Dirk Bradler

kTC - Robust and Adaptive Wireless Ad-Hoc Topology Control

Topology control for Wireless Sensor Networks (WSN) is a frequently tackled challenge, for which no satisfying general solution for realistic deployments has been found to the current day. Aiding to minimize unnecessary transmissions, it nevertheless represents a crucial function of WSN, in the light of their pursuit of efficiency. kTC is a new WSN topology control that unlike prior art neither relies on location information, nor on complex geometric structures, which could leave doubts about a practical feasibility. Even though location-free approaches have been proposed to circumvent systematic problems, they do not address issues like robustness and adaptability satisfyingly, which may lead to disconnection in real world deployments. kTC is a location-free approach that adapts topologies dynamically in face of changing environmental influences. It is based on a local, pattern-based heuristic, and transmitting only two messages per node to construct the topology it is highly scalable. The graphs kTC creates are symmetric, connected, and planar; they have bounded degree and nodes are θ-separated. Simulative evaluations indicate that kTC outperforms known topology control schemes. A preliminary deployment on a sensor testbed corroborates the obtained results and acts as proof of concept for kTC.

GTNA: a framework for the graph-theoretic network analysis

Concise and reliable graph-theoretic analysis of complex networks today is a cumbersome task, consisting essentially of the adaptation of intricate libraries for each specific problem instance. The growing number of complex metrics that have been proposed in the last years, which mainly gain significance due to the increasing computational capabilities at hand, have led to important new insights in the field. However, they have solely been implemented as single algorithms, each specialized for the purpose of calculating exactly the targeted metric for a selected type of network graph. A comprehensive, extensible tool for the concise evaluation of graphs is currently not available. For this purpose we introduce the Graph-Theoretic Network Analyzer (GTNA), an efficient, Java-based toolkit for the comprehensive analysis of complex network graphs. GTNA, while already including the main metrics that are used to analyze the complex networks in computer science today, is simple to extend through a well defined plugin interface for metrics, network descriptions and network generator models. Throughout the paper we present the design and simple extensibility of GTNA, as well as the network models and metrics that are already implemented and give examples of its scalability and performance.

Leveraging Network Motifs for the Adaptation of Structured Peer-to-Peer-Networks

Topology adaptation is a vital operation in tech- nological networks. It is frequently implemented as either an external process or a distributed online optimization that relies on gathering knowledge on the overall state of the system. In this work we propose MBO, a novel approach that uses network motifs (a local, stochastic metric) for distributed topology optimization of arbitrary, adaptable networks. In order to give a proof of concept we chose to optimize structured Peer-to-Peer overlays towards a fair load balancing. MBO is parametrized using target motif signatures of networks, which are derived from exemplary, generated topologies with the desired properties - a fair load balancing in the demonstrated case. Extensive simulations indicate that for CAN and Kademlia, two different types of P2P systems, MBO leads to a well balanced load, while being minimally intrusive.

First response communication sandbox

First response communication is tackled by several independent research groups. While there are existing prototypes and simulated results, comparison of first response solutions is hardly possible so far. We have built an universal XML based description format to handle all relevant settings and actions typical for first response scenarios. In addition we implemented a user-friendly movement and environment simulator which interacts with the network simulation on top of the simulated movement. The chosen data structure have proven to be well suited for describing settings and actions found in a first response scenario. The simulator combines movement and network simulation and therefore enables both, fine grained movement models and location aware network models with reciprocal interdependencies. The simulation results of the chosen communication approach are therefore finer grained than using a network or movement simulator separately.

Self-organized aggregation in irregular wireless networks

Gossip-based epidemic protocols are used to aggregate data in distributed systems. This fault-tolerant approach does neither require maintenance of any global network state nor knowledge of network structure. However, although gossip-based aggregation algorithms scale well for graphs with good expansion, their efficiency for sparse graphs is unexamined. In this paper we analyze the feasibility and efficiency of a gossip aggregation protocol in wireless networks with low expansion. We propose a modification of the existing aggregation algorithm for use in locality-aware, sparse, static wireless networks. Our protocol terminates autonomously, uses less bandwidth than the original version, and removes the need for the leader election process while counting network nodes. Aggregates are calculated only over nodes placed in the vicinity, and nodes communicate only with their immediate neighbors by using a wireless broadcast. We evaluate our approach by simulation on sparse, irregular graphs with low expansion for the simplified system model. Furthermore, we analytically assess the worst-case convergence time of this protocol for sparse wireless networks and also for the simplified system model.

Evaluation of Peer-to-Peer Overlays for First Response

Efficient communication architectures are vital for handling larger scale first response scenarios, and existing mechanisms have several shortcomings due to the heterogeneity of first response groups. In this paper, we consider using peer-to-peer-based communication architectures for first response scenarios. We evaluated different network overlays in environments found in first response -like scenarios. A first response P2P system needs to address both, reliability in high churn situations in network infrastructure mode as well as reasonable usability in wireless ad-hoc networks. Our evaluation shows that a superpeer architecture based on peer capabilities has superior performance when compared with purely unstructured or DHT-based overlays.

Systematic first response use case evaluation

Efficient communication architectures are vital for handling larger scale disaster management, and existing communication mechanisms have several shortcomings due to the heterogeneity of the first response groups. In this paper, we present requirements leading to FRCS, a sandbox environment for simulating all kinds of communication approaches in a first response scenario. Through extensive telephone interviews and from existing reports, we have identified several use cases which a first response system must be able to handle. Only by combining both, a unified infrastructure scenario and standardized use cases, becomes a fair evaluation of different kinds of first response solutions possible.

Demonstration of a Peer-to-Peer Approach for Spatial Queries

This demo paper presents an prototype implementation of a decentralized and distributed approach for spatial queries. The main focus is the location-based search for all the objects or information in the particular geographical area.

BridgeFinder: Finding communication bottlenecks in distributed environments

Nodes in mobile networks are usually unevenly distributed over space. Several dense clusters of nodes are interconnected by a few nodes in sparsely occupied areas. Removing vital nodes along such bridges would partition the network and severely reduce the overall connectivity. Consequently, detecting and protecting those few vital nodes is crucial for keeping the network operational. In order to achieve this task, we present our novel approach: BridgeFinder. Most importantly, BridgeFinder allows us to calculate good estimates for global graph measures, while operating as a fully distributed algorithm and causing only very little messaging overhead. It is based on an extended gossiping protocol and is significantly faster and more precise than existing mechanisms. The results of our extensive evaluation show that BridgeFinder is indeed very effective in detecting the few crucial for the network operation nodes.

PathFinder: efficient lookups and efficient search in peer-to-peer networks

Peer-to-Peer networks are divided into two main classes: unstructured and structured. Overlays from the first class are better suited for exhaustive search, whereas those from the second class offer very efficient key-value lookups. In this paper we present a novel overlay, Path-Finder, which combines the advantages of both classes within one single overlay for the first time. Our evaluation shows that PathFinder is comparable or even better in terms of lookup and complex query performance than existing peer-to-peer overlays and scales to millions of nodes.