tim hieu cong nghe ip muliticast 4291

7/16/2019 Tim Hieu Cong Nghe Ip Muliticast 4291

1/91

TRNG.

KHOA.

----------

Bo co tt nghip

ti:

TM HIU CNG NGH IP MULITICAST


2/91

LI CM N

Ti xin chn thnh cm n TS. Ng Khnh Vn, ngi tn tnh hng

dn, ch bo ti trong sut thi gian di thc hin ti.

Ti xin chn thnh cm n PGS.TS Nguyn Vn Tam, cng tc ti Vin

cng ngh thng tin, ch bo v cho ti nhng li khuyn qu bu hon

thin lun vn.

Ti xin chn thnh cm n cc thy c trong trng i Hc Cng Ngh,

i Hc Quc Gia H Ni ging dy, truyn t v to iu kin hc tp tt

nht cho ti trong sut thi gian hc tp cng nh trong qu trnh thc hin lun

vn.

H Ni, thng 08 nm 2009

Trng Cng i


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I

MC LC

LI CM NMC LCDANH MC CC TVIT TTDANH SCH HNH VDANH SCH CC BNGMU................................................................................................................ 1

1. t vn .................................................................................................. 12. i tng v mc tiu lun vn................................................................. 13. Hng tip cn ........................................................................................... 24. Kt cu ca lun vn .................................................................................. 2

CHNG 1 ........................................................................................................... 3C BN V IP MULTICAST.............................................................................. 3

1.1 Mu ......................................................................................................... 31.2 Cc thnh phn tham gia vo truyn thng multicast .................................. 51.3 a ch multicast .......................................................................................... 71.4 Cy phn phi multicast............................................................................... 9

1.4.1 Cy ngun ............................................................................................. 91.4.2 Cy chia s .......................................................................................... 10

1.5 Chuyn tip multicast................................................................................. 131.6 ng trc multicast.................................................................................. 151.7 Giao thc qun l nhm Internet ............................................................... 17

1.7.1 Giao thc IGMPv1.............................................................................. 171.7.1.1 Thng ip Host Membership Report.......................................... 181.7.1.2 Thng ip Host Membership Query........................................... 19

1.7.2 Giao thc IGMPv2.............................................................................. 191.7.2.1 La chn router truy vn.............................................................. 201.7.2.2 Thng ip ri nhm.................................................................... 211.7.2.3 Truy vn cho tng nhm.............................................................. 21

1.7.3 Giao thc IGMPv3.............................................................................. 21


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1.7.3.1 Lc d liu ................................................................................... 211.7.3.2 Thng ip IGMPv3 Host Membership Query ........................... 221.7.3.3 Thng ip IGMPv3 Host Membership Report........................... 23

CHNG 2 ......................................................................................................... 25NH TUYN MULTICAST ............................................................................. 25

2.1 Giao thc nh tuyn multicast vctkhong cch ................................... 252.1.1 Tm kim hng xm ............................................................................ 252.1.2 Trao i thng bo nh tuyn ............................................................ 262.1.3 Ct nhnh ............................................................................................ 292.1.4 Ghp nhnh ......................................................................................... 31

2.2 Giao thc PIM Dense Mode ...................................................................... 332.2.1 Tm kim hng xm ............................................................................ 33

2.2.1.1 Thng ip Hello ......................................................................... 332.2.1.2 Routerc chnh.................................................................... 332.2.1.3 Cy phn phi multicast............................................................... 34

2.2.2 Ct nhnh ............................................................................................ 352.2.3 Cch xc nhn .................................................................................. 372.2.4 Ghp nhnh ......................................................................................... 38

2.3 PIM Sparse Mode....................................................................................... 392.3.1 M hnh tham gia ................................................................................ 392.3.2 Cy chia s .......................................................................................... 40

2.3.2.1 Tham gia cy chia s .................................................................... 402.3.2.2 Ct nhnh trn cy chia s............................................................ 43

2.3.3 Cy ng i ngn nht ...................................................................... 452.3.3.1 Tham gia cy ng i ngn nht................................................ 452.3.3.2 Ct nhnh trn cy ng i ngn nht ....................................... 47

2.3.4 Thng ip Join/Prune ........................................................................ 482.3.5 ng k ngun d liu........................................................................ 49

2.3.5.1 Thng ip PIM Register............................................................. 492.3.5.2 Thng ip PIM Register Stop.................................................. 50

2.3.6 Chuyn t cy chia s sang cy ng i ngn nht .......................... 50


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2.4 Giao thc Multicast Open Shortest Path First ........................................... 542.4.1 nh tuyn multicast trong vng......................................................... 542.4.2 nh tuyn multicast trn nhiu vng................................................. 562.4.3 nh tuyn multicast trn cc vng t tr............................................ 59

CHNG 3 ......................................................................................................... 61SDNG ACCESS GRID XY DNG .......................................................... 61H THNG HI NGH TRUYN HNH DA TRN IP MULTICAST........ 61

3.1 Cc khi nim chung v dch v hi ngh truyn hnh .............................. 613.1.1 H thng hi ngh truyn hnh ............................................................ 623.1.2 Cc thnh phn cbn ca hi ngh truyn hnh ................................ 63

3.2 Giao thc RTP............................................................................................ 643.2.1 Khun dng RTP header ..................................................................... 643.2.2 Cc ng dng s dng RTP ............................................................... 65

3.2.2.1 Thoi hi nghn gin ............................................................... 653.2.2.2 Thoi v truyn hnh hi ngh ...................................................... 673.2.2.3 B trn v b bin dch ................................................................ 67

3.3 ng b lung hnh nh v m thanh ........................................................ 683.4 S dng Access Grid xy dng mt hi ngh truyn hnh......................... 70

3.4.1 Cc thnh phn ca Access Grid......................................................... 703.4.2 S dng Access Grid client tham gia vo hi ngh truyn hnh..... 73

KT LUN.......................................................................................................... 76HNG PHT TRIN CA TI ............................................................... 77TI LIU THAM KHO


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II

DANH MC CC TVIT TT

T vit tt Vit y Ngha ting Vit

ABR Area Border Router Router bin vng

AG Access Grid Phn mm h trxy dng ng dng

hi ngh truyn hnh

AS Autonomous System Vng t tr

ASBR Autonomous System

Border Routers

Router trn bin vng t tr

DR Designated Router Routerc la chn

DVMRP Distance Vector Multicast

Routing Protocol

Giao thc nh tuyn multicast vc-

tkhong cch

IGMP Internet Group

Management Protocol

Giao thc qun l nhm Internet

LAN Local Area Network Mng ni b

LSA Link-State Advertisement Thng ip qung b trng thi lin

kt

MABR Multicast Area Border

Router

Router bin vng multicast

MBONE Multicast Backbone ng trc multicast

MOSPF Multicast Open Shortest

Path First

Giao thc nh tuyn multicast da

trn thut ton ng i ngn nht

MCU Multipoint Control Unit Biu khin a im

OSPF Open Shortest Path First Giao thc nh tuyn unicast da

trn thut ton ng i ngn nht


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II

PIM Protocol Independent

Multicast

Giao thc nh tuyn multicast c

lp

PIM-DM Protocol Independent

Multicast Dense Mode


lp theo m hnh tp trung

PIM-SM Protocol Independent

Multicast Sparse Mode


lp theo m hnh phn tn

RAT Robust Audio Tool Cng c truyn m thanh trong ng

dng hi ngh truyn hnh

RIP Routing Information

Protocol

Giao thc thng tin nh tuyn

RPF Reverse Path Forwarding Kim tra ng dn ngc

RP Rendezvous Point im hn

RTCP Real Time Transport

Control Protocol

Giao thc iu khin truyn thng

thi gian thc

RTP Realtime Transport

Protocol

Giao thc truyn thng thi gian

thc

SPT Shortest Path Tree Cy ng i ngn nht

TTL Time To Live Thi gian tn ti gi tin

VIC Video Conference ng dng video trong hi ngh

truyn hnh


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III

DANH SCH HNH V

Hnh 1.1: Truyn thng unicast v multicast ......................................................... 3Hnh 1.2: Cc thnh phn tham gia vo truyn thng multicast ............................ 6Hnh 1.3: nh dng ca a ch IP lp D.............................................................. 7Hnh 1.4: nh xa ch IP multicast sang a ch MAC...................................... 8Hnh 1.5: Cy ng i ngn nht ca host A ....................................................... 9Hnh 1.6: Cy ng i ngn nht ca host B ..................................................... 10Hnh 1.7: Cy chia s ........................................................................................... 11Hnh 1.8: Cy chia s hai chiu............................................................................ 12Hnh 1.9: Cy chia s mt chiu s dng cy SPT.............................................. 12Hnh 1.10: Cy chia s mt chiu s dng nh tuyn unicast ............................ 13Hnh 1.11: Gii hn TTL ..................................................................................... 14Hnh 1.12: Cchng hm lin kt cc c o multicast............................... 15Hnh 1.13: ng gi IP multicast theo cch tunneling..................................... 16Hnh 1.14: Cchng hm lin kt cc MRouter .......................................... 16Hnh 1.15: Thng ip IGMPv1 .......................................................................... 18Hnh 1.16: Thng ip IGMPv2 .......................................................................... 19Hnh 2.1: Tm hng xm trong DVMRP ............................................................. 26Hnh 2.2: Trao i nh tuyn DVMRP bc 1................................................... 27Hnh 2.3: Trao i nh tuyn DVMRP bc 2................................................... 28Hnh 2.4: Trao i nh tuyn DVMRP bc 3................................................... 29Hnh 2.5: Ct nhnh trong DVMRP bc 1 ........................................................ 30Hnh 2.6: Ct nhnh trong DVMRP bc 2 ........................................................ 31Hnh 2.7: Ghp nhnh trong DVMRP bc 1 ..................................................... 32Hnh 2.8: Ghp nhnh trong DVMRP bc 2 ..................................................... 32Hnh 2.9: Cy phn phi PIM-DM ...................................................................... 35Hnh 2.10: Ct nhnh trong PIM-DM bc 1 ...................................................... 36Hnh 2.11: Ct nhnh trong PIM-DM bc 2 ...................................................... 36Hnh 2.12: Ct nhnh trong PIM-DM bc 3 ...................................................... 37Hnh 2.13: Xc nhn trong PIM-DM ................................................................... 38


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Hnh 2.14: Ghp nhnh trong PIM-DM............................................................... 39Hnh 2.15: Tham gia cy chia s PIM bc 1...................................................... 40Hnh 2.16: Tham gia cy chia s PIM bc 2...................................................... 41Hinh 2.17: Tham gia cy chia s PIM bc 3...................................................... 42Hnh 2.18: Tham gia cy chia s PIM bc 4...................................................... 42Hnh 2.19: Tham gia cy chia s PIM bc 5...................................................... 43Hnh 2.20: Tham gia cy chia s PIM bc 6...................................................... 43Hnh 2.21: Ct nhnh trn cy chia s bc 1 ..................................................... 44Hnh 2.22: Ct nhnh trn cy chia s bc 2 ..................................................... 44Hnh 2.23: Ct nhnh trn cy chia s bc 3 ..................................................... 45Hnh 2.24: Tham gia cy ng i ngn nht bc 1.......................................... 46Hnh 2.25: Tham gia cy ng i ngn nht bc 2.......................................... 46Hnh 2.26: Tham gia cy ng i ngn nht bc 3.......................................... 47Hnh 2.27: Ct nhnh trn cy ng i ngn nht bc 1 ................................. 47Hnh 2.28: Ct nhnh trn cy ng i ngn nht bc 2 ................................. 48Hnh 2.29: Ct nhnh trn cy ng i ngn nht bc 3 ................................. 48Hnh 2.30: Chuyn sang cy SPT bc 1 ............................................................ 51Hnh 2.31: Chuyn sang cy SPT bc 2 ............................................................ 51Hnh 2.32: Ct b ngun khi cy chia s bc 3 ............................................... 52Hnh 2.33: Ct b ngun khi cy chia s bc 4 ............................................... 53Hnh 2.34: Ct b ngun khi cy chia s bc 5 ............................................... 53Hnh 2.35: Vng MOSPF cha ngun v thnh vin nhm G ............................ 55Hnh 2.36: Cy ng i ngn nht MOSPF SPT cho mng N3 v N4.............. 56Hnh 2.37: Thng ip nhm tm tt trong vng ng trc.............................. 57Hnh 2.38: Cy ng i ngn nht SPT trong vng ng trc ........................ 58Hnh 2.39: Ngun trong vng khng phi ng trc......................................... 59Hnh 2.40: Lu lng multicast xung cc min MOSPF .................................. 60Hnh 3.1: Thnh phn ca hi ngh truyn hnh .................................................. 63Hnh 3.2: Khun dng RTP header...................................................................... 64Hnh 3.3: Cc thnh phn ca Access Grid ......................................................... 70Hnh 3.4: Desktop node........................................................................................ 71


