Getting Started

This section is aimed at getting a user to a working state starting with a machine that may never have had ns-3 installed. It covers supported platforms, prerequisites, ways to obtain ns-3, ways to build ns-3, and ways to verify your build and run simple programs.

Overview

ns-3 is built as a system of software libraries that work together. User programs can be written that links with (or imports from) these libraries. User programs are written in either the C++ or Python programming languages.

ns-3 is distributed as source code, meaning that the target system needs to have a software development environment to build the libraries first, then build the user program. ns-3 could in principle be distributed as pre-built libraries for selected systems, and in the future it may be distributed that way, but at present, many users actually do their work by editing ns-3 itself, so having the source code around to rebuild the libraries is useful. If someone would like to undertake the job of making pre-built libraries and packages for operating systems, please contact the ns-developers mailing list.

In the following, we’ll look at three ways of downloading and building ns-3. The first is to download and build an official release from the main web site. The second is to fetch and build development copies of a basic ns-3 installation. The third is to use an additional build tool to download more extensions for ns-3. We’ll walk through each since the tools involved are slightly different.

Experienced Linux users may wonder at this point why ns-3 is not provided like most other libraries using a package management tool? Although there exist some binary packages for various Linux distributions (e.g. Debian), most users end up editing and having to rebuild the ns-3 libraries themselves, so having the source code available is more convenient. We will therefore focus on a source installation in this tutorial.

For most uses of ns-3, root permissions are not needed, and the use of a non-privileged user account is recommended.

Prerequisites

The entire set of available ns-3 libraries has a number of dependencies on third-party libraries, but most of ns-3 can be built and used with support for a few common (often installed by default) components: a C++ compiler, an installation of Python, a source code editor (such as vim, emacs, or Eclipse) and, if using the development repositories, an installation of Git source code control system. Most beginning users need not concern themselves if their configuration reports some missing optional features of ns-3, but for those wishing a full installation, the project provides a wiki that includes pages with many useful hints and tips. One such page is the “Installation” page, with install instructions for various systems, available at https://www.nsnam.org/wiki/Installation.

The “Prerequisites” section of this wiki page explains which packages are required to support common ns-3 options, and also provides the commands used to install them for common Linux or macOS variants.

You may want to take this opportunity to explore the ns-3 wiki a bit, or the main web site at https://www.nsnam.org, since there is a wealth of information there.

As of the most recent ns-3 release (ns-3.29), the following tools are needed to get started with ns-3:

Prerequisite Package/version
C++ compiler clang++ or g++ (g++ version 4.9 or greater)
Python python2 version >= 2.7.10, or python3 version >=3.4
Git any recent version (to access ns-3 from GitLab.com)
tar any recent version (to unpack an ns-3 release)
bunzip2 any recent version (to uncompress an ns-3 release)

To check the default version of Python, type python -V. To check the default version of g++, type g++ -v. If your installation is missing or too old, please consult the ns-3 installation wiki for guidance.

From this point forward, we are going to assume that the reader is working in Linux, macOS, or a Linux emulation environment, and has at least the above prerequisites.

Downloading a release of ns-3 as a source archive

This option is for the new user who wishes to download and experiment with the most recently released and packaged version of ns-3. ns-3 publishes its releases as compressed source archives, sometimes referred to as a tarball. A tarball is a particular format of software archive where multiple files are bundled together and the archive is usually compressed. The process for downloading ns-3 via tarball is simple; you just have to pick a release, download it and uncompress it.

Let’s assume that you, as a user, wish to build ns-3 in a local directory called workspace. If you adopt the workspace directory approach, you can get a copy of a release by typing the following into your Linux shell (substitute the appropriate version numbers, of course)

$ cd
$ mkdir workspace
$ cd workspace
$ wget https://www.nsnam.org/release/ns-allinone-3.29.tar.bz2
$ tar xjf ns-allinone-3.29.tar.bz2

Notice the use above of the wget utility, which is a command-line tool to fetch objects from the web; if you do not have this installed, you can use a browser for this step.

Following these steps, if you change into the directory ns-allinone-3.29, you should see a number of files and directories

$ cd ns-allinone-3.29
$ ls
bake      constants.py   ns-3.29                            README
build.py  netanim-3.108  pybindgen-0.17.0.post58+ngcf00cc0  util.py

You are now ready to build the base ns-3 distribution and may skip ahead to the section on building ns-3.

Downloading ns-3 using Git

The ns-3 code is available in Git repositories on the GitLab.com service at https://gitlab.com/nsnam/. The group name nsnam organizes the various repositories used by the open source project.

