TRUYN HNH CP DIGITAL I. Tng qut h thng truyn hnh cp Digital :

Truyn hnh s l truyn hnh c cht lng cao tha mn c nhu cu ca ngi xem cng nh gip cho cc trung tm truyn hnh d dng qun l cc thu bao, pht trin ln cng ngh truyn hnh s th cc trung tm truyn hnh cn phi ci thin h thng ca mnh, nng cp cc phng tin k thut cng nh cn phi lp t cc u thu truyn hnh s v iu ch cc tn hiu s pht i khi cc thu bao cng s c lp t mt Set top box s, Cu to ca mt h thng truyn hnh cp s cng tng t nh h thng truyn hnh cp tng t, Tng qut ca mt h thng truyn hnh cp s bao gm cc khi chc nng nh: thu tn hiu s, nn v m ha, iu ch v sau s c ghp knh v truyn i n thu bao, Ti thu bao s c lp t mt Set-top-box s thu tn hiu v gii m,

Thu tn hiu Nn v m ha iu ch

Node quang Hub Headend(ni qun l mng) Amplifier H thng truy cp c iu kin

S khi tng qut ca mt h thng truyn hnh cp s

Nguyn l hat ng ca h thng

Theo s tng qut ca h thng truyn hnh cp s th tn hiu c pht i ti trung tmv i n thu bao s l tn hiu s, Ti trung tm ca h thng tn hiu s c thu nhn t nhiu ngun khc nhau, Cc tn hiu c my thu thu nhn s c a qua khi nn v m ha ti y tn hiu s c chuyn i hon tan thnh tn hiu s, Tn hiu ny sau s c a qua b iu ch s iu ch tn hiu s thnh mt tn hiu hon chnh, Sau tn hiu ny s c ghp knh v pht i trn si cp quang n node quang, T node quang tn hiu c khuch i v a n thu bao, Ti thu bao ca truyn hnh cp s s c mt h thng truy cp c iu kin, Tin b ca truyn hnh

cp s l c th kt ni gia my tnh vi my thu hnh v hp gii m Set-top-box s v c kh nng truyn trong Internet. Mng hat ng ca h thng trn u da trn c s ca mng HFC v c gi l HFC s, HFC l cng ngh cp quang lai ghp, s dng cu hnh mng dng cp quang v cp ng trc, c s dng phn phi li cc dch v bng rng, Cc dch v bng rng ny bao gm: in thai, a phng tin tng tc, truy cp Iternet tc cao, VOD (Video-on demand video theo yu cu) v hc t xa, Cc lai dch v cung cp cho thu bao thay i gia cc cng ty cp, Nhiu cng ty truyn hnh cp chnh Chu u, M v Chu M La Tinh, ng Nam s dng HFC s, Cc mng s dng cng ngh HFC c c trng: thc hin mt cch l tng cc dch v thng tin cho th h mi, HFC tha mn cc yu cu v tng kh nng m rng v thc hin cc dch v ph m khng cn thay i c s h tng,

II .H thng Headend s: 1./ S h thng Headend Digital:

Headend l trung tm thu v pht tn hiu, T y tn hiu s c thu nhn v qua qu trnh s l sau s c pht i, Khc vi Headend Analog l tn hiu ti trung tm pht i l tn hiu s, Do s dng cng ngh mng HFC nn h thng Headend s vn da trn c s h tng c sn ch cn u t thm trang thit b x l tn hiu.

` 2./ Chc nng cc khi trong h thng Headend s:

A./ SIGNAL ACQUISITION: tn hiu thu Tn hiu thu y rt a dng,cc tn hiu thu gm: tn hiu v tinh, truyn

hnh s mt t, mng, cc i a phngty theo tng loi tn hiu m ta c cc b gii iu ch khc nhau bng cch s dng cc card ri gn trn cc rack cm

c im: - Cc tn hiu sau khi thu c s c x l v truyn tn hiu s

trn mt bng tn c s ( ASI) - Yu cu c trng ca tn hiu l: linh ng, n gin, nng

lng thp v vn hnh mt cch c lp - Cht lng hin th ca tn hiu: cn x l tn hiu mt cch y

v chnh xc, trnh lan truyn tn hiu b trc trc, - Yu t d phng: c tm quan trng i vi cc tn hiu thu c

v n s t ng backup d liu khi b phn trc xy ra s c a./ Thu tn hiu t v tinh: ( card TITAN)

- Tn hiu thu t v tinh s c a qua b gii iu ch QBSK vi ng ra l tn hiu ASI

- c im: + tc d liu t 1 n 45 Mbaud

+ c th la chn ch t ng hay l th cng cc thng s cn iu ch + Hai ng ra ASI vi tc ln n 90 Mbps + chc nng hin th c ci tin nh: SNR, mc ng vo, BER, khng sa

c li. b./ Thu tn hiu truyn hnh s mt t ( card ATLAT II)

-Tn hiu thu c c a qua b gii iu ch C-OFDM - c im: + h tr FFT kch thc 2K v 8K

+ c th chn c bng thng 7 MHz hoc 8MHz + c h tr bng tn UHF v VHF + hai ng ra ASI vi tc ln n 31.7 Mbps + ch hin th c ci tin (MER) + giao din s dng n gin

c./ Tng thch vi mng ATM/SDH/SONET

* c im ca card AXIT: - C th gn nhiu card trn rack ca headend s GALAXY ( t nht l 3

card) - Vn hnh theo AAAL v PVC - Giao tip vi mng qua lun STM_1/SONET tc 155 Mbit/s - Giao tip vi mng SDH (E3/DS3) - C n 10 i ASI ng vo v ra - c t 10base-T cho cc a ch IP c v iu khin - C thm giao din cho ngi dng v my tnh bng ha l JAVA GUI

v SNMP

d./ Tng thch vi mng /SDH/SONET ( card NEON Rx)

- B phn ny c chc nng l chuyn tn hiu E3/DS3 sang ASI v truyn trn 1 ng truyn - c im:

+ H tr tn hiu DS3 hoc tn hiu E3 hoc khng cn khung fram + Tun theo chun ITU-T G703 v G832/G751 + Hai ng ra ASI d phng + Ng ra nh dng 204 gi tin, khng cn FEC

+ Mn hnh LCD pha trc iu khin trng thi thng tin cho chnh xc

e./ Thu tn hiu cc i a phng: ( card SPECTRA)

- Tn hiu s c anten Yagi thu nhn v c a qua b gii

iu ch QAM ( iu ch pha) - c im:

+ Tn s RF ng vo t 45 n 860 MHz + C th chn la ch t ng hay bng th cng cc thng s cn iu ch + M rng chc nng hin th tn hiu + Hai ng ra ASI + Hon ton c ch to bi ROSA

B PROCESSING ( x l tn hiu)

Tn hiu sau khi thu c s c a qua khi PROCESSING x l. Gm cc khi: Decrambling, Routing, Remuxing, Processing, Scrambling,

a DESCRAMING ( phn loi tn hiu) - Cc tn hiu sau khi vo khi ny s c gii m x l - c im: + phc hi tn hiu ch xy ra vi tn hiu l s + S phc hi da trn chun m:

Cable- POD v DVB-CI Gn lin vi chun ASI C th thay i h thng CA v n d v r

+ Vn hnh mt cch c lp v bn c th xo tn hiu sau khi hon tt cng vic truyn.