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Hnh 3.5: Office node........................................................................................... 72Hnh 3.6: Room node ........................................................................................... 72Hnh 3.7: Mi quan h gia multicast v Access Grid ........................................ 73Hnh 3.8: Profile Dialog....................................................................................... 73Hnh 3.9: in a ch virtual venue kt ni ................................................... 73Hnh 3.10: Venue client ....................................................................................... 74Hnh 3.11: Ca s video....................................................................................... 74Hnh 3.12: Ca s audio....................................................................................... 75


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IV

DANH SCH CC BNG

Bng 1.1: Cc trng trong thng ip IGMPv1................................................. 18Bng 1.2: Cc trng trong thng ip IGMPv2................................................. 20Bng 1.3: Cc trng trong thng ip IGMPv3 Host Membership Query........ 22Bng 1.4: Cc trng trong thng ip IGMPv3 Host Membership Report ....... 24


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1

MU

1. t vn Ngy nay mng Internet v cc ng dng trn mng ngy cng tr nn

thng dng, v th c mt lng rt ln cc thng tin cn phi chuyn tip n

nhiu ni trong cng mt thi gian. Phn ln cc ng dng trn mng hin nay

s dng phng php truyn d liu unicast, y l phng php truyn d liu

tim ti im, tc l dc truyn t mt ngi gi ti mt ngi nhn.

Tuy nhin vi mt sng dng yu cu phi thng xuyn gi d liu t mt

im ti nhiu im, d liu c gi t mt ngi gi ti nhiu ngi nhn,phng php truyn d liu unicast trnn khng hiu qu. Trong trng hp

ny, cc ng dng s dng unicast phi ng gi cng mt d liu nhiu ln v

ln lt gi chng tim ti im. Mt cch khc thc hin vic truyn d

liu tim n nhiu im l s dng broadcast, y l phng php gi d

liu t mt im n tt c cc im. D thy rng c hai phng php trn u

gy nn nhng s lng ph ti nguyn mng, khi multicast l mt s thay th

tt nht, phng php ny gip ta tit kim c bng thng mng cng nh ci

thin c tc truyn d liu. Multicast l phng php truyn d liu t

im ti nhiu im, trong mt ngun gi s gi lu lng ti mt nhm

ngun nhn thng qua a ch nhm multicast. Trong phng php multicast c

cc giao thc cho php cc my tnh c th gia nhp vo nhm nhn d liu

hay ri b nhm mt cch d dng, cc giao thc nh tuyn cng c xy dng

cho php cc ng dng c th gi d liu mt cch hiu qu trn mng.

2. i tng v mc tiu lun vn

Xut pht t vn nu trn, lun vn xc nh IP multicast l i tng

nghin cu vi nhng vn tp trung ch yu nh sau:

Tm hiu cc thnh phn cbn ca qu trnh truyn d liu multicast gm:

a ch multicast, cy multicast, chuyn tip multicast cng nh qu trnh


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tham gia nhm multicast thng qua giao thc Internet Group Management

Protocol.

Tm hiu cc giao thc nh tuyn cbn c s dng trong truyn thng

multicast nh giao thc nh tuyn Distance Vector Multicast Routing

Protocol, giao thc nh tuyn Protocol Independent Multicast v giao thc

nh tuyn Multicast Open Shortest Path First.

Tm hiu kh nng p dng ca multicast trong ng dng thi gian thc.

3. Hng tip cn

Vi mc tiu l tm hiu cng ngh IP multicast, lun vn c tip cn

theo hng tp trung nghin cu cc khi nim, tm hiu cc giao thc ph bin

ca multicast t ch ra c cc u im, nhc im cng nh kh nng pdng ca IP multicast vo cc ng dng.

4. Kt cu ca lun vn

Lun vn gm phn mu, 03 chng v kt lun.

Chng 1: Trnh by cc vn c bn ca IP multicast nh a ch

multicast, cy phn phi multicast, chuyn tip multicast v qu trnh tham

gia nhm multicast.

Chng 2: Trnh by cc giao thc nh tuyn c s dng trong truyn

thng multicast gm giao thc nh tuyn Distance Vector Multicast

Routing Protocol, giao thc nh tuyn Protocol Independent Multicast theo

hai m hnh tp trung v phn tn v giao thc nh tuyn Multicast Open

Shortest Path First.

Chng 3: Tm hiu v hi ngh truyn hnh, ng dng phn mm Access

Grid xy dng h thng hi ngh truyn hnh da trn IP multicast.

Cui cng l kt lun v hng nghin cu tip theo ca lun vn.


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3

CHNG 1

CBN V IP MULTICAST

1.1 Mu

IP multicast l mt nhm cc cng ngh v tiu chun cho php vic truyn

ti a im a im nh hi ngh, hay truyn ti im a im nh vic

qung b m thanh, video trn Internet. Vic ng dng cng ngh ny ngy cng

pht trin do nhu cu ngy cng cao i vi cc ng dng a phng tin v s

ci tin cng ngh IP multicast.

Multicast l thut ng k thut, c ngha mt gi tin c thc gi n

nhiu ni trong cng thi im. Cch thc thng thng trong vic truyn thng

tin trn Internet l s dng cc giao thc unicast, cc giao thc ny gi cc gi

tin n mi im thu ti mt thi im. Trn mng multicast, mt gi tin c th

c gi t mt my tnh n mt vi my tnh khc, thay v gi gi tin ln

lt n tng my tnh. Do 5, 10 hay 100 my c th nhn c cng gi tin nn

bng thng c tit kim. Khi s dng multicast gi i gi tin th khng cn

thit phi bit a ch ca nhng ngi cn nhn lung tin multicast : d liuc qung b theo mt phng thc m nhng ngi quan tm n n c th

nhn c.

Hnh 1.1: Truyn thng unicast v multicast

Cc mng h trmulticast cung cp nhiu dch v v cc ng dng cho

ngi s dng u cui. Nhiu ng dng h trmulticast l cc ng dng a


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phng tin, tuy nhin cn c nhiu loi ng dng khc nhau s dng cng ngh

IP multicast cho cc mc ch khng phi a phng tin. Cc ng dng thi

gian thc bao gm: truyn hnh trc tip, i pht thanh, hi ngh truyn hnh,

cc ng dng khng phi thi gian thc nh truyn file, d liu, video theo yu

cu

Truyn ti multicast a li nhiu u im so vi unicast truyn thng.

Bng thng ca mng c tn dng hiu qu hn do nhiu lung d liu c

thay th bi mt lung d liu multicast. Cng ngh ny em li cht lng ti

u do cn t bn sao d liu chuyn i v x l ti cc nt mng. c th c

c cc u im ca IP multicast, th kh nng nh tuyn multicast phi c

h trti cc nt mng. Ty thuc vo chnh sch s dng v nhu cu ca ngi

s dng, th cc vn lin quan n nh tuyn, tin cy, nh a ch mngv cc giao thc truyn ti a phng tin c tm quan trng i vi nh vn

hnh mng.

Multicast khng chem li li ch cho ngi s dng u cui. Hu ht

cc ng dng multicast l da trn UDP, vic s dng giao thc ny c th dn

n cc nh hng ph khng mong mun (cc gi tin c th b hy) so vi cc

ng dng unicast tng t da trn TCP. Tuy nhin, vic thiu kim sot nghn

c th dn n vic suy gim cht lng mng tng th. Cc gi tin trng c ththnh thong c to ra khi cc topo mng multicast thay i. Trong tng lai

vic trin khai IPv6 sem li multicast c sn cho ngi s dng mng. Phn

mm nh tuyn tin cy hn vi cc giao thc mi s tn dng c h tng

mng. Vi multicast c sn, cc vn nh tuyn sc gii quyt d dng

hn v bng thng sc tit kim hn.

Multicast l mt cng ngh tng i mi cho php cc khch hng c

hng li t cc ng dng thi gian thc m ng ra phi yu cu mt lng

bng thng cc ln. Cng ngh ny cho php nhiu loi cng ty a cc sn

phm ca hn cc nhm ngi vi chi ph thp so vi unicast. Multicast gim

lu lng mng v tit kim bng thng cho php ngi dng khai thc kh nng

s dng cc i c th ca Internet. Multicast cung cp cho cc ngi s dng

lin quan n Internet (cc ngi s dng u cui, nh vn hnh mng, ISP v


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cc cng ty lin quan khc) gii php kh thi kinh t v k thut cho vn

truyn ti khi lng thng tin ln n cc nhm ngi dng c la chn.

c c multicast trn Internet hay cc mng Intranet, cch u tin l

kt ni cc c o mng h trmulticast vi cc ng hm IP multicast. Do cc

ng hm ny khng kh phn cp v khng a li cc u im k tha ca

multicast, bc k tip l thay th h tng ng hm vi h tng nh tuyn

multicast thc s. Cng ngh multicast hin ti a ra cc thch thc khc nhau

cho vic nh tuyn v nh a ch, hin nay th thch ln nht l thit lp h

tng ton cu c tnh tin cy v c tnh kh phn cp tng t nh h tng mng

Internet unicast ngy nay.

Trong khi giao thc mng IP t bn thn n cung cp cc cch k tha

i vi IP multicast, cc giao thc lp cao hn khng h trn. Mc d cc giaothc khng tin cy nh UDP, RTP c th s dng trn nc ca IP multicast, TCP

v cc giao thc truyn ti tin cy hn trong cc mi trng unicast khng h tr

multicast. Do vy cc giao thc truyn ti multicast phi c pht trin v v th

khng c giao thc truyn ti mc ch chung cho mi trng hp, tuy nhin li

xut hin cc giao thc kh cu hnh cao v cc giao thc c chuyn bit cao

cho cc mc ch truyn ti tin cy c bit trong mi trng IP multicast.

1.2 Cc thnh phn tham gia vo truyn thng multicast

tham gia vo qu trnh trao i d liu cc my tnh v router cn h tr

giao thc multicast, khi cc my c th gi hay nhn lu lng multicast.

My ngun gi d liu multicast ti mt a ch nhm, y l mt a ch lp D.

Cc my trm mun nhn cc gi tin multicast s lin h vi router cc b

ng k tham gia nhm v nhn d liu. Cc router s s dng mt giao thc

nh tuyn multicast xc nh cc mng con c cc thnh vin ca nhm v

chuyn d liu multicast ti cc my nhn. Nu mng con khng c thnh vin

ca nhm, router s khng chuyn d liu ti mng . Ta s tm hiu cc thnh

thnh phn tham gia vo truyn thng multicast v hot ng ca chng trong

mng qua minh ho trn hnh 1.2:


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Hnh 1.2: Cc thnh phn tham gia vo truyn thng multicast

Trong m phng trn hnh 1.2 cc hot ng din ra nh sau:

Host A trong Subnet 1 l mt ngun multicast v gi d liu multicast ti

a ch nhm.

Host B trong Subnet 1 gi yu cu tham gia nhm ti router cc b ca n.

