Stephen John Turner

Time-space consistency in large-scale distributed virtual environments

Maintaining a consistent view of the simulated world among different simulation nodes is a fundamental problem in large-scale distributed virtual environments (DVEs). In this paper, we characterize this problem by quantifying the time-space inconsistency in a DVE. To this end, a metric is defined to measure the time-space inconsistency in a DVE. One major advantage of the metric is that it may be estimated based on some characteristic parameters of a DVE, such as clock asynchrony, message transmission delay, the accuracy of the dead reckoning algorithm, the kinetics of the moving entity, and human factors. Thus the metric can be used to evaluate the time-space consistency property of a DVE without the actual execution of the DVE application, which is especially useful in the design stage of a DVE. Our work also clearly shows how the characteristic parameters of a DVE are interrelated in deciding the time-space inconsistency, so that we may fine-tune the DVE to make it as consistent as possible. To verify the effectiveness of the metric, a Ping-Pong game is developed. Experimental results show that the metric is effective in evaluating the time-space consistency property of the game.

A scalable architecture for supporting interactive games on the internet

This paper presents a scalable architecture for supporting large-scale interactive Internet games. In order to support a large number of participants and to divide the workload, the virtual world is divided into partitions. Each partition is then assigned to a server. A client (i.e., a player or a participant) will join a server according to the position of the avatar it controls. Compared to a centralized architecture, this distributed client-server architecture is more scalable. In addition, compared to a fully distributed, peer-to-peer architecture, it also provides a means for detecting cheating in distributed games. Since interactions and accounting information must be forwarded directly to one of the servers for qualification and verification, cheating amongst distributed players of the game will be minimized. To support secured communication for interactions and accounting information as well as to speedup periodic update messages (e.g., position updates), a hybrid communication scheme using both TCP and IP multicast is used between clients and the associated server. The communication among servers is enabled by the Run-Time Infrastructure (RTI) services. The High Level Architecture (HLA) Data Distribution Management (DDM) is employed to limit the amount of communication between the servers. In addition, the Ownership Management (OM) is also employed to implement the need for transferring the avatars between servers. In this paper, the design detail of the architecture will be presented. An experimental interactive Internet game realized using the architecture will be also described in the paper.

A load management system for running HLA-based distributed simulations over the grid

Running a large-scale distributed simulation may need a large amount of computing resources at geographically different locations. These resources may be from different organizations. The simulation may run for a long period of time and the availability and amount of computing resources available may change during the course of simulation execution. Therefore, coordinating and managing resources for distributed simulation to complete the simulation efficiently and effectively is a critical issue. This paper describes a load management system for HLA-based distributed simulation. The system is constructed on top of a grid computing environment supported by Globus. The overall structure of the system is presented in the paper and how the system saves and restores a federate is also discussed in detail.

Load balancing for conservative simulation on shared memory multiprocessor systems

Load balancing is a crucial factor in achieving good performance for parallel discrete event simulations. We present a load balancing scheme that combines both static partitioning and dynamic load balancing. The static partitioning scheme maps simulation objects to logical processes before simulation starts while the dynamic load balancing scheme attempts to balance the load during runtime. The static scheme involves two steps. First, the simulation objects that contribute to small lookahead are merged together by using a merging algorithm. Then a partitioning algorithm is applied. The merging is needed to ensure a consistent performance for our dynamic scheme. Our dynamic scheme is tailor-made for an asynchronous simulation protocol that does not rely on null messages. The performance study on a supply chain simulation shows that the partitioning algorithm and dynamic load balancing are important in achieving good performance.

Large scale agent-based simulation on the grid

The development of many complex simulation applications requires collaborative effort from researchers with different domain knowledge and expertise, possibly at different locations. These simulation systems often require huge computing resources and data sets, which can be geographically distributed. In order to support collaborative model development and to cater for the increasing complexity of such systems, it is necessary to harness distributed resources over the Internet. The emergence of Grid technologies provides exciting new opportunities for large-scale distributed simulation, enabling collaboration and the use of distributed computing resources, while also facilitating access to geographically distributed data sets. This paper presents HLA_Grid_RePast, a middleware platform for executing large scale collaborating RePast agent-based models on the Grid. The paper also provides performance results from a deployment of the system between UK and Singapore.

