1. Introduction

1.1. What is RTI Connext Micro?

RTI Connext Micro is network middleware for distributed real-time applications. It provides the communications service programmers need to distribute time-critical data between embedded and/or enterprise devices or nodes. Connext Micro uses the publish-subscribe communications model to make data distribution efficient and robust. Connext Micro simplifies application development, deployment and maintenance and provides fast, predictable distribution of time-critical data over a variety of transport networks. With Connext Micro, you can:

  • Perform complex one-to-many and many-to-many network communications.

  • Customize application operation to meet various real-time, reliability, and quality-of-service goals.

  • Provide application-transparent fault tolerance and application robustness.

  • Use a variety of transports.

Connext Micro implements the Data-Centric Publish-Subscribe (DCPS) API within the OMG’s Data Distribution Service (DDS) for Real-Time Systems. DDS is the first standard developed for the needs of real-time systems. DCPS provides an efficient way to transfer data in a distributed system.

With Connext Micro, systems designers and programmers start with a fault-tolerant and flexible communications infrastructure that will work over a wide variety of computer hardware, operating systems, languages, and networking transport protocols. Connext Micro is highly configurable so programmers can adapt it to meet the application’s specific communication requirements.

1.1.1. RTI Connext Cert versus RTI Connext Micro

RTI Connext Micro and RTI Connext Cert originate from the same source base, but as of Connext Micro 2.4.6 the two are maintained as two independent releases. The latest release with certification evidence is Connext Cert 2.4.5. However, features that exist in Connext Micro and Connext Cert behave identically and the source code is written following identical guidelines. Connext Cert only supports a subset of the features found in Connext Micro. In the API reference manuals, APIs that are supported by Connext Cert are clearly marked.

1.1.2. Optional Certification Package

An optional Certification Package is available for systems that require certification to DO-178C or other safety standards. This package includes the artifacts required by a certification authority. The Certification Package is licensed separately from Connext DDS Cert.

To use an existing Certification Package, an application must be linked against the same libraries included in the Certification Package. Contact RTI Support, support@rti.com, for details.

1.1.3. Publish-Subscribe Middleware

Connext Micro is based on a publish-subscribe communications model. Publish-subscribe (PS) middleware provides a simple and intuitive way to distribute data. It decouples the software that creates and sends data—the data publishers—from the software that receives and uses the data—the data subscribers. Publishers simply declare their intent to send and then publish the data. Subscribers declare their intent to receive, then the data is automatically delivered by the middleware. Despite the simplicity of the model, PS middleware can handle complex patterns of information flow. The use of PS middleware results in simpler, more modular distributed applications. Perhaps most importantly, PS middleware can automatically handle all network chores, including connections, failures, and network changes, eliminating the need for user applications to program of all those special <cases. What experienced network middleware developers know is that handling special cases accounts for over 80% of the effort and code.

1.2. Supported DDS Features

Connext Micro supports a subset of the DDS DCPS standard. A brief overview of the supported features are listed here. For a detailed list, please refer to the C API Reference and C++ API Reference.

1.2.1. DDS Entity Support

Connext Micro supports the following DDS entities. Please refer to the documentation for details.

1.3. Standards and Interoperability

Connext Micro implements the Object Management Group (OMG) Data Distribution Service (DDS) standard (version 1.4), and the Real-Time Publish-Subscribe (RTPS) wire interoperabilty protocol standard (version 2.2).

Connext Micro supports a subset of the submessages defined by the Real-Time Publish-Subscribe (RTPS) interoperability specification. Data fragment submessages are not supported. The messages are compatible with Wireshark and its RTPS packet dissector.

Connext Micro, RTI Connext Micro, and Connext are wire-interoperable, unless stated otherwise (see below), and API compatible for APIs specified by the DDS standard. For non-standard APIs, Connext Micro, RTI Connext Micro, and Connext are incompatible. Please refer to Working with RTI Connext Micro and RTI Connext for more information.

1.3.1. DDS Wire Compatibility

Connext Micro is compliant with RTPS 2.2, but does not support and ignore the following RTPS sub-messages:

Submessage

Supported

DDS Standard

Connext DDS Core

DATA_FRAG

No

Yes

Yes

NACK_FRAG

No

Yes

Yes

HEARTBEAT_FRAG

No

Yes

No

INFO_SRC

No

Yes

Yes

INFO_REPLY

No

Yes

Yes

INFO_REPLY_IPV4

No

Yes

Yes

1.3.2. Profile / Feature

Connext Micro does not support mutable Qos policies.

