.Nhng t chc ln hn v cc nh cung cp dchv Internet cp php cho hu ht hoc gn htcc a ch ny. V d v a ch lp B: 132.6.2.24,trong , 132.6 ch ra mng, 2.24 ch ra host.


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C

Mng lp C c a ch c s u tin c gi tr t192 n 223. S ny tng ng vi mt a chmng 21 v a ch cc b 8 bit. Gi tr 1,1 v 0c gn cho 3 bit c th t cao nht. C gn 2triu a ch mng lp C, mi mng c kh nngh tr nh a ch cho 254 thit b mng.

DL phn u tin ca a ch c gi tr t 224 n239. Nhng a ch IP ny c s dng cho mcch truyn a im

Ea ch mng lp E c gi tr t 240 n 247 vc t trc s dng sau ny

Hnh 3.18 cc lp a ch IP

d) Mng con IPTV:

Trong cc mng ln IPTV vi hng ngn IPTVCD tri rng trn 1 khu vc a lrng., mng da trn IP ny cn c chia thnh cc mng nh hn gi l mng con.Mng con ca mng IPTV cho php nh cung cp dch v nh ngha v gim st ccphn ring bit trong mng m khng cn a ch IPv4 mi. Ngi iu hnh mng cngs dng a ch mng con giu i cu trc mng ni b trch b tn cng t mng


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Internet cng cng. Ngi qun tr mng IPTV s dng cc s ring bit ccj gi l ach subnet mask to cc mng con trong mi trng IPTV. Subnet mask l a chIP32 bit. Gi tr mc nh cu subnet mask ca lp A, B, C l:

Class A----- 255.0.0.0

Class B----- 255.255.0.0

Class C-----255.255.255.0

Cc tin trnh chy trn mng con thng c qun l bi thit b phn cng gil router. Mt router c th ni vi nhiu mng v quyt nh thng tin s c gi nu trong mng.

e) Tng lai ca a ch IP:

Khi cu trc a ch IP ca mng Internet mi c pht trin trong nhngnm u ca thp k 80, ngi ta cho rng n p ng c nhu cu cangi dng hin ti v trong tng lai. a ch IP 32 bit trong vesion IPv4 c thnh a ch cho hn 4 t my trm trong khong 16,7 triu mng khc nhau.ach IPv4 khng p ng c nhu cu tc pht trin ca mng Internet nhhin nay.Tc pht trin ca mng Internet nm ngoi d on ca nhngngi pht trin giao thc IP v s lng mng kt ni vi mng Internet tng lntng thng.

tm gii php cho hn ch ca a ch IPv4, Nhm K S mng Internet a ravesion mi IPv6 vi 128 bit a ch. . IPv6 c th cung cp lng a ch gp hng t ln sa ch IPv4. IPv6 c c cc kh nng cung cp h tr vic xc thc, tnh ton vn QoS, mha v b mt. Vic s dng IPv6 trn mng IPTV l thch hp bi v c ch QoS bn trongn v c kh nng h tr s lng khng gii hn cc IPTVCD.Trong 5 ti 10 nm t, IPv6

s dn thay th IPv4.Ti sao li s dng IPv6 khi trin khai IPTV ? IPv6 c tnh nng vt tri hn

so vi IPv4. Cc nguyn nhn chnh khin cc nh cung cp dch v xem xt vic sdng IPv6:

Quy m c tng ln: IPv4 dng a ch 32 bit trong khi IPv6 dng a ch128 bit, ln hn gp 4 ln. iu ny cho php nh cung cp dch v IPTV m rngs lng thit b c th qun l .

Cu trc header n gin: IPv6 gim kch thc header xung cn 40byte c nh v n gin cu trc ca trng header. Cc thnh phn c bnca IPv6 header c m t trong hnh 3.19 v bng 3.13.

Tng mc bo v: IPv6 c 2 c im gip tng mc bo v:

(1) Bao gm header xc thc----- bao gm cc bn tin xc nhn v kim trangi gi gi.

(2) Payload bo mt c ng gi----- c im ny m bo tnh ton vn cad liu IPTV v bo mt gia cc my ch trung tm d liu IPTV v cc IPTVCD khc.


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Lu lng thi gian thc tt hn: kh nng dn nhn lung ca IPv6cho php nh cung cp dch v nh du cc gi ring, ph thuc vo tng loidch v. Trong mi trng triple-play, cc router c th coi cc gi IP c dnnhn vi mt nhn dng video l cc gi IP c dn nhn khi mang ni dungweb.

T ng cu hnh: Kh nng plug and play ca IPv6 gip gim bt phctp khi ci t dch v IPTV ti nh ca khch hng.

