diff --git a/doc/fig_topologies_rs.txt b/doc/fig_topologies_rs.txt
new file mode 100644
index 0000000..0bd1730
--- /dev/null
+++ b/doc/fig_topologies_rs.txt
@@ -0,0 +1,5 @@
+(RF1)  (RF2)
+    \  /
+    [RS]
+    /  \
+(RF3)  (RF4)