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I.Gii thiuS pht trin ca mng Internet ton cu ni ring v cng ngh thng tin n

chung em li tin b v pht trin vt bc ca khoa hc k thut. Internkhng nhng rt ngn khong cch v khng gian, thi gian m cn mng lcho mi ngi, mi quc gia v c th gii nhng li ch to ln. Tc pht trinhanh chng ca cng ngh thng tin l mt trong nhng li ch to ln, c vai trquan trng v tm nh hng rng khp.

Vi s pht trin nhanh chng ca mng Internet bng rng cn lm thay c v ni dung v k thut truyn hnh. Hin nay truyn hnh c nhiu dng khnhau: truyn hnh s, truyn hnh v tinh, truyn hnh cp, truyn hnh Internet vIPTV. IPTV ang l cp cao nht v l cng ngh truyn hnh ca tng lai. Svt tri trong k thut truyn hnh ca IPTV l tnh nng tng tc gia h thvi ngi xem, cho php ngi xem ch ng v thi gian v kh nng trin khnhiu dch v gi tr gia tng tin ch khc trn h thng nhm p ng nhu cu cngi s dng.

Hin nay trn th gii c mt s quc gia trin khai thnh cng IPTVTheo cc chuyn gia d bo th tc pht trin thu bao IPTV s tng theo cp snhn theo tng nm. Vit Nam hin nay, mt s nh cung cp ang th nghidch v IPTV trn mng bng rng ADSL.

II.IPTV l g?IPTV - Internet Protocol TV - l mng truyn hnh kt hp cht ch v

mng vin thng. Ni rng hn IPTV l dch v gi tr gia tng s dng mng bnrng IP phc v cho nhiu ngi dng (user). Cc user c th thng qua my vi tnPC hoc my thu hnh ph thng cng vi hp phi ghp set topbox s dn

dch v IPTV.H thng IPTV cung cp cho thu bao s dng TV mt di rng cho vic lchn ni dung qung b v ni dung la chn ring ca thu bao. Gii php todin bao gm Live TV, Video on Demand (VOD), Digital Rights Management(DRM) v Middleware. Ni dung truyn hnh c pht thng qua kt ni IP bmt s dng cc set-top box da trn cng ngh IP chun.

IPTV c 2 c im c bn l: da trn nn cng ngh IP v phc v thenhu cu. Vi khch hng u cui, IPTV thng cung cp dch v VoD (Video oDemand) v c th kt hp vi cc dch v Internet nh truy cp web v VoIP. Vikt hp ny c gi l dch v "Triple Play" (thm mobility th c gi l"Quadruple Play").

Nh vy IPTV ng vai tr phn phi cc d liu, k c hnh nh, m thanhvn bn qua mng s dng giao thc Internet. iu ny nhn mnh vo viInternet khng ng vai tr chnh trong vic truyn ti thng tin truyn hnh hay bk loi ni dung truyn hnh no khc. Thay vo , IPTV s dng IP l c ch ph phi m theo c th s dng Internet, i din cho mng cng cng da trn Ihay c th s dng mng ring da trn IP.

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So vi VOD (video theo yu cu) IPTV c u th l:

1. S dng d dng, hin th trn tivi hiu qu cao hn mn my vi tnh, thaotc trn hp ghp ni + bn phm n gin, thc hin chuyn i nhanh lung caotc/chng trnh.

2. D qun l, d khng ch, s dng hp kt ni lm u cui nh cung cdch v tin hnh nh ch i vi hp kt ni khng cn n nghip v an tov kim tra cht lng. y cng l c s k thut d thu ph.

IPTV c th thc hin cc dch v multimedia. Cn c vo s la chn cangi dng, IPTV cung cp rt nhiu loi hnh dch v. S dng hp kt ni vitivi, ch nhn ngi trc my n phm iu khin c th xem cc tit mc videoang hot ng, thc hin m thoi IP c hnh, nghe m nhc, tra tm tin tc dulch trn mng, gi v nhn e-mail, thc hin mua sm gia nh, giao dch tri

phiu... Nh IPTV cht lng sinh hot gia nh c ci thin rt nhiu.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. d, set top box IPTV c th thng qua phn mm cho php xem ng thi chng trnh truyn hnh trn mn hin th, hay c th nhn tin nhn sms, e mail.Tim nng ca IPTV l rt ln.

III. S lc v lch s ra i ca IPTV: Nm 1994, World News Now ca ABC c bui trnh chiu truyn hnh

qung b qua mng Internet u tin, s dng phn mm CU-SeeMevideoconferencing.

T chc lin quan n IPTV u tin xut hin l vo nm 1995, vi sthnh lp Precept Software bi Judith Estrin v Bill Carrico. H thit k v xydng mt sn phm internet video gi l "IP/TV". IP/TV l mt MBONE tnthch vi cc ng dng trn Windows v Unix, thc hin truyn m thanh, hnh nthng qua c giao thc unicast v IP multicast RTP/RTCP. Phn mm ny c vi bi Steve Casner, Karl Auerbach, v Cha Chee Kuan. H thng ny c CiscoSystems mua vo nm 1998 v Cisco d li tn "IP/TV".

Cng ty v tuyn Internet AudioNet bt u tin hnh nghin cu livewebcasts vi WFAA-TV trong thng 1 nm 1998, v KCTU-LP vo mng 10 thng1 nm 1998.

Kingston Communications, mt nh cung cp dch v vin thng Anh,trin khai KIT (Kingston Interactive Television), mt dch v truyn hnh tng ttrn nn mng bng rng DSL vo thng 9 nm 1999 sau khi th nghim dch vTV v VoD. Nh cung cp ny thm dch v VoD vo h thng trong thng 10nm 2001 vi Yes TV, mt nh cung cp cc gii php v dch v VoD trn nn IP.

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Kingston l mt trong nhng cng ty u tin trn th gii trin khai IPTV v IPVoD trn ng truyn ADSL.

Hin nay, IPTV pht trin mnh trung v ng u.

IV. 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 lodch v c truyn ti thng qua mt dch v IPTV c th bao gm TV trc tichun, TV cht lng cao (HDTV), tr chi tng tc, v kh nng duyt Interntc cao.

- S dch thi gian:IPTV kt hp vi mt my ghi video k thut s cho phpdch thi gian ni dung chng trnh mt c ch cho vic ghi v lu tr ni duIPTV xem sau.

- C nhn ha: Mt th thng IPTV t kt cui n kt cui h tr truyn thntin hai chiu v cho php ngi dng kt cui c nhn ha nhng thi quen xemTV ca h bng cch cho php h quyt nh nhng g h mun xem v khi no hmun xem.

- Yu cu v bng thng thp:Thay v phn phi trn mi knh ti mingi dng, cng ngh IPTV cho php nh cung cp dch v ch truyn trn mknh m ngi dng yu cu. c im hp dn ny cho php nh iu hnh mc th tit kim bng thng ca mng.

- C th truy xut qua nhiu thit b:Vic xem ni dung IPTV by gi khngch gii hn vic s dng TV. Ngi dng c th s dng my PC hay thit bng truy xut vo cc dch v IPTV.

V. M hnh kin trc h thng cung cp dch v IPTV:

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Mng truy nhp bng rng: H tng mng IP bng rng truyn dch vnh cung cp dch v IPTV n khch hng. Mng truy nhp s tn dng phn tng mng xDSL c sn. cung cp dch v vi cht lng tt v tiu th t bthng khi c ng thi nhiu truy nhp n h thng, mng truy nhp bng rng (RAS/MSS v DSLAM) cn phi c h tr multicast. i vi DSLAM, ngoi htr multicast, DSLAM cn cn h tr IGMP version 2. Ngoi ra, B-RAS/MSS vDSLAM cng cn h tr cc giao tip Ethernet chun (FE, GE). Mng cng phi ckh nng h tr QoS t u cui n u cui, m bo c bng thng cn tv u tin cho cc knh truyn hnh qung b cng nh cc phin Video theo yucu ang s dng (phi t c mt gi v jitter ti thiu). Bng thng xDdo cc DSLAM cung cp n khch hng phi c kh nng ln n 4-5 Mbps.

H thng cung cp ngun d liu: Thu, nhn v x l cc d liu chtrnh t cc ngun khc nhau nh v tinh, truyn hnh mt t v cc ngun khc

chuyn sang h thng Video Headend.H thng Video Headend: Thu, iu ch v gii m ni dung hnh nh v

m thanh t cc ngun khc nhau v s dng cc thit b m ha (encoder) chuyn i ni dung ny thnh cc lung IP multicast khun dng m ha mongmun. Yu cu phi c thit b u cui cho vic pht ni dung qung b. Thitu cui ny c kh nng m ho mt chui cc hnh nh theo thi gian thc bnk thut nn dng MPEG-4 Part 10 hoc H.264. Hnh nh m ho c th ly t vtinh, truyn hnh cp, h thng truyn hnh mt t, my ch video, tape playouv.v... Sau khi m ho, cc chui (nh dng ASI, SPTS) truyn MPEG s c n

gi bng cch s dng IP Streamer. Sau s truyn nhng chui gi IP bng ccs dng giao thc UDP/IP. u vo ca h thng Video Headend l cc chntrnh truyn hnh qung b, cc knh truyn hnh mua bn quyn thu t v tinh, cknh truyn hnh cp, cc phim t cc ngun khc nh t sn xut, t cc thit VCD/DVD player, v.v...

H thng Middleware: Cung cp kh nng qun l thu bao, ni dung v bo co hon chnh cng vi cc chc nng qun l EPG v STB, ng thi vnduy tr tnh m cho vic tch hp cc dch v trong tng lai. Middleware l mgiao din ca h thng cung cp dch v IPTV vi ngi s dng, n xc nh datnh cho ngi dng. Hin th mt danh sch cc dch v m thu bao c th sdng v tr gip la chn dch v ny sau khi xc thc danh tnh ca ngdng. Middleware lu li mt profile cho tt c cc dch v. Middleware m bcc hot ng bn trong ca dch v truyn hnh mt cch hon ho. Middleware khng gii hn bt k hot ng ring r no trong h thng, nhng s giao tip ttip vi mi thnh phn c h thng h tr. Middleware h tr API cho php mrng cc chc nng mi v truyn d liu gia cc h thng.

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H thng phn phi ni dung: Bao gm cc cm my ch VoD v h thnqun l VoD tng ng, cho php lu tr cc ni dung c m ha v thit lcc chnh sch phn phi ni dung mt cch mm do. H thng ny cng cho phnh khai thc m rng mt cch kinh t, ph hp vi ti v yu cu dch v ca cthu bao. My ch VoD s lu ni dung thc v cung cp cho thu bao khi n nhc s xc thc danh tnh t Middleware. N cho php cc thu bao t v xemnhng b phim cht lng cao v chng trnh theo yu cu (chng trnh nc lu trn my dch v v truyn ti theo yu cu). H thng ny cng cung cnhng chc nng iu khin VCR nh fast-forward, pause, v rewind.

H thng qun l bn quyn s (DRM): DRM gip nh khai thc bo v ndung ca mnh, nh trn cc tn hiu truyn hnh hay m ha ni dung VoD, khtruyn i trn mng Internet v tch hp vi tnh nng an ninh ti STB pha thu bao. DRM dng bo mt ni dung cc kha gii m ca cc thu bao. Nhng ndung c ti trn nhng my ch ni dung s c m ha trc bng h th

DRM v n cng cng ch m ha ni dung broadcast bo mt s phn b Set-top Box (STB). H thng c kh nng h tr chc nng m ho trong ccHeadend tng ng v cung cp kho mt m cho cc Headend ny. H thngDRM cha kho cho phn ni dung ca mt c s d liu kho ng thi b m phn phi c s d liu ny ti STB. H thng DRM cng s h tr thm vo phni dung cc chc nng th thut trong khi xem (tua nhanh, tua li, v.v...). H thnDRM s da trn cc khi nim ca h thng c s h tng kho cng cng (PubKey Infrastructure, PKI). PKI dng cc th k thut s X.509 xc nhn mthnh t trong h thng DRM ng thi m ho an ton d liu c dng cc khochung/ring.

H thng qun l mng v tnh cc: H thng ny qun l v tnh cdch v truy cp ca thu bao IPTV.

Set-top Box (STB): Thit b u cui pha khch hng, cho php thu, giim v hin th ni dung trn mn hnh TV. STB cn h tr cc chun MPEG-4/H.264. Ngoi ra, STB cng c th h tr HDTV, c kh nng kt ni vi cc thi b lu tr bn ngoi, video phone, truy nhp web (Walled garden), v.v... STB cungcp cc ng dng truyn thng v gii tr. STB s h tr kt ni gia thit b tivmng in thoi, cng nh Internet v th vin nh o ca nh cung cp dch v N c th gii m nhng chui d liu v hnh nh n da vo a ch IP, nthi th hin cc hnh nh ny trn TV. STB s h tr chun H.264/MPEG-4 Part 1v phn mm client Middleware ca n s c da trn mt cu trc thick clieniu c ngha l ng dng v d liu th hin s lu trn STB.

VI. Cc cu trc ng dng.

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Di y l m t vic ci t cc ng dng IPTV nh cc c s h tnmng khc nhau.

a) IPTV khi dng ADSL.

ADSL c th h tr bng thng t 512 kb/s n 6 Mb/s on t tr schnh (Central Office-CO) n end point. on ny thng c gi l last mil(dm cui). Bng thng c sn thc t ph thuc vo khong cch gia end pov ADSL DSLAM. Ph thuc vo bng thng last mile c sn, khch hng c ththu 2 knh video, khi hai IP/STB s c b tr end point (mt STB cho mknh). Bng thng c sn ph thuc vo khong cch t DSLAM n end point.

