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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Design of a Scalable Path Service for the Internet

Ascigil, Mehmet O 01 January 2015 (has links)
Despite the world-changing success of the Internet, shortcomings in its routing and forwarding system have become increasingly apparent. One symptom is an escalating tension between users and providers over the control of routing and forwarding of packets: providers understandably want to control use of their infrastructure, and users understandably want paths with sufficient quality-of-service (QoS) to improve the performance of their applications. As a result, users resort to various “hacks” such as sending traffic through intermediate end-systems, and the providers fight back with mechanisms to inspect and block such traffic. To enable users and providers to jointly control routing and forwarding policies, recent research has considered various architectural approaches in which provider- level route determination occurs separately from forwarding. With this separation, provider-level path computation and selection can be provided as a centralized service: users (or their applications) send path queries to a path service to obtain provider- level paths that meet their application-specific QoS requirements. At the same time, providers can control the use of their infrastructure by dictating how packets are forwarded across their network. The separation of routing and forwarding offers many advantages, but also brings a number of challenges such as scalability. In particular, the path service must respond to path queries in a timely manner and periodically collect topology information containing load-dependent (i.e., performance) routing information. We present a new design for a path service that makes use of expensive pre- computations, parallel on-demand computations on performance information, and caching of recently computed paths to achieve scalability. We demonstrate that, us- ing commodity hardware with a modest amount of resources, the path service can respond to path queries with acceptable latency under a realistic workload. The ser- vice can scale to arbitrarily large topologies through parallelism. Finally, we describe how to utilize the path service in the current Internet with existing Internet applica- tions.


Wu, Xiongqi 01 January 2015 (has links)
A common feature of emerging future Internet architectures is the ability for applications to select the path, or paths, their packets take between a source and destination. Unlike the current Internet architecture where routing protocols find a single (best) path between a source and destination, future Internet routing protocols will present applications with a set of paths and allow them to select the most appropriate path. Although this enables applications to be actively involved in the selection of the paths their packets travel, the huge number of potential paths and the need to know the current network conditions of each of the proposed paths will make it virtually impossible for applications to select the best set of paths, or just the best path. To tackle this problem, we introduce a new Network Path Advising Service (NPAS) that helps future applications choose network paths. Given a set of possible paths, the NPAS service helps applications select appropriate paths based on both recent path measurements and end-to-end feedback collected from other applications. We describe the NPAS service abstraction, API calls, and a distributed architecture that achieves scalability by determining the most important things to monitor based on actual usage. By analyzing existing traffic patterns, we will demonstrate it is feasible for NPAS to monitor only a few nodes and links and yet be able to offer advice about the most important paths used by a high percentage of traffic. Finally, we describe a prototype implementation of the NPAS components as well as a simulation model used to evaluate the NPAS architecture.

Clear-air analytical and empirical K-Factor determination and characterization for terrestrial microwave LOS link applications.

Nyete, Abraham Mutunga. 30 October 2014 (has links)
The transmission media, that is, the atmosphere, through which terrestrial and satellite signals traverse, is irregular. Thus, one requires proper knowledge on how variations in atmospheric refractive conditions will affect the optimal performance of terrestrial and satellite links. Under clear-air conditions, atmospheric changes will mainly involve variations in atmospheric pressure, relative humidity and temperature, which are the key to defining the way signals are refracted as they travel from the transmitter to the receiver. Accurate knowledge of these variations can be acquired through proper modeling, characterization and mapping of these three atmospheric quantities, in terms of the refractive index, refractivity gradient or the effective earth radius factor (k-factor). In this dissertation, both parametric and non-parametric modeling and characterizing, interpolation and mapping of the k-factor for South Africa is done. Median (k50%) and effective (k99.9%) k-factor values are the ones that determine antenna heights in line of sight (LOS) terrestrial microwave links. Thus, the accurate determination of the two k-factor values is critical for the proper design of LOS links by ensuring that adequate path clearance is achieved, hence steering clear of all obstacles along the radio path. Thus, this study is critical for the proper design of LOS links in South Africa. One parametric method (curve fitting) and one non-parametric method (kernel density estimation) are used to develop three-year annual and seasonal models of the k-factor for seven locations in South Africa. The integral of square error (ISE) is used to optimize the model formulations obtained in both cases. The models are developed using k-factor statistics processed from radiosonde measurements obtained from the South African Weather Service (SAWS) for a three year period (2007-2009). Since the data obtained at the seven locations is scattered, three different interpolation techniques are then explored to extend the three-year annual and seasonal discrete measured k-factor values for the seven locations studied to cover the rest of the country, and the results of the interpolation are then presented in the form of contour maps. The techniques used for the interpolation are kriging, inverse distance weighting (IDW) and radial basis functions (RBFs). The mean absolute error (MAE) and the root mean square error (RMSE) are the metrics used to compare the performance of the different interpolation techniques used. The method that produces the least error is deemed to be the best, and its interpolation results are the ones used for developing the contour maps of the k-factor. / M. Sc. Eng. University of KwaZulu-Natal, Durban 2013.