* CARD Indus MKII Transport Stream Descrambler: - Ngy nay hu ht cc chng trnh u c m ha s dng chng trnh truy cp h thng DVB. Trong nhiu trng hp cc chng trnh cn c phn loi cho vic x l c nhanh hn. - Indus MKII hon ton da trn tiu chun DVB chng hn nh giao din chung cho cc ng dng ca CA v ASI tng thch vi nhiu thit b khc. Ngoi ra vi giao din chung th Indus cho php vn hnh giao din CA vi cc thnh phn c la chn mt cch d dng, ng thi cng khng cn sn xut hng lot cc phin bn khc nhau m ch cn thay th Module CI v th thng minh ( Smart Card) l . - Qua giao din HTML th ta c th vn hnh h thng mt cch tng qut vi cc mc c sn v mt trong nhng phn Descrambling c la chn trc . Sauk hi x l xong th ng ra l ASI. - Indus MKII tng thch vi Rack GALAXI v nhiu h thng Headend s khc

b ROUTING ( nh tuyn)

- L h thng chuyn mch thng minh c s dng rng ri trong nhiu lnh vc ni m im ni im hay a im ni a im th con ng d phng l rt cn thit. - Mc ch chnh ca phn ny l chn ng i lm sao khi tn hiu truyn i trn ng ny b mt cn c ng khc thay th th c gi l Redundance swiching

- Phng php d phng c xem l kh quan trng v: + Tt c cc thit b lm vic lp transport nn nhiu chng trnh c th b mt + S gin on l nguyn nhn gay mt tn hiu + Mng s thng cung cp nhiu dch v hn nh pay-per-view

* Card Redus MKII: - c tch hp nhiu dng chun khc nhau s dng cho nhiu ng dng ch vi 1 card kt ni th Redus MKII nh l mt h thng khuch i nh vi 4 ng ra - N rt ph hp vi Rack GALAXI v c trang b vi h thng qun l iu khin bng Remote qua giao din ROSA hoc h thng giao din Third-party s dng SNML. Mn hnh LSD pha trc cho php iu khin mt cch d dng hn.

c REMUXING: phn knh - S chn la v trn tn hiu li vi nhau trong 1 lung truyn - Da trn giao din chun + S thch hp gia cc thit b vi ASI

+ Giao din s dng hin th v iu khin l Web v SNMP - Qu trnh x l n gin

+ Phn mm PSI/SI c th thc hin 1 cch t ng pha sau + Ch cn 1 sai phm nh s hot ng sai

d PROCESSING: x l

- X l PSI/SI xem nh l 1 cch iu chnh ca tn hiu - Tht s PSI/Si rt ph hp vi ng TS ( Transport Stream) + a s c thc hin bi khi Re-multiplexer

- Mt khc PSI/SI gip thng tin khng b gin on v mi 1 lun TS cha thng tin v chng trnh

e SCRAMBLING: xo trn

- Chng trnh Scrambling xy ra trong s thiu lin lc vi iu kin truy

cp h thng - B xo trn da trn tiu chun m

+ N cho php nhiu thnh phn CA trong h thng trn li vi nhau ging nh lun TS

+ Giao tip vi ASi -Cc thit b vn hnh khng tt cng ging nh 1 b trn c ci t sn

+ Khng c a cng v ch thng gi + Chng trnh x l c gn vo chy vi thi gian thc OS.

C TRANSMISSION: Truyn ti tn hiu

- a tt c cc tn hiu vo 1 ch truyn i vi mng - Vi cc k thut iu ch:

64 & 256 QAM 8VBS &C-OFDM QBSK, 8PSK,16PSK

- Tng thch vi mng: + PDH/SDH/SONET DS3/E3 + ATM

+ a ch IP - K thut nn MPEG

+ Audio/Video + SDI

3./ Nn v m ha tn hiu truyn hnh:

Trung tm ca mt mng pht sng video s bao gm h thng nn, n cung cp chng trnh video v audio cht lng cao cho ngi xem bng cch ch s dng mt phn nh rng bng tn mng, Mc ch chnh ca nn l ti thiu ha kh nng lu tr v truyn dn pht sng thng tin (ghp nhiu tn hiu chng trnh truyn hnh vo mt dng truyn) . H thng nn tn hiu gm cc b m ha s (digital encodes) v cc b ghp knh (multiplexers), Cc b encodes c nhim v chuyn i tn hiu tng t (video/audio) sang dng s (digitizing), nn (compressing) v xo trn (scrambling) thnh mt dng audio, video v d liu (data) khc di dng s c nn, M ha s cho php truyn dn, pht sng nhiu chng trnh video/audio cht lng cao qua cng rng bng tn nh mt knh sng video/audio tng t (v d 8Mhz Vit Nam). Tn hiu c m ha v nn thnh mt dng tn hiu MPEG-2 (Moving Pictures Experts Group: chun nn tn hiu video/audio ca Chu u, s dng cho Vit Nam) s c a n b ghp knh, Nhm chuyn gia MPEG nh ngha mt tp cc tiu chun nn v nh dng file, bao gm c h thng ha video MPEG-2.Tiu chun nn tn hiu video s MPEG-2 c chp nhn 190 nc, l tiu chun nn video s, C nhiu tiu chun nn video/audio: MPEG-1, MPEG-2, MPEG-3, MPEG-4, MPEG-5, MPEG-6, MPEG-7, MPEG-J(JAVA),Tuy nhin, truyn hnh s qung b ch s dng tiu chun MPEG-2, Chun nn MPEG-1 v MPEG-3 c hp nht vo tiu chun MPEG-2 (my VCD s dng chun nn MPEG-1 cn DVD s dng chun nn MPEG-2, do DVD c c c a VCD (MPEG-1) va a DVD (MPEG-2), 4./ K thut nn nh s: a./ Khi qut v k thut nn: Cng vi s pht trin mnh m ca my tnh v s ra i ca Internet th vic tm mt phng php nn nh gim bt khng gian lu tr thng tin v truyn thng tin trn mng nhanh chng ang l mt yu cu cn thit. Trong nhng nm gn y, c rt nhiu cc phng php v ang c nghin cu rng ri thc hin nn nh, Tt c u vi mt mc ch chung l lm th no biu din mt nh vi t bit nht c th ti thiu ha dung lng knh truyn v khng gian lu tr trong khi vn gi c tnh trung thc ca nh, iu ny tng ng vi vic biu din nh c tin cy cao nht vi tc bit nh nht, Tc bit c o bng s bit trn mt im nh (pixel). Tc bit i vi nh en trng khi cha c nn l 8bit/pixel v i vi nh mu l 24bit/pixel, Cc k thut nn hin nay cho php dung lng nh c nn gim 30 n 50

ln so vi nh gc m nh vn gi c trung thc cao, trung thc ca nh c nh gi da trn tiu ch nh li trung bnh bnh phng (MSE: Mean Square Error) hoc t s tn hiu trn tp m (SNR: Signal-to-Noise rotio) gia nh gc v nh nn,

