Multicast Routing and RMT

1
Multicast Routing and RMT

• Jung, Chan-Yoon
• jucys_at_emerald.yonsei.ac.kr

2
Contents

• Introduction
• Multicast Application
• Evolution of Multicast Routing
• Reliable Multicast Transport

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Introduction

• Multicasting
• Efficient way to distribute from a single source
  to multiple destinations
• Efficiency in multicast
• Number of transmissions from a source
• Number of packets generated within the network

4
Multicast Fundamentals

• IP Multicast Address
• Class D
• IGMP (Internet Group Management Protocol)
• Used between a host on a subnet and the
  corresponding router for the subnet
• A host informs the router(Designated Router IGMP
  Querier) that it want to join a particular IP
  multicast group
• Tree
• Shortest Path Tree algorithm
• used actually in internet multicast routing
  protocol
• Minimum Cost Tree algorithm
• Constrained Tree algorithm

5
Multicast Applications

• Category by
• One-to-Many, Many-to-Many
• Latency, reliability

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One-to-Many
Latency-unconstrained reliable multicast
large file transfer
Latency-constrained reliable multicast
distribution of financial information
Resilient multicast
non-interactive real-time application, such as
streaming of video, audio)
Many-to-Many
Latency-constrained reliable multicast
distribution of multimedia information
Non-resilient multicast
interactive games, conferencing
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Standard IP Multicast Model

• Stephen Deering, 1991
• Model
• IP-style semantics
• Open groups
• Source only need to know a multicast address
• Dynamic groups
• Join or leave a multicast group at will

8
The Birth of the Multicast Backbone

• Creation of Mbone
• March 1992
• Main Idea
• mrouted
• IP-encapsulated tunnel
• Encapsulate IP multicast packet in regular IP
  packet
• Routed across non-multicast-capable router
• DVMRP (Distance Vector Multicast Routing Protocol)

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DVMRP

• Broadcast-and-prune
• Source broadcast
• Each router perform RPF(Reverse Path Forwarding)
  check
• Leaf Router decide to forward this packet to the
  subnet
• By Information gathered by IGMP
• Prune
• By leaf router which does not have m-group member
• To all interface
• By Router in multicast path
• to Non-RPF interface

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The Evolution of Intradomain Multicast

• Dense-Mode
• MOSPF
• PIM-DM
• Sparse-Mode
• CBT
• PIM-SM

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Problem in Multicast

• Problems in current DVMRP MBone
• Poor scalability (6000 routes)
• Poor convergence
• Limited policy control
• Resulting in limited acceptance in commercial ISP
• Waste of bandwidth for periodic route updates in
  both directions of a link

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The Evolution of Interdomain Multicast

• Provide scalable, hierarchical internet-wide
  multicast
• Near-term solution
• MBGP Inter-Domain Topology Discovery
• PIM-SM
• MSDP Multicast Source Discovery Protocol
• Long-term solution
• BGMP Inter-Domain Distribution Tree Construction
• MASC Multicast Address-Set Claim

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MSDP

• Idea connect domains together
• Rather than connecting tree, connect sources
  known to all trees
• An RP in a domain has a MSDP peering
  session(over TCP)
• How it works
• Source goes active in PIM-SM domain
• Its packets get PIM registered to domains RP
• RP sends SA message to its MSDP peers
• Those peers forward the SA to their peers away
  from the originating RP
• If a peer in another domain has receivers for the
  group to which the source is sending, it joins
  the source (Flooding-and-Join model

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BGMP

• Uses shared tree between PIM domains
• Bi-directional trees
• Joins sent toward root PIM domain
• Single root domain per group
• Each domain assigns multicast group addresses
• MASC is the currently proposed group address
  assignment mechanism

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Evolution of Multicast Routing

• Past
• MBone
• DVMRP backbone
• Current
• Internet2 vBNS, Abilene, APAN-KR
• MSDP / PIM-SM /other m-IGPs
• Future
• MASC / BGMP / other m-IGPs

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Reliable Multicast Transport

• Problem of TCP in Reliable Multicast
• ACK-Implosion
• New Transport Protocol for Reliable Multicast
• RMT

Multicast Application
Multicast Application
RMT
TCP
UDP
UDP
TCP
RMT
IP
IP
Link Layer
Link Layer
Physical Layer
Physical Layer
Reliable Multicast Transport Protocol Stack
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Relevant Technology in RMT

• Error Control
• Error detection, retransmission request,
  retransmission
• (N)ACK implosion
• scalability
• Flow Control
• How to select one receivers buffer capacity
  among many receivers
• Congestion control
• Rate control according loss rate, RTT

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Error Control in RMT

• What is it ?
• Retransmission of lost packets to group members
  in a multicast group
• Objects
• scalable
• Avoid (N)ACK implosion and duplicate replies
• Reduce recovery latency
• Achieve recovery isolation
• Adaptive to dynamic membership changes

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Congestion Control in RMT

• Object
• Multicast applications respond to network
  congestion in a TCP-friendly manner in order to
  coexist with TCP flows
• Design Goal
• TCP-friendly
• Scalable
• Require as little router support as possible
• Judiciously detect network congestion and respond
  accordingly based on acknowledgments from
  receivers

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RMT Protocol

• One size fits all" protocol will be unable to
  meet the requirements of all applications
• 4 Classes of RMT Protocol
• A NACK-based protocol
• A Tree-based ACK protocol
• An Asynchronous Layered Coding protocol that uses
  Forward Error Correction
• GRA (Generic Router Assist)
• Note
• Actual protocols may use a combination of the
  mechanisms belonging to different classes

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NACK-based protocol

• Protocol families
• SRM, MDP2
• Issues
• NACK suppression

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Tree-based ACK protocol

• Protocol Families
• RMTP, RMTP-II, TRAM
• Issues
• Tree configuration

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ACK aggregation of RMTP
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Open-Loop delivery

• Protocol Families
• RMDP
• Features
• Use sender-based Forward Error Correction (FEC)
  methods
• No feedback from receivers or the network
• Very good at Asynchronous Network such as
  satellite network
• Highest theoretical scalability

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GRA

• Protocol Families
• PGM
• Features
• These protocols take advantage of new router
  software to do constrained negative
  acknowledgments and retransmissions
• Router assist protocols can also provide other
  functionality more efficiently than end to end
  protocols
• Each router is required to interpret transport
  message and store state information

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Conclusion

• Multicast Routing
• Intradomain Multicast Routing Protocol
• Interdomain Multicast Routing Protocol
• Reliable Multicast Transport
• Error Control
• Flow/Congestion Control
• Multicast Application

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Reference

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  on Networking, Dec. 1997
• Brian Whetten, An Overview of Reliable Multicast
  Trnasport Protocol II, IEEE Network, Jan. 2000
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• ???, ???, ????? ???? ?? ? ??? ??, ?????? 944?,
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