RealTime OnLine Network Simulation

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Real-Time On-Line Network Simulation

• Bolek Szymanski
• Kiran Mandani, Anand Sastry and Yu Liu
• Rensselaer Polytechnic Institute, Troy, NY
• http//www.cs.rpi.edu/szymansk/sonms.html
• email szymansk_at_cs.rpi.edu
• DARPA PI Meeting
• April 2, 2001

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Novel goals of the research

• On-Line Network Modeling and Simulation scalable
• to multiple domains and hundreds of thousands
  of flows
• Second order traffic and routing control

Topic of this poster
Experiment Design
Network Abstraction And Decomposition
Parallel Discrete Event Simulation
Performance
Processor 1
Processor 2
Domain 2
Domain 1
Parameter 2
Parameter 1
P1min
P1max
Processor 3
Processor 4
Current operating point
Domain 3
Trial operating point triggering simulation
router
Link, simulated at packet level
Models of Inter-domain flows
Links crossing processor Boundary may cause
rollback
All three trial points can be Evaluated
concurrently
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Real-Time On-Line Network Simulation

• Space decomposition partition large network into
  disjoined individual domains, each simulated
  independently and concurrently with others.
• Time decomposition partition simulation time
  into separate intervals, each interval iterated
  over until all domain simulators converge.
• Synchronization exchange packet delay and loss
  information on flows originated externally to
  each domain at the end of each interval
  simulation (iteration). Message passing via
  sockets is used in farmer-worker parallel
  architecture.
• Basic domain simulation uses currently ns to
  support portability of the results.

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Global view - abstract configuration
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Extensions to ns

• Domain definition in network simulation
  definition (Tcl script)
• Fake source and fake link definition to
  represent inflow and outflows to the domain and
  account for packet delay and drop outside the
  domain
• Checkpointing of the simulation state to enable
  iterations over time intervals
• Freeze event to enable synchronizing simulations
  and exchange of data at the end of each iteration

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Concurrent simulations of domains freeze,
exchange of messages, checkpointing
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Experiments with 64-node network
Linear Speedups As compared to Single Domain
Simulation Runs 4 Domain 4.83 times 16 Domain
14.251 times
64-node configuration
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Experiments with 27-node network
Linear Speedups As compared to Single Domain
Simulation Runs 3 Domain 1.90 times 9 Domain
5.71 times
27-node configuration
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Advantages of the Approach

• Efficiency execution time t(n) of network of
  size n is growing faster than n
• nlogn term from processing future event queue
• nn term from processing routing
• An iteration with n processors, each running a
  domain of 1/n of nodes run faster than 1/n of
  entire network simulation time.
• Fault tolerance if a domain processor fails,
  the data from last iteration can be used
• Integration of models into simulation a cloud
  of unknown structure could be represented by path
  delays and packet drop probabilities
• Full processing distribution processors
  simulating each domain can be located in the
  domain

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Whats Next?

• Improvements in implementation
• Synchronization in a tree-like structure
• Checkpointing to local disks
• Aggregating external sources into single external
  link
• Experiments with TCP traffic
• Integration with fast domain simulators (ROSS)
• Linking with an On-line Data Collection
• Integration with Experiment Design component for
  network management