CC NGUYN TC CA NN NH:

Mt tnh cht chung nht ca tt c cc nh s l tng quan gia cc pixel cnh nhau ln, iu ny dn n d tha thng tin biu din nh, D tha thng tin s lm cho vic m ha khng ti u, Do cng vic cn lm nn nh l phi tm c cc biu din nh vi tng quan nh nht gim thiu d tha thng tin ca nh, Thc t, c hai kiu d tha thng tin c phn lai nh sau: D tha trong min khng gian: tng quan gia cc gi tr pixel ca nh, iu ny c ngha rng cc pixel ln cn ca nh c gi tr gn ging nhau (tr nhng pixel gip ng bin nh) . D tha trong min tn s: Tng quan gia cc mt phng mu hoc di ph khc nhau, Trng tm ca vic nghin cu v nn nh l tm cch gim s bit cn biu din nh bng vic lai b d tha trong min khng gian v min tn s cng nhiu cng tt,

CC K THUT NN NH C S DNG: - Nn nh khng mt thng tin: vi phng php ny sau khi gii nn ta khi phc c chnh xc nh gc, Cc phng php nn ny bao gm m ha Huffman, m ha thut tan - Nn nh c mt thng tin: nh gii nn c mt s sai khc nh so vi nh gc, Cc phng php ny bao gm:

o Lng t ha v hng: PCM v DPCM o Lng t ha vector o M ha bin i: bin i cosin ri rc (DTC), bin i Fourier

nhanh (FFT) o M ha bng con

nh cha nn nh nn

S khi mt h thng nn nh in hnh b./ Chun nn MPEG MPEG (Motion Picture Expert Group, tc nhm Lo lng v hnh ng). Nhm ny do vin nh chun Quc T (ISO = International Standard

Bin i Lng t M ha

Organization) thnh lp cui nm 1988 nhm nh ra cc dng thc video s ti u, dng c cho nhiu lnh vc, Khi t dng thc DVI (Digital Video Interactive, 1988) ghi hnh trn CD-ROM ca vin i hc Sarhoff Princeton, n nm 1990 nhm san xong dng thc MPEG1, ch p dng cho video s SIF (352x288x25 hoc 352x240x30 khng xen k) , vi bit rate trung bnh c 1.5MHz, C th tm xem MPEG1 l php nn ni hnh JPEG (Intra Frame) + php nn lin hnh (Inter Frame), bng cch suy ra mt hnh gia, t dch chuyn ca c hnh sau ln trc n (B = Bi-Directional Frame), ng dng ni bt ca MPEG1 l vic ghi hnh cng lc vi hai ng m thanh ni trn a CD, t cht lng tng ng bng t VHS, gi l VCD, vn cn tn ti n nay, T l nn ca MPEG1 t khang 20:1 l mt thnh tu ln, m ra trin vng da vo MPEG1 pht trin ng dng cho truyn hnh i chng (Broadcast TV, tv PAL,NTSC,SECAM). Nm 1991, nhm san xong MPEG2 vn trn nn c php ca MPEG1 nhng thm vo b cng c xen k (Interlace Tool).B cng c chn tm (Scalable Mode), chng hn chn t l khun hnh 4x3 hay 16x9, chn nhm hnh( GOP) nhiu hay t, chn tm d bo chuyn ng (macro block) rng hay hp, B cng c phm cp (Profiles-Levels), ty chn nhiu phm cp cht lng khc nhau, Thnh cng ca MPEG2 m nn n , nh ban u chn MPEG3 dnh ring cho HDTV khng cn lm na v chnh MPEG2 p ng c tt c,

Cui nm 1992, MPEG4 c san xong, y l mt php nn hiu qu cc cao nhng ch dnh cho cc hnh c cnh nn c nh bit trc, Chng hn tan cnh sn banh trong mt trn bng , tan cnh vn phng ca mt in thai c hnh - Nm 1995 MPEG1 v MPEG2 v nm 1999 MPEG4 c cng nhn l chun quc t, Cc c im cn lu :

o MPEG khng ohi tn hiu m ch l c php nn v gii nn lung bit, o MPEG2 khng nh ngha c nh cc thut tan, m m rng kh

nng cho tng pht kin ring, tng ng dng ring, Chng hn thng s nh gi chuyn dch ca hnh (Motion Estimation), thng s GOP (Group Of Picture: nhm hnh) , t l nn (Rate Control), u c th ty chn,

o MPEG2 m rng kh nng pht trin trong tng lai, tng thch c vi tt c cc b gii nn,

MPEG-2 MPEG-2 = MPEG- Syntax Elements

Interlace Tool Scalable Modes Profiles & Levels

o MPEG2 khng i xng, Nn MPEG rt phc tp, trong qu trnh nn c km sn thng s gii nn cho u thu, i hi tnh tan rt nhiu, gii nn MPEG n gin, cn t tnh tan hn tc r tin hn,

Nhm hnh _ GOP (Group Of Picture):

MPEG t hiu qu nn cao, ch yu nh lai b d tha thi gian tc nn lin hnh (inter frame), bng cch khng truyn lp li phn ging nhau ca hnh sau so vi hnh trc, Ni cch khc la ch truyn nhng cho a khc i (cc ch dch chuyn) ca hnh sau so vi hnh trc, C 3 lai hnh c MPEG truyn i:

Hnh I (Intra frame): c sau mt thi gian nht nh, li truyn i mt hnh y gi l hnh I, Ni cch khc, I l hnh c nn ni hnh v truyn i y ,

Hnh P (Prediction frame) : c suy ra t hnh I trc , tc suy ra t chiu thi gian pha trc, Ni r hn, trong thi gian ca hnh P, ch truyn thng tin khc nhau ca n so vi hnh I trc n m thi,

Hnh B (B- Directional frame) : c suy ra t c hnh I (hoc P) trc v sau n, tc l suy ra t c hai chiu thi gian, Ni r hn, trong thi gian ca hnh B, truyn i cc ch khc nhau gia n vi hnh I (hoc P) trc n,hoc hnh P (hay I) sau n, hoc c hai, ty theo kt qu d tm dch chuyn,

S hnh c trong khang t mt hnh I n hnh I k tip gi l mt

nhm hnh, hay mt GOP, Tnh cht ca GOP k hiu bi NM, N l s hnh tng cng ca nhm, M l s hnh c t mt hnh P n hnh P k tip, MPEG cho php ty chn nhm hnh, GOP nh hay N nh, s hnh I c nhiu, hay s khng nn c nhiu, Nh vy, vi ng truyn c bit rate cho trc khng i, vi s hnh / giy c nh theo chun, GOP nh c ngha l hnh truyn i s km cht lng, Ngc li, GOP ln hay N ln, nn c nhiu hn gip hnh truyn i cht lng hn, nhng li gy kh khn cho cc b dng (phi gii nn ra tng hnh y ri mi ni, chn vo cc ch cn ni) , M ln cn i hi mch MPEG tnh tan nhiu hn v lm chm (delay) video nhiu hn,

