+------------------------
+
+As a SMPI user, you are supposed to provide a description of your
+virtual platform, that is mostly a set of simulated hosts and network
+links with some performance characteristics. SimGrid provides a plenty
+of :ref:`documentation <platform>`_ and examples (in the
+`examples/platforms <https://framagit.org/simgrid/simgrid/tree/master/examples/platforms>`_
+source directory), and this section only shows a small set of introductory
+examples.
+
+Simple Example with 3 hosts
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+At the most basic level, you can describe your simulated platform as a
+graph of hosts and network links. For instance:
+
+.. image:: /tuto_smpi/img/3hosts.png
+ :align: center
+
+.. literalinclude:: /tuto_smpi/3hosts.xml
+ :language: xml
+
+Note the way in which hosts, links, and routes are defined in
+this XML. All hosts are defined with a speed (in Gflops), and links
+with a latency (in us) and bandwidth (in MBytes per second). Other
+units are possible and written as expected. Routes specify the list of
+links encountered from one route to another. Routes are symmetrical by
+default.
+
+Cluster with a Crossbar
+^^^^^^^^^^^^^^^^^^^^^^^
+
+A very common parallel computing platform is a homogeneous cluster in
+which hosts are interconnected via a crossbar switch with as many
+ports as hosts, so that any disjoint pairs of hosts can communicate
+concurrently at full speed. For instance:
+
+Cluster with a Shared Backbone
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