Bi v Host B gia nhp vo nhm nn giao din mng ca n s lngnghe cc gi d liu gi ti a ch nhm. Cc my tnh cn li trong

Subnet 1 khng tham gia nhm nn chng s lc b cc lu lng gi ti

a ch nhm multicast.

Router s chuyn d liu multicast ti tt c cc mng con c thnh vin

ca nhm. Trong trng hp ny, router s chuyn d liu t Subnet 1 ti

Subnet 3.

Host C trong Subnet 3 tham gia vo nhm do n s nhn d liu

multicast.

Host D trong Subnet 3 gi yu cu ti router tham gia nhm, sau khi

tham gia nhm giao din mng ca n s lng nghe v nhn cc d liu gi

ti a ch nhm.

Cc thnh phn tham gia vo truyn thng multicast:


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Host (bao gm ngun hoc ch): l cc l cc my tnh tham gia kt ni

vo mng v h trqu trnh gi v nhn d liu multicast.

Router: l cc router h trgiao thc multicast, n c kh nng x l cc

yu cu tham gia hay ri nhm v c giao thc nh tuyn multicast xc

nh v chuyn d liu ti cc mng con.

a ch multicast: l a ch lp D, n chnh l a ch ca nhm multicast.

Nhm multicast: l mt tp cc thit bu cui lng nghe d liu gi ti

mt a ch multicast.

MBone: vit tt ca t Internet multicast backbone l mt phn ca Internet

h trqu trnh nh tuyn v gi d liu multicast.

1.3 a ch multicastCc router phi c phng thc phn bit d liu dng multicast vi

dng unicast hay broadcast. iu ny thc hin thng qua vic gn a ch IP,

bng cch dng a ch lp D t 224.0.0.0 n 239.255.255.255 cho multicast cc

thit b mng c th nhanh chng lc ra cc a ch multicast bng cch c 4 bit

bn tri ca mt a ch. Bn bit ny ca mt a ch multicast lun lun bng

1110, hnh 1.3 th hin nh dng ca mt a ch lp D.

Hnh 1.3: nh dng ca a ch IP lp D

Lm th no mt router kt hp mt a ch multicast ca IP vi mt a

ch MAC. Do khng c cch tng ng vi giao thc phn gii a ch nh

trong truyn thng unicast, mt dng gi trc bit dnh ring cho a ch MAC

ca multicast sc dng. Cc a ch ny bt u bng 01005E, phn 28 bitsau ca a ch IP multicast sc nh x vo 23 bit thp ca a ch MAC

bng mt gii thut n gin.

Multicast Group ID0111Class D

28 bits


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Hnh 1.4: nh xa ch IP multicast sang a ch MAC

Hnh 1.4 cho thy cch nh xa ch, ch c 23 bit cui ca a ch l

c chp ta ch IP sang a ch MAC. Tuy nhin ch rng c 5 bit ca a

ch IP khng c chuyn sang a ch MAC. nh x ny lm ny sinh mt vn

l c th c 32 a ch multicast khc nhau c th nh x vo cng mt a ch

MAC. S nhp nhng ny dn n mt vn nh khi host multicast nhn mt

Ethernet frame ca a ch multicast. Mt a ch MAC c th tng ng vi 32

a ch IP multicast khc nhau. V vy, khi mt host nhn d liu n kim tra tt

c cc frame c MAC m n quan tm. Sau host ny phi kim tra phn a

ch IP bn trong mi frame nhn ra phn a ch ca tng nhm multicast. Sau

y l mt s khng gian a chc dnh ring ca multicast:

Ton b khng gian a ch multicast: 224.0.0.0 - 239.255.255.255.

a ch link-local: 224.0.0.0 - 224.0.0.255 c dng bi cc giao thc nh

tuyn. Router s khng chuyn cc gi tin c a ch ny. Cc a ch bao

gm a ch tt c cc host 224.0.0.1, tt c cc router 224.0.0.2, tt c cc

OSPF router 224.0.0.5 y l a ch cc nhm cnh v cc a ch ny

c xc nh trc.

Khong a ch dnh cho qun tr 239.0.0.0 - 239.255.255.255 c dng

trong cc min multicast khc nhau, ging nh dy a ch dnh ring trong

RFC1918. a ch ny khng c s dng gia cc min multicast nn n

c thc dng li nhiu ln.

28 bit

nh x sang a ch MAC

Multicast

MAC Address0 0 0 0 0 0 0 1 0 0000 00 00 10 11 10 10

1110

5 bit

Khng s dng

01 00 5E X Y Z

X Y Z

IP Multicast

224 - 239


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a ch ton cc 224.0.1.0 - 238.255.255.255 c dng bi bt c i

tng no. Cc a ch ny c s dng trn Internet v vy a ch ny

phi duy nht.

1.4 Cy phn phi multicast phn phi d liu multicast ti ti tt c cc my nhn, cy phn phi

multicast c s dng, n c tc dng iu khin ng i ca d liu truyn

trn mng. C hai loi cbn ca cy phn phi multicast l cy ngun v cy

chia s.

1.4.1 Cy ngun

Dng n gin nht ca cy phn phi l cy ngun,vi gc ca n chnh l

ngun d liu multicast v cc nhnh ca n dn ti cc u cui nhn d liu

trn mng. Do loi cy ny s dng ng i ngn nht nn cn c tn l cy

ng i ngn nht (Shortest Path Tree SPT). Hnh 1.5 biu din mt v d ca

cy SPT cho nhm 224.1.1.1 c gc ti host A l ngun d liu v hai my nhn

l host B v host C.

Hnh 1.5: Cy ng i ngn nht ca host A


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Hnh 1.6: Cy ng i ngn nht ca host B

K hiu c bit (S, G) ch ra mt cy SPT trong S l a ch IP ca

ngun d liu v G l a ch ca nhm multicast. p dng cho mng nh trn

hnh 1.5 k hiu c thc vit nh sau (192.1.1.1, 224.1.1.1). Mi k hiu (S,

G) ng vi mt ngun gi d liu v th nu host B cng gi d liu ti nhm224.1.1.1 v cc host A v C l cc my nhn th k hiu (S, G) ng vi ngun B

s l (192.2.2.2, 224.1.1.1) nh trong hnh 1.6.

1.4.2 Cy chia s

Khng c gc ng vi tng ngun nh cy ngun, cc cy chia s s dng

mt gc chung duy nht ti mt im chn trn mng. Gc chia s ny cn

c gi l im hn (Rendezvous Point RP). Hnh 1.7 th hin mt cy chia

s cho nhm 224.2.2.2 vi gc cy ti router D. Khi s dng cy chia s, ngun

phi gi lu lng ca n ti gc v sau lu lng ny c chuyn tip theo

cc nhnh ca cy n cc u cui nhn d liu.

Trong hnh 1.7 d liu multicast t host A v host D c gi ti gc cy l

router D v theo nhnh cy n hai my nhn l host B v host C. Bi v tt c


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cc ngun trong nhm multicast cng s dng chung mt cy chia s, mt k

hiu (*, G) c s dng biu din cy. Trong k hiu * c ngha l tt c

cc ngun v G biu din a ch nhm multicast. V th cy chia s trong hnh

1.7 c thc vit (*, 224.2.2.2).

Hnh 1.7: Cy chia sCy chia sc chia lm hai loi: cy mt chiu v cy hai chiu. Trong

cy hai chiu d liu c th truyn ln v xung ti tt c cc my nhn. Hnh

1.8 th hin mt v d ca cy chia s hai chiu, trong d liu t host B c

gi ngc ln gc cy v t gc cy c gi xung router B n router A v

n my nhn.

Cy chia s mt chiu ch cho d liu multicast i xung theo chiu t gc

cy n cc my nhn. V th ngun d liu cn s dng mt cch khc gi

d liu ti gc cy v t chuyn ti cc my nhn. Mt phng php c s

dng l cho gc ca cy chia s tham gia vo mt cy SPT c gc l ngun d

liu. Hnh 1.9 minh ha mt cy chia s mt chiu trong gc ca cy tham gia

vo cy SPT c gc l host B v d liu c gi t B ti gc. Khi gc cy nhn


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d liu n s gi d liu xung cc nhnh ti cc my nhn. Giao thc nh

tuyn PIM s dng phng php ny ly d liu t ngun ti router RP.

Hnh 1.8: Cy chia s hai chiu

Hnh 1.9: Cy chia s mt chiu s dng cy SPT


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Hnh 1.10: Cy chia s mt chiu s dng nh tuyn unicast

Mt cch khc gi d liu multicast ti gc cy l cho gc cy kt ni

trc tip vi ngun v d liu c gi ti gc thng qua phng thc unicast.

Giao thc nh tuyn CBT s dng phng php ny khi mt my ngun ch gi

d liu ti nhm (my ngun ch gi d liu v khng nhn d liu t nhm).Trong hnh 1.10 host A l ngun ch gi d liu n khng tham gia vo nhm

multicast v th n khng thuc mt nhnh trn cy chia s.

Trong v d trn router A ng gi d liu multicast t host A v s dng

nh tuyn unicast gi gi tin trc tip n gc cy. Ti gc cy d liu c

mgi v gi xung cc nhnh cy ti my nhn.

1.5 Chuyn tip multicast

Trong c ch nh tuyn unicast, lu lng c chuyn tip qua mng

theo mt ng duy nht t ngun ti ch. Router unicast khng thc s quan

tm n a ch ngun, n ch quan tm n a chch v cch chuyn tip

lu lng ti ch. Router qut bng nh tuyn ca n v chuyn tip mt bn

sao duy nht qua giao din hng n ch. Trong cch multicast ngun gi d


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liu ti mt nhm cc my thng qua a ch nhm c lu trong trng a ch

ch ca mt gi tin IP. V th cc gi tin multicast khng th chn gin xc

nh ng i tip theo cho gi tin da vo a chch nh trong giao thc nh

tuyn unicast. Cc router thng phi gi d liu ln nhiu giao din ca n

n c tt c cc my nhn. Chnh v th giao thc nh tuyn multicast phc

tp hn so vi nh tuyn unicast.

Hu ht cc phng php nh tuyn multicast s dng chuyn tip theo

ng dn ngc (Reverse Path Forwarding RPF) nh l mt cch kim tra

chnh quyt nh chuyn tip hay loi b mt gi tin. Khi mt gi tin multicast

n router, router s thc hin kim tra RPF i vi gi tin. a ch ngun ca

gi tin sc kim tra bit rng gi tin c c nhn t giao din c

ng i ngn nht trli ngun (giao din RPF) hay khng. Nu kim tra RPFthnh cng gi tin c chuyn tip, nu kim tra tht bi router s loi b gi tin

. Cch thc router xc nh giao din l RPF i vi mt gi tin ph thuc

vo giao thc nh tuyn c s dng. Mt s giao thc multicast duy tr mt

bng nh tuyn multicast ring ca n s dng vo kim tra RPF nh giao

thc DVMRP. C nhng giao thc khc s dng bng nh tuyn unicast trn

router xc nh giao din RPF nh giao thc PIM hay CBT.

Mi ln mt gi tin multicast c chuyn tip bi router gi tr trngTTL (Time To Live) trong IP header s gim i mt. Nu gi tr TTL ca gi tin

gim v khng, router s loi gi tin. Gii hn TTL c thc p dng cho mt

giao din c th ca mt router multicast ngn chn cc gi tin multicast c

gi tr TTL nh hn ngng c chuyn qua giao din. Trong hnh 1.11 minh

ha mt router p dng gii hn TTL cho cc giao din ca n.

Hnh 1.11: Gii hn TTL


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Trong hnh 1.11, gi tin multicast n router t cng Serial0, gi s rng

kim tra RPF thnh cng v cc cng cn li ca routeru c trong danh sch

cng ra cho nhm multicast, v th d liu sc chuyn tip n cc cng. Tuy

nhin do router p dng gii hn ngng TTL ti cc giao din v th gi tin ch

c chuyn tip ra cc cng Serial1 v Ethernet0, cn cng Serial2 ngng

TTL l 64 ln hn gi tr TTL ca gi tin l 23 v th gi tin khng c chuyn

tip.

