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Re: Node throughput and packet delay
Sean,
i agree with you: dumping everything to the tracefile is an easy
solution and it takes a lot of space.
However there are flow monitor objects that can be used to collect
statistics without much postprocessing.
I also agree on the fact that if you want to collect specific data, well
you may as well derive your own monitor object. But still if you are a new user
it might just be easier to use trace-all and postprocess with awk than go on
the darkside of ns: C++. I think that working on the C++ part of ns requires a
strong knowledge of ns internals.
> Date: Sun, 10 Oct 1999 12:21:58 +0100 (BST)
> From: Sean Murphy <[email protected]>
> X-Sender: murphys@lofn
> To: Tarik Alj <[email protected]>
> cc: [email protected], [email protected]
> Subject: Re: Node throughput and packet delay
> MIME-Version: 1.0
>
> Tarik,
>
> > > > Another solution that doesn't involve modifying ns is to create trace
> > > > files for your simulation and perform filtering on the trace file using
> > > > awk, for example to obtain the info you want. I've never done this, so I
> > > > don't know exactly what it entails.
> >
> > Ignorance maybe a bliss... but awk (or Perl) really isn't that hard to learn
> > (besides you can find a lot of example scripts in the test and ex
directories0.
> > You can learn more about the tracefiles in ns: notes & documentation,
chapter 16
> > in the Support section (as of april 1 99). And instprocs like trace-all and
> > trace-queue.
>
> Yep, I'm familiar with both awk and perl and yes, these are certainly very
> important and probably necessary tools for postprocessing data. However, I
> still think that it would be useful to have more intelligent monitoring
> components in ns than simply dumping *all* the simulation events to a file
> and performing filtering.
>
> This would have a number of advantages:
>
> 1. new users could be able to obtain the info they want more easily - I
> think that ns is quite a comprehensive and possibly daunting piece of s/w
> - I think many new users have to get their heads around (a) tcl, (b) otcl,
> (c) otcl & c++ linkage, (d) the ns library and possibly more - having to
> learn awk and perl on top of all that should not be necessary to obtain
> quite common but useful (eg packet delays and variations) results.
>
> 2. Entire trace files often take up a very large amount of space, increase
> simulation times, because large amounts of data are written to files, and
> often require post processing to extract the information you want. I think
> it would be better to have some of the filtering done throughout the
> simulation, which decreases the amount of data output, hence the
> simulation time, and hopefully requires less (or none) post-processing.
> (Of course, if you always animate your sim, then this doesn't really
> apply).
>
> 3. I think that it is more natural and possibly easier (depending on the
> interface) to configure a monitoring object and have it log the relevant
> info, rather than logging everything, and fiddling around with the trace
> files, which were not really written for this purpose (I guess). It's also
> faster to have this logging done at the c++ level, rather than the tcl
> level - hence it is useful to implement such functionality in c++.
>
> I'm not saying that my approach is better, just that it has some
> advantages, and no real disadvantages (that I can see) for certain cases.
> Of course situations can arise in which, say, you run a reasonably long
> simulation and you want to obtain many different results. In a situation
> such as this, I think that it may be better to obtain a trace file, and
> run filtering programs on the output to obtain the different sets of
> results.
>
> > some people work on saturdays!
>
> some people work on sundays aswell - some people have no life :-).
>
> Just my $0.02 (as always),
> Sean.
>
> -----
> Sean Murphy, Email: [email protected]
> Teltec Ireland, Phone: +353-1-7045080
> DCU, Dublin 9, Fax: +353-1-7045092
> Ireland.
>
Tarik Alj
INRS-Telecommunications
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