Mt vn quan trng l cu hnh CO phi m bo rng ADSL DSLAM htr multicast. Nu khng th dng c mc III phi p ng tt c cc stream chmi knh yu cu. iu ny c kh nng gy ra nghn mch DSLAM.

V d nu DSLAM CO phc v 20 end point v tt c end point yucu knh 3 th thit b lelvel III phi cung cp knh 3 n DSLAM 20 ln. NDSLAM h tr multicast n s nhn mt stream ca knh 3 v gi n cho mi en point. Trong hnh 3 mt streaming server (MGW 5100) c t head end vmt CO. MGW CO nhn thm cung cp t v tinh gm ni dung a ph(local content) cho phn b n mt din tch hoc mt nhm s dng c bit.

b) IPTV khi dng VDSL

Cu hnh VDSL da trn kt ni si quang trn mng khung tc bit 15Mb/s hoc hn. Tc truyn dn t nt mng last mile n end point kho10 40 Mb/s. Cc bng thng cao v VDSL h tr cho php khch hng nhn nhiuknh xem trn nhiu my thu hnh. Vi VDSL, c s h tng mng khun(backbone) da trn si quang n trm chnh (basement / crub) trong khi gii phplast mile dng VDSL trn si cp ng thoi.

c) IPTV dng FTTH (Fibre To The Home).

Cu hnh FTTH da trn kt ni cp t headend n endpoint. Trong cuhnh ny video c truyn qua mng khung si quang tc ln hn 155 Mb/Cu hnh chng cui (last mile) gm mng 100 Base T. Bng thng mng ln nhvy cho php khch hng thu nhiu knh, c xem trn my thu hnh qua IP/STB.

VII. Phng thc pht truyn tn hiu ca IPTVa. Tng quan :

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Ni mt cch gin n, trong h thng IPTV hnh nh video do cc phncng thu thp theo thi gian thc (real time), thng qua phng thc m ha(nh MPEG 2/4...) to thnh cc lung tn hiu s. Sau , thng qua h thn phn mm, IPTV pht truyn vo mng cp. u cui ca cc user tip nhla chn, gii m v khuch i.

b. Phn loi :Trong h thng IPTV c 2 phng thc truyn a tn hiu c d

nh trc (scheduled programs). l: Pht qung b (broadcasting), truyn pht ti mi ni Pht n a im theo yu cu (on demand).

c. Nguyn l hot ng: Nguyn l hot ng ca h thng qung b :

Cc chng trnh c v trn hnh 1. Trong MBone (mng xngsng ca h thng a im) chnh l ng trc Internet. Tuy nhin ngi sdng ch theo lnh ca b qun l ni dung (content manager) c githiu ni dung chng trnh hu quan. Chng trnh c th do rt nhiu bIPTV server thu thp c hoc cng do cc server ca mng MBone cung cp

Hnh 1

Nguyn l hot ng ca h thng phc v theo yu cu(VOD)

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Hnh 2.

Hnh 2 minh ha s hot ng ca h thng IPTV phc v theo yu c(VOD) c gi l IPTV n im. Trong cc server ca b qun l ndung c t chc thnh cm server (server cluster) tng hp kho d liu(database) ca cc chng trnh.

Cch b tr cm server phc v c cc user c hiu qu s ni r trn s tng th di y. Cc bc thc hin VOD nh sau:

Mt thu bao c chng nhn nhp mng v chu s qun l ca b qun l EPGThu bao mun yu cu mt ni dung no . Thu bao gi yu

cu n EGPEGP cho bit a ch ca server cn tmThu bao gi yu cu ti server Server da theo yu cu ca thu bao m cung cp ni dung.

VIII. Mng tng th IPTV

S khi biu th cc chc nng ca nghip v IPTV nh hnh 3. Tngun ni dung ti u cui ngi dng c h chia lm: nghip v cung cp gii thiu cc ni dung, nghip v chuyn ti, nghip v tip ni u cuinghip v qun tr.

a. Mng ni dung :

Mng ny cung cp v gii thiu ni dung gm x l ni dung truynhnh trc tip/truyn hnh VOD (theo im) v x l, gii thiu cc ng dngia tng (phc v tin tc, in thoi c hnh, email, nhn tin...). Ngun ni duntruyn hnh trc tip/truyn hnh VOD khng qua h thng x l ni dung

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m ha ph hp vi lung media theo yu cu qua mng chuyn ti a clung ny cung cp ti cc ngi dng u cui.

b. Mng truyn ti:

y l mng cp IP. i vi lung media c hnh thc nghip v khngging nhau c th dng phng thc chuyn a hng (multicast) cng c thchuyn theo phng thc n knh. Thng thng, truyn hnh qung b BTtruyn a hng ti user u cui, truyn hnh theo yu cu VOD thng qumng cp phn pht ni dung CDN (Content Distribution Network) ti a imngi dng u cui.

c. Mng u cui (cn gi l mng cp gia nh):

Theo cc nh khai thc vin thng, th mng ny l mng tip ni bng

rng xDSL, FTTx+LAN hoc WLAN.d. B qun tr :

B qun tr bao gm qun l ni dung, qun l cp truyn, tnh cc phqun l cc thu bao, qun l cc hp ghp ni STB.

Ta thy trong mng IPTV c 3 dng lung tn hiu: lung qung b BTVlung truyn n a im theo yu cu VOD v lung nghip v gi tr gitng. Nh biu din trn hnh 3. Ta xt cc phng thc truyn tn hiu th tnC 3 phng thc truyn trc tip hin trng, truyn qung b c nh thgian v truyn ti im VOD. Khi truyn hnh trc tip ng thi ta ly ndung ny lu vo b nh pht li vo truyn hnh qung b nh thi giahoc lm ngun cc tit mc cho truyn hnh VOD. i vi tit mc qung bc nh thi IPTV dng phng php truyn pht a im IP c tit kim bntn tc l phng thc multicast. Phng thc ny thc hin "nht pht, a thuDng phng thc ny, mi tit mc mng cp ch pht mt lung s liu thgian thc (real time) khng lin quan ti s ngi xem tit mc ny. Phngthc ny c th truyn pht cho hng nghn thu bao.

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Hnh 3

IPTV cung cp ng thi hnh nh (video) v m thanh (audio) trnmng cp. m bo cht lng ca 2 loi tn hiu trn IPTV dng ph

php ng b A/V thng qua mt server duy nht thu thp cc d liu ti hitrng, vn bn s dng theo khuyn ngh truyn dn thi gian thc RTP. IPTdng k thut nn th tn c hiu sut cao nn bng tn truyn dn ti 800kbc th tip cn vi bng tn thu DVD nn to iu kin cho cc nh khai thc ddng pht trin cc dch v video. Mng chuyn ti CDN gm nhiu servecache phn b ti cc khu vc tp trung thu bao, Khi c yu cu ca thu baocache server chuyn ln VOD server trong mng ngun cung cp, tm ni dung ph hp v chuyn ti cho thu bao s hot ng ca cc server trong mnchuyn ti da trn k thut cn bng ph ti ton cc (GSLB). Trong qu trntruyn a multimedia IPTV c th dng kha mt m m bo an ton c

ni dung truyn dn. IPTV p dng cc khuyn ngh quc t v tiu chun, nh khuynngh v truyn dn thi gian thc (RTP), khuyn ngh v khng ch thi giathc (RTCP)...

IPTV cng cng lm vic vi my tnh dng h iu hnh UNIX,VIC/VAT, Apple v Quick Time.

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Hin nay cch thc m ha video ca lung ch ca IPTV theoMPEG-2, MPEG-4, H.264/AVC; Real Microsoft UWMV-9. Trong , MPEG-2v MPEG-4 c pht trin mnh. H.264 l lut m ha th tn ca ITU-T xut thch hp cho cc h thng cng cng. Do H.264 c kh nng thnhcch m ha chnh ca IPTV.

Nh nu trn, nghip v IPTV chnh l phc v cho cc h gianh. Phng thc tip nhp bng rng ti gia nh thng dng phng phtruy nhp ADSL, nhng v IPTV thit lp ti user nghip v multimedia thgian thc v tng tc nn ADSL khng tha mn cc yu cu ca IPTV. Cpquang truyn dn ti tn nh FTTH c cng nhn l phng thc chuyn tti u. Cp quang c bng tn rt rng v c kh nng truyn dn hai hng xng m bo c yu cu truyn hnh nh ng theo hai hng vi chlng cao.

Thit b u cui IPTV trong gia nh c 2 loi: mt l my vi tnhPC, hai l my TV + hp kt ni STB.

Hp STB thc hin 3 chc nng sau:Ni tip vo mng bng tn rng, thu pht v x l s liu IP v

lung video.Tin hnh gii m lung video MPEG-2, MPEG-4, WMV, Real...

m bo video VOD hin th ln mn hnh ti vi cc s liu...Phi hp vi bn phm m bo HTML du lch trn mng, tin

hnh gi nhn email. Hp STB m nhim cc nhim v trn chyu da vo b vi x l.

kt lun ta thy IPTV ng dng k thut streaming media, thng qumng bng rng truyn dn tn hiu truyn hnh digital n cc thu bao. Cthu bao ch cn c thit b u cui l my tnh PC hoc TV+STB l c ththng thc c cc chng trnh truyn hnh phong ph. Hot ng ca IPTl hot ng tng tc trn mng khng ch c cc chng trnh truyn hnqung b m cn thc hin truyn hnh n a im theo yu cu (VOD). IPTcn c cc dch v tng tc khc nh truyn thoi c hnh, email, du lch trnmng, hc tp t xa...

IPTV cng cc hot ng thng tin trn bng tn rng kt hp c 3mng (my tnh + vin thng + truyn hnh) biu th xu th pht trin ca mtruyn thng tng lai. Cc nh kinh doanh dch v vin thng bng rng khngch cc nc tin tin nh M, Nht... m cc nc trong khu vc nhTrung Quc, Hn Quc, Hng Kng... ang pht trin mnh dch v IPTV.

IX. Tng quan v m hnh truyn thng IPTV (IPTVCD)M hnh truyn thng trong IPTV c 7 lp (v mt lp ty chn) c xp

chng ln nhau.Cc d liu video pha thit b gi c truyn t lp cao xung lp th

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trong m hnh IPTV, v c truyn i trong mng bng rng bng cc giao thc clp vt l. thit b nhn, d liu nhn c chuyn t lp thp nht n lpcng trong m hnh IPTV.

Hnh3.1: m hnh truyn thng IPTVDo , nu 1 b m ha gi chng trnh video n 1 thit b IPTV ca

khch hng, th phi chuyn qua cc lp trong m hnh IPTV c pha thit b nh

v thit b gi. Mi lp trong m hnh IPTV c lp vi nhau v c chc nng rinKhi chc nng ny c thc hin , d liu j video c chuyn n lp tip thtrong m hnh IPTV. Mi lp s thm vo hoc b i phn thng tin iu khin ccc gi video trong quad trnh x l. Thng tin iu khin cha cc thng tin gipthit b c th s dng gi d liu ng chc nng ca n, v thng c dng nh cc header hoc trailer. Bn cnh vic truyn thng gia cc lp, cn ccc lin kt o gia cc tng cng mc. 7 lp v 1 lp b sung trong m hnh IPTc th c chia lm 2 loi: cc lp cao v lp thp. cc tng cao hn th quan tnhiu hn ti cc ng dng ca IPTV v cc nh dng file, trong khi cc tng thhn th quan tm ti vic truyn ti cc ni dung.

a. M hnh IPTV v truyn ti cc ni dung MPEG: Ni dung video c nn qua cc lp nh th no khi s dng h thn

MPEG khi chuyn t lp trn xung lp di :

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Hnh 3.2 ng gi cc lp trong m hnh IPTV

b. Lp m ha video:Qu trnh truyn thng bt u lp m ha, cc tn hiu tng t hoc s

c nn. Tn hiu li ra ca b nn l cc dng Mpeg c bn. cc dng MPEG c bn c nh ngha l cc tn hiu s lin tc thi gian thc. C nhiu loi dng 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 d lic t chc thnh cc khung ti lp ny. Cc thng tin cha trong mt dng c bc th bao gm:

Loi khung v tc V tr ca nhng block d liu trn mn hnhT s cnh

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

c.Lp ng gi Video: truyn cc dng c bn m thanh, d liu v hnh nh qua mng s

mi PES c nh du thi gian (PES-packetized Element Stream). Mtdng PES dng c bn ny phi c chuyn i sang mt dng c chn cgi ch bao gm 1 loi d liu t 1 ngun. Mt gi PES c th c kch thkhi c nh hoc thay i, c th ln ti 65536 byte/gi. Bao gm 6 byte

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header, v s byte cn li cha ni dung chng trnh. nh dng ca 1 PES headc minh ha trong hnh 3.4 v gii thich trong bng 3.4.

Hnh 3.4 nh dng gi MPEG PES

Bng 3.1 Cu trc ca mt gi MPEG PES

Tn trng Chc nng

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

Nhn dng dng(1 byte)

Trng ny nhn dng loi payload trong gi. Mtmu bit 111x xxxx cho bit l gi audio, cn mu bit 1110 xxxx cho bit rng l gi video. 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 video vaudio

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C header PES

Trng 14 bit cha cc b ch th PES khc nhau haycc c, cung cp phn cng hay phn mm b gii mca set - top box IP vi thng tin thm vo. Cc loic gm:

iu khin tranh chp PES: C ny bo cho b giim gi c c bo m hay khng thng qua x ltranh chp u tin PES: C ny cung cp cho b gii mthng tin v mc u tin ca gi PESB ch th sp xp d liu: B ch th ny quyt nhPayload ca PES bt u vi bit video hay audioThng tin bn quyn: Khi bit ny c thit t, nidung video c bo v bi bn quynBn gc hay bn sao: C ny ch ra ni dung ny l bn gc hay bn sao

di d liuheader ca PES

Trng ny nhn ch ra tng s byte b chim bi cctrng header khc nhau

Trng header ca PES Trng ny cha mt s cc bt ty chn

Payload ca PES Payload ca PES gm cc dng audio hay d liuvideo

Do bn cht ca mng, th t hay chui cc khung video t li ra ca truntm d liu IPTV c th khc th t cc khung do cc thit b ca ngi dng nhc. do , gip qu trnh ng b, cc h thng da trn MPEG thng dnhn cc gi PES khc nhau trong chui video.