1.6 ng trc multicast

Mng ng trc multicast MBone c xy dng nhm nh gi cc

ng dng cng nh cc giao thc c xy dng phc v truyn thng multicast

d liu, audio v video. MBone c thit k hot ng lp trn ca Internetv c cu thnh bi mng li cc c o multicast. Cc c o giao tip vi

mng bn ngoi thng qua mt b nh tuyn c kh nng x l cc gi IP

multicast thng qua h trgiao thc qun l nhm Internet IGMP v cc giao

thc nh tuyn khc c xc nh l mt MRouter hay IP multicast router. Tip

gip vi cc c o l cc bnh tuyn IP truyn thng ch h trx l cc gi

IP unicast c xc nh l cc URouter (IP unicast router). Cc MRouter ca

cc mng khc nhau kt ni thng qua cc lin kt o tim ti im thng qua

cchng hm tunneling. Kt qu l MBone c hnh thnh nh tp hp

cc MRouterc ni vi nhau bi cc ng hm bao ph ton mng.

Hnh 1.12: Cchng hm lin kt cc c o multicast


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ng hm l c ch cho php chuyn gi d liu multicast t MRouter

ngun n MRouterch thng qua cc bnh tuyn. MRouter ngun thc hin

ng gi v chuyn tip d liu. Vic ng gi theo cchng hm thc hin

b sung thm phn tiu IP mi vi a ch ch l a ch IP unicast ca

MRouteru bn kia ca ng hm v a ch ngun l a ch IP unicast ca

MRouterang gi gi tin .

Hnh 1.13: ng gi IP multicast theo cch tunneling

Cc bnh tuyn trung gian nm trn tuyn lin kt t MRouter ngun n

MRouterch s xem gi ny nh gi d liu unicast bnh thng v truyn i

theo thng tin trong bng nh tuyn unicast. c o multicast ch pha bn

kia ca ng hm s nhn gi unicast ny v tch phn header c thm

vo ri sau gi gi d liu i mt cch thch hp. Vi bnh tuyn cc

gi d liu c xem nhn t MRouter ln cn v trong sut i vi cc b

nh tuyn trung gian. ng i trung gian bn i i vi bnh tuyn ny.

Khi cc MRouter x l cc gi IP multicast tng t nh cc bnh tuyn

x l cc gi IP unicast nh th hin trn hnh 1.13.

Hnh 1.14: Cchng hm lin kt cc MRouter


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Nh th hin trn hnh 1.14, MRouter R2 mun gi mt gi tin IP a hng

ti MRouter R5. Trc ht, R2 sng v gi tin (chuyn t gi IP a hng

thnh gi IP n hng) ri chuyn tip ti URouter R3. Gi a hng ny si

theo tuyn R3-R7-R8-R5. Nh vy, theo cchng hm, vi MRouter R5 th

gi tin ny c x l vi a ch ngun n t R2.

1.7 Giao thc qun l nhm Internet

nhn d liu multicast t mt ngun, cc my nhn u tin phi tham

gia vo mt nhm multicast, nhm ny c xc nh thng qua a ch

multicast. Mt host c th tham gia vo mt nhm multicast bng cch gi cc

yu cu n router gn nht. Tc v ny c thc hin thng qua giao thc qun

l nhm Internet - IGMP (Internet Group Management Protocol). Giao thcIGMP pht trin t giao thc Host Membership Protocol, c m t trong ti

liu ca Deering. IGMP pht trin t IGMPv1 (RFC 1112) n IGMPv2 (RFC

2236) v phin bn mi nht IGMPv3 (RFC 3376). Cc thng ip IGMP c

ng gi trong IP datagram vi trng protocol number bng 2, trong trng

TTL c gi tr bng 1. Cc gi IGMP chc truyn trong mng LAN v khng

c tip tc chuyn sang LAN khc do gi tr TTL ca n. Hai mc ch quan

trng nht ca IGMP l:

Thng bo cho router multicast bit rng c mt my mun nhn d liu t

mt nhm multicast.

Thng bo cho router bit c mt my mun ri nhm multicast (ni cch

khc, my khng cn quan tm n vic nhn d liu multicast na).

Cc router thng dng IGMP duy tr thng tin cho tng giao din

bit nhng nhm multicast no router cn phi truyn d liu v nhng host

no mun nhn.

1.7.1 Giao thc IGMPv1

Giao thc IGMP phin bn 1 bao gm 2 loi thng ip l Host

Membership Report v Host Membership Query. nh dng ca thng ip

IGMPv1 c th hin nh trong hnh 1.15:


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Hnh 1.15: Thng ip IGMPv1

Gi tr ca cc trng trong IGMPv1 c m t trong bng 1.1:

Bng 1.1: Cc trng trong thng ip IGMPv1

Tn trng di M t

Version 4 bit Ch nh phin bn ca giao thc v lun c

gi tr l 1

Type 4 bit Xc nh 2 kiu thng ip c gi tr:

0x1 cho Host Membership Query

0x2 cho Host Membership Report

Unused 8 bit Cha gi tr 0 khi gi v b b qua khi nhn

Checksum 16 bit Dng kim tra li trong qu trnh truyn d

liu

Group Address 32 bit c gn v gi tr 0.0.0.0 khi router gi gitin Host Membership Query v c gn gi tr

a ch nhm multicast khi mt my gi thng

ip Host Membership Report

1.7.1.1 Thngip Host Membership Report

tham gia vo mt nhm, host s gi mt thng ip Host Membership

Report ti router cc b, n khng cn quan tm c cc host khc trn mng con

l thnh vin ca nhm hay cha. Thng ip ny s dng a ch 224.0.0.1

(a ch all-hosts) nha chch v cha a ch nhm m host mun tham gia.

0 3 4 7 8 15 16 31

UnusedTypeVersion Checksum

Group Address


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1.7.1.2 Thngip Host Membership Query

Mt router IGMPv1 s gi mt cch nh k (mi 60 giy) thng ip Host

Membership Query n tt c cc host kim tra xem cc host ny c cn quan

tm nhn d liu multicast na khng. Cc host c th tham gia vo cc nhm

multicast bt k thi im no. IGMPv1 khng c cch cho php mt host

ri khi mt nhm nu host khng cn mun nhn d liu t nhm multicast.

Thay vo , router s kt lun l mt cng ca n khng cn thuc v mt nhm

multicast no nu cng khng nhn c thng ip Host Membership Report

trong ba chu k truy vn lin tip. iu ny c ngha l, d liu multicast vn gi

vo mt phn on mng trong ba chu k truy vn lin tip sau khi tt c cc

thnh vin ca nhm khng cn lng nghe d liu multicast na.


Giao thc IGMP phin bn 2 l s mrng cc chc nng ca IGMP phin

bn 1 bao gm:

Mt phng thc xc nh router no s gi cc thng ip truy vn

multicast khi c nhiu router cng kt ni vo mt mng con.

Mt thng ip mi c s dng khi mt host mun ri nhm.

Mt thng ip mi cho php router truy vn cho tng nhm c th thay v

tt c cc nhm.

Phin bn mi ca thng ip Host Membership Report.

nh dng ca thng ip IGMPv2 c th hin nh trong hnh 1.16:

Hnh 1.16: Thng ip IGMPv2

0 7 8 15 16 31

Max RTimeType Checksum

Group Address


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Gi tr ca cc trng trong IGMPv1 c m t trong bng 1.2:

Bng 1.2: Cc trng trong thng ip IGMPv2

Tn trng di M t



0x12 cho IGMPv1 Host Membership Report


0x17 cho Leave Group Message

Maximum

Response Time

8 bit Ch ra khong thi gian ti a (tnh bng giy)

m mt host c th phn hi thng tin truy vn,

ch s dng trong cc thng ip truy vn


liu

Group Address 32 bit c gn gi tr 0.0.0.0 trong gi tin truy vn

v gn a ch nhm nu thng ip l cho tng

nhm c th. Cc thng ip Host MembershipReport hoc thng ip Leave Group c th

mang a ch ca nhm trong trng ny

1.7.2.1 La chn router truy vn

Khc vi IGMPv1, trong giao thc nh tuyn multicast s la chn

router truy vn, IGMPv2 s dng mt phng thc la chn n gin chn

mt router trn mi mng con gi nh k cc thng ip Host Membership

Query. Routerc chn l router c a ch IP nh nht. Khi mt router nhn

c mt gi tin truy vn t mt router no , n s kim tra a ch ngun ca

gi tin . Nu a ch ngun ca router cc b nh hn a ch ngun trong gi

tin va n, router s vn tip tc gi gi tin query v n bit rng n s gi vai


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tr truy vn. Cn nu a ch ngun ca gi tin truy vn nh hn, router s t b

vai tr truy vn v khng gi gi tin.

1.7.2.2 Thngip ri nhm

Khi mt host mun ri nhm, n s gi mt thng ip ti a ch 224.0.0.2(a ch all-routers). Khi nhn c thng ip ri nhm, router s gi truy vn

cho tng nhm c th ti mng con cha host. Nu router khng nhn c c

tr li ca truy vn n s quyt nh rng trn mng con khng cn thnh vin

no ca nhm v khng y d liu multicast ti na. Nu router nhn c

phn hi, ngha l trn mng con vn cn host l thnh vin ca nhm v n

s tip tc chuyn d liu ti. S dng thng ip ri nhm lm gim i cc d

liu tha m router chuyn n cc mng con khi khng cn thnh vin no canhm.

1.7.2.3 Truy vn cho tng nhm

Mt thng ip Host Membership Query c gi ti a ch 224.0.0.1

tm ra cc nhm multicast c thnh vin trn mng con. Trong IGMPv2 cc

router cn c th gi thng ip cho tng nhm c th ti mt a ch nhm

xc nh nhm c thnh vin trn mt mng con hay khng.


IGMP phin bn 3 m rng chc nng ca IGMPv2 bng vic h tr tnh

nng multicast cho tng ngun cho php cc host lc d liu i vo da trn a

ch IP ngun. Vi IGMPv3 c th c nhiu ngun cho mt dng d liu multicast

v th cc host c th gia nhp nhm v nhn d liu t cc ngun gn nht.

IGMPv3 cn ci tin thng ip Host Membership Query v thm phin bn mi

ca Host Membership Report.

1.7.3.1 Lc dliu

y l kh nng cho php mt host ch ra n s nhn ngun d liu

multicast ta ch ngun xc nh. Vi IGMPv1 v IGMPv2 mt host thng

bo nhm thnh vin m khng quan tm ngun ca d liu gi ti nhm. Nu

d liu multicast gi ti nhm t nhiu ngun, mt mng con c th nhn d liu


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multicast t mi ngun. IMGPv3 cho php mt host ch r hai thuc tnh sau y

cho cc nhm multicast c th:

Danh sch cc ngun m host nhn d liu.

Danh sch cc ngun m host khng nhn d liu.

Cc multicast router v cc giao thc nh tuyn multicast s dng thng

tin cho tng ngun c th trong IGMPv3 Host Membership Report ngn vic

chuyn cc thng ip multicast t mt ngun ti mt mng con khng c thnh

vin ca nhm.

