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rmw_connext

Implementation of the ROS Middleware (rmw) Interface using RTI's Connext DDS.

DEPRECATION NOTICE: rmw_connextdds is a new RMW implementation for RTI Connext DDS, which supersedes the one contained in this repository (rmw_connext_cpp). This new implementation was developed by RTI in collaboration with the ROS 2 community, and it resolves several performance issues that are present in this implementation. rmw_connextdds is included in ROS 2 releases starting with Galactic. This rmw implementation will be supported until the end-of-life of the ROS distributions it is available in (ROS 2 Dashing and Foxy).

Working with rmw_connext

To use rmw_connext with ROS2 applications, set the environment variable RMW_IMPLEMENTATION=rmw_connext_cpp and run your ROS2 applications as usual:

Linux:
export RMW_IMPLEMENTATION=rmw_connext_cpp
or prepend on ROS2 command line, such as: RMW_IMPLEMENTATION=rmw_connext_cpp ros2 run rviz2 rviz2

Windows:
set RMW_IMPLEMENTATION=rmw_connext_cpp

Binary Installation

Pre-built binaries for RTI Connext DDS are available for x86_64 (Debian/Ubuntu) Linux platform using the steps outlined in the ROS2 installation wiki, available under a non-commercial license.
Other platforms must be built from source, using a separately-installed copy of RTI Connext DDS.

How to get RTI Connext DDS

This implementation of rmw_connext requires version 5.3.1 of RTI Connext DDS, which can be obtained through the RTI University Program, purchase, or as an evaluation. Note that the RTI website has Free Trial offers, but these are typically for the most-current version of RTI Connext DDS (6.0.1 as of this writing), which does not build with this implementation of rmw_connext.

Building

Refer to the Install DDS Implementations page for details on building rmw_connext for your platform.

Using Connext XML QoS settings

QoS profiles can be specified in XML according to the load order specified here. url_profile and string_profile cannot be used.

ROS will use the profile with the is_default_qos="true" attribute. The policies defined in the ROS QoS profile will override those in the default profile, except when rmw_qos_profile_system_default is used.

For example:

<?xml version="1.0"?>
<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://community.rti.com/schema/5.3.1/rti_dds_qos_profiles.xsd" version="5.3.1">
  <qos_library name="Ros2TestQosLibrary">
    <qos_profile name="Ros2TestDefaultQos" base_name="BuiltinQosLib::Baseline.5.3.0" is_default_qos="true">
      <participant_qos>
        <property>
          <value>
            <!-- 6.25 MB/sec (52 Mb/sec) flow controller -->
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.max_tokens</name>
              <value>8</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.tokens_added_per_period</name>
              <value>8</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.bytes_per_token</name>
              <value>8192</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.period.sec</name>
              <value>0</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.period.nanosec</name>
              <value>10000000</value>
            </element>
          </value>
        </property>
      </participant_qos>

      <datawriter_qos topic_filter="rt/my_large_data_topic">
        <reliability>
          <kind>RELIABLE_RELIABILITY_QOS</kind>
        </reliability>
        <publish_mode>
          <flow_controller_name>dds.flow_controller.token_bucket.slow_flow</flow_controller_name>
        </publish_mode>
      </datawriter_qos>
    </qos_profile>
  </qos_library>
</dds>

That will force all publishers in the my_large_data_topic to use the slow_flow flow controller, but the reliability specified in the ROS QoS profile will be used except if its value is RMW_QOS_RELIABILITY_POLICY_SYSTEM_DEFAULT. See Topic Name Mangling section to understand the rt/ prefix.

See RTI Connext docs to understand topic filters.

Overriding ROS specified QoS policies for a topic

To use this feature, you must first set the following environment variable:

:: Windows
set RMW_CONNEXT_ALLOW_TOPIC_QOS_PROFILES=1
# Linux/MacOS
export RMW_CONNEXT_ALLOW_TOPIC_QOS_PROFILES=1

If the environment variable is set, when a profile name matches the dds topic name, it will be used and the ROS specified profile will be ignored.

