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ROS 2 Distributed Communication (Part 1: Basics)

1. Concept​

Multi-machine communication, also known as distributed communication, refers to a communication strategy that enables data exchange between different hosts over a network.

ROS 2 itself is a distributed communication framework. The middleware underlying ROS 2 is DDS (Data Distribution Service). When running on the same network, distributed communication is achieved through the DDS Domain ID mechanism (ROS_DOMAIN_ID).

How It Works​

Before starting a node, you can set a domain ID value. Nodes with the same domain ID can freely discover and communicate with each other. If the domain IDs are different, communication is not possible.

By default, all nodes start with:

ROS_DOMAIN_ID=0

This means that as long as devices are on the same network, distributed communication works automatically without extra configuration.

2. Typical Applications​

Distributed communication is widely used in scenarios such as:

  • Unmanned vehicle platooning\
  • Drone swarms\
  • Remote robot control

All of these rely on distributed data exchange.

3. Implementation​

3.1 Default Implementation​

Distributed communication is achieved simply by placing all devices on the same network, such as:

  • The same WiFi network\
  • The same router

On Windows, setting a virtual machine to bridge mode places it on the same network as the host.

4. Test Setup​

Assume two hosts:

  • Host A
  • Host B

These can be:

  • Virtual machines\
  • Raspberry Pi\
  • Jetson devices\
  • x86/ARM hosts

All that is required is that they run the same ROS 2 version.

Step 1: Execute on Host A​

ros2 run demo_nodes_py talker

Step 2: Execute on Host B​

ros2 run demo_nodes_py listener

If the listener successfully receives messages from the talker, then multi-machine communication is working.

5. Remote Turtle Control Example​

Host A​

ros2 run turtlesim turtlesim_node

Host B​

ros2 run turtlesim turtle_teleop_key

The turtle on Host A can now be controlled remotely from Host B.