Submessage

Supported

DDS Standard

Connext DDS Core

USER_DATA

No

Yes

Yes

TOPIC_DATA

No

Yes

Yes

DURABILITY

Partially (1)

Yes

Yes

PRESENTATION

Partially (2)

Yes

Yes

DEADLINE

Yes

Yes

Yes

LATENCY_BUDGET

No

Yes

Yes

LIVELINESS

Partially (3)

Yes

Yes

TIME_BASED_FILTER

No

Yes

Yes

PARTITION

No

Yes

Yes

RELIABILITY

Yes (4)

Yes

Yes

TRANSPORT_PRIORITY

No

Yes

Yes

LIFESPAN

No

Yes

Yes

DESTINATION_ORDER

Partially (5)

Yes

Yes

HISTORY

Partially (6)

Yes

Yes

RESOURCE_LIMITS

Yes (7)

Yes

Yes

ENTITY_FACTORY

Yes

Yes

Yes

WRITER_DATA_LIFECYCLE

No

Yes

Yes

READER_DATA_LIFECYCLE

No

Yes

Yes

OWNERSHIP

Yes

Yes

Yes

OWNERSHIP_STRENGTH

Yes

Yes

Yes

DURABILITY_SERVICE

No

Yes

Yes

ContentFilteredTopic

No

Yes

Yes

QueryCondition

No

Yes

Yes

MultiTopic

No

Yes

No

ASYNCHRONOUS_PUBLISHER

No

No

Yes

AVAILABILITY

No

No

Yes

BATCH

Only reception

No

Yes

DATA_READER_PROTOCOL

rtps_object_id

No

Yes

DATA_WRITER_PROTOCOL

Partially (8)

No

Yes

DISCOVERY

Yes

No

Yes

DISCOVERY_CONFIG

No

No

Yes

ENTITY_NAME

Partially (9)

No

Yes

EVENT

No

No

Yes

LOCATORFILTER

No

No

Yes

LOGGING

No

No

Yes

MULTICHANNEL

No

No

Yes

PROPERTY

No

No

Yes

PUBLISH_MODE

No

No

Yes

RECEIVER_POOL

No

No

Yes

SERVICE

No

No

Yes

TYPE_CONSISTENCY_ENFORCEMENT

No

No

Yes

TYPESUPPORT

Yes

No

Yes

WIRE_PROTOCOL

Yes

No

Yes

NOTES:

  1. VOLATILE and TRANSIENT_LOCAL

  2. No, DW offers access_scope = TOPIC, coherent_access = FALSE and ordered_access = TRUE DR requests access_scope = INSTANCE, coherent_access = FALSE and ordered_access = FALSE

  3. AUTOMATIC (infinite only), MANUAL_BY_PARTICIPANT (infinite only), MANUAL_BY_TOPIC (finite and infinite)

  4. BEST_EFFORT and RELIABLE, only max_blocking_time=0

  5. DataWriter: Yes, DataReader only supports BY_RECEPTION_TIMESTAMP

  6. Only KEEP_LAST

  7. Only finite resource limits

  8. The following are supported:

    • heartbeat_period

    • heartbeats_per_max_samples

    • max_heartbeat_retries

    • max_send_window_size

    • rtps_object_id

  9. DomainParticipant only

1.3.3. DDS API Support

For supported APIs, please refer to:

1.4. RTI Connext DDS Documentation

Throughout this document, we may suggest reading sections in other RTI Connext DDS documents. These documents are in your RTI Connext DDS installation directory under rti-connext-dds-<version>/doc/manuals. A quick way to find them is from RTI Launcher’s Help panel, select “Browse Connext Documentation”.

Since installation directories vary per user, links are not provided to these documents on your local machine. However, we do provide links to documents on the RTI Documentation site for users with Internet access.

New users can start by reading Parts 1 (Introduction) and 2 (Core Concepts) in the RTI Connext DDS Core Libraries User’s Manual. These sections teach basic DDS concepts applicable to all RTI middleware, including RTI Connext Professional and RTI Connext Micro. You can open the RTI Connext DDS Core Libraries User’s Manual from RTI Launcher’s Help panel.

The RTI Community provides many resources for users of DDS and the RTI Connext family of products.

1.5. OMG DDS Specification

For the original DDS reference, the OMG DDS specification can be found in the OMG Specifications under “Data Distribution Service”.

1.6. Other Products

RTI Connext Micro is one of several products in the RTI Connext family of products:

RTI Connext Cert is a subset of RTI Connext Micro. Connext Cert does not include the following features because Certification Evidence is not yet available for them. If you require Certification Evidence for any of these features, please contact RTI.

  • C++ language API.

  • Multi-platform support.

  • Dynamic endpoint discovery.

  • delete() APIs (e.g. delete_datareader()).

  • Batching.

  • UDP Transformations.

RTI Connext Professional addresses the sophisticated databus requirements in complex systems including an API compliant with the Object Management Group (OMG) Data Distribution Service (DDS) specification. DDS is the leading data-centric publish/subscribe (DCPS) messaging standard for integrating distributed real-time applications. Connext Professional is the dominant industry implementation with benefits including:

  • OMG-compliant DDS API

  • Advanced features to address complex systems

  • Advanced Quality of Service (QoS) support

  • Comprehensive platform and network transport support

  • Seamless interoperability with rtime

RTI Connext Professional includes rich integration capabilities:

  • Data transformation

  • Integration support for standards including JMS, SQL databases, file, socket, Excel, OPC, STANAG, LabVIEW, Web Services and more

  • Ability for users to create custom integration adapters

  • Optional integration with Oracle, MySQL and other relational databases

  • Tools for visualizing, debugging and managing all systems in real-time

RTI Connext Professional also includes a rich set of tools to accelerate debugging and testing while easing management of deployed systems. These components include:

  • Administration Console

  • Distributed Logger

  • Monitor

  • Monitoring Library

  • Recording Service