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OPNET Technologies © 2008 OPNET Technologies, Inc. |
Research: During the second half of 2008, the OPNET modeler has been proficiently applied in two main areas: 1.The first one has been carrier sense adaptation. In this area, we continued to study the dependence between the density of nodes in an IEEE 802.11 based network and the carrier sense threshold that maximizes aggregate throughput. OPNET has been a very convenient tool to have a fast and accurate evaluation of theoretical predictions. The relationship between density and carrier sense threshold has been confirmed, and this link led to the creation of a fully distributed and adaptive protocol that can leverage this feature. 2. The second research activity is concerned with the modeling of Industrial Real Time communication systems. The following networks have been considered:
2.1 Ethernet Powerlink 2.2 EtherCAT Simulation models have been developed for EtherCAT, which is a very popular Real-Time Ethernet network. Some preliminary outcomes of the simulations are presented in the paper: "A simulation approach to a real-time Ethernet protocol", by L. Seno and C. Zunino, published on the Proceedings of the ETFA '08 IEEE International Conference.Abstract: In the last years the use of Ethernet as the communication technology for automation systems has been sensibly increasing. In particular, Real-Time Ethernet networks have become widely adopted. In this paper we consider one of the most popular Real-Time Ethernet networks, namely EtherCAT. We firstly provide a short outline of the protocol, along with a description of a simulation model we have developed. Subsequently, we focus on some typical network configurations and provide some insights on their performance by means of both theoretical analysis and numerical simulations. Moreover, the simulation models of EtherCAT and Powerlink have been employed to study the possibility of controlling electrical motors. In particular, we carried out simulations in which the networks were used to deliver the velocity set points to electrical drives. The analysis has been executed under different operational conditions. Specifically, we assessed the behavior of the systems for error prone environments in which some messages could get lost due to several reasons (communication errors, cable breaks, component failures, etc). 2.3 IEEE 802.11 The IEEE 802.11 g/e wireless LAN has been adopted in order to implement wireless extensions of wired networks for real-time applications. In particular, wireless extensions of Ethernet Powerlink have been investigated. The analysis has been carried out for different scenarios. Indeed, we took into account the presence of interfering networks as well as fading. Most of the results we obtained have been summarized in the paper: "Analysis of Ethernet Powerlink Wireless Extensions based on the IEEE 802.11 Wireless LAN" by L. Seno, S. Vitturi and C. Zunino submitted for possible publication on the IEEE Transactions on Industrial Informatics. Abstract: The industrial communication scenario is experiencing the introduction of wireless networks at all levels of factory automation systems. The benefits deriving from such an innovation are manifold, even if wireless systems can not be thought as a complete replacement of wired networks. Rather, they will be even more used in the near future to realize hybrid (wired/wireless) configurations. In particular, it is envisaged that wireless networks may be employed to implement extensions of (possibly already installed) wired systems. In this paper we consider wireless extensions of Ethernet Powerlink, a very popular Real-Time Ethernet network, implemented by means of the IEEE 802.11 WLAN. Specifically, we focus on a widespread network configuration and address two types of extensions based on, respectively, bridge and gateway devices. In the second part of the paper we provide an analysis of the hybrid networks aimed at evaluating the most relevant performance indexes. Since the reliability of wireless networks may represent a critical aspect, the analysis is carried out taking into account the presence of interference as well as fading in the wireless segment. The results we show, obtained from a theoretical analysis and validated by numerical simulations, allow to get some useful insights on the overall performance of the hybrid networks. Teaching: The course, offered to under-graduated students, deals with principles and performance evaluation of telecommunications networks, including TCP/IP, LAN and WAN architectures, and queueing theory. The deailed course syllabous follows. Introduction to the Telecommunications Networks. Circuit switched vs message/packet switched networks. Layering and OSI model. Physical layer functionalities. Error detection and retransmission strategies (ARQ). Delay models in data networks. Basic of random variables and processes. Poisson processes. Markov chains analysis. Chapman-Kolmogorov formulae. Little's theorem. Queueing models (M/M/1, M/M/infinity, M/M/C, M/M/1/K, M/G/1). Description and analysis of the most common MAC strategies (TDMA, FDMA, Aloha, Slotted Aloha, CSMA, Polling). Introduction to IEEE 802.x (Ethernet, IEEE 802.11, IEEE 802.5). Network layer functionalities (Dijkstra, Link State Routing, Distance Vector Routing). Introduction to Internet protocols: IP, UDP, TCP. Flow and congestion control mechanisms. The laboratory assignments require the use of OPNET to simulate simple packet switched networks and provide evidence of some theoretical analysis. OPNET is also used as a demonstration tool during lectures and discussion sections. In particular, the following experiences have been proposed:
Following these links you can see some lab reports written by students of the course:
OPNET Technologies, Inc. is a leading provider of solutions for managing networks and applications. OPNET's best-in-class solutions address application troubleshooting, application monitoring, network monitoring, network configuration management, network planning , and network simulation. OPNET’s solutions have been operationally proven in thousands of customer environments worldwide, including corporate and government enterprises, government and defense agencies, network service providers, and network equipment manufacturers. For more information about OPNET and its products, visit www.opnet.com. |