The simplest way to get started using Git repositories is to fork or clone the ns-3-allinone environment. This is a set of scripts that manages the downloading and building of the most commonly used subsystems of ns-3 for you. If you are new to Git, the terminology of fork and clone may be foreign to you; if so, we recommend that you simply clone (create your own replica) of the repository found on GitLab.com, as follows:

$ cd
$ mkdir workspace
$ cd workspace
$ git clone https://gitlab.com/nsnam/ns-3-allinone.git
$ cd ns-3-allinone

At this point, your view of the ns-3-allinone directory is slightly different than described above with a release archive; it should look something like this:

$ ls
build.py  constants.py   download.py  README  util.py

Note the presence of the download.py script, which will further fetch the ns-3 and related sourcecode. At this point, you have a choice, to either download the most recent development snapshot of ns-3:

$ python download.py

or to specify a release of ns-3, using the -n flag to specify a release number:

$ python download.py -n ns-3.29

After this step, the additional repositories of ns-3, bake, pybindgen, and netanim will be downloaded to the ns-3-allinone directory.

Downloading ns-3 Using Bake

The above two techniques (source archive, or ns-3-allinone repository via Git) are useful to get the most basic installation of ns-3 with a few addons (pybindgen for generating Python bindings, and netanim for network animiations). The third repository provided by default in ns-3-allinone is called bake.

Bake is a tool for coordinated software building from multiple repositories, developed for the ns-3 project.  Bake can be used to fetch development versions of the ns-3 software, and to download and build extensions to the base ns-3 distribution, such as the Direct Code Execution environment, Network Simulation Cradle, ability to create new Python bindings, and various ns-3 “apps”. If you envision that your ns-3 installation may use advanced or optional features, you may wish to follow this installation path.

In recent ns-3 releases, Bake has been included in the release tarball. The configuration file included in the released version will allow one to download any software that was current at the time of the release. That is, for example, the version of Bake that is distributed with the ns-3.29 release can be used to fetch components for that ns-3 release or earlier, but can’t be used to fetch components for later releases (unless the bakeconf.xml package description file is updated).

You can also get the most recent copy of bake by typing the following into your Linux shell (assuming you have installed Git):

$ cd
$ mkdir workspace
$ cd workspace
$ git clone https://gitlab.com/nsnam/bake.git

As the git command executes, you should see something like the following displayed:

Cloning into 'bake'...
remote: Enumerating objects: 2086, done.
remote: Counting objects: 100% (2086/2086), done.
remote: Compressing objects: 100% (649/649), done.
remote: Total 2086 (delta 1404), reused 2078 (delta 1399)
Receiving objects: 100% (2086/2086), 2.68 MiB | 3.82 MiB/s, done.
Resolving deltas: 100% (1404/1404), done.

After the clone command completes, you should have a directory called bake, the contents of which should look something like the following:

$ cd bake
$ ls
bake  bakeconf.xml  bake.py  doc  examples  generate-binary.py  test  TODO

Notice that you have downloaded some Python scripts, a Python module called bake, and an XML configuration file. The next step will be to use those scripts to download and build the ns-3 distribution of your choice.

There are a few configuration targets available:

  1. ns-3.29: the module corresponding to the release; it will download components similar to the release tarball.
  2. ns-3-dev: a similar module but using the development code tree
  3. ns-allinone-3.29: the module that includes other optional features such as Click routing, Openflow for ns-3, and the Network Simulation Cradle
  4. ns-3-allinone: similar to the released version of the allinone module, but for development code.

The current development snapshot (unreleased) of ns-3 may be found at https://gitlab.com/nsnam/ns-3-dev.git. The developers attempt to keep these repositories in consistent, working states but they are in a development area with unreleased code present, so you may want to consider staying with an official release if you do not need newly- introduced features.

You can find the latest version of the code either by inspection of the repository list or by going to the “ns-3 Releases” web page and clicking on the latest release link. We’ll proceed in this tutorial example with ns-3.29.

We are now going to use the bake tool to pull down the various pieces of ns-3 you will be using. First, we’ll say a word about running bake.

bake works by downloading source packages into a source directory, and installing libraries into a build directory. bake can be run by referencing the binary, but if one chooses to run bake from outside of the directory it was downloaded into, it is advisable to put bake into your path, such as follows (Linux bash shell example). First, change into the ‘bake’ directory, and then set the following environment variables:

$ export BAKE_HOME=`pwd`
$ export PATH=$PATH:$BAKE_HOME:$BAKE_HOME/build/bin
$ export PYTHONPATH=$PYTHONPATH:$BAKE_HOME:$BAKE_HOME/build/lib

This will put the bake.py program into the shell’s path, and will allow other programs to find executables and libraries created by bake. Although several bake use cases do not require setting PATH and PYTHONPATH as above, full builds of ns-3-allinone (with the optional packages) typically do.

