[Ns-developers] Internal Time Keeping Question

[Hagen Paul Pfeifer]

On Tue, 22 Jul 2008 08:50:15 -0700, Tom Henderson <tomh at tomh.org> wrote:

>> @George: should I adopt the concept of Ghost in this scenario? Build a
>> lightweight infrastructure based on federate information? This will lead
> to
>> huge infrastructure changes in ns-3, as far as I can estimate.
>>
>>
> Hagen,
> Your last sentence above concerns me.  Are you on a path that is
> compatible with our current architecture?

Until now there is really no code impact, except ~10 lines of code. So far
so good!

The challenge now is that ns-3 was not designed to run in a strictly
parallelized mode. The question to George aimed on an optimization
technique. The challenge what I realized is that if I parallelize the whole
the scenario in a dumb manner every physical instance must setup the whole
scenario! For example: if there are 40 simulated nodes and we are working
on a quad-core processor we must set up all 40 nodes on all cores which
will result in 160 allocated nodes! My question to George concerns about a
optimization technique.

Another challenge is that there is no uniform API to inject Packets into
the simulator. The whole simulator is based on a object method call
principle. For disadvantage is that this requires the reference to this
object - but how could a central place (where the Packet is received)
should know the object reference? The idea is to store register devices in
a collector class (whatever) and fetch the reference based on the device
ID. The ID of the device must be unique across the simulated plattform.

> I reviewed your example code also (simple-point-to-point-udp-discard).
> On the wiki, you state that there is nothing to do from the API level
> except call Simulator::EnableParallelSimulation().  However, I expected
> to see (and didn't see) some kind of mapping of nodes to physical
> machines.  Is there really no script-level impact of running MPI-based
> simulations?  I do not understand how this could be.

No, you should see an output where the federates are mapped to! Did you
start with -np 2?
No, there is no scripting impact at the moment - thats a feature!

See http://colabti.org/irclogger/irclogger_log/ns-3?date=2008-07-15,Tue for
an longer discussion on lost Tuesday!


Hagen 

PS: I will answer the other question later!