48 research outputs found
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
Species delimitation 4.0: integrative taxonomy meets artificial intelligence
Although species are central units for biological research, recent findings in genomics are raising awareness that what we call species can be ill-founded entities due to solely morphology-based, regional species descriptions. This particularly applies to groups characterized by intricate evolutionary processes such as hybridization, polyploidy, or asexuality. Here, challenges of current integrative taxonomy (genetics/genomics + morphology + ecology, etc.) become apparent: different favored species concepts, lack of universal characters/markers, missing appropriate analytical tools for intricate evolutionary processes, and highly subjective ranking and fusion of datasets. Now, integrative taxonomy combined with artificial intelligence under a unified species concept can enable automated feature learning and data integration, and thus reduce subjectivity in species delimitation. This approach will likely accelerate revising and unraveling eukaryotic biodiversity.K.K., L.K., P.M., and J.W.’s research is supported by the German Federal Ministry of Education and Research (BMBF) grant 01IS20062, M.H. by the German Ministry of Agriculture and Food (BMEL-BLE) grant 2819NA106, and L.H. by the German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety, and Consumer Protection grant 67KI2086. K.K. also received funding from the German Research Foundation (DFG) Priority Program Taxon-Omics SPP1991 funding line Seed Money for Post-Doc Grants. E.H., S.T., and N.W. are supported by the DFG priority program Taxon-Omics SPP1991 grants Ho4395/10-2, To1400/1-1, and Wa3684/2-1, respectively. J.d.V. is supported by the DFG priority program SPP 2237 MAdLand grant VR 132/4-1. J.d.V. further thanks the European Research Council for funding under the EU Horizon 2020 Research and Innovation Program (Grant Agreement No. 852725; ERC-StG ‘TerreStriAL’). H.L. is supported by the National Natural Science Foundation of China grant 32171813.Peer reviewe
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