Impact of Topology on

Overlay Multicast

Suat Mercan

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Outline Multicast IP Multicast Overlay Multicast

Performance Metrics

Simulator

Topology Generator

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One to many communication Multiple Unicast Multicast

S

R

R

R

S

R

R

R

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Why Multicast

Better bandwidth utilization (eliminates traffic redundancy) For the equivalent amount of multicast traffic, the sender needs

much less processing power and bandwidth

Less host/router processing (reduces server and network load) Multicast packets do not impose as high a rate of bandwidth

utilization as unicast packets, so there is a greater possibility that they will arrive almost simultaneously at the receivers

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IP Multicast Rely on network layer to replicate and deliver data packets to

receivers

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IP Multicast

Advantage:efficient data distribution Difficulties:

Limited router supportPer-group/source state in routersReliability difficultiesCongestion-control difficultiesUndefined pricing model

Alternative:application layer multicast, to control and maintain an efficient overlay for data transmission

Multicast Topology: Overlay

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A virtual network

Multicast Topology: Overlay Flexible Easy to implement Not as efficient as IP Multicast Mesh-based, tree-based

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Mesh-based multiple paths exist between any

sender and receiver pair Quick reconfigurable and robust Excessive message overhead

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Tree-based Shared Multicast Tree Less control overhead Vulnerable to node failure

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Overlay techniques

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Overlay techniques Narada Yoid HostCast Directional Multicast

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Factors that affect choice of multicast technique

Scalability Fault tolerance Performance Quality of service Security

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Performance

Quality of data path Stress Stretch Recovery from failure

Control traffic overhead

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Performance

Stress Number of identical packets sent by the protocol over the

same link. For IP Multicast there is no redundant packet replication

Stretch Resource usage Control Overhead Each member on the overlay exchanges refresh

messages with all its peers.

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Simulation

P2P Sim OverSim PlanetSim GPS NS2

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NS2 Academic project over 10 years old freely distributed, open source Based on C++ and TCL Discrete event simulator NAM, the Network AniMator pre-processing:traffic and topology generators post-processing:simple trace analysis

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NS2

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Topology Generation BRITE PLRG INET GT-ITM

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GT-ITM Georgia Tech Internet Topology Models

A collection of routines to generate and analyze graphs using a wide variety of models for internetwork topology

Waxman method, Transit-Stub method Included as part of NS-2

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GT-ITM

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Our Project Implement ‘Directional Multicast’ in NS-2

Generate different topologies

Measure performance metrics under different topologies

Analyze how underlying topology affects performance

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Thank You!