====== Messaging WG ======
===== Overview =====
Evaluate middleware solutions for communication between GCS, drone, cloud, and between processes running on the vehicle. Select the best solution and evaluate ROS compatibility. 

Some requirements include:
  * Robust, SW messaging solution for commercial deployments of PX4
  * Needs to scale to optimally support remote connections over an unreliable link, to onboard interprocess communication, and in-process communication. 
  * On-board heterogeneous compute (i.e. between different types of SoC core running parts of the flight stack) to be handled by a communication bridge. 
  * Extensible serialization format

**Weekly Messaging WG Meetings:** Google Hangout, Thurs mornings PT.

===== Current Status =====

The majority of the work to date has been done by eProsima on creating a bridge between uORB and RTPS. There are repositories on Github and videos on YouTube of the progress to date:

  * https://github.com/eProsima/Fast-RTPS
  * https://github.com/ros2/rmw_fastrtps
  * https://github.com/eProsima/Fast-CDR
  * https://github.com/eProsima/PX4-FastRTPS-PoC
  * https://www.youtube.com/watch?v=NF65EPD-6aY&feature=youtu.be

Intel is actively working on support FastRTPS on Aero:
  *  https://github.com/edersondisouza/Firmware/commits/test-rtps-share

===== Open Issues =====
There are a few open issues to resolve:
  * Whether to support ROS via full ROS2 support and existing ROS2 to ROS bridge or create a MAVROS impelmentation that works with RTPS
  * PX4 Integration plan
    * The details of the PX4 integration plan need to be flushed out
  * Snapdragon FastRPC support, OMG IDL and DDS RPC
    * Investigate the best architecture for integration of FastRTPS with FastRPC
  * Serialization format
    * ROS2 uses ROS serialization format which is currently not extensible
    * 3DR had selected Cap n' Proto for serialization


===== Previous Analysis =====

3DR analysis and discussion on Middleware:
  * https://lists.dronecode.org/pipermail/dronecode-tsc/2015-August/000107.html
  * https://gist.github.com/liamstask/1bf35b0cf5c73c787d45
  * http://discuss.dronecode.org/t/messaging-systems/87
  * http://discuss.dronecode.org/t/message-format-options/88
  * http://diydrones.com/profiles/blogs/3d-robotics-selects-eprosima-fast-rtps-for-system-infrastructure
3DR analysis of serialization protocols:
  * https://docs.google.com/document/d/1HDOfb3cQ6WiYm9M02RjAgyXRRNhMlGJF1iaLBAVp-T8/edit

OSRF Analysis of RTPS and why it was selected for ROS2:
  * http://design.ros2.org/articles/ros_with_zeromq.html
  * http://design.ros2.org/articles/ros_on_dds.html

Links to other middleware comparisons:
  * https://www.slideshare.net/RealTimeInnovations/comparison-of-mqtt-and-dds-as-m2m-protocols-for-the-internet-of-things
  * http://www.eejournal.com/archives/articles/20150420-protocols/
  * http://electronicdesign.com/iot/understanding-protocols-behind-internet-things
  * http://mnb.ociweb.com/mnb/MiddlewareNewsBrief-201004.html

The benefits of RTPS over alternatives is:
  * Industry standard with several commercial and open source providers
  * Can handle unreliable links
  * Performance is good, and better performers have fewer needed features
  * Potential compatibility with ROS2 (depends on serialization used)