This article reviews the state of the art in Open Source (OS) Discrete Event Simulation (DES) software used for decision support in Operations Research (OR) focusing on the modelling of manufacturing, services, supply chain management and logistics. DES is arguably one of the most popular OR techniques. Commercial-Off-The-Shelf (COTS) DES software has been around for decades and it has considerably helped in the wider adoption and use of DES, providing the user with tools for modelling, debugging and experimentation. However, such tools often have limitations regarding their aspects such as cost, flexibility and reusability and OS DES seems to be a strong alternative in order to fill those gaps. The scope of our review is to present the state of the art in OS DES and identify future areas of research. The paper concludes with the desired features that an OS DES project should have in order to become a notable competitor against COTS equivalents in the OR domain.

A review of open source discrete event simulation software for operations research

Precise time synchronization becomes a vital constituent due to the rigorous needs of several time-sensitive applications. The clock synchronization protocol is one of the fundamental factors that can define the quality of communication. Our study starts with a brief discussion on the application domain of precise time synchronization and comes with an in-depth study of the synchronization with the main focus on the IEEE 1588 Precision Time Protocol (PTP). We have compared the well-known synchronization techniques and conclude that the PTP is the most appropriate answer to robust clock synchronization though challenges are there that requires thoughtful efforts and modification in the current version. The working mechanism and main components of the PTP network are discussed. We have established a testbench using commercially available devices and development boards to evaluate the PTP performance under different configurations. Major sources of synchronization error and other aspects contributing to precision are examined. This paper discussed numerous approaches that could enhance the performance of the PTP protocol. Structures for PTP based wireless clock synchronization required by advanced applications has also been discussed. In the end, paper focuses on the main industrial application areas in which PTP plays an important role, including WLAN, optical data centers, Smart grid, IEC 61850, etc. We conclude the paper by identifying the future trends and research directions for PTP based clock synchronization.

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IEEE 1588 for Clock Synchronization in Industrial IoT and Related Applications: A Review on Contributing Technologies, Protocols and Enhancement Methodologies

This paper presents the development of a simulator, TS2 time-synchronization simulator, for realistically simulating and studying the performance of the IEEE 1588 precise time protocol PTP in IEEE 802.15.4 TI CC2420 chip-based mobile wireless sensor networks WSNs. The PTP has the advantage of achieving high time precision at a low cost. It was designed for a wired Ethernet with requirements of symmetric communication paths and accurate time stamping, which is difficult for the low-cost WSNs to meet, as WSNs suffer more from overwhelming transmission delay jitters. An analytic solution to the performance of the PTP in WSNs is not possible, and it is of importance to evaluate the performance by realistic simulation. Based on the open-source OMNeT++ simulation engine, a realistic simulator was developed to simulate the PTP in IEEE 802.15.4 networks. There are two main contributions and benefits of the developed simulator. 1 Reality and fidelity: the WSN node's various layers including radio channels and TI CC2420 chip, drifting oscillator clocks and PTPs are simulated realistically. The drifting clock is simulated at an adjustable and higher resolution. 2 Support to both hardware and software time stamping, and the time-stamping uncertainties, by using a separated modular time-stamping module. It also has other features such as extendibility and code-reusability, mobile WSN nodes, scalability for multi-node, multi-hop simulation. Finally, to demonstrate the simulator's application to evaluating a PTP-based clock correction algorithm, a direct servo clock adjustment algorithm i.e., a P controller for a TI CC2420-based WSN was simulated and its performance was analyzed.

TS2: a realistic IEEE1588 time-synchronization simulator for mobile wireless sensor networks

A datacenter, which is a highly distributed multiprocessing system, needs to keep accurate track of time across a large number of machines. Precise time synchronization has become a critical component due to stringent requirements of several time critical applications such as real-time big data analytics, high-performance computing, and financial trading. Our study starts with a survey on the most relevant time synchronization techniques for datacenter networks. Then, we propose a zero-overhead microsecond-accuracy solution to synchronize a packet-switched optical network for datacenters. To achieve the desired time accuracy, we consider precision time protocol to synchronize the server clocks with a central controller clock. Zero-overhead is maintained by using data traffic to carry the time messages instead of a separate control channel. Through simulation, we show that microsecond level of time accuracy can be achieved. We also discuss the dependency of the accuracy on different traffic loads, traffic distributions, and packet lengths.

A survey on high-precision time synchronization techniques for optical datacenter networks and a zero-overhead microsecond-accuracy solution

Clock synchronization is a necessary feature in in-vehicle time- and safety-critical networks. The reason is that exact timing information has to be maintained in nodes, for instance for time stamps of messages that are important for safety-critical functions. A common time base has to be established at start-up time before time-sensitive data handling can begin. In vehicular applications, this clock initialization phase is only one part of tasks that have to be finished before the vehicle is fully functional. To avoid lengthy delays after vehicle ignition, this start-up phase has to be very short depending on the requirements of functions. Advanced driver assistance systems require high-bandwidth communication such as Ethernet Audio Video Bridging (AVB). Its corresponding IEEE 802.1 AS time synchronization protocol is, however, not able to guarantee fast synchronization start-up in conformance with automotive applications. This paper thus proposes and analyzes several variants of the time synchronization protocol to achieve a shorter start-up time. Simulation-based performance analysis shows that start-up times can be reduced by a factor of 40 compared to the standard IEEE 802.1 AS with the proposal, without considerably affecting synchronization error.

Improved clock synchronization start-up time for Ethernet AVB-based in-vehicle networks

Time synchronization has played an important role in modern measurement and control systems which require high time accuracy to maintain optimal performance in sample acquisition, signal control and safety protection. The Ethernet/IP based IEEE 1588 precise time protocol (PTP) provides us a prospective solution. By means of taking hardware timestamps, the time synchronization accuracy can be kept in the range of sub-microsecond with minimal network load and low demand on computing resources. Based on the OMNeT++ simulator, we build the PTP ordinary clock model and simulate the typical process of the PTP clock synchronization. The complete clock synchronization process and its performance are both analyzed and evaluated.

OMNeT++ based modeling and simulation of the IEEE 1588 PTP clock

A novel network layer management protocol for the low-voltage power line communication (PLC) network is proposed, focusing on the dynamic network address assignment mechanism of the PLC network with a multi-master topology. The remarkable feature of the presented protocol is that it enables the equipments to claim, configure and maintain their network addresses autonomously within the PLC network. Data communications can also be performed freely without the interferences of the network management equipments. Experimental results verified its flexibility and reliability. This protocol is tailored for the PLC networks composed of various flexible and plug-and-play equipments, which make it suitable and promising in the areas of smart home and office automation, as well as the industrial networks with low data transfer rate and soft real time requirements.

Yingshu Liu

Papers

OMNeT++ based modeling and simulation of the IEEE 1588 PTP clock

A novel network layer management protocol for the multi-master low-voltage power line communication network