Peter Janacik

ShoX: An Easy to Use Simulation Platform for Wireless Networks

For the evaluation of wireless network protocols, simulation has established itself as a good compromise between cost and complexity, on the one hand, and accuracy of results, on the other hand. Most established network simulators, however, were originally developed for wired networks and only later extended to the wireless domain. Some simulators like Opnet are not even restricted to communication networks at all, but can be used to simulate all kinds of networked systems. In this paper, we present ShoX, a network simulator explicitly designed for the simulation of wireless networks. Together with its strong GUI support, this allows a very efficient development and evaluation of network protocols without any considerable learning curve. All relevant concepts known from the domain of wireless networks like nodes, links, OSI layers, packets, mobility, signal propagation and traffic models are directly available. Defining new layers, packets or models is as easy as subclassing the existing abstract classes which ensures at compile time that all required methods are provided by the user. ShoX is completely based on Java and XML, thus superseding to learn unfamiliar languages like Tcl or NED. It features an integrated GUI for configuration, visualization and statistics.

Comparative Study of Wireless Network Simulators

In order to evaluate the behavior and performance of protocols for wireless networks, simulations are a good compromise between cost and complexity, on the one hand, and accuracy of the results, on the other hand. Since there are many simulators for wireless networks, it is often difficult to decide which simulator to choose. To help shed light on this issue, we present a case study in which four popular wireless network simulators were used to evaluate a well-known topology control protocol (SPAN). Within the case study, we describe outstanding and desirable but missing features of the simulators, outlining their strengths and weaknesses. Further, we compare the amount of effort needed for installation, familiarization, implementation (needed lines of code and lines for configuration) and visualization. As opposed to other simulator comparisons, we do not focus on the correlation of the individual simulation results, but try to compare the simulators from feature and usability point of view. This paper can help other researchers to quickly identify which simulator is most suitable for their needs.

BASIC CONCEPTS OF REAL TIME OPERATING SYSTEMS

Real-time applications usually are executed on top of a Real-time Operating System (RTOS). Specific scheduling algorithms can be designed. When possi- ble, static cyclic schedules are calculated off-line. If more flexibility is needed on-line techniques are applied. These algorithms are bound to priorities which can be assigned statically or dynamically. Designing a proper RTOS architec- ture needs some delicate decisions. The basic services like process manage- ment, inter-process communication, interrupt handling, or process synchroniza- tion have to be provided in an efficient manner making use of a very restricted resource budget. Various techniques like library-based approaches, monolithic kernels, microkernels, or virtual machines/exokernels are applied, based on spe- cific demands. Safety critical application can be supported by separation of ap- plications either in the time or the space domain. Multi-core architectures need special techniques for process management, memory management, and synchro- nization. The upcoming Wireless Sensor Networks (WSN) generate special de- mands for RTOS support leading to dedicated solutions. Another special area is given by multimedia applications. Very high data rates have to be supported un- der (soft) RT constraints. Based on the used encoding techniques (e.g. MPEG) dedicated solutions can be created.

Emergent Topology Control Based on Division of Labour in Ants

Advances in the area of wireless sensor networks enable a myriad of new applications. Communication is however still the most costly function in these networks. Regions with higher node density lead to a greater amount of energy waste through overhearing, collisions, etc., while not increasing the networks capacity. Therefore, we propose an emergent approach to topology control reducing the number of active nodes in such areas. Facing the necessity to minimize the amount of data exchanged for achieving this goal, given the high cost of communication, the approach is motivated by the division of labour observed in ants promising lower overhead, more robustness and better scalability. Nodes actively involved in network operation are modeled as transporters, other nodes as workers. State changes are realized using a response function incorporating a response threshold and stimulus. The response threshold determines the tendency of a node to respond to a stimulus and reflects the ability to perform a state change. The intensity of stimulus is determined by quantitative cues perceived

Performance of wireless network simulators: a case study

Designing protocols for wireless networks is a challenging task. Combined with the fact that such networks are often deployed for critical missions like forest fire detection in the WSN scenario or have to function properly and efficiently for an extended period of time, it is desirable to thoroughly test, analyze and evaluate newly developed communication protocols before deployment. In order to do this, simulations are a good compromise between cost/complexity and accuracy of the results. Since there are many simulators for wireless networks, it is often difficult to decide which one to choose. Therefore, we present a case study in which four common wireless network simulators were used to evaluate a well-known topology control protocol (SPAN). Within the case study, we describe the strengths and weaknesses of the examined network simulators: First, we evaluate the usability of the simulators in terms of different parts of the protocol developers work process. Moreover, we also focus on the simulators support for reusability and maintainability of simulation models by measuring particular model properties. For this purpose, we have proposed a model of quality for network simulators. The model of quality defines which properties of models to measure and how to interpret them. As opposed to other simulator comparisons, we do not focus on the correlation of the individual simulation results. Through this paper, we aim at providing a basis for finding an adequate simulator for a particular task.

