ns3, Avoiding random value collision

[Dorice Diane Ngueguia]

Hi,

I am trying to simulate a network application that uses random values. I have 10 000 nodes and during the simulation, each node can generate up to 100 random integer values. I would like all my 1 000 000 (10 000 nodes * 100 values per node) random integers to be distinct trough the simulation. So this is what I did :

The application installed on each node has a uniform random value,  0..1 000 000
          m_hit_generator = UniformVariable(0, 1000000);
To avoid collisions, I have divided my value space in 10 000 parts of 100 possible integer values. Each application has a parameter named HITRange ( = 0, 1, 2,...9999). So to have a random value from each application I do
          m_tag_hit = m_hit_generator.GetInteger(m_hitRange*100,(m_hitRange+1)*100);
Can see that for the first node, range 0, I will be doing GetInteger(0, 100); for the second node GetInteger(100, 200); for the last GetInteger(9900, 10 000)

I thought it was sufficient to avoid collision, but I am still having redundancy.

Does someone know what I should do ?

Tank.

[francesco]

Are you having collisions on the border values, such as 100, 200...?
If this is the case, it's due to the fact that the return value of
GetInteger(a,b) falls in [a,b], including both ends; so the intervals
GetInteger is called on every nodes do overlap.
In other words, consider adding a "-1" somewhere, in order to call
GetInteger(0,99) on node 0, GetInteger(100,199) on node 2 and so on.

[vaibhav tayal]

how do you will get to know about those collisions...
Regards
Vaibhav Tayal

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[Mathieu Lacage]

A random distribution of numbers is not a set of unique numbers. What you appear to want is a random permutation of a fixed set of numbers. My knuth book explains how to do this but wikipedia has a nice discussion of this topic:

http://en.wikipedia.org/wiki/Random_permutation
http://en.wikipedia.org/wiki/Knuth_shuffle

Mathieu

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Mathieu Lacage <mathieu...@gmail.com>

[vaibhav tayal]

Can you please elaborate your explaination??


Regards
Vaibhav Tayal

[Mathieu Lacage]

On Tue, Dec 22, 2009 at 3:56 PM, vaibhav tayal <vaibhav...@gmail.com> wrote:

Can you please elaborate your explaination??

Did you read the wikipedia articles I pointed out ?

http://en.wikipedia.org/wiki/Random_permutation
http://en.wikipedia.org/wiki/Knuth_shuffle

Mathieu

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Mathieu Lacage <mathieu...@gmail.com>