C 2 loi nhn thi gian c s dng i vi mi gi PES: nhn thi giatrnh din(PTS), v nhn thi gian gii m(DTS): PTS---- nhn thi gian trnh din c gi tr thi gian 33 bit, c t trong trnPES header. Mc ch ca vic s dng PTS cho mi gi l xc nh xem khi nv theo trt t no th gi c xem (bi ngi xem).

DTS---nhn gii m s dng gip b gii m thit b cngi s dng bit khi no x l gi .d. Lp cu trc dng truyn ti:Lp tip theo trong m hnh truyn thng IPTV lm nhim v to nn dng

truyn ti, bao gm 1 dng lin tip cc gi. Nhng gi ny thng c gi l cgi TS, c to ra bng cch ngt cc gi PES thnh cc gi TS c kch thc cnh l 188 byte c lp vi thi gian. S dng thi gian c lp ny lm gim k

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nng mt gi tin trong qu trnh truyn v gim n. Mi gi TS bao gm 1 trong nh dng truyn thng: d liu, m thanh, hnh nh. Do , cc gi TS mang c nh1 loi hnh truyn thng. Mi gi TS bao gm 184 byte payload v 4 byte header. Ccthnh phn ca TS header c m t trong hnh 3.7 v gii thch trong bng 3.2

Hnh 3.5 nh dng gi MPEG TSBng 3.2 Cu trc gi MPEG TS

Tn trng Chc nng

Trng ng bPhn header thng bt u bng cc bit ng b (8 bit), thng l cc bit 0. Trng ny dng xcnh im bt u ca 1gi IPTV.

Trng ch th li bit c ny s ch ra 1 li (nu c) lin quan n dngtruyn ti

Trng ch thim bt u khitruyn ti

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

Mc u tin Khi t c ny s ch ra mc u tin khi payload

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truyn ti

ID chng trnh

Trng quan trng nht trong phn header l13 bit xc nh ID chng trnh. N s ch ra gi no thucdng no.Cc gi thuc dng no th s c cng IDchng trnh.B phn knh trong b ca ngi sdng dng thng tin phn bit cc loi gi khcnhau.ch rng cc gi null c ID chng trnh =8191. Cc gi khng c ID chng trnh th s b thit b nhn IPTV loi b

iu khin victranh chp cctruyn ti

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

Trng iukhin thch nghi

trng 2 bit ny s cho bit liu header ca gi dliu c lin quan ti dng truyn ti c bao gmtrng thch nghi v payload khng

B m tinB m tin s m tng ln 1 khi 1 gi dng truynti vi cng mt ID chng trnh. Nh c th xcnh c nu c mt hoc b lp gi. iu ny c thnh hng hnh nh.

Trng thch nghi

Trng ny c th c hoc khng c trong phnheader.Trng thch nghi ny bao gm nhiu thng tin khcnhau c s dng nh thi v iu khin, baogm c PCR. PCR c s dng ng b ng hIPTVCD vi ng h b m ha. Gi tr PCR c di 42 bit v c tng theo tc ng h chun,27MHz. Ngay sau khi ng b, vic gii m MPEG -2 IPTV c tin hnh

Trng thch nghi

Trng ny c th c hoc khng c trong phnheader.

Trng thch nghi ny bao gm nhiu thng tin khcnhau c s dng nh thi v iu khin, baogm c PCR. PCR c s dng ng b ng hIPTVCD vi ng h b m ha. Gi tr PCR c di 42 bit v c tng Theo tc ng h chun,27MHz. Ngay sau khi ng b, vic gii m MPEG -2 IPTV c tin hnh.

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Bn cnh cc ni dung hnh nh v m thanh c nn, dng truyn ti bagm nhiu thng tin c trng ca chng trnh hoc metadata m t cc dng bThng tin ny c cha trong 4 bng PSI.

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

Bng nh x chng trnh: Bng nh x chng trnh cng l bt buc vmang co thng tin v mt chng trnh c th. Bng nh x chng trnh lit k ID chng trnh cho cc gi mang cc thnh phn ca 1 chng trnh c th (mthanh, hnh nh, d liu, v cc thng tin PCR).Hnh 3.8 m t 1 v d v mi quan 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 nh nh ngha cc IP chng trnh v gi m thanh, hnh nh v d liu lin kt vchng trnh . Trong v d ny, thu bao la chn chng trnh1 v thit b IPTVca ngi s dng nh v ton b cc gi truyn ti vi ID chng trnh l 36 i v phn hnh nh ca chng trnh v cc gi vi ID chng trnh l 3 vi cc phn thanh ca chng trnh. Nu d liu l qung b vi chng trnh, th bng nh chng trnh s bao gm cc chi tit trn xc nh cc gi d liu truyn ti.

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Hnh 3.8 Mi lin h gia PMT v PAT

Bng iu kin truy cp(CAT)- bng iu kin truy cp l 1 bng ty chn P bao gm cc ID chng trnh ca EMMs (cc tin qun l quyn truy cp). Tin qunquyn truy cp bao gm cc thng tin v mc cho php i vi h thng truy c bng iu kin truy cp(CAT) thng c cha trong 1 gi gi vi ID chng trl 1.

Bng thng tin mng (NIT)- Bng thng tin mng NIT l 1 bng ty chn ltr cc thng tin nh tn s knh v s dng truyn ti. Set top box s s dng thtin ny chnh sng ti cc chng trnh c th.

Khi TS c cu trc v nh dng, n s c chuyn xung lp truyn t

trc tip hoc ti lp s dng giao thc truyn ti thi gian thc (RTP).e. 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 nnMPEG-2, H.264/AVC lp cao hn v c lp thp hn trong m hnh IPTV.Giao thc RTP chnh l li ca lp ny v thng l block c s h tr truydng ni dung theo thi gian thc qua mng IP.

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Giao thc truyn ti thi gian thc phn pht cc dng m thanh v hnhnh bng cch ng gi cc ni dung ny trong mt nh dng ring bit gi gi.Mi gi bao gm phn header v payload(d liu IPTV). s dnhiu 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 cncc d liu thi gian thc qua mng. header ca RTP c th nhn bit vi headca UDP c gi tr l 5004, v bao gm rt nhiu trng.Chi tit v cc trnkhc 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 cuncp loi thng tin ny. Nh miu t trong bng 3.6, li ch chnh ca vichn cc ni dung video c nn v trong cc gi RTP l:

Thm s chui vo gi gip c b gii m pha nh cung cpv thit b ngi dng c th sp xp li cc gi nhn c tmng IP.

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

Hnh 3.9 nh dng RTP header

Khi header truyn ti thi gian thc c thm vo payload video, gitruyn ti thi gian thc c gi ti giao thc TCP hoc UDP tip tc x Bng 3.3: Cu trc ca gi IPTV da trn RTP

Tn trng Chc nng

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

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

Phn m rng (X) Nu bit ny c t bng 1 th phn m rng theo ngay satiu c nh

Tng s ngungp (CSRC) Trng ny cha thng tin s b nhn din CSRC c trong gi

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

Loi Payload (PT)Trng ny ch thng tin v nh dng payload ca IPTV. Vd, gi tr 34 ch ra ni dung video c m ha s dng H.263

S th t gi

Trng ny gip tm ra c nhng gi b mt, li. Gip choIPTVCD sp xp li cc gi c gi ti khng theo th t, xnh ng knh thc gi khng ng v ch ra gi b lp. Gitr trong trng c tng ln mt mi ln mt gi RTP gi qua mng. Khi dng IPTV bt u, mt gi tr bt k gn cho trng ny gim ri ro b hacker tn cng

Du thi gianTrng ny gi du thi gian ca gi, c khi to t mng h ng tin cy. Trng ny c sd thm vo trongcc gi m thanh v hnh nh ng theo th t thi gian cadng IPTV

Ngun ng b(SSRC)

Mc ch ca trng ny ch ra ngun ng b trong mnIPTV. Trng ny thng c s dng kt hp vi trng sth t gi sa nhng vn xy ra trong chui IPTV

Danh sch CSRC Mc ch ca trng 32 bit ny ch ra nhng ngun video vaudio gp vo payload IPTV

Hnh 3.10 Cc gi MPEG TS

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f. Lp truyn ti:Thng thng cc gi RTP l dng u vo ca lp truyn ti. iu n

ch l c th nh x trc tip cc gi MPEG-TS sang payload giao thc calp truyn ti.

Lp truyn ti IPTV c thit k m bo cc kt ni u cui lcy. Nu d liu ti thit b ngi nhn ng. Lp truyn ti s truyn li. Ltruyn ti thng 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 : S dng TCP nh tuyn cc gi IPTV :

TCP l giao thc ct li ca b giao thc internet v c xp vo lonh hng kt ni. iu ny c bn c ngha l kt ni c thit lp gia cui nh cung cp v thit b IPTV cua ngi s dng truyn cc chntrnh 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 gtrong m trng truyn IPTV. x l cc tnh hung ny, TCP s dng hthng cc s lin tc cho php thit b gi c th gi li cc d liu hnh b mt hoc hng. H thng s lin tc ny l trng c di 32 bit trong ctrc gi. trng u tin cha chui s bt u ca d liu trong gi v trth hai cha gi tr ca chui s tip theo m video server ang i (mong) nhtr li t IPTVCD

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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 dungvideo qua mng IP bng rng, TCP cn c iu khin lung d liu. iu ny cth t c bng cch s dng trng kch thc ca s, vi thut ton gi l ca s trt. Gi tr trong trng ny xc nh s cc byte c th truyn qua mng trc khi nhn c xc nhn t pha thit b nhn.

Trong mi trng IPTV, gi tr trng kch thc ca s chnh l kchthc vng m trong IPTVCD tr i lng ni dung c trong vng m tmt thi im. D liu ny s c gi cho ti khi bn tin thng bo nhc 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 chvideo server dng hoc lm chm li tc gi cc gi d liu ti IPTVCDiu ny s m bo rng IPTVCD s khng b trn cc gi d liu ti. KhIPTVCD x l xong cc cc gi d liu trong vng mv video server bit c iu th gi tr ti vng m s tng ln, v video server s bt truyn tip cc ni dung. Trong mi trng IPTV l tng, s ca ca s bo v t IPTVCD s bo cho server bit khng gian vng m cn trng chn

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la tc m ti cc ni dung video c gi i t video server.Cc cng TCP v Socket: Mi im cui ca 1 lin kt IPTV th c 1 a

ch IP v 1 gi tr cng lin quan. V th mi lin kt c 4 thnh phn khc nhaua ch IP ca video server S ca cng ca video server a ch IP ca IPTVCDS ca cng ca IPTVCD

Vic kt hp a ch IP v s ca cng cho php 1 tin trnh trn IPTVCDc th lin lc trc tip vi tin trnh ang chy trn mt trong cc my servec t trung tm d liu IPTV. Mt cng gm 16 bit nh ngha hn truyn cc thng bo gia cc lp mng. C 2 loi cng :

Cng well known c gi tr t 1 n 1023. Loi cng ny thngc cc server s dng v c qun l bi IANACng Ephemeral c thiu lp bi IPTVCD trng thi tm th

khi lin lc vi IPTV server. Cc cng thng c nh trongngn xp phn mm IP. Cc gi tr ny thng ln hn 1024 vnh hn65535. Cng ny khng chu s qun l ca IANA.

Socket cng l mt thnh phn quan trng khc trong m hnh truynthng 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 trnthit b IP. Mt socket c thit t bng cch kt hp a ch IP vi s c

cng. hiu hn v mi lin h gia a ch IP v socket xt cc bc thi

lp 1 knh truyn thng gia 1 tin trnh chy trn IPTVCD v 1 tin trnh chtrn trung tm cung cp d liu IPTV. Bc c m t nh sau:

Chun b d liu: Tin trnh gi chy trn h thng server dongIPTV chun b ni dung v gi module truyn thng TCP/IP truyn cc d liu ti 1 tin trnh ang chy trn mt IPTVCD. Cctin trnh truyn thng bt u v thng tin header c thm voni dung khi truyn qua cc lp trong IPTVCM.

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

- Giao thc- a ch IP ca my ch IPTV

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- ID ca tin trnh chy trn my ch IPTV- a ch IP ca IPTVCD- ID ca tin trnh chy trn IPTVCD

Truyn d liu: Truyn thng bt u thng qua socket gia 2tin trnh t pha IPTV server n IPTVCDQun l cc dng ni dung IPTV: giao thc TCP qun l cc dng

IPTV trong khi kt ni c thit lpHy 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 mngHeader: Thng tin ny gip cho segment c truyn i t ngun n

ch. 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

t 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 csegment.

