tim hieu cong nghe ip muliticast 4291
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TRNG . KHOA.
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Bo co tt nghip
ti:
TM HIU CNG NGH IP MULITICAST
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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 N
MC LC
DANH MC CC T VIT TT
DANH SCH HNH V
DANH SCH CC BNG
M U................................................................................................................ 1
1. t vn .................................................................................................. 1
2. i tng v mc tiu lun vn................................................................. 1
3. Hng tip cn ........................................................................................... 2
4. Kt cu ca lun vn .................................................................................. 2
CHNG 1 ........................................................................................................... 3
C BN V IP MULTICAST.............................................................................. 3
1.1 M u ......................................................................................................... 3
1.2 Cc thnh phn tham gia vo truyn thng multicast .................................. 5
1.3 a ch multicast .......................................................................................... 7
1.4 Cy phn phi multicast............................................................................... 9
1.4.1 Cy ngun ............................................................................................. 9
1.4.2 Cy chia s .......................................................................................... 10
1.5 Chuyn tip multicast................................................................................. 13
1.6 ng trc multicast.................................................................................. 15
1.7 Giao thc qun l nhm Internet ............................................................... 17
1.7.1 Giao thc IGMPv1.............................................................................. 17
1.7.1.1 Thng ip Host Membership Report.......................................... 18
1.7.1.2 Thng ip Host Membership Query........................................... 19
1.7.2 Giao thc IGMPv2.............................................................................. 19
1.7.2.1 La chn router truy vn.............................................................. 20
1.7.2.2 Thng ip ri nhm.................................................................... 21
1.7.2.3 Truy vn cho tng nhm.............................................................. 21
1.7.3 Giao thc IGMPv3.............................................................................. 21
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I
1.7.3.1 Lc d liu ................................................................................... 21
1.7.3.2 Thng ip IGMPv3 Host Membership Query ........................... 22
1.7.3.3 Thng ip IGMPv3 Host Membership Report........................... 23
CHNG 2 ......................................................................................................... 25
NH TUYN MULTICAST ............................................................................. 25
2.1 Giao thc nh tuyn multicast vct khong cch ................................... 25
2.1.1 Tm kim hng xm ............................................................................ 25
2.1.2 Trao i thng bo nh tuyn ............................................................ 26
2.1.3 Ct nhnh ............................................................................................ 29
2.1.4 Ghp nhnh ......................................................................................... 31
2.2 Giao thc PIM Dense Mode ...................................................................... 33
2.2.1 Tm kim hng xm ............................................................................ 33
2.2.1.1 Thng ip Hello ......................................................................... 33
2.2.1.2 Router c ch nh.................................................................... 33
2.2.1.3 Cy phn phi multicast............................................................... 34
2.2.2 Ct nhnh ............................................................................................ 35
2.2.3 C ch xc nhn .................................................................................. 37
2.2.4 Ghp nhnh ......................................................................................... 38
2.3 PIM Sparse Mode....................................................................................... 39
2.3.1 M hnh tham gia ................................................................................ 39
2.3.2 Cy chia s .......................................................................................... 40
2.3.2.1 Tham gia cy chia s .................................................................... 40
2.3.2.2 Ct nhnh trn cy chia s............................................................ 43
2.3.3 Cy ng i ngn nht ...................................................................... 45
2.3.3.1 Tham gia cy ng i ngn nht................................................ 45
2.3.3.2 Ct nhnh trn cy ng i ngn nht ....................................... 47
2.3.4 Thng ip Join/Prune ........................................................................ 48
2.3.5 ng k ngun d liu........................................................................ 49
2.3.5.1 Thng ip PIM Register............................................................. 49
2.3.5.2 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 ........................................... 54
2.4.1 nh tuyn multicast trong vng......................................................... 54
2.4.2 nh tuyn multicast trn nhiu vng ................................................. 56
2.4.3 nh tuyn multicast trn cc vng t tr............................................ 59
CHNG 3 ......................................................................................................... 61
S DNG ACCESS GRID XY DNG .......................................................... 61
H THNG HI NGH TRUYN HNH DA TRN IP MULTICAST ........ 61
3.1 Cc khi nim chung v dch v hi ngh truyn hnh .............................. 61
3.1.1 H thng hi ngh truyn hnh ............................................................ 62
3.1.2 Cc thnh phn c bn ca hi ngh truyn hnh ................................ 63
3.2 Giao thc RTP............................................................................................ 64
3.2.1 Khun dng RTP header ..................................................................... 64
3.2.2 Cc ng dng s dng RTP ............................................................... 65
3.2.2.1 Thoi hi ngh n gin ............................................................... 65
3.2.2.2 Thoi v truyn hnh hi ngh ...................................................... 67
3.2.2.3 B trn v b bin dch ................................................................ 67
3.3 ng b lung hnh nh v m thanh ........................................................ 68
3.4 S dng Access Grid xy dng mt hi ngh truyn hnh......................... 70
3.4.1 Cc thnh phn ca Access Grid......................................................... 70
3.4.2 S dng Access Grid client tham gia vo hi ngh truyn hnh..... 73
KT LUN.......................................................................................................... 76
HNG PHT TRIN CA TI ............................................................... 77
TI LIU THAM KHO
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II
DANH MC CC T VIT TT
T vit tt Vit y Ngha ting Vit
ABR Area Border Router Router bin vng
AG Access Grid Phn mm h tr xy 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 Router c la chn
DVMRP Distance Vector Multicast
Routing Protocol
Giao thc nh tuyn multicast vc-
t khong 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 B iu 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
Giao thc nh tuyn multicast c
lp theo m hnh tp trung
PIM-SM Protocol Independent
Multicast Sparse Mode
Giao thc nh tuyn multicast c
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 ......................................................... 3
Hnh 1.2: Cc thnh phn tham gia vo truyn thng multicast ............................ 6
Hnh 1.3: nh dng ca a ch IP lp D.............................................................. 7
Hnh 1.4: nh x a ch IP multicast sang a ch MAC...................................... 8
Hnh 1.5: Cy ng i ngn nht ca host A....................................................... 9
Hnh 1.6: Cy ng i ngn nht ca host B ..................................................... 10
Hnh 1.7: Cy chia s ........................................................................................... 11
Hnh 1.8: Cy chia s hai chiu............................................................................ 12
Hnh 1.9: Cy chia s mt chiu s dng cy SPT .............................................. 12
Hnh 1.10: Cy chia s mt chiu s dng nh tuyn unicast ............................ 13
Hnh 1.11: Gii hn TTL ..................................................................................... 14
Hnh 1.12: C ch ng hm lin kt cc c o multicast............................... 15
Hnh 1.13: ng gi IP multicast theo c ch tunneling..................................... 16
Hnh 1.14: C ch ng hm lin kt cc MRouter .......................................... 16
Hnh 1.15: Thng ip IGMPv1 .......................................................................... 18
Hnh 1.16: Thng ip IGMPv2 .......................................................................... 19
Hnh 2.1: Tm hng xm trong DVMRP ............................................................. 26
Hnh 2.2: Trao i nh tuyn DVMRP bc 1................................................... 27
Hnh 2.3: Trao i nh tuyn DVMRP bc 2................................................... 28
Hnh 2.4: Trao i nh tuyn DVMRP bc 3................................................... 29
Hnh 2.5: Ct nhnh trong DVMRP bc 1 ........................................................ 30
Hnh 2.6: Ct nhnh trong DVMRP bc 2 ........................................................ 31
Hnh 2.7: Ghp nhnh trong DVMRP bc 1 ..................................................... 32
Hnh 2.8: Ghp nhnh trong DVMRP bc 2 ..................................................... 32
Hnh 2.9: Cy phn phi PIM-DM ...................................................................... 35
Hnh 2.10: Ct nhnh trong PIM-DM bc 1...................................................... 36
Hnh 2.11: Ct nhnh trong PIM-DM bc 2...................................................... 36
Hnh 2.12: Ct nhnh trong PIM-DM bc 3...................................................... 37
Hnh 2.13: Xc nhn trong PIM-DM................................................................... 38
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III Hnh 2.14: Ghp nhnh trong PIM-DM............................................................... 39
Hnh 2.15: Tham gia cy chia s PIM bc 1...................................................... 40
Hnh 2.16: Tham gia cy chia s PIM bc 2...................................................... 41
Hinh 2.17: Tham gia cy chia s PIM bc 3...................................................... 42
Hnh 2.18: Tham gia cy chia s PIM bc 4...................................................... 42
Hnh 2.19: Tham gia cy chia s PIM bc 5...................................................... 43
Hnh 2.20: Tham gia cy chia s PIM bc 6...................................................... 43
Hnh 2.21: Ct nhnh trn cy chia s bc 1 ..................................................... 44
Hnh 2.22: Ct nhnh trn cy chia s bc 2 ..................................................... 44
Hnh 2.23: Ct nhnh trn cy chia s bc 3 ..................................................... 45
Hnh 2.24: Tham gia cy ng i ngn nht bc 1.......................................... 46
Hnh 2.25: Tham gia cy ng i ngn nht bc 2.......................................... 46
Hnh 2.26: Tham gia cy ng i ngn nht bc 3.......................................... 47
Hnh 2.27: Ct nhnh trn cy ng i ngn nht bc 1 ................................. 47
