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ZeroMQ
The control of Atacama Large Millimeter/submillimeter Array (ALMA) is done using software built on a distributed object-oriented framework, specially designed for this job, called ALMA Common Software (ACS). ACS offers several services and common design patterns for applications developed on it. In general, ACS is based on Common Object Request Broker Architecture (CORBA) offering an abstraction of CORBA for services, making more easy the construction and deployment of distributed applications.
One of the services offered is the ACS Notification Channel based on CORBA Notification Service. This service is responsible of handling asynchronous messages between objects using ACS. There are alternatives for the CORBA Notification Service that could offer better performance and scalability.
- ALMA: Atacama Large Millimeter/submillimeter Array
- ACS: ALMA Common Software
- 0MQ: ZeroMQ
- DDS: Data Distribution Service
- TAO: The ACE ORB (open source CORBA implementation written entirely in C/C++)
The ALMA is a major collaboration effort between European (ESO), North American (NRAO) and East Asian countries (NAOJ), under operations on the Chilean Chajnantor plateau, at 5.000 meters of altitude. Currently, it is the largest radio-telescope on Earth, it has 66 antennas of 12-meter and 7-meter diameter, distributed over a wide extension, with up to 16 kilometers of baseline separation. ALMA has three types of 12-meters antennas: Vertex, Alcatel and Mitsubishi.
ALMA Software uses ACS as its main framework. ACS provides a software infrastructure common to all partners and consists of a documented collection of common patterns in and of components, which implement those patterns. The heart of ACS is based on a distributed component model, with ACS components implemented as CORBA objects in any of the supported programming languages. The teams responsible for the control system's development use ACS Components as the basis for control high level entities and for the implementation of devices such as an antenna mount control. ACS provides common CORBA-based services such as logging, error and alarm management, configuration database and lifecycle management.
Currently ACS relies on a CORBA Notification Service implementation (TAO Notify_Service) for its messaging system (a distributed and decoupled implementation of the Publish-subscribe architectural pattern), which is part of CORBA 2.x standard. It is known that this standard is not widely used in the industry. At this moment there are other alternatives (i.e. JMS, DDS, AMQP, ZeroMQ, etc) that may offer better message broker. Better could means either better throughput, less network overhead, better management and/or monitoring, more reliable or better support from the open-source community. However the current ACS Notification Channel API must be kept, to allow to do a seamless transition to the new messaging broker.
For both performance and features, it may be an advantage for ACS to use ZeroMQ instead of Notify Service as the underlying mechanism for message based communication.
- Become familiar with ZeroMQ framework.
- Compare ZeroMQ and Notify Service interfaces and see if a common abstraction can be found, to allow ACS to run either of these in a way that is transparent to code using ACS. Such an abstraction would probably be built into the "SimpleSupplier" and related ACS classes which offer messaging functionality to ACS components.
- Implementation shall be done in C++, Java an optionally in python.
- Set up a test, ideally with some measurement of throughput and other performance indicators, which uses DDS for communication.
| Milestone | Planned Completion Date | Status |
|---|---|---|
| Read documentation of the requirements for this project | Week 0 | 🆗 |
| Become familiar with ZeroMQ framework | Week 1 | 🆗 |
| Compare ZeroMQ and Notify Service interfaces | Week 2 | 🆗 |
| Prototype design | Week 4 | 🆗 |
| Implementation of ZeroMQ as test | Week 6 | 🆗 |
| ZeroMQ integrated into the build system | Week 9 | ⏳ |
| Tests | Week 11 | ❎ |
| Write the thesis and Presentation | Week 14 | ❎ |
- Framework able to carry atomic messages asynchronously.
- Avalaible for most SO (Linux, Windows, OSX) and support various programming languages (C, C++, Java, Python, Ruby,...) and comunication protocols (TCP, IPC, inproc, PGM, SOCKS5).
- Has it own communication protocol (ZMTP - ZeroMQ Message Transport Protocol), which describes how two pieces talk, over TCP or IPC.
- Works with different type of patterns (Pub-Sub, Request-Reply, Router-Dealer).
- Is used for one-to-many distribution of data or events from a single publisher to multiple subscribers.
- 5[ms] to stablish connection between subscriber and publisher.
- 1K messages for 1 [ms].
- Subscriber always miss the first messages that the publisher sends.
- Sub socket MUST set a subscription using zmq_setsockopt().
- One subscriber can be connected to many publishers.
- Recomendation: sub socket starts first and then the pub socket
http://github.com/diegorz/ZeroMQ-ACS
- Read Documentation of the ZeroMQ
- Write on Wiki of ACS-Community
- Read Documentation of the ZeroMQ
- Study ZeroMQ - The Guide
- Study ZeroMQ - The Guide
- Study SOCKET API
- Compile ACS on Ubuntu
- Study Messaging Patterns
- Study Pub-Sub Pattern
- Study Advanced Pub-Sub Patterns
- ZeroMQ into ACS
- https://github.com/ACS-Community/ACS/issues/6 (Issue on ACS-Community)
- http://zguide.zeromq.org/page:all (ZeroMQ Guide)
- https://csrg.inf.utfsm.cl/twiki/pub/ACS/AlmaTheses/thesis-javarias08.pdf (Jorge Avarias Thesis)