Bng 3.4 nh 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 dy

Ch ra ch s dy ca on TCP. iu ny gip TCP theo

c vt ca mi gi IPTVchuyn qua mngCh s chpnhn

cha ch s dy tip theo m thit b gi mong munnhn c. Trng ny ch cha gi tr ny nu bt iukhin ACK c thit lp

di d liu trng ngn ny ch ra v tr trong on m d liu video bt uc t trc Trng ny c t trc s dng sau ny v c gitr bng 0

Cc bit iukhin

Trng ny gm c 6 bt iu khin:

URG: Urgent pointer ACK: AcknowledgmentPSH: Push

RST: Reset (t li lin kt)SYN: Synchronize (ng b ch s dy)

FIN: khng c thm d liu t bn giCa s Ch ra kch thc ca s cho d liu phn phi gianhng ln nhn

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Checksum Kim tra li bo v d liu c gi qua mngcon tr khn cp Ch c dch khi trng con tr khn cp c cho php

Cc ty chn vm

Cc ty chn l cc bi s 8 bit c sn v c th cha cckiu bin khc nhau. Cc ty chn c la chn squyt nh di ca on TCP. m l phn cui cngca tiu v to thnh bi cc s 0

TCP nh x segment sang giao thc IP sau khi chn cc thng tin cn thit votrong phn header.Nh m t trn, TCP cung cp ton b cc chc nng truyn ti cc d liu qua mng IP.

S dng UDP nh hng cc gi IPTV:UDP l giao thc thuc v b giao thc Internet. UDP cho php my ch k

ni vi mng bng rng gi ti cc IPTVCD dch v truyn hnh qung b c c

lng hi lng ngi dng. UDP ging vi TCP nhng l phin bn s lc hn, ra cho s lng ti thiu cc dch v truyn ti. UDP l giao thc khng lin kt, c ngha l kt ni gia video server v IPTVCD ko cn phi thit lp trc khi liu c truyn i. Video server dn gin ch thm vo a ch IP ch v s cnvo datagram v gi ti c s mng phn pht ti a ch IP ch. Khi trn mnUDP sd cch tt nht c gng thu c d liu v im ch ca n. Ch rUDP s dng cc khi d liu c gi l cc datagram truyn ni dung qua m

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:

- 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 Ngc li, khi s dng TCP, c th xy ra s ngt qung khi phi ch cc g b tr v cc khung 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 trongkhi TCP header chim ti 20 byte.- Tc thit lp kt ni: thi gian thit lp v hy b kt ni gia IPTV

v cc thit b trung tm d liu IPTV ngn. Do , vic phn phi cc gs dng 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 ccng ty s dng v tinh c th truyn ni dung IPTV truyn a im ti khchng ca mnh.

Nhc im ca UDP:

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

- Tnh ton vn ca d liu: Tnh ton vn ca d liu khi s dng UDP khng c bo m khi UDP ch cung cp 1 dch v duy nht l kim tr

tng v multiplexing thng qua s cng. bt k vn no cng c th xy rtrong qu trnh truyn thng ti u cui no cn c iu khin c lvi cc ng dng. Cc vn thng gp nh l pht li, ng gi v lp rli, truyn li cc gi b mt, s tc nghn, v iu khin lung nm ngoi knng sa li ca UDP.- 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 ncng nh hng ti cc cng ty cung cp dch v Internet TV.

Hnh 3.16 nh dng datagram da trn UDP

Bng 3.5 Cu trc datagram IPTV da trn UDPTn trng Chc nng

Ca ngun ch ra ch s ca ca qu trnh gi datagram. N l caty chn v nu khng cdng th s c in y bng cc s 0

Ca ch Ch ra ch s ca ca qu trnh ch ang chy trnIPTVCD

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diGip cho IPTVCD xc nh di v kch thc cadatagram UDP ang n. Trng di bao gm mt gi tr h 8, bao gm c tiu v dliu video thc s.

ChecksumTrng ny di 2 byte cha s c nh trc, cho php mt IPTVCD kim li tnhnguyn vn ca UDP ang n da trn datagram 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 nh dng bi giao thc dng video vaudio m c s dng ti u cui IPTV

i vi IPTV, UDP t ra hu ch khi trung tm d liu cn gi cc ni

dung video IP ti nhiu IPTVCD v l giao thc mc truyn ti ph bin nhm cc nh cung cp dch v IPTV.g. Lp IP:Sau lp truyn ti l lp IP(cn c gi l lp lin mng ) Nhim v

chnh ca lp ny l a cc d liu ti cc v tr mng ring bit thng qunhiu mng c lp c lin kt vi nhau c gi l lin mng. Lp nc s dng gi cc d liu thng qua cc ng khc nhau ti ch. IP giao thc tt nht c s dng trong lp lin mng. giao thc ny cung cdch v phn pht gi c bn cho tt c cc dch v IPTV. Cc loi dch v nvi h thng truyn n im, ni cc gi c truyn t ngun ti 1 IPTVCch, 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 ngynay. Nhim v chnh ca IP l phn pht cc bit d liu trong cc gi t ngunti ch. IP s dng k thut c hiu qu cao nht phn pht d liu. Ni ckhc khng c tin trnh no m bo qu trnh phn pht thng tin qua mngCc khi c s ca giao thc IP l cc on bit d liu c t trong cc gi vc nh a ch.

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 lchui 4 s c ngn cch vi nhau bng cc du chm nh ngha 1 ccchnh xc v tr vt l ca 1 thit b, v d nh set-top box, trong mng. a chIPv4 gm 32 bit trong 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 khot 0 n 255. Mi octet c ngn cch bi 1 du chm trong h thp phn. ch IP c t chc thnh 2 phn:

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a ch mng dng nh ngha mng bng rng mIPTVCD kt ni ti.

a ch host dng nh ngha cc thit b IPTV.

Hnh 3.17 nh dng gi video IPv4

Bng 3.6: Cu trc gi video IPv4

Tn trng Chc nngPhin bn Ch ra phin bn ca IP c s dng trn mng _ IPv4hay IPv6 di Header M t kch thc ca header, gip cho IPTVCD nhn ra payload ca d liu video bt u u

Loi dch v

Cn c bit l im m phn bit dch v(DSCP_Differentiated services code point). Trng nykh quan trng cho vic phn phi ni dung IPTV bi vn cho nh cung cp dch v thit t loi ni dung cmang trong gi d liu. Thng tin ny sau c x l bi b nh tuyn IP trong h thng mng. iu ny cho php cc b nh tuyn chp nhn v lm cho mc chtlng dch v thch hp vi nhng loi lu lng khcnhau

Tng chiu diBo cho IPTVCD bit ton b chiu di ca gi IPTV.Gi tr ny c di 16bit, c ngha l mt gi c th ckch thc ti a l 65535 byte

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Th nhn dngc b nh tuyn s dng phn mt gi ln thnhnhiu mnh nh. Khi c phn mnh, b nh tuyn sdng trng ny phn bit cc mnh khc nhau cagi ban u

C Cc c xc nh cc kiu phn mnh khc nhau, hocgi l mt mnh, hoc n c cho php phn mnh,hoc gi l mnh cui cng hay c thm mnh khc.

di camnh

Khi mt gi IPTV c phn mnh v chuyn i quamng th chc nng ca IPTVCD l tng hp cc mnhtheo ng th t. Trng ny nh s mi mnh, cho php IPTVCD tng hp li theo ng th t

Thi gian sng

V mt gi IP chuyn qua mng, trng thi gian sngs c mi b nh tuyn dc theo ng truyn kimtra v gi tr bn trong trng ny s c gim dn.Qu trnh ny tip tc cho n khi gi tr trng nygim v 0. Khi iu ny xy ra c ngha l gi ny hthn v s b loi b. Chc nng chnh ca trng ny l loi b cc gi trn mng m khng c kh nngtruyn n ch. iu ny s lm gim tc nghn trnmng. Gi tr ca trng ny trong khong t 30 n 32.

Giao thc

Trng di 8 bit, ch ra loi giao thc ng gi bntrong datagram IP. Nu gi tr l mt th sau ICMPc dng, l hai tng ng vi IGMP, l 6 c sdng cho lu lng TCP, v 17 c s dng cho ngdng 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. Trong mitrng IPTV, thit b gi thng l my ch VoD hocl b m ha.

a ch ch Cha a ch ca thit b nhn c ch nh. Trong mitrng IPTV, a ch ny thng l a ch ca IPTVCDTy chn vm

c nh cung cp IPTV s dng cung cp thm ccc im khc

D liu L ni dung video

h. Lp lin kt d liu:Lp lin kt d liu ly cc d liu th t lp IP v nh dng chng

thnh cc gi ph hp truyn qua mng vt l. Ch , lp lin kt d likhc vi cc giao thc mng. K thut Ethetnet l mt trong nhng k thut ph bin hn c s dng trong h thng IPTV. Lp lin kt d liu bao gm cchc nng dnh cho cc mng da trn Ethernet:

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Encapsulation---- Lp ny thm vo cc gi IPTV 1 header.Ethernet header l loi Encapsulation ph bin nht dng trong lp lin kd liu ca IPTVCD. Cc thnh phn c bn ca Ethernet header c githch trong bng 3.9.

nh a ch---- Lp lin kt d liu x l cc a ch vt l camng ngi s dng v cc thit b ch. H thng a ch khc nhau vi ctopo mng. V d, a ch MAC c s dng trong mng Ethernet. Mthit b kt ni vi mng IPTV th c 1 a ch MAC. di ca a chMAC l 48 bit v thng c biu din bng 12 s trong h 16. Trong 1s h 16 ny, 6 s u tin dnh cho nh sn xut thit b IPTV v cc scn li c dng nh ngha giao din mng o.

Kim tra li----- chc nng kim tra li c dng trong vilp ca m hnh IPTV, bao gm c lp lin kt d liu. Cc gi b ngt lli thng gp trong qu trnh truyn cc ni dung video qua mng da trIP. Phng php sa li thng dung l kim tra d tha vng (CRC) trongIPTV tm v loi b cc gi b ngt. S dng k thut CRC thit b gIPTV thc hin vic tnh ton trn cc gi v lu tr kt qu trong gi. C php tnh ton tng t cng c thc hin trn thit b nhn khi nhc cc gi. Nu kt qu tnh ton l nh nhau, th cc gi c x l bnhthng. Tuy nhin, nu kt qu ny l khc nhau, th gi b li s b lo b.Thit b gi s to mt gi mi v gi li n. Thng bo vi lp trtrong m hnh IPTV khi c li xy ra l nhim v chnh ca lp lin kt dliu trong k thut kim tra li m cc h thng IPTV end to end.

iu khin lung---- iu khin lung l mt trong chc nngca lp truyn ti. Trong mng IPTV, iu khin lung cho thit b IPTVca ngi s dng khng b trn bi cc ni dung. Lp lin kt d liu cnvi lp truyn ti thc hin bt k yu cu iu khin lung no.

i. Lp vt l:Lp vt l quy nh lut l truyn cc bit s qua mng. N cp

vic a cc d liu qua cc mng vt l ring bit nh x DSL, v khng dyLp ny nh ngha cu hnh mng vt l, thng s k thut, in trong mtrng truyn.

Khi dng bit c truyn qua mng, cc gi c chuyn t lp thpn lp cao trong m hnh truyn thng IPTV. V d lp lin kt d liu s kitra cc gi v loi b i phn header Ethernet v trng sa li CRC. Tip skim tra trng kiu m ca Ethernet header v xc nh gi cn c x k bgiao thc IP. Do gi d liu c chuyn ln lp mang. Lp mng kim trv loi b i phn IP header v chuyn gi ln lp truyn ti. Phng ph b i phn header khi qua cc lp khc nhau gi l bc gi. Qu trnh ny tiptc c thc hin cho ti khi gi d liu ln n tng trn cng trong m hn

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Hnh nh gc c th hin trn mn hnh TV ca ngi xem.

Bng 3.11 Tng kt cc lp trong m hnh IPTV

Sth t lp

Tn lp Tng quan

1 Vt lXc nh cc thuc tnh ca cc phng tin truynthng trong mng chu trch nhim truyn cc bit dliu IPTV

2 Lin kt d

liu

Qun l cc c ch c s dng truy cp thit btruyn thng trong mng. Kim sot li, ng b v

iu khin lung l nhng chc nng khc m lpny cung cp.

3 IPChc nng ca lp ny c quan h vi vic nhtuyn cc gi IP truyn trn mng. Cc c ch nh lnh a ch v iu khin tc nghn thng clp IPTVCM ny s dng

4 Giao vnChc nng chnh ca lp ny l m bo rng ccgi IPTV n c ch. TCPv UDP u vn hnh ti lp ny

5 RTP (tychn)

Mc d UDP l giao thc c lp giao vn u tins dng hn cho vic phn phi ni dung IPTV trnmng bng rng, nhng n cng ko phi l giao thcang tin cy v n khng h tr vic sa li hay giiquyt vn cc gi n IPTVCD khng theo ngth t. Do , mt s cc nh cung cp dch v sdng RTP gii quyt nhng thiu ht c hutrong giao thc UDP.

6Xy dngdngtruyn ti

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

7Lp ng giVideo

Lp ny to mt dng cc gi PES c nhdu thi gian

8 M ha VideoCc dng audio v video c bn lm thnh nn tngcho lp IPTVCM. nh dng ca dng truyn cs dng lp ny ph thuc vo thut ton nn sdng bi b m ha

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X. Gii thiu cng ngh ADSLCng ngh ADSL (Asymetric Digital Subscriber Line) c pht trin t

u nhng nm 1990 khi xut hin nhu cu truy cp Internet tc cao, cc dcv trc tuyn, video theo yu cuADSL cung cp tc truyn dn khng xng : t 16 - 640 Kbps vi lung ln v ti 8 Mbps vi ng xung (t tngi n khch hng) vi khong truyn ti a l 50 km. u im ca ADSL lcho php ngi s dng dng ng thi ng dy in thoi cho c hai loidch v l thoi v s liu v ADSL truyn min tn s cao (20 Khz - 1 Mhz)nn khng nh hng ti tn hiu thoi. Cc b lc c t hai u mchvng tch tn hiu thoi v s liu theo hai hng khc nhau. Mch ADSLto nn ba knh thng tin i dy thu bao : mt knh tc cao t tng iti thu bao, mt knh tc trung bnh hai chiu v mt knh thoi hoc mtknh N-ISDN. Modem ADSL tng thch vi truyn dn ATM, giao thc IP bng vic thay i tc truyn dn ph hp vi cc mu ca ATM, IP.

