1. Introduction

1.1. What is RTI Connext DDS Micro?

RTI Connext DDS 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 DDS Micro uses the publish-subscribe communications model to make data distribution efficient and robust. Connext DDS Micro simplifies application development, deployment and maintenance and provides fast, predictable distribution of time-critical data over a variety of transport networks. With Connext DDS 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 DDS 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 DDS 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 DDS Micro is highly configurable so programmers can adapt it to meet the application’s specific communication requirements.

1.1.1. RTI Connext DDS Micro Cert versus RTI Connext DDS Micro

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

• DomainParticipantFactory

• DomainParticipant

• Topic

• Publisher

• Subscriber

• DataWriter

• DataReader

1.2.2. DDS QoS Policy Support

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

• DDS_DataReaderProtocolQosPolicy

• DDS_DataReaderResourceLimitsQosPolicy

• DDS_DataWriterProtocolQosPolicy

• DDS_DataWriterResourceLimitsQosPolicy

• DDS_DeadlineQosPolicy

• DDS_DiscoveryQosPolicy

• DDS_DomainParticipantResourceLimitsQosPolicy

• DDS_DurabilityQosPolicy

• DDS_DestinationOrderQosPolicy

• DDS_EntityFactoryQosPolicy

• DDS_HistoryQosPolicy

• DDS_LivelinessQosPolicy

• DDS_OwnershipQosPolicy

• DDS_OwnershipStrengthQosPolicy

• DDS_ReliabilityQosPolicy

• DDS_ResourceLimitsQosPolicy

• DDS_RtpsReliableWriterProtocol_t

• DDS_SystemResourceLimitsQosPolicy

• DDS_TransportQosPolicy

• DDS_UserTrafficQosPolicy

• DDS_WireProtocolQosPolicy

1.3. Standards and Interoperability

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

1.3.1. DDS Wire Compatibility

Connext DDS 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 DDS 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:

• C API Reference

• C++ API Reference

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

RTI Connext DDS Micro Cert is a subset of RTI Connext DDS Micro. Connext DDS Micro 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 DDS 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 DDS 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 DDS 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 DDS 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