For example:

<?xml version="1.0"?>
<dds xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://community.rti.com/schema/5.3.1/rti_dds_qos_profiles.xsd" version="5.3.1">
  <qos_library name="Ros2TestQosLibrary">
    <qos_profile name="Ros2TestDefaultQos" base_name="BuiltinQosLib::Baseline.5.3.0" is_default_qos="true">
      <participant_qos>
        <property>
          <value>
            <!-- 6.25 MB/sec (52 Mb/sec) flow controller -->
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.max_tokens</name>
              <value>8</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.tokens_added_per_period</name>
              <value>8</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.bytes_per_token</name>
              <value>8192</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.period.sec</name>
              <value>0</value>
            </element>
            <element>
              <name>dds.flow_controller.token_bucket.slow_flow.token_bucket.period.nanosec</name>
              <value>10000000</value>
            </element>
          </value>
        </property>
      </participant_qos>
    </qos_profile>
    <qos_profile name="rt/my_large_data_topic" base_name="BuiltinQosLib::Baseline.5.3.0">
      <datawriter_qos>  <!--Don't use topic filters here-->
        <publish_mode>
          <flow_controller_name>dds.flow_controller.token_bucket.slow_flow</flow_controller_name>
        </publish_mode>
        <reliability>
          <kind>RELIABLE_RELIABILITY_QOS</kind>
        </reliability>
      </datawriter_qos>
    </qos_profile>
  </qos_library>
</dds>

In this case, all publishers in the topic /my_large_data_topic will use the specified slow flow controller and have a reliable reliability (regardless of the reliability specified in ROS code).

Caveats:

  • If you want to override the QoS profiles used for all publishers in a topic, the subscription profiles in the same topic will also be overriden. If you don't explicitly provide one, a default will be used.
  • RTI Connext will log an error each time that it tries to find a profile that doesn't exist. Your will see a lot of these logs in your terminal when using RMW_CONNEXT_ALLOW_TOPIC_QOS_PROFILES option.

Specifying an specific QoS library

If you only provided one QoS library to the process, that one will be used. If not, the RMW_CONNEXT_QOS_PROFILE_LIBRARY must be used:

:: Windows
set RMW_CONNEXT_QOS_PROFILE_LIBRARY=Ros2TestQosLibrary
# Linux/MacOS
export RMW_CONNEXT_QOS_PROFILE_LIBRARY=Ros2TestQosLibrary

Specifying a different default QoS profile

You can use the RMW_CONNEXT_DEFAULT_QOS_PROFILE environment variable for this. It overrides the profile marked with is_default_qos="true" when set. The profile is looked up in the QoS profile library RMW connext is using.

Using user provided publish mode

ROS is always overriding the QoS profile of datawriters to use ASYNCHRONOUS_PUBLISH_MODE_QOS. To avoid that from being overriden, you can set the following environment variable:

:: Windows
set RMW_CONNEXT_DO_NOT_OVERRIDE_PUBLICATION_MODE=1
# Linux/MacOS
export RMW_CONNEXT_DO_NOT_OVERRIDE_PUBLICATION_MODE=1

ROS topic name mangling

ROS uses the following mangled topics when the ROS QoS policy avoid_ros_namespace_conventions is false, which is the default:

  • Topics are prefixed with rt. e.g.: /my/fully/qualified/ros/topic is converted to rt/my/fully/qualified/ros/topic.
  • The service request topics are prefixed with rq and suffixed with Request. e.g.: /my/fully/qualified/ros/service request topic is rq/my/fully/qualified/ros/serviceRequest.
  • The service response topics are prefixed with rr and suffixed with Response. e.g.: /my/fully/qualified/ros/service response topic is rr/my/fully/qualified/ros/serviceResponse.

Quality Declaration (per REP-2004)

See RTI Quality Declaration file, hosted on RTI Community website.

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Implementation of the ROS Middleware (rmw) Interface using RTI's Connext DDS.

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