The ability of self-reconfigurable robots to solve a variety of robot tasks comes in part from their use of a large number of modules. Effective use of these systems requires parallel actuation and planning, both for ...
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The ability of self-reconfigurable robots to solve a variety of robot tasks comes in part from their use of a large number of modules. Effective use of these systems requires parallel actuation and planning, both for efficiency and independence from a central controller. This paper presents the PacMan algorithm, a technique for distributed actuation and planning. This algorithm was developed for systems with unit-compressible modules, such as the crystalline robot. We also describe some analytical properties of the PacMan planning and actuation, and discuss simulation and hardware experiments.
One of the six categories of management services provided in the Run Time Infrastructure (RTI) to federated simulations is time management. Currently, it provides only two message ordering policies, that is, time stam...
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ISBN:
(纸本)076951104X
One of the six categories of management services provided in the Run Time Infrastructure (RTI) to federated simulations is time management. Currently, it provides only two message ordering policies, that is, time stamp ordering and receipt ordering. Temporal anomalies occurring during the execution of federation due to the heterogeneous latencies in the communication network are not handled in receipt ordering. While time stamp ordering eliminates the temporal anomalies entirely, it incurs great communication latency, and huge bandwidth requirement. The paper presents a novel time management mechanism which provides a less costly message ordering service, namely causal ordering, to federates. It does not require the specification of lookahead and allows federates that do not require stringent message ordering properties to achieve much more efficient execution. A series of experiments has been carried out to benchmark the performance of this new time management mechanism and the results show that it includes a slight overhead compared to the receipt ordering mechanism but achieves significant performance improvement over the time stamp ordering mechanism.
The Time Warp synchronization protocol allows causality errors and then recovers from them with the assistance of a cancellation mechanism. Cancellation can cause the rollback of several other simulation objects that ...
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ISBN:
(纸本)076951104X
The Time Warp synchronization protocol allows causality errors and then recovers from them with the assistance of a cancellation mechanism. Cancellation can cause the rollback of several other simulation objects that may trigger a cascading rollback situation where the rollback cycles back to the original simulation object. These cycles of rollback can cause the simulation to enter an unstable (or thrashing) state where little real forward simulation progress is achieved. To address this problem, knowledge of causal relations between events can be used during cancellation to avoid cascading rollbacks and to initiate early recovery operations from causality errors. In this paper we describe a logical time representation for Time Warp simulations that is used to disseminate causality information. The new timestamp representation, called Total Clocks, has two components: (i) a virtual time component, and (ii) a vector of event counters similar to Vector clocks. The virtual time component provides a one dimensional global simulation time and the vector of event counters records event processing rates by the simulation objects. This time representation allows us to disseminate causality information during event execution that can be used to allow early recovery, during cancellation. We propose a cancellation mechanism using Total Clocks that allows cascading rollbacks in Time Warp simulations that have FIFO communication channels.
The Data Distribution Management (DDM) service is one of the six services provided in the Runtime Infrastructure (RTI) of High Level Architecture (HLA). Its purpose is to perform data filtering and reduce irrelevant d...
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ISBN:
(纸本)076951104X
The Data Distribution Management (DDM) service is one of the six services provided in the Runtime Infrastructure (RTI) of High Level Architecture (HLA). Its purpose is to perform data filtering and reduce irrelevant data communicated between federates. The two DDM schemes proposed for RTI, region based and grid based DDM, are oriented to send as little irrelevant data to subscribers as possible, but only manage to filter part of this information and some irrelevant data is still being communicated. Previously (G. Tan et al., 2000), we employed intelligent agents to perform data filtering in HLA, implemented an agent based DDM in RTI (ARTI) and compared it with the other two filtering mechanisms. The paper reports on additional experiments, results and analysis using two scenarios: the AWACS sensing aircraft simulation and the air traffic control simulation scenario. Experimental results show that compared with other mechanisms, the agent based approach communicates only relevant data and minimizes network communication, and is also comparable in terms of time efficiency. Some guidelines on when the agent based scheme can be used are also given.
One of the six categories of management services provided in the Run Time Infrastructure (RTI) to federated simulations is Time Management. Currently, it provides only two message ordering policies, that is, time stam...
详细信息
ISBN:
(纸本)9780769511047
One of the six categories of management services provided in the Run Time Infrastructure (RTI) to federated simulations is Time Management. Currently, it provides only two message ordering policies, that is, time stamp ordering and receive ordering. Temporal anomalies occurred during the execution of federation due to the heterogeneous latencies in the communication network are not handled in receive ordering. White time stamp ordering eliminates the temporal anomalies entirely, it incurs great communication latency and huge handwidth requirement. This paper presents a new time management mechanism which provides a less costly message ordering service, namely causal ordering, to federates. It does not require the specification of lookahead and allows federates that do not require stringent message ordering properties to achieve much more efficient execution. A series of experiments has been carried out to benchmark the performance of this new time management mechanism and the results show that if incurs a slight overhead compared to receive ordering mechanism but achieves significant performance improvement over time stamp ordering mechanism.
