The paper introduces OMNeT++, a C++-based discrete event simulation package primarily targeted at simulating computer networks and other distributed systems. OMNeT++ is fully programmable and modular, and it was designed from the ground up to support modeling very large networks built from reusable model components. Large emphasis was placed also on easy traceability and debuggability of simulation models: one can execute the simulation under a powerful graphical user interface, which makes the internals of a simulation model fully visible to the person running the simulation: it displays the network graphics, animates the message flow and lets the user peek into objects and variables within the model. These features make OMNeT++ a good candidate for both research and educational purposes. The OMNeT++ simulation engine can be easily embedded into larger applications. OMNeT++ is opensource, free for non-profit use, and it has a fairly large user

The omnet++ discrete event simulation system

SUMMARY Clusters, Grids, and peer-to-peer (P2P) networks have emerged as popular paradigms for next generation parallel and distributed computing. They enable aggregation of distributed resources for solving largescale problems in science, engineering, and commerce. In Grid and P2P computing environments, the resources are usually geographically distributed in multiple administrative domains, managed and owned by different organizations with different policies, and interconnected by wide-area networks or the Internet. This introduces a number of resource management and application scheduling challenges in the domain of security, resource and policy heterogeneity, fault tolerance, continuously changing resource conditions, and politics. The resource management and scheduling systems for Grid computing need to manage resources and application execution depending on either resource consumers’ or owners’ requirements, and continuously adapt to changes in resource availability. The management of resources and scheduling of applications in such large-scale distributed systems is a complex undertaking. In order to prove the effectiveness of resource brokers and associated scheduling algorithms, their performance needs to be evaluated under different scenarios such as varying number of resources and users with different requirements. In a Grid environment, it is hard and even impossible to perform scheduler performance evaluation in a repeatable and controllable manner as resources and users are distributed across multiple organizations with their own policies. To overcome this limitation, we have developed a Java-based discrete-event Grid simulation toolkit called GridSim. The toolkit supports modeling and simulation of heterogeneous Grid resources (both time- and space-shared), users and application models. It provides primitives for creation of application tasks, mapping of tasks to resources, and their management. To demonstrate suitability of the GridSim toolkit, we have simulated a Nimrod-G

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GridSim: a toolkit for the modeling and simulation of distributed resource management and scheduling for Grid computing

A number of library based parallel and sequential network simulators have been designed. The paper describes a library, called GloMoSim (Global Mobile system Simulator), for parallel simulation of wireless networks. GloMoSim has been designed to be extensible and composable: the communication protocol stack for wireless networks is divided into a set of layers, each with its own API. Models of protocols at one layer interact with those at a lower (or higher) layer only via these APIs. The modular implementation enables consistent comparison of multiple protocols at a given layer. The parallel implementation of GloMoSim can be executed using a variety of conservative synchronization protocols, which include the null message and conditional event algorithms. The paper describes the GloMoSim library, addresses a number of issues relevant to its parallelization, and presents a set of experimental results on the IBM 9076 SP, a distributed memory multicomputer. These experiments use models constructed from the library modules.

GloMoSim: a library for parallel simulation of large-scale wireless networks

The OMNeT++ discrete event simulation environment has been publicly available since 1997. It has been created with the simulation of communication networks, multiprocessors and other distributed systems in mind as application area, but instead of building a specialized simulator, OMNeT++ was designed to be as general as possible. Since then, the idea has proven to work, and OMNeT++ has been used in numerous domains from queuing network simulations to wireless and ad-hoc network simulations, from business process simulation to peer-to-peer network, optical switch and storage area network simulations. This paper presents an overview of the OMNeT++ framework, recent challenges brought about by the growing amount and complexity of third party simulation models, and the solutions we introduce in the next major revision of the simulation framework.

