14,873 research outputs found
Buffer Overflow Management with Class Segregation
We consider a new model for buffer management of network switches with
Quality of Service (QoS) requirements. A stream of packets, each attributed
with a value representing its Class of Service (CoS), arrives over time at a
network switch and demands a further transmission. The switch is equipped with
multiple queues of limited capacities, where each queue stores packets of one
value only. The objective is to maximize the total value of the transmitted
packets (i.e., the weighted throughput).
We analyze a natural greedy algorithm, GREEDY, which sends in each time step
a packet with the greatest value. For general packet values , we show that GREEDY is -competitive, where . Furthermore, we show a lower bound of on the competitiveness of any deterministic online algorithm.
In the special case of two packet values (1 and ), GREEDY is shown
to be optimal with a competitive ratio of
Spectral analysis of the truncated Hilbert transform with overlap
We study a restriction of the Hilbert transform as an operator from
to for real numbers . The
operator arises in tomographic reconstruction from limited data, more
precisely in the method of differentiated back-projection (DBP). There, the
reconstruction requires recovering a family of one-dimensional functions
supported on compact intervals from its Hilbert transform measured
on intervals that might only overlap, but not cover . We
show that the inversion of is ill-posed, which is why we investigate the
spectral properties of .
We relate the operator to a self-adjoint two-interval Sturm-Liouville
problem, for which we prove that the spectrum is discrete. The Sturm-Liouville
operator is found to commute with , which then implies that the spectrum
of is discrete. Furthermore, we express the singular value
decomposition of in terms of the solutions to the Sturm-Liouville
problem. The singular values of accumulate at both and , implying
that is not a compact operator. We conclude by illustrating the
properties obtained for numerically.Comment: 24 pages, revised versio
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