How can I disable multicasting and enable unicasting in ROS2

asked 2018-08-30 11:33:10 -0500

aks
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I am integrating ROS2 with another native DDS based application, both located on different laptops but in the same network. My problem is that I cannot use multicasting due to certain limitations. So, I opted for unicasting for the discovery process. I configured the native DDS based application as unicast as explained here. But my ROS2 based machine still uses multicasting. It is obvious that once I find the ROS2 based machine through unicasting, both discover each other and the communication works in both direction. But how can i configure ROS2 to use unicasting ?

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answered 2018-09-07 03:02:52 -0500

aks
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There are not many QoS settings made in the ROS2 RMW code; the Connext libs will look for a source of user QoS settings using the normal search order (detailed here) - meaning you can provide your own QoS settings to the Connext libs under ROS2, using a variety of methods. Here's what I did:

To disable multicast in ROS2, create a file named "NDDS_DISCOVERY_PEERS" in a directory from which your ROS2 application(s) will be launched (directory where the ros2 command is entered and run). Place in this file a list of the initial peers for discovery (make sure to exclude multicast and shmem) format as detailed here.
My file had: localhost,192.168.1.44 For other QoS settings, place in the same directory as above a "USER_QOS_PROFILES.xml" file containing the QoS settings you'd like to use in ROS2. These settings will affect the ROS2 applications launched from that directory.

this is the answer i received from a RTI colleague.

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That's a good answer. I just would like to add that this answer is Connext DDS specific. Changing this setting for eProsima fastrtps works different by creating a DEFAULT_FASTRTPS_PROFILES.xml with an initialPeersList.

machinekoder ( 2019-08-26 04:46:49 -0500 )edit

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answered 2018-08-30 11:42:05 -0500

Dirk Thomas
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Currently ROS 2 doesn't provide that option. You might want to check for the DDS implementation you are using if it supports that option through a vendor specific configuration file.

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I am using RTI connext. They do support it and that is why I have configured in their native application. What do you mean by vendor specific configuration file ? Could i use it to enable unicasting in ROS2 as well ?

aks ( 2018-08-30 11:48:40 -0500 )edit

When you use Connext with ROS 2 the RTI specific configuration files are still being used and applies for publisher / subscribers / topics created by ROS - as long as the configuration value is not explicitly set from the ROS 2 code.