Hnh 3.19 Cu truc header ca IPv6

Bng 3.8 M t trng ca IPv6

Tn trng Chc nngM bt uca gi

Cc gi PES bt u bng cc bit 0

nh dngdng

Trng ny dng nh ngha loi payload chatrong gi. Dng 111x xxxxl ch gi m thanh, v 1110 xxxx ch cc gi hnhnh. x l s dng MPEG

di gi

PES

2 byte ca trng ny dng nh ngha di

gi

M ng b

Trng ny c s dng ng b m thanhv ni dung video cung cp phn cngv phn mm trong b m ha t trong set- topbox IP vi cc thng tin thm. Trongtrng ny cn bao gm cc c:C iu khin trn m PES: bo cho b m ha


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bit liu gi c c m bo khng trong qutrnh x l trn m.C u tin PES: Cung cp thng tin v mc utin ca gi PES cho b gii m.Data_alignment_indicator : C ch th ny s xcnh xem phn payload ca PES bt u vi bitm thanh hay hnh nh,Thng tin bn quyn: khi bit nay c thit lp,chng trnh l chng trnh c bn quyn.C nguyn bn hay bn sao: C ny ch th liuchng trnh c phi l bn gc, hay la bnsao.

di d liuheader

trng ny dng nh ngha tng s byte cs dng bi cctrng headerkhc.

Cc trng

headertrong PES Trng ny cha cc s cc bit ty chnTrngpayload vd liu video

Trng payload ca PES cha cc dng c bnm thanh

V nhng u im k trn IPv6 c xem nh gii php lu di h trtrin khai cc thit b s quy m ln, c th s dng nhiu loi ng dng datrn IP.

Nhc im chnh khi s dng giao thc IP l khng c g m bo rng

khi no cc gi ti ng ch hay gi c n ng lc khng.ngay c th t ccgi c chuyn n cng khng c xc nh. Do , lp IP lm vic cng vigiao thc lp truyn ti m bo rng cc gi n IPTVCD ng lc v theotrt t ng. IP cng lm cho qu trnh phn pht ni video b tr.

3.2.7 Lp lin kt d liu:

Lp lin kt d liu ly cc d liu th t lp IP v nh dng chng thnhcc gi ph hp truyn qua mng vt l. Ch , lp lin kt d liu khc vicc giao thc mng. K thut Ethetnet l mt trong nhng k thut ph bin hnc s dng trong h thng IPTV. Lp lin kt d liu bao gm cc chc nngdnh cho cc mng da trn Ethernet:

Encapsulation---- Lp ny thm vo cc gi IPTV 1 header. Ethernet headerl loi Encapsulation ph bin nht dng trong lp lin kt d liu ca IPTVCD.Cc thnh phn c bn ca Ethernet header c gii thch trong bng 3.9.

nh a ch---- Lp lin kt d liu x l cc a ch vt l ca mng ngis dng v cc thit b ch. H thng a ch khc nhau vi cc topo mng. V


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d, a ch MAC c s dng trong mng Ethernet. Mi thit b kt ni vimng IPTV th c 1 a ch MAC. di ca a ch MAC l 48 bit v thngc biu din bng 12 s trong h 16. Trong 12 s h 16 ny, 6 s u tin dnh cho nh sn xut thit b IPTV v cc s cn li c dng nh nghagiao din mng o.

Kim tra li----- chc nng kim tra li c dng trong vi lp ca m hnhIPTV, bao gm c lp lin kt d liu. Cc gi b ngt l li thng gp trong qu trnhtruyn cc ni dung video qua mng da trn IP. Phng php sa li thng dung l kimtra d tha vng (CRC) trong IPTV tm v loi b cc gi b ngt. S dng kthut CRC thit b gi IPTV thc hin vic tnh ton trn cc gi v lu tr kt qu tronggi. Cc php tnh ton tng t cng c thc hin trn thit b nhn khi nhn ccc gi. Nu kt qu tnh ton l nh nhau, th cc gi c x l bnh thng. Tuynhin, nu kt qu ny l khc nhau, th gi b li s b loi b.Thit b gi s to mtgi mi v gi li n. Thng bo vi lp trn trong m hnh IPTV khi c li xy ra lnhim v chnh ca lp lin kt d liu trong k thut kim tra li m cc h thng IPTVend to end.

iu khin lung----iu khin lung l mt trong chc nng ca lp truynti. Trong mng IPTV, iu khin lung cho thit b IPTV ca ngi s dng khngb trn bi cc ni dung. Lp lin kt d liu cng vi lp truyn ti thc hin bt kyu cu iu khin lung no.

