scholarly journals Assessing Contact Graph Routing Performance and Reliability in Distributed Satellite Constellations

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
J. A. Fraire ◽  
P. Madoery ◽  
S. Burleigh ◽  
M. Feldmann ◽  
J. Finochietto ◽  
...  
Keyword(s):  
State Of The Art ◽  
Satellite Constellations ◽  
Internet Protocols ◽  
Communication Architecture ◽  
Contact Graph ◽  
Routing Performance ◽  
Distributed Satellite ◽  
Space Environments ◽  
Disruption Tolerant Networking ◽  
Carry And Forward

Existing Internet protocols assume persistent end-to-end connectivity, which cannot be guaranteed in disruptive and high-latency space environments. To operate over these challenging networks, a store-carry-and-forward communication architecture called Delay/Disruption Tolerant Networking (DTN) has been proposed. This work provides the first examination of the performance and robustness of Contact Graph Routing (CGR) algorithm, the state-of-the-art routing scheme for space-based DTNs. To this end, after a thorough description of CGR, two appealing satellite constellations are proposed and evaluated by means of simulations. Indeed, the DtnSim simulator is introduced as another relevant contribution of this work. Results enabled the authors to identify existing CGR weaknesses and enhancement opportunities.

scholarly journals Towards Intelligent Caching and Retrieval Mechanisms for Upcoming Proposals on Vehicular Delay-Tolerant Networks

2011 ◽  
Vol 7 (1) ◽  
pp. 1 ◽  
Author(s):  
Bruno M. C. Silva ◽  
Vasco N. G. J. Soares ◽  
Joel J. P. C. Rodrigues
Keyword(s):  
Network Performance ◽  
Ad Hoc ◽  
Storage Capacity ◽  
State Of The Art ◽  
Delay Tolerant Networks ◽  
Opportunistic Networks ◽  
Network Nodes ◽  
Intermittent Connectivity ◽  
Delay Tolerant ◽  
Carry And Forward

Vehicular delay-tolerant networks (VDTNs) are opportunistic networks that enable connectivity in challenged scenarios with unstable links where end-to-end communications may not exist. VDTN architecture handles non-real timeapplications using vehicles to relay messages between network nodes. To address the problem of intermittent connectivity, network nodes store messages on their buffers, carrying them through the network while waiting for transfer opportunities. The storage capacity of the nodes affects directly the network performance. Therefore, it is important to incorporate suitable network protocols using self-contained messages to improve communication that supports store-carry-and-forward operation procedures. Clearly, such procedures motivate content cachingand retrieval. This paper surveys the state-of-the art on intelligent caching and retrieval mechanisms focusing on ad-hoc and delay tolerant networks (DTN). These approaches can offer important insights for upcoming proposals on intelligent caching and retrieval mechanisms for VDTNs.

scholarly journals Multi-threaded ASP solving with clasp

2012 ◽  
Vol 12 (4-5) ◽  
pp. 525-545 ◽  
Author(s):  
MARTIN GEBSER ◽  
BENJAMIN KAUFMANN ◽  
TORSTEN SCHAUB
Keyword(s):  
Experimental Analysis ◽  
State Of The Art ◽  
Data Representation ◽  
The State ◽  
Communication Architecture ◽  
Answer Set

AbstractWe present the new multi-threaded version of the state-of-the-art answer set solverclasp. We detail its component and communication architecture and illustrate how they support the principal functionalities ofclasp. Also, we provide some insights into the data representation used for different constraint types handled byclasp. All this is accompanied by an extensive experimental analysis of the major features related to multi-threading inclasp.

scholarly journals Analysis of Information Interaction Efficiency in Low-Orbit Satellite Constellations

2019 ◽  
Vol 18 (4) ◽  
pp. 858-886 ◽  
Author(s):  
Oleg Karsaev
Keyword(s):  
Effective Interaction ◽  
Network Control ◽  
Necessary Condition ◽  
Satellite Constellations ◽  
Autonomous Planning ◽  
Orbit Satellite ◽  
Information Interaction ◽  
Interaction Efficiency ◽  
Disruption Tolerant Networking ◽  
Networking Technology

