Time warp discrete event simulation booklet

It uses a series of instantaneous occurrences, or discrete events. Scaling time warpbased discrete event execution to 10 4. The middle layer is a parallel discrete event simulation kernel, ooctw, which is an objectoriented version of clustered time warp ctw1. An assessment of the modsimtwos parallel simulation. Discrete event simulation is a simple, yet versatile, way of describing a dynamic system. Tay, s c, y m teo and s t kong, a throttled time warp scheme for parallel discrete event simulation. This article describes a time warp simulation algorithm for discrete event models that are described in terms of the discrete event system specification devs.

On constructing optimistic simulation algorithms for the. Apr 05, 2017 remove the earliest event e in the event list. The performance of a distributed combat simulation with the time. Here, we describe our experiences in developing two pcs simulation models on a general purpose distributed simulation platform based on the time warp mechanism. Pdf the local time warp approach to parallel simulation. Jobs arrive at random times, and the job server takes a random time for each service. The book is a reasonably full, theory based, introduction to the technique of discrete event simulation. Event scheduling schemes for time warp on iistributed systems. Time warp simulation using time scale decomposition acm. Applications abound not only in the analysis of complex systems such as transportation or the nextgeneration internet, but also in computergenerated virtual. In the simulation education homepage simulation tools list by william yurcik there were more than 200 simulation products, including noncommercial tools. Time warp is an optimistic synchronization protocol for parallel discrete event simulation that coordinates the available parallelism through its rollback and antimessage mechanisms. It also supports any other distributed applica tions that are synchronized by virtual time. This time requirement could decrease through the usage of parallel or distributed computing systems.

Bagrodia r perils and pitfalls of parallel discrete event simulation proceedings of the 28th conference on winter simulation, 6143 avril h and tropper c clustered time warp and logic simulation proceedings of the ninth workshop on parallel and distributed simulation, 112119. In this paper, we investigate two major factors in order to design an efficient event scheduling strat egy for time warp on distributedmemorysystems. Distributed simulation and the time warp operating system. Discrete event simulation goals of this class understand discrete event simulation see how it applies to assembly systems understand its strengths and weaknesses see some statistics about real systems simulation 11202002 daniel e whitney 19972004 1. Lately, important largescale simulation applications, such as emergency event planning and response, are emerging that are based on discrete event models. Des is being used increasingly in healthcare services2426 and the increasing speed and memory of computers has allowed the technique to be applied to problems of increasing size and complexity. In particular, the direct cancellation mechanism is proposed that eliminates the need for antimessages and provides an efficient. Optimizing time warp simulation with reinforcement learning techniques, proceedings of the 39th winter simulation conference, 577584 34.

Discrete event simulation is used to simulate components which normally operate at a higher level of abstraction than components simulated by continuous simulators. November 6 event driven simulation if events arent guaranteed to occur at regular intervals, and we dont have a good bound on the time step it shouldnt be so small as to make the simulation run too long, nor so large as to make the number of events unmanageable, then its more appropriate to use an event driven simulation. Within the context of discrete event simulation, an event is defined as an incident which causes the system to change its state in some way. A discrete event simulation starts with an abstract model of the real system to be simulated, expressed in terms of transitions of the system state that occur at discrete points in time. The note first presents the fundamental issues in concurrent discrete event simulation.

As a consequence, a priori knowledge of the control flow of the overall. A new strategy, called breathing time warp, has been developed in the synchronous parallel environment for emulation and discrete event simulation speedes operating sytem. We have adopted middle layer approach in stockyard to support millions of agents and to run it for a larger time span days, weeks, months and years. Several world views have been developed for des programming, as seen in the next few sections.

Using basic concepts like entities, queues, gates, and servers, you can build complex models to explore fundamental questions such as latency, utilization, and bottlenecks. The timewarp machine, has emerged as the most effective parallel execution environment for discrete event simulation applications where parallelism or sequentiality of programmed interactions cannot be determined at program design stage. Jul 12, 2012 discreteevent simulation is a very useful tool when it comes to simulating alternative scenarios for current of future business operations. Simpler than des to code and understand fast, if system states change very quickly or many events happening in short time period.

