[e2e] Simulator for wireless network

[Giuseppe Bianchi]

At 00.40 15/04/2007, U.Shanker wrote:
>Detlef Bosau wrote:
>>Jeroen Massar wrote:
>>>Durga Prasad Pandey wrote:
>>>
>>>>What would be considered the best network simulator(s) for wireless
>>>>networks, particularly for TCP experiments?
>>>>
>>>
>>>A large amount (>40) old laptops spread around a site.
>>>
>>>Don't simulate, use real live setups.
>>
>>Unfortunately, that´s not always possible.
>Agreed

And don't neglect the fact that, at least for 
802.11 networks (the area which I'm 
experimentally more confident), there is a strong 
dependence on the network cards / Drivers / OSs 
employed. For at least two reasons (at least  = 
limiting to what I'm personally aware of):

1. it is not granted that ALL cards will exactly 
behave as specified by the 802.11 standard (e.g. 
some use different CWmin,  different EIFS, in 
some cases odd behavior do emerge e.g. because of 
possible implementation issues)

2. they may also employ proprietary algorithms, 
either expected (such as rate adaptation) or, and 
this is the case that may really play havoc with 
your experiments, unexpected (e.g. one ongoing 
finding is that some cards seem to use 
undocumented proprietary power control solutions 
which you would not nearly expect from a wire-powered device!).

This implies that, in order to have a reasonable 
confidence that the experimental trial is 
meaningful (at least from a qualitative point of 
view, e.g., to assess e.g. dependence from a set 
of system parameters), you have to use 
homogeneous systems, and it is quite costly to 
deploy more than a few identical boards/PCs, with 
identical card model and driver version... 
Another possibility is to repeat the experiment 
with different HW/SW and HOPE that results are 
the same. Not only this doubles the cost and 
labor, but in many cases this is not even 
technically possible (e.g. when your solution 
uses some driver-level mechanism or requires 
driver modification). In any case, some 
care  (and, most important, the understanding if 
the hardware/software you are using shows some 
odd behavior) is needed before taking 
conclusions, especially in stressful conditions 
(e.g. many terminals, outdoor links).

Giuseppe.