[e2e] Simulator for wireless network
awo at ieee.org
Sun Apr 15 02:57:58 PDT 2007
> 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
> So the question: throughput of an 802.11 is in fact unspecified -
> 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!
> 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.
>> 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
>> 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
>> 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).
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