The time warp operating system university of california. Thus, the warpiv simulation kernel articulates an infrastructure based on concepts from time warp. Fujimoto compiles and consolidates research results in the field spanning the last twenty years, discussing the use of parallel and distributed computers in both the modeling and analysis of system behavior and the creation of distributed virtual environments. Gtw utilizes a number of optimizations to maximize performance including direct cancellation, fast gvt algorithms, onthefly. An introduction to discrete event simulation peter w. In this chapter, we will also learn about queuing simulation, which is a very important aspect in discrete event simulation along with simulation of time sharing system. A discrete event simulation hereafter called a simulation proceeds by producing a sequence of system snapshots or system images which represent the evolution of the system through time. Optimistic parallel discrete event simulations of physical.

The time warp operating system twos has been the focus of significant research in parallel, discrete event simulation pdes. Tay, s c, y m teo and c h ng, a globally optimised checkpointing scheme for time warp. With an emphasis on parallel and distributed discrete event simulation technologies, dr. Determine the next transition event time at the time of transition event. It provides services such as rollback, state saving and restoration, gvt computation and fossil collection to the top layer.

Time warp simulation related conferences, publications, and organizations. It also supports any other distributed applica tions that are. It achieves high speedup on discrete event simulations by running them in parallel on multiple nodes of a parallel processor, or on several sun workstations connected by an ethernet. Then the authors give a detailed description of the local control part of the time warp mechanism, the part concerned with the actual mechanics of discrete event. The simulation method known as a monte carlo simulation is similar to discrete event simulation, but is static, meaning that time does not factor into simulating leemis and park, 2006.

Discrete event simulation modeling should be used when the system under analysis can naturally be described as a sequence of operations at a medium level of abstraction. The rollback framework, event management services, and time management layers provide the basic infrastructure that is necessary to support both discrete event simulation and real time scheduling applications executing on single or multiple cpu machines. Time warp simulation on multicore platforms winter simulation. Parallel discrete event simulation pdes is a field concerned with the execution of discrete event simulation programs on a parallel computer. Using new distributed real time agent framework with time warp draft agents can enhance the development of multi. Using discreteevent simulation to simulate hospital. The field began with work in the 1970s and 1980s in first defining the synchronization problem along with associated terminology e. Its primary goal is concurrent execution of large, irregular discrete event simulations at maximum speed. A discrete event simulation is a computer model that mimics the operation of a real or proposed system, such as the daytoday operation of a bank, the running of an assembly line in a factory, or the staff assignment of a hospital or call center.

The simulation is driven by the exchange of timestamped message by the lps. It is also a useful reference for professionals in operations research, management science, industrial engineering, and information science. The event is invalid if one of the particles has participated in a collision since the time the event was inserted onto the priority queue. Optimistic synchronization of parallel simulations in. The coupling of modsim and twos is an attempt to address the development of largescale.

While other books on pads concentrate on applications, parallel and distributed simulation systems clearly shows how to implement the technology. Simevents integrates discreteevent system modeling into the simulink timebased framework. Consistency in the processing of messages requires that all events be. Discrete event system simulation is ideal for junior and seniorlevel simulation courses in engineering, business, or computer science. The model used in a discrete system simulation has a set of numbers to represent the state of the system, called as a state descriptor. Tradeoff between sequential and time warpbased parallel. It explains in detail the synchronization algorithms needed to properly realize the simulations, including an indepth discussion of time warp and advanced optimistic techniques. This chapter is about the history of the time warp algorithm and optimistic approaches to parallel discrete event simulation. The time warp operating system includes a complete implementation of the time warp mechanism, and is a substantial departure from conventional operating. The applications are characterized by their scale several millions of simulated entities, their finegrained nature of computation microseconds per event, and. In 1985 jefferson introduced the optimistic synchronization protocol, which was utilized in parallel discrete event simulations, known as time warp. Discrete event simulation software is widely used in the manufacturing, logistics, and healthcare fields. A comparative study of state saving mecanisms for time warp. A stateoftheart guide for the implementation of distributed simulation technology.