Step into the workspace directory and type the following into your shell:

$ ./bake.py configure -e ns-3.29

Next, we’ll ask bake to check whether we have enough tools to download various components. Type:

$ ./bake.py check

You should see something like the following:

> Python - OK
> GNU C++ compiler - OK
> Mercurial - OK
> Git - OK
> Tar tool - OK
> Unzip tool - OK
> Make - OK
> cMake - OK
> patch tool - OK
> Path searched for tools: /usr/local/sbin /usr/local/bin /usr/sbin /usr/bin /sbin /bin ...

In particular, download tools such as Mercurial, CVS, Git, and Bazaar are our principal concerns at this point, since they allow us to fetch the code. Please install missing tools at this stage, in the usual way for your system (if you are able to), or contact your system administrator as needed to install these tools.

Next, try to download the software:

$ ./bake.py download

should yield something like:

>> Searching for system dependency setuptools - OK
>> Searching for system dependency libgoocanvas2 - OK
>> Searching for system dependency gi-cairo - OK
>> Searching for system dependency pygobject - OK
>> Searching for system dependency pygraphviz - OK
>> Searching for system dependency python-dev - OK
>> Searching for system dependency qt - OK
>> Searching for system dependency g++ - OK
>> Downloading pybindgen-0.19.0.post4+ng823d8b2 (target directory:pybindgen) - OK
>> Downloading netanim-3.108 - OK
>> Downloading ns-3.29 - OK

The above suggests that three sources have been downloaded. Check the source directory now and type ls; one should see:

$ cd source
$ ls
netanim-3.108  ns-3.29  pybindgen

You are now ready to build the ns-3 distribution.

Building ns-3

As with downloading ns-3, there are a few ways to build ns-3. The main thing that we wish to emphasize is the following. ns-3 is built with a build tool called Waf, described below. Most users will end up working most directly with Waf, but there are some convenience scripts to get you started or to orchestrate more complicated builds. Therefore, please have a look at build.py and building with bake, before reading about Waf below.

Building with build.py

Note: This build step is only available from a source archive release described above; not from downloading via git or bake.

When working from a released tarball, a convenience script available as part of ns-3-allinone can orchestrate a simple build of components. This program is called build.py. This program will get the project configured for you in the most commonly useful way. However, please note that more advanced configuration and work with ns-3 will typically involve using the native ns-3 build system, Waf, to be introduced later in this tutorial.

If you downloaded using a tarball you should have a directory called something like ns-allinone-3.29 under your ~/workspace directory. Type the following:

$ ./build.py --enable-examples --enable-tests

Because we are working with examples and tests in this tutorial, and because they are not built by default in ns-3, the arguments for build.py tells it to build them for us. The program also defaults to building all available modules. Later, you can build ns-3 without examples and tests, or eliminate the modules that are not necessary for your work, if you wish.

You will see lots of compiler output messages displayed as the build script builds the various pieces you downloaded. First, the script will attempt to build the netanim animator, then the pybindgen bindings generator, and finally ns-3. Eventually you should see the following:

Waf: Leaving directory '/path/to/workspace/ns-allinone-3.29/ns-3.29/build'
'build' finished successfully (6m25.032s)

Modules built:
antenna                aodv                      applications
bridge                 buildings                 config-store
core                   csma                      csma-layout
dsdv                   dsr                       energy
fd-net-device          flow-monitor              internet
internet-apps          lr-wpan                   lte
mesh                   mobility                  mpi
netanim (no Python)    network                   nix-vector-routing
olsr                   point-to-point            point-to-point-layout
propagation            sixlowpan                 spectrum
stats                  tap-bridge                test (no Python)
topology-read          traffic-control           uan
virtual-net-device     visualizer                wave
wifi                   wimax

Modules not built (see ns-3 tutorial for explanation):
brite                  click                     openflow

Leaving directory ./ns-3.29

Regarding the portion about modules not built:

Modules not built (see ns-3 tutorial for explanation):
brite                     click

This just means that some ns-3 modules that have dependencies on outside libraries may not have been built, or that the configuration specifically asked not to build them. It does not mean that the simulator did not build successfully or that it will provide wrong results for the modules listed as being built.

