ex-7.md

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

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 }):

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.