Strange simulation behaviour

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Strange simulation behaviour

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as a part of my project concerning the usage of ns2, I've frequently stumbled upon simulations that performed poorly without any straightforward reason so I decided to ask someone to maybe explain to me what was going on and how can I correct the problem. My original TCL script creates a random topology and communication scheme, but I extracted an instance where weird things happen. Here are the files:


The TCL file has two variables at the very start: cbr_scenario and pck_scenario. When both equal 0, the simulation generates a PDR of 18.26%, but when either or both equal 1, it jumps to about 99%. The only thing the variables control are the CBR packet size (70 vs 100), and communication start times.

This seems rather arbitrary. There seems to be no concrete reason for the result of one simulation to differ so much from the other three, and when generating random simulation scenarios this posses a problem. I find this kind of behavior far too frequently.

So, can anyone  explain what is going on?