2.1 Quick Overview

ns-3 random numbers are provided via instances of class RandomVariable.

• by default, ns-3 simulations use a fixed seed; if there is any randomness in the simulation, each run of the program will yield identical results unless the seed and/or run number is changed.
  • in ns-3.3 and earlier, ns-3 simulations used a random seed by default; this marks a change in policy starting with ns-3.4
• to obtain randomness across multiple simulation runs, you must either set the seed differently or set the run number differently. To set a seed, call SeedManager::SetSeed (uint32_t) at the beginning of the program; to set a run number with the same seed, call SeedManager::SetRun (uint32_t) at the beginning of the program; See section Seeding and independent replications
• each RandomVariable used in ns-3 has a virtual random number generator associated with it; all random variables use either a fixed or random seed based on the use of the global seed (previous bullet);
• if you intend to perform multiple runs of the same scenario, with different random numbers, please be sure to read the section on how to perform independent replications: See section Seeding and independent replications.

Read further for more explanation about the random number facility for ns-3.

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