Zenoh for ROS2 WiFi Communication

Overview

This guide helps you configure Zenoh to optimize ROS2 communications over WiFi networks. Zenoh serves as a more efficient alternative to standard DDS for wireless robot communication, reducing bandwidth usage and improving reliability.

Why Zenoh for ROS2 WiFi?

• Bandwidth Efficiency: Zenoh uses a more compact protocol than DDS, reducing network traffic
• Improved Reliability: Better handling of intermittent connectivity in wireless environments
• Simplified Multi-Robot Setup: Namespace configuration at the bridge level instead of per-node
• Fine-Grained Control: Manage topic frequency, prioritization, and filtering
• Lower Latency: Optimized for wireless environments with minimal overhead

Installation

Option 1: Debian/Ubuntu (Recommended)

```bash

Add Eclipse Zenoh repository

echo "deb [trusted=yes] https://download.eclipse.org/zenoh/debian-repo/ /" | sudo tee -a /etc/apt/sources.list > /dev/null sudo apt update

Install standalone bridge

sudo apt install zenoh-bridge-ros2dds

Or install plugin for existing Zenoh router

sudo apt install zenoh-plugin-ros2dds ```

Option 2: Docker

bash docker pull eclipse/zenoh-bridge-ros2dds:latest

Basic Configuration

Zenoh bridges use JSON5 configuration files. Here's the basic structure:

json5 { "plugins": { "ros2dds": { "nodename": "zenoh_bridge_ros2dds", "namespace": "/robot_name" } }, "mode": "router", "listen": { "endpoints": ["tcp/0.0.0.0:7447"] }, "connect": { "endpoints": ["tcp/192.168.1.100:7447"] } }

Configuration Examples

Robot-Side Configuration

json5 { "plugins": { "ros2dds": { "nodename": "zenoh_bridge_robot", "namespace": "/robot1", "domain": 0, "pub_max_frequencies": [ ".*/camera/image_raw=5", ".*/lidar_scan=10" ] } }, "mode": "router", "listen": { "endpoints": ["tcp/0.0.0.0:7447"] } }

Lab/Control Station Configuration

json5 { "plugins": { "ros2dds": { "nodename": "zenoh_bridge_lab", "namespace": "/" } }, "mode": "router", "connect": { "tcp/<ROBOT_IP_ADDRESS>:7447" } }

Multi-Robot Configuration

json5 { "plugins": { "ros2dds": { "nodename": "zenoh_bridge_central", "namespace": "/" } }, "mode": "router", "connect": { "endpoints": [ "tcp/192.168.1.101:7447", // Robot 1 "tcp/192.168.1.102:7447", // Robot 2 "tcp/192.168.1.103:7447" // Robot 3 ] } }

Advanced Configuration Options

Namespace Management

The namespace parameter is critical for multi-robot setups:

• Robot Bridge: Set to a unique identifier (e.g., /robot1, /jazzy)

  • Topics within the robot (like /camera/image) will automatically be prefixed when seen by the lab (/robot1/camera/image)
  • When the lab sends to /robot1/cmd_vel, the robot sees it as just /cmd_vel

• Lab Bridge: Usually set to root namespace (/)

  • Allows interaction with all robots without adding extra prefixes
  • Makes multi-robot visualization and monitoring easier

json5 "namespace": "/robot1" // For robot bridge "namespace": "/" // For lab bridge

Topic Filtering

Control which topics traverse the network using allow or deny lists:

json5 "allow": { "publishers": [".*/laser_scan", "/tf", ".*/pose"], "subscribers": [".*/cmd_vel"], "service_servers": [".*/.*_parameters"], "action_servers": [".*/navigate_to_pose"] }

json5 "deny": { "publishers": ["/rosout", "/parameter_events", ".*/raw_image"], "subscribers": ["/rosout"] }

You cannot use both allow and deny in the same configuration. The best approach is: - Use allow when you want to limit traffic to a small set of known topics - Use deny when you want to block just a few problematic topics

Frequency Control

Limit how often high-bandwidth topics cross the network:

json5 "pub_max_frequencies": [ ".*/camera/image_raw=5", // Limit to 5 Hz ".*/lidar_scan=10", // Limit to 10 Hz "/tf=20", // Limit to 20 Hz "/battery_status=0.1" // Once every 10 seconds ]

Frequency control should be applied at the source of the data (typically on the robot bridge), not at the destination.

Message Prioritization

Ensure critical messages get through even during network congestion:

json5 "pub_priorities": [ "/emergency_stop=1:express", // Highest priority, immediate delivery "/cmd_vel=2:express", // High priority, immediate delivery "/pose=3", // Medium-high priority "/diagnostic=7" // Lowest priority ]

Priority values range from 1 (highest) to 7 (lowest), with 5 as default. The express option bypasses batching for lower latency.

Network Configuration Options

```json5 // Configure Zenoh to operate as a router "mode": "router",

// Listen for incoming connections "listen": { "endpoints": ["tcp/0.0.0.0:7447"] },

// Connect to other bridges/routers "connect": { "endpoints": ["tcp/192.168.1.100:7447"] },

// Enable auto-discovery (for more dynamic setups) "scouting": { "multicast": { "enabled": true, "autoconnect": { "router": ["router"] } } } ```

Running Zenoh Bridge

Run the Zenoh bridge with your configuration file:

bash zenoh-bridge-ros2dds -c your_config.json5

To prevent DDS traffic from going over WiFi, set:

```bash

For ROS2 Iron and later:

export ROSAUTOMATICDISCOVERY_RANGE=LOCALHOST

Testing Your Configuration

To verify bridges are communicating properly:

```bash

List topics from all robots

ros2 topic list

Publish a test message

ros2 topic pub /testtopic stdmsgs/msg/String "{data: 'Jazzy robot is online'}" --rate 1

Subscribe to a topic with the robot's namespace

ros2 topic echo "/namespace"/test_topic ```

Troubleshooting

Common Issues

1. Bridges not connecting:

   • Verify IP addresses and port numbers
   • Check for firewalls blocking port 7447
   • Ensure both bridges are running

2. Topics not appearing:

   • Check namespace configuration
   • Verify topics aren't filtered by allow/deny settings
   • Confirm ROS nodes are publishing

3. Port conflicts when testing locally:

   • Use different ports for each bridge: json "listen": { "endpoints": ["tcp/127.0.0.1:7448"] }

Best Practices

1. Limit high-bandwidth topics: Use pub_max_frequencies to reduce network load from cameras, lidars, and other sensors.

2. Prioritize control messages: Give motion and safety commands the highest priority with pub_priorities.

3. Configure namespaces carefully: Use unique namespaces for each robot, and root namespace for the lab.

4. Use localhost isolation: Set ROS_LOCALHOST_ONLY=1 to prevent DDS from communicating directly over WiFi.

5. Start simple, then optimize: Begin with basic connectivity, then fine-tune with frequency controls and filtering.

6. Monitor bandwidth usage: Use network monitoring tools to identify bandwidth-heavy topics that need additional controls.

Additional Resources

• Zenoh Documentation
• Zenoh-ROS2-DDS GitHub Repository
• ROS2 Middleware Report on Zenoh