197 research outputs found
Compact Routing on Internet-Like Graphs
The Thorup-Zwick (TZ) routing scheme is the first generic stretch-3 routing
scheme delivering a nearly optimal local memory upper bound. Using both direct
analysis and simulation, we calculate the stretch distribution of this routing
scheme on random graphs with power-law node degree distributions, . We find that the average stretch is very low and virtually
independent of . In particular, for the Internet interdomain graph,
, the average stretch is around 1.1, with up to 70% of paths
being shortest. As the network grows, the average stretch slowly decreases. The
routing table is very small, too. It is well below its upper bounds, and its
size is around 50 records for -node networks. Furthermore, we find that
both the average shortest path length (i.e. distance) and width of
the distance distribution observed in the real Internet inter-AS graph
have values that are very close to the minimums of the average stretch in the
- and -directions. This leads us to the discovery of a unique
critical quasi-stationary point of the average TZ stretch as a function of
and . The Internet distance distribution is located in a
close neighborhood of this point. This observation suggests the analytical
structure of the average stretch function may be an indirect indicator of some
hidden optimization criteria influencing the Internet's interdomain topology
evolution.Comment: 29 pages, 16 figure
Enhancing AIS to Improve Whale-Ship Collision Avoidance and Maritime Security
Whale-ship strikes are of growing worldwide concern due to the steady growth of commercial shipping. Improving the current situation involves the creation of a communication capability allowing whale position information to be estimated and exchanged among vessels and other observation assets. An early example of such a system has been implemented for the shipping lane approaches to the harbor of Boston, Massachusetts where ship traffic transits areas of the Stellwagen Bank National Marine Sanctuary frequently used by whales. It uses the Automated Identification Systems (AIS) technology, currently required for larger vessels but becoming more common in all classes of vessels. However, we believe the default mode of AIS operation will be inadequate to meet the long-term needs of whale-ship collision avoidance, and will likewise fall short of meeting other current and future marine safety and security communication needs. This paper explores the emerging safety and security needs for vessel communications, and considers the consequences of a communication framework supporting asynchronous messaging that can be used to enhance the basic AIS capability. The options we analyze can be pursued within the AIS standardization process, or independently developed with attention to compatibility with existing AIS systems. Examples are discussed for minimizing ship interactions with Humpback Whales and endangered North Atlantic Right Whales on the east coast, and North Pacific Right Whales, Bowhead Whales, Humpback Whales, Blue Whales and Beluga Whales in west coast, Alaskan and Hawaiian waters
09071 Abstracts Collection -- Delay and Disruption-Tolerant Networking (DTN) II
From 08.02. to 11.02.2009, the Dagstuhl Seminar 09071 ``Delay and Disruption-Tolerant Networking (DTN) II \u27\u27 was held in Schloss Dagstuhl~--~Leibniz Center for Informatics.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
05142 Abstracts Collection -- Disruption Tolerant Networking
From 03.04.05 to 06.04.05, the Dagstuhl Seminar 05142 ``Disruption Tolerant Networking\u27\u27 was held in the International Conference and Research Center (IBFI),
Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
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The Characteristics of Psychological Safety in Group Counseling
Psychological safety is a concept mentioned throughout the literature as a necessary component in the process of change in group counseling. Despite its frequent mention, no study has examined the characteristics of psychological safety. The purpose of this study was to lay the groundwork for a definition of the concept of psychological safety using self reports of group leaders and group members on a constructed Likert format psychological safety questionnaire of three attributional categories: self, other members, and leader. The study utilized group members (n = 44) and group leaders (n = 4) participating in laboratory groups as a part of a counseling related masters curriculum. The questionnaires were filled out on the first, eighth (middle), and fourteenth (last) sessions. Hierarchies for characteristics and attribution were constructed by using a summing procedure of the Likert responses. Results on the attribution of psychological safety by group members showed a consistent pattern over the three time measures. Group members reported leaders as the most attributed to facilitating psychological safety, other members as second, and self as least attributed to facilitate psychological safety. Group leaders showed no apparent agreement between groups, but each group leader attributed psychological safety consistently over time within one's own group. Results on the characteristics of psychological safety yielded a comprehensive list of characteristics, arranged in hierarchical format, as reported by both group members and leaders. Results indicated that psychological safety has some core concepts in each of the attributional categories. For group members, the characteristics of "warmth and support" and "active listening" were stable across every attributional category and time measure. For group leaders, "self disclosing feelings", "warmth and support", and "responding in an emotional, feeling manner" were reported in every time measure and attributional category. Characteristics that had a negative effect on psychological safety and recommendations for future research were also discussed
Self-Positioning Smart Buoys, The \u27Un-Buoy\u27 Solution: Logistic Considerations Using Autonomous Surface Craft Technology and Improved Communications Infrastructure
