OpenDDS

OpenDDS is an open-source C++ implementation of the Object Management Group's specification "Data Distribution Service for Real-time Systems". Although OpenDDS is itself developed in C++, Java and JMS bindings are provided so that Java applications can use OpenDDS.

OpenDDS is built on the ACE abstraction layer to provide platform portability. OpenDDS also leverages capabilities of TAO, such as its IDL compiler and as the basis of the OpenDDS DCPS Information Repository (DCPSInfoRepo).

The primary development of OpenDDS was done by the ACE/TAO development team at Object Computing, Incorporated in St. Louis and Phoenix. It is released under the same generous license terms as ACE, TAO and MPC. See the LICENSE file for details.

Features

OpenDDS is based on version 1.4 of OMG Data Distribution Service (DDS) for Real-Time Systems specification (formal/2015-04-10) and version 2.2 of the Real-time Publish-Subscribe Wire Protocol DDS Interoperability Wire Protocol Specification (DDSI-RTPS) (formal/2014-09-01).

It offers the following default transport protocols (IPv4 and IPv6):

  • TCP/IP
  • RTPS/UDP
  • UDP/IP
  • IP multicast
The pluggable transport framework allows anyone to create a transport to fit custom requirements.

OpenDDS has been found to perform better than other TAO services (notification and real-time event channel) by a factor of two or three. The features offered by the Real-Time Event Channel and Notification Service are similar to DDS, but not identical, so carefully examine your use-cases before choosing one service over another. Speed is not the only criterion.

Compliance with the DDS Specification

OpenDDS supports the following capabilities defined in the DDS Specification:

All profiles (including optional profiles) of the DCPS layer are implemented.

The Built-In Topic functionality is available and enabled by default. To disable Built-in Topic support pass "-NOBITS" option to DCPSInfoRepo and "-DcpsBit 0" to all clients.

Developers can define a structure in IDL that will be used as a DDS data type. The structure may include basic scalar types, strings, sequences, arrays, enumeration and unions. It may not contain interfaces or value types. Zero or more keys can be specified for a data type.

Compliance with the DDS-RTPS Specification

OpenDDS supports the following capabilities defined in the DDS-RTPS Specification:

  • Support of all RTPS Messages
  • Support of RTPS Discovery by implementation of the Simple Participant Discovery Protocol (SPDP) and Simple Endpoint Discovery Protocol (SEDP)
  • Implementation of all elements have tunable timing properties
  • Support of all required RTPS Reader and RTPS Writer behaviors
  • Support of all required RTPS QoS functionality

Peformance Testing

Performance testing of OpenDDS can be performed using the OpenDDS-Bench performance testing framework. This framework is currently located at:

$DDS_ROOT/performance-tests/Bench

in the OpenDDS source code distribution. Detailed information about the OpenDDS-Bench framework is located at:

$DDS_ROOT/performance-tests/Bench/doc/userguide.html

Tests are configured using files. The configuration files for some tests are included in the OpenDDS distribution and can be used to repeat the testing reported here in a user's environment. This way, users can compare existing or other candidate data transport mechanisms in their specific target environment to these results. The test environments include both OCI and customer test labs.

Some testing was performed in the OCI training laboratory. These tests are representative of performance in a busy, user-driven environment of many desktop hosts with other tasks sharing the processing and network resources along with the test execution. Testing in this environment leads to noisy results, but demonstrates the performance of OpenDDS under actual, adverse, conditions.

Additional testing was performed on a single, multi-core box. While this configuration is unlikely to be commonly deployed, its purpose is to establish the baseline behavior of OpenDDS in a non-networked environment. Therefore, the latency numbers are those that directly result from the running of the publisher and subscriber, in different threads, on the same box, in loopback mode so as to ensure that the entire transport stack is exercised.

This baseline behavior on a single host can, of course, be improved by employing shared memory transport and other techniques. Therefore, the performance characteristics reported in the single-host case do not represent the lowest possible latency for OpenDDS. They are intended to provide a reference measurement. For instance, testing with various processor speeds shows that OpenDDS improves in almost a directly proportional manner. Further testing will be performed on boxes with faster processor speeds as they become available to reaffirm this conclusion.

When OpenDDS is introduced into a more typical network setting, additional latency will accrue, of course, depending on the network protocol, topology, distance and network hardware, etc. In general, when measuring the latency in networked settings, these other factors may well swamp the baseline results seen here. The testing in the OCI training lab shows that latency might be two to three times greater on a general purpose LAN. (See the actual results of tests performed at "OCI Lab".)

Further performance testing will be performed on racked systems using the standard protocols supported such as TCP/IP. This configuration is increasingly commonly deployed for certain types of easily distributed tasks that require close cooperation. The advertised latency between boxes on Infinband, for example, is a few hundred nanoseconds. (Other rack fabrics offer similar numbers.) Therefore this should not cause much noticeable additional latency. Testing will confirm this.

Comparison of the latency of OpenDDS with that of proprietary offerings indicates OpenDDS performs about the same as the fastest of its competitors. There is no advantage to be gained by purchasing a proprietary implementation. The bottom line appears to be that when using the open source DDS product, the savings from license fees can be applied to network hardware, racks for co-located systems, etc. All these investments will yield a commensurate return.