2.1. ROS 2 network statistics inspection with ROS 2 Monitor

2.1.1. Background

Vulcanexus integrates the ROS 2 Monitor, a powerful tool for monitoring and studying ROS 2 networks. Since ROS 2 relies on the DDS specification for communication between nodes, this tool simplifies the process of observing network activity. With automatic entity discovery within a local network, users can easily identify active Participants, their Endpoints, the Topics they utilize, and even the network interfaces used for communication. Moreover, the ROS 2 Statistics Module enables the collection of statistical data from every endpoint in the network. This data is very useful for analyzing the DDS network performance and diagnosing possible communication issues.

This tutorial provides step-by-step instructions to use Vulcanexus for monitoring a ROS 2 talker/listener demo.

2.1.2. Prerequisites

Ensure that the Vulcanexus installation includes Vulcanexus Tools (either vulcanexus-jazzy-desktop, vulcanexus-jazzy-tools, or vulcanexus-jazzy-base). Also, remember to source the environment in every terminal in this tutorial.

source /opt/vulcanexus/jazzy/setup.bash

2.1.3. Launch ROS 2 Monitor

Initiate ROS 2 Monitor running the following command:

fastdds_monitor

Once ROS 2 Monitor is launched, start a monitor in domain 0 (default domain).

../../../../_images/Init_domain.png

2.1.4. Execute ROS 2 demo nodes with statistics

In order to activate the publication of statistical data, eProsima Fast DDS requires an environment variable specifying which kinds of statistical data are to be reported. Consequently, before launching the ROS 2 nodes, remember to set FASTDDS_STATISTICS environment variable. Run the following commands in different terminals (remember to source the Vulcanexus environment):

export FASTDDS_STATISTICS="HISTORY_LATENCY_TOPIC;NETWORK_LATENCY_TOPIC;PUBLICATION_THROUGHPUT_TOPIC;\
SUBSCRIPTION_THROUGHPUT_TOPIC;RTPS_SENT_TOPIC;RTPS_LOST_TOPIC;\
HEARTBEAT_COUNT_TOPIC;ACKNACK_COUNT_TOPIC;NACKFRAG_COUNT_TOPIC;\
GAP_COUNT_TOPIC;DATA_COUNT_TOPIC;RESENT_DATAS_TOPIC;SAMPLE_DATAS_TOPIC;\
PDP_PACKETS_TOPIC;EDP_PACKETS_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC"

ros2 run demo_nodes_cpp listener

export FASTDDS_STATISTICS="HISTORY_LATENCY_TOPIC;NETWORK_LATENCY_TOPIC;PUBLICATION_THROUGHPUT_TOPIC;\
SUBSCRIPTION_THROUGHPUT_TOPIC;RTPS_SENT_TOPIC;RTPS_LOST_TOPIC;\
HEARTBEAT_COUNT_TOPIC;ACKNACK_COUNT_TOPIC;NACKFRAG_COUNT_TOPIC;\
GAP_COUNT_TOPIC;DATA_COUNT_TOPIC;RESENT_DATAS_TOPIC;SAMPLE_DATAS_TOPIC;\
PDP_PACKETS_TOPIC;EDP_PACKETS_TOPIC;DISCOVERY_TOPIC;PHYSICAL_DATA_TOPIC"

ros2 run demo_nodes_cpp talker

2.1.5. Monitoring network

Now, the two new Participants are visible in the ROS 2 Monitor’s DDS Panel.

../../../../_images/Participants.png

2.1.5.1. Domain View

To easily inspect the structure of the DDS network created, open the Domain View in the Main Panel. In this tab, we can see a graph describing the structure of our network: our single Host contains our single User, which in turn contains both our Processes, each containing a number of DataReaders and DataWriters. We can see a number of Topics, presented as vertical gray lines, related to the code of the listener and talker. Only one of them, rt/chatter, relates two entities, a DataWriter and a DataReader: this is the Topic that is being used to exchange information.

../../../../_images/Domain_Graph.png

The Domain View allows us to access different possibilities. By pressing right-click on top of the Topic name, we can find several options, such as filtering the graph by the Topic (selecting Filter topic graph). Clicking on the rt/chatter Topic, we can easily see the entities exchanging information.

../../../../_images/Topic_filter.png

Additionally, we can access the we can access the IDL representation of any of the Topics, by pressing right-click over the Topic name, and choosing Data type IDL view. This opens a new Tab with the required information, which can be copied and pasted. Note that for ROS 2 topics, the IDL representation is demangled by default (can be undone in View->Revert ROS 2 Demangling).

../../../../_images/IDL_img_jazzy2.png

2.1.5.2. Alias

Participants in ROS 2 are named / by default. In order to differentiate them, it is possible to change the Participant’s aliases within the ROS 2 Monitor. This can be done either from the Explorer Panel, or from the Domain View panel, by pressing righ click on top of the entity. The talker would be the one with a chatter DataWriter, and the listener the one with a chatter DataReader. Since we’re not going to be using this Tab anymore, click on the X to return to the New Tab view.

../../../../_images/Alias_new.png

2.1.5.3. Statistical data

To show statistical data about the communication between the talker and the listener, follow the steps to create dynamic series chart.

../../../../_images/Statistics.png

2.1.5.4. Introspect metatraffic topics

ROS 2 Monitor filters by default the topics used for sharing metatraffic, as well as the endpoints related to them, so users can inspect their network easily. These topics are the ones that ROS 2 uses for discovery and configuration purposes, such as ros_discovery_info, as well as those used by Fast DDS to report statistical data.

In order to see these topics in the monitor, click View->Show Metatraffic menu button. Now, these topics are shown in the logical panel. Furthermore, the Readers and Writers associated to them are now listed under their respective Participants.

../../../../_images/Metatraffic.png