Digital interruptions amongst the Millennial generation : task performance and emotional effects

Swihart, Joshua K. 09 July 2011 (has links)
The use of portable digital devices in the United States is increasing. With this increase in digital technology use comes an increase in interruptions between digital users. This study explores whether interruptions caused by a digital device evoke an emotion from members of the Millennial generation. In addition, this research aims to determine whether an interruption during a task causes a reduction in task efficiency amongst Millennials. The findings from this study can provide corporations and educational institutions with information about how portable digital technologies might affect the productivity of Millennial employees and students. / Department of Telecommunications

A study of error control techniques and the use of an enhanced X.25 LAPB protocol on a pseudo-random frequency-hopped anti-jam satellite link

Fairhurst, Godred January 1987 (has links)
The Skynet IV satellite will provide a medium for an integrated digital communications network. This will use the packet-oriented techniques employed in many modern communications systems. One important role of the system will be to provide jam-resistant services. The advent of sophisticated electronic jammers has required the application of complex error-correcting codes and data interleaving techniques. When the satellite link forms part of a wider network, these have profound effects upon the performance of the data link protocol. This project has examined some of these effects. Terrestrial data link control protocols were found to be very inefficient, and a number of enhancements to these protocols have been proposed. An implementation of the enhanced protocols has been tested within a simulation environment. The simulator was written in Simula, an object-oriented programming language. The performance of the link was observed to be highly dependent upon the error environment presented by the underlying physical layer service (in this case a frequency-hopped spread spectrum anti-jam satellite circuit). A model of the physical layer was combined with a link layer simulator. The model used an unusual technique to reduce the computational requirements of the simulator. The project revealed that a conventional anti-jam satellite circuit is unsuitable for carriage of packetised data services. However, a number of simple changes to the protocol and error control techniques may yield a significant increase in the performance, permitting use of the service even in the harsh error environments presented by hostile jammers. These results are to be used in the specification of future satellite modems.

Automatic-repeat-request systems for error control in digital transmission

Miller, Michael Joseph January 1982 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 1982. / Bibliography: leaves 188-191. / Microfiche. / xi, 191 leaves, bound ill. 29 cm

Network journalism : journalistic practice in interactive spheres

Heinrich, Ansgard, n/a January 2008 (has links)
Today�s globalized network communication initiates new interactive formats, transforming not only the dissemination, but - increasingly - the production of news. The �one-way� flow of news from a news outlet to the audience has been replaced by a network structure. Following Castells� concept of the �network� (1996) as the central model of information structures, I perpetuate this paradigmatic shift and suggest that networks also transform the professional journalism sphere in many world regions. A revised sphere of journalism is taking shape in which an increasingly global flow of news is evolving and a multiple platform structure of journalism is taking shape in which boundaries between traditional media outlets of print, radio, and television and between national and �foreign� journalism are blurring. Furthermore, I argue that a globalized journalistic network sphere is emerging which involves �traditional� journalistic outlets and bloggers, media activists, so-called citizen journalists, or user-generated content providers alike. These new journalistic spheres of connectivity establish new (and continuous) links between journalists, their sources as well as their audiences. This fundamental change creates new professional levels of connectivity on one hand and on the other, has severe strategic and organizational implications for the management of print, broadcast and online news outlets. Within this new �network� sphere of journalistic practice, the roles of journalistic outlets change. This work suggests a framework that helps to understand journalistic organization today, with innovative work structures based on digital technologies transforming the character and in effect substituting the model of �top-down� journalism models by a model that is far more complicated. I argue that within an evolving global news sphere, information flows are multidirectional. Decentralization and non-linearity become the key parameters defining news flows at the beginning of the twenty-first century. The character of this network in the journalism sphere is transnational, crossmedia, and cross professions. Based on results of thirteen qualitative interviews with media practitioners in Germany, the US and the UK, I argue that a new geography of journalism is taking shape in which journalistic outlets are being transformed into nodes. These nodes are arranged in a dense net of information gathers, producers and disseminators and the interactive connections among them constitute what I want to call network journalism.

Comparative performance of forward error correction using diversity in indoor mobile radio communications /

Munodawafa, Jacob. Unknown Date (has links)
Thesis (MEng (Research))--University of South Australia, 1993

A maximum likelihood approach to symbol timing recovery in digital communications /

Sabel, Lesley Phillip. Unknown Date (has links)
Thesis (PhD)--University of South Australia, 1993.

Non-binary cyclic codes and its applications in decoding of high dimensional trellis-coded modulation

Zhou, Biyun. January 2000 (has links)
Thesis (M.S.)--Ohio University, March, 2000. / Title from PDF t.p.

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