7th Annual Conference on Systems Engineering Research 2009 (CSER 2009)
A DDS Based Framework for Remote Integration over the Internet Yu-Hong Wang1, Shuang-Hua Yang1, Alan Grigg2, Julian Johnson2 1 2
Computer Science, Loughborough University, UK,
[email protected],
[email protected] Systems Engineering Innovation Centre, UK,
[email protected],
[email protected]
Abstract A framework is developed to allow multiple development teams to collaborate over the Internet on the development, integration and testing of complex system. The proposed framework is based on the Service Oriented Architecture concept and implemented in the form of data-centric publisher/subscriber architecture, employing Data Distribution Service middleware (DDS) for communications. A prototype realization of the proposed framework has been developed using a Process Control Unit rig. In the prototype, embedded real time software has been developed. Before being delivered to the integrator of the rig or a central service, the embedded software remains at the developer’s facility and has been remotely integrated and tested with operational software running in the PCU rig located remotely from the software developer. This paper presents the adopted software architecture and the middleware and rig employed to realize the framework prototype. Basic functionality for remote integration and testing is also described in the paper. Keywords - Remote integration, Distributed development, the Internet, SOA, DDS are using System Integration Laboratories (SILs) [4, 15]. An extension of the this approach is to link SILs in different 1 Introduction locations together and to link remote equipments into SILs In modern manufacturing industries, component using high bandwidth communication links to form Virtual developments of a complex system are becoming System Integration Laboratories (VSILs) [15]. SILs are increasingly fragmented over geographically distributed used to address the integration of systems and so focus on locations. Whilst the components are tested in isolation by the system level rather than software level. There are some suppliers prior to delivery to the central integrator, other successful integration architectures and platforms, problems are invariably encountered during system such as Integrated System Technologies (INSYTE) [5] integration that could have been identified earlier. The from BAE Systems, Joint and Multi-National ability to perform an initial stage of component integration Interoperability Assessment Network (JMNIAN) [6], the whilst some components are still physically located at the UK’s high-speed national secure data highway, owned by supplier’s site could be invaluable and save significant time MoD. JMNIAN provides for integration at system of during later stages of integration. systems level, rather than for software level integration. 1.1 Existing Applications There are many applications in the area of remote integration, maintenance and testing. Relevant applications can be found in software engineering [1-3], military and defence [4-6], industrial applications [7-10] and business [11-12], etc. In software engineering, it is now common practice for nonreal time software to be developed and integrated by geographically distributed teams and organizations. Such an approach can access the global resource pools and profit from around-the-clock development, hence reducing costs and time-to-market. Two notable platforms for distributed software development are the Rational Software Suit [13] and the V-Design System (VDS) [14]. These support the specification definition, design, realisation and configuration of system and software components. In the military and defence area, with the increasing complexity of modern military ground vehicles and weapon systems, distributed development and integration of such systems is becoming more common. Many organizations
In the industry applications area, the current main focus is on E-Manufacturing and E-Maintenance. Distributed and collaborative CAD aims to meet the increasing demands of globally collaborative design and outsourcing trends in manufacturing [9]. Due to the large volumes of CAD data that are needed to be transferred over the Internet, real time collaboration is a big challenge for collaborative CAD systems. 1.2 Available Frameworks Remote maintenance is becoming important because of its role in maintaining and improving system availability and safety, as well as product quality. In [7], PROTEUS, a web based framework for remote maintenance for large and medium scale industrial installation has been developed. In the above mentioned applications areas, a software framework plays a key role. A software framework provides "the skeleton of an application that can be customized by an application developer” [17]. A software framework for remote integration, maintenance and testing Loughborough University – 20th - 23rd April 2009
7th Annual Conference on Systems Engineering Research 2009 (CSER 2009) can be seen as a collaboration environment connected (over the Internet) with distributed rigs. Developing an ideal generalised framework to cater for all purposes is a difficult task – the framework will face shifts in customer expectations, evolving requirements, rapidly changing technologies, the increasing significance of real-time information, increasing reliance on legacy systems, escalating system development, support and maintenance costs and compatibility with emerging standards [18]. Consequently, most existing frameworks are aimed at specific application areas. From the point of view of adopted technology, five such frameworks can be summarized from relevant applications. There are web service based framework, Grid based framework, SOA (Service Oriented Architecture) based framework, data centric framework and HIL (Hardware in Loop) framework. In a web services based framework, different functions are published as services on the Internet (or intranet), and services are registered and discovered in the Universal Description, Discovery, and Integration (UDDI) registry. Remote integration, maintenance and testing applications publish their services and subscribe to other services. Requests to remote systems are processed by using common transport protocols such as Hyper Text Transfer Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP). Web services use the Simple Object Access Protocol (SOAP) for exchanging XML-based messages. This approach tends to result in high end-to-end latencies and consequential difficulty in achieving adequate real-time performance [19]. In a Grid based framework, Grid applications are often developed as Grid services. Different functions are published as Grid services on the Internet. Remote integration, maintenance and testing applications