2,959 research outputs found

    Design of Overlay Networks for Internet Multicast - Doctoral Dissertation, August 2002

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    Multicast is an efficient transmission scheme for supporting group communication in networks. Contrasted with unicast, where multiple point-to-point connections must be used to support communications among a group of users, multicast is more efficient because each data packet is replicated in the network – at the branching points leading to distinguished destinations, thus reducing the transmission load on the data sources and traffic load on the network links. To implement multicast, networks need to incorporate new routing and forwarding mechanisms in addition to the existing are not adequately supported in the current networks. The IP multicast are not adequately supported in the current networks. The IP multicast solution has serious scaling and deployment limitations, and cannot be easily extended to provide more enhanced data services. Furthermore, and perhaps most importantly, IP multicast has ignored the economic nature of the problem, lacking incentives for service providers to deploy the service in wide area networks. Overlay multicast holds promise for the realization of large scale Internet multicast services. An overlay network is a virtual topology constructed on top of the Internet infrastructure. The concept of overlay networks enables multicast to be deployed as a service network rather than a network primitive mechanism, allowing deployment over heterogeneous networks without the need of universal network support. This dissertation addresses the network design aspects of overlay networks to provide scalable multicast services in the Internet. The resources and the network cost in the context of overlay networks are different from that in conventional networks, presenting new challenges and new problems to solve. Our design goal are the maximization of network utility and improved service quality. As the overall network design problem is extremely complex, we divide the problem into three components: the efficient management of session traffic (multicast routing), the provisioning of overlay network resources (bandwidth dimensioning) and overlay topology optimization (service placement). The combined solution provides a comprehensive procedure for planning and managing an overlay multicast network. We also consider a complementary form of overlay multicast called application-level multicast (ALMI). ALMI allows end systems to directly create an overlay multicast session among themselves. This gives applications the flexibility to communicate without relying on service provides. The tradeoff is that users do not have direct control on the topology and data paths taken by the session flows and will typically get lower quality of service due to the best effort nature of the Internet environment. ALMI is therefore suitable for sessions of small size or sessions where all members are well connected to the network. Furthermore, the ALMI framework allows us to experiment with application specific components such as data reliability, in order to identify a useful set of communication semantic for enhanced data services

    Sequels to the Chicago Aviation Conference

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    This research aims to explore and propose a more effective management of rail and road infrastructure and the possibility of a more resource-efficient road and rail infrastructure by applying business models based on performance and a life-cycle perspective. There is a lack of efficiency in the Swedish rail and road infrastructure industries - at the same time as the availability of the rail tracks and roads is essential. Rail and road infrastructure have long lifetimes, around 40-60 years, and during these decades regular maintenance and reconstruction are needed to ensure proper function. Large amounts of resources are required to construct the infrastructure, and the overall environmental pressure depends substantially on this. This research is largely based on interviews conducted with the buyer, contractors and design consultants for rail and road infrastructure in Sweden. Literature reviews have been conducted to develop the framework needed to analyze the empirical findings. This research contributes by building on theory in areas such as Integrated Product Service Offerings (IPSOs) and eco-design, and this abstract presents a brief summary of the overall conclusions. Several challenges for rail and road infrastructure in Sweden have been identified, such as the lack of information and knowledge transfer between different projects and actors. This is due to e.g. the use of traditional short-term contracts and conservative cooperate cultures, creating sub-optimizations in management. Increased collaboration, through e.g. partnering, seems to be a promising way to increase the information and knowledge transfer between actors by increasing trust and interaction. In this way, management would be more effective, and by involving contractors in the design phase, more efficient technical solutions could be developed and used. Additionally, increased involvement by the design consultants and an iterative information loop between design, construction and maintenance could also be beneficial. The research indicates that increased cooperation increases trust. In this way, there is a possibility to remove the detailed requirements that prevent new ways of working. Rail and road infrastructure have characteristics, such as the resources used and the importance of availability, that are well-suited for IPSOs. This performance-based business model with a life-cycle perspective provides incentives to optimize the use of resources and provide a holistic view for management that is lacking today for rail and road infrastructure. However, a long-term contract such as an IPSO creates uncertainties. The actors are risk-averse, which is an obstacle in the development of new business models and contract forms. Most of the risks and uncertainties identified are due to lack of experience. This implies that an implementation of IPSOs will have a steep learning curve. Additionally, risk allocation between the actors is important for effective management: too much risk for the suppliers will make them reluctant in developing new solutions, and they will use a risk premium to cover up for the risk

