Merge branch 'main' of github.com:ZettaScaleLabs/roscon2024_workshop

README.md

@@ -91,3 +91,5 @@ The docker directory contains several scripts to help manage the container:
 ### [Exercise 5 - Discovery via UDP multicast](exercises/ex-5.md)
 
 ### [Exercise 6 - Access Control](exercises/ex-6.md)
+
+### [Exercise 7 - Downsampling](exercises/ex-7.md)

exercises/ex-7.md

@@ -0,0 +1,49 @@
+# Exercise 7 - Downsampling
+
+By configuration the Zenoh router can perform downsampling (i.e. reducing the frequency of messages) for some topics published via a specified interface.
+
+## Configuration
+
+<p align="center"><img src="pictures/downsampling.png"  height="300" alt="downsampling"/></p>
+
+Follow up with the same partner than the previous exercise.
+
+In container A add this `downsampling` configuration at the end of your `zenoh_confs/ROUTER_CONFIG.json5` file (just before the last `}`):
+
+```json5
+downsampling: [
+  {
+    // Downsampling publications in egress on WiFi interface
+    interfaces: ["<YOUR_WIFI_INTERFACE>"],
+    flow: "egress",
+    rules: [
+      // 0.5Hz for the Zenoh key expression used for the "/chatter_public" topic
+      {
+        key_expr: "0/chatter_public/std_msgs::msg::dds_::String_/RIHS01_df668c740482bbd48fb39d76a70dfd4bd59db1288021743503259e948f6b1a18",
+        freq: 0.5
+      },
+    ],
+  },
+],
+```
+
+## Running the Test
+
+Run the same commands than for previous exercise:
+
+* In container A:
+  * Start the router (with the custom configuration): `ZENOH_ROUTER_CONFIG_URI=/ros_ws/zenoh_confs/ROUTER_CONFIG.json5 ros2 run rmw_zenoh_cpp rmw_zenohd`
+    You can also add this environment variable to see the router applying the access control:
+    `RUST_LOG=info,zenoh::net::routing::interceptor=debug`
+  * Start the publisher on the denied topic:
+    `ros2 topic pub /chatter std_msgs/msg/String "data: Hello just me!"`
+  * Start another publisher on an allowed topic:
+    `ros2 topic pub /chatter_public std_msgs/msg/String "data: Hello World!"`
+* In container B:
+  * Start the router (with the default configuration): `ros2 run rmw_zenoh_cpp rmw_zenohd`
+  * Start the listener on the denied topic:
+    `ros2 topic echo /chatter`
+  * Start the listener on an allowed topic:
+    `ros2 topic echo /chatter_public`
+
+And see the result in the listener on `/chatter_public`.