NS-3 Third Example-RandomWalk2dMobilityModel

[Erdem Tuna]

Hello everyone,

I am working on the examples provided by NS-3. In the "third.cc", some nodes are installed with RandomWalk2dMobilityModel with the following codes: 

MobilityHelper mobility;

mobility.SetPositionAllocator ("ns3::GridPositionAllocator",
  "MinX", DoubleValue (0.0),
  "MinY", DoubleValue (0.0),
  "DeltaX", DoubleValue (5.0),
  "DeltaY", DoubleValue (10.0),
  "GridWidth", UintegerValue (3),
  "LayoutType", StringValue ("RowFirst"));
mobility.SetMobilityModel ("ns3::RandomWalk2dMobilityModel",
  "Bounds", RectangleValue (Rectangle (-50, 50, -50, 50)));
mobility.Install (wifiStaNodes);

The problem is when I track the position of one of the such nodes, they always end up at the same destination point every time I run time simulation. Isn't this a conflict with a random model?

[pdbarnes]

All random numbers in ns-3 are pseudo-random: the sequence appears random, but it is in fact reproducible. That’s why you get the same sequence, and hence same motion, each time you execute a script.

To get different motion each time you need to change the Run number.

$ NS_GLOBAL_VALUE="RngRun=3" ./waf --run ...

See the manual chapter for more information:
https://www.nsnam.org/docs/manual/html/random-variables.html

Peter