[Click] nsclick rng support for ns3

[Sascha Alexander Jopen]

Hi Eddie,

I did not implement a fallback method, because i was not sure how to
handle CLICK_RAND_MAX in case a fall back is necessary. In
include/click/glue.hh CLICK_RAND_MAX is defined as the maximum value
supported by the ns3 implementation. However, if we find the simulator
not supporting random numbers at runtime, falling back to random() or
rand() could lead to a RAND_MAX, which is different from the defined
CLICK_RAND_MAX. This could lead to unexpected simulation behaviour. Any
comments, how to handle this?

Regarding the CLICK_RAND_MAX value itself, i can change the maximum
value to 0xFFFFFFFFU.

I used 0xFFFFFFFEU in the first place, because, although the ns3
documentation says, that calling

  uint32_t GetInteger(uint32_t min, uint32_t max)

returns an integer in the range [min,max], this seems not to be true for
max = 0xFFFFFFFFU. Because this calls internally another method, with
GetValue(min, max + 1), this results in an overflow. So 0xFFFFFFFEU
would be the largest possible integer. See around line 187 in file
src/core/model/random-variable-stream.cc. Either i'm wrong, or this is
something to report to the ns3 team.

However, i certainly missed the alternative call with a cast of the max
value 0xFFFFFFFFU to double and back to uint32_t after a call to the
double based GetValue function. This would lead to a RAND_MAX of
0xFFFFFFFFU. I will fix this.

Thanks for reviewing,
Sascha

On 23.01.2013 16:52, Eddie Kohler wrote:
> Hey,
> 
> Two comments.
> - Breaking random numbers except for nses that export random numbers
> considered lame. Why not fall back to the normal random number
> generator?
> - The RAND_MAX value seems odd. (-2??) Why this value?
> 
> Eddie
> 
> On Wed, Jan 23, 2013 at 3:52 AM, Lalith Suresh <suresh.lalith at gmail.com> wrote:
>> Hi,
>>
>> On Mon, Jan 21, 2013 at 12:16 PM, Sascha Alexander Jopen
>> <jopen at informatik.uni-bonn.de> wrote:
>>> Hey,
>>>
>>> please find attached a patchset for click and ns3 which adds support for
>>> drawing random numbers within click simulations from the underlying ns3
>>> random number generator. Each simulated click node has its own uniformly
>>> distributed random number stream (as opposed to my previously submitted
>>> patch). This way all nodes have independent random number streams.
>>>
>>> Setting the seed or run numbers is done within the simulation by means of
>>>
>>> RngSeedManager::SetSeed ();
>>> RngSeedManager::SetRun ();
>>>
>>> or with environment variables or command line parameters.
>>> See http://www.nsnam.org/docs/manual/html/random-variables.html
>>>
>>> I still have no ns2 available. Currently, missing rng support from the
>>> simulator side is detected and reported but no random numbers are
>>> available to the simulation. Implementing a fallback method should be
>>> possible, however. Maybe someone who uses ns2 could provide this?
>>>
>>> click-ns3-rng.diff is for the click side and ns3-nsclick-rng.diff for
>>> the ns3 side.
>>>
>>
>> I had a look through this patch. For clarity, my comment is to rename
>> the simclick command to SIMCLICK_GET_RANDOM_INT and the
>> Ipv4ClickRouting method's name to GetRandomVariable(). Otherwise, it
>> looks good.
>>
>> I can push this to ns-3-dev when the click side gets committed.
>>
>>> Regards,
>>> Sascha
>>>
>>> --
>>> Dipl.-Inform. Sascha Jopen
>>>
>>> University of Bonn                     Tel.:   +49-228-73-54219
>>> Institute of Computer Science 4        Fax:    +49-228-73-4571
>>> Friedrich-Ebert-Allee 144              E-mail: jopen at cs.uni-bonn.de
>>> D-53113 Bonn, Germany
>>>
>>> _______________________________________________
>>> click mailing list
>>> click at amsterdam.lcs.mit.edu
>>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>>>
>>
>>
>>
>> --
>> Lalith Suresh
>> www.lalith.in
>> _______________________________________________
>> click mailing list
>> click at amsterdam.lcs.mit.edu
>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click


-- 
Dipl.-Inform. Sascha Jopen

University of Bonn                     Tel.:   +49-228-73-54219
Institute of Computer Science 4        Fax:    +49-228-73-4571
Friedrich-Ebert-Allee 144              E-mail: jopen at cs.uni-bonn.de
D-53113 Bonn, Germany