5./ iu ch tn hiu s: Dng tn hiu s video/audio sau b ghp knh ch c 2 trng thi gi tr

l 0 v 1.Tn hiu s s i qua khi iu ch trc khi pht sng, Khi tn hiu i qua qu trnh iu ch, th mt s trng thi s c cng li, lm tng tc truyn d liu, C 3 lai iu ch s chnh dng cho truyn hnh l: QAM (Quadrature Amplitude Modulation) , QPSK (Quadrature Phase Shift Keying), COFDM (Coded Orthogonal Frequency Division Multiplexing). Trong truyn hnh cp ta s dng hai dng iu ch l QAM v QPSK,

a./ iu ch QAM: K thut iu ch QAM cho php truyn tn hiu s vi tc cao trong

mt bng tn hp, n c th t tc truyn n 40Mbit/s v c tnh min nhiu tt i vi cc knh khc nhau cng truyn chung trn mt ng truyn, Thng thng ta c cc Mode iu ch: 16,32,64,128 hoc 256 QAM, c biu din trong s chm sao (s chm sao tng trng cho tn hiu truyn trong h thng cp), Mode iu ch thp c tnh min nhiu rt cao (thng thng dng mode 16-QAM), Ngc li, mode iu ch cao (mode 256-QAM) rt d b nhiu nn vic gii m tn hiu bn thu khng n nh,

S chm sao ca mode iu ch 16-QAM c biu din trong hnh sau, Cc im trn chm sao thuc gc phn t th nht s c chuyn sang gc phn t th hai, th ba, th t bng cch thay i 2 bit c trng s cao nht MSB (c ngha l Ik v Qk) v quay bit c trng s thp nht LSB theo quy tc cho bi bng sau:

Gc phn t MSB Xoay LSB 1 00 2 10 /2 3 11 4 01 3/2

16 QAM Q

Qk Ik = 10 QkIk= 00 1011 1001 0010 0011 1010 1000 0000 0001

I 1101 1100 0100 0110 1111 1110 0101 0111 QkIk= 11 QkIk= 01

S chm sao ca 16-QAM

Vic xc nh mode QAM no c s dng c cn c vo tnh hnh c th v ty mi quc gia, V d ni cn truyn nhiu chng trnh th dng QAM mode cao (64-QAM, 256-QAM), nhng lc i hi thit b phi c cht lng cao v di ng truyn thch hp, Ni khng cn truyn nhiu chng trnh th dng QAM mode thp c tin cy cao v tit kim gi thnh,

Kt lun: Vic iu ch QAM cho truyn hnh s qua cp c nhiu u im:

Vi mode iu ch QAM thp, ng truyn s qua cp c tnh khng nhiu cao.Nhiu ng truyn hu nh khng nh hng n cht lng tn hiu khi gii m (mode iu ch c th dng l 16-QAM). Tn hiu gii m pha thu ch c hai mc: gii m c (cht lng hnh nh tt) v khng gii m c (hnh nh lc gii m lc c lc khng, dng hnh) , Hay ni cch khc: hoc thu c rt r hoc khng thu c, Vic khuch i tn hiu s iu ch QAM cn c quan tm, v y l tc nhn chnh gy nn li ng truyn, Tn hiu s iu ch QAM sau khi khuch i phi c x l sao cho trit c nhiu xy ra, Phi lai b nhiu sinh ra trong qu trnh khuch i, nu khng my thu s khng gii m c tn hiu, Cc knh s c th ghp k nhau (m khng tc ng ln nhau), i vi knh tng t khi ghp vi knh s iu ch QAM cn ch n chng ph trong sng mang hnh v sng mang ting, Tn hiu iu ch s QAM truyn i trn h thng phn phi b suy hao, Tuy nhin, nu mc khuch i va th tn hiu iu ch QAM vn c gii m tt, C th s dng h thng phn phi cp cho truyn hnh tng t phn phi knh truyn s iu ch QAM. i vi mt h thng truyn hnh cp thc t, mng phn phi thng dng l mng HFC, Cc knh tng t v knh s truyn chung trn mt h thng phn phi, khng xy ra s chng ph ca cc knh k nhau (d l knh tng t hay knh s) . Cc tn hiu sau khi c khuch i my pht cn ch trng n vic x l nhiu, Sau , c th ghp cc knh tng t v knh s ri truyn i trn cp quang.Khi ghp nn thc hin nh sau: +Nn ghp theo tng nhm cc knh tng t v nhm cc knh s

+ Cc knh s ghp bng tng cao, cc knh tng t ghp bng tng thp hn do knh s c tnh khng nhiu tt,

b./ iu ch QPSK:

QPSK l k thut iu ch s c kh nng chng nhiu in t trng tt hn QAM, thng c s dng trong mi trng v tinh hoc knh phn hi (knh ngc) ca mng truyn hnh cp, QPSK lm vic da trn nguyn l dch tn hiu s khng c pha trong tn hiu ra, QPSK lm tng mnh ca mng, Tuy nhin s iu ch QPSK c th truyn d liu ti 10Mbit/s,

6./ H thng qun l mng:

Trung tm pht sng bao gm nhiu thnh phn phc tp, cung cp nhiu dch v, cc vn mng cn c pht trin nhanh chng v gii quyt cc vn iu khin v kim tra cc dch v cung cp cho thu bao, H thng kim tra v iu khin mng c t ti cc trung tm pht sng, Mc ch chnh ca mt h thng nh vy l ti thiu ha s gin an cc dch v i vi thu bao truyn hnh s, H thng qun l mng s qun l cc knh truyn hnh cung cp cho thu bao, Ti cc trung tm truyn hnh cp y l h thng c vai tr c bit quang trng, n cho php hay khng cho php thu bao xem cc kng truyn hnh, c trng ca mt h thng iu khin Headend s tiu biu bao gm:

Kim tra kh nng cc thit b Tp hp thng k Thng bo v bo ng v cc vn thng k D bo t xa Hn nay cc h thng ny chy trn cc h iu hnh WindowsNT

hoc UNIX, III.H thng truy cp c iu kin CA:

Ngy nay, cc nh iu hnh, sn xut chng trnh v pht sng truyn hnh c th trc tip tng tc vi ngi xem nhiu mc khc nhau, cung cp mt s lng ln chng trnh la chn, Mc tiu chnh ca h thng truy cp c iu kin CA l iu khin s truy cp ca thu bao i vi truyn hnh s c tr tin v bo mt cc dng video/audio s i vi nh qun l v iu hnh, Nh vy, ch cc thu bao c h thng CA mi lin lc c hiu qu vi nh iu hnh mng truy cp vo dch v c th, S dng cc h thng CA cc nh iu hnh mng c th trc tip lp trnh (target programming),qung co, khuyn khch cho thu bao trong khu vc (th trng) hoc cho c nhn, Do h thng CA l hng quang trng ca truyn hnh s, Truy cp gii hn vo mt dch v c th c thc hin bng cch dng k thut mt m (cryptography).K thut mt m bo v dch v s bng cch bin i tn hiu thnh mt dng khng c c. Qu trnh bin i c gi l kha m (encryption) trong mi trng s v xo trn (Scrambling) trong

mi trng tng t, Khi tn hiu c kha m (encrypted) th ch c th gii kha m (decrypted) bng b gii kha m gn vo Set-top-box s, Gii kha m l qu trnh bin i ngc tn hiu (message) v dng gc thng qua kha m (decryption), Kha (key) c hiu nh l mt gi tr mt m (secret), bao gm mt vng bit ngu nhin (s dng my tnh cng cc thut tan kha m v gii kha m thng tin) . Set-top-box kt hp phn cng v phn mm cn thit thu nhn v gii m tn hiu, Cc thnh phn ny c thit k gm 1 chip gii kha m v kha m, 1 b x l bo mt (secure processor) v mt vi b iu khin phn cng (hardware driver) thch hp, Chip gii kha m v kha m m bo chn gii thut CA, B x l bo mt c th gn vo mch in trong Set-top-box hoc km theo card gii kha m (smart card-card gii kha m, cn gi l card thng minh) . Card thng tin l card plastic, ging nh th tn dng ngn hng (credit card), B x l ny gm cc kha (key)cn cho gii m cc dch v khc nhau, Ngoi ra m ha cc dch v s, CA phi giao din vi cc h thng con SMS, SAS, a./ H thng SMS: SMS (Subscriber Management System) l h thng qun l thu bao, cn lm giao din cc h thng k thut ca cc nh iu hnh truyn hnh, SMS cung cp cc h tr cn thit qun l chng xc m hnh truyn hnh s thng mi, N thc hin c s d liu ca thu bao v gi cc yu cu ca thu bao cho h thng SAS (Subscruber Authorization System l h thng qun l k thut ca h thng CA). Chc nng c trng ca SMS c cung cp bng mt h thng ng dng phn mm SMS, bao gm:

Ghi dch (register), ci bin v xa cc cuc ghi ca thu bao Phn u cho cc chin dch th trng Qun l, kim k cc Set-top-box v card thng minh Theo di vic s dng ca thu bao Bn cho (cross-selling) cc dch v Giao din vi ngn hng v cc cng ty th tnh dng Qun l s c C kh nng dng nhiu lai ngn ng v nhiu lai tin t Sa v to dng ha n Trnh by ha n in t Cc kh nng tnh tan

Nhiu phn mm trn th trng c kh nng h tr lm tng dch v tng tc cho thu bao, Mc ch chnh ca SMS l bo m thu bao xem c ng chng trnh m h tr tin, b./ H thng SAS: SAS (Subscriber AUthorization System) l h thng quyn tc gi i vi thu bao, c nhim v truyn cc yu cu n t SMS vo EMM

(Entitlement Management Message bc in qun l quyn truy cp) , Tip n, cc bc in quyn tc gi EMM ny c ghp knh s (digital multiplex) n card thng minh SC (smart card) t Set-top-box. Chng c gi n thu bao theo cc khang thi gian u n (v d mi thng) cp nht quyn truy cp cho thu bao trn SC, Trong trng hp dng PPV(pay-per-view), h thng SAS gi mt s du hiu in t nht nh (tokens) cho SC cho php thu bao tr tin cho cc s kin PPV khc nhau, SAS cha c s d liu, c kh nng lu tr cc thng tin sau:

Thng tin v sn phm pay-TV D liu h tr hng dn truyn hnh bng in t (EPG) S nhn dng SC D liu danh mc (schedule)

Ngoi ra, c th nng cao vic bo mt SAS bng cch thay i theo chu k cc kha quyn tc gi truyn n c s thu bao Sau y l mt s h thng CA thng gp:

Cryptoworks ca Phillips Viacess ca France Telecom Nagra ca Nagra Vision VideoGuard ca NDS Digicipher ca General Instruments Iredeto ca Mindport

IV.Set-top-box s : Truyn hnh s v cc dch v tng tc c pht trin nhiu nc, Trong qu trnh chuyn dch ln truyn hnh s (khang 10 nm nay), cc nh khai thc truyn hnh vn tip tc pht sng tn hiu truyn hnh tng t song song vi truyn hnh s mi, Trung tm ca vic chuyn dch t thu truyn hnh tng t ln thu truyn hnh s l Set-top-box, Hp en nh t trn my thu hnh tiu chun cho php thu truyn hnh s, Set-top-box s c th cung cp cht lng hnh nh tt hn nhiu so vi h thng truyn hnh tng t hin nay, T nh , ta c th xem truyn hnh, truy cp Internet, gi/nhn E-mail cho bn b ng nghip, mua hng,chi game a phng tin, Set-top-box th h 1 ch c kh nng thu tn hiu hnh v khng kha m (unsrambling-khng xo trn hoc khng kha m) , Cc phin bn mi ca Set-top-box c nhiu c trng hin i hn, cho php ngi xem truy cp mt s lng hn ch cc dch v tng tc, Set-top-box th h th 2 ging vi bn sao th h th 1 nhng cho php thu bao truy cp c cc dch v truyn hnh s, Set-top-box th h th 2thc hin gii m MPEG, c mt CPU (n v iu khin trung tm) , mt s lng nh b nh (1Mbyte), 1 knh truyn ngc tn hiu tc thp (nh modem in thai) v phn h tr c hn ch cho ni kt Set-top-box vo cc thit b xa, Vo nm 2000,xp x 8 triu set-top-box th h 2 c s dng Chu u, M, Ngoi vic thu tn hiu truyn hnh s, hu ht cc set-top-box cn c kh nng thu v x l tn hiu truyn hnh, Nhng thu bao mun s dng my thu

hnh truy cp cc ng dng tng tc a phng tin, th i hi set-top-box phi c kh nng tnh tan hin i, Cui 1998 xut hin mt th h set-top-box mi, Set-top-box th h mi ny (th h 3) c kh nng tng tc y , s dng mt s cc tnh nng ging my tnh PC, bao gm cc giao din d liu tc cao (c bit l b nh) , CPU mnh, knh truyn ngc tc cao v c kh nng s l cc ni dung da trn c s a phng tin (multimedia), Cc set-top-box th h th 3 cho php ngi xem truyn hnh truy cp cc ng dng v Internet v truyn hnh , bao gm: th truyn hnh (TV-mail), VOD (video-on-demand: video theo yu cu) , home shopping (mua hng t nh) , qung co tng tc (interactive adversiting: qung co tng tc, trong ngi xem c th yu cu hoc cht vn trc tip li) ,tr chi in t vi nhiu ngi chi, cc hng dn chng trnh in t EPG, Vic trin khai thc t lai set-top-box ny cn nhiu tr ngi do gi thnh ca n rt cao nn cha c ph bin rng ri,

I./ Internet trong truyn hnh cp : Internet l mt tp hp s cc mng cng cng v cc c nhn, ni kt hng triu cng ty, vin nghin cu, th vin, v cc chng trnh tc v c nhn trn th gii, N cho php mt phm vi nhiu lai ngi s dng my tnh khc nhau ni kt vi nhau theo cc mc ch: kinh doanh, o to, nghin cu v gii tr, internet khng t chc tp trung v khng c 1 ngi hoc 1 t chc no s hu ring internet,