Building with bake

If you used bake above to fetch source code from project repositories, you may continue to use it to build ns-3. Type:

$ ./bake.py build

and you should see something like:

>> Building pybindgen-0.19.0.post4+ng823d8b2 - OK
>> Building netanim-3.108 - OK
>> Building ns-3.29 - OK

Hint: you can also perform both steps, download and build, by calling ``bake.py deploy``.

There may be failures to build all components, but the build will proceed anyway if the component is optional. For example, a recent portability issue has been that castxml may not build via the bake build tool on all platforms; in this case, the line will show something like:

>> Building castxml - Problem
> Problem: Optional dependency, module "castxml" failed
  This may reduce the  functionality of the final build.
  However, bake will continue since "castxml" is not an essential dependency.
  For more information call bake with -v or -vvv, for full verbose mode.

However, castxml is only needed if one wants to generate updated Python bindings, and most users do not need to do so (or to do so until they are more involved with ns-3 changes), so such warnings might be safely ignored for now.

If there happens to be a failure, please have a look at what the following command tells you; it may give a hint as to a missing dependency:

$ ./bake.py show

This will list out the various dependencies of the packages you are trying to build.

Building with Waf

Up to this point, we have used either the build.py script, or the bake tool, to get started with building ns-3. These tools are useful for building ns-3 and supporting libraries, and they call into the ns-3 directory to call the Waf build tool to do the actual building. An installation of Waf is bundled with the ns-3 source code. Most users quickly transition to using Waf directly to configure and build ns-3. So, to proceed, please change your working directory to the ns-3 directory that you have initially built.

It’s not strictly required at this point, but it will be valuable to take a slight detour and look at how to make changes to the configuration of the project. Probably the most useful configuration change you can make will be to build the optimized version of the code. By default you have configured your project to build the debug version. Let’s tell the project to make an optimized build. To explain to Waf that it should do optimized builds that include the examples and tests, you will need to execute the following commands:

$ ./waf clean
$ ./waf configure --build-profile=optimized --enable-examples --enable-tests

This runs Waf out of the local directory (which is provided as a convenience for you). The first command to clean out the previous build is not typically strictly necessary but is good practice (but see Build Profiles, below); it will remove the previously built libraries and object files found in directory build/. When the project is reconfigured and the build system checks for various dependencies, you should see output that looks similar to the following:

