repeater_example.rst

Repeater Example

A |ddsrouter| could work as a Repeater to forward messages by the same Participant. If you are interested in understanding the use case of a Repeater please refer to the following section :ref:`use_case_repeater`.

Configuration

Allowed Topics

This section lists the :term:`Topics <Topic>` that the DDS Router will route from one Participant to the other. Topic HelloWorldTopic and ROS 2 topic rt/chatter will be forwarded from one domain to the other, allowing different DDS domains to interact with each other.

.. literalinclude:: ../../resources/examples/repeater_server.yaml
    :language: yaml
    :lines: 9-11

Repeater Participant

The Repeater Participant is the one that will be used to forward messages by the same Participant. It must be a :ref:`WAN <user_manual_participants_wan>` Participant, configured with :ref:`WAN configuration <user_manual_wan_configuration>`, or an :ref:`XML <user_manual_participants_xml>` Participant.

.. literalinclude:: ../../resources/examples/repeater_server.yaml
    :language: yaml
    :lines: 21-27

Client Participants

Every Client can connect to a Repeater Participant as if it was a normal WAN Participant. The Repeater admits as many edge |ddsrouter| connections as desired, so several |ddsrouter| can use the same or similar configuration to communicate across it.

.. literalinclude:: ../../resources/examples/repeater_client.yaml
    :language: yaml
    :lines: 29-34

Execute example

Please refer to this :ref:`section <user_manual_user_interface>` for a detailed explanation on how to execute the |ddsrouter|.

In order to run these examples, there must be three different hosts located in different local networks:

• host H_A with private IP 192.168.1.2 connected to network router R_A with public IP 1.1.1.1.
• host H_B with private IP 192.168.2.2 connected to network router R_B with public IP 2.2.2.2.
• host H_C with private IP 192.168.2.3 connected to network router R_C with public IP 3.3.3.3.

These examples could be run in localhost or with two hosts in the same LAN, but it will not use the WAN communication features of the |ddsrouter|.

Host H_A

This host runs the |ddsrouter| Repeater Server, which will receive data from both edges and redirect the messages between them. Execute |ddsrouter| using file <path/to/ddsrouter_tool>/share/resources/configurations/examples/repeater.yaml. Remember to change the IP and port on the configuration file to the actual public IP of R_A, and be sure that the port forwarding rules are configured in R_A so H_A is accessible from the outside.

Hosts H_B and H_C

These hosts run the |ddsrouter| WAN Clients, which will connect to the previously launched Repeater Server. Execute |ddsrouter| using file <path/to/ddsrouter_tool>/share/resources/configurations/examples/wan_client.yaml. Remember to change the IPs and ports on the configuration file to the actual public IPs of R_A and R_B. In this example the port forwarding is not required, as the Repeater will allow the communication through it, and TCP protocol is being used..

Execute with ROS 2 demo nodes

Both clients can execute ROS 2 demo nodes, which will publish and subscribe in topic rt/chatter. Execute a talker in one of them and a listener in the other. It is recommended to use different ROS_DOMAIN_ID in each node, so in case both nodes are accessible (under same network) no loop is created. In order to do so, change the YAML configuration files to use different domains, and use the following ROS2 commands:

# Hb
ROS_DOMAIN_ID=0 ros2 run demo_nodes_cpp talker

# Hc
ROS_DOMAIN_ID=1 ros2 run demo_nodes_cpp listener

Result

After executing the three |ddsrouter| applications in hosts, and talker and listener applications, the listener in H_C will start receiving and printing data from the talker in H_B. You are communicating DDS via WAN.

Note

If H_B can access H_C due to port forwarding or because both are under the same network, the listener will receive duplicated messages, as one of them will arrive from H_B and the other from H_A.

Execute with Fast DDS HelloWorld Example

Both clients can create Fast DDS endpoints , which will publish and subscribe in topic HelloWorldTopic. Execute a publisher in one of them and a subscriber in the other. It is recommended to use different domains in each endpoint, so in case both endpoints are accessible (under same network) no loop is created. In order to do so, change the YAML configuration files to use different domains.

Execute a |fastdds| configuration example publisher in domain 0:

./<path/to/fastdds_installation>/share/fastdds/examples/cpp/configuration/bin/configuration publisher --domain 0 --name HelloWorldTopic

Execute a |fastdds| configuration example subscriber in domain 1:

./<path/to/fastdds_installation>/share/fastdds/examples/cpp/configuration/bin/configuration subscriber --domain 1 --name HelloWorldTopic

Result

After executing the three |ddsrouter| applications in hosts, and publisher and subscriber applications, the subscriber in H_C will start receiving and printing data from the publisher in H_B. You are communicating DDS via WAN.

Note

If H_B can access H_C due to port forwarding or because both are under the same network, the subscriber will receive duplicated messages, as one of them will arrive from H_B and the other from H_A.