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Impact of Topology
on
Overlay Multicast
Suat Mercan
Outline
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Multicast
IP Multicast
Overlay Multicast
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Performance Metrics
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Simulator
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Topology Generator
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One to many communication
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Multiple Unicast
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Multicast
R
S
R
S
R
R
R
R
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Why Multicast
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Better bandwidth utilization (eliminates traffic redundancy)
For the equivalent amount of multicast traffic, the sender needs
much less processing power and bandwidth
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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
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Rely on network layer to replicate and deliver data packets to
receivers
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IP Multicast
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Advantage:efficient data distribution
Difficulties:
Limited router support
Per-group/source state in routers
Reliability difficulties
Congestion-control difficulties
Undefined pricing model
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Alternative:application layer multicast, to control and
maintain an efficient overlay for data transmission
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Multicast Topology: Overlay
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A virtual network
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Multicast Topology: Overlay
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Flexible
Easy to implement
Not as efficient as IP Multicast
Mesh-based, tree-based
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Mesh-based
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multiple paths exist between any
sender and receiver pair
Quick reconfigurable and robust
Excessive message overhead
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Tree-based
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Shared Multicast Tree
Less control overhead
Vulnerable to node failure
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Overlay techniques
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Overlay techniques
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Narada
Yoid
HostCast
Directional Multicast
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Factors that affect choice of
multicast technique
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Scalability
Fault tolerance
Performance
Quality of service
Security
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Performance
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Quality of data path
Stress
Stretch
Recovery from failure
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Control traffic overhead
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Performance
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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
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P2P Sim
OverSim
PlanetSim
GPS
NS2
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NS2
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Academic project over 10 years old
freely distributed, open source
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Based on C++ and TCL
Discrete event simulator
NAM, the Network AniMator
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pre-processing:
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traffic and topology generators
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post-processing:
simple trace analysis
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NS2
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Topology Generation
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BRITE
PLRG
INET
GT-ITM
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GT-ITM
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Georgia Tech Internet Topology Models
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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
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Implement ‘Directional Multicast’ in NS-2
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Generate different topologies
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Measure performance metrics under different topologies
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Analyze how underlying topology affects performance
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Thank You!
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