Mt dng ADSL khc gi l ADSL.lite hay ADSL khng s dng b

chia ti nh thu bao xut hin t nm 1998. K thut ny khng i hi blc pha thu bao nn gi thnh thit b v chi ph lp t gim i gip cho tc trin khai Internet bng thng rng nhanh hn nhng tc lung ch cn1,5 Mbps.

Thng 7/2002 ITU-T ban hnh tiu chun u tin v ADSL2 trongkhuyn ngh G.992.3 nhm ci tin tt c ng dng trn ADSL c v thoi vliu :

ADSL2 h tr ch truyn dn ng b ST, ch truyn dn bng b ATM, ch truyn dn Packet v h tr thoi khng gi

(thoi c a vo dng d liu ADSL2 khng cn qua b IAD). Mc tiu ca qun l ngun ADSL2 thc hin tit kim nng ln

cho tnh nng always on ca ngun ADSL. ADSL2 thay i v di tn truyn dn theo hai chiu downstream v

upstream vi s phn b mt ph cng sut thch hp trn cc d bng tn. Nh s ci thin ny m di ng dy cho mt tc c nh tng n 300m.

ADSL2 cho php nhiu ng dy ADSL2 to thnh ng dyADSL2 tc cao. Cc ng dy ADSL2 ghp c s dng thayth cho gii php VDSL vi c ly di hn nhng vi s i dy nhiuhn.

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ADSL2 s dng c ch thch ng tc SRA (Seamless RateAdaption) cho php thay i tc d liu m khng b ngt qung,khng b rt mch, khng b nh hng ti t s sai bt.

3.2Cc phng php truyn thng a phng tini vi cc ng dng truyn thng Internet cho truyn hnh, hnh

thc phn phi d liu mt n nhiu im l cn thit, trong dng d licn c truyn i t mt my pht n nhiu my thu ng thi, nhng khc php i n ton b mng con. V l do ny nn gii php IP Broadcasthng khng c s dng trong truyn hnh Internet. Cc ng dng truyhnh Internet hin nay thng s dng phng php IP Unicast v IP Multicasttrong IP Multicast hin l gii php ph bin nht hin nay.

3.2.1 IP UnicastMt s ng dng truyn thng Internet cho truyn hnh giai on u

s dng phng php truyn d liu IP Unicast. Trong trng hp ny, ctruyn ti theo dng c nh hng kt ni c s dng phn phi d n mi my thu mt cch ring l.

Hnh 6 : Gii php truyn thng IP Unicast

Cc ng dng ny hin cn mang nhiu hn ch v hin nay tc ng dng v nhng l do sau : Bng thng ca mng b lng ph

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Dch v khng th m rng phc v khi s lng my thu tng ln Khng th s dng trong cc thit b gii hn thi gian, do s cung cp nmi my thu phi theo trnh t xp hng.

3.2.2 IP Multicast3.2.2.1 Truyn thng IP Multicast trn mng InternetPhng php IP Multicast cng cho php truyn d liu t mt

my pht sender n nhiu my thu, nhng khng ging nh IP Unicast, con scc bn sao (copy) d liu ging nhau truyn i c gim mc ti thiTt c cc my thu ca mt nhm multicast (lp mng D) c ci t cu hnging nhau. My pht sender truyn mt gi IP n mt a ch multicast v cho php gi chuyn tip mt bn copy ca gi d liu n my ch ca mi nh

Nh vy con s cc bn copy di ra qu mc cn thit truyn n cc mng cdi (subnet) c gim thiu v IP Multicast c hiu qu hn IP Unicast, dtit kim c nhiu bng thng my ch server.

Hnh 7 : Gii php truyn thng IP MulticastGiao thc c s dng trong truyn thng IP Multicast c

thc hin ti cc Router mng, khng phi trong cc my ch Server. Cc

Router mng t ng to ra mt bn copy ca mi gi multicast cho mi mthu. Vic nh tuyn trong truyn thng IP Multicast i hi cc Router c bit : cc router trung gian gia my pht sender v cc my thu receiver cn phi c kh nng IP Multicast.

IP Multicast khng phi l mt phng thc truyn thng kt ninh hng : my pht sender gi d liu n nhiu my thu thng qua giao

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thc gi d liu ngi dng UDP (User Datagram Protocol). UDP cng l mtgiao thc thuc lp giao vn (Transport Layer) nh TCP. Nhng khc vi TCP,UDP l loi giao thc khng lin kt, khng i hi phi thit lp lin kt loggia hai thit b trao i thng tin vi nhau, m cho php truyn s liu thngqua s hiu cng m khng cn thit lp mt phin kt ni logic. Kh nng ncho php rt ngn c thi gian truyn s liu, nhng li khng m bo chchn gi d liu c gi i s n ch. Nu mi li xut hin trong qu trtruyn th gi d liu s b hu b. Vic phc hi cc gi d liu b mt s thc hin thng qua cc yu cu phn hi n my pht sender (iu ny tnhin s lm cho s truyn thng phc tp hn hnh trn v ny sinh yu c bng thng mng cao hn).

Trong nhiu trng hp, khi cc my thu nm trong cc mngcon c ngn cch vi cc mng Internet bng cc bc tng la (fire wall)nhng bc tng la ny cn c c kh nng v c ci t cu hnh c php cc dng IP Multicast i qua.

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Hnh 8 : Mng truyn thng vi cc phn t c kh nng IP Multicast

c th thu c v hin th cc dng truyn thng IPMulticast cc my thu cn p ng cc yu cu sau : H tr truyn thng (truyn v nhn d liu) IP Multicast theo nhm giao

thc TCP/IP Ci t phn mm h tr giao thc mng Internet IGMP gi cc yu c

hy b hay tham gia kt ni multicast n cc my thu multicast trong nhm. Card giao din mng c th lc mt cch hiu qu cc a ch lp kt ni d

liu mng Lan c nh x t ng a ch.

3.2.2.2 nh tuyn trong truyn thng IP Multicastnh tuyn cc dng lu thng multicast l mt vn phc

tp, v cc a ch multicast cn c nhn bit nh l a ch ca phin truyn dliu c bit, ch khng n thun ch l mt a im vt l cn gi d liu Mt s k thut mi c pht trin gii quyt c hiu qu vn nh tu

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dng lu thng multicast. Do con s my thu trong mt phin multicast ln, nnngun pht khng cn thit phi bit r tt c cc a ch ny. Thay vo cc bnh tuyn mng cn phi c kh nng chuyn cc a ch multicast vo trong ch chnh (host addresses). trnh lp li cc hot ng ny, mt thit b ntuyn duy nht c chn lm b nh tuyn chnh (designated router) cho mmng, v t thit b nh tuyn chnh ny s to ra mt cu trc m rng hnh ckt ni tt c cc thnh vin ca mt nhm IP Multicast.

Hnh 9 : Cu trc hnh cy m rng trong IP MulticastMt cu trc m rng dng cy ch c kt ni vi phm vi va sao ch

ch c mt ng kt ni duy nht gia tng cp router.Tu theo tnh hnh mt phn b cc my thu trn mng, truyn thng IPMulticast s dng mt trong hai giao thc (v thut ton) nh tuyn sau :

Giao thc nh tuyn mt cao (Dense-mode routing protocol) : c sdng khi cc thnh vin nhm Multicast c phn b dy c trn tonmng. N to ra s lu thng trn ngp trn mng trong tng giai on cd liu multicast trin khai v duy tr cu trc hnh cy m rng.

Giao thc nh tuyn mt thp (Sparse-mode routing protocol) : cs dng khi cc thnh vin nhm multicast phn b tha tht trn mng,cn s dng cc k thut chn lc hn t chc v duy tr cu trmulticast dng cy. Trong trng hp ny nu lu thng trn ngp cc dliu multicast trn mng s gy lng ph bng thng v c th gy ra nhngvn nghim trng trong vn hnh mng.

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Hnh 10 : ng nhp v nhn dng video qua Internet

Nhn chung, d phng thc truyn thng IP Multicast cho php phn phid liu t mt n nhiu im hiu qu hn IP Unicast rt nhiu, nhng vn tmt s vn cha gii quyt c nh :

Cc b nh tuyn trung gian cn phi c kh nng Multicast Tnh nng v vn cu hnh li (reconfiguration) cc tng la trong ccmng con Vn tin cy v kh nng kim sot li trong truyn d liu Cc yu cu lin quan n cc my thu, cn c card mng v phn mm c

bit h tr IP Multicast

3.2.4 Mt s giao thc, ngn ng v chun k thut s dng trongtruyn thng a phng tin trn mng Internet

Giao thc l mt tp cc tiu chun trao i thng tin gia hai h thnmy tnh vi nhau, cc chun ny c s dng v chi phi qu trnh truyn thntrn mng. Tt c cc my tnh c lin quan n mt qu trnh truyn thng u ph

c ci t v tun th cng nhng tiu chun nh nhau trnh sai li.Internet l mt tp hp cc mng my tnh c ni kt v truyn thng vnhau trn c s giao thc chung TCP/IP. Cc chng trnh truyn hnh trc tuyntrn mng Internet s hin th cho ngi xem trn nhng my tnh v cc thit bhin th khc nhau, c ni Internet qua cc mng con khc nhau. V vy cc gia

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thc v chun k thut s dng cho truyn thng truyn hnh trc tuyn cn phc chp nhn v c kh nng truyn thng trn tt c cc thit b v mng ny.

Bc t ph to nn cuc cch mng trong lnh vc video (v c audio) trtuyn l s xut hin cc giao thc truyn dn Internet mi nh UDP (UseDatagram Protocol), RTP (Realtime Tranfer Protocol), v RTSP (RealTimeStreaming Protocol) cho php truyn ni dung audio/video trn Internet hiu quhn cc giao thc Internet truyn thng trc y.

Trc khi c UDP, d liu c truyn trn web ch yu dng giao thc TC(Transmission Control Protocol). TCP c thit k nhm m bo tin cy vton vn thng tin cho vic truyn d liu, email, cc trang web HTML trn mnInternet. C ch sa li ca TCP m bo truyn chnh xc tng bit d liu, lun gng gi li gi d liu b trc trc (do s c ng truyn hoc l do k thut

) trc khi gi tip gi khc, v vy gy nn thi gian tr ln v nh hng cht lng audio/video. V nguyn tc chng ta vn c th thc hin videstreaming vi cc giao thc HTTP (HyperText Transport Protocol) hay FTP (FileTransfer Protocol), nhng do cc giao thc ny vn da giao thc truyn thng TCnn cng khng thch hp cho vic truyn video trc tuyn vn c yu cu cao vyu t thi gian. Giao thc UDP c thit k u tin cho vic truyn d liu ltc hn l nhm m bo tnh ton vn d liu, v vy c bit thch hp cho vtruyn pht online trn mng. Khng ging giao thc TCP, khi gi d liu videotruyn theo giao thc UDP b trc trc (hoc b mt), my ch vn gi tip cc gd liu khc. Phng thc ny cng ph hp vi nguyn tc cm nhn ca tri gi

con ngi, cho php b qua nhng sai bit nh do khng nhn bit c hay dnm trong mc chp nhn c (v d nh mt mt vi m tit hay khung hging nh hin tng nhiu trong truyn dn tn hiu truyn hnh).

Cc giao thc RTP v RTSP u da trn giao thc UDP. RTP l phng thctruyn 1 chiu, cn RTSP cho php truyn 2 chiu, cho php ngi s dng c thtng tc vi my ch iu khin quay lui, tin ti... ging chc nng b ikhin t xa ca u VCR hay DVD. y l 2 giao thc chun m c t chIETF (Internet Engineering Task Force) ph chun chnh thc v c cc cng tyln trong lnh vc truyn thng trc tuyn ng h. Ngoi giao thc RTP v RTSPcn c mt s giao thc khc nh MMS (Microsoft Media Service) ca Microsoftgiao thc ny c th truyn theo UDP hay TCP v c kh nng truyn c 2 chiging nh giao thc RTSP.

Mt s giao thc v chun k thut ang c s dng ph bin trong truyhnh trc tuyn Internet l :

3.2.4.1 Giao thc khi to phin SIP (Session Initiation Protocol):

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SIP l mt giao thc mi xut hin nhng c ng dng rng ri. Trong ccu trc mng NGN, SIP c la chn lm giao thc bo hiu chnh.

I. Gii thiuSIP l mt giao thc bo hiu mi xut hin thc hin iu khin phin ch

cc kt ni a dch v. V c bn, hot ng iu khin bao gm khi to, thayv kt thc mt phin c lin quan n cc phn t a phng tin nh video, thotin nhn, game trc tuyn, vn vn.

SIP em li ba nng lc chnh cho mng vin thng. Th nht, n kch thchs pht trin ca cc m hnh ng dng v dch v da trn web. y l mt iht sc thut li cho nh cung cp dch v do c th s dng mt ngun ti nguydi do cc cng c sn c, ng thi cng thun li i vi ngi s dng kngi s dng quen thuc vi k thut web v n cng c trin khai tr phn ln cc thit b thng minh ngy nay. iu ny tng cng kh nng cung ccc dch v mi mt cch nhanh chng.

Nng lc th hai l kh nng m rng, do SIP l giao thc bo hiu ng cv c tnh phn b cao. Khc vi cc giao thc bo hiu truyn thng thng ctnh x l tp trung cao, in hnh l SS7, trong hot ng ca n tp trung tmt s im bo hiu trong mt cu trc mng bo hiu phc tp; cc phn t SIP phn tn n tn bin ca mng v c nhng ti tn cc im u cui.

