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Challenges in Simulating the Internet

This paper discusses the difficulties in simulating the behavior of the global Internet due to its sheer size, heterogeneity, evolving topology and link properties, and changing traffic patterns. The paper also explores various coping strategies and the need for analyzing a wide range of parameters in order to create realistic simulations.

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Challenges in Simulating the Internet

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  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 4/598N: Computer Networks

  2. 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 1996 - 9 million computers • Jan 1997 - 16 million computers • Dec 2000 - 100 million computers • Internet changes in drastic ways • Growth (80%) can be traced back to 1984 4/598N: Computer Networks

  3. 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? 4/598N: Computer Networks

  4. 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 4/598N: Computer Networks

  5. 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 4/598N: Computer Networks

  6. 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!! 4/598N: Computer Networks

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

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