1. Vern Paxson and Sally Floyd, "Why We Don't Know How To Simulate The Internet", Proceedings of the 1997 Winter Simulation Conference, Dec1997
Sally Floyd and Vern Paxson “Difficulties in Simulating the Internet”, 2001
Realistic BGP Traffic for Test Labs. Olaf Maennel and Anja Feldmann, SIGCOMM 02
Network Topology Generators: Degree-Based vs. Structural. H. Tangmunarunkit, R. Govindan), S. Jamin, S. Shenker and W. Willinger, SIGCOMM02
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2. Simulating how the global Internet behaves is important
Motivation
Simulating how the global Internet behaves is important
Validate new protocols before deploying them
Immensely hard task
Sheer diversity of the hosts
Internet is big
Jan million computers
Jan million computers
Dec million computers
Internet changes in drastic ways
Growth (80%) can be traced back to 1984
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4/598N: Computer Networks

3. Growth affects usage statistics with time
Motivation (cont)
Growth affects usage statistics with time
ftp median size went from 4500 bytes to 2100 bytes!!
New protocols take over the traffic
Web traffic was unknown before 1992, Napster, Gnutella, Mbone grew on short notice. Napster traffic disappeared overnight
What are we trying to achieve with simulations
Faithfully model the internet or capture its global scale behaviour?
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4/598N: Computer Networks

4. Topology and link properties
Heterogeneity
Topology and link properties
What is the network topology - hierarchical or power law distributions
Network is also evolving continuously
Link properties also change (DSL, cable, and other technologies)
Links can be asymmetric - especially with large topologies
Protocol differences
TCP implementations are evolving too (with their own set of bugs!!)
Depends on the application goals for simulation
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4/598N: Computer Networks

5. How do we generate representative traffic
Traffic generation
How do we generate representative traffic
Trace-driven simulation is tempting
Internet uses adaptive congestion control
Traces depend on the time when it was collected
Trace driven source-level simulation is promising
Todays network is not tomorrow’s
New pricing structure could make QoS take off
Routing protocols may introduce QoS models
Native multicast rather than tunnelled
CDNs changed the web dynamics
Next killer application can change everything
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6. Carefully exploring the parameter space
Coping stategies
Search for invariants
Carefully exploring the parameter space
Choosing a random topology does not “prove” anything
Need to analyze fro a wide range of “viable” parameters!!
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4/598N: Computer Networks

7. BGP traffic generators Network topology generators
Other papers
BGP traffic generators
Network topology generators
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4/598N: Computer Networks