1.7.3.2 Thngip IGMPv3 Host Membership Query

IGMPv3 Host Membership Query c cng gi tr kiu v c cng nh dng

vi IGMPv2 Host Membership Query ngoi tr n thm mt s trng sautrng a ch nhm. Cc trng ny cung cp cc tham s truy vn cho router v

ch r cc ngun c chp nhn v khng c chp nhn ng vi mi nhm

multicast. Danh sch cc ngun c chp nhn v khng chp nhn chc s

dng cho truy vn ti mt nhm c th c s dng tnh nng lc d liu. Bng

1.3 m t cc trng trong thng ip IGMPv3 Host Membership Query:

Bng 1.3: Cc trng trong thng ip IGMPv3 Host Membership Query

Tn trng di M t





0x17 cho Leave Group Message

Maximum

Response Time

8 bit Ch ra khong thi gian ti a (tnh bng giy)

m mt host c th phn hi thng tin truy vn,

ch s dng trong cc thng ip truy vn


liu


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Group Address 32 bit c gn gi tr 0.0.0.0 trong gi tin truy vn

v gn a ch nhm nu thng ip l cho tng

nhm c th. Cc thng ip Membership

Report hoc thng ip Leave Group c th

mang a ch ca nhm trong trng ny

Reserved (Dnh

ring)

4 bit Cha gi tr 0 khi gi v b b qua khi nhn

Suppress 1 bit Gn gi tr 1 chi r cc router nhn dng

cp nht thi gian khi nhn mt truy vn

Queriers

Robustness

Variable (QRV)

3 bit Ch ra cc gi datagram mong i trn mng.

IGMP c th ly li QRV-1 gi datagram b

mt

Queriers Query

Interval

Code(QQIC)

8 bit Ch ra khong thi gian tnh bng giy m

routeri gia hai truy vn thng thng

Number of

Sources

16 bit Ch s lng a ch ngun cha thng ip

truy vn

Source Addresses 32 bit Cha a ch IP ca ngun multicast

1.7.3.3 Thngip IGMPv3 Host Membership Report

Host s dng thng ip IGMPv3 Host Membership Report ch r cc

nhm multicast m n mun gia nhp, vi mi a ch nhm km theo danh sch

nhng a ch ngun m host mun nhn d liu multicast v ngun no hostkhng mun nhn. Thng ip IGMPv3 Host Membership Report cha mt dy

cc bn ghi nhm. Mi nhm cha a ch nhm multicast v mt danh sch lin

kt cc ngun. Thng ip IGMPv3 Host Membership Report c gi ti a

ch 224.0.0.22, y l a ch dnh ring cho router multicast h trIGMPv3.


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Bng 1.4: Cc trng trong thng ip IGMPv3 Host Membership Report

Tn trng di M t





Reserved 8 bit Cha gi tr 0 khi gi v b b qua khi nhn


liu

Reserved 16 bit Cha gi tr 0 khi gi v b b qua khi nhn

Number of

Records

16 bit Cha s lng ca nhm bn ghi trong thng

ip

Group Records Variable Mi bn ghi ch ra a ch IP cho nhm

multicast tham gia hay ri v danh sch cc

ngun nhn d liu v khng nhn d liu


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CHNG 2

NH TUYN MULTICASTCc giao thc nh tuyn multicast c chia lm ba loi chnh gm: giao

thc hot ng theo m hnh tp trung (dense mode) nh DVMRP v PIM-DM,

cc giao thc hot ng theo m hnh phn tn (sparse mode) nh PIM-SM v

giao thc hot ng theo m hnh trng thi lin kt (link-state) nh MOSPF.

Cc giao thc dense mode hot ng theo cch qung b v loi b trong

cc router cho rng trn cc mng con tn ti t nht mt my nhn d liu

multicast, v th chng gi d liu xung tt c cc mng cho n khi nhn cthng bo dng gi d liu. Vi cch ny cc giao thc dense mode ph hp

vi cc mng my tnh nh, trong lu lng multicast c truyn ti hu ht

cc my trn mng. Cc giao thc sparse mode hot ng theo cch ngc li,

cc router s khng gi d liu ln mng tr khi n nhn c yu cu gi d

liu t cc my nhn. iu ny lm gim d liu d tha truyn trn mng, gip

cho cc giao thc sparse mode ph hp vi cc mng ln, vi s lng cc my

tham gia nhn d liu nhiu nhng nm ri rc trn cc mng con.

2.1 Giao thc nh tuyn multicast vctkhong cch

Giao thc nh tuyn multicast vct khong cch (Distance Vector

Multicast Routing Protocol DVMRP) l giao thc nh tuyn multicast u tin

c s dng ph bin. DVMRP c pht trin da trn giao thc nh tuyn

unicast Routing Information Protocol (RIP) vi mt s thay i ph hp vi

cch multicast.

2.1.1 Tm kim hng xm

Tm kim router hng xm l mt qu trnh quan trng bi v cc router s

dng giao thc DVMRP cn phi duy tr mt danh sch cc router hng xm

thc hin chuyn tip multicast. iu ny c bit ng khi DVMRP hot ng

trn mng a truy cp nh mng Ethernet, bi v trn mng c th c nhiu router


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DVMRP cng tham gia. thc hin iu , cc thng ip thm d DVMRP

Probe c cc router gi mt cch nh k ti a ch all-DVMRP-router

(224.0.0.4). Trn hnh 2.1 th hin c ch tm kim hng xm thng qua hot

ng ca 2 router.

Hnh 2.1: Tm hng xm trong DVMRP

Cc bc hot ng ca cch tm kim c minh ha trn hnh 2.1 gm:

u tin router 1 gi mt gi tin thm d, lc ny router 1 cha pht hin

c cc hng xm v th danh sch hng xm trong gi tin l rng.

Router 2 nhn c thng ip thm d t router 1, n thm a ch IP ca

router 1 vo danh sch cc router hng xm ca giao din nhn gi tin.

Router 2 gi thng ip thm d ln mng, trong c cha a ch IP carouter 1 trong danh sch hng xm.

Router 1 nhn c thng ip t router 2 thm a ch IP ca router 2 vo

danh sch hng xm. V chu k gi gi tin tip theo tip theo, router 1

gi thng ip ln mng vi a ch IP ca router 2 trong danh sch hng

xm.

Khi mt router nhn c thng ip thm d trong a ch IP ca n c

trong danh sch hng xm, router bit rng c mt kt ni hai chiu c thit

lp thnh cng gia n v hng xm, khi hai router c th trao i d liu vi

nhau.

2.1.2 Trao i thng bo nh tuyn


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Cc thng bo nh tuyn ca DVMRP c gi mt cch nh k theo

cch ging vi giao thc nh tuyn unicast RIP. Mt im khc bit quan trng

l DVMRP qung b cc ng i cng vi subnet mask cho php DVMRP hot

ng c trn giao thc classless. Trn hnh 2.2 th hin mt mng multicast

bao gm 2 router s dng DVMRP kt ni vi nhau.

Hnh 2.2: Trao i nh tuyn DVMRP bc 1

Trong bng nh tuyn ca 2 router c cha mt sng i m cc router

hc c thng qua giao din S0. Gi s router 2 gi thng ip thng bo

trc nh trn hnh 2.3.


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Thng bo nh tuyn t router 2 cha hai ng i v c gi ti router

1. Router 1 thm mt thc th cho mng 204.1.16.0/24 vo bng nh tuyn ca

n, ngoi ra v router 2 c gi tr metric ti mng 151.10.0.0 nh hn nn router 1

cp nht thc th c trong bng nh tuyn vi gi tr metric mi l 4 v giao

din ra l E0. Sau router 1 phn hi bng cch gi thng ip thm d ca n

ln mng ti router 2.

Trong gi tin gi ti router 2, router 1 s dung k thut Poison Reverse

vi hai ng i m n nhn trn cng E0 bng cch thm gi tr ngng (32)

vo gi tr metric hin ti. K thut Poison Reverse trong DVMRP c s dng

thng bo ti mt router l c mt router khc ph thuc vo n trong vic

nhn d liu t mt nhm multicast. V th router 2 bit rng router 1 pha di

trong cy multicast ca ngun d liu v mong mun nhn d liu multicast thai mng ny thng qua router 2. Router 2 nhn thng bo v thm vo bng

nh tuyn ca n mt thc th mi cho mng 198.14.32.0/24 nh trong hnh 2.4.


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Sau khi cp nht bng nh tuyn router 2 s gi mt thng bo Poison

Reverse cho ng i 198.14.32.0/24 nhn t router 1 bng cch thm ngng

vo gi tr metric. iu ny cho router 1 bit router 2 l pha di v nhn d

liu multicast t mng ngun 198.14.32.0/24 thng qua router 1.

2.1.3 Ct nhnh

DVMRP s dng cy ngun iu khin ng i ca lung d liu, banu d liu multicast c gi xung tt c cc nhnh ca cy. gim lu

lng d tha cn c mt cch ct cc nhnh cy m trn khng c cc my

nhn d liu. V th ti cc router l khng c my nhn d liu kt ni trc tip,

mt thng ip DVMRP Prune c gi ngc ln cy multicast yu cu

dng gi d liu khng mong mun v ct b nhnh khi cy multicast. Trn

hnh 2.5 m t mng vi mt ngun hot ng S gi d liu multicast ti nhm

G.


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Hnh 2.5: Ct nhnh trong DVMRP bc 1

My nhn 1 tham gia vo nhm multicast G v nhn d liu t S. Cc

ng mi tn ch ra lung lu lng (S, G) ban u i xung cy multicast

(c th hin bi cc mi tn t nt) trc khi thc hin qu trnh ct nhnh.

router C khng phi l routerc chn gi d liu (Designated Router DR)

cho mng c my nhn 1 kt ni v th n trthnh mt router l. V th router C

gi mt thng ip DVMRP Prune ti router B yu cu dng gi d liu

khng cn thit (S, G). Khi nhn c thng ip router B phn hi bng cch

ct bng i ti router C.

Lc ny c hai router X v Y cng l router l v th n gi thng ip

Prune ti router E yu cu ct khi cy multicast. Router E bit rng n ch c

2 router hng xm, v v c hai router gi thng ip ct nhnh nn router E

cng gi thng ip Prune cho lu lng (S, G) ln router D. Router D nhn

thng ip t E s ct bng i ti router E nh trong hnh 2.6.


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Hnh 2.6: Ct nhnh trong DVMRP bc 22.1.4 Ghp nhnh

Mi thng ip ct b nhnh c mt gi tr thi gian timeout, v th nu mt

nhnh b ct b khi cy multicast sau khi ht thi gian timeout n li c th

nhn d liu t ngun. Tuy nhin DVMRP cn h trmt cch cho php cc

nhnh cy b ct b c th ghp tr li m khng cn phi i ht khong thi

gian ny. thc hin iu ny, router gi mt thng ip DVMRP Graft ti

router pha trn thng bo n mun c ghp tr li cy multicast. Sau khirouter pha trn nhn c n s phn hi li bng thng ip Graft-Ack v

chuyn tip lu lng multicast xung router pha di. Trn hnh 2.7 tip tc

m t mng nh phn trc, gi s lc ny my nhn 2 trn router Y tham gia

vo nhm multicast v nhn d liu t ngun S gi ti nhm G. Router Y bit

rng n ang trng thi b ct b khi cy multicast ca ngun S v th n gi

mt thng ip Graft ti router E. Khi router E nhn c thng ip, router E

chuyn trng thi cho cng kt ni vi router Y t trng thi ct b sang trngthi chuyn tip d liu v gi mt thng ip xc nhn Graft-Ack trli router

Y.


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Hnh 2.7: Ghp nhnh trong DVMRP bc 1

Sau router E tip tc gi ti router D mt thng ip Graft yu cu

nhn d liu multicast gi ti nhm G. Cui cng khi router D nhn c thng

ip t router E n phn hi bng mt thng ip Graft-Ack v chuyn tip d

liu multicast qua giao din ca n n router E nh trn hnh 2.8.

Hnh 2.8: Ghp nhnh trong DVMRP bc 2


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2.2 Giao thc PIM Dense Mode

Giao thc PIM (Protocol Independent Multicast) c tn l giao thc

multicast c lp bi v n hot ng c lp vi giao thc nh tuyn IP unicast.

