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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
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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!