Khaldoon Al-Zoubi

Distributed simulation of DEVS and Cell-DEVS models in CD++ using Web-Services

Abstract Discrete event system specification (DEVS) is a modeling and simulation formalism that has been widely used to study the dynamics of discrete event systems. Cell-DEVS is a DEVS-based formalism that defines spatial models as a cell space assembled of a group of DEVS models connected together. CD++ is a modeling and simulation toolkit capable of executing DEVS and Cell-DEVS models that has proven to be useful for executing complex models. We present the design and implementation of a distributed simulation engine, known as D-CD++, which exposes CD++ simulation utilities as machine-consumable services. In addition, we present the design and implementation of the Web-Service components which enable D-CD++ to expose the simulation functionalities to remote users. Enabling CD++ with Web-Services technology provides a solid framework for interoperating different DEVS implementations in order to achieve a standard DEVS Modeling Language and simulation protocols. This paves the road towards DEVS standardization, while providing a mashup approach, which can lead to higher degree of reuse and reduced time to set up and run experiments, and making sharing among remote users more effective. To prove this fact, we integrate it within larger services (such as a 3D visualization engine), showing the mechanism to incorporate to other environments (including geographical information systems, web-based applications and other modeling and simulation tools) through using standard Web-Service tools. Performance of D-CD++, major bottlenecks and communication overheads are analyzed.

Using REST Web-Services Architecture for Distributed Simulation

In recent years, Web Services technologies have been successfully used for simplifying interoperability while providing scalability and flexibility in multiple applications, including distributed simulation software. The RESTful-CD++ simulation Server provides Web Services according to the REST principles by exposing services as URIs and consumed via HTTP messages. Therefore, the server becomes a service part of the Web that can be easily mashed-up with other applications and simulation software. In contrast, RPC-style SOAP-based Web Services use the Web as a transmission medium by exposing few URIs and many RPCs. RESTful-CD++ is (to our best knowledge) the only existing RESTful system in this area. Further, this distributed simulation package provides pioneering distributed simulation services using the Web architectural style. We present an overview of the principles, design and implementation of the RESTful-CD++ HTTP server and DCD++ simulation. We show that REST fulfills WS objectives with a much better and easier style than the SOAP-based systems.

RISE: A general simulation interoperability middleware container

In recent years, new services on the Internet have enabled global cooperation; in particular, the Web has enabled new distributed simulation technology. Much research has been devoted to develop middleware interoperability methods on the Web. However, most existing methods have constraints in the structural rules that are placed on the design of middleware interoperability methods. For example, such constraints make it difficult to enhance interoperability via decoupling systems implementations and design, which is essential in open computing networks, as in the case of the Web. In order to achieve such objectives we present the RISE (RESTful Interoperability Simulation Environment) middleware. This all-purpose WS-based distributed simulation middleware decouples design and implementation while allowing composition scalability and dynamicity. Furthermore, it supports experiment-oriented frameworks and has the ability to put Web 2.0 services in the simulation loop. RISE is the first existing middleware to achieve such objectives, and the first to employ RESTful Web-services. We present the foundations for meeting the above objectives, and the distinct characteristics of RISE from existing Web-based approaches.

Interfacing and Coordination for a DEVS Simulation Protocol Standard

We propose a flexible and scalable message-oriented mechanism allowing interoperability between seven different DEVS implementations towards DEVS standardization. The main objective of the proposed protocol is to enable different DEVS implementations to interface and coordinate among each other to simulate the same model structure across their diverse domains. To do so, the proposed simulation protocol uses SOAP-based Web-Services technology as the communication framework to exchange control and simulation messages. The objective is achievable with minimum design changes to each DEVS implementation, mainly by hiding the detailed implementation behind a wrapper and focusing only on the exchanged messages.

Performing distributed simulation with RESTful web-services

Distributed simulations are mainly used to interoperate heterogeneous simulators or geographically distributed models. We present here RESTful-CD++, the first distributed simulation middleware based on REST (Representational State Transfer) Web-services. RESTful-CD++ middleware enables heterogeneous independent-developed simulation components to intero-perate with much flexibility and simplicity. REST has the potential to advance distributed simulation state-of-the-art towards plug-and-play or automatic/semi-automatic interoperability. This because of its lightweight approach hides internal software implementation by using universal uniform interface and describing connectivity semantics in form of messages, usually XML. In contrast, other approaches expose functionalities in heterogeneous RPCs that often reflect internal implementation and describe semantics in form of procedure parameters. Further, REST enables simulations to mashup with Web 2.0 applications, which makes simulation in link with any device attached to the Web dynamically at runtime. The CD++ tool is now the first simulation engine to use RESTful middleware to perform distributed simulation in large-scale.

