904 research outputs found
Transient analysis of a Markovian Single Vacation Feedback Queue with an Interrupted Closedown Time and Control of Admission During Vacation
This paper analyzes the transient behavior of an M/M/1 queueing model with single vacation, feedback, interrupted closedown time and control of admission during vacation. The time-dependent system size probabilities for the proposed model are obtained using generating function in the closed form. Further, the system performance measures like mean and variance of system size are also obtained for the time-dependent case. Finally, numerical illustrations are presented to understand the effect for various system parameters
Performance Modelling and Optimisation of Multi-hop Networks
A major challenge in the design of large-scale networks is to predict and optimise the
total time and energy consumption required to deliver a packet from a source node to a
destination node. Examples of such complex networks include wireless ad hoc and sensor
networks which need to deal with the effects of node mobility, routing inaccuracies, higher
packet loss rates, limited or time-varying effective bandwidth, energy constraints, and the
computational limitations of the nodes. They also include more reliable communication
environments, such as wired networks, that are susceptible to random failures, security
threats and malicious behaviours which compromise their quality of service (QoS) guarantees.
In such networks, packets traverse a number of hops that cannot be determined
in advance and encounter non-homogeneous network conditions that have been largely
ignored in the literature. This thesis examines analytical properties of packet travel in
large networks and investigates the implications of some packet coding techniques on both
QoS and resource utilisation.
Specifically, we use a mixed jump and diffusion model to represent packet traversal
through large networks. The model accounts for network non-homogeneity regarding
routing and the loss rate that a packet experiences as it passes successive segments of a
source to destination route. A mixed analytical-numerical method is developed to compute
the average packet travel time and the energy it consumes. The model is able to capture
the effects of increased loss rate in areas remote from the source and destination, variable
rate of advancement towards destination over the route, as well as of defending against
malicious packets within a certain distance from the destination. We then consider sending
multiple coded packets that follow independent paths to the destination node so as to
mitigate the effects of losses and routing inaccuracies. We study a homogeneous medium
and obtain the time-dependent properties of the packet’s travel process, allowing us to
compare the merits and limitations of coding, both in terms of delivery times and energy
efficiency. Finally, we propose models that can assist in the analysis and optimisation
of the performance of inter-flow network coding (NC). We analyse two queueing models
for a router that carries out NC, in addition to its standard packet routing function. The
approach is extended to the study of multiple hops, which leads to an optimisation problem
that characterises the optimal time that packets should be held back in a router, waiting
for coding opportunities to arise, so that the total packet end-to-end delay is minimised
Strategic queueing behavior for individual and social optimization in managing discrete time working vacation queue with Bernoulli interruption schedule
In this paper, we consider a discrete time working vacation queue with a utility function
for the reward of receiving the service and the cost of waiting in the system. A more
flexible switching mechanism between low and regular service states is introduced to enhance
the practical value of the working vacation queue. Under different precision levels
of the system information, namely observable, almost unobservable and fully unobservable
cases, the utility function is studied from both the individual customer’s and the system
administrator’s points of view. By analyzing the steady-state behavior of the system, the
associated optimal joining decisions under different information scenarios are obtained. We
find that for the fully observable queue, the joining threshold for individual optimization
may be less than the one for social optimization in working vacation period. A similar
situation also appears in almost unobservable case. Such phenomenon is not possible for
the classic first come first served queue due to the fact that there is no vacation time and
thus will not cause large fluctuations in customers’ conditional waiting time. Additionally,
we also conduct some numerical comparisons to demonstrate the effect of the information
levels as well as system parameters on customer joining behavior.This research was partially supported
by grant from NSERC DAS programs, National Natural Science Foundation of China
(Nos.71301111, 71571127, 71402072) and the FSUSE (No.2012RC23).http://www.elsevier.com/locate/caor2017-09-30hb2016Electrical, Electronic and Computer Engineerin
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