1,953 research outputs found
A bibliography on formal methods for system specification, design and validation
Literature on the specification, design, verification, testing, and evaluation of avionics systems was surveyed, providing 655 citations. Journal papers, conference papers, and technical reports are included. Manual and computer-based methods were employed. Keywords used in the online search are listed
A hybrid queueing model for fast broadband networking simulation
PhDThis research focuses on the investigation of a fast simulation method for broadband
telecommunication networks, such as ATM networks and IP networks. As a result of
this research, a hybrid simulation model is proposed, which combines the analytical
modelling and event-driven simulation modelling to speeding up the overall
simulation.
The division between foreground and background traffic and the way of dealing with
these different types of traffic to achieve improvement in simulation time is the major
contribution reported in this thesis. Background traffic is present to ensure that proper
buffering behaviour is included during the course of the simulation experiments, but
only the foreground traffic of interest is simulated, unlike traditional simulation
techniques. Foreground and background traffic are dealt with in a different way.
To avoid the need for extra events on the event list, and the processing overhead,
associated with the background traffic, the novel technique investigated in this
research is to remove the background traffic completely, adjusting the service time of
the queues for the background traffic to compensate (in most cases, the service time
for the foreground traffic will increase). By removing the background traffic from the
event-driven simulator the number of cell processing events dealt with is reduced
drastically.
Validation of this approach shows that, overall, the method works well, but the
simulation using this method does have some differences compared with experimental
results on a testbed. The reason for this is mainly because of the assumptions behind
the analytical model that make the modelling tractable.
Hence, the analytical model needs to be adjusted. This is done by having a neural
network trained to learn the relationship between the input traffic parameters and the
output difference between the proposed model and the testbed. Following this
training, simulations can be run using the output of the neural network to adjust the
analytical model for those particular traffic conditions.
The approach is applied to cell scale and burst scale queueing to simulate an ATM
switch, and it is also used to simulate an IP router. In all the applications, the method
ensures a fast simulation as well as an accurate result
Discrete events: Perspectives from system theory
Systems Theory;differentiaal/ integraal-vergelijkingen
Random Fluid Limit of an Overloaded Polling Model
In the present paper, we study the evolution of an overloaded cyclic polling
model that starts empty. Exploiting a connection with multitype branching
processes, we derive fluid asymptotics for the joint queue length process.
Under passage to the fluid dynamics, the server switches between the queues
infinitely many times in any finite time interval causing frequent oscillatory
behavior of the fluid limit in the neighborhood of zero. Moreover, the fluid
limit is random. Additionally, we suggest a method that establishes finiteness
of moments of the busy period in an M/G/1 queue.Comment: 36 pages, 2 picture
Dynamic priority allocation via restless bandit marginal productivity indices
This paper surveys recent work by the author on the theoretical and
algorithmic aspects of restless bandit indexation as well as on its application
to a variety of problems involving the dynamic allocation of priority to
multiple stochastic projects. The main aim is to present ideas and methods in
an accessible form that can be of use to researchers addressing problems of
such a kind. Besides building on the rich literature on bandit problems, our
approach draws on ideas from linear programming, economics, and multi-objective
optimization. In particular, it was motivated to address issues raised in the
seminal work of Whittle (Restless bandits: activity allocation in a changing
world. In: Gani J. (ed.) A Celebration of Applied Probability, J. Appl.
Probab., vol. 25A, Applied Probability Trust, Sheffield, pp. 287-298, 1988)
where he introduced the index for restless bandits that is the starting point
of this work. Such an index, along with previously proposed indices and more
recent extensions, is shown to be unified through the intuitive concept of
``marginal productivity index'' (MPI), which measures the marginal productivity
of work on a project at each of its states. In a multi-project setting, MPI
policies are economically sound, as they dynamically allocate higher priority
to those projects where work appears to be currently more productive. Besides
being tractable and widely applicable, a growing body of computational evidence
indicates that such index policies typically achieve a near-optimal performance
and substantially outperform benchmark policies derived from conventional
approaches.Comment: 7 figure
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