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An overview of the OMNeT++ simulation environment

An ad-hoc network is the cooperative engagement of a collection of (typically wireless) mobile nodes without the required intervention of any centralized access point or existing infrastructure. To provide optimal communication ability, a routing protocol for such a dynamic self-starting network must be capable of unicast, broadcast, and multicast. In this paper we extend Ad-hoc On-Demand Distance Vector Routing (AODV), an algorithm for the operation of such ad-hoc networks, to offer novel multicast capabilities which follow naturally from the way AODV establishes unicast routes. AODV builds multicast trees as needed (i.e., on-demand) to connect multicast group members. Control of the multicast tree is distributed so that there is no single point of failure. AODV provides loop-free routes for both unicast and multicast, even while repairing broken links. We include an evaluation methodology and simulation results to validate the correct and efficient operation of the AODV algorithm.

http://www.dcc.ic.uff.br/~celio/classes/cmovel/slides/royer%201999%20_multicast.pdf

Multicast operation of the ad-hoc on-demand distance vector routing protocol

Design and development costs for extremely large systems could be significantly reduced if only there were efficient techniques for evaluating design alternatives and predicting their impact on overall system performance metrics. Due to the systems' analytical intractability, simulation is the most common performance evaluation technique for such systems. However, the long execution times needed for sequential simulation models often hampers evaluation. The slow speeds of sequential model execution have led to growing interest in the use of parallel execution for simulating large-scale systems. Widespread use of parallel simulation, however; has been significantly hindered by a lack of tools for integrating parallel model execution into the overall framework of system simulation. Another drawback to widespread use of simulations is the cost of model design and maintenance. The simulation environment the authors developed at UCLA attempts to address some of these issues. It consists of three primary components: a parallel simulation language called Parsec (parallel simulation environment for complex systems), its GUI, called Pave, and the portable runtime system that implements the simulation algorithms.

Parsec: a parallel simulation environment for complex systems

A flexible simulator has been developed to simulate a two-level metropolitan area network which uses wormhole routing. To accurately model the nature of wormhole routing, the simulator performs discretebyte rather than discrete-packet simulation. Despite the increased computational workload that this implies, it has been possible to create a simulator with acceptable performance by writing it in Maisie, a parallel discrete-event simulation language. The simulator provides an accurate model of an actual high-speed, source-routing, wormhole network (the Myrinet) and is the first such simulator. The paper describes the simulator and reports on the performance of parallel implementations of the simulator on a 24-node IBM SP 2 multicomputer. The parallel implementations yielded reasonable speedups. For instance, on 12 nodes, the conservative algorithm yielded a speed-up of about 6 whereas an optimistic algorithm yielded a speed-up of about 4.

Parallel simulation of a high-speed wormhole routing network

This paper presents the results of an experimental study to evaluate the effectiveness of parallel simulation in reducing the execution time of gate-level models of VLSI circuits. Specific contributions of this paper include (i) the design of a gate-level parallel simulator that can be executed, without any changes on both distributed memory and shared memory parallel architectures, (ii) demonstrated speedups with both conservative and optimistic simulation protocols (almost all previous studies on circuit simulation have failed to extract speedups with conservative protocols); in particular we showed that a speedup of about 3 was obtained on 8 processors of Sparc1000 for conservative algorithms and about 2 for optimistic algorithms for circuits in the ISCAS85 benchmark suite; and (iii) performance comparison between shared memory and distributed memory implementations of the simulator.

Parallel gate-level circuit simulation on shared memory architectures

Interest in the exploitation of parallelism in circuit simulation has been increasing steadily. In this paper, we study parallel logic level simulation of combinational VLSI Boolean networks using both conservative and optimistic simulation algorithms. In particular, we describe a logic level circuit simulator that uses an acyclic multi-way network partitioning algorithm to decompose Boolean networks and an algorithm-independent simulation language that allows a discrete-event simulation model to be executed using a variety of simulation algorithms. The simulator has been implemented on an IBM SP1 supercomputer and was used to simulate a set of combinational Boolean circuits from the ISCAS85 benchmark suite. Our results show that it is feasible to obtain speedups for even relatively small circuits using both conservative and optimistic methods.

Parallel logic level simulation of VLSI circuits

This paper presents the results of an experimental study to evaluate the effectiveness of multiple synchronization protocols and partitioning algorithms in reducing the execution time of switch-level models of VLSI circuits. Specific contributions of this paper include: (i) parallelizing an existing switch-level simulator such that the model can be executed using conservative and optimistic simulation protocols with minor changes, (ii) evaluating effectiveness of several partitioning algorithms for parallel simulation, and (iii) demonstrating speedups with both conservative and optimistic simulation protocols for seven circuits, ranging in size from 3K transistors to about 87K transistors.

Yu-an Chen

Papers

Parsec: a parallel simulation environment for complex systems

Parallel simulation of a high-speed wormhole routing network

Parallel gate-level circuit simulation on shared memory architectures

Parallel logic level simulation of VLSI circuits

A multidimensional study on the feasibility of parallel switch-level circuit simulation