[Ns-developers] [ns3] socket API

[Gustavo Carneiro]

On 21/04/2008, George Riley <riley at ece.gatech.edu> wrote:
>
>
>
>
>
> The larger issue here seems to be what will be the prevailing model for
>
> applications that we will use as examples of how to do things in ns-3? I'm
>
> not sure that many people have looked closely at Mathieu's ns-3-simu but
> one
>
> possibility would be that the process code (see examples/process.cc) would
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> be the most widely used API,
>
>
>
> See, this is what I was afraid of.  You are opening the door for any and
> every simulation model to use simulated processes, yet the performance
> implications of this approach have not been studied.  We have already seen
> that the only portable implementation of simulated processes is through
> POSIX threads, namely one thread per simulated process.  Now suppose you
> have 500 nodes, each running 2 routing protocols using synchronous socket
> API.  NS-3 will then create 1000 threads.  And what will the performance
> of
> that look like?...
>
> HI Gustavo,
> I don't think Tom is suggesting that we would drop the so-called
> asynchronous
> API; rather he thinks the process-based one might be more popular.
>  Whether
> or not this is comes about does not seem significant at the moment.  I'm
> very
> much with you, that performance will suffer if a user models 10,000
> peer-to-peer
> applications, each with a separate thread and private stack.  Anyway, rest
> assured the async approach is and will remain an integral part of ns-3,
> and
> in my opinion the method of choice for most users.
>

Yes, of course.  I would consider simulated processes and blocking sockets a
feature that does not perform well but acceptable as means of rapid
prototyping some model.  It would be on par with Python, in that respect.

But unlike Python models, in which it is clear that the performance is going
to be poor when compared to C++, with blocking sockets it is not at all
apparent the performance penalty a user is incurring.

So I really have nothing against blocking sockets as long as they are not
widespread used.  It would be better if there was a decision, followed by
documentation, that writing new simulation models (e.g. new protocols) on
top of blocking sockets is to be discouraged.

-- 
Gustavo J. A. M. Carneiro
INESC Porto, Telecommunications and Multimedia Unit
"The universe is always one step beyond logic." -- Frank Herbert