3 ns-3 as a SimGrid model
4 #######################
6 You can use the well-known `ns-3 packet-level network simulator
7 <http://www.nsnam.org>`_ as a SimGrid model, for example to investigate the
8 validity of your simulation. Just install ns-3 and recompile SimGrid
11 The SimGrid/ns-3 binding only contains features that are common to both systems.
12 Not all ns-3 models are available from SimGrid (only the TCP and WiFi ones are),
13 while not all SimGrid platform files can be used in conjunction ns-3 (routes
14 must be of length 1). Also, the platform built in ns-3 from the SimGrid
15 description is very basic. Finally, communicating from a host to
16 itself is forbidden in ns-3, so every such communication completes
17 immediately upon startup.
20 Compiling the ns-3/SimGrid binding
21 **********************************
26 SimGrid requires ns-3 version 3.26 or higher, and you probably want the most
27 recent version of both SimGrid and ns-3. While the Debian package of SimGrid
28 don't have the ns-3 bindings activated, you can still use the packaged version
29 of ns-3 by grabbing the ``libns3-dev ns3`` packages. Alternatively, you can
30 install ns-3 from scratch (see the `ns-3 documentation <http://www.nsnam.org>`_).
32 Enabling ns-3 in SimGrid
33 ========================
35 SimGrid must be recompiled with the ``enable_ns3`` option activated in cmake.
36 Optionally, use ``NS3_HINT`` to tell cmake where ns3 is installed on
41 cmake . -Denable_ns3=ON -DNS3_HINT=/opt/ns3 # or change the path if needed
43 By the end of the configuration, cmake reports whether ns-3 was found,
44 and this information is also available in ``include/simgrid/config.h``
45 If your local copy defines the variable ``SIMGRID_HAVE_NS3`` to 1, then ns-3
46 was correctly detected. Otherwise, explore ``CMakeFiles/CMakeOutput.log`` and
47 ``CMakeFiles/CMakeError.log`` to diagnose the problem.
49 Test that ns-3 was successfully integrated with the following (from your SimGrid
50 build directory). It will run all SimGrid tests that are related to the ns-3
51 integration. If no test is run at all, you probably forgot to enable ns-3 in cmake.
60 If you use a version of ns-3 that is not known to SimGrid yet, edit
61 ``tools/cmake/Modules/FindNS3.cmake`` in your SimGrid tree, according to the
62 comments on top of this file. Conversely, if something goes wrong with an old
63 version of either SimGrid or ns-3, try upgrading everything.
67 Using ns-3 from SimGrid
68 ***********************
70 Platform files compatibility
71 ============================
73 Any route longer than one will be ignored when using ns-3. They are
74 harmless, but you still need to connect your hosts using one-hop routes.
75 The best solution is to add routers to split your route. Here is an
76 example of an invalid platform:
81 <!DOCTYPE platform SYSTEM "https://simgrid.org/simgrid.dtd">
82 <platform version="4.1">
83 <zone id="zone0" routing="Floyd">
84 <host id="alice" speed="1Gf" />
85 <host id="bob" speed="1Gf" />
87 <link id="l1" bandwidth="1Mbps" latency="5ms" />
88 <link id="l2" bandwidth="1Mbps" latency="5ms" />
90 <route src="alice" dst="bob">
91 <link_ctn id="l1"/> <!-- !!!! IGNORED WHEN USED WITH ns-3 !!!! -->
92 <link_ctn id="l2"/> <!-- !!!! ROUTES MUST CONTAIN ONE LINK ONLY !!!! -->
97 This can be reformulated as follows to make it usable with the ns-3 binding.
98 There is no direct connection from alice to bob, but that's OK because ns-3
99 automatically routes from point to point (using
100 ``ns3::Ipv4GlobalRoutingHelper::PopulateRoutingTables``).
104 <?xml version='1.0'?>
105 <!DOCTYPE platform SYSTEM "https://simgrid.org/simgrid.dtd">
106 <platform version="4.1">
107 <zone id="zone0" routing="Full">
108 <host id="alice" speed="1Gf" />
109 <host id="bob" speed="1Gf" />
111 <router id="r1" /> <!-- routers are compute-less hosts -->
113 <link id="l1" bandwidth="1Mbps" latency="5ms"/>
114 <link id="l2" bandwidth="1Mbps" latency="5ms"/>
116 <route src="alice" dst="r1">
120 <route src="r1" dst="bob">
126 Once your platform is OK, just change the :ref:`network/model
127 <options_model_select>` configuration option to `ns-3` as follows. The other
128 options can be used as usual.