Cui cng l kh nng ph cp ca SIP. c pht trin bi IETF, SIP k thcc c im ca hai giao thc Internet c pht trin rt ph bin: l HypText Transport Protocol (HTTP) s dng cho Web v Simple Mail TransportProtocol (SMTP) s dng cho e-mail. Da vo cc nguyn tc c c t mitrng IP, SIP c thit k l giao thc c lp vi ng dng, rt mm do vkh nng p dng trong nhiu mi trng khc nhau v cung cp cc dch v dng.

Tm li, c im ca SIP l n gin, m, d dng trin khai, v tng thvi cc giao thc IP c.

1.1 S pht trin ca SIPSIP c pht trin bi SIP Working Group trong IETF. Phin bn u tin

c ban hnh vo nm 1999 trong ti liu RFC 2543. Sau , SIP tri qua nhiuthay i v ci tin. Phin bn mi nht hin nay c ban hnh trong IETF RF

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3261. RFC 3261 hon ton tng thch ngc vi RFC 2543, do cc h thngthc thi theo RFC 2543 hon ton c th s dng vi cc h thng theo RFC 3261.

Mt bn tin SIP c hai phn, phn mo u v phn thn. Phn thn cho php phc v cc ng dng khc nhau mt cch linh hot. Ban u phn thn ch dng

chuyn ti cc tham s miu t phin SDP nh codec, a ch IP u cui, ... Phnthn c s dng m rng cc ng dng ca khc nhau ca SIP v d nh SIPT cho lin vn PSTN-SIP-PSTN hoc MSCML (Media Server Control MarkupLanguage) cho dch v hi ngh.

S ph cp ca SIP dn ti vic mt lot nhm lm vic lin quan n SIPc thnh lp. Nhm SIPPING (Session Initiation Protocol investigation workinggroup) c thnh lp vi mc ch nghin cu cc ng dng v pht trin cc yucu m rng cho SIP. Nhm SIMPLE (SIP for Instant Messaging and PresenceLeveraging Extensions) c nhim v chun ho cc giao thc cho cc ng dngnhn tin tc thi. Cc nhm lm vic khc l PINT (PSTN and InternetInternetworking), SPIRITS (PSTN/IN requesting Internet Services).

1.2 Cc c im ca SIP thc hin chc nng iu khin phin, SIP h tr 5 chc nng sau:

- User location Xc nh v tr thit b u cui khch hng.- User availability Xc nh trng thi v tnh sn sng ca thu bao b gi

bt u thit lp ng truyn.- User capabilities Xc nh phng tin v cc thng s c s dng.- Session setup Thit lp cc thng s ca phin cho c thu bao ch gi v

thu bao b gi.- Session management To, kt thc, v sa i phin.

SIP khng phi l mt h thng truyn thng c trin khai theo chiu dcm n l mt thnh phn c s dng cng vi cc giao thc khc ca IETF tnn mt cu trc a phng tin hon chnh. Mc d SIP c s dng kt hp vcc giao thc khc, nhng cc hot ng v tnh nng c bn ca n khng phthuc vo cc giao thc ny.

C bn loi thc th chnh c nh ngha trong SIP:- User Agent (UA) ng vai tr ca thit b u cui trong bo hiu SIP. UA bao

gm hai loi User Agent Client (UAC) v User Agent Server (UAS). UAC khi tocuc gi v UAS tr li cuc gi. iu ny cho php thc hin cuc gi ngang hthng qua m hnh client-server.

- Redirect Server tip nhn yu cu nhng khng chuyn sang server k bn mgi tr li n ch gi ch ra a ch ca b gi.

- Proxy Server tip nhn cc yu cu, quyt nh ni gi n v chuyn chngsang server k tip (s dng nguyn tc nh tuyn next hop).

- Registrar tip nhn ng k t cc UA cp nht thng tin v v tr ca chn

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Thng 11 nm 2000, SIP c chp nhn nh mt giao thc bo hiu ca 3GPP vtr thnh mt thnh phn chnh thc ca cu trc IMS. Tiu chun mi nht cho phn li ca SIP (SIP-core) c ban hnh bi IETF trong ti liu RFC 3261. SauSIP-core, nhiu m rng ca SIP c pht trin nh cc m rng ca SIP chomng NGN nh SIP-profile trong cu trc IMS ca 3GPP, SIP-profile cho dch vVoIP ca MSF.

SIP khng phi l mt giao thc bo hiu hot ng c lp. Hot ng ca SIP cs phi hp vi mt s giao thc bo hiu khc. Cc giao thc l SDP (giao thmiu t phin) (RFC 2327) s dng SIP nh mt phng tin chuyn ti v RTP(giao thc truyn ti thi gian thc) c s dng lm phng tin chuyn tSIP. SDP c s dng m t c tnh ca phin. SDP c chuyn ti trong phn thn ca bn tin SIP.

SDP-Session Description Protoco lSDP c nh ngha bi RFC 2327, c pht trin bi IETF MMUSIC. SDPc SIP s dng nh mt phng tin m t phin. Mc ch ban u l m tvic thit lp cc multicast session thng qua MBONE.ng dng u tin ca SDPl giao thc Session Announcement Protocol(SAP)s dng cc port v nhn ccthng bo ca cc MBONE session.SDP cha cc thng tin v media session: IP Address(IPv4 address hoc host name). Port Number(s dng UDP hoc TCP truyn ti).

Media type(audio,video,tng tc whiteboard,). Media Encoding scheme(PCM A-Law,MPEG II video,).Thm vo, SDP cn cha cc thng tin: Ch ca cc session. Bt u v kt thc mi thi im. Lin h thng tin v cc session.Ging nh SIP, SDP d dng m ha vn bng. Mt SDP message c son lmt series ca cc dng, cc trng called, v n yu cu order d dng phntch.SDP th khng c gn c th m rng d dng, v phn tch cc qui tc mtcch chnh xc. Mt ngi phn tch SDP khng phi ti cc trng cha bin, cc trng missing, hoc mt dng out-of-sequence.

Giao thc dnh ring ti nguyn mng RSVP (ResourceReservation

Protocol)

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RSVP l giao thc dnh ring ti nguyn trn mng Internet, c phttrin bi t chc tiu chun mng quc t IETF (Internet Engineering Task Force) nhm nng cao cht lng cc dch v truyn thng trn h tngInternet hin ti. RSVP cho php truyn pht d liu trn mng theo mt trnht thi gian chnh xc (thi gian thc) trn c s duy tr mt quan h thi gianvi ng h ch clock, xc nh dung sai cho php ca tc bit (bit rate), tr (Jitter) v t l li bit BER. RSVP c kh nng yu cu cc thit b nhtuyn Router dnh ring bng thng nht nh cho cc lung lu thng c bi(truyn hnh trc tuyn ) gia cc mng kt ni, qua xc nh trc vm bo cht lng ti thiu ca dch v v to iu kin s dng bng thmt cch hiu qu nht. y l iu khng thc hin c i vi giao thcmng Internet thng thng TCP/IP.

V thc cht, RSVP ch hot ng theo nguyn tc iu khin vpht tnhiu, ch khng trc tip nh tuyn: khi bt u mt dch v truyn thngmy ch (ngun d liu) s a ra mt lnh PATH t cc Router ny qua cc

Router khc (c tnh nng h tr giao thc RSVP) ti mt hay nhiu a chch. Lnh PATH bao gm mt nh danh lung xc nh phin ni kt RSVP,a ra yu cu vloi lung dliu vrng bng thng cn thit. Nu mt bnh tuyn dc trn ltrnh i qua khng p ng c yu cu, n s phitm kim mt ltrnh khc cho lnh PATH i qua. Khi lnh PATH i qua, nucc Router ng gia nhp phin ni kt, chng s nh p v thi hnh cc yucu cha trong lnh PATH ny, sau gi tr v my ch mt lnh RESVtheo tuyn ng c. trnh vic ngi dng chim ot bng thng choring h, cn ci t cc chc nng kim sot bng thng v quyn u tin mngi s dng c trn mng. Cc Router nh tuyn skim tra tnh trng

bng thng v quyn u tin ny khi c mt lnh PATH c gi n. Vicdnh ring ti nguyn trn mng thng c tr chi phb sung bi nhcungc p dch vmng.

2. Giao thc truyn ti thi gian thc RTP (Real-Time TransportProtocol) v Giao thc kim sot thi gian thc RTCP (Real TimeControl Protocol).

RTP l giao thc dng truyn thng trn cc mng truyn thng khngm bo, tc l khng chc chn 100% gi d liu gi i s n ch do btht lc hay tr (nh mng Internet). y l mt giao thc to kh nng ng b v sa li nhm khc phc vn tn tht v tr d liu. RTP cng xcnh mt nh dng cho vic m ho audio v video thc y s lin tcgia cc nn chun my tnh, cc h thng vn hnh, cc sn phm phn mmng dng khc nhau. Nh cc trng d liu c bit (specific data fields)c ng du thi gian (time stamp) v c cha cc thng tin v trnh t phnon d liu (sequence information), cc my tnh thu d liu c th s dngtrng ny ti to cc c tnh thi gian ca dng d liu. Nh qui nhthng nht cch thc truyn dliu a phng tin thi gian thc tmy ny

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sang my khc trn mng (Internet hoc intranet), nn giao thc truyn ti thigian thc RTP c kh nng xlcc dng dliu lin tc, m phng phn b tng tc, cc chng trnh ng dng iu khin. Giao thc ny c ngdng kh ph bin trong cc dch vnh nhn bit loi thanh ton, nh sth t, nh du thi gian, vgim st vic truyn dliu Mt giao thc khclin quan n RTP l giao thc kim sot thi gian thc RTCP. y l giaothc kim sot trng thi ca dng truyn thng thi gian thc. Bng vic sdng RTCP, cc bo co thu v pht c truyn i lin tc trong sut thigian truyn thng sao cho cc ng dng s dng giao thc RTP c th thuc cc bo co v vic d liu ang c cung cp nh th no. C hai giathc trn c a ra bi IETF.

3. Giao thc truyn a dng tin cy cao RMP (Reliable MulticastProtocols).

c thit k bi IETF nhm m bo s cung cp ton vn 100% d litrn mt mng khi cn thit. Khi truyn cc chng trnh truyn hnh hayvideo, do nhy ca mt v tai con ngi c gii hn, nn chng ta khngcn s truyn ti hon ho (100%) d liu v c th b qua nhng tn tht nkhng quan trng, cng nh s can nhiu trong cc hnh nh v m thanh. Nhng truyn cc c s d liu chun hay cc phn mm, th khng c php c bt k tn tht d liu no. Trong trng hp cn s dng giaothc truyn a dng tin cy cao RMP trong truyn thng trn mng Internet.

4. Ngn ng nh du m rng XML (Extansible Markup

Language).XML l nh dng file di dng text c c, c W3C pht trin t

ngn ng nh du siu vn bn HTML (Hypertext Markup Language). XMLc thit kthc hin lu tr, pht hnh d liu trn cc Web site mtcch d dng v p mt hn v l ngn ng linh hot hn nhiu so viHTML, cho php ngi thit k Web nh ngha r ni dung ca d liu bngcch to ui m rng theo mnh (HTML ch kha thnh mt t p cc uimrng theo chun cng nghi p). XML cho php s dng ngn ng nh dutng qut chun SGML (Standard Generalized Markup Language) trn web, vcho php xc nh, nhn dng v s dng cu trc, loi v ni dung ca cc tliu. XSL c th ch nh cho tng thit b u cui th hin hay khng thhin ni dung, hay ch th hin phn no ca ni dung. XML thm ch cth trnh by ni dung trong mi trung truyn thng khc (v d ch ni hayaudio thay cho text hoc hnh nh) v h tr kt ni cc c s d liu, truynv hin th cc thng tin/thng bo di dng vn bn text trc tip.

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Trong ng dng Truyn hnh trc tuyn trn mi trng mng, s phntch v x l cc file XML c th bt u ngay khi cc phn u tin c thu bi my thu thay cho vic phi i n lc thu c y file c pht iS phn tch c php ca cu trc file XML c thc hin song song ngaylp tc trong sut qu trnh thu. Cc thng bo c to ra kim sot ccng dng bn ngoi. Nh vy vic lu tr tc th mt file XML nguyn th lkhng cn thit v s hin th c th bt u ngay lp tc.

5. Ngn ng tch hp truyn thng a phng tin ng b SMIL(Synchronized Multimedia Integration Language).

SMIL l kt qu ca "D n truyn thng a phng tin ng b nhmthit lp chun k thut c kh nng ng b cc truyn thng d liu khcnhau (text, ho, audio v video) sao cho vic hin th ni dung truyn thngc thc hin theo mt phng thc kt hp, m bo tnh nng a truyn

thng. D n c thc hin bi t hp cng nghip quc t W3C (WorldWide Web Consortium). SMIL c kh nng trn ghp cc d liu truyn thngtrong cc nh dng khc nhau, nh vy c th tch hp cc truyn thng trongcng mt frame, ng b chng trong mt chng trnh. Kh nng ny tothun li cho cc nh thit k web thit k v b sung (ghp) cc chng trnhtruyn thng khc nhau ln cng Website. SMIL c xy dng trn c s ngn ng nh du m rng XML.