Moored buoys have long served national interests, but incur high development, construction, installation, and maintenance costs. Buoys which drift off-location can pose hazards to mariners, and in coastal waters may cause environmental damage. Moreover, retrieval, repair and replacement of drifting buoys may be delayed when data would be most useful. Such gaps in coastal buoy data can pose a threat to national security by reducing maritime domain awareness. The concept of self-positioning buoys has been advanced to reduce installation cost by eliminating mooring hardware. We here describe technology for operation of reduced cost self-positioning buoys which can be used in coastal or oceanic waters. The ASC SCOUT model is based on a self-propelled, GPS-positioned, autonomous surface craft that can be pre-programmed, autonomous, or directed in real time. Each vessel can communicate wirelessly with deployment vessels and other similar buoys directly or via satellite. Engineering options for short or longer term power requirements are considered, in addition to future options for improved energy delivery systems. Methods of reducing buoy drift and position-maintaining energy requirements for self-locating buoys are also discussed, based on the potential of incorporating traditional maritime solutions to these problems. We here include discussion of the advanced Delay Tolerant Networking (DTN) communications draft protocol which offers improved wireless communication capabilities underwater, to adjacent vessels, and to satellites. DTN is particularly adapted for noisy or loss-prone environments, thus it improves reliability. In addition to existing buoy communication via commercial satellites, a growing network of small satellites known as PICOSATs can be readily adapted to provide low-cost communications nodes for buoys. Coordination with planned vessel Automated Identification Systems (AIS) and International Maritime Organization standards for buoy and vessel notificat- - ion systems are reviewed and the legal framework for deployment of autonomous surface vessels is considered
Systematic Topology Analysis and Generation Using Degree Correlations
We present a new, systematic approach for analyzing network topologies. We
first introduce the dK-series of probability distributions specifying all
degree correlations within d-sized subgraphs of a given graph G. Increasing
values of d capture progressively more properties of G at the cost of more
complex representation of the probability distribution. Using this series, we
can quantitatively measure the distance between two graphs and construct random
graphs that accurately reproduce virtually all metrics proposed in the
literature. The nature of the dK-series implies that it will also capture any
future metrics that may be proposed. Using our approach, we construct graphs
for d=0,1,2,3 and demonstrate that these graphs reproduce, with increasing
accuracy, important properties of measured and modeled Internet topologies. We
find that the d=2 case is sufficient for most practical purposes, while d=3
essentially reconstructs the Internet AS- and router-level topologies exactly.
We hope that a systematic method to analyze and synthesize topologies offers a
significant improvement to the set of tools available to network topology and
protocol researchers.Comment: Final versio
Arterial hypoxaemia and its impact on coagulation:significance of altered redox homeostasis
AimsArterial hypoxaemia stimulates free radical formation. Cellular studies suggest this may be implicated in coagulation activation though human evidence is lacking. To examine this, an observational study was designed to explore relationships between systemic oxidative stress and haemostatic responses in healthy participants exposed to inspiratory hypoxia.ResultsActivated partial thromboplastin time and international normalised ratio were measured as routine clinical biomarkers of coagulation and ascorbate free radical (A•−) as a direct global biomarker of free radical flux. Six hours of hypoxia activated coagulation, and increased formation of A•−, with inverse correlations observed against oxyhaemoglobin saturation.ConclusionsThis is the first study to address the link between free radical formation and coagulation in vivo. This ‘proof-of-concept’ study demonstrated functional associations between hypoxaemia and coagulation that may be subject to redox activation of the intrinsic pathway. Further studies are required to identify precisely which intrinsic factors are subject to redox activation.</jats:sec
On Compact Routing for the Internet
While there exist compact routing schemes designed for grids, trees, and
Internet-like topologies that offer routing tables of sizes that scale
logarithmically with the network size, we demonstrate in this paper that in
view of recent results in compact routing research, such logarithmic scaling on
Internet-like topologies is fundamentally impossible in the presence of
topology dynamics or topology-independent (flat) addressing. We use analytic
arguments to show that the number of routing control messages per topology
change cannot scale better than linearly on Internet-like topologies. We also
employ simulations to confirm that logarithmic routing table size scaling gets
broken by topology-independent addressing, a cornerstone of popular
locator-identifier split proposals aiming at improving routing scaling in the
presence of network topology dynamics or host mobility. These pessimistic
findings lead us to the conclusion that a fundamental re-examination of
assumptions behind routing models and abstractions is needed in order to find a
routing architecture that would be able to scale ``indefinitely.''Comment: This is a significantly revised, journal version of cs/050802
Evaluating the Suitability of Server Network Cards for Software Routers
The advent of multicore CPUs has led to renewed interest in software routers built from commodity PC hardware. However, fully exploiting the parallelism due to multiple cores requires the ability to efficiently parallelize the delivery of packets to cores. I.e., traffic arriving (departing) on an incoming (outgoing) link at a router is inherently serial and hence we need a mechanism that appropriately demultiplexes (multiplexes) traffic between a serial link and a set of cores. Recent efforts point to modern server network interface cards (NICs) as offering the required mux/demux capability through new hardware classification features. However, there has been little evaluation of the extent to which these features match the requirements of software routing from the standpoint of both, performance and functionality. This paper takes a first step towards such an evaluation, comparing a commodity server NIC to both, an idealized "parallel" NIC and a "serial only" NIC. We show that although commodity NICs do improve on serial-only NICs they lag an ideal parallel NIC. We find similar gaps in the classification features these NICs offer. We thus conclude with recommendations for NIC modifications that we believe would improve their suitability for software routers
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