Setting top to                           : /home/ns3user/workspace/bake/source/ns-3-dev
Setting out to                           : /home/ns3user/workspace/bake/source/ns-3-dev/build
Checking for 'gcc' (C compiler)          : /usr/bin/gcc
Checking for cc version                  : 7.3.0
Checking for 'g++' (C++ compiler)        : /usr/bin/g++
Checking for compilation flag -march=native support : ok
Checking for compilation flag -Wl,--soname=foo support : ok
Checking for compilation flag -std=c++11 support       : ok
Checking boost includes                                : headers not found, please provide a --boost-includes argument (see help)
Checking boost includes                                : headers not found, please provide a --boost-includes argument (see help)
Checking for program 'python'                          : /usr/bin/python
Checking for python version >= 2.3                     : 2.7.15
python-config                                          : /usr/bin/python-config
Asking python-config for pyembed '--cflags --libs --ldflags' flags : yes
Testing pyembed configuration                                      : yes
Asking python-config for pyext '--cflags --libs --ldflags' flags   : yes
Testing pyext configuration                                        : yes
Checking for compilation flag -fvisibility=hidden support          : ok
Checking for compilation flag -Wno-array-bounds support            : ok
Checking for pybindgen location                                    : ../pybindgen (guessed)
Checking for python module 'pybindgen'                             : 0.19.0.post4+g823d8b2
Checking for pybindgen version                                     : 0.19.0.post4+g823d8b2
Checking for code snippet                                          : yes
Checking for types uint64_t and unsigned long equivalence          : no
Checking for code snippet                                          : no
Checking for types uint64_t and unsigned long long equivalence     : yes
Checking for the apidefs that can be used for Python bindings      : gcc-LP64
Checking for internal GCC cxxabi                                   : complete
Checking for python module 'pygccxml'                              : not found
Checking for click location                                        : not found
Checking for program 'pkg-config'                                  : /usr/bin/pkg-config
Checking for 'gtk+-3.0'                                            : not found
Checking for 'libxml-2.0'                                          : yes
checking for uint128_t                                             : not found
checking for __uint128_t                                           : yes
Checking high precision implementation                             : 128-bit integer (default)
Checking for header stdint.h                                       : yes
Checking for header inttypes.h                                     : yes
Checking for header sys/inttypes.h                                 : not found
Checking for header sys/types.h                                    : yes
Checking for header sys/stat.h                                     : yes
Checking for header dirent.h                                       : yes
Checking for header stdlib.h                                       : yes
Checking for header signal.h                                       : yes
Checking for header pthread.h                                      : yes
Checking for header stdint.h                                       : yes
Checking for header inttypes.h                                     : yes
Checking for header sys/inttypes.h                                 : not found
Checking for library rt                                            : yes
Checking for header sys/ioctl.h                                    : yes
Checking for header net/if.h                                       : yes
Checking for header net/ethernet.h                                 : yes
Checking for header linux/if_tun.h                                 : yes
Checking for header netpacket/packet.h                             : yes
Checking for NSC location                                          : not found
Checking for 'sqlite3'                                             : not found
Checking for header linux/if_tun.h                                 : yes
Checking for python module 'gi'                                    : 3.26.1
Checking for python module 'gi.repository.GObject'                 : ok
Checking for python module 'cairo'                                 : ok
Checking for python module 'pygraphviz'                            : 1.4rc1
Checking for python module 'gi.repository.Gtk'                     : ok
Checking for python module 'gi.repository.Gdk'                     : ok
Checking for python module 'gi.repository.Pango'                   : ok
Checking for python module 'gi.repository.GooCanvas'               : ok
Checking for program 'sudo'                                        : /usr/bin/sudo
Checking for program 'valgrind'                                    : not found
Checking for 'gsl'                                                 : not found
python-config                                                      : not found
Checking for compilation flag -fstrict-aliasing support            : ok
Checking for compilation flag -fstrict-aliasing support            : ok
Checking for compilation flag -Wstrict-aliasing support            : ok
Checking for compilation flag -Wstrict-aliasing support            : ok
Checking for program 'doxygen'                                     : /usr/bin/doxygen
---- Summary of optional NS-3 features:
Build profile                 : optimized
Build directory               :
BRITE Integration             : not enabled (BRITE not enabled (see option --with-brite))
DES Metrics event collection  : not enabled (defaults to disabled)
Emulation FdNetDevice         : enabled
Examples                      : enabled
File descriptor NetDevice     : enabled
GNU Scientific Library (GSL)  : not enabled (GSL not found)
Gcrypt library                : not enabled (libgcrypt not found: you can use libgcrypt-config to find its location.)
GtkConfigStore                : not enabled (library 'gtk+-3.0 >= 3.0' not found)
MPI Support                   : not enabled (option --enable-mpi not selected)
NS-3 Click Integration        : not enabled (nsclick not enabled (see option --with-nsclick))
NS-3 OpenFlow Integration     : not enabled (Required boost libraries not found)
Network Simulation Cradle     : not enabled (NSC not found (see option --with-nsc))
PlanetLab FdNetDevice         : not enabled (PlanetLab operating system not detected (see option --force-planetlab))
PyViz visualizer              : enabled
Python API Scanning Support   : not enabled (Missing 'pygccxml' Python module)
Python Bindings               : enabled
Real Time Simulator           : enabled
SQlite stats data output      : not enabled (library 'sqlite3' not found)
Tap Bridge                    : enabled
Tap FdNetDevice               : enabled
Tests                         : enabled
Threading Primitives          : enabled
Use sudo to set suid bit      : not enabled (option --enable-sudo not selected)
XmlIo                         : enabled
'configure' finished successfully (6.387s)

Note the last part of the above output. Some ns-3 options are not enabled by default or require support from the underlying system to work properly. For instance, to enable XmlTo, the library libxml-2.0 must be found on the system. If this library were not found, the corresponding ns-3 feature would not be enabled and a message would be displayed. Note further that there is a feature to use the program sudo to set the suid bit of certain programs. This is not enabled by default and so this feature is reported as “not enabled.” Finally, to reprint this summary of which optional features are enabled, use the --check-config option to waf.

Now go ahead and switch back to the debug build that includes the examples and tests.

$ ./waf clean
$ ./waf configure --build-profile=debug --enable-examples --enable-tests

The build system is now configured and you can build the debug versions of the ns-3 programs by simply typing:

$ ./waf

Although the above steps made you build the ns-3 part of the system twice, now you know how to change the configuration and build optimized code.

