Introduction to IP Multicast Routing

2002.01.31Yun Chan Phill

Yunmir@postech.ac.kr

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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)