Optimally Efficient Prefix Search and Multicast in Structured P2P Networks

Searching in P2P networks is fundamental to all overlay networks. P2P networks based on Distributed Hash Tables (DHT) are optimized for single key lookups, whereas unstructured networks offer more complex queries at the cost of increased traffic and uncertain success rates. Our Distributed Tree Construction (DTC) approach enables structured P2P networks to perform prefix search, range queries, and multicast in an optimal way. It achieves this by creating a spanning tree over the peers in the search area, using only information available locally on each peer. Because DTC creates a spanning tree, it can query all the peers in the search area with a minimal number of messages. Furthermore, we show that the tree depth has the same upper bound as a regular DHT lookup which in turn guarantees fast and responsive runtime behavior. By placing objects with a region quadtree, we can perform a prefix search or a range query in a freely selectable area of the DHT. Our DTC algorithm is DHT-agnostic and works with most existing DHTs. We evaluate the performance of DTC over several DHTs by comparing the performance to existing application-level multicast solutions, we show that DTC sends 30-250% fewer messages than common solutions

Peer-to-Peer Concepts for Emergency First Response

Peer-to-peer (P2P) technology has already been established in several application domains, e.g., IP telephony, file sharing, and content distribution. It is considered to be distributed, ad-hoc, robust and scalable approach for digital information transfer. In this thesis, the P2P communication paradigm is proposed as an alternative communication approach in the first response application domain. Disaster relief efforts, after larger scale catastrophes, suffer from damaged or destroyed communication infrastructure. Satellite connection equipment is hardly available and costly, and therefore rescue workers tend to send foot messengers to relay messages between the on-site organizations. A P2P-inspired communication approach for first responders would relieve the overloading of communication channels, can function as a completely self-contained method and remove the need for centrally managed communication approaches, which might be damaged or destroyed after catastrophes. In this thesis, we investigate a breakdown of the P2P-inspired communication approach in four distinct layers. We identify the key challenges for each layer and propose novel approaches for the most important challenges in each layer. The main contributions are: (i) a systematic breakdown of the communication concept in four distinct layers, and (ii) a mechanism called 'BridgeFinder', which increases the robustness of the communication network. The overlay network (iii) 'Pathfinder' provides key functionalities like routing, lookup and exhaustive search. The application-level multicast (iv) provides an efficient way of sending messages to multiple recipients. The novel mechanism (v), called DCC, provides reliable command and control structure management in a distributed fashion. Besides the technical concept, we developed a simulation environment with working prototypes for each contribution. Further, we evaluated the robustness, scalability and efficiency of these communication approaches. We show that they meet the stipulated requirements of first responders and perform at least equally or better than the current approaches

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 time and message complexity of this protocol for sparse wireless networks and also for the simplified system model

Öffentliche Sicherheit: IKT-Unterstützung für hochkritische Aufgaben in Großschadenslagen

Bei einer Großschadenslage, wie z.B. einem Chemieunfall oder einem Großbrand, werden extreme Anforderungen an die Belastbarkeit der menschlichen Einsatzkräfte, an die Schnitt-stelle zwischen Mensch und Technik sowie an die Technik selbst gestellt. Notwendige Absprachen der Rettungskräfte sind aufgrund der von Stress geprägten Situation besonders fehleranfällig, dabei nicht selten überlebenskritisch, sie kosten wertvolle Zeit und lenken viel Aufmerksamkeit von der ei-gentlichen Aufgabe ab. Informations- und Kommunikations-technik (IKT) für die Öffentliche Sicherheit kann auf ver-schiedene Weise helfen, diese Probleme zu reduzieren. Der folgende Beitrag gibt einen kurzen Überblick über entspre-chende IKT-Einsatzfelder und bespricht zwei davon genauer

Optimally Efficient Multicast in Structured Peer-to-Peer Networks

The Distributed Tree Construction (DTC) algorithm is designed for optimally efficient multicast tree construction over structured peer-to-peer networks. It achieves this by creating a spanning tree over the peers in the multicast group, using only information available locally on each peer. Furthermore, we show that the tree depth has the same upper bound as a regular DHT lookup which in turn guarantees fast and responsive runtime behavior. Our DTC algorithm is DHT-agnostic and works with most existing DHTs. We evaluate the performance of DTC over several DHTs by comparing the performance to existing application-level multicast solutions, we show that DTC sends 30–250% fewer messages than common solutions

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