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Zenoh Communication

Starting from OPENMANIPULATOR package version 5.0.0, OMY changes its default ROS 2 middleware from Fast DDS to Zenoh RMW. This enables more stable communication between robot-side nodes, Docker containers, and external PCs. This page explains how to connect an external PC to the robot and how rmw_zenoh fits into the ROS 2 communication stack.
warning

At least one Zenoh daemon must be running in the communication network. If no Zenoh daemon is running, ROS 2 nodes cannot discover or communicate with each other. For OMY, we recommend running the Zenoh daemon inside the robot-side container. This requirement is noted at the top of each operation manual.

To start the Zenoh daemon manually, run zenohd in a terminal inside the robot-side container.

External PC Control​

To control OMY from an external PC, set up the open_manipulator Docker container on the external PC. Then connect the container's Zenoh client to the Zenoh router running on the robot.

Inside the external PC's open_manipulator container, set the following environment variable:

export ZENOH_CONFIG_OVERRIDE='transport/shared_memory/enabled=true;mode="client";connect/endpoints=["tcp/robot_ip:7447"]'

Replace robot_ip with the real IP address of the OMY robot. Use the robot's Wi-Fi IP address when both devices are connected over Wi-Fi, or use the robot's LAN IP address when the external PC is connected through Ethernet.

For example, if the robot's IP address is 192.168.0.42:

export ZENOH_CONFIG_OVERRIDE='transport/shared_memory/enabled=true;mode="client";connect/endpoints=["tcp/192.168.0.42:7447"]'

The open_manipulator Docker image enables Zenoh RMW by default. You can check or manually set it with:

export RMW_IMPLEMENTATION=rmw_zenoh_cpp

Keep ROS_DOMAIN_ID consistent across terminals and containers when the OMY environment expects a specific ROS domain. Even though Zenoh does not rely on DDS multicast discovery, the ROS 2 process environment should remain consistent across the robot-side stack.

What is rmw_zenoh?​

rmw_zenoh is the ROS 2 RMW (ROS Middleware) implementation for Zenoh. The implementation package is rmw_zenoh_cpp, and it maps the ROS 2 middleware API onto Zenoh APIs. Existing ROS 2 publishers, subscribers, services, clients, parameters, and command-line tools can keep using normal ROS 2 interfaces while Zenoh handles discovery and transport.

Zenoh is a pub/sub/query protocol designed to move data efficiently across local processes, robot networks, edge computers, and cloud systems. For OMY, this means the robot control software can use normal ROS 2 topics while Zenoh provides a lightweight communication layer that is easier to route across containers and hosts than multicast-heavy DDS discovery.

Main Components​

ComponentRole
rmw_zenoh_cppROS 2 RMW implementation selected by RMW_IMPLEMENTATION=rmw_zenoh_cpp.
rmw_zenohdZenoh router executable packaged with rmw_zenoh_cpp. It provides discovery information and host-to-host routing.
Zenoh sessionCommunication session used internally by ROS 2 contexts. Publishers, subscribers, services, and clients share the session.
Zenoh router configurationControls how routers listen, connect, and bridge communication between containers, the robot, and remote PCs.

How Communication Works​

  • ROS 2 nodes continue to publish and subscribe to normal topics such as /joint_states, /tf, or controller command topics.
  • rmw_zenoh_cpp converts the ROS 2 middleware calls into Zenoh operations.
  • A local Zenoh router is normally started so nodes can discover each other.
  • On the same host, message data can use direct peer-to-peer paths instead of forcing every sample through the router.
  • Across multiple hosts, configure the external PC container as a Zenoh client connected to the robot's Zenoh router endpoint.

Quick Checks​

Use these commands inside the open_manipulator container to confirm that Zenoh RMW is active and that the ROS graph is visible:

echo $RMW_IMPLEMENTATION
echo $ZENOH_CONFIG_OVERRIDE
ros2 node list
ros2 topic list
ros2 topic echo /joint_states

If topics appear but messages are not flowing, check that:

  • ZENOH_CONFIG_OVERRIDE uses the robot's real IP address.
  • The robot and external PC are on the same reachable network.
  • Port 7447 is reachable from the external PC.
  • The open_manipulator container is running with the expected network configuration.
  • Old ROS 2 daemon state has been stopped with ros2 daemon stop.

References​