Experiments with Biologically-Inspired Methods for Service Assignment in Wireless Sensor Networks

Given the scarcity of energy in wireless sensor networks (WSNs), in-network data processing by distributed, cooperating services is often used to reduce the amount of information that has to be routed to the base station and thereby to reduce communication and energy consumption. However, to minimize the amount of communication between services and their requesters, the locations of services in the network have to be selected carefully. Therefore, this paper proposes an efficient biologically-inspired heuristic for service assignment in WSNs. In order to reduce the amount of information exchange necessary for our heuristic, we use a concept observed in ant colonies that utilizes only local information. We model packets as ants (depositing pheromones at the visited nodes), services as food sources and requesters as formicaries. To optimize an objective function (reduction of communication distance between services and requesters), an explorer agent makes local service assignment decisions based on solely local information: the pheromones deposited by the ants. Furthermore, our paper presents the formal definition of the problem of service assignment and a thorough analysis and discussion of the results of our experiments, which show the efficiency of our approach.

A Survey of Ant Colony Optimization-Based Approaches to Routing in Computer Networks

Nature has provided an elegant solution for the routing problem millions of years ago, when ant colonies started to use swarm intelligence to discover food and route it reliably to their formicaries. The approach utilized by ants has several advantages that are also useful in computer networks: complete distribution, load balancing, finding shortest paths with a high probability. Several routing protocols designed for the area of computer networks have made use of this approach, called ant colony optimization. This paper provides first a broad overview of ant colony optimization-based routing protocols, while focusing on four selected approaches in later sections, describing their operation and discussing their properties in detail.

Multi-view Communication Visualization for Wireless Network Simulations

In this paper, we present a novel multi-view visualization tool for trace files generated by network simulations, currently supporting the ns-2 and ShoX trace formats. As the first tool in this area, it shows simultaneously three synchronized views (or perspectives) of the current network state in one window: (a) An enriched text view showing events line-by-line, marked up using colors and symbols in order to improve readability, (b) the 2-D bird’s eye view known from other simulators, (c) a newly proposed view depicting the development of network state as a graph focusing on the visualization of communication patterns on intra- and internode level. Using this synchronized multi-view, as well as, our novel graph view, we aim at increasing the speed of the analysis and evaluation processes during the development of communication protocols.

A routing approach using swarm-intelligence for resource sharing in wireless ad hoc networks

Many current applications for wireless networks are based on a static infrastructure and only operate within the range of access points to a wired network. The inflexibility of these hierarchical solutions yields problems like bottlenecks, limited scalability and congestions. In this paper we present the routing technique Stigmergy based on swarm-intelligence to share resources in wireless ad hoc networks. We present a simulation platform for Stigmergy which provides resource sharing where n resource requestors relate to m resource providers, with n,m ⩾ 1. It routes messages between one of the n resource requesting nodes and one of the m resource providing nodes.

Self-organizing resource-aware clustering for ad hoc networks

This paper proposes an efficient heuristic for solving the minimum-intracommunication clustering problem in energy- and resource-constrained ad hoc networks. The heuristic organizes the network in clusters aiming to minimize a given cost function. The function used measures the total communication cost between all nodes within the cluster, keeping a minimum amount of resources per cluster. The clusterhead selection of the proposed heuristic is based on the division of labor encountered in social insects. The idea is that each node has probabilistic tendencies to assume a determined role in the network. For example, nodes with good connectivity and high energy level are good candidates for being clusterheads. The probability of assuming a determined role is based on a nodes fitness for the specific role and the actual necessity (reflected by stimulus) of the role in the current network context. After becoming clusterhead, a node starts recruiting members in order to reach a minimum amount of resources that have to be available in the cluster. The procedure is based on a membership fitness function that evaluates the suitability of a node for the cluster. The realized simulations demonstrate that the proposed heuristic performance was about in average 25% inferior to the global optimum.