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.

Compiling the ns-3/SimGrid binding

Installing ns-3

SimGrid requires ns-3 version 3.26 or higher, and you probably want the most recent version of both SimGrid and ns-3. While the Debian package of SimGrid don’t have the ns-3 bindings activated, you can still use the packaged version of ns-3 by grabbing the libns3-dev ns3 packages. Alternatively, you can install ns-3 from scratch as follows:

# Download the source
wget http://www.nsnam.org/release/ns-allinone-3.29.tar.bz2
tar -xf ns-allinone-3.29.tar.bz2
cd ns-allinone-3.29/ns-3.29/
# 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 ns-3 in SimGrid

SimGrid must be recompiled with the enable_ns3 option activated in cmake. Optionally, use NS3_HINT to hint cmake about where to find ns-3.

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. Otherwise, explore CMakeFiles/CMakeOutput.log and CMakeFiles/CMakeError.log to diagnose the problem.

Test your installation after compilation as follows:

ctest -R ns3

Troubleshooting

If you use a version of ns-3 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. Conversely, if something goes wrong with an old version of either SimGrid or ns-3, try upgrading everything.

Using ns-3 from SimGrid

The SimGrid/ns-3 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.

Platform files compatibility

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>

This can be reformulated as follows to make it usable with the ns-3 binding. There is no direct connexion from alice to bob, but that’s OK because ns-3 automatically routes 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 “ns-3” as follows. The rest is unchanged.

./network-ns3 --cfg=network/model:ns-3 (other parameters)

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/deprecated/msg/network-ns3/network-ns3.tesh to see which ones are used in our regression tests.

Limitations

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 ns-3 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. If you come up with interesting improvements, please contribute them back

Troubleshooting

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.