3.2.4.6 Giao thc dng d liu thi gian thc RTSP (Real-TimeStreaming

Protocol)RTSP l giao thc mc ng dng kim sot vic cung cp v lu trni dung ca cc d liu c c tnh thi gian thc trn Internet v Intranet,RTSP c pht trin bi Real Networks, Netscape, Columbia University vc IETF chun ho. Giao thc ny lm vic bng cch bnhcc gi dliu ty theo tc bng thng cho ph p gia client vserver. Khi mclientnhn va lng d liu thplayer sgii nn, play gi d liu u risau ti p tc download gi d liu ti p theo vti p tc play gi d liu k ti p vcti p tc nh vy. Giao thc RTSP giy c thgii ha v p dng trong hu ht cc ng dng streaming. RTSP c th truyn m thanhv hnh nh trc tip hay c thu t trc. Cho php tng tc hai chiu htr cho IP Multicast vi chi ph truyn thng thp, an ton caoRTSP hinang c trn cc nn my tnh ph bin hin nay. RTSP ngy nay c xem l giao thc chun trong knghmultimedia streaming.

7. nh dng dng tin tin ASF (Advanced Streaming Format).ASF c xy dng bi Microsoft xc nh nh dng lu tr i vi

cc truyn thng theo dng (streaming media). ASF l nh dng file chun m

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trong ni dung multimedia s c lu gi, to dng (streamed) v hin thnh cc cng c, cc my ch server, v my trm ca nh cung cp truynthng a phng tin trong cng file chung, thay cho vic phi s dng ccfile video, ha, text v audio ring bit.

3.2.4.7 Giao thc qun l nhm Internet IGMP (Internet GroupManagement Protocol)

Giao thc IGMP pht trin t giao thc Host Membership Protocol, cm t trong ti liu ca Deering. IGMP pht trin t IGMPv1 (RFC1112) nIGMPv2 (RFC2236) v n phin bn cui cng IGMPv3 (RFC3376). Ccthng ip IGMP c gi bn trong gi tin IP vi trng protocol number bng 2, trong trng TTL c gi tr bng 1. Cc gi IGMP ch c truyntrong LAN v khng c tip tc chuyn sang LAN khc do gi tr TTL can. Hai mc ch quan trng nht ca IGMP l:

- Thng bo cho router multicast rng c mt my mun nhn multicasttraffic ca mt nhm c th.

- Thng bo cho router rng mt c mt my mun ri mt nhm multicast(ni cch khc, c mt my khng cn quan tm n vic nhn multicasttraffic na). Cc router thng dng IGMP duy tr thng tin cho tng cngca router l nhng nhm multicast no router cn phi chuyn v nhng hostno mun nhn.

Trc khi mt host c th nhn bt k mt multicast traffic no, mt ngdng multicast phi c ci t v chy trn host . Sau khi mt host thamgia vo mt nhm, phn mm s tnh ton a ch multicast v sau cardmng s bt u lng nghe a ch multicast MAC. Trc khi mt host hoc

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mt ngi dng mun tham gia vo mt nhm, ngi dng cn phi bit nhno ang tn ti v lm th no tham gia vo nhm . i vi cc ngdng mc doanh nghip, ngi dng ch cn n gin nhp vo mt link trnmt trang web hoc a ch multicast c th cu hnh trc trn client. V d,mt ngi dng c th c yu cu log vo mt my ch v xc thc btn v ngi dng. Nu tn ngi dng c xc thc, ng dng multicast st ng ci trn PC ca ngi dng, ngha l ngi dng tham gia vonhm multicast. Khi ngi dng khng cn mun dng ng dng multicastna, ngi dng phi ri khi nhm. V d, ngi dng n gin ch cn nng dng multicast ri khi nhm. i vi c ch multicast, mt ngidng cn phi tm ra ng dng no h mun chy, a ch multicast c dn bi ng dng.

Lm th no mt router bit c cc my cn nghe multicast traffic? nhn multicast traffic t mt ngun, c ngun v cc my nhn u tin phi

gia nhp (join) vo mt nhm multicast. Nhm ny c xc nh thng quaa ch multicast. Mt host c th tham gia vo mt nhm multicast bng cchgi cc yu cu n router gn nht. Tc v ny c thc hin thng qua giathc IGMP. IGMPv1 c nh ngha trong RFC1112 v bn ci tin ca n,IGMPv2 c nh ngha trong RFC2236. Khi c vi host mun tham gia vonhm, giao thc PIM s thng bo cho nhau gia cc router v hnh thnh nncy multicast gia cc routers. IGMP v ICMP c nhiu im tng ng,cng chia s mt vi chc nng tng t. IGMP cng ng gi trong gi tin IP(protocol number 2), nhng IGMP gii hn ch trong mt kt ni lp 2. m bo router khng bao gi tip tc chuyn gi tin i, trng TTL ca

IGMP lun c gi tr bng 1.IGMPv1

C mi 60 giy, mt router trn mi phn on mng s gi truy vn ntt c cc host kim tra xem cc host ny c cn quan tm nhn multicasttraffic na khng? Router ny gi l router truy vn IGMPv1 Querier v chcnng ca n l mi cc host tham gia vo nhm.

Nu mt host mun tham gia vo mt nhm, hoc n mun tip tc nhntraffic t mt nhm m n tham gia, n phi tr li li bng thng ipmembership-report. Cc host c th tham gia vo cc nhm multicast bt kthi im no.

Tuy nhin IGMPv1 khng c c ch cho php mt host ri khi mtnhm nu host khng cn quan tm n ni dung ca nhm multicast .Thay vo , router s kt lun l mt cng giao tip ca b khng cn thucv mt nhm multicast no nu router khng nhn c thng ip

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membership-report trong ba chu k truy vn lin tip. iu ny c ngha l, ch mc nh, cc lu lng multicast vn gi vo mt phn on mngtrong ba chu k truy vn lin tip sau khi tt c cc thnh vin ca nhm khngcn lng nghe multicast traffic na.

Ngoi ra, router khng c gi mt danh sch y cc my thnh vincho tng nhm multicast. Thay vo , n cn phi lu nhng nhm multicastno l ang tn ti trn nhng cng no ca n.

tham gia vo mt nhm multicast, mt host s gi mt thng ip ngk tham gia vo nhm n router cc b ca n. Thng ip ny c tn lMembership Report IGMP. Thng ip ny s thng bo cho router v a chnhm multicast m host mun tham gia vo. a ch multicast tng trng chott c cc my 224.0.0.1 c dng nh a ch ch. Trong thng ip ny ccha a ch nhm multicast.

Mt thng ip IGMPv1 c nm trng:1. Version: trng ny c di 4-bit, lun lun gn gi tr bng 1.2. Type: Trng gi tr 4bit, ch ra hai loi thng ip c nh ngha bi

IGMPv1. Type = 0x1 l kiu Host Membership Query, c dng ch birouter. Type = 0x2 l kiu Host Membership report c dng ch bi host.

3. Unused: trng ny c di 8bit cha gi tr 0 khi c gi v b bqua khi c nhn.

4. Checksum: mang gi tr 16bit checksum c tnh ton bi ngun cathng ip IGMP. Thit b nhn thng kim tra gi tr checksum v nu gitr ny khng ng bng gi tr tnh ton, my nhn s loi b frame.

5. a ch nhm (Group Address): di 32bit, c gn v gi tr 0.0.0.0 khirouter gi ra gi tin Membership query. Gi tr ny c gn gi tr a chnhm multicast khi mt my gi thng ip Membership report.

Lu rng khi kt hp hai trng version v trng type, gi tr dng thplc phn ca mt gi tin IGMPv1 Host Membership Query s l 0x11 v

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IGMPv1 Host Membership report l 0x12. Cc gi tr ny s c so snh vicc gi tr ca IGMPv2.

Router truy vn IGMPv1 Querier

tng tnh d phng, ta c th trin khai nhiu router multicast trn cngmt mng. Tuy nhin nu tt c cc router gi gi tin truy vn mi 60 giy ths rt lng ph bng thng . Nh vy, nn c mt router c gn vai tr gigi tin truy vn v truyn lu lng multicast vo hoc ra subnet. Nu mtrouter b down, router th hai c th m nhn trch nhim. IGMPv1 thngda vo cc thng tin nh tuyn ca multicast gii quyt vn bu chnrouter ny.

2.2 Internet Group Management Protocol, IGMP Version 2

2.2.1 nh dng thng ip IGMPv2

IGMP version 2 c m t chi tit trong RFC 2236. nh dng thng ipIGMP version 2 nh hnh sau:

Trng Type di 8 bit, mi gi tr trng Type ng vi mi loi thngip:

-Type = 0x11: Thng ip truy cn thnh vin Membership Query-Type = 0x12: Thng ip bo co thnh vin Membership Report Version

1-Type = 0x16: Thng ip bo co thnh vin Membership Report Version

2-Type = 0x17: Thng ip ri khi nhm Leave Group

Thng ip Membership Query, ng vi gi tr Type = 0x11, mang 2 nidung. Th nht thng ip General Query dng xc nh nhm no trnmng c thnh vin hot ng. Th hai l thng ip Group-Specific Querydng xc nh mt nhm multicast c th c thnh vin hot ng.

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Trng Maximum Response Time (Max. Rtime) ch p dng cho thngip Membership Query. Trng ny ch ra thi gian ln nht m trm con phi ch trc khi nhn thng ip hi p Membership Query.

Trng Checksum di 16 bit dng kim tra li header.

Trng Group Address cha a ch nhm. i vi thng ip GeneralQuery, trng ny mang gi tr 0.0.0.0. i vi thng ip Group Specfic,trng ny s cha a ch ca nhm multicast c truy vn.

2.2.2 So snh IGMPv2 v IGMPv1

-IGMPv1 khng c thng ip Group Leave nn thi gian nhn bit trmcui cng ri khi nhm v thi gian router ngng gi d liu multicast luhn so vi IGMPv2. Trong khi IGMPv2 gim thiu thi gian ch khi xc nh

trm con ri nhm v nhanh chng b qua lu lng khng mong mun.-IGMPv2 c s dng thng ip truy vn Group-Specific Query trong khi

IGMPv1 th khng c thng ip ny.

-IGMPv1 khng ch nh khong thi gian Maximum Response Time trongcc thng ip Membership Query m c nh thi gian ny l 10 giy.

-IGMPv1 khng chn ra router no gi thng ip Membership Query nnc th c nhiu router gi thng ip ny trn cng mng con.

- Mt ci tin ca IGMP version 2 so vi version 1 lin quan n mng atruy cp (multi-access networks) v d nh mng ethernet c nhiu hn 1router multicast trong mng. Do ch cn 1 router gi thng ip MembershipQuery, IGMP version 2 thm mt tnh nng l xc nh c router s chutrch nhim gi thng ip Membership Query gi l Querier router v ccrouter khc tr thnh Non-Querier router.

VD: Gi s rng router A gi thng ip Membership Query vo mngtrc router B. Router B nhn thng ip ny v bi v router A c a ch IPthp hn router B nn router A vn l Querier router v router B tr thnh Non-Querier router . Nu router B gi thng ip Membership Query trcrouter A, iu ny khng ngn cn c thng ip Membership Query trouter A v router A c a ch IP thp hn. Router A s gi thng ipMembership Query v router B(trong lc nhn thng ip ny) s tr thnh Non-Querier router trong mng.

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im mi na ca IGMP version 2 so vi IGMP version 1 l c thmthng ip Leave Group. Khi trm con quyt nh ri khi nhm v nu trmcon l trm hi p thng ip Membership Query cui cng, th trm con sgi thng ip Leave Group n a ch multicast ca tt c cc router trongmng 224.0.0.2. Nu trm con cha phi l trm cui cng gi thng ipMembership Query, th thng ip Leave Group cha gi i. RFC cng cho php gi thng ip Leave Group n nhm multicast c th thay v gi na ch multicast ca tt c cc router. Li ch ca vic gi thng ip LeaveGroup n a ch multicast ca tt c cc router l cc trm con khc khng lthnh vin ca nhm khng phi x l thng ip ny.

M ha thi gian th v s vn chuyn thi gianthc trong IPTV

Vi s hi t ca vic truy cp Internet, TV, in thoi, th cc cng ngh nn ang vai tr ch cht trong vic pht trin cc dch v v sn phm mi cho cc ncung cp dch v v cc nh kinh doanh thit b. Sau y l cc cng ngh nn mnnht c s dng trong h thng IPTV nh l: MPEG-2, H.264/AVC v VC-1Trong phn ny cung cp chi tit m hnh truyn thng IPTV (IPTVCM), IPTVCM lmi trng gm 7 lp v gii thch cc giao thc h tr cho trch nhim ca mi ltrong m hnh.

Gii thiu v m ha thi gian thc:- Trc khi tm hiu v m ha, th tht c li khi ta hiu c hai qu trnh l c

c ni dung video v giai on m ha. u tin l qu trnh lin quan n vis dng camera chp v ghi li ni dung video nh dng tng t v ni duvideo cn phi qua mt qu trnh c gi l s ha chuyn i tn hiu tht lin tc thnh cc chui bit s. Mt phn cng c it c gi l b chuynA/D c s dng trong qu trnh ny.

- K thut ly mu v lng t ha c s dng trong sut qu trnh x l tn hiLy mu y c ngha l s lng mu c ly ra t tn hiu tng t, tc mu c tnh bng ps. Lng t ha l qu trnh quy nh s bit trn mi mu thiu. T cc dng bit video cha c nn chun b cho qu trnh m ha.

- Qu trnh m ha cc dng bit s yu cu s dng phn cng c bit l cc b mha, qu trnh m ha ti cc trung tm d liu IPTV bao gm cc bc sau:

(1) Mt ngun cung cp video c nhn t mt ngun c bit. nh dng ca ngun cung cp ny c th l t cc tnhiu tng t cht lng thp n cc dng bit s chtlng cao.

(2) Khi nhn c ri, b m ha p dng mt chun nnc bit n ni dung video.

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(3) Khi c nn ri, video c chun b cho vic truynti, chun b y c ngha l ni dung c chn vo ccgi d liu bao gm vic phn thnh cc gi v ng gini dung video.

