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-.. _platform:
-
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+.. _platform:
+
 Describing your Simulated Platform
-==================================
+##################################
+
+In SimGrid, platforms are usually described in XML. This formalism has
+some drawbacks, but using a specific format ensures that the platform
+is not mixed with the tested application. This separation of concern
+:ref:`is a must <howto_science>` for your Modeling and Simulation (M&S)
+work. When XML is too limiting, you may describe your platforms using
+the :ref:`lua bindings <platform_lua>` (it is not yet possible to do so in
+python or directly in C++).
+
+Any simulated platform must contain **basic elements**, such as
+:ref:`pf_tag_host`, :ref:`pf_tag_link`, :ref:`pf_tag_disk`, and similar.
+SimGrid makes no assumption about the **routing of your platform**, so you must declare
+explicitly the network path taken between each pair of hosts. 
+This can be done through a flat list of :ref:`pf_tag_route` for each pair of hosts (routes
+are symmetrical by default), or you may use the advanced concept of :ref:`networking zone <platform_routing>`
+to efficiently express the routing of your platform.
+Finally, you may also describe an **experimental scenario**, with qualitative (e.g., bandwidth variations representing
+an external load) and qualitative (e.g., representing how some elements fail and restart over time) changes.
+
+The most efficient way to learn about platform description is to look at the
+:ref:`many examples <platform_examples>` included in the archive and described
+in the next section. This documentation also contains some :ref:`hints and
+howtos <howto>`, as well as the full :ref:`XML reference guide
+<platform_reference>`.
+
+..  LocalWords:  SimGrid