Transcript Introduction to Multicast

Introduction to Multicast
Spencer Tsai
Mobile Communication & Broadband Network Lab
Multicast
CSIE
Fu-Jen Catholic University
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Multicast
Outline
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Overview
IGMP
Multicast Routing on the Internet
Multicast Routing between Domains
Reference
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Multicast
Overview
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Unicast
Multicast
Multicast Characteristic
IP Multicast Address
Examples of permanent groups
Architecture of Multicast
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Unicast
Receiver
Host
Router
Multicast
．Point to point
．N receivers, send n times
．Not suitable for group communication
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Multicast
Receiver
Host
Router
Multicast
．1 sender and n receivers
．N receivers, only send 1 times
．Suitable for group communication
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Benefits of Multicast
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
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Multicast
Multicast Characteristic
• RFC 1112
• Each multicast group identified by classD 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
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IP Multicast Address
Multicast
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Class A
0
Class B
1
0
Class C
1
1
0
Class D
1
1
1
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Net ID
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IP system
IP system
Net ID
IP system
Net ID
0
Multicast address
•Multicast address range
Class D IP Address-higher order 4 bits are set
224.0.0.0 ---239.255.255.255
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Multicast
Examples of permanent groups
224.0.0.0
Reserved
224.0.0.1
All systems in a subnet
224.0.0.2
All routers in a subnet
224.0.0.3
Not allocated
224.0.0.4
All DVMRP routers in a subnet
224.0.0.9
Routers with RIP Version 2 in a
subnet
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Architecture of Multicast
Sender
Multicast Routing
Multicast
Router
IGMP
IGMP version 2
Receiver
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Multicast
Outline
•
•
•
•
•
Overview
IGMP
Multicast Routing on the Internet
Multicast Routing between Domains
Reference
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IGMP
•Internet Group Management Protocol (IGMP)
•Group management within edge networks
•RFC 1112 – IGMP version 1
•RFC 2236 – IGMP version 2 (widely uesd)
Multicast
•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
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IGMP – Join a Group
Multicast Router
Report
Report
Multicast
Host 1
224.2.2.2
Host 2
Host 3
224.2.2.3
•Joining members sends report
•Different hosts can join different multicast group
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IGMP – General Query
Multicast Router
Multicast
General query to
224.0.0.1
Host 1
Host 2
Host 3
•Router periodically sends general query to
224.0.0.1(all systems in a subnet)
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IGMP – Maintaining a Group
Multicast Router
General query to
224.0.0.1
Report
224.2.2.2
suppress
224.2.2.2
Host 1
Multicast
224.2.2.2
Host 2
Host 3
224.2.2.2
•Two steps:
First, router sends general query
Second, member send report
•Only one member needs to send report
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IGMP – Leaving a Group
Multicast Router
General query to
224.0.0.1
Multicast
Host 1
Host 2
Host 3
•Router continue to send general query periodically
•Members silently leave group
• No report receive by router
•Group times out
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IGMP - Querier Selection
MRouter 1
1.1.1.1
Multicast
Host 1
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Host 2
MRouter 2
1.1.1.2
Host 3
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
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Multicast
Outline
•
•
•
•
•
Overview
IGMP
Multicast Routing on the Internet
Multicast Routing between Domains
Reference
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Multicast
Multicast Routing on the Internet
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DVMRP
MOSPF
PIM-DM
PIM-SM
CBT
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Multicast
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
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DVMRP (cont.)
• Graft is used to reconnect an old area or
connect a new area
– Member to source
Multicast
• 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
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MOSPF
• Multicast Extensions to Open Shortest Path
First
• OSPF
Multicast
– 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)
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MOSPF (cont.)
Autonomous System
Domain
Boundary AS
router
BR
AS
R
Multicast
R
Domain
BR
Backbone
BR
Domain
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Multicast
PIM-DM
• Protocol Independent MulticastingDense 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
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PIM-DM (cont.)
Initial
Source
A
Multicast
B
C
D
E
Receiver 1
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PIM-DM (cont.)
Source
Flooding
A
Multicast
B
C
D
E
Receiver 1
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PIM-DM (cont.)
Source
Pruning
A
Pruning
B
D
Multicast
Pruning
C
E
Pruning
Receiver 1
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PIM-DM (cont.)
Source
Steady state
A
Multicast
B
C
D
E
Receiver 1
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PIM-DM (cont.)
Source
A receiver is joining
Graft
A
B
D
Multicast
Graft
C
Receiver 1
E
Receiver 2
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PIM-DM (cont.)
Source
Steady state
A
Multicast
B
D
C
Receiver 1
E
Receiver 2
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Multicast
PIM-SM
• Protocol Independent MulticastingSparse Mode (PIM-SM)
• Based on that systems are located far
away from each other, density of group
member is low=>B.W. tends to be small
• Membership is based on explicit join
operations
• Data is sent to the rendezvous point
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PIM-SM (cont.)
• Bootstrap routers distribute information
about rendezvous points
Multicast
PIM router
PIM router
Multicast
border
router
Non-PIM
enabled domain
PIM router
Bootstrap router
PIM domain
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PIM-SM (cont.)
Sender
Data
PIM Router 3
PIM resister
data unit
PIM join
PIM Router 2
Rendezvous
Multicast
PIM join
PIM join
PIM Router 1
IGMP join
Receiver
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PIM-SM (cont.)
Sender
PIM Router 3
delete
Multicast
PIM Router 2
PIM Router 1
Rendezvous
PIM join
Pruning data unit
Data
Receiver
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CBT
• Core-Based Trees(CBT)
• Based on concept of rendezvous point, in this
case called cores
• Uses a bidirectional multicast tree
Multicast
– PIM is unidirectional
• Use of Hello mechanism
• Restriction to one rendezvous point
• Bootstrap mechanism
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Multicast
Outline
•
•
•
•
•
Overview
IGMP
Multicast Routing on the Internet
Multicast Routing between Domains
Reference
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Multicast Routing Between
Domains
Multicast
Domain
Multicast
Multicast
Domain
BGMP
Router
Multicast
Domain
BGMP
Router
BGMP
Router
BGMP routing
BGMP
Router
Multicast
Domain
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Multicast Routing Between
Domains (cont.)
Multicast
• BGMP(Border Gateway Multicast Protocol)
– Based on CBT and PIM-SM(avoid flooding)
– BGMP join and prune data unit are transmitted
over TCP
– Multicast routing can throughout the internet by
using BGMP
– Connection between multicast domain
autonomous system
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Multicast
Reference
• Multicast Communication, writed by
Ralph Wittmann and Martina Zitterbart,
Morgan Kaufmann publish
• http://www.ietf.org/html.charters/pimcharter.html
• http://www.cs.ucsb.edu/~almeroth
• http://www.cisco.com
• http://www.cs.wisc.edu/~lhl/
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