3.4. Configuring ROS 2 Router’s Topic QoS¶

Background
Prerequisites
Deploy ROS 2 nodes
- Environment setup
- Running ROS 2 nodes
Deploying a ROS 2 Router
- Configuration
- Running the ROS 2 Router
Deploy ROS 2 nodes on topic secret
- Running ROS 2 nodes
Next steps

3.4.1. Background¶

eProsima ROS 2 Router, a.k.a DDS Router, is an end-user software application that enables the connection of distributed ROS 2 networks (see the ROS 2 Router documentation here). That is, ROS 2 nodes such as publishers and subscriptions, or clients and services, deployed in one geographic location and using a dedicated local network will be able to communicate with other ROS 2 nodes deployed in different geographic locations on their own dedicated local networks as if they were all on the same network through the ROS 2 Router.

This tutorial explains how to apply some configurations to individual DDS Topics forwarded by the ROS 2 Router. In particular, we will configure two participants in different domains and communicate them with a ROS 2 Router. The ROS 2 Router will configure a specific Topic for one of the participants using this new topic settings option. In particular, in this tutorial, we will fix the maximum transmission rate (max-tx-rate) of one of the topics for a specific participant, so that only this participant will apply this maximum publication rate only to this topic.

Note

This tutorial is similar to the Change ROS 2 Domain Id tutorial, since we will launch a talker and a listener on different domains and connect them with a ROS 2 Router. The difference between both tutorials is that, in this one, we will limit the transmission rate for a participant on a topic to avoid clogging the connection.

The DDS protocol defines the Domain Id as a parameter for every DomainParticipant. Different entities in different Domain Ids will never discover each other, and thus they will not communicate with each other. The ROS 2 Router can be used as a bridge between ROS 2 Domains, so that every node in a domain can communicate with every other node on another domain, as illustrated in the following figure:

../../../../_images/change_domain_topic_qos.png

This tutorial will use the demo_nodes_cpp package, available in the Vulcanexus Desktop distribution. Two ROS 2 nodes, a talker and a listener, will be launched on different ROS 2 Domains, so that they cannot communicate between each other. Then, the ROS 2 Router will be used as a bridge between the two Domains, allowing the listener to receive the messages from the talker.

3.4.2. Prerequisites¶

To proceed, please install Vulcanexus with one of the following installation methods:

3.4.3. Deploy ROS 2 nodes¶

Let us start by running the ROS 2 talker and listener nodes.

3.4.3.1. Environment setup¶

To run the nodes, we need to set up the Vulcanexus environment so that the demo_nodes_cpp package is available. There are two ways to achieve this:

Running the Vulcanexus Docker image.

Run the Vulcanexus Docker image by executing:
```
docker run -it ubuntu-vulcanexus:iron-desktop
```
The Docker container will automatically setup the Vulcanexus environment on start up, but in case you installed Vulcanexus from binaries please do not forget to source the Vulcanexus installation first by executing:
```
source /opt/vulcanexus/iron/setup.bash
```
Setting up a development environment on the local host.

To do this, the vucanexus-iron-desktop package is needed, since it includes all the simulation tools, demos, and tutorials.

Set up the Vulcanexus environment by executing:
```
source /opt/vulcanexus/iron/setup.bash
```

3.4.3.2. Running ROS 2 nodes¶

3.4.4. Deploying a ROS 2 Router¶

To deploy the ROS 2 Router, we need to create its configuration file.

3.4.4.1. Configuration¶

The following YAML configuration file configures a ROS 2 Router with two Simple Participants in domains 0 and 1, and a topic configuration to limit the transmission rate on one of the participants for a specific topic.

Note

This configuration enables listeners in domain 1 to subscribe to messages published in domain 0, at a frequency of 1 Hz on topic secret, and at an unlimited frequency on any other topic. It also enables listeners in domain 0 to subscribe to messages published in domain 1 at an unlimited frequency on any topic.

version: v4.0

topics:
  - name: rt/secret
    qos:
      max-tx-rate: 1
    participant:
      - Ros_2_Domain_1

participants:
  - name: ROS_2_Domain_0
    kind: local
    domain: 0

  - name: ROS_2_Domain_1
    kind: local
    domain: 1

3.4.4.1.1. Simple Participants¶

The Simple Participants are configured with a name, a kind (local), and a domain id (0 and 1).

participants:
  - name: ROS_2_Domain_0
    kind: local
    domain: 0

  - name: ROS_2_Domain_1
    kind: local
    domain: 1

3.4.4.1.2. Topic Configuration¶

We define the topic under the tag topics. This topic is configured so that ROS_2_Domain_1 will publish at a maximum frequency of 1 Hz on topic secret, and at an unlimited frequency on any other topic.

topics:
  - name: rt/secret
    qos:
      max-tx-rate: 1
    participant:
      - Ros_2_Domain_1

3.4.4.2. Running the ROS 2 Router¶

Run the DDS Router with the configuration file available at <path/to/file>/ros_2_router_with_manual_topics.yaml.

ddsrouter -c <path/to/file>/ros_2_router_with_manual_topics.yaml

The output from the ROS 2 Router should be something like:

Starting DDS Router Tool execution.
DDS Router running.

If so, the ROS 2 Router has started correctly and it is currently running. In order to close the execution, press ^C or send a signal (SIGINT 2 or SIGTERM 15) to close it.

The listener should now receive the messages sent by the talker at an unlimited rate as they are communicating through the chatter topic.

3.4.5. Deploy ROS 2 nodes on topic secret¶

Let us now run the ROS 2 talker and listener nodes on the topic secret.

3.4.5.1. Running ROS 2 nodes¶

3.4.6. Next steps¶

For all possible configurations that can be applied to the ROS 2 Router topics please refer to the Topic QoS section of the DDS Router documentation.