PIM khng quan trng giao thc no c s dng to ra bng nh tuynunicast (bao gm c bng nh tuyn tnh) trn router, m n s dng thng tin t

bng nh tuyn unicast thc hin qu tnh kim tra Reverse Path Forwarding

(RPF) t a ra quyt nh gi d liu. Bi v PIM khng phi duy tr d liu

ca bng nh tuyn, n s khng cn thc hin cc qu trnh gi v nhn cc

thng bo cp nht ng i trong bng nh tuyn gia cc router nh cc giao

thc khc, iu lm gim ng k lu lng truyn trn mng.

PIM c th cu hnh hot ng theo hai cch l dense mode v sparse

mode, trong phn ny chng ta s tm hiu v PIM dense mode (PIM DM) bao

gm cc qu trnh cbn nh: tm kim hng xm, ct b v ghp thm nhnh

trn cy phn phi multicast, cch xc nhn.

2.2.1 Tm kim hng xm

2.2.1.1 Thngip Hello

Cng ging nh giao thc DVMRP, PIM-DM s dng c ch tm kim

hng xm thit lp mi lin kt vi router hng xm. Trong PIM-DMv1 thng

ip tm kim c tn l Router Query c ng gi trong thng ip IGMP v

c gi ti a ch 224.0.0.2 (a ch all-routers). Trong PIM-DMv2 thng ip

thm d c tn l Hello c gi theo chu k 30 giy ti a ch 224.0.0.13 (a

ch all-PIM-routers). Trong thng ip Hello cha mt gi tr Holdtime thng

bo cho cc my nhn bit khong thi gian hiu lc ca kt ni gia hai my b

ht nu khng c thng ip Hello khc c gi trong thi gian .

2.2.1.2 Routerc chnh

Ngoi vic thit lp mi lin kt hng xm, thng ip PIM Hello cng

c s dng tm ra routerc chnh gi d liu (Designated Router

DR) cho mng a truy cp. Thng qua thng ip Hello cc router s bit c

router no trn mng c gi tra ch IP cao nht, v router c chn lm


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DR cho mng. Khi trong mt phn on mng c nhiu router cng tn ti, ngi

qun tr mng thng thng cn chnh mt router l DR. Tuy nhin vic thay

i a ch IP ca router chnh mt router l DR thng kh khn hoc

khng th thc hin. thc hin iu ny, trong thng ip PIMv2 Hello thm

vo mt la chn vu tin DR-Priority. Khi cc router c u tin cao

sc chn lm DR, nu c hai hay nhiu router cng u tin th gi tr IP

c so snh bu chn.

2.2.1.3 Cy phn phi multicast

Bi v PIM-DM l mt giao thc dense mode, cy ngun (hay cy ng i

ngn nht) c s dng ch ra qu trnh phn phi d liu ti cc my nhn

trn mng. Cc cy ngun c xy dng bng cch s dng cch qung b vloi b (flood and prune) ngay khi ngun multicast bt u truyn d liu. Khng

nh DVMRP l giao thc s dng bng nh tuyn multicast ca ring n, PIM-

DM s dng thng tin v hng xm ca n xy dng cy ngun. Trong PIM-

DM cc router kt ni vi ngun c cho l trn cy ng i ngn nht SPT

v cc hng xm PIM-DM khc cc nhnh pha dui ca ngun d liu. Cy

SPT ban u chnh l cy qung b (broadcast tree) bi v router gi d liu ti

tt c cc hng xm ca n, m khng bit trn cc router c tn ti cc my

nhn d liu hay khng. Hnh 2.9 th hin mt v d v vic qung b d liu

multicast trn mng PIM-DM xung cy qung b multicast.

Trong mng trn hnh 2.9, ngun d liu multicast gi d liu ti router A

v B t gi tip xung cc router PIM-DM pha di l router C v D. Ta

thy rng lung d liu ban u trc khi c cc hot ng ct nhnh c nhiu

ng i d tha, nh l router C nhn hai lung d liu ging nhau, hay router

C v D cng gi d liu ti mt phn on mng. Cy qung b ny sc iu

chnh loi b d tha khi qu trnh loi b nhnh c hon tt.


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Hnh 2.9: Cy phn phi PIM-DM

2.2.2 Ct nhnh

Cc router PIM-DM gi thng ip ct nhnh Prune ln router pha trn ca

n khi c mt trong cc iu kin sau: khi d liu n t mt giao din khng

phi l giao din RPF hay khi mt router nhn thy phn on mng pha sau n

khng tn ti cc my nhn mun nhn d liu t nhm multicast. Trn hnh

2.10, gi s metric cho ng i t router A n C tt hn ng i t router Bn C, lc router C gi thng ip Prune ti router B v d liu n n trn

giao din khng phi l giao din RPF i vi ngun.

bc tip theo, router B phn hi li thng ip Prune c gi t C v

ng i t router B n router C b loi b khi cy multicast. Ngoi ra router I

l mt router l khng c cc my nhn d liu kt ni ti, v th n gi mt

thng ip Prune ti router E. Router E phn hi li bng cch loi bng i

ti router I v bi v router E cng khng c cc my nhn d liu kt ni trctip n cng s gi d liu ti router C v D. Tuy nhin v my nhn 1 kt ni

trc tip ti cng giao din, router C v D s b qua thng ip Prune t E. iu

c ngha d liu t ngun vn tip tc c gi ti router E v E tip tc gi

thng ip Prune ln router C v D.


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Hnh 2.10: Ct nhnh trong PIM-DM bc 1


Trong cch ct nhnh trn mng a truy cp, cc router PIM-DM mongmun nhn thng ip Join t cc hng xm phn hi li thng ip Prune ca

hng xm khc trn cng mt giao din. Router G v H trong hnh 2.12 l mt v

d ca cch hot ng trn.


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G l mt node l v khng c cc my nhn d liu kt ni ti v th n gi

thng ip Prune ln mng ti router F. Tuy nhin thng ip Prune c gi ti

a ch all-PIM-router v th router H cng nhn c thng ip gi ti F. Bi

v H c cc my nhn yu cu nhn d liu, H s gi mt thng ip PIM Join v

n s hy b thng ip Prune c gi t G. m bo qu trnh Prune hot

ng hiu qu cc router PIM-DM khi nhn mt thng ip Prune s khng x l

ngay m i 3 giy cc router khc gi thng ip Join. Nu sau khong thi

gian ny, router khng nhn c thng ip Join th n s thc hin qu trnh

ct nhnh.

2.2.3 Cch xc nhn

Tr li mng trong hnh 2.12, ngun d liu by gi ch gi ti cc my

nhn trn mng. Tuy nhin vn cn mt vn na, l vic trng lp d liu

c gi bi router C v D ln mng ti my nhn 1. gii quyt vn trn, PIM s dng mt c ch xc nhn bnh chn ra mt router DR cho

ngun multicast. C ch xc nhn hot ng theo quy tc sau: nu mt router

nhn d liu multicast trn cng m cng cng gi d liu t ngun, th router

s gi mt thng ip PIM Assert ti cng m n nhn d liu tm ra router

c la chn. Trong thng ip PIM Assert cha gi tr metric ti ngun, lc


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cc router trn mng kim tra gi tr metric v router no c gi tr metric tt nht

sc chn lm router gi d liu. Cc router khc s ngng gi d liu v loi

b cng ca n ra khi cy multicast. Trong trng hp c nhiu router c cng

metric, a ch IP sc kim tra v router no c a ch IP cao nht sc

chn.

Mng trong hnh 2.13 router C v D cng gi thng ip PIM Assert ln

mng, gi s router C v D c cng metric v router C c a ch IP ln hn. Lc

ny router C sc chn lm router gi d liu cn router D s ngng gi d

liu v loi b giao din ca n ra khi cy multicast.

Hnh 2.13: Xc nhn trong PIM-DM

2.2.4 Ghp nhnh

PIM-DM cng h trkh nng ghp trli cy multicast mt nhnh cy

b ct b trc . Hnh 2.14 th hin mt mng vi mt my nhn th 3 tham

gia vo nhm multicast trn router I.


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Hnh 2.14: Ghp nhnh trong PIM-DM

Khi router I nhn thng ip gia nhp nhm multicast IGMP t my nhn 3,

router I gi mt thng ip Graft ti router E yu cu nhn d liu. Router E

nhn thng ip Graft t router I n tr li bng cch gi li I mt thng ip

Graft-Ack. Bi v trc router E gi thng ip ct b khi cy

multicast v th n cng gi mt thng ip Graft ti router C. Tng t router C

s gi li E mt thng ip Graft-Ack, v lc ny d liu multicast c gi t

router C qua router E v I ti my nhn 3.

2.3 PIM Sparse Mode

2.3.1 M hnh tham gia

PIM-SM tun theo hot ng ca giao thc sparse mode, trong d liu

multicast chc gi ti cc my nhn trn mng khi c yu cu. Trong PIM-

SM yu cu c thc hin thng qua c ch tham gia tng minh (Explicit

Join), thng ip PIM Join sc gi qua tng chng n c gc ca cy

multicast (gc ca cy multicast trong PIM-SM l router RP i vi cy chia s

hay l router kt ni trc tip vi ngun d liu trong cy ng i ngn nht).

Khi thng ip Join i theo cy ln ti gc, cc router trn ng i to mt

trng thi gi d liu multicast v th d liu multicast yu cu sc gi tr


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li cy. Tng t, khi d liu multicast khng c yu cu na, router s gi

thng ip Prune ln gc cy ct b cc lung d liu khng cn thit. Khi

thng ip Prune i qua cc chng trn cy cc router cng cp nht trng thi

ca n, bi trng thi gi d liu tng ng vi nhm multicast. im quan

trng trong m hnh tham gia tng minh l trng thi gi d liu trong cc

routerc to ra nh l kt qu ca thng ip Join. l s khc bit quan

trng so vi giao thc dense mode, l cc giao thc m trng thi gi d liu ca

routerc to bi d liu multicast n router.

2.3.2 Cy chia s

Cc hot ng ca PIM-SM xoay quanh mt cy chia s mt chiu, trong

gc cy c gi l im hn RP (Rendezvous Point). Cy chia s cn c mttn khc l cy RP c vit tt l RPT v gc ca n ti im RP. Router

chng cui (router kt ni trc tip vi my nhn d liu) mun nhn d liu t

mt nhm multicast n s tham gia vo cy chia s. Khi router khng mun nhn

d liu t nhm multicast na, n s ct b khi cy chia s.

2.3.2.1 Tham gia cy chia s

Trn hnh 2.15 th hin bc u tin trong qu trnh tham gia vo cy chia

s, trong bc ny my nhn 1 tham gia vo nhm multicast G bng cch githng ip IGMP Report.

Hnh 2.15: Tham gia cy chia s PIM bc 1


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Bi v my nhn 1 l my u tin tham gia vo nhm multicast, router C

to mt trng thi (*, G) trong bng nh tuyn multicast ca n cho nhm G.

Router C t giao din ca n vo danh sch cc cng ra ca thc th (*, G) nh

trn hnh 2.16 (c th hin bng mi tn). Bi v router C to mt thc th

trng thi mi (*, G) n cng gi mt PIM (*, G) Join ti router RP tham gia

vo cy chia s (c th hin bng mi tn t nt trong hnh 2.16). gi gi

tin ti RP router C s dng bng nh tuyn unicast xc nh giao din cn

chuyn gi tin.


Router RP nhn thng ip (*, G) Join v bi v n cha c trng thi cho

nhm multicast G. Router RP s to mt thc th trng thi (*, G) trong bng

nh tuyn multicast ca n v thm mt ng i ti router C vo danh sch cc

cng ra. Lc ny, cy chia s cho nhm G c xy dng t router RP ti C v

my nhn 1 nh trn hnh 2.17, d liu multicast cho nhm G c gi ti router

RP v theo cy chia si xung my nhn 1.


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Hinh 2.17: Tham gia cy chia s PIM bc 3

Tip tc v d v gi s rng c mt my nhn 2 tham gia vo nhm

multicast nh trn hnh 2.18. Tng t my nhn cng thng bo n mun nhn

d liu multicast trn nhm G bng cch gi thng ip IGMP ti router E.