The objects of the research are networks and information interactions in low-orbit satellite constellations performing tasks of remote sensing of the Earth. Research of network creation questions in this case is a necessary condition as opportunities and efficiency of information interaction directly depend on opportunities of a network. DTN (Delay-and-Disruption Tolerant Networking) technology is a basis of the network creation and CGR (Contact Graph Routing) approach is a basis of message routing. DTN technology and CGR approach are originally developed and used to provide communication with spacecraft located in a deep space. Therefore, the article discusses issues and problems arising in the context of their use in relation to low-orbit satellite constellations. The purpose of the information interaction study is development of effective interaction schemes (protocols). In the paper, the schemes of information interaction that can be used by a group of satellites in case of autonomous planning are considered. Along with autonomous planning, the paper also considers information interaction that can be used to implement network control of a satellite constellation in the case of ground planning. The effectiveness of the information interaction schemes are assessed by efficiency of orders’ execution. Measurement of efficiency is estimated via simulation of the communication network and the corresponding scheme of information interaction.

Modifi cation of the CGR-Algorithm on Data Routing in a Communication Network of Satellite Constellation

2020 ◽  
Vol 21 (2) ◽  
pp. 75-85 ◽  
Author(s):  
O. V. Karsaev
Keyword(s):  
Communication Networks ◽  
Data Storage ◽  
Communication Channels ◽  
Adaptive Method ◽  
Satellite Constellations ◽  
Network Nodes ◽  
Contact Graph ◽  
Data Routing ◽  
Promising Solution ◽  
Contact Graphs

Communication networks in space systems involving the use of satellite constellations are DTN networks (Delay and Disruption Tolerant Networks). The establishment of communication channels in space communication networks has certain specifics: communication channels can be planned. In this regard, the CGR approach (Contact Graph Routing) is considered as the most promising solution to the problem of data routing. At the basis of this approach, taking into account this specificity, the calculation of the contact plan is considered. On the basis of this plan in the network nodes contact graphs are calculated, which are used to search the shortest data transmission routes. The paper proposes two interrelated solutions as a modification of this approach: the route search based on the contact plan, i.e. without calculation and use of the contact graph, and an adaptive method of finding the set of shortest routes required for routing. The essence of the first solution is as follows. In the standard CGR approach, the graph vertices correspond to the planned contacts between the network nodes, and the edges correspond to the data storage processes in the network nodes. In contrast, in the proposed approach, the vertices of the graph correspond to the nodes of the network, and the edges of the graph and their weight are determined dynamically, in the process of finding the shortest routes. The second solution is based on the concept of the planning front, which means a list of the closest contacts in time. The required routes are divided into a certain number of pools. Each pool combines the routes that use the specified contact from the planning front. The planning front is updated in two cases. If the network topology changes, the completed or not established contacts are replaced by subsequent ones with the same network nodes that are closest in time. If message traffic grows, a certain extension of the planning front and the use of additional route pools are performed. The article concludes with a description and justification of the expected advantages of the proposed approach.

scholarly journals Motif-h: a novel functional backbone extraction for directed networks

2021 ◽  
Author(s):  
Yiguang Bai ◽  
Qian Li ◽  
Yanni Fan ◽  
Sanyang Liu
Keyword(s):  
Large Scale ◽  
State Of The Art ◽  
Weak Ties ◽  
The Novel ◽  
Directed Networks ◽  
Communication Architecture ◽  
Dense Networks ◽  
Edge Strength ◽  
Social Analytics ◽  
Large Scale Networks

AbstractDense networks are very pervasive in social analytics, biometrics, communication, architecture, etc. Analyzing and visualizing such large-scale networks are significant challenges, which are generally met by reducing the redundancy on the level of nodes or edges. Motifs, patterns of the higher order organization compared with nodes and edges, are recently found to be the novel fundamental unit structures of complex networks. In this work, we proposed a novel motif h-backbone (Motif-h) method to extract functional cores of directed networks based on both motif strength and h-bridge. Compared with the state-of-the-art method Motif-DF and Entropy, our method solves two main issues which are often found in existing methods: the Motif-h reconsiders weak ties into our candidate set, and those weak ties often have critical functions of bridges in networks; moreover, our method provides a trade-off between the motif size and the edge strength, which quantifies the core edges accordingly. In the simulations, we compare our method with Motif-DF in four real-world networks and found that Motif-h can streamline the extraction of crucial structures compared with the others with limited edges.