use service data to invoke different services [20, 21]. The drawback is the complexity of Grid software tools, this means that it is often hard to design applications and to deploy software tools using a Grid based framework. Furthermore, services are confined to Grid services and this creates a barrier to the introduction of third party services to expand system capabilities. SOA is an effective paradigm for addressing integration of software components and is becoming an increasingly popular solution for integrating distributed applications [2225]. It is possible to categorise the Web service based framework and Grid based framework as valid implementations of SOA. It is preferable, however, to pursue a more generic SOA model and technology directly as a primary solution to realizing and evaluating a distributed integration framework in order to leverage the benefits of a more general solution. For the distributed integration framework, real-time performance is rapidly becoming a key issue. Real-time issues in SOA include repository of services, reserved bandwidth, and computing capacity, trade-off between performance and cost and QoS control. Recently real time SOA issues have attracted more attention and are becoming a challenging research topic. Loughborough University – 20th - 23rd April 2009
For example, the first IEEE International Workshop On Real-Time Service-Oriented Architecture and Applications has recently been held in August 2008 in Finland [26]. In the work reported here, it is primarily the technologies associated with SOA, specifically DDS, which is of direct relevance in supporting remote integration for military system development integrations, rather than the wider SOA capabilities. Data-centric frameworks are being developed for distributed database applications as a result of the recent availability of high performance messaging and database technologies and, to a certain extent, the increasing adoption of SOA and Web Services in software applications. The data-centric model is characterized by distributed participants together with data-centric interactions between these participants, and the use of the publish/subscribe model for large volumes of data. Middleware is used to implement the data centric architecture. Message-Oriented Middleware (MOM) is more effective for performance-critical applications. Comparing with JMS, a high-performance MOM, Data Distribution Service (DDS) can explicitly control the latency and efficient use of network resources, which is a critical issue in real-time application integration, maintenance and testing over the Internet [27-29] The HIL framework is used for simulation and distributed development of system prototype using a combination of simulation models and real physical rigs [30]. This framework is being used increasingly in the development and testing of complex real-time embedded systems and provides an effective platform for testing by adding the complexity of the real system to the test platform. From a technical perspective, HIL integration, maintenance and testing services are carried out locally. From the above review, we can see there is no mature framework for the remote integration, maintenance and testing for the distributed components of a complex system. Some frameworks have partly addressed the requirements. No one however, has provided a solution for real time remote integration, maintenance and testing. Remote Method Invocation (RMI) based applications [16, 31] show some potential but, because of the problem of using remote procedure calls over the Internet, it is hard to achieve satisfactory performance. A data centric solution is a potential way to tackle the real-time issue [28] and there are already some applications which use MOM for remote integration. Of these, only DDS supports explicit control over the communication latency and efficient use of network resources. These limitations of relevant framework and applications inspire us to develop a framework for realtime remote integration, maintenance and testing by adopting an SOA-compliant approach based on the datacentric publish-subscribe model. The rest of the paper is organized as follows: In Section 2, the objectives and specifications of the framework are presented. In Section 3, a framework for remote integration
7th Annual Conference on Systems Engineering Research 2009 (CSER 2009) earlier distributed integration, where subsets of software under development have to remain physically in close proximity to associated elements of hardware. This would be the case for instance, where a developer is developing both hardware and its associated specific software. In addition, the framework should meet the following more specific requirements:
and remote testing is presented, including the introduction of enabling technologies of SOA and DDS. Section 4 describes the prototype of the framework by using a PCU, and section 5 contains the conclusions. 2
Objectives and Specifications of the Proposed Framework Usually a large and complex system needs to be developed by geographically dispersed teams. Different parts of the system may be developed by using different development tools and development software languages. The system is characterized as consisting of multiple processors connected by appropriate communication media. The functionality of the system can be partitioned in the manner that supports distributed development and integration. For remote integration, communication between distributed rigs is via the Internet or an intranet. However, the different partners’ development environments will clearly require some minimal level of compatibility with the framework such as compliant interfaces and related protocols.
•
The framework must be implemented using an open architecture based on mainstream computer technologies and non-proprietary standards. Implementations will then be possible for any platform conforming to the standards on which the tool is based;
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The framework should allow each participant to join and depart from the infrastructure without effecting other (independent) users;
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The framework should support real-time qualityof-service requirements as far as possible for integration over the Internet but also, given inherent limits such as Internet latency and packet loss, support further practical mechanisms for the compensation and masking of these deficiencies sufficient for integration de-risking purposes;
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The framework will need to support the identification of operational bounds over which use of such distributed integration is valid, and indeed, where results of such integration can be relied upon.
