Madrid, April 2022

Content Filtered Topics in Fast DDS

Fast DDS now provides the Content Filtered Topic feature (CFT) that provides the Topic with filtering capabilities, enabling users to segment the data of their interest when subscribing to a topic.

This new feature, both on data reader and data writer sides, has been developed for Fast DDS in collaboration with Sony.

This Fast DDS feature has been developed in compliance with the DDS specification, and now offers the possibility of creating data readers in topics with filtering capabilities, i.e. Content Filtered Topics, in which the filtering properties consist of an expression and a set of parameters. Thus the CFT brings benefits to the communications performance by conserving the network traffic.

Fast DDS 2.6 also provides filtering capabilities on the data writer side, meaning that the data writer can apply the data reader’s filter and only send those specific samples for which the filter’s criteria is met. This is made possible by the data readers sharing their filtering information during the discovery phase.

CFT is not a data reader QoS, but instead it is a “specialized” topic or topic with filtering properties. In this topic the user creates data readers that will be displaying the information in accordance with the filter settings, which can be modified at runtime.

When applying a Content Filtered Topic, only the subset of all samples that fulfill the filter criteria are notified. Thus, only the data of interest is received by the application, which may help to conserve network resources and avoid unnecessary noise. In this way, CFT API will only improve the high standard performance KPIs already provided by Fast DDS implementation. 

The Content Filtered Topic API allows the data reader to indicate which topic data is of interest. For instance, if there is a Topic: motor temperature, a subscriber with no CFT will simply display temperature while a subscriber with CFT (temperature higher than 21º)  will only display temperature when it is higher than 21º.



eProsima is an SME company specialized in middleware solutions targeting robotic, IoT and automotive sectors. eProsima develops middleware implementations for larger robotic systems like Fast DDS and Micro XRCE-DDS, the default middleware for ROS 2 and for micro-ROS. Follow us on LinkedIn, Twitter and YouTube.



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