Great effort has been devoted to the design of optimized checkpointing strategies for optimistic parallel discrete event simulators. On the other hand there is less work in the direction to improve the execution mode ...
ISBN:
(纸本)9780769511047
Great effort has been devoted to the design of optimized checkpointing strategies for optimistic parallel discrete event simulators. On the other hand there is less work in the direction to improve the execution mode of any single checkpoint operation. Specifically, checkpoint operations are typically charged to the CPU, thus leading to freezing of the simulation application while checkpointing is in progress, i.e. the execution mode of the checkpointing protocol is typically synchronous. In this paper we focus on improvements of the execution mode and present a software architecture, designed for myrinet based Network of Workstations (NOWs), to avoid application freezing during any checkpoint operation, thus moving the execution itself towards an asynchronous mode. This is done by charging checkpoint operations to a hardware component distinct from the CPU, namely a DMA engine. On the other hand, totally asynchronous checkpointing could suffer from data inconsistency whenever the content of a state buffer is accessed for further modifications while a checkpoint operation involving it is not yet completed. To avoid this, the architecture includes functionalities for resynchronization on demand. We have used these functionalities to implement an execution mode of the checkpointing protocol we refer to as semi-asynchronous. By the results of an experimental study we argue that the semi-asynchronous mode can be an effective solution to almost completely remove the delay associated with any checkpoint operation from the completion time of the simulation.
Algorithms for simulating an ATM switch on a distributed memory multiprocessor are described. These include parallel generation of bursty arrival streams, along with the marking and deleting of lost cells due to buffe...
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ISBN:
(纸本)0769506771
Algorithms for simulating an ATM switch on a distributed memory multiprocessor are described. These include parallel generation of bursty arrival streams, along with the marking and deleting of lost cells due to buffer overflows. These algorithm increase the amount of computation carried out independently by each processor and reduce the communication between the processors. When the number of cells lost is relatively small, the nln time of the simulation is approximately O(N/P), where N is the total number of cells simulated and P is the number of processors. The cells are processed in intervals of fixed length;that length affects the structure and the performance of the algorithms.
Multi-agent systems comprise multiple, deliberative agents embedded in and recreating patterns of interactions. Each agent's execution consumes considerable storage and calculation capacities. For testing multi-ag...
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ISBN:
(纸本)0769506771
Multi-agent systems comprise multiple, deliberative agents embedded in and recreating patterns of interactions. Each agent's execution consumes considerable storage and calculation capacities. For testing multi-agent system, distributedparallelsimulation techniques are required that take the dynamic pattern of composition and interaction of multi-agent systems into account. Analyzing the behavior of agents in virtual, dynamic environments necessitates relating the simulation time to the actual execution time of agents. Since the execution time of deliberative components can hardly be foretold, conservative techniques based on lookahead are nor applicable. On the other hand, optimistic techniques become very expensive if mobile agents and the creation and deletion of model components are affected by a rollback. The developed simulation layer of JAMES (a Java Based Agent Modeling Environment for simulation) implements a moderately optimistic strategy which splits simulation and external deliberation into different threads and allows simulation and deliberation to proceed concurrently by utilizing simulation events as synchronization points.
While the PADS community has traditionally focused on - and done a great job with - the technical aspects of developing simulations that run fast and can be connected to other simulations, it has paid little or no att...
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ISBN:
(纸本)0769506771
While the PADS community has traditionally focused on - and done a great job with - the technical aspects of developing simulations that run fast and can be connected to other simulations, it has paid little or no attention to the overall strategies required to produce a marketable, useful, and successful parallelsimulation. This lack of market focus has led to many fears of the demise of the PADS community, complaints of its lack of general acceptance by the broader simulation community, and predictions that it will become merely another venue for simulation interconnection. These fears, complaints, and predictions are unnecessary. There are several examples of successful parallelsimulations - in domains as far apart as aviation modeling and wargames. What can we learn from their successes? How can we translate their general acceptance into other parallelsimulation domains? Are there market opportunities that we are missing? In short, what is the parallelsimulation community lacking, and what does it need to do in order to be more successful? The purpose of this talk is to begin a discussion on the answers to these questions (as opposed to definitively answering them). We will draw on numerous examples of successful applications, and make some concrete suggestions for furthering the community.
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