[e2e] Simulator for wireless network

[U.Shanker]

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
>
> In addition, there are always two ways to produce wrong results.
>
> The first is: Simulate. As you never know, what you´re simulating, 
> your results will be wrong for sure.
Interesting. But probably I just want effect of one or other parameters 
on the whole system. In that case, simulation is the best.
> The second is: Conduct real experiments. As you never know, what 
> you´re really doing, your results will be wrong for sure.
>
> So, the best way is, and somewhere I heard this were an old jiddish 
> saying: If you have only two impossible choices, choose the third.
What about taking some real network data and using simulations based on 
that. We use this using Opnet modeler etc. I think this is one of the 
best approach.
>
> So, in my opinion, you should have a very precise idea what you want 
> to find out, either by real experiments or by simulation.
> Some questions are:
>
> - are you interested in 802.11 networks?
> - are you interested in cellular networks?
> - is mobility (beyond pedestrian) allowed in your network?
> - which design questions are not yet fully discussed?
>
> I´m writing an RLP agent for the NS2 myself at the moment and I have 
> much more questions than answers here.
> And I´m often quite upset, when I read "papers" which refer to "well 
> known simulators" and present some funny tables and columns of 
> numbers, called "results" and it´s in fact not even clear, which 
> question is actually answered.
>
> One basic lessen, I´ve always learned from dealing with mobile 
> networks / wireless networks and the like:
> Even the best answer is at least as bad as the question.
>
> Why I choose the NS2: It´s quite easy. I´m quite familiar with the NS2 
> and it´s widely accepted. And because I´m quite familiar with the NS2, 
> it´s quite easy for me to add new classes and protocols there and I´m 
> well aware of a huge number of pitfalls which are around nearly each 
> corner. E.g. the first time, you get a null pointer exception or 
> segmentation violation or something like that will cause you a 
> nightmare of debugging the code day and night in the debugger - o.k., 
> this afternoon I consumed a "one way event" with delete instead of 
> free, but after some hours, I remembered I did something simular some 
> years ago and looked at my own old source code - which solved the 
> problem.
> (As you can imagine, I got some funny error messages before ;-))
I think, here you made very good point. I tried ns2 and spend most of 
the time between understand the whole NS2 system and debugging between 
C++ and otcl code. Finally I moved to the OPNET (free for the 
universities !). It really solved most of the my problems and I was just 
able to concentrate on simulation only. But if somebody can master a 
tool like NS2, then better to use that. I know there a big ns2 community 
and forums is quite useful.
>
> If you´re completely new to simulation and have the time, you will 
> perhaps start with the NS 3. I don´t know.
>
> But first of all: You should make perfectly clear, what you want to 
> simulate and what´s your precise question.
> Because good questions are often more than half the answer.
>
> Detlef
>
Finally, as Detlaf said,  it will really depend what exactly you want to 
do. Want to see effects of some standard parameters within the complex 
WLAN/UMTS/WIMAX environment, then OPNET could be very fast in providing 
results. If want to do changed in the standard TCP implementations 
together with WLAN etc, then may be NS2 will be faster. Looking for the 
complex environment and some changes in the TCP, then you have to take 
the time and probably use the OPNET.

I was really very fast with NS2 and TCP and WLAN simulation. But when it 
comes to the UMTS and WiMAX etc together with TCP/WLAN then it appeared 
that, I have to move back from ns2 2.29 to 2.27, as UMTS implementation 
was based on the older NS2 version and so on. If you plan to spend next 
few years with this kind of simulations work then probably its worth 
start using NS2/NS3.

-- 

regards,
Uma Shanker,

PhD Student, Center for Telecommunications Research
King's College London, Strand, London WC2R 2LS, UK.
Tel: +44-20-7848-2889 Email: uma.shanker(at)kcl.ac.uk