Truyn hnh cp c a vo internet l mt bc pht trin vt bc trong truyn hnh , N p ng c nhu cu ngy cng cao ca ngi s dng khi truy cp internet, Khi truy cp vo internet ngi s dng c th xem cc chng trnh truyn hnh m mnh yu thch, Vic xem cc chng trnh truyn hnh trn th gii tr thnh nhu cu cn thit ca nhiu ngi, a h thng cp vo internet i hi phi c mt h thng kt ni vo my tnh ca ngi s dng, Lc ny cn c s lin kt cht ch gia my tnh, tivi v set-top-box, a internet vo truyn hnh cp cn phi c mt k thut kt ni tht tin tin gia truyn hnh v internet, Khi thu bao truy cp vo h thng internet xem truyn hnh cp th lc ny tn hiu truyn hnh cng s c truyn ti xung thu bao truy cp vo, 1./ Trin khai h thng cp truyn internet:

a./ Modem cp: Mt lai modem c s dng rng ri trong set-top-box nng cao cht lng thng tin hai chiu l modem cp, Khi nim modem cp dn n giao din mng qua h thng truyn hnh cp tiu chun, Modem cp cho cc nh cung cp dch v kh nng v internet tc cao, trin khai c hng lat trn th trng cn pht trin cc tiu chun Tp an MCNS (Multimedia Cable Network System) M pht trin tiu chun thng tin hai chiu qua mng cp, gi l tiu chun DOCSIS (Data Over Cable System Interface Specification) .

Nhiu cng ty v mng a ra sn phm thng mi da trn tiu chun DOCSIS, im hi t chnh ca tiu chun DOCSIS l cung cp cc dch v cho ngi s dng my tnh, Chu u, tp an DVB (Digital Video Broardcasting) sn xut thit b c cc c trng gi l DAVIC (Digital Audio Visual Council), tip cn vi DVB v tp trung cho vic truyn d liu tc cao trong mi trng truyn hnh, Nhiu nh sn xut kt hp sn xut set-top-box dng modem cp theo chun DVB, Thi gian u, modem cp c s dng thu v truyn TCP/IP bao gm ni dung a phng tin v d liu truy cp Web, Nghi thc (Protocol) TCP/IP l mt tiu chun dng cho hat ng internet, pht v thu d liu theo hai kiu khc nhau, D liu pht t Headend n modem cp dng xung (downstream) s dng iu ch QAM, ph tn nm gia 50-750MHz. Khi set-top-box cn pht dng d liu ln (upstream) n headend, th modem cp s dng bng tn 8MHz v 40MHz, Phm vi tn s ny c xu hng b nhiu hon tan (can nhiu n t cc CB(cable box) v thit b dng trong gia nh) .Do hu ht cc nh sn xut set-top-box mun s dng lai iu ch QPSK chiu dng ln (knh ngc). Modem cp c 2 cng ni tip: 1 cng ni ra bn ngoi my thu hnh v 1 cng ni vo PC ca thu bao, Modem cp thng thng tin qua mng cp n thit b CMTS(Cable Modem Termination System) .Tc ca modem cp ph thuc vo mc giao thng v cu trc mng, V l thuyt, modem cp c th t tc dng xung trn 30bit/s. Tuy nhin, trong thc t thu bao c th hy vng cho thng tin ti xung nm gia 1 v 1,5 MB/s. Khi ni v dng xung, tc l truyn tn hiu t headend n modem cp, Modem cp thch hp cho cc ng dng c yu cu v knh ngc tc cao.V l do ny cc nh sn xut bt u gi modem cp vi set-top-box (t gia 1999). Set-top-box dng modem cp ch thch hp cho mng truyn hnh cp v khng dng cho cc mng khc, cung cp tng tc hai chiu cc mng k trn thu bao cn muaset-top-box c phn knh ngc qua ng in thai, b./ a ch TCP/IP: Nu ni 1 set-top-box vo mt mng truyn hnh cp th s khng bo m thng tin thnh cng gia thu bao v h thng headend ca nh cung cp dch v, V d 1 set-top-box cn c thng bo l bao gi truyn tn hiu qua mt mng truyn hnh s v truyn nh th no.Set-top-box cn phn mm thng tin mng thng bo cho set-top-box bit l truyn tn hiu qua mng cp nh th no, hiu 1 set-top-box hat ng v thng tin bng rng trn mng nh th no,u tincn kim tra TCP/IP ca cc dy nghi thc thng tin. Dy ny(suite)biu din thng tin t 1 ng dng phn mm (chy trn my tnh t ti headend ca nh iu hnh) chuyn ng nh th no qua mi trng mng n ng dng phn mm chy trn 1 set-top-box ca thu bao. TCP v IP l 2 nghi thc ring c quan h cht ch vi nhau cho mc ch truyn d liu bng mt phng tin hiu qu, p ng chnh ca TCP l tch d liu thnh cc gi, Nghi thc IP th cung cp chnh xc cc gi ny cho cc a im, Nghi thc

TCP tp hp cc gi ny li ti u cui, N c nhm ARPA (M) pht trin u nhng nm 1980. V s bt u ca n m TCP/IP tr thnh nghi thc thng tin de-facto(nghi thc thc t) chi internet, Vic s dng rng ri TCP/IPtrn internet gip cho cc nh pht sng truyn hnh v iu hnh cp s dng nghi thc ny nh l mt khi nh c s trong vic cung cp cc dch v gii tr cho khch hng, M hnh thng tin TCP/IP l mt m hnh nguyn l, bao gm 4 lp c gi li vi nhau, mi lp c trng cho chc nng mng ring, Thit b pht Thit b thu (set-top-box s) (my tnh headend)

Cp, MMDS Mt t, v tinh

M hnh TCP/IP D liu i t trn xung, t lp ny n lp tip theo trn thit b pht cho n khi no n c truyn qua mng bng rng bng nghi thc lp truy cp mng, Mi lp m hnh thng tin cng vi thng tin iu khin (v d nh a ch n v cc digits sa li) m bo vic cung cp ng, Ti u cui (t xa)d liu i ln m hnh thng tin n ng dng thu, Bn lp ca m hnh TCP/IP bao gm:lp truy cp mng, lp mng internet, lp truyn v lp ng dng(t di ln) Lp truy cp mng(network access layer) c quan h vi cc ch xc nh ta cc lut (rules) truyn cc bit s trn mng bng rng, N c lin quan vi vic nhn d liu qua 1 lai mng vt l dc trng (v d HFC,v tinh, pht sng trn mt t, hoc MMDS). N xc nh cc cu trc mng vt l(topologies), cc t trng c hc v in cho vic s dng mi trng truyn.Phn cng kt ni mng di y thng c lin quan vi lp truy cp mng, modem in thai v cp, mch khuch i v cc b pht li (repeaters) trn 1mng HFC v cc kt ni

