Svilen Ivanov

Real-Time Network Emulation with ns-2

The network simulator ns-2 implements both wireless networks and emulation — a feature that allows to simulate a network environment among real stations. However, the real-time requirements of a network emulation introduce an inaccurate timing behavior of the simulator scheduler. These timing errors have a negative impact on the performance of network protocols in ns-2. Even more, they lead to false simulation results in the IEEE 802.11 protocol implementation. In this paper we present performance improvements in ns-2, that increase the accuracy of its virtual clock and the the exactness of the real-time simulation. Then we describe a simple time monitoring and correction technique that ensures a timely correct execution of network protocols and enables wireless network emulation in ns-2.

Adjusting the ns-2 Emulation Mode to a Live Network

The network simulator ns-2 implements both wireless networks and emulation — a feature that allows to simulate a network environment among real stations. In contrast to a discrete event simulation an emulation is affected by various system parameters. The understanding of the impact of those parameters is crucial to obtain valid results from an emulation experiment. In this paper we evaluate a modified version of the ns-2 that has been optimized for emulations. We analyze the effect of different parameter settings in various experiments and compare the results with measurements in a live network.

Automatic WLAN localization for industrial automation

The increasing WLAN deployment in industrial environments opens possibilities for location based services such as asset-tracking and workflow optimization. This paper presents our current research to develop a WLAN-localization system that fulfils the requirements of industrial automation: scalability and 5-10 m localization accuracy. Our envisaged system produces the training data automatically using automatic measurements, and model calibration. The suggested approach avoids the effort for walk-around and extensive manual measurements and is stable under environmental changes, while still achieving an accuracy equivalent to state-of-the art technology. Preliminary evaluation shows an average accuracy of 3.7 m (12ft).

Precise Admission Control for Bandwidth Reservation in Wireless Mesh Networks

Quality of service in wireless mesh networks is an often requested feature for various kinds of applications. A common approach is the establishment of routes based on hop-by-hop reservation of bandwidth. In this paper we address the problems of admission control in wireless mesh networks. We show that the existing solutions suffer from temporal inconsistencies during the distributed admission process, which lead to high admission failure rates of approximately 2% to 10% in typical topologies, even with the best approach. A solution for this problem is presented, based on the two phase commit protocol. It prevents inconsistencies and the corresponding admission failures.

PLANNING AVAILABLE WLAN IN DYNAMIC PRODUCTION ENVIRONMENTS

Abstract What is still missing in the convergence of IT and automation technologies is the integration of wireless communication. In this paper we consider the problem of planning available Wireless LAN (WLAN) in production environments with dynamic radio-propagation properties. Our approach is an autonomic control loop with feedback simulation and optimization. We present in detail the simulation and calibration module which automatically keeps the knowledge about the current radio coverage up-to-date. Evaluation showed that the constrained least squares calibration method results in a more accurate model compared to other methods. The results are general to planning WLAN availability in production environments. Copyright

Localization-Based Radio Model Calibration for Fault-Tolerant Wireless Mesh Networks

Wireless mesh networks offer flexibility for industrial automation, but, in these environments with changing propagation conditions, it is challenging to guarantee the radio coverage and connectivity. This paper contributes a new localization-based method for the calibration of radio propagation models. The idea is to find the locations of the mobile stations via localization and to use radio signal strength measurements from them for adjusting the radio model parameters until the model better fits to the real environment. This calibration method is integrated in our previously published fault-tolerance framework for guaranteeing the availability of radio coverage and connectivity of wireless mesh networks. It is used to automatically detect environmental dynamics (errors) at run-time and to propose a network reconfiguration before they lead to service failures. An evaluation in a real industrial scenario shows the practicability of our approach.

Fault-tolerant base station planning of Wireless Mesh Networks in dynamic industrial environments

Wireless Mesh Networks are infrastructure networks with a wireless multi-hop backbone. In this paper we present an innovative algorithm for fault-tolerant base station planning in wireless mesh networks. The algorithm determines a close-to-minimal number and the positions of base stations to be installed such that the radio coverage is correct in the presence of faults (base station crash or link outage). The algorithm considers both the connectivity of the multi-hop backbone and the connectivity of the mobile stations. The presented algorithm produces correct results, in limited number of iterations under realistic network size and in acceptable time. The provided fault-tolerance is sufficient in most practical situations.

Fault-Tolerant Coverage Planning in Wireless Networks

Typically wireless networks coverage is planned with static redundancy to compensate temporal variations in the environment. As a result, the service still is delivered but the network coverage could have entered a critical state, meaning that further changes in the environment may lead to service failure. Service failures have to be explicitly notified by the applications. Therefore, in this paper we propose a methodology for fault-tolerant coverage planning. The idea is detecting the critical state and removing it by on-line system reconfiguration, and restoration of the original static redundancy. Even in case of a failure the system automatically generates a new configuration to restore the service, leading to shorter repair times. We describe how this approach can be applied to wireless mesh networks, often used in industrial applications like manufacturing, automation and logistics. The evaluation results show that the underlying model used for error detection and system recovery is accurate enough to correctly identify the system state.

Measurement-Based Detection of Interfering Neighbors for QoS in Wireless Mesh Networks

Communication in wireless mesh networks based on the IEEE 802.11 WLAN standard is mainly governed by the carrier sensing based medium access. Knowledge about, which nodes influence each other, can improve the performance and is essential for QoS provision in terms of bandwidth guarantees. However, until now only approximations for the determination of station in carrier sense range are used. We present an exact solution by measuring the carrier sense in static wireless mesh networks. Simulation studies and measurements are done that verify the correctness of the protocol and reveal some significant properties of the carrier sense. It is shown that the carrier sense relation is neither strict nor symmetric in the general case, in opposite to the assumptions normally found in literature. We further conclude that for evaluation better simulation models are required that match these properties.

Dependable wireless mesh networks: An integrated approach

Wireless Mesh Networks (WMNs) are replacing wireless Infrastructure networks in many areas because of their lower cost and higher flexibility. However, applications in the Process Industry and Telerobotics field require not only flexible but also dependable service, which is not provided by existing solutions. To make a WMN dependable, many problems have to be solved on different layers. With this paper, we describe our ongoing work to provide an integrated solution to increase the dependability of WMNs. Our approach combines network coverage planning on the physical layer, bandwidth management on the link layer and live network monitoring to improve the reliability, availability and maintainability of a WMN. We provide fine-grained means to improve the predictability of the network components, thus making the WMN more dependable. In this paper, we present first results of our ongoing work, and describe how they are interleaved.