Introduction to IP Multicast Routing
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Transcript of Introduction to IP Multicast Routing
POSTECHNetworking and Distributed Systems Lab. - 2 -
References
Introduction to IP Multicast Routing-An IP Multicast Initiative White Paper
Stardust Technologies, Inc Multicast Routing Algorithms and Protocols:A Tutorial
Laxman H. Sahasrabuddhe & Biswanath Mukerjee IEEE Network, Jan./Feb. 2000
Intra- And Inter- Domain Multicast Routing Protocols: A Survey And Taxonmy
Maria Ramalho IEEE Communications Surveys & Tutorials, vol.3, no.1, 2000.
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Contents
Introduction Multicast Routing Tree Multicast Routing Protocols
Intra-Domain Inter-Domain
Conclusion
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What is Multicasting
Ability of Communication Networks Send packets from a source To a group of Receivers at different
locations With shared routes
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Multicast
Why Multicasting Better bandwidth Less Host/Router processing
Applications video/audio conferencing for remote meetings News feed/ File distribution Interactive games service advertisement
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Compare To Unicast
Unicast
Multicast
Source D
C
B
A
Source D
C
B
A
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Multicast Group Address
Multicasting uses group address for Identify
Managed by IGMP protocols Use Class D IP address
224.0.0.2 –239.255.255.255 224.0.0.0 – not assigned to any group 224.0.0.1 – assigned to permanent
group(IGMP query)
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Contents-MR Tree
Properties Classification Steiner Tree Problem
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Multicast Routing Tree
an acyclic(loopless) spanning tree for support multicasting routing
All Route Multicasting Tree Route
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Properties of Good MR Tree
High Priority Low cost Low delay Scalability Support for dynamic multicast groups
Low Priority Survivability Fairness
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Classes of MR Trees
Source-based Tree One Source for each MR Tree Dense Mode, Not Scalable App: real time multimedia
Group Shared Tree Multi Source exist for each MR Tree Sparse Mode, Scalable App: software distribution
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Source Based Tree
A Tree Required per Source Flood and Prune
Not scalable Heavy control message Hard to manage group
Dense mode DVMRP,MOSPF, PIM-DM
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Source Based Tree
All Route Multicasting Tree Route
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Group Shared Tree
A Tree Required per Group Center based Tree Constructing
Scalable Light control message Easy to Manage group Traffic Concentration Steiner Tree Problem occurred
Sparse Mode CBT, PIM-SM
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Group Shared Tree
All Route Multicasting Tree Route
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Steiner Tree Problem
The Optimization Problem in MR Group shared multicast tree STP is a NP-complete problem Steiner node
A MR tree nodes which do not belongs to multicast group(e.g.:node D, E in fig)
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Two Steiner Trees
All Route 1st Steiner Tree Route2nd Steiner Tree Route
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Properties of Good MR Protocols
Efficiency
Scalability
Easy to Implement
Incrementally deployable
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Classes of MR Protocols
Host–to–Router IGMP
Intra-Domain DVMRP, MOSPF, PIM-DM/SM, MIP
Inter-Domain YAM, QosMIC, BGMP, PTMR-, EXPRESS
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Example of MR protocols
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Internet Group Management Protocol
Exist at IP module of host IGMP messages
Enables a MR to keep track of group Host membership query Host membership reply Join-group report Leave-group report
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ContentsIntra Domain MR Protocol
RPF DVMRP MOSPF CBT PIM-DB PIM-SM
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Reverse Path Forwarding
A method to Find shortest path from one source to many receivers
flood & prune Uses unicast routing table Employed in many MR protocol
DVMRP, MOSPF, PIM-DM, etc.
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Steps of RPF
Unicast Route
All Route
F irst F looding
Second F loodiing
Third F loodiing
Fourth F loodiing
MR1
MR2 MR3
MR5
MR6
MR4
MR7 MR8
MR9
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Distance-Vector Multicast Routing Protocol
Intra-Domain Protocol of Dense Mode
Construct source-based multicast tree
Depends on RIP, the Unicast protocol
Flood & Prune for construct tree by the first packet
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Constructing DVMRP Tree
Unicast Route
All Route
F irst F looding
Second F loodiing
Third F loodiing
Fourth F loodiing
MR1
MR2 MR3
MR5
MR6
MR4
MR7 MR8
MR9
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Resulting Spanning Tree
MR1
MR3
MR5MR4
MR7
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Merits of DVMRP
Minimize the packet delivery costs No routing loops Support incremental deployment
Use DVMRP Tunnel for inter domain Easy to implement Low computational complexity
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Drawbacks of DVMRP
Big memory usage Poor scalability Waste bandwidth Hard to Mange Group(flooding)
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Multicast Open Shortest Path First
Intra-Domain Protocol of Dense Mode Depends on OSPF, Unicast Protocol Tree is built on demand by First Packet Every routers knows complete routing top
ology Make Source-based Tree Dijkstra Algorithm for computing Paths
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Constructing MOSPF Tree
Unicast Route
All Route
F irst Step
Second Step
Third Step
MR1
MR2 MR3
MR5
MR6
MR4
MR7 MR8
MR9
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Resulting Spanning Tree
MR1
MR3
MR5MR4
MR7
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Merits of MOSPF
Tree state required only on tree node
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Drawbacks of MOSPF
Heavy computation Poor Scalability Not support incremental
deployment No tunnels nor any feature for support
it Hard to Mange Group(flooding)
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Core Based Trees
Intra-Domain Protocol of Sparse Mode
Uses only one tree per group To Overcome the scalability Do not use RPF
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Joining a CBT Group
existing route
added routesource path
join REQ
join AC K
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Merits of CBT
Small Usage of router’s memory space Independent of unicast routing protocol Scalable Easy to manage Multicast Group
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Drawbacks of CBT
Concentrates traffic(e.g.: Core Node)
Can occur routing loop Include NP-complete problem
Selecting Core
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Protocol Independent Multicast
To overcome the drawbacks of DVMRP, CBT DVMRP: protocol dependant CBT: traffic concentration
Two modes of operations PIM- Dense Mode PIM – Sparse Mode
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PIM-DM
Similar to DVMRP RPF checks Construct source-based tree Data driven
Differences from DVMRP Do not save the packet routes Independent of unicast routing protocol
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Constructing PIM-DM Tree
Unicast Route
All Route
F irst F looding
Second F loodiing
Third F loodiing
Fourth F loodiing
MR1
MR2 MR3
MR5
MR6
MR4
MR7 MR8
MR9
Differs from DVMRP
P run message
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PIM-SM
Similar to CBT Construct group shared tree with core
Differences from CBT PIM-SM can construct source-based
tree Semi-soft state
Wide deployed
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Construct PIM-SM SB Tree
existing route
added routesourc e path
join REQ
prune message
deleted route
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Result of Tree
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Inter-Domain MR Protocols
For Communicate Between different ASes Most Protocols in research only steps Based on Sparse Mode assumption
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Border Gateway Multicast Protocol
for inter-operate with any intra-domain MR protocols
Similar to PIM-SM Two Components
MIGP – Intra-Domain MR part BGMP – Join/Prune etc.
Use TCP for Control message
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BGMP Simplification
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Conclusion
“What is a multicast tree, how does one construct it?”
Design choice Network performance
considerations
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IP Address Classes
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Tunnel
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Terminologies
IGMP: Internet Group Management Protocols
Domain: Routers run the same routing protocols(ex: postech)