[e2e] Simulator for wireless network

Detlef Bosau detlef.bosau at web.de
Mon Apr 16 03:36:57 PDT 2007

U.Shanker wrote:
> Detlef Bosau wrote:
>> I even don´t know whether the source code for the Opnet modeler is 
>> available. The NS2 code is, and so I can see what I´m doing.
> But you can not expect to have source code of every-thing we use. 

Of course I can!

I remember a remark by a professor for software engineering, Hans-Jochen 
Ludewig, who once told us that the most important part in a program, if 
not the ony important one, is the specification! In case of a disaster, 
fire, earthquake all backups lost etc., the only important part which 
must be kept by all circumstances is the specification! Anything else 
may get lost.

So, when you analyze wireless networks, it´s exactly the same story: The 
only important thing is the specification!
Anything else is a crude mixture of bugs and  beginner´s first steps to 
programming - and to hide the mess from the public, it is claimed to be 
"company confidential".

Whether we use open and well known specifications and implement them in 
a manner that anyone can check whether the implementation matches the 
specification or not makes the very difference whether we are doing 
science or whether we are just kidding.

It´s not the purpose of science / universities to promote mediocre 
products from the industry. There is a new buzzword each and every day. 
And lots of people are eager to keep track with all the new 
"developments". But this is not my attitude to thoroughful, proper science.

If you have a simulator with a code you do not know or do not 
understand, you will _NEVER_ be able to defend your "results" gained by 
this product - it´s simply useless.

It is inevitable to use a simulator which is carefuly specified and 
implemented - or the outcome of your simulation is poor luck. Artifacts 
caused by bugs, useless stuff. It´s waste of time to loose a word on it.

> I think, some kind of black-box(es) in the whole environment is better 
> to have. This is to hide the complexity.

If you want to hide complexity, you don´t use _black_ boxes but you use 
_specified_ boxes. You use boxes with a specified behaviour.
When the behaviour is properly specified and there is evidence (not only 
by one test run but _evidence_) that a certain component behaves in the 
specified manner, you may well use it. That´s were scientists should 
stand upon each others shoulders. And not on their toes. (Refer to the 
well known quote by Hamming, IIRC, you will find it in Wesleys signature 
> Generally not every had a skill and knowledge to understand the whole 
> system. 

Generally not everyone is a computer scientist, and not everyone is 
pursuing a PhD and not everyone is professor and not everyone does research.

If I were to review a paper with simulation results where it becomes 
clear that the authors don´t have a perfect and reliable understanding 
of what they are doing - I would reject it without further consideration.

We´ve seen enough cold fursions and successful clone experiments by this 
famous professor in South Korea, the name of whom I just forgot.
Not only that this is no science, the problem is even worse: All these 
"happenings" have absolutely destructive consequences for the 
reputation  of a discipline and science in general.

Do it - or leave it. But plese do nothing in betewen.

> In telecommunication from physical layer to application layer, it 
> really hard to find people with all the skills(of all the layers). So, 
> if I am

I know.

And if you listen to the German government, it´s extremely hard to find 
those people.
(If the German government were not as stupid as it is, it would have a 
look at the job market. We have 4 millions of unemployed people here. 
Perhaps not everybody is as skilled as we request in this discussion. 
But I think, the 40 to 50 adequately skilled persons which are really 
needed can be found here without any problems.)

Many of the participants in this list, I expect it is the vast majority, 
hold a PhD in computer science, electrical engineering or communication 
engineering. If we assume, that this is not earned by luck or as a gift 
but it is _deserved_, these people _are_ adequately skilled.
Otherewise we would have to put academic degrees in question.

> just a Transport layer person, then its better to have a good (well 
> recognized) black-box with standard APIs for other layers, then just 
> the source code of the physical layer. So, as even if the source code 
> is available for physical layer, for me its useless.
You may well use a component written by someone else. But there must be 
evidence that this component behaves as requested.

(And by all means - I did not say that science is a nine-to-five job.)

> Just to make it short, most of the problems in this world are solved 
> by abstracting(the other parts) and not by going in details to the 
> whole system.

Yes. There is a quick, and wrong, answer to nearly any question in the 

>> And BTW: I´m absolutely not convinced of actually availalbe RLP / 
>> mobile network simulators for the NS2, perhaps I don´t know all of them.
>> Of course, this is due to the questions I´m actually trying to find 
>> an answer to. So, I have to write my own simulator classes. Of 
>> course, it´s always a concern that no one will believe my results 
>> produced with this classes, this matches Craig´s experiences. The 
>> only thing I can do is to make the classes available to the public 
>> and to request comments on this code.
> I think, this is also a kind of abstraction for your RLP work.
At least, I did not find one - during the last seven years.

It may be my fault - or my claims are too high, I don´t know.

Just in the beginning of this year, I was about to start with a paper - 
when a colleague told me after a first glance, he would not believe my 


Where do artifacts end? Where do results begin?

So I learned a basic lesson in wireless networking: Do not believe in 
_any_ abstraction which you do not completely understand.
And if this takes to attend some lessons in physics, it _takes_ to 
attend these. And if you have to reproduce a proof of lentgh 20 pages in 
a textbook of communiation engineering, you simply have to do it.

Perhaps, that way a PhD study is not finished within two years.

Perhaps, you will receive criticism because you were not ambitioned 
because you do not write enough papers.

What is your attitude? Proper science? Or a well known reputation? There 
are extremely few persons who receive both. And the people who _deserve_ 
both, in the whole history of science, may be easily counted with one hand.

Detlef Bosau
Galileistrasse 30
70565 Stuttgart
Mail: detlef.bosau at web.de
Web: http://www.detlef-bosau.de
Mobile: +49 172 681 9937

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