Bng 3.9 Cu trc ca Ethernet header

Tntrngtrong

Header

Kchthc(bit)

Chc nng

a chch mngEthernet

48 Ch ra a ch ca giao din ch

a chngunmngEthernet

48 Ch ra a ch ca giao din ngun

Loi m 16Ch ra giao thc c s dng trong vicnh dng gi. V d kiu gi "TCP/IP"cha gi tr kiu hex "0 x 80 0 x 00"


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Bng 3.10: Cu trc khung Ethernet c dng mang ni dungMPEG-2

M t Kch thcCc dng gitruynti MPEG by

Mi gi c kch thc 188 byte (184 byte chani dung video, cng vi 4 byte cdng lm thng tin header). Gi MPEG - TS byny chim 1316 byte (10528 bit) ca khung

Tiu RTP Tiu ny chim 12 byte ca khung EthernetTiu UDP Tiu ny chim 8 byte ca khung EthernetTiu IP Tiu ny chim 20 byte ca khung EthernetTiu Ethernet

Tiu ny chim 14 byte ca khung Ethernet

3.2.8 Lp vt l:

Lp vt l quy nh lut l truyn cc bit s qua mng. N cp n vica cc d liu qua cc mng vt l ring bit nh x DSL, v khng dy. Lp nynh ngha cu hnh mng vt l, thng s k thut, in trong mi trng truyn.

Khi dng bit c truyn qua mng, cc gi c chuynr t lp thp n lpcao trong m hnh truyn thng IPTV. V d lp lin kt d liu s kim tra cc gi vloi b i phn header Ethernet v trng sa li CRC. Tip s kim tra trngkiu m ca Ethernet header v xc nh gi cn c x k bi giao thc IP. Do

gi d liu c chuyn ln lp mang. Lp mng kim tra v loi b i phn IP headerv chuyn gi ln lp truyn ti. Phng php b i phn header khi qua cc lpkhc nhau gi l bc gi. Qu trnh ny tip tc c thc hin cho ti khi gi d liuln n tng trn cng trong m hnh. Hnh nh gc c th hin trn mn hnh TVca ngi xem.


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Bng 3.11 Tng kt cc lp trong m hnh IPTV

sthtlp

Tn lp Tng quan

1 Vt lXc nh cc thuc tnh ca cc phng tintruyn thng trong mng chu trch nhimtruyn cc bit d liu IPTV

2 Lin kt dliu

Qun l cc c ch c s dng truy cpthit b truyn thng trong mng. Kim sot li,ng b v iu khin lung l nhng chcnng khc m lp ny cung cp.

3 IP

Chc nng ca lp ny c quan h vi vicnh tuyn cc gi IP truyn trn mng. Ccc ch nh l nh a ch v iu khin tcnghn thng c lp IPTVCM ny s dng

4 Giao vnChc nng chnh ca lp ny l m borng cc gi IPTV n c ch. TCPv UDP u vn hnh ti lp ny

5RTP (tychn)

Mc d UDP l giao thc c lp giao vnu tin s dng hn cho vic phn phi nidung IPTV trn mng bng rng, nhng ncng ko phi l giao thc ang tin cy v nkhng h tr vic sa li hay gii quyt vn cc gi n IPTVCD khng theo ng th t.

Do , mt s cc nh cung cp dch v sdng RTP gii quyt nhng thiu ht chu trong giao thc UDP.

6Xy dngdngtruyn ti

Lp ny ng gi cc dng bt video v audio.Cc gi c di 188 byte

7Lp ng giVideo

Lp ny to mt dng cc gi PES cnh du thi gian

8M haVideo

Cc dng audio v video c bn lm thnhnn tng cho lp IPTVCM. nh dng cadng truyn c s dng lp ny ph

thuc vo thut ton nn s dng bi b mha


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Ti liu tham kho:

Ting Vit:

[1]. Hong TinDng Thanh Phng, (2004), Truyn hnh k thuts, NXB Khoa hc v K thut.

[2]. Ng Thi Tr, (2004), Truyn hnh s, NXB i hc Quc gia H Ni.

Ting Anh:

[3]. Iain E G Richardsob, (2003), H.264 and MPEG-4 Video Compression,NXB Wiley.

[4]. Gerard O Driscoll, (2008), Next Generation IPTV Services andTechnologies, John Wiley & Sons, Inc., Hoboken, New Jersey.

[5]. Thomas Wiegand, Gary J. Sullivan, Gisle Bjontegaard, and Ajay Luthra,(2003), Overview of the H.264/ AVC Video Coding Standard, IEEE transactions

on curcuit and system for video technology.[6]. Wes Simpson and Howard Greenfield, (2007), IPTV and Internet Video

Expanding the Reach Television Broadcasting, Focal Press.


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