scholarly journals Review on Free-Space Optical Communications for Delay and Disruption Tolerant Networks

Electronics ◽  
2021 ◽  
Vol 10 (13) ◽  
pp. 1607
Author(s):  
Mafalda Goncalves Teixeira ◽  
Julio Ramirez Molina ◽  
Vasco N. G. J. Soares
Keyword(s):  
Free Space ◽  
State Of The Art ◽  
Data Driven ◽  
Satellite Network ◽  
Transmission Protocol ◽  
Optical Wireless ◽  
Free Space Optical ◽  
Optical Links ◽  
Data Rates ◽  
Disruption Tolerant Networking

The increase of data-rates that are provided by free-space optical (FSO) communications is essential in our data-driven society. When used in satellite and interplanetary networks, these optical links can ensure fast connections, yet they are susceptible to atmospheric disruptions and long orbital delays. The Delay and Disruption Tolerant Networking (DTN) architecture ensures a reliable connection between two end nodes, without the need for a direct connection. This can be an asset when used with FSO links, providing protocols that can handle the intermittent nature of the connection. This paper provides a review on the theoretical and state-of-the-art studies on FSO and DTN. The aim of this review is to provide motivation for the research of an optical wireless satellite network, with focus on the use of the Licklider Transmission Protocol. The assessment presented establishes the viability of these networks, providing many examples to rely on, and summarizing the most recent stage of the development of the technologies addressed.

Practical Picture Processing

1974 ◽  
Vol 32 ◽  
pp. 338-339
Author(s):  
T. A. Welton
Keyword(s):  
Radiation Damage ◽  
Coherence Length ◽  
Spatial Information ◽  
State Of The Art ◽  
Coherent Radiation ◽  
The State ◽  
Energy Spread ◽  
Electron Micrograph ◽  
Picture Processing ◽  
Molecular Skeleton

Various authors have emphasized the spatial information resident in an electron micrograph taken with adequately coherent radiation. In view of the completion of at least one such instrument, this opportunity is taken to summarize the state of the art of processing such micrographs. We use the usual symbols for the aberration coefficients, and supplement these with £ and 6 for the transverse coherence length and the fractional energy spread respectively. He also assume a weak, biologically interesting sample, with principal interest lying in the molecular skeleton remaining after obvious hydrogen loss and other radiation damage has occurred.

A Macintosh Interface for the Cameca Camebax-Micro Electron Microprobe

1990 ◽  
Vol 48 (1) ◽  
pp. 438-439
Author(s):  
Carl E. Henderson
Keyword(s):  
Electron Microprobe ◽  
Processing Speed ◽  
Word Processing ◽  
State Of The Art ◽  
Computer Control ◽  
Third Party ◽  
Disk Storage ◽  
The Past ◽  
User Facility ◽  
Instrument Control

Over the past few years it has become apparent in our multi-user facility that the computer system and software supplied in 1985 with our CAMECA CAMEBAX-MICRO electron microprobe analyzer has the greatest potential for improvement and updating of any component of the instrument. While the standard CAMECA software running on a DEC PDP-11/23+ computer under the RSX-11M operating system can perform almost any task required of the instrument, the commands are not always intuitive and can be difficult to remember for the casual user (of which our laboratory has many). Given the widespread and growing use of other microcomputers (such as PC’s and Macintoshes) by users of the microprobe, the PDP has become the “oddball” and has also fallen behind the state-of-the-art in terms of processing speed and disk storage capabilities. Upgrade paths within products available from DEC are considered to be too expensive for the benefits received. After using a Macintosh for other tasks in the laboratory, such as instrument use and billing records, word processing, and graphics display, its unique and “friendly” user interface suggested an easier-to-use system for computer control of the electron microprobe automation. Specifically a Macintosh IIx was chosen for its capacity for third-party add-on cards used in instrument control.

Sign in / Sign up

Export Citation Format

Share Document