# ROS2 Overview ## Distros ROS2 was first announced at ROSCon 2014 | Distro | Release date | | ------ | ------------ | | alpha1 | Aug 31st, 2015 | | beta1 | Dec 19th, 2016 | | beta2 | Jul 5th, 2017 | | beta3 | Sep 13th, 2017 | | Ardent Apalone (Ver 1) | Dec 8th, 2017 | Latest distro and future release | Name | Release date | EOL date / Support for | | ----------------- | -------------- | -------------------- | | ==Dashing Diademata== | May 31st, 2019 | May 2021 | | Eloquent Elusor | November 22nd, 2019 | 1 year | | Foxy Fitzroy | June 5th, 2020 | 3+ years (Target Ubuntu 20.04) | ## Why ROS2 Known issues and limits of ROS1 - **Master** (roscore): a major one - Realtime performance - Node management :::info - Multi-robots capability (Swarm) Use ROS namespace would sometimes cause problems ::: - Small processors - Communication Priority - Communication Security - Unreliable network connectivity ROS1 使用 TCPROS(預設)/UDPROS 的通訊協定，並且需要 master 管理所有系統上的節點，當 master 下線將失去對系統的掌握，且 master 一旦重新啟動，雖然舊有的節點仍然可以溝通，但是之後新增的節點就無法與舊有的節點溝通，這些特性是 ROS1 在從原型機到最後產品化時最大的困難。 ![](https://i.imgur.com/ydvaxa3.png) ROS2 use cases - Teams of multiple robots (scalability) - Small embedded platforms: support “bare-metal” micro controllers. - Real-time systems: make real-time control directly in ROS, including inter-process and inter-machine communication. - Non-ideal networks: from poor-quality WiFi to ground-to-space communication links. - **Production environments**: while it is vital that ROS continue to be the platform of choice in the research lab, we want to ensure that ROS-based lab prototypes can evolve into ROS-based products suitable for use in real-world applications. ![](https://i.imgur.com/HqT6Whq.png) ## ROS2 architecture ### ROS1 ROS2 architecture comparsion ![](https://i.imgur.com/9VBoPDp.png) > left: ROS1 &nbsp;&nbsp;&nbsp;&nbsp; right: ROS2 ### ROS2 詳細架構圖 ![](https://i.imgur.com/PPxzXNv.png) ### ROS2 Core Stack * Build System * The `ament_package` Package * The `ament_cmake` Repository * The `ament_lint` Repository * Build tools * Internal ROS Interfaces * Type Specific Interfaces * ==The `rcl` Repository== * ==The `rmw` Repository== * The `rosidl` Repository * The `rcutils` Repository * ROS Middleware Implementations * Common Packages for DDS Middleware Packages * Structure of ROS Middleware Implementations * ROS Client Interfaces (Client Libraries) * ==The `rclcpp` Package== * ==The `rclpy` Package== --- ## DDS in ROS2 DDS stands for Data Distribution Service, is a set of specifications standardized by the Object Management Group (OMG). | Specification | Description | |-|-| | DDS | Specification of the **programming model**, **QoS**, and **language APIs** used to program a Data-Centric Publish-Subscribe application. | | DDS-RTPS (Data Distribution Service Real-Time Publish-Subscribe Interoperability Wire Protocol) | Specification of the wire protocol used by DDS to exchange information. It includes ==**discovery**==, **data encapsulation**, **reliability**, **multicast**, and many selectable QoS parameters. | ### DDS/RTPS vendors | Product name | License | RMW implementation | Status | | ------------ | ------- | ------------------ | ------ | | eProsima Fast RTPS | Apache 2 | `rmw_fastrtps_cpp` | Full support (for `rmw` interface). **Default `rmw`**. Packaged with binary releases. | | RTI Connext | commercial, research | `rmw_connext_cpp` | Full support. Support included in binaries, but Connext installed separately. | | ADLINK Opensplice | Apache 2, commercial | `rmw_opensplice_cpp` | Partial support. Support included in binaries, but OpenSplice installed separately. | ### QoS QoS policies of ROS2 | Policy | Description | | -------- | ----------- | | History | ==Keep last==: only store up to N samples, configurable via the queue <ins>**depth**</ins> option. <p></p> ==Keep all==: store all samples, subject to the configured resource limits of the underlying middleware. | Reliability | ==Best effort==: attempt to deliver samples, but may lose them if the network is not robust. <p></p> ==Reliable==: guarantee that samples are delivered, may retry multiple times. | Durability | ==Transient local==: the publisher becomes responsible for persisting samples for “<ins>late-joining</ins>” subscribers. <p></p> ==Volatile==: no attempt is made to persist samples. | ### Technologies relevant to ROS - Zeroconf - Protocol Buffers - ZeroMQ (and the other MQs) - Redis - WebSockets --- References: ROS2 wiki - Overview of ROS2 concept: https://index.ros.org/doc/ros2/Concepts/Overview-of-ROS-2-concepts/ - Quality of Service Settings: https://index.ros.org/doc/ros2/Concepts/About-Quality-of-Service-Settings/ - Exploring the performance of ROS2: https://ieeexplore.ieee.org/document/7743223/metrics#metrics - Hypha ROS2 introdution https://drive.google.com/file/d/1MW_w7MS1DNg1EzhprgbJKY2cqmxksPaw/view - DDS Best Practices https://www.rti.com/hubfs/docs/DDS_Best_Practices_WP.pdf - ROS core http://docs.ros2.org/crystal/index.html - Current Status of ROS2 https://static1.squarespace.com/static/51df34b1e4b08840dcfd2841/t/5ce6c85ca4222fe0ccbd5309/1558628472094/2019-05-07_Current_Status_of_ROS_2.pdf - Autoware migration from ROS1 to ROS2: https://apex-ai.docsend.com/view/bzyahhy