    A simulation model for public bike-sharing systems

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    Urban areas are in need of efficient and sustainable mobility services. Public bicycle sharing systems stand out as a promising alternative and many cities have invested in their deployment. This has led to a continuous and fast implementation of these systems around the world, while at the same time, research works devoted to understand the system dynamics and deriving optimal designs are being developed. In spite of this, many promoting agencies have faced the impossibility of evaluating a system design in advance, increasing the uncertainty on its performance and the risks of failure. This paper describes the development of an agent-based simulation model to emulate a bike-sharing system. The goal is to obtain a tool to evaluate and compare different alternatives for the system design before their implementation. This tool will support the decision-making process in all the stages of implementation, from the strategical planning to the daily operation. The main behavioral patterns and schemes for all agents involved are designed and implemented into a Matlab programming code. The model is validated against real data compiled from the Barcelona’s Bicing system showing good accuracy.Postprint (published version

    Topological Design of Multiple Virtual Private Networks UTILIZING SINK-TREE PATHS

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    With the deployment of MultiProtocol Label Switching (MPLS) over a core backbone networks, it is possible for a service provider to built Virtual Private Networks (VPNs) supporting various classes of services with QoS guarantees. Efficiently mapping the logical layout of multiple VPNs over a service provider network is a challenging traffic engineering problem. The use of sink-tree (multipoint-to-point) routing paths in a MPLS network makes the VPN design problem different from traditional design approaches where a full-mesh of point-to-point paths is often the choice. The clear benefits of using sink-tree paths are the reduction in the number of label switch paths and bandwidth savings due to larger granularities of bandwidth aggregation within the network. In this thesis, the design of multiple VPNs over a MPLS-like infrastructure network, using sink-tree routing, is formulated as a mixed integer programming problem to simultaneously find a set of VPN logical topologies and their dimensions to carry multi-service, multi-hour traffic from various customers. Such a problem formulation yields a NP-hard complexity. A heuristic path selection algorithm is proposed here to scale the VPN design problem by choosing a small-but-good candidate set of feasible sink-tree paths over which the optimal routes and capacity assignments are determined. The proposed heuristic has clearly shown to speed up the optimization process and the solution can be obtained within a reasonable time for a realistic-size network. Nevertheless, when a large number of VPNs are being layout simultaneously, a standard optimization approach has a limited scalability. Here, the heuristics termed the Minimum-Capacity Sink-Tree Assignment (MCSTA) algorithm proposed to approximate the optimal bandwidth and sink-tree route assignment for multiple VPNs within a polynomial computational time. Numerical results demonstrate the MCSTA algorithm yields a good solution within a small error and sometimes yields the exact solution. Lastly, the proposed VPN design models and solution algorithms are extended for multipoint traffic demand including multipoint-to-point and broadcasting connections

    Live Migration of Virtualized Carrier Grade SIP Server

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    The concept of network virtualization, such as network functions virtualization, has attracted considerable attention from telecom carriers and a live migration technique is a key feature of virtualization technology. However, there are some challenges associated with applying server virtualization technology including live migration to a SIP server. Previous work has not dealt with the performance or behavior of a SIP server during live migration. Neither has it targeted a carrier grade SIP server for live migration. In this paper we present a virtualized carrier grade SIP server running on a virtual machine, which is configured with Carrier Grade Linux, HA middleware and SIP-AS application. We also assess its performance to investigate the impact of throughput degradation and suspension on a SIP layer and HA cluster configuration

    Perceived importance of national occupational CADD skill standards among faculty of NAIT accredited institutions

