User FAQ

2008-01-02T22:22:24Z

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<center><big>The Network Simulator ns-3: Frequently Asked Questions (FAQ)</big> </center>

This wiki page is devoted to questions for <b>users</b> of the simulator. There is a similar [[Developer_FAQ]] page for ns-3 <b>software developers and maintainers</b>.

__TOC__

== What is the difference between ns-2 and ns-3? ==

[http://www.isi.edu/nsnam/ns ns-2] is a popular discrete-event network simulator developed under several previous research grants and activities. It remains in active use and will continue to be maintained.

[http://www.nsnam.org ns-3] is a new software development effort focused on improving upon the core architecture, software integration, models, and educational components of ns-2. The project commenced in July 2006 and there have not yet been any releases (pre-alpha stage).

If you are looking for a simulator to currently use for research, please use ns-2.

== Will ns-2 scripts run on ns-3? ==
No. ns-2 uses OTcl as its scripting environment. ns-3 will use C programs or python scripts to define simulations.

== I found a bug in ns-3. How do I report it? ==

Please consult [http://www.nsnam.org/contributing.html#bugs this page]. Also, please consider fixing the bug, not just reporting it :)

== Mercurial ==

=== merging a separate repository with a main repository ===

Q. I want to incorporate some code from a mercurial branch (repository) that is off the main repository.

A. (from Mathieu Lacage)

You can create a local clone of the repository and pull into it from the main repository:
you can push these yourself by creating a
local clone of that repo and then pushing it back to the main repo. It
will keep the original history; e.g.:

<pre>
hg clone http://code.nsnam.org/mathieu/ns-3-ptr
cd ns-3-ptr
# merge from main ns-3 repository into this other repository
hg pull http://code.nsnam.org/ns-3
hg merge
</pre>

Pushing this new merged repository into another repository will then keep the original change history:
<pre>
# push back-- must have privileges to push to the repository
hg push ssh://code@code.nsnam.org/repos/ns-3
</pre>

=== working with subsets of repositories ===

Q. Is there a way with mercurial to pull/merge/push subsets of the repositories? For instance, suppose I wanted only to grab the samples directory from a repo and merge that alone.

A. (from Mathieu Lacage) You cannot cherry-pick individual changesets other than by exporting
them to patches first. The reason is that each Changeset contains a
single hash which is, among others, based on the hash of the 'parent'
changeset hash. So, if you 'reparent' a changeset, you change its hash
id because the id of the parent changes. If the hash id of a changeset
changes, it is a different changeset so, mercurial cannot really manage
these individual changesets. There is, however, the [http://www.selenic.com/mercurial/wiki/index.cgi/TransplantExtension transplant extension] that lets you do just that.

So, the idea is that merging happens from one repo to another, and
cannot be done on a sub-dir basis. The other alternatives are:

1) the latest mercurial has support for in-repo branches: you can
maintain multiple branches within a single repository but each branch
represents a branch for the whole repository.

2) the latest mercurial contains the [http://www.selenic.com/mercurial/wiki/index.cgi/ForestExtension forest extension] which is a way
to make mercurial manage a 'forest' of repos: each repo is independent
but they also behave as a single big repo through the forest extension.

== WAF (new build process) ==
See also the [http://www.nsnam.org/wiki/index.php/Developer_FAQ#The_WAF_build_system WAF developers FAQ]
=== How to build NS-3 ===
First choose the debug level that you want. To select the debug level, you have to ''configure'' NS-3 first with the command:<pre>
./waf configure -d debuglevel
</pre>
Where ''debuglevel'' is one of:
* ''debug'' (the default): builds NS-3 with the most suited options for debugging. This includes disabling of all optimization, since it confuses the debugger and makes debugging very difficult. It also activates NS-3 internal assertions to catch all programming errors, as well as enabling support for debugging messages (NS_DEBUG and NS_DEBUG_UNCONDITIONAL). This mode should be used initially for development, until you are happy that the code runs correctly and does not contain any serious programming mistake.
* ''optimized'': this compiles NS-3 with optimization, but disabled assertions and debugging messages. Use this when the program is correct and you just want to extrat results.

It is also possible to customize the C compilation flags through the CXXFLAGS environment variable. Example:
<pre>
CXXFLAGS='-O3' ./waf configure -d optimized
</pre>

See [http://code.google.com/p/waf/wiki/EnvironmentVariables here] for a list of additional environment variables that can be used to control waf configure. After configuration, NS-3 can be built with the command:
<pre>
./waf build
</pre>
[ The waf command ''build'' can be omitted, since it is the default command. ]

'''WARNING''': even though the -d option is accepted outside "waf configure", it is completely ignored unless applied together with the configure command.

=== How to run NS-3 programs ===
First, the builtin NS-3 [http://en.wikipedia.org/wiki/Unit_test unit tests] can be executed with the command:
<pre>
./waf check
</pre>

To run the remaining programs, there are three different ways to do it.
# The hard way: because NS-3 is built as a set of shared library (dll) files, it requires you to manually configure LD_LIBRARY_PATH, PATH, or DYLD_LIBRARY_PATH, depending on your platform, to make them point to each ns-3 module directory. Only then can you run the programs that were built as <code>build/<debuglevel>/path/to/program</code>.
# Easy way #2: run <code>./waf --shell</code>. You will then have a new nested shell from which programs can be run, e.g. <code>gdb ./build/debug/examples/simple-p2p</code>.
# Easy way #1: <code>./waf --run programname</code>, or <code>./waf --run "programname args"</code>. To find out available program names, run <code>./waf --run non-existent-program-name</code>.

=== How to run NS-3 programs under another tool ===
For running ns-3 programs with gdb or valgrind, try the following:
* Use the "command-template" argument; e.g.
** <code> waf --run csma-cd-one-subnet --command-template="gdb %s"</code>
** <code> waf --run csma-cd-one-subnet --command-template="valgrind %s"</code>

== Scons (old build process) ==

=== Library not loaded error ===
Question: On Apple osX, I built ns-3 successfully, but when I try to run a sample program I get something like:
<pre>
> ./sample-packet
dyld: Library not loaded: build-dir/dbg-shared/lib/libcommon.dylib
Referenced from: /tmp/ns-3/build-dir/dbg-shared/bin/./sample-packet
Reason: image not found
Trace/BPT trap
</pre>

Answer: This is because the library path variable of your environment does not include the location where the ns-3 modules (libraries) are located.

In OS X, you need to set the DYLD_LIBRARY_PATH variable to include the library directory. These need to include the lib/ directory where these ns-3 libraries are built. On Linux and Solaris systems, you should never warnings of this kind. If you do, please, report a bug.

In this example, setting
DYLD_LIBRARY_PATH=/tmp/ns-3/build-dir/dbg-shared/lib/
will work.

=== How do I do the equivalent of a "make clean"? ===
<pre>
scons -c
</pre>

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