A command exists for checking which profile is currently active for an already configured project:

$ ./waf --check-profile
Waf: Entering directory \`/path/to/ns-3-allinone/ns-3.29/build\'
Build profile: debug

The build.py script discussed above supports also the --enable-examples and enable-tests arguments, but in general, does not directly support other waf options; for example, this will not work:

$ ./build.py --disable-python

will result in:

build.py: error: no such option: --disable-python

However, the special operator -- can be used to pass additional options through to waf, so instead of the above, the following will work:

$ ./build.py -- --disable-python

as it generates the underlying command ./waf configure --disable-python.

Here are a few more introductory tips about Waf.

Handling build errors

ns-3 releases are tested against the most recent C++ compilers available in the mainstream Linux and macOS distributions at the time of the release. However, over time, newer distributions are released, with newer compilers, and these newer compilers tend to be more pedantic about warnings. ns-3 configures its build to treat all warnings as errors, so it is sometimes the case, if you are using an older release version on a newer system, that a compiler warning will cause the build to fail.

For instance, ns-3.28 was released prior to Fedora 28, which included a new major version of gcc (gcc-8). Building ns-3.28 or older releases on Fedora 28, when Gtk2+ is installed, will result in an error such as:

/usr/include/gtk-2.0/gtk/gtkfilechooserbutton.h:59:8: error: unnecessary parentheses in declaration of ‘__gtk_reserved1’ [-Werror=parentheses]
 void (*__gtk_reserved1);

In releases starting with ns-3.28.1, an option is available in Waf to work around these issues. The option disables the inclusion of the ‘-Werror’ flag to g++ and clang++. The option is ‘–disable-werror’ and must be used at configure time; e.g.:

./waf configure --disable-werror --enable-examples --enable-tests

Configure vs. Build

Some Waf commands are only meaningful during the configure phase and some commands are valid in the build phase. For example, if you wanted to use the emulation features of ns-3, you might want to enable setting the suid bit using sudo as described above. This turns out to be a configuration-time command, and so you could reconfigure using the following command that also includes the examples and tests.

$ ./waf configure --enable-sudo --enable-examples --enable-tests

If you do this, Waf will have run sudo to change the socket creator programs of the emulation code to run as root.

There are many other configure- and build-time options available in Waf. To explore these options, type:

$ ./waf --help

We’ll use some of the testing-related commands in the next section.

Build Profiles

We already saw how you can configure Waf for debug or optimized builds:

$ ./waf --build-profile=debug

There is also an intermediate build profile, release. -d is a synonym for --build-profile.

The build profile controls the use of logging, assertions, and compiler optimization:

Feature Build Profile
debug release optimized
Enabled Features
NS3_BUILD_PROFILE_DEBUG
NS_LOG...
NS_ASSERT...
NS3_BUILD_PROFILE_RELEASE NS3_BUILD_PROFILE_OPTIMIZED
Code Wrapper Macro NS_BUILD_DEBUG(code) NS_BUILD_RELEASE(code) NS_BUILD_OPTIMIZED(code)
Compiler Flags -O0 -ggdb -g3 -O3 -g0 -fomit-frame-pointer -O3 -g -fstrict-overflow -march=native

As you can see, logging and assertions are only available in debug builds. Recommended practice is to develop your scenario in debug mode, then conduct repetitive runs (for statistics or changing parameters) in optimized build profile.

If you have code that should only run in specific build profiles, use the indicated Code Wrapper macro:

NS_BUILD_DEBUG (std::cout << "Part of an output line..." << std::flush; timer.Start ());
DoLongInvolvedComputation ();
NS_BUILD_DEBUG (timer.Stop (); std::cout << "Done: " << timer << std::endl;)

By default Waf puts the build artifacts in the build directory. You can specify a different output directory with the --out option, e.g.

$ ./waf configure --out=my-build-dir

Combining this with build profiles lets you switch between the different compile options in a clean way:

$ ./waf configure --build-profile=debug --out=build/debug
$ ./waf build
...
$ ./waf configure --build-profile=optimized --out=build/optimized
$ ./waf build
...

This allows you to work with multiple builds rather than always overwriting the last build. When you switch, Waf will only compile what it has to, instead of recompiling everything.

