docs: Add comment on problems when communicating in between different…

… DDS vendors

doc/Ros.md

@@ -194,7 +194,7 @@ A new alternative to DDS-based communication in ROS 2 Iron is [Zenoh](https://ze
 
 ## 4. Bridging ROS 1 and ROS 2
 
-Setting the DDS middleware as described above is in particular important for cross-distro communication as **different ROS distros** ship with [**different default DDS implementations**](https://docs.ros.org/en/humble/Installation/DDS-Implementations.html). Neither communication between different DDS implementations nor different ROS 2 distributions is currently officially supported (for more details see [here](https://github.com/ros2/ros2_documentation/issues/3288)) but similarly to ROS 1 if the **messages have not changed** (or you compile the messages as well as the packages using them from source) and you are **using the same DDS vendor across all involved distros** generally communication between the different distros can be achieved. This can also be useful for **bridging ROS 1 to ROS 2**. The last Ubuntu version to support both ROS 1 (Noetic) and ROS 2 (Galactic) is Ubuntu 20.04. You can use the corresponding [**Galactic ROS 1 bridge Docker**](https://hub.docker.com/layers/library/ros/galactic-ros1-bridge/images/sha256-a2f06953930b0a209295138745d606b1936f0b0564106df9230e2a6612b8b9a2?context=explore). In case message definitions have changed from Galactic to the distro that you are using (the ROS 2 API is not stable yet!) you might have to compile the corresponding messages from source. The main advantage over other solutions for having the two run alongside is that unlike to other solutions ([here](https://docs.ros.org/en/humble/How-To-Guides/Using-ros1_bridge-Jammy-upstream.html) or [here](https://github.com/TommyChangUMD/ros-humble-ros1-bridge-builder/tree/main)) you will have none or only very few repositories that have to be compiled from source and can't be installed from a Debian package.
+Setting the DDS middleware as described above is in particular important for cross-distro communication as **different ROS distros** ship with [**different default DDS implementations**](https://docs.ros.org/en/humble/Installation/DDS-Implementations.html). Neither communication between different DDS implementations nor different ROS 2 distributions is currently officially supported (generally it works but there can be problems with lower frequency etc., for more details see [here](https://github.com/ros2/ros2_documentation/issues/3288)) but similarly to ROS 1 if the **messages have not changed** (or you compile the messages as well as the packages using them from source) and you are **using the same DDS vendor across all involved distros** generally communication between the different distros can be achieved. This can also be useful for **bridging ROS 1 to ROS 2**. The last Ubuntu version to support both ROS 1 (Noetic) and ROS 2 (Galactic) is Ubuntu 20.04. You can use the corresponding [**Galactic ROS 1 bridge Docker**](https://hub.docker.com/layers/library/ros/galactic-ros1-bridge/images/sha256-a2f06953930b0a209295138745d606b1936f0b0564106df9230e2a6612b8b9a2?context=explore). In case message definitions have changed from Galactic to the distro that you are using (the ROS 2 API is not stable yet!) you might have to compile the corresponding messages from source. The main advantage over other solutions for having the two run alongside is that unlike to other solutions ([here](https://docs.ros.org/en/humble/How-To-Guides/Using-ros1_bridge-Jammy-upstream.html) or [here](https://github.com/TommyChangUMD/ros-humble-ros1-bridge-builder/tree/main)) you will have none or only very few repositories that have to be compiled from source and can't be installed from a Debian package.
 
 ## 5. CUDA and ROS