Lp ng dng

Lp truyn

Lp truy cp mng

Lp internet

Lp ng dng

Lp truyn

Lp internet

Lp truy cp mng

Lp trn ca lp truy cp mng l Internetwork layer. Nhim v u tin ca n l truyn d liu n cc v tr c trng ca mng qua cc mnh Internetworks (cc mng multiple, interconnected, c lp). IP l nghi thc tt nht (t ti lp internetworks layer), cung cp dch v gi c bn cho tt c cc mngTCP/IP. Nghi thc IP thc hin 1 h thng cc a ch logic host (gi l IP addresses). Lp nghi thc (protocol layer)trn lp internetwork layer l lp transport layer. N c thit che y tnh phc tp (intricacy) ca cu trc mng truyn hnh s t cc qu trnh ca lp trn. Cc tiu chun ti lp ny cung cp vic iu khin thng tin(end-to-end) cho thc t v tch hp, V d nu cp b t, th lp truyn khng th m bo cung cp d liu. Nu d liu khng th cung cp ng cho thit b thu, th lp truyn c th truyn li t u, N c th thng tin cho cc lp trn thc hin vic sa cha cn thit, TCP l nghi thc quan trng nht, c dng ti lp ny cho b thng tin TCP/IP, Lp trn cng trong m hnh thng tin TCP/IP l lp ng dng (application layer). Lp ny cung cp cc dch v m thu bao s dng thng tin qua mng truyn hnh s, Cc dch v ny bao gm cc kh nng truyn file, iu khin truy cp, hng dn truyn hnh, in,

c./ Phn mm ca set-top-box (STB) Proxy Server:

Khi s dng thit b c hn ch v ti nguyn (v d 1STB xem lt trang Web), th phi lin hat 1 proxy server vi cu trc h thng, Mt proxy server l mt my tnh, chy chng trnh phn mm, hat ng nh mt gateway gia mng truyn hnh s v internet. N cho php nh iu hnh truyn hnh xc nh cc thnh phn ca c s thu bao c th truy cp internet v cc dch v, Ni mt cch khc, chng trnh proxy server quyt nh yu cu no c th c cho qua v yu cu no cn xa, Qu trnh ny khng nhn thy c, Proxy server thng tin bt k yu cu no cho internet, Proxy server c s dng tng tc truy cp ca thu bao vo www bng cch nhn (caching) cc trang web theo chu k, Caching (bt ly)l mt k thut c proxy server s dng lu cc b cc trang web thng dng, Khi mt thu bao cn mt trang web, th u tin STB brower kim tra proxy server trong headend xem nu c 1 copy trang web c lu cc b, Nu ng nh vy, th proxy server chun b teang hin th trn mn hnh v gi ngc trang web v STB, Khi nhn c, th n c STB browser tr li v hin th trn mn hnh ca thu bao, Vic ny xy ra nhanh hn ti mt trang web xung t mt web site trn internet cng cng, Nu khng tn ti mt bng copy trang web yu cu ti proxy server, hoc nu trang ny mt d liu, th proxy server yu cu trang ny t internet, Yu

cu t proxy server i vi web site xa c th gy ra tr, tuy nhin tr phi nh hn so vi thi gian ti xung trang web, Nu c trang ny, th n s quay ngc li thu bao, Nhng nu trang ny b lai khi web server, th th in bo li s hin th trn mn hnh ca thu bao, Vic bt (caching) ni dung internet s nng cao vic thc hin ca ngi s dng v gim vic s dng rng bng tn ti ni kt internet, Nhiu phin bn modem ca STB proxy server c kh nng t ng khi phc v bt cc trang yu cu trong cc chu k hat ng thp m khng lm tng ti ca server, Lai caching t ng ny cho php proxy server bit c cc yu cu ca internet m ngi s dng set-top-box phi lm. Th in c li NO YES NO YES

Ngi s dng Set-top yu cu trang web

Proxy server kim tra kh nng ca trang web trong

cache cc b

Chun b hin th trn my thu

hnh

Yu cu trang Web t internet

Kh nng

Chun b hin th

trn mn hnh

Chun b in th

c li

S dng d liu ca STB v khi phc cc trang t proxy server

d../ K hach pht trin STB proxy server: Vi cc nh iu hnh mng truyn hnh, lp k hach lp t STB proxy server l bt u thc hin phn tch cc yu cu, Bc u l xc nh cc khch hng truyn hnh s yu cu truy cp vo internet cng cng nh th no ? V h cn truy cp theo mc no? V d mt s khch hng cn truy cp c nh, trong khi s khc li ch cn thnh thang truy cp. Ngoi cc thi quen truy cp, nh cung cp dch v cn xc nh cc ng dng no s chy qua mng bng rng v cc phn t no ca proxy server cn h tr cc ng dng ny? V d, hu ht ngi s dng STB cn nghi thc HTTP xem lt ti liu t Internet, tuy nhin proxy server cn chy dch v web proxy tha mn cc yu cu ny. Bc tip theo l xc nh cc yu cu v dung lng ca proxy server d trn c s giao thng qua mng. V d, mt nhm 1000 users (ngi s dng) ti xung cc file a phng tin qua mng bng rng, i hi dung lng server ln hn so vi users ti xung cc ti lu HTML gc. Trong trng hp ny, nh cung cp dch v cn lp t nhiu hn 1 proxy server cn bng qu ti v giao thng trn mng. Khi nh iu hnh truyn hnh quyt nh cc yu cu ca khch hng, th proxy server cn c a vo mi trng truyn hnh, l tng chy chy kim tra beta bng cch s dng mt s hn ch cc khch hng truyn hnh s v thc hin vic kim tra qua mt chu k thi gian my, N cho nh qun l c hi chuyn cu hnh trong khi ch phi h tr mt s hn ch ngi s dng, Khi thc hin thnh cng nh cung cp dch v s da nhiu thu bao hn vo h thng STH browser.

e./ Ghp ni Internet tc :

Proxy server h tr tt c giao thng vo Internet bng cch s dng mt ng n c dung lng cao. Thay v tng ngi s dng mt ng ring nt vo Internet, th ch cn s dung mt kt ni chung. Kt ni dung lng cao vo internet phi c kh nng hat ng 24 gi/ngy, 7 ngy/tun, p ng cho cc thu bao mun xem lt v gi e-mail ti mi thi im, tha mn cc yu cu v thng mi v k thut, cn xc lp mt kt ni thng xuyn gia headend v internet, iu ny thng c nh cung cp dch v internet ISP (internet service provider) v cng ty in thai a phng thc hin, ISP l mt cng ty cung cp truy cp vo internet. ISP thng i thu bao tr tin hng thng hoc hng nm. ISP c gateway bo m cho nhiu ngi s dng, truy cp internet, C th chia ISP thnh 4 nhm khc nhau, * a phng (Local): nh a phng cung cp cho ngi s dng trong phm vi a l gii hn, H thng nhn truy cp mng t cc nh cung cp a