Router E cha c trng thi cho nhm G, n s to mt thc th trng thi

mi trong bng nh tuyn multicast ca n v thm cng vo danh sch cng ra

(c th hin bng mi tn trong hnh 2.19). Router gi mt thng ip (*, G)

Join ti router C gia nhp cy chia s (th hin bng mi tn t nt trong

hnh 2.19).


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Khi router C nhn thng ip (*, G) t router E n nhn thy rng tn ti

trng thi (*,G) cho nhm G. V th router C n gin ch cn thm ng i ti

router E vo danh sch cng ra. Trong hnh 2.20 th hin kt qu ca cy chia s,

bao gm router C v E vi cc ng i ti cc my nhn d liu.


2.3.2.2 Ct nhnh trn cy chia s

Bi v PIM-SM s dng m hnh Explicit Join xy dng cy multicast v

th n cng s dng thng ip Prune ct b cc nhnh cy khi chng khngcn nhn d liu na. Trn hnh 2.21 my nhn 2 ri nhm multicast G bng

cch gi thng ip IGMP Leave.


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Hnh 2.21: Ct nhnh trn cy chia s bc 1

Router E ch c mt my nhn tham gia vo nhm multicast v th cng

b loi b khi danh sch cng ra ca trng thi (*, G), iu ny c th hin

bng cch b mi tn t router E trn hnh 2.22. Khi giao din b loi b, danh

sch cng ra cho thc th (*, G) l rng, iu ch ra router E khng cn nhn

d liu cho nhm multicast G na. Lc router E gi mt thng ip (*, G)

Prune ti router RP yu cu ct b n khi nhnh cy multicast.


Khi router C nhn thng ip Prune, n loi bng i ti router E trong

danh sch cc cng ra ca thc th (*, G). Tuy nhin router C vn cn my nhn

1 kt ni v nhn d liu multicast t nhm G, v th router C vn tip tc duy tr

cy chia s do thng ip Prune s khng c gi tip ti router RP.


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2.3.3 Cy ng i ngn nht

Khng ging nh giao thc sparse mode khc, giao thc PIM-SM khnggii hn ngi dng phi nhn d liu multicast thng qua cy chia s. Cc my

nhn cng c th nhn d liu multicast thng qua cy ng i ngn nht SPT.

Bng cch tham gia cy SPT, d liu multicast sc a trc tip ti my

nhn m khng thng qua router RP, iu gip gim ti trn router RP. Nhc

im ca cy SPT l router phi to v duy tr cc thc th trng thi (S, G) trong

bng nh tuyn multicast ca chng. Tuy nhin, vic duy tr thng tin trng thi

trn cc router PIM-SM s dng cy ng i ngn nht vn t hn so cc routers dng giao thc dense mode. L do l cch qung b v loi bc s dng

bi cc giao thc dense mode yu cu cc router duy tr trng thi (S, G) trong

bng nh tuyn cho tt c cc ngun hot ng, cho d khng c cc my nhn

yu cu nhn d liu. iu l gii ti sao giao thc PIM-SM c khuyn

khch s dng hn so vi cc giao thc dense mode.

2.3.3.1 Tham gia cy ngi ngn nht

Bng cch gi mt thng ip (S, G) Join ti ngun, router c th tham gia

vo cy ng i ngn nht cho ngun S v c th nhn d liu multicast

c gi t ngun ti nhm multicast G. Trn hnh 2.24 th hin mt v d ca

thng ip (S, G) Join c gi ti ngun tham gia cy SPT. Trong my

nhn 1 tham gia vo nhm G v yu cu nhn d liu t nhm.


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Hnh 2.24: Tham gia cy ng i ngn nht bc 1Bi v router E mun tham gia cy SPT cho ngun S n gi mt thng ip

(S, G) Join ti ngun. Khi router C nhn thng ip tham gia n to mt thc th

(S, G) vo bng nh tuyn ca n v thm giao din nhn gi tin vo danh

sch cng ra (c th hin bng mi tn trn hnh 2.25). Bi v router to mt

trng thi mi (S, G) v vy n cng gi mt thng ip (S, G) Join ti ngun

(c th hin bng mi tn t nt trn hnh 2.25).

Hnh 2.25: Tham gia cy ng i ngn nht bc 2


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Cui cng khi router A nhn c thng ip (S, G) Join n thm ng i

vo danh sch cng ra ca thc th (S, G) v hnh thnh cy ng i ngn nht

SPT t ngun S ti my nhn nh hnh 2.26.

Hnh 2.26: Tham gia cy ng i ngn nht bc 3

2.3.3.2 Ct nhnh trn cy ngi ngn nht

PIM-SM cng c th ct b cc nhnh trn cy SPT thng qua thng ip

(S, G) Prune tng t nh qu trnh ct nhnh trn cy chia s. Xt mng nh

trn hnh 2.27, gi s lc ny router E khng cn cc my nhn d liu na, v

th khng cn thit gi d liu n n. V vy router E gi mt thng ip (S, G)

Prune ti ngun yu cu ct b n khi cy SPT.

Hnh 2.27: Ct nhnh trn cy ng i ngn nht bc 1


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Router C nhn c thng ip (S, G) Prune n loi b cng nhn thng

ip ra khi danh sch cng ra ca thc th (S, G). Lc ny danh sch cng ra

cho thc th (S, G) l rng v th router C gi mt thng ip (S, G) Prune ti

ngun yu cu ct b n ra khi cy multicast.


Khi router A nhn c thng ip (S, G) Prune t C n loi b cng

nhn thng ip ra khi danh sch cng ra. Tuy nhin, v router A l router kt

ni trc tip vi ngun S nn router A khng gi thng ip Prune na, m n

chn gin loi b cc gi tin c gi n t S v danh sch cng ra ca (S, G)

by gil rng.


2.3.4 Thng ip Join/Prune

Cc phn trc y chng ta nhc n thng ip PIM Join v PIM

Prune nh hai thng thng ip khc nhau vi mc ch lm sng t qu trnh


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tham gia hay ct b nhnh. Tuy nhin thc t PIM ch s dng mt thng ip

n Join/Prune cho c hai chc nng. Mi thng ip Join/Prune cha c hai

danh sch Join v Prune v mt trong hai danh sch c th rng. Cc thc th

Join v Prune trong thng ip Join/Prune c cng mt nh dng chung, bao

gm cc thng tin nh sau:

a ch ngun multicast: a ch IP ca ngun multicast thc hin qu

trnh Join hay Prune, nu cWildcard c bt th trng ny cha a ch

ca router RP.

a ch nhm multicast: a ch nhm multicast thc hin qu trnh Join

hay Prune.

C Wildcard (WC bit): ch ra rng thc th l mt thng ip (*, G)

Join/Prune.

CRP Tree (RP bit): thng ip Join/Prune l thch hp v cn c gi

ln cy chia s.

2.3.5 ng k ngun dliu

Trong cy chia s PIM-SM chng ta bit cch router gi thng ip (*,

G) ti cy chia s cho nhm multicast G. Tuy nhin PIM-SM s dng cy chia s

mt chiu nn d liu multicast ch c thi theo chiu t gc cy xung cc

nhnh. V th ngun d liu cn phi c mt cch khc gi d liu ca n ti

router RP. Tuy nhin trc tin router RP cn phi c thng bo v ngun

ang tn ti. lm iu ny PIM-SM s dng thng ip PIM Register v

Register-Stop thc hin qu trnh ng k ngun d liu. Qu trnh ny s

thng bo vi router RP mt ngun ang hot ng trn mng v phn phi cc

gi tin multicast u tin ti RP tip tc c gi xung cc nhnh cy.

2.3.5.1 Thngip PIM RegisterThng ip PIM Registerc gi t router DR kt ni vi ngun d liu

ti router RP, vi hai mc ch l:

Bo cho router RP bit rng S l ngun hot ng v ang gi d liu ti

nhm G.


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Gi cc gi tin multicast u tin t S (cc gi tin c ng gi trong mt

thng ip PIM Register) ti RP gi xung cy chia s ti my nhn.

V th khi mt ngun multicast bt u gi d liu, router DR nhn gi tin

multicast t ngun v to mt thc th trng thi (S, G) trong bng nh tuyn

multicast. Tip router DRng gi mi gi tin multicast trong cc thng ip

PIM Register ring r v gi ti router RP. Khi router RP nhn mt thng ip

PIM Register, u tin n s mgi thng ip v nhn c gi tin multicast

trong . Nu gi tin l ca mt nhm multicast c cc my nhn RP gi gi tin

xung cc nhnh cy ph hp. Sau router RP tham gia vo cy ng i ngn

nht ca ngun S v c th nhn d liu trc tip t ngun m khng cn nhn

thng qua thng ip PIM Register na. Nu nh gi tin multicast trong thng

ip PIM Register khng c my no yu cu nhn (lc danh sch cng ra cho

trng thi (S, G) l rng) th router RP s loi b thng ip multicast v khng

gi thng ip Join trli ngun.

2.3.5.2 Thngip PIM Register Stop

Router RP s dng thng ip PIM Register-Stop thng bo vi router

DR ngng vic gi cc thng ip PIM Register khi tha mn mt trong hai iu

kin sau:

Khi router RP bt u nhn d liu multicast t ngun thng qua cy (S, G)

SPT gia ngun v RP.

Khi router RP khng cn nhn d liu na v trn n khng cn tn ti cc

my yu cu nhn d liu multicast.

Khi router DR nhn thng ip Register-Stop n bit router RP khng cn

nhn d liu na v th n ngng vic ng gi v gi cc thng ip Register.

2.3.6 Chuyn tcy chia s sang cy ng i ngn nht

PIM-SM h trkh nng cho php router DR chng cui (l router kt

ni trc tip vi cc my nhn d liu) c th chuyn t cy chia s sang cy

SPT cho mt ngun multicast. iu ny c thc hin tng thng qua vic

t ra mt ngng SPT-Threshold ca bng thng mng, khi gi tr bng thng

t ngng router DR s tham gia vo cy SPT.


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Xt mng c hai ngun v hai my nhn nh trn hnh 2.30, bi v router C

l router DR chng cui n c mt la chn chuyn sang cy SPT cho ngun

S1 v S2. lm router C gi thng ip (S1, G) Join ti ngun G nhc

th hin bng mi tn t nt trn hnh 2.30.

Hnh 2.30: Chuyn sang cy SPT bc 1

Khi router A nhn thng ip Join, n thm cng nhn thng ip vo danh

sch cng ra cho thc th (S1, G) vo bng multicast ca n. Lc ny ng i

t router A n router C c thit lp v d liu c th truyn trc tip ti

router C theo cy (S1, G) SPT.

Hnh 2.31: Chuyn sang cy SPT bc 2


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Chng ta c th thy ti thi im ny c hai ng i i vi lung d liu

multicast (S1, G) n router C, l thng qua cy chia s v cy SPT iu ny

gy trng lp d liu cng nh lng ph bng thng mng. V th cn c cch

thng bo vi router RP ct b d liu multicast (S1, G) khi cy chia s.

thc hin iu ny mt kiu c bit ca thng ip Prune c s dng. Thng

ip ny c tn l (S, G) RP-bit Prune bi v n c cRP c gn trong danh

sch cc thc th Prune. Nh phn trc ta bit cRP ch ra rng thng ip

l ph hp vi cy chia s v cn c gi ln trn ti router RP. S dng c

ny trong thng ip (S1, G) Prune v gi n ln cy chia s thng bo ti cc

router trn cy loi b ngun d liu multicast S1 ra khi cy.

Trn hnh 2.32 router C gi mt thng ip (S1, G) RP-bit Prune ti router

RP loi b ngun d liu S1 khi cy multicast. Sau khi nhn c thng iprouter RP trng thi gi d liu multicast ca n v th d liu (S1, G) s khng

c gi xung nhnh cy n router C. Tuy nhin sau khi loi bng i ti

router C danh sch cng ra cho trng thi (S1, G) trn router RP l rng v th n

khng cn nhn d liu multicast t ngun na.

