Bandwidth Aggregation-Aware Dynamic QoS Negotiation for Real-Time Video Streaming in Next-Generation Wireless Networks

In next generation wireless networks, Internet service providers (ISPs) are expected to offer services through several wireless technologies (e.g., WLAN, 3G, WiFi, and WiMAX). Thus, mobile computers equipped with multiple interfaces will be able to maintain simultaneous connections with different networks and increase their data communication rates by aggregating the bandwidth available at these networks. To guarantee quality-of-service (QoS) for these applications, this paper proposes a dynamic QoS negotiation scheme that allows users to dynamically negotiate the service levels required for their traffic and to reach them through one or more wireless interfaces. Such bandwidth aggregation (BAG) scheme implies transmission of data belonging to a single application via multiple paths with different characteristics, which may result in an out-of-order delivery of data packets to the receiver and introduce additional delays for packets reordering. The proposed QoS negotiation system aims to ensure the continuity of QoS perceived by mobile users while they are on the move between different access points, and also, a fair use of the network resources. The performance of the proposed dynamic QoS negotiation system is investigated and compared against other schemes. The obtained results demonstrate the outstanding performance of the proposed scheme as it enhances the scalability of the system and minimizes the reordering delay and the associated packet loss rate.     

A comprehensive study of queue management as a DoS counter-measure

The purpose of a denial of service (DoS) attack is to render a network service unavailable for legitimate users. We address the problem of DoS attacks on connection-oriented protocols where the attacker tries to deplete the server connection by initiating communication with the server and then abandoning the communication. The most exploited attack in this category is the SYN-flood attack but other attacks using the same approach in stateful communication protocols also fall into this category. Our goals are twofold: first, to develop a mathematical model allowing us to analyse the trade-off between the attacker and the defender resources and second, to offer prevention mechanisms that can be used to defend against this category of attacks. We model the server queue of connections using Markov chains to establish a relationship between the server capacity, the attack rate and the impact on the service level. We analyse two methods of adjusting the timeout, threshold and linear, and we couple them with three policies of assigning the timeout to connections: the deterministic policy, the deferred policy and the utopian Poisson policy. First, theoretical modelling confirms that for any given strategy, there exists a linear trade-off between attack rate and targeted server queue size. However, the ratio that needs to be kept between them in order to maintain a similar level of quality of service differs between strategies; in that sense some are better than others. In particular, theoretical modelling also indicates that the linear deferred timeout strategy is very similar in performance to the linear Poisson timeout strategy, which in turn outperforms all the other dynamic timeout strategies. The dynamic timeout strategies always outperform the classical fixed timeout method. Our model is very general and can be used to capture the behaviour of the server queue during connection depletion attacks at various levels in the TCP protocol stack. We confirm the theoretical findings using stochastic simulations and network experiments of SYN-flood attacks. We also show how the model can be used when analysing a TCP connection establishment flood or a ticket reservation flood. The protection strategies we suggest are robust to changes in the attack model and our implementation is very efficient and transparent with respect to the server and applications it tries to protect. The strategies could therefore be easily integrated into existing operating systems and applications, or implemented in separate network devices.     

Oxidation of arsenopyrite (FeAsS) in acid Part I: Reactivity of arsenopyrite

The oxidation reactivity of arsenopyrite FeAsS in dilute acid determines the recovery of gold from arsenopyritic gold ores by slurry electrolysis. Stoichiometric,sulfur- and arsenic- deficient arsenopyrite have practically the same oxidation rate. Arsenopyrite is covered with a metal deficient sulfide layer which appears to determine the restpotential of the electrode. This layer can be separately oxidized and reduced during bulk-oxidation of arsenopyrite. Arsenopyrite oxidation is accelerated by dissolved Na₂SO₄ and by high electrode potentials and solution acidity. The rate is controlled by a surface reaction with an apparent activation energy of 33kJmol^–1.     

Semantic enhancement for media asset management systems

The socio-economic development of the World Wide Web gathered a large momentum through Web 2.0 and currently, the Web of Data is adding a further technological driver to this. The tremendous growth of media data combined with structured (linked) data promises further opportunities for digital market places. Although the integration of media content with linked data is only beginning there are already working groups and projects addressing this issue. We show how media and existing data sets can be seamlessly integrated and thus give possibilities for an extended user experience while interacting with media content on the web. We focus on automatic semantic enhancement services that can link arbitrary and open accessible data and introduce opportunities for media annotation, fragmentation and presentation. Our use case scenario is based on the Red Bull Content Pool, a media management system for videos, images and articles about Red Bull related content covering a multitude of sports events.     

Cytotoxic Phosphinoarsino and Diphosphino Pd(II) Complexes of Thiolate Amino Acids and Glutathione

The novel complexes [Pd(L-L')(SR)Cl] where L-L' is Ph(2)PCH(2)CH(2)PPh(2) (dppe) or Ph(2)AsCH(2)CH(2)PPh(2) (dadpe) and RSH is glutathione, L-cysteine, or N-acetyl-L-cysteine, have been prepared and characterised. Their structures in the solid-state and in solution are discussed. The introduction of cysteine or glutathione as a ligand in these complexes greatly improved their aqueous solubility compared with the hydrophobic parent dichloro complexes. The cytotoxicities of the glutathione complexes towards the cell-lines L1210, ADJ/PC6 and CH1 were investigated. Their cytotoxicities towards L1210 cells were comparable to those of the parent dichloro complexes.     

Russian gas exports have potential to grow through 2020

This paper analyzes the potential for Russian gas export growth through the next decade and concludes that supply for exports will continue to grow, albeit moderately. The greater or lesser intensity of that growth will depend on the evolution of both production and internal consumption. From the production side, the pace of growth depends on the status of gas reserves and, more importantly, on the investment program pursued by the State-owned gas giant Gazprom. From the demand side, evolution depends on the way Russia's wide potential for gas savings is managed. Through this analysis, we find three likely scenarios for Russian gas exports. In the most positive, diversification of exports will be possible. In the most negative, Russia will have scant opportunity to develop an export diversification strategy.     

Input current shaper based on the series connection of a voltagesource and a loss-free resistor

A new input current shaper is proposed in this paper. The operating principle is based on the connection of a voltage source and a loss-free resistor (LFR) between the input rectifier and the bulk capacitor in a conventional switching mode power supply with no power-factor correction. Both the voltage source and the LFR are obtained as an additional output from the converter's transformer. This additional output is a forward-type one with one extra inductor. With the final topology, a good tradeoff between capacitor voltage, recycling energy, and harmonic content can be established in order to comply with IEC 1000-3-2 specifications