- Vic m ha ni dung video cho mi trng mng IPTV c vi im thun lnh:

+ Gim c s lng ln khng gian a cng lu tr cc tp tinvideo.

+ Vic p dng cc k thut nn cho ni dun g video gim s lngcc lnh ca b vi x l trong qu trnh x l v hin th ra mn hnh.

+ Kch thuc tp tin oc nn 3n kch thc ban 9u nn thi giangi n qua mng c gim.

+ Kt ni bng thng rng vi kh nng thp c th c s dng

truyn ti ni dung IPTV. V d: Mt dng c 4 ho cho mt knh SDTV th xx 1.5Mbps, trong khi mt knh HDTV th xp x 8Mbps. Trong khi vi chunnn c th yu cu 3.5Mbps cho SDTV v 20-25 Mbps cho HDTV, cho ta thy thunli ca cchun nn hin i l rt r.

- Tuy nhin c vi bt li khi s dng cng ngh nn khi truyn ti cc dch vIPTV nh:

+ Qu trnh nn v gii nn mt tn hiu s xut hin thi gian tr.+ Mt vi thng tin b ct b trong qu trnh nn, cho nn tng quan

th cht lng hnh nh s gim so vi lc cc tn hiu cha b nn.

+ Vic chuyn m ca cc tn hiu xut ra v chuyn t nh dng nny sang nh dng nn khc c th nh hng n cht lng ca tn hiu.V vy chng ta cn cn nhc vic m ha tn hiu truyn ti qua mng IP.

Cc chun nn MPEG:Cng ngh MPEG l mt chun nn, c s dng rng ri trong cc

h thng truyn hnh nh: mt t, cp, v tinh. MPEG l ch vit tt ca MovPicture Experts Group, l mt hip hi cng nghip chuyn nghin cu v pht tricc chun nn thch hp cho vic truyn ti video. Nhm ny c to ra bi T ChTiu Chun Quc t (ISO) v y Ban K S Quc T (IEC). T khi c thnh lMPEG a ra cc chun nn nh: MPEG-1, MPEG-2, MPEG-4(Part 2 v Part 10),MPEG-7, v MPEG-21. Trong cc chun ny, MPEG-2 v MPEG-4 Part 10 c sdng rng ri trong IPTV.

Bng tm tt cc nh dng MPEG

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nh dngMPEG M t

MPEG-1

nh dng MPEG-1 cpht trin u tin vo nm1988 v c s dng chnh nn video ti tc bit l 1.5Mbps. Ni dung MPEG-1 c s dng chodch v nh pht thanh s(DAB). MPEG-1 l nhdng c bn ca chun MP3, c s dng rng richo nhc trn Internet.

MPEG-2

MPEG-2 c xy dng trn kh nng nn mnh mca chun MPEG-1. MPEG-2 c s dng rng ritrong truyn ti ca truyn hnh qung b cht lngv lu tr ni dung video trn cc a DVD. Mt scc chun truyn hnh quc t da vo nh dng nnny.

MPEG-4 Part 2

MPEG-4 l nh dng thit k chnh thc caISO/IEC vo thng 10/1998 v tr th nh chun quct vo nm 2000. Chun Part 2 th c chia votrong mt s thng tin m a ch yu cu ca mt sng dng video trong in thoi di ng n cc mycamera theo di.

MPEG-4 Part 10MPEG-4 Part 10 hay cn gi l H.264/AVC cthit k truyn video qung b v video cht lngDVD ti tc d liu thp nht.

Chun nn video.

Tuy c nhng t ph v giao thc truyn nhng vic truyn video trc tuyn skhng th tr thnh hin thc nu khng c nhng tin b vt bc trong k thum ha, nn v gii nn d liu video. Cc tp tin ni dung video gc hay cha nnthng rt ln, c th lm tc nghn bt k ng truyn no, v vy vic nn nhd liu gim yu cu bng thng c ngha v cng quan trng i vi k thustreaming.

C mt s cch gim yu cu bng thng ca dng d liu truyn dn. V d vi video, ngi ta c th gim tn sut khung hnh (ch dng 15 khung hnh/giythay cho 30 khung hnh/giy) v phn gii (v d gim phn gii t 640x480 pixels xung cn 320x240 pixels). Tuy nhin, nhng phng php ny lm gimnhiu cht lng hnh nh v vn cha gip gim bng thng truyn dn n

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mong mun. V vy ngi ta cn phi s dng cc k thut m ha nn ni dunggc, sau gii m my thu client.

Hin c nhiu k thut m ha nn d liu audio v video, nhng tu trung c th phn theo 2 k thut c bn. Mt l tm cch th hin hiu qu thng tin d thatrong ni dung, theo cch ny, khi c ti to li d liu kt qu ging tng bit vni dung gc. Tuy nhin, cch thc nn khng tn tht ny ch gip gim s bitkhng ng k. a phn k thut m ha v nn video s dng trn mng Internethin nay s dng k thut c tn tht, tc l ngi ta s lc b bt i mt s thtin m cc c quan tri gic con ngi (tai v mt) khng nhn bit c. Cc kthut ny cng cho php m ha nn vi nhiu t l bit khc nhau mt cch linhhot, c th cho php truyn ti ty theo bng thng kt ni khc nhau v khi ,trn my thu client cng phi c cng c gii m tng ng gip gii m ni dungth mi c th hin th c. y thng l cc cng c gii m c cung cpmin ph, khch hng c th ti v t cc my ch ca nh cung cp dch v video

online trn mng nh Windows Media (wmv, wma, avi v asf), Realplayer (rm,ram), QuickTime (mov) v MPEG-4 (ISO, DivX)...

Bng 1: Mt s chun nn v gii m dng video ph bin trn mng Internet hinnay.

H.264

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H.264 gim yu cu bng thng trong khi cht lng nh tng ng MPEG-2 vMPEG-4. Cng ngh ny gip cho tng cng kh nng nn khng gian v nn thgian, cho hnh nh truyn rt nhanh trn mng LAN, internet. Vi nhng u vit cmnh, H.264 ang c ng dng rt nhiu vo ngnh an ninh.

1. Gii thiu chung

K t khi mi xut hin vo u nhng nm 90, chun nn video MPEG-2 honton thng lnh th gii truyn thng. Cng trong thp k ny, chun nn MPEG-2 c ci tin v nhiu mt. Gi y n c tc bit thp hn v vic ng dnn c m rng hn nh c cc k thut nh on chuyn ng, tin x l, x l

i ngu v phn b tc bit ty theo tnh hung thng qua ghp knh thng k.

Tuy nhin, chun nn MPEG-2 cng khng th c pht trin mt cch v hnnh. Thc t hin nay cho thy chun nn ny t n ht gii hn ng dng mnh trong lnh vc truyn truyn hnh t sn xut tin k n hu k v lu trVideo s. Bn cnh , nhu cu nn Video li ang ngy mt tng cao km theo s pht trin mnh m ca mng IP m tiu biu l mng Internet. Khi lng nidung m cc cng ty truyn thng cng nh cc nh cung cp dch v thng tin c

th mang li ngy cng ln, ngoi ra h cn c th cung cp nhiu dch v theo ycu thng qua h thng cp, v tinh v cc h tng vin thng t bit l mngInternet.

Cc tiu chun m ho Video ra i v pht trin vi mc tiu cung cp cc phntin cn thit to ra s thng nht gia cc h thng c thit k bi nhngsn xut khc nhau i vi mi loi ng dng Video; Nh vy th trng Video ciu kin tng trng mnh. Chnh v l do ny nn nhng ngi s dng b giim cn c mt chun nn mi i tip chng ng m MPEG-2 b d.

Hip hi vin thng quc t (ITU) v t chc tiu chun quc t/ U ban k thuin t quc t (ISO/IEC) l hai t chc pht trin cc tiu chun m ho Video.Theo ITU-T, cc tiu chun m ho Video c coi l cc khuyn ngh gi tt l

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chun H.26x (H.261, H.262, H.263 v H.264). Vi tiu chun ISO/IEC, chng cgi l MPEG-x (nh MPEG-1, MPEG-2 v MPEG-4).

Nhng khuyn ngh ca ITU c thit k dnh cho cc ng dng truyn thngVideo thi gian thc nh Video Conferencing hay in thoi truyn hnh. Mt khcnhng tiu chun MPEG c thit k hng ti mc tiu lu tr Video chng hnh trn a quang DVD, qung b Video s trn mng cp, ng truyn s DSL,truyn hnh v tinh hay nhng ng dng truyn dng Video trn mng Internet hothng qua mng khng dy (wireless).

Vi i tng truyn dn Video l mng Internet th ng c vin hng u l

chun nn MPEG-4 AVC, cn c gi l H.264, MPEG-4 part 10, H.26L hocJVT.

2. Tnh k tha ca chun nn H.264

Mc tiu chnh ca chun nn H.264 ang pht trin nhm cung cp Video c cht

lng tt hn nhiu so vi nhng chun nn Video trc y. iu ny c th tc nh s k tha cc li im ca cc chun nn Video trc y. Khng chth, chun nn H.264 cn k tha phn ln li im ca cc tiu chun trc lH.263 v MPEG-4 bao gm 4 c im chnh nh sau:

Phn chia mi hnh nh thnh cc Block (bao gm nhiu im nh), do vyqu trnh x l tng nh c th c tip cn ti mc Block.

Khai thc trit s d tha v mt khng gian tn ti gia cc hnh nh litip bi mt vi m ca nhng Block gc thng qua d on v khng gian, php bin i, qu trnh lng t v m ho Entropy (hay m c di thayi VLC).

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Khai thc s ph thuc tm thi ca cc Block ca cc hnh nh lin tip bvy ch cn m ho nhng chi tit thay i gia cc nh lin tip. Vic nyc thc hin thng qua d on v b chuyn ng. Vi bt k Block nocng c th c thc hin t mt hoc vi nh m ho trc hay nhc m ho sau quyt nh vc t chuyn ng, cc vc t ny cs dng trong b m ho v gii m d on cc loi Block.

Khai thc tt c s d tha v khng gian cn li trong nh bng vic m c block d tha. V d nh s khc bit gia block gc v Block d on sc m ho thng qua qu trnh bin i, lng t ho v m ho Entropy.

3. C ch nn nh ca H.264 (MPEG-4 AVC)

Vi chun nn H264, mi hnh nh c phn chia thnh nhiu Block, mi block

tng ng vi mt s lng nht nh cc MacroBlock. V d mt hnh nh c phn gii QCIF (tng ng vi s lng im nh 176x144) s c chia thn99 MacroBlock vi kch c 16x16. Mt s phn on cc MacroBlock tng tc s dng cc kch c nh khc. Thnh phn chi ca nh c ly mu tnng vi phn gii ca nh , trong khi thnh phn mu CR v CB c lymu vi tn s thp hn theo 2 chiu ngang v dc. Thm vo mi hnh nh cth c phn thnh s nguyn ln cc lt mng (slice), vic ny rt c gi tr chovic ti ng b trong trng hp li d liu.

Mi hnh nh thu c c xem nh mt nh I. nh I l nh c m ho bi vip dng trc tip cc php bin i ln cc MacroBlock khc nhau trong nh. Ccnh I c m ho s c kch c ln bi n c xy dng t mt khi lng lnthng tin ca bn thn nh hin ti m khng s dng bt c thng tin no t mithi gian trong qu trnh x l m ho tng hiu qu x l m ho bn trongtrong H.264.

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3.1. Gim bt d tha

Cng ging nh cc b lp gii m khc, H.264 nn video bng cch gim bt d tha c v khng gian v thi gian trong hnh nh. Nhng d tha v mt thigian l nhng hnh nh ging nhau lp i lp li t khung (frame) ny sang khungkhc, v d nh phn phng nn khng chuyn ng ca mt chng trnh i thotrn truyn hnh. D tha v khng gian l nhng chi tit ging nhau xut hintrong cng mt khung, v d nh nhiu im nh ging nhau to thnh mt bu trxanh. Hnh 1 biu din mt cch s lc cc bc m b lp gii m MPEG-4 phtin hnh nn khng gian v thi gian.

3.2. Chn ch , phn chia v ch ng

B lp gii m bt u bng vic quyt nh loi khung cn nn ti mt thi inht nh v chn ch m ho ph hp. Ch "trong khi" to ra nh "I", trokhi ch "gia khi" to ra khung "P" hoc "B". Sau , b m ho s chia nhthnh hng trm hng v ct cc im nh ca nh video s cha nn thnh cc kh

nh hn, mi khi c cha mt vi hng v ct im nh.

3.3. Nn theo min thi gian

Khi b m ho ang hot ng ch "gia khi" (inter), khi ny s phi quacng on hiu chnh chuyn ng. Qu trnh ny s pht hin ra bt k chuynng no din ra gia khi v mt khi tng ng mt hoc hn mt nh thchiu c lu tr t trc, sau to ra mt khi "chnh lch" hoc "li". Thtc ny s gim bt d liu trong mi block mt cch hiu qu do ch phi trnh bchuyn ng ca n m thi. Tip n l cng on bin i csin ri rc (DCT) bt u nn theo min khng gian. Khi b m ho hot ng ch "trong khi(intra), khi ny s b qua cng on hiu chnh chuyn ng v ti thng cngon DCT.

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3.4. Nn theo min khng gian

Cc khi thng c cha cc im nh tng t hoc thm ch ging ht nhau.Trong nhiu trng hp, cc im nh thng khng thay i my (nu c). Nhvy c ngha l tn s thay i gi tr im nh trong khi ny l rt thp. Nhngkhi nh th c gi l khi c tn s khng gian thp. B lp m li dng cim ny bng cch chuyn i cc gi tr im nh ca khi thnh cc thng tin ts trong cng on bin