Hnh 2.32: Ct b ngun khi cy chia s bc 3

ngng lung d liu khng cn thit t ngun gi ti, router RP gi

thng ip (S1,G) Prune tr li ngun. Thng ip Prune (c th hin bng


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mi tn t nt trn hnh 2.33) c gi theo tng chng v qua router B trc

khi n router A.


By gicy (S1, G) SPT c ct b nhnh ch cn ng i gia router

A v router C. Router E vn tip tc nhn d liu t router C v n khng bit

router C chuyn qua cy ng i ngn nht. D liu t ngun S2 vn tip tc

c gi qua cy chia s ti cc my nhn 1 v 2 nhng mi tn trn hnh

2.34.



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2.4 Giao thc Multicast Open Shortest Path First

Giao thc Multicast Open Shortest Path First (MOSPF) c nh ngha

trong RFC 1584 l mt mrng ca giao thc nh tuyn unicast trng thi lin

kt Open Shortest Path First (OSPF). MOSPF cung cp s mrng vnh dngd liu v cc c t hot ng t OSPF. S m rng ny cho php d liu

multicast c truyn trn mng OSPF bng cch s dng cy ng i ngn

nht nh l mt phn ca cc router MOSPF. Trong phn ny chng ta s tm

hiu cc khi nim v cch ca hot ng MOSPF bao gm cc phn sau: nh

tuyn multicast trong vng, nh tuyn multicast nhiu vng v nh tuyn

multicast trn nhiu vng t tr (autonomous system - AS).

2.4.1 nh tuyn multicast trong vngMOSPF l m rng ca giao thc nh tuyn unicast OSPF v do vy i

hi OSPF nh giao thc nh tuyn c s. Khi nim c bn ca nh tuyn

MOSPF trong vng da vo gi thit trng thi trong m t OSPF l nu cc

router trong mt vng bit cc phn on mng c cc thnh vin ca nhm

multicast, cc router c th s dng thut ton Dijkstra xy dng cy

ng i ngn nht cho bt k cc cp nhm, mng ngun trong vng.

Mt m rng quan trng ca MOSPF trong nh dng d liu h trmulticast l s dng mt thng ip qung b trng thi lin kt ca nhm (group

Link-State Advertisement LSA nhm). Thng ip LSA nhm ny c pht

tn nh k trong c vng ging nh LSA ca giao thc OSPF. Mi LSA nhm

c cc thng tin cbn sau: a ch nhm multicast, nh danh router qung b,

danh sch cc giao din mng ca router (xc n bi a ch IP) c cc thnh

vin ca nhm.

Sau khi c

sd liu ca cc router trong vng c ng b, s kt hpca LSA nhm vi router v mng LSA cung cp cho mi router MOSPF thng

tin cn thit xy dng cy ng i ngn nht cho cc cp nhm v mng

trong vng. xy dng cy ny mi router MOSPF s dng thut ton Dijkstra

xy dng mt cy ng i ngn nht multicast n c gc ti mng ngun.

Hnh 2.35 l mt v d ca mt vng OSPF c ba ngun multicast v cc thnh


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vin hot ng ca nhm G trn cc v tr khc nhau ca mng. Sau khi cs

d liu c ng b mi router c kh nng xy dng mt cy SPT cho ngun

1, 2 v 3. Lu rng cy SPT ny l ring bit cho cc cp ngun v mng con,

v khng phn bit cc ngun trn mt mng. V th mc d c 3 ngun trn

mng N3 cho nhm G ch c mt cy SPT cho ngun mng c xy dng.

Hnh 2.35: Vng MOSPF cha ngun v thnh vin nhm G

Hnh 2.36A ch ra kt qu ca cy ng i ngn nht MOSPF (N4, G)

SPT vi gc l mng ngun N4 v cha ngun 1 v 3. Hnh 2.36.B ch ra kt qu

cy (N3, G) SPT vi gc ti mng ngun N3 c cha ngun 2.


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Hnh 2.36: Cy ng i ngn nht MOSPF SPT cho mng N3 v N4

2.4.2 nh tuyn multicast trn nhiu vng

phn trn chng ta tm hiu cch MOSPF nh tuyn trong mt vng

OSPF. Phn ny minh ha cch m MOSPF thc hin chuyn tip gi tin

gia cc vng OSPF. iu ny xy ra khi mt ngun multicast trong mt vng

trong khi ngi nhn trong vng khc. Cch thc MOSPF s dng qun l

nh tuyn multicast trn nhiu vng c nhiu im ging vi cch OSPF thchin. Trong OSPF cc router lin kt mt vng thuc lp th hai ti vng ng

trc c gi l ABR (area border router- router trn bin ca vng) v c

chu trch nhim chuyn tip thng tin nh tuyn (trong dng ca mt thng

ip tm tt LSA - summary LSA) v d liu unicast gia hai vng. Cc router

ABR khng truyn tuyn ng hay cc thng ip LSA gia cc vng, m ch

truyn cc thng ip LSA tm tt gia cc vng.

h trmulticast trn nhiu vng, RFC 1584 nh ngha chuyn tipmulticast lin vng l mt tp con ca cc OSPF ABR trong mng v c cu

hnh thc hin cc tc v multicast lin quan nh: tm tt thng tin thnh vin

nhm trong vng 0 v chuyn tip gi tin multicast gia cc vng. Cc router

thc hin chc nng ny c gi l router multicast trn bin ca vng

(multicast area border routers MABR).


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d liu multicast theo cu trc phn cp ca OSPF (t vng ng trc

ti cc vng lp th hai) router trn vng ng trc cn bit cc router multicast

trn bin ca vng (MABR) no ang c kt ni c thnh vin hot ng ca

nhm multicast. Cc router MABR tm tt thng tin ca thnh vin nhm

multicast trong vng v pht tn ti vng ng trc thng qua LSA nhm. Tuy

nhin, khng nh OSPF LSA tm tt c pht tn i xng xuyn qua bin ca

vng, cc LSA nhm tm tt pht tn khng i xng v ch theo chiu t vng

khng ng trc sang vng ng trc.

Hnh 2.37: Thng ip nhm tm tt trong vng ng trc

Trong v d trn hnh 2.37, vng 1 cha mt thnh vin ca nhm A ( )

v hai thnh vin nhm B ( ). Thng tin thnh vin trong nhm c tm tt

trong thng ip MABR1 v c pht tn n vng ng trc (vng 0) thng

qua LSA nhm. Tng t vng 2 cha hai thnh vin nhm A v thng tin ctm tt v pht tn ti vng ng trc thng qua MABR2.

Hnh 2.38 ch ra 2 ngun hot ng S1 v S2 gi d liu ti cc nhm

multicast tng ng B v A. Thng tin thnh vin nhm c pht tn ti vng

ng trc bi cc router MABR1 v MABR2 cho bit ng i t ngun ti

cc nhm. Theo cy (S1, B) v cy (S2, B) c xy dng trong vng ng


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trc cho php lu lng nhm A v B c truyn ti vng 1 v 2 mt cch thch

hp.

Hnh 2.38: Cy ng i ngn nht SPT trong vng ng trc

Trong v d trn ngun nm trn vng ng trc v d liu c ly

xung ti cc vng khng phi ng trc. Tuy nhin trong thc t thng

xuyn gp phi trng hp cc ngun khng nm trn vng ng trc, trong

trng hp ny MOSPF x l bng cch nh ngha mt c bo hiu ngi

nhn multicast. Cbo hiu ch ra router mong mun nhn tt c cc d liu

multicast. Tt c cc router multicast trn bin vng (MABR) nhn d liu

multicast t cc ngun trong vng khng phi ng trc v t c th chuyn

tip ti cc router trn vng ng trc nu cn. Trn hnh 2.39 th hin mng

vi ngun (S1, B) v (S2, A) by gi trong mng khng phi ng trc.

Ngun (S2, A) trn vng 2 v cy ng i ngn nht cho trng hp nhtuyn cho nhiu vng vn c xy dng bnh thng, tuy nhin lc ny

MABR2 nh du nhn d liu muticast v th n c thm vo cy SPT (S2,

A). Tng t trn vng 1 MABR1 cng c thm vo cy ng i ngn nht

(S1, B). Lc ny da vo cy ng i ngn nht trn vng ng trc cc router

MABR1 v MABR2 c th ti cc vng.


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Hnh 2.39: Ngun trong vng khng phi ng trc

Trn hnh 2.39 ta thy ngun B khng c cc thnh vin ca nhm

multicast hot ng pha ngoi vng 1 tuy nhin lu lng vn c gi ti

MABR1 do kt qu ca vic s dng cbo nhn trn MABR1, iu ny lm

tng bng thng trn mng cng nh cc x l trn router.

2.4.3 nh tuyn multicast trn cc vng ttr

Trong phn ny chng ta s tm hiu v cch m MOSPF thc hin kh

nng nh tuyn trn cc vng t tr (autonomous system - AS). Trong nh tuyn

unicast OSPF s dng cc router ti bin ca cc vng t tr (autonomous system

border routers - ASBR) chuyn tip d liu ti cc min OSPF. Tng t

MOSPF cng s dng cc router multicast trn vng bin (Multicast AS Border

Routers - MASBR) chuyn tip d liu muticast ti cc router trn vng

ng. Khi lu lng vo t mt min khc thng qua MASBR lu lng ny

c chuyn qua ng trc ti MABR da vo LAS nhm rt gn. Tip theo

d liu t cc router MABR tip tc c pht tn ti cc thnh vin nhm

multicast da vo cy ng i ngn nht c minh ha nh trn hnh 2.40.


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Hnh 2.40: Lu lng multicast xung cc min MOSPF


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CHNG 3

SDNG ACCESS GRID XY DNG

H THNG HI NGH TRUYN HNH DA TRN

IP MULTICAST

3.1 Cc khi nim chung v dch v hi ngh truyn hnh

Hi ngh truyn hnh cng cng ln u tin c t chc vo thng

04/1903 gia tr sAT&T v Bell Laboratory. Vo thi im m thanh v

hnh nh c truyn i vi cht lng chp nhn c. V t vn trao

i trc tip qua khong cch xa c quan tm nhiu. n nm 1934 cuc chin

v chun gia cc cng ty bt u v kt thc l chun tivi tng t vi bng

thng 4,2MHz (525 dng, 30 nh/giy). Ti nm 1964 AT&T gii thiu sn

phm hi ngh truyn hnh u tin l Picturephone. H thng ny ch yu cu

cng sut x l l 1MHz v cung cp tnh nng s dng chung d liu u tin.

Ti nm 1971 c hi ngh truyn hnh vt i dng vi h thng LME ca

Ericsson. V ti nhng nm 1990 vi s ra i v pht trin mnh ca mngInternet, hi ngh truyn hnh trn my tnh c gii thiu.

Hi ngh truyn hnh dng cbn nht l vic truyn hnh nh v li ni

mt cch ng b gia hai hay nhiu a im xa nhau ging nh cc nhm trao

i thng tin ti cng mt a im. Vic ny c thc hin bng cch s dng

my quay ( lu tr v truyn hnh nh ti cc a im khc), microphone (

bt v chuyn li ni ti cc a im khc) v loa ( c th nghe c t cc

a im khc). Mc d c th c nhiu yu t phc tp ha h thng, tuy nhinv cbn mt h thng hi ngh truyn hnh vn cn thit cc yu t nu trn.

Cc ng dng ca trng hp u bao gm o to t xa, cc cuc hp, hi

tho, t vn v thng tin t xa. Cc ng dng cho trng hp sau bao gm vic

truy cp ti cc vng su, vng xa nh y t t xa, o to t xa, truy cp vo cc

thit b nguyn t, trm v tr Hi ngh truyn hnh cng c dng quan


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st ng vt

tim hieu cong nghe ip muliticast 4291

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