Distributed Simulation Using RESTful Interoperability Simulation Environment (RISE) Middleware

Distributed simulation practice outside the military sector is still limited. Having plug-and-play or automatic middleware interoperability is one of the main challenges is needed to advance distributed simulation, as indicated by several surveys; hence, interoperability must be achieved effortlessly with rational cost. They further indicate the need of having general pluggable container where lightweight commercial-off-the-shelf (COTS) simulation components can be plugged into the container with minimal development time. However, existing middleware solutions have been complex so far to overcome these distributed simulation issues. The RESTful Interoperability Simulation Environment (RISE) is the first existing middleware to be based on RESTful Web-services. RISE uses the Web plug-and-play interoperability style to overcome distributed simulation issues. Our focus here on plugging simulation components into RISE and on interoperating independent-developed simulation engines to perform the same distributed simulation session.

Standardizing DEVS Model Representation

As discussed in the previous chapter, the idea of Standardizing DEVS model representation is to allow a platform-independent DEVS model representation to be executed by a DEVS-based simulator. In this case, a DEVS model is executed in a single processor or parallel/distributed simulation environment. This allows model reusability without the need for performing longdistance distributed simulation. Typically, models are stored in repositories and retrieved as needed. This type of interoperability is very important to achieve, because often modelers already have or can easily install a DEVS simulator on their machine. However, it is much more difficult for them to retrieve and reuse already existing models that were intended to run on a specific DEVS environment. Therefore, we need some way to provide access and share these numerous models. Having a platform independent DEVS model representation format allows us to go a step further in automatic model transformations and generate entire local copies of distant models.

Simulation in the Cloud Using Handheld Devices

In recent years, numerous applications have been deployed into mobile devices. However, until now, there have been no attempts to run simulations on handheld devices. We want investigate different architectures for running and man-aging simulations on handheld devices, and putting the simulation services in the Cloud. We propose a hybrid simulation and visualization approach, where a dedicated mobile application is running on the client side and the RISE simulation server is hosted in the Cloud. In particular, with our prototype, we explore the remote management of a simulation tool using a dedicated native application running on an Android Smartphone, and showing the evolution of a simulation model for a forest fire spread, mashing-up the generated graphics with online GIS services.

RISE: REST-ing heterogeneous simulations interoperability

Interoperating heterogeneous simulation models and tools is becoming a necessity in todays cross-enterprise collaboration market. Nevertheless, simulation models and engines have evolved apart in many directions, making their interoperability extremely complex. We present the RESTful Interoperability Simulation Environment (RISE), which provides the means for interoperating simulation heterogeneous assets. RISE uses Service-Oriented RESTful web-services, and it is based on three aspects: the framework architecture, the modeling level and the simulation synchronization level. RISE is independent of any simulation engine, theory or an algorithm. However, it provides different rules for simulation domains with conservative or optimistic synchronization algorithms. Further, RISE does not require any implementation changes related to domain modeling or simulation methods. Furthermore, it hides domain internal specifics, giving freedom to define different internal implementation and algorithms. The presented work here is part of the on-going effort in the DEVS community to interoperate different DEVS-based simulation assets.

Distributed simulation of DEVS and Cell-DEVS models using the RISE middleware

Abstract With the expansion of the Web, the desire toward global cooperation in the distributed simulation technology has also been on the rise. However, since current distributed simulation interoperability methods are coupled with system implementations, they place constraints on enhancing interoperability and synchronization algorithms. To enhance simulation interoperability on the Web, we implemented the RISE (RESTful Interoperability Simulation Environment) middleware, the first existing simulation middleware to be based on RESTful Web-services (WS). RISE is a general middleware that serves as a container to hold different simulation environments without being specific to a certain environment. RISE can hold heterogeneous simulations, and it exposes them as services via the Web. One of such services is called Distributed CD++ (DCD++) simulation system, an extension of the CD++ core engine that allows executing DEVS and Cell-DEVS models. Here, we introduce a proof-of-concept design and implementation of DCD++ using the distributed simulation using the RISE environment. We show how the RESTful WS interoperability style in RISE has improved the design, implementation and the performance of the DCD++ simulator. We also discuss a substantial performance improvement of the implementation of the RISE-based DCD++ presented here, showing many advantages of the RESTful WS presented here: improved interoperability, a seamless method to be connected into a cloud computing environment, and performance improvement when compared to our SOAP-based DCD++ in a similar testing environment.