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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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