Practical Algorithms for Multicast Support in Input Queues Switches

Abstract — This paper deals with multicast flow support in N × N Input Queued switch architectures. A practical approach to support multicast traffic is presented, assuming that O(N) queues are available at each input port. The focus is on dynamic queueing policies, where, at each input port, multicast flows are assigned to one among the available queues when flows become active: flows are assigned to queues according to switch queue status and, possibly, to flow information. We discuss queueing assignments, scheduling algorithms and flow activity definition models. We explain why dynamic queueing disciplines may outperform static policies, and we show that, even in the most favorable conditions for static policies, they provide comparable performance. I

Measurement Based Reconfigurations in Optical Ring Metro Networks

Single-hop wavelength division multiplexing (WDM) optical ring networks operating in packet mode are one of themost promising architectures for the design of innovative metropolitan network (metro) architectures. They permit a cost-effective design, with a good combination of optical and electronic technologies, while supporting features like restoration and reconfiguration that are essential in any metro scenario. In this article, we address the tunability requirements that lead to an effective resource usage and permit reconfiguration in optical WDM metros.We introduce reconfiguration algorithms that, on the basis of traffic measurements, adapt the network configuration to traffic demands to optimize performance. Using a specific network architecture as a reference case, the paper aims at the broader goal of showing which are the advantages fostered by innovative network designs exploiting the features of optical technologies

The Gulf Cooperation Council Monarchies After 2011: Redefining Security Perceptions and Rethinking Threat Analysis

Since 2011, a series of events – including popular upheavals, civil wars, the empowerment of non-state actors, economic volatility and increased geopolitical confrontation between states – hinted at the beginning of a transformative period for the Middle East and North Africa (MENA) region. Notwithstanding the region’s modern history has provided several instances of treacherous conjunctures, seldom like in the aftermath of 2011 so many different challenges of different types have risen simultaneously on a regional and domestic scale. As this transformative wave spread towards the countries of the Gulf Cooperation Council (GCC), challenging the existing balance of power, the local regimes’ security perceptions were profoundly impacted. Arguably, these became so substantially divergent at the level of each state that, in the span of only six years, the GCC was hit by two of the gravest internal political crises in its history. Hence, new questions emerged regarding the existence of a shared prioritization of threats and the interaction of endogenous and exogenous dangers when they materialize simultaneously, that don’t seem to find answers in the existing body of scholarship yet. Focusing on the post-2011 environment and the issues emerged as crucial amid the 2014 and 2017 intra-GCC crises, this thesis aims to provide new analytical tools for addressing such questions and enhancing the understanding of evolving security perceptions. In order to do so, drawing from the literatures of security studies and area studies, an original theoretical framework is elaborated, which introduces a distinction between threats and risks and a categorization system addressing the emergence of multidimensional, ‘intermestic’ threats. The framework is subsequently applied to perform an analysis of threat perceptions in each of the six GCC states. Finally, the author will attempt to draw conclusions on threat prioritization in the region and the status of the much-debated notion of ‘Gulf security’

GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?

On the basis of the recent understanding of GRB050315 and GRB060218, we return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow. We proposed it as the prototype for a new class of GRBs with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". Detailed theoretical computation of the GRB970228 light curves in selected energy bands for the prompt emission are presented and compared with observational BeppoSAX data. From our analysis we conclude that GRB970228 and likely the ones of the above mentioned new class of GRBs are "canonical GRBs" have only one peculiarity: they exploded in a galactic environment, possibly the halo, with a very low value of CBM density. Here we investigate how GRB970228 unveils another peculiarity of this class of GRBs: they do not fulfill the "Amati relation". We provide a theoretical explanation within the fireshell model for the apparent absence of such correlation for the GRBs belonging to this new class.Comment: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28, 2007, C.L. Bianco, S.-S. Xue, Editor

The Amati relation in the "fireshell" model

(Shortened) CONTEXT: [...] AIMS: Motivated by the relation proposed by Amati and collaborators, we look within the ``fireshell'' model for a relation between the peak energy E_p of the \nu F_\nu total time-integrated spectrum of the afterglow and the total energy of the afterglow E_{aft}, which in our model encompasses and extends the prompt emission. METODS: [...] Within the fireshell model [...] We can then build two sets of ``gedanken'' GRBs varying the total energy of the electron-positron plasma E^{e^\pm}_{tot} and keeping the same baryon loading B of GRB050315. The first set assumes for the effective CBM density the one obtained in the fit of GRB050315. The second set assumes instead a constant CBM density equal to the average value of the GRB050315 prompt phase. RESULTS: For the first set of ``gedanken'' GRBs we find a relation E_p\propto (E_{aft})^a, with a = 0.45 \pm 0.01, whose slope strictly agrees with the Amati one. Such a relation, in the limit B \to 10^{-2}, coincides with the Amati one. Instead, in the second set of ``gedanken'' GRBs no correlation is found. CONCLUSIONS: Our analysis excludes the Proper-GRB (P-GRB) from the prompt emission, extends all the way to the latest afterglow phases and is independent on the assumed cosmological model, since all ``gedanken'' GRBs are at the same redshift. The Amati relation, on the other hand, includes also the P-GRB, focuses on the prompt emission only, and is therefore influenced by the instrumental threshold which fixes the end of the prompt emission, and depends on the assumed cosmology. This may well explain the intrinsic scatter observed in the Amati relation.Comment: 4 pages, 5 figures, to appear on A&A Letter

On the physical processes which lie at the bases of time variability of GRBs

The relative-space-time-transformation (RSTT) paradigm and the interpretation of the burst-structure (IBS) paradigm are applied to probe the origin of the time variability of GRBs. Again GRB 991216 is used as a prototypical case, thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is found that with the exception of the relatively inconspicuous but scientifically very important signal originating from the initial ``proper gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be explained by the interaction of the accelerated-baryonic-matter pulse with inhomogeneities in the interstellar matter. This can be demonstrated by using the RSTT paradigm as well as the IBS paradigm, to trace a typical spike observed in arrival time back to the corresponding one in the laboratory time. Using these paradigms, the identification of the physical nature of the time variablity of the GRBs can be made most convincingly. It is made explicit the dependence of a) the intensities of the afterglow, b) the spikes amplitude and c) the actual time structure on the Lorentz gamma factor of the accelerated-baryonic-matter pulse. In principle it is possible to read off from the spike structure the detailed density contrast of the interstellar medium in the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure