Giới thiệu tổng quan về multicast
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Multicast
1
Spencer Tsai
Mobile Communication & Broadband Network Lab
CSIE
Fu-Jen Catholic University
Introduction to Multicast
Multicast
2
Outline
•
Overview
•
IGMP
•
Multicast Routing on the Internet
•
Multicast Routing between Domains
•
Reference
Multicast
3
Overview
•
Unicast
•
Multicast
•
Multicast Characteristic
•
IP Multicast Address
•
Examples of permanent groups
•
Architecture of Multicast
Multicast
4
Unicast
Host
Router
． Point to point
． N receivers, send n times
． Not suitable for group communication
Receiver
Multicast
5
Multicast
Host
Router
． 1 sender and n receivers
． N receivers, only send 1 times
． Suitable for group communication
Receiver
Multicast
6
Benefits of Multicast
•
Saves bandwidth by enhancing network
efficiency in distribution of data
•
Group communication and services
•
Supports distributed applications
–
distance learning
–
videoconferencing
•
Reduces the cost to deploy applications
Multicast
7
Multicast Characteristic
•
RFC 1112
•
Each multicast group identified by class-
D IP address
•
Receivers can present anywhere
•
Receivers can join and leave anytime
•
Sender don’t need to be a member
•
No membership list exist, use routers to
manage groups
Multicast
8
IP Multicast Address
•
Multicast address range
Class D IP Address-higher order 4 bits are set
224.0.0.0 239.255.255.255
1 1 1 0
Multicast address
1 1 0
Net ID
8 16 24
32
IP system
1 0
Net ID
IP system
0
Net ID IP system
Class D
Class C
Class B
Class A
Multicast
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Examples of permanent groups
All DVMRP routers in a subnet224.0.0.4
Not allocated224.0.0.3
Routers with RIP Version 2 in a
subnet
224.0.0.9
All routers in a subnet224.0.0.2
All systems in a subnet224.0.0.1
Reserved224.0.0.0
Multicast
10
Architecture of Multicast
Sender
Router
Receiver
IGMP
IGMP version 2
Multicast Routing
Multicast
11
Outline
•
Overview
•
IGMP
IGMP
•
Multicast Routing on the Internet
•
Multicast Routing between Domains
•
Reference
Multicast
12
IGMP
•
Internet Group Management Protocol (IGMP)
•
Group management within edge networks
•
RFC 1112 – IGMP version 1
•
RFC 2236 – IGMP version 2 (widely uesd)
•
Similar to the ICMP(Internet Control Message Protocol)
•
Router sends query to their directly hosts to manage group
membership
•
Different Hosts may join more than one multicast group
Multicast
13
IGMP – Join a Group
•
Joining members sends report
•
Different hosts can join different multicast group
Multicast Router
Host 1 Host 2 Host 3
224.2.2.3
ReportReport
224.2.2.2
Multicast
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IGMP – General Query
Host 1 Host 2 Host 3
General query to
224.0.0.1
Multicast Router
•
Router periodically sends general query to
224.0.0.1(all systems in a subnet)
Multicast
15
IGMP – Maintaining a Group
suppress
Host 1 Host 2 Host 3
224.2.2.2224.2.2.2
Report
224.2.2.2
224.2.2.2
•
Two steps:
First, router sends general query
Second, member send report
•
Only one member needs to send report
Multicast Router
General query to
224.0.0.1
Multicast
16
IGMP – Leaving a Group
Host 1 Host 2 Host 3
General query to
224.0.0.1
Multicast Router
•
Router continue to send general query periodically
•
Members silently leave group
•
No report receive by router
•
Group times out
Multicast
17
IGMP - Querier Selection
Host 1 Host 2 Host 3
MRouter 1
1.1.1.1
MRouter 2
1.1.1.2
•
Initially, all routers are querier and send query
•
Then, only one router with the lowest IP address is
selected as the actual Querier
•
The other routers are Non-Querier
Multicast
18
Outline
•
Overview
•
IGMP
•
Multicast Routing on the Internet
Multicast Routing on the Internet
•
Multicast Routing between Domains
•
Reference
Multicast
19
Multicast Routing on the Internet
•
DVMRP
•
MOSPF
•
PIM-DM
•
PIM-SM
•
CBT
Multicast
20
DVMRP
•
Distance Vector Multicast Routing Protocol
(DVMRP)
•
Distance vector algorithm that determines the
shortest path (hop count)
•
Like RIP, maintains a routing table
•
Uses RPF(Reverse Path Forwarding)
–
The first data is flooded to the entire network
–
No members or terminating membership, do pruning
Multicast
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DVMRP (cont.)
•
Graft is used to reconnect an old area or
connect a new area
–
Member to source
•
Graft ack. Indicates that a graft has been
received correctly
–
Source to member
•
Designated forwarder
–
First, lowest metric to a source
–
Second, lowest IP address
Multicast
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MOSPF
•
Multicast Extensions to Open Shortest Path
First
•
OSPF
–
Hello
–
Synchronize database description
–
Link state advertisement
•
MOSPF
–
Local group membership must be known in the routers
–
A separate multicast tree has to be calculated for each
pair consisting of sender and group G(S,G)
Multicast
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MOSPF (cont.)
Autonomous System
BR
BR
BR
R
Boundary AS
router
R
Domain
Domain
Domain
Backbone
AS
Multicast
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PIM-DM
•
Protocol Independent Multicasting-
Dense Mode (PIM-DM)
•
Members are not widely distributed,
density of group member is very high
•
Uses flooding, pruning and graft
•
Similar to DVMRP
–
Without the routing information exchange part
–
Differs in some details
Multicast
25
PIM-DM (cont.)
Source
B
Receiver 1
C
A
D
E
Initial