Integrating heterogeneous distributed COTS discrete-event simulation packages: an emerging standards-based approach

This paper reports on the progress made toward the emergence of standards to support the integration of heterogeneous discrete-event simulations (DESs) created in specialist support tools called commercial-off-the-shelf (COTS) discrete-event simulation packages (CSPs). The general standard for heterogeneous integration in this area has been developed from research in distributed simulation and is the IEEE 1516 standard The High Level Architecture (HLA). However, the specific needs of heterogeneous CSP integration require that the HLA is augmented by additional complementary standards. These are the suite of CSP interoperability (CSPI) standards being developed under the Simulation Interoperability Standards Organization (SISO-http://www.sisostds.org) by the CSPI Product Development Group (CSPI-PDG). The suite consists of several interoperability reference models (IRMs) that outline different integration needs of CSPI, interoperability frameworks (IFs) that define the HLA-based solution to each IRM, appropriate data exchange representations to specify the data exchanged in an IF, and benchmarks termed CSP emulators (CSPEs). This paper contributes to the development of the Type I IF that is intended to represent the HLA-based solution to the problem outlined by the Type I IRM (asynchronous entity passing) by developing the entity transfer specification (ETS) data exchange representation. The use of the ETS in an illustrative case study implemented using a prototype CSPE is shown. This case study also allows us to highlight the importance of event granularity and lookahead in the performance and development of the Type I IF, and to discuss possible methods to automate the capture of appropriate values of lookahead.

A Service Oriented HLA RTI on the Grid

Modeling and simulation permeate all areas of business, science and engineering. To promote the interoperability and reusability of simulation applications and link geographically dispersed simulation components, distributed simulation was introduced. While the high level architecture (HLA) is the IEEE standard for distributed simulation, a run time infrastructure (RTI) provides the actual implementation of the HLA. With increased size and complexity of simulation applications, large amounts of distributed computational and data resources are required. The Grid provides a flexible, secure and coordinated resource sharing environment which can facilitate distributed simulation execution. In this paper, we propose a service oriented HLA RTI (SOHR) framework which provides the functionalities of an RTI as Grid services and enables large scale distributed simulations to be conducted on a heterogeneous Grid environment. The various services in SOHR can be dynamically deployed, discovered and undeployed, leading to a scalable distributed simulation environment. While the communications between simulators are through Grid service invocations, the standard HLA interface is provided as a library to increase simulator reusability and interoperability. A subset of HLA specifications was implemented in a SOHR prototype based on GT4 and the experimental results have verified the feasibility of SOHR.

Symbiotic Simulation Systems: An Extended Definition Motivated by Symbiosis in Biology

Although various forms of symbiosis are known in biology, only mutualism has been considered in the context of symbiotic simulation systems. In this paper, we explain why the original definition of symbiotic simulation systems is narrow and why it is important to consider other forms of symbiosis as well. As a consequence we propose an extended definition of symbiotic simulation systems motivated by symbiosis in biology. By using this extended definition, we identify five different types of symbiotic simulation systems which can be applied in various applications. We describe how single systems can be combined and propose a hybrid symbiotic simulation system in the context of semiconductor manufacturing.

Federate Migration in a Service Oriented HLA RTI

The High Level Architecture provides a general framework for distributed simulation, promoting reusability and interoperability of simulation components (federates). Large scale distributed simulation, in which federates run on many heterogenous computing machines may benefit from migrating federates among these machines for load- balancing and fault-tolerance. However, the HLA framework does not provide formal support for federate migration currently. We have previously developed a Service Oriented HLA RTL (SOHR) framework, which provides HLA RTL functionalities via the cooperation of a set of Grid services. SOHR is developed with migration support features by using a decoupled federate design. In this paper, a basic federate migration protocol is first proposed to illustrate the process of federate migration in SOHR. Then two optimized protocols are further developed to overlap federate migration with federate execution for the purpose of reducing migration overhead. Experiments show that the migration overhead is reduced considerably in the optimized protocols.

Hierarchical federations: an architecture for information hiding

In a distributed simulation, simulation components of various types are executed at geographically different locations, forming a simulation federation to create a common virtual environment. Under the High Level Architecture (HLA), information that will be produced and consumed by a simulation component is defined in its object model, and how that information is produced and consumed is well encapsulated inside the simulation components implementation. However in the current implementation of the HLAs Runtime Infrastructure (RTI), information hiding between groups of simulation components in a simulation federation is not addressed. The authors discuss how hierarchical federation architectures can be used to tackle this problem. The hierarchical federation architecture adopted in the paper differs from the existing architectures in that it is based on a hybrid approach for interoperability between simulation federations. To demonstrate information hiding using the architecture, a distributed semiconductor supply-chain simulation is also described.