Hnh 2.28: Ct nhnh trn cy ng i ngn nht bc 2 ................................. 48
Hnh 2.29: Ct nhnh trn cy ng i ngn nht bc 3 ................................. 48
Hnh 2.30: Chuyn sang cy SPT bc 1 ............................................................ 51
Hnh 2.31: Chuyn sang cy SPT bc 2 ............................................................ 51
Hnh 2.32: Ct b ngun khi cy chia s bc 3 ............................................... 52
Hnh 2.33: Ct b ngun khi cy chia s bc 4 ............................................... 53
Hnh 2.34: Ct b ngun khi cy chia s bc 5 ............................................... 53
Hnh 2.35: Vng MOSPF cha ngun v thnh vin nhm G ............................ 55
Hnh 2.36: Cy ng i ngn nht MOSPF SPT cho mng N3 v N4.............. 56
Hnh 2.37: Thng ip nhm tm tt trong vng ng trc.............................. 57
Hnh 2.38: Cy ng i ngn nht SPT trong vng ng trc ........................ 58
Hnh 2.39: Ngun trong vng khng phi ng trc......................................... 59
Hnh 2.40: Lu lng multicast xung cc min MOSPF .................................. 60
Hnh 3.1: Thnh phn ca hi ngh truyn hnh .................................................. 63
Hnh 3.2: Khun dng RTP header ...................................................................... 64
Hnh 3.3: Cc thnh phn ca Access Grid ......................................................... 70
Hnh 3.4: Desktop node........................................................................................ 71
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III Hnh 3.5: Office node........................................................................................... 72
Hnh 3.6: Room node ........................................................................................... 72
Hnh 3.7: Mi quan h gia multicast v Access Grid ........................................ 73
Hnh 3.8: Profile Dialog....................................................................................... 73
Hnh 3.9: in a ch virtual venue kt ni ................................................... 73
Hnh 3.10: Venue client ....................................................................................... 74
Hnh 3.11: Ca s video....................................................................................... 74
Hnh 3.12: Ca s audio....................................................................................... 75
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III
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IV
DANH SCH CC BNG
Bng 1.1: Cc trng trong thng ip IGMPv1................................................. 18
Bng 1.2: Cc trng trong thng ip IGMPv2................................................. 20
Bng 1.3: Cc trng trong thng ip IGMPv3 Host Membership Query........ 22
Bng 1.4: Cc trng trong thng ip IGMPv3 Host Membership Report ....... 24
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1
M U
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
t im ti im, tc l d c truyn t mt ngi gi ti mt ngi nhn.
Tuy nhin vi mt s ng 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 tr nn 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 t im ti im. Mt cch khc thc hin vic truyn d
liu t im 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 c bn 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 c bn 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 p
dng ca IP multicast vo cc ng dng.
4. Kt cu ca lun vn
Lun vn gm phn m u, 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
C BN V IP MULTICAST
1.1 M u
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 th c 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 liu
c 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 tr multicast cung cp nhiu dch v v cc ng dng cho
ngi s dng u cui. Nhiu ng dng h tr multicast l cc ng dng a
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4 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 tr ti 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 mng
v cc giao thc truyn ti a phng tin c tm quan trng i vi nh vn
hnh mng.
Multicast khng ch em 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 th
thnh thong c to ra khi cc topo mng multicast thay i. Trong tng lai
vic trin khai IPv6 s em 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 s c gii quyt d dng
hn v bng thng s c 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 h n 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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5 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 tr multicast 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 c ch k tha
i vi IP multicast, cc giao thc lp cao hn khng h tr n. Mc d cc giao
thc 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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6
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 lng
nghe 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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7 Host (bao gm ngun hoc ch): l cc l cc my tnh tham gia kt ni
vo mng v h tr qu trnh gi v nhn d liu multicast.
Router: l cc router h tr giao 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 b u 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 tr qu trnh nh tuyn v gi d liu multicast.
1.3 a ch multicast
Cc 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 c ch tng ng vi giao thc phn gii a ch nh
trong truyn thng unicast, mt dng gi tr c bit dnh ring cho a ch MAC
ca multicast s c dng. Cc a ch ny bt u bng 01005E, phn 28 bit
sau ca a ch IP multicast s c nh x vo 23 bit thp ca a ch MAC
bng mt gii thut n gin.
Multicast Group ID 0 1 1 1 Class D
28 bits
-
8
Hnh 1.4: nh x a ch IP multicast sang a ch MAC
Hnh 1.4 cho thy c ch nh x a ch, ch c 23 bit cui ca a ch l
c chp t a 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 ch c 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 c nh 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 th c dng li nhiu ln.
28 bit
nh x sang a ch MAC Multicast
MAC Address 0 0 0 0 0 0 0 1 0 0000000010111010
1110
5 bit
Khng s dng
01 00 5E X Y Z
X Y Z
IP Multicast
224 - 239
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