In 1993, a new scheduling approach was developed in speedes to integrate the strengths of pure time warp with the riskfree flow control benefits of btb. From our point of view, statistical fundamentals and evaluation of simulation results is a mandatory requirement for every scientific researcher. Georgia tech time warp gtw is a general purpose parallel discrete event simulation executive using optimistic synchronization techniques. Discreteevent simulation in r discrete event simulation des is widely used in business, industry, and gov ernment. Introduction parallel simulation with multiple computers enables largescale and possibly fast simulation beyond a. I assume the next message in the queue is the true next message i messages may arrive asynchronously i when a message with time stamp t less than what has executed, time warp must. A case study in simulating pcs networks using time warp. The top layer is the distributedsimulation engine, which. General principles of discreteevent simulation systems. If the event corresponds to an invalidated collision, discard it.

In this paper we propose the local time warp method for parallel discreteevent simulation and present a novel synchronization scheme for it called hctw. In this paper, we analyze the time warp synchronization protocol for parallel discrete event simulation and present an analytical model evaluating the upper bound on the completion time of a time warp simulation. Participants will learn the basics of monte carlo and discrete event simulation. A few years later, david jefferson and henry sowizral at the rand corporation came up with an entirely different approach known as time warp jefferson 1985. A discreteevent simulation des involves the execution of a sequence of event handlers dynamically scheduled at runtime. Scaling time warp based discrete event execution to 104 processors on a blue gene supercomputer, proceedings of the 4th international conference on computing frontiers, 6976 35. Cloud computing offers the potential to make parallel discrete event simulation capabilities more widely accessible to users who are not experts in this technology and do not have ready access to high performance computing equipment.

The basic time warp mechanism, which is at the heart of twos, was invented by henry sowizral and david jefferson then at the rand corporation and the uni versity of southern california respectively as a method for speeding up discrete event simulations jefferson 82. Fremont, california94538 distributed simulation offers afaster means of executing com plex and time consuming discrete event simulations than does conventional simulation. The result was the breathing time warp btw algorithm that reduced message. Fast concurrent simulation using the time warp mechanism. A variation of the time warp parallel discrete event simulation mechanism is presented that is optimized for execution on a shared memory multiprocessor. Index termsparallel discrete event simulation, time warp, peertopeer, data processing engine, mapreduce i. Efficient execution of time warp programs on heterogeneous. Discrete event simulation in r and, why r is different. A discrete event simulation consists of a collection of logical processes lps, which may execute on different processors pes.

Vme rollback hardware for time warp multiprocessor systems. However, many problems remain to be solved before distributed simulation can become commonplace. Introduction to simulation ws0102 l 04 2240 graham horton the event list the future event list fel controls the simulation the fel contains all future events that are scheduled the fel is ordered by increasing time of event notice example fel at some simulation time. In timebased systems, a signal changes value in response to the simulation clock, and state updates occur synchronously with time. To date, the technique known as reverse computation has only been applied in software for optimistically synchronized, parallel discrete event simulation. A dynamically configurable discrete event simulation framework for manycore chip multiprocessors. Discreteevent simulation in r discreteevent simulation des is widely used in business, industry, and government. The time warp mechanism speeds up objectoriented discrete event simulation by providing a synchronization protocol for multiprocessor computer systems jefb2, jefb5. Parallel discrete event simulation pdes 2 is a powerful tool of program ming on. Time warp mechanism i takes an optimistic approach. Gtw utilizes a number of optimizations to maximize performance including direct cancellation, fast gvt algorithms, onthefly fossil collection, and memorybased control of optimism.

Time warp connection oriented time warp connection oriented kalantery, nasser 20040516 00. Discrete event simulation jerry banks marietta, georgia. Operationally, a discrete event simulation is a chronologically nondecreasing sequence of event occurrences. Introduction time warp algorithms for simulating devs models are relatively uncommon in the parallel discrete event simulation literature see, e. Devs, parallel simulation, time warp, discreteevent simulation 1. The looping continues until the userspecified maximum simulation time is exceeded. Distributed discrete event and pseudo realtime combined. Introduction to discreteevent simulation and the simpy language. Discrete event modeling anylogic simulation software. The term discrete event refers to the fact that the state of the system changes only in discrete quantities, rather than changing continuously. Time warp simulation ieee conferences, publications, and.

