[e2e] Simulator for wireless network

[Adam Wolisz]

> ALl,
> Giuseppe has addressed a very important point.
>
> In fact the following question is a basic one: what is to be 
> investigated - an ideal behavior of the envisioned,
> precisely defined solution - or THE behavior of really deployed products?
>
> In the WINTECH 2006 workshop The First ACM International Workshop on 
> Wireless Network Testbeds, Experimental evaluation and 
> CHaracterization - one of the MOBICOM 2006 workshops -
> a very interesting paper presents
> "An Empirical ANalysis of Heterogeneity in IEEE 802.11 MAC protocol 
> implementations and it implications"
>
> Surprisingly enough, besides of a long list of differences which are 
> to be expected _ e.g. rate adaptation
> algorithms are NOT defined by the standard, propreitary solutions have 
> to be used! -  also
> very clear violations of the standard have been observed within 
> products of major manufactureres.
>
> In particular the list of observed differences (and violations of the 
> standard!)  has been given,
> along with a demonstration, that due to this differences unfairness in 
> bandwidth sharing exists among terminals
> using products of different manufactures.  And the differences ARE 
> SIGNIFICANT!
>
> So the question: throughput of an 802.11 is in fact unspecified  -   
> sorry....
>                                
> On the other hand : throughput of an 802.11 implementation by Company 
> XXX model YYYY  from August 200z
>                 is probably not what one is necessarily looking at.... 
> or perhaps exactly what one is looking at!
>
> Best
> adam wolisz
>
>
>
> Giuseppe Bianchi wrote:
>
>> 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.
>>
>>
>>
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