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    This study presents a descriptive survey that examined the importance and relevance of National Occupational CARD Skills based on the perceptions of faculty teaching at National Association of Industrial Technology (NAIT) accredited institutions. The major goal of the study was to determine what National Occupational CADD Skill Standards are relevant and important to faculty teaching CARD courses. The study was also designed to determine ratings of the perceived importance and relevance of National Occupational CADD Skill Standards by faculty teaching CADD courses at NAIT accredited institutions based on their area of specialization, professional ranking, and teaching experience. This study provided NAIT accredited programs, professionals, and affiliated organizations a reflection of CADD standards developed, adopted, and practiced by faculty teaching CADD courses at NAIT accredited institutions in relation to National Occupational CADD Skill Standards. The population used for this study includes faculty teaching CADD courses in various Industrial Technology programs. For testing hypothesis I, a single sample was used for survey responses. Independent samples were used for survey responses in hypotheses II, III, and V. A single survey instrument was developed for this study. The survey instrument has five sections representing: demographics, fundamental drafting skills, fundamental computer skills, basic CADD skills, and advanced CADD skills. A research hypothesis (H1 : μ ≠ 3) was established for hypothesis I for each item. Research hypotheses (H1 At least one pair of the category means would be different) were established for hypotheses II, III, and IV. Hypothesis I was tested using a single sample t -test at the .O5 level of significance for each of the CADD skill standard item. The ANOVA was used to test hypotheses II, III, and IV. The results of the statistical analyses were used to arrive at inferences on the importance and relevance of National Occupational CADD Skill Standards developed by National Coalition for Advanced Manufacturing (NACFAM) by faculty teaching at NAIT accredited institutions. Statistical analyses also checked on the balance of opinions on importance and relevance of National Occupational CADD Skill Standards between industry and educators. Statistical analyses failed to establish significant mean differences on how faculty teaching CADD at NAIT accredited institutions perceive the importance and relevance of National Occupational CADD Skill Standards in the four hypotheses tested. The four hypotheses are stated in Chapter 1 of the study. Recommendations for further studies are provided in Chapter 5

    Development of a moderate-cost device for teaching numerical control programming

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    The study was undertaken to develop a machine which could be used to provide a realistic experience in the operation of a numerically controlled machine at moderate cost. The machine was designed to be used in the high school industrial arts laboratory. The machine was controlled by a microcomputer which was interfaced to stepping motors which powered a plotting table and the quill feed of a drill press. A router bit was placed in the chuck, so student selected designs could be cut in wood or plastic;The development of the machine and computer program was followed by a study of the effects of its use in a high school industrial arts curriculum on the students\u27 acquisition of numerical control and automated manufacturing concepts, on their development of numerical control programming skills, and on their attitudes toward numerical control and the unit of study;The results of data analysis of the posttest and attitude instruments did not support use of the prototype machine to enhance concept acquisition, skill development, or positive attitudes toward the unit of study, although it was noted that all but four of the approximately 230 students participating in the study or pilot studies developed skills sufficient to complete at least one numerical control programming project successfully

    Competition in a Pure World of Internet Telephony

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    From the angle of competition policy, Voice over IP looks like a panacea. It not only brings better service, but it also increases competitive pressure on former telecommunications monopolists. This paper points to the largely overlooked downside. In a pure world of Internet telephony, there would be no charge for individual calls, nor for telephony, as distinct from other services running over the uniform network. Specifically, establishing property rights for either of these would be costly, whereas these property rights were automatic and free of charge in switched telephony. Giving voice over IP providers classic telephone numbers would enhance systems competition with switched telephony. But this would make it more difficult for clients to swap providers. The anti-competitive caller pays principle would extend to IP telephony.property right, non-linear pricing, pure bundling, club good, cross-subsidisation, packet switched telephony

    Modelling and Optimisation of GSM and UMTS Radio Access Networks

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    The size and complexity of mobile communication networks have increased in the last years making network management a very complicated task. GSM/EDGE Radio Access Network (GERAN) systems are in a mature state now. Thus, non-optimal performance does not come from typical network start-up problems, but, more likely, from the mismatching between traffic, network or propagation models used for network planning, and their real counterparts. Such differences cause network congestion problems both in signalling and data channels. With the aim of maximising the financial benefits on their mature networks, operators do not solve anymore congestion problems by adding new radio resources, as they usually did. Alternatively, two main strategies can be adopted, a) a better assignment of radio resources through a re-planning approach, and/or b) the automatic configuration (optimisation, in a wide sense) of network parameters. Both techniques aim to adapt the network to the actual traffic and propagation conditions. Moreover, a new heterogenous scenario, where several services and Radio Access Technologies (RATs) coexist in the same area, is now common, causing new unbalanced traffic scenarios and congestion problems. In this thesis, several optimisation and modelling methods are proposed to solve congestion problems in data and signalling channels for single- and multi-RAT scenarios

    Basic graphics : an introduction to rudimentary graphic design

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    These notes were compiled from several authorities to be used for teaching and learning purposes here at QUT, with the focus on first and second year landscape architecture design studio units
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