Discrete event simulation modelling and simulation of. The time warp multiprocessing scheme promises speedup for objectoriented discrete event simulation. Parallel discrete event simulation pdes is concerned with the parallel and distributed execution. Department of information systems and computer science, national university of singapore, 30 november 1996. This paper analyzes the performance of a discreteevent combat simulation executed on a parallel processor under control of the time warp operating system. Designing multiagent systems for power plant control can be approached numerous ways, but it is important to enhance the flow of development to implementation. To achieve performance in a multiuser network of workstation now environment, time warp must continue to operate efficiently in the presence of external workloads caused by other users, processor heterogeneity, and irregular internal workloads caused by the simulation model.

At the same time, there is a strong need to develop a new generation of discrete event simulation software by taking account of changes in application environments. Time warp divides a simulation into multiple objects running on separate nodes which schedule events for each other. Parallel discreteevent simulation on data processing engines. Modeling methods based on discrete algebraic systems. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Discrete event simulation models include a detailed representation of the actual internals. The simulation must keep track of the current simulation time, in whatever measurement units are suitable for the system being modeled. A typical example would involve a queuing system, say people. System is composed of objects called entities that have certain properties called attributes state a collection of attributes or state variables that represent the entities of the system. What is discrete event simulation des a discrete event simulation models a system whose state may change only at discrete point in time. A critical analysis of the methods for concurrent simulation proposed in the literature follows. A comparative study of state saving mechanisms for time warp synchronized parallel discrete event simulation. Parallel and distributed simulation systems richard m. In time series analysis, dynamic time warping dtw is one of the algorithms for measuring similarity between two temporal sequences, which may vary in speed.

Sassy is a scalable agent simulation system for discrete event simulation that provides a middleware between an agentbased api and a parallel des simulation kernel. This book covers the whole life cycle of the discrete event simulation process. These models utilize two widely used approaches to simulating pcs networks. Teo, y m, s c tay and ne mastorakis, modeling and simulation of interconnection networks a conservative parallel approach. Events are classified as instances of a finite number of types, each of which. Nonpreemptive time warp scheduling algorithms rand. Introduction to monte carlo and discreteevent simulation. Services hosted within the ldquocloudrdquo can potentially incur processing delays due to load sharing among other active services, and can cause optimistic. Frequently, for problems that fit the discrete event simulation model well in my career, this has been physicsbased modeling, this is not a problem. The concurrent processing for advanced simulation project has constructed a lispbased time warp system for implementing simulations with many large, complex objects. Simulation symposium ass96, mar 1996, new orleans, united states. The time warp mechanism is an implementation of the virtual time paradigm proposed by jefferson jefferson 1985. A discrete event simulation is the modeling over time of a system all of whose state changes occur at discrete points in time those points when an event occurs. Reverse computation is a software application of the concept of reversible computing.

The basic time warp mechanism, which is at the heart of twos, was invented by henry sowizral and david jefferson then at the rand corporation and the uni versity of southern california respectively as a method for speeding up. The development of the course discrete event simulation modelling and simulation of computer networks is driven by the fact that many publications show lack of meaningful statistical evaluation. In a time warp simulation, the system under investigation is decomposed into a set of lps that operate as asynchronously communicating discrete event simulators jefferson 1985. The time warp operating system twos is a optimistic parallel discrete event simulation engine based on david jeffersons concept of virtual time. Development, testing, simulation, and validation of complex real time distributed systems is a challenge on many levels. Perhaps the earliest was the colliding pucks application developed for the time warp operating system twos 5. Most mathematical and statistical models are static in that they represent a system at a fixed point in time. This work, modeling a set of pucks traveling over a frictionless plane, was used to benchmark an early implementation of the time warp protocol. In discreteevent simulations, as opposed to continuous simulations, time hops because events are instantaneous the clock skips to the next event start time as the simulation proceeds. The rapid expansion of the internet and commodity parallel computers has made parallel and distributed simulation pads a hot technology indeed.

Update the current simulated time to the time in e. Patients of an outpatient diabetes clinic are complaining about long waiting times, this seems to have an adverse effect on patient satisfaction and patient retention. The main event driven simulation loop works as follows. Specifically, they will learn to identify realworld problem types appropriate for simulation, and will develop skills and intuition for applying monte carlo and discrete event simulation techniques. Each state such transition corresponds to an event. State duration time for the transition node in the right. A new language, modsim, has been developed for use in conjunction with twos.