130 .. code-block:: shell
132 ./network-ns3 --cfg=network/model:ns-3 (other parameters)
134 Many other files from the ``examples/platform`` directory are usable with the
135 ns-3 model, such as `examples/platforms/dogbone.xml <https://framagit.org/simgrid/simgrid/tree/master/examples/platforms/dogbone.xml>`_.
136 Check the file `examples/s4u/network-ns3/network-ns3.tesh <https://framagit.org/simgrid/simgrid/tree/master/examples/s4u/network-ns3/network-ns3.tesh>`_
137 to see which ones are used in our regression tests.
142 In SimGrid, WiFi networks are modeled as regular links with a specific
143 attribute, and these links are then added to routes between hosts. The main
144 difference When using ns-3 WiFi networks is that the network performance is not
145 given by the link bandwidth and latency but by the access point WiFi
146 characteristics, and the distance between the access point and the hosts (called
147 station in the WiFi world).
149 So, to declare a new WiFi network, simply declare a link with the ``WiFi``
150 sharing policy as you would do in a pure SimGrid simulation (you must still
151 provide the ``bandwidth`` and ``latency`` attributes even if they are ignored,
152 because they are mandatory to the SimGrid XML parser).
156 <link id="net0" bandwidth="0" latency="0" sharing_policy="WIFI"/>
158 To declare that a given host is connected to this WiFi zone, use the
159 ``wifi_link`` property of that host. The property value must be the link id that
160 you want to use as a WiFi zone. This is not needed when using pure SimGrid wifi,
161 only when using ns-3 wifi, because the wifi performance is :ref:`configured <ns3_wifi_perf>`.
165 <host id="alice" speed="1Gf">
166 <prop id="wifi_link" value="net0"/>
169 To connect the station node to the access point node, simply create a route
174 <route src="alice" dst="bob">
175 <link_ctn id="net0" />
180 WiFi network performance
181 ^^^^^^^^^^^^^^^^^^^^^^^^
184 The performance of a wifi network is controlled by 3 property that can be added
185 to the a host connected to the wifi zone:
187 * ``wifi_mcs`` (`Modulation and Coding Scheme <https://en.wikipedia.org/wiki/Link_adaptation>`_)
188 Roughly speaking, it defines the speed at which the access point is
189 exchanging data with all stations. It depends on its model and configuration,
190 and the possible values are listed for example on Wikipedia.
191 |br| By default, ``wifi_mcs=3``.
192 * ``wifi_nss`` (Number of Spatial Streams, or `number of antennas <https://en.wikipedia.org/wiki/IEEE_802.11n-2009#Number_of_antennas>`_)
193 defines the amount of simultaneous data streams that the AP can sustain.
194 Not all value of MCS and NSS are valid nor compatible (cf. `802.11n standard <https://en.wikipedia.org/wiki/IEEE_802.11n-2009#Data_rates>`_).
195 |br| By default, ``wifi_nss=1``.
196 * ``wifi_distance`` is the distance from the station to the access point. Each
197 station can have a specific value.
198 |br| By default, ``wifi_distance=10``.
200 Here is an example of host changing all these values:
204 <host id="alice" speed="100.0Mf,50.0Mf,20.0Mf" pstate="0">
205 <prop id="wifi_link" value="net0"/>
206 <prop id="wifi_mcs" value="5"/>
207 <prop id="wifi_nss" value="2"/>
208 <prop id="wifi_distance" value="30" />
214 A ns-3 platform is automatically created from the provided SimGrid
215 platform. However, there are some known caveats:
217 * The default values (e.g., TCP parameters) are the ns-3 default values.
218 * ns-3 networks are routed using the shortest path algorithm, using ``ns3::Ipv4GlobalRoutingHelper::PopulateRoutingTables``.
219 * End hosts cannot have more than one interface card. So, your SimGrid hosts
220 should be connected to the platform through only one link. Otherwise, your
221 SimGrid host will be considered as a router (FIXME: is it still true?).
223 Our goal is to keep the ns-3 plugin of SimGrid as easy (and hopefully readable)
224 as possible. If the current state does not fit your needs, you should modify
225 this plugin, and/or create your own plugin from the existing one. If you come up
226 with interesting improvements, please contribute them back.
231 If your simulation hangs in a communication, this is probably because one host
232 is sending data that is not routable in your platform. Make sure that you only
233 use routes of length 1, and that any host is connected to the platform.
234 Arguably, SimGrid could detect this situation and report it, but unfortunately,
235 this is still to be done.