When you do switch build profiles like this, you have to be careful to give the same configuration parameters each time. It may be convenient to define some environment variables to help you avoid mistakes:

$ export NS3CONFIG="--enable-examples --enable-tests"
$ export NS3DEBUG="--build-profile=debug --out=build/debug"
$ export NS3OPT=="--build-profile=optimized --out=build/optimized"

$ ./waf configure $NS3CONFIG $NS3DEBUG
$ ./waf build
...
$ ./waf configure $NS3CONFIG $NS3OPT
$ ./waf build

Compilers and Flags

In the examples above, Waf uses the GCC C++ compiler, g++, for building ns-3. However, it’s possible to change the C++ compiler used by Waf by defining the CXX environment variable. For example, to use the Clang C++ compiler, clang++,

$ CXX="clang++" ./waf configure
$ ./waf build

One can also set up Waf to do distributed compilation with distcc in a similar way:

$ CXX="distcc g++" ./waf configure
$ ./waf build

More info on distcc and distributed compilation can be found on it’s project page under Documentation section.

To add compiler flags, use the CXXFLAGS_EXTRA environment variable when you configure ns-3.

Install

Waf may be used to install libraries in various places on the system. The default location where libraries and executables are built is in the build directory, and because Waf knows the location of these libraries and executables, it is not necessary to install the libraries elsewhere.

If users choose to install things outside of the build directory, users may issue the ./waf install command. By default, the prefix for installation is /usr/local, so ./waf install will install programs into /usr/local/bin, libraries into /usr/local/lib, and headers into /usr/local/include. Superuser privileges are typically needed to install to the default prefix, so the typical command would be sudo ./waf install. When running programs with Waf, Waf will first prefer to use shared libraries in the build directory, then will look for libraries in the library path configured in the local environment. So when installing libraries to the system, it is good practice to check that the intended libraries are being used.

Users may choose to install to a different prefix by passing the --prefix option at configure time, such as:

./waf configure --prefix=/opt/local

If later after the build the user issues the ./waf install command, the prefix /opt/local will be used.

The ./waf clean command should be used prior to reconfiguring the project if Waf will be used to install things at a different prefix.

In summary, it is not necessary to call ./waf install to use ns-3. Most users will not need this command since Waf will pick up the current libraries from the build directory, but some users may find it useful if their use case involves working with programs outside of the ns-3 directory.

One Waf

There is only one Waf script, at the top level of the ns-3 source tree. As you work, you may find yourself spending a lot of time in scratch/, or deep in src/..., and needing to invoke Waf. You could just remember where you are, and invoke Waf like this:

$ ../../../waf ...

but that gets tedious, and error prone, and there are better solutions.

One common way when using a text-based editor such as emacs or vim is to open two terminal sessions and use one to build ns-3 and one to edit source code.

If you only have the tarball, an environment variable can help:

$ export NS3DIR="$PWD"
$ function waff { cd $NS3DIR && ./waf $* ; }

$ cd scratch
$ waff build

It might be tempting in a module directory to add a trivial waf script along the lines of exec ../../waf. Please don’t. It’s confusing to newcomers, and when done poorly it leads to subtle build errors. The solutions above are the way to go.

Testing ns-3

You can run the unit tests of the ns-3 distribution by running the ./test.py script:

$ ./test.py

These tests are run in parallel by Waf. You should eventually see a report saying that

92 of 92 tests passed (92 passed, 0 failed, 0 crashed, 0 valgrind errors)

This is the important message to check for; failures, crashes, or valgrind errors indicate problems with the code or incompatibilities between the tools and the code.

You will also see the summary output from Waf and the test runner executing each test, which will actually look something like:

Waf: Entering directory `/path/to/workspace/ns-3-allinone/ns-3-dev/build'
Waf: Leaving directory `/path/to/workspace/ns-3-allinone/ns-3-dev/build'
'build' finished successfully (1.799s)

Modules built:
aodv                      applications              bridge
click                     config-store              core
csma                      csma-layout               dsdv
emu                       energy                    flow-monitor
internet                  lte                       mesh
mobility                  mpi                       netanim
network                   nix-vector-routing        ns3tcp
ns3wifi                   olsr                      openflow
point-to-point            point-to-point-layout     propagation
spectrum                  stats                     tap-bridge
template                  test                      tools
topology-read             uan                       virtual-net-device
visualizer                wifi                      wimax

PASS: TestSuite ns3-wifi-interference
PASS: TestSuite histogram

...

PASS: TestSuite object
PASS: TestSuite random-number-generators
92 of 92 tests passed (92 passed, 0 failed, 0 crashed, 0 valgrind errors)

This command is typically run by users to quickly verify that an ns-3 distribution has built correctly. (Note the order of the PASS: ... lines can vary, which is okay. What’s important is that the summary line at the end report that all tests passed; none failed or crashed.)

