Why We Don’t Know How to
Simulate the Internet
Presented by Sui-Yu Wang
Introduction
• Explain why the network is hard to
simulate:
– Great heterogeneity
– Rapid change
• Propose strategies for developing
meaningful simulation
Reasons why the internet is hard
to characterize
• IP does not uniform behavior
• The internet is too big to ignore small
fraction of atypical behaviors
• The internet changes in drastic way over
time
Heterogeneity that can not be
ignored
• Topology and link property
– Topology is constantly changing
– Entities are not necessarily willing to provide
information
– Bandwidth may vary
– Different type of link
– Dynamic routing
– Asymmetric routes
• Protocol difference
– Different implementation
Traffic Generation
• Trace-driven simulation
– Trace at packet level may not be reused safely
– Trace at source level perform better
• Characterize traffic in abstract term
How the Internet might Evolve in
the future
• Changes in the internet might undermine
result of simulation
– Marketing strategies affects user and router
pattern
– New technology
Coping Strategies
• The search for invariants
– Self-similarity for packet arrivals
– Poisson processes for network user session
– The distribution of connection sizes or duration is lognormal
– Network activity distribution has heavy-tail property
– Pattern of network packets generated by user typing at a
keyboard has an invariant distribution
• Carefully exploring the parameter space
The Role of Simulation
• Provides a check on the assumptions of the
model and on the correctness of the analysis
• Allowing exploration of complicated
scenarios that would be either difficult of
impossible to analyze
• Address questions of internet dynamics
• Examining particular aspects of proposed
protocols