This paper reports the develop of a framework to allow multiple system development teams to collaborate over the Internet on remote integration, maintenance and testing. The proposed framework is to enable: •
•
The remote integration of system hardware/software components over the Internet so that distributed teams can collaborate on the integration of newly developed or modified components in order to de-risk their subsequent integration into a centralized rig and help identify and resolve potential conflicts over component design and implementation details
An application scenario of this framework can be illustrated in Figure 1. In this figure, we suppose the components App1, App-2, App-3, and App-5 are locally available for the main system integrator but the module APP-4 is being developed remotely. Figure 1 shows a potential remote integration scenario for this case. The remote integration of App-4 is done via a local App-4 ‘stub’ linked via the Internet with the real implementation of App-4 which is running on remote hardware (either a real target hardware module or as part of a host development environment).
The remote testing and maintenance of system hardware and software components over the Internet, for example system hardware or software component upgrade.
Most specifically we target the case where, in earlier stages of systems developments, there are advances in performing
App-3 App-1
App-2
App-5 App-4 stub
Local node
Local node
App-4
Remote node
Figure 1 - Application Scenario of the Proposed Framework.
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7th Annual Conference on Systems Engineering Research 2009 (CSER 2009) 3
QoS contract and an associated listener to be alerted if any significant status changes. DDS can automatically discover publishers and subscribers.
The Proposed Framework
3.1 SOA and DDS Technologies SOA encompasses service creation, interaction, presentation, and integration infrastructure capabilities to build software at a more abstract level based on reusable components. SOA, as a set of development patterns, focuses on service design, reuse, and accessibility to build highly flexible and agile software systems. SOA is an architectural approach that can be implemented in many different ways. Key elements in the SOA model are the service producer, service consumer and service registry [32].
3.2 The Proposed Framework From the previous sections, it appears that SOA is becoming an over-arching approach for distributed integration in which numerous, more specific approaches based on web service, Grid technology and data-centric frameworks can be categorized as SOA-compliant and implemented accordingly. For example, the typical compromise in web-service and Grid based frameworks is to develop function entities as services. In data-centric frameworks, data producers (publishers) and consumers (subscribers) can similarly be developed as services. For the remote integration framework, we should consider how to utilize the SOA guiding principles of reuse, granularity, modularity, composability, componentization, interoperability and standards compliance to the design of a framework to meet the critical performance requirement.
Messaging middleware is the key enabler of real-time SOA [33]. There are several high-performance standards-based messaging middleware solutions including JMS and DDS. DDS goes further, however, to explicitly address the problems of controlled latency and efficient use of the network resources; both critical issues in supporting realtime applications. DDS allows user level control over network QoS parameters so that designers can fine tune network behaviour to best suit the distributed system performance requirements.
A framework adopting a SOA-compliant approach based on the data-centric publish-subscribe model is developed in this paper as shown in Figure 2. The data-centric model can be viewed as a SOA for real-time development and end-toend integration of disparate independently developed software components. This architecture results in “loosely coupled” software components with data-oriented interfaces that can be seamlessly integrated using a high-performance standards-based communication middleware infrastructure [33].
DDS middleware sits on top of a networking stack. Applications based on DDS can act as a data publisher or a data subscriber or both. A publisher declares information it has and specifies the Topic, the offered QoS contract and an associated data writer. A subscriber declares the information it wants and specifies the Topic, the requested Integration Agent
Testing Agent
Maintenance Agent
Workbench
Model Service Software Service
Simulation Service Performance Service
Model Identification Service
Assembling/Integrating Platform
SOA Based Middleware
SOA Based Middleware
SOA Based Middleware
SOA Based Middleware
INTERNET
SOA Based Middleware
SOA Based Middleware
Embedded Software Service Diagnosis Service Data Acquisition/ Operational Software
Embedded Software Service Diagnosis Service Data Acquisition/ Operational Software
Distributed Component/Rig
Distributed Component/Rig
Figure 2 - Architecture of the Proposed Framework. As shown in Figure 2, the software functionalities of the distributed rigs are developed as services. The integration agent, testing agent, and maintenance agent provide different services, such as model service, software service, simulation service, performance service, and model identification service. A workbench is developed to present a unified platform for remote integration, maintenance and Loughborough University – 20th - 23rd April 2009
testing. Detail descriptions of the different services are as follows: •
Model Services encapsulate functional models of components where these are used in place of real components.
7th Annual Conference on Systems Engineering Research 2009 (CSER 2009) •
Software Services encapsulate some newly developed software components to be published as service for remote integration and testing before installation.
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Simulation Services can provide simulation functions of corresponding real components before interacting with corresponding real components.
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Model Identification Services provide the tools to build the model services and, where appropriate, to gather model configuration data from rigs.
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Performance Services provide operating performance indication functions by capturing appropriate traffic or metrics. During system operation.
