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General queueing networks with priorities. Maximum entropy analysis of general queueing network models with priority preemptive resume or head-of-line and non-priority based service disciplines.
Priority based scheduling disciplines are widely used by existing
computer operating systems. However, the mathematical analysis and
modelling of these systems present great difficulties since priority
schedulling is not compatible with exact product form solutions of
queueing network models (QNM's). It is therefore, necessary to employ
credible approximate techniques for solving QNM's with priority
classes.
The principle of maximum entropy (ME) is a method of inference
for estimating a probability distribution given prior information in
the form of expected values. This principle is applied, based on
marginal utilisation, mean queue length and idle state probability
constraints, to characterise new product-form approximations for
general open and closed QNM's with priority (preemptive-resume,
non-preemtive head-of-line) and non-priority
(first-come-first-served, processor-sharing, last-come-first-served
with, or without preemtion) servers. The ME solutions are interpreted
in terms of a decomposition of the original network into individual
stable GIG11 queueing stations with assumed renewal arrival
processes. These solutions are implemented by making use of the
generalised exponential (GE) distributional model to approximate the
interarrival-time and service-time distributions in the network. As a
consequence the ME queue length distribution of the stable GE/GEzl
priority queue, subject to mean value constraints obtained via
classical queueing theory on bulk queues, is used as a 'building
block' together with corresponding universal approximate flow
formulae for the analysis of general QNM's with priorities. The
credibility of the ME method is demonstrated with illustrative
numerical examples and favourable comparisons against exact,
simulation and other approximate methods are made.Algerian governmen
Scheduling in CDMA-based wireless packet networks.
Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.Modern networks carry a wide range of different data types, each with its own individual
requirements. The scheduler plays an important role in enabling a network to meet all
these requirements. In wired networks a large amount of research has been performed
on various schedulers, most of which belong to the family of General Processor Sharing
(GPS) schedulers. In this dissertation we briefly discuss the work that has been done on a
range of wired schedulers, which all attempt to differentiate between heterogeneous traffic.
In the world of wireless communications the scheduler plays a very important role, since
it can take channel conditions into account to further improve the performance of the
network. The main focus of this dissertation is to introduce schedulers, which attempt to
meet the Quality of Service requirements of various data types in a wireless environment.
Examples of schedulers that take channel conditions into account are the Modified Largest
Weighted Delay First (M-LWDF), as well as a new scheduler introduced in this dissertation,
known as the Wireless Fair Largest Weighted Delay First (WF-LWDF) algorithm.
The two schemes are studied in detail and a comparison of their throughput, delay, power,
and packet dropping performance is made through a range of simulations. The results are
compared to the performance offour other schedulers. The fairness ofM-LWDF and WFLWDF
is determined through simulations. The throughput results are used to establish
Chernoff bounds of the fairness of these two algorithms. Finally, a summary is given of the
published delay bounds of various schedulers, and the tightness of the resultant bounds is
discussed