Both Waf and test.py will split up the job on the available CPU cores of the machine, in parallel.

Running a Script

We typically run scripts under the control of Waf. This allows the build system to ensure that the shared library paths are set correctly and that the libraries are available at run time. To run a program, simply use the --run option in Waf. Let’s run the ns-3 equivalent of the ubiquitous hello world program by typing the following:

$ ./waf --run hello-simulator

Waf first checks to make sure that the program is built correctly and executes a build if required. Waf then executes the program, which produces the following output.

Hello Simulator

Congratulations! You are now an ns-3 user!

What do I do if I don’t see the output?

If you see Waf messages indicating that the build was completed successfully, but do not see the “Hello Simulator” output, chances are that you have switched your build mode to optimized in the Building with Waf section, but have missed the change back to debug mode. All of the console output used in this tutorial uses a special ns-3 logging component that is useful for printing user messages to the console. Output from this component is automatically disabled when you compile optimized code – it is “optimized out.” If you don’t see the “Hello Simulator” output, type the following:

$ ./waf configure --build-profile=debug --enable-examples --enable-tests

to tell Waf to build the debug versions of the ns-3 programs that includes the examples and tests. You must still build the actual debug version of the code by typing

$ ./waf

Now, if you run the hello-simulator program, you should see the expected output.

Program Arguments

To feed command line arguments to an ns-3 program use this pattern:

$ ./waf --run <ns3-program> --command-template="%s <args>"

Substitute your program name for <ns3-program>, and the arguments for <args>. The --command-template argument to Waf is basically a recipe for constructing the actual command line Waf should use to execute the program. Waf checks that the build is complete, sets the shared library paths, then invokes the executable using the provided command line template, inserting the program name for the %s placeholder.

If you find the above to be syntactically complicated, a simpler variant exists, which is to include the ns-3 program and its arguments enclosed by single quotes, such as:

$ ./waf --run '<ns3-program> --arg1=value1 --arg2=value2 ...'

Another particularly useful example is to run a test suite by itself. Let’s assume that a mytest test suite exists (it doesn’t). Above, we used the ./test.py script to run a whole slew of tests in parallel, by repeatedly invoking the real testing program, test-runner. To invoke test-runner directly for a single test:

$ ./waf --run test-runner --command-template="%s --suite=mytest --verbose"

This passes the arguments to the test-runner program. Since mytest does not exist, an error message will be generated. To print the available test-runner options:

$ ./waf --run test-runner --command-template="%s --help"

Debugging

To run ns-3 programs under the control of another utility, such as a debugger (e.g. gdb) or memory checker (e.g. valgrind), you use a similar --command-template="..." form.

For example, to run your ns-3 program hello-simulator with the arguments <args> under the gdb debugger:

$ ./waf --run=hello-simulator --command-template="gdb %s --args <args>"

Notice that the ns-3 program name goes with the --run argument, and the control utility (here gdb) is the first token in the --command-template argument. The --args tells gdb that the remainder of the command line belongs to the “inferior” program. (Some gdb’s don’t understand the --args feature. In this case, omit the program arguments from the --command-template, and use the gdb command set args.)

We can combine this recipe and the previous one to run a test under the debugger:

$ ./waf --run test-runner --command-template="gdb %s --args --suite=mytest --verbose"

Working Directory

Waf needs to run from its location at the top of the ns-3 tree. This becomes the working directory where output files will be written. But what if you want to keep those files out of the ns-3 source tree? Use the --cwd argument:

$ ./waf --cwd=...

It may be more convenient to start with your working directory where you want the output files, in which case a little indirection can help:

$ function waff {
    CWD="$PWD"
    cd $NS3DIR >/dev/null
    ./waf --cwd="$CWD" $*
    cd - >/dev/null
  }

This embellishment of the previous version saves the current working directory, cd’s to the Waf directory, then instructs Waf to change the working directory back to the saved current working directory before running the program.

We mention this --cwd command for completeness; most users will simply run Waf from the top-level directory and generate the output data files there.

Running without Building

As of the ns-3.30 release, a new Waf option was introduced to allow the running of programs while skipping the build step. This can reduce the time to run programs when, for example, running the same program repeatedly through a shell script, or when demonstrating program execution. This option, --run-no-build, behaves the same as the -run option, except that the program and ns-3 libraries will not be rebuilt.

$ ./waf --run-no-build '<ns3-program> --arg1=value1 --arg2=value2 ...'