-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.
+The elements basic elements (with :ref:`pf_tag_host` and
+:ref:`pf_tag_link`) are described first, and then the routes between
+any pair of hosts are explicitely given with :ref:`pf_tag_route`.
+
+Any host must be given a computational speed in flops while links must
+be given a latency and a bandwidth. You can write 1Gf for
+1,000,000,000 flops (full list of units in the reference guide of
+:ref:`pf_tag_host` and :ref:`pf_tag_link`).
+
+Routes defined with :ref:`pf_tag_route` are symmetrical by default,
+meaning that the list of traversed links from A to B is the same as
+from B to A. Explicitely define non-symmetrical routes if you prefer.
