OverSim and Churn

OverSim uses churn generators for simulating non-static networks. The different churn generators simulate different user behaviour and can be configured individually.

Churn Generators

• NoChurn (will be added in the next release)
  • Node behaviour: No churn. Nodes will be added until targetOverlayTerminalNum is reached; after that, the network will remain static.
  • Parameters: None
• RandomChurn
  • Node behaviour: In fixed intervalls a random number is drawn. Depending on this number, a random node is either added, deleted or migrated.
  • Parameters:
    • targetMobilityDelay: Timespan in seconds between two actions.
    • creationProbability, migrationProbability, removalProbability: Changes the probability of the actions taken when a number is drawn. Example: creationProbability=0.5, removalProbability=0.5, migrationProbability=0. In this case, every targetMobilityDelay seconds a node is added or removed with a probability of 50%. Other example: creationProbability=0.6, removalProbability=0.4, migrationProbability=0. In this example, nodes are created with a probability of 60% and removed with a probability of 40%. This will result in a constantly growing network.
  • Notes: This churn generator can be used to simulate static networks if all probabilities are set to 0.
• LifetimeChurn
  • Node behaviour: On creation of a node, his lifetime will be drawn randomly from a given probability function. When this time is reached, the node is removed. A new node will be created after a dead time drawn from the same probability function.
  • Parameters:
    • lifetimeMean: The mean lifetime.
    • lifetimeDistName: The function used for drawing the lifetimes (default: weibull)
• ParetoChurn
  • Node behaviour: Similar to LifetimeChurn, a node's lifetime is drawn on creation. However, this is done in a two-stepped process. For details, please read Yao, Z.; Leonard, D.; Wang, X. & Loguinov, D. "Modeling Heterogeneous User Churn and Local Resilience of Unstructured P2P Networks" Proceedings of the 2006 14th IEEE International Conference on Network Protocols, 2006. ICNP '06. 2006, pp. 32--41
  • Parameters:
    • lifetimeMean: The mean lifetime.
    • deadtimeMean: The mean deadtime.
  • Notes: This churn generator results in heavy tailed session times similar to empirical results from P2P filesharing networks or MMOGs.