Real-Time DDS Examination & Evaluation Project (RT-DEEP)

Table of Contents

• 1. DDS Overview
  
• 2. RT_DEEP Overview
  
• 3. Examaination & Evaluation Objective
  
• 4.Benchmark Design
  
  • 4.1 Evaluation targets
  • 4.2 Benchmark scenario
  • 4.3 Testbed overview
• 5. Empirical Results

1. DDS Overview

The Object Management Group's (OMG) Data Distribution Service(DDS) specification (OMG DDS formal/04-12-02) provides a new data distribution interoperability standard  for a plethora of diverse real-time computing environments ranging from small networked embedded systems to large-sclae information backbones. Based on a  publisher-subscriber architecture, the specification defines clear interfaces that enable applications running on heterogeneous platforms to communicate with each other simply by publishing and subscribing the information they need. By pervasive use of  Quality of Service (QoS) parameters, DDS also allows applications to configure the publish-subscribe system in a highly flexible manner,  thus providing performance predicability and resource control required by misson-critical environments.Compared to CORBA and DCOM which are client-server communication model, Publish-Subscribe is more efficient in both latency and bandwith for periodic data exchange because it is designed as a pure data-centric model. Figure 1 gives a overall architacture of DDS.

figure 1 architecture of DDS

2. RT-DEEP Overview

The goal of RT-DEEP is to get familar with different flavors of COTS DDS implementations, examine the capabilities they provide, and evaluate real-time DDS performance by comparing different DDS implementations as well as by comparing DDS with other pub/sub mechanisms.

Comparing different DDS Implementations - Right now there are several primary COTS DDS middleware vendors. Open-source DDS development projects include OpenDDS . OpenDDS provides an open-source C++ implementation of the DDS specification based ACE. After a year of beta testing, OpenDDS is now being used in production systems and has achieved a formal version 1 release.

As other DDS implementations become available users will need to choose the right one(s) to meet their application QoS requirements. Different implementations may address certain parts of the DDS specifications with different methods, thus affecting the QoS of those part in different ways. It is the goal of RT-DEEP to investigate these variants and discover the architectural differences in various products that may affect ability of products to scale to large number of processors & processes.

Comparing DDS with other pub/sub mechanisms - As a powerful communication pattern, Publish/Subscribe mechanism has been commonly offered by many distrbuted systems as core system services. Examples include Java Messaging Service,  Web Service Pub-Sub Notification, and CORBA Notificaton Service. Sun's Java Messaging Service (JMS) is a message-oriented middleware standard that defines common ways for Java programs to create, send, receive and read enterprise messaging system's messages. One of the most common messaging models JMS provides is a Pub/Sub model in which Java objects/components that represent publishers publish enterprising messages to a topic, and all the subscribers (Java objects/components) to the topic will receive the messages sent to that topic. Publish-Subscribe Notification for Web Services (WS-pubsub) is part of Web Service Resource Framework which defines standard web services approach to publish/subscribe pattern. In the WS-PubSub model, a publisher is represented by a web service NotifiationProducer, and a subscriber by a web service NotificationConsumer. In a typical application scenario, a service requestor, as a subscriber, sends a subscription to NotificationProducer webservice, indicating the interest topic and the address of a NotifciationConsumer.When certain situation is triggered, the NotificationProducer will send out NotificaitionMessages associated with a topic to the interst parties. CORBA notification service is a OMG event service standards which allows multiple event suppliers to send events to multiple consumers. It decouples event suppliers from event consumers by using event channels. As we can see, all the three services mentioned above provides similar pub/sub mechanisms for real-time applications, and both JMS and WS-PubSub reply on topics to connect publishers to subscribers and vice versa, which is simialr to DDS. So it is also the goal of RT-DEEP to compare DDS with all the existing pub/sub mechanisms.

3. Examination & Evaluation objectives

• Evaluate the latency performance of different DDS implementations

• Evaluat the throughput performance of different DDS implemnetations
  
  
• Evaluate the ease of programming using different DDS interfaces
  
  
• Evaluate the performance of DDS compared with other pub/sub mechanisms
  To achive this objective, we will adapt our model used in evaluating different DDS implementations to compare DDS with JMS, WS-PubSub and CORBA notification service.
  

4. Benchmark Design

• Latency test
  
  
  

• Throughput test

5. Emperical Results