phng ln hn v bn li rng bng tn, Gi thnh truy cp internet qua mt nh cung cp a phng tng i thp v truy cp c khuch i theo cuc gi in thai a phng, * Vng (Regional): Vic ghp ni vo mt nh cung cp vng s cho php cung cp cho cc cng ty nhiu dch v internet hin i hn, v d cc trang thng mi in t hosting, Chi ph ca cc cng ty thnh vin i vi cc lai ISP ny ni chung l cao hn, * Ti chnh (Backbone carrier): cc ti chnh c kh nng cung cp tan phm vi truy cp tc cao bng cch s dng cc sn phm internet sau nht vo cc t chc ln, * Cable ISP (ISP cp) :Lai ISP ny cung cp dch v tc cao cho cc thu bao s qua mng truyn hnh cp, Hai lai ISP tt nht M tp trung vo cng ngh cp l RoadRunnen v Excite@Home, Bc 1 xc lp ni kt internet l xp x rng bng tn, yu cu ni kt mi internet h tr ngi tiu dng truy cp cc dch v internet bng STB. rng bng tn tham chiu s lng thng tin c ti qua thit b c nh, rng bng tn thng c tnh theo n v kilo-bit/giy (Kb/s) hoc l megabit/giy (Mb/s), Nu ta c khi nim v ln cc ti liu v trang Web cn truyn v s lng xp x cc ni kt trong mt ngy, th c th s dng cng thc biu din sau y xp x rng bng tn cn h tr cho cc vic c lt tan b trang web qua STB: rng bng tn xp x = (s ni kt internet trung bnh 1 ngy/s giy ca mt ngy) x ln trung bnh ca ti liu theo Kb/s, V d mt nh iu hnh MMDS v cp hin cung cp cc dch v truyn hnh s cho 400000 khch hng, Cng ty lp k hach cung cp mt dch v c lt internet y cho cc khch hng ca cng ty v cn xc nh dung lng ca mt ng dy cung cp gia mng truyn hnh s ring ca h v internet, Cng ty gi thit nh sau: 1, Cng ty d bo dng t l (rate) 25% cho dch v mi 2, Tt c cc khch hng ni kt t nht 1 ln /ngy 3, ln trung bnh ca mt trang web tiu biu l 25 KB 4, Cng ty d bo vic thu nhn cc trang web ti headend ca h s m bo 60% yu cu 5, Thi gian c lt s l 1 gi/ngy v mt ngi xem truyn hnh s s xem 20trang web ni dung Cng thc tnh tan rng bng tn nh sau: ln file 25 KB nhn vi 1024 xc lp s byte (1024bit =1KB) v kt qu nhn vi 8 tnh s bit, Kt qu l 204.800 bit thng tin, By gi i ra n v Kilobit ta li chia cho 1024, kt qu cho ta ln trung bnh ca ti liu

200Kb/s, Kt qu ny c nhn vi 20 c tan b d liu c ti xung 1 ngy/1 ngi s dng cho STB, Thng s tip theo cn tnh l s thi gian c lt trung bnh trong mt ngy, Ta tnh 25 % ca 400.000 thu bao l 100.000 ngi, S giy trong mt ngy l 86.400 giy, rng bng tn c tnh bng cch o ngc cc gi tr ny thnh: 100.000/86.400 x 4000Kb = 4296 Kbit, xp x s Mbit cn thit, ta chia kt qu ny cho 1024 v s c yu cu rng bng tn l 4,5Mb/s (tc truyn) . Theo mt trong cc gi thuyt ni trn, ti thiu 60% cc yu cu internet s c phc v bng cch s dng proxy server thu nhn (caching).Do , nh lng rng bng tn yu cu l 40% ca 4,5 Mb/s, tc l 1,8 Mb/s, C th dng tnh tan ny xc nh lai ng truyn cn thit cung cp cc dch v internet tc cao cho STB, Hai lai ng truyn c bn i vi cc nh iu hnh mng l ng truyn tng t v ng truyn s. ng truyn tng t l mt ng dy in thai tiu chun c nh, thc hin gii php ng truyn tng t, cn phi lp t cc modem ti cc u ni kt cui, Modem bin i tn hiu s t mng bng rng ca nh iu hnh thnh tn hiu tng t, Tc truyn d liu ca ng truyn tng t ph thuc vo tc ca cc modem , Hin nay, cc modem nhanh trn th trng c tc truyn d liu l 56,6Kb/s, Ta bit ng truyn tng t khng phi l gii php thch hp cho cc nh iu hnh mng mun cung cp cc ng dng internet tc cao cho cc thu bao dng STB, C nhiu ng truyn s da trn c s tiu chun ISDN (Intergrated Services Digital Network), ISDN l mng thng tin s ph bin trn th gii so vi mng in thai cng cng PSTN, N nhanh v an tan hn nhiu cho vic truyn d liu so vi ni kt tng t, v n s dng cc ng truyn thai s, Mt ng truyn dng giao din tc c bn BRI(basic rate interface) ca ISDN c phn thnh 2xknh d liu v 1xknh iu khin 16Kb/s, Ccknh ny c th lin kt li thnh 1 ng 128 kb/s.ng truyn dng giao din PRI (Primary Rate Interface) ca ISDN c dung lng cao hn nhiu v l m option(ph lc) ph bin hn i vi cc cng ty ln mun ni kt cc mng bng rng ni b vi internet cng cng, Lai ng truyn ny cho php kt hp 30knh d liu v 1 knh kim tra. M, PRI-ISDN c gi l ni kt T1, T1 c dung lng ca rng bng tn l 1,544 Mb/s, Chu u, ni kt tng t c gi l E1 v T1 t hn nhiu so vi vic chy trn ISDN hoc ng in thai, nhng gi thnh ang ngy cng gim,

S KHI CA H THNG HEADEND

* Mt s thit b trong phng Headend: GII M DECODER MY PHT QUANG ACI COMMUNICATION

U ENCODE

VI./ H thng qun l tn hiu cung cp n thu bao Encoder v Decoder:

Khi ng phn mm: - User: HTVC

Device Management

Decoder Managerment

Channel Managerment

1. DEVICE MANAGEMENT: Thng bo trng thi ca tt c cc knh c a vo h thng m ha, Click here

a ch IP ca mi my Encode- 1 Encode m ha 4 knh

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Kha tn hiu ca 1 knh gm c 5 cch: - Phase Krypt: kha pha - Inversion: tn hiu mu - Horizontal Overlay: mt ng b ngang - Vertical Overlay: mt ng b ngang - Audio: kha ting

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2.CHANNEL MANAGER: Qun l knh

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Lu : - La chn:

Prepare dng sa thng tin qun l knh trn phn mm Active dng truyn thng tin qun l knh n decoder

- Gn th t knh cho Decoder: + Display: s th t knh hin th trn Decoder + RF : knh RF (VHF/UHF) c thu +ng vi 1 s th t knh hin th trn Decoder l 1 knh RF c thu - Xc nh knh h thng (System channel): + Home CH: Knh lin lc thng tin + Not Auth CH: khng ng k th chuyn v knh ny +No pay Ch: khng tr ph th chuyn v knh ny

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3. DECODER MANAGER: Qun l b gii m Key 1: nhm A Key 2: nhm B

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Kha / M nhm knh

Thit lp Master /Slave

Khi to trng thi ban u cho Decoder

S c t trn Decoder,mi Decoder c 1 s ring

M knh

Kha knh

ENCODER

DECODER