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Embedded Software Services provide useroriented and rig-oriented functions, respectively, including calibration and adjustment of rig parameters and components and testing of component software and gathering/reporting testing results.
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Diagnosis Services determine the run-time status of the operating rigs and software components.
4 Framework Prototyping Based on PCU The PCU (Process Control Unit) rig has been chosen to act as a hardware device working with a PID controller locally and with embedded optimizer software remotely. The PCU rig comprises a process tank, a sump, a pump, a cooler and a number of drain valves. This rig is basically used to illustrate the dynamic control of fluid level in an open tank. The tank is filled by the inlet flow controlled by a pump and is emptied into a drainage tank through a connection pipe and hand valve. The inlet flow is controlled by the PID controller operational software to maintain the fluid level of the tank at a desired value. In order to enhance the control performance, the optimiser software is needed to be developed and cascaded to the PID controller. In the prototype, the optimiser software is designed and developed away from the PCU rig’s location. Before downloaded to the PCU rig’s site, the optimizer software need to be integrated and tested remotely with the PCU rig. Based on the proposed framework, a prototype was developed to demonstrate this remote integration, remote testing and remote monitoring functions. The architecture of the prototype is shown in Figure 3.
Figure 3 - Architecture of Prototype. The prototype provides the function of remote integration, remote testing and remote monitoring of the optimiser software. In the prototype, the PID controller operational software includes a data acquisition module and a manipulating module. The data acquisition module acquires data from the rig and transfers the data to the optimiser software for integrated operation. As the optimiser software is not available on the local side, the data will be transferred to it via the optimiser software stub. In this particular context, the optimiser software is an optimal control algorithm to work with the PID controller operational software to control the rig. In detail, the optimiser software works as an optimizer and determines an optimised reference for the rig. The optimised reference is then passed to the PID controller operational software, which then operates and maintains the rig to reach the desired level. The optimiser software stub is the key component for remote integration, which will receive data from the PID
controller operational software and publish the data produced through a DDS interface. It will also subscribe the optimised reference of the rig published by optimizer software located remotely through the DDS interface. After remote integration, the optimiser software will take the place of the optimiser software stub. The workbench is a platform for integration, testing and maintenance. The workbench has two communication interfaces. One is a DDS interface, which is used to publish and subscribe real time data over the Internet using the optimiser software stub. . The other communication interface is between the optimiser software and the workbench itself. The DDS interface is the key section for remote integration. Once the remote integration has been completed, the optimiser software can be shipped to the local side to replace the optimizer software stub and integrated with the PID controller operational software seamlessly. Loughborough University – 20th - 23rd April 2009
7th Annual Conference on Systems Engineering Research 2009 (CSER 2009) Basing on the above integration prototype, it is possible to re-design and upgrade the optimiser software by specialized experts away from the PCU rig. Currently, the prototype allows one main integrator to integrate the optimiser software over the Internet, while it can enable distributed testing and monitoring simultaneously using the same workbench by multiple geographically distributed users (the approach and functionality for handling multiple user contention during testing is the subject of current research work). Using the prototype, various functions have been performed. The scenarios investigated involve integrating the optimizer software with the rig remote to the developer, remotely monitoring the performance of the optimizer software, remotely testing the optimizer software, Control Action
submitting the optimizer software to a central service, obtaining the optimizer software from the central service, and performing local integration and testing with the rig. Two experiment result graphs are present here, one is control performance without the optimiser software as shown in Figure 4(a); the other is the control performance with remote integration of the optimiser software as shown in Figure 4(b). Comparing Figure 4(a) and Figure 4(b), reveals a significant discrepancy between the desired reference and measured value in Figure 4(a). The Root Mean Square (RMS) between desired reference and measured value in Figure 4(a) is 7.2 while that in Figure 4(b) is only 0.19.
Desired Reference
Measured Value
a
b
Figure 4 - Control Performance without Optimiser Software (a) and with Remote Integration of the Optimiser Software (b). 5 Conclusion This paper presents a software architecture, the middleware and rig employed to realize a framework prototype for remote integration, testing and maintenance. DDS middleware is chosen for communications over the Internet explicitly to provide the controlled latency and efficient use of the network resources, which is a critical issue in realtime applications. Though the case study of the framework is based on the integration of developed embedded software with remote operational software in the rig, the proposed framework provides a concurrent, distributed environment for development, integration and testing of modern complex systems. It offers the possibility of integrating and testing the complex system over the Internet before various parts of the complex system – software and hardware - are physically shipped to a factory and assembled together. Development of a complex system will benefit from early integration testing of the suppliers’ components in the context of the evolving integration rig. This framework also provides a means of de-risking later centralized integration, both leading to lower downstream costs and improved customer satisfaction. Loughborough University – 20th - 23rd April 2009
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