SimGrid  3.17
Versatile Simulation of Distributed Systems
ns-3 as a SimGrid model

You can use the well-known ns-3 packet-level network simulator as a SimGrid model, for example to investigate the validity of your simulation. Just install ns-3 and recompile SimGrid accordingly.

Installing ns-3

The easiest is to install it with the package manager. Under Debian/Ubuntu, simply type as root:

apt-get install libns3-dev ns3

You can also install it from scratch with the following commands:

# Download the source
wget http://www.nsnam.org/release/ns-allinone-3.26.tar.bz2
tar -xf ns-allinone-3.26.tar.bz2
cd ns-allinone-3.26/ns-3.26/
# Configure, build and install
./waf configure --prefix="/opt/ns3" # or give another path if you prefer
./waf
./waf install

For more information, please refer to the ns-3 documentation (official website).

Enabling SimGrid's support for ns-3

Normally, you just have to enable ns-3 in ccmake or cmake as follows. If you installed ns-3 in a regular path, just drop the NS3_HINT configuration item.

cmake . -Denable_ns3=ON -DNS3_HINT=/opt/ns3 # or change the path if needed

By the end of the configuration, cmake reports whether ns-3 was found, and this information is also available in include/simgrid_config.h If your local copy defines the variable SIMGRID_HAVE_NS3 to 1, then ns-3 was correctly detected. If it's defined to 0, then something went wrong. Explore CMakeFiles/CMakeOutput.log and CMakeFiles/CMakeError.log to diagnose the problem.

Afterward, you can test your installation as follows:

$ ctest -R ns3

Using ns-3 from SimGrid

The SimGrid-ns3 binding only contains features that are common to both systems: ns-3 wireless models are not available, while SimGrid routes cannot be longer than 1. Also, the platform built in ns-3 from the SimGrid description is very basic.

Any route longer than one will be ignored when using ns-3. They are harmless, but you still need to connect your hosts using one-hop routes. The best solution is to add routers to split your route. Here is an example of invalid platform:

<platform>
<host id="alice" speed="1Gf" />
<host id="bob" speed="1Gf" />
<link id="l1" bw="1Mbps" />
<link id="l2" bw="1Mbps" />
<route src="alice" dst="bob">
<link_ctn id="l1"/> <!-- INVALID WITH NS-3 -->
<link_ctn id="l2"/> <!-- length=2 IS TOO MUCH -->
</route>
</platform>

Here is the same platform expressed in a way that ns-3 will understand. There is no direct connexion from alice to bob, but that's OK because ns-3 will find the path from point to point.

<platform>
<host id="alice" speed="1Gf" />
<host id="bob" speed="1Gf" />
<router id="r1" /> <!-- routers are compute-less hosts -->
<link id="l1" bw="1Mbps" />
<link id="l2" bw="1Mbps" />
<route src="alice" dst="r1">
<link_ctn id="l1"/>
</route>
<route src="r1" dst="bob">
<link_ctn id="l2"/>
</route>
</platform>

Once your platform is OK, just change the "network/model" configuration option to "NS3" as follows. The rest remains unchanged.

./network-ns3 ../../platforms/small_platform_one_link_routes.xml 3hosts_2links_d.xml --cfg=network/model:NS3

Many other files from the examples/platform directory are usable with the ns-3 model, such as examples/platforms/dogbone.xml. Check the file examples/msg/network-ns3/network-ns3.tesh to see which ones are used in our regression tests. You may also be interested in the ns-3/SimGrid examples.

Shortcomings of the ns-3 bindings in SimGrid

A ns-3 platform is automatically created from the provided SimGrid platform. However, there are some known caveats:

  • The default values (e.g., TCP parameters) are the ns3 default values.

  • ns-3 networks are routed using the shortest path algorithm, using ns3::Ipv4GlobalRoutingHelper::PopulateRoutingTables.

  • End hosts cannot have more than one interface card. So, your SimGrid hosts should be connected to the platform through only one link. Otherwise, your SimGrid host will be considered as a router.

Our goal is to keep the ns-3 plugin of SimGrid as easy (and hopefully readable) as possible. If the current state does not fit your needs, you should modify this plugin, and/or create your own plugin from the existing one.

Troubleshooting with ns-3 and SimGrid

I fail to compile ns-3 within SimGrid

If you have a ns-3 version that is not known to SimGrid yet, edit tools/cmake/Modules/FindNS3.cmake in your SimGrid tree, according to the comments on top of this file.

If the compilation fails on Debian/Ubuntu when linking the library because of some .a file that cannot be used dynamically, then you are probably using a very old (and buggy) libns3-dev package. Update it, or install libns3-3 manually.

The simulation hangs at some point

If your simulation hangs in a communication, this is probably because one host is sending data that is not routable in your platform. Make sure that you only use routes of length 1, and that any host is connected to the platform.

Arguably, SimGrid could detect this situation and report it, but unfortunately, this is still to be